304-28-9Relevant articles and documents
Stereoselective Postassembly CH Oxidation of Self-Assembled Metal-Ligand Cage Complexes
Holloway, Lauren R.,Bogie, Paul M.,Lyon, Yana,Julian, Ryan R.,Hooley, Richard J.
, p. 11435 - 11442 (2017)
Self-assembled Fe-iminopyridine cage complexes containing doubly benzylic methylene units such as fluorene and xanthene can be selectively oxidized at the ligand backbone with tBuOOH, with no competitive oxidation observed at the metal centers. The self-assembled cage structure controls the reaction outcome, yielding oxidation products that are favored by the assembly, not by the reactants or functional groups. Whereas uncomplexed xanthene and fluorene control ligands are solely oxidized to the ketone equivalents with tBuOOH, the unfavorability of the self-assembled ketone cages forces the reaction to form the tbutyl peroxide and alcohol-containing oxidation products, respectively. In addition, the oxidation is diastereoselective, with only single isomers of the cage assemblies formed, despite the presence of as many as 10 stereocenters in the final product. The self-assembled structures exploit self-complementary hydrogen bonding and geometrical constraints to direct the postassembly reactions to outcomes not observed in free solution. This selectivity is reminiscent of the fine control of post-translational modification seen in biomacromolecules.
Tetraguanidino-functionalized phenazine and fluorene dyes: Synthesis, optical properties and metal coordination
Bindewald, Elvira,Lorenz, Roxana,Hübner, Olaf,Brox, Dominik,Herten, Dirk-Peter,Kaifer, Elisabeth,Himmel, Hans-J?rg
, p. 3467 - 3485 (2015/03/05)
In this work the first phenazine derivatives with guanidino substituents were prepared and their structural and electronic properties studied in detail. The guanidino groups decrease the HOMO-LUMO gap, massively increase the quantum yield for fluorescence and offer sites for metal coordination. The yellow-orange colored 2,3,7,8-tetraguanidino-substituted phenazine shows intense fluorescence. The wavelength of the fluorescence signal is strongly solvent dependent, covering a region from 515 nm in Et2O solution (with a record quantum yield of 0.39 in Et2O) to 640 nm in water. 2,3-Bisguanidino-substituted phenazine is less fluorescent (maximum quantum yield of 0.17 in THF), but exhibits extremely large Stokes shifts. In contrast, guanidino-functionalized fluorenes emit only very weakly. Subsequently, the influence of coordination on the electronic properties and especially the fluorescence of the phenazine system was analysed. Coordination first takes place at the guanidino groups, and leads to a blue shift of the luminescence signal as well as a massive decrease of the luminescence lifetime. Luminescence is almost quenched completely upon CuI coordination. On the other hand, in the case of ZnII coordination the fluorescence signal remains strong (quantum yield of 0.36 in CH3CN). In the case of strong zinc Lewis acids, an excess of metal compound leads to additional coordination at the phenazine N atoms. This is accompanied by significant red-shifts of the lowest-energy transition in the absorption and fluorescence spectra. Pentanuclear complexes with two phenazine units were isolated and structurally characterized, and further aggregation leads to chain polymers. This journal is
Selective Preparation of Fluorene Derivatives Using the t-Butyl Function as a Positional Protective Group
Kajigaeshi, Shoji,Kadowaki, Toshiya,Nishida, Akiko,Fujisaki, Shizuo
, p. 97 - 104 (2007/10/02)
Several 4-substituted 2,7-di-t-butylfluorene derivatives (3) were prepared by electrophilic substitutions of 2,7-di-t-butylfluorene (1). 4-Substituted fluorene (4), such as 4-bromo- (4a), 4-methyl (4e), and 4-aacetylaminofluorene (4j), were obtained by the trans-t-butylations of 3.Although we attempted to synthesize 1,8-disubstituted fluorene from 3,6-di-t-butylfluorene (2) which was derived from 2,2'-diiodo-4,4'-di-t-butyldiphenylmethane (5), by the same methods, we obtained only 2,7-disubstituted fluorene derivatives (8); it turned out electrophilic substitutions of 2 gave 2,7-disubstituted 3,6-di-t-butylfluorene derivatives.
