Aluminum Complexes of Octahydrophenanthroline‐Based Salophan Ligands: Coordination Chemistry and Activity in the Ring‐Opening Polymerization of Lactide

Abstract

Salophan ligands featuring the octahydrophenanthroline core are described for the first time. Two ligand precursors featuring either di-tert-butylphenolate or dichlorophenolate were prepared by 1,10-phenanthroline hydrogenation followed by reaction with bromomethyl-substituted phenols. The ligand precursors react with AlMe 3 to give the [{ONNO}Al-Me]-type complexes as single stereoisomers of averaged C s -symmetry on the NMR timescale. The reactivity of the [a] 5048 Scheme 3. The reactivity of the salophan {ONNN}Al-Me complexes with benzyl alcohol.

The Dual‐Stereocontrol Mechanism: Heteroselective Polymerization of rac‐Lactide and Syndioselective Polymerization of meso‐Lactide by Chiral Aluminum Salan Catalysts

“…[19][20][21][22][23] In contrast, aluminum complexes of salan ligands assembled around the chiral diaminocyclohexane core were obtained as mixtures of diastereomers which led to low levels of stereocontrol in rac-a nd meso-lactide polymerization. [24] Aiming at higher stereoselectivity while not retarding reactivity, [25,26] we targeted two new ligand precursors:t he C 2 -symmetric Lig 1 H 2 bearing ortho-phenyl substituents on the two phenolates,and the hybrid C 1 -symmetric Lig 2 H 2 bearing an ortho-phenyl phenolate and a2 ,4-dichlorophenolate (Scheme 3). Thet wo ligand precursors were prepared as pure enantiomers by at wo-step reduction-amination of the two enantiomers of bipyrrolidine with the substituted salicylaldehydes (see the Supporting Information), and were obtained as crystalline solids in high yields.R eacting the ligand precursors Lig 1 H 2 and Lig 2 H 2 with triethylaluminum followed by benzyl alcohol gave the [{ONNO}Al-OBn] complexes as single diastereomers according to 1 HNMR and 13 CNMR spectra.…”