Zinc Complexes with Cyanoxime: Structural, Spectroscopic, and Catalysis Studies in the Pivaloylcyanoxime-Zn System

Abstract

Reaction of 2-hydroxyimino-4,4-dimethyl-3-oxo-pentanenitrile (common abbreviation HPiCO, pivaloyl-cyanoxime) with zinc sulfate in an aqueous solution results in the formation of the two new complexes: [Zn(PiCO){H(PiCO)2}(H2O)] (I) and tetranuclear Zn complex [Zn4(μ3-OH)2(PiCO)6 (H2O)4] (II). Both complexes were characterized by elemental analysis, IR- and UV-visible spectra, DSC/TGA studies, and X-ray analysis. In complex II, the PiCO- cyanoxime anion adopts three bidentate binding modes: O-monodentate, chelating (κ2), and bridging (2) coordinations. Also, the ligand represents the mixture of two diasteromers (cis-anti and cis-syn) that form five- and six-membered chelate rings with Zn atoms and cocrystallize in one unit cell at population of 0.57-0.43. There are two crystallographically different Zn-centers in the ASU, and two μ3-bridging hydroxo-groups arrange via inversion center the formation of an elegant tetranuclear complex. Each Zn atom has a molecule of coordinated water and is in the distorted octahedral environment. Because of the structural flexibility and multidentate propensity of the pivaloyl-cyanoxime, complex II may act as a structural model of naturally occurring Zn-containing enzymes. Indeed, compound I exhibits an efficient catalytic performance for transesterification reaction of various esters in ethanol under mild reaction conditions. Therefore, obtained results allow assignment of observed activity as green catalysis.

Department(s)

Chemistry and Biochemistry

Document Type

Article

DOI

https://doi.org/10.1021/acs.inorgchem.7b01891

Publication Date

11-20-2017

Journal Title

Inorganic Chemistry

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