[2 + 2] Cycloaddition of Carbon Disulfide to NCN-Chelated Organoantimony(III) and Organobismuth(III) Sulfides: Evidence for Terminal Sb−S and Bi−S Bonds in Solution

The organoantimony(III) and organobismuth(III) sulfides (LMS)2 (L = NCN chelating ligand, C6H3-2,6-(CH2NMe2)2; M = Sb (1), Bi (2)) are dimeric in the solid state. Nevertheless, their monomeric structures with terminal Sb−S and Bi−S bonds present in solution were trapped by [2 + 2] cycloaddition reactions with CS2, giving the molecular trithiocarbonates LMS2CS (M = Sb (3), Bi (4)). Both compounds were characterized in the solid state by X-ray diffraction techniques on both single crystals and powder material and by IR spectroscopy. Carbon disulfide can be easily eliminated from the trithiocarbonates 3 and 4 by heating to 120 °C (for 3) and 160 °C (for 4) to recover the starting sulfides 1 and 2. In solution, trithiocarbonates 3 and 4 exist in equilibrium with starting sulfides 1 and 2, but this equilibrium may be shifted to pure 3 and 4 by addition of an excess of CS2, as shown by 1H NMR spectroscopy.