Synthesis, Crystal Structure Determination and Electrochemistry of Homoleptic Pd(0) Complexes Supported by Normal and Abnormal N-Heterocyclic Carbene Ligands

Abnormal carbene complex of Pd(L1)(2), where L1 =1,3-Bis(2,6-diisopropylpheny1)-2,4-diphenylimidazole and normal carbene complex of Pd(L2)(2), where L2 =1,3-dimesityl-4,9-dioxonaphtho-2,3-diimidazole were prepared from a Pd(0) precursor Pd(COD)(CH2TMS)(2). Both the complexes crystalize in the triclinic space group P-1 and cell parameters of Pd(L1)(2) and Pd(L2)(2) are a= 12.0477 angstrom, b= 17.5269 angstrom, c =18.9786 angstrom, alpha = 114.4855 degrees, beta =92.5295 degrees, gamma =107.9472 degrees and a= 11.5007 angstrom, b = 15.2316 angstrom, c =17.9007 angstrom, alpha = 67.061 degrees, beta =72.143 degrees, gamma =72.183 degrees respectively. In both case N-heterocyclic ligands are distorted towards palladium direction. Further, crystal structures reveal that the palladium atom is covalently bonded to the two aNHC and nNHC ligands respectively. The electrochemical properties of these complexes were determined by cyclic voltammetry analysis in THE solution under argon atmosphere. The enunciated reversibility of the complexes can be explained by sequential one electron oxidations of the palladium centre from Pd(0) to Pd(I) and then Pd(II). [GRAPHICS] .