Thermal Generation and Structures of the Unsaturated Doubly Bridged

Jan 10, 2011 - Thermal Generation and Structures of the Unsaturated Doubly Bridged Complex [Mo2Cp2Cl2(μ-SMe)2] and Its Quadruply Bridged Isomer ...
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Organometallics 2011, 30, 649–652 DOI: 10.1021/om101061y

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Thermal Generation and Structures of the Unsaturated Doubly Bridged Complex [Mo2Cp2Cl2( μ-SMe)2] and Its Quadruply Bridged Isomer [Mo2Cp2( μ-Cl)2(μ-SMe)2] Wilfried-Solo Ojo,† John E. McGrady,*,‡ Franc-ois Y. Petillon,*,† Philippe Schollhammer,*,† and Jean Talarmin† †

Universit e de Brest, CNRS, UMR 6521, “Chimie, Electrochimie Mol eculaires et Chimie Analytique”, CS 93837, 29238 Brest-Cedex 3, France, and ‡Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QR, U.K. Received November 11, 2010 Summary: The doubly and quadruply bridged isomers [Mo2Cp2Cl2(μ-SMe)2] (4) and [Mo2Cp2(μ-Cl)2(μ-SMe)2] (3) have been obtained as side-products when the dicarbonyl precursor [Mo2Cp2(CO)2(μ-SMe)3]Cl (1) is warmed in toluene solution, the main product being the tris-thiolato-bridged compound [Mo2Cp2(μ-Cl)(μ-SMe)3] (2). Complex 4 is stable at room temperature but can be transformed into 3 at elevated temperatures. 3 and 4 have been crystallographically characterized, and both contain equivalent molybdenum centers. The Mo-Mo separations of 2.5909(11) and 2.4507(2) A˚ in 3(syn) and 4 are consistent with single and triple Mo-Mo bonds, respectively.

Introduction Unsaturated dinuclear organometallic complexes with a {Mo2Cp0 2} core (Cp0=η5-C5H5, η5-C5Me5, η5-C5H4Me) and 32- and 30-electron counts display remarkable reactivity associated with their multiple Mo-Mo bonds, and, as a result, these compounds have been exploited extensively in the context of molecular activation.1 However, despite their generally high reactivity, some of these unsaturated derivatives show unexpected stability even under forcing thermal or photochemical conditions.2 A striking example of this is the *To whom correspondence should be addressed. E-mail: schollha@ univ-brest.fr, [email protected], john.mcgrady@chem. ox.ac.uk. (1) Selected recent references: (a) Petillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Coord. Chem. Rev. 1998, 178-180, 203, and references therein. (b) Adams, H.; Gill, L. J.; Morris, M. J. J. Chem. Soc., Dalton Trans. 1998, 2451. (c) Adams, H.; Allott, C.; Bancroft., M. N.; Morris, M. J. Inorg. Chim. Acta 2003, 350, 277. (d) Wong, R. C. S.; Ooi, M. L.; Tan, G. H.; Ng, S. W. Inorg. Chim. Acta 2007, 360, 3113. (e) García, M. E.; García-Viv o, D.; Ruiz, M. A.; Herson, P. Organometallics 2008, 27, 3879. (f) Li, Q.; Luo, C.; Song, L. C. Chin. J. Chem. 2009, 27, 1711. (g) Alvarez, M. A.; García, M. E.; Ramos, A.; Ruiz, M. A. J. Organomet. Chem. 2009, 694, 3864. (h) Alvarez, M. A.; García, M. E.; Martínez, M. E.; Ramos, A.; Ruiz, M. A. Organometallics 2009, 28, 6293. (i) Alvarez, M. A.; García, M. E.; Martínez, M. E.; Menendez, S.; Ruiz, M. A. Organometallics 2010, 29, 710. (j) Alvarez, M. E.; García, M. E.; Martínez, M. E.; Ruiz, M. A. Organometallics 2010, 29, 904. (2) (a) Garcı´ a-Viv o, D.; Garcı´ a, M. E.; Ruiz, M. A. Organometallics 2008, 27, 169. (b) García, M. E.; Melon, S.; Ramos, A.; Ruiz, M. A. Dalton Trans. 2009, 8171. (3) Benson, I. B.; Killops, S. D.; Knox, S. A. R.; Welch, A. J. J. Chem. Soc., Chem. Commun. 1980, 1137. (4) (a) Petillon, F. Y.; Le Quere, J. L.; Roue, J.; Guerchais, J. E.; Sharp, D. W. A. J. Organomet. Chem. 1981, 204, 207. (b) Guerchais, J. E.; Le Quere, J. L.; Petillon, F. Y.; Manojlovic-Muir, Lj.; Muir, K. W.; Sharp, D. W. A. J. Chem. Soc., Dalton Trans. 1982, 283. r 2011 American Chemical Society

