Metal multiple

Metal-metal multiple bonds in dinuclear clusters. F. A. Cotton and R. A. Walton, Struct. Bonding (Berlin), 1985, 62,1 (188). 

In the second chapter, Phil Power continues his remarkable and continuously successful search for new main group metal multiple bonding. The chapter is entitled Multiple Bonding Between Heavier Group 13 Elements, and covers the astounding new developments that have occurred in this area in... 

This statement applies to the representative elements. Multiple bonding is also important for some transition elements. For a review of metal-metal multiple bonds, see Cotton, F.A. J. Chem. Educ., 1983, 60, 713. 

Cotton FA, Walton RA (1985) Metal-Metal Multiple Bonds in Dinuclear Clusters. 62 1-49... 

Not included in the present review is the fascinating new chemistry which results from reaction between diazo compounds and low-valent transition-metal complexes bearing easily displaceable two-electron ligands as well as with metal-metal multiple bonds and metal hydrides whereby a variety of novel organometallic molecules could be obtained. This field has been covered, in accord with its rapid development, by successive reviews of Hermann 19 22) and Atbini23). 

One approach to the production of high-performance dielectrics relies on the use of mixed-metal, multiple-component oxides. These oxides provide convenient means for controlling the dielectric-constant breakdown-field product through incorporation of components that specifically contribute to performance via dielectric constant or breakdown. At the same time, the mixed materials can inhibit crystallization, resulting in deposition of amorphous films with extremely flat surfaces. Common candidates, base oxides for tuning these properties, are listed in Table 4.1. 

The term carbometallation was most probably coined only about a quarter of a century ago.1 However, the history of those reactions that can be classified as carbometallation reactions is much older. If one includes not only the Ziegler-Natta-type organometallic alkene polymerization reactions2 but also various types of organometallic conjugate addition reactions,3 carbometallation collectively is easily more than a century old. In its broadest definition, carbometallation may be defined as a process of addition of a carbon-metal bond to a carbon-carbon multiple bond. As such, it may represent either a starting material-product relationship irrespective of mechanistic details or an actual mechanistic microstep of carbon-metal bond addition to a carbon-carbon metal multiple bond irrespective of the structure of the product eventually formed. 

Figure 5. An oxidation state diagram for Mo, Cr, Fe and Mn. For Mo and Cr, N = III for Fe and Mn, N = II. Potentials are given at standard states in acid solution relative to the hydrogen electrode. On such a diagram, die slope between any two points equals the redox potential. In conh ast to most other metals, multiple Mo oxidation states are accessible over a small range of potentials. Note also that Mo is oxidized to Mo(VI) at relatively low potential (similar to Fe(III). Figure modified after Frausto da Silva and Williams (2001).

The apparently unanimous verdict in favour of halogen metal multiple-bond character given by nuclear quadrupole resonance methods is unfortunately somewhat shaken by the results of Grayheal and Green (5) who measured (Table 4) the Chlorine asymmetry parameters of the... 

Among the more interesting metal-metal multiple bonded complexes are the hexaalkoxo dinuclear tungsten and molybdenum complexes, fM,(OR),J [Pg.418]

A detailed account of the descriptive chemistry of the heavier transition metals is beyond the scope of this book. Many aspects of the chemistry of these elements such as metal-metal multiple bonds, metal clusters, organometallic chemistry, and coordination chemistry are discussed in other chapters. The present discussion will be limited to a comparison of the similarities and differences of the heavier metals and their lighter congeners. 

VIII. COMPOUNDS WITH METAL-METAL MULTIPLE BONDS.126... 

II. STRONG METAL-METAL MULTIPLE BOND PROPERTIES.214... 

The reactions discussed in this section include those in which monomeric reagents are converted into dimeric species containing quadruple bonds. Later sections of this review consider reactions in which substitution or redox processes occur with retention, alteration, or cleavage of the metal—metal multiple bond. In very general terms, it is the initial formation of the quadruple bond that is common to the reactions below, and the number and variety of... 

A is a reflection of electronic factors due to the added electron weakening the metal—metal multiple bond slightly and hence shifting the metal atom separation toward the high side of observed quadruple bond values, a compounding of this effect would be anticipated in the more reduced Re2 Cl4(PEt3)4 case. Such is not observed. The separation actually decreases to... 

In some cases, alkoxide displacements at a metal center proceed sequentially and at different rates so that, if redistribution processes do not intervene, mixed diketonates can be obtained by adjusting the ratios of reactants.190,191 Recently, bimetallic / -diketonates of the type M2(diketonate)2(OR)4 (M = Mo, W R = alkyl) have been prepared from diketones and M2(OR)6. X-Ray studies show that one diketonate is attached to each metal atom so that unbridged M=M units are retained although rapid rotation about this multiple bond can occur.192 Diketonate complexes with metal-metal multiple bonds are rather uncommon, one other example being C2v CK-Mo2(Me-COCHCOMe), (02 CMe)2.193... 

The t2sTe nucleus is amenable to study by Mossbauer spectroscopy as well as by NMR, but far fewer studies dealing with the former have been reported. We are aware of one report by Jones (192) that reports isomer shift and quad-rupole splitting data for 153,164,165, and 154. The isomer shifts are found to be essentially the same regardless of whether the tellurium acts as a two-, four-, or six-electron donor, and the small values observed for the quadru-pole splittings in 153,164, and 165 are indicative of tellurium-metal multiple bonding. 

Reactions of isocyanides with metal-metal multiple-bonded dimers of molybdenum, rhenium, ruthenium, and rhodium have effected cleavage of... 

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