Abstract:
Access to multicarbene complexes of a fused thienothiophene substrate was obtained by the use of the
tetrabrominated thieno[2,3-b]thiophene precursor in a lithium–bromide exchange reaction, followed by
nucleophilic attack on metal hexacarbonyls (M = Cr, W). Subsequent alkylation afforded unique triscarbene
complexes [M(CO)4{{C(OEt)}2C6H1S2C(OEt)}M(CO)5] (M = Cr 12, W 13) featuring three non-equivalent
carbene ligands on a single thiophene linker, as well as the bischelated tetracarbene complexes
[M(CO)4{{C(OEt)}2C6S2{C(OEt)}2}M(CO)4] (M = Cr 14, W 15). The triscarbene complexes 12 and 13 are the
first examples of multi-alkoxycarbene complexes featuring three non-equivalent carbene ligands. The
reaction also afforded the chelated mononuclear biscarbene complexes [M(CO)4{C(OEt)}2C6H2S2] (M =
Cr 10, W 11) in low yields. Similarly, employing tetrabromothiophene as precursor yielded the mononuclear
chelate biscarbene complexes [M(CO)4{C(OEt)}2C4H2S] (M = Cr 6, W 7) and the dinuclear tetracarbene
complexes [M(CO)4{{C(OEt)}2C4S{C(OEt)}2}M(CO)4] (M = Cr 8, W 9). Modification of the classic
Fischer carbene synthetic methodology to a process of stepwise additions of lithiating agent and metal
carbonyls to thieno[2,3-b]thiophene, facilitates the formation of the mixed metal biscarbene complex
[W(CO)5C(OEt){C6H2S2}C(OEt)Cr(CO)5] 5, as analogue of the homonuclear biscarbene complexes
[M(CO)5C(OEt){C6H2S2}C(OEt)M(CO)5], (M = Cr 3, W 4). The monocarbene complexes [M(CO)5{C(OEt)-
C6H3S2}], (M = Cr 1, W 2) were also obtained in high yields, and the molecular structures of the tungsten
complexes, with the exception of 9 and 11, were confirmed by single crystal X-ray diffraction studies.
