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Application of Pd(II) Complexes with Pyridines as Catalysts for the Reduction of Aromatic Nitro Compounds by CO/H2O

“…Mechanism of the Reduction of Nitro Compounds to Amines by CO/H 2 O in the Presence of Pd(II) Complexes. On the basis of our previous studies of the catalytic carbonylation 21,23 and reduction 27,29 of NB, we propose the following mechanism. Before the cyclic mechanism shown in Scheme 1 starts, a trace amount of the central atom in PdCl 2 (X n Py) 2 is reduced to palladium(0) by CO/H 2 O: Pd 2+ → Pd 0 .…”

“…The most promising method for this employs the inexpensive and easily accessible mixture of CO/H 2 O as the reducing agent. − Our previous studies on the carbonylation of nitrobenzene to ethyl N -phenylcarbamate (EPC) by carbon monoxide in the presence of PdCl 2 (X n Py) 2 complexes (where X = Cl or CH 3 , and n = 0–2) showed that the activity of the catalyst increases as the basicity of the X n Py ligand increases. , Thus, the activity of PdCl 2 (X n Py) 2 catalyst is strongly correlated with the electron density on the nitrogen atom of the X n Py ligand. Recently, we proposed a mechanism for this carbonylation: the process starts from the reduction of NB to aniline, which is subsequently carbonylated to EPC. ,− The carbonylation can be stopped at this “initial aniline” step if the process is carried out in the presence of water, and this method can be convenient for the synthesis of aromatic amines. ,− The results of the carbonylation carried out in the presence of water allowed us to hypothesize that electron transfer from Pd(0) to the nitro compound is the rate-determining step (RDS), as was previously observed for the carbonylation of NB to EPC in the absence of water. , If electron transfer from palladium to NB is indeed the RDS, then an increase in the electron density on Pd by introducing electron-donating substituents in the X n Py ligand would result in improved catalyst activity. In this work, we verify this hypothesis in a series of reduction processes of various nitro compounds (YC 6 H 4 NO 2 ) catalyzed by 12 PdCl 2 (X n Py) 2 complexes ( I – XII ), where X n Py = pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine, 2,4-dimethylpyridine, 3,5-dimethylpyridine, 2-chloropyridine, 3-chloropyridine, 2,6-dichloropyridine, 2,4-dichloropyridine, and 3,5-dichloropyridine.…”

Crystal structure, electronic properties and cytotoxic activity of palladium chloride complexes with monosubstituted pyridines

“…11 Our studies have long been concerned with the structural effects of substrates on the yield of carbonylation of amines and nitrocompounds. [24][25][26][27][28] We described the substituent effects in the nitrobenzene and aniline ring on the yield of ethyl N-fenylcarbamate (EPC) in the carbonylation of a nitrobenzene (NB), mixture NB/AN or AN (where AN is aniline), respectively. 29,30 However, our previous studies were limited to PdCl 2 and PdCl 2 Py 2 complexes without detailed research on the nature of a ligand and structure of a catalyst.…”

Iridium Nanoparticles Confined within Partially Carbonized Hyperbranched Polymers for Selective Hydrogenation of Nitroarenes at Room Temperature

“…Considerable attention has always been paid to the catalytic hydrogenation of aromatic nitro compounds owing to the importance of their selective reduction into aromatic amines in synthetic organic chemistry. − The main method to synthesize aromatic amines by the reduction of aromatic nitro compounds is catalytic reduction with hydrogen − or hydrogen donors. − Among them, catalytic hydrogenation with hydrogen is one of the most important industrial approaches to prepare aromatic amines due to the advantages of less environmental pollution, high yield, good purity, simple process, and so on . To date, however, the selective synthesis of aromatic amines from aromatic nitro compounds by direct hydrogen reduction requires a long reaction time, a high reaction temperature, or a high hydrogen pressure .…”