Luo Derong, Zeng Yi, Chen Xiong, Xia Ping, Xie Guangyong, You Qingliang, Zhang Li, Li Tingcheng, Li Xiangdan, Zhang Aiqing
Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission, Ministry of Education Hubei Province, South-Central University for Nationalities Wuhan 430074 China
Key Laboratory of Optoelectronic Chemical Materials and Devices, Ministry of Education, School of Chemical and Environmental Engineering, Jianghan University Wuhan 430056 China.
RSC Adv. 2018 Feb 13;8(13):6954-6964. doi: 10.1039/c8ra00071a. eCollection 2018 Feb 9.
Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [ONS] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (TiL-TiL) were synthesized and characterized by H NMR, C NMR, FTIR and elemental analysis. The molecular structure of ligand L (R = Pr) and its corresponding Ti complex TiL were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 10 g mol (Ti) h atm) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex TiL bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.
与单核配合物相比，双核和多核配合物因其在烯烃聚合中独特的催化性能而备受关注。在本工作中，合成了一系列苯基桥联的双-β-羰基烯胺[ONS]（R = 烷基或苯基）三齿配体及其双核钛配合物（TiL-TiL），并通过¹H NMR、¹³C NMR、FTIR和元素分析对其进行了表征。通过单晶X射线衍射进一步研究了配体L（R = ⁱPr）及其相应的钛配合物TiL的分子结构，结果表明，随着配体从β-羰基烯胺转变为β-亚氨基烯醇形式，每个钛与六个原子配位形成扭曲的八面体构型。在MMAO的活化下，这些配合物催化乙烯聚合以及乙烯/α-烯烃共聚，具有极高的活性（超过10 g mol⁻¹(Ti)⁻¹ h⁻¹ atm⁻¹），可生产高分子量聚乙烯。同时，与单核对应物TiL相比，观察到更宽的多分散性，表明可能存在两个活性催化中心，这与双核钛配合物的不对称晶体结构一致。此外，这些配合物比其单核类似物具有更好的热稳定性。与带有烷硫基侧链的配合物相比，带有苯硫基侧链的配合物TiL对乙烯聚合表现出更高的催化活性，并且生产出分子量高得多的聚乙烯，但1-己烯的插入率明显较低。然而，与亚甲基桥联的双水杨醛亚胺基双核钛配合物相比，这些双-β-羰基烯胺衍生的双核钛配合物表现出更高的乙烯/1-己烯共聚活性和1-己烯插入率，并且分子量和1-己烯插入率可通过α-烯烃共聚单体的初始进料和催化剂结构进行灵活调节。
