om301060h_si_002.cif (306.59 kB)

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

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posted on 10.12.2012, 00:00 by Nicholas Phillips, Johnny Rowles, Michael J. Kelly, Ian Riddlestone, Nicholas H. Rees, Athanasia Dervisi, Ian A. Fallis, Simon Aldridge
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.