Study On The Reaction Of Substituted Pyrazoles With 1-Alkynyl Fischer Carbene Complexes (CO)₅M=C(OEt)C≡CPh (M=Cr, W)

β-Pyrazolyl alkenyl Fischer carbene complexes have both the virtues of multiple reactivity in carbene fragment and high bioactivity in pyrazole fragment, which attracts our interest in their synthesis and application from a theoretical and applied viewpoint. In the thesis a series ofβ-pyrazolyl-α,β-unsaturated Fischer carbene complexes were synthesized and structurally characterized by NMR, IR and X-ray crystallographic determinations. Based on the dynamic nuclear magnetic resonance (DNMR) and density functional calculation (DFT) results, a three-step mechanism is proposed for the Michael type addition of pyrazoles to the alkynyl carbene complexes. Substituent effect of pyrazoles was also investigated by DNMR and DFT.We successfully synthesized these intermediates with exclusively (E)-conformations in a mild condition. X-ray results show that substituents in the pyrazolyl ring affect greatly on the structures of products, especially theπdelocation of the fragment 1-metal-butadiene.DNMR and DFT were applied to investigate the syn-/anti- interconversion of the alkynyl carbene complexes derived from the partial double-bond property of the bond Ccarbene-O. The syn-conformer is more stable than the anti-analogue by 6.5 kJ·mol^-1 with an activation barrier of 62.5 kJ·mol^-1. The predominant syn-conformation may determine the reaction pathway under kinetic control.Michael addition of 3-methyl-5-phenyl-pyrazole (and 3-phenyl-5-methyl- pyrazole) to the alkynyl Fischer carbene complex was investigated as a model reaction by the density functional theory. The transition state structures and the activation barriers from the complete LST/QST search results indicate a three-step process: (1) Formation of C-N bond via transition state TS1; (2) Conformation conversion from In1 to In2, which is very important but was ignored before; (3) Intramolecular proton transfer via transition state TS2 to form the product. The first step is rate-determining with an activation barrier of 73.0 kJ·mol^-1, while the experimental value is 89.6 kJ·mol^-1 from the dynamic NMR measurements.With NMR and DFT methods, the Michael additions of alkynyl Fischer carbene complex with a series of substituted pyrazoles as nucleophiles were also studied. All reactions follow the same three-step pathway mechanism described above. Substituents on 3-, 4- and 5- positions of the pyrazolyl ring affect the reaction in the steric and electronic manners, even to change the rate-determining step.