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Oxidation of Ammonia in Osmium Polypyridyl Complexes

Coia, George M. and Demadis, Konstantinos D. and Meyer, Thomas J. (2000) Oxidation of Ammonia in Osmium Polypyridyl Complexes. Inorganic Chemistry, 39 (10). pp. 2212-2223. ISSN 0020-1669. doi:10.1021/ic0000505.

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The oxidations of cis- and trans-[Os^(III)(tpy)(Cl)_2(NH_3)](PF_6), cis-[Os^(II)(bpy)_2(Cl)(NH_3)](PF_6), and [Os^(II)(tpy)(bpy)(NH_3)](PF_6)_2 have been studied by cyclic voltammetry and by controlled-potential electrolysis. In acetonitrile or in acidic, aqueous solution, oxidation is metal-based and reversible, but as the pH is increased, oxidation and proton loss from coordinated ammonia occurs. cis- and trans-[Os^(III)(tpy)(Cl)_2(NH_3)](PF_6) are oxidized by four electrons to give the corresponding Os^(VI) nitrido complexes, [Os^(VI)(tpy)(Cl)_2(N)]^+. Oxidation of [Os(tpy)(bpy)(NH_3)](PF_6)_2 occurs by six electrons to give [Os(tpy)(bpy)(NO)](PF_6)_3. Oxidation of cis-[Os^(II)(bpy)_2(Cl)(NH_3)](PF_6) at pH 9.0 gives cis-[Os^(II)(bpy)_2(Cl)(NO)](PF_6)_2 and the mixed-valence form of the μ-N_2 dimer {cis-[Os(bpy)_2(Cl)]_2(μ-N_2)}(PF_6)_3. With NH_4^+ added to the electrolyte, cis-[Os^(II)(bpy)_2(Cl)(N_2)](PF_6) is a coproduct. The results of pH-dependent cyclic voltammetry measurements suggest Os^(IV) as a common intermediate in the oxidation of coordinated ammonia. For cis- and trans-[Os^(III)(tpy)(Cl)_2(NH_3)]^+, Os^(IV) is a discernible intermediate. It undergoes further pH-dependent oxidation to [Os^(VI)(tpy)(Cl)_2(N)]^+. For [Os^(II)(tpy)(bpy)(NH_3)]_2^+, oxidation to Os^(IV) is followed by hydration at the nitrogen atom and further oxidation to nitrosyl. For cis-[Os^(II)(bpy)_2(Cl)(NH_3)]^+, oxidation to Os^(IV) is followed by N−N coupling and further oxidation to {cis-[Os(bpy)_2(Cl)]_2(μ-N_2)}^(3+). At pH 9, N−N coupling is competitive with capture of Os^(IV) by OH- and further oxidation, yielding cis-[Os^(II)(bpy)_2(Cl)(NO)]^(2+).

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Additional Information:© 2000 American Chemical Society. Received 18 January 2000. Published online 26 April 2000. Published in print 1 May 2000. The authors acknowledge the National Science Foundation for funding this research under Grant CHE-9503738 and Dr. Martin Devenney for obtaining the Raman spectrum of cis,cis-[(bpy)_2(Cl)Os^(II)(N⋮N)Os^(II)(Cl)(bpy)_2]^(2+).
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Official Citation:Oxidation of Ammonia in Osmium Polypyridyl Complexes George M. Coia, Konstantinos D. Demadis, and Thomas J. Meyer Inorganic Chemistry 2000 39 (10), 2212-2223 DOI: 10.1021/ic0000505
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76854
Deposited By: Ruth Sustaita
Deposited On:24 Apr 2017 20:31
Last Modified:15 Nov 2021 17:03

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