Anisotropic 11B and 13C NMR Interaction Tensors in Decamethylcyclopentadienyl Boron Complexes

Abstract

Solid-state double-resonance and triple-resonance 13C, 11B, and 1H NMR experiments are used to investigate two main group metallocene complexes: the decamethylcyclopentadienylborinium cation, [Cp*2B]+, and bis(pentamethylcyclopentadienyl)methylborane, Cp*2BMe. The crystal structure for the latter complex is reported herein. A combination of magic-angle-spinning and static 11B{1H} NMR experiments are used to measure 11B nuclear quadrupole coupling constants (CQ) and rare instances of anisotropic boron chemical shielding tensors. Boron-11 nuclear quadrupole coupling constants reflect the higher spherical symmetry of [Cp*2B]+ compared to Cp*2BMe, with CQ(11B) = 1.14 MHz in the former and CQ(11B) = 4.52 MHz in the latter. Chemical shielding tensor spans are measured for [Cp*2B]+ and Cp*2BMe as Ω = 73.0 and 146.0 ppm, respectively. Hartree−Fock and hybrid density functional theory (B3LYP) calculations of electric field gradient and chemical shielding tensors are in quantitative agreement with experiment, and ...