Alkyl ligands nucleophilic attack

The mechanism of the reaction is a combination of the simple steps we have seen before. The phosphine ligands reversibly dissociate and associate, and an oxidative addition occurs. The new step that occurs in catalytic allylic alkylation is nucleophilic attack on an allyl ligand coordinated to a metal. 

Irreversible inhibition is probably due to the alkylation of a histidine residue.43 Chymotrypsin is selectively inactivated with no or poor inhibition of human leukocyte elastase (HLE) with a major difference the inactivation of HLE is transient.42,43 The calculated intrinsic reactivity of the coumarin derivatives, using a model of a nucleophilic reaction between the ligand and the methanol-water pair, indicates that the inhibitor potency cannot be explained solely by differences in the reactivity of the lactonic carbonyl group toward the nucleophilic attack 43 Studies on pyridyl esters of 6-(chloromethyl)-2-oxo-2//-1 -benzopyran-3-carboxylic acid (5 and 6, Fig. 11.5) and related structures having various substituents at the 6-position (7, Fig. 11.5) revealed that compounds 5 and 6 are powerful inhibitors of human leukocyte elastase and a-chymotrypsin thrombin is inhibited in some cases whereas trypsin is not inhibited.21... 

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. 

As already discussed (Section 3.1.1) the elimination of, for instance, neopentane from penta(neopentyl)tantalum corresponds to an a-deprotonation of one alkyl ligand by another, the latter being eliminated as neopentane. Hence in the reverse reaction the carbene carbon atom of the (nucleophilic) carbene complex must formally deprotonate the incoming alkane with simultaneous electrophilic attack of the metal at the newly formed, carbanionic alkyl group (Figure 3.36). 

N==Ca+—Aua which makes the isocyanide ligands susceptible to nucleophilic attack and has led to formation of carbene complexes, iminoalkyl complexes and catalytic conversion of isocyanides to formamidines using alkyl or aryl isocyanide complexes of gold(I).301,402 4(y7-409-415 A review of this significant work has been published.16... 

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-... 

Complexes containing unusual isocyanide ligands have evolved from attempts to alkylate the anions [M(CN)6]4 (M = Fe, Ru, Os) with [Et3OJBF4 in acetone solution. The compounds isolated [M CNCMe2 CH2COMe)6](BF4)2 resulted from an initial acid-catalyzed aldol condensation of the acetone solvent followed by a nucleophilic attack of the carbon-... 

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