Organometallic Chemistry: Definition, Properties & Structure

Organometallic chemistry is a branch of science that combines features of inorganic and organic chemistry. Organometallic chemistry deals with chemical compounds that include at least one chemical bond between an organic molecule's carbon atom and a metal, such as alkali, alkaline earth, transition metals, as well as metalloids like boron, silicon, and selenium. Along with the links to organyl fragments or molecules, organometallic linkages to inorganic carbon, like carbon monoxide, cyanide, or carbide, are also common. Metal -diketonates, alkoxides, dialkyl amides, and metal phosphine complexes are also members of this category.

Key Terms: Organometallic compounds, metalloids, transition metals, organyl group, organic ligands, hapticity.

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What are Organometallic Compounds?

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Organometallic compounds (e.g., organopalladium compounds) are any compounds that contain a bond between a metal atom and a carbon atom of an organyl group. Organometallic compounds include lanthanides, actinides, semimetals, elements boron, silicon, arsenic, and selenium, in addition to classical metals (alkali metals, alkali earth metals, transition metals, and post transition metals). Gilman reagents, which are having lithium and copper, and Grignard reagents, which are having magnesium, are some examples of organometallic compounds.

• Organometallic compounds which include transition metals include tetracarbonyl nickel and ferrocene. 
• Organolithium compounds like n-butyllithium (n-BuLi), organozinc compounds like diethylzinc (Et2Zn), organotin compounds like tributyltin hydride (Bu3SnH), organoborane compounds like triethylborane (Et3B), and organoaluminum compounds like trimethylaluminum are all examples of organometallic compounds (Me3Al). 
• Methylcobalamin (a type of Vitamin B12) is a in nature occurring organometallic complex which comprises a cobalt-methyl link. 
• The subfield of bioorganometallic chemistry frequently discusses this complex, as well as other biologically related complexes.

Concept Map of Organometallic Chemistry

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Distinction From Coordination Compounds With Organic Ligands

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Coordination bonds between metal and organic ligands are found in many complexes. 

• Coordination compounds (e.g Heme A and Fe (acac)3) are complexes in which the organic ligands attach to the metal via a heteroatom such as oxygen or nitrogen. 
• However, the complex is called organometallic if any of the ligands create a direct metal-carbon (M-C) link.
• Despite the lack of a formal definition by the IUPAC, some chemists use the word "metalorganic" to designate any coordination molecule with an organic ligand, regardless of whether or not a direct M-C bond exists. 
• The nature of the anionic moiety, the metal ion, and possibly the medium can affect the status of compounds in which the canonical anion has a negative charge that is shared between a carbon atom and an atom more which is electronegative than carbon (e.g. enolates). 
• Such compounds are not termed organometallic in the absence of direct structural evidence for a carbon–metal connection. 
• Lithium enolates, for example, frequently only have Li-O bonds and are not organometallic, but zinc enolates (Reformatsky reagents) have both Zn-O and Zn-C links and are organometallic.

Coordination Compound

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Properties of Organometallic Compounds

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Here are some properties of Organometallic Compounds-

1. In most organometallic complexes, the metal-carbon link is extremely covalent. The carbon ligands of highly electropositive elements, such as lithium and sodium, have carbanionic properties, while free carbon-based anions, such as cyanide, are extremely rare. 
2. At normal temperature, the majority of organometallic compounds are solids, although some are liquids, such as methylcyclopentadienyl manganese tricarbonyl, or even volatile liquids, such as nickel tetracarbonyl. 
3. As many organometallic compounds are air sensitive (reactive to oxygen and moisture), they must be handled in a controlled environment. 
4. Some organometallic compounds, such as triethylaluminum, are pyrophoric, igniting when exposed to air.

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Structure of Organometallic Compounds

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Following are the diagrammatic representations of Organometallic Compounds such as Ferrocene, Cobaltocene, Lithium diphenylcuprate, Iron pentacarbonyl, etc.

Diagram of Organometallic Compounds

Also Read- Electrophile

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Other Concepts about Organometallic Compounds

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Here are some other Concept of Organometallic Compounds-

1. Electron Countings

Electron counting, like in other areas of chemistry, is beneficial for organizing organometallic chemistry. 

• The stability of organometallic complexes, such as metal carbonyls and metal hydrides, can be predicted using the 18-electron rule. Ionic and neutral (also known as covalent) ligand models are two sample electron counting models in the 18e rule.
• The electron count can be influenced by the hapticity of a metal-ligand combination. 
• The amount of continuous ligands coordinated to a metal is referred to as hapticity (η, Greek Letter eta). 
• For example, ferrocene [(η₅-C₅H₅)₂Fe] has two cyclopentadienyl ligands, giving it a hapticity of 5, with each of the C₅H₅ ligand's five carbon atoms contributing one electron to the iron core.

2. Symbols

The Greek symbol kappa, κ is used to represent ligands that bind noncontiguous atoms. 

• A good example is chelating κ2-acetate. 
• The covalent bond categorization approach divides ligands into three categories: X, L, and Z, based on the ligand's electron donating interactions.

3. Other Rules

The 18e rule is not followed by many organometallic compounds. 

• The d electron count and oxidation state of metal atoms in organometallic compounds are widely used to define them. 
• These ideas can aid in predicting their reactivity and preferred geometry. 
• The isolobal concept is frequently used to discuss chemical bonding and reactivity in organometallic compounds.

4. The Structure, Composition, and Characteristics

The structure, composition, and characteristics of organometallic compounds are determined using a range of physical approaches.

•  X-ray diffraction is a crucial technique for locating atom locations inside a solid compound and providing a thorough description of its structure. 
• Other methods for obtaining information on the structure and bonding of organometallic compounds include infrared spectroscopy and nuclear magnetic resonance spectroscopy.

5. Other Important Concept

The use of ultraviolet-visible spectroscopy to gather information on the electronic structure of organometallic compounds is a widespread practice. 

• It's also used to keep track of the progress of organometallic processes and figure out their kinetics.
• Dynamic NMR spectroscopy can be used to investigate the dynamics of organometallic compounds. X-ray absorption spectroscopy, electron paramagnetic resonance spectroscopy, and elemental analysis are among the other notable techniques.

Also Read- Lassaigne’s Test

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Things to Remember

• Organometallic chemistry is the study of chemical compounds that have at least one chemical bond between a carbon atom of an organic molecule and a metal, such as alkali, alkaline earth, and transition metals, as well as metalloids like boron, silicon, and selenium.
• Metal-containing compounds that lack direct metal-carbon bonds but contain organic ligands are referred to as "metalorganic compounds," a related but different concept. 
• Coordination bonds between a metal and organic ligands, found in many complexes. Coordination compounds (e.g Fe(acac)3), are complexes in which the organic ligands attach to the metal via a heteroatom such as oxygen or nitrogen.
• In most organometallic complexes, the metal-carbon link is extremely covalent. 
• Electron counting, like in other areas of chemistry, is beneficial for organizing organometallic chemistry. 
• The structure, composition, and characteristics of organometallic compounds are determined using a range of physical approaches. X-ray diffraction is a crucial technique for locating atom locations inside a solid compound and providing a thorough description of its structure.