| Abstract
| - Oxidative addition of different imidazolium cations to zerovalent group 10 metals, to affordheterocyclic carbene complexes, has been investigated by both density functional theory (DFT) and experimentalstudies. The theoretical analysis shows that addition of imidazoliums to Pt0 and Ni0 is more exothermic thanto Pd0, and Ni0 is predicted to react with a much lower barrier than either Pt0 or Pd0. Strongly basic supportingligands on the metal, as well as cis-chelating ligands, increase the exothermicity of the reaction and also lowerthe activation barrier. The addition of 2-H imidazoliums is easier and more exothermic than addition of2-alkylimidazoliums, and a halo-imidazolium is expected to further lower the barrier to oxidative addition andincrease the exothermicity. The DFT results show that all three of the metals should be able to oxidatively addimidazolium cations under appropriate conditions. Experimental studies confirmed that oxidative addition ispossible, and a number of Pt− and Pd−carbene complexes were prepared via oxidative addition of imidazoliumsalts to M0 precursors. Most significantly, oxidative addition of 2-H azolium salts was found to readily occur,and the reaction of 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPh3)2 and Pt(PCy3)2 affords[PtH(dmiy)(PPh3)2]BF4 (10) and [PtH(dmiy)(PCy3)2]BF4 (11), while reaction between 3,4-dimethylthiazoliumtetrafluoroborate and Pt(PCy3)2 yields [PtH(dmty)(PCy3)2]BF4 (12) (dmiy = 1,3-dimethylimidazolin-2-ylidene,dmty = 3,4-dimethylthiazolin-2-ylidene). Addition of 2-iodo-1,3,4,5-tetramethylimidazolium tetrafluoroborateto Pt(PPh3)4 or Pd(dcype)(dba) yields [PtI(tmiy)(PPh3)2]BF4 (9) and [PdI(tmiy)(dcype)]BF4 (14), respectively(tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, dcype = 1,3-bis(dicyclohexylphosphino)ethane)). X-ray crystalstructures are reported for complexes 9 and 11 (cis and trans). These studies clearly show for the first timethat oxidative addition of imidazolium and thiazolium cations is possible, and the results are discussed interms of the ramifications for catalysis in imidazolium-based ionic liquids with both carbene-based and non-carbene-based complexes.
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