Unusual bonding and properties in main group element chemistry: rational synthesis, characterization, and experimental electron density determination of mixed-valent tetraphosphetes.
Unusual bonding and properties in main group element chemistry: rational synthesis, characterization, and experimental electron density determination of mixed-valent tetraphosphetes.
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DOI：
10.1002/chem.201406131
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发表时间：
2015-03
期刊：
影响因子：
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通讯作者：
Verena Breuers;C. Lehmann;W. Frank
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文献类型：
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作者：
Verena Breuers;C. Lehmann;W. Frank
五种二螺环 λ(3),λ(5)-四亚磷酸酯 [{R2Si(NR(1))(NR(2))P2}2]（R(1) = R(2) 和 R(1) ≠ R(2)）通过在强可见光下光解各自的双（三甲基硅基）膦酰基二氮杂磷酸酯，可以轻松地以几乎定量的产率制备。这些深黄色低配位磷化合物可以被认为是众所周知的环二磷腈的第一个高级同系物。四磷酸酯在空气中非常稳定，并表现出与中心四π电子四元磷环的独特键合情况相关的意想不到的分子特性。由于 σ(2)-磷原子处存在异常锐角，中心 P4 环的菱形畸变程度非常显着。所有 P-P 键的长度大致相等。距离位于磷单键和双键给出的范围的中间。在[{Me2Si(NtBu)(NtBu)P2}2]的黄色/无色二向色晶体的情况下很容易观察到可见光的各向异性吸收和σ(2)-磷原子的特殊(31)P NMR化学位移是λ(3),λ(5)-四亚磷酸盐最显着的特征。对于 [{Me2Si(NtBu)(NtBu)P2}2]，应用 Hansen-Coppens 多极模型从 100 K 下获得的高分辨率 X 射线衍射数据中提取电子密度。静态变形密度和拓扑分析揭示了中心不饱和 P4 片段中独特的成键情况，其特征是极性 σ 键合、σ(2)-磷原子上明显的环外非键合孤对电子密度，以及额外的非经典三中心背键贡献。
Five dispirocyclic λ(3),λ(5)-tetraphosphetes [{R2Si(NR(1))(NR(2))P2}2] (R(1) = R(2) and R(1) ≠ R(2)) are easily prepared in almost quantitative yields via photolysis of the respective bis(trimethylsilyl)phosphanyldiazaphosphasiletidines with intense visible light. These deep-yellow low-coordinate phosphorus compounds can be considered as the first higher congeners of the well-known cyclodiphosphazenes. The tetraphosphetes are remarkably stable in air and show unexpected molecular properties related to the unique bonding situation of the central four-π-electron four-membered phosphorus ring. The extent of rhombic distortion of the central P4 ring is remarkable due to an unusually acute angle at the σ(2)-phosphorus atoms. All of the P-P bonds are approximately equal in length. The distances are in the middle of the range given by phosphorus single and double bonds. The anisotropic absorption of visible light that can easily be observed in the case of the yellow/colorless dichroic crystals of [{Me2Si(NtBu)(NtBu)P2}2] and the exceptional (31)P NMR chemical shift of the σ(2)-phosphorus atoms are the most remarkable features of the λ(3),λ(5)-tetraphosphetes. In the case of [{Me2Si(NtBu)(NtBu)P2}2], the Hansen-Coppens multipole model is applied to extract the electron density from high-resolution X-ray diffraction data obtained at 100 K. Static deformation density and topological analysis reveal a unique bonding situation in the central unsaturated P4 fragment characterized by polar σ-bonding, pronounced out-of-ring non-bonding lone pair density on the σ(2)-phosphorus atoms, and an additional non-classical three-center back-bonding contribution.