Functionalised azetidines as ligands: Species derived by selective alkylation at substituent-nitrogen

Selective functionalisation of the tridentate ligand 1-(2-aminoethyl)-3- methyl-3-(2-pyridyl)azetidine at its terminal amino-nitrogen atom can be readily achieved by both reductive alkylation and simple alkylation reactions to give tri-, quadri-, quinque- and sexi-dentate derivatives. Simple alkylation by 2-picolinyl chloride provides the only example of a second reaction pathway where the azetidine ring of the reactant has undergone activation towards ring opening. Structural characterisation of the Cu(ii) complexes of these ligands has revealed several remarkable aspects of their solid-state coordination chemistry, including the formation of infinite helical aggregates through π-stacking and tetramerisation through carboxylate bridging, as well as further examples of the crystallisation of mixed species found to be rather common with complexes of the parent ligand.