HOMOGENEOUS CATALYSIS IN WATER .3. THE CATALYTIC-HYDROGENATION OF PROPIONALDEHYDE WITH (RUCL2L2)2, RUHCLL3, RUH(OAC)L3, RUH2L4, RUHIL3, RUCL2(CO)2L2 AND [RU(OAC)(CO)2L]2, (L=P(C6H4-MSO3NA)3.3H2O) - A KINETIC INVESTIGATION OF THE SALT EFFECT IN WATER

Seven water-soluble ruthenium complexes (RuCl2L2)2 1, RuHClL3 2, RuH(OAc)L3 3, RuH2L4 4, RuHIL3 5, RuCl2(CO)2L2 6 and [Ru(OAc)(CO)2L]2 7 (L=P(C6H4-mSO3Na)3.3H2O) have been tested in the catalytic hydrogenation of propionaldehyde. Their catalytic performances have been compared to those of their organosoluble analogues (1'-7', L=PPh3). The non-carbonylated complexes 1-5 exhibit comparable rates of propionaldehyde hydrogenation in water at 100-degrees-C, as determined by their first-order rate constants. In contrast, the rates observed with 1'-4' are different from one another and extremely solvent dependent. With 1, the reaction is first order in aldehyde, catalyst and hydrogen pressure, as is found for the organosoluble complex RuH(CO)Cl(PPh3)3. Starting with 1-4, various equilibria have been observed which lead to the same complex RuH2L3(H2O). These equilibria suggest that the real catalyst precursor in water is RuH2L3. Whatever the precursor (1-5) used, addition of alkaline, alkaline-earth and ammonium salt dramatically increases the activity without any loss of selectivity. The rate equation is drastically modified in the presence of salt. It has been established that the salt acts by both its cation and its anion. For a given anion, the rate increases in the order: NR4+ (R=Et, n-Bu)<Na+<Li+<K+<Mg2+<Ca2+. For a given cation, the rate increases in the order: SiF62-<NO3-<Cl-<Br-<I-. In the presence of NaI, the coordination spheres of 2-4 are modified in water and lead to the same complex RuHIL3 5. The role of the cation has been verified by adding to the catalytic solution a specific sodium cryptand, which resulted in a dramatic drop in activity. A mechanism has been proposed which takes into account the kinetic equation as well as the various observations which were made on the different catalyst precursors.