Palladium(II) and Platinum(II) Complexes of Disubstituted Imidazo[1,5-a]Pyridine and Imidazolylpyridine: Coordination Chemistry, Versatile Catalysis, Biophysical Study

Abstract

Some pincer type mono- and poly-nuclear Pd(II) and Pt(II) complexes bearing imidazo[1,5-a]pyridine and imidazolylpyridine moiety were synthesized and characterized by using several spectroscopic methods. Determination of molecular structures of all complexes by single crystal X-ray diffraction studies revealed a distorted square planar geometry around the bivalent palladium and platinum in all complexes. These Pd(II) complexes have been observed to display high catalytic activity in various reaction such as Suzuki-Miyaura cross-coupling reaction, transfer hydrogenation reaction, and alkyne homocoupling. The theoretical study was also well matched with experimental data of all catalysts. Substantial deviations in the catalytic activity were observed by changing the co-ligand, binding mode of the ligand and the number of metal centre. Under optimal conditions, Suzuki cross-coupling and the transfer hydrogenation reaction were accomplished proficiently with wide functional group possibility by taking only 0.1 mol% of tetranuclear Pd(II) complex (5) as catalyst. Intermediates in Suzuki coupling reaction were also detected by using mass spectroscopy. Among all studied complexes, the tetra nuclear palladium complex exhibited high catalytic activity. Further Pd(II) complexes were tested in a model reaction of homocoupling of phenylacetylene and produce diphenylbutadiyne in excellent yield. Also, interaction study of all the complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were investigated using electronic spectroscopy Absorption study showed minor groove binding of DNA with these complexes while intercalative binding was observed by all complexes through displacement of ethidium bromide (EB) in EB-DNA by quenching of fluorescence intensity. The complexes were also displayed high binding affinity toward BSA confirmed by emission, synchronous fluorescence, and steady state fluorescence anisotropy measurement. Moreover, the pharmacokinetic properties of two bioactive compounds (3s and 3t) obtained from Suzuki coupling reaction were calculated and to evaluate their activity as leukotriene A4 hydrolase (LTA4H) inhibitor, these molecules were docked with human LTA4H enzyme.