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Yttrium amidate complexes : fundamental reactivity and applications in catalysis and polymerization Stanlake, Louisa Janet Easton 2008

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YTTRIUM AMIDATE COMPLEXES: FUNDAMENTAL REACTIVITY AND APPLICATIONS IN CATALYSIS AND POLYMERIZATION  by  Louisa Janet Easton Stanlake B.Sc. (Honours), University of Victoria, 2003  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY  in  The Faculty of Graduate Studies (Chemistry)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) October 2008 © Louisa Janet Easton Stanlake, 2008  Abstract Rare-earth complexes are attractive catalyst systems due to their low cost, low toxicity and high reactivity. Modular ligand sets are ideal for complex formation since the steric and electronic properties of the resultant metal complexes can be easily varied.  This thesis  explores the structure and reactivity of new yttrium amidate complexes, which combine the highly reactive metal with the modular amidate ligand set. mono(amidate)  yttrium  complexes  have  been  directly  A library of tris, bis and synthesized  from  yttrium  tris(trimethylsilyl)amidate and simple amide proligands. The tris(amidate) yttrium complexes are highly active initiators of ring-opening polymerization of -caprolactone, yielding some of the largest molecular weight values for poly(-caprolactone) reported. The initiation of this polymerization is proposed to be ligand initiated; however, a side-reaction is postulated where formation of a -caprolactone-enolate yttrium complex results in broad polydispersity values of the resultant polymers. The  bis(amidate)  yttrium  complexes  are  also  excellent  precatalysts  for  the  hydroamination of aminoalkenes. Simple modification to the amidate backbone to include electron-withdrawing groups was found to significantly enhance reaction efficiency. These catalysts can mediate cyclohydroamination with both primary and secondary amine containing substrates. The mono(amidate) yttrium complexes were also investigated as novel precursors for the synthesis of the elusive terminal yttrium imido complex.  Mixed anilido/amidate yttrium  complexes were synthesized in high yield and a-H abstraction and deprotonation reactions were attempted in the hopes of isolating a crystalline compound.  The addition of  11  monodentate and neutral donors was required for isolation and characterization of the key reactive intermediates. This new family of yttrium complexes has proven to be very successful in preliminary catalytic studies. The ease with which the complexes can be synthesized and their steric and electronic properties make these complexes ideal for further catalytic investigations.  É 111  Table of Contents Abstract  .  Table of Contents  ii iv  viii  List of Tables  x  List of Figures List of Abbreviations  xiv xviii  Foreword Acknowledgements  xix  Co-Authorship Statement  xx  Chapter 1. Amidates as Tunable Ligand Set for Group 3 Metals  1  1.1  Ligand Design for Group 3 Metal Catalysts  1  1.2  Non-cyclopentadienyl Ligand Systems for Group 3 Metals  2  1.3  Amidinate Complexes of Yttrium  5  1.4  Guanidinate Complexes of Yttrium  11  1.5  Salicylaldiminate and Dialkoxy-Diimino Complexes of Yttrium  14  1.6  Scope of Thesis  17  1.7  References  19  Chapter 2. Synthesis, Structure and Stability of Yttrium Amidate Complexes  26  2.1  Introduction  26  2.2  Amide Proligands  29  2.2.1  Introduction  29  2.2.2  Results and Discussion  30  Tris(amidate) Yttrium Complexes  31  2.3 2.3.1  Introduction  31  2.3.2  Results and Discussion  32  Bis(amidate) Yttrium Complexes  42  2.4 2.4.1  Introduction  42  2.4.2  Results and Discussion  43  2.5 2.5.1  2.6  Mono(amidate) Complexes of Yttrium Results and Discussion Comparison of Yttrium Amidate Complexes  49 49 55  iv  2.7  Summary and Conclusions  2.8  Experimental  .  59 61  2.8.1  Starting Materials and Reagents  61  2.8.2  Synthesis  62  2.9  References  78  Chapter 3. Yttrium Amidate Complexes as Effective Initiators for the Ring-Opening Polymerization of -Capro1actone 3.1  Introduction  81 81  3.1.1  Mechanistic Introduction  86  3.1.2  Scope of Chapter  89  Yttrium Amidate Complexes as Initiators  3.2  Results and Discussion  3.2.1  90 90  3.2.1.1  Comparison of Tris, Bis and Mono(amidate) Complexes  91  3.2.1.2  Effect of Monomer to Initiator Ratio  96  3.2.1.3  Effect of Amidate Ligand on Initiator  98  3.2.1.4  Effect of Temperature on Initiation  3.3  Mechanistic Investigations  101 104  3.3.1  Results and Discussion  104  3.3.2  Mechanistic Investigation Summary  115  3.4  Conclusions  116  3.5  Experimental  118  3.5.1  Starting Materials and Reagents  118  3.5.2  Synthesis  119  3.6  References  122  Chapter 4. Yttrium Amidate Complexes as Effective Precatalysts for the Cyclohydroamination of Aminoalkenes 4.1 4.1.1 4.2  Introduction Scope of Chapter Yttrium Amidate Complexes as Precatalysts  128 128 132 133  4.2.1  Results and Discussion  133  4.2.2  Summary  145  V  4.3  Conclusions  .145  4.4  Experimental  146  4.4.1  Starting Materials and Reagents  146  4.4.2  Synthesis  147  4.5  References  Chapter 5. Yttrium Amidate Complexes as Imido Precursors  148 152  5.1  Introduction  152  5.2  Anilido Complexes  156  5.2.1  Introduction  156  5.2.2  Results and Discussion  157  5.3  Attempted ct-H Abstraction Routes to Imido Complexes  164  5.4  Attempted Deprotonation Routes  170  5.5  Conclusions  174  5.6  Experimental  175  5.6.1  Starting Materials and Reagents  175  5.6.2  Synthesis  176  5.7  References  Chapter 6. Conclusions and Future Work  181 183  6.1  Summary and Conclusions  183  6.2  Future Work  184  6.2.1  Yttrium Amidates as Polymerization Initiators for other Oxygen-containing  Monomers  184  6.2.2  Intermolecular Hydroamination  185  6.2.3  Amidate Complexes as Imido Precursors  187  6.2.4  Yttrium Amidates as Atomic Layer Deposition Precursors  188  6.2.5  Imidates (O,N,O chelate) as a Ligand Set for Rare Earths  189  6.3  Summary  192  6.4  Experimental  193  6.4.1  Starting Materials and Reagents  193  6.4.2  Synthesis  193  6.5  References  197  vi  Appendix I  .199  Appendix 11.201 Appendix III  202  vii  List of Tables  Table 2.2.  (A) and angles (°) for complex 2.17 Selected bond lengths (A) and bond angles (°) for complex 2.18  39  Table 2.3.  Selected bond lengths and angles for complex 2.24, and 2.25  48  Table 2.4.  Selected bond lengths and bond angles for complex 2.27  54  Table 2.5.  Selected bond lengths and bond angles for complex 2.28  55  Table 2.6.  Comparison table of tris, bis and mono(amidate) complexes 2.18, 2.24 and  Table 2.1.  34  Selected bond lengths  2.27  56  Table 3.1.  Comparison of yttrium initiators for the ROP of 8-caprolactone  85  Table 3.2.  Comparison of initiators for the ROP of-caprolactone using a [M]/[I] of 225. 93  Table 3.3.  Summary of ring-opening polymerization of -capro1actone for initiator 3.19..  97 Table 3.4.  Comparison of initiator ability for the ROP of -capro1actone for tris(amidate) complexes 3.23, 3.24, 3.25 and 3.26 using a [M]/[I] of 225  Table 3.5.  Comparison of initiator ability for the ROP of -caprolactone at 0 °C for tris(amidate) complex 3.19  Table 3.6.  101  102  Comparison of initiator ability (225:1 [M]/{I]) for the ROP of E-caprolactone at 0 °C for tris(amidate) complex 3.19, the -capro1actone complex 3.27, and the proposed enolate complex 3.28  114  Table 4.1.  Hydroamination of 4-pentenylamine (4.6)  131  Table 4.2.  Hydroamination of 2,2-diphenyl-4-pentenylamine (4.1)  134  Table 4.3.  Hydroamination of various aminoalkenes using bis(amidate) complexes 4.8, 4.9and4.1O  Table 4.4.  135  Hydroamination of aminoalkenes with terminal substituents using bis(amidate) complexes 4.8, 4.9 and 4.10  138  Table 4.5.  Hydroamination of 2-allyl-2-methyl-4-pentenylamine (4.29)  140  Table 4.6.  Hydroamination using complexes 4.11 and 4.12 as precatalysts (10 mol%).143  Table 5.1.  Selected bond length and bond angles for the solid-state molecular structure of 5.16  163 viii  Table 5.2.  Selected bond length and bond angles for the solid-state molecular structure of 5.18  Table 6.1.  Selected bond lengths  167  (A) and angles (°) for complex 6.12  191  ix  List of Figures Figure 1.1.  The cobalt ammine coordination complex proposed by Werner  Figure 1.2.  Selected examples of ligands that have been used in yttrium complex  1  synthesis. (R = aryl or alkyl substituent)  4  Figure 1.3.  Synthesis of selected amidinate yttrium complexes  6  Figure 1.4.  Synthesis of yttrium amidinate complexes with either a bridging amidinate or amido donor  8  Figure 1.5.  Hydrosilylation using complexes 1.13 as catalyst  9  Figure 1.6.  Isoprene polymerization using amidinate yttrium complex 1.14  10  Figure 1.7.  Lactone ring-opening polymerization examples  10  Figure 1.8.  Synthesis of selected guanidinate yttrium complexes  12  Figure 1.9.  Synthesis of yttrium hydrido complex supported by guanidinate ligands  13  Figure 1.10.  ROP of lactones using guanidinate supported yttrium complexes  14  Figure 1.11.  Synthesis and reactivity of yttrium salicylaldiminate complexes  15  Figure 1.12.  Synthesis of fluorous dialkoxy-diimino yttrium complex 1.35  16  Figure 1.13.  Lactide ring-opening polymerization using complex 1.35  16  Figure 2.1.  N-containing ancillary ligand sets  26  Figure 2.2.  Isocyanate insertion into a En-C bond  28  Figure 2.3.  Synthesis of amide proligands  30  Figure 2.4.  ORTEP of 3 Ph) (2.17) with the probability ellipsoids ) [Y(tBu{O,N](CH 2 ] drawn at the 50% level  33  Figure 2.5.  Synthesis of tris(amidate) complexes  35  Figure 2.6.  ORTEP diagram of the solid-state molecular structure of Ph) (2.18) with the probability ellipsoids drawn at [(THF)Y(Nap[O,N](iPr) 2 ] 3 the 50% level  Figure 2.7.  39  Synthesis of complex 2.23 and ball and stick representation of molecular solid-state structure of complex 2.23  41  x  Figure 2.8.  ‘H NMR spectrum (from  6.0 ppm to 9.5 ppm) in C D of crude product after 6  synthesis of complex 2.20 in THF at room temperature  44  Figure 2.9.  Synthesis of bis(amidate) complexes  45  Figure 2.10.  ORTEP structure of complex 2.24 and 2.25 with the probability ellipsoids  drawn at the 50% level  48  Figure 2.11.  Synthesis of mono(amidate) complexes  50  Figure 2.12.  ORTEP structure of complex 2.27 and 2.28, with the probability ellipsoids drawn at the 50% and 30% level, respectively  54  Figure 3.1.  Ring-opening polymerization of -caprolactone  81  Figure 3.2.  Proposed mechanism for the ring-opening polymerization of -caprolactone. 82  Figure 3.3.  Initiators for -caprolactone ring-opening polymerization  84  Figure 3.4.  Known yttrium complexes of varying ligands that have been used as initiators for -caprolactone ROP  85  Figure 3.5.  Initiation of ROP of -caprolactone using complex 3.7  87  Figure 3.6.  Samarium tris(13-diketiminate) complex 3.14  87  Figure 3.7.  Initiation of -caprolactone ROP using Zr(acac) 4 (3.15)  88  Figure 3.8.  Tris, bis and mono(amidate) complexes of yttrium  90  Figure 3.9.  Intermolecular and intramolecular transesterification reactions for chain 94  termination with poly(E-caprolactone) Figure 3.10.  M values of poly(-caprolactone) at different [Ml/[I] ratios using complex 3.19 as the initiator at room temperature  97  Figure 3.11.  Yttrium amidate complexes containing varying amidate backbones  99  Figure 3.12.  M values of poly(-caprolactone) at different [Mi/El] ratios using complex 3.19 as the initiator at 0 °C  Figure 3.13.  103  ) of poly(-caprolactone) using 3 ‘H NMR (600 MHz) spectrum (in CDC1 initiator 3.19 at 0 °C with 10:1 [Mi/Fl] ratio  105  xi  Figure 3.14.  Yield of polymer during ROP of -caprolactone using initiator 3.19 ([M]/[I]  =  225,0°C)  106  Figure 3.15.  Formation of monodentate 8-caprolactone yttrium complex 3.27  107  Figure 3.17.  Possible reaction after second equivalent of -caprolactone is added  109  Figure 3.19.  Formation of 2-(hydroxyphenylmethyl)cyclohexan-1-one (3.32) and 2benzylidenecyclohexanone (3.33)  Figure 3.20.  112  Proposed mechanism for 8-caprolactone ROP using complex 3.19 as initiator. 114  Figure 4.1.  Examples of inter- and intramolecular alkene hydroamination  128  Figure 4.2.  G-Bond insertion mechanism for hydroamination of aminoalkenes using rareearth catalysts  130  Figure 4.3.  Known yttrium complexes used as catalysts for hydroamination  131  Figure 4.4.  Yttrium amidate complexes as precatalysts for cyclohydroamination of aminoalkenes  133  Figure 4.5.  cr-Bond insertion step with terminal substitution on aminoalkene  137  Figure 4.6.  Preliminary screen of secondary amines for hydroamination  139  Figure 4.7.  Intermolecular hydroamination using precatalyst 4.9  141  Figure 4.8.  Hydroamination of 1-methyl-4-pentenylamine (4.31)  144  Figure 5.1.  Examples of imido complexes  152  Figure 5.2.  Formation of lanthanide imido complex 5.4  153  Figure 5.3.  Synthesis of Yb bridging imido complexes 5.5 and 5.6  154  Figure 5.4.  Postulated scandium imido intermediate  155  Figure 5.5.  Anilido phosphinimine (5.9) and amino phosphine (5.10) supported yttrium bis(anilido) complexes  156  Figure 5.6.  Synthesis of aryl/amidate yttrium complex 5.13  157  Figure 5.7.  Synthesis of mixed amidate/anilido complex 5.16  160  Figure 5.9.  ORTEP diagram of the solid-state molecular structure of 5.16 with the probability ellipsoids drawn at the 50% level  162  Figure 5.10.  Synthesis of bipy complex 5.18  164  Figure 5.11.  ORTEP diagram of the solid-state molecular structure of 5.18 with the probability ellipsoids drawn at the 50% level  166 xii  Figure 5.12.  Synthesis of bis(anilido) yttrium complex 5.19  168  Figure 5.13.  ‘H NMR spectrum (600 MHz) of complex 5.19 in C D 6  169  Figure 5.14.  Insertion reaction into proposed imido complex  173  Figure 6.1.  Tris(amidate) yttrium complex 6.1  185  Figure 6.2.  Structure of rac-lactide (6.2)  185  Figure 6.3.  Potential new amide proligand  186  Figure 6.4.  Possible alkene sources for intermolecular hydroamination  187  Figure 6.5.  Amide proligands introduced in Chapter 2  189  Figure 6.6.  Synthesis of imide proligands 6.10 and 6.11  189  Figure 6.7.  Synthesis of imidate complex 6.12  190  Figure 6.8.  Solid-state molecular structure of complex 6.12  191  xiii  List of Abbreviations [M]/[I]  Monomer to initiator ratio Approximately  >  Greater than  O  Degree symbol  o  C  Degrees Celsius Transition state  A  Angstrom  acac  Acetylacetonate  Anal.  Analysis  Ar  Aryl  atm  Atmosphere  b  Broad (NMR or IR spectrum)  bipy  2,2’-Bipyridine  Calcd.  Calculated  cat.  Catalyst  1 cm  Wavenumber  cony.  Conversion  Cp  Cyclopentadienyl  Cp*  Pentamethylcyclopentadienyl  Cp’  Methylcyclopentadienyl  Cy  Cyclohexyl Delta, chemical shift  d  Doublet  DCM  Dichloromethane  z\G  Gibbs Free Energy  Dipp  Diisopropylphenyl  Dmp  Dimethylphenyl  dr  Diastereomeric ratio  E  Energy  xiv  8  Molar absorptivity  El  Electron impact  equiv.  Equivalents  g  Gram  gem  Geminal  GPC  Gel permeation chromatography  h  Hours  HSAB  Hard-Soft Acid-Base Theory  Hz  Hertz,  I  Initiator  iPr  iso-propyl  IR  Infrared  J  Coupling constant  K  Kelvin  kcal  Kilocalorie  kJ  Kilojoules  L  Ligand  LLCT  Ligand to ligand charge-transfer  LLS  Laser-light scattering  max 2  Maximum wavelength  LMCT  Ligand to metal charge-transfer  Ln  Lanthanide  m  multiplet (NMR spectroscopy)  M  Metal  M  Molar  M  Metal  mlz  Mass to charge ratio  M  Molecular ion  Me  Methyl  mg  Milligrams  MHz  Megahertz  xv  mm  Minute  mL  Millilitres Microlitre  MLCT  Metal-ligand charge transfer  mmol  Millimole Number-average molecular weight  mol  Mole  mol%  Mole percent  MS  Mass spectrometry Weight-average molecular weight  n  Number (integer)  v  Frequency  Nap  Naphthyl  n-Bu  n-Butyl  nm  Nanometre  NMR  Nuclear magnetic resonance  NR  No reaction  o  Ortho  ORTEP  Oakridge Thermal Ellipsoid Program  p  Para  P  Polymer  PDI  Polydispersity Index  Ph  Phenyl  ppm  Parts per million  R  Aryl or alkyl substituent  R  Rectus (Configurational)  RDS  Rate-determining step  ROP  Ring-opening polymerization  rt  Room temperature  s  Strong (JR spectrum)  xvi  s  Singlet (NMR spectroscopy)  sec-butyl  Secondary-butyl  sh  Sharp, Shoulder (JR spectrum)  t  Triplet (NMR spectroscopy)  tBu  tert-Butyl  temp.  Temperature  THF  Tetrahydrofuran  TPPO  Triphenylphosphine oxide  TM  Trademark  w  Weak (JR spectrum)  Xy  Xylide  xvii  Foreword The work reported in this thesis involves the investigation of novel yttrium amidate complexes. This thesis is a manuscript-based thesis, where each chapter is considered as a stand-alone document.  Consequently, there will be some reiteration of introductory  information within separate chapters. Furthermore, there are several compounds that are used throughout the entire thesis; however, numbering is consistent within each chapter and therefore some compounds will be linked to more than one number in this thesis.  xviii  Acknowledgements First and foremost I would like to thank Dr. Laurel Schafer for all the support over the years. I truly appreciate that she always treated me like an equal, and always made me believe in my abilities. The Schafer lab is one of the best environments that I have ever worked in and I owe great gratitude to the Schafer group members, past and present.  I  especially have to thank Dave for the great chemistry discussions, the introduction into quality music, and for spending the time to read this thesis. I would like to thank the mechanical shop, the electronics shop, the glassblower, the NMR staff and the analytical staff; especially Ken Love for spending countless hours helping fix a troublesome glovebox. I would also like to thank Brian Patrick, Rob Thomson, and Neal Yonson for assistance with X-ray crystallography. Also, thank you to the chemistry department and MEC for funding during my Ph. D. studies. Girlfriends, wine, and ANTM are a great stress reliever, so thanks to “team models” (Ali, Bronwyn, Courtney, Jenn, Jackie and Shiva) for taking the edge off, and always being there over the years. Thanks to Howie, for always making your “appearance” and to Mark, for always keeping me entertained. I would like to thank my parents, who were right when they told me that graduate school would be the best time of my life. I also appreciate their great support, financially and psychologically throughout my Ph. D. I have to thank my brother and his family, Mel and K Dub, for believing in me. Also, thank you to Jesse, for all your love and support and for trying really hard to understand what I do.  xix  Co-Authorship Statement All of the work contained herein was performed by Louisa J. E. Stanlake, except for the synthesis of compound 2.17 in Chapter 2, which was synthesized by J. David Beard. Consequently, J. David Beard is a co-author on the published paper, Rare-Earth Amidate Complexes. Easily Accessed Initiators For -Capro1actone Ring-Opening Polymerization. Louisa J. E. Stanlake, J. David Beard and Laurel L. Schafer, Inorg. Chem. 2008, 47, 8062. Laurel L. Schafer is the principle investigator for this work and assisted with identification and design of the research program, data analyses, and manuscript preparation; however, she did not assist in any experimental research within this thesis.  xx  Chapter 1. Amidates as Tunable Ligand Set for Group 3 Metals 1.1  Ligand Design for Group 3 Metal Catalysts In 1893 Alfred Werner postulated the “coordination theory” for bonding to explain the  structure of a cobalt ammine complex, 3 •6NH CoC1 .  He proposed an octahedral cobalt  complex with six NH 3 “ligands” at the vertices, and the chloride groups as counter ions (1.1, Figure 1.1). This theory garnered him the Nobel Prize in Chemistry in 1913. Since then, the term “ligand” has been synonymous with coordination chemistry.” 2 3+  1.1  Figure 1.1. The cobalt ammine coordination complex proposed by Werner. A ligand (L) is any molecule or atom that is bound to a central metal centre. A ligand can be monodentate, bridging or chelating. A chelating ligand has more than one atom bound to a metal centre. The bonding to the metal can be more ionic, or more covalent in nature depending upon the metal and ligands involved. Ligands that contain “hard” atoms, such as oxygen, tend to bind to hard metal centres, while the opposite is true for low oxidation state late transition metals that are best described as “soft” metals. These trends are in accordance 3 with hard-soft acid base (HSAB) theory. Group 3 metals are hard metals and tend to bind hard donors. Furthermore, group 3 catalysts are almost exclusively in the 3+ oxidation state, and are best described as having an ionic bonding motif. 46 This 3+ oxidation state is the major difference between group 3 metals and the rest of the transition metal block. Most transition metals have a range of  1  oxidation states, whereas group 3 only exhibits the +3 (d°) oxidation state. Yttrium is very similar in reactivity to the lanthanide metals and is often referred to as a “rare-earth” (a term used to include group 3 and the lanthanide metals in one group). Yttrium has a similar ionic radius to some lanthanides (for example, Y 3 1.00  A, Lu 3  0.977  1.04  A, Nd 3  =  1.12  A, Gd 3  1.07  A, Er 3  7 and is frequently included in reviews of lanthanide chemistry. A),  =  8-13  Group 3 or rare-earth complexes are very attractive catalyst systems due to their low toxicity, 4 and are often used in catalysis and are used in reactions such low cost and high reactivity,’ 6 hydrosilylation,’ ’ 5 8 aldol condensation’°” as well as ’ 6 as, hydroamination,’ 5 hydrogenation, 2 ’ 20 polymerization of olefins,’ 9 lactones and lactides. Like the lanthanides, yttrium often has very high coordination numbers, up to  92224  Complex formation and reactivity between yttrium and the smaller lanthanides also are very similar. However, one significant difference is that yttrium is diamagnetic, which renders NMR spectroscopy useful in the ch aracterization of compounds, and the monitoring of catalytic  reactions.  Early research into yttrium  complexes  was  dominated by  cyclopentadienyl complexes) 534 but easily accessed and modular ligand sets are becoming 25 In this introduction only easily more common for the optimization of catalytic activity. varied complexes of yttrium that have been exploited in various catalytic applications will be reviewed.  1.2  Non-cyclopentadienyl Ligand Systems for Group 3 Metals Yttrium complexes containing cyclopentadienyl-based ancillary ligands are very  2658 The chemistry involving these complexes has been explored extensively for ’ 8 common. 57 and ’ 38 29 polymerization, 3 4 5 0 but also polar monomer polymerization, 9 2 mainly olefin ’  2  other catalytic processes such as ’ 42 and hydroamination.’ 28 hydrosilylation ° 5 5 However, the cyclopentadienyl ligand is not a modular ligand set, and can be synthetically difficult to functionalize.  Due to limited synthetic flexibility, ligand sets that allow for easy  modification of steric and electronic properties are attractive in group 3 complex synthesis. An auxiliary ligand that can be varied for tunable reactivity in the resultant complex is an ideal feature for catalyst design. There is a wide variety of ligand sets that are used in the 5962 synthesis of yttrium complexes that include monodentate ancillary ligands such as amido, 6365 bidentate (vide infra), tridentate and tetradentate ligands. alkoxides, 6674 modular ligand sets are common and include aminotroponimates (1 3)78  13 -diketiminates  Bidentate  aminotroponates  (1 •4),7986 acetylacetonates (1 •5)879o bisoxazolinates (1.6)9192  alkoxydimethylsilylamides (1  •7),9394  phosphoramidates (1  amidinates (1  guanidinates (1.1O),hb0h18 and salicylaldiminates (1.11)80h19122 (Figure 1.2).  9),981 09  This thesis  explores the synthesis and reactivity of yttrium amidate (1.12) complexes; however, up until now, these complexes have never been systematically explored for their reactivity in either stoichiometric or catalytic investigations.  3  R IY  R {YR  1.9  2 Y(PR  R IYNR2  1.10  R Y(  1.11  (YR 1.12  Figure 1.2. Selected examples of ligands that have been used in yttrium complex synthesis. (R = aryl or alkyl substituent)  The ligands shown in Figure 1.2 are all monoanionic ligand sets and many of these ligand sets are modular, where the R groups can be easily changed during the synthesis of the ligand. Most of these ligand sets use N and 0 donors, because of the desirable hard-hard match with yttrium. Furthermore, examples of four (1.7, 1.8, 1.9, 1.10 and 1.12), five (1.2 and 1.3) and six-membered (1.4, 1.5, 1.6 and 1.11) rings are observed in the yttrium metallacycles formed upon chelation. T here is a, vast number of ligand sets and recent 23 24 9 Yttrium amidinate (1.9), guanidinate (1.10) 5 10 available. 