Artificial Chiral Trinuclear Zn Catalysts: Design, Self-Assembly and Unprecedented Efficiency in Asymmetric
Jingxi He1, Shuxin Jiang1, Yu Qiu1
1State Key Laboratory of Organometallic Chemistry and Shanghai Hongkong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
Abstract:
The development of artificial catalysts with efficiency that can rival those of Nature's enzymes represents one of the foremost yet challenging goals in homogeneous metal catalysis. Inspired by the exceptional performance of metalloenzymes, the design and development of highly efficient bi/multinuclear catalysts via judicious ligand design, by taking advantage of the cooperative action of the proximal catalytic sites, has attracted great attention. Herein, we report the self-assembly of a chiral hexadentate BINOL-dipyox ligand with zinc acetate into a well-defined trinuclear zinc complex, which demonstrated ultrahigh catalytic productivity in the enantioselective hydroboration of ketones with an unprecedented turnover number (TON) of 19,400 at an extremely low catalyst loading (0.005 mol %). Mechanistic investigations reveal that a cooperative Lewis acid activation mode is operating in the catalytic process, hence, underscoring the unique advantages of the trinuclear architecture.
More Related Videos
Related Concept Videos
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
02:36Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:05Prochirality
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.