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In the few past years, the chemistry of frustrated Lewis pairs (FLP) has enabled a plethora of transformations that would otherwise only be possible using transition metal catalysts. Of particular interest are C–H bond activation and borylation reactions, which are the subject of this review. The FLP borylation chemistry is compared with the early borylation methodologies using strongly electrophilic borenium ions. We present the mechanism of the C–H borylation using inter- and intramolecular Lewis pairs, along with some applications of these transformations.1 Introduction2 Electrophilic Borylation3 Intramolecular or Directed Electrophilic Borylation4 Intermolecular FLP-Mediated C–H Borylation5 Stoichiometric Borylation by Intramolecular FLPs5.1 Csp–H Borylation5.2 Csp2–H Borylation5.3 Csp3–H Borylation6 Catalytic Borylation by Intramolecular FLPs7 Catalytic Borylation by Self-Assembled FLPs8 Conclusion

Exploiting the steric incompatibility of the tris-(alkyl)gallium GaR3 (R = CH2SiMe3) and the bulky N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu), here we report the B−H bond activation of pinacolborane (HBPin), which has led to the isolation and structural authentication of a novel ion pair, [{ItBu-BPin}+{GaR3(μ-H)-GaR3}−] (2). Contrastingly, neither ItBu or GaR3 was able to react with HBPin under the conditions of this study. Combining an NHC-stabilized borenium cation, [{ItBu-BPin}+], with an anionic dinuclear gallate, [{GaR3(μ-H)GaR3}−], 2 proved to be unstable in solution at room temperature, evolving to the abnormal NHC-Ga complex [BPinC{{N(tBu)]2CHCGa(R)3}] (3). Interestingly, the structural isomer of 2, with the borenium cation residing at the C4 position of the carbene, [{aItBu-BPin}+{GaR3(μ-H)GaR3}−] (4), was obtained when the abnormal NHC complex [aItBu·GaR3] (1) was heated to 70 °C with HBPin, demonstrating that, under these forced conditions, it is possible to induce thermal frustration of the Lewis base/Lewis acid components of 1, enabling the activation of HBPin. Building on these stoichiometric studies, the frustrated Lewis pair (FLP) reactivity observed for the GaR3/ItBu combination with HBPin could then be upgraded to catalytic regimes, allowing the efficient hydroboration of a range of aldehydes and ketones under mild reaction conditions. Mechanistic insights into the possible reaction pathway involved in this process have been gained by combining kinetic investigations with a comparative study of the catalytic capabilities of several gallium and borenium species related to 2. Disclosing a new cooperative partnership, reactions are proposed to occur via the formation of a highly reactive monomeric hydride gallate, [{ItBu- BPin}+{GaR3(H)}−] (I). Each anionic and cationic component of I plays a key role for success of the hydroboration, with the nucleophilic monomeric gallate anion favoring the transfer of its hydride to the C=O bond of the organic substate, which in turn is activated by coordination to the borenium cation.

ConspectusZeolites, accompanied by their initial discovery as natural mines and the subsequent large-scale commercial production, have played indispensable roles in various fields such as petroleum refining and the chemical industry. Understanding the characteristics of zeolites, in contrast to their counterparts with similar chemical compositions and the origin thereof, is always a hot and challenging topic. Zeolites are known as intrinsic confined systems with ordered channels on the molecular scale, and structural confinement has been proposed to explain the unique chemical behaviors of zeolites. Generally, the channels of zeolites can regulate the diffusion of molecules, leading to a visible difference in molecular transportation and the ultimate shape-selective catalysis. On the other hand, the local electric field within the zeolite channels or cages can act on the guest molecules and change their energy levels. Confinement can be simply interpreted from both spatial and electronic issues; however, the nature of zeolite confinement is ambiguous and needs to be clarified.In this Account, we make a concise summary and analysis of the topics of confinement in a zeolite and zeolite catalysis from two specific views of spatial constraint and a local electric field to answer two basic questions of why zeolites and what else can we do with zeolites. First, it is shown how to construct functional sites including Bronsted acid sites, Lewis acid sites, extraframework cation sites, and entrapped metal or oxide aggregates in zeolites via confinement and how to understand the specific role of confinement in their reactivity. Second, the multiple impacts of confinement in zeolite-catalyzed reactions are discussed, which rationally lead to several unique processes, namely, Bronsted acid catalysis confined in zeolites, Lewis acid catalysis confined in zeolites, catalysis by zeolite-confined coordinatively unsaturated cation sites, and a cascade reaction within the confined space of zeolites. Overall, confinement effects do exist in zeolite systems and have already played extremely important roles in adsorption and catalysis. Although confinement might exist in many systems, the confinement by zeolites is more straightforward thanks to their well-ordered and rigid structure, deriving unique chemical behaviors within the confined space of zeolites. A zeolite is a fantastic scaffold for constructing isolated sites spatially and electrostatically confined in its matrix. Furthermore, zeolites containing well-defined transition-metal sites can be treated as inorganometallic complexes (i.e., a zeolite framework as the ligand of transition-metal ions) and can catalyze reactions resembling organometallic complexes or even metalloenzymes. The local electric field within the confined space of zeolites is strong enough to induce or assist the activation of small molecules, following the working fashion of frustrated Lewis pairs. The tactful utilization of structural confinement, both spatially and electronically, becomes the key to robust zeolites for adsorption and catalysis.

Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4 − salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2BDI ligand (R1,R2BDI=HC[C(R1)N(R2)]2) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPPBDI, A series of strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4 − salts. Their catalytic activity in imine hydrogenation depends strongly on the substituents in the BDI ligand. DFT calculations on the mechanism reveal two interconnected catalytic cycles. Hydrogen is activated either by Al⋅⋅⋅imine or Al⋅⋅⋅amine Frustrated‐Lewis‐Pairs.

Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.

Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications have been demonstrated to be one of emerge research topics in the field of catalysis. Previous studies have shown that the thermodynamics of these reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated the systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H2 activation by both inter- and intra-molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H-H cleavage elemental step, while disfavored the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra-molecular FLPs are more effected compared to the inter-molecular FLPs.

A three-component Lewis acid-base (Lewis trio) involving a bulky chiral primary amine, B(C6 F5 )3 and a bulky tertiary amine has been developed as an effective enamine catalyst for enantioselective disulfuration reactions. The bulky tertiary amine was found to activate a bulky primary-tertiary diamine-borane Lewis pair for enamine catalysis via frustrated interaction. The resulted chiral bulky Lewis trio (BLT) allows for the construction of chiral disulfides via direct disulfuration with β-ketocarbonyls or α-branched aldehydes in a practical and highly stereocontrolled manner.

De introductie van een chemisch additief aan supramoleculaire polymeren heeft een groot potentieel voor de ontwikkeling van nieuwe structuren en functies. In dit opzicht zijn verschillende op donor- en acceptor gebaseerde moleculen toegepast bij het ontwerp van deze niet-covalente polymeren. De opname van door borium en stikstof gefrustreerde Lewis-paren in dergelijke architecturen is echter nog steeds zeldzaam, ondanks hun vele intrigerende eigenschappen in katalyse en materiaalwetenschap. De beperkte keuzes van geschikte boorderivaten vormen een van de belangrijkste beperkingen voor de vooruitgang in deze richting. Hier onderzoeken we het gebruik van het in de handel verkrijgbare tris (pentafluorfenyl) boraan met verschillende trifenylaminederivaten om supramoleculaire B-N-ladingsoverdrachtsystemen te creëren. Onze resultaten benadrukken het belang van een goede balans tussen de donor-/acceptorsterkte en de drijvende kracht voor supramoleculaire polymerisatie om stabiele B-N-systemen op lange afstand te bereiken. Gedetailleerde analyses met behulp van paramagnetische elektronenresonantie en optische spectroscopie suggereren dat tris(pentafluorfenyl)boraan complex gedrag vertoont met de op amide gebaseerde trifenylamine supramoleculaire polymeren en kan interageren in dimeren of grotere chirale aggregaten, afhankelijk van de specifieke structuur van de trifenylaminen.

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis., An Outlook on the rich chemistry of phosphorus, focusing on nucleophilic phosphine catalysis, organophosphorus catalysis to prevent phosphine oxide waste, and phosphorus-mediated radical processes.

The intramolecular "inverse" frustrated Lewis pairs (FLPs) of general formula 1-BR2 -2-[(Me2 N)2 C=N]-C6 H4 (3-6) [BR2 =BMes2 (3), BC12 H8 , (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-BR2 )-2-[(Me2 N)2 C=NH]-C6 H4 (R=Ph, H) and reacted with ammonia, BnNH2 and pyrrolidine, to generate the FLP adducts 1-(R2 HN→BR2 )-2-[(Me2 N)2 C=NH]-C6 H4 , 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 H2 CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H2 , HBPin and PhSiH3 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.

