Theoretical Studies On C-N, N-N And N-O Bond Formation From Aryl Azide Catalyzed By The Transition Metals

In recent years, organic azides participate in transition metal catalyzed reactionsthat construct new C-N, N-N and N-O bonds, which is a late-model area of intenseresearch interest by the synthetic community. Although there are some metalcomplexes have been reported for catalytic formation of these new bonds from vinylor aryl azides by experimental observation, the true mechanism details remainsinconclusive from viewpoint of theory. In this paper, we set out to investigate thereaction mechanism of transition-metal-catalyzed routes for the formation of C-N,N-N and N-O bonds with the aid of DFT calculations at the B3LYP level. Our hope isthat a systematically study of the factors influencing the mechanism ofmetal-catalyzed these new bonds formation reactions will lead to a fundamentalunderstanding of these factors that will assist experimental efforts in finding bettercatalysts.In Chapter3, we carry out a systematic DFT study to examine how catalysts withdifferent metals influence the C-H amination mechanism of biaryl azides. Themechanisms of （cod）Ir（OMe）, RuC_l3（DME）（DME=CH₃OCH₂CH₂OCH₃, a solventmolecule）, Rh₂（O₂CCF₃）₄, and ZnI₂were investigated in our study. The calculationsindicated that the C-H amination reactions mainly proceeded through a stepwisemechanism regardless of the metal center （Ru, Ir, Rh, or Zn）. The energetic span （δE）model proposed by Shaik et al. has been applied to reveal the kinetic behavior of thefour catalytic cycles. The results indicate that the ruthenium specie exhibit highercatalytic performance than the other three ones. The investigation of magneticproperties suggest that no matter what the metal center was–Ir, Ru, Rh, or Zn–theC-N bond formation step is pseudoelectrocyclization with an orbital disconnection onthe nitrogen atom （N1） in the pseudopericyclic transition structure.In Chapter4, we study the reaction mechanism on the C-H amination reactionunder [FeⅢ（F₂0TPP）Cl] catalysis. The calculations show that the classical three-stepmechanism for other metals （Ru, Rh, Ir and Zn）, including N₂liberation, C-N bondformation and1,2hydrogen-shift, only takes place along the doublet state for the iron（Ⅲ）-catalyzed system. In the quartet state, the favorable reaction pathway for theiron（Ⅲ）-catalyzed system is a1,2-hydrogen shift preceding C-N bond formation, i.e.,a H-abstraction/radical rebound mechanism after N₂liberation.In Chapter5, we carried out to study the reaction mechanism on N O or N Nbond formation from aryl azide catalyzed by iron（Ⅱ） bromide complex. We found thatthe reaction proceeds along the quintet pathway. The calculation results indicate thatthe iron-catalyzed N-N or N-O bond formation reaction is mainly initiated by Fecoordinating to internal N atom of azide, which gives an iron nitrene intermediate.