1 2 ’ reviews of this field are 1 and salicylaldiminate (1.11) complexes are known and display important structural similarities to the proposed amidate complexes. Previous to the work of this thesis, there were no examples of yttrium amidate complexes for comparison; however, these similar ligand sets provide useful benchmarks for reactivity trends. In particular, the amidinate and  4  guanidinate ligand sets have been studied for yttrium complex formation, and provide useful comparisons to the work presented in this thesis because they have a similar binding motif to the amidate. The salicylaldiminate ligand will also be reviewed because it is a popular N,O chelate for yttrium, and shares the asymmetric N,O donor atoms of the proposed amidate ligand.  1.3  Amidinate Complexes of Yttrium Although amidinate complexes of yttrium can be formed in situ, by insertion of a  carbodiimide into a reactive Y-C bond,’° 8 a direct route where the amidinate lithium salt is first isolated is more commonly used. The amidinate ligand is directly synthesized from a carbodiimide (R-N=C=N-R) (Figure 1.3) and a lithium reagent, alkyl, aryl or silyl. The amidinate salt can be reacted directly in a salt metathesis reaction with yttrium trichloride. The amidinate salt can also be protonated with water to form the amidine to yield the corresponding proligand for a protonolysis reaction with various yttrium starting materials to give the yttrium amidinate complexes. The protonolysis route was used in the synthesis of mono(amidinate) complexes 1.13 and 1.15. These complexes were fully characterized and explored for their application in olefin polymerization 99 (for complex 1.13) and 3 (for complex 1.15) (vide infra). Furthermore, Hessen and coworkers found hydrosilylation’° that the ligand in complexes 1.13 and 1.15 is able to support cationic complexes for a range of group 3 and lanthanide metals (Sc, Lu, Y, Gd, Nd, and La).’°°  5  R—NCN--R RLi  R-NN-R  0 2 H Salt Metathesis 3 YCI  R /L R_j N—R  Protonolysis S 2 Y(CH ( ) 3 THF) IMe or 4 CsH 2 Y(o-CH N ,//  1.14  1.13  iPriPr  tBu  3 /S1Me  tBu  3 \SiMe  (Me3Si<  L  iPrj_iPr  1.15  *  /2  1.16  Figure 1.3. Synthesis of selected amidinate yttrium complexes.  The salt metathesis route was used in the formation of yttrium amidinate complexes 1.14 and 1.16. In the case of complex 1.16, the bis(amidinate)mono(chloro) complex was first synthesized and then used in a metathesis reaction with phenoxide salt to form complex  6  1.16.98  Both complexes 1.14 and 1.16 have been explored for the ring-opening  polymerization of lactones (vide infra). 5 ”° 98 Hessen and coworkers have synthesized variations of tethered amidinate ligands for complex synthesis with yttrium (Figure  1.4).101b02  The tethered bis(amidinate) ligand in  complex 1.18 changes the orientation of the amidinate groups in the resultant complex giving it a more open metal coordination sphere in comparison to un-tethered bis(amidinate) 2 Shen and coworkers’° complexes.’° 7 used complex 1.18, first synthesized by Hessen and coworkers, to form the bridged yttrium dimer 1.19. This complex was studied for its ability to initiate the ring-opening polymerization of -caprolactone (vide infra). An alternative tethered ligand motif, the amino-amidinate ancillary ligand in complex 1.20 gives additional electronic stabilization to a highly electropositive metal centre.’ ’ 0  Without this extra  stabilization, a mono(amidinate) complex was difficult to synthesize due to ligand redistribution  7  SiN 3 Me +.  Li  2 equiv. PhCN  3 NSiMe +.  Li  N N -)>-—Ph Ph—<( L:i N N Si’ 3 Me ‘SiMe 3 1.17  qiv. 1.17  Ph  Ph  N NV Ph—K(——Y——)>---Ph N / N SI’ CI THF iMe 3 Me 3 1.18  (THF) YCI 3  NN Si 3 Me  /c  Me S 3 I-N )—N 7 Ph  3 SiMe ;;Y\ )>—Ph Ph—<( 3 J\JSIMe N N 3 Me SiMe Si 3 N—J\ Ph 1.19  /  N N  Li  1. 3 (THF) YCI ] 2 ) 3 2. 2 equiv. Li[CH(SiMe  Si’ 3 Me  N / ph_(___y__CH(SMe 2 ) 3 Si’ 3 Me  2 ) 3 CH(SiMe 1.20  Figure 1.4. Synthesis of yttrium amidinate complexes with either a bridging amidinate or  amido donor.’°”° 2  These selected examples illustrate that mono, bis and tris(amidinate) complexes of yttrium can be synthesized directly with varying substituents. Tethered amidinate ligands can be used to isolate either monomeric or dimeric species. Furthermore, by modifying the amidinate ligand to include an amino donor, isolation of a solvent free alkyl yttrium complex is possible (complex 1.20).  The yttrium amidinate complexes presented here have been  studied for hydrosilylation, as well as olefin and ring-opening polymerization. Hydrosilylation is the addition of an Si-H bond across a C-C unsaturation and can be 6 mediated by a wide range of transition and lanthanide metals including yttrium complexes.’ 18  For example, only 2 mol% of mono(amidinate) bis(alkyl) yttrium complex 1.13 (Figure  1 •5)1 in the reaction of phenylsilane with a variety of alkenes (R  =  butane, hexane,  8  cyclohexyl, cyclohexene, tert-butyl) results in nearly 100% yield of the linear hydrosilylation product in less than 5 minutes at 23 °C. Complex 1.13 has a notably higher turnover rate (> 600 h’) for this transformation when compared to other rare-earth or early transition metal catalysts. 103  Ph 2 RSiH +  PhSiH  2 mol°/ 113 ,23°C D 6 C  Linear product  +  R  —  T  Branched product  Ph 2 SiH  <5 mm, 100% conversion > 99% linear product  3 Figure 1.5. Hydrosilylation using complexes 1.13 as catalyst.’°  The polymerization of substituted alkenes, such as isoprene, is not as well-developed for 09 Interestingly, alkyl amidinate complexes rare-earth catalysts as ethylene polymerization.’ 9 Complex 1.14 can be activated by have been explored for the polymerization of isoprene.’° CI[B(C and reacted with isoprene to give greater than 90% selectivity of iso-3,43 [Ph ] 4 ) 5 F 6 poly(isoprene). This polymerization at room temperature results in 100% yield of iso-3,4poly(isoprene), and narrow polydispersity values (1.30). Interestingly, if complex 1.14 is first reacted with trimethylaluminum and then 6 C][B(C is added, polymerization of 3 [Ph 1 4 ) 5 F isoprene results in greater than 90% selective formation of cis-1,4-poly(isoprene).  This  polymerization at room temperature also results in 100% yield, and narrow polydispersity values (1.50  —  1.70).  By a small change in the activation step, two different types of  poly(isoprene) can be selectively formed using the same yttrium amidinate complex.  9  3 1.14+AIMe CJ[B(C 3 [Ph ] 4 ) 5 F 6  cis- 1 ,4-poly(isoprene)  1.14 isoprene  C][B(C 3 [Ph ] 4 ) 5 F 6  n iso-3,4-poly(isoprene)  Figure 1.6. Isoprene polymerization using amidinate yttrium complex 1.14.109  Another popular application of rare-earth complexes is the initiation of the ring-opening polymerization (ROP) of lactones. The most used monomers are lactide and s-caprolactone, which both produce biodegradable polyester after ROP.  Phenoxide amidinate yttrium  complex 1.15 and bridging amidinate yttrium dimer 1.19 have been explored for the ROP of D,L-lactide and s-caprolactone, respectively (Figure 1  7)98107  Both complexes give high-  yielding polymer with very high molecular weights and moderate polydispersity indices. A more detailed overview of ROP using a range of yttrium complexes will be presented in Chapter 3.  1 equ.BnH  o  25°C,6Omin  D, L-Iactide  a  -caproIactone  PoIy(Iactide)  2500 [M]/[I] 25 0 C 30 mm  M =2,30,000 PDI = 2.20 PoIy(6-caprolactone)  Figure 1.7. Lactone ring-opening polymerization examples.  Amidinate complexes of yttrium can be synthesized in two different ways starting from carbodiimides, salt metathesis or protonolysis.  Selective formation of mono, bis or tris  10  amidinate yttrium complexes is readily achieved through control of reaction stoichiometry. Modifications to form tethered amidinates are reported to give a range of monomeric and bridged bimetallic complexes. The amidinate complexes of yttrium have been used in multiple catalytic applications including, hydrosilylation of alkenes, polymerization of isoprene and the ROP of lactones. These results demonstrate the usefulness of a readily accessed, modular, ancillary ligand set for yttrium. Furthermore, they illustrate that 4-membered metallacyclic complexes formed upon chelation are sufficiently robust for a range of catalytic reactions.  1.4  Guanidinate Complexes of Yttrium The guanidinate ligand is very similar to the amidinate ligand, except for the addition of a  2 group to the backbone (Figure 1.8). The synthesis starts from a carbodiimide molecule, NR and a lithium amide reagent is added to obtain the guanidinate lithium salt. Synthesis of complexes is most often performed via the salt metathesis route.  It is evident that the  guanidinate ligand can support different types of yttrium complexes including chloro (1.21),h14h15  aryl (1.22),h14 alkyl (1.23),” alkoxide (1.24)110 and amido (1.25) complexes. 116  11  F L1NR 2 rJ R  R N N—K(-I 2 R’ FJ R  ‘ci  Pr  / R—Y ))—N(SiMe 2 ) 3 \iPr 1.21 R=CI 1.22 R Ph 1.23 R = tBu  /2  1.24ROiPr 1.25 R = N1Pr 2  Figure 1.8. Synthesis of selected guanidinate yttrium complexes.  These complexes can be used as starting materials for a variety of catalytic investigations. For example, complex 1.21 can be used in a metathesis reaction to form an yttrium alkyl complex 1.26 (Figure 1.9). This alkyl complex can then be reacted with a hydride source to form the guanidinate supported yttrium hydrido complex  1.27.112  This is a rare example of a  well-characterized non-cyclopentadienyl hydrido complex of yttrium,” 2 and shows that the guanidinate ligand set is capable of providing the steric and electronic environment that is comparable to the cyclopentadienyl ligand.  Furthermore, preliminary experiments with  hydrido yttrium complex 1.27 show it can be used as a moderately active ethylene polymerization catalyst.” 2 As in the case of amidinate yttrium complexes, guanidinate yttrium complexes can be used in a vast range of catalytic reactions, including the ROP of lactones.  12  Complex 1.21  S1Me 2 LiCH  1.26  C 3 -SiMe S P 2 1H H h  Z27 ) 3 )N(SiMe  Si) 3 Me N 2 (  1.27  Figure 1.9. Synthesis of yttrium hydrido complex supported by guanidinate ligands.  Selected recent examples of ROP of D,L-lactide’ ° and E-caprolactone” 1 6 are shown in Figure 1.10. The alkoxide complex 1.24 produces poly(lactide) in high yield with narrow polydispersity values in mild conditions.  The amido complex 1.25 produces poly(c  caprolactone) in high yield with very large molecular weights. Interestingly, in comparison with amidinate yttrium complexes, guanidinate examples show reduced poly(lactide) polymer molecular weights yet comparable poly(-caprolactone) molecular weights. These selected examples provide a useful point of reference for comparing and contrasting the amidate yttrium complexes investigated here.  13  _______  D, L-Iactide  PoIy(Iactide)  0  /  1.25 1000 [M]/[I] 1500, 5 mm  \  -caproIactone  0  (1  o\  -  100%yield M = 2,430,000 PDI = 2.36  PoIy(e-caprolactone)  Figure 1.10. ROP of lactones using guanidinate supported yttrium complexes.  In Summary, guanidinate ligands are similar to the amidinate ligand set, but have -NR 2 group in the backbone.  Yttrium guanidinate complexes are typically synthesized via salt  metathesis and a wide range of bis(guanidinate) yttrium complexes can be synthesized, such as chloro, alkyl, aryl, alkoxide and amido species. Interestingly, yttrium hydrido complexes have been reported for this class of complexes. Another major application of guanidinate yttrium complexes is the ring-opening polymerization of selected lactones.  1.5  Salicylaldiminate and Dialkoxy-Diimino Complexes of Yttrium Another N,O-chelating ligand for yttrium chelation is the salicylaldiminate. This ligand  motif has the similar N,O-asymmetric binding motif to the amidate ligand. In contrast to the amidinate and guanidinate ligands, the salicylaldiminate ligand forms a 6-membered ring upon chelation, and has much less bulk close to the metal centre after binding (resulting from the binding of an 0 instead of NR group) than either amidinate or guanidinate complexes. The salicylaldiminate proligands can be synthesized from the condensation reaction between 25 Salicylaldiminate hydroxyl substituted benzaldehyde and substituted aniline compounds.’  14  _____ _____________  _  proligand 1.28 has been extensively used by Piers and coworkers for the synthesis of new yttrium salicylaldiminate compounds (Figure 1.11).”  2equiv.  SiMe 2 Y(CH P 2 (THF) 3 h)  2  LH  SIMe /—CH P 2 h 1.29  LH, 1.28  1.30 4  N  0  atm,>/  Ph  1 atm No reaction  ri  0  2equiv. Ph C=0 2 —  CN-ND  -  1.32  0u 1.31  H  excess —SiMe 3  N1:T  3 EESiMe  +  3 SiMe  19 Figure 1.11. Synthesis and reactivity of yttrium salicylaldiminate complexes.’  Bis(salicylaldiminate) mono(alkyl) yttrium complex 1.29 can easily be fonned via a protonolysis reaction.  Also, a tris(salicylaldiminate) yttrium complex (1.30) can be  synthesized in the same manner. A salicylaldiminate supported yttrium hydrido complex (1.31) can be formed directly from the yttrium alkyl complex and hydrogen gas. Hydrido  complex 1.31 did not catalyze the polymerization of ethylene, but did hydrogenate stoichiometric amounts of alkyne, and diphenylketone.  Notably, complex 1.31 is not  catalytic and was only investigated for stoichiometric chemistry.  15  A similar ligand set to the salicylaldiminate that has been recently synthesized is the dialkoxy-diimino  ligand  1.34  (Figure  1.l2).122126  In a similar reaction to the  salicylaldiminate proligand, the dialkoxy-diimino proligand 1.34 is synthesized from the 3 groups result condensation of f3-hydroxy ketones and a bridging primary diamine. The CF 122 and thus a in a tethered ligand where the tendency to form oligomers is reduced, monomeric yttrium complex 1.35 can be synthesized in high yield.  (THF) 3 ] ) 2 Y[N(SiHMe F C 3 -)-—OH C 3 F  HO—--CF 3 3 CF I .35  1.34  Figure 1.12. Synthesis of fluorous dialkoxy-diimino yttrium complex 1.35.  3 groups in complex 1.35 promote higher reactivity for The electron-withdrawing CF lactide polymerization (Figure 1.13). Complex 1.35 initiates the ROP of lactide obtaining poly(lactide) in high yield, with a narrow polydispersity value and is thought to be a living catalyst for the ROP of D,L-lactide.  20 D, L-Iactide  00,  60n  DI=13 PoIy(Iactide)  Figure 1.13. Lactide ring-opening polymerization using complex 1.35.  16  N,O-chelates such as salicylaldiminate and dialkoxy-diimino ligands have been shown to form yttrium complexes in high yield. Proligand 1.28 was used in the synthesis of bis-ligated and tris-ligated yttrium complexes, and bis(salicylaldiminate) yttrium complex 1.29 can be reacted with hydrogen gas to give a hydrido complex that can reduce silylalkyne and diphenyl ketone stoichiometrically.  The dialkoxy-diimino proligand 1.34 gives the  monometallic yttrium complex 1.35. This complex was found to be a controlled initiator for the ROP of lactide. Comparing the smaller amidate N,O-chelate with the salicylaldiminate reactivity trends in various catalytic and stoichiometric reactions provides insight into the effect of the metallacycle ring size.  1.6  Scope of Thesis Previous  work  on  yttrium  complexes  supported  by  arnidinate,  guanidinate,  salicylaldiminate and the dialkoxy-diimino ligands, show that these complexes can be used in a range of applications. However, previous to the work of this thesis, no yttrium amidate complexes have been directly synthesized using either salt metathesis or protonolysis routes. The amidate ligand (1.12, Figure 1.2) is similar in many ways to the presented ligand sets in that it would chelate to give a 4-membered metallacycle of yttrium (as in amidinate and guanidinate yttrium complexes) and it is an N,O-chelate as in salicylaldiminate and dialkoxy diimino complexes. The literature precedent established suggests that amidate ligands will be suitable for supporting reactive yttrium complexes. Furthermore, in the Schafer group, 127-13 1 amidate complexes of group 4 metals have been synthesized in high-yield.  In this thesis the extension of this work to yttrium, a group 3 metal, is investigated. Fundamental coordination modes. structure, bonding and stability investigations are  17  performed in the synthesis of novel tris, bis and mono(amidate) complexes of yttrium (Chapter 2). The catalytic applications of these yttrium amidate complexes will be explored in the ROP of E-caprolactone (Chapter 3) and the hydroamination reaction (Chapter 4). Finally, stoichiometric reactivity investigations in the pursuit of a terminal yttrium imido complex will also be presented (Chapter 5).  18  1.7  References  (1)  Marusak, R. A.; Doan, K.; Cummings, S. D. Integrated Approach to Coordination  Chemistry; John Wiley & Sons, Inc.: Hoboken, New Jersey, 2007, 1-21. 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A.; Schafer, L. L. Organometallics 2006, 25, 4069. (131) Li, C. Y.; Thomson, R. K.; Gillon, B.; Patrick, B. 0.; Schafer, L. L. Chem. Commun.  2003, 2462.  25  Chapter 2. Synthesis, Structure and Stability of Yttrium Amidate 1 Complexes 2.1  Introduction Substantial research with group 3 and lanthanide complexes containing ancillary nitrogen  donor ligands such as amido (2.1)’ 13-diketiminate (2.2),’ amidinate (2.3),’’ guanidinate (2.4),1824  and ureate  (2.5)25  ligand sets has been conducted (Figure 2.1).  These are all  attractive ligands that can be assembled using a modular strategy to vary steric and electronic properties.  M)R  M-NR2  2.1  2.2  2.3  MNR2  2.4  MNR2 MR  2.5  2.6  Figure 2.1. N-containing ancillary ligand sets.  The synthesis of discrete rare earth complexes can be difficult due to low energy ligand redistribution pathways. The high Lewis acidity of these rare earth metals, in combination with their larger radii means that synthetic approaches using multidentate ligands often 2628 Typically, the formation of discrete results in dimer formation or even higher aggregates. species is most commonly controlled by creating a sterically demanding ligand. Furthermore, facile modification of steric and electronic properties of the ancillary ligand of new complexes is desirable for tuning reactivity profiles. ‘A version of this has been published Stanlake, L. J. E., Beard, J. D. and Schafer, L. L. Inorg. Chern. 2008, 47, 8062-8068. Reproduced in part with permission from Inorg. Chem. 2008, 47, 8062-8068. Copyright 2008 American Chemical Society.  26  A similar ancillary ligand set to those shown in Figure 2.1 is the amidate ligand (2.6). Amidates have been largely overlooked as an auxiliary ligand set capable of providing selective metal complex reactivity.  The research presented here focuses on new high-  yielding preparative methods to access crystalline, discrete yttrium amidate complexes that will be investigated for catalytic activity. Due to the facile synthesis of organic amides, from acid chlorides and primary amines, the amide proligands can be easily varied for desired steric and electronic properties. Previous examples of amidate complexes of the rare-earth metals have been synthesized via isocyanate insertion into a reactive M-C bond of rare-earth alkyl complexes (Figure 2.2).2931 This preparative approach typically yields amidate bridged bimetallic complexes (2.7), which 30 have been fully characterized.  The corresponding tetrahydrofuran (THF) adduct (2.8)  could not be analyzed by X-ray crystallography, but was characterized by elemental analysis, mass spectrometry and JR spectroscopy. Moreover, a decomposition product of an attempted isocyanate insertion reaction led to the only previous report of a homoleptic lanthanide ° a Ho[(n-Bu)[OCN]Ph1 3 amidate complex, 3 complex, which was characterized by elemental 30 analysis and JR spectroscopy; no structural information was provided.  While the  isocyanate insertion method is well established, the requisite lanthanide alkyl starting materials are non-trivial to synthesize and handle and often result in complex or ill-defined species. Furthermore, this route has been typically exploited for the reactivity of M-C bonds, rather than using the resultant amidate complexes as potential tunable catalytic systems.  27  LnCI 2 Cp Cp’  =  n-Bu Li, -3O°C THF  C H CH  Ln(n-Bu)(TH F) 2 Cp PhCNO,-1O°C TH F  0—I  n-Bu  +THF n Ph Cp L 2 -THF Ln=Sm,Dy,Er 2.8  2.7  ° 3 Figure 2.2. Isocyanate insertion into a Ln-C bond.  To date, there are no examples of molecular structures of yttrium amidate complexes. However, there is a reported solid-state structure of a similar ureate complex Y(THF)(N(iPr) [O,NIPh) ) 4 H 5 (MeC 2  25  For purposes of this thesis, this monoureate yttrium  complex will be used for comparison to the yttrium amidate complexes synthesized here. As an alternative synthetic protocol, this work has focused on using organic amides as proligands in the direct preparation of yttrium amidate complexes. Using a high-yielding protonolysis reaction between organic amides and commercially available yttrium , the first examples of monomeric crystalline (Y[N(SiMe ) ] 2 ) tris(bis(trimethylsilyl))amide 3 tris, bis and mono(amidate) complexes of yttrium can be obtained. The structural properties and reactivity of these easily isolable complexes have also been investigated.  28  2.2  Amide Proligands  2.2.1 Introduction Ligand design is a crucial aspect of catalyst synthesis. A ligand backbone needs to be tunable in order to vary the steric and electronic properties of the synthesized complexes. The amide proligand is an ideal candidate for catalyst preparation, since the synthesis is short, high-yielding and modular. Section 2.2 shows that a broad range of substituents, and electron-withdrawing groups can easily be installed on the amidate backbone. When bound to a metal centre, the substituent on the nitrogen is placed close to the metal centre, in contrast to the carbonyl substituent, which is further removed. As mentioned previously, rare-earth complexes are prone to dimerization or oligomerization; however, with sufficient steric bulk on the N-substituent, dimerization can be disfavoured, if not eliminated. In the Schafer group, the majority of monomeric group 4 bis(amidate)bis(amido) complexes that have been crystallographically determined contain either Dipp or dimethylphenyl (Dmp) as the N-substituent. 3234  Consequently, electronic properties of the amide proligands are  typically varied by modifying the carbonyl substituent. H Another practical advantage to the amide proligand is the diagnostic N-H signal in the 1 NMR spectrum (a singlet between in the JR spectrum  (‘  3300 cm’).  6.1 and 6.6 ppm) and the broad N-H stretch absorption The progress of the protonolysis reaction can be  monitored by the disappearance of these signals.  The ease in synthesis, variability and  characterization of the amide proligands make them ideal candidates for investigating yttrium complex formation.  29  2.2.2 Results and Discussion As mentioned before, the amide proligands can be easily synthesized from acid chlorides and primary amines (Figure 2.3) in a dichioromethane (DCM) solution with triethylamine ) as a base. After workup a pale yellow solid is isolated that can be recrystallized from 3 (NEt  hot toluene and hexanes to give amide product in high yield (76  -  9 1%). These proligands  must be thoroughly dried by heating under vacuum before use in metal complexation reactions.  A CI R  +  N—R’ 2 H  1.2 equi NEt 3 RANR H 2.9-2.16  DCM  2.9, 91%  2.10, 85%  2.11, 84%  C 3 F 3  2.12, 79%  2.14, 80%  2.13, 70%  2.15, 82%  2.16, 76%  Figure 2.3. Synthesis of amide proligands.  As shown in Figure 2.3, the series of proligands have a broad range of the steric and electronic properties. Amide 2.9 (which is extensively used throughout this thesis, vide  30  infra) contains a naphthyl substituent, which has a diagnostic doublet signal in the 1 H NMR spectrum at  8.86 ppm for the naphthyl ortho-proton. Amide proligands 2.12 and 2.13  include trifluoromethyl groups that result in a more electron-withdrawing amidate backbone. Furthermore, yttrium complexes resulting from these proligands are expected to be more Lewis acidic. Amides 2.14, 2.15 and 2.16 contain alkyl substituents, in contrast to the aryl substituents on all the other proligands. The advantage of using alkyl groups is increased solubility, lower melting points, and a lower molecular weight. The lower melting point may allow sublimation to be used as a purification technique. The library of compounds shown in Figure 2.3 illustrates the variety of amide proligands that have been investigated during the course of this work. Formation of yttrium complexes using these proligands results in complexes with variable reactivity (vide infra). Synthesis of tris, his and mono(amidate) complexes using this library of amide proligands will be presented, as well as their structural features, stability and reactivity.  