Theoretical Studies On The Mechanism Of Rh(Ⅲ)-catalyzed C-H Bond Functionalization Of N-Phenoxyacetamide

The use of oxidizing directin groups as internal oxidants has recently emerged as an attractive strategy in transition metal-catalyzed C-H functionalization reactions,which has been used in the formation of C-C/C-X bond. With the fast development of oxidizing directing groups, this type of reactions appears to be more and more diversifiec. By contrast, the development of its theory research lagging behind slightly.And the mechanism details involed in these reactions remain unclear from the viewpoint of theory. In this paper, we set out to investigate the reaction mechanism of rhodium(Ⅲ)-catalyzed C-H acticvation of N-phenoxyacetamide with the aid of density functional theory calculations at the M06 leval.In Chapter 3, a density functional theory(DFT) study has been conducted to elucidate the mechanism of the rhodium(Ⅲ)-catalyzed C-H activation of N-phenoxyacetamide, where the amido component of an internal oxidant serves as a leaving group. The impact of different substrates(alkynes versus cyclopropenes) on the reaction mechanism has been discussed in detail. The pathway for cyclopropene substrate proceeded via a Rh(V) nitrene, whilst Rh(Ⅲ) retained unchanged throughout the pathway for alkyne substrate. The C-O bond-forming reductive elimination and O-N bond cleavage steps simultaneously occurred for the alkyne substrate. However, the C-O bond was formed by an electrocyclization from a Rh(Ⅲ)intermediate for the cyclopropene substrate. The energy profiles for the cyclopropene substrate were accompanied by a change in spin-state because the triplet spin state of a Rh(V) nitrene complex is lower than that of the singlet spin state.In Chapter 4, a systematic density function theory study has been conducted to examine the mechanisms involved in the rhodium(Ⅲ)-catalyzed alkenylation of N-phenoxyacetamide with two different substrates(i.e, styrene and N-tosylhydrazone).The density function theory calculations indicated that the reaction of the N-tosylhydrazone substrate resulted in the formation of a Rh(V)–nitrene intermediate via the cleavage of the O–N bond of N-phenoxyacetamide, whereas the styrene substrate resulted in an Rh(I) species through consecutive β-H elimination and Hmigration steps to the internal oxidant. The differences observed between the N-tosylhydrazone and styrene systems were attributed to differences in the reactivity of their Rh(V)–nitrene intermediates. For example, the N-tosylhydrazone formed a five-membered Rh(V)–nitrene intermediate, which was readily reduced to a Rh(Ⅲ)species by tautomerization, whereas this pathway was energetically unfavorable for the styrene substrate.