Syntheses and structures of dimesitylbismuth(III) bromide, Mes 2BiBr, and bis(diphenyldithiophosphinato)mesitylbismuth(III), MesBi(S 2PPh 2) 2

Abstract

Addition of BiBr 3 to Mes 3Bi (Mes = 2, 4, 6-Me 3C 6H 2) in Et 2O gives 86% of Mes 2BiBr ( 1) as yellow crystals. Reaction of 1 with Ph 2PS 2NH 4 in a 1 : 1 molar ratio gives a quantitative yield of MesBi(S 2PPh 2) 2 ( 2) rather than the expected dimesitylbismuth compound. The crystal and molecular structures of 1 and 2 were determined at 153 K and 173 K, respectively. They contain Mes 2BiBr molecules with trigonal pyramidal coordination around Bi. The mean BiC bond distance is 2.27 Å and the BiBr bond distance is 2.690(2) Å. The angles around Bi vary between 89.4 and 106.4°. Intermolecular Bi…Br contacts of 3.795 Å, indicating weak secondary bonding, give rise to zig-zag shaped (BiBr) x chains. In the polymeric chain the coordination geometry around bismuth atoms can be described as pseudo-trigonal bipyramidal. The crystals of 2 consist of discrete monomeric MesBi(S 2PPh 2) 2 molecules with a symmetry plane containing the metal atom and the aromatic ring of the attached mesityl group. The dithiophosphinato ligands exhibit an anisobidentate coordination pattern with long and short phosphorus—sulfur bonds, i.e. P(1)S(1) 2.051(31) Å and P(1)S(2) 1.980(3) Å, related to short and long bismuth—sulfur distances, respectively, i.e. BiS(1) 2.662(2) Å and BiS(2) 3.123(3) Å. This leads to a square-pyramidal geometry around the bismuth atom, with the metal lying 0.33 Å above the basal plane formed by the four sulfur atoms.