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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.
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Mapping C−H⋅⋅⋅M Interactions in Confined Spaces: (α‐ICyD Me )Au, Ag, Cu Complexes Reveal “Contra‐electrostatic H Bonds” Masquerading as Anagostic Interactions**
Abstract What happens when a C−H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as “contra‐electrostatic” H‐bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H‐bonding with an unusual contra‐electrostatic component. While electrostatics is strongly stabilizing component in the conventional C−H⋅⋅⋅X bonds where X is an electronegative main group element, it is destabilizing in the C−H⋅⋅⋅M contacts when M is Au(I), Ag(I), or Cu(I) of NHC−M−Cl systems. Such remarkable C−H⋅⋅⋅M interaction became experimentally accessible within (α‐ICyDMe)MCl, NHC‐Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C−H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set ofd‐orbitals. A combination of experimental and computational data demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C−H bond to point toward the metal, and reveals a still attractive “contra‐electrostatic” H‐bonding interaction.
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- Award ID(s):
- 1800329
- PAR ID:
- 10226913
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 27
- Issue:
- 31
- ISSN:
- 0947-6539
- Format(s):
- Medium: X Size: p. 8127-8142
- Size(s):
- p. 8127-8142
- Sponsoring Org:
- National Science Foundation
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