Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex Induced by Intramolecular Metal-to-Ligand Alkyl Migration: Models for Hydrodenitrogenation Catalysis

Gray, Steven D.; Weller, Keith J.; Bruck, Michael A.; Briggs, Paula M.; Wigley, David E.

doi:10.1021/ja00148a010

Cited by 120 publications

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“…The aromatic heterocycles were distilled or recrystallized before use; all other materials were used as received. 1 H NMR spectra were recorded on Bruker300 or Bruker500 spectrometers (supported by the NSF grant CHE-9974928) at room temperature in C 6 D 6 unless otherwise specified. Chemical shifts are reported with respect to solvent residual peak, 7.16 ppm (C 6 D 6 ).…”

Section: Methodsmentioning

confidence: 99%

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Ring opening of aromatic heterocycles by uranium complexes

Duhović

Monreal

Diaconescu

2010

Journal of Organometallic Chemistry

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Section: Methodsmentioning

confidence: 99%

“…The brown-yellow oil was redissolved in fresh hexanes, passed through Celite, and stored at À35 C as a highly concentrated solution. Brown, block crystals suitable for X-ray structure analysis formed after 3 d. 1 …”

Section: Synthesis Of 7 Mbi -Qn(ch 2 Ph)mentioning

confidence: 99%

Ring opening of aromatic heterocycles by uranium complexes

Duhović

Monreal

Diaconescu

2010

Journal of Organometallic Chemistry

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“…32 The seminal works by Wigley 24, 33,34,37 and Wolczanski 35,36,38 provide the only examples of well-defined homogeneous HDN models capable of promoting the C-N bond cleavage of pyridine. 28 Common to both systems is the formation of an η 2 (N,C)-bound pyridine complex with a highly reducing group 5 metal center, while the C-N bond cleavage step entails divergent pathways such as alkyl migration 33,34 and reduction 35,36 in the Wigley and Wolczanski Scheme 1. Preparation of the η 2 (N,C)-Pyridine Complex b through a [2 þ 2 þ 2] Cyclotrimerization, while Salt Metathesis and Alkyl Migration to the R-C systems, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Wigley's C-N bond cleavage is not the result of the activation of free pyridine from a, but rather the result of a preassembled η 2 (N,C)-pyridine moiety via a set of stepwise reactions (Scheme 1): cycloaddition of two terminal alkynes, followed by isomerization and insertion of a nitrile, to give the pyridine moiety. 39 Once the η 2 (N,C) motif was assembled onto the tantalum metal center to form the "activated" η 2 -pyridine complex b, transmetallation of one chloride with either a hydride or alkyl nucleophile, followed by migration of the latter, resulted in the formal cleavage of the C-N bond to afford the ring-opened product c. 34 A series of elegant and systematic studies revealed that c further undergoes several interesting transformations such as β-hydride elimination, reinsertion of the pendant olefin group, an electrocyclic rearrangement, [2 þ 2] retrocycloaddition, and finally dimerization to afford the dinuclear metallapyridine species g. 34 We discuss the work of Wigley, since their work shares transformations similar to those in the work presented herein.…”

Section: Introductionmentioning

confidence: 99%

Synthetic and Mechanistic Studies of the Ring Opening and Denitrogenation of Pyridine and Picolines by Ti−C Multiple Bonds

