Reactions of the unsaturated methyl-bridged complexes [Mo2Cp2(μ-CH3)(μ-PtBu2)(CO)x] (x = 1, 2) towards transition metal carbonyls: convenient dehydrogenative route to heterometallic methylidyne-bridged clusters

Abstract

The unsaturated dicarbonyl complex [Mo2Cp2(μ-CH3)(μ-PtBu2)(CO)2] (1) reacted with [W(CO)6] under photolytic conditions to give three isomers of formula [Mo2WCp2(μ3-CH)(μ-PtBu2)(CO)7] (cis-3, cis-3´ and trans-3 in a ratio ca. 10:1:3), these differing in the relative disposition of the Cp, CO and methylidyne ligands, as inferred from the available spectroscopic data and the crystal structure of trans-3 (Mo−Mo = 2.8931(4) Å). The cis isomers are thermally unstable species which could not be isolated as pure solids as they either decomposed upon manipulation (cis-3´) or rearranged into the corresponding trans isomer (cis-3). In contrast, no reaction was observed between this compound and [W(THF)(CO)5] in the absence of photochemical activation, yet a rapid reaction occurred between this fragment and the monocarbonyl [Mo2Cp2(μ-CH3)(μ-PtBu2)(μ-CO)] (2) to give the cis-3 isomer exclusively. The reaction of 2 with [Fe2(CO)9] at room temperature led to a mixture of two trinuclear clusters: the 46-electron methylidyne-bridged [Mo2FeCp2(μ3-CH)(μ-PtBu2)(CO)5] (4a) and the acetyl-bridged [Mo2FeCp2{μ3-κ1:η2:κ1-C(O)CH3}(μ-PtBu2)(CO)5] (5) in a ca. 3:1 ratio. A symmetrical coordination of the methylidyne group is found in compound 4a, while the electronic unsaturation is mainly located at the Mo−Mo edge (2.667(1) Å). In contrast, an asymmetric 5-electron donor coordination of the acetyl group is observed in compound 5 and, accordingly, the intermetallic lengths are consistent with the formulation of single bonds in a 48-electron trinuclear cluster (Mo−Mo = 2.8235(4) Å and Mo−Fe ca. 2.76 Å). Finally, the reaction of compound 2 with [Ru3(CO)12] required photochemical activation and then led to the formation of the corresponding unsaturated methylidyne cluster [Mo2RuCp2(μ3-CH)(μ-PtBu2)(CO)5] (4b) in high yield.