Tungsten complexes carboxylic acid

Tungsten(II) complexes carboxylic acid, 441 cyanides synthesis, 9... 

Molybdenum and tungsten compounds have long been known to catalyze the transformations of alkenes into epoxides and diols by hydrogen peroxide.171"173 This reaction was found to be suitable for the epoxidation of water-soluble alkenes such as allylic alcohols (equation 30)174,175 or unsaturated carboxylic acids (equation 31).171 Tungsten catalysts were found to be more active and selective in aqueous solution than molybdenum complexes. 

The trisneopentyl neopentylidyne complexes 144 of molybdenum and tungsten react with trifluoroacetic acid [Eq. (130)] and with other carboxylic acids [Eq. (131)] to afford the triscarboxylate systems 145 and 146... 

Upon interaction of the Jt-basic metal fragment (W(Tp)(NO)(L/) with L (L = Melm or PMe3 L = benzene, acetaldehyde, acetone, ethyl acetate, methyl formate, and N,N-dimethylformamide) stable [W(Tp)(NO)(PMe3)(r]2-L)] complexes formed. When the tungsten fragment is combined with a carboxylic acid, oxidative addition yields the seven-coordinate hydride complex [W(Tp)(NO)(H)(PMe3)C(=0)R] (Fig. 2.43).108... 

Hydrogen atom donors such as non-nucleophilic tertiary thiols or tri-n-butyltin hydride are extremely efficient traps for the capture of the alkyl radical R derived from O-acyl thiohydroxamates, thus providing a very efficient method for reductive decarboxylation (Scheme 3). In practical terms, the use of the mercaptan is preferred since the tertiary alkyl pyridyl disulfide can be easily removed during work up by a simple acid extraction. The reaction has been successfully applied to a very wide range of complex substrates [8] possessing primary, secondary, or tertiary aliphatic carboxylic acids, and reactions at room temperature or below require only photolysis from a simple tungsten lamp and often involve in situ O-acyl thiohy-droxamate derivatization. 

Usually the COOH functional groups act both as hydrogen-bond donors and acceptors. The dinuclear tungsten complex [(C5H4COOH)W(CO)3]2, 52 [118], is not a supramolecular compound but it is shown here as an example of hydrogenbonding between carboxylic acid functions and THE. 

Treatment of the complexes NMe4[Cr(CO)5) =C(0)Me ] with iodine in the presence of base and alcohols affords carboxylic acid esters in reasonable yield. Use of water or an amine in place of the alcohol provides the carboxylic acid or the amide. The molybdenum and tungsten derivatives... 

---