2.3  Tris(amidate) Yttrium Complexes  2.3.1 Introduction The importance of ligand design is evident in the synthesis of new, discrete, monometallic yttrium compounds as amidate ligands are known to promote the formation of ligand bridged species. The proligand library shown in Figure 2.3 explores a range of steric and electronic environments in this new class of complexes. Initial results show that placing larger groups (e.g. 2,6-diisopropylphenyl, Dipp) on the N-substituent had a positive effect in the isolation of the desired pure monomeric yttrium amidate species. Using amide proligands with smaller substituents (as in compounds 2.14, 2.15 and 2.16) resulted in uncharacterizable  31  H NMR spectra and inconclusive mass spectra). yttrium species (as indicated by complex 1 This is most likely due to a lack of steric bulk close to the metal centre, resulting in oligomerization. To date, the results of complex formation using amides 2.14, 2.15 and 2.16 are inconclusive and consequently, this chapter will focus on complexes of amides 2.9 2.13. -  Notably, resultant complexes of 2.9 2.13 all have sterically bulky aryl groups on the N and -  the Dipp or Dmp (2,6-dimethylphenyl) groups were found to be essential in synthesis of pure, monomeric yttrium tris(amidate) complexes.  2.3.2 Results and Discussion In the Schafer group, the protonolysis route for complex formation has been used to make 5 6 ’ 32 metals. crystalline bis(amidate) complexes of group 4 3  Traditional salt metathesis  37 do not work well routes, which are very useful for group 3 amidinate complex formation, for preparing group 4 amidate complexes, often resulting in amorphous material.  Initial  preparative efforts by J. D. Beard toward yttrium amidate complexes using salt metathesis revealed the propensity for amidate ligands to promote the formation of bridged dimeric or 38 However, one example of a bridged amidate complex ill-defined multi-metallic species. (2.17) can be formed in low yield by salt metathesis using the sodium amidate salt of N-2’,6’, in (Na(N(SiMe ) 2 ) dimethylphenyl(tert-butyl)amide (2.11), formed from deprotonation with 3 a 3:1 molar ratio with yttrium trichloride. This material can be recrystallized from hexanes, 38 Unfortunately full and a solid-state molecular structure of complex 2.17 was obtained. characterization was not possible as this low yielding crystalline sample was not representative of the bulk material which had complex NMR spectra consistent with a highly 38 Figure 2.4 shows the solid fluxional species of ill-defined structure in the solution phase.  32  state molecular structure of 2.17, which is a centrosymmetric dimer, with each yttrium atom having three amidate ligands.  One amidate ligand is bridging to another yttrium atom  through the amidate oxygen.  Notably, the use of the large sodium counter-ion and bulky  base were found to be necessary, as deprotonation of 2.11 with n-butyllithium and subsequent reaction with yttrium trichloride resulted in the formation of completely insoluble 38 materials.  01  Ph} (2.17) with the probability ellipsoids drawn [Y{tBu[O,N]Me 2 ] Figure 2.4. ORTEP of 3 38 at the 50% level. tert-Butyl groups omitted for clarity.  33  Table 2.1. Selected bond lengths (A) and angles (°) for complex 2.17. Bond Length (A) Bond Angle(°) Yl-Ol 2.260(4) Yl-Ol-Ci 99.6(4) Yl-Ni 2.449(5) 01-Cl-Ni 115.0(6) 01-Cl 1.286(8) Cl-Ni-Yi 90.3(4) Ni-Cl 1.299(9) Ni-Yl-Ol 54.99(17) 2.270(4) Yl-02-C14 99.8(4) Yl-02 Yi-N2 2.492(5) 02-C14-N2 116.3(6) 02-Ci4 1.286(8) C14-N2-Y1 88.9(4) N2-Y1 -02 54.90(18) N2-Ci 4 1.309(9) 97.2(4) 2.384(4) Yl -03-C27 Yi-03 03-C27-N3 114.8(6) Yl-N3 2.483(5) C27-N3-Y1 93.4(4) 03-C27 1.327(8) 1.302(9) N3-Y1-03 54.08(16) N3-C27  Since salt metathesis preparation of yttrium amidate complexes has been difficult, and protonolysis is effective in formation of bis(amidate) complexes of group 4, protonolysis preparative methods were extended to yttrium in hopes of making crystalline, monomeric yttrium amidate species.  39 discovered that Furthermore, Livinghouse and coworkers  chelating bis(thiophosphinic amidate) yttrium complexes can be formed cleanly from thiophosphinic  amide  proligands  and  yttrium  The  tris(bis(trimethylsilyl)amide).  bis(thiophosphinic amidate) yttrium complexes have a similar 3-member chelate ring (N-P-S) as the amidate complexes (N-C-0).  Also, these complexes are highly active for  intramolecular hydroamination of aminoalkenes when formed in situ. Homoleptic yttrium complexes can be made from proligands 2.9, 2.10, 2.11, 2.12 and , ] 2 ) 3 2.13 using a simple protonolysis reaction (Figure 2.5). The starting material Y[N(SiMe ° is dissolved in 4 which is commercially available or can be easily synthesized, tetrahydrofuran (THF) at room temperature. Separately, the amide proligand is dissolved in ] in THF. The reaction 2 ) 3 THF and is added dropwise to a stirring solution of Y[N(SiMe  34  mixture is stirred at 60 °C for 2 hours, and after work-up pale yellow solids (2.18, 2.19, and 2.20) or yellow oils that solidify over time (2.21, 2.22) are obtained. The complexes formed are recrystallized from hexanes to give colourless crystals in high yield (Figure 2.5). These moisture sensitive complexes have been fully characterized and are soluble in all common hydrocarbon solvents.  3 equiv.)lR 2.9  C°  -  2.13  2 ) 3 Y(N(SEMe 600C,2h -3 equiv. HN(SiMe 2 ) 3  C0YR) 3 2.18 2.22 -  Y)  2.19, 91%  2.18, 94%  2.21, 79%  2.20, 88%  2.22, 88%  Figure 2.5. Synthesis of tris(amidate) complexes. The ‘H NMR spectra of complexes 2.18, 2.19, 2.20, 2.21 and 2.22 have very similar 3 symmetric structures in the solution characteristics, and all spectra show time averaged C  phase and bind one equivalent of THF. Interestingly, the ‘H NMR spectrum of complex 2.19 at room temperature contains broad signals compared to the other tris(amidate) complexes. The signals in the ‘H NMR spectrum of 2.19 sharpened at higher temperatures (77 °C, in  35  ) and maintained C 8 D 7 C 3 symmetry. In complexes 2.18, 2.20, 2.21 and 2.22, the signals observed for the THF methylene protons are shifted (ö 4.08 ppm and 1.41 ppm for 2.18,  o 3.46 ppm and  1.46 ppm for 2.19, 0 3.89 ppm, and 1.42 ppm for 2.20, 0 3.71 ppm and 1.32  ppm for 2.22) and broadened from typical residual THF solvent signals (0 3.57 ppm and 1.40 ’ This data is consistent with labile, coordinated THF that is rapidly exchanging on 4 ppm). the NMR time scale.  Variable temperature NMR spectroscopic experiments on complex  2.18 failed to yield any energetic parameters for this exchange, as no line-broadening was observed, even at -45 °C.  Furthermore, the overall C 3 symmetry of this complex is  maintained at these lower temperatures, also with no observable line broadening, consistent with either a highly fluxional complex, or a static structure. A key feature of the ‘H NMR spectrum for complex 2.18 is the diagnostic doublet signal at 0 9.26 ppm for the ortho-proton of the naphthyl substituent, which can be used to differentiate between tris, bis and mono(amidate) complexes (vide infra). The THF ligand of complexes 2.18, 2.19, 2.21 and 2.22 is retained even after extended exposure to high vacuum, as evidenced by ‘H NMR spectroscopy and combustion analysis. However, this is not the case for complex 2.20, which retains THF after exposure to vacuum overnight at 25 °C, but after exposure for more than three days, the THF can be partially removed, as evidenced by the decreased integration of the THF proton signals. Complex 2.20 has less steric bulk around the metal centre, and potentially converts to complex 2.17 under extensive vacuum. JR spectroscopy is very diagnostic for the formation of these complexes as the disappearance of the N-H stretch absorption from proligands and a shift of the C0 stretch absorption bands are consistently observed.  For example, from proligand 2.9 to the  36  formation of complex 2.18, the disappearance of the N-H stretch band (3253 cm 1 for 2.9) and the shifting of the C=O stretch band from 1643 cm 1 to 1513 cm 1 is observed. This weakening of the C=O bond is consistent with both amidate delocalization and metal 1 complexation. Furthermore, the appearance of a weak CN stretch absorption at 1406 cm supports the formation of the desired complex with the delocalized monoanionic ligand. These JR trends are mirrored in complexes 2.19, 2.20, 2.21 and 2.22 (CO v: 1647 cm 1 to 1 1618 cm for 2.10 to 2.19, 1650 cm 1 to 1541 cm 1 for 2.11 to 2.20, 1648 cm to 1528 cm for 2.12 to 2.21, and 1647 cm 1 to 1534 cm 1 for 2.13 to 2.22). Finally, mass spectrometry of 2.18, 2.19, 2.20, 2.21 and 2.22 results in molecular ion peaks corresponding to the complex without THF in all cases. As well, the fragmentation patterns for these complexes show signals for the loss of one ligand and for the free ligand itself. X-ray quality crystals of complex 2.18 can be grown from hexanes at -35 °C and the solid-state molecular structure is shown in Figure 2.6.  The 7-coordinate C 1 symmetric  -amidate backbone as 2 structure of 2.18 confirms electron delocalization through the K indicated by the similar C-O and C-N bond lengths (average C-O is 1.290 N is 1.310  A and average C-  A) (Table 2.2). The average Y-O (amidate) and Y-N (amidate) bond length are  2.3 03 and 2.411  A, respectively. It is reasonable for the Y-O bond to be slightly shorter than  the Y-N bond length, as shown in the previously mentioned and a structurally similar ureate Y ) 4 H 5 (MeC [ 2 O,N]Ph). (THF)(N(iPr) This may be attributed to greater complex of yttrium 25 anionic charge density on oxygen and the oxophilic nature of yttrium. Also, there is a lack of steric bulk around the oxygen relative to the nitrogen making it sterically more favourable for  o  to approach the metal centre.  Since there are no previous structurally characterized  yttrium amidate complexes, the solid-state molecular structure of the monoureate yttrium  37  complex  will  be  used  for  comparison.  This  monoureate  complex,  Y ) 4 H 5 (MeC [ 2 O,N]Ph), (THF)(N(iPr) has similar Y-O and Y-N bond lengths to 2.18 (2.285(2)  A and 2.401(2) A). Interestingly, in 2.18 one amidate metallacycle is further  removed from the yttrium metal than the others, as evidenced by the much longer Yl-03 and Y1-N3 bond lengths. This is likely due to the presence of the bulky groups on nitrogen. The average amidate bite angle (O-Y-N) for complex 2.18 is 55.90°, which is similar to YO,N]Ph) ) 4 H 5 (MeC [ 2 (THF)(N(iPr) (55.96(9)0).25 The average sum total of the four angles of each amidate metallacycle is 3 59.5°, indicating the yttrium and amidate N-C-O backbone are all in the same plane. Complexes 2.19, 2.20, 2.21 and 2.22 can be synthesized easily in high yield, but X-ray quality structure determinations have proven to be difficult. The composition and proposed structure of these complexes was based upon other characterization techniques, such as ‘H and ‘ C NMR spectroscopy, JR spectroscopy, mass spectrometry, and elemental analysis. 3 These data are then compared to those of complex 2.18.  38  C25  Figure 2.6. ORTEP diagram of the solid-state molecular structure of 3 P [(THF)Y{Nap[O,N](iPr) 2 ] h} (2.18) with the probability ellipsoids drawn at the 50% level. Naphthyl groups (except for ipso-carbon) and the carbons of the THF groups omitted for 42 clarity. Table 2.2. Selected bond lengths (A) and bond angles (°) for complex 2.18. Bond Length (A) Bond Angle(°) Yl-Ol 2.334(3) Y1-01-Cl 95.8(3) Y1-Nl 2.386(4) 0l-Cl-Nl 115.5(4) 01-Cl 1.292(5) Cl-Nl-Y1 93.0(3) Ni-Cl 1.304(5) Nl-Y1-01 55.44(12) Y1-02 2.307(3) Y1-02-C24 94.8(3) Y1-N2 2.3 69(3) 02-C24-N2 1 17.0(4) 02-C24 1.272(5) C24-N2-Yi 90.8(3) N2-C24 N2-Yi-02 1.318(5) 56.38(1 1) 2.268(3) Yl-03-C47 Yi-03 97.6(3) Yi-N3 2.479(4) 03-C47-N3 1 18.5(4) 03-C47 1.293(6) C47-N3-Y1 87.8(3) N3-C47 1.304(6) N3-Yl -03 55.87(12) Y1-04 2.332(3)  In an attempt to prepare a 6-coordinate (THF free), monomeric tris(amidate) complex, three equivalents of proligand 2.9 were reacted with Y[N(SiMe ] in a non-coordinating 2 ) 3 solvent at 60 °C.  The resultant moisture sensitive microcrystalline product (2.23) was  39  isolated from warm toluene in poor yield (12%). The residual material from the reaction was insoluble in common organic solvents, consistent with the formation of aggregate species. Complex 2.23 could not be fully characterized, although the data from the X-ray crystallographic studies of a poor quality crystal were satisfactory for establishing connectivity (Figure 2.7).  Two of the ligands are bound as bidentate amidates, as seen  previously, while one monodentate amidate ligand, bound through the oxygen oniy, displays the hemi-labile coordination mode that can be adopted by this ligand framework. Finally, the fourth ligand is a neutral amide, also bound through the oxygen. It is evident by ‘H NMR spectroscopy that one neutral amide is incorporated as a donor ligand, as the amide N-H signal can be seen as a highly deshielded broad singlet at approximately ö 11. Also in the ‘H NMR spectrum, the methyl groups and the methine protons for all diisopropylphenyl substituents are broad singlets or multiplets respectively, indicating the rapid exchange of proton and coordination modes between all the ligands on the NMR timescale.  40  R  3 to 4 equiv. 2.9  1 equ.Y(N(SiMe 2 ) 3  Y)R)  2.23  ()  Figure 2.7. Synthesis of complex 2.23 and ball and stick representation of molecular solid-  state structure of complex 2.23. Naphthyl groups (except for iso-.carbon) are omitted for clarity.  In non-coordinating solvent, even strict control of the reaction stoichiometry (3 proligands to 1 Y) consistently gave evidence (signal at ö 11 in the ‘H NMR spectrum) for formation of product 2.23 in poor yield. Interestingly, product 2.23 can also be prepared in situ on NMR tube scale by addition of one further equivalent of proligand 2.9 to complex 2.18, via THF displacement by the neutral amide group. Furthermore, pyridine has also been shown to add to complex 2.18, also resulting in displacement of coordinated THF.  41  As demonstrated by NMR spectroscopic investigations, the ancillary amidate ligands in complex 2.18 are highly fluxional and additional donors can be easily introduced to the metal center. Thus, when complex 2.18 was reacted with complex 2.19, a rapid redistribution of the ligands occurred, as seen by ‘H NMR spectroscopy.  The signals for the methylene  protons of the THF molecules shifted from ö 4.08 ppm to ö 3.57 ppm, indicating free THF, and multiple signals were observed for the diisopropyl substituents, as well as naphthyl aryl signals. This reaction occurred immediately at room temperature, and no further change in the ‘H NMR spectrum was seen when the solution was heated to 110 °C. Attempts to isolate a mixed amidate yttrium complex have been unsuccessful. In solution phase, it is apparent that the amidate ligands are rapidly exchanging and are thought to exchange through a mechanism that takes advantage of the potential bridging mode of the ligand as seen in complex 2.17 and ligand hemi-lability as observed in complex 2.23.  2.4  Bis(amidate) Yttrium Complexes  2.4.1 Introduction The direct synthesis of tris(amidate) complexes using the protonolysis reaction is very successful in forming crystalline, monomeric complexes.  However, the tris(amidate)  complexes lack a reactive ligand (such as N(SiMe 2 at the metal centre during catalytic ) 3 44 With the success of the bis(amidate) complexes of group 4 as hydroamination ’ 43 processes. precatalysts, synthesis of group 3 analogues are desirable.  Furthermore, hydroamination  43 ’ 39 precatalysts of group 3 are typically formed in situ, and are not fully characterized. Without adequate steric protection about the metal centre oligomerization can occur and/or 7 group 3 mixed-ligand complexes have the tendency to undergo ligand redistribution.  42  However, the protonolysis route used in formation of tris(amidate) complexes of yttrium can also be used successfully for the preparation of bis(amidate) complexes.  2.4.2 Results and Discussion The first example of a fully characterized bis(amidate) yttrium complex has been synthesized using amide 2.9 and Y(N(SiMe 2 in THF at room temperature. The amide ) 3 proligand 2.9 was dissolved in THF and added dropwise to a stirring solution of ] in THF. 2 ) 3 Y[N(SiMe  The reaction mixture was stirred at 25 °C, and after work-up,  concentrated in vacuo to obtain a pale yellow solid. As mentioned previously, the signal corresponding to the ortho-proton on the naphthyl substituent is very useful, and as shown in Figure 2.8 there are two separate ortho-proton doublets in the ‘H NMR spectrum (signal ‘a’ and ‘b’ in Figure 2.8) for the crude compound. This indicates that there are two discrete compounds in solution that contain the naphthyl substituent. There are no N-H signals at approximately ö 6.6 ppm (free proligand) or 1 1 ppm (coordinated proligand) in the ‘H NMR spectrum, so these two discrete compounds are both amidate complexes. Furthermore, there is a singlet at approximately 3 0.3 ppm for the methyl protons in residual ] or LY(N(SiMe 2 ) 3 Y[N(SiMe 2 (where L ) 3  =  amidate ligand). The doublet at 3 9.26 ppm  matches the chemical shift for the ortho-proton on the naphthyl substituent in the analogous tris(amidate) complex 2.18. The same reaction was repeated in THF at 60 °C for 2 hours, and the amount of tris(amidate) was decreased (as evidenced by the decrease in integration of the doublet ‘a’ compared to doublet ‘b’ in the ‘H NMR spectrum of the crude material). Heating the crude mixture dissolved in toluene to 90 °C resulted in clean bis(amidate)  43  complex formation.  This was verified by the full removal of peak ‘a’ in the ‘H NMR  spectrum of the product.  b a 9.0  8.5  8.0  7.5  7.0  6.5  D of crude product after 6 Figure 2.8. ‘H NMR spectrum (from ö 6.0 ppm to 9.5 ppm) in C synthesis of complex 2.20 in THF at room temperature.  The discovery that heating the crude sample dissolved in toluene at 90 °C leads to the clean formation of bis(amidate) complex 2.24, resulted in a synthetic protocol that gives the compound in high yield (82%) (Figure 2.9). This synthetic approach can also be used in the formation of bis(amidate) complexes 2.25, and 2.26, in 80% and 84% yield respectively. ] and proligands 2.12 and 2.13 respectively in THF at 60 2 ) 3 Initial reaction with Y[N(SiMe °C results in bis(amidate) formation as well as tris(amidate) by-product (as evidenced by the crude ‘H NMR spectra).  As in the formation of complex 2.24, heating the crude material  dissolved in toluene at 90 °C and subsequent recrystallization gives clean crystalline bis(amidate) complexes 2.25, and 2.26.  44  2euIv.JlR’ H  2.9, 2.12 or 2.13  1. 3 Y(N(SiMe ) THE 600C,2h 2. Toluene, 90 OC  2.24 2.26 -  2.25, 80%  2.24, 82%  3 CE  2.26, 84% Figure 2.9. Synthesis of bis(amidate) complexes.  When the same reaction is carried out using a proligand with a less sterically bulky substituent on the N, such as dimethyiphenyl instead of diisopropylphenyl, single product formation is not observed. Isolation of the bis(amidate) product proved very difficult in these cases and was subsequently abandoned.  This shows that it is necessary to have the steric  bulk of the diisopropylphenyl substituent on the N of the amidate when synthesizing highyielding crystalline, monomeric bis(amidate) complexes of yttrium. The complexes are moisture sensitive, and in the solid-state can be stored at -30 °C for more than 4 months. Furthermore, these complexes are stable in solution at 110 °C for an extended period of time, but after 16 hours at 145 °C, solid precipitates out of solution and degradation of product signals are seen in the ‘H NMR spectrum. The ‘H NMR spectra of all  45  2 symmetric the bis(amidate) complexes at room temperature are consistent with C compounds in solution. No line broadening is evident by ‘H NMR spectroscopy when a solution of complex 2.24 is cooled to -50 °C, indicating no loss in symmetry at these lower temperatures. As in the case for the tris(amidate) complexes, the bis(amidate) complexes all have one molecule of THF bound to the metal centre. It is evident that the THF is bound from the shift of the methylene signals of THF in the ‘H NMR spectra for 2.24,  3.94 and 1.15 ppm for 2.25 and  ( 3.94 and  1.23 ppm  3.90 and 1.05 ppm for 2.26). These proton  signals are broad due to the fluxionality of the chemical environment. The THF molecule remains bound even after exposing the bis(amidate) complexes to full vacuum overnight, since the ‘H NMR signals for the THF methylene protons maintain the same integration. Complex formation and amidate delocalization is confirmed in the JR spectroscopic data for the bis(amidate) complexes. In all cases, the loss of the N-H stretching band from the 1 to 1511 proligand, and the shift of the C0 stretching band is evident (CO v: 1643 cm 1 to 1623 cm’ for 1 to 1626 cm’ for 2.12 to 2.25, and 1647 cm 1 for 2.9 to 2.24, 1648 cm cm 2.13 to 2.26). The weakening of the C=O bond is not as drastic in the complexes that contain the electron-withdrawing trifluoromethyl group.  This suggests that the anionic charge  density is retained by the amidate ligand for complexes 2.25 and 2.26. The mass spectra of compounds 2.24, 2.25 and 2.26 each have molecular ion peaks associated with their respective complexes without THF; the fragmentation pattern shows an 2 group. ) 3 initial loss of the N(SiMe X-ray quality crystals of complexes 2.24 and 2.25 were grown at -35 °C from hexanes with a few drops of toluene. Their respective solid-state molecular structures are shown in Figure 2.10. Complexes 2.24 and 2.25 are six-coordinate, Cj symmetric, pseudo pentagonal  46  pyramidal complexes with the amido ligand as the axial group.  There is electron  delocalization through the ic -amidate backbone as indicated by the C-O and C-N bond 2 lengths (average C-O, C-N for 2.24 is 1.291 respectively). 2.444  A, 1.312 A and for 2.25 is 1.294 A, 1.301 A,  The Y-O(amidate) and Y-N(amidate) average bond lengths are 2.282 and  A for complex 2.24 and 2.286 and 2.428 A for complex 2.25. The binding of the  amidate ligand is more distorted in the bis(amidate) complexes than the tris(amidate) complex 2.18, as the Y-O bond is shorter and the Y-N bond longer. As in the tris(amidate) complex, this is attributed to the greater electronegativity of the oxygen in combination with 2 bond length for both 2.24 (2.255(3) ) 3 steric bulk around the nitrogen. The Y-N(SiMe and 2.25 (2.23 5(3)  A)  A) are very similar to the reported value for the pentamethyl  Y(N(SiMe (Cp* Cp* 2 ) cyclopentadienyl yttrium complex 3 angles of the amidate ligand (O-Y-N) are 55.71  °  and 55.98  =  °  Me (2.255 C ) 5  45 The bite A).  for 2.24 and 2.25, respectively.  These values are very similar to the tris(amidate) complex 2.18. The average sum of the angles of the amidate metallacycles is 359.5° for 2.24 and 359.7° for 2.25, indicating the yttrium and amidate backbone are in the same plane.  47  Figure 2.10. ORTEP structure of complex 2.24 and 2.25 with the probability ellipsoids drawn at the 50% level. For both structures the THF ring carbons have been omitted for clarity, and from the structure of 2.24, two molecules of toluene were also omitted.  Table 2.3. Selected bond lengths and angles for complex 2.24, and 2.25.  Complex  Yl-Ol Yl-Ni 01-Cl Ni-Cl Y1-02 Yl-N2 02-C2 N2-C2 Y1-03 Yl-N3  2.24 Bond Length (A) 2.285(3) 2.450(3) 1.288(4) 1.313(5) 2.279(3) 2.437(3) 1.293(4) 1.310(5) 2.350(3) 2.255(3)  2.25 Bond Length (A) 2.313(2) 2.391(3) 1.294(4) 1.306(5) 2.259(3) 2.464(3) 1.294(5) 1.295(5) 2.352(3) 2.235(3)  Complex Bond Angle(°) Yl-Ol-Ci 01-Cl-Ni Ci-Ni-Yl Ni-Yl-Ol Y1-02-C2 02-C2-N2 C2-N2-Y1 N2-Y1-02 Y1-N3-Sil Y1-N3-Si2 Sil-N3-Si2  2.24 Bond Angle(°) 97.6(2) 116.8(3) 89.4(2) 55.65(10) 97.6(2) 116.2(3) 89.9(2) 55.77(10) 124.58(17) 116.62(17) 118.75(18)  2.25 Bond Angle(°) 95.1(2) 117.0(4) 91.2(3) 56.19(10) 97.9(3) 117.8(4) 88.5(3) 55.77(11) 121.50(18) 115.07(16) 122.87(19)  48  It was found with the tris(amidate) complexes that the amidate ligands were highly fluxional. The solution NMR spectra of the crystalline bis(amidate) complexes maintain the appearance of C 2 symmetry, even at cooler temperatures (-50 °C). This suggests that the amidate ligand is also highly fluxional in the bis(amidate) compounds. To further probe this, complex 2.24 and 2.25 were dissolved separately in C D and combined in a J-Young NMR 6 tube. Immediately, ligand redistribution occurs, as indicated by multiple aryl, methylene, and methyl signals in the ‘H NMR spectrum. These new signals do not match the signals associated with complex 2.24 or 2.25. This redistribution occurs further when the sample is heated to 65 °C, and at 110 °C. After overnight at 110 °C, no further change occurs but isolation and characterization of a mixed complex was not possible. This indicates that the amidate ligands in the bis(amidate) complexes are as fluxional as they are in the tris(amidate) complexes.  