Metal-Catalyzed Cyclization Reactions of Hydrocarbons

This chapter emphasizes on the metal-catalyzed cyclization reactions, with reference to oxide and dual-function catalysts. Product cycles may contain five or six carbon atoms. A common feature of any cyclization reaction is that a new intramolecular C-C bond is produced that would not have been formed in the absence of the catalyst. Those reactions in which one ring closure step is sufficient to explain the formation of a given cyclic product will be called "simple" cyclization processes, although their mechanism is, as a rule, complex. As few as six different kinds of adsorption are proposed in the chapter as being responsible for a great variety of hydrocarbon transformations over metal catalysts. This approach is fully accepted that the character of primary adsorption determines the structure of the product. One of the main points that is stressed is that very different reactions may often be concealed behind the expression "cyclization." An attempt is made in the chapter to correlate primary adsorption (consequently the reactions expected) with two main factors: the nature of the metal and the amount of hydrogen available during the catalytic process. The latter may be of paramount importance: the amount of surface hydrogen may govern which type of chemisorbed species is formed and, by doing so, determine catalytic selectivity.