Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins

• Published in: European journal of organic chemistry Vol. 2019; no. 14; pp. 2448 - 2452
• Main Authors: Kielmann, Marc, Grover, Nitika, Kalisch, Werner W., Senge, Mathias O.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 16.04.2019
• Subjects: Basicity; Catalysis; Catalytic activity; Correlation analysis; Density functional theory; Hydrogen bonds; Macrocycles; Molecular engineering; Organocatalysis; Porphyrins
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201801691

To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β‐ethyl substitution (“H2EtxTPPs” 1–6; x = 0, 2, 4, 6, 8) was applied in organocatalyzed reactions. The macrocycles display incrementally increasing nonplanarity due to repulsive peri‐interactions. This creates an out‐of‐plane vector and better accessibility of the core amine and imine groups as the number of alkyl substituents increases. Following such a molecular engineering approach, the inner core system could be used to activate small molecules as a result of significant saddle distortion. The potential organocatalyst “H2EtxTPPs” were used in benchmark sulfa‐Michael reactions and we found a distinct relationship between nonplanarity and conversion. These observations were attributed to the combined effect of enhanced basicity and increased H‐bonding potential that could facilitate bifunctional organocatalysis. Ultimately, density functional theory (DFT) calculations were performed on 1–6 to monitor some electronic properties of the title compounds. To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β‐ethyl substitution was applied in organocatalyzed reactions. This was aided by DFT calculations in order to explain the distinct relationship between distortion and catalytic competence.