Controlled/Living Cationic Polymerization of p-Methoxystyrene Using Tellurium-Based Chalcogen Bonding Catalyst─Discovery of a New Water-Tolerant Lewis Acid Catalyst

Halogen, Chalcogen, Pnictogen, and Tetrel Bonding in Non-Covalent Organocatalysis: An Update

The use of noncovalent interactions based on electrophilic halogen, chalcogen, pnictogen, or tetrel centers in organocatalysis has gained noticeable attention. Herein, we provide an overview on the most important developments in the last years with a clear focus on experimental studies and on catalysts which act via such non-transient interactions.

Recent Developments on Cationic Polymerization of Vinyl Ethers

In recent times, the evolution of cationic polymerization has taken a multidirectional approach, with the development of cationic reversible addition-fragmentation chain transfer (RAFT) polymerization. In contrast to the conventional cationic polymerization methods, which were typically carried out under inert atmospheres and low temperatures, various novel polymerization techniques have been developed where the reactions are carried out in open air, operate at room temperature, are cost-effective, and are environmentally friendly. Besides, several external stimuli, such as heat, light, chemicals, electrical potential, etc. have been employed to activate and control the polymerization process. It also enables the combination of cationic polymerization with other polymerization methods in a single reaction vessel, eliminating the necessity for isolation and purification during intermediate steps. In addition, significant advancements have been made through various modifications in catalyst systems, resulting in polymers with an exceptionally high level of stereoregularity. This review article comprehensively analyses the recent developments in cationic polymerization, encompassing their applications and offering insights into future perspectives.

Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental-Theoretical Joint Study

Telluronium salts [Ar2 MeTe]X were synthesized, and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. Structural X-ray diffraction analysis of 21 different salts revealed the electrophilicity of the Te centers in their interactions with anions. Telluroniums' propensity to form Lewis pairs was investigated with OPPh3 . Diffusion-ordered NMR spectroscopy suggested that telluroniums can bind up to three OPPh3 molecules. Isotherm titration calorimetry showed that the related heats of association in 1,2-dichloroethane depend on the electronic properties of the substituents of the aryl moiety and on the nature of the counterion. The enthalpies of first association of OPPh3 span -0.5 to -5 kcal mol-1 . Study of the affinity of telluroniums for OPPh3 by state-of-the-art DFT and ab-initio methods revealed the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar2 MeTe]+ cations and OPPh3 are deemed insufficient on their own to ensure the cohesion of [Ar2 MeTe ⋅ Bn ]+ complexes in solution (B=Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4/MBD-vdW thermodynamics of formation of higher [Ar2 MeTe ⋅ Bn ]+ complexes revealed significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.

Bidentate selenium-based chalcogen bond catalyzed cationic polymerization of p-methoxystyrene

The application of selenium-based non-covalent bond catalysis in living cationic polymerization has rarely been reported. In this work, the cationic polymerization of p-methoxystyrene (pMOS) was performed using a bidentate selenium bond catalyst - a new water-tolerant Lewis acid catalyst. A polymer with controllable molecular weight and narrow molecular weight distribution can be obtained at room temperature, with a maximum molecular weight of 23.3 kDa. This selenium bond compound can also catalyze the controllable cationic polymerization of p-methoxy styrene under environmental conditions. By changing the monomer feeding ratio, a secondary feeding experiment and DFT analysis, it is shown that the selenium bond catalyst can induce polymer chain growth by reversibly activating dormant covalent bonds (C-OH).

Chalcogen Bonding Catalysis: Tellurium, the Last Frontier?

Chalcogen bonding (ChB) is the non-covalent interaction occurring between chalcogen atoms as Lewis acid sites and atoms or groups of atoms able to behave as Lewis bases through their lone pair or π electrons. Analogously to its sister halogen bonding, the high directionality of this interaction was implemented for precise structural organizations in the solid state and in solution. Regarding catalysis, ChB is now accepted as a new mode of activation as demonstrated by the increased number of examples in the last five years. In the family of ChB catalysts, those based on tellurium rapidly appeared to overcome their lighter sulfur and selenium counterparts. In this review, we highlight the Lewis acid properties of tellurium-based derivatives in solution and summarize the start-of-the-art of their applications in catalysis.