32-electron, doubly bridged complexes [Mo2Cp2(CO)2(μSR)2] (R = t-Bu,3 Me4), which are prepared under drastic conditions3-5 and are unreactive toward carbonyl,3 phosphines, phosphites, or alkynes.5 In this paper, we report that the unsaturated 30-electron dimolybdenum complex [Mo2Cp2Cl2(μ-SMe)2] (4) can be obtained, along with isomeric [Mo2Cp2(μ-Cl)2(μ-SMe)2] (3) and the quadruply bridged species [Mo2Cp2(μ-Cl)(μ-SMe)3] (2), by heating toluene solutions of the 34-electron triply bridged derivative [Mo2Cp2(CO)2(μ-SMe)3]Cl (1). We also show a rare example of isomerization of a terminal halide unsaturated 30-electron compound (4) into a bridged 34-electron derivative (3) by heating; such an isomerization is known to depend on the nature of the bridged or nonbridged ligands.6 This could, in addition, have a direct impact on the reactivity of such products. Compounds 3 and 4 have been characterized by X-ray diffraction.

Results and Discussion In earlier papers we reported the synthesis and spectroscopic5 and X-ray crystallographic characterization7 of the μ-trithiolato-μ-chloro-bridged complex [Mo2Cp2(μ-Cl)(μ-SMe)3] (2) as the sole product of the heating of [Mo2Cp2(CO)2(μ-SMe)3]Cl (1) in toluene at low temperature. On reinvestigating the thermal transformations of 1 in toluene at higher temperature, two further chloro compounds, [Mo2Cp2(μ-Cl)2(μ-SMe)2] (3) and [Mo2Cp2Cl2(μ-SMe)2] (4), are obtained in low yields in addition to 2, which is the major product of the reaction (Scheme 1 and Experimental Section). The three derivatives 2, 3, and 4 have been cleanly separated by conventional chromatographic techniques and obtained as analytically pure samples. 3 has previously been synthesized via an alternative route by treating a dichloromethane solution of the salt [Mo2Cp2(CH3CN)4(μ-SMe)2](BF4)2 with Et4NCl, but the product was characterized only through analytical and spectroscopic data.7 Compound 4, on the other hand, is entirely new. Prolonged heating of 4 in toluene solution results in its conversion to 3, suggesting that the small amounts of 3 obtained in the original reaction mixture arise from the thermal transformation of 4. (5) Gomes de Lima, M. B.; Guerchais, J. E.; Mercier, R.; Petillon, F. Y. Organometallics 1986, 5, 1952. (6) Green, M. L. H.; Mountford, P. Chem. Soc. Rev. 1992, 29. (7) Cabon, N.; Petillon, F. Y.; Schollhammer, P.; Talarmin, J.; Muir, K. W. Dalton Trans. 2004, 2708. Published on Web 01/10/2011

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Ojo et al.

Scheme 1

Figure 1. View of the molecule of [Mo2Cp2(μ-Cl)2(μ-SMe)2] (3). Non-hydrogen atoms are shown with ellipsoids at the 30% level. H atoms bonded to C atoms are omitted for clarity.

