Synthesis, structure and norbornene polymerization behavior of neutral palladium complexes
摘要:
A series of neutral palladium(II) complexes bearing non-symmetric bidentate pyrrole-iminato or salicylaldiminato chelate ligands have been synthesized, and the structure of representative complexes (3a, 4a, and 5a) have been confirmed by X-ray crystallographic analysis. These palladium complexes have been investigated as catalysts for the polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display high activities and produce vinyl-addition polynorborenes. Catalytic activity of up to 8.52 x 10(3) kg/mol(Pd) h has been observed. Wide-angle X-ray diffraction (WAXD) has been used to investigate the polymer microstructure and it has been found that they are non-crystalline. (C) 2004 Elsevier Ltd. All rights reserved.
elimination of Ln[N(TMS)2]3 with the bulky bidentate Schiffbase HL′ (L′ = 3,5-But2-2-(O)-C6H2CH═N-2,6-Pri2-C6H3) afforded the monoamido lanthanide complexes L′2LnN(TMS)2 (Ln = Yb (9), Y (10), Nd (11), and La (12)). While the amine elimination with the less bulky Schiffbase HL′′ (L′′ = 3,5-But2-2-(O)-C6H2CH═N-2,6-Me2-C6H3) yielded the desired monoamido complexes with the small metals of Y and Yb, L′′2LnN(TMS)2
Metal and Ligand-Substituent Effects in the Immortal Polymerization of<i>rac</i>-Lactide with Li, Na, and K Phenoxo-imine Complexes
作者:Francisco M. García-Valle、Robert Estivill、Carlos Gallegos、Tomás Cuenca、Marta E. G. Mosquera、Vanessa Tabernero、Jesús Cano
DOI:10.1021/om501000b
日期:2015.1.26
A series of lithium, sodium, and potassium complexes with phenoxo-imine ligands M[(O-2-(RN=CH)-C6H4] [R = C6H5; 2-(BuC6H5)-Bu-t; 2,6-(Pr2C6H3)-Pr-i] and [O-2-(RN=CH)-4,6-(Bu2C6H4)-Bu-t] [R = C6H5; 2-(BuC6H5)-Bu-t; 2,6-(Pr2C6H3)-Pr-i] 1-3(a-f) have been synthesized. The molecular structures in the solid state of some of these complexes have been determined by X-ray diffraction. These compounds show different nuclearities and geometries around the metal center depending on the nature and the pocket of the ligand substituents. Of particular interest is the structure of compound 3e, being the first example of a potassium cubane complex obtained with this kind of ligand. The structural behavior in solution has also been studied by diffusion-ordered NMR spectroscopy (DOSY), showing a direct correlation between aggregation behavior and polymerization activity. Compounds 1-3(a-f) are extremely active catalysts in the ring-opening polymerization (ROP) of rac-lactide, achieving conversions of 100% in less than 1 min and heterorich-PLA that is modified by the metal atom and the ligand substituents. BnOH was used as co-initiator, and the presence of large amounts of the alcohol produces the immortal polymerization of rac-lactide in a more controlled process. Stoichiometric reactions involving the catalysts, BnOH, and lactide demonstrated an activated monomer mechanism for the polymerization of rac-lactide.