Formation pathway of a Mn(IV),Mn(IV) bis(μ-oxo) dimer that incorporates alkali and alkaline earth cations and electron transfer properties of the dimer

Abstract

The oxidation of (3,3′-17-crown-6-SALPN)Mn(II) with O 2 in CH 3CN resulted in formation of the corresponding Mn(IV),Mn(IV) bis(μ-oxo) dimer ( 2). A 16O 2/ 18O 2 labeling experiment, in which the product was analyzed by FT-IR spectroscopy and electrospray ionization mass spectrometry (ESI-MS), showed no detectable quantity of the mixed-isotope product [(3,3′-17-crown-6(SALPN))Mn(IV)] 2(μ- 16O)(μ- 18O), suggesting a simple O–O bond cleavage/bis(μ-oxo) dimer formation pathway that does not include Mn–O monomers. Alkali or alkaline earth cations were incorporated into the crown ether portion of each ligand. Upon addition of 2 equiv. of NaPF 6, KPF 6, CaTf 2, or BaTf 2 (Tf is [SO 3CF 3] −) to a slurry of 2 in CH 3CN, 2·2NaPF 6, 2·2KPF 6, 2·2CaTf 2, or 2·2BaTf 2 formed. All of the complexes were characterized by cyclic voltammetry. Anodic potential shifts were recorded for the Mn(IV),Mn(IV/III)(μ-O) 2 and Mn(IV/III),Mn(III)(μ-O) 2 redox processes upon cation incorporation into 2. The voltammetry of some of the complexes was suggestive of cation motion toward the Mn 2O 2 core following the injection of the first electron.