2.5  Mono(amidate) Complexes of Yttrium  2.5.1 Results and Discussion An efficient route for the formation of tris and bis(amidate) complexes has been determined, and to further study the reactivity of amidate complexes of yttrium, mono(amidate) complexes were synthesized. Initially, proligand 2.9 was used to synthesize a mono(amidate) complex so the progress of reaction could be monitored using the diagnostic ortho-naphthyl signal in the ‘H NMR spectrum (vide supra). The reaction was performed using the same protonolysis route as the tris and bis(amidate) complex synthesis, but at room temperature. The proligand was dissolved in THF, and added very slowly to a stirring solution of the starting material Y[N(SiMe 1 dissolved in THF. After stirring, 2 ) 3  49  __________  filtering and concentrating in vacuo, a pale yellow solid was obtained. The crude ‘H NMR spectrum shows two separate ortho-naphthyl peaks, a major signal at 8 9.16 ppm, and a very minor signal at 3 9.09 ppm, indicating a small amount of bis(amidate) product present. If the same reaction is repeated with more dilute solutions (each in 10 mL THF instead of 5 mL), after workup the crude ‘H NMR spectrum contains only one signal for the ortho-naphthyl signal at 6 9.16 ppm. Thus, an effective synthetic route to mono(amidate) complexes of yttrium has been developed (Figure 2.11).  2 ) 3 Y(N(SiMe  1 equiv. RNR  TH F 25°C, 2h -1 equiv. HN(SiMe 2 ) 3  2.9, 2.lOand 2.12  o  R’  Si) 3 ((Me N 2 )  2.27 -2.29  Si) 3 (Me N 2 , Si) 3 (Me N 2  /  2.28, 82%  2.27, 77%  Si 3 (Me  2.29, 82%  Figure 2.11. Synthesis of mono(amidate) complexes.  50  Mono(amidate) complexes 2.27, 2.28 and 2.29 can be easily recrystallized from a minimum amount of hexanes at -35 °C to yield colourless plate-like crystals in high yield. These compounds are soluble in all common hydrocarbon solvents, and are very moisture sensitive. The solid samples can be stored at -30 °C for greater than 4 months without decomposition; however, these compounds undergo ligand redistribution in solution at higher temperatures. For example, heating a solution of complex 2.27 to 65 °C results in no change of the ortho-naphthyl signal at  H NMR spectrum, but at 110 °C after even 9.16 ppm, in the 1  a short amount of time a doublet appears at ö 9.09 ppm (matching that of bis(amidate) complex 2.24). After overnight at 110 °C the intensity of the doublet at ö 9.09 ppm increases and the doublet at  9.16 ppm decreases. This indicates that heating the mono(amidate) will  cause selective formation of the bis(amidate) complex with no evidence for tris(amidate) formation. At a lower temperature (65 °C) it is evident that the mono(amidate) complex is 2 groups ) 3 stable in solution, and on the NMR timescale the proton signals for the -N(Si(CH 2 groups ) 3 are rendered equivalent. This is postulated to occur by exchange of the -N(Si(CH on the NMR timescale through a mono dentate amidate intermediate.  The observed  2 groups is maintained at lower temperatures (-70 °C), ) 3 symmetry of the -N(Si(CH suggesting a highly fluxional structure. Interestingly, complex 2.28 displays dramatically different solution phase behaviour at H NMR spectrum, all signals are very broad and when the sample room temperature. In the 1 is warmed to 65 °C it is apparent that there are two species in solution, as evidenced by two separate broad septet signals at ö 3.39 and 3.25 ppm in a 1:2 integration ratio. This is similar to the tris(amidate) complex 2.19, with the same amidate ligand, which also displays broadened signals in the ‘H NMR spectrum. Unfortunately, heating this sample past 65 °C  51  causes ligand redistribution, so a higher temperature ‘H NMR spectrum could not be obtained. It is known that in the solid-state, the molecular structure of complex 2.28 is a monomeric mono(amidate) complex (vide infra), and isolation of another species has not been possible to date. It is postulated that the two species are different geometric isomers (vide infra). The mono(amidate) complexes are similar to the tris(amidate) and bis(amidate) complexes in that there is one molecule of bound THF on the yttrium centre indicated by ‘H NMR spectroscopy.  The JR spectra of the mono(amidate) complexes 2.27, 2.28 and 2.29  shows a loss of N-H stretch band, a shifted C=O stretch band and a new C=N stretch band. The electron-impact mass spectra of the mono(amidate) samples all show a typical fragmentation pattern, including the molecular ion peak (without THF) followed by [M  -  1 fragments. 2 ) 3 I and [M N(SiMe 3 CH -  X-ray quality crystals can be obtained at -35 °C for the mono(amidate) complexes 2.27 and 2.28 (from a minimum amount of hexanes) (Figure 2.12).  The mono(amidate)  complexes formed crystals much more readily than the tris and bis(amidate) complexes. Both 2.27 and 2.28 are isostructural, 5-coordinate, Cj symmetric and pseudo square-based pyramidal structures with one amido ligand as the axial group.  This low coordination  number is rare for yttrium due to the previously discussed ligand redistribution pathways, ° 4 2 ligand stabilizes this species. ) 3 although the steric bulk of the —N(SiMe  Electron  delocalization is evident through the amidate backbone since the C-O and C-N bond lengths are 1.280(4)  A, 1.316(4) A for 2.27 and 1.295(6) A, 1.310(6) A for 2.28, respectively) (Table  2.4 and Table 2.5). The Y-O(amidate) bond lengths are slightly shorter than those for the  analogous tris and bis(amidate) complexes (2.2 15(2)  A for complex 2.27 and 2.222(4) A for  52  complex 2.28),  whereas the Y-N(amidate) bond length is much longer (2.519(3)  complex 2.27 and 2.540(3)  A for complex 2.28) consistent with the asymmetry seen in  2 bond length for both 2.27 (2.223 ) 3 amidate bonding. The average Y-N(SiMe (2.242  A for  A) and 2.28  A) are very similar to the bis(amidate) complexes 2.24 and 2.25. The amidate bite  angle in complexes 2.27 and 2.28 are also similar to the tris and bis(arnidate) complexes at 55.52(8)  and 54.62(12)  0  respectively.  The mono(amidate) complexes were studied by ‘H NMR spectroscopy to explore the degree of ligand redistribution. It is evident that ligand redistribution occurs for a solution sample of 2.27 at 110 °C, but not at room temperature or 65 °C.  Interestingly, when  complexes 2.27 and 2.29 were combined in solution, no ligand redistribution occurred at room temperature or 65 °C, as evidenced by no change in the ‘H NMR spectrum of each respective complex. However, at 110 °C ligand redistribution is clear by formation of new naphthyl ortho-proton signals at ö 9.07 and 9.02 ppm.  These signals do not match the  bis(amidate) complex 2.24 ortho-naphthyl proton signal and therefore must be an indication of mixed compound formation.  This result is in contrast to the tris and bis(amidate)  complexes of yttrium that show ligand redistribution between complexes occurring immediately at room temperature.  This indicates that ligand redistribution between  mono(amidate) yttrium complexes is less favoured than in tris or bis(amidate) complexes, 2 ligand blocking the approach of ) 3 possibly due to the more sterically protecting —N(SiMe potential bridging amidate ligands. The mono(amidate) yttrium complexes may be less stable than the tris and bis(amidate) counterparts (such as the ligand redistribution above 65 °C), but the ease of isolation and  53  crystallization of these compounds makes them ideal for reactivity investigations and catalytic applications.  Figure 2.12. ORTEP structure of complex 2.27 and 2.28, with the probability ellipsoids drawn at the 50% and 30% level, respectively. THF ring carbons omitted for clarity in both structures, and isopropyl methyl substituents omitted in 2.28.  Table 2.4. Selected bond lengths and bond angles for complex 2.27. Bond Angle(°) Bond Length -  (A) Yl-Ol Yl-Nl 01-Cl Ni-Cl Y1-02 Yl-N2 Yl-N3  2.215(2) 2.519(3) 1.280(4) 1.316(4) 2.343(2) 2.214(2) 2.231(2)  Yl-Ol-Ci 01-Cl-Ni Ci-Ni-Yl N1-Y1-0i Yl-N2-Sii Yl-N2-5i2 Sil-N2-Si2 Yl-N3-5i3 Y1-N3-Si4 5i3-N3-Si4  100.65(18) 117.6(3) 85.80(19) 55.52(8) 120.56(14) 119.90(15) 119.48(15) 112.36(13) 126.58(13) 120.85(15)  54  Table 2.5. Selected bond lengths and bond angles for complex 2.28. Bond Length Bond Angle(°) -  (A) Y001 -02 Y00 i-Ni 02-C 13 Ni-C13 0i(THF) Y1-N2 Y1-N3  2.6  2.222(4) 2.540(3) 1.295(6) 1.310(6)  Y001-02-Ci 3 02-C 13-Ni Cl 3-N1-Y001 N1-Y001-02  102.5(3) 115.5(4) 87.3(3) 54.62(12)  2.388(4)  Y001-N2-Si5  135.6(3)  2.259(4) 2.224(5)  Y001-N2-Si7 Si5-N2-Si7 Y00i-N3-Si2 Y001-N3-Si3 5i2-N3-Si3  113.7(3) 1 10.5(3) 1 18.6(3) 116.6(2) 123.8(3)  Comparison of Yttrium Amidate Complexes These first examples of yttrium amidate complexes bearing the same naphthyl  derivatized  ligand  (tris(amidate)  complex  2.18,  bis(amidate)  complex  2.24  and  mono(amidate) complex 2.27) lend themselves to a comparison within this family of compounds (Table 2.6).  These complexes may all have the same amidate ligand, but  structural and stability trends are noticeable due to the different ligand stoichiometries. A decrease in substitution from 3 amidate ligands to 1 amidate ligand, results in a coordination number decrease from 7 to 5.  Furthermore, the yield, the chemical shift of the ortho  naphthyl proton signal, the C-N JR stretching frequency, the Y-0 and C-N bond lengths and the amidate bite angle all decrease with decreasing amidate coordination.  55  Table 2.6. Comparison table of reaction data, ‘H NMR, JR and X-ray crystallographic data for tris, bis and mono(amidate) complexes 2.18, 2.24 and 2.27. 2.27 2.24 2.18 Complex  Number of amidate ligands  3  2  1  Coordination number  7  6  5  94%  82%  77%  ö9.26 ppm  9.09 ppm  69.l6ppm  1513, 1406cm’  1511, 1400cm’  1 1516, 1399 cm  Yield Chemical shift of ortho .  ) D 6 naphthyl H signal (in C C-O,C-NlRstretch Average* Y-O bond length Average* Y-N bond length Average* C-O bond length Average* C-N bond length Y-O(THF) bond length  2.303  A  A 1.290 A 1.310 A 2.332(3) A 2.411  Average* Y-N(SiMe 2 bond ) 3 -  A 2.444 A 1.291 A 1.312 A 2.282  *  55.90  A 1.316(4) A 1.280(4)  A  2.343 (2)  2.25 5(3)  A  2.223  55.71  °  A  2.519(3)A  2.3 50(3)  length Average* N-Y-O bond angle  2.2 15(2)  A  A  55.52(8)  Calculated averages do not include errors.  56  _________iLlUi  *  ortho naphthyl signals %THFO 2 signals CH # CH(CH) signals  ) i) 2 S 3 ((Me N  %  *  2.18.n3 2.2n=2 2.27. n=l •9_ ‘‘!‘‘‘I’’’’’’’’I’’’’!.’’’i’’’’!’’ _J’,-  90  85  80  7.5  70  6,5  6,0  55  !!]!!!!!!!!!!1!!!!!!!I•!!!!’!  5O 45 Chett,tcJ Shift (ppr)  40  35  30  25  20  15  1.0  05  Figure 2.1. ‘H NMR (400 MHz, C , 25 °C) of tris(amidate) complex 2.18, D 6 D at room 6 bis(amidate) complex 2.24, and mono(amidate) complex 2.27 in C temperature.  H NMR spectra for tris(amidate) complex 2.18, bis(amidate) Figure 2.13 shows the 1 complex 2.24 and mono(amidate) complex 2.27 overlaid. The major differences are seen in the ortho-naphthyl signal (* in Figure 2.13), the THF chemical shifts (% in Figure 2.13), and the methine peak of the isopropyl groups (# in Figure 2.13). These diagnostic signals are critical in the interpretation of spectra with multiple species. Both the tris(amidate) and bis(amidate) complexes were found to have very labile amidate ligands, and underwent ligand redistribution when another amide or complex was introduced into a reaction mixture.  Also, the mono(amidate) complex undergoes ligand  redistribution to form small amounts of bis(amidate) when heated above 65 °C. Interestingly, when one equivalent of tris(amidate) complex 2.18 is added to mono(amidate) complex 2.27 in solution, immediate redistribution is noted in the ‘H NMR spectrum. 57  Immediately there are three separate doublets for the ortho-naphthyl substituent at 6 9.26 ppm, 9.16 ppm and a minor doublet at 9.09 ppm. The first two signals match those of a tris(amidate) complex 2.18 and mono(amidate) complex 2.27, and the minor doublet is form the bis(amidate) complex 2.24. When the solution was heated to 65 °C for 48 hours, the same ortho-naphthyl signals were still evident, and the ortho-naphthyl signal matching that of the bis(amidate) complex grew in intensity. After 48 hours at 110 °C, the bis(amidate) complex is the major product (doublet at 6 9.09 ppm), and there is no evidence of mono(amidate) complex, but a small doublet associated with the tris(amidate) complex at 6 9.26 ppm is still present in the ‘H NMR spectrum. This may be due to a small difference in stoichiometry when the initial reaction was prepared. This confirms that the bis(amidate) complex is the thermodynamic product for this system. All the complexes are soluble in common hydrocarbon solvents, but vary in their thermal stability. The tris(amidate) complexes are known to be stable up to 110 °C in solution and are highly fluxional. The bis(amidate) complexes are stable in solution up to 110 °C, but at 145 °C decomposition is noted as evidenced by degradation of signals in the ‘H NMR spectrum.  2 symmetry, and is also The bis(amidate) complex in solution maintains C  fluxional.  The mono(amidate) complexes on the other hand are stable only to 65 °C in  solution, and were determined to be less fluxional than the corresponding tris or bis(amidate) complexes. The asymmetry of the amidate binding increases from tris to mono(amidate) complex The  formation, meaning the Y-O bonds get shorter and the Y-N bonds get longer.  mono(amidate) yttrium complex has two bulky trimethylsilylamide groups that sterically repel the Dipp substituent on the N, causing the elongation of the Y-N bond. To compensate  58  for this, more charge is localized on the 0 of the amidate, causing a shorter Y-0 bond in the mono(amidate) complex.  The Y-O(THF) bond length is quite similar for all three  complexes, not displaying any notable trends.  In the mono(amidate) complex, the Y  2 are on average shorter than the corresponding bis(amidate) complex 2.24. This ) 3 N(SiMe structural data correlates with the observed solution phase behaviour for these complexes.  2.7  Summary and Conclusions A direct synthesis of amidate complexes of yttrium has been accomplished using amide  proligands and Y[N(SiMe . ] 2 ) 3  The amide proligands are easily synthesized from acid  chlorides and primary amines in high yield and large quantities.  Also, variations to the  substituents on the amide proligand, such as adding steric bulk or electron-withdrawing groups, is incredibly straightforward. Ligand design was an important aspect of this chapter and the amide proligands used were designed to include steric bulk on the N substituent, as this was found to be essential in the formation of pure, isolable yttrium amidate complexes. Minor modifications, mainly stoichiometry, temperature and dilution, to the simple ] allows selective formation and high-yielding 2 ) 3 protonolysis reaction with Y[N(SiMe preparations of crystalline tris, bis and mono(amidate) complexes.  It is ideal to use  coordinating solvent for synthesis, since one molecule of THF is bound to all yttrium amidate complexes and early attempts to exclude exogenous donors were unsuccessful. However, it should be noted the synthesis of bis and mono(amidate) complexes were not attempted in non-coordinating solvents. Solid-state molecular structures of tris, bis and mono(amidate) complexes were obtained and trends in bond lengths were evident.  From the tris(amidate) complexes to the  59  mono(amidate) complexes, the Y-O bond length decreases and the Y-N bond length increases. The amidate ligand was found to be very fluxional in the tris and bis(amidate) complexes. When two tris or bis(amidate) complexes were combined in solution, ligand redistribution was immediately evident at room temperature. This was not the case for mono(amidate) complexes as ligand redistribution did not occur at room temperature or 65 °C.  This is  2 ligand providing more steric protection from an approaching ) 3 possibly due to the —N(SiMe complex. The hemi-lability of the amidate scaffold, and the ease with which the donor ligand can be displaced led us to consider tris, bis and mono(amidate) complexes of yttrium as being sterically accessible Lewis acids for a range of potential Lewis basic donors. Consequently, amidate complexes of yttrium have been investigated as initiators in E-caprolactone ring opening  polymerization  and  compared  with  other known  yttrium  -caprolactone  polymerization initiators (Chapter 3). 2 and are ) 3 The bis and mono(amidate) complexes have reactive amido groups (-N(SiMe ideal candidates for hydroamination catalysis (Chapter 4). The different amidate ligands can be compared for their reactivity rates during hydroamination. The mono(amidate) complexes can be used in mixed amidate/anilido complex formation. These complexes are studied and tested for possible yttrium imido formation in Chapter 5.  60  2.8  Experimental  2.8.1 Starting Materials and Reagents All operations were performed under an inert atmosphere of nitrogen using standard Schlenk-line or glovebox techniques. THF, toluene, pentane, and hexanes were all purified by passage through an alumina column and sparged with nitrogen.  1 was 2 ) 3 Y[N(SiMe  40 or purchased from Aldrich and recrystallized from synthesized as described in literature, hexanes before use. All other chemicals were commercially available and used as received H and ‘ C NMR spectra were recorded on Bruker AV300, AV400 3 unless otherwise stated. 1  or AV600 spectrometers.  Shifts are reported in parts per million (ppm) relative to  tetramethylsilane (TMS) and calibrated against residual solvent signal, coupling constants J J unless otherwise stated). are given in Hertz (Hz) (all couplings are 3  ‘JCF  coupling for some  C NMR 3 3 groups could not be reported due to the complicated aryl region of the ‘ CF spectrum. Infrared spectra were measured on a Nicolet 4700 spectrometer using KBr pellets and IR bands v are reported in cm’. Elemental analyses and mass spectra were performed by the microanalytical laboratory of the Department of Chemistry at the University of British Columbia.  Some elemental analyses gave low carbon content for yttrium complexes,  46 X-ray crystallography was conducted at the University possibly due to carbide formation. of British Columbia by Dr. Brian Patrick, Dr. Rob Thomson, or Neal Yonson. Compounds 2.9, 2.10, 2.11, 2.14, 2.15, and 2.16 have been previously synthesized, but complete  4752 characterization data were not provided.  61  2.8.2 Synthesis Synthesis of N-(diisopropylphenyl)naphthyl amide (2.9)  To a 250 mL round-bottom flask was added 2,6-diisopropylaniline (4.95 mL, 26.2 mmol) dissolved in 125 mL of dichioromethane. The  \  /  —  NH  reaction mixture was cooled to 0 °C, and triethylamine (8 mL) was added dropwise by syringe. The resulting solution was stirred for 5 minutes with subsequent dropwise addition of 1-naphthoyl chloride (3.95 mL, 26.2 mmol). The reaction was stirred overnight and then was washed with 1 M aqueous HC1 (3 x 50 mL), followed by 1M aqueous NaOH (30 mL), and brine (30 mL). The organic layer was dried over MgSO , filtered, and then concentrated under reduced pressure to obtain a beige solid. 4 The solid was recrystallized twice from hot toluene to obtain a white powder. Yield: 7.94 g, J , 400 MHz, 293 K) ö 8.86 (d, 3 D 6 91%. ‘H NMR (C  =  6 Hz, 1H, 9-naphthyl-H), 7.62  J = 5 Hz, 1H, 2J = 6 Hz, 2H, 6-naphthyl-H and 4-naphthyl-H), 7.52 (d, 3 (overlapping d, 3 J = 6 Hz, 1H, 4-diisopropylphenyl-I]), naphthyl-I]), 7.32 (m, 3H, 8,7,3-naphthyl-IJ), 7.24 (t, 3 7.11 (m, 3 J  J= 5Hz, 6Hz, 2H, 3,5-diisopropylphenyl-II), 6.60 (s, 1H, N-I]), 3.25 (septet, 3  , 1.25 (d, J 2H, 3 CH(CH ) 2 )  , 75.5 MHz, 293K) ö 3 C NMR (CDC1 3 . ‘ CH(CH ) 2 ) 5 Hz, 12H, 3  170.4 (C=O), 147.8, 135.6, 135.3, 132.5, 132.2, 131.9, 130.1, 129.8, 128.8, 128.0, 126.8, . JR data (KBr, cm’): 3253 25.2(CH(CH ) 2 ) ,3 (CH(CH ) 2 ) 126.2, 126.1, 125.0 (aryl C), 30.4 3 (br), 3047 (w), 2961 (s), 2865 (w), 1643 (s), 1591 (w), 1517 (s), 1297 (w), 913 (w), 785 (w), 3 C 83.74% 5 N0): C 2 734 (w), 654 (w). ElMS (m/z): 331 {M]. Anal. Found (calcd for H (83.34%), N 4.55% (4.23%), H 7.54% (7.60%).  62  Synthesis of N-(2,6-diisopropylphenyl)tert-butyl amide (2.10)  The experimental method described for 2.9 was used in the preparation of 2.10  using  2,6-diisopropylaniline  (5.00  trimethylacetyl chloride (3.26 mL, 0.027 mol).  mL,  0.027  mol)  and  Yield: 5.86 g, 85%. ‘H  NMR (C , 400 MHz, 293 K) ö 7.23 (m, 1H, phenyl-If), 7.11 (m, 2H, D 6 J phenyl-H), 6.26 (s, 1H, N-I]), 3.07 (septet, 3  7 Hz, 2H, CH(CH ), 1.21 (d, 3 2 ) 3 J  7 Hz,  , 100 MHz, 293K) ö 177.3 (CO), D 6 12H, CH(CH ), 1.13 (s, 9H, C(CH 2 ) 3 ). ‘ ) 3 C NMR (C 3 ), 24.5 2 ) 3 ), 29.8 (CH(CH ) 3 ), 28.5 (CH(CH 2 ) 3 147.5, 133.2, 124.3 (aryl C’s), 39.8 (C(CH ). JR data (KBr, cm’): 3317 (s), 2962 (s), 2865 (w), 1647 (s), 1508 (s), 1498 (s), ) 3 (C(CH 790 (s), 736 (w). ESI (m/z): 284 [M  +  Na], 262 [M  +  H]  .  Anal. Found (calcd for  27 C 77.93% (78.11%), N 5.47% (5.36%), H 10.59% (10.41%). H 7 C, N0):  Synthesis of N-(2,6-dimethylphenyl)tert-butyl amide (2.11)  The experimental method described for 2.9 was used in the preparation of 2.11 using 2,6-dimethylaniline (5.10 mL, 0.041 mol) and trimethylacetyl  chloride (5.05 mL, 0.041 mol). MHz, 293 K)  / \ —  , 400 D 6 Yield: 7.07 g, 84%. ‘H NMR (C  7.05 (m, 1H, phenyl-I]), 6.95 (m, 2H, phenyl-If), 6.17 (s,  , 100 MHz, 293K) ö D 6 ). ‘ ) 3 C NMR (C 3 ), 1.08 (s, 9H, C(CH 3 1H, N-I]), 2.09 (s, 6H, CH ), 18.0 ) 3 ), 27.3 (C(CH ) 3 175.6 (C0), 135.6, 135.1, 127.7, 126.6 (phenyl C), 38.7 (C(CH ). JR data (KBr, cm’): 3295 (br), 3021 (w), 2956 (s), 2921 (w), 1650 (s), 1593 (w), 3 (CH 1506 (s), 1278 (w), 1221 (m) 938 (w), 768 (s), 722 (w), 647 (w). ElMS (m/z): 205 [M]. C 1 H 3 9 Anal. Found (calcd for NO):  C 76.12% (76.06%), N 7.00% (6.82%), H 9.09%  (9.33%).  63  Synthesis of N-(2,6-diisopropylphenyl)p-(trifluoromethyl)phenyl amide (2.12)  The experimental method described for 2.9 was used in the preparation of 2.12 using 2,6-diisopropylaniline (6.30 mL, 33.4 mmol) and p-(trifluoromethyl)benzoyl chloride (5.00 mL, 33.6 , 600 MHz. 293 K) D 6 mmol). Yield: 9.24 g, 79%. ‘H NMR (C J’ 12 Hz, 2H, aryl-ff), 7.25 (m, 2H, aryl-I]), 7.14 (m, 3H, aryl-I]), 6.68 (s, 1H, ö 7.47 (d, 3 J N-I]), 3.08 (septet, 3  , 1.21 (d, 3 CH(CH ) 2 ) J 6 Hz, 2H, 3  C 3 . ‘ CH(CH ) 2 ) 6 Hz, 12H, 3  , 375 MHz, 293K) ö 164.1 (C0), 146.10, 137.2, 132.5, 130.8, 128.3, 125.1, D 6 NMR (C : 3300 (br), 2966 (s), cm ) . JR data (KBr, 1 (CH(CH ) 2 ) ), 23.2 3 2 ) 3 123.2 (aryl C), 28.6 (CH(CH 2929 (s) 1648 (s), 1580 (w), 1530 (s), 1500 (s), 1330 (m), 1317 (w), 1158 (w), 1116 (w), 862 (w), 801 (w). ElMS (rn/z): 349 [M].  0): 0 2 F C 2 H N Anal. found (calcd for 3  C 68.75%  (68.75%), N 4.30% (4.0 1%), H 6.64% (6.35%).  Synthesis of N-(2,6-.diisopropylphenyl)(3,5-bis(trifluoromethyl))phenyl amide (2.13)  To  a  250  mL  round-bottom  flask  were  added  2,6-  diisopropylaniline (3.50 mL, 18.5 mmol) and 125 mL of dichloromethane.  The reaction mixture was cooled to 0 °C  using an ice bath, and triethylamine (3.20 mL, 23.0 mmol) was added dropwise by syringe. The resulting solution was stirred for 5 minutes with subsequent dropwise addition of 3,5-bis(trifluoromethyl)benzoyl chloride (5.00 mL, 18.0 mrnol), which fumed upon addition.  The reaction was stirred overnight in which time a white solid  precipitated from the solution. The solid was isolated by filtration and recrystallized by dissolving in warm dichloromethane, with subsequent addition of hexanes and then cooling  64  H NMR to 0 °C. A white fibrous solid was isolated by filtration. Yield: 5.29 g, 70%. 