Carbon−Sulfur and Carbon−Halogen Bond Cleavage of Acyclic or

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Organometallics 2010, 29, 448–462 DOI: 10.1021/om900901s

Carbon-Sulfur and Carbon-Halogen Bond Cleavage of Acyclic or Cyclic Thioethers, Thiophenes, and Dihaloalkanes with the Trithiolato-Bridged Cation [Mo2Cp2(μ-SMe)3(MeCN)2]þ Wilfried-Solo Ojo, Franc-ois Y. P
etillon,* P. Schollhammer,* and Jean Talarmin Universit
e Europ
eenne de Bretagne, Universit
e de Brest, CNRS, UMR 6521, “Chimie, Electrochimie Mol
eculaires et Chimie Analytique”, ISSTB, CS 93837, 29238 Brest-Cedex 3, France Received October 14, 2009

Reactions of the trithiolato-bridged complex [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with acyclic (e.g., Et2S) or cyclic (e.g., thiirane, thietane, tetrahydrothiophene, 1,4-dithiane, and 1,4-thioxane) thioethers and chalcogenophenes (benzothiophene, benzoselenophene, and dibenzothiophene) in dihaloalkanes led to either the thioether- and halide-bridged compounds [Mo2Cp2(μ-SMe)2(μSRR0 )(μ-X)](BF4) (R=R0 =Et, X=Cl (3); RR0 =C4H8, X=Cl (10), X=Br (11) ; RR0 =C4H8O, X = Cl (14)), and dithioether- and chloro-bridged derivatives [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S), κ1(S)-(SR00 x(CH2)nSR00 x}](BF4) (x=1, R00 =Me, n=1 (4); x=0, n=4 (13)) or the μ-sulfido complex [Mo2Cp2(μ-SMe)3(μ-S)](BF4) (6) and the methyl 1,3-propylthiolate thioether-bridged compound [Mo2Cp2(μ-SMe)2{μ-κ2(S),κ2(S)-S(CH2)3SMe}](BF4) (8), according to the structural features of the organic sulfur reagents. Ring-opening reaction through the cleavage of C-S bonds occurred when small-ring thioethers (e.g., thiirane and thietane) are used as reagents, whereas facile C-X (X = Cl, Br) bond cleavage was observed for other sulfur molecules. Some reactions that were conducted in chlorocarbon solvents (e.g., CH2Cl2, (CH2)2Cl2) gave rise to the formation of the oxo-bridged complex [Mo2Cp2(μ-SMe)3(μ-O)](BF4) (7) as a byproduct with moderate yields. All new complexes have been characterized by elemental analyses and spectroscopic methods, supplemented for the tetraphenylborate or hexafluorophosphate salts of 4, 6-8, 10, and 13 by X-ray diffraction.

Introduction Metal-mediated activation of strong bonds, including C-C, C-H, and C-X (X = halogen), is a current research subject that involves transformation of organic molecules through stoichiometric and catalytic processes.1 In particular, the activation of the somewhat inert C-Cl bond of chloroalkanes remains a good challenge of chemical and environmental relevance,2 as illustrated by very recent works devoted to this topic.3 Carbon-sulfur bonds are also known to be efficiently activated on transition metal centers to lead, *To whom correspondence should be addressed. E-mail: francois. [email protected]. (F.Y.P.); [email protected] (P.S.). (1) Recent reviews on the subject: (a) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36, 1173. (b) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107, 174. (c) Satoh, T.; Mitsudo, T. Top. Organomet. Chem. 2005, 14, 1. (d) Jun, C.-H. Chem. Soc. Rev. 2004, 33, 610. (e) van de Boorn, M. E.; Mildstein, D. Chem. Rev. 2003, 103, 1759. (f) Ritleng, V.; Sirlini, C.; Pfeffer, M. Chem. Rev. 2002, 35, 1731. (g) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826. (2) Kliegman, S.; McNeill, K. Dalton Trans. 2008, 4191. (3) (a) Pattacini, R.; Jie, S.; Braunstein, P. Chem. Commun. 2009, 890. (b) Vetter, A. J.; Rieth, R. D.; Brennessel, W. W.; Jones, W. D. J. Am. Chem. Soc. 2009, 131, 10742. (c) Blank, B.; Glatz, G.; Kempe, R. Chem. Asian J. 2009, 4, 321. (d) Csok, Z.; Vechorkin, O.; Harkins, S. B.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc. 2008, 130, 8156. (e) Tan, R.; Jia, P.; Rao, Y.; Jia, W.; Hadzovic, A.; Yu, Q.; Li, X.; Song, D. Organometallics 2008, 27, 6614. (f) Xiang, X.; Shen, Q.; Wang, J.; Zhu, Z.; Huang, W.; Zhou, X. Organometallics 2008, 27, 1959. (g) Zeng, J. Y.; Hsieh, M.-H.; Lee, H. M. J. Organomet. Chem. 2005, 690, 5662. pubs.acs.org/Organometallics

Published on Web 12/23/2009

via C-S bond cleavages, to novel sulfur compounds,4 allowing insight into related transformations that may occur during heterogeneous catalytic processes. Thus, there is still substantial interest in metal-mediated activation of C-S bonds, especially because its importance for hydrodesulfurization (HDS) processes as well as synthetic organic (4) (a) Uddin, M. N.; Mottalib, M. A.; Begum, N.; Gosh, S.; Raha, A. K.; Haworth, D. T.; Lindeman, S. V.; Siddique, T. A.; Bennett, D.; Hogarth, G.; Norlander, E.; Kabir, S. E. Organometallics 2009, 28, 1514. (b) Grochowski, M. R.; Brennessel, W. W.; Jones, W. D. Organometallics 2009, 28, 2661. (c) Torres-Nieto, J.; Brennessel, W. W.; Jones, W. D.; García, J. J. Am. Chem. Soc. 2009, 131, 4120. (d) Atesin, T. A.; Jones, W. D. Inorg. Chem. 2008, 47, 10889. (e) Uddin, M. N.; Begum, N.; Hassan, M. R.; Hogarth, G.; Kabir, S. E.; Miah, M. A.; Norlander, E.; Torcher, D. A. Dalton Trans. 2008, 6219. (f) Iwasa, K.; Seino, H.; Mizobe, Y. J. Organomet. Chem. 2008, 693, 3197. (g) Shibue, M.; Hirotsu, M.; Nishioka, T.; Kinoshita, I. Organometallics 2008, 27, 4475. (h) Schaub, T.; Backes, M.; Radius, H. Chem. Commun. 2007, 2037. (i) Nova, A.; Novio, F.; Gonzales-Duarte, P.; Lledos, A.; Mas-Ballest
e, R. Eur. J. Inorg. Chem. 2007, 5707. (j) Goj, L. A.; Lail, M.; Pittard, K. A.; Riley, K. C.; Gunnoe, T. B.; Petersen, J. L. Chem. Commun. 2006, 982. (k) Cabeza, J. A.; del Río, I.; S
anchez-Vega, M. G.; Su
arez, M. Organometallics 2006, 25, 1831. (5) (a) S
anchez-Delgado, R. A. Organometallic Modeling of the Hydrodesulfurization and Hydrodenitrogenation Reactions; Kluwer Academic: Dordrecht, The Netherlands, 2002. (b) Li, H.; Watson, E. J.; Virkaitis, K. L.; D'Acchioli, J. S.; Carpenter, G. B.; Sweigart, D. A. Organometallics 2002, 21, 1262. (c) Angelici, R. J. Organometallics 2001, 20, 1259. (d) Bianchini, C.; Meli, A. Acc. Chem. Res. 1998, 31, 109. (e) Angelici, R. J. Polyhedron 1997, 16, 3073. (f) Jones, W. D.; Vicic, D. A.; Chin, R. M.; Roache, J. H.; Myers, A. W. Polyhedron 1997, 16, 3115. (g) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259. (h) Angelici, R. J. Acc. Chem. Res. 1988, 21, 387. r 2009 American Chemical Society

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chemistry. Indeed, the cleavage of carbon-sulfur bonds is considered as a necessary step in the HDS process, which is the process that removes organic sulfur compounds (e.g., thiols, thioethers, alkyl sulfides, and thiophenes) from fossil fuels.5 Many late transition metals (Mn, Ru, Os, Ir, Re, Pt, Pd) have been shown to be substantially active as C-S bond cleavage promoters.5c,6 In contrast, only a few examples of soluble molybdenum complexes have been reported to act as carbon-sulfur activation promoters,7 as molybdenum-cobalt/nickel mixtures are usually employed in industrial heterogeneous HDS processes.8 The reactions of cyclic thioethers with several transition metals (Nb,9 Ta,10 Ti,11 Zr,12 W,13 Mn,14 Re,15 Fe,16 Ru,17 and mainly Os18) are well-known; they induce interesting ring-opening processes in some cases. However, to the best of our knowledge only one example of a dinuclear thiomolybdenum complex19 has been reported to act in such reactions. In a systematic study, we have, in the past decade, investigated the reactivity of several ligands, having various functions, toward thiolato-bridged dimolybdenum complexes, thus supplying an interesting scale of ligand transformations.20 (6) (a) Angelici, R. J. Bull. Soc. Chim. Belg. 1995, 104, 265and references cited therein. (b) Adams, R. D.; Falloon, S. B. Chem. Rev. 1995, 95, 2587and references cited therein. (c) Zhang, X.; Dullaghan, C. A.; Watson, E. J.; Carpenter, G. B.; Sweigart, D. A. Organometallics 1998, 17, 2067. (7) (a) Rakowski DuBois, M. Polyhedron 1997, 16, 3089. (b) Riaz, U.; Curnow, O. J.; Curtis, M. D. J. Am. Chem. Soc. 1994, 116, 4357. (c) Curtis, M. D.; Riaz, U.; Curnow, O. J.; Kampf, J. W.; Rheingold, A. L.; Haggerty, B. S. Organometallics 1995, 14, 5337. (d) Curtis, M. D.; Druker, S. H. J. Am. Chem. Soc. 1997, 119, 1027. (e) Adams, H.; Allot, C; Bancroft, M. N.; Morris, M. J. Dalton Trans. 2000, 4145. (f) Churchill, D. G.; Bridgewater, B. M.; Parkin, G. J. Am. Chem. Soc. 2000, 122, 178. (g) Janak, K. E.; Tanski, J. M.; Churchill, D. V.; Parkin, G. J. Am. Chem. Soc. 2002, 124, 4182. (h) Hossain, M. M.; Lin, H.-M.; Shyu, S.-G. Organometallics 2003, 22, 3262. (i) Buccella, D.; Janak, M. E.; Parkin, G. J. Am. Chem. Soc. 2008, 12, 3630. (j) Herbst, K.; Monari, M.; Brorson, M. Inorg. Chem. 2002, 41, 1336. (8) Friend, C. M.; Roberts, J. T. Acc. Chem. Res. 1988, 21, 399. (9) (a) Kakeya, M.; Fujihara, T.; Kasaya, T.; Nagasawa, A. Organometallics 2006, 25, 4131. (b) Etienne, M.; Mathieu, R.; Donnadieu, B. Organometallics 1997, 119, 3218. (10) (a) Sadorge, A.; Sauvageot, P.; Blacque, O.; Kubicki, M.; Moı¨ se, C.; Leblanc, J.-C. J. Organomet. Chem. 1999, 575, 278. (b) Nelson, J. E.; Parkin, G.; Bercaw, J. E. Organometallics 1992, 11, 2181. (c) Proulx, G.; Bergman, R. G. Organometallics 1996, 15, 133. (11) Park, J. W.; Henling, L. M.; Schaefer, W. P.; Grubbs, R. H. Organometallics 1990, 9, 1650. (12) Baranger, A. M.; Hanna, T. A.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 10041. (13) (a) Boorman, P. M.; Gao, X.; Fait, J. F.; Parvez, M. Inorg. Chem. 1991, 30, 3886. (b) Boorman, P. M.; Langdon, N. L.; Mozol, V. J.; Parvez, M. Inorg. Chem. 1998, 37, 6023. (c) Adams, R. D.; Perrin, J. L. J. Am. Chem. Soc. 1999, 121, 3984. (d) Morrow, J. R.; Tonker, T. L.; Templeton, J. L. Organometallics 1985, 4, 745. (14) Adams, R. D.; Belinski, J. A.; Chen, L. Organometallics 1992, 11, 4104. (15) (a) Adams, R. D.; Belinski, J. A.; Schierlmann, J. J. Am. Chem. Soc. 1991, 113, 9004. (b) Kanney, J.; Noll, B. C.; Rakowski DuBois, M. Organometallics 2000, 19, 4925. (16) (a) Adams, R. D.; Chen, G.; Sun, S.; Wolfe, T. A. J. Am. Chem. Soc. 1990, 112, 868. (b) Kuhn, N.; Schuman, H. J. Organomet. Chem. 1986, 315, 93. (17) (a) Adams, R. D.; Babin, J. E.; Tasi, M. Inorg. Chem. 1986, 25, 4514. (b) Amarasekera, J.; Rauchfuss, T. B.; Wilson, S. R. J. Am. Chem. Soc. 1988, 110, 2332. (c) Rondon, D.; Delbeau, J.; He, X.-D.; Sabo-Etienne, S; Chaudret, B. J. Chem. Soc., Dalton Trans. 1994, 1895. (18) Selected references: (a) Adams, R. D.; Pompeo, M. P. Organometallics 1990, 9, 1718. (b) Adams, R. D.; Pompeo, M. P. J. Am. Chem. Soc. 1991, 113, 1619. (c) Adams, R. D.; Pompeo, M. P. Organometallics 1992, 11, 1460. (d) Adams, R. D.; Pompeo, M. P.; Wu, W.; Yamamoto, J. H. J. Am. Chem. Soc. 1993, 115, 8207. (e) Adams, R. D.; Chen, L.; Yamamoto, J. H. Inorg. Chim. Acta 1995, 229, 47. (19) Gabay, J.; Dietz, S.; Bernatis, P.; Rakowski DuBois, M. Organometallics 1993, 12, 3630.

