A dibenz[a,c]phenazine-supported N-heterocyclic carbene and its rhodium and iridium complexes

A new polycyclic N-heterocyclic carbene featuring a fused dibenz[a,c]phenazine moiety was generated in situ from the corresponding tetrafluoroborate salt. The synthesis and NMR data of its corresponding precursors, its sulfur adduct and dimer are reported. Complexes of type [MCl(COD)(1)] and [MCl(CO)2(1)] (M = Rh and Ir, 1 = 1,3-dibutyldibenzo[a,c]phenazino[11,12-d]imidazol-2-ylidene) were prepared and characterized using spectroscopic and crystallographic methods. The electron-releasing capacity of this new carbene was investigated by evaluation of its corresponding IrCl(COD) and IrCl(CO)2 complexes by IR spectroscopy (νav) and cyclic voltammetry (E1/2). These studies revealed that the electron donicity of this ligand is comparable to that of the previously reported naphthoquinone-annulated imidazolin-2-ylidene. Some preliminary studies of the photophysical properties and catalytic activity of these metal complexes are reported.