Coordinated ligands, nucleophilic

Chiral pyridine-based ligands were, among various Ar,AT-coordinating ligands, more efficient associated to palladium for asymmetric nucleophilic allylic substitution. Asymmetric molybdenum-catalyzed alkylations, especially of non-symmetric allylic derivatives as substrates, have been very efficiently performed with bis(pyridylamide) ligands. 

J. E. Backvall, Nucleophilic Attack on Coordinated Alkenes , in Reaction of Coordinated Ligands (Ed. P. S. Braterman), Plenum Press, London 1986, pp. 679-731. 

Hydrolysis of coordinated ligands is a special case of nucleophilic attack. Two examples involving inorganic ligands have already been given in Section II. A on aquation of cobalt(III) complexes. Many further examples will be found in the following Section VII.B on catalysis of hydrolysis of organic substrates by metal ions and complexes. 

Schulz E (2005) Use of JV,JV-Coordinaling Ligands in Catalytic Asymmetric C-C Bond Formations Example of Cyclopropanation, Diels-Alder Reaction, Nucleophilic Allylic Substitution. 15 93-148... 

Having established a very effective method for the synthesis of tricar-bonyl(T74-vinylketene)iron(0) complexes, Thomas has subsequently undertaken the most comprehensive study on the reactivity of these complexes to date. The reactions of 221 with phosphoramidate anions,90134 coordinating ligands such as phosphines3 and isonitriles,69,87,89,135,142,143 a variety of nucleophiles,86,89135142 phosphonoacetate anions,88,89 alkynes,108,109,144,145 and al-kenes146,147 have ah been investigated. Crucially, Thomas has also developed a method138 for the kinetic resolution of the vinylketene complexes (221) that ultimately yields enantiomerically pure samples of the complex. This... 

A cis-coordinating ligand is apparently required to bind and activate MeOH so that a methoxy group is transferred to the polyketone chain and a hydride remains on palladium. Two mechanisms are possible for this reaction (i) nucleophilic attack by the oxygen at the acyl carbonyl with concerted formation of Pd-H (ii) formation of a Pd(acyl) (methoxy) complex and H, followed by reductive elimination and subsequent proton attack on a Pd center. No experimental evidence favoring either mechanism in ethene/CO copolymerisation has been provided so far. 

L = CO, ethylene, propene, pent-l-ene, butadiene, H2S, THF, acetone, acetonitrile, nitromethane). The moiety [Re(CO)5] + can also be added to a nucleophilic atom of a coordinated ligand, which provides a systematic way to prepare ligand-bridged complexes,12 for example,... 

The organic chemistry of benzene is dominated by electrophilic substitution reactions, but as a coordinated ligand, it undergoes nucleophilic substitution. This dramatic change in chemical behavior is a good example of the powerful influence coordination can have on the chemistry of a molecule and is illustrated in the following functionalization of benzene.1< 1... 

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... 

In contrast to electrophiles, nucleophiles are expected to react preferentially with n -bonded heteroaldehyde and -ketone ligands. The site of attack is expected to be the carbon atom of the E = C group, -coordinated ligands should be less reactive. 

The synthetic utility of reactions of coordinated ligands is an important and varied subject. It is based on the enhancement in reactivity of organic ligands as a consequence of metal coordination. For example, the metal can act as a super add and cause enhanced nucleophilic attack on coordinated carbonyl and imine ligands. The metal ion can also enable the ligand itself to act as a nucleophile, sometimes by direct activation, sometimes by protecting other parts of the ligand and sometimes by a combination of both. 

Most of the reactions which will be discussed lead to carbonyl compounds with a stereogenic center in the 3-position. This is illustrated in Scheme 1 a substrate molecule (1 X = heteroatom or heteroatom-based functional group), having an electron-deficient double bond, is attacked by a nucleophilic reagent (possibly in the presence of a coordinating ligand or a catalyst) to form an anionic intermediate (2), which is then converted to the product (3) on hydrolytic work-up. 

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