Mechanistic insights into the Nb2O5 and niobium phosphate catalyzed in situ condensation of a fluorescent halochromic assembly

Abstract

[EN] Solid niobium oxides (Nb2O5 center dot nH(2)O) and niobium phosphate were used as heterogeneous acid catalysts to promote the condensation between a switchable oxazine and a fluorescent coumarin in an aprotic solvent. The catalysts were found to promote the generation of an active methylene from the enamine-based portion of the oxazine, which was followed by a nucleophilic attack on the aldehyde functionality of the coumarin reagent. In the resulting system, the emission of the conjugated fluorophore can be observed at 670 nm and, thus, the processes occurring at the catalyst surface can be monitored in real time by total internal reflection fluorescence microscopy (TIRFM). ; The authors wish to thank the Natural Sciences and Engineering Research Council (NSERC) and the Canada Research Chairs program. The University of Ottawa International Office provided grants to study niobium. Thanks are due to the Government of Canada and NSERC for a Banting Postdoctoral Fellowship to S. Impellizzeri and a Vanier Scholarship to C. Fasciani. S. Simoncelli acknowledges a DFAIT fellowship from ELAP (Emerging Leaders in the Americas Program) to support her visit to Canada. M. L. Marin thanks the financial support of the Generalitat Valenciana (BEST/2012/233) and the Distinguished Visiting Professor program of the University of Ottawa. We thank Dr. Jose-Carlos Netto-Ferreira of INMETRO (Rio de Janeiro, Brazil) for providing chemicals from CBMM. ; Impellizzeri, S.; Simoncelli, S.; Fasciani, C.; Marín García, ML.; Hallett-Tapley, GL.; Hodgson, GK.; Scaiano, JC. (2015). Mechanistic insights into the Nb2O5 and niobium phosphate catalyzed in situ condensation of a fluorescent halochromic assembly. Catalysis Science and Technology. 5(1):169-175. https://doi.org/10.1039/C4CY00703D ; S ; 169 ; 175 ; 5 ; 1