The synthesis and molecular and crystal structures of 1-methyl-2-carboxy-1,2-dicarba-closo-dodecaborane(12), 1-phenyl-2-carboxy-1,2-dicarba-closo-dodecaborane(12) and 1-phenyl-2-benzoyl-1,2-dicarba-closo-dodecaborane(12)

摘要

The structures of 1-Me-2-COOH-1,2-closo-C2B10H10 (1), 1-Ph-2-COOH-1,2-closo-C2B10H10 (2) and 1-Ph-2-COPh-1,2-closo-C2B10H10 (3) have been determined by X-ray crystallography. In 1 the orientation of the COOH group is defined by theta(COOH) = 65.0(2)(syn)degrees, and this group H-bonds to that in a second molecule via a centrosymmetric eight-membered ring, R-2(2)(8). DFT calculations on the parent species 1-COOH-1,2-closo-C2B10H11 reveal that the structure with theta(COOH) = 90(syn)degrees is preferred, with a barrier to COOH rotation of approximate to 17 kJ mol(-1). Similar calculations on 1 yield a lower rotational barrier, approximate to 7 kJ mol(-1), because internal H-bonding is now denied. In compound 2 the COOH group is twisted to lower theta values [5.0(3)degrees and 39.7(3)degrees] but both crystallographically independent molecules exist as dimers in the solid state by virtue of R-2(2) (8) rings. Compound 2 crystallises from wet solvent as a monohydrate, the structure of which reveals a non-planar centrosymmetric R-4(4)(12) ring and near-orthogonal Ph and COOH substituents [theta(Ph) = 6.7(2) and theta(COOH) = 78.0(2)(syn)degrees]. In compound 3 molecular association by H-bonding is blocked, so 3 serves as a useful comparative structure for 2. (C) 2003 Elsevier Ltd. All rights reserved.