Nickel(II) heterocyclic carbene complexes of the formula NiI2(carbene)2 (carbene = 3-methyl-1-propylimidazolin-2-ylidene (1), 1-butyl-3-methylimidazolin-2-ylidene (2), 1-isopropyl-3-methylimidazolin-2-ylidene (3), 1,3-diisopropylimidazolin-2-ylidene (4)) have been prepared and fully characterized by both spectroscopic methods and single-crystal X-ray structure analysis. All complexes have “square-planar” nickel environments, with the donor atoms pairwise trans, all obligate, except for one of the two independent molecular types found in 2, in which, with different substituents at the nitrogen atoms, the two rotamers are observed as independent molecules in the one crystal. Complexes 1−4 were tested as catalysts for propene and 1-butene dimerization in both toluene and an imidazolium−chloroaluminate ionic liquid. While the complexes are inactive to sparingly active in toluene, highly active catalysts are produced in the ionic liquid. In all cases the complexes are more active toward 1-butene dimerization than is NiCl2(PCy3)2 in the ionic liquid. The results are interpreted in terms of catalyst stabilization by the imidazolium-based ionic liquid. In toluene the complexes decompose rapidly via reductive elimination of imidazolium cations, while in the ionic liquid no decomposition is observed. While reductive elimination of imidazolium is possible in the ionic liquid, a rapid reoxidation via addition of the solvent imidazolium cation seems possible and may prevent the formation of Ni0 deposits associated with catalyst deactivation.

The synthesis and characterization of a series of azolium-linked cyclophanes are reported. The cyclophanes consist of two azolium groups (17 examples) or three imidazolium groups (1 example) linked to two benzenoid units (benzene, naphthalene, p-xylene, mesitylene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, 2,6-pyridine, and p-tert-butylphenol) via methylene groups. Cyclophanes containing ortho-, meta-, and para-substitution patterns in the benzenoid units were examined. The conformations of the cyclophanes were examined in solution by variable-temperature NMR studies and in the solid state by crystallographic studies. The p-cyclophanes and mesitylene-based m- and o/m-cyclophanes are rigid on the NMR time scale, as indicated by sharp (1)H NMR spectra at all accessible temperatures. The non-mesitylene-based m-cyclophanes and the o-cyclophanes are fluxional on the NMR time scale at high temperatures, but in most cases, specific conformations can be "frozen out" at low temperatures. Many structures deduced from solution studies were consistent with those in the solid state.

A novel nickel complex in which the nickel center is bonded to two pyridine units and two heterocyclic carbene units in an imidazolium linked meta-cyclophane skeleton has been synthesized and structurally characterized. Both the parent imidazolium-linked cyclophane and the nickel complex undergo H/D exchange reactions in D2O solutions.

A new pyranone, 5-hydroxy-3-methoxy-4H-pyran-4-one (1), was isolated from the aerial parts of the desert shrub Haloxylon salicornicum. The structure was elucidated by X-ray structural analysis, NMR spectroscopy, and mass spectrometry. The monoacetate was also prepared, and molecular modeling studies and full NMR data were recorded.