N,S-Heterocyclic Carbene Containing Benzothiazol-2 and Pd (II) New Complexes Functionalized with Butyl Linked Carbazole Moiety: Synthesis, Characterization and Their Catalytic Efficiency and Electropolymerizations

Abstract

In contrast to the large number of polymeric N-heterocyclic carbenes (NHCs) there are relatively few examples of NHCs-containing conductive polymers. However, conducting polymers (CPs) could be excellent hosts for NHC compounds, as they can easily form polymer films electrochemically, and their optical & electrical properties can be easily tuned by electrochemically or changing bonding groups in their structure. In this work, the N,S-heterocyclic carbene (NHC) ligand precursor, N-(4-butylcarbazole)benzothiazolium bromide (1) was prepared by solvent-free alkylation of benzothiazole by 9-(4-bromobutyl)carbazole with high efficiency. The air- and moisture-stable new piano-stool Ru(II)-N,S-NHC (2) and PEPPSI type Pd(II)-N,S-NHC (3) complexes, were synthesized and characterized by H-1- and C-13 NMR, FT-IR, UV-vis and ESI-MS spectroscopic methods and elemental analysis. Further confirmations of structural details for benzothiazolium salt (1) and its Ru(II)-N,S-NHC complex (2) were determined by X-ray single-crystal diffraction. The catalytic performance of the complexes (2 and 3) in transfer hydrogenation (TH) of acetophenone and Suzuki-Miyaura cross-coupling reactions of aryl bromides were also investigated, respectively. All compounds (1-3) were electrochemically polymerized and conducting polymer films with pendant carbene complex moieties were obtained. The electrical and optical properties of the resulting polymers were characterized via spectroelectrochemical studies.