Transition-metal derivatives of the functionalized cyclopentadienyl ligand. XVI. Synthesis of the bridged complexes [ (l-g5- (M = Cr, Mo, W). X-Ray crystal structure of C5H4PPh2)M(CO)2 ] 2 the dihydride derivative [ (l-g5-C5H4PPh2)W(CO)2H] 2 Brigitte Brumas-Soula, Dahan and Reneç Poilblanc* Franc” oise L aboratoire de chimie de coordination du CNRS,§ 205 route de Narbonne, 31077 T oulouse cedex, France Four synthetical methods, implying basically the oxidation of the anionic species [(g5-C5H4PPh2)M(CO)3]~ [M\Cr, (2a~), Mo (2b~), W (2c~)] to produce the new homobimetallic derivatives [(l,g5- (MwM), [M\Cr (1a), Mo (1b), W (1c)] of the heterodifunctional C5H4PPh2)M(CO)2]2 diphenylphosphinocyclopentadienyl bridging ligand, have been investigated.The –rst approach proceeds in two steps : thus the electrochemical oxidation of the complexes 2a~and 2b~ leads to the metal»metal bonded dimetallic complexes [(g5- (MwM), [M\Cr (5a), Mo (5b)] ; the irradiation of these C5H4PPh2)M(CO)3]2 complexes 5a and 5b with a high-pressure Hg lamp aÜords the corresponding decarbonylated bridged complexes 1a and 1b.The second method, using silver tetra—uoroborate as the oxidant of the anions 2a~ to 2c~, leads to the formation of tetrametallic cyclic complexes of silver and Group 6 transition metals [(l-g5- [M\Cr (6a), Mo (6b), W (6c)] but the splitting of these compounds into bimetallic C5H4PPh2[M(CO)3Ag]2 , complexes 1a»c and metallic silver appears neither easy nor selective.As a third procedure, the hydrido complexes (g5- [M\Cr (3a), Mo (3b), W (3c)] are irradiated with a high-pressure Hg C5H4PPh2)M(CO)3H lamp.This procedure is useful to prepare 1b but is non-selective in the two other cases, aÜording mainly bimetallic dihydrido-bridged complexes [(l-g5- [M\Mo (7b), W (7c)] and 1a or 1b, as C5H4PPh2)M(CO)2H]2 a result of the expected competition between the dehydrogenation and the decarbonylation processes. The X-ray molecular structure of 7c points out the transoïé d disposition of the hydrido ligands, which could well be a factor of its inertness in a spontaneous dehydrogenation process towards 1c.Finally, the most efficient method requires the preliminary preparation of the iodo complexes (g5- [M\Cr (4a), Mo (4b), W (4c)], C5H4PPh2)M(CO)3I which are reacted in toluene with their anionic parents 2~.This last method is particularly useful for preparing 1a and 1c. Complexes des meç taux de transition avec les ligands cyclopentadienyles fonctionnaliseç s. XVI. Synthe` se des complexes dimeç talliques (M = Cr, Mo, W). Structure moleç culaire du deriveç [ (l-g5-C5H4PPh2)M(CO)2 ] 2 dihydrure dœacceç der a` la seç rie des complexes homobimeç talliques ponteç s [ (l-g5-C5H4PPh2)W(CO)2H] 2 .A–n [(l-g5- (MwM), [M\Cr (1a), Mo (1b), W (1c)] du ligand heç teç rodifonctionnel pontant C5H4PPh2)M(CO2)]2 dipheç nylphosphinocyclopentadienyle, quatre possibiliteç s de preç parations ontç eteç eç tudieç es. Elles impliquent fondamentalement lœoxydation des anions [(g5- [M\Cr (2a~), Mo (2b~), W (2c~)]. La C5H4PPh2)M(CO)3]~ premie` re approche met dœabord en jeu lœoxydation eç lectrochimique de 2a~ et 2b~ conduisant aux complexes a` liaison meç tal»meç tal [(g5- (MwM), [M\Cr (5a), Mo (5b)] dont lœirradiation sous UV C5H4PPh2)M(CO3)]2 conduit aux deç rives rechercheç s 1a et 1b.La deuxie` me, utilisant comme oxydant le teç tra—uoborate dœargent, conduit a` la formation de complexes teç trameç talliques cycliques [(l-g5- [M\Cr (6a), C5H4PPh2)M(CO)3Ag]2 Mo (6b), W (6c)].La troisie` me voie met en jeux lœirradiation UV des hydrures (g5-C5H4PPh2)M(CO)3H, [M\Cr (3a), Mo (3b), W (3c)]. Celle-ci se traduit par la deshydrogeç nation de 3b en 1b, mais la deç carbonylation de 3c, conduit au complexe dihydrure ponteç [(l-g5- 7c dont la structure a eç teç C5H4PPh2)W(CO)2H]2 , deç termineç e. Finalement, la quatrie` me meç thode exige la preç paration preç alable des iodures (g5- [M\Cr (4a), Mo (4b), W (4c)] qui reç agissent aiseç ment avec les anions correspondants C5H4PPh2)M(CO)3I 2a~»2c~.We are currently involved in the synthesis of various dinuclear compounds in which two functionalized cyclopentadienyls, acting as eight-electron ligands, bridge the two metallic centers. This bridging forces the metallic atoms to remain in close proximity and has been shown, specially in the case of rhodium(I) complexes,1 to promote reactions in which the two metal centers cooperate.2 In extending these studies to metal» metal bonded dimers of the Group 6 transition metals, we anticipated that bridging might stabilize new dimetallic § UPR 8241 lieç e par convention a` lœUniversiteç Paul Sabatier et a` lìInstitut National Polytechnique de Toulouse.species and modify the course of reactions in which homolytic or heterolytic splittings of the metal»metal bond play a prominent part.3 In the present paper, we shall describe and compare synthetic processes aÜording the dinuclear complexes of the general formula [(l-g5- [M\Cr C5H4PPh2)M(CO)2]2 (1a), Mo (1b), W (1c)]. Using the monometallic anionic complexes [(g5- (2a~), Mo (2b~), W (2c~)] as C5H4PPh2)M(CO)3]~[M\Cr starting materials, four synthetic attempts implying basically oxidative processes were investigated, namely: (i) electro- and photo-chemical transformations of the anions 2a~, 2b~ and 2c~; (ii) chemical oxidation of the anions 2a~, 2b~ and 2c~ by New J.Chem., 1998, Pages 15»23 151a–1c silver tetra—uoroborate; (iii) photochemical dehydrogenation of the hydrides (g5- [M\Cr (3a), Mo C5H4PPh2)M(CO)3H (3b), W (3c)] ; and (iv) metal»metal bond formation by reaction of the lithium salts [Li][2] with the corresponding iodo complexes (g5- [M\Cr (4a), Mo (4b), W C5H4PPh2)M(CO)3I (4c)].Interestingly, the –rst process includes the primary formation of metal»metal bonded complexes [(g5- [M\Cr (5a), Mo (5b)], the second one C5H4PPh2)M(CO)3]2 aÜords novel tetrametallic MwAg cyclic complexes [(l-g5- [M\Cr (6a), Mo (6b), W (6c)] and C5H4PPh2)M(CO)3Ag]2 the third one also leads to novel dimetallic dihydrides [(l-g5- [M\Mo (7b), W (7c)].The X-ray C5H4PPh2)M(CO)2H]2 molecular structure of the dihydride 7c is also presented and discussed in comparison with the already known parent compounds [(g5- (WxW ), related to the C5H5)W(CO)2(l-H)]2 series of non-bridged complexes.4 Preparations of the molybdenum complex 1b and its X-ray crystal structure, together with that of one of the tetrametallic cyclic complexes [(l-g5- have C5H4PPh2)Mo(CO)3Ag]2 , already been reported in two preliminary communications5,6 Results The