Photochemistry of RuII 4,4′-Bi-1,2,3-triazolyl (btz) Complexes: Crystallographic Characterization of the Photoreactive Ligand-Loss Intermediate trans-[Ru(bpy)(κ2-btz)(κ1-btz)(NCMe)]2+

We report the unprecedented observation and unequivocal crystallographic characterization of the metastable ligand loss intermediate solvento complex trans-[Ru-(bpy)(kappa(2)-btz)(kappa(1)-btz)(NCMe)](2+) (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(NN)(btz)(2)](2+) (1a-d: btz=1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl; NN=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(NN)(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 rearrange-ment such that they become coplanar. X-ray crystal structure of 3a and 3d confirmed the co-planar arrangement of the NN 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 degrees C) 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 kappa(2)-btz ligands in 2a coordinate in a square-planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.