Gold(I) and gold(III) complexes supported by a pyrazine / pyrimidine wingtip N-heterocyclic carbene: Synthesis, structure and DFT studies

Starting from pyrazine and pyrimidine functionalized N-heterocyclic carbene (NHC) proligand 1-(2-Pyrazinyl)-3(methyl) imidazolium chloride (1.HCl), 1-(2-Pyrimidyl)-3(methyl) imidazolium chloride (2.HCl), four novel gold complexes [Au(1)Cl], (1a); [Au(1)Cl₃], (1b), [Au(2)Cl], (2a) and [Au(2)Cl₃] (2b) were synthesized and characterized using NMR spectroscopic techniques and elemental analysis. Additionally, the solid state structures of 1a & 2b were elucidated using single crystal X-ray diffraction analysis, which revealed that in 1a, the carbene nucleus and the chloride ion bound to Au(I) nearly linear having C-Au-Cl bond angle 178.84°. Where as in 2b, the carbene nucleus and the chloride ion bound to the Au(III) adopts the square planar geometry surrounding Au(III). A series of DFT calculations were also performed to gain further insight into the respective structures of the complexes to relate the crystallographic parameters and electronic distribution.