Homogeneous ruthenium catalyst

In the most economically efficient route to indoles reported this past year, Al-substituted anilines 68 were reacted with triethanolamine in the presence of a homogeneous ruthenium catalyst to give the corresponding 1-substituted indoles 69 <96SC1349>. 

Hydrogenation of Carbon Monoxide to Methanol and Ethylene Glycol by Homogeneous Ruthenium Catalysts... 

Notwithstanding these excellent results, there is still some room for further improvement. All of these systems require anaerobic conditions, owing to their air sensitivity, and consequently cannot be reused. Indeed all of these systems involve significant (from a cost point of view) amounts (2-5 mol%) of a homogeneous ruthenium catalyst, which is difficult to recycle. An interesting recent development in this context is the report, by Kim and coworkers [19], of an air-stable, recyclable catalyst that is applicable to DKR at room temperature (Fig. 9.8). 

A remarkable application of reactions of this type would be if carbonylation with CO is replaced by reaction with CO2. An example of this is the use of sc CO2 in the catalytic production of dimethylformamide (DMF), a very important organic solvent. The present industrial production of DMF is based on the carbonylation of dimethylamine in the presence of methanol. Recent studies have shown that DMF can also be produced by reacting dimethylamine, sc CO2, and hydrogen in the presence of a homogeneous ruthenium catalyst (Jessop et al., 1994a). Reactions of this type can add a new dimension to the more conventional carbonylation by CO in the presence of a homogeneous catalyst (see Chapter 8). 

Initial attempts were made by ter Halle et al.[7] to convert the homogeneous ruthenium catalyst into a heterogeneous catalyst by incorporating the metal center in a solid support using polymerizable diamine ligands. Unfortunately, both the conversions and % ee s for the transfer hydrogenations were low compared to the... 

For the cross-metathesis reactions we used two different homogeneous ruthenium catalysts one multicomponent catalyst prepared in situ, and the other catalyst consisting of one single component. Both are based on ruthenium(II) and the latter can be isolated in pure form. Figure 1 shows the ruthenium catalysts that were used in cross-metathesis reactions to synthesize silicon-containing ot,(o-dienes. 

This chapter will focus almost exclusively on alkene metathesis catalyzed by well-defined homogeneous ruthenium-catalyst systems and is divided into three sections (1) a discussion of how precatalyst structure affects the rate and mechanism of initiation in two key series of metathesis precatalysts (2) a discussion of how substrate structure, both close to and remote from the alkene termini, affects the rate and selectivity of alkene metathesis in synthetic chemistry and (3) the tools that have been used by experimental and theoretical chemists to study alkene metathesis reactions. In each case, the discussion will be focused on the specific topics interested readers are referred to a recent article which covers a wider range of the mechanistic aspects of alkene metathesis with ruthenium complexes, albeit in less depth. 

Bui The K, Concilio C, Porzi G (1981) Cyclization of alpha, omega aliphatic diamines and conversion of primary amines to symmetrical tertiary amines by a homogeneous ruthenium catalyst. J Org Chem 46(8) 1759-1760... 

Another alternative to the in situ generation of syngas is the reaction of carbon dioxide with hydrogen (reversed water gas shift = RWGS). A particular activity in this respect displays homogeneous ruthenium catalysts (see also Section 1.6). 

Additional examples of nitrile hydration reactions catalyzed by homogeneous ruthenium catalysts in organic media are (Scheme 8) (1) The hydration of benzoxazolylacetonitrile by the arene-ruthenium(II) dimer [ RuCl(p-Cl)(r -p-cymene) 2], which led to benzoxazolylacetamide in high yield [58], and (2) the asymmetric hydration of a-benzyl-a-methylmalononitrile by the chiral catalysts 13 [59]. Modest yields and low enantiomeric excesses were obtained in this latter reaction. However, we must note that this is the first example of a nonenzymatic asymmetric nitrile hydration process reported to date in the literature. 

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