Ferrocenylsiloxane chemistry: Synthesis and characterization of hexaferrocenylcyclotrisiloxane and tetraferrocenyldisiloxanediol

Base-catalyzed condensation of diferrocenylsilanediol, Fc(2)Si(OH)(2) (3; Fc = (eta-C5H4)Fe(eta-C5H5)), in refluxing 95% ethanol (ca. 90 degrees C) affords a novel cyclotrisiloxane with six ferrocenyl substituents, [Fc(2)SiO](3) (4), in 74% yield. At 60 degrees C, the intermediate tetraferrocenyldisiloxanediol, [HOSiFc(2)](2)O (5), could be isolated in 78% yield. NMR, IR, Raman, and UV-vis data for 4 and 5 were consistent with the! proposed structures. Electrochemical studies of 4 showed that there are substantial interactions between the ferrocenyl groups attached to the same Si atom and weaker interactions between the ferrocenyl groups attached to adjacent Si atoms. Furthermore, single-crystal X-ray diffraction studies of these compounds revealed an essentially planar Si3O3 ring in 4 and a novel hydrogen-bonded chain motif for disiloxanediol 5. Surprisingly, 4 and 5 cocrystallize in a 1:3 ratio from a CH2Cl2/hexanes mixture to afford an interesting helical hydrogen-bonding structure for the siloxanediol 5.