The stability of metal carbonyl complexes falls off markedly as we go to the right of group 10 in the periodic table. For example, Cu complexes only bind CO weakly. Why is this? What oxidation state, of the ones commonly available to copper, would you expect to bind CO most strongly?
The metal atom in metal carbonyls is in low oxidation state. This is because if the fact that there is a higher electronic density (electronic charge) on the metal atom in its lower oxidation state than in its higher oxidaton state.
Some metal carbonyls are prepared by the reduction of metal halides in the presence of high pressure of carbon monoxide. A variety of reducing agents are employed, including copper, aluminum, hydrogen, as well as metal alkyls such as triethylaluminium.
Metal carbonyls are thermodynamically unstable. They undergo aerial oxidation with different rates. Co2(CO)8 and Fe2(CO)9 are oxidized by air at room temperature while chromium and molybdenum hexacarbonyls are oxidized in air when heated. The metal carbonyls give a variety of chemical reactions.