Types of Metal Carbonyl Complexes

Metal carbonyl complexes are readily available and serve as starting materials for the preparation of many other organometallic compounds. Numerous reviews and books discuss their preparation and structure. The common stable metal carbonyls are given in Table 2.1, and the commercially available ones are marked with an asterisk.  

Metal carbonyl complexes can be prepared in some cases from the bulk metal and from the reduction of complexes in higher oxidation states. For example, the highly toxic Ni(CO) can be prepared directly from nickel metal and carbon monoxide at one atmosphere pressure, and small amoimts of Fe(CO)j are found in carbon monoxide that has been stored under pressure in steel cylinders. However, most metal carbonyls are best made in an ordinary laboratory by reductive carbonylation, as shown in Equations 2.1 and 2,2. The reducing agents used include electropositive metals and aluminum alkyls, as well as carbon monoxide itself. 

Homoleptic carbonyl complexes of metals in the second and third rows of the transition series form polynuclear carbonyl complexes more often than they form mononuclear carbonyl complexes. For example, Fe(CO)5 is stable and is the most common iron carbonyl, but Os(CO)j is much less stable Os3(CO)jj is more stable. 

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