Etude du mode de liaison et des propriétés d’oxydo-réduction dans les complexes Organométalliques aux ligands riches en électrons π

Abstract

The work presented in this thesis deals with the theoretical study of organometallic complexes investigating the electronic and molecular structures of synthesized and interesting hypothetical mono-metallic, bi-metallic and hetero-bimetallic complexes. The study establishes a relationship between the electronic account, the coordination mode of bimetallic and hetero-bimetallic complexes. All calculations were carried out at different theoretical levels using the DFT method. The manuscript is divided into four parts; the first one is an introduction to the theory of density functional theory (DFT). The outline of this method of quantum chemistry are described and compared with those of ab initio Hartree-Fock, the second part presents the findings of the DFT calculations using BP86 and B3LYP* concerning the low-energy structures of mixed [M(Ind)Cp]+1/0/- 1 (M = Ti-Ni) sandwich complexes of indenyl and cyclopentadienyl ligands. The electronic configuration of cationic, neutral and anionic metal-ligand complexes and their structures are discussed depending on the metal nature, the spin state and the metal valence electrons, where a complete rationalization of the bonding has been provided for the [M(Ind)Cp]+1/0/-1 complexes. The indenyl ligand adopts different coordination modes including h3,h5,h5+2 and h9 according to the number of metal valence electrons and the spin state of the complex. These complexes present different total numbers of electrons (TNE = 16,17,……,25). We discussed in the the third part a series of homo- and heterobimetallic compounds of the type [(RuCp)2(Ind)]+, [(CoCb)2(Ind)]+and [(RuCp)(CoCb)(Ind)]+ (Ind = Indenyl, Cp = Cyclopentadienyl and Cb = cyclobutadiene) of 34-TNE (Total number of electrons) and their oxidized of 32- and 33- TNEs and their reduced of 35- and 36-TNEs species. Depending on the ancillary Cp or Cb ligand to the metal, the electronic and molecular structures and metal-metal bonding of this family of compounds have been analyzed. The syn and anti-configurations are possible for the studied binuclear complexes, which are related to the metal nature, where mostly steric constraints of the Cp or the Cb ligand appear to control its spatial disposition favouring the anti-configuration despite of its electronic deficiency for the 32- and 33-TNEs species. The flexibility of the indenyl ligand which is related to the metal hapticity favors the possibility of existence of several syn and anti-isomers of closeness energies. This study showed quite similar behaviours of the (RuCp)+ and (CoCb)+ of 12-electrons regarding their change or their permutation. The current study shows the ease of the reduction with regard to the oxidation, particularly that of the two-electrons one. The used three functionals gave comparable tendencies of the stability sequences between isomers favouring the low-spin structures and provided comparable findings regarding the low-spin/high-spin energy splittings. Withn the fourth part, DFT calculations have been performed on a series of hypothetical bi-metallic complexes of the type: [(Cp)M)2-(pyr)] :(Ti ,V,Cr,Mn,Fe,Ru,Co,Ni).The flexibility of the pyrene ligand favors the possibility of the existence of several isomers. The molecular and electronic structures of this large family of compounds were analyzed with respect to their total number of electrons (TNE) and the nature of the ancillary ligands. The structures with electron count lower than 34-TNE shows the possibility of the formation of metal-to-metal bonds relative the syn (b) conformation, which offers a stability of about 10 kcal/mol compared to other isomers.