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

We report the synthesis, characterization, and photochemical reactivity of the triazole-containing complex [Ru­(pytz)­(btz)2]2+ (1, pytz = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole, btz = 1,1′-dibenzyl-4,4′-bi-1,2,3-triazolyl). The UV–vis absorption spectrum of 1 exhibits pytz- and btz-centered 1MLCT bands at 365 and 300 nm, respectively. Upon photoexcitation, acetonitrile solutions of 1 undergo conversion to the ligand-loss intermediate, trans-[Ru­(pytz)­(κ2-btz)­(κ1-btz)­(NCMe)]2+ (2, Φ363 = 0.013) and ultimately to the ligand-loss product trans-[Ru­(pytz)­(btz)­(NCMe)2]2+ (3), both of which are observed and characterized by 1H NMR spectroscopy. Time-dependent density functional theory calculations reveal that the S1 state of the complex has primarily HOMO → LUMO pytz-based 1MLCT character. Data show that the 3MLCT and 3MC states are in close energetic proximity (≤0.11 eV to 2 d.p.) and that the T1 state from a single-point triplet state calculation at the S0 geometry suggests 3MC character. Optimization of the T1 state of the complex starting from the ground state geometry leads to elongation of the two Ru–N­(btz) bonds cis to the pytz ligand to 2.539 and 2.544 Å leading to a pseudo-4-coordinate 3MC state rather than the 3MLCT state. The work therefore provides additional insights into the photophysical and photochemical properties of ruthenium triazole-containing complexes and their excited state dynamics.