We have been able to obtain crystals of 3 and 4 suitable for X-ray analysis (see below) from cold toluene/hexane and CH2Cl2/pentane solutions of the complexes, respectively. It should be noted that attempts to crystallize 3 from a CH2Cl2/ pentane mixture led to its transformation into crystals of a bimetallic compound identified as [Mo2Cp2Cl3(μ-SMe)2(μ-OH)] 3 CH2Cl2 (5 3 CH2Cl2) by an X-ray diffraction study. The values of the interatomic distances for the bimetallic unit in 5 3 CH2Cl2 are similar to those reported previously8 for the related solvate 5 3 0.5 C7H8, so the crystallographic data of 5 3 CH2Cl2 will not be discussed further here. The results of the X-ray analysis of 3 are consistent with a structure based on a {Mo2Cp2} core bridged by two thiolato and two chloro ligands. As is usual in this group of compounds, the thiolato and chloro bridges in 3 are all nearly symmetrical and adopt a mutually cis arrangement with a syn orientation of the methyl groups at sulfur with respect to the S---S vector (Figure 1 and Table 1). The relatively short Mo-Mo distance of 2.5909(11) A˚ and acute Mo-X-Mo (X = Cl, S) bridging angles (62.21(6)-64.29(6)°) are consistent with the presence of direct metal-metal bonding.1a The Mo-Mo bond length of 2.5909(11) A˚ in the unit cell is typical of single (Cp)Mo(III)-Mo(III)(Cp) bonds in related quadruply bridged species containing three-electron-donor halide or pseu(8) Couldwell, C.; Meunier, B.; Prout, K. Acta Crystallogr. B 1979, 35, 603. (9) (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. (c) McKenna, M.; Wright, L. L.; Miller, D. J.; Tanner, L.; Haltiwanger, R. C.; Rakowski DuBois, M. J. Am. Chem. Soc. 1983, 105, 5329. (d) Schollhammer, P.; Guenin, E.; Poder-Guillou, S.; Petillon, F. Y.; Talarmin, J.; Muir, K. W.; Baguley, P. J. Organomet. Chem. 1997, 539, 193. (10) (a) Grebenik, P. B.; Green, M. L. H.; Izquierdo, A.; Mtetwa, V. S. B.; Prout, K. J. Chem. Soc., Dalton Trans. 1987, 9. (b) Fromm, K; Hey-Hawkins, E. Z. Anorg. Allg. Chem. 1993, 619, 261. (c) Abugideiri, F.; Fettinger, J. C.; Poli, R. Inorg. Chim. Acta 1995, 229, 445. (11) Desai, J. U.; Gordon, J. C.; Kraatz, H.-B.; Owens-Waltermire, B. E.; Poli, R.; Rheingold, A. L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1486. (12) Shin, J. H.; Parkin, G. Polyhedron 1994, 13, 1489. (13) Tucker, D. S.; Dietz, S.; Parker, K. G.; Carperos, V.; Gabay, J.; Noll, B.; Rakowski DuBois, M.; Campana, C. F. Organometallics 1995, 14, 4325. (14) Le Roy, C.; Petillon, F. Y.; Muir, K. W.; Schollhammer, P.; Talarmin, J. J. Organomet. Chem. 2006, 691, 898.

