Tanaka Koji, Kushi Yoshinori, Tsuge Kiyoshi, Toyohara Kiyotsuna, Nishioka Takanori, Isobe Kiyoshi
Institute for Molecular Science, Myodaiji, Okazaki 444, Japan, and Department of Material Science, Faculty of Science, Osaka City University, Sugimotochou, Sumiyoshi-ku, Osaka 558, Japan.
Inorg Chem. 1998 Jan 12;37(1):120-126. doi: 10.1021/ic9702328.
Electrochemical reduction of (Ir(eta(5)-C(5)Me(5)))(3)(&mgr;(3)-S)(2)(2) (Ir(3)S(2)(2)) in CO(2)-saturated CH(3)CN at -1.30 V (vs Ag/AgCl) produced C(2)O(4)(2)(-) and (Ir(eta(5)-C(5)Me(5)))(2)(Ir(eta(4)-C(5)Me(5))CH(2)CN)(&mgr;(3)-S)(2) (Ir(3)S(2)CH(2)CN). The crystal structure of Ir(3)S(2)CH(2)CN by X-ray analysis revealed that a linear CH(2)CN group is linked at the exo-position of a C(5)Me(5) ligand, and the C(5)Me(5)CH(2)CN ligand coordinates to an Ir atom with an eta(4)-mode. The cyclic voltammogram of Ir(3)S(2)CH(2)CN in CH(3)CN under CO(2) exhibited a strong catalytic current due to the reduction of CO(2), while that of Ir(3)S(2) did not show an interaction with CO(2) in the same solvent. The reduced form of Ir(3)S(2)CH(2)CN works as the active species in the reduction of CO(2). The IR spectra of Ir(3)S(2)CH(2)CN in CD(3)CN showed a reversible adduct formation with CO(2) and also evidenced the oxalate generation through the reduced form of the CO(2) adduct under the controlled potential electrolysis of the solution at -1.55 V. A coupling reaction of two CO(2) molecules bonded on adjacent &mgr;(3)-S and Ir in Ir(3)S(2)CH(2)CN is proposed for the first catalytic generation of C(2)O(4)(2)(-) without accompanying CO evolution.
在 -1.30 V（相对于 Ag/AgCl）下，(Ir(η⁵-C₅Me₅))₃(μ₃-S)₂₂（Ir₃S₂₂）在 CO₂ 饱和的 CH₃CN 中进行电化学还原，生成了 C₂O₄²⁻ 和 [(Ir(η⁵-C₅Me₅))₂(Ir(η⁴-C₅Me₅)CH₂CN)(μ₃-S)₂]⁺（[Ir₃S₂CH₂CN]⁺）。通过 X 射线分析得到的 Ir₃S₂CH₂CN 的晶体结构表明，一个线性的 CH₂CN 基团连接在一个 C₅Me₅ 配体的外位，并且 C₅Me₅CH₂CN 配体以 η⁴ 模式与一个 Ir 原子配位。在 CO₂ 存在下，[Ir₃S₂CH₂CN]⁺ 在 CH₃CN 中的循环伏安图显示出由于 CO₂ 还原而产生的强催化电流，而 [Ir₃S₂]²⁺ 在相同溶剂中未显示出与 CO₂ 的相互作用。[Ir₃S₂CH₂CN]⁺ 的还原形式在 CO₂ 还原中作为活性物种起作用。[Ir₃S₂CH₂CN]⁺ 在 CD₃CN 中的红外光谱显示与 CO₂ 形成可逆加合物，并且还证明了在 -1.55 V 对溶液进行控制电位电解时，通过 CO₂ 加合物的还原形式生成草酸盐。首次提出在 [Ir₃S₂CH₂CN]⁰ 中，两个键合在相邻 μ₃-S 和 Ir 上的 CO₂ 分子发生偶联反应，用于催化生成 C₂O₄²⁻ 而不伴随 CO 释放。
