Synthesis and photochemical reactivity of bilirubin model compounds

Intermolecularly Hydrogen-Bonded Dimeric Helices. Tripyrrindiones

A rare and unusual class of tripyrrolic compounds, violet-colored tripyrrin-1,14-diones, can be prepared easily and in moderately high yields from base (piperidine)-catalyzed condensation of 3-pyrrolin-2-ones with 2,5-diformylpyrroles. Dipyrrinones adopt the all syn-Z conformation leading to helical, lock-washer like structures, which form dimers that are held together by intermolecular hydrogen bonds in nonpolar solvents and in the crystal. Strong bathochromic spectral shifts of the tripyrrindione approximately 480 nm long wavelength UV-visible absorption band are seen with added base: DBU, 615 nm; TFA, 573 nm; and Zn (OAc)(2), 586 nm.

2-pyrrolylthiones as monoanionic bidentate N,S-chelators: synthesis and molecular structure of 2-pyrrolylthionato complexes of nickel(II), cobalt(III), and mercury(II)

The metal-chelating ability of 2-pyrrolylthiones is described. The readily available ligands di-2-pyrrolyl thione (6), 2-thioacetylpyrrole (10), and 2-thiobenzoylpyrrole (11) constitute examples of monoanionic ligands with N,S-donor atom sets, although di-2-pyrrolyl thione (6) could theoretically also achieve chelation through an N,N-donor set. A square planar Ni(II) complex, 14, an octahedral Co(III) complex, 18, and a tetrahedral Hg(II) complex, 17, with the di-2-pyrrolyl thionato chelate have been prepared, and their structures have been characterized by 1H NMR, UV-vis, MS, IR, elemental analysis, and single-crystal X-ray diffraction. Crystal data for 14: C18H14N4NiS2.0.28H2O, trigonal, R3, a = 18.467(1) A, b = 18.467(1) A, c = 26.404(2) A, V = 7797(1) A3; Z = 18, R = 3.2%. Crystal data for 18-mer: C27H21CoN6S3.C3H6O (acetone), monoclinic, P21/n, a = 9.569(1) A, b = 23.152(1) A, c = 13.659(1) A, beta = 100.882(8) degrees, V = 2971.6(5) A3, Z = 4, R = 4.3%. Crystal data for 17: C18H14HgN4S2, triclinic, P1, a = 8.443(2), b = 14.278(1) A, c = 7.445(1) A, alpha = 90.561(9) degrees, beta = 97.64(1) degrees, gamma = 104.250(9) degrees, V = 861.3(2) A3, Z = 2, R = 4.2%. The bond lengths and angles of these metal complexes are comparable to those of known N,S-chelates. A comparison of the structural parameters of the ligand in the metal complexes with those for the free ligand 6 demonstrates the preorganization of the free ligand for complexation and demonstrates the spectator role of the noncoordinating pyrrolic unit. Chelation of Ni(II) by 2-thioacetylpyrrole (10) and 2-thiobenzoylpyrrole (11) to provide complexes 12 and 13 with structures analogous to complex 14 is also described.