Core-insertion of palladium in naphthalenediimides: Opto-electronic properties, structural insights and coupling studies

Abstract

Synthesis and isolation of palladium inserted functional π-scaffold is considered a major challenge due to its high instability and reactivity towards molecular oxygen. Herein, we report two σ-bonded compounds (1 and 2) between Naphthalenediimide (NDI) and palladium triphenylphosphine. Both these core-substituted NDI-palladium compounds have been characterized as NDI-{Pd(PPh3)2Br}2 having two Pd(PPh3)2 (1) and (C3H7)NH-NDI-Pd(PPh3)2Br having one Pd(PPh3)2 and n-propylamine as a donor moiety (2). Both the NDI-Pd compounds have been prepared by oxidative addition of Pd(0) triphenylphosphine with their respective core-brominated NDI having axially substituted n-hexyl groups. Interestingly, both these compounds showed remarkable stability towards column chromatography. Syntheses of 1 and 2 have been well characterised by different spectroscopic and analytical techniques. Cyclic voltammetry experiments were performed to understand the redox properties of the isolated NDI-Pd compounds. The structures of 1 and 2 have been crystallographically characterised. Solid state packing of both the compounds display strong intramolecular π-π stacking interactions between the electron-deficient NDI scaffold and the phenyl rings of the PPh3 unit(s). Moreover, both 1 and 2 exhibits interesting self-assembled architectures via intermolecular hydrogen and halogen bonding. Theoretical calculations were performed to evaluate frontier molecular orbitals and the intramolecular interactions. Furthermore, compound 1 was further utilized for the synthesis of Suzuki coupled bis-cyanophenyl compound in high yield.