Synthesis and Structure of Binuclear O/S‐Bridged Organobismuth Complexes and Their Cooperative Catalytic Effect on CO2 Fixation

In the synthesis of binuclear organobismuth complexes (1–6) through treatment of organobismuth chlorides with NaOH or Na2S⋅9H2O, the two 5,6,7,12-tetrahydrodibenz [c,f][1,5]azabismocine frameworks are cross-linked by either a sulfur or an oxygen atom. The complexes (1–6) show high catalytic efficiency in the synthesis of cyclic carbonates from 2-(chloromethyl)oxirane and CO2. Compared with their precursor chlorides (7–9), methoxide 10 and methanethioate 11 which are mononuclear organobismuth complexes, the binuclear organobismuth complexes show higher cooperative catalytic effect. However, the complexes with an oxygen bridge (1–3) are not stable in air and lose their catalytic efficiency because of hydrolysis or CO2 adsorption (forming organobismuth carbonates in the latter case). Nonetheless, the binuclear organobismuth complexes (4–6) with a sulfur bridge are highly stable in air and can be applied in the synthesis of cyclic carbonates (with the co-presence of Bu4NI) across various kinds of epoxides, thus exhibiting satisfactory efficiency and selectivity.