Ligand mới cho hóa học phối hợp Lanthanide - Luận án tiến sĩ

Copyright by Jennifer Anne Moore 2006 The Dissertation Committee for Jennifer Anne Moore Certifies that this is the approved version of the following dissertation: Exploring New Ligand Environments for Lanthanide Coordination Chemistry Committee: Alan H.Cowley, Supervisor Richard A. Gordon Exploring New Ligand Environments for Lanthanide Coordination Chemistry by Jennifer Anne Moore, B. Dissertation Presented to the Faculty of the Graduate School of The University of Texas at Austin in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The University of Texas at Austin May 2006 UMI Number: 3244338 UMI Microform 3244338 Copyright 2007 by ProQuest Information and Learning Company. All rights reserved.

This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 Acknowledgements First, I would like to thank Professor Alan H. I am constantly amazed by his enthusiasm for all types of chemistry and hopefully that will now include f-block chemistry.

I enjoyed his “open door policy” and whenever I had a question or idea, I would walk into his office and always be welcomed warmly thank you for all your support. Next, I want to thank all the Cowley group members that I have encountered over the last four years, I appreciate the conversation and support, I thank you, Dr. Robert Wiacek, Dr. Jeffery Pietryga, Dr.

Piyush Shukla, Silvia Filliponi, Lucy Mullins, Zheng Lu, Dr. Christopher Entwhistle, Micheal Findlater, Kalyan Vasudevan, Clint Hoberg and Dr. I wanted to thank Dr. Vince Lynch for all the help and advice.

I enjoyed his sense of humor, which never failed to make me laugh and groan at the same time. Next, I want to thank Professor Richard Jones for answering my endless questions whenever the Boss was not available and for the all the equipment I have borrowed none of which was ever broken. Thank you Professor Brad Holiday and Professor Chris Bielawski for agreeing to be on my committee. I would especially like to thank Dr.

John Gordon for all his advice, suggestions and help regarding Lanthanide chemistry you were an invaluable asset to me. Drasko Vidovic, who was my desk buddy since day one, I want to thank you for all the Reese’s Peanut Buttercups and some days I don’t think I would have made it through the day without them Next, I would like to thank Dr. Jamie Jones, little did I know that when I was recruited by her to join the Cowley group, that she would play such an instrumental role in my life and I will never to able to express how much iv she helped me. I could not ask for a better friend thank you Dr.

I also want to thank Dr. Nick Hill, for his endless patience on trying to improve my writing skills, listening to me complain and the never-ending lunches he endure at the same restaurants. Most of all I would like to thank my wonderful husband, who had to tolerate me through my graduate experience. Rondall you helped me to keep going, gave me endless encouragement and loved me no matter what.

Thank you Honey Bunny. v Exploring New Ligand Environments for Lanthanide Coordination Chemistry Publication No._____________ Jennifer Anne Moore, Ph. The University of Texas at Austin, 2006 Supervisor: Alan H. Cowley The recent surge of interest in Lanthanide (Ln) chemistry is focused on the synthesis and characterization of new families of mixed-valence Ln complexes for potential applications in electronics.

Accessing mixed-valence systems in Ln chemistry has so far been difficult due to the lack of information available on these elements in an oxidation state other than the common Ln(III) state. We are interested in devising a series of complexes that feature two discrete Ln(II) metals ions and, via controlled intramolecular electron transfer, we aim to oxidize one of the Ln(II) species to a Ln(III), thus generating a mixed-valence complex. Although intramolecular electron transfer has been reported previously for a handful of Ln complexes, the transfer was spontaneous. vi The reaction of the Ln(II) precursors (C5Me5)2Ln·OEt2 (Ln = Sm, Eu and Yb) with various 1,4-diaza 1,3-butadiene R1N=CR2–CR2=NR1 (DAD) ligands has led to the isolation of Ln(II) and Ln(III) complexes that are dependant on the nature of the R1 groups.

