Tracking the Progress and Mechanism Study of a Solvothermal in Situ Domino N-Alkylation Reaction of Triethylamine and Ammonia Assisted by Ferrous Sulfate.

Atom economic in situ domino N-alkylation reactions of triethylamine/ammonia with 2-(hydroxymethyl)quinolin-8-ol (HL-OH) assisted by FeSO·7HO were realized under mild solvothermal conditions at 120 °C in acetonitrile. The resulting tripodal 2,2',2″-[nitrilotris(methylene)]tris(quinolin-8-ol) (HL-N) forms a linear trimer [Fe(L-N)] (1). Electrospray ionization mass spectrometry of the reaction solution provides evidence for the intermediates of three steps, while crystallography and X-ray photoelectron spectroscopy characterize the trimer. Shortening the time of the reaction allowed for the organic intermediates to be isolated, which led to a proposed mechanism. The method provides a facile way to produce symmetric tertiary amine from widely used NEt and NH. The results represent an example of the in situ Fe-catalyzed domino reaction in which Fe is coordinated by the generated ligands and is involved in each step until the final cluster 1.