1、Chapter 8 Nucleophilic and Electrophilic Addition,Types of Reaction,Nucleophiles: Me-, OH-, Et-, CH2CH-,etc. Electrophiles: Me+, H+, Ph3C+, etc. Nucleophilic addition Nucleophilic abstraction Electrophilic addition Electrophilic abstraction,Unsaturated ligands: carbon monoxide, isonitriles, olefins,
2、 dienes, and arenes do not normally react with nuc- in “free” form (e- rich ligands). Coordination to metal (especially e- deficient metals): ligands push e- density to metal and ligandsbecome e- deficient, “activated,” for nuc- attack. Factors to facilitate nucleophilic attack on unsaturated ligand
3、:a) High reactivity of nucleophiles b) Coordinative saturation of the metalc) Formal positive charge on metal d) -Acceptor “ancillary” ligands,Nucleophilic addition,Nucleophilic abstraction,Electrophilic addition,Electrophilic abstraction,Nucleophilic addition to CO and carbenes,CO is very sensitive
4、 to nucleophilic attack when coordinated to metal sites of low basicity. Hydride reagents, organolithium and Grignard reagents, alkoxides, hydroxide, amines, and amide anions.,Nucleophilic addition to polyene and polyenyl ligands,Green-Davies-Mingos Rules: Polyenes (even or Ln ligands) react before
5、polyenyls (odd or LnX ligands) Open ligands before closed Open polyenes: terminal addition in all cases. Open polyenyls: usually terminal attack, but nonterminal if LnM is electron-donating. Rule 1 takes precedence over rule 2 whenever they conflict.,Taking some examples: exo addition,This rules do
6、very well in most cases. The situation can sometimes be much more complicated, however, as shown by the following equation:,Cyclohexadienyl complexes react with nucleophiles to give 1,3-diene complexes:,Diene complexes give allyls on nucleophilic attack:,Note that the amine acts as a carbon, not as
7、a nitrogen nucleophile.,3-Allyls are also readily attacked.,Electronphilic Addition,An electrophile can attack the ligand, or the M-L bonds, or the metal-even in an 18e complex. AlMe3, BF3, HgCl2, Cu+, etc The mechanism is complex and is less well understood.,Addition to the Metal,Addition to a Meta
8、l-Ligand Bond,Protonation are the most common,Addition to Ligand,For soft electrophiles, an endo attack is also possible as a result of initial attack of the electrophile at the metal, followed by transfer to the endo face of the ligand.,For a hard electrophile such as CH3CO+, direct exo attack at the ligand tends to be seen, as in acetylation of ferrocene.,