1,1- and 1,3-Diiodo Neopentanes on Pt(111): Intermediates during Hydrocarbon Catalytic Conversion Reactions

The chemistry of 1,1- and 1,3-diiodo neopentanes, precursors to neopentylidene and 2,2-dimethyl propane-1,3-diyl intermediates, respectively, was probed on a Pt(111) single-crystal surface by temperature-programmed desorption (TPD) and reflection–adsorption infrared spectroscopy (RAIRS). The sequential surface activation of the two C–I bonds in those compounds is manifested by the formation of neopentyl iodide and neopentane in TPD experiments. Dosing of the 1,3-diiodo compound at 230 K leads to the formation of the expected cyclic 2,2-dimethyl propane-1,3-diyl intermediate, with the main ring perpendicular to the surface. Activation of the 1,1-isomer, on the other hand, leads to the formation of 2,2-dimethyl propane-1-yl-3-ylidene, presumably via γ-H elimination from neopentylidene. The surface species that result from 1,1-diiodo neopentane are more reactive and dehydrogenate to a larger extent than those from the 1,3-diiodo analog, but both eventually convert to neopentylidyne. The implications of this chemistry to hydrocarbon catalytic processes such as oil reforming are discussed.