Ten-Vertex Polyhedral Rhodadicarbaborane Chemistry. Molecular Structure, NMR Properties, and Cluster Dynamic Behaviour of [2,2,2-(PPh3)2H-closo-2,1,6-RhC2B7H9]

Abstract

The compound previously described as [6,6,6-(PPh3)2H-closo-6,3,3-RhC2B7H9] is shown by detailed multielement NMR studies and single-crystal X-ray diffraction analysis to be its isomer [2,2,2-(PPh3)2H-closo-2,1,6-RhC2B7H9] Crystals (from pentane-diethyl ether) were monoclinic, space group P21/n, with Z = 4, and with a = 1 222.2(1) pm, b = 1 598.7(2) pm, c = 1 836.7(1) pm, and β = 91.86(1)°. The structure was refined to R(Rw) 0.0295(0.0414)using 6 819 observed data [I > 2.0 σ(I)] out of 8 541 collected at 200 K. The {RhC2B7} cluster structure is to a first approximation classically closo, with the metal and two carbon atoms in adjacent 2, 1, and 6 positions, respectively. Both enantiomers exist in the unit cell, and variable temperature NMR studies show that the molecule is fluxional (∆G355 ≈ 60 kJ mol-1) between enantiomers via a diamond-square diamond cluster rearrangement.