Syntheses and Studies of Group 6 Terminal Pnictides, Early-Metal Trimetaphosphate Complexes, and a New bis-Enamide Ligand by MASSACHUSMS INSTITUTE Christopher Robert Clough OF TECHNOLOGY B.S., Chemistry (2002) JUN 072011 M.S., Chemistry (2002) The University of Chicago Submitted to the Department of Chemistry ARCHIVES in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2011 @ Massachusetts Institute of Technology 2011. All rights reserved. Author.. .. .. .. .. ... .. .. .. .. .... Department of Chemistry May 6,2011 Certified by............. Christopher C. Cummins Professor of Chemistry Thesis Supervisor Accepted by ........ Robert W. Field Chairman, Department Committee on Graduate Studies 2 This Doctoral Thesis has been examined by a Committee of the Department of Chemistry as follows: Professor Daniel G. Nocera ..................... Henry Dreyfus Profe~ssofof Energy and Pr6fessor of Chemistry Chairman Professor Christopher C. Cummins............................ .................. Professor of Chemistry Thesis Supervisor Professor Richard R. Schrock .................. Frederick G. Keyes Professor of Chemistry Committee Member 4 For my Grandfather: For always encouraging me to do my best and to think critically about the world around me. 6 Alright team, it's the fourth quarter. The Lord gave us the atoms and it's up to us to make 'em dance. -Homer Simpson 8 Syntheses and Studies of Group 6 Terminal Pnictides, Early-Metal Trimetaphosphate Complexes, and a New bis-Enamide Ligand by Christopher Robert Clough Submitted to the Department of Chemistry on May 6, 2011, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract Investigated herein is the reactivity of the terminal-nitrido, trisanilide tungsten complex, NW(N[i- Pr]Ar) 3 (Ar = 3,5-Me 2C6H3, 1). Nitride 1 has been shown to undergo an "N for (O)C1 metathesis with a variety of acid chlorides to form oxochloride (Ar[i-Pr]N) 3W(O)C1 (2) and the corresponding nitriles. The reaction of 1 with acid chlorides has been shown to proceed through an acylimido chloride intermediate. Furthermore, oxochloride 2 has been converted to a terminal phosphido trisanilide tungsten complex, PW(N[i-Pr]Ar) 3 (9) by treatment with the anionic niobium phosphide complex [Na(OEt2)][PNb(N[Np]Ar) 31. Nitride 1 and oxochloride 2 have been converted to pseudo-octahedral complexes through the use of electrophilic reagents such as oxalyl chloride and phosphorus pentachloride. (Ar[i- Pr]N)3W(OCN)(Cl) 2 (10) and (Ar[i-Pr]N)3W(N=PCl 3)(Cl) 2 (11) are synthesized by treating compound 1 with oxalyl chloride and PCl5, respectively. Similarly, (Ar[i-Pr]N) 3W(Cl) 3 (12) is formed by treatment of oxochloride 2 with PC15 with concomitant loss of oxyphosphorus trichloride. Reaction studies of trichloride 12 undertaken in the attempt to generate a low-coordinate tungsten species are also presented. Also reported presently is a new procedure for synthesis of the terminal phosphoryl complex (Ar[t-Bu]N)3MoPO (17) by treating phosphide (Ar[t-Bu]N) 3MoP (16) with the potent oxygen atom transfer (OAT) reagent mesitylnitrile oxide (MesCNO). In conjunction with collaborators, the thermodynamic and kinetic aspects of MesCNO as an OAT reagent with phosphide 16 and phosphines have been investigated. Density Functional Theory calculations of OAT reactions of MesCNO are also shown. In an effort to further develop the coordination chemistry of the trianionic, tridentate ligand trimetaphosphate, studies are described whereupon trimetaphosphate is metallated with molybdenum. (MeCN)3Mo(CO) 3 reacts with [PPN] 3[P30 9] -H20 ([PPN] = [Ph3P=N-PPh3]') to form the trimetaphosphate salt [PPN] 3[(P30 9)Mo(CO) 3] ([PPN] 3[18]) in high yield. Efforts to generate trimetaphosphate vanadium oxo ((P30 9)V--O, 19) are also revealed. Finally, the synthesis of a new bis-enamide ligand class is described by the double addition of ketenimines to dilithium arylphosphanides. Formation of [Li(thf)]2 {PhP[C(CPh2)NPh] 21 ([Li(thf)] 2[20]) and [Li(thf)]2{MesP[C(CPh2)NPh] 2} ([Li(thf)]2[21]) are presented. The synthesis of tantalum species utilizing these new bis-enamide ligands is also demonstrated. Thesis Supervisor: Christopher C. Cummins Title: Professor of Chemistry 10 Acknowledgements It has been said that it takes a village to raise a child. In this case, it has taken a small metropolis to help an imbecile like me finish my Ph.D. In my opinion, the acknowledgements section is the most important part of this document. First off, this may be the only section that most people read. More importantly, none of the work in this dissertation would be possible without the love, support, encouragement, guidance, advice