¹¹B Solid-State NMR Interaction Tensors of Linear Two-Coordinate Boron: The Dimesitylborinium Cation

Borinium cations (R₂B⁺) are of particular fundamental and applied interest in part due to their pronounced Lewis acidity which enables unique chemical transformations. Solid-state NMR spectroscopy of magic-angle spinning and stationary powdered samples of the dicoordinate boron cation in the recently reported dimesitylborinium tetrakis­(pentafluorophenyl)­borate compound (Shoji et al. Nature Chem. 2014, 6, 498) is applied to characterize the ¹¹B electric field gradient (EFG) and chemical shift (CS) tensors. The experimental data are consistent with linear CB⁺C geometry. The ¹¹B quadrupolar coupling constant, 5.44 ± 0.08 MHz, and the span of the CS tensor, 130 ± 1 ppm, are both particularly large relative to literature data for a variety of boron functional groups, and represent the first such data for the linear CB⁺C borinium moiety. The NMR data are similar to those for the neutral tricoordinate analogue, trimesitylborane, but contrast with those of the Cp*₂B⁺ cation. Quantum chemical calculations are applied to provide additional insights into the relationship between the NMR observables and the molecular and electronic structure of the dimesitylborinium cation.