Reactivity of a kinetically stabilized 1,3,6-triphosphafulvene toward some nucleophiles

Main Group Pentafulvenes: Challenges and Opportunities in Heavy Main Group Isolobal Substitution of Pentafulvene

Heterofulvenes based on isolobal substitution of carbon fragments by (heavier) main group motifs provide a rich source of structurally interesting building blocks with electronic situations that can vastly differ from all-carbon congeners. Group 13, heavier 14 & 16 fulvenes are rare and pose significant stability challenges, while group 15 derivatives, particularly phosphorus and arsenic, have led to many derivatives with intriguing opto-electronic properties.

Synthesis of phosphorus ylides bearing a P-H bond from a kinetically stabilized 1,3,6-triphosphafulvene

In mixing 2,4,6-tris(2,4,6-tri-tert-butylphenyl)-1,3,6-triphosphafulvene with alkyllithium compounds and acetic acid, both of nucleophilic alkylation and electrophilic protonation occurred at the exo sp2-phosphorus atoms to afford [2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclopentadienylidene](alkyl)(2,4,6-tri-tert-butylphenyl)phosphoranes which are phosphorus ylides that bear a P-H bond. A phosphorus ylide bearing both P-H and P-F bonds was obtained by reaction of 2,4,6-tris(2,4,6-tri-tert-butylphenyl)-1,3,6-triphosphafulvene with hydrogen tetrafluoroborate, and the structure was determined by X-ray crystallography. Both P=C double bond and P(+)-C(-) zwitterionic character was indicated by the metric parameters. The isolated phosphorus ylide bearing a P-H bond, [2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclopentadienylidene](2,4,6-tri-tert-butylphenyl)phosphorane, showed no isomerization by H-migration to the corresponding phosphinodiphospholes, probably due to the pi-accepting ability of the unsaturated PC bonds and aromaticity of the C3P2 ring. The ylide structure and aromaticity of 2,4-diphosphacyclopenta-2,4-dienylidenephosphorane was characterized by theoretical calculations. In addition, the regioselective protonation of the lithiated phosphinodiphospholes generated from the 1,3,6-triphosphafulvene is discussed.