Intramolecular Homolytic Translocation Chemistry: An ab Initio Study of 1,n-Silyl, Germyl, and Stannyl Group Transfer and Related Ring-Closure Reactions

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Abstract
Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-ζ pseudopotential (DZP) basis set, with (MP2, QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (B3LYP) predict that 1,n-homolytic transfers (n = 1−5) of silyl, germyl, and stannyl groups from group IV heteroatoms to carbon radicals can proceed via a frontside attack mechanism. At the B3LYP/DZP level of theory, energy barriers (ΔE⧧) of 101.2, 98.8, 58.9, and 63.4 kJ/mol are calculated for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively, of SiH3 between silicon atoms. Similar results are obtained for reactions involving germanium and tin with energy barriers (ΔE⧧) of 85.9−113.1, 84.4−109.0, 41.7−73.3, and 48.5−78.2 kJ/mol for the 1,2-, 1,3-, 1,4-, and 1,5-translocation reactions, respectively. This study also predicts that four- and five-membered ring-closure reactions can be competitive with the 1,4- and 1,5-translocation reactions. These results suggest that while 1,2- and 1,3-translocation four-membered ring-formation reactions are unlikely to be synthetically viable, 1,4- and 1,5-transfers and five-membered ring-formation have synthetic possibilities.

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