NEW MODES OF THIOPHENE COORDINATION AND REACTIVITY - STRUCTURES OF CP-STAR IR(ETA-2-THIOPHENE), AN IRIDATHIABENZENE, AND CP-STAR IR(ETA-4-THIOPHENE.BH3)

The [Cp*Ir(η5-2,5-Me2T)](BF4)2 complex (1d), where Cp* is η5-C5Me5 and 2,5-Me2T is 2,5-dimethylthiophene (other thiophenes react similarly), undergoes a two-electron reduction using Na[H2Al(OCH2CH2OMe)2] to give Cp*Ir-(η4-2,5-Me2T) (2d). Basic Al2O3 catalyzes the isomerization of 2d to the more stable and novel 3d. X-ray and NMR studies [inlineformulaomitted] support a structure for 3d in which the π-system of the six-membered ring is delocalized and may best be described as an iridathiabenzene. Oxidation of both 2d and 3d (surprisingly) yield Id. In addition to 2d and small amounts of 3d, the BH3 adduct Cp*Ir(η4-2,5-Me2T·BH3) (4d) in which the BH3 is coordinated to the sulfur of 2d was isolated in trace amounts from the reduction of 1d; the structure of 4d was established by an X-ray diffraction investigation. © 1990, American Chemical Society. All rights reserved.