Tungsten complexes applications

The aminocarbonylation of alkynes has been less explored as compared to that of alkenyl and (hetero)aryl halides. Nevertheless, several noteworthy applications of this reaction have been reported, including the syntheses of 2-ynamides, chiral 2-carbamoyl-7r-allylic tungsten complexes, angular triquinanes, 2-(carbamoylmethylene)tetrahydrofurans, alle-nyl amides, and others. ... 

Recent applications of X/Y correlation techniques to measure chemical shifts of low- , spin-1/2 transition metal nuclei other than rhodium focused mainly on the analysis of silver and tungsten complexes in addition, the use of 13C-relayed H/195Pt correlations for the stereochemical analysis of some platinum complexes was explored.44 A report on the application of 31P/51V correlation spectroscopy demonstrated further the possibility of indirect detection of rapidly relaxing quadrupolar metal nuclei and the feasibility of the... 

This study reports an immobilization process leading to the stable, noncovalent anchoring of a hydride tungsten complex within the new mesoporous structure of AlTUD-1. As expected, the porous volume of the AlTUD-1 is reduced as a consequence of the immobilization. These materials have potential applications in heterogeneous catalysis in mild conditions namely for hydrogenation catalysis. Further research in this direction is in progress. 

In an interesting departure from the otherwise exclusive applications of the D-HMBC experiment in natural product structure elucidation that have been cited above, Carbajo etal. used the D-HMBC experiment in a study of alkenylcarbyne- and alkenylvinylidene-tungsten complexes. Using both H- - W and inverse detection methods, the authors demonstrated an approxi-... 

The chemical uses of tungsten have increased substantially in more recent years. Catalysis (qv) of photochemical reactions and newer types of soluble organometaUic complexes for industrially important organic reactions are among the areas of these new applications. 

Dimethyl sulfoxide has found application as a solvent for electrochemical studies of Mo(VI) and Mo(V) complexes of quinol derivatives (287). Sulfoxides have also been examined as extractants for the separation of molybdenum and tungsten from acid solutions (218). 

Metal alkylidene complexes find application in the metathesis of alkenes, the cvclopropanation of alkenes (Grubbs, Schrock), Wittig type reactions, and the McMurry reaction. In suitable complexes a-elimination can occur twice yielding alkylidync complexes. See Figure 2.21 for an example with tungsten. 

Heteroatom-substituted (Fischer-type) carbene complexes are mostly used as stoichiometric reagents. For this reason only carbene complexes of reasonably cheap metals, such as chromium, molybdenum, tungsten, or iron have found broad application in organic synthesis. 

Inter- and intramolecular (cyclometallation) reactions of this type have been ob-.served, for instance, with titanium [408,505,683-685], hafnium [411], tantalum [426,686,687], tungsten [418,542], and ruthenium complexes [688], Not only carbene complexes but also imido complexes L M=NR of, e.g., zirconium [689,690], vanadium [691], tantalum [692], or tungsten [693] undergo C-H insertion with unactivated alkanes and arenes. Some illustrative examples are sketched in Figure 3.37. No applications in organic synthesis have yet been found for these mechanistically interesting processes. 

The application of tungsten-<7r-allyl complexes provided yet another elegant and efficient access to paraconic acids (Scheme 29) [68]. The propargylic al-... 

In 1994, Quayle et al. reported the application of this cyclic Fischer-carbene synthesis from 3-butynols to spirolactone synthesis, although the process was stepwise and a stoichiometric amount of the complex was employed [17]. The key transformation was the chromium or tungsten carbene complex formation followed by the CAN oxidation of the complex to give y-lactone. The reaction was further applied to the synthesis of andirolactone and muricatacin, the former being shown in Scheme 5.14. 

Chemical routes involving the use of tungsten salts have been reported. W2C was claimed to be formed by the pyrolysis of an organometallic complex containing cyclopentadiene and carbonyl groups.8 The W2C formed was useful for ceramic applications such as wear resistant surfaces and cutting tools. The same phase was also prepared by the reduction of WC14 with sodium triethylborohydride.9 The material was formed as 1-5 nm-sized crystallites as shown by SEM and TEM. 

Tungsten j4-diene cations in both s-trans and s-cis forms have been synthesized and the influence of the diene conformation on the regiochemistry of nucleophilic attack has been demonstrated488. Application of nucleophilic additions to Mo-complexed olefins in the construction of quaternary carbon centres has been summarized489. 

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