Base-Free Pd-Catalyzed C−Cl Borylation of Fluorinated Aryl Chlorides

Catalytic C−X borylation of aryl halides containing two ortho-fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho-fluorine substituents. Herein, we report that a combination of Pd(dba)₂ (dba=dibenzylideneacetone) with SPhos (2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl) as a ligand is efficient to catalyze the C-Cl borylation of aryl chlorides containing two ortho-fluorine substituents. This method, conducted under base-free conditions, is compatible with the resulting di-ortho-fluorinated aryl boronate products which are sensitive to base.     

Pentamethylcyclopentadienylruthenium(II) Complexes: Synthesis,Characterization and Catalytic Activity in Aryl–Aryl Coupling

Ruthenium(II) complexes of the type [Ru(PPh₃)( ⁵-C₅Me₅)L] have been synthesized by the reactions of [RuCl(PPh₃)₂( ⁵-C₅Me₅)] with Schiff bases having the (N, O) donor atoms. The Schiff bases used in this study were prepared by condensing the appropriate aniline with salicylaldehyde or 2-hydroxy-1-naphthaldehyde in a 1:2 molar ratio respectively. The complexes were characterized by analytical, spectral (i.r., electronic and ¹H-n.m.r.) data. The new complexes have been used as catalysts in aryl–aryl coupling reactions.     

11C-Cyanation of Aryl Fluorides via Nickel and Lithium Chloride-Mediated C−F Bond Activation

Aryl fluorides are expected to be useful as radiolabeling precursors due to their chemical stability and ready availability. However, direct radiolabeling via carbon-fluorine (C−F) bond cleavage is a challenging issue due to its significant inertness. Herein, we report a two-phase radiosynthetic method for the ipso-¹¹C-cyanation of aryl fluorides to obtain [¹¹C]aryl nitriles via nickel-mediated C−F bond activation. We also established a practical protocol that avoids the use of a glovebox, except for the initial preparation of a nickel/phosphine mixture, rendering the method applicable for general PET centers. This method enabled the efficient synthesis of diverse [¹¹C]aryl nitriles from the corresponding aryl fluorides, including pharmaceutical drugs. Stoichiometric reactions and theoretical studies indicated a significant promotion effect of lithium chloride on the oxidative addition, affording an aryl(chloro)nickel(II) complex, which serves as a precursor for rapid ¹¹C-cyanation.     

C−H Bond Activation by Iridium(III) and Iridium(IV) Oxo Complexes

Oxidation of an iridium(III) oxo precursor enabled the structural, spectroscopic, and quantum-chemical characterization of the first well-defined iridium(IV) oxo complex. Side-by-side examination of the proton-coupled electron transfer thermochemistry revealed similar driving forces for the isostructural oxo complexes in two redox states due to compensating contributions from H⁺ and e⁻ transfer. However, C−H activation of dihydroanthracene revealed significant hydrogen tunneling for the distinctly more basic iridium(III) oxo complex. Our findings complement the growing body of data that relate tunneling to ground state properties as predictors for the selectivity of C−H bond activation.     

Easy Access to Versatile Catalytic Systems for C−H Activation and Reductive Amination Based on Tetrahydrofluorenyl Rhodium(III) Complexes

On the basis of the 1,2,3,4-tetrahydrofluorenyl ligand, a simple approach was developed to new effective rhodium catalysts for the construction of C−C and C−N bonds. The halide compounds [(η⁵-tetrahydrofluorenyl)RhX₂]₂ ( 2 a : X=Br; 2 b : X=I) were synthesized by treatment of the bis(ethylene) derivative (η⁵-tetrahydrofluorenyl)Rh(C₂H₄)₂ ( 1 a ) with halogens. An analogous reaction of the cyclooctadiene complex (η⁵-tetrahydrofluorenyl)Rh(cod) ( 1 b ) with I₂ is complicated by the side formation of [(cod)RhI]₂. The reaction of 2 b with 2,2′-bipyridyl leads to cation [(η⁵-tetrahydrofluorenyl)Rh(2,2′-bipyridyl)I]⁺ ( 3 ). The halide abstraction from 2 a , b with thallium or silver salts allowed us to prepare sandwich compounds with incoming cyclopentadienyl, dicarbollide and mesityleneligands [(η⁵-tetrahydrofluorenyl)RhCp]⁺ ( 4 ), (η⁵-tetrahydrofluorenyl)Rh(η-7,8-C₂B₉H₁₁) ( 5 ), and [(η⁵-tetrahydrofluorenyl)Rh(η-mesitylene)]²⁺ ( 6 ). The structures of 1 b , 2 b ⋅ 2I₂, 3 PF₆, 4 TlI₄, 5 , and [(cod)RhI]₂ were determined by X-ray diffraction. Compounds 2 a , b efficiently catalyze the oxidative coupling of benzoic acids with alkynes to selectively give isocoumarins or naphthalenes, depending on the reaction temperature. Moreover, they showed moderate catalytic activity in other annulations of alkynes with aromatic compounds (such as benzamide, acetanilide, etc.) which proceed through CH activation. Compound 2 b also effectively catalyzes the reductive amination of aldehydes and ketones in the presence of carbon monoxide and water via water-gas shift reaction, giving amines in high yields (67–99 %).     

