Selective halogenation at the pnictogen atom in Lewis-acid/base-stabilised phosphanylboranes and arsanylboranes

Abstract

The halogenation of Lewis-acid/base-stabilised phosphanylboranes ( 1a) and arsanylboranes ( 1b) with CX4 (X = Cl, Br) leads selectively to the substitution of both protons at the pentel atom and the new compounds [(CO)5W(X2PBH2·NMe3)] ( 2a: X = Cl, 2b: X = Br) and [(CO)5W(X2AsBH2·NMe3)] ( 3a: X = Cl, 3b: X = Br), respectively, are obtained. The new products were comprehensively characterised by spectroscopic methods and by X-ray crystallography. While compounds 2a and 2b show an antiperiplanar arrangement of the Lewis acid (W(CO)5) and the Lewis base (NMe3) in the solid state, a synclinal arrangement in 3a and 3b, respectively, was observed. Computational calculations of the optimised antiperiplanar and synclinal geometries of the compounds 2 and 3 in the gas phase slightly favour the antiperiplanar arrangement of the Lewis acid and the Lewis base for both compounds.