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The burgeoning field of frustrated Lewis pair (FLP) heterogeneous catalysts has garnered significant interest in recent years, primarily due to their inherent ability to activate H-source molecules, such as H2, thereby facilitating hydrogenation reactions. However, the application of single metal atom catalysts incorporating FLP sites has been relatively under-explored. In this study, non-precious transition metal atoms were anchored onto a C2N framework with an intrinsic cavity and a defective N-C sheet. Theoretical calculations substantiated energy barriers as low as 0.10 eV for isopropanol activation, thereby positioning these catalysts as highly promising candidates for catalytic transfer hydrogenation of furfural. Electronic structure analyses revealed that the H-O bond breakage in isopropanol molecules was significantly facilitated by the presence of FLP sites within the catalysts. Notably, both Ni-C2N and Ni-N6-C demonstrated exceptional potential as selective catalysts for the hydrogenation of furfural into furfuryl alcohol, exhibiting remarkably low barriers of only 0.65-0.72 eV for the rate-determining steps, which are notably lower than those observed in many traditional catalysts. Theoretical investigations strongly imply that the construction of single atom catalysts with FLP sites could significantly enhance the activity and selectivity for hydrogenation reactions, thus stimulating the experimental synthesis of such catalysts., (© 2024 Wiley‐VCH GmbH.)

Gas molecules, as a family of unique polyatomic building blocks, have long been considered hard to involve in molecular assembly or construct assembled materials due to their structural simplicity yet paucity of defined interacting sites. To solve this non-trivial challenge, a core idea is to break the limit of current ways of bonding gas molecules, endowing them with new modes of interactions that match the basic requirements of molecular assembly. In recent years, a new concept, named the dynamic gas-bridged bond (DGB), has emerged, which allows for gas molecules to constitute a dynamic bridging structure between other building blocks with the aid of frustrated Lewis pairs. This makes it possible to harness gas in a supramolecular or dynamic manner. Herein, this perspective discusses distinct dynamic natures of DGBs and manifests their particular functions in various fields, including the control of molecular/polymeric self-assembly nanostructures, creation of multidimensional assembled materials, and recyclable catalysts. The future research direction and challenges of dynamic gas-bridged chemistry toward gas-programmed self-assembly and gas-constructed adaptive materials are highlighted.

Xanthene-backbone FLPs featuring secondary borane functions -B(Ar X )H (where Ar X =C 6 F 5 (Ar F ) or C 6 Cl 5 (Ar Cl )) have been targeted through reactions of the dihydroboranes Me 2 S ⋅ BAr X H 2 with [4,5-xanth(PR 2 )Li] 2 (R=Ph, i Pr), and investigated in the synthesis of related cationic systems via hydride abstraction. The reactivity of these systems (both cationic and charge neutral) with ammonia have been probed, with a view to probing the potential for proton shuttling via N-H bond 'activation.' We find that in the case of four-coordinate boron systems (cationic or change neutral), the N-H linkage remains intact, supported by a NH⋅⋅⋅P hydrogen bond which is worth up to 17 kcal mol -1 thermodynamically, and enabled by planarization of the flexible xanthene scaffold. For cationic three coordinate systems, N-to-P proton transfer is viable, driven by the ability of the boron centre to stabilise the [NH 2 ] - conjugate base through N-to-B π bonding. This proton transfer can be shown to be reversible in the presence of excess ammonia, depending on the nature of the B-bound Ar X group. It is viable in the case of C 6 F 5 substituents, but is prevented by the more sterically encumbering and secondary donor-stabilising capabilities of the C 6 Cl 5 substituent., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Interest is growing in transition metal-free compounds for small molecule activation and catalysis. We discuss the opportunities arising from synthesizing sodium-doped amorphous silicon-boron-nitride (Na-doped a-SiBN). Na + cations and 3-fold coordinated B III moieties were incorporated into an amorphous silicon nitride network via chemical modification of a polysilazane followed by pyrolysis in ammonia (NH 3 ) at 1000 °C. Emphasis is placed on the mechanisms of hydrogen (H 2 ) activation within Na-doped a-SiBN structure. This material design approach allows the homogeneous distribution of Na + and B III moieties surrounded by SiN 4 units contributing to the transformation of the B III moieties into 4-fold coordinated geometry upon encountering H 2 , potentially serving as frustrated Lewis acid (FLA) sites. Exposure to H 2 induced formation of frustrated Lewis base (FLB) N - = sites with Na + as a charge-compensating cation, resulting in the in situ formation of a frustrated Lewis pair (FLP) motif (≡B FLA ⋅⋅⋅H δ- ⋅⋅⋅H δ+ ⋅⋅⋅:N - (Na + )=). Reversible H 2 adsorption-desorption behavior with high activation energy for H 2 desorption (124 kJ mol -1 ) suggested the H 2 chemisorption on Na-doped a-SiBN. These findings highlight a future landscape full of possibilities within our reach, where we anticipate main-group-mediated small molecule activation will have an important impact on the design of more efficient catalytic processes and the discovery of new catalytic transformations., (© 2024 Wiley-VCH GmbH.)