complex [(l-g5- 1b, is an inter- C5H4PPh2)Mo(CO)2]2 , esting example of a dinuclear complex having a metal»metal bond supported by ì—exibleœ bridging ligands.As described hereafter chromium and tungsten analogs have now been prepared. Beside elemental analysis data, the three compounds 1a»1c have been identi–ed by their mass spectra (DCI/NH3), which are in good agreement with the expected isotopic pattern calculated for dimetallic complexes.In addition, they were also easily characterized by spectroscopic methods as shown below. As shown in Table 1, the most evident analogies appear in the IR spectra in the CwO stretching frequency region, where the observation of four bands agrees with the expected C2v symmetry. Moreover, comparison of these spectra with that of the centrosymmetric metal»metal bonded complex [(g5- [1850 (s), 1831(vs) cm~1] suggests C5H5)Mo(CO)2PPh3]2 7 the assignment of the two higher frequency bands of the C2v bridged complexes 1a»1c, to the in-phase stretching modes.The observed spectra of 1a»1c are also comparable with that exhibited by the [l- com- (Ph2P)CH2][M(g5-C5H5)(CO)2]2 plexes, which nevertheless, interestingly show a low frequency shift [1919(s), 1882(vs), 1848(m), 1828(s) for M\Mo8a and 1911(s), 1875(vs), 1837(m), 1815(s) for M\W8b] in the same solvent.In the 1H NMR spectra, the four protons of each cyclopentadienyl ligand are non-equivalent, con–rming the absence Table 1 Spectral characteristics of the bridged complexes 1a-1c IR/cm~1 a 31PM1HN NMR/ppm [(l-g5-C5H4PPh2)Cr(CO)2]2 1941 vs 88.5b 1a 1890 vs 1864 w 1844 s [(l-g5-C5H4PPh2)Mo(CO)2]2 1943 vs 68.2c 1b 1888 vs 1868 w 1846 s [(l-g5-C5H4PPh2)W(CO)2]2 1938 vs 39.9 (JPvW\140 Hz)b 1c 1892 vs 35.0 (JPvW\164 Hz)c 1863 w 1838 s a In toluene solution.b 81.015 MHz, c 32.40MHz, [2H6]acetone [2H6]benzene. Scheme 1 of a symmetry plane in the fragment as shown in C5H4wP Scheme 1. From the values of the coupling constants, it is JHvP also suggested that the two signals at higher –eld in the three complexes 1a»1c correspond to the protons in the a positions to the phosphorus atoms.Noticeably, the four cyclopentadienyl signals exhibit an important solvent eÜect (see Experimental). This last phenomena is most clearly observed with 1a and 1b. A last argument in favor of the equivalency of the two [(g5- fragments in 1a»1c is pro- C5H4PPh2)M(CO)2] vided by the 31PM1HN NMR spectra, which exhibit only one signal (Table 1).In all three cases, the chemical shifts appear as characteristic of the coordination of the phosphorus atom to the metal atom. In compound 1c, each 31P nucleus is coupled with one 183W leading to a low intensity doublet that brackets the uncoupled singlet ; the isotopic –gure corresponds to the isotopic ratio 183W/W (14.28%). Preparation of the diphenylcyclopentadienyl monometallic starting materials Fig. 1 sums up the various synthetic pathways used to prepare the three dimetallic complexes 1a»1c via four methods, each starting from the anionic complexes [(g5- 2a~»2c~. These anions were prepared C5H4PPh2)M(CO)3]~, from the lithium diphenylphosphinocyclopentadienyde using tricarbonyl metal derivatives since the reactions with the hexacarbonyl complexes produce largely the monomeric pentacarbonyl anion [(g1- (in which the PPh2C5H4)M(CO)5]~ phosphorus atom is bonded to the metal).By using the heptatrienyl tricarbonyl complexes (g6- (M\Cr, Mo) in re—ux with THF, the anions C7H8)M(CO)3 2a~ and 2b~ were obtained in good yield (99 and 91%, respectively, with respect to (g6- Neverthe- C7H8)M(CO)3).9 less, the synthesis of (g6- itself is slow (it needs C7H8)Cr(CO)3 about 20 h of re—ux) ; in addition the substitution reaction of (g6- with needs a three-day C7H8)Cr(CO)3 Li(C5H4PPh2) period of re—ux to reach completeness.Moreover, the product [Li][2a] was formed along with a pyrophoric compound whose separation is awkward and decreases its yield (60%).These constraints prompted us to use the complex as the starting material. In our hands, (CH3CH2CN)3Cr(CO)3 the preparation of this complex following the published procedure10 also gave a modest yield (60%), but its reaction in toluene with a suspension of very conveniently Li(C5H4PPh2) aÜords [Li][2a], which precipitated in high purity and good yield [99% with respect to (CH3CH2CN)3Cr(CO)3].The preparation of 2c~, starting from the cycloheptatrienyl complex (g6- has also been tested. In addition C7H8)W(CO)3 , to the slowness of the preparation of this starting material, its reaction with in THF re—ux is accompanied by Li(C5H4PPh2) decomposition. Therefore a second method of preparation was preferred using as the starting (CH3CN)3W(CO)3 material.11 As in the case of the chromium compound, the use of suspensions in toluene of the reactants (CH3CN)3W(CO)3 and aÜords easily a precipitate of the product Li(C5H4PPh2) [Li][2c] in high purity and good yield with respect to (97%).(CH3CN)3W(CO)3 The lithium salts [Li][2a], [Li][2b] and [Li][2c] were identi–ed in 31PM1HN NMR by signals at chemical shifts (2a~, 16 New J.Chem., 1998, Pages 15»23Fig. 1 The four synthetic reaction paths aÜording the bridged homobimetallic derivatives [(l-g5- [M\Cr (1a), Mo (1b), C5H4PPh2)M(CO)2]2 W (1c)] d[17.0(s) ; 2b~, d[18.2 (s) ; 2c~, d[17.2 (s]d, 2JPvW\41 Hz) in consistent with a non-coordinated phos- [2H6]benzene, phorus arm and in the infrared, surprisingly, by four CwO stretching bands.The occurrence of four bands instead of the three normally expected for tricarbonyl compounds has been attributed to the formation of a species in which an interaction occurs between the CO groups and a lithium cation.12 The new hydrido complexes (g5-C5H4PPh2)M(CO)3H [M\Cr (3a), Mo (3b), W (3c)] were readily prepared by adding one equivalent of glacial acetic acid to toluene solutions of the lithium salts [Li][2].The solutions (from orange for chromium to yellow for the tungsten derivatives) instantaneously turned red (from bright red for chromium to orange red for the tungsten derivatives) together with the formation of a light precipitate of lithium acetate. The hydrido complexes were identi–ed in 31PM1HN NMR spectra by singlets at chemical shifts consistent with a dangling phosphino group (3a, d[19.8 ; 3b, d[19.5 ; 3c, d[19.8), in 1H NMR spectra by their hydride signals at high –eld [3a, d[5.39(s) ; 3b, d[5.26(s) ; 3c, d[7.28 (s]d, Hz)] and in infra- 1JHvW\36 red by two bands that compare quite well with those of their parent compounds (g5- The formation of C5H5)M(CO)3H.byproducts was also observed and