Synthesis of [Bis(hexamethylene)cyclopentadienone]iron Tricarbonyl and its Application to the Catalytic Reduction of C=O Bonds

Herein, we report the synthesis of [bis(hexamethylene)cyclopentadienone]iron tricarbonyl (1b) by the reaction of cyclooctyne with Fe(CO)(5) and the investigation of its catalytic properties in C=O bond reduction. As a result of the peculiar reactivity of cyclooctyne, 1b was formed in good yield (56%) by intermolecular cyclative carbonylation/complexation with Fe(CO)(5). Compound 1b was characterized fully and its crystal structure was determined by using XRD. Catalytic tests revealed that, upon in situ activation with Me3NO, 1b promotes the hydrogenation of ketones, aldehydes, and activated esters as well as the transfer hydrogenation of ketones and shows a higher activity than the classical "Knolker complex" (1a). Studies on the hydrogenation kinetics in the presence of 1a and 1b (respectively) suggest that this difference in activity is probably caused by the better stability of the 1b-derived complex than that of the in situ generated Knolker-Casey catalyst.