Aggregation Effects in Visible‐Light Flavin Photocatalysts: Synthesis, Structure, and Catalytic Activity of 10‐Arylflavins. Issue 3 (29th November 2012)

• Record Type: Journal Article
• Authors: Daďová, Jitka; Kümmel, Susanne; Feldmeier, Christian; Cibulková, Jana; Pažout, Richard; Maixner, Jaroslav; Gschwind, Ruth M.; König, Burkhard; Cibulka, Radek
• Is Part Of: Chemistry. Volume 19:Issue 3(2013)
• Page Start: 1066
• Page End: 1075
• Publication Date: 2012-11-29
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201202488
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>A series of 10‐arylflavins (10‐phenyl‐, 10‐(2′, 6′‐dimethylphenyl)‐, 10‐(2′, 6′‐diethylphenyl)‐, 10‐(2′, 6′‐diisopropylphenyl)‐, 10‐(2′‐<italic>tert</italic>‐butylphenyl)‐, and 10‐(2′, 6′‐dimethylphenyl)‐3‐methylisoalloxazine (<bold>2 a</bold>–<bold>f</bold>)) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with <sup>1</sup>H‐DOSY NMR spectroscopic experiments in CD<sub>3</sub>CN, CD<sub>3</sub>CN/D<sub>2</sub>O (1:1), and D<sub>2</sub>O confirm the decreased ability of 10‐arylflavins <bold>2</bold> to form aggregates relative to tetra‐<italic>O</italic>‐acetyl riboflavin (<bold>1</bold>). 10‐Arylflavins <bold>2 a</bold>–<bold>d</bold> do not interact by π–π interactions, which are restricted by the 10‐phenyl ring oriented perpendicularly to the isoalloxazine skeleton. On the other hand, N3H⋅⋅⋅O hydrogen bonds were detected in their crystal structures. In the structure of 10‐aryl‐3‐methylflavin (<bold>2 f</bold>) with a substituted N3 position, weak CH⋅⋅⋅O bonds and weak π–π interactions were found. 10‐Arylflavins <bold>2</bold> were tested as photoredox catalysts for the aerial oxidation of 4‐methoxybenzyl alcohol to the corresponding aldehyde (model reaction), thus showing higher efficiency relative to <bold>1</bold>. The quantum yields of 4‐methoxybenzyl alcohol oxidation reactions mediated by arylflavins <bold>2</bold> were higher by almost one order of magnitude relative to values in the presence of <bold>1</bold>.</p> </abstract>