Comparative properties of coordinated H-2 and H2S at a ruthenium(II) centre

Thermodynamic data for the reversible formation of cis-RuCl2(P-N)(PPh3)(eta(2)-H-2) (2a) from trans-RuCl2-(P-N)(PPh3) in C6D6 are determined by variable temperature P-31{H-1} and H-1 NMR spectroscopy; P-N = o-diphenylphosphino-N,N'-dimethylaniline. Values of Delta H degrees = -26 +/- 4 kJ mol(-1), Delta S degrees = -40 +/- 15 J mol(-1) K-1, and Delta G degrees (at 25 degrees 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 similar to 20 kJ mol(-1), but this is counteracted by a more unfavourable entropy change, and overall the K and Delta G degrees values at 25 degrees C are close. For loss of H-2 from 2a in the solid state, whose X-ray structure is presented, Delta H degrees is 50 +/- 3 kJ mol(-1) as measured by Differential Scanning Calorimetry. The pK(a) values of the coordinated H-2 (similar to 11) and H2S (similar to 14) are estimated by reactions of 2a and 4a with proton sponge (1,8-bis(dimethylamino)naphthalene) in CD2Cl2 at 20 degrees 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.