Synthesis of ureas from titanium imido complexes using CO2 as a C-1 reagent at ambient temperature and pressure

Abstract

The coordinatively unsaturated 12-electron complex dichloro t-butylimido bispyridine titanium(IV) (2a) has been shown to react with CO₂ to give N,N-bis-t-butyl urea. Two analogous sterically hindered coordinatively saturated 14-electron complexes dichloro t-butylimido trispyridine titanium(IV) (10a) and dichloro 2,6-(i-Pr)₂phenylimido trispyridine titanium(IV) (10b) also gave their corresponding symmetrical ureas upon treatment with CO₂. Further experiments support the intermediary of metallocycles formed from heterocumulene metathesis reactions. The unsymmetrical ureaN-benzyl, N-t-butyl urea (11) was produced from treatment of 2,6-(i-Pr)₂phenylimido trispyridine titanium(IV) (10b) with CO₂ and interception with BnNH₂. Equimolar quantities of N,N-bistrimethylsilybenzylamine or N,N-bistrimethylsilyphenethylamine were shown to promote the reaction between t-butylimido bispyridine titanium(IV) (2a) and CO₂ to give near quantitative yields of symmetrical urea. Other symmetrical ureas could be produced from TiCl₄, amine and CO₂ in moderate to quantitative yields depending on the stoichiometry of amine present.