HYDROGENOLYSIS AND HOMOLOGATION OF 3,3-DIMETHYL-1-BUTENE ON RU SIO2 CATALYST - IMPLICATIONS FOR THE MECHANISM OF CARBON-CARBON BOND FORMATION AND CLEAVAGE ON METAL-SURFACES/

The reactions of 3,3-dimethyl-1-butene (neohexene) with hydrogen in th e presence of zero-valent ruthenium metal particles supported on silic a are reported. The predominant reaction is the hydrogenation of neohe xene to neohexane. Simultaneous but slower homologation and hydrogenol ysis reactions are reported. The homologation and hydrogenolysis react ions run at approximately equal rates, suggesting a mechanistic link b etween the two processes. The relative quantities of C-1-C-5 and C-7 p roducts and the variation of these quantities with respect to varying temperature, neohexene/hydrogen ratio, and contact time are reported. The distribution of the primary products, neopentane, isobutene, and m ethane for hydrogenolysis and 2,2-dimethyl pentane, 2,2,3-trimethyl bu tane, and 4,4-dimethyl-1-pentene for homologation is discussed in term s of current thought on the mechanism of homologation and hydrogenolys is of alkanes. The most likely and strongly indicated mechanism for th e hydrogenolysis of neohexene involves the deinsertion of a methyliden e fragment from a ruthenium-neohexyl intermediate which is also an int ermediate in the hydrogenation of neohexene. The distribution of C-7 h omologation products does not allow one to distinguish between a simpl e insertion mechanism and a mechanism passing through a metallacyclic intermediate. (C) 1995 Academic Press, Inc.