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]).