External attack on coordinated substrates

The nature of an unsaturated compound is modified by formation of a tt bond with a transition metal. Since catalytic processes in organic synthesis are often associated with conversion of unsaturated substrates, alteration of the character of free unsaturated compounds by binding to a transition metal affords a quite useful means in designing the strategy of organic synthesis. For example, the usually electron-rich and nucleophilic properties of unsaturated compounds such as alkenes are modified by formation of a tt bond with an electrophiUc metal center such as Pd(ll). 

Attack of nucleophiles on jf-, and r/ -bonded ligands has found extensive use in catalytic processes. Catalytic processes using the attack on r -, rf-, and J7 -ligands have been less developed, although some stoichiometric synthetic applications using the reactivities of these tt-complexes with external nucleophiles have been reported [101]. Details of the additions to coordinated unsaturated ligands are dealt with in Chapter 8. 

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