Intermediate Oxidation State Tungsten Acetylacetonate Complexes

Intermediate Oxidation State Tungsten Acetylacetonate Complexes Chetna Khosla A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry. Chapel Hill 2009 Approved by: Advisor: Professor Joseph L. Templeton Reader: Professor Maurice Brookhart Reader: Professor Cynthia Schauer Professor Valerie Ashby Professor H. Holden Thorp ABSTRACT Chetna Khosla: INTERMEDIATE OXIDATION STATE TUNGSTEN ACETYLACETONATE COMPLEXES (Under the direction of Professor Joseph L. Templeton) Previous work with tungsten(II) acetylacetonate complexes has focused on synthesis of complexes with -bound ligands (alkyne, nitrile, imine, ketone, aldehyde). In this work, 2 addition of methyl triflate (MeOTf) to W(CO)(acac)2(η -N≡CPh) produces the iminoacyl 2 complex [W(CO)acac)2(η -MeN=CPh)][OTf]. Displacement of the carbon monoxide in 2 + [W(CO)(acac)2(η -MeN≡CPh)] by isonitriles, bulky phosphines, and alkynes has been accomplished. The substitution of carbon monoxide by alkyne relieves the iminoacyl ligand of its role as a four-electron donor and enables further reduction of the C-N based ligand. Use 2 + of Na[HB(OMe)3] as a hydride source that attacks [W(RC≡CR′)(acac)2(η -MeN=CPh)] 2 yields the imine complex W(RC≡CR′)(acac)2(η -MeN=CHPh) with a diastereoselective ratio of 2:1. Addition of MeOTf leads to the final tungsten(II) iminium complex 2 [W(RC≡CR′)(acac)2(η -Me2N=CHPh)][OTf]. 2 Addition of m-chloroperoxybenzoic acid (MCPBA) to W(CO)(acac)2(η -N≡CR) 2 2 results in oxidation of the metal center to form the W(IV) d metal complex W(O)(acac)2(η - N≡CR). Similar results are obtained with alkyne, imine, ketone, or aldehyde ligands in the 2 2 coordination sphere. Methylation of W(O)(acac)2(η -N≡CPh) to produce [W(O)(acac)2(η - MeN≡CPh)][OTf] is accomplished using MeOTf. Subsequent addition of Na[HB(OMe)3] 2 produces W(O)(acac)2(η -MeN≡CHPh) with diastereoselectivity of 10:1. ii (Trimethylsilyl)diazomethane addition to W(CO)3(acac)2 results in end-on coordination through nitrogen, producing the tungsten(IV) d2 complex W(CO)(acac)2(N2CHSiMe3) with nitrogen triply-bound to tungsten. Similar results are observed with diphenyldiazomethane and ethyl diazoacetate. Addition of Na[HB(OMe)3] to - + W(CO)(acac)2(N2CHSiMe3), followed by treatment with HBF4 results in H and H addition across the C=N bond to form the tungsten(IV) complex W(CO)(acac)2(N2HCH2TMS). 2 Addition of PMe3 to a CH2Cl2 solution of W(CO)(acac)2(η -N≡CR) leads to displacement of nitrile and one equivalent of acetylacetonate to produce the tungsten(II) complex W(CO)(acac)(Cl)(PMe3)3. Reaction of NaN3 with W(CO)(acac)(Cl)(PMe3)3 produces loss of carbon monoxide and dinitrogen prior to protonation to form the 2 + tungsten(IV) d imido complex [W(NH)(acac)(PMe3)3] . Aryl isocyanate insertion into the NH bond occurs at high temperatures to the form new C-N bonds. 2 t W(CO)(acac)2(η -P≡CR) (R = Ad, Bu) is synthesized upon addition of P≡CR (R = t Ad, Bu) to W(CO)3(acac)2. The phosphorus lone pair is utilized to bind Lewis acidic metal complexes, W(CO)5(thf) or [PtCl2(PEt3)]2, to produce dinuclear metal complexes. iii ACKNOWLEDGEMENTS I would first like to thank my advisor Professor Joseph Templeton for all of his support. Joe has always managed to be there when I needed guidance, even if he was busy in DC or with important faculty meetings. Joe has challenged me to think more critically about my work and made me a better graduate student. He has supported my activities at UNC, even when I would be out of lab due to these obligations. Joe is also one of the nicest and most sincere people that I have ever met with a great concern for his students. I could not ask for a better mentor. The many Templeton lab members I have worked with have helped me greatly throughout graduate school. Dr. Andy Jackson helped me get off to a great start in my project doing tungsten bis(acac) chemistry. His excitement about his work was transferred to me and I owe him many thanks for all his help. Dr. Andrew Garrett taught me the basics of working in the lab and always provided a kind ear and a good laugh. Dr. Ned West has a great mind for chemistry and is always providing ideas to anyone who would listen, even if he no longer works in the Templeton Lab. Kristi Engelman has been a great lab mate and friend for the last three years as we helped keep each other sane. Dr. Margaret MacDonald, Anne Saunders, Rob Foster, Bryan Frauhiger, Leah Pranger, and Elise Traversa have been great co-workers for the my tenure at UNC and I thank them for all their help and support. Drs. Wes Bernkoetter and Marc Walter in the Brookhart Lab have provided me with great project ideas that have advanced my graduate career. They are two of the most knowledgeable chemists I iv know and I admire them greatly. Many thanks