Alcohol Complexes of Tungsten Prepared by Ionic Hydrogenations of Ketones

Abstract

Ionic hydrogenation of acetone by Cp(CO)3WH and HOTf (OTf = OSO2CF3) gives the 2-propanol complex [Cp(CO)3W(HOiPr)]+OTf-. 1H NMR data suggest O−H···O hydrogen bonding between the alcohol OH and an oxygen of the triflate anion in solution, and a crystal structure of this complex shows that hydrogen bonding also exists in the solid state. The short O···O distance of 2.63(1) Å indicates a strong hydrogen bond. Hydrogenation of other ketones and aldehydes gives related [Cp(CO)3W(alcohol)]+OTf- complexes. Aldehydes are selectively hydrogenated over ketones, and alkyl ketones are selectively hydrogenated over aromatic ketones. Hydrogenation of acetophenone gives ethylbenzene, with no intermediate tungsten complexes being observed. Reaction of 1-phenyl-1,3-butanedione with Cp(CO)3WH and HOTf gave {Cp(CO)3W[CH3CH(OH)CH2C(O)Ph]}+OTf -, the structure of which was determined by X-ray diffraction. The alcohol complexes [Cp(CO)3W(alcohol)]+OTf- decompose in solution to give free alcohols and Cp(CO)3WOTf. The cationic dihydride [Cp(CO)2(PMe3)W(H)2]+OTf- hydrogenates aldehydes and ketones; in these reactions a metal hydride serves as both the proton and hydride donor