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Schrock tungsten alkylidyne

At the same time, Filrstner used tungsten alkyUdene complex 150 developed by Schrock for ring-closing alkyne metathesis. He compared the reactivities of tungsten alkylidyne complex 150 and Mo(CO)6-p-ClC6H40H (Table 6.4) and showed that both catalysts work well, although a higher reaction temperature is required in the case of Mo(CO)6-p-chlorophenol. [Pg.198]

This mechanism was later confirmed experimentally in 1981 by Schrock and others, who reported the first example of alkyne metathesis by tungsten(vi)-alkylidyne complex. They have prepared tungsten alkylidyne complex 120 (Equation (21)) and found that it reacts with diphenylacetylende to give tungsten alkylidyne complex 121 and another alkyne 122 (lequiv.) (Equation (22)). Furthermore, complex 121 works as a catalyst for the alkyne metathesis reaction. [Pg.301]

At the same time, Fiirstner and others used Schrock s tungsten alkylidyne complex 120 for ring-closing alkyne metathesis. They compared 120 with the Mo(CO)6-/>-ClC6H40H system (Table 4) in reactivity and found that... [Pg.301]

R. R. Schrock, High-Oxidation-State Molybdenum and Tungsten Alkylidyne Complexes, Acc. Chem. Res. 19, 342-348 (1986). [Pg.288]

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 preparation of high-valent, Schrock-type alkylidyne complexes containing poly(pyrazolyl)borate ligands may also be achieved by ligand substitution reactions. For example, the (dry) air-stable tungsten complexes Tp W( = CR)X2... [Pg.7]

Bunz group, and Grela et al. found the beneficial effects of certain phenolic additive such as 2-fluorophenol or 2-fiu-oro-5-methylphenol. Schrock et al. have developed well-defined tungsten alkylidyne complexes, of which the commercially available catalyst [W]-I (Figure 24.7) shows high activity under mild conditions. ... [Pg.720]

The first examples of catalytic RCAM for the synthesis of functionalized macrocycles were reported by Ftirstner and Seidel [7]. Two catalyst systems were employed in this study the instant system prepared by reaction of catalytic amounts of Mo(CO)6 1 with stoichiometric quantities of phenols, and the well-defined tungsten-alkylidyne 2 first prepared by Schrock in 1981 [5, 8]. Subsequent applications of RCAM, particularly in natural product synthesis, have either utilized these two systems or a molybdenum system developed by Fiirstner that employs in situ reaction of trisamido molybdenum complex 3 [9] and CH2CI2 (Figure 7.1) [10]. [Pg.207]

Our interest in dimetallacyclobutadienes was triggered when Schrock reported the synthesis of alkylidyne tungsten compounds in a metathesis-like reaction involving W=W bonds [Eq. (2)] (18). [Pg.98]

R. R. Schrock, M. L. Listemann, and L. G. Sturgeoff, Metathesis of Tungsten-Tungsten Triple Bonds with Acetylenes and Nitriles To Give Alkylidyne and Nitrido Complexes, J. Am. Chem. Soc. 104, 4291 1293 (1982). [Pg.289]

M. L. Listemann, and R. R. Schrock, A General Route to Tri-lerl-butoxytungsten Alkylidyne Complexes. Scission of Acetylenes by Tungsten Hexa-lerl-butoxide, Orga-nometallics 4, 74-83 (1985). [Pg.289]

Schrock RR, Czekelius C. Recent advances in the syntheses 136. and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. [Pg.2135]

Krouse, S.A., Schrock, R.R., and Cohen, R.E. (1989) Preparation of polycyclooctyne by ring-opening polymerization employing dO tungsten and molybdenum alkylidyne complexes. Macromolecules, 22, 2569-2576. [Pg.151]

Schrock, R.R. and Czekelius, C. (2007) Recent advances in the syntheses and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. Adv. Synth. Catal, 349, 55-77. Zhang, W. and Moore, J.S. (2007)... [Pg.151]

Carbene complexes have also been shown to undergo a-hydrogen elimination, in this case to form alkylidyne complexes. This reaction is much less common than the reaction of alkyl complexes to form alkylidenes, but a few examples are well documented. Two examples of this transformation are shown in Equations 10.39 and 10.40. Schrock reported the first direct observation of this transformation (Equation 10.39). ° In this first example, an isolated carbene complex converted to an alkylidyne hydride complex upon abstraction of a chloride ligand with trimethylaluminum. In a second example, a double C-H activation process by two sequential a-hydrogen elimination reactions converts the starting tungsten-methyl complex in Equation 10.40 into a methylidyne complex. ... [Pg.413]

In the preparative section 3.2 devoted to metal-carbene complexes, it is shown how the a-elimination reaction from high oxidation state early-transition-metal-alkyl complexes is one of the general methods of synthesis of Schrock s Ta and Nb alkylidene complexes. The other direction, formation of an alkylidene from an alkylidyne complex, can also be a valuable route to metal alkylidenes. For instance, Schrock s arylamino-tungsten-carbynes can be isomerized to imido-tungsten-carbene by using a catalytic amount of NEts as a base. These compounds are precursors of olefin metathesis catalysts by substitution of the two Cl ligands by bulky alkoxides (dimethoxyethane then decoordinates for steric reasons), and this route was extended to Mo complexes ... [Pg.211]


See other pages where Schrock tungsten alkylidyne is mentioned: [Pg.275]    [Pg.353]    [Pg.28]    [Pg.387]    [Pg.440]    [Pg.137]    [Pg.1039]    [Pg.134]    [Pg.721]    [Pg.628]    [Pg.253]    [Pg.4989]    [Pg.4988]    [Pg.318]    [Pg.151]    [Pg.151]    [Pg.488]    [Pg.1036]    [Pg.417]    [Pg.473]    [Pg.384]    [Pg.206]   
See also in sourсe #XX -- [ Pg.137 ]




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