1 , 600 MHz, 293 K) ö 8.14 (s, 2H, aryl-I]), 7.73 (s, 1H, aryl-I]), 7.23 (t, J= 6Hz, 1H, D 6 (C aryl-I]), 7.11 (d, J  =  6 Hz, 2H, aryl-II), 6.49 (s, 1H, N-fl), 2.95 (septet, J  6 Hz, 2H,  , 375 MHz, 293K) D 6 C NMR (C 3 . ‘ CH(CH ) 2 ) , 1.18 (d, J= 6 Hz, 12H, 3 CH(CH ) 2 ) 3 (C—O), 146.0, 136.3, 131.6 (q, J  =  162.59  , 130.4, 128.5, 126.9, 124.5, 123.2(aryl C’s), 86Hz, 3 CCF )  . JR data (KBr, cm’): 3306 (br), 2967 (s), 2930 (s) 1647 (CH(CH ) 2 ) , 23.1 3 (CH(CH ) 2 ) 28.6 3 (s), 1589 (w), 1525 (s), 1465 (s), 1374 (m), 1333 (w), 1274 (s), 1193 (s), 1140 (s), 911 (w),  1 C 60.52% (60.43%), F C 2 H N O): 797 (w). ElMS (m/z): 417 [M]. Anal. found (calcd for 6 N 3.60% (3.36%), H 5.28% (5.07%).  Synthesis of N-(tert-butyl)tert-butyl amide (2.14) The experimental method described for 2.9 was used in the preparation of 2.14 using tert-butylamine (2.63 mL, 25.0 mmol) and trimethylacetyl , 400MHz, 293K) ö D 6 chloride (3.08 mL, 25.0 mmol). Yield: 3.14 g, 80%. ‘H NMR (C . ElMS (m/z): 157 C(CH ) ) , 1.05 (s, 9H, 3 C(CH ) ) 5.10 (s, 1H, N-I]), 1.26 (s, 9H, 3  9 NO): 1 H 9 Anal. found (calcd for C  EM1.  C 68.86% (68.74%), N 8.95% (8.91%), H 12.20%  (12.18%). Melting Point: 112-113 °C.  Synthesis of N-(tert-butyl)sec-butyl amide (2.15)  The experimental method described for 2.9 was used in the preparation of 2.15 using tert-butylamine (1.32 mL, 12.6 mmol) and sec-butyl acid , 400MHz, 293K) 6 4.84 D 6 chloride (1.56 mL, 12.6 mmol). Yield: 1.63 g, 82%. ‘H NMR (C H , 1.38 (m, 2H, )CH 3 CH(CH C 2 H , 1.62 (m, 2H, ) )CH 3 CH(CH C 2 (s, 1H, N-I]), 1.80 (m, 1H, )  65  H , 0.95 (t, )CH 3 CH(CH C 2 , 1.16 (d, J= 6 Hz, 3H, ) C(CH ) ) H , 1.35 (s, 9H, 3 )CH 3 CH(CH C 2 ) J  =  H . JR data (KBr, cm’): 3306 (s), 2963 (s), 1646 (s), 1547 6 Hz, 3H, ) )CH 3 CH(C11 C 2  (w), 1451 (s), 1390 (w), 1272 (m), 1250 (w), 1228 (w), 1109 (s), 967 (s), 676 (w). ElMS 19 C 68.88% (68.74%), N 8.99% (8.91%), H 9 C (m/z): 157 [Mf. Anal. found (calcd for NO): H 12.22% (12.18%). Melting Point: 108-109 °C.  Synthesis of N-(tert-butyl)sec-butyl amide (2.16)  The experimental method described for 2.9 was used in the preparation of 2.16 using sec-butylamine (2.53 mL, 25.0 mmol) and trimethylacetyl , 400MHz, 293K) D 6 chloride (3.08 mL, 25.0 mmol). Yield: 2.99 g, 76%. ‘H NMR (C H , 1.13 (s, )CH 3 CH(CH C 2 H , 1.29 (m, 211, ) )CH 3 CH(CH C 2 5.48 (s, 1H, N-Il), 4.04 (m, 1H, ) , 0.98 (d, J C(CH ) ) 9H, 3 H . )CH 3 CH(CH C 2 )  =  H , 0.79 (t, J )CH 3 CH(CH C 2 6 Hz, 3H, )  , 150 MHz, 293K) D 6 C NMR (C 13  =  6 Hz, 3H,  177.2 (C0), 46.8, 38.9, 30.2,  28.2, 20.9, 11.0. JR data (KBr, cm’): 3336 (s), 2967 (s), 1634 (s), 1534 (w), 1478 (s), 1459 (w), 1210 (m), 669 (w).  19 H 9 C ElMS (m/z): 157 [M]. Anal. found (calcd for NO):  C  68.91% (68.74%), N 8.94% (8.91%), H 12.26% (12.18%). Melting Point: 96-97 °C.  Synthesis  tris(N-2 ‘ ,6’ -diisopropylphenyl(naphthyl)amidate)yttrium  of  mono(tetrahydrofuran) (2.18)  Inside a nitrogen filled glovebox, a vial was charged yttrium tris(bis(trimethylsilyl)amide) (0.118 mmol) and a stirbar.  g,  0.206  To this, 5 mL of tetrahydrofuran  (THF) was transferred to the reaction vessel at room  66  temperature. Amide 2.9 (0.205 g, 0.618 mmol) was dissolved in 5 mL THF and transferred dropwise to the stirring solution of yttrium tris(bis(trimethylsilyl)amide in THF.  The  solution was stirred within the glovebox for 2 hours at 60 °C, and then filtered through CeliteTM and concentrated under reduced pressure to a pale yellow powder. The product was recrystallized by dissolving in a minimum amount of hexanes and then left at -30 °C to yield colorless crystals. Yield: 0.223 g, 94%. Refer to Figure 2.6, Table 2.2 and Appendix I for crystallographic data. ‘H NMR (300 MHz, C ) D 6 =  9.26 (d, J 9 Hz, 3H, aryl-R), 7.53 (d, J  8 Hz, 3H, aryl-I]), 7.49-7.43 (m, 1OH, aryl-I]), 7.38 (d, J= 8 Hz, 3H, aryl-H), 7.26 (t, J= 8  Hz, 3H, aryl-I]), 6.98 (s, 5H, aryl-H), 6.85 (t, J= 7 Hz, 3H, aryl-R), 4.08 (broad m, 4H, 0), 3.73 (septet, J = 7 Hz, 6H, CH(CH 2 CL! ), 1.41 (m, 4H, 2 2 ) 3 CH O-CH ) , 1.04 (d, J = 7 Hz, 18H, CH(CH ), 0.77 (d, J 2 ) 3  7 Hz, 18H, CH(CH ). 13 2 ) 3 C NMR (100.6 MHz, C ) ö 180.1 D 6  (C=0), 142.3, 141.6, 134.3, 132.1, 132.0, 130.1, 129.4, 128.3, 127.8, 127.5, 127.4, 127.3, CH (O-CH ) , 25.0 126.3, 125.4, 124.3, 123.9, 123.6, 123.5 (aryl-C), 69.6 (O-CH ), 28.1 2 2 ), 23.5 (CH(CH 2 ) 3 (CH(CH ). JR data (KBr, cm’): 3052 (w), 2960 (s), 2860 (w), 1573 (w), 2 ) 3 1513 (vs), 1406 (vs), 1382 (vs), 1318 (w), 1251 (s), 1191 (s), 1024 (s), 915 (s), 840 (w), 800 . ElMS (m/z): 1079 1 (w), 779 (s), 761 (w), 657 (w), 621 (w), 564 (w), 506 (w), 459 (w) cm [MtY(Nap[0,N]Dipp) ] . Anal. found [Mj, 952 [M-Nap], 749 [MtNap[O,N]Dipp], 331 2  70 C 8 H Y 4 0 3 3 ): C 75.70% (76.09%), H 6.6 1% (7.00%); N 3.68% (3.65%). (calcd. for N  67  of  Synthesis  tris(N-2’ ,6’-diisopropylphenyl(tert-butyl)amidate)yttrium  mono(tetrahydrofuran) (2.19)  The experimental method described for 2.18 was used in the preparation of 2.19 using 2.10 (0.200 g, 0.766 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.146 g, 0.256 mmol) to give a pale yellow solid. The product was recrystallized by dissolving in a minimum amount of pentane and then left at -30 °C to give a white crystalline , 25 °C) D 6 solid. Yield: 0.207 g, 91%. ‘H NMR (600 MHz, C  7.07 (broad m, 9H, aryl-R),  , CH 2 O-CH ), 1.46 (broad s, 4H, ) 2 ) 3 ), 3.07 (broad m, 6H, CH(CH 2 3.46 (broad s, 4H, O-CH 1.34 (d, J  . C(CH ) ) 2 and 3 ) 3 , 1.12 (overlapping d and s, 27H, CH(CH CH(CH ) 2 ) 6 Hz, 18H, 3  , 77 °C) 8 D 7 ‘H NMR (400 MHz, C 3.31 (septet, J  =  , O-CH ) 6.98 (broad m, 9H, aryl-I]), 3.48 (broad s, 4H, 2  , 1.30 (d, J CH 2 O-CH , 1.36 (broad s, 4H, ) CH(CH ) 2 ) 7 Hz, 6H, 3  , 1.14 (overlapping d and s, J 18H, 3 CH(CH ) 2 )  =  7 Hz,  C 3 . ‘ C(CH ) ) 2 and 3 ) 3 7 Hz, 27H, CH(CH  , 25 °C) ö 186.3 (C=O), 140.7, 124.7, 122.8, 121.5 (aryl-C), 69.2 D 6 NMR (100.6 MHz, C , (0-CR ) 2  , 23.0 (CT-I (CR ) ). JR 3 , 25.0 3 (C(CH ) ) , 28.7 3 (CH(CH ) 2 ) , 25.0 3 CH 2 (O-CH 41.6 )  data (KBr, cm’): 2961 (s), 2861 (w), 1618 (s), 1508 (s), 1474 (s), 1395 (w), 1351 (w), 1213 . ElMS (m/z): 1 (w), 931 (w), 805 (w) cm [tBu[0,N]Dipp].  869 [Mj, 686 [M- tBu[0,N]Dipp], 261  ): 5 6 N 5 C 8 H Y 4 0 Anal. found (calcd for 3  C 69.19% (70.11%), N 4.52%  (4.46%), H 9.20% (9.26%).  68  Synthesis  tris(N-2’ ,6’ -dimethylphenyl(tert-butyl)amidate)yttrium  of  mono(tetrahydrofuran) (2.20)  The experimental method described for 2.18 was used in the preparation of 2.20 using 2.11 (0.201 g, 0.981 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.187 g, 0.327 mmol) to give a pale yellow solid.  The product was recrystallized by  dissolving in a minimum amount of hexanes and then left at -30 °C to give a white crystalline solid. Yield: 0.223 g, 88%. ‘H NMR (300 MHz, C ) ö 6.88 (m, 9H, aryl-I]), 3.67 (m, 4H, D 6 ), 2.24 (s, 18H, CH 2 0-CH ), 1.28 (m, 4H, 2 3 CH 0-CH ) , 1.08 (s, 27H, C(CH ). ‘ ) 3 C NMR 3 ), 41.2 2 (100.6 MHz, C ) ö 185.2 (C=0), 145.8, 130.8, 127.4, 122.7 (aryl-C), 68.7 (0-CR D 6  CH (0-CH ) 2 , 28.0 (C(CH ), 19.2 (CH 3 ). JR data (KBr, cm’): 2986 (w), 2951 3 ), 25.0 (CR ) 3 (s), 2904 (w), 1541 (s), 1522 (s), 1477 (s), 1398 (s), 1352 (w), 1219 (s), 1183 (s), 927 (s), 759 (s), 605 (w) cm . ElMS (m/z): 1 (tBu[O,N]Dmp].  701 [Mj, 686 [M-CH 1, 644 [M-tBu], 497 [M 3  Anal. found (calcd for N 42 C 6 H Y 4 0 3 3 ):  C 66.70% (66.75%), N 6.25%  (5.99%), H 7.89% (7.76%).  Synthesis of tris(N-2’ ,6’ -diisopropylphenyl(p-(trifluoromethylphenyl) amidate)yttrium mono(tetrahydrofuran) (2.21)  The experimental method described for 2.18 was used in the preparation of 2.21 with amide 2.12 (0.40 1 g, 1.15 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.220 g, 0.386 mmol) to give a yellow oil which  3  solidified over time. The product was recrystallized by dissolving in a minimum amount of  69  hexanes and then left at -30 °C to give a white crystalline solid. Yield: 0.365 g, 79%. ‘H NMR (400 MHz, C ) D 6  7.65 (d, J= 8 Hz, 6H, aryl-IJ), 7.20 (m, 6H, aryl-H), 7.12 (m, 9H,  , 3.46 (septet, 6H, J O-CH ) aryl-fl), 3.89 (m, 4H, 2 , 1.12 (d, 18H, J CH 2 CH )  =  , 1.41 (m, 4H, 07 Hz, 3 CH(CH ) 2 )  7 Hz, CH(CH ), 0.89 (d, 18H, J 2 ) 3  C NMR . 13 CH(CH ) 2 ) 7 Hz, 3  ) ö 175.7 (C0), 142.5, 141.2, 137.6, 132.4 (q, J D 6 (100.6 MHz, C  32 Hz, C(CF )), 130.5, 3  , 24.6 CH 2 (0-CH , 25.4 ) (CH(CH ) 2 ) ), 28.5 3 2 125.4, 124.7, 124.3 (aryl-C), 71.5 (O-CH ). JR data (KBr, cm’): 2964 (w), 1617 (s), 1528 (s), 1503 (s), 2 ) 3 , 24.0 (CH(CFI (CH(CH ) 2 ) 3 1 1409 (s), 1325 (s), 1167 (w), 1129 (s), 1066 (s), 925 (w), 858 (s), 764 (w), 697 (w) cm ElMS (m/z):  phenyl[0,NjDippJ. 3 phenyl[0,N]Dipp], 349 [pCF 3 1133 [Mj, 785 [M- pCF  ): C 62.36% (63.73%), N 3.43% (3.48%), H 6.16% 4 1 F 6 C 7 H Y 4 0 3 N Anal. found (calcd for 9 (5.93%).  Synthesis  of  tris(N-2 ‘,6 ‘-diisopropylphenyl((3,5-bis(trifluoromethyl)  phenyl)amidate)yttrium mono(tetrahydrofuran) (2.22)  The experimental method described for 2.18 was used in the preparation of 2.22 with amide 2.13 (0.200 g, 0.479 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.0918 g, 0.16 1 mmol) to give a yellow oil which solidified over  3 CF  time. The product was recrystallized by dissolving in a minimum amount of hexanes and then left at -30 °C to give a white crystalline solid. Yield: 0.200 g, 88%. ‘H NMR (400 ) D 6 MHz, C  8.05 (s, 6H, aryl-If), 7.61 (d, J= 8 Hz, 3H, aryl-If), 7.10 (m, 3H, aryl-R), 7.04  , 1.32 (m, 4H, 0CH(CH ) 2 ) , 3.38 (broad m, 6H, 3 0-CH ) (m, 6H, aryl-I]), 3.71 (broad s, 4H, 2 , 0.83 (d, 18H, J CH(CH ) 2 ) , 1.04 (broad s, 18H, 3 CH 2 CH )  . JR data (KBr, 7 Hz, 3 CH(CH ) 2 )  70  cm’): 2966 (w), 1534 (s), 1459 (s), 1351 (s), 1278 (s), 1187 (w), 1137 (s), 1066 (s), 909 (w), 847 (s), 800 (w), 702 (w) cm . 1  ElMS (m/z):  1337  )phenyl [O,N]Dipp], 417 [3 ,5-bis(CF 3 bis(CF )phenyl [O,N]Dipp]. 3  [Mj, 925  [M- 3,5-  Anal. found (calcd for  C 6 H 1 F Y 4 O 3 N 7 3 8 ): C 56.90% (57.07%), N 3.16% (2.98%), H 4.82% (4.86%).  Synthesis  of  tris(N-2’ ,6’-diisopropylphenyl(naphthyl)amidate)mono(N-2 ‘  -  diisopropylphenyl(naphthyl)amide) yttrium (2.23)  Note:  Only partial characterization data could be obtained, due to difficulty in  recrystallization. Inside a nitrogen filled glovebox, a 500 mL round bottomed Schlenk flask was charged with amide 2.9 (0.501g, 1.51 mmol), yttrium tris(bis(trimethylsilyl)amide) (0.317g, 0.550 mmol) and a stirbar. To this, 100 mL of toluene was transferred to the reaction vessel at room temperature. The solution was stirred overnight at 65 °C, and then filtered through Celite and concentrated under reduced pressure to a white powder. The product was recrystallized by dissolving in a minimum amount of hot toluene, layered with pentane and then left at -30 °C.  Yield: 0.093g, 12%.  Poor quality crystals were grown from warm toluene/pentane  mixture. ‘H NMR (400 MHz, CDC1 ) ö 11.1 (s, 1H, bound amide N-I]), 8.47 (d, J= 8 Hz, 3 3H, aryl-I]), 7.97 (d, J= 8 Hz, 1H, aryl-I]), 7.89 (d, J  8 Hz, 1H, aryl-I]), 7.83 (d, J 8 Hz,  1H, aryl-I]), 7.66-7.60 (m, 8H, aryl-I]), 7.53 (m, 6H, aryl-R), 7.34-6.94 (m, 20H, aryl-I]), ), 0.65 (broad s, 24H, CH(CH 2 ) 3 ), 0.42 (broad s, 24H, 2 ) 3 3.90 (broad m, 8H, CH(CH 1 (br, N-H), 3058 (w), 2961 (s), 2866 (s), 1629 ). JR data (KBr, cm’): 3266 cm 2 ) 3 CH(CH and 1615 (s, CO), 1490 (w), 1319 (s), 1253 (s), 1911 (s), 920 (s), 841 (s), 800 (s), 779 (s), . 1 760 (s) cm  71  _________________________  Synthesis  of  bis(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate)  mono(trimethylsilyl  amido) yttrium mono(tetrahydrofuran) (2.24)  Inside a glovebox, a parallel synthetic apparatus tube was charged with yttrium tris(bis(trimethylsilyl)amide) (0.345 g, 0.605 mmol) 5 mL of tetrahydrofuran and a stirbar. The reaction mixture was stirred until all solid was dissolved and N-(diisopropylphenyl)naphthyl amide 2.9  (0.401 g,  1.21 mmol) dissolved in 5 mL of tetrahydrofuran was added dropwise. The solution was stirred within the glovebox for 2 hours at 60 °C, and then filtered through a pipette plug of CeliteTM and concentrated under reduced pressure to a pale yellow solid. This solid was redissolved in toluene and stirred at 90 °C for a subsequent 2 hours. The product was then concentrated again to a pale yellow solid and recrystallized by dissolving in hexanes with a few drops of toluene to dissolve all solid and then left at -30 °C to give a white crystalline solid.  Yield: 0.450 g, 82%.  Refer to Figure 2.10, Table 2.3 and Appendix I for  ) D 6 crystallographic data. ‘H NMR (300 MHz, C  9.09 (d, J  9 Hz, 2H, aryl-IJ), 7.49 (m,  4H, aryl-R), 7.36 (d, J= 8 Hz, 2H, aryl-I]), 7.24 (m, 2H, aryl-If), 7.14 (m, 2H, aryl-I]), 7.03 (m, 2H, aryl-H), 6.96 (m, 4H, aryl-I]), 6.81 (t, J= 8 Hz, 2H, aryl-I]), 3.94 (broad t, J= 6 Hz, ), 1.23 (overlapping t and d, 16H, 02 ) 3 4H, O-CH ), 3.67 (broad septet, 4H, J= 7 Hz, CH(CH 2 ), 0.65 (d, J 2 ) 3 CH and CH(CH CH 2  =  ). 2 ) 3 6 Hz, l2H, CH(CH ), 0.53 (s, 18H, N(Si(CH 2 ) 3  ) ö 179.6 (d, J D 6 C NMR (100.6 MHz, C 3 ‘  2 Hz, C0), 141.9, 141.4, 137.5, 134.3, 131.9,  131.5, 130.4, 128.9, 128.4, 126.8, 126.3, 125.5, 125.3, 124.5, 123.8, 123.6 (aryl-C’s), 69.9 ), 4.6 2 ) 3 CH (O-CH ) , 24.9 (CH(CH ), 23.5 (CH(CH 2 ) 3 ), 25.4 2 2 ) 3 ), 28.0 (CH(CH 2 (0-CR ). IR data (KBr, cm’): 2962 (w), 1511(s), 1496 (s), 1400 (s), 1382 (s), 1245 2 ) 3 (N(Si(CH  72  ElMS (m/z):  . 1 (s), 964 (w), 842 (w), 828 (w), 779 (w) cm , 331 [naphthyl[O,N]Dipp]. N(Si(CH ] 2 ) 3  909 [M], 749 [M  -  C  ): i 6 4 2 5 C 7 H S O 3 N Anal. found (calcd for Y  68.15% (68.47%), N 4.65% (4.28%), H 7.97% (7.59%).  Synthesis  bis(N-2 ‘,6 ‘-diisopropylphenyl(p-(trifluoromethylphenyl)amidate)  of  mono(trimethylsilyl amido) yttrium mono(tetrahydrofuran) (2.25)  The experimental method described for 2.24 was used in the preparation of 2.25 using 2.12 (0.400 g, 1.15 mmol)  and  yttrium  tris(bis(trimethylsilyl)amide)  (0.326 g, 0.572 mmol) to give a pale yellow solid.  (Me3Si)2N\  ) 3 CF  C  2  The product was recrystallized by dissolving in a minimum amount of hexanes, with a few drops of toluene, and then left at -30 °C to give a white crystalline solid. Yield: 0.432 g, 80%. Refer to Figure 2.10, Table 2.3 and Appendix I for crystallographic data. ‘H NMR (400 MHz, C ) ö 7.48 (d, J D 6  8 Hz, 4H, aryl-I]), 7.10 (m, 6H, aryl-II), 7.01 (d, 4H, aryl-H),  , 1.18 (d, J = 7 Hz, 1 2H, CH(C11 ) 2 ) , 3.40 (septet, J = 7 Hz, 4H, 3 O-CH ) 3.94 (broad s, 4H, 2 , 0.81 (d, J CH 2 O-CH , 1.15 (m, 4H, ) CH(CH ) 2 ) 3  =  7 Hz, 12H, CH(CH ), 0.47 (s, 18H, 2 ) 3  ) ö 175.0 (C0), 141.4, 140.4, 136.5, 131.8 (q, J D 6 . ‘ N(Si(CH ) 2 ) 3 C NMR (100.6 MHz, C 3 =  , (CH(CH ) 2 ) , 27.8 3 (0-CR ) )), 129.8, 125.2, 124.1, 123.7 (aryl-C’s), 69.9 2 3 32 Hz, C(CF  . JR data (KBr, cm’): 2964 (w), 1626 (CH(CH ) 2 ) , 23.4 3 (CH(CH ) 2 ) , 24.0 3 CH 2 (O-CH 24.4 ) (s),  1528 (s), 1503 (s), 1410 (s), 1325 (s), 1170 (w), 1132 (s), 1067 (s), 1016 (w), 857 (s), 786  . 1 (w), 764 (w) cm  ElMS (m/z):  phenyl[O,N]Dipp], 3 pCF  349  2 ) 3 , 639 [Mt N(SiMe 945 [Mj, 784 3 [M-N(SiMe ] 2 )  phenyl[O,N]Dipp]. 3 [pCF  Anal.  found  (calcd  ): i C 58.33% (58.98%), N 4.00% (4.13%), H 6.56% (6.73%). 0 8 2 5 C 6 H S O 3 N 6 F Y  73  -  for  Synthesis of bis(N-2 ‘,6 ‘-diisopropylphenyl((3,5-bis(trifluoromethyl) phenyl)amidate) mono(trimethylsilyl amido) yttrium mono(tetrahydrofuran) (2.26)  The experimental method described for 2.24 was used in the preparation of 2.26 using 2.13 (0.201 g, 0.48 1 NF3) mmol) and yttrium tris(bis(trimethylsilyl)amide) (0. 138 g, 0.242 mmol) to give a pale yellow solid.  SD 3 (Me N 2 N  The  CF  2  product was recrystallized by dissolving in a minimum amount of hexanes, with a few drops of toluene, and then left at -30 °C to give a white crystalline solid. Yield: 0.2 19 g, 84%. 1 H NMR (600 MHz, C ) D 6  8.00 (s, 4H, aryl-I]), 7.60 (s, 2H, aryl-R), 7.06 (m, 2H, aryl-I]),  7.02 (d, J= 6 Hz, 4H, aryl-R), 3.91 (broad s, 4H, O-CH ), 3.38 (broad septet, 4H, J 2 ), 1.16 (d, J 2 ) 3 CH(CH J  =  6 Hz,  6 Hz, 12H, CH(CH ), 1.05 (broad s, 4H, 2 2 ) 3 CH 0.78 (d, 12H, O-CH )  ), 0.40 (s, 18H, N(Si(CH 2 ) 3 ). ‘ 2 ) 3 C NMR (150.9 MHz, C 3 ) ö 173.0 D 6 6 Hz, CH(CH  (C0), 140.7, 140.3, 135.3, 130.8 (q, J 123.5, 122.7 (q, J  =  =  33 Hz, C(CF )), 129.7, 127.6, 127.2, 125.6, 124.0, 3  270 Hz, C(CF )) (aryl-C’s), 69.9 (O-CH 3 ), 27.7 (CH(CH 2 ), 24.2 (02 ) 3  ). JR data (KBr, cm’): 2963 2 ) 3 CH CH ) 2 , 23.9 (CH(CH ), 23.2 (CH(CH 2 ) 3 ), 4.1 (N(Si(CH 2 ) 3 (w), 1623 (w), 1529 (s), 1463 (w), 1400 (s), 1349 (s), 1279 (s), 1185 (s), 1136 (s), 961 (w), . ElMS (m/z): 1 908 (w), 839 (w), 801 (w), 702 (w), 682 (w) cm  1082 [Mj, 1066 [M  -  (phenyl)[O,N]Dippl, 3 ], 665 [M N(Si(CH 2 ) 3 2 and 3,5-bisCF ) 3 ], 921 {M N(Si(CH 3 CH -  [O,N]Dipp]. 3 416 {3,5-bisCF  -  52 C 6 H 1 F S 0 3 N Y 6 ): i Anal. found (calcd for 2  C 54.50%  (54.11%), N 3.75% (3.64%), H 5.81% (5.76%).  74  Synthesis  of  mono(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate)bis(trimethylsilyl  amido) yttrium mono(tetrahydrofuran) (2.27)  Inside a glovebox, a parallel synthetic apparatus tube was charged with yttrium tris(bis(trimethylsilyl)amide) (0.40 1 g, 0.701 mmol) 10 mL of tetrahydrofuran and a stirbar.  The  reaction mixture was stirred until all solid was dissolved and 2.9  (0.401  g,  1.21  mmol)  dissolved  in  10  mE  of  tetrahydrofuran was added very slowly (approximately over 10 minutes) to the stirring solution of yttrium tris(bis(trimethylsilyl)amide) at room temperature. The solution was stirred within the glovebox for 2 hours and then filtered through a pipette plug of Celite and concentrated under reduced pressure to a white solid.  The product was recrystallized by  dissolving in minimum amount of hexanes and then left at -30 °C to give colourless plates. Yield: 0.443 g, 77%. Refer to Figure 2.12, Table 2.3 and Appendix I for crystallographic ) D 6 data. ‘H NMR (600 MHz, C 1]), 7.48 (d, J  9.16 (d, J= 6 Hz, 1H, aryl-I]), 7.54 (t, J= 6 Hz, 1H, aryl  6 Hz, 1H, aryl-I]), 7.33 (t, J  II), 6.97 (m, 3H, aryl-H), 6.75 (t, J  6 Hz, 2H, aryl-H), 7.23 (t, 1H, J  6 Hz, 1H, aryl-If), 3.81 (broad t, J  6 Hz, aryl  , O-CH ) 6 Hz, 4H, 2  , 1.13 (broad t, J CH(CH ) 2 ) , 1.20 (d, 6H, J = 6 Hz, 3 CH(CH ) 2 ) 3.48 (septet, 4H, J = 6 Hz, 3  6  . ‘ N(Si(CH ) 2 ) C 3 , 0.49 (s, 32H, 3 CH(CH ) 2 ) , 0.70 (d, J = 6 Hz, 6H, 3 CH 2 O-CH Hz, 4H, ) ) D 6 NMR (150.9 MHz, C  179.9 (C0), 142.8, 141.9, 135.1, 132.7, 132.0, 131.9, 131.2,  , 28.3 (O-CH ) 129.2, 128.7, 128.6, 127.6, 127.3, 126.4, 125.5, 125.0, 124.2 (aryl-C’s), 72.4 2  . IR (N(Si(CH ) 2 ) , 6.1 3 (CH(CH ) 2 ) , 24.5 3 (CH(CH ) 2 ) , 25.2 3 CH 2 (O-CH , 26.2 ) (CH(CH ) 2 ) 3 data (KBr, cm’): 2963 (w), 1516 (s), 1497 (s), 1399 (s), 1379 (s), 1245 (s), 956 (w), 863 (w), . ElMS (m/z): 739 [Mj, 724 [M 1 844 (w), 668 (w) cm  -  . N(Si(CH ] 2 ) ], 578 [M 3 3 CH -  75  ): i C 57.82% (57.67%), N 5.46% (5.17%), H 8.38% 9 8 4 3 C 6 H S 2 O 3 N Anal. found (calcd for Y (8.44%).  Synthesis  of  mono(N-2 ‘,6 ‘-diisopropylphenyl(tert-butyl)amidate)bis(trimethylsilyl  amido) yttrium mono(tetrahydrofuran) (2.28)  The experimental method described for 2.27 was used in the preparation of 2.28 using 2.10 (0.100 g, 0.384 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.219 g, 0.384 mmol) to give a pale yellow solid.  The product was recrystallized by  dissolving in minimum amount of pentane and then left at -30 °C to give a colourless plates. Yield: 0.234 g, 82%. Refer to Figure 2.12, Table 2.5 and , 65 °C, mixture of two D 6 Appendix I for crystallographic data. ‘H NMR (400 MHz, C compounds a and b in a  1:2 ratio) ö 7.08 (s, 1H, aryl-H, compound a), 7.01 (s, 2H, aryl-H,  compound a), 7.00 (s, 2H, aryl-H, compound b), 6.70 (m, 1H, aryl-H, compound b), 3.81 , compound a), 3.25 (septet, 2H, 2 ) 3 , 3.39 (septet, 2H, J = 6 Hz, CH(CH O-CH ) (broad s, 4H, 2 , compound a), 1.34 (d, 2 ) 3 , compound b), 1.42 (d, 6H, J = 6 Hz, CH(CH 2 ) 3 J = 6 Hz, CH(CH 2 for compound b ) 3 , compound a), 1.31 (d, 1 OH, J = 6 Hz, CH(CH 2 ) 3 6H, J = 6 Hz, CH(CH , 1.22 (d, 15H, J CH 2 O-CH overlapping with )  =  2 for compound b ) 3 6 Hz, CH(CH  ) for compound b), 0.36 (s, 3 ) for compound a), 1.10 (s, 9H, C(CH 3 overlapping with C(CH C NMR (150.9 MHz, 3 2 for both compound a and b). ‘ ) 3 36H for a, 36H for b, N(Si(CH , 25 °C, broad and complicated) ö 186.3 (C0), 140.7, 140.6, 124.7, 124.2, 123.1 (br), D 6 C , 29.5 (br), 28.6 C}1 2 (O-CH ), 41.7 ) 2 121.4 (br), 121.4 (br), 120.5 (br) (aryl-C’s), 71.2 (0-CR 2 ) 3 (br), 27.9, 27.6 (br), 25.4 (br), 24.9 (br), 24.1 (br) 23.6 (br), 22.9 (br), 21.6 (br) (CR(CH  76  _____________________________  and C(CI-{ ), 5.12 (br), 4.34 (br) (N(Si(CH ) 3 ). JR data (KBr, cm’): 2961 (s), 1513 (s), 2 ) 3 1477 (s), 1399 (s), 1348 (s), 1313 (w), 1246 (s), 1176 (w), 942 (s), 830 (s), 767 (w) cm . 1 ElMS (m/z): 669 [M], 654 [M  -  ], 509 [M N(Si(CH 3 CH ]. Anal. found (calcd for 2 ) 3 -  30 C 7 H S 2 O 3 N Y 4 3 ): i C 52.35% (53.40%), N 5.48% (5.66%), H 9.11% (9.51%).  Synthesis of mono(p-(trifluoromethylphenyl)amidate)bis(trimethylsilylamido) yttrium mono(tetrahydrofuran) (2.29)  The experimental method described for 2.27 was used in the preparation of 2.29 using 2.12 (0.100 g, 0.287 mmol) and yttrium tris(bis(trimethylsilyl)amide) (0.163  SI) 3 (Me N 2 \  g, 0.286 mmol) to give a pale yellow solid. The product  SI) 3 (Me N 2  N  /X)o  —  3 \/CF  was recrystallized by dissolving in minimum amount of pentane and then left at -30 °C to give a white solid. Yield: 0.194 g, 82%. ‘H NMR (600 MHz, C ) D 6  7.50 (d, J  6 Hz, 2H, aryl-I]), 7.07 (m, 3H, aryl-I]), 6.96 (d, J  =  ), 3.31 (septet, J 2 aryl-I]), 3.69 (broad s, 4H, O-CH  =  6 Hz, 2H,  6Hz, 2H, CH(CH ), 1.17 (d, J 2 ) 3  6Hz,  ), 2 ) 3 CH O-CH ) , 0.82 (d, J= 6 Hz, 6H, CH(CH 6H, CH(CH ), 1.11 (broad s, J= 6 Hz, 4H, 2 2 ) 3 C NMR (150.9 MHz, C 3 ) ö 174.6 (C0), 143.1, 141.6, D 6 0.46 (s, 36H, N(Si(CH ). ‘ 2 ) 3 137.5, 132.8 (q, J  =  )), 131.0, 126.2, 125.5, 125.4 (q, J 3 33 Hz, C(CF  =  169 Hz, C(CF )), 3  ), 28.5 (CH(CH 2 ), 25.2 (overlapping 2 2 ) 3 CH and O-CH 125.2, 124.9 (aryl-C’s), 72.1 (O-CH ). JR data (KBr, cm’): 2962 (w), 1528 (s), 2 ) 3 ), 24.4 (CH(CH 2 ) 3 CH(CH ), 6.0 (N(Si(CH 2 ) 3 . ElMS (m/z): 1 1501 (s), 1410 (s), 1327 (s), 1247 (s), 1132 (s), 1067 (w), 833 (s), 668 (w) cm 742 [M  -  I, 596 [M 3 CH  -  35 C 6 H S 2 O N 3 F Y 6 ): i C ]. Anal. found (calcd for 4 2 ) 3 N(Si(CH  5 1.74% (52.08%), N 4.86% (5.06%), H 7.49% (7.89%).  77  2.9  References  (1)  Burgstein, M. R.; Berberich, H.; Roesky, P. W. Chem. Eur. .1 2001, 7, 3078.  (2)  Kim, Y. K.; Livinghouse, T.; Bercaw, J. E. Tetrahedron Lett. 2001, 42, 2933.  (3)  Tredget, C. S.; Lawrence, S. C.; Ward, B. D.; Howe, R. G.; Cowley, A. R.;  Mountford, P. Organometallics 2005, 24, 3136. (4)  Arnold, P. L.; Mungur, S. A.; Blake, A. J.; Wilson, C. Angew. Chem.,  mt.  Ed. 2003,  42, 5981.  (5)  Yao, Y. M.; Zhang, Z.  Q.; Peng, H. M.; Zhang, Y.; Shen, Q.; Lin, J. Inorg. Chem.  2006, 45, 2175.  Q.; Yao, Y. M.; Shen, Q.; Zhang, Y. I Organomet. Chem. 2005, 690, 4685.  (6)  Xue, M.  (7)  Sanchez-Barba, L.  L.; Humphrey,  S. A.; Bochmann, M.  Sanchez-Barba, L. F.; Hughes, D. L.; Humphrey,  S. M.; Bochmann, M.  F.; Hughes, D.  Organometallics 2005, 24, 3792. (8)  Organometallics 2006, 25, 1012. (9)  Chai, J.; Jancik, V.; Singh, S.; Zhu, H.; He, C.; Roesky, H. 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Scand. B: Org. Chem. Biochem. 1984, B38,  397. (50)  Joergensen, K. A.; Ghattas, A. B.; Lawesson, S. 0. Bull. Chem. Soc. Chim. Fra.  1984, 204. (51)  Budzelaar, P. H. M.; van Oort, A. B.; Orpen, G. Eur. I Inorg. Chem. 1998, 10, 1485.  (52)  Leonard, N. J.; Nommensen, E. W. I Am. Chem. Soc. 1949, 71, 2808.  80  Chapter 3. Yttrium Amidate Complexes as Effective Initiators for the Ring-Opening Polymerization of -Caprolactone’ 3.1  Introduction Plastic products have become essential to the modern economy, being utilized in  everything from packaging to electronic devices. Currently, most plastics are made from petroleum sources, meaning fossil fuel consumption.  A more sustainable option is the  utilization of biodegradable polymers, which can re-enter the carbon cycle upon decomposition. Synthetic biodegradable polymers (green plastics) can be used for a variety of consumer needs such as biomedical applications and plastic substitutes.’ 5  The most  common synthetic green polymers are variations of polyesters, which can be synthesized in multiple ways. Polycondensation of diols and dicarboxylic acids is one method, but usually 6 requires high temperatures and long reaction times to obtain high molecular weight polymer. A more efficient method for high molecular weight polyester formation is ring-opening polymerization (ROP) of lactones or lactides, since the chain length can be controlled and the 6 The ring-opening polymerization of reactions are typically done at modest temperatures.  -  caprolactone (3.1) is widely used, and the resulting polyester (3.2) is already used extensively in the biomedical industry (eg. surgical sutures, drug delivery media) (Figure 3. l).  Initiator  e-caprolactone 3.1  poly(E-caprolactone) 3.2  Figure 3.1. Ring-opening polymerization of -caprolactone. 