Effect of Ligands on the Lewis Acidity of the Metal and the Binding of N-Bases to Iridium Pincer Complexes

The coordination of pyridine (Py) and benzonitrile (PhCN) to benzene based pincer hydridochlorides [(PCP)IrH(Cl)] (1), [(POCOP)IrH(Cl)] (2), [{EtO(O)C-POCOP}IrH(Cl)] (3), and [(PCN)IrH(Cl)] (4) was studied spectroscopically and computationally to deduce the ligand influence. The variable temperature NMR ( 1 H, 31 P, 15 N) and UV/Visible spectroscopic measurements revealed preferential coordination of these N-donor ligands in the apical position of 1–4 and gave the formation enthalpies for the hexacoordinate complexes, which follow the order: 1 ≈ 4 > 3 > 2. This order nicely agrees with the order of Lewis acidity obtained for these complexes in DFT calculations. The orbital and electron density distribution analysis were performed at the DFT/M06 theory level for 1–4 and a series of p-substituted PCP-based hydridochlorides. The increasing Lewis acidity of iridium [as a maximum energy, V S,max , of molecular electrostatic potential (MEP)] correlates with decreasing basicity of Cl-ligand (as MEP minimum, V S,min ) as well as with Hammett σ p parameters of p-substituents. Importantly, these properties are conserved upon conversion into the corresponding dihydrides, as shown on the example of 1 and 4. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim