Selective Derivatization and Characterization of Bifunctional “Janus-Type” Cyclotetrasiloxanes

Stereoregular all-cis cyclotetrasiloxanes
[R-Si­(O)-R′]4 with different functional groups attached
to the opposite
faces of the ring skeleton were derivatized without stereoisomerization
or cleavage of the (SiO)4 ring and with high selectivity
using standard synthetic methods. The solid-state structures obtained
for the iodophenyl-substituted starting material 16 ([p-I-C6H4-Si­(O)-OSiMe2Vin]4) and for the coupling product 21 ([biphenyl-CC-C6H4-Si­(O)-OSiMe2Vin]4) show
a pronounced differentiation in the steric requirements of the different
sides of the ring, resulting in characteristic crystal packing. In
combination with the observed high thermal and chemical stability,
these data demonstrate the high potential of cyclotetrasiloxanes for
a wide range of applications.

通式为[R-Si(O)-R′]₄的立构规整全顺式环四硅氧烷（cyclotetrasiloxanes），当不同官能团连接于其环骨架的相对两侧时，可通过标准合成方法实现高选择性衍生化，且反应过程未发生立体异构化，也未出现(SiO)₄环的断裂。对碘苯基取代的起始原料16（[p-I-C₆H₄-Si(O)-OSiMe₂Vin]₄）以及偶联产物21（[联苯-CC-C₆H₄-Si(O)-OSiMe₂Vin]₄）的固态结构表征结果显示，环不同侧面的空间位阻需求存在显著差异，进而形成特征性的晶体堆积模式。结合观测到的优异热稳定性与化学稳定性，上述数据证明了环四硅氧烷在诸多应用领域具备极高的应用潜力。