First examples of dipyrido(1,2-c:2′,1′-e)imidazolin-7-ylidenes serving as NHC-ligands: synthesis, properties and structural features of their chromium and tungsten pentacarbonyl complexes - Nonnenmacher, Michael; Kunz, Doris; Rominger, Frank; Oeser, Thomas (Journal of organometallic chemistry, 2005)