Synthesis and Properties of Oxo-carboxylato- and Dioxo-Bridged Diosmium Complexes of Tris(2-pyridylmethyl)amine

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• 作者：Hideki Sugimoto ; Kazuhiro Kitayama ; Kenji Ashikari ; Chikako Matsunami ; Naomi Ueda ; Keisuke Umakoshi ; Yuko Hosokoshi ; Yoichi Sasaki ; Shinobu Itoh
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：September 19, 2011
• 年：2011
• 卷：50
• 期：18
• 页码：9014-9023
• 全文大小：1009K
• 年卷期：v.50,no.18(September 19, 2011)
• ISSN：1520-510X

文摘

A series of oxo-bridged diosmium complexes with tpa ligand (tpa = tris(2-pyridylmethyl)amine) are synthesized. The hydrolytic reaction of the mononuclear osmium complex [Os^IIICl₂(tpa)]PF₆ in aqueous solution containing a sodium carboxylate yields a 渭-oxo-渭-carboxylato-diosmium(III) complex, [Os^III₂(渭-O)(渭-RCOO)(tpa)₂](PF₆)₃ (R = C₃H₇ (1), CH₃ (2), or C₆H₅ (3)). One-electron oxidation of 1 with (NH₄)₂Ce^IV(NO₃)₆ gives a mixed-valent [Os^IIIOs^IV(渭-O)(渭-C₃H₇COO)(tpa)₂](PF₆)₄ complex (4). A mixed-valent di-渭-oxo-diosmium complex, [Os^IIIOs^IV(渭-O)₂(tpa)₂](PF₆)₃ (5), is also synthesized from 1 in an aerobic alkaline solution (pH 13.5). All the complexes exhibit strong absorption bands in a visible鈥搉ear-infrared region based on interactions of the osmium d蟺 and oxygen p蟺 orbitals of the Os鈥揙鈥揙s moiety. The X-ray crystallographic analysis of 1, 3, and 4 shows that the osmium centers take a pseudo-octahedral geometry in the 渭-oxo-渭-carboxylato-diosmium core. The mixed-valent osmium(III)osmium(IV) complex 4 has a shorter osmium鈥搊xo bond and a larger osmium鈥搊xo鈥搊smium angle as compared with those of the diosmium(III) complex 1 having the same bridging carboxylate. Crystal structure of 5 reveals that the two osmium ions are bridged by two oxo groups to give an Os₂(渭-O)₂ core with the significantly short osmium鈥搊smium distance (2.51784(7) 脜), which is indicative of a direct osmium鈥搊smium bond formation with the bond order of 1.5 (蟽²蟺²未²未*²蟺*¹ configuration). In the electrochemical studies, the 渭-oxo-渭-carboxylato-diosmium(III) complexes exhibit two reversible Os^IIIOs^III/Os^IIIOs^IV and Os^IIIOs^IV/Os^IVOs^IV oxidation couples and one irreversible redox wave for the Os^IIIOs^III/Os^IIOs^III couple in CH₃CN. The irreversible reductive process becomes reversible in CH₃CN/H₂O (1:1 Britton鈥揜obinson buffer; pH 5鈥?1), where the {1H⁺/2e^{鈥?/sup>} transfer process is indicated by the plot of the redox potentials against the pH values of the solution of 1. Thus, the 渭-oxo-渭-butyrato-diosmium(III) center undergoes proton-coupled electron transfer to yield a 渭-hydroxo-渭-butyrato-diosmisum(II) species. The di(渭-oxo) complex 5 exhibits one reversible OsIIIOsIV/OsIVOsIV oxidation process and one reversible OsIIIOsIV/OsIIIOsIII reduction process in CH₃CN. The comproportionation constants K_com of the OsIIIOsIV states for the present diosmium complexes are on the order of 1019. The values are significantly larger when compared with those of similar oxo-bridged dimetal complexes of ruthenium and rhenium.}