1  A version of this has been published Stanlake, L. J. E., Beard, J. D. and Schafer, L. L. Inorg. Chem. 2008, 47, 8062-8068. Reproduced in part with permission from Inorg. Chem. 2008, 47, 8062-8068. Copyright 2008 American Chemical Society.  81  Generally, polymerization can be explained in three different steps, initiation, propagation and finally, termination.  Specifically for ring-opening polymerization of  caprolactone, the initiation step is believed to involve the ring-opening of one molecule of  -  -  caprolactone, which is promoted by the coordination of the second molecule of c caprolactone (Figure  3.2).8  Propagation begins when the third equivalent of E-caprolactone  coordinates and concurrently another molecule of -caprolactone is inserted into the growing polymer chain. The metal complex is known as an initiator (I) because its presence is required to begin the polymerization.  M-R  a Further propagation, followed by quenching  R14H  8 Figure 3.2. Proposed mechanism for the ring-opening polymerization of -caprolactone.  7 denoting ’ 9 Many rare-earth initiators of ROP of -caprolactone are “living” initiators, that the rate of initiation is much larger than the rate of propagation.  Furthermore, the  termination step is insignificant, which results in a well-behaved catalyst that can generate block copolymers,’ 824 and produce polymer with controlled molecular weights paired with  82  low molecular weight distributions as measured by the polydispersity index, PDI. For the purposes of this thesis, the latter properties represent what will be referred to as a “controlled” polymerization (where PDI is close to one). Most often the molecular weight values of poly(-caprolactone) correlate very well with calculated values which arise from the molecular weight of -capro1actone (114 gmol’) multiplied by the monomer to initiator ratio ([MI/El]).  Living initiators typically have a linear relationship between 1) percent  conversion and time of the reaction and 2) molecular weight (of polymer obtained) and the monomer to initiator ratio. 25 Many metal-based initiators have been used in the synthesis of poly(-caprolactone) such as tin, 2628 aluminum, 30 and rare-earth metals (lanthanides, and group 3 4 ’ 29 metals). 137 Tin ’ 3 ” and aluminum compounds are very successful in this transformation, but due to their acute toxicity they are not ideal for commercial use. 39 Rare-earth complexes are very attractive ’ 38 catalyst systems due to their low toxicity, low cost and high activity. 40 These features make group 3 and the lanthanides popular for use as initiators in -caprolactone ROP. Interestingly, homoleptic amidinate complexes (3.3), and bis(guanidinate) complexes (3.4) of the lanthanides and group 3 metals have been modestly successful in ROP of caprolactone (Figure  33)4143  -  An example is the homoleptic neodymium amidinate  complex, [CyNC(Me)NCy] Nd that forms poly(-capro1actone) of a moderate molecular 3 weight (7.98 x iü gmoF ) with a PDI value of 1.8 1.41 Also, aryloxo lanthanide compounds 1 (3.5) supported by 13-diketiminato ligands were found to be living initiators for this transformation.”  83  R  F  Ln 3 R  Ar  (R2NLn Li(TMEDA) 2 R  Ar  3.4  3.3  3.5  Figure 3.3. Initiators for -caprolactone ring-opening polymerization. (Ln lanthanides).  =  Y or the  Selected examples of known yttrium complexes that initiate the ring-opening polymerization of E-caprolactone are shown in Figure 3.4, and some polymerization results are shown in Table 3.1.  Polymer characteristics are very dependant on polymerization  conditions (temperature, concentration, [M]/[I1 ratio, rate of addition of monomer etc.), so the reported examples provide a guide for yttrium initiator ability for ROP of 8-caprolactone. Compounds  3•725  and  are variations of yttrium metallocenes, where one is an  yttrium alkoxide (3.7), and the other contains a linked amido-cyclopentadienyl ligand (3.8). Both 3.7 and 3.8 gave reasonable polydispersity values (<2) and molecular weights typical for group 3 complexes (Table 3.1, Entry 1 and 2).  The isopropoxy yttrium diethyl  acetoacetate complex 3.9 is shown to be a well-controlled living polymerization catalyst with molecular weights that match calculated values, and a polydispersity value very close to one (Table 3.1, Entry 3). The bisQhosphinimino) methanide yttrium complex 3.10 (Table 3.1, Entry 4) produced higher molecular weight polymer with larger polydispersity values than complex 3.7, 3.8 or 3.9. Interestingly, the yttrium pyrrolyl complex 3.6, the only homoleptic complex described here, was unable to initiate polymerization (Table 3.1, Entry 5), which Matsuo and co-workers attribute to the Y-N(pyrrolyl) bond being too strong to initiate polymerization. 15  84  2 Me NOMe OMe 2 SiMe Ar  =  3.7  -OMe-p 4 H 6 C 3.6  3.8 3 ,SiMe Ph N 2 N ,CI cc\ /YNPPh 2 P—N 2 Ph N\ 3 PPh S1Me 2 3.10  Figure 3.4. Known yttrium complexes of varying ligands that have been used as initiators for E-caprolactone ROP.  Table 3.1. Comparison of yttrium initiators for the ROP of s-caprolactone. Entry  Initiator  [M]/[Ij  TeIUP.  Time  515  3.6 3.7 3.8 3•9 3.10  100 20 197 200 289  20 0 25 20 25  5 10 1.5 0.5 2  125 323  445 a  Yield = weight of polymer obtained/weight of monomer used. polystyrene samples.  b  (x1o gmol )  trace 90 92 94 94  PDI  -  -  9.97 7.20 2.48 10.2  1.12 1.80 1.08 2.10  b  Measured by GPC calibrated with standard  Taking a look at the above rare-earth complexes it is apparent that vastly different metal complexes can mediate this desirable reaction.  It has been realized that the ligand can  polymers. 1,46 4 ’ influence the molecular weight, polydispersity values, and yield of resultant 40 ‘ Therefore, easily accessed and modular ligand sets suitable for rare-earth complexation are also ideal targets for the optimization of the synthesis of requisite metal complexes and their inherent catalytic activity.  85  3.1.1 Mechanistic Introduction The mechanism for the ROP of -caprolactone using rare-earth initiators (Figure 3.2) is thought to proceed via a coordination-insertion mechanism which involves formation of a metal-alkoxide species by cleavage of the oxygen-acyl bond that then regenerates a metal alkoxide species and promotes further polymerization.  The mechanism involves  coordination of one molecule of -caprolactone, and subsequently a second incoming equivalent promotes the ring-opening. Also, the terminus of the growing polymer contains the ligand that was originally bound to the metal centre.  The coordination-insertion route is  most probable for rare-earth metal centres, as compounds can be isolated with -caprolactone as a donor molecule through its carbonyl oxygen’ 75 and end-group analysis most often ’ 4 determines that the ligand terminates the ’ 48 polymer.’°’ 8 2 Furthermore, this mechanism was 3 calculated to be favoured over the route where ring-opening occurs at the oxygen-alkyl position on -capro1actone.’ To further elucidate the ROP mechanism, Yasuda and co-workers studied the initiation step with a living initiator yttrium cyclopentadienyl alkoxide complex 3.7 (Figure  35)25  Complex 3.7 reacted with one equivalent of -caprolactone to give a coordination complex where -caprolactone can initially bind as a monodentate ligand (3.11). After quenching,  -  caprolactone was re-isolated. If two equivalents of -caprolactone are reacted with complex 3.7 and then quenched, one equivalent of -caprolactone is returned and one equivalent of ring-opened ester alcohol (3.13) is produced. This indicates that the intermediate species after initiation is complex 3.12.  Therefore, polymerization is perceived to start with the  coordination of 6-caprolactone to form the 2:1 complex. In the initiation step, the alkoxide  86  attacks to C=O group to generate the ring-opened complex with E-caprolactone coordinated. 14  H  3 0ç  N0Me  OMe +  2equiv. 0ç 3 3.12  a 0  H0 3.13  +  Figure 3.5. Initiation of ROP of-capro1actone using complex  3•7•25  To emphasize the importance of coordination of s-caprolactone as the initial step, a samarium tris(3-diketiminate) complex (Figure 3.6, 3.14) was found to be inactive for the polymerization of -capro1actone. Barbier-Baudry and coworkers interpret the solid-state molecular structure of 3.14 as having no open coordination site for monomer coordination. 16  3.14  Figure 3.6. Samarium tris(j3-diketiminate) complex 3.14.  87  Another potential initiation mechanism has been proposed for the ROP of —caprolactone using as Zr(acac) 4 (3.15, acac  =  acetylacetonate) (Figure  3•7)39  The polymer obtained using  4 as an initiator contained no evidence of acetylacetonate derivatives at the chain Zr(acac) end.  Additionally Dobrzynski observed enolate formation in the ‘H NMR spectrum as  indicated by signals arising at  4.05 and 3.63, corresponding to the CH O, and CHC(O) 2  protons in deprotonated capro1actone, as well as diagnostic peaks associated with 4 was protonated acetylacetonate ligand (3.18). The ROP of -caprolactone using Zr(acac) found to have an almost linear relationship between conversion of monomer and time of reaction, and slightly higher than calculated molecular weights of po1y(-capro1actone) were obtained with quite low polydispersity values (< 1.50).  (  (zr+Ô 3.15  3.16  DH  3.18  3.17  6 4 (3.15). Figure 3.7. Initiation of -capro1actone ROP using Zr(acac)  88  Another potential enolate mechanism has been described using rare-earth phenyl 76 These complexes are believed to initiate by enolization of the s-caprolactone ’ 38 compounds. monomer, followed by insertion into the lanthanide-oxygen bond by another molecule of  -  caprolactone. The evidence for the proposed mechanism presented by Deng and coworkers is the lack of aryl signals in the end-group analysis, indicating that the ligand is not terminating the polymer. In all investigated cases, rare-earth ROP of 8-caprolactone started by coordination of  -  caprolactone. It was shown in Chapter 2 that the THF molecule in complex 3.19 is easily displaced by multiple donors making it an intriguing potential initiator for ROP of  -  caprolactone.  3.1.2 Scope of Chapter Similarities can be drawn between the reported yttrium initiators and the yttrium amidate complexes that were introduced in Chapter 2. The rare earth amidate complex replaces one nitrogen donor for an oxygen donor when compared to the amidinate complexes (3.3), and bis(guanidinate) complex (3.4). Stevels and coworkers propose that a hard oxygen donor can stabilize the highly electropositive nature of the rare earth metal centre, thereby reducing the possibility of acid-base type side reactions that can occur with substrates containing activated hydrogen atoms. 32  Tetrahydrofuran (THF) occupies a seventh coordination site in 3.5 as  well as 3.19, and as shown in Chapter 2, the THF molecule can be displaced by a range of Lewis base donors. The modifiability of the amidate scaffold, and the ease with which the donor THF is displaced led us to consider the amidate complexes of yttrium as  -  caprolactone ring-opening initiators. As shown in Section 3.1, varying stoichiometries of  89  ligands can be used to give rare-earth complexes that are initiators in the ROP of  g  caprolactone. For this reason, tris, bis and mono(amidate) complexes of yttrium (3.19, 3.20 and 3.21, respectively, Figure 3.8) are explored as -caprolactone ring-opening initiators. The desirable amidate ligand features are determined by varying substituents on the amidate backbone and testing the initiator ability of the varied yttrium complexes. Furthermore, this chapter will include the results for mechanistic investigations for ROP of -caprolactone.  2 S 3 (Me N i) \ 77\\ /Y ) / SD 3 (Me N 2 o /\  t  3.20  3.19  3.21  Figure 3.8. Tris, bis and mono(amidate) complexes of yttrium. 3.2  Yttrium Amidate Complexes as Initiators  3.2.1 Results and Discussion Research on ROP of 8-caprolactone is very dependant on the characterization of the resultant polymer.  The polymer is characterized by yield, molecular weight and  polydispersity indices, where the latter two results are obtained from gel permeation chromatography (GPC).  It should be noted that the molecular weight (Mw) and  polydispersity indices (PDI) are reported two separate ways in this thesis 1) versus a polystyrene standard curve and 2) using a triple-detection laser-light scattering (LLS) detector. Most literature values for M and PDI for rare-earth initiation of -caprolactone  90  ROP are reported versus a polystyrene standard curve (including selected results presented in Section 3.1), but this is known to give misleading results for M and PDT due to the very 77 Results in this thesis for M using a polystyrene different nature of the two polymers. standard curve are typically twice the value received for M using triple-detection laser-light scattering results.  Using the triple-detection LLS technique molecular weights can be  determined directly without a standard curve. These results are more accurate than using a standard curve, but in order to compare results to literature values, both the polystyrene standard curve results and the LLS results will be reported. Furthermore, it must be emphasized that all results have good reproducibility and are averaged values from duplicate, or presented triplicate polymerization runs. Polymerizations were initially done in duplicate, and if there was more than ± 5% difference in yield, M or PDI values, further polymerization runs were performed until the data was precise.  3.2.1.1  Comparison of Tris, Bis and Mono(amidate) Complexes  Amidate  complexes  mono(tetrahydrofuran)  tris(N-2’,  (3.19),  6 ‘-diisopropylphenyl(naphthyl)amidate)yttrium  bis(N-2’,  6 ‘-diisopropylphenyl(naphthyl)amidate)  mono(trimethylsilyl amido) yttrium mono(tetrahydrofuran) (3.20), and mono(N-2’, 6’diisopropylphenyl(naphthyl)amidate)  bis(trimethylsilyl  amido)  yttrium  mono(tetrahydrofuran) (3.21), were found to have similarities to known -caprolactone ring opening polymerization initiators.  Since they have the same amidate ligand, a direct  comparison between tris, bis and mono(amidate) complexes was undertaken to see which complex would be the ideal initiator for the ROP of -caprolactone.  91  Initial experiments for the ROP of -caprolactone were carried out using complexes 3.19, 78 3.20 and 3.21 as initiators. The experimental procedure was adapted from literature results with an optimized [M]/[I] of 225 (vide infra). Under an inert atmosphere, -caprolactone was added directly to a stirring solution of initiator in 10 mL dry toluene. The reactions were stirred vigorously for 15 mm, subsequently exposed to air, quenched with 1 M aqueous hydrochloric acid (HC1) and the polymer can be isolated by precipitation with cold petroleum ether. The polymerization data of initiators 3.19, 3.20 and 3.21 are shown in Table 3.2. As shown in chapter two, these complexes were directly synthesized from yttrium tris(trimethylsilyl) amide (3.22), which is a known -capro1actone polymerization initiator. Thus polymerization results are also compared to 3.22 to note the effect of the amidate ligand on polymerization.  Furthermore, a control experiment, where the sodium salt of N  (diisopropylphenyl)naphthyl amide was isolated and used as an initiator has been completed. This control experiment tests the possibility that the anionic amidate ligand is sufficient to mediate polymerization on its own. This control experiment only produced trace amounts of polymer, indicating the presence of the yttrium centre is required for effective polymerization.  92  Table 3.2. Comparison of initiators for the ROP of s-caprolactone using a [MI/Fl] of 225. MwC Entry Initiator 4 PD! d (x i0 4 PD! C (x i0 ‘ °‘ ) 1 gmol gmo1) 10.7 1.28 91 32.5 2.12 3.19 1 3.8 6.33 2.04 12.8 2 3.20 99 2.43 5.81 1.86 99 11.8 3.21 3 3.214 2.46 94 9.6 16.0 4 3.22 a  weight of polymer General polymerization conditions: in toluene, 15 mm. of stirring, 25 °C. b Yield d obtained/weight of monomer used. C Measured by GPC calibrated with standard polystyrene samples. Measured by GPC (triple detection) equipped with differential refractometer (Waters), viscometer, and laserlight scattering detectors (Wyatt). =  Although the yield using the tris(amidate) complex 3.19 is somewhat lower than its bis and mono(amidate) counterparts, the M value is much larger. Also the PDI values for complex 3.19 are narrower in comparison to complexes 3.20 and 3.21. It is well established that a more shielded active site on the metal centre can block transesterification, which is a major contribution to chain termination, and also molecular weight distribution broadening, 9 The PDI enlargement is due in part 2 70 2 values. 6 ’ which consequently results in larger PDI 8 to the randomization of the polymer, which can occur with intermolecular transesterification, or the formation of cyclic polymers from intramolecular transesterification reactions (Figure 3.9). 19 Another possible reason for molecular weight distribution broadening is that more than one active species may be present, with initiation and propagation occurring at different rates. 16  93  OMl R 1 0  lnteolecular Transesterification  R,OM1 +  R  ntramoiecuiar Transesterification  +  0M] jM]  =  Metal  =  Polymer  Figure 3.9. Intermolecular and intramolecular transesterification reactions for chain 9 termination with poly(-caprolactone).’  Interestingly, using the same polymerization conditions as for initiators 3.19, 3.20, and 3.21, complex 3.22 was found to produce polymers with a much larger PDI than any amidate complex, but a smaller molecular weight than that obtained with complex 3.19 (Table 3.2, Entry 4). Hultzch et. al hypothesize that the large molecular weights and broad PDI are due to the absence of an inert spectator ligand, as well as the monodentate nature of the amido 1 ligands. 8 ’ 44 The amidate ligands help influence the control over the polymerization as shown by the lower PDI values compared to complex 3.22. The calculated molecular weight value for a , which is much lower than the values in Table 3.2 for 1 4 gmof [MI/El] of 225:1 is 2.57 x i0 the amidate complexes.  This indicates the amidate complexes are not polymerizing in a  controlled manner. The tris(amidate) complex 3.19 had the lowest PDI value paired with the  94  highest molecular weight, and is thought to be the better initiator over the corresponding bis and mono(amidate) complexes. Compared to known rare-earth initiators (3.7, 3.8, 3.9 and 3.10 (Figure 3.4)) for ROP of -caprolactone, complex 3.19 produces poly(-caprolactone) with some of the highest molecular weights with a fast reaction time of 15 mm. The polydispersity values are similar to the values obtained by complexes 3.8, and 3.10, but are much higher than known living initiator 3.9. Complex 3.19 produces polymer with a much higher molecular weight than neodymium amidinate complex [CyNC(Me)NCy] Nd, but has similar polydispersity values. 3 Although the analogous yttrium amidinate complex was prepared, no polymerization results were reported. Polymerization reactivity of rare-earth metal derived initiators has been found to increase with increasing metal radii, since a less crowded coordination environment (resulting from a larger metal radius) facilitates monomer coordination and presumably faster 82 This indicates similar neodymium compounds should be more reactive than ’ 40 insertion. yttrium (since Nd is larger than Y). Thus, the tris(amidate) complex 3.19 compares very well to the neodymium complex, suggesting that the amidate scaffold can result in an increase in reactivity over the amidinate ligand set. When used as an initiator, tris(amidate) complex 3.19 produces polymer with optimized properties (high molecular weight, narrow PDI) compared to the bis and mono(amidate) analogues 3.20 and 3.21. Resultant polymer properties suggest that complex 3.19 has better control during polymerization than the starting material yttrium tris(bis(trimethylsilyl)amide) 3.22. Also, complex 3.19 yields larger polymer molecular weights at room temperature than the other reported yttrium complexes (Table 3.1), as well as moderate PDI values. Improvements to this class of initiators could result in a more controlled polymerization,  95  which would be denoted by molecular weights that approach calculated values, as well as polydispersity values close to one. Further studies of ROP of -caprolactone were carried out using varying [M]/[I] ratios to find the optimized conditions. Additionally, modifications were made to the amidate ligand to vary the steric and electronic properties in order to evaluate the potential for tuning the activity of the polymerization initiator.  3.2.1.2  Effect of Monomer to Initiator Ratio  Varying monomer to initiator ratios can have a profound effect on the polymer produced.  When an initiator is a living catalyst, the molecular weight of the obtained polymer will increase with increasing monomer to initiator ratio. Thus, initial experiments for varying the [M]/[Ij ratio were carried out to explore complex 3.19 as a living catalyst, since complex  3.19 was found to be the optimal amidate complex for ring-opening polymerization of s caprolactone. The polymerization reactions were carried out with the same conditions as described in section 3.2.1.1 except the monomer to initiator ratios ([M]/[I]) were varied as shown in Table 3.3.  96  Table 3.3. Summary of ring-opening polymerization of -capro1actone for initiator 3.19. MwC  .  Entry  [M]/jI]  1 2 3  10 20 30 40 50 100  4  5 6 7  o)  70 73 84 74 95 96  225 500  (x iO ) 1 gmol 5.52 6.43 9.46 10.1 24.7 27.8 32.5  PD!  1.61 1.61 1.94 1.70 2.56 2.40 2.12  (x i0 4 gmol’) 4.36 4.59 7.25 7.39 11.8 10.2 10.7  91 63 31.7 2.20 10.7 General polymerization conditions: in toluene, 15 mm, of stirring, 25 °C. 8  a  (  d  PD!  1.17 1.14 1.44 1.18 1.62 1.38 1.28 b  1.28 Yield = weight of polymer  obtained/weight of monomer used. Measured by GPC calibrated with standard polystyrene samples. d Measured by GPC (triple detection) equipped with differential refractometer (Waters), viscometer, and laserlight scattering detectors (Wyatt).  100000  90000  80000  70000  60000  Experimental  50000  40000  30000  20000  Calculated  10000  0 0  10  20  30  40  50  60  Monomer to Initiator Ratio  •  L  Calculated Experimental Data (using LLS data) Experimental Data (versus polystyrene)  • —  -  —  —  —  —  Experimental Data (versus polystyrene) Calculated Experimental Data (using LLS data)  Figure 3.10. M values of po1y(-capro1actone) at different [Mj/{I] ratios using complex 3.19 as the initiator at room temperature.a a  Experimental plot uses averaged data, error bars are 2a and trendline is in place to guide the eye.  97  Comparing entries 1-6, the yield of the polymer is increased as the [M]/[I] is increased to a maximum at [MJ/[I] of 100, where the yield of polymer starts to decline at higher {M]/[Ij ratios (Table 3.3, Entries 7 and 8). From the graph (Figure 3.10), the M values on average increase with increasing [M]/[I] ratio, but the relationship is much larger than calculated values (calculated line in Figure 3.10). The 1i4 and PDI values of polymer obtained when complex 3.19 was employed as an initiator is an indication of uncontrolled or slow initiation, or possible side-reactions.  This may be due to an increase in chain terminationlcatalyst  84 The molecular ’ 83 decomposition events as the concentration of monomer is increased. weights obtained (against a polystyrene standard curve) in entries 5-8, are among the highest molecular weights observed for rare-earth metal initiated -caprolactone ring-opening 2 polymerization.’ 6 8 ’ 3 4 5  However, the PDI values are typical for yttrium initiated ring  opening polymerization of -caprolactone. The [Mj/{I] ratio of 225 was regarded as the optimized reaction conditions (as shown in entry 7 where polymer yield and molecular weight were maximized for compound 3.19) and was used for comparison studies with other yttrium amidate complexes.  3.2.1.3  Effect of Amidate Ligand on Initiator  As mentioned before, the ligand can influence the molecular weight, polydispersity 4 40 polymers. 