Understanding the binding and activation of thiophenic molecules in transition metal complexes and clusters

Organometallic complexes and clusters provide examples of binding modes of thiophenic molecules, activation of the C-S bond in thiophene, and actual desulfurization of thiophenic molecules. Our molecular orbital calculations on these complexes are aimed toward understanding how the binding and reactivity of the thiophenic ligands are influenced by the electronic structures of the various complexes. Results of Fenske-Hall molecular orbital calculations for complexes incorporating both eta(5) and eta(1) thiophene ligands show that although the thiophene ligand acts primarily as a donor, thiophene can and does act as a pi acceptor under certain conditions. These results suggest how binding of a thiophenic ligand and/or activation of the C--S bond might be optimized in eta(5) or eta(1) complexes. Results for metal-inserted or ring opened complexes show distinct differences in the electronic structure of saturated and unsaturated complexes. The orbital structures and charge distributions provide explanations for the different reactivities of a number of these complexes. Comparisons of the electronic structures and reactivities of the metal-inserted complexes and the butterfly cluster (Cp')(2)Mo-2 Co2S3(CO)(4), which is known to remove sulfur from thiophene, suggest similarities in the mechanism of binding and activation of a thiophene ring in the complexes and the butterfly cluster. (C) 1997 Elsevier Science Ltd.