Nina Elfferding

Michael Linder

Nina Susanne Hillesheim

Michael Elfferding

Thomas Linder

Jörg Sundermeyer

Bernd Harbrecht

Geburtstag

Neuartige Cyclopentadienyl-N-silylphosphazen-Komplexe der Seltenerdmetalle Yttrium und Lutetium

Keywords: Constrained Geometry complexes, Cyclopentadienyl ligands, Phosphazene, Rare earth metals Constrained Geometry complexes, Cyclopentadienyl ligands, Phosphazene, Rare earth metals

We report the investigation of four new monoanionic cyclopentadienyl-N-silylphosphazene ligands [C 5 R 4 -SiMe 2 -NPR' 3 ] - (CpSiNP -) 1-4. In this system the amido moiety of the classical dianionic chelate ligand (CpSiN 2-) is displaced by an isoelectronic phosphazene donor function (CpSiNP -). The iminophosphoranefunctionalized tetramethylcyclopentadiene ligands have been prepared by the reaction of two equivalents of tri-(tertbutyl)iminophosphorane or tris-(dimethylamino)iminophosphorane with tetramethyl or tertbutyl substituted chlorodimethylsilyl-1,3-cyclopentadiene. The molecular structures of the protonated species of two representatives 1-H and 2-H have been established by X-ray diffraction analysis. Furthermore the metallation of the ligand [C 5 R 4 -SiMe 2 -NPtBu 3 ]H 2-H was explored by the aryl elimination pathway using chelate stabilized arene complexes of rare earth metals (RE) [RE(dmba) 3 ]

(RE = Y, Lu;

(dmba -) = ortho metalated N,Ndimethylbenzylamine). The resulting cyclopentadienyl diaryl complexes of the type [(η 5 -C 5 Me 4 -SiMe 2 -NPtBu 3 )RE(dmba) 2 ] (RE = Y (5); Lu(6)) were completely characterized by NMR spectroscopy, elemental analysis and X-ray diffraction analysis. The coordination number of the central atom in each case is nine. Five RE-C bonds to the Cp fragment, two RE-C bonds to the aryl-C atom and two RE-N bonds to the chelating amino function are realized. The phosphazene unit with uncommonly large Si-N-P angles of 173° (5) and 166° (6) do not form a bond in terms of the Constrained-Geometry ligand concept at least in these complexes. It seems that on the one hand the high coordination number and on the other hand the stable chelate structure of the coordinated amino-aryl ligand is responsible for this result.

6

Abbildung 5: Molekülstrukturen der Komplexe 5 und 6. [START_REF] Baisch | [END_REF] mit Thionylchlorid in THF durchgeführt. Der Metallgehalt der solvatisierten Lanthanidtrichloride wurde durch komplexometrische Titration mit EDTA in Anwesenheit von Xylenolorange als Indikator bestimmt. [33] Die folgenden Verbindungen wurden nach Literaturvorschriften dargestellt: Dimethylfulven (CH 3 ) 2 C=C 5 H 4 , [34] Li(C 5 H 4 tBu), [35] Li(C 5 Me 4 H), [ 36 ] (C 5 H 4 tBu)Me 2 SiCl, [ 37 ] (C 5 Me 4 )Me 2 SiCl, [ 38 ] Benzylkalium, [ 39 ] TMSN=P(NMe 2 ) 3 , [ 40 ], TMSN=PtBu 3 ,[22] HN=PtBu 3 [ 41 ], N,N-Dimethylbenzylamin, [ 42 ] Li(dmba), [ 43 ] [Y(dmba) 3 ], [28] [Lu(dmba) 3 ]. [29] n-BuLi (1.6 M Lösung in Hexan) wurde von p. A. Qualität bei den Firmen ALDRICH und ACROS, bezogen. Die NMR-Spektren wurden an folgenden Geräten bei 25°C gemessen: BRUKER ARX 300, BRUKER AMX 300, BRUKER DRX 400, BRUKER DRX 500. Als interner Standard für die 1

Kristallstrukturanalyse:

Die Sammlung der Röntgenstrukturdaten erfolgte an Flächendetektordiffraktometersystemen des Typs IPDS-I und IPDS-II der Firma STOE. Als Strahlungsquelle diente eine Mo-Anode mit nachgeschaltetem Graphitmonochromator (Mo-Kα-Strahlung, λ = 71.073 pm). Die Datensammlung erfolgte mit der IPDS Software X-Area der Firma STOE. [ 44 ] Absorptionskorrekturen erfolgten empirisch unter Verwendung von Multiscans. [45] Für die Strukturlösung wurden direkte Methoden verwendet (Sir-97). [46] Die Lagen fehlender Atome wurden aus Differenzfouriersynthesen bestimmt. Für die Verfeinerung wurde die Methode der kleinsten Fehlerquadrate verwendet (SHELXL-97). [START_REF] Sheldrick | SHELXL-97[END_REF] Die Programme PLATON [START_REF] Spek | [END_REF] und PLUTON [START_REF] Spek | Platon: A Multi-Purpose Crystallographic Tool[END_REF] kamen zur Überprüfung der Strukturauswertung zum Einsatz. Zur graphischen Darstellung der Verbindungen wurde das Programm Diamond verwendet. [START_REF] Brandenburg | Diamond, Release 3.0[END_REF] Die kristallographischen Daten der in dieser Veröffentlichung beschriebenen Strukturen wurden als supplementary publication no. CCDC-763416 bis 763419 beim Cambridge Crystallographic Data Centre hinterlegt. Eine tabellarische Zusammenfassung der wichtigsten Kristallstrukturdaten befindet sich im supporting information file. (2,3,4,5- 3 J H,H = 6.7 Hz, 2H, CpH ar ), 7.36 (t, 3 J H,H = 7.02 Hz, 2H, CpH ar ), 7.24 (t, 3 J H,H = 6.4 Hz, 2H, CpH ar ), 7.03 (d, 3 J H,H = 7.5 Hz, 2H, CpH ar ), 4.15 (d, 2 J H,H = 14.0 Hz, 2H, CH 2 ), 3.02 (d, 2 J H,H = 13.7 Hz, 2H, CH benzyl ), 2.50 (s, 6 H, NCH 3 ), 2.35 (s, 3 H, C ipso CCH 3 ), 2.30 (s, 3 H, C ipso CCH 3 ), 2.02 (s, 6H, NCH 3 ), 1.94 (s, 3H, H 3 CCCCH 3 ), 1.82 (s, 3H, H 3 CCCCH 3 ), 1.07 (d, 27H, 3 J H,P = 12.6 Hz, C(CH 3 ) 3 ), 0.68 (s, 3 H, SiCH 3 ), 0.47 (s, 3H, SiCH 3 ). Die Signale der quartären Kohlenstoffatome des Cp-Rings sind im 13 C-NMR-Spektrum nicht zu beobachten. 31 P-NMR (C 6 D 6 , 121.5 MHz): δ/ppm = 29.6. EI/MS: m/z (%) = 395 (7) [Ligand] + , 274 (100), 218 (10), 160 (6), 105 (11).

P-Tri-tertbutyl-N-(dimethyl-(4-tertbutyl-cyclopenta-2,4-dienyl) silanyl)-iminophosphoran (1-H): Zu einer Suspension von

P-Tri-tertbutyl-N-(dimethyl-

P-Tris(dimethylamino)-N-(dimethyl-(4-tertbutyl-cyclopenta-

Inhaltsübersicht.Abb. 1 :

 1 Abb. 1: . Bisher in der Literatur bekannte Strukturmortive für Liganden, die zur Synthese von Constrained-Geometry-Komplexe eingesetzt werden (A, B, D) und die neue Ligandenklasse C CpSiNP.

Abb. 3 :

 3 Abb. 3: Molekülstrukturen der Liganden 1-H und 2-H. Thermische Ellipsoide sind für eine Aufenthaltswahrscheinlichkeit von 50% dargestellt. Tabelle 1. Ausgewählte Bindungslängen (Å) und -winkel (°) von C 5 H 4 tBu-SiMe 2 NPtBu 3 (1-H) und C 5 Me 4 H-SiMe 2 NPtBu 3 (2-H).

  Abbildung 1 zeigt das Ergebnis der Kristallstrukturanalyse, und in Tabelle 1 sind ausgewählte Bindungslängen und -winkel angegeben. Verbindung 1-H kristallisiert in der orthorhombischen Raumgruppe Pbca, während Verbindung 2-H in der monoklinen Raumgruppe P2 1 /n vorliegt. Die Bindungsabstände P1-N1 betragen 1.540(1) Å bzw. 1.541(1) Å und sind somit erwartungsgemäß vergleichbar mit der P-N-Bindungslänge in anderen N-Silyliminophosphoranen wie Me 3 SiNPtBu 2 (2-C 6 H 4 Ph) (1.531(2) Å) [ 24 ] oder 1,3-(Me 3 SiNPtBu 2 CH 2 ) 2 -C 6 H 4 (1.538(2) Å bzw. 1.531(2) Å).[ 25 ] Die Werte für die N1-Si1-Bindungslängen betragen 1.658 Å bzw. 1.652 Å. Da übliche Bindungslängen für reine Si-N-Einfachbindung bei etwa 1.8 Å liegen, kann davon ausgegangen werden, dass bei beiden Verbindungen die Si-N-Bindung durch negativhyperkonjugative Wechselwirkung ähnlich der P-N Bindung partiellen Doppelbindungscharakter besitzt.[26] Ähnliche N-Si-Bindungslängen werden in den oben erwähnten Referenzverbindungen gefunden. Die Bindungswinkel P1-N1-Si1 sind mit 166.7° bzw. 166.0° gegenüber dem idealen Wert für ein sp 2 -hybridisiertes Stickstoffatom stark aufgeweitet und vergleichbar mit dem P-N-Si-Winkel der Referenzverbindung 1,3-(Me 3 SiNPtBu 2 CH 2 ) 2 -C 6 H 4 (165.05(16)° bzw. 175.12(17)°)).[ 27 ] Aufgrund des hohen sterischen Anspruchs der tertButyl-bzw. Tetramethyl-cyclopentadien-Einheit ist dieser P-N-Si-Winkel deutlich näher an 180° als z. B. in der artverwandten Verbindung Me 3 SiNPtBu 2 (2-C 6 H 4 Ph) (vgl. d(P1-N1-Si1) = 160.76(15)°).[24] Unerwarteter Weise ließ sich die protonierte Form dieser Cyclopentadiene 1-H -4-H nicht mit homoleptischen

2 -H 5 (

 25 Abb.4: Syntheseroute zur Darstellung neuartiger Cyclopentadienyl-N-silylphosphazen-Komplexe des Yttriums und Lutetiums.

