<i>Rac/</i><i>m</i><i>eso</i> Transformations of Disiloxane-bis(1-indenyl)-<i>a</i><i>nsa</i>-ferrocenes:  An X-ray Crystallographic and NMR Study

Both stereoisomers of disiloxane-bis(1-indenyl)-<i>ansa</i>-ferrocene, Fe(η<sup>5</sup>-inden-1-yl-SiMe<sub>2</sub>)<sub>2</sub>O, <b>1</b>, were prepared by the reaction of disiloxane-bis-1,3-inden-1‘-yl anion with FeCl<sub>2</sub>; the diastereomers were separated by column chromatography and recrystallized from <i>n</i>-heptane. A single-crystal X-ray diffraction study confirmed that each stereoisomer, <i>racemic</i> <b>1</b><b><i><sub>r</sub></i></b> and <i>meso</i> <b>1</b><b><i><sub>m</sub></i></b>, involves parallel bis-indenyl coordination to the Fe metal center. These isomers were also characterized by <sup>1</sup>H, <sup>13</sup>C, and <sup>29</sup>Si NMR and IR spectroscopy. Compounds <b>1</b><b><i><sub>r</sub></i></b> and <b>1</b><b><i><sub>m</sub></i></b> could each be transformed into the other diastereomer:  the conversion was retarded by base, but accelerated under weakly acidic conditions. The mechanism of this process, investigated using deuterium labeling experiments, is consistent with a series of successive 1,5-suprafacial, sigmatropic silicon shifts. Compound <b>1</b> was also copolymerized with 1,1,3,3,5,5,7,7-octamethylcyclotetrasiloxane (D<sub>4</sub>) and 1,1,1,3,3,5,5,5-octamethyltrisiloxane (MDM) to produce green organometallic polymers.