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DALTON FULL PAPER J. Chem. Soc. Dalton Trans. 1999 867–873 867 Half-sandwich molybdenum compounds with phosphine– alkylthiolate and phosphine–thioether ligands. Crystal structure of [CpMo(SCH2CH2PPh2)2][BPh4] Dolores Morales Rinaldo Poli,* Philippe Richard Jacques Andrieu and Edmond Collange Laboratoire de Synthèse et d’Electrosynthèse Organométalliques Faculté des Sciences “Gabriel” Université de Bourgogne 6 Boulevard Gabriel 21100 Dijon France. E-mail Rinaldo.Poli@u-bourgogne.fr Received 21st December 1998 Accepted 21st January 1999 The reaction of CpMoCl2 with Ph2PCH2CH2SR (R = H CH3) yields the corresponding addition products CpMoCl2(Ph2PCH2CH2SR) but only the derivative with R = CH3 (compound 5) is suYciently stable to be isolated as a crystalline solid. The derivative with R = H evolves rapidly to aVord a mixture of compounds [CpMo(SCH2CH2- PPh2)2]1Cl2 1 and [CpMoCl(SCH2CH2PPh2)]2 2 the former being favored by a larger ligand :Mo ratio.Compound 1 undergoes metathesis with NaBPh4 to aVord [CpMo(SCH2CH2PPh2)2]1BPh4 2 3 which has been characterized by X-ray crystallography. The reaction of CpMoCl2 with 2 equivalents of Ph2PCH2CH2S2Li1 aVords the paramagnetic complex CpMo(SCH2CH2PPh2)2 4 which is readily oxidized by Cp2Fe1 or by H1 to the corresponding cation. The salts 1 and 3 in turn may be reduced by Na amalgam MeLi or ButOK to compound 4. The reversible redox process interconverting 4 and its cation occurs at E2� 1 = 21.23 V relative to the ferrocene standard while compound 5 shows a reversible oxidation process at E2� 1 = 0.12 V by cyclic voltammetry. The comparison between these potentials and that previously reported for CpMoCl2(dppe) indicates relative donor abilities in the order Ph2P > MeS and RS2 > Cl2.Compound 5 can also be synthesized by Na amalgam or Zn reduction of CpMoCl4(Ph2PCH2CH2SCH3) 6 which is obtained by addition of the ligand to CpMoCl4. Introduction Molybdenum complexes with sulfide thiolate or thioether ligands are extensively used models for understanding the mechanism of action of fossil fuel hydrotreating catalysts and metalloenzymes involved in the nitrogen cycle.1–10 In both areas useful information has been obtained from fundamental investigations of the eVect of the coordination environment on the stability redox properties and reactivity. A great many studies have been devoted to dinuclear half-sandwich complexes of Mo(III) and Mo(IV),6,7,10 generally containing only anionic ligands (halides thiolates sulfide) or a combination of these and neutral p-acceptor ligands (carbonyl isocyanides thioethers).In our laboratory we have investigated in detail reactivity and redox properties as a function of the ligands for a class of mononuclear complexes of formula CpMoX2L2 where X is a halide ligand and L is typically a tertiary phosphine.11–18 These are stable paramagnetic compounds characterized by a 17-electron configuration and sharp room temperature isotropic EPR resonances. Here we extend the above class to thiolate and thioether derivatives. Results Reactions with the Ph2PCH2CH2SH ligand The reaction between CpMoCl2 and the bifunctional ligand Ph2PCH2CH2SH in a 1 1 or 1 2 ratio produces compounds [CpMo(SCH2CH2PPh2)2]Cl 1 and [CpMoCl(SCH2CH2PPh2)]2 2 [eqn.(1)]. The interaction initially aVords an EPR active CpMoCl2 1Ph2PCH2CH2SHæÆ[CpMo(SCH2CH2PPh2)2]Cl 1 1 [CpMoCl(SCH2CH2PPh2)]2 (1) 2 intermediate which disappears within a few minutes. The EPR properties of this intermediate indicate its probable composition as the addition product CpMoCl2(Ph2PCH2CH2SH) by comparison with those of the stable thioether analogue CpMoCl2(Ph2PCH2CH2SCH3) compound 5 see below. When a larger excess of the ligand was used (3.5 equivalents) however compound 1 was recovered in a greater yield (57% relative to 40% when 2 equivalents were used) and product 2 was absent. The yield of compound 1 was even lower (20%) when using a 1 1 Mo ligand ratio. Compound 1 which is obtained as a yellow precipitate from the reaction mixture is insoluble in all common solvents and only slightly soluble in MeOH.A 31P-{1H} NMR spectrum in MeOH shows a single resonance at d 85.1 indicating its diamagnetic nature. Methathesis of 1 with NaBPh4 yields a more soluble tetraphenylborate