THEORETICAL STUDIES ON OXIDATIVE ADDITION OF AMMONIA TO IRIDIUM COMPLEXES AND METATHESIS REACTIONS OF TRIPLE BONDS INVOLVING TUNGSTEN, MOLYBDENUM, CARBON AND NITROGEN EMPLOYING DENSITY FUNCTIONAL THEORY Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Shentan Chen, M.S. ***** The Ohio State University 2009 Dissertation Committee: Approved by Professor Bruce E. Bursten, Advisor Professor Malcolm H. Chisholm, Advisor Professor Sheldon G. Shore _______________________________ Professor Patrick M. Woodward Advisor Graduate Program in Chemistry ABSTRACT Activation and cleavage of element-hydrogen bonds, E-H, where E = H, C, N and O, via oxidative addition to a transition metal complex is an important step in many catalytic cycles. Hence, an understanding of the factors that influence the oxidative addition and reductive elimination of H–E bonds is necessary to develop efficient catalysts. Density functional theory (DFT) has been used to investigate the oxidation addition of an N-H bond to iridium complexes. Both the electronic properties and steric properties of the ancillary ligands (Ln) play important roles in affecting the relative stability of LnIr(III)(NH2)H and LnIr(I)(NH3). Under similar steric effects, LnIr(I)(NH3) is more stable than LnIr(III)(NH2)H when Ln is a poor electron donating ligand and LnIr(III)(NH2)H becomes more stable than LnIr(I)(NH3) when Ln is a good donating ligand. The relative stability of LnIr(III)(NH2)H and LnIr(I)(NH3) can thus be manipulated by changing the electronic donating ability of Ln. Like metal-alkylidyne complexes that are active as catalysts for alkyne metathesis reactions, metal-nitride complexes can undergo metathesis reactions with M≡M complexes, nitriles and alkynes. Theoretical studies employing DFT methods on the ii reactions between the model compounds (MeO)3M≡N and CH3C≡N, where M = Mo and W, show that the reactions proceed through a cyclobutadiene-like transition state. The calculated energy of the transition state for M = Mo is 13 kcal/mol higher than that for M = W. This is consistent with the experimental observation that nitrogen atom exchange only occurs at elevated temperatures for M = Mo. The reactivity of metal-nitride molecules is greatly influenced by the metal, the electron configuration of the metal, and the particular set of attendant ligands. The t electronic structures of the molecules ( BuO)3M≡N(M = Cr, Mo, W) have been studied by using the gas phase photoelectron spectroscopy and the density functional calculations. It is found that the alkoxide orbitals mix strongly with the M≡N triple bond orbitals and contribute substantially to the valence electronic structure. The first ionization of t ( BuO)3Cr≡N is from an orbital of a2 symmetry that is oxygen based and contains no metal or nitrogen character by symmetry. In contrast, the first ionizations of the molybdenum and tungsten analogs are from orbitals of a1 and e symmetry that derive form the highest occupied M≡N σ and π orbitals mixed with the appropriate symmetry combinations of the oxygen p orbitals. The polarity of the M≡N bond increases down the group such that W≡N has the highest charge separation. In addition to investigation of the effects of the metals, the electronic influences of substitution at the alkoxide ligands have been examined for the molecules (RO)3Mo≡N (R=C(CH3)2H, C(CH3)3, and C(CH3)2CF3). The introduction of CF3 groups stabilizes the molecular orbital energies, iii but does not alter the overall electronic structure. DFT has been applied to study the metathesis reaction between W2(OMe)6 and MeCN. The reaction begins with the coordination of acetonitrile to W2(OMe)6 to give an adduct with a planar cyclobutadiene-like W2CN core and is then followed by the cleavage of the C-N and W-W bond in this adduct to give tungsten alkylidyne and tungsten nitride. The rate-determining step is the cleavage step. The ditungstenazacyclobutadiene t intermediate that is structurally related to ( BuO)6Mo2(NCNMe2) can also be readily obtained from the starting reagents. This structure is calculated to be thermodynamically unfavorable relative to the metathesis products and thus no such analogue for tungsten is observed in experiment. iv DEDICATION To my parents and Lu v ACKNOWLEDGEMENTS Fist of all, I would like to express my gratitude and thanks to two of my advisors, Dr. Bruce E. Bursten and Dr. Malcolm H. Chisholm, not only for their patient guidance through the course of this dissertation but also for their encouragement and support throughout my Ph.D. study. I also would like to thank Dr. Russell M. Pitzer for providing helpful suggestions and lots of education in quantum chemistry. I appreciate that many faculty members in chemistry department