Carbon-Sulfur Bond Cleavage Reactions of Quinolyl-Substituted Thiophenes with Iron Carbonyls

Thermal reactions of quinolyl-substituted thiophenes (2-(8'-quinolyl)thiophene (QT), 2-methy1-5-(8'-quinolyl)thiophene (MeQT), 2-(8'-quinolyl)-5(trimethylsily)thiophene (TMSQT)) with [Fe-3(CO)(12)] gave the corresponding thiolate-bridged diiron complexes [Fe-2(mu-L-R)(CO)(5)] (R = H, Me, SiMe3), where L-H, L-Me, and L-TMS are dianionic N,C,S-tridentate ligands (SC(R)CHCHC(Q)(2-), Q=8-quinolyl) formed by the oxidative addition of the C-S bond in QT, MeQT, and TMSQT, respectively. In contrast, the formation of photoreaction products of the quinolyl-substituted thiophenes with [Fe(CO)(5)] was dependent on the R group of the thiophene ring. The photoreaction of QT gave the sulfur-free diiron complex [Fe-2{CHCHCHC(Q)}(CO)(5)], whereas the photoreactions of MeQT and TMSQT gave the thiolate-bridged triiron complex [Fe-3(mu-L-R)(CO)(8)] and diiron complex [Fe-2(mu-L-TMS)(CO)(5)], respectively, as the major products. In the triiron complexes [Fe-3(mu-L-R)(CO)(8)], an Fe(CO)(3) unit is bound to the C(R)CHCH moiety in the S-metallacycle of the diiron complexes [Fe-2(mu-L-R)(CO)(5)]. The difference in the photoreaction products is described on the basis of the reactivity of the thiolate complexes [Fe-2(mu-L-R)(CO)(5)] and [Fe-3(mu-L-R)(CO)(8)]. Although the photoreactions of the diiron complexes [Fe-2(mu-L-R)(CO)(5)] with [Fe(CO)(5)] produced the corresponding triiron complexes [Fe-3(mu-L-R)(CO)(8)], desulfurization leading to the formation of [Fe-2{CHCHCHC(Q)}(CO)(5)] was predominant for R = H, and a fast conversion of the triiron complex to a CO elimination product was observed for R = SiMe3.