salt 3 which was amenable to a more detailed characterization. The 31P-{1H} NMR resonance of 3 compares with that of 1 while the triplet 1H NMR resonance for the Cp ring at d 4.40 (JPH = 1.83 Hz) is direct evidence for the presence of two ligands per metal atom. These spectral data suggest a four-legged piano stool structure for the cation leaving uncertain the stereochemistry (cis vs. trans). The trans configuration is shown by the X-ray structural characterization (see below). Compound 2 is obtained as a microcrystalline brown solid by diVusion of pentane into the CH2Cl2 solution after separation of compound 1.This compound is insoluble in hydrocarbon solvents but soluble in CH2Cl2 CHCl3 and THF. Elemental analyses (C H S) and NMR investigations (1H and 31P) help in the structural assignment of the compound. The doublet Cp resonance in the 1H NMR spectrum indicates the presence of only one ligand per metal atom and the diamagnetism requires a dimeric formulation since mononuclear half-sandwich Mo(III) complexes are paramagnetic and EPR active.17 A saturated electronic configuration can be reached by adopting a 868 J. Chem. Soc. Dalton Trans. 1999 867–873 bridged structure with a metal–metal bond as described for the isoelectronic complex {[CpMo(m-SBut)(CO)2]2}21.19 In principle either the two chloride ligands or the two thiolate functions may occupy the bridging positions.The superior bridging ability of thiolates relative to halides lead us to propose structure I for compound 2. The isoelectronic Mo(III) complexes [CpM(SMe)X(CO)]2 (M = Mo W; X = Cl Br) have also been proposed to adopt a thiolato-bridged structure with terminal halide ligands,20 and complexes with bridging thiolato or hydrosulfide and terminal chlorides are known for other metals.21,22 The single 31P-{1H} NMR resonance at d 78.5 indicates the equivalence of the two phosphorus atoms and the chelating nature of the ligand but cannot distinguish between the P–S and the P–(m-S) binding modes. Unfortunately suitable crystals for an X-ray investigation could not be obtained. The reaction between CpMoCl2 and 1 equivalent of Ph2PCH2CH2S2Li1 leads to a mixture of unidentified paramagnetic products.However the reaction with 2 equivalents of the same reagent produces a stable paramagnetic Mo(III) compound namely CpMo(SCH2CH2PPh2)2 4 see eqn. (2). Compound 4 CpMoCl2 1 2 Ph2PCH2CH2S2Li1 æÆ CpMo(SCH2CH2PPh2)2 1 2 LiCl (2) 4 also forms upon treatment of compound 2 with Ph2PCH2- CH2S2Li1 see eqn. (3). The identity of this complex as a 17- [CpMoCl(SCH2CH2PPh2)]2 1 2 Ph2PCH2CH2S2Li1 æÆ 2 2 CpMo(SCH2CH2PPh2)2 1 2 LiCl (3) 4 electron monomer is confirmed by the EPR spectrum which shows a binomial triplet (g = 1.987 aP = 3.9 G aMo = 32.4 G) in hexane (other solvents yield a broader resonance which does not permit the observation of the phosphorus coupling). It is interesting to note the unusually small phosphorus hyperfine coupling.In previously reported bis(phosphine) dichloro complexes of half-sandwich Mo(III) the aP values are smaller when the two P donors adopt a relative trans configuration (in the 9–16 G range) than when they are located cis to each other (greater than 23 G).12,14,23 A trans geometry seems therefore most reasonable for compound 4. This compound can be also synthesized by reduction of compounds 1 and 3 eqn. (4). The reduction of the THFsoluble 3 can be easily accomplished with sodium while the reduction of the insoluble 1 can conveniently be carried out by the use of THF-soluble reducing agents. One such reagent is MeLi which is known to display single electron transfer properties. 24 The reduction process with this reagent is instantaneous in THF.Somewhat surprisingly a clean reduction process also occurs albeit more slowly (12 h) with ButOK. Cosely compound 4 can be chemically oxidized to the corresponding cation by a ferrocenium salt [Cp2Fe]BF4 or by the proton of HBF4?OEt2 as shown by EPR and NMR spectroscopic monitoring. Oxidation with HBF4?OEt2 in C6D6 led to the immediate evolution of H2 which was identified by the characteristic NMR resonance at d 4.5. The reversibility of the redox process in eqn. (4) can also be Mo S S Mo Cl Ph2P P Cl Ph2 I witnessed by electrochemical investigations. The cyclic voltammogram of compound 