Herein, we present the first example of the activation of small molecules by P–B–P bond systems. The reactivity study involves reactions of two selected diphosphinoboranes, (t-Bu2P)2BPh (1′) and (Cy2P)2BNiPr2 (2), that differ in terms of their structural and electronic properties for the activation of dihydrogen, carbon dioxide, and phenyl isocyanate. Diphosphinoborane 1′ activates H2 under very mild conditions in the absence of a catalyst with the formation of the dimer (t-Bu2PB(Ph)H)2 and t-Bu2PH. Conversely, diphosphinoborane 2 did not react with H2 under the same conditions. The reaction of 1′ with CO2 led to the formation of a compound with an unusual structure, where two phosphinoformate units were coordinated to the PhBOBPh moiety. In addition, 2 reacted with CO2 to insert two CO2 molecules into the P–B bonds of the parent diphosphinoborane. Both diphosphinoboranes activated PhNCO, yielding products resulting from the addition of two and/or three PhNCO molecules and the formation of new P–C, B–O, B–N, and C–N bonds. The products of the activation of small molecules by diphosphinoboranes were characterized with nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, single-crystal X-ray diffraction, and elemental analysis. Additionally, the reaction mechanisms of the activation of small molecules by diphosphinoboranes were elucidated by theoretical methods., The first example of the activation of dihydrogen, carbon dioxide, and phenyl isocyanate by diphosphinoboranes is presented.

Selective hydrogenation of aromatic amines, especially chemicals such as aniline and bis(4-aminocyclohexyl)methane for non-yellowing polyurethane, is of particular interests due to the extensive applications. To conquer the existing difficulties in selective hydrogenation, the Ru0-Ruδ+/CeO2 catalyst with solid frustrated Lewis pairs was developed for aromatic amines hydrogenation with excellent activity and selectivity under relative milder conditions. The morphology, electronic and chemical properties, especially the Ru0-Ruδ+ clusters and reducible ceria were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), CO2 temperature programmed desorption (CO2-TPD), H2 temperature programmed reduction (H2-TPR), H2 diffuse reflectance Fourier transform infrared spectroscopy (H2-DRIFT), Raman, etc. The 2% Ru/CeO2 catalyst exhibited good conversion of 95% and selectivity greater than 99% toward cyclohexylamine. The volcano curve describing the activity and Ru state was found. Owning to the "acidic site isolation" by surrounding alkaline sites, condensation between the neighboring amine molecules could be effectively suppressed. The catalyst also showed good stability and applicability for other aromatic amines and heteroarenes containing different functional groups.

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., B for cooperation: The term boron–ligand cooperation (BLC) describes a specific mode of action by which distinctive intramolecular borane‐based frustrated Lewis Pairs (FLPs) activate chemical bonds. The central aspect of this concept is that the substituent at the borane that is involved in the bond activation becomes a datively bound ligand upon bond activation. The reactivity of systems that operate via BLC can complement those of classic intramolecular FLPs.

Titanium dioxide (TiO2) alone is rarely reported to have exciting performance towards heterogeneous hydrogenation reactions. In this work, we demonstrate via density functional theory (DFT) calculations that anatase TiO2 with oxygen vacancies (Ovs), which provides frustrated Lewis pairs (FLPs) from surface Ti and O atoms for the heterolytic dissociation of hydrogen, can effectively hydrogenate acetylene to ethylene. Meanwhile, the mechanisms of H2 activation and acetylene hydrogenation with several structure–reactivity correlations are well established, suggesting the potential catalytic reactivity in the presence of Ovs on anatase TiO2 surfaces. Then, the reactivity of anatase TiO2 towards acetylene hydrogenation is preliminarily confirmed by experimental studies which show that the existence of Ovs after reduction leads to higher reactivity. These results can provide important implications for the further development of selective hydrogenation catalysts based on earth-abundant materials.

The reactivity of the geminal frustrated Lewis pair (FLP) (F5C2)3SnCH2P(tBu)2 (1) was explored by reacting it with a variety of small molecules (PhOCN, PhNCS, PhCCH, tBuCCH, H3CC(O)CH=CH2, Ph[C(O)]2Ph, PhN=NPh and Me3SiCHN2), featuring polar or non‐polar multiple bonds and/or represent α,β‐unsaturated systems. While most adducts are formed readily, the binding of azobenzene requires UV‐induced photoisomerization, which results in the highly selective complexation of cis‐azobenzene. In the case of benzil, the reaction does not lead to the expected 1,2‐ or 1,4‐addition products, but to the non‐stereoselective (tBu)2PCH2‐transfer to a prochiral keto function of benzil. All adducts of 1 were characterised by means of multinuclear NMR spectroscopy, elemental analyses and X‐ray diffraction experiments., A highly selective complexation of cis‐azobenzene was found when reacting the isomeric compound with the intramolecular frustrated Lewis pair (F5C2)3SnCH2P(tBu)2 under UV‐induced photoisomerization conditions.

