RuII(a-diimine) or RuIII(a-diimine·-)? Structural, Spectroscopic, and Theoretical Evidence for the Stabilization of a Prominent Metal-to-Ligand Charge-Transfer Excited-State Configuration in the Ground State

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European Journal of Inorganic Chemistry, 2014 (1): 110--119 (2014)
DOI: 10.1002/ejic.201301206


The new compds. Ru(R-DAB)(acac)2 (R-DAB = 1,4-diorganyl-1,4-diazabuta-1,3-diene; R = tert-Bu, 4-methoxyphenyl, 2,6-dimethylphenyl; acac- = 2,4-pentanedionate) exhibit intrachelate ring bond lengths 1.297 \textless d(CN) \textless 1.344 \AA and 1.382 \textless d(CC) \textless 1.425 \AA, which suggest a RuIII(R-DAB·-) oxidn. state formulation. This notion is confirmed by the negligible solvatochromism of the intense (e $\approx$ 104M-1 cm-1) charge-transfer absorption band in the visible region and by DFT calcns. Oxidn. of the compds. occurs mainly at the R-DAB·- radical ligand to produce UV/Vis/NIR and ESR spectroelectrochem. detectable RuIII species, whereas the redn. proceeds less reversibly and yields predominantly (R-DAB)-ligand-based spin for the 4-methoxyphenyl deriv., measured at low temp. The results are discussed with respect to metal-to-ligand charge-transfer (MLCT) excited states of conventional (a-diimine)ruthenium(II) complexes and in view of other (a-diimine)metal complexes with ambiguous oxidn.-state assignments. on SciFinder(R)



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