A Dissertation Entitled the Study of Lanthanides for Organometallic And

Home , Lanthanocene, Organomercury, Organometallic chemistry

A Dissertation

entitled

The Study of Lanthanides for Organometallic and Separations Chemistry

Andrew Charles Behrle

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Chemistry

______Dr. Joseph A. R. Schmidt, Committee Chair

______Dr. Mark R. Mason, Committee Member

______Dr. Steven J. Sucheck, Committee Member

______Dr. Constance A. Schall, Committee Member

______Dr. Patricia R. Komuniecki, Dean College of Graduate Studies

The University of Toledo December 2012

This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author.

An Abstract of

The Study of Lanthanides for Organometallic and Separations Chemistry

Andrew Charles Behrle

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Chemistry The University of Toledo

December 2012

Part 1. The effective use of f-element complexes as catalysts for reactions such as hydroamination and hydrophosphination has been demonstrated in many recent reports.

Unfortunately, the homoleptic starting materials underpinning this chemistry are generally derived from only a handful of ligands. That is, of the homoleptic lanthanide complexes that exist, the majority make use of alkylsilane (-CH2SiMe3), silylamide (-

N(SiMe3)2), or benzyl (-CH2C6H5) derivatives.

The paucity of tri-alkyl lanthanide complexes can be attributed to the required extended coordination sphere and high Lewis acidity or electrophilicity of these metals.

While these properties make lanthanum alkyl complexes very reactive, in turn they also make their synthesis and manipulation quite challenging. Our efforts have focused on the development of unexplored homoleptic tri-alkyl rare-earth metal complexes utilizing simple ligands that fulfill both the electronic and steric requirements of these metal

iii centers. Herein, we report our findings of a new class of homoleptic tri-alkyl rare-earth metal complexes using alpha-metallated N,N-dimethylbenzylamine ligands as stable benzyl ligand derivatives to form lanthanide complexes free of coordinating solvent.

We have also expanded the reactivity scope of these homoleptic lanthanide complexes to include stoichiometric insertion and catalytic hydrophosphination reactions involving heterocumulenes. The tris alpha-metallated N,N-dimethylbenzylamine lanthanum and yttrium complexes [α-La(DMBA)3, α-Y(DMBA)3] have proven to be capable starting materials that undergo triple insertion reactions with a variety of carbodiimide ligands. In addition α-La(DMBA)3 demonstrated excellent catalytic activity for the room temperature hydrophosphination of a wide array of heterocumulenes.

Part 2. Another current focus of the Schmidt group involves development of a class of lower rim functionalized calix[4]arenes containing ligands that have been previously shown to selectively separate lanthanides. These calix[4]arenes will be attached to a solid support through an alkyl linker at the methylene position and separation will be based primarily on the ionic radius of the metal cation.

In summary, we report the synthesis and derivatization of a series of 2-(ω-

(alkyl))tetramethoxy-p-tert-butylcalix[4]arenes. These calix[4]arenes represent intermediates in a multi-step synthesis for the design of lower rim modified

iv calix[4]arenes that will be evaluated for the separation of lanthanide ions with the future goal of attachment to a solid support.

Acknowledgements

First and foremost I want to acknowledge my family. I have been blessed and fortunate to have parents who stressed the importance of an education throughout my life.

I cannot find the words to fully express my gratitude for my parents loving and caring support throughout my life and their help with the endeavors I have overcome. I also want to thank my sisters, Catherine and Kristen. I would like to acknowledge three people who were instrumental in my decision to pursue chemistry: Fr. John Ebenhoeh,

O.S.F.S, Dr. Hongcai Zhou, and Dr. Joseph A. R. Schmidt. Joe not only pushed me to be the best synthetic chemist I can be, but encouraged me to always remember to try new reactions. I thank Joe for his seemingly bottomless chasm of chemistry knowledge, help and his willingness to always give advice. I want to acknowledge and thank my committee members for their input and suggestions throughout my graduate career. I also acknowledge my co-workers over the past five years. I want to thank Dr. Andrew R.

Shaffer, Dr. John F. Beck, Dr. Tamam Baiz, Matt Hertel, Danielle Samblanet, Nick

Zingales, and Sreejit Menon for all their help in and outside the lab. Finally I want to thank my wife Natalie for all her love, support, and patience. I am very blessed to have you in my life. You have been with me since I began this journey and continue to remain at my side. I love you more than words can describe.

Contents

Abstract iii

Acknowledgements vi

Contents vii

List of Tables ix

List of Figures x

List of Schemes xii

Chapter 1 An Introduction to Lanthanides and Their Chemistry

1.1 General Properties 1

1.2 Inorganic Complexes 5

1.3 Organometallic Chemistry of the Lanthanides 9

1.4 Catalysis 24

Chapter 2 Synthesis and Protonolysis Reactivity of Homoleptic Alpha- Metallated N,N- Dimethylbenzylamine Rare-Earth Metal Complexes

2.1 Introduction 27

2.2 Results and Discussion 29

2.3 Conclusion 41

2.4 Experimental 42

vii

2.4.1 General Considerations and Instrumentation 42

2.5 Crystallography 54

Chapter 3 Insertion Reactions and Catalytic Hydrophosphination of Heterocumulenes using Alpha-Metallated N,N- Dimethylbenzylamine Rare-Earth Metal Complexes

3.1 Introduction 60

3.2 Results and Discussion 62

3.3 Conclusion 73

3.4 Experimental 74

3.4.1 General Considerations and Instrumentation 74

3.4.2 General Procedures for the Hydrophosphination of 79 Heterocumulenes

3.4.2.1 Method A 79

3.4.2.2 Method B 80

3.4.2.3 Method C 80

3.5 Crystallography 87

Chapter 4 Modification and Synthesis of 2-(ω-Chloroalkyl)- 91 Tetramethoxy-p-tert-Butylcalix[4]arenes

4.1 Introduction 91

4.2 Results and Discussion 96

4.3 Conclusions 102

4.4 Experimental Details 103

References 113

viii

List of Tables

1.1 Abundance of Lanthanides 2

1.2 Selected Properties of Lanthanides and Their Ions 3

1.3 Colors and Electronic Ground States of M3+ Ions 5

2.1 Selected Bond Distances and Angles for (2-1)-(2-8) 33

2.2 Crystal Data and Collection Parameters (2-1)-(2-5) 58

2.3 Crystal Data and Collection Parameters (2-6)-(2-9) 59

3.1 Catalytic Addition of Phosphines to Heterocumulenes 69

3.2 Crystal Data and Collection Parameters (3-3) and (3-5) 90

List of Figures

1.1 Multiple coordination modes of carbonates to rare-earth metals 7

1.2 Coordination mode of phosphates to rare-earth metals 7

1.3 Coordination mode of sulfate to lanthanum ions 8

1.4 Bidentate secondary phosphine ligands 21

2.1 1H NMR spectrum of 2-1 30

2.2 1H NMR spectrum of 2-8 31

2.3 ORTEP diagram of 2-1 32

2.4 ORTEP diagram of 2-8 33

2.5 ORTEP diagram of 2-2 35

2.6 ORTEP diagram of 2-3 35

2.7 ORTEP diagram of 2-4 36

2.8 ORTEP diagram of 2-5 36

2.9 ORTEP diagram of 2-6 37

2.10 ORTEP diagram of 2-7 37

2.11 ORTEP diagram of 2-9 40

2.12 ChemDraw figure of 2-1 44

2.13 ChemDraw figure of 2-8 48

3.1 ORTEP diagram of 3-3 65

3.2 ORTEP diagram of 3-5 72

4.1 The four conformations of p-tert-butylcalix[4]arene 92

4.2 Location of the three possible positions for modification of calix[4]arene 93

4.3 1H NMR spectrum of 4-3 98

4.4 1H NMR spectrum of 4-5 100

4.5 1H NMR spectrum of 4-9 102

List of Schemes

1.1 Synthesis of rare-earth metal borates 9

1.2 Synthesis of (trimethylsilyl)methyl rare-earth metal complexes 11

1.3 Synthesis of Ln(CH2SiMe3)3 11

1.4 Synthesis of rare-earth metal cationic complexes 12

1.5 Synthesis of heteroleptic rare-earth alkyl complexes 12

1.6 Synthesis of homoleptic lanthanide tribenzyl complexes 14

1.7 Synthesis of donor functionalized benzyl divalent lanthanide complexes 14

1.8 Synthesis of Ln(II) phenyl substituted complexes 16

1.9 Synthesis of organometallic triphenyl lanthanide complexes 16

1.10 Formation of anionic and neutral rare-earth phenyl complexes 17

1.11 Synthesis of cationic, dicationic, and tris(cyclopentadienyl) rare-earth metal complexes 18

1.12 Synthesis of N-methylimidazole samarium complexes 19

1.13 Synthesis of salen yttrium(III) complex 20

1.14 Synthesis of rare-earth metal phosphide complexes 20

1.15 Salt metathesis reactions to generate rare-earth metal hydrides 22

1.16 β-Hydride elimination to form rare-earth metal hydrides in situ 23

1.17 Hydride transfer reactions to yield lanthanide hydrides 23

xii

1.18 Hydrogenolysis of lanthanide alkyls to yield hydrides 23

1.19 Catalytic cycles of hydroamination and hydrosilylation 25

1.20 Proposed hydrophosphination mechanism 26

2.1 Synthesis of α-Ln(DMBA) [(2-1)-(2-8)] 3 29

2.2 Protonolysis reactions of α-Ln(DMBA) [(2-9)-(2-18)] 3 39

3.1 Stoichiometric insertion of carbodiimides [(3-1)-(3-3)] 63

3.2 Synthesis of N,N-dimethylbenzylamine amidinate (3-4) 64

3.3 Synthesis of homoleptic lanthanum phosphaguanidinate (3-5) 70

3.4 Proposed catalytic cycle for the hydrophosphination of N,N- diisopropylcarbodiimide 73

4.1 Synthesis of p-tert-butylcalix[4]arene 92

4.2 Fragment condensation reaction to form a methylene-substituted calix[4]arene 94

4.3 Addition of chloro-alkyl group to tetramethoxy-p-tert-butylcalix[4]arene 94

4.4 Synthesis of tetramethoxy-p-tert-butylcalix[4]arene 96

4.5 Synthesis of 2-(ω-(2,5-dichloroanilino)alkyl)tetramethoxy-p-tert- butylcalix[4]arenes 97

4.6 Synthesis of 2-(ω-phthalimidoalkyl)tetramethoxy-p-tert-butylcalix[4]arenes 99

4.7 Synthesis of 2-(ω-phthalimidoalkyl)tetrahydroxy-p-tert-butylcalix[4]arenes 101

xiii

Chapter 1

An Introduction to Lanthanides and Their Chemistry

1.1 General Properties

The lanthanides, or rare-earth elements (REE), have a rich and colorful history which began with the discovery of a black mineral, yttria, by Johann Gadolin in

Scandinavia in the year 1794.1,2 Further analysis revealed yttria to be composed of yttrium, terbium, ytterbium, scandium, holmium, thulium, gadolinium, dysprosium, and lutetium oxides. In 1803 M.H. Klaproth and independently J.J. Berzelius and W. Hisinger isolated a new oxide (“ceria”) composed of lanthanum, cerium, praseodymium, neodymium, and europium. After the development of the atomic number, Henry Moseley used X-ray spectroscopy to demonstrate there were 15 rare-earth elements from lanthanum to lutetium.1,2 Ironically, the term “rare-earth element” does not accurately describe their abundance in the Earth’s crust. Table 1.1 depicts the abundance of the 15 rare-earth elements plus yttrium.3 Today, the largest known reserves are located in China

(51%), the USA (15%), Australia (6%), and India (3%).4

Table 1.1. Abundance of Lanthanides3

Y La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Crust 31 35 66 9.1 40 0.0 7.0 2.1 6.1 1.2 4.5 1.3 3.5 0.5 3.1 0.8 (ppm)

The lanthanides exhibit a number of characteristics in their chemistry that distinguish them from the d-block metals. The first and foremost feature is the +3 oxidation state, which is the root of the inherent difficulty in separating ores into individual metals. The second most noteworthy feature is the decrease in the ionic radius for each Ln3+ ion from left to right across the series, also known as the lanthanide contraction. This phenomenon is the result of insufficient shielding by the 4f electrons. The 4f electrons are located inside and penetrate the 5s and 5p orbitals. The consequence is inadequate shielding of the 5s and 5p electrons from the increased nuclear charge. Hence, there is a contraction of the electron cloud and decrease in ionic radius because of the increased effective nuclear charge (Table 1.2).3 Because the 4f electrons are core-like in their behavior, their ability to form bonds is significantly reduced as noted by their small ligand field stabilization energies.

Table 1.2. Selected Properties of Lanthanides and Their Ions3

Neutral M3+ Ionic Atomic Name Symbol Valence Valence Radius Number Electrons Electrons (M3+, Å) 57 Lanthanum La 5d16s2 - 1.17 58 Cerium Ce 4f15d16s2 4f1 1.15 59 Praseodymium Pr 4f36s2 4f2 1.13 60 Neodymium Nd 4f46s2 4f3 1.12 61 Promethium Pm 4f56s2 4f4 1.11 62 Samarium Sm 4f66s2 4f5 1.10 63 Europium Eu 4f76s2 4f6 1.09 64 Gadolinium Gd 4f75d16s2 4f7 1.08 65 Terbium Tb 4f96s2 4f8 1.06 66 Dysprosium Dy 4f106s2 4f9 1.05 67 Holmium Ho 4f116s2 4f10 1.04 68 Erbium Er 4f126s2 4f11 1.03 69 Thulium Tm 4f136s2 4f12 1.02 70 Ytterbium Yb 4f146s2 4f13 1.01 71 Lutetium Lu 4f145d16s2 4f14 1.00

While the +3 oxidation state is most common for the lanthanides, some of the rare-earth elements have readily accessible +2 and +4 oxidation states, most notably Ce4+,

Eu2+ and Yb2+. These alternative oxidation states can be attributed to the emptied, half- occupied or full 4f electron shell (Ce4+ (4f0), Eu2+ (4f7), Yb2+ (4f14)).

Another notable attribute of the lanthanides is their ability to form chemical bonds with various non-metals. In terms of hard-soft acid-base theory (HSAB), lanthanides can be described as hard acids that prefer to bind to hard bases such as oxygen and nitrogen

group atoms.5 The coordination number of transition metals is generally 4-6; however, for the lanthanides the number ranges from 3 to 12 with 8 and 9 being the most common.

The reasons for this are twofold; the large ionic radius of the lanthanide elements can accommodate the increase in the coordination number and the sum of the 6s, 6p, and 5d orbitals is close to the coordination number of 12. The crystal field stabilization energy of lanthanides is very small compared to the transition metals (4.18 kJ/mol vs. > 418 kJ/mol).6 As a result, the bonds are not directional (fully electrostatic in nature) and the coordination number can range from 3-12.6

The magnetism and absorption spectroscopy of the lanthanides also exhibit different features than the d-block transition metals. The absorption spectra of the lanthanides are often line-like, originating from f-f transitions.7 This comes about as a result of the core-like behavior of the 4f electrons. As a result the surrounding elements have little effect on the 4f electrons giving rise to absorption spectra closely resembling free ions.8 This is the opposite of the d-block transition metals. The d orbitals are not shielded from the ligands and thus are influenced by the ligand field, resulting in broad- line spectra. Most Ln3+ elements have very weak or no absorption in the visible range, with transitions found in the near UV range.9 The colors and ground state configurations are given in Table 1.3.10 The susceptibilities and magnetic moments of the Ln3+ ions can be determined with equations using the J state.11 The experimental values closely match the expected values with two exceptions, Sm3+ and Eu3+. Both of these M3+ ions have excited J states close to the ground state at room temperature, resulting in an underestimation of their magnetic moments.12

Table 1.3. Colors and Electronic Ground States of M3+ Ions10

Ground Color Ground Color Ion (M3+) Ion (M3+) State State

1 1 La S0 Colorless Lu S0 Colorless

2 2 Ce F5/2 Colorless Yb F7/2 Colorless

3 3 Pr H4 Green Tm H6 Green

4 4 Nd I9/2 Lilac Er I15/2 Lilac

5 5 Pm I4 Pink, Ho I8 Pink, yellow yellow

6 6 Sm H5/2 Yellow Dy H15/2 Yellow

7 7 Eu F0 Pale Pink Tb F6 Pale Pink

8 Gd S7/2 Colorless

1.2 Inorganic Complexes

Rare-earth hydroxides, RE(OH)3•nH2O, are precipitated from high pH solutions as gels. They are not thermally stable and lose water upon heating to form REO(OH) or

13 RE2O3. Single crystals of rare-earth hydroxides can be grown using hydrothermal

13 conditions. The crystal system of Ln(OH)3 (Ln = La-Yb) is hexagonal with two

14 Ln(OH)3 units in each unit cell. Each hydroxide group acts as a μ3-bridge linking three

rare-earth ions resulting in a coordination number of nine for each Ln metal center. The overall geometry can be described as a tricapped trigonal prism.

15 Rare-earth chlorides easily adsorb water to form hydrates, RECl3•nH2O. Non- hydrated rare-earth halides can be obtained from the reaction of the rare-earth metal with the corresponding halogen gas or with a mercury salt.15 Dehydration reactions with

16 excess SOCl2 will also yield the dehydrated chloride salt. Simple heating of a

RECl3•nH2O will not yield the non-hydrated chloride (RECl3), but will instead form

17 REOCl. The crystal structures of LnCl3•nH2O are different depending on the metal.

Lanthanum, cerium, and praseodymium are triclinic while neodymium-lutetium are

17 4+ monoclinic. In CeCl3•7H2O, each unit cell has the dimeric structure [Ce2Cl2(H2O)14] .

The two cerium atoms are connected by μ2-bridging chlorides and seven water molecules are coordinated to each metal center resulting in a coordination number of nine with four ionic chlorides.17

Rare-earth carbonates exhibit fairly low solubilities (10-5 – 10-6 mol/L).6 The generation of a rare-earth carbonate is achieved from the reaction between ammonium carbonate and a water soluble rare-earth salt.18 The coordination environment of the carbonate varies depending on the metal. For La2(CO3)3•8H2O, the carbonate anion has three different bonding modes (a,b,c; Figure 1.1) while for Nd(OH)CO3 the carbonate only has one mode (d; Figure 1.1).

Figure 1.1. Multiple coordination modes of carbonates to rare-earth metals.

Rare-earth nitrates can be prepared using nitric acid and the respective metal oxide, hydroxide, or carbonate.19 They usually have the molecular formula

RE(NO3)3•nH2O where n = 6 for La-Nd and n = 5 for Eu-Lu. The nitrate coordinates to the metal center in a bidentate fashion through two oxygen atoms.19

Rare-earth phosphates exhibit similar solubilities to those of the carbonates and can be generated in an analogous manner. The product formula is REPO4•nH2O where n

= 0.5-4.20 The structures of the rare-earth phosphates can be split into two classes depending on the metal. La-Gd are monoclinic, while Tb-Lu are tetragonal.21,22 The coordination of the phosphate for each crystal system is shown below (Figure 1.2).

Figure 1.2. Coordination modes of phosphates to rare-earth metals.

In the monoclinic system, five oxygen atoms form an equatorial plane with the metal ion and two phosphate groups cap the top and bottom of the equatorial plane giving rise to a distorted pentangular bi-pyramid.

Rare-earth sulfates are made from the reaction of rare-earth oxides, hydroxides, or

23 carbonates with dilute sulfuric acid. The molecular formula is RE2(SO4)3•nH2O where n

= 3-6, 8, or 9. Dehydration can occur by heating to 155-260 °C.6 The lanthanum atoms in the structure of La2(SO4)3•9H2O are in two different coordination environments (Figure

1.3).23 La1 is coordinated to 12 oxygen atoms from six bidentate sulfate groups and La2 is bound to 3 monohapto sulfate groups and six water molecules giving a coordination number of 9. The geometry of La2(SO4)3•9H2O is a tri-capped prism with the remaining three water molecules hydrogen bonded to the oxygens throughout the network.

Figure 1.3. Coordination mode of sulfate to lanthanum ions.

Rare-earth borates are synthesized from the reaction between a rare-earth metal oxide and boric acid (Scheme 1.1).24 The ratio of RE/B is dependent on the metal’s ionic radius. Larger cations tend for form hydrated octaborates while smaller cations form hydrated nonaborates (Scheme 1.1). These individual units can form one-dimensional chains, two-dimensional planes, or three-dimensional networks through sharing of corners or edges.25

Scheme 1.1. Synthesis of rare-earth metal borates.

The information discussed thus far is to educate the reader about the unique properties of the rare-earth metals, such as the contraction of their ionic radii, larger coordination number, high magnetic moments, and hard Lewis acidic character, as well as to give a broad overview of the inorganic chemistry of the lanthanides. The main development of these complexes has been for their uses in luminescent materials,25 molecule-based magnets,26 polar/chiral networks,19 and fundamental coordination chemistry.20,23

1.3 Organometallic Chemistry of the Lanthanides

The purpose of this section is to provide a detailed overview about the history of lanthanide organometallic chemistry highlighting the most important discoveries and to bring the reader up-to-date with recent results. This will in turn put the results presented in this dissertation into proper context within this field of chemistry.

As stated previously, the 4f electrons are the valence electrons, but seem to exhibit very minimal interaction with ligands. Therefore, much of the bonding in lanthanides was originally described as primarily ionic, to maintain charge balance. As a result, lanthanide organometallic chemistry was significantly overlooked until the

27 discovery of Cp3Ln (Cp = cyclopentadienyl), which exhibited a great deal of covalent

ligand-lanthanide bonding character and inspired continued research into organometallic lanthanide chemistry.

In recent years, there has been a reinvigorated focus on organometallic lanthanide chemistry with distinct interest in developing non-cyclopentadienyl ligands and investigating their reactivity and general properties.28-30 Lanthanide alkyl and aryl complexes have been greatly researched over the past decades. There are three major ligand classes used in these rare-earth metal complexes: (trimethylsilyl)alkyl, phenyl, and benzyl. The synthesis and reactivity of each class will be discussed.

Trialkyl lanthanide complexes with sterically small groups like methyl have been found to be thermally unstable because of their inability to satisfy the coordination number of the lanthanide cation.31 In addition alkyl groups must be free of β-hydrogen atoms in order to prevent ligand decomposition through β-hydride elimination. Therefore, bulky (trimethylsilyl)alkyl groups were sought to stabilize the metal center in early efforts to create trialkyl lanthanide organometallic complexes. There are three types of

(trimethylsilyl)alkyl groups: (trimethylsilyl)methyl [-CH2SiMe3]; bis(trimethylsilyl)methyl [-CH(SiMe3)2]; and tris(trimethylsilyl)methyl [-C(SiMe3)3]. The first yttrium alkyl(trimethylsilyl) complex was synthesized by Lappert and co-workers,32 while lutetium,33 ytterbium,34 thulium,34 erbium,34 and terbium34 complexes were synthesized soon thereafter. Several synthetic procedures exist, but all make use of stoichiometric salt metathesis reactions to form the lanthanide trialkyl complexes

(Scheme 1.2).

Scheme 1.2. Synthesis of (trimethylsilyl)methyl rare-earth metal complexes.

Since the (trimethylsilyl)methyl ligands do not provide sufficient steric bulk, solvent molecules, such as THF, are coordinated to the metal center. The number of THF molecules increases with the size of the metal’s ionic radius. A significant deterrent to using these complexes is their thermal instability. At ambient temperature,

Ln(CH2SiMe3)3 complexes have been shown to decompose in hours to form insoluble

33 products and SiMe4. Furthermore, the (trimethylsilyl)methyl ligand can only be used for middle to small rare-earth metal elements because of ligand degradation for larger size lanthanides. A second drawback to using (trimethylsilyl)methyl ligands is their ability to

+ - 34 form lanthanates or [Li] [Ln(R)4] . The lanthanates exhibit no solubility in non-polar solvents, but reasonable solubility in coordinating solvents such as diethyl ether and THF.

Salt formation of this type can be avoided through the stoichiometric reaction of

35 lanthanide aryloxides with LiCH2SiMe3 (Scheme 1.3).

Scheme 1.3. Synthesis of Ln(CH2SiMe3)3.

Despite the drawbacks mentioned, the -CH2SiMe3 ligand remains one of the most widely used in the generation of many active lanthanide complexes. Protonolysis of 1-3 ligands to lose SiMe4 and synthesize new active organolanthanide alkyl complexes remains a staple in the organometallic chemistry of rare-earth metals. To list every lanthanide 11

complex synthesized from the Ln(CH2SiMe3)3(THF)x precursor would go well beyond the scope of this chapter; however, a short list will be compiled. Ln(CH2SiMe3)3(THF)x complexes have been reacted with various Lewis acids and weak Brønsted acids to form an array of cationic complexes (Scheme 1.4).36,37

Scheme 1.4. Synthesis of rare-earth metal cationic complexes.

In addition to cationic complexes, Ln(CH2SiMe3)3 has been treated with various weakly acidic ligand precursors to create a collection of heteroleptic lanthanide complexes through alkane elimination (Scheme 1.5). These half-sandwich and amidinate complexes have been used in ethylene polymerization and intramolecular hydroamination.38,39

Scheme 1.5. Synthesis of heteroleptic rare-earth alkyl complexes.

The bis(trimethylsilyl)methyl ligand proved to be a major stepping stone in organolanthanide chemistry as it allowed for synthesis of the first solvent free

40 homoleptic lanthanide alkyl complex Y[CH(SiMe3)2]3. The steric bulk of the bis(trimethylsilyl)methyl ligand was large enough to also stabilize divalent ytterbium.41

The synthetic route used is analogous to that which formed lanthanates in the case of the

(trimethylsilyl)methyl ligand. However, solvent free compounds can be achieved in this case using a diethyl ether/toluene mixture. Alternatively, using a lanthanide aryloxide as a precursor will also yield the solvent free trialkyl complex. A distinct advantage of the bis(trimethylsilyl)methyl ligand is the stabilization of early lanthanide metals (La and

35,42 Ce). The utility of Ln[CH(SiMe3)2]3 as a starting material for the generation of more sophisticated complexes is mostly limited to early and middle rare-earth metals.

43 Reaction of (C5Me5)H with Y[CH(SiMe3)2]3 did not yield the desired product. On the

t other hand the reaction between Lu[CH(SiMe3)2]3 and (C5Me4H)Me2Si( BuNH) yielded

44 the corresponding constrained geometry complex. In general, Ln[CH(SiMe3)2]3 is very sensitive to the acidity and steric bulk of the reactants employed.

To finish off the alkyl-silyl series, tris(trimethylsilyl)methyl ligands [-C(SiMe3)3] were also developed. The highest degree of substitution in the collection results in the largest steric bulk and completely suppresses lanthanate formation.45 Consequently [-

46,47 C(SiMe3)3] is large enough to stabilize solvent free divalent europium and samarium.

In an effort to find suitable complexes to use as a universal entry point for the generation of early lanthanide species, benzyl ligands [-CH2Ph] were investigated. The first definitive report of tribenzyl lanthanide complexes came about from the salt metathesis reaction between an anhydrous metal halide and benzyl potassium (Scheme

1.6).48

Scheme 1.6. Synthesis of homoleptic lanthanide tribenzyl complexes.

The Ln(CH2Ph)3(THF)3 series was later expanded to include Ce, Pr, Sm, Gd, Dy, and

Er.49 Crystal structures of these complexes revealed that the benzyl and THF ligands each adopt a fac arrangement. Although the geometry of each lanthanide complex is the same, there are subtle differences in the coordination environment of the benzyl ligand. For the early lanthanides (La-Nd) the ipso-carbon coordinates to the metal resulting in an η2- interaction.49 Due to the lanthanide contraction, the ipso-carbon no longer coordinates to the metal center for middle to late lanthanides (Sm-Lu) giving rise to an η1-interaction.49

The tribenzyl complexes have been subjected to a number of reactions to investigate their reactivity and properties. Protonolysis reactions with various amidines,

i t ArN=CRNHAr (Ar = C6H3-2,6- Pr2; R = Ph, Bu), led to the formation of the respective monoamidinate-bisbenzyl complexes.48,50

The progression to donor functionalized benzyl ligands came about in an effort to find other suitable ligands to stabilize divalent rare-earth cations.51 For example the stoichiometric salt metathesis reaction between SmI2 and K[CH(SiMe3)C6H4-o-NMe2] resulted in the Sm[CH(SiMe3)C6H4-o-NMe2]2(THF)2 product in which the neutral nitrogen donor is bound to the metal center (Scheme 1.7).51,52

Scheme 1.7. Synthesis of donor functionalized benzyl divalent lanthanide complexes.

Benzyl groups with amines such as [CH2C6H4-o-NMe2] and [CH(NMe2)C6H5] have recently garnered attention as suitable donor ligands for the stabilization of rare- earth metal complexes.51,53-55 One notable feature apparent in the solid state structures of these complexes is that as the ionic radius of the metal decreases, one of the benzyl ligands will reposition itself “upside-down” to alleviate steric repulsions resulting from the decrease in the Ln-C σ-bond length, ultimately destroying the 3-fold symmetry observed with the larger metals.55,56 Two constitutional isomers exhibit this behavior: (o-

Me2N-C6H4-CH2)3La and La[CH(NMe2)C6H5]3. Both La complexes maintain a 3-fold symmetry at low temperature, but when the metal center is changed to yttrium {(o-Me2N-

C6H4-CH2)3Y and Y[CH(NMe2)C6H5]3} both lose their 3-fold symmetry, even at low temperature.

The reactivity of these amino-stabilized benzyl ligands has been probed through various protonolysis and acid-base reactions with weak Brønsted acids.55,57 In addition, such complexes have been used as precursors for polymerization reactions and cross- coupling of terminal alkynes with isocyanides.58,59

The generation of phenyl substituted rare-earth metal complexes

R R 60-62 {[Ln(Ph )2(THF)x] and [Ln(Ph )3(THF)x]} is prevalent throughout the literature; however, the synthetic routes vary widely. For divalent lanthanide complexes, salt metathesis is not preferable, but rather redox transmetallation/ligand substitution reactions are used.63 Redox transmetallation reactions between organomercury species and elemental rare-earth metals remain the dominant method (Scheme 1.8).

Scheme 1.8. Synthesis of Ln(II) phenyl substituted complexes.

R The type of Hg(Ph )2 employed should be carefully considered when designing this type of reaction. HgPh2 is less reactive than Hg(C6F5)2 and requires activation of the metal

64,65 (Hg or CH2I2); on the other hand, HgPh2 is a weaker oxidizing agent and is preferred when working with metals containing competing divalent and trivalent oxidation states.66

67 A third criterion to consider is pKa. Reagents with high pKa’s (HN(SiMe3)2 = 25.8)

68 should be reacted with HgPh2 because of its high pKa (40) and not Hg(C6F5)2 (26).

Because of the instability of LnPh2, its solid state structure has not been isolated, and it is often generated in situ followed by reaction with a protic reagent. Several reactivity studies have been undertaken using various protic reagents (cyclopentadienes, phenol, and heterocyclic amines).66,69,70

The first trivalent organometallic phenyl lanthanide complex was produced from the salt metathesis reaction between the metal chloride and phenyl lithium (Scheme

1.9).71

Scheme 1.9. Synthesis of organometallic triphenyl lanthanide complexes.

