Synthesis of a DMPM and Hydrido-Bridged Diiridium Complex, [(Cp*Ir)2(μ-dmpm)(μ-H)2][OTf]2, and Its Reactivity toward Alkynes and Isocyanides

Abstract

Reaction of [Cp*IrCl(μ-H)]2 (2) (Cp* = pentamethylcyclopentadienyl) with equimolar amounts of bis(dimethylphosphino)methane (dmpm) in THF followed by 2 equiv of AgOTf gives a new binuclear iridium complex, [(Cp*Ir)2(μ-dmpm)(μ-H)2][OTf]2 (1). Complex 1 reacts with ethyne to give a μ-vinyl complex, [(Cp*Ir)2(μ,η1,η2-CHCH2)(μ-dmpm)(μ-H)][OTf]2 (4), via addition of the iridium hydride to the carbon−carbon triple bond. Reactions of 1 with terminal alkynes give mixtures of α-isomers of a μ-vinyl complex, [(Cp*Ir)2(μ,η1,η2-CRCH2)(μ-dmpm)(μ-H)][OTf]2 [R = Ph (5a), PhCH2 (5b), nBu (5c)], and β-trans isomers [(Cp*Ir)2(μ,η1,η2-CHCHR)(μ-dmpm)(μ-H)][OTf]2 [R = Ph (6a), PhCH2 (6b), nBu (6c)]. The μ-vinyl ligand in 6a−c undergoes a fluxional process. Heating the α-isomers 5a−c at 120 °C results in isomerization to β-trans isomers 6a−c. Complex 1 reacts with tert-butylisocyanide to give the simple adduct [(Cp*Ir)(CNtBu)(μ-dmpm)(μ-H)(Cp*Ir)(H)][OTf]2 (7), while reaction of 1 with phenylisocyanide or cyclohexylisocyanide gives μ-aminocarbyne complexes [(Cp*Ir)2(μ,η1-CN(H)R)(μ-dmpm)(μ-H)][OTf]2 [R = Ph (8a), Cy (8b)]. The structures of 1, 5c, 6a, 7, and 8a have been determined by X-ray diffraction methods.