Preparation and characterization of diruthenium(II,III) compounds containing terminal olefin groups

4-Vinylbenzoic acid reacted with Ru₂(D(3,5-Cl₂Ph)F)₃(OAc)Cl and cis-Ru₂(D(3,5-Cl₂Ph)F)₂(OAc)₂Cl (D(3,5-Cl₂Ph)F is N,N′-bis(3,5-dichlorophenyl)formamidinate) to yield Ru₂(D(3,5-Cl₂Ph)F)₃(4-vinylbenzoate)Cl (1) and cis-Ru₂(D(3,5-Cl₂Ph)F)₂(4-vinylbenzoate)₂Cl (2), respectively. Ru₂(D(3,5-Cl₂Ph)F)₃(OAc)Cl reacted with 5-hexenoic acid and 6-heptenoic acid to afford Ru₂(D(3,5-Cl₂Ph)F)₃(5-hexenoate)Cl (3) and Ru₂(D(3,5-Cl₂Ph)F)₃(6-heptenoate)Cl (4), respectively. All new compounds were characterized using voltammetric and Vis–NIR spectroscopic techniques, and the structures of 1 and 2 were also established through X-ray single crystal diffractions.     

Frustrated Lewis Pairs Comprising Nitrogen Lewis Acids for Si–H Bond Activation

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.     

New Reactivity Patterns in 3H-Phosphaallene Chemistry [Aryl-P=C=C(H)-tBu]: Hydroboration of the C=C Bond,Deprotonation and Trimerisation

3H-Phosphaallenes, R−P=C=C(H)C−R’ ( 3 ), are accessible in a multigram scale on a new and facile route and show a fascinating chemical reactivity. BH₃(SMe₂) and 3 a (R=Mes*, R’=tBu) afforded by hydroboration of the C=C bonds of two phosphaallene molecules an unprecedented borane ( 7 ) with the B atom bound to two P=C double bonds. This compound represents a new FLP based on a B and two P atoms. The increased Lewis acidity of the B atom led to a different reaction course upon treatment of 3 a with H₂B-C₆F₅(SMe₂). Hydroboration of a C=C bond of a first phosphaallene is followed in a typical FLP reaction by the coordination of a second phosphaallene molecule via B−C and P−B bond formation to yield a BP₂C₂ heterocycle ( 8 ). Its B−P bond is short and the B-bound P atom has a planar surrounding. Treatment of 3 a with tBuLi resulted in deprotonation of the β-C atom of the phosphaallene ( 9 ). The Li atom is bound to the P atom as demonstrated by crystal structure determination, quantum chemical calculations and reactions with HCl, Cl-SiMe₃ or Cl-PtBu₂. The thermally unstable phosphaallene Ph−P=C=C(H)-tBu gave a unique trimeric secondary product by P−P, P−C and C−C bond formation. It contains a P₂C₄ heterocycle and was isolated as a W(CO)₄ complex with two P atoms coordinated to W ( 15 ).     

Stoichiometric and Catalytic C−C and C−H Bond Formation with B(C6F5)3 via Cationic Intermediates

This work showcases a new catalytic cyclization reaction using a highly Lewis acidic borane with concomitant C−H or C−C bond formation. The activation of alkyne‐containing substrates with B(C₆F₅)₃ enabled the first catalytic intramolecular cyclizations of carboxylic acid substrates using this Lewis acid. In addition, intramolecular cyclizations of esters enable C−C bond formation as catalytic B(C₆F₅)₃ can be used to effect formal 1,5‐alkyl migrations from the ester functional groups to unsaturated carbon–carbon frameworks. This metal‐free method was used for the catalytic formation of complex dihydropyrones and isocoumarins in very good yields under relatively mild conditions with excellent atom efficiency.     

