Theoretical investigation of the metal-metal interaction in dimolybdenum complexes with bridging hydride and methyl ligands

DFT calculations on dinuclear molybdenum complexes with bridging hydride and methyl ligands, namely [CpMo(mu-O2CH)](2)(mu-PH2)(mu-H) and [CP*MO(mu-O2CMe)](2)(mu-PMe2)(mu-Me), indicate that the bonding is best described in terms of. (i) a 2-center-2-electron Mo-Mo single bond and (ii) a 3-center-2-electron Mo-H-Mo or Mo-Me-Mo bond. The presence of a 2-center-2-electron Mo-Mo single bond is in accord with an electron counting procedure that views the bridging hydride and methyl ligands as mu-LX ligands; in contrast, an electron counting procedure which apportions half of the valence electron of the hydrogen atom or methyl radical to each metal dictates a Mo=Mo double bond, a result that is contrary to the theoretical calculations. Consideration of a variety of other bridging hydride complexes indicates that the mu-LX electron counting method provides the best general description of the bonding by clearly distinguishing between the number of 3-center-2-electron M-H-M interactions and direct 2-center-2-electron M-M interactions. (C) 2004 Elsevier Ltd. All rights reserved.