Synthesis and Characterization of Aryl Acylguanidines and Their Copper(Ⅱ) Complexes

A series of eight N-mono-substituted aryl acylguanidines L~(1～8) were synthesized from the reactions of their parent acylthioureas and respective primary amines, including five R~1C(O)N=C(NHR~2)_2 with balanced arms(denoted as R~1–R~2–R~2: Ph–Ar'–Ar', L~1(1); Ph–Ar'–Ar', L~2(2); 1-Naph–Ar'–Ar', L~3(3); 1-Naph–Ar'–Ar', L~4(4); 2-Naph–Ar'–Ar', L`5(5); Ar' = 2,6-Me_2C_6H_3, Ar' = 2,6-iPr_2C_6H_3) and three R~1C(O)N=C(NHR~2)NHR~3 with unbalanced arms(denoted as R~1–R~2–R~3: Ph–Ar'–Ph, L~6(6); Ph–Ar' –Ph, L~7(7); Ph–Ar' –Ar', L~8(8)). Treatment of L~(1～5)(1～5) with copper acetate in a molar ratio of 2:1 in dichloromethane led to the formation of homoleptic Cu(Ⅱ) complexes trans-L_2~(n')Cu(9～13), in which the Cu(Ⅱ) center was stabilized by deprotonated ligands Ln'(n = 1～5) in the O,N-bidentate mode. When similar reactions of L~6(Ph–Ar'–Ph)(6) and L~7(Ph–Ar'–Ph)(7) that contain unbalanced arms were investigated, the Cu(Ⅱ) products trans-L_2~(6')Cu(14) and trans-L_2~(7')Cu(15) were formed by deprotonating the bulky amine groups in Ln(-NHAr' for L~6 and-NHAr' for L~7) rather than the-NHPh group. In sharp contrast, trans-L_2~(8')Cu(16) was obtained from two-arm unbalanced L~8(Ph–Ar'–Ar')(8) not by deprotonating the more bulky-NHAr' group but the relatively less bulky-NHAr' group. In a further exploration, the reaction of 1:1 mixed ligands Ln and Lm with copper acetate was found to give only homoleptic Cu(Ⅱ) complex L_2~(n')Cu instead of the heteroleptic one L~(n')CuL~(m'). The in vitro antibacterial activity of L~n was evaluated against S. aureus, E. coli and C. albicans by determining the minimum inhibitory concentrations(MICs) using Kirby-Bauer test.     

Selective Activation of Ar–Cl and Ar–C Bonds with Iron(II) Complexes

The electrophilic iron–carbene chelate complexes 1 and 2 react with alkoxides RO⁻ to give the neutral chelate complex 3 and the carbene complex 4 , respectively. Depending on the nature of the chelating ortho substituent, selective activation of the Ar–Cl or Ar–C bond occurs; these processes are promoted by the chelation.     

Rhodium Indenyl NHC and Fluorenyl-Tethered NHC Half-Sandwich Complexes: Synthesis,Structures and Applications in the Catalytic C−H Borylation of Arenes and Alkanes

