Methanolysis of nitrile-functionalised pendant arm derivatives of 1,4,7-triazacyclononane upon coordination to CuII

Abstract

The three ligands 1,4,7-tris(cyanomethyl)-1,4,7-triazacyclononane (L¹), 1,4,7-tris(2-cyanoethyl)-1,4,7-triazacyclononane (L²) and 1,4-bis(2-cyanoethyl)-7-methyl-1,4,7-triazacyclononane (L³) have been treated with Cu(BF₄)₂·4H₂O in refluxing MeOH to afford complexes [Cu(1)](BF₄)₂, [Cu(2)](BF₄)₂·H₂O and [Cu(3)](BF₄)₂, respectively, where 1, 2 and 3 have two nitrile groups of each starting L¹, L² and L³ ligand transformed into imino-ether groups via nucleophilic attack of MeOH at the the CN triple bond. [Cu(1)](BF₄)₂ and [Cu(2)](BF₄)₂ have been structurally characterised and show distorted square-based pyramidal coordination at Cu^II with the N-donors from the imino-ether groups occupying two basal positions. Interestingly, one nitrile group does not undergo methanolysis and remains unbound to the metal centre in [Cu(1)]²⁺ and [Cu(2)]²⁺. L² and L³ have also been treated with CuCl₂·2H₂O in CH₃CN at room temperature to give the 1 ∶ 1 complexes [Cu(L²)Cl₂] and [Cu(L³)Cl₂]·½MeNO₂. X-Ray diffraction studies confirm that in each case the two chloride anions and the three N-donors from the [9]aneN₃ framework coordinate to the metal centre in a distorted square-based pyramidal geometry. All the complexes have been characterised by electronic and EPR spectroscopy. The reaction of L² with CuCl₂·2H₂O has also been carried out in refluxing MeOH and followed by electronic spectroscopy in order to investigate whether the methanolysis of the two nitrile groups is effected by the presence of more strongly coordinating anions such as chloride. The complex [Cu(4)Cl](BF₄) where 4 is derived from L² by methanolysis of only one nitrile group, has been isolated after addition of an excess of Me₄NBF₄.