Photochemically Induced Intramolecular Six‐Electron Reductive Elimination and Oxidative Addition of Nitric Oxide by the Nitridoosmate(VIII) Anion

UV photolysis of the nitridoosmate(VIII) anion, OsO₃N^?, in low‐temperature frozen matrices results in nitrogen–oxygen bond formation to give the Os^II nitrosyl complex OsO₂(NO)^?. Photolysis of the Os^II nitrosyl product with visible wavelengths results in reversion to the parent Os^VIII complex. Formally a six‐electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation. DFT modelling of this reaction proceeds through a step‐wise mechanism taking place through a side‐on nitroxyl Os^VI intermediate, OsO₂(η²‐NO)^?.     

Computational Study of Bridge Splitting,Aryl Halide Oxidative Addition to PtII,and Reductive Elimination from PtIV: Route to Pincer-PtII Reagents with Chemical and Biological Applications

Density functional theory computation indicates that bridge splitting of [Pt^IIR₂(μ-SEt₂)]₂ proceeds by partial dissociation to form R₂Pt^a(μ-SEt₂)Pt^bR₂(SEt₂), followed by coordination of N-donor bromoarenes (L-Br) at Pt^a leading to release of Pt^bR₂(SEt₂), which reacts with a second molecule of L-Br, providing two molecules of PtR₂(SEt₂)(L-Br-N). For R=4-tolyl (Tol), L-Br=2,6-(pzCH₂)₂C₆H₃Br (pz=pyrazol-1-yl) and 2,6-(Me₂NCH₂)₂C₆H₃Br, subsequent oxidative addition assisted by intramolecular N-donor coordination via Pt^IITol₂(L-N,Br) and reductive elimination from Pt^IV intermediates gives mer-Pt^II(L-N,C,N)Br and Tol₂. The strong σ-donor influence of Tol groups results in subtle differences in oxidative addition mechanisms when compared with related aryl halide oxidative addition to palladium(II) centres. For R=Me and L-Br=2,6-(pzCH₂)₂C₆H₃Br, a stable Pt^IV product, fac-Pt^IVMe₂{2,6-(pzCH₂)₂C₆H₃-N,C,N)Br is predicted, as reported experimentally, acting as a model for undetected and unstable Pt^IVTol₂{L-N,C,N}Br undergoing facile Tol₂ reductive elimination. The mechanisms reported herein enable the synthesis of Pt^II pincer reagents with applications in materials and bio-organometallic chemistry.     

Oxidative Addition of Carbon–Carbon Bonds to Gold

The oxidative addition of strained C? C bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino‐carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)? C(O) or C(alkyl)? C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation.     

A Monoaryllead Trichloride That Resists Reductive Elimination

Transmetallation of Pb(OAc)₄ with R₂Hg ( 1 ), followed by treatment with HCl in Et₂O, provided RPbCl₃ ( 2 ), the first kinetically stabilized monoorganolead trihalide that resists reductive elimination under ambient conditions. The kinetic stabilisation relies on an intramolecularly coordinating O‐donor substituent (R=6‐Ph₂P(O)‐Ace‐5‐). The gram‐scale preparation of 2 was key for the synthesis of unsymmetrically substituted diaryllead dichlorides RR′PbCl₂ ( 3 a , R′=Ph; 3 b , R′=4‐MeOC₆H₄; 3 c , R′=4‐Me₂NC₆H₄).     

Syntheses of Tetrasubstituted [10]Cycloparaphenylenes by a Pd‐catalyzed Coupling Reaction. Remarkable Effect of Strain on the Oxidative Addition and Reductive Elimination

A small library of tetrasubstituted [10]cycloparaphenylene ([10]CPP) derivatives bearing alkyl, alkenyl, alkynyl and aryl substituents was constructed by a Pd‐catalyzed cross‐coupling reaction starting from tetratriflate [10]CPP 5 e , which was readily available in high yields on a >2 g scale. The CPP skeleton increases the reactivity of aryl triflate for oxidative addition to the Pd species, and 5 e is 10 times more reactive than its linear paraphenylene analogue, as determined by competition experiments. Theoretical calculations suggest that the accumulation of the small strain relief from each paraphenylene unit not involved in the reaction is responsible for the observed enhanced reactivity.     

Oxidative Addition Reactions of Element–Hydrogen Bonds with Different Polarities to a Gallium(I) Compound

The gallium(I) derivative [Ga({N(dipp)CMe}₂CH)] ( 1 ; dipp=2,6‐diisopropylphenyl) undergoes facile oxidative addition reactions with various element–hydrogen bonds including N? H, P? H, O? H, Sn? H, and H? H bonds. This was demonstrated by its reaction with triphenyltin hydride, ethanol, water, diethylamine, diphenylphosphane, and dihydrogen. All products were characterized by means of single‐crystal X‐ray structure determination, NMR spectroscopy, IR spectroscopy, and mass spectrometry.     

