Amine oxidation is one of the fundamental reactions in organic synthesis as it leads to a variety of value-added products such as oximes, nitriles, imines, and amides among many others. These products comprise the key N-containing building blocks in the modern chemical industry, and such transformations, when achieved in the presence of molecular oxygen without using stoichiometric oxidants, are much preferred as they circumvent the production of unwanted wastes. In parallel, the versatility of ruthenium catalysts in various oxidative transformations is well-documented. Herein, this review focuses on aerobic oxidation of amines specifically by using ruthenium catalysts and highlights the major achievements in this direction and challenges that still need to be addressed.

Chemical noninnocence" of metal-coordinated 2-picolylamine (PA) derivatives has been introduced upon its reaction with the metal precursor [Ru II (Cl)-(H)(CO)(PPh 3 ) 3 ] under basic conditions. This in effect leads to the facile formation of metalated amide, imine, ring-cyclized pyrrole, and an N-dealkylated congener based on the fine-tuning of an amine nitrogen (N amine ) and a methylene center (C α ) at the PA backbone. It develops oxygenated L1′ in 1 and cyclized L4′ in 4 upon switching of the N amine substituent of PA from aryl to an electrophilic pent-3-en-2-one moiety. On the other hand, imposing the substituent at the C α position of PA modifies its reactivity profile, leading to a dehydrogenation (2/3) or N-dealkylation (6) process. The divergent reactivity profile of metalated PA is considered to proceed through a common dianionic intermediate. Further, a competitive scenario of C−H bond functionalization of coordinated PA versus the ligand-exchange process has been exemplified in the presence of external electrophile such as benzyl bromide or methylene iodide. Authentication of the product formation as well as elucidation of the reaction pathway has been addressed by their crystal structures and spectroscopic features in conjunction with the transition-state (TS) theory.

Reaction of 3,6-bis(2-pyridyl)-diketopyrrolopyrrole (H2-BPDPP) with two equivalents of [Ru(H)(CO)(Cl)(PPh3)3] in EtOH produced two symmetrical dinuclear isomers, (μ-BPDPP)[Ru(CO)H(PPh3)2]2, green 1 and blue 2, which could be separated chromatographically and characterised spectroscopically (1H and 31P NMR, IR, and UV-VIS). Isomeric forms of 1 and 2 were authenticated using their single crystal X-ray structures. In addition to the essentially planar bis-chelating bridge BPDPP2- and the mutually trans positioned axial PPh3 ligands in both complexes, compound 1 was established with the CO groups trans to the pyrrolate-N atoms, whereas 2 has the π acceptors CO and pyridine-N situated trans to each other. While the reduction of 1 and 2 proceeds irreversibly at negative potentials, the reversible oxidations at rather low potentials could be monitored by EPR and UV-VIS-NIR absorption measurements. Together with TD-DFT calculations, these results reveal that the primary electron transfers are largely confined to the BPDPP ligand. Despite the bridge centred processes, small differences between the isomers 10/+ and 20/+ were found, affecting e.g. the near infrared absorption of the radical cation species.

The article examines the newly designed and structurally characterized redox-active BIAN-derived [Ru(trpy)(R-BIAN)Cl]ClO4 ([1a]ClO4-[1c]ClO4), [Ru(trpy)(R-BIAN)(H2O)](ClO4)2 ([3a](ClO4)2-[3c](ClO4)2), and BIAO-derived [Ru(trpy)(BIAO)Cl]ClO4 ([2a]ClO4) (trpy = 2,2':6',2''-terpyridine, R-BIAN = bis(arylimino)acenaphthene (R = H (1a(+), 3a(2+)), 4-OMe (1b(+), 3b(2+)), 4-NO2 (1c(+), 3c(2+)), BIAO = [N-(phenyl)imino]acenapthenone). The experimental (X-ray, (1)H NMR, spectroelectrochemistry, EPR) and DFT/TD-DFT calculations of 1a(n)-1c(n) or 2a(n) collectively establish {Ru(II)-BIAN(0)} or {Ru(II)-BIAO(0)} configuration in the native state, metal-based oxidation to {Ru(III)-BIAN(0)} or {Ru(III)-BIAO(0)}, and successive electron uptake processes by the α-diimine fragment, followed by trpy and naphthalene π-system of BIAN or BIAO, respectively. The impact of the electron-withdrawing NO2 function in the BIAN moiety in 1c(+) has been reflected in the five nearby reduction steps within the accessible potential limit of -2 V versus SCE, leading to a fully reduced BIAN(4-) state in [1c](4-). The aqua derivatives ({Ru(II)-OH2}, 3a(2+)-3c(2+)) undergo simultaneous 2e(-)/2H(+) transfer to the corresponding {Ru(IV)═O} state and the catalytic current associated with the Ru(IV)/Ru(V) response probably implies its involvement in the electrocatalytic water oxidation. The aqua derivatives (3a(2+)-3c(2+)) are efficient and selective precatalysts in transforming a wide variety of alkenes to corresponding epoxides in the presence of PhI(OAc)2 as an oxidant in CH2Cl2 at 298 K as well as oxidation of primary, secondary, and heterocyclic alcohols with a large substrate scope with H2O2 as the stoichiometric oxidant in CH3CN at 343 K. The involvement of the {Ru(IV)═O} intermediate as the active catalyst in both the oxidation processes has been ascertained via a sequence of experimental evidence.