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The bis(nitrile) dinuclear thiomolybdenum derivative [Mo2Cp2(μ-SMe)3(MeCN)2](BF4)21 (1) offers a good opportunity to systematically study these reactions with dialkyl sulfide (e.g., diethyl sulfide), cyclic thioethers of increasing ring size (e.g., thiirane, thietane, tetrahydrothiophene, 1,4-dithiane, and 1,4-thioxane), and chalcogenophenes (e.g., 1-benzothiophene, 1-benzoselenophene, and dibenzothiophene), providing relevant comparisons between these various systems. Most of the reactions of thioethers or thiophenes toward transition-metal complexes are carried out in alkanes, aromatics, or tetrahydrofuran as solvents, but only a few experiments have been carried out in dihaloalkanes. Here, we have chosen to work in dichloromethane, dichloroethane, or dibromoethane in order to verify the influence of a halo solvent on the reactivity of these sulfurized ligands toward the thiolato complex 1. Surprisingly, both C-S and C-X bond activations (X = Cl, Br) are observed in several reactions.

Results and Discussion Reaction of 1 with Diethyl Sulfide in Dichloroalkanes. Reaction of 1 with Et2S under various conditions did not give products resulting from C-S bond scission as expected, but it has been found from 1H NMR criteria that the substitution reaction mainly takes place. Thus, the heating of a 1,2-dichloroethane [(CH2)2Cl2] solution of 1 and diethyl sulfide afforded only one product, 3, as a purple solid in approximately 76% yield (Scheme 1a). Compound 3 has been fully characterized from spectroscopic and analytical data (see the Experimental Section). 1H NMR spectroscopy indicated that 3 was obtained in this experiment as a single isomer, 3a. When the reaction (Scheme 1b) was conducted in dichloromethane instead of dichloroethane, compound 3 was still obtained as the major product, but together with relatively low yields of the new complex 4 and small amounts of the already known tetrakis(nitrile)dimolybdenum derivative 5.22 Thus, formation of 4 in Scheme 1b occurs as a side (20) Selected references: (a) Ojo., W.-S.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. Organometallics 2008, 27, 4207. (b) Le Goff, A.; Le Roy, C.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. Organometallics 2007, 26, 3607. (c) Ojo, W.-S.; Capon, J.-F.; Le Goff, A.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. J. Organomet. Chem. 2007, 692, 5351. (d) Le Goff, A.; Le Roy, C.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. New J. Chem. 2007, 31, 265. (e) Cabon, N.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. J. Organomet. Chem. 2006, 691, 566. (f) Le Goff, A.; Le Roy, C.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. New J. Chem. 2006, 30, 929. (g) Ojo, W.-S.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Organometallics 2006, 25, 5503. (h) Ojo, W.-S.; Paugam, E.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Organometallics 2006, 25, 4009. (i) Cabon, N.; Le Goff, A.; Le Roy, C.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; McGrady, J. E.; Muir, K. W. Organometallics 2005, 24, 6268. (j) Cabon, N.; P
etillon, F. Y.; Orain, P.-Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. J. Organomet. Chem. 2005, 690, 4583. (k) LeH
enanf, M.; Le Roy, C.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. Eur. J. Inorg. Chem. 2005, 3875. (l) Cabon, N.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Dalton Trans. 2004, 2708. (m) Schollhammer, P.; Cabon, N.; Kervella, A.-C.; P
etillon, F. Y.; Rumin, R.; Talarmin, J.; Muir, K. W. Inorg. Chim. Acta 2003, 350, 495. (n) Le Grand, N.; Muir, K. W.; P
etillon, F. Y.; Pickett, C. J.; Schollhammer, P.; Talarmin, J. Chem. Eur. J. 2002, 8, 3115. (o) Schollhammer, P.; Didier, B.; Le Grand, N.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W.; Teat, S. J. Eur. J. Inorg. Chem. 2002, 658. (p) Schollhammer, P.; Le H
enanf, M.; Le Roy-Le Floch, C.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W. Dalton Trans. 2001, 1573. (q) Schollhammer, P.; Cabon, N.; Capon, J.-F.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W. Organometallics 2001, 20, 1230. (21) Barriere, F.; Le Mest, Y.; P
etillon, F. Y.; Poder-Guillou, S.; Schollhammer, P.; Talarmin, J. J. Chem. Soc., Dalton Trans. 1996, 3967. (22) Schollhammer, P.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W. Inorg. Chim. Acta 1999, 284, 107.

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Ojo et al. Scheme 1

reaction to a relatively small extent. In typical experiments, compounds 3-5 were respectively obtained in about an 11:4:1 ratio; each of these products was collected in a pure form from cold dichloromethane-hexane solutions. Therefore, they were identified by comparing their 1H NMR patterns with those of pure samples obtained either here in other reactions besides this one (3 and 4) (see Schemes 1a and 8), or in previous work (5).22 The NMR data provided evidence for the presence of two isomers in solution for 3 (Scheme 1b), 3a and 3b, which probably differ only in the orientations (syn or anti) of the bridging SMe groups. 1H NMR spectroscopy (see the Experimental Section) indicates the presence of a methylene and two thioether methyl groups, as well as two bridging SMe ligands in 4. Therefore, this compound was identified as a molybdenum dimer containing a bis(methylthio)methane ligand, a chloride, and two SMe groups on the basis of these spectroscopic and analytical data as depicted in Scheme 1b. The formulation of 4 was confirmed by X-ray analysis of a single crystal of 40 (Figure 1), obtained at room temperature from a dichloromethane solution of the hexafluorophosphate salt of 4, layered with diethyl ether. The cation of 40 consists of two CpMo fragments, bridged by one dithioether ligand, two thiolates in an anti orientation, and one chloride atom. For the cationic quadruply bridged Mo(III)-Mo(III) species 40 , a direct metal-metal bond is compatible with the fairly long Mo-Mo distance of 2.7929(5) A˚.20l,23 The Mo-S-Mo angles (average 70.25(3)°) in 40 are somewhat higher than those generally observed (63-64°) for tetrakis(μ-thiolato) compounds;20a,24 this is an outcome of the replacement of one three-electron-donor pseudohalide (SR) by a four-electron-donor dithioether ligand. The bridging Mo-Cl bond distances, average 2.4911(11) A˚, fall in the range of Mo-Cl distances found in the related quadruply bridged trithiolato compound [Mo2Cp2(μ-SMe)3(μ-Cl)] (average 2.483(3) A˚). In the coordinated dithioether ligand, the S-C distances, average 1.790(5) A˚, are close to those found in the two dinuclear dithioether complexes of rhodium (average 1.816(7) A˚)25a (23) Gomes de Lima, M. B.; Guerchais, J. E.; Mercier, R.; P
etillon, F. Y. Organometallics 1986, 5, 1952. (24) (a) Connelly, N. G.; Dahl, L. F. J. Am. Chem. Soc. 1970, 92, 7470. (b) Miller, W. K.; Haltiwanger, R. C.; Van Derveer, M. C.; Rakowski DuBois, M. Inorg. Chem. 1983, 22, 2973. (25) (a) Valderrama, M.; Contreras, R.; Arancibia, V.; Boys, D. J. Organomet. Chem. 2001, 620, 256. (b) Connolly, J.; Goodban, G. W.; Reid, G.; Slawin, A. M. Z. J. Chem. Soc., Dalton Trans. 1998, 2225.

