Plommer Hart, Murphy Jennifer N, Dawe Louise N, Kerton Francesca M
Department of Chemistry , Memorial University of Newfoundland , St. John's , NL A1B 3X7 , Canada.
Department of Chemistry and Biochemistry , Wilfrid Laurier University , Waterloo , ON N2L 3C5 , Canada.
Inorg Chem. 2019 Apr 15;58(8):5253-5264. doi: 10.1021/acs.inorgchem.9b00347. Epub 2019 Apr 4.
The first structures exhibiting bidentate (N, O) chelation of a morpholine group to a p-block element (aluminum) have been prepared and characterized by X-ray diffraction methods: Al[L] [WCA], where [L] = 4-(2-aminoethyl)morpholinylamino- N, N-bis(2-methylene-4,6- tert-butylphenolate) and [WCA] is a weakly coordinating anion. These compounds are easily synthesized by reacting Al[L]Cl with an equimolar amount of anhydrous Lewis acid and were characterized by elemental analyses, ESI-MS, MALDI-TOF MS, H, C{H}, and multinuclear NMR spectroscopy. DFT calculations showed that Al[L] cations containing bidentate NO coordination of the morpholine group are at least 21.1 kJ/mol more stable when compared to hypothetical monodentate (N bound) structures. When combined with protic co-initiators (EtOH, glycerol carbonate), the cationic complexes, where [WCA] = [GaCl] or [InCl], are living catalyst systems for the polymerization of ε-caprolactone, producing polycaprolactone with narrow dispersity ( D̵ = 1.00-1.05). Employing glycidol as a co-initiator furnished polymers with narrow dispersity ( D̵ = 1.01-1.07) but experimental molecular weights diverged considerably from the calculated values. Similar reactivity toward ROP was observed for all complexes containing a stable [WCA] but where [WCA] = [AlCl], upon combination with alcohols, alcoholysis was observed. Kinetic studies (Eyring analyses) allowed the determination of activation parameters, which were consistent with a coordination-insertion mechanism for the catalysts containing [WCA] = [GaCl] or [InCl]. End group analyses using MALDI-TOF mass spectrometry and H NMR spectroscopy showed hydroxyl and ester end groups within the polymer, corroborating the proposed mechanism. Stoichiometric reactions of EtOH, glycidol or tert-butyl alcohol with the complex, where [WCA] = [GaCl], showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.
通过X射线衍射方法制备并表征了首例展现出吗啉基团与p区元素（铝）形成双齿（N，O）螯合作用的结构：Al[L][WCA]，其中[L] = 4-(2-氨基乙基)吗啉基氨基-N，N-双(2-亚甲基-4,6-二叔丁基苯酚盐)，[WCA]为弱配位阴离子。这些化合物通过使Al[L]Cl与等摩尔量的无水路易斯酸反应易于合成，并通过元素分析、电喷雾电离质谱（ESI-MS）、基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）、氢谱、碳谱{氢谱}和多核核磁共振光谱进行表征。密度泛函理论（DFT）计算表明，与假设的单齿（N配位）结构相比，含有吗啉基团双齿NO配位的Al[L]阳离子稳定性至少高21.1 kJ/mol。当与质子型共引发剂（乙醇、碳酸甘油酯）结合时，其中[WCA] = [GaCl]或[InCl]的阳离子配合物是ε-己内酯聚合的活性催化剂体系，能生成分散度窄（Đ = 1.00 - 1.05）的聚己内酯。以缩水甘油作为共引发剂可得到分散度窄（Đ = 1.01 - 1.07）的聚合物，但实验分子量与计算值有很大偏差。对于所有含有稳定[WCA]的配合物都观察到了类似的对开环聚合（ROP）的反应活性，但当[WCA] = [AlCl]时，与醇结合会发生醇解反应。动力学研究（艾林分析）确定了活化参数，这与含有[WCA] = [GaCl]或[InCl]的催化剂的配位插入机理一致。使用MALDI-TOF质谱和氢谱进行的端基分析表明聚合物中存在羟基和酯端基，证实了所提出的机理。乙醇、缩水甘油或叔丁醇与[WCA] = [GaCl]的配合物的化学计量反应表明配体在N-吗啉位点发生质子化，这导致该侧基解离。
