Kim J H, Lindeman S V, Kochi J K
Department of Chemistry, University of Houston, Houston, Texas 77204-5641, USA.
J Am Chem Soc. 2001 May 30;123(21):4951-9. doi: 10.1021/ja010108u.
Electron donor/acceptor (EDA) interactions are found to be a versatile methodology for the engineering of reactive heteromolecular crystals. In this way, a series of the charge-transfer pi-complexes between bis(alkylimino)-1,4-dithiin acceptors and anthracene donors are shown to form heteromolecular (1:1) crystalline solids that spontaneously undergo stereoselective [2 + 4] Diels--Alder cycloadditions. The flexible nature of the 1,4-dithiin moiety allows this homogeneous topochemical transformation to proceed with minimal distortion of the crystal lattice. As a result, a unique (single) crystal phase of the Diels--Alder adduct can be produced anti-thermodynamically with a molecular arrangement very different from that in solvent-grown crystals. Such a topochemical reaction between bis(methylimino)-1,4-dithiin and anthracene proceeds thermally and homogeneously up to very high conversions without disintegration of the single crystal. This ideal case of the mono-phase topochemical conversion can be continuously monitored structurally (X-ray crystallography) and kinetically (NMR spectroscopy) throughout the entire range of the crystalline transformation. The resultant "artificial" crystal of the Diels--Alder adduct is surprisingly stable despite its different symmetry and packing mode compared to the naturally grown (thermodynamic) crystal.
电子供体/受体（EDA）相互作用被发现是一种用于构建反应性异分子晶体的通用方法。通过这种方式，双（烷基亚氨基）-1,4-二噻因受体与蒽供体之间的一系列电荷转移π-络合物被证明能形成异分子（1:1）晶体固体，这些固体能自发地进行立体选择性的[2 + 4]狄尔斯-阿尔德环加成反应。1,4-二噻因部分的柔性使得这种均相拓扑化学转化能够在晶格最小程度变形的情况下进行。因此，狄尔斯-阿尔德加合物的独特（单一）晶相可以以反热力学的方式产生，其分子排列与溶剂生长晶体中的排列非常不同。双（甲基亚氨基）-1,4-二噻因与蒽之间的这种拓扑化学反应在热作用下均匀地进行，直至非常高的转化率，而单晶不会分解。这种单相拓扑化学转化的理想情况可以在整个晶体转变范围内通过结构（X射线晶体学）和动力学（核磁共振光谱）进行连续监测。所得的狄尔斯-阿尔德加合物的“人工”晶体尽管与自然生长（热力学）晶体相比具有不同的对称性和堆积模式，但却出奇地稳定。
