The suitability and accuracy of the Huynh electronic parameter (HEP) was further tested to reveal remote substituent effects in pyridines, which are located five or six bonds away from the reporter probe. These values show an excellent correlation to Hammett σ‐constants of the respective substituents with coefficients of R2=0.9856 (σm) and R2=0.9857 (σp). Based on this observation, a methodology for the re‐evaluation of certain Hammett constants with larger uncertainties has been proposed and demonstrated. Moreover, the scope of HEP was extended to various neutral pnictogen and chalcogen donors during which “transphobia effects” were revealed for mixed NHC complexes containing phosphites, arsine and stibine for the first time.
A library of 12 palladium(II) complexes of the type [PdBr( i Pr 2 -bimy)(L∧X)] comprising 10 dithiocarbamato (R 2 NCS 2 − ) and two xanthato (ROCS 2 − ) ligands have been prepared and fully characterized. With these complexes in hand, the electronic and steric properties of the bidentate, monoanionic ligands were evaluated using the HEP2 and %V bur methodologies. Moreover, the construction of the first stereoelectronic map for dithiocarbamates enabled the in-principle identification of optimal ligand parameters for enhanced cytotoxic activities of their gold(III) complexes. This application of the stereoelectronic map showcases its viability as a useful tool to establish structure−activity relationships for rational ligand design.
14 mono-, di-, and tetranuclear palladium complexes were prepared to study the coordination chemistry of symmetrical and unsymmetrical azole-derived diimines and their anions. The diverse range of complexes obtained highlights the structural and electronic diversities imposed by these ligands. Using the monopalladium species, the electronic properties of selected bidentate ligands were determined, ranked, and compared by 13 C NMR spectroscopy, extending the scope of the HEP2 (Huynh electronic parameter 2) scale, which can detect even subtle differences. Moreover, the %V bur (percentage volume buried) values as an estimate for the steric bulk of some ligands were determined using the solid-state molecular structures of their complexes, and a preliminary stereoelectronic map was established.
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