The structure and aromaticity of lithium azaphospholide complexes

Abstract

The structure and aromaticity of lithium-1,3-azaphospholide molecules have been investigated by ab initio methods using HF and MP2/6-311++G(2d,p) levels of theory. Twelve stable isomers have been found on the potential energy surface. The most important factor of stability is the coordination of phosphorus: molecules 1– 5 containing σ 2,λ 3-phosphorus (type I) are considerably more stable than the σ 2,λ 3-derivatives 6– 12 (type II). The most stable isomer is the lithium η 5-complex 1. Isomers containing divalent carbon atoms are the least stable derivatives. Three different aspects of the aromaticity have been studied, the molecular geometry, the Bird and the NICS indices. Although 3H-azaphosphole is not aromatic, complex formation enhances the aromaticity and most of the corresponding type II Li-complexes are highly aromatic ( 8– 10, 12). No correlation can be found between the position of lithium, the aromaticity and the stability of the molecules.