Ruthenium(II)-Complex-Catalyzed Acceptorless Double Dehydrogenation of Primary Amines to Nitriles

Abstract

Acceptorless dehydrogenative oxidation of primary amines into nitriles using an in situ complex derived from commercially available dichloro(1,5-cyclooctadiene) ruthenium(II) complex and simple hexamethylenetetramine has been demonstrated. The synthetic protocol is highly selective and yields the nitrile compounds in moderate to excellent yields and produces hydrogen as the sole byproduct.

Key words

ruthenium - amine - nitrile - dehydrogenation

• References and Notes

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• 11 General Procedure for the Dehydrogenation of Amine Ruthenium(II) chloride 1,5-cyclooctadiene 1 (3 mol%), HMTA (2, 3 mol%), amine 3 (0.25 mL), and dry toluene (1.0 mL) were placed in a Schlenk tube. The reaction mixture was stirred under open conditions to nitrogen and refluxed for 24 h. After completion of the reaction all toluene were evaporated under vacuo, the oxidized products 4 were isolated from crude mixture with the help of column chromatography using hexane/EtOAc as eluent. The formation of products was confirmed by comparing the ¹H NMR data with literature reports.
• 12 General Procedure for the Dehydrogenation of Benzylamine 3 in the Presence of Cyclohexene In a 50 mL closed-vessel reactor, ruthenium(II) chloride 1,5-cyclooctadiene 1 (0.004 g, 0.013 mmol), HMTA (2, 0.002 g, 0.013 mmol), amine 3 (0.05 mL, 0.5mmol), cyclohexene (0.4 mL, 5 mmol), and dry toluene (0.6 mL) were taken. The resulting mixture was heated at 110 °C for 24 h. After completion of the reaction, the solution was cooled to room temperature and extracted with CH₂Cl₂ then analyzed through gas chromatography; yield of benzonitrile 4 49% and cyclohexane 24%.
• 13 General Procedure for in situ ¹H NMR Study to Show Formation of Imine Intermediate In N₂ atmosphere benzylamine 3 (0.05 mL, 0.46 mol), ruthenium(II) chloride 1,5-cyclooctadiene (1, 0.004 g, 3 mol%) HMTA (2, 0.002 g, 3 mol%), and toluene-d ₈ as a solvent (0.4 mL) were taken in the NMR tube. The reaction mixture was heated at 110 °C for 12 h, and then the reaction mixture was cooled to room temperature before collecting the NMR data.