Transition-metal-carbon bond, preparation

A recipe for the preparation of Prussian Blue was published 20 years after its discovery.10 " Since materials containing iron, potash and nitrogenous matter such as blood or animal hooves may have been heated together in more remote times, ferrocyanides [hexacyanoferrates(II)] probably antedate Diesbach s discovery. They contain Fe—CN bonds and may thus possibly be considered as the first known examples of coordination compounds containing transition metal—carbon bonds (organometallic compounds). 

A (triphenylene)Cr(CO)3 complex and its crystal structure212 has been described in which the Cr—C distance of this -complex is around 2.2 A, common for transition-metal-carbon bond distances. A redox-tunable near-IR dye based on a trinuclear ruthenium-(II) complex of hexahydroxytriphenylene 87 has been prepared.220 Here, the absorption maximum of the... 

Many other soluble catalysts were developed over the last thirty years. Most of these materials must be prepared and used at low temperatures. The polymerization mechanism is also believed to take place by an initial coordination of the monomers with the transition metals. This is followed by a four-center insertion reaction of the monomer into the transition metal-carbon bond. 

Transmetallation is probably the most frequently employed preparative procedure in organometallic chemistry, and perhaps the commonest variant on this route to new metal-carbon bonds is the interaction of a transition-metal halide MX and a hydrocarbyl derivative of a (usually) more electropositive metal M R ... 

Organogold compounds.34 Alkyl derivatives of gold were among the first organometallic compounds of transition metals to be prepared. Both gold(i) and gold(m) compounds with cr-bonds to carbon, as well as olefin complexes, are known. 

In the absence of experimental thermochemical evidence about the strength of the metal-carbon bonds in metal carbonyl carbide systems, we can turn to the binary compounds formed between transition metals and carbon for information about the last point, the strength of metal-carbon bonds to core carbon atoms. Transition metal carbides are important. They include, in substances such as tungsten carbide, WC, some of the hardest substances known, and the capacity of added carbon to toughen metals has been known since the earliest days of steel-making. Information about them is, however, patchy. They are difficult to prepare in stoichiometric compositions of established structure and thermochemistry the metals we are most interested in here (osmium, rhenium, and rhodium) are not known to form thermodynamically stable binary phases MC and the carbides of some other metals adopt very complicated structures. Enough is, however, known about the simple structures of the carbides of the early transition metals to provide some useful pointers. 

The first alkylidyne-metal complexes were prepared by Fischer et al. more than 30 years ago. Since this pioneering event, the chemistry of the transition metal-carbon triple bond present in such complexes has developed into a major field of research and though the poly(pyrazolyl)borate ligands were discovered 7 years prior to the synthesis of the first alkylidyne complexes, their importance and significance in this field has only more recently been truly appreciated. 

A variety of compounds with metal metal bonds have been prepared. Mercurous compounds which contain the [Hg-Hg] " unit have long been known. More recent examples include compounds in which carbon monoxide is a ligand such as (Co)sMn Re(CO)s and (C6H5)3PAu-Co(CO)4. A number of complexes with transition metal tin bonds have been prepared. One of these, [Pt(SnCl3)5], contains five-coordinated platinum(ll) and is an excellent hydrogenation catalyst. 

Preparation of transition metal-carbon a-bonded compounds... 

Alkynyl complexes contain metal-carbon bonds in which the metal is bound to the sp-hybridized carbon at the terminus of a metal-carbon triple bond. The materials properties of these complexes have been investigated extensively. The properties of these complexes include luminescence, optical nonlinearity, electrical conductivity, and liquid crystallinity. These properties derive largely from the extensive overlap of the metal orbitals with the ir-orbitals on the alkynyl ligand. The M-C bonds in alkynyl complexes appear to be considerably stronger than those in methyl, phenyl, or vinyl complexes. Alkynyl complexes are sometimes prepared from acetylide anions generated from terminal alkynes and lithium bases (e.g., method A in Equation 3.42), but the acidity of alkynyl C-H bonds, particularly after coordination of the alkyne to the transition metal, makes it possible to form alkynyl complexes from alkynes and relatively weak bases (e.g., method B in Equation 3.42). Alkynyl copper complexes are easily prepared and often used to make alkynylnickel, -palladium, or -platinum complexes by transmetallation (Equation 3.43). This reaction is a step in the preparation of Ni, Pd, or Pt alkynyl complexes from an alkyne, base, and a catalytic amoimt of Cul (Equation 3.44). This protocol for... 

By varying the metal complex anion and RX, a wide variety of metal compounds containing transition metal-carbon cr-bonds have been prepared directly by this reaction. In addition, acyl metal derivatives prepared by this method may be decarbonylated to give alkyl and aryl metal complexes. 

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