Synthetic, structural and computational studies on adducts of the4,1,2-SnC_2B_(10)supraicosahedral stannacarborane

摘要

The stannacarborane 1,2-μ,-(CH_2)_3-4,1,2-closo-SnC_2B_(10)H_(10) (1) and its adducts with 2,2'-bipyridine(bipy), 1,10-phenanthroline (o-phen) and 4,4'-diphenyl-2,2'-bipyridine (Ph2bipy), 1,2-μ-(CH_2)_3-4-(bipy)-4,1,2-closo-SnC_2B_(10)H_(10) (2), 1,2-μ-(CH_2)_3-4-(o-phen)-4,1,2-c/oso-SnC2BloHl0(3)and 1,2-μ-(CH_2)_3-4-(Ph2bipy)-4,1,2-closo-SnC_2B_(10)H_(10) (4), respectively, together with the analogouscompound 1,2-μ.-{C_6H_4(CH_2)_2}-4-(bipy)-4,1,2-closo-SnC_2B_(10)H _(10)(5) have been prepared andcharacterised. In solution at ambient temperature, compounds 1-5 all display NMR spectra which areinterpreted in terms of (time-averaged) C, molecular symmetry, but whilst (effectively) C, symmetry isretained in the structures of 2-5 in the crystal (i.e. henicosahedral cage structures are observed), 1 has a(C1-symmetric) docosahedral structure. A method for quantifying the "percentage docosahedralcharacter" of 13-vertex 1,2-C_2heteroboranes is described, based on the angles around the C1C2B9B5quadrilateral. The structures of "carbons adjacent" 1-5 all reveal less slipping of the Sn atom (or{SnL,} fragment) across the C2B4 carborane face than has previously been observed in analogous"carbons apart" 4,1,6-closo-SnC_2B_(10) species, a surprising result in the context of previous studies ofslipping in icosahedral platinacarboranes. A computational study of "carbons adjacent" and "carbonsapart" icosahedral and supraicosahedral platinacarboranes has revealed that the origin of thisobservation is steric control of the slipping distortion in both "carbons apart" species and in the"carbons adjacent" 13-vertex species, with orbital interactions proving dominant only in the case of the"carbons adjacent" icosahedral compound