Characterization of H2-Splitting Products of Frustrated Lewis Pairs: Benefit of Fast Magic-Angle Spinning

Proton spectroscopy in solid-state NMR on catalytic materials offers new opportunities in structural characterization, in particular of reaction products of catalytic reactions such as hydrogenation reactions. Unfortunately, the H-1 NMR line widths in magic-angle spinning solid-state spectra are often broadened by an incomplete averaging of H-1-H-1 dipolar couplings. We herein discuss two model compounds, namely the H-2-splitting products of two phosphane-borane Frustrated Lewis Pairs (FLPs), to study potentials and limitations of proton solid-state NMR experiments employing magic-angle spinning frequencies larger than 100 kHz at a static magnetic field strength of 20.0 T. The H-1 lines are homogeneously broadened as illustrated by spin-echo decay experiments. We study two structurally similar materials which however show significant differences in H-1 line widths which we explain by differences in their H-1-H-1 dipolar networks. We discuss the benefit of fast MAS experiments up to 110 kHz to detect the resonances of the H+/H- pair in the hydrogenation products of FLPs.