Novel Thiophene-Based Cycloruthenated Compounds: Synthesis, Characterization, and Reactivity

The reactions between a series of thiophene-based imines with [(η6-C6H6)RuCl(μ-Cl)]2, in a basic medium, and in MeCN give a family of ruthenacycles of stoichiometry [Ru(C∧N)(NCMe)4]PF6 (C∧N = orthometalated thiopheneimine). In these species, the C−H activation process is produced in most cases at the thiophene ring. When two C−H bonds are competing (thiophene vs aryl), the cyclometalation can be driven regioselectively to the thiophene unit or to the aryl ring as a function of the location of the iminic CN bond. Cyclometalation can also be oriented to positions 2 or 3 of the thiophene depending on the situation of the imine in the heterocycle (3 or 2, respectively). In all studied cases, the η6-C6H6 ligand was substituted by acetonitrile. The X-ray structures of two representative complexes have been determined. These thiophene-based metallacycles react with iodine under very mild conditions affording, after hydrolysis, substituted 3-iodo-2-formyl(benzo)thiophenes or substituted 2-iodo-3-formyl(benzo)thiophenes, as a function of the organometallic precursor.