Ab initio molecular orbital study of organometallic complexes containing benzo[b]thiophene

Ab initio molecular orbital calculations have been carried out an 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 far 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, call 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.