Synthesis and Study of Palladium(II) and Platinum(II) Complexes Supported by a Common "Wingtip" N-Heterocyclic Carbene

Abstract

Two annulated imidazolium salts, 2-(phenyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate 1 center dot H(PF6) and 1-methyl-2-(phenyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate 2 center dot H(PF6), were synthesized via formylative cyclization of the corresponding Schiff bases followed by anion metathesis with KPF6. Independently treating 1 center dot H(PF6) or 2 center dot H(PF6) with silver oxide and then palladium chloride in acetonitrile led to the formation of the complexes [Pd(1)(2)Cl(CH3CN)]PF6 (1a) and [Pd(2)(2)Cl(CH3CN)]PF6 (2a), respectively. Likewise, [Pt(1)(2)Cl(CH3CN)]PF6 (1b) and [Pt(2)(2)Cl(CH3CN)]PF6 (2b) were synthesized using similar transmetallation chemistry. The complexes were characterized using various spectroscopic techniques and the solid state structures of 1-H(PF6) as well as 2a were elucidated using X-ray diffraction analyses. A series of DFT calculations were also performed to gain further insight into the respective structures of the complexes. Complexes 1a and 2a were found to facilitate Suzuki coupling reactions under relatively mild conditions.