Organometallic Compounds - Examples, Preparation, Properties. Structure, FAQs

Organometallic compounds are a special and dynamic class of chemical compounds with at the minimum of one direct metal-carbon (M–C) bond. These compounds serve as a link between inorganic chemistry (compounds including metals) and organic chemistry (molecules based on carbon), and they are very useful in the field of industrial operations, material science, medicines, and catalysis.

This Story also Contains

1. Organometallic Compounds
2. Classification of Organometallic Compounds
3. Types And Examples of Organometallic Compounds
4. Applications: Organometallic Compounds in Real Life
5. Some Solved Examples

In this article, the topic of organometallic compounds is covered, that are very important topic of chapter Coordination Compounds from the board exam point of view and also for the JEE Mains Exam, NEET Exam, and many other entrance exams like SRMJEE, BITSAT, WBJEE, BCECE, and more

Organometallic Compounds

Organometallics are a class of chemical species defined by the presence of at least one bond between a carbon atom and a metal atom. Species of this kind are of interest and show properties that clearly distinguish them from organic and inorganic pure compounds. They can be as simple as alkali and alkaline earth metals or connected with different transition metals and metalloids, such as silicon and tin. The very metal-carbon bond is different in nature; it changes from covalent to ionic and even multicenter, which alters the reactivity and stability of the compounds.

The role of organometallic compounds in chemistry cannot be overestimated. They entered this field most importantly in the area of catalysis, where chemical reactions are enabled to proceed at extremely high turnover long before any mediators are consumed. Another striking example in this respect is Grignard reagents and metal carbonyls that have been used in organic synthesis with wider applications. Thus, the platform is provided by the chemist or scientist to understand the properties and behavior of such compounds and further develop processes and optimize them.

Compounds that contain at least one carbon-metal bond are called organometallic compounds. Zeise, in 1830, prepared the first organometallic compound by the action of ethylene on a solution of Potassium chloroplatinate(II). In the last four decades, enormous work has been done in this field and many fascinating compounds have been synthesized and investigated. Grignard reagent, RMgX is a familiar example of organometallic compounds where R is an alkyl group. Diethyl zinc [Zn(C₂H₅)₂], lead tetraethyl [Pb(C₂H₅)₄], ferrocene [Fe(C₅H₅)₂], dibenzene chromium[Cr(C₆H₆)₂], metal carbonyls are other examples of organometallic compounds. The compounds of metalloids such as germanium and antimony and non-metallic elements such as boron and silicon are also included under this classification.

Classification of Organometallic Compounds

Sigma(σ) bonded Complexes:

These complexes contain a metal and carbon atom attached with a sigma bond e.g. Tetramethyl Tin, Trimethyl aluminum, etc.

Bonding in Trimethyl aluminum is shown below

Pi(π) Bonded Complexes:

These complexes contain a metal and carbon atom attached to a Pi Bond. e.g. Ferrocene, Dibenzene Chromium, etc. Bonding in Ferrocene and Dibenzene Chromium is shown below:

Complexes Containing Both σ and π Bonding Characteristics:

These complexes contain both σ as well as π bonding characteristics. e.g. Metal Carbonyls. The M−Cσ bond is formed by the donation of the lone pair of electrons of the carbonyl group into the vacant d orbital of metal while the M−Cπ bond is formed by the back donation of the lone pair of electrons from the metal into vacant antibonding π∗ molecular orbital of CO. This synergic bonding leads to the formation of stronger bonds and stable metal carbonyl complexes. The bonding in metal carbonyls is shown below:

Types And Examples of Organometallic Compounds

Organometallic compounds can be classified depending on the particular metal or the type of carbon-metal bond.