  NPtBu 3 )Y(dmba) 2 ] kristallisiert in der monoklinen Raumgruppe P2 1 /n. Die Molekülstruktur zeigt, dass es sich um einen Halbsandwichkomplex handelt, in der nur der Cp-Ring des potentiellen Chelatliganden an das Yttriumatom gebunden ist. Der sterische Anspruch der beiden dmba-Chelatliganden ist derart groß, dass selbst das basische Stickstoffatom der Phosphazeneinheit des Liganden nicht in der Lage ist, an das abgeschirmte Zentralatom zu koordinieren. Stattdessen geht dieses sterisch sehr anspruchsvolle Iminophosphoran-Fragment in der Kristallpackung der Koordinationssphäre so gut wie möglich aus dem Weg und ordnet sich mit einem Winkel von 87.5(4)° fast rechtwinklig zur Ebene des Cp-Rings an. Das Yttriumatom besitzt eine Koordinationszahl von neun und bildet mit den koordinierenden Stickstoff-und Kohlenstoff-Atomen der beiden dmba-Liganden sowie dem Zentroid des η 5 -koordinierten Cp-Rings als Koordinationspolyeder eine Pyramide mit angenähert tetragonaler Grundfläche aus. Die Abstände der zum Zentralatom koordinierenden Atome sowie die Bisswinkel C33-M-N3 innerhalb der dmba-Liganden lassen sich mit Winkeln von 71.0(4)° (5) und 69.9(2)° (6) mit denen der homoleptischen Verbindung [Y(dmba) 3 ] (68.0(3)° bis 70.1(4)°) vergleichen.[30] Die Aromatisierung des Cp-Rings ist deutlich am Winkel zwischen der C1-Si-Bindung und der Ebene des Cp-Rings erkennbar. Liegt das C1-Atom im Liganden noch tetraedrisch koordiniert vor, so ist die C1-Si-Bindung im Komplex nur noch um 12(5)° aus der Cp-Ebene ausgelenkt. Allerdings macht sich auch hier der hohe sterische Anspruch des gesamten Ligandenregimes dadurch bemerkbar, dass zum einen der Cp-Ring nicht perfekt planar ist und zum anderen auch die Methyl-Substituenten des Cyclopentadienylrings leicht aus der Ebene ausgelenkt sind. Die gleichen Trends in den NMR-spektroskopischen und strukturellen Eigenschaften finden sich auch in dem diamagnetischen Lutetiumkomplex 6. Es handelt sich aufgrund der gleichen Anordung der sterisch anspruchsvollen chelatisierenden dmba-Liganden um einen Halbsandwichkomplex, wobei der Phosphazenrest nicht koordiniert vorliegt. Die geringfügig unterschiedlichen Bindungslängen und -winkel (Tab. 2) von 6 im Vergleich zu [(C 5 Me 4 SiMe 2 NPtBu 3 )Y(dmba) 2 ] (5) lassen sich auf den kleineren Ionenradius des Lutetiums als Zentralatom zurückführen. So ist z. B. der Abstand zwischen dem Lutetiumatom und dem Centroid des Cp-Rings kürzer als im verwandten Yttriumkomplex. Die Methylgruppen der SiMe 2 -Brücke stehen nicht mehr in einer Ebene mit dem Cp-Ring, sondern sind leicht aus dieser heraus gedreht (Abb. 5). Dies ist vermutlich auf die höhere sterische Repulsion der Liganden in Folge der kürzeren Abstände zu den dmba-Liganden sowie dem Cp-Ring zurückzuführen. Der Winkel der Si-N-P-Einheit im Yttriumkomplex beträgt 173.2(7)°, im Falle des Lutetiumkomplexes 166.4(3)°, wobei Unterschiede sehr wahrscheinlich auf Packungseffekten beruhen. Beide Komplexe 5 und 6 ähneln sich nicht nur strukturell, sondern auch in ihrer thermischen Stabilität: Sie sind 3 Tage bei 80°C in Benzol stabil. Somit erwarten wir ein ähnliches Reaktivitätsmuster dieser Diaryl-Halbsandwich-Verbindungen, das in kommenden Studien untersucht werden soll. Aufgrund der starken Luft-und Hydrolyseempfindlichkeit dieser Systeme konnten keine zufriedenstellenden Ergebnisse in der Massenspektroskopie wie auch in der Elementaranalyse erzielt werden. Zusammenfassung In diesem Beitrag präsentierten wir die Synthese von neuen Iminophosphoran-funktionalisierten Cyclopentadienylliganden als potentielle Kandidaten für Constrained-Geometry Komplexe. Die Ligandvorläufer 1-H bis 4-H lassen sich unerwarteter Weise nicht mit gängigen reaktiven Metallkomplexen metallieren, etwa homoleptischen Alkylen und Amiden von Metallen der Gruppe 3 und 4. Die offenbar zu geringe thermodynamische und kinetische Acidität dieser Liganden steht im krassen Gegensatz zu dem protischen Charakter der in der eigenen Arbeitsgruppe entwickelten Cyclopentadienyl-phosphazen-Liganden (B) mit innerzyklischer Phosphazen-Einheit. Dennoch konnte die Metallierung des Liganden [C 5 Me 4 -SiMe 2 -NPtBu 3 ]H 2-H unter Verwendung chelat-stabilisierter Triarylkomplexe der Seltenerdmetalle (SE) [SE(dmba) 3 ] (SE = Y, Lu) erreicht werdenmit 2 als Liganden konnten isoliert und vollständig durch NMR-Spektroskopie, Elementaranalyse und XRD-Strukturanalyse charakterisiert werden. Eine Koordination der Iminophosphoran-Funktionalität, die große Si-N-P Winkel von 166° bzw. 173° aufweist, scheint aufgrund sterischer Aspekte zumindest in den hier vorgestellten Komplexen mit neunfach koordiniertem Zentralatom nicht möglich zu sein. Derzeitige Arbeiten beschäftigen sich mit dem Koordinationsverhalten der sterisch weniger anspruchvollen, aber deutlich basischeren Tris(dimethylamino)iminphosphoran-Liganden gegenüber Seltenerdmetallen mit dem Ziel, die Koordinationszahl am Zentralatom durch nichtchelatisierende Organylliganden sowie durch Organylabstraktion und Bildung kationischer SEM-Organyle herab zu setzen. Somit könnte sich eventuell der Weg zu Constrained-Geometry Katalysatoren für die Olefin-Hydroaminierung oder Polymerisation eröffnen. Experimenteller Teil Alle Versuche wurden in heiß zusammengesetzten und im Ölpumpenvakuum (ca. 10 -2 mbar) abgekühlten Glasapparaturen (Schlenkrohrtechnik) unter einer Schutzgasatmosphäre von nachgereinigtem Argon 4.8 (Trocknung mit P 4 O 10 -Granulat) durchgeführt. Die Probenvorbereitung für die Spektroskopie, die Einwaage sowie die längerfristige Lagerung von luftempfindlichen Ausgangsverbindungen erfolgte in Gloveboxen (Typen MB150B-G-II und LabMaser 130, Fa. M. Braun) unter einer nachgereinigten Stickstoffatmosphäre. Die Lösungsmittel für luft-oder feuchtigkeitsempfindliche Reaktionen wurden nach Standardverfahren getrocknet[31] oder mittels Absorptionssäulen über Aluminiumoxid/Molsieb 3 Å/R3-11G-Katalysator (Fa. BASF) absolutiert. Die deuterierten Lösungsmittel für NMR-Messungen wurden ebenfalls nach Standardmethoden getrocknet und über Molsieb 3 Å gelagert. Die Ausgangsverbindungen der Seltenerdchloride wurden durch Lösen der entsprechenden Oxide in konzentrierter Salzsäure (p. A.) und anschließendes Abrauchen bei 90°C hergestellt. Die sich anschließende Entwässerung wurde nach der Methode von BAISCH et al.

  6 : δ = 7.16 ppm, d 8 -THF: δ = 3.58 ppm, 1.73 ppm. Die 13 C-NMR-Spektren wurden breitbandentkoppelt aufgenommen und auf das Lösungsmittelsignal kalibriert: C 6 D 6 : δ = 128.2 ppm, d 8 -THF: δ = 67.4 ppm, 25.2 ppm, CD 3 CN: 118.2 ppm. 31 P-NMR-Spektren wurden breitbandentkoppelt aufgenommen und extern gegen 85%ige Phosphorsäure kalibriert. Kopplungen zwischen Kern X und Kern Y mit Kernspin ½ über n Bindungen werden durch die Kopplungskonstante n J XY in Hz angegeben. Eine genaue Zuordnung der Signale erfolgte mittels 2D-NMR-Spektroskopie (COSY, HMQC und HMBC Experimente). Die Aufnahme der Massenspektren erfolgte an einem Finnigan MAT CH 7 (Elektronenenergie = 70 eV) und die Elementaranalysen (C, H, N) an einem Gerät des Typs CHN-Rapid der Firma Heraeus in der Analytikabteilung des Fachbereichs Chemie der Universität Marburg. Aufgrund der extremen Luftempfindlichkeit der Arylkomplexe konnten nicht immer zufriedenstellende Ergebnisse in der Massenspektroskopie wie auch in der Elementaranalyse erzielt werden.

  tBu 3 P=NH (3.71 g, 17.1 mmol) in 50 mL Hexan wurde bei 0°C (3-tertButyl-cyclopentadienyl)dimethylchlorosilan (1.87 g, 8.8 mmol) hinzugegeben. Über Nacht wurde die Suspension langsam auf RT gebracht und für 16 h gerührt. Der farblose Feststoff wurde über einer Umkehrfritte abfiltriert, zweimal mit Hexan gewaschen, und das Lösungsmittel des Filtrats wurde im Feinvakuum entfernt. Der entstehende Feststoff wurde aus Hexan bei -30°C kristallisiert. Es wurden 2.30 g (5.80 mmol, 66%) des Liganden 1-H in Form von farblosen Kristallen erhalten. Das Produkt ist gut löslich in Hexan, Benzol und Toluol. C 23 H 46 SiNP (M 395.3) C 69.57 (calc. 69.82), H 10.18 (11.72), N 3.62 (3.48)%.1 H-NMR (C 6 D 6 , 300.1 MHz): δ/ppm = 6.86 (m, 2H, CpH olef ), 6.52 (m, 1H, CpH olef ), 3.72 (s, 1H, CpH sp3 ), 1.39 (s, 9H, CptBu) 1.15 (d, 3 J H,P = 13.0 Hz, 27H, P(CMe 3 ) 3 ), 0.27 (s, 3H, SiCH 3 ), 0.22 (s, 3H, SiCH 3 ). 13 C-NMR (C 6 D 6 , 75.5 MHz): δ/ppm = 154.3, 135.5, 129.4, 125.6 (Cp), 56.5 (C ipso ), 40.1 (d, 1 J C,P = 54.0 Hz, P(CMe 3 ) 3 ), 32.5 (CpCMe 3 ), 31.0 (CpCMe 3 ), 29.7 (P(CMe 3 ) 3 ), 2.4 (SiCH 3 ), 1.7 (SiCH 3 ). 31 P-NMR (C 6 D 6 , 81.0 MHz): δ/ppm = 35.1. EI/MS: m/z (%) = 338 (1.0) [M-tBu] + , 274 (100.0), 218 (17), 160 (14), 104 (12), 59 (2).

  13 C-NMR (C 6 D 6 , 75.5 MHz): δ/ppm = 40.6 ((CH 3 ) 3 C Cq ), 30.4 ((CH 3 ) 3 C),16.6 (C ipso -CCH 3 ), 12.8 (CH 3 C=CCH 3 ), 6.9 (Si(CH 3 ) 2 ). Die drei Signale der Cq des C 5 Me 4 -Rings und des ipso-Cs sind nicht zu beobachten. 31 P-NMR (C 6 D 6 , 81.0 MHz): δ/ppm = 33.6. EI/MS: m/z (%) = 395 (1.0) [M] + , 290 (1.0), 274 (100.0), 218 (5.2), 160 (11.2), 104 (11.2), 59 (40.1).

  13 C-NMR (C 6 D 6 , 202.3 MHz): δ/ppm = 188.0 (d, 1 J C,Y = 44.0 Hz, C ar -Y), 146.3 (Cipso ar ), 138.8 (CH ar , m' ), 129.2 (CH ar , m ), 127.2 (CH ar, o ), 125.2 (CH ar, p ), 70.1 (CH 2, benzyl ), 46.8 (NCH 3 ), 45.6 (NCH 3 ), 40.3 (d, 1 J C,P = 54.1 Hz, PC(CH 3 ) 3 ), 29.7 (PC(CH 3 ) 3 ), 15.48 (C ipso CCH 3 ), 15.46 (C ipso CCH 3 ), 12.1 (H 3 CCCCH 3 ), 11.9 (H 3 CCCCH 3 ), 8.3 (SiCH 3 ), 7.8 (SiCH 3 ). Die Signale der quartären Kohlenstoffatome des Cp-Rings sind im 13 C-NMR-Spektrum nicht zu beobachten. 31 P-NMR (C 6 D 6 , 121.5 MHz): δ/ppm = 29.7. EI/MS: m/z (%) = 395 (7) [Ligand] + , 275 (23), 274 (100.0), 218 (8), 120 (13), 105 (11.2), 91 (7), 44 (8). [(C 5 Me 4 SiMe 2 NPtBu 3 )Lu(dmba) 2 ] (6) Lu(dmba) 3 (181 mg, 0.31 mmol) und C 5 Me 4 HSiMe 2 NPtBu 3 (95.0 mg, 0.24 mmol) wurden in Benzol (5 mL) gelöst. Die Lösung wurde 24 h bei 80°C gerührt. Benzol und H(dmba) wurden bei 40°C im Vakuum aus der Reaktionsmischung entfernt. Der zurückgebliebene braune Feststoff wurde in Hexan (5 mL) aufgenommen. Die Suspension wurde bei -30°C über Nacht gelagert. Dabei setzte sich ein farbloser Feststoff ab. Die Suspension wurde bei 2000 U/min für 20 min zentrifugiert, daraufhin wurde das Lösungsmittel dekantiert und der gelbliche Rückstand im Feinvakuum getrocknet. C 41 H 69 LuN 3 PSi (M 838.03) C 54.64 (calc. 58.76), H 8.20 (8.30), N: 4.27 (5.01)%. 1 H-NMR (C 6 D 6 , 300.1 MHz): δ/ppm = 8.00 (d,

  13 C-NMR (C 6 D 6 , 202.3 MHz): δ/ppm = 195.8 (C ar -Lu), 146.4 (Cipso ar ), 139.9 (CH ar , m' ), 129.2 (CH ar , m ), 125.2 (CH ar, o ), 124.7 (CH ar, p ), 70.2 (CH 2, benzyl ), 47.3 (NCH 3 ), 45.9 (NCH 3 ), 40.0 (d, 1 J C,P = 54.3 Hz, PC(CH 3 ) 3 ), 29.7 (PC(CH 3 ) 3 ), 16.7 (C ipso CCH 3 ), 15.7 (C ipso CCH 3 ), 12.3 (H 3 CCCCH 3 ), 12.1 (H 3 CCCCH 3 ), 8.3 (SiCH 3 ), 8.0 (SiCH 3 ).

  Über Nacht wurde die Suspension auf RT gebracht und bei RT 16 h gerührt. Das Lösungsmittel wurde im Vakuum entfernt, wobei ein hellgelber Feststoff erhalten wurde. Dieser wurde in Hexan (20 mL) aufgenommen, wobei eine gelbe Suspension entstand. Der farblose Feststoff wurde über eine Umkehrfritte abfiltriert, zweimal mit Hexan gewaschen, und das Lösungsmittel vom Filtrat wurde im Vakuum entfernt. Der zitronengelbe Rückstand wurde aus Hexan bei -30°C kristallisiert. Es wurden 387 mg (0.98 mmol, 53%) Ligand 2-H in Form von farblosen Kristallen erhalten. Das Produkt ist gut löslich in Hexan, Benzol und Toluol und schwerlöslich in Diethylether und THF. C 23 H 46 SiNP (M 395.3) C 66.84 (calc. 69.82), H 11.23 (11.72), N 3.17 (3.54)%. 1 H-NMR (C 6 D 6 , 300.1 MHz): δ/ppm = 2.86 (s, 1H, CH), 2.20 (s, 6H, HC ipso -CCH 3 ), 1.91 (s, 6H, CH 3 C=CCH 3 ), 1.08 (d, 3 J H,P = 12.7 Hz, 27H, C(CH 3 ) 3 ), 0.52 (s, 6H, Si(CH 3 ) 2 ).

	tetramethyl-cyclopenta-
	2,4-dienyl)-silanyl)-iminophosphoran (2-H)
	Zu einer Suspension von tBu 3 P=NH (699 mg, 3.22 mmol) in
	Toluol (30 mL) wurde bei 0°C Chloro-dimethyl-(2,3,4,5-
	tetramethyl-cyclopenta-2,4-dienyl)-silan (395 mg, 1.84 mmol)
	hinzugegeben.

