Search for: All records

Not AvailableAmphidynamic crystals are a type of condensed matter that blends two extremes of the dynamic spectrum: rigid components forming a static lattice and rapidly moving parts. Among them, ordered rotor arrays within metal-organic frameworks (MOFs) constitute a promising platform to explore unchartered territories, such as gas phase-like dynamics in the crystalline state. Through quantum mechanical (QM) calculations and molecular dynamics (MD) simulations we verified that nearly barrierless cubane rotators in CUB-5 display rotational dynamics that transitions from continuous or inertial at high tempera-ture, to chaotic behavior, and ultimately to discrete jumps, as the temperature decreases from room temperature down to cry-ogenic conditions. 1H NMR spin-lattice (T1) relaxation measurements corroborate our theoretical predictions, with experi-mental rotational activation energy of 0.17 kcal/mol and an attempt frequency of 1.03×1012 s-1 that compare well with calcu-lated values of 0.15 kcal/mol and 0.38×1012 s-1, respectively. 

Abstract A kinetic, product, and computational study on the reactions of the cumyloxyl radical (CumO•) with 1,4-dimethyl- and 1,4-diphenylcyclohexanes is reported. The rate constants for hydrogen atom transfer (HAT) from the C–H bonds of these substrates to CumO•, together with the corresponding oxygenation product distributions reveal the role of strain release on reaction site selectivity. Transition structures and activation barriers obtained by DFT calculations are in excellent agreement with the experimental results. Tertiary/secondary ratios of oxygenation products of 0.6, 1.0, and 3.3 were observed, for trans-1,4-dimethyl-, cis-1,4-dimethyl-, and trans-1,4-diphenylcyclohexane, respectively. With cis-1,4-diphenylcyclohexane, exclusive formation of the diastereomeric tertiary alcohol products was observed. Within the two diastereomeric couples, the tertiary equatorial C–H bond in the cis- isomer is ca. 6 and 27 times more reactive, respectively, than the tertiary axial ones, a behavior that reflects the release of 1,3-diaxial strain in the HAT transition state. The tertiary axial C–H bonds of the four substrates show remarkably similar reactivities in spite of the much greater stabilization of the benzyl radicals resulting from HAT from the 1,4-diphenylcyclohexanes. The lack of benzylic acceleration is discussed in the framework of Bernasconi’s ‘principle of nonperfect synchronization’. 

Abstract The transition‐metal‐catalyzed Suzuki‐Miyaura cross‐coupling (SMC) reaction of organoboron nucleophiles with aryl (pseudo)halide electrophiles is a reliable method for carbon‐carbon bond formation. This reaction generally requires the use of an exogenous base to promote transmetalation process, which limits the substrate scope of the reaction due to undesired protodeboronation and functional group incompatibilities. Here, we established a base‐free SMC reaction via a conceptually different electrophilic substitution transmetalation (EST). This transformation is applicable to a wide range of base‐sensitive and sterically hindered organoborons. Key to this advance is the formation of a stable cationic palladium(II) or nickel(II) intermediate via experimental and theoretical investigations. In a broader context, this research further expands the synthetic boundary of cross‐coupling chemistry. 

Group 13 aminoxy complexes, (L)E(TEMPO)₃(TEMPO = 2,2,6,6-tetramethylpiperidine 1-oxyl; L = THF (tetrahydrofuran) or Py (pyridine); E = Al, Ga, In), display ambiphilic reactivity with H₂and function as synthons for the preparation of materials. 

Storing sunlight in a compact and rechargeable form remains a central challenge for solar energy utilization. Molecular solar thermal (MOST) energy storage systems, which harness photon energy and release it as heat on demand, provide a direct approach, but have long failed to meet practical benchmarks. Inspired by the architecture of DNA, we report a pyrimidone-based MOST system that stores energy in the strained Dewar photoisomer upon excitation at 300 nm. Designed with sustainability in mind, the system operates solvent-free and remains compatible with aqueous environments while overcoming one of the field’s greatest hurdles: the controlled extraction and transfer of stored heat. When catalyzed by acid, the Dewar isomer releases enough heat to boil water (~0.5 mL). These advances help point the way toward decentralized solar heat storage and off-grid energy solutions. 

Abstract Radical substitution is a useful method to functionalize heterocycles, as in the venerable Minisci reaction. Empirically observed regiochemistries indicate that the CF₂H radical has a nucleophilic character similar to alkyl radicals, but the CF₃radical is electrophilic. While the difference between •CH₃and •CF₃is well understood, the reason that one and two Fs make little difference but the third has a large effect is puzzling. DFT calculations with M06-2X both reproduce experimental selectivities and also lead to an explanation of this difference. Theoretical methods reveal how the F inductive withdrawal and conjugative donation alter radical properties, but only CF₃becomes decidedly electrophilic toward heterocycles. Here, we show a simple model to explain the radical orbital energy trends and resulting nucleophilicity or electrophilicity of fluorinated radicals.