Comparative properties of coordinated H2 and H2S at a ruthenium(ii) centre

Abstract

Thermodynamic data for the reversible formation of cis-RuCl₂(P–N)(PPh₃)(η²-H₂) (2a) from trans-RuCl₂(P–N)(PPh₃) in C₆D₆ are determined by variable temperature ³¹P{¹H} and ¹H NMR spectroscopy; P–N = o-diphenylphosphino-N,N′-dimethylaniline. Values of ΔH° = −26 ± 4 kJ mol⁻¹, ΔS° = −40 ± 15 J mol⁻¹ K⁻¹, and ΔG° (at 25 °C) = −13.8 ± 0.2 kJ mol⁻¹ are compared with recently reported data for the corresponding H₂S adduct (4a), where the exothermicity is greater by ∼20 kJ mol⁻¹, but this is counteracted by a more unfavourable entropy change, and overall the K and ΔG° values at 25 °C are close. For loss of H₂ from 2a in the solid state, whose X-ray structure is presented, ΔH° is 50 ± 3 kJ mol⁻¹ as measured by Differential Scanning Calorimetry. The pK_a values of the coordinated H₂ (∼11) and H₂S (∼14) are estimated by reactions of 2a and 4a with proton sponge (1,8-bis(dimethylamino)naphthalene) in CD₂Cl₂ at 20 °C; the mono-hydrido and -mercapto products are identified in situ. A corresponding H₂O adduct is not deprotonated under the same conditions. Related dihydrido, mercapto and hydroxy species are formed by in situ reactions of 1a with NaH, NaSH, and NaOH, respectively.