Stabilization of {RuNO}6 and {RuNO}7 States in [RuII(trpy)(bik)(NO)]n+ {trpy = 2,2′:6′,2″-terpyridine, bik = 2,2′-bis(1-methylimidazolyl) ketone} – Formation, Reactivity, and Photorelease of Metal-Bound Nitrosyl
✍ Scribed by Prinaka De; Biprajit Sarkar; Somnath Maji; Atanu Kumar Das; Ece Bulak; Shaikh M. Mobin; Wolfgang Kaim; Goutam Kumar Lahiri
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 527 KB
- Volume
- 2009
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Ruthenium nitrosyl complexes have been isolated in the {RuNO}^6^ and {RuNO}^7^ configurations, employing the following reaction pathway for [Ru(trpy)(bik)(X)]^n+^: X = Cl^–^, 1 → X = CH~3~CN, 2~2~ → X = NO~2~^–^, 3 → X = NO^+^, 4~3~ → X = NO^·^, 4~2~. The single‐crystal X‐ray structures of 1·(C~6~H~6~)·H~2~O, 2~2~·H~2~O, and 3·H~2~O have been determined. The successive NO^+^/NO^·^ (reversible) and NO^·^/NO^–^ (irreversible) reduction processes of [4]^3+^ appear at +0.36 and –0.40 V vs. SCE, respectively. While the ν(C=O) frequency of the bik ligand at about 1630 cm^–1^ is largely invariant on complexation and reduction, the ν(NO) frequency for the {RuNO}^6^ state in [4]^3+^ at 1950 cm^–1^ shifts to about 1640 cm^–1^ on one‐electron reduction to the {RuNO}^7^ form in [4]^2+^, reflecting the predominant NO^+^ → NO^·^ character of this electron transfer. However, a sizeable contribution from ruthenium with its high spin‐orbit coupling constant to the singly occupied molecular orbital (SOMO) is apparent from the enhanced g anisotropy in the EPR spectrum [4]^2+^ (g~1~ = 2.015, g~2~ = 1.995, g~3~ = 1.881; g~av~ = 1.965; Δ__g__ = 0.134). The {RuNO}^6^ unit in [4]^3+^ reacts with OH^–^ via an associatively activated process (Δ__S^#^__ = –126.5 ± 2 J K^–1^ mol^–1^) with a second‐order rate constant of k = 3.3 × 10^–2^ M^–1^ s^–1^, leading to the corresponding nitro complex [3]^+^. On exposure to light both {RuNO}^6^ and {RuNO}^7^ in [4]^3+^ and [4]^2+^ undergo Ru–NO photocleavage in CH~3~CN via the formation of [Ru(trpy)(bik)(CH~3~CN)]^2+^, [2]^2+^. The rate of photocleavage of the Ru^II^–NO^+^ bond in [4]^3+^ (k~NO~, 8.57 ×10^–1^ s^–1^, t~1/2~ = 0.80 s) is found to be much faster than that of the Ru^II^–NO^·^ bond in [4]^2+^, [k~NO~·, 5.45 × 10^–4^ s^–1^, t~1/2~ = 21.2 min (= 1272 s)]. The photoreleased nitrosyl can be trapped as an Mb‐NO adduct.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)