Abstract
We report the unprecedented observation and unequivocal crystallographic characterization of the meta-stable ligand loss intermediate solvento complex trans-[Ru(bpy)(κ2-btz)(κ1-btz)(NCMe)]2+ (1 a) 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()(btz)2]2+ (1 a–d: btz=1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl; =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, 1 a–d eventually convert to the bis-solvento complexes trans-[Ru()(btz)(NCMe)2]2+ (3 a–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 3 a and 3 d confirmed the co-planar arrangement of the and btz ligands and the trans coordination of two solvent molecules. These conversions proceed via the observed intermediate complexes 2 a–d, which are formed quantitatively from 1 a–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 °C) allowed the isolation of 2 a in the solid state, and the complex to be crystallographically characterized. Similarly to the structures adopted by complexes 3 a and d, the bpy and κ2-btz ligands in 2 a coordinate in a square-planar fashion with the second monodentate btz ligand coordinated trans to an acetonitrile ligand.
Highlights
The photophysics of ruthenium(II) polypyridyl complexes,[1] and other d6 complexes containing OsII, ReI and IrIII, have been the subject of intense investigation over the past four decades
There has been renewed interest in the investigation of the photophysics of these complexes and the tuning of the relative energies of the 3MLCT and 3MC states.[3]. In which these states are brought into close proximity, the thermal population of 3MC from photoexcited 3MLCT states has been exploited for the light-activated formation of anticancer agents for photodynamic therapy.[3e,4] In systems analogous to the classic complex [Ru(bpy)3]2+, inclusion of steric congestion
Two singlet resonances were observed corresponding to the triazole ring protons of the btz ligands reflecting the C2 symmetry of the complexes
Summary
The photophysics of ruthenium(II) polypyridyl complexes,[1] and other d6 complexes containing OsII, ReI and IrIII, have been the subject of intense investigation over the past four decades. The 1H NMR spectrum of the photochemical product complex 3 a in [D3]acetonitrile showed four resonances for the bpy ligand demonstrating that the two pyridine rings maintain magnetic equivalence.
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