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 Ligand Design for the Reductive Elimination of ArCF3 from a Small Bite Angle PdII Complex: Remarkable Effect of a Perfluoroalkyl Phosphine

To date only three ligands are known to trigger the challenging reductive elimination of ArCF₃ from Pd^II. We report the computational design of a bidentate trifluoromethylphosphine ligand that although exhibiting a generally ineffective small bite angle is predicted to give facile reductive elimination. Our experimental verification gave quantitative formation of ArCF₃ at 80 °C within 2 h. This highlights the distinct effect of P‐CF₃ in organometallic reactivity and constitutes a proof‐of‐principle study of computational reactivity design.     

BrettPhos Ligand Supported Palladium‐Catalyzed CO Bond Formation through an Electronic Pathway of Reductive Elimination: Fluoroalkoxylation of Activated Aryl Halides

We report an unprecedented BrettPhos ligand supported Pd‐catalyzed C?O bond‐forming reaction of activated aryl halides with primary fluoroalkyl alcohols. We demonstrate that the Phosphine ligand (BrettPhos) possesses the property of altering the mechanistic pathway of reductive elimination from nucleophile to nucleophile. The Pd/BrettPhos catalyst system facilitates the reductive elimination of the oxygen nucleophile through an electronic pathway.     

Acceleration of Reductive Elimination of [Ar‐Pd‐C] by a Phosphine/Electron‐Deficient Olefin Ligand: A Kinetic Investigation

Dramatic rate enhancement of reductive elimination of [Ar‐Pd‐C] was observed in the presence of a phosphine/electron‐deficient olefin ligand. Through systematic kinetic investigations of the Negishi coupling of ethyl 2‐iodobenzoate with alkylzinc chlorides (see scheme), the rate constants for reductive elimination of [Ar‐Pd‐C] were determined to be greater than 0.3 s^?1, which is about four or five orders of magnitude greater than values reported previously.

     

Mechanistic Insights into C(sp2)−C(sp)N Reductive Elimination from Gold(III) Cyanide Complexes

A new family of phosphine‐ligated dicyanoarylgold(III) complexes has been prepared and their reactivity towards reductive elimination has been studied in detail. Both, a highly positive entropy of activation and a primary ^12/13C KIE suggest a late concerted transition state while Hammett analysis and DFT calculations indicate that the process is asynchronous. As a result, a distinct mechanism involving an asynchronous concerted reductive elimination for the overall C(sp²)?C(sp)N bond forming reaction is characterized herein, for the first time, complementing previous studies reported for C(sp³)?C(sp³), C(sp²)?C(sp²), and C(sp³)?C(sp²) bond formation processes taking place on gold(III) species.     

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.     

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.     

Photolytic Reductive Elimination of White Phosphorus from a Mononuclear cyclo‐P4 Transition Metal Complex

Elemental white phosphorus (P₄) is well recognized as a critical precursor to organophosphorus compounds. However, regulatory constraints stemming from the toxic and pyrophoric nature of white phosphorus have significantly limited its accessibility. Herein is described a new approach to white phosphorus storage and release based on a unique example of photolytic reductive elimination of the tetrahedral P₄ molecule from a mononuclear cyclo‐P₄ molybdenum complex. The latter functions as an air‐stable, chemically‐deactivated source of white phosphorus. The system features efficient photo‐release of white phosphorus using inexpensive violet LED sources. Additionally, high‐yield recapture of unspent white phosphorus by the molybdenum center can be achieved by post‐photolysis heating at convenient temperatures.     

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.     

Reductive Aromatization of Quinols with B2pin2 as Deoxidizing Agent

We have demonstrated B₂pin₂ as superior deoxidizing agent for the reductive deoxygenation of quinol derivatives under basic conditions. A wide range of highly functionalized phenols were obtained in good yields including a complex drug molecule, which revealed the high functional group tolerance of this protocol.     

A Key Intermediate in Copper‐Mediated Arene Trifluoromethylation, [nBu4N][Cu(Ar)(CF3)3]: Synthesis,Characterization, and C(sp2)−CF3 Reductive Elimination

The synthesis, characterization, and C(sp²)?CF₃ reductive elimination of stable aryl[tris(trifluoromethyl)]cuprate(III) complexes [nBu₄N][Cu(Ar)(CF₃)₃] are described. Mechanistic investigations, including kinetic studies, studies of the effect of temperature, solvent, and the para substituent of the aryl group, as well as DFT calculations, suggest that the C(sp²)?CF₃ reductive elimination proceeds through a concerted carbon–carbon bond‐forming pathway.     

A DFT Study on the Conversion of Aryl Iodides to Alkyl Iodides: Reductive Elimination of R−I from Alkylpalladium Iodide Complexes with Accessible β‐Hydrogens

DFT calculations have been performed on the palladium‐catalyzed carboiodination reaction. The reaction involves oxidative addition, alkyne insertion, C?N bond cleavage, and reductive elimination. For the alkylpalladium iodide intermediate, LiOtBu stabilizes the intermediate in non‐polar solvents, thus promoting reductive elimination and preventing β‐hydride elimination. The C?N bond cleavage process was explored and the computations show that PPh₃ is not bound to the Pd center during this step. Experimentally, it was demonstrated that LiOtBu is not necessary for the oxidative addition, alkyne insertion, or C?N bond cleavage steps, lending support to the conclusions from the DFT calculations. The turnover‐limiting steps were found to be C?N bond cleavage and reductive elimination, whereas oxidative addition, alkyne insertion, and formation of the indole ring provide the driving force for the reaction.     

