Effect of ring strain on nucleophilic substitution at selenium: a computational study of cyclic diselenides and selenenyl sulfides.
Nucleophilic substitution reactions of small rings incorporating selenium are examined using computational methods. The potential energy surfaces of HS- and HSe- with 1,2-diselenirane, 1,2-diselenetane, 1,2-diselenolane, and 1,2-diselenane were computed at B3LYP/6-31+G(d) and MP2/6-31+G(d). The reactions of three-, four-, five-, and six-membered rings incorporating the S-Se bond with HS- were computed at B3LYP/6-31+G(d). The strained three- and four-membered diselenides and selenenyl sulfide rings undergo SN2 reactions, while the five- and six-membered rings react via the addition-elimination pathway, a path that invokes a hypercoordinate selenium intermediate. The strain in the small rings precludes the addition of a further ligand to either heteroatom. Substitution at selenium is both kinetically and thermodynamically favored over attack at sulfur.
Bachrach
Steven M
SM
Department of Chemistry, Trinity University, 1 Trinity Place, San Antonio, Texas 78212, USA. sbachrach@trinity.edu
Walker
Claire J
CJ
Lee
Fiona
F
Royce
Sarah
S