Group 4 Metallocene Mediated Homo- and Heterocoupling of Heteroaromatic Nitriles

Abstract

Coupling of different heterocyclic nitriles at group 4 metallocenes was investigated. The product of 2,6-dicyanopyridine coupling at [Cp*2Ti] (1Ti) reacts with [Cp*2Zr(η2-Me3SiC2SiMe3)] to yield the novel trinuclear TiZr2 complex 2, which further reacts with smaller heteroaromatic nitriles 2-cyanofuran and 2-cyanothiophene to form the homocoupling products 3Zr and 4Zr. Similar products were formed in the direct coupling of these nitriles at [Cp*2M] (M = Ti, Zr). Mixed 1-metalla-2,5-diazacyclopenta-2,4-dienes 5Ti and 5Zr can be accessed by using mixtures of both nitriles, or in the case of 5Zr by stepwise addition of different nitriles to [Cp*2Zr(η2-Me3SiC2SiMe3)]. Metallacycle transfer using titanocene complexes 3Ti and 4Ti and SOCl2 yields the corresponding thiadiazole oxides 3SO and 4SO, as well as the mixed thiadiazole oxide 5SO, which were isolated and fully characterized. DFT calculations were done to further look into the process of nitrile exchange at metallocene.