LIVING a -OLEFIN POLYMERIZATION BY CATIONIC ZIRCONIUM AND HAFNIUM COMPLEXES CONTAINING CHELATING DIAMIDOPYRIDINE LIGANDS by PARISA MEHRKHODAVANDI B.Sc. (Honours) in Chemistry, University of British Columbia (1998) Submitted to the Department of Chemistry In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2002 ã Massachusetts Institute of Technology, 2002 Signature of Author _______________________________________________________________________ Department of Chemistry August 5, 2002 Certified by___________________________________________________________________________ Richard R. Schrock Thesis Supervisor Accepted by___________________________________________________________________________ Robert W. Field Chairman, Departmental Committee on Graduate Students 2 This doctoral thesis has been examined by a Committee of the Department of Chemistry as follows: Professor Daniel G. Nocera _______________________________________________________________________ Chairman Professor Richard R. Schrock ______________________________________________________________________ Thesis Supervisor Professor Joseph P. Sadighi_______________________________________________________________________ For Sohrab and Doulat, with love. For Bamas Jahangir, my inspiration. In memory of Memas Khorshid. 4 LIVING a -OLEFIN POLYMERIZATION BY CATIONIC ZIRCONIUM AND HAFNIUM COMPLEXES CONTAINING CHELATING DIAMIDOPYRIDINE LIGANDS by PARISA MEHRKHODAVANDI Submitted to the Department of Chemistry, September 2002, in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry ABSTRACT Chapter 1 2- 2- Arylated diamidopyridine ligands [H3CC(2-C5H4N)(CH2NAr)2] ([ArNpy] ) were synthesized via a Buchwald coupling between H3CC(2-C5H4N)(CH2NH2)2 and ArBr. Dimethyl complexes [MesNpy]ZrMe2 (1) and [TripNpy]ZrMe2 (8) were prepared. Synthesis of 1 was complicated by the formation of ether adducts such as [MesNpy]Zr(THF)Me2 (2) and zirconates such as [Li·OEt2][(MesNpy)ZrMe3] (3). In all of these complexes, the ligand was coordinated with fac geometry, creating a face with open coordination geometry. Methyl group exchange between neutral dimethyl complexes 1 and 8 was observed. Activation of 1 or 8 with 1.0 or 0.5 equiv of [Ph3C][B(C6F5)4] led to dinuclear monocations {[(MesNpy)Zr]2Me3}{B(C6F5)4} (11) and {[(TripNpy)Zr] 2Me3}{B(C6F5)4} (12). These dinuclear complexes were unreactive towards dimethyl compounds, [Ph3C][B(C6F5)4], or ethers at 25 ˚C, but showed limited reactivity at 40 ˚C. The JCH values for all three methyl groups in 11 and 12 was 109 Hz, which suggests a structure with three bridging methyl groups for these complexes. The hafnium complex [MesNpy]HfMe2 (16) was synthesized. Activation of 16 with [Ph3C][B(C6F5)4] yielded {[(MesNpy)Hf]2Me3}{B(C6F5)4} (17), similarly to 11 and 12. Activation of 16 with B(C6F5)3 - resulted in {[(MesNpy)Hf]2Me3}{MeB(C6F5)3} (18). No interaction between [MeB(C6F5)3] and the metal center was observed. Chapter 2 Zirconium complexes [MesNpy]ZrMe2 (1) and [TripNpy]ZrMe2 (8) were activated with [Ph3C][B(C6F5)4] and reaction of the resulting activated species with 1-hexene was examined by kinetics studies. In polymerization reactions with these species, unreacted {[(ArNpy)Zr]2Me3}{B(C6F5)4} was observed after complete consumption of the olefin. In reactions involving activated 1, 2,1 insertion of 1-hexene was observed. 2,1-Insertion of olefin and unreacted dinuclear species led to low catalyst efficiency and high polymer Mn values. The dibenzyl, [MesNpy]ZrBn2 (20), and dineopentyl, [MesNpy]ZrNp2 (22), complexes were prepared and activated with [Ph3C][B(C6F5)4] to yield [(MesNpy)ZrBn][B(C6F5)4] (21) and [(MesNpy)ZrNp][B(C6F5)4] (23), respectively. NMR studies of 21 show that the ligand pyridyl ring is not coordinated to zirconium. Complex 21 showed low reactivity towards 1-hexene. Complex 23 polymerized 1-hexene, but decomposed at 0 ˚C. Complexes [MesNpy]Zr(i-Bu)2 (24) and [TripNpy]Zr(i-Bu)2 (26) were prepared and activated with [Ph3C][B(C6F5)4] to yield 5 [(MesNpy)Zr(i-Bu)][B(C6F5)4] (25) and [(TripNpy)Zr(i-Bu)][B(C6F5)4] (27), respectively. Polymerization reactions with 25 showed first order kinetics, but the catalyst decomposed at 0 ˚C in a first order manner. Polymer Mn values are higher than expected for polymerizations with both 25 and 27. Chapter 3 Dialkyl hafnium complexes [MesNpy]HfR2 (R = Et (28), n-Pr (31), n-Bu (32), i-Pr (37)) and mixed alkyl complexes [MesNpy]Hf(i-Pr)R’ (R’ = Me (35), Cl (36)) were prepared. Activation of 28 with [Ph3C][B(C6F5)4] led to both alkyl and b-hydride abstraction, and formation of [(MesNpy)HfEt][B(C6F5)4] (29) and [(MesNpy)Hf(n-Bu)][B(C6F5)4] (30), the product of ethylene insertion into 29. Activation of 31 and 32 with [Ph3C][B(C6F5)4] resulted in b-hydride