REACTION OF A TANTALUM ALKYLIDENE COMPLEX WITH DINUCLEAR METAL-CARBONYLS - FORMATION OF C3 LIGANDS

The mechanisms of reactions that deoxygenate carbon monoxide (CO) and convert it into longer chain hydrocarbons are not well understood. A series of reactions between ''early'' and ''late'' transition metal complexes that result in CO coupling reactions in a homogeneous solution are reported. In one example, the Schrock tantalum-methylene complex (eta5-C5H5)2Ta(CH2)(CH3) reacts with the dinuclear metal carbonyls Co2(CO)8 and Fe2(CO)9 in a novel fashion to yield a C3H2O2 ligand bridging three metal centers. Reaction of the tantalum-methylene complex with Re2(CO)10 leads to an even more substantial change in which extensive rearrangement along with three-carbon coupling occurs. An oxygen atom is removed from one CO group, leading to the novel oxotantalum compound (eta-5-C5H5)2(CH3)Ta=O. Simultaneously, the carbon atom from the transformed CO couples with two CH2 groups initially bound to tantalum and the CH2 hydrogens are rearranged to produce a CH3-CC ligand. Low-temperature nuclear magnetic resonance and isotope tracer experiments have provided preliminary information about the mechanisms of these unusual carbon-carbon bond-forming reactions.