Deciphering the Influence of Alkylene Bridged and Chelating Mode on Pd—C and Pd—X (X = Cl, Br, and I) Bonding Interaction Within Bis-(NHC)-Palladium Complexes Using Quantum Chemistry Tools

Abstract

In this paper, we have explored the influence of alkylene-bridged length and coordination mode on the reactivity of a series of 24 alkylene-bridged palladium complexes using computational tools (B3PW91/LANL2DZ//6-31G(d) level) in gas phase and DMSO. These palladium complexes prefer a boat and chair configuration for methylene and ethylene bridge length, respectively. In addition, phenyl and nitro complexes present a higher activation for Pd—C bonds while the most stable Pd⋯C interactions are observed for abnormal mode with methylene bridge. According to the energy decomposition analysis (EDA), hydrogen and phenyl complexes in both chelation modes present a better electrostatic character. Moreover, Pd⋯C interactions are stronger compared to the Pd⋯X ones for ethylene-bridged abnormal complexes (in gas phase). Finally, the donation/back-donation ratio (d/b) values reveal the Fischer carbene character of these [bis(NHC)]⋯[PdX₂] interactions. Concerning the hybridization around the metal cation for the Pd—C bond, the sp²d type is observed for methylene-bridged palladium complexes while the sp³ one is observed for ethylene bridge complexes.