Organometallic compounds are compounds that have one or more metal-carbon bonds. Therefore, when organic groups are bonded with metalloids such as Arsenic (As), Germanium (Ge), Boron (B), the resulting compound is called Organometallic.
Metals include a lot of elements except phosphorus, nitrogen, halogens, rare gases, and all the group 16 elements. In the year 1827, the first organometallic compound K[ptCl3(CH=CH2)] was synthesized by the Danish pharmacist William C. Zeise. The compounds have grown enormously since the first one was synthesized in 1827 and its application was figured out decades after.
They are used as catalysts (substance that alters the rate of a chemical reaction and is unchanged at the end of the reaction). Inorganic catalyst is called an enzyme. The majority of the catalysts used in the chemical industry and laboratory are organometallic compounds. An example of an organometallic compound is trimethyl boron B(CH3)3 that has three boron-carbon bonds.
Organometallic compounds differ greatly in their physical and chemical properties. Some of them are liquid while some are gases and those whose hydro-carbon groups are aromatic or ring-shaped are mostly solid. Heats and oxidation stability vary among these compounds. Volatile organometallic compounds are highly toxic.
The properties of organometallic compounds are determined by the type of carbon-metal bonds present. We have normal covalent bonds, multicenter bonds, and ionic bonds. Normal covalent bonds include the sharing of a pair of electron between two atoms while multicenter covalent bonds are the sharing of electrons among more than two atoms. Ionic bond is the bond between metals and non-metals.
Organometallic compounds can be used as homogeneous catalysts in reactions where all the reacting compounds are present in one phase, usually the liquid phase. The complexes of transition metals act in different ways in a catalytic reaction. Transition metal activates the substrate by coordinating the metal and lowering the activation energy of the substrate in the reaction. The reactant reacts with a new complex, thereby giving the homogeneous catalyst a new pathway.
Organometallic compounds can help increase the rate of chemical reaction in the catalysis of reactions in which the molecules are polymer or pharmaceuticals. It has also been of great help in the investigation of catalytic C-H bond and it also gives an expansion to the industrial application in recent times.
The catalytic result of the hydrogenation of alkenes is the addition of molecular hydrogen across the double bond in alkenes. The reactant goes into reaction with complex to produce hydrido complex and an alkenes complex simultaneously. Finally, the hydrogenated product leaves the mixture, the regeneration of the unsaturated Rh complex and it goes on until hydrogen gas and ethylene are depleted.
Addition of Hydrogen with Carbon monoxide to alkenes to form an aldehyde that has more carbon than the usual alkenes. This catalytic reaction is utilized in a petrochemical company.
1. Metal-carbon atom has covalent bonds
2. A good number of organometallic compounds exist in the solid-state most especially, those whose hydro-carbon groups are aromatic or ring-shaped are mostly solid.
3. Organometallic compounds act as reducing agents, especially the ones formed with highly electro-positive metals.
4. Volatile organometallic compounds are toxic to humans
RBr +R’Li RLi + R’Br
The formation of the organometallic compound is favored by the equilibrium in the reaction. This method is used in the preparation of organic-lithium compounds derived from unreactive halides like ethynyl, aryl, or ethenyl halides. These halides do not react readily with lithium metal.
RLi + Cul RCu + Lil
R is connected to the less electropositive metal. The reaction forms a less reactive organometallic compound from a reactive one. The reaction is favor by equilibrium.
Applications
1. Organometallic compounds are used in the production of LEDs (light-emitting diodes)
2. They are used to manufacture semiconductors, which make use of compounds such as trimethyl antimony, trimethylindium, trimethylgallium, and trimethylaluminum.
3. They are used in the production of margarine i.e. bulk hydrogenation.
4. Their complex form such as alkyl aluminum, organoboron, and organolithium is utilized in the synthesis of many organic compounds.
5. They are also used as catalysts and reagents in the synthesis of organic compounds.
6. They are used as stoichiometric reagents in both industrial and research-based chemical reactions.
7. They are utilized as homogeneous catalysts
Organometallic compounds that contain Lead, Mercury, and Tin are used commercially. Organic-tin compounds are used as pesticides, pharmaceuticals, stabilizers for polyvinyl chloride, and fire retardants. The toxicity of methyl mercury has caused severe pollution. Carbon monoxide reacts with a transition metal to form metal carbonyls which are an example of organometallics. Tetracarbonylnickel which is a volatile nickel is employed in the purification of nickel. Carbonyls are used as catalysts in petrochemical reactions. Organomagnesium halides (Grignard reagents) are used in synthetic organic chemistry.
Active metals such as Sodium, Magnesium, and Aluminum (Al) forms organometallic compounds that are highly sensitive to air and water. e.g. A12(CH3)6 react violently with water to liberate methane gas which burst into flames immediately when it gets in contact with air. Organometallic are not water-sensitive for elements in group 14 and 15. For example, tetramethylsilicon, at room temperature, does not react with air and water. Grignard reagents combine with a halogen-substituted hydrocarbon to give simple organometallic compounds. Methyl lithium is produced in a large amount by the following reaction:
2Li +CH3Cl LiCH3 + LiCl
With metals such as Magnesium, Zinc, and Aluminum, the reactions normally yield organic-metal halide.
Organometallic reagents such as B(CH3)3, Zn(CH3)2, and Li(CH3) are flammable in air
Organometallic (MR) and binary halide (EX, where E can be a metal or a non-metal and X is a halogen) synthesize organometallic compounds by double displacement. This synthetic procedure is used in the laboratory and commercially.
4Li(CH3) + SiCL4 4LiCl + Si(CH3)4
Al2(CH3)6 + 2BF3 2AlF3 + 2B(CH3)3
In the above reactions, the organic group on the more active metal is given to the less active metal. The common active metals are Magnesium, Lithium
, and Aluminum.
All organometallic compounds can undergo oxidation thereby making them a good reducing agent.
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