Its crystal structure was determined 30 years later with a slight modification to the

72 3+ original procedure (THF/Et2O solvent mixture). Salt metathesis reactions with Ln chlorides and aryllithium reagents still remain the dominant method for the production of 16

triphenyl substituted products. The product produced in this type of reaction is dependent on the size of the metal and the stoichiometric amount of the lithiated species used

(Scheme 1.10).

Scheme 1.10. Formation of anionic and neutral rare-earth phenyl complexes.

As with most salt metathesis reactions involving lithium, the larger rare-earth metals often form anionic salts (Scheme 1.10).61,73 Neutral homoleptic triphenyl complexes can be readily achieved using middle or late lanthanides and the appropriate amount of lithium reagent (Scheme 1.10). The reactivity of triphenyl complexes has been investigated through reactions with weak Brønsted acids. A series of cationic and dicationic rare-earth complexes have been made through arene elimination (Scheme

1.11).62 Redox-transmetallation/ligand exchange reactions have also been used to synthesize tris(Cp) complexes of trivalent lanthanides (Scheme 1.11).74,75

Scheme 1.11. Synthesis of cationic, dicationic, and tris(cyclopentadienyl) rare-earth

metal complexes.

There is a plethora of N-donor ligands including, but not limited to silylamides,

N-heterocycles, pyrroles, and Schiff-base ligands that have been used in organometallic rare-earth metal chemistry. Silylamides were first developed because of the large steric encumbrance provided by their silyl groups. The classical route using salt metathesis of an anhydrous rare-earth metal chloride with an alkali metal silylamide remains the preferred synthetic method of choice.76 To date, amide complexes using the bis(trimethylsilyl)amide ligand exist for the following metals: Sc3+, La3+, Ce3+, Pr3+,

Nd3+, Eu2+, Eu3+, Dy3+, Er3+, Yb2+, and Yb3+.77-82 Such complexes have been used as building blocks for the generation of more elaborate compounds found in various

83-85 3- catalytic processes. Tetradentate triamidoamines [N(CH2CH2NR)3] have been used

3- t as well. Lanthanum and yttrium complexes using [N(CH2CH2NR)3] (R = SiMe2 Bu)

have been generated from the salt metathesis reaction between the lithated amide and the anhydrous metal chlorides.86

In the family of N-heterocyclic ligands, imidazoles have recently received a great deal of attention because of their abundance in biological systems. Additionally, the development of a new class of neutral ligands that can stabilize and satisfy the electronic and steric requirements of the rare-earth metals is continually sought after. The first structurally characterized imidazole rare-earth metal complex was from the reaction of

87 SmI2 with 4 eq. of N-methylimidazole (Scheme 1.12).

Scheme 1.12. Synthesis of N-methylimidazole samarium complexes.

Surprisingly, the imidazole was able to displace all of the THF and iodide ligands in the

Sm(III) complex (Scheme 1.12), demonstrating the imidazole’s ability to stabilize the metal center and its potential to be a suitable ligand for the synthesis of a wide range of lanthanide complexes.

The ease and cost-effectiveness of Schiff-base ligands make them one of the most widely used ligand scaffolds for lanthanide and actinide chemistry.88 The advantages of

Schiff-base ligands include coordination through the imine nitrogen as well as any possible hard-donor substituent on the phenyl ring such as phenolic oxygen in salen

complexes. Evans and co-workers synthesized an yttrium salen complex using salt metathesis (Scheme 1.13).89

Scheme 1.13. Synthesis of salen yttrium(III) complex.

The isolated yttrium complex shows that the salen ligand is a suitable alternative to the cyclopentadienyl ligand and further broadens the field of organometallic lanthanide chemistry.

Because of the hard ionic nature of the lanthanides much research has been conducted using hard donor ligands such as nitrogen and oxygen, while ligands making use of soft donors (P or As) remains limited. The development of phosphorus ligands has its roots in lanthanide amido chemistry. The earliest known isolated rare-earth metal

90 phosphide was a (CH3C5H4)2SmPPh2 complex. The first structurally characterized rare-

91 earth metal triphosphide complex was Tm[P(SiMe3)2]3(THF)2. The two most common methods used to synthesize rare-earth metal phosphides are salt metathesis and protonolysis of an alkyl or aryl ligand (Scheme 1.14).92-94

Scheme 1.14. Synthesis of rare-earth metal phosphide complexes.

Salt metathesis with alkali metal phosphides is the most common route to generate lanthanide phosphides; however, there are the usual drawbacks to using lithium salts,

t t such as lanthanate formation. When La(OTf)3 was reacted with Bu2PLi, [( Bu2P)2La(μ-

t 92 P Bu2)2][Li(THF)] was formed. Surprisingly, the same product results even when the reaction stoichiometry was changed from 1:4 to 1:3. The family of monodentate

t phosphide ligands has grown to include the many PR2 moieties (R = Ph, Bu, SiMe3,

Mes).92,95-97 Considering that there are 16 rare-earth elements (including yttrium), only seven different metals (La, Nd, Eu, Sm, Tm, Yb, and Lu) have been isolated in the solid state with phosphide ligands according to the Cambridge Structural Database.92,94,95,98-101

Recently, there has been a change in focus from monodentate to bidentate secondary phosphine substituted ligands, as seen with the incorporation of dimethylbenzylamine and silyl-linked cyclopentadienyl moieties (Figure 1.4).93,102

Figure 1.4. Bidentate secondary phosphide ligands.

All of the aforementioned rare-earth metal phosphide complexes are potential precatalysts for the catalytic hydrophosphination of unsaturated hydrocarbons. While this discipline of organolanthanide chemistry is still developing, further research into tunability of the electronic and steric environment to gain a better understanding of the reactivity is strongly warranted.

In the area of organolanthanide chemistry, the synthesis of hydrides has seen recent interest due to their high reactivity and their presence as possible catalytic intermediates for a number of organic transformation reactions.83,103,104 The reactivity of lanthanide hydrides has been investigated in terms of many stoichiometric and catalytic reactions including addition, σ-bond metathesis, isomerization, and hydrogenation.105-107

Essentially, there are four routes to synthesize rare-earth metal hydrides: metathesis reactions, β-hydride elimination, hydrogenolysis, and hydride transfer. Reaction with an alkali metal hydride is a classical way to generate a rare-earth metal hydride (Scheme

1.15).108 Alkali metals containing borohydrides are generally avoided because of their

- 108 stability, often resulting in BH4 complexes, rather than hydrides and byproduct BH3.

Scheme 1.15. Salt metathesis reactions to generate rare-earth metal hydrides.

Another synthetic route to a hydride is via β-hydride elimination from an alkyl ligand. Careful selection of the appropriate alkyl group can lead to hydride formation at or above room temperature. tert-Butyl and isobutyl groups have demonstrated that at room temperature, β-hydride elimination will occur to form trimetallic and mono-hydride complexes (Scheme 1.16).109,110

Scheme 1.16. β-Hydride elimination to form rare-earth metal hydrides in situ.

Alkyl and aryl organometallic lanthanide complexes can also react with hydrides of silicon, germanium, or tin to yield rare-earth metal hydride complexes. Such reactions can be described as hydrogen transfer reactions (Scheme 1.17).111

Scheme 1.17. Hydride transfer reactions to yield lanthanide hydrides.

The most common synthetic method to generate a hydride is hydrogenolysis of an alkyl compound.112-114 The first isolated lanthanide hydride made use of the hydrogenolysis reaction (Scheme 1.18).115

Scheme 1.18. Hydrogenolysis of lanthanide alkyls to yield hydrides.

The reaction is dependent on a number of factors including size of the metal, size of the ligand, and coordinating ability of the solvent. Monomeric lanthanide complexes such as

t Cp2Y( Bu)(THF) will not undergo σ-bond metathesis with H2 in THF; however, they will

produce the resulting hydride in toluene. This has been hypothesized to result from the

t 115,116 dissociation of THF to form the more reactive species Cp2Y( Bu) in solution. In contrast, dimeric complexes like [Cp2Y(μ-Me)]2 will not react in the presence of toluene,

116 but do react in THF because of formation of the monomer Cp2Y(Me)THF.

1.4 Catalysis

The IUPAC Gold book defines a catalyst as the following: “A substance that increases the rate of reaction without modifying the overall standard Gibbs energy change in the reaction; the process is called catalysis.”117 Catalysis can also be described as homogeneous (only one phase is involved) or heterogeneous (two phases are involved and the reaction occurs at the interface between the two). Many of the organometallic lanthanide complexes already described are actually precatalysts or intermediates used in various homogeneous catalytic processes such as hydroamination, hydrosilylation, and hydrophosphination reactions. A distinct and major advantage of all three of these reactions is that there is 100% atom economy.118 The common theme for all three of these catalytic processes is the creation of a new heteroatom-carbon bond while reducing the bond order of the unsaturated C-C bond by one. Hydroamination is defined as the addition of an N-H bond across an unsaturated carbon-carbon bond. Research into hydroamination among the scientific community has risen and continues to develop as nitrogen-containing compounds (amines, enamines, and imines) are utilized in more and more bulk/specialty chemicals and pharmaceuticals.119,120 The general reaction mechanism is shown below (A, Scheme 1.19). Of the known catalysts, there is a healthy

balance between lanthanocene and non-lanthanocene complexes.121 One notable feature of the lanthanocene complexes is that as the ionic radius of the metal increases so does the catalytic activity.122 Hydrosilylation is defined as the addition of a Si-H bond across a carbon-carbon unsaturated bond (B, Scheme 1.19). Early work in catalyzed hydrosilylation reactions made use of lanthanocene and its derivatives, while more recent publications have focused on using non-lanthanocene ligand frameworks.123-127

Scheme 1.19. Catalytic cycles of hydroamination and hydrosilylation.

Hydrophosphination can be described as the addition of a P-H bond across an unsaturated C-C bond (Scheme 1.20).94 Of the three listed catalytic processes, hydrophosphination is the most underdeveloped. Traditionally late transition metal complexes have dominated the field, but early transition metals and rare-earth metals are starting to emerge as useful catalysts.94,128-133 Benefits of catalytic hydrophosphination include 100% atom economy and a straightforward route for the synthesis of unsymmetrical phosphines.

Scheme 1.20. Proposed hydrophosphination mechanism.

1.5 Conclusion

In summary, the general properties of the rare-earth metals have been described, as well as a brief synopsis of their inorganic and organometallic chemistry by drawing attention to relevant discoveries. This has been provided to the reader in order for them have a better understanding of the research presented in this dissertation.

Chapter 2

Synthesis and Protonolysis Reactivity of Homoleptic Alpha-Metallated N,N- Dimethylbenzylamine Rare-Earth Metal Complexes

2.1 Introduction

The effective use of f-element complexes as catalysts for reactions such as hydroamination,134-137 ring-opening polymerization of lactide,49,138-141 and hydrosilylation,125,142-144 as well as precursors for the generation of thin films,145-148 has been demonstrated in many recent reports. Unfortunately, the homoleptic starting materials underpinning this chemistry are generally derived from only a handful of ligands. That is, of the homoleptic lanthanide complexes that exist, the majority make use of alkylsilane (-CH2SiMe3), silylamide (-N(SiMe3)2), or benzyl (-CH2C6H5) derivatives

(see section 1.3).30,32,76,149-153 The preparation of these homoleptic starting materials via salt metathesis reactions between rare-earth metal chlorides and lithium salts often leads

- 33 to the generation of lanthanate ions ([LnR4] ). Furthermore, alkylsilane complexes require careful sublimation to purify and have been shown to exhibit only moderate

thermal stability.34 In contrast, while the lanthanide tri-benzyl complexes do not often form the lanthanate ion, they instead retain coordinated solvent, making them not truly homoleptic complexes and limiting their potential as starting materials in some cases.48

Thus, the discovery of new homoleptic lanthanide complexes with easy isolation protocols and effective protonolysis reactivity would represent a significant advance in the field of lanthanide chemistry.

The paucity of tri-alkyl lanthanide complexes can be attributed to the required extended coordination sphere and high Lewis acidity or electrophilicity of these metals.

The ionic radii of Ln3+ ions range from 1.00-1.17 Å (Table 1.2).12 While these properties make lanthanum alkyl complexes very reactive, in turn they also make their synthesis and manipulation quite challenging. Our efforts have focused on the development of unexplored homoleptic tri-alkyl rare-earth metal complexes utilizing simple ligands that fulfill both the electronic and steric requirements of these metal centers. The N,N- dimethylbenzylamine ligand scaffold is not unknown in the literature; however, nearly all of its previous uses have been limited to ortho-metallated complexes.154,155 There is only a single example of a crystallographically-characterized alpha-metallated transition metal complex, a zirconium species by Norton and coworkers.156 For the rare-earth metals, only ortho-metallated N,N-dimethylbenzylamine complexes exist and of these, only the middle and late lanthanides proved to be stable enough for isolation.54,157 Herein, we report our findings of a new class of homoleptic tri-alkyl rare-earth metal complexes using alpha-metallated N,N-dimethylbenzylamine ligands as stable benzyl ligand derivatives to form lanthanide complexes free of coordinating solvent.

2.2 Results and Discussion

A series of homoleptic alpha-metallated N,N-dimethylbenzylamine (DMBA) Ln complexes (Ln = La, Ce, Pr, Nd, Sm, Gd, Ho and Y) was synthesized following a simple procedure56 involving salt metathesis of rare-earth metal chlorides with alpha-potassiated dimethylbenzylamine at -50 °C in THF (Scheme 2.1).

Scheme 2.1. Synthesis of α-Ln(DMBA)3 (Ln = La (2-1), Ce (2-2), Pr (2-3), Nd (2-4), Sm

(2-5), Gd (2-6) Ho (2-7; Cs isomer), and Y (2-8; Cs isomer)).

α-La(DMBA)3 (2-1) was isolated by recrystallization from THF/pentane at -25

°C, affording orange crystals in 77% yield. α-Y(DMBA)3 (2-8) was synthesized in a similar manner to 2-1, except the THF solvent was removed under reduced pressure at 0

°C in order to prevent product decomposition. Subsequently, 2-8 was recrystallized from a concentrated solution of pentane at room temperature to give yellow crystals in 79% yield. The La complex (2-1) showed no evidence of decomposition in THF at room temperature, while 2-8 decomposed readily in this solvent. Spectroscopically, 2-1 exhibited fluxional behavior at room temperature, but upon cooling to -78 °C, it displayed much sharper resolution with resonances indicative of a C3-symmetric species

(Figure 2.1).

N M e T ol T ol, H B T ol 2

N M e 2

T ol

H C H D

H E

H A

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Chemical Shif t (ppm)

1 Figure 2.1. The H NMR spectrum of 2-1 at -78 °C displaying C3 symmetry.

At low temperature, 2-1 adopted an ABCDX splitting pattern for the five protons of the phenyl rings, with a significantly upfield shifted resonance at 3.10 ppm in its 1H NMR spectrum, assigned to the ortho-proton closest to the metal center. This upfield chemical shift is indicative of a disruption of the aromatic system and can be attributed to η2- coordination of the phenyl ring to the lanthanum giving rise to an overall η4-binding mode and resulting in a pseudo-allylic arrangement for the three carbon atoms interacting with the metal center. In contrast, the yttrium complex (2-8) did not exhibit fluxional behavior at room temperature; however, unlike complex 2-1, its 1H NMR displayed two independent isomers in a nearly 1:1 ratio with one having C3 symmetry and the other Cs symmetry (Figure 2.2).

C 6D 6

H B N M e 2, N M e 2' C H ', C H

H A N M e 2

H 'B

H C

H 'C

H'A

7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shif t (ppm)

1 Figure 2.2. The H NMR spectrum of 2-8 at room temperature displaying Cs and C3

symmetric isomers.

The 1H NMR spectrum of each isomer of 2-8 showed AA’BB’C coupling patterns for each inequivalent phenyl group. This indicates rapid rotation of these phenyl groups in solution, implying an η2-coordination from the DMBA ligands to the yttrium metal center, unlike the η4-coordination observed in 2-1.

X-ray quality crystals were achieved for both 2-1 and 2-8 and their crystal structures were solved. Both 2-1 and 2-8 crystallized in monoclinic space groups. The structure of compound 2-1 confirmed its approximate C3 symmetry (Figure 2.3).

Figure 2.3. ORTEP diagram of 2-1, showing the pseudo-three fold rotation axis in these

lanthanide complexes (thermal ellipsoids at 50% probability).

The La-Cbenzyl average bond distance in 2-1 is 2.648(3) Å (Table 2.1), which is significantly shorter than the average La-Cbenzyl bond distance of 2.755(2) Å in

48 La(CH2Ph)3(THF)3. Similarly, the average La-Cipso bond distance is 2.834(3) Å, somewhat shorter than the average La-Cipso bond distance of 2.873(6) Å for (o-Me2N-

51,56 C6H4-CH2)3La. The shorter bond distances observed for the α-DMBA ligands in 2-1 reflect the allylic nature of the 3-carbon anionic fragment in these ligands, causing the entire unit to be closer to the metal center to properly bind in this allylic motif. The average bite angle for 2-1 is 63.98(7)° for N-La-Cortho. The tilt of the phenyl group can be measured as the Ln-Cbenzyl-Cipso angle, with an average phenyl tilt angle for 2-1 of

82.7(2)°.

Table 2.1. Selected Bond Distances and Angles for (2-1)-(2-8)a

Ln-C Ln-C Ln-C Ln-N C -C -Ln Bite angle benzyl ipso ortho ipso benzyl La 2.648(3) 2.834(3) 2.856(2) 2.652(2) 82.65(15) 63.98(7) Ce 2.617(3) 2.814(3) 2.840(3) 2.624(3) 82.99(19) 64.57(9) Pr 2.597(4) 2.797(3) 2.830(3) 2.605(3) 82.93(19) 64.91(11) Nd 2.588(3) 2.785(3) 2.818(3) 2.603(3) 82.73(18) 65.24(9) Sm 2.555(4) 2.760(4) 2.803(4) 2.568(4) 83.0(2) 65.79(12) Gd 2.545(3) 2.790(3) 2.743(3) 2.518(3) 84.49(17) 69.82(8) Ho 2.54(1) 2.74(1) 2.75(1) 2.461(9) 84.5(7) 69.4(3) Y 2.516(4) 2.758(4) 2.751(4) 2.471(3) 84.2(2) 69.53(12) a All values are averages of those observed in the α-Ln(DMBA)3 complex.

In contrast, we were fortunate to crystallize the low-symmetry isomer of complex 2-8, in which one of the three DMBA ligands is oriented in the opposite direction from the other two (Figure 2.4).

Figure 2.4. ORTEP diagram of 2-8, lacking the approximate C3 symmetry observed in

(2-1)-(2-6) (thermal ellipsoids at 50% probability).

The formation of this lower symmetry isomer is due to the smaller ionic radius of Y3+, with reorientation necessary to relieve steric stress resulting from the decreased Y-Cbenzyl bond distances, which are more than 0.1 Å shorter than those observed in 2-1.

Specifically, the Y-Cbenzyl bond distances fall in the range of 2.488(4)-2.552(4) Å and are slightly elongated compared to the Y-Cbenzyl bond distances of Y(CH2Ph)3(THF)3

153 (2.452(3)-2.463(3) Å). The Y-Cipso bond distances are also shorter, ranging from

2.714(4)-2.824(4) Å. The average Y-Cipso bond distance is 2.758(4) Å and is somewhat shorter than the average Y-Cipso bond distance of 2.801(3) Å for (o-Me2N-C6H4-

56 CH2)3Y. The closer approach to the metal center also results in larger bite angles for 2-8

(66.9(1) to 72.4(1)°), while the phenyl tilt angles span a wide range (81.9(2) to 87.5(2)°).

The remaining α-Ln(DMBA)3 complexes (Ln = Ce, Pr, Nd, Sm, Gd, and Ho) were synthesized using procedures analogous to those used for 2-8, and each was recrystallized from toluene/pentane at -25 °C (Figures (2-5)-(2-10)). As expected, complexes (2-2)-(2-7) were paramagnetic, and their 1H NMR spectra revealed only broad and uninterpretable signals. The magnetic moment of each complex was determined using the Evans NMR method11 and showed no anomalous values.158 The solid state structures of (2-2)-(2-6) were each very similar to that of α-La(DMBA)3 (2-1), containing a 3-fold axis of rotation and η4-coordination to the metal centers; however, the solid state structure of α-Ho(DMBA)3 (2-7) revealed an “upside-down” ligand with loss of the C3 axis.

Figure 2.5. ORTEP diagram of 2-2, showing the pseudo-three fold rotation

(thermal ellipsoids at 50% probability).

Figure 2.6. ORTEP diagram of 2-3, showing the pseudo-three fold rotation (thermal

ellipsoids at 50% probability).

Figure 2.7. ORTEP diagram of 2-4, showing the pseudo-three fold rotation

(thermal ellipsoids at 50% probability).

Figure 2.8. ORTEP diagram of 2-5, showing the pseudo-three fold rotation (thermal

ellipsoids at 50% probability).

Figure 2.9. ORTEP diagram of 2-6 showing the pseudo-three fold rotation

(thermal ellipsoids at 50% probability).

Figure 2.10. ORTEP diagram of 2-7, lacking the approximate C3 symmetry observed in

(2-1)-(2-6) (thermal ellipsoids at 50% probability).

The formation of the lower symmetry isomer can be explained for the same reasons as complex 2-8. As anticipated, the Ln-Cbenzyl bond distance decreased as the metal’s ionic radius became smaller due to the lanthanide contraction (Table 2.1). One noticeable feature of complexes (2-2)-(2-7) is the increase in the phenyl tilt angle as the

Ln-Cbenzyl bond length decreased. This phenyl tilt angle implies that as the ionic radius of the metal shrinks, the phenyl group becomes more orthogonal to the metal. Also, as the metal’s radius decreases, the ligands move closer to the metal, resulting in larger ligand bite angles. Based on a comparison of the Ln-Cbenzyl bond distances and the phenyl tilt angles of 2-6 and 2-8, α-Gd(DMBA)3 (2-6) may represent the absolute minimum radius necessary to fully preserve the three-fold symmetry.

In order to demonstrate the utility of α-Ln(DMBA)3 complexes as effective precursors in lanthanide chemistry, the reactivity of 2-1 and 2-8 was investigated through a series of protonolysis reactions. Initial attempts consisted of treatment of these complexes with 1 eq. of 2,6-di-tert-butylphenol. The expected mono-aryloxide product was not formed, but rather a disubstituted product, La(DMBA)(OAr)2(THF) (2-9), was generated in low yield. As a means to increase the yield of 2-9, the reaction was repeated with nearly 2 eq. of 2,6-di-tert-butylphenol to more appropriately reflect product stoichiometry (Scheme 2.2).

Scheme 2.2 Protonolysis reactions of α-Ln(DMBA)3. Ln = La, Y; Ar = 2,6-di-tert-

butylphenyl, 4-tert-butylphenyl; Ar’ = 2,6-diisopropylphenyl, 4-tert-butylphenyl.

Complex 2-9 was recrystallized from a THF/pentane solution at room temperature. Its 1H NMR spectrum and X-ray crystal structure (Figure 2.11) revealed a decrease in hapticity of the N,N-dimethylbenzylamine ligand from η4→η2. The 1H NMR spectrum of 2-9 displayed a classical AA’BB’C splitting pattern for the phenyl group of the N,N-dimethylbenzylamine ligand. This decrease in hapticity is likely a result of minimization of the steric interactions caused by the very bulky aryloxides. The La-Cbenzyl and La-N bond distances are 2.602(2) and 2.664(2) Å, respectively, which are quite similar to those in the homoleptic α-La(DMBA)3 precursor. While the generation of 2-9 was initially unanticipated, it provided insight into the donor capabilities and Lewis basicity of N,N-dimethylbenzylamine. The lanthanum clearly preferred the more basic aryloxide and neutral tetrahydrofuran ligands over neutral N,N-dimethylbenzylamine, which is present in solution as a reaction byproduct. This result stems from the fact that the aryloxide and tetrahydrofuran are both harder bases than the tertiary amine, and THF has less steric bulk than the neutral N,N-dimethylbenzylamine.

Figure 2.11. ORTEP diagram of 2-9 with tert-butyl methyl groups removed for clarity

(thermal ellipsoids at 50% probability).

As a means to more readily demonstrate the breadth of ligands amenable to protonolysis reactions with α-Ln(DMBA)3, we turned our attention to full protonolysis of

2-1 and 2-8, in which all three DMBA ligands were displaced by other anionic ligands, such as bulky aryloxides, anilides, or silylamides. Overall, 2-1 and 2-8 showed excellent reactivity in full protonolysis reactions to very simply generate numerous other homoleptic lanthanide complexes (Scheme 2.2). As expected for the less sterically- encumbered aryloxides, La(OAr)3 (2-10) and Y(OAr)3 (2-12) exhibited dimeric behavior in solution (Ar = 4-tert-butylphenyl). In each case, to achieve full protonolysis, 2-1 was treated with 3 eq. of protonating agent in THF at room temperature, while the analogous reactions of 2-8 were conducted at -78 °C in order to prevent decomposition of 2-8 in

THF. Product isolation consisted of either simply washing the solid with pentane or

extracting the product into pentane after the THF had been removed under reduced pressure, followed by crystallization at -25 °C. No traces of liberated neutral N,N- dimethylbenzylamine could be found in any of the products after isolation, confirming that full protonolysis had occurred and that no tertiary amine remained coordinated to the metal. Thus, protonolysis of α-Ln(DMBA)3 proved to be a very effective and simple means of generating homoleptic aryloxide and amide complexes.

2.3 Conclusion In conclusion, we have disclosed the synthesis of a new series of solvent-free homoleptic rare-earth metal complexes [α-Ln(DMBA)3]. These complexes were readily produced via salt metathesis with no formation of the corresponding “-ate” species. The size of the metal’s ionic radius determined whether a three-fold axis of symmetry was produced at the metal center, while the α-DMBA ligand showed η4 coordination in virtually every case. The reactivity of 2-1 and 2-8 was probed via protonolysis reactions.

A heteroleptic lanthanide complex (2-9) was isolated, revealing that lanthanum preferred coordination of a THF molecule to the neutral N,N-dimethylbenzylamine ligand. Full protonolysis reactions with several phenols and amines resulted in easily isolated homoleptic complexes, demonstrating the utility and versatility of the α-Ln(DMBA)3 compounds as precursors to other Ln complexes. Further investigation of the organometallic reactivity of α-Ln(DMBA)3 complexes and their use in catalysis is underway.

2.4 Experimental

2.4.1 General Considerations and Instrumentation

Compounds (2-1)-(2-18) were prepared using standard Schlenk and drybox techniques. Lanthanum(III) chloride, praseodymium(III) chloride, neodymium(III) chloride, and gadolinium(III) chloride were purchased from Strem and used without further purification. Cerium(III) chloride hexahydrate, holmium(III) chloride hexahydrate, and samarium(III) chloride hexahydrate were purchased from Strem and dried as described previously.16 N,N-Dimethylbenzylamine (DMBA-H), 2,6-di-tert- butylphenol, and p-tert-butylphenol were purchased from Acros and used without further purification. 2,6-Diisopropylaniline and 1,1,1,3,3,3-hexamethyl-disilazane were purchased from Acros and dried over calcium hydride, freeze-pump-thawed three times, distilled, and stored under nitrogen. Potassium tert-butoxide was purchased from Fisher and used without further purification. C6D6 and C7D8 were purchased from Cambridge

Isotope Laboratories and were vacuum-transferred from sodium/benzophenone ketyl and degassed with three freeze-evacuate-thaw cycles. C5D5N was purchased from Cambridge

Isotope Laboratories and was vacuum-transferred from calcium hydride and degassed with three freeze-evacuate-thaw cycles. All other solvents were purchased from either

VWR or Fisher. Pentane and toluene were purified by passage through columns of alumina and activated 4 Å molecular sieves and degassed prior to use. Tetrahydrofuran was dried over a sodium/benzophenone ketyl and distilled prior to use. All 1H and 13C

NMR data were obtained on a 400 MHz VXRS or a 600 MHz Inova spectrometer. 1H

NMR shifts given were referenced internally to the residual solvent peaks at δ 7.16 ppm

13 (C6D5H), 2.08 ppm (C7D7H), and 8.74 ppm (C5D4HN). C NMR shifts given were

referenced internally to the residual peaks at δ 128.0 ppm (C6D6), 20.4 ppm (C7D8), and

150.3 ppm (C5D5N). IR samples were prepared as Nujol mulls and taken between KBr plates on a Perkin-Elmer XTL FTIR spectrophotometer. Melting points were observed on a capillary Mel-Temp apparatus in sealed capillary tubes under nitrogen and are uncorrected. Elemental analyses were determined by Galbraith Laboratories, Knoxville,

TN or Atlantic Microlabs, Inc., Norcross, GA. Single-crystal X-ray structure determinations were performed at The University of Toledo.

α-Potassiated-N,N-dimethylbenzylamine (α-K(DMBA)).

Following a modified procedure from Sebastian, J.F.159 an oven dried 100 mL flask was charged with potassium tert-butoxide (2.91 g, 25.9 mmol). THF (50 mL) was added in order to dissolve the potassium tert-butoxide completely. N,N- dimethylbenzylamine (3.90 g, 28.8 mmol) was added to the 100 mL flask to yield a yellow solution. The 100 mL flask was cooled to -78 °C and n-BuLi (25.3 mL, 1.14 M,

28.8 mmol) was added dropwise. The reaction was stirred at -78 °C for 1.5 h, removed from the cold bath, placed in an ice bath (0 °C) and the solvent removed under vacuum.

The resulting sticky dark red solid was placed in the freezer (-25 °C) overnight. The solid was washed with copious amounts of pentane and filtered to yield a pyrophoric bright red solid (4.16 g, 93%). Flame tests revealed no trace amounts of lithium tert-butoxide.

Rather, the pentane extracts were found to contain significant amounts of lithium tert- butoxide.

α-La(DMBA)3 (2-1).

Figure 2.12. ChemDraw figure of 2-1 depicting the positions of H and H’.

