Acyl coordinated ligands, electrophilic

Electrophilic attack on coordinated cyclopentadienyl rings, particularly those in ferrocene, is well established. This process occurs in a similar fashion to electrophilic attack on arenes and was used to establish the binding mode of the Cp ligand in ferrocene (see Equation 3.88). These reactions of the Cp ligand with electrophiles are described in more detail in Chapter 12, which covers electrophilic attack on coordinated ligands. Friedel-Crafts acylation, formylation, aminomethylation, and mercuration are all known. - ... 

Mononuclear acyl Co carbonyl complexes ROC(0)Co(CO)4 result from reaction of Co2(CO)8 with RO-.77 These also form via the carbonylation of the alkyl precursor. The ROC(0)Co(CO)4 species undergo a range of reactions, including CO ligand substitution (by phosphines, for example), decarbonylation to the alkyl species, isomerization, and reactions of the coordinated acyl group involving either nucleophilic attack at the C or electrophilic attack at the O atom. 

At the present, the most straightforward mechanism for the formation of J5 from 1 is via insertion of CO into the Th-C(acyl) bond to form a ketene (H, (eq. (4)) which subsequently dimerizes. Presumably, initial CO interaction could involve coordination either to the metal ion as shown or to the electrophilic vacant "carbene p atomic orbital. Considering the affinity of the Th(IV) ion for oxygenated ligands, interaction of the ketene oxygen atom with the metal ion seems reason-... 

These ligand have already been met (Chapter 3), including the three key synthetic routes migratory insertion of o-organyl/carbonyl complexes, electrophilic attack at electron rich metals by acyl halides or anhydrides and nucleophilic attack at coordinated CO (Figure 4.12). 

In its reactions, coordinated cyclobutadiene exhibits aromatic character, undergoing electrophilic substitution, e.g. Friedel-Crafts acylation. A S5mthetic apphcation of (r " -C4H4)Fe(CO)3 in organic chemistry is as a stable source of cyclobutadiene oxidation releases the ligand making it available for reaction with, for example, alkynes as in scheme 23.117. 

First, coordinatively unsaturated active palladium catalyst, PdL2, is produced via dissociation of the ligands, which then reacts with acyl halide to give the acylpalladium intermediate. Since deinsertion of CO of the acylpalladium derivatives may occur simul-taneously, the next step, transmetallation (so-called metathesis), is the most crucial for the efficiency of the overall reaction. A variety of organometallic compounds, such as boron, aluminum, copper, zinc, mercury, silicon, tin, lead, zirconium, and bismuth, are used as the partner in this coupling reaction without loss of CO. In this section, the important features of the cross-coupling reactions of a variety of organometallic compounds with acyl halides and related electrophiles are discussed. 

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