Delavaux-Nicot

Agne `s Bigeard

Azzedine Bousseksou

Bruno Donnadieu

´rard Commenges

Reactivity of the Acyclic Diazadioxa Redox Active Ligand [(C 5 H 5 )Fe(C 5 H 4 CH 2 N(CH 3 )(CH 2 ) 2 OCH 2 -)] 2 : NMR, Electrochemical, and Mo 1ssbauer Studies. Crystal Structure of Its Copper Complex Be ´atrice

Keywords: Found: C, 42.09, H, 4.93 N, 3.31 . Found: C, 54.15, H, 6.33 N, 3.89

 ]( M)Zn, Hg) (9, 10) are reported. The crystal structure of complex 7 has been determined by X-ray analysis at 180 K. Crystal data: monoclinic

.1(2)°). In cyclic voltammetry, 4a-c undergo two quasi-reversible (Fe(II)/Fe(III)) redox processes at 0.1 V s -1 . Electrochemical studies of 3a-c, 5, 7, and 8 show that diprotonation and dialkylation of 2 or complexation of a Cu (Ag) salt induces an anodic shift ranging from 240 to 110 mV. Chemical oxidation of 2 (5 equiv of Ag(I)) produces the cation [2(H) 2 ] 4+ (11). The quantitative two-step electrochemical oxidation of 2 at controlled potential in CH 3 CN also leads to 11: an ECE mechanism, in which the diprotonated species plays a key role, is proposed. Mo ¨ssbauer data of 2, 3c, 6, 7, 8, and 11 are also presented.

Introduction

The design of receptors containing ferrocenyl groups for electrochemical recognition is a recurrent theme in contemporary chemistry. 1,2 One of our goals in this regard has been to synthesize new 1,2-disubstituted ferrocenyl compounds containing both a (Ph)P(S)(NMeNdCH-) 2 anda(-CH 2 NMe(CH 2 ) 2 -OCH 2 -) 2 moiety. Recently, we have shown that it is possible to selectively synthesize acyclic phosphorus-containing ferrocenyl ligands Ph 3-n PX(NMeNdCHC 5 H 4 FeCp) n (X ) O, S; n ) 2, 3), in high yield. These ligands show a remarkable ability to yield electroactive complexes with a copper(I) salt and ZnCl 2 . 3 Our preliminary results have provided us with the opportunity to synthesize the new diferrocenyl compound [(C 5 H 5 )Fe(C 5 H 4 -CH 2 N(CH 3 )(CH 2 ) 2 OCH 2 -)] 2 (2). 4 The most interesting feature of 2 is the combination of an electrochemically active ferrocene and a simple organic ether chain within the same molecule. In the neutral form, the diferrocene can bind a cation through its nitrogen and (or) oxygen donor sites; upon oxidation to ferrocenium, however, the unfavorable interaction of two cations in close proximity can lead to a destabilization of the complex, as shown for PhPS(NMeNdCHC 5 H 4 FeCp) 2 (1), and can provide an opportunity to recover both the ligand and cation. Except for crown ether chemistry, few studies of ether-cation complexation have been undertaken because ether-cation interactions are weak and therefore difficult to assess. 5 In order to better understand the complexing and redox properties of the novel dimetallic complex 2 we decided to study its reactivity and to examine the electrochemical behavior of this ligand and of its new cationic derivatives. The synthesis and characterization of complexes obtained through protonation and methylation reactions of 2 are described in this paper. The electrochemical behavior of these compounds has allowed us to suggest a mechanism for the electrochemical oxidation of complex 2 in CH 3 CN. The complexation reactions of 2 with Na(I), Cu(I), Ag(I), Zn(II), and Hg(II) compounds are reported, and the X-ray structure of the heterotrimetallic iron-copper complex [2Cu][CF 3 SO 3 ] is presented.

Results and Discussion

1. Protonation and Methylation Reactions of Compound 2. Organic crown ethers and cryptands containing several diazaoxa chains are known to be easily protonated, and some of them may be used as pH sensors. 6 Recently, Plenio et al., in order to better understand the influence of the hardness (charge-to-radius ratio) of a complexed cation on the electrochemistry of several ferrocene crowns and aza cryptands, investigated the effect of the hardest possible cation, H + ,o n these systems. 7 In the case of compound 2, the reaction with H + was particularly interesting since the stable diprotonated species seemed to play a key role in the electrochemical oxidation process of this starting complex (vide infra).

The one-pot synthesis of compound 2 was realized by reacting [(C 5 H 5 )Fe(C 5 H 4 CH 2 NMe 3 )][I] with 0.5 equiv of 1,8-bis(methylamino)-3,6-dioxaoctane in water. 4 2 reacts with 2 equiv of HX (X ) CF 3 SO 3 ,B F 4 ) to afford, after purification, [2(H) 2 ]-[X] 2 (X ) CF 3 SO 3 (3a) and X ) BF 4 (3b), in high yield (95-97%) as oils (Scheme 1). The structure of these molecules has been deduced from spectroscopic data. In particular, the protonation reaction has been confirmed by the appearence of a new signal at δ ≈ 7 ppm ( 1 H NMR, CD 3 CN) attributed to the protons of the NH + groups. 8 2D NMR experiments have been carried out for compound 2 and for the diprotonated complex 3a and clearly verify the assignments. Elemental analyses and mass spectra are also in agreement with the proposed formulation (See Experimental Section).

Addition of NH 4 PF 6 to a solution of compound 2 could lead to the new adduct [2NH 4 ][PF 6 ] with N + H---N and N + H---O (salt/ligand) interactions. 9 Attempts to crystallize this species from mixtures of NH 4 PF 6 and 2, in 1:1 and 1:2 stoichiometry in CH 3 CN, according to established procedures, 9a were unsuccessful. 10 However, when complex 2 was reacted with 2 equiv of NH 4 PF 6 , the product isolated after treatment was the diprotonated species [2(H) 2 ][PF 6 ] 2 (3c). In contrast to 3a,b, the product was obtained as a powder, and in the solid state, the ν (N + H) (KBr) absorptions could be clearly located at 3199 cm -1 . 11 Reaction of compound 2 with HCF 3 SO 3 , HBF 4 'Et 2 O, or NH 4 PF 6 in 1:1 stoichiometry affords respectively the N-H-N monoprotonated species [2H][X] (X ) CF 3 SO 3 (4a), BF 4 (4b), PF 6 (4c)). 4b and 4c were isolated in good yield (70-90%). Compound 4a was characterized in solution.

