Synthesis, structure and characterisation of amido derivatives of [9]aneN3(1,4,7-triazacyclononane)

Abstract

The amido species OHC[9]aneN₃(1-formyl-1,4,7-triazacyclononane), [OHC[9]aneN₃H]BPh₄, (OHC)₃[9]aneN₃(1,4,7-triformyl-1,4,7-triazacyclononane) and (PhOC)₃[9]aneN₃(1,4,7-tribenzoyl-1,4,7-triazacyclononane) have been synthesised, characterised and their crystal structures determined. The conformations of these compounds are discussed in terms of their solid-state structures and of their ¹H and ¹³C NMR spectra in solution. Symmetric isomers derived from hindered rotation about the N–C (amide) bond are generally preferred to asymmetric ones, with the N–C(O)R (R = H or Ph) forming a planar unit exo to the triazamacrocycle. Complexation of Pd^II with OHC[9]aneN₃ confirms the bidentate binding of this ligand and affords [Pd(OHC[9]aneN₃)₂][B(C₆F₅)₄]₂·2H₂O, the single-crystal structure of which shows the Pd atom at an inversion centre with Pd–N 2.057(13) and 2.065(10)Å. The amide functions lie above and below the square-planar metal centre with Pd ⋯ N (amide) 3.021(12)Å. The retention of planarity within the amide function upon complexation [torsion angle for C(2)–N(1)–C(10)–O(11)–6(2)°] suggests that there is no interaction between the amide group and the metal centre.