Alkaline-Earth-Metal-Induced Liberation of Rare Allotropes of Elemental Silicon and Germanium from N-Heterocyclic Metallylenes

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• 作者：Burgert Blom ; Amro Said ; Tibor Szilv谩si ; Prashanth W. Menezes ; Gengwen Tan ; Judith Baumgartner ; Matthias Driess
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：54
• 期：17
• 页码：8840-8848
• 全文大小：530K
• ISSN：1520-510X

文摘

The synthesis and striking reactivity of the unprecedented N-heterocyclic silylene and germylene (鈥渕etallylene鈥? alkaline-earth metal (Ae) complexes of the type [(畏⁵-C₅Me₅)₂Ae鈫?E(N^tBuCH)₂] (3, 4, and 7鈥?b>9; Ae = Ca, E = Ge 3; Ae = Sr, E = Ge 4; Ae = Sr, E = Si 7; Ae = Ba, E = Si 8; Ae = Ba, E = Ge 9) are reported. All complexes have been characterized by spectroscopic means, and their bonding situations investigated by density functional theory (DFT) methods. Single-crystal X-ray diffraction analyses of examples revealed relatively long Si鈥揂e and Ge鈥揂e distances, respectively, indicative of weak E:鈫扐e (E = Si, Ge) dative bonds, further supported by the calculated Wiberg bond indices , which are rather low in all cases (鈭?.5). Unexpectedly, the complexes undergo facile transformation to 1,4-diazabuta-1,3-diene Ae metal complexes of the type [(畏⁵-C₅Me₅)₂Ae(魏²-{N^tBu鈺怌HCH鈺怤^tBu})] (Ae = Sr 10, Ae = Ba 11) or in the case of calcium to the dinuclear complex [(畏⁵-C₅Me₅)₂Ca鈫?N(^tBu)鈺怌HCH鈺?^tBu)N:鈫扖a(畏⁵-C₅Me₅)₂] (12) under concomitant liberation of elemental silicon and germanium. The formation of elemental silicon and germanium is proven by inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray spectroscopy. Notably, the decomposition of the Si(II)鈫払a complex 8 produces allo-silicon, a rare allotropic form of elemental silicon. Similarly, the analogous Ge(II)鈫払a complex 9, upon decomposition, forms tetragonal germanium, a dense and rare allotrope of elemental germanium. The energetics of this unprecedented alkaline-earth-metal-induced liberation of elemental silicon and germanium was additionally studied by DFT methods, revealing that the transformations are pronouncedly exergonic and considerably larger for the N-heterocyclic germylene complexes than those of the corresponding silicon analogues.