Imidate

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Ian J S Fairlamb - One of the best experts on this subject based on the ideXlab platform.

  • mechanistic examination of auiii mediated 1 5 enyne cycloisomerization by aubr2 n Imidate nhc agx precatalysts is the active catalyst auiii or aui
    Catalysis Science & Technology, 2014
    Co-Authors: Jonathan P. Reeds, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-Imidate)(NHC) catalysts {where N-Imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-Imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

  • Mechanistic examination of AuIII-mediated 1,5-enyne cycloisomerization by AuBr2(N-Imidate)(NHC)/AgX precatalysts – is the active catalyst AuIII or AuI?
    Catal. Sci. Technol., 2014
    Co-Authors: Jonathan P. Reeds, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-Imidate)(NHC) catalysts {where N-Imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-Imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

  • Synthesis and Reactivity of N-Heterocyclic Carbene Gold(I) and Gold(III) Imidate Complexes and Their Catalytic Activity in 1,5-Enyne Cycloisomerization
    Organometallics, 2013
    Co-Authors: Jonathan P. Reeds, Adrian C. Whitwood, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    The effects of substituting (pseudo)halide for anionic Imidate ligands in Au(I) and Au(III) (i.e. [AuBr(NHC)] and [AuBr3(NHC)]) complexes have been investigated. [Au(N-Imidate)(NHC)] and [AuBr2(N-Imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-Imidate)(NHC)] complexes, in combination with Ag salts, were tested for catalytic activity in the cycloisomerization of 1,5-enynes and found to be more effective than the tribromide analogues (e.g. [AuBr3(NHC)]). Subtle changes to the anionic Imidate ligand structure had a pronounced effect on the catalytic activity of the Au(III) complexes.

  • mono and binuclear cyclometallated palladium ii complexes containing bridging n o and terminal n Imidate ligands air stable thermally robust and recyclable catalysts for cross coupling processes
    Dalton Transactions, 2004
    Co-Authors: Ian J S Fairlamb, Anant R Kapdi, Adam F Lee, Gregorio Sanchez, Gregorio Lopez, Jose Luis Serrano, Luis F Garcia, Jose Perez, Eduardo Perez
    Abstract:

    Novel dinuclear cyclometallated palladium complexes [{Pd(µ-NCO)(C⁁N)}2], containing asymmetric imidato –NCO– bridging units have been synthesised [C⁁N = 7,8-benzoquinolyl; –NCO– = succinImidate (1c), phthalImidate (2c) or maleImidate (3c)]. The reaction of these complexes, and the previously reported analogous Imidate precursors containing a phenylazophenyl (1a–3a) or 2-pyridylphenyl (1b–3b) backbone, with tertiary phosphines provides novel mononuclear N-bonded Imidate derivatives of the general formula [Pd(C⁁N)(Imidate)(L)] [L = PPh3, P(4-F-C6H4)3 or P(4-MeO-C6H4)3]. The single crystal structures of [Pd(azb)(phthalImidate)(P(4-MeO-C6H4)3)] (9a) and [Pd(bzq)(phthalImidate)(PPh3)] (7c) have been established. Dinuclear complexes (1a–3a, 1b–3b, 1c–3c) demonstrate outstanding thermal stability in the solid-state, as shown by thermoanalytical techniques. A marked influence of bridging Imidate groups on the initial decomposition temperature is observed. The dinuclear and mononuclear derivatives are shown to be active catalysts/precatalysts for the Suzuki–Miyaura cross-coupling reactions of aryl bromides with aryl boronic acids, and the Sonogashira reactions of aryl halides with phenyl acetylene (in the presence and absence of Cu(I) salts). The conversions appear to be dependent, to some extent, on the type of Imidate ligand, suggesting a role for these pseudohalides in the catalytic cycle in both cross-coupling processes. Lower catalyst loadings in ‘copper-free’ Sonogashira cross-couplings favour higher turnover frequencies. We have further determined that these catalysts may be recycled using a poly(ethylene oxide) (PEO)/methanol solvent medium in Suzuki–Miyaura cross-coupling. Once the reaction is complete, product extraction into a hexane/diethyl ether mixture (1 ∶ 1, v/v) gives cross-coupled products in good yields (with purity > 95%). The polar phase can then be re-used several times without appreciable loss of catalytic activity.

Alexei V. Demchenko - One of the best experts on this subject based on the ideXlab platform.

