Dual Emission and Excited-State Mixed-Valence in a Quasi-Symmetric Dinuclear Ru-Ru Complex

作者：Kreitner Christoph; Grabolle Markus; Resch Genger Ute; Heinze Katja^*

来源：Inorganic Chemistry, 2014, 53(24): 12947-12961.

DOI：10.1021/ic5020362

The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)](4+) 3(4+) of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)](2+) 1(2+) are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)](2+) 4(2+) carrying the same functional groups. 3(4+) is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UVvis absorption and NMR spectroscopy as well as cyclic voltammetry. 4(2+) and 3(4+) are emissive at room temperature, as expected. Moreover, 3(4+) exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [Ru-II(tpy-NHCO-tpy(center dot-))Ru-III] and [Ru-III(tpy-NHCO-tpy(center dot-))Ru-II] states leading to an unprecedented excited-state (RuRuIII)-Ru-II mixed-valent system via the radical anion bridge tpy-NHCO-tpy(center dot-). The mixed-valent cation 35+, on the other hand, shows no measurable interaction of the (RuRuIII)-Ru-II centers via the neutral bridge tpy-NHCO-tpy (RobinDay class I). Reduction of 3(4+) to the radical cation 33(+) by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 33(+) via NMR and UVvis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H3(+) in which the bridging amide is deprotonated. Hence 3-H3(+) (and 4-H+) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 4(2+) and 3(4+) to 4-H+, 3-H3(+), and 3-2H(2+) was demonstrated using a strong base and was studied using NMR and UV-vis absorption spectroscopies. The equilibrating excited triplet states of 3(4+) are reductively quenched by N,N-dimethylaniline assisted by hydrogen bonding to the bridging amide.

• 出版日期2014-12-15