et al. 2010

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The neopentylidene-neopentyl complex (PNP)TidCH t Bu(CH 2 t Bu) (1; PNP -= N[2-P(CHMe 2 ) 2 -4-methylphenyl] 2 ) extrudes neopentane in neat pyridine or picoline (3-or 4-picoline) under mild conditions (25°C), to generate the transient titanium alkylidyne intermediate (PNP)TitC t Bu (A), which subsequently ring-opens the pyridine by ring-opening metathesis of the aromatic NdC bond across the TitC linkage, generating the metallaazabicycles (PNP)Ti(C( t Bu)C 5 H 3 RNH) (R = H (2), 3-Me (3), 4-Me (4)). Kinetic studies suggest that the C-N activation process obeys a pseudo-first-order process in titanium, with R-hydrogen abstraction being the rate-determining step (the KIE for 1/1-d 3 conversion to 2 was 3.8(3) at 25°C). The activation parameters are ΔH q = 23(3) kcal/mol and ΔS q = -4(3) cal/(mol K). The intermolecular k H /k D ratio is close to unity, 1.07(3) at 25°C, for the conversion of 1 to 2 in pyridine versus pyridine-d 5 . Detailed theoretical studies suggest the 1 f 2 transformation proceeds in the following order: (i) formation of A in an overall endergonic step by R-hydrogen abstraction, (ii) an exergonic binding of pyridine, and (iii) concerted, exergonic [2 þ 2] cycloaddition followed by (iv) exergonic ring-opening metathesis and finally (v) a concerted hydrogen atom migration. Complexes 2-4 can denitrogenate, that is, completely remove N of the heterocycle at 65°C over 72 h, when treated with silyl chlorides such as ClSiR 3 (R = Me, i Pr, Ph) to cleanly afford the titanium silylimides (PNP)TidNSiR 3 (Cl) (R = Me (8), i Pr (9), Ph (10)) and the corresponding t Bu-arene organic byproduct. [Et 3 Si][B(C 6 F 5 ) 4 ] also promotes denitrogenation of 2 to yield t Bu-benzene, but the metal complex could not be characterized from such a reaction. The conversion 2 f 8 was found to have activation parameters ΔH q = 30(6) kcal/mol and ΔS q = 10(2) cal/(mol K), therefore yielding ΔG q ≈ 27 kcal/mol at 298.15 K. A KIE of 1.6(2) at 85°C was observed when 2/2-d 5 were denitrogenated to 8 in the presence of ClSiMe 3 , with the rate of the reaction being insensitive to both the steric nature and concentration of the trialkylsilyl chloride. Denitrogenation leading to 8-10 is proposed to occur via a series of steps including a 1,3-hydrogen migration, an electrocyclic rearrangement, a retrocycloaddition, and a Si-Cl addition. The transformations 1 f 2/3/4 and 2/3/4 f 8 can be made cyclic by a series of steps such as deimination of the imide moiety in 8 with 2 equiv of MoCl 5 , followed by reduction and transmetalation with LiCH 2 t Bu and then oxidatively induced R-hydrogen abstraction. The reactivity of 1 with other heterocycles such as THF, thiophene, and piperidine is also discussed.

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“…The ring opening of aromatic N heterocycles has been restricted to a few examples involving transition metals, such as niobium, tantalum, titanium, scandium, yttrium, and rhenium; [1][2][3][4][5][6][7][8][9] strong actinide-oxygen bonds could also drive the ring opening of pyridine N-oxides. [10] Our interest in the reactions of electrophilic alkyl complexes [11,12] supported by a ferrocene (fc) diamide ligand with aromatic N heterocycles [13][14][15] prompted us to investigate the reactivity of the uranium dibenzyl complex 1-(CH 2 Ph) 2 ((NN fc )U(CH 2 Ph) 2 ; NN fc = 1,1'-fc(NSitBuMe 2 ) 2 ) [11,16] with imidazoles.…”

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confidence: 99%

Beyond CH Activation with Uranium: A Cascade of Reactions Mediated by a Uranium Dialkyl Complex

2009

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A neutral uranium dibenzyl complex mediated the CH activation of two aromatic N heterocycles, followed by a cascade of reactions which led to the opening and functionalization of imidazole rings (see scheme). This double CH activation and the sequence of transformations succeeding it are unique to uranium and point to the use of this element for the cleavage of other strong carbon–heteroatom bonds.

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Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex Induced by Intramolecular Metal-to-Ligand Alkyl Migration: Models for Hydrodenitrogenation Catalysis

Cited by 120 publications

References 0 publications

Ring opening of aromatic heterocycles by uranium complexes

Ring opening of aromatic heterocycles by uranium complexes

Synthetic and Mechanistic Studies of the Ring Opening and Denitrogenation of Pyridine and Picolines by Ti−C Multiple Bonds

Beyond CH Activation with Uranium: A Cascade of Reactions Mediated by a Uranium Dialkyl Complex

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