An oven dried 100 mL flask was charged with anhydrous LaCl3 (2.26 g, 9.21 mmol). A second oven dried 100 mL flask was charged with α-K(DMBA) (4.91 g, 28.3 mmol). THF (40 mL) was added to the LaCl3 and cooled to -50 °C. The α-K(DMBA) was cooled to -50 °C and dissolved in THF (40 mL). The α-K(DMBA) was slowly added to the LaCl3 and stirred at -50 °C for 2.5 h. The reaction was allowed to warm to room temperature, stirred for 3 h and filtered over a bed of celite. The solution was concentrated under vacuum and cooled to -25 °C. The resulting precipitate was filtered, washed with pentane (50 mL) at -78 °C and dried under vacuum to yield an orange solid

1 3 ’ 3 (3.85 g, 77%). H NMR (C7D8, -78 °C): δ 6.99 (t, JH-H = 7.6 Hz, 3H, m-H ), 6.92 (t, JH-H

3 3 = 7.6 Hz, 3H, m-H), 6.47 (t, JH-H = 7.6 Hz, 3H, p-H), 6.38 (d, JH-H = 7.6 Hz, 3H, o-H),

3 ’ 3.46 (s, 3H, CH), 3.10 (d, JH-H = 7.6 Hz, 3H, o-H ), 1.88 (s, 9H, NCH3), 1.60 (s, 9H,

13 1 NCH3). C{ H} NMR (C7D8, -78 °C): δ 139.27, 136.26, 129.74, 120.39, 111.86, 100.97,

87.90, 45.85, 44.70. IR (Nujol, cm-1): 2922 (s), 2850 (s), 2778 (w), 2336 (m), 1916 (w),

1695 (w), 1649 (w), 1592 (m), 1525 (m), 1458 (m), 1380 (m), 1330 (m), 1302 (m), 1249

(w), 1167 (m), 1075 (w), 1029 (m), 1008 (w), 969 (m), 859 (m), 733 (s), 701 (m). Anal.

Calcd for C27H36LaN3: C, 59.89; H, 6.70; N, 7.76. Found: C, 57.66; H, 6.39; N, 8.13. Mp:

170 °C dec.

α-Ce(DMBA)3 (2-2).

An oven dried Schlenk tube was charged with anhydrous CeCl3 (227 mg, 0.921 mmol). A second oven dried Schlenk tube was charged with α-K(DMBA) (495 mg, 2.86 mmol). THF (15 mL) was added to the CeCl3 and cooled to -50 °C. The α-K(DMBA) was cooled to -50 °C and dissolved in THF (15 mL). The α-K(DMBA) was slowly added to the CeCl3 and stirred at -50 °C for 2.5 h. The Schlenk tube was removed from the cold bath, placed in an ice bath (0 °C) and solvent removed under vacuum. The solid was extracted into toluene, filtered over celite, and solvent removed under vacuum to yield a dark red solid (235 mg, 47%). IR (Nujol, cm-1): 2905 (s), 2779 (m), 2125 (m), 1596 (s),

1528 (s), 1465 (s), 1376 (m), 1334 (m), 1303 (m), 1250 (w), 1225 (m), 1083 (m), 1035

(m), 1008 (m), 971 (m), 863 (m), 845 (m), 807 (m), 735 (m), 638 (m), 604 (m). Anal.

Calcd for C27H36CeN3: C, 59.75; H, 6.69; N, 7.74. Found: C, 56.70; H, 6.59; N, 7.10. μeff

= 2.33 μB. Mp: 175 °C dec.

α-Pr(DMBA)3 (2-3).

Same procedure as 2-2 using PrCl3 (227 mg, 0.918 mmol) and α-K(DMBA) (494 mg, 2.85 mmol) to yield 2-3 as a bright red solid (255 mg, 51%). IR (Nujol, cm-1): 2927

(s), 2851 (s), 1591 (w), 1524 (w), 1451 (s), 1376 (m), 1306 (w), 1249 (w), 1223 (w),

1166 (w), 1073 (w), 1031 (w), 1000 (w), 964 (w), 860 (w), 808 (w), 730 (m), 704 (w).

Anal. Calcd for C27H36N3Pr: C, 59.67; H, 6.68; N, 7.73. Found: C, 56.63; H, 6.26; N,

7.12. μeff = 2.86 μB. Mp: 167 °C dec.

α-Nd(DMBA)3 (2-4).

Same procedure as 2-2 using NdCl3 (229 mg, 0.914 mmol) and α-K(DMBA) (490 mg, 2.83 mmol) to yield 2-4 as an orange-red solid (260 mg, 52%). IR (Nujol, cm-1):

2924 (s), 2843 (s), 1592 (m), 1527 (m), 1456 (s), 1376 (m), 1330 (w), 1305 (w), 1255

(w), 1220 (w), 1170 (m), 1074 (w), 1034 (w), 968 (w), 858 (w), 797 (w), 732 (m), 702

(w), 641 (w), 601 (w). Anal. Calcd for C27H36N3Nd: C, 59.30; H, 6.64; N, 7.68. Found:

C, 57.15; H, 6.42; N, 7.34. μeff = 3.84 μB. Mp: 168 °C dec.

α-Sm(DMBA)3 (2-5).

Same procedure as 2-2 using SmCl3 (232 mg, 0.904 mmol) and α-K(DMBA) (485 mg, 2.80 mmol) to yield 2-5 as a black solid (149 mg, 30%). IR (Nujol, cm-1): 2919 (s),

1918 (w), 1598 (s), 1531 (s), 1463 (s), 1378 (s), 1333 (m), 1306 (m), 1255 (m), 1224 (m),

1172 (s), 1037 (s), 1008 (m), 972 (m), 954 (m), 863 (m), 805 (m), 737 (s), 705 (s), 642

(s), 606 (s). Anal. Calcd for C27H36N3Sm: C, 58.65; H, 6.56; N, 7.60. Found: C, 54.13; H,

6.31; N, 6.54. μeff = 2.25 μB. Mp: 155 °C dec.

α-Gd(DMBA)3 (2-6).

Same procedure as 2-2 using GdCl3 (235 mg, 0.891 mmol) and α-K(DMBA) (480 mg, 2.77 mmol) to yield 2-6 as an orange-red solid (270 mg, 54%). IR (Nujol, cm-1):

2926 (s), 2833 (s), 1918 (w), 1789 (w), 1680 (w), 1597 (m), 1529 (m), 1462 (s), 1374 (s),

1332 (m), 1311 (m), 1249 (m), 1218 (m), 1176 (m), 1156 (m), 1078 (m), 1026 (m), 1005

(m), 969 (m), 948 (m), 860 (m), 808 (m), 725 (s), 699 (m), 637 (m), 606 (m). Anal. Calcd for C27H36GdN3: C, 57.92; H, 6.48; N, 7.50. Found: C, 55.70; H, 6.48; N, 7.09. μeff =

8.59 μB. Mp: 124 °C dec.

α-Ho(DMBA)3 (2-7).

Same procedure as 2-2 using HoCl3 (239 mg, 0.881 mmol) and α-K(DMBA) (473 mg, 2.73 mmol) to yield 2-7 as an orange-red solid (215 mg, 43%). IR (Nujol, cm-1):

2937 (s), 2847 (s), 1597 (m), 1527 (m), 1456 (s), 1376 (s), 1336 (m), 1310 (m), 1255 (s),

1220 (m), 1179 (m), 1154 (m), 1094 (w), 1074 (m), 1023 (m), 1003 (m), 968 (m), 943

(w), 862 (w), 837 (m), 802 (m), 731 (s), 696 (m). Anal. Calcd for C27H36HoN3: C, 57.14;

H, 6.39; N, 7.40. Found: C 55.45; H, 6.01; N, 7.03. μeff = 8.80 μB. Mp: 139 °C dec.

α-Y(DMBA)3 (2-8).

’ Figure 2.13 ChemDraw figure of 2-8 depicting H and H for Cs isomer.

Same procedure as 2-2 using YCl3 (1.99 g, 10.2 mmol) and α-K(DMBA) (5.46 g,

31.5 mmol) to yield 2-8 as a yellow solid (3.95 g, 79%; C3 isomer (45%), Cs isomer

1 3 (55%)). H NMR (C6D6, 20 °C) C3 isomer: δ 6.87 (m, 6H, m-H), 6.32 (t, JH-H = 7.2 Hz,

3 3H, p-H), 6.04 (d, JH-H = 7.2 Hz, 6H, o-H), 3.68 (s, 3H, CH), 2.02 (br s, 18H, NCH3); Cs

3 ’ 3 isomer: δ 6.85 (m, 4H, m-H), 6.77 (t, JH-H = 7.2 Hz, 2H, m-H ), 6.43 (t, JH-H = 7.2 Hz,

’ 3 3 1H, p-H ), 6.20 (t, JH-H = 7.2 Hz, 2H, p-H), 6.00 (d, JH-H = 7.2 Hz, 4H, o-H), 5.90 (d,

3 ’ ’ ’ JH-H = 7.2 Hz, 2H, o-H ), 3.70 (s, 1H, CH ), 3.69 (s, 2H, CH), 2.07 (br s, 6H, NCH3 ),

13 1 1.86 (br s, 12H, NCH3). C{ H} NMR (C6D6, 20 °C): C3 isomer: δ 141.85, 132.38,

112.77, 106.80 (br), 82.97, 45.37; Cs isomer: 140.57, 139.64, 132.80, 132.31, 113.71,

111.95, 106.80 (br), 105.47 (br), 81.07, 80.54, 48.29, 40.78. IR (Nujol, cm-1): 2926 (s),

2850 (s), 1596 (m), 1530 (m), 1454 (s), 1372 (m), 1334 (m), 1312 (w), 1252 (w), 1220

(m), 1181 (m), 1154 (w), 1078 (w), 1023 (m), 1001 (w), 969 (w), 947 (w), 860 (w), 832

(w), 805 (w), 729 (s), 701 (m), 631 (s), 598 (m). Anal. Calcd for C27H36N3Y: C, 65.98; H,

7.38; N, 8.55. Found: C, 64.81; H, 7.54; N, 8.36. Mp: 135 °C dec.

La[(DMBA)(OAr)2(THF)] [Ar = 2,6-di-tert-butylphenyl] (2-9).

An oven dried Schlenk tube was charged with 2-1 (359 mg, 0.663 mmol). A second oven dried Schlenk tube was charged with 2,6-di-tert-butylphenol (219 mg, 1.06 mmol). THF (20 mL) was added to both Schlenk tubes and the Schlenk tube containing

2-1 was cooled to -78 °C. The 2,6-di-tert-butylphenol solution was added dropwise to 2-

1. The reaction was stirred at -78 °C for 1 h and warmed to room temperature to yield a yellow colored solution. The THF was removed under vacuum and the solid was extracted twice with pentane, filtered, and the solvent removed under vacuum to yield a

1 3 yellow solid (283 mg, 71%). H NMR (C6D6, 20 °C): δ 7.36 (d, JH-H = 7.8 Hz, 4H, m-H

3 3 of OAr), 6.99 (t, JH-H = 7.8 Hz, 2H, p-H of OAr), 6.85 (t, JH-H = 7.2 Hz, 2H, m-H of

3 3 DMBA), 6.35 (d, JH-H = 7.2 Hz, 2H, o-H of DMBA), 6.30 (t, JH-H = 7.2 Hz, 1H, p-H of

t DMBA), 3.40 (s, 1H, CH), 3.18 (br s, 4H, THF), 2.37 (s, 6H, NCH3), 1.54 (s, 36H, Bu),

13 1 1.04 (br s, 4H, THF). C{ H} (C6D6, 20 °C): δ 162.93, 144.52, 137.30, 132.19, 125.50,

117.35, 114.45, 114.33, 88.25, 69.93, 35.16, 35.07, 32.36, 25.40. IR (Nujol, cm-1): 2911

(s), 1595 (m), 1576 (m), 1539 (m), 1459 (s), 1407 (s), 1379 (s), 1299 (m), 1257 (s), 1233

(s), 1101 (m), 1021 (m), 1003 (m), 979 (w), 885 (w), 857 (s), 815 (s), 739 (s), 697 (m),

674 (m), 641 (s), 603 (m). Anal. Calcd for C41H62LaNO3: C, 65.15; H, 8.27; N, 1.85.

Found: C, 64.35; H, 8.20; N, 2.29. Mp: 157 °C dec.

La(OAr)3 [Ar = p-tert-butylphenyl] (2-10).

An oven dried Schlenk tube was charged with 2-1 (415 mg, 0.766 mmol). A second oven dried Schlenk tube was charged with p-tert-butylphenol (345 mg, 2.30

mmol). THF (10 mL) was added to each Schlenk tube and the p-tert-butylphenol solution was added slowly to 2-1. The solution was stirred overnight to yield a colorless solution.

The solvent was removed under vacuum and the solid was washed with pentane (60 mL) at -78 °C to yield a white solid. The solid was dried under vacuum and collected (135 mg,

1 30%). Spectroscopic data indicates that 2-10 exists as a dimer: [(ArO)2La(μ-OAr)]2. H

3 3 NMR (C6D6, 20 °C): δ 7.95 (d, JH-H = 8.4 Hz, 4H, o-H), 7.68 (d, JH-H = 8.4 Hz, 4H, m-

3 3 H), 7.28 (d, JH-H = 7.8 Hz, 8H, o-H), 6.76 (d, JH-H = 7.8 Hz, 8H, m-H), 1.34 (s, 54H, t 13 1 Bu). C{ H} NMR (C6D6, 20 °C): δ 163.87, 162.46, 140.37, 138.31, 127.46, 126.90,

119.69, 119.03, 34.25, 34.07, 32.16, 32.07. IR (Nujol, cm-1): 2899 (s), 1875 (w), 1598 (s),

1502 (s), 1462 (s), 1362 (s), 1266 (s), 1175 (s), 1110 (m), 1029 (m), 919 (w), 858 (m),

831 (s), 672 (m), 556 (s). Anal. Calcd for C30H39LaO3: C, 61.42; H, 6.70. Found: C,

62.00; H, 7.50. Mp: 160 °C dec

La(OAr)3 [Ar = 2,6-di-tert-butylphenyl] (2-11).

Same procedure as 2-10 using 2-1 (359 mg, 0.662 mmol) and 2,6-di-tert- butylphenol (410 mg, 1.99 mmol) to yield 2-11 as a white solid (353 mg, 71%).

Compound 2-11 has been previously reported, although no spectral data were given.160

1 3 3 H NMR (C6D6, 20 °C): δ 7.30 (d, JH-H = 7.8 Hz, 6H, m-H), 6.83 (t, JH-H = 7.8 Hz, 3H,

t 13 1 p-H), 1.55 (s, 54H, Bu). C{ H} NMR (C6D6, 20 °C): δ 162.82, 137.17, 125.34, 117.16,

34.93, 32.22.

Y(OAr)3 [Ar = p-tert-butylphenyl] (2-12).

An oven dried Schlenk tube was charged with 2-8 (458 mg, 0.932 mmol). A second oven dried Schlenk tube was charged with p-tert-butylphenol (420 mg, 2.80 mmol). The Schlenk tube containing 2-8 was cooled to -78 °C and THF (10 mL) was added. The p-tert-butylphenol was dissolved in THF (15 mL) and slowly added to 2-8.

The reaction was stirred at -78 °C for 30 min and allowed to warm to room temperature to yield a colorless solution. The solvent was removed under vacuum and the solid extracted with pentane. After filtration, the solvent was removed to yield a yellow

1 precipitate (327 mg, 65%; monomer (33%), dimer (67%)). H NMR (C6D6, 20 °C)

3 3 monomer: δ 8.14 (d, JH-H = 8.4 Hz, 6H, o-H), 6.99 (d, JH-H = 8.4 Hz, 6H, m-H), 1.01 (s,

t 3 3 27H, Bu); dimer: δ 7.81 (d, JH-H = 8.4 Hz, 4H, o-H), 7.29 (d, JH-H = 8.4 Hz, 8H, o-H),

3 3 t 7.27 (d, JH-H = 8.4 Hz, 4H, m-H), 6.84 (d, JH-H = 8.4 Hz, 8H, m-H), 1.38 (s, 36H, Bu),

t 13 1 1.13 (s, 18H, Bu). C{ H} NMR (C6D6, 20 °C) monomer: δ 156.74, 143.50, 127.08,

122.13, 34.20, 31.78; dimer: 161.44, 159.65, 141.98, 139.67, 127.37, 126.50, 120.03,

118.91, 34.18, 34.14, 32.20, 31.88. IR (Nujol, cm-1): 2902 (s), 1882 (w), 1755 (w), 1605

(m), 1459 (s), 1379 (s), 1308 (s), 1172 (m), 1111 (m), 1017 (m), 960 (w), 932 (w), 876

(m), 829 (m), 735 (m), 697 (w), 674 (w), 641 (w). Anal. Calcd for C30H39O3Y: C, 67.16;

H, 7.33. Found: C, 67.98; H, 7.85. Mp: 150 °C dec.

Y(OAr)3 [Ar = 2,6-di-tert-butylphenyl] (2-13).

An oven dried Schlenk tube was charged with 2-8 (349 mg, 0.709 mmol). A second oven dried Schlenk tube was charged with 2,6-di-tert-butylphenol (439 mg, 2.13

mmol). The Schlenk tube containing 2-8 was cooled to -78 °C and THF (10 mL) was added. The 2,6-di-tert-butylphenol was dissolved in THF (10 mL) and slowly added to 2-

8. The reaction was stirred at -78 °C for 30 min and allowed to warm to room temperature. The solvent was removed under vacuum and the solid was extracted with pentane. After filtration, the solvent was removed to yield a white solid (296 mg, 59%).

Spectroscopic properties matched those previously recorded.161

La(NHAr’)3 [Ar’ = 2,6-diisopropylphenyl] (2-14).

An oven dried Schlenk tube was charged with 2-1 (324 mg, 0.598 mmol). A second oven dried Schlenk tube was charged with 2,6-diisopropylaniline (324 mg, 1.83 mmol). THF (10 mL) was added to both Schlenk tubes and the 2,6-diisopropylaniline solution was added dropwise to 2-1. The reaction was stirred at room temperature overnight to yield an orange colored solution. The THF was removed under vacuum and the product was washed with pentane (12 mL) at -78 °C, filtered, and dried under vacuum to yield a tan colored solid (268 mg, 67%). Spectroscopic properties matched those previously recorded.162

La(NHAr’)3 [Ar’ = p-tert-butylphenyl] (2-15).

Same procedure as 2-14 using 2-1 (464 mg, 0.856 mmol) and 4-tert-butylaniline

1 (384 mg, 2.57 mmol) to yield 2-15 as a white solid (275 mg, 55%). H NMR (C5D5N, 20

3 3 °C): δ 7.04 (d, JH-H = 7.8 Hz, 6H, o-H), 6.91 (d, JH-H = 7.8 Hz, 6H, m-H), 4.89 (s, 3H,

t 13 1 NH), 1.29 (s, 27H, Bu). C{ H} NMR (C5D5N, 20 °C) δ 130.33, 130.03, 119.18,

118.46, 37.22, 35.84. IR (Nujol, cm-1): 2912 (m), 1599 (s), 1544 (w), 1497 (s), 1459 (m),

1361 (m), 1333 (m), 1291 (s), 1263 (s), 1186 (s), 1105 (w), 1000 (w), 882 (m), 665 (m),

557 (m). Anal. Calcd for C30H42LaN3: C, 61.75; H, 7.25; N, 7.20. Found: C, 57.66; H,

7.20; N, 6.57. Mp: 164 °C dec.

Y(NHAr’)3 [Ar’ = 2,6-diisopropylphenyl] (2-16).

An oven dried Schlenk tube was charged with 2-8 (318 mg, 0.647 mmol). A second oven dried Schlenk tube was charged with 2,6-diisopropylaniline (350 mg, 1.97 mmol). The Schlenk tube containing 2-8 was cooled to -78 °C and THF (10 mL) was added. THF (10 mL) was added to the 2,6-diisopropylaniline and the solution was added dropwise to 2-8. The reaction was stirred at -78 °C for 30 min and allowed to warm to room temperature and stirred overnight to yield a golden yellow colored solution. After filtration, the solvent was removed under vacuum and the solid was washed with pentane twice to yield a white solid (237 mg, 59%). Spectroscopic properties matched those previously recorded.163

La[N(SiMe3)2]3 (2-17).

An oven dried Schlenk tube was charged with 2-1 (349 mg, 0.645 mmol). A second oven dried Schlenk tube was charged with 1,1,1,3,3,3-hexamethyl-disilazane (317 mg, 1.97 mmol). THF (10 mL) was added to both Schlenk tubes and the 1,1,1,3,3,3-

hexamethyl-disilazane was slowly added to 2-1. The reaction was stirred overnight and the solvent was removed under vacuum. The solid was extracted into pentane, filtered, and the solvent removed under vacuum to yield an off-white solid (390 mg, 98%).

Spectroscopic properties matched those previously reported.76

Y[N(SiMe3)2]3 (2-18).

An oven dried Schlenk tube was charged with 2-8 (345 mg, 0.702 mmol). A second oven dried Schlenk tube was charged with 1,1,1,3,3,3-hexamethyl-disilazane (345 mg, 2.14 mmol). The Schlenk tube containing 2-8 was cooled to -78 °C and THF (10 mL) was added. THF (10 mL) was added to the 1,1,1,3,3,3-hexamethyl-disilazane and the solution was slowly added to 2-8. The reaction was stirred at -78 °C for 30 min and allowed to warm to room temperature and stirred overnight to yield a vibrant orange- yellow colored solution. The solvent was removed under vacuum and the solid was extracted with pentane. After filtration, the pentane was removed under vacuum to yield an off-white solid (310 mg, 77%). Spectroscopic properties matched those previously recorded.76

2.5 Crystallography.

Summaries of crystal data and collection parameters for the crystal structures of

(2-1)-(2-5) and (2-6)-(2-9) are provided in Tables 2.2 and 2.3, respectively. Detailed descriptions of data collection, as well as data solution, are provided below. ORTEP

diagrams were generated with the ORTEP-3 software package.164 For each sample, a suitable crystal was mounted on a pulled glass fiber using Paratone-N hydrocarbon oil.

The crystal was transferred to a Siemens SMART165 diffractometer with a CCD detector, centered in the X-ray beam, and cooled to 140 K using a nitrogen-flow low temperature apparatus that had been previously calibrated by a thermocouple placed at the same position as the crystal. An arbitrary hemisphere of data was collected using 0.3° ω scans, and the data were integrated by the program SAINT.166 The final unit cell parameters were determined by a least-squares refinement of the reflections with I > 10σ(I). Data analysis using Siemens XPREP167 and the successful solution and refinement of the structure determined the space group. An empirical absorption correction was applied using SADABS.168 Equivalent reflections were averaged, and the structures were solved by direct methods using the SHELXTL software package.169 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included as fixed atoms, but not refined.

2-1. X-ray quality crystals were grown from a layered solution of THF and pentane at -25

°C. The final cycle of full-matrix least-squares refinement was based on 5589 observed reflections and 280 variable parameters and converged, yielding final residuals: R =

0.0251, Rall = 0.0292, and GOF = 1.067.

2-2. X-ray quality crystals were grown from a layered solution of toluene and pentane at -

25 °C. The final cycle of full-matrix least-squares refinement was based on 5230 observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0330, Rall = 0.0422, and GOF = 1.047.

2-3. X-ray quality crystals were grown from a layered solution of toluene and pentane at -

25 °C. The final cycle of full-matrix least-squares refinement was based on 5931 observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0381, Rall = 0.0392, and GOF = 1.136.

2-4. X-ray quality crystals were grown from a layered solution of toluene and pentane at -

25 °C. The final cycle of full-matrix least-squares refinement was based on 5809 observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0309, Rall = 0.0328, and GOF = 1.109.

2-5. X-ray quality crystals were grown from a layered solution of toluene and pentane at -

25 °C. The final cycle of full-matrix least-squares refinement was based on 3191 observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0253, Rall = 0.0289, and GOF = 1.084.

2-6. X-ray quality crystals were grown from a layered solution of toluene and pentane at

-25 °C. The final cycle of full-matrix least-squares refinement was based on 5619 observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0275, Rall = 0.0307, and GOF = 1.088.

2-7. X-ray quality crystals were grown from a layered solution of toluene and pentane at -

25 °C. The final cycle of a full-matrix least-squares refinement was based on 5403 observed reflections and 559 variable parameters and converged, yielding final residuals:

R = 0.0768, Rall = 0.0901, and GOF = 1.034.

2-8. X-ray quality crystals were grown from a concentrated pentane solution at room temperature. The final cycle of full-matrix least-squares refinement was based on 4855

observed reflections and 280 variable parameters and converged, yielding final residuals:

R = 0.0593, Rall = 0.0712, and GOF = 1.124.

2-9. X-ray quality crystals were grown from a layered solution of THF and pentane at room temperature. The final cycle of full-matrix least-squares refinement was based on

9253 observed reflections and 415 variable parameters and converged, yielding final residuals: R = 0.0271, Rall = 0.0276, and GOF = 1.058.

Table 2.2. Crystal Data and Collection Parameters

2-1 2-2 2-3 2-4 2-5 Formula C27H36LaN3 C27H36CeN3 C27H36N3Pr C27H36N3Nd C27H36N3Sm Fw 541.50 542.71 543.50 546.83 552.94 Space Group P21/c P21/c P21/c P21/c P21/c Temp (K) 140 140 140 140 140 a(Å) 14.4333(4) 14.390(1) 14.3591(6) 14.366(1) 14.281(3) b(Å) 11.6644(3) 11.603(1) 11.5768(4) 11.577(1) 11.527(2) c(Å) 14.9842(4) 14.999(1) 15.0116(6) 15.049(1) 15.021(3) α(deg) 90.000 90.000 90.000 90.000 90.000 β(deg) 94.422(1) 93.817(2) 93.622(1) 93.878(2) 93.181(4) γ(deg) 90.00 90.000 90.000 90.000 90.000 V(Å3) 2515.2(1) 2498.8(4) 2490.4(2) 2497.1(4) 2468.9(8)

Z 4 4 4 4 4 Calcd density 3 1.430 1.443 1.450 1.455 1.488 (g/cm ) Siemens Siemens Siemens Siemens Siemens Diffractometer SMART SMART SMART SMART SMART Mo Kα (λ = Mo Kα (λ = Mo Kα (λ = Mo Kα (λ = Mo Kα (λ = Radiation 0.71073 Å) 0.71073 Å) 0.71073 Å) 0.71073 Å) 0.71073 Å) Monochromator Graphite Graphite Graphite Graphite Graphite CCD area CCD area CCD area CCD area CCD area Detector detector detector detector detector detector Scan type, ω, 0.3 ω, 0.3 ω, 0.3 ω, 0.3 ω, 0.3 Width (deg) Scan speed 20 20 20 20 20 (s/frame)

No of reflns Hemisphere Hemisphere Hemisphere Hemisphere Hemisphere measd 2θ range (deg) 2.84-56.56 4.44-56.66 4.44-56.64 2.84-56.56 2.86-46.54 Cryst dimens 0.30 x 0.30 x 0.40 x 0.20 x 0.30 x 0.20 x 0.40 x 0.40 x 0.50 x 0.40 x (mm) 0.30 0.10 0.20 0.20 0.10 No of reflns 28062 23475 26240 27022 19892 measd No of unique 6243 6206 6178 6184 3547 reflns No of obsd refln 5589 5230 5931 5809 3191 (I > 2σ(I))

Rint 0.0242 0.0525 0.0358 0.0384 0.0377 No of params 280 280 280 280 280 0.0251, 0.0330, 0.0381, 0.0309, 0.0253, R, Rw, Rall 0.0629, 0.0818, 0.0976, 0.0794, 0.0629, 0.0292 0.0422 0.0392 0.0328 0.0289 GoF 1.067 1.047 1.136 1.109 1.084

Table 2.3. Crystal Data and Collection Parameters

2-6 2 -7 2-8 2-9 Formula C27H36GdN3 C27H36HoN3 C27H36N3Y C41H62LaNO3 Fw 559.84 567.52 491.50 755.83 Space Group P21/c P -1 P21/n Cc Temp (K) 140 140 140 140 a(Å) 14.9873(8) 9.405(3) 15.004(3) 14.2150(6) b(Å) 9.8170(5) 17.268(5) 10.626(2) 13.9201(5) c(Å) 16.9075(9) 17.336(6) 15.155(3) 19.6337(8) α(deg) 90.000 108.565(8) 90.000 90.000 β(deg) 93.241(1) 105.566(6) 97.07(3) 90.442(1) γ(deg) 90.000 100.822(6) 90.000 90.000 3 V(Å ) 2483.6(2) 2453.1(1) 2397.9(8) 3884.9(3) Z 4 4 4 4 Calcd density 3 1.497 1.537 1.361 1.292 (g/cm ) Siemens Siemens Siemens Siemens Diffractometer SMART SMART SMART SMART Mo Kα (λ = Mo Kα (λ = Mo Kα (λ = Mo Kα (λ = Radiation 0.71073 Å) 0.71073 Å) 0.71073 Å) 0.71073 Å) Monochromator Graphite Graphite Graphite Graphite CCD area CCD area CCD area CCD area Detector detector detector detector detector Scan type, ω, 0.3 ω, 0.3 ω, 0.3 ω, 0.3 Width (deg) Scan speed 20 20 20 20 (s/frame) No of reflns Hemisphere Hemisphere Hemisphere Hemisphere measd 2θ range (deg) 2.72-56.60 2.60 -46.66 3.60-56.78 4.10-56.58 Cryst dimens 0.30 x 0.20 x 0.40 x 0.40 x 0.40 x 0.40 x 0.30 x 0.20 x (mm) 0.10 0.40 0.40 0.10 No of reflns 27011 16410 21038 20656 measd No of unique 6156 6973 5803 9469 reflns No of obsd refln 5619 5403 4855 9253 (I > 2σ(I))

Rint 0.0435 0.0771 0.0566 0.0310 No of params 280 559 280 415 0.0275, 0.0768, 0.0593, 0.0271, R, R , R 0.0709, 0.1905, 0.1430, w all 0.0663, 0.0276 0.0307 0.0901 0.0712 GoF 1.088 1.034 1.124 1.058

Chapter 3

Insertion Reactions and Catalytic Hydrophosphination of Heterocumulenes using Alpha-Metallated N,N- Dimethylbenzylamine Rare-Earth Metal Complexes

3.1 Introduction

In the ever-growing discipline of catalysis, the improvement of carbon-heteroatom bond- forming reactions remains at the forefront. The effective catalysis of hydroamination,121,170 hydrosilylation,126,142,171 and hydrophosphination94,172-174 is very attractive due to the 100% atom economy involved in these reactions.118 In contrast to the myriad reported catalysts for hydroamination and hydrosilylation reactions, the number of known hydrophosphination catalysts remains small, although they span the entire periodic table, with several reports involving late transition metals.133,175-179 Early metal catalysts, such as those of Waterman and Mindiola, have been utilized in the intermolecular hydrophosphination of alkynes.130,180 Main group metals can also be effective, as noted in Cui, Stephan, and Hill’s reports on alkaline earth metal catalyzed hydrophosphination reactions.173,181,182 Furthermore, the Marks and Hou groups have

shown that even f-elements can be employed, as demonstrated in the hydrophosphination of olefins and carbodiimides using constrained geometry lanthanide catalysts.132,183 We were especially intrigued by the use of lanthanides due to the various possible advantages available with these metals, such as their electrophilicities, the ability to tune the steric environment about these metal centers through the proper choice of supporting ligands, and their absence of unproductive oxidative addition/reductive elimination reaction pathways.

