A spectroscopic investigation of carbon-carbon bond formation by methylene insertion on a Ag(111) surface: mechanism and kinetics.
Using reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed reaction spectroscopy (TPRS), we have investigated the cross-coupling reaction between CH(2)(a) and CF(3)(a) on a Ag(111) surface. CH(2)(a) and CF(3)(a) are generated by thermal decomposition of adsorbed CH(2)I(2) and CF(3)I. RAIRS results unambiguously demonstrate that CH(2)(a) inserts into the Ag-CF(3) bond to produce adsorbed CF(3)CH(2)(a), which upon heating selectively undergoes beta-fluorine elimination to form CH(2)=CF(2). Increasing the CH(2)(a) and CF(3)(a) coverage leads to the sequential insertion of CH(2)(a) into Ag-CF(3), as evidenced by CH(2)CH(2)CF(3)(a) formation detected with RAIRS. Prior to the insertion reaction, the evidence favors islanding of fragments. The methylene insertion reaction is so facile that it occurs at cryogenic temperatures (120 K). Time-resolved RAIRS (TR-RAIRS) results at selected temperatures reveal an activation energy of 5.8 kJ/mol. Our results provide, for the first time, direct spectroscopic information about the mechanism and kinetics of the methylene insertion reaction.
Huang
Weixin
W
Department of Chemistry and Biochemistry, Center for Materials Chemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
White
John M
JM