The actions of halogens on phosphine-substituted Group VI metal carbonyls. Part IV. The preparation of some triphenylphosphonium halogenocarbonyl molybdenum and tungsten derivatives

Abstract

Halogens act on some of the triphenylphosphine derivatives of hexacarbonyl-molybdenum and -tungsten to yield phosphonium complexes rather than phosphine derivatives. Treatment of 1 mole of M(CO)₃(PPh₃)₃(M = Mo and W) with 3 equivalents of iodine in dichloromethane yields the compounds (Ph₃PH)[M(CO)₃(PPh₃)l₃], identified by analyses and infrared spectra. These complexes are diamagnetic and uni-univalent electrolytes in nitrobenzene, indicating that they are seven-co-ordinate derivatives of molybdenum(II) and tungsten(II). Treatment of either trans-M(CO)₄(PPh₃)₂ or M(CO)₃(PPh₃)₃ with 3 equivalents of bromine affords the seven-co-ordinate diamagnetic derivatives (Ph₃PH)[M(CO)₃(PPh₃)Br₃], which can be initially isolated as dichloromethane adducts. The differences in behaviour towards oxidation by halogens between these and the diphosphine-substituted molybdenum and tungsten carbonyls are discussed.