Carbynes transition metals

H. Fi.scher, C. Troll, and J. Schleu, in Transition Metal Carbyne Complexes, (F. R. Kreissl ed.), p.79. Kluwer Academic Publishers, Dodrecht, 1993. 

The importance of transition metal carbene complexes (compounds with formal M=C bonds) and of transition metal carbyne complexes (compounds with formal M=C bonds) is now well appreciated. Carbene complexes are involved in olefin metathesis (7) and have many applications in organic synthesis (2), while carbyne complexes have similar relevance to... 

BONDING MODELS AND REACTIVITY PATTERNS FOR TRANSITION METAL CARBENE AND CARBYNE COMPLEXES... 

The wealth of empirical information collected for transition metal carbene and carbyne complexes may be best interpreted within the framework of sound theoretical models for these compounds. Perhaps the most significant contribution made by the theoretical studies of carbene and carbyne complexes concerns an understanding of the reactivity patterns they display. In this section the relationship between bonding and reactivity is examined, with particular emphasis being given to the ways in which studies of Ru, Os, and Ir compounds have helped unify the bonding models applied to seemingly diverse types of carbene and carbyne complexes. 

The chemistry of transition metal-carbyne complexes is rather less developed than the chemistry of carbene complexes. This is almost certainly because reactions which form new carbyne complexes are relatively rare when compared with those forming metal carbenes. The few theoretical studies of carbyne complexes which are available indicate that close parallels exist between the bonding in carbene and carbyne compounds. These parallels also extend to chemical reactivity, and studies of Group 8 complexes again prove instructive. 

The similarity, then, between carbene and carbyne complex chemistry of Group 8a transition metals, as well as of Group 6a and 7a metals, is apparent. 

Transition metal carbyne complexes are still relatively uncommon as only a few synthetic approaches to these compounds has proved generally applicable. In addition to making the initial characterization (723), the Fischer group has made the largest contribution to carbyne complex chemistry, with some 200 mononuclear complexes of Group 6 and 7 metals having been prepared. 

There are, broadly speaking, three general routes to transition metal carbyne complexes ... 

The similarity between the bonding models for transition metal carbene and carbyne complexes was noted in Section II. That the reactivity of the metal-carbon double and triple bonds in isoelectronic carbene and carbyne complexes should be comparable, then, is not surprising. In this section, the familiar relationship between metal-carbon bond reactivity and metal electron density is examined for Ru and Os carbyne complexes. 

Couturier JL, Leconte M, Basset JM (1993) Transition Metal Carbyne Com 392 39... 

Table 7.10 Calculated BDEs De (Do) (kcal/mol) of transition metal carbyne complexes.3...

A major breakthrough in the synthesis of transition metal methylene and methylidyne complexes has been achieved by Stone and his group it originates from the simple idea that M=C double bonds in Fischer-type carbenes and M=C triple bonds in carbyne systems should add to low valent metal complexes as do C=C and C=C linkages, respec-... 

The rapid development of the chemistry of transition metal complexes containing terminal carbene (A) or carbyne (B) ligands (7) has been followed more recently by much research centered on bridged methylene compounds (C) (2). The importance of /t-methylidyne complexes, whether in recently established binuclear examples (D), the well-known trinuclear derivatives (E), or the unusual complexes (F), has also become apparent. All are based on one-carbon (C,) fragments, and considerable interest is centered on their possible significance as models for intermediates in surface-catalyzed reactions between carbon monoxide and hydrogen (Fischer -Tropsch reactions) and related processes. These topics have been extensively ... 

I hope that I have been able to demonstrate, with this small selection of our newest research results, what a variety of reaction possibilities the chemistry of transition metal carbene complexes display. In the following I review an area whose development we have made most recently our special task, namely that of transition metal-carbyne complexes. 

In the realm of all-carbon ligands in the formation of transition-metal complexes, the naked carbon atom holds a special position. Based on the geometry of metal-carbon interaction, these compounds can be divided into four classes terminal carbide (I), 1,3-dimetallaallene (II), C-metalated carbyne (III), and carbido cluster (IV) ... 

Note that the transformation of metal carbene vice versa, during polymerisation occurs as in the case of cycloalk-ene ring-opening metathesis polymerisation. Considering the mechanism of metathesis polymerisation of acetylenic monomers, it is worth noting that catalysts containing a transition metal carbyne bond (Mt=C) can induce polymerisation only when this bond is transformed into the respective metal carbene bond (Mt=C) [39],... 

A number of transition metal-induced acetylene-vinylidene rearrangements44 54 and a carbene-carbyne rearrangement53 involving 1,2-silyl migration have been reported. 

From a mechanistic point of view (Scheme 3), a transition metal carbyne undergoes a [2+2] cydoaddition with an alkyne to form a metallacydobutadiene as an intermediate, or possibly as a transition state. The four-membered ring then cycloreverts, expelling a di-substituted alkyne with regeneration of a catalytically active carbyne complex. In a subsequent... 

Scheme 8.5 Preparation of the first Fischer-type transition metal carbyne 19 from the...

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. 

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