The 1 H NMR spectra of 4a indicate that it is symmetrical, with the NH + group being observed at 7.9 ppm (CD 3 CN, 293 K) as a broad signal. This may be attributed to an NH + group interacting with the second N atom. 8a,11 Lowering the temperature to 193 K in CD 2 Cl 2 shows a broadening of the signals of 4a in 1 H and 13 C NMR spectra. A single signal is clearly observed for the methyl groups in the 1 H and 13 C NMR spectra (at δ ) 2.5 ppm, 243 K and δ ) 36.9 ppm, 193 K, respectively), suggesting that an H + exchange occurs between the two N atoms and that it is not blocked at low temperature. In the solid state, the ν (N + H) (KBr) frequencies, observed in the 2400-2340 cm -1 range of the IR spectrum of 4c, are also consistent with an additional hydrogen interaction with the second nitrogen. 11,12 The mass spectrum of 4b indicates monoprotonation. It is worth noting that compound 4b is cleanly obtained when compound 2 is reacted with the diprotonated complex 3b with a 1:1 stoichiometry in CD 2 Cl 2 . The later experiment leads us to suggest that an exchange mechanism involving N + H---N interand intramolecular interactions exists (Scheme 2). The flexibility of the (-N(CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 N-) chain in compound 2 (vide infra) may favor this type of exchange, which is probably assisted by the presence of the oxygen atoms of the chain. 11,12 Subsequent addition of 1 equiv of HBF 4 'Et 2 Otothe monoprotonated species affords 3b.

In order to compare the electrochemical properties of a methylated species with the diprotonated forms, we synthesized a dimethylated derivative of 2. Treatment of 2 with 2 equiv of CF 3 SO 3 Me in CH 3 CN affords [2(Me) 2 ][CF 3 SO 3 ] 2 (5), which was isolated in 50% yield as a yellow powder. Characterization was achieved by 1 H, 13 C, and 19 F{ 1 H} NMR experiments in CD 3 CN.

Complexation Reactions.

To check the bonding ability of complex 2, we have investigated its reactivity with Na, Cu, Ag, Zn, and Hg salts.

When either 1 equiv or an excess of NaPF 6 salt is added to 2 in CH 3 CN, the [2Na][PF 6 ] adduct (6) is the unique species isolated after purification. The 31 P{ 1 H}, 19 F{ 1 H}, and 23 Na NMR spectra in CDCl 3 allow confirmation of the complexation of the NaPF 6 salt, which is normally insoluble in this solvent. In the solid state, mass spectroscopy confirms that the 1:1 adduct is the unique product of the reaction.

The coordination mode of the Na + ion in compound 6 is not clear. Generally Na + requires more than four bonds in its coordination sphere; however, tetrahedral coordination with a N 2 O 2 donor set is possible. 13 Na + presents a good affinity for N and O atoms in diazacrown ether compounds. Mass spectra show that 7 is the unique complexation adduct formed under these experimental conditions. The most important 1 H deshielding is observed for the FcCH 2 N protons (∆δ ) 0.75 ppm in CDCl 3 ) and is associated with a broadening of the resonances. When complex 7 is dissolved in acetonitrile, ligand 2 is displaced by the solvent. This copper complex is prone to rapid oxidation in solution in the presence of dioxygen but was found to be sufficiently stable to allow characterization. Crystals of 7 suitable for X-ray analysis were obtained by recrystallization from a 1:3 CH 2 Cl 2 /Et 2 O mixture. An X-ray structure determination realized at 293 K shows very large thermal ellipsoids especially for the C atoms in the ether chain; this initially hampered a good refinement of the structure (R ) 0.095, R w ) 0.111). A perspective view of the molecule from data obtained at 180 K is shown in Figure 1. Selected bond lengths and interatomic angles are listed in Tables 1 and2, respectively. 2 is symmetrically coordinated to the copper atom through its N and O donor atoms with the N-C, C-O and C-C distances within the normal ranges. 1e,16 Usual Cu-N distances (Cu-N(1) ) 1.966(4) Å, Cu-N(2) ) 1.953(4) Å) are observed, 3a,17a but the Cu-O distances (Cu-O(1) ) 2.517-(4) Å, Cu-O(2) ) 2.610(4) Å) are elongated by the ligand architecture and are close to those found in copper(II) complexes bound to a similar diazadioxa organic chain. 18,19 The consequence for the copper atom is a very distorted tetrahedral geometry with a large N(1)-Cu(1)-N(2) angle (163.1 (2)°). The presence of two nitrogen atoms in a tetrahedral environment together with the stereochemical requirement of the methyl and ferrocenyl groups may enforce this particular geometry.

Cu(I) and Ag(I) compounds are known 17 to prefer tetrahedral geometry, but few examples of ferrocenyl silver compounds have been reported. 1e,20 With this in mind, along with the fact that Ag(I) can accommodate N and O ligands in a tetrahedral geometry, 21,22 formation of a silver adduct of 2 was conceivable. The compound [Ag2][CF 3 SO 3 ]( 8 ) has been isolated in 50% yield from the 1:1 reaction of compound 2 with AgCF 3 SO 3 in THF. Mass spectra carried out on a pure sample confirmed the proposed formula. As for the copper compound 7, the 1 H NMR signals in CDCl 3 are broad, but in contrast to 7 the Ag adduct is stable in CD 3 CN. 1 H NMR spectra in this solvent show a weak deshielding of the signals (0.1-0.2 ppm) when compared to those of the starting material, and they show illresolved multiplets for NCH 2 CH 2 O and FcCH 2 N protons. Lowtemperature NMR experiments of 8 (CD 2 Cl 2 , 193 K) are not informative, and the complex decomposes upon heating to 333 KinCD 3 CN. Attempts to crystallize 8 were unsuccessful, and a detailed mode of coordination cannot be proposed, though a structure similar to that of 7 may be suggested.

When a slight excess of AgCF 3 SO 3 was added to a solution of 2, the mixture turned green. This fact suggested to us that the extra silver salt could act as an oxidizing agent toward the Fe(II) centers (vide infra).

Recently, addition of Zn(CF 3 SO 3 ) 2 to a solution of an aminoferrocene complex has been shown to induce the largest anodic shift ever observed for the redox potential of the Fe(II)/Fe(III) couple. 23e With the aim of synthesizing [Fe-Zn] 2+ complexes, reaction of compound 2 with 1 equiv of Zn-(CF 3 SO 3 ) 2 was carried out. After purification, the diprotonated complex 3a was identified by NMR and mass spectroscopy as the unique product of the reaction, demonstrating the easy protonation of the chain. To our knowledge, neutral ferrocenyl iron-zinc and ironmercury complexes are scarce 23,24 and only a few complexes have been structurally characterized. 3d,23c,e,24a Reaction of 2 with ZnCl 2 and HgCl 2 led us to successful isolation of the respective metal ligand complexes [2ZnCl 2 ]( 9 ) and [2HgCl 2 ]( 10), the elemental analyses of which suggested a 1:1 ligand:metal stoichiometry. Coordination of these units to ligand 2 also involves a weak 1 H NMR deshielding of the signals (0.2-0.3 ppm). In the case of the Zn adduct, the signals are broad and lowtemperature NMR experiments indicate that complex phenomena operate in solution. To achieve a tetrahedral geometry, 3d,23c-e,24 these two metals need only two of the four donor atoms (N or O) of the amino ether chain. Due to the flexibility and the symmetry of the chain, an exchange phenomenon involving decoordination of one of the two coordinated atoms of the organic chain and simultaneous coordination of an other atom is possible. 3c,d 3. Electrochemical studies. A. Protonated and Methylated Species 3a-c, 4a-c, and 5. Typical voltammograms of these species are presented in Figure 2. They can also be obtained by stepwise addition of an appropriate number of equivalents of reactant to an acetonitrile solution of 2.

