Synthesis and structural characterisation of the palladium N-heterocyclic carbene cluster complexes [Pd3(μ-CO)3(NHC)3] and [Pd3(μ-SO2)3(NHC)3]

The reduction of trans-[Pd(NHC)2Cl2] (NHC = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IiPr2 = 1,3-bis-isopropylimidazol-2-ylidene) with potassium graphite under an atmosphere of CO affords the palladium NHC carbonyl clusters [Pd3(μ-CO)3(NHC)3] (NHC = IMes, 1; IiPr2, 3). Treatment of 1 with SO2 at room temperature yields the bridging SO2 complex [Pd3(μ-SO2)3(IMes)3] (4) in quantitative yield. Complexes 1, 3 and 4 have been structurally characterised by X-ray crystallography.