Catalytic hydrophosphination of an unsaturated species yields product phosphines with one more substituent than the related reactant (e.g. a secondary phosphine is converted to a tertiary phosphine). In addition to its atom efficiency, this reaction serves as a convenient way to make unsymmetrically substituted phosphines (e.g. R2PR’; R ≠

R’). The hydrophosphination products are valuable due to their utility in various applications such as use as ligands for stabilization of metals,184 and in medicine,185 complex organic synthesis,186 and materials chemistry.187 The hydrophosphination of heterocumulenes has recently come under scrutiny as a convenient means to synthesize phosphorus analogues of guanidines, ureas, thioureas, and amidines.59,188-192 Recent work has shown that constrained geometry lanthanide catalysts are useful for the hydrophosphination of carbodiimides at elevated temperatures (80°C).132 The product phosphaguanidines are known to be a versatile ligand class for Al, La, Y, Ti, Zr, Nb, Cu, and Zn species with broadly tunable properties.193-196 Direct synthesis of phosphaguanidines from phosphines and carbodiimides does not work; therefore, metal catalyzed hydrophosphination of carbodiimides, in which the P-H bond is added across

the diimine reducing the bond order by one, represents a useful new method to produce these compounds.

Although Hou has shown that silyl-bridged cyclopentadienyl-amido lanthanide complexes efficiently catalyze the hydrophosphination of carbodiimides, these reactions required elevated temperatures for catalysis.132 To date, there have been no reports of successful hydrophosphination of heterocumulenes at room temperature using a rare- earth-metal catalyst. As our recent efforts have focused on the production of new lanthanide complexes,55 we set out to explore their possible utility in catalytic hydrophosphination reactions. Herein, we report the room temperature hydrophosphination of carbodiimides and isocyanates using homoleptic alpha-metallated

N,N-dimethylbenzylamine (DMBA) rare-earth complexes.

3.2 Results and Discussion

In Chapter 2, we reported the synthesis and preliminary protonolysis reactivity of a new class of non-cyclopentadienyl homoleptic rare-earth-metal complexes utilizing exclusively α-metallated dimethylbenzylamine supporting ligands.55 In our ongoing experiments, we sought to expand the reactivity scope of the α-Ln(DMBA)3 (Ln = La, Y) complexes by investigating stoichiometric insertion reactions, as well as the related catalytic processes utilizing both insertion and protonolysis reactions. As such, complex

3-1 was synthesized via the stoichiometric reaction of α-La(DMBA)3 with three equivalents of N,N-diisopropylcarbodiimide in THF at ambient temperature (Scheme

3.1). In the course of 12 hours, this reaction underwent a color change from an orange-red

to a golden yellow hue. The product was isolated from a concentrated solution of diethyl ether as a microcrystalline powder. Its NMR spectrum at ambient temperature was broad and uninterpretable, indicating significant fluxionality. Upon warming to 78°C, the spectrum sharpened and was consistent with the single insertion product 3-1. We attribute the fluxional behavior at ambient temperature to slow intramolecular ligand exchange processes in which the NMe2 unit is transiently coordinated to the metal center instead of one of the amidinate nitrogen donor atoms. The overall composition was further supported by elemental analysis data.

Scheme 3.1. Stoichiometric insertion of carbodiimides.

A pair of single insertion yttrium complexes (3-2 and 3-3; Scheme 3.1) were prepared in a similar manner to that used for 3-1. As in the previous case, each of these two complexes exhibited fluxional NMR spectra at room temperature that sharpened nicely at elevated temperatures. Thus, we assigned 3-2 and 3-3 analogous structures to that of 3-1, with compositions that were confirmed by elemental analysis data.

Furthermore, for the cyclohexyl derivative (3-3), we were able to obtain X-ray quality crystals from a concentrated solution of pentane/diethyl ether at room temperature. The

X-ray structure of 3-3 revealed a homoleptic tris-amidinate complex (Figure 3-1). To accurately describe the geometry of 3-3, the torsion angle N1-Q1-Q2-N2, where Q1 and Q2

are centroids formed by the N1N4N7 and N2N5N8 planes from Figure 3.1, was determined.

A perfect trigonal prism and octahedron will have torsion angles of 0° and 60°, respectively. In the case of 3-3, the torsion angle N(1)-Q(1)-Q(2)-N(2) is 28.15° and

i compares well to other yttrium guanidinates Y[(N Pr)2CNMe2]3 (20.77°) and

i 197 Y[(N Pr)2CNEt2]3 (21.43°). The Ln-N bond distances vary from 2.371(3) to 2.405(4) Å and are comparable to other amidinate and guanidinate complexes:

t t Y2[Me3SiNC(Ph)N(CH2)3NC(Ph)NSiMe3]3 (2.307(2)-2.354(2) Å), Y[ BuNC(CH3)N Bu]3

i (2.379(3)-2.389(3) Å), Y[(N Pr)2CNMe2]3 (2.362(2)- 2.373(2) Å), and

i i i 147,197-199 (C5H5)2Y[ PrNC(N Pr2)N Pr] (2.316(3)-2.321(3) Å).

Further derivatives of these insertion products were explored through two additional reactants: bis(trimethylsilyl)carbodiimide and N,N-di-tert-butylcarbodiimide.

The latter showed no insertion into the Ln-C bond for either La or Y even at elevated temperatures, while the former appeared to insert one equivalent of the carbodiimide, yielding complex 3-4 (Ln = Y) (Scheme 3.2).

Scheme 3.2. Synthesis of N,N-dimethylbenzylamine amidinate (3-4; R = SiMe3).

In the NMR spectrum of 3-4, the benzyl amidinate contained three aryl resonances (7.47, 7.20, and 7.09 ppm) that were shifted significantly from those of the phenyl group of the dimethylbenzylamine ligand (7.24, 6.64, and 6.25 ppm). Also, the

4 methine hydrogen of the newly formed amidinate ligand displayed a doublet with JY-H =

1.9 Hz, while the methine of the DMBA ligand was a broad singlet. The 13C{1H} NMR

3 of 3-4 displayed two doublets with coupling constant of JY-C = 4.8 Hz for the methine

1 carbon of the amidinate ligand and JY-C = 6.7 Hz for the methine carbon of the dimethylbenzylamine ligand. These values are well within the wide range of coupling constants observed previously for yttrium non-metallocene complexes.56,200

N2 N1

N7 Y1 N5 C45 C23

N8 N4

Figure 3.1. ORTEP diagram of 3-3 with cyclohexyl groups from two ligands removed for clarity (thermal ellipsoids at 30% probability). Selected bond lengths (Å) and angles

(deg): Y1-N7 2.375(3), Y1-N8 2.371(3), N7-Y1-N8 56.2(1).

In a recent report, Hou and coworkers demonstrated that

[{Me2Si(C5Me5)(NC6H2Me3-2,4,6)}La(CH2C6H4NMe2-o)(THF)] functioned as a useful precatalyst for the hydrophosphination of a variety of carbodiimides at elevated temperatures (80°C).132 Given the results involving carbodiimide insertion reactions

presented herein and our previous investigation into protonolysis reactions of α-

55 Ln(DMBA)3 (see Chapter 2), we felt that these new complexes were perfectly suited for use in catalytic hydrophosphination reactions. To test this hypothesis, we first added N,N- diisopropylcarbodiimide to a solution of α-La(DMBA)3 (5 mol%) and THF at room temperature, followed by the addition of one equivalent of diphenylphosphine. While we did observe excellent conversion to the phosphaguanidine product, in accordance with the aforementioned results, this product was contaminated with the amidine i i ( PrN=C(NH Pr)CHPhNMe2), which was likely formed by insertion of the carbodiimide into the La-DMBA bond, followed by subsequent protonolysis by the Ph2PH. Thus, this order of addition of reactants is limited to a maximum yield of 85% due to the initial formation of the triply inserted product (3-1). Therefore the order of addition was reversed in our subsequent experiments; that is, diphenylphosphine was added to α-

La(DMBA)3 followed by the N,N-diisopropylcarbodiimide. Additionally, 1.15 equivalents of Ph2PH were used to offset the 15% loss of product. Using this reversed order of addition, we found that DMBA-H was produced (via initial protonolysis of α-

La(DMBA)3 by Ph2PH) instead of the amidine observed previously, and this byproduct was much more easily removed from the desired phosphaguanidines, improving isolated yields greatly. A control experiment was performed in which the catalyst was withheld from the reaction mixture, and no hydrophosphination product was observed, even after heating the reaction to 90°C for 48 hours.

Prior to full-scale catalytic screening, we investigated a series of NMR scale catalyses using [D8]THF in order to determine the optimal conditions for this reaction.

There was a distinct color change upon addition of N,N-diisopropylcarbodiimide to the

mixture of α-La(DMBA)3 and diphenylphosphine at room temperature. After ten minutes, 1H NMR spectroscopy indicated that the reaction was >90% complete. For this and various other heterocumulenes, it was found that the reaction was essentially complete after 6h at room temperature in THF. Noncoordinating reaction solvents such as

C6D6 or C7D8 were screened, but no catalytic activity was observed. Alternate lanthanide complexes, such as α-Y(DMBA)3 and α-Ce(DMBA)3 demonstrated moderate catalytic activity (42% and 40% with diisopropylcarbodiimide, respectively), but both proved to be inferior to α-La(DMBA)3. This was attributed to the decomposition of α-Y(DMBA)3

55 and α-Ce(DMBA)3 in THF as noted previously (Chapter 2).

To further develop the substrate scope of this catalytic reaction, hydrophosphination of a wide range of heterocumulenes was undertaken (Table 3.1).

Additionally, a few commercially available phosphines were investigated.

Hydrophosphination of unhindered carbodiimides was very efficient and the resulting phosphaguanidines (3-6a and 3-6b) were isolated in excellent yields. In contrast, attempted hydrophosphination of N,N-di-tert-butylcarbodiimide with diphenylphosphine did not result in production of the desired phosphaguanidine, but rather only starting materials were observed. This is consistent with the stoichiometric insertion results where

N,N-di-tert-butylcarbodiimide was unable to insert because of the larger steric bulk of the tert-butyl groups. The hydrophosphination reaction also worked well with isocyanates and isothiocyanates and it was tolerant of both electron withdrawing and electron donating nitrogen substituents on these heterocumulenes ((3-6c)-(3-6l)). In fact, for most of the isocyanates, NMR spectroscopic observation of the crude reaction products indicated virtually quantitative conversion to the desired phosphaureas. The reduced yield

is generally reflective of losses upon isolation and purification. A decrease in reaction yield with 1-adamantyl isocyanate can be attributed to the larger steric bulk of the adamantyl group, hindering insertion into the La-phosphide bond and consequently reducing conversion to the product. Hydrophosphination of the slightly larger tert- butylisocyanate was even worse, with the desired phosphaurea compound afforded in very low yield (<20%), again demonstrating the deleterious effect of steric hindrance on this reaction.

The acidity of the phosphine employed was also found to significantly affect the catalysis. Attempted hydrophosphination of N,N-diisopropylcarbodiimide with di-tert- butylphosphine gave no product even when heated to 80 °C for 36h. Given its much lower acidity,201 it is likely that the di-tert-butylphosphine is unable to protonate off the product phosphaguanidinate ligand, preventing catalytic turnover. Small amounts of (4-

MeOC6H4)2PH and di-p-tolylphosphine were obtained from commercial sources for comparison. In both cases, the related phosphaureas (3-6m and 3-6n) were produced and isolated in very similar yields to those obtained with the unsubstituted diphenylphosphine, indicating little or no sensitivity to electronic effects at this position.

Table 3.1. Catalytic addition of phosphines to heterocumulenes.a

Yieldb Entry R PH R’-N=C=X Product 2 [%]

3-6a 1 Ph PH iPrN=C=NiPr 2 (93)

3-6b 2 Ph PH CyN=C=NCy 2 (74)

3-6c 3 Ph PH PhN=C=O 2 (60)

3-6d 4 Ph PH CyN=C=O 2 (54)

3-6e 5 Ph PH AdN=C=O 2 (38)c

3-6f 6 Ph PH NaphN=C=O 2 (76)c

3-6g 7 Ph PH PhN=C=S 2 (91)

3-6h 8 Ph PH (4-FC H )N=C=O 2 6 4 (83)d

3-6i 9 Ph PH (4-ClC H )N=C=O 2 6 4 (83)

3-6j 10 Ph PH (4-BrC H )N=C=O 2 6 4 (49)

3-6k 11 Ph PH (4-MeOC H )N=C=O 2 6 4 (62)

3-6l 12 Ph PH (4-F CC H )N=C=O 2 3 6 4 (88)

3-6m 13 (4-MeOC H ) PH (4-BrC H )N=C=O 6 4 2 6 4 (45)

3-6n 14 (4-MeC H ) PH (4-F CC H )N=C=O 6 4 2 3 6 4 (65) a Conditions: phosphine (1.15 mmol), heterocumulene (1.00 mmol), catalyst (0.05 mmol), THF (3 mL). b Isolated yield. c Reaction stirred at 55°C. d Product isolated as a 3:1 ratio of phosphaurea 3-6h and trimerized isocyanate.

Scheme 3-3. Synthesis of homoleptic lanthanum phosphaguanidinate (3-5).

To gain insight into the possible catalysis mechanism, α-La(DMBA)3 was treated with three equivalents of diphenylphosphine in THF (15 mL), followed by three equivalents of N,N-diisopropylcarbodiimide (Scheme 3.3). After removal of THF under vacuum, the mixture was triturated with pentane (10 mL), washed twice with pentane (12 mL) at -78 °C, and dried under vacuum. The resulting product (3-5) was then recrystallized from a concentrated solution of toluene at room temperature. Its X-ray crystal structure revealed a homoleptic complex in which three phosphaguanidinate ligands are bound to the metal center through their chelating nitrogen atoms (Figure 3.2).

The La-N bond distances of 3-5 (2.502(1) and 2.566(1) Å) are slightly shorter than those

i i found in [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}La{ PrNC(PPh2)N Pr}(OEt2)] (2.557(2) and 2.570(2) Å)132 and marginally longer than the guanidinate bond distances of

132,202 [La{MeC(NCy)2}3] (2.493(4) and 2.501(4) Å). Complex 3-5 proved to be a competent hydrophosphination catalyst. For example, the hydrophosphination of N,N- diisopropylcarbodiimide with diphenylphosphine using a catalytic amount of 3-5 (5 mol%) yielded the phosphaguanidine, 3-6a (93%) supporting 3-5 as a possible catalytic intermediate. Given the results discussed in this chapter, we propose the mechanism shown in Scheme 3.4 for this catalytic reaction. Overall, the catalysis proceeds via insertion of the heterocumulene into the La-PR2 bond, followed by protonolysis to yield the hydrophosphination product and regenerate the active species. Transformation of the

α-La(DMBA)3 complex to the active catalyst likely occurs via protonolysis by the phosphine substrate. This protonolysis initiation step produces either DMBA-H or the protonated product after heterocumulene insertion into the La-DMBA bond. In either case, the functional catalyst involves a La-PR2 active moiety.

N3 C18 N4 C19

C10 N2 La1 C17 C11 N6 C9 N1 C1 N5 C12 C8 P1 C16 P3 C13 C14 C2 C3 C15 C7 C4

C6 C5 Figure 3-2. ORTEP diagram of 3-5 (thermal ellipsoids at 30% probability). Selected bond lengths (Å) and angles (deg): La1-N1 2.566(1), La1-N2 2.502(1), C1-N1 1.328(2),

C1-N2 1.338(2), P1-C1 1.907(2), P1-C2 1.834(2), P1-C8 1.837(2), N1-C14 1.463(2), N2-

C17 1.467(2), N1-La1-N2 52.87(4), N1-C1-N2 115.66(1), C2-P1-C8 106.63(7).

Scheme 3.4. Proposed catalytic cycle for the hydrophosphination of N,N-

diisopropylcarbodiimide.

3.3 Conclusions

We have broadened the reactivity scope of alpha-metallated N,N- dimethylbenzylamine rare-earth-metal complexes, α-La(DMBA)3 and α-Y(DMBA)3.

Both complexes have been shown to undergo single insertion reactions to form homoleptic amidinate and phosphaguanidinate complexes ((3-1)-(3-5)). Additionally, the

La and Y homoleptic complexes serve as useful catalytic precursors for the addition of a

P-H bond across the C=N bond of heterocumulenes. α-La(DMBA)3 demonstrated excellent catalytic activity at room temperature for the hydrophosphination of a wide variety of heterocumulenes. It showed broad tolerance to electron donating and electron withdrawing substituents on aryl isocyanates. The catalytic effectiveness appeared to be dependent on both the acidity of the phosphine and the steric bulk of the heterocumulene.

The catalytic mechanism likely begins with formation of a metal phosphide, followed by insertion of a heterocumulene, and subsequent protonation yielding the hydrophosphination product. The most important aspect of the results reported herein is

the development of a new hydrophosphination catalyst with broad substrate tolerance that functions effectively at ambient temperature. Further catalytic studies involving catalytic hydrophosphination of α,β-unsaturated alkenes and allenes will be investigated in due course.

3.4 Experimental

3.4.1 General Considerations

Compounds (3-1)-(3-5) and 3-6a-n were prepared using standard Schlenk and drybox techniques. Lanthanum(III) chloride and yttrium(III) chloride were purchased from Strem and used without further purification. α-La(DMBA)3 and α-Y(DMBA)3 were synthesized as previously described.55 Diphenylphosphine was synthesized according to the literature report for diisopropylphosphine as previously described.203

Diisopropylcarbodiimide, cyclohexyl isocyanate, phenyl isothiocyanate, and 1-naphthyl isocyanate were purchased from Acros, dried over 4 Å molecular sieves, freeze-pump- thawed three times, distilled, and stored under nitrogen. Dicyclohexylcarbodiimide was purchased from Acros and sublimed. Phenyl isocyanate was purchased from Aldrich, dried over 4 Å molecular sieves, freeze-pump-thawed three times, distilled, and stored under nitrogen. 1-Adamantyl isocyanate, 4-fluorophenyl isocyanate, 4-chlorophenyl isocyanate, 4-bromophenyl isocyanate, 4-(trifluoromethyl)phenyl isocyanate, 4- methoxyphenyl isocyanate, and di-p-methoxyphenyl phosphine were purchased from

Aldrich, stored under nitrogen and used without further purification. Di-p-tolylphosphine was purchased from Strem as a 10% by mass solution in hexane and the hexane was

removed in vacuo prior to use. C6D6 and C7D8 were purchased from Cambridge Isotope

Laboratories and were vacuum-transferred from sodium/benzophenone ketyl and degassed with three freeze-evacuate-thaw cycles. C4D8O was purchased from Cambridge

Isotope Laboratories and was vacuum-transferred from 4 Å molecular sieves and degassed with three freeze-evacuate-thaw cycles. All other solvents were purchased from either VWR or Fisher. Pentane, methylene chloride, and toluene were purified by passage through columns of activated 4 Å molecular sieves and degassed prior to use. Diethyl ether was purified by passage through a column of activated alumina and degassed prior to use. Tetrahydrofuran was dried over a sodium/benzophenone ketyl and distilled prior to use. All 1H, 13C, and 31P NMR data were obtained on a 400 MHz VXRS, 600 MHz

Inova or 600 MHz Avance III Bruker spectrometer. 1H NMR shifts given were referenced internally to the residual solvent peaks at δ 7.16 ppm (C6D5H), 2.08 ppm

13 (C7D7H), and 3.58 ppm (C4D7HO). C NMR shifts given were referenced internally to the residual peaks at δ 128.0 ppm (C6D6) and 20.4 ppm (C7D8). Phosphorus NMR spectra were externally referenced to 0.00 ppm with 5% H3PO4 in D2O. IR samples were prepared as Nujol mulls and taken between KBr plates on a Perkin-Elmer XTL FTIR spectrophotometer. Melting points were observed on a capillary Mel-Temp apparatus in sealed capillary tubes under nitrogen and are uncorrected. Elemental analyses were determined by Atlantic Microlabs, Inc., Norcross, GA. Single-crystal X-ray structure determinations were performed at The University of Toledo.

i i La[ PrNC(DMBA)N Pr]3 (3-1).

An oven dried Schlenk tube was charged with α-La(DMBA)3 (400 mg, 0.739 mmol). THF (15 mL) was added to the α-La(DMBA)3 followed by diisopropylcarbodiimide (355 μL, 0.288 g, 2.28 mmol). The mixture was stirred at room temperature for 12 h. The THF was removed under vacuum and the solid was extracted with diethyl ether, filtered, and concentrated. The flask was placed in a freezer at -20°C

1 to yield a white precipitate after three days (516 mg, 76%). H NMR (C7D8, 78 °C): δ

3 3 7.48-7.44 (m, 6H, o-H), 7.41 (t, JH-H = 6.4 Hz, 6H, m-H), 7.00 (t, JH-H = 6.4 Hz, 3H, p-

H), 4.49 (s, 3H, CH(C6H5)(NMe2)), 4.38 (bs, 6H, CH(CH3)2)), 2.33 (s, 18H,

CH(C6H5)(NMe2)), 1.33-1.22 (m, 18H, CH(CH3)2), 0.93-0.85 (m, 18H, CH(CH3)2).

13 1 C{ H} NMR (C7D8, 78 °C): δ 171.37, 140.96, 129.12, 128.29, 126.34, 68.85, 46.88,

45.15, 27.37. IR (Nujol, cm-1): 2924 (s), 2767 (s), 2592 (m), 1645 (w), 1600 (m), 1471

(s), 1318 (s), 1254 (s), 1180 (s), 1120 (s), 1023 (s), 940 (m), 894 (s), 862 (m), 839 (m),

811 (m), 737 (s), 701 (s), 640 (m). Anal. Calcd for C48H78LaN9: C, 62.66; H, 8.54; N,

13.70. Found: C, 61.60; H, 8.59; N, 13.35. Mp: 187 °C dec.

i i Y[ PrNC(DMBA)N Pr]3 (3-2).

An oven dried Schlenk tube was charged with α-Y(DMBA)3 (282 mg, 0.575 mmol). Toluene (15 mL) was added to the α-Y(DMBA)3 followed by diisopropylcarbodiimide (276 μL, 224 mg, 1.77 mmol). The mixture was stirred at room temperature for 12 h. The toluene was removed under vacuum and the solid was extracted with pentane, filtered, and concentrated. The flask was placed in a freezer at -20

1 °C to yield a white precipitate after three days (208 mg, 42%). H NMR (C7D8, 78 °C): δ

3 3 3 7.45 (d, JH-H = 7.2 Hz, 6H, o-H), 7.11 (t, JH-H = 7.2 Hz, 6H, m-H), 7.01 (t, JH-H = 7.2

Hz, 3H, p-H), 4.54 (bs, 3H, CH(C6H5)(NMe2)), 4.50-4.30 (m, 6H, CH(CH3)2)), 2.27 (s,

18H, CH(C6H5)(NMe2)), 1.39-1.29 (m, 9H, CH(CH3)2), 1.09-1.00 (m, 18H, CH(CH3)2),

13 1 0.83-0.79 (m, 9H, CH(CH3)2). C{ H} NMR (C7D8, 78 °C): δ 173.33, 140.31, 129.53,

128.35, 126.58, 69.53, 46.55, 45.39, 27.67. IR (Nujol, cm-1): 2896 (s), 2627 (s), 2352 (w),

1646 (w), 1595 (m), 1461 (s), 1337 (s), 1259 (s), 1189 (s), 1125 (s), 1093 (m), 1051 (s),

1018 (s), 940 (m), 917 (w), 894 (s), 867 (m), 839 (s), 816 (m), 738 (s), 701 (s), 650 (w).

Anal. Calcd for C48H78N9Y: C, 66.26; H, 9.04; N, 14.49. Found: C, 65.75; H, 9.13; N,

14.19. Mp: 180 °C dec.

Y[CyNC(DMBA)NCy]3 (3-3).

An oven dried Schlenk tube was charged with α-Y(DMBA)3 (266 mg, 0.540 mmol). Toluene (15 mL) was added to the α-Y(DMBA)3 followed by dicyclohexylcarbodiimide (346 mg, 1.68 mmol). The mixture was stirred at room temperature for 36 h. The toluene was removed under vacuum and the solid was extracted with pentane, filtered and concentrated. Colorless crystals grew from a

1 concentrated pentane solution at room temperature (388 mg, 65%). H NMR (C7D8, 78

°C): δ 7.65-7.57 (m, 6H, o-H), 7.29-7.18 (m, 6H, m-H), 7.07-7.02 (m, 3H, p-H), 4.74-

4.70 (m, 3H, CH(C6H5)(NMe2)), 4.08 (bs, 6H, CH-cyclohexyl), 2.38-2.35 (m, 18H,

13 1 CH(C6H5)(NMe2)), 1.80-1.25 (m, 60H, CH2-cyclohexyl). C{ H} NMR (C7D8, 78 °C): δ

173.16, 140.53, 128.30, 126.63, 126.32, 68.23, 55.67, 45.44, 35.39, 32.40, 29.84. IR

(Nujol, cm-1): 2884 (s), 2758 (s), 2116 (s), 1598 (m), 1446 (s), 1344 (s), 1260 (s), 1176

(s), 1130 (s), 1024 (s), 990 (s), 957 (w), 923 (m), 889 (s), 843 (m), 830 (m), 805 (m), 741

(s), 699 (s), 623 (m). Anal. Calcd for C66H102N9Y: C, 71.38; H, 9.26; N, 11.35. Found: C,

71.05; H, 9.40; N, 10.96. Mp: 178-181 °C.

Y[{Me3SiNC(DMBA)NSiMe3}(DMBA)2] (3-4).

An oven dried Schlenk tube was charged with α-Y(DMBA)3 (368 mg, 0.749 mmol). Toluene (15 mL) was added followed by bis(trimethylsilyl)carbodiimide (188 μL,

154 mg, 0.826 mmol). The mixture was stirred at room temperature for 48 h. The toluene was removed under vacuum and the solid was extracted with hot diethyl ether, filtered and concentrated. The flask was placed in a freezer at -20°C to yield a yellow precipitate

1 3 after three days (429 mg, 84%). H NMR (C6D6, 23 °C): δ 7.47 (d, JH-H = 7.4 Hz, 2H, o-

3 3 H(amidinate)), 7.24 (t, JH-H = 7.0 Hz, 4H, m-H(DMBA)), 7.20 (t, JH-H = 7.4 Hz, 2H, m-

3 3 H(amidinate)), 7.09 (t, JH-H = 7.4 Hz, 1H, p-H(amidinate)), 6.64 (t, JH-H = 7.0 Hz, 2H, p-

3 4 H(DMBA)), 6.25 (d, JH-H = 7.0 Hz, 4H, o-H(DMBA)), 4.16 (d, JY-H = 1.9 Hz, 1H,

CH(amidinate)), 3.53 (s, 2H, CH(DMBA)), 2.20 (bs, 12H, NMe2(DMBA)), 2.09 (s, 6H,

13 1 2 NMe2(amidinate)), 0.100 (s, 18H, SiMe3). C{ H} NMR (C6D6, 23 °C): δ 177.89 (d, JY-

C = 4.4 Hz, amidinate), 139.98, 137.30, 131.99, 131.91, 128.45, 128.41, 114.73, 110.14,

1 3 80.08 (d, JY-C = 6.7 Hz, DMBA), 77.61 (d, JY-C = 4.8 Hz, amidinate), 46.11, 41.07, 3.48.

IR (Nujol, cm-1): 2928 (s), 2845 (s), 2129 (w), 1598 (m), 1535 (w), 1463 (s), 1374 (m),

1307 (w), 1245 (m), 1177 (w), 1151 (w), 1042 (w), 1011 (m), 975 (w), 868 (w), 835 (s),

731 (m), 695 (m), 674 (w), 638 (w), 607 (w). Anal. Calcd for C34H54N5Si2Y: C, 60.24; H,

8.03; N, 10.33. Found: C, 57.96; H, 7.84; N, 9.93. Mp: 149-153 °C.

i i La[ PrNC(PPh2)N Pr]3 (3-5).

An oven dried Schlenk tube was charged with α-La(DMBA)3 (542 mg, 1.00 mmol). THF (15 mL) was added followed by diphenylphosphine (568 mg, 3.05 mmol).

The mixture was stirred until the solution was a ruby red color. A second oven dried

Schlenk tube was charged with diisopropylcarbodiimide (472 μL, 385 mg, 3.05 mmol) and THF (5 mL), which was then added to the initial reaction mixture. The reaction was allowed to stir at room temperature overnight to yield a yellow colored solution. The

THF was removed under vacuum and the mixture was triturated with pentane (10 mL) to yield a yellow precipitate. The precipitate was washed twice with pentane (12 mL) at -78

°C and dried under vacuum. The solid was dissolved in toluene (15 mL). Colorless X-ray quality crystals were grown at room temperature from a concentrated solution of toluene

1 3 3 (697 mg, 65%). H NMR (C6D6, 23 °C): δ 7.72 (t, JH-H = JP-H = 7.2 Hz, 12H, o-H), 7.14

3 3 3 (t, JH-H = 7.2 Hz, 12H, m-H), 7.06 (t, JH-H = 7.2 Hz, 6H, p-H), 4.35 (sept, JH-H = 6.0 Hz,

13 1 6H, CH(CH3)2), 1.17 (bs, 36H, CH(CH3)2). C{ H} NMR (C6D6, 23 °C): δ 171.52 (d,

1 1 2 3 JP-C = 54.6 Hz), 135.65 (d, JP-C = 28.6 Hz), 134.29 (d, JP-C = 19.8 Hz), 132.38 (d, JP-C

4 3 31 1 = 17.8 Hz), 128.70 (d, JP-C = 5.5 Hz), 49.88 (d, JP-C = 21.1 Hz), 26.87. P{ H} NMR

-1 (C6D6, 23 °C): δ -18.86. IR (Nujol, cm ): 2918 (s), 2842 (s), 1948 (w), 1581 (s), 1433 (s),

1362 (s), 1311 (s), 1164 (s), 1117 (s), 1062 (m), 990 (s), 940 (w), 910 (w), 872 (w), 843

(w), 813 (w), 737 (s), 691 (s), 636 (s). Anal. Calcd for C57H72LaN6P3: C, 63.80; H, 6.76;

N, 7.83. Found: C, 63.95; H, 6.72; N, 8.02. Mp: 201-204 °C.

3.4.2 General Procedures for the Hydrophosphination of Heterocumulenes.

3.4.2.1 Method A. An oven dried Schlenk tube was charged with α-La(DMBA)3 (27.0 mg, 0.0500 mmol) and THF (2 mL). Diphenylphosphine (214 mg, 1.15 mmol) and THF

(1 mL) were added. The mixture was stirred until the solution turned a ruby red color.

The carbodiimide (1.00 mmol) was then added. The mixture was allowed to stir for 6 h at room temperature. The THF was removed under vacuum and triturated with 3 mL of pentane. The solid was extracted with pentane, filtered, and concentrated. The Schlenk tube was placed in a freezer at -20° C to yield a white solid. Spectroscopic data for 3-6a and 3-6b matched previously reported material.132

3.4.2.2 Method B. An oven dried Schlenk tube was charged with α-La(DMBA)3 (27.0 mg, 0.0500 mmol) and THF (2 mL). The phosphine (1.15 mmol) and THF (1 mL) were added to the reaction mixture. The mixture was stirred until the solution turned a ruby red color. The heterocumulene (1.00 mmol) was then added. The mixture was allowed to stir for 6 h at room temperature. The THF was removed under vacuum and triturated with 3 mL of pentane. The solid was washed with cold pentane (5 mL), filtered, and dried under vacuum, yielding a white or yellow precipitate.

