Bioinspired manganese(ii) complexes with a clickable ligand for immobilisation on a solid support

Abstract

Clickable ligands like N,N′-bis((pyridin-2-yl)methyl)prop-2-yn-1-amine (L¹) and N-((1-methyl-1H-imidazol-2-yl)methyl)-N-(pyridin-2-ylmethyl)prop-2-yn-1-amine (L²) have been used to synthesise a series of manganese(II) complexes for grafting onto appropriate solid supports. These ligands mimic the 2-His-1-carboxylate facial chelation present in the active site of the manganese-dependent dioxygenase (MndD), while the alkyne side function allows grafting of the ligand onto an azido-functionalised support using “click chemistry” methodologies. Such synthetic analogues of the MndD crystallise in the solid state as double halide or pseudohalide-bridged dinuclear manganese(II) complexes of the general formula [Mn₂(μ-X)₂X₂L₂] [L = L¹ with X = Cl (1), Br (2), and N₃ (3); L = L² with X = N₃ (4)]. Complexes 1–4 are characterised by a weak magnetic exchange interaction between the two high-spin Mn^II ions through the two X⁻ bridges (J in the range of −0.059 to +5.30 cm⁻¹, H = −J·S_Mn1·S_Mn2 with S_Mn1 = S_Mn2 = 5/2). A new magneto-structural correlation of superexchange bis(μ_1,1-azido)dimanganese(II) complexes has been proposed using both structural parameters, the Mn–N–Mn bridging angle and the Mn–N_azido distance. In MeOH–EtOH solution the dimeric species are present together with few percents of mononuclear manganese(II) complexes as evidenced by electron paramagnetic resonance (EPR) spectroscopy. Grafting the complexes onto mesoporous silica of MCM-41 type stabilises both dimers and monomers in the nanopores of the solid.