This review aims to look past tris(pentafluorophenyl)borane to its halogenated triarylborane siblings, to give a greater understanding as to how modification to their aryl rings can lead to improved reactivity.

This year marks the 350th anniversary of the discovery of phosphorus by the alchemist Hennig Brand. However, this element was not included in the p-block of the periodic table until more recently. 2019 also marks the 150th anniversary of the preliminary tabular arrangement of the elements into the periodic system by Mendeleev. Of the 63 elements known in 1869, almost one-third of them belonged to what ultimately became the p-block, and Mendeleev predicted the existence of both gallium and germanium as well. The elements of the p-block have a disparate and varied history. Their chemical structure, reactivity, and properties vary widely. Nevertheless, in recent years, a better understanding of trends in p-block reactivity, particularly the behavior of those elements not typically found in biological systems, has led to a promising array of emerging applications, highlighted herein.

As main-group chemistry, in particular boron chemistry, has expanded and developed over the past 20 years, one reagent has risen to prominence as well. Tris(pentafluorophenyl)borane, B(CF) (commonly known as BCF), has demonstrated extensive applications in a wide variety of reactions, including borylation, hydrogenation, hydrosilylation, frustrated Lewis pair (FLP) chemistry, Lewis acid catalysis, and more. The high Lewis acidity of B(CF) is derived from the electronic effects of its three CF rings, rendering it a versatile reagent for a great number of reactions. In addition, the steric bulk of these rings also allows it to function as the Lewis acid in a FLP, granting this reagent yet another synthetically useful application. However, as main-group chemistry continues to evolve as a field, new reagents are required that go beyond BCF, increasing not only the range of reactions available but also the breadth of compounds attainable. Great strides have already been made in order to accomplish this task, and this review will highlight modern advances in boron chemistry relating to borylation reactions. Herein, we will show the recent uses of B(CF) in borylation reactions while also focusing on current advances in novel borane and borocation usage that eclipses that of the stalwart B(CF).

Contents 1. Introduction………………………………………………………………………………………………... 1 2. Group 2-catalyzed Mannich reactions…………………………………………………………………...... 3 3. Group 2-catalyzed 1,4-addition reactions…………………………………………………………………. 5 4. Silylation of ketones and imines…………………………………………………………………………... 8 5. Hydrogenation reactions using group 13 Lewis acids and frustrated Lewis pairs…………………………12 6. Hydroamination reactions with s-block elements………………………………………………………… 14 7. Aluminum-centered catalysts in phosphonylation reactions……………………………………………… 17 8. Domino reactions…………………………………………………………………..……………………….21 9. Conclusions……………………………………………………………………………………………….. 24 This review highlights a number of recent developments in the field of main group enantioselective catalysis. Many essential transformations can be effected catalytically such as hydrosilylation, hydroamination and hydrogenation reactions, amongst others, in an asymmetric fashion using earth abundant sand p-block elements such as calcium, strontium, boron and aluminum. Recent work in this area has shown that these systems are not only active in catalysis but may also have the potential to compete with transition metal based systems with the reduced cost and toxicity often associated with main group chemistry. Keywords: enantioselective main group catalysis chiral asymmetric | 7 Scheme 8. Catalytic malonate addition reaction using calcium PyBOX complex [66]. Scheme 9. Proposed catalytic cycle of calcium-catalyzed addition reaction to nitro-styrene [66].

Dehydrocoupling reactions, i.e. reactions involving elimination of H2 between two E-H bonds, provide a clean route to E-E bonds within the main group. The products afforded from these reactions have applications in organic synthesis and materials chemistry, and in addition the H2 released during these reactions can also be useful as an energy source. Previous methods for dehydrocoupling involve both thermal and transition metal catalysed routes but recent developments have shown that main group compounds can be used as catalysts in these reactions. This tutorial review will focus on the development of main group catalysed dehydrocoupling reactions as a route to heteronuclear element-element bonds.