Kinetics and mechanism of mercuriation of aromatic compounds by mercury trifluoroacetate in trifluoroacetic acid

Abstract

The mercuriation of a series of aromatic derivatives by mercury(l1) trifluoroacetate in trifluoroacetic acid has been studied using titrirnetric and spectrophotornetric methods. The latter method has revealed the presence of a rapidly formed x-complex intermediate and values of the thermodynamic parameters of its formation have been computed. Only small kinetic isotope effects were found for the complex-forming step in contrast to the large values obtained for the slow step. The effect of added salts was investigated and the mechanism of the reaction discussed in detail in the light of these results. Mercuriation by a readily synthesised mixed acetate, Hg(OCOCF,)-(OCOCH,), is also reported as well as some preliminary studies of triptycene derivatives.

Overview of the Mechanistic Work on the Concerted Metallation–Deprotonation Pathway

“…This is especially the case for studies on the mercuration of benzene 9,12 and the cyclopalladation of DMBA-H. 17,19 Moreover, the S E Ar mechanism cannot justify why 3-fluorobenzothiophene reacts preferentially over the more nucleophilic benzothiophene in a direct arylation competition reaction (Scheme 12). 40 Computationally, palladiumarenium complexes were not located for any of the heteroarenes investigated.…”

“…8 Interestingly, before Roberts and co-workers published an elegant mechanistic study on the subject, 9 there were no in-depth kinetic studies performed on the mechanism of the mercuration of simple arenes. Earlier mechanistic proposals suggested an S E Ar mechanism based on the electrophilic character of mercury.…”

“…9 They showed that the intermediate was indeed a ³ complex rather than a · complex, based on the experimental free energy of formation. In the second step of the reaction (k 2 , eq 1), the discrete KIEs of the reaction indicated that the CH bond was cleaved at that step.…”

Organometallics aspects of C–H bond activation/functionalization

“…This observation was later confirmed by Roberts and co-workers who predicted the presence of p-complex as the intermediate. 119 An important aspect of CMD is the role of acetato ligand or a carboxylate ion, that has shown to provide assistance for the cleavage of the C-H bond by acting as an intramolecular base for its deprotonation. 120 One of the first examples suggesting the role of acetato ligand in C-H bond activation of N,N-dimethylbenzylamine 74 was reported by Ryabov.…”

Untersuchungen zu Synthese und Reaktionen von Fluorphenylquecksilber-Derivaten mit den Liganden 2-FC6H4, 2,6-F2C6H3 und 2,4,6-F3C6H2

“…Nachdem sich das Quecksilberoxid vollsta È ndig gelo È st hatte, wurden 1,0 ml (9,7 mmol) 1,3,5-Trifluorbenzol zugetropft und die Reaktionsmischung auf 80°C erwa È rmt. Nach dreita È-gigem Ru È hren bei dieser Temperatur konnte 1,3,5-F 3 C 6 H 3 in den 19 …”