Metal complexes have extensive applications in catalysis, however, the efficient evaluation of Lewis acidity of metal complexes is still a challenge. Herein, we report a method by using electrospray ionization mass spectrometry (ESI-MS) to evaluate the Lewis acidity of metal complexes in the presence of a reference Lewis base, in which the value of the Lewis acidity can be quantized by the bond dissociation energy (BDE) of the resultant Lewis acid-base pairs. Using this method, the Lewis acidity of tetradentate Schiff-base metal complexes (designated as salenMX), a class of common metal complexes in the homogeneous catalysis, was studied in detail. For the salenM(III)X complexes (M = Al, Cr, Fe, Co), the Lewis acidity tendency is Al > Cr > Fe > Co due to a strong affinity between the Al complex and the reference Lewis base while a weak affinity concerning on the Co complex. Additionally, the effect of ligand steric and electronic nature on the Lewis acidity was studied by using Co complex. Furthermore, density functional theory (DFT) was employed to calculate the BDE, which consists with the results obtained from ESI-MS. The ESI-MS method provides a convenient and efficient method for evaluating the Lewis acidity of metal complexes.

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使用 ESI 质谱法评估金属配合物的路易斯酸度

金属配合物在催化方面有着广泛的应用，然而，有效评估金属配合物的路易斯酸度仍然是一个挑战。在此，我们报告了一种使用电喷雾电离质谱 (ESI-MS) 在参考路易斯碱存在下评估金属配合物的路易斯酸度的方法，其中路易斯酸度的值可以通过键离解能来量化(BDE) 所得路易斯酸碱对。使用该方法，详细研究了均相催化中常见的一类金属络合物四齿席夫碱金属络合物（命名为 salenMX）的路易斯酸度。对于 salenM(III)X 配合物 (M = Al, Cr, Fe, Co)，路易斯酸度趋势是 Al > Cr > Fe > Co 是由于 Al 配合物与参考路易斯碱之间的强亲和力而与 Co 配合物的弱亲和力。此外，通过使用 Co 配合物研究了配体空间和电子性质对路易斯酸度的影响。此外，密度泛函理论 (DFT) 被用来计算 BDE，它与从 ESI-MS 获得的结果一致。ESI-MS 方法为评估金属配合物的路易斯酸度提供了一种方便有效的方法。