为了使芳香族硝基化合物大规模转化为胺的成本最小化,已经进行了许多努力。为此,使用CO / H 2 O作为还原剂代替分子氢似乎是一种有前途的方法,并且该过程可以由Pd(II)配合物催化。在这项工作中,研究了具有一般结构PdCl 2(X n Py)2(其中X n Py =吡啶衍生物)的方形平面配合物的催化活性。尤其要注意X n Py(配体)的芳环和要还原的硝基化合物(YC 6 H 4 NO 2)中取代基的作用)。在YC 6 H 4 NO 2的芳香环中引入吸电子Y会提高转化率,这表明该过程的动力学类似于在不存在水的情况下用CO羰基合成硝基苯氮烯的过程(见J. Mol 。CATAL A:化学2011,337,9-16)。令人惊讶地,吸电子取代基掺入X n Py配体的芳环中也增加了YC 6 H 4 NO 2的转化率(与YC 6 H 4 NO 2底物的结构无关)。
为了使芳香族硝基化合物大规模转化为胺的成本最小化,已经进行了许多努力。为此,使用CO / H 2 O作为还原剂代替分子氢似乎是一种有前途的方法,并且该过程可以由Pd(II)配合物催化。在这项工作中,研究了具有一般结构PdCl 2(X n Py)2(其中X n Py =吡啶衍生物)的方形平面配合物的催化活性。尤其要注意X n Py(配体)的芳环和要还原的硝基化合物(YC 6 H 4 NO 2)中取代基的作用)。在YC 6 H 4 NO 2的芳香环中引入吸电子Y会提高转化率,这表明该过程的动力学类似于在不存在水的情况下用CO羰基合成硝基苯氮烯的过程(见J. Mol 。CATAL A:化学2011,337,9-16)。令人惊讶地,吸电子取代基掺入X n Py配体的芳环中也增加了YC 6 H 4 NO 2的转化率(与YC 6 H 4 NO 2底物的结构无关)。
The position and number of substituents in pyridine ligands (XnPy) were correlated with structural, physical, and chemical properties of PdCl2(XnPy)(2) complexes applied as catalysts for the carbonylation of aromatic nitrocompounds (phosgene-free method of carbamates production). Thermal stability and catalytic activity of PdCl2(XnPY)(2) complexes without steric hindrance increases with increasing XnPy's basicity whereas a decrease of thermal stability and catalytic activity of the complexes is observed for sterically crowded complexes (with the ortho-substituted XnPy). The complexes with X = Cl in meta- position of XnPy decompose to a mixture of PdCl2 and metallic Pd (similarly to complexes with MenPy) whereas complexes with ortho-chlorine (in XnPy) decompose to the organopalladium products. Therefore, two different mechanisms of thermal decomposition are proposed for PdCl2(ClnPy)(2) and PdCl2(MenPy)(2). The results of complex thermal and structural analysis of a series of PdCl2(XnPy)(2) complexes allow us to get insight into the mechanism of nitrobenzene (NB) carbonylation catalyzed by PdCl2(XnPY)(2) at 150-180 degrees C. We conclude that the electron transfer from Pd(0) to nitrobenzene is the rate determining step of catalytic cycle of NB carbonylation. (C) 2014 Elsevier B.V. All rights reserved.
Catalytic activity of PdCl2 complexes with pyridines in nitrobenzene carbonylation
Synthesis of square planar palladium(II) complexes of general structure PdCl2(XnPy)(2) (where: Py = pyridine; XnPy = 2-MePy: 3-MePy; 4-MePy; 2,4-Me2Py; 2,6-Me2Py; 2-CIPy; 3-CIPy and 3,5-Cl2Py) has been performed in order to study activity of these complexes as catalysts of nitrobenzene (NB) carbonylation - a process of industrial importance leading to production of ethyl N-phenylcarbamate (EPC). Electron withdrawing/electron donating properties of XnPy ligands (described by experimentally determined acidity parameter pK(a)) have been correlated with activities of PdCl2(X Py)2 complexes during NB carbonylation in presence of catalytic system PdCl2(XnPy)(2)/Fe/I-2/XnPy. We observed that conversions of substrates and yields of EPC increase within increasing basicity of XnPy ligand (for not sterically hindered XnPy's). On the basis of current work and our previous studies a detailed mechanism of catalytic carbonylation of NB is proposed. (C) 2011 Elsevier B.V. All rights reserved.
One pot synthesis of ureas and carbamates via oxidative carbonylation of aniline-type substrates by CO/O2 mixture catalyzed by Pd-complexes
作者:Agnieszka Krogul、Grzegorz Litwinienko
DOI:10.1016/j.molcata.2015.06.027
日期:2015.10
Carbonylation of aromatic amines by direct insertion of carbon monoxide is catalyzed by PdCl2(XnPY)(2) complexes (where Py = pyridine, X=-CH3, -Cl; n=0-2) and gives, depending on the conditions, ethyl N-phenylcarbamates or N,N'-diphenylureas. For carbonylation of aniline, a proper choice of XnPy ligands in PdCl2(XnPY)(2)catalyst and application of molecular oxygen instead of nitrobenzene (conventionally used oxidant for carbonylations) allow to carry out the process under mild conditions with high yield and selectivity. The best results (75% yield of the main product with selectivity of catalyst above 90%) were obtained for the process catalyzed by PdCl2(XnPY)(2) complex at 100 degrees C and they were greatly improved in comparison to 41% yield and 68% selectivity obtained for CO/nitrobenzene used at 180 degrees C. (C) 2015 Elsevier B.V. All rights reserved.