Catalytic activity of polynuclear platinum carbonyl anions in homogeneous hydrogenation reactions

Abstract

The homogeneous hydrogenation of benzaldehyde, heptanal, cyclohexanone, cyclohexene, acetonitrile, and benzonitrile has been studied using [NBuⁿ₄]₂[{Pt₃(CO)₆}⁵](1) as the catalyst over a range of temperature (40- 80 °C) and pressure (20-64 lbf in^-2). Infrared spectroscopic studies suggest the formation of a common intermediate in reactions carried out at ≥60 °C. Benzaldehyde is the most readily hydrogenated; the nature of the products depends on the pressure of hydrogen used and is selective to either benzyl alcohol or a mixture of benzene and methanol. Kinetic studies on the rate of benzyl alcohol formation indicate a first-order dependence of the rate on the concentration of (1). While the rate shows a Michaelis-Menten type of dependence on the PhCHO concentration, it seems to be independent of Hz pressure in the range 20-25 lbf in^-2. Under these conditions, a value of 63.81 kJ mol^-1 for the activation energy is obtained from the Arrhenius plot. A tentative mechanism for PhCHO hydrogenation is discussed.