The performance of particle‐catalyzed reactions using heterogenized organocatalysts is typically assessed in bulk‐scale systems like packed‐bed or stirred‐tank reactors. However, such ensemble measurements only yield average values across millions of particles, potentially masking substantial variability in individual catalytic performance. To address this limitation, we developed a droplet microfluidic mass spectrometry approach for studying the catalytic performance of discrete catalyst particles in nL‐sized droplets. These silica particles, functionalized with a covalently bonded Ley–Arvidsson–Yamamoto catalyst, were applied to catalyze a Mannich reaction. Using this method, droplets containing single or a few particles were generated in acetonitrile, and product formation was studied by electrospray ionization mass spectrometry. A total of 100 reactions of individual particles in nL droplets were investigated using this method. These single‐particle reactions revealed a high degree of heterogeneity in catalytic activity, underscoring the importance of single‐particle resolution for accurate catalyst characterization and targeted method development.
Protoboration exhibits inverse chemoselectivity relative to classical hydroboration and proceeds via a nucleophilic boron species. Although well established for alkenes and alkynes, its application to carbonyl (C═O) compounds remains unexplored, and all reported methods to date rely on metal catalysis. Herein, we report the first protoboration of carbonyl compounds and the first metal‐free variant of this transformation. An N‐heterocyclic carbene (NHC)‐catalyzed protocol enables the direct protoboration of unactivated dialkyl ketones to afford α‐hydroxyboronate esters in high yields under mild conditions, using readily available bis(pinacolato)diboron (B2pin2) and isopropyl alcohol (IPA). Mechanistic investigations, including control and sequential addition experiments, variable‐temperature nuclear magnetic resonance, and density functional theory calculations, reveal cooperative activation by the NHC, diboron reagent, and alcohol. A nucleophilic boron species derived from an NHC–borane complex, previously limited to conjugate borylation, is shown here to directly activate relatively unreactive dialkyl ketones, a reactivity previously considered inaccessible without metal catalysis. This work establishes a sustainable, metal‐free strategy for protoboration and significantly expands the scope of nucleophilic boron chemistry to carbonyl functionalization.
A new family of pentamethylcyclopentadienyl (C5Me5, Cp*) iridium(III), rhodium(III), and ruthenium(III) complexes bearing bidentate 1,2‐dioxime ligands was developed as a promising platform for aqueous‐phase catalysis. A modular series of piano‐stool complexes of general formula [MX(η5‐Cp*)(κ2N‐dioxime)]+ (M = Ir, Rh, Ru; X = Cl, I) was obtained in excellent yields from inexpensive and readily available dioximes. Spectroscopic and crystallographic analyses showed that dioxime coordination strongly affects the acid–base behavior and water solubility of the complexes, while D2O speciation studies revealed sequential deprotonation equilibria (pKa1 ≈ 3.3; pKa2 ≈ 6.5–7.1) and halide lability, highlighting the dynamic behavior of these systems under catalytic conditions. The catalytic performance of the complexes was evaluated in amine H/D exchange using D2O as both solvent and deuterium source. Iridium derivatives, particularly [IrCp*X(κ2N‐nioxime)]+ (X = Cl, I), achieved >95% deuterium incorporation in pyrrolidine under optimized conditions. Cyclic, acyclic, and benzylic amines underwent efficient isotopic exchange, including incorporation at positions remote from the nitrogen, demonstrating broad but substrate‐dependent reactivity. These results identify Cp*Ir‐dioxime complexes as effective proton‐responsive catalysts for H/D exchange in water, and 1,2‐dioxime ligands provide a useful and tunable framework for the development of aqueous isotope‐exchange catalysis.
