New dinuclear, pyrazolato-bridged cationic complexes of ruthenium and rhodium were synthesized from N-heterocyclic carbene (NHC) precursors 3,5-bis(methylimidazolium-1-ylmethyl]-1H-pyrazole bishexafluorophosphate and the  metal precursors [Ru(p-cymene)Cl2]2 and [Rh(Cp*)Cl2]2. Depending on the reaction conditions, either dinuclear bis(imidazolium) complexes or the corresponding bis(NHC)-complexes were formed. The obtained compounds were fully characterized by means of NMR, elemental analysis and single crystal X-ray diffraction. The metal-metal distances are in the range of 3.85 � and 3.92 �, therefore, a direct metal-metal bond can be excluded in all cases. Futhermore, the electronic properties were examined by cyclic voltammetry (CV) to detect possible electronic coupling between the metal centers. Only in the case of the Ru-bis(NHC) complex three reversible redox processes can be detected. The Ru-complexes show good activity in the catalytic transfer hydrogenation of acetophenone, while the Rh-complexes catalyze the formation of chromon- and isochinolin- derivatives through aryl-C-H activation.

Synthesis, characterization, and catalytic applications of new pyrazolato bridged complexes of ruthenium and rhodium

245th National Meeting (2013)

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