will be discussed further.The three complexes 3a»3c have been obtained as crystalline solids by concentrating and cooling their solutions in toluene (or THF) to [18 °C. The transformation of the preceding anionic compounds 2a~»2c~ into the iodo derivatives (g5-C5H4PPh2)M(CO)3I, (4a»4c) has been easily performed, by simply adding iodine to a toluene solution of 2a~»2c~. The three new complexes 4a»4c were easily identi–ed, namely in 31PM1HN NMR spectra, which show singlets at d [14.0 and [12.8 in [2H6]acetone, respectively, for 4a and 4b and at [16.1 (s]d, Hz) JPvW\71 in for 4c, fully consistent with a pendant phos- [2H6]benzene phorus atom.Electro- and photo-chemical processes leading to the bridged dinuclear complexes 1a and 1b: method A The transformation of the mononuclear anionic complexes 2a~»2c~, into the dinuclear neutral complexes 1a»1c can be regarded as the succession of two processes, the oxidative coupling of the anions, then the substitution of a carbonyl ligand bonded to one of the metal centers by the phosphino group bonded to the other metal center.We have already reported our observations in the case of the molybdenum complexes. 6 We mention that in this case, the primary formation of a dimetallic neutral species [(g5-C5H4PPh2)Mo(CO)3]2 (MwM), 5b (Fig. 1), resulted directly from the electrochemical oxidation of the mononuclear anionic complexes 2b~. We have attempted to apply the same processes to the chromium compounds. An oxidative electrolysis of 2a~ was performed at 0 mV on a platinum-gauze electrode in acetone with 0.1 M Noticeably, as in the case of the molyb- Et4NBF4 .denum compounds, a phenomenum of saturation of the electrode occurred, limiting the number of electrons exchanged per mole of 2a~ during the exhaustive electrolysis. Therefore, for purposes of electron counting and electrosynthesis, an electrolytic cell without a frit was used. After the electrolysis, the acetone solution showed complicated infrared and New J.Chem., 1998, Pages 15»23 1731PM1HNNMR spectra, from which the bridged complex 1a was easily identi–ed. Additionally, a peak at d[19.0 suggests the presence of a complex bearing a dangling phosphine arm. To this signal observed in the 31PM1HN NMR spectra, one can associate, in respect of the concomitant intensity variations during various essays, two bands in the infrared spectra at 1978 and 1908 cm~1.These data were –nally assigned to the metal»metal bonded complex 5a resulting probably from the dimerization of the electrogenerated radical M(g5- Attempts to transform 5a into 1a C5H4PPh2)Cr(CO)3N.13 failed, leading to the precipitation of an unidenti–ed green powder. We have also tried to use the considered two-phase electrophotochemical process to get the tungsten compound 1c.In this case the electrolysis, performed at 600 mV, also on a platinium-gauze electrode in acetone with 0.1 M Et4NBF4 , stopped after the consumption of only 0.5 Faraday mol~1. The absence in the infrared spectra of any band in the 2000» 1800 cm~1 region where 5b was characterized and the presence in the 31PM1HN NMR spectra of peaks without the characteristic satellites due to the coupling with 183W show that the expected products, 5c and 1c, do not form.Considering this result, we thought it useless to perform further photochemical experiments. An attempt to oxidize the anion by silver tetra—uoroborate : method B A further possibility to get the dimeric complexes 1a»1c is chemically to oxidize the anionic complexes 2a~»2c~.Considering the value of the oxidation potential of 2b~ (Ep\100 mV), it is advisable to use ferrocenium as an oxidizing reagent ; unfortunately we were unable to get a clean reaction. For this reason, we extended the investigation using silver cation as the oxidant. As already reported in the case of the molybdenum compounds, 5 when 1 equiv of silver tetra—uoroborate crystals was added to a toluene solution of one of anions 2a~»2c~, a grey precipitate of lithium tetra—uoroborate appeared, which was easily removed. In each case one can obtain from the resulting solution, in moderate yield, yellow crystals of the crown-like complexes [(l-g5- [M\Cr (6a), Mo C5H4PPh2)M(CO)3Ag]2 (6b), W (6c)].These complexes have been fully characterized by elemental analysis, MS, IR and NMR spectroscopies and their crystal structures have been solved.14 The scheme shown in Fig. 1 is based on the results of this study. As far as the synthesis of the complexes 1a»1c is concerned, it was eÜectively possible to observe their formation by heating at re—ux the toluene solutions of their respective silver derivatives 6a»6c.But these reactions are non-selective and unidenti–ed products form through a decomposition process. Synthesis of the hydrido complexes (g5-C5H4PPh2)M(CO)3H [M= Cr (3a), Mo (3b), W (3c) ] and [ (l-g5- [M= Mo (7b), W (7c) ] : some C5H4PPh2)M(CO)2H] 2 observations on the photochemical dehydrogenation processes : method C The hydrido complexes (g5- [M\Cr C5H4PPh2)M(CO)3H (3a), Mo (3b), W (3c)] were expected to be the direct precursors of the dimeric compounds 1a»1c and lead to efficient pathways for their dehydrogenation and decarbonylation reactions.The preparation of these hydrido compounds was attempted from the lithium salt [Li][2] through reaction with acetic acid. In the case of the chromium complex, the reaction in toluene at room temperature aÜords mainly the monometallic hydrido complex 3a, but the formation of small quantities of 1a suggests also a spontaneous multistep transformation of 3a into 1a.In the case of the molybdenum complex the reaction of [Li][2b] with acetic acid aÜords similarly the hydrido complex (g5- 3b, but C5H4PPh2)Mo(CO)3H, in addition gives noticeable amounts of a compound 7b that was characterized in 1H NMR spectra by a high-–eld signal at d[5.29 and in 31PM1HN NMR spectra by a singlet at d 59.37, suggesting the coordination of the phosphine arm.In the tungsten case, analogous mixtures were obtained, from which the hydrido complex (g5- 3c, was easily C5H4PPh2)W(CO)3H, identi–ed by its IR and 1H NMR spectra. Moreover, by slow evaporation of an acetone solution of 3c, crystals of the compound 7c were obtained, suggesting the occurrence of a substitution process, even in absence of irradiation : *, ~CO (g5-C5H4PPh2)W(CO)3H 3c »»»’ 12 [(l-g5-C5H4PPh2)W(CO)2H]2 7c The crystals of 7c were suitable for X-ray analysis which con–rmed the dimetallic phosphino-bridged molecular structure [(l-g5- (see below).C5H4PPh2)W(CO)2H]2 To support