Sterically Encumbered Iridium Bis(N-heterocyclic carbene) Complexes: Air-Stable 14-Electron Cations and Facile Degenerate C–H Activation

Cationic Ir­(III) systems supported by a bis­(expanded NHC) framework and featuring both agostic C–H and cis alkyl/hydride ligand sets have been targeted by protonation of the corresponding bis­(alkyl) hydride complexes. Remarkably, the steric shielding afforded by the NHC substituents is such that these and related putative 14-electron cations are air and moisture stable. In solution, degenerate fluxional exchange is brought about by reversible σ-bond activation within the agostic alkyl C­(sp3)–H bond; a non-dissociative mechanism is implied by the activation parameters ΔH⧧ = 8.8(0.4) kcal mol–1 and ΔS⧧ = −12.2(1.7) eu.