Furthermore, we have examined the electronic structure of the free ligand by Density Functional Theory (DFT), exploring the relationships between the size of the HOMO/LUMO gap and/or the absolute energies of the LUMO and the occurrence of electron transfer. The development of new non-cyclopentadienyl (Cp) Ln catalysts is also explored. Since the nature of the auxiliary ligands influences the reactivity of a complex, the replacement of Cp-type ligands with nitrogen-based ligands will increase the electophilicity of the metal center and permit greater control over the steric environment at the reactive site, thus allowing for the generation of a more active catalyst. One nitrogen-based ligand system of current interest is a β- diketiminate containing electron withdrawing substituents such as C6F5.

The purpose of the study is to develop a series of new Ln compounds featuring one or more β- diketiminate ligands and to investigate their catalytic activity in ethylene polymerization. vii Table of Contents CHAPTER 1: LANTHANIDE DIAZABUTADIENE COMPLEXES 1 Overall Introduction .14 Results and Discussion .74 viii General Procedures .85 Tables of X-ray Crystallographic Data .156 CHAPTER 2: A COMPUTATIONAL STUDY OF N,N'-DISUBSTITUED 1, 4 -DIAZA 1,3-BUTADIENES LIGANDS 161 Overall Introduction .161 Results and Discussion .167 HOMO/LUMO Gap .172 Molecular Orbital Pictures.179 ix Geometry of Optimized Structures .199 CHAPTER 3: LANTHANIDE β – DIKETIMINATE COMPLEXES 201 Overall Introduction .207 Results and Discussion .252 Results and Discussion .252 Summary of Polymerization Studies .262 Polymerization Studies without a co-catalyst.263 Polymerization Studies with a co-catalyst .264 Tables of X-ray Crystallographic Data .291 xi CHAPTER 1 LANTHANIDE DIAZABUTADIENE COMPLEXES INTRODUCTION Mixed valence complexes have been of interest to scientists over the last five decades due to the potential applications of these compounds, including energy conversion, new materials, better catalysts and molecular electronics.1-4 The field has seen an explosion of new mixed valence transition metal systems, allowing the isolation of complexes that features two discrete metals centers bridged by a variety of different ligand systems. These mixed-valence systems have permitted scientist to gain an understanding of the flow of electron between metal centers. However, so far lanthanide (Ln) mixed-valence systems have remained elusive.

Of particular interest in Ln mixed valence systems are discrete assemblies in which two metal centers are connected by a bridging ligand and show an electronic communication between the metal centers. Such interactions allow the possibility of delocalization of election density over fairly long distances and in the emerging field of molecular electronics, represent one of the simplest electronic building blocks, namely a molecular wire. An enhanced understanding of the mechanism of communication could potentially 1 lead to the ability of controlling oxidation states, which is essential for the development of the basic elements of molecular and quantum computing devices. Accessing mixed valence systems in Ln chemistry has so far been difficult due to the lack of information available on these elements in an oxidation state other then the common +3 state.

An objective of the present work was to devise a series of complexes that feature two discrete Ln(II) metals ions such that via controlled intramolecular electron transfer, one of the Ln (II) moieties is converted to a Ln (III), thus generating a mixed valence complex (Figure 1. L Ln2+ Ln2+ L L Ln3+ Ln2+ L controlled oxidation L = Auxiliary ligand = 'conjugated' = 'conjugated' L = Auxiliary ligand ligand system ligand system Figure 1.1 Schematic showing controlled oxidation of a Ln(II) metal to a Ln(III) metal thus generating a mixed metal complex. In particular, the present study is focused on the interaction of Ln(II) metal moieties with ligand systems that are able to oxidize the metal center with the objective of understanding and controlling this spontaneous electron transfer. Although the generality of the metal-to-ligand charge transfer process is now established for Ln(II) to Ln(III) metal conversion the fundamentally interesting, questions as to its origin are just beginning to be addressed.