General Broad Categories Include:

• Main-Group Organometallic: They are compounds that react actively with alkali and alkaline earth metals to form organolithium and organomagnesium compounds. For instance, Grignard reagents are of paramount importance in organic synthesis due to the fact that they can form carbon-carbon bonds.
• Transition Metal Organometallics: A class of compounds of transition metals with carbon atoms includes ferrocene and metal carbonyls. Ferrocene is an example of a metallocene; that is, it is a substance that contains a central iron atom sandwiched between two cyclopentadienyl anions. It is highly stable and also shows electronic properties.
• Apart from this, organometallics are also classified by functional groups and by the reactivity character of these groups. For example, organotin compounds are found in plastics, stabilizers, and biocides, while organocuprates are one of the dominating compounds in most nucleophilic substitution reactions.

Examples of tetra hepto ligands are Cycloheptatriene and cyclooctatetraene.

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Applications: Organometallic Compounds in Real Life

The importance of organometallic compounds does not merely lie within the laboratories; they are also relevant in industries and real-life applications.

• Catalysis: Organometallic compounds act as catalysts in chemical reactions that more or less take place in the enhancement of reaction rate and selectivity. For example, organometallic complexes, such as Ziegler–Natta, are of paramount importance in the polymerization of alkenes, which in turn are used in making polyethylene and polypropylene. Pharmaceuticals: Organometallic compounds work as important mediums in the synthesis of many drugs in the pharmaceutical industry. They are important in that they can provide proper carbon-carbon bond formation so that highly complex organic molecules can be developed.
• Environmental Concerns: These compounds can either be of great utility or can be a great threat to health and the environment. An example is the very toxic compound methylmercury with one application that has caused very serious ecological and health problems and is under very stringent regulatory control on its use and disposal.
• Semiconductors and Electronics: Organometallic compounds are used extensively today in the production of semiconductors and other electronic devices. For example, trimethylgallium for LED and solar cell MOCVD thin-film deposition.
• Organometallic compounds have so many and so varied applications that they underline their relevance both in academic research and practical, industrial applications. Their special properties and reactivity make organometallic compounds powerful tools in the promotion of chemistry and technology.

Some Solved Examples

Example 1
Question: Mn₂(CO)₁₀ is an organometallic compound due to the presence of:

1) Mn-C bond
2) Mn-Mn bond
3) Mn-O bond
4) C-O bond

Solution: Mn₂(CO)₁₀ is classified as an organometallic compound because it contains a Mn-C bond. Therefore, the correct answer is option (1).

Example 2
Question: The number of bridging CO ligands in [Mn₂(CO)₁₀] is __________.

1) 0
2)1
3)3
4)2

Solution: There are zero bridging CO ligands present in [Mn₂(CO)₁₀]. Thus, the answer is 0.

Example 3 Which of the following is not true for metal carbonyls?

1) The oxidation state of the metal in the carbonyls is generally zero

2) Metal carbonyls generally follow the Effective atomic number rule

3) Metal carbonyls have a bond order that is greater than 1 between the metal and the carbonyl carbon

4) (correct)$d\pi -p\pi$ overlap is observed in metal carbonyls

Solution

Metal carbonyls do not show $d\pi -p\pi$ overlapping.

The back donation takes place from the d orbital of the metal to the vacant ${\pi }^{\ast }$ molecular orbital of the carbonyl ligand.

All other statements are correct.

Hence, the answer is the option (4).

Example 4
Question: The number of complexes that will exhibit synergic bonding among [Cr(CO)₆], [Mn(CO)₅], and [Mn₂(CO)₁₀] is ________.

1) 3
2) 4
3) 8
4) 5

Solution: All three complexes are metal carbonyl complexes and exhibit synergic bonding. Hence, the answer is 3.

Example 5
Question: The oxidation states of iron atoms in compounds (A), (B), and (C), respectively, are x, y, and z. What is the sum of x, y, and z?

1) 6
2) 9
3) 4
4) 5

Solution: The sum of the oxidation states of iron atoms in compounds (A), (B), and (C) is 6. Therefore, the correct answer is 6.