Solution kinetic and mechanistic studies were performed on the abstraction of sulfur from Pd2X2(ti-S)(ti-dpm)2 [X = Cl (2a), Br (2b), I (2c)] using bis(diphenylphosphino)methane (dpm) to give, respectively, Pd2X2(dpm)2 [X = Cl (la), Br (lb), I (lc)] and dpm(S). The reaction is first-order in both 2 and dpm with the reactivity trend in CHCI3 being X = Cl > Br > I. The activation parameters for the chloride system are AH* -41 ± 3 kJ mol-1 and AS* = -127 ± 10 J K-1 mol-1, and for the bromide, AH* = 38 ± 1 kJ mol-1 and AS* --144 ±41 K-1 mol-1, showing the entropy term is dominant in governing reactivity. Low-temperature NMR studies did not reveal the presence of observable intermediates. 2b and lb undergo rapid diphosphine ligand exchange with dpm-i/2; with 2b, prior to any S-abstraction, Pd2Br2(M-S)(dpm)(dpm-d2) (7b) and Pd2Br2(¿í-S)(dpm-íi2)2 (8b) are present, while Pd2Br2(dpm)(dpm-¿2) (3b) and Pd2Br2(dpm-£?2)2 (4b) are formed, as well as lb and dpm(S)-¿2, in the abstraction reaction of 2b with dpm-i/2• The distribution of products is close to statistical on the basis of the stoichiometries of the reactants. Reaction of 2b with 1,l'-bisídiphenylphosphinojethane (dpmMe) proceeds in an analogous way generating lb, Pd2Br2(dpm)(dpmMe) (5b), Pd2Br2(dpmMe)2 (6b), dpm(S), and dpmMe(S). In contrast, lb undergoes slow diphosphine ligand exchange with dpmMe to form 5b and 6b; 2b undergoes no ligand exchange with dpmMe prior to the S-abstraction reaction. The findings are rationalized in terms of postulated intermediates and transition states that include formulations with three equivalent diphosphines. No sulfur abstraction occurs on treating 2b with PPI13, PPh2Me, or Ph2P(CH2)3PPh2.

Kinetic and low temperature nmr data are presented for the reaction of hydrogen sulfide with PdzX2(k-dpm)2 species in dichloromethane solution (X = halide, dpm = bis(dipheny1phosphino)methane. The reactions form the corresponding bridgedsulfide, A-frame complex via oxidative-addition of H2S across the Pd-Pd bond to give a hydrido(mercapto) intermediate, that subsequently liberates H, to give Pd2X2(p-S) (~-d p m )~ species. Quantitative kinetic data showing first order behaviour in both Pd2 dimer and H2S concentrations are given for the bromide system over the temperature range 0-3S°C, as well as more limited data for the photosensitive iodide system; plausible mechanisms are discussed. Some qualitative findings are presented for related systems containing 1 ,1-bis(dipheny1phosphino)ethane.Key words: palladium complexes, hydrogen sulfide, bis(dipheny1phosphino)methane.A. FREDDY BARNABAS, DOMINIQUE SALLIN et BRIAN R. JAMES. Can. J. Chem. 67,2009Chem. 67, (1989.On prksente des donnkes relatives a la cinktique ainsi qu'i la rmn a basse tempkrature pour la rkaction du sulfure d'hydrogkne avec les espkces Pd2X2(k-dpm)2 (dans lesquelles X = halogknure et dpm = bis(diphknylphosphino)mkthane), en solution dans le dichloromkthane. Par le biais d'une addition oxydative du H2S a travers la liaison Pd-Pd, les rkactions foment le complexe correspondant, de structure en A et comportant un pont sulfure, qui conduit a un intermkdiaire hydrido(mercapto) et qui libkie par la suite du H2 pour foumir des espkces Pd2X2(k-S) ( k -d~r n )~. Des donnkes cinktiques quantitatives dkmontrent que, pour le systkme du bromure i d e s ternpkratures allant de 0 a 30°C et pour des donnkes plus limitkes relatives au systkme photosensibilisk de l'iodure, les rkactions sont du premier ordre relativement aux concentrations tant du dimkre Pd2 que du H2S; on discute de divers mkcanismes plausibles. On presente quelques donnkes qualitatives concemant des systkmes apparentks contenant du 1 , 1-bis(diphCny1phosphino)Cthane.