Isolation of a 16π-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4 P2 Ring.

Abstract

Herein, we report the first 1,4‐diphosphinine‐1,4‐diide compound [(ADCPh)P]2 (5‐Ph) (ADCPh=PhC{(NDipp)C}2; Dipp=2,6‐iPr2C6H3) derived from an anionic dicarbene (ADCPh) as a red crystalline solid. Compound 5‐Ph containing a 16π‐electron planar fused‐tricyclic ring system was obtained by the 4e reduction of [(ADCPh)PCl2]2 (4‐Ph) with Mg (or KC8) in a quantitative yield. Experimental and computational results imply that the central 8π‐electrons C4P2 ring of 5‐Ph, which is fused between two 6π‐electrons C3N2 aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5‐Ph has two electron‐lone‐pairs, one in a p‐type orbital is in conjugation with the C=C bonds of the C4P2 ring, while the second resides in a σ‐symmetric orbital. This can be shown with the gold complex [(ADCPh)P(AuCl)2]2 (6‐Ph) obtained by reacting 5‐Ph with (Me2S)AuCl. A mixture of 5‐Ph and 4‐Ph undergoes comproportionation in the presence of MgCl2 to form the intermediate oxidation state compound [(ADCAr)P]2(MgCl4) (7‐Ph), which is an aromatic species.