Regulation of the Rate of Dinucleation of a Monocopper(I) Complex Containing Bipyrimidine Rotary Units by Restricted Double Pyrimidine Rotation

New copper(I) complexes with coordinated 2-(4′-methyl)pyrimidinyl moieties were fabricated, and the isomerism of their pyrimidine ring linkage was investigated. The ligands bis[2-(diphenylphosphino)phenyl] ether (DPEPhos) and 4,4′-dimethyl-2,2′-bipyrimidine (dmbpm) were used to synthesize a heteroleptic copper(I) complex, [CuI(DPEPhos)(dmbpm)]·BF4 (1·BF4), and a dinuclear copper(I) complex, [(CuI)2(DPEPhos)2(μ-dmbmp)](BF4)2 [2·(BF4)2]. The X-ray crystallographic structures, UV–vis absorption spectra, and luminescence properties of the complexes were analyzed. The thermodynamic and kinetic aspects of the isomerism of 1·BF4 were examined by variable-temperature NMR. Double pyrimidine ring rotation was found to be restricted sterically by the bulky DPEPhos ligands. This limited the number of the possible isomers: 1·BF4 showed only isomers with either one (io isomer) or both (oo isomer) of the two methyl groups positioned away from the copper center, while dinuclear 2·(BF4)2 was only found as a symmetric (io–...