“Activation of Small Molecules at N-heterocyclic Carbenes and their Application to Metal-organic Materials”
N-Heterocyclic Carbenes (NHCs) have been intensively explored for stabilizing unstable species such as radicals and zerovalent nonmetal species, and for activating small molecules such as CO, H2, NH3, N2O, NO, etc.1,2 Such a capability of NHCs can be attributed to their strong donor characters and steric tunability that lead to the remarkable reactivity. Recently, we reported N-heterocyclic carbene nitric oxide (NHCNO) radicals, which can be also considered as iminoxyl radicals. NHCNO radicals react with silyl and alkyl triflate to generate the corresponding radical cations.3 The structures of the unprecedented oxime ether radical cations were determined by X-ray crystallography. Furthermore, we also found that triazenyl cations stabilized by NHC form the corresponding triazenyl radicals upon the treatment of elemental potassium as a reductant.4 The triazenyl radicals were fully characterized by single-crystal X-ray analysis and electron paramagnetic resonance (EPR) spectroscopy. The details of synthesis, characterization, and formation mechanisms of the compounds will be discussed.
With the novel reactivity of NHCs, we also have also been exploring porous metal–organic frameworks (MOFs) and cages (MOCs) with various N-heterocyclic carbene precusors, imidazolium salts, and metal ions due to their potential applications such as catalysis, gas storage, molecular separations, etc. Since MOFs and MOCs can be constructed with a variety of structural and functional diversity via a modular approach, the facile tunability of the materials is available for appropriate applications. I will discuss the synthetic progress for MOFs and MOCs.
Reference
[1] Park, J.; Song, H.; Kim, Y.; Eun, B.; Kim, Y.; Bae, Y.; Park, D. S.; Rhee, Y. M.; Kim, W. J.; Kim, K.; Lee, E. J. Am. Chem. Soc. 2015, 137, 4642.
[2] Song, H.; Kim, Y.; Park, J.; Kim, K.; Lee, E. Synlett. 2016, 27, 477.
[3] Kim, Y.; Kim, K.; Lee, E. submitted.
[4] Back, J.; Park, J.; Y. Kim, Y.; Kim, K.; Lee, E. submitted.