Металл-карбон байланыстары: Құрамы, түрлері және қолданылуы

Class of organometalic compounds

A transition metal carbene complex is an organometallic compound featuring a divalent carbon ligand, itself also called a carbene. Carbene complexes have been synthesized from most transition metals and f block metals, using many different synthetic routes such as nucleophilic addition and alpha hydrogen abstraction.

Metal carbene complexes are often classified into two types. The Fischer carbenes, named after Ernst Otto Fischer, feature strong π acceptors at the metal and are electrophilic at the carbene carbon atom. Schrock carbenes, named after Richard R. Schrock, are characterized by more nucleophilic carbene carbon centers; these species typically feature higher oxidation state (valency) metals. N Heterocyclic carbenes (NHCs) were popularized following Arduengo's isolation of a stable free carbene in 1991. Reflecting the growth of the area, carbene complexes are now known with a broad range of different reactivities and diverse substituents. Often it is not possible to classify a carbene complex solely with regards to its electrophilicity or nucleophilicity.

Metal carbene complexes have applications in hetereogeneous and homogeneous catalysis, and as reagents for organic reactions.

The dominant application of metal carbenes involves none of the above classes of compounds, but rather heterogeneous catalysts used for alkene metathesis for the synthesis of higher alkenes. A variety of related reactions are used to interconvert light alkenes, e. g. butenes, propylene, and ethylene. Carbene complexes are invoked as intermediates in the Fischer–Tropsch route to hydrocarbons.

Fischer carbenes are used with alkynes as the starting reagents for the Wulff–Dötz reaction, forming phenols.

The first metal carbene complex to have been reported was Chugaev's red salt, first synthesized as early as 1925, although it was never identified to be a carbene complex. In 1968, Hans Werner Wanzlick and Karl Öfele separately reported metal bonded N heterocyclic carbenes. The synthesis and characterization of ((CH3)3CCH2)Ta=CHC(CH3)3 by Richard R. Schrock in 1974 marked the first metal alkylidene complex. In 1991, Anthony J. Arduengo synthesized and crystallized the first persistent carbene, an NHC with large adamantane alkyl groups, accelerating the field of N heterocarbene ligands to its current use.