Synthesis, characterization, and coordination chemistry of a phenanthridine-containing N-heterocyclic carbene ligand

An N-heterocyclic carbene ligand precursor bearing a π-extended phenanthridine (3,4-benzoquinoline) unit is presented. The proligand was isolated as the imidazolium salt of chloride (1•HCl), bromide (1•HBr), or hexafluorophosphate (1•HPF 6 ) counterions. These salts can be deprotonated and the carbene installed on silver centres using Ag 2 O as both a base and a source of metal ion. The resulting Ag(I) complex (1)AgCl can be used in a transmetalation reaction to generate a Pd(II) coordination complex (1)Pd(CH 3 CN)Cl 2 . The characterization and photophysical properties of these complexes is presented, along with a demonstration of the utility of (1)Pd(CH 3 CN)Cl 2 in mediating a catalytic C-N cross-coupling reaction for the preparation of the pharmaceutical Piribedil.