Computational Elucidation of Electrocatalytic Mechanism in Mono-Ni Complexes with Pendant Amines and Structural Insights into Diosmium Sawhorse Complexes

Abstract

With the significant achievements in quantum mechanical methodologies, such as Hartree-Fock-Roothaan (HFR) Theory and Density Functional Theory (DFT), along with the boost in computational power, the field of computational chemistry, also referred to as theoretical chemistry, has greatly expanded its importance. Presently, DFT is widely adopted due to its computational efficiency, remarkable accuracy, and its applicability to diverse problems.

This dissertation is centered on the theoretical investigations of the structural properties and catalytic reactivity in organometallic systems by application of the DFT calculations. This dissertation is comprised of five chapters. The first chapter gives an overview of the principal quantum mechanical methodologies in theoretical chemistry studies, including the HFR self-consistent field theory and DFT. Related topics including the basis set, solvent effect, and relativistic effect also are discussed.

Chapters II and III investigated the reaction mechanism, along with the corresponding experimental results, of a mono-Ni system, [Ni(PR 2NR 2)(CH3CN)2] 2+(R or R’=Ph, Bn or tBu), which electrocatalytically oxidizes alcohols into their corresponding aldehydes or ketones in the presence of an external base. The computational results summarize the catalytic cycle into three distinct phases: the first deprotonation, subsequent beta-hydride elimination, and a second deprotonation, which with oxidation regenerates the initial active species.

Chapters IV and V focus on studies of the diosmium carbonyl sawhorse complex Os2(μ-O2CH)2(CO)6. Chapter IV examines an exchange process of the terminal CO, which represents a rare example of the poorly understood transition from a dissociative process with a CO-loss intermediate to a dissociative interchange process with a transition state involving both the incoming and the leaving COs.

Chapter V explores the rationale behind linear relationships between the O-Os-OsO dihedrals and the Os-Os distance among 9 selected diosmium complexes, which are grouped into two based on the presence or absence of terminal phosphine ligands. A derived mathematical expression shows that this relationship depends on three additional geometric parameters. Among these parameters the dihedral is the most responsive, while the other factors respond systematically to produce the observed linear trend. The packing of the molecules in the crystal environment has a major impact on the dihedral and a minor impact on the Os-Os distance. Finally, the phosphine ligand is found to buffer the impact of packing on the Os-Os distance, which results in the separation of the trend into two lines.