Organometallic chemistry

Organometallic chemistry is responsible for the study, synthesis, and reactivity of organometallic compounds, those chemical compounds that have at least one bond between a carbon atom of an organic ligand and a metal atom. In this context, the term metal can be defined using an electronegativity scale, assigning the word metal to that element that presents a less electronegative character than carbon. From this point of view, elements known as metalloids, such as silicon, are designated as metals.

It can be considered a part of chemistry that is different from organic chemistry (in which carbon is covalently bonded to non-metal atoms such as hydrogen, oxygen, nitrogen, phosphorus, sulfur, or halogens) and also different from organic chemistry. inorganic chemistry.

Several metals where different transition metals appear attached to cycles of carbon atoms and other atoms or ligands.

Organometallic chemistry is a discipline that encompasses other subdisciplines of chemistry, such as: organic chemistry, inorganic chemistry, physical chemistry, electrochemistry. This transdiscipline of organometallic chemistry means that it has technological applicability in various chemical industries. To mention just a few cases: catalytic hydrogenation of olefins using homogeneous systems, at lower pressure and temperature, polymerization of ethylene and propylene that generate plastic polymers with a higher degree of tacticity, etc.

History

Its beginning can be established in the middle of the XIX century with the synthesis of diethylzinc by Edward Frankland in 1849, mixing ethyl iodide with zinc.

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Its real takeoff took place from 1900 with the development of Grignard reagents, organomagnesium halides.

In 1909, Pope and Peachey prepared trimethylplatinum iodide, the first alkyl of a transition metal.

In 1910, the first organometallic medicine, salvarsan, was marketed to treat syphilis patients.

In the second half of the XX century, many industrial processes where knowledge about these compounds was applied, such as Ziegler-Natta catalysis for the manufacture of polyethylene, a plastic of great interest.

Concepts and techniques

As in other areas of chemistry, electron counting is useful for organizing organometallic chemistry. Generally, these compounds do not follow the octet rule, but rather the 18-electron rule, very useful for predicting the stabilities of metal carbonyls and other related compounds. The chemical bonding and reactivity of organometallic compounds is often discussed from the perspective of the isolobal or isolobularity principle.

NMR and infrared spectroscopy are the most common techniques used to determine the structure of these organometallic compounds. The dynamic properties of organometallic compounds are often tested by programming experiments at variable temperature in NMR and with chemical kinetics experiments.

Organometallic chemistry classification

The main classifications that are made are:

By groups

Depending on the metal used:

• Organometallic compounds of alkaline metals: Although it is classified with the name of the group, actually the lithium (Li) is the only participant of the group, forming the organolithium compounds. Sodium (Na), potassium (K), blond (Rb), cesium (Cs)... form ionic links, so they do not form organometallic compounds. An example of organolitiates and their use is the N-butil-litio used in organic synthesis. Although organic salts of alkaline metals are used in organometallic chemistry, these compounds are salts, not organometallic (sodium cylopentadyenide, potassium terc-butoxide...).
• Organometallic compounds of alkalinetheran metals: Organomagnesians of Grignard Regents stand out, and to a lesser extent organoberilio compounds. The latter are highly toxic and very sensitive to air and humidity, so they are not as used or studied as the first. In the case of using heavier alkalinetherree metals (calcium (Ca), strontium (Sr), barium (Ba)...), they have covalents of a marked ionic character, due to their greater electropositiveness and greater ionic radius, their organometallic chemistry more resembles that of divalent ions of lanthanides such as yterbium (Ybium).²⁺), samario (Sm²⁺), europio (Eu²⁺... than to his counterparts of the Berry group (Beryllium)²⁺) and magnesium (Mg²⁺).
• Organizational compositions of Group 12: These elements are often included within the organometallic compounds of group 2, since they have the full d layer, and do not have acceptor or giver properties such as the other transitional elements. They highlight mainly zinc and mercury, although the latter due to its toxicity, it is increasingly falling into disuse. Cadmium compounds have also been studied to a lesser extent, and are also toxic.
• Organizational compositions of the Boro group (group 13): Although in this group all the organometallic compounds of the boro (B), aluminum (Al), galio (Ga), Indian (In) and Talio (Tl) are included, the most widely studied organometallic chemistry of this group is relative to the boro and aluminium. Unlike the rest of the group, the B and the Al tend to form several links from the same central atom, forming clusters like organoborans. In the case of aluminum, the DIBAL used in the hydrogenation of organic compounds stands out.
• Organometallic compounds of the Carbon Group (Group 14): The organosilitium compound, whose silicones open a new world of material chemistry, and the organostatins and organoplomos that have been widely used in the chemical industry (e.g. tetraethylplom was used for years as antidetonant in gasoline). To a lesser extent, the [organogermanio responsible for organogermanio] have been studied, which a priori seem to have intermediate properties between the organoestaños and the organosilicio.
• Organometallic compounds of the Nitrogen Group (Group 15): Since phosphorus is a non-metal, the organometallic chemistry of the elements of the Group 15 includes only arsenic (As), antimony (Sb) and biscuit (Bi). Because of this, this group does not have great differences between the organometallic compounds of the different elements of the group, as they are intimately related to each other. Although it was started using arsenic derivatives (arsfenamine, etc) in pharmacology, due to the high toxicity of the organometallic compounds of this group, the only current use is limited to the production of organoarsenic compounds of semiconductors.
• Organizational compositions of Group 16: As in group 15, oxygen and sulfur are non-metallic, so they cannot form organometallic compounds. In addition, the polonium is radioactive. Because of this, in this group we only have selenium (Se) and telury (Te). Selenium has been studied in more depth, is found in biomolecules of living beings, and even very interesting organic synthesis reactions have been found, such as the elimination of selenoxide, which is used for the synthesis of compounds with carbonyl groups α β-unsaturated
• Organizational compositions of Group 11: Copper (Cu), silver (Ag) and gold (Au) are always separated from other transitional elements because they tend to have certain particularities that differentiate them from the rest. The organometallic chemistry of copper and silver is exclusive of the oxidation state (I), although a compound is known, a tetraorganoargentate (III), [Ag(CF)₃)₄]^-which owes its existence thanks to the electro-negativity of the CF groups₃. In the case of organometallic gold compounds, oxidation (I) and (III) compounds may be found.
• Organometallic compounds of transition metals: The core of organometallic chemistry is in this particular group. Due to the variety of oxidation states, ways to fill the empty orbitals d, possibility of multiple links to metal, complexes with ligands dadores and/or acceptors, etc. this group presents a very wide organometallic chemistry.

By structure

Depending on how the metal is linked to the organic molecules, we can have different types of organometallic structures:

• Sandwich compounds: Among those who stand out the metalocenes.
• Metallic carves: They are characterized by a double metal-carbon link, among which are Fisher's carvens and Schrock's carvens.
• Metal carbonyl: Used in various industrial applications.

Synthesis of organometallic compounds

Organometallic compounds can be obtained from several important reactions, among them are:

• oxidant attachment and reducer removal
• Direct synthesis
• Metalling
• Mercury (metalation with mercury)
• Transmetal
• Carbometal
• Hydrometalization
• Electronic transfer
• Beta-elimination
• Metases reaction: Metal exchange, metal-halogen exchange, lease...
• Olephin metastases
• Activation of the C-H link
• Cyclometalization
• Carbene insertion
• Downloadboxylation
• Migratory insertion
• nucleophilic aggregation