Tungsten, complexes with

The electrocatalytic properties of several parent dinitrogen or hydrazido-containing molybdenum and tungsten complexes with dppe ligand have also been investigated. Each of these complexes yielded NH3, in chemical yields which ranged from 1% to 36% per mole of complex.318... 

Etherification using a metal vinylidene has also been combined with G-G bond formation through the reaction of an alkynyl tungsten complex with benzaldehyde (Scheme 14). The addition of an internal alcohol to the incipient /3,/Udialkylvinylidene that is generated leads to dehydration and the formation of a Fischer-type alkylidene complex. Further reactions of this carbene with a range of nucleophiles have provided access to various furan derivatives.374,375... 

Scheme 5.3 The reaction of a benzylidene tungsten complex with keteneimine.

A family of molybdenum and tungsten complexes with the formula [M(Cp)(C0)2(PR3)(0=CEt2)]BAr4 [Ar = 3,5-6isftrifluoro-methyl)phenyl] are known to operate through this mechanism. In most of the cases, the rate-limiting step was the ketone displacement for H2 in order to form the active dihydride (55,56). An... 

Molybdenum and tungsten complexes with three crown ether benzenedithio-lene ligands (21) have been reported (105) and the effect of alkali ion binding has been probed by CV (106). Upon binding with Li+, Na+, or K+, positive shifts in the redox potential have been observed for all complexes. This observation suggests that the tris(crown ether benzodithiolene) complexes of Mo and W may potentially be useful as sensors for alkali metal cations (106). 

The fact that the substitution reactions of the tungsten complex with monodentate ligands (see Table VII) are about 1000 times faster than those with bidentate ligands (2-picolinic acid) (214), whereas the kinetic results point to a dissociative mechanism (see Section IIIDl), is... 

As we discovered that bulky electrophilic terminal phosphinidene tungsten complexes with CsMes or CH(SiMe3)2 at the phosphoms do not dimerize in the absence of trapping reagents [16, 17], we became interested in their fate. 

Half-Sandwich Tungsten Complexes with Silyl-Functionalized r -Cyclopentadienyl Ligand ... 

Very few examples on the cleavage of C-O bonds in alcohols except for allylic alcohols have been reported. The highly oxophilic nature of tungsten chlorides causes abstraction of oxygen from methanol or ethanol yielding oxotungsten and bis(alkoxide)tungsten complexes with liberation of alkanes (Eq. 46) [107, 108]. 

The C=0 bond in ketones can be cleaved by tungsten complexes with formation of a very strong oxo-tungsten multiple bond as has been studied extensively [119]. 

The sample solution, containing not more than 150 pg of W should be slightly alkaline or neutral. If it contains tartrate, it may also be acidic. Add 2.5 ml of thiocyanate solution, 5 ml of SnCh solution, and enough cone. HCl to bring its concentration in the solution to 8-9 M.. The total volume of the solution should be -25 ml. After 15 min extract the tungsten complex with two portions of isoamyl alcohol. Dilute the extract with the solvent in a 25-ml standard flask, and measure the absorbance at 403 nm, using the solvent as reference. 

Dichloroiodo)benzene is commonly used as a reagent for the chlorination or oxidation of various transition metal complexes. Numerous examples of oxidative chlorination of various molybdenum and tungsten complexes with PhICl2 have been reported in the literature [67-74]. In a representative example, oxidative decarbonylation of the cyclopentadienyl complexes 83 with one equivalent of PhICh selectively yields the respective molybdenum(IV) or tungsten(IV) complexes 84 in excellent yields (Scheme 3.31) [73]. 

Chisholm, M.H. Foiling. K. Streib. W.E. Wu, D.-D. Preparation and characterization of the kinetic and thermodynamic isomers of dinuclear molybdenum and 26. tungsten complexes with metal-metal triple bonds supported by p-tert-butylcalix[4]arene anions. Chem. Commun. 1998, 379-380. 

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