4 shows a reversible oxidation wave at E2� 1 = 21.23 V which is quite close to the potential of the reversible reduction wave measured for compound 3 (E2� 1 = 21.25 V). This value is an indicator of the electron richness of this system relative to the CpMoCl2L2 complexes (L = tertiary phosphine) whose oxidation potentials are in the range 20.33 V (for L2 = dppe) to 20.63 V (for L = PPrn 3).14 This illustrates the greater donor capability of a thiolate ligand relative to a chloride.Since compound 3 is shown by the X-ray analysis to adopt a trans geometry the reversibility of the redox process indicates the same relative configuration for compound 4 confirming the prediction previously made on the basis of the aP value in the EPR spectrum. A view of the cation of compound 3 is shown in Fig. 1 and bond lengths and angles in Table 1. The geometry can be described as a four-legged piano stool with the pairs of sulfur and phosphorus atoms occupying relative trans positions to yield an approximate C2 local symmetry.The CNT–Mo–L angles (CNT = center of gravity of the Cp ring) are larger for Fig. 1 An ORTEP45 view of the cation of compound 3 with thermal ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Mo S P P S Mo S P P S + (ii) 4 (i) [Cp2Fe]BF4 or HBF4 (X= BF4) (ii) Na (X= BPh4) or 2MeLi (X=Cl) or ButOK (X=Cl) Ph2 Ph2 Ph2 Ph2 X – (4) 1 (X = Cl) 3 (X = BPh4) (i) J. Chem. Soc. Dalton Trans. 1999 867–873 869 the thiolate donors than for the phosphorus donors as predicted on the basis of the p-donor/acceptor properties of these ligands and the diamagnetic configuration of the complex.25 The geometry and metric parameters can be best compared with those of the isoelectronic oxo compound MoO(SCH2- CH2PPh2)2.26 Both are compounds of Mo(IV) with the same bifunctional ligand the O22 and Cp2 ligands being both capable of establishing three bonding interactions (s 1 2p) and therefore being able to donate 6 electrons to the metal center.The Mo–P distances are comparable in the two compounds whereas the Mo–S distances are significantly shorter in the cation of 3 relative to the oxo analogue (2.372(4) Å and 2.348(4) Å).26 This diVerence can be rationalized by the stronger electron donating capability of the O22 ligand relative to the Cp2 as also indirectly established from other comparisons.27 Reactions with the Ph2PCH2CH2SCH3 ligand The reaction between CpMoCl2 and the phosphine–thioether ligand Ph2PCH2CH2SCH3 leads to the addition product 5 see Scheme 1 which was isolated as a microcrystalline brown-red solid and characterized by elemental analysis EPR spectroscopy and cyclic voltammetry.The compound is indefinitely stable under an argon atmosphere at 280 8C but decomposes at room temperature rather quickly even under an inert atmosphere. The EPR spectrum shows the expected doublet due to coupling with a phosphorus atom (g = 1.973 aP = 24.7 G aMo = 35.9 G). These properties compare quite well with those of the diphosphine derivatives CpMoCl2(L–L) (L–L = dppe dmpe) for which a four legged piano-stool structure with a cis arrangement of the two phosphorus donors was demonstrated. 12,28 An analogous structure is therefore also proposed for compound 5. In particular the phosphorus hyperfine coupling constant of 5 is only slightly smaller than those of the diphosphine analogues (26 G for the dppe complex and 28 G for the dmpe complex) and the Mo hyperfine coupling constant Scheme 1 Mo S Cl P Cl Me 5 6 2Na–Hg or Zn Ph2 CpMoCl4(Ph2PCH2CH2SMe) Ph2PCH2CH2SMe Ph2PCH2CH2SMe CpMoCl2 CpMoCl4 Table 1 Selected bond distances (Å) and angles (8) for compound 3a Mo–CNT Mo–S(1) Mo–P(2) CNT–Mo–S(1) CNT–Mo–S(2) CNT–Mo–P(1) CNT–Mo–P(2) S(1)–Mo–S(2) 1.98(2) 2.3261(9) 2.4824(9) 125(1) 116(1) 111(1) 108(1) 118.82(3) Mo–S(2) Mo–P(1) S(1)–Mo–P(1) S(1)–Mo–P(2) S(2)–Mo–P(1) S(2)–Mo–P(2) P(1)–Mo–P(2) 2.3134(9) 2.4770(9) 77.84(3) 82.22(3) 82.72(3) 77.64(3) 140.56(3) a CNT is the centroid of the cyclopentadienyl ring.is correspondingly slightly greater (29 and 33 G for dppe and dmpe analogues respectively). The alternative trans arrangement observed for the bulkier Cp*MoCl2(dppe) derivative leads to completely diVerent spectral parameters.23 The g factor was shown to be highly dependent on the nature of the halide ligands but rather independent of the