μ-Carbon−Carbon Bonds of Dinuclear Manganese Half-Sandwich Complexes as Electron Reservoirs

The mononuclear vinylidene complexes of the type Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)(CC(R1)(SnMe3)) were obtained by the reaction of Mn(C5H4R‘)(η6-cycloheptatriene) (R‘ = H, 1a; CH3, 1b) with 1 equiv of R1−C⋮C−SnMe3 (R1 = SnMe3, C6H5, C4H3S, C6H4CH3) and R‘ ‘2PCH2CH2PR‘ ‘2 (R‘ ‘ = CH3 (dmpe), C2H5 (depe)) in toluene at 50 °C for 3 h. The reactions of these tin-substituted complexes with 1 equiv of 1.0 M TBAF yielded the corresponding parent vinylidene species Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)(CC(R1)(H)). Treatment of some of these vinylidene species with 1 equiv of [Cp2Fe][PF6] led to the oxidative coupling product [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CHR1−CHR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2 (R‘ = CH3, R‘ ‘ = CH3, R1 = H; R‘ = CH3, R‘ ‘ = CH3, R1 = C6H5; R‘ = CH3, R‘ ‘ = CH3, R1 = C4H3S; R‘ = H, R‘ ‘ = C2H5, R1 = H; R‘ = H, R‘ ‘ = C2H5, R1 = C6H5; R‘ = H, R‘ ‘ = C2H5, R1 = C4H3S). In some cases these products of oxidative coupling, [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CHR1−CHR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2, were accompanied by formation of dinuclear complexes of the type [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CR1CR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2 and of the cationic carbyne complexes [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CH2R1][PF6] obtained by proton transfer. Reduction of these dinuclear complexes with Cp2*Co yielded back the corresponding mononuclear precursor complexes involving a reductive decoupling process. Both the reductive coupling and the oxidative coupling are fully reversible, which is supported by DFT calculations. The mononuclear and the dinuclear compounds were characterized by NMR, IR, and cyclic voltammetric studies. X-ray diffraction studies have been performed on complexes 3a, 11, 13a, 15a, and 22b.