Sterically hindered frustrated Lewis pairs (FLPs) have the ability to activate hydrogen molecules, and their reactivity is strongly determined by the geometric parameters of the Lewis acids and bases. A recent experimental study showed that ionic liquids (ILs) could largely improve the effective configuration of FLPs. However, the detailed mechanistic profile is still unclear. Herein, we performed molecular dynamics (MD) simulations to reveal the effects of ILs on the structures of FLPs, in particular, the association of Lewis acids and bases. For this purpose, mixed systems were adopted consisting of the ILs [Cnmim][NTf2] (n = 6, 10, 14), [C6mim][PF6] and [C6mim][CTf3] and the typical FLP (tBu)3P/B(C6F5)3 for MD simulations. Radial distribution functions (RDFs) results show that toluene competes with (tBu)3P to interact with B(C6F5)3, resulting in a relatively low effective (tBu)3P/B(C6F5)3 complex, while [C10mim][NTf2] shows less competition with (tBu)3P, which increases the amount of effective FLPs. Spatial distribution functions (SDFs) results show that toluene forms a continuum solvation-shell, which hinders the interactions between (tBu)3P and B(C6F5)3, while [C10mim][NTf2] leaves relatively large empty spaces, which are accessible for (tBu)3P or B(C6F5)3 molecules, resulting in higher probabilities of effective FLP structures. Lastly, we find that the longer alkyl chain length of [Cnmim]+ cations, the higher the amount of effective (tBu)3P/B(C6F5)3 pairs, and the anion [CTf3]- shows negative effects, for which even less effective (tBu)3P/B(C6F5)3 pairs have been found compared to those of toluene.

Frustrated Lewis Pairs (FLPs) as the zwitter compound is not only an effective catalyst in the hydrogenation process, but also a potential excellent hydrogen-storage material. Therefore, the activity and the reversibility of the ab-/desorbing hydrogen process of FLPs are generally determined by the acidity of the Lewis acid (LA) and the alkalinity of the Lewis base (LB). Herein, we learn three classic B/N intramolecular FLPs composed by Pier's acid and N-heterocyclic groups to evaluate the relationship between the energy of deformation of LA/LB and the reactivity of FLPs in the hydrogenation. The acidity is determined by the energy of structural transformation in activating hydrogen, while the alkalinity of LB is determined by the electron density of connected groups. Different from the traditional point that the strong LA and LB form a perfect FLPs, the excellent FLPs appears reversibility and fast reaction rate in the hydrogenation when it composed by a strong LA (72.97 = GA ≤ 120.15 kcal/mol) and a relative weak LB (GB ≥ 155.28 kcal/mol). The results help us to establish a quantitative relationship between the deformation energy of FLPs and the reversibility/activity in the Ab-/Desorbing hydrogen process of the intramolecular B/N FLPs.

Adducts of the parent iminoborane isomers, HBNH and NBH2, have been prepared, each stabilized by the frustrated Lewis pair (FLP) chelate iPr2P(C6H4)BCy2 (PB). PB{HBNH} was accessed via dehydrohalogenation, while the corresponding isomer PB{NBH2} was obtained from the borylation of the formal nitrene-FLP complex PB{NH}.

Stoichiometric carbon dioxide reduction to highly reduced C1 molecules, such as formic acid (2e- ), formaldehyde (4e- ), methanol (6e- ) or even most-reduced methane (8e- ), has been successfully achieved by using organosilanes, organoboranes, and frustrated Lewis Pairs (FLPs) in the presence of suitable catalyst. The development of renewable organohydride compounds could be the best alternative in this regard as they have shown promise for the transfer of hydride directly to CO2 . Reduction of CO2 by two electrons and two protons to afford formic acid by using renewable organohydride molecules has recently been investigated by various groups. However, catalytic CO2 reduction to ≥2e- -reduced products by using renewable organohydride-based molecules has rarely been explored. This Minireview summarizes important findings in this regard, encompassing both stoichiometric and catalytic CO2 reduction.

