Regiocontrolled one-step synthesis of 3,3 '-disubstituted 2,2 '-bipyridineligands by cobalt(I)-catalyzed cyclotrimerization

A one-step, regioselective synthesis of annelated symmetric and asymmetric 3,3'-disubstituted 2,2'-bipyridines by cobalt(I)-catalyzed [2+2+2] cycloadd itions between 5-hexynenitrile and 1,3-divnes is described. In the symmetri c case, the total regioselectivity of the first cycloaddition is ensured el ectronically by the conjugation of the triple bonds, and for aminomethylate d diynes that of the second is ensured by the cobalt coordinating to the am ino-methyl rather than to the hexynenitrile nitrogen. In the asymmetric cas e, the first cycloaddition took place chemoselectively, which in the case o f bis(trimethylsilyl)-1,3,5-hexatriyne (viewed as a 1,3-diyne) is explained by semiempirical calculation of LUMO coefficients. The copper(I) complex o f 6b, constituting the first reported complex of the form ML, (L is a symme tric 3,3'-disubstituted 2,2'-bipyii dine), has been prepared. It had UV/Vis and NMR spectra reflecting the 3-substituent-induced mutual torsion of the bipyridine rings in the cis conformation, as was confirmed by x-ray diffra ctometric determination. The bipyridine 6c forms the dinuclear complex [Cu- 2(6c)(2)(CH3CN)(2)](2+) in the solid state.