dohalide (Y) ligands (Y=SR,9 Cl,10 Br,11 I,12 Cl/SR,7,13 Br/ SR,14 I/SR,14 SR/PR2,7 Cl/PR2,10b,15 SR/NdNR,16 SR/Nd CR2,17 SR/CCR,18 SR/Cl/PR2,7 and SR/PR2/NdCR27), which lie in the range 2.574(1)-2.708(3) A˚. The Mo-Mo bond length in 3 is also very similar to that in 2 (Mo-Mo=2.601(1) A˚),7 suggesting that replacement of one bridging SMe group by a chlorine has little influence on the molybdenum-molybdenum bonding. Complex 4 has been characterized by NMR and IR spectroscopy, microanalysis, and single-crystal X-ray diffraction. Elemental analyses are consistent with the formula C12H16Cl2Mo2S2, and the 1H NMR pattern indicates the presence of two cyclopentadienyl and two SMe groups. The IR spectrum in KBr pellets shows a band at 310 cm-1, which is characteristic of a terminal Mo-Cl stretch. These analytical data are fully compatible with the structure of 4 revealed by X-ray crystallography (Figure 2 and Table 1): the molecule contains two {CpMoCl} units symmetrically bridged by two SMe groups (with a syn arrangement of the methyl groups), which are cis to the terminal chloro ligands. The Cl2, Mo2, Mo1, and Cl1 atoms are almost planar (torsion angle=-1.16(2)°), and the remarkably short Mo-Mo separation of 2.4507(2) A˚ in 4 is consistent with the triple Mo-Mo bond required by the EAN formalism for the 30electron complex 4. Although a relatively large number of binuclear cyclopentadienyl molybdenum complexes have been reported, only a few of them feature Mo-Mo triple bonds, and most of these contain at least one phosphido- or phosphinidene-bridged ligand.20,21 Compound 4 represents the first example of a crystallographically characterized triply bonded cyclopentadienyl dimolybdenum complex containing a thiolato-bridged ligand. The Mo-Mo distance in 4 is (15) Felsberg, R.; Blaurock, S.; Junk, P. C.; Kirmse, R.; Voigt, A.; Hey-Hawkins, E. Z. Anorg. Allg. Chem. 2004, 630, 806. (16) Schollhammer, P.; Guenin, E.; Petillon, F. Y.; Talarmin, J.; Muir, K. W.; Yufit, D. S. Organometallics 1998, 17, 1922. (17) Schollhammer, P.; Pichon, M.; Muir, K. W.; Petillon, F. Y.; Pichon, R.; Talarmin, J. Eur. J. Inorg. Chem. 1999, 221. (18) Schollhammer, P.; Cabon, N.; Capon, J.-F.; Petillon, F. Y.; Talarmin, J.; Muir, K. W. Organometallics 2001, 20, 1230. (19) Le Goff, A.; Le Roy, C.; Petillon, F. Y.; Schollhammer, P.; Talarmin, J. Organometallics 2007, 26, 3607. (20) (a) Alvarez, C. M.; Alvarez, M. A.; Garcia, M. E.; Ramos, A.; Ruiz, M. A.; Lafranchi, M.; Tiripicchio, A. Organometallics 2005, 24, 7. (b) Garcia, M. E.; Ramos, A.; Ruiz, M. A.; Lafranchi, M.; Marchio, L. Organometallics 2007, 26, 6197. (21) (a) Kyba, E. P.; Mather, J. D.; Hassett, K. L.; McKennis, J. S.; Davis, R. E. J. Am. Chem. Soc. 1984, 106, 5371. (b) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1989, 1555. (c) Amor, I.; García, M. E.; Ruiz, M. A.; Saez, D.; Hamidov, H.; Jeffery, J. C. Organometallics 2006, 25, 4857. (d) García, M. E.; Melon, S.; Ramos, A.; Ruiz, M. A. Dalton Trans. 2009, 8171.

