Département de Chimie Moléculaire , UMR CNRS 5250, Université Grenoble Alpes , B.P. 53, 38041 Grenoble Cedex 9 , France.
Department of Chemistry , University of the Fraser Valley , Abbotsford , British Columbia V2S 7M8 , Canada.
Inorg Chem. 2018 Aug 20;57(16):9708-9719. doi: 10.1021/acs.inorgchem.8b00044. Epub 2018 Apr 4.
The sterically hindered bis(phenol)-dipyrrin ligands LH and LH were reacted with 1 equiv of copper(II) under ambient conditions to produce the copper radical complexes [Cu(L)] and [Cu(L)]. Their X-ray crystal structures show relatively short C-O bond distances (mean bond distances of 1.287 and 1.291 Å), reminiscent of mixed pyrrolyl-phenoxyl radical species. Complexes [Cu(L)] and [Cu(L)] exhibit rich electronic spectra, with an intense near-IR (NIR) band (ε > 6 mM cm) at 1346 and 1321 nm, respectively, assigned to a ligand-to-ligand charger-transfer transition. Both show a reversible oxidation wave ( E = 0.05 and 0.04 V), as well as a reversible reduction wave ( E = -0.40 and -0.56 V versus ferrocenium/ferrocene, respectively). The cations ([Cu(L)] and [Cu(L)]) and anions ([Cu(L)] and [Cu(L)]) were generated. They all display an axial ( S = /) signal with a copper hyperfine structure in their electron paramagnetic resonance spectra, consistent with ligand-centered redox processes in both reduction and oxidation. Complex Cu(L) was cocrystallized with [Cu(L)]. Oxidation is accompanied by a slight contraction of both the C-O bonds (mean bond distance of 1.280 Å) and the C-C bonds connecting the peripheral rings to the dipyrrin. The cations show vis-NIR bands of up to 1090 nm due to their quinoidal nature. The anions do not show a significant band above 700 nm, in agreement with their bis(phenolate)-dipyrrin character. The radical complexes efficiently catalyze the aerobic oxidation of benzyl alcohol, 1-phenylethanol, and unactivated 2-phenylethanol in basic conditions.
空间位阻双（苯酚）-二吡咯配体 LH 和 LH 在环境条件下与 1 当量的铜（II）反应，生成铜自由基配合物 [Cu(L)] 和 [Cu(L)]。它们的 X 射线晶体结构显示出相对较短的 C-O 键距离（平均键距离为 1.287 和 1.291 Å），类似于混合吡咯-苯氧基自由基物种。配合物 [Cu(L)] 和 [Cu(L)] 表现出丰富的电子光谱，在 1346 和 1321 nm 处分别具有强烈的近红外（NIR）带（ε>6 mM cm），归因于配体到配体的电荷转移跃迁。两者都显示出可逆的氧化波（E = 0.05 和 0.04 V），以及可逆的还原波（E = -0.40 和 -0.56 V 相对于 ferrocenium/ferrocene）。生成了阳离子([Cu(L)] 和 [Cu(L)])和阴离子([Cu(L)] 和 [Cu(L)])。它们在电子顺磁共振光谱中都显示出轴向（S = /）信号和铜超精细结构，与还原和氧化过程中的配体中心氧化还原过程一致。配合物Cu(L)与[Cu(L)]共结晶。氧化伴随着两个 C-O 键（平均键距离为 1.280 Å）和连接外围环到二吡咯的 C-C 键的轻微收缩。阳离子由于其醌型性质显示出高达 1090 nm 的可见近红外带。阴离子在 700 nm 以上没有明显的带，这与它们的双（苯氧）-二吡咯性质一致。自由基配合物在碱性条件下有效地催化苄醇、1-苯乙醇和未活化的 2-苯乙醇的有氧氧化。
