Reactions of alkyl intermediates on copper surfaces

Alkyls bound to copper surfaces are potential intermediates in reactions such as the catalytic reductive coupling of alkyl halides and the competing disproportionation pathway. To investigate the chemistry of such intermediates, we have generated a variety of alkyls on a Cu(110) single crystal surface under ultra-high vacuum conditions using alkyl iodides as precursors. The authors deduce that when methyl groups and hydrogen atoms are coadsorbed on a Cu(110) surface reductive elimination to give methane is favored over methyl group coupling or hydrogen atom recombination. Second, methylene coupling is much more facile than methyl coupling. Third, α and β C-H bonds are broken at enormously different rates, the ratio being 10⁷ at 300K assuming equal preexponential factors of 10¹³ sec^-1.