Revisiting Isomerism in Square Planar Palladium NHC\nComplexes with NacAc Chelators

Quantifying the donor ability of\nbidentate ligands in inorganic\nchemistry is not straightforward, and the Huynh electronic parameter\nfor chelators (HEP2) presents a rare solution to the task. Aiming\nto extend the ligand scope in this work, the soundness and practicality\nof HEP2 was further scrutinized with seven stereoelectronically diverse\nβ-ketiminato (“NacAc”) chelators using palladium\ncomplexes of the type [PdBr(<sup><i>i</i></sup>Pr<sub>2</sub>-bimy)(<sup>Ar</sup>NacAc)] (<sup><i>i</i></sup>Pr<sub>2</sub>-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene). Notably,\nthe unsymmetrical nature of this κ<sup>2</sup>-<i>N</i>,<i>O</i> ligand family allowed for an intriguing exploration\ninto isomerism in the square planar Pd<sup>II</sup> products, which\ndepends on the <i>N</i>-aryl <i>ortho</i>- and <i>para</i>-substituents based on experimental and theoretical\nfindings. The HEP2 values of both isomeric forms correlate well with\nthe widely used σ<sub>p</sub> Hammett constants, which reinforces\nthe reliability of this modern methodology.