Homogeneous Catalysis by Pt(Il)-Sn(II) Chloride Complex: Part 2.—Mechanism of the Isomerization of n-Butenes

Abstract

The mechanism of the isomerization of n-butencs catalyzed by a methanolic solution of Pt(II)- Sn(II) chloride complex has been studied by kinetic, mass-spcctromctric and microwave-spectro scopic measurements. This isomerization proceeds in the presence of hydrogen. The initial rate of isomerization of 1-butcnc is of half-order with respect to hydrogen and of first-order with respect to 1-butene in the temperature range 0-20’C and total pressures up to 100 Torr. The deuterium distributions in reactants and products have been measured at 20°C in C4H84-D^-f-CH3OD systems. It was found that cis-CH2DCH=CHCH3 and cis-CH3CD=CHCH3 arc formed from 1-C4H8 and trans-2-C4H8, respectively, and CH2=CHCHDCH3 is produced from both cis- and trans-2-C4H8, and that “ simple exchange reaction ” of 1-C4H8 proceeds faster than the isomcrizations, while those of 2-butcnes scarcely occur. Double-bond migration and “ simple exchange reaction ” of propylene in the C3H64-D24-CH3OD system have been studied for comparison with those of n-butene isomerization. Hydrogen atoms in propylene exchanged with different rates depending on their positions. On the basis of these results, a detailed mechanism is proposed, which involves coordination of olefins to platinum hydride complex, formation of alkyl-platinum, and regeneration of olefins.