trans Bis-N-heterocyclic carbene bis-acetylide palladium(II) complexes

A series of square planar trans bis-N-heterocyclic carbene palladium(II) bis(acetylide) complexes of the type [(iPr2-bimy)2Pd(Ctriple bond; length of mdashC–R)2] (bimy = benzimidazolin-2-ylidene) (R = C6H5, C6H4F, C6H4OMe, SiMe3, C4H3S, C5H4N, C6H4Ctriple bond; length of mdashCC6H5 and 1-pyrene) were prepared by the addition of the corresponding lithium acetylides to the starting (iPr2-bimy)2PdBr2 complex in good to modest yields. The molecular structures of (iPr2-bimy)2Pd(Ctriple bond; length of mdashC–C6H5)2 (1) and [(iPr2-bimy)2Pd(Ctriple bond; length of mdashC–SiMe3)2] (4) were determined by single-crystal X-ray diffraction studies. UV/vis absorption studies reveal significant spectral changes depending on the nature of the acetylide ligands bound to the palladium center.