Synthesis and characterisation of manganese(II) compounds with tetradentate ligands based on the bispidine backbone

Abstract

Reaction of the tetradentate ligand dimethyl 3,7-dimethyl-9-oxo-2,4-bis(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate (L¹) with manganese(II) chloride or iodide in methanol yielded [MnL¹Cl₂] and [MnL¹I₂], respectively. Reaction with silver(I) triflate Ag(O₃SCF₃) converted these compounds into [MnL¹(O₃SCF₃)₂]. Reduction of L¹ with NaBH₄ in MeOH and LiAlH₄ in THF led to the triol 1,5-bis(hydroxymethylene)-3,7-dimethyl-2,4-bis(2-pyridyl)-3,7-diazabicyclo[3.3.1]nonan-9-ol (L²); the reduction is stereoselective and yields the syn isomer. Complexation of manganese(II) chloride and iodide with L² produced [MnL²Cl₂] and [MnL²I₂] and these have a higher thermal stability than [MnL¹X₂]. The complexes [MnL¹Cl₂], [MnL¹I₂], [MnL¹(O₃SCF₃)₂], [MnL²Cl₂] and [MnL²I₂] are characterised spectroscopically, electrochemically and by their magnetic, conductometric, thermal and structural properties (X-ray analyses of [MnL¹Cl₂] and [MnL²Cl₂]).

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