Ruthenium catalysis coupling

Under the conditions of ruthenium catalysis, alcohols and allylic acetates couple to form enones,... 

Intramolecular variants of the Alder-ene type couplings between alkynes and alkenes have been extensively explored by means of palladium catalysis [73]. Recently, such a cycloisomerization of enynes was also accomplished with ruthenium catalysis (Scheme 4.32) [74]. 

A protocol for cross-dehydrogenative oxidative coupling of the 2-arylpyridine 4 with the cycloalkane 5 under ruthenium catalysis was elegantly developed by Li and... 

Scheme 17.4 C-H/C-X coupling of 2-phenylpyridine derivatives with aryl halides under ruthenium catalysis.

Scheme 3.10 Tandem alkene-alkyne cross-coupling reaction-intramolecular het-erocyclisation reaction catalysed hy a combination of ruthenium catalysis and chiral palladium catalysis.

Direct Silylation of Heteroarylcarbonyl Compounds. Under ruthenium catalysis vinyltrimethylsilane reacts to ortho silyl-ate heteroaryl carbonyl compounds directly in good yields (eqs 32 and 33). The reaction only works with heteroaromatic systems. The resulting aryltrimethylsilanes can be used to introduce electrophiles regioselectively through electrophilic desilyla-tion. The reaction also works with vinyltriethoxysilane, opening the possibility of silicon-based cross-coupling reactions. 

Trimethylsilylation of Vinylboronates. Vinylboronate esters react with vinyltrimethylsilane under ruthenium catalysis to give the I trimethylsilyl-l-boronylethylene (eq 34). Such a species could be used in Suzuki-type cross coupling reactions to prepare various a-substituted vinyltrimethylsilanes. ... 

Under ruthenium catalysis, oxidative coupling of a,a-disubstituted benzy-lamines with acrylates can be performed efficiently at room temperature to produce (isoindol-l-yl)acetic acid derivatives (Eq. (7.48)) [58]. The reaction takes place accompanied by free amino group-directed orffio-alkenylation and successive intramolecular cyclization. 

In general, an ester (or a carboxylate) is borne by the alkyne 80 (except for nickel where a second olefin inserts and extends the metaUacycle) while the substituents on the olefin 81 vary a great deal, depending on the catalyst. Scheme 42 illustrates the synthetic utility of this coupling in the case of ruthenium catalysis [75]. Here, the dienes 82 are recovered regioselectively, the stereoselectivity depending on the olefin stracture. 

Techniques for attaching such ruthenium electrocatalysts to the electrode surface, and thereby realizing some of the advantages of the modified electrode devices, have been developed.512-521 The electrocatalytic activity of these films have been evaluated and some preparative scale experiments performed. The modified electrodes are active and selective catalysts for oxidation of alcohols.5 6-521 However, the kinetics of the catalysis is markedly slower with films compared to bulk solution. This is a consequence of the slowness of the access to highest oxidation states of the complex and of the chemical reactions coupled with the electron transfer in films. In compensation, the stability of catalysts is dramatically improved in films, especially with complexes sensitive to bpy ligand loss like [Ru(bpy)2(0)2]2 + 51, 519 521... 

In this paper we disclose the syngas homologation of carboxylic acids via ruthenium homogeneous catalysis. This novel homologation reaction involves treatment of lower MW carboxylic acids with synthesis gas (C0/H2) in the presence of soluble ruthenium species, e.g., Ru02, Ru3(C0)12, H4Ru4(C0)12, coupled with iodide-containing promoters such as HI or an alkyl iodide (1). 

A number of transition metal complexes will catalyze the dehydrogenative coupling of organotin tin hydrides, R SnI I, to give the distannanes, RjSnSnRj.443 These metals include palladium,449 gold,450, hafnium,451 yttrium, and ruthenium.452 The catalyst that is most commonly used is palladium, often as Pd(PPh3>4, and the most active catalysts appear to be the heterobimetallic Fe/Pd complexes, in which both metals are believed to be involved in the catalysis.443... 

So far, catalytic systems in which the mediator plays the role of both catalyst and electron carrier have been considered. Figure 4.21 shows an example where these two roles are dissociated.21 The catalyst, in the sense of a chemical catalyst, is the Co(II) porphyrin embedded in the Nafion (a trademark of Dupont) film, while the electron are shuttled by the ruthenium hexamine 3 + /2+ couple attached electrostatically to the Nafion backbone. The catalytic reaction now involves two successive steps, as expected for a chemical catalysis process (see Sections 4.2.1 and 4.3.1), calling for the definition of two characteristic currents. One has the same... 

Ruthenium, cobalt and halogen are the key elements of this catalysis (2), although ruthenium in combination with halogen-containing zirconium and titanium derivatives is also effective (3). In the case of the Ru-Oo couple, the highest yields of acetic acid may generally be achieved with ruthenium oxide, carbonyls and complex derivatives in combination with various cobalt halides dispersed in low-melting quaternary phosphonium halide salts (2). 

While platinum and rhodium are predominantly used as efficient catalysts in the hydrosilylation and cobalt group complexes are used in the reactions of silicon compounds with carbon monooxide, in the last couple of years the chemistry of ruthenium complexes has progressed significantly and plays a crucial role in catalysis of these types of processes (e.g., dehydrogenative silylation, hydrosilylation and silylformylation of alkynes, carbonylation and carbocyclisation of silicon substrates). 

The unique versatility of ruthenium as an oxidation catalyst continues to provide a stimulus for research on a variety of oxidative transformations. Its juxtaposition in the periodic table and close similarity to the biological redox elements, iron and manganese, coupled with the accessibility of various high-valent oxo species by reaction of lower-valent complexes with dioxygen make ruthenium an ideal candidate for suprabiotic catalysis. 

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