Reaction rates ruthenium catalysis

The ruthenium catalyst system, 14, shown in Fig. 3, also carries out ADMET condensation chemistry, albeit with higher concentrations being required to achieve reasonable reaction rates [32]. The possibility of intramolecular compl-exation with this catalyst influences the polymerization reaction, but nonetheless, ruthenium catalysis has proved to be a valuable contributor to overall condensation metathesis chemistry. Equally significant, these catalysts are tolerant to the presence of alcohol functionality [33] and are relatively easy to synthesize. For these reasons, ruthenium catalysis continues to be important in both ADMET and ring closing metathesis chemistry. 

Sandell and others described determinations of ruthenium and osmium based on catalysis of the Ce(IV)-As(III) reaction. In both cases, the reaction rate is proportional to catalyst concentration. However, with ruthenium the rate is independent of [As(III)] and dependent on [Ce(IV)], whereas with osmium the rate is independent of [Ce(iy)] and dependent on [As(III)]. Although the complete reaction mechanisms have not been eluddated, one may infer that the rate-determining steps... 

The carbonyl [Ru3(CO),2] is a good cocatalyst for the low pressure hydroformylation of internal alkenes using the classic rhodium phosphine [HRh(CO)(PPh3),] system in the presence of an excess of triphenylphosphine (P/Rh = 200) (22). Starting from a mixture of hex-2- and hex-3-ene, the addition of [Ru3(CO),2l (Rh/Ru = 1/1) increased both the reaction rate and the n/iso ratio of heptanals. More recently, Poilblanc and coworkers (23) have prepared a mixed ruthenium-rhodium complex formulated as [CIRh(/i-CO)(//-dppm)2Ru(CO)2] (dppm is Ph2PCH2PPh2). This species shows catalytic activity in the hydroformylation of pent-l-ene at 40 bar (H2/C0= 1/1) and 75°C. Conversion to hexanals was 90% in 24 hours and the linearity reached 70%. No further report has appeared to determine the role of the two metals in this catalysis. 

Reactions of arenes carrying a coordinating substituent with alkenes may give alkylated derivatives when catalysed by ruthenium biscarboxylate complexes. Experiments with deuterium-labelled compounds indicate that carbon-hydrogen metallation is reversible, so that reductive elimination from intermediates such as (90) is rate determining. Carboxylate-assisted ruthenium catalysis also allows the reaction of 2-arylpyridines with methylenecyclopropane to give derivatives, (91), in which the cyclopropane ring is conserved. ... 

There has been considerable recent interest in the reductions of [Fe(CN)6]. The electron exchange with A -propyl-l,4-dihydronicotinamide is catalyzed by alkali metal ions. The increase in reaction rate is attributed to the polarizability of M and the observed linear free energy relationship is discussed. An outer-sphere mechanism is postulated in the oxidation of phenothiazines. A free radical mechanism involving the alcohol anion is invoked in the reaction of 1-and 2-propanol in aqueous alkaline media, the kinetic order being unity for [Fe(CN)6], OH, and alcohol concentrations. Catalysis by metal ions has also been observed in the presence of copper(II) and ruthenium(III) complexes. In the oxidation of a-hydroxypropionic acid in alkaline media,a Cu(II)-ligand complex is formed which is oxidized slowly to a copper(III) species. Alkaline ferricyanide oxidizes butanol, the process being catalyzed by chlororuthenium complexes.The rate law is consistent with oxidation of the alcohol by the Ru(III) followed by reoxidation of the catalyst by [Fe(CN)6]. The rate law is of the form ... 

However, the intermediate product during the oxidation of methanol makes the catalysis complicated, and the reaction rate for making CO out of methanol solution is slow. Moreover, a second metal such as Ruthenium (Ru) is required, which is explained by the bifunctional mechanism. In other words, activation of water or surface oxides at lower potentials makes the CO absorption bond weaker on the PtRu alloy catalyst. In the meantime, oxidative methanol dehydrogenation occurs on Pt by oxygen-like species on Ru, so that species on Pt-Ru pair sites enables the continuous oxidation of CO to CO. ... 

Solutions of ruthenium carbonyl complexes in acetic acid solvent under 340 atm of 1 1 H2/CO are stable at temperatures up to about 265°C (166). Reactions at higher temperatures can lead to the precipitation of ruthenium metal and the formation of hydrocarbon products. Bradley has found that soluble ruthenium carbonyl complexes are unstable toward metallization at 271°C under 272 atm of 3 2 H2/CO [109 atm CO partial pressure (165)]. Solutions under these conditions form both methanol and alkanes, products of homogeneous and heterogeneous catalysis, respectively. Reactions followed with time exhibited an increasing rate of alkane formation corresponding to the decreasing concentration of soluble ruthenium and methanol formation rate. Nevertheless, solutions at temperatures as high as 290°C appear to be stable under 1300 atm of 3 2 H2/CO. 

The iodide reaction was first studied by incremental addition of thiosulphate ( The method of constant rates ) . This use of the method was attacked by Bell . Bray s work established the two rate terms shown in Table 28. The reaction has also been studied in the presence of arsenite , which does not interfere as thiosulphate does, and kj =3.3x10 l .mole .sec at 25 °C. Catalysis of the reaction has been demonstrated in presence of vanadium(IV) , ruthenium(III) , rhenium(II) osmium tetroxide " and iron(III) , together with retardation by Mn(II) - Ni(II) and chloride . These measurements were made at moderate acidities and appear to involve quite different dependence of rate on acid concentration from the reaction in absence of catalyst (half-order for Ru(OH), first-order for Re ). The mechanisms may also be quite different. 

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