Cleavage of carbon–nitrogen bond in 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane by copper(I) bromide

• Cleavage of C–N bond in 1,3,5-triazacyclohexanes by copper halides are studied.
• Copper(I) bromide cleaves the C–N bond in 1,3,5-triazacyclohexanes in any solvent.
• Copper(II) bromide and copper(I) chloride forms the amidinium cation.
• Solution stability of the copper amidinium complexes is studied.

Reactions of CuCl, CuCl2 and CuBr2 with 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane (tBu3tach) resulted in the formation of [(tBu3tach-H)+(CuCl2)] (1), [(tBu3tach)(CuCl2)] (2) and [(tBu3tach-H)+(CuBr2)] (3) respectively. Interestingly, CuBr was found to mediate the cleavage of the C–N bonds of tBu3tach in a vast range of solvents, namely, chloroform, dichloromethane, tetrahydrofuran, acetonitrile and methanol to yield [Cu4Br4(tBuNCH2)4] (4) and stands as an example of C–N bond cleavage of 1,3,5-triazacyclohexane rings by copper salts. Compounds 1 and 3 contains amidinium cations and are unstable in solution towards the release of copper. The release of copper from 3 in solution was confirmed by the isolation of the compound, [CuBr(MeCN)] (5). Formation of the amidinium cations [(tBu3tach-H)+] in 1 and 3 may be avoided by the use of PPh3 to yield [(tBu3tach)Cu(PPh3)](PF6) (6), while the coordinated N-tert-butylmethanimine (tBuNCH2) in 4 could be replaced by PPh3 to yield [Cu4Br4(PPh3)4] (7). Complexes 1–7 are characterized by a combination of single crystal X-ray structure determination and/or elemental analysis, NMR, IR, and UV–Vis spectroscopy, and Mass spectrometry.

CuIBr has been shown to mediate the cleavage of the C–N bonds in 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane (tBu3tach) to yield [CuI4Br4(tBuNCH2)], while CuIIBr2, CuICl and CuIICl2 yielded [(tBu3tach-H+)(CuIBr2)], [(tBu3tach-H+)(CuICl2)] and [(tBu3tach)(CuIICl2)] respectively. A systematic comparative study of such C–N bond cleavage is presented.Figure optionsDownload as PowerPoint slide