3.4.2.3 Method C. An oven dried Schlenk tube was charged with α-La(DMBA)3 (27.0 mg, 0.0500 mmol) and THF (2 mL). Diphenylphosphine (214 mg, 1.15 mmol) and THF

(1 mL) were added to the reaction mixture. The mixture was stirred until the solution turned a ruby red color. The isocyanate (1.00 mmol) was then added. The mixture was

allowed to stir for 12 h at 55 °C. The THF was removed under vacuum and triturated with 3 mL of pentane. The solid was washed with pentane (5 mL), filtered, and dried under vacuum, yielding a white precipitate.

i i 132 PrN=C(PPh2)(NH Pr) (3-6a). Method A. White solid (290 mg, 93%). Anal. Calcd for

C19H25N2P: C, 73.05; H, 8.07; N, 8.97. Found: C, 71.37; H, 7.98; N, 8.85. HRMScalc:

+ 313.1834 for C19H26N2P [M + H] ; HRMSmeas: 313.1825.

132 CyN=C(PPh2)(NHCy) (3-6b). Method A. White solid (290 mg, 74%). Anal. Calcd for

C25H33N2P: C, 76.50; H, 8.47; N, 7.14. Found: C, 74.81; H, 8.56; N, 6.93. HRMScalc:

+ 393.2460 for C25H34N2P [M + H] ; HRMSmeas: 393.2456.

1 O=C(PPh2)(NHPh) (3-6c). Method B. White solid (184 mg, 60%). H NMR (C6D6, 23

3 3 °C): δ 7.57-7.55 (m, 4H, Ph-P), 7.34 (d, JH-H = 7.8 Hz, 2H, o-H), 7.22 (d, JP-H = 8.4 Hz,

3 3 1H, N-H), 7.03-7.02 (m, 6H, Ph-P), 6.97 (t, JH-H = 7.8 Hz, 2H, m-H), 6.81 (t, JH-H = 7.8

13 1 1 Hz, 1H, p-H). C{ H} NMR (C6D6, 23 °C): δ 175.49 (d, JP-C = 15.4 Hz), 149.02, 135.06

2 1 3 (d, JP-C = 19.3 Hz), 134.64 (d, JP-C = 17.5 Hz), 130.20, 129.61, 129.51 (d, JP-C = 2.9

31 1 -1 Hz), 124.87, 119.74. P{ H} NMR (C6D6, 23 °C): δ 0.77. IR (Nujol, cm ): 3247 (m),

2941 (s), 2843 (s), 1701 (w), 1688 (w), 1590 (m), 1531 (m), 1455 (s), 1433 (s), 1348 (s),

1303 (m), 1236 (m), 1169 (w), 1088 (w), 1066 (w), 1026 (w), 990 (w), 914 (w), 887 (w),

757 (m), 735 (s), 690 (s), 650 (w), 587 (m). Anal. Calcd for C19H16NOP: C, 74.74; H,

5.28; N, 4.59. Found: C, 70.23; H, 4.89; N, 5.22. HRMScalc: 306.1048 for C19H17NOP [M

+ + H] ; HRMSmeas: 306.1041.

1 O=C(PPh2)(NHCy) (3-6d). Method B. White solid (167 mg, 54%). H NMR (C6D6, 23

3 °C): δ 7.67-7.65 (m, 4H, Ph-P), 7.10-7.06 (m, 6H, Ph-P), 5.49 (bd, JH-H = 6.0 Hz, 1H, N-

H), 3.96-3.95 (m, 1H, CH), 1.65-1.62 (m, 2H, CH2), 1.29-1.21 (m, 2H, CH2), 1.04-0.98

13 1 (m, 2H, CH2), 0.80-0.78 (m, 2H, CH2), 0.71-0.69 (m, 2H, CH2). C{ H} NMR (C6D6, 23

1 1 2 °C): δ 174.92 (d, JP-C = 12.3 Hz), 135.39 (d, JP-C = 12.7 Hz), 134.65 (d, JP-C = 18.8 Hz),

3 31 1 129.57, 129.00 (d, JP-C = 7.0 Hz), 48.69, 32.82, 25.58, 24.70. P{ H} NMR (C6D6, 23

°C): δ -3.35. IR (Nujol, cm-1): 3251 (m), 2918 (s), 2285 (m), 1974 (w), 1957 (w), 1898

(w), 1883 (w), 1624 (s), 1497 (s), 1438 (s), 1370 (m), 1337 (m), 1303 (m), 1256 (m),

1218 (s), 1185 (m), 1151 (m), 1092 (m), 1024 (m), 999 (m), 919 (w), 885 (m), 839 (m),

805 (w), 739 (w), 746 (s), 695 (s). Anal. Calcd for C19H22NOP: C, 73.29; H, 7.12; N,

+ 4.50. Found: C, 71.97; H, 7.12; N, 4.39. HRMScalc: 312.1517 for C19H23NOP [M + H] ;

HRMSmeas: 312.1522.

1 O=C(PPh2)(NHAd) (3-6e). Method C. White solid (138 mg, 38%). H NMR (C6D6, 23

°C): δ 7.69-7.66 (m, 4H, Ph-P), 7.11-7.08 (m, 4H, Ph-P), 7.06-7.04 (m, 2H, Ph-P), 5.35

(bs, 1H, N-H), 1.86 (bs, 6H, Ad-H), 1.79 (bs, 3H, Ad-H), 1.44-1.40 (m, 6H, Ad-H).

13 1 1 1 C{ H} NMR (C6D6, 23 °C): δ 174.86 (d, JP-C = 13.6 Hz), 135.69 (d, JP-C = 12.1 Hz),

2 3 134.53 (d, JP-C = 18.1 Hz), 129.34, 128.92 (d, JP-C = 6.0 Hz), 53.33, 41.66, 36.35,

31 1 -1 29.74. P{ H} NMR (C6D6, 23 °C): δ -2.20. IR (Nujol, cm ): 3258 (m), 2933 (s), 2852

(s), 1625 (s), 1491 (s), 1455 (s), 1432 (s), 1375 (m), 1352 (m), 1308 (m), 1290 (m), 1276

(m), 1205 (s), 1182 (m), 1088 (m), 1026 (w), 999 (w), 941 (w), 887 (w), 856 (w), 802

(w), 748 (s), 722 (w), 695 (s). Anal. Calcd for C23H26NOP: C, 76.01; H, 7.21; N, 3.85.

+ Found: C, 74.50; H, 7.41; N, 4.17. HRMScalc: 364.1830 for C23H27NOP [M + H] ;

HRMSmeas: 364.1833.

1 O=C(PPh2)(NHNaph) (3-6f). Method C. White solid (271 mg, 76%). H NMR (C6D6,

3 23 °C): δ 8.70 (d, JH-H = 8.4 Hz, 1H, 2-Naph), 7.83 (s, 1H, N-H), 7.61 (m, 4H, Ph-P),

3 3 3 7.52 (d, JH-H = 8.4 Hz, 1H, 8-Naph), 7.34 (d, JH-H = 8.4 Hz, 1H, 4-Naph), 7.21 (t, JH-H

3 = 8.4 Hz, 1H, 3-Naph), 7.13 (t, JH-H = 8.4 Hz, 1H, 7-Naph), 7.06 (m, 7H, Ph-P and 6-

3 13 1 Naph), 6.79 (d, JH-H = 8.4 Hz, 1H, 5-Naph). C{ H} NMR (C6D6, 23 °C): δ 175.46 (d,

1 2 1 JP-C = 15.2 Hz), 134.82 (d, JP-C = 19.1 Hz), 134.39, 134.29 (d, JP-C = 12.8 Hz), 132.60

3 3 (d, JP-C = 2.1 Hz), 129.88, 129.29 (d, JP-C = 7.1 Hz), 129.14, 128.68, 126.29, 126.06,

31 1 -1 125.80, 125.20, 119.54, 118.41. P{ H} NMR (C6D6, 23 °C): δ -0.36. IR (Nujol, cm ):

3257 (s), 2936 (s), 2849 (s), 1717 (w), 1630 (s), 1530 (s), 1469 (s), 1430 (s), 1400 (m),

1378 (m), 1339 (s), 1265 (m), 1248 (s), 1196 (s), 1161 (s), 1083 (w), 1026 (w), 952 (w),

909 (w), 888 (w), 856 (w), 793 (s), 771 (s), 740 (s), 692 (s), 644 (m). Anal. Calcd for

C23H18NOP: C, 77.74; H, 5.11; N, 3.94. Found: C, 75.43; H, 5.08; N, 4.48. HRMScalc:

+ 356.1204 for C23H19NOP [M + H] ; HRMSmeas: 356.1206.

1 S=C(PPh2)(NHPh) (3-6g). Method B. Yellow solid (292 mg, 91%). H NMR (C6D6, 23

3 °C): δ 8.67 (bs, 1H, N-H), 7.67 (d, JH-H = 7.8 Hz, 2H, o-H), 7.49-7.46 (m, 4H, Ph-P),

3 3 7.03-7.00 (m, 6H, Ph-P), 6.96 (t, JH-H = 7.8 Hz, 2H, m-H), 6.86 (t, JH-H = 7.8 Hz, 1H, p-

13 1 1 1 H). C{ H} NMR (C6D6, 23 °C): δ 206.39 (d, JP-C = 39.3 Hz), 139.78, 135.80 (d, JP-C =

2 3 17.0 Hz), 134.74 (d, JP-C = 21.1 Hz), 130.07, 129.34 (d, JP-C = 6.0 Hz), 129.01, 126.60,

31 1 -1 121.80. P{ H} NMR (C6D6, 23 °C): δ 20.86. IR (Nujol, cm ): 3300 (m), 2953 (s), 2857

(s), 2284 (w), 1960 (w), 1886 (w), 1821 (w), 1660 (w), 1595 (m), 1521 (m), 1465 (s),

1443 (s), 1373 (s), 1204 (m), 1152 (m), 1083 (m), 1026 (m), 996 (m), 978 (m), 926 (w),

905 (m), 852 (w), 796 (m), 722 (s), 692 (s). Anal. Calcd for C19H16NPS: C, 71.01; H,

5.02; N, 4.36. Found: C, 68.58; H, 5.27; N, 3.99. HRMScalc: 322.0819 for C19H17NPS [M

+ + H] ; HRMSmeas: 322.0811.

O=C(PPh2){N(H)C6H4F-4} (3-6h). Method B. White solid in a 3:1 ratio of product and trimerized isocyanate (193 mg, 83%), purified by passing through a plug of silica gel. 1H

NMR (C6D6, 23 °C): δ 7.57-7.54 (m, 4H, Ph-P), 7.12 (bs, 1H, N-H), 7.09-7.07 (m, 2H, o-

3 3 13 1 H), 7.05-7.04 (m, 6H, Ph-P), 6.60 (t, JF-H = JH-H = 9.0 Hz, 2H, m-H). C{ H} NMR

1 1 2 (C6D6, 23 °C): δ 174.94 (d, JP-C = 15.6 Hz), 159.57 (d, JF-C = 242.0 Hz), 134.66 (d, JP-C

1 3 = 19.7 Hz), 134.39 (br), 134.09 (d, JP-C = 11.3 Hz), 129.89, 129.13 (d, JP-C = 7.1 Hz),

3 2 31 1 121.06 (d, JF-C = 7.7 Hz), 115.62 (d, JF-C = 22.2 Hz). P{ H} NMR (C6D6, 23 °C): δ

0.55. IR (Nujol, cm-1): 3210 (m), 2929 (s), 2848 (s), 1881 (w), 1811 (w), 1630 (m), 1605

(m), 1529 (m), 1509 (m), 1464 (m), 1434 (m), 1399 (m), 1379 (m), 1298 (m), 1253 (m),

1208 (m), 1168 (m), 1153 (m), 1097 (m), 1022 (w), 886 (w), 851 (w), 826 (m), 735 (m),

+ 690 (m), 640 (m). HRMScalc: 324.0954 for C19H16FNOP [M + H] ; HRMSmeas: 324.0948.

1 O=C(PPh2){N(H)C6H4Cl-4} (3-6i). Method B. White solid (281 mg, 83%). H NMR

3 (C6D6, 23 °C): δ 7.55-7.52 (m, 4H, Ph-P), 7.31 (s, 1H, N-H), 7.08 (d, JH-H = 9.0 Hz, 2H,

3 13 1 o-H), 7.07-7.04 (m, 6H, Ph-P), 6.92 (d, JH-H = 9.0 Hz, 2H, m-H). C{ H} NMR (C6D6,

1 3 2 23 °C): δ 175.28 (d, JP-C = 16.1 Hz), 136.80 (d, JP-C = 4.2 Hz), 134.68 (d, JP-C = 19.6

1 3 Hz), 133.92 (d, JP-C = 10.9 Hz), 129.95, 129.49, 129.15 (d, JP-C = 7.6 Hz), 129.08,

31 1 -1 120.68. P{ H} NMR (C6D6, 23 °C): δ 1.00. IR (Nujol, cm ): 3239 (m), 2935 (s), 2857

(s), 1899 (w), 1690 (w), 1625 (m), 1591 (m), 1525 (m), 1460 (s), 1378 (s), 1300 (s), 1282

(m), 1235 (m), 1169 (m), 1091 (m), 1013 (m), 896 (w), 833 (m), 808 (m), 737 (m), 697

+ (m), 658 (m). HRMScalc: 340.0658 for C19H16ClNOP [M + H] ; HRMSmeas: 340.0648.

1 O=C(PPh2){N(H)C6H4Br-4} (3-6j). Method B. White solid (190 mg, 49%). H NMR

3 (C6D6, 23 °C): δ 7.54-7.51 (m, 4H, Ph-P), 7.06 (d, JH-H = 8.8 Hz, 2H, o-H), 7.05-7.03

3 13 1 (m, 6H, Ph-P), 7.00 (bs, 1H, N-H), 6.97 (d, JH-H = 8.8 Hz, 2H, m-H). C{ H} NMR

1 3 2 (C6D6, 23 °C): δ 175.68 (d, JP-C = 16.4 Hz), 137.63 (d, JP-C = 3.9 Hz), 135.06 (d, JP-C =

1 3 19.6 Hz), 134.27 (d, JP-C = 10.9 Hz), 132.43, 130.34, 129.53 (d, JP-C = 7.6 Hz), 121.38,

31 1 -1 117.46. P{ H} NMR (C6D6, 23 °C): δ 1.28. IR (Nujol, cm ): 3265 (m), 2927 (s), 2857

(s), 1630 (m), 1599 (m), 1534 (m), 1460 (s), 1378 (m), 1308 (m), 1243 (m), 1169 (w),

1070 (w), 1004 (m), 822 (m), 731 (m), 692 (m). HRMScalc: 384.0153 for C19H16BrNOP

+ [M + H] ; HRMSmeas: 384.0144.

O=C(PPh2){N(H)C6H4OMe-4} (3-6k). Method B. Recrystallized from a

1 CH2Cl2/pentane mixture. White solid (208 mg, 62%). H NMR (C6D6, 23 °C): δ 7.61-

3 7.58 (m, 4H, Ph-P), 7.28 (d, JH-H = 9.0 Hz, 2H, o-H), 7.11 (s, 1H, N-H), 7.05-7.04 (m,

3 13 1 6H, Ph-P), 6.61 (d, JH-H = 9.0 Hz, 2H, m-H), 3.20 (s, 3H, OCH3). C{ H} NMR (C6D6,

1 2 23 °C): δ 174.47 (d, JP-C = 14.4 Hz), 156.85, 134.70 (d, JP-C = 19.6 Hz), 134.52, 134.27

1 3 31 1 (d, JP-C = 17.7 Hz), 129.76, 129.09 (d, JP-C = 7.4 Hz), 121.01, 114.25, 54.82. P{ H}

-1 NMR (C6D6, 23 °C): δ 0.18. IR (Nujol, cm ): 3257 (m), 2927 (s), 2831 (s), 1690 (s),

1607 (s), 1590 (s), 1507 (s), 1497 (s), 1377 (s), 1299 (s), 1251 (s), 1164 (s), 1104 (m),

1025 (s), 891 (w), 821 (s), 752 (m), 730 (m), 691 (m), 636 (m). HRMScalc: 336.1153 for

+ C20H19NO2P [M + H] ; HRMSmeas: 336.1149.

1 O=C(PPh2){N(H)C6H4CF3-4} (3-6l). Method B. White solid (329 mg, 88%). H NMR

3 3 (C6D6, 23 °C): δ 7.55-7.52 (m, 4H, Ph-P), 7.16 (d, JH-H = 8.5 Hz, 2H, o-H), 7.07 (d, JH-H

13 1 = 8.5 Hz, 2H, m-H), 7.06 (s, 1H, N-H), 7.06-7.04 (m, 6H, Ph-P). C{ H} NMR (C6D6,

1 3 2 23 °C): δ 175.92 (d, JP-C = 17.5 Hz), 140.95 (d, JP-C = 3.6 Hz), 134.68 (d, JP-C = 19.1

1 3 3 Hz), 133.60 (d, JP-C = 10.5 Hz), 130.08, 129.21 (d, JP-C = 7.5 Hz), 126.32 (q, JF-C = 4.0

2 1 31 1 Hz), 126.08 (q, JF-C = 32.8 Hz), 124.76 (q, JF-C = 272.0 Hz), 119.09. P{ H} NMR

-1 (C6D6, 23 °C): δ 1.63. IR (Nujol, cm ): 3220 (m), 2916 (s), 2838 (s), 1950 (w), 1898 (w),

1629 (s), 1525 (s), 1460 (s), 1403 (m), 1377 (m), 1316 (m), 1273 (m), 1208 (m), 930 (s),

856 (m), 761 (m), 708 (m), 665 (m), 635 (m), 600 (m). HRMScalc: 374.0922 for

+ C20H16F3NOP [M + H] ; HRMSmeas: 374.0920.

O=C[(4-MeOC6H4)2P]{N(H)C6H4Br-4} (3-6m). Method B. White solid (200 mg,

1 3 3 45%). H NMR (C6D6, 23 °C): δ 7.54 (t, JH-H = JP-H = 8.6 Hz, 4H, o-H), 7.18 (s, 1H, N-

3 3 3 H), 7.09 (d, JH-H = 9.0 Hz, 2H, o-H), 7.06 (d, JH-H = 9.0 Hz, 2H, m-H), 6.72 (d, JH-H =

13 1 1 8.6 Hz, 4H, m-H), 3.21 (s, 6H, OCH3). C{ H} NMR (C6D6, 23 °C): δ 177.12 (d, JP-C =

3 2 1 15.8 Hz), 161.92, 137.89 (d, JP-C = 3.9 Hz), 136.81 (d, JP-C = 21.1 Hz), 135.87 (d, JP-C =

4 3 18.6 Hz), 132.45, 125.29 (d, JP-C = 7.7 Hz), 121.34, 115.35 (d, JP-C = 8.1 Hz), 55.09.

31 1 -1 P{ H} NMR (C6D6, 23 °C): δ -1.97. IR (Nujol, cm ): 3299 (m), 2933 (s), 2838 (s),

2274 (w), 1894 (w), 1659 (s), 1594 (s), 1564 (s), 1520 (s), 1494 (s), 1455 (s), 1390 (s),

1282 (s), 1247 (s), 1182 (s), 1147 (m), 1099 (s), 1073 (m), 1012 (m), 960 (w), 943 (w),

891 (w), 821 (s), 791 (m), 717 (w), 630 (w). HRMScalc: 444.0364 for C21H20BrNO3P [M

+ + H] ; HRMSmeas: 444.0355.

O=C[(4-MeC6H4)2P]{N(H)C6H4CF3-4} (3-6n). Method B. White solid (262 mg,

1 3 3 65%). H NMR (C6D6, 23 °C): δ 7.53 (t, JH-H = JP-H = 8.0 Hz, 4H, o-H), 7.31 (s, 1H, N-

3 3 3 H), 7.17 (d, JH-H = 9.6 Hz, 2H, o-H), 7.15 (d, JH-H = 9.6 Hz, 2H, m-H), 6.94 (d, JH-H =

13 1 1 8.0 Hz, 4H, m-H), 2.01 (s, 6H, CH3). C{ H} NMR (C6D6, 23 °C): δ 176.76 (d, JP-C =

3 2 1 17.3 Hz), 141.15 (d, JP-C = 3.2 Hz), 140.28, 134.82 (d, JP-C = 19.8 Hz), 130.39 (d, JP-C =

3 3 2 9.0 Hz), 130.01 (d, JP-C = 7.8 Hz), 126.30 (q, JF-C = 3.5 Hz), 125.94 (q, JF-C = 32.8 Hz),

1 31 1 124.80 (q, JF-C = 272.0 Hz), 119.11, 20.74. P{ H} NMR (C6D6, 23 °C): δ 0.24. IR

(Nujol, cm-1): 3263 (s), 2925 (s), 2881 (s), 1906 (w), 1632 (s), 1602 (s), 1524 (s), 1459

(s), 1403 (s), 1372 (m), 1312 (s), 1246 (s), 1173 (s), 1147 (s), 1116 (s), 1064 (s), 1012

(m), 964 (w), 903 (m), 838 (m), 799 (m), 751 (w), 712 (m), 630 (m). HRMScalc: 402.1235

+ for C22H20F3NOP [M + H] ; HRMSmeas: 402.1237.

3.5 Crystallography

Summaries of crystal data and collection parameters for the crystal structures of 3-3 and

3-5 are provided in Table 3.2. Detailed descriptions of data collection, as well as data solution, are provided below. ORTEP diagrams were generated with the ORTEP-3 software package.164 For each sample, a suitable crystal was mounted on a micro-mesh

crystal loop using Paratone-N hydrocarbon oil. The crystal was transferred to a Bruker

Apex II Duo diffractometer with a CCD detector, centered in the X-ray beam, and cooled to 110 K using a nitrogen-flow low temperature apparatus that had been previously calibrated by a thermocouple placed at the same position as the crystal. An arbitrary hemisphere of data was collected using 0.5° ω scans, and the data were integrated by the program SAINT.166 The final unit cell parameters were determined by a least-squares refinement of the reflections with I > 10σ(I). Data analysis using Siemens XPREP167 and the successful solution and refinement of the structure determined the space group. An empirical absorption correction was applied using SADABS.168 Equivalent reflections were averaged, and the structures were solved by direct methods using the SHELXTL software package.169 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included as fixed atoms, but not refined, unless otherwise noted.

3-3. X-ray quality crystals were grown from a concentrated solution of pentane and diethyl ether at room temperature. A cyclohexyl ring and four methyl groups were disordered over two positions each. Carbon atoms that contained less than 50% occupancy were refined isotropically. A rigid group constraint was employed to maintain connectivity of the disordered cyclohexyl ring. An ether molecule was modeled in at 50% occupancy with the carbons refined anisotropically. The final cycle of full-matrix least- squares refinement was based on 10701 observed reflections and 790 variable parameters and converged, yielding final residuals: R = 0.0724, Rall = 0.0841, and GOF = 1.056.

3-5. X-ray quality crystals were grown from a concentrated solution of pentane at room temperature. One phenyl ring was disordered over two positions in a nearly 1:1 ratio. The occupancies and thermal parameters were refined. Restraints were used to ensure a planar

arrangement of the carbon atoms and a rigid group fitting was employed to force a hexagonal structure. The final cycle of full-matrix least-squares refinement was based on

10029 observed reflections and 668 variable parameters and converged, yielding final residuals: R = 0.0201, Rall = 0.0238, and GOF = 1.022.

Table 3.2. Crystal Data and Collection Parameters

3-3 3-5

Formula C68H107N9O0.5Y C57H72LaN6P3 Fw 1147.54 1073.03

Space Group P21/n P-1 Temp (K) 110 110 Color of Crystal Colorless Colorless a (Å) 14.4154(3) 10.057(1) b (Å) 22.0275(3) 12.789(1) c (Å) 21.5060(4) 21.968(3) α (deg) 90.00 82.324(2) β (deg) 97.955(1) 83.209(2) γ (deg) 90.00 80.949(2) V (Å3) 6762.9(2) 2571.6(6) Z 4 2 Calcd density (g/cm3) 1.127 1.295 Diffractometer Bruker Apex Duo Bruker Apex Duo

Radiation Cu-Kα (λ = 1.54178) Mo-Kα (λ = 0.71073 Å) Monochromator Graphite Graphite Detector CCD area detector CCD area detector Scan type, width (deg) ω, 0.5 ω, 0.5 Scan speed (s/frame) 30 20 No of reflns measd Hemisphere Hemisphere 2θ range (deg) 5.78-141.28 3.24-52.16 Cryst dimens (mm) 0.20 x 0.20 x 0.20 0.20 x 0.10 x 0.02 No of reflns measd 115671 32673 No of unique reflns 12801 10895 No of obsd refln (I > 2σ(I)) 10701 10029

Rint 0.0485 0.0256 No of params 790 668

R1, Rw, Rall 0.0724, 0.2152, 0.0841 0.0201, 0.0462, 0.0238 GOF 1.056 1.022

Chapter 4

Modification and Synthesis of 2-(ω- Chloroalkyl)-Tetramethoxy-p-tert- Butylcalix[4]arenes

4.1 Introduction Calix[n]arenes are a class of phenolic metacyclophanes generated from the base catalyzed condensation of phenols and aldehydes.204 C. D. Gutsche derived the name from the Greek word ‘calix’ because of the chalice-like shape these macrocycles display when all aromatic rings are positioned in the same direction. The bracketed number indicates the number of aromatic rings within the macrocycle and determines its size (n =

4, 6, 8). Of the parent calix[n]arenes listed, the calix[4]arene is the only calixarene of interest in the current project and will be the only type discussed further.

Calix[4]arenes can exhibit four different structural conformations (Figure 4.1, A-

D). The different conformations are as follows full-cone: (Figure 4.1, A), partial cone

(Figure 4.1, B), 1,2-alternate (Figure 4.1, C), and 1,3-alternate

(Figure 4.1, D). Of the four different conformers, the full-cone is most preferred because of the intramolecular hydrogen bonding between the phenolic units.

Figure 4.1. The four conformations of p-tert-butylcalix[4]arene.

The general route for the synthesis of p-tert-butylcalix[4]arene is a base catalyzed condensation reaction between p-tert-butylphenol and formaldehyde (Scheme 4.1).204

Scheme 4.1. Synthesis of p-tert-butylcalix[4]arene.

p-tert-Butylcalix[4]arenes are tritopic molecular structures on which functional groups can be attached at three different positions (Figure 4.2).

Figure 4.2. Location of the three possible positions for modification of a calix[4]arene. 92

The “upper rim” or “wide rim” is where the C-alkyl groups are located. The “lower rim” or “narrow rim” is the location of the phenols, and the third position is at the methylene linkers. Numerous reports have been published on derivatization reactions at the upper and lower positions of p-tert-butylcalix[4]arene.205,206 Typical reactions for upper rim modification are electrophilic aromatic substitution or sulfonization of the aromatic ring.207,208 Lower rim reactions generally begin with the tetrahydroxy-p-tert- butylcalix[4]arene and involve deprotonation followed by salt-metathesis.209-211 In contrast, the number of publications about substitution at the methylene linker position is few.212-217 Early works made use of fragment condensation reactions in which two small units, one containing a substituted methylene carbon, were brought together to form a calix[4]arene (Scheme 4.2).212

Scheme 4.2. Fragment condensation reaction to form a methylene-substituted

calix[4]arene (R = Me, Et, iPr, tBu, p-Tol, p-Nitro; R’ = tBu, Me; R’’ = tBu).

The work of the Schmidt and Fantini groups utilizes a more streamlined approach to attach various functional groups to the methylene bridge.218-220 Specifically, in collaboration, these research groups have developed a more efficient methodology to

attach one functional group at the methylene bridge enabling the calix[4]arene to maintain its general properties (Scheme 4.3).

Scheme 4.3. Addition of chloro-alkyl group to tetramethoxy-p-tert-butylcalix[4]arene (R

= Me, n = 3-6).

Following a previously published report on the mono-lithiation of tetramethoxy-p-tert- butylcalix[4]arene,218 a series of 2-(ω-chloroalkyl)-calix[4]arenes were synthesized using a stepwise procedure (Scheme 4.3).219 The tetramethoxy-p-tert-butylcalix[4]arene was lithiated using n-butyllithium in THF to give a blood red colored solution followed by addition of an α,ω-dihaloalkane. The reaction was stirred overnight to yield a yellow colored solution. The THF was removed under vacuum and the solid was washed with pentane and diethyl ether to yield a white precipitate. The product was purified by recrystallization from pentane to yield a white solid in reasonable yields (68-83%). The use of a symmetrically substituted dihaloalkane such as 1,5-dibromopentane resulted in a mixture of products as well as unreacted starting material. After separation of the products, their identities were found to be the desired product as well as a bis- calix[4]arene with the alkyl chain linking the two calix[4]arenes. To avoid production of the bis-calix[4]arene product, α,ω-chlorobromoalkanes were used instead.

The applicability of calix[4]arenes spans the world of chemistry from luminescence through catalysis to extraction.205,209,221,222 For extraction studies, especially 94

with metal cations, calix[4]arenes have received much attention.223-228 Numerous works have been published detailing the increase in separation efficiency between lanthanides and actinides as well as the greater extraction capabilities when using lower-rim functionalized calix[4]arenes.222,223,229-231

As demand for the rare-earth elements (REE) continues to grow, their supply is decreasing. As noted in Chapter 1, China’s reserve accounts for 51% of the rare-earth metals located in the Earth’s crust and they have 90% of the current production of REE today. Because of the increase in demand due to the numerous applications of the rare- earth metals, China has reduced the amount of REE exported to other countries. The resulting price increases have forced many countries to seek alternative sources to fulfill their demand. While private companies continue to prospect various landmasses for rare- earth metals, countries like France have turned to nuclear fuel reprocessing. Spent nuclear fuel contains up to 20% of recoverable rare-earth metals.232 A process that would allow the separation of the rare-earth metals individually or into groups (early, middle, late) would be a significant advancement in the recovery of the lanthanides from nuclear fuel and decrease the amount of nuclear waste generated. One current focus of the Schmidt group is to develop a class of lower rim functionalized calix[4]arenes containing ligands that have been previously shown to separate the lanthanides. These calix[4]arenes will be attached to a solid support through a carbon tail linker at the methylene position. The advantage of the linker at the rim position is that the calix[4]arene will not lose any of its inherent properties and separation will be determined based almost entirely on the ionic radius of the metal cation. The work presented herein focuses on the synthesis and

derivatization of p-tert-butylcalix[4]arenes. Further lower rim modification and separation efficiency will be further investigated by future Schmidt group members.

4.2 Results and Discussion

The first step in attachment of the orthogonal alkyl tail at the methylene-bridge position is protection of the lower rim by utilizing a modified version of the Williamson ether synthesis (Scheme 4.4).233

Scheme 4.4. Synthesis of tetramethoxy-p-tert-butylcalix[4]arene (R = methyl).

