3d Element Complexes of Pentadentate Bipyridine-Pyridine-Based Ligand Scaffolds: Structures and Photocatalytic Activities

The synthesis of the two penta-pyridyl
type ligands pyridine-2,6-diylbis­(dipyridin-2-ylmethanol) (PPy, 1) and bis-2,2′'-bipyridine-6-yl­(pyridine-2-yl)­methanol
(aPPy, 2) is described. Both ligands coordinate rapidly
to the 3d element cations MnII, FeII, CoII, NiII, CuII, and ZnII,
thereby yielding complexes of the general composition [MBr­(1)]+ and [MBr­(2)]+, respectively.
Further, the X-ray structures of selected complexes with ligands 1 and 2 are described. They show metal center
dependent structural features and complexes with 2 exhibiting
distinctly distorted octahedral geometries. Moreover, photocatalytic
water reduction with [CoIIBr­(PPy)]Br (1c)
and [CoIIBr­(aPPy)]Br (2c) as water reducing
catalysts (WRC) was investigated. Both complexes showed catalytic
activity in water when in presence of ascorbic acid as sacrificial
electron donor and [Re­(py)­(bpy)­(CO)3]+ (3) as photosensitizer (PS). Turnover numbers, TONs (H2/Co), up to 11 000 were achieved. Complex 2c was more active than 1c, whereas none of the other
complexes showed any activity.

本文报道了两种五吡啶类配体——吡啶-2,6-二基二(二吡啶-2-基甲醇)（PPy, 1）与双-2,2′'-联吡啶-6-基(吡啶-2-基)甲醇（aPPy, 2）的合成。两种配体均可与3d族金属阳离子（二价锰MnII、二价铁FeII、二价钴CoII、二价镍NiII、二价铜CuII及二价锌ZnII）快速配位，分别得到通式为[MBr(1)]+和[MBr(2)]+的配合物。此外，本文还对配体1和2的部分代表性配合物的X射线晶体结构进行了表征，结果显示其结构特征依赖于金属中心；其中含配体2的配合物呈现出显著畸变的八面体几何构型。以[CoIIBr(PPy)]Br（1c）和[CoIIBr(aPPy)]Br（2c）作为水还原催化剂（WRC）开展了光催化水还原反应研究：当以抗坏血酸作为牺牲电子给体、[Re(py)(bpy)(CO)3]+（3）作为光敏剂（PS）时，两种配合物均在水相体系中表现出催化活性，其转化数（TONs，H2/Co）最高可达11000，且配合物2c的催化活性优于1c；其余配合物均未表现出催化活性。