Applications of Catalysis in Hydroboration and Hydrosilylation of Unsaturated Organic Molecules

Transition metal catalysis is a powerful methodology now widely used in both academia and industry in the transformation of organic molecules into value-added materials. The advantages of any catalyzed reaction over an uncatalyzed one typically includes a measure of control over regio, chemo-, and stereoselectivity. Precious metals, such as Platinum (Pt), Palladium (Pd), Rhodium (Rh), Ruthenium (Ru), and Iridium (Ir), have been the frontiers of new achievements and breakthroughs in catalysis for decades; however, one major drawback associated with employing precious metals in industrial applications would be the excessive cost and limited availability. Nevertheless, base metal catalysis has seen an explosion of interest in recent times as “greener” alternatives for similar applications. The growth in all these strategies can be attributed to the low toxicity, relatively lower costs of operation, and inherent sustainability associated with such an approach. First-row transition metals are prone to single electron transfer, which can often lead to non-productive side reactions, limiting catalytic efficiency. Several novel approaches have been explored to help circumvent this shortcoming. For example, metal-ligand cooperativity has played a significant role in enabling first-row transition metal catalysis to undergo two-electron reaction processes. Catalysis can be broadly divided into distinct categories including homogenous catalysis, heterogeneous catalysis, organocatalysis and, enzymatic catalysis. Hydroboration and hydrosilylation are examples of homogenous catalysis that have been explored for several years. In these reactions, the boron or silicon containing group function as a functional handle to form a new carbon–carbon bond or to introduce functional groups such as alcohols, amides, amines, or halogens. The first section of this dissertation focuses on the catalytic hydroboration of imines, nitriles, and carbodiimides as a powerful method of preparing amines. Initial developments in catalytic hydroboration of imines and nitriles employed precious metals and typically required harsh reaction conditions. More recent advances have shifted toward the use of base metal and main group element catalysis and milder reaction conditions. The TON and TOF of imine hydroboration catalysts are reported with a brief overview of recent advances in this field. The second part of this dissertation describes the catalytic hydroboration of imines and nitriles using dppBIANFe(Tol) as precatalyst and hydroboration of esters using a lanthanum-based catalyst in the presence of HBpin. Secondary amines obtained from imine/nitrile hydroboration are key synthetic intermediates in the synthesis of bactericides, herbicides, rubber accelerators and many clinically applied drugs. The hydroboration of carbonyl groups of esters into the corresponding alcohols is also a potentially industrially important transformation to construct the synthetic building blocks of fine chemicals. The third part of this dissertation discusses the hydrosilylation catalysis of amides using a recyclable zinc catalyst. A metalla-GAP strategy (GAP = Group-Assisted-Purification) is used in homogeneous catalysis, which allows simple recovery and re-use of homogeneous metal catalyst. By making homogenous catalysts recyclable or by designing systems that facilitate better separability the key advantage of heterogenous catalysis can be incorporated into homogenous systems. The m-GAP strategy is further expanded to the reduction of ketones using the recyclable zinc catalyst. The final part of this dissertation deals with the base metal catalyzed cross-coupling reactions. Several base metal salts are investigated in Suzuki–Miyaura coupling catalysis in conjugation with a nitrogenous ligand. The reaction condition optimized using Ni(COD)2 as the base metal catalyst and 2,2’- Bipyridine as the ligand. A recyclable Chan−Evans−Lam coupling catalyst is also designed by incorporating a phosphoramide motif in the presence of a copper salt_Cu(OAC)2. Inspired by group-assisted purification ligand, this catalytic system designed to facilitate better separability by simple filtration.

Embargo status: Restricted until 06/2024. To request the author grant access, click on the PDF link to the left.