Demetalation deprotonation

Scheme 4. Proposed general mechanism of demetalation of 1 by picolinic acid accounting for first (la, in the box) and second (lm) orders in the buffer acid concentration. The charge of the Fem-TAML complex is shown outside the bracket and localized charges are shown for the deprotonated pyridine carboxylates. From Ref. (27).

Based on these reactivities various derivatives of carbenes, such as the aminocarbene 238, are prepared by displacement of the OR group in 237 with amine via addition elimination, analogous to transesterification [74,75], As an example the carbanion 240, generated by deprotonation of 239, attacks ethylene oxide to give the lactone equivalent 241, which is further alkylated by chloromethyl methyl ether, again at the -position. Finally the oc-methylene-y-lactone 242 is obtained by oxidative demetallation with a Ce(TV) salt [76],... 

Selective nucleophilic substitution of one of the chlorides in (dichloroben-zene)FeCp complexes can be achieved with a variety of nucleophiles. The first substitution is fast while the resulting complex is typically less electrophilic so that the second substitution is slower [75]. In the case of a primary amine nucleophile, the product is deprotonated by excess of amine and thereby made completely unreactive towards a second substitution [66,76]. A second substitution can be achieved after neutralization with an equivalent amount of acid. If the first nucleophile is attached to the solid phase, a library of substituted arenes can be generated [77]. With q -(o-dichlorobenzene)FeCp and a bis-heteroatom nucleophile, benzo-fused heterocycles (e.g., 34) are obtained after pyrolytic demetallation [78]. 

As a mechanism of this MCR process, it is proposed that the Au-catalyst effects (1) a three-component coupling of pyridine-2-aldehyde, amine, and alkyne to give the (2-propargyl)pyridine 33 and (2) enhancement of the triple-bond activity by Au-coordination in favor of the cyclization 33 34 finally the Au-heterocycle 34 should undergo deprotonation ( 35) and demetalation to give the products 32. 

Covalent capsules 127-129 with donor pyri-dyl groups and their 1 1 cage complexes with an encapsnlated potassium(I) cation have been synthesized in [96] using similar synthetic approaches (Scheme 2.84). These complexes underwent demetalation with hydrochloric and nitric acids. A reversible protonation-deproton-... 

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