Nucleophilic attack at coordinated ligand

Carbonyl ligands may also be removed by treatment with an amine oxide this oxidizes coordinated CO to C02, which does not coordinate strongly and is displaced by the (labile) amine (Figures 3.15 and 3.5a). Since this involves nucleophilic attack at coordinated CO, it is most effective for carbonyl ligands bound to less 7i-basic metal centres (higher vco). 

Figure 3.20 Nucleophilic attack at coordinated CO and related ligands...

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). 

The coordination of a ligand to a metal can sometimes make the ligand itself more susceptible to nucleophilic attack. This is especially true when the metal has a high oxidation number and/or electron-withdrawing ligands. Some examples of nucleophilic attack at the ligand are shown in Figure 19.18. 

Related catalytic processes are discussed elsewhere (Chapter 14) as are intramolecular ligand rearrangements (Chapter 13). Quantitative studies of nucleophilic attack on carbonyl ligands are also generally outside the scope of this chapter, and are discussed only where attack at carbon monoxide occurs competitively with reaction at a coordinated hydrocarbon. A short section on nucleophilic attack at coordinated isocyanides is included for the first time. 

Although deprotonation at the benzylic position of arenes coordinated to ruthenium and chromium was reported,27 in the case of the coordinated oxo-ri5-dienyl unit, nucleophilic attack at one terminus of the complexed r 5-dienyl ligand, rather than deprotonation, was expected.28 The reason for the successful deprotonation (even at relatively hindered isopropyl sites) is, according to the authors, the cationic nature of the Cp M fragment. In addition, the transition state for the deprotonation might involve stabilization by the metal (Scheme 3.15). 

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. 

In the postulated transition state, the y-phosphorus atom is penta-coordinated, whereby the ligands are configmed in the form of a triagonal bipyramid. Mg is indispensable for the catalysis it is needed for binding of substrate and product, as well as for the catalysis itself. Activation of the water molecule for nucleophilic attack at the y-phosphate requires involvement of side groups of the protein in the sense of a general base catalysis. 

Alkenes bonded to platinum(II) can be displaced by strongly coordinating ligands such as cyanide ion or tertiary phosphines. The displacement of ethylene from Zeise s salt by phosphines is a useful method of preparation of complexes trawa-PtCl2(PR3)2.711 Amines will also displace alkenes from coordination to platinum(II), but this reaction can compete with nucleophilic attack at the coordinated alkenic carbon. The stability of platinum(II) alkene complexes follows the sequence C2H4 > PhCH=CH2 > Ph2C=CH2 555 Ph(Me)C=CH2.712... 

Backwall and coworkers have extensively studied the stereochemistry of nucleophilic additions on 7r-alkenic and ir-allylic palladium(II) complexes. They concluded that nucleophiles which preferentially undergo a trans external attack are hard bases such as amines, water, alcohols, acetate and stabilized carbanions such as /3-diketonates. In contrast, soft bases are nonstabilized carbanions such as methyl or phenyl groups and undergo a cis internal nucleophilic attack at the coordinated substrate.398,399 The pseudocyclic alkylperoxypalladation procedure occurring in the ketonization of terminal alkenes by [RCC PdOOBu1], complexes (see Section 61.3.2.2.2)42 belongs to internal cis addition processes, as well as the oxidation of complexed alkenes by coordinated nitro ligands (vide in/ra).396,397... 

Terminal monoalkenes were alkylated by stabilized carbanions (p a 10-18) in the presence of 1 equiv. of palladium chloride and 2 equiv. of triethylamine, at low temperatures (Scheme l).1 The resulting unstable hydride eliminate to give the alkene (path b), or treated with carbon monoxide and methanol to produce the ester (path c).2 As was the case with heteroatom nucleophiles, attack at the more substituted alkene position predominated, and internal alkenes underwent alkylation in much lower (=30%) yield. In the absence of triethylamine, the yields were very low (1-2%) and reduction of the metal by the carbanion became the major process. Presumably, the tertiary amine ligand prevented attack of the carbanion at the metal, directing it instead to the coordinated alkene. The regiochemistry (predominant attack at the more sub-... 

Very few reactions of C02 complexes with nucleophiles have been reported. One of the rare examples of nucleophilic attack at C02 has been provided by Aresta et al. [81], in a study of the coordination chemistry of phenoxide ligands to Mn ... 

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