Dynamics of H-atom exchange in stable cis-dihydrogen/hydride complexes of ruthenium(ii) bearing phosphine and N–N bidentate ligands

Abstract

Synthesis and characterization of cis,trans-[RuH(η²-H₂)(PPh3)2(N–N)][OTf] (N–N = 2,2′-bipyridyl (bpy) 1a, 2,2′-bipyrimidine (bpm) 2a; OTf = trifluoromethane sulfonate (CF₃SO₃)) complexes are reported. The cis-H₂/hydride ligands are involved in H-atom site exchange between the two moieties. This dynamics was investigated by variable temperature NMR spectral studies based on which the mechanism of the exchange process was deduced. The ΔG≠ for the exchange of H-atoms between the η²-H₂ and hydride ligands was determined to be around 8 and 13 kJ mol⁻¹, respectively, for 1a and 2a. The H–H distances (d_HH, Å) in complexes 1a and 2a have been calculated from the T₁(minimum) and ¹J(H,D) and are found to be 1.07 Å (slow) and 0.95 Å for 1a and 1.04 Å (slow) and 0.94 Å for 2a, respectively. The molecular structure of 1a was determined by X-ray crystallography.