Oxidation State Analysis of a Four-Component Redox Series Os(pap)2(Q)n Involving Two Different Non-Innocent Ligands on a Redox-Active Transition Metal
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Inorganic Chemistry 50 (15): 7090--7098 (2011)

Complexes Os(pap)2(Q) (1-4) were obtained and structurally characterized for pap = 2-phenylazopyridine and Q = 4,6-di-tert-butyl-N-aryl-o-iminobenzoquinone (aryl = Ph (1), 3,5-dichlorophenyl (2), 3,5-dimethoxyphenyl (3), or 3,5-di-tert-butylphenyl (4)). The oxidized form (3)(ClO4)2 was also crystallog. characterized while the odd-electron intermediates Os(pap)2(Q)+ (1+-4+) and Os(pap)2(Q)- (2-) were studied by EPR and UV-visible-NIR spectroelectrochem. in conjunction with d. functional theory (DFT) spin d. and time-dependent DFT (TD-DFT) calcns. The results from the structural, spectroscopic, and electrochem. expts. and from the computational studies allow for the assignments OsII(pap0)2(Q0)2+, OsII(pap0)2(Q·-)+, OsIV(pap·-)2(Q2-), and OsII(pap·-)(pap0)(Q2-)-, with comproportionation consts. Kc $\approx$ 103.5, 1010, 1018, and 105, resp. The redox potentials and the comproportionation consts. exhibit similarities and differences between Ru and Os analogs. While the Q-based redox reactions show identical potentials, the more metal-involving processes exhibit cathodic shifts for the osmium systems, leading to distinctly different comproportionation consts. for some intermediates, esp. to a stabilization of the neutral osmium compds. described. The example Os(pap)2(Q)n illustrates esp. the power of combined structural and EPR anal. with support from DFT towards the valence state description of transition metal complexes incorporating redox non-innocent ligands. on SciFinder(R)
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