Tungsten clusters, reactivity

Structure and Reactivity of Some Unusual Molybdenum and Tungsten Cluster Systems... 

A major difference in reactivity of the tungsten cluster as compared to the molybdenum clusters is evidenced by the extreme sensitivity of the former to decomposition in air. Further work on the synthesis and reactions of the tungsten clusters is in progress. 

The kinetics and thermodynamics of the exchange of halide ions (X) in cluster compounds of the type [MgCyXe have been reported for M = Mo and W. Replacement of chloride ion (X ) by bromide ion involves aquation in the rate-determining step followed by rapid bromide-ion anation of the aqua-intermediate. The activation energies for the forward and reverse reactions are both reported to be ca. 18 kcal mol. The molybdenum clusters are about ten times as reactive as the analogous tungsten clusters. 

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... 

Tungsten coordination has recently been comprehensively reviewed in Comprehensive Coordination Chemistry, particularly in the areas of mononuclear complexes, dinu-clear species containing single and multiple W-W bonds, polyoxometaUate synthesis, structure, and reactivity, and chalcogen-containing cluster complexes. ... 

The methods for the preparation of the triply bonded dimers, (C5Hj)2M2(CO)4, of molybdenum and tungsten involve either the photolysis or thermolysis of (C5H5)2M2(C0)6. The photolysis route is appropriate only for the preparation of very small amounts of (CjHj)2Mo2(CO)4. An improved version of the thermolysis route is presented that shortens the reaction time and produces (C5H,)2M2(CO)4 in high yield and purity. These compounds are of interest in catalysis, as precursors to sulfided clusters, and in preparative chemistry due to the broad reactivity of the metal-metal triple bond. ... 

R.D. Adams, I.T. Horvath - The Unusual Structures, Bonding, and Reactivity of Some Sulfido-Bridged Tungsten-Osmium Carbonyl Cluster Compounds,... 

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