Indenyl (Ind) rhodium N-heterocyclic carbene (NHC) complexes [Rh(η⁵-Ind)(NHC)(L)] were synthesised for 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) with L=C₂H₄ ( 1 ), CO ( 2 a ) and cyclooctene (COE; 3 ), for 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes) with L=CO ( 2 b ) and COE ( 4 ), and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) with L=CO ( 2 c ) and COE ( 5 ). Reaction of SIPr with [Rh(Cp*)(C₂H₄)₂] did not give the desired SIPr complex, thus demonstrating the “indenyl effect” in the synthesis of 1 . Oxidative addition of HSi(OEt)₃ to 3 proceeded under mild conditions to give the Rh silyl hydride complex [Rh(Ind){Si(OEt)₃}(H)(SIPr)] ( 6 ) with loss of COE. Tethered-fluorenyl NHC rhodium complexes [Rh{(η⁵-C₁₃H₈)C₂H₄N(C)C₂H_xNR}(L)] (x=4, R=Dipp, L=C₂H₄: 11 ; L=COE: 12 ; L=CO: 13 ; R=Mes, L=COE: 14 ; L=CO: 15 ; x=2, R=Me, L=COE: 16 ; L=CO: 17 ) were synthesised in low yields (5–31 %) in comparison to good yields for the monodentate complexes (49–79 %). Compounds 3 and 1 , which contain labile alkene ligands, were successful catalysts for the catalytic borylation of benzene with B₂pin₂ (Bpin=pinacolboronate, 97 and 93 % PhBpin respectively with 5 mol % catalyst, 24 h, 80 °C), with SIPr giving a more active catalyst than SIMes or IMes. Fluorenyl-tethered NHC complexes were much less active as borylation catalysts, and the carbonyl complexes were inactive. The borylation of toluene, biphenyl, anisole and diphenyl ether proceeded to give meta substitutions as the major product, with smaller amounts of para substitution and almost no ortho product. The borylation of octane and decane with B₂pin₂ at 120 and 140 °C, respectively, was monitored by ¹¹B NMR spectroscopy, which showed high conversions into octyl and decylBpin over 4–7 days, thus demonstrating catalysed sp³ C−H borylation with new piano stool rhodium indenyl complexes. Irradiation of the monodentate complexes with 400 or 420 nm light confirmed the ready dissociation of C₂H₄ and COE ligands, whereas CO complexes were inert. Evidence for C−H bond activation in the alkyl groups of the NHC ligands was obtained.     

Influence of the Flexibility of Nickel PCP-Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium C_sp2−H bond with [Ni(cod)₂] affording a carbanionic ligand in [NiCl(PC_sp3^HP)] ( 8 ) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PC^NHCP)]PF₆ ( 9 ) upon halide abstraction; 3) ethylene insertion into the Ni−H bond of the latter and ethyl migration to the N−C−N carbon atom of the heterocycle in [Ni(PC^EtP)]PF₆ ( 10 ); and 4) an unprecedented C−P bond activation transforming the P−C^NHC−P pincer ligand of 8 in a C−C^NHC−P pincer and a terminal phosphanido ligand in [Ni(PPh₂)(CC^NHCP)] ( 15 ). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.     

Preparation of Copolymer of Salen-crown Ether Complexes and its Catalytic Activation for Molecular Oxygen

In order to mimic the function of cytochrome P-450, synthetic porphyrin and quasi-porphyrin metal complexes have been employed1. This kind of metal complexesshowed high activity and stability in catalytic oxidation of hydrocarbon compound withmolecular ox…     

Triangle Cl−Ag1−Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO₂ emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl−Ag₁−Cl sites on a Cl-terminated, (001) facet-exposed BiOCl can selectively promote one-electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O₂⁻), and also shift the adsorption configuration of product NO₃⁻ from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl−Ag₁−Cl-landen BiOCl achieved >90 % NO conversion to favorable NO₃⁻ of high selectivity (>97 %) in 10 min under visible light, with the undesired NO₂ concentration below 20 ppb. Both the activity and the selectivity of Cl−Ag₁−Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO₃⁻ selectivity) or control O−Ag₁−O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO₃⁻ selectivity). This study develops new single-atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.     

Nickel Complexes of a Pincer Amidobis(amine) Ligand: Synthesis,Structure, and Activity in Stoichiometric and Catalytic C?C Bond‐Forming Reactions of Alkyl Halides

Get a grip! Ni^II complexes of the new pincer amidobis(amine) ligand are described. The Ni chloride complex catalyzes Kumada–Corriu–Tamao coupling of unactivated alkyl halides with alkyl Grignard reagents, as well as double C–C coupling of CH₂Cl₂ with alkyl Grignard reagents (see schemes).

     

C−H Activation and Olefin Insertion in d8 and d0 Complexes: Same Elementary Steps,Different Electronics

Metallocene alkyl complexes with d⁰ electron configuration and d⁸-configured square planar α-diimine late transition metal alkyl complexes show activity in both C−H activation through σ-bond metathesis and olefin insertion. Herein, we show by analysis of their M−CH₃ ¹³C chemical shift tensors that these reactions involve a π(M−C) interaction in the horizontal plane of the complex for both d⁰ and d⁸ systems. While in the case of d⁰ systems the interaction of an empty metal d-orbital and a filled carbon p-orbital causes partial alkylidene character of the M−C bond, the corresponding metal d-orbital is filled in d⁸ systems, thus generating a filled π*(M−C) orbital that increases the anionic character of the methyl group. This entails fundamentally different reaction mechanisms for d⁰ and d⁸ systems, which are reflected in the structures of the transition states: While d⁰ olefin insertion can be viewed as a [2+2] cycloaddition reaction, d⁸ olefin insertion rather resembles methyl group migration onto a positively polarized olefin, thus explaining the observed differences in regioselectivity. These findings are translated to σ-bond metathesis, a reaction which is isolobal to olefin insertion for both early and late transition metals.     