phosphine substituents (in the 1.978–1.994 range for the dichloride complexes).The g value recorded for compound 5 is at the low end of this range and a direct comparison with the value for CpMoCl2(dppe) (g = 1.986) 12 indicates a rather small low-field shift caused by the replacement of a PPh2 donor with a SMe donor. Compound 5 shows a reversible oxidation wave at E2� 1 = 0.12 V in the cyclic voltammogram. This is 0.45 V more positive relative to the oxidation process of the analogous CpMoCl2(dppe) complex,14 indicating that the SMe group is a weaker electron donor relative to the PPh2 group as expected from the diVerent electronegativity of the two donor elements.Compound 5 has also been prepared by an alternative procedure (Scheme 1). The reaction between CpMoCl4 and one equivalent of the ligand in CH2Cl2 aVords the corresponding addition product CpMoCl4(Ph2PCH2CH2SCH3) 6 in good yields. Reduction of compound 6 in THF with either 2 equivalents of sodium amalgam or 1 equivalent of Zn gives the Mo(III) complex 5. The EPR spectrum of compound 6 does not show coupling to the phosphorus atom (singlet at g = 1.954 aMo = 51.8 G). Previously reported phosphine adducts of alkylsubstituted cyclopentadienyl derivatives of Mo(V) display rather large phosphorus hyperfine constants (greater than 24 G),29–31 thus indicating the possibility that the bifunctional ligand binds the metal in a monodentate fashion via the sulfur donor in compound 6.However we find that the addition of the electronically similar PMePh2 ligand to CpMoCl4 aVords an EPR spectrum which consists of a single resonance with no observable hyperfine coupling to the P nucleus. The g value and aMo hyperfine coupling of this spectrum are very similar to those of the Ph2PCH2CH2SMe adduct (see Experimental section). Therefore phosphorus coordination to the metal center remains a structural possibility. We have also considered the possibility of a bidentate coordination mode for the phosphine– thioether ligand. This alternative arrangement would likely induce the displacement of a chloro ligand to aVord an ionic isomer [CpMoCl3(h2-Ph2PCH2CH2SMe-P,S)]1Cl2. Electrical conductivity measurements indicate the presence of ionic species (L• = 9.3 and 90.5 S cm2 mol21 in THF and MeCN solutions respectively).The values measured however are slightly smaller than those typically observed for fully dissociated 1 1 salts.32 A possible rationalization of this result is the existence of an equilibrium between ionic and neutral isomeric forms. An attempt was made to methylate compound 5 with methyllithium. The reaction with 1 equivalent of MeLi carried out at 280 8C in THF led to the disappearance of the starting material without the appearance of new EPR-active species. The 31P-{1H} NMR spectrum showed the formation of a complex mixture of several products which was not further investigated. When 2 equivalents of MeLi were used the immediately recorded EPR spectrum showed a new doublet resonance (g = 1.987 aP = 24.3 G aMo = 38.6 G) which we tentatively assign to the dimethyl product CpMo(CH3)2(Ph2PCH2CH2- SMe) but the signal dared after ca.1/2 h at room temperature. The 31P-{1H} NMR spectrum showed the release of the free ligand Ph2PCH2CH2SMe. An analogous alkylation attempt had been carried out previously for the compound CpMoCl2(PMe3)2 also resulting in decomposition of the alkylation product,13 whereas the alkylation of CpMoCl2(h4- C4H6) aVords thermally stable dialkyl derivatives.33 The positive shift of the g value upon methylation of compound 5 (from 1.973 to 1.987) parallels those observed upon methylation of CpMoCl2(PMe3)2 (from 1.982 to 2.003) and CpMoCl2(h4-C4- H6) (from 1.994 to 2.012). 870 J. Chem. Soc. Dalton Trans. 