The first bridged, bifunctional cyclopentadienyl-imidazolylidene ligand and complexes with titanium and zirconium

Starting from imidazole, 1-[2-(cyclopenta-2,4-dienyl)ethyl]-3-methylimidazolium iodide (3) was obtained as a mixture of isomers by a simple three-step synthesis. The reaction of 3 with Ti(NEt2)4 or Zr(NEt2)4 by double deprotonation of the imidazolium salt led to the isomerically pure cationic complexes [{eta(5)-C5H4-(CH2)(2)-NHC}M(NEt2)(2)]I-+(-) (NHC = N-heterocyclic carbene) 4a (M = Ti) and 4b (M = Zr), respectively, in which a cyclopentadienyl and a methylimidazol-2-ylidene unit are linked by an ethy lidene-1,2 bridge to form a novel chelating ligand system. In the case of the reaction of 3 with Zr(NEt2)(4) the neutral compound [{eta(5)-C5H4-(CH2)(2)-NHC}Zr(NEt2)I-2] (5) is formed as an additional product. According to the X-ray structure analyses, the titanium atom of 4a is tetra-coordinated while no coordinative interaction exists with the iodide anion; on the other hand, in 5 the zirconium centre is pentacoordinated.