Osmium Hydrazido and Dinitrogen Complexes
1997; American Chemical Society; Volume: 36; Issue: 11 Linguagem: Inglês
10.1021/ic961025v
ISSN1520-510X
AutoresGeorge M. Coia, Martin Devenney, Peter S. White, Thomas J. Meyer, David A. Wink,
Tópico(s)Magnetism in coordination complexes
Resumo[Os(tpy)(bpy)(NH3)](PF6)2 (1) was oxidized electrochemically in the presence of a series of amines in aqueous solutions buffered to pH 7. With secondary aliphatic amines, electrolysis gave [Os(tpy)(bpy)(NNR2)](PF6)3 (3); number of electrons n = 4.6−5.0. 3 was reduced to [Os(tpy)(bpy)(NNR2)](PF6)2 (2) in aqueous and nonaqueous solutions with n = 1.0. The structures of 2 were determined by X-ray crystallography for NR2 = diethylamide (2a) and morpholide (2c) and were found to exhibit bent hydrazido(2−) coordination (Os−N−N = 137°). The salts crystallized in the triclinic system, space group P1̄. For 2a, a = 9.004(1) Å, b = 9.796(1) Å, c = 20.710(2) Å, α = 88.78(2)°, β = 85.43(2)°, γ = 86.22(2)°, and Z = 2. For 2c, a = 9.632(8) Å, b = 21.229(9) Å, c = 9.039(5) Å, α = 97.41(4)°, β = 94.28(5)°, γ = 85.07(5)°, and Z = 2. Solutions of 2 were protonated in strongly acidic media to give hydrazido(1−) complexes. The pKa of the protonated form of 2a is 0.90 ± 0.01. Reduction of 2 in aqueous solutions of pH <1 gave 1 and NH2R2+ with n = 4.0. At higher pH, there is evidence for an Os(II) hydrazine intermediate. Oxidation of 3 by one electron afforded transiently stable species which decomposed to give [Os(tpy)(bpy)(NCCH3)]3+ in acetonitrile solution. Pseudo-first-order rate constants of 8.1 ± 0.9 s-1 and 0.200 ± .005 s-1 were estimated by cyclic voltammetry on solutions of 2a and 2b (NR2 = piperidide), respectively. Oxidation of 1 at pH 7, in the presence of primary aliphatic amines or ammonia, occurred with n = 5.9−6.2, and generated [OsII(tpy)(bpy)(N2)](PF6)2 (4).
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