Structure and reactivity in highly halogenated ketazines

Lai, E. C. K.; Mackay, Donald; Taylor, Nicholas J.; Watson, Kenneth

doi:10.1139/v88-440

Cited by 10 publications

(4 citation statements)

References 21 publications

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“…In addition, at high concentrations of 1 (>5 mM) a new stable IR band appears at 1746 cm -1 . This signal, which grows at the same rate as carbene IR bands decay, is assigned to azine 4 on the basis of these kinetics and comparison with the reported IR spectrum of its phenyl analogue …”

Section: Resultsmentioning

confidence: 71%

Time-Resolved IR Studies of 2-Naphthyl(carbomethoxy)carbene: Reactivity and Direct Experimental Estimate of the Singlet/Triplet Energy Gap

et al. 1999

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To clarify the role of diazocarbonyl excited states in Wolff rearrangement chemistry, time-resolved infrared (TRIR) spectroscopy has been used to study methyl 2-diazo-(2-naphthyl) acetate (1) and the subsequently produced 2-naphthyl(carbomethoxy)carbene (2). TRIR analysis of the growth rate of the ketene rearrangement product following laser excitation of diazoester 1 demonstrates that in this case ketene is formed almost exclusively from the carbene. The absence of reaction from the diazoester excited state is likely due to the highly preferred anti relationship between the diazo and carbonyl groups in 1. In addition, the detection of IR bands from both the singlet and triplet states of spin-equilibrated carbene 2 has allowed a direct experimental estimate of the singlet/triplet energy gap in solution at ambient temperature. This work represents the first TRIR detection and study of a carbene intermediate and demonstrates the potential value of TRIR spectroscopy in structural and mechanistic aspects of carbene chemistry.

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Section: Resultsmentioning

confidence: 71%

Time-Resolved IR Studies of 2-Naphthyl(carbomethoxy)carbene: Reactivity and Direct Experimental Estimate of the Singlet/Triplet Energy Gap

et al. 1999

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“…The structure of the Z,Zisomer of 3 was verified by an analysis of single-crystal X-ray diffraction data with metrical parameters that matched published molecular structures. 7,8 High yields of 1 were achieved using elevated temperatures and dropwise addition of MPDA. Increasing the catalyst loading to 5.0 mol % also significantly increased the yield of product 1, but such a high catalyst loading is not practical given the cost of Ir(TTP)CH 3 .…”

Section: ■ Results and Discussionmentioning

confidence: 99%

C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate

et al. 2012

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C-H insertion reactions between different substrates and diazo reagents were catalyzed by tetratolylporphyrinato methyliridium (Ir(TTP)CH 3). The highest yields were achieved for reactions between the bulky diazo reagent methyl 2-phenyldiazoacetate (MPDA) and substrates containing electron-rich C-H bonds. An intermediate metalloporphyrin complex was identified as a metal-carbene complex, Ir(TTP)(═C[Ph]CO 2 CH 3)(CH 3) (4), using 1 H NMR and UV/vis absorption spectroscopy. The presence of 4 was further supported by computationally modeling the absorption spectra with time-dependent DFT (6-31G(d,p)/SBKJC basis set, PBE0 functional). Kinetic studies for C-H insertion reactions using different substrates showed substantial differences in the rate of MPDA consumption, suggesting that carbene transfer is rate-limiting. Furthermore, primary kinetic isotope effects of 3.7 ± 0.3 and 2.7 ± 0.4 were measured using toluene and cyclohexane, respectively. These data are consistent with a mechanism that involves direct C-H insertion rather than a radical rebound pathway. Disciplines

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“…Upon addition of N 2 CPh 2 to this molecule, the end-on η 1 -N 2 CPh 2 uranium compound, [{( Ad ArO) 3 tacn}U(η 1 -NNCPh 2 )], is isolated. [40,41] Analogous reactivity with benzophenone has been observed for the uranium(IV) imido species CpЈ 2 U{N(p-tolyl)} [CpЈ = η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] [24] to form CpЈ 2 U(O) and the corresponding imine product Ph 2 C[N(p-tolyl)]. [8] Reactivity studies with aldehydes and ketones also provide insight into the various isomeric forms of 2.…”

Section: Resultsmentioning

confidence: 99%

Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

2012

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The reactivity of the uranium(III) alkyl Tp*2UCH2Ph (1) toward diazoalkanes is reported. Addition of 1 equiv. N2CPh2 produces 0.5 equiv. bibenzyl, along with Tp*2U(N2CPh2) (2). This species is dynamic in solution at room temperature and rapidly interconverts between the η1‐ and η2 isomers as determined by variable‐temperature 1H NMR spectroscopy. X‐ray crystallographic analysis at low temperature shows exclusively the η2 isomer, which features a short U–N multiple bond analogous to an imido species. The η1 isomer reacts quantitatively with aldehydes and ketones through multiple bond metathesis to produce Tp*2U(O) and the corresponding ketazine. Treatment of 1 with N2CHSiMe3 generates 0.5 equiv. bibenzyl and the η1 isomer Tp*2U(N2CHSiMe3) (3). This species is unstable over the course of hours, and there is no spectroscopic evidence for the η2 isomer. Tp*2U(η1‐N2CHSiMe3) can be trapped by addition of phenylacetylene by a [2+2] cycloaddition to afford the uranium(IV) metallacycle Tp*2U[(N‐N = CHSiMe3)CHCPh] (4). Crystallographic data for 4 are presented.

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Structure and reactivity in highly halogenated ketazines

Cited by 10 publications

References 21 publications

Time-Resolved IR Studies of 2-Naphthyl(carbomethoxy)carbene: Reactivity and Direct Experimental Estimate of the Singlet/Triplet Energy Gap

Time-Resolved IR Studies of 2-Naphthyl(carbomethoxy)carbene: Reactivity and Direct Experimental Estimate of the Singlet/Triplet Energy Gap

C–H Insertion Catalyzed by Tetratolylporphyrinato Methyliridium via a Metal–Carbene Intermediate

Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

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