Methanol-Mediated Formation of an Iridium(III) NHC/Azolato Chelate Complex: An Experimental and Theoretical Study

Abstract

One equivalent of methanol-d4 reacts with the iridium(III)-carbonato-NHC complex [Ir(Cp*)(NHC-theo)(O2CO)] [1] containing an N-heterocyclic carbene ligand with an N-tethered C8-iodotheophylline group (NHC-theo) to form the iridium(III) chelate complex [Ir(Cp*)(theophyllinato^NHC)I] [2] that bears a theophyllinato^NHC chelate ligand, an iodo ligand, and the pentamethylcyclopentadienyl ligand (Cp*). The methanol-d4 solvent is oxidized to formaldehyde-d2 that was identified by a detailed LC–MS study using the 2,4-dinitrophenylhydrazine (DNPH) method. A plausible rearrangement involving the unusual oxidative addition of the C8–I bond of the theophylline group to an iridium(III) center to give a seven-coordinate iridium(V) intermediate is supported by density functional theory calculations.