Evaluating stereoelectronic properties of bulky dialkylterphenyl phosphine ligands

Abstract

The stereoelectronic properties of a series of sterically hindered phosphines containing a terphenyl substituent, PR2Ar’ (R = alkyl; Ar’ = C6H3-2,6-Ar2), 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)2(PR2Ar’)] and rhodium [Rh(acac)(CO)2(PR2Ar’)] (acac = acetylacetonate) complexes, as well as by measuring 31P–77Se scalar coupling constants (1JSeP) for the corresponding phosphine selenides (Se=PR2Ar’). In turn, the steric profile of terphenyl phosphines has been gauged by calculating Tolman Cone Angle (TCA), ligand shielding (G) and percent buried volume (%VBur) 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.