Hydroboranes are versatile reagents in synthetic chemistry, but their synthesis relies on energy-intensive processes. Herein, we report a new method for the preparation of hydroboranes from hydrogen and the corresponding haloboranes. Triethylamine (NEt 3 ) form with dialkylchloroboranes a Frustrated Lewis Pair (FLP) able to split H 2 and afford the desired hydroborane with ammonium salts. Unreactive haloboranes were unlocked using a catalytic amount of Cy 2 BCl, enabling the synthesis of commonly used hydroboranes such as pinacolborane or catecholborane. The mechanisms of these reactions have been examined by DFT studies, highlighting the importance of the base selection. Finally, the system's robustness has been evaluated in one-pot B-Cl hydrogenolysis/hydroboration reactions of C=C unsaturated bonds., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

This study employs computational methods to investigate the mechanism of H 2 activation by frustrated Lewis pair (FLP) species, including both intermolecular and intramolecular nitrothane/borane FLP systems. Previous studies have proposed two qualitative reactivity mechanism models to explain the facile cleavage of H 2 by FLPs. The findings of this study support the electric field mechanism as the favorable pathway for H 2 cleavage. Utilizing frontier molecular orbital theory and energy decomposition analysis, the study explores the electronic structure and nature of the reactions under an external electric field (EEF). Analysis using the activation strain model highlights the significant influence of geometrical deformation energies of FLPs on the activation barriers of H 2 activation reactions. Computational results suggest that H 2 activation by FLP molecules follows the electric field mechanism, indicating the potential of the FLP/EEF combination as an effective activator for inert molecules., (© 2024 Wiley-VCH GmbH.)

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect on the activation of H 2 and diverse organic substrates. Reactions of RE(OAr) 3 (RE=La, Sm, and Y; Ar=2,6- t Bu 2 -C 6 H 3 ) with unsaturated NHC I t Bu (:C[N(R)CH] 2 , R= t Bu) isolated abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr) 3 were treated with NHO (R 2 C=C[N(R)C(R)] 2 , R=CH 3 ). Both RE/aNHC and RE/NHO Lewis pairs enabled cooperative H 2 activation. Furthermore, RE(OAr) 3 were found to catalyze the hydrogenation of the exocyclic C=C double bond of NHO under mild conditions. Moreover, treatment of the La/aNHC complex with benzaldehyde produced a La/C4 1,2-addition product. The La/NHO Lewis pair could react with (trimethylsilyl)diazomethane and α, β-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively., (© 2024 Wiley-VCH GmbH.)

The strategic installation of a [ 18 F]fluorine atom at the specific position of the lead molecule is a never-ending challenge for radiochemists in their endeavour to develop novel positron emission tomography (PET) imaging applications. Although the radiosynthesis of [ 18 F]CF 2 H-containing molecules has been explored in the past decade, more methods need to be explored for various well-functionalized compounds. Recently, two novel strategies of radiodifluoromethylation were reported, namely the utilization of [ 18 F]difluorocarbene building block and frustrated Lewis pair-mediated C- 18 F bond formation, respectively. These methods provide an efficient radiofunctionalization of complex CF 2 H-containing molecules for drug discovery and PET ligand development., Competing Interests: None., (AJNMMI Copyright © 2024.)

Understanding the structure-performance relationships of a frustrated Lewis pair (FLP) at the atomic level is key to yielding high efficiency in activating chemically "inert" molecules into value-added products. A sound strategy was developed herein through incorporating oxygen defects into a Zr-based metal-organic layer (Zr-MOL-D) and employing Lewis basic proximal surface hydroxyls for the in situ formation of solid heterogeneous FLP (Zr 4-δ -V O -Zr -OH ). Zr-MOL-D exhibits a superior CO 2 to CO conversion rate of 49.4 μmol g -1 h -1 in water vapor without any sacrificing agent or photosensitizer, which is about 12 times higher than that of pure MOL (Zr-MOL-P), with extreme stability even after being placed for half a year. Theoretical and experimental results reveal that the introduction of FLP converts the process of the crucial intermediate COOH* from an endothermic reaction to an exothermic spontaneous reaction. This work is expected to provide new prospects for developing efficient MOL-based photocatalysts in FLP chemistry through a sound defect-engineering strategy.

A method of desymmetrization of geminal difluoroalkanes using frustrated Lewis pair (FLP) mediated monoselective C-F activation where a chiral sulfide is the Lewis base component is reported. The stereoselective reaction provides generally high yields of diastereomeric sulfonium salts with dr of up to 95:5. The distribution of diastereomers is found to be thermodynamically controlled via facile sulfide exchange. The use of enantiopure chiral sulfides allows for high stereospecificity in nucleophilic substitution reactions and the formation of stereoenriched products., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

CO 2 hydrogenation to methane is gaining increasing interest as one of the most promising ways to store intermittent renewable energy in the form of chemical fuels. Ni particles supported on CeO 2 represent a highly efficient, stable and inexpensive catalyst for this reaction. Herein, Ni-doped CeO 2 nanoparticles were tested for CO 2 methanation showing an extremely high Ni mass-specific activity and CH 4 selectivity. Operando characterization reveals that this performance is tightly associated with ionic Νi and Ce 3+ surface sites, while formation of metallic Ni does not seem to considerably promote the reaction. Theoretical calculations confirmed the stability of interstitial ionic Ni sites on ceria surfaces and highlighted the role of Ce-O frustrated Lewis pair (FLP), Ni-O classical Lewis pair (CLP) and Ni-Ce pair sites to the activation of H 2 and CO 2 molecules. To a large extent, the theoretical predictions were validated by in situ spectroscopy under H 2 and CO 2  : H 2 gaseous environments., (© 2023 Wiley-VCH GmbH.)

