Solid-state phosphorus-31 NMR spectroscopy of a multiple-spin system: an investigation of a rhodium–triphosphine complex

Abstract

Phosphorus-31 NMR spectra of solid [tris(dimethylphenylphosphine)](2,5-norbornadiene) rhodium(I) hexafluorophosphate have been acquired at several applied magnetic field strengths. The phosphorus nuclei of the three phosphine ligands are spin–spin coupled to each other and to ¹⁰³Rh, resulting in complex NMR spectra; however, the three phosphorus chemical shift (CS) tensors were determined through the analysis of NMR spectra of slow magic angle spinning and stationary samples. Spectra of spinning samples in rotational resonance and two-dimensional ³¹P NMR spectra were particularly useful for determining the magnitudes of the indirect spin–spin couplings, and to probe their signs. Despite being in similar environments, the three phosphorus nuclei of the phosphine ligands have distinct CS tensors. In particular, the spans of these tensors, δ₁₁–δ₃₃, range from 80 to 176 ppm. The phosphorus CS tensors have been assigned to specific sites determined by X-ray crystallography, based on a combination of the experimental results and the results of quantum chemical calculations of the phosphorus shielding and ²J(³¹P,³¹P) values. The effect of coordination of dimethylphenylphosphine with rhodium has been investigated by comparing calculated phosphorus CS tensors for the uncoordinated ligand with those obtained for the ligands in the complex.