Singlet Diradical Complexes of Ruthenium and Osmium: Geometrical and Electronic Structures and their Unexpected Changes on Oxidation
, , , , , und .
Inorganic Chemistry 47 (5): 1625--1633 (2008)

Reaction of HL, HLa (2-(2-N-phenylamino)phenylazopyridine), HLb (2-2-N-(4-methylphenyl)aminophenylazopyridine), or HLc (2-2-N-(4-chlorophenyl)aminophenylazopyridine), 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)2I3, 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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