the discussion of the photochemical transformation of the preceding compound, it is worth summarizing some aspects of the photoreactivity of the parent complexes (g5- (M\Cr, Mo, W).Fig. 2 recalls part of C5H5)M(CO)3H the published observations in this –eld.4b,c The various pathways postulated for the photolysis of these complexes diÜer essentially, depending on the experimental conditions (in CO matrice, in gas phase, in n-pentane solution, .. .), in the nature of the dihydrogen elimination processes. They are postulated to occur either (i) from monometallic or (ii) from bimetallic species. Therefore, the CO dissociation»association equilibrium (iii) can be regarded as dispatching the system into one or the other process. Interestingly, the hydrido-bridged complexes [(g5- 8 can lose reversibly C5H5)M(CO)2(l-H)]2 H2 upon UV irradiation, forming the dimers [(g5- (M\Mo and W).These dimers are known C5H5)M(CO)2]2 to add CO in a dark reaction, forming the saturated [(g5- complexes. C5H5)M(CO)3]2 Concerning the presently studied hydrido complexes 3a»3c, the presence of a pendant ligand led us to anticipate PPh2 photoprocesses notably diÜerent from those described in Fig. 2. Because of the spontaneous decarbonylation of 3b into 7b (or of 3c into 7c), it was not expected to be easy to get signi–- cant data for the separate pathways. Therefore we restricted Fig. 2 Photoreactivity in the parent series of non-bridged cyclopentadienyl hydrido tricarbonyl complexes (g5-C5H5)M(CO)3H (M\Mo and W) as summarized from references 4 18 New J.Chem., 1998, Pages 15»23C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) H(1) W P Cp P¢ C(3¢) W¢ O(1) O(2) ourself to preliminary experiments. Thus the solutions containing both 3b and 7b (or 3c and 7c) have been irradiated with a UV high-pressure lamp. The mixture of molybdenum complexes transformed in toto into complex 1b, aÜording no additional observations.In contrast, in the case of the tungsten complexes, monitoring by infrared spectroscopy of the progress of the photoreaction showed the characteristic CwO stretching bands of the complexes 1c and 5c [this compound being identi–ed by its bands at 1963(s) and 1906(s) cm~1, similar to those of 5b at 1959 and 1913 cm~1]. The appearance of 5c shows that the irradiation of 3c induces a dehydrogenation process, which ends with the formation of a metal»metal bonded complex:15 hl, ~H2 (g5-C5H4PPh2)W(CO)3H 3c »»»’ 12 [(g5-C5H4PPh2)W(CO)3]2 (WwW ) 5c Finally in the case of the chromium compounds, the irradiation of 3a (in fact of a mixture containing in addition small amounts of 1a) aÜorded a light green powder.This green product, which apparently from its ponderal analysis, does not contain the diphenylphosphinocyclopentadienyl ligand, was not considered for further studies.To sum up, as regards the efficiency, the preparation of compounds 1a»1c by the irradiation of the hydrido complexes (method C) appears limited to the previously described case of the molybdenum compound 1b, which was obtained with high yield (90%).6 The X-ray molecular structure of 7c [ (l,g5-C5H4PPh2)W(CO)2H] 2 , The noticeable stability of the dihydrido complex 7c with respect to the dehydrogenation process led us to try to obtain a better understanding of its structure.Therefore an X-ray crystallographic investigation of a suitable crystal of 7c was carried out. The molecular geometry and atomic numbering scheme of 7c are shown in Fig. 3 and selected bond lengths and angles are given in Table 2. In a perspective view the most prominent features are the dinuclear nature of the complex and the headto- tail disposition of the bridging ligands. The geometry of Fig. 3 Perspective view of the dihydrido complex [(l-g5- 7c C5H4PPh2)W(CO)2H]2, Table 2 Selected bond lengths and angles (deg) with e.s.d.s in (”) parentheses for the complex [(l-g5- (7c) C5H4PPh2)W(CO)2H]2 W… … …W@ 4.5408(6) WwP 2.413(2) WwC(1) 1.923(10) WwCp 2.004(8) WwC(2) 1.942(10) WwH(1) 1.65(5) WwC(3) 2.294(7) C(3)wC(4) 1.443(10) WwC(4) 2.323(7) C(4)wC(5) 1.421(12) WwC(5) 2.358(9) C(5)wC(6) 1.372(13) WwC(6) 2.367(8) C(6)wC(7) 1.400(11) WwC(7) 2.312(8) C(7)wC(3) 1.360(10) C(1)wO(1) 1.145(13) C(2)wO(2) 1.195(12) PwWwCp 125.4(2) CpwWwC(2) 125.6(4) PwWwC(1) 103.2(3) CpwWwH(1) 119(2) PwWwC(2) 79.4(3) C(1)wWwC(2) 77.7(4) PwWwH(1) 66(2) C(1)wWwH(1) 61(2) CpwWwC(1) 127.5(4) C(2)wWwH(1) 116(2) @ denotes the 1[x, [y, 1[z symmetry operation.Cp is the centroid of the C(3)C(4)C(5)C(6)C(7) cyclopentadienyl ring. each (g5- moiety conforms to the C5H4w)W(CO)2(Ph2Pw)H ìfour-legged piano stoolœ description with the four ì legs œ including one phosphine, two carbonyl ligands and the hydride ligand.The two carbonyl groups are in cisoïé d positions. Those two moieties are related by centrosymmetry and, in particular, the two MwH bonds occupy transoïé d positions with respect to the molecular center of symmetry. The metal» metal distance, 4.5408(6) is long enough to prevent any ”, metal»metal interaction.There have been numerous studies of the cyclopentadienyl complexes that adopt a ìfour-legged piano stoolœ geometry but, among the hydrido-substituted complexes of the type (g5- whose structures are similar to the frag- C5R5)M(CO)2LH, ment (g5- of7c, only the structure C5H4w)W(CO)2(Ph2Pw)H of the chromium derivative (g5-C5H5)Cr(CO)2(PPh2Cy)H (Cy\cyclohexyl)16 and of the molybdenum derivatives (g5- and (g5- C5Me5)Mo(CO)2(CNBut)H 17 C5Me5)Mo(CO)3H 18 have been reported.In the former molybdenum compound a MowH distance of 1.63(4) was observed while the neutron ” diÜraction study of the latter aÜords 1.789(7) Our determi- ”. nation of a WwH distance of 1.65(5) is coherent with the ” former observation as the covalent radius of tungsten is only 0.01 longer than that of molybdenum; nevertheless the ” lower precision of our result precludes any comparison with the latter neutron diÜraction determination.To our knowledge, 7c is the –rst reported structure of a tungsten derivative of the type (g5- and this C5R5)M(CO)2LH, limits therefore the comparisons that can be made. The average WwCO distance of 1.93 in 7c appears, as expected, ” some 0.05 shorter than the values generally observed in ” [(g5- complexes (R\R@\Me; R\H, C5R4R@)W(CO)3] R@\various groups).19 Concerning the CwO distances, it would be unwise, in view of their e.s.d.s, to try a precise comparison ; we will just consider that they lie in the normal range.The angles between the ì legsœ and the (Cp)wW axis and also between them indicate no signi–cant