Electron Transfer Induced C-S Bond Cleavage in Rhenium and Technetium Thioether Complexes: Structural and Chemical Evidence for it Back-Donation to C-S sigma* Orbitals

摘要

The ability of tertiary phosphane ligands to act as pi-acceptor ligands is well-established. It has been suggested that a model in which P- C sigma* orbitals are the primary contributor to the Jt-ac-ceptor capacity of the phosphane ligand is a more useful description of the back-bonding than the model in which the phosphorus d oibitals are the primary acceptor. This is supported by structural and computational evidence. The analogy between tertiary phosphanes and thioethers suggests that thioethets too may act as it acceptors in transition metal complexes, although the relative instability of thioether complexes has been an obstacle to substantive investigation of the bonding At issue are whether thioethers possess significant it-acceptor properties, and whether C-S sigma* prbitals have a significant role in the description of the back-bonding, if it exists. The relative scarcity of suitable thioether complexes has in the past prevented experimental verification of theoretical calculations, but inthe last decade a large series of homoleptic hexathioether complexes has become available with the macrocyclic ligahd 1,4,7-trithiacyclononane (9S3). This has led to an accumulation of spectroscopic evidence for pi acidity of thioether ligands. If C-S sigma* orbitals participate in this bonding structural manifestations would also be expected.