  • S-Benzimidazolyl (SBiz) Imidates as a Platform for Oligosaccharide Synthesis via Active-Latent, Armed-Disarmed, Selective, and Orthogonal Activations.
    The Journal of organic chemistry, 2017
    Co-Authors: Scott J. Hasty, Mithila D. Bandara, Nigam P. Rath, Alexei V. Demchenko
    Abstract:

    This article describes the development of S-benzimidazolyl (SBiz) Imidates as versatile building blocks for oligosaccharide synthesis. The SBiz Imidates have been originally developed as a new platform for active-latent glycosylations. This article expands upon the utility of these compounds. The application to practically all common concepts for the expeditious oligosaccharide synthesis including selective, chemoselective, and orthogonal strategies is demonstrated. The strategy development was made possible thanks to our enhanced understanding of the reaction mechanism and the modes by which SBiz Imidates interact with various promoters of glycosylation.

  • OFox Imidates as versatile glycosyl donors for chemical glycosylation
    Organic & biomolecular chemistry, 2017
    Co-Authors: Swati S Nigudkar, Keith J. Stine, Tinghua Wang, Salvatore G. Pistorio, Jagodige P. Yasomanee, Alexei V. Demchenko
    Abstract:

    Previously we communicated 3,3-difluoroxindole (HOFox) – mediated glycosylations wherein 3,3-difluoro-3H-indol-2-yl (OFox) Imidates were found to be key intermediates. Both the in situ synthesis from the corresponding glycosyl bromides and activation of the OFox Imidates could be conducted in a regenerative fashion. Herein, we extend this study with the main focus on the synthesis of various OFox Imidates and their investigation as glycosyl donors for chemical 1,2-cis and 1,2-trans glycosylation.

  • regenerative glycosylation under nucleophilic catalysis
    Journal of the American Chemical Society, 2014
    Co-Authors: Swati S Nigudkar, Keith J. Stine, Alexei V. Demchenko
    Abstract:

    This article describes 3,3-difluoroxindole (HOFox)-mediated glycosylation. The uniqueness of this approach is that both the in situ synthesis of 3,3-difluoro-3H-indol-2-yl (OFox) glycosyl donors and activation thereof can be conducted in a regenerative fashion as is a typical reaction performed under nucleophilic catalysis. Only a catalytic amount of the OFox Imidate donor and a Lewis acid activator are present in the reaction medium. The OFox Imidate donor is constantly regenerated upon its consumption until glycosyl acceptor has reacted.

  • O-Benzoxazolyl Imidates as versatile glycosyl donors for chemical glycosylation
    Organic & biomolecular chemistry, 2013
    Co-Authors: Swati S Nigudkar, Keith J. Stine, Archana R. Parameswar, Papapida Pornsuriyasak, Alexei V. Demchenko
    Abstract:

    Herein, we report a new class of glycosyl donors, benzoxazolyl Imidates, for chemical glycosylation. The O-benzoxazolyl (OBox) leaving group was designed with an aim to compare the relative reactivity and stability of similarly structured S-benzoxazolyl (SBox) glycosides (thioImidates) developed in our lab and glycosyl trichloroacetImidates (TCAI, O-Imidates) developed by Schmidt. Novel OBox donors can be activated under catalytic conditions and provided excellent yields in glycosylation. The OBox Imidates were found to be more reactive than either SBox or TCAI donors. The high reactivity profile was confirmed in direct competitive experiments and was found beneficial for HPLC-assisted solid-phase synthesis.

Jonathan P. Reeds - One of the best experts on this subject based on the ideXlab platform.

  • mechanistic examination of auiii mediated 1 5 enyne cycloisomerization by aubr2 n Imidate nhc agx precatalysts is the active catalyst auiii or aui
    Catalysis Science & Technology, 2014
    Co-Authors: Jonathan P. Reeds, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-Imidate)(NHC) catalysts {where N-Imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-Imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

  • Mechanistic examination of AuIII-mediated 1,5-enyne cycloisomerization by AuBr2(N-Imidate)(NHC)/AgX precatalysts – is the active catalyst AuIII or AuI?
    Catal. Sci. Technol., 2014
    Co-Authors: Jonathan P. Reeds, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    Gold(III) catalysts mediate 1,5-enyne cycloisomerization or tandem nucleophilic substitution-1,5-enyne cycloisomerization processes in an efficient manner. This study examines the reaction kinetics of 1,5-enyne cycloisomerization, mediated by AuBr2(N-Imidate)(NHC) catalysts {where N-Imidate = N-tetrafluorosuccinimide (N-TFS) or N-phthalimide (N-phthal) and NHC = N,N′-di-tert-pentylimidazol-2-ylidene (ItPe)}, in the presence of AgOTf, in comparison with AuIIIBr3(NHC) and AuIBr(NHC). The nature of N-Imidate anion influences catalyst efficacy. NMR spectroscopic investigations have allowed the ease of reduction of AuBr2(N-TFS)(NHC) to AuIX(NHC) (where X = N-TFS or Br) to be examined. Br2 is liberated from AuIII, which has been trapped by a sacrificial alkene. Under working catalyst conditions cationic AuIII is reduced to AuI.

