Walvoord Ryan R, Huynh Phuong N H, Kozlowski Marisa C
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
J Am Chem Soc. 2014 Nov 12;136(45):16055-65. doi: 10.1021/ja5086244. Epub 2014 Nov 4.
A spectrophotometric sensor is described that provides a useful assessment of the LUMO-lowering provided by catalysts in Diels-Alder and Friedel-Crafts reactions. A broad range of 33 hydrogen-bonding catalysts was assessed with the sensor, and the relative rates in the above reactions spanned 5 orders of magnitude as determined via (1)H- and (2)H NMR spectroscopic measurements, respectively. The differences between the maximum wavelength shift of the sensor with and without catalyst (Δλ(max)(-1)) were found to correlate linearly with ln(k(rel)) values for both reactions, even though the substrate feature that interacts with the catalyst differs significantly (ketone vs nitro). The sensor provides an assessment of both the inherent reactivity of a catalyst architecture as well as the sensitivity of the reaction to changes within an architecture. In contrast, catalyst pK(a) values are a poor measure of reactivity, although correlations have been identified within catalyst classes.
本文描述了一种分光光度传感器，它能有效评估狄尔斯-阿尔德反应和傅里德-克拉夫茨反应中催化剂降低最低未占分子轨道（LUMO）的能力。使用该传感器评估了33种广泛的氢键催化剂，通过¹H-和²H NMR光谱测量分别确定，上述反应中的相对速率跨度达5个数量级。发现有催化剂和无催化剂时传感器的最大波长位移之差（Δλ(max)(-1)）与两个反应的ln(k(rel))值均呈线性相关，尽管与催化剂相互作用的底物特征有显著差异（酮基与硝基）。该传感器既能评估催化剂结构的固有反应活性，也能评估反应对结构内变化的敏感性。相比之下，尽管已在催化剂类别中确定了相关性，但催化剂的pKa值并不能很好地衡量反应活性。
