Unsymmetrical Imidazopyrimidine-based Bimetallic Ligand and Complexes

With bimetallic catalysts becoming increasingly important, the development of electronically and structurally diverse binucleating ligands is desired. This work describes the synthesis of unsymmetric ligand 2,7-di(pyridin-2-yl)imidazo[1,2-a]pyrimi-dine (dpip) that is achieved in four steps on a multi-gram scale in an overall 54% yield. The ability of dpip to act as a scaffold for the formation of bimetallic complexes is demonstrated with the one-step syntheses of the dicopper complex Cu2(dpip)(µ-OH)(CF3COO)3 (4), the dipalladium complex [Pd2(dpip)(µ-OH)(CF3COO)2][(CF3COO)2H] (5), and the dinickel complex [{Ni2(dpip)(µ-Cl)Cl2(MeOH)3}2][2Cl] (6) in good yields (79-92%). All bimetallic complexes were characterized by spectroscopic methods and x-ray crystallography which revealed metal-metal distances between 3.4821(9)−4.106(2) Å. Additionally, quantum-chemical calculations were conducted on complex 4 and an analogous 1,8-naphthyridine-based dicopper complex to investigate the differences between the imidazopyrimidine motif reported here and the widely used 1,8-naphthyridine motif. Natural bonding orbital (NBO) and Mayer Bond order (MBO) analyses validated the ability of dpip to coordinate metals more strongly. Finally, NBO cal-culations quantified the differences in the binding energy between the two pockets of the unsymmetrical dpip ligand.