Formation of a Ruthenium(IV)-Oxo Complex by Electron-Transfer Oxidation of a Coordinatively Saturated Ruthenium(II) Complex and Detection of Oxygen-Rebound Intermediates in C–H Bond Oxygenation

Abstract

A coordinatively saturated ruthenium(II) complex having tetradentate tris(2-pyridylmethyl)amine (TPA) and bidentate 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)](2+) (1), was oxidized by a Ce(IV) ion in H(2)O to afford a Ru(IV)-oxo complex, [Ru(O)(H(+)TPA)(bpy)](3+) (2). The crystal structure of the Ru(IV)-oxo complex 2 was determined by X-ray crystallography. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated. The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to -20 ppm, was determined to be an intermediate spin (S = 1) by the Evans' method with (1)H NMR spectroscopy in acetone-d(6). The reaction of 2 with various oraganic substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex, [Ru(H(+)TPA)(bpy)(CH(3)CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated C-H bonds with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12, respectively. The second-order rate constants of C-H oxygenation in the first step exhibited a linear correlation with bond dissociation energies of the C-H bond cleavage.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…Radicals can be generated in the solvent cage, as in the so-called "oxygen rebound mechanism" [279][280][281][282] (21)/RCOOH system has been assumed to oxidize via a "crypto-radical" ("hydroperoxo-rebound") mechanism (Figure 19) [283]. …”

“…Radicals can be generated in the solvent cage, as in the so-called "oxygen rebound mechanism" [279][280][281][282] (21)/RCOOH system has been assumed to oxidize via a "crypto-radical" ("hydroperoxo-rebound") mechanism (Figure 19) [283]. m-Chloroperbenzoic acid in the presence of certain metal compounds efficiently oxidizes alkanes at low temperature with a very high degree of stereoselectivity (trans/cis << 1) [160,227,284,285].…”

Synthesis and structural analyses of phenylethynyl-substituted tris(2-pyridylmethyl)amines and their copper(ii) complexes

“…7E. These eight contacts are classified into three types-two [Ph centroid ⋯ H-C sp 2] 4 , crystallizes in a monoclinic crystal system with a P2 1 /n space group (Fig. 8), and its unit cell has four asymmetric units which contain a [Cu(1)MeOH]·2ClO 4 complex, shown in Fig.…”

“…Contact 1 is a typical slipped π⋯π stack with a distance of 3.25 Å. Two types of C-H⋯π interactions also connect cationic species together; a [C sp 3- 4 , crystalizes in a triclinic system with a P1 space group (Fig. 9).…”

“…Two of C Ph -CuC-C Py are slightly deformed with C- 4 , also assembled into a triclinic crystal system with a P1 space group (Fig. 10).…”