Electronegative elements nucleophilic attack

You see in Chapter 10 that aldehydes and ketones contain a carbonyl group attached to carbon or hydrogen atoms. In the case of carboxylic acids and their derivatives, a carbonyl group is attached to an electronegative element such as oxygen, chlorine, or nitrogen. The presence of these elements tends to increase the 5+ charge on the carbonyl carbon, which makes the carbon atom more susceptible to nucleophilic attack. 

Nucleophilicity decreases with increasing electronegativity of the attacking atom. This is true both in comparisons of atomic centers that belong to the same period of the periodic table of the elements... 

The main differences between using an iron cation and Pd(ll) to activate an olefin are (a) Pd(ll) reactions are often catalytic processes (b) the C-Pd a bond that results from nucleophilic attack on the coordinated olefin is reactive and undergoes either decomposition or further transformations, usually with reduction of the Pd species to Pd(0). There are numerous examples of arylation reactions of Pd(ll)-coordinated olefins, but only a few simple alkylation reactions. Pd-catalyzed reactions are usually more important for forming C-X bonds where X is an electronegative element (Section IV). Some examples of typical Pd-catalyzed C-C bond-forming reactions-are given in Eqs.(ll)-(15)(Heck, 1968, 1969), Eq. (16) (Heck, 1972), and Eq. (17) (Brown, 1974) (see also S. Tsuji, 1969 J. Tsuji, 1972 Bird, 1972, Henry, 1973). 

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