N-Heterocyclic carbenes have numerous applications in synthetic chemistry. We detail the reactivity and chemistry of these molecules including investigations into their reactions with small reagents, their use for the preparation of polarised azines and their potential application as NLO materials. The chemistry of imidazolium salts, which are related to NHCs by the addition of a proton, is also discussed. New chemistry for ionic liquids is also revealed.

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We have developed a multistep inorganic synthesis experiment for our second-year undergraduate teaching laboratory that introduces students to modern organometallic chemistry. The ligands are prepared in two simple steps and the preparation of an air-stable silver carbene complex is accomplished in the third step. The students are introduced to multinuclear NMR (1H and 13C) spectroscopy and a modern area of chemistry, as well as prepare an important class of ligand, namely N-heterocyclic carbenes. We have used this experiment to introduce students to novel coordination geometries and valence states of carbon.

Addition of Re(CO)5(H) to Os4(CO)14 in solution at room temperature affords ReOs4(μ-H)(CO)19 (1). Careful pyrolysis of 1 in hexane at 85 °C initially yields ReOs4(μ-H)(μ-CO)(CO)17 (2), which on further heating gives ReOs4(μ-H)(CO)16 (3). There was no evidence for ReOs4(μ-H)(CO)17. The four osmium atoms in 1 have a planar kite arrangement with the Re(CO)5 in an equatorial site, that is, a spiked kite metal skeleton. The H ligand is believed to bridge the OsOs bond (length 2.892(1), 2.904(1) Å; two independent molecules) that is cis to the Re atom, rather than one of the longer OsOs bonds. Cluster 2 has a distorted tetrahedral Os4 nucleus with the Re(CO)5 again acting as a spike ligand (i.e., a spiked tetrahedral metal skeleton). Compound 3 has the expected trigonal bipyramidal core of metal atoms with the Re(CO)4 unit in the equatorial plane. The structures of 1−3 are compared to those of the analogous Os5(CO) n (n = 19, 18, 16) clusters. The solution behavior of the new clusters was also investigated by variable-temperature 13C NMR spectroscopy.