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Organometallics

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An organometallic compound is generally defined as one that possesses a metal carbon bond. It deals with molecules that contain a metal carbon bond. While many chemists prefer to say that for a compound to be classified as an organometallic compound, the type of metal carbon bonding in a molecule should be covalent or partially covalent in nature.


Based on periodic table one can broadly classify organometallic chemistry further into transition metal, main group metal and lanthanide/actinides based organometallics. Among these the most well developed, mechanistically understood and widely utilized in catalysis is transition metal organometallic chemistry.

Organometallic Reagents

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Organic chemists use organometallic compounds as reagents a well as catalysts. The usefulness of organometallic compounds especially the alkali and alkaline earth compounds such as butyllithium and organomagnesium (Grignard) reagents, is the most visible face of organometallics to organic chemists.

Organosilicon protecting groups such as trimethylsilyl or tertiarybutyl dimethylsilyl and triisopropylsilyl also form an integral part of the organic chemists. Organic chemists use many organometallic reagents and catalysts for very specific applications. Some of the organometallic reagents are given below.

Organozinc Reagent

Organozinc compounds are much less nucleophilic than grignard reagents. The Reformatsky reaction which converts $\alpha$-haloesters and aldehydes to $\beta$-hydroxyesters also goes through an intermediate organozinc halide. In the Simmons-Smith reaction the carbenoid zinc iodide reacts with alkenes to form cyclopropanes.

Organocopper Reagents

The most useful organocopper reagents are lithium dialkylsuprates R2CuLi. These are formed by the reaction of two equivalents of an organolithium compound with a copper(I) halide.

Organocadmium Reagents

The alkyl groups present in the organocadmium compounds are less nucleophilic than those in the organozinc compounds due to the general increase in electronegativity going down group 12.

Organoiron Reagents

The efficiency of the Fe(CO)3 moiety in protecting 1,3-dienes and its use as a stereo directing group in various types of reactions is well documented.

Inorganic chemists also explore the synthesis of new organometallic compounds their stability and structural studies and then determine their potential applications especially as catalysts.

Organometallic Catalysts

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Some common organometallic compounds are listed below.

S.No Organometallic compounds
Remarks
1
Dibutyltin dilaurate Standard compound
2
Stannous octoate
Polysther-based slabstock foams
3
Dibutyltin diacetate
4
Dibutyltin dimercaptide
5Lead naphthenate
6
Lead octoate
7
Dibutyltin bis(4-hydroxyphenylacetate)
8
Dibutylin bis(2,3-dihydroxypropylmercaptide) Hydrolytically stable
9
Ferric acetylacetonate Elastomers

Organic and inorganic chemists are the key players agree the industrial importance of homogeneous catalysts has played a very important role in the development and application of organometallic compounds.

Classical organometallic chemistry is typically non-aqueous. The water phase variants have prominently problems with the solubility of catalyst complexes. Organometallic catalysts frequently operate in zero oxidation state, which excludes the solubilizing action of ionization on the metal.

Organometallic Synthesis

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Organometallic compounds refer to those containing at least one metal carbon bond. They are in an interdisciplinary area between inorganic and organic chemistry. Organometallic compounds have played a critical role in catalysis and organic synthesis often leading to more efficient use of reagents, higher yields of products and less use of energy.

Synthesis of M-C containing compounds plays a central role in the field of organometallic chemistry. Both the metals and ligands are diverse. The former include those of main group, transition metals and lanthanide and actinide elements. The latter range from CO to multidentate organic molecules.

Since organometallic compounds contain metals and ligands the synthetic methods are in general grouped into two types.
  1. Reactions between metal species and preformed ligands or ligand precursors.
  2. Reactions of ligands in organometallic compounds yielding new ligands.


The former is used in the preparation of Grignard reagents, organolithium reagents and MeCo(CO)4. The latter is typified by the synthesis of Fischer carbene and carbyne complexes containing M=C and M triple bond C bonds. Some of the Organometallic Reactions are given below.

R-X + Mg $\rightarrow$ RMgX

MCl4 + 4LiCH2Bu $\rightarrow$ M(CH2BU)4 (M = Ti, Zr, Hf)

Na+[Co(CO)4]- + MeI $\rightarrow$ MeCo(CO)4

Organometallics Compounds

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The designation "organometallic" generally denotes compounds in which organic group are linked directly to the metal through at least one carbon atom. Compounds like Ti(OC4H9)4, Ca[N(CH3)2]2 and Fe(SC5H11)3 are therefore not included in the list of organometallic compounds.

The number of organometallic compounds is almost unlimited. On the industrial side although only few organometallic compounds like tetraethyllead and silicone's have been used in bulk quantities, organometallic catalysts have begun to make unprecedented dents in a number of important industrial processes like those named after Fischer and Tropsch or Ziegler and Natta.

Grignard Reagent

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The use of organomagnesium halides, Grignard reagents, was developed early by the French chemist Victor Grignard who for that reason got Nobel prize in 1912. The Grignard reaction has proved to be one of the most versatile methods for the formation of carbon-carbon bonds.

Grignard reagents possess significant nucleophilic character because of the highly polarized carbon-metal bond that results in considerable carbanionic character at carbon. Grignard reagents have found great utility and widespread use in organic synthesis.