Further investigation on the nitration of BODIPY with cupric nitrate: crystal structures of 4,4-difluoro-1,3,5,7,8-pentamethyl-2-nitro-4-bora-3a,4a-diaza-s-indacene, 4,4-difluoro-3-nitro-8-phenyl-4-bora-3a,4a-diaza-s-indacene, and 3-chloro-6-ethyl-5,7,8-trimethyl-2-nitro-4,4-diphenyl-4-bora-3a,4a-diaza-s-indacene

Abstract

The treatment of non-fully substituted 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with cupric nitrate leads to the introduction of a nitro group at different positions of the BODIPY core, depending on the substitution pattern. This methodology complements the treatment of fully substituted BODIPY with cupric nitrate that was previously reported. The crystal structures of 4,4-difluoro-1,3,5,7,8-pentamethyl-2-nitro-4-bora-3a,4a-diaza-s-indacene, C14H16BF2N3O2 (5a) 4,4-difluoro-3-nitro-8-phenyl-4-bora-3a,4a-diaza-s-indacene, C15H10BF2N3O2 (5b) and 3-chloro-6-ethyl-5,7,8-trimethyl-2-nitro-4,4-diphenyl-4-bora-3a,4a-diaza-s-indacene, C26H25BClN3O2 (5d) are presented. In all three structures, the fused ring system is in a very flattened `V-shape', with dihedral angles between the two outer five membered rings of 8.12 (14), 6.67 (9) and 12.30 (18) Å for 5a, 5b and 5d, respectively. In each case, the central six-membered ring is in a flattened sofa conformation. In the crystal of 5a, molecules are linked by weak C—H...O and C—H...F hydrogen bonds forming sheets parallel to (10-1). In the crystal of 5b molecules are linked by weak C—H...O and C—H...F hydrogen bonds and π–π interactions forming sheets parallel to (001). In the crystal of 5d, weak C—H...O hydrogen bonds link molecules into chains along [001]. In compound 5d, the atoms of the nitro group were refined as disordered over two sets of sites with occupancies 0.618 (12) and 0.382 (12).