Trioxorhena(VII)carborane Anion and Its Methyl-Substituted Analogue: Synthesis, Structure, DFT, and Catalytic Studies

Synthesis and characterization of trioxorhena­(VII)­carborane
[Bu4N]­[(η1-C2B9H11)­ReO3] (1a) and its methyl-substituted
analogue
[Bu4N]­[(7,8-Me2-η1-C2B9H11)­ReO3] (1b) are
reported. The single-crystal X-ray structures of 1a and 1b display η1 coordination between Re and
the carborane cage. Density functional theory computations at B3LYP/LANL2DZ
(Gaussian 09 suite) level show that the strong π donor character
of the oxo ligands results in a weak interaction between the d orbitals
on Re and the π orbitals of the boron cage, the consequence
of which is favoring η1 Re–B coordination.
Complexes 1a and 1b exhibit reversible one-electron
reduction in cyclic voltammetry experiments at E1/2 potentials of −1.83 and −1.88 V versus Cp2Fe/Cp2Fe+, respectively. Complex 1a catalyzes the hydrosilylation of aldehydes and ketones
in excellent yields and with high tolerance to a variety of functional
groups. Mechanistic investigation of the hydrosilylation reaction
revealed potential involvement of multirhenium–boron cluster.