Evaluating stereoelectronic properties of bulky dialkylterphenyl phosphine ligands

Abstract

The stereoelectronic properties of a series of sterically hindered phosphines containing a terphenyl substituent, PRAr’ (R = alkyl; Ar’ = CH-2,6-Ar), have been evaluated by various methods. Their σ-donating capacity has been assessed on the basis of the carbon monoxide stretching frequencies in benchmark iridium [IrCl(CO)(PRAr’)] and rhodium [Rh(acac)(CO)(PRAr’)] (acac = acetylacetonate) complexes, as well as by measuring P–Se scalar coupling constants (J) for the corresponding phosphine selenides (Se=PRAr’). In turn, the steric profile of terphenyl phosphines has been gauged by calculating Tolman Cone Angle (TCA), ligand shielding (G) and percent buried volume (%V) parameters. These calculations have been carried out from both X-ray diffraction and DFT-optimized structures. We have also examined several of the widely used biaryl phosphines for comparative purposes.