The first polyoxometalates (POMs) composed of Mo IV , Mo V 2 , discrete d 1 -Mo V and Mo VI , [Mo IV 3 Mo V 6 Mo VI 4 O 32 (μ 2 -OH)(μ 3 -OH)py 9 ] (1), was prepared from the solvothermal partial oxidation of [Mo IV 3 O 2 (O 2 CCH 3 ) 6 (H 2 O) 3 ]ZnCl 4 in a mixture of pyridine and water. The Mo V =O adduct-free unit [H 2 Mo 12 O 33 py 9 ] presents the 11e-reduced Mo derivative of the paratungtic archetype. The use of methanol, ethanol, n-propyl alcohol and triglycol instead of water produced the isostructural [Mo IV 3 Mo V 6 Mo VI 4 O 32 (μ 3 -OH)(μ 2 -OR)py 9 ](R=CH 3 , 2; C 2 H 5 , 3; C 3 H 7 , 4; C 2 H 4 OH, 5), providing the first examples of Mo IV 3 -POMs containing bridging alkoxyl groups. The addition of [Cr III Mo 6 O 24 ] 9- led to the substitution of {Mo V =O} 3+ with {Cr III -py} 3+ in the allomer [Mo IV 3 Mo V 5 Mo VI 4 Cr III O 32 (μ-OH) 2 py 10 ] (6). Using a mixture of Mo 3 and MoW 2 precursors afforded W VI -incorporated allomer [Mo IV 3 Mo V 6 Mo VI W VI 3 O 32 (μ-OH) 2 py 9 ] (7). The complete substitution of Mo VI with W VI by using a mixture of the Mo 2 W, MoW 2 and W 3 precursors produced the diamagnetic [Mo IV 3 Mo V 6 W VI 4 O 33 (μ 3 -OH)py 9 ] - (syn-8) resulting from the anti→syn conversion between the top and bottom M 3 triads concomitant with Mo V -Mo V bonding. Both anti-1-7 and syn-8 have been characterized by X-ray single crystal structural analyses. The spin distribution and magnetic interactions have been investigated by temperature-dependent magnetic susceptibility and DFT theoretical calculations. Heterogeneous hydrogen transfer catalysis has been examined by the Lewis catalysis field (LCF) theory., (© 2023 Wiley-VCH GmbH.)

To overcome the thermodynamic and kinetic impediments of the Sabatier CO 2 methanation reaction, the process must be operated under very high temperature and pressure conditions, to obtain an industrially viable conversion, rate, and selectivity. Herein, we report that these technologically relevant performance metrics have been achieved under much milder conditions using solar rather than thermal energy, where the methanation reaction is enabled by a novel nickel-boron nitride catalyst. In this regard, an in situ generated HOB⋅⋅⋅B surface frustrated Lewis's pair is considered responsible for the high Sabatier conversion 87.68 %, reaction rate 2.03 mol g Ni -1 h -1 , and near 100 % selectivity, realized under ambient pressure conditions. This discovery bodes well for an opto-chemical engineering strategy aimed at the development and implementation of a sustainable 'Solar Sabatier' methanation process., (© 2023 Wiley-VCH GmbH.)

Frustrated Lewis pairs (FLPs), discovered in the last few decades for homogeneous catalysts and in the last few years also for heterogeneous catalysts, are stimulating the scientific community's interest for their potential in small-molecule activation. Nevertheless, how an FLP activates stable molecules such as CO 2 is still undefined. Through a careful spectroscopic study, we here report the formation of FLPs over a highly defective CeO 2 sample prepared by microwave-assisted synthesis. Carbon dioxide activation over FLP is shown to occur through a bidentate carbonate bridging the FLP and implying a Ce 3+ -to-CO 2 charge transfer, thus enhancing its activation. Carbon dioxide reaction with methanol to form monomethylcarbonate is here employed to demonstrate active roles of FLP and, eventually, to propose a reaction mechanism clarifying the role of Ce 3+ and oxygen vacancies.

Frustrated Lewis pairs (FLPs) have been widely investigated as promising catalysts due to their metal-free feature and ability to activate small molecules. Since their discovery, many works have been investigating how these Lewis pairs (intermolecular pairs) are held together in an encounter complex. This prompted several studies based on theoretical investigations, but experimental ones are limited yet. In this communication we show evidence of weak intermolecular interactions between Lewis acids and Lewis bases, distinguishing the Lewis adduct from FLPs, by probing fluorine-carbon vibrational modes using infrared spectroscopy. The main evidence is based on the band shifts occurring in FLPs due to weak hydrogen bonds between the hydrogen atoms of the Lewis base and the fluorine atoms of Lewis acid., (© 2022 Wiley-VCH GmbH.)

The development and application of new organoboron reagents as Lewis acids in synthesis and metal-free catalysis have dramatically expanded over the past 20 years. In this context, we will show the recent uses of the simple and relatively weak Lewis acid BPh 3 -discovered 100 years ago-as a metal-free catalyst for various organic transformations. The first part will highlight catalytic applications in polymer synthesis such as the copolymerization of epoxides with CO 2 , isocyanate, and organic anhydrides to various polycarbonate copolymers and controlled diblock copolymers as well as alternating polyurethanes. This is followed by a discussion of BPh 3 as a Lewis acid component in the frustrated Lewis pair (FLP) mediated cleavage of hydrogen and hydrogenation catalysis. In addition, BPh 3 -catalyzed reductive N-methylations and C-methylations with CO 2 and silane to value-added organic products will be covered as well along with BPh 3 -catalyzed cycloadditions and insertion reactions. Collectively, this mini-review showcases the underexplored potential of commercially available BPh 3 in metal-free catalysis.

Asymmetric hydrogenation, a seminal strategy for the synthesis of chiral molecules, remains largely unmet in terms of activation by non-metal sites of heterogeneous catalysts. Herein, as demonstrated by combined computational and experimental studies, we present a general strategy for integrating rationally designed molecular chiral frustrated Lewis pair (CFLP) with porous metal-organic framework (MOF) to construct the catalyst CFLP@MOF that can efficiently promote the asymmetric hydrogenation in a heterogeneous manner, which for the first time extends the concept of chiral frustrated Lewis pair from homogeneous system to heterogeneous catalysis. Significantly, the developed CFLP@MOF, inherits the merits of both homogeneous and heterogeneous catalysts, with high activity/enantio-selectivity and excellent recyclability/regenerability. Our work not only advances CFLP@MOF as a new platform for heterogeneous asymmetric hydrogenation, but also opens a new avenue for the design and preparation of advanced catalysts for asymmetric catalysis., (© 2022 Wiley-VCH GmbH.)

