Dihydrogen bonding formed by (hydrido)[hydrotris(pyrazolyl)borato]ruthenium. The effect of ligands on the proton-accepting ability of ruthenium complexes

Abstract

Reactions of [1,2-bis(diphenylphosphino)ethane](hydrido)[hydrotris(pyrazolyl)borato]-ruthenium with proton donors were studied by IR and 1H NMR spectroscopy in CH2Cl2 over a wide temperature range. Dihydrogen bonding to CF3CH2OH was detected; its spectral and thermodynamic parameters (ΔH° =–3.3±0.2 kcal mol–1, ΔS° =–6.7±0.6 cal mol–1 K–1) were determined. The basicity factor E j of the hydride ligand is 0.81. The H⋯H distance in the dihydrogen-bonded complex (2.05 A) was estimated from the changes in the spin-lattice relaxation time T 1min of the hydride resonance. Comparison of the results obtained with the literature data revealed a correlation between the length and enthalpy of formation of the dihydrogen bond as well as a correlation between the basicity of the hydride ligand and the tendency of the fragment [ML n ] toward stabilization and oxidative addition of H2.