Cyclometalated Complexes of Ru(II) with 2-Aryl Derivatives of Quinoline and 1,10-Phenanthroline

Difficulty in cyclometalating 1-(2‘-quinolinyl)pyrene and 1,3-di-(2‘-quinolinyl)pyrene with Ru(II) led to a more
detailed study of the cyclometalation process. A series of 2-aryl-1,10-phenanthrolines, where aryl = phenyl,
2-naphthyl, 1-anthracenyl, and 1-pyrenyl, were treated with [Ru(tpy)Cl3] to provide either the N5Cl complex
[Ru(tpy)(L)Cl]+ or this same material as a mixture with the N5C cyclometalated species [Ru(tpy)L]+. Steric
effects appear to govern the ability of the ligand to attain the near planar conformation required for cyclometalation.
The bridged ligand 3,1‘-dimethylene-2-(2‘-pyrenyl)-1,10-phenanthroline was prepared along with a quinoline
analogue. The former species was found to cyclometalate at the C1 of pyrene and afford the N5Cl complex. Both
the N5C (P21/n (monoclinic), a = 28.1102(11), b = 8.4638(3), c = 31.2908(12) Å, Z = 8) and N5Cl (P-1
(triclinic), a = 11.7235 (10), b = 14.5306(12), c = 14.5725(12) Å, Z = 2) complexes were analyzed by X-ray
crystallography, and the N5Cl species evidenced a congested environment for pyrene, which is apparently stabilized
by π stacking with tpy. Similar reactions with a series of three 3,2‘-bridged derivatives of 2-phenyl-1,10-phenanthroline provide both N5Cl and cyclometalated products in proportions which support the importance of
π stacking. The electronic absorption spectra and redox potentials for these complexes evidence strong σ donation
by the cyclometalated ligand and an apparant insensitivity to the orthogonal 2-aryl group.