to all the other Templeton and Brookhart group members that I haven’t mentioned. My two roommates at UNC, Chrissie Fecenko and Alison Campbell, have been great friends to me over the past years and helped me make it through graduate school. Even as they have moved on past UNC, their friendships have been invaluable to me. Anthony Chianese has given me essential support during my graduate career. He helped me study for my exams, given me research ideas and lab tips, and been the best friend I could ask for. My family has been my greatest supporters over the past five years. My mom, dad, sisters Shalini and Anjali, and my brother-in-law Puran have encouraged me in my studies even when I thought I couldn’t keep going. Thank you all. v TABLE OF CONTENTS LIST OF FIGURES AND SCHEMES ......................................................................................x LIST OF TABLES................................................................................................................. xiii LIST OF ABBREVIATIONS AND SYMBOLS .................................................................. xiv I. Structural Design of W(II) and W(IV) Complexes with Anionic Bidentate Ligands .........1 Introduction....................................................................................................................1 Molecular Design to Promote η2-Coordination of Nitriles............................................3 Synthesis and Reactivity of W(CO)3(acac)2 ..................................................................6 Summary......................................................................................................................10 References....................................................................................................................11 II. Reduction of a π-Bound Nitrile Ligand to a π-Bound Iminium Ligand in a Tungsten(II) Bis(Acetylacetonate) Coordination Sphere ..................................................14 Introduction..................................................................................................................14 Results and Discussion................................................................................................16 Summary......................................................................................................................36 Experimental Section...................................................................................................36 References....................................................................................................................47 III. Reactivity Patterns of Bis(Acetylacetonate) Tungsten(IV) Complexes Containing a π-Basic Diazoalkane or Oxo Ligand ............................................................51 vi Introduction..................................................................................................................51 Results and Discussion................................................................................................52 Summary......................................................................................................................70 Experimental Section...................................................................................................71 References....................................................................................................................78 IV. Synthesis and Reactivity Studies of a Tungsten(IV) Imido Complex Formed From W(CO)(acac)(X)(PMe3)3 ............................................................................82 Introduction..................................................................................................................82 Results and Discussion................................................................................................83 Summary....................................................................................................................103 Experimental Section.................................................................................................104 References..................................................................................................................114 2 V. Synthesis and Reactivity of W(CO)(acac)2(η -P≡CR) Complexes Containing π-Bound Phosphaalkyne Ligands..................................................................118 Introduction................................................................................................................118 Results and Discussion..............................................................................................119 Summary....................................................................................................................128

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