Theoretical Prediction Of Ir-H Bond Cleavage Energies Of Cyclopentadienyl Iridium Complexes

In Chapter 1,a review about half-sandwish complexes is present.In addition,more details about cyclopentadienyl iridium complexes are present,which about C-H bond activations,Diels-Alder reactions,(asymmetric)hydrogen transfers,and carbon dioxide reduction.Meanwhile,an outline of this thesis also is present.Chapter 2 includes an introduction to computation chemistry and two analysis methods.The introduction to computation chemistry includes ab inito method,density function theory,solvent effect and basis.NBO population analysis and distortion-interaction energy analysis have been stated.In Chapter 3,the main work finished in my graduated period is present.Iridium hydride complexes are ubiquitous in Ir-catalyzed reactions as catalysts or critical intermediates and the cleavage or formation of Ir-H bonds are usually involved in these transformations.In this work the bond dissociation enthalpies and the hydride-generating heterolytic dissociation enthalpies of the Ir-H bonds in various cyclopentadienyl iridium complexes were studied with the aid of density functional theory method TPSS.Computational results show that the deficient-electron iridium center benefits homolytic cleavage of Ir-H bonds while electron withdrawing groups as well as strong electron acceptors result in weakened electron density of central iridium.Rigid chelate rings and large steric substituents could reduce bond energies by releasing steric hindrance.Such as 2-phenylpyridine bipyridyl coordinated iridium hydride compounds could use d orbitals to form delocalization bonds with the aromatic system of the ligands thereby decreases the hydride-generating heterogeneous cleavage enthalpies of these species.Olefin ligands promoted homolysis reactions and restrained heterolysis reactions.Phosphine ligands have little influence on homolysis while significantly reduce the hydride ion cleavage enthalpies.Deficient-electron boron atoms favor the homolysis and disfavor the heterolysis because the later reaction would form Ir-H-B bridge bonds.Silicon atoms are relatively electron-rich which result in higher enthalpies of both processes.