  • Synthesis and Reactivity of N-Heterocyclic Carbene Gold(I) and Gold(III) Imidate Complexes and Their Catalytic Activity in 1,5-Enyne Cycloisomerization
    Organometallics, 2013
    Co-Authors: Jonathan P. Reeds, Adrian C. Whitwood, Mark Patrick Healy, Ian J S Fairlamb
    Abstract:

    The effects of substituting (pseudo)halide for anionic Imidate ligands in Au(I) and Au(III) (i.e. [AuBr(NHC)] and [AuBr3(NHC)]) complexes have been investigated. [Au(N-Imidate)(NHC)] and [AuBr2(N-Imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-Imidate)(NHC)] complexes, in combination with Ag salts, were tested for catalytic activity in the cycloisomerization of 1,5-enynes and found to be more effective than the tribromide analogues (e.g. [AuBr3(NHC)]). Subtle changes to the anionic Imidate ligand structure had a pronounced effect on the catalytic activity of the Au(III) complexes.

  • Exploiting Imidate ligand effects in transition metal-mediated C-C bond forming processes
    2010
    Co-Authors: Jonathan P. Reeds
    Abstract:

    The effects of substituting (pseudo)halide for Imidate ligands in Au(I) and Au(III) ([AuBr(NHC)] and [AuBr3(NHC)]), Ru(II) ([RuCl2(CHR)(L2)]) and Pd(II) ([Pd(OAc)2]) complexes has been investigated. The activity of these complexes as (pre)catalysts in enyne cycloisomerisation and propargylic nucleophilic substitution, diene ring-closing metathesis and ring-opening metathesis polymerisation and direct arylation reactions, respectively, has been determined. [Au(N-Imidate)(NHC)] and [AuBr2(N-Imidate)(NHC)] complexes were prepared and the structure and bonding of the complexes examined spectroscopically and crystallographically. The [AuBr2(N-Imidate)(NHC)] complexes, in combination with co-catalytic silver salts, were tested for activity in the cycloisomerisation of 1,5- and 1,6- enynes and found to be more effective than tribromide analogues. Kinetic analysis of the reactions showed subtle changes to the Imidate structure had a pronounced effect on the activity of the complexes and the use of the silver salt Ag[Al(OC(CF3)3)4] as a co-catalyst greatly increased catalytic activity. The complexes were also found to catalyse a unique tandem nucleophilic substitution-cycloisomerisation of propargyl alcohols and allylsilanes. [AuBr2(N-tfs)(ItPe)] was found to be an effective precatalyst for this reaction whilst Au(III) tribromide and Au(I) complexes were ineffective. 1,3-Diarylbicyclo[3.1.0]hexenes products were found to undergo a post-reaction ambient temperature 1,3-carbon shift isomerisation. The complex [Ru(N-tfs)2(o-iPrO-CHPh)(IMesH2)] was prepared and characterised spectroscopically and crystallographically. The complex was found to be inactive in the ring-closing metathesis and ring-opening metathesis polymerisation of alkenes. Attempts to selectively substitute chloride for Imidate ligands derived from imides with higher pKa’s of 8.3-9.7 (in water) resulted in decomposition of the alkylidene or benzylidene ligand. [Pd(Imidate)2(MeCN)] and [Pd(Imidate)2(THT)] complexes were prepared and analysed by NMR and infra-red spectroscopy. The complexes were tested for activity in the direct arylation of imidazole with iodoarenes without added base or neutral ligands. The activity of the complexes was to some degree dependant on the structure of the Imidate ligand, possessing moderate activity in comparison with [Pd(OAc)2]. The activity of other palladium sources and conditions for this reaction were investigated and it was found that the formation of Pd nanoparticles may be key to reaction progression.

David A. Nagib - One of the best experts on this subject based on the ideXlab platform.

  • catalytic β c h amination via an Imidate radical relay
    Chemical Science, 2019
    Co-Authors: Leah M. Stateman, Kohki M. Nakafuku, Kara M. Edwards, Ethan A Wappes, David A. Nagib
    Abstract:

    The first catalytic strategy to harness Imidate radicals for C–H functionalization has been developed. This iodine-catalyzed approach enables β C–H amination of alcohols by an Imidate-mediated radical relay. In contrast to our first-generation, (super)stoichiometric protocol, this catalytic method enables faster and more efficient reactivity. Furthermore, lower oxidant concentration affords broader functional group tolerance, including alkenes, alkynes, alcohols, carbonyls, and heteroarenes. Mechanistic experiments interrogating the electronic nature of the key 1,5 H-atom transfer event are included, as well as probes for chemo-, regio-, and stereo-selectivity.

