Harkins Seth B, Peters Jonas C
Contribution from the Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, USA.
J Am Chem Soc. 2004 Mar 10;126(9):2885-93. doi: 10.1021/ja037364m.
A novel Cu(2)N(2) diamond core structure supported by an SNS ligand (1) (SNS = bis(2-tert-butylsulfanylphenyl)amido) has been prepared. This dicopper system exhibits a fully reversible one-electron redox process between a reduced Cu(1)Cu(1) complex, [SNS][Cu] (2), and a class III delocalized Cu(1.5)Cu(1.5) state, [[SNS][Cu]][B(3,5-(CF(3))(2)C(6)H(3))(4)] (3). Structural snapshots of both redox forms have been obtained to reveal remarkably little overall structural reorganization. The Cu...Cu bond distance nonetheless undergoes an appreciable compression (approximately 0.13 A) upon oxidation, providing a Cu...Cu distance of 2.4724(4) A in the mixed-valence state that is virtually identical to the Cu...Cu distance observed in the reduced form of the Cu(A) site of thiolate-bridged cytochrome c oxidase. Despite the low structural reorganization evident between 2 and 3, the SNS ligand is quite flexible. For example, square-planar geometries can prevail for divalent copper ions supported by SNS as evident from the crystal structure of [SNS]CuCl (4). Physical characterization for the mixed valence complex 3 includes electrochemical, magnetic (SQUID), EPR, and optical data. The complex has also been examined by density functional methods. An attempt was made to measure the rate of electron self-exchange k(s) between the Cu(1)Cu(1) and the Cu(1.5)Cu(1.5) complexes 2 and 3 by NMR line-broadening analysis in dichloromethane solution. While the system is certainly in the fast-exchange regime, the exchange process is too fast to be accurately measured by this technique. The value for k(s) can be bracketed with a conservative lower boundary of > or =10(7) M(-1) s(-1), a value that appears to be larger than other low molecular weight copper model complexes for which similar data is available. The unusually large magnitude of k(s) likely reflects the minimal structural reorganization that accompanies Cu(1)Cu(1) <--> Cu(1.5)Cu(1.5) interchange.
已制备出一种由[SNS]⁻配体（1）（[SNS]⁻ = 双（2 - 叔丁基硫苯基）酰胺）支撑的新型Cu₂N₂金刚石核结构。这种二铜体系在还原态的Cu(Ⅰ)Cu(Ⅰ)配合物[[SNS][Cu]]₂（2）与Ⅲ类离域的Cu₁.₅Cu₁.₅态[[[SNS][Cu]]₂][B(3,5-(CF₃)₂C₆H₃)₄]（3）之间呈现出完全可逆的单电子氧化还原过程。已获得两种氧化还原形式的结构快照，以揭示总体结构重排非常少。然而，Cu…Cu键距在氧化时会发生明显压缩（约0.13 Å），在混合价态下提供了2.4724(4) Å的Cu…Cu距离，这与在硫醇盐桥连细胞色素c氧化酶的Cu(A)位点还原形式中观察到的Cu…Cu距离几乎相同。尽管在2和3之间明显存在低结构重排，但[SNS]⁻配体相当灵活。例如，由[SNS]⁻支撑的二价铜离子可以呈现平面正方形几何构型，这从[SNS]CuCl（4）的晶体结构中可以明显看出。混合价配合物3的物理表征包括电化学、磁性（超导量子干涉仪）、电子顺磁共振和光学数据。该配合物也已通过密度泛函方法进行研究。尝试通过二氯甲烷溶液中的核磁共振线宽分析来测量Cu(Ⅰ)Cu(Ⅰ)和Cu₁.₅Cu₁.₅配合物2和3之间的电子自交换速率kₛ。虽然该体系肯定处于快速交换区域，但交换过程太快以至于无法通过该技术准确测量。kₛ的值可以用保守的下限≥10⁷ M⁻¹ s⁻¹来界定，该值似乎比其他可获得类似数据的低分子量铜模型配合物的值要大。kₛ异常大的数值可能反映了伴随Cu(Ⅰ)Cu(Ⅰ)⇌Cu₁.₅Cu₁.₅互换的最小结构重排。
