Experimental and Computational Studies of Phosphine Ligand Displacement in Iridium-Pincer Complexes Employing Pyridine or Acetonitrile

This report describes the synthesis, characterization, and ligand exchange studies of iridium-based, pincer complexes. (tBuPOCOP)Ir(PPh3) (tBuPOCOP = 2,6-bis(di-tert-butylphosphonito)benzene) serves as a convenient source of the latent Ir(I), 14-electron species [(tBuPOCOP)Ir] and is susceptible to ligand exchange chemistry; reactions with acetonitrile and pyridine afford the corresponding (tBuPOCOP)Ir(NCMe) (2) and (tBuPOCOP)Ir(Py) (3) complexes, respectively. Varying concentrations of both pyridine and acetonitrile, the kinetic and thermodynamic parameters of the ligand exchange process between (tBuPOCOP)Ir(PPh3) and L (L = MeCN or pyridine) were determined by employing NMR, UV-vis spectroscopy, and density functional theory (DFT) calculations to measure the relevant equilibria. A discussion of these results allows us to address whether phosphine displacement occurs via an associative or a dissociative pathway.