We herein present four new ruthenium(II) mesoinic carbene complexes that show high activities as homogeneous catalysts towards the N-alkylation of nitroarenes to the respective secondary amines. We incorporate chelating triazolylidenes as strong donating ligands. The complexes were synthesised from the corresponding 1,2,3-triazolium salts via a transmetallation route as has previously been established in our group. For comparative reasons, both the 1,4- as well as the 1,5-regioisomer (of the starting triazoles) of pyridyl- and bicarbene ligands are utilized to investigate the influence on the catalytic activity. The complexes were then tested in the reductive N-alkylation of nitrobenzene with benzyl alcohol according to the “borrowing hydrogen” concept. Optimization of the reaction conditions revealed potassium tert-amylate as base to be crucial for a fast and clean conversion towards the secondary amine. Under our optimized reaction conditions, excellent conversions and selectivities were achieved for the test substrate. A selected scope of substrates was chosen to demonstrate the compatibility of fuctional groups both on the nitroarene as well as for the primary alcohol. We therefore want to introduce this new catalytic system as one of the most effective systems for this reaction until today.

1,5-Regioisomer of the click reaction: Valuable ligand precursors for new Ru-MIC complexes

253rd National Meeting (2017)

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