Synthesis, structural characterization, and catalytic behaviour in Heck coupling of palladium(II) complexes containing pyrimidine-functionalized N-heterocyclic carbenes

[Pd(L1)(2)(CH3CN)](PF6)(2) (L-1 = 1-n-butyl-3-(2-pyrimidyl) imidazolylidene, 3) and [Pd(L-2)(2)](PF6)(2) (L-2 = 1-(2-picolyl)-3-(2-pyrimidyl) imidazolylidene 4), prepared via carbene transfer reactions of [Ag(L1)(2)] PF6 (1) and [Ag-2(L2)(2)](PF6)(2) (2) with palladium salts, respectively, have been fully characterized by H-1 and C-13 NMR spectroscopy and elemental analysis. The X-ray crystal structures of complexes 1-4 are reported. Complex 3 is an unusual pentacoordinated palladium complex, in which the palladium is coordinated by two imidazolylidene, two pyridine, and one acetonitrile molecule in a square-pyramidal geometry. The apical position is occupied by a pyrimidine nitrogen atom with a relatively long Pd-N distance (2.762(6) angstrom). Complex 4 is a typical square-planar palladium complex with palladium surrounded by two pairs of cis-arranged pyridine and imidazolylidene ligands. The complexes exhibit good catalytic activities in the Heck coupling reaction of aryl bromides and activated aryl chlorides under mild conditions.