A low temperature hydrogen borrowing approach to generate secondary amines using benzimidazole-based N-heterocyclic carbene (BNHC) ruthenium complexes is reported. A series of the piano-stool complexes of the type [(η6 -p-cymene)(BNHC)RuCl2 ] (1a-g) were synthesized via one-pot reaction of the NHC salt precursor, Ag2 O, and [RuCl2 (p-cymene)]2 and characterized using conventional spectroscopic techniques. The geometry of two precursors, [(η6 -p-cymene)(Me4BnMe2 BNHCCH2OxMe)RuCl2 ] (1f) and [(η6 -p-cymene)(Me5BnMe2 BNHCCH2OxMe)RuCl2 ] (1g), was studied by single crystal X-ray diffraction. These catalysts were found to dehydrogenate alcohols efficiently at temperatures as low as 50 °C to allow Schiff-base condensation and subsequent imine hydrogenation to afford secondary amines. Notably, this ruthenium-based procedure enables the N-alkylation of aromatic and heteroaromatic primary amines with a wide range of primary alcohols in excellent yields of up to 98%. The present methodology is green and water is liberated as the sole byproduct.
Benzimidazol-2-ylidenes, ruthenium complexes, amine alkylation, C-N bond formation, mild conditions
NAWAZ, ZAHID; GÜRBÜZ, NEVİN; ZAFAR, MUHAMMED NAVEED; ÖZDEMİR, NAMIK; ÇETİNKAYA, BEKİR; and ÖZDEMİR, İSMAİL
"Benzimidazol-2-ylidene ruthenium complexes for C-N bond formation through alcohol dehydrogenation,"
Turkish Journal of Chemistry: Vol. 47:
5, Article 26.
Available at: https://journals.tubitak.gov.tr/chem/vol47/iss5/26