2,4-dienyl-silanyl)-iminophosphoran (3-H)

  ) 2 ). 13 C-NMR (C 6 D 6 , 75.5 MHz): δ/ppm = 154.3, 135.4, 129.2, 125.3 (Cp), 56.1 ( 3 J C,P = 2.76 Hz, C ipso ), 32.5 (CpCMe 3 ), 37.3 (d, 2 J C,P = 3.3 Hz, P(NMe 2 ) 3 ), 32.4 (CpC q Me 3 ), 31.0 (CpCMe 3 ), 1.65 (Si(CH 3 ) 2 ). 31 P-NMR (C 6 D 6 , 161.9 MHz): δ/ppm = 15.2. für weitere 2 h gerührt. Über Nacht wurde die Lösung langsam auf RT gebracht und 14 h gerührt. Das Lösungsmittel wurde im Vakuum entfernt. Dabei wurde ein hellgelbes Öl erhalten. Der Rückstand wurde in Hexan (10 mL) suspendiert. Der farblose Feststoff wurde über eine Umkehrfritte abfiltriert, zweimal mit Hexan gewaschen, und das Lösungsmittel wurde vom Filtrat im Vakuum entfernt. Es wurden 745 mg (2.04 mmol, 82%) Ligand 4-H in Form einer gelben Flüssigkeit erhalten. Dieser ist gut mischbar mit Hexan, Benzol und Toluol. C 17 H 37 SiNP (M 356.3) C 49.37 (calc. 57.26), H 10.59 (10.46), N 17.64 (15.71)%. 1 H-NMR (C 6 D 6 , 300.1 MHz): δ/ppm = 3.05 (s, 1H, CpCH), 2.37 (d, 3 J H,P = 10.3 Hz, 18H, (N(CH 3 ) 2 ), 2.26 (s, 6H, HC-CCH 3 ), 1.95 (s, 6H, CH 3 C=CCH 3 ), 0.24 (s, 6H, Si(CH 3 ) 3 ). NMR (C 6 D 6 , 75.5 MHz): δ/ppm = 134.2 (Cq), 134.1 (Cq), 59.7 (d, 3 J C,P = 4.6 Hz, CH), 37.3 (d, 2 J C,P = 3.5 Hz, N(CH 3 ) 2 ), 15.2 (HC ipso -CCH 3 ), 11.6 (CH 3 C=CCH 3 ), 2.8 ((CH 3 ) 3 Si).

	Zu einer Lösung von (Me 2 N) 3 P=NH (0.43 mL, 2.37 mmol) in Hexan (8 mL) wurde bei 0°C (3-tertButyl-cyclopentadienyl) dimethylchlorosilan (255 mg, 1.19 mmol) hinzugegeben. Es fiel sofort ein farbloser Niederschlag aus. Über Nacht wurde die Suspension langsam auf RT gebracht und für 16 h gerührt. Der farblose Feststoff wurde über einer Umkehrfritte abfiltriert, zweimal mit Hexan gewaschen, und das Lösungsmittel wurde vom Filtrat im Feinvakuum entfernt. Es wurden 340 mg (0.95 mmol, 80%) von 3-H in Form eines gelben Öls erhalten. Das Produkt ist gut mischbar mit Hexan, Benzol und Toluol. C 17 H 37 N 4 PSi (M 356.3) C 50.61 (calc. 57.71), H: 9.35 (10.46), N: 16.83 (15.71)%. 1 H-NMR (C 6 D 6 , 300.1 MHz): δ/ppm = 6.78 (m, 2H, CpH olef ), 6.41 (m, 1H, CpH olef ), 3.62 (s, 1H, CpH sp3 ), 2.40 (d, 3 J H,P = 10.0 Hz, 18H, P(NMe 2 ) 3 ), 1.34 (s, 9H, CptBu), 0.15 (s, 6H, Si(CH 3 EI/MS: m/z (%) = 356 (14) [M] + , 298 (1.0), 235 (68), 192 (100.0), 149 (66), 102 (20.8), 44 (22). P-Tris(dimethylamino)-N-(dimethyl-(2,3,4,5-tetramethylcyclo-penta-2,4-dienyl-silanyl)-iminophosphoran (4-H) Zu einer Lösung von (Me 2 N) 3 P=NH (0.9 mL, 5.0 mmol) in Toluol (15 mL) wurde bei 0°C Chloro-dimethyl-(2,3,4,5-tetramethyl-cyclopenta-2,4-dienyl)-silan (540 mg, 2.5 mmol) hinzugegeben, und es wurde 31 P-NMR (C 6 D 6 , 81.0 MHz): δ/ppm = 14.9. EI/MS m/z (%) = 342 (1.0), 298 (1.0), 235 (66.8), 192 (100.0), 149 (46.7), 102 (20.8), 59 (5.4), 44 (18.9). [(C

13

C-

5 Me 4 SiMe 2 NPtBu 3 )Y(dmba) 2 ] (5)

  Y(dmba) 3 (317 mg, 0.64 mmol) und HC 5 Me 4 SiMe 2 NPtBu 3 (229 mg, 0.58 mmol) wurden in 7 mL Benzol gelöst. Die Lösung wurde 3 h bei 40°C und über Nacht bei 80°C gerührt. Benzol und H(dmba) wurden bei 40°C im Vakuum entfernt. Der zurückgebliebene braune Feststoff wurde mit Hexan (5 mL) aufgenommen. Nach 4 min im Ultraschallbad wurde die Suspension bei -30°C über Nacht gelagert. Die Suspension wurde bei 2000 U/min für 20 min zentrifugiert, daraufhin wurde das Lösungsmittel dekantiert. Der farblose Feststoff wurde im Vakuum getrocknet. C 41 H 69 YN 3 PSi (M 751.9) C 56.88 (calc. 65.49), H 6.92 (9.25), N 4.63 (5.59)%. 1 H-NMR (C 6 D 6 , 300.1 MHz) δ/ppm = 7.94 (d, 3 J H,H = 6.7 Hz, 2H, CpH ar ), 7.31 (t, 3 J H,H = 6.9 Hz, 2H, CpH ar ), 7.24 (t, 3 J H,H = 7.3 Hz, 2H, CpH ar ), 6.99 (d, 3 J H,H = 7.4 Hz, 2H, CpH ar ), 4.09 (d, 2 J H,H = 14.0 Hz, 2H, CH benzyl ), 3.01 (d, 2 J H,H = 13.7 Hz, 2H, CH benzyl ), 2.44 (s, 6H, NCH 3 ), 2.36 (s, 3H, C ipso CCH 3 ), 2.34 (s, 3H, C ipso CCH 3 ), 2.07 (s, 6H, NCH 3 ), 2.01 (s, 3H, H 3 CCCH 3 ), 1.82 (s, 3H, H 3 CCCCH 3 ), 1.07 (d, 27H, 3 J H,P = 12.6 Hz, C(CH 3 ) 3 ), 0.72 (s, 3H, SiCH 3 ), 0.43 (s, 3H, SiCH 3 ).

Danksagung

Der Deutschen Forschungsgemeinschaft danken wir für finanzielle Unterstützung im Rahmen des SPP 1166 (Lanthanoidspezifische Funktionalität), der Firma Chemetall, Frankfurt für die Spende von Lithiumorganylen und Herrn Dr. Ulrich Wietelmann, Chemetall, für interessante Diskussionen.


Bernhard Aicher

Kathrin Öxler

Prof. Dr Wolfgang Petz

Florian Öxler

Kathrin Aicher

Prof. Dr Bernhard Neumüller

Formation and Crystal Structures of Lewis Acid Adducts of Ph 3 PCHP(O)Ph 2 ; New Neutral and Cationic Species

Keywords: carbodiphosphorane, hydrolysis product, Lewis acid adducts, crystal structures Carbodiphosphorane, Hydrolysis product, Lewis acid adducts, Crystal structures

The carbodiphosphorane C(PPh 3 ) 2 (1) is easily hydrolyzed from wet air to give the ylide Ph 3 PCHP(O)Ph 2 (2), which forms addition compounds with various Lewis acids to give neutral or cationic compounds. According to pairs of electrons at the central carbon atom and the oxygen atom, respectively, addition compounds with coordination modes A (via oxygen), B (via carbon), and C (via carbon and oxygen) were isolated either as by-products from reactions of Lewis acids with 1 (contaminated with some 2) or directly with 2. The crystal structures and the spectroscopic properties of 2 and of the addition

Ph 3 PCH 2 P(OBI 3 )Ph 2 ][BI 4 ] (7), [Ph 3 PCHP(OSnCl 2 )Ph 2 ] (8), and [Ph 3 PCH 2 P(O)Ph 2 ] 2 [Hg 2 I 6 ] (9) are reported. Ph 3 PCHC(O)R in which the P(O)Ph 2 group of 2 is replaced by C(O)R and which exhibits rich coordination chemistry [5].

Introduction

The carbodiphosphorane C(PPh 3 ) 2 (1) and its hydrolysis product Ph 3 PCHP(O)Ph 2 (2) were first described in 1961 by Ramirez et al. [1]. Whereas various addition compounds of 1 have been synthesized up to now [2], the chemistry of 2 remained unexplored for many years. An earlier reported platinum complex with a side on bounded C(PPh 3 ) 2 ligand [3] was later identified as pure 2 [4]. 2 can be seen as an ylide derived from the ylide CH 2 PPh 3 by replacing one proton by the P(O)Ph 2 group or as a derivative of the phosphane oxide OPPh 3 in which one Ph group is replaced by the ylidic group CHPPh 3 . To our knowledge, further compounds of the type Ph 3 PCHP(E)Ph 2 with E other than O have not been reported so far.

Thus, the chemistry of 2 should be related to both, CH 2 PPh 3 and OPPh 3 . In principle, 2 is endowed with two anchor points for Lewis acids (LA), the free pair of electrons at the ylidic carbon atom between the P atoms and a pair of electrons at the oxygen atom. Therefore, 1:1 adducts with sp 2 (A) and sp 3 carbon atoms (B) or 1:2 adducts with an sp 3 (C) carbon atom are expected as depicted in Scheme 1. Coordination modes A and B represent hard and soft coordination sites, respectively, of the ylide. In the coordination mode C, the ylide 2 can also act as a chelating ligand. In principle, 2 is related to the carbonyl-stabilized ylides of the type with wet air; the resulting 2 is soluble in toluene and can be precipitated by addition of n-pentane. However, direct addition of water to 1 is not successful; only decomposition products were obtained.

C(PPh 3 ) 2 + H 2 O → Ph 3 PCHP(O)Ph 2 + C 6 H 6 (1)

1 2
The 31 P NMR spectrum of 2 exhibits two characteristic doublets with coupling constants 2 J(P,P) = 19 Hz indicating chemically different phosphorus atoms; the low field signal can be attributed to the PO group. A strong solvent dependency of the shifts is observed, and the shift difference ∆ between the doublets range between 4.4 and 7.4 ppm, depending on the nature of the solvent. In the IR spectrum the PO stretching vibration cannot be assigned with certainty, because in the region between 1250 and 1100 cm -1 several strong bands were recorded. However, a very strong band at 1171 cm -1 seems to be reliable; the P-O vibration of Ph 3 PO appears at about 1190 cm -1 [8,9].

The majority of compounds based on 2 were obtained in small amounts as side-products during our efforts to prepare addition compounds LA←1 between the double ylide and various Lewis acids LA, such as compounds of group 13 elements, and attempts to obtain crystals from the crude reaction products. In general, the reactions with 1 were carried out in toluene, because the use of halogenated hydrocarbons or even THF, DME, or DMSO led to deprotonation of the solvents with formation of the cations (HC{PPh 3 } 2 ) +

or (H 2 C{PPh 3 } 2 ) 2+ . Unfortunately, the resulting adducts LA←1 were insoluble in toluene and other nonpolar solvents, preventing sufficient characterization by NMR and X-ray analyses; however, few crystals were sporadically obtained from freshly prepared filtered toluene solutions. In most cases the precipitates from toluene are soluble in DMSO or halogenated solvents, but the 31 P NMR spectra show only the signal of the cation (HC{PPh 3 } 2 ) + , indicating reaction with the solvent with proton abstraction. This is confirmed by IR experiments in which the spectra changed after the precipitates had got contact to polar solvents showing the characteristic medium intense bands of the cation at 1032, 1013, and 991 cm - (5,8), B (9), and C (6,7).

Thus, the type A compound [Ph 3 PCHP(OBF 3 )Ph 2 ] (5) formed when 1, containing small amounts of 2 (as shown by 31 P NMR spectroscopy), was allowed to react with gaseous BF 3 in toluene; colorless crystals of 5 separated in low yield from the toluene solution, and the desired adduct F 3 B←1 precipitated without forming crystals suitable for an X-ray analysis. Upon coordination of BF 3 at the O atom of 2, both doublets experienced a high field shift in the 31 P NMR spectrum of 5. Attempts to prepare 5 directly from 2 and 7) was obtained as the only crystalline product, and the desired adduct I 3 B←1 could not be identified; instead, only the salt (H 2 C{PPh 3 } 2 )[I 3 ]I [10] was isolated upon attempts to recrystallize the crude material from acetonitrile. The HI needed for protonation probably

Wiley-VCH

ZAAC

formed upon borylation and deprotonation of the appropriate solvents. The 31 P NMR spectrum of 7 in DCM exhibits a doublet at 16.20 ppm ( 2 J(P,P) = 20.35 Hz) and a multiplet at 54.55 Hz, according to PPh 3 and P(OBI 3 )Ph 2 phosphorus atoms, respectively. Relative to the starting compound 2, the low field signal has become more deshielded, whereas the high field signal has experienced a high field shift in going to the addition compounds 6 and 7. As yet, only type C compounds were detected in which the Lewis acid at the carbon atom is H + , thus producing salt like compounds. Solvent reactions with proton abstraction of addition compounds with 1 and other Lewis acids were reported recently [11].

If 2 was allowed to react with anhydrous SnCl 2 in DCM the neutral type A addition complex [Ph 3 PCHP(OSnCl 2 )Ph 2 ] ( 8) could be prepared in high yields and characterized by X-ray analysis. The 31 P NMR spectrum of a freshly prepared sample in DCM exhibits two doublets at 38.74, 18.18 ppm (set A) which disappeared within some hours in favor of doublets at 22.96, 21.33 (set B). The set B persisted and was observed as the only signals after isolation of the product indicating the formation of only one type of compounds. The initial signals of set A apparently belong to an intermediate which could not be identified so far. The IR spectrum of 8 exhibits a new strong band at 1018 cm -1 not found in 2, which can be assigned to the P-OSn vibration.

