Silylium cation initiated sergeants-and-soldiers type chiral amplification of helical aryl isocyanide copolymers

A series of silylium cations [(R 1 R 2 R 3 Si) 2 H] + [B(C 6 F 5 ) 4 ] − ( 1-6 ) ( 1 : R 1 = R 2 = R 3 = Et; 2 : R 1 = R 3 = H, R 2 = Ph; 3 : R 1 = R 3 = Me, R 2 = Ph; 4 : R 1 = R 2 = R 3 = Ph; 5 : R 1 = R 2 = R 3 = i Pr; 6 : R 1 = R 2 = R 3 = OEt) serve as highly efficient metal-free single-component cationic initiators for the cationic polymerization and copolymerization of chiral and achiral aryl isocyanides R-N&z.tbd;C ( a-k ) ( a : R = 2-C 10 H 7 (NI); b : R = 4-(COOEt)-C 6 H 4 (EPI); c : R = 3-[COO i Pr]-C 6 H 4 (IPI); d : R = 4-{COO-[(1 S ,2 R ,5 S )-(2- i Pr-5-Me-C 6 H 6 )]}-C 6 H 4 ( d -IMCI); e : R = 4-{COO-[(1 R ,2 S ,5 R )-(2- i Pr-5-Me-C 6 H 6 )]}-C 6 H 4 ( l -IMCI); f : R = 4-[4-(Ph)C&z.dbd;C(Ph) 2 -C 6 H 4 ]-C 6 H 4 (ITPB); g : R = 4-{COO-(CH 2 ) 9 -O-[4-(4-Ph-2-C 9 H 5 N)-C 6 H 4 ]}-C 6 H 4 (BNB); h : R = 4-{COO-[4-(4-Ph-2-C 9 H 5 N)-C 6 H 4 ]}-C 6 H 4 (PQPI); i : R = 4-(4-Ph-2-C 9 H 5 N)-C 6 H 4 (IPQ); j : R = 4-{COO-(CH 2 ) 9 -O-[4-(Ph)C&z.dbd;C(4-N(C 2 H 5 ) 2 -C 6 H 4 ) 2 -C 6 H 4 ]}-C 6 H 4 (PPNI); k : R = 4-(N&z.dbd;N-Ph)-C 6 H 4 (IPD)). Nine homopoly(aryl isocyanide)s are prepared, in which optically active poly( d ) and poly( e ) exhibit obvious negative and positive Cotton effects at 364 nm and adopt one-handed helical conformations, the poly( f ) containing tetraphenylethylene (TPE) substituent shows an aggregation-induced emission (AIE) nature, and the poly( g ) containing 2,4-diphenylquinoline (DPQ) substituent serves as a new fluorescent probe for the detection of Fe 3+ or Fe 2+ ions. By fine-tuning the types of chiral and achiral aryl isocyanides, different degrees of chiral amplification of copolymer helicity can be achieved in the copolymerization of chiral aryl isocyanides d and e with achiral aryl isocyanides b , c , f , and k . Such chiral amplifications of the helical poly( e - co - b )s, poly( d / e - co - c )s, poly( d / e - co - f )s, and poly( d / e - co - k )s with the same helical sense as the corresponding poly( d ) and poly( e ) obey the "sergeants-and-soldiers" rule. Determination of reactivity ratios of these copolymerizations demonstrates that the different nonlinear relationship between the intensity of CD signals at 364 nm and the d / l -IMCI contents of these copolymers depends on the sequence distribution of chiral aryl isocyanide monomers in these copolymers. Based on the in situ 1 H NMR, FT-IR, and high resolution ESI-MS spectra, a possible cationic (co)polymerization mechanism is proposed. Silylium cati