Iron Carbonyl Complexes Containing N,C,S-Tridentate Ligands with Quinoline, Vinyl, and Benzenethiolate Units

Iron­(III) carbonyl complexes of N,C,S-tridentate ligands containing quinoline-N, vinyl-C, and benzenethiolate-S donors were synthesized by three steps from quinolyl-substituted benzothiophenes via C–S bond cleavage, and their photoreactivity was investigated. The starting complexes [Fe2(μ-L)­(CO)5] (L = qvbt and qvbt-OMe) were synthesized by the photoreactions of the ligand precursors with [Fe­(CO)5], where qvbt and qvbt-OMe are a doubly deprotonated form of 2-[2-(quinolin-8-yl)­vinyl]­benzenethiol and its methoxy derivative, respectively. The methoxy group is bound to the vinyl moiety of the ligand, which is the β-position to Fe in the C,S-chelate. The N,C,S-pincer iron­(II) carbonyl complexes trans-[Fe­(L)­(CO)­(PMe3)2] were obtained by treatment of [Fe2(μ-L)­(CO)5] with PMe3. One-electron oxidation of the iron­(II) complexes afforded the N,C,S-pincer iron­(III) carbonyl complexes trans-[Fe­(L)­(CO)­(PMe3)2]­PF6. The iron­(III) carbonyl complex of qvbt was adequately stable in both the solid and solution state, whereas the qvbt-OMe complex underwent thermal decomposition in solution. The instability is related to the steric demand of the methoxy group in the coordinated ligand. Both iron­(III) complexes showed the CO-releasing properties induced by visible light in dichloromethane, which is enhanced by the methoxy group on the vinyl moiety.