 However, only a small subset of naturally-occurring metal complexes and synthetically prepared pharmaceuticals are "organometallic"; that is, they feature a direct covalent bond between the metal(loid) and a carbon atom.The first, and for a long time, the only examples of naturally occurring bioorganometallic compounds were the cobalamin cofactors (vitamin B12) in its various forms.Due to the recent (21st century) discovery of new systems containing carbon-metal bonds in biology, bioorganometallic chemistry is rapidly emerging as a distinct subdiscipline of bioinorganic chemistry that straddles organometallic chemistry and biochemistry.