Slow homolytic substitution reactions at selenium: 2-Selenabicyclo[1.1.1]pentane

• Published in: Computational and theoretical chemistry Vol. 1068; pp. 128 - 133
• Main Authors: Wallace, Claire M., Schiesser, Carl H., Hancock, Amber N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2015
• Subjects: Computational chemistry; Free radical; Homolytic substitution; Kinetics; Computational chemistry; Homolytic substitution; Kinetics; Free radical
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2015.06.026

[Display omitted] •Radical substitution to form 2-selenabicyclo[1.1.1]pentane explored.•Rate constants of 5×10−14 to 2×10−8s−1 calculated using G3(MP2)-RAD.•Slowest homolytic substitution at selenium atom containing lone pair.•Reaction not synthetically useful. Ab initio molecular orbital and density functional calculations predict that 3-(alkylseleno)cyclobutyl radicals (12) undergo intramolecular homolytic substitution chemistry to form 2-selenabicyclo[1.1.1]pentane (14) with energy barriers (ΔE1‡) that depend on both level of theory and nature of the leaving radical. In the absence of electron correlation, HF/6-311G(d,p) calculations provide values of ΔE1‡ that range from 170.6 (t-Bu) to 206.5kJmol−1 (Me). Inclusion of electron correlation (QCISD, CCSD(T)) serves to reduce these barriers by 30–40kJmol−1. At the highest level (G3(MP2-RAD)), activation energies of 150.0 (Me), 143.3 (Et), 138.0 (i-Pr), 129.7 (t-Bu) and 108.4 (Bn) kJmol−1 are calculated. G3(MP2)-RAD also provides rate constants for ring-closure (kc) that range from 5×10−14 (Me) to 2×10−8s−1(Bn) suggesting that this chemistry is unlikely to be useful for constructing these interesting ring systems. Data for the cyclization for the analogous sulfur-containing system, the 3-(alkylthio)cyclobutyl radicals (15) are also provided.