title: Porphyrin Cobalt(III) "Nitrene Radical" Reactivity; Hydrogen Atom Transfer from Ortho-YH Substituents to the Nitrene Moiety of Cobalt-Bound Aryl Nitrene Intermediates (Y = O, NH).
abstract: In the field of cobalt(II) porphyrin-catalyzed metallo-radical reactions, organic azides have emerged as successful nitrene transfer reagents. In the pursuit of employing ortho-YH substituted (Y = O, NH) aryl azides in Co(II) porphyrin-catalyzed nitrene transfer reactions, unexpected hydrogen atom transfer (HAT) from the OH or NH₂ group in the ortho-position to the nitrene moiety of the key radical-intermediate was observed. This leads to formation of reactive ortho-iminoquinonoid (Y = O) and phenylene diimine (Y = NH) species. These intermediates convert to subsequent products in non-catalyzed reactions, as is typical for these free organic compounds. As such, the observed reactions prevent the anticipated cobalt-mediated catalytic radical-type coupling of the nitrene radical intermediates to alkynes or alkenes. Nonetheless, the observed reactions provide valuable insights into the reactivity of transition metal nitrene-radical intermediates, and give access to ortho-iminoquinonoid and phenylene diimine intermediates from ortho-YH substituted aryl azides in a catalytic manner. The latter can be employed as intermediates in one-pot catalytic transformations. From the ortho-hydroxy aryl azide substrates both phenoxizinones and benzoxazines could be synthesized in high yields. From the ortho-amino aryl azide substrates azabenzene compounds were obtained as the main products. Computational studies support these observations, and reveal that HAT from the neighboring OH and NH₂ moiety to the nitrene radical moiety has a low energy barrier.
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. m.goswami@uva.nl.
authors.forename: Monalisa
authors.initials: M
authors.lastname: Goswami
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. C.Rebreyend@uva.nl.
authors.forename: Christophe
authors.initials: C
authors.lastname: Rebreyend
authors.affiliation: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. b.debruin@uva.nl.
authors.forename: Bas
authors.initials: B
authors.lastname: de Bruin
mesh_terms: D000475:Alkenes / Q000737:chemistry; D001386:Azides / Q000737:chemistry; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*
chemical_list: D000475:Alkenes; D001386:Azides; D011166:Porphyrins; D003035:Cobalt; D006859:Hydrogen
keywords: aryl azides; azabenzenes; cobalt(II) porphyrins; hydrogen atom transfer; nitrene radicals; ortho-iminoquinonoid; phenylene diimine