Theoretical Studies On Thermodynamic Properties Of Transition Metal Compounds

Transition-metal compounds play a very important role in a large range of catalytic processes.Therefore,research on the thermodynamic properties of transition metal complexes is one of the hottest topics in modern bioinorganic chemistry and transition-metal catalysis.However,due to the limitations of experimental conditions and lack of appropriate experimental methods,quantum chemistry and theoretical methods becomes urgent and quite important.In recent years,quantum chemistry and its application in organic chemistry have been developed quickly,but it is still challenging to accurately model bulky transition metal complexes in solution.This dissertation focuses on developing a scientific methodology based on first principle to deal with the transition metal compounds in solution and quantitatively predict the properties of these compounds,so as to make the precisions comparable to the experimental ones.With solid data,other fundamental issues in physical organic chemistry,such as ligand effects,substituent effects and solvation effects,are also discussed.In the first chapter,the background,recent development and prospect on the theoretical studies of transition metal complexes were reviewed.In the second chapter,some computational methods including quantum chemistry method,Molecular Mechanics,Molecular Dynamic simulation,Monte Carlo method and so on,were briefly reviewed.In the chapter 3,the chemical accuracy calculations of pK_αof transition metal hydrides in acetonitrile were performed.We utilized several theoretical methods to predict pK_αof transition metal hydrides in acetonitrile.By assessing their performances,we are able to obtain one effective methodology based on first principles to predict the pK_αof transition,metal hydrides in acetonitrile with a precision of 1.5 pK_αunits.With solid data in hand,we further explored the structure-property relationships of the transition metal hydrides.(Published in Organometallics 2006,25,5879-5886.)In the chapter 4,a new theoretical protocol was developed to accurately predict the hydricities of transition metal hydrides in acetonitrile.In this work,we successfully established an effective tool with higher precision and less computational consumption through combination of some popular DFT methods with the relativistic effect.This generally-applicable theoretical approach is independent on the structure and can be successfully utilized to predict the hydricities,the acidities of the metal-hydrogen bond and the redox potentials of the corresponding metal complexes. Based on the systematic data,we studied the structure-activity relationships in the hydricities of transition metal hydrides and analysed the ligand effects,substituent effects and periodic trends on hydricities.The theoretical results can guide us to design new catalytic reactions.(Published in Organometallics 2007,26,4197-4203.)In the chapter 5,the Co-C bond dissociation energy(BDE)of organocobalt complexes was predicted with the theoretical approaches.Calibrated with experimental data,a generally-applicable,first-principle protocol was developed, which successfully predicted the Co-C BDE's of 28 structurally-unrelated organocobalt compounds with a precision of 2.2 kcal/mol.Equipped with this useful tool,we examined the effects of the in-plane ligands on the Co-C BDEs in a systematic fashion and observed the correlation between the spin density of the radical center and the bond strength for the first time,which can help us get a better understanding of the fundamental concepts in physical organic chemistry. (Organometallics,2008,In press.)Theoretical quantum chemical study is reliable contributing to its first principle. It is of great importance especially in resolving the problems difficult for experiments. The research results of this dissertation have provided valuable and fundamental information to the development of the bioinorganic chemistry as well as the transition-metal catalysis.