Methylene Bridging Effect on the Structures,Lewis Acidities and Optical Properties of Semi-planar Triarylboranes

Three synthetic methods towards semi-planar triarylboranes with two aryl rings connected by a methylene bridge have been developed. The fine-tuning of their stereoelectronic properties and Lewis acidities was achieved by introducing fluorine, methyl, methoxy, n-butyl and phenyl groups either at their exocyclic or bridged aryl rings. X-ray diffraction analysis and quantum-chemical calculations provided quantitative information on the structural distortion experienced by the near planar hydro-boraanthracene skeleton during the association with Lewis bases such as NH₃ and F⁻. Though the methylene bridge between the ortho-positions of two aryl rings of triarylboranes decreased the Gibbs free energies of complexation with small Lewis bases by less than 5 kJ mol⁻¹ relative to the classical Lewis acid BAr₃, the steric shielding of the CH₂ bridge is sufficient to avoid the formation of Lewis adducts with larger Lewis bases such as triarylphosphines. A newly synthesized spirocyclic amino-borane with a long intramolecular B−N bond that could be dissociated under thermal process, UV-irradiation, or acidic conditions might be a potential candidate in Lewis pairs catalysis.     

A Frustrated and Confused Lewis Pair

We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates ^iPr2ArNCO (^iPr2Ar=2,6‐iPr₂C₆H₃) and ^Ph2tBuArNCO (^Ph2tBuAr=2,6‐Ph₂‐4‐tBuC₆H₂) with Piers’ borane (HB(C₆F₅)₂). While hydroboration of smaller isocyanates such as ^iPr2ArNCO leads to isocyanate—N/B FLP adducts, hydroboration of the bulkier ^Ph2tBuArNCO allows isolation of the substrate‐free aminoborane with a short, covalent N?B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a “normal” FLP along the reaction pathway, supported by high‐level DFT studies and variable‐temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid–base interaction.     

N-Heterocyclic Carbene Derived 3-Azabutadiene as a π-Base in Classic and Frustrated Lewis Pair Chemistry

N-Heterocyclic carbene (NHC) derived 3-azabutadienes 1 and 2 have been prepared by a single-step reaction of the corresponding NHC with cyclohexyl isocyanide. Compound 1 features π-basic, delocalized nucleophilic sites over the 3-azabutadiene moiety, therefore allowing for coordinating with small Lewis acids, such as AlCl₃, GaCl₃, and Me₂SAuCl, to form diverse classic Lewis adducts 3 – 5 . Combination of 1 with B(C₆F₅)₃ or [Ph₃C][B(C₆F₅)₄] resulted in single-electron transfer and the obtained radical cation was detected by EPR. In addition, a frustrated Lewis pair comprised of the π-basic 1 and BPh₃ effects the splitting of the O−H bond of phenol and the N−H bond of imidazole to give 7 and 8 , respectively. An intrinsic bond orbital (IBO) analysis of the pathway leading to 8 showcases the transformation of the delocalized π-electrons of 1 to a newly formed C−H localized σ-bond.     

Bis[N,N′‐diisopropylbenzamidinato(−)]silicon(II): Lewis Acid/Base Reactions with Triorganylboranes

Reaction of the donor‐stabilized silylene 1 (which is three‐coordinate in the solid state and four‐coordinate in solution) with BEt₃ and BPh₃ leads to the formation of the Lewis acid/base complexes 2 and 3 , respectively, which are the first five‐coordinate silicon compounds with an Si?B bond. These compounds were structurally characterized by crystal structure analyses and by multinuclear NMR spectroscopic studies in the solid state and in solution. Additionally, the bonding situation in 2 and 3 was analyzed by quantum chemical studies.     

Directed Synthesis and Chemistry of Unsymmetric Dicationic Diboranes and Their Use in Frustrated Lewis Pair-like Chemistry

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 B₂(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.     

