Synthesis, Electrochemistry, and Reactivity of New Iridium(III) and Rhodium(III) Hydrides
journal contributionposted on 2016-02-20, 16:36 authored by Yue Hu, Ling Li, Anthony P. Shaw, Jack R. Norton, Wesley Sattler, Yi Rong
Two new iridium hydride complexes, Cp*Ir(2-phenylpyridine)H (Cp* = pentamethylcyclopentadienyl) and Cp*Ir(benzo[h]quinoline)H, and their rhodium analogues Cp*Rh(2-phenylpyridine)H and Cp*Rh(benzo[h]quinoline)H have been prepared from the corresponding chlorides. The X-ray structures of Cp*Ir(2-phenylpyridine)H and Cp*Rh(2-phenylpyridine)H have been determined. The electrochemistry of all four hydride complexes and the corresponding chlorides has been studied by cyclic voltammetry; all exhibit irreversible M(III/IV) (M = Ir, Rh) oxidations. The hydride complexes are more easily oxidized than their chloride analogues, and the rhodium hydrides are more easily oxidized than their iridium analogues. The hydride complexes transfer H– to the N-carbophenoxypyridinium cation at room temperature, giving mixtures of the 1,2- and 1,4-dihydropyridine products. In CD3CN all four hydrides give these products in nearly the same ratio, which results from kinetic control; the thermodynamic ratio of the products has been calculated, and isomerization in that direction has been observed. In weakly coordinating solvents the cations left after H– transfer catalyze this isomerization. Acetonitrile can trap these cations, slowing isomerization substantially. The X-ray structures of [Cp*Ir(2-phenylpyridine)(CH3CN)][PF6] and [Cp*Rh(2-phenylpyridine)(CH3CN)][PF6] have also been determined.