Chromium carbonyl, also known as chromium hexacarbonyl, is the chemical compound with the formula Cr(CO)6. At room temperature the solid is stable to air, although it does have a high vapor pressure and sublimes readily. Cr(CO)6 is zerovalent, meaning that Cr has a formal charge of zero, and it is called a homoleptic complex, which means that all the ligands are the same.

Organocobalt compounds are involved in several organic reactions and the important biomolecule vitamin B12 has a cobalt-carbon bond. Many organocobalt compounds are investigated for catalytic properties [1]. An early example of organocobalt chemistry is the carbonylation of azobenzene with dicobalt octacarbonyl as described by Murahashi & Horiie in 1956

Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.

Tungsten hexacarbonyl (also called tungsten carbonyl) is the chemical compound with the formula W(CO)6. This complex gave rise to the first example of a dihydrogen complex.