Abstract
Reaction of HL, HLa (2-[(2-N-phenylamino)phenylazo]pyridine), HLb (2-[2-N-(4-methylphenyl)aminophenylazo]pyridine), or HLc (2-[2-N-(4-chlorophenyl)aminophenylazo]pyridine), with KRuO4 or OsO4 and PPh3 under exhaustive deoxygenation (PPh3 $\rightarrow$ OPPh3) yields diamagnetic compds. ML2. Crystal structure detn. for M(La)2 indicates the ligand radical dianion state, L.bul.2-, as evident from a typical N-N bond length of $\sim$1.33 \AA for a 1-electron reduced azo function. The resulting spin-coupled complexes, MIV(L.bul.2-)2, can be oxidized in two reversible 1-electron steps, as probed by cyclic voltammetry and UV-visible-NIR spectroelectrochem. The paramagnetic intermediates, [M(La)2]+, are distinguished by intense NIR absorption, largely metal-centered spin as revealed by EPR, and, in the case of [Os(La)2]I3, by crystallog. detd. shortening of the N=N bond to $\sim$1.30 \AA, corresponding to a coordinated unreduced azo function. Thus, oxidn. of MIV(L.bul.2-)2 involves partial redn. of the metal in [MIII(L-)2]+ because intramol. double electron transfer is offsetting the external charge removal. D.-functional theory calcns. were employed to confirm the structural features and to support the spectroscopic assignments. [on SciFinder(R)]
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