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. [ABSTRACT FROM AUTHOR]