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.