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Photoinduced Electron Transfer in Ruthenium Bipyridyl Complexes: Evidence for the Existence of a Cage with Molecular Oxygen

Yavin, Eylon and Weiner, Lev and Arad-Yellin, Rina and Shanzer, Abraham (2004) Photoinduced Electron Transfer in Ruthenium Bipyridyl Complexes: Evidence for the Existence of a Cage with Molecular Oxygen. Journal of Physical Chemistry A, 108 (42). pp. 9274-9282. ISSN 1089-5639. doi:10.1021/jp048235a.

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Ruthenium complexes with three bipyridyl ligands, one of which is modified by attaching one or two hydroxamic acids groups (Ru-1 and Ru-2, respectively), were synthesized. Using EPR spectroscopy, we have found that photoexcitation leads to formation of nitroxyl radicals. The nitroxyl radical concentration in Ru-2 increased dramatically in the presence of spin traps DMPO (5,5‘-dimethyl-1-pyrroline-N-oxide) and PBN (N-tert-butyl-α-phenylnitrone) characterized by strong affinity to superoxide radicals. We have attributed this behavior to the formation of a cage complex between Ru-2 and the superoxide radical. This paper concerns the study of cages formed between ruthenium complexes and molecular oxygen and the effect of functional groups attached to modified bipyridyl ligands on cage formation. The complex between Ru-2 and O_2 was formed in the ground state, probably with participation of the hydroxamic acid groups. The equilibrium constant of this complex was determined by EPR as K_(eq) ∼ 3 M^(-1). The formation of the Ru-2−O_2 complex is supported by the temperature-dependent rate of appearance of the EPR signal in the presence of PBN. Additional evidence comes from observation of paramagnetic shifts of the peaks in the 1H NMR spectrum of specific aromatic protons in the substituted bipyridyl ring upon exposure to O_2. Similar shifts were observed in the spectrum of Os-2, with osmium replacing ruthenium. Model compounds with functional groups that replace the hydroxamic acid or compounds without the metal center, but with the two hydroxamic acids, were synthesized. No shifts in the ^1H NMR spectra of these derivatives were observed in the presence of O_2. These results lead to the conclusion that both metal ions, Ru(II) or Os(II), and hydroxamic acid groups are essential components for the formation of the oxygen cage.

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Additional Information:© 2004 American Chemical Society. Received: April 22, 2004; In Final Form: July 30, 2004. Publication Date (Web): September 18, 2004. The authors thank Dr. Leonid Konstantinovski for his helpful advice in conducting NMR experiments and Prof. Anatoly Burshtein for useful discussions. Support from the Helen and Martin Kimmel Center for Molecular Design is greatly acknowledged. A.S. holds the Siegfried and Irma Ulmann professorial chair.
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Helen and Martin Kimmel Center for Molecular DesignUNSPECIFIED
Siegfried and Irma Ulmann professorial chairUNSPECIFIED
Issue or Number:42
Record Number:CaltechAUTHORS:20170510-100233559
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Official Citation:Photoinduced Electron Transfer in Ruthenium Bipyridyl Complexes:  Evidence for the Existence of a Cage with Molecular Oxygen Eylon Yavin, Lev Weiner, Rina Arad-Yellin, and Abraham Shanzer The Journal of Physical Chemistry A 2004 108 (42), 9274-9282 DOI: 10.1021/jp048235a
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77338
Deposited By: Tony Diaz
Deposited On:16 May 2017 20:31
Last Modified:15 Nov 2021 17:30

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