Frustrated Lewis Pair Chemistry Enables N2 Borylation by Formal 1,3-Addition of a B−H Bond in the Coordination Sphere of Tungsten

The first example of a formal 1,3-B−H bond addition across the M−N≡N unit of an end-on dinitrogen complex has been achieved. The use of Piers’ borane HB(C₆F₅)₂ was essential to observe this reactivity and it plays a triple role in this transformation: 1) electrophilic N₂-borylation agent, 2) Lewis acid in a frustrated Lewis pair-type B−H bond activation, and 3) hydride shuttle to the metal center. This chemistry is supported by NMR spectroscopy and solid-state characterization of products and intermediates. The combination of chelate effect and strong σ donation in the diphosphine ligand 1,2-bis(diethylphosphino)ethane was mandatory to avoid phosphine dissociation that otherwise led to complexes where borylation of N₂ occurred without hydride transfer.     

Alkylation of aromatic compounds with multi-component Lewis acid catalysts of ZnCl2 and ionic liquids with different organic cations

Alkylation of aromatic compounds with various alkylating agents such as benzyl chloride, benzyl alcohol and isopropyl chloride were investigated using ZnCl₂ based ionic liquid (ILs) Lewis acid catalysts. Multi-component Lewis acid catalysts of ZnCl₂ and ionic liquids such as 1-butyl-3-methylimidazolium bromide, 1-butylpyridinium bromide, cholin chloride and tetrabutylammonium bromide were prepared, supported on silica gel, and compared for alkylation reactions with various alkylating agents. Among the IL-based catalysts, 1-butyl-3-methyl imidazolium-bromide-ZnCl₂ and 1-butylpyridinium bromide-ZnCl₂ are highly active.     

Reactions of Rhenium and Technetium Nitrido Complexes with ER3 Fragments (E = B,Ga, Al,C, P; R = H,Alkyl, Aryl)

Terminal ‘N^3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used. Air‐stable compounds with Re≡N‐ER₃ bridges are formed when ER₃ is BR₃ (R = H, Cl, Br, Ethyl, Phenyl, C₆F₅), BCl₂Ph, GaCl₃, CPh₃⁺, or PPh₃. The six‐co‐ordinate rhenium(V) complexes [ReNX₂(PMe₂Ph)₃] (X = Cl, Br), [ReN(X)(Et₂dtc)(PMe₂Ph)₂] (Et₂dtc^— = diethyldithiocarbamate) and [ReN(Et₂dtc)₂(PMe₂Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl₂(PPh₃)₂], [ReN(Et₂dtc)₂], [ReN{Ph₂P(S)NP(S)Ph₂}₂] or [ReNCl₄]^— only react with the most reactive Lewis bases of the examples mentioned above such as BCl₂Ph or B(C₆F₅)₃. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors. Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms. EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d¹) [ReNX₄]^— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl₄]^— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge. The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH₃ and BPhCl₂ have been established.     

Selective Activation of Aromatic Aldehydes Promoted by Dispersion Interactions: Steric and Electronic Factors of a π-Pocket within Cage-Shaped Borates for Molecular Recognition

Selective bond formations are one of the most important reactions in organic synthesis. In the Lewis acid mediated electrophile reactions of carbonyls, the selective formation of a carbonyl–acid complex plays a critical role in determining selectivity, which is based on the difference in the coordinative interaction between the carbonyl and Lewis acid center. Although this strategy has attained progress in selective bond formations, the discrimination between similarly sized aromatic and aliphatic carbonyls that have no functional anchors to strongly interact with the metal center still remains a challenging issue. Herein, this work focuses on molecular recognition driven by dispersion interactions within some aromatic moieties. A Lewis acid catalyst with a π-space cavity, which is referred to as a π-pocket, as the recognition site for aromatic carbonyls is designed. Cage-shaped borates 1 B with various π-pockets demonstrated significant chemoselectivity for aromatic aldehydes 3 b – f over that of aliphatic 3 a in competitive hetero-Diels–Alder reactions. The effectiveness of our catalysts was also evidenced by intramolecular recognition of the aromatic carbonyl within a dicarbonyl substrate. Mechanistic and theoretical studies demonstrated that the selective activation of aromatic substrates was driven by the preorganization step with a larger dispersion interaction, rather than the rate-determining step of the C−C bond formation, and this was likely to contribute to the preferred activation of aromatic substrates over that of aliphatic ones.     

