Ethylene and Styrene Carbon Monoxide Copolymerization Catalyzed by Pyrazolyl Palladium(II) Complexes

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand

Zn(II), Pd(II), and Cd(II) complexes, [L _TH MCl ₂ ] (M = Zn, Pd; X = Br, Cl) and [L _TH Cd(μ-X)X] _n (X = Cl, Br; n = n, 2), supported by the (E)-N ¹,N ¹-dimethyl-N ²-(thiophen-2-ylmethylene)ethane-1,2-diamine (L _TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl^- or Br^-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L _TH MCl ₂ ]/LiO ⁱ Pr (M = Zn, Pd) and [L _TH Cd(μ-Cl)Cl] _n /LiO ⁱ Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L _TH ZnCl ₂ ]/LiO ⁱ Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L _TH ZnCl ₂ ]/LiO ⁱ Pr producing PLA with higher heterotactic bias (P _r up to 0.74 at 0 °C).

Effect of chalcogens on CO insertion into the palladium-methyl bond of [(N^N^X)Pd(CH3)](+) (X = O, S, Se) and on CO/ethylene copolymerisation

Neutral chloromethylpalladium(II) complexes, [Pd(Cl)(CH3)(L)] (1a-5a) with ligands κ(2)-N^S-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L1), κ(2)-N^S-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L2), κ(2)-N^Se-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L3), κ(2)-N^Se-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L4), and κ(2)-N^N-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenoxymethyl)pyridine (L5) have been synthesised and characterised by various spectroscopic techniques. Ligands L1-L4 exhibit Npy^S/Se bidentate coordination whereas L5 shows an Npy^Npz bidentate coordination mode in their corresponding neutral palladium complexes. Abstraction of chloride in neutral palladium complexes with NaBAr4 (BAr4 = tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate) resulted in the formation of the cationic palladium complexes 1b-5b, in which L1-L4 adopt a tridentate Npz^Npy^X (X = S or Se) coordination mode in their respective cationic palladium complexes (1b-4b) whilst L5 in complex 5b adopts a Npy^Npz bidentate coordination mode and the palladium centre is stabilized by the weakly coordinating acetonitrile. Compounds 1b-5b readily undergo CO insertion into the Pd-CH3 bond to form Pd-acyl that determines their ability to catalyse CO/ethylene copolymerisation to polyketones.

Ferrocenylpyrazolyl palladium complexes as catalysts for the polymerisation of 1-heptene and 1-octene to highly branched polyolefins

(Ferrocenylpyrazolyl)palladium complexes that catalyse the polymerization of 1-heptene and 1-octene to highly branched polyolefins are reported.