4 674 1 Thus, varying the substituents of the amidate values, and yield of resultant ’ ligand is expected to result in modified polymer properties. The advantage to the amidate backbone is the ease with which steric or electronic properties can be varied. Figure 3.11 shows four different yttrium complexes that have been synthesized using different amidate ligands. Complex 3.23 has a slightly more electron-donating group than complex 3.19 (tert  98  butyl group versus naphthyl). Complex 3.24 has less bulk shielding the active site than any of the other yttrium amidate complexes (vide supra), which provides insight into the effect of sterically protecting the active site during polymerization. Both complexes 3.25 and 3.26 have electron-withdrawing groups on the amidate backbone, which results in more ligand charge localized on the ligand as opposed to donating to the yttrium centre. The outcome of this is the yttrium centre being more electropositive than in complex 3.23 or 3.24, and being therefore more Lewis acidic.  CO_Y)3 3.23  C0Y) 3.24  CF3  CoYcF3)3 3.25  3.26  Figure 3.11. Yttrium amidate complexes containing varying amidate backbones.  Each of the complexes in Figure 3.11 are used in polymerization studies and the results are shown in Table 3.4. Complex 3.23 (Table 3.4, Entry 1) has a slightly more electron donating group than complex 3.19 (tert-butyl group versus naphthyl) but similar steric bulk about the reactive metal centre, resulting in lower molecular weight values yet similar polydispersity values. The more sterically accessible complex 3.24 gave a reduced yield in comparison to 3.23 and 3.19, but also a higher molecular weight and slightly broader PDI.  99  This is consistent with a more open active site that can lead to more side reactions, such as 23 transesterification. When a more electron-withdrawing amidate ligand is installed, such as compounds 3.25 and 3.26, the yields of polymer are reduced dramatically.  The molecular weight of the  polyester produced is also lower than when compound 3.19 is used as initiator, indicating a reduced efficiency of initiating the ROP of -caprolactone. Possibly the yttrium complexes 3.25 and 3.26 are too Lewis acidic resulting in sluggish initiation and/or propagation. Modest variations to ligand structure investigated here result in notable changes in polymerization initiation activity.  These results show that tris(amidate) complexes 3.19,  3.23, 3.24, 3.25 and 3.26 are good initiators of ring-opening -caprolactone, with 3.19 giving the best combination of yield, high molecular weight and low PDI.  A more sterically  protected active site on the initiator, by using bulkier diisopropyl (Dipp) groups as opposed to dimethyiphenyl (Dmp) groups on the amidate ligand, imparts a narrower molecular weight distribution in resultant poly(s-caprolactone) (Entries 1 and 2).  When using a more  electropositive yttrium centre as an initiator, low molecular weights, and poor yield of polymer are produced (Entries 4 and 5). The ideal yttrium amidate initiator, in terms of sterics and electronics on the amidate ligand, was found to be complex 3.19.  100  Table 3.4. Comparison of initiator ability for the ROP of E-caprolactone for tris(amidate) complexes 3.23, 3.24, 3.25 and 3.26 using a [M]/[I1 of 225. Mw’ Yw1l Entry Initiator PDI (x iø (x iO PD! d o) ( gmol’) gmol’) 1 91 3.19 32.5 2.12 10.7 1.28 2 89 3.23 13.2 2.17 7.9 1.49 3 72 3.24 38.6 2.49 14.0 1.45 4 3.25 56 17.8 2.47 5.6 1.41 5 30 3.26 5.0 2.00 3.19 1.30 a  General polymerization conditions: in toluene, 15 mm. of stirring, 25 0 c• b Yield weight of polymer obtained/weight of monomer used. Measured by GPC calibrated with standard polystyrene samples. d Measured by GPC (triple detection) equipped with differential refractometer (Waters), viscometer, and laserlight scattering detectors (Wyatt) =  3.2.1.4  Effect of Temperature on Initiation  The M of the poly(-caprolactone) obtained by tris(amidate) complexes as initiators is much larger than calculated, and the PDI values show broad molecular weight distribution, suggesting slow initiation followed by rapid polymerization by small quantities of catalytically active species. Temperature was shown to have an effect on the polymerization (Table 3.5). Firstly, the ROP reaction using complex 3.19 as an initiator was performed at 0 °C, with a reaction time of 15 minutes. The polymerizations were carried out in Schlenk flasks containing the initiator in 10 mL of dry toluene, cooled to 0 °C using an ice bath. The monomer was syringed directly into the stirring solution of initiator, stirred for 1 hour, quenched with a few drops of I M aqueous hydrochloric acid, and then precipitated from cold petroleum ether. The polymer was isolated by vacuum filtration and dried in vacuo overnight at room temperature before GPC analysis. After 15 minutes of reaction time only trace amounts of polymer were obtained, however, once the reaction time was increased to 1 hour at 0 °C, polymer yield increased greatly for a [Mj/[I] ratio of 225. The reported lower  101  yields for polymer with smaller [M]/[I] ratios is most likely due to the smaller scale on which the reaction is performed, which results in a challenging polymer isolation step. At 0 °C, the polymerization produces polymer with lower molecular weights than the same study at room temperature, but the molecular weights are still substantially larger than calculated values (Figure 3.12). The PDT values are also slightly narrower than at room temperature, indicating that side reactions are less prevalent at lower temperatures. These results are all consistent with the observation that tris(amidate) complex 3.19 is not a living initiator at room temperature or at 0 °C. The effect of temperature on the initiation and propagation steps of the polymerization is further studied in section 3.3.  Table 3.5. Comparison of initiator ability for the ROP of -caprolactone at 0 °C for tris(amidate) complex 3.19. Me Md Temp. d PD! PD! (x 1O) (x 1O jM]/[Ij Entry gmol ) gmol )  3 4 5 6 7  25 0 0 0 0 0 0  10.7 3.32 1.82  1.28 1.34  5.15  2.12 1.77 1.55 1.62  2.63  1.42  48  5.17  1.96  2.58  1.24  42  6.02  1.78  3.08  1.43  55  4.65  1.65  2.43  1.53  225 225 10 20 30 40  91 93  32.5 6.24  55  3.219  54  50  1.19  ing. C Yield = weight of b Conditions: in toluene, 15 mill, of stirring. Conditions: in toluene, 1 hour of stiff d polymer obtained/weight of monomer used. Measured by GPC calibrated with standard polystyrene samples. Measured by GPC (triple detection) equipped with differential refractometer (Waters), viscometer, and laser light scattering detectors (Wyatt). a  102  ___________  50000  40000  30000  2OOOO  10000  -  -  Calculated  0  -10000  -____________________________________  10  0  • •  20  40  30  60  50  Monomer to Initiator Ratio • Experimental Data (using LLS data) Experimental Data (versus polystyrene) Experimental Data (versus polystyrene) Calculated Cculated Experimental Data (using LLS data) —  -  —  Figure 3.12. M values of po1y(-caprolactone) at different [M]/[I] ratios using complex C. 3.19 as the initiator at 0 0 a  Experimental plot uses averaged data, error bars are 2a and trendline is in place to guide the eye.  It has been shown that the tris(amidate) complex 3.19 was a better initiator than the analogous bis and mono(amidate) complexes 3.20 and 3.21, at the optimized [M]/[I] ratio of 225.  Variations on the amidate ligand of the initiator did have an effect on the  polymerization results.  When less bulk (complex 3.24) or when electron-withdrawing  groups (complexes 3.25 and 3.26) were installed on the amidate ligand of the initiator, polymerization was less controlled than when complex 3.19 was used. Temperature was found to have an effect on the polymerization, and at 0 °C the polymerization results were closer to the calculated values than results obtained from room temperature experiments.  I (•\  ‘U-,  Overall, complex 3.19 was deemed to be the optimized initiator and is used for further investigation into the polymerization mechanism.  3.3  Mechanistic Investigations  3.3.1 Results and Discussion From the results in Section 3.2, it is evident that tris(amidate) complexes are prone to promote uncontrolled ROP of s-caprolactone (high molecular weights paired with moderate PDI values).  The initiators formed in situ are highly active, but more insight into the  mechanism is needed in order to better understand and improve upon these initiators. Firstly, the terminus of the poly(s-caprolactone) was identified in order to deduce which initiation mechanism is most likely involved for amidate complex 3.19.  The polymer  produced using initiator 3.19 at 0 °C and a 10:1 monomer to initiator ratio was evaluated using end group analysis by ‘H NMR spectroscopy, as shown in Figure 3.13.  The  incorporation of one ligand in the polymer chain is observed, as evidenced by the signal at OH terminus of the polymer, signal ‘a’) that integrates for 2 protons, as 2 3.66, (for the CH does the multiplet at  3.33 for the methine protons of the ligand isopropyl substituents (also  2 protons, signal ‘g’). This is consistent with the mechanism of polymerization proceeding through ligand promoted initiation to produce a polymer with N-(diisopropylphenyl)naphthyl amide as the terminus.  104  ____________J  C  H 0  e, c  h•  b  *  --:-  H  a g  I  -______  r  r.!frm  85  80  75  70  6.5  r I!!!•![I. 60 55  5.0 4.5 40 Chernic& Shift (ppn)  3.5  3.0  2.5  2.0  1.5  1.0  05  0  Figure 3.13. ‘H NMR (600 MHz, CDC1 , 25 °C) spectrum of poly(-caprolactone) using 3 initiator 3.19 at 0 °C with 10:1 [MJ/[I] ratio.  As noted earlier, complex 3.19 does not display living catalyst behaviour, potentially due to small amounts of initiation occurring. To examine this, the progress of the reaction was studied. This was completed at 0 °C because the polymerization occurs too rapidly at room temperature (>90% yield after 4 minutes). Multiple polymerization reactions were carried out simultaneously and then quenched at varying times during the reaction. The yield of polymer was graphed against reaction time to monitor the course of polymerization (Figure 3.14). As indicated by the reaction profile there is a notable induction period (only trace amounts of polymer were obtained after 10 minutes). This induction period may be required to form the active initiator from complex 3.19. Relatively slow initiation often results in a broad molecular weight distribution. 38 After the induction period, polymerization occurs 105  almost in a linear fashion to give greater than 90% yield.  The inset confirms that the  molecular weight of the polymer increases as the yield of reaction increases. The maximum molecular weight and maximum polymer yield were reached after 50 minutes of reaction time, indicating the reaction is proceeding throughout the entire hour. To understand the reason for the induction period, the initiation step using complex 3.19 was probed. 100  90  80  70  60  V  50  >40  30  20  10  0 0  10  20  30  40  50  60  70  Time (mm)  Figure 3.14. Yield of polymer during ROP of -caprolactone using initiator 3.19 ([Mj/[l] 225, 0 °C). Inset shows tendency of M 11 values as yield increases.a a  =  Trendlines are only in place to guide the eye.  Following the method employed by Yasuda and co-workers, 25 one equivalent of  -  caprolactone was added slowly to a stirring solution of complex 3.19 in hexanes at room temperature (Figure 3.15). The product was dried in vacuo to give a -caprolactone yttrium tris(amidate) complex 3.27 as a white solid that is quite soluble in deuterated benzene. The coordination of -capro1actone is indicated in the ‘H NMR spectrum, which shows a shift in  106  signals from that of uncoordinated 8-caprolactone, and there is no evidence of the tetrahydrofuran present in 3.27 (Figure 3.16).  The a-hydrogens 2 C(O)OCH and (CH )  hydrogens 2 C(O)OCH in 8-caprolactone are shifted from (CH ) respectively in uncoordinated -caprolactone, to  -  3.46 and 2.12 ppm  3.44 and 2.50 ppm in complex 3.27. This  is in accordance to already published complexes where -capro1actone is bound monodentate through the carbonyl oxygen to 4 yttrium.’ 7 ’ 5 The mass spectrum was the same as the parent complex 3.19 with a M of 1079, indicating loss of bound -caprolactone during analysis just as the bound THF molecule is lost during analysis of complex 3.19. Attempts at recrystallization from several solvents have been unsuccessful in producing crystalline 3.27 suitable for X-ray crystallographic analysis.  o_ +  3.19  hexanes, rt  3.27  Figure 3.15. Formation of monodentate 8-caprolactone yttrium complex 3.27.  107  _________________________________________________________________________________  *  I  Bound caprolactone  Toluene  -  I  *  _.____.________J JLi 9.5  8.5  8.0  7.5  _ .  7.0  6.5  6.0  5.5  5.0 4.5 Chemic Shift (ppm)  4.0  3.5  3.0  2.5  2.0  1.5  1.0  C  Figure 3.1. ‘H NMR spectrum (600 MHz, C , 25 °C) of complex 3.27. D 6  The ‘H NMR spectrum of 3.27 showed quite broad signals (note broadened signals at ö 9.53, 3.81 and 0.75 for the ortho-naphthyl, CH(CH 2 and CH(CH ) 3 2 protons for complex ) 3 3.27, respectively) in comparison to the parent complex 3.19, but attempts to heat the sample (65 °C in a J-Young NMR tube) to sharpen signals caused decomposition, as indicated by precipitate forming, and two diagnostic proton signals at approximately ö 11 and 6.5 ppm resulting from protonated amide bound to the yttrium centre, and the N-H signal for the free amide proligand respectively (vide supra). The precipitate is thought to contain insoluble yttrium containing compounds that are not characterizable.  Solid 3.27 also very slowly  degrades in the same fashion at room temperature when stored in the inert atmosphere glovebox, but it is stable when stored at -30 °C for greater than a month. When 2 equivalents of 8-caprolactone are reacted with 3.19 at room temperature, protonated amide is immediately apparent in the ‘H NMR spectrum of the crude sample.  108  When the crude sample is heated in solution at 65 °C overnight a solid precipitates, and in the ‘H NMR spectrum the only detectable species is amide proligand.  Since the s  caprolactone is extensively dried and does not have a deleterious effect upon 3.19 in significant excess (during polymerization runs), presumably decomposition is not originating from adventitious trace amounts of water. One possibility is that decomposition is due to the enolization of -caprolactone. The coordination of the second molecule of -capro1actone may somehow promote the enolization (Figure 3.16). The ‘H NMR spectrum of the crude reaction shown in Figure 3.16 does have similarities to a reported spectrum for the proposed enolization of s-caprolactone using Zr(acac) . There are signals arising at 4 ppm, which are very similar to reported values of  4.00 and 3.61  4.05 and 3.63 ppm for the CH O, and 2  CH=C(O) protons in deprotonated -caprolactone using Zr(acac) . 4  +  hexanes, rt Insoluble material +  3.27  3.29  Figure 3.17. Possible reaction after second equivalent of E-caprolactone is added.  Rare-earth enolate compounds are rarely isolated, 87 but are more typically formed in ’ 86 8895 Unfortunately, -caprolactone situ for catalytic reactions such as the aldol condensations.  109  is not used as a reagent in aldol reactions but other cyclic ketones, such as cyclohexanone, are very commonly used. For this reason, complex 3.19 was probed for its reactivity with cyclohexanone. The reaction was performed by adding two equivalents of cyclohexanone slowly to a stirring solution of complex 3.19 in hexanes at room temperature. A precipitate formed after 2 hours of stirring, and after drying in vacuo, the crude product was obtained as a white solid that was moderately soluble in aromatic hydrocarbon solvents. Attempts to fully characterize this material in the solid-state were unsuccessful due to its resistance to single crystal formation.  The ‘H NMR spectrum of the crude material clearly shows  evidence of protonated ligand bound to the yttrium centre by the diagnostic N-H signal at approximately 6 11.2 ppm (signal ‘a’, Figure 3.18). Signal b and c are indicative of the ortho-proton on the naphthyl substituent of the residual complex and the protonated ligand (3.29). Signal ‘b’ is very broad, potentially due to oligomeric yttrium species forming in solution that are sparingly soluble in deuterated benzene. If enolate is forming, and the bulky amidate ligand is lost, the resulting metal complexes will likely form proposed compound 3.30 and/or dimers or oligomers. Signal ‘d’ is proposed to be the CH=C(O) signal of the bound cyclohexanone enolate (3.30) and attempts to quench the enolization product using 0, and CF 2 D COOD have thus far been inconclusive. 3  Using D 0 and CF 2 COOD as 3  quenching reagents did show incorporation of deuterium, indicated by a small broad triplet at approximately 6 3.56 ppm, 97 but incorporation was not quantitative and full ’ 96 characterization proved problematic.  110  3.29 +  Insoluble material  c a  d  b  115  115  155  100  85  90  85  80  75 70 Chemical Shift (ppm)  65  60  55  50  45  40  35  30  Figure 3.2. Proposed product formation (3.30, 3.29 and insoluble material) and ‘H NMR spectrum (400 MHz, C , 25 °C) of the crude material obtained after direct reaction of D 6 complex 3.19 with cyclohexanone.  The aldol reaction using the proposed yttrium enolate compound 3.30 (formed using cyclohexanone) was attempted by quenching using benzaldehyde (3.31) (Figure 3.18). The expected initial product is 2-(hydroxyphenylmethyl)cyclohexan-1-one (3.32), which in the presence of a Lewis acid can easily dehydrate to form 2-benzylidenecyclohexanone  (3•33)•98  111  lOequiv. 0  rn\  31 Q  3.30  0 2 -H  3.32  3.33  Figure 3.19. Formation of 2-(hydroxyphenylmethyl)cyclohexan-1-one (3.32) and 2benzylidenecyclohexanone (3.33).  The proposed enolate complex was formed by stirring a solution of complex 3.19 dissolved in toluene inside an inert atmosphere glovebox and slowly adding dropwise two equivalents of cyclohexanone. This crude solution was transferred to a Schlenk flask and then cooled to -78 °C, where dry benzaldehyde was added dropwise by syringe.  The  resulting mixture was warmed to room temperature before quenching with 1 M aqueous Rd. The organic layer was isolated and dried in vacuo to give a crude mixture, which was analyzed by mass spectrometry and NMR spectroscopy.  The electron-impact (El) mass  spectrum contained a fragmentation pattern of that for free proligand (M  =  331, 2O%), and  a signal at 204 (mass for 3.32, 5%) and a mass at 187 (mass for 3.33, 5%). By comparing the literature values for the ‘H NMR spectrum of  3.32100  and  compound 3.33 in the sample as indicated by a multiplet at and a triplet at  333101103  there is evidence for  2.88 ppm for the ‘y-hydrogens,  2.50 ppm for the CH C(O) hydrogens. However, isolation of the small 2  amount of product in the presence of excess ligand and starting material proved problematic. Thus preliminary evidence supports formation of an enolate, which is presumably occurring during reaction of complex 3.19 with -caprolactone or cyclohexanone. The enolization of -caprolactone is not thought to be an initiation step, since using end group analysis the polymer was found to be terminated by an amide proligand, but instead a competing side-reaction during polymerization initiation. To test this theory, the yttrium  112  enolate of -capro1actone product 3.28 was tested as an initiator for the ROP of  -  caprolactone (Table 3.6). The yield of polymer for 3.28 is much lower than for the parent complex 3.19. Also, the resultant polymer has lower M values and larger polydispersity values than when complex 3.19 is used as an initiator. This gives an indication that the material 3.28 that is proposed to contain an enolate complex, is not as efficient an initiator as complexes 3.19 and may be involved in a competing process. As mentioned before, initiation of -caprolactone ROP is proposed to begin with coordination of -caprolactone, such as in complex 3.27. Therefore, complex 3.27 was also tested for its initiator ability for the ROP of -caprolactone. The polymer yield using 3.27 as an initiator was much lower than for the parent complex 3.19. This could be due to complex 3.27 forming more complex 3.28 under the polymerization conditions.  The M for the  complex 3.27 are similar to the parent complex 3.19, with comparable polydispersity values. Combining all the data presented above a proposed mechanism of ring-opening polymerization of -caprolactone using initiator 3.19 is shown in Figure 3.20.  113  Table 3.6. Comparison of initiator ability (225:1 [M]/[I]) for the ROP of E-caprolactone at 0 °C for tris(amidate) complex 3.19, the E-caprolactone complex 3.27, and the proposed a enolate complex 328 Entryb  Initiator  Reaction Time (mm)  1 2  3.19 3.19 3.27 3.27 3.28 3.28  30 60 30 60 30 60  3 4  5 6  d  e  .  d  (x iO gmo1)  56 93 28 50 15 36  4.36 6.24 4.36 5.76 3.201 3.225  2.24  1.77 2.13 2.18 2.55 3.7  M (x gmol’)  3.48 3.32 2.17 3.42 1.86 1.92  PD!  e  1.59 1.34 1.32 1.24 1.47 1.68  a  Crude material used, and molecular weight based on complex 3.28 ‘ Conditions: in toluene, 1 hour of stirring, °C. Yield = weight of polymer obtained/weight of monomer used. d Measured by GPC calibrated with standard polystyrene samples. e Measured by GPC (triple detection) equipped with differential refractometer (Waters), viscometer, and laser-light scattering detectors (Wyatt).  o  (THF)YL 3 3.19  3.28  3 c=OYL +  LH  3.27  3.34  L=*\  Figure 3.20. Proposed mechanism for E-caprolactone ROP using complex 3.19 as initiator.  Initially, one molecule of -caprolactone displaces a THF molecule to form complex 3.27. This complex can coordinate another molecule of s-caprolactone and initiate the ring-  114  opening of the first molecule of -caprolactone (Complex 3.34), or form an enolate complex 3.28 and consequently a protonated ligand is displaced. When the complex 3.27 is isolated and used as an initiator, perhaps it more easily forms more of complex 3.28 explaining the lower yield of polymer in Table 3.6 (Entry 3 and 4). Complex 3.28 is thought to reversibly form complex 3.27, such as in Zr(acac) 4 initiated polymerization, 39 which competes with the formation of complex 3.34 and subsequent further propagation. This rationalizes the nonliving character of complex 3.19 and the induction period observed for the polymerization. These competing reactions (formation of 3.28 and 3.34) result in species polymerizing at different rates giving broader molecular weight distributions in the obtained polymers.  3.3.2 Mechanistic Investigation Summary ROP of -capro1actone using yttrium amidate complex 3.19 was found to be an efficient initiator at room temperature and at 0 °C. By end group analysis, it was found that the amide proligand terminated the polymer. sodium  salt  It was also found that alone, the anionic ligand (the  of N-(diisopropylphenyl)naphthyl  amide)  was  incapable  of efficient  polymerization. The combination of both these results indicates polymerization occurs via the coordination-insertion mechanism. Studies of the progress of reaction indicated a slow initiation followed by an almost linear polymerization, with full conversion of monomer after 60 minutes of reaction at 0 °C. Further studies into the initiation step showed that complex 3.19 could coordinate one equivalent of -capro1actone easily, but was prone to possible  enolization, to produce protonated amide ligand and uncharacterizable potential enolate complexes of yttrium. A possible mechanism for initiation proposes an equilibrium between the bound yttrium complex of -caprolactone, and an enolate complex, causing an induction  115  period during the initiation of polymerization.  Despite the induction period, the yttrium  amidate complex 3.19 is a highly active initiator for ROP of -caprolactone.  3.4  Conclusions Amidate complexes of group 3 metals were found to be very active initiators for the ROP  of -caprolactone. The tris(amidate) complexes were found to have more control over the polymerization compared to bis and mono(amidate) complexes.  The polymer properties  were varied by changing the substituents on the amidate scaffold of the initiating complex. The optimum amidate ligand for tris(amidate) complexes for desirable polymer properties (high molecular weight, moderate PDI values) combined steric bulk at the metal centre with slightly electron-withdrawing capabilities.  Therefore, the optimum tris(amidate) complex  investigated was complex 3.19, which in comparison to other reported group 3  E  caprolactone ROP initiators is highly active, but has moderate control over polymerization. Tris(amidate) complex 3.19 was found to be a non-living initiator with a significant induction period, leading to broader PDI values. The polymerization mechanism is thought to follow the coordination-insertion pathway, since by end group analysis the polymer was found to be terminated by an amide group and it is known that the anionic ligand is incapable of efficient initiation. Initiation studies indicate that a molecule of -caprolactone can coordinate the yttrium centre, supporting the coordination mechanism; however, the monomer has been 9 This may contribute to the non-living 36 ’ 38 others. observed to be enolizable, by us and 7 behaviour of the initiator, the induction period for initiation of polymerization, as well as broad polydispersity values.  