Figure 1. View of the [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S),κ1(S)SMe(CH2)SMe}]þ cation in crystals of 40 . Here and elsewhere, non-hydrogen atoms are shown with ellipsoids at the 30% probability level. H atoms bonded to C atoms are omitted for clarity. Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Mo2 = 2.7929(5), Mo1-S1 = 2.4365(12), Mo1S2=2.4221(13), Mo2-S1=2.4219(12), Mo2-S2=2.4275(12), Mo1-S4 = 2.5061(13), Mo2-S5 = 2.5194(12), Mo1-Cl1 = 2.4944(11), Mo2-Cl1 = 2.4878(11), C3-S4 = 1.790(5), C3S5 = 1.791(5), C4-S4 = 1.813(5), C5-S5 = 1.804(5); Mo1S1-Mo2 = 70.18(3), Mo1-S2-Mo2 = 70.33, Mo1-Cl1Mo2 = 68.19(3), C3-S4-C4 = 101.7(2), Mo1-S4-C3 = 110.05(17), Mo1-S4-C4 = 114.67(19), C3-S5-C5 = 102.5(2), Mo2-S5-C3 = 110.41 (16), Mo2-S5-C5 = 112.16(17), S4-C3-S5=118.9(3); S5-C3-S4-Mo1= -43.067(2), Mo2S5-S4-Mo1=13.329(1), Mo2-Cl1-Mo1-S1 = -15.684(1), S1-Mo1-Mo2-S2 = -99.381(1).

and manganese (average 1.806(10) A˚),25b which have been previously characterized by crystallography. In view to check the effect of the diethyl sulfide over the formation of 4, we conducted the reaction of 1 with dichloromethane in the absence of Et2S. As shown in Scheme 1c, complex 4 was obtained in valuable yields (∼55%, on the basis of 1H NMR analysis) together with some unknown byproduct and small amounts of tetrakis(nitrile) derivative 5. On comparison of the products of reaction c with those of reactions a and b (Scheme 1), it appears that the formation of the dithioether compound 4 does not depend on the presence

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or absence of diethyl sulfide in dichloroalkane solution, although we show below that higher yields of 4 are obtained when 1 is heated in CH2Cl2 in the presence of sulfur compounds: e.g., 1-benzothiophene, 1-benzoselenophene, and dibenzothiophene. Therefore, formation of 4 in reactions involving 1 and dichloroalkanes indicates that this μ-trithiolato-bridged molybdenum(III) complex is able to cleave all C-Cl bonds in CH2Cl2, under relatively mild conditions, but not those in (CH2)2Cl2. These reactions show that activation of CH2Cl2 to generate a dithioether-bridged molybdenum derivative is not limited to very electron rich, low-oxidation-state transition-metal complexes: e.g. Rh(I) and Ir(I) complexes. Most significantly, these reactions yield exclusively the C-S coupled product in which each chlorine atom has been replaced by a thiolate group originating from the thiolato-molybdenum species. However, the formation of 4 from 1 and CH2Cl2 involves the elimination of only one chlorine atom, concomitant with simultaneous SMe- addition to Mo and insertion of the CH2 fragment into the (MeS)Mo-Mo(SMe) unit. To the best of our knowledge, this is the first time that such a transformation implying a dinuclear molybdenum(III) complex has been observed, leading to efficient double thiolate-thiolate coupling of CH2Cl2. Moreover, it should be noted that all the known mono- or polynuclear complexes possessing dithioethers as ligands reported in the literature25,27 resulted from reactions of transition-metal compounds with preformed dithioether reagents. This contrasts strongly with our data, which indicate clearly that the dithioether ligand is formed in the coordination sphere of the dimolybdenum derivative 1. Finally, it should be pointed out that relatively few examples of double C-Cl bond activation in CH2Cl2 by transitionmetal complexes have been reported.3a,c,d,28-30 Proposed Routes for the Formation of 3 and 4 from 1 and Dihaloalkanes. Possible Pathways for the Formation of 3. It appears from the reactions summarized in Scheme 1 that complexes 3 and 4 are formed independently. Thus, a possible route for the formation of 3 is depicted in Scheme 2. The initial step may involve the replacement of the two nitriles in 1 by a diethyl sulfide molecule to give the transient thioether complex A. Although such an intermediate is not detected here, the related μ-tetrahydrothiophene derivative 9 has been isolated when 1 reacted with tetrahydrothiophene in CH2Cl2 (see Scheme 6 below). Electrophilic addition of chloroalkyl at the sulfur atom of a thiolato-bridged ligand next gives the chloroalkyl methyl sulfide intermediate B. Indeed, the nucleophilic character of the sulfur atom of a thiolate and its susceptibility to electrophilic attack20e,26 are well established. (26) Abasq, M.-L.; P
etillon, F. Y.; Schollhammer, P.; Talarmin, J. New J. Chem. 1996, 20, 1221. (27) (a) Black, J. R.; Champness, N. R.; Levason, W.; Reid, G. Inorg. Chem. 1996, 35, 4432. (b) Genge, A. R. J.; Levason, W.; Reid, G. J. Chem. Soc., Dalton Trans. 1997, 4479. (c) Chiffey, A. F.; Evans, J.; Levason, W.; Webster, M. J. Chem. Soc., Dalton Trans. 1994, 2835. (d) Abel, E. W.;  V. J. Chem. Soc., Dalton Trans. Khan, A. R.; Kite, K.; Orrell, K. G.; Sik, 1980, 1169. (28) Alcock, N. W.; Pringle, P. G.; Bergamini, P.; Sostero, S.; Traverso, O. J. Chem. Soc., Dalton Trans. 1990, 1553. (29) (a) Brunet, J.-J.; Couillens, X.; Daran, J.-C.; Diallo, O.; Lepetit, C.; Neibecker, D. Eur. J. Inorg. Chem. 1998, 349. (b) Ciriano, M. A.; Tena, M. A.; Oro, L. A. J. Chem. Soc., Dalton Trans. 1992, 2123. (c) Ball., G. E.; Cullen, W. R.; Fryzuk, M. D.; James, B. R.; Rettig, S. J. Organometallics 1991, 10, 3767. (30) (a) Sugawara, K; Hickichi, S.; Akita, M. Chem. Lett. 2001, 1094. (b) Burns, E. G.; Chu, S. C.; de Meester, P.; Lattman, M. Organometallics 1986, 5, 2383. (c) Lin, Y. C.; Calabrese, J. C.; Wreford, S. S. J. Am. Chem. Soc. 1983, 105, 1679.

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Scheme 2. Proposed Pathway for the Formation of 3 from 1

Finally, nucleophilic substitution on B affords product 3. Thus, we can conclude that complex 1 is unable to cleave any carbon-sulfur bond in the diethyl sulfide molecule, which acts only as a double 2e-donor ligand. Possible Pathways for the Formation of 4. As no intermediate has been detected, the mechanism of the reaction leading to 4 can only be a matter of speculation at present. The crucial question was whether electrophilic chloroalkyl reagents attack a coordinated thiolato group, thus enabling a path for the formation of 4 such as that summarized in Scheme 3a, or the molybdenum atoms, according to a route such as that proposed in Scheme 3b. The pathway involving direct reaction of a nucleophilic thiolato group in 1 with CH2Cl2, leading to a chloromethyl methyl sulfide ligand (intermediate C in Scheme 3a, step i), appears to be quite sound. Indeed, the formation of the related sulfenyl chloride ligand in similar reactions has been previously demonstrated.20a,31 For example, such a ligand has been obtained by reaction of dichloromethane with the μ-sulfido dimolybdenum complex [{Mo(CO)Cp0 }2(μ-S)(μ-SMe)2] (Cp0 = C5H5, C5Me5), yielding [{Mo(CO)Cp0 }2(μ-SCH2Cl)(μ-SMe)2]Cl derivatives.20a,31 In this case, the nucleophilic character of the sulfido ligand was thought to promote the oxidative addition of CH2Cl2, involving a single C-Cl bond activation. The second step (ii) may imply the substitution of a nitrile ligand by a chloride to give the intermediate D. Then, the replacement of Cl- from Mo by a thiolato group can account for the formation of the intermediate E (step iii). This nucleophilic substitution reaction could be promoted by the presence in solution of SMe- arising from the releasing of either one or two/three SMe- groups per unit of 1 to generate the coproduct 3 (Scheme 1b) or unknown products (Scheme 1c), respectively. Finally, the last step (iv) should involve concomitant “CH2” and chloride transferal to, respectively, sulfur and molybdenum atoms, affording the dithioether-bridged derivative 4. A mechanism for the formation of 4 implying oxidative addition of CH2Cl2 to molybdenum centers cannot be excluded. Indeed, it could be thought that the presence in 1 of three-electron-releasing SMe groups promotes the oxidation power of the molybdenum atoms. Therefore, pathway b such as that summarized in Scheme 3 could also be proposed to account for the (31) Schollhammer, P.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W.; Fun, H. K.; Chinnakali, K. Inorg. Chem. 2000, 39, 5879.

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Scheme 3. Proposed Routes for the Formation of 4 from 1

formation of 4, even if no transient species has been detected during the reactions. Indeed, there is precedent for most steps described in pathway b (Scheme 3). The first step (a) may involve oxidative addition of CH2Cl2 to Mo to form the Cl-Mo-CH2Cl species F through a two-electron two-fragment process. Examples of such a simple oxidative addition of CH2X2 to form M-CH2X units have already been reported for low-valent mononuclear, electron-rich transition-metal complexes (M = Rh(I),3b,g,32 Ir(I),32g Pt(0),33 Pt(II),28 and Pd(0).33a). In contrast, double oxidative additions of halomethanes to metals are observed when lowvalent dinuclear transition-metal complexes (M = Ir,34 Rh3c,29) are employed. These last reactions undergo a fourelectron three-fragment process, due to the high nucleophilic (32) (a) Dorta, R.; Shimon, L. J. W.; Rozenberg, H.; Milstein, D. Eur. J. Inorg. Chem. 2002, 1827. (b) Hunt, C., Jr.; Fronczek, F. R.; Billodeaux, D. R.; Stanley, G. G. Inorg. Chem. 2001, 40, 5192. (c) Bradd, K. J.; Heaton, B. T.; Jacob, C.; Sampanthar, J. T.; Steiner, A. J. Chem. Soc., Dalton Trans. 1999, 1109. (d) Haarman, H.; Ernsting, J. M.; Kranenburg, M.; Kooijman, H.; Veldman, N.; Spek, A. L.; van Leeuwen, P. W.; Vrieze, K. Organometallics 1997, 16, 887. (e) Kashiwabara, K.; Morikawa, A.; Suzuki, T.; Isobe, K.; Tatsumi, K. J. Chem. Soc., Dalton Trans. 1997, 1075. (f) Nishiyama, H.; Horihata, M.; Hirai, T.; Wakamatsu, S.; Itoh, K. Organometallics 1991, 10, 2706. (g) Marder, T. B.; Fultz, W. C.; Calabrese, J. C.; Harlow, R. L.; Mildstein, D. J. Chem. Soc., Chem. Commun. 1987, 1543. (h) Werner, H.; Paul, W.; Feser, R.; Zolk, R.; Thometzek, P. Chem. Ber. 1985, 118, 261. (i) Werner, H.; Hofmann, L.; Feser, R.; Paul, W. J. Organomet. Chem. 1985, 281, 317. (j) Yoshida, T.; Ueda, T.; Adachi, T.; Yamamoto, K.; Higuchi, T. J. Chem. Soc., Chem. Commun. 1985, 1137. (33) (a) Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini, A.; Ramirez, J. A. J. Chem. Soc., Chem. Commun. 1989, 304. (b) Ghilardi, C. A.; Midollini, S.; Moneti, S.; Orlandini, A.; Scapacci, G.; Traversi, A. J. Chem. Soc., Dalton Trans. 1990, 2293. (34) El Amane, M.; Maisonnat, A.; Dahan, F.; Pince, R.; Poilblanc, R. Organometallics 1985, 4, 773.

character of the complexes and the close proximity of the metal centers, affording characteristic methylene-bridged halo derivatives.3c,29,34 We think that in our case the chloromethyl intermediate F rather than a methylene-bridged species might be formed by reacting CH2Cl2 with the trithiolato-bridged molybdenum(III) complex 1. Indeed, the sole reported example we are aware of, involving the reaction of CH2X2 (X = I) with a μ-thiolato transition-metal complex, e.g. [{Ir(CO)(PR3)(μ-StBu)2], gave a methylene-bridged derivative34 instead of the dithioether-bridged compound that is obtained here as the final product. Therefore, the formation of the chloromethyl intermediate F could result from the valuable nucleophilic character of the metal centers induced by the good σ-donating thiolato groups. The replacement of Cl- from Mo in F by a SMe- group (step b), to give the intermediate G, coud be promoted by the presence in solution of SMe-. The following step (c) involves the isomerization reaction, giving the transient species H, which is induced by the presence of a SMe- ligand trans to the chloromethyl group, consistent with the buildup of positive charge on the R-carbon during the thiolate-chloride exchange. Similar dyotropic rearrangements,35 involving phosphine and halide ligands, have been previously observed with mononuclear systems.3a,32i,g The release of a nitrile ligand (step d) is accompanied by an intramolecular rearrangement to yield the chlorine-bridged, thioformaldehyde transient derivative I. A previous study by Werner et al. on a carbenoid-rhodium system demonstrated the possibility of formation of (35) Black, T. H.; DuBay, W. J.; Tully, P. S. J. Org. Chem. 1988, 53, 5922.

