Wang Chaopan, Chen Jue, Xu Wei, Mou Zehuai, Yao Yingming, Luo Yunjie
School of Material Science and Chemical Engineering, Ningbo University, Ningbo 315211, P. R. China.
School of Biological and Chemical Engineering, Ningbo Institute of Technology, Zhejiang University, Ningbo 315100, P. R. China.
Inorg Chem. 2020 Mar 2;59(5):3132-3141. doi: 10.1021/acs.inorgchem.9b03495. Epub 2020 Feb 19.
Bimetallic complexes are expected to offer unique catalytic property, by facilitating cooperative effects between proximate functional groups or adjacent active metal centers, and thus have attracted increasing attention in the chemical community. Treatment of Ln(CHSiMe)(THF) or Ln(CHCHNMe-) with 1,4-(CHNH)CH in a 2:1 molar ratio in tetrahydrofuran (THF) generated a series of bimetallic arylamide-ligated rare-earth metal alkyl complexes [1,4-(CHN)CH][Ln(CHSiMe)(THF)] (Ln = Sc (), Lu (), Y ()), and aminobenzyl complexes [1,4-(CHN)CH][Ln(CHCHNMe-)(THF)] (Ln = Sc (), = 0; Lu (), Y (), = 1) in 65-73% isolated yields. To reveal the polymerization difference between bimetallic and monometallic rare-earth metal complexes, the monoarylamide-ligated scandium bis(aminobenzyl) complex [(CH)N]Sc(CHCHNMe-) () was prepared by the reaction of Sc(CHCHNMe-) with 1 equiv of diphenylamine (CH)NH. All these rare-earth metal complexes were characterized by elemental analysis and NMR spectroscopy. The molecular structures of complexes and were authenticated by single-crystal X-ray diffraction. Complexes , , , and alone were highly active for 2-vinylpyridine (2VP) polymerization at room temperature, giving poly-2VP with good iso-selectivity (). After activation with 2 equiv of [PhC][B(CF)] or [PhNHMe][B(CF)], these complexes demonstrated an improved iso-selectivity ( up to 96%) toward 2VP polymerization compared to their neutral analogues. In comparison, the bimetallic scandium complexes and showed relatively poor activity toward 2VP polymerization under the same conditions. However, the stereoselectivity of the polymerization could be switched from iso-tacticity to syndio-rich selectivity solely by tuning active species from only one scandium precatalyst. The catalyst system of complex /[PhNMeH][B(CF)] was able to promote a controlled syndio-specific polymerization of 2VP. The polymerization was experimentally verified to proceed via group transfer mechanism. Preliminary results indicated that the bimetallic rare-earth metal complexes showed a higher polymerization activity than the corresponding monometallic species mostly resulting from the cooperative effect.
双金属配合物有望通过促进相邻官能团或相邻活性金属中心之间的协同效应而展现出独特的催化性能，因此在化学领域引起了越来越多的关注。在四氢呋喃（THF）中，将Ln(CHSiMe)(THF)或Ln(CHCHNMe-)与1,4-(CHNH)CH以2:1的摩尔比进行反应，得到了一系列双金属芳基酰胺配位的稀土金属烷基配合物[1,4-(CHN)CH][Ln(CHSiMe)(THF)]（Ln = Sc（），Lu（），Y（））以及氨基苄基配合物[1,4-(CHN)CH][Ln(CHCHNMe-)(THF)]（Ln = Sc（）， = 0；Lu（），Y（）， = 1），分离产率为65 - 73%。为了揭示双金属和单金属稀土金属配合物之间的聚合差异，通过Sc(CHCHNMe-)与1当量的二苯胺(CH)NH反应制备了单芳基酰胺配位的钪双(氨基苄基)配合物[(CH)N]Sc(CHCHNMe-)（）。所有这些稀土金属配合物均通过元素分析和核磁共振光谱进行了表征。配合物 和 的分子结构通过单晶X射线衍射得以确证。配合物 、 、 和 单独在室温下对2 - 乙烯基吡啶（2VP）聚合具有高活性，生成具有良好等规选择性（）的聚2VP。在用2当量的[PhC][B(CF)]或[PhNHMe][B(CF)]活化后，与它们的中性类似物相比，这些配合物对2VP聚合表现出更高的等规选择性（高达96%）。相比之下，双金属钪配合物 和 在相同条件下对2VP聚合表现出相对较差的活性。然而，仅通过调节单一钪预催化剂的活性物种，聚合的立体选择性就可以从等规性转变为富含间同立构的选择性。配合物 /[PhNMeH][B(CF)]的催化体系能够促进2VP的可控间同立构特异性聚合。实验证明该聚合通过基团转移机理进行。初步结果表明，双金属稀土金属配合物比相应的单金属物种表现出更高的聚合活性，这主要是由于协同效应。
