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.