Effect of butterfly-shaped sulfur-bridged ligand and counter anions on the catalytic activity and diastereoselectivity of organobismuth complexesElectronic supplementary information (ESI) available: experimental details and characterization data. CCDC reference numbers 724767(1), 728508(2), 755139(3), 791966(4). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0dt01419b

In the direct Mannich reaction and synthesis of α,β-unsaturated ketones, the use of organobismuth complexes as catalysts leads to high diastereoselectivity and products of single transconformation. In this paper, we illustrate the relationship between structure and catalytic activity as well as diastereoselectivity of organobismuth complexes having a 5,6,7,12-tetrahydrodibenz [c,f][1,5]thiobismocine framework as well as bearing a butterfly-shaped sulfur-bridged ligand and tunable anions. With the exposed bismuth center acting as a Lewis acid site and the uncoordinated lone pair electrons of sulfur as a Lewis base site, the cationic organobismuth complexes work as bifunctional Lewis acid/base catalysts. Due to the steric influence of the butterfly-shaped structure and synergistic effect of Lewis acid and Lewis base centers, the complexes can direct substrate attack in organic synthesis. By adjusting the electron-withdrawing ability of the counter anions, the S–Bi bond strength can be regulated, leading to a significant change in Lewis acidity and Lewis basicity as well as catalytic activity. Through synergistic modulation of the above effects, one can control the diastereoselectivity of the organobismuth complexes for the generation of a single diastereoisomer. [ABSTRACT FROM AUTHOR]