Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV–Vis/ATR‐IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas‐Liquid Phase Reactions
Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV–Vis/ATR‐IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas‐Liquid Phase Reactions
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DOI：
10.1002/chem.202000436
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发表时间：
2020-03
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通讯作者：
J. Rabeah;V. Briois;S. Adomeit;C. La Fontaine;U. Bentrup;A. Brückner
中科院分区：
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作者：
J. Rabeah;V. Briois;S. Adomeit;C. La Fontaine;U. Bentrup;A. Brückner
首次将OPANDO EPR、XANES/EXAFS、UV-Vis和ATR-IR光谱方法在相同的实验装置上联用，用于研究铜/TEMPO催化体系(TEMPO=2，2，6，6-四甲基哌啶氧基)选择性好氧氧化苯甲醇的未知机理。通过同时记录的XAS和UV-Vis数据的多元曲线分辨和交替最小二乘拟合，发现最初形成的(Bpy)(Nmi)CuI络合物(bpy=2，2‘-联吡啶，nmi=N-甲基咪唑)被转化为两种不同的CuII物种，一种是EPR和ESI-MS可检测到的单核(Bpy)(Nmi)(CH3CN)CuII-OOH，另一种是EPR沉默的双核(Ch3CN)(Bpy)(Nmi)II(μ-OH)2⋅CuII(Bpy)(NMI)。后者在进一步的反应过程中被切割成(BPY)(NMI)(HOO)CuII-TEMPO单体，由于与结合TEMPO的偶极相互作用，这些单体也是EPR沉默的。铜单体和铜二聚体在反应的初始阶段都具有催化活性，但二聚体既不是主要的活性物种，也不是休眠状态，因为它在反应过程中被不可逆地裂解，同时保持了催化活性。在延长的反应时间内，不可还原的CuII的逐渐形成导致轻微的失活。
Abstract Operando EPR, XANES/EXAFS, UV‐Vis and ATR‐IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6‐tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least‐squares fitting (MCR‐ALS) of simultaneously recorded XAS and UV‐Vis data sets, it was found that an initially formed (bpy)(NMI)CuI‐ complex (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole ) is converted to two different CuII species, a mononuclear (bpy)(NMI)(CH3CN)CuII‐OOH species detectable by EPR and ESI‐MS, and an EPR‐silent dinuclear (CH3CN)(bpy)(NMI)CuII(μ‐OH)2 ⋅CuII (bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)CuII‐TEMPO monomers that are also EPR‐silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non‐reducible CuII leads to slight deactivation at extended reaction times.