Abstract
A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.
Highlights
Palladium compounds are known as the most attractive catalysts for many important organic transformations.[1,2,3,4,5,6,7]. As these reactions involve organometallic intermediates in different oxidation states, the catalytic cycles can be elucidated by electrochemical methods
The purpose of this paper is to reveal structure-electrochemical properties correlation for cyclometalated palladium(II) complexes
In this work a combination of electrochemical techniques, ESR spectroscopy and quantum chemical calculations in the study of a series of cyclometalated Pd(II) complexes was used to reveal the dependence of their electrochemical properties on their structures
Summary
Palladium compounds are known as the most attractive catalysts for many important organic transformations.[1,2,3,4,5,6,7] As these reactions involve organometallic intermediates in different oxidation states (which are generally redox active), the catalytic cycles can be elucidated by electrochemical methods. To date this strategy was successfully used to study Pd(II)/Pd(0) crosscouplings.[3] Contrariwise, electrochemical data for Pd(II)/Pd(III) and Pd(II)/Pd(IV) redox couples and for reactions based on these shuttles is extremely poor. Cyclometalated palladium(II), (III), (IV) complexes are proposed to be key intermediates in oxidative ligand-directed aromatic C–H functionalizations.[4,5] this approach is adapted to introduce diverse functional groups into aromatic substrates in C(sp2)–H halogenation, acetoxylation, arylation and some other reactions,[6,7] examples of effective formation of carbon–phosphorus and carbon–fluoroalkyl bonds are still rare[8,9,10] compounds with these structure units are important and relevant as pharmaceuticals.[11,12,13,14]
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