A quite different reaction pathway was found upon reacting 2 with HgI 2 in THF. The clear solution showed a set of two doublets at 21.58 and 20.79 ppm ( 2 J(P,P) = 14.35 Hz) along with a set of two broad signals at 27.8 and 26.0 ppm in about 1:1 ratio. Attempts to grow crystals gave colorless crystals suitable for X-ray analysis and a pale yellow micro crystalline material which was unsuitable for X-ray analysis. The colorless crystals turned out to be the salt like compound [Ph 3 PCH 2 P(O)Ph 2 ] 2 [Hg 2 I 6 ] (9). The salt can be considered as the first compound of the type B containing a "free" PO group as in 2 but a protonated ylidic carbon atom, thus being its conjugated acid. An alternative pathway, the addition of HgCl 2 at the carbon atom, as expected, could not be found. However, the formation of such kind of adduct as intermediate can neither be excluded nor be established; no other type of crystals was found. It could be responsible for the unusual Wiley-VCH ZAAC deprotonation of the solvent. The IR spectrum of 9 exhibits a strong band at 1184 cm -1 , which probably can be assigned to the P-O vibration.

Crystal structures

For comparison and for documentation of the changes in the parameters upon adduct formation we have also studied the crystal structure of 2; colorless crystals separated from a toluene solution after layering with npentane. Crystals of 5 (adduct of the type A) were obtained as described above. The related H[HOB 2 F 6 ] adduct 6 was obtained from the reaction of 2 with [F 3 1; bond lengths and angles are summarized in Tables 2 to 7.

3.1 Crystal structure of Ph 3 PCHP(O)Ph 2 (2) The unit cell of 2 contains two independent molecules, the parameters of which, however, differ only slightly, and only one molecule is depicted in Figure 1. As expected, the C-P distances to the ylidic carbon atom are different. The C-PPh 3 bond length amounts to 168.8(3) pm while the C-P(O)Ph 2 bond is longer with 171.7(3) pm. The short P-C bond is located between that of C(PPh 3 ) 2 (163.5) [12] and that of the cation (HC{PPh 3 } 2 ) + (mean value of 169.9 pm from about 10 compounds) [7], indicating a decreasing

-17 ≤ k ≤ 17 -22 ≤ l ≤ 22 -14 ≤ h ≤ 14 -17 ≤ k ≤ 17 -20 ≤ l ≤ 20 -12 ≤ h ≤ 12 -13 ≤ k ≤ 13 -19 ≤ l ≤ 19 -13 ≤ h ≤ 13 -17 ≤ k ≤ 18 -17 ≤ l ≤ 17 -15 ≤ h ≤ 18 -25 ≤ k ≤ 25 -21 ≤ l ≤ 22 -14 ≤ h ≤ 12 -13 ≤ k ≤ 13 -31 ≤ l ≤

SHELXS-97

direct methods SIR-92 [START_REF] Altomare | Sir-92[END_REF] direct methods SIR-92 [START_REF] Altomare | Sir-92[END_REF] direct methods

SHELXS-97

direct methods SIR-92 [START_REF] Altomare | Sir-92[END_REF] direct methods SHELXS-97 [START_REF] Sheldrick | SHELXS-97, Programm zur Lösung von Kristallstrukturen[END_REF] Page 9 of 50

Wiley-VCH ZAAC 10 [15] [15]
Refinement against F 2 SHELXL-97 [START_REF] Sheldrick | SHELXL-97, Program for the refinement of Crystal Structures[END_REF] SHELXL-97 [START_REF] Sheldrick | SHELXL-97, Program for the refinement of Crystal Structures[END_REF] SHELXL-97 [START_REF] Sheldrick | SHELXL-97, Program for the refinement of Crystal Structures[END_REF] SHELXL-97 [START_REF] Sheldrick | SHELXL-97, Program for the refinement of Crystal Structures[END_REF] SHELXS-97 [START_REF] Sheldrick | SHELXS-97, Programm zur Lösung von Kristallstrukturen[END_REF] SHELXL-97 [START_REF] Sheldrick | SHELXL-97, Program for the refinement of Crystal Structures[END_REF] Flack (2) with thermal ellipsoids at 40% probability, the hydrogen atoms are omitted for clarity. 2) 1) 116( 2 bonded to the oxygen atom instead of BF 3 , however, the related P-C bond lengths are those of 2, but according to large standard deviations in the tungsten complex, these values should be discussed with caution [6]. 4)

P(2) -C(1) -H(
C( 1) -H( 1) 87( 3) C( 1) -H( 2) 97( 3)

F(4) -B(2) 137.8(4) F(5) -B(2)
137.8( 4) 20) 175( 1) 26) 178( 1) O( 1) -B( 1) 148( 1) 2) 228( 1) I( 5) -B( 2) 222( 2) 2) 224( 2) I( 7) -B( 2) 222( 1 pm, which is shorter than that in the comparable complex [Cl 2 Sn(OC(O)C{PPh 3 } 2 )] (214.3(4) pm) described by us recently [22]. Similar Sn-O bond lenghts in SnCl 2 addition compounds vary between 252 pm in the dioxane adduct [23] and 230 pm in the dihydrate [24]; the structures of other compounds with the simple Table 6. Selected bond lengths/pm and angles/° in 8.

F(6) -B(2) 135.3(4) F (
P(2) -C(
C(1) -H(1) 99 C(1) -H(2) 99 I(4) -B(
I(6) -B(

P(1) -O(1)

156( 1

Conclusion

The majority of the compounds presented here are side-products which were obtained with low yields during various runs for preparing addition compounds of the type LA←1 and not as a result of specific syntheses. Although 2 was only present in trace amounts in the starting material the adducts preferentially crystallized. It turned out that these are more soluble, less sensitive to polar solvents, and show better crystallization properties than those with 1. In part, this was also the case during the reaction of AlBr Here we could show that the neutral compound Ph 3 PCHP(O)Ph 2 (2) has a free pair of electrons at the carbon atom and can be protonated; the results of attempted alkylation will be reported elsewhere. Other Lewis acids such as group 13 or group 14 electron deficient compounds prefer the PO oxygen atom. Thus, adducts of the type A, B, and C of Scheme 1 could be realized with Lewis acids at the oxygen atom, the carbon atom, and at both atoms, respectively. In addition to the results reported, 2 is assumed to act as a chelating ligand with formation of a four-membered MCPO ring; however, no such compound could be isolated so far. Those compounds would have a constrained geometry and may act as catalysts for olefin polymerization

[25]. [Ph 3 PCP(O)Ph 2 ] -← Ph 3 PCHP(O)Ph 2 → [Ph 3 PCH 2 P(O)Ph 2 ] + (2) 2 9
In addition, the proton at the carbon atom of 2 may also be replaced with strong Lewis bases to produce a double ylide-like anion (equation 2 left side) such as in complexes with the dianion [Ph 2 (E)P-C-P(E)Ph 2 ] 2- (E = NR, S) [26], but as yet, the acidity of this proton and the assumed amphoteric character of 2 is still unexplored. Further studies on the chemistry of 2 are currently in progress.

Experimental Details

All operations were carried out under an argon atmosphere in dried and degassed solvents using Schlenk techniques. The solvents were thoroughly dried and freshly distilled prior to use. The IR spectra were run on a Nicolet 510 spectrometer in Nujol mull. For the 31 P NMR spectra we used the instrument Bruker AC 200.

Elemental analyses were performed by the analytical service of the Fachbereich Chemie at the Philipps Universität Marburg (Germany). The carbodiphosphorane C(PPh 3 ) 2 (1) was prepared according to a

Page 26 of 50

Wiley-VCH ZAAC modified literature procedure [27]. [BF 3 (OEt 2 )] was commercially obtained and used without further purification. BI 3 was obtained according to the procedure described in [START_REF] Brauer | Handbuch der Präparativen Anorganischen Chemie[END_REF].

Ph 3 PCHP(O)Ph 2 (2).

A suspension of 2.3 g of 1 (4.3 mmol) in about 40 ml toluene was stirred in a 100 ml flask. The neck was closed by glass wool to allow a slow admission of moist air. After about 2 h the yellow color of 1 had disappeared and a colorless suspension was obtained. The solution was filtered from small amounts of an insoluble material. From the clear solution 1 could be precipitated as colorless crystals by layering with n-pentane. Yield 1.9 g (4.0 mmol, 95% yield). 31 Formation of [Ph 3 PCHP(OBF 3 )Ph 2 ] (5). A solution of 0.59 g of 1 (1.1 mmol) containing small amounts of 2 (identified by 31 PNMR spectroscopy) in 20 ml of toluene was admitted to an atmosphere of gaseous BF 3

for about 1 hour and the mixture was stirred mechanically. A colorless precipitate formed immediately.

After several days of standing, colorless whiskers of 5 had grown from the filtered solution. 31

F 3

 3 B←OEt 2 or BF 3 in toluene gave a precipitate which upon recrystallization from CH 2 Cl 2 /n-pentane produced the type C compound [Ph 3 PCH 2 P(OBF 3 )Ph 2 ][(µ-OH)B 2 F 6 ] (6) in good yields; source for the additional proton are the solvent or impurities in [F 3 B(OEt 2 )]. In the 31 P NMR spectrum of 6 a doublet at 17.53 ppm ( 2 J(P,P) = 17.80 Hz) and a multiplet at 45.63 ppm were measured, which were assigned to PPh 3 and P(OBF 3 )Ph 2 phosphorus atoms, respectively. Similarly, from the reaction of 1 with BI 3 in toluene the type C complex [Ph 3 PCH 2 P(OBI 3 )Ph 2 ][BI 4 ] (

) 3 . 2

 32 Crystal structure of [Ph 3 PCHP(OBF 3 )Ph 2 ] (5) The molecular structure of 5 is shown in Figure 2. The coordination of a BF 3 molecule at the oxygen atom of 2 leads to an elongation of the P-O bond length by about 8 pm to 157.3(3) pm indicating a dramatic loss of π character; this is less operative in [(Ph 3 PO)BF 3 ], where the elongation amounts to 4 pm only [18]. A similar elongation is found in the compounds [(Ph 3 PO)AlX 3 ] (X = Cl, Br) [19]. As counterweight, the B-O bond length in 5 of 148.8(6) pm is appreciably shorter than that in [(Ph 3 PO)BF 3 ] (151.6(6) pm). The P-O-B angles in both compounds are close together with 133.4(3) in 5 and 134.5(2) in the phosphane oxide adduct. In going from 2 to 5 the P-C-P angle opens to 131.7(3)°. The influence of the Lewis acid induces also changes in the P-C bonding situation. With the C-P(O)Ph 2 bond length of 168.1(4) and the C-PPh 3 bond length of 171.6(4) a reverse situation to 2 occurs with a shifting of the partial double bond to the other side, more directed to the PO group. The same effects on the P-O bond are observed in 2 were a W(CO) 5 group is

Figure 2 .

 2 Figure 2. Molecular structure of [Ph 3 PCHP(OBF 3 )Ph 2 ] (5) with thermal ellipsoids at 40% probability, the

3

 3 Crystal structure of [Ph 3 PCH 2 P(OBF 3 )Ph 2 ][(µ-OH)B 2 F 6 ] (6) In the solid state the compound forms a centrosymmetric dimer and the two units are linked by H⋅⋅⋅⋅F bridges. A further H⋅⋅⋅⋅F bridge exists between H(2) and F(4) of the anion with a C(1)-H(2)⋅⋅⋅⋅F(4) distance of 326.1(4) pm. The complex can be seen as a protonation product upon addition of the hypothetical acid H[HOB 2 F 6 ] at the Lewis base 5, and the crystal structure of the dimer unit is shown in Figure 3. The unusual Page 14 of 50 Wiley-VCH ZAACand as yet unique anion [HOB 2 F 6 ] -was described earlier with a carbenoid counter cation[20]. The bonding situation around the P-C-P group changed dramatically upon conversion of the central sp 2 carbon atom into a sp 3 carbon atom on protonation to give a type C salt. According to a missing back donation, the P-C bond lengths increased to 181.3(3) and 179.9(3) pm and correspond to normal single bonds. The P-O bond length amounts to 152.9(2) and is in between that of 1 and 5. Relative to 5 the B-O bond length increased by about 5 pm to 154.2(4) pm, while the P-O-B angle remained unchanged. The P-C-P angle moved into the direction of that of an sp 3 carbon atom but with 119.9(2)º remains still large, probably according to steric repulsion between the phenyl groups. The other angles in the distorted tetrahedral environment of the carbon atom range between 100° (H-C-H) and 111° (P-C-H).

Figure 3 .

 3 Figure 3. Molecular structure of [Ph 3 PCH 2 P(OBF 3 )Ph 2 ][(µ-OH)B 2 F 6 ] (6). The two cations and two anions

F( 1 ) 4

 14 -B(1) -F(2) 110.4(3) F(1) -B(1) -F(3) 110.8(4) F(1) -B(1) -O(1) 106.9(3) F(2) -B(1) -F(3) 114.9(4) Crystal structure of [Ph 3 PCH 2 P(OBI 3 )Ph 2 ][BI 4 ] (7⋅C 7 H 8 ) The compound crystallizes with one disordered toluene molecule without contacts to the salt-like compound and the molecular structure of 7 is shown in Figure 4. The replacement of the BF 3 group by the BI 3 group has no dramatic effect on the parameters of the cation; only the B-O bond is about 5 pm shorter and close to that of 5 which is due to the stronger Lewis acidity of BI 3 relative to BF 3 . The P-C bond lengths show the same trend as reported for the cation of 6. Weak H bridges between H(2) of the cation and I(4) of the anion exist (C(1)-H(2)⋅⋅⋅⋅I(4) = 399(1) pm), which lead to a long B(2)-I(4) distance of 228(1) pm relative to the three others with a mean B-I distance of 223 pm; all B-I distances are about 10 pm longer than those in the planar BI 3 molecule [21].

Figure 4 .

 4 Figure 4. Molecular structure of [Ph 3 PCH 2 P(OBI 3 )Ph 2 ][BI 4 ] (7). The ellipsoids are drawn at a 40%

5 ,

 5 the tin derivative 8 can be considered as type A compound; the molecular structure is depicted in Figure5. Thus, the relevant bond lengths P(1)-O, P(1)-C(1), and P(2)-C(1), which are influenced by the coordination of the tin atom, show the same trend in shifting of the partial double bond more directed to the PO bond relative to the starting compound 2. The Sn-O bond length amounts to 212(1)

Cl 2 Figure 5 .

