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Carbyne Alkylidyne Complexes

Carbyne complexes have metal-carbon triple bonds they are formally analogous to alkynes. Many carbyne complexes are now known examples of carbyne ligands include the following  [Pg.501]

the Lewis acid attacks the oxygen, the basic site on the carbene  [Pg.501]

Subsequently, the intermediate loses CO, with the halogen coordinating in a position trans to the carbyne  [Pg.501]

The best evidence for the carbyne nature of the complex is provided by X-ray crystallography, which gives a Cr — C bond distance of 168 pm (for X = Cl), considerably shorter than the 204 pm for the parent carbene complex. The Cr = C — C angle is, as expected, 180° for this complex however, slight deviations from linearity are observed for many complexes in crystalline form, in part a consequence of the manner of packing in the crystal. [Pg.501]

The carbyne ligand has a lone pair of electrons in an sp hybrid on carbon this lone pair can donate to a suitable orbital on Cr to form a a bond. In addition, the carbon has two p orbitals that can accept electron density from d orbitals on Cr to form tt bonds. Thus, the overall function of the carbyne ligand is as both a a donor and tt acceptor. (For electron counting purposes, a CR ligand can be considered a 2-electron donor it is usually more convenient to count neutral CR as a 3-electron donor.) [Pg.501]

FIGURE 13.47 Complexes Containing Alkyl, Carbene, and Carbyne Ligands. Data from (a) M. R. Churchill, [Pg.518]

Carbyne complexes can be synthesized in a variety of ways in addition to Lewis acid attack on carbene complexes. Synthetic routes for carbyne complexes and the reactions of these complexes have been reviewed.  [Pg.518]


Molybdenum and tungsten carbyne (alkylidyne) complexes frequently undergo 2+2 cycloaddition reactions with alkynes to give the corresponding metallacyclobutadiene... [Pg.594]

One route to a carbyne (alkylidyne) complex was reaction 23.40 equation 23.91 illustrates the initial method of Fischer. The abstraction of an ot-H atom from a Schrock-type carbene yields the corresponding carbyne complex (equation 23.92). [Pg.730]

Carbyne (alkylidyne) complexes are implicated in the metathesis of alkynes (p. 377). [Pg.236]

Fischer synthesized his carbyne (alkylidyne) complexes upon attempting to make halogenocarbene complexes using the following reaction ... [Pg.216]

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. [Pg.173]

Since the Schrock carbyne is active in the transalkylidynation reaction, the possibility of ring-opening polymerisation of cycloalkynes by acetylene transalkylidynation catalysts (metal alkylidyne complexes) has been evaluated [151]. Unfortunately, cyclooctyne is one of the few relatively stable strained cyclic acetylenes, but it is not strained enough to react selectively with the catalyst and yield a polymer according to the scheme... [Pg.388]

Osmium carbyne (see Carbyne Complexes) or aUcylidyne complexes have a triple bond between the metal and the carbon atom of the ligand. Carbyne complexes are related to singlet carbenes. They are analogous to linear nitrosyl (see Nitrosyl Complexes) complexes and the osmium is usually in a lower oxidation state. Alkylidyne complexes are related to triplet carbenes and the bonding between the osmium and the carbon atom is similar to the C-C bond in an alkyne. [Pg.3368]

The oldest route to carbyne (CR) complexes involves a Lewis acid (A+) attack on Fischer-type carbenes (equation 15). In this way, several Re carbyne derivatives under the general formula [[Re](CR)]° + have been prepared. The leading examples are [ReCp(CO)2(CR)]+ (R = Ph, SiPhs) because the analogous alkyl carbynes (alkylidynes) are much less stable due to facile deprotonation as elegantly shown by the spontaneous near-quantitative proton loss shown in equation (16). ... [Pg.4021]

NMR resonances of the alkylidyne carbon atom and selected IR absorptions for new carbyne complexes are given in Table 11. In other studies, the Mo and NMR spectra of molybdenum and tungsten alkylidyne complexes were determined by Enemark and co-workers (23). The metal atoms in the alkylidyne complexes were found to be less shielded than those in nitrido complexes but more shielded than those in compounds containing metal-metal multiple bonds. [Pg.228]

Bocarsly et al. reported the electronic absorption and emission spectra of a series of tungsten alkylidyne complexes of the type W(CR)X(CO)2L2 (R = Ph, CMe3, and 2-naphthyl X = halide Lj = tmeda, 2py, dppe) 24). For example, the absorptions at 450 and 327 nm for the complex W(CPh)Br(CO)2(tmeda) were assigned to d n Mc and transitions. Emission from the excited state occurs at 630 nm. The lifetime of the electronically excited state was measured to be 0.180 //seconds. Emission was observed only for the aryl-substituted carbyne complexes. (The photoreactivity of these compounds is discussed in Section IV, B.)... [Pg.228]

Metal alkylidyne complexes undergo a variety of oxidation and reduction reactions as well as redox-induced transformations of the alkylidyne ligands. A method for the direct transformation of Fischer-type carbyne complexes into Schrock-type alkylidyne complexes was developed in our laboratory. Bromine oxidation of the /ra/7, -carbyne bromo tetracarbonyl complexes 49 of molybdenum and tungsten in the presence of dimethox-yethane affords the dme-stabilized alkylidyne tribromo metal complexes 50 [Eq. (42)] (81). For alkyl-substituted complexes (R = Me, CH2CMe3)... [Pg.259]

The tungsten alkylidyne complexes 141 are reactive toward borane reagents Treatment with BH3 affords the dinuclear complexes 142 [Eq. (128)], and reaction with borabicyclononane gives complex 143 [Eq. (129)]. Complex 143 contains both fragments of the hydroboration reagent attached to the carbyne carbon. [Pg.286]

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. [Pg.317]

Alkylidyne-metal complexes have traditionally been divided into two categories, according to the oxidation state of the metals, in a manner directly analogous to the classification of the very large number of known alkylidene-metal species (19a,b). Hence Fischer-type alkylidyne complexes involve metals in low oxidation states, while Schrock-type complexes generally involve more electropositive metals with higher oxidation states (13). However, the properties of some of the numerous carbyne-metal complexes that have been characterized since the early days have in many cases blurred the distinction between the two classes (12a). [Pg.139]

It has been noted that metal-carbon triple bonds behave in a similar way as alkynes with respect to jr-complex formation13,15. Various heterometallic gold complexes with bridging carbyne ligands reflect this analogy. Alkylidyne complexes like [W(=CR)(CO)2( 5-C5H5)], [W(=CR)(CO)2( 75-C2B9H9R )] (R = alkyl, aryl, amino R = H, Me) readily... [Pg.293]


See other pages where Carbyne Alkylidyne Complexes is mentioned: [Pg.594]    [Pg.79]    [Pg.501]    [Pg.170]    [Pg.182]    [Pg.517]    [Pg.280]    [Pg.594]    [Pg.79]    [Pg.501]    [Pg.170]    [Pg.182]    [Pg.517]    [Pg.280]    [Pg.17]    [Pg.281]    [Pg.288]    [Pg.116]    [Pg.4989]    [Pg.4991]    [Pg.250]    [Pg.274]    [Pg.304]    [Pg.306]    [Pg.317]    [Pg.237]    [Pg.722]    [Pg.4988]    [Pg.151]   


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Alkylidyne

Alkylidynes

Carbyn

Carbyne

Carbyne complexes

Carbynes

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