The field of heme‐catalyzed oxidation chemistry predominantly focuses on oxidations performed by Compounds 0, I, and II. In the past 50 years, a number of alternative high‐valent iron porphyrin species have been identified wherein the porphyrin holds all the oxidative equivalents. Little is known regarding their potential to perform oxidations of small molecules nor their possible role in catalytic pathways. One avenue of particular interest to us is the use of isoporphyrins for the umpolung of chloride (J. Am. Chem. Soc. 2012, 134, 4469–4472; Inorg. Chem. 2022, 61, 8105–8111; Angew. Chem. Int. Ed. 2023, 62, e202313006). Here we have further explored the viability of such catalytic reactivity and found that chlorination yields remain rather low. One main complication with such reactivity is the presence of a competing pathway. Namely, we are able to efficiently transform 1,3,5‐trimethoxybenzene (TMB) to 2,6‐dimethoxybenzoquinone (DMBQ). The two pathways diverge at the iron(III) π‐dication, as TMB is capable of reducing the π‐dication to a radical π‐cation. We have further investigated the breadth of reactivity of the iron(III) π‐dication and provide comprehensive characterization of the radical π‐cation including UV–vis, resonance Raman, and Mössbauer spectroscopies, as well as mass spectrometry.
Visible‐light‐gated catalysis enables control over chemical reactivity, yet single transition‐metal system for intermolecular [2 + 2 + 2] cycloadditions of alkynes remain underdeveloped. Here, we report a visible‐light‐gated Rh‐catalyzed intermolecular [2 + 2 + 2] cycloaddition of internal and terminal alkynes using spiro‐fluorene–indenoindenyl (SFI)–Rh(cod) complexes (cod = 1,5‐cyclooctadiene). Under blue‐light irradiation, a range of alkynes undergo cyclotrimerization under mild conditions to afford substituted benzenes. In contrast, under dark conditions, reactivity is suppressed or diverted to polymerization, highlighting a divergence in reaction pathways. Mechanistic studies suggest that this divergence arises from coordination‐state‐dependent reactivity of the Rh catalyst. Photoinduced ligand dissociation generates coordinatively unsaturated Rh species capable of binding multiple alkynes, thereby enabling cyclotrimerization, whereas the dark‐state reactivity is consistent with predominance of mono‐alkyne‐coordinated species. DFT calculations indicate that cyclotrimerization proceeds on the ground‐state surface, supporting a mechanism in which light modulates catalyst speciation rather than altering the reaction pathway. This coordination‐state control regulates competing reactivity through kinetic control of pathway selection.
This study reports the synthesis, structures, and bonding of silver(I) and gold(I) carbonyl complexes supported by a bulky, mesityl-group-decorated, electron-rich tris(pyridyl)borate ligand. This ligand offers steric protection and strong sigma-donation, allowing isolation of classical carbonyls [MeB(6-(Mes)Py)3]Ag(CO) and [MeB(6-(Mes)Py)3]Au(CO). Both show notably low CO stretching frequencies (2115 and 2063 cm-1), lowest for structurally authenticated Ag(I)-CO and Au(I) species, respectively, indicating enhanced metal -> CO pi-backbonding. X-ray crystallography shows tetrahedral kappa 3-NNN coordination and linear M-C-O fragments (M = Ag, Au), while 13C NMR spectrum of the silver complex reveals 1 07/109Ag-13C coupling. Computational studies indicate that electrostatic interactions dominate the interaction between M and CO, but gold(I) shows stronger orbital contributions and pi-backdonation than silver(I), consistent with experimental trends. Buried-volume calculations highlight the ligand's steric bulk. These findings expand the chemistry of isolable Ag(I) and Au(I) carbonyls, providing examples of classical CO complexes and insights into bonding and stabilization strategies. Spectroscopic data on the copper analog, [MeB(6-(Mes)Py)3]Cu(CO), have also been included for comparison.
Planar hydrocarbon‐based tropyl radicals remain elusive because seven‐membered open‐shell systems readily undergo structural deformation and intermolecular reactions. Herein, we report the design, isolation, and structural characterization of dibenzotropyl radicals bearing anthryl‐based π‐systems. Density functional theory (DFT) calculations predicted that bianthryl and teranthryl substituents stabilize orthogonally twisted conformations containing a planar dibenzotropyl radical unit while suppressing the formation of reactive folded structures. One‐electron reduction of the corresponding dibenzotropyliums afforded persistent neutral radicals for both the bianthryl and teranthryl derivatives, which are stable under ambient conditions. Single‐crystal X‐ray diffraction analysis of the bianthryl‐substituted radical revealed a sterically unperturbed planar dibenzotropyl structure, providing the first crystallographic evidence for a planar hydrocarbon‐based tropyl radical. Spectroscopic, electrochemical, and theoretical studies revealed reversible redox interconversion between the cationic and radical states while retaining the planar seven‐membered framework. These findings provide insight into redox‐active seven‐membered π‐systems and establish a design strategy for stable open‐shell hydrocarbons.
