Zinc, aluminum and group 3 metal complexes of sterically demanding naphthoxy-pyridine ligands: Synthesis, structure, and use in ROP of racemic lactide and beta-butyrolactone

摘要

New potentially tridentate, bulky ortho-Ph3Si-substituted naphthol-pyridine proligands a-f were synthesized and introduced onto zinc, aluminum and group 3 metal centers (M = Sc, Y, La) using straightforward one-step alkane or amine elimination protocols. The solid-state structures of these mononuclear zinc (1a, 1c, 1d, 2c and 2e) and aluminum (3c) complexes were determined by single-crystal X-ray diffraction studies, while the solution structures were established using H-1, C-13{H-1} and Si-29/Si-29{H-1} (when appropriate) NMR spectroscopy. For all complexes, only one species (isomer) of C-1 symmetry was observed by NMR spectroscopy in the broad temperature range. Most of these complexes are effective initiators for the ring-opening polymerization (ROP) of racemic lactide (rac-LA) at 25-100 degrees C, affording poly(lactides)s (PLAs) generally with unimodal dispersities and molecular weights in good agreement with calculated values. An yttrium complex (4e) proved the most active (TOF = 1840 mol(LA) mol(Y)(-1) h(-1) at 25 degrees C) and yielded heterotactic-enriched PLAs (P-r up to 0.80) in toluene, while atactic PHBs were formed in the ROP of racemic beta-butyrolactone (rac-BBL) under the same conditions. (C) 2014 Elsevier B.V. All rights reserved.