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Scheme 4

thioformaldehyde complexes.36 Finally, the key step (e) in these reactions could be the “CH2” transferal to sulfur atom in the transient compound I, affording product 4, by analogy to related late-transition-metal mononuclear systems involving phosphine and phosphoramide ligands.28,30b,32g,37 At this stage, it should be said that until now most of the reactions of electrophiles with the bis(nitrile) complex 1 gave products that resulted from attack at a sulfur atom.20e,q,38 This behavior suggests that the nucleophilic character of the molybdenum centers is probably not high enough to allow direct reaction with electrophiles, being advised moreover that very electron rich systems are required to produce rupture of the strong C-Cl bond in CH2Cl2. Thus, the proposed pathway for the formation of 4 summarized in Scheme 3a appears to be more likely than that shown in Scheme 3b, even if there is precedent in the literature for almost each intermediate postulated in the latter case. Reaction of 1 with Thiirane, Thietane, and S8 in Dichloromethane. It is generally admitted that the ring-opening reaction is an important step in the desulfurization of cyclic thioethers, which are sulfur-containing contaminants of fossil fuels. Several transition-metal complexes have been found to promote such a process. Because of their intrinsic strain, small-ring thioethers, such as thiirane and thietane, show a high tendency to undergo ring opening and even complete desulfurization. In this regard, most of the investigations concerning the reactions of thiiranes or thietanes with transition-metal complexes have involved mononuclear derivatives (M = Nb, Ta, Ti, W, Re, Pt),39 triosmium,40 and dimolybdenum-dicobalt7b clusters; in contrast, very (36) Paul, W.; Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 316. (37) (a) Werner, H.; Hofmann, L.; Paul, W.; Schubert, U. Organometallics 1988, 7, 1106. (b) Werner, H.; Zolk, R. Organometallics 1985, 4, 601. (38) Capon, J.-F.; Schollhammer, P.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W. Organometallics 1999, 18, 2055. (39) (a) Myers, A. W.; Dong, L.; Ates-in, T. A.; Skugrud, R.; Flaschenriem, C.; Jones, W. D. Inorg. Chim. Acta 2008, 361, 3263. (b) Komiya, S.; Muroi, S.; Furuya, M.; Hirano, M. J. Am. Chem. Soc. 2000, 122, 170. (c) Etienne, M.; Mathieu, R.; Donnadieu, B. J. Am. Chem. Soc. 1997, 119, 3218. (d) Park, J. W.; Henling, L. M.; Schaefer, W. P.; Grubbs, R. H. Organometallics 1990, 9, 1650. See also refs 10a-c, 13d, 15b, 17b, and 18c. (40) (a) Adams, R. D.; Queisser, J. A.; Yamamoto, J. H. J. Am. Chem. Soc. 1996, 118, 10674. (b) Adams, R. D.; Belinski, J. A.; Pompeo, M. P. Organometallics 1992, 11, 2016. (c) Adams, R. D.; Pompeo, M. P. Organometallics 1992, 11, 103; 1990, 9, 2651; 1990, 9, 1718. (d) Adams, R. D.; Babin, J. E.; Tasi, M. Organometallics 1987, 6, 1717. See also refs 14, 16a, 17a, and 18b.

Figure 2. View of the [Mo2Cp2(μ-SMe)3(μ-S)]þcation in crystals of 60 . Disorder is not shown, to aid clarity. Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Moi=2.5304(7), Mo-S1=2.462(2), Mo-S2 = 2.450(2), Mo-S3 = 2.456(4), Mo-S4 = 2.347(6); Mo-S1-Moi = 61.85(6), Moi-S2Mo = 62.17(7), Mo-S3-Moi = 62.02(12), Moi-S4-Mo = 65.25(11); S4 -Moi-S3-Mo = -1.255(1), S1-Moi-S2Mo = -1.907(1), S1-Mo-Moi-S4 = 89.767(1).

few works have been devoted to those implying dinuclear complexes.12,19 Thus, it should be instructive to investigate the reactions in dichloromethane of small rings of a thiirane and a thietane with the dinuclear bis(nitrile) μ-trithiolato molybdenum derivative 1 and to compare our results with those reported by Rakowski DuBois,19 which involved a related tetrasulfur-bridged molybdenum complex. Accordingly, compound 1 was treated with an excess of thiirane in dichloromethane under reflux for 1 h. Two different outcomes were observed by the dryness quality of the solvent. In dry dichloromethane, only the product 6 was isolated in high yield (Scheme 4a), whereas in wet CH2Cl2 the two complexes 6 and 7 were formed in variable ratios depending on the wetness of the dichloromethane (Scheme 4b). The formulation of compound 6 was deduced from spectroscopic and analytical data (see the Experimental Section). It was shown by 1H NMR spectroscopy that in solution the complex is present in two isomeric forms, 6a and 6b, apparently differing only in the orientations (syn and anti) of the bridging SMe groups. The structure of 6 was confirmed by X-ray analysis of a single crystal of 60 (Figure 2): i.e., the tetraphenylborate salt of 6. The structural analysis of the cation of 60 revealed that the bridging groups are disordered and occupy four sites, each of them having an occupancy factor of 25%. The superposition of the four equally likely Mo-S and Mo-S-C orientations displays a structure which is symmetrical related to the Cp mirror (Mo, Moi, C1, C1i) and quasi-symmetrical related to the pseudobinary (C4-C4ii) axis. The cation of 60 is structurally related to the quadruply bridged dimolybdenum species [Mo2Cp2(μSMe)3(μ-X)] (X = Cl,20l Br,41 I,41 SMe24a), containing threeelectron-donor halide or pseudohalide. The cation consists of two CpMo fragments which are directly connected by a Mo-Mo bond of 2.5304(7) A˚ in addition to being bridged by three thiolates and one sulfido ligand. The Mo-S (sulfido) distances (2.347(6) A˚) are notably shorter than the Mo-SR (R = alkyl) distances (∼2.456(3) A˚); this is strong indirect confirmation that S4 is neither methylated nor protonated, (41) Le Roy, C.; P
etillon, F. Y.; Muir, K. W.; Schollhammer, P.; Talarmin, J. J. Organomet. Chem. 2006, 691, 898.

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Figure 3. View of the [Mo2Cp2(μ-SMe)3(μ-O)]þ cation in crystals of 70 . Disorder is not shown, to aid clarity. Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Mo1j = 2.5250(4), Mo1-S1 = 2.446(3), Mo1-S2 = 2.462(4), Mo1S3 = 2.461(2), Mo1-O1 = 1.919(12), Mo1j-O1 = 1.919(12); Mo1j-O1-Mo1=82.3(6), Mo1j-S1-Mo1=62.14(7), Mo1jS2-Mo1 = 61.70(12), Mo1j-S3-Mo1 = 61.73(7); Mo1jO1-Mo1-S2 = 6.112(1), Mo1j-S3-Mo1-S1 = -2.685(1), Mo1j-S3-Mo1-S2 = -63.38(1).

since μ-S(sulfido)-Mo distances are typically ca. 0.1 A˚ shorter than μ-SR-Mo distances.42 Compound 7 was formed as a mixture of the two isomers 7a and 7b in about a 5:1 ratio, in the reaction of Scheme 4b; it was characterized by comparing its 1H NMR pattern with that of a pure sample obtained previously.20c,p However, to ascertain the structure of this complex, we have independently synthesized 7 in high yields (83%) by reaction of [Mo2Cp2(μ-SMe)3(μ-Cl)](BF4)21 (2) with H2O, in order to get crystals suitable for X-ray analysis. Only crystals of [Mo2Cp2(μ-SMe)3(μ-O)](BPh4) (70 ), the tetraphenylborate salt of 7, have been obtained, which has nevertheless allowed us to confirm by X-ray diffraction the structure proposed for 7 by spectroscopy. The cation of 70 , where disorders are observed, is shown in Figure 3; it contains two CpMo fragments bridged symmetrically by one oxygen atom and three SMe ligands, so that each metal atom has a four-legged piano-stool coordination, as in the cation of 60 . A mirror plane is defined by the bridging S1, S2, S3 (from which methyl carbons C1, C2, and C1i are only slightly displaced), and O atoms. The Mo-S distances (average 2.456 A˚), Mo-S-Mo angles (average 61.85°), and Mo-Mo bond length (2.5250 A˚) are close to the values found in the μ-sulfido cation of 60 (see above), indicating that the replacement of one sulfur atom by one oxygen has little influence on these parameters. The Mo-O distances (1.919(12) A˚) in 70 compared to the Mo-S(sulfido) bond lengths (2.347(6) A˚) in 60 are strong indirect proof that 70 contains a μ-oxo ligand and not a μ-sulfido one. These distances are close to those (42) (a) Green, M. H. L.; Mountford, P. Chem. Soc. Rev. 1992, 29. (b) Casewit, C. J.; Haltiwanger, R. C.; Hoordik, J.; Rakowski DuBois, M. Organometallics 1985, 4, 119. (c) Schollhammer, P.; P
etillon, F. Y.; Pichon, R.; Poder-Guillou, S.; Talarmin, J.; Muir, K. W.; Manojlovi
c-Muir, L. Organometallics 1995, 14, 2277.

found in related μ-oxomolybdenum complexes, e.g [Mo2Cp2*Br2(μ-SMe)(μ-Br)(μ-O)]43a (average 1.910 A˚), [{Mo2Cp2Br(μ-O)(μ-SMe)2}2(μ-MoO4)]41 (average 1.935 A˚), and [(MoCpCl)2(μ-Cl)(μ-CO3H)(μ-O)].43b In view to verify that the μ-sulfido compound 6 could be formed via a way other than that indicated in Scheme 4a,b, i. e. from an episulfide, we refluxed a dichloromethane solution of 1 in the presence of an excess of sulfur (S8). Effectively, good yields of 6 (76%) were obtained together with some amounts of 7 by the addition of sulfur to the trithiolato compound 1, concomitant with the loss of two nitrile ligands (Scheme 4c). When the bis(nitrile) complex 1 was heated with another small-ring thioether, e.g. thietane (2.3 equiv), under conditions similar to those used in Scheme 4a for thiirane, the new complex 8 was obtained in good yields (77%) (Scheme 5). Elemental analysis and NMR spectroscopy indicate the presence of a thietane unit and three thiolate ligands in 8. The formulation of this compound was provided by X-ray analysis of a single crystal of 80 3 H2O, the tetraphenylborate salt of 8, obtained from a CH2Cl2 solution layered with diethyl ether. Because of disorder the cation of 80 3 H2O occupies two sites and is depicted in only its major site (occupancy 75%) in Figure 4. The structure contains two CpMo fragments bridged by the bidentate methyl 1,3-propylthiolate thioether and two SMe ligands, so that each Mo atom has a four-legged piano-stool coordination. The metal atoms are nearly coplanar with S2 and S4, the thiolate sulfur atoms (Mo1-S4-Mo2-S2 = 2.268(3)°), and with S1 and S3, the methyl thioether and the methanethiolate sulfur atoms (Mo1-S1-Mo2-S3 = -3.705°); moreover, these two “Mo2S2” planes are nearly normal (dihedral angle 94.83°). Trends in bond angles at C4, C5, and C6 reflect some constraint imposed by the attachment of the propane unit to Mo1 and Mo2 through both S4 (thiolate sulfur atom) and S1 (thioether sulfur atom), respectively. The Mo-S bond lengths that involve the thioether groups (average 2.386 A˚) are slightly shorter than those involving thiolate ligands (average 2.458 A˚), and inversely the Mo-S(thioether)-Mo angle (66.37(9)°) is somewhat larger than the Mo-S(thiolate)-Mo angles (average 64.53°). 1H NMR data for 8 are in accord with the formulation proposed from the X-ray study. In particular, the SMe pattern displays one deshielded resonance and two typical thiolate-bridged peaks at δ 1.71 and 1.65, thus suggesting thioether character for the lower field SMe resonance observed at δ 2.47. Moreover, the 1 H NMR spectrum of 8 shows only one cyclopentadienyl resonance (δ 5.91), typical for a symmetrical molecule. Thus, thermal reactions of the bis(nitrile) trithiolato complex 1 with the strained rings of thiirane or thietane in dichloromethane led to their ring opening to form the sulfide-bridged dimolybdenum compound 6 or the μ-methyl (43) (a) Poder-Guillou, S.; Schollhammer, P.; P
etillon, F. Y.; Talarmin, J.; Muir, K. W.; Baguley, P. Inorg. Chim. Acta 1995, 257, 153. (b) Bottomley, F.; Chen, J. Organometallics 1992, 11, 3404.

