Polyurethanes (PUs) have many applications resulting from their preeminent properties, but being commonly used toxic catalysts, and the lack of processability for PU thermosets cause limitations. Herein, we report a new class of the PU-like dynamic covalent polymers, poly(oxime-urethanes) (POUs), which are prepared from the uncatalyzed polyaddition of multifunctional oximes and hexamethylene diisocyanate (HDI) at ambient temperature. Kinetics studies reveal that almost complete polymerization (∼99% conversion) can be achieved in 3 h at 30 °C in dichloromethane (DCM), the most effective among the solvents evaluated, producing linear POUs with comparable molecular weights to the catalyzed PUs. We find that the oxime-carbamate structures are reversible at about 100 °C through oxime-enabled transcarbamoylation via a thermally dissociative mechanism. The cross-linked POUs based on oxime-carbamate bonds show efficient catalyst-free healable/recyclable properties. Density functional theory (DFT) calculations suggest that the fast oxime-urethanation and the mild thermoreversible nature are mediated by the characteristic nitrone tautomer of the oxime. Given widespread urethane-containing materials, POUs are of promising potential in applications because of the excellent mechanical performances, facile preparation, and dynamic property without using catalysts.

The asymmetric O-H insertion reaction is an ideal synthetic strategy for preparing optically pure alpha-alkoxy, alpha-aryloxy, and alpha-hydroxy carboxylic acid derivatives, which are valuable building blocks for the construction of natural products and other biologically active molecules. Surprisingly, to date there have been no reports of significant levels of enantiocontrol in the O-H insertions using chiral dirhodium(II) catalysts, which are powerful for asymmetric C-H insertions. Only recently, through the use of chiral copper catalysts, have highly enantioselective insertions of alpha-diazocarbonyl compounds into O-H bonds been achieved. To explain these interesting phenomena, density functional theory calculations have been conducted. The results show that in the Cu(I)-catalyzed system, the [1,2]-H shift process (the stereocenter formation step) favors the copper-associated ylide pathway. This ensures that when a chiral copper complex is used as the catalyst, the stereocenter forms in a chiral environment, which is the prerequisite for achieving enantioselectivity. In contrast, the free-ylide pathway is favored in the Rh(II)-catalyzed system. This significant difference renders the copper(I) complexes more competent than the dirhodium(II) complexes in catalytic asymmetric O-H insertions. In addition, it has been found for the first time that in transition-metal-catalyzed X-H insertions, water acts as an efficient proton-transport catalyst for the [1,2]-H shift.

Through the joint forces of computation and experiment, the detailed mechanism of the Lu phosphine catalyzed (3 + 2) cycloaddition of allenoates and alkenes has been elucidated. The overall potential energy surface of the Lu (3 + 2) reaction has been computed. More importantly, theory and experiment have confirmed that a trace amount of water plays a critical role in assisting the process of [1,2] proton shift in the Lu reaction.