Structural and Chemical Effects of the PtBu2 Bridge at Unsaturated Dimolybdenum Complexes Having Hydride and Hydrocarbyl Ligands

A high-yield synthetic route for the preparation of the unsaturated anion [Mo2Cp2(μ-PtBu2)(μ-CO)2]− (2) was implemented, via two-electron reduction of the chloride complex [Mo2Cp2(μ-Cl)(μ-PtBu2)(CO)2] (1). Reaction of 2 with [NH4][PF6] led to the formation of the 30-electron complex [Mo2Cp2(H)(μ-PtBu2)(CO)2] (3), in which the hydride ligand adopts an uncommon terminal disposition. DFT analysis of the electronic structure of 3 gave support to the presence of a M≡M triple bond in this complex following from a σ2δ2δ2 configuration, a view also supported by the high electron density accumulated at the corresponding Mo–Mo bond critical point. In contrast, reactions of 2 with IMe or ClCH2Ph gave the alkyl-bridged complexes [Mo2Cp2(μ-κ1:η2-CH2R)(μ-PtBu2)(CO)2] (R = H (4a), Ph (4b)), which in solution display agostic Mo–H–C interactions. Decarbonylation of 4a took place rapidly under photochemical conditions to give the 30-electron complex [Mo2Cp2(μ-κ1:η2-CH3)(μ-PtBu2)(μ-CO)] (7), with a stronger agostic coordina...