Electronic structure of aryl- and alkylphosphines

The electronic structure of tertiary arylphosphines and methylphosphines are explored, using ab initio calculations and a detailed analysis of properties based on the electron distribution rho(r). The comparison concentrates on the topology of rho and del(2) rho in the vicinity of the phosphorus atom, and the integrated atomic properties (energies, multipole moments) of this atom. Some trends are revealed which are consistent with the known relative basicities of these compounds, whereas others are unexpected. In particular (i) neither methyl nor aryl substituents substantially alter the charge on phosphorus, (ii) and the phosphorus-phenyl P-C bond of triarylphosphines, phenylphosphabicyclo[3.3.1]nonane and its [4.2.1] analogue indicate a significant conjugative effect, unlike in phenyl or pyridylphosphine.