Direct syngas conversion to light olefins on bifunctional oxide-zeolite (OX-ZEO) catalysts is of great interest to both academia and industry, but the role of oxygen vacancy (Vo) in metal oxides and whether the key intermediate in the reaction mechanism is ketene or methanol are still not well-understood. To address these two issues, we carry out a theoretical study of the syngas conversion on the typical reducible metal oxide, CeO2, using density functional theory calculations. Our results demonstrate that by forming frustrated Lewis pairs (FLPs), the VOs in CeO2 play a key role in the activation of H2 and CO. The activation of H2 on FLPs undergoes a heterolytic dissociative pathway with a tiny barrier of 0.01 eV, while CO is activated on FLPs by combining with the basic site (O atom) of FLPs to form CO22−. Four pathways for the conversion of syngas were explored on FLPs, two of which are prone to form ketene and the other two are inclined to produce methanol suggesting a compromise to resolve the debate about the key intermediates (ketene or methanol) in the experiments. Rate constant calculations showed that the route initiating with the coupling of two CO* into OCCO* and ending with the formation of ketene is the dominant pathway, with the neighboring FLPs playing an important role in this pathway. Overall, our study reveals the function of the surface FLPs in the activation of H2 and CO and the reaction mechanism for the production of ketene and methanol for the first time, providing novel insights into syngas conversion over OX-ZEO catalysts.

Development of metal-free strategies for stereoselective hydrogenation of unsaturated substrates is of particular interest in asymmetric synthesis. The emerging chemistry of frustrated Lewis pairs offers a promising approach along this line as demonstrated by recent achievements. However, the stereocontrol elements in these reactions are not clearly recognized thus far. Herein, we analyze the origin of stereoinduction in direct hydrogenation of imines catalyzed by a set of chiral boranes. We use the tools of computational chemistry to describe the elementary steps of the catalytic cycle, and we pay special attention to the stereoselectivity-determining hydride transfer process. The enantioselectivities predicted by the applied computational approach are in very good agreement with previous experimental observations. We find that the stereoselectivity is governed by a thermodynamically less favored conformer of the borohydride intermediate and not by the experimentally observed form. The most favored hydride transfer transition states are stabilized by specific aryl-aryl and alkyl-aryl noncovalent interactions, which play an important role in stereoinduction. This computational insight is exploited in proposing additional borane variants to improve the enantioselectivity, which could be demonstrated experimentally

Bond activation and catalysis are central to the development of a sustainable energy system. Frustrated Lewis Pairs have conceptually revolutionized the activation of inert chemical bonds. Far less...

A new efficient metal-based frustrated Lewis pair constructed by (Pt Bu3 )2 Pt and B(C6 F5 )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 H2 liberation, which occurs through the cooperative functions of the Pt(0) center and the B(C6 F5 )3 moiety. Two equivalents of H2 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.

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, i Pr2 P(C6 H4 )BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2 }] and [PB{GeH2 }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH2 }] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2 }] was also prepared, and shown to release poly(dimethylsilane) [SiMe2 ]n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

N-heterocyclic nitrogen Lewis acids are a recent addition to the field of organic chemistry. Based on nitrenium cations, these acids where previously shown to generate Lewis adducts when combined with the appropriate Lewis bases. Herein, a triazinium-based Lewis acid was combined with tBu3P to generate a frustrated Lewis pair (FLP) capable of cleaving, for the first time, Si-H bonds in silanes. Whereas low yields were initially encountered owing to insufficient Lewis acidity, a new nitrenium-based Lewis acid was synthesized, and its superior Lewis acidity was experimentally and computationally confirmed. A FLP based on this acid cleaved the Si-H bond in PhSiH3, generating the triazane product in a quantitative yield. This unprecedented N-H triazane was fully characterized by multinuclear NMR techniques and single-crystal X-ray crystallography. A new class of compounds, N-H triazanes display the potential capacity to participate in hydride transfer reactions.

We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis (pentafluorophenyOboryl] phenyl -2, 2,6,6-tetrame-thylpiperidine (KCAT). The gas-solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 h at 300 K under a flow of H-2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4-200 K did not provide evidence for the formation of polarized H-2 in a precursor complex within the crystal at low temperatures and high pressures. However, at 300 K, the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Calculations suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H-2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2, and a possible precursor complex of H-2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H-2 diffusion into the FLP crystal with a rate-limiting movement of H-2 from inactive positions to reactive sites.

Organoboron compounds are essential reagents in modern C−C coupling reactions. Their synthesis via catalytic C−H borylation by main group elements is emerging as a powerful tool alternative to transition metal based catalysis. Herein, a straightforward metal‐free synthesis of aryldifluoroboranes from BF3 and heteroarenes is reported. The reaction is assisted by sterically hindered amines and catalytic amounts of thioureas. According to computational studies the reaction proceeds via frustrated Lewis pair (FLP) mechanism. The obtained aryldifluoroboranes are further stabilized against destructive protodeborylation by converting them to the corresponding air stable tetramethylammonium organotrifluoroborates., C−H activation: Indoles, pyrroles and indolenines undergo C−H borylation by boron trifluoride with assistance of base and thiourea additives.

