Revisiting Isomerism in Square Planar Palladium NHC Complexes with NacAc Chelators

Quantifying the donor ability of bidentate ligands in inorganic chemistry is not straightforward, and the Huynh electronic parameter for chelators (HEP2) presents a rare solution to the task. Aiming to extend the ligand scope in this work, the soundness and practicality of HEP2 was further scrutinized with seven stereoelectronically diverse β-ketiminato ("NacAc") chelators using palladium complexes of the type [PdBr(^<i>i</i>Pr₂-bimy)(^ArNacAc)] (^<i>i</i>Pr₂-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene). Notably, the unsymmetrical nature of this κ²-<i>N</i>,<i>O</i> ligand family allowed for an intriguing exploration into isomerism in the square planar Pd^II products, which depends on the <i>N</i>-aryl <i>ortho</i>- and <i>para</i>-substituents based on experimental and theoretical findings. The HEP2 values of both isomeric forms correlate well with the widely used σ_p Hammett constants, which reinforces the reliability of this modern methodology.