Labrum Nicholas S, Curtin Gregory M, Jakubikova Elena, Caulton Kenneth G
Department of Chemistry, Indiana University, Bloomington, Indiana, 47405, USA.
Department of Chemistry, North Carolina State University, Raleigh, North Carolina, 27695, USA.
Chemistry. 2020 Aug 3;26(43):9547-9555. doi: 10.1002/chem.202000457. Epub 2020 Jul 9.
Dimeric [CrL] , where L is the conjugate base of bis-pyrazolyl pyridine, is evaluated for its ability to undergo inner sphere and outer sphere redox chemistry. It reacts with Cp Fe to give [Cr (HL) (μ -O)] , still containing divalent Cr. Reduction (KC ) of [CrL] by two electrons gives [K (THF) Cr L (μ -O)], and by four electrons gives [K (THF) Cr L (μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K (THF) Cr L (μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L and Cr , illustrating that this pincer is proton-responsive, redox active, and a versatile donor to associated K ions here. The K electrophiles interact with electron-rich oxo, but do not significantly (>5 kcal mol ) alter spin state energies. Inner sphere oxidation of [CrL] with a quinone gives [Cr L (semiquinone) ], while pre-reduced [CrL] reacts with quinone to give [K (THF) Cr L (catecholate) (μ-OH)], a product of capture of two undercoordinated LCr(catecholate) by hydroxide.
二聚体[CrL]（其中L是双吡唑基吡啶的共轭碱）因其进行内球和外球氧化还原化学的能力而受到评估。它与Cp Fe反应生成[Cr(HL)(μ -O)]，其中仍含有二价铬。用两个电子还原[CrL]（KC）得到[K(THF)Cr L(μ -O)]，用四个电子还原得到[K(THF)Cr L(μ -O)]，由于配位不足的铬具有亲电性，它们各自从玻璃表面清除了（氢）氧化物。通过全面的DFT计算和配体内键长分析表明，[K(THF)Cr L(μ -O)]包含一个吡啶基自由基L和Cr，这表明这种钳形配体对质子有响应、具有氧化还原活性，并且在此处是与相关钾离子结合的多功能供体。钾亲电试剂与富电子的氧相互作用，但不会显著（>5 kcal mol）改变自旋态能量。用醌对[CrL]进行内球氧化得到[Cr L(半醌)]，而预先还原的[CrL] 与醌反应得到[K(THF)Cr L(儿茶酚)(μ -OH)]，这是两个配位不足的LCr(儿茶酚)被氢氧化物捕获的产物。