Selective 3,3-Rearrangement of Azobenzenes upon Complexation by a Frustrated Lewis Pair

The reaction of the oxygen-bridged frustrated Lewis pairs (FLPs) tBu₂P−O−Si(C₂F₅)₃ ( 1 ) and tBu₂P−O−AlBis₂ ( 2 ) with azobenzene, promoted by UV irradiation, led to a selective complexation of the cis-isomer. The addition product of 2 is stable, while the adduct of 1 isomerizes in solution in an ortho-benzidine-like [3,3]-rearrangement by cleavage of the N−N bond, saturation of the nitrogen atoms with hydrogen atoms and formation of a new bond between two phenyl ortho-carbon atoms. Similar rearrangements take place with different para-substituted azobenzenes (R=Me, OMe, Cl) and di(2-naphthyl)diazene, while ortho-methylated azo compounds do not form adducts with 1 . All adducts were characterized by multinuclear NMR spectroscopy and elemental analyses and the mechanism of the rearrangement was explored by quantum-chemical calculations.     

A Neutral “Aluminocene” Sandwich Complex: η1‐ versus η5‐Coordination Modes of a Pentaarylborole with ECp* (E=Al,Ga; Cp*=C5Me5)

The pentaaryl borole (Ph*C)₄BXyl^F [Ph*=3,5‐tBu₂(C₆H₃); Xyl^F=3,5‐(CF₃)₂(C₆H₃)] reacts with low‐valent Group 13 precursors AlCp* and GaCp* by two divergent routes. In the case of [AlCp*]₄, the borole reacts as an oxidising agent and accepts two electrons. Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral η⁵‐Cp*,η⁵‐[(Ph*C)₄BXyl^F] complex of Al^III revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole‐cyclopentadienyl “aluminocene” leads to significant changes in the ¹³C NMR chemical shifts within the borole unit. In the case of the less‐reductive GaCp*, borole (Ph*C)₄BXyl^F reacts as a Lewis acid to form a dynamic adduct with a dative 2‐center‐2‐electron Ga?B bond. The Lewis adduct was also studied structurally, spectroscopically, and computationally.     

Al/P- and Ga/P-Based Frustrated Lewis Pairs and Electronically Unsaturated Substrates: Ring Cleavage and Ring Closure,C−C and C−N Bond Formation

Al/P- and Ga/P-based frustrated Lewis pairs (FLPs) reacted with an azirine under mild conditions under cleavage of the heterocycle on two different positions. Opening of the C−C bond yielded an unusual nitrile–ylide adduct in which a C−N moiety coordinated to the FLP backbone. Cleavage of a C−N bond afforded the thermodynamically favored enamine adduct with the N atom bound to P and Al or Ga atoms. Ring closure was observed upon treatment of an Al/P FLP with electronically unsaturated substrates (4-(1-cyclohexenyl)-1-aza-but-1-en-3-ynes) and yielded by C−N bond formation hexahydroquinoline derivatives, which coordinated to the FLP through P−C and Al−C bonds. Diphenylcyclopropenone showed a diverse reactivity, which depending on steric shielding and the polarizing effect of Al or Ga atoms afforded different products. An AltBu₂/P FLP yielded an adduct with the C=O group coordinated to P and Al. The dineopentyl derivative gave an equilibrium mixture consisting of a similar product and a simple adduct with O bound to Al and a three-coordinate P atom. Both compounds co-crystallize. The Ga/P FLP only formed the simple adduct with the same substrate. Rearrangement resulted in all cases in C₃-ring cleavage and migration of a mesityl group from P to a former ring C atom by C−C bond formation. Diphenylthiocyclopropenone (evidence for the presence of P=C bonds) and an imine derivative afforded similar products.     

