Synthesis, Characterization, and Properties of Mononuclear and Dinuclear Ruthenium(II) Complexes Containing Phenanthroline and Chlorophenanthroline

The study of photophysical and photochemical properties of ruthenium complexes is of great interest for fundamental practical reasons. Ruthenium complexes have been investigated for use in artificial photosynthesis. This paper deals with the synthesis and spectroscopic investigation of custom-designed ruthenium complexes containing phenanthroline and chloro-phenanthroline ligands. These complexes maybe useful for biological electron-transfer studies. The heteroleptic ruthenium monomer complex Ru(phen)2(Cl-phen) (where phen = 1,10-phenanthroline and Cl-phen=5-chloro-1,10-phenanthroline) was prepared in a two-step procedure previously developed in our laboratory. This monomer complex was used to prepare the ruthenium homometallic dimer complex, (phen)2Ru(phen-phen)Ru(phen)2, by utilizing the Ni-catalyzed coupling reaction. Both complexes were purified by extensive column chromatography. The identity and the integrity of the monomer complex were confirmed by elemental analysis. The calculated and the experimental values for the elemental analysis were in good agreement for the monomer complex. UV/Vis absorption spectroscopy, emission spectroscopy, and cyclic voltammetry were used to investigate the properties of both the complexes

Modulation of internuclear communication in multinuclear Ruthenium(II) polypyridyl complexes

The syntheses and characterisation of a series of mononuclear and dinuclear ruthenium polypyridyl complexes based on the bridging ligands 1,3-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 1,4-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]benzene, 2,5-bis-[5-(2-pyridyl)-1H-1,2,4-triazol-3-yl]thiophene, 2,5-bis-[5-pyrazinyl-1H-1,2,4-triazol-3-yl]thiophene are reported. Electrochemical studies indicate that in these systems, the ground state interaction is critically dependent on the nature of the bridging ligand and its protonation state, with strong and weak interactions being observed for thiophene- and phenylene-bridged complexes, respectively

Towards the Design and Syntheses of Novel Triads Comprising Single Robson-Type Macrocyclic Dicopper(II) Cores Flanked by Two Terminal Polypyridyl Ruthenium(II) Complexes.

Progress toward the syntheses of new tetranuclear bimetallic complexes of copper(II) and ruthenium(II) was realized. The designed triads comprise a central binuclear copper(II) complex with a tetraiminodiphenolate macrocyclic Robson-type compartmental ligand. In the envisioned complexes, the macrocyclic core is further functionalized by attachment of two polypyridyl ruthenium(II) complexes. A novel dibrominated dicopper(II) Robson complex was formed by the 2:2:2 condensation reaction of 4-bromo-2,6-diformylphenol and 1,3- diaminopropane with cupric chloride. Similarly, a new dibrominated dizinc(II) was synthesized from zinc tetrafluoroborate and the same diamine and dialdehyde. The new dicopper(II) complex did not heterocouple with borylated substrates under explored Suzuki reaction conditions. 5-Bromo-2-(methoxymethoxy)benzene-1,3-dicarboxaldehyde successfully heterocoupled with 4-tert-butylphenylboronic acid under Suzuki conditions. 4\u27-(4-Neopentylglycolatoboronphenyl)-2,2\u27:6\u27,2-terpyridine also coupled with 5-bromo-2-(methoxymethoxy)benzene-1,3-dicarboxaldehyde to give, after deprotection, 2,6-diformyl-4-(4-[2,2\u27:6\u27,2 -terpyridin]-4\u27-ylphenyl)phenol. This new dialdehyde, a precursor to the title complexes, was treated with (4\u27-(4-methylphenyl)-2,2\u27:6\u27,2 -terpyridine)RuCl3 under reducing conditions; however, the desired [(4\u27-(4-methylphenyl)-2,2\u27:6\u27,2 -terpyridine)Ru(4\u27-(3,5-diformyl-4-hydroxyphenyl)-2,2\u27:6\u27,2 -terpyridine)]2+ was neither isolated from nor detected in the reaction mixture

An Investigation of the Electronic Coupling in Some Dimeric Ruthenium (II) Polypyridine Complexes

A detailed understanding of respiration at the molecular level requires an understanding of the many electron transfer steps involved in the process. These electron transfer processes are extremely fast and are impossible to measure by simple rapid mixing techniques. In order to get around this problem, scientists have used laser flash photolysis. This technique relies on the fact that under proper conditions, a reactant can be generated by a very short laser pulse. Once generated, the course of the reaction can be monitored by various techniques capable of very rapid time response. Many applications of this methodology rely on the use of ruthenium (II) polypyridine complexes to initiate the reactions of interest. This approach has been used to study the rates of electron transfer between cytochrome c, and cytochrome b5, cytochrome peroxidase and cytochrome oxidase and the bc1 complex. The latter are key components in the respiration process. In these investigations special emphasis was placed on the design of ruthenium complexes that were efficient and compatible with the biological components. A thorough understanding of the design parameters are critical to continued success in this area. Dimeric ruthenium complexes at the current time appear to be among the best candidates for photochemical initiators. The photophysical properties of these complexes, however, have not yet been examined. In particular the excited-state lifetime of some of the monomers of interest appears to be comparable or even longer than the corresponding dimers. This observation is inconsistent with the single covalent bond that links the two monomeric units which would provide strong electronic coupling and rapid excited state decay. Preliminary observations suggest a very weak electronic coupling. The underlying basis of this inconsistency is important in future design endeavors and may provide useful information for the use of these complexes in other areas such as solar energy conversion. In order to investigate the magnitude of the electronic coupling, both symmetric and asymmetric ruthenium (II) dimeric complexes were synthesized. The ligands used in the synthesis of these dimers were limited to either those commercially available or those that could be easily synthesized. The symmetric ruthenium (II) bipyridine dimer ([Ru(bpy)2diphen(bpy)2](PF6)4)and ([Ru(TAP)2diphen(TAP)2](PF6)4 were synthesized through a nickel catalyzed coupling reaction . The asymmetric dimer ([Ru(bpy)2diphen(dmbpy)2](PF6)4 ) on the other hand was synthesized by decarbonylating [Ru(dmbpy)2(CO)2](PF6)2 with three fold of excess trimethylamine N-oxide in the presence of 2-methoxy ethanol and reacting it with [Ru(bpy)2diphen](PF6)2. Emission measurements confirmed that there is no significant difference in the excited state lifetime of the monomers and the dimers (both symmetric and asymmetric) used in this study. The result from our electrochemical studies showed that the mixed dimer complex was made up of two metal centers with different redox potentials. The symmetric dimer on the other hand has the same redox potential for each of the two metal centers and they do not interact with each other thus giving a single two electron oxidation at the same potential. Finally, our result from the emission study of the mixed dimer showed that the emission energy of the mixed dimer was equal to the average of the bpy and dmbpy dimers. From the photochemical studies, one can conclude that the mixed dimer and the symmetric dimers behaved as the monomers because there was no significant change in the excited state life time This indicates that the metal center of both the mixed dimer and the symmetric dimers are weakly coupled by the bridging ligand and there is no significant coupling between the two metal centers