What is the Difference Between Organometallic Compounds and Metal Carbonyls

The key difference between organometallic compounds and metal carbonyls is that organometallic compounds form from the combination of a metal center with carbon atoms of organic ligands through covalent bonding, whereas metal carbonyl compounds contain a metal center bound to carbon monoxide ligands.

Organometallic compounds and metal carbonyls are coordination complexes containing a metal center and ligands surrounding the metal atom/ion. The ligands are bonded to the metal center through a metal-carbon covalent bond.

CONTENTS

1. Overview and Key Difference
2. What are Organometallic Compounds  
3. What are Metal Carbonyls
4. Organometallic Compounds vs Metal Carbonyls in Tabular Form
5. Summary – Organometallic Compounds vs Metal Carbonyls 

What are Organometallic Compounds?

Organometallic compounds can be defined as complex compounds having one or more Metal-Carbon covalent bonds. These chemical compounds contain covalent bonds between carbon and metal atoms. However, there are some exceptions as well, which include metal-cyano bonds, which are not considered organometallic bonds.

The metal involved in the formation of the organometallic chemical bond can be an alkali metal, alkaline earth metal, a transition metal or a metalloid such as Boron. Some common examples for organometallic compounds are Grignard reagents containing either Lithium (Li) or Magnesium (Mg), ferrocene, tetracarbonyl nickel, etc. Boron is a metalloid, but it also forms organometallic compounds such as organoborane compounds.

Organometallic compounds are good sources of nucleophilic carbon atoms. This is because the electronegativity of the metal is very low compared to carbon. Therefore, the metal atom can form a cation easily by giving bond electrons to the carbon atom. Now, the carbon atom is rich with electrons, and it can act as a nucleophile. This carbon nucleophile can attack electrophilic carbon atoms and form new Carbon-Carbon bonds.

What are Metal Carbonyls?

Metal carbonyl compounds are coordination complexes having transition metal atoms bonded to carbon monoxide ligands. These compounds are very important in organic synthesis reactions and are also useful as catalyst or catalyst precursors in homogenous catalysis (this process includes hydroformylation and Reppe chemistry). Moreover, metal carbonyls are significant in preparing organometallic compounds.

Importantly, when in contact with the skin, the metal carbonyl is usually toxic and can be toxic when inhaled or ingested. This is because of the ability of these compounds to carbonylate hemoglobin, forming carboxyhemoglobin. Therefore, it can prevent the binding of oxygen with hemoglobin in the blood.

Furthermore, most metal carbonyl compounds are colorless or pale yellow in color. These are either volatile liquids or solids at room temperature. In addition, metal carbonyls are flammable and toxic. However, there can be some deep-colored solid metal carbonyls as well; for example, vanadium hexacarbonyl compound is a blue-black colored solid.

There are different ways to prepare metal carbonyls. For example, the direct reaction of the metal with carbon monoxide, reduction of metal salts and oxides, photolysis and thermolysis, salt metathesis, metal carbonyl cations and carbonylates, etc.

What is the Difference Between Organometallic Compounds and Metal Carbonyls?

Organometallic compounds are complex compounds having one or more Metal-Carbon covalent bonds, whereas metal carbonyl compounds are coordination complexes having transition metal atoms bonded with carbon monoxide ligands. The key difference between organometallic compounds and metal carbonyls is that organometallic compounds contain a metal center with carbon atoms of organic ligands, whereas metal carbonyl compounds contain a metal center bound to carbon monoxide ligands.

The following table presents the difference between organometallic compounds and metal carbonyls in tabular form.

Summary – Organometallic Compounds vs Metal Carbonyls

Organometallic compounds and metal carbonyls are coordination complexes containing a metal center and ligands surrounding the metal atom/ion. The key difference between organometallic compounds and metal carbonyls is that organometallic compounds are formed from the combination of a metal center with carbon atoms of organic ligands through covalent bonding, whereas metal carbonyl compounds contain a metal center bound to carbon monoxide ligands.

Reference:

1. “8.1: Metal Carbonyls.” Chemistry LibreTexts, Libretexts, 14 July 2020.

Image Courtesy:

1. “N-butyllithium-tetramer-3D-balls” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia
2. “Iron-pentacarbonyl-from-xtal-3D-balls” By Ben Mills – Own work (Public Domain) via Commons Wikimedia