Molybdenum complexes, anion, with

The group of potential 0,N-two-center ligands includes oximes (>C=N-OH), as well as hydroxylamine NH2OH, and its derivatives. The iri -coordination of simple oximes and substituted hydroxylamines in d transition metal complexes was reported almost simultaneously in Russia [9] and elsewhere [42,43]. More speciflcally, it was found [9,44,45] that the flnal product of the reaction between tungsten (molybdenum) oxotetrafluoride and simple oximes and p-phenylhydroxylamine is a complex anion with the deprotonated organic ligand [M0F4L] (where M=Mo, W HL stands for acetoxime, acetaldoxime, benzal-doxime, 2- and 4-pyridinaldoxime, and p-phenylhydroxylamine). 

When methylene chloride was used as a solvent, it was found that 28 are obtained in minor amounts, while the dominating product is the -coordinated chloro-carbyne species [(> -Tp )Mo(CO)2(=CCl)], whose yield increases abruptly with substitution in the pyrazol-l-yl fragments (3-methyl-, 3,4,5-trimethyl-, and 3,5-dimethyl-4-chloro derivatives) [90AX(C)59,95JCS(D) 1709]. The tungsten analog can be prepared similarly. The chlorocarbyne molybdenum complex follows also from the reaction of the parent anion with triphenylsulfonium cation but conducted in dichloromethane. The bromo- and iodocarbyne derivatives are made similarly. 

Simple anions are those that exist only in one oxidation state in soil and generally are only assodated with water. Complex anions are typically oxyanions of nonmetals, although molybdenum occurs as an oxyanion. 

Upon acidification or neutralization of solutions containing phosphate anions with other anions, such as those of molybdenum and tungsten, complexes are formed which can readily be crystallized as salts, called phosphomolybdates, phosphotiingstates, etc. 

There are two well-characterized examples of a naked carbon atom bound by a triple bond to a metal center (Fig 14.3.8). The molybdenum carbide anion [CMo N(R)Ar 3]- (R = C(CD3)2(CH3), Ar = C6H3Me2-3,5), an isoelectronic analog of NMo N(R)Ar 3, can be prepared in a multistep procedure via deprotonation of the d° methylidyne complex HCMo N(R)Ar 3. The Mo=C distance of 171.3(9) pm is at the low end of the known range for molybdenum-carbon multiple bonds. In the diamagnetic, air-stable terminal ruthenium carbide complex Ru(=C )C12(LL/)(L = L = PCy3, or L = PCy3 and L = l,3-dimesityl-4,5-dihydroimidazol-2-ylidene), the measured Ru-C distance of 165.0(2) pm is consistent with the existence of a very short Ru=C triple bond. 

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