Electrophilic attack of coordinated ligands

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. - ... 

Propene is also proposed as a product of the reaction of the same Rh-siloxy organometaUic fragment with CO, as a consequence of an electrophilic attack of a proton in or near the coordination sphere of rhodium on one of the allyl ligands (Scheme 7.3). 

In reaction (93) the black isomer is initially formed electrophilic attack of NO followed by coordination of the N202 ligand to a second Co(II) center may then be proposed to yield the red isomer. This sequence is shown as (94). 

Asymmetric addition of PhLi, coordinated by the chiral ligand 200, to the prochiral imine complex 199 generates 201. Discrimination between enantiotopic sites at C(2) and C(6) occurs. Then the 5,6-mmv-disubstituted 1,3-cyclohexadienal 202 was prepared with 93% ee by electrophilic attack of propargyl bromide [50],... 

Perdenteration of the methylene hnker affords a relatively kinetically stable complex, which allows for the monitoring of exogenons snbstrate oxidations. When (7) is exposed to cold (-95 °C) acetone solntions of the lithium salts of para-substituted phenolates, clean conversion to the corresponding o-catechols is observed. Deuterium kinetic isotope effects (KIEs) for these hydroxylation reactions of 1.0 are observed, which is consistent with an electrophilic attack of the peroxo ligand on the arene ring. An electrophilic aromatic substitution is also consistent with the observation that lithium jo-methoxy-phenolate reacts substantially faster with (7) than lithium / -chloro-phenolate. Furthermore, a plot of observed reaction rates vs. / -chloro-phenolate concentration demonstrated that substrate coordination to the metal center is occurring prior to hydroxylation, and thus may be an important feature in these phenolate o-hydroxylation reactions. 

The cationic dinitrosyl complexes (146) are apparently much more electrophilic than (143). Studies of the reactivity of (146) have been focused on attack of coordinated organic ligands of other transition metal complexes, such as the cyclooctatetraene ligand in L3M(cot) complexes (M = Fe, Ru) and Cp Co(cot) complexes (Cp = Cp, Cp ), the cyclopenta-dienyl ligand of CpRh(cot) complexes, and the cyanide ligand... 

A newer approach toward the enantioselective electrophilic fluorination of jS-ketoesters is based on enolization of the substrate under neutral conditions by coordination to a chiral titanium catalyst [211]. The catalyst, a chiral titanium TADDOLato complex (TADDOL = a,a,a, a -tetraaryl-2,2-dimethyl-1,3-dioxolan-4,5-dimethanol) [212, 213], coordinates to the -ketoester, enolizes it, and thus renders it susceptible to electrophilic fluorination (Scheme 2.95). One face of the prochiral enolate substructure is covered by a bulky naphthyl substituent from the TADDOL ligand, impeding electrophilic attack of F-TEDA. 

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