Evaluating stereoelectronic properties of bulky dialkylterphenyl phosphine ligands.

The stereoelectronic properties of a series of sterically hindered phosphines containing a terphenyl substituent, PR 2 Ar' (R = alkyl; Ar' = C 6 H 3 -2,6-Ar 2), 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 (PR 2 Ar')] and rhodium [Rh(acac)(CO) 2 (PR 2 Ar')] (acac = acetylacetonate) complexes, as well as by measuring 31P–77Se scalar coupling constants (1 J SeP) for the corresponding phosphine selenides (Se=PR 2 Ar'). 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. Image 1 • The stereoelectronic properties of dialkylterphenyl phosphines have been evaluated. • Evaluating σ-donating capacity by ν CO frequencies should be handled with caution. • Evaluating σ-donating capacity by 1 J PSe values fails for ligands with large front-strain. • Steric protection of terphenyl phosphines is considerably superior than biaryl counterparts. [ABSTRACT FROM AUTHOR]