Kira Mitsuo, Ishida Shintaro, Iwamoto Takeaki
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
Chem Rec. 2004;4(4):243-53. doi: 10.1002/tcr.20019.
Recent studies of the synthesis, structures, spectroscopic properties, and reactions of a series of isolable metallylenes (R2E:, E = Si (1), Ge (2), and Sn (3); R2 = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) are summarized. Because these group-14 metallylenes bear the same helmet-like ligand, a straightforward discussion of the element-dependence of the intrinsic properties of the group-14 element divalent compounds is possible. All these metallylenes were monomeric both in solution and in the solid state, indicating the effective steric protection by the ligand against dimerization. A small sigma-pi conjugation between C-Si(substituent) sigma orbitals and the vacant npz orbitals of divalent atoms in R2E: exists and the extent decreases in the order E = Si > Ge > Sn, as evidenced by UV-vis and NMR spectroscopies and X-ray crystallography. However, the extent of the sigma-pi conjugation in metallylenes 1-3 was much smaller than the electron-donating effects of neighboring nitrogen atoms in known stable cyclic diamino-substituted metallylenes, and hence metallylenes 1-3 are regarded as the least electronically perturbed. Comparative studies of the unique reactions among these metallylenes are also discussed.
总结了一系列可分离的亚金属化合物（R2E:，E = Si (1)、Ge (2) 和 Sn (3)；R2 = 1,1,4,4-四（三甲基硅基）丁烷-1,4-二亚基）的合成、结构、光谱性质及反应的近期研究。由于这些第14族亚金属化合物带有相同的头盔状配体，因此可以直接讨论第14族元素二价化合物固有性质的元素依赖性。所有这些亚金属化合物在溶液和固态中均为单体，表明配体对二聚化具有有效的空间保护作用。R2E: 中C-Si（取代基）σ轨道与二价原子的空npz轨道之间存在小的σ-π共轭，且共轭程度按E = Si > Ge > Sn的顺序降低，紫外可见光谱、核磁共振光谱及X射线晶体学证明了这一点。然而，亚金属化合物1-3中的σ-π共轭程度远小于已知稳定的环状二氨基取代亚金属化合物中相邻氮原子的给电子效应，因此亚金属化合物1-3被认为是电子干扰最小的。还讨论了这些亚金属化合物之间独特反应的比较研究。
