U UNIVERSITY OF CINCINNATI Date: 08/19/2009 I, Seher Kuyuldar (Tastan) , hereby submit this original work as part of the requirements for the degree of: Doctor of Philosophy (Ph. D) in Chemistry It is entitled: Synthesis, Characterization and Redox Studies of Platinum and Palladium Complexes with mer-Coordinating Ligands Seher Kuyuldar Student Signature: This work and its defense approved by: Dr. William B. Connick Committee Chair: Dr. Michael Baldwin Dr. Carl Seliskar Approval of the electronic document: I have reviewed the Thesis/Dissertation in its final electronic format and certify that it is an accurate copy of the document reviewed and approved by the committee. Committee Chair signature: Dr. William B. Connick Synthesis, Characterization and Redox Studies of Platinum and Palladium Complexes with mer-Coordinating Ligands A dissertation submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of DOCTORATE OF PHILOSOPHY (Ph.D.) In the Department of Chemistry of the College of Arts and Sciences 2009 by Seher Kuyuldar (Tastan) B.S., Fatih University, 2002 Committee Chair: Dr. William B. Connick I Abstract Synthetic, structural, spectroscopic, and redox studies of platinum(II) and palladium(II) compounds with mer-coordinating ligands have been undertaken in an effort to better understand the role of the metal and the ligands in controlling d6/d8 electron-transfer reactions. A series of Pd(pip2NCN)X (pip2NCNH=1,3- bis(piperdylmethyl)benzene) and [Pd(pip2NNN)X]X (X=Cl, Br, I) (pip2NNN=2,6- bis(piperdyl-methyl)pyridine) complexes are reported. Electronic spectra are consistent with stabilization of ligand-to-metal-charge-transfer states as the ancillary ligand is varied along the Cl<Br<I series. On the other hand, 1H NMR spectra in chloroform show that the piperidyl ligand resonances are deshielded along the Cl<Br<I series, which is attributed to decreasing filled/filled repulsions between the d(Pd) orbitals and the halide lone pair orbitals along this series. For [Pd(pip2NNN)X]X, the furthest downfield - piperidyl resonance is sensitive to changes in the counter-anion. Conductivity and 1H NMR spectroscopic measurements are consistent with the presence of an interaction - - - + 1 between the exogenous anion (Cl , Br , BF4 ) and Pd(pip2NNN)X (X=Cl, Br). H NMR, mass and electronic spectra, as well as elemental analyses, establish that 2+ [Pd(pip2NNN)X][PdnX2n+2] salts (n=1, 2) form during the procedure used to prepare t [Pd(pip2NNN)X]X. The crystal structure of [Pd(pip2NNN)( Bu3tpy)](BF4)2. t 2(ClCH2CH2Cl) ( Bu3tpy=4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine) reveals a short Pd...N(piperidyl) distance (3.33 Å). Solution spectra also are consistent with interaction between the Pd(II) center and the dangling piperidyl group. However, this and the tpy analog are irreversibly oxidized near 1.5 V vs. Ag/AgCl. In order to investigate the role of metal acidity on the redox chemistry of + + Pt(pip2NCN)(tpy) , a series of Pt(Z-pip2NCN)(Rn-tpy) complexes were prepared with II electron-releasing and/or withdrawing groups at the para-positions of the phenyl (Z=OMe, H, NO2) and pyridyl groups (Rn=t-butyl, H, tolyl). The synthesis and properties of these two-electron reagents, as well as the Z-pip2NCNBr ligand precursors and their platinum(II) halide adducts, are described. In the solid state, each + Pt(Z-pip2NCN)(R-tpy) complex exhibits at least one short Pt...N(piperidyl) distance (3.19-3.69 Å). The solution electronic spectra show a band at ~550 nm that is tentatively -N)4 -transfer-transition, resulting from the weak interaction of a piperidyl group with the metal center. In acetonitrile solution, each complex exhibits a two-electron metal-centered oxidation process near 0.4 V and two Pt(tpy)-centered reductions near -1.0 and -1.5 V vs. Ag/AgCl. The scan rate dependences of the peak potentials are consistent with large structural reorganization accompanying electron transfer, as expected for interconversion between Pt(II) and Pt(IV). Variations in the Z- and R-substituents cause the Pt(IV/II) couple (E°') to vary over a range of 200 mV. These data establish that oxidation of the metal center becomes more difficult as the electron withdrawing character of the substituents increases. There is an approximately linear relationship between E°' and an effective Hammet parameter, and the slope is similar to that observed for the Ru(III/II) couple of ruthenium bipyridyl complexes. 