Construction of Reaction Center by Reductive Cleavage of Metal-Metal Bonds

[（MC_p^**&gt;）_3（μ 3-S）_2]（BPh_4）_2（M=Co，Rh）催化CO_2的电化学还原，<2->在均相体系中选择性地生成了草酸根的第一个例子C_2O_4 ~（2-）。在[（IrC_p^**&gt;）_3（mu 3-S）_2]（BPh_4）_2（[Ir_3S_2]（BPh_4）_2）存在下，在-1.30V（vs.Ag/AgCl）的CH_3CN溶液中，CO_2的类似电化学还原也产生了C_2O_4^<2->，电流效率为60%，但[（IrC_p^**&gt;）_2（Ir-eta^<4->Cp^**&gt;CH_2CN）（mu 3-S）_2]^+（[Ir_3S_2CH_2CN]^+）从电解质溶液中分离出来。[Ir_3S_2CH_2CN]（BPh_4）的晶体结构表明，在Cp^**&gt;配体的外位上连接了一个线性的CH_2CN基团，Cp^**&gt;CH_2CN基团以η ^模式与Ir原子配位<4->。[Ir_3S_2CH_2CN]^+在CH_3CN中的循环伏安图显示出很强的催化电流，这是由于CO_2的还原，而[Ir_3S_2]^&lt;2+&gt;在相同的溶剂中没有显示出与CO_2的相互作用。因此，[Ir_3S_2CH_2CN]^+的还原态在CO_2的还原过程中起着活性物种的作用。[Ir_3S_2CH_2CN]^+在CD_3CN中与CO_2形成可逆加合物。[Ir_3S_2CH_2CN]^+在-1.50V的CO_2条件下的控制电位电解证明了[Ir_3S_2CH_2CN<2->]^+与CO_2之间通过1：2的加合物生成C_2O_4^+。本文提出了在Ir_3S_2CH_2CN]^0中两个CO_2分子在相邻μ_3-S和Ir上活化的偶联反应首次选择性生成C_2O_4^<2->。

Electrochemical reduction of CO_2 catalyzed by [(MC_p^<**>) _3 (mu3-S)_2] (BPh_4)_2 (M=Co, Rh) selectively produced C_2O_4^<2-> as the first example of oxalate formation in homogeneous syatem and the original trinuclear clusters are recovered intact after the electrolysis. Similar electrochemical reduction of CO_2 in the presence of [(IrC_p^<**>)_3 (mu3-S)_2] (BPh_4)_2 ([Ir_3S_2] (BPh_4)_2) in CH_3CN at -1.30V (vs.Ag/AgCl) also produced C_2O_4^<2-> with a current efficiency of 60%, but [(IrC_p^<**>)_2 (Ir-eta^<4->Cp^<**>CH_2CN) (mu3-S)_2]^+ ([Ir_3S_2CH_2CN]^+) was isolated from the electrolyte solution. The crystal structure of [Ir_3S_2CH_2CN] (BPh_4) by X-ray analysis revealed that a linear CH_2CN group is linked at the exo-position of a Cp^<**> ligand, and the Cp^<**>CH_2CN group coordinates to an Ir atom with an eta^<4->mode. The cyclic voltammongram of [Ir_3S_2CH_2CN]^+ in CH_3CN under CO_2 exhibited a strong catalytic current due to the reduction of CO_2, while that of [Ir_3S_2]^<2+> did not show an interaction with CO_2 in the same solvent. Thus, the reduced form of [Ir_3S_2CH_2CN]^+ works as the active species in the reduction of CO_2. The IR spectra of [Ir_3S_2CH_2CN]^+ in CD_3CN showed a reversible adduct formation with CO_2. The controlled potential electrolysis of [Ir_3S_2CH_2CN]^+ at -1.50V under CO_2 evidenced the generation of C_2O_4^<2-> through a 1 : 2 adduct between [Ir_3S_2CH_2CN]^0 and CO_2. A coupling reaction of two CO_2 molecules activated on adjacent mu3-S and Ir in Ir_3S_2CH_2CN]^0 is proposed for the first selective generation of C_2O_4^<2->.