deviations worth mention.Considering the dehydrogenation processes in 7c, it is worth noticing the transoïé d geometry of the hydrido ligands. Such a mutual position could well be a considerable endergonic hindrance to a reductive elimination process of dihydrogen and it was surprising that both complexes 3c and 7c disappear when they are irradiated.Nevertheless, the existence of a facile pathway to the cisoïé d isomer, based on the cis» trans rearrangement observed20 in the related monometallic hydride (g5- is not excluded C5H5)W(CO)2(PMe3)H, and could provide a reasonable explanation of the observations reported above in the description of ììmethod Cœœ. New J. Chem., 1998, Pages 15»23 19Formation of metalñmetal bonds by reaction of the lithium salts [Li] [2] with the corresponding iodo complexes (g5- [M= Cr (4a), Mo (4b), W (4c) ] : C5H4PPh2)M(CO)3I method D Such syntheses of some dinuclear metal»metal bonded complexes of molybdenum and tungsten, bridged by one or two heterodifunctional ligands have already been C5H4PPh2 , reported.21 Following this method, T HF was used as solvent.Thus, by heating at re—ux solutions of 2b~ with one equivalent of (g5- (M\Mo, W) for 16 h, the mono- C5H5)M(CO)3I bridged (M\Mo, (CO)3Mo(l-g5-C5H4PPh2)M(g5-C5H5) W) were obtained but in low yield. Following this process using 2b~ with one equivalent of 4b, the dibridged complex 1b was obtained, also in a low yield (32%). Overall this method appears to be non-selective and all products need to be puri- –ed by column chromatography.We have used the above principle to synthesize the three complexes 1a»1c, in toluene solution. First, iodo complexes 4a»4c were obtained with a good yield from solutions of anionic complexes 2a~»2c~ with one equivalent of iodine. 4a»4c were added to the corresponding anionic species 2a~»2c~ and the resulting toluene solutions were re—uxed during 16 h for the chromium and molybdenum complexes and 24 h for the tungsten complex.This method appears quite selective, the three complexes 1a, 1b and 1c are obtained as crystalline powders without puri–cation, with excellent yields of 95, 95 and 99%, respectively. Experimental General methods and materials All reactions of water- or air-sensitive compounds were conducted under a dry argon atmosphere using Schlenck techniques.Solvents were puri–ed as follows : toluene, diethyl ether and tetrahydrofuran were distilled under nitrogen over Na/benzophenone. Dichloromethane was distilled over CaH2. Starting materials (g6- (M\Cr, Mo),9 C7H8)M(CO)3 and as well (CH3CH2CN)3Cr(CO)3 10 (CH3CN)3W(CO)3,11 as the cyclopentadienide were prepared as Li(C5H4PPh2),22 described in the literature.All irradiations were performed by a 500-watt, highpressure, water-cooled, mercury lamp with a Hanau power supply. Infrared spectra were obtained on a 1725 X Perkin Elmer FT-IR spectrometer. 1H, 13C and 31P NMR spectra were recorded using 80-, 200-, or 250-MHz Bruker instruments. Mass spectra were recorded on a Nermag R10 instrument. Elemental analyses (%) were performed by the Microanalytical Laboratory of the Coordination Chemistry Laboratory (Toulouse, France).Syntheses Only the selected methods of preparation of compounds 1 are described hereafter in detail. 1a. Method D: To an [ (l-g5-C5H4PPh2)Cr(CO)2 ] 2 , orange solution of 1.44 mmol of 2a~ in 20 mL of toluene was added a red solution of 1.44 mmol of 4a in 20 mL of toluene. The resulting violet solution was re—uxed for 16 h, then cooled to room temperature. After concentration and –ltration, dark metallic crystals were obtained, giving 0.977 g of 1a (95% yield). 1H NMR (200 MHz, d 7.90 and 7.75 (2m, 8H, C6D6) : ortho), 7.13 (m, 12H, meta and para), 4.64 (s, 2H, 4.38 C5H4), (s, 2H, 3.81 (s, 2H, 3.34 (s, 2H, 1H NMR C5H4), C5H4), C5H4) ; (200 MHz, d 8.05 and 7.70 (2m, 8H, ortho), [2H6]acetone) : 7.65 (m, 12H, meta and para), 5.15 (s, 2H, 4.48 (s, 2H, C5H4), 3.58 (m, 2H, 3.41 (s, 2H, 31P M1HN C5H4), C5H4), C5H4) ; NMR (32.40 MHz, d 83.6 (s) ; 31P M1HN NMR (81.015 C6D6) : MHz, d 88.5 (s) ; IR 1940 (vs), [2H6]acetone) : (CH2Cl2 , mCO) : 1889 (vs), 1864 (w), 1842 (s) cm~1; IR (toluene, 1941 (vs), mCO) : 1890 (vs), 1864 (w), 1844 (s) cm~1; MS m/z 714 (DCI/NH3), [MH`] showing an isotopic pattern characteristic for a dichromium compound.Anal. calcd for C, Cr2C38H28O4P2: 63.87 ; H, 3.95. Found: C, 63.45 ; H, 3.69. [Li] [2a] . First method: To a Li[ (g5-C5H4PPh2)Cr(CO)3 ] , yellow solution of 1.20 g (4.68 mmol) of in 130 Li(C5H4PPh2) mL of THF was added 1.07 g of (g6- (4.68 C7H8)Cr(CO)3 mmol). The resulting red solution was re—uxed for 3 days, giving an orange solution that was cooled to room temperature. The solvent was removed in vacuo to give a brown yellow residue, which was washed with pentane to give 1.82 g of [Li][2a] as a beige solid (99% yield).Second method: To a heterogeneous yellow solution of 0.128 g (0.5 mmol) of in 15 mL of toluene was added a green solu- Li(C5H4PPh2) tion of 0.150 g (0.5 mmol) of in 15 mL (CH3CH2CN)3Cr(CO)3 of toluene.The heterogeneous mixture was heated and when the re—ux temperature was obtained the solution became homogeneous. A white precipitate rapidly appeared. The new mixture was cooled to room temperature and the suspension was –ltered and washed with pentane. [Li][2a] was obtained as 0.160 g of a dried white product (82% yield). 1H NMR (200 MHz, d 7.84 (2m, 4H, ortho), 7.66 to 7.08 (m, 6H, meta C6D6) : and para), 5.02 (s, 4H, 31P M1HN NMR (32.40 MHz, C5H4) ; d [17.0 (s) ; IR (THF, 1903 (vs), 1811 (vs), 1788 C6D6) : mCO) : (s), 1725 (s) cm~1. Anal. calcd for C, 61.24 ; LiCrC20H14O3P: H, 3.57. Found: C, 60.82 ; H, 4.28. 3a. To a dark orange solution of (g5-C5H4PPh2)Cr(CO)3H, 0.12 g (0.31 mmol) of [Li][2a] in 30 mL of toluene was added 18 lL of glacial acetic acid (0.31 mmol, one equivalent).The solution, which had turned bright red, was stirred for 10 min. After –ltration and elimination of the solution CH3COOLi, was concentrated and cooled to [18 °C. A red solid precipitated and the suspension was –ltered. 3a was obtained as 0.11 g of a dried red powder (92% yield). 1H NMR (200 MHz, d 7.70 and 7.45 (2m, 4H, ortho), 7.20 (m, 6H, meta and C6D6) : para), 4.98 (s, 2H, 4.74 (s, 2H, [5.39 (s, C5H4), C5H4), hydride) ; 31P M1HN NMR (32.40 MHz, d [19.8 (s) ; IR C6D6) : (toluene, 2012 (vs), 1927 (vs) cm~1. Anal. calcd for mCO) : C, 62.18 ; H, 3.91. Found: C, 62.34 ; H, 3.79. CrC20H15O3P: 4a. To an orange solution of [ (g5-C5H4PPh2)Cr(CO)3I ] , 1.78 mmol of 2a~ in 40 mL of toluene was added 0.451 g of I2 (1.78 mmol).The resulting red solution was stirred for 10 min. After –ltration, the solution was concentrated and cooled to [18 °C. An orange solid precipitated, and the suspension was –ltered. 