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 (M n > 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) (M n = 4.20 × 105 to 1.08 × 106, PDI = 1.39−2.08) and poly(carbosilane-r-ferrocenylsilane) (8) copolymer (M n = 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 species represents the first phosphine-ligated catalyst for the ROP of 1a, and moreover, in this case no subsequent depolymerization of the resulting poly(ferrocenyldimethylsilane) (2a) was detected. The cleavage of the polyferrocene backbone in the presence of [Rh(1,5-cod)2]OTf was modeled through the catalytic reaction of Fc2SiMe2 (Fc = Fe(η5-C5H5)(η5-C5H4)) with the rhodium complex (9 mol %), which resulted in Cp−Si bond cleavage affording ferrocene as the sole, isolable product. The presence of 1,5-cod inhibited the catalytic activity of both [Rh(1,5-cod)2]OTf and [Rh(1,5-cod)(dmpe)]PF6, suggesting that elimination of a 1,5-cod ligand is necessary to generate the true active catalytic species. The addition of dmpe effectively arrested the catalytic activity with [Rh(1,5-cod)(dmpe)]PF6; this is presumably a result of the displacement of the 1,5-cod ligand by dmpe, which would generate catalytically inactive [Rh(dmpe)2]PF6.

Polyferrocenylsilanes: synthesis, properties, and applications

“…Catalytic ROP. 37 Catalytic amounts of [Rh (1,5-cod) 2 ]A (cod = 1,5-cyclooctadiene, A = [OTf] À , [PF 6 ] À ) initiated the ROP of sila [1]ferrocenophanes with quantitative conversion within 2 minutes. 33,34 Complexes used as precatalysts feature platinum (Pt 0 , Pt II ), [33][34][35][36] for example Karstedt's catalyst (platinum divinyltetramethyldisiloxane complex), 36 palladium (Pd 0 , Pd II ), 33,34 and rhodium (Rh I ).…”

“…In 1995 it was discovered that a variety of late transition metal complexes catalysed the ROP of sila [1]ferrocenophanes, to yield high molecular weight PFSs both in solution and at room temperature. 37 In the case of Pt, it has been reported that heterogeneous metal colloids form as the active catalysts, and postulated that oxidative-addition and reductive-elimination reactions at the metal surface resulted in formation of the polymer. 37 Catalytic amounts of [Rh (1,5-cod) 2 ]A (cod = 1,5-cyclooctadiene, A = [OTf] À , [PF 6 ] À ) initiated the ROP of sila [1]ferrocenophanes with quantitative conversion within 2 minutes.…”

Polyferrocenylsilane‐Based Polymer Systems

“…[103] Later on, similar copolymers were obtained by [Rh(1,5-cod) 2 ] OTf-catalyzed copolymerization. [104] Transition-metal-catalyzed ROP in the presence of varying amounts of Et 3 SiH allows convenient control of the molecular weight over the range M n = 2000-45 000, with polydispersity index values in the range of 1.1-2.3 (Scheme 19). [105] The observed M n value is greater than expected from the feed ratio of monomer/Et 3 SiH, implying that [fcSiMe 2 ] is more reactive towards the catalytic metal center compared to Et 3 SiH.…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…32,33 Complexes used as precatalysts feature platinum (Pt 0 , Pt II ), 34 for example Karstedt's catalyst (platinum divinyltetramethyldisiloxane complex), 35 palladium (Pd 0 , Pd II ), and rhodium (Rh I ). 36 In the case of Pt, it has been reported that heterogeneous metal colloids form as the active catalysts, and postulated that oxidative-addition and reductive-elimination reactions at the metal surface resulted in formation of the polymer. 37 For silicon-bridged ferrocenophanes in which one Cp ring is methylated, Pt II -catalysed ROP proceeds solely by selective cleavage of the Si-Cp H (Cp H = C5H4)bond to yield a regioregular, crystalline PFS, unlike thermal ROP which affords a regioirregular amorphous material.…”