Ab Initio and DFT Study of Homolytic Substitution Reactions of Acyl Radicals at Silicon, Germanium, and Tin

Abstract

Ab initio calculations using the 6-311G(d,p), cc-pVDZ, aug-cc-pVDZ, and (valence) double-ζ pseudopotential (DZP) basis sets, with (MP2, ROMP2, QCISD, CCSD(T)) and without (HF) the inclusion of electron correlation, and density functional (BHandHLYP) calculations predict that homolytic substitution reactions of acetyl radicals at the silicon atoms in dimethylsilane 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 110.4 and 107.5 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 97.6−191.7 and 100.8−171.3 kJ mol−1 for the backside and frontside mechanisms, respectively. These data suggest that both homolytic substitution mechanisms are feasible for homolytic reactions of acetyl radicals at silicon, germanium, and tin. BHandHLYP calculations provide geometries and energy barriers for backside and frontside transition states in good agreement with those obtained by traditional ab initio techniques.

Rate coefficients for intramolecular homolytic substitution of oxyacyl radicals at selenium

“…While acyl radicals have been extensively used in homolytic addition chemistry [7,8], there are many fewer examples of their use in substitution chemistry [1,9] and even fewer examples exist for oxyacyl radicals; we showed that radical 1 cyclized efficiently to afford the cyclic selenocarbonate (2), a previously unknown functional group (Scheme 2) [10]. Work in our laboratories has been directed toward the understanding and utilization of free-radical homolytic substitution chemistry [2], and as such we have published several ab initio and DFT studies with the aim of increasing our understanding of the factors that affect and control the mechanism of radical reactions involving main-group heteroatoms [2,11,12].…”

Bimolecular Reaction Dynamics in the Phenyl–Silane System: Exploring the Prototype of a Radical Substitution Mechanism

“…Later, Kulicke et al proposed that in the liquid phase, silanes may undergo substitution reactions via carbon-silicon bond formation, which compete effectively with hydrogen abstraction. 20 Condensed-phase kinetics 18,[20][21] and computational studies [22][23][24][25][26][27][28] with silanes suggest that monosilane (SiH4) is unreactive toward substitution reactions with alkyl radicals, however, that substitution reactions with disilane might be feasible, i.e. the reaction H + Si2H6 → SiH4 + SiH3 is competitive with hydrogen abstraction 18,[20][21] ; similar substitution reactions were also proposed for germanium-, tin-, and sulfur-centered molecules.…”

Bimolecular Reaction Dynamics in the Phenyl - Silane System: Exploring the Prototype of a Radical Substitution Mechanism

“…Later, Kulicke et al proposed that in the liquid phase, silanes may undergo substitution reactions via carbon-silicon bond formation, which compete effectively with hydrogen abstraction. 20 Condensed-phase kinetics 18,[20][21] and computational studies [22][23][24][25][26][27][28] with silanes suggest that monosilane (SiH4) is unreactive toward substitution reactions with alkyl radicals, however, that substitution reactions with disilane might be feasible, i.e. the reaction H + Si2H6 → SiH4 + SiH3 is competitive with hydrogen abstraction 18,[20][21] ; similar substitution reactions were also proposed for germanium-, tin-, and sulfur-centered molecules.…”