 25 Figure 5. Molecular structure of [Ph 3 PCHP(OSnCl 2 )Ph 2 ] (8). The ellipsoids are drawn at a 40% probability

6

 6 Crystal structure of [Ph 3 PCH 2 P(O)Ph 2 ] 2 [Hg 2 I 6 ] (9) The protonation of 2 produces the cation of 9, its conjugated acid and a change in rehybridization of the carbon atom from planar sp 2 to tetrahedral sp 3 occurred with interruption of the π conjugation in the P-C-P-O spine. The molecular structure is shown in Figure 6. Upon protonation, both P-C bond lengths have increased by about 10 pm with respect to 2 being now in the range of a normal P-C single bond; however, the prevailing C-P(O) bond lengths in 2 and 9 are about 2 to 3 pm longer. The P-O bond length remains nearly unchanged. The addition of a further Lewis acid at the oxygen atom as in 6 or 7 leads to an increase of the P-O bond by about 5 pm. In the crystals of 9 ion triples are present, held together by H•••••I bridges (C(1)•••••I(2) = 388.6(8) pm) which are stacked along H•••••H-O bridges as shown in Figure 7. The dianion is located around an inversion center causing the fourmembered Hg-I-Hg-I ring to be completely planar, and both Hg atoms are in a distorted tetrahedral environment.

Figure 6 .

 6 Figure 6. Molecular structure of [Ph 3 PCH 2 P(O)Ph 2 ] 2 [Hg 2 I 6 ] (9). The ellipsoids are drawn at a 40%

Figure 7 .

 7 Figure 7. Crystal packing diagram of compound 9 viewed along the b axis; hydrogen contacts are indicated

3 with 1

 1 in toluene, where a couple of colorless crystals of the adduct Br 3 Al←1 have grown from a saturated toluene solution overnight and among them very few yellow crystals of 3[7]. However, in the majority of reactions with C(PPh 3 ) 2 and Lewis acids in toluene or benzene no crystals of the appropriate addition compounds from the saturated solutions as yet and attempts to get crystals have failed according to the properties mentioned above.

  P NMR (CH 2 Cl 2 , 200 MHz, 298 K): 25.8 (d, PO), 19.2 (d, PPh 3 ) ppm, 2 J(P,P) = 19.7 Hz, ∆ = 6.66 ppm); similar values were obtained in CHCl 3 (25.3, 18.6 ppm, 2 J(P,P) = Hz, ∆ = 7.39 ppm), THF (26.7, 21.5 ppm, 2 J(P,P) = Hz, ∆ = 4.15 ppm), DMSO (25.2, 19.0 ppm, 2 J(P,P) = 20.4 Hz, ∆ = 6.15 ppm), and toluene (25.3, 20.6 ppm, 2 J(P,P) = 19.7 Hz, ∆ = 4.65 ppm) solutions. Remarkable is the shift difference ∆ between the two doublets in the respective solvents. IR (Nujol mull, cm -1 ): 1479 s, 1435 vs, 1306 w, 1198 s, 1184 sh, 1171 vs, 1165 s, 1150 s, 1113 vs, 1100 vs, 1069 m, 1028m, 995 sh, 984 s, 964 s, 806 w, 789 w, 764 m, 750 s, 743 s, 714 vs, 694 vs, 569 m, 536 vs, 518 s, 500 s, 444 w.

Figure 1 .Figure 2 .

 12 Figure 1. Molecular structure of Ph 3 PCHP(O)Ph 2(2) with thermal ellipsoids at 40%

Figure 3 .Figure 4 .Figure 5 .Figure 6 .Figure 7 .

 34567 Figure 3. Molecular structure of [Ph 3 PCH 2 P(OBF 3 )Ph 2 ][(µ -OH)B 2 F 6 ] (6). The two cations

  . In this contribution we concentrate on the discussion of addition products of 2 either obtained as side-products by reactions of 1 with Lewis acids or upon reaction of 2 with Lewis acids, and the results are sketched in Scheme 2.

			H		H		H
			C	O	LA	C		O	LA
		Ph 3 P		P Ph 2	Ph 3 P		P Ph 2
	LA	_	BF 3	SnCl 2	LA	_	BF 3	BI 3
		2	5	8		9	6	7

+

Scheme 2. Compounds of the coordination modes A

compound 8 and the type B salt 9. The structures of 2, 5, 6, 7⋅

	B(OEt 2 )], and crystals of 7⋅ ⋅ ⋅ ⋅C 7 H 8 formed from a
	toluene solution; the adducts are of the type C. Additionally, we have obtained crystals of the type A
	⋅ ⋅ ⋅C 7 H 8 , 8, and 9 are shown in Figures 1 to 6;
	crystallographic data are collected in Table

Table 1 .

 1 Crystal data and structure refinement details for the compounds 2

	P-C double

, 5, 6, and 7⋅

							ZAAC						Page 8 of 50
	Temperature/K	193		100		193		173		⋅ ⋅ ⋅C 7 H 8 , 8, and 9. 100	193
	µ /cm -1	2.1	2	2.1	5	2.2	6	48.9	7⋅C 7 H 8	12.35	8	76.36	9
	Formula 2θ max /°	C 31 H 26 OP 2 52.34	C 31 H 26 BF 3 OP 2 C 31 H 28 B 3 F 9 O 2 P 2 C 38 H 35 B 2 I 7 OP 2 C 31 H 26 Cl 2 OP 2 Sn C 62 H 45 Hg 2 I 6 O 2 P 4 52.10 55.22 52.12 52.10 52.42
	Mw/g•mol -1 Index range	476.49 -12 ≤ h ≤ 12	544.30		697.92		1479.56	666.05		2117.51
	a/pm	1004.8(1)	1151.7(2)	988.6(2)	1108.0(1)	1496.9(2)	1194.0(1)
	b/pm	1476.5(2)	1392.1(2)	1059.4(2)	1476.5(2)	2061.0(3)	1094.2(1)
	c/pm	1832.9(3)	1653.8(3)	1722.5(2)	1444.4(2)	1825.0(2)	2552.1(2)
	α/°	107.93(1)	90		79.46(2)	90		90		90
	β/°	98.55(1)	97.63(1)	78.46(2)	106.50(1)	90		100.36(1)
	γ/°	101.09(1)	90		65.68(2)	90		90		90
	Crystal size/mm 0.32×0.14×0.08 0.17×0.17×0.04 0.14×0.06×0.05 0.24×0.09×0.05 0.13×0.12×0.04 0.18×0.11×0.09
	Volume/pm 3 ⋅10 6 2475.2(6)	2628.0(8)	1600.5(5)	2265.7(5)	5630(1)		3279.9(5)
	Z	4		4		2		2		8		2
	d calc /g•cm -3	1.279		1.376		1.448		2.169	1.571		2.144
	Crystal system	triclinic	monoclinic	triclinic		monoclinic	orthorhombic	monoclinic
	Space group	Pī (No. 2)	P2 1 /n (No. 14) Pī (No. 2)	P2 1 (No. 4)	Pbca (No. 61)	P2 1 /n (No. 14)
	Diffractometer	IPDS I (Stoe)	IPDS II (Stoe) IPDS I (Stoe)	IPDS II (Stoe) IPDS II (Stoe)	IPDS I (Stoe)
	Radiation	Mo-K α		Mo-K α		Mo-K α		Mo-K α	Mo-K α		Mo-K α
							Wiley-VCH

Table 2

 2 Selected bond lengths/pm and angles/° in one of the two independent molecules of 2

	Page 11 of 50		ZAAC
	P(1) -O(1)	148.9(2)	P(1) -C(1)	171.7(3)
			Wiley-VCH

P(1) -C(2) 181.2(3) P(1) -C(8) 182.2(3) P(2) -C(1) 168.8(3) P(2) -C(14) 182.0(3)

Table 3 .

 3 Selected bond lengths/pm and angles/° in 5.

	Page 13 of 50		ZAAC
	P(1) -O(1)	157.3(3)	P(1) -C(1)	168.1(4)
	P(1) -C(2)	179.7(4)	P(1) -C(8)	179.7(4)
			Wiley-VCH

C(1) -P(2) -C(26) 112.0(2) C(14) -P(2) -C(20) 104.8(2) C(14) -P(2) -C(26) 107.2(2) C(20) -P(2) -C(26) 108.2

Table 4 .

 4 Selected bond lengths/pm and angles/° in 6.

	P(1) -O(1)	152.9(2)	P(1) -C(1)	179.9(3)
	P(1) -C(2)	178.5(3)	P(1) -C(8)	177.3(3)
	P(2) -C(1)	181.3(3)	P(2) -C(14)	178.6(3)
	P(2) -C(20)	177.7(3)	P(2) -C(26)	178.2(3)
	F(1) -B(1)	138.8(4)	F(2) -B(1)	134.2(4)
	F(3) -B(1)	133.6(4)	O(1) -B(1)	154.2(

Table 5 .

 5 Selected bond lengths/pm and angles/° in 7⋅ ⋅ ⋅ ⋅C 7 H 8 .

	I(1) -B(1)	221(1)	I(2) -B(1)	222(1)
	I(3) -B(1)	229(1)	P(1) -C(1)	180(1)
	P(1) -C(2)	177.0(9)	P(1) -C(8)	179(1)
	P(1) -C(14)	176(1)	P(2) -O(1)	154.5(1)
	P(2) -C(1)	180.4(8)	P(2) -C(

Table 7 .

 7 Selected bond lengths/pm and angles/° in 9.

Ph 3 PCH 2 P(OBF 3 )Ph 2 ][HOB 2 F 6 ] (6).

  The main product, probably the adduct F 3 B←1, dissolves in DMSO, and the 31 P NMR shows a signal at 20.8 ppm indicating the formation of the cation (HC{PPh 3 } 2 ) + via proton abstraction from the solvent. Similar behavior was observed with other polar solvents such as DCM, DCE, and THF, therefore the structure of the precipitate could not be identified as yet. From 2 and [BF 3 (OEt 2 )]: 0.1 ml of [BF 3 (OEt 2 )] (0.8 mmol) was layered in a Schlenk tube with 2 ml of toluene. This mixture was layered with a solution of 0.05 g of 2 (0.11 mmol) in ca 1 ml of toluene and allowed to stand overnight. Colorless crystals of 6 separated. and BF 3 : A solution of 0.20 g of 2 (0.42 mmol) in about 20 ml of toluene was contacted with a bulb containing gaseous BF 3 . After some days crystals of 6 formed at the surface of the solution. The precipitate was filtered and dried in vacuum.31 P NMR (CD 2 Cl 2 , 200 MHz, 298 K): 45.69 (m, PO), 17.55 (d, PPh 3 ), 2 J(P,P) = 17.80 Hz. Another set of two doublets at 23.54 and 18.75 ppm ( 2 J(P,P) =

	P NMR (CH 2 Cl 2 , 200 MHz, 298 K): 21.02, 19.38 ppm, 2 J(P,P) = 12.71 Hz. IR (Nujol mull, cm -1 ): 1613 m, 1588 w, 1487 w, 1441 st, 1358 m, 1196 st, 1154 st, 1113 st, 997 m, 922 w, 903 w, 862 m, 883 st, 797 st, 739 st, 710 w, 685 st, 660 w, 579 m, 564 w, 507 m, 501 m, 488 m. C 31 H 36 BF 3 OP 2 , found C 67.4, H 5.1, calcd C 68.4, H ZAAC Formation of [31 P NMR (CH 2 Cl 2 , 200 MHz, 298 K): 45.63 (m, PO), 17.54 (d, PPh 3 ), 2 J(P,P) = 17.80 Hz. IR (Nujol mull, cm -1 ): 2723 m, br (ν(OH)), 1589 w, 1485, w, 1439 s, 1406 w, 1367 m, 1341 w, 1173 to 1117 vs (ν(BF)), 1034 m, 999 m, 856 s, 847 s, 801 s, 781 s, 743 vs, 731 s, 689 s, 600 w, 579 w, 557 w, 505 m, 490 m. 6 was also obtained from 2 13.99 Hz) belongs to 5. 4.8%. Page 27 of 50 Formation of [
	Wiley-VCH

Ph 3 PCH 2 P(OBI 3 )Ph 2 ][BI 4 ] (7) and (H 2 C{PPh 3 } 2 )[I 3 ]I

	. Solutions of 0.24g (0.45 mmol) of 1
	and of 0.84 g (2.14 mmol) of BI 3 , each in about 10 ml of toluene, were combined at room temperature. The
	resulting precipitate was filtered. In the filtrate small yellow crystals had formed after several days which
	turned out to be 7⋅C 7 H 8 . 31 P NMR (CH 2 Cl 2 , 200 MHz, 298 K): 54.55 (m, PO), 16.20 (d, PPh 3 ), 2 J(P,P) =
	16.35 Hz). IR (Nujol mull, cm -1 ): 1558 m, 1480 m, 1439 s, 1339 w, 1312 w, 1213 m, 1181 s, 1161 m, 1099
	w, 1074 w, 1028 w, 997 w, 963 m, 745 m, 735 m, 721 s, 710 w, 696 m, 687 m, 648 w, 536 s, 509 s. Part of
	the precipitate was dissolved in MeCN. After five days needle-like orange red crystals separated which
	turned out to be the salt (H 2 C{PPh 3 } 2 )[I 3 ]I. 31 P NMR (MeCN): 18.30 ppm.

