Synthesis and crystal structures of carbene complexes with conjugated thiophene units

Binuclear carbene complexes of chromium and tungsten containing a conjugated thiophene spacer, dithieno[3,2-b:2′,3′-d]thienylene (TTT), were synthesized according to the Fischer method for the synthesis of carbene complexes. Biscarbene complexes of the type [(CO)5M{C(OEt)TTTC(OEt)}M(CO)5] (M=Cr, 2; W, 5) were afforded together with the corresponding monocarbene complexes [M{C(OEt)TTTH}(CO)5] (M=Cr, 1; W, 4) and decomposition products [M{C(OEt)TTTC(O)OEt}(CO)5] (M=Cr, 3; W, 6), formed in the reaction of the biscarbene complexes with trace amounts of oxygen. X-ray crystallographic determinations were performed on compounds 1, 2 and 6 to assess the influence of the different substituents in the C9 position of the TTT carbene complexes on the structural features of the condensed rings. The crystallographic data of these three complexes are reported in this paper.