1999 867–873 Scheme 2 Mo S Cl P Cl H Mo S S Mo Cl Ph2P P Cl Mo S P Cl Mo S P P S Mo S P P S CpMoCl2 HCl 1 1/2 H2 Ph2PCH2CH2SH Ph2 Ph2 2 Ph2 x 2 4 II III Ph2 Ph2 + Ph2 Ph2 Cl- Ph2PCH2CH2SH HCl HCl Discussion The addition of neutral ligands to CpMoCl2 to form 17- electron CpMoCl2L2 adducts had previously been established when L = tertiary phosphine 11,14 or L2 = diphosphine 12 or diene.34 In this contribution we have analyzed the results of the addition of the bifunctional ligands Ph2PCH2CH2SR (R = H CH3).An isolable addition product (compound 5) is only obtained for R = CH3. When R = H the addition intermediate (which can be spectroscopically observed) rapidly evolves to lead to the isolation of two diVerent products 1 and 2 in a relative ratio that depends on the amount of ligand used. The results of the electrochemical investigations help us formulate a mechanism for the formation of these compounds (see Scheme 2).The diVerence between the two addition products is likely due to the acidity of the SH function especially once this is coordinated to the metal center. Thus deprotonation of the intermediate II and loss of chloride would lead to the unsaturated complex III. A related deprotonation process has been described for a very similar reaction namely the addition of HS(CH2)nSH (n = 2 3) to Cp2Mo2(m-SMe)3(m-Cl) whereby the dinuclear product Cp2Mo2(m-SMe)3[m-S(CH2)nSH] is obtained with elimination of HCl.35 Compound CpMoCl2 is also a dinuclear compound with four bridging chloro ligands.36–38 Intermediate III can evolve to a saturated product either by dimerization leading directly to the observed product 2 or by addition of a second molecule of the ligand Ph2PCH2- CH2SH.Further deprotonation and chloride loss would aVord compound 4 but the redox properties of this 17-electron Mo(III) product make it susceptible to oxidation by the available protons as it has independently been verified to aVord the observed Mo(IV) product 1. The essential features of this proposed mechanism are consistent with the observation that the use of an increased amount of the ligand Ph2PCH2CH2SH increases the yield of 1 and decreases the yield of 2. In addition compound 2 converts into compound 4 upon treatment with Ph2PCH2CH2S2. It is notable that intermediate II has the same electronic configuration as compound 4 but is not oxidized under the reaction conditions that lead to products 1 and 2.The electrochemical investigation of the analogous thioether complex 5 indicates that the potential at which its oxidation would occur is much more positive relative to that of compound 4 (ca. 1.3 V more positive) revealing a dramatic eVect of the ligand’s nature on the redox properties in this system. A comparison of the redox potentials for the Mo(III)/Mo(IV) processes in compounds 3/4 and 5 with that already reported in the literature for compound CpMoCl2(dppe) (20.33 V) shows trends in ligand donor properties in the order RS2 > Cl2 and RSMe < RPPh2. Both these two eVects contribute to render compound 4 much more easily oxidized relative to compound 5. Conclusions The present study is relevant in comparison with previous investigations of electron-poor half-sandwich Mo(III) complexes which by and large prefer to adopt a dinuclear structure with a metal–metal bond.The combination of a sulfur ligand (alkylthiolate or thioether) with a phosphorus donor in a chelating bifunctional ligand leads to stable mononuclear electron-rich compounds. This greater electron-richness is clearly manifested in the oxidation of Mo(III) to Mo(IV) by the protons generated from coordinated mercaptans to yield H2. Similar oxidation of dinuclear thiolate-bridged cyclopentadienyl derivatives of Mo(III) by the proton have been reported.7 Experimental All reactions were carried out in dry solvents under a dinitrogen or argon atmosphere by the use of Schlenk line or glove-box techniques. The solvents were dried by conventional methods (CH2Cl2 from CaH2 THF from Na–K pentane and toluene from Na–benzophenone) and distilled under nitrogen prior to use.Deuteriated solvents were dried over molecular sieves and degassed by 3 freeze–pump–thaw cycles prior to use. 1H and 31P-{1H} NMR measurements were carried out on a Bruker AC200 spectrometer. The peak positions are reported with positive shifts downfield of SiMe4 as calculated from the residual solvent peaks (1H) or downfield of external 85% H3PO4 (31P). EPR measurements were carried out at the X-band microwave frequency on a Bruker ESP300 spectrometer. The spectrometer frequency was calibrated with diphenylpicrylhydrazyl (g = 2.0037). Cyclic voltammograms were carried out at room temperature with a Radiometer digital electrochemical analyzer (model DEA332). The electrochemical cell was fitted with an SCE reference electrode a platinum disc working electrode and a Pt wire