Tungsten organic ligands

Reactivity studies of organic ligands with mixed-metal clusters have been utilized in an attempt to shed light on the fundamental steps that occur in heterogeneous catalysis (Table VIII), although the correspondence between cluster chemistry and surface-adsorbate interactions is often poor. While some of these studies have been mentioned in Section ll.D., it is useful to revisit them in the context of the catalytic process for which they are models. Shapley and co-workers have examined the solution chemistry of tungsten-iridium clusters in an effort to understand hydrogenolysis of butane. The reaction of excess diphenylacetylene with... 

X-ray structural analysis of 2,2-dimethyl-3-phenyl-l-methylenecyclopropane tungsten pentacarbonyl reveals an octahedral complex with characteristic W—C bond distance of 238 pm. The typical bond distances within the organic ligand are 138 (complexed C=C), 148 (proximal C—C), 154 (distal C—C) pm, compared e.g. with 140, 148 and 154 pm, respectively, for the Feist s ester iron complex analogue (see above). 

Consequently, these topics are not specifically discussed in this article, which focuses primarily on the chemistry of mononuclear tungsten complexes containing organic ligands. 

The oxidation state of tungsten in compounds may vary between —2 and -1-6, the latter being the most common. Lower oxidation state compounds exhibit basic properties while higher ones are acidic. The maximum coordination number is 8, but it may attain 13 in coordination compounds with cyclic organic ligands. Chapter 4 treats tungsten compoimds in detail. 

The number of compounds synthesized so lar is exttemely large. The organic ligands can be classified by the number of carbon atoms (1-7) interacting with tungsten, as will be shown in Table 4.11. 

Alkyl ligands form metal-carbon o bonds. Often they occur in conjunction with other organic ligands or CO, but can be found on their own, as in tungsten hexamethyl (1), and in [Ti(CH2SiMe3)4] where... 

J. W. Johnson, A. J. Jacobson, S. M. Rich, and J. F. Brody, New layered compounds with transition-metal oxide separated by covalently bound organic ligands. Molybdenum and tungsten trioxide-pyridine, J. Am. Chem. Soc., 103, 5246-5247 (1981). 

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). 

Bis(3,5-dimethylpyrazol-l-yl)cyclotriphosphazene containing phenyl substituents at the phosphorus atoms (R) reacts with molybdenum and tungsten hexacar-bonylstogive34(R = Ph M = Mo, W) [94JCS(D)63]. IfRj = N(Me)(CH2)20, compounds 34 (R2 = N(Me)(CH2)20 M = Mo, W) having better solubility in organic solvents are produced. Their structures show the novel tridentate NNN feature of the ligands. 

Cyclopentadienyl-manganese, -molybdenum and -tungsten anions react with organic halides to give species with five independent ligands - (Scheme 16) ... 

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