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Table 1. Selected Bond Lengths (A˚), Angles (deg), and Dihedral and Torsion Angles (deg) for syn-3 and 4 syn-3

Mo1-Mo2 Mo1-Cl1 Mo2-Cl1 Mo1-Cl2 Mo2-Cl2 Mo1-S1 Mo2-S1 Mo1-S2 Mo2-S2 Mo2-S1-Mo1 Mo2-S2-Mo1 Mo2-Cl1-Mo1 Mo2-Cl2-Mo1 Mo1-S1-Mo2/ Mo1-S2-Mo2

4

X-ray (A˚/deg)

DFT (A˚/deg)

2.5909(11) 2.494(2) 2.521(2) 2.511(2) 2.501(2) 2.433(2) 2.436(2) 2.446(2) 2.443(2) 64.29(6) 64.00(6) 62.21(6) 62.26(5) 94.15

2.63 2.56

2.48

64.0 61.9

X-ray (A˚/deg)

DFT (A˚/deg)

Mo1-Mo2 Mo1-Cl1 Mo2-Cl2 Mo1-S1 Mo2-S1 Mo1-S2 Mo2-S2 Mo1-S1-Mo2 Mo1-S2-Mo2 S1-Mo1-S2 S1-Mo2-S2 Cl2-Mo2-Mo1 Cl1-Mo1-Mo2 Cl2-Mo2-Mo1-Cl1

2.4507(2) 2.3749(4) 2.3959(4) 2.4198(4) 2.4116(4) 2.4135(4) 2.4158(4) 60.96(1) 60.99(2) 114.93(1) 115.14(1) 112.75(1) 111.90(1) -1.16(2)

2.41 2.39

Mo1-S1-Mo2-S2

22.36(2)

2.46

58.6

Figure 2. View of a molecule of [Mo2Cp2Cl2(μ-SMe)2] (4) showing 30% probability ellipsoids. H atoms bonded to C atoms are omitted for clarity.

somewhat shorter than those in the related doubly bridged unsaturated (30-electron) neutral cyclopentadienyl dimolybdenum complexes, which lie in the range 2.528(2)-2.580(1) A˚ (average = 2.5595 A˚). The Mo-Mo bond length in neutral cyclopentadienyl compounds of this type generally decreases as the number of bridging ligands increases, but the distance of 2.4507(2) A˚ in the doubly bridged 4 is, in fact, even shorter than those found in typical triply bridged cyclopentadienyl complexes with Mo-Mo triple bonds (2.464(1)-2.5322(3) A˚, average = 2.5044 A˚).1i,20,21 Thus it appears that the thiolato bridge supports a remarkably short Mo-Mo separation. Notably, it is ca. 0.27 A˚ shorter than the corresponding distance in a 32-electron doubly bridged derivative, [Mo2Cp2(O)(Cl)(μ-SMe)(μ-MeSCCH2Ph)], for which a Mo-Mo bond order of 2 had been proposed.19 In order to explore the changes in metal-metal bonding associated with the isomerization of syn-3 to 4, we have conducted a series of calculations using density functional theory. The ground states of both compounds are closedshell singlets, with optimized bond lengths very similar to experiment (see Table 1): Mo-S and Mo-Cl bond lengths are uniformly overestimated by approximately 0.05 A˚, but most significantly, the substantial contraction of the Mo-Mo separation on going from syn-3 to 4 is reproduced (0.22 A˚ (comp) vs 0.14 A˚ (expt)). The energies of the two isomers, syn-3 and 4, differ by less than 1 kcal/mol, consistent with the observation that both can be isolated from the same reaction mixture. Analysis of the Kohn-Sham orbitals (Figure 3) of 3 and 4 reveals a qualitative picture fully

Figure 3. Doubly occupied Kohn-Sham orbitals of syn-3 and 4, illustrating the formal bond orders of 1 and 3, respectively.

