Synthesis, electrochemistry, and reactivity of half-sandwich ruthenium complexes bearing metallocene-based bisphosphines

The bimetallic complexes CpRu(P-P)X [Cp = n ⁵-C ₅H ₅; X = Cl, H; P-P = dppf (1,1′-bis(diphenylphosphino)ferrocene) , dppr (1,1′-bis(diphenylphosphino)ruthenocene), dppo (1,1′- bis(diphenylphosphino)-osmocene), dippf (1,1′-bis(diisopropylphosphino) ferrocene), dcpf (1,1′-bis(dicyclohexylphosphino)ferrocene)], Cp*Ru(P-P)X [Cp* = n ⁵-C ₅Me ₅; X = Cl, H; P-P = dppf, dippf, dppomf (1,1′-bis(diphenylphosphino) octamethylferrocene), dppc (1,1′-bis(diphenylphosphino)cobaltocene)], [Cp*Ru(P-P)X] ⁺ (X = H, CCPh; P-P = dppc ⁺), and [Cp*Ru(P-P)L] ²⁺ (L = CH ₃CN, t-BuCN; P-P = dppc ^-) have been synthesized. Most of the chloride and hydride complexes have been studied by cyclic voltammetry. The X-ray structures of [Cp*Ru(dppc)CH ₃CN][PF6] ₂ and [Cp*Ru(dppc)CCPh] [PF ₆] have been determined. Protonation of [Cp*Ru(dppc)CCPh] ⁺ gives the vinylidene complex [Cp*Ru(dppc)CCHPh] ²⁺. The Co(III/II) potential of the dppc ⁺ ligand undergoes a cathodic shift upon coordination in [Cp*Ru-(dppc)H] ⁺ and an anodic shift upon coordination in [Cp*Ru(dppc)CH3CN] . The ¹H NMR spectrum of Cp*Ru(dppc)H is consistent with its formulation as a Co(II)/Ru(II) complex. As gauged by their reactivity toward iminium cations, the hydride complexes are poor hydride donors; proton and electron transfer are dominant. CpRu(dippf)H and CpRu(dcpf)H deprotonate iminium cations with acidic a-hydrogens. Cp*Ru(dppc)H is oxidized by the N-(benzylidene)pyrrolidinium cation, giving [Cp*Ru-(dppc)H] ^- and the vicinal diamine 1,2-bis(N-pyrrolidino)-1,2-diphenylethane. Most of the hydride complexes give rraw-dihydride cations upon protonation; an exception is [Cp*Ru(dppc)H] ⁺, which forms a dihydrogen complex [Cp*Ru(dppc)(H2)]2+ with surprising kinetic stability. This dihydrogen complex is more acidic and less thermodynamically stable than its dihydride isomer. The H ₂ ligand in [Cp*Ru(dppc)-(H ₂)] ²⁺ is readily replaced by nitriles; the reaction with t-BuCN occurs by a dissociative mechanism.