Phosphazenes and phosphazanes-the nature of the P-N bond

Abstract

Synthetic, spectroscopic and X-ray structural studies on linear and cyclic λ³-diphosphazanes, λ³-cyclotriphosphazanes, λ⁵-cyclotriphosphazenes and a bicyclic P₄N₅ derivative are summarised. Transition metal organometallic chemistry of linear and cyclic λ³-phosphazanes and suitably functionalised λ⁵-cyclotriphosphazenes is also investigated. Novel mono- and dinuclear palladium complexes have been isolated from spirocyclic λ⁵ cyclotriphosphazenes by facile hydrolytic cleavage of a λ⁵-diazaphospholane ring. The structural data on P-N compounds and their complexes and ab initio molecular orbital calculations on selected model systems provide strong evidence for "negative hyperconjugation" as a dominant feature of multiple bonding between phosphorus and nitrogen.