Chromium and tungsten carbene complexes of thieno [3,2-b]thiophene

Dinuclear carbene complexes with 3,6-dimethylthieno[3,2b]thienylene (T'T') and thieno[3,2-b]thienylene (TT) spacers were prepared using the classical Fischer method. Their reactivity in solution towards oxygen, as well as the ir structural features were investigated. Chromium and tungsten carbene com plexes were synthesized via dilithiation of the thienothiophene, followed b y the addition of the appropriate metal carbonyl complex and subsequent alk ylation with triethyloxonium tetrafluoroborate. Monocarbene [M{C(OEt)T'T'H} -(CO)(5)], (M = Cr, 1; W, 4), biscarbene [(CO)(5)M{C-(OEt)T'T'C(OEt)}M(CO)( 5)], (M = Cr, 2; W, 5), and the products [M{C(OEt)T'T'C(O)OEt} (CO)(5)], (M = Cr, 3; W, 6), where a metal moiety of 2 and 5 has been replaced by an es ter functionality, were isolated. The reaction product afforded in the reac tion of Cr(CO)(6) with lithiated thieno[3,2-b]thiophene, [Cr{C(OEt)TTC(O)Bu }(CO)(5)], 7, did not resemble any of the products isolated in the similar reaction of Cr(CO), with lithiated 3,6-dimethylthieno[3,2-b]thiophene.