Metal—carbon triple bonds synthesis

Kreis from 16 and BI3) [43] that the seminal paper about the synthesis and characterization of the first carbyne metal complex was submitted to Angewandte Chemie. When Fischer went to Stockholm in December 1973, he had a ball-and-stick model of Cr(CCH3)(CO)4l in his luggage, demonstrating to the audience of his Nobel Lecture that a transition metal compound with a metal-carbon triple bond is not a fantasy, but really exists. 

The chemistry of metal-carbon triple bonds has developed considerably during the late 1980s. The synthetic basis was broadened, the utility of high-valent metal alkylidynes in metathesis reactions was further developed and refined, and the potential of low-valent carbyne complexes for applications in organic synthesis has become more apparent. The discovery of novel iridium alkylidyne complexes indicates that the full range of metal-carbon triple bonds is not yet known. We can therefore expect that future work in this area of organometallic chemistry will lead to new discoveries with fundamental implications and practical applications. 

Transition metal carbyne complexes are described by the general formula L M=CR where the carbyne ligand (=CR) is bonded to the metal by a metal-carbon triple bond. Transition metal carbene complexes have found numerous applications in synthetic organic chemistry through a variety of carbene transfer and cycloaddition reactions [17]. In contrast, carbyne (L M=CR) and vinylidene (L M=C=CRR ) complexes have far fewer applications, in part because their overall chemistry is significantly less developed [18]. Addition reactions to transition metal vinylidene complexes will be discussed in Chapter 21. The first successful synthesis of a carbyne complex was reported by Fischer and co-workers in 1973 [Eq. (8) 19]. Subsequently, many other carbyne complexes have been synthesized by the classic route of Fischer or by new synthetic methods [20]. 

Nine years after Fischer s report of the first stable transition metal-carbene complex, the first report was made of the synthesis of complexes containing a transition metal-carbon triple bond fittingly this report was also made by the Fischer group.15 Carbyne complexes have metal-carbon triple bonds, and they are formally analogous to alkynes.16 Many carbyne complexes are now known examples of carbyne ligands include the following. 

The first alkylidyne-metal complexes were prepared by Fischer et al. more than 30 years ago. Since this pioneering event, the chemistry of the transition metal-carbon triple bond present in such complexes has developed into a major field of research and though the poly(pyrazolyl)borate ligands were discovered 7 years prior to the synthesis of the first alkylidyne complexes, their importance and significance in this field has only more recently been truly appreciated. 

Nucleophiles react with carbyne complexes to promote (or trap) carbyne-carbonyl coupling products, attack the metal-carbon triple bond, or displace a substituent on the carbyne carbon. Complexes of the form Tp M( = CR)(CO)2 are coordinatively saturated and in the case of Tp = Tp, the metal also enjoys a substantial degree of steric protection. Accordingly, the reaction of these complexes with nucleophiles does not, in general, involve attack at the metal but rather at a coligand. Attempted synthesis of Tp W( = CMe)(CO)2 via reaction of MeLi with the... 

The first synthesis of a complex containing a metal-carbon triple bond was reported in 1973 [1]. Since then, numerous carbyne complexes have been prepared. In recent years, the study of the reactivity of these complexes has attracted considerable interest [2]. E.g. carbyne complexes have extensively been used as building blocks in the synthesis of transition metal clusters [3]. The coupling of carbyne ligands with CO or isocyanide ligands has also been studied in detail [4]. However, the number of reports on the use of carbyne complexes in synthetic organic chemistry is rather limit in contrast to carbene complexes which have found many applications in the synthesis of carbo- and heterocycles [5]. 

Compared to their carbene cousins, carbyne complexes, containing a metal-carbon triple bond, have seen very little development. One example is an interesting phenol synthesis by the reaction of a diyne 8.478 with a carbyne complex (Scheme 8.128). The reaction is remarkable for the low temperature at which it proceeds. " As in the Dotz reaction, the aromatic carbon atom bearing the hydroxyl substituent is derived from a carbon... 

Haloboration Reactions. The haloboration of carbon-carbon triple bonds provides another entry point for the synthesis of organoboranes. A wide variety of haloboranes including BBrs, 9-BBN-Br, and 9-BBN-l has been found to react with terminal alkynes to produce (Z)-2-halo-l-aIkenylboranes. The reaction occurs in a stereo-, regio-, and chemoselective fashion specifically with terminal alkynes and has been used to synthesize numerous substituted olefins and related compounds. Diboration reactions of alkynes with B2CI4 are also well known. However, more convenient transition-metal-catalyzed procedures with the less reactive aUcoxy substituted diboranes B2(OR)4 have recently been developed. 

Ohmura, K. Kijima, M. Shirakawa, H. Synthesis of conducting polymers with conjugated carbon-carbon triple bonds by electrochemical condensation of acetylene derivatives catalyzed by copper complex. Synth. Metals 1997, 84, 417-418. 

Hoffmaim-La Roche has produced -carotene since the 1950s and has rehed on core knowledge of vitamin A chemistry for the synthesis of this target. In this approach, a five-carbon homologation of vitamin A aldehyde (19) is accompHshed by successive acetalizations and enol ether condensations to prepare the aldehyde (46). Metal acetyUde coupling with two molecules of aldehyde (46) completes constmction of the C q carbon framework. Selective reduction of the internal triple bond of (47) is followed by dehydration and thermal isomerization to yield -carotene (21) (Fig. 10). 

Silver belongs to the late transition metals and, like gold, favors coordination to C=C triple bonds. A lot of silver-containing organometallic complexes, where silver-alkyne interactions assist the assembly of the complexes, are known. None of these complexes, however, was applied to efficient carbon-carbon bond formation in organic synthesis. 

For reviews of hydrocarboxylation of double and triple bonds catalyzed by acids or metallic compounds, see Lapidus Pirozhkov Russ. Chem. Rev. 1989, 58. 117-137 Anderson Davies, in Hartley Patai, Ref. 422, vol. 3, pp. 335-359, pp. 335-348 in Falbe New Syntheses with Carbon Monoxide Springer New York, 1980, the articles by Mullen, pp. 243-308 and Bahrmann, pp. 372-413 in Wender Pino Organic Syntheses via Metal Carbonyls, vol. 2 Wiley New York, 1977, the articles by Pino, Piacenti Bianchi, pp. 233-296 and Pino Braca pp. 419-516 Eidus Lapidus Puzitskii Nefedov Russ. Chem. Rev. 1973, 42, 199-213, Russ. Chem. Rev, 1971, 40. 429-440 Falbe Carbon Monoxide in Organic Synthesis, Springer Berlin. 1970, pp. 78-174. 

Metal-mediated intramolecular addition of silyl enolates to alkynes is also valuable for the synthesis of cyclic ketones. A stoichiometric amount of HgCl2 or EtAlCl2 effectively promotes the cycloalkenylation via anti-addition to alkynes (Equations (87) and (88)).319 320a The -addition mode can be explained by a metal coordination to the triple bond and subsequent attack of the enolate moiety from the opposite side to the metal. The resultant alkenylmetals can be used for carbon-carbon and carbon-heteroatom bond formation as well as protonation. 

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