Organometallic Compounds - Definition, Structure, Properties and Applications

How much do you know about Vitamin B12? It is required for the production of red blood cells and DNA. It's also important for brain and nerve cell function and growth. It means it is very important for the human body. This compound is a naturally occurring organometallic coordination compound and is also known as Cobalamin. It has cobalt metal attached to a carbon in the molecule. 

Nickel is obtained in pure form from nickel carbonyls. It is also an organic compound. But what is this organometallic?

Table of Contents

• Organometallic Compounds
• Metal carbonyls
• Synergic Bond
• Practice Problems
• Frequently Asked Questions

Organometallic Compounds

Organometallic compounds have one or more of a bond between a metallic element and a carbon atom of an organic or inorganic molecule. Metallic elements can donate electrons ot form ionic bonding with electronegative elements and at the same time use their empty d-orbitals for electron acceptance to form covalent bonding.

For example, organomagnesium compounds in which carbon is directly bonded to magnesium.

Below are a few examples of organometallic compounds:

Organozinc(RZnX), Organocadmium[(R)₂Cd], Organolithium (RLi) and Organoboron (BR₃) etc. where X is a halide ion.

Metal carbonyls

Metal carbonyls are carbon monoxide transition metal complexes with metal-carbon (M-C) bonds.

Example: Ni(CO)₄, Fe(CO)₅ & Co(CO)₆

Some important examples of multi centred organometallic compounds:

The two types of bonding found in metal carbonyls are described here:

• Type-1: A metal-carbon σ bond is created as a result of the carbonyl molecules donating electrons from non-bonding molecular orbital (NBMO) to metal's empty orbitals.
  

• Type-2: A metal-carbon bond is created when a pair of electrons from a filled d orbital of metal are donated to the unoccupied antibonding π* orbital of the carbonyl ligand.

Synergic Bond

A synergic bond is a π-bond established between a metal atom/ion and a ligand by reverse donation of a metal atom/ion.

Synergic Effect

Synergic bonding causes the internal bond length of a ligand and the metal-ligand bond length to vary, which is known as the synergic effect.

The synergic effect is caused by a self-strengthening link that involves electron transfers from 

Ligand to metal 

Metal to ligand

Synergic Bonding in the case of Alkenes

The metal's filled d-orbitals overlap with the ethylene molecule's vacant π* molecular orbital to generate a back bond/synergic bond.

General properties of organometallic compounds-

1. Since organometallic compounds have covalent bonds, the compounds are insoluble in aqueous solvents but soluble in nonpolar organic solvents..
2. The compounds have large molecular weight and exist as solids.
3. These compounds are very active. So, they are either prepared in situ for reactions or stored in inert solvents if needed.. 
4. Exhibit lower melting points. 
5. Are toxic to humans and need precautions during preparations and uses.

Applications of organometallic compounds

Organometallic compounds are critical to the advancement of science. They have a wide range of applications and are commonly employed in laboratories and the chemical industry.

1. Organomagnesium halides (Grignard reagents), as well as organolithium and organoboron compounds, are commonly utilised in synthetic organic chemistry. 
2. Organic synthesis uses alkyl aluminum compounds as well. They are essential catalysts in the polymerization of unsaturated hydrocarbons like ethylene and propylene when combined with titanium salts. The interaction between the titanium atoms and the double bonds of the hydrocarbons is most likely the mechanism of action of titanium-aluminum alkyl catalysts which are known as Ziegler -Natta catalyst in the polymerisation of alkenes.
3. Pharmaceuticals, insecticides, polyvinyl chloride stabilizers, and fire retardants are just a few of the applications for organotin chemicals.
4.  Because of its toxicity, methylmercury has wreaked havoc on the environment. As a result of this, mercury flow from chemical factories into rivers, lakes, and oceans is strictly regulated.

Practice Problems

Q1. Why is Co₄(CO)₁₂ known as an organometallic compound?

