Photochemistry of Ru^II 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⁺

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.

An overview of photosubstitution reactions of Ru(II) imine complexes and their application in photobiology and photodynamic therapy

“…39,40 Recently, the single crystal structure of a monodentate intermediate species was obtained following photolysis of solutions of various bis-di-1,2,3-triazole complexes. 41 Figure 2a shows the structure of the starting bis-triazole and 2b illustrates the structure of the monodentate intermediate. What is most interesting is that the incoming acetonitrile ligand is trans to the coordinated singly bound bis-triazole.…”

Photochemistry of [Ru(pytz)(btz)2]2+ and Characterization of a κ1-btz Ligand-Loss Intermediate

“…These energies can be determined or inferred spectroscopically, electrochemically and computationally and as [Ru(N^N) 3 ] 2+ complexes invariably have a highest occupied molecular orbital of predominantly metallic 4d character, and hence effectively the same ground state, these excited state energies can be readily compared). Work in our laboratory, [26][27][28] and those of others, [29][30][31][32] has shown that complexes containing 1,2,3-triazole rings that lack such steric promotion can also lead to photochemical reactivity, possibly through destabilisation of the 3 MLCT state with respect to the 3 MC state when compared to those states of the archetypal complex [Ru(bpy) 3 ] 2+ . We recently reported the series of complexes [Ru(bpy) 3-n (btz) n ] 2+ (btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, n = 1 to 3) 33 in which an increasing number of btz ligands leads to destabilisation of the 1 MLCT bands in the visible absorption spectrum, significantly so for the homoleptic complex [Ru(btz) 3 ] 2+ .…”

Labilizing the Photoinert: Extraordinarily Facile Photochemical Ligand Ejection in an [Os(N^N)3]2+ Complex

“…[8] Here,presence of the btz ligand appears to induce adestabilization of the 3 MLCT state,b ringing it into closer energetic proximity to the 3 MC state thereby enabling thermal population of the 3 MC state with consequential photochemical btz ligand ejection in acetonitrile solutions.Inthe case of the latter of these complexes,t his is accompanied by the unprecedented observation of am etastable ligand-loss intermediate, trans-[Ru(bpy)(k 2 -btz)(k 1 -btz)(NCCH 3 )] 2+ ,w hich can be formed quantitatively by photolysis in an NMR tube within minutes and has been crystallographically characterized. [9] Theb tz ligand has also been observed to induce photochemical decomposition in the iridium(III) complex [Ir(dfptz) 2 (btz)] + (dfptzH = 4-(2,4-difluorophenyl)-1,2,3-triazole) [10] which one would expect to be far more inert due to the typically higher lying 3 MC states associated with the 5d metal center.…”