Organic Superbases in Catalytic Antimony-Carbon Bond Formation and Frustrated Lewis Pair Hydrogenation of Imines.

Organic bases are essential tools used in synthetic chemistry, but many are considered weak compared to their inorganic or metalorganic counterparts, mainly when abstracting weakly acidic protons. However, organic bases have been developed to exhibit stronger Brønsted basicity and increased structural diversity, expanding their application range. Notably, with the development of 1,8-bis-dimethylaminonapthalene (DMAN), also known by its more common trade name, Proton Sponge, organic bases have gained a metric of basicity and activity that many now refer to as super-basicity for organic bases. Organic superbases offer several advantages, including reversible protonation and the formation of conjugate acid-ion pairs, which enable metal-free catalysis that is more environmentally friendly. They also demonstrate increased solubility in most organic solvents compared to inorganic bases and can be structurally tuned to adjust their steric and electronic properties. In this work, we report the use of organic superbases in the synthesis of various organometallic antimony compounds via catalyzed antimony-carbon bond formation protonolysis. Using electron-deficient stibines such as Sb(C6F5)3 and weakly acidic aromatic, heteroaromatic, and terminal alkyne compounds as substrates, we selectively formed a range of new aromatic, heteroaromatic, as well as alkynyl-substituted stibines, using C6F5 as a leaving group, with liberation of C6HF5 upon formal proton transfer. Kinetic studies were performed to gain mechanistic insights, and DFT calculations suggest a possible reaction pathway wherein the base catalyst activates the Sb-C bond through secondary bond interactions. Organic superbases are also valuable in frustrated Lewis pair (FLP) catalysis, where they act as a strong base component when paired with weakly Lewis acidic aryl-9-borabicyclo[3.3.1]nonane (aryl-9-BBN) compounds. We report the catalytic hydrogenation of a wide range of functionalized imines through the cooperative use of aryl-9-BBN compounds and organic superbases, along with spectroscopic studies that examine their interactions.