Abstract: Structure of the product of imidazolidine (1,3,5,7-tetra-tert-butyloctahydro-1H,4аH-imidazo[4ʹ,5ʹ:5,6]dioxino[2,3-d]imidazole) ether cocrytallization with 1,3-di-tert-butylimidazol-2-one and 1,3-di-tert-butylimidazolin-2-ylidene was established by single crystal X-ray diffraction. The co-crystal is the product of the oxidation-hydrolysis of the 1,3-di-tert-butylimidazolin-2-ylidene complex with AlH₃.