Structure and Conformation of Novel BODIPY Ugi Adducts

• DOI: 10.1002/open.202200197
• Publication Date: 2022-10-26T03:17:29Z
• Authors: Ismael Javier Arr...; Gonzalo Gamboa‐Ve...; Claudia Gabriela ...; Marco A. Leyva‐Ra...; María Teresa Cort...; Marco A. García‐R...; Diana E. Ramírez‐...; Eduardo Peña‐Cabrera; Eusebio Juaristi
• Keywords: BODIPY; Ring flip; Chemical shift

Abstract Two novel BODIPY‐Ugi (boron dipyrromethene) adducts exhibit peculiar room temperature (T=20 °C) H‐1 NMR spectra in that several protons located at the aromatic aniline‐type ring are lost baseline. This observation revealed existence of a dynamic conformational process where rotation around C−N bond is hindered. Variable‐temperature and C‐13 spectroscopic analysis confirmed this conclusion; is, low‐temperature show distinct signals for all four below coalescence, whereas average recorded above coalescence (T=+120 °C). Particularly interesting was rather large difference chemical shifts ortho Δδ=1.45 ppm, which explained based on DFT computational analysis. Indeed, calculated lowest‐energy gas‐phase conformation BODIPY Ugi locates one half shielding anisotropic cone bridge phenyl segment. contrast to solid‐state established by X‐ray diffraction shows nearly parallel arrangement rings, probably induced crystal packing forces.