FORMATION OF CARBONYL CARBONATE COMPLEXES OF MOLYBDENUM BY REDUCTIVE DISPROPORTIONATION OF CARBON-DIOXIDE - X-RAY STRUCTURE OF MO4(MU-4-CO3)(CO)2(O)2(MU-2-O)2(MU-2-OH)4(PME3)6

The reaction of carbon dioxide with the bis(dinitrogen) complex cis-Mo(N2)2(PMe3)4, in coordinating solvents, gives the carbonyl-carbonate complexes [Mo(mu-2-eta-1,eta-2-CO3)(CO)CPMe3)3]2 (2) and Mo(CO3)(CO)(PMe3)4 (3) derived from the metal-induced reductive disproportionation of CO2. The use of Et2O or THF as the reaction solvent leads to the preferential formation of binuclear 2 whereas in acetone monomeric 3 is the preferred product. Compounds 2 and 3 interconvert readily by association or dissociation of PMe3, and their solution stabilities have been found to be strongly solvent dependent. Interaction of 3 with the chelating phosphines dmpe or dmpm (dmpe = Me2PCH2CH2PMe2; dmpm = Me2PCH2PMe2), under appropriate conditions, affords the related complexes Mo(CO3)(CO)(P-P)(PMe3)2 (P-P = dmpe, 4; P-P = dmpm, 5) and Mo(CO3)(CO)(dmpe)2 (6). Compounds 2 and 3 react with H2O with formation of an unusual tetrametallic, mixed-valence Mo(II)-Mo(V) complex Mo4(mu-4-CO3)-(CO)2(O)2(mu-2-O)2(mu-2-OH)4(PMe3)6 (7) that contains a unique carbonate ligand engaged in a novel type of bonding. The structure of 7 has been determined by X-ray crystallography. Crystals of 7 are orthorhombic, Pbcn, with unit cell constants a = 26.866 (9) angstrom, b = 12.934 (4) angstrom, c = 11.965 (2) angstrom, and D(calcd) = 1.74 g cm-3 for Z = 4.