Photochemistry of Ru 4,4’-Bi-1,2,3-triazolyl (btz) Complexes: Crystallographic Characterization of the Photoreactive Ligand- Loss Intermediate trans-[Ru(bpy)(k-btz)(k-btz)(NCMe)]

We report the unprecedented observation and unequivocal crystallographic characterization of the metastable ligand loss intermediate solvento complex trans-[Ru(bpy)(k-btz)(k-btz)(NCMe)] (1a) that contains a monodentate chelate ligand. This and analogous complexes can be observed during the photolysis reactions of a family of complexes of the form [Ru(N _ N)(btz)2] 2+ (1a–d : btz=1,1’-dibenzyl-4,4’-bi-1,2,3-triazolyl ; N _ N=a) 2,2’-bipyridyl (bpy), b) 4,4’dimethyl-2,2’-bipyridyl (dmbpy), c) 4,4’-dimethoxy-2,2’-bipyridyl (dmeobpy), d) 1,10-phenanthroline (phen)). In acetonitrile solutions, 1a–d eventually convert to the bis-solvento complexes trans-[Ru(N _ N)(btz)(NCMe)2] 2+ (3a–d) along with one equivalent of free btz, in a process in which the remaining coordinated bidentate ligands undergo a new rearrangement such that they become coplanar. X-ray crystal structure of 3a and 3d confirmed the co-planar arrangement of the N _ N and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2a–d, which are formed quantitatively from 1a–d in a matter of minutes and to which they slowly revert back on being left to stand in the dark over several days. The remarkably long lifetime of the intermediate complexes (>12 h at 40 8C) allowed the isolation of 2a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3a and d, the bpy and k-btz ligands in 2a coordinate in a square-planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.