Stereoselective Ring-Opening Metathesis Polymerization with Molybdenum Imido Alkylidenes Containing O-Chelating N-Heterocyclic Carbenes: Influence of Syn/Anti Interconversion and Polymerization Rates on Polymer Structure
Stereoselective Ring-Opening Metathesis Polymerization with Molybdenum Imido Alkylidenes Containing O-Chelating N-Heterocyclic Carbenes: Influence of Syn/Anti Interconversion and Polymerization Rates on Polymer Structure
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DOI：
10.1021/acs.macromol.7b00841
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发表时间：
2017-08-08
期刊：
影响因子：
5.5
通讯作者：
Buchmeiser, Michael R.
中科院分区：
文献类型：
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作者：
Lienert, Christina;Frey, Wolfgang;Buchmeiser, Michael R.
研究了基于O-螯合NHC的中性和阳离子钼亚氨基亚烷基N-杂环卡宾（NHC）络合物在异丙基烯衍生物开环易位聚合（ROMP）中的第一插入产物（顺式/反式，顺式/反式）的结构，即，【莫（N-2，6-Me-2-C6H3）（N-亚苄基-N '-2-O-1-C6 H4-咪唑啉-2-亚基）（CHCMe2Ph）（OTf）]（1）、[Mo（N-2，6-Pr-2-C6H3）（N-2-，6-'Pr-2-C6 H3 N'-2-O-1-C6 H4-咪唑啉-2-亚基）-（CHCMe 2 Ph）（OTf）]（2）和[Mo（N-2，6-'Pr-2-C6 H3）（N-2，6'-C6 H3-N '-2-O-1-C6 H4-咪唑啉-2-亚基）（CH 3CN）（CHMe 2 Ph）（B（Ar-F）（4）（-））]（3）。此外，在乙腈中测定了催化剂1-3的顺/反互变速率。这些值与多晶型化的速率常数的相关性揭示了这两个值之间的平衡比率的重要性。通过改变溶剂或单体或通过切换到类似但更具ROMP活性的催化剂来破坏该平衡导致所得聚合物的顺式/反式含量的显著变化。尽管螯合和庞大的配体的性质，一个机制，需要在聚合过程中的催化剂的金属中心的转化提出。因此，借助于3制备了高度顺式-间同立构开环易位聚合衍生的聚合物。在此基础上，我们提出了一个综合性的机理，即含O-螯合剂的钼酰亚胺配合物形成顺式和反式构型的聚合物
The structures of the first insertion products (syn/anti, cis/trans) in the ring-opening metathesis polymerization (ROMP) of norbornene derivatives using both neutral and cationic molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes based on an O-chelating NHC, i.e., [Mo(N-2,6-Me-2-C6H3)(N-nnesityl-N'-2-O-1-C6H4-imidazo-lin-2-ylidene)(CHCMe2Ph)(OTf)] (1), [Mo (N-2,6-Pr-2-C6H3) (N-2-,6-'Pr-2-C6H3N'-2-O-1-C6H4-imidazolin-2-ylidene)-(CHCMe2Ph)(OTf)] (2), and [Mo(N-2,6-'Pr-2-C6H3)(N-2,6'-C6H3-N'-2-O-1-C6H4-imidazolin-2-ylidene) (CH3CN)(CHMe2Ph) (B(Ar-F)(4)(-))] (3), have been identified. Also, syn/anti interconversion rates of catalysts 1-3 have been determined in acetonitrile. Correlation of these values with the rate constants of polymorization revealed the importance of a balanced ratio between these two values. Disrupting that balance by changing the solvent or the monomer or by switching to a similar, but more ROMP-active catalyst leads to significant changes in the cis/trans contents of the resulting polymers. Despite the chelating and bulky nature of the ligands, a mechanism that entails inversion at the metal center of the catalyst during polymerization is proposed. Thus, highly cis-syndiotactic ring-opening metathesis polymerization-derived polymers have been prepared with the aid of 3. On the basis of our results, we propose a comprehensive mechanism for the formation of cis- and trans-configured polymers with molybdenum imido complexes containing an O-chelating