Design, Synthesis and Aromaticity of an Alternating Cyclo[4]Thiophene[4]Furan.

A new class of conjugated macrocycle, the cyclo[4]thiophene[4]furan hexyl ester (C4TE4FE), is reported. This cycle consists of alternating α-linked thiophene-3-ester and furan-3-ester repeat units, and was prepared in a single step using Suzuki-Miyaura cross-coupling of a 2-(thiophen-2-yl)furan monomer. The ester side groups help promote a syn conformation of the heterocycles, which enables formation of the macrocycle. Cyclic voltammetry studies revealed that C4TE4FE could undergo multiple oxidations, so treatment with SbCl5 resulted in formation of the [C4TE4FE]2+ dication. Computational work, paired with 1 H NMR spectroscopy of the dication, revealed that the cycle becomes globally aromatic upon 2e- oxidation, as the annulene pathway along the outer ring becomes Hückel aromatic. The change in ring current for the cycle upon oxidation was clear from 1 H NMR spectroscopy, as the protons of the thiophene and furan rings shifted downfield by nearly 6 ppm. This work highlights the potential of sequence control in furan-based macrocycles to tune electronic properties.

Chemoselective Rhodium-Catalyzed Borylation of Bromoiodoarenes Under Mild Conditions.

A chemoselective rhodium-catalyzed borylation has been developed for the preparation of aryl boronate esters. The reaction proceeds under mild conditions with excellent selectivity for C-I bonds in bromoiodoarenes and exhibits broad functional group tolerance. This procedure can act as a complementary approach toward bifunctional arenes along with other metal-catalyzed borylations. Additionally, the reaction's utility in the preparation of monomers for metal-catalyzed cross-coupling polymerization is demonstrated.

Photostable Helical Polyfurans.

This report describes the design and synthesis of a new class of polyfurans bearing ester side chains. The macromolecules can be synthesized using catalyst-transfer polycondensation, providing precise control over molecular weight and molecular weight distribution. Such obtained furan ester polymers are significantly more photostable than their alkyl analogues owing to the electron-withdrawing nature of the attached subunit. Most interestingly, they spontaneously fold into a compact π-stacked helix, yielding a complex multilayer cylindrical nanoparticle with a hollow, rigid, conjugated core composed of the polyfuran backbone and a soft, insulating outer layer formed by the ester side chains. The length of polymer side chains dictates the outer diameter of such nanoparticles, which for the hexyl ester groups used in the present study is equal to ∼2.3 nm. The inner cavity of the conjugated core is lined with oxygen atoms, which set its effective diameter to 0.4 nm. Furthermore, installation of bulkier, branched chiral ester side chains on the repeat unit yields structures that, upon change of solvent, can reversibly transition between an ordered chiral helical folded and disordered unfolded state.

Probing the Kinetic Origin of Varying Oxidative Stability of Ethyl- vs. Propyl-spaced Amines for Direct Air Capture.

Amine-based adsorbents are promising for direct air capture of CO2 , yet oxidative degradation remains a key unmitigated risk hindering wide-scale deployment. Borrowing wisdom from the basic auto-oxidation scheme, insights are gained into the underlying degradation mechanisms of polyamines by quantum chemical, advanced sampling simulations, adsorbent synthesis, and accelerated degradation experiments. The reaction kinetics of polyamines are contrasted with that of typical aliphatic polymers and they elucidate for the first time the critical role of aminoalkyl hydroperoxide decomposition in the oxidative degradation of amino-oligomers. The experimentally observed variation in oxidative stability of polyamines with different backbone structures is explained by the relationship between the local chemical structure and the free energy barrier of aminoalkyl hydroperoxide decomposition, suggesting that its energetics can be used as a descriptor to screen and design new polyamines with improved stability. The developed computational capability sheds light on radical-induced degradation chemistry of other organic functional materials.

Enhanced hydrogen bonding via epoxide-functionalization restricts mobility in poly(ethylenimine) for CO2 capture.

Free energy sampling, deep potential molecular dynamics, and characterizations provide insights into the impact of epoxide-functionalization on the hydrogen bonding and mobility of poly(ethylenimine), a promising CO2 sorbent. These findings rationalize the anti-degradation effects of epoxide functionalization and open up new avenues for designing more durable CO2 sorbents.

Chain-Growth Polymerization of Benzotriazole Using Suzuki-Miyaura Cross-Coupling and Dialkylbiarylphosphine Palladium Catalysts.

Electron-deficient (n-type) conjugated materials are commonly prepared via step-growth methods with limited control over the molecular weight and molecular weight distribution of the resulting polymers. In this communication, we demonstrate that Pd-dialkylbiarylphosphine catalysts enable the chain-growth polymerization of benzo[1,2,3]triazole using Suzuki-Miyaura coupling with molecular weight control and modest molecular weight distributions (D ∼ 1.2-1.6). The importance of a free ligand in the reaction mixture during polymerization was established by analysis of polymer samples using GPC and MALDI-TOF mass spectrometry. A block copolymer with poly(3-hexylthiophene) was also synthesized by sequential monomer addition. The success of these commercially available catalysts for polymerization of benzotriazole highlights their potential for chain-growth reactions with other bicyclic arenes in the future.