Chuanzhi Wei,Binghao Han,Dejuan Zheng,Quande Zheng,Shaofeng Liu,Zhibo Li
The aluminum complexes LAlMe2 (Al1–Al5: LH = 2,6-(R1)2-4-R2-C6H2NHCH2C6H4-2-PPh2; Al1, R1 = H, R2 = H; Al2, R1 = Me, R2 = H; Al3, R1 = iPr, R2 = H; Al4, R1 = Ph2CH, R2 = iPr; Al5, R1 = Cl, R2 = H) have been synthesized and characterized by elemental analysis and 1H, 13C, and 31P NMR. NMR analysis in solution reveals an interesting hemilabile coordination of the soft P donor. The molecular structures of Al2–Al4 were defined by X-ray diffraction studies, showing a distorted-tetrahedral geometry around the aluminum center in all structures. Careful comparison of these crystal structures suggested that different substituents on the ligands could lead to unignorable changed coordination environments around the Al center, thus affecting their catalytic properties. In the presence of BnOH, complexes Al1–Al5 efficiently catalyzed the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) with high conversions in a controlled manner, and high molecular weights (Mn up to 118.6 kg mol–1) of polycaprolactones (PCLs) were readily prepared. Immortal polymerizations by Al4 having bulky Ph2CH groups were also studied with up to 20 equiv of alcohols and 2000 equiv of monomers, without sacrificing polymerization control.
Shaofeng Liu,Jie Zhang,Weiwei Zuo,Wenjuan Zhang,Wen-Hua Sun,Hongqi Ye,Zhibo Li
The stoichiometric reactions of 8-(2,6-R1-4-R2-anilide)-5,6,7-trihydroquinoline (LH) with AlR3(R = Me or Et) afforded the aluminum complexesLAlR2(Al1–Al5,Al1: R1=iPr, R2= H, R = Me;Al2: R1= Me, R2= H, R = Me;Al3: R1= H, R2= H, R = Me;Al4: R1= Me, R2= Me, R = Me;Al5: R1= Me, R2= Me, R = Et) in high yields. All aluminum complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexesAl4andAl5were determined by single-crystal X-ray diffractions and revealed a distorted tetrahedral geometry at aluminum. In the presence of BnOH, complexesAl1–Al5efficiently initiated the ring-opening homopolymerization ofε-caprolactone (ε-CL) andrac-lactide (rac-LA), respectively, in a living/controlled manner.Keywords:aluminum complexes;crystal structures;ring-opening polymerization;biodegradable polyesters
Mengting Zang,Wenyao Cao,Xingwang Zhang,Shaofeng Liu,Zhibo Li
Catalysts drive innovation in sustainable polymers because of their reactivity and selectivity. In this context, the synthesis and characterization of a series of Al complexes ( Al1 − Al5 ) bearing N,N-bidentate amino-quinoline ligands are described, as well as their applications in ring-opening polymerization (ROP) of ε -caprolactone ( ε -CL). The amido-coordination Al complexes were directly synthesized by reactions of imino-quinoline compounds with AlMe 3 via methyl migration from Al to the carbon atom of imine, as indicated by both NMR spectroscopy and X-ray diffraction. In the presence of BnOH, complexes Al1 − Al5 showed significant reactivity for ROP of ε -CL with good control over molar mass ( M n ) and dispersity ( Đ < 1.2), and polycaprolactones (PCLs) with high molecular weights ( M n up to 129 kDa) were readily synthesized. Remarkably, immortal catalysis with excess of BnOH (up to 20 equiv. to Al) was achieved to prepare PCLs with predictable M n s, low dispersities, and end groups using an extremely low loading of Al complex (0.05 mol% to ε -CL monomer).
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