The reduction of nitro compounds to the corresponding amines is one of the most utilized catalytic processes in the fine and bulk chemical industry. The latest development of catalysts with cheap metals like Fe, Co, Ni and Cu has led to their tremendous achievements over the last years prompting to their greater application as "standard" catalysts. In this review we will comprehensively discuss the use of homogeneous and heterogeneous catalysts based on non-noble 3d-metals for the reduction of nitro compounds using various reductants. The different systems will be revised considering both the catalytic performances and synthetic aspects highlighting also their advantages and disadvantages.

‡ These authors contributed equally to this work.Abstract: Ar-BIANs and related α-diimine Co complexes were wet impregnated onto Vulcan® XC 72 R carbon black powder and used as precursors for the synthesis of heterogeneous supported nanoscale catalysts by pyrolysis under argon at 800 °C. The catalytic materials feature a core-shell structure composed of metallic Co and Co oxides decorated with nitrogen-doped graphitic layers (NGr). These catalysts display high activity in the liquid phase hydrogenation of aromatic nitro compounds (110 °C, 50 bar H2) to give chemoselectively substituted aryl amines. The catalytic activity is closely related to the amount and type of nitrogen atoms in the final catalytic material, which suggests a heterolytic activation of dihydrogen.Keywords: cobalt, hydrogenation, nitro compounds, kinetic, heterolytic activation IntroductionCatalysis is a key-technology for the manufacturing of all kinds of bulk and fine chemical products. It allows for producing chemicals avoiding the formation of undesired and useless stoichiometric side products which leads to additional cost and energy consumption [1][2][3]. Many of the industrially relevant catalytic processes in the fine chemical industry are still based on expensive and rare late transition metals such as Pd, Pt, Rh, Ru and Ir [4,[1][2][3][4][5]. Although these metals exhibit very good catalytic performance for advanced organic substrates, the decreasing availability of these elements requires the development of efficient alternative metal-based catalysts [6]. In this regard, the design of catalytic systems based on abundant and biocompatible metals is an important goal for the implementation and progress of green and sustainable chemistry. Hence, transition metals such as Fe, Co and Cu are ideal candidates, which meet these requirements [7][8][9][10]. As a matter of fact, these elements are among the most abundant metals in the Earth's upper crust, thus being readily accessible [11]. Recently, heteroatom-doped carbon materials attracted major interest in the field of metal supported heterogeneous catalysts for both chemical synthesis [12][13][14] and/or energy-relevant transformations [15,16]. Indeed, doping graphene with heteroatoms such as N, B, P, or S leads to a radical modification of the electronic properties of both the support and the supported metal [17][18][19]. Consequently, it is possible to modify the activity and adjust the selectivity of the final catalytic material towards the desired transformation. Among the various dopants, nitrogen attracted most interest [15,[20][21][22]. and applications of transition metal/N-doped graphene (NGr) based catalytic systems ranges from oxygen reduction reactions (ORR) [23][24][25][26], hydrogen evolving reactions (HER) [27,28], photocatalysis [29,30], oxidation [31][32][33][34][35][36][37][38], and reduction [39][40][41][42][43][44] reactions of organic

Ar-BIANH2 bearing different substituents on the aryl rings have been synthesized in high yield by reduction of the corresponding bis(aryl)acenaphthenequinonediimine (Ar-BIAN) compounds. The structure of p-CH3 C6 H4 -BIANH2 in the solid state was determined by X-ray diffraction. An exhaustive voltammetric investigation of the two parallel BIAN and BIANH2 series afforded a first rationalization of the redox properties of these molecules, highlighting their analogies with quinone/hydroquinone systems. Such analogies, in combination with the much more negative reduction potential range of Ar-BIAN compounds with respect to quinones, can afford to extend the range of reduction potentials so far obtainable by the use of quinones.

An active and renewable catalyst for olefin hydrogenation was obtained by inclusion of cobalt in a carbon matrix derived from the pyrolysis of chitosan.

Inspired by the results of a previous mechanistic study, a series of mostly new nonsymmetric phenanthrolines were synthesized and tested as ligands in the palladium-catalyzed reductive carbonylation reaction of nitrobenzene to methyl phenylcarbamate. Very good results were obtained when the asymmetry was of an electronic nature (a donating substituent in the para position of one of the two pyridinic rings and an electron-withdrawing or no substituent on the para position of the other pyridinic ring), but steric hindrance in the ortho or meta position retarded the reaction. The TOF for the modified system is the highest ever reported for any carbonylation reaction of nitroarenes.

A mechanism for the aziridination of olefins by aryl azides (ArN3), promoted by ruthenium(ii) porphyrin complexes, is proposed on the basis of kinetic and theoretical studies. All the recorded data support the involvement of a mono-imido ruthenium complex as the active intermediate in the transfer of the nitrene moiety "ArN" to the olefin. The selectivity of the aziridination vs. the uncatalysed triazoline formation can be enhanced by fine-tuning the electronic features of the porphyrin ligand and the olefin/azide catalytic ratio. The DFT study highlights the importance of an accessible triplet ground state of the intermediate ruthenium mono-imido complex to allow the evolution of the aziridination process.

An efficient catalytic cyclization of β‐nitrostyrenes to indoles was developed. The reaction was applied to the synthesis of 3‐arylindoles and 2‐alkylindoles. Given that in the latter case the starting β‐nitrostyrenes can be easily obtained by a Henry reaction, the present method allows indoles to be obtained in a two‐step sequence starting from cheap reactants.

Reaction of neutral palladium(II) complexes with chelating nitrogen ligands of the phenanthroline family had been earlier found to proceed through the formation of a CO adduct, which is then reduced to another observable complex before decomposing to metallic palladium. We have now extended this study and completely characterized by single-crystal X-ray diffraction one member of this class of compounds. The intermediate is an unprecedented type of palladium(I) dimer with two bridging COs. The same complex could also be obtained by a conproportionation reaction of a Pd0 with a PdII complex. The picture of the reactivity of neutral palladium(II) complexes with phenanthroline ligands in a CO atmosphere was completed by the identification of two byproducts of the main reaction.