a ) 11.511(2) Å monoclinic, space group P2 1/c b ) 19.613(2) Å T )-93 °C c ) 14.493(2) Å λ(Mo KR 1) ) 0.710 73 Å β ) 88.32(2)°F calcd ) 1.59 g cm -3 V ) 3273.2(1) Å 3 µ ) 15.44 cm -1 Z ) 4 R a ) 0.034 Rw b ) 0.039 a R ) ∑||Fo| -|Fc||/∑|Fo|. b Rw ) [∑w(|Fo| -|Fc|) 2 /(∑w|Fo| 2 )] 1/2 .
The electrochemical properties of the ligand 2 and of the diprotonated 3a-c and dimethylated 5 complexes have been investigated in CH 3 CN (Table 3). The waves observed in cyclic voltammograms are due to oxidation of the ferrocene part of the molecule and correspond to quasi-reversible processes. A detailed analysis of the electrochemical oxidation of compound 2 is presented in the following section.

Concerning compound 3a, under stationary conditions, a study of the limiting current versus the square root of the electrode rotating speed showed a linearity indicating a diffusioncontrolled process (D ) 5.3 × 10 -6 cm 2 s -1 at 25 °C). The electron transfer rate constant k°calculated by the Nicholson and Shain method 25 was close to 10 -2 cm s -1 , typical of a pseudoreversible process. Two faradays per mole of complex were involved in each electrochemical oxidation process for compounds 3a-c as measured by exhaustive electrolysis of solutions of the compounds at controlled potential (0.8 V) on a platinum grid working electrode. The initially yellow solutions turned blue during the electrolysis. These observations suggest that the electron transfer takes place on the ferrocene part of the molecule (the two redox centers are independent). Electrochemical reduction (at 300 mV) of the oxidized forms of 3a-c regenerates the initial compounds. The electrochemical oxidation of these cationic complexes [2(H) 2 ] 2+ can be written Significant anodic perturbations of the ferrocenyl oxidation potentials are induced by protonation and methylation of the amine groups of the chain (205-240 mV) when compared to the parent compound 2. These values are in the same range as those obtained for the protonation and methylation of the simple ferrocenyl amine (C 5 H 5 FeC 5 H 4 CH 2 NMe 2 ): 185 and 190 mV, respectively. 16 These results indicate a comparable Fe-N distance and probably reflect the good flexibility of the organic chain, which prevents a strong Fe-N interaction. The difference in the redox shifts between related protonated 3b and methylated 5 species is rather small and in agreement with the literature data. 16 The voltammograms of the isolated monoprotonated species show, at 0.1V s -1 , two well-defined one-electron reversible oxidation waves of equal intensity which correspond to the presence of two different chemical environments for the ferrocene groups (for example, E 1/2 ) 0.41, 0.59 for 4b): the first one is similar to that of the starting complex (vide infra), and the second one (more anodic potential value) is closer to that of the diprotonated species. Taking into account the proposed exchange phenomenon (Scheme 2), the first wave can be attributed to the nonprotonated ferrocenyl part of a molecule and the second one to the protonated part. In compounds 4ac, the proton exchange is rapid as discussed below, but once the nonprotonated part of the molecule has been oxidized, it is not basic enough to accept (via its N atom) the proton of the nonoxidized protonated part of the molecule. An electrostatic repulsion occurs and prevents the H + exchange. If the proton exchange still occurred, a single oxidation peak would be observed at ≈ 0.4 V. As we have already noted, electrochemistry appears to be a convenient tool for detecting exchange phe- [2(H) 2 ] 2+ h [2(H) 2 ] 4+ + 2e also been investigated in CH 2 Cl 2 (Table 4). As for compound 3a (vide supra), we have verified that the quasi-reversible oxidation process is diffusion-controlled (D ) 3.3 × 10 -6 cm 2 s -1 at 20 °C). About 2 faradays/mol were consumed during controlled potential electrolysis of 2 at 0.8 V, and the initial yellow solution turned green. In contrast with the case of the diprotonated species 3a-c, or the phosphodihydrazide ligand 1, electrochemical reduction of the oxidized species has not been possible. Passivation phenomena attributed to nonconducting deposits have been observed.

To gain a better understanding of this oxidation process, the chemical oxidation of compound 2 has been undertaken. Remembering the previous observation concerning reaction of 2 with a slight excess of Ag salt (vide supra), and considering its well-known oxidation properties, 26 we chose Ag + as oxidizing agent. When 2 equiv of Ag + was added to 2 in CH 2 Cl 2 ,a green solid (similar in color to the electrochemical solution after oxidation) was obtained. Mo ¨ssbauer studies of the solid (Figure 3) indicated the presence of two iron sites in equal proportion. The first one is characterized by a doublet (isomer shift, IS ) 0.519(2) mm s -1 , quadrupole splitting, QS ) 2.368(3) mm s -1 , at 80 K) attributed to the presence of low-spin Fe(II); the second one is a broad singlet (IS ) 0.53(1) mm s -1 , Γ/2 ) 0.39(5) mm s -1 at 80 K) consistent with those previously published for iron (III). 27 The green solid is not stable in solution, but its mass spectrum clearly indicates the presence of the cation 8. The green solid corresponds thus to a mixture of products: one of them has been identified as complex 8 (solid state and solution); the other one could be the desired oxidized form of 2 responsible for the broad Fe(III) singlet observed in the Mo ¨ssbauer spectrum.

In order to verify this hypothesis, reactions of compound 2 with variable amounts of AgCF 3 SO 3 (>2 equiv), according to a precise procedure (see Experimental Section), were undertaken. The products were isolated in solid form and analyzed by Mo ¨ssbauer spectrometry (Figure 3). When 5 equiv of silver salt was added, the Mo ¨ssbauer spectrum exhibited only a broad singlet 28 and the color of the isolated product was deep blue. Microanalyses of this sample are in agreement with the proposed formula [2(H) 2 ][CF 3 SO 3 ] 4 (11), where the N atoms of the chain have been protonated. Mo ¨ssbauer spectra of 11 are very similar to those of the isolated product [2(Me) 2 ]-[BF 4 ] 4 (12) obtained after electrochemical oxidation of the dimethylated compound 5 at0.8VinCH 3 CN. Protonation of the nitrogen atoms during an oxidation reaction with a Ag salt has also been reported recently for a neutral azathiaferrocenophane. 29 In conclusion, an excess of silver salt pushes further the complexation reaction and favors the formation of the blue oxidation product 11. Electrochemical synthesis of this species appeared thus as a new challenge, and the electrochemical oxidation was reinvestigated.