A. There are carbon and metal present in the coordination compounds.
B. Whenever there is a carbonyl present, that compound form organometallic compounds
C. There is a direct bond of Cobalt metal and carbon present in the compound
D. All statements are true.

Solution: Organometallic compound has at least one bond between a metallic element and the carbon atom of an organic molecule. 

In option (A), only the presence of carbon and metal is not enough to become an organometallic compound. So it is incorrect.

In option (B), Carbonyl alone is not a sign of an organometallic compound, metal should be attached to the carbon of carbonyl. So this option is also incorrect.

In option (C), the statement is correct as a direct bond of metal and carbon is a basic condition of an organometallic compound. So this option is correct.

The correct answer is (C).

Q2. How many metal-metal bonds and bridged bonds are present in the organometallic compounds Fe₃(CO)₁₂ ?

A. 3,2
B. 3,3
C. 4,3|
D. 4,2

Solution: As we can see from the structure, there are 3 metal-metal bonds present in between iron atoms and two bridge bond present via carbonyl. So, the correct answer should be 3, 2 (A).

Q3. Why is Mn2(CO)10 known as an organometallic compound?

A. There are carbon and metal present in the coordination compounds.
B. There is one metal-metal bond present
C. There is a direct bond of manganese metal and carbon present in the compound
D. There is synergic bonding present in the molecule.

Solution: Organometallic compound has at least one bond between a metallic element and the carbon atom of an organic molecule. 

In option (A), only the presence of carbon and metal is not enough to become an organometallic compound. So it is incorrect.

In option (B), the Metal-Metal bond is not a basic condition of organometallic compounds. So this option is also incorrect.

In option (C), The statement is correct as a direct bond of metal and carbon is a basic condition of organometallic compound. So this option is correct.

In option (D), The statement is correct as a synergic bond is present in the molecule but it is not a basic condition of an organometallic compound.

The correct answer is (C).

Q4. Which of the following statements are true for Fe₂(CO)₉(gas phase)?

A. There are 3 bridge bonds present in the compound.
B. There is one metal-metal bond present
C. There is synergic bonding present in the molecule.
D. All are true.

Solution: Organometallic compound has at least one bond between a metallic element and the carbon atom of an organic molecule. 

In option (A), there are three bridge bonds present in the compound.

In option (B), the Metal-Metal bond is also present in this organometallic compound. 

In option (C), The statement is correct as a synergic bond is present in the molecule between metal's filled d-orbitals overlaps with the carbonyl molecule's vacant π* molecular orbital.

Hence, all the statements are true. Here, The correct answer is (D).

Frequently Asked Questions

Question 1. What are the applications of Organometallics compounds?
Answer: Organometallic compounds are widely used as stoichiometric catalysts in research and industrial chemical reactions, as well as in the role of catalysts to increase the rates of such reactions (e.g., inhomogeneous catalysis), with target molecules including polymers, pharmaceuticals, and a wide range of other practical products. One of the earliest organometallic compounds to be identified and utilized in cancer treatment was Zeise's salt.

Question 2. What are the applications of organometallic compounds in medicine?
Answer: In general, synthetic organometallic compounds are poisonous or incompatible with biological systems. Despite this impression, the therapeutic effects of organometallic compounds, particularly organo-transition metal complexes, have long been studied, and the field has expanded significantly in recent years. They're useful in cancer treatment and diagnosis, as well as the treatment of viral, fungal, bacterial, and parasitic diseases.

Question 3. What is the nature of the link between the metal atom and the organic compound's carbon?
Answer: In most cases, the bond between the metal atom and the carbon in the organic complex is covalent. The carbon linked to the central metal atom has a carbanionic character when metals with relatively high electropositivity (such as sodium and lithium) create these combinations.

Question 4. Discuss the reducing nature of organometallic compounds?
Answer: Because the metal gives up electrons to the carbon, resulting in a polar M-C bond with a partial positive charge on the metal and a negative charge on the carbon, electropositive components of organometallic compounds such as lithium, sodium, and aluminium are particularly good reducing agents.

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