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Carbyne reactions with nucleophiles

The reactions of Fischer and Schrock carbyne complexes are of interest because they may act as intermediates in chemical synthesis. Typical reactivity of carbyne complexes with nucleophiles (i.e., alkyl lithium reagents and metal(I) alkoxides) are consistent with the electronics and molecular orbital calculations for these types of complexes [Eq. (9) 22]. The nucleophile adds to the carbyne-carbon, resulting in the formation of a carbene complex. The reaction of a Grignard reagent with a carbyne complex is expected to demonstrate similar reactivity. [Pg.379]

On the other hand, neutral Os alkylidyne 82 undergoes reaction with methanol to give carbene complex 83 (equation 10.56).96 It would appear that 82 undergoes reaction with nucleophilic methanol at 0 first, which is followed by proton transfer to Os. Such reactivity would be consistent with that associated with Fischer carbyne complexes, yet the metal center is more electron-rich than the group 6 metal complex reactant in equation 10.55. [Pg.448]

The methoxycarbyne complex Tp W( = COMe)(CO)2 also reacts at the carbyne substituent with nucleophiles attacking the methoxide Me group, delivering Me and generating [Tp W(CO)3] via an Sn2 reaction.The reactivity of the methoxycarbyne complex Tp W( = COMe)(CO)2 thus differs considerably from that of the methylthiocarbyne complex Tp W( = CSMe)(CO)2, which reacts with phosphines at the carbyne carbon to undergo nucleophilic displacement of the methylthiolate substituent to produce phosphoniocarbyne complexes.The... [Pg.71]

Many carbene complexes undergo nucleophilic attack at the carbene carbon. This chemistry is presented in more detail in Chapter 13 on metal-ligand multiple bonds. In brief, cationic carbene complexes tend to imdergo simple addition processes to generate neutral products (Equation 11.8), whereas neutral complexes can react by either addition (Equation 11.9) or by a sequence of addition and elimination reactions (Equation 11.10). Fischer has shown that the aminolysis of alkoxycarbene complexes occurs by initial attack at the carbene carbon by a mechanism similar to that for the aminolysis of organic esters. Although less studied than reactions of carbenes with nucleophiles, reactions of carbyne complexes with nucleophiles are also known, and these reactions generate carbene complexes. ... [Pg.421]

In carbyne osmium compounds such as [Os3(/i-COMe)(/z-H)(CO)io] nucleophilic attack on the carbyne carbon atom also takes place. By carrying out sequential reactions with nucleophiles and electrophiles, it is possible to break the C—O bond (Table 3.14, footnote reference A). The reaction furnishes an isolable carbene complex, [Os3(M-CHOMe)(/i-H)(CO)io]... [Pg.189]

E. O. Fischer and G. Besl, Z. Naturforsch., Teil B, 1980, 34, 1186. Novel carbene complexes of manganese obtained by reaction of cationic carbyne complexes with nucleophiles. [Pg.219]

Dihalocarbene complexes are useful precursors to new carbenes by nucleophilic displacement of the chlorine substituents. This has been nicely illustrated for Fe(TPP)(=CCl2) by its reaction with two equivalents of Re(CO)5J to give the unusual /t-carbido complex Fe(TPP)=C=Re(CO)4Re(CO)5 which also contains a rhenium-rhenium bond. " The carbido carbon resonance was observed at 211.7 ppm in the C NMR spectrum. An X-ray crystal structure showed a very short Fe=C bond (1.605(13) A, shorter than comparable carbyne complexes) and a relatively long Re=C bond (1.957( 12) A) (Fig. 4, Table III). " ... [Pg.260]

Some carbyne complexes, in particular cationic ones with good Ji-accepting ligands, can react with nucleophiles to give carbene complexes [187,521]. Several reductions of carbyne complexes to carbene complexes by treatment with metal hydrides have been reported. Similarly, organolithium or other carbanionic reagents can react with electrophilic carbyne complexes to yield carbene complexes. Illustrative examples of both reactions are sketched in Figure 3.23. [Pg.94]

The reaction of nucleophilic Pt(0), Pd(0), and Ni(0) complexes with unsaturated metal-metal bonds has been extended by Stone and coworkers (18, 19) to include carbene and carbyne derivatives, Eqs. (21) (18) and (22) (19). [Pg.231]

The electron-rich thiocarbyne complex 479 (R = Me, 2,4-dinitrophenyl) is not susceptible to nucleophilic attack at the carbyne carbon, and reaction with PEtj causes carbonylation to give the / -ketenyl complex 480 (257). The same reaction occurs in the complex containing the ligand HC(pz)3 instead of HB(pz)3 (258). [Pg.91]