Syntheses and Crystal Structures of Zinc(II) and Nickel(II) Complexes Involving Reduced Nitroxide Radicals

1 INTRODUCTION The synthesis of new molecular magnetic mate- rials that combine transition metal ions and pure organic radicals as ligating sites has attracted much more attention in the last few years[1~4]. Nitronyl ni- troxide radicals, independently or in combination with metal ions, have been one of the most studied systems in molecular magnetism for understanding the radical-radical or metal-radical interactions as well as for synthesizing organic ferromagnets and metal-radical magne…     

Ethylene Oligomerization Catalyzed by Nickel(II) Diimine Complexes

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Synthesis of Dinuclear Mo−Fe Hydride Complexes and Catalytic Silylation of N2

Two transition-metal atoms bridged by hydrides may represent a useful structural motif for N₂ activation by molecular complexes and the enzyme active site. In this study, dinuclear Mo^IV-Fe^II complexes with bridging hydrides, Cp^RMo(PMe₃)(H)(μ-H)₃FeCp* ( 2 a ; Cp^R=Cp*=C₅Me₅, 2 b ; Cp^R=C₅Me₄H), were synthesized via deprotonation of Cp^RMo(PMe₃)H₅ ( 1 a ; Cp^R=Cp*, 1 b ; Cp^R=C₅Me₄H) by Cp*FeN(SiMe₃)₂, and they were characterized by spectroscopy and crystallography. These Mo−Fe complexes reveal the shortest Mo−Fe distances ever reported (2.4005(3) Å for 2 a and 2.3952(3) Å for 2 b ), and the Mo−Fe interactions were analyzed by computational studies. Removal of the terminal Mo−H hydride in 2 a – 2 b by [Ph₃C]⁺ in THF led to the formation of cationic THF adducts [Cp^RMo(PMe₃)(THF)(μ-H)₃FeCp*]⁺ ( 3 a ; Cp^R=Cp*, 3 b ; Cp^R=C₅Me₄H). Further reaction of 3 a with LiPPh₂ gave rise to a phosphido-bridged complex Cp*Mo(PMe₃)(μ-H)(μ-PPh₂)FeCp* ( 4 ). A series of Mo−Fe complexes were subjected to catalytic silylation of N₂ in the presence of Na and Me₃SiCl, furnishing up to 129±20 equiv of N(SiMe₃)₃ per molecule of 2 b . Mechanism of the catalytic cycle was analyzed by DFT calculations.     

Catalytic Behavior of Mono-N-Protected Amino-Acid Ligands in Ligand-Accelerated C−H Activation by Palladium(II)

Mono-N-protected amino acids (MPAAs) are increasingly common ligands in Pd-catalyzed C−H functionalization reactions. Previous studies have shown how these ligands accelerate catalytic turnover by facilitating the C−H activation step. Here, it is shown that MPAA ligands exhibit a second property commonly associated with ligand-accelerated catalysis: the ability to support catalytic turnover at substoichiometric ligand-to-metal ratios. This catalytic role of the MPAA ligand is characterized in stoichiometric C−H activation and catalytic C−H functionalization reactions. Palladacycle formation with substrates bearing carboxylate and pyridine directing groups exhibit a 50–100-fold increase in rate when only 0.05 equivalents of MPAA are present relative to Pd^II. These and other mechanistic data indicate that facile exchange between MPAAs and anionic ligands coordinated to Pd^II enables a single MPAA to support C−H activation at multiple Pd^II centers.     

Preparation and Characterization of Uranium–Iron Triple-Bonded UFe(CO)3− and OUFe(CO)3− Complexes

We report the preparation of UFe(CO)₃⁻ and OUFe(CO)₃⁻ complexes using a laser-vaporization supersonic ion source in the gas phase. These compounds were mass-selected and characterized by infrared photodissociation spectroscopy and state-of-the-art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe-to-U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(−II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df–d multiple-bonded f-element-transition-metal compounds that have not been fully recognized to date.     

Dioxygen Affinities and Catalytic Oxidation Performance of Cobalt （Ⅱ）Complexes with N—Aryl Hydroxamic Acid

The oxygenation of cobalt(Ⅱ) hydroxamates(CoL2) and its catalytic performance in oxidation of p-xylene to p-toluic acid (PTA) were examined.The effects of X and Y bonded to hydroxamate group on dioxygen affinities and catalytic oxidation performance were also investigated.