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(H) 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)Cl-3] 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 Cl of pyrene and afford the N5Cl complex. Both the N5C (P2(1)/n (monoclinic), a = 28.1102(11), b = 8.4638(3),- c = 31.2908(12) Angstrom, Z = 8) and N5Cl (P-1 (triclinic), a = 11.7235 (10), b = 14.5306(12), c = 14.5725(12) Angstrom, Z = 2) complexes were analyzed by X-ray crystallography, and the N5Cl species evidenced a congested environment for pyrene, which is apparently stabilized by pi 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,7 stacking. The electronic absorption spectra and redox potentials for these complexes evidence strong sigma donation by the cyclometalated ligand and an apparant insensitivity to the orthogonal 2-aryl group.