skip to main content

Explore Research Products in the NSF-PAR

Title: Copper( ii ) ketimides in sp 3 C–H amination
Commercially available benzophenone imine (HNCPh 2 ) reacts with β-diketiminato copper( ii ) tert -butoxide complexes [Cu II ]–O t Bu to form isolable copper( ii ) ketimides [Cu II ]–NCPh 2 . Structural characterization of the three coordinate copper( ii ) ketimide [Me 3 NN]Cu–NCPh 2 reveals a short Cu-N ketimide distance (1.700(2) Å) with a nearly linear Cu–N–C linkage (178.9(2)°). Copper( ii ) ketimides [Cu II ]–NCPh 2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R–NCPh 2 products in a process that competes with N–N coupling of copper( ii ) ketimides [Cu II ]–NCPh 2 to form the azine Ph 2 CN–NCPh 2 . Copper( ii ) ketimides [Cu II ]–NCAr 2 serve as intermediates in catalytic sp 3 C–H amination of substrates R–H with ketimines HNCAr 2 and t BuOO t Bu as oxidant to form N -alkyl ketimines R–NCAr 2 . This protocol enables the use of unactivated sp 3 C–H bonds to give R–NCAr 2 products easily converted to primary amines R–NH 2 via simple acidic deprotection.  more » « less
Award ID(s):
1955942
NSF-PAR ID:
10322281
Author(s) / Creator(s):
;  ; ; ; ; ;
Date Published:
Journal Name:
Chemical Science
Volume:
12
Issue:
47
ISSN:
2041-6520
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ( , Angewandte Chemie International Edition)
    Abstract

    Undirected C(sp3)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ2‐N,O‐NC(O)Ar) to provide carbon‐based radicals R.and copper(II)amide intermediates [CuII]‐NHC(O)Ar that subsequently capture radicals R.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups.

     
    more » « less
  2. ; ; ; ; ; ( , Angewandte Chemie)
    Abstract

    Undirected C(sp3)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ2‐N,O‐NC(O)Ar) to provide carbon‐based radicals R.and copper(II)amide intermediates [CuII]‐NHC(O)Ar that subsequently capture radicals R.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups.

     
    more » « less
  3. ; ; ; ( , Inorganic Chemistry Frontiers)
    null (Ed.)
    HN(CH 2 CH 2 PR 2 ) 2 -ligated copper borohydride complexes, ( R PN H P)Cu(BH 4 ) (R = i Pr, Cy, t Bu), which can be prepared from ( R PN H P)CuBr and NaBH 4 , are capable of catalyzing the hydrogenation of aldehydes in an alcoholic solvent. More active hydrogenation catalysts are ( R PN H P)CuBr mixed with KO t Bu, allowing various aldehydes and ketones to be efficiently reduced to alcohols except those bearing a nitro, N -unprotected pyrrole, pyridine, or an ester group, or those prone to aldol condensation ( e.g. , 1-heptanal). Modifying the catalyst structure by replacing the NH group in ( i Pr PN H P)CuBr with an NMe group results in an inferior catalyst but preserves some catalytic activity. The hexanuclear copper hydride cluster, ( i Pr PN H P) 3 Cu 6 H 6 , is also competent in catalyzing the hydrogenation of aldehydes such as benzaldehyde and N -methyl-2-pyrrolecarboxaldehyde, albeit accompanied by decomposition pathways. The catalytic performance can be enhanced through the addition of a strong base or i Pr PN H P. The three catalytic systems likely share the same catalytically active species, which is proposed to be a mononuclear copper hydride ( R PN H P)CuH with the NH group bound to copper. 
    more » « less
  4. ; ; ; ; ( , Dalton Transactions)
    Reduction of Cp′ 3 ThCl, Cp′ 3 ThBr, and Cp′ 3 ThI (Cp′ = C 5 H 4 SiMe 3 ) with potassium graphite generates dark blue solutions with reactivity and spectroscopic properties consistent with the formation of Cp′ 3 Th. The EPR and UV-visible spectra of the solutions are similar to those of crystallographically-characterized tris(cyclopentadienyl) Th( iii ) complexes: [C 5 H 3 (SiMe 3 ) 2 ] 3 Th, (C 5 Me 4 H) 3 Th, (C 5 t Bu 2 H 3 ) 3 Th, and (C 5 Me 5 ) 3 Th. Density functional theory (DFT) analysis indicates that the UV-visible spectrum is consistent with Cp′ 3 Th and not [Cp′ 3 ThBr] 1− . Although single crystals of Cp′ 3 Th have not been isolated, the blue solution reacts with Me 3 SiCl, I 2 , and HCCPh to afford products expected from Cp′ 3 Th, namely, Cp′ 3 ThCl, Cp′ 3 ThI, and Cp′ 3 Th(CCPh), respectively. Reactions with MeI give mixtures of Cp′ 3 ThI and Cp′ 3 ThMe. Evidence for further reduction of the blue solutions to a Cp′-ligated Th( ii ) complex has not been observed. The crystal structures of Cp′ 3 ThMe and (Cp′ 3 Th) 2 (μ-O) were also determined as part of these studies. 
    more » « less
  5. ; ; ( , Dalton Transactions)
    The reduction potentials (reported vs. Fc + /Fc) for a series of Cp′ 3 Ln complexes (Cp′ = C 5 H 4 SiMe 3 , Ln = lanthanide) were determined via electrochemistry in THF with [ n Bu 4 N][BPh 4 ] as the supporting electrolyte. The Ln( iii )/Ln( ii ) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f 7 , 4f 14 , 4f 6 , and 4f 13 Ln( ii ) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f n 5d 1 Ln( ii ) ions ( n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln( ii ) compounds [K(2.2.2-cryptand)][Cp′ 3 Ln] (Ln = Pr, Sm, Eu) match those of the Cp′ 3 Ln complexes. The reduction potentials of nine (C 5 Me 4 H) 3 Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′ 3 Ln compounds. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email