High-resolution 2H MAS NMR applied to deuterium analogs of hydrido η 2-dihydrogen complexes

Abstract

2H solid-state, variable temperature magic angle spinning (MAS) NMR spectra of precipitated samples of the deutero dideuterium complexes Ru(D) 2(η 2-D 2) 2(PCy 3) 2 and RuD(η 2-D 2)I(PCy 3) 2 [Cy=cyclohexyl] are presented. They show that even at moderate MAS speed, high resolution is achieved at 7 and 14 T allowing 2H chemical shifts and quadrupole couplings to be obtained and assigned to different solid and gaseous 2H species. These two parameters allow identifying chemically different hydrogen species in the material. The analysis of these parameters in this study reveals the presence of three different species in the sample, namely the complexes RuD(η 2-D 2)I(PCy 3) 2 and RuD(η 2-D 2) 2I(PCy 3) 2, and highly mobile HD/D 2. These assignments are supported by 2H T 1 relaxation times and 31P MAS NMR spectra. Moreover, variable temperature MAS NMR spectra reveal temperature-dependent line-shape changes, which are clear indications of intramolecular hydrogen exchange of the deutero and the dideuterium ligands and which give an estimate for the activation energy of this process.