The effective atomic number of metal in metal carbonyl is equal to that of rare gas, and metal-carbon bond is characterized by having doable bonding of σ-and π-bon-dings.This evidence shows the existence of stable metal carbonyl compounds with diffierent steric configuration by various kinds of metals.
In the oxo reaction typical of various reactions in using the metallic carbonyl as catalyst, from the kinetic equation, products, isomerization and steric hindrance, a mechanism is postulated of the reaction that olefine is first coordinated to HCo (CO)
4 with Co
2 (CO)
8 as catalyst. Reppe's alcohol synthesis can be well explained from this reaction mechanism.
The diffence between metallic carbonyl and metallic solid catalyst is that the former soluble to organic solvent acts as homogenous catalyst and as such all metal atom has equal activity.
Thus the metallic carbonyl gives selective and typical catalytic reaction.The cyclization reaction of acetylenes with the use of so-called Ziegler type catalyst such as AlR
3-TiCl
4, and AlR
3-TiCl
3 is very similar to that with metal carbonyl.
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