The chemical conversion of CO 2 to long-chain chemicals is considered as a highly attractive method to produce value-added organics, while the underlying reaction mechanism remains unclear. By constructing surface vacancy-cluster-mediated solid frustrated Lewis pairs (FLPs), the 100 % atom-economical, efficient chemical conversion of CO 2 to dimethyl carbonate (DMC) was realized. By taking CeO 2 as a model system, we illustrate that FLP sites can efficiently accelerate the coupling and conversion of key intermediates. As demonstrated, CeO 2 with rich FLP sites shows improved reaction activity and achieves a high yield of DMC up to 15.3 mmol g -1 . In addition, by means of synchrotron radiation in situ diffuse reflectance infrared Fourier-transform spectroscopy, combined with density functional theory calculations, the reaction mechanism on the FLP site was investigated systematically and in-depth, providing pioneering insights into the underlying pathway for CO 2 chemical conversion to long-chain chemicals., (© 2022 Wiley-VCH GmbH.)

Olefin-borane π-complexes have been postulated as intermediates for the addition of frustrated Lewis pairs (FLP) to olefins. In the present study, we have employed this weak interaction to modulate the electronic properties of boron-based π-electron materials. A series of donor-π-acceptor (D-π-A) fluorophores that contain an alkenyl-bridged diarylboryl group is synthesized. A crystallographic analysis revealed that the olefin and boron moieties are held in close proximity. Upon addition of a Lewis base to a solution of these D-π-A fluorophores, an FLP-type addition occurs with concurrent significant changes in the absorption and emission properties. The FLP-type reaction shifts the reaction site from the Lewis-acidic boron atom to a carbocationic center, and thereby even facilitates a reaction with bulky Lewis bases. For example, a tricyclohexylphosphine adduct thus generated exhibits temperature-dependent reversible dissociation/association behavior. These results provide a design strategy for stimuli-responsive emissive boron-based materials., (© 2022 Wiley-VCH GmbH.)

The trapping reactions of carbene analogs G14F 2 (G14 = group 14 element) by the benzene-bridged B/P-Rea frustrated Lewis pair (FLPs) molecule are studied using density functional theory (B3LYP-D3(BJ)/def2-TZVP). Our theoretical investigations predict that only the CF 2 intermediate rather than other heavy carbene analogs can be trapped by the B/P-Rea FLP-type molecule. Energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) analyses indicate that the bonding nature of the G14F 2 catching reactions by the B/P-Rea FLP-type molecule is a donor-acceptor (singlet-singlet) interaction rather than an electron-sharing (triplet-triplet) interaction. Moreover, EDA-NOCV and frontier molecular orbital (FMO) theory findings strongly suggest that the lone pair (LP) (P) → vacant p-π-orbital (G14F 2 ) interaction rather than the empty σ-orbital (B) ← sp 2 -σ-orbital (G14F 2 ) interaction plays a predominant role in establishing its bonding condition during the G14F 2 trapping reaction with the B/P-Rea FLP-associated molecule. Our activation strain model findings reveal that the atomic radius of the G14 element of G14F 2 plays a key role in determining the activation barrier of the G14F 2 trapping reactions by the benzene-bridged B/P-Rea FLP. The valence bond state correlation diagram (VBSCD) model developed by Shaik is used to rationalize the calculated results. The VBSCD findings demonstrate that in the present trapping reactions, the singlet triplet splitting of G14F 2 plays a significant role in influencing its reaction barrier and reaction enthalpy. Our theoretical results demonstrate that the relationship between the geometrical parameters of the transition states and the corresponding reaction free energy barriers agrees well with the findings based on the Hammond postulate., (© 2022 Wiley Periodicals LLC.)

Molybdenum(VI) bis(imido) complexes [Mo(NtBu) 2 (L R ) 2 ] (R=H 1 a; R=CF 3 1 b) combined with B(C 6 F 5 ) 3 (1 a/B(C 6 F 5 ) 3 , 1 b/B(C 6 F 5 ) 3 ) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H-H, Si-H and O-H bonds. Cleavage of H 2 and Et 3 SiH affords ion pairs [Mo(NtBu)(NHtBu)(L R ) 2 ][HB(C 6 F 5 ) 3 ] (R=H 2 a; R=CF 3 2 b) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H 2 O leads to [Mo(NtBu)(NHtBu)(L R ) 2 ][(HO)B(C 6 F 5 ) 3 ] (R=H 3 a; R=CF 3 3 b). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a. Mechanistic elucidation revealed insertion of the aldehyde into the B-H bond of [HB(C 6 F 5 ) 3 ] - . We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L R ) 2 ][{PhCH 2 O}B(C 6 F 5 ) 3 ] (R=H 4 a; R=CF 3 4 b). Catalysis occurs at [HB(C 6 F 5 ) 3 ] - while [Mo(NtBu)(NHtBu)(L R ) 2 ] + (R=H or CF 3 ) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC)., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Heteroaryl boronic acids and esters are extremely important and valuable intermediates because of their wide application in the synthesis of marketed drugs and bioactive compounds. Over the last couple of decades, the construction of highly important heteroaryl carbon-boron bonds has created huge attention. The transition-metal-free protocols are more green, less sensitive to air and moisture, and also economically advantageous over the transition-metal-based protocols. The transition-metal-free C-H borylation of heteroarenes and C-X (X=halogen) borylation of heteroaryl halides represents an excellent approach for their synthesis. Also, various cyclization and alkyne activation protocols have been recently established for their synthesis. The goal of this review article is to summarize the existing literature and the current state of the art for transition-metal-free synthesis of heteroaryl boronic acid and esters., (© 2022 Wiley-VCH GmbH.)

