Comparative Study of Aluminum Complexes Bearing N,N′-Diaryldioxalamidate and N,N′-Diaryldithiooxalamidate Ligands in Ring-Opening Polymerization of ε-Caprolactone

Abstract

A series of Al catalysts with N,N′-diaryloxalamidate and N,N′-diaryldithiooxalamidate ligands were synthesized, and their εcaprolactone polymerization rates were determined in this study. Of the Al complexes bearing N,N′-diaryldithiooxalamidate, [Ph H NCS] 2 Al 2 Me 4 exhibited the highest catalytic activity (conv. of poly-ε-caprolactone = 94%; [ε-caprolactone]:[[Ph H NCS] 2 Al 2 Me 4 ]:[benzyl alcohol] = 100:0.5:2 with [ε-caprolactone] = 2 M at 25 °C after 20 min), and of the Al complexes bearing N,N′-diaryldioxalamidate, [Ph H NCO] 2 Al 2 Me 4 exhibited the highest catalytic activity (conv. of poly-ε-caprolactone = 94%; [εcaprolactone]:[O H Al 2 Me 4 ]:[benzyl alcohol] = 100:0.5:2 with [ε-caprolactone] = 2 M at 25 °C after 30 min). The Al complexes bearing N,N′diaryldithiooxalamidate demonstrated a greater catalytic activity (1.4−7.3fold) than Al complexes bearing N,N′-diaryldioxalamidate. Density functional theory calculations revealed that [Ph iPr NCS] 2 Al 2 (OMe) 4 with a weaker Al−OMe bond and less repulsion of the highest transition state TS1 revealed the lower potential energy of TS1 compared to [Ph iPr NCO] 2 Al 2 (OMe) 4 and further exhibited a higher polymerization rate than [Ph iPr NCO] 2 Al 2 (OMe) 4 .

Improvement of catalytic activity of aluminum complexes for the ring-opening polymerization of ε-caprolactone: aluminum thioamidate and thioureidate systems

“…A review of CL polymerization using Al complexes bearing N,O and N,S bidentate ligands, including aminophenolate, 25 benzotriazole phenolate, 25 Schiff base, 25,26 thio-Schiff base, 27 N -(2-diphenylphosphinophenyl)-2,6-dialkylaniline, 28 hydroquinolin-8-olate, 29 2,2-bis(3,5-dimethylpyrazol-1-yl)-1- para -tolylethoxide, 30 N -phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)-acetamide, 31 arylamide, 11 anilinate, 8 g ,32 2-(benzo[ d ]oxazol-2-yl)phenolate, 33 ketiminate, 34 N , N ′-dimethyloxalamidates, 35 pyrazolyl-phenolate, 36 2-(benzo[ d ]thiazol-2-yl)phenolate, 37 β-pyrazylenolate, 38 and 8-quinolinolates, 39 is presented in Fig. 14.…”

Effects of Aluminum Complexes Bearing β-Thioketiminate and β-Ketiminates on ε-Caprolactone Ring-Opening Polymerization Reactivity

“…However, the overall catalysis comparison can still be made as a preliminary comparison. From Figure (polymerization at 25 °C), Al complexes bearing anilinate, aminophenolate, and N , N ′-dimethyloxalamidates exhibited high catalytic activity with less 30 min polymerization time. The mediocre Al complexes bearing ketiminate, arylamide, and pyrazolyl-phenolater have good catalytic ability with 40–60 min polymerization.…”