Tungsten complexes alkylidyne

In the last several years tungsten alkylidyne complexes [60], W(CCMe3) (CH2CMe3)3 and W(CCMe3)Cl2(dimethoxyethane) in particular, have been a source of alkylidene complexes bound to oxide surfaces as a consequence of protonation of the alkylidyne ligand by a surface-bound hydroxyl group [112-114]. 

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. 

Although the structure of the complex arising from I52/CH2CI2 is not clear, this catalyst is excellent in terms of ease of preparation. The catalyst is very active for formation of cycloalkynes with ring sizes different from those of diynes (Table 6.5). In contrast to tungsten alkylidyne complex 150, catalyst 152/ CH2CI2 is sensitive toward an acidic proton such as amide proton and exhibited remarkable tolerance towards many polar functional groups (Table 6.5). 

Alkyne Metathesis with Tungsten Alkylidyne Complex 301... 

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. 

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... 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

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

Ring-closing metathesis (RCM) is not restricted to alkenes similar reactions are also known for alkynes. The tungsten alkylidyne complex W(=CCMe3)(OCMc3)3 has been used to catalyze such reactions. Predict the structures of the cyclic products for metathesis of... 

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. 

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.)... 

Protonation of several molybdenum and tungsten alkylidyne complexes of the type M(CR)(f) -C5H5)(CO)L with acids such as HCI or CFjCOjH was reported by KreissI et al. to afford the / -acyl complexes 121 [Eq. (104)] (134). The formation of the acyl complexes I2I presumably in-... 

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. 

The tungsten alkylidyne complex (t-BuO)3W(C-t-Bu) [130-132] is capable of catalyzing alkyne metathesis polymerization of cyclic alkynes. In addition, it can be used in acyclic diene metathesis (ADIMET) [133, 134]. The synthesis of the corresponding Mo-compound Mo(CCH2SiMe3)(OAd)3 (Ad=adamantyl) has been reported by C.C. Cummins et al. [135]. Though the active species is not known yet, a mixture of Mo(CO)6 and 4-chlorophenol is nowadays used for purposes of convenience [136]. 

It is also possible to make aikyiidene hydride complexes of W by hydrogenation of tungsten alkylidyne complexes. ... 

Beer, S., Hrib, C.G., Jones, P.G., Brandhorst, K., Grunenberg, ]., and Tamm, M. (2007) Efficient room-temperature alkyne metathesis with well-defined imidazolin-2-iminato tungsten alkylidyne complexes. Angew. Chem. Int. Ed., 46, 8890-8894. 

In attempts to synthesize tungsten alkylidyne complexes containing chelating anionic donor ligands we investigated the reactions of the bis-pyridine-substituted complex 1 with dithiocarbamate ligands and with pyrrole-2-carboxaldehyde methylimine in the presence of... 

The tungsten alkylidyne complex W(=CBu )(OBu )3, which, if monomeric, is only 12-electron, catalyses the metathesis of 3-heptyne at a spectacular rate. Note that the presence of strongly Ti-donating alkoxy groups destabilizes some of the metal d-orbitals (p. 1 51) so that the 18-electron rule is no longer expected to hold. In this case the reactions are too fast to obtain evidence for tungstenacy-clobutadiene intermediates. Another route to the catalysts, however, is provided by the remarkable reaction between the triply bonded tungsten alkoxides W IOR) and alkynes. 

LFnlike 3, tungsten-alkylidyne complexes of the type (OR)3W -t-Bu having... 

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. ... 

Beer S, Brandhorst K, Grunenberg J, Hrib CG, Jones PG, Tamm M. Preparation of cyclophanes by room-temperature ring-closing alkyne metathesis with imidazolin-2-iminato tungsten alkylidyne complexes. Org. Lett. 2008 10 981 984. 

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