Zeolites have found tremendous applications in the chemical industry. However, the dynamic nature of their active sites under the flow of adsorbate molecules for adsorption and catalysis is unclear, especially in operando conditions, which could be different from the as-synthesized structures. In the present study, we report a structural transformation of the adsorptive active sites in SAPO-34 zeolite by using acetone as a probe molecule under various temperatures. The combination of solid-state nuclear magnetic resonance, in situ variable-temperature synchrotron X-ray diffraction, and in situ diffuse-reflectance infrared Fourier-transform spectroscopy allow a clear identification and quantification that the chemisorption of acetone can convert the classical Brønsted acid site adsorption mode to an induced Frustrated Lewis Pairs adsorption mode at increasing temperatures. Such facile conversion is also supported by the calculations of ab-initio molecular-dynamics simulations. This work sheds new light on the importance of the dynamic structural alteration of active sites in zeolites with adsorbates at elevated temperatures., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The metal-free catalytic hydrogenolysis of silyl triflates and halides (I, Br) to hydrosilanes is unlocked by using arylborane Lewis acids as catalysts. In the presence of a nitrogen base, the catalyst acts as a Frustrated Lewis Pair (FLP) able to split H 2 and generate a boron hydride intermediate capable of reducing (pseudo)halosilanes. This metal-free organocatalytic system is competitive with metal-based catalysts and enables the formation of a variety of hydrosilanes at room temperature in high yields (>85 %) under a low pressure of H 2 (≤10 bar)., (© 2022 Wiley-VCH GmbH.)

Frustrated Lewis pair (FLP) chemistry is an alternative strategy in the area of metal-free organic catalysis. This study reports adamantane as FLP molecular scaffold used to design new FLP (ambiphilic molecule) for the metal-free catalytic reduction of CO 2 to methoxy borane (CH 3 O[B]) via hydroboration process. The DFT [B97D/6-31G(d,p), (SMD,benzene)//B3PW91/6-31G(d,p),SDD] calculations have been employed to examine the reaction. The saturated hydrocarbon showed a marked improvement in the energetics of the reduction process compared to the unsaturated phenylene FLPs employed for such reactions. The saturated scaffold improves the Lewis acid and base characters in adamantyl-derived FLPs. The gauche arrangement of Lewis pairs in the adamantyl FLP system is critical to lower the energy barriers in the potential energy surfaces compared to the unsaturated phenylene FLPs. The adamantyl scaffold FLP lowered the activation barriers by ∼6.0 kcal/mol in the key steps of the reduction of CO 2 with the reducing agent compared to the phenylene FLPs. These calculated results corroborate the activation of the reducing agent and carbon dioxide to function as efficient catalysis in all steps. The enhancement in the Lewis characters of FLPs with adamantane scaffold was elucidated with conceptual density functional theory (CDFT) calculations., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The frustrated Lewis pair (FLP) concept in homogeneous catalysis was extended to heterogeneous catalysis via the supramolecular system of FLP between deprotonated zeolite framework oxygens and confined carbocations in methanol-to-olefin (MTO) reactions. In this FLP, the polymethylbenzenium (PMB + ) functioned as the Lewis acid to accept an electron pair, and the deprotonated framework oxygen site acted as the Lewis base to donate an electron pair. This FLP theoretically demonstrated the ability to undergo H 2 heterolysis and alkanes dehydrogenation, and this was further confirmed by gas chromatography-mass spectrometer (GC-MS) catalytic experiments inside FLP-containing chabazite zeolites. All these findings not only bring new recognition to the carbocation chemistry in zeolite cages but also put forward a new reaction pathway as one part of MTO reactions., (© 2022 Wiley-VCH GmbH.)

The chemistry of dicationic diboranes with two B II atoms that are engaged in direct B-B bonding is by enlarge unexplored, although these molecules have intriguing properties due to their combined Lewis acidic and electron-donor properties. Unsymmetric dicationic diboranes are extremely rare, but especially attractive due to their polarized B-B bond. In this work we report the directed synthesis of several stable unsymmetric dicationic diboranes by reaction between the electron-rich ditriflato-diborane B 2 (hpp) 2 (OTf) 2 (hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-α]pyrimidinate) and phosphino-pyridines, establishing B-N and B-P bonds with the diborane concomitant with triflate elimination. In the case of 2-((ditertbutylphosphino)methyl)pyridine, the B-N bond is formed instantly, but the B-P bond formation requires (due to steric constraints) several days at ambient conditions for completion, creating an intermediate that could be used for frustrated Lewis pair (FLP)-like chemistry. Here we test its reaction with an aldehyde, and propose a new type of FLP-like chemistry., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The frustrated Lewis pair (FLP) derived from 2,6-lutidine and B(C 6 F 5 ) 3 is shown to mediate the catalytic hydrogenation of CO 2 using H 2 as the reductant and a silylhalide as an oxophile. The nature of the products can be controlled with the judicious selection of the silylhalide and the solvent. In this fashion, this metal-free catalysis affords avenues to the selective formation of the disilylacetal (R 3 SiOCH 2 OSiR 3 ), methoxysilane (R 3 SiOCH 3 ), methyliodide (CH 3 I) and methane (CH 4 ) under mild conditions. DFT studies illuminate the complexities of the mechanism and account for the observed selectivity., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The metal-free catalytic hydrogenation of secondary carboxylic acid amides is developed. The reduction is realized by two new catalytic reactions. First, the amide is converted into the imidoyl chloride by triphosgene (CO(OCCl 3 ) 2 ) using novel phosphorus(V) catalysts. Second, the in situ generated imidoyl chlorides are hydrogenated in high yields by an FLP-catalyst. Mechanistic and quantum mechanical calculations support an autoinduced catalytic cycle for the hydrogenation with chloride acting as unusual Lewis base for FLP-mediated H 2 -activation., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Carbodicarbene (CDC), unique carbenic entities bearing two lone pairs of electrons are well-known for their strong Lewis basicity. We demonstrate herein, upon introducing a weak Brønsted acid benzyl alcohol (BnOH) as a co-modulator, CDC is remolded into a Frustrated Lewis Pair (FLP)-like reactivity. DFT calculation and experimental evidence show BnOH loosely interacting with the binding pocket of CDC via H-bonding and π-π stacking. Four distinct reactions in nature were deployed to demonstrate the viability of proof-of-concept as synergistic FLP/Modulator (CDC/BnOH), demonstrating enhanced catalytic reactivity in cyclotrimerization of isocyanate, polymerization process for L-lactide (LA), methyl methacrylate (MMA) and dehydrosilylation of alcohols. Importantly, the catalytic reactivity of carbodicarbene is uniquely distinct from conventional NHC which relies on only single chemical feature of nucleophilicity. This finding also provides a new spin in diversifying FLP reactivity with co-modulator or co-catalyst., (© 2021 Wiley-VCH GmbH.)

