Le Gendre Pierre, Comte Virginie, Ondel-Eymin Marie-Joëlle, Moïse Claude, Pousson Eveline, Richard Philippe, Mugnier Yves, Fortin Daniel, Boeré René T, Harvey Pierre D
Institut de Chimie Moléculaire de l'Université de Bourgogne UMR CNRS 5260, Faculté des Sciences Mirande, 9 avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France.
Inorg Chem. 2009 Apr 6;48(7):3095-103. doi: 10.1021/ic8023869.
The heterotrinuclear complexes, (CpTiCl(2)Cp-PPh(2))(2)Cu (2) (as PF(6)(-) salt) and CpTiCl(2)Cp-PPh(2)CuCl (3), containing two electron-poor Ti(IV) fragments and one electron-rich Cu(I) center, and a tetrametallic species, (CpTiCl(2)Cp-PPh(2))Cu(mu-Cl) (4), were synthesized and characterized. The trinuclear nature of 2 and 3 was demonstrated by X-ray crystallography for which the three metallic centers are held together by two CpPPh(2) ligands. Weak Cl...Cu interactions are noted in 3, whereas two stronger Cl-Cu bridges are depicted in the cationic complex 2. The tetranuclear complex 4 contains two Cu atoms bridged together by two chloride ligands and connected to one Ti atom by one CpPPh(2) ligand and one mu-Cl ligand. Despite the short distances in the Ti-Cl-Cu bridges, notably in 2 and 4, the NMR spectra reveals evidence of fluxion in solution attributed to the lability of the mu-Cl ligands. Electrochemical experiments performed on 2 (rotating disk electrode and cyclic voltammograms) demonstrated the presences of two successive 1-electron reductions generating a first structurally unsymmetrical paramagnetic species (CpTiCl(2)Cp-PPh(2))(2)Cu (2'), confidently characterized by electron paramagnetic resonance (EPR) as a Ti(III)-Cu(I)-Ti(IV) system, and a second one, which is tentatively assigned to a symmetric neutral complex formulated as CpTiClCp-PPh(2)CuCl (5) with an EPR signature indistinguishable from that of 2' (i.e., Ti(III)-Cu(I)-Ti(III) system with a similar electronic environment). Density functional theory (DFT) computations examining the nature of the frontier orbitals and the geometry confirmed the presence and lack of symmetry in 2 and 2', respectively. The detection of chemical/electrochemical mechanisms in the electrochemical studies provides a clear explanation for the stepwise reduction behavior in these systems through chloride ligand transfer from Ti to Cu prior to the first reduction step. This transfer process is fully reversible upon re-oxidation. The electrochemical properties of complexes 3 and 4 are also reported.
合成并表征了异三核配合物[（CpTiCl₂Cp - PPh₂）₂Cu]⁺（2，作为PF₆⁻盐）和[CpTiCl₂Cp - PPh₂]₂CuCl（3），它们含有两个贫电子的Ti（IV）片段和一个富电子的Cu（I）中心，以及一个四金属物种[（CpTiCl₂Cp - PPh₂）Cu（μ - Cl）]₂（4）。通过X射线晶体学证明了2和3的三核性质，其中三个金属中心通过两个CpPPh₂配体连接在一起。在3中注意到弱的Cl...Cu相互作用，而在阳离子配合物2中描绘了两个更强的Cl - Cu桥。四核配合物4包含两个通过两个氯配体桥连在一起的Cu原子，并通过一个CpPPh₂配体和一个μ - Cl配体与一个Ti原子相连。尽管在Ti - Cl - Cu桥中距离较短，特别是在2和4中，但NMR光谱揭示了溶液中存在由于μ - Cl配体的不稳定性导致的通量现象。对2进行的电化学实验（旋转圆盘电极和循环伏安图）表明存在两个连续的1电子还原过程，生成第一个结构不对称的顺磁性物种[（CpTiCl₂Cp - PPh₂）₂Cu]⁰（2'），通过电子顺磁共振（EPR）可靠地表征为Ti（III） - Cu（I） - Ti（IV）体系，以及第二个，暂定为对称中性配合物，化学式为[CpTiClCp - PPh₂]₂CuCl（5），其EPR特征与2'无法区分（即具有相似电子环境的Ti（III） - Cu（I） - Ti（III）体系）。研究前沿轨道性质和几何结构的密度泛函理论（DFT）计算分别证实了2和2'中对称性的存在和缺失。电化学研究中化学/电化学机制的检测为这些体系中的逐步还原行为提供了清晰的解释，即通过在第一个还原步骤之前氯配体从Ti转移到Cu。这种转移过程在再氧化时是完全可逆的。还报道了配合物3和4的电化学性质。