In 2005, a facile dihydrogen activation was reported by the Power group using an alkyne analog of germanium [ArGe≡GeAr; Ar=2,6-Trip2 -C6 H3 (Trip=2,4,6-i Pr3 -C6 H2 )]. After that, a significant progress has been made in the activation of various small molecules by main-group compounds, and a variety of stoichiometric and catalytic processes have been formulated using the p-block elements. In this regard, compounds containing low-valent main-group elements with a frontier orbitals of relatively small energy gaps or compounds forming frustrated Lewis pair (FLP) became quite successful. In spite of these promising stoichiometric and catalytic transformations, redox-cycling catalysts based on main-group elements remain extremely rare. Recently, it has been observed that pincer type ligands supported geometry constrained main-group compounds are capable of acting as redox catalysts similar to those of the transition metals. In this review, we focus on the synthesis and the structural aspects of the geometry constrained main-group compounds using pincer ligands. Emphasis has been placed on their applications on catalytic activity and small molecules activation.

International audience; A novel architecture of phosphine-stabilized silylium ions is described. The peculiar moderate flexible framework allows an efficient donation of the phosphine group toward the electron deficient silicon center thus providing a very good stabilization of the corresponding silylium ions. The P-Si interaction was studied in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis, respectively. The reactivity of silylium ions is easily improved using less donating phosphine ligands. Of particular interest, thanks to the flexible ligand framework, phosphine-stabilized silylium ion 5f behaves as a frustrated Lewis pair instead of a simple Lewis acid and exhibits an original ambiphilic reactivity with carbonyl derivatives that allows the synthesis of seven-to nine-membered ring heterocycles.

Phosphagallenes (1 a/1 b) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a, which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound (2) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H2 and forms a 1:1 adduct with CO2., We describe the synthesis of compounds exhibiting gallium–phosphorus double bonds. The stability of these species is dependent on the saturation of the phosphanyl moiety, and the saturated variant behaves as a frustrated Lewis pair that is capable of activating H2 and forms a 1:1 adduct with CO2.

Two covalent organic frameworks comprising Lewis basic P(III) centers and Lewis acidic boron atoms were prepared by poly‐condensation reactions of newly obtained tris(4‐diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11‐hexahydroxytriphenylene and 2,3,6,7‐tetrahydroxy‐9,10‐dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm3g‐1 at 1 bar at 77 K), methane (20 cm3g‐1 at 1 bar at 273 K) and carbon dioxide (50 cm3g‐1 at 1 bar at 273 K). They were exploited as solid‐state ligands for coordination of Pd(0) centers. Alternatively, in bottom‐up approach, boronated phosphine was treated with Pd2dba3 and poly‐condensated yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P–Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework‐guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.

The geminal frustrated Lewis pair (F5C2)3SnCH2P(tBu)2 (1) reacted with N‐sulfinylaniline PhNSO to afford the first sulfur monoxide adduct of a main group metal, (F5C2)3SnCH2P(tBu)2⋅SO (2), which contains a SnCPSO ring. The second product is a phenylnitrene adduct of 1. The surprising stability of 2 was compared with the stabilities of the so far inaccessible O2 and S2 adducts of 1. Attempts to prepare these from 1 and the elemental chalcogens (O2, S8, Se∞, Te∞) led to four‐membered SnCPE ring systems. Quantum‐chemical investigations of 2 demonstrate the bond polarity of the SO unit to stabilize 2., The first adduct of SO to a main group metal system was found by reacting PhNSO with an intramolecular Sn/P frustrated Lewis pair; the exceptional stability of the adduct is attributed to the polarity of the incorporated SO unit.

Bulky phosphines and their redox properties have received increased attention in the view of useful auxiliary ligands for transition metal catalysts and Lewis-base components of frustrated Lewis pairs for chemical transformations. Herein we report the synthesis, structure, and properties of a series of trialkylphosphines 2R (R = methyl, ethyl, isopropyl, tert-butyl, 1-adamantyl) that possess the bulky 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane as a structural backbone. Among these phosphines, 2Ad, which contains an adamantyl moiety, has a very large buried volume (%Vbur) for a trialkylphosphine (62.0) and shows a quasi-reversible oxidative wave at a lower oxidation potential (-0.12 V in CH2Cl2, vs ferrocene/ferrocenium couple) by cyclic voltammetry. The reaction of 2Ad with AgPF6 afforded a cationic silver aquo complex [Ag(2Ad)(H2O)]+[PF6]-, whereas the reaction with NOSbF6 gave a persistent phosphine radical cation [2Ad]•+. Based on the EPR spectra and DFT studies, the spin and positive charge of [2Ad]•+ are localized on the phosphorus atom.

