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

Reactions of Cu(ClO 4 ) 2 ⋅6H 2 O 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 (NO 2 ‐dmpz‐py) ( 3 ) yield the corresponding metal complexes: [Cu(dmpz‐py)(H 2 O)(ClO 4 )]ClO 4 ( 4 ), [Cu(I‐dmpz‐py)(H 2 O)](ClO 4 ) 2 ( 5 ) and [Cu(NO 2 ‐dmpz‐py)(H 2 O)(ClO 4 ) 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.