Evaluating stereoelectronic properties of bulky dialkylterphenyl phosphine ligands

The stereoelectronic properties of a series of sterically hindered phosphines containing a terphenyl substituent, PR2Ar' (R = alkyl; Ar' = C6H3-2,6-Ar-2), have been evaluated by various methods. Their sigma-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 P-31-Se-77 scalar coupling constants ((1)JSeP) 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 (%V-Bur) 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. (c) 2019 Elsevier B.V. All rights reserved.