Cationic Cobalt Porphyrin-Catalyzed Allylation of Aldehydes with Allyltrimethylsilanes.

Cationic cobalt porphyrin-catalyzed allylation of aldehydes with allyltrimethylsilanes is developed. The formation of the aldehyde-cobalt porphyrin complex, the key intermediate for the addition of allylsilanes, is confirmed by theoretical studies and synchrotron-based X-ray absorption fine-structure measurements. Facile dissociation of the product by allylation from the cobalt complex regenerates the active complex with the aldehyde. The readily obtainable [Co(TPP)]SbF6 complex serves as an efficient catalyst for this allylation.

Asymmetric Aza-Diels-Alder Reaction with Ion-Paired-Iron Lewis Acid-Brønsted Acid Catalyst.

The development and use of a multiple-activation catalyst with ion-paired Lewis acid and Brønsted acid in an asymmetric aza-Diels-Alder reaction of simple dienes (non-Danishefsky-type electron-rich dienes) was achieved by utilizing the [FeBr2 ]+ [FeBr4 ]- combination prepared in situ from FeBr3 and chiral phosphoric acid. Synergistic effects of the highly active ion-paired Lewis acid [FeBr2 ]+ [FeBr4 ]- and a chiral Brønsted acid are important for promoting the reaction with high turnover frequency and high enantioselectivity. The multiple-activation catalyst system was confirmed using synchrotron-based X-ray absorption fine structure measurements, and theoretical studies. This study reveals that the developed catalyst promoted the reaction not only by the interaction offered by the ion-paired Lewis acid and the Brønsted acid but also noncovalent interactions.

FeCl3 as an Ion-Pairing Lewis Acid Catalyst. Formation of Highly Lewis Acidic FeCl2+ and Thermodynamically Stable FeCl4- To Catalyze the Aza-Diels-Alder Reaction with High Turnover Frequency.

The aza-Diels-Alder reaction of nonactivated dienes and imines was realized through the action of the ion-paired Lewis acid catalyst [FeCl2]+[FeCl4]- generated by the in situ disproportionation of FeCl3. The uniquely high reactivity of [FeCl2]+[FeCl4]- was attributed to both the highly Lewis acidic FeCl2+ and thermodynamically stable FeCl4- acting as an ion-paired catalyst. Synchrotron-based X-ray absorption fine structure measurements provided fundamental insights into the disproportionation and structure of the resulting ion-paired iron complex. A theoretical study was performed to analyze the catalytic reaction and better understand the "ion-pairing effect" which transforms simple FeCl3 into a high turnover frequency Lewis acid catalyst in the aza-Diels-Alder reaction of nonactivated dienes and imines.