consistent with early work by Hoffmann and others on doubly22 and quadruply bridged species23 and confirms the assignments of Mo-Mo bond order proposed above on the basis of simple electron-counting procedures. The approximately octahedral geometry about the molybdenum centers in 4 leads to a characteristic three-below-two splitting of the metal d orbitals, and linear combinations of the three lowlying singly occupied orbitals generate filled bonding orbitals with local σ and mixed π/δ symmetry and hence a formal MotMo triple bond. The quadruple bridge in syn-3 destabilizes a further orbital on each metal center, leaving only linear combinations with local σ and δ symmetry to accommodate the six metal-based electrons. Occupation of the σ, δ, and δ* combinations leaves a net Mo-Mo bond order of 1, as required by the EAN rule. In conclusion complex 4 is the first example of a double thiolato-bridged compound with a Mo-Mo triple bond. Compound 4 converts into its quadruply bridged isomer 3, with a Mo-Mo single bond, at high temperatures. (22) Tremmel, W.; Hoffmann, R.; Jemmis, E. D. Inorg. Chem. 1989, 28, 1213. (23) Shaik, S.; Hoffmann, R.; Fisel, C. R.; Summerville, R. H. J. Am. Chem. Soc. 1980, 102, 4555.

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Our analysis of the structure and electronic properties of 3 and 4 suggests that the conversion of 4 to 3 can be viewed as an intramolecular nucleophilic attack of a chloride on the triple bond of 4. In light of this, the stability of 4 that allows it to be stored under nitrogen for several days and characterized by spectroscopic and X-ray diffraction methods is remarkable.

Experimental Section General Procedures. The reactions were routinely carried out under a nitrogen atmosphere using standard Schlenk techniques. Solvents were distilled immediately before use under nitrogen from appropriate drying agents. A literature method was used for the synthesis of [Mo2Cp2(CO)2(μ-SMe)3]Cl (1).5 Infrared spectra were recorded on a Nicolet-Nexus FTIR spectrophotometer from KBr pellets. 1H NMR spectra were recorded in CDCl3 on a Bruker AMX 400 and were referenced to SiMe4. Chemical analyses were performed by the” Service de Microanalyse” ICSN-CNRS, Gif sur Yvette (France). Thermal Transformation of [Mo2Cp2(CO)2(μ-SMe)3]Cl (1): Formation of [Mo2Cp2(μ-Cl)(μ-SMe)3] (2), [Mo2Cp2(μ-Cl)2(μ-SMe)2] (3), and [Mo2Cp2Cl2(μ-SMe)2] (4). Crystallization of [Mo2Cp2Cl3(μ-SMe)2(μ-OH)] 3 CH2Cl2 (5 3 CH2Cl2). The heating (160 °C) of 1 (1 g, 1.8 mmol) in toluene for 24 h was carried out almost (reduced reaction time) as described previously.5 The 1 H NMR analysis of CDCl3 solutions of the crude solid indicated the presence of two new products, 3 and 4, in addition to that of 2, the only organometallic species characterized in these reactions previously.5 The three complexes were separated cleanly by chromatography on silica gel. Elution with a mixture of CH2Cl2/hexane (1:4) removed a brown band from which compound 2 was obtained, after evaporation of the volatiles, as the major product (500 mg, 65% yield); 2 was previously characterized by spectroscopic5 and crystallographic7 data. Further elution with a mixture of CH2Cl2/hexane (1:1.5) afforded a greenish-brown band; the eluate was concentrated to dryness to give 3 as a light brown solid (ca. 50 mg, 5.5% yield). Compound 3 was identified by comparison of its 1H NMR spectrum with that of a pure sample.7 Finally, a last green band was removed with CH2Cl2/hexane (4:1), which gave, after evaporation of the solvent, the new complex 4 as a green powder (ca. 70 mg, 7.5% yield). Light brown crystals (plates) of 3 suitable for X-ray diffraction analysis were grown from a cold toluene/hexane (1.5:1) solution (-18 °C) of the complex. Attempts to crystallize 3 in a CH2Cl2/pentane mixture (1:1) led to its transformation into crystals of [Mo2Cp2Cl3(μ-SMe)2(μ-OH)] 3 CH2Cl2 (5 3 CH2Cl2), which have been analyzed by X-ray diffraction. Green crystals of 4 suitable for X-ray analysis were obtained at room temperature by slow evaporation from a CH2Cl2/pentane solution (1:1) of 4. Prolonged heating of a toluene solution of 4, for a few hours, led to its complete transformation into compound 3. Data for 4 are as follows. Anal. Calcd for C12H16Cl2Mo2S2: C, 29.58; H, 3.31; Cl, 14.55; S, 13.16. Found: C, 29.04, H, 3.41; Cl, 14.41; S, 11.90. 1H NMR (CDCl3): δ 5.58 (s, 10H, C5H5), 3.04 (s, 6H, SCH3). IR (KBr, cm-1): ν(MoCl) 310(s).

