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.
Highlights
In the context of homogeneously catalyzed organic transformations carbene and nitrene transfer reactions provide interesting possibilities [1,2,3,4,5,6,7]
Another iron based example is limited in the sense that only azides with bulky substitutents like mestiyl groups result in formation of aza compounds [41]
We further evaluated the changes in spin density distribution during the hydrogen atom transfer (HAT) process
Summary
In the context of homogeneously catalyzed organic transformations carbene and nitrene transfer reactions provide interesting possibilities [1,2,3,4,5,6,7]. Organic azides are potentially more interesting quite common to use iminoiodanes or haloamine-T compounds as nitrene sources fornitrene-transfer transfer to other [3,5,6], molecules most convenientformed and benign nitrene as of reagents as [29,30,31,32,33] They areThese moreare, soluble andnot thethe only byproduct during the sources, generation they are poorly soluble and lead to the formation of undesirable side products like phenyl iodide and nitrenes from azides is dinitrogen. The detailed mechanistic amination of ethylbenzene, toluene, and tetralin (1,2,3,4tetrahydronaphthalene) studiedbywith aspects of two such catalytic nitrene transfer reactions with cobalt porphyrins have beenwas elucidated a variety of organic azides like N1) C(O)OMe, density functionaloftheory (DFT) and
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