Unconventional Approach to the Synthesis of Nickel and Platinum Complexes of 1,3,6-Azadiphosphacycloheptanes

A new method has been proposed for the synthesis of bis(phosphine sulfides) and nickel and platinum chelate complexes of 1,3,6-azadiphosphacycloheptanes. The method is based on the ability of 14-membered 3,6,10,13-diazadiphosphacyclotetradecanes to undergo a reversible transformation in solutions into a mixture of meso- and rac-isomers of seven-membered bis-phosphines. The reaction of 3,6,10,13-diazadiphosphacyclotetradecanes with elementary sulfur results in 14-membered tetrakis(phosphine sulfides) or seven-membered bis(phosphine sulfides), depending on the reaction conditions. The reaction of 1,3,6-azadiphosphacycloheptanes, resulting from the reversible dissociation of 14-membered tetraphosphines in chloroform, with Ni(CH₃CN)₆(BF₄)₂ and Pt(COD)Cl₂ gives the corresponding chelate complexes. The structures of the meso-isomer of 1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane-3,6-disulfide, bis-(κ²-1-isopropyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)nickel bis(tetrafluoroborate), bis-(κ²-1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)chloronickel tetrafluoroborate, and cis-dichloro-(κ²-1-cyclohexyl-3,6-diphenyl-1-aza-3,6-diphosphacycloheptane)platinum(II), isolated in crystalline form, have been confirmed by single crystal X-ray diffraction.