Synthesis and Structural Characterization of a Series of Novel Polyaromatic Ligands Containing Pyrene and Related Biscyclometalated Iridium(III) Complexes^†

A series of novel polyaromatic ligands containing pyrene with different types of substitution around the central pyridine ring were synthesized via Suzuki cross-coupling reactions. The series consists of 4-methyl-2-pyren-1-ylpyridine (5), in which the pyrene ring is attached to the 2-position of pyridine; 2-(3,5-bis(trifluoromethyl)phenyl)-5-pyren-1-ylpyridine (16), in which the pyrene ring is attached to the 5-position of pyridine; and 4-methyl-2-(3-pyren-1-ylphenyl)pyridine (30), in which the pyrene ring is attached to the 3-position of the 2-phenylpyridine moiety. The novel, sterically bulky di-tert-butyl(pyren-1-yl)phosphine (25) was used for the first time as a ligand in the Suzuki coupling reaction. The palladium complexes 6, 7, and 31 were also isolated as catalyst degradation products from the corresponding Suzuki reactions. Some of the largest cyclometalated systems to date have been synthesized by the biscycloiridation of the above three types of pyrene-containing phenylpyridine ligands in trimethyl phosphate. The systems include complexes 10 and 12, in which the pyrene ring is cyclometalated by iridium; complex 19, in which the pyrene ring is attached to a pyridine moiety; and complex 32, in which the pyrene is attached to a cyclometalated phenyl moiety. In the solid state, complexes 12 and 19 exhibit π-stacking arrangements through the large aromatic systems of the pyrene rings. The plane-to-plane distances of the π−π stacked complexes 12 and 19 vary from 3.40 to 3.53 Å. The π-stacking distance can be affected by the size of the solvent molecules incorporated in the cavities formed by the pyrene rings. Complex 32 does not have π-stacked aromatic rings.