Organometallic compounds

Organometallic compounds (MOS) are organic compounds in the molecules of which there is a bond between a metal atom and a carbon atom / atoms.

Content

Types of Organometallic Compounds

By the nature of the bond, they are divided into 2 types: 1) with a σ bond (for example, (СН ₃ ) ₃ Al, C ₂ H ₅ MgI, C ₄ H ₉ Li) and 2) with a π bond (for example, ferrocene and bis -π-allyl-nickel). Compounds of the first type form predominantly transition metals, compounds of the second type - transition. Full MOS are known that contain only carbon-metal bonds and transitional ones that also contain a metal-heteroatom bond (usually halogen). Organometallic compounds are widely used for a wide variety of syntheses and in various industries.

In the first type of MOC, the polarity and reactivity of metal-carbon bonds in heterolytic reactions decreases with a top-down transition for compounds of groups IIb and III of the periodic system and increase for compounds of groups I, IIa, IV, and V. Thermal stability decreases from top to bottom for compounds of groups III and IV, as well as during the transition from aromatic compounds to aliphatic. Chemical transformations (reactions with acids, halogens, salts of other metals, addition by multiple bonds, disproportionation, exchange of anion-like residues) are usually accompanied by rupture of the MC bond and, to a lesser extent, metal-heteroatom bonds.

The main type of MOS of the second type is π-complexes - transition metal compounds containing pi-linked organic ligands - olefin, acetylene, allyl, cyclopentadienyl, carboran. By the nature of the bond, carbonyl, isonitrile, cyanide and carbene derivatives of transition metals are adjacent to them. In such MOS, the metal – organic ligand bond occurs as a result of the interaction of the filled ligand orbitals with the vacant metal orbitals (donor – acceptor component) and as a result of the reverse supply of electrons from the metal orbitals to the lower vacant ligand orbitals (the native component). In complexes, the metal can interact with all carbon atoms of the pi-electron system or only with some of them. The stoichiometry of most pi-complexes obeys the effective atomic number rule: the sum of the electrons of an atom or metal ion and the electrons provided to it by the ligand should equal the number of electrons in the atom of the nearest inert gas. The chemical properties of pi-complex MOSs depend mainly on the nature of the ligand and to a lesser extent on the nature of the central metal atom. Reactions of these MOS are possible both with partial or complete conservation of the metal-ligand bond, and with its rupture.

The most known Grignard reagents that are used to introduce hydrocarbon radicals into various parts of the molecule. Organolithium compounds are often used. Organometallic compounds include Ziegler-Natta ((C ₂ H ₅ ) ₃ Al and TiCl ₄ ) catalysts used in industry to produce polyethylene. Tetraethyl lead , an antiknock additive to gasoline , is the main source of harmful lead pollution along highways. Vitamin B ₁₂ , as well as hemoglobin and hemocyanin oxygen carriers in red blood cells, belong to natural MOS.

Ways to get

1) from alkyl or aryl halides:

{\mathsf {CH_{3}Br+2Li\rightarrow CH_{3}Li+LiBr}}

{\ displaystyle {\ mathsf {CH_ {3} Br + 2Li \ rightarrow CH_ {3} Li + LiBr}}}

{\mathsf {CH_{3}Br+Mg\rightarrow CH_{3}MgBr}}

{\ displaystyle {\ mathsf {CH_ {3} Br + Mg \ rightarrow CH_ {3} MgBr}}}

2) the reaction of metal salts with MOS lithium, magnesium and aluminum. This process is sometimes called remapping. The driving force of the process is the desire for the formation of an ionic salt of a more electropositive metal.

{\mathsf {2CH_{3}+HgBr_{2}\rightarrow (CH_{3})_{2}Hg+2MgBr_{2}}}

{\ displaystyle {\ mathsf {2CH_ {3} + HgBr_ {2} \ rightarrow (CH_ {3}) _ {2} Hg + 2MgBr_ {2}}}}

{\mathsf {PhMgBr+CuBr\rightarrow PhCu+MgBr_{2}}}

{\ displaystyle {\ mathsf {PhMgBr + CuBr \ rightarrow PhCu + MgBr_ {2}}}}

3) the reaction of MOC with hydrocarbons, metals or other MOC

{\mathsf {(CH_{3})_{2}Hg+2Na\rightarrow 2CH_{3}Na+Hg}}

{\ displaystyle {\ mathsf {(CH_ {3}) _ {2} Hg + 2Na \ rightarrow 2CH_ {3} Na + Hg}}}

{\mathsf {CH_{3}MgBr+CH_{3}C\equiv CCH_{3}\rightarrow CH_{3}C\equiv CMgBr+CH_{4}}}

{\ displaystyle {\ mathsf {CH_ {3} MgBr + CH_ {3} C \ equiv CCH_ {3} \ rightarrow CH_ {3} C \ equiv CMgBr + CH_ {4}}}}

{\mathsf {2CH_{3}Li+CuI\rightarrow (CH_{3})_{2}Cu+2LiI}}

{\ displaystyle {\ mathsf {2CH_ {3} Li + CuI \ rightarrow (CH_ {3}) _ {2} Cu + 2LiI}}}

{\mathsf {RR'NCH_{2}SnBu_{3}+BuLi\rightarrow RR'NCH_{2}Li+Bu_{4}Sn}}

{\ displaystyle {\ mathsf {RR'NCH_ {2} SnBu_ {3} + BuLi \ rightarrow RR'NCH_ {2} Li + Bu_ {4} Sn}}}

4) derivatives of less active metals are obtained by the interaction of their alloys with sodium with alkyl halides:

{\mathsf {4C_{2}H_{5}Br+4Na/Pb\rightarrow (C_{2}H_{5})_{4}Pb+4NaBr}}

{\ displaystyle {\ mathsf {4C_ {2} H_ {5} Br + 4Na / Pb \ rightarrow (C_ {2} H_ {5}) _ {4} Pb + 4NaBr}}}

{\mathsf {2CH_{3}Br+2Na/Hg\rightarrow (CH_{3})_{2}Hg+2NaBr}}

{\ displaystyle {\ mathsf {2CH_ {3} Br + 2Na / Hg \ rightarrow (CH_ {3}) _ {2} Hg + 2NaBr}}}

5) metallization of compounds with a mobile hydrogen atom.

