A Series of Bis(phosphinic)diamido Yttrium Complexes As Initiators for Lactide Polymerization

Phosphasalalen Rare-Earth Complexes for the Polymerization of rac-Lactide and rac-β-Butyrolactone

A series of new phosphasalalen pro-ligands, analogues of salalen but with an iminophosphorane replacing the imine functionality, and their corresponding rare-earth alkoxide and siloxide complexes were synthesized. The multinuclear NMR spectra and X-ray diffraction analyses revealed that, for the tert-butoxide and ethoxide complexes, the resulting phosphasalalen rare-earth product was composed of a mononuclear alkoxide and a binuclear complex containing bridged alkoxo and hydroxo groups, while an analogous binuclear complex was isolated as the sole product for the siloxide complex. All the complexes could catalyze the heteroselective ring-opening polymerization (ROP) of rac-lactide (P_r up to 0.77) with high catalytic activities and a controlled polydispersity. Remarkably, the yttrium and lutetium phosphasalalen complexes could also efficiently catalyze the ROP of rac-β-butyrolactone to produce syndiotactic polymers (P_r up to 0.73) while their salalen analogues were inert, revealing the special effects of the iminophosphorane moiety. Detailed end-group analyses and kinetic investigations suggested that the alkoxo-hydroxo-bridged complexes maintained their binuclear structures in the polymerization.

N-Benzoylbenzamidinate complexes of aluminium: highly efficient initiators for the ring-opening polymerization of ε-caprolactone

A series of aluminium complexes supported by amidinate-based N,O-chelate ligands are synthesized and characterized. While complexes [L(Dipp)AlMe2] () and [L(Ph)AlMe2] () are prepared by treating N-benzoyl-N'-2,6-diisopropylphenylbenzamidine (L(Dipp)H) and N-benzoyl-N'-phenylbenzamidine (L(Ph)H) with a slight excess of 1 equiv. of AlMe3, complexes [(L(Dipp))2AlMe] () and [(L(Ph))3Al] () can be obtained using the ligands and AlMe3 in 2 : 1 and 3 : 1 molar ratios respectively. Complexes have been characterized by (1)H/(13)C NMR spectroscopy and elemental analysis. The molecular structures of complexes , and have also been determined by single crystal X-ray diffraction technique. , and are highly active initiators for the ring opening polymerization (ROP) of ε-caprolactone and produce polycaprolactone with very high molecular weight and narrow molecular weight distribution. These complexes are also active toward the ROP of cyclohexene oxide.

Dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands: synthesis, structures, and catalysis toward the ring-opening polymerization of ε-caprolactone and rac-lactide

Synthesis and characterization of novel dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands and their catalysis toward the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) were carried out. The ligand precursors [(5-Bu(t)-2-C4H2NH)CH=N(CH2)2]2NH (H2L(Bu), 1) and [(2-C4H3NH)CH=N(CH2)2]2NH (H2L(H), 2) were prepared by condensation of diethylene triamine with 5-tert-butyl-1H-pyrrole-2-carbaldehyde and 1H-pyrrole-2-carbaldehyde, respectively. Treatment of 1 with 2 equiv. of Bu(n)MgOBn in toluene at 70 °C produced dinuclear magnesium complex [(μ-OBn)2Mg2L(Bu)] (3). Similar treatment of 1 with EtZnOBn generated [(μ-OBn)2Zn2L(Bu)] (4). Reaction of 2 with 2 equiv. of Me2AlOBn in toluene at 70 °C afforded aluminum complex [Me2Al(μ-OBn)2AlL(H)] (5). Complexes 3-5 were characterized by (1)H and (13)C NMR spectroscopy, elemental analyses, and single crystal X-ray diffraction techniques. Each of complexes 3-5 is active for the ROP of ε-CL and rac-LA. Kinetic studies of the polymerization reactions were performed.

Chiral lanthanide complexes: coordination chemistry, spectroscopy, and catalysis

Luminescent lanthanide complexes bearing amido-bisoxazoline ligands are reported. They were studied using time-resolved luminescence spectroscopy, and were probed for their activity in hydroamination/cyclisation and ring-opening polymerisation catalysis.

Mechanism of living lactide polymerization by dinuclear indium catalysts and its impact on isoselectivity

A family of racemic and enantiopure indium complexes 1-11 bearing bulky chiral diaminoaryloxy ligands, H(NNO(R)), were synthesized and fully characterized. Investigation of both the mono- and the bis-alkoxy-bridged complexes [(NNO(R))InX](2)[μ-Y][μ-OEt] (5, R = (t)Bu, X = Y = Cl; 8, R = Me, X = I, Y = OEt) by variable temperature, 2D NOESY, and PGSE NMR spectroscopy confirmed dinuclear structures in solution analogous to those obtained by single-crystal X-ray crystallography. The dinuclear complexes in the family were highly active catalysts for the ring-opening polymerization (ROP) of lactide (LA) to form poly(lactic acid) (PLA) at room temperature. In particular, complex 5 showed living polymerization behavior over a large molecular weight range. A detailed investigation of catalyst stereoselectivity showed that, although (R,R/R,R)-5 is highly selective for l-LA, only atactic PLA is obtained in the polymerization of racemic LA. No such selectivity was observed for complex 8. Importantly, the selectivities obtained for the ROP of racemic LA with (R,R/R,R)-5 and (R,R/R,R)-8 are different and, along with kinetics investigations, suggest a dinuclear propagating species for these complexes.