UC Davis

Two compounds containing a Sn(II) atom supported by a bidentate biscarborane ligand have been synthesized via salt metathesis. The synthetic procedures for (bc)Sn·THF (bc = 1,1' (ortho-carborane) (1) and K₂[(bc)Sn]₂ (2) involved the reaction of K₂[bc] with SnCl₂ in either a THF solution (1) or in a benzene/dichloromethane solvent mixture (2). Using the same solvent conditions as those used for 2 but using a shorter reaction time gave a dibiscarboranyl ethene (3). The products were characterized by ¹H, ¹³C, ¹¹B, ¹¹⁹Sn NMR, UV-vis, and IR spectroscopy, and by X-ray crystallography. The diffraction data for 1 and 2 show that the Sn atom has a trigonal pyramid environment and is constrained by the bc ligand in a planar five-membered C₄Sn heterocycle. The ¹¹⁹Sn NMR spectrum of 1 displays a triplet of triplets pattern signal, which is unexpected given the absence of a Sn-H signal in the ¹H NMR, IR spectrum, and X-ray crystallographic data. However, a comparison with other organotin compounds featuring a Sn atom bonded to carboranes reveal similar multiplets in their ¹¹⁹Sn NMR spectra, likely arising from long-range nuclear spin-spin coupling between the carboranyl ¹¹B and ¹¹⁹Sn nuclei. Compound 3 displays structural and spectroscopic characteristics typical of conjugated alkenes.