title: Comparative study of C^N and N^C type cyclometalated ruthenium complexes with a NAD+/NADH function.
abstract: Cyclometalated ruthenium complexes having C(^)N and N(^)C type coordinating ligands with NAD(+)/NADH function have been synthesized and characterized by spectroscopic methods. The variation of the coordinating position of σ-donating carbon atom leads to a drastic change in their properties. Both the complex Ru(phbn)(phen)(2)]PF(6) ([1]PF(6)) and [Ru(pad)(phen)(2)]PF(6) ([2]PF(6)) reduced to Ru(phbnHH)(phen)(2)]PF(6) ([1HH]PF(6)) and [Ru(padHH)(phen)(2)]PF(6) ([2HH]PF(6)) by chemical and electrochemical methods. Complex [1]PF(6) photochemically reduced to [1HH]PF(6) in the presence of the sacrificial agent triethylamine (TEA) upon irradiation of visible light (λ ≥ 420 nm), whereas photochemical reduction of [2]PF(6) was not successful. Both experimental results and theoretical calculations reveal that upon protonation the energy level of the π* orbital of either of the ligands phbn or pad is drastically stabilized compared to the nonprotonated forms. In the protonated complex [Ru(padH)(phen)(2)](PF(6))(2) {[2H](PF(6))(2)}, the Ru-C bond exists in a tautomeric equilibrium with Ru═C coordination and behaves as a remote N-heterocyclic carbene (rNHC) compex; on the contrary, this behavior could not be observed in protonated complex [Ru(phbnH)(phen)(2)](PF(6))(2) {[1H](PF(6))(2)}.
authors: Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 5-1, Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors: Sumanta Kumar
authors: SK
authors: Padhi
authors: Ryoichi
authors: R
authors: Fukuda
authors: Masahiro
authors: M
authors: Ehara
authors: Koji
authors: K
authors: Tanaka
mesh_terms: D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D005021:Ethylamines; D007700:Kinetics; D008024:Ligands; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives / Q000737:chemistry; D008958:Models, Molecular; D009243:NAD / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D055668:Photochemical Processes; D011522:Protons; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D005021:Ethylamines; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; D009243:NAD; C030011:carbene; D012428:Ruthenium; D008697:Methane; C016162:triethylamine