Archetypal phosphine/borane frustrated Lewis pairs (FLPs) are famed for their ability to activate small molecules. The mechanism is generally believed to involve two‐electron processes. However, the detection of radical intermediates indicates that single‐electron transfer (SET) generating frustrated radical pairs could also play an important role. These highly reactive radical species typically have significantly higher energy than the FLP, which prompted this investigation into their formation. Herein, we provide evidence that the classical phosphine/borane combinations PMes3/B(C6F5)3 and PtBu3/B(C6F5)3 both form an electron donor–acceptor (charge‐transfer) complex that undergoes visible‐light‐induced SET to form the corresponding highly reactive radical‐ion pairs. Subsequently, we show that by tuning the properties of the Lewis acid/base pair, the energy required for SET can be reduced to become thermally accessible., Exciting FLPs! The radical‐ion pairs of the archetypal frustrated Lewis pair (FLP) systems PMes3/B(C6F5)3 and PtBu3/B(C6F5)3 can be accessed by visible‐light‐induced single‐electron transfer. Varying the FLP system shows this process is general for a range of donor–acceptor combinations and can be tuned to proceed thermally.

The reaction of the intramolecular frustrated Lewis pair (FLP) tBu2PCH2BPh2 with the amine-boranes NH3 center dot BH3 and Me2NH center dot BH3 leads to the formation of the corresponding FLP-H2 adducts as well as novel five-membered heterocycles that result from capturing the in situ formed amino-borane by a second equivalent of FLP. The sterically more demanding tBu2PCH2BMes2 does not form such a five-membered heterocycle when reacted with Me2NH•BH3 and its H2 adduct liberates dihydrogen at elevated temperatures, promoting the metal-free catalytic dehydrogenation of amine-boranes.

Aromaticity and frustrated Lewis pairs (FLP), two important concepts in chemistry, have attracted considerable attention from theoretical and experimental chemists. However, combining these two con...

Described herein is the development of a borane-catalyzed cine-silylative ring-opening of α-methyl azacycles. This transformation involves four-step cascade processes: (i) exo-dehydrogenation of alicyclic amine, (ii) hydrosilylation of the resultant enamine, (iii) silylium-induced cis-β-amino elimination to open the ring skeleton, and (iv) hydrosilylation of the terminal olefin. The present borane catalysis also works efficiently for the C-N bond cleavage of acyclic tertiary amines. On the basis of experimental and computational studies, the silicon atom was elucidated to play a pivotal role in the β-amino elimination step.

Summary This Perspective describes the development of the field of catalysis and the advent of metal-free catalysis by focusing on the use of main-group species as frustrated Lewis pair catalysts. In addition to outlining the major advances in this area, it also discusses how these advances could evolve and affect the future of catalysis.

Introducing transition metals into frustrated Lewis pair systems has attracted considerable attention in recent years. Here we report a selection of three metal-only frustrated systems based on Au(I)/Pt(0) combinations and their reactivity towards alkynes. We have inspected the activation of the simplest alkyne, namely acetylene, as well as of other internal and terminal triply bonded hydrocarbons. The gold(I) fragments are stabilized by three bulky phosphines bearing terphenyl groups. We have observed that subtle modifications on the substituents of these ligands proved critical to control the regioselectivity of acetylene activation and the product distribution resulting from C(sp)—H cleavage of phenylacetylene. A mechanistic picture based on experimental observations and computational analysis is provided. As a result of the cooperative action of the two metals of the frustrated pairs, several uncommon heterobimetallic structures have been fully characterized.

Three molybdenum(VI) dioxido complexes [MoO2(L)2] bearing Schiff base ligands were reacted with B(C6F5)3 to afford the corresponding adducts [MoO{OB(C6F5)3}(L)2], which were fully characterized. They exhibit Frustrated Lewis‐Pairs reactivity when reacting with silanes. Especially, the [MoO{OB(C6F5)3}(L)2] complex with L=2,4‐dimethyl‐6‐((phenylimino)methyl)phenol proved to be active as catalyst for the hydroalkylation of aryl alkenes with organohalides and for the Atom‐Transfer Radical Addition (ATRA) of organohalides to aliphatic alkenes. A series of gem‐dichloride and gem‐dibromide compounds with potential for further derivatization were synthesized from simple alkenes and organohalides, like chloroform or bromoform, using low catalyst loading.

