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Sesin 1 RWU STUDENT RESEARCH PROPOSAL Name of applicant: Lindsey Sesin General area of research: Inorganic Chemistry Title of research project: The study of ruthenium dimers based on trans(dppm)2ClRuCCPh. Abstract The purpose of this project is to synthesize linear ruthenium complexes and study the interactions between bridged ruthenium metal centers. This will be accomplished by synthesizing systems based on the dimeric compound trans-trans-( R-PhCC-Ru(dppm)2BL-Ru(dppm)2-CCPh-R’), where BL are the bridging ligands pyrazine, 4,4’ bipyridine, 4,4’ bipyridyl ethane, 4,4’ bipyridyl ethene, and 4,4’ bipyridyl ethyne. The R and R’ subtituents in the para position on the ligand formally trans to BL are various electron donating and electron accepting groups. Multinuclear complexes based on trans-trans-( R-PhCC-Ru(dppm)2 are of interest because its linear geometry allows potential fabrication of, and subsequent investigation of, extended molecular architectures that may ultimately find utility in a wide variety of molecular electronic devices. Date of submission of proposal to committee: November 30, 2005 Amount of funding required: $1004.00 Final Report Due: November 31, 2006 Sesin 2 Introduction Many research groups have investigated the ability of transition metal complexes to transfer electrons from both their ground and electronically exited states.1 One particularly interesting result is the use of ruthenium-based chromphores to convert light energy into electrical energy or stored chemical energy.1 Since complexes based on ruthenium exhibit various stable oxidation states, absorbs light, and is synthetically versatile, it is an attractive complex for a wide variety of studies.2 Research has shown ruthenium’s ability to function efficiently in liquid-based photovolatic cells by absorbing light and transferring electrons into conduction bands of solid state semiconductors.3 This has been an important factor in advancing the studies of converting solar energy into electricity. Transition metals in general have been linked together with a wide variety of bridging ligands.4 Many groups have shown that the π network of orbitals on the bridging ligand provides a pathway for delocalization of electron density between the metal and ligand creating an efficient mechanism for communication between two or more metal centers.4 In addition, it has also been postulated that geometrically linear ruthenium bridged ligand complexes, when properly exploited, can display a more efficient transfer of electrons than those with non-linear geometries.5 Over the past five years, chemistry students at RWU have made significant progress exploring a related ruthenium complex, trans-[Cl(pyridine)4RuL]+ (Fig 1A). A previous study carried out by by Amanda Kuber (RWU ‘01) examined different ruthenium complexes where L = pyridine, pyrazine, 4, 4’-bipyridine. However, Kuber’s attempts to remove the chloride ligand trans to the L ligand were unsuccessful because of pyridine’s inherent ability to remove large amounts of electrons density from the ruthenium metal center. This makes it virtually impossible to remove the chloride ligand from the highly positive ruthenium center without decomposing the complex. Changing pyridine ligands to diphenylphosphino methane (dppm) ligands dramatically alters the electronics of the system to our advantage. (Fig. 1B) Py Cl Ru Cl Ph2P Py Py L Py A PPh2 Ru Ph2P L PPh2 B Figure 1. trans-LRuCl2py4 (A) where L = pyridine, prazine or 4,4’-bipyridine and trans-L-RuCl(dppm)2 (B) where L = phenylacetylide ligand Synthetically altering the electronic nature of the ruthenium center has allowed us to successfully remove the chloride ligand. This has been demonstrated recently by Mr. Jason Hill (RWU ’05). Mr. Hill explored the rate in which the chloride ligand can be extracted from the ruthenium metal center in trans-(ClRu(dppm)2CCPh) by reacting the Sesin 3 halide containing metal complex with Tl+ ion. (Fig. 2). Understanding the kinetics of this complex is an important foundation for my research because it is has not only elucidated the kinetic parameters associated with removing the chloride ligand but has unequivocally demonstrated that it is possible to remove the halide without decomposing the metal complex. PPh2 Cl Tl+ PPh2 Ph2P Ru C PPh2 C R Ph2P Abstraction S Ru C C R + TlCl S= solvent Ph2P PPh2 Ph2P Figure 2. Abstraction of Cl- using Tl + Mr. Hill’s results elegantly revealed that the abstraction of the trans chloride ligand depended linearly on the electron accepting/donating characteristics of the para substituent (R) attached to the phenyl acetylide ligand (Fig. 3). Mr. Hill’s results are useful because it provides insight into the role R plays in the ability to remove the chloride ligand. H C C R R=NH2, H, Cl, COH, CN, NO2 Figure 3. Phenyl acetylene ligand with para- substituent R The results of this study strongly suggest that the nature of the electronic communication between two bridged