4a was obtained as 0.738 g of a dried orange powder (81% yield). 1H NMR (200 MHz, d 7.98 to 7.30 (m, C6D6) : 10H, ortho, meta and para), 5.82 (s, 2H, 5.38 (s, 2H, C5H4), 31P M1HN NMR (32.40 MHz, d [16.1 (s) ; 31P C5H4) ; C6D6) : M1HN NMR (81.015 MHz, d [14.0 (s) ; IR [2H6]acetone) : (toluene, 2029 (vs), 1975 (vs) with a shoulder at 1955 (s) mCO) : cm~1. Anal.calcd for C, 46.90 ; H, 2.76. CrC20H14O3PI: Found: C, 46.77 ; H, 2.81. 1b. Method A: The hydride [ (l-g5-C5H4PPh2)Mo(CO)2 ] 2 , 3b (in fact a mixture also containing 7b can be used) was dissolved in 30 mL of toluene and the solution was irradiated with a low-pressure Hg lamp for 5 h.The red solution was then concentrated and cooled to [18 °C. A red solid precipitated and the suspension was –ltered. The product was washed with pentane and dried under vacuum. 1b was obtained as 0.17 g of a dried red powder (99% yield). Method B: After linear voltametry of Li[(g5-C5H4PPh2)Mo(CO)3], [Li][2b], on a platinum-gauze electrode in acetone with 0.1 M electrolyte, electrolysis at 100 mV was performed. Et4NBF4 The bright orange solution turned progressively dark red when one electron/mol of 2b~ was exchanged.The supporting electrolyte was eliminated through two cycles of evaporation 20 New J. Chem., 1998, Pages 15»23to dryness and redissolution in diÜerent solvents, from acetone to THF in which is not soluble, and then from THF Et4NBF4 to toluene.The 31P M1HN NMR (32,40 MHz, spectrum C6D6) shows the presence of [(g5- 5b, at d C5H4PPh2)Mo(CO)3]2 , [17.0 (s), of 1b at d 68.1 (s) and of unidenti–ed species at d 62.5 (s) ; in IR (THF, the bands at 1959(s), 1913 (s) cm~1 mCO) were assigned to 5b (main product) by comparison with [(g5- which are at 1960(s), 1914 (s) cm~1 C5H5)Mo(CO)3]2 for mCO in The red solution was irradiated with a high-pressure CCl4.Hg vapor lamp for 3 h. It was then concentrated, –ltered, and cooled to [18 °C. The precipitate was washed with pentane and dried under vacuum. A dried red powder of 1b was obtained with a 40 to 50% yield for electrolysis and irradiation. Method D: To an orange solution of 1 mmol of 2b~ in 50 mL of toluene was added a red solution of 1 mmol of 4b in 50 mL of toluene.The dark solution was re—uxed for 16 h and then cooled to room temperature. After concentration and –ltration, 0.761 g of 1b were obtained (95% yield). 1H NMR (200 MHz, d 7.90 and 7.75 (2m, 8H, ortho), 7.13 (m, C6D6) : 12H, meta and para), 4.89 (s, 2H, 4.42 (s, 2H, C5H4), C5H4), 3.73 (s, 2H, 3.15 (s, 2H, 31P M1HN NMR (32.40 C5H4), C5H4) ; MHz, d 68.2 (s) ; 13C M1HN NMR (50.323 MHz, C6D6) : C6D6) : d 244.5 (d, Hz, 2CO), 232.3 (s, 2CO), 140.4 (d, 1JCP\27 Hz, 4C, ipso), 134.3 and 133.4 (2s, 4C, para), 135.2 1JCP\41 and 132.2 (2d, Hz, 8C, ortho), 131.6 and 130.7 (2s, 1JCP\10 8C, meta), 94.1 and 88.2 (2s, of 91.8 and 88.6 (2d, 4C3 C5H4P), Hz, of 53.6 (d, Hz, of 1JCP\11 4C2 C5H4P), 1JCP\41 2C1 IR (THF, 1941 (vs), 1896 (vs), 1865 (w), 1843 (s) C5H4P); mCO) : cm~1; IR (toluene, 1943 (vs), 1898 (vs), 1868 (w), 1846 (s) mCO) : cm~1; MS m/z 802 [MH`] showing an isotopic (DCI/NH3), pattern characteristic for a dimolybdenum compound.Anal. calcd for C, 56.87 ; H, 3.52. Found: C, 57.0 ; Mo2C38H28O4P2 : H, 3.56.[Li] [2b] . To a yellow solu- Li[ (g5-C5H4PPh2)Mo(CO)3 ] , tion of 2.40 g (9.37 mmol) of in 275 mL of THF Li(C5H4PPh2) was added 2.55 g of (g6- (9.37 mmol). The red C7H8)Mo(CO)3 solution was re—uxed for 3 h and the resulting yellow solution was cooled to room temperature. The solvent was removed in vacuo to give a brown yellow residue, which was washed with pentane to give 3.72 g of [Li][2b] as a beige solid (91% yield). 1H NMR (200 MHz, d 7.70 and 7.46 (2m, 4H, ortho), C6D6) : 7.14 (m, 6H, meta and para), 5.50 (br s, 4H, 31P M1HN C5H4) ; NMR (32.40 MHz, d [18.2 (s) ; IR (THF, 1909 C6D6) : mCO) : (vs), 1813 (vs), 1790 (s), 1724 (s) cm~1; IR (KBr, 1980 (s), mCO) : 1901 (vs), 1789 (vs), 1763 (s) cm~1. Anal. calcd for C, 55.1 ; H, 3.2. Found: C, 52.2 ; H, 3.9.LiMoC20H14O3P: 3b and (g5-C5H4PPh2)Mo(CO)3H, [ (l-g5- 7b. An orange solution of 0.21 g C5H4PPh2)Mo(CO)2H] 2 , (0.48 mmol) of [Li][2b] in 30 mL of toluene was treated with 28 lL of glacial acetic acid (0.48 mmol, one equivalent). The bright orange solution was stirred for 10 min. After –ltration and elimination of the solution was concentrated CH3COOLi, and cooled to [18 °C. An orange solid precipitated and the suspension was –ltered.A dried orange powder (0.18 g) was obtained. Spectroscopic analyses showed that the monometallic hydride compound 3b and the dimetallic dihydride compound 7b were present in an approximate ratio of 6 : 1. 1H NMR (200 MHz, d 7.70 and 7.45 (2m, 32H, ortho), C6D6) : 7.20 (m, 48H, meta and para), 4.98 (s, 24H, 3b) and C5H4 of 4.74 (s, 8H, 7b), [5.26 (s, 6H, hydride of 3b) and C5H4 of [5.29 (s, 2H, hydrides of 7b) ; 31P M1HN NMR (32.40 MHz, d [19.5 (s, 3b) and 59.4 (s, 7b) ; IR (toluene, 2024 C6D6) : mCO) : (s), 1937 (s) cm~1.Anal. calcd for 6 and 1 MoC20H15O3P C, 53.4 ; H, 3.4. Found: C, 54.1 ; H, 3.9. Mo2C36H30O4P2 : 4b. To an orange solution of 1 (g5-C5H4PPh2)Mo(CO)3I, mmol of 2b~ in 30 mL of THF was added 0.254 g of (1 I2 mmol).The red solution was stirred for 10 min. After –ltration, the solution was concentrated and cooled to [18 °C. An orange solid precipitated and the suspension was –ltered. 4b was obtained as 0.500 mg of a dried orange product (90% yield). 1H NMR (200 MHz, d 7.57 to 7.45 (m, [2H6]acetone) : 10H, ortho, meta and para), 6.24 (m, 2H, 5.81 (m, 2H, C5H4), 31P M1HN NMR (81.015 MHz, d [12.8 C5H4) ; [2H6]acetone) : (s) ; IR (THF, 2039 (vs), 1964 (vs) cm~1.Anal. calcd for mCO) : C, 43.19 ; H, 2.54. Found: C, 43.01 ; H, 2.65. MoC20H14O3PI: 1c. Method D: To a solu- [ (l-g5-C5H4PPh2)W(CO)2 ] 2 , tion of 0.120 g of [Li][2c] (0.23 mmol) in 15 mL of toluene was added a red solution of 0.147 g of 4c (0.23 mmol) in 15 mL of toluene. The solution was re—uxed for 16 h.and then cooled to room temperature. After concentration and –ltration, a red powder was obtained, giving 0.224 g of 1c (99% yield). Red crystals of 1c were obtained by slow diÜusion of diethyl ether in a saturated dichloromethane solution. 