Deibel Naina, Hohloch Stephan, Schweinfurth David, Weisser Fritz, Grupp Anita, Sarkar Biprajit
Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart (Germany).
Chemistry. 2014 Nov 10;20(46):15178-87. doi: 10.1002/chem.201403276. Epub 2014 Sep 22.
Reversible proton- and electron-transfer steps are crucial for various chemical transformations. The electron-reservoir behavior of redox non-innocent ligands and the proton-reservoir behavior of chemically non-innocent ligands can be cooperatively utilized for substrate bond activation. Although site-decoupled proton- and electron-transfer steps are often found in enzymatic systems, generating model metal complexes with these properties remains challenging. To tackle this issue, we present herein complexes [(cod-H)M(μ-L(2-)) M(cod-H)] (M = Pt(II), [1] or Pd(II), [2], cod = 1,5-cyclooctadiene, H2L = 2,5-di-[2,6-(diisopropyl)anilino]-1,4-benzoquinone), in which cod acts as a proton reservoir, and L(2-) as an electron reservoir. Protonation of [2] leads to an unusual tetranuclear complex. However, [1] can be stepwise reversibly protonated with up to two protons on the cod-H ligands, and the protonated forms can be stepwise reversibly reduced with up to two electrons on the L(2-) ligand. The doubly protonated form of [1] is also shown to react with OMe(-) leading to an activation of the cod ligands. The site-decoupled proton and electron reservoir sources work in tandem in a three-way cooperative process that results in the transfer of two electrons and two protons to a substrate leading to its double reduction and protonation. These results will possibly provide new insights into developing catalysts for multiple proton- and electron-transfer reactions by using metal complexes of non-innocent ligands.
可逆的质子和电子转移步骤对于各种化学转化至关重要。氧化还原非无辜配体的电子储存行为和化学非无辜配体的质子储存行为可以协同用于底物键的活化。尽管在酶系统中经常发现位点解耦的质子和电子转移步骤，但生成具有这些性质的模型金属配合物仍然具有挑战性。为了解决这个问题，我们在此展示配合物[(cod-H)M(μ-L(2-)) M(cod-H)]（M = Pt(II)，[1]或Pd(II)，[2]，cod = 1,5-环辛二烯，H2L = 2,5-二-[2,6-(二异丙基)苯胺基]-1,4-苯醌），其中cod作为质子储存体，L(2-)作为电子储存体。[2]的质子化导致一种不寻常的四核配合物。然而，[1]可以在cod-H配体上逐步可逆地质子化，最多可接受两个质子，并且质子化形式可以在L(2-)配体上逐步可逆地还原，最多可接受两个电子。[1]的双质子化形式也显示与OMe(-)反应，导致cod配体的活化。位点解耦的质子和电子储存源在一个三向协同过程中协同工作，导致两个电子和两个质子转移到底物上，使其发生双还原和质子化。这些结果可能会为利用非无辜配体的金属配合物开发用于多质子和电子转移反应的催化剂提供新的见解。