  • Catalytic β C–H amination via an Imidate radical relay
    Chemical science, 2019
    Co-Authors: Leah M. Stateman, Kohki M. Nakafuku, Ethan A. Wappes, Kara M. Edwards, David A. Nagib
    Abstract:

    The first catalytic strategy to harness Imidate radicals for C–H functionalization has been developed. This iodine-catalyzed approach enables β C–H amination of alcohols by an Imidate-mediated radical relay. In contrast to our first-generation, (super)stoichiometric protocol, this catalytic method enables faster and more efficient reactivity. Furthermore, lower oxidant concentration affords broader functional group tolerance, including alkenes, alkynes, alcohols, carbonyls, and heteroarenes. Mechanistic experiments interrogating the electronic nature of the key 1,5 H-atom transfer event are included, as well as probes for chemo-, regio-, and stereo-selectivity.

  • Catalytic Alkene Difunctionalization via Imidate Radicals
    Journal of the American Chemical Society, 2018
    Co-Authors: Kohki M. Nakafuku, Stacy C. Fosu, David A. Nagib
    Abstract:

    The first catalytic strategy to harness Imidate radicals has been developed. This approach enables alkene difunctionalization of allyl alcohols by photocatalytic reduction of their oxime Imidates. The ensuing Imidate radicals undergo consecutive intra- and intermolecular reactions to afford (i) hydroamination, (ii) aminoalkylation, or (iii) aminoarylation, via three distinct radical mechanisms. The broad scope and utility of this catalytic method for Imidate radical reactivity is presented, along with comparisons to other N-centered radicals and complementary, closed-shell Imidate pathways.

  • Catalytic Alkene Difunctionalization via Imidate Radicals
    2018
    Co-Authors: Kohki M. Nakafuku, Stacy C. Fosu, David A. Nagib
    Abstract:

    The first catalytic strategy to harness Imidate radicals has been developed. This approach enables alkene difunctionalization of allyl alcohols by photocatalytic reduction of their oxime Imidates. The ensuing Imidate radicals undergo consecutive intra- and intermolecular reactions to afford (i) hydroamination, (ii) aminoalkylation, or (iii) aminoarylation, via three distinct radical mechanisms. The broad scope and utility of this catalytic method for Imidate radical reactivity is presented, along with comparisons to other N-centered radicals and complementary, closed-shell Imidate pathways

  • Directed β C–H Amination of Alcohols via Radical Relay Chaperones
    2017
    Co-Authors: Ethan A. Wappes, Kohki M. Nakafuku, David A. Nagib
    Abstract:

    A radical-mediated strategy for β C–H amination of alcohols has been developed. This approach employs a radical relay chaperone, which serves as a traceless director that facilitates selective C–H functionalization via 1,5-hydrogen atom transfer (HAT) and enables net incorporation of ammonia at the β carbon of alcohols. The chaperones presented herein enable direct access to Imidate radicals, allowing their first use for H atom abstraction. A streamlined protocol enables rapid conversion of alcohols to their β-amino analogs (via in situ conversion of alcohols to Imidates, directed C–H amination, and hydrolysis to NH2). Mechanistic experiments indicate HAT is rate-limiting, whereas intramolecular amination is product- and stereo-determining

Salima Boughdiri - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical study of the mechanism and regioselectivity in the formation of pyrazolo[1,5-a]- [1,3,5]-triazines and pyrazolo[1,5-a]-[1,3,5]triazinones: a DFT study
    Chemical Physics Letters, 2019
    Co-Authors: Marwa Manachou, Christophe Morell, Henry Chermette, Salima Boughdiri
    Abstract:

    To shed more insight into the regioselectivities observed in the reactions between 3,5-diaminopyrazoles and N-acyl Imidates or N-ethoxy Imidate yielding the corresponding substituted pyrazolo[1,5-a]-[1,3,5] triazines or pyrazolo[1,5-a][1,3,5] triazinones, DFT calculations are carried out using B3LYP/6- 31++G (d, p) method. The favored mechanism and the experimental regioselectivity of this reaction are rationalized by calculations of activation energy, natural atomic charge, and Fukui indexes derived from density functional theory. The present study shows that the experimental trends of the relative reactivities and regioselectivities of these reactions are correctly predicted using these computational levels.