Synthesis and Reactivity Studies of Cationic Ir(III) Alkylidines. α-Hydride Abstraction Reactions

The chemistry of late transition metal alkylidenes [M=CR₂], where R is H a hydrocarbyl group, have attracted widespread attention although mainly with reference to complexes of metals in low oxidation state. We focus in this paper on reactions based on electrophilic attacks by Ph₃C⁺ that allow either isolation of stable cationic Ir(III) alkylidenes, considerably more attractive than well-known Ir(I) counterparts, or the generation of very reactive variants that experience fast migratory insertion into existing Ir-C and Ir-H sigma bonds. The present studies are based on (η⁵-C₅Me₅)Ir(III) complexes that bear a cyclometalated PMeXyl₂ ligand (Xyl = 2,6-Me₂C₆H₃). The contribution of different monoanionic ligands (chloride, alkyl or hydride) to either stabilize the Ir=CR₂ linkage or provide facile reactivity routes has been investigated, including the use of various deuterium isotopologues of the iridium complex precursors.