Ab Initio Molecular Orbital Study of Organometallic Complexes Containing Benzo[b]thiophene

Ab initio molecular orbital calculations have been carried out on benzo[ b ]thiophene (BT), 2-methylbenzo[ b ]thiophene (2-MeBT), 3-methylbenzo[ b ]thiophene (3-MeBT), and a number of organometallic complexes containing these thiophenic moieties in an attempt to understand the usual preference for insertion of metal fragments into the sulfur−carbon(vinyl) bond of BT and the recent observations of insertion into the sulfur−carbon(aryl) bond. The results indicate that insertion selectivity is governed by several factors, including the orbital structure of BT, steric interactions between the metal and the heterocycle, and the metal−carbon bond strengths of the inserted products. In most cases, all three factors support the experimentally observed preference for insertion into the S−C(vinyl) bond. Subtle structural changes, however, can lead to S−C(aryl) metal-inserted products. For instance, steric factors inhibiting insertion of metal fragments into the sulfur−carbon(aryl) bond of BT can be overcome by “tied back” or relatively small metal fragments. In addition, the strength of the metal−carbon bond of the inserted product, which appears to be a determining factor leading to the otherwise unexpected sulfur−carbon(aryl) metal-inserted adducts, can be influenced by derivatizing BT or coordinating metals to the arene ring of BT.