title: Aggregation effects in visible-light flavin photocatalysts: synthesis, structure, and catalytic activity of 10-arylflavins.
abstract: 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, N3-H⋅⋅⋅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 C-H⋅⋅⋅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.
authors.affiliation: Institute of Organic Chemistry, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany.
authors.forename: Jitka
authors.initials: J
authors.lastname: Daďová
authors.forename: Susanne
authors.initials: S
authors.lastname: Kümmel
authors.forename: Christian
authors.initials: C
authors.lastname: Feldmeier
authors.forename: Jana
authors.initials: J
authors.lastname: Cibulková
authors.forename: Richard
authors.initials: R
authors.lastname: Pažout
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Maixner
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Gschwind
authors.forename: Burkhard
authors.initials: B
authors.lastname: König
authors.forename: Radek
authors.initials: R
authors.lastname: Cibulka
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D005415:Flavins / Q000138:chemical synthesis* / Q000737:chemistry*; D008027:Light; D008958:Models, Molecular; D015394:Molecular Structure; D055668:Photochemical Processes
chemical_list: D005415:Flavins