We report two BNB-type frustrated Lewis pairs which feature an acceptor-donor-acceptor functionalized cavity, and which differ in the nature of the B-bound fluoroaryl group (C 6 F 5 vs. C 6 H 3 (CF 3 ) 2 -3,5, Ar f ). These receptor systems are capable of capturing gaseous CO, and in the case of the -BAr f 2 system this can be shown to occur in reversible fashion at/above room temperature. For both systems, the binding event is accompanied by migration of one of the aryl substituents to the electrophilic carbon of the CO guest. Experiments utilizing an additional equivalent of P t Bu 3 allow the initially formed (non-migrated) CO adduct to be identified and trapped (via demethylation), while also establishing the reversibility of the B-to-C migration process. When partnered with the slightly less Lewis acidic -BAr f 2 substituent, this reversibility allows for release of the captured carbon monoxide in the temperature range 40-70 °C, and the possibility for CO sensing, making use of the associated colourless to orange/red colour change., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The intramolecular "inverse" frustrated Lewis pairs (FLPs) of general formula 1-BR 2 -2-[(Me 2 N) 2 C=N]-C 6 H 4 (3-6) [BR 2 =BMes 2 (3), BC 12 H 8 , (4), BBN (5), BBNO (6)] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X-ray analysis. These novel types of pre-organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via an ortho-phenylene linker, are capable of activating H-H, C-H, N-H, O-H, Si-H, B-H and C=O bonds. 4 and 5 deprotonated terminal alkynes and acetylene to form the zwitterionic borates 1-(RC≡C-BR 2 )-2-[(Me 2 N) 2 C=NH]-C 6 H 4 (R=Ph, H) and reacted with ammonia, BnNH 2 and pyrrolidine, to generate the FLP adducts 1-(R 2 HN→BR 2 )-2-[(Me 2 N) 2 C=NH]-C 6 H 4 , where the N-H functionality is activated by intramolecular H-bond interactions. In addition, 5 was found to rapidly add across the double bond of H 2 CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H 2 , HBPin and PhSiH 3 to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules., (© 2021 Wiley-VCH GmbH.)

The term boron-ligand cooperation was introduced to describe a specific mode of action by which certain metal-free systems activate chemical bonds. The main characteristic of this mode of action is that one covalently bound substituent at the boron is actively involved in the bond activation process and changes to a datively bound ligand in the course of the bond activation. Within this review, how the term boron-ligand cooperation evolved is reflected on and examples of bond activation by boron-ligand cooperation are discussed. It is furthermore shown that systems that operate via boron-ligand cooperation can complement the reactivity of classic intramolecular frustrated Lewis pairs and applications of this new concept for metal-free catalysis are summarized., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A classical Lewis adduct derives from a covalent bond between a Lewis acid and a base. When the adduct formation is precluded by means of steric hindrance the association of the respective acid-base molecular system is defined as a frustrated Lewis pair (FLP). In this work, the archetypal FLP Mes 3 P/B(C 6 F 5 ) 3 was characterized for the first time by resonance Raman spectroscopy, and the results were supported by density functional theory (DFT) calculations. The charge transfer nature of the lowest energy electronic transition, from phosphine to borane, was confirmed by the selective enhancement of the Raman bands associated to the FLP chromophore at resonance condition. Herein, we demonstrate the use of resonance Raman spectroscopy as a distinguished technique to probe the weak interaction involved in FLP chemistry., (© 2021 Wiley-VCH GmbH.)

Progress in frustrated Lewis pair (FLP) chemistry has revealed the importance of the main group elements in catalysis, opening new avenues in synthetic chemistry. Recently, new reactivities of frustrated Lewis pairs have been uncovered that disclose that certain combinations of Lewis acids and bases undergo single-electron transfer (SET) processes. Here an electron can be transferred from the Lewis basic donor to a Lewis acidic acceptor to generate a reactive frustrated radical pair (FRP). This minireview aims to showcase the recent advancements in this emerging field covering the synthesis and reactivities of frustrated radical pairs, with extensive highlights of the results from Electron Paramagnetic Resonance (EPR) spectroscopy to explain the nature and stability of the different radical species observed., (© 2020 Wiley-VCH GmbH.)

