A novel samarium(ii) complex bearing a dianionic bis(phenolate) cyclam ligand: synthesis, structure and electron-transfer reactions

Abstract

The reaction of the hexadentate dianionic 1,4,8,11-tetraazacyclotetradecane-based bis(phenolate) ligand, (^tBu₂ArO)₂Me₂-cyclam²⁻, with [SmI₂(thf)₂] in thf resulted in the formation of the divalent samarium complex [Sm(κ⁶-{(^tBu₂ArO)₂Me₂-cyclam})] (1). X-ray diffraction studies revealed that after recrystallization from n-hexane/thf complex 1 has a monomeric structure and does not contain thf molecules coordinated to the Sm(II) center. However, UV-vis and ¹H NMR spectroscopy of 1 evidenced the formation of thf-solvated complexes in neat thf. Reductive studies show that complex 1 can act as a single electron-transfer reagent and form well-defined Sm(III) species. The reaction of 1 with several substrates, namely, TlBPh₄, pyridine N-oxide, OPPh₃, SPPh₃ and bipyridines, are reported. Spectroscopy studies, including NMR, and single crystal X-ray diffraction data are in agreement with the formation of cationic Sm(III) species, monochalcogenide bridged Sm(III) complexes and Sm(III) complexes with bipyridine radical ligand, respectively.