Carbene complex chromium ruthenium

Initial reports of cross-metathesis reactions using well-defined catalysts were limited to simple isolated examples the metathesis of ethyl or methyl oleate with dec-5-ene catalysed by tungsten alkylidenes [13,14] and the cross-metathesis of unsaturated ethers catalysed by a chromium carbene complex [15]. With the discovery of the well-defined molybdenum and ruthenium alkylidene catalysts 3 and 4,by Schrock [16] and Grubbs [17],respectively, the development of alkene metathesis as a tool for organic synthesis began in earnest. 

Barbier reaction Samarium(II) iodide, 270 Benzoannelation Chromium carbene complexes, 82 Dicarbonylcyclopentadienylcobalt, 96 Ethyl (Z)-3-bromoacryIate, 130 Grignard reagents, 138 Methyl acrylate, 183 Methyllithium, 188 Ruthenium(III) chloride, 268 Benzoin condensation Benzyltriethylammonium chloride, 239 3-EthyIbenzothiazolium bromide, 130 Benzoylation (see also Acylation) Cadmium, 60 Dibutyltin oxide, 95 Birch reduction Birch reduction, 32... 

Enyne intramolecular metathesis reactions, of the type shown in equation 61, can be very useful in organic synthesis. A number of such reactions, catalysed by tungsten or chromium carbene complexes, have been reported634,635,737 - 740. The ruthenium carbene catalysts 18-20 (Table 2) are likely to be increasingly used for this purpose because of their stability, ease of handling and good yields, as in the synthesis of various 5-, 6- and 7-membered heterocycles, e.g. equation 67741. 

Ring closing metathesis using Grubbs ruthenium catalyst has also been used in a novel preparation of the Fischer-type chromium carbene complex 10 from the precursor 9 in >98% yield [01SL757], Similarly, the TV-substituted tetrahydroazepine 12 could be accessed in near quantitative yield from 11 [01JOC3564],... 

The reaction mechanism is similar to the one employed by Raubenheimer el al. for their chromium(O) thiazol-2-ylidene complex [48], In the case of the ruthenium imidazol-2-ylidene complexes, 4,5-dimethylimidazole stabilised the carbene complex compared with unsubstituted imidazole. Likewise, the carbonyl ligand in trans position was necessary to isolate and crystallise the complex. This can be expected, when an excellent o-donor (NHC) is trans to an excellent tr-acceptor (CO). 

Katz and Sivavec, who used a Fischer tungsten carbene complex as a catalyst. After the report of a chromium-catalyzed reaction by Mori et al., they disclosed the utility of ruthenium-carbene complexes for the enyne metathesis (Scheme 24.44). The Ru-carbene-catalyzed reaction under the ethylene atmosphere brought about good results in the case of terminal alkyne substrates such as 164b. ... 

The first ene-yne metathesis was reported by Katz etal. [3], who used a Fischer tungsten-carhene complex. Then, Mori et al. reported a chromium-catalyzed ene-yne metathesis [4]. It was later found that the ruthenium-carhene complexes [Ru]-IV and [Ru]-I were very effective for ene-yne metathesis [5]. The reaction would proceed via a [2 -T 2]-cycloaddition of a ruthenium-carhene complex 3 with an alkyne part to produce ruthenacyclobutene 4, and ring opening of this latter species affords a ruthenium carbene complex 5, which reacts with an alkene part to produce ruthenacyclobutane 6. Subsequent ring opening of 6 gives a cychzed compound 2, and a ruthenium-carbene complex is regenerated (Scheme 6.1, Route 1). The other mechanism considered also involves at first reaction of the... 

Beyond the use of the Fischer-type chromium carbenes as stoichiometric reagents and the Grubbs-type ruthenium carbenes as versatile catalysts for the preparation of organic compounds, Schrock s molybdenum and tungsten complexes of the general composition M(CHR)(NAr)(OR )2 (and derivatives thereof) and... 

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