Understanding the Effect of Ancillary Ligands on Concerted Metalation–Deprotonation by (dmPhebox)Ir(OAc)2(H2O) Complexes: A DFT Study

A DFT study of (dmPhebox)Ir(OAc)2(H2O) was undertaken to understand ligand effects that control the propensity of this complex to undergo intermolecular alkane C–H activation by a concerted metalation–deprotonation (CMD) mechanism. Substitution of electronically diverse substituents at the para position of the aryl ring and exchange of the pincer oxazolinyl arms with other donor groups were calculated to minimally impact the barriers to C–H activation. It is suggested that these modifications do not influence the orbitals directly involved in the six-membered CMD transition state. The base and spectator carboxylate ligands were calculated to play two distinct roles in the activation with different electronic preferences, namely, their intrinsic basicity and trans influence/effect, respectively. Heteroaryl linkers in the pincer backbone were identified as a promising lead, yielding noticeably lower computed C–H activation barriers, due to increased electrophilicity of the cationic metal center.