Article,

Filling Gaps in the Series of Noninnocent Hetero-1,3-diene Chelate Ligands: Ruthenium Complexes of Redox-Active a-Azocarbonyl and a-Azothiocarbonyl Ligands RNNC(R')E, E = O or S

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Inorganic Chemistry, 51 (11): 6237--6244 (2012)
DOI: 10.1021/ic300439h

Abstract

4-Center unsatd. chelate ligands A=B-C=D with redox activity to yield -A-B=C-D- in two steps were complemented by two new combinations RNNC(R')E, E = O or S, R = R' = Ph. The ligands N-benzoyl-N'-phenyldiazene = LO, and N-thiobenzoyl-N'-phenyldiazene = LS, (obtained in situ) form structurally characterized compds. (acac)2Ru(L) (1) with L = LO, and (3) with L = LS, and (bpy)2Ru(L)(PF6), (2(PF6)) with L = LO, and (4(PF6)) with L = LS (acac- = 2,4-pentanedionato; bpy = 2,2'-bipyridine). According to spectroscopy and the N-N distances around 1.35 \AA and N-C bond lengths of $\sim$1.33 \AA, all complexes involve the monoanionic (radical) ligand form. For 1 and 3, the antiferromagnetic spin-spin coupling with electron transfer-generated RuIII leads to diamagnetic ground states of the neutral complexes, whereas the cations 2+ and 4+ are EPR-active radical ligand complexes of RuII. The complexes are reduced and oxidized in reversible 1-electron steps. EPR and UV-visible-NIR spectroelectrochem. in conjunction with time-dependent d. functional theory (TD-DFT) calcns. allowed the authors to assign the electronic transitions in the redox series, revealing mostly ligand-centered electron transfer: (acac)2RuIII(L0)+ .rdblhar. (acac)2RuIII(L·-) .rdblhar. (acac)2RuIII(L2-)-/(acac)2RuII(L·-)-, and (bpy)2RuIII(L·-)2+/(bpy)2RuII(L0)2+ .rdblhar. (bpy)2RuII(L·-)+ .rdblhar. (bpy)2RuII(L2-)0. The differences between the O and S contg. compds. are rather small in comparison to the effects of the ancillary ligands, acac- vs. bpy. on SciFinder(R)

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