[Ph

3 PCHP(OSnCl 2 )Ph 2 ]

  (8): To a solution of 0.21 g of 2 (0.44 mmol) in about 4 ml DCM 0.27 g of anhydrous SnCl 2 (0.88 mmol) was added, and the mixture was treated for 30 min in an ultrasonic bath at room temperature. The resulting suspension was filtered from some insoluble material. The 31 P NMR solution showed two doublets at 38.74, 18.18 ppm ( 2 J(P,P) = 19.67 Hz). After about 24 h the signals had disappeared in favor of two new doublets at22.96, 21.33 ( 2 J(P,P) = 12.52 Hz. Layering of the solution with n-pentane gave colorless crystals after about three days which turned out to be the addition compound 8; the product was filtered and dried in vacuum; the yield was not determined.31 P NMR: 23.01,

	ZAAC
	spectrum of the 21.40 (d's, 2 J(P,P) = 14.3 Hz) in DCM and 23.32. 21.79 (d's, 2 J(P,P) = 14.3 Hz) in DMSO. IR (Nujol mull,
	cm -1 ): 1481 m, 1447 s, 1194 m, 1181 m, 1157 w, 1117 s, 1107 s, 1030 s, 1018 s, 997 s, 972 s, 806 m, 758
	m, 747 s, 737 s, 723 s, 718 m, 702 m, 692 s, 596 m, 527 s, 515 s, 494 m, 480 m, 467 w, 467 w, 434 w.
	C 31 H 26 Cl 2 OP 2 Sn (MW 666.07), found C 54.7, H 4.1, calcd C 55.90, H 3.94 %.
	[Ph 3
	Wiley-VCH

PCH 2 P(O)Ph 2 ] 2 [Hg 2 I 6 ]

  (9): To a solution of 0.07 g of 2 (0.15 mmol) in about 3 ml THF 0.09 g (0.2 mmol) of HgI 2 was added; a clear solution was obtained. The 31 P NMR spectrum of the solution showed two doublets at 21.79, 21.07 ppm (d`s, 2 J(P,P) = 12.51 Hz) along with two broad bands at 27.1 and 26.3 ppm.Layering of the solution with n-pentane gave colorless crystals overnight which turned out to be the salt 9.

	ZAAC	Page 32 of 50
	31 P NMR (DMSO, 300 MHz, 298 K): 23.34, 21.92 (d's, 2 J(P,P) = 14.3 Hz). IR (Nujol mull, cm -1 ): 1588 m,
	1484 m, 1437 s, 1375 m, 1334 m, 1185 s, 1118 s, 1071 m, 998 m, 799 s, 783 s, 743 m 743 s, 729 s, 712 s,
	689 s, 556 m, 503 s, 484 m. C 31 H 27 HgI 3 OP 2 (MW 1058.77), found C 35.05, H 2.63, calcd C 35.17, H 2.57
	%.
	Crystallographic data for the structures have been deposited with the Cambridge Crystallographic Data
	Centre, 12 Union Road, Cambridge CB21EZ. Copies of the data can be obtained on quoting the depository
	numbers CCDC 757261 (2), CCDC 757262 (5), CCDC 757263 (6), CCDC 757264 (7⋅ ⋅ ⋅ ⋅C 7 H 8 ), CCDC 757265
	(8), and CCDC 757266 (9) (Fax: (+44)1223-336-033; E-mail: deposit@ccdc.cam.ac.uk).
	Wiley-VCH

Table 1 .

 1 Crystal data and structure refinement details for the compounds 2, 5, 6, and 7⋅ ⋅ ⋅ ⋅C 7 H 8 , 8, and 9. OP 2 C 31 H 28 B 3 F 9 O 2 P 2 C 38 H 35 B 2 I 7 OP 2 C 31 H 26 Cl 2 OP 2 Sn C 62 H 45 Hg 2 I 6 O 2 P 4

	Page 33 of 50				ZAAC
		2	5	6	7⋅C 7 H 8	8	9
	Formula C 31 H 26 BF 3 Mw/g•mol -1 C 31 H 26 OP 2 476.49 544.30	697.92	1479.56	666.05	2117.51
	a/pm	1004.8(1)	1151.7(2)	988.6(2)	1108.0(1)	1496.9(2)	1194.0(1)
	b/pm	1476.5(2)	1392.1(2)	1059.4(2)	1476.5(2)	2061.0(3)	1094.2(1)
	c/pm	1832.9(3)	1653.8(3)	1722.5(2)	1444.4(2)	1825.0(2)	2552.1(2)
	α/°	107.93(1)	90	79.46(2)	90	90	90
	β/°	98.55(1)	97.63(1)	78.46(2)	106.50(1)	90	100.36(1)
	γ/°	101.09(1)	90	65.68(2)	90	90	90
	Crystal size/mm 0.32×0.14×0.08 0.17×0.17×0.04 0.14×0.06×0.05 0.24×0.09×0.05 0.13×0.12×0.04 0.18×0.11×0.09
	Volume/pm 3 ⋅10 6 2475.2(6)	2628.0(8)	1600.5(5)	2265.7(5)	5630(1)	3279.9(5)
	Z	4	4	2	2	8	2
	d calc /g•cm -3	1.279	1.376	1.448	2.169	1.571	2.144
	Crystal system	triclinic	monoclinic	triclinic	monoclinic	orthorhombic	monoclinic
					Wiley-VCH

Table 2

 2 Selected bond lengths/pm and angles/° in one of the two independent molecules of 2

Acknowledgement. We thank the Deutsche Forschungsgemeinschaft for financial support. W. P. is also grateful to the Max-Planck-Society, Munich, Germany, for supporting this research project.


Christine Lausser

Michael U Kumke

Markus Antonietti

Helmut Cölfen
email: coelfen@mpikg.mpg.de

Rüdiger Kniep

Fabrication of EuF3-Mesocrystals in a gel matrix

Keywords:

come

INTRODUCTION

The control over the mutual self-organization of nanoparticles towards superstructures and well organized arrays is a next step in nanosciences. Recently, non classical crystallization was found to be a tool for controlled nanoparticle organization to superstructures or single crystals, thus generating so-called mesocrystals, superstructures built up by nanocrystals which are in mutual alignment [1][START_REF] Cölfen | Mesocrystals and Non Classical Crystallization[END_REF][START_REF] Zhou | [END_REF] . Often the crystalline building blocks are in perfect three-dimensional crystalline registry. The properties of mesocrystal materials, such as single crystalline-behaviour, high crystallinity and high porosity are very useful for functional materials. Such combination of properties in a single material is unique compared to singlecrystalline, polycrystalline and amorphous materials. A number of desirable characteristics can be found within a mesocrystal that cannot be obtained for the same material in amorphous or single-crystalline form or as a polycrystalline aggregate. For example, it can be very advantageous to use a catalyst-material in form of a mesocrystal. It combines high crystallinity with small particle size, high surface area and high porosity as well as good handling as the mesocrystal has a size in the micrometer range. Examples for mesocrystals of functional materials are NH 4 TiOF 3 mesocrystals and their topotactic conversion to Anatasemesocrystals [4,5] as well as superparamagnetic Magnetite mesocrystals [6] .

In the present study, mesocrystals of Europium(III)fluoride (EuF 3 ) are described. Compounds based on rare-earth elements are among the most common luminescent materials, due to high photochemical stability, characteristic sharp emission lines of lanthanide ions and high quantum efficiencies [7] . They are applied for high-performance luminescent displays, optical communication and biochemical probes to laser materials [8][9][10][11] . Therefore, it is desirable to develop bottom up strategies for the design of these materials with a controlled nanostructure.

Wang et al prepared a variety of EuF 3 nanostructures with different crystalline phases and morphologies via a simple solution route employing different fluoride sources [12,13] , and new morphologies of crystalline Europium(III)fluoride were addressed more and more often in the last few years [14,15] . The optical properties of EuF 3 were analyzed in detail by Jayasankar using fluorescence microscopy. He detected the typical magnetic dipole transition ( 5 D 0 → 7 F 1 ) and the typical electric dipole transitions ( 5 D 0 → 7 F 2 , 5 D 0 → 7 F 3 , 5 D 0 → 7 F 4 ) [16] .

Following the pioneering work of Kniep on oriented superstructure synthesis in structured biopolymers, e.g. synthesis and analysis of a hexagonal-prismatic seed crystal of fluorapatite formed in a gelatin gel [17,18] , we made the current mesocrystals of EuF 3 by using a polymer gel as template. Using a structured organic matrix is an obvious mechanism for mesocrystal formation since the crystalline nanoparticles could align along the organic matrix [START_REF] Cölfen | Mesocrystals and Non Classical Crystallization[END_REF], [19] . There are two possibilities for the formation of a mesocrystal: either the nanoparticles are formed first and then attach to the polymer and get oriented, or they nucleate directly on the organic matrix which could act as an oriented, heterogeneous nucleation site [20] . A large number of examples of ordered macromolecular structures are also known in the world of biomacromolecules. Mesocrystal formation along a pre-structured organic matrix seems to be especially valid in biomineralization processes, as could also be demonstrated by biomimetic mineralization experiments [21][22][23][24][25] . Typical examples for a matrix-mediated nanoparticle growth are the formation and growth of bones as well as the growth of nacre [25][26][27] . Here we report on the exploitation of such principles for the generation of an EuF 3 mesocrystal.

RESULTS AND DISCUSSIONS

As soon as Eu(NO 3 ) 3 • 5H 2 O solution is added to the Accusol / NaBF 4 solution, nanoparticles composed of polymer and mineral precursors are formed in solution. The particle size is increasing in the first 3 h to a value of about 500 nm and then drops because of the sedimentation of the formed particles when they grew further (Figure 1). This is also expressed in the decrease of the intensity, which reaches 0 after 8 hours. After a reaction time of 3 hours and isolation of crystals, platelet-like agglomerates with flat surfaces, expressed angularity, and with different sizes and thicknesses were obtained. They are obviously built up by small primary nanoparticles with an average size between 30 and 50 nm, as evidenced by SEM (Figure 2). XRD measurements (Figure 3) show that the primary particles are completely crystalline; the diffraction peaks can be indexed to the hexagonal In addition, polarisation microscopy with crossed polarisers shows a strong, very homogeneous birefringence with uniform colour over distances > 100 µm, which is a proof for the iso-orientation of the nanoparticle aggregates even on the micron scale. Therefore, the obtained nanoparticle superstructure is a mesocrystal [1], [START_REF] Cölfen | Mesocrystals and Non Classical Crystallization[END_REF], [19] .

The formation reaction of EuF 3 is literature described as follows [15] Eu 3+ + 3BF 4 -→ EuF 3 + 3BF 3 (1)

BF 3 + 3H 2 O → 3H + 3F -+ H 3 BO 3 (2) Eu 3+ +3F -→ EuF 3 (3)
The release of the protons (equation 2) and thus the formation of EuF 3 can therefore be followed via pH-measurements. The pH value varied in the experiment from 2.6 at the beginning of the reaction to 2.2 after reaction of 3 hours. This indicates continuous formation of EuF 3 .

At these pH values, the carboxylic acid part of the polymer template is clearly protonated, but the strongly acidic sulfonic acid residues (14.7 mol-%) are still deprotonated. As a consequence, a gel is formed via electrostatic interactions of the sulfonated copolymer with Eu 3+ . Gel formation was demonstrated by swelling experiments under a light microscope and gravimetric comparison of the swollen and deswollen gel.

To investigate a possible templating mechanism of the Accusol-Eu gel, we performed a control experiment. By slowly adding an aqueous Eu(NO 3 ) 3 solution to an aqueous ACUSOL 588G solution, the gel was formed. The mixture became turbid immediately, and colloidal gel particles were formed. The precipitate was centrifuged. SEM images of dried gel samples showed a primary nanostructure similar to the final Europium(III)fluoride-mesocrystals. It is built up by small particles with similar average size of 50 nm as the building units of a layered gel film (Figure 5). This confirms the assumption that the microgel particles serve as templates for the subsequent crystallisation. The electron diffraction of the control gel particles demonstrates the amorphous character of the polymer-metal ion adducts. Upon addition of NaBF 4 aqueous solution to the as formed reference particles, the gel dissolved after three days. After further two days, a transformation to a crystalline precipitate took place and could clearly be followed by naked eye. This shows that the Europium-ions which were initially bound by the polymer reacted with the fluoroborate-ions weakening the

a) b) c)
gel structure, while EuF 3 formed. As only those Eu 3+ ions, which crosslinked the gel structure, were available for EuF 3 formation, the gel was destroyed, and no templating took place in the reference experiment. Therefore, under the standard reaction conditions, an Eu 3+ excess with respect to the amount needed to crosslink the gel was mandatory for mesostructure formation.

In another control, the experiment was repeated under the same conditions except the removal of the supernatant reaction solution. In that case the Europium-polymer-complex was not dissolved due to the Eu 3+ excess. This shows that the fluoroborate-ions react primarily with the Europium-ions in the solution. However, since light scattering (Figure 1) shows that the particles sediment after 3h when they have reached a radius of 500 nm. It is likely that these larger particles are the centers for further growth to the structures several tens of micrometer in size as observed by SEM (Figure 2). The polymer and Europium-ions needed for this growth are supplied from the solution phase, and the gel can act as a template for the formation of the EuF 3 mesocrystal.

Increasing the reaction time from 3 hours to 16 hours led to some different structures. Round and disc shaped structures with rough surfaces and an average size of 500 nm were obtained as it is typical for a reaction of NaBF 4 and Eu(NO 3 ) 3 without any additive (Figure 6a,b) [12] .

The crystallinity of the particles was proven by XRD (data not shown) and the diffraction peaks can be indexed to the hexagonal phase of EuF 3 . These structures are also polycrystalline, and electron diffraction shows again a mutual order as it is typical for mesocrystals (Figure 6c). However, the order is lower than in the case of the mesocrystals formed in the polymer gel template (Figure 4). A time dependent observation of the formed structures (3h, 5h, 7h, 9h, 11h and 16h) shows that the gel structure controls structure formation up to 7h (Figure SI 2). After 9h, the particles with the rough surface begin to form on cost of the polymer gel since the gel gets depleted in the areas where particles are observed (Figure SI 1). After 16h, this process has advanced to a stage, where the entire gel was consumed and only the secondary species were left. We assume that with increasing time Eu 3+ gets depleted, and also the Eu 3+ crosslinking the polymer is consumed. This leads to the observed dissolution of the gel structure and formation of the round and disk shaped mesocrystals.