A two-step oxidation was undertaken: a first electrolysis was carried out at 0.45 V (CH 3 CN, Et 4 NBF 4 ), followed by a second one at 0.8 V (Scheme 3). The value of the first potential was chosen in order to selectively oxidize compound 2 and to prevent oxidation of other products formed during this electrolysis.

During the first electrolysis (0.45 V), the yellow solution turned orange and two electrons were exchanged. After electrolysis, the cyclic voltammogram showed a wave corresponding to a quasi-reversible oxidation process (E 1/2 ) 0.60 V). The intensity of this wave was nearly the same as that measured for the starting compound; an orange solution was obtained on extraction with THF. 1 H and 13 C NMR spectra of this solution proved that the diprotonated species 3b (yellow) was the main product. 30 During the second electrolysis (0.8 V), the solution turned blue and again two electrons were exchanged. The linear voltammogram was indicative of the presence of the Fe(III) species (cathodic current). This species can be reduced at 0.2 V to regenerate the orange solution, through a two-electron exchange. a Conditions: [complexes], 1 mmol L -1 ; Pt electrode in CH2Cl2, Bu4NPF6 (0.1 mmol L -1 ); scan rate in cyclic voltammetry, 0.1 V s -1 ; ∆Ep,R ,I p , and n, have the same signification as in Table 3. b An additional wave at ca. 0.69 V was also observed (see text).

Scheme 3

but it was impossible to prepare a sample suitable for Mo ¨ssbauer experiments. However, as mentioned above, electrochemical oxidation of the dimethylated compound 5 at0.8VinCH 3 CN allowed us to obtain the blue cation [2(Me) 2 ] 4+ (12) as a sticky but more tractable oil.

Studies of the oxidation of organic amines have shown that the primary electrode process is the transfer of one electron from the lone pair of nitrogen to the anode to form a cationic radical; in wet acetonitrile, after oxidation, the original aliphatic amine R 3 N is mainly recovered as the ammonium ion R 3 NH + . 31 In the case of the organometallic compound 2, we propose the formation of a similar dicationic radical which abstracts hydrogen atoms (H • ) from the electrochemical medium to yield the diprotonated species. Oxidation of the ferrocenyl moiety then occurs to afford the blue complex.

A minor irreversible wave detected at 1.3 V in the cyclic voltammogram of 2 can be attributed to the oxidation of the amine. This implies that, during the first electrolysis, formation of the dicationic radical occurred after oxidation of the ferrocenyl parts and rapid electron transfer from the nitrogen to the iron centers. A similar mechanism has recently been proposed by Simpson et al. for azadiferrocenyl compounds. 32 It is clear now that the two-step electrochemical oxidation of compound 2 corresponds to the following ECE (electrochemical, chemical, electrochemical) mechanism.

With respect to the result of the former electrolysis carried out at 0.8 V and affording a green solution, another mechanism can be proposed (Scheme 4). It involves the following steps: (a) rapid formation of the diprotonated tetracationic blue species 11 either by the path illustrated in Scheme 3 or after formation of the tetracationic nonprotonated species (13); (b) fast reaction of 11 with the starting yellow compound 2 to afford, through a rapid rearrangement and a new abstraction of H • , the more stable diprotonated dicationic complex 3. This proposed mechanism can explain why only 2 faradays/mol (or less) is necessary under these conditions to yield 3. Unlike the two-step electrochemical oxidation, 11 can react with 2 in solution as soon as it is formed. The green color observed corresponds to a mixture of 11 and 2 and/or 3. It is worth noting that the presence of a minor iron-(III) species and of the major diprotonated species 3 has been detected after electrolysis. Furthermore, the blue species 11 is not very stable in solution and decomposes, yielding a green or yellow solution (depending on the solvent) containing the diprotonated species 3. Passivation phenomena may be ascribed to minor decomposition processes due to the nature of the tetracationic species.

A judicious choice of the oxidation potential has allowed us to prove that a selected oxidation pathway can be favored and that the diprotonated product is a key intermediate.

C. Compounds 6-8. Electrochemical results obtained for complexes 6-8 are gathered in Table 4.

Previous electrochemical studies on polymetallic phosphohydrazone ferrocenyl complexes have shown that the variation in the electrochemical properties of the ferrocene centers is a sensitive probe for evaluating the complexation of the ferrocenyl phosphodihydrazone ligand 1. 3c,d Complex 6 undergoes a quasireversible oxidation process at a potential value (E 1/2 ) 0.45 mV) that is nearly coincident with that of the free ligand 2. This probably reveals a weak binding between 2 and Na + . Complexes 7 and 8 undergo a reversible two-electron oxidation step in dichloromethane at potentials very close to each other (0.54 and 0.55 V), which demonstrates the lack of interaction between the two ferrocenyl centers of each of the species. Complexation of copper and silver ions in CH 2 Cl 2 solution causes the two-electron oxidation of the ferrocene fragment to shift anodically by 120 and 130 mV, respectively. The ∆E 1/2 value obtained for the copper compound is in the same range as that obtained for the diferrocenyl phosphohydrazone derivatives of copper(I). 3c,33 The ∆E 1/2 value obtained for the silver compound is very close to that obtained for the diferrocenyl crown silver cation 1e but larger than that observed for the formation of the recently reported azadiferrocenyl disilver macrocyclic cation [(Fe (C 5

[(Fc-L a -Fc)Ag] + (L a )-CH 2 N- ((CH 2 ) 2 O(CH 2 ) 2 O(CH 2 ) 2 ) 2 NCH 2 -) (110mV)
H 4 -L b - C 5 H 4 ) 2 Fe)Ag 2 ] 2+ (L b )-CH 2 NH(CH 2 ) 4 NHCH 2 -) (45 mV)
(when compared to their respective parent compounds). 20 The perturbation observed in the cyclic voltammograms is probably due to a secondary effect resulting from the close approach of silver coordinated to the nitrogen atom. The similar electrochemical behavior of 7 and 8 probably reflects the same type of phenomenon and similar coordination modes for 2Cu + and 2Ag + .

Electrolyses of compounds 6-8 have been carried out at different oxidation potentials, producing unstable green mixtures containing diprotonated species.

4. Mo 1ssbauer Spectra of Compounds 2, 3c, and 6-8. Mo ¨ssbauer studies of ferrocene derivatives have previously established correlations between QS values and the redox potential of the Fe(II)/Fe(III) couple of disubstituted ferrocenes. 34 Several groups have also used this technique in order to investigate the possible interaction of complexed cations with different ferrocene-base ligands (cryptands, macrocycles) leading to correlations between the Mo ¨ssbauer parameters and the Fe-M n+ internuclear distance, or the strength of this interaction. 1d,35,36 In light of these results, Mo ¨ssbauer studies of compounds 2, 3c, and 6-8 have been undertaken, the results of which are gathered in Table 5

4 2 -2e f 2 2(•+) E 2 2(•+) + 2H • f 3 C 3 -2e f 11 E
examined consist of a temperature independent quadrupole split doublet, typical of low-spin Fe(II), which presents approximately the same parameters as those of ligand 2 at 80 K (IS ) 0.527-(1) mm s -1 ,Q S)2.397(2) mm s -1 ).

