Experimental and computational studies of Zn (II) complexes structured with Schiff base ligands as the efficient catalysts for chemical fixation of CO2 into cyclic carbonates

Chemical CO2 fixation by a heterogenised Zn(ii)-hydrazone complex

A new Zn(ii) coordination compound, [Zn(HL)(OAc)2] (1), with ONN-donor hydrazone ligand (HL = (E)-4-amino-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide) was synthesized and structurally characterized by using spectroscopic techniques and X-ray analysis. These analyses indicated that the Zn(ii) ion in the resulting coordination compound is five coordinated and the compound has a free amine functionality on the phenyl ring. Thus, [Zn(HL)(OAc)2] (1) was immobilized on the surface of propionylchloride functionalized silica gel through an amidification process via the reaction of the aniline part of compound 1 and the acyl chloride group of the support. The synthesized heterogeneous catalyst, Si-[Zn(HL)(OAc)2], was characterized by several analytical methods and the results confirmed the successful support of 1 on the surface of the support. Si-[Zn(HL)(OAc)2] was used in a chemical CO2 fixation reaction and styrene epoxide was used as a model substrate to investigate the catalytic performance of the supported Zn(ii) catalyst. Si-[Zn(HL)(OAc)2] can efficiently catalyze the formation of cyclic carbonate from the reaction of epoxide and CO2 in the presence of TBAB as a co-catalyst.

Chemical CO2 fixation using a cyanido bridged heterometallic Zn(II)-Mn(II) 2D coordination polymer

A new cyanido bridged Zn(II)-Mn(II) mixed-metal coordination polymer, {[Zn(μ-L)(μ-CN)2Mn0.5]·(CH3OH)}n (1), has been synthesized by the reaction of Zn(CN)2, Mn(II) salts and a hydrazone ligand (HL = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinohydrazide) in methanol. Compound 1 was characterized using various analytical methods (including elemental analysis, photoluminescence, FT-IR, XRD, SEM, and EDX analyses, and TGA), and its structure was determined by X-ray analysis. These analyses confirmed the formation of a mixed metal Zn(II)-Mn(II) coordination polymer containing both cyanide and hydrazone bridging ligands. This mixed metal coordination polymer exhibits interesting emission spectra by having several emissions via excitation at 230, 270, 375 and 385 nm. The catalytic activity of compound 1 in chemical CO2 fixation was investigated in the presence of epoxides, and the effects of various parameters on its catalytic performance were evaluated. The results of catalytic studies show that compound 1 can efficiently catalyze the chemical CO2 fixation reaction under mild conditions. The amount of co-catalyst, temperature of the reaction, nature of the solvent and also the substituent connected to the epoxide ring are some of the important parameters that have considerable effects on the catalytic activity of 1.

Synthesis, Crystal Structure, Hirschfeld Surface Analysis and Catalytic Activity of a New Binuclear Zn(II) Complex Based on Homophthalic Acid and 2,2'-Bipyridine Ligands

A new binuclear Zn(II) complex, [Zn2L2(BIPY)2(H2O)2](1) (H2L = homophthalic acid, BIPY = 2,2'-bipyridine) has been synthesized by one-pot method of homophthalic acid, 2,2'-bipyridine, zinc acetate dihydrate, and NaOH in water/ethanol (v:v = 1:1) solution. The structure of complex (1) was characterized by IR and X-ray single-crystal diffraction analysis. The results show that each Zn(II) ion is five-coordinated with two carboxylic O atoms from two homophthalate ligands (O2, O3 or O2a, O3a), two N atoms from two 2,2'-bipyridine ligands (N1, N2 or N1a, N2a) and one O atom from coordinated water molecule (O5 or O5a), and forms a distorted trigonal bipyramid coordination geometry. Complex (1) forms 1D chained structure and 3D network structure by the p-p interaction of 2,2'-bipyridine ligands. The Hirschfeld surface analysis of complex (1) was calculated. The catalytic performance of complex (1) has also been investigated for the oxidation of benzyl alcohol under O2 atmosphere. The optimal reaction temperature and pressure were 100 °C and 0.3 MPa for complex (1). Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Synthesis, Crystal Structure and Catalytic Activity of Tri-Nuclear Zn(II) Complex Based on 6-Phenylpyridine-2-carboxylic Acid and Bis(4-pyridyl)amine Ligands

A new trinuclear Zn (II) complex, [Zn3(L1)4(L2)2(CH3COO)2] (1) (HL1 = 6-phenylpyridine-2-carboxylic acid, L2 = bis(4-pyridyl)amine) has been synthesized by 6-phenylpyridine-2-carboxylic acid, NaOH, bis(4-pyridyl)amine and Zn(CH3COO)2•2H2O. The complex 1 has also been structural characterized by elemental analysis and single crystal X-ray diffraction. The results reveals that complex 1 is made up of three Zn(II) ions, four L1 ligands, two L2 ligands and two CH3COO- anions. In 1, both Zn1 ion and Zn1a ion are five-coordinated with two O atoms from two different L1 ligands, two N atoms from two different L1 ligands, and one N atoms from bis(4-pyridyl)amine ligand, respectively, and forms a distorted trigonal biyramid geometry. And Zn2 ion is four-coordinated with two O atoms from two different CH3COO− anions and two N atoms from two different L2 ligands, forming a distorted tetrahedral geometry. Complex 1 displays a 3D network structure by the intermolecular N−H···O hydrogen bonds. The catalytic performance for oxidation of benzyl alcohol with O2 was studied under mild reaction conditions using complex 1 as catalyst. The results demonstrated that the catalysts were very active, and the yield of benzaldehyde was 50.8% at 90 °C with THF as solvent under 0.5 MPa O2 within 3 h. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).