Binaphthol-derived phosphoric acids as efficient chiral organocatalysts for the enantiomer-selective polymerization of rac-lactide

Abstract

A high enantiomer-selectivity for the polymerization of rac-lactide was achieved using chiral binaphthol-derived monophosphoric acids as organocatalysts. During the polymerization, d-lactide (DLA) preferentially polymerized via kinetic resolution with the maximum selectivity factor (kD/kL) of 28.3. The selective polymerization of DLA was derived from a dual activation, i.e., monomer activation and chain-end activation.

Highly Active and Iso‐Selective Catalysts for the Ring‐Opening Polymerization of Cyclic Esters using Group 2 Metal Initiators

“…The tacticity of the PLA obtained from catalysts 5 a , b – 7 a , b was determined with the help of homonuclear‐decoupled 1 H NMR spectra of the methine region (Figures FS97–FS102 in the Supporting Information) . It was observed that the PLA obtained from catalysts 5 a , 5 b , 6 a , and 6 b at 298 K were highly isotactic in nature, whereas the PLAs formed by catalysts 7 a and 7 b at 298 K were atactic in nature.…”

“…The tacticityo ft he PLA obtained from catalysts 5a,b-7a,b was determined with the help of homonuclear-decoupled 1 HNMR spectra of the methine region ( Figures FS97-FS102 in the Supporting Information). [38] It was observed that the PLA obtained from catalysts 5a, 5b, 6a,a nd 6b at 298 Kw ere highly isotactic in nature, whereas the PLAs formed by catalysts 7a and 7b at 298 Kw ere atactic in nature. The significant steric bulk of the phosphiminol igands (1 and 2), along with the achiral nature of the Ae metal complexes induce stereoselectivity in the PLA through ac hain-endc ontrol mechanism.…”

Understanding the phosphoric acid catalysed ring opening polymerisation of β-Butyrolactone and other cyclic esters

“…This behaviour contrasts strikingly with the ROP of with ɛ-caprolactone and rac-lactide, with conversions of 80 and 84% respectively were obtained, in agreement with previously published results. [20,22] As electron withdrawing power increases on the substituent (entries 9-17), a clear and expected increase in conversion is observed. Molecular weight determination by mass spectrometry revealed an initiator residue at the chain end, confirmed the oligomers formed are linear.…”

“…[20] Kakuchi and coworkers also reported diphenyl phosphate as a potential catalyst for ɛ-caprolactone and δ-valerolactone polymerisation, including kinetic studies showing good control up to 24 h, [21] and binapthol phosphoric acids that catalysed the stereoselective ROP of lactide. [22] Chakraborty and coworkers claimed to have synthesised substituted phosphoric acids and showed that electron withdrawing halogen substituents improved activity in ɛ-caprolactone polymerisations. [23] Hillmyer reported using diphenyl phosphate as a catalyst with a wide range of alkylsubstituted δ-valerolactones.…”

Isoselective Lactide Ring Opening Polymerisation using [2]Rotaxane Catalysts

“…[2] All tacticities of PLA are produced by the ring opening polymerization (ROP) of lactide.Acurrent challenge is to deliver stereoblock PLA from racemic lactide (rac-LA) using selective catalysis. [8] Fore xample, binaphthol-derived phosphoric acid (k D /k L = 28), [9] chiral synthetic prolines (P i = 0.87-0.96) [10] and ac hiral thiourea (P i = 0.82) [11] operate by enantiomorphic site control. [7] Very few organocatalysts are isoselective (rac-LA) and the most successful are chiral.…”