Experimental and theoretical views on catalytic silver chemistry
Over the past decades, transition metal catalysis have become an important and the frontier research direction of synthetic organic chemistry. The outer d orbitals of transition metal ions are incompletely filled with electrons, thus they can give and take electrons. This creates transition metals prime candidates for catalysis, so we have to study specific transition metals to establish unique catalysis. Generally, transition metal with variable oxidation states and its strong coordination (for example, rhodium, ruthenium, palladium, iridium, copper, gold, etc.) occupies the prominent position. These metals have high catalytic activity and are commonly used to catalyze various organic transformations; but, the low coordinating transition metals having invariable valence exhibit low catalytic activity. Although, these kinds of metals exhibit unique catalysis, it is very difficult to establish catalytic reactions of those metals. Therefore, it is highly desirable to explore the catalytic potential of such metals
Silver is such a type of transition metal with the outer most electronic configuration 4d105s1. Based on the electronic structure and orbital characteristics, silver is the only transition metal that exist in a stable mono positive oxidation state and have certain similarities to proton. The organo silver reagents are usually used as acid equivalents; the organic silver intermediates are unstable and prone to undergo proto desilveration. Silver reagents are nontoxic and less expensive than other precious noble metals, behave like protons, and are stable under ambient conditions. Generally, silver salts are mostly utilized as either σ-Lewis acid or π-Lewis acid. They are also employed as cocatalysts, halophiles, general oxidants, SET oxidants, weak bases, and radical precursors. However, the development of catalytic silver chemistry remains very scarce, and also lacks the deeper understanding of the role of silver in synthetic chemistry. Therefore, establishing a unique silver-catalyzed reaction system and enlightening its catalytic principle is an important and difficult issue in the study of transition metal catalysis. Over the past ten years, Bi’s research group has focused on the exploration of the catalytic performance of silver and has performed systematic and in-depth research on the many silver-catalyzed organic transformations, including in the perspective of theoretical context. Particularly, his work has focused on the catalytic activation of alkynes and carbene carbon by silver and has achieved innovative research results, including proposed the catalytic σ-activation strategy for alkyne, established a silver-catalyzed alkyne hydroazidation reaction and further applied this strategy in multi-component reaction for accessing N-containing compounds, which was internationally christened as “Bi’s Ag(I) catalysed hydroazidation methodology”. Moreover, proposed the activation of carbene carbon through a weak coordination concept of silver, developed silver-catalyzed reaction between isonitrile and silver carbene using sulfonylhydrazone as a precursor, which allows the development of a series of silver-catalyzed carbene reactions. Based on the theoretical results, it has proposed that the proton-like nature and weak coordination activation of silver, which creates a new perception of silver catalysis.