Highly Active Cationic Rhodium(I) Precatalysts for the Ambient Temperature Ring-Opening Polymerization of [1]Silaferrocenophanes and Tetramethyldisilacyclobutane

Abstract

The cationic rhodium(I) complexes [Rh(1,5-cod)2]A (A = OTf, PF6, 1,5-cod = 1,5-cyclooctadiene) have been shown to exhibit high catalytic activity for the transition metal-mediated ring-opening polymerization (ROP) of silicon-bridged [1]ferrocenophanes (e.g., fcSiMe2 (1a), fc = Fe(η5-C5H4)2), to quantitatively afford high molecular weight (Mn > 105) polyferrocenylsilanes (e.g., [fcSiMe2]n (2a)). However, prolonged exposure of the resulting polyferrocene solution to the catalyst resulted in a dramatic molecular weight decline. Transition metal-catalyzed ROP of tetramethyldisilacyclobutane (6) and copolymerization of this species with 1a also proved readily feasible with [Rh(1,5-cod)2]OTf forming high molecular weight polycarbosilane homopolymer (7) (Mn = 4.20 × 105 to 1.08 × 106, PDI = 1.39−2.08) and poly(carbosilane-r-ferrocenylsilane) (8) copolymer (Mn = 4.63 × 105, PDI = 1.86), respectively. While [Rh(1,5-cod)(dmpe)]PF6 (dmpe = bis(dimethylphosphinoethane)) proved less active as a ROP catalyst, this spec...