Mononuclear MnIII and MnIV Bis-terpyridine Complexes: Electrochemical Formation and Spectroscopic Characterizations

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• 作者：Sophie Romain ; Carole Baffert^† ; ; Carole Duboc ; Jean-Claude Leprtre^‡ ; ; Alain Deronzier* ; Marie-Nolle Collomb*
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：April 6, 2009
• 年：2009
• 卷：48
• 期：7
• 页码：3125-3131
• 全文大小：259K
• 年卷期：v.48,no.7(April 6, 2009)
• ISSN：1520-510X

文摘

The electrochemical behavior of two mononuclear Mn^II bis-terpyridine complexes, [Mn^II(L)₂]²⁺ (L = terpy (2,2′:6′,2′′-terpyridine) and ^tBu₃-terpy (4,4′,4′′-tritert-butyl-2,2′:6′,2′′-terpyridine)), has been investigated in dry CH₃CN. Under these conditions, the cyclic voltammograms of these complexes exhibit not only the well-known Mn^II/Mn^III oxidation system but also a second metal-based oxidation one, corresponding to the Mn^III/Mn^IV redox couple. These oxidative processes are located at E_1/2 = +0.96 and +1.77 V vs Ag/Ag⁺ (+1.26 and +2.07 V vs SCE) for the terpy complex and E_1/2 = +0.85 and +1.56 V vs Ag/Ag⁺ (+1.15 and +1.86 V vs SCE) for the ^tBu₃-terpy derivative. The one-electron oxidized form of these complexes, [Mn^III(L)₂]³⁺, has been quantitatively generated by exhaustive electrolyses at E = 1.30 V, as previously observed in the case of the oxidation of [Mn^II(tolyl-terpy)₂]²⁺ (tolyl-terpy = 4′-(4-Methylphenyl)-2,2′:6′,2′′-terpyridine) (Romain, S.; Duboc, C.; Neese, F.; Rivire, E.; Hanton, L. R.; Blackman, A. G.; Leprtre, J.-C.; Deronzier, A.; Collomb, M.-N. Chem.Eur. J. 2009, 15, 980−988). Further electrolyses at E = 1.65−1.80 V of [Mn^III(L)₂]³⁺ solutions have shown that the [Mn^IV(L)₂]⁴⁺ species is only stable for L = ^tBu₃-terpy because of the strong electron-donating properties of the tert-butyl substituents. These electrogenerated high-valent complexes are rare examples of mononuclear Mn^III and Mn^IV complexes stabilized solely by neutral N ligands. They have been fully characterized in solution by UV−visible and electron paramagnetic resonance (EPR) spectroscopies. A detailed investigation of the EPR spectra of the [Mn^II(^tBu₃-terpy)₂]²⁺ and [Mn^IV(^tBu₃-terpy)₂]⁴⁺ has allowed the determination of the spin Hamiltonian parameters for both systems (for Mn^II: |D| = 0.059 cm⁻¹; |E| = 0.014 cm⁻¹; E/D = 0.259; g_x = g_y = g_z = 2.00 and for Mn^IV: |D| = 1.33(6) cm⁻¹; |E| = 0.36(4) cm⁻¹; E/D = 0.27; g_x = 1.96(4); g_y = 1.97(4); g_z = 1.98(4)).