Formation and Electrochemical Properties of a 1,4-Diphosphafulvene Including Formal Dimerization of Phosphaallene

Reactions of sterically protected 2-bromo-3-phenyl-1-phosphapropenes with bases such as tert-butyllithium and potassium tert-butoxide successfully afforded a bulky 1,4-diphosphafulvene (Mes = 2,4,6-tBu(3)C(6)H(2)) through a novel and formal dimerization pathway of 1-phosphaallene, together with small amounts of 3-phenyl-1-phosphaallene and 3,4-diphosphanylidenecyclobutene. The structure of the 1,4-diphosphafulvene was confirmed by X-ray crystallography indicating somewhat flattened phosphorus atoms due to the bulky Mes groups. The electrochemical properties of the 1,4-diphosphafulvene were investigated to show promising suitability as an electron donor, and indeed, it afforded a charge-transfer complex with TCNQ. Preparation and structural elucidation of an alkoxy-functionalized 1-phosphaallene was also performed, and the effect of the alkoxy group on the 1-phosphaallene moiety was characterized.