This chapter will focus on the nucleophilic addition reactions of transiton metal carbene and carbyne complexes with Grignard reagents. The synthesis and some general reactions of these carbene and carbyne complexes will be presented. A more detailed description of the chemistry of these complexes can be found in the literature [1]. This chapter, although not exhaustive, is descriptive of the prototypical nucleophilic addition reactions of metal-carbon (M-C) multiple bonds with Grignard reagents. [Pg.373]

Reactions of electrophilic metal carbenes and carbynes with nucleophilic metal centers are used to prepare a large number of clusters, most containing two or more different metals. The metal-metal bond formed is usually bridged by the carbene or carbyne ligand, but ligand transfer can lead to homometallic products. ... [Pg.81]

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... [Pg.59]

Herein we report on their reactions with a variety of nucleophiles and the transformation of the p.-carbyne groups into the Fischer type carbene ligands. Our attention will be focused on the methods that lead to aminocarbenes and to the electronic and steric factors which stabilize this currently unknown class of complexes. [Pg.138]

The pattern of chemical reactions observed for these compounds clearly sets them apart from "Fischer-type" carbyne complexes of GroupVI e.g., W(hCR)X(CO)4. Whereas the "Fischer-type" complexes typically react with nucleophiles at the carbyne carbon all of the reactions observed for the five coordinate mthenium and osmium complexes, including the cationic examples, are electrophilic additions to the MsC bond. The following sections deal individually with, protonation, addition of halides of the coinage metals, addition of chlorine and chalcogens, and finally an attempted nucleophilic addition where the nucleophile is directed to a remote site on the aryl ring of the carbyne substituent. [Pg.158]

The reluctance of the carbyne carbon to react with nucleophiles is revealed by the reaction with LiEt3BH (see Scheme 6). Here the most electrophilic site is not the carbyne carbon but the ipara position of the aryl ring in the carbyne substituent Both ruthenium and osmium five coordinate, cationic, carbyne complexes undergo this reaction. The structure of a representative example, the osmium compound derived from the p-tolyl carbyne complex, has been determined by X-ray crystallography [16]. The unusual vinylidene complex reacts with HCl to produce a substituted benzyl derivative. The reaction may proceed through the intermediate a-vinyl complex depicted in Scheme 6 although there is also the possibility that the vinylidene compound is in equilibrium with the carbene tautomer as shown below. [Pg.161]

The formal similarity of these ruthenium and osmium compounds to the octahedral Group VI carbyne compounds would lead to an expectation of reactivity towards nucleophiles. In fact the neutral octahedral complexes prove to be rather unreactive compounds but the cationic complexes do react with nucleophiles. Mention has already been made of the hydrolysis of [Ru(=CPh)ClI(CO)(PPh3)2]I to RuPhCl(CO)2g Ph3)2. A very clear-cut example is provided by the reaction of [0s(sCR)Cl2(CNR )(PPh3)2]C104 (R=p-dimethylaminophenyl, R =p-tolyl) with NaSH. [Pg.164]

Carbynes, (RCj), are 2e ligands and their carbon atoms have sp hybridization (two p orbitals are not hybridized). Therefore, in carbyne complexes L M —CR, two molecular orbitals d -p are formed. Thus, formally, the metal-carbon bond is triple. Calculations of electronic structures of [(OC)5Cr = CH] and [(OC)4ClCr=CH] show that the carbyne carbon charge is negative. Because in cationic carbyne complexes the carbon atom reacts with nucleophiles, this carbon s reactivity is not controlled by the charge, contrary to these calculations. The contradictions between calculations and experiments may be explained " by means of the frontier orbital theory (reactions controlled by frontier orbitals). Nucleophiles react with the atom of a molecule on which the LUMO is located, while electrophiles react with the atom of a molecule on which the HOMO is mainly localized. In the case of [(OC)5Cr = CH], the maximal coefficient in LUMO is at the carbyne carbon atom, and therefore it reacts with the nucleophile despite the fact that it is negative. [Pg.280]


See other pages where Carbyne reactions with nucleophiles is mentioned: [Pg.541]    [Pg.541]    [Pg.176]    [Pg.94]    [Pg.71]    [Pg.40]    [Pg.539]    [Pg.263]    [Pg.271]    [Pg.90]    [Pg.114]    [Pg.539]    [Pg.3369]    [Pg.4019]    [Pg.378]    [Pg.447]    [Pg.10]    [Pg.39]    [Pg.3368]    [Pg.4018]    [Pg.15]    [Pg.17]    [Pg.20]    [Pg.64]    [Pg.88]    [Pg.144]    [Pg.155]   
See also in sourсe #XX -- [ Pg.32 , Pg.33 , Pg.94 , Pg.95 ]




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