1,2-Diphosphetene, 1,2-Diphosphete, and 1,3-Diphosphete Metal Complexes: Novel Access by Ring Contraction, Cyclodimerization, and Intramolecular Redox Reactions†

The reaction of [Cr(CO)5(THF)] and pentaphenyl-1,2,3-triphospholene affords a single stereoisomer of [(pentaphenyl-1,3-η-1,2,3-triphospholene)(Cr(CO)5)2] (6). Visible light photolysis of 6 causes a ring contraction and [(trans-tetraphenyl-1,2-η-1,2-diphosphetene)(Cr(CO)5)2] (7a) is formed, whose stereochemistry was elucidated by X-ray crystallography. trans-1,2-Dichloro-3,4-di-tert-butyl-1,2-diphosphetene (2a) and [Fe2(CO)9] form the σ complexes [(trans-1,2-dichloro-3,4-di-tert-butyl-1-η-1,2-diphosphetene)Fe(CO)4] (8a) and [(trans-1,2-dichloro-3,4-di-tert-butyl-1,2-η-1,2-diphosphetene)(Fe(CO)4)2] (8b), depending on the relative concentration of the starting materials. 8a has been proven to be an intermediate in the formation of 8b. Heating of neat 8b in a vacuum leads to the elimination of the chlorine substituents in an intramolecular redox reaction and [(3,4-di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3] (9a) is formed. This is the first specific reaction, leading to a 1,2-diphosphete complex. 9a and its 1,3...