Oxidative Addition of Water and Methanol to a Dicationic Trivalent Phosphorus Centre

Our recently synthesised phosphorus dication is observed to activate water (and methanol) under reactions conditions atypical for other systems containing a non‐metal centre. This particular activation described as oxidative addition is quite rare and has been reserved exclusively for a couple of metal‐based compounds.     

Chiral Amine Catalyzed Reductive Aldol/Reductive Michael Addition Cascade Towards Enantioselective Synthesis of Benzannulated Diquinanes

Disclosed here an amine-catalyzed reductive aldol-condensation followed by an intramolecular reductive Michael-addition cascade employing Hantzsch ester as hydride source to a keto-bis-enone to provide enantio- and diastereoselective benzannulated diquinanes having three consecutive stereocenters, one of which is an all-carbon quaternary formyl stereocenter. Interestingly, on changing a tether connecting the ketone and an enone moiety from an aliphatic to an aromatic, a change in reactivity is observed. In this case, instead of the above-mentioned reductive aldol condensation, an asymmetric aldol reaction occurs, followed by an iminium/enamine isomerization and, finally diastereoselective Michael addition reaction occurs. As a result, a bis-benzannulated diquinane is obtained with vicinal congested quaternary chiral centers.     

Superionic Conduction in Co‐Vacant P2‐NaxCoO2 Created by Hydrogen Reductive Elimination

The layered P2‐Na_xMO₂ (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2‐Na_xCoO₂ created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm^?1 at 25 °C. Using in situ synchrotron X‐ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na_0.61(H₃O)_0.18Co_0.93O₂. Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co‐stoichiometric compound Na_x(H₃O)_yCoO₂ does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.     

Cooperative Reductive Elimination: The Missing Piece in the Oxidative‐Coupling Mechanistic Puzzle

The reaction between benzoic acid and methylphenylacetylene to form an isocoumarin is catalyzed by Cp*Rh(OAc)₂ in the presence of Cu(OAc)₂(H₂O) as an oxidant and a leading example of oxidative‐coupling reactions. Its mechanism was elucidated by DFT calculations with the B97D functional. The conventional mechanism, with separate reductive‐elimination and reoxidation steps, was found to yield a naphthalene derivative as the major product by CO₂ extrusion, contradicting experimental observations. The experimental result was reproduced by an alternative mechanism with a lower barrier: In this case, the copper acetate oxidant plays a key role in the reductive‐elimination step, which takes place through a transition state containing both rhodium and copper centers. This cooperative reductive‐elimination step would not be accessible with a generic oxidant, which, again, is in agreement with available experimental data.     

Photochemically Induced Reductive Elimination as a Route to a Zirconocene Complex with a Strongly Activated N2 Ligand

The zirconocene dinitrogen complex [{(η⁵‐C₅Me₄H)₂Zr}₂(μ₂,η²,η²‐N₂)] was synthesized by photochemical reductive elimination from the corresponding zirconium bis(aryl) or aryl hydride complexes, providing a high‐yielding, alkali metal‐free route to strongly activated early‐metal N₂ complexes. Mechanistic studies support the intermediacy of zirconocene arene complexes that in the absence of sufficient dinitrogen promote C? H activation or undergo comproportion to formally Zr^III complexes. When N₂ is in excess arene displacement gives rise to strong dinitrogen activation.     

Hydrogen activation by an intramolecular boron lewis acid/zirconocene pair

Let's split: Reaction of the zirconium complex A with Piers' borane [HB(C(6) F(5) )(2) ] yields the unusual borylalkyne zirconocene complex B which reacts with dihydrogen, activating it to give the doubly hydrido bridged alkyne zirconium complex C.     

A Zwitterionic Phosphonium Stannate(II) via Hydrogen Splitting by a Sn/P Frustrated Lewis-Pair and Reductive Elimination

The reactivity of the frustrated Lewis pair (FLP) (F₅C₂)₃SnCH₂P(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) (F₅C₂)₂SnCH₂PH(tBu)₂ ( 3 ). It was characterized by means of multinuclear NMR spectroscopy and single crystal X-ray diffraction. NMR experiments with the two isotopologues H₂ and D₂ showed it to be formed via an H₂ adduct (F₅C₂)₃HSnCH₂PH(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 H₂, [HP(tBu)₂Me][Sn(C₂F₅)₃] ( 4 ), in ¹H NMR spectra, whereas 2 was not detected due to its transient nature.     

Oxidative Addition at a Carbene Center: Synthesis of an Iminoboryl–CAAC Adduct

The reaction of a cyclic (alkyl)(amino)carbene (CAAC) with dichloro‐ and dibromobis(trimethylsilyl)aminoborane results in the formation of haloiminoborane–CAAC adducts. When the iodo analogue is used, an oxidative addition at the carbene center affords a cationic iminoboryl–CAAC adduct, featuring a boron–nitrogen triple bond. Similar salts are also obtained by halide abstraction from the chloro‐ and bromoiminoborane–CAAC adducts. The reactivity of all of these compounds towards CO₂ is discussed.     