In 2002 Anderson et al. reported that the ytterbocene bis-pyridine adduct [(Me5C5)Yb(py)2], (py = pyridine), is a green diamagnetic complex as expected since Yb(II) has a closed shell electronic structure.5 However, a surprising result for 2 similar stoichiometrically related complexes of decamethylytterbocene bipyridine (Me5C5)Yb(byp)2, (bpy = bipyridine) and the related decamethylytterbocene and 1,10-phenanthroline complex (Me5C5)Yb(phen)2 (phen = 1,10-phenanthroline) is that chemical and physical properties are different from those of [(Me5C5)Yb(py)2]. The (Me5C5)Yb(byp)2 and (Me5C5)Yb(phen)2 complexes are able to undergo a spontaneous electron transfer, resulting in oxidation of the metal center and consequent reduction of the ligand.5 John et al. a recently reported similar terpyridine complex of ytterbium, ((Me5C5)Yb(typ)2 (typ = terpyridine)6,7 which has similar chemical and physical properties to those reported by Anderson et al.

for (Me5C5)Yb(byp)2 and (Me5C5)Yb(phen)2, thus showing greater generality for the process shown in Scheme 1. 3 Me5 Me5 A 2 eq. N N Yb2+•OEt2 Yb2+ N Me5 Me5 Me5 Me5 N N N B Yb2+•OEt2 Yb3+ N Me5 Me5 Me5 Me5 N C N N Yb2+•OEt2 Yb3+ N Me5 Me5 Scheme 1.1 Scheme illustrating the reactions of Ln(II) complexes with (a) two equivalents pyridine (b) bipyridine (c) 1, 10-phenanthroline. The decamethylytterbocene adducts shown in B and C in Scheme 1.1 cannot be simply represented as (C5Me5)2YbIII(L-), with non-interacting Ln and ligand spins and in fact, their magnetic behavior is not fully understood.

The issue will be explored in the present study. Similar behavior has been reported for diazabutadiene DAD(R1, R2) (Figure 1.2) complexes of ytterbium and samarium. However, their chemical and physical properties have not been investigated as thoroughly as the pyridine complexes. In general, no systematic trends related to the diimine ligand structures or redox behavior have been identified that would shed light on the origin 4 of the charge-transfer process or the resulting spin interactions.

It stands to reason that in order to gain further insight into the origin of the charge-transfer process it would be necessary to undertake systematic structural variations. Anderson and co- workers have examined the effects of changing the substituents on the cyclopentadienide rings of ytterbocene complexes by investigating the magnetic moments of the resulting complexes. In the present study a series of N, N’- disubstituted 1,4-diaza- 1,3-dienes (DAD, R1, R2) (Figure 1.2) ligands will be used to probe the behavior of the Ln(II)/Ln(III) redox couples. Particular emphasis is placed on varying the R1 substituents because of the proximity of the nitrogen atoms to the Ln centers.2 N, N’-disubstituted 1,4-diaza- 1,3-butadienes (DAD, R1, R2).

Diazabutadiene ligands (DAD, R1, R2) used extensively in d- and p-block chemistry on account of their diversity of coordination modes and interesting redox properties. Significantly, less information is available for (DAD, R1, R2) complexes of the Ln elements. The known organo-Ln (DAD, R1, R2) derivatives can be classified into three types depending on the degree of the reduction of the (DAD, R1, R2) ligand (Figure 1. In the first class (a) the (DAD, R1, R2) ligands function as a neutral bis(imine) donors, while in (b) the (DAD, R1, R2) ligands exists as anion 5 radicals.

In the third class, (c) the (DAD, R1, R2) ligands are doubly reduced to a dianion. R1 R1 R1 R2 R2 R2 N N N LnM LnM LnM N N N R2 R2 R2 R1 R1 R1 a b c Figure 1.3 The three possible bonding modes for Ln diazabutadiene complexes. In terms of Ln chemistry, the previously reported diazabutadiene complexes are formed either by reaction of a neutral diazabutadiene with an organometallic Ln fragment or via metathesis reactions of diazabutadiene radical anions and/or dianions with a Ln(II) or Ln(III) halides. The first Ln diazabutadiene complex was reported by Cloke et al.8 using co-condensation of the vapors of Y0, Nd0, Sm0 and Yb0 with an excess of DAD(t-Bu, H) in heptanes.