- Functionalization of the Aryl Moiety in the Pincer Complex (NCN)NiIIIBr2: Insights on NiIII-Promoted Carbon-Heteroatom Coupling
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This report describes the C-O, C-N, and C-halogen functionalization of the NiIII-Ar moiety stabilized within a pincer framework that serves as a model system for studying C-heteroatom coupling reactions promoted by high-valent Ni compounds. Treating van Koten's pincer complex (NCN)NiIIIBr2 under a nitrogen atmosphere with water, 1° or 2° alcohols, 1° amines, HCl, or HBr results in heterofunctionalization at the ipso-C of the pincer ligand's aryl moiety. The yields of these heterofunctionalizations are generally a comproportionation reaction between the trivalent precursor and a NiI species arising from the reductive elimination step in the functionalization process. Other side-reactions include a C-OH coupling with residual water and C-H coupling (net protonation) that is prevalent with mineral acids, some alcohols, and aqueous NH3. Kinetic measurements have established that the reaction with MeOH is first-order with respect to [(NCN)NiIIIBr2], and a kinetic isotope effect of 0.47 has been obtained for functionalization with CH3OH/CD3OD. These and other observations have allowed us to propose two different mechanistic postulates for the involvement of trivalent intermediates in the functionalization reactions under discussion. Tetravalent species such as [(NCN)NiIVBr2]+ can be generated in situ under strongly oxidative conditions and they do promote C-Br coupling, but such species play no role in the C-heteroatom coupling reactions under nonoxidative conditions.
- Cloutier, Jean-Philippe,Zargarian, Davit
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- Aerobic oxidation-functionalization of the aryl moiety in van Koten's pincer complex (NCN)Ni(ii)Br: Relevance to carbon-heteroatom coupling reactions promoted by high-valent nickel species
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The growing popularity of metal-promoted C-H functionalization methodologies has led to increased efforts aimed at improving our understanding of the mechanistic underpinnings of C-C and C-heteroatom bond forming steps. One approach to such mechanistic studies involves probing the reactivities of model complexes featuring chelate-stabilized M-hydrocarbyl moieties. The present study uses van Koten's (NCN)Ni(ii)Br compound as a model for probing C-heteroatom coupling with protic substrates HX (X = NHR, OR). Our results establish the crucial importance of aerobic (oxidative) conditions for promoting reactivities that give the functionalized ligands NC(X)N. The importance of oxidation for the C-heteroatom bond formation is further deduced from the reaction of the structurally authenticated complex (NCN)Ni(OSiMe3) with CuBr2 to give the C-O functionalization product NC(OSiMe3)N. This journal is
- Cloutier, Jean-Philippe,Zamani, Fahimeh,Zargarian, Davit
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p. 1800 - 1807
(2022/01/31)
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- Triethylsiloxymethyl-N,N-dimethylamine, Et3SiOCH2NMe2: A Dimethylaminomethylation (Mannich) Reagent for O–H, S–H, P–H and Aromatic C–H Systems
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Triethylsiloxymethylamine, Et3SiOCH2NMe2, readily synthesized in high yield by the hydrosilylation reaction between Et3SiH and DMF, is an excellent (N,N-dimethylamino)methyl transfer agent to a representative range of aliphatic alcohols, thiols, and Ph2PH (E–H) materials. The reactions are almost instantaneous at room temperature in inert solvents and require no activating agents to produce E–CH2NMe2 products in high yields and illustrate the title compound as an excellent addition to the family of organic reagents. For aromatic alcohols, electrophilic substitution of the aromatic ring occurs in high yield. Crystal structures of new materials such as the cholestero–CH2NMe2 derivative, 2–4-[bis(N,N-dimethylamino)methyl]-1-naphthol, and the phosphine oxide derived from Ph2PCH2NMe2 are reported.
- Gonzalez, Paulina E.,Sharma, Hemant K.,Chakrabarty, Sanchita,Metta-Maga?a, Alejandro,Pannell, Keith H.
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p. 5610 - 5616
(2017/10/13)
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- Capillary supercritical fluid chromatography/mass spectrometry of phenolic mannich bases with dimethyl ether modified ethane as the mobile phase
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The analysis of phenolic Mannich bases-which are used as hardeners and accelerators for epoxy resins-by capillary supercritical fluid chromatography (SFC) with dimethyl ether modified ethane as the mobile phase is described. The elution properties of several different mobile phases with respect to amines are shown. SFC with UV detection is coupled via a custom-built interface to a mass spectrometer with atmospheric pressure chemical ionization. Two technically important Mannich bases prepared by different production processes are characterized and compared with respect to their byproducts. The role of dimethyl ether during the ionization process and the fragmentation of phenolic Mannich bases is discussed.
- Fuchslueger, Ulf
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p. 2324 - 2333
(2007/10/03)
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