Reaction of a Tantalum Alkylidene Complex with Dinuclear Metal Carbonyls: Formation of C 3 ligands

Abstract

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 (η 5 -C 5 H 2 ) 2 Ta(CH 2 )(CH 3 ) reacts with the dinuclear metal carbonyls CO 2 (CO) 8 and Fe 2 (CO) 9 in a novel fashion to yield a C 3 H 2 O 2 ligand bridging three metal centers. Reaction of the tantalum-methylene complex with Re 2 (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 (η 5 -C 5 H 5 ) 2 (CH 3 )Ta=O. Simultaneously, the carbon atom from the transformed CO couples with two CH 2 groups initially bound to tantalum and the CH 2 hydrogens are rearranged to produce a CH 3 -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.