Homoleptic Rhodium Pyridine Complexes for Catalytic Hydrogen Oxidation.

The homoleptic rhodium pyridine complex [Rh(py)4]+ ([1]+) is prepared from simple precursors. Lacking good π-acceptor ligands but being sterically protected, [1]+ reversibly oxidizes to colorless [Rh(py)4(thf)2]2+. This monomeric S = 1/2 Rh(II) complex activates H2 to give [HRh(py)4L]2+, which can also be generated by protonation of [1]+. The Rh(III)-H bond is weak, being susceptible to H atom abstraction as well as deprotonation. These results underpin a novel catalytic system for the oxidation of H2 by ferrocenium.