Alcohol Complexes of Tungsten Prepared by Ionic Hydrogenations of Ketones

Ionic hydrogenation of acetone by Cp(CO) 3 WH and HOTf (OTf = OSO 2 CF 3 ) gives the 2-propanol complex [Cp(CO) 3 W(HO i Pr)] + OTf - . 1 H 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) 3 W(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) 3 WH and HOTf gave {Cp(CO) 3 W[CH 3 CH(OH)CH 2 C( O)Ph]} + OTf -, the structure of which was determined by X-ray diffraction. The alcohol complexes [Cp(CO) 3 W(alcohol)] + OTf - decompose in solution to give free alcohols and Cp(CO) 3 WOTf. The cationic dihydride [Cp(CO) 2 (PMe 3 )W(H) 2 ] + OTf - hydrogenates aldehydes and ketones; in these reactions a metal hydride serves as both the proton and hydride donor.