N−N Bond Forming Reductive Elimination via a Mixed‐Valent Nickel(II)–Nickel(III) Intermediate

Natural products containing N–N bonds exhibit important biological activity. Current methods for constructing N?N bonds have limited scope. An advanced understanding of the fundamental N?N bond formation/cleavage processes occurring at the transition‐metal center would facilitate the development of catalytic reactions. Herein we present an N?N bond‐forming reductive elimination, which proceeds via a mixed‐valent Ni^II–Ni^III intermediate with a Ni–Ni bond order of zero. The discrete Ni^II–Ni^III oxidation states contrast with the cationic dimeric Ni analogue, in which both Ni centers are equivalent with an oxidation state of 2.5. The electronic structures of these mixed‐valent complexes have implications for the fundamental understanding of metal–metal bonding interactions.     

Fluoride‐Catalyzed Methylation of Amines by Reductive Functionalization of CO2 with Hydrosilanes

An effective and inexpensive organocatalyst tetrabutylammonium fluoride (TBAF) was developed for the reductive functionalization of CO₂ with amines to selectively afford formamides or methylamines by employing hydrosilanes. Hydrosilanes with different substituents show discriminatory reducing activity. Thus, the formation of formamides and further reduction products, that is, methylamines could be controlled by elegantly tuning hydrosilane types. Formamides were obtained exclusively under an atmospheric pressure of CO₂ with triethoxysilane. Using phenylsilane as a reductant, methylamines were attained with up to 99 % yield at 50 °C coupled to a complete deoxygenation of CO₂. The crucial intermediate silyl formate in the formylation step was identified and thereby a tentative mechanism involving the fluoride‐promoted hydride transfer from the hydrosilane to CO₂/formamide was proposed. Striking features of this metal‐free protocol are formylation and methylation of amines by reductive functionalization of CO₂ with hydrosilanes and mild reaction conditions.     

Plasmon‐Induced Ammonia Synthesis through Nitrogen Photofixation with Visible Light Irradiation

We have successfully developed a plasmon‐induced technique for ammonia synthesis that responds to visible light through a strontium titanate (SrTiO₃) photoelectrode loaded with gold (Au) nanoparticles. The photoelectrochemical reaction cell was divided into two chambers to separate the oxidized (anodic side) and reduced (cathodic side) products. To promote NH₃ formation, a chemical bias was applied by regulating the pH value of these compartments, and ethanol was added to the anodic chamber as a sacrificial donor. The quantity of NH₃ formed at the ruthenium surface, which was used as a co‐catalyst for SrTiO₃, increases linearly as a function of time under irradiation with visible light at wavelengths longer than 550 nm. The NH₃ formation action spectrum approximately corresponds to the plasmon resonance spectrum. We deduced that plasmon‐induced charge separation at the Au/SrTiO₃ interface promotes oxidation at the anodic chamber and subsequent nitrogen reduction on the cathodic side.     

How a Redox‐Innocent Metal Promotes the Formal Reductive Elimination of Biphenyl Using Redox‐Active Ligands

One of the most compelling strategies for utilizing redox‐active ligands is to perform redox events at the ligands to avoid accessing prohibitively high energy oxidation states at the metal center. This has been demonstrated experimentally in many systems, yet there is little understanding of the fundamental electronic structures involved with these transformations or how to control them. Here, the reductive elimination of biphenyl from [M(isq)₂Ph₂] (M=Ti, Zr, and Hf and isq=2,4‐di‐tert‐butyl‐6‐tert‐butyliminosemiquinone) was studied computationally. It was found that the metal remains in the +IV oxidation state and all redox chemistry was mediated by the redox‐active ligands. Two types of electron‐transfer mechanisms were identified, an asymmetric unpaired electron transfer (UET) and a symmetric pairwise electron transfer (PET), the former always being lower in energy. The energetic differences between these two mechanisms were explained through simple molecular orbital theory arguments. Despite the metal’s redox‐inactivity, it still has a marked influence on the calculated energetics of the reaction, with the Ti systems being much more reactive than the Zr/Hf systems. This primarily originates from the shorter Ti?Ph bond, which leads to a stronger filled‐filled interaction between these ligands at the reactant state. This greater reactant destabilization leads to the lower activation energies.     

Catalytic HgCl2—Samarium System Induced Reductive Coupling of Nitriles with Nitro Compounds

The intermolecular coupling of a nitro group with a cyano group mediated by a Sm(Hg) amalgam prepared from metal samarium powder and catalytic mercury dichloride was studied.     

羰基钴催化烯烃醛化反应中RCOCo(H)2(CO)3还原消去关键步骤的理论研究

在其催化循环过程中,RCOCo(CO)_3与H2_氧化加成生成RCOCO(H)_2(CO)_3,此中间体进一步还原消去生成醛是涉及氢在整个醛化反应催化循环中活化作用的关键步骤,文献[2]认为它是整个循环的控制步骤,由于反应的各中间物光谱无法准确测定,无法分别考察这两个步