Theoretical Studies Of The Mechanism Of C-H Bond Amination Reaction, Based On Amidines As Nitrogen Source

An efficient method for synthesis of heterocyclic compounds has been de veloped via transition metal-catalyzed C-H functionalization reaction. However, the development of its theory research, by contrast, slightly lagging behind,and the mechanism details involved in these reactions remain unclear from the viewpoint of theory. In this paper, we set out to investigate the reaction mechanism of transition-metal(Cu or Pd)-catalyzed C-H amination reaction with the aid of DFT calculations at the B3 LYP level.In Chapter 3, we carry out a systematic study to investigate the Cu(OAc)2- and [Pd Cl2(Ph CN)2]-catalyzed syntheses of benzimidazoles from amidines, using DFT calculations at the B3 LYP level. The caculations indicated that(1) For the Cu-catalyzed system, our calculations supported a four-step-cascade reaction involving C–H activation with Cu(II) via concerted metalation–deprotonation(CMD), followed by oxidation of the Cu(II) intermediate and deprotonation of the imino group by Cu(III), and finally reductive elimination from Cu(III);(2) In our calculations, the CMD step has the same barrier as deprotonation of the imino group;(3) On the basis of the calculation results for the Pd-catalyzed system, C–H bond breaking by CMD occurs firstly, followed by the rate-determining C–N bond formation and N-H deprotonation;(4) Pd(III) species is not involved in the Pd-catalyzed syntheses of benzimidazoles from amidines.In Chapter 4, we study the reaction mechanism on the C–H functionalization reaction under Pd(OAc)2 catalysis involving CO/isonitrile insertion. Since isonitrile is isoelectronic with CO, it shows some similarities, which include(1) the C–H activation reaction mainly both proceeded through the anagostic bonding mechanism;(2) the CO/isonitrile insertion step is the rate-determining step;(3) the C–H activation and CO/isonitrile insertion steps are accomplished with Pd(II) and Pd(III), respectively. For reaction including CO insertion, the arene C–H activation step is the first step of the reaction mechanism. However, for the reaction including isonitrile insertion, the arene C–H activation step occurs after deprotonation of the imino group. The reason lies in the different oxidants. In the reactions including isonitrile insertion, the high endergonicity of the oxidation step suppresses prior C–H activation and favors prior deprotonation of the imino group. While, in the reactions including CO insertion, the low endergonicity of the oxidation step allows a prior C–H activation to occur, which in favor of CO insertion reaction.