The influence of reaction time on the sample properties is also found in the luminescence properties. In Figure 7 the luminescence spectra of the samples (reaction time 3 h and 16 h) and of a reference EuF 3 sample are compared. A clear difference in the spectral intensity distribution was observed for the samples isolated after 3h and 16h: i) for the sample isolated after 3h the luminescence transition corresponding to the 5 D 0 -7 F 0 transition is well pronounced in contrast to the sample isolated after 16 h. The luminescence spectrum of the sample isolated after 16h is very similar to a EuF 3 reference sample. The spectral intensity distribution of the europium luminescence is mainly determined by the symmetry of the local coordination sphere and the charge density as well as the covalency of the bonds. While in a highly symmetric complex the 5 D 0 -7 F 0 transition (around λ em = 579 nm) is forbidden and therefore should not be observed in the luminescence spectrum, distortion of the symmetry lower the forbiddance and subsequently, this transition can be observed in the luminescence spectrum. In case of the reference sample and the sample isolated after 16h, the intensity of the 5 D 0 -7 F 0 transition is very weak, indicating a high degree of symmetry in crystals (the minor intensity may be due to matrix vibrations, which lower the symmetry and consequently also the forbiddance of the 5 D 0 -7 F 0 transition) (see Figure 7, Inset). For the sample isolated after 3h a much higher intensity of the 5 D 0 -7 F 0 transition is observed indicating a relaxed europium symmetry in the presence of the polymer gel template. A similar trend is also found for the asymmetry ratio (intensity ratio of the 5 D 0 -7 F 1 and the so-called hypersensitive 5 D 0 -7 F 2 transition at λ em = 595 nm and 615 nm, respectively, see also Figure 8). Furthermore, the differences in the europium environment are also reflected in the small spectral shift of the non-degenerate 5 D 0 -7 F 0 transition (see Inset of Figure 7), which is representative for a europium species. [28] In Figure 8 the time-resolved luminescence decays at λ em = 595 nm and the asymmetry ratios are shown, which further support the results of the luminescence spectra analysis. While the reference and the sample isolated after 16h are very similar, the luminescence decay as well as the time dependence of the asymmetry ratio of the sample isolated after 3h are distinctly different: i) the luminescence decays much faster and ii) the asymmetry ratio continuously changes with time after the laser flash (in contrast to the sample isolated after 16h, which approaches a limiting value similar to the reference sample (see right side of Figure 8)). In the luminescence decays, quenching contributions from ligands are seen. The luminescence decays of all samples are multiexponential, which may be connected to different species in the sample (e.g., surface and bulk europium ions interacting differently with surrounding water molecules, which are strong luminescence quenchers due to the effective coupling to OHvibrations). The presence of two species (bulk and surface) can be seen in the timedependence of the asymmetry ratio of the reference and the sample isolated after 16h, which both approach a plateau at long times after the laser flash (right side of Figure 8, top and middle) [29] . Striking is the fast (compared to the other samples) luminescence decay of the mesocrystal sample isolated after 3h, which may be attributed to a strong coupling to the presence of the polymer gel matrix and the subsequent efficient luminescence quenching (e.g, via matrix vibrations).

The whole reaction pathway reminds of other, related observations of mesocrystal formation via crystallisation in a gel-template. One of the best investigated examples of mesocrystal development in a gel is the formation of the hexagonal-prismatic seed crystal of fluorapatite in gelatin [30] . The crystallization in a gel is very suited for the formation of mesocrystals as the crystal growth takes place at a high level of supersaturation and in the absence of flow and mechanical distortion [31] . This results on the one hand in an increase of the nucleation of small nanoparticles, which in addition are able to interact unperturbed and to arrange.

Furthermore, the reduced diffusion in the gel ensures sufficiently slow growth [31] . The level of supersaturation of Eu 3+ -ions along the Europium-ACUSOL-gel is very high and nucleation occurs since the Accusol gel acts as an "ion sponge". Small EuF 3 nanoparticles develop in the polymer gel, which then form the mesocrystals. Since EuF 3 has a hexagonal crystal structure, it has by symmetry no dipole moment, which could generate the mutual alignment of the nanocrystals in the mesocrystal. However, EuF 3 has polar faces, namely {001}, {110} and {011} (see Figures SI 3-5), which can be Europium-terminated and therefore strongly positive. This is favourable for the adsorption of the negatively charged copolymer. If a particle is nucleated in the vicinity of the polymer, the polymer can adsorb on one of these charged faces and block them from further growth. However, adsorption can -for energetic reasons-only occur on one side of a particle, thus creating two oppositely charged faces, as was already discussed earlier for CaCO 3 [12] and BaCrO 4 [32] This leads to the formation of a strong dipole, resulting in the mutual alignment of adjacent nanoparticles. We propose this mechanism also to hold true for the formation of the EuF 3 mesocrystals in the copolymer gel.

It is interesting to note that our case is different from the fluoroapatite mesocrystals formed in a gelatin gel [33] . Gelatin triple helices carry a dipole moment, which generates the intrinsic electric field aligning the nanoparticles. In the present example, this cannot be the case, and dipole fields can only be generated by unsymmetrical polymer adsorption.

CONCLUSIONS

In conclusion we have succeeded in fabrication of Europium(III)fluoride mesocrystals by a simple reaction in an organic matrix. It was demonstrated that Eu 3+ -ions react with the polymer ACUSOL 588G to a gel. Adsorption of the polyanion on a charged face of a particle nucleated in the vicinity of the polymer leads to oppositely charged faces resulting in a dipole moment. Due to this dipole field, the arrangement of the particles takes place according to the particular dipole-dipole-interactions. This is supported by the luminescence results, which confirm the presence of a modified Eu-ion surrounding in presence of the polymer gel matrix.

The polymer gel has multiple roles in this complex structuration process. It acts as an ion sponge that generates the high supersaturation in the gel phase leading to particle nucleation in the gel only. Secondly, it leads to the formation of a dipole field by adsorption onto a charged polymer face in the vicinity of the gel. In the present case, the mesocrystal gel structure is however only transient. With time, the gel dissolves again after the crosslinking Europium-ions were consumed for particle growth. Our example shows that complex functional mesocrystal structures can be assembled in very simple self-organized reaction schemes.

Nanostructured materials have received extensive attention due to their unusual properties and potential applications. For example, Europium(III)fluoride is used for high-performance luminescence displays or for laser materials. The here shown mesocrystaline material might be advantageous for these applications since a mesocrystal combines high crystalinity with a small particle size. The luminescence of the crystals was measured using combined Nd:YAG OPO laser (Quanta-Ray, Spectra Physics) OPO system operated at 20 Hz (versaScan, GWU Lasertechnik) for excitation at λ ex = 395 nm. The emission of the samples was detected in the wavelength range of 550 nm < λ em < 800 nm by a spectrograph (MS257, Oriel Instruments) equipped with an iCCD camera (DH720-18H-13, Andor Technology). In the luminescence measurements timeresolved emission spectra (TRES) were recorded based on a gated (box-car) detection scheme. In a typical experiment the luminescence signal was integrated for a gate time ∆t = 100 µs at variable gate step δt after the laser pulse in the time range of 10 µs < δt < 5000 µs with a gate step of 40 µs. The luminescence measurements were performed on suspensions of the samples at room temperature.

EXPERIMENTAL SECTION

Materials

Figure 1 :

 1 Figure 1: Time dependent dynamic light scattering data of forming EuF 3 in presence of Accusol. Left: Hydrodynamic radius r H and right: Intensity

phase of EuF 3 (

 3 JCPDS 32-0373). The particle size of 30 nm from Scherrer evaluation agrees well with the SEM results. Comparison of the obtained WAXS data with the reference for hexagonal EuF 3 shows that the peak intensities are very similar. No preferred orientation can be deduced from the WAXS data.

Figure 2 :Figure 3 : 1 :Figure 4 :

 2314 Figure 2: SEM images after a reaction time of 3 hours. a) Agglomerates different in size and form occur. b) and c) the agglomerates are built up by small particles with an average size of 50 nm.

Figure 5 :

 5 Figure 5: a) -b) SEM-images of the Eu-ACUSOL-gel. c) The TEM-measurement and electron diffraction of the amorphous gel, which is built up by small particles.

Figure 6 :

 6 Figure 6: a) and b) The SEM images show a network of round and disc shaped particles after a reaction time of 16h. c) TEM shows that these particles are polycrystalline and exhibit a short range order

Figure 7

 7 Figure 7 Comparison of the Eu-luminescence spectra of the samples at 3h and 16h. The samples were measured in suspension at room temperature (λ λ λ λ ex = 395 nm) in a time-gate detection mode at δ δ δ δt = 20 µs after the laser excitation pulse. Inset: Shown is the 5 D 0 -7 F 0 transition of europium for the three samples.

FFigure 8

 8 Figure 8 Luminescence decay at λ λ λ λ em = 395 nm (left) and time-resolved asymmetry ratio (right) of the different samples (λ λ λ λ ex = 395 nm) in water suspension. The asymmetry ratio is calculated as the intensity ratio of the 5 D 0 -7 F 1 and the 5 D 0 -7 F 2 transition at λ λ λ λ em = 595 nm and 615 nm, respectively.

:

  Sodium fluoroborate (NaBF 4 , Fluka, ≥ 98%), Europium(III) nitrate pentahydrate (Eu(NO 3 ) 3 • 5H 2 O, Aldrich, 99.9%) and the Polymer ACUSOL 588G (Acrylic acid / sulfonic acid copolymer, likely with 2-acrylamido-2-methylpropanesulfonic acid, AMPS content from elemental analysis = 14.7 mol-%, M w = 12000 g/mol, a well known antiscale additive donated by Benckiser, were used without further purification. Synthesis: 25 mL of ACUSOL aqueous solution (c = 0.4 g/L) were mixed with 25 mL of NaBF 4 aqueous solution (c = 160 mM) under stirring in a beaker. After a few minutes 50 mL of Eu(NO 3 ) 3 • 5H 2 O aqueous solution (c = 20 mM) were added. The mixture became turbid immediately. The reaction mixture was stirred at room temperature for 3 h respectively 16 h. Afterwards the supernatant solution was removed by centrifugation. The precipitate was washed with distilled water several times as well as twice with ethanol via centrifugation.Between the centrifugation steps, the sample was treated by ultrasonics for a few minutes to dissolve the precipitate in water. The final product was dried at 70°C under vacuum over night.Characterisation:The crystals were characterized with different microscope techniques. The light microscope images were obtained with a Leica microscope type DMR B with and without crossed polarisers. The microstructure was also analyzed by a scanning electron ) LEO 1550-Gemini-System. The transmission electron microscope (TEM) images were recorded on a Zeiss EM 912Ω microscope operated at 120kV. The XRD data were measured in reflection mode (Cu-K α radiation) on a Bruker D8 diffractometer equipped with scintillation counter.

ACKNOWLEDGEMENT

We thank Rona Pitschke and Heike Runge for SEM-and TEM-measurements as well as Christina Diehl and Ina Dambowsky for discussions about the chemical structure of the polymer, Peter Cernoch for DLS-Measurements, and Katlen Brennenstuhl for the measurement of the TRES. The Max-Planck-society is acknowledged for financial support.


Tobias Kloubert

Helmar Görls

Matthias Westerhausen

Synthesis and Crystal Structures of Dinuclear Zinc Complexes with the 3,5-Bis(pyridine-2-yl)pyrazolato Ligand

Keywords: zinc, metallation reaction, pyrazolate, crystal structure

Zincation of 3,5-bis(pyridine-2-yl)pyrazole with Zn[E(SiMe 3 ) 2 ] 2 in tetrahydrofuran yields dimeric 3,5-bis(pyridine-2-yl)pyrazolato zinc bis(trimethylsilyl)amide (E = N, 1) and bis(trimethylsilyl)methanide (E = CH, 2). These complexes crystallize in the space groups P2 1 /n and P ī, respectively. The zinc atoms are in distorted tetrahedral environments. In the solid state the 3,5-bis(pyridine-2-yl)pyrazolato anions act as bridging tridentate bases with one pyridyl group not participating in the coordination behaviour. In solution exchange processes fast on the NMR time scale lead to a single set of resonances for the pyridyl substituents.

Introduction

Dinuclear zinc complexes play an important role in biomimetic models for enzymes and catalysts [1]. Often pyridyl groups are used to mimic N-bound histidine bases. In the course of our investigations of dinuclear zinc complexes with multi-dentate ligands such as 1,2bis(pyridine-2-yl)-1,2-diamidoethanes [2] or bis(2-pyridylmethyl)amides [3] we included studies with tetradentate 3,5-bis(2-pyridyl)pyrazolato anions. Pyrazolyl and imidazolyl units also play a crucial role in bioinorganic chemistry of zinc in order to mimic active sites of zinc enzymes [4]. 3,5-Substituted pyrazolate ligands represent valuable bridging units between two zinc ions with a strong influence of the side arms (length and nature of functional groups) on the catalytic activity [5]. An easily accessible ligand offering pyrazolyl as well as pyridyl functionalities is the well-known 3,5-bis(pyridine-2-yl)pyrazolate anion. This ligand forms complexes with the late 3d transition metals from Cr to Cu whereas no examples are known for the earlier transition metals [6]. Only hydrates of 3,5-bis(2-pyridyl)pyrazole zinc halide [7] and nitrate [7,8] and their homologous cadmium derivatives are reported, however, the molecular structures remained unknown. The rigidity of this 3,5-bis(2-pyridyl)pyrazolyl ligand enables the formation of dinuclear metal complexes and in some cases even complexes of higher nuclearity via self-assembly [9]. In general, the 3,5-bis(pyridine-2-yl)pyrazolato ligand acts as a bridging ligand and in bidentate fashion to both the metal cations as displayed in Scheme 1. In these complexes the metals often show hexa-coordination in distorted octahedral environments. These isotypic compounds were recrystallized from concentrated thf solutions to grow single crystals suitable for X-ray structure determinations.

N N N N H N N N N M M N N N N E E Me 3 Si Me 3 Si SiMe 3 SiMe 3 + Zn[E(SiMe 3 ) 2 ] 2 -HE(SiMe 3 ) 2 1 2 E = N (1), CH (2) (1)
NMR spectroscopic data are summarized in Table 1. The numbering scheme is in accordance with the IUPAC recommendation. The amide or methanide groups show nearly no influence on the 1 H NMR data of the 3,5-bis(pyridine-2-yl)pyrazolato anions of 1 and 2. However, the 13 C{ 1 H} NMR parameters of the central pyrazolato ring differ strongly. This fact can be explained by a reduced charge on the zinc atoms for the bis(trimethylsilyl)methyl derivative 2. The zinc atoms bind tightly to the nitrogen bases and therefore the charge on the metal atoms influences the chemical shifts of the N-bound carbon atoms the most.

