Site-selective substitution and vinylidene–alkylidyne–vinylidene interconversion in dimolybdenum–ruthenium clusters

Abstract

The thermal reaction of the dimolybdenum-ruthenium vinylidene clusters [Mo 2 Ru(µ 3 -C᎐ ᎐ CHR)(CO) 7 (η-C 5 H 5 ) 2 ] (R = H 1a, Me 1b, Ph 1c or CO 2 Me 1d) with the tertiary phosphine PPh 2 Me afforded the monosubstituted complexes [Mo 2 Ru(µ 3 -C᎐ ᎐ CHR)(CO) 6 (PPh 2 Me)(η-C 5 H 5 ) 2 ] 2a-2d in excellent yields. The products exist as single isomers in which site-selective substitution of a CO ligand has occurred exclusively at the ruthenium atom. The crystal structure of 2b has been determined by X-ray diffraction; the geometry of the vinylidene ligand is identical to that previously found in the parent compound 1b, but a slightly different pattern of semi-bridging carbonyls is present. The reactions of 1a and 1b with diphenylphosphine are more complex. Depending on the stoichiometry and conditions employed, three different types of cluster have been isolated: the substitution product [Mo 2 Ru-(µ 3 -C᎐ ᎐ CH 2 )(CO) 6 (PPh 2 H)(η-C 5 H 5 ) 2 ] 2e; the 46-electron monophosphido compounds [Mo 2 Ru(µ 3 -CCH 2 R)-(µ-PPh 2 )(CO) 5 (η-C 5 H 5 ) 2 ] 3a, 3b and the saturated bis(phosphido) species [Mo 2 Ru(µ 3 -C᎐ ᎐ CHR)(µ-PPh 2 ) 2 (CO) 4 -(η-C 5 H 5 ) 2 ] 4a, 4b. Separate experiments have established that these products are formed sequentially, thus demonstrating the conversion of the initial vinylidene into an alkylidyne ligand and then back to a vinylidene. The structures of 3b and 4a have been confirmed by X-ray diffraction, showing that the phosphido groups bridge one or both of the Mo᎐Ru edges respectively.

Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 3. Formation and Cleavage of C−C and C−O Bonds in the Reactions of the Complexes [Mo2Cp2(µ-COMe)(µ-COR)(µ-PCy2)]BF4(R = Me, Et)

“…All this suggests that the electronic unsaturation of the trinuclear cluster is essentially localized on this pair of metal atoms. Yet, the Mo−Ru separations, 2.813(1) and 2.846(1) Å, are also somewhat shorter than those measured in related compounds having Mo−Ru single bonds (2.90–3.1 Å), perhaps as an effect of the positive charge of cluster. The coordination sphere of the molybdenum centers is completed by one Cp ligand and the dicyclohexylphosphide ligand bridging the Mo−Mo edge.…”

Heterometallic Derivatives of the Unsaturated Methyl-Bridged Complex [Mo2(η5-C5H5)2(μ-CH3)(μ-PCy2)(CO)2]. Photochemical Generation of Methylidyne-Bridged Clusters

“…The 13 C NMR spectrum displays a strongly deshielded carbyne resonance at 401.5 ppm, a chemical shift significantly higher than those measured in the triply bridged clusters [Mo 2 Ru(μ 3 -CR)(μ-PPh 2 )(CO) 5 ] (R = Me, Et; δ C ca. 350 ppm), this being suggestive that the carbyne ligand retains in solution the almost edge-bridging coordination found in the crystal. Besides, the Fe-bound carbonyls give rise to a single resonance at room temperature, with this indicating the operation of a fast fluxional process within the Fe(CO) 3 fragment, as found for the clusters 7 and 9 .…”

Reactivity of the Unsaturated Hydride [Mo2(η5-C5H5)2(μ-H)(μ-PCy2)(CO)2] toward 17- and 16-Electron Metal Carbonyl Fragments: Rational Synthesis of Electron-Deficient Heterometallic Clusters

“…Thus, the large difference in the 31 P chemical shifts of isomers 4a and 4b is taken as an indication that the PCy 2 ligand might be bridging a Mo 2 vector in one isomer ( 4b , by comparison with the shifts for 2b ) and a MoRu one in the other isomer ( 4a , this structure being comparable to that of 3 , after replacing the Mn(CO) 3 fragment in the latter by the isoelectronic RuCp one). We can compare the shift in 4a with those of the Mo 2 Ru clusters [Mo 2 RuCp 2 (μ 3 -CCRH)(μ-PPh 2 ) 2 (CO) 4 ] and [Mo 2 RuCp 2 (μ 3 -CCH 2 R)(μ-PPh 2 )(CO) 5 ] (R = H, Me), ranging from 188 to 202 ppm …”

“…Finally, we should note that while a number of trinuclear clusters having Mo 2 Ru cores have been reported previously, most of them are electron-precise species (48 electrons). In fact, we are only aware of another family of 46-electron Mo 2 Ru species, these being the above-mentioned [Mo 2 RuCp 2 (μ 3 -CCH 2 R)(μ-PPh 2 )(CO) 5 ] clusters (R = H, Me) …”