counter electrode.Bu4NPF6 (ca. 0.1 M) was used as supporting electrolyte. All potentials are reported relative to the ferrocene standard which was added to each solution and measured at the end of the experiments. The solution conductivity measurements were carried out at 25 8C with a Tacussel type CD6 N conductimeter equipped with an XE 110 cell which had been calibrated with a 0.1 M KCl solution. The elemental analyses were carried out by the analytical service of the Laboratoire de Synthèse et d’Electrosynthèse Organométalliques. NaBPh4 HBF4?OEt2 MeLi (1 M solution in diethyl ether) BunLi (1.6 M solution in hexanes) ButOK and J. Chem. Soc. Dalton Trans. 1999 867–873 871 Zn powder were used as received without further purification.CpMoCl4,39 CpMoCl2,40 Ph2PCH2CH2SH,26 and [Cp2Fe]BF4,41 were prepared according to literature procedures. Ph2PCH2- CH2SCH3 was prepared by a slight modification of the method described in the literature:42 to a solution of Ph2PCH2CH2SH (1.057 mL 4.57 mmol) in 20 mL of THF at 0 8C was added a solution of 1.6 M BunLi (2.85 mL 4.57 mmol) and MeI (284 ml 4.57 mmol). The mixture was stirred overnight. The solvent was evaporated in vacuo the residue was extracted with pentane filtered through Celite and concentrated in vacuo to ca. 20 mL. Cooling to 280 8C for 24 h aVorded white crystals of Ph2- PCH2CH2SCH3. The 1H and 31P NMR properties of this product are identical with those previously reported.42 Yield 0.845 g 71%. Synthesis of [CpMo(SCH2CH2PPh2)2]Cl 1 A solution of Ph2PCH2CH2SH (474 mL 2.17 mmol) in 5 mL of CH2Cl2 was added to a suspension of CpMoCl2 (0.143 g 0.62 mmol) in 10 mL of CH2Cl2 and the mixture was stirred overnight at room temperature.An immediate analysis of the supernatant solution by EPR spectroscopy revealed a doublet resonance (aP = 26.20 G) at g = 1.982. After a few minutes this EPR signal was no longer present. Compound 1 precipitated as a very insoluble yellow solid which was collected on a filter washed with CH2Cl2 (4 × 5 mL) and dried in vacuo. Yield 0.244 g 57%. (Calc. for C33H33ClMoP2S2 C 57.69; H 4.84; S 9.33. Found C 57.27; H 4.87; S 8.96%). 31P-{1H} NMR (CH3OH with external D2O capillary) d 85.1. Synthesis of [CpMoCl(SCH2CH2PPh2)]2 2 A solution of Ph2PCH2CH2SH (628 mL 2.88 mmol) in 5 mL of CH2Cl2 was added to a suspension of CpMoCl2 (0.668 g 2.88 mmol) in 20 mL of CH2Cl2 and the mixture was stirred overnight at room temperature.A yellow microcrystalline precipitate corresponding to compound 1 was filtered oV (yield 0.402 g 20%). The solution was filtered again through Celite concentrated in vacuo to ca. 5 mL layered with pentane (20 mL) and kept in a refrigerator at 220 8C for several days. When the diVusion was complete compound 2 was obtained as a microcrystalline brown solid. Yield 0.589 g 46%. (Calc. for C19H19- ClMoPS C 51.66; H 4.33; S 7.26. Found C 51.28; H 4.69; S 6.97%). 31P-{1H} NMR (CDCl3) d 78.5. 1H NMR (CDCl3) d 7.88–7.32 (m 10H Ph) 4.92 (d JPH = 2.20 Hz 5H Cp) 4.08– 3.07 (m 4H SCH2CH2P). Synthesis of [CpMo(SCH2CH2PPh2)2]BPh4 3 To a suspension of [CpMo(SCH2CH2PPh2)2]Cl (0.034 g 0.05 mmol) in 10 mL of THF was added NaBPh4 (0.016 g 0.05 mmol) and the mixture was stirred overnight at room temperature resulting in the solubilization of the yellow starting material to yield an orange solution.After evaporation the residue was redissolved in 10 mL of CH2Cl2. The resulting orange solution was filtered through Celite and concentrated under reduced pressure to ca. 5 mL. Slow diVusion of pentane into this solution at 220 8C produced orange crystals after 3 days. Yield 0.038 g 80%. A suitable crystal obtained in this way was used for the X-ray analysis. (Calc. for C57H53BMoP2S2 C 70.52; H 5.50; S 6.60. Found C 70.37; H 5.40; S 6.31%). 31P-{1H} NMR (CD2Cl2) d 83.4. 1H NMR (CD2Cl2) d 7.48– 6.79 (m 40H Ph) 4.40 (t JPH = 1.83 Hz 5H Cp) 3.68– 2.90 (m 8H SCH2CH2P).Cyclic voltammetry (THF room temperature) reversible reduction at E2� 1 = 21.25 V. Synthesis of CpMo(SCH2CH2PPh2)2 4 (A) From CpMoCl2 and 2 equivalents of Ph2PCH2CH2S2Li1. A solution of Ph2PCH2CH2S2Li1 prepared in situ from Ph2PCH2CH2SH (496 mL 2.15 mmol) and MeLi (2.15 mL 2.15 mmol) in 10 mL of THF was added to a suspension of CpMoCl2 (0.255 g 1.07 mmol) in 40 mL of THF. The mixture was stirred overnight at room temperature. The brown-red solution was evaporated under reduced pressure. The residue was extracted in toluene and filtered through Celite. The solvent was evaporated in vacuo the residue was washed with cold pentane (3 × 5 mL) and dried under vacuum. Yield 0.382 g 55%. EPR (hexane) g = 1.987 (triplet with Mo satellites aP = 3.94 G aMo = 32.4 G). Cyclic voltammetry (THF room temperature) reversible oxidation at E2� 1 = 21.23 V.