Attachment of the chloroalkyl tails was then achieved following the previous published procedure (Scheme 4.3).219 Conversion of the chloride to a secondary amine was accomplished by first deprotonating an aniline with KH, and then adding the resulting reagent to the 2-chloroalkyl-tetramethoxy-p-tert-butylcalix[4]arene in THF

(Scheme 4.5).219

Scheme 4.5. Synthesis of 2-(ω-(2,5-dichloroanilino)alkyl)tetramethoxy-p-tert-

butylcalix[4]arenes (R = Me; Ar = 2,5-dichlorophenyl; n = 3-5).

The reaction underwent a variety of color changes, beginning from yellow and ending with dark purple. Excess KH was quenched with water and a standard organic workup was completed to isolate the product. When necessary, excess aniline was removed through distillation to yield a glassy solid. One notable feature of these calix[4]arenes is their fluxionality in solution at room temperature.234 Since the methyl group is small enough to pass through the center of the macrocycle, the calix[4]arene will exhibit different structural conformers (Figure 4.1), making interpretation of the 1H NMR difficult. To circumvent this, the NMR spectra of (4-1)-(4-3) were taken in a 3:1 mixture of CDCl3/CD3CN saturated with NaI. The sodium iodide was present to be coordinated by the lower-rim oxygen atoms, forcing the calix[4]arene to maintain the full-cone conformer in solution and resulting in readily interpreted NMR spectra. The diagnostic peaks in the 1H NMR spectra were the protons on the chlorophenyl ring at the 3-, 4-, and

6- positions. The chemical shifts for these protons ranged from 7.20-6.50 ppm with splitting patterns representative of a 2,5-disubstituted phenyl ring (Figure 4.3).

H O CD CN t Ar OCH 3 2 3 Bu

Ar (axial)-C H 2

(equi)-C H 2

H C H CH A 2 CH CH C H  2 CH2 2 H B N H CH2

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shif t (ppm)

Figure 4.3. 1H NMR spectrum of 2-(5-(2,5-dichloroanilino)pentyl)tetramethoxy-p-tert-

butylcalix[4]arene (4-3; R = CH3).

The second diagnostic peak in the 1H NMR spectrum was the NH peak. Due to the electron withdrawing effects of the phenyl ring, the NH resonance was a full 1 ppm further downfield when compared to the chemical shifts of the 2,6-dialkylaniline derivatives.219

In an effort to generate suitable 2-(ω-alkyl)-tetramethoxy-p-tert- butylcalix[4]arenes capable of undergoing modification of the lower-rim without competing reactions at the terminus of the alkyl tail, a phthalimide protecting group was chosen to act as a masked amine (Scheme 4.6).

Scheme 4.6. Synthesis of 2-(ω-phthalimidoalkyl)tetramethoxy-p-tert-butylcalix[4]arenes

(R = Me; n = 4-6).

The phthalimide group was selected because it can be easily cleaved to generate a primary amine that can then undergo further reactions to generate more sophisticated tethers capable of attachment to solid supports. Each 2-(ω-chloroalkyl)-tetramethoxy-p- tert-butylcalix[4]arene was treated with 10 equivalents of potassium phthalimide in DMF and heated to 80 °C for five days. The reaction was then made biphasic and the organic phase was washed with copious amounts of NH4Cl (aq) and 0.5 M NaOH to remove

DMF and excess potassium phthalimide. The organic phase was dried and solvent was removed under reduced pressure. The crude product was washed with methanol and dried on a Schlenk line overnight to yield a white solid. The 1H NMR spectrum of the product was again taken using CDCl3/CD3CN saturated with NaI and revealed two multiplets with chemical shifts ranging from 7.72-7.60 ppm representing the four protons of the phthalimide group (Figure 4.4)

t Ar OCH 3 Bu

CDCl3

(axial)-C H 2 (equi)-C H 2 phth -CH 2 CH phth 2

CH2

C H CH2 -CH 2

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shif t (ppm)

Figure 4.4. 1H NMR spectrum of 2-(5-phthalimidopentyl)tetramethoxy-p-tert-

butylcalix[4]arene (4-5; R = CH3).

After attachment of the protecting group, lower rim modification begins with removal of the methyl groups to regenerate the tetrahydroxycalix[4]arene. Demethylation

235 is accomplished using BBr3 (Scheme 4.7).

Scheme 4.7. Synthesis of 2-(ω-phthalimidoalkyl)tetrahydroxy-p-tert-butylcalix[4]arenes

(R = Me; n = 3-6).

The reaction conditions were as follows: under Schlenk conditions, the 2-(ω- phthalimidoalkyl)-tetramethoxy-p-tert-butylcalix[4]arene was dissolved in methylene chloride and cooled to -78 °C. The dropwise addition of neat BBr3 resulted in a color change of the solution to pale yellow. The mixture was stirred for 1 hr at -78 °C, removed from the cold bath, and allowed to reach room temperature overnight. Excess BBr3 was

100

quenched with NaHCO3 (aq). The organic phase was washed twice with NaHCO3 (aq), twice with brine solution and dried over MgSO4. The methylene chloride was removed under reduced pressure and the solid was dissolved in THF and layered with pentane.

Finally, the solution was placed in a freezer at -20 °C and a white precipitate resulted

1 after three days. Its H NMR spectrum was taken in CDCl3 because of the intramolecular hydrogen bonding of the hydroxyl groups, resulting in the full cone conformation without the need for NaI (Figure 4.5).

t (axial)-C H (equi)-C H Bu phth phth Ar 2 -CH 2 2

CH2 O H -CH C H 2 CH2

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shif t (ppm)

Figure 4.5. 1H NMR spectrum of 2-(5-phthalimidopentyl)tetrahydroxy-p-tert-

butylcalix[4]arene (4-9).

A broad singlet at 10.30 ppm is characteristic of the OH resonance and the absence of the resonances from 4.10-4.00 ppm demonstrates that all four methoxy groups have been removed. Further evidence for the formation of (4-7)-(4-10) was obtained through HRMS

(Section 4.4). 101

4.3 Conclusions

In summary, a collection of 2-(ω-anilidoalkyl)-tetramethoxy-p-tert- butylcalix[4]arenes, 2-(ω-phthalimidoalkyl)-tetramethoxy-p-tert-butylcalix[4]arenes and

2-(ω-phthalimidoalkyl)-tetrahydroxy-p-tert-butylcalix[4]arenes with alkyl chains ranging from 3-6 carbons has been synthesized and characterized using 1H and 13C NMR, IR, and

HRMS. These calix[4]arenes represent intermediates in a multi-step synthesis for the design of lower rim modified calix[4]arenes that will be evaluated for the separation of lanthanide ions with the future goal of attachment to a solid support.

4.4 Experimental Details

Compounds [(4-4)-(4-6)] were synthesized under ambient atmospheric conditions.

Compounds [(4-1)-(4-3)] and [(4-7)-(4-10)] were synthesized using standard Schlenk and drybox techniques. Tetrahydroxy-p-tert-butylcalix[4]arene was synthesized as previous described and tetramethoxy-p-tert-butylcalix[4]arene was synthesized using a

233,236 modified procedure to that previously published. CDCl3 and CD3CN were purchased from Cambridge Isotope Laboratories and used as received. All 1H and 13C

NMR data were obtained on a 600 MHz Inova or 600 MHz Avance III Bruker spectrometer. NMR spectra of compounds [(4-1)-(4-6)] were obtained using a mixture of

CDCl3/CD3CN (3:1) containing NaI (1 g per 80 mL solution). Pentane, methylene chloride, and toluene were purified by passage through columns of activated 4 Å molecular sieves and degassed prior to use. Diethyl ether was purified by passage through a column of activated alumina and degassed prior to use. Tetrahydrofuran was dried over

102

a sodium/benzophenone ketyl and distilled prior to use. High resolution mass spectrometry, using electrospray ionization, was performed at the University of Illinois

Mass Spectrometry Laboratory, Urbana, IL. IR samples were prepared by dissolving the analyte in CH2Cl2, placing a drop on a KBr salt plate and evaporating the solvent to yield a thin film. IR spectra were taken on a Perkin-Elmer XTL FTIR spectrophotometer.

Modified procedure for tetramethoxy-p-tert-butylcalix[4]arene: Tetrahydroxy-p-tert- butylcalix[4]arene was dissolved in a 10:1 ratio of THF/DMF, followed by addition of the base (NaH, 4.1 equiv) and the electrophile (CH3I, 10 equiv). The mixture was heated to reflux for 1hr and then allowed to cool to room temperature. The THF was removed under reduced pressure using the rotavap and the resulting white solid was washed with

H2O to remove any trace DMF. The solid was then dried under reduced pressure and methanol was added (30 mL) and stirred for 20 minutes. The mixture was placed in a freezer at -20 °C overnight, filtered, and dried on a Schlenk line to yield a white microcrystalline solid.

General procedure for the 2-(ω-(2,5-dichloroanilino)alkyl)tetramethoxy-p-tert- butylcalix[4]arenes: An oven dried Schlenk tube was charged with a 2-(ω- chloroalkyl)tetramethoxycalix[4]arene and placed under vacuum for several hours. THF

(15 mL) was added followed by KH (4 equiv) and 2,5-dichloroaniline (4 equiv). A yellow suspension resulted, followed by evolution of H2. The solution eventually changed to a purple color after 12 h. Several drops of water were added to quench the 103

unreacted KH and convert any deprotonated product back to the protio species. All volatiles were removed in vacuo prior to extraction into pentane. Filtration yielded a dark brown solution and volatiles were again removed in vacuo. Excess aniline was removed by vacuum distillation producing a dark brown colored glassy solid.

2-(3-(2,5-Dichloroanilino)propyl)tetramethoxy-p-tert-butylcalix[4]arene (4-1).

Reagents: 2-(3-chloropropyl)tetramethoxy-p-tert-butylcalix[4]arene (0.200 g, 0.230 mmol); KH (0.041 g, 1.0 mmol); 2.5-dichloroaniline (0.165 g, 1.02 mmol). Yield: 0.125

1 4 g (59.9%). H NMR (23 °C): δ 7.11 (d, JH-H = 2.0 Hz, 2H, Ph), 7.09-7.04 (m, 6H, Ph),

3 4 3 7.01 (d, JH-H = 8.0 Hz, 1H, Ph), 6.66 (d, JH-H = 2.0 Hz, 1H, Ph), 6.49 (dd, JH-H = 8.0

4 3 Hz, JH-H = 2.0 Hz, 1H, Ph), 4.55 (t, JH-H = 8.0 Hz, 1H, CH), 4.36 (m, 1H, NH), 4.15 (d,

2 JH-H = 12.0 Hz, 3H, CH2), 4.02 (s, 6H, OCH3), 4.01 (s, 6H, OCH3), 3.49 (m, 2H, CH2),

2 3.32 (d, JH-H = 12.0 Hz, 3H, CH2), 2.17 (m, 2H, CH2), 1.74 (m, 2H, CH2), 1.07 (s, 36H, tBu). 13C{1H} NMR (23 °C): δ 150.50, 148.73, 148.58, 145.84, 144.93, 137.31, 134.40,

134.37, 134.36, 129.55, 127.86, 125.82, 125.80, 125.62, 122.14, 116.20, 64.79, 64.45,

45.05, 44.81, 43.28, 34.85, 34.20, 31.04, 30.87, 22.34. IR (cm-1): 3422 (m), 2962 (s),

1764 (m), 1596 (s), 1481 (s), 1362 (s), 1296 (s), 1206 (s), 1178 (m), 1120 (s), 1005 (s),

872 (s), 807 (s), 738 (s), 703 (m).

2-(4-(2,5-Dichloroanilino)butyl)tetramethoxy-p-tert-butylcalix[4]arene (4-2).

Reagents: 2-(4-chlorobutyl)tetramethoxy-p-tert-butylcalix[4]arene (1.093 g, 1.199

104

mmol); KH (0.144 g, 3.59 mmol); 2,5-dichloroaniline (0.583 g, 3.60 mmol). Yield: 0.662

1 4 g (60.0%). H NMR (23 °C): δ 7.35-7.33 (m, 6H, Ph), 7.28 (d, JH-H = 2.0 Hz, 2H, Ph),

3 4 3 7.15 (d, JH-H = 8.0 Hz, 1H, Ph), 7.00 (d, JH-H = 2.0 Hz, 1H, Ph), 6.67 (dd, JH-H = 8.0

4 3 Hz, JH-H = 2.0 Hz, 1H, Ph), 4.73 (m, 1H, NH), 4.60 (t, JH-H = 8.0 Hz, 1H, CH), 4.19 (d,

2 2 JH-H = 12.0 Hz, 3H, CH2), 4.04 (s, 12H, OCH3), 3.60 (m, 2H, CH2), 3.53 (d, JH-H = 12.0

Hz, 3H, CH2), 2.19 (m, 2H, CH2), 1.83 (m, 2H, CH2), 1.43 (m, 2H, CH2), 1.16 (s, 36H, tBu). 13C{1H} NMR (23 °C): δ 151.54, 151.52, 149.51, 149.50, 149.44, 139.92, 135.68,

135.50, 134.47, 130.92, 127.05, 126.85, 126.70, 123.41, 116.56, 115.49, 111.34, 65.03,

64.89, 45.70, 43.45, 36.42, 35.04, 31.39, 31.20, 31.04, 30.01, 26.59. IR (cm-1): 3854 (w),

3746 (w), 3674 (w), 3387 (m), 3046 (m), 2959 (s), 2823 (m), 2362 (m), 2033 (w), 1699

(w), 1596 (s), 1480 (s), 1362 (m), 1264 (s), 1206 (s), 1119 (m), 1023 (s), 873 (m), 792

+ (m), 739 (m). HRMS calculated for C58H76Cl2NO4 [M+H] : 920.5151, found: 920.5141.

2-(5-(2,5-Dichloroanilino)pentyl)tetramethoxy-p-tert-butylcalix[4]arene (4-3).

Reagents: 2-(5-chloropentyl)tetramethoxy-p-tert-butylcalix[4]arene (0.925 g, 1.00 mmol); KH (0.120 g, 3.00 mmol); 2,5-dichloroaniline (0.486 g, 3.00 mmol). Yield: 0.683

1 4 g (73.0%). H NMR (23 °C): δ 7.33-7.30 (m, 6H, Ph), 7.21 (d, JH-H = 2.0 Hz, 2H, Ph),

3 4 3 7.14 (d, JH-H = 8.0 Hz, 1H, Ph), 6.56 (d, JH-H = 2.0 Hz, 1H, Ph), 6.51 (dd, JH-H = 8.0

4 3 3 Hz, JH-H = 2.0 Hz, 1H, Ph), 4.72 (t, JH-H = 7.0 Hz, 1H, NH), 4.54 (t, JH-H = 7.0 Hz, 1H,

2 CH), 4.14 (d, JH-H = 12.0 Hz, 3H, CH2), 4.01 (s, 6H, OCH3), 4.00 (s, 6H, OCH3), 3.49

2 3 3 (d, JH-H = 12.0 Hz, 3H, CH2), 3.06 (q, JH-H = 7.0 Hz, 2H, CH2), 2.10 (q, JH-H = 7.0 Hz,

3 3 2H, CH2), 1.54 (pent, JH-H = 7.0 Hz, 2H, CH2), 1.39 (pent, JH-H = 7.0 Hz, 2H, CH2),

105

3 t t 13 1 1.29 (pent, JH-H = 7.0 Hz, 2H, CH2), 1.11 (s, 18H, Bu), 1.10 (s, 18H, Bu). C{ H}

NMR (23 °C): δ 151.50, 151.47, 151.40, 149.48, 149.34, 149.32, 139.06, 139.03, 135.63,

135.48, 127.04, 126.64, 123.45, 123.37, 111.28, 64.84, 64.80, 45.93, 43.41, 36.33, 35.06,

34.84, 32.76, 31.30, 31.21, 31.15, 31.10, 30.03, 27.42. IR (cm-1): 3847 (w), 3746 (w),

3660 (w), 3422 (w), 3172 (w), 3073 (m), 2958 (s), 2819 (m), 2362 (m), 2034 (w), 1740

(w), 1694 (w), 1596 (s), 1479 (s), 1362 (m), 1260 (s), 1206 (s), 1112 (s), 1022 (s), 872

+ (m), 803 (m), 738 (m). HRMS calculated for C59H78Cl2NO4 [M+H] : 934.5308, found:

934.5269.

General procedure for the 2-(ω-phthalimidoalkyl)tetramethoxy-p-tert- butylcalix[4]arenes: A 500 mL round bottom flask was charged with 2-(ω-chloroalkyl)- tetramethoxy-p-tert-butylcalix[4]arene. DMF (300 mL) was added, followed by potassium phthalimide (10 equiv). The reaction was stirred at 80 °C for five days. Diethyl ether (150 mL) was added. The organic phase was washed four times with NH4Cl (aq) and four times with NaOH (aq). The aqueous layers were combined and back extracted twice with pentane. The organic layers were combined, dried over MgSO4, and the solvent was removed on the rotary evaporator to yield a crude white solid. The crude solid was washed with MeOH to yield a white precipitate.

2-(4-Phthalimidobutyl)tetramethoxy-p-tert-butylcalix[4]arene (4-4). Reagents: 2-(4- chlorobutyl)tetramethoxy-p-tert-butylcalix[4]arene (3.51 g, 4.41 mmol), potassium phthalimide (8.17 g, 44.1 mmol). Yield 2.72 g (68%). NMR (23 °C): δ 7.72-7.71 (m, 2H, 106

Nphth), 7.70-7.69 (m, 2H, Nphth), 7.08 (br s, 2H, Ph), 7.06 (br s, 4H, Ph), 7.03 (br s, 2H,

3 2 Ph), 4.64 (t, JH-H = 8.4 Hz, 1H, CH), 4.27 (d, JH-H = 12.0 Hz, 3H, CH2), 4.17 (s, 6H,

3 2 OCH3), 4.14 (s, 6H, OCH3), 3.68 (t, JH-H = 8.4 Hz, 2H, CH2), 3.35 (d, JH-H = 12.0 Hz,

3H, CH2), 2.15-2.10 (m, 2H, CH2), 2.06-2.02 (m, 2H, CH2), 1.81-1.76 (m, 2H, CH2), 1.12

(s, 18H, tBu), 1.11 (s, 18H, tBu). 13C{1H} NMR (23 °C): δ 168.26, 154.91, 147.54,

144.57, 137.43, 134.24, 133.97, 133.87, 133.72, 131.98, 131.87, 125.61, 125.30, 123.01,

122.17, 65.08, 64.94, 37.90, 37.43, 35.57, 34.02, 33.80, 33.52, 31.30, 31.13, 29.76, 28.74.

IR (cm-1): 3040 (s), 2925 (s), 2820 (s), 2024 (w), 1772 (s), 1715 (s), 1614 (m), 1600 (m),

1480 (m), 1394 (m), 1365 (m), 1265 (m), 1207 (m), 1121 (m), 1035 (m), 948 (m), 872

+ (s), 805 (m), 742 (m), 709 (m). HRMS calculated for C60H76NO6 [M+H] : 906.5673, found: 906.5676.

2-(5-Phthalimidopentyl)tetramethoxy-p-tert-butylcalix[4]arene (4-5). Reagents: 2-(5- chloropentyl)tetramethoxy-p-tert-butylcalix[4]arene (4.00 g, 4.94 mmol); potassium phthalimide (9.15 g, 49.4 mmol). Yield 3.27 g (72%). 1H NMR (23 °C): δ 7.71-7.69 (m,

4 2H, Nphth), 7.62-7.61 (m, 2H, Nphth), 7.09 (d, JH-H = 2.4 Hz, 2H, Ph), 7.08 (s, 4H, Ph),

4 3 2 7.05 (d, JH-H = 2.4 Hz, 2H, Ph), 4.50 (t, JH-H = 7.8 Hz, 1H, CH), 4.15 (d, JH-H = 12.0

3 Hz, 3H, CH2), 4.04 (s, 6H, OCH3), 4.00 (s, 6H, OCH3), 3.54 (t, JH-H = 7.2 Hz, 2H, CH2),

2 3 3.32 (d, JH-H = 12.0 Hz, 3H, CH2), 2.00-1.97 (m, 2H, CH2), 1.54 (pent, JH-H = 7.2 Hz,

t 2H, CH2), 1.33-1.30 (m, 2H, CH2), 1.23-1.21 (m, 2H, CH2), 1.08 (s, 18H, Bu), 1.07 (s,

18H, tBu). 13C{1H} NMR (23 °C): δ 168.44, 155.16, 154.18, 144.81, 144.15, 137.88,

137.12, 133.90, 133.23, 132.82, 132.25, 126.50, 125.86, 125.56, 123.20, 121.78, 60.66,

107

60.03, 37.90, 37.04, 35.57, 33.99, 33.87, 33.74, 31.54, 31.34, 28.51, 28.09, 27.04. IR

(cm-1): 3048 (s), 2937 (s), 2857 (s), 1774 (s), 1713 (s), 1602 (m), 1587 (m), 1487 (m),

1401 (m), 1361 (s), 1270 (m), 1200 (s), 1124 (s), 1048 (m), 1028 (m), 867 (m), 807 (s),

741 (m), 721 (m).

2-(6-Phthalimidohexyl)tetramethoxy-p-tert-butylcalix[4]arene (4-6). Reagents: 2-(6- chlorohexyl)tetramethoxy-p-tert-butylcalix[4]arene (6.70 g, 8.13 mmol); potassium phthalimide (15.1 g, 81.3 mmol). Yield 5.32 g (70%). 1H NMR (23 °C): δ 7.71-7.70 (m,

4 2H, Nphth), 7.63-7.61 (m, 2H, Nphth), 7.10 (br s, 2H, Ph), 7.09 (s, 4H, Ph), 7.06 (d, JH-H

3 2 = 1.8 Hz, 2H, Ph), 4.50 (t, JH-H = 7.8 Hz, 1H, CH), 4.16 (d, JH-H = 12.0 Hz, 1H, CH2),

2 3 4.15 (d, JH-H = 12.0 Hz, 2H, CH2), 4.04 (s, 6H, OCH3), 4.00 (s, 6H, OCH3), 3.53 (t, JH-H

2 3 = 7.2 Hz, 2H, CH2), 3.34 (d, JH-H = 12.0 Hz, 3H, CH2), 2.00 (q, JH-H = 7.8 Hz, 2H, CH2-

3 ), 1.53 (pent, JH-H = 7.8 Hz, 2H, CH2), 1.35-1.31 (m, 2H, CH2), 1.30-1.25 (m, 2H, CH2),

t t 13 1 1.24-1.21 (m, 2H, CH2), 1.09 (s, 18H, Bu), 1.08 (s, 18H, Bu). C{ H} NMR (23 °C): δ

168.23, 154.77, 150.40, 147.45, 144.48, 137.61, 136.91, 134.14, 133.67, 132.94, 132.51,

131.91, 129.07, 126.50, 125.76, 122.94, 64.90, 60.19, 39.72, 37.81, 36.93, 36.37, 35.60,

34.65, 33.92, 31.42, 29.65, 29.50, 28.47, 26.83. IR (cm-1): 3279 (m), 2963 (s), 2857 (s),

1715 (s), 1633 (m), 1556 (m), 1475 (s), 1394 (s), 1360 (m), 1302 (m), 1245 (m), 1202 (s),

1173 (m), 1121 (m), 1020 (s), 948 (w), 871 (s), 800 (m), 737 (m), 713 (m).

General procedure for 2-(ω-phthalimidoalkyl)tetrahydroxy-p-tert-butylcalix[4]arenes. An oven dried 150 mL Kjeldahl flask was charged with 2-(ω- 108

phthalimidoalkyl)tetramethoxy-p-tert-butylcalix[4]arene dissolved in CH2Cl2 and was then cooled to -78 °C. BBr3 (10 equiv) was added dropwise and the solution turned a dark brown color. The reaction was stirred for one hour at -78 °C then allowed to warm to room temperature and stirred overnight. The reaction was quenched with NaHCO3 (aq) resulting in a purple solution. The organic phase was washed twice with NaHCO3 (aq), twice with brine solution, dried over MgSO4, and the solvent removed using a rotary evaporator. The resulting white solid was dissolved in THF, layered with pentane, and placed in a freezer at -20 °C to yield a white precipitate after 3 days.

2-(3-Phthalimidopropyl)tetrahydroxy-p-tert-butylcalix[4]arene (4-7). Reagents: 2-(3- phthalimidopropyl)tetramethoxy-p-tert-butylcalix[4]arene (1.54 g, 1.73 mmol); BBr3

1 (1.66 mL, 17.3 mmol). Yield 1.01 g (69.8%). H NMR (CDCl3, 23 °C): δ 10.29 (s, 4H,

4 OH), 7.83-7.81 (m, 2H, Nphth), 7.67-7.65 (m, 2H, Nphth), 7.11 (d, JH-H = 2.1 Hz, 2H,

4 4 4 Ph), 7.09 (d, JH-H = 2.3 Hz, 2H, Ph), 7.07 (d, JH-H = 2.3 Hz, 2H, Ph), 7.01 (d, JH-H = 2.1

3 2 Hz, 2H, Ph), 4.59 (t, JH-H = 8.0 Hz, 1H, CH), 4.27 (d, JH-H = 14.1 Hz, 1H, CH2), 4.25 (d,

2 3 2 JH-H = 14.1 Hz, 2H, CH2), 3.78 (t, JH-H = 7.0 Hz, 2H, CH2), 3.52 (d, JH-H = 14.1 Hz,

2 1H, CH2), 3.50 (d, JH-H = 14.1 Hz, 2H, CH2), 2.26-2.24 (m, 2H, CH2), 1.77-1.72 (m, 2H,

t t 13 1 CH2), 1.23 (s, 18H, Bu), 1.21 (s, 18H, Bu). C{ H} NMR (CDCl3, 23 °C): δ 168.33,

146.75, 146.68, 144.39, 144.19, 133.82, 132.02, 130.45, 127.69, 127.44, 127.29, 125.90,

125.28, 123.12, 121.57, 37.59, 35.03, 34.12, 33.98, 32.63, 31.53, 31.37, 29.23, 27.13. IR

(cm-1): 3209 (s), 2947 (s), 2856 (s), 1769 (m), 1708 (s), 1607 (m), 1567 (m), 1471 (m),

1401 (m), 1366 (m), 1300 (m), 1260 (m), 1124 (m), 1088 (m), 1033 (m), 948 (w), 872

109

+ (m), 812 (m), 782 (m), 736 (m), 701 (m). HRMS calculated for C55H66NO6 [M+H] :

836.4890, found: 836.4885.

2-(4-Phthalimidobutyl)tetrahydroxy-p-tert-butylcalix[4]arene (4-8). Reagents: 2-(4- phthalimidobutyl)tetramethoxy-p-tert-butylcalix[4]arene (2.52 g, 2.78 mmol); BBr3 (2.68

1 mL, 27.8 mmol). Yield 1.70 g (71.9%). H NMR (CDCl3, 23 °C): δ 10.32 (s, 4H, OH),

4 7.86-7.84 (m, 2H, Nphth), 7.70-7.68 (m, 2H, Nphth), 7.13 (d, JH-H = 2.0 Hz, 2H, Ph),

4 4 4 7.12 (d, JH-H = 2.3 Hz, 2H, Ph), 7.10 (d, JH-H = 2.3 Hz, 2H, Ph), 7.02 (d, JH-H = 2.0 Hz,

3 2 2 2H, Ph), 4.56 (t, JH-H = 8.0 Hz, 1H, CH), 4.30 (d, JH-H = 14.1 Hz, 1H, CH2), 4.28 (d, JH-

3 2 H = 14.1 Hz, 2H, CH2), 3.71 (t, JH-H = 7.6 Hz, 2H, CH2), 3.54 (d, JH-H = 14.1 Hz, 1H,

2 3 CH2), 3.52 (d, JH-H = 14.1 Hz, 2H, CH2), 2.29 (q, JH-H = 8.0 Hz, 2H, CH2), 1.83 (pent,

3 3 t JH-H = 7.6 Hz, 2H, CH2), 1.44 (pent, JH-H = 7.6 Hz, 2H, CH2), 1.26 (s, 18H, Bu), 1.23

t 13 1 (s, 18H, Bu). C{ H} NMR (CDCl3, 23 °C): δ 168.30, 146.72, 146.61, 144.27, 144.15,

133.74, 131.99, 130.71, 127.70, 127.43, 127.16, 125.86, 125.82, 125.11, 123.07, 121.66,

37.73, 35.17, 34.07, 33.94, 32.63, 32.58, 31.45, 31.31, 28.24, 25.01. IR (cm-1): 3199 (s),

2947 (s), 2857 (s), 1769 (s), 1708 (s), 1602 (s), 1477 (s), 1396 (s), 1366 (s), 1300 (m),

1260 (s), 1194 (s), 1119 (w), 1064 (w), 1038 (m), 948 (w), 872 (m), 812 (m), 782 (m),

+ 732 (m), 701 (m). HRMS calculated for C56H68NO6 [M+H] : 850.5047, found: 850.5038.

2-(5-Phthalimidopentyl)tetrahydroxy-p-tert-butylcalix[4]arene (4-9). Reagents: 2-(5- phthalimidopentyl)tetramethoxy-p-tert-butylcalix[4]arene (4.00 g, 4.35 mmol); BBr3

1 (4.19 mL, 43.5 mmol). Yield 3.59 g (95.5%). H NMR (CDCl3, 23 °C): δ 10.27 (s, 4H, 110

4 OH), 7.86-7.85 (m, 2H, Nphth), 7.72-7.71 (m, 2H, Nphth), 7.10 (d, JH-H = 2.1 Hz, 2H,

4 4 4 Ph), 7.08 (d, JH-H = 2.2 Hz, 2H, Ph), 7.06 (d, JH-H = 2.2 Hz, 2H, Ph), 6.99 (d, JH-H = 2.1

3 2 Hz, 2H, Ph), 4.47 (t, JH-H = 8.0 Hz, 1H, CH), 4.27 (d, JH-H = 14.0 Hz, 1H, CH2), 4.23 (d,

2 3 2 JH-H = 14.0 Hz, 2H, CH2), 3.69 (t, JH-H = 7.2 Hz, 2H, CH2), 3.51 (d, JH-H = 14.0 Hz,

2 3 1H, CH2), 3.50 (d, JH-H = 14.0 Hz, 2H, CH2), 2.19 (q, JH-H = 8.0 Hz, 2H, CH2), 1.68

3 (pent, JH-H = 7.2 Hz, 2H, CH2), 1.44-1.41 (m, 2H, CH2), 1.40-1.37 (m, 2H, CH2), 1.23 (s,

t t 13 1 18H, Bu), 1.20 (s, 18H, Bu). C{ H} NMR (CDCl3, 23 °C): δ 168.55, 146.84, 146.71,

144.39, 144.28, 133.93, 132.17, 131.02, 127.83, 127.54, 127.23, 125.99, 125.34, 125.21,

123.22, 121.82, 37.94, 35.30, 34.12, 33.98, 32.65, 32.63, 31.89, 31.35, 28.42, 27.46,

26.70. IR (cm-1): 3159 (s), 2947 (s), 2857 (s), 1774 (m), 1708 (s), 1602 (w), 1476 (m),

1456 (m), 1396 (m), 1295 (m), 1260 (m), 1200 (m), 1129 (w), 1048 (w), 940 (w), 867

+ (w), 817 (w), 787 (w), 736 (m), 716 (m). HRMS calculated for C57H70NO6 [M+H] :

864.5203, found: 864.5220.