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Figure 4. View of the [Mo2Cp2(μ-SMe)2{μ-S(CH2)3SMe}]þ cation in crystals of 80 3 H2O. Disorder is not shown to aid clarity; only the form relative to that observed in the major site (75%) is depicted here. Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Mo2 = 2.6126(12), Mo1-S2 = 2.482(4), Mo2-S2 = 2.460(4), Mo1-S3 = 2.441(3), Mo2-S3 = 2.450(4), Mo1-S4=2.413(4), Mo2-S4=2.438(3), Mo1-S1=2.371(3), Mo2-S1 = 2.402(3), S4-C4 = 1.864(11), C4-C5 = 1.468(17), C5-C6 = 1.562(18), C6-S1 = 1.783(10); Mo1-S2Mo2 = 63.82(9), Mo1-S3-Mo2 = 64.59(9), Mo1-S4-Mo2 = 65.18(9), Mo1-S1-Mo2 = 66.37(9), Mo1-S4-C4 = 115.6(4), Mo2-S4-C4 = 117.4(4), Mo1-S1-C6 = 122.6(4), Mo2-S1C6 = 123.6(4), C6-S1-C1 = 99.5(6), S4-C4-C5 = 116.8(9), C4-C5-C6 = 116.4(11), C5-C6-S1 = 114.4(8); Mo1-S4Mo2-S2=2.268(3), Mo1-S1-Mo2-S3=-3.705(3), S4-Mo2Mo1-S1=-94.834(3), S4-C4-C5-C6=-62.357(7), C4-C5C6-S1 = 58.160(7).

1,3-propylthiolate thioether dimer 8, respectively. The formation of 6 can be understood as following from the addition of the corresponding cyclic thioether to an unsaturated “Mo2(μ-SMe)3” center, resulting from 1 by loss of MeCN, and further spontaneous olefin elimination (no effort was made to characterize the leaving C2H4). No intermediate could be detected in this reaction, and complete desulfurization readily occurred. Until this work, only one example of desulfurization of thiirane induced by a dimer, e.g. [MoCp2(μ-S2CH2)(μ-SMe)(μ-SMe2)]X, was known.19 The reaction described here shows close similarity to that reported by Rakowski DuBois et al. Indeed, both complexes used to activate the C-S bonds in thiirane have labile ligands, e.g. thioether or MeCN groups, leading to unsaturated systems that promote attack by a thioether. The reaction of 1 with thietane might also proceed initially by a simple displacement of the MeCN ligands with the thioether to give an unobserved intermediate containing an S-coordinated bridging thietane. Then, two possible ways could be considered to account for the formation of 8. First, the ringopening reaction could be promoted by the coordination of the thietane to two metal centers, which causes an alteration of Lewis acidity at the metals, to afford a metallacyclic intermediate. Then, this thiametallacycle is susceptible to nucleophilic addition because of its proximity to a SMe group, to finally give compound 8. Alternatively, direct addition of a nucleophile (e.g., bridging SMe) to one of the R-methylene carbon atoms on the bridging ring might open the thietane ring through cleavage of a carbon-sulfur bond, to afford 8. In contrast with our results, Rakowski DuBois

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et al. showed that a μ-sulfido compound and the corresponding cyclopropane were formed when the thioether complex [MoCp2(μ-S2CH2)(μ-SMe)(μ-SMe2)](BF4) reacted with thietane.19 Such a different behavior might be due to different coordination modes of the thietane in the intermediates formed in the course of the initial step of the reactions of the dimolybdenum complexes with the thioether. It should be emphasized that here there was no evidence of either cyclopropane elimination or sulfide-bridged dimer formation. Quite extensive studies of the reactions of metal (Os, Re, Mn) clusters with related thietanes have been reported by Adams et al. Most of them were devoted to the formation of new complexes containing intact thietanes.14,15a,18a-c,40b However, further thermo- or phototreatment of these complexes showed that the coordinated thietanes are capable to undergo either ring-opening reactions to afford thiometallacycle derivatives or ring-opening oligomerization of thietanes.15a,18a,b,40b,c To the best of our knowledge, 8 is the first example of formation of a complex resulting formally from a ring-opening reaction of thietane concomitant with an intramolecular attack of one of the R-methylene carbon atoms by a nucleophile (bridging SMe) to give a bidentate methyl 1,3-propylthiolate thioether bridged ligand. Finally, it shoud be noted that the chlorocarbon solvent (e.g., CH2Cl2) played no active role in these reactions. Reaction of 1 with Tetrahydrothiophene, 1,4-Dithiane, and 1,4-Thioxane in Dihaloalkanes. We have shown above that intramolecular nucleophilic attack at one R-methylene carbon atom of a coordinated thietane, by an adjacent bridging thiolate in a precursor of 8, induces ring opening via μ-S-C bond cleavage to produce the desired ring-opened complex. In the light of this result, we examined the reactivity of unstrained five- or six-membered heterocycles of tetrahydrothiophene, 1,4-dithiane, and 1,4-thioxane to see if, once synthesized, the related complexes were suitable candidates for ring opening. Reaction of 1 with Tetrahydrothiophene in Dihaloalkanes. The reaction of 1 with 2 equiv of tetrahydrothiophene in refluxing dichloromethane for 2 h led to the formation in good overall yields of two thioether complexes of tetrahydrothiophene, 9 and 10, and the μ-chloro dithioether derivative 4 in low yield (Scheme 6a). When the heating time was prolonged (18 h), only the μ-thioether 10 was formed in high yields; however, its production was accompanied by that of compound 4 in low yields (Scheme 6b). Complex 10 was thought to result from 9; in order to verify such an assumption, we have modified the experimental conditions of the reaction by increasing the quantities of added tetrahydrothiophene (15 equiv) and reducing the reaction time (30 min). As expected, only compound 9 was formed in high yields under these conditions (Scheme 6c). Then, when dichloromethane solutions of 9 were heated under reflux for 1 h, more this compound transformed mainly into 10, together with complexes 4 and 7 (Scheme 6d). Syntheses differ in overall yields, product distribution, and reaction time on exchanging the dichloromethane for dichloroethane, as shown in Scheme 6e. Finally, when the reaction was conducted in dibromomethane at 70 °C for 30 min, the related μ-bromo complex 11 was obtained as the major product, together with low yields of its precursor 9. The X-ray crystal structure of 100 , the hexafluorophosphate salt of 10, proves unequivocally that two thiolates, one chloride, and one intact tetrahydrothiophene bridge nearly symmetrically two CpMo fragments in 100 (see Figure 5). The metal

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atoms are nearly coplanar with Cl1 and S2, the chlorine and methane thiolate sulfur atoms (Mo1-Cl1-Mo2-S2 = -2.807(6)°), and with S3 and S1, the tetrahydrothiophene

Figure 5. View of the [Mo2Cp2(μ-SMe)2(μ-Cl){μ-SC4H8}]þ cation in crystals of 100 . Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Mo2 = 2.6069(10), Mo1-Cl1 = 2.510(2), Mo2-Cl1=2.512(2), Mo1-S1=2.439(3), Mo1-S2 = 2.439(2), Mo2-S1=2.431(2), Mo2-S2 = 2.439(2), Mo1-S3 = 2.394(2), Mo2-S3=2.419(2), S3-C3=1.811(10), S3-C6=1.830(9), C3-C4=1.467(16), C4-C5=1.408(17), C5-C6=1.513(15); Mo1-S1-Mo2=64.73(7), Mo1-S2-Mo2=64.61(6), Mo1-S3Mo2 = 65.60(7), Mo1-Cl1-Mo2 = 62.55(6), Mo1-S3-C3 = 122.1(4), Mo2-S3-C3 = 124.9(3), Mo2-S3-C6 = 126.3(3), C3-S3-C6 = 96.0(5), S3-C6-C5 = 104.9(7), C5-C4-C3 = 117.5(11), C4-C3-S3=104.3(8); Mo1-Cl1-Mo2-S2= -2.807(6), Mo1-S3-Mo2-S1 = -0.342(6), Mo1-Cl1-Mo2-S3 = -61.774(5), Cl1-Mo1-Mo2-S3 = 87.337(6).

and methane sulfur atoms (Mo1-S3-Mo2-S1 = -0.342(6)°); these two “Mo2S2” planes are nearly normal (dihedral angle 87.337(6)°). We finally note that, apart from the dinuclear niobium compound [Cl2(C4H8S)Nb(μ-Cl)2(μC4H8S)Nb(C4H8S)Cl2]9a and the anionic tungsten derivative [Cl3W{μ-S-(CH2)4Cl}(μ-C4H8S)2WCl3]-,13a no other structurally characterized dinuclear transition-metal complexes having bridging tetrahydrothiophene were reported previously. It was shown by 1H NMR spectroscopy that in solution the complex is present in two isomeric forms, 10a and 10b, which differ in the syn and anti orientations of the bridging methanethiolate ligands. Spectroscopic data for isomers 10a and 10b are very similar to each other (see the Experimental Section), and they are also consistent with the structure of 100 (syn) in the crystal. The formulation of compound 9 (isomers 9a and 9b) was deduced from the spectroscopic and analytical data (see the Experimental Section). More significantly, the 1H NMR spectra of 9a and 9b in the methylene region resemble those of 10a and 10b but with an apparent doubling of all resonances; this difference results probably from the exchange of a bridging chloride for a bridging thiolate. Finally, the observation of three typical resonances in the methanethiolate region confirms our hypothesis as to the formulation of 9. Complex 11 was characterized from spectroscopic and analytical data (see the Experimental Section). 1H NMR spectroscopy indicates that compounds 11 (isomers 11a and 11b) and 10 have similar patterns; thus, we deduced that 11 can be formulated as 10, with a bridging bromide instead of chloride, as shown in Scheme 6f. The reactions leading to the formation of 9 (Scheme 6a,c,e,f) are not unprecedented in the coordination chemistry of tetrahydrothiophene. For example, earlier work by Rakowski DuBois et al. showed that the replacement of a thioether (SMe2) for a bridging tetrahydrothiophene from the dinuclear cationic complex [Mo2Cp2(μ-S2CH2)(μ-SMe)(μ-SMe2)]þ took place in