(B) By reduction of compound 1. By MeLi. To a suspension of compound 1 (0.091 g 0.132 mmol) in 20 mL of toluene was added dropwise 264 mL (0.264 mmol) of a MeLi solution (1 M in diethyl ether) causing the dissolution of the yellow starting material within 30 min and formation of a brown-red solution. The solution was evaporated under reduced pressure to ca. 10 mL and filtered through Celite. The solvent was further evaporated to dryness and the residue was washed with cold pentane (3 × 5 mL) and dried under reduced pressure. Yield 0.060 g 69.83%. This product had spectroscopic (EPR) and electrochemical properties identical to those of the material obtained by method A. By ButOK. To a suspension of compound 1 (0.084 g 0.122 mmol) in 20 mL of THF was added ButOK (0.027 g 0.244 mmol).After 24 h of stirring at room temperature the solvent was removed in vacuo. The residue was extracted with toluene and filtered through Celite the solution was evaporated to dryness under reduced pressure and the residue was washed with cold pentane (3 × 5 mL) and dried under vacuum. Yield 0.185 g 72.88%. (Calc. for C33H33MoP2S2 C 60.83; H 5.10; S 9.84. Found C 61.15; H 5.36; S 9.31%). (C) By reduction of compound 3. To a solution of [CpMo- (SCH2CH2PPh2)2]BPh4 (0.010 g 0.01 mmol) in 2 mL of THF was added Na (0.023 g 0.01 mmol) and the mixture was stirred at room temperature for 45 min. During this time the yellow solution became red and the EPR spectrum showed the signal corresponding to compound 4. The EPR properties matched those described above for the product of method A.(D) From compound 2 and 2 equivalents of Ph2PCH2- CH2S2Li1. To a solution of compound 2 (0.007 g 0.009 mmol) in 1mL of THF was added a solution of Ph2PCH2CH2S2Li1 prepared in situ from Ph2PCH2CH2SH (5 mL 0.018 mmol) and MeLi (18 mL 0.018 mmol) in 1 mL of THF. The brown solution became red. The EPR spectrum shows the signal corresponding to compound 4. NMR study of the chemical oxidation of compound 4 (A) By ferrocenium. To a solution of compound 4 (0.006 g 0.01 mmol) in 5 mL of THF was added [Cp2Fe]BF4 (0.027 g 0.01 mmol) and the mixture was stirred for 15 min. The red solution changes to yellow and it becomes EPR silent. The 31P-{1H} NMR (THF) shows one sharp peak at d 84.7 attributed to [CpMo(SCH2CH2PPh2)2]BF4. (B) By HBF4.To a solution of compound 4 (41.65 g 0.064 mmol) in 1 mL of C6D6 was added HBF4?OEt2 (0.064 mmol 69 mL) at 0 8C. Gas evolution was immediately observed discharging the red colour of the solution and yielding a yellow precipitate. 1H NMR (C6D6) d 4.50 (s H2). The suspension was filtered and the yellow solid was dissolved in THF. 31P-{1H} NMR (THF) d 84.7. Synthesis of CpMoCl2(Ph2PCH2CH2SCH3) 5 from CpMoCl2 and Ph2PCH2CH2SCH3 To a suspension of CpMoCl2 (0.185 g 0.8 mmol) in 15 mL of CH2Cl2 was added a solution of Ph2PCH2CH2SCH3 (0.209 g 0.8 mmol) in 5 mL of CH2Cl2 at room temperature. The mix- 872 J. Chem. Soc. Dalton Trans. 1999 867–873 ture was stirred for 2 h filtered through Celite and concentrated under reduced pressure to ca. 5 mL. Addition of pentane (20 mL) gave 6 as a brown-red microcrystalline solid.Yield 0.324 g 82% (Calc. for C20H22Cl2MoPS C 48.80; H 4.50; S 6.51. Found C 48.76; H 4.87; S 5.91%). EPR (hexane) g = 1.973 (doublet with Mo satellites aP = 24.7 G aMo = 35.9 G). Cyclic voltammetry (CH2Cl2 room temperature) reversible oxidation at E2� 1 = 0.12 V. Synthesis of CpMoCl4(Ph2PCH2CH2SCH3) 6 A solution of Ph2PCH2CH2SCH3 (0.551 g 2.11 mmol) in 5 mL of CH2Cl2 was added to a suspension of CpMoCl4 (0.669 g 2.21 mmol) in 20 mL of CH2Cl2 at 280 8C. The solution was warmed to room temperature stirred for 3 h and filtered through Celite. The filtrate was concentrated under reduced pressure to ca. 5 mL. Addition of pentane (20 mL) gave 6 as a brown-red microcrystalline solid. Yield 1.152 g 