Modified ruthenium catalysts

Only a few publications dealing with this subject can be found in the literature. Hydrogenation of diketo esters A with chirally modified ruthenium catalysts resulted in mixtures of syn- and anti-dihydroxy esters C with varying enantiomeric excesses [5], A notable exception to this is represented by the recent work of Car-pentier et al., who succeeded in controlling the reduction of methyl 3,5-dioxohex-anoate at the initial step, namely the reduction of the P-keto group. The enantiomeric excess achieved was, nevertheless, limited to 78% at best [5a]. 

Because propylene is frequently quite expensive and in short supply, BASF has applied for a patent on a new route to n-butyraldehyde and/or n-butanol starting from butadiene. They found that a homogeneous palladium acetonylacetonate catalyst with phosphine ligands would allow butadiene to react with n-butanol to produce l-n-butoxy-2-butene (nBB). nBB will then react with more n-butanol to produce the acetal, using a homogeneous phosphine modified ruthenium catalyst. The acetal can be hydrolyzed to n-butyraldehyde, or hydrogenated and hydrolyzed to n-butanol using the same Ru catalyst. 

Ramaswamy N, Allen RJ, Mukerjee S (2011) Electrochemical kinetics and X-ray absorption spectroscopic investigations of oxygen reduction on chalcogen-modified ruthenium catalysts in alkaline media. J Phys Chem C 115(25) 12650-12664. 

Triphenylphosphine-Modified Ruthenium Catalyst. The mechanism of olefin hydroformylation using Ru(CO)3(P(C6H5)3)2 as the catalyst precursor has been explained by the classical hydride-, alkyl-, and acyl-complex sequence involving Ru(H)2(CO)(P(C6H5)3) as the principal active catalytic species (125). 

In 1987, Murata s group [12] showed the potential of modified ruthenium catalysts. Ru3(CO)j 2 mixed with l-methyl-3-ethyl-benzimidazolium bromide and NEtg gave at 150 °C and a syngas pressure of 10 MPa up to 70% yield of ethylene glycol. 

The modified BINAP catalyst 5 has been used for the hydrogenation of a number of analogues of substrate 1 (substrates 32-35, Fig. 30.8 Table 30.6), though again, enantioselectivities were modest [4]. Substrate 31 has also been hydrogenated with a ruthenium-BINAP-hydride cluster with low selectivity (11% ee) [27]. 

Nickel, cobalt, copper, ruthenium, and copper-ruthenium catalysts modified with optically active amino acid or hydroxy acid have been extensively investigated by Klabunovskii s group since 1964 (82). However, those catalysts have been reported to have lower EDA than that of MRNi. 

In some instances removal of ruthenium from the desired product has proved difficult. To overcome this problem, there are several reported ways to remove the ruthenium catalyst after the olefin metathesis reaction is complete. The first and most common is addition of a modifier or adsorbent followed by chromatography. The additives include dimethyl sulfoxide (DMSO), triphenylphos-phine oxide,74 or activated carbon.75 Although this is generally not suitable for commercial production, it can be quite effective. A convenient alternative is the use of Brockmann I basic alumina, followed by simple filtration through a bed of filter agent such as activated carbon. This method is capable of reducing ruthenium levels down to less than 20 ppm.76... 

It appears that an electronic effect may be modifying the nature of the active sites on the catalyst. The increased selectivity observed on adding alkali ions to ruthenium catalysts supports this conclusion. 5-118... 

The fact that water-soluble sulfonated phosphines may combine the properties of a ligand and a surfactant in the same molecule was first mentioned in 1978 by Wilkinson etal. [11] in their study of the hydroformylation of 1-hexene using rhodium and ruthenium catalysts modified with TPPMS (triphenylphosphine mono-... 

J Struijk, JJF Scholten. Selectivity to cyclohexenes in the liquid phase hydrogenation of benzene and toluene over ruthenium catalysts, as influenced by reaction modifiers. Appl Catal A 82 277-287,1992. 

Cyclohexene can be produced by partial hydrogenation of benzene over a ruthenium catalyst at ambient temperature and pressure. In the presence of reaction modifiers, selectivities up to only 10% have been achieved [1,2]. 

When supported on y-alumina (modified with 30% w/w K as KOH) this [Ru3Ni] catalyst had activity in ammonia synthesisj It was again more effective than the corresponding [OssNi] catalyst (prepared from the analogous [Os3Ni(/<3-H)Cp(CO)9]) but the monometallic ruthenium catalyst derived from [Ru3(CO)i2] was the most active. ... 

Coq, Figueras and their associates have conducted wide-ranging investigations of surface modification of supported platinum, rhodium, and especially ruthenium catalysts by treating them when hydrided with alkyl compounds of aluminium, zinc, antimony, germanium, tin or lead. The purpose of this work was to explore the locations of the modifying atoms on the surface of the active metal particles, and to see whether in any case there was evidence for the selective blocking of sites on either low co-ordination number... 

Chapter 4 contains the background of the development of effective modified Ni catalysts, discusses the methods of preparation of different types of stable and active metal catalysts, and discusses the selection of effective modifiers and the most suitable substrate molecules having practical interests. On the basis of these studies a reaction mechanism for the new effective catalytic systems was suggested and experimentally examined. The Chapter discusses the preparation variables for the development of this new type of effective chiral modified Ni catalyst, the supported metal catalysts, the chiral modified bimetal and multimetal catalysts including rare earth metals, and the new chiral modified nickel-ruthenium and palladium catalysts. Attempts are undertaken to elucidate the mechanism of enantioselectivity and to reveal the general regularities of asymmetric actions. 

---