Synthesis and Structural Analysis of Four Coordinate (Arylimido)niobium(V) Dimethyl Complexes Containing Phenoxide Ligand: MAO-Free Ethylene Polymerization by the Cationic Nb(V)?Methyl Complex
Synthesis and Structural Analysis of Four Coordinate (Arylimido)niobium(V) Dimethyl Complexes Containing Phenoxide Ligand: MAO-Free Ethylene Polymerization by the Cationic Nb(V)?Methyl Complex
复制标题
含酚盐配体的四配位(芳基酰亚氨基)铌(V)二甲基配合物的合成与结构分析：阳离子Nb(V)甲基配合物的无MAO乙烯聚合
DOI：
10.1021/acs.organomet.0c00567
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发表时间：
2020
期刊：
影响因子：
2.8
通讯作者：
Nomura Kotohiro
中科院分区：
文献类型：
--
作者：
Koide Koji;Yi Jun;Kuboki Masaharu;Yamazoe Seiji;Nakatani Naoki;Nomura Kotohiro
以二（二甲酰胺）类似物Nb（NAr）（NMe 2）2（O-2，6-tBu 2C 6 H3）（2a-c）为原料，通过与AlMe 3反应，合成了四个含2，6-二叔丁基苯氧基配体的（芳酰亚胺）铌（V）二甲基配合物Nb（NAr）Me 2（O-2，6-tBu 2C 6 H3）[Ar = 2，6-iPr 2C 6 H3（5a），2，6-Me 2C 6 H3（5 b），2-MeC 6 H4（5c）].通过X射线晶体学确定了双（二甲基酰胺）配合物（2a-c）和二甲基配合物（5 b，c）的具有扭曲四面体几何形状的结构。溶液Nb K边XANES谱（X射线吸收近边结构，在甲苯中，25 °C）显示，二甲基络合物（5a，B）中的边前强度高于双（5 a，5 b）中的边前强度。（二甲基酰胺）配合物（2a，B）及其边前衍生物（包括它们的肩部边缘突起）受到所采用的配体组的高度影响;通过TD-DFT（时间相关密度泛函理论）模拟，这些峰的分配被很好地解释为s-d跃迁和随后d-p杂化程度的结果。二甲基配合物（5a-c）在甲基铝氧烷（MAO）的存在下，特别是在80 °C（约100 ° C）下，对正辛烷中的乙烯聚合显示出良好的催化能力。808-1140 kg-PE/mol-Nb·h）。用[Ph 3C][B（C6 F5）4]在THF中处理5a得到阳离子[Nb（N-2，6-iPr2C6H3）Me（O-2，6-tBu 2C 6 H3）（THF）]+[B（C6 F5）4]−（6a），其在添加Al（n-C8 H17）3时在80 ℃下聚合乙烯，得到具有单峰分子量分布的高分子量聚合物（Mn= 1.04-1.21 × 106，Mw/Mn= 1.60-1.86），表明聚合是通过阳离子烷基物种进行的。
Four coordinate (arylimido)niobium(V) dimethyl complexes containing 2,6-di-tert-butylphenoxy ligand, Nb(NAr)Me2(O-2,6-tBu2C6H3) [Ar = 2,6-iPr2C6H3(5a), 2,6-Me2C6H3(5b), 2-MeC6H4(5c)], were prepared from the bis(dimethylamide) analogues, Nb(NAr)(NMe2)2(O-2,6-tBu2C6H3) (2a–c), by treatment with AlMe3. Structures with a distorted tetrahedral geometry of the bis(dimethylamide) complexes (2a–c) and the dimethyl complexes (5b,c) were determined by X-ray crystallography. The solution Nb K-edge XANES spectra (X-ray absorption near edge structure, in toluene at 25 °C) showed that pre-edge intensities in the dimethyl complexes (5a,b) were higher than those in the bis(dimethylamide) complexes (2a,b) and their pre-edge absorptions (including their shoulder edge absorptions) were highly affected by the ligand sets employed; these peak assignments are well explained by TD-DFT (time dependent density functional theory) simulation as a results of s–d transition and degree in subsequent d–p hybridization. The dimethyl complexes (5a–c) showed good catalysis capabilities for ethylene polymerization inn-octane in the presence of methylaluminoxane (MAO) especially at 80 °C (ca. 808–1140 kg-PE/mol-Nb·h). Treating5awith [Ph3C][B(C6F5)4] in THF gave the cationic [Nb(N-2,6-iPr2C6H3)Me(O-2,6-tBu2C6H3)(THF)]+[B(C6F5)4]−(6a), which polymerized ethylene at 80 °C upon addition of Al(n-C8H17)3to afford ultrahigh molecular weight polymers with unimodal molecular weight distributions (Mn= 1.04–1.21 × 106,Mw/Mn= 1.60–1.86); the results strongly suggest that the polymerization proceeded via the cationic alkyl species.