Mechanistic snapshots of rhodium-catalyzed acylnitrene transfer reactions

Science, Год журнала: 2023, Номер 381(6657), С. 525 - 532

Опубликована: Июль 20, 2023

Rhodium (Rh) acylnitrene complexes are widely implicated in catalytic C-H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral Rh complex with bidentate dioxazolone ligand, which photoinduced metal-to-ligand charge transfer initiates amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone allowed elucidation targeted Rh-acylnitrenoid provided firm evidence that singlet nitrenoid species is primarily responsible for acylamino reactions. We also monitored crystallo reaction nucleophile situ-generated Rh-acylnitrenoid, crystallographically traceable system to capture mechanistic snapshots transfer.

Язык: Английский

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Nitrogen Atom Transfer Catalysis by Metallonitrene C−H Insertion: Photocatalytic Amidation of Aldehydes

Angewandte Chemie International Edition, Год журнала: 2021, Номер 61(9)

Опубликована: Дек. 14, 2021

C-H amination and amidation by catalytic nitrene transfer are well-established typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion (formal) terminal nitride ligands into bonds is much less developed nitrogen atom remains unknown. We here report synthesis a formal complex palladium. Photocrystallographic, magnetic, computational characterization support assignment as an authentic metallonitrene (Pd-N) with diradical ligand that singly bonded to Pd

Язык: Английский

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A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(6), С. 2637 - 2656

Опубликована: Фев. 4, 2022

Herein, we study the mechanism of iron-catalyzed direct synthesis unprotected aminoethers from olefins by a hydroxyl amine derived reagent using wide range analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational resonance Raman) along with high-level quantum chemical calculations. The triflic acid salt acts as "oxidant" well "amino" group donor. It activates high-spin Fe(II) (St = 2) catalyst [Fe(acac)2(H2O)2] (1) to generate 5/2) intermediate (Int I), which decays second II) St 2. analysis computational data leads formulation Int I [Fe(III)(acac)2-N-acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, II is formed N–O bond homolysis. However, it does not high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead Fe(III) center strongly antiferromagnetically coupled (J −524 cm–1) an iminyl radical, [Fe(III)(acac)2-NH·], giving Though Fe(NH) complexes isoelectronic surrogates Fe(O) functionalities are known, detection Fe(III)-N-acyloxy undergoes cleavage active iron–nitrogen II), unprecedented. Relative centers, features weak elongated Fe–N which, together unpaired electron density vector, helps rationalize its propensity for N-transfer reactions onto styrenyl olefins, resulting in overall formation aminoethers. This thus demonstrates potential utilizing iron-coordinated nitrogen-centered radicals powerful reactive intermediates catalysis.

Язык: Английский

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Synthesis and Reactivity of a Cobalt-Supported Singlet Nitrene

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(25), С. 13650 - 13662

Опубликована: Июнь 13, 2023

The synthesis, characterization, and reactivity of a series cobalt terminal imido complexes supported by an N-anchored tripodal tris(carbene) chelate is described, including Co-supported singlet nitrene. Reaction the CoI precursor [(TIMMNmes)CoI](PF6) (TIMMNmes = tris-[2-(3-mesityl-imidazolin-2-ylidene)-methyl]amine) with p-methoxyphenyl azide yields CoIII imide [(TIMMNmes)CoIII(NAnisole)](PF6) (1). Treatment 1 equiv [FeCp2](PF6) at -35 °C affords formal CoIV complex [(TIMMNmes)Co(NAnisole)](PF6)2 (2), which features bent Co-N(imido)-C(Anisole) linkage. Subsequent one-electron oxidation 2 AgPF6 provides access to tricationic [(TIMMNmes)Co(NAnisole)](PF6)3 (3). All were fully characterized, single-crystal X-ray diffraction (SC-XRD) analyses, infrared (IR) vibrational, ultraviolet/visible (UV/vis) electronic absorption, multinuclear NMR, X-band electron paramagnetic resonance (EPR), nuclear double (ENDOR), high-energy-resolution fluorescence-detected absorption spectroscopy (HERFD XAS). Quantum chemical calculations provide additional insight into structures all compounds. dicationic exhibits doublet ground state considerable imidyl character as result covalent Co-NAnisole bonding. At room temperature, readily converts CoII amine involving intramolecular C-H bond amination. Electronically, 3 can be understood nitrene bound significant radical character. Verifying pronounced electrophilicity, nucleophiles such H2O tBuNH2 add 3─analogous parent free nitrene─in para position aromatic substituent, thus, clearly corroborating nitrene-type reactivity.

