Synthesis and reactivity of cationic bis(N-heterocyclic dicarbene) ruthenium(II) complexes

Four ruthenium(II) N-heterocyclic dicarbene complexes of general formula [Ru{MeIm(CH2)nImMe}2(RCN)2][PF6]2 (1: n=1,R=Me;2: n=1,R=Ph;3: n=2,R=Me;4: n=2,R=Ph; MeIm = 3-methylimidazol-2-yliden-1-yl) have been synthesised by transmetalation of the dicarbene ligand from a dicarbene silver complex with [RuCl2(COD)]x (COD = 1,5-cyclooctadiene) or [RuCl2(p-cymene)]2as ruthenium precursors. The relative position of the coordinated nitrile molecules (cisortrans) depends on the group that links the two carbene moieties: the dicarbene with the methylene bridge affords thetransisomer, whereas theciscomplex is obtained with the ethylene bridge. The lability of coordinated nitriles towards entering nucleophiles, in particular, cyclohexyl and tert-butyl isocyanide, has been carefully checked, and the corresponding substitution complexes [Ru{MeIm(CH2)nImMe}2(RNC)2][PF6]2(6: n=1,R=Cy;7: n=2,R=Cy;8: n=2,R=tBu) have been synthesised. The transcomplexes are more inert than thecisones, and benzonitrile is a better leaving group than acetonitrile; these characteristics allow a proper tuning of the coordination set and the stereoelectronic properties of these dicarbene ruthenium complexes. The Xray crystal structures of1and7have also been determined.