Manganese(III) complexes of the ligand ethylenebis[(o-hydroxyphenyl)glycine], Mn(EHPG)-, are shown to oxidatively decarboxylate in methanol, DMF, and acetone solutions to generate derivatives of [ethylenebis(salicylideneaminato)]manganese(III), Mn(SALEN)+. This process occurs via air oxidation of MnIII(EHPG)- to form MnIV(EHPG), which subsequently loses CO2 and one proton, forming [N-(2-(o-salicylideneamino)ethyl)(o-hydroxyphenyl)glycinato]manganese(III), MnIII(EHGS). MnIII-(EHGS) is also air sensitive and will further decarboxylate to MnIII(SALEN)+. When this reaction is completed in acetone, X-ray-quality crystals of MnIII(SALEN)[2-(3-oxobutenyl)phenolate] are recovered. This very loosely associated solid-state dimer contains a rare example of monodentate phenolate coordination to Mn(III). The generation of MnIII(SALEN)+ has been followed by electrochemistry and paramagnetic NMR spectroscopy. MnIII(EHPG)- shows an oxidative wave in methanol with E0 = +450 mV and in DMF with E0 = +300 mV (vs SCE). Bulk electrolysis at +600 mV in methanol quantitatively (by the passage of four electrons) generates MnIII(SALEN)+, which has an Mn(III)/Mn(II) reduction at -250 mV. The paramagnetic NMR spectrum, of a mixture of rac and meso isomers of MnIII(EHPG)- in CD3OD shows resonances at +26.3, -18.6 and -34.6 ppm (rac isomer) and +27.8, +24.0, -2.4, -16.5, -22.5, -32.5, and -35.5 ppm (meso isomers). After 9 days, the spectrum of MnIII(SALEN)+ has developed completely with resonances at -4.1, -23.2, and -28.9 ppm. MnIII(EHGS) is not produced in sufficient quantities to be detected under these conditions. In contrast, DMF solutions of MnIII(EHPG)- (shifts at +27.3, +24.8, -2.4, -18.0, -21.6, -32.0, and -35.5 ppm, meso isomer) slowly form MnIII(EHGS) with features at +45.6, +28.6, +13.1 -9.4, -19.5, and -27.7 ppm, and ultimately one recovers MnIII(SALEN)+ with peaks at +29.5, -2.4, -22.3, and -25.4 ppm. In contrast, the FeIII(EHPG)-, CuII(EHPG)2-, and GaIII(EHPG)- complexes are air stable. This metal-assisted, oxidative decarboxylation is analogous to that previously described for VVO(HEHPG), which was shown to generate V(III) species as intermediates. Therefore, this facile decarboxylation reaction appears to be promoted by using ions that can cycle through three oxidation states and suggests that a cycle for the manganese-facilitated process includes both Mn(IV) and Mn(II) X-ray parameters for MnIII(SALEN)[2-(3-oxobutenyl)phenolate]: MnC26H23N2O4, mol wt 482.4, monoclinic (P21/c), a = 12.200 (4) ? b = 14.104 (4) ?, c = 13.584 (3) ?, β = 103.74 (2)°, V = 2270 (1) ?3, Z = 4, 3503 unique data collected with 0 3σ(I). The best model gave R = 0.044 and Rw = 0.039.