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Aggregation Effects in Visible‐Light Flavin Photocatalysts: Synthesis, Structure, and Catalytic Activity of 10‐Arylflavins
Author(s) -
Daďová Jitka,
Kümmel Susanne,
Feldmeier Christian,
Cibulková Jana,
Pažout Richard,
Maixner Jaroslav,
Gschwind Ruth M.,
König Burkhard,
Cibulka Radek
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202488
Subject(s) - chemistry , flavin group , catalysis , crystal structure , aryl , alcohol , photochemistry , ring (chemistry) , aldehyde , medicinal chemistry , hydrogen bond , crystallography , stereochemistry , molecule , organic chemistry , alkyl , enzyme
A series of 10‐arylflavins (10‐phenyl‐, 10‐(2′,6′‐dimethylphenyl)‐, 10‐(2′,6′‐diethylphenyl)‐, 10‐(2′,6′‐diisopropylphenyl)‐, 10‐(2′‐ tert ‐butylphenyl)‐, and 10‐(2′,6′‐dimethylphenyl)‐3‐methylisoalloxazine ( 2 a – f )) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with 1 H‐DOSY NMR spectroscopic experiments in CD 3 CN, CD 3 CN/D 2 O (1:1), and D 2 O confirm the decreased ability of 10‐arylflavins 2 to form aggregates relative to tetra‐ O ‐acetyl riboflavin ( 1 ). 10‐Arylflavins 2 a – d 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, N3H⋅⋅⋅O hydrogen bonds were detected in their crystal structures. In the structure of 10‐aryl‐3‐methylflavin ( 2 f ) with a substituted N3 position, weak CH⋅⋅⋅O bonds and weak π–π interactions were found. 10‐Arylflavins 2 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 1 . The quantum yields of 4‐methoxybenzyl alcohol oxidation reactions mediated by arylflavins 2 were higher by almost one order of magnitude relative to values in the presence of 1 .