Scheme 6

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Scheme 7

refluxing acetonitrile after 6-7 days of heating.19 Quite less drastic conditions are required here to obtain the similar bridging tetrahydrothiophene compound 9 in high yields. Moreover, it should be noted that, in contrast with 9, the bridging tetrahydrothiophene cationic complex [Mo2Cp2(μ-S2CH2)(μSMe)(μ-C4H8S)]þ was not isolated in these experiments and was only characterized by NMR spectroscopy.19 Thus, the trithiolato-bridged complex 1 reacts with tetrahydrothiophene under mild conditions in CH2Cl2 (Scheme 6c), with neither C-S nor C-X (X = Cl, Br) activation occurring; only the μ-thioether species 9 was formed by displacement of the two labile MeCN ligands followed by coordination of the tetrahydrothiophene. However, under more forcing conditions (prolonged heating time (CH2Cl2) or higher temperature ((CH2)2Cl2 and CH2Br2)) the activation of the solvents (haloalkanes) by either the tris(thiolato) bridged compound 1 (Scheme 6a-c) or the bis(thiolato) thioether bridged intermediate 9 was allowed, with formation of the μ-halo derivatives (10 and 11) and the μ-dithioether complex 4. Reaction of 1 with 1,4-Dithiane and 1,4-Thioxane in Dichloroalkanes. The behavior of the bis(nitrile)thiolato compound 1 toward six-membered heterocyles of 1,4-dithiane and 1,4-thioxane was also examined. The reaction of 1 with 1,4-dithiane gave the bridging bis(thioether)complex [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S),κ1(S)-S(CH2)4S}](BF4) (13), where the dithiane ligand acts as a bidentate ligand, after heating for 1 h in dichloromethane (Scheme 7a). In contrast to this reaction, that with 1,4-thioxane afforded the bridging mono(thioether) derivative [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ2(S)-S(C4H8)O}](BF4) (14), where the thioxane ligand acts only as a monodentate via its sulfur atom, after heating for 2 h in dichloromethane (Scheme 7b). In both reactions complex 1 was able to activate the C-Cl bonds in CH2Cl2 to give the bridging chloro compounds 13 and 14. Complex 13 was formed in good yield (70%, after treatment) as the sole product of the reaction, whereas 14 was obtained only in moderate yield (51%), since significant amounts of other byproducts, 4 (22%) and 5 (2%), were also present in the crude reaction mixture. However, somewhat higher yields (60%, after treatment) were obtained when the reaction was conducted in (CH2)2Cl2 instead of CH2Cl2 (Scheme 7c). Both complexes 13 and 14 were present in solution as mixtures of isomers (13a and 13b; 14a and 14b), which probably differ only in the orientations (syn and anti) of the bridging thiomethyl groups. The X-ray crystal structure of 130 , the tetraphenylborate salt of 13, proves unequivocally that 1,4-dithiane in the corresponding

Figure 6. View of the [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S),κ1(S)-S(CH2)4S}]þ cation in crystals of 130 . Selected distances (A˚), angles (deg), and torsion angles (deg): Mo1-Mo2 = 2.7924(4), Mo1S1=2.4410(9), Mo2-S1=2.4134(9), Mo1-S2=2.4318(9), Mo2S2 = 2.4301(9), Mo1-Cl1 = 2.4884(9), Mo2-Cl1 = 2.5002(9), Mo1-S2=2.4318(9), Mo2-S4=2.4894(9), C3-C4 = 1.525(5), C5-C6 = 1.539(5); Mo1-S3-C3 = 117.66(13), Mo1-S3-C5 = 117.18(14), Mo2-S4-C4 = 117.46(12), Mo2-S4-C6 = 115.76(13), C3-S3-C5 = 98.06(18), S3- C3-C4 = 116.0(3), S3-C5C6 = 114.8(3), C4-S4-C6 = 98.70(18), C3-C4-S4 = 116.1(3), C5-C6-S4 = 116.8(3); Mo1-S3-S4-Mo2 = 3.314(2), S2Mo1-S3-S4 = -4.053(4), Mo1-Cl1-Mo2-S1 = -13.440(2), S2-Mo1-Mo2-S1 = -96.375(2), S3-C5-C6-S4 = 3.647(4).

cation bridges two dimolybdenum(III) centers using its two sulfur atoms and adopts a boat conformation (see Figure 6). This structure of the cation of 130 differs significantly from that of the related neutral molybdenum complex [Mo2Cp2(CO)4{μ-S(CH2)4S}],44 where the dithiane ring lies perpendicular to the metal-metal bond in a chair conformation. More precisely, the cation of 130 contains two CpMo fragments bridged by the 1,4dithiane and two SMe and one chloride ligand. In the solid state the orientations of the bridging SMe groups in 130 are syn. The S-C distances (average value of 1.80 A˚) in the dithiane ring are close to those found in the free molecule (ca. 1.811 A˚),45 whereas the related C-C bonds are somewhat elongated: 1.539(5) and 1.525(5) A˚ versus 1.490(18)A˚. The observation that the C-S-C angles of the coordinated 1,4-dithiane (98.70(18) and 98.06(18)°) are only slightly weaker than those of the free molecule (ca. 99.0(6)°)45 strongly suggests that electronic density of the sulfur atoms was little withdrawn upon coordination. Only a few compounds with 1,4-dithiane as a bidentate ligand have been crystallographically characterized. The examples of discrete metal-organic compounds with a chelating 1,4-dithiane found in the literature are either mononuclear transition-metal complexes46 or a triosmium cluster involving only one active metal center.47 As in 13, in these compounds the dithiane molecule must (44) Bock, H.; Nuber, B.; Korswagen, R. P.; Ziegler, M. L. Bol. Soc. Quim. Peru 1988, 54, 211. (45) (a) Marsh, R. E. Acta Crystallogr. 1955, 8, 91. (b) Rosso, T. E.; Ellzy, M. W.; Jensen, J. O.; Hameka, H. F.; Zeroka, D. Spectrochim. Acta 1999, 8A, 91. (46) (a) Johansson, M. H.; Engelbrecht, H. P. Acta Crystallogr. 2001, E57, m114–m116. (b) Green, M.; Draganjac, M.; Jiang, Y.; Nave, P. M.; Cordes, A. W.; Bryan, C. D.; Dixon, J. K.; Folkert, S. L.; Yu, C.-H. J. Chem. Crystallogr. 2003, 33, 473. (c) Santiago, M. O.; Sousa, J. R.; Di
ogenes, I. C. N.; Lopes, L. G. F.; Meyer, E.; Castellano, E. E.; Ellena, J.; Batista, A. A.; Moreira, I. S. Polyhedron 2006, 25, 1543. (47) Adams, R. D.; Chen, L.; Yamamoto, J. H. Inorg. Chim. Acta 1995, 229, 47.

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adopt the boat conformation to be able to bind as a bidentate ligand. The proton NMR spectra of 13 are essentially consistent with the structure proposed by the X-ray analysis of crystals of 130 , since a single resonance for the Cp ligands is observed in the pattern. The formulation of 14 was deduced from spectroscopic (1H NMR) and analytical data (see the Experimental Section). In particular, the 1H patterns of 14a and 14b both exhibit a single resonance for the Cp ligands, which excludes for 14 a structure where the 1,4-thioxane ligand adopts a boat conformation. On the other hand, the 1,4-thioxane proton pattern of the major isomer 14a is very similar to that of the ditungsten thioxanebridged complex (PPh4)[W2(Cl)6(μ-Cl){μ-κ2(S)-S(C4H8)O}2] (previously characterized by X-ray methods13b), where 1,4-thioxane bridges two ditungsten(III) centers using only its sulfur atom. Thus, this observation strongly suggests a similar mode of coordination of the 1,4-thioxane in these two species, which adopts a chair conformation. The molybdenum(III) centers are insufficiently weak oxophiles to bind the 1,4-thioxane through its oxygen atom, which explains the absence of boat conformations in the related complexes. Compounds 13 and 14 were obtained by displacement of the two MeCN groups in 1, coordination of sulfur atoms to the two metal atoms, and then replacement of one of the three bridging thiolato groups by a chloride ligand arising from the halogenated solvent. Unhappily, in spite of more severe heating conditions the six-membered ring 1,4-dithiane or thioxane cannot be opened through the cleavage of a carbon-sulfur bond when the molecule is coordinated to dimolybdenum centers. Finally, it was interesting to observe that only the reaction of 1 with 1,4-dithiane led to a selective carbon-chlorine bond activation; this is probably related to the initial coordination mode of the dithiane on [Cp2Mo2]þ via a boat conformation. Reaction of 1 with Thioselenophenes in Dichloroalkanes. It is thought that rational pathways in the desulfurization reactions of organic sulfur derivatives, which are present in fossil fuels, may involve the cleavage of carbon-sulfur bonds as a necessary step in the HDS process.5 Thiophenes are some of the most important species among these organic sulfur compounds. In this context, it appeared interesting to examine the reaction of the soluble dimolybdenum complex 1 with several thiophenes, possibly to get some more insights on the mechanism of C-S cleavage reactions. Thus, when faced to several thiophenes (benzothiophene, benzoselenophene, and dibenzothiophene) the cation 1 gave in dichloromethane the dithioether derivative 4 and occasionally low yields of the μ-oxo species 7 (Scheme 8). When the reaction is

conducted in (CH2)2Cl2 instead of CH2Cl2 (Scheme 8), the oxo compound 7 was mainly formed together with low yields of a byproduct, only characterized by its Cp signal at 6.86 ppm. All the products (4, 5, and 7) obtained here have already been characterized by spectroscopy or X-ray methods in previous parts of this work (see above). Formation of the dithioether complex 4 in the reactions in dichloromethane is indicative of the occurrence of a dominant C-Cl bond cleavage process. Unhappily, no C-S(thiophene) bond was cleaved by 1 under our experimental conditions. In other respects, when 1 reacts with selenophene, no product containing selenium atom was formed; this clearly indicates that the fourth chalcogen atom in 4 came from partial decomposition of the starting tris(thiolato) complex 1. This observation confirms the mechanism of formation of 4, proposed above in Scheme 3. It may be thought that 4 simply results from thermal activation of CH2Cl2 by 1 without the chalcogenophene step in these reactions, since the dithioether compound was also formed by refluxing dichloromethane solutions of 1 (Scheme 1c). However, 4 was collected in higher yields when the reactions were conducted in the presence of chalcogenophenes (Scheme 8) rather than in their absence (Scheme 1c). This observation suggests that these chalcogenophenes could interfere in the formation of 4, but at this stage of the work no mechanism could be proposed. Finally, it should be noted that complex 1 is unable to activate any C-Cl bond in (CH2)2Cl2 when we operate in the presence of chalcogenophenes; instead the -oxo species 7 was mainly detected in the crude products.