From these data, we can conclude that protonation or complexation reactions have no effect on the Mo ¨ssbauer parameters observed for compound 2 and that no direct interaction occurs between the complexed cation and the iron center. In each molecule, both iron sites are in the same local environment. Considering now the different oxidation potentials observed for these molecules, it is clear that no correlation with Mo ¨ssbauer parameters can be made.

Conclusion

As for the phosphodihydrazone complex 1, complex 2 is an efficient ligand for many metals; 1:1 adducts are obtained with small (Na + ) and larger cations (Ag + ) and also with neutral units (MCl 2 ,M)Zn, Hg). This may be due to the relative flexibility of the organic chain as shown for the copper compound (X-ray structure). NMR, Mo ¨ssbauer, and electrochemical data show that all new molecules are symmetric in nature. Cyclic voltammetry has shown that the complexation reactions induce small anodic shifts of the redox potential of the Fe(II)/Fe(III) couple for the cationic species.

Ligand 2 can be easily and cleanly mono-or diprotonated. The synthesis of the monoprotonated species provides us the opportunity to electrochemically detect a proton exchange between the two nitrogen atoms of the ligand.

The two-step electrochemical oxidation of 2 can lead to the same cation 11 as its chemical oxidation by AgCF 3 SO 3 (5 equiv). The complementary use of different techniques (electrochemistry, NMR, Mo ¨ssbauer, and so on) has allowed us to propose an ECE mechanism for this oxidation process.

This study shows that, in contrast to 1, ligand 2 cannot be recovered after successive controlled electrochemical oxidation/ reduction processes of a (2)M + derivative. Unlike the phosphohydrazone chain, the novel N 2 O 2 organic chain has a key role during the oxidation process and is protonated. The use of this ligand for electrochemical recognition of cations would require its deprotonation after oxidation of the complexed cationic species in order to be recycled.

Experimental Section

Tetrahydrofuran and diethyl ether were distilled over sodium/ benzophenone, dichloromethane was distilled over P 2O5, and pentane and CH 3CN were distilled over CaH2 and stored under argon. [CH3-NH(CH 2)2O(CH2)-]2 (Acros), HBF4 (85% in Et2O), HCF3SO3 (98%), MeCF 3SO3,N H 4 PF6 (95%), NaPF6 (98%), Ag(CF3SO3) (99+%), Zn(CF 3SO3)2 (98%) (Aldrich), anhydrous ZnCl2 (98%) (Prolabo), HgCl2 (Ega Chimie), Cu(CF3SO3)'0.5C6H6 (90%) (Fluka), and FcCH2NMe2 (Lancaster) were used without further purification. FcCH2NMe3I 37 and [(C 5H5)Fe(C5H4CH2NCH3(CH2)2OCH2-)]2 4 (2) were prepared according to published procedures. All syntheses were performed under a nitrogen or argon atmosphere using standard Schlenk tube techniques. IR spectra were recorded on a Perkin-Elmer 983 spectrophotometer. Samples were run as KBr pellets prepared in a glovebox. Elemental analyses were carried out on a Perkin-Elmer 2400 B analyzer at the L. C. C. Microanalytical Laboratory in Toulouse. Mass spectra (fast atom bombardment, FAB>0; or desorption chemical ionization, DCI) were performed on a Nermag R10 at the Service Commun de Spectrometrie de Masse de l'Universite ´Paul Sabatier et du CNRS in Toulouse. 1 H, 13 C, and 31 P NMR spectra have been performed on Bruker AC 80, AC 200, AM 250, and AMX 400 spectrometers. 31 P NMR spectra are referenced to external 85% H 3PO4 in D2O, 1 H and 13 C NMR spectra are referenced to tetramethylsilane, 19 F NMR spectra are referenced to external CF 3COOH (10% in C6D6), and 23 Na NMR spectra are referenced to NaCl,4Mi nD 2 O. Variable-temperature and selective decoupling experiments were carried out on an AMX 400 spectrometer equipped with a multinuclear probe. The observation and decoupling frequencies were in the range 400.13 MHz for 1 H, 161.98 MHz for 31 P, 100.62 MHz for 13 C, and 105.84 MHz for 23 Na.

Electrochemical Studies. Electrochemical measurements were carried out with a home-made potentiostat using an interfacing hardware with a PC-compatible microcomputer. The positive feedback or interrupt method was used to compensate for IR drop. A conventional electrochemical cell was used, including three electrodes: a Pt disk (diameter 1 mm) working electrode, a Pt wire auxiliary electrode, and a SCE reference electrode for cyclic voltammetry (scan rate, 0.1 V s -1 ). A rotating disk electrode of Pt with a diameter of 2 mm (EDI Tacussel) was used for analytical purposes (scan rate, 5 mV s -1 ; rotation speed, 1000 rpm). For electrolysis experiments, a Pt grid or a Pt foil was used. The reference electrode consisted of an SCE separated from the solution by a bridge compartment filled with the same solvent and supporting electrolyte solution. All solutions measured were 1.0 × 10 -3 M in the organometallic complex and 0.1 M in supporting electrolyte. Analogous solutions were used for controlled potential coulometry. The supporting electrolyte Bu 4NPF6 or Et4NBF4 (Aldrich analytical grade) was used as received. Dichloromethane (SDS, purex) was refluxed on CaH 2 and distilled under an argon atmosphere prior to use. CH 3CN (Aldrich 99+%) was dried over molecular sieves. The solutions were degassed by bubbling argon during experiments. With the above reference, E°) 0.42 V vs SCE was obtained for 1 mM ferrocene.

Mo 1ssbauer

Studies. Measurements were obtained on a constantacceleration conventional spectrometer with a 25 mCi source of 57 Co (Rh matrix). Isomer shift values (IS) throughout the paper are given with respect to metallic iron at room temperature. The absorber was a sample of 80 mg of microcrystalline powder enclosed ina2c m diameter cylindrical plastic sample holder, the size of which had been determined to optimize the absorption. Variable-temperature spectra were obtained in the 300-4.2 K range, by using a MD 306 Oxford cryostat, the thermal scanning being monitored by an Oxford ITC4 servocontrol device ((0.1 K accuracy). A least-squares computer program 38 was used to fit the Mo ¨ssbauer parameters and determine their standard deviations of statistical origin (given in parentheses).

[(C 5H5)Fe(C5H4CH2N(CH3)(CH2)2OCH2-)]2 (2

Synthesis of [2(H)2][CF3SO3]2 (3a)

. Method A. 168 mg (1.1 mmol) of HCF 3SO3 was added to a solution of 2 (310 mg, 0.5 mmol) in5mLofCH 3CN. The mixture was stirred for 0.5 h, and the solvent was evaporated to dryness. The yellow oil obtained was purified by diffusion in a 2:3 CH 2Cl2/pentane mixture. The solvent was filtered

Method B.

