Synthesis and Properties of Bridgehead-Functionalized Permethylbicyclo[2.2.2]octasilanes

A series
of previously unknown bridgehead-functionalized bicyclo[2.2.2]­octasilanes,
Me3Si-Si8Me12-X, X-Si8Me12-X, and X-Si8Me12-Y [X, Y =
−SiMenPh3–n (n = 1, 2) (2, 3, 10), −SiMe2Fc (Fc = ferrocenyl)
(4, 11, 13, 14), −COR (R = Me, tBu) (6, 7, 12), COOMe (8), COOH (9)], have been prepared by the reaction of the silanides Me3Si-Si8Me12–K+ or
K+–Si8Me12–K+ with proper electrophiles and fully characterized.
The molecular structures of 2, 3, 4, 6, 8, 9, 10, and 13 as determined by single-crystal X-ray diffraction
analysis exhibit a slightly twisted structure of the bicyclooctasilane
cage. Endocyclic bond lengths, bond angles, and dihedral angles are
not influenced considerably by the substituents attached to the bridgehead
silicon atoms. Due to σ­(SiSi)/π­(aryl) conjugation, a 20–30
nm bathochromic shift of the longest wavelength UV absorption band
relative to Me3Si-Si8Me12-SiMe3 (1) is evident in the UV absorption spectra
of the phenyl and ferrocenyl derivatives. Otherwise, UV absorption
data do not support the assumption of aryl/aryl or aryl/CO
interaction via the σ­(SiSi) bicyclooctasilane framework.

本研究制备了一系列此前未被报道的桥头官能化双环[2.2.2]辛硅烷（bicyclo[2.2.2]octasilanes），其通式为Me₃Si-Si₈Me₁₂-X、X-Si₈Me₁₂-X及X-Si₈Me₁₂-Y，其中X、Y的取代基涵盖：-SiMeₙPh₃₋ₙ（n=1、2，对应化合物2、3、10）、-SiMe₂Fc（Fc为二茂铁基（ferrocenyl），对应化合物4、11、13、14）、-COR（R为甲基、叔丁基，对应化合物6、7、12）、-COOMe（对应化合物8）与-COOH（对应化合物9）；该系列化合物通过硅烷化物（silanides）Me₃Si-Si₈Me₁₂⁻K⁺或K⁺-Si₈Me₁₂-K⁺与适宜亲电试剂的反应合成，并完成了全面表征。经单晶X射线衍射（single-crystal X-ray diffraction）分析测定的化合物2、3、4、6、8、9、10及13的分子结构表明，双环辛硅烷笼状骨架呈现轻微扭曲的构型。桥头硅原子所连取代基对环内键长、键角及二面角均无显著影响。得益于σ(Si-Si)/π(芳基)共轭作用，苯基与二茂铁基取代衍生物的紫外吸收光谱中，最长波长紫外吸收带相较于参比化合物Me₃Si-Si₈Me₁₂-SiMe₃（1）出现了20~30 nm的红移（bathochromic shift）。除此之外，紫外吸收数据未能支持芳基/芳基或芳基/C=O通过σ(Si-Si)双环辛硅烷骨架发生相互作用的假设。