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Zinc Complexes with Tridentate Pyridyl‐Pyrrole Ligands and their Use as Catalysts in CO 2 Fixation into Cyclic Carbonates
Author(s) -
Chen JingJing,
Xu YaoChun,
Gan ZhiLiang,
Peng Xiao,
Yi XiaoYi
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201801246
Subject(s) - chemistry , pyridine , zinc , ligand (biochemistry) , pyrrole , catalysis , octahedron , toluene , medicinal chemistry , crystallography , polymer chemistry , inorganic chemistry , crystal structure , organic chemistry , biochemistry , receptor
Pyridyl‐pyrrole ligands usually mimic the polypyridine ligand, and their metal complexes are interesting due to their rich coordination chemistry and their use in molecular devices, biological therapeutics, and catalytic transformations. C s ‐symmetric H L 3 ligand Br‐substituted on one of the pyridyl rings was designed and synthesized by Paal–Knorr pyrrole condensation. Ligand H L 4 was synthesized by Suzuki‐coupling reaction between H L 3 and 2‐thiopheneboronic acid in the presence of K 2 CO 3 and Pd(PPh 3 ) 4 in degassed THF/H 2 O solution. Zinc complexes 1 – 5 with H L 1 to H L 5 were prepared by treatment of the corresponding pyridyl‐pyrrole ligands with diethylzinc in toluene at 0 °C in high yield. Ligand H L 3 and all zinc complexes are characterized by X‐ray diffraction analysis. The structure of free H L 3 is planar. The geometries at Zn in 1 , 2 , and 5 are compressed octahedra, while in 3 and 4 they are perhaps best described as being between cis ‐divacant octahedral and distorted tetrahedral. In these zinc complexes, shorter Zn–N pyrrole [1.878(5)‐1.950(4) Å] and longer Zn–N pyridine [2.108(5)‐2.509(3) Å], Zn‐N pendant pyridine [2.802(2)‐3.039(3) Å] bond lengths are observed. Complexes 2 and 3 were used as catalysts to promote the coupling reaction of CO 2 and various epoxides under solvent‐free conditions, and the catalytic mechanism was investigated by 1 H NMR spectroscopy.