Hydrogen Transfer of 2-Cyclohexen-l-ol Catalyzed by Active Species Photogenerated from a Stable Hydridocobalt(I) Complex

Abstract

A thermally stable complex [CoH{PPh (OEt)₂}₄] was irradiated with a 400 W high-pressure Hg lamp equipped with a Pyrex filter to generate a coordinatively unsaturated active hydrido species "CoH{PPh(OEt)₂}₃". The species catalyzed intramolecular hydrogen transfer of 2cyclohexen-1-ol to give cyclohexanone. The reaction of 2-cyclohexen-1-ol yielded four byproducts: 3-cyclohexen-1-ol through double-bond migration and small amounts of cyclohexanol, 2-cyclohexen-1-one, and 3-cyclohexen-1-one through intermolecular hydrogen transfer. The reaction was virtually "photoassisted" rather than "true photocatalytic". Upon interuption of irradiation, the coordinatively unsaturated hydrido species was assumed to be recombined with the photodissociated phosphonite to give the stable starting complex. In the photoassisted catalytic reaction of 2-cyclohexen-1-ol, addition of free phosphonite decreased the conversion to cyclohexanone.
The reciprocal in itial rate of cyclohexanone formation was plotted against the reciprocal concentration of the substrate charged, and a linear relationship was observed between them at several reaction temperatures. From the Arrhenius equation, a value of 29.6 kJ⋅mol-1was obtained as the overall activation energy of the present reaction.