Bonds tungsten complexes

As expected, the Sb—Sb bond distance in this complex is significandy shoitei than the Sb—Sb single bond distance. Chioinium and tungsten complexes of dialkyldistibines have also been isolated (132). 

Very recently, synthesis and structure of molybdenum and tungsten complexes of the relatively unhindered disilene Si2Me4 were reported. The x-ray structure of 84 shows a metallacyclosilane structure with W — Si = 2.606(2) A and Si —Si = 2.260(3) A. The W — Si bond length is within the range of various estimates of the Si and W covalent radii and the Si —Si distance falls midway between the expected values for a single (2.35 A) and a double bond (2.14 A) (Fig. 13). 

The tungsten complex Cp (CO)2(PMe3)WSiPh2OH has no HO- HO hydrogen bonds, but it is not clear whether there are OH---CO or OH- aryl interactions (29). The iron complex Cp(CO)2FeSi(p-tolyl)2OH (248) has also been reported to have no intra- or intermolecu-lar hydrogen bonds. 

Geometrical parameters provide much more information than simple identification. The phosphorus-carbon distance of 1.686(6) A in this tungsten complex is consistent with there being a double bond, as it is close to those observed in open chain phosphaalkenes. But how much better it would have been if the parent compound could have been studied uncomplexed, so that the strain in this unusual ring system could have been investigated. The geometrical parameters would then have provided very useful information about the likely reactivity of the compound, and information about the changes on... 

Other derivatives can effect such functionalizations, including iron, ruthenium, rhodium, and tungsten complexes. Excellent regioselectivities were observed in catalytic thermal processes involving unfunctionalized alkanes and primary alkyl C-H bonds were functionalized (Equation (20)).31... 

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... 

By far, the most W-Si bonds reported in the period that this review covers involve W(CO)n or (t]S-CsRs)W-containing compounds. A significant development has been that of a recyclable catalyst for the hydrosilylation of ketones the system begins with a polar liquid substrate (ketone or ester) and finishes with a non-polar liquid product (alkoxysilane). The rest state of the catalyst is a mixture of the [BlCgFsTH salts of 36 and 37 the tungsten complex is far more active than its molybdenum analog. 

Various alkylgermanes add across the Si-C double bond in the silylene complex 116 to yield germyl(silyl)tungsten complexes (Equation (201), Table 25).248... 

The complexes [W2CI4L4] undergo a reversible one-electron oxidation. A comparison of the oxidation potential of analogous molybdenum and tungsten compounds clearly shows that the tungsten compounds are considerably easier to oxidize. This ease of oxidation is believed to be responsible for the fact that it is difficult, if not impossible, to obtain quadruply bonded tungsten compounds by synthetic procedures which are known for molybdenum.339... 

The first examples of a chalcogen insertion into a transition metal-carbene bond were reported in 1981. Stirring solutions of the pentacarbonyl-(diarylcarbene)tungsten complexes 39 in pentane in the presence of solid sulfur afforded the thioketone complexes 40 [Eq. (8)].171 The reaction rate increased considerably when pentane was replaced by CS2 as the solvent due to the higher solubility of elemental sulfur in CS2. 

Further confirmation of the structure comes from the X-ray crystal structure analysis of the cyclopropylcarbinyl tungsten complex CpW(CO)3(C5FI9) which reveals a tetragonal bipyramidal geometry at the metal, and a typical bisected conformation of the cyclo-propylcarbinyl-M moiety. The sigma C—M bond distance of 234 pm is expectedly much longer than the W—CO bonds (115 pm). 

A number of reactions between M2(OR)6 compounds and alkynes have been found to give alkylidyne compounds by a metathesis of the M=M and C=C bonds (see Sections 15.3.6.4) and evidence has been presented275 for an equilibrium between a ditungstatetrahedrane and a methyl-idyne-tungsten complex supported by BulO ligands (equation 72). 

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