Facile CH Bond Formation by Reductive Elimination at a Dinuclear Metal Site

The electronically unsaturated dirhenium complex [Re₂(CO)₈(µ‐AuPPh₃)(µ‐Ph)] ( 1 ) was obtained from the reaction of [Re₂(CO)₈{µ‐η²‐C(H)?C(H)nBu}(µ‐H)] with [Au(PPh₃)Ph]. The bridging {AuPPh₃} group was replaced by a bridging hydrido ligand to yield the unsaturated dirhenium complex [Re₂(CO)₈(µ‐H)(µ‐Ph)] ( 2 ) by reaction of 1 with HSnPh₃. Compound 2 reductively eliminates benzene upon addition of NCMe at 25 °C. The electronic structure of 2 and the mechanism of the reductive elimination of the benzene molecule in its reaction with NCMe were investigated by DFT computational analyses.     

Proton‐Assisted Hydrogen Activation on Polyhedral Cations

The treatment of [1,1‐(PR₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] (PR₃=PMe₃ ( 2 ) or PPh₃ and PMe₃ ( 3 ); Py=pyridine) with triflic acid (TfOH) affords [1,3‐μ‐(H)‐1,1‐(PR₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ (PR₃=PMe₃ ( 4 ) or PMe₃ and PPh₃ ( 5 )). These products result from the protonation of the 11‐vertex closo‐cages along the Rh(1)? B(3) edge. These unusual cationic rhodathiaboranes are stable in solution and in the solid state and they have been fully characterized by multinuclear NMR spectroscopy. In addition, compound 5 was characterized by single‐crystal X‐ray diffraction. One remarkable feature in these structures is the presence of three {Rh(PPh₃)(PMe₃)}‐to‐{ηⁿ‐SB₉H₈(Py)} (n=4 or 5) conformers in the unit cell, thus giving an uncommon case of conformational isomerism. [1,1‐(PPh₃)₂‐3‐(Py)‐closo‐1,2‐RhSB₉H₈] ( 1 ), that is, the bis‐PPh₃‐ligated analogue of compounds 2 and 3 , is also protonated by TfOH, but, in marked contrast, the resulting cation, [1,3‐μ‐(H)‐1,1‐(PPh₃)₂‐3‐(Py)‐1,2‐RhSB₉H₈]⁺ ( 6 ), is attacked by a triflate anion with the release of a PPh₃ ligand and the formation of [8,8‐(OTf)(PPh₃)‐9‐(Py)‐nido‐8,7‐RhSB₉H₉] ( 9 ). The result is an equilibrium that involves cationic species 6 , neutral OTf‐ligated compound 9 , and [HPPh₃]⁺, which is formed upon protonation of the released PPh₃ ligand. The resulting ionic system reacts readily with H₂ to give cationic species [8,8,8‐(H)(PPh₃)₂‐9‐(Py)‐nido‐8,7‐RhSB₉H₉]⁺ ( 7 ). This reactivity is markedly higher than that previously found for compound 1 and it introduces a new example of proton‐assisted H₂ activation that occurs on a polyhedral boron‐containing compound.     

Effect of Hydrogen or Syngas Addition on Light Alkene Production by the Catalytic Oxidative Cracking of Hexane 氢气/合成气添加对正己烷催化氧化裂解制低碳烯烃反应的影响

 采用0.1%Pt/MgAl2O4催化剂研究了H2或合成气的添加对高碳烷烃模型化合物正己烷氧化裂解制低碳烯烃反应的影响. 添加H2实验中,随n(H2)/n(O2)从0增加到3,产物中COx的选择性迅速由22.4%降到4.3%,低碳烯烃的选择性则从61.5%增加到73.8%,正己烷的转化率从62.0%增加到72.8%. 添加合成气对低碳烯烃和CO选择性的影响与添加H2的影响相同,只是添加合成气时正己烷的转化率下降了6%左右. 添加合成气的正己烷氧化裂解过程可提供组成可调的产物(含有低碳烯烃、H2和CO),可不经分离直接用作加氢甲酰化生产低碳烯烃衍生物过程的原料.     

Simple Synthesis of Eudesmin through Oxidative Coupling of Carbanions and Reductive Catalytic Hydrogenation of Diketo Diester

A simple synthesis of eudesmin (1) is described. The key fragments were diol 13, dicarbethoxyethane 4, and diketo diester 5, which were prepared via reductive catalytic hydrogenation and oxidative intermolecular coupling of carbanions. This method is useful to generate the core skeleton of an endo–endo furofuran ring.