Concluding Remarks The reactivity of the thiolato-bridged complex [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) toward acyclic or cyclic thioethers and thiophenes in chlorocarbon solvents (CH2Cl2, (CH2)2Cl2, and CH2Br2) is presented and compared. The structural features of the organic sulfur derivatives are crucial regulators of their chemical reactivity. Our results indicate that the ring-opening reaction (through the cleavage of a C-S bond) in cyclic thioethers or thiophenes occurred only with small-ring thioethers, e.g. thiirane and thietane, proceeding by either a desulfurization reaction of the cyclic thioether to give the μ-sulfido compound [Mo2Cp2(μ-SMe)3(μ-S)](BF4) (6) or nucleophilic addition to afford the methyl 1,3-propylthiolate thioether-bridged complex [Mo2Cp2(μSMe)2{μ-κ2(S):κ2(S)-S(CH2)3SMe}](BF4) (8). Otherwise, when five- or six-membered cyclic thioethers or thiophenes were used,

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dominant, facile C-X bond cleavage (X = Cl, Br) occurred in CH2Cl2, (CH2)2Cl2, and CH2Br2 to give thioether- and halide-bridged complexes [Mo2Cp2(μ-SMe)2(μ-SRR0 )(μ-X)](BF4) (R=R0 =Et, X = Cl (3); RR0 = C4H8, X = Cl (10), Br (11); RR0=C4H8O, X=Cl (14)) and dithioether- and chlorobridged derivatives [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S):κ1(S)-SR00 x(CH2)nSR00 x}](BF4) (x = 1, R00 = Me, n = 1 (4); x = 0; n = 4 (13)). In the last cases no carbon-sulfur bond cleavage was observed; instead carbon-halogen bond activation took the lead in the reactions. A similar feature was found when an acyclic thioether compound, namely Et2S, was employed; only carbonchlorine bond cleavage was observed, giving the thioether-bridged derivative [Mo2Cp2(μ-SMe)2(μ-SEt2)(μ-Cl)](BF4) (3) and the μ-dithioether complex 4. The results reported here clearly show that the choice of the solvent, used to examine the carbon-sulfur bond activation reactions, is of prime importance.

Experimental Section General Procedures. All reactions were routinely carried out under either a nitrogen or an argon atmosphere using standard Schlenk techniques. Solvents were distilled immediately before use under nitrogen from appropriate drying agents. The starting materials [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) and [Mo2Cp2(μ-SMe)3(μ-Cl)](BF4) (2) were prepared as described previously.21 All other reagents were purchased commercially and used as received. Infrared spectra were recorded on a NicoletNexus FT IR spectrophotometer from KBr pellets. Chemical analyses were performed either by the Service de Microanalyse ICSN-CNRS, Gif sur Yvette, France, or by the Service Central d’Analyze, Vernaison, France. Yields of all products are relative to the starting dimolybdenum complexes. The NMR spectra (1H) were recorded at room temperature in (CD3)2CO or CD2Cl2 solutions with a Bruker AMX 400 spectrometer and were referenced to SiMe4. Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Diethyl Sulfide in Dichloroethane: Synthesis of [Mo2Cp2(μ-SMe)2(μSEt2)(μ-Cl)](BF4) (3). A mixture of 1 (100 mg, 0.158 mmol) and diethyl sulfide (34 μL, 2 equiv) was heated in (CH2)2Cl2 (15 mL) at 45 °C for 2 h. After this time, the solution had turned from red to purple-red. The solvent was then removed, and the crude products were analyzed in acetone-d by 1H NMR spectroscopy. Only one organometallic complex was detected in the spectrum. The residue was redissolved in dichloromethane (5 mL), and 20 mL of pentane was added. A purple solid precipitated. It was collected by filtration and then washed with pentane (3  15 mL), affording a purple powder of 3 (75.5 mg, 76% yield). 3 was obtained here as the single isomer 3a. Data for 3a are as follows. Anal. Calcd for C16H26BClF4Mo2S3: C, 30.56; H, 4.17; Cl, 5.64; Found: C, 30.49; H, 3.73; Cl, 5.32. 1H NMR (acetone-d): δ 6.09 (s, 10H, C5H5), 2.98 (q, JH-H= 8.0 Hz, 2H, CH2CH3), 2.90 (q, JH-H = 8.0 Hz, 2H, CH2CH3), 1.80 (s, 3H, SCH3), 1.68 (s, 3H, SCH3), 1.20 (m, 6H, CH2CH3). IR (KBr, cm-1): ν(BF) 1090-1010 (s). Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Diethyl Sulfide in Dichloromethane: Formation of 3 and 4. Complex 1 (92 mg, 0.142 mmol) and diethyl sulfide (31 μL, 2 equiv) were heated with stirring in CH2Cl2 (15 mL) at reflux for 1 h. The solution turned from red to maroon and then was concentrated. To this reduced solution was added 20 mL of pentane, giving a maroon precipitate that was analyzed in acetone-d by 1H NMR. The spectrum indicated that the reaction was incomplete, since signals due to 1 were detected. Compounds 3-5 and 1 were respectively obtained in about an 11:4:1:3.5 ratio. 3 was formed here as a mixture of the two inseparable isomers 3a and 3b in about a 10:1 ratio. 5 was identified as [Mo2Cp2(μ-SMe)2(MeCN)4](BF4)(Cl) by comparison of its 1H NMR data with those of a pure sample.22 The formulation of 4 was proven by

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comparison of its 1H NMR pattern with that of an analytically pure form, obtained in a further experiment (see below). Data for 3b are as follows. 1H NMR (acetone-d): δ 6.22 (s, 10H, C5H5), 3.06 (m, 4H, CH2CH3), 1.28 (m, 6H, CH2CH3); the peaks attributable to the SMe groups in 3b are obscured by the related ones observed in 3a. Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Thiirane in Dry Dichloromethane: Synthesis of [Mo2Cp2(μ-SMe)3(μS)](BF4) (6). Complex 1 (200 mg, 0.320 mmol) and 1.5 equiv of thiirane (28 μL) were heated in dry dichloromethane (20 mL) at reflux for 1 h. The solution turned from red to orange. Then, the solution was concentrated and 30 mL of diethyl ether was added to give an orange solid. After filtration the resultant residue was washed with pentane (2  15 mL), affording an orange powder of 6 (151 mg, 82% yield). 6 was obtained as a mixture of the two inseparable isomers 6a and 6b in about a 44:1 ratio. Crystals of 60 , suitable for X-ray analysis, were grown from a dichloromethane solution of the tetraphenylborate complex [Mo2Cp2(μSMe)3(μ-S)](BPh4) (60 ), formed via a metathetical reaction involving 6 as starting material, layered with diethyl ether. Data for 6 are as follows. Anal. Calcd for C13H19BF4Mo2S4: C, 26.81; H, 3.27. Found: C, 27.78; H, 3.54. 1H NMR (acetone-d): 6a, δ 6.96 (s, 10H, C5H5), 2.38, 1.94, and 1.74 (s, 3H, SCH3); 6b, δ 6.87 (s, 10H, C5H5), 2.48, 1.94, and 1.75 (s, 3H, SCH3). IR (KBr, cm-1): ν(BF) 1110-1050 (s). Reaction of 1 with Thiirane in Wet Dichloromethane: Formation of 6 and 7. In a similar manner, the above reaction was conducted in wet dichloromethane instead of dry CH2Cl2. The 1 H NMR spectra of acetone-d solutions of the orange powders obtained in four experiments indicated the presence of the four products 6a, 6b, 7a, and 7b, in variable molar ratios in the range of (154-2):(3-1):(125-1):(43-1), respectively. All these complexes were characterized by NMR spectroscopy (see above and below). Reaction of [Mo2Cp2(μ-SMe)3(μ-Cl)](BF4) (2) with H2O: Independent Synthesis of [Mo2Cp2(μ-SMe)3(μ-O)](BF4) (7). Complex 7 has previously been synthesized and partially characterized by spectroscopy and elemental analysis.20c,p Here, we have prepared 7 via a slightly modified method, in order to fully characterize (1H NMR and X-ray diffraction study) this complex. A solution of complex 2 (100 mg, 0.171 mmol) in warm water (5 mL) was stirred for 30 min at 50 °C. The solution turned from brownish green to light green, and diethyl ether (20 mL) was added, affording a green solid that was collected by filtration, washed with pentane (2  15 mL), and then dried under vacuum. Compound 7 was isolated as a green powder (80 mg, 83% yield). 7 was obtained as a mixture of the two inseparable isomers 7a and 7b in about a 5:1 ratio. Crystals of 70 , suitable for X-ray analysis, were obtained at room temperature from a dichloromethane solution of the tetraphenylborate complex [Mo2Cp2(μ-SMe)3(μ-O)](BPh4) (70 ), formed via a metathetical reaction involving 7 as starting material, layered with diethyl ether. New NMR data for 7 are as follows. 1H NMR (acetone-d): 7a, δ 7.01 (s, 10H, C5H5), 2.36, 1.86, and 1.81 (s, 3H, SCH3); 7b, δ 6.99 (s, 10H, C5H5), 2.45, 1.86, and 1.81 (s, 3H, SCH3). 1H NMR (CD3CN): 7a, δ 6.81 (s, 10H, C5H5), 2.26, 1.73, and 1.72 (s, 3H, SCH3); 7b, δ 6.78 (s, 10H, C5H5), 2.37, 1.95, and 1.94 (s, 3H, SCH3). Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Sulfur S8: Formation of 6 and 7a. To a solution of 1 (100 mg, 0.158 mmol) in dichloromethane (10 mL) was added 2 equiv of sulfur S8 (127 mg, 0.316 mmol). The mixture was stirred for 1 h 30 min at 45 °C, and the solution turned from red to orange. After filtration to eliminate the excess sulfur, the solution was concentrated, and 15 mL of pentane was added to give an orange solid. After further filtration the resultant residue was washed with pentane (2  15 mL), affording an orange powder (87 mg), which was analyzed by 1H NMR spectroscopy. The spectrum showed that the crude product contained a mixture of three compounds: 7a (11%), 6 (78%), and an unidentified complex

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(11%). The latter was only characterized by its 1H NMR signals at 6.66 (Cp) and 1.87 and 1.61 (SMe) ppm. Compound 6 was formed as a mixture of the two isomers 6a and 6b in a 6:1 ratio. On the basis of the 1H NMR spectra of the mixture the yields of 6 were estimated at 76%. Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Thietane: Synthesis of [Mo2Cp2(μ-SMe)2{μ-κ2(S):κ2(S)-S(CH2)3SMe}](BF4) (8). Complex 1 (150 mg, 0.237 mmol) was treated with 2.3 equiv of thietane (40 μL) in refluxing dichloromethane (15 mL) for 1 h. The solvent was then removed under reduced pressure. The resulting residue was washed three times with cold pentane (3  15 mL), affording a purple solid. The 1H NMR spectrum of the resultant powder in (CD3)2CO indicated the presence of only one product, 8 (114 mg, 77% yield). However, in some experiments small amounts of the oxo compound 7 ( 2σ(I)) R1 (all data) wR2 (all data) goodness of fit on F2 ΔFmax, ΔFmin/e A˚-3

40

60

70

80 3 H2O

100

130

C15H24ClF6Mo2PS4 704.88 0.18  0.10  0.02 orthorhombic P212121 12.7338(3) 13.3930(3) 13.9952(4) 90 90 90 2386.8(1) 4 1.962 170(2) 1.628 2.64-24.71 15 187 3842, 266 0.0320 0.0254 0.0371 0.0528 0.990 0.524, -0.329

C37H39BMo2S4 814.61 0.20  0.20  0.20 tetragonal P421/m 14.6955(4) 14.6955(4) 7.7749(4) 90 90 90 1679.05(11) 2 1.611 170(2) 1.023 3.82-33.05 19 843 3185, 125 0.0497 0.0500 0.0571 0.1248 1.085 2.107, -1.872