The reactivity of the frustrated Lewis pair (FLP) (F 5 C 2 ) 3 SnCH 2 P(tBu) 2 (1) was investigated with respect to the activation of elemental hydrogen. The reaction of 1 at elevated hydrogen pressure afforded the intramolecular phosphonium stannate(II) (F 5 C 2 ) 2 SnCH 2 PH(tBu) 2 (3). It was characterized by means of multinuclear NMR spectroscopy and single crystal X-ray diffraction. NMR experiments with the two isotopologues H 2 and D 2 showed it to be formed via an H 2 adduct (F 5 C 2 ) 3 HSnCH 2 PH(tBu) 2 (2) and the subsequent formal reductive elimination of pentafluoroethane; this is supported by DFT calculations. Parahydrogen-induced polarization experiments revealed the formation of a second product of the reaction of 1 with H 2 , [HP(tBu) 2 Me][Sn(C 2 F 5 ) 3 ] (4), in 1 H NMR spectra, whereas 2 was not detected due to its transient nature., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

A new efficient metal-based frustrated Lewis pair constructed by (P t Bu 3 ) 2 Pt and B(C 6 F 5 ) 3 was designed through density functional theory calculations for the catalytic dehydrogenation of ammonia borane (AB). The reaction was composed by the successive dehydrogenation of AB and H 2 liberation, which occurs through the cooperative functions of the Pt(0) center and the B(C 6 F 5 ) 3 moiety. Two equivalents of H 2 were predicted to be liberated from each AB molecule. The generation of the second H2 is the rate-determining step, with a Gibbs energy barrier and reaction energy of 27.4 and 12.8 kcal/mol, respectively., (© 2020 Wiley-VCH GmbH.)

The metal-free cis selective hydrogenation of alkynes catalyzed by a boroxypyridine is reported. A variety of internal alkynes are hydrogenated at 80 °C under 5 bar H 2 with good yields and stereoselectivity. Furthermore, the catalyst described herein enables the first metal-free semihydrogenation of terminal alkynes. Mechanistic investigations, substantiated by DFT computations, reveal that the mode of action by which the boroxypyridine activates H 2 is reminiscent of the reactivity of an intramolecular frustrated Lewis pair. However, it is the change in the coordination mode of the boroxypyridine upon H 2 activation that allows the dissociation of the formed pyridone borane complex and subsequent hydroboration of an alkyne. This change in the coordination mode upon bond activation is described by the term boron-ligand cooperation., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a W II alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ 5 -phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31 P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Integrating gas as a main building block into nanomaterial construction is a challenging mission that remains elusive. Herein, we report a gas-constructed vesicular system formed by CO 2 gas and frustrated Lewis pairs (FLPs). Two molecular triads bearing three bulky borane and phosphine groups are designed as trivalent disc-like FLP monomers. CO 2 , as a gas cross-linker, can drive the two-dimensional polymerization of these two FLP monomers, leading to the generation of planar FLP networks that further transform into a thermodynamically favored membranous vesicle structure. Gas-guided vesicle formation is also applicable to other inert but FLP-activatable gases. Different gas linkages can form vesicles with distinct architectures, sizes, and morphologies. We envisage that this study would suggest a new concept that exploits gases to fabricate tunable nanomaterials., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A set of novel, easily synthesized aluminum complexes, Al[κ 2 - N , N- 2-(methylamino)pyridine] 2 R (R = Et, i Bu) are reported. When subjected to 1 atm of CO 2 pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO 2 substrate reminiscent of a Frustrated Lewis Pair. This reaction has limited precedent for Al/N based Lewis Pair systems, and this is the first system readily shown to sequester multiple equivalents of CO 2 per aluminum center. The ethyl variant then reacts further, inserting a third equivalent of CO 2 into the aluminum alkyl to generate an aluminum carboxylate. Examples of this type of reactivity are rare under thermal conditions. A joint experimental/computational study supports the proposed reaction mechanism.

The noble gas (Ng) binding ability of a monocationic [(FLP)Au] + species has been investigated by a computational study. Here, the monocationic [(FLP)Au] + species is formed by coordination of Au(I) cation with the phosphorous (Lewis base) and the boron (Lewis acid) centers of a frustrated Lewis pair (FLP). The bonds involving Au and P, and Au and B atoms in [(FLP)Au] + are partially covalent in nature as revealed by Wiberg bond index (WBI) values, electron density analysis and energy decomposition analysis (EDA). The zero point energy corrected bond dissociation energy (D 0 ), enthalpy and free energy changes are computed for the dissociation of Au-Ng bonds to assess the Ng binding ability of [(FLP)Au] + species. The D 0 ranges from 6.0 to 13.3 kcal/mol, which increases from Ar to Rn. Moreover, the dissociation of Au-Ng bonds is endothermic as well as endergonic for Ng = Kr-Rn, whereas the same for Ng = Ar is endothermic but exergonic at room temperature. The partial covalent character of the bonds between Au and Ng atoms is demonstrated by their WBI values and electron density analysis. The Ng atoms get slight positive charges of 0.11-0.23 | e |, which indicates some amount of charge transfer takes place from it. EDA demonstrates that electrostatic and orbital interactions have equal contributions to stabilize the Ng-Au bonds in the [(FLP)AuNg] + complex., (Copyright © 2020 Ghara and Chattaraj.)

