A 19F NMR study of the transmission of electronic effects in triarylphosphines

Abstract

The nature and efficiency of transmission of electronic effects of substituents through the bridging phosphorus atom in systems of the Ar 2PC 6H 4F-4 type have been investigated by 19F NMR. Correlation of the obtained data on the fluorine chemical shifts in triarylphosphines with those in the correspondingtriarylmethanes and tetraarylsilanes indicated that the bridging phosphorus atom shows a higher transmitting ability than carbon and silicon. On the basis of the data on two-parameter correlation of the fluorine chemical shifts with the inductive (σ I) and resonance (σ R) parameters of the substituents in the aromatic rings for systems with bridged phosphorus, carbon, silicon, tin, nitrogen, and bismuth atoms it has been established that phosphorus occupies an intermediate position between nitrogen and bismuth as regards the nature of transmission of electronic effects, i.e. interactions through the PC ar bonds occur both by an inductive and, to some extent, a resonance mechanism.