Bis(diethylphosphino)methane As a Bridging Ligand in Complexes of Ir2, Rh2, and IrRh: Geminal C–H Activation of α-Olefins

Bis­(diethylphosphino)­methane (depm, Et2PCH2PEt2) is used as a new bridging ligand for the syntheses of a series of diiridium, dirhodium, and iridium/rhodium complexes, starting from trans-[MM′Cl2(CO)2(depm)2] (M = M′ = Ir (1); M = M′ = Rh (11); M = Ir, M′ = Rh (19)). The reduction of all three chloro compounds in aqueous KOH under an atmosphere of CO produces the neutral tricarbonyl complexes [MM′(CO)3(depm)2] (M = M′ = Ir (2); M = M′ = Rh (12); M = Ir, M′ = Rh (20)). Protonation of these tricarbonyl complexes by triflic acid (HOTf) or Brookhart’s acid (HBArF 4) yields the hydride-bridged tricarbonyl complexes [MM′(CO)3(μ-H)­(depm)2]­[X] (M = M′ = Ir (9); M = M′ = Rh (16); M = Ir, M′ = Rh (25); X = SO3CF3 or B­(3,5-(CF3)2C6H3)4). Reaction of 2 with methyl triflate yields the methylene/hydride product [Ir2(H)­(CO)3(μ-CH2)­(depm)2]­[OTf] (4), while the same reaction with the dirhodium analogue (12) produces the methyl complex [Rh2(CH3)­(CO)3(depm)2]­[OTf] (14) at below −20 °C, which upon warming to above −20 °C results in migratory insertion to yield an acetyl-bridged species, [Rh2(CO)2(μ-C­(CH3)­O)­(depm)2]­[OTf] (14a). The analogous Rh/Ir species (20) reacts with methyl triflate to give the methyl-tricarbonyl product [IrRh­(CH3)­(CO)3(depm)2]­[OTf] (22). Removal of a carbonyl from 4 and 22 yields [MIr­(CH3)­(CO)2(depm)2]­[OTf] (M = Ir (5); M = Rh (23)), which are highly susceptible to hydrolysis; however the dirhodium species 14 and 14a are not susceptible to CO loss under the conditions investigated. The reaction of [Ir2(CO)3(μ-H)­(depm)2]­[BArF 4] (9) with a number of α-olefins results in double C–H bond activation of the geminal hydrogens to give the vinylidene-bridged trihydride products of the form [Ir2(H)2(CO)2(μ-H)­(μ-CCRR′)­(depm)2]­[BArF 4].