Oxo- and imido-alkoxide vanadium complexes as precatalysts for the guanylation of aromatic amines

Abstract

Vanadium oxo-alkoxide complexes [V(O)(Cl)_3−x(OR)_x] (x = 1, R = Me (1), Et (2), n-Pr (3); x = 2, R = Me (4), Et (5), n-Pr (6)) were obtained by a clean reaction between [V(O)Cl₃] and different excesses of ROSiMe₃ silicon ethers. Imido complexes [V(NAr)(Cl)_3−x(OR)_x]₂ (Ar = 2,6-i-Pr₂C₆H₃; x = 1, R = Me (7), Et (8), n-Pr (9); x = 2, R = Me (10), Et (11), n-Pr (12)) were prepared in excellent yields by reaction of the oxo-alkoxide precursors and ArNCO. X-Ray crystal structure determinations for 7, 8 and 12 revealed dimeric structures with alkoxide bridges. Complexes 7–12 are precursor of highly active guanylation catalysts. The study of the catalytic reaction allow us to propose the non-participation of the imido moiety. This was confirmed when complexes 1–6 gave better catalysts under the same conditions. The simple and commercial [V(O)Cl₃] (16) can be proposed as the most effective catalyst in this series of vanadium complexes.