1H NMR (200 MHz, d 7.92 and 7.41 (2m, 8H, ortho), 7.23 C6D6) : to 7.09 (m, 12H, meta and para), 4.64 (s, 2H, 4.38 (s, C5H4), 2H, 3.81 (s, 2H, 3.34 (s, 2H, 1H NMR C5H4), C5H4), C5H4) ; (200 MHz, d 8.08 and 7.81 (2m, 8H, ortho), [2H6]acetone) : 7.67 to 7.30 (m, 12H, meta and para), 5.45 (s, 2H, 5.00 C5H4), (s, 2H, 4.19 (s, 2H, 3.89 (s, 2H, 31P M1HN C5H4), C5H4), C5H4) ; NMR (32.40 MHz, d 35.0 (s]d, Hz); IR C6D6) : JPvW\328 1940 (vs), 1889 (vs), 1864 (w), 1842 (s) cm~1; IR (CH2Cl2 , mCO) : (toluene, 1938 (vs), 1892 (vs), 1863 (w), 1838 (s) cm~1; IR mCO) : (THF, 1936 (vs), 1890 (vs), 1862 (w), 1835 (s) cm~1; MS mCO) : m/z 978 [MH`] showing an isotopic pattern (DCI/NH3), characteristic for a ditungsten compound.Anal. calcd for C, 46.65 ; H, 2.89. Found: C, 46.20 ; H, 3.00. W2C38H28O4P2: [Li] [2c] . To a yellow solu- Li[ (g5-C5H4PPh2)W(CO)3 ] , tion of 0.835 g (3.26 mmol) of in 50 mL of Li(C5H4PPh2) toluene was added a solution of 1.275 g of (CH3CN)3W(CO)3 (3.26 mmol) in 50 mL of toluene.The heterogeneous mixture was heated and when the re—ux temperature was obtained, the solution became homogeneous. After 15 min a beige precipitate appeared. The new mixture was cooled to room temperature and the suspension was –ltered. [Li][2c] was obtained as 1.655 g of a dried white powder (97% yield). 1H NMR (200 MHz, d 7.56 to 7.48 (m, 4H, ortho), [2H6]acetone) : 7.45 to 7.38 (m, 6H, meta and para), 5.25 (s, Hz, 2H, JHvP\2.3 5.04 (s, Hz, 2H, 31P M1HN NMR C5H4), JHvP\1.9 C5H4) ; (32.40 MHz, d [17.2 (s]d, Hz); IR C6D6) : 2JPvW\41 (THF, 1903 (vs), 1808 (vs), 1786 (s), 1724 (s) cm~1. Anal. mCO) : calcd for C, 45.84 ; H, 2.69. Found: C, 46.12 ; LiWC20H14O3P: H, 3.27. 3c. To a yellow solution of 0.290 (g5-C5H4PPh2)W(CO)3H, g (0.55 mmol) of [Li][2c] in 30 mL of THF was added 30 lL of glacial acetic acid (0.55 mmol). The resulting red solution was stirred for 10 min. After –ltration and elimination of the solution was concentrated and cooled to CH3COOLi, [18 °C. An orange solid precipitated, and the suspension was –ltered. 3c was obtained as 0.275 g of a dried orange powder (96% yield). 1H NMR (200 MHz, d 7.57 to [2H6]acetone) : 7.37 (m, 10H, 6.03 (s, 2H, 5.75 (s, 2H, C6H5), C5H4), C5H4), [7.23 (s]d, hydride, Hz); 1H NMR (200 MHz, JHvW\36 d 7.45 to 7.25 (m, 10H, 5.59 (s, 2H, CDCl3) : C6H5), C5H4), 5.40 (s, 2H, [7.28 (s]d, hydride, Hz); 31P C5H4), 1JHvW\36 M1HN NMR (32.40 MHz, d[19.8 (s]d, C6D6) : 2JPvW\63 Hz); IR (THF, 2019 (vs), 1926 (vs) cm~1. Anal.calcd for mCO) : C, 62.18 ; H, 3.91. Found: C, 62.34 ; H, 3.79. WC20H15O3P: 4c. To a yellow solution of 0.315 (g5-C5H4PPh2)W(CO)3I, g (0.60 mmol) of [Li][2c] in 30 mL of THF was added 0.152 g of (0.60 mmol). The resulting red solution was stirred for 10 I2 min. After –ltration, the solution was concentrated and cooled to [18 °C. An orange solid precipitated and the suspension was –ltered. 4c was obtained as 0.314 g of a dried orange powder (81% yield). 1H NMR (200 MHz, d 7.40 and C6D6) : New J. Chem., 1998, Pages 15»23 21Table 3 Crystal Data for [(l-g5- 7c C5H4PPh2)W(CO)2H]2 Chemical formula C38H30O4P2W2 FW 980.3 Crystal system Orthorhombic Space group Pbca (no.61) a/” 12.042(1) b/” 16.535(2) c/” 16.871(2) U/”3 3359(1) F(000) 1872 Z 4 qcalc/g cm~3 1.938 Radiation MoKa (j\0.71073 ”) l(MoKa)/mm~1 6.70 T&»T' 0.922»1.000 2h range/deg 3»46 Scan mode x[2h No.of data collected 2328 (all unique) No. of observed data 1193 [Fo2[3r(Fo2)] No. of variable params 128 S 1.093 w [r2(Fo)]0.0011Fo2]~1 (*/r)max 0.008 R\&[(oFo o[ oFc o)/&oFo o 0.030 Rw\[&w(oFo o[oFc o)2/&woFo o2]1@2 0.034 (*/q)max, min/e ”~3 0.55, [0.53 7.31 (2m, 4H, ortho), 7.17 to 7.12 (m, 6H, meta and para), 5.07 (quint., 2H, 4.87 (t, 2H, 31P M1HN NMR (32.40 C5H4), C5H4) ; MHz, d [16.1 (s]d, Hz); IR (THF, C6D6) : 2JPvW\71 mCO) : 2033 (vs), 1951 (vs) cm~1.Anal. calcd for C, WC20H14O3PI: 37.30 ; H, 2.19. Found: C, 37.52 ; H, 2.24. Formation of the complex [ (l-g5-C5H4PPh2)W(CO)2H] 2 , 7c. In the 1H NMR tube of a 3c solution in [2H6]acetone, orange crystals of 7c were obtained by slow concentration MS m/z 980 [MH`] showing an [2H6]acetone.(DCI/NH3), isotopic pattern characteristic for a ditungsten compound. Anal. calcd for C, 46.56 ; H, 3.08. Found: C, W2C38H30O4P2 : 46.42 ; H, 3.01. Table 4 Atomic coordinates for 7c Atom x/a y/b z/c W 0.51845(2) 0.12256(2) 0.44077(2) H(1) 0.4614(62) 0.1285(41) 0.3522(21) P 0.3671(2) 0.0294(1) 0.4198(1) C(1) 0.4576(7) 0.2245(6) 0.4072(6) O(1) 0.4262(7) 0.2885(5) 0.3940(5) C(2) 0.4224(8) 0.1510(6) 0.5289(6) O(2) 0.3677(6) 0.1747(4) 0.5832(4) C(3) 0.6529(6) 0.0465(4) 0.5018(4) C(4) 0.6857(6) 0.1301(4) 0.5089(5) C(5) 0.7071(7) 0.1596(7) 0.4313(5) C(6) 0.6919(7) 0.0962(5) 0.3800(5) C(7) 0.6581(5) 0.0283(5) 0.4233(4) C(8) 0.2335(4) 0.0803(3) 0.4119(3) C(9) 0.1480(4) 0.0638(3) 0.4654(3) C(10) 0.0452(4) 0.1015(3) 0.4567(3) C(11) 0.0277(4) 0.1557(3) 0.3946(3) C(12) 0.1131(4) 0.1722(3) 0.3411(3) C(13) 0.2160(4) 0.1345(3) 0.3498(3) C(14) 0.3631(4) [0.0301(4) 0.3289(3) C(15) 0.4514(4) [0.0297(4) 0.2754(3) C(16) 0.4450(4) [0.0748(4) 0.2057(3) C(17) 0.3502(4) [0.1204(4) 0.1895(3) C(18) 0.2618(4) [0.1209(4) 0.2430(3) C(19) 0.2683(4) [0.0757(4) 0.3127(3) X-Ray crystallography for 7c DiÜraction data were collected on an Enraf-Nonius CAD-4 diÜractometer at room temperature using MoKa graphitemonochromated radiation (k\0.71073 Accurate unit cell ”).parameters were obtained from least-squares re–nement of 25 re—ections in the 11»15° h range. The intensities were corrected for Lorentz and polarization eÜects and for a slight ([6.3%) linear decay.23 Empirical absorption corrections24 were made from w scans.The structure was solved by Patterson techniques.25a Relevant crystallographic data for 7c are listed in Table 3. Full-matrix least-squares re–nement25b minimizing was performed with non-hydrogen &w(oFc o[oFc o)2 atoms anisotropic but those of phenyl rings re–ned as isotropic rigid groups.The hydride ligand H(1) was located on a diÜerence-Fourier map. Its position agreed with that obtained by seeking sites of potential energy minima.26 It was re–ned isotropically. All other H atoms were introduced in calculated positions. Final atomic coordinates are given in Table 4. CCDC reference number 440/002. Conclusions The possibility to obtain in very good yields a series of bridged metal»metal bonded complexes now opens opportunities to study comparatively the structures and physical properties in that series. Chemical properties, in particular the electrochemical behavior, are currently extended from the case of the molydenum complex5 to the chromium and tungsten ones.Acknowledgements authors would like to express their gratitude to Suzy The Richelme and Dr.D. de Montauzon for helpful contributions and comments on the mass spectra and electrochemical determinations, respectively and to Dr. Andreç Maisonnat for helpful discussions. References 1 (a) A. Iretskii, M. C. Jennings and R. Poilblanc, Inorg. Chem., 1996, 35, 1266. (b) J. B. Tommasino, D. de Montauzon, X. He, A. Maisonnat, R. Poilblanc, J.N. Verpeaux and C. Amatore, Organometallics, 1992, 11, 4150. 