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

The first use of dipyridocarbenes as Arduengo-Wanzlick type carbene ligands for transition metal complexes is reported. The complexes M(CO)(5)L (L = dipyridoimidazolinylidene, di-tert-butyldipyridoimidazolinylidene, M = Cr, W) were synthesized and their spectroscopic and structural properties compared with the literature known N-heterocyclic carbene (NHC) group 6 metal pentacarbonyl complexes. This reveals that the C-13 NMR carbene signals of theses complexes with dipyrido carbene ligands show the strongest high-field shift ever observed for M(CO)5(NHC) (M = Cr, W) complexes. The structural characterization shows alternating single and double bonds in the conjugated dipyrido moiety of the ligand. (c) 2005 Elsevier B.V. All rights reserved.