Triarylborane Lewis acids with indole or phenol group: B/H hybrid receptors for fluoride
摘要:
Triarylboranes bearing an indole ((indol-7-yl)Mes(2)B, 1) or phenol ((phenol-2-yl)Mes(2)B, 2) group were prepared and characterized as a novel class of boron/hydrogen bond (B/H) hybrid receptors for fluoride. X-ray crystal structures revealed the presence of proximal X-H bond (X = N, O) to the trigonal boron center. UV/Vis absorption titrations of 1 and 2 with fluorides resulted in the corresponding fluoride adduct with high binding constants (4.0 x 10(7) M-1 in DMSO for 1 and 3.0 x 10(7) M-1 in THF for 2). Comparative fluoride binding experiments with the triarylboranes lacking an X-H bond showed the enhanced fluoride binding affinity of 1 and 2 with an increase of one order of magnitude. H-1 NMR spectroscopic titrations confirmed that the dative B-F interaction was assisted by X-H center dot center dot center dot F hydrogen bonding. (C) 2014 Elsevier B.V. All rights reserved.