Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

Abstract

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-(2aminoethyl)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, 1 H, 13 C{ 1 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 4 ] − or [InCl 4 ] − , 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 4 ] − , 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 4 ] − or [InCl 4 ] − . End group analyses using MALDI−TOF mass spectrometry and 1 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 4 ] − , showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.

Non-Nucleophilic Electrolyte Based on Ionic Liquid and Magnesium Bis(diisopropyl)amide for Rechargeable Magnesium-Ion Batteries

“…Raman spectroscopic studies performed on the electrolyte to identify [Mg 2 (μ-Cl) 3 (THF) 6 ] + yielded an unresolved spectrum initially due to strong fluorescence interferences from the solvent molecules, which is in accordance with the earlier reported studies . However, the spectra (Figure S3) obtained from the solidified electrolyte after removing the THF solvent that shows a characteristic peak at around 242 cm –1 corresponds to MgCl 3 + in the [Mg 2 (μ-Cl) 3 (THF) 6 ] + complex. , Besides, the characteristic peak of AlCl 4 – is observed at 311 cm –1 . However, the peak for its dimer Al 2 Cl 7 – (347 cm –1 ) is not observed in the electrolyte .…”

“…54 However, the spectra (Figure S3) obtained from the solidified electrolyte after removing the THF solvent that shows a characteristic peak at around 242 cm −1 corresponds to MgCl 3 + in the [Mg 2 (μ-Cl) 3 (THF) 6 ] + complex. 33,55 Besides, the characteristic peak of AlCl 4…”

Progress in the catalytic reactions of CO2 and epoxides to selectively provide cyclic or polymeric carbonates

“…6e). 15 Li and coworkers have reported the preparation of monometallic aluminum alkyl complexes viz. LAlMe 2 (Fig.…”

Collaboration between Trinuclear Aluminum Complexes Bearing Bipyrazoles in the Ring-Opening Polymerization of ε-Caprolactone

“…Al catalysts are frequently used for ROP because they are strong Lewis acids, are easy to synthesize, and have inexpensive precursors. Ligands are essential for catalyst design because they can influence the catalytic activity through electronic, − steric, ,, chelating, ,− and dinuclear cooperation effects ,− and reduce transesterification. , Recently, Al complexes − bearing pyrazolyl-containing ligands and their application in ROP have been reported; these complexes exhibit moderate catalytic activity for cyclic ester polymerization. Importantly, dinuclear Al complexes bearing pyrazolide derivatives (Figure a) with high catalytic activities for CL ROP have been reported.…”