The carbonylation of benzyl chloride to phenylacetic acid catalyzed by carbonyl cobalt is discussed in great detail.

Carbonyl groups readily attach themselves to nickel or cobalt atoms, but not so strongly that they cannot link to other molecules and jump ship to form larger molecules.

When we conduct experiments using nickel or cobalt sulfides, we see that carbon addition occurs primarily by carbonylation-the insertion of a carbon and oxygen molecule, or carbonyl group.