Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4 '-di-tert-butyl-2,2 '-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(IV)

摘要

This article reports on the stabilization of organic radical anions promoted by the oxidovanadium(IV) ion. A 3,5-di-tert-butylcatecholate ((tBu)catH(-)) complex of oxidovanadium(V) of the type [(L-ONO(a2-))(VO3+((tBu)CatH(-)] (1) was isolated using tridentate (E)-N'-((3-hydroxynaphthalen-2-yl)methylene)benzohydrazide ((LONOH2)-H-a) as a coligand, whereas o-benzosemiquinonate (sq(center dot-)) and p-nitro-o-iminobenzosemiquinonate ((NO2)isq(center dot-)) radical anion complexes of oxidovanadium(IV) of the types [(L-NNO(-))(VO2+)(sq(center dot-))1 (2) and [(L-NNO(-))(VO2+((NO2)isq(center dot-))1 (3) were successfully isolated using (1Z,N'E)-N'-(phenyl(pyridin-2-yl)methylene)benzohydrazonic acid (LNNOH) as a coligand. Oxidovanadium(IV) complexes of the types [(L-ONO(b2-))(VO2+(phen)1 (4) and [(L-ONO(b2-))(VO2+)((tBu)bpy)] (5), which undergo reversible reduction to the 4,4'-di-tert-butyl-2,2'-bipyridine radical anion ((tBu)bpy(center dot-)) and the 1,10-phenanthroline radical anion (phen(center dot-)) to afford the coupled states [(L-ONO(b2-))(VO2+(phen(center dot-))(-) (4(-)) and [(L-ONO(b2-))(VO2(+))((tBu)bpy(center dot-))](-) (5(-),) respectively, were isolated ((LONOH2)-H-b = (E)-N'-(2-hydroxybenzylidene)benzohydrazide). The molecular geometries of the complexes were confirmed by the single-crystal X-ray structure determinations of 1, 3 and 4. In 1, the V-O-phenotato length cis to V=O is 1.879(2) angstrom and the dissimilar V-O and V-OH lengths corresponding to the (tBu)catH(-) are 1.832(2) and 2.312(2) angstrom, respectively. In 1, the average C-O lengths in (tBu)catH(-) are 1.351(3) angstrom, whereas in 3 the average C-O and C-N lengths in (NO2)isq(center dot-) are 1.293(4) and 1.355(5) angstrom, respectively. In 4, the V-O-phenolato length cis to V=O (1.937(3) angstrom) is relatively longer. The V-51 NMR spectrum of 1 displays a signal at -337.2 ppm, whereas the signals for 2 and 3 are deshielded to +382.4 and +71.8 ppm, respectively. The closed-shell singlet (CSS) solutions of 3 and 5(-) at the B3LYP/DFT level are unstable and the open-shell singlet (OSS) solutions are 0.5 and 7.3 kcal mol(-1) lower in energy, respectively, than the CSS solutions. In 3 and 5(-) the alpha spin (100%) is localized on the vanadium ion, whereas the beta spin is delocalized across the aminophenol and bipyridine fragments. 2 and 3 exhibit lower energy absorption bands at 785 and 585 nm, which are defined as CSS -> OSS perturbation transitions.