Ojo et al. X-ray Structural Determination and Crystallographic Data. Measurements for 3, 4, and 5 3 CH2Cl2 were carried out on an Oxford Diffraction X-Calibur-2 CDD diffractometer, and the structures were solved and refined by standard procedures,24 as described previously.25 X-ray crystal data for 3: C12H16Cl2Mo2S2, fw=487.15, T= 170(2) K, triclinic, space groupe P1, a = 7.7777(7) A˚, b = 13.2903(12) A˚, c = 15.2420(13) A˚, R = 95.693(7)°, β = 97.602(7)°, γ=90.944(8)°, V=1553.3(2) A˚3, Z=4, dcalcd =2.083 g/cm3; 6324 unique, absorption-corrected intensities with θ < 26.37°. R(F)=0.0611 for 6324 reflections with I>2σ(I), and wR(F2) (all data) = 0.1341 after refinement of 329 parameters. |ΔF | < 1.001 e A˚-3. X-ray data for 4: C12H16Cl2Mo2S2, fw = 487.15, monoclinic, space group P21/n, a = 7.9955(3) A˚, b=14.5964(5) A˚, c=13.7702(4) A˚, β = 102.560(3)°, V = 1568.60(9) A˚-3, T=170(2) K, Z=4, dcalcd =2.063 g/cm3; 4785 unique, absorption-corrected intensities with θ(Mo KR) < 30.51°. R(F) = 0.0167 for 4785 reflections with I > 2σ(I), and wR(F2) (all data) = 0.0394 after refinement of 165 parameters. |ΔF | < 0.462 e A˚-3. Selected bond lengths and angles are given in Table 1. The X-ray crystallographic data for 5 3 CH2Cl2 are given in the Supporting Information. Computational Methodology. All calculations described in this paper were performed using density functional theory as implemented in the Gaussian program.26 Geometry optimizations on 3 and 4 were carried out using the BP86 functional,27 in combination with the Lanl08 pseudopotential and associated basis set for Mo, 6-31þG* on Cl, S, and the carbon atoms of the Cp ring, and 6-31G* elsewhere. The absence of imaginary frequencies confirmed the stationary points to be minima.

Acknowledgment. We are grateful to Dr. Franc-ois Michaud for the X-ray crystal analysis and to Mrs. Jacqueline L’Helgouarc’h for technical assistance. We also thank Mr. Alexandre Diascorn, undergraduate. The Universite Europeenne de Bretagne-Universite de Brest (France) and the CNRS are acknowledged for financial support. We also thank the Ministere de l’Enseignement Superieur et de la Recherche du Gabon for providing studenships (W.-S.O.). Supporting Information Available: CIF files giving X-ray crystallographic data for 3 and 4 and tables giving details of the structure determination of 5 3 CH2Cl2. Cartesian coordinates of the DFT-optimized structures of 3 and 4. This material is available free of charge via the Internet at http://pubs.acs.org. (24) (a) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112. (b) Farrugia, L. J. WinGX-A Windows Program for Crystal Analysis. J. Appl. Crystallogr. 1999, 32, 837. (25) Ojo, W.-S.; Petillon, F. Y.; Schollhammer, P.; Talarmin, J. Organometallics 2010, 29, 448. (26) Frisch, M. J.; et al. Gaussian 03, Revision D.02; Gaussian, Inc.: Wallingford, CT, 2004. Complete citation is given in the Supporting Information. (27) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 1372.