The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1,1-carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1,1-Carboboration has been proposed to proceed through a zwitterionic intermediate. We report the isolation and spectroscopic, structural and computational characterization of the zwitterionic intermediates generated by reaction of B(C6 F5 )3 with alkynes. The stepwise reactivity of the zwitterion provides new mechanistic insight for 1,1-carboboration and wider B(C6 F5 )3 catalysis. Making use of intramolecular stabilization by a ferrocene substituent, we have characterized the zwitterionic intermediate in the solid state and diverted reactivity towards alkyne cyclotrimerization.

A set of novel, easily synthesized aluminum complexes, Al[κ2-N,N-2-(methylamino)pyridine]2R (R = Et, iBu) are reported. When subjected to 1 atm of CO2 pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO2 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 CO2 per aluminum center. The ethyl variant then reacts further, inserting a third equivalent of CO2 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.

An immortal N-(diphenylphosphanyl)-1,3-diisopropyl-4,5-dimethyl-1,3-dihydro-2H-imidazol-2-imine/diisobutyl (2,6-di-tert-butyl-4-methylphenoxy) aluminum (P(NIi Pr)Ph2 /(BHT)Ali Bu2 )-based frustrated Lewis pair (FLP) polymerization strategy is presented for rapid and scalable synthesis of the sequence-controlled multiblock copolymers at room temperature. Without addition of extra initiator or catalyst and complex synthetic procedure, this method enabled a tripentacontablock copolymer (n=53, k=4, dpn =50) to be achieved with the highest reported block number (n=53) and molecular weight (Mn =310 kg mol-1 ) within 30 min. More importantly, this FLP polymerization strategy provided access to the multiblock copolymers with tailored properties by precisely adjusting the monomer sequence and block numbers.

The cycloaddition of ethylene, cyanoethylene, and propylene to a five-membered P/B frustrated Lewis pair (FLP) is shown to be highly favorable under normal conditions, as confirmed by the computed thermodynamic and kinetic data. All of these cycloaddition reactions are concerted as highlighted by the intrinsic reaction coordinate (IRC) and Wiberg bond index calculations. Almost 70% of the reaction force is required for structural orientation to initiate electronic activity. The reactions are interpreted by the frontier molecular orbital (FMO) analysis and conceptual density functional theory (DFT)-based reactivity descriptors. It appears that ethylene and propylene will act as nucleophiles, while the FLP will act as an electrophile throughout the cycloaddition reaction, however, cyanoethylene will act as an electrophile and the FLP as a nucleophile. Regioselectivities of the cycloadditon of cyanoethylene and propylene to the FLP are further verified through philicity and dual descriptors. It is demonstrated that an FLP can be forced to act as an electrophile or a nucleophile by intelligently selecting its partner in a cycloaddition reaction. Even the P and B centers would behave differently within the same FLP. This strategy may be properly exploited by the experimentalists in designing a suitable reaction for the synthesis of any useful molecule possessing the desired property.

The reaction between H2 and CO2 catalyzed by an intramolecular frustrated Lewis pair, which is covalently bonded to a UiO-66 metal–organic framework (MOF), is considered in this work. Free energy s...

Herein, we present the first transformation of borylphosphine into borylphosphinite using nitrous oxide. Borylphosphine reacts with N2O via insertion of a single oxygen atom into the P–B bond and f...

Frustrated Lewis pairs consisting of diphenylphosphino and boryl groups located at the ortho-position can trap difluorocarbene affording stable zwitterionic adducts. The reaction can be reversed to release difluorocarbene at elevated temperatures.

Polyfluoromethyl groups generally suffer from over-reaction, where multiple C–F bonds are uncontrollably functionalized. The use of a frustrated Lewis pair (FLP)-mediated C–F bond activation permits selective monodefluorination through base capture of intermediate fluorocarbocations. FLP-mediated C–F bond activation can be applied to aromatic, heteroaromatic, or nonaromatic difluoro and trifluoromethyl groups to generate selectively fluoride-substituted phosphonium and pyridinium salts. These salts can be further functionalized by Wittig coupling, nucleophilic substitution, photoredox alkylation, nucleophilic transfer, or hydrogenation reactions to install a range of functional groups into the activated C–F position.1 Introduction2 Frustrated Lewis Pair C–F Activation3 Conclusion

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.