Nickel tetracarbonyl and iron pentacarbonyl can be prepared according to the following equations by reaction of finely divided metal with carbon monoxide:
:Ni + 4 CO → Ni(CO) (1 bar, 55 °C)
:Fe + 5 CO → Fe(CO) (100 bar, 175 °C)
Nickel tetracarbonyl is formed with carbon monoxide already at 80 °C and atmospheric pressure, finely divided iron reacts at temperatures between 150 and 200 °C and a carbon monoxide pressure of 50–200 bar. Other metal carbonyls are prepared by less direct methods.