Sustainable catalysis using iron based catalysts for hydrofunctionalization of c=x (x = o, n) unsaturated bonds
Transition metal complexes are capable of catalyzing organic transformations with exceptional efficiency and are rightly considered as indispensable tools in organic synthesis. High catalytic activity (especially at low catalyst loadings), selectivity, and stability are some of the important benchmarks used in assessing the performance of a transition metal catalyst. Generally, choosing an appropriate ligand helps in meeting the above criteria, moreover rational changes in the ligand structure can result in modification of the catalytic properties of the metal center. Therefore binding of a well-designed ligand system to the metal center, gives the opportunity to vary the metal properties in a controlled manner. Most of the protocols used in organic transformations are carried out in the presence of noble metals. The price of the noble metals is almost 1000 times higher than that of the nonprecious metals, which has a direct effect on the price of the products synthesized with these catalysts. Therefore, the replacement of these catalysts with earth abundant cheap alternatives like iron is highly demanded. Iron has been known for a long time as a catalyst for physiological (hemoglobin) and large scale industrial process such as the Haber process for ammonia production, but it is significantly underdeveloped in homogeneous catalysis as compared to other transition metals. Over the last two decades, remarkable breakthroughs have been made in the development and applications of iron catalysis: many of the transformations achieved with noble metals can now be performed with iron‐based catalysts, allowing bond constructions without the use of costly precursors. Pincer ligands are one of the most successful ligand design currently known and their precious metal complexes have been the focus of various stoichiometric as well as catalytic studies. Motivated by increased research efforts in the area of base-metal catalysis using metal-ligand cooperativity, we wanted to examine the catalytic efficiency of novel iron and cobalt based pincer complexes in hydrosilylation of aldehydes and ketones. Within the field of organic chemistry, the carbonyl moiety is central to many broadly used synthetic modifications and fragment coupling steps, including Grignard reactions and Wittig olefinations. Hydrosilylation protocols to reduce carbonyl compounds have recently emerged as attractive complements to traditional methods that employ molecular hydrogen and hydride transfer reagents. In the first part of this dissertation, we describe synthesis, characterization and their ablility to catalytically reduce carbonyl moieties via hydrosilylation technology. In the second and third part of this dissertation we report the catalytic applications of BIAN (bis-(arylimino) acenaphthene) based iron complexes for the hydrosilylation of aldimines. Conversion of aldimines into amines is one of the most important chemical reactions in synthetic organic chemistry. Amines have been widely used for the production of bulk and fine chemicals, such as dyes, agrochemicals, pharmaceuticals, pesticides, and polymers. This catalytic system was also applicable for hydroboration of a range of aldehydes, ketones and aldimines. With this work, we have demonstrated the versatility of pincer and BIAN based iron complexes in the emerging field of research using homogeneous iron catalysis.