Elusive Terminal Copper Arylnitrene Intermediates

• Published in: Angewandte Chemie (International ed.) 2017-06, Vol.56 (23), p.6426-6430
• Main Authors: Bakhoda, Abolghasem (Gus), Jiang, Quan, Bertke, Jeffery A., Cundari, Thomas R., Warren, Timothy H.
• Format: Article
• Language: English
• Subjects: Copper; C−H amination; Ethylbenzene; group transfer; Hydrogen bonds; Intermediates; ketimide; nitrenes; Organic compounds; triazenide
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201611275

We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β‐diketiminate. Addition of N3ArX3 (ArX3=2,4,6‐X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β‐diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p‐position to give the dicopper(II) diketimide 4 (Ar=2,6‐iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4‐Ph‐2,6‐iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. Attempts at isolating terminal arylnitrenes [Cu]=NAr result in a dicopper diketimide (see scheme, left) formed through reversible C−C coupling at the para position of the NAr group or acetonitrile insertion to give a diazametallacyclobutene (right). Experimental and theoretical studies reveal that both intermediates serve as “masked” sources of the corresponding terminal nitrene [Cu]=NAr that undergoes nitrene transfer to PMe3, CNtBu, and benzylic C−H bonds.