96% (Calc. for C20H22Cl4MoPS C 42.65; H 3.94; S 5.69.Found C 42.28; H 3.82; S 5.65%). EPR (CH2Cl2) g = 1.954 (s with Mo satellites aMo = 51.82 G). Molar conductivity (L S cm2 mol21) in THF 2.6 (8.9 × 1023 M) 7.2 (8.9 × 1024 M) L• = 9.3 S cm2 mol21; in MeCN 48.9 (9.05 × 1023 M) 75.7 (9.05 × 1024 M) L• = 90.5 S cm2 mol21. Reduction of compound 6 to compound 5 (A) With sodium amalgam. Compound 6 (0.400 g 0.71 mmol) was dissolved in THF (20 mL) and the solution was cooled to 0 8C. Freshly prepared sodium amalgam (1% w/w 0.032 g 1.42 mmol) was added and the mixture was stirred for 45 min. The mixture was decanted and the solution was filtered (via cannula). The solvent was removed in vacuo and the solid residue was extracted with CH2Cl2 and filtered through Celite. The solution was evaporated and the precipitate was washed with pentane and dried under vacuum.Yield 0.162 g 46%. This product had spectroscopic (EPR) properties identical to those of the material obtained from CpMoCl2 and Ph2PCH2- CH2SMe as described above. (B) With Zn. A solution of compound 6 (0.010 g 0.017 mmol) in 5 mL of THF was cooled to 0 8C and then Zn powder (0.001 g 0.025 mmol) was added. The mixture was stirred for 3 h. An EPR investigation of this solution showed an identical spectrum to that observed for compound 5 as obtained by the two methods described above. Reactions of compound 5 with MeLi (A) With 1 equivalent. A solution of compound 5 (0.030 g 0.11 mmol) in 10 mL of THF was cooled to 280 8C and then a solution of MeLi (109 mL 0.109 mmol) was added dropwise via a microsyringe. The EPR spectrum showed a decrease in intensity of the EPR signal of the starting material until 5 was completely consumed but no EPR-active products were observed.(B) With 2 equivalents. To a cooled (280 8C) solution of compound 5 (0.046 g 0.16 mmol) in 10 mL of THF was added dropwise a solution of MeLi (320 mL 0.32 mmol). The EPR spectrum recorded immediately showed a new doublet resonance with Mo satellites g = 1.987 aP = 24.3 G aMo = 38.6 G. Reaction between CpMoCl4 and Ph2PMe To a suspension of CpMoCl4 (0.028 g 0.092 mmol) in 10 mL of THF cooled to 0 8C was added Ph2PMe (17.20 m2 mmol) via a microsyringe. The red starting compound completely dissolved to yield a brown solution. The EPR spectrum showed a new resonance with Mo satellites at g = 1.947 aMo = 51.5 G. The EPR signal decreased in intensity and after 3 h the solution became EPR silent.Crystal structure determination of compound 3 Crystal data. C57H53BMoP2S2 M = 970.80 monoclinic a = 18.943(2) b = 12.397(1) c = 20.508(2) Å b = 91.138(7)8 U = 4815.1(8) Å3 T = 293(2) K space group = P21/c (no. 14) Z = 4 m = 0.463 mm21 8365 reflections measured up to sinq/l = 0.59 Å21 8108 unique (Rint = 0.0302) which were used in all the calculations. The data were corrected for absorption (y scan).43 No decay was observed. The structure was solved via a Patterson search program44 and refined (space group P21/c) with full-matrix least-squares methods 44 based on |F2|. All non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms of the complex were included in their calculated positions and refined with a riding model. The cyclopentadienyl ligand was found to be disordered around its geometrical center and was modelled as lying in two positions with occupancies m1 = 0.624 and m2 = 1 2 m1 = 0.376.The cyclopentadienyl rings were refined as variable metric groups (the shape is retained but the group may shrink or expand uniformly). The final agreement indices are Rw(F2) = 0.0885 and R(F) = 0.0987 for all data and 600 parameters; R(F) = 0.0336 for 5311 data with I > 2s(I); goodness of fit = 1.043. The final Fourier diVerence map is featureless Dr = 0.335 and 20.273 e Å23. CCDC reference number 186/1324. See http://www.rsc.org/suppdata/dt/1999/867/ for crystallographic files in .cif format. Acknowledgements We are grateful to the Conseil Régional de Bourgogne the MENRT and the CNRS for support of this work. We also thank the Conseil Régional de Bourgogne and the II Plan Regional de Investigation del Principado de Asturias (Spain) for postdoctoral fellowships to D.M. References 1 R. R. Chianelli Catal. 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ISSN:1477-9226    

DOI:10.1039/a809903k

出版商:RSC    

年代:1999

数据来源: RSC