Synthesis and Characterization of Pd Complexes of a Carbazolyl/Bis(Imine) NNN Pincer Ligand

A serendipitously discovered construction of a carbazole nucleus by lithiation of N-methylated bis(4-methyl-2,6-dibromophenyl)amine is described. It was used to synthesize an NNN pincer-type ligand that combines a central carbazole site (N-methylated in the precursor ligand) with two flanking aldimine donors bearing mesityl substituents. The installation of this ligand on Pd was accomplished via an N−Me cleaving reaction with (COD)PdCl2 producing MeCl and (NNN)PdCl (where NNN is an anionic carbazolyl/bis(imine) pincer ligand). Several (NNN)PdX complexes were characterized spectroscopically. (NNN)PdOTf (−OTf = triflate or −O3SCF3) readily reacted with stoichiometric amounts of water in benzene or dichloromethane to give a cationic water adduct [(NNN)Pd(OH2)]OTf. An X-ray diffraction study on a single crystal of (NNN)PdCl revealed an almost perfectly square planar environment about Pd and an almost perfectly planar carbazole/bis(imine) conjugated system. Cyclic voltammetry of (NNN)PdCl showed quasi-reversible oxidation at E1/2 = 0.72 V vs Fc/Fc+ which is most likely ligand-based.