Reactivity of Amine/E(C6F5)3 (E = B, Al) Lewis Pairs toward Linear and Cyclic Acrylic Monomers: Hydrogenation vs. Polymerization.
Reactivity of Amine/E(C6F5)3 (E = B, Al) Lewis Pairs toward Linear and Cyclic Acrylic Monomers: Hydrogenation vs. Polymerization.
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DOI：
10.3390/molecules20069575
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发表时间：
2015-05-26
期刊：
影响因子：
--
通讯作者：
Chen EX
中科院分区：
文献类型：
--
作者：
Chen J;Chen EX
本工作揭示了胺/E（C6 F5）3（E = B，Al）刘易斯对对线性和环状丙烯酸单体、甲基丙烯酸甲酯（MMA）和可生物再生的γ-甲基-α-亚甲基-γ-丁内酯（γMMBL）的对比反应性。2，2，6，6-四甲基哌啶（TMP）与B（C6 F5）3混合后形成受抑的刘易斯对（FLP），Et 3 N与B（C6 F5）3反应生成双硼酸铵离子对和亚胺两性离子对。另一方面，TMP或Et 3 N与Al（C6 F5）3的化学计量反应导致经典的刘易斯加合物（CLA）的干净形成。TMP和Et 3 N在与E（C6 F5）3配对时均不聚合MMA，但Et 3 N/2B（C6 F5）3对促进MMA的转移氢化以形成异丁酸甲酯。相比之下，胺/E（C6 F5）3对促进携带更具反应性的环外亚甲基部分的γMMBL的快速聚合，即使在0.0625摩尔%的低催化剂负载下也在不到3分钟内实现完全转化。TMP与硼烷或铝烷配对时比Et 3 N对于聚合更有效，而铝烷与Et 3 N配对时比硼烷表现出更高的聚合活性。总的来说，TMP/Al（C6 F5）3体系表现出最高的聚合活性，在0.125 mol %的催化剂负载量下实现了96，000 h−1的最大转换频率，产生了Mn = 1.29 × 105 g·mol−1的高分子量PγMMBL。
This work reveals the contrasting reactivity of amine/E(C6F5)3 (E = B, Al) Lewis pairs toward linear and cyclic acrylic monomers, methyl methacrylate (MMA) and biorenewable γ-methyl-α-methylene-γ-butyrolactone (γMMBL). While mixing of 2,2,6,6-tetramethylpiperidine (TMP) and B(C6F5)3 leads to a frustrated Lewis pair (FLP), Et3N reacts with B(C6F5)3 to form disproportionation products, ammonium hydridoborate ionic pair and iminium zwitterion. On the other hand, the stoichiometric reaction of either TMP or Et3N with Al(C6F5)3 leads to clean formation of a classic Lewis adduct (CLA). Neither TMP nor Et3N, when paired with E(C6F5)3, polymerizes MMA, but the Et3N/2B(C6F5)3 pair promotes transfer hydrogenation of MMA to form methyl isobutyrate. In contrast, the amine/E(C6F5)3 pairs promote rapid polymerization of γMMBL carrying the more reactive exocyclic methylene moiety, achieving full conversion in less than 3 min even at a low catalyst loading of 0.0625 mol %. TMP is more effective than Et3N for the polymerization when paired with either the borane or the alane, while the alane exhibits higher polymerization activity than the borane when paired with Et3N. Overall, the TMP/Al(C6F5)3 system exhibits the highest polymerization activity, achieving a maximum turn-over frequency of 96,000 h−1 at 0.125 mol % of catalyst loading, producing high molecular weight PγMMBL with Mn = 1.29 × 105 g∙mol−1.
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