Moshe Kol

Gradient Isotactic Multiblock Polylactides from Aluminum Complexes of Chiral Salalen Ligands

Aluminum complexes of enantiomerically pure aminomethylpyrrolidine-based salalen ligands and their application in the stereoselective polymerization of lactide are described. Poly(lactic acid) featuring the new gradient isotactic multiblock microstructure was synthesized by isoselective catalysts, which operate by a combination of enantiomorphic-site and chain-end control mechanisms.

New facets of an old ligand: titanium and zirconium complexes of phenylenediamine bis(phenolate) in lactide polymerisation catalysis

Phenylenediamine bis(phenolate) binds in the reduced dianionic form to titanium and zirconium alkoxides giving either mononuclear or bridging dinuclear complexes depending on the metal precursors; the fluxional mononuclear titanium complex is found to exhibit extremely high activity in polymerisation of rac-lactide in the melt.

Titanium and Zirconium Complexes of Robust Salophan Ligands. Coordination Chemistry and Olefin Polymerization Catalysis

The synthesis of [ONNO]-type robust Salophan ligands featuring tertiary nitrogen donors is described for the first time. By varying the substitution pattern on the aromatic bridge and on the phenol...

Single-step synthesis of salans and substituted salans by Mannich condensation

Abstract A convenient route for the synthesis of a variety of salan-type compounds is introduced. The synthesis is based on a single-step Mannich condensation between readily available starting materials: primary or secondary amines, formaldehyde and substituted phenols. This methodology is suitable for the preparation of chiral salans as well, which may find applications in asymmetric catalysis.

Titanium complexes of chelating dianionic amine bis(phenolate) ligands: an extra donor makes a big difference

Abstract Two dianionic amine bis(phenolate) ligands are introduced and their reactions with titanium tetra(iso-propoxide) studied; ligand 1 having a single N-donor group leads exclusively to a homoleptic Lig2Ti type complex whereas ligand 3 having an additional N-donor on a side arm leads exclusively to a LigTi(OPri)2 type complex.

Titanium(IV) complexes of trianionic amine triphenolate ligands

Abstract Two trianionic amine triphenolate ligands are introduced and their isopropoxide Ti(IV) complexes synthesized. The two complexes are mononuclear and C3-symmetrical on the NMR timescale. High barriers to inversion ( ΔG ‡ >65 KJ mol −1 ) between the enantiomers of each complex were found. The complex derived from the bulkier tripodal ligand shows a better resistance to hydrolysis.

Group IV complexes of an amine bis(phenolate) ligand featuring a THF sidearm donor: From highly active to living polymerization catalysts of 1-hexene

Abstract A new amine bis(phenolate) ligand bearing a THF donor on a sidearm and several dialkyl complexes of the group IV triad are introduced. The crystal structures of a zirconium dibenzyl complex and a titanium dibenzyl complex were solved, and revealed a strong binding of the oxygen donor of the THF group to the metal center. Upon activation with tris(pentafluorophenyl)borane the zirconium and the hafnium dibenzyl complexes lead to highly active 1-hexene polymerization catalysts. In comparison, titanium complexes (a dibenzyl complex and a dimethyl complex) lead to slower but living polymerization of 1-hexene at room temperature. Polymerization of neat 1-hexene under high dilution conditions was found to be living for an exceptionally long time of 6 days, leading to poly(1-hexene) of Mw=816 000 and PDI=1.09. A block copolymerization of 1-hexene and 1-octene at room temperature could be obtained using the titanium catalysts.

Dithiodiolate Ligands: Group 4 Complexes and Application in Lactide Polymerization

Dithiodiolate ligands were synthesized by reacting 1,2-ethanedithiol or 1,2-benzenedithiol with 2,2-bis(trifluoromethyl)oxirane, led selectively to mononuclear octahedral group 4 complexes of the type [{OSSO}M(OR)(2)], which features C(2) symmetry and fluxional behavior, and were highly active in the ring-opening polymerization of rac- and L-lactide.

Zirconium Complexes of Phenylene-Bridged {ONSO} Ligands: Coordination Chemistry and Stereoselective Polymerization of rac-Lactide

Sequential tetradentate dianionic thio-imine diphenolate ligands featuring an ortho-phenylene core and their zirconium complexes are described for the first time. Ligands that include different combinations of bulky-alkyl groups and halo groups on the two phenol arms were prepared by a substitution/condensation reaction sequence. An unexpected fac-fac wrapping mode was found in the solid state for the ligands in the octahedral [{ONSO}Zr(O(t)Bu)2] complexes. The complexes were all fluxional, and the barrier for enantiomer interconversion was found to depend on the phenolate substituents. The complexes were found to catalyze the polymerization of rac-lactide to poly(lactic acid) in solution with polymer tacticities varying from heterotactic to atactic which showed correlation to the nature of phenolate substituents but not to the degree of complex fluxionality.

Controlled stereoselective polymerization of lactide monomers by group 4 metal initiators that contain an (OSSO)-type tetradentate bis(phenolate) ligand

Group 4 metal complexes Zr-1 to Zr-4, Ti-4 and Ti-4a that contain an (OSSO)-type tetradentate bis(phenolate) ligand were found to initiate the ring-opening polymerization of meso-, rac-, and L-lactides in toluene solution. The polymerizations were controlled with initiator efficiency values around one and gave polymers with low polydispersity (Mw/Mn < 1.2). The polylactides were atactic when rac-lactide was used as the monomer and heterotactic biased when meso-lactide was used. Kinetic measurements showed that meso-lactide was polymerized generally faster than rac- and L-lactide.