Fluorinated β‐Ketoiminate Zinc Complexes: Synthesis, Structure and Catalytic Activity in Ring Opening Polymerization of Lactide

Abstract

Dedicated to Prof. H. Schnöckel on the occasion of his 80th birthday.Complexes LZnR (L = C 6 F 5 NC(CF 3 )C(H)C(CF 3 )O; R = Me 1; Et 2) and L 2 Zn(thf) 2 (3) were synthesized and analyzed by NMR ( 1 H, 13 C, 19 F) and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. Complexes 1 and 2 are dinuclear in the solid state but monomeric in toluene solution according to diffusion-ordered spectroscopy (DOSY-NMR). They showed poor activity in the ring opening polymerization (ROP) of lactide (LA) but moderate activity in the presence of benzyl alcohol (BnOH), yielding polymers with high number average molecular weight (M n ) and moderately controlled molecular weight distribution (PDI). Homonuclear-decoupled 1 H NMR analysis of polylactic acid (PLA) obtained from rac-LA showed isotactic enrichment of the polymer microstructure, and kinetic studies of the ROP of L-LA with complex 2 showed a first order dependence of the monomer concentration. Analyses of low molecular weight polymers by 1 H NMR and MALDI-ToF mass spectrometry demonstrated the coordination-insertion mechanism (CIM).

Reductive Dimerization of Alkenes and Allenes Enabled by Photochemically Activated Zinc–Zinc Bonded Compounds

“…The zinc center exhibits a distorted tetrahedral coordination geometry, chelated by the NNP ligand in a κ 3 -N,N,P coordination . 50,51 Moreover, the addition of 2 equiv of TEMPO to the reaction of 1a and styrene under UV irradiation led to the formation of 9a exclusively and inhibited the formation of 3a (for details, see the Supporting Information). Treatment of complex 1a with two equivalents of 2,2′bipyridine under UV irradiation produced 2,2′-bipyridyl zinc complex 10 as a dark-red crystalline solid in 58% isolated yield (Scheme 4).…”

“…The zinc center exhibits a distorted tetrahedral coordination geometry, chelated by the NNP ligand in a κ 3 - N , N , P coordination mode and coordinated by the oxygen atom. The bond length of Zn–O was found to be 1.8566(13) Å, which is in the normal range of a Zn–O single bond [Zn–O, 1.80–2.18 Å]. , Moreover, the addition of 2 equiv of TEMPO to the reaction of 1a and styrene under UV irradiation led to the formation of 9a exclusively and inhibited the formation of 3a (for details, see the Supporting Information).…”

Zinc 8-aminotrihydroquinolines appended with pendant N-diphenylphosphinoethyl arms as exceptionally active catalysts for the ROP of ε-CL

“…While zinc catalysts bound by tridentate ligands have been central to developments in this area, there were also many reports concerned with zinc complexes bearing bidentate N^N ( 12–20 , Chart 1) 32–37 or N^O ( 21–25 , Chart 1) 38 ligands, which are in most cases formed as dimeric species. 32 For example, N^N-containing 12–16 bearing N-heterocyclic donors can efficiently catalyze the ROP of ε-CL and LA, 8 a ,33,34 while those containing sterically encumbered pyridylamido ligands ( 14 ) can mediate the formation of stereodiblock poly(LLA- b -DLA).…”