Metal dinuclear transition

Prospects for dinuclear transition metal chemistry illustrated by recent advances in the chemistry of dimolybdenum and ditungsten. M. H. Chisholm, Transition Met. Chem. (Weinheim, Ger.), 1978, 3, 321-333 (91). 

In Fig. 1 some of the most common metal-dioxygen binding modes found for mononuclear and dinuclear transition metal complexes are diagrammed. Note that the terms superoxo and peroxo ultimately... 

Eliminations from Os(CO)4RR occur by dinuclear mechanisms only if either R or R is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO)4H2, the vacant site is created by dissociation of CO. With Os(CO)4-(H)CH the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO)4(H)C2H and various polynuclear ethyl osmium derivatives show that (3-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 

As stated above, no information about the actual microscopic coupling mechanism can be extracted from the exchange energy Jex. As a consequence, numerous studies have explored the relevant structure-property correlations of dinuclear transition metal complexes LaM(/r-Lb)M Lc, namely the relation between the value of /ex and the geometry of the M(/r-Lb)M link. 

With mononuclear transition metal carbonyls, photochemically induced substitutions of one or two carbonyl ligands by a diene can be expected to be the only reactions. Dinuclear transition metal carbonyls or carbonyl... 

Studies on dinuclear transition-metal compounds containing metal-metal bonds have deeply enriched our understanding of chemical bonding. The nature and... 

Dinuclear transition-metal complexes conforming to the 1 8-electron rule... 

A trans-n- 1,2-Peroxo Dicopper(II) Complex. Our own efforts have resulted in the structural and spectroscopic characterization of five types of copper-dioxygen complexes (6), distinguished on the basis of the ligands used for their synthesis and on their distinctive structures or physical properties. Thus, the manner in which hemocyanin binds 02 is not the only one possible, and it is of considerable interest to deduce the structures, along with associated spectroscopy and reactivity of a variety of types. Dioxygen can bind to dinuclear transition metals in a variety of structural modes, shown in Figure 2. As mentioned, mode C is present in oxy-Hc and Kitajima s model complex (Scheme 1), whereas we have structural and spectroscopic evidence for types A (30-32), B (33-35), and F (36-38) for peroxo 022- binding, and mode D (39, 40) in the case of hydroperoxo (OOH ) complexes. 

Dare we push on with the same simple idea to group 14 Well, the chemist s approach is to push an idea until it fails. Then one tries to figure out why it does so and see what modifications to the model are needed. An electron configuration of ( s)2( p)2 implies a four-hole connector and four two-center-two-electron bonds. A quadruple bond comes to mind, but for a main-group species this is not observed. The tinker-toy theory fails. However, quadruple bonds are possible - just not for main-group atoms. As will be seen in Chapter 1, examples are observed in dinuclear transition-metal systems. 

I should like to propose that all the types of reactions which have been established for mononuclear transition metal complexes will also occur for dinuclear transition metal complexes, and furthermore, that the latter will show additional modes of reactivity which are uniquely associated with the metal-metal bond. In this article, I shall support this proposal by illustrations taken from the reactions of dinuclear compounds of molybdenum and tungsten, two elements which enter into extensive dinuclear relationships (J ). 

The time is ripe for truly exciting developments in the reactivity of dinuclear transition metal compounds. The potential for cyclic sequences of reactions, as is required for catalytic reactions, has already been realized. (1) It has been shown, by Muetterties, et al. (53), that alkynes can be selectively hydrogenated to alkenes (cU 2H-addition) by Cp2Mo2(C0) the rate determining step involves CO dissociation from the acetylene adducts Cp2MO2(C0) (R2C2). (2) We have found that... 

W U-H fOPr1) will isomerize olefins it selectively takes 1-butene to cis-2-butene, for example (54). While one can but speculate about the ultimate impact of dinuclear transition metal chemistry, it is surely fair to say that the elucidation of the intimate mechanisms of reactions at dinuclear metal centers will prove more challenging and fascinating than did their analogues at mononuclear centers. 

Dinuclear Transition Metal Trifluorophosphine Complexes Containing PF2-Bridging Ligands... 

Hydrocarbon or hydrocarbyl bridged dinuclear transition metal complexes. ... 

Carbonyl Complexes of the Transition Metals Cluster Compounds Inorganometalhc Compounds Containing Transition Metal Main Group Elements Cyanide Complexes of the Transition Metals Dinuclear Organometallic Cluster Complexes Gold Inorganic Coordination Chemistry. 

Dinuclear transition metal complexes see Dinuclear) in which two reactive metal centers are maintamed in close proximity have been largely studied owing to the opportunity provided to observe a synergism effect, hi many cases, interest has focused on complexes containing early (electron deficient) and late (electron rich) transition metals in different oxidation states in which such interactions are more probable. They can combine the Lewis acidity of the early metals and the known ability of the late metals to activate small molecules. ... 

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