Organometallic Mixed-Valence Systems. Two-Center and Three-Center Compounds with meta Connections around a Central Phenylene Ring

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• 作者：Tania Weyland ; Karine Costuas ; Loic Toupet ; Jean-Franç ; ois Halet ; and Claude Lapinte
• 刊名：Organometallics
• 出版年：2000
• 出版时间：October 16, 2000
• 年：2000
• 卷：19
• 期：21
• 页码：4228 - 4239
• 全文大小：209K
• 年卷期：v.19,no.21(October 16, 2000)
• ISSN：1520-6041

文摘

The bi- and trinuclear mixed-valence complexes [{Cp*(dppe)Fe(CC-)}₂(1,3-C₆H₄)][PF₆] (2⁺),[{Cp*(dppe)Fe(CC-)}₃(1,3,5-C₆H₃)][PF₆] (3⁺), and [{Cp*(dppe)Fe(CC-)}₃(1,3,5-C₆H₃)][PF₆]₂(3²⁺) were prepared either by oxidation of [{Cp*(dppe)Fe(CC-)}₂(1,3-C₆H₄)] (2) or [{Cp*(dppe)Fe(CC-)}₃(1,3,5-C₆H₃)] (3) with 1 or 2 equiv of [(C₅H₅)₂Fe][PF₆] or by reaction betweenthe homovalent species 2 and 2²⁺ or 3 and 3³⁺. After crystallization (CH₂Cl₂/pentane) at-20 C, the mixed-valence complexes 2⁺, 3⁺, and 3²⁺ were isolated in good yields (80-93%).The well-resolved separations between the redox processes in the cyclic voltammogramsenabled computation of the comproportionation constants (K_c ) and the molar fraction (xⁿ⁺)for all the species 2ⁿ⁺ (n = 0, 1, 2) and 3ⁿ⁺ (n = 0, 1, 2, 3) present in solution. The X-raycrystal structure of 2⁺ revealed that the two iron atoms are not equivalent, suggestinglocalized Fe(II) and Fe(III) sites. IR, Mössbauer, ESR, and UV-vis spectroscopies also provideevidence for localized oxidation states. Analyses of the NIR spectra showed both a forbiddenligand field transition specific to the Cp*(dppe)Fe(III) fragment and a unique ICT band forthe weakly coupled mixed-valence system 2⁺ and 3⁺ (V_ab = 161 and 143 cm^-1, respectively).In the case of the diradical trinuclear mixed-valence 3²⁺, two distinct ICT bands wereobserved and attributed to the two possible independent ways to transfer an electron in thesinglet and triplet states of such a mixed-valence compound. Density functional molecularorbital calculations provide the electronic structure of these mixed-valence systems.