Supramolecular first-row transition metal complexes of 3-(3,5-dimethylpyrazol-1-yl)propanamide: Three different coordination modes

Abstract

Michael addition of 3-tert-butylpyrazole (1) or 3,5-dimethylpyrazole (2) to acrylamide afforded the pyrazolylpropanamide-type ligands 3-(3-tert-pyrazol-1-yl)propanamide (3, = tBuPPA) and 3-(3,5-dimethylpyrazol-1-yl)propanamide (4, = Me2PPA), respectively, in high isolated yields (3: 80%, 4: 76%). Reactions of 4 with selected first-row transition-metal chlorides (MnCl2·4H2O, CoCl2·6H2O, ZnCl2, CuCl2·2H2O) afforded the new complexes MnCl2(Me2PPA)2 (5), [MCl2(Me2PPA)]2 (M = Co (6), Zn (7)), and CuCl2(Me2PPA)2·2H2O (8). Ligand 3 and all four new complexes 5–8 have been structurally characterized though single-crystal X-ray diffraction. Surprisingly, the crystal structure determinations revealed three different coordination modes for the pyrazole-based ligand in these complexes. Seven-membered κN,κO-chelate rings are present in the manganese(II) complex 5. In contrast, κN: κO-bridging coordination of Me2PPA in compounds 6 and 7 leads to formation of dimers comprising 14-membered ring systems. Furthermore, unusual κN-monodentate coordination of Me2PPA has been found in the structure of the hydrated copper(II) complex Cu(Me2PPA)2Cl2·2H2O (8). In the crystalline state, all four complexes 5–8 form one- or two-dimensional supramolecular structures assembled through different types of hydrogen bonding.