Theoretical studies on structure and bonding of transition-metal complexes and mechanisms of stoichiometric and catalytic organometallic reactions are reported in this thesis. _{3 2 2 3 2 3 2 2 2 2 2 2 3 2 3 2 6 5 3 3}...[ Read more ]

Theoretical studies on structure and bonding of transition-metal complexes and mechanisms of stoichiometric and catalytic organometallic reactions are reported in this thesis.

Part I: The trans influence of boryl ligands, together with that of other ligands commonly believed to have a strong trans influence, has been investigated theoretically via DFT calculations on a series of square planar platinum(II) complexes of the form trans-[PtL(Cl)(PMe₃)₂]. The following order of trans influence has been obtained: –BMe₂ > –SiMe₃ > – BH₂ > –SnMe₃ ~ –BNHCH₂CH₂NH > –Bpin > –BOCH₂CH₂O > –BOCH=CHO ~ –Bcat ~ –BCl₂ ~ –BBr₂ ~ –SiH₃ > –CH₂CH₃ > –CH=CH₂ > –H ~ –Me > –C₆H₅ > –SiCl₃ > –SnCl₃ > –C≡CH. How the subsituents at the boron center affect the trans influence properties of the boryl ligands has been thoroughly investigated. The major factor is the σ-donor strength of the boryl ligand.

Part II: The nonplanarity found in metallabenzene complexes has been investigated theoretically via DFT calculations. A metallabenzene has four occupied π molecular orbitals (8 π electrons) instead of three that benzene has. The extra occupied π molecular orbital, which is the highest occupied molecular orbital (HOMO) in many metallabenzenes, has antibonding interactions between the metal center and the metal-bonded ring-carbon atoms, providing the electronic driving force toward nonplanarity. Our calculations indicate that the electronic driving force toward nonplanarity, however, is relatively small. Therefore, other factors such as steric effects also play important roles in determining the planarity of these metallabenzene complexes. How the various electronic and steric factors interplay with each other has been discussed.

Part III: The insertion reactions of allenes with MHCl(CO)(PPh₃)₃ and MHCl(PPh₃)₃ (M = Ru, Os), which lead to very different insertion products (allyl complexes and vinyl complexes, respectively), have been theoretically investigated via the aid of DFT calculations. The calculation results show that the observed different reactivity can be related to the significant difference in the electron gaining at the central carbon of the allene ligand upon coordination to metal fragments.

Part IV: Mechanism of alkyne metathesis catalyzed by W/Mo alkylidyne complexes has been theoretically investigated with the aid of DFT calculations. Calculations on various model alkylidyne complexes M(≡CMe)(OR)₃ (M = W, Mo; R = Me, CH₂F), W(≡CMe)(NMe₂)₃ and W(≡CMe)(Cl)₃ allow us to examine the factors that influence the reaction barriers. In the reaction mechanism, metallacyclobutadienes are initially formed from a ring-closing step between alkynes and alkylidyne complexes. A ring-opening step then gives the metathesis products. The factors that determine the metathesis reaction barriers have been examined. The reaction paths leading to the formation of Cp complexes, a possible path deactivating catalytic activity, were also studied.