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[Co_3Cp_3(Mu_3-CPH)_2{muAg(X)}](X=Cf_3CO_2-(2)，NO_3-(3))的银(I)加合物。由Ag原子桥联的Co-Co键比1(2.38)长。2和3在Cd_2Cl_2中的1H核磁共振谱表明AgX基团部分解离。Cd_3CN溶液的~1H核磁共振谱和冰冻的CH_3CN溶液中的ESR谱表明，1~+离子的生成没有沉积金属银。结果表明，在乙腈中，Ag^+、1与Ag^0、1^+建立平衡，在CH2Cl2中，I与卤素(X_2=Cl2、Br2、I2)反应生成卤素桥联络合物{Co3Cp3(mu3-CPH)2(MuX)]^+。卤素桥联的Co-Co距离延长，无卤桥的Co-Co距离与1(2.38“A”)保持不变。[Co_3Cp_3(Mu_3-CPH)_2(Mu-Cl)]PF_6在0.1MnBu_4NPF_6底液中的循环伏安曲线显示一个不可逆的还原峰(-0.49V vs Fc/Fc~+)。为探讨卤素桥联络合物的形成机理，用循环伏安法研究了1在0.1MnBu_4NC]/CH_3CN体系中的反应。在100 mVS~(-1)扫描速率下，在与1在0.1Mn-Bu_4NPF_4/CH_3CN中的准可逆氧化相同的EPA值下观察到不可逆氧化波，其电流值是0.1Mn-Bu_4NPF_6/CH_3CN的1.3倍，并在-0.46V与Fc/Fc^+处出现一个新的不可逆还原峰，对应于[Co_3Cp_3(Mu_3-CPH)_2(Mu-Cl)]^+的还原。当扫描速度为500 MVS^~(-1)~(-1)时，氧化峰的电流值与0.1M_n-Bu_4NPF_6/CH_3CN的氧化峰电流非常接近，在-0.09V与Fc/Fc^+处有一个较小的还原峰，这是由于[Co3Cp_3(Mu_3-CPH)_2]~+被还原所致。结果表明，1的氧化遵循氯离子的配位，并立即氧化成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^+.