Methyl radical also reacts by the frontside mechanism: An ab initio study of some homolytic substitution reactions of methyl radical at silicon, germanium and tin

Abstract

Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-ζ pseudopotential (DZP) basis sets, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional (B3LYP) calculations predict that homolytic substitution reactions of the methyl radical at the silicon atom in disilane can proceed via both backside and frontside attack mechanisms. At the highest level of theory (CCSD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ), energy barriers (ΔE^‡) of 47.4 and 48.6 kJ mol⁻¹ are calculated for the backside and frontside reactions respectively. Similar results are obtained for reactions involving germanium and tin with energy barriers (ΔE^‡) of between 46.5 and 67.3, and 41.0 and 73.3 kJ mol⁻¹ for the backside and frontside mechanisms, respectively. These data suggest that homolytic substitution reactions of methyl radical at silicon, germanium, and tin can proceed via either homolytic substitution mechanism.