Ligand effects on NiII-catalysed alkane-hydroxylation with m-CPBA
Ligand effects on NiII-catalysed alkane-hydroxylation with m-CPBA
复制标题
DOI：
10.1039/b615503k
复制
发表时间：
2007-01-01
影响因子：
4
通讯作者：
Itoh, Shinobu
中科院分区：
文献类型：
--
作者：
Nagataki, Takayuki;Ishii, Kenta;Itoh, Shinobu
一系列吡啶基烷基胺配体负载的镍（II）配合物[tris（2-吡啶甲基）胺（TPA;络合物1a和1b）、三[2-（三氟甲基）苯基]氨基甲酸酯（tris[2-（三氟甲基）苯基]氨基甲酸酯）（2-吡啶基）乙胺（TEPA;络合物2a和2b），6-[N，N-双（2-吡啶基甲基）氨基甲基]-2，4-二叔丁基苯酚（（Dtbp）Pym 2 H;配合物3a和3b）、6-[N，N-双[2-（2-甲氧基苯基）-2-甲基-N-（2-甲氧基苯基）-3-甲基-N，N-二氧杂环戊烯]-1-基]-N，N-二氧杂环己基]-N，N-二氧杂环己基]-N，（2-吡啶基）乙基]氨基甲基]-2，4-二叔丁基苯酚（（Dtbp）Pye 2 H;络合物4a和4 b），N-苄基-双（2-吡啶基甲基）胺（（Bz）Pym 2;络合物5a）和N-苄基-双[ 2-（三氟甲基）苯基]-N-（2-吡啶基甲基）胺（（Bz）Pym 2;络合物5a）。（2-吡啶基）乙基]胺（（Bz）Pye 2;配合物6a）]的合成和结构表征的X-射线晶体学分析[配位抗衡阴离子配合物na（n = 1 - 6）的配位体为AcO-，配合物nb（n = 1 - 4）的配位体为NO3-]。所有的配合物，除了1b，得到一个单核镍（II）配合物表现出扭曲的八面体几何形状，而配合物1b被隔离为双核镍（II）配合物桥接由两个硝酸根阴离子。以环己烷为氧化剂，考察了镍（II）配合物的催化活性。在所有情况下，氧化反应都以催化方式进行，得到作为主要产物的环己醇以及作为次要产物的环己酮。含有吡啶基甲胺（Pym）金属结合基团的配合物（1a，3a，5a）比含有吡啶基乙胺（Pye）金属结合基团的配合物（2a，4a，6a）显示出更高的转换数（TON），而后者（Pye系统）的醇/酮（A/K）选择性比前者（Pym系统）高得多。另一方面，NO3-共配体（1b，2b和3b）的存在导致了催化反应早期的滞后期。根据X-射线衍射结构，讨论了配体的电子效应和空间位阻效应以及共配体的化学行为对镍配合物催化活性的影响。
Nickel(II) complexes supported by a series of pyridylalkylamine ligands [tris(2-pyridylmethyl) amine (TPA; complexes 1a and 1b), tris[2-(2-pyridyl) ethyl] amine (TEPA; complexes 2a and 2b), 6-[N, N-bis(2-pyridylmethyl) aminomethyl]-2,4-di-tert-butylphenol ((Dtbp)Pym2H; complexes 3a and 3b), 6-[N, N-bis[2-(2-pyridyl) ethyl] aminomethyl]-2,4-di-tert-butylphenol ((Dtbp)Pye2H; complexes 4a and 4b), N-benzyl-bis(2-pyridylmethyl) amine ((Bz)Pym2; complex 5a) and N-benzyl-bis[ 2-( 2- pyridyl) ethyl] amine ((Bz)Pye2; complex 6a)] have been synthesized and structurally characterized by X-ray crystallographic analysis [ coordinating counter anion (co-ligand) of complexes na ( n = 1 - 6) is AcO- and that of complexes nb ( n = 1 - 4) is NO3-]. All complexes, except 1b, were obtained as a mononuclear nickel( II) complex exhibiting a distorted octahedral geometry, whereas complex 1b was isolated as a dinuclear nickel( II) complex bridged by two nitrate anions. Catalytic activity of the nickel( II) complexes were examined in the oxidation of cyclohexane with m-CPBA as an oxidant. In all cases, the oxygenation reaction proceeded catalytically to give cyclohexanol as the major product together with cyclohexanone as the minor product. The complexes containing the pyridylmethylamine (Pym) metal-binding group ( 1a, 3a, 5a) showed higher turnover number ( TON) than those containing the pyridylethylamine (Pye) metal-binding group ( 2a, 4a, 6a), whereas the alcohol/ketone (A/K) selectivity was much higher with the latter ( Pye system) than the former ( Pym system). On the other hand, the existence of the NO3- co-ligand (1b, 2b and 3b) caused a lag phase in the early stage of the catalytic reaction. Electronic and steric effects of the supporting ligands as well as the chemical behavior of the co-ligands on the catalytic activity of the nickel( II) complexes have been discussed on the basis of their X-ray structures.