Salt metathesis of 1-methyl-2,4,6-triphenylphosphacyclohexadienyl lithium and chlorobis(pentafluorophenyl)borane affords a 1-phospha-7-bora-norbornadiene derivative 2. The C≡N triple bonds of nitriles insert into the P-B bond of 2 with concomitant C-B bond cleavage, whereas the C≡C bonds of phenylacetylenes react with 2 to form λ 4 -phosphabarrelenes. Even though 2 must formally be regarded as a classical Lewis adduct, the C≡N and C≡C activation processes observed (and the mild conditions under which they occur) are reminiscent of the reactivity of frustrated Lewis pairs. Indeed, NMR and computational studies give insight into the mechanism of the reactions and reveal the labile nature of the phosphorus-boron bond in 2, which is also suggested by detailed NMR spectroscopic studies on this compound. Nitrile insertion is thus preceded by ring opening of the bicycle of 2 through P-B bond splitting with a low energy barrier. By contrast, the reaction with alkynes involves formation of a reactive zwitterionic methylphosphininium borate intermediate, which readily undergoes alkyne 1,4-addition., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The concept of frustrated Lewis pairs (FLPs) has been widely applied in various research areas, and metal-free hydrogenation undoubtedly belongs to the most significant and successful ones. In the past decade, great efforts have been devoted to the synthesis of chiral boron Lewis acids. In a sharp contrast, chiral Lewis base derived FLPs have rarely been disclosed for the asymmetric hydrogenation. In this work, a novel type of chiral FLP was developed by simple combination of chiral oxazoline Lewis bases with achiral boron Lewis acids, thus providing a promising new direction for the development of chiral FLPs in the future. These chiral FLPs proved to be highly effective for the asymmetric hydrogenation of ketones, enones, and chromones, giving the corresponding products in high yields with up to 95 % ee. Mechanistic studies suggest that the hydrogen transfer to simple ketones likely proceeds in a concerted manner., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This contribution reports an unprecedentedly efficient dimerization and the first successful polymerization of lignocellulose-based β-angelica lactone (β-AL) by utilizing a selective Lewis pair (LP) catalytic system, thereby establishing a versatile bio-refinery platform wherein two products, including a dimer for high-quality gasoline-like biofuel (C 8 -C 9 branched alkanes, yield=87 %) and a heat- and solvent-resistant acrylic bioplastic (M n up to 26.0 kg mol -1 ), can be synthesized from one feedstock by one catalytic system. The underlying reason for exquisite selectivity of the LP catalytic system toward dimerization and polymerization was explored mechanistically., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient deuteration process of α -C-H bonds in various carbonyl-based pharmaceutical compounds has been developed. Catalytic reactions are initiated by the action of Lewis acidic B(C 6 F 5 ) 3 and D 2 O, converting a drug molecule into the corresponding boron-enolate. Ensuing deuteration of the enolate by in situ-generated D 2 O + -H then results in the formation of α -deuterated bioactive carbonyl compounds with up to >98% deuterium incorporation.

Generating desired efficiency enhancements in organic solar cells (OSCs) by charge-transfer doping requires to obtain modified optoelectronic properties while retaining the favorable nanomorphology. We report a thermally assisted doping based on Lewis acid tris(pentafluorophenyl)-borane (BCF) as a p-dopant for two groups of OSCs comprising the PBDB-TF and PBDB-T donors and a nonfullerene acceptor IT-4F. We found that the face-on molecular packing in the PBDB-TF:IT-4F blend or neat PBDB-TF donor films is favorably modified with the formation of frustrated Lewis pairs (FLPs) in the donor, which is in contrast to the hampered π-π stacking in the doped PBDB-T film. The different impacts of BCF dopants on the morphology lead to contrasting photovoltaic behaviors where the PBDB-TF-based devices receive enhanced power conversion efficiencies (PCEs) in the presence of BCF, while reduction of efficiencies is observed in the PBDB-T device. In the best doping conditions with the proposed hot-film deposition, we achieve a boosted PCE of 14.1% in PBDB-TF:IT-4F solar cells at low BCF concentrations. Based on the same fluorinated donor, the described BCF doping also applies to NF-solar cells based on the NF-acceptor Y6, leading to an increase in the PCE to 16.0%. Our results suggest that controlling the degree of FLP formation in the donor component with the addition of BCF is key to obtaining desired improvements on nanomorphology and relevant photophysical properties in OSCs.

Extensive DFT calculations provide detailed mechanistic insights into the metal-free reduction of phosphine oxide Ph 3 P=O by using chlorination reagents O=CClX (X=COCl, Cl, OCCl 3 and Ph) and H 2 . Fast electrophilic attack to the P=O group oxygen atom is favored by exergonic CO 2 release to form phosphonium Ph 3 PCl + and chloride Cl - , which may slowly cleave H 2 by an unstable HPh 3 PCl complex yielding Ph 3 PH + and Cl - ions in solution. Moderate heating is required to accelerate the slow H 2 -activation step and to eliminate HCl to form phosphine Ph 3 P instead of Ph 3 PH + Cl - salt as the desired product. Though partially quenched by Ph 3 P (and reactant Ph 3 P=O if present), borane B(2,6-F 2 C 6 H 3 ) 3 can be still combined with Cl - and Ph 3 P as reactive frustrated Lewis pair (FLP) catalysts., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Proton spectroscopy in solid-state NMR on catalytic materials offers new opportunities in structural characterization, in particular of reaction products of catalytic reactions such as hydrogenation reactions. Unfortunately, the 1 H NMR line widths in magic-angle spinning solid-state spectra are often broadened by an incomplete averaging of 1 H- 1 H dipolar couplings. We herein discuss two model compounds, namely the H 2 -splitting products of two phosphane-borane Frustrated Lewis Pairs (FLPs), to study potentials and limitations of proton solid-state NMR experiments employing magic-angle spinning frequencies larger than 100 kHz at a static magnetic field strength of 20.0 T. The 1 H lines are homogeneously broadened as illustrated by spin-echo decay experiments. We study two structurally similar materials which however show significant differences in 1 H line widths which we explain by differences in their 1 H- 1 H dipolar networks. We discuss the benefit of fast MAS experiments up to 110 kHz to detect the resonances of the H + /H - pair in the hydrogenation products of FLPs., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)