ruthenium complexes can be modulated by the R substituent (Fig. 3). Thus, it is of interest to evaluate the extent of electronic interactions between ruthenium dimers such as the ones proposed and to determine how R impacts the distribution of electron density in the molecule. My specific research will synthesize and investigate various dimeric Ru(dppm) complexes that are tied together with a bridging ligand. An important part of this study will be the successful abstraction of the trans-chloride ligand attached to the metal ruthenium with Ag+ followed by reactions with bridging ligands that can link the metal centers. This work has not been previously attempted here at RWU. Mr. Hill demonstrated that the chloride can be removed and that the open coordination site could be replaced with a solvent molecule (acetonitrile) but he did not generate any other monomeric or dimeric complexes based on the Ru(dppm)2 metal centers. Sesin 4 Once the trans-chloride ligand is abstracted, a desired ligand containing an immine nitrogen (pyridine, pyrazine, etc..) will replace it to confirm that the ruthenium complex will not decompose. The lone pair of electrons on nitrogen allows the pyridyl ligand to coordinate to metal ions. Also, the anti bonding -type orbitals on the nitrogen, that caused much grief in previous studies, in this case will actually increase the strength of the resulting M-L bond thus stabilizing our desired product. Once pyridine is successfully attached to the ruthenium complex without destroying the compound, other proposed bridging ligands (Fig 4) will be attempted. If I am able to make significant progress on this project, I am hoping to present this research at the National ACS conference in Chicago, Illinois in the Spring of 2007. N N C H2 C H2 N 4,4' bipyridyl ethane N C H C H N 4,4' bipyridyl ethene N C C N 4,4' bipyridyl ethyne N pyrazine N N 4,4'-bipyridine Figure 4. Commercially available bridging ligands Detailed Project Description The starting material, trans-(ClRu(dppm)2CCPh-4-R) ,will be prepared from published procedures.7 R is NH2, H, Cl, COH, CN, or NO2. Each trans-(RuCl(dppm)2CCPh-4-R) monomer will then be reacted with Ag+ to remove the chloride ligand as shown in figure 5. Results for varying substituent R will be studied and documented to find the best way to remove the chloride ion. PPh2 PPh2 Ph2P Ph2P Abstraction Cl Ru C Ag C S R Ru C S= solvent + PPh2 Ph2P PPh2 Ph2P Figure 5. Abstraction of Cl- using Ag+ C R + AgCl Sesin 5 Subsequent addition of 0.5 equivalents of a desirable bridging ligand (Fig. 4) should result in a high yield of the proposed bridged species. Products will be purified via column chromatography and recrystallized from DMF/Et2O solutions using standard procedures. One desired product in particular will be: PPh2 N Ph2P R PPh2 C C Ru Ph2P Ru C C R PPh2 Ph2P N PPh2 Ph2P O Figure 6. trans-trans-[Ru(CCHC6H4-4-R]Cl(dppm)2 bridged with 1,5-dipyridyl-1,4-pentadiene-3-one The bridging ligand 1,5-dipyridyl-1,4-pentadiene-3-one (Fig. 6) is the subject of another proposal (Ramkamur ’06/ von Riesen) being submitted concurrently. This bridging ligand is intriguing as it should exhibit proton induced switching by taking advantage of the pH induced keto/enol equilibria. Protonation of the keto-oxygen should disrupt the conjugation between the metal centers thus diminishing the extent of electron interaction that can take place between ruthenium centers. This should be evident in both the spectroscopy of the dimer as well as in the electrochemical behavior (cyclic voltammograms) of the complex. Research Methods and Procedures Using a published procedure and Mr. Hill’s lab notebook containing his kinetics study of Ru(dppm), [Ru(CCHC6H4-4-R]Cl(dppm)2 will be obtained through a series of successive reactions with toluene, [RuCl2(MeSO)4], dppm, CH2Cl2, 4-HCCC6H4R, NH4PF6, NEt3 and hexane, which are all available through the Aldrich Chemical Company. All reactions take place under positive pressure of argon gas. All reactions will be studied using RWU’s instruments. Laboratory Space Required All procedures will be carried out in the lab facilities at RWU. Sesin 6 References 1. Roundhill, D.M. Photochemistry and Photophysics of Coordination Compounds, Wiley, New York, 1994. 2. Juris, A.; Campogna, S.; Balzani, V.; Belser, P.; von Zelewsky, A. Cord. Chem. Rev., 1988, 84, 85. 3. Kalyanasundaram, K. Photochemistry of Polypyridine and Porphyrin Complexes, Academic Press, London, 1992 4. McGrady J.; Lovell T.; Stranger R.; Humphrey M.G. Organometallics. 1997, 16,4004. 5. Lampert, C.M., Solar Energy Materials and Solar Cells, 1994, 32, 221 6. Miessler, G.; Tarr, D.; Inorganic Chemistry, 3rd Ed., Pearson Prentice Hall, 2004. 7. Zakeeruddin, S.; Nazeeruddin, M.; Rotzinger, F.; Kalyanasundaram, K.;Gratzel, M.; Inor. Chem. Rev., 1988, 84, 85. 8. McDonagh, A.M.; Deeble, G.J.; Hurst, S.; Cifuentes, M.P.; Humphrey, M.G.; J Chem. Ed. 2001, 78, 232. 9. Choua, S.; Jovaiti, A.; Geoffroy, M.; Physical Chemistry Chemical Physics, 1999, 1, 3557.