Flexible N,N,N-chelates as supports for iron and cobalt chloride complexes; synthesis, structures, DFT calculations and ethylene oligomerisation studies
作者:Richard Cowdell、Christopher J. Davies、Stephen J. Hilton、Jean-Didier Maréchal、Gregory A. Solan、Owen Thomas、John Fawcett
DOI:10.1039/b409827g
日期:——
The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH2CH2)(2-C5H4N)CH2}NH and (ArNHCH2CH2)2NH (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2), have been prepared by employing palladium-catalysed N–C(aryl) coupling reactions of the corresponding primary amines with aryl bromide. Treatment of MCl2 with (ArNHCH2CH2)(2-C5H4N)CH2}NH affords [(ArNHCH2CH2)((2-C5H4N)CH2)NH}CoCl2]
(Ar = 2,6-Me2C6H31a; 2,4,6-Me3C6H21b) and [(ArNHCH2CH2)((2-C5H4N)CH2)NH}FeCl2]n
(n
= 1, Ar = 2,6-Me2C6H32a; n
= 2, 2,4,6-Me3C6H22b) in high yield. The X-ray structures of 1a and 1b are isostructural and reveal the metal centres to adopt distorted trigonal bipyramidal geometries with the N,N,N-chelates adopting fac-structures. A facial coordination mode of the ligand is also observed in bimetallic 2b, however, in 2a the N,N,N-chelate adopts a mer-configuration with the metal centre adopting a geometry best described as square pyramidal. Solution studies indicate that mer–fac isomerisation is a facile process for these systems at room temperature. Quantum mechanical calculations (DFT) have been performed on 1a and 2a, in which the ligands employed are identical, and show the fac- to be marginally more stable than the mer-configuration for cobalt (1a) while for iron (2a) the converse is evident. Reaction of (ArNHCH2CH2)2NH with CoCl2 gave the five-coordinate complexes [(ArNHCH2CH2)2NH}CoCl2]
(Ar = 2,6-Me2C6H33a, 2,4,6-Me3C6H23b), in which the ligand adopts a mer-configuration; no reaction occurred with FeCl2. All complexes 1–3 act as modest ethylene oligomerisation catalysts on activation with excess methylaluminoxane (MAO); the iron systems giving linear α-olefins while the cobalt systems give mixtures of linear and branched products.
通过钯催化相应伯胺与芳基溴的 N-C(芳基)偶联反应,制备了芳基取代的 N-十六烷基乙二胺和二乙烯三胺配体 (ArNHCH2CH2)(2-C5H4N)CH2}NH 和 (ArNHCH2CH2)2NH(Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2)。MCl2 与 (ArNHCH2CH2)(2-C5H4N)CH2}NH 处理后得到 [(ArNHCH2CH2)((2-C5H4N)CH2)NH}CoCl2] (Ar = 2,6-Me2C6H31a;2,4,6-Me3C6H21b)和[(ArNHCH2CH2)((2-C5H4N)CH2)NH}FeCl2]n(n = 1,Ar = 2,6-Me2C6H32a;n = 2,2,4,6-Me3C6H22b)的高产率。1a 和 1b 的 X 射线结构是同构的,并显示金属中心采用扭曲的三叉双锥体几何结构,N,N,N-螯合物采用面结构。在双金属 2b 中也观察到了配体的面配位模式,但在 2a 中,N,N,N-螯合物采用的是 Mer 构型,金属中心采用的是方形金字塔几何结构。溶液研究表明,在室温下,mer-fac 异构化是这些体系的一个简单过程。我们对 1a 和 2a 进行了量子力学计算(DFT),其中使用的配体完全相同,计算结果表明,钴(1a)的面-构型比美拉-构型略微稳定,而铁(2a)的面-构型则明显相反。(ArNHCH2CH2)2NH 与 CoCl2 反应生成了五配位络合物 [(ArNHCH2CH2)2NH}CoCl2](Ar = 2,6-Me2C6H33a, 2,4,6-Me3C6H23b),其中配体采用了 Mer 构型;与 FeCl2 没有发生反应。在过量甲基铝氧烷(MAO)的活化作用下,所有配合物 1-3 都可作为适度的乙烯低聚催化剂;铁系统可生成线性 α-烯烃,而钴系统则可生成线性和支化产物的混合物。