2-(6-Phthalimidohexyl)tetrahydroxy-p-tert-butylcalix[4]arene (4-10). Reagents: 2-(6- phthalimidohexyl)tetramethoxy-p-tert-butylcalix[4]arene (2.08 g, 2.23 mmol); BBr3 (2.15

1 mL, 22.3 mmol). Yield 1.48 g (75.6%). H NMR (CDCl3, 23 °C): δ 10.31 (s, 4H, OH),

4 7.85-7.84 (m, 2H, Nphth), 7.71-7.69 (m, 2H, Nphth), 7.11 (d, JH-H = 2.2 Hz, 2H, Ph),

4 4 4 7.09 (d, JH-H = 2.3 Hz, 2H, Ph), 7.07 (d, JH-H = 2.3 Hz, 2H, Ph), 7.00 (d, JH-H = 2.2 Hz,

3 2 2 2H, Ph), 4.48 (t, JH-H = 8.0 Hz, 1H, CH), 4.27 (d, JH-H = 14.0 Hz, 1H, CH2), 4.25 (d, JH-

3 2 H = 14.0 Hz, 2H, CH2), 3.69 (t, JH-H = 7.3 Hz, 2H, CH2), 3.51 (d, JH-H = 14.0 Hz, 1H,

2 3 CH2), 3.50 (d, JH-H = 14.0 Hz, 2H, CH2), 2.19 (q, JH-H = 8.0 Hz, 2H, CH2), 1.67 (pent,

111

3 t JH-H = 7.3 Hz, 2H, CH2), 1.44-1.40 (m, 2H, CH2), 1.34-1.30 (m, 4H, CH2), 1.23 (s, Bu,

t 13 1 18H), 1.21 (s, Bu, 18H). C{ H} NMR (CDCl3, 23 °C): δ 168.45, 146.75, 146.59,

144.30, 144.18, 133.82, 132.07, 131.04, 127.74, 127.62, 127.46, 127.13, 125.88, 125.07,

123.12, 121.76, 37.91, 35.43, 34.08, 33.97, 32.66, 32.53, 31.37, 31.36, 29.11, 28.57,

27.85, 26.72. IR (cm-1): 3169 (s), 2957 (s), 2869 (m), 1769 (w), 1713 (s), 1602 (w), 1482

(m), 1461 (m), 1396 (m), 1361 (w), 1300 (w), 1260 (w), 1240 (w), 1200 (w), 872 (w),

811 (w), 782 (w), 741 (w), 716 (w). HRMS calculated for C58H72NO6 [M+H]: 878.5360, found: 878.5352.

112

References

(1) Moeller, T. The Chemistry of the Lanthanides.; Reinhold Publishing Corporation: New York, 1965, 1-3.

(2) Kaltsoyannis, N.; Scott, P. The f-Elements.; Oxford University Press: London, 1999, 1-3.

(3) Cotton, S. Lanthanide and Actinide Chemistry.; John Wiley & Sons, Ltd: West Sussex, 2006, 2-3.

(4) Falconnet, P. The rare-earth industry - A world of rapid change. J. Alloys. Comp. 1993, 192, 114-117.

(5) Cotton, S. Lanthanide and Actinide Chemistry.; John Wiley & Sons: West Sussex, 2006, 35-56.

(6) Akaska, T.; Bian, Z.; Chan, K. W.; Chen, Z.; Gao, S.; Hu, H.; Huang, C.; Jiang, J.; Jiang, S.; Li, F.; Lu, X.; Lu, Y.; Nagase, S.; Shen, Q.; Wang, B.; Wand, E.; Wang, K.; Wang, R.; Wang, X.; Wong, W.; Xu, H.; Yang, H.; Yao, Y.; Zhang, X.; Zheng, Z. Rare Earth Metal Coordination Chemistry. Fundamentals and Applications.; John Wiley & Sons: Singapore, 2010, 18-36.

(7) de Bettencourt-Dias, A.; Barber, P. S.; Bauer, S. A water-soluble pybox derivative and its highly luminescent lanthanide ion complexes. J. Am. Chem. Soc. 2012, 134, 6987-6994.

(8) Bunzli, J. C. G.; Klein, B.; Chapuis, G.; Schenk, K. J. Crystal structure and emission spectrum of the undecacoordinate complex tris(nitrato)-1,4,7,10,13- pentaoxacyclopentadecaneeuropium(III). Inorg. Chem. 1982, 21, 808-812.

113

(9) O'Laughlin, J. W. In Handbook on the Physics and Chemistry of Rare Earths.; Karl A. Gschneidner, Jr., LeRoy, E., Eds.; Elsevier: 1979; Vol. 4, p 341-358.

(10) Akaska, T.; Bian, Z.; Chan, K. W.; Chen, Z.; Gao, S.; Hu, H.; Huang, C.; Jiang, J.; Jiang, S.; Li, F.; Lu, X.; Lu, Y.; Nagase, S.; Shen, Q.; Wang, B.; Wand, E.; Wang, K.; Wang, R.; Wang, X.; Wong, W.; Xu, H.; Yang, H.; Yao, Y.; Zhang, X.; Zheng, Z. Rare Earth Metal Coordination Chemistry. Fundamentals and Applications.; John Wiley & Sons: Singapore, 2010, 6.

(11) Evans, D. F. The determination of the paramagnetic susceptibility of substances in solution by nuclear magnetic resonance. J. Chem. Soc. 1959, 2003-2005.

(12) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry.; 6th ed.; John Wiley & Sons, Inc.: New York, 1999, 1109.

(13) Mullica, D. F.; Milligan, W. O. Structural refinement of cubic Lu(OH)3. J. Inorg. Nucl. Chem. 1980, 42, 223-227.

(14) Beall, G. W.; Milligan, W. O.; Wolcott, H. A. Structural trends in the lanthanide trihydroxides. J. Inorg. Nucl. Chem. 1977, 39, 65-70.

(15) Cotton, S. Lanthanide and Actinide Chemistry.; John Wiley & Sons: West Sussex, 2006, 23-33.

(16) Freeman, J. H.; Smith, M. L. The preparation of anhydrous inorganic chlorides by dehydration with thionyl chloride. J. Inorg. Nucl. Chem. 1958, 7, 224-227.

(17) Peterson, E. J.; Onstott, E. I.; Vondreele, R. B. Refinement of cerium(III) trichloride heptahydrate in space group P1. Acta. Crystallogr., Sect. B: Struct. Sci. 1979, 35, 805-809.

(18) Beall, G. W.; Milligan, W. O.; Mroczkowski, S. Ytrrium carbonate hydroxide. Acta Crystallogr., Sect. B: Struct. Sci. 1976, 32, 3143-3144.

114

(19) Krishnamohan Sharma, C. V.; Rogers, R. D. 'Molecular chinese blinds': Self-organization of tetranitrato lanthanide complexes into open, chiral hydrogen bonded networks. Chem. Commun. 1999, 83-84.

(20) Wang, R. C.; Zhang, Y. P.; Hu, H. L.; Frausto, R. R.; Clearfield, A. Preparation of lanthanide arylphosphonates and crystal structures of lanthanum phenyl- phosphonates and benzylphosphonates. Chem. Mater. 1992, 4, 864-871.

(21) Mullica, D. F.; Grossie, D. A.; Boatner, L. A. Coordination geometry and structural determinations of SmPO4, EuPO4, and GdPO4. Inorg. Chim. A-F-Block 1985, 109, 105-110.

(22) Milligan, W. O.; Mullica, D. F.; Beall, G. W.; Boatner, L. A. Structural investigations of YPO4, ScPO4, and LuPO4. Inorg. Chim. A-Articles 1982, 60, 39-43.

(23) Xing, Y.; Shi, Z.; Li, G. H.; Pang, W. Q. Hydrothermal synthesis and structure of [C2N2H10][La2(H2O)4(SO4)4]•2H2O, a new organically templated rare earth sulfate with a layer structure. Dalton Trans. 2003, 940-943.

(24) Li, L.; Jin, X.; Li, G.; Wang, Y.; Liao, F.; Yao, G.; Lin, J. Novel rare earth polyborates. 2. Syntheses and structures. Chem. Mater. 2003, 15, 2253-2260.

(25) Li, L. Y.; Jin, X. L.; Li, G. B.; Wang, Y. X.; Liao, F. H.; Yao, G. Q.; Lin, J. H. Novel rare earth polyborates. 2. Syntheses and structures Chem. Mater. 2003, 15, 2253-2260.

(26) Tanase, S.; Reedijk, J. Chemistry and magnetism of cyanido-bridged d-f assemblies. Coord. Chem. Rev. 2006, 250, 2501-2510.

(27) Wilkinson, G.; Birmingham, J. M. Cyclopentadienyl compounds of Sc, Y, La, Ce and some lanthanide elements. J. Am. Chem. Soc. 1954, 76, 6210.

(28) Cotton, S. A. Aspects of the lanthanide-carbon σ-bond. Coord. Chem. Rev. 1997, 160, 93-127. 115

(29) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Synthesis and structural chemistry of non-cyclopentadienyl organolanthanide complexes. Chem. Rev. 2002, 102, 1851-1896.

(30) Zimmermann, M.; Anwander, R. Homoleptic rare-earth metal complexes containing Ln−C σ-bonds. Chem. Rev. 2010, 110, 6194-6259.

(31) Dietrich, H. M.; Raudaschl-Sieber, G.; Anwander, R. Trimethylyttrium and trimethyllutetium. Angew. Chem. Int. Ed. 2005, 44, 5303-5306.

(32) Lappert, M. F.; Pearce, R. Stable silylmethyl and neopentyl complexes of scandium(III) and yttrium(III). J. Chem. Soc., Chem. Commun. 1973, 126.

(33) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Organometallic compounds of the lanthanides. 157 The molecular structure of tris(trimethylsilylmethyl)samarium, -erbium, -ytterbium, and -lutetium. Z. Anorg. Allg. Chem. 2002, 628, 2422-2426.

(34) Atwood, J. L.; Hunter, W. E.; Rogers, R. D.; Holton, J.; McMeeking, J.; Pearce, R.; Lappert, M. F. Neutral and anionic silylmethyl complexes of group 3A and lanthanoid metals. X-ray crystal and molecular structure of Li(THF)4Yb[CH(SiMe3)2]3Cl (THF = tetrahydrofuran). J. Chem. Soc., Chem. Commun. 1978, 140-142.

(35) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G.; Bartlett, R. A.; Power, P. P. Synthesis and structural characterization of 1st neutral homoleptic lanthanide metal(III) alkyls - LnR3 (Ln = La or Sm, R = CH(SiMe3)2). J. Chem. Soc., Chem. Comm. 1988, 1007-1009.

(36) Arndt, S.; Spaniol, T. P.; Okuda, J. The first structurally characterized cationic lanthanide-alkyl complexes. Chem. Commun. 2002, 896-897.

(37) Elvidge, B. R.; Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Cationic rare-earth metal trimethylsilylmethyl complexes supported by THF and 12- crown-4 ligands: Synthesis and structural characterization. Inorg. Chem. 2005, 44, 6777- 6788. 116

(38) Hultzsch, K. C.; Spaniol, H. P.; Okuda, J. Half-sandwich alkyl and hydrido complexes of yttrium: Convenient synthesis and polymerization catalysis of polar monomers. Angew. Chem. Int. Ed. 1999, 38, 227-230.

(39) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. One ligand fits all: Cationic mono(amidinate) alkyl catalysts over the full size range of the group 3 and lanthanide metals. J. Am. Chem. Soc. 2004, 126, 9182-9183.

(40) Barker, G. K.; Lappert, M. F. Stabilization of transition-metals in a low coordinative environment using bis(trimethylsilyl)methyl ligand; Monomeric Cr(III) alkyl, Cr[CH(SiMe3)2]3, and related complexes. J. Organomet. Chem. 1974, 76, C45- C46.

(41) Hitchcock, P. B.; Holmes, S. A.; Lappert, M. F.; Tian, S. Synthesis, structures and reactions of ytterbium(II) alkyls. J. Chem. Soc., Chem. Comm. 1994, 2691- 2692.

(42) Avent, A. G.; Caro, C. F.; Hitchcock, P. B.; Lappert, M. F.; Li, Z. N.; Wei, X. H. Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium gamma-diketiminates. Dalton Trans. 2004, 1567-1577.

(43) Booij, M.; Kiers, N. H.; Heeres, H. J.; Teuben, J. H. On the synthesis of monopentamethylcyclopentadienyl derivatives of yttrium, lanthanum, and cerium. J. Organomet. Chem 1989, 364, 79-86.

(44) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J. Constrained geometry organolanthanide catalysts. Synthesis, structural characterization, and enhanced aminoalkene hydroamination/cyclization activity. Organometallics 1999, 18, 2568-2570.

(45) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Smith, J. D. A monomeric solvent- free bent lanthanide dialkyl and a lanthanide analog of a Grignard reagent. Crystal structures of Yb{C(SiMe3)3}2 and [Yb{C(SiMe3)3}I•OEt2]2. J. Am. Chem. Soc. 1994, 116, 12071-12072.

117

(46) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Lu, Z.-R.; Smith, J. D. Alkyl derivatives of europium(+2) and ytterbium(+2). Crystal structures of Eu[C(SiMe3)3]2, Yb[C(SiMe3)2(SiMe2CHCH2)]I·OEt2 and Yb[C(SiMe3)2(SiMe2OMe)]I·OEt2. Organometallics 1996, 15, 4783-4790.

(47) Qi, G. Z.; Nitto, Y.; Saiki, A.; Tomohiro, T.; Nakayama, Y.; Yasuda, H. Isospecific polymerizations of alkyl methacrylates with a bis(alkyl)Yb complex and formation of stereocomplexes with syndiotactic poly(alkyl methacrylate)s. Tetrahedron 2003, 59, 10409-10418.

(48) Bambirra, S.; Meetsma, A.; Hessen, B. Lanthanum tribenzyl complexes as convenient starting materials for organolanthanum chemistry. Organometallics 2006, 25, 3454-3462.

(49) Wooles, A. J.; Mills, D. P.; Lewis, W.; Blake, A. J.; Liddle, S. T. Lanthanide tri-benzyl Complexes: Structural variations and useful precursors to phosphorus-stabilised lanthanide carbenes. Dalton Trans. 2010, 39, 500-510.

(50) Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.; Meetsma, A.; Hessen, B. Strategies for the synthesis of lanthanum dialkyl complexes with monoanionic ancillary ligands. Organometallics 2008, 27, 704-712.

(51) Harder, S.; Ruspic, C.; Bhriain, N. N.; Berkermann, F.; Schuermann, M. Benzyl complexes of lanthanide(II) and lanthanide(III) metals: Trends and comparisons. Z. Naturforsch., B: Chem. Sci. 2008, 63, 267-274.

(52) Harder, S. The chemistry of Ca-II and Yb-II: Astoundingly similar but not equal! Angew. Chem. Int. Ed. 2004, 43, 2714-2718.

(53) Manzer, L. E. New chelated C,N-benzyllithium reagent and some organometallic derivatives of selected early transition metals. J. Organomet. Chem. 1977, 135, C6-C9.

(54) Petrov, A. R.; Rufanov, K. A.; Harms, K.; Sundermeyer, J. Re- investigation of ortho-metalated N,N-dialkylbenzylamine complexes of rare-earth metals. 118

First structurally characterized arylates of neodymium and gadolinium Li(LnAr)4. J. Organomet. Chem. 2009, 694, 1212-1218.

(55) Behrle, A. C.; Schmidt, J. A. R. Synthesis and reactivity of homoleptic α- metalated N,N-dimethylbenzylamine rare-earth-metal complexes. Organometallics 2011, 30, 3915-3918.

(56) Harder, S. Syntheses and structures of homoleptic lanthanide complexes with chelating o-dimethylaminobenzyl ligands: Key precursors in lanthanide chemistry. Organometallics 2005, 24, 373-379.

(57) Jaroschik, F.; Shima, T.; Li, X.; Mori, K.; Ricard, L.; Le Goff, X.-F.; Nief, F.; Hou, Z. Synthesis, characterization, and reactivity of mono(phospholyl)lanthanoid(III) bis(dimethylaminobenzyl) complexes. Organometallics 2007, 26, 5654-5660.

(58) Li, X.; Nishiura, M.; Mori, K.; Mashiko, T.; Hou, Z. Cationic scandium aminobenzyl complexes. Synthesis, structure and unprecedented catalysis of copolymerization of 1-hexene and dicyclopentadiene. Chem. Commun. 2007, 4137-4139.

(59) Zhang, W.-X.; Nishiura, M.; Hou, Z. Synthesis of (Z)-1-aza-1,3-enynes by the cross-coupling of terminal alkynes with isocyanides catalyzed by rare-earth metal complexes. Angew. Chem. Int. Ed. 2008, 47, 9700-9703.

(60) Deacon, G. B.; Koplick, A. J. Bis(phenylethynyl)ytterbium - A novel organolanthanide. J. Organomet. Chem. 1978, 146, C43-C45.

(61) Ihara, E.; Adachi, Y.; Yasuda, H.; Hashimoto, H.; Kanehisa, N.; Kai, Y. Synthesis of 2,6-dialkoxylphenyllanthanoid complexes and their polymerization catalysis. J. Organomet. Chem. 1998, 569, 147-157.

(62) Zeimentz, P. M.; Okuda, J. Cationic aryl complexes of the rare-earth metals. Organometallics 2007, 26, 6388-6396.

119

(63) Deacon, G. B.; Koplick, A. J.; Raverty, W. D.; Vince, D. G. Organolanthanoids 2. Preparation and identification of some organolanthanoid species in solution. J. Organomet. Chem. 1979, 182, 121-141.

(64) Suleimanov, G. Z.; Khandozhko, R. N.; Mekhdiev, R. I.; Petrovskii, P. V.; Agdamskii, T. A.; Kolobova, N. E.; Beletskaia, I. P. Synthesis and properties of benzenechromiumtricarbonyl derivatives of bivalent lanthanoids. Dokl. Akad. Nauk 1985, 284, 1376-1378.

(65) Starostina, T. A.; Shifrina, R. R.; Rybakova, L. F.; Petrov, E. S. Diphenylytterbium. Zh. Obshch. Khim. 1987, 57, 2402.

(66) Deacon, G. B.; Forsyth, C. M. The synthesis of a new soluble samarium(II) diorganoamide. Inorg. Chim. Acta 1988, 154, 121-122.

(67) Fraser, R. R.; Mansour, T. S.; Savard, S. Acidity measurements on pyridines in tetrahydrofuran using lithiated silylamines. J. Org. Chem. 1985, 50, 3232- 3234.

(68) Streitwieser, A.; Chang, C. J.; Reuben, D. M. E. Acidity of hydrocarbons. XLIV. Equilibrium ion-pair acidities of 9-alkylfluorenes in cyclohexylamine. J. Am. Chem. Soc. 1972, 94, 5730-5734.

(69) Deacon, G. B.; Newnham, R. H. Organolanthanoids. 8. Some ligand- exchange reactions of pentafluorophenyllanthanoids and bis(phenylethynyl)ytterbium(II). Aust. J. Chem. 1985, 38, 1757-1765.

(70) Deacon, G. B.; Forsyth, C. M.; Newham, R. H. Synthesis of divalent aryloxy-lanthanides diorganoamidolanthanides from Bis(pentafluorophenyl)lanthanides(II) complexes. Polyhedron 1987, 6, 1143-1145.

(71) Hart, F. A.; Saran, M. S. Triphenylscandium and related compounds. Chem. Commun. 1968, 1614.

120

(72) Putzer, M. A.; Rogers, J. S.; Bazan, G. C. Intramolecular nucleophilic substitution on coordinated borabenzenes: A new entry into borabenzene complexes. J. Am. Chem. Soc. 1999, 121, 8112-8113.

(73) Hart, F. A.; Massey, A. G.; Saran, M. S. Phenyls and alkyls of group 3A metals. J. Organomet. Chem. 1970, 21, 147-154.

(74) Deacon, G. B.; Forsyth, C. M.; Newnham, R. H.; Tuong, T. D. Organolanthanoids. 10. Syntheses of cyclopentadienyllanthanoids by transmetalation reactions in pyridine, acetonitrile, and ethers. Aust. J. Chem. 1987, 40, 895-906.

(75) Qayyum, S.; Haberland, K.; Forsyth, C. M.; Junk, P. C.; Deacon, G. B.; Kempe, R. Small steric variations in ligands with large synthetic and structural consequences. Eur. J. Inorg. Chem. 2008, 557-562.

(76) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. Low coordination numbers in lanthanide and actinide compounds. 1. Preparation and characterization of tris bis(trimethylsilyl)amido lanthanides. J. Chem. Soc., Dalton Trans. 1973, 1021-1027.

(77) Ghotra, J. S.; Hursthouse, M. B.; Welch, A. J. 3-Coordinate scandium(III) and europium(III). Crystal and molecular structures of their trishexamethyldisilylamides. J. Chem. Soc., Chem. Commun. 1973, 669-670.

(78) Andersen, R. A.; Templeton, D. H.; Zalkin, A. Structure of tris[bis(trimethylsilyl)amido]neodymium(III), Nd[N(SiMe3)2]3. Inorg. Chem. 1978, 17, 2317-2319.

(79) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Divalent lanthanide chemistry. Preparation and crystal structures of sodium tris[bis(trimethylsilyl)amido]europate(II) and sodium tris[bis(trimethylsilyl)amido]ytterbate(II), NaM[N(SiMe3)2]3. Inorg. Chem. 1984, 23, 2271-2276.

(80) Fjeldberg, T.; Andersen, R. A. Gas-phase electron-diffraction studies of two sterically hindered 3-coordinate lanthanide amides.

121

Tris[bis(trimethylsilyl)amido]cerium(III) and praseodymium, M[N(SiMe3)2]3, M = Ce and Pr. J. Mol. Struct. 1985, 129, 93-105.

(81) Herrmann, W. A.; Anwander, R.; Munck, F. C.; Scherer, W.; Dufaud, V.; Huber, N. W.; Artus, G. R. J. Lanthanoid complexes. 9. Reactivity control of lanthanoid amides through ligand effects. Synthesis and structures of sterically congested alkoxy complexes. Z. Naturforsch., B: Chem. Sci. 1994, 49, 1789-1797.

(82) Rees, W. S.; Just, O.; Van Derveer, D. S. Molecular design of dopant precursors for atomic layer epitaxy of SrS : Ce. J. Mater. Chem. 1999, 9, 249-252.

(83) Jeske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann, H.; Marks, T. J. Highly reactive organolanthanides. Systematic routes to and olefin chemistry of early and late bis(pentamethylcyclopentadienyl) 4f hydrocarbyl and hydride complexes. J. Am. Chem. Soc. 1985, 107, 8091-8103.

(84) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. Alpha-bond metathesis for C-H bonds of hydrocarbons and Sc-H, Sc-alkyl, Sc-aryl bonds of permethylscandocene derivatives. Evidence for noninvolvement of the pi-system in electrophilic activation of aromatic and vinylic C-H bonds. J. Am. Chem. Soc. 1987, 109, 203-219.

(85) Li, Y. W.; Fu, P. F.; Marks, T. J. Organolanthanide catalyzed carbon- heteroatom bond formation. Observations on the facile, regiospecific cyclization of aminoalkynes. Organometallics 1994, 13, 439-440.

(86) Roussel, P.; Alcock, N. W.; Scott, P. Triamidoamine complexes of scandium, yttrium and the lanthanides. Chem. Commun. 1998, 801-802.

(87) Evans, W. J.; Rabe, G. W.; Ziller, J. W. Utility of N-methylimidazole in isolating crystalline lanthanide iodide and hydroxide complexes: Crystallographic characterization of octasolvated [Sm(N-MeIm)8]I3 and polymetallic [SmI(μ-I)(N- MeIm)3]2, [(N-MeIm)5Sm(μ-OH)]2I4, and {[(N-MeIm)4Sm(μ-OH)]3(μ3-OH)2}I4. Inorg. Chem. 1994, 33, 3072-3078.

122

(88) Alexander, V. Design and synthesis of macrocyclic ligands and their complexes of lanthanides and actinides. Chem. Rev. 1995, 95, 273-342.

(89) Evans, W. J.; Fujimoto, C. H.; Ziller, J. W. Synthesis and structure of arene soluble N,N '-bis(di-tert-butylsalicylidene)ethylenediamine yttrium complexes. Chem. Commun. 1999, 311-312.

(90) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. Synthesis of organosamarium complexes containing samarium-carbon and samarium-phosphorus bonds. Crystallographic characterization of [(MeC5H4)2SmC≡CCMe3]2. Organometallics 1983, 2, 709-714.

(91) Rabe, G. W.; Ziller, J. W. Phosphido complexes of the lanthanides. Synthesis and X-ray crystal structure determination of a tris(phosphido) species of neodymium: Nd[P(SiMe3)2]3(THF)2. Inorg. Chem. 1995, 34, 5378-5379.

(92) Rabe, G. W.; Riede, J.; Schier, A. Synthesis, X-ray crystal structure determination, and NMR spectroscopic investigation of two homoleptic four-coordinate t t lanthanide complexes: Trivalent ( Bu2P)2La[(μ-P Bu2)2][Li(THF)] and divalent [Yb[(μ- t P Bu2)2][Li(THF)]2. Inorg. Chem. 1996, 35, 40-45.

(93) Izod, K.; Liddle, S. T.; McFarlane, W.; Clegg, W. Synthesis and reactions of sterically encumbered, heteroleptic lanthanum phosphides. Structural characterization of [{(Me3Si)2CH}-(C6H4-2-CH2NMe2)P]2La(OR) and [{(Me3Si)2CH}-(C6H4-2- i t CH2NMe2)P]La(THF)[P(C6H4-2-CH2NMe2)-{CH(SiMe3)(SiMe2CH2)} [R= Pr, Bu]. Organometallics 2004, 23, 2734-2743.

(94) Douglass, M. R.; Stern, C. L.; Marks, T. J. Intramolecular hydrophosphination/cyclization of phosphinoalkenes and phosphinoalkynes catalyzed by organolanthanides: Scope, selectivity, and mechanism. J. Am. Chem. Soc. 2001, 123, 10221-10238.

(95) Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L. Divalent lanthanide chemistry: Three synthetic routes to samarium(II) and ytterbium bis(phosphido) species

123

including the structural characterization of Yb[PPh2]2(THF)4 and Sm[PPh2]2(N-MeIm)4. Inorg. Chem. 1995, 34, 4521-4522.

(96) Izod, K.; Liddle, S. T.; Clegg, W.; Harrington, R. W. Amino- functionalised diarylphosphide complexes of the alkali metals and lanthanum. Dalton Trans. 2006, 3431-3437.

(97) Nief, F.; Ricard, L. New examples of lanthanide(II) phosphides and arsenides with planar coordination at the heteroatom: Crystal structures of [(mesityl)2P]2Sm(THF)4 and of [(mesityl)2As]2Sm(THF)4. J. Organomet. Chem. 1997, 529, 357-360.

(98) Nief, F.; Ricard, L. Synthesis and molecular structure of bis(pentamethylcyclopentadienyl) phospholyl- and arsolylsamarium(III) complexes: Influence of steric and electronic factors. Organometallics 2001, 20, 3884-3890.

(99) Schumann, H.; Palamidis, E.; Schmid, G.; Boese, R.; Manecke, G. [(Cp2Lu{μ-PPh2})2Li(tmeda)]•1/2 C6H5CH3, The first organolanthanoid-phosphane compound to be characterized by X-ray structure analysis. Angew. Chem. Int. Ed. 1986, 25, 718-719.

(100) Rabe, G. W.; Riede, J.; Schier, A. Synthesis and structural characterization of the first lanthanide tris(phosphido) complex: Tm[P(SiMe3)2]3(THF)2. J. Chem. Soc., Chem. Commun. 1995, 577-578.

(101) Rabe, G. W.; Yap, G. P. A.; Rheingold, A. L. Lanthanide phosphido t complexes: A comparison of the divalent homoleptic species Ln[(μ-P Bu2)2Li(THF)]2 (Ln = Yb, Eu, Sm) including the structural characterization and a europium-151 t Mossbauer spectrum of Eu[(μ-(P Bu2)2Li(THF)]2. Inorg. Chem. 1997, 36, 3212-3215.

(102) Tardif, O.; Hou, Z. M.; Nishiura, M.; Koizumi, T.; Wakatsuki, Y. Synthesis, structures, and reactivity of the first silylene-linked cyclopentadienyl- phosphido lanthanide complexes. Organometallics 2001, 20, 4565-4573.

124

(103) Evans, W. J.; Bloom, I.; Engerer, S. C. Catalytic activation of molecular- hydrogen in alkyne hydrogenation reactions by lanthanide metal vapor reaction products. J. Catal. 1983, 84, 468-476.

(104) Sakakura, T.; Lautenschlager, H. J.; Tanaka, M. Hydrosilylation catalyzed by organoneodymium complexes. J. Chem. Soc., Chem. Commun. 1991, 40-41.

(105) Yasuda, H.; Yamamoto, H.; Yokota, K.; Miyake, S.; Nakamura, A. Synthesis of monodispersed high molecular weight polymers and isolation of an organolanthanide(III) intermediate coordinated by a penultimate poly(MMA) unit. J. Am. Chem. Soc. 1992, 114, 4908-4910.

(106) Bunel, E.; Burger, B. J.; Bercaw, J. E. Carbon-carbon bond activation via β-alkyl elimination. Reversible branching of 1,4-pentadienes catalyzed by scandocene hydride derivatives. J. Am. Chem. Soc. 1988, 110, 976-978.

(107) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T. J. Highly reactive organolanthanides: A mechanistic study of catalytic olefin hydrogenation by bis(pentamethylcyclopentadienyl) and related 4f complexes. J. Am. Chem. Soc. 1985, 107, 8111-8118.

(108) Laske, D. A.; Duchateau, R.; Teuben, J. H.; Spek, A. L. Synthesis of new bis(cyclopentadienyl)yttrium complexes with ether functionalized cyclopentadienyl ligands. Crystal structure of [(C5H4CH2OMe)2Y(μ-H)2BH2]. J. Organomet. Chem. 1993, 462, 149-153.

(109) Evans, W. J.; Meadows, J. H.; Hanusa, T. P. Organolanthanide and organoyttrium hydride chemistry. 6. Direct synthesis and proton NMR spectral analysis of the trimetallic yttrium and yttrium-zirconium tetrahydride complexes, {[(C5H5)2YH]3H}{Li(THF)4} and {[(CH3C5H4)2YH]2[(CH3C5H4)2ZrH]H}. J. Am. Chem. Soc. 1984, 106, 4454-4460.

(110) Watson, P. L. Ziegler-Natta polymerization: The lanthanide model. J. Am. Chem. Soc. 1982, 104, 337-339.

