DFT Applications in Rationalizing Boron-based Catalytic Reactions for Industrially Valuable Chemicals

Abstract

Density Functional Theory (DFT) is extensively applied to rationalize catalytic reactions that produce valuable chemicals, offering significant insights into the reaction mechanism. The thesis is divided into the following six chapters. Chapter 1 provides an introduction to various boron-containing catalytic reactions. These boron-containing compounds mainly include boron oxide (B2O3), hexagonal boron nitride (h-BN), and pinacol boron (HBpin). B2O3 and h-BN catalysts perform the oxidation of light alkanes such as methane, ethane, propane and butane to their oxidized products. Furthermore, the objectives carried out in the next chapters are shown at the end. Chapter 2 demonstrates the reaction mechanism of oxidation of methane to formaldehyde over a small BOB model. Two active sites were explored to react with methane and dioxygen. Chapter 3 depicts the usage of an actual periodic model of boron oxide to investigate methane oxidation. The periodic model of boron oxide contains six active sites available on the surface. However, out of six sites, only two active sites contain the boron p-orbitals rightly oriented towards the upcoming molecules. These sites were employed to obtain various routes for methane oxidation to HCHO, CO and CO2 in the presence of singlet and triplet dioxygen. Chapter 4 discusses the DFT-derived mechanistic routes for the methane oxidation to HCHO and CO over a h-BN catalyst. Various h-BN active sites were explored to determine the surface catalytic-space of methane to HCHO and CO conversion. Orbital analysis reveals that methane activation over h-BN in presence of dioxygen follows a standard hydrogen atom transfer mechanism. Chapter 5 is related to the mechanastic investigation of zinc, palladium and titanium-catalysed reduction of carbonyl moetites using a boron containing compound HBpin. In zinc-mediated reaction, DFT studies reveal three different mechanism for the reduction of aldehyde. A six-membered transition state is key stationary point in the potential energy surface. In palladium-catalysed reaction, computations unravlled that HBpin shows dual role during the reaction. In rate determining step, while HBpin acts as a hydride donor, it also plays the role of a carbonyl species receiver to transfer the hydride from Pd to the carbonyl carbon. The titanium catalyst reduces the ester molecule and DFT studies reveal that the rate-limiting step is the cleavage of the C–O bond of an ester.Chapter 6 presents two distinct problems. The first problem involves a metal-free borylation reaction of α‑naphthamides and phenylacetic acid molecules in presence of BBr3. In this work, α‑naphthamides contain C2 and C8 positions through which the reaction can proceed. The computations show that borylation at the C8 position of α‑naphthamides is preferred over the C2 position. Moreover, in case of phenylacetic acid, the computations unveil that the overall activation barrier is affordable if the bulky substituents at the nitrogen and α-position of phenyl acetamide are present. The second problem focuses on the computation of a green process for the synthesis of α- aminophosphonates, through the reaction of aldehydes, amines, and phosphine oxide in the presence of an indium complexe. The calculations demonstrated that barrier-less transition states play a crucial role in the reaction, so such transition states should not be ignored. The computations also unraveled the fact that in place of phosphine oxide, its tautomerized species phophinous acid takes part in the reaction.