Regioselectivity and Chemoselectivity in the Reactions of Aromatic C-h Bonds Activation of Toluene and Anisole by Platinum (ii) Phenanthroline Complex
Year: 2026
Type: article
Abstract: The reactions of direct arylation of toluene and anisole with the platinum (II) phenanthroline complex were considered in this work. A possible reaction mechanism includes the formation “in situ” of aryl complexes of platinum (II), which are capable to reactions with aryl iodide and forms diaryl complexts of platinum. Unsymmetric biphenyls are formed from this complexes as a result of reductive elimination reaction. This approach is an example of the direct arylation of arenes that does not require their prior functionalization. Potassium tetrachloroplatinite is ineffective in the cross-coupling reactions. The ligand-controlled selectivity of the cross-coupling reactions was explained in terms of the nucleophilicity and electrophilicity of these platinum complexes. The DFT method is used for calculate the energies of the frontier molecular orbitals of platinum complexes and, based on them, the reactivity indices of the complexes (Mulliken charges on platinum, electrophilicity, and nucleophilicity). It has been established that the phenanthroline complex exhibits a relatively higher electrophilicity than the tetrachloride complex. This means that in the reaction, this complex can act as electrophiles and is advisable to use in the metalation reactions of arenes. Replacement of one of the chloride ligands in the coordination sphere of the phenanthroline complex by a ϭ-aryl ligand leads to an increase in its nucleophilicity compared with the precursor complex. The reaction of oxidative addition of aryliodide to this complex formally represents aromatic nucleophilic substitution. The nucleophilicity of the complex is important here and the activation of the C–I bond becomes predominant. It has been established that the phenanthroline complex of platinum (II) is a chemoselective catalyst for the reaction of a cross-coupling of arenes and p-iodonitrobenzene. Low reactivity of the C-H bonds of arenes required prolonged boiling of the reaction mixtures. The structure of the obtained compounds was determined by 1H NMR-spectroscopy. It was not possible to achieve 100 % regioselectivity. This is due to the different reactivity of the C-H bonds of the aromatic ring. The main product of the cross-coupling reactions is the o-isomer, the p-isomer is formed with a slight advantage relative to the m-isomer. The predominant formation of the o- isomer is explained by the o-p activating effect of CH3 and CH3O- groups and, on the other hand, by the directing effect of CH3 and CH3O-groups.
Author: Bezbozhnaya, T. V.
Language: Russian
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7225205359