Redox process of Group 9 trimetal cluster complexes

[Co_3Cp_3（mu_3-CPh）_2]（1）与强配位阴离子（CF_3CO_2-，NO_3-）的盐反应，得到1的银（I）加合物[Co_3Cp_3（mu_3-CPh）_2{muAg（X）}]（X= CF_3CO_2-（2），NO_3-（3））。Ag原子桥连的Co-Co键比1（2.38）长。2和3在CD_2Cl_2中的^1HNMR谱表明AgX基团部分解离。CD_3CN溶液的^1H NMR谱和化合物2和3在冷冻CH_3CN溶液中的ESR谱表明，在没有Ag金属沉积的情况下，产生了1^+。在乙腈中，Ag^+和I与Ag^0和I ^+建立了平衡，I与卤素（X_2 = Cl_2，Br_2，I_2）在CH_2Cl_2中反应生成卤素桥联配合物{Co_3Cp_3（mu_3-CPh）_2（mu-X）]^+。卤素桥连的Co-Co距离被拉长，而没有卤素桥连的Co-Co距离与1（2.38“A”）相比没有变化。[Co_3Cp_3（mu_3-CPh）_2（mu-Cl）]PF_6在乙腈中以0.1 M n-Bu_4 NPF_6为支持电解质的循环伏安图显示一个不可逆还原波（-0.49 V vsFc/Fc^+）。不可逆的减少导致恢复1。为了研究卤桥络合物的形成机理，用循环伏安法研究了1在0.1 M n-Bu_4 NC]/CH_3CN中的电化学行为。在100 mVs/s<-1>扫描速率下，在0.1 Mn-Bu_4 NPF_4/CH_3CN中，在与1的准可逆氧化相同的Epa值处观察到不可逆氧化波，波的电流值是0.1 Mn-Bu_4 NPF_6/CH_3CN中的1.3倍，在-0.46 VvsFc/Fc^+处出现一个新的不可逆还原峰，对应于[Co_3Cp_3]的还原（mu_3-CPh）_2（mu-Cl）]^+。当扫描速度为500 mVs^时<-1>，氧化峰的电流值与0.1 M n-Bu_4 NPF_6/CH_3CN中的氧化峰非常相似，在-0.09 V vsFc/Fc^+处有一个小的还原峰，这是由于[Co_3Cp_3（mu_3-CPh）_2]^+的还原所致。结果表明，1的氧化反应是先与Cl^-配位，然后立即氧化为2^+。

Reaction of [Co_3Cp_3 (mu_3-CPh)_2] (1) with the salts of strongly-coordinating anions (CF_3CO_2-, NO_3-) gives silver (I) adducts of 1, [Co_3Cp_3(mu_3-CPh)_2{muAg(X)}] (X= CF_3CO_2- (2), NO_3- (3)). The Co-Co bonds bridged by the Ag atom are longer than that of 1 (2.38). ^1HNMR spectra of 2 and 3 in CD_2Cl_2 indicates partial dissociation of the AgX group. The ^1H NMR spectra of CD_3CN solutions and the ESR spectra in frozen CH_3CN solutions of 2 and 3 shows generation of 1^+ without deposition of Ag metal. It suggests that equilibrium of Ag^+ and 1 with Ag^0 and 1^+ is established in acetonitrile.Reaction of I with halogens (X_2 = Cl_2, Br_2, I_2) in CH_2Cl_2 gives halogen-bridged complex {Co_3Cp_3(mu_3-CPh)_2(mu-X)]^+. The halogen-bridged Co-Co distance is elongated and the Co-Co distances without halogen-bridge remaine unchanged from that of 1 (2.38"A"). Cyclic voltammogram of [Co_3Cp_3(mu_3-CPh)_2(mu-Cl)]PF_6 in CH_3CN with 0.1 M n-Bu_4NPF_6 as supporting electrolyte shows an irreversible reduction wave (-0.49 V vs Fc/Fc^+). The irreversible reduction causes recovery of 1. To examine the mechanism of formation of the halogen-bridged complex, cyclic voltammetry of 1 in 0.1 M n-Bu_4NC]/CH_3CN is carried out. At 100 mVs^<-1> scan rate the irreversible oxidation waveis observed at the same Epa value as the quasi-reversible oxidation of 1 in 0.1 Mn-Bu_4NPF_4/CH_3CN.The current value of the wave is 1.3 times bigger than that in 0.1 M n-Bu_4NPF_6/CH_3CN and a new irreversible reduction peak is appeared at -0.46 V vs Fc/Fc^+ that is corresponding to reduction of [Co_3Cp_3(mu_3-CPh)_2(mu-Cl)]^+. When the scan speed is 500 mVs^<-1>, the current value of the oxidation peak is very similar to that in 0.1 M n-Bu_4NPF_6/CH_3CN and the small reduction peak at -0.09 V vs Fc/Fc^+ which was due to the reduction of [Co_3Cp_3(mu_3-CPh)_2]^+. It indicated that the oxidation of 1 follows coordination of Cl^- and immediate oxidation to 2^+.