Copper(II) Complexes with Tridentate Bis(pyrazolylmethyl)pyridine Ligands: Synthesis, X‐ray Crystal Structures and ϵ‐Caprolactone Polymerization

Abstract

Reactions of Cu(ClO4)2⋅6H2O with 2,6‐bis(3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (dmpz‐py) (1), 2,6‐bis(4‐iodo‐3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (I‐dmpz‐py) (2) and 2,6‐bis(4‐nitro‐3,5‐dimethylpirazol‐1‐ylmethyl)pyridine (NO2‐dmpz‐py) (3) yield the corresponding metal complexes: [Cu(dmpz‐py)(H2O)(ClO4)]ClO4 (4), [Cu(I‐dmpz‐py)(H2O)](ClO4)2 (5) and [Cu(NO2‐dmpz‐py)(H2O)(ClO4)2] (6). The complexes were isolated in high yields as stable solids at room temperature and characterized by melting point, electrical conductivity, and infrared and ultraviolet/visible spectroscopy. In addition, the crystal structures of the new complexes were determined by single‐crystal X‐ray diffraction and showed square‐base pyramidal (4), distorted square‐planar (5) and octahedral (6) geometries. All three complexes were active in the ring opening polymerization of ϵ‐caprolactone under solvent‐free conditions, producing polycaprolactones of narrow polydispersity and high crystallinity. The results obtained show an important increase in polymerization speed compared with analogous azole‐derived copper (II) complexes.

Polymers of ε-Caprolactone Using New Copper(II) and Zinc(II) Complexes as Initiators: Synthesis, Characterization and X-Ray Crystal Structures

“…Therefore, these polymers could be applied or implemented in the design of biodegradable packaging [42]. In general, the PCLs obtained showed a lower dispersion, a higher molecular weight and high degrees of crystallinity compared with other polycaprolactones obtained using previously reported metal catalysts by the authors’ research group and PCLs that are commercially available [9,10,13,16,42].…”

“…CL (0.01 mol, 1.14 g) was added to glass-tube reactors under solvent-free conditions with magnetic stirring at 110 °C. The polymers were purified following a previously reported procedure from the literature and characterized by physico-chemical and spectroscopic methods [10,13]. Characterization of the PCL produced the following results: mp: 59–61.5 °C.…”

“…The PCL that was obtained exhibited a crystallinity up to 89% and a decomposition temperature above 470 °C [9]. Related Zn(II) and Cu(II) complexes have shown activity in ROP of CL at 110 °C, producing polymers with moderate molecular weights and molecular weight distributions [10,11].…”