Bisurea and Bisthiourea H-Bonding Organocatalysts for Ring-Opening Polymerization: Cues for the Catalyst Design

Abstract

A series of conformationally flexible bis(thio)urea H-bond donors plus base cocatalyst were applied to the ringopening polymerization (ROP) of lactones. The rate of the ROP displays a strong dependence on the length and identity of the tether, where a circa five methylene-unit long tether exhibits the fastest ROP. Any constriction to conformational freedom is deleterious to catalysis. For the ROP of δ-valerolactone (VL) and ε-caprolactone (CL), the bisurea H-bond donors are more effective, but for lactide, the bisthioureas are more active catalysts. The ROP reactions are rapid and controlled across a wide range of reaction conditions, including solvent-free conditions, exhibiting excellent weight control from low M n to high polymers. The active mechanism is highly dependent on the identity of the base cocatalyst, and a mechanistic rationale for the observations is discussed. Implications for the design of future generation catalysts are discussed.

Rapid and Controlled Organocatalyzed Ring-Opening Polymerization of 3S-(Isobutyl)morpholine-2,5-dione and Copolymerization with Lactide

“…Indeed, 1,8-diazabicyclo­(5,4,0)­undec-7-ene (DBU) and 1,5,7-triazabicyclo­(4,4,0)­dec-5-ene (TBD) can effectively catalyze the ROP of morpholine-2,5-diones with initiators such as benzyl alcohol. , Unfortunately, transesterification reactions occurred when the monomer conversion exceeds 50% . It has been demonstrated that the use of a thiourea cocatalyst prevents such effects for many cyclic esters including morpholine-2,5-dione derivatives carrying substitutions on the 6 position. ,− Complementary to this previous study, the present work evaluates the influence of the amount of a thiourea cocatalyst (3-[3,5-bis­(trifluoromethyl)­phenyl]-1-cyclohexylthiourea) (TU) on the ROP of 3S-(isobutyl)­morpholine-2,5-dione (MD), derived from l -leucine and more importantly, devoid of substituents on the 6 position, which readily alter the reactivity of the propagating chain-end. Moreover, the results obtained lead us to propose new mechanistic pathways for the ROP of MD depending on the initial ratio of TU and MD.…”

Organoselenium chemistry-based polymer synthesis

“…In recent years, because of its high efficiency, ring-opening polymerization has become a prominent research area. [65][66][67][68][69][70] In particular, the method is used in the synthesis of polyester materials, including β-butyrolactone, γ-butyrolactone, ε-capro-lactone, etc. 71,72 Accordingly, some selenium-containing polymers were also prepared in this way with Se monomers.…”

Pharmacokinetics, Mechanism, and Docking Study of Antioxidant Aryl‐Bisthiourea Derivatives for Alzheimer's Disease

“…[18,19] Dithiourea has three unique structural properties (a) complementary (C=S), (b) hydrogen bonding area (NÀ H group), and (c) additional 1,3-disubstituted pattern. [20] The lipophilic property of bis thiourea is more than mono thiourea and mono urea which help for cell internalization. [21] That is why thiourea derivatives show better biological activities than mono thiourea .…”

“…[21] That is why thiourea derivatives show better biological activities than mono thiourea . [20] Furthermore, the biological activity of these derivatives is enhanced by incorporate substitutions on aryl ring. [22] These electrifying structures show a noteworthy part in the improvement of inhibition activity and constructing lead-molecule for drug designing.…”