| Abstract
| - The hydrido-ruthenium(II) complexes of 1,3,5-triaza-7-phosphaadamantane (PTA), [RuH(PTA)5]+, [RuH2(PTA)4], and [RuH(PTA)4X] (X = Cl- or H2O) are observed to be formed in aqueous solution under H2 pressure. The complex [RuCl2(PTA)4] is catalytically active in the hydrogenation of CO2/HCO3- into formate anion under mild conditons: HCO3- + H2 → HCO2- + H2O
- The water-soluble tertiary phosphine complex of ruthenium(II), [RuCl2(PTA)4], (PTA = 1,3,5-triaza-7-phosphaadamantane) was used as catalyst precursor for hydrogenation of CO2 and bicarbonate in aqueous solution,in the absence of amine or other additives, under mild conditions. Reaction of [RuCl2(PTA)4] and H2 (60 bar)gives the hydrides [RuH2(PTA)4] (at pH = 12.0) and [RuH(PTA)4X] (X = Cl- or H2O) (at pH = 2.0). In presenceof excess PTA, formation of the unparalleled cationic pentakis-phosphino species, [HRu(PTA)5]+, wasunambiguously established by 1H and 31P NMR measurements. The same hydrides were observed when [Ru(H2O)6][tos]2 (tos = toluene-4-sulfonate) reacted with PTA under H2 pressure. The rate of CO2 hydrogenationstrongly depends on the pH. The highest initial reaction rate (TOF = 807.3 h-1) was determined for a 10%HCO3-/90% CO2 mixture (pH = 5.86), whereas the reduction was very slow both at low and high pH (CO2 andNa2CO3 solutions, respectively). 1H and 31P NMR studies together with the kinetic measurements suggested thatHCO3- was the real substrate and [RuH(PTA)4X] the catalytically active hydride species in this reaction.Hydrogenation of HCO3- showed an induction period which could be ascribed to the slow formation of thecatalytically active hydride species.
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