Theoretical Studies On Transition Metal Mediated Organic Reactions

The recent development of quantum chemistry and theoretical methods enables the deep understanding of the detailed mechanism of organic reactions. This thesis mainly focuses on the mechanistic studies on transition metal complexes mediated organic reactions. The main contents include:Chapter 1 gives a brief introduction to different methodologies used in mechanistic studies of organic reactions.Chapter 2 mainly reviews the recent development in mechanistic studies of Cu(I) catalyzed C-X cross coupling reactions.Chapter 3 to Chapter 5 described the research topics of the mechanistic studies on transition metal mediated organic reactions, which were accomlished in my PhD studies in USTC.In Chapter 3, we mainly focus on the theoretical studies on Cu(I) catalyzed highly selective C-X (X=N, O) cross coupling reactions of aminoalcohols with arylhylides. With the aid of DFT (B3LYP) calculations, we are able to compare the energy demands of different pathways quantitatively and finally summarized the energetically most favorable one. On the basis of the electronic and structural analysis of the key intermediates and transistion states, we futher clarified the intrinsic releationship between the electronic character of ligand and the C-X coupling selectivities. This paper is published on J. Am. Chem. Soc. 2010, 132, 18078.In Chapter 4, DFT calculations have been carried out to study the mechanisms of reactions of O2 with a series of metal complexes, including d6 CpRuL2, d6 ML5, and d8 ML4 complexes. The calculation results indicate that the reaction is initiated by an end-on coordination of O2 to the metal center, which gives an (η1-O2)[M] intermediate. The uncoordinated oxygen atom of theη1-O2 ligand then approaches the metal center to give a newη1-O2 intermediate in which the O2 ligand is oriented approximately the same as the one defined in the product. An intersystem conversion from the triplet to singlet energy surface (MECP) then occurs to enable the metal peroxide product to be formed. This paper is published on Organometallics, 2009, 28, 4443.In Chapter 5, we mainly focus on the mechanistic study of Pd(OAc)2 catalyzed intramolecular diaminations in presence of base and oxidants. On the basis of the DFT (B3LYP) calculations, we concluded that the diamination tends to occur via an anti-aminopalladation/syn-C-N bond formation pathway, rather than the previously proposed syn-aminopalladation/anti-C-N bond formation pathway. This paper is published on Organometallics, 2009, 28, 4507.All research work in Chapter 3-5 show good correlations between the calculation results and the experimental observations, which not only validate the reliability of the calculation methods, but also provide information that is difficult to gain from experimental measurements. We wish the conclusions provided in this thesis could be helpful for the desighing of new catalyst system and new organometallic reactions in the future.