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

Abstract

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 (1H, 31P, 15N) 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, VS,max, of molecular electrostatic potential (MEP)] correlates with decreasing basicity of Cl‐ligand (as MEP minimum, VS,min) as well as with Hammett σp parameters of p‐substituents. Importantly, these properties are conserved upon conversion into the corresponding dihydrides, as shown on the example of 1 and 4.