全氟烷基磺酰亚胺盐催化芳香化合物硝化反应的研究

利用系列全氟烷基磺酰亚胺盐[M(NPf₂)_n]作为一种新型的Lewis酸催化剂，用于催化芳香化合物与等摩尔65% (m∶m)硝酸的硝化反应. 通过考察不同的催化剂、反应时间、反应温度和反应介质效应等因素对甲苯硝化的影响，以及比较1 mol% Yb[N(C₄F₉SO₂)₂]₃催化不同结构的取代芳烃硝化反应的效果，表明全氟烷基磺酰亚胺盐不仅具有环境友好和原子经济的特点，而且是一类比常规Lewis酸更有效的、芳香化合物硝化反应的催化剂.     

Tweaking Photo CO2 Reduction by Altering Lewis Acidic Sites in Metalated-Porous Organic Polymer for Adjustable H2/CO Ratio in Syngas Production

Herein, we have specifically designed two metalated porous organic polymers ( Zn-POP and Co-POP ) for syngas (CO+H₂) production from gaseous CO₂. The variable H₂/CO ratio of syngas with the highest efficiency was produced in water medium (without an organic hole scavenger and photosensitizer) by utilizing the basic principle of Lewis acid/base chemistry. Also, we observed the formation of entirely different major products during photocatalytic CO₂ reduction and water splitting with the help of the two catalysts, where CO (145.65 μmol g⁻¹ h⁻¹) and H₂ (434.7 μmol g⁻¹ h⁻¹) production were preferentially obtained over Co-POP & Zn-POP , respectively. The higher electron density/better Lewis basic nature of Co-POP was investigated further using XPS, XANES, and NH₃-TPD studies, which considerably improve CO₂ activation capacity. Moreover, the structure–activity relationship was confirmed via in situ DRIFTS and DFT studies, which demonstrated the formation of COOH* intermediate along with the thermodynamic feasibility of CO₂ reduction over Co-POP while water splitting occurred preferentially over Zn-POP .     

Heavy Chains: Synthesis,Reactivity and Decomposition of Interpnictogen Chains with Terminal Diaryl Bismuth Fragments

In this work, we report the preparation of multiple interpnictogen chain compounds with three consecutive pnictogen atoms and terminal Ar₂Bi fragments (Ar=Ph, Mes). Symmetrical compounds of the form Ar₂Bi−E(tBu)−Bi₂Ar ( 1 : Ar=Ph, E=P; 2 : Ar=Ph, Mes, E=As) as well as ternary interpnictogen compounds of the form Ar₂Bi−E¹(tBu)−E²tBu₂ (Ar=Ph, Mes; 4 : E¹=P, E²=As; 5 : E¹=P, E²=Sb; 6 : E¹=As, E²=P) were prepared. The decomposition in solution at room temperature and under the influence of light was studied for compounds 1 – 6 . The reactivity of 1_Ph and 2_Ph with the small N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene (Me₂IMe) was also studied. In the case of 1_Ph , the formation and consecutive decomposition of Me₂IMe=PtBu ( 8 ) was observed in solution. Hence, it was shown that 1_Ph can react as a “masked phosphinidene”. In the case of 2_Ph , no reaction with Me₂IMe was observed. All isolated compounds were analysed by NMR and IR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray diffraction.     

Pnictogen-Bonding Catalysis: An Interactive Tool to Uncover Unorthodox Mechanisms in Polyether Cascade Cyclizations

Pnictogen-bonding catalysis and supramolecular σ-hole catalysis in general is currently being introduced as the non-covalent counterpart of covalent Lewis acid catalysis. With access to anti-Baldwin cyclizations identified as unique characteristic, pnictogen-bonding catalysis appeared promising to elucidate one of the hidden enigmas of brevetoxin-type epoxide opening polyether cascade cyclizations, that is the cyclization of certain trans epoxides into cis-fused rings. In principle, a shift from S_N2- to S_N1-type mechanisms could suffice to rationalize this inversion of configuration. However, the same inversion could be explained by a completely different mechanism: Ring opening with C−C bond cleavage into a branched hydroxy-5-enal and the corresponding cyclic hemiacetal, followed by cascade cyclization under conformational control, including stereoselective C−C bond formation. In this report, a pnictogen-bonding supramolecular Sb^V catalyst is used to demonstrate that this unorthodox polyether cascade cyclization mechanism occurs.