125

(111) Voskoboynikov, A. Z.; Parshina, I. N.; Shestakova, A. K.; Butin, K. P.; Beletskaya, I. P.; Kuzmina, L. G.; Howard, J. A. K. Reactivity of lanthanide and yttrium hydrides and hydrocarbyls toward organosilicon hydrides and related compounds Organometallics 1997, 16, 4041-4055.

(112) Venugopal, A.; Fegler, W.; Spaniol, T. P.; Maron, L.; Okuda, J. Dihydrogen addition in a dinuclear rare-earth metal hydride complex supported by a metalated TREN ligand. J. Am. Chem. Soc. 2011, 133, 17574-17577.

(113) Takenaka, Y.; Hou, Z. Lanthanide terminal hydride complexes bearing two sterically demanding C5Me4SiMe3 ligands. Synthesis, structure, and reactivity. Organometallics 2009, 28, 5196-5203.

(114) Konkol, M.; Okuda, J. Non-metallocene hydride complexes of the rare- earth metals. Coord. Chem. Rev. 2008, 252, 1577-1591.

(115) Evans, W. J.; Meadows, J. H.; Wayda, A. L.; Hunter, W. E.; Atwood, J. L. Organolanthanide hydride chemistry. 1. Synthesis and X-ray crystallographic characterization of dimeric organolanthanide and organoyttrium hydride complexes. J. Am. Chem. Soc. 1982, 104, 2008-2014.

(116) Evans, W. J.; Dominguez, R.; Hanusa, T. P. Organolanthanide and organoyttrium hydride chemistry. Part 8. Structure and reactivity studies of bis(cyclopentadienyl)ytterbium and ytterbium alkyl complexes including the X-ray crystal structure of (C5H5)2Yb(CH3)(THF). Organometallics 1986, 5, 263-270.

(117) McNaught, A. D.; Wilkinson, A. IUPAC Compendium of Chemical Terminology Goldbook.; 2.3.1 ed.; Blackwell Science, 1997, 220.

(118) Trost, B. M. The atom economy - A search for synthetic efficiency. Science 1991, 254, 1471-1477.

(119) Haggins, J. Chemists seek greater recognition for catalysis. Chem. Eng. News 1993, 71, 23-27.

126

(120) Brunet, J. J.; Neibecker, D. Catalytic Heterofunctionalization from Hydroamination to Hydrozirconation.; VCH: Weinheim, Germany, 2001, 91-141.

(121) Mueller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Hydroamination: Direct addition of amines to alkenes and alkynes. Chem. Rev. 2008, 108, 3795-3892.

(122) Gagne, M. R.; Stern, C. L.; Marks, T. J. Organolanthanide-catalyzed hydroamination. A kinetic, mechanistic, and diastereoselectivity study of the cyclization of N-unprotected amino olefins. J. Am. Chem. Soc. 1992, 114, 275-294.

(123) Sakakura, T.; Lautenschlager, H. J.; Nakajima, M.; Tanaka, M. Dehydrogenative condensation of hydrosilanes catalyzed by an organoneodymium complex. Chem. Lett. 1991, 913-916.

(124) Molander, G. A.; Julius, M. Selective hydrosilylation of alkenes catalyzed by an organoyttrium complex. J. Org. Chem. 1992, 57, 6347-6351.

(125) Trambitas, A. G.; Panda, T. K.; Jenter, J.; Roesky, P. W.; Daniliuc, C.; Hrib, C. G.; Jones, P. G.; Tamm, M. Rare-earth metal alkyl, amido, and cyclopentadienyl complexes supported by imidazolin-2-iminato ligands: Synthesis, structural characterization, and catalytic application. Inorg. Chem. 2010, 49, 2435-2446.

(126) Abinet, E.; Spaniol, T. P.; Okuda, J. Olefin hydrosilylation catalysts based on allyl bis(phenolato) complexes of the early lanthanides. Chem. Asian J. 2011, 6, 389- 391.

(127) Konkol, M.; Kondracka, M.; Voth, P.; Spaniol, T. P.; Okuda, J. Rare-earth metal alkyl and hydrido complexes containing a thioether-functionalized bis(phenolato) ligand: Efficient catalysts for olefin hydrosilylation. Organometallics 2008, 27, 3774- 3784.

(128) Costa, E.; Pringle, P. G.; Smith, M. B.; Worboys, K. Self-replication of tris(cyanoethyl)phosphine catalysed by platinum group metal complexes. J. Chem. Soc., Dalton Trans. 1997, 4277-4282. 127

(129) Shulyupin, M. O.; Kazankova, M. A.; Beletskaya, I. P. Catalytic hydrophosphination of styrenes. Org. Lett. 2002, 4, 761-763.

(130) Roering, A. J.; Leshinski, S. E.; Chan, S. M.; Shalumova, T.; MacMillan, S. N.; Tanski, J. M.; Waterman, R. Insertion reactions and catalytic hydrophosphination by triamidoamine-supported zirconium complexes. Organometallics 2010, 29, 2557- 2565.

(131) Takaki, K.; Koshoji, G.; Komeyama, K.; Takeda, M.; Shishido, T.; Kitani, A.; Takehira, K. Intermolecular hydrophosphination of alkynes and related carbon-carbon multiple bonds catalyzed by organoytterbiums. J. Org. Chem. 2003, 68, 6554-6565.

(132) Zhang, W.-X.; Nishiura, M.; Mashiko, T.; Hou, Z. Half-sandwich o-N,N- dimethylaminobenzyl complexes over the full size range of group 3 and lanthanide metals. Synthesis, structural characterization, and catalysis of phosphine P-H bond addition to carbodiimides. Chem. Eur. J. 2008, 14, 2167-2179.

(133) Sadow, A. D.; Togni, A. Enantioselective addition of secondary phosphines to methacrylonitrile: Catalysis and mechanism. J. Am. Chem. Soc. 2005, 127, 17012-17024.

(134) Mueller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Hydroamination: Direct Addition of Amines to Alkenes and Alkynes Chem. Rev. 2008, 108, 3795-3892.

(135) Yuen, H. F.; Marks, T. J. Phenylene-bridged binuclear organolanthanide complexes as catalysts for intramolecular and intermolecular hydroamination. Organometallics 2009, 28, 2423-2440.

(136) Stanlake, L. J. E.; Schafer, L. L. Bis- and mono(amidate) complexes of yttrium: Synthesis, characterization, and use as precatalysts for the hydroamination of aminoalkenes. Organometallics 2009, 28, 3990-3998.

128

(137) Bambirra, S.; Tsurugi, H.; van Leusen, D.; Hessen, B. Neutral versus cationic group 3 metal alkyl catalysts: Performance in intramolecular hydroamination/cyclisation. Dalton Trans. 2006, 1157-1161.

(138) Stanford, M. J.; Dove, A. P. Stereocontrolled ring-opening polymerisation of lactide. Chem. Soc. Rev. 2010, 39, 486-494.

(139) Platel, R. H.; Hodgson, L. M.; Williams, C. K. Biocompatible initiators for lactide polymerization. Polym. Rev. 2008, 48, 11-63.

(140) Miao, W.; Li, S. H.; Cui, D. M.; Huang, B. T. Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: synthesis, characterization and catalysis on the ring-opening polymerization of L-lactide. J. Organomet. Chem. 2007, 692, 3823- 3834.

(141) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Controlled ring- opening polymerization of lactide and glycolide. Chem. Rev. 2004, 104, 6147-6176.

(142) Molander, G. A.; Romero, J. A. C. Lanthanocene catalysts in selective organic synthesis. Chem. Rev. 2002, 102, 2161-2186.

(143) Ge, S.; Meetsma, A.; Hessen, B. Highly efficient hydrosilylation of alkenes by organoyttrium catalysts with sterically demanding amidinate and guanidinate ligands. Organometallics 2008, 27, 3131-3135.

(144) Molander, G. A.; Dowdy, E. D.; Noll, B. C. Investigation of the regioselectivity of alkene hydrosilylation catalyzed by organolanthanide and group 3 metallocene complexes. Organometallics 1998, 17, 3754-3758.

(145) Edelmann, F. T. Lanthanide amidinates and guanidinates: From laboratory curiosities to efficient homogeneous catalysts and precursors for rare-earth oxide thin films. Chem. Soc. Rev. 2009, 38, 2253-2268.

129

(146) Daly, S. R.; Kim, D. Y.; Yang, Y.; Abelson, J. R.; Girolami, G. S. Lanthanide N,N-dimethylaminodiboranates: Highly volatile precursors for the deposition of lanthanide-containing thin films. J. Am. Chem. Soc. 2010, 132, 2106-2107.

(147) Paivasaari, J.; Dezelah, C. L.; Back, D.; El-Kaderi, H. M.; Heeg, M.; Putkonen, M.; Niinisto, L.; Winter, C. H. Synthesis, structure and properties of volatile lanthanide complexes containing amidinate ligands: Application for Er2O3 thin film growth by atomic layer deposition. J. Mater. Chem. 2005, 15, 4224-4233.

(148) Lim, B. S.; Rahtu, A.; Park, J.-S.; Gordon, R. G. Synthesis and characterization of volatile, thermally stable, reactive transition metal amidinates. Inorg. Chem. 2003, 42, 7951-7958.

(149) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A.; Hessen, B.; Saliu, K.; Takats, J. Synthesis and structures of scandium and lutetium benzyl complexes. Organometallics 2008, 27, 1501-1505.

(150) Ge, S.; Meetsma, A.; Hessen, B. Scandium, yttrium, and lanthanum benzyl and alkynyl complexes with the N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amido ligand: Synthesis, characterization, and Z-selective catalytic linear dimerization of phenylacetylenes. Organometallics 2009, 28, 719-726.

(151) Carver, C. T.; Monreal, M. J.; Diaconescu, P. L. Scandium alkyl complexes supported by a ferrocene diamide ligand. Organometallics 2008, 27, 363-370.

(152) Carver, C. T.; Diaconescu, P. L. Ring-opening reactions of aromatic N- heterocycles by scandium and yttrium alkyl complexes. J. Am. Chem. Soc. 2008, 130, 7558-7559.

(153) Mills, D. P.; Cooper, O. J.; McMaster, J.; Lewis, W.; Liddle, S. T. Synthesis and reactivity of the yttrium-alkyl-carbene complex [Y(BIPM)(CH2C6H5)(THF)] (BIPM = {C(PPh2NSiMe3)2}). Dalton Trans. 2009, 4547- 4555.

130

(154) Abicht, H. P.; Issleib, K. Cyclometallated Pd and Pt complexes of (ortho- lithiobenzyl)diorganophosphines . J. Organomet. Chem 1980, 185, 265-275.

(155) Wayda, A. L.; Atwood, J. L.; Hunter, W. E. Homoleptic organolanthanoid hydrocarbyls. The synthesis and X-ray crystal structure of tris[o- ((dimethylamino)methyl)phenyl]lutetium. Organometallics 1984, 3, 939-941.

(156) Lubben, T. V.; Plossl, K.; Norton, J. R.; Miller, M. M.; Anderson, O. P. Synthesis and structure of two organozirconocenes with alpha nitrogen substituents. Organometallics 1992, 11, 122-127.

(157) Petrov, A. R.; Thomas, O.; Harms, K.; Rufanov, K. A.; Sundermeyer, J. Dramatic enhancement of the stability of rare-earth metal complexes with alpha-methyl substituted N,N-dimethylbenzylamine ligands. J. Organomet. Chem. 2010, 695, 2738- 2746.

(158) Jones, C. J. d-and f-Block Chemistry; Wiley-Interscience: New York, 2002, 148-149.

(159) Oakes, F. T.; Sebastian, J. F. Direct observation of metallated N,N- dimethylbenzylamines by FT NMR-spectroscopy. J. Organomet. Chem. 1978, 159, 363- 371.

(160) Lappert, M. F.; Singh, A.; Smith, R. G.; Stecher, H. A.; Sen, A. Hydrocarbon-soluble homoleptic bulky aryl oxides of the lanthanide metals: [Ln(OAr)3]. Inorg. Synth. 1990, 27, 164-168.

(161) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G. Tris(2,6-di-tert- butylphenoxo)yttrium: A 3-coordinate hydrocarbon soluble aryloxide of yttrium. Inorg. Chim. Acta 1987, 139, 183-184.

(162) Giesbrecht, G. R.; Gordon, J. C.; Clark, D. L.; Hay, P. J.; Scott, B. L.; Tait, C. D. A comparative study of arene-bridged lanthanum arylamide and aryloxide dimers. Solution behavior, exchange mechanisms, and X-ray crystal structures of

131

i i i La2(NH-2,6- Pr2C6H3)6, La(NH-2,6- Pr2C6H3)3(THF)3, and La(NH-2,6- Pr2C6H3)3(py)2. J. Am. Chem. Soc. 2004, 126, 6387-6401.

(163) Evans, W. J.; Ansari, M. A.; Ziller, J. W.; Khan, S. I. Utility of arylamido ligands in yttrium and lanthanide chemistry. Inorg. Chem. 1996, 35, 5435-5444.

(164) Farrugia, L. ORTEP-3 for Windows - A version of ORTEP-III with a graphical user interface (GUI). J. Appl. Crystallogr. 1997, 30, 565.

(165) SMART: Area-Detector Software Package, v5.625, Bruker AXS, Inc., Madison, WI, 1997-2001.

(166) SAINT: SAX Area-Detector Integration Program, v6.22, Bruker AXS, Inc., Madison, WI, 1997-2001.

(167) XPREP: Reciprocal Space Exploration Program, v6.12, Bruker AXS, Inc, Madison, WI, 2001.

(168) SADABS: Bruker/Siemens Area Detector Absorption Program, v2.03, Bruker AXS, Inc., Madison, WI, 2001.

(169) SHELXTL-97: Structure Solution Program, v6.10, Bruker AXS, Inc., Madison, WI, 2000.

(170) Otero, A.; Lara-Sánchez, A.; Nájera, C.; Fernández-Baeza, J.; Márquez- Segovia, I.; Castro-Osma, J. A.; Martínez, J.; Sánchez-Barba, L. F.; Rodríguez, A. M. New highly active heteroscorpionate-containing lutetium catalysts for the hydroamination of aminoalkenes: Isolation and structural characterization of a dipyrrolidinide–lutetium complex. Organometallics 2012, 31, 2244-2255.

(171) Oyamada, J.; Nishiura, M.; Hou, Z. Scandium-catalyzed silylation of aromatic C-H bonds. Angew. Chem. Int. Ed. 2011, 50, 10720-10723.

132

(172) Zhao, D.; Wang, R. Recent developments in metal catalyzed asymmetric addition of phosphorus nucleophiles. Chem. Soc. Rev. 2012, 41, 2095-2108.

(173) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A. Calcium-catalyzed intermolecular hydrophosphination. Organometallics 2007, 26, 2953-2956.

(174) Wicht, D. K.; Kovacik, I.; Glueck, D. S.; Liable-Sands, L. M.; Incarvito, C. D.; Rheingold, A. L. Chiral terminal platinum(II) phosphido complexes: Synthesis, phosphorus inversion, and acrylonitrile insertion. Organometallics 1999, 18, 5141-5151.

(175) Yuan, M.; Pullarkat, S. A.; Li, Y.; Lee, Z.-Y.; Leung, P.-H. Novel synthesis of chiral 1,3-diphosphines via palladium template promoted hydrophosphination and functional group transformation reactions. Organometallics 2010, 29, 3582-3588.

(176) Zhao, D.; Yuan, Y.; Chan, A. S. C.; Wang, R. Highly enantioselective 1,4- addition of diethyl phosphite to enones using a dinuclear Zn catalyst. Chem. Eur. J. 2009, 15, 2738-2741.

(177) Pullarkat, S. A.; Yi, D.; Li, Y.; Tan, G.-K.; Leung, P.-H. A novel approach toward asymmetric synthesis of alcohol functionalized c-chiral diphosphines via two- stage hydrophosphination of terminal alkynols. Inorg. Chem. 2006, 45, 7455-7463.

(178) Kovacik, I.; Wicht, D. K.; Grewal, N. S.; Glueck, D. S.; Incarvito, C. D.; Guzei, I. A.; Rheingold, A. L. Pt(Me-Duphos)-catalyzed asymmetric hydrophosphination of activated olefins: Enantioselective synthesis of chiral phosphines. Organometallics 2000, 19, 950-953.

(179) Pringle, P. G.; Smith, M. B. Platinum(0)-catalyzed hydrophosphination of acrylonitrile. J. Chem. Soc. Chem. Comm. 1990, 1701-1702.

(180) Zhao, G.; Basuli, F.; Kilgore, U. J.; Fan, H.; Aneetha, H.; Huffman, J. C.; Wu, G.; Mindiola, D. J. Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, 133

and catalytic studies addressing the Ti-P multiple bond. J. Am. Chem. Soc. 2006, 128, 13575-13585.

(181) Hu, H.; Cui, C. Synthesis of calcium and ytterbium complexes supported by a tridentate imino-amidinate ligand and their application in the intermolecular hydrophosphination of alkenes and alkynes. Organometallics 2012, 31, 1208-1211.

(182) Greenberg, S.; Stephan, D. W. Phosphines bearing alkyne substituents: Synthesis and hydrophosphination polymerization. Inorg. Chem. 2009, 48, 8623-8631.

(183) Motta, A.; Fragalà, I. L.; Marks, T. J. Energetics and mechanism of organolanthanide-mediated phosphinoalkene hydrophosphination/cyclization. A density functional theory analysis. Organometallics 2005, 24, 4995-5003.

(184) Shaikh, T. M.; Weng, C.-M.; Hong, F.-E. Secondary phosphine oxides: Versatile ligands in transition metal-catalyzed cross-coupling reactions. Coord. Chem. Rev. 2012, 256, 771-803.

(185) Xu, Q.; Han, L.-B. Palladium-catalyzed asymmetric hydrophosphination of norbornenes. Org. Lett. 2006, 8, 2099-2101.

(186) Glueck, D. S. Metal-catalyzed asymmetric synthesis of P-stereogenic phosphines. Synlett 2007, 2627-2634.

(187) Smith, R. C.; Protasiewicz, J. D. Conjugated polymers featuring heavier main group element multiple bonds: A diphosphene-ppv. J. Am. Chem. Soc. 2004, 126, 2268-2269.

(188) Elorriaga, D.; Carrillo-Hermosilla, F.; Antiñolo, A.; López-Solera, I.; Menot, B.; Fernández-Galán, R.; Villaseñor, E.; Otero, A. New alkylimido niobium complexes supported by guanidinate ligands: Synthesis, characterization, and migratory insertion reactions. Organometallics 2012, 31, 1840-1848.

134

(189) Casely, I. J.; Ziller, J. W.; Evans, W. J. C–H activation via carbodiimide insertion into yttrium–carbon alkynide bonds: An organometallic Alder-ene reaction. Organometallics 2011, 30, 4873-4881.

(190) Cao, Y.; Du, Z.; Li, W.; Li, J.; Zhang, Y.; Xu, F.; Shen, Q. Activation of carbodiimide and transformation with amine to guanidinate group by Ln(OAr)3(THF)2 (Ln: lanthanide and yttrium) and Ln(OAr)3(THF)2 as a novel precatalyst for addition of amines to carbodiimides: Influence of aryloxide group. Inorg. Chem. 2011, 50, 3729- 3737.

(191) Zhang, J.; Zhou, X. Selective insertions of unsaturated organic molecules into the Ln-N or N-H bonds of biscyclopentadienyl lanthanide complexes. Dalton Trans. 2011, 40, 9637-9648.

(192) Sun, Y.; Zhang, Z.; Wang, X.; Li, X.; Weng, L.; Zhou, X. Lanthanide- induced diinsertion of isocyanates into the N−H bond: Synthesis, structure, and reactivity of organolanthanides containing diureido ligands. Organometallics 2009, 28, 6320-6330.

(193) Mansfield, N. E.; Grundy, J.; Coles, M. P.; Hitchcock, P. B. Phospha(III)guanidinate complexes of titanium(IV) and zirconium(IV) amides. Polyhedron 2010, 29, 2481-2488.

(194) Edelmann, F. T. Advances in the coordination chemistry of amidinate and guanidinate ligands.; Elsevier Academic Press Inc.: San Diego, 2008; Vol. 57, 183-352.

(195) Rowley, C. N.; Ong, T.-G.; Priem, J.; Richeson, D. S.; Woo, T. K. Analysis of the critical step in catalytic carbodiimide transformation: Proton transfer from amines, phosphines, and alkynes to guanidinates, phosphaguanidinates, and propiolamidinates with Li and Al catalysts. Inorg. Chem. 2008, 47, 12024-12031.

(196) Grundy, J.; Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Phosphaguanidines as scaffolds for multimetallic complexes containing metal- functionalized phosphines. Inorg. Chem. 2008, 47, 2258-2260.

135

(197) Milanov, A. P.; Fischer, R. A.; Devi, A. Synthesis, characterization, and thermal properties of homoleptic rare-earth guanidinates: Promising precursors for MOCVD and ALD of rare-earth oxide thin films. Inorg. Chem. 2008, 47, 11405-11416.

(198) Wang, J.; Sun, H.; Yao, Y.; Zhang, Y.; Shen, Q. Bridged bis(amidinate) lanthanide complexes: Synthesis, molecular structure and reactivity. Polyhedron 2008, 27, 1977-1982.

(199) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Insertion of a carbodiimide into the Ln−N σ-bond of organolanthanide complexes. Isomerization and rearrangement of organolanthanides containing guanidinate ligands. Organometallics 2004, 23, 3303-3308.

(200) Zhang, W.-X.; Nishiura, M.; Hou, Z. Catalytic addition of terminal alkynes to carbodiimides by half-sandwich rare earth metal complexes. J. Am. Chem. Soc. 2005, 127, 16788-16789.

(201) Li, J. N.; Liu, L.; Fu, Y.; Guo, Q. X. What are the pKa values of organophosphorus compounds? Tetrahedron 2006, 62, 4453-4462.

(202) Villiers, C.; Thuery, P.; Ephritikhine, M. A comparison of analogous 4f- and 5f-element compounds: Synthesis, X-ray crystal structures and catalytic activity of the homoleptic amidinate complexes [M{MeC(NCy)2}3] (M = La, Nd, or U). Eur. J. Inorg. Chem. 2004, 4624-4632.

(203) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.; Goldman, A. S. Highly effective pincer-ligated iridium catalysts for alkane dehydrogenation. DFT calculations of relevant thermodynamic, kinetic, and spectroscopic properties. J. Am. Chem. Soc. 2004, 126, 13044-13053.

(204) Gutsche, C. D. Monographs in Supramolecular Chemistry.; The Royal Society of Chemistry: Cambridge, 1989; Vol. 1.

(205) Creaven, B. S.; Donlon, D. F.; McGinley, J. Coordination chemistry of calix[4]arene derivatives with lower rim functionalisation and their applications. Coord. Chem. Rev. 2009, 253, 893-962. 136

(206) Harvey, P. D. Wide-rim and outer-face functionalizations of calix[4]arene. Coord. Chem. Rev. 2002, 233, 289-309.

(207) Arduini, A.; Casnat, A. Macrocycle Synthesis: A Practical Approach.; Oxford University Press: Oxford, 1996; Vol. 1, 165-166.

(208) Arduini, A.; Casnat, A. Macrocycle Synthesis: A Practical Approach.; Oxford University Press: Oxford, 1996; Vol. 1, 167-168.

(209) Steyer, E.; Jeunesse, C.; Harrowfield, J.; Matt, D. Bis-phosphites and bis- phosphinites based on distally-functionalised calix[4]arenes: Coordination chemistry and use in rhodium-catalysed, low-pressure olefin hydroformylation. Dalton Trans. 2005, 1301-1309.

(210) Kleij, A. W.; Souto, B.; Pastor, C. J.; Prados, P.; de Mendoza, J. Multinuclear calixarene synthons with covalently linked aryl-palladium(II) complexes. J. Org. Chem. 2004, 69, 6394-6403.

(211) Dorta, R.; Shimon, L. J. W.; Rozenberg, H.; Ben-David, Y.; Milstein, D. A new ligand system based on a bipyridine-functionalized calix[4]arene backbone leading to mono- and bimetallic complexes. Inorg. Chem. 2003, 42, 3160-3167.

(212) Biali, S. E.; Böhmer, V.; Cohen, S.; Ferguson, G.; Grüttner, C.; Grynszpan, F.; Paulus, E. F.; Thondorf, I.; Vogt, W. Alkanediyl bridged calix[4]arenes: Synthesis, conformational analysis, and rotational barriers. J. Am. Chem. Soc. 1996, 118, 12938-12949.

(213) Biali, S. E.; Böhmer, V.; Brenn, J.; Frings, M.; Thondorf, I.; Vogt, W.; Wöhnert, J. Conformation, inversion barrier, and solvent-induced conformational shift in exo- and endo/exo-calix[4]arenes. J. Org. Chem. 1997, 62, 8350-8360.

(214) Bergamaschi, M.; Bigi, F.; Lanfranchi, M.; Maggi, R.; Pastorio, A.; Pellinghelli, M. A.; Peri, F.; Porta, C.; Sartori, G. Stepwise synthesis and structural characterization of calix[4] and calix[5]arenes bearing a functionalized arm on the methylene bridge. Tetrahedron 1997, 53, 13037-13052. 137

(215) Sartori, G.; Bigi, F.; Porta, C.; Maggi, R.; Peri, F. Solvent effect in the fragment condensation synthesis of calix[4]arenes and temperature dependent 1H NMR studies of new dihomomonoxacalixarenes. Tetrahedron Lett. 1995, 36, 8323-8326.

(216) Middel, O.; Greff, Z.; Taylor, N. J.; Verboom, W.; Reinhoudt, D. N.; Snieckus, V. The first lateral functionalization of calix[4]arenes by a homologous anionic ortho-Fries rearrangement. J. Org. Chem. 2000, 65, 667-675.

(217) Agbaria, K.; Biali, S. E. Spirodienone route for the stereoselective methylene functionalization of p-tert-butylcalix[4]arene. J. Am. Chem. Soc. 2001, 123, 12495-12503.

(218) Scully, P. A.; Hamilton, T. M.; Bennett, J. L. Synthesis of 2-alkyl- and 2- carboxy-p-tert-butylcalix[4]arenes via the lithiation of tetramethoxy-p-tert- butylcalix[4]arene. Org. Lett. 2001, 3, 2741-2744.

(219) Hertel, M. P.; Behrle, A. C.; Williams, S. A.; Schmidt, J. A. R.; Fantini, J. L. Synthesis of amine, halide, and pyridinium terminated 2-alkyl-p-tert- butylcalix[4]arenes. Tetrahedron 2009, 65, 8657-8667.

(220) Hardman, M. J.; Thomas, A. M.; Carroll, L. T.; Williams, L. C.; Parkin, S.; Fantini, J. L. Synthesis and 'click' cycloaddition reactions of tetramethoxy- and tetrapropoxy-2-(-azidoalkyl)calix[4]arenes. Tetrahedron 2011, 67, 7027-7034.

(221) Halouani, H.; Dumazet-Bonnamour, I.; Duchamp, C.; Bavoux, C.; Ehlinger, N.; Perrin, M.; Lamartine, R. Synthesis, conformations and extraction properties of new chromogenic calix[4]arene amide derivatives. Eur. J. Org. Chem. 2002, 4202-4210.

(222) Dieleman, C. B.; Matt, D.; Jones, P. G. Arranging phosphoryl ligands on a calixarene platform. J. Organomet. Chem. 1997, 545, 461-473.

(223) Yaftian, M. R.; Burgard, M.; Matt, D.; Dieleman, C. B.; Rastegar, F. Solvent extraction of the rare-earth metal ions by a cone-shaped calix[4]arene substituted at the lower rim by four -CH2P(O)Ph2 ligands. Solvent Extr. Ion Exch. 1997, 15, 975-989. 138

(224) Talanova, G. G.; Hwang, H. S.; Talanov, V. S.; Bartsch, R. A. Calix[4]arenes with hard donor groups as efficient soft cation extractants. Remarkable extraction selectivity of calix[4]arene n-(x)sulfonylcarboxamides for Hg-II. Chem. Commun. 1998, 1329-1330.

(225) Alpoguz, H. K.; Memon, S.; Ersoz, M.; Yilmaz, M. Transport of metals through a liquid membrane containing calix[4]arene derivatives as carrier. Sep. Sci. Technol. 2002, 37, 2201-2213.

(226) Talanov, V. S.; Talanova, G. G.; Gorbunova, M. G.; Bartsch, R. A. Novel cesium-selective, 1,3-alternate calix[4]arene-bis(crown-6-ethers) with proton-ionizable groups for enhanced extraction efficiency. J. Chem. Soc., Perkin Trans. 2 2002, 209-215.

(227) Bozkurt, S.; Karakucuk, A.; Sirit, A.; Yilmaz, M. Synthesis of two calix[4]arene diamide derivatives for extraction of chromium(VI). Tetrahedron 2005, 61, 10443-10448.

(228) Tu, C.; Surowiec, K.; Bartsch, R. A. Efficient divalent metal cation extractions with di-ionizable calix[4]arene-1,2-crown-4 compounds. Tetrahedron 2007, 63, 4184-4189.

(229) Malone, J. F.; Marrs, D. J.; McKervey, M. A.; O'Hagan, P.; Thompson, N.; Walker, A.; Amaud-Neu, F.; Mauprivez, O.; Schwing-Weill, M. J.; Dozol, J. F.; Rouquette, H.; Simon, N. Calix[n]arene phosphine oxides. A new series of cation receptors of extraction of europium, thorium, plutonium, and americium in nuclear waste treatment. J. Chem. Soc., Chem. Commun. 1995, 2151-2153.

(230) Arnaud-Neu, F.; Browne, J. K.; Byrne, D.; Marrs, D. J.; McKervey, M. A.; O'Hagan, P.; Schwing-Weill, M. J.; Walker, A. Extraction and complexation of alkali, alkaline earth, and f-element cations by calixaryl phosphine oxides. Chem. Eur. J. 1999, 5, 175-186.

(231) Yaftian, M. R.; Taheri, R.; Matt, D. Lower-rim polyphosphorylated calix[4]arenes. Their use as extracting agents for thorium (IV) and europium (III) ions. Phosphorus, Sulfur Silicon Relat. Elem. 2003, 178, 1225-1230.

139

(232) Choppin, G. R. R., J. Treatment of Spent Nuclear Fuel. In Radiochemistry and Nuclear Chemistry; 1st ed.; Pergamon Press Ltd.: Oxford, 1980.

(233) Arduini, A.; Casnat, A. Macrocycle Synthesis: A Practical Approach.; Oxford University Press: Oxford, 1996, 147-149.

(234) Gutsche, C. D.; Dhawan, B.; Levine, J. A.; No, K. H.; Bauer, L. J. Calixarenes-9 - Conformational isomers of ethers and esters of calix[4]arenes. Tetrahedron 1983, 39, 409-426.

(235) McOmie, J. F. W.; Watts, M. L.; West, D. E. Demethylation of aryl methyl ethers by boron tribromide. Tetrahedron 1968, 24, 2289-2292.

(236) Arduini, A.; Casnat, A. Macrocycle Synthesis: A Practical Approach.; Oxford University Press: Oxford, 1996, 159-160.

140