Rhenium(V) Complexes with Selenolato- and Tellurolato-Substituted Schiff Bases - Released PPh3 as a Facile Reductant

The salicylidene Schiff bases of bis(2-aminophenyl)diselenide and -ditelluride react with [ReOCl3(PPh3)(2)] or the arylimidorhenium(V) compounds [Re(NPhR)Cl-3(PPh3)(2)] (R = H, F, CF3) with formation of rhenium(V) complexes with tridentate {O,N,Se/Te} chalcogenolato ligands. The ligands adopt a facial coordination mode with the oxygen donors trans to the multiply bonded O2- or NPhR2- ligands. The reduction of the dichalcogenides and the formation of the chalcogenolato ligands occurs in situ by released PPh3 ligands. The absence of additional reducing agents provides good yields of products with rhenium in the high formal oxidation state +5. A mechanism for the dichalcogenide reduction is proposed on the basis of the experimental results. In accordance with the proposed mechanism, best yields are obtained with a strict exclusion of oxygen, but in the presence of water.