Pivotal Role of a Pentacoordinate 3MC State on the Photocleavage Efficiency of a Thioether Ligand in Ruthenium(II) Complexes: A Theoretical Mechanistic Study

• Published in: Inorganic chemistry Vol. 55; no. 9; pp. 4448 - 4456
• Main Authors: Göttle, Adrien J, Alary, Fabienne, Boggio-Pasqua, Martial, Dixon, Isabelle M, Heully, Jean-Louis, Bahreman, Azadeh, Askes, Sven H. C, Bonnet, Sylvestre
• Format: Journal Article
• Language: English
• Published: American Chemical Society 02.05.2016
• Subjects: Chemical Sciences; Coordination chemistry; or physical chemistry; Theoretical and
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.6b00268

A mechanistic study of the photocleavage of the methylthioethanol ligand (Hmte) in the series of ruthenium complexes [Ru­(tpy)­(N-N)­(Hmte)]2+ (tpy = 2,2′:6′,2″-terpyridine, N-N = bpy (2,2′-bipyridine), biq (2,2′-biquinoline), dcbpy (6,6′-dichloro-2,2′-bipyridine), dmbpy (6,6′-dimethyl-2,2′-bipyridine)) was performed using density functional theory. These studies reveal the decisive role of two quasi-degenerate triplet metal-centered states, denoted 3MChexa and 3MCpenta, on the lowest triplet potential energy surface. It also shows how the population of the specific pentacoordinate 3MCpenta state, characterized by a geometry more accessible for the attack of a solvent molecule, is a key step for the efficiency of the photosubstitution reaction. The difference in the photosubstitution quantum yields experimentally observed for this series of complexes (from φ = 0.022 for N-N = bpy up to φ = 0.30 for N-N = dmbpy) is rationalized by the existence of this 3MCpenta photoreactive state and by the different topologies of the triplet excited-state potential energy surfaces, rather than by the sole steric properties of these polypyridinyl ligands.