C37H39BMo2OS3 798.58 0.33  0.19  0.08 tetragonal P421/m 14.6783(4) 14.6783(4) 7.7906(4) 90 90 90 1678.5(1) 2 1.580 170(2) 0.963 3.10-26.37 13 619 1809, 124 0.0342 0.0304 0.0310 0.0754 1.181 0.537, -0.356

C40H47 BMo2OS4 874.71 0.21  0.17  0.02 monoclinic P21/c 17.8598(12) 10.0786(6) 22.2717(19) 90 107.308(8) 90 3827.4(5) 4 1.518 170(2) 0.905 2.67-20.82 11 385 3863, 353 0.0503 0.0529 0.0829 0.1539 1.029 1.364, -0.367

C16H24ClF6Mo2PS3 684.83 0.55  0.41  0.14 triclinic P1 10.8501(8) 13.5873(15) 17.1418(10) 68.456(7) 89.075(5) 81.857(8) 2325.1(3) 4 1.956 170(2) 1.581 2.66-23.26 12 430 5776, 527 0.0212 0.0514 0.0754 0.1507 1.058 1.966, -1.103

C40H44BClMo2S4 891.13 0.17  0.14  0.08 monoclinic P21/n 9.4536(5) 30.7462(12) 12.7894(6) 90 90.258(4) 90 3717.4(3) 4 1.592 170(2) 1.001 2.67-25.35 23 625 5876, /435 0.0283 0.0286 0.0448 0.0750 1.064 0.672, -0.338

a

Legend: Nmeasd = total number of intensity measurements; Nunique = number of intensity measurements after averaging according to point symmetry.

together with small amounts of an uncharacterized byproduct in about a 11.5:5.5:2:1 ratio, respectively. Thermal Transformation of 1 in Dichloromethane: Formation of 4 and 5. The heating of the bis(nitrile) complex 1 (92 mg, 0.142 mmol) in dichloromethane at reflux for 2 h gave a red-brown solution, which was reduced under vacuum. Addition of pentane (20 mL) to this solution afforded a red-brown precipitate (m = 84 mg) that was analyzed by 1H NMR spectroscopy. Complexes 4 and 5 were formed together with two other unknown byproducts in about a 10:2:3:1 ratio. On the basis of 1 H NMR spectra of the mixture the yields of 4 and 5 were estimated at 55% and 8%, respectively. Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with 1,4Dithiane: Synthesis of [Mo2Cp2(μ-SMe)2(μ-Cl){(μ-κ1(S):κ1(S)S(CH2)4S}](BF4) (13). A mixture of 1 (200 mg, 0.316 mmol) and 1,4-dithiane (57 mg, 1.5 equiv) was heated in dichloromethane (15 mL) at reflux for 1 h under stirring. The solution turned from brick red to orange-yellow. The volume of the solution was then reduced under vacuum, and diethyl ether (30 mL) was added to precipitate an orange solid. After filtration and washing with cold pentane (2  15 mL) the solid was analyzed by 1H NMR spectroscopy in acetone-d. Complex 13 was formed as the major product together with small amounts of 14 and a byproduct in about a 23:1:1 ratio. By crystallization in cold dichloromethane-hexane (1:1), compound 13 was obtained as an analytically pure sample in good yield (m = 146 mg, 70%). Complex 13 was formed as a mixture of two isomers, 13a and 13b, in a 6:1 ratio. Crystals of 130 , suitable for X-ray analysis, were obtained at room temperature from a dichloromethane solution of the tetraphenylborate compound [Mo2Cp2(μ-SMe)2(μ-Cl){μ-κ1(S):κ1(S)-S(CH2)4S}](BPh4) (130 ), formed via a metathetical reaction involving 13 as starting material, layered with diethyl ether. Data for 13 are as follows. Anal. Calcd for C16H24BF4Mo2S4Cl: C, 29.17; H, 3.67; Cl, 5.38. Found: C, 29.28; H, 3.65; Cl, 4.80. 1 H NMR (acetone-d): 13a, 5.54 (s, 10H, C5H5), 3.27 (m, 4H, CH2), 3.20 (m, 4H, CH2), 2.08 and 1.55 (s, 3H, SCH3); 13b, δ 5.55 (s, 10H, C5H5), 2.96 (m, 4H, CH2), 2.93 (m, 4H, CH2), 2.13 and 1.67 (s, 3H, SCH3). IR (KBr, cm-1): ν(BF) 1131- 994 (s), ν(CS) 631 (s). Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with 1,4-Thioxane: Synthesis of [Mo2Cp2(μ-SMe)2(μ-Cl){(μ-κ2(S)-S(C4H8)O}](BF4) (14) and Formation of 4 and 5. In a typical experiment, a

mixture of 1 (92 mg, 0.142 mmol) and 1,4-thioxane (68 μL, 5 equiv) was heated in dichloromethane (15 mL) at reflux for 2 h. After this time, the solution turned from red to purple. The solvent was then concentrated, and pentane (20 mL) was added to give a violet solid. The 1H NMR analysis of the insoluble product (m = 75 mg) in acetone-d indicated the presence of compounds 14, 4, and 5 together with small amounts of a byproduct in about a 21:9.5:2:1 ratio. On the basis of 1H NMR spectra of the mixture the yields of 14, 4, and 5 were estimated at 51%, 22% and 2%, respectively. Compound 14 was obtained as a mixture of two isomers, 14a and 14b, in about a 4:1 ratio. Similarly, compound 1 (100 mg, 0.158 mmol) was treated with 5 equiv of 1,4-thioxane (74 μL) in (CH2)2Cl2 (15 mL) at 60 °C for 20 min. After the usual treatments, a violet powder (m = 78 mg) was obtained and analyzed by 1H NMR spectroscopy. The spectra indicated that the solid contains mainly compound 14a (estimated yield 60%), together with minor byproduct. After several recrystallizations of the above mixture of products in cold dichloromethane-hexane (1:1), an analytically pure powder of 14a was collected. Data for 14 are as follows. Anal. Calcd for C16H24BClF4Mo2OS3: C, 29.90; H, 3.76; Cl, 5.51. Found: C, 29.61; H, 3.55; Cl, 4.96. 1H NMR (acetone-d): 14a, δ 6.14 (s, 10H, C5H5), 3.96, 3.87, 3.14, and 3.03 (m, 2H, CH2), 1.80 and 1.68 (s, 3H, SCH3); 14b, δ 6.22 (s, 10H, C5H5), 3.91 and 3.22 (m, 4H, CH2), 1.64 (s, 6H, SCH3). IR (KBr, cm-1): ν(BF) 1128- 992 (s). Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with Benzothiophene: Synthesis of 4 and Formation of 5 and 7. To a dichloromethane solution (15 mL) of 1 (100 mg, 0.158 mmol) was added an excess of 1-benzothiophene (106 mg, 5 equiv), and the mixture was heated under reflux for ca. 16 h. After this time, a red precipitate was obtained, separated from the solution by filtration, and washed with diethyl ether (3  10 mL), affording a red powder of 5 (17 mg, 15% yield). The volume of the filtrate was then reduced under vacuum, and diethyl ether (20 mL) was added to precipitate a violet powder of 4, which was washed with pentane (3  15 mL). After drying, 4 was obtained in 66% yield (67.5 mg) as an analytically pure solid. Crystals of 40 , suitable for X-ray analysis, were obtained at room temperature from a dichloromethane solution of the hexafluorophosphate complex [Mo2Cp2(μ-SMe)2(μ-Cl){μ-S(Me)CH2S(Me)}](PF6) (40 ), formed

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via a metathetical reaction involving 4 as starting material, layered with diethyl ether. Similarly, compound 1 (100 mg, 0.158 mmol) was treated with 5 equiv of 1-benzothiophene (74 μL) in (CH2)2Cl2 (15 mL) at 60 °C for 20 min. After the usual treatments, a greenish precipitate (m = 78 mg) was obtained by addition of pentane. The 1H NMR analysis of the solid indicated the formation of two products, which were identified as the oxo compound 7 (71%) and an unknown derivative (29%), characterized by its cyclopentadienyl signal at δ 6.86 ppm. On the basis of 1H NMR spectra of the mixture the yield of 7 was estimated at 62%. Data for 4 are as follows. Anal. Calcd for C15H24BClF4Mo2S4: C, 27.85; H, 3.74; Cl, 5.48. Found: C, 27.78; H, 3.62; Cl, 5.92. 1H NMR (acetone-d): δ 5.55 (s, 10H, C5H5), 4.11 (AB, JH-H = 16.0 Hz, 2H, CH2), 2.48 (s, 6H, -CH2SCH3), 2.13 and 1.67 (s, 3H, SCH3). Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with 1-Benzoselenophene: Formation of 4, 5, and 7. Complex 1 (100 mg, 0.158 mmol) was treated with 2 equiv of benzoselenophene (57 mg) in refluxing CH2Cl2 (15 mL) for 2 h 30 min. The solvent was then removed, and the crude products were analyzed by 1H NMR spectroscopy, which indicated the presence of three NMR-detectable organometallic complexes, e.g. 4 (57%), 5 (3%), and 7 (11%), together with unidentified byproduct. When the reaction was conducted in dichloroethane instead of dichloromethane, only 7 (78%) and an unidentified product having a cyclopentadienyl signal at 6.86 ppm were formed. Reaction of [Mo2Cp2(μ-SMe)3(MeCN)2](BF4) (1) with 1-Dibenzothiophene: Formation of 4, 5, and 7. To a dichloromethane solution (20 mL) of 1 (300 mg, 0.474 mmol) was added 5 equiv of dibenzothiophene (437 mg), and the mixture was heated under reflux for 1 h. The solution was then cooled to 0 °C, and after 1 h (48) (a) Sheldrick, G. M. SHELX-97; University of G€ottingen, G€ ottingen, Germany, 1998. (b) Farrugia, L. J. WinGX-A Windows Program for Crystal Analysis. J. Appl. Crystallogr. 1999, 32, 837.

Ojo et al. at this temperature a red precipitate was obtained and separated from the solution by filtration. This solid was then washed three times with diethyl ether (3  15 mL), affording a red powder of 5 (143.2 mg, 43% yield). The volume of the filtrate was then reduced under vacuum, and diethyl ether (20 mL) was added to precipitate a violet powder that was washed with pentane. After drying, 4 was obtained in 50.5% yield (155 mg). X-ray Structural Determinations. Measurements for compounds 40 , 60 , 70 , 80 3 H2O, 100 , and 130 were carried out on a Oxford Diffraction X-Calibur-2 CDD diffractometer equipped with a jet cooler device. Graphite-monochromated Mo KR radiation (λ = 0.710 73 A˚) was used in all experiments. The structures were solved and refined by standard procedures.48 Selected bond lengths and angles are collected in the captions to Figures 1-6. Crystal and data collection and processing parameters are given in Table 1.

Acknowledgment. We are grateful to Dr. F. Michaud for the crystallographic measurements and helpful discussions and to Dr. K. W. Muir (University of Glasgow) for handling the structure of complex 60 . We also thank Mrs J. L’Helgouarc’h for technical assistance. The Universit
e Europ
eenne de Bretagne-Universit
e de Brest and the CNRS are acknowledged for financial support. The Ministere de l’Enseignement Sup
erieur et de la Recherche du Gabon is acknowledged for providing studenships (W.-S.O.). Supporting Information Available: CIF files giving X-ray crystallographic data for 40 , 60 , 70 , 80 3 H2O, 100 , and 130 and tables giving details of the structure determination, non-hydrogen atomic positional parameters, all bond distances and angles, anisotropic parameters, and hydrogen atomic coordinates. This material is available free of charge via the Internet at http:// pubs.acs.org.