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

The oxidation of (3,3'-17-crown-6-SALPN)Mn(II) with O-2 in CH3CN resulted i n formation of the corresponding Mn(IV),Mn(IV) bis(mu-oxo) dimer (2). A O-1 6(2)/O-18(2) labeling experiment, in which the product was analyzed by FT-I R spectroscopy and electrospray ionization mass spectrometry (ESI-MS), show ed no detectable quantity of the mixed-isotope product [(3,3'-17-crown-6(SA LPN))Mn(IV)](2)(mu-O-16)(mu-O-18), suggesting a simple O-O bond cleavage/bi s(mu-oxo) dimer formation pathway that does not include Mn-O monomers. Alka li or alkaline earth cations were incorporated into the crown ether portion of each ligand. Upon addition of 2 equiv. of NaPF6, KPF6, CaTf2, or BaTf2 (Tf is [SO3CF3](-)) to a slurry of 2 in CH3CN, 2.2NaPF(6), 2.2KPF(6), 2.2Ca Tf(2), or 2.2BaTf(2) formed. All of the complexes were characterized by cyc lic voltammetry. Anodic potential shifts were recorded for the Mn(IV), Mn(I V/III)(mu-O)(2) and Mn(IV/III), Mn(III)(mu-O)(2) redox processes upon catio n incorporation into 2. The voltammetry of some of the complexes was sugges tive of cation motion toward the Mn2O2 core following the injection of the first electron. (C) 1999 Elsevier Science S.A. All rights reserved.