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Oxidation of CS 2 by AsBr 4 + : The Unexpected Formation of the Simple CS 2 Br 3 + Carbenium Ion
Author(s) -
Gonsior Marcin,
Krossing Ingo
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400046
Subject(s) - exergonic reaction , delocalized electron , chemistry , ion , solvation , carbocation , computational chemistry , crystallography , photochemistry , organic chemistry , catalysis
During the preparation of AsBr 4 + [Al(OR) 4 ] − , the novel carbocation CS 2 Br 3 + was synthesized by reaction of AsBr 3 , Br 2 , CS 2 , and Ag[Al(OR) 4 ] (R=C(CF 3 ) 3 ). CS 2 Br 3 + [Al(OR) 4 ] − was characterized by its crystal structure, NMR and IR spectroscopy, and quantum chemical calculations (including COSMO solvation enthalpies). Additional experiments as well as the computed thermodynamics indicated two likely reaction pathways: Ag + +2 Br 2 +CS 2 →CS 2 Br 3 + +AgBr and the direct 4 e − oxidation reaction AsBr 4 + +CS 2 →CS 2 Br 3 + +1/6As 6 Br 6 . Both reactions were observed experimentally and were calculated to be exergonic in solution by −226 and −56 kJ mol −1 respectively. As a result of charge delocalization the CS and CBr distances in the cation are shortened by 0.06 to 0.08 Å; the SBr distances are also slightly shortened indicating a delocalization of the charge also to the bromine atoms in the (S)Br moieties. Based on an analysis of the cation–anion contacts as well as quantum chemical MP2 calculations, a delocalization model as a planar 10 π electron system is discussed and the π molecular orbitals are given. It will be shown that the electronic situation of CS 2 Br 3 + is very close to that in CBr 3 + , that is, the properties of SBr moieties and Br atoms as π donors towards a formal C + center are comparable.