Язык: Английский

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Palladium Terminal Imido Complexes with Nitrene Character

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(20), С. 8897 - 8901

Опубликована: Май 16, 2022

Whereas triplet-nitrene complexes of the late transition metals are isolable and key intermediates in catalysis, singlet-nitrene ligands remain elusive. Herein we communicate three such palladium terminal imido with singlet ground states. UV–vis–NIR electronic spectroscopy broad bands up to 1400 nm as well high-level computations (DFT, STEOM-CCSD, CASSCF/NEVPT2, EOS analysis) reactivity studies suggest significant palladium(0) character. Although aliphatic nitrene proved be too reactive for isolation analytically pure form a result elimination isobutylene, aryl congener could characterized by SC-XRD, elemental analysis, IR-, NMR spectroscopy, HRMS. The complexes' distinguished ambiphilicity allows them activate hexafluorobenzene, triphenylphosphine, pinacol borane, catalytically dehydrogenate cyclohexene, aminate ethylene via transfer at or below room temperature.

Язык: Английский

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Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Chemical Science, Год журнала: 2022, Номер 13(26), С. 7907 - 7913

Опубликована: Янв. 1, 2022

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C-H bonds as well aziridination olefines. We report on synthesis trigonal imido iron complexes [Fe(NMes)L2]0,- (L = -N{Dipp}SiMe3); Dipp 2,6-diisopropyl-phenyl; Mes (2,4,6-trimethylphenyl) via reaction mesityl azide (MesN3) with linear precursors [FeL2]0,-. UV-vis-, EPR-, 57Fe Mössbauer spectroscopy, magnetometry, computational methods suggest for reduced form electronic structure a ferromagnetically coupled iron(ii) imidyl radical, whereas oxidation leads to mixed iron(iii) electrophilic character. Reactivity studies show that both are capable H atom abstraction from bonds. Further, [Fe(NMes)L2]- reacts nucleophilically CS2 by inserting into bond, electrophilically CO under transfer. The neutral [Fe(NMes)L2] complex shows enhanced behavior evidenced transfer phosphine, yet combination overall reactivity.

Язык: Английский

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A Borane Lewis Acid in the Secondary Coordination Sphere of a Ni(II) Imido Imparts Distinct C–H Activation Selectivity

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(34), С. 15793 - 15802

Опубликована: Авг. 16, 2022

Two borane-functionalized bidentate phosphine ligands that vary in tether length have been prepared to examine cooperative metal-substrate interactions. Ni(0) complexes react with aryl azides at low temperatures form structurally unusual κ2-(N,N)-N3Ar adducts. Warming these adducts affords products of N2 extrusion and one case, a Ni-imido compound is capped by the appended borane. Reactions 1-azidoadamantane (AdN3) provide distinct outcome, where proposed nickel imido intermediate activates sp2 C-H bonds arenes, even presence benzylic sites. Combined experimental computational mechanistic studies demonstrate unique reactivity consequence Lewis-acid-induced polarization Ni-NR bond, potentially providing synthetic strategy for chemoselective reaction engineering.