abstraction. Activation of 35 with [Ph3C][B(C6F5)4] or [HNMe2Ph][B(C6F5)4] led to formation of methyl-bridged dinuclear species. Activation of 37 with [Ph3C][B(C6F5)4] led to b- hydride abstraction to yield [(MesNpy)Hf(i-Pr)][B(C6F5)4] (38) and the product of propene insertion into 38, [(MesNpy)Hf(CH2CH(CH3)(i-Pr))][B(C6F5)4] (39). The secondary alkyl cation, 38, decomposes significantly faster the primary alkyl cation, 39. Complex 38 was prepared independently by reaction of 37 with [HNMe2Ph][B(C6F5)4]. This complex decomposed by C-H activation of the NMe2Ph by-product to yield [(MesNpy)Hf(C6H4NMe2)][B(C6F5)4] (40). Reaction of 37 with B(C6F5)3 yielded [(MesNpy)Hf(CH2CH(CH3)(i-Pr))][HB(C6F5)3] (41). Polymerization of 1-hexene with 41 followed first order kinetics. Chapter 4 Hafnium complexes [MesNpy]Hf(i-Bu)2 (42) and [TripNpy]Hf(i-Bu)2 (46) were synthesized and activated with [Ph3C][B(C6F5)4] to yield the alkyl cations [(MesNpy)Hf(i- Bu)][B(C6F5)4] (43) and [(TripNpy)Hf(i-Bu)][B(C6F5)4] (47). Complex 43 catalyzed the living polymerization of 1-hexene, as shown by kinetics and bulk polymerization studies. Molecular weights of the polymers obtained with 47 are higher than expected. 13C-labeling studies with these neutral and cationic complexes showed that there is alkyl exchange between cations, but that it is promoted by neutral dialkyl complexes. Activation of 42 with B(C6F5)3 led to [(MesNpy)Hf(i-Bu)][HB(C6F5)3] (48). The rate of polymerization with 48 was lower that that with 43, demonstrating an anion effect. The effect of inhibitors on 1-hexene polymerization was studied. The NMe2Ph inhibitor was prone to C-H activation of the aryl ring, and the C-H activation product, [(MesNpy)Hf(C 6H4NMe2)][HB(C6F5)3] (50), was independently prepared and characterized. Suitable inhibitors were bulky ethers and amines that did not contain aryl groups. Appendix 1 Tantalum complexes [MesNpy]TaMe3 (51) and [TripNpy]TaMe3 (52) were synthesized by reaction of Li2[ArNpy] with TaMe3Cl2. The synthesis was complicated by formation of a by- product (53) in which only one of the amido arms is coordinated and the ligand backbone is interacting with the metal center. Activation of 51 with [Ph3C][B(C6F5)4] led to the mononuclear cation [(MesNpy)TaMe2][B(C6F5)4] (54). Thesis Supervisor: Dr. Richard R. Schrock Title: Frederick G. Keyes Professor of Chemistry 6 TABLE OF CONTENTS Title Page......................................................................................................................................... 1 Signature Page................................................................................................................................. 2 Dedication ....................................................................................................................................... 3 Abstract ........................................................................................................................................... 4 Table of Contents ............................................................................................................................ 6 List of Abbreviations....................................................................................................................... 8 List of Compounds ........................................................................................................................ 10 List of Figures ............................................................................................................................... 12 List of Schemes ............................................................................................................................. 15 List of Tables................................................................................................................................. 16 General Introduction .................................................................................................................. 17 Chapter 1. Synthesis and activation of dimethyl zirconium and hafnium complexes of arylated diamidopyridine ligands: The importance of methyl bridges in a system with an open coordination environment ................................................................................................. 22 1.1 Introduction ................................................................................................................ 23 1.2 Ligand synthesis......................................................................................................... 25 1.3 Complication during synthesis of [MesNpy]ZrMe2 .................................................. 27 1.4 Synthesis of [ArNpy]ZrMe2 .....................................................................................