and ass-whipping that the people listed here have supplied. I am making every effort to thank each and every person who has made an impact on me, no matter how small, while I pursued my studies at MIT. In no way will I make any attempt at brevity in this section. My deepest apologies to anyone whom I forget to thank-in no way was the omission deliberate. Finishing this degree has truly been the hardest thing that I've ever done in my life and is one of the accomplishments of which I am most proud. To anyone reading this and especially to those listed in this section, I thank you from the bottom of my heart and am forever indebted to you. Science has always fascinated me-it was the one subject I always looked forward to in school for as long as I can remember. When most children wanted to be police officers, truck drivers or ballplayers, I dreamed of becoming a scientist. From the moment I could pronounce the word, I wanted to be a paleontologist. As most childhood dreams die, so did mine-I settled for chemistry. As I look back upon my career in chemistry, I feel it is best to proceed chronologically throughout my development as a scientist. I seriously doubt that I would have become a chemist had it not been for Mr. Quigel, my chemistry teacher sophomore year of high school. Mr. Quigel challenged us not just to learn the material presented, but to truly understand it-to understand why. I still recall the lab where we measured the freezing point of p-dichlorobenzene... The idea was simple enough, melt the material and then observe the temperature as a function of time while it cooled back down to room temperature. If people had simply read the material in the textbook, they would know that upon reaching the freezing point of the dichlorobenzene, the temperature would stabilize until the material had frozen fully. When Mr. Quigel was asked why the temperature had suddenly stopped decreasing at ca. 53 C, he simply gave the answer, "Maybe the thermometer is broken. Here, try this one." Not only did this save him from having to answer the question 20-some odd times (along with lecturing each student for not doing the required reading), it forced people to actually THINK about what's going on. I had the pleasure of taking Quigel's class for a full year my sophomore year and his AP chemistry class my senior year. It's because of him that things like HONClBrIF and the charge of every conceivable ion are burned into my head forever. Throughout all the pain and frustration of learning things like stoichiometry for the first time, Mr. Quigel helped (forced) me to think about why things are the way they are. It was then that I realized the beauty of chemistry. I can honestly say that by the end of my sophomore year of high school that I knew I wanted to be a chemist. After High School, I took a short trip down the Kennedy to attend the University of Chicago. I suppose at this point I should thank Prof. Viresh Rawal for putting me down the path to be an inorganic chemist. Here is my dark secret-I became an inorganic chemist not as an act of rebellion for hating Prof. Rawal's organic chemistry class, truly the opposite. I became an inorganic chemist entirely by accident. Early in my second year of college, I approached Prof. Rawal about joining his laboratory as an undergraduate researcher. He kindly explained to me that he already had four undergraduates working for him and he suggested four other faculty members in chemistry that were looking for undergraduates: Hillhouse, Hopkins, Jordan and Piccirilli. Alphabetically, "Hillhouse" comes first, so I went to talk to Greg. (Admittedly, three out of the four are inorganic chemists, so Prof. Rawal had stacked the deck...) Greg Hillhouse gave me several reprints of his articles and told me to go home, read them over and then decide if that's the sort of thing that I wanted to do. I tried. I really did. But never having taken an inorganic chemistry course, it was like trying to read Greek. I remember how bizarre it looked seeing carbons bound to nickel. After about a week, Greg called me up and asked what I thought. (Eleven years later, I'm paraphrasing the conversation that took place.) "Dude, wondering if you wanted to sign up. I had another girl come by after you asking if she could join the lab. I only want to take one undergrad this quarter and since you were here first, the choice is yours." Without hesitation, I said yes. And it was perhaps the best decision I have made in my life. Working in Greg's lab was a wonderful experience. I had figured that I would be treated as a glorified lab tech-washing glassware, allowed to run an occasional reaction..