A mixture of 2 (330 mg, 0.58 mmol) and 1 equiv of Zn(CF 3SO3)2 (213 mg, 0.59 mmol) was dissolved in THF (13 mL). The solution was stirred for 48 h at room temperature (20 °C). The solution was filtered and the solvent evaporated to dryness. The orange residue was dissolved in CH 2Cl2 (15 mL). The solution was filtered and evaporated to dryness and the residue washed with pentane (2 × 15 mL) and dried under vacuum.

Synthesis of [2(H) 2][BF4]2 (3b). Two equivalents of HBF4'Et2O

was syringed into a solution of 2 (340 mg, 0.59 mmol) in CH 2Cl2 (10 mL). The mixture was stirred for1ha t2 0°C. The solvent was evaporated to dryness under vacuum, and the yellow product was washed with diethyl ether (2 × 20 mL) and pentane (2 × 20 mL): 1031, 638 (ν CF3SO3). Anal. Calcd for 7,C31H40N2O5SF3Fe2Cu: C, 47.45; H, 5.14; N, 3.57. Found: C, 47.41; H, 5.00 N, 3.51.

Synthesis of [2Ag][CF 3SO3] (8).

A light-protected mixture of Ag-(CF 3SO3) (184 mg, 0.72 mmol) and 2 (410 mg, 0.72 mmol) was prepared in a glovebox; 15 mL of THF was rapidly added. The mixture was stirred for 15 h. After filtration, the solution was evaporated to dryness and the orange powder was washed with pentane and dried under vacuum: 310 mg, 52% yield. 1 H NMR (400 MHz, CD3CN): δ 2.40 (s, 6H, CH 3), 2.76 (br s, 4H, NCH2CH2O), 3.44 (br s, 4H, FcCH 2N), 3.63 (s, 4H, OCH2CH2O), 3.66 (t, J ) 4.9 Hz, 4H, NCH 2CH2O), 4.22, 4.30 (each br s, 18H, C5H5FeC5H4). 13 C NMR (62.9 MHz, CD 3CN): δ 44.9 (q, JCH ) 133 Hz, NCH3), 59.0 (t, JCH ) 136 Hz), 59.8 (t, J CH ) 137 Hz), 65. 4

Synthesis of [2HgCl 2] (10).

A mixture of 1 equiv of HgCl2 (204 mg, 0.75 mmol) and 1 equiv of 2 (430 mg, 0.75 mmol) was rapidly dissolved in 20 mL of THF. The mixture was stirred for 29 h at 60 °C, and the solution was filtered and evaporated to dryness. After diffusion in a CH 2Cl2/pentane mixture, the solid was washed with pentane and dried under vacuum, yielding an orange powder: 600 mg, 95% yield. (ZnCl 2 and HgCl2 were weighed under argon.) 1 H NMR (200 MHz, CDCl 3): δ 2.33 (s, 6H, CH3), 2.71 (br s, 4H, NCH2CH2O), 3.63 (br s, 4H, FcCH 2No rO C H 2 CH2O), 3.70 (t, J ) 5.6 Hz, 4H, NCH 2CH2O), 3.71 (br s, 4H, FcCH2NorOCH2CH2O), 4.13, 4.23 (each m, 18H, C 5H5FeC5H4). 13 C NMR (62.9 MHz, CDCl3): δ 41.5 (q, JCH ) 136 Hz, NCH3), 55.2, (t, JCH ) 138 Hz), 57.5 (t, JCH ) 138 Hz), 68.0 (t, J CH ) 136 Hz), 70. Experiments were carried out in the absence of light, and reactants were weighed in a glovebox; n equiv of Ag(CF 3SO3)( n)2 -5) was dissolved in 15 mL of CH 2Cl2 and the mixture vigorously stirred. A solution of compound 2 (200 mg) in 15 mL of CH 2Cl2 was slowly added dropwise. After 0.5 h, the solution was filtered with a cannula under argon and rapidly evaporated to dryness. The product was dried under vacuum for several hours: 339 mg, 83% yield (n ) 5). Anal. Calcd for 11,C 34H42N2O14Fe2S4F12: C, 34.89; H, 3.62; N, 2.39. Found: C, 34.48; H, 3.76; N, 2.52.

Electrochemical Oxidation of 5: Synthesis of [2(Me)2][BF4]4 (12).

After a controlled-potential electrolysis at 0.8 V of a solution of 5 (75.4 mg in 10 mL of CH 3CN, Et4NBF4), the blue electrochemical mixture was immediately evaporated to dryness for 4 h. The product was extracted with several fractions of CH 2Cl2 (15, 10, 5, and 3 mL). The solvent was evaporated, yielding a blue product. Anal. Calcd for 12, C 32H46N2O2Fe2B4F16: C, 40.41; H, 4.88; N, 2.95. Found: C, 40.24; H, 4.78; N, 2.75.

Crystallographic Study of Compound (7).

The data collection was performed at low temperature (T )-93 °C) on an I.P.D.S. STOE using graphite-monochromatized Mo KR radiation and equipped with an Oxford Cryostream cooling device. The structure was solved by direct methods using SIR92 [START_REF] Altomare | SIR92, a program for automatic solution of crystal structures by direct methods[END_REF] and subsequent Fourier maps. The refinement was performed by using the full-matrix least-squares technique with the CRYSTALS package. [START_REF] Watkin | CRYSTALS Issue 10[END_REF] All hydrogen atoms were found on difference Fourier maps, but they were included in the refinement process as fixed contributors with C-H ) 0.96 Å and isotropic thermal parameters fixed 20% higher than those of their carbon atoms. Their positions were calculated after each refinement cycle. All non-hydrogen atoms were anisotropically refined. Full-matrix leastsquares refinement was carried out by minimizing the function ∑w(|F o| -|F c|) 2 , where Fo and Fc are the observed and calculated structure factors. Models reached convergence with R and R w values mentioned in Table 1. The molecule was drawn using CAMERON. [START_REF] Watkin | [END_REF] Acknowledgment. Dr. Rene ´Mathieu (Toulouse, France) is gratefully acknowledged for fruitful discussion. We gratefully acknowledge Dominique de Montauzon (Service d'Electrochimie du LCC, CNRS) for expert technical assistance and fruitful discussion. We thank Dr. Jean Claude Daran (Toulouse, France) for helpful discussions about the X-ray data, and Dr. Paul-Louis Fabre (Castres) is acknowledged for fruitful discussion. The suggestion provided by one of the reviewers, concerning the CV perturbation for the [Fe-Ag] compound, is also acknowledged.

