Siah, P. S.; Xie, X. K.; Gnanaprakasam, B.; Dang, T. T.; Ramalingam, B.; Huynh, H. V.; Seayad, A. M., Benzimidazolin-2-ylidene N-heterocyclic carbene complexes of ruthenium as a simple catalyst for the N-alkylation of amines using alcohols and diols. RSC Advances 2015, 5 (6), 4434-4442.
Abstract:
Simple air and moisture stable ruthenium complexes 1–3 and 3a were synthesized from readily available benzannulated N-heterocyclic carbene ligands (bimy = benzimidazolin-2-ylidene). These complexes were found to be efficient catalysts for the alkylation of amines using alcohols as alkylating agents. Catalysts 1, 2 and 3a gave excellent yields of up to 99% for the alkylation of various amines using benzylic and aliphatic alcohols at 130 °C for 18 h under solventless conditions. Catalyst 3a bearing both phosphine and carbene ligands gave excellent yields of up to 98% for the synthesis of heterocyclic amines by double alkylation of primary amines using linear diols. The practical utility of these catalysts was demonstrated for the synthesis of pharmaceutically important amines in a more environmentally benign way under solventless conditions.
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Funding Info:
This work was funded by “GSK-EDB Singapore Partnership for Green and Sustainable manufacturing and the Institute of Chemical and Engineering Sciences (ICES), Agency for Science, Technology and Research (A*STAR), Singapore and National University of Singapore (NUS, WBS R143-000-513-592).