Pentacoordination at antimony via endocyclic and exocyclic intramolecular interactions in dibenzostibocine diorganodithiophosphates [{D(C6H4S)2}Sb{S2P(OR)2}] (D=O, S)

Treatment of [{D(C6H4S)2}SbCl] (D=O, 1; D=S, 2) with MS2P(OR)2 afforded the stable dibenzostibocine dithiophosphate compounds [{D(C6H4S)2}Sb{S2P(OR)2}] with D=O, R=1,2-C6H4 (3); for D=S, R=1,2-C6H4 (4), Et (5), nPr (6), iPr (7), and Ph (8). The compounds were characterized by IR and 1H, 13C{1H}, and 31P{1H} NMR spectroscopy in solution. The 31P{1H} NMR data are consistent with an anisobidentate coordination mode of the dithiophosphate ligand to the Sb atom. Single crystal X-ray diffraction analyses of compounds 3, 4, 7, and 8 revealed that the antimony atom acts as an acceptor atom exhibiting endocyclic and exocyclic intramolecular interactions with the donor D atom and with both sulfur atoms of the dithiophosphate ligand, expanding its coordination sphere from four in the starting materials to five and displaying a skew-trapezoidal pyramidal local geometry.