Supporting Information Available: Complete crystal data, data collection, and refinement parameters (Table S1), fractional atomic coordinates and equivalent thermal parameters (Table S2), full list of interatomic distances (Table S3) and bond angles (Table S4), fractional atomic coordinates and isotropic thermal parameters for the H atoms (Table S5), anisotropic thermal parameters for the non-hydrogen atoms (Table S6) for 7, 2D NMR data and selected spectra for 2 and 3a, and expanded 1 H NMR (CD3CN, 200 MHz) spectra at δ ) 1.5-5.0 ppm for 2, 3a, 4a, and 5 (14 pages). Ordering information is given on any current masthead page. Observed and calculated structure factors have been deposited at the Cambridge Crystallographic Data Center. Copies of the data can be obtained, free of charge, on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EC, U.K.

Figure 1 .

 1 Figure 1. Molecular view of the structure of compound (2) (CAM-ERON) with 30% thermal ellipsoids.

Figure 2 .

 2 Figure 2. Cyclic voltammograms of (a) 2, (b) 2 + 1 equiv of NH4-PF6, and (c) 2 + 2 equiv of NH4PF6 at 0.1 V s -1 . Experimental conditions: Pt electrode (1 mm) in 0.1 mol L -1 solution of n NBu4PF6 in CH3CN, complex concentration 10 -3 M.

Figure 3 .

 3 Figure 3. 57 Fe Mo ¨ssbauer spectrum of (a) 2, (b) 2 + 2 equiv of Ag + , (c) 2 + 4 equiv of Ag + , and (d) 2 + 5 equiv of Ag + , at 80 K (isolated samples).

Scheme

  Scheme 4

  2 (t, JCH ) 135 Hz) (NCH2CH2O, FcCH2N, OCH 2CH2O, and NCH2CH2O), 68.5 (m, 1 JCH ) 176 Hz) , 68.6 (m, 1 JCH ) 176 Hz), 70.7 (m, 1 JCH ) 174 Hz) (C5H5FeC5H4). MS-FAB: m/z 844 [M] + , 809 [M -Cl] + . MS-DCI: 809 [M -Cl] + . Anal. Calcd for 10,C 30H40N2O2Fe2HgCl2: C, 42.70; H, 4.78; N, 3.32. Found: C, 42.71; H, 4.79; N, 3.26. Chemical Oxidation of 2: Synthesis of [2(H) 2][CF3SO3]4 (11).

  8b,14 In 6

	Scheme 1	Scheme 2
	additional coordination could be provided from the PF 6 coun-teranion through its F atoms. 15 However, 31 P{ 1 H} (161.98 MHz,
	CD 2 Cl 2 ) variable temperature NMR experiments down to 183 K do not show significant variation of the spectra, thus lending
	no support to this proposal (the heptuplet at -141.72 ppm is
	not modified). Yellow crystals of the pure compound were
	obtained, but they were not suitable for X-ray diffraction
	studies.
	When treated with CuCF 3 SO 3 '0.5C 6 H 6 in 1:1 stoichiometry in CH 2 Cl 2 or THF, 2 afforded the adduct [2Cu][CF 3 SO 3 ]( 7 ).
	(7) Plenio, H.; El-Desoky, H.; Heinze, J. Chem. Ber. 1993, 126, 2403. (8) (a) Cheney, J.; Lehn, J. M. J. Chem. Soc., Chem. Commun. 1972, 487. (b) Plenio, H.; Diodone, R. J. Organomet. Chem. 1995, 492, 73. (9) (a) Beer, P. D.; Crowe, D. B.; Ogden, M. I.; Drew, M. G. B.; Main,
		(12) Cheney, J.; Kintzinger, J. P.; Lehn, J. M. NouV. J. Chim. 1978, 2, 411. (13) Crescenzi, R.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1996, 35, 2413. (14) (a) Plenio, H. Inorg. Chem. 1994, 33, 6123. (b) Plenio, H.; Diodone, R. Inorg. Chem. 1995, 34, 3964 and references therein.

B. J. Chem. Soc., Dalton Trans. 1993, 2107. (b) Graf, E.; Kintzinger, J. P.; Lehn, J. M.; LeMoigne, J. J. Am. Chem. Soc. 1982, 104, 1672. (c) Graf, E.; Lehn, J. M. HelV. Chim. Acta 1981, 64, 1040. (d) Graf, E.; Hosseini, M. W.; Ruppert, R.; De Cian, A.; Fischer, J. J. Chem. Soc., Chem. Commun. 1995, 1505. (10) Monitoring first this reaction with electrochemical methods allowed us to observe that addition of 2 equiv of NH 4PF6 produces an anodic shift (220 mV) of the Fe(II)/Fe(III) couple; this could be ascribed to the formation of the adduct [2NH4][PF6]. 9a (11) Bru ¨gge, H.-J.; Carboo, D.; von Deuten, K.; Kno ¨chel, A.; Kopf, J.; Dreissig, W. J. Am. Chem. Soc. 1986, 108, 107.

Table 1 .

 1 Crystal and Intensity Data for 7

	empirical formula: C30H40N2O2Fe2Cu	formula wt: 784.96

Table 2 .

 2 Selected Bond Lengths (Å) and Bond Angles (deg) for 7,

	with Esd's in Parentheses
	Cu-O(1) Cu-O(2) Cu-N(1) Cu-N(2) N(1)-C(1) N(1)-C(2) N(1)-C(10) C(1)-C(120) C(8)-C(121)	Bond Lengths (Å) 2.517(4) C(2)-C(3) 2.610(4) C(3)-O(1) 1.966(4) O(1)-C(4) 1.953(4) C(4)-C(5) 1.512(6) C(5)-O(2) 1.484(7) O(2)-C(6) 1.490(7) C(6)-C(7) 1.500(7) C(7)-N(2) 1.495(7) N(2)-C(8)	1.483(9) 1.419(7) 1.422(8) 1.515(9) 1.431(8) 1.413(7) 1.50(1) 1.499(8) 1.515(6)

  nomena, which are not always easily or cleanly detected by other techniques.

3d B. Electrochemical and Chemical Oxidation of Compound 2. The electrochemical behavior of compound 2 has (23) (a) Bracci, M.; Ercolani, C.; Floris, B.; Basseti, M.; Chiesi-Villa, A.; Guastini, C. J. Chem. Soc., Dalton Trans. 1990, 1357. (b) Fleishmann, W.-D.; Fritz, H. P. Z. Naturforsch. 1973, 28b, 383. (c) Kawamoto, T.; Kushi, Y. J. Chem. Soc., Dalton Trans. 1992, 3137. (d) Corain, B.; Longato, B.; Favero, G.; Ajo, D.; Pilloni, G.; Russo, U.; Kreissl, F. R. Inorg. Chim. Acta 1989, 157, 259. (e) Plenio, H.; Dirk, B. Organometallics 1996, 15, 4054. (24) (a) Houlton, A.; Ibrahim, S. K.; Dilworth, J. R.; Silver, J. J. Chem. Soc., Dalton Trans. 1990, 2421 and references therein. (b) Mann, K. R.; Morrison, W. H.; Hendrikson, D. N. Inorg. Chem. 1974, 13, 1180. (25) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706.

Table 3 .

