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⋅H(PF6) and 1‐methyl‐2‐(phenyl)imidazo[1,5‐a]pyridin‐4‐ylium hexafluorophosphate 2⋅H(PF6), were synthesized via formylative cyclization of the corresponding Schiff bases followed by anion metathesis with KPF6. Independently treating 1⋅H(PF6) or 2⋅H(PF6) with silver oxide and then palladium chloride in acetonitrile led to the formation of the complexes [Pd(1)2Cl(CH3CN)]PF6 (1 a) and [Pd(2)2Cl(CH3CN)]PF6 (2 a), respectively. Likewise, [Pt(1)2Cl(CH3CN)]PF6 (1 b) and [Pt(2)2Cl(CH3CN)]PF6 (2 b) 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 2 a 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 1 a and 2 a were found to facilitate Suzuki coupling reactions under relatively mild conditions.