2 (a) M. J. Hostetler, M. D. Butts and R. G. Bergman, J. Am. Chem. Soc., 1993, 115, 2743. (b) D. Baudry, A. Dormond and A. Ha–d, New J. Chem., 1993, 17, 465. (c) M. Visseaux, A. Dormond, M. M. Kubichi, C. Moïé se, D. Baudry and M. Ephritikine, J. Organomet. Chem., 1992, 433, 95. (d) M. Ogasa, M. D. Rausch and R. D.Rogers, J. Organomet. Chem., 1991, 403, 279. (e) X. He, A. Maisonnat, F. Dahan and R. Poilblanc, Organometallics, 1991, 10, 2443. ( f ) A. Dormond, P. Hepiegne, A. Ha–d and C. Moïé se, J. Organomet. Chem., 1990, 398, C1. (g) M. El Amane, R. Mathieu and R. Poilblanc, New J. Chem., 1988, 12, 661. (h) G. K. Anderson and M. Lee, Organometallics, 1988, 7, 2285. (i) K. W. Lee, W. T. Pennington, A.W. Cordis and T. L. Brown, J. Am. Chem. Soc., 1985, 107, 631. ( j) F. Faraone, S. Lo Schiaoo, G. Bruno and G. Bombieri, J. Chem. Soc., Chem. Commun., 1984, (k) G. Bruno, S. Lo Schiavo, P. Priraino and F. Faraone, Organometallics, 1985, 4, 1098. (l) P. Kalk, J.-M. Frances, P. M. P–ster, T. G. Southern and A. Thorez, J. Chem. Soc., Chem. Commun., 1983, 510. (m) M. El Amane, R.Mathieu and R. Poilblanc, Organometallics, 1983, 2, 1618. 3 (a) J. R. Knorr and T. L. Brown, J. Am. Chem. Soc., 1993, 115, 4087. (b) S. C. TenhaeÜ, K. J. Covert, M. P. Castellani, J. Grunkemeier, C. Kunz, T. J. R. Weakley, T. Koenig and D. R. Tyler, Organometallics, 1993, 12, 5000. (c) S. L. Scott, J. H. Espenson and W.-J. Chen, Organometallics, 1993, 12, 4077. (d) Q. Yao, A.Bakac and J. H. Espenson, Organometallics, 1993, 12, 2010. (e) W. C. Watkins, T. Jaeger, C. E. Kidd, S. Fortier, M. C. Baird, G. Kiss, G. C. Roper and C. D. HoÜ, J. Am. Chem Soc., 1992, 114, 907. ( f ) S. Fortier, M. C. Baird, K. F. Preston, J. R. Morton, T. Ziegler, T. J. Jaeger, W. C. Watkins, J. H. MacNeil, K. A. Watson, K. Hensel, Y. Le Page, J.-P. Charland and A. J. Williams, J.Am. Chem. Soc., 1991, 113, 542. (g) S. J. McLain, J. Am. Chem. Soc., 1988, 110, 643. (h) R. H. Hooker, K. A. Mahmoud and A. J. Rest, J. Organomet. 22 New J. Chem., 1998, Pages 15»23Chem., 1983, 254, C25. (i) R. J. Kazlauskas and M. S. Wrighton, J. Am. Chem. Soc., 1982, 104, 6005. ( j) D. S. Ginley, C. R. Bock and M. S. Wrighton, Inorg. Chim. Acta, 1977, 23, 85. (k) R.M. Laine and P. C. Ford, Inorg. Chem., 1977, 16, 388. (l) M. S. Wrighton and D. S. Ginley, J. Am. Chem. Soc., 1975, 97, 4246. (m) J. L. Hughey IV, C. R. Bock and T. J. Meyer, J. Am. Chem. Soc., 1974, 97, 4440. (n) R. D. Adams, D. E. Collins and F. A. Cotton, J. Am. Chem. Soc., 1974, 96, 749. 4 (a) H. G. Alt, T. Frister, E. E. Trapl and H. E. Engelhardt, J. Organomet. Chem., 1989, 362, 125.(b) K. A. Mahmoud, A. J. Rest and H. G. Alt, J. Chem. Soc., Dalton T rans., 1984, 187. (c) H. G. Alt, K. A. Mahmoud and A. J. Rest, Angew. Chem., Int. Ed. Engl., 1983, 22, 544. 5 B. Brumas, F. Dahan, D. de Montauzon and R. Poilblanc, J. Organomet. Chem., 1993, 453, C13. 6 B. Brumas, D. de Caro, F. Dahan, D. de Montauzon and R. Poilblanc, Organometallics, 1993, 12, 1503. 7 M.A. Bennett, L. Pratt and G. Wilkinson, J. Chem. Soc., 1961, 2037. 8 (a) A. Alvarez, E. Garcia, V. Riera, M. A. Ruiz, C. Bois, Y. Jeannin, V. Riera and M. A. Ruiz, Angew. Chem., Int. Ed. Engl., 1993, 32, 1156. (b) V. Riera, M. A. Ruiz and F. Villafane, Organometallics, 1992, 11, 2854. 9 (a) R. B. King and A. Fronzaglia, Inorg. Chem., 1966, 5, 1837. (b) E. W. Abel, M. A. Bennett, R. Burton and G.Wilkinson, J. Chem. Soc., 1958, 919, 4559. (c) E. W. Abel, M. A. Bennett and G. Wilkinson, Proc. Chem. Soc., 1958. 152. 10 G. J. Kubas, L. S. van der Sluys, R. A. Doyle and R. J. Angelici, Inorganic Syntheses, ed. R. J. Angelici, Wiley, vol. 28, p. 32. 11 (a) T. J. McNeese, J. Chem. Educ., 1991, 68, 678. (b) R. B. King, Organomet. Synth., 1965, 1, 109. 12 M. Y. Darensbourg, Prog. Inorg. Chem., 1985, 33, 221. 13 (a) Following the suggestion of Baird et al., brace brackets will be used to distinguish the 17-electron species from the closed-shell compounds of similar formulae. (b) T. A. Huber, D. H. Macerney and M. C. Baird, Organometallics, 1993, 12, 4715. 14 B. Brumas-Soula, G. Commenges, F. Dahan and R. Poilblanc unpublished results. 15 In addition, a species characterized by two low frequency stretching bands at 1753 and 1728 cm~1, whose concentration increased with the duration of the experiment, was attributed to the formation of CO-bridged dimetallic species. 16 W. C. Watkins, K. Hensel, S. Fortier, D. H. Macartney, M. C. Baird and S. J. MacLain, Organometallics, 1992, 11, 2418. 17 H. G. Alt, H. E. Engelhardt, T. Frister and R. D. Rogers, J. Organomet. Chem., 1989, 366, 297. 18 L. Brammer, D. Zhao, R. M. Bullock and R. K. McMullan, Inorg. Chem., 1993, 32, 4819. 19 (a) H. G. Alt, J. S. Han and R. D. Rogers, J. Organomet. Chem., 1993, 454, 165. (b) T. J. R. Weakley, A. Avey Jr. and D. R. Tyler, Acta Crystallogr., Sect. C, 1992, 48, 154. (c) A. L. Rheingold and J. R. Harper, Acta Crystallogr., Sect. C, 1991, 47, 184. (d) T. E. Bitterwolf and A. L. Rheingold, Organometallics, 1991, 10, 3856. (e) A. Avey, S. C. TendeÜ, T. J. R. Weakley and D. R. Tyler, Organometallics, 1991, 10, 3607. ( f ) I. R. Lyatifov, T. K. Casanov, T. K. Kurbanov, A. N. Shnulin and V. K. Shilœnikov, Koord. Khim., 1990, 16, 1343 (Chem. Abstr., 1991, 114(15), 336k). (g) W. Abriel and J. Heck, J. Organomet. Chem., 1986, 302, 363. 20 B. Wrackmeyer, H. G. Alt and H. E. Maisel, J. Organomet. Chem., 1990, 399, 125. 21 T. J. Duckworth, M. J. Mays, G. Conole and M. McPartlin, J. Organomet. Chem., 1992, 439 327. 22 F. Mathey and J.-P. Lampin, J. Organomet. Chem., 1975, 31, 2685. 23 C. K. Fair, MolEn Molecular Structure Procedures, Enraf-Nonius, Delft, Holland 1990 24 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 21, 351. 25 (a) G. M. Sheldrick, SHEL XS86 Program for Crystal Structure Solution, University of Goé ttingen, Goé ttingen, 1986. (b) G. M. Sheldrick, SHEL X76 Program for Structure Determination, University of Cambridge, Cambridge, 1976. 26 A. G. Orpen, J. Chem. Soc., Dalton T rans., 1980, 2509. Received 29th January 1997; Paper 7/06746A New J. Chem., 1998, Pages 15»23 23