gave me a tremendous education. I would give my special thanks to Dr. Shore and Dr. Woodward as my committee members. I would like to extend my gratitude to all group members in Bursten and Chisholm group, for their friendship, encouragement, and discussions. Sharing an office with Mike Mrozik was a wonderful experience. He gave me a lot help both within and outside the office. I thank Dr. Benjamin Lear for teaching me how to use the Schlenk line techniques and dry box as well as some other experimental techniques. I thank Chandrani Chatterjee for helping me with the mass spectrum. I appreciate Lacey O'Neal for her help. Finally I would like to thank my parents and my wife for their unconditional love and support, all the other family members and all my friends, for their encouragement. vi VITA May 18, 1977………………………....Born – Fujian, P. R. China 1994 – 1998…………………………..B.S. Chemistry Nankai University, Tianjin, China 1998 – 2000…………………………..Analyst, Xiamen 3-Circles Battery Co., LTD Fujian, China 2000 – 2003…………………….…….M.S. Chemistry Nankai Univeristy, Tianjin, China 2003 – 2009………………………..…Graduate Teaching and Research Associate, The Ohio State University PUBLICATIONS Research publication 1. Chen, Shentan; Chisholm, Malcolm H.; Davidson, Ernest R.; English, Jason B.; Lichtenberger, Deenis L. Theoretical and Spectroscopic Investigations of the Bonding and Reactivity of (RO)3M≡N Molecules, where M = Cr, Mo and W. Inorganic Chemistry 2009, 48, 828-837. 2. Burroughs, Beth A.; Bursten, Bruce E.; Chen, Shentan; Chisholm, Malcolm H.; Kidwell, Andy R. Metathesis of Nitrogen Atoms within Triple Bonds Involving Carbon, Tungsten, and Molybdenum. Inorganic Chemistry 2008, 47, 5377-5385. 3. Bursten, Bruce E.; Chen, Shentan; Chisholm, Malcolm H. Ligand effects on the stability of the insertion products: A DFT study of oxidative addition of NH3 to iridium(I) complex. Journal of Organometallic Chemistry 2008, 693,1547-1551. vii 4. Du, Miao; Chen, Shen-Tan; Guo, Ya-Mei; Bu, Xian-He; Ribas, Joan. Synthesis, crystal structure, spectroscopy and magnetic properties of a dinuclear Cu(II) complex with 3,5-bis(2-pyridyl)pyrazole bridging ligand. Journal of Molecular Structure 2005, 737,17-21. 5. Du, Miao; Guo, Ya-Mei; Chen, Shen-Tan; Bu, Xian-He; Batten, Stuart R.; Ribas, Joan; Kitagawa, Susumu. Preparation of Acentric Porous Coordination Frameworks from an Interpenetrated Diamondoid Array through Anion-Exchange Procedures: Crystal Structures and Properties. Inorganic Chemistry 2004, 43, 1287-1293. 6. Huang, Zheng; Song, Hai-Bin; Du, Miao; Chen, Shen-Tan; Bu, Xian-He; Ribas, Joan. Coordination Polymers Assembled from Angular Dipyridyl Ligands and CuII, CdII, CoII Salts: Crystal Structures and Properties. Inorganic Chemistry 2004, 43, 931-944. 7. Du, Miao; Bu, Xian-He; Huang, Zheng; Chen, Shen-Tan; Guo, Ya-Mei; Diaz, Carmen; Ribas, Joan. From Metallacyclophanes to 1-D Coordination Polymers: Role of Anions in Self-Assembly Processes of Copper(II) and 2,5-Bis(3-pyridyl)-1,3,4- oxadiazole. Inorganic Chemistry 2003, 42, 552-559. 8. Du, Miao; Chen, Shen-Tan; Bu, Xian-He; Ribas, Joan. Crystal structure and properties of a CuII coordination polymer with 2-D grid-like host architecture for the inclusion of organic guest molecule. Inorganic Chemistry Communications 2002, 5(11), 1003-1006. 9. Du, Miao; Chen, Shen-Tan; Bu, Xian-He. {[Cd(bpo)(SCN)2]CH3CN}n: A Novel Three-Dimensional (3D) Noninterpenetrated Channel-Like Open Framework with Porous Properties. Crystal Growth & Design 2002, 2(6), 625-629. FIELDS OF STUDY Major Field: Chemistry viii LIST OF TABLE Table page 2.1 Selected bond lengths and bond angles of complexes 1a, 1b, 2a and 2b …….….. 35 2.2 Relative energies and relative Gibbs free energies (298K) were given in kcal/mol. Ir-NH3 refers to ammonia coordinated compound while HIr-NH2 refers to hydrido amido compound. …………………………….. 38 4.1 Relative areas of the He I spectra regions (A, A*, B+C) of t t BuOH and ( BuO)3M≡N relative to the total area (A+A*+B+C) …….………… 90 4.2 Prominent features in the He I photoelectron spectra, and the calculated lowest ionization potentials (IP) by ADF2007.01. See Figure 4.4 for definitions of peaks. ……………………………………….… 92 4.3 Comparison of the ADF2007.01 optimized geometrical parameters t with the crystal structure parameters for ( BuO)3M≡N…………………………..100 4.4 The calculated orbital energies (in eV) of the highest six occupied t orbitals for ( BuO)3M≡N. …………………………………………………...….101 t 4.5 Calculated primary orbital characters for ( BuO)3M≡N. ………………………. 102 4.6 Mulliken charges, molecular dipole moment (µ) and M≡N bond dissociation energies (BDE) calculated by ADF2007.01 for (RO)3M≡N. ……... 107 5.1 Free energies (kcal/mol) and selected bond distance (Å) for intermediates