Flash Communication: Synthesis and Isolation of Neutral Pyridine Bis(carbene) Calcium Complexes

A series of 2,6-bis(3-mesitylimidazol-2-ylidene)pyridine (MesCNC) calcium dihalide (X = Cl, Br) complexes have been synthesized by direct treatment of the corresponding imidazolium salt precursor with calcium bis(trimethylsilyl(amide)) (Ca[N(SiMe3)2]2(thf)2), in contrast to previously reported methods. Structural evaluation showed that generating the analogous ligand with substitutions at the 3- and 5-positions of the central pyridine moiety resulted in the 3,5-dimethyl-2,6-bis(3-mesitylimidazol-2-ylidene)pyridine (3,5-Me2-MesCNC)CaI2 complex, which shows puckering of the ligand that has not been observed previously. Attempts to characterize these complexes by solution-state NMR spectroscopy have been previously elusive; herein, we report full characterization of a suite of pyridinebis(carbene) calcium complexes along with single crystal X-ray diffraction studies.