The chemistry of tantalum hydride compounds containing ancillary aryloxide ligation

In recent years, Rothwell et al. have shown that mixed hydrido, aryloxide derivatives of tantalum catalyze the regio- and stereo-selective hydrogenation of arene substrates such as naphthalene and anthracene. A high priority is to obtain a better understanding of the mechanism by which the hydrogenation is occurring. This involves the isolation and study of organometallic compounds that may be intermediates within the catalytic cycle. This work describes the synthesis and characterization of a series of tantalum hydride complexes as well as their solid state structures. These isolated hydride complexes were shown to be reactive towards organic isocyanide reagents to form new organometallic complexes from the initial insertion of RNC through the metal-hydride bond. The hydride complexes also react with olefins such as styrene to form new organometallic derivatives which indicate that the ancillary aryloxide ligand has a strong influence on the reaction path that is followed. With cyclic olefin reagents such as 1,3-cyclohexadiene, the hydride complexes form coordinated cyclohexyl and cyclohexyl, cyclohexadiene complexes. These new characterized organometallic derivatives are shown to be intermediates within the proposed hydrogenation mechanism