Rac/meso transformations of disiloxane-bis(1-indenyl)-ansa-ferrocenes:: An X-ray crystallographic and NMR study

Both stereoisomers of disiloxane-bis(1-indenyl)-ansa-ferrocene, Fe(eta(5)-inden-1-yl-SiMe2)(2)O, 1, were prepared by the reaction of disiloxane-bis-1,3-inden-1'-yl anion with FeCl2; the diastereomers were separated by column chromatography and recrystallized from n-heptane. A single-crystal X-ray diffraction study confirmed that each stereoisomer, racemic 1, and meso 1(m), involves parallel bis-indenyl coordination to the Fe metal center. These isomers were also characterized by H-1, C-13, and Si-29 NMR and IR spectroscopy. Compounds 1(r) and 1(m) 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 I was also copolymerized with 1,1,3,3,.5,5,7,7-octamethylcyclotetrasiloxane (D-4) and 1,1,1,3,3,5,5,5-octamethyltrisiloxane (MDM) to produce green organometallic polymers.