HYDRATION OF CONJUGATED DIENES TO PRODUCE KETONES CATALYZED BY RUTHENIUM COMPLEXES

A class of ruthenium catalysts has been developed for the hydration of conjugated dienes to produce ketones directly. One application of int erest is the conversion of 1,3-butadiene to methyl ethyl ketone. Where as the acid component of the catalyst systems is responsible for the i ntermediate formation of both 3-buten-2-ol and 2-buten-1-ol, the ruthe nium component can selectively and directly convert only the former al cohol to methyl ethyl ketone by intramolecular hydrogen transfer. Howe ver, the latter alcohol, being in hydration-dehydration equilibrium wi th 1,3-butadiene, is, indirectly, also converted to the same product. This reaction thus allows methyl ethyl ketone yields above 90% based o n 1,3-butadiene. The essential feature of the new catalyst systems is that they are formed by the combination of Bronstedt acids, containing weakly or non-coordinating anions, with a ruthenium(III) source and c helating bipyridyl type ligands. It is suggested that a cationic ruthe nium species, coordinated to a single chelating bipyridyl type ligand, fulfills a key role in the catalysis of the most critical step in the overall conversion, i.e. the catalysis of the intramolecular hydrogen transfer of intermediate allylic alcohols under acid catalyzed diene hydration conditions.