Department of Chemistry, Western Michigan University , Kalamazoo, Michigan 49008, United States.
J Org Chem. 2017 Oct 6;82(19):10549-10562. doi: 10.1021/acs.joc.7b02070. Epub 2017 Sep 20.
The reaction of amines with aldehydes and ketones has been exploited for over 150 years to produce Schiff bases, one of the most popular classes of compounds in both organic and coordination chemistry. In certain cases, however, compounds other than Schiff bases have been reported to result from such reactions. After conducting a representative reaction under various different conditions and identifying several reaction intermediates by NMR spectroscopy, mass spectrometry and X-ray crystallography, we now report a unified picture that explains the scattered and often inconsistent results obtained with 3(5)-aminopyrazole derivatives and other related molecules. Acid catalysis, which is often employed in Schiff base synthesis, radically changes the course of reaction and leads to bis(pyrazol-4-yl)methane derivatives instead of the expected Schiff base products. The stoichiometry of the reaction is also found to be crucial for obtaining quantitative conversions. A total of 31 new compounds have been isolated and characterized as a result of this study, including a reaction intermediate, 2 Schiff bases, and 28 bis- or tris(pyrazol-3(4)-yl)methane ligands. The latter defines a new class of "non-scorpionate" ligands, with three nonchelating pyrazole moieties, as opposed to the well-known "scorpionate" tris(pyrazol-1-yl)-borate and -methane ligands.
胺与醛和酮的反应已经被开发了超过 150 年，用于生产席夫碱，这是有机和配位化学中最受欢迎的化合物之一。然而，在某些情况下，除了席夫碱之外，还有其他化合物被报道是由这些反应产生的。在各种不同条件下进行了代表性反应，并通过 NMR 光谱、质谱和 X 射线晶体学鉴定了几种反应中间体后，我们现在提出了一个统一的观点，解释了 3(5)-氨基吡唑衍生物和其他相关分子的分散且经常不一致的结果。席夫碱合成中经常采用的酸催化从根本上改变了反应的进程，导致生成双(吡唑-4-基)甲烷衍生物，而不是预期的席夫碱产物。反应的化学计量也被发现对获得定量转化率至关重要。由于这项研究，总共分离和表征了 31 种新化合物，包括一个反应中间体、2 种席夫碱和 28 种双或三(吡唑-3(4)-基)甲烷配体。后者定义了一类新的“非冠醚”配体，具有三个非螯合的吡唑部分，而不是众所周知的“冠醚”三(吡唑-1-基)-硼酸和甲烷配体。