 3 Electrochemical Ep c -Ep a .R I p )| I p (backward)/Ip(forward)| ) |Ip red /Ip ox |. n ) number of exchanged electrons in the electrochemical process. P ) slope of the linear regression of E ) f(log |i/id-i|). b See text section 4. Conditions: [complexes], 1 mmol L -1 ; Pt electrode; rotating electrode 1000 rpm; scan rate in cyclic voltammetry, 0.1 V s -1 ; solvent CH3CN, Bu4NPF6 (0.1 mol L -1 ).

			Data for Complexes 2, 3a-c, and 5
	compd	E1/2 (V)	P (mV)	nE p a (V)	∆Ep (mV)	RIp
	2 3a 3b 3c 5	0.38 0.59 0.59 0.60 0.62	63 56 58 57 55	2 2 2 2 2	0.43 0.64 0.66 0.67 0.67	85 89 99 75 80	1.0 1.0 1.0 1.0 1.0

a ∆Ep ) Ep(backward) -Ep(forward) )

Table 4 .

 4 Electrochemical Data for Complexes 2 and 6-8

	compd	E1/2 (V)	Ep a (V)	Ep r (V)	∆Ep (mV)	RIp
	2 6 7 b 8	0.42 0.45 0.54 0.55	0.47 0.48 0.58 0.59	0.40 0.41 0.51 0.52	70 70 70 70	1.0 1.0 1.0 1.0

  . At 297 K, no spectra are obtained for 2 and 7. From 200 K to 4 K, the spectra for all complexes

(31) Ross, S. D.; Finkelstein, M.; Rudd, E. J. In Anodic Oxidation; Academic Press: New York, 1975; Vol. 32, Chapter 8, p 189. (32) Spescha, M.; Duffy, N. W.; Robinson, B. H.; Simpson, J. Organometallics 1994, 13, 4895. (33) The novel copper compound 7 also presents a wave of lower intensity at 0.69 V vs SCE resulting from the oxidation of Cu(I) as previously observed for the above mentioned iron-copper compounds. 3c (34) Roberts, R. M. G.; Silver, J. J. Organomet. Chem. 1984, 263, 235. (35) Hall, C. D.; Danks, I. P.; Hammond, P. J.; Sharpe, N. W.; Thomas, M. J. K. J. Organomet. Chem. 1990, 388, 301. (36) (a) Akabori, S.; Shibahara, S.; Habata, Y.; Sato, M. Bull. Chem. Soc. Jpn 1984, 57, 63. (b) Akabori, S.; Habata, Y.; Sato, M. Bull. Chem. Soc. Jpn 1984, 57, 68. (c) Akabori, S.; Habata, Y.; Sakamoto, Y.; Sato, M.; Ebine, S. Bull. Chem. Soc. Jpn. 1983, 56, 537.

Table 5 .

 5 Least-Squares Fitted Mo ¨ssbauer Data a,b for Compounds IS: isomer shift. QS: quadrupole splitting. Γ/2: half-hight width of line.b With their statistical standard deviation given in parentheses; isomer shift values refer to metallic iron at 300 K. off and the oil dried under vacuum: 448 mg, 95% yield. 1 H NMR (400 MHz, CD 3CN): δ 2.77 (m, 6H, CH3), 3.21 (dm, 4H, NCH2CH2O), 3.66 (s, 4H, OCH 2CH2O), 3.75 (t, 4H, J ) 15.0 Hz, NCH2CH2O), 4.23 (br s, 4H, FcCH 2N), 4.30 (s, 10 H, C5H5), 4.39, 4.50, 4.52 (8H, each br s, C 5H4), 7.42 (s, 2H, NH). 13 C{ 1 H} NMR (100.62 MHz, CD3CN): δ 40.14 (s, CH 3), 54.21, 54.26 (each s, NCH2CH2O), 57.43 (s, FcCH2N), 64.39 (s, NCH 2CH2O), 69.72 (s, C5H5), 70.58, 70.70, 71.92, 72.20, 74.11 (each s, C 5H4), 70.46 (s, OCH2CH2O); (CD2Cl2, 193 K): δ 119.4 (q, J CF ) 319 Hz). MS-FAB: 723 [M -CF3SO3] + , 573 [M -2CF3-SO 3 -H] + . Anal. Calcd for 3a,C 32H42N2O8S2F6Fe2: C, 44.05; H, 4.85; N, 3.21. Found: C, 43.72; H, 4.90; N, 3.25.

	2, 3c, and 6-8 at 80 K
	compd	IS (mm/s)	QS (mm/s)	Γ/2 (mm/s)
	2 3c 6 7 8	0.527(1) 0.510(2) 0.520(1) 0.523(1) 0.520(1)	2.397(2) 2.390(5) 2.382(2) 2.389(2) 2.378(2)	0.128(2) 0.115(4) 0.116(2) 0.121(1) 0.133(1)

a

  was dissolved in 20 mL of THF, and 95 mg (0.70 mmol) of ZnCl 2 was added to the orange solution. The mixture was stirred for 20 h at 60 °C. After filtration, pentane (40 mL) was added. After filtration and evaporation to dryness, the yellow product obtained was washed with pentane and dried under vacuum: 479 mg, 97% yield.1 H NMR (200 MHz, CDCl 3): δ 2.39 (s, 6H, CH3), 2.76 (br s, 4H, NCH2CH2O), 3.73, 3.80 (br s, 12H, NCH 2CH2O, FcCH2N, OCH2CH2O), 4.14, 4.22 (each br s, 18H, C 5H5FeC5H4). 13 C{ 1 H} NMR (50.3 MHz, CDCl3): δ 40.6 (s, NCH 3), 53.9, 57.0, 65.3, 70.2 (each br s, NCH2CH2O, FcCH2N, OCH 2CH2O, NCH2CH2O), 69.1, 69.6, 71.5 (each s, C5H5FeC5H4). MS-FAB: [M + H] + 709. MS-DCI: [M + H] + 709. Anal. Calcd for 9,C 30H40N2O2Fe2ZnCl2: C, 50.85; H, 5.69; N, 3.95. Found: C, 51.23; H, 6.03; N, 3.83.

	(t, JCH ) 142 Hz), 69.4 (t, JCH ) 143
	Hz) (NCH 2CH2O, OCH2CH2O NCH2CH2O, FcCH2N), 69.1 (m 1 JCH
	) 176 Hz), 69.5 (m, 1 JCH ) 176 Hz), 70.8 (m, 1 JCH ) 175 Hz), 82.8
	(s) (C 5H5FeC5H4). MS-FAB: m/z 828 [M] + , 679 [M -CF3SO3] + .IR
	(KBr, ν,c m -1 ): 1268, 1032, 641 (ν,C F 3 SO3). Anal. Calcd for 8,
	C 31H40N2O5SF3Fe2Ag: C, 44.93; H, 4.87; N, 3.38. Found: C, 44.82;
	H, 4.88 N, 3.37.
	Synthesis of [2ZnCl 2] (9). A 400 mg (0.70 mmol) sample of 2