Meghan M Gordon, Michael R Reardon , Cliff J. Timpson, and Daniel Von Riesen

1. Synthesis, characterization, and study of a series of metal complexes based on trans-[Cl(pyridine)4Ru-L]+ (L= NCArX) Meghan M Gordon, Michael R Reardon, Cliff J. Timpson, and Daniel Von Riesen Roger Williams University, One Old Ferry Road, Bristol, Rhode Island 02809 Abstract Over the past three years, a number of studies in our group have been aimed at exploring the photochemical and electrochemical properties of monomeric and dimeric complexes based on trans-[Cl(pyridine)4Ru-L]+. Our current efforts involve the synthesis, characterization, and study of a new series of monomeric complexes of the type trans-[Cl(pyridine)4Ru-L]+ where L is a cyanobenzene derivative, NCArCOOH, NCArCOMe and NCArCHO. The work presented here will detail our efforts to prepare and to purify each of the complexes. Results of the spectroscopic and electrochemical characterization will be presented as well as an assessment of the thermal and photochemical stabilities of each complex. Electrochemical & Infrared Properties of Complexes Complex E1/2mV v Ag-AgCl (∆Ep, mV) IR(cm-1) trans-[Cl(py)4Ru(PhCN)]PF6 995* (95) 2200 (moderate) trans-[Cl(py)4Ru(NCArCHO)]PF6 1021.5 (61) 2192 (strong) trans-[Cl(py)4Ru(NCArCOMe)]PF6 1009.5 (61) 2204 (moderate) trans-[Cl(py)4Ru(NCArCOOH)]PF6 1011.5 (63) 2194 (weak) trans-[Cl(py)4Ru(NCArBr)]PF6 995 (70) *converted from v SCE Introduction Ruthenium polypyridyl complexes have received considerable attention in the chemical literature due in part to their ability to function as efficient photosensitizers in photovoltaic devices.1-4 In the course of these studies, researchers have come to appreciate the critical role molecular geometry plays in the operation of these devices.3,4 The work presented here seeks to explore the chemistry of trans-[Cl(pyridine)4Ru(L)]+ (L = 4-cyanobenzaldehyde, 4-acetlybenzonitrile, and 4-cyanobenzoic acid ) complexes as potential “building blocks” for larger oligomeric complexes which might exhibit interesting photochemical and/or redox active properties.  The trans- geometry of the tetrapyridine ruthenium monomer, combined with appropriate bridging ligands, should ultimately allow fabrication of supramolecular complexes that exhibit linear or pseudo-linear geometries. Spectroscopic Properties of Complexes Complex λmax, nm(ε, M-1cm-1) Assignment trans-[Cl(py)4Ru(MeCN)]PF6 226 (22 650) π to π* 244 (23 250) π to π* 355 (29550) dπ to π* (py) trans-[Cl(py)4Ru(ArCN)]PF6 202 (33 200) π to π* 241 (32 000) π to π* 351 (27 400) dπ to π* (py) trans-[Cl(py)4Ru(NCArCHO)]PF6 198 (25 754) π to π* 247 (18 493) π to π* 347 (9 647) dπ to π* (py) 429 (5 660) dπ to π* (L) trans-[Cl(py)4Ru(NCArCOMe)]PF6 200 (27 245) π to π* 246 (25 553) π to π* 349 (13 759) dπ to π* (py) 416 (7 842) dπ to π* (L) trans-[Cl(py)4Ru(NCArCOOH)]PF6 200 (~22 000) π to π* 246 (~20 000) π to π* 349* (~10 000) dπ to π* (py) Results and Conclusions • A variety of N-bound aromatic nitrile complexes of the form trans-[Cl(py)4RuL]+ can be easily obtained from versatile starting material complex trans-[Cl(py)4Ru(NO)](PF6)2.  • Efforts to obtain pure samples of the complex trans-[Cl(py)4Ru(NCArCOOH)]+ were complicated by the carboxylic acid functionality makes the complex difficult to chromatograph on silica and alumina. Efforts in our labs are currently underway to purify the trans-[Cl(py)4Ru(NCArCOOH)]+ complex. • For the complexes trans-[Cl(py)4RuNCArCHO]+ and trans-[Cl(py)4RuNCArCOMe]+, the low energy absorption features present in CH3CN solution at 429 and 416 respectively can be assigned as a MLCT type, dpp*(NCArX) transitions. A similar absorption feature is clearly evident as a low energy shoulder (~400nm) on trans-[Cl(py)4RuNCArCOOH]+. • Each of the complexes of trans-[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH ) were shown to be thermally stable in CH3CN solution at 298K. • Irradiation of the complexes trans-[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH )  with visible light (l > 355nm) in CH3CN at 298K leads to changes in the UV-Visible spectra which can be ascribed to photochemically induced cleavage of the Ru-NC-ArX bond. • Based on our results of investigating related systems, we expect that extended (3 hr) irradiation of the complexes trans-[Cl(py)4RuL]+ (L = NCArCHO, NCArCOMe, and NCArCOOH ) will lead quantitatively to formation of the solvent substituted complex trans-[Cl(py)4Ru(CH3CN)]+ when irradiated in CH3CN. • Extended (3 hr) irradiation of the solvent complex trans-[Cl(py)4Ru(NCCH3)]+ at l > 355 nm does not lead to an appreciable photochemical loss of pyridine, nor do we find any UV-Vis evidence for trans to cis isomerization. Methods and Materials Spectroscopic grade solvents (Burdick and Jackson, Aldrich, Fisher) and reagents (Aldrich) were obtained commercially and used as supplied. All reactions were conducted under an argon atmosphere and were shielded from ambient light. The complex trans-[ClRu(py)4(NO)](PF6)2 was prepared according to procedures  previously reported by Coe.5,6 Column chromatography was carried out using silica gel 60 (70-230 mesh) (Aldrich) with varying proportions of acetone:dichloromethane (5% to 50% acetone) as the eluent.  All products were dried at room temperature in a vacuum dessicator for a minimum of 24 h before use.  UV-Vis spectra and kinetic data were collected on a Hewlett-Packard HP-8453 Diode Array spectrophotometer.  Infrared data was collected on a Perkin-Elmer 1600 series FT-IR, and cyclic voltammetric measurements were obtained using a Bio-Analytical Systems (BAS) CV-50W.  Photolysis studies were accomplished by irradiating the complexes (ca. 10-5 M) in CH3CN with a 50W halogen light source equipped with a 355 nm cutoff filter.  The irradiating light was passed through 5 cm of water to minimize heating of the photolysis solution. Complexes Studied References 1. Roundhill, D.M. Photochemistry and Photophysics of Coordination Compounds, Wiley, New York, 1994. Juris, A; Campanga,S; Balzani, V.; Belser, P.;von Zelewsky, A. Coord. Chem. Rev., 1988, 84, 85. 2. Zakeeruddin, S.; Nazeeruddin, M.; Rotzinger, F.; Kalyanasundaram, K., Grätzel, M., Inorg. Chem., 1997, 36, 5937. 3. Frank, A; et al., Presentation at IEEE Photovoltaic Conference, Sept. 1997, available via www.nrel.gov/ncpv/ndf/ieee.pdf. See also Solar Energy Materials and Solar Cells, Lampert, C.M. Ed., Vol. 32, No. 3, March 1994. 4. Balzani, V.; Scandola, F. Supermolecular Photochemistry; Wiley, Chinchester, UK, 1991. 5. Coe, B.; Meyer, T. J.; White, P.S. Inorg. Chem., 1993, 32, 4012. 6. Coe, B.; Meyer, T. J.; White, P.S. Inorg. Chem., 1995, 34, 593. 7. Hansch, C; Leo, A. Exploring QSAR: Fundamentals and Applications in Chemistry and Biology. American Chemical Society; Salem, MA: 1995. Page 17 Synthetic Scheme Acknowledgments MMG and MRR gratefully acknowledge: Kate Dedeian and Hannah Nandor for the synthesis of trans-[Ru(py)4Cl(NO)](PF6)2 Steve Hira for collecting electrochemical data Randy Petrichko for the synthesis of trans- [Ru(DMSO)4(Cl)2] complex CJT and DVR gratefully acknowledge: Financial support from a grant from the RWU Faculty Research Foundation www.rwu.edu