Adducts of the supraicosahedral stannacarborane 1,6-Me2-4,1,6-closo-SnC2B10H10; synthetic, structural and computational studies.

The 13-vertex stannacarborane 1,6-Me(2)-4,1,6-closo-SnC(2)B(10)H(10) reacts with the Lewis bases 2,2'-bipyridine, 1,10-phenanthroline, 4,4'-dimethybipyridine and 4,4'-diphenylbipyridine, in toluene, to precipitate bright-yellow adducts 1,6-Me(2)-4-(L(2))-4,1,6-closo-SnC(2)B(10)H(10) (, respectively) in good yield. Compounds have been characterised by NMR spectroscopy and single-crystal X-ray diffraction. Compound is somewhat less stable in solution but has also been studied crystallographically. Adduct formation retains the docosahedral structure of 1,6-Me(2)-4,1,6-closo-SnC(2)B(10)H(10) but is accompanied by polyhedral distortion arising from significant increases in Sn-C and Sn-B2 distances. This distortion is described in terms of either a slipping or hinging of the {SnL(2)} fragment. In the molecular structures of it is evident that the Sn lone pair of electrons is stereochemically active since the L(2) ligand is clearly inclined with respect to the polyhedron. Both the inclination and orientation of L(2) are rationalised by the results of DFT calculations on 4,1,6-closo-SnC(2)B(10)H(12). Calculations on models of the adducts , and reproduce the structural distortion that accompanies adduct formation, but appear to underestimate somewhat the strength of Sn-L(2) bonding.