{\mathsf {(CH_{3})_{3}CH+Cu[NH_{3})_{2}]OH\rightarrow (CH_{3})_{3}CCu+2NH_{3}+H_{2}O}}

{\ displaystyle {\ mathsf {(CH_ {3}) _ {3} CH + Cu [NH_ {3}) _ {2}] OH \ rightarrow (CH_ {3}) _ {3} CCu + 2NH_ {3} + H_ {2} O}}}

6) the addition of metal salts and hydrides to organic compounds containing multiple bonds C = C

7) the effect of metal powders on the double diazonium salts of the corresponding metals.

Building

MOS are divided by the type of S-Metal connection into

1. With an ionic bond : CH ₃ ^- Na ⁺

2. With covalent polar bond : Grignard reagents, organolithium compounds

3. With a covalent non-polar bond : MOS of most metals, the most known compounds are Zn , Cu , Hg , Sn , Pb .

Application

MOCs have a wide range of applications in organic chemistry. Lithium and organomagnesium compounds can be used as strong bases or as reagents for nucleophilic alkylation or arylation.

Another area of application of MOS is catalysis. So, the composition used in industry for the production of polyethylene catalyst Ziegler-Natta includes MOS (C ₂ H ₅ ) ₃ Al.

MOS are used in the manufacture of a number of electronics products. Highly pure organometallic compounds are used in a wide range of different areas of both industry and consumer goods, in the production of lasers, photocells, LEDs and mobile phones.

MOS in the last decade are increasingly used in the national economy. They are widely used in organic synthesis as substances with high chemical activity. They are used as well as catalysts for various polymers. They are added to motor fuels as antiknock agents.

Among the MOC there are drugs, antioxidants and stabilizers of high molecular weight compounds.

Organotin compounds are used in paints that prevent the fouling of ships and underwater structures, and as catalysts in the production of some plastics. Organotin compounds are widely used as polymer stabilizers. Organic compounds of alkali metals allow the synthesis of vitamins and antibiotics. Ultra-high purity metals are obtained from organometallic compounds.

Organic mercury compounds are used in the preservation of wood, in the synthesis of organometallic compounds, as pesticides, to protect plastic materials, paper pulp and textiles, casein adhesives from molds. Organo-mercury compounds used to be fungicides in agriculture, but their use is prohibited in many countries for environmental reasons, as Organo-mercury compounds are converted by microorganisms into the water-soluble and toxic methylmercury ion CH3Hg + (which caused an ecological disaster in Minamata, Japan). In nature, an important role is played by vitamin B12, a cobaltorganic compound, the deficiency of which in the body leads to anemia.

Organolithium compounds are widely used in the pharmaceutical industry to produce a variety of organic compounds.

Organoboron compounds are used mainly for the production of boron hydrides, which serve as raw materials for the production of high-calorie fuels for jet engines; complex compounds of the NaB (C ₆ H ₅ ) _{4 type} are used in analytical chemistry for the deposition of K, Pb, Cs, NH ₄ ions.

They find the use of beryllium compounds, for the most part, in nuclear energy as a moderator and neutron reflector and as a structural material. The possibility of using organometallic compounds of beryllium to increase the calorific value of hydrocarbon fuel is currently being studied.

A significant amount of lithium compounds is used to produce glasses having properties such as increased chemical resistance, transparency for ultraviolet and infrared radiation, and photosensitivity. The introduction of lithium compounds contributes to the production of high-voltage porcelain. According to foreign experts, a possible field of application of lithium compounds is rocket technology. It is worth mentioning the use of LiOH as an additive to alkaline batteries, which increases the battery capacity by 12%. Lithium soaps impregnate water-repellent fabrics.

A completely special place among organometallic compounds belongs to tetraethyl lead. The use of this substance as a highly effective antiknock agent in light motor fuels has led to the creation of special production facilities of high power in several countries.

But there are still a number of applications for organometallic substances, for example, in microelectronics for creating thin-layer metal conductive layers, as well as for creating semiconductors. There are developments of various metal-containing coatings and glasses having protective properties against all kinds of radiation.

Due to the high reactivity, many organometallic compounds (especially compounds of metals of the first and second groups of the periodic system) are widely used in organic synthesis. Introduction to the composition of organic compounds of metals has expanded the synthetic possibilities of organic chemistry. So, their ability to produce alcohols, thioalcohols and other derivatives of hydrocarbons is based on the ability of organometallic compounds to interact with sulfur, oxygen, halogens, selenium, tellurium.

Catalytic reactions in which organometallic compounds occur in the form of unstable intermediates (intermediate substances with a short lifetime, formed during the chemical reaction and then reacting further to the reaction products) are of great importance in industry.

Literature

March J. Organic Chemistry. Reactions, mechanisms and structure. 3 volume
Chemical Encyclopedia in 5 volumes. ed. I.L. Knunyants. 1.volume.
Kerry. Sandberg Organic chemistry. Reaction mechanisms. 2 volume
Elshenbroich K. Organometallic chemistry. - M .: BINOM. Knowledge laboratory. - 2011. - ISBN 978-5-9963-0203-1