3 1 $ - $ -tpy)](BF4)2.1/4Et2Oand [Pt(tpy)(CH3COO)3](PF6) were structurally characterized. The former is the first example of a crystallographically characterized d8- ! " $1- and $3-terpyridyl ligands. The latter is the first example of a platinum(IV) terpyridyl complex. III IV Acknowledgements There are many people I have to acknowledge, so that the age range is from above 65 years to minus 10 days. I can neither name all of them nor state the reasons why I am so grateful. So the fallowing is an abridged version that is expressed in limited wording. I would like to start with Dr. Bill Connick, who has been a great mentor as well as a wonderful advisor. He has helped me grow personally and academically. His enthusiasm for the field, encouragement and thoughtful advice have made me more devoted to my studies and motivated me through rough times. I appreciate that he was always considerate of my different background and respectful to my preferences and life- style. Also, I would like to thank Dr. Baldwin and Dr. Seliskar for their expertise and guidance through this process and Dr. Stalcup for her last minute-save by attending my public defense as a substitute. In addition, I am fortunate to have had the opportunity to interact with many helpful members on the faculty and staff in the chemistry department. In particular, I am grateful to Jeanette for helping me with crystallography, Dr. Sallans and Dr. Macha for always having time to go through less than obvious mass spectra, Dr. Brooks and Dr. Ding for helping me utilize different functions of NMR instruments. I feel like it has been an honor and a privilege to have been a member of the Connick group. I would like to thank them all for the friendly and helpful environment they created. In closing, I am eternally grateful to my parents and brothers. They have endured long separations and once-in-a-year visits for several years and kept me in their prayers. Finally, I thank my dear husband for his continuous encouragement, optimism and support …and the about minus ten days old for bearing with me until the end. V TABLE OF CONTENTS Table of Contents I List of Figures IV List of Tables IX List of Schemes XI List of Abbreviations and Symbols XII CHAPTER 1: Introduction. Synthesis, Characterization and Redox Studies of 1 Palladium and Platinum Complexes with mer-Coordinating Ligands. References 11 CHAPTER 2: Synthesis, Structures and Spectroscopic Properties of Palladium(II) Complexes with Tridentate Piperidyl-Containing Pincer Ligands Introduction 15 Experimental 16 X-ray Crystallography 20 Results and Discussion 22 Synthesis 22 1H NMR Spectroscopy 22 Crystal Structures 27 Electronic Spectroscopy 35 Conclusions 41 References 42 I CHAPTER 3: Palladium(II) Halide Complexes with a Pyridyl Pincer Ligand Introduction 49 Experimental 50 X-ray Crystallography 54 Results and Discussion 55 + Synthesis of Pd(pip2NNN)X Salts 55 Crystal Structures 62 Electronic Spectroscopy 73 1H NMR Spectroscopy 77 Anion Dependence of the Chemical Shift 80 Conclusions 94 References 96 CHAPTER 4: Palladium(II) Complexes with Two Potentially Tridentate Pyridyl Ligands Introduction 103 Experimental 105 X-ray Crystallography 107 Results and Discussion 108 Synthesis 108 Crystal Structures 111 1H NMR Spectroscopy 118 Electronic Spectroscopy 123 Cyclic Voltammetry 128 Conclusions 134 II References 135 CHAPTER 5: Synthesis, Characterization and Redox Tuning of Platinum (II) Pincer Complexes with Terpyridine Introduction 141 Experimental 143 X-ray Crystallography 150 Results and Discussion 152 Synthesis 152 Crystal Structures 155 1H NMR Spectroscopy 167 Electronic Spectroscopy 181 Cyclic Voltammetry 187 Conclusions 200 References 202 III LIST OF FIGURES 1 Figure 2.1 H NMR spectra of Pd(pip2NCN)Cl, Pd(pip2NCN)Br, 26 Pd(pip2NCN)I, [Pd(pip2NNN)Cl]Cl and [Pd(pip2NNN)Cl]Cl. Figure 2.2 ORTEP diagrams of Pd(pip2NCN)Br. 30 Figure 2.3 ORTEP diagrams of [Pd(pip2NCN)(phpy)](BF4). 31 Figure 2.4 ORTEP diagrams of [Pd(pip2NNN)Cl]Cl 32 Figure 2.5 UV-visible absorption spectra of [Pd(pip2NNN)Cl]Cl, 36 [Pd(pip2NCN)(py)](BF4), Pd(NCN)Cl, Pd(NCN)Br and Pd(NCN)I. Figure 2.6 UV-visible absorption spectra of [Pd(NCN)(phpy)](BF4) and 37 [Pd(NCN)(py)](BF4). 2- Figure 3.1 UV-visible absorption spectra of solutions containing PdnX2n+2 57 + (n=1, 2); the tan salt of Pd(pip2NNN)Cl , the orange-brown salt + + of Pd(pip2NNN)Br and the burgundy salt of Pd(pip2NNN)I . Figure 3.2 UV-visible absorption spectra of the [Pd(pip2NNN)I]2[PdnI2n+2] 61 products, assuming [Pd(pip2NNN)I]2[Pd2I6] and [Pd(pip2NNN)I]2[Pd2I8]0.5 formulations. Figure 3.3 ORTEP diagrams of [Pd(pip2NNN)Br](BF4). 65 Figure 3.4 ORTEP diagrams of molecule A of [Pd(pip2NNN)Br]Br.H2O 66-67 Ball-and-stick representations for molecules A and B of [Pd(pip2NNN)Br]Br.H2O. Figure 3.5 ORTEP diagrams and ball-and-stick representation of 68 [Pd(pip2NNN)I]I. IV Figure 3.6 ORTEP diagrams and ball-and-stick representation of 69 [Pd(pip2NNN)I]2[Pd2I6]. Figure 3.7 UV-visible absorption spectra of [Pd(pip2NNN)Cl]Cl, 75 [Pd(pip2NNN)Br]Br and [Pd(pip2NNN)I]I.