Guodong Du

Zinc-Catalyzed Highly Isoselective Ring Opening Polymerization of rac-Lactide

A family of chiral zinc amido-oxazolinate complexes are shown to be highly active and isoselective initiators for the ring-opening polymerization (ROP) of rac-lactide, yielding isotactic stereoblock polylactides (PLA) with Pm up to 0.91. This represents the highest isoselectivity observed with zinc-based catalysts for ROP of rac-lactide.

Ring-Opening Polymerization of rac-Lactide with Aluminum Chiral Anilido-Oxazolinate Complexes.

A series of dimethylaluminum complexes (L1a–i)AlMe2 (2a–i, where HL1a–i = 2-(2′-ArNH)phenyl-4-R1-oxazoline) bearing chiral, bidentate anilido-oxazolinate ligands have been prepared and characterized. Six of the complexes, in the presence of an alcohol cocatalyst, are shown to be active initiators for the stereoselective ring-opening polymerization of rac-lactide in toluene solution and under bulk conditions, yielding polylactides with a range of tacticity from slightly isotactic to moderately heterotactic. The reactivity and selectivity of these catalysts are discussed on the basis of the effect of their substituents.

Dehydrogenative coupling of alcohols and carboxylic acids with hydrosilanes catalyzed by a salen–Mn(V) complex

A Mn(V)–salen complex was found to be an effective catalyst for the dehydrogenative coupling of hydroxyl groups with hydrosilane. The reaction conditions were optimized with different silanes and efficient dehydrogenative coupling was achieved by using triethoxysilane and diphenylsilane. Various alcohols and phenols and a limited number of carboxylic acids were converted into the corresponding silyl ethers and silyl esters. A range of functional groups such as chloro, nitro, methoxy, carbonyl and carbon–carbon multiple bonds are tolerated in the reaction.

Ring‐Opening Copolymerization of Styrene Oxide and Cyclic Anhydrides by using Highly Effective Zinc Amido–Oxazolinate Catalysts

Polyesters have been widely applied owing to their biodegradability and biocompatibility. Recently, catalytic ring‐opening copolymerization of cyclic anhydrides and epoxides has emerged as an effective approach for the synthesis of polyesters. Herein, we report a series of amido–oxazolinate zinc complexes as highly active catalysts for the ring‐opening copolymerization of styrene oxide and cyclic anhydrides. Turnover frequencies up to 4000 h−1 were achieved in the reaction of styrene oxide and maleic anhydride. Analysis of the end groups provides a useful probe for the preference at the electron‐poor methine site of styrene oxide for the ring‐opening process.

Renewable Isohexide-Based, Hydrolytically Degradable Poly(silyl ether)s with High Thermal Stability

Several degradable poly(silyl ether)s (PSEs) have been synthesized by dehydrogenative cross-coupling between bio-based 1,4:3,6-dianhydrohexitols (isosorbide and isomannide) and commercially available hydrosilanes. An air-stable manganese salen nitrido complex [MnV N(salen-3,5-tBu2 )] was employed as the catalyst. High-molecular-weight polymer was obtained from isosorbide and diphenylsilane (Mn up to 17000 g mol-1 ). Thermal analysis showed that these PSEs possessed high thermal stability with thermal decomposition temperatures (T-5 % ) of 347-446 °C and glass transition temperatures of 42-120 °C. Structure-property analysis suggested that steric bulk and molecular weight have a significant influence to determine the thermal properties of synthesized polymers. Importantly, these polymers were degraded effectively to small molecules under acidic and basic hydrolysis conditions.