Язык: Английский

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From Divalent to Pentavalent Iron Imido Complexes and an Fe(V) Nitride via N–C Bond Cleavage

Journal of the American Chemical Society, Год журнала: 2022, Номер 145(2), С. 873 - 887

Опубликована: Дек. 30, 2022

As key intermediates in metal-catalyzed nitrogen-transfer chemistry, terminal imido complexes of iron have attracted significant attention for a long time. In search versatile model compounds, the recently developed second-generation N-anchored tris-NHC chelating ligand tris-[2-(3-mesityl-imidazole-2-ylidene)-methyl]amine (TIMMNMes) was utilized to synthesize and compare two series mid- high-valent alkyl complexes, including reactive Fe(V) adamantyl intermediate en route an isolable nitrido complex. The chemistry toward imides achieved by reacting Fe(I) precursor [(TIMMNMes)FeI(N2)]+ (1) with 1-adamantyl azide yield corresponding trivalent imide. Stepwise chemical reduction oxidation lead isostructural low-spin [(TIMMNMes)Fe(NAd)]0,1+,2+,3+ (2Ad–5Ad) states II V. imide [(TIMMNMes)Fe(NAd)]3+ (5Ad) is unstable under ambient conditions converts air-stable nitride [(TIMMNMes)FeV(N)]2+ (6) via N–C bond cleavage. stability pentavalent can be increased derivatizing [(TIMMNMes)FeIV(N)]+ (7) ethyl group using triethyloxonium salt Et3OPF6. This gives access analogous [(TIMMNMes)Fe(NEt)]0,1+,2+,3+ (2Et–5Et), stable Iron exist manifold different electronic structures, ultimately controlling their diverse reactivities. Accordingly, these were characterized single-crystal X-ray diffraction analyses, SQUID magnetization, electrochemical methods, as well 57Fe Mössbauer, IR vibrational, UV/vis absorption, multinuclear NMR, X-band EPR, absorption spectroscopy. Our studies are complemented quantum calculations, thus providing further insight into structures all complexes.

Язык: Английский

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Open-Shell Early Lanthanide Terminal Imides

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(9), С. 4102 - 4113

Опубликована: Фев. 25, 2022

Group 3- and 4f-element organometallic chemistry reactivity are decisively driven by the rare-earth-metal/lanthanide (Ln) ion size associated electronegativity/ionicity/Lewis acidity criteria. For these reasons, synthesis of terminal "unsupported" imides [Ln═NR] smaller, closed-shell Sc(III), Lu(III), Y(III), increasingly covalent Ce(IV) has involved distinct reaction protocols while derivatives "early" large Ln(III) have remained elusive. Herein, we report such open-shell lanthanide cations Ce(III), Nd(III), Sm(III) according to a new protocol. Lewis-acid-stabilized methylidene complexes [TptBu,MeLn(μ3-CH2){(μ2-Me)MMe2}2] (Ln = Ce, Nd, Sm; M Al, Ga) react with 2,6-diisopropylaniline (H2NAriPr) via methane elimination. The formation arylimide is governed size, Lewis group 13 metal alkyl, steric factors, presence donor solvent, sterics (pKa) aromatic amine. Crucially, arylimides [TptBu,MeLn(═NAriPr)(THF)2] Sm) formed only for Ga, [TptBu,MeLn(NAriPr)(AlMe3)] persistent. In stark contrast, [GaMe3]-stabilized imide [TptBu,MeLn(NAriPr)(GaMe3)] reversibly in noncoordinating solvents.

Язык: Английский

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Photoinduced Metallonitrene Formation by N₂ Elimination from Azide Diradical Ligands

Angewandte Chemie International Edition, Год журнала: 2023, Номер 62(42)

Опубликована: Авг. 7, 2023

Transition-metal nitrides/nitrenes are highly promising reagents for catalytic nitrogen-atom-transfer reactivity. They typically prepared in situ upon optically induced N2 elimination from azido precursors. A full exploitation of their potential, however, requires in-depth knowledge the primary photo-induced processes and structural/electronic factors mediating loss with birth terminal metal-nitrogen core. Using femtosecond infrared spectroscopy, we elucidate here molecular-level mechanisms responsible formation a unique platinum(II) nitrene triplet ground state closed-shell azide precursor. The spectroscopic data combination quantum-chemical calculations provide compelling evidence that product initial occupation singlet excited an anionic diradical ligand is bound to low-spin d8 -configured PtII ion. Subsequent intersystem crossing generates Pt-bound diradical, which smoothly evolves into via near barrierless adiabatic dissociation. Our highlight importance productive, -releasing possessing ππ* character as design principle accessing efficient N-atom-transfer catalysts.

Язык: Английский

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