The title complexes were isolated as structurally characterised compounds [Os(9-OP)L]ClO, L = 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap), and were compared with ruthenium analogues. A reversible one-electron oxidation and up to three reduction processes were observed by voltammetry (CV, DPV) and spectroelectrochemistry (UV-vis-NIR, partially EPR). Supporting calculations (DFT, TD-DFT) were used to assess the oxidation state combinations of the different redox active ligands and of the metal, revealing the effects of Os versus Ru exchange and of bpy versus pap acceptor ligation. Several unexpected consequences of these variations were observed for members of the new osmium-containing redox series. Remarkably, the EPR results exhibit a clear dichotomy between the complex ion [Os(9-OP)(bpy)] and the radical species [Os(9-OP˙)(pap)], which has not been similarly observed for the analogous [Ru(9-OP)L] systems. This difference, unprecedented for 5d systems, is attributed to the superior stabilisation of the Os state by the strongly π-accepting pap ligands. The reduced forms [Os(9-OP)(pap˙)(pap)] and [Os(9-OP)(pap˙)] exhibit strong inter-ligand interactions, leading to spin isomers and electron hopping.

Reports on aerobic oxidation of amines to amides are rare, and those reported suffer from several limitations like poor yield or selectivity and make use of pure oxygen under elevated pressure. Herein, we report a practical and an efficient ruthenium-catalyzed synthetic protocol that enables selective oxidation of a broad range of primary aliphatic, heterocyclic and benzylic amines to their corresponding amides, using readily available reagents and ambient air as the sole oxidant. Secondary amines instead, yield benzamides selectively as the sole product. Mechanistic investigations reveal intermediacy of nitriles, which undergo hydration to afford amide as the final product.

We have synthesized a low-spin Co(III) complex of 5,15-bis(4nitrophenyl)-10-(2-methylcarboxyphenyl)corrole with an Sbound dimethylsulfoxide (DMSO) ligand (1DMSO) and determined the coordination mode through X-ray diffraction for the first time. UV-vis-NIR spectral data show that the DMSO ligand does not dissociate in MeCN solution, and EPR results indicate that the first oxidation is ligand centered and suggest that not only DMSO remains bound but a second apical ligand, possibly MeCN, binds to the cobalt center. Multiconfigurational wavefunction electronic structure methods (CASSCF/NEVPT2) al-lowed us to determine that in the neutral complex the corrole behaves as an innocent trianionic ligand and that the σ-donor effect of the S atom determines the low-spin configuration by raising the energy of the Co 3dz 2 orbital. While DFT calculations predict a ground open-shell singlet for both S-bound and Obound DMSO variants, CASSCF/NEVPT2 calculations predict a closed-shell singlet ground state in both cases. These calculations reproduce considerably well the UV-vis-NIR spectrum of 1DMSO in solution, validating the closed-shell singlet description.

Metal complexes of multi‐porphyrins and multi‐corroles are unique systems that display a host of extremely interesting properties. Availability of free meso and β positions allow formation of different types of directly linked bis‐porphyrins giving rise to intriguing optical and electronic properties. While the fields of metalloporphyrin and corroles monomer have seen exponential growth in the last decades, the chemistry of metal complexes of bis‐porphyrins and bis‐corroles remain rather underexplored. Therefore, the impact of covalent linkages on the optical, electronic, (spectro)electrochemical, magnetic and electrocatalytic activities of metal complexes of bis‐porphyrins and ‐corroles has been summarized in this review article. This article shows that despite the (still) somewhat difficult synthetic access to these molecules, their extremely exciting properties do make a strong case for pursuing research on these classes of compounds.