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

摘要

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(#mu#-oxo) dimer (2). A ~(16)O_2/~(18)O_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(#mu#-~(16)O)(#mu#-~(18)O), suggesting a simple O-O bond cleavage/bis(#mu#-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, 2.3NaPF_6, 2 centre dot 2KPF_6, 2 centre dot 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)(#mu#-O)_2 and Mn(IV/III),Mn(III)(#mu#-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.