Unveiling the Latent Reactivity of Cp* Ligands (C5Me5-) toward Carbon Nucleophiles on an Iridium Complex

The divergent reactivity of the cationic iridium complex [(??5-C5Me5)IrCl(PMe2ArDipp2)]+ (ArDipp2 = C6H3???2,6-(C6H3???2,6-iPr2)2) toward organolithium and Grignard reagents is described. The noninnocent behavior of the Cp* ligand, a robust spectator in the majority of stoichiometric and catalytic reactions, was manifested by its unforeseen electrophilic character toward organolithium reagents LiMe, LiEt, and LinBu. In these unconven-tional transformations, the metal center is only indirectly involved by means of the Ir(III)/Ir(I) redox cycle. In the presence of less nucleophilic organolithium reagents, the Cp* ligand also exhibits noninnocent behavior undergoing facile deprotonation, which is also concomitant with the reduction of the metal center. In turn, the weaker alkylating agents EtMgBr and MeMgBr effectively achieve the alkylation of the metal center. These reactive iridium(III) alkyls partake in subsequent reactions: while the ethyl complex undergoes ??-H elimination, the methyl derivative releases methane by a remote C???H bond activation. Computational studies, including the quantum theory of atoms in molecules (QTAIM), support that the preferential activation of the non-benzylic C???H bonds takes place via sigma-bond metathesis.

Automated summary

The divergent reactivity of a cationic iridium complex toward organolithium and Grignard reagents is discussed. The Cp* ligand exhibits unexpected electrophilic behavior towards organolithium reagents and can also undergo facile deprotonation in the presence of less nucleophilic organolithium reagents. Weaker alkylating agents effectively achieve alkylation of the metal center, and the reactive iridium(III) alkyls participate in subsequent reactions.