Metal-alkyne complexe reactions

Schore, N. E. Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 703-739. 

Schore NE (1991) Org React 40 1 Schore NE (1991) The Pauson-Khand reaction. In Trost BM (ed) Comprehensive organic synthesis, vol 5. Pergamon Press, Oxford, p 1037 Pauson PL (1985) Tetrahedron 41 5855 Schore NE (1995) Transition metal alkyne complexes Pauson-Khand reaction. In Abel EW, Stone EGA, Wilkinson G (eds) Comprehensive organometallic chemistry II, vol 12. Pergamon Press, Oxford, p 703 Iwasawa N (1992) Chem Lett 473... 

Chung CY. Transition metal alkyne complexes the Pauson-Khand reaction. Coord. Chem. Rev. 1999 188 297-341. Brummond KM, Kent JL. Recent advances in the Pauson-Khand reaction and related (2 + 2+1) cycloadditions. Tetrahedron 2000 56 3263-3283. 

Keun Chung, Y. Transition metal alkyne complexes the Pauson-Khand reaction. Coord. Chem. Rev. 1999, 188, 297-341. 

Eor a recent review, see Schore NE (1995) Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Louis Hegedus (vol ed), Abel EW, Stone EGA,Wlkmson G (eds) Comprehensive OrganometaUic Chemistry II. Pergamon, Kidlington, vol 12,703... 

The resulting expansiveness of this field prevents a comprehensive review. It is our intention, therefore, to highlight some of the most important and recent developments in the chemistry of metal-alkyne complexes. We will largely limit our coverage to that chemistry which clearly involves the intervention of metal- i-bonded alkyne complexes. We thus exclude the chemistry of metal-acetylide derivatives and mention only briefly the burgeoning number of metal-catalyzed reactions for which alkyne complexes are only presumed intermediates. Prior reviews of metal-alkyne chemistry may be consulted for more complete coverage of the older literature [3]. 

Alkynes enter into a remarkable variety of metal-promoted coupling reactions with olefins, alkynes, and other unsaturated species leading to a diversity of cyclization, oligomerization, and polymerization products of synthetic value. In many instances alkyne complexes are presumed intermediates in these reactions but often this has not been proven. The reader is referred to other reviews [95-97] for more complete coverage of this topic. We briefly summarize here the most useful of these processes, highlighting those systems in which metal-alkyne complexes have been demonstrated as intermediates. 

We conclude our reaction survey with Scheme 4-66, which summarizes the known reactivity characteristics of metal-alkyne complexes. 

Reaction of a metal alkyne complex or cluster with additional metal fragments. 

Certain metal alkyne complexes are capable of initiating the polymerization of dialkylacetylenes, no doubt first being converted into metal carbene complexes. For complexes of the type Mo(=CCMe3)(OR)3 the nature of OR is critical for a substrate such as EtC=CPr. If OR is OCMe3, there is no reaction if OR is OCMe(CF3)2, the acetylene is metathesized only if OR is OCHMe2 or OCH2CMe3 does the acetylene polymerize (McCullough 1984, 1985). 

Transition metal alkyne complexes also react with nucleophiles, in this case to generate CT-vinyl complexes. There are fewer stable alkyne complexes of higher oxidation state or cationic metals than olefin complexes. Because these types of alkyne complexes are most susceptible to nucleophilic attack, less information is available on tfiis reaction than on nucleophilic attack on coordinated alkenes. Nevertheless, reactions of several cationic alkyne complexes with nucleophiles have been reported, and a few examples are presented here. 

Reaction of the cyclopropylalkynes (151) with water (or methanol), catalysed by (Tf2N)3Fe, proceeds with the cyclopropane opening, which generates the homo allenic cation (153), whose hydration affords (154). By contrast, catalysis by (Tf2N)Au, (Tf2N)Ag, and/or (Tf2N)2Hg proceeds as an uneventful hydration to produce ketones (155). This example clearly demonstrates the subtle electtonic differences in the intermediate metal-alkyne complexes 152). ... 

It is our intent in this chapter to point out the potential utility of transition metal-alkyne complexes and cluster compounds which may be derived from them as reagents in organic synthesis. In the interests of brevity, we have chosen to limit the discussion to the organic chemistry of isolable acetylene complexes. Those reactions of particular synthetic promise for which alkyne complexes have not been demonstrated to be intermediates, but whose course very likely involves such complexes, will be mentioned only briefly. 

The reaction of alkenes with alkenes or alkynes does not always produce an aromatic ring. An important variation of this reaction reacts dienes, diynes, or en-ynes with transition metals to form organometallic coordination complexes. In the presence of carbon monoxide, cyclopentenone derivatives are formed in what is known as the Pauson-Khand reaction The reaction involves (1) formation of a hexacarbonyldicobalt-alkyne complex and (2) decomposition of the complex in the presence of an alkene. A typical example Rhodium and tungsten ... 

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