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-tBu3C6H2) 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.