Activity of ruthenium catalyst

Although the activities of ruthenium catalysts are much lower than that of chloroplatinic acid in the hydrosilylation of alkenes, RuCl2(PPh3)3 turned out to be an excellent... 

A. N. Basinska, L. KelpinAski, F. Domka, The effect of support on WGSR activity of ruthenium catalysts, Appl. Catal. A Gen. 183 (1999) 143-153. 

TOF of ammonia synthesis reaction and isotopic equilibrium rate of nitrogen molecule follow the order shown in Table 6.8. We can roughly estimate the performance of promoters from chemical property of element itself. The activity of ruthenium catalysts supported on AI2O3 is very low, while almost no activity is observed on activated carbon due to the acidicity of AI2O3 and absorption of electrons by activated carbon. 

It is reported that catal3dic activity of ruthenium catalyst is 10-20 times higher than that of iron catalyst by many sources including BP and Kellogg companies. For example, Kowalczyk et considered that the reaction rate on Ba-Cs-Ru 9.1/C is 25 times faster and on Ba-Cs-Ru 23.1/C is 50 times faster than that on iron catalyst (KMI) (Table 6.42). 

At 350°C (Fig. 6.68), the activity of ruthenium catalyst increases from 9.33% to 15% when the H2/N2 ratio is 3 and 0.5, indicating that the relative activity increases by 60%. Fishel et has also investigated the effect of H2/N2 ratio on the turnover frequency of ammonia (TOF). Similar results are shown in Fig. 6.69. The TOF increases in linearity with decrease of H2 molar fraction and increase of N2 molar fraction at 350° C. 

The influence of preparation procedure on structural and surface properties of magnesium fluoride support and on the activity of ruthenium catalysts for selective hydrogenation of chloronitrobenzene... 

Novel catalytic systems, initially used for atom transfer radical additions in organic chemistry, have been employed in polymer science and referred to as atom transfer radical polymerization, ATRP [62-65]. Among the different systems developed, two have been widely used. The first involves the use of ruthenium catalysts [e.g. RuCl2(PPh3)2] in the presence of CC14 as the initiator and aluminum alkoxides as the activators. The second employs the catalytic system CuX/bpy (X = halogen) in the presence of alkyl halides as the initiators. Bpy is a 4,4/-dialkyl-substituted bipyridine, which acts as the catalyst s ligand. 

The initial steep rise can be attributed simply to activation of the catalyst precursor. The amount of base corresponds approximately to one equivalent of KOH for the ruthenium catalyst and two equivalents for the rhodium catalyst. Activation could result from hydroxide attack as in (5) and (6) for rhodium and (10) for ruthenium ... 

We found little difference between the activities of this catalyst with K2CO3 and with KOH. However, a pronounced dependence on pressure was seen for a six-fold decrease in CO pressure, the activity increased by a factor of 2.5. This tendency is in marked contrast to the activity increase with increasing CO pressure observed with ruthenium carbonyl. 

Synthesis, Structure, Mechanism and Activity of Ruthenium-Based Metathesis Catalysts... 

The olefin binding site is presumed to be cis to the carbene and trans to one of the chlorides. Subsequent dissociation of a phosphine paves the way for the formation of a 14-electron metallacycle G which upon cycloreversion generates a pro ductive intermediate [ 11 ]. The metallacycle formation is the rate determining step. The observed reactivity pattern of the pre-catalyst outlined above and the kinetic data presently available support this mechanistic picture. The fact that the catalytic activity of ruthenium carbene complexes 1 maybe significantly enhanced on addition of CuCl to the reaction mixture is also very well in line with this dissociative mechanism [11] Cu(I) is known to trap phosphines and its presence may therefore lead to a higher concentration of the catalytically active monophosphine metal fragments F and G in solution. 

There is much current excitement and activity in the field of homogeneous hydrogenation using ruthenium catalysts. This is reflected in the recent, explosive increase in the number of research publications in this area, now rivaling those for rhodium catalysts (Fig. 3.1). Meanwhile, the price of rhodium metal has risen dramatically, becoming about ten times that of ruthenium, on a molar basis. The number of reports on the use of osmium catalysts has remained low, partly because of the higher price of osmium compounds - about ten times that of ruthenium - and partly because the activity of osmium catalysts is often lower. 

Water has been shown to enhance the activity of ruthenium and rhodium catalysts in both the TEAF and potassium formate systems [34, 36, 52]. The aqueous systems enable much simpler control of pH this is important, as Xiao has found that a low pH markedly slows the reaction [52]. The pH at which this occurs corresponds with the pKa of formic acid (i.e., 3.7), implying that the formate anion is required for complexation with the catalyst. Xiao has proposed two possible catalytic cycles - one that provides poor ee-values at low pH as a result of ligand decomplexation, and another that gives high ee-values at high pH. 

Recent mechanistic work has shown that 16 e Ru methylene complexes (such as bisphosphine 11) are slow to re-enter the catalytic cycle. Their reluctance to initiate can result in competitive decomposition see Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts, M.S. Sanford, J.A. Love, R.H. Grubbs,/. 

These observations led to the catalytic application of well-defined ruthenium alkyUdenes, some of them freely soluble and sufficiently stable in water (Scheme 7.9) although their stability was found somewhat less in aqueous solutions than in methanol [21,27,28], With these catalysts a real living ROMP of water-soluble monomers could be achieved, i.e. addition of a suitable monomer to a final solution of a quantitative reaction resulted in further polymerization activity of the catalyst [28], This is particularly important in the preparation of block copolymers. 

Ruthenium(n) systems containing imidazol-2-ylidene or imidazolidin-2-ylidene have been used to catalyze the synthesis of 2,3-dimethylfuran starting at (Z)-3-methylpent-2-en-4-yn-l-ol [Eq. (54)]. The activity of the catalyst strongly depends on the nature of the NHC ligand. Benzimidazolin-2-ylidenes give the best results for this transformation. Similar systems have also been used for olefin metathesis reactions. ... 

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