The unusual oxidation of a 1,5,2,4‐diazadiphosphorinan‐6‐one with tetrachloro‐ortho‐benzoquinone

Abstract

AbstractThe oxidation of 2,4‐bis(diethylamino)‐1,5‐dimethyl‐1,5,2,4‐diazadiphosphorinan‐6‐one (1b) with two equivalents of tetrachloro‐ortho‐benzoquinone (TOB) (2) leads to the cleavage of the original heterocycle and to the formation of a mixture of compounds, including the 1,3,2‐diazaphosphetidine 6 (“λ6P‐”) and the spirophosphorane 7. Compound 7 exists as two isomers that undergo slow spontaneous transformation in solution to compound 9, containing a six‐coordinate phosphorus atom. When the oxidation of 1b is carried out in two stages, with the second equivalent of TOB being added after an interval of four days, the cleavage of the original molecule does not occur, and compound 17, containing a seven‐membered ring with two phosphorus atoms of opposite formal charge and different coordination number (“λ4P+,λ6P‐”) is formed. The structures of 6, 7, 9, and 17 were established by low‐temperature X‐ray analysis. Compound 6 displays crystallographic twofold symmetry; the coordination at phosphorus is octahedral, but distorted by the phosphetidine ring. The phosphorus atom in 7 possesses square pyramidal coordination geometry, the pyramid base being defined by the four oxygen atoms. Compound 9 (“λ6P‐”) crystallized with two molecules of CDCl3. Compound 17 crystallized as a dichloromethane solvate. Distorted octahedral and tetrahedral geometries were observed for P1 and P2, respectively. The four‐membered ring is planar. The bridging hydroquinone ligand displays much wider O–C–C(–O) and C–O–P angles than the chelating hydroquinone.