High‐entropy alloy nanoparticles (HEA NPs) have attracted significant interest due to their multielement interactions and high surface areas, making them promising candidates for heterogeneous catalysis. Their broader implementation, however, is often limited by restrictive synthesis conditions and challenges in scalable production. Laser‐based strategies have recently emerged as versatile, green approaches enabling the preparation of colloidal, support‐free HEA NPs under ambient conditions. Pulsed laser techniques exploit ultrafast heating and rapid quenching in liquids, affording kinetic control that promotes single‐phase formation with homogeneous elemental distributions. Some approaches also offer significant potential for scale‐up and high‐throughput production, as well as access to amorphous HEA NPs. This focused review summarizes and critically compares recent advances in laser‐based fabrication of HEA NPs in the liquid phase, focusing on laser reduction in liquid, laser ablation in liquid, and microparticle laser fragmentation in liquid. We highlight advantages and limitations with respect to I) compositional flexibility, II) nanoparticle size, phase structure and elemental composition, and III) convenience and scalability of the method. Finally, emerging applications of laser‐synthesized HEA NPs in heterogeneous catalysis and magnetism are highlighted, underscoring the need for further developments toward fundamental understanding, large‐scale production, and practical deployment.
The development of multifunctional organic pi-conjugated molecules has been of great interest due to their potential use in sustainable energy applications. Some progress has been made in the development of n-type, electron-acceptor molecules with very low LUMO levels, but the diversity of suitable molecular scaffolds remains strictly limited. Along similar lines, phosphorus incorporation into ring-fused organic scaffolds has proven to create molecules with beneficial optical and electrochemical properties and electron-acceptor character, as well as exceptional tunability. Herein, we report a detailed structure-property study of the dithieno[2,3-b;3 ',2 '-e]-4-keto-1,4-dihydrophosphinine system, an intriguing scaffold that has remained largely unexplored to date. Through various targeted approaches, we comprehensively explore a series of dithienoketophosphinine-based electron-acceptor species functionalized at the phosphorus center, the carbonyl group, and the thieno-backbone to explore and more deeply understand the impact on the electrochemical, optical, and structural properties of the system. Our study convincingly establishes the superior electron-acceptor properties of the scaffold that outcompete state-of-the-art materials, as well as its high degree of tunability that also unlocks valuable emission features upon extension of the core.
Conventional carbonate‐based electrolytes take merits of cost‐efficiency, high‐voltage stability, and Al current collector passivation, while their application in lithium metal batteries (LMBs) is severely hindered by issues such as lithium (Li) dendrite growth and unstable interfaces. Herein, we report that lithium difluoroacetate (LiDFA) with a partially fluorinated structure and strongly bonded Li+ can act as a multifunctional electrolyte additive to stabilize LMBs in carbonate‐based electrolytes. The Lewis base property of DFA− can effectively suppress the hydrolysis of LiPF6, thereby improving the storage stability of the electrolyte. In addition, LiDFA can enhance the solubility of LiNO3 in carbonate electrolytes, and the synergistic effect of the LiDFA and LiNO3 contributes to the formation of an inorganic‐rich solid electrolyte interphase, facilitates dense and uniform Li deposition morphology, as well as accelerates the interfacial kinetics. Consequently, the designed additive‐modified electrolyte improves the reversibility of Li plating/stripping with a high Coulombic efficiency of 99.14% and enables long‐term cycling of Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) over 150 cycles with a capacity retention of 82.72% under the condition of lean electrolyte, limited Li source, and conventional Li‐salt concentration. This work provides an effective and low‐cost strategy for designing high‐performance electrolytes for advanced battery systems.
