Biologically important organometallic compounds are molecules where a metal atom is directly bonded to a carbon atom of an organic group. In living systems, certain organometallic compounds play crucial roles in enzymatic reactions, energy production, and biosynthesis. Some notable examples are:
- Vitamin B₁₂ (Cobalamin)
- Contains a cobalt (Co) atom coordinated to a corrin ring.
- The biologically active form, methylcobalamin or adenosylcobalamin, features a direct Co–C bond.
- It is essential for DNA synthesis, fatty acid metabolism, and the conversion of homocysteine to methionine.
- [Fe]-Hydrogenase (Iron–Carbonyl Complexes)
- In hydrogenase enzymes, iron is bonded to carbon monoxide (CO) and cyanide (CN⁻) ligands, forming metal–carbon bonds.
- These complexes help in reversible hydrogen (H₂) metabolism in microorganisms.
- Nickel–Carbon Bonds in Enzymes
- Found in methyl-coenzyme M reductase (MCR), a key enzyme in methanogenesis.
- Involves a Ni–CH₃ organometallic intermediate that participates in methane formation.
- Iron–Sulfur Clusters (Fe–C Interactions in Radical SAM Enzymes)
- Though primarily Fe–S bonded, certain radical SAM enzymes generate organometallic intermediates where iron forms transient Fe–C bonds with organic radicals.
- Hemoproteins (Special Cases)
- While hemoglobin and cytochromes mainly involve Fe–N and Fe–O bonds, some heme enzymes (like cytochrome P450) can transiently form Fe–C bonds with organic substrates during catalysis.
In summary:
The most classical and widely recognized biologically important organometallic compound is Vitamin B₁₂ (with its stable Co–C bond). Others include Fe–CO complexes in hydrogenases and Ni–C intermediates in methane metabolism.