Insert Table 1 Molecular structures and numbering schemes of isoelectronic 1 and 2 are shown in Figures 1 and2, respectively. The molecular structures are very similar even though they do not crystallize isomorphous. In both compounds the 3,5-bis(pyridine-2-yl)pyrazolato anions show a rather unique coordination behaviour. The bridging pyrazolato moiety is bound to two zinc cations. The metal atoms also coordinate to one pyridyl group (forming a five-membered ZnN 2 C 2 heterocycle) whereas the other pyridyl substituent is not involved in the ligand sphere of the zinc atom as shown in equation 1.

Insert Figures 1 and 2

Insert Table 2 Selected structural data of 1 and 2 are compared in Table 2. In both complexes the endocyclic Zn1-N1/N2 and Zn2-N5/N6 bond lengths are significantly larger than the exocyclic Zn1-N7 and Zn2-N3 distances. Ring formation also leads to narrow N1-Zn1-N2 and N5-Zn2-N6 bond angles of 76.9°. In 1 the Zn-N bonds to the bis(trimethylsilyl)amide anions show the smallest values due to a rather large electrostatic attraction. Nevertheless, in Zn[N(SiMe 3 ) 2 ] 2 with a two-coordinate zinc atom significantly smaller Zn-N bond lengths are observed (Zn-N, solid state: 183.3 (11) pm [10], gas phase: 182.4( 14) pm [11]). The influence of the coordination numbers of Zn and N on the Zn-N distances is nicely shown for a number of homoleptic zinc amides of the type Zn[N(SiR 3 )R'] 2 [12] and Zn(NPh 2 ) 2 [13]. The bulkiness of the E(SiMe 3 ) 2 ligands ( E = CH, N) induces steric pressure and enhanced N-Zn-E angles in 1 and 2. The negative charge of the pyrazolato anions are delocalized within this five-membered aromatic ring which reduces the negative charge on the nitrogen atoms N2, N3 as well as N6, N7. Even though the 3,5-bis(pyridine-2-yl)pyrazolato ligand displays a nearly planar arrangement there is nearly no charge delocalization into the pyridyl moieties; the C-C bonds between the aromatic rings show values of approximately 146.6 pm which is characteristic for single bonds between sp 2 hybridized carbon atoms. The Zn-C distances of 201.3 pm are rather large and represent a characteristic value for dialkylzinc with tetra-coordinate metal atoms [14].

Conclusion and Perspective

In the solid state only one of the pyridyl groups of the anion is bound to zinc. However, in solution an exchange reaction, which is fast on the NMR time scale, leads to two chemically equivalent pyridyl substituents and one set of resonances. The tendency of zinc to favour tetra-coordination leads to unique molecular structures for 1 and 2 which were unknown for the 3,5-bis(pyridine-2-yl)pyrazolato anions as of yet but they are comparable to complexes of the type [RZn-N(CH 2 Py) 2 ] 2 [3]. In these compounds only one set of NMR signals was found for the pyridyl groups but in the solid state only one pyridyl substituent was acting as a Lewis base to the zinc cations.

The catalytic activity of [RZn-N(CH 2 Py) 2 ] 2 is based on the fact that the pyridyl groups can act as hemilabile Lewis bases [15]. However, the hydrogen atoms at the α-methylene units are rather acidic and deprotonation reactions can occur leading to by-products [3]. This kind of side-reaction is impossible for the 3,5-bis(pyridine-2-yl)pyrazolato ligand. Therefore further investigations are in progress in order to evaluate the catalytic activity of 1 and 2 because these complexes fulfil the pre-condition that hemilabile ligands offer access to the metal centers.

Experimental

All manipulations were carried out in an anaerobic argon atmosphere and the solvents were thoroughly dried. IR spectra were recorded with Nujol solutions between KBr windows. The values of the elemental analysis deviate from theoretical values because weighing of these moisture sensitive compounds was challenging due to the easy loss of cocrystallized thf and also due carbonate formation during combustion even though V 2 O 5 was added. Starting 3,5bis(pyridine-2-yl)pyrazole [8], Zn[N(SiMe 3 ) 2 ] 2 [16], and Zn[CH(SiMe 3 ) 2 ] 2 [17] were prepared according to literature procedures. Synthesis of 3,5-bis(pyridine-2-yl)pyrazolato zinc bis(trimethylsilyl)amide (1): 3,5-Bis(pyridine-2-yl)pyrazole (570 mg, 5.56 mmol) were dissolved in 15 ml of thf and cooled to -30°C. Zinc bis[bis(trimethylsilyl)amide] (2.5 g, 6.49 mmol), dissolved in 15 ml of thf and also cooled to -30°C, was added dropwise. The reaction mixture was stirred for further 5 h and then warmed to r.t. The formed precipitate was redissolved at 50°C and the solution slowly cooled again to r.t. Crystallization of 1 was completed by storing of the reacton mixture at 4 °C for 2 d. Yield: 980 mg of 1 (2,19 mmol 85,5%). -Dec. above 238°C. -1 H NMR ([D8]THF) δ = 8.93 (d, 3 J(H 8,14 ,H 9,15 ) = 4.8 Hz, 2H, Pyr 8,14 ); 7.83 (ddd, 3 J(H 10,16 ,H 9,11;15,17 ) = 7.7 Hz, 4 J(H 10,16 ,H 8,14 ) = 1.5 Hz, 2H, Pyr 10,16 ); 7.66 (d, 3 J(H 11,17 ,H 10,16 ) = 7.9 Hz, 2H, Pyr 11,17 ); 7.35 (ddd, 3 J(H 9,15 ,H 10,16;8,14 ) = 5.4 Hz, 4 J(H 9,15 ,H 11,17 ) = 0.8 Hz, 2H, Pyr 9,15 ); 7.05 (s, 1H, H 4 ); 0.06 (s, 18H, H Me ). - 13 C NMR ([D8]THF) δ = 146.7 (Pyr 8,14 ); 144.7 (Pyr 6,12 ); 136.4 (Pyr 10,16 ); 133.6 (C 3,5 ); 120.1 (Pyr 9,15 ); 117.5 (Pyr 11,17 C 53.11, H 6.98, N 13.46; found: C 52.28, H 6.16, N 13.62.

Synthesis of 3,5-bis(pyridine-2-yl)pyrazolato zinc bis(trimethylsilyl)methanide (2): A solution

of zinc bis[bis(trimethylsilyl)methanide] (400 mg, 1.04 mmol) in 5 ml of toluene was dropped into a solution of 3,5-bis(pyridine-2-yl)pyrazole (228 mg, 1.03 mmol) in 5 ml of thf. Then the reaction mixture was heated to 60 °C for 30 min and thereafter slowly cooled to r.t. The product crystallized in the shape of colorless cubes. Yield: 420 mg of 2 (0,94 mmol, 91%). -Dec. above 260°C. -1 H NMR ([D8]THF) δ = 8.92 (d, 3 J(H 8,14 ,H 9,15 ) = 5.0 Hz, 2H, Pyr 8,14 ); 7.78 (ddd, 3 J(H 10,16 ,H 9,11;15,17 ) = 7.1 Hz, 4 J(H 10,16 ,H 8,14 ) = 1.8 Hz, 2H, Pyr 10,16 ); 7.65 (d, 3 J(H 11,17 ,H 10,16 ) = 8.0 Hz, 2H, Pyr 11,17 ); 7.29 (ddd, 3 J(H 9,15 ,H 10,16;8,14 ) = 6.6 Hz, 4 J(H 9,15 ,H 11,17 ) = 1.6 Hz, 2H, Pyr 9,15 ); 7.02 (s, 1H, H 4 ); 0, 10 (s, 1H, H 19 ); -0.14 (s, 18H, H Me ). -13 C-NMR ([D8]THF) δ = 152.4 (Pyr 6,12 ); 151.1 (Pyr 8,14 ); 138.9 (Pyr 10,16 ); 122.7 (Pyr 9,15 ); 120.6 (Pyr 11,17 ); 109.6 (C 3,5 ); 100.0 (C 4 ); 4.9 (C Me ); 1.3 (C 19 ). -IR (Nujol, cm - Crystal structure determination: The intensity data for the compounds were collected on a Nonius KappaCCD diffractometer, using graphite-monochromated MoK α radiation [START_REF] Collect | Data Collection Software[END_REF][START_REF]Processing of X-Ray Diffraction Data Collected in Oscillation Mode[END_REF].

The structures were solved by Direct Methods (SHELXS [START_REF] Sheldrick | [END_REF]) and refined by full-matrix leastsquares techniques against F o 2 (SHELXL-97 [21]). All hydrogen atoms were included at calculated positions with fixed thermal parameters. All non-disordered, non-hydrogen atoms were refined anisotropically [21]. Crystallographic data as well as structure solution and refinement details are summarized in Table 3. XP (Siemens Analytical X-ray Instruments, Inc.)

was used for structure representations.

Insert Table 3 Acknowledge

Acknowledge Acknowledge Acknowledgement ment ment ment

This work was generously supported by the Deutsche Forschungsgemeinschaft (DFG, Bonn-Bad Godesberg, Germany). We are also grateful to the Fonds der Chemischen Industrie (Frankfurt/Main, Germany) for supporting our research.

Supporting

Scheme 1 :

 1 Scheme 1: Common coordination modes of the 3,5-bis(pyridine-2-yl)pyrazolate anion as a bridging ligand. The value of m depends on the oxidation state on M and on the charge of L (which can be solvent molecules and counter anions).

  ); 96.4 (C 4 ); 3.5 (C Me ). -IR (Nujol, cm -1 ): ν = 3378 w, 3115 w, 3053 m, 2920 vs, 2720w, 2683 m, 2609 w, 2532 w, 2308 m, 1979 m, 1850 m, 1767 m, 1705 m, 1652 w, 1606 vs, 1568 s, 1536 s, 1456 s, 1436 s, 1378s, 1366 w, 1345 s, 1274 w, 1249 vs, 1180 m, 1151s, 1141 m, 1095 m, 1074 m, 1048 w, 1020 w, 1009 w, 987 s, 884 s, 766 s, 738 m, 696 m, 663 s, 639 m, 625 m, 613 m, 552 m, 504 w, 497 m, 470 m, 462w. -MS (EI): m/z (%) = 384 * (1.4), 369 * (9), 275 (48), 161 (7), 147 (29), 146 (100) [(Me3Si)2, HNSi2Me5, Si2Me6] + , 130 (41), (signals with an asterisk * show the isotopic pattern of Zn). -Elemental analysis (C19H27N5Si2Zn(thf), 519.13): calcd.:

1 )

 1 : ν = 3556 vw, 3118 w, 3046 w, 2852 s, 2722 w, 2667 w, 2309 vw, 1976 w, 1912 w, 1842 w, 1766 w, 1686 w, 1649 w, 1606 vs, 1590 w, 1565 s, 1533 s, 1454 vs, 1435 vs, 1377 s, 1343 m, 1276 m, 1255 w, 1236 vs, 1150 m, 1135 m, 1095 w, 1072 m, 1049 m, 1027 s, 1019 s, 1007 s, 989 m, 974 m, 897 s, 853 s, 801 m, 765 s, 742 s, 708 w, 695 w, 671 s, 638 m, 622 m, 609 m, 550 m, 497 m, 476 w, 467 m. -MS (EI): m/z (%) = 444 * (28) [M] + , 429 * (100) [M-CH3] + , 367 * (8) [M-Pyridyl] H+ , 357 * (11) [429H-SiMe3] H+ , 335 (23), 286 * (12), 273 (16), 145 (34), 129 (42), (signals with an asterisk * show the isotopic pattern of Zn). -Elemental analysis (C20H28N4Si2Zn, 446.05): calcd.: C 53.74,H 6.54, N 12.53; found: C 53.56, H 6.35, N 12.61.

Figure 1 :Figure 2 :

 12 Figure 1: Molecular structure and numbering scheme of 3,5-bis(pyridine-2-yl)pyrazolato zinc bis(trimethylsilyl)amide (1). The ellipsoids represent a probability of 40%, H atoms are neglected for clarity reasons.

Table 1 :

 1 NMR data of 3,5-bis(pyridine-2-yl)pyrazolato zinc bis(trimethylsilyl)amide (E = N,

	Information available: Crystallographic data (excluding structure factors) has
	been deposited with the Cambridge Crystallographic Data Centre as supplementary
	publication CCDC-773037 for 1, and CCDC-773037 for 2. Copies of the data can be obtained
	free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [E-mail:
	deposit@ccdc.cam.ac.uk].

Table 2 :

 2 Structural parameters of the metal environments in 1 and 2 (bond lengths [pm] and angles [deg.]).

	1 (E = N)	2 (E = CH)

Table 3 :

 3 Crystal data and refinement details for the X-ray structure determinations of 1 and 2.

		1 (E = N)	2 (E = CH)
	Formula	C 38 H 54 N 10 Si 4 Zn 2 , 2(C 4 H 8 O)	C 40 H 56 N 8 Si 4 Zn 2 , 1.5(C 4 H 8 O)
	Fw (g•mol -1 )	1038.22	1000.18
	T/K	-140(2)	-90(2)
	Crystal system	monoclinic	triclinic
	Space group	P 2 1 /n	P ī
	a/ Å	13.3555(3)	13.7044(4)
	b/ Å	26.3010(5)	14.1141(5)
	c/ Å	15.1101(2)	15.5526(6)
	α/°	90	74.086(1)
	β/°	95.157(1)	70.244(2)
	γ/°	90	85.002(2)
	V/Å 3	5286.13(17)	2722.64(16)
	Z	4	2
	σ (g•cm -3 )	1.305	1.220
	µ (cm -1 )	10.44	10.09
	Measured data	35385	19659
	Data with I > 2σ(I)	8038	8875
	unique data / R int	12098/0.0621	12342/0.0331
	wR 2 (all data, on F 2 ) a)	0.0929	0.1512
	R 1 (I > 2σ(I)) a)	0.0407	0.0484
	s b)	0.995	1.013
	Res. dens./e•Å -3	0.686/-0.417	1.039/-0.547
	CCDC No.

Wiley-VCH ZAAC

Wiley-VCH

ZAAC

Wiley-VCH ZAAC