New bidentate cationic and zwitterionic relatives of Crabtree's hydrogenation catalyst.

Inspired by the monodentate P,N ligation strategy featured in Crabtree's catalyst [(COD)Ir(PCy3)(Py)]+PF6-([1]+PF6-), a new class of bidentate cationic ([2]+X-) and zwitterionic (3) Ir complexes have been developed, which are capable of mediating the hydrogenation of alkenes under mild conditions and in a wider range of solvents than is possible for [1]+PF6-.