Perturbing the Copper(III)-Hydroxide Unit through Ligand Structural Variation.
Perturbing the Copper(III)-Hydroxide Unit through Ligand Structural Variation.
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DOI：
10.1021/jacs.5b10985
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发表时间：
2016-01-13
影响因子：
15
通讯作者：
Tolman WB
中科院分区：
文献类型：
--
作者：
Dhar D;Yee GM;Spaeth AD;Boyce DW;Zhang H;Dereli B;Cramer CJ;Tolman WB
两个新的配体组，pipMeLH 2和NO2 LH 2（pipMeL = N，N′-双（2，6-二异丙基苯基）-1-甲基哌啶-2，6-二甲酰胺，NO 2L = N，N′-双（2，6-二异丙基-4-硝基苯基）吡啶-2，6-二甲酰胺），报道了旨在扰乱氢氧化铜（III）核心的整体电子学以及对其氢原子夺取（HAT）的热力学和动力学产生的影响反应.键离解能（BDEs）的O-H键的相应的Cu（II）-OH 2配合物进行了测量，揭示了在氧化还原电位的变化的Cu（III）/Cu（II）对只有部分抵消相反的变化pKa，导致适度的差异BDE之间的三种化合物。这些变化的影响，进一步探讨通过评估HAT率由相应的Cu（III）-氢氧化物配合物从基板与C-H键的可变强度。这些研究揭示了log k（其中k为二级速率常数）与反应ΔH之间的关系呈总体线性趋势。然而，测量速率中的其他微妙之处与氢原子提取势垒高度和隧穿效率在−80 ° C至−20 °C温度范围内的变化有关，这是从测量的动力学同位素效应和相应的基于电子结构的过渡态理论计算推断的。
Two new ligand sets, pipMeLH2 and NO2LH2 (pipMeL = N,N′-bis(2,6-diisopropylphenyl)-1-methylpiperidine-2,6-dicarboxamide, NO2L = N,N′-bis(2,6-diisopropyl-4-nitrophenyl)pyridine-2,6-dicarboxamide), are reported which are designed to perturb the overall electronics of the copper(III)–hydroxide core and the resulting effects on the thermodynamics and kinetics of its hydrogen-atom abstraction (HAT) reactions. Bond dissociation energies (BDEs) for the O–H bonds of the corresponding Cu(II)–OH2 complexes were measured that reveal that changes in the redox potential for the Cu(III)/Cu(II) couple are only partially offset by opposite changes in the pKa, leading to modest differences in BDE among the three compounds. The effects of these changes were further probed by evaluating the rates of HAT by the corresponding Cu(III)–hydroxide complexes from substrates with C–H bonds of variable strength. These studies revealed an overarching linear trend in the relationship between the log k (where k is the second-order rate constant) and the ΔH of reaction. Additional subtleties in measured rates arise, however, that are associated with variations in hydrogen-atom abstraction barrier heights and tunneling effciencies over the temperature range from −80 to −20 °C, as inferred from measured kinetic isotope effects and corresponding electronic-structure-based transition-state theory calculations.