116  Overall, rare-earth amidate complexes are highly active initiators for the ROP of  -  caprolactone. The ease with which the tris(amidate) complexes can be formed makes them ideal candidates for further study in ROP of other lactones as well as lactides. On-going research will take advantage of the tunable amidate ligand set to generate new rare-earth amidate complexes as optimized initiators for the ring-opening polymerization of a variety of cyclic lactones including E-caprolactone and lactide.  117  3.5  Experimental  3.5.1 Starting Materials and Reagents All operations were performed under an inert atmosphere of dinitrogen using standard Schienk-line or glovebox techniques. Toluene was purified by passage through an alumina column and sparged with nitrogen. 8-Caprolactone was dried by stirring over CaH 2 for 4 days, allowed to settle for 2 days, decanted to a new flask and then distilled under reduced pressure, and stored over molecular sieves. Y[N(SiMe ] was synthesized as described in 2 ) 3 the literature.’ 04 All other chemicals were commercially available and used as received unless otherwise stated. ‘H and ‘ C NMR spectra were recorded on Bruker AV300, AV400 3 and AV600 spectrometers.  Molecular weights were estimated by triple detection gel  permeation chromatography (GPC  -  LLS) using a Waters liquid chromatograph equipped  with a Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel columns (4.6 x 300 mm) HR5E, HR4 and HR2, Waters 2410 differential refractometer, Wyatt tristar miniDAWN (laser light scattering detector) and a Wyatt ViscoStar viscometer. A flow rate of 0.5 mL  was used and samples were dissolved in THF (ca. 4 mg mL’). Molecular  weights were determined by comparison to a polystyrene standard curve, and absolute molecular weights were determined using a dnldc (change in refractive index/change in concentration) of 0.079 mL 6 ”° Elemental analyses and mass spectra were performed 5 g’.’° by the microanalytical laboratory of the Department of Chemistry at the University of British Columbia.  118  3.5.2 Synthesis General Procedure for c-caprolactone ring-opening polymerization (225:1 monomer to initiator ratio) at room temperature.  Inside a dinitrogen filled glovebox, complex 3.19 (13.5 mg, 0.0 117 mmol) was dissolved in 10 mL toluene (measured by volumetric flask). The colorless solution was transferred to a 10 mL vial, equipped with a stir bar.  -Caprolactone (0.28 mL, 0.3012 g, 2.64 mmol) was  transferred by syringe directly into the vigorously stirring solution of complex 3.19. The reaction was stirred for 15 minutes within the glovebox and then exposed to air and quenched with several drops of a 1 M aqueous HC1 solution. The polymer was precipitated from cold petroleum ether. The polymer was isolated by vacuum filtration, and then dried overnight in vacuo. Yield: 0.274 g, 91%.  General Procedure for E-caprolactone ring-opening polymerization (225:1 monomer to initiator ratio) at 0 °C.  Inside a dinitrogen filled glovebox, complex 3.19 (13.5 mg, 0.0117 mmol) was dissolved in 10 mL toluene (measured by volumetric flask). The colorless solution was transferred to a TM stopper and a stir bar. The Schlenk flask tube Schlenk flask, equipped with a rubber Suba was brought out of the glovebox and cooled in an ice bath for 15 minutes. s-Caprolactone (0.28 mL, 0.3012 g, 2.64 mmol) was syringed directly into the vigorously stirring solution of complex 3.19. The reaction was stirred for 1 hour at 0 °C, then exposed to air and quenched with several drops of a 1 M aqueous HC1 solution. The polymer was precipitated from cold petroleum ether. The polymer was isolated by vacuum filtration, and then dried overnight in vacuo. Yield: 0.280 g, 93%.  119  General Procedure for E-caprolactone ring-opening polymerization (10:1, 20:1, 30:1, 40:1, 50:1 monomer to initiator ratio) at room temperature.  Inside a dinitrogen filled glovebox, complex 3.19 (0.333 g, 0.289 mmol) was dissolved in 10 mL toluene (measured by volumetric flask) to make a stock solution (0.0289 M).  The  solution was transferred via syringe (10:1 (3.04 mL), 20:1 (1.52 mL), 30:1 (1.01 mL), 40:1 (0.76 mL), 50:1 (0.61 mL) to a 10 mL volumetric flask, diluted to 10.00 mL and then transferred to 20 mL vial, equipped with a stir bar.  8-Caprolactone (0.100 g, 0.876 mmol)  was transferred by syringe directly into the vigorously stirring solution of complex 3.19. The reaction was stirred for 15 minutes within the glovebox and then exposed to air and quenched with several drops of a 1 M aqueous HC1 solution. The polymer was precipitated from cold petroleum ether. The polymer was isolated by vacuum filtration, and then dried overnight in vacuo. Yield: 10:1 (0.086 g, 86%), 20:1 (0.079 g, 80%), 30:1 (0.095 g, 94%), 40:1 (0.100 g,  100%), 50:1 (0.100 g, 100%).  Synthesis  of  tris(N-2’,  6’ -diisopropylphenyl(naphthyl)amidate)yttrium  mono(  caprolactone) (3.27)  A solution of complex 3.19 (0.129 g, 0.112 mmol) was dissolved in 5 mL hexanes in a 20 mL glass vial equipped with a stir bar. -Caprolactone (12.7 mg, 0.111 mmol) was dissolved in 2 mL hexanes and added dropwise to a stirring solution of complex 3.19. The reaction was stirred overnight at room temperature at which time a fine white solid precipitated out of the solution. The reaction was dried in vacuo to give a white solid. Yield: 0.109 g, 82%. ‘H ) ö 9.53 (broad s, 3H, aryl-H), 7.48 (broad m, 6H, aryl-R), 7.23-7.40 D 6 NMR (600 MHz, C (m, 12H, aryl-II), 7.05 (s, 6H, aryl-I]), 6.83 (broad m, 3H, aryl-I]), 3.211 (broad s, 6H,  120  ), 3.44 (broad s, 2H, O-CH 2 ) 3 CH(CH ), 2.50 (broad s, 2H, OC(O)CH 2 ), 1.23 (d, J = 7 Hz, 2 18H, CH(CH ), 1.13 (broad s, 2H, 2 2 ) 3 CH O-CH ) , 0.88 (broad s, 4H, 2 OC(O)CH C ) H ,  ). ‘ 2 ) 3 C NMR (150 MHz, C 3 ) ö 180.7 (C0), 142.7, 135.0, D 6 0.75 (broad s, 18H, CH(CH 133.4, 132.5, 130.4, 128.9, 128.7, 127.5, 126.7, 126.0, 125.1, 124.7, 124.4 (aryl-C), 71.7 (0CH (OC(O)CH ) , 26.0 ), 34.7 (CH(CH 2 CH ), 28.9 2 2 ) 3 CH (O-CH ) , 28.7 (CH(CH ), 28.5 2 2 ) 3 ), 24.5 (OC(O)CH 2 ) 3 (CH(CH ), 24.3 2 2 (0C(0)CH C ) H . MS (El): 1079 (M), 952 (M Nap), 749 (MtNap[O,N]Dipp), 331 (M-Y(Nap[0,N]Dipp) ). 2  Anal. found (calcd. for  72 C 8 H Y 5 0 3 N 5 ): C 73.55% (75 .42%), H 7.30% (6.92%); N 3.44% (3.52%).  General Procedure for quenching reaction with benzaldehyde. Inside an inert atmosphere glovebox, at room temperature, complex 3.19 (0.142 g, 0.123 mmol) was dissolved in toluene in a 20 mL vial equipped with a stir bar. Cyclohexanone (24.2 mg, 0.247) was dissolved in toluene and added dropwise to the stirring solution of complex 3.19. The crude solution was transferred to a Schienk flask equipped with a Suba seal cap, and attached to a vacuum manifold and cooled to -78 °C. Dry benzaldehyde (0.13 mL, 1.28 mmol) was added dropwise by syringe. The resulting mixture was warmed to room temperature and stirred overnight before quenching with 1 M HC1. The organic layer was H isolated, dried over Mg50 , filtered and dried in vacuo to give a crude mixture (0.155 g). 1 4 NMR (400 MHz, C ) Complicated, but notable peaks at D 6  7.20-8.20 (aryl-H of 3.29), 3.30  2 of 3.29), 2.88 (m, y-hydrogens of 3.33), and 2.50 ppm (t, ) 3 (septet, J = 6 Hz, 2H, CH(CH C(0) of 3.33), 1.50-2.50 (multiple multiplets), 1.24 (d, J 2 CH  2 of ) 3 6 Hz, 12H, CH(CH  3.29). 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R.; He, A.; Reddy, L. M.; Kundu, A.; Barma, D. K.; Bandyopadhyay, A.; Kamila, S.; Akella, R.; Bejot, R.; Mioskowski, C. Org. Lett. 2006, 8, 4645.  126  (104) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton Trans. 1973, 2228. (105) Knecht, M. R.; Elias, H.-G. Die Makro. Chem. 1972, 157, 1. (106) Dostal, J.; Simek, L.; Kasparkova, V.; Bohdanecky, M. I Appi. Polym. Sd. 1998, 68, 1917.  127  Chapter 4. Yttrium Amidate Complexes as Effective Precatalysts for the Cyclohydroamination of Aminoalkenes’ 4.1  Introduction The synthesis of nitrogen-containing molecules is a much sought after process in the  pharmaceutical and fine chemical industries.’  A catalytic route to nitrogen-containing  molecules is hydroamination, which is the formal addition of nitrogen and hydrogen atoms across a carbon-carbon unsaturation.  The carbon-carbon multiple bond can include  ° or alkenes,”’ allenes, ’ 2 3 alkynes,” 6 and the amine source can be either primary or secondary amines.  Hydroamination is atom-economical, can occur in an inter- or  ° requires a catalyst. 72 intramolecular fashion, and excluding some highly active substrates,’ Alkene hydroamination is a thermodynamically less favourable process than alkyne or allene ’ and therefore constitutes a greater challenge (Figure 4.1). The addition of 2 hydroamination, ammonia to ethylene is described as virtually thermoneutral with AG° estimated at -14.7 kJ 2 However, this reaction has a high activation barrier arising from bringing two mof’. 2 ’ 21 electron-rich molecules together and thus requires a catalyst to overcome this barrier.  Intermolecular Hydroamination =  +  3 NH  catalyst  Intramolecular Hydroamination catalyst  4.1  Ph Ph 4.2  Figure 4.1. Examples of inter- and intramolecular alkene hydroamination.  ‘A version of this chapter will be submitted for publication. Stanlake, L. J. E.; Schafer, L. L. 2008.  128  Metal-based catalysts for alkene hydroamination include examples from across the 39 ’ 3 gold,’ ° 3538 4 copper,  2324 group 4 periodic table, including calcium, 5 6 14 zinc. 4 4 and ’ rhodium’ 4 ’ 43 6 2 palladium, platinum, 4 ’ 41  The rare-earth metals are also  072 hydroamination intermolecular 7 ’ 4769 and 22 attractive, as they are very active for the intraof alkenes.  Although intermolecular hydroamination is the ultimate goal, intramolecular  hydroamination allows preliminary investigation into catalyst efficiency to give nitrogencontaining heterocycles.  Geminally-substituted aminoalkenes are most often used for  intramolecular hydroamination (such as 4.1, Figure 4.1) due to enhanced reactivity. This is known as the gem-disubstituent effect, which is a combination of the Thorpe-Ingold effect 73 The substrate, 2,2-diphenyl-4-pentenylamine (4.1), is and the reactive rotamer hypothesis. commonly  used  because  its  large  phenyl  substituents  facilitate  intramolecular  hydroamination.  129  N(SiMe YL 2 ) 3 H2N)( HN(SiMe) Ph Ph >çz H N 2  ) 11  7Ir  H N  Ph JPh  //  [  Ph  RDS  Figure 4.2. a-Bond insertion mechanism for hydroamination of aminoalkenes using rareearth catalysts. 72 ’ 57  In contrast to group 4 metals which are proposed to catalyze the hydroamination of 5 rare-earth catalysts are thought to intermediate, 7 ’ aminoalkenes through a metal-imido 74 proceed via a a-bond insertion mechanism (Figure 4.2).5772 The insertion is thought to be 2 Ligand design is important to enhance the turnover rate (RDS). 7 ’ the rate-determining step 57 of the reaction, and to this end, rare-earth catalyzed intramolecular hydroamination has been catalyzed by organometallic complexes, amido complexes and phenoxides.  Also,  hydroamination of aminoalkenes produces a chiral centre, which has led to research using 6169 for asymmetric catalysis. chiral ligands,  Examples of some well known yttrium  complexes used as pre-catalysts for hydroamination are shown in Figure 4.3.  130  /  cI  4.3  4.4 DMP  =  4.5 dimethyiphenyl  Figure 4.3. Known yttrium complexes used as catalysts for hydroamination. ansa-Metallocene complex 4.3 has a labile (reactive) amido ligand, whereas 4.4 and 4.5 both employ labile aryl ligands, and all compounds have two auxiliary ligands.  All  complexes 4.3, 4.4 and 4.5 are successful hydroamination pre-catalysts and their reactivity towards the cyclohydroamination of the substrate 4-pentenylamine (4.6) is shown in Table 4.1.  Table 4.1. Hydroamination of 4-pentenylamine (4.6) Cat.  2 NH  Entry  Cat.  mol /o  172  4.3 4.4 4.5 ] 2 ) 3 Y[N(SiMe  5 3 4 3  2° 364 450  a  Temp [°C1 60 60 22 80  Timea [h] 0.34 60 20 216  Cony. j%] 100 97 94 6  Time for conversion.  Substrate 4.6, which lacks any substitution on the alkyl chain, is a challenging hydroamination substrate relative to 4.1. Complex 4.3, which contains a labile amido rather than an aryl, showed high reactivity with substrate 4.6 (Table 4.1, Entry 1), while complex 4.4 at the same temperature required drastically longer reaction times in order to obtain 2 The binaphthol complex 4.5 catalyzed the hydroamination of 4.6 conversion. 7 ’ comparable 50  131  at a lower temperature, but required a much longer reaction time than complex 4.3 (Table 4.1, Entry  3)64  ] was a 2 ) 3 A common starting material for yttrium complexes, Y[N(SiMe  poor pre-catalyst for the hydroamination of substrate 4.6 (Table 4.1, Entry 4), obtaining only 6% conversion after 216 hours at 80  50 0C  In the Schafer lab, bis(amidate)bis(amido) complexes of group 4 have been shown to be 4 and the successful aminoalkenes 3 ’ active pre-catalysts in the cyclohydroamination of 32 synthesis of amidate complexes has now been extended to group 3 (shown in Chapter 2). Interestingly, substrate 4.6 continues to be a challenging substrate for group 4 hydroamination  catalysts.  This  chapter  will  involve  studies  of intramolecular  hydroamination of aminoalkenes using amidate complexes of group 3.  4.1.1 Scope of Chapter Due to the success of group 4 amidate complexes for the cyclohydroamination of aminoalkenes, it is of interest to investigate the reactivity of related group 3 complexes. As shown in Chapter 2, crystalline bis(amidate) complexes of yttrium can be synthesized in high yield. This is ideal, as synthesis of known rare-earth precatalysts for hydroamination can be 4 56 ’ 51 low-yielding. lengthy and 6  Another advantage to the facile synthesis of group 3  amidates is the ease with which the substituents can be varied on the amidate backbone. It has been shown using group 4 amidate complexes that electron-withdrawing substituents on 29 It is of interest to compare and the amidate can shorten hydroamination reaction times. contrast reactivity trends in yttrium catalyzed cyclohydroamination of aminoalkenes. The three bis(amidate) complexes investigated in this Chapter are shown in Figure 4.4. comparison, homoleptic 4.11 and mono(amidate) 4.12 were also tested for reactivity.  132  For  4.8  n O CF3) 2 S 3 (Me N  CF3  i) ’7%_ 2 S 3 (Me N 3 2 CF 4.10  4.9  i) 2 S 3 (Me  Qo Y)  4.11  i) 2 S 3 (Me N  0 a 4.12  Figure 4.4. Yttrium amidate complexes as precatalysts for cyclohydroamination of aminoalkenes.  4.2  Yttrium Amidate Complexes as Precatalysts  4.2.1 Results and Discussion Initially, to test the reactivity of the bis(amidate) complexes, the hydroamination of 2,2diphenyl-4-pentenylamine (4.1) was performed (Table 4.2). The precatalyst, standard (1,3,5trimethoxybenzene), and substrate were weighed out separately in an inert atmosphere glovebox, and dissolved in approximately 0.7 g of deuterated benzene. The reaction was monitored until greater than 99% conversion was observed in the ‘H NMR spectrum, indicated by complete depletion of substrate alkene proton multiplets at 6 5.73 and 5.10, and H(CH and 1.92 (-CthCH(CH NH-) 3 C 2 (-CH )NH-) 3 the appearance of product peaks at 6 2.47 )  133  H(CH NH-). 3 C 2 (-CH and 1.09 )  After full conversion, NMR yields were obtained by  comparison between the standard proton signals (aryl and methyl protons) and the product 4.2 proton signals in the ‘H NMR spectrum.  Table 4.2. Hydroamination of 2,2-diphenyl-4-pentenylamine (4.1). Yieidd  Eflb,a  Aminoalkene  Product  Ph Ph NH 4 2  Ph\,”  1 2 3  4.1  _H Ph \ 2  4.2  Cat.b  Time’  Ehi  [%] (isolated)e  4.8  <0.25  >95 (95)  4.9  <0.25  >95 (94)  4.10  <0.25  >95 (93)  d C H reactions performed at 25 °C b 10 mol% precatalyst Time for >99% conversion. Yield determined by 1 standard.e yield. Isolated internal as an l,3,5-trimethoxybenzene using NMR spectroscopy  The bis(amidate) complexes were highly efficient in the conversion of compound 4.1 to the heterocycle (4.2) (Entry 1-3, Table 4.2) at room temperature. These reactions resulting in high NMR yields of product, which correlated well to the isolated yields obtained.  1—,  1.,  Table 4.3. Hydroamination of various aminoalkenes using bis(amidate) complexes 4.8, 4.9 and 4.10.  Entry  Aminoalkene  Product  Cat.  Temp. [°C1  4.8 1 4.13  25  NH  2 NH  4.14  4.10  Timea [h] <0.25  >95  <0.25  >95  <0.25  >95  1.8 2  3  4  25  NH2  4.15  4.16  NH2  >c  4.17  4.18  2 NH  D4—  47 Ph Ph  4.19  6  Ph  4.21  1  >95  4.10  2.5  93  4.8  24  >95  6  4.10 25  4.10  6  >95 88c  4.8  1.8  >95  0.8  >95  4.10  0.8  >95  4.8  30  81  21  85  19  82  49  4.6  ‘4.22  : :  4.9  4.9 4.10  110  65  110  b H NMR spectroscopy using l,3,5-trimethoxybenzene as Time for >99% conversion. Yield determined by 1 an internal standard. Percent conversion  a  In order to determine the substrate scope of the bis(amidate) precatalyst, a variety of aminoalkenes were tested (Table 4.3). Entries 1-4 contain substrates that have a decrease in geminal-substituent steric properties, from a cyclohexyl group (4.13) to no gem disubstituents at all (4.19). The gem-disubstituent effect is evident when comparing entries 1-4, as an increase in reaction time is noted; in the case of entry 4, an increase in temperature is also needed to achieve full conversion. For the hydroamination of substrate 4.13, all bis(amidate) complexes give high yield in less than 15 minutes. When the size of the ring in  135  the gem-position on the substrate is reduced to a cyclopentyl group (4.15), reaction time is increased to at least an hour, but still provides high yields. This reaction reveals a reactivity difference between the amidate complexes, with the CF 3 substituted bis(amidate) complexes 4.9 and 4.10 giving the fastest times (1 hr). The ring substituents in substrates 4.13 and 4.15 facilitate the transition state (shown in Fig. 4.2), more than the methyl substituents of 4.17, because of the lack of the reactive rotamer effect.  This is evidenced by the increase in  reaction time (Entry 3, Table 4.3) for the cyclization of substrate 4.17. The use of complex 4.8 as a precatalyst results in a reaction time 2 hours longer than the other bis(amidate) complexes (4.9 and 4.10). The substrate 4.19 contains no substituents and requires the use of higher temperatures (110 °C) in order to achieve full conversion (Entry 4, Table 4.3). Again, complexes 4.9 and 4.10 result in faster reaction times, compared to complex 4.8. The same reaction using complex 4.8 as a precatalyst at 25 °C results in no evidence of reaction after 24 hours.  Compared to the known yttrium catalysts (Figure 4.3, Table 4.1) amidate  complexes 4.8, 4.9, and 4.10 are precatalysts for hydroamination of compound 4.19 at higher reaction temperatures. However, the amidate complexes have much shorter reaction times and good conversion compared to the starting material used to synthesize them, . ] 2 ) 3 Y{N(SiMe For hydroamination of aminoalkenes, 5-membered ring formation is the most facile, but this can be extended to more challenging 6- and 7-membered rings (substrates 4.19 and 4.21). As expected from hydroamination results presented above, the hydroamination of substrates 4.19, and 4.21, proceeded with a faster reaction time using precatalysts 4.9 and 4.10 (Entry 5 and 6, Table 4.3).  136  The same hydroamination reaction as in Entry 5 (Table 4.3, using precatalyst 4.8) was also carried out with an in situ catalyst preparation. Firstly, 20 mol% of the ligand, N-2’, 6’diisopropylphenyl(naphthyl)amide, and 10 mol% of yttrium tris(bis(trimethylsilyl)amide) J were combined in approximately 0.7 g of deuterated benzene, and the 2 ) 3 (Y[N(SiMe substrate 4.19 was added after a 15 minute delay. After 1.8 hours the reaction was completed with greater than 95% conversion, as evidenced by the disappearance of alkene signals at S 5.72 and 4.92 and the growth of product 4.20 proton signals at 5 3.75 (NHCHH) and 2.90 (NHCHH),  2.50  )NH), 3 (CH(CH  2.43  3 C 2 (CHHCH ) H(CH NH)  and  2.03  C 2 (CHHCH ) 3 NH), H(CH 1.33 ) 3 C 2 (CH HHCH(CH NH) and 1.11 ) 3 C 2 (CH HHCH(CH NH) and 0.84 (CH(CH )NH) in the ‘H NMR spectrum. 3  This result correlates well to the  hydroamination outcome where precatalyst 4.8 was isolated prior to reaction (Entry 5, Table 4.3). This demonstrates that the reaction can be affected with the commercially available starting material 3 (Y[N(SiMe ) ] 2 ) , and an easily prepared amide with no need to isolate the bis(amidate) complex. Another challenge is the hydroamination of substrates of internal alkenes. As mentioned before, the rate determining step of the hydroamination cycle is proposed to be the G-bond insertion step. Thus, a substituent at the terminal end of the alkene sterically impedes this step (Figure 4.5). 2 R 1 R 2 R2NH  [RR1]  RlH  Figure 4.5. cs-Bond insertion step with terminal substitution on aminoalkene.  137  Substrates 4.23 and 4.25, which both contain terminal substituents, were cyclized using complexes 4.8, 4.9 and 4.10 as precatalysts and the results are shown in Table 4.4. For the substrate with a phenyl substituent on the terminus (4.23), reaction rates were very fast producing high yields for the CF 3 containing bis(amidate) complexes 4.9 and 4.10. Much longer reaction times and higher temperatures are needed when the phenyl terminus is replaced with a methyl substituent (compound 4.25).  High yields are obtained for this  reaction, and all amidate complexes give similar reaction times.  Table 4.4. Hydroamination of aminoalkenes with terminal substituents using bis(amidate) complexes 4.8, 4.9 and 4.10. Yield” Timea Entry Aminoalkene Product Cat. Temp. [°C1 j%j jhl (isolated)c Ph  1  2 PhNH  Ph  4.23  4.24  Ph Ph 2 )<NH  2  Ph  >95 (99)  <0.25  >95  4.10  <0.25  >95  4.8  18  >95 (85)  18  >95 (81)  17  >95 (82)  4.9  4.9  Ph  4.25  6  4.8  NH  4.26  4.10  25  65  b  a  Time for >99% conversion. Yield determiied by ‘H NMR spectroscopy using l,3,5-trimethoxybenzene as an internal standard. C Isolated yield.  Hydroamination using rare-earth metals as catalysts can tolerate the use of secondary amine substrates. This is in contrast to neutral group 4 catalyzed hydroamination which requires a primary amine to form the proposed imido intermediate. 33 In a preliminary screen using substrate 4.27 and precatalyst 4.8 (Figure 4.6), reactivity was noticed by product methyl proton signals at ö 2.07 (N(Cj)) and 1.11 (CH(CH )) and diastereotopic proton 3 signals at  3.10 and 3.02 (CjCH(CH )) and 2.35 and 2.03 (N(CH 3 )Cffi) in the ‘H NMR 3  spectrum.  138  Ph Ph -/ii 4.27  1OmoI%4.9  Ph Ph 4.28  Figure 4.6. Preliminary screen of secondary amines for hydroamination.  The reactivity of secondary amines was then extended to a tandem reaction using the substrate 1 -amino-2,2-diallylpropane (4.29), which contains two alkene groups Table  45)•58  Neutral group 4 catalyzed hydroamination generally stops at the formation of the 5membered heterocycle, whereas rare-earth catalyzed hydroamination can instead do a tandem cyclization to form the tertiary amine 4.30. The bis(amidate) complexes 4.8, 4.9 and 4.10 were used in the hydroamination of 4.29 initially at 65 °C. After 11 hours, the conversion values using precatalysts 4.8, 4.9 and 4.10 were 68%, 61% and 69%, respectively. In all cases, these conversion values were mostly achieved after only 6 hours at 65 °C.  The  reaction was repeated at 110 °C, and after 1 hour using precatalysts 4.8, 4.9 and 4.10 the conversion values reached 86%, 71% and 71% respectively. After longer reaction times at 110 °C no further reactivity was noted; however, if more precatalyst was added the reaction 57 In would go to completion. This reaction “stalling” may be due to product inhibition. order to verify this, the product 4.30 was isolated by vacuum distillation and a small amount was purposely added to a hydroamination reaction to monitor the reaction rate in presence of the product. Two hydroamination reactions were prepared concurrently using precatalyst 4.8 and substrate 4.29, where one reaction had product 4.30 added. Both reactions were run at 110 °C concurrently for 1 hour. The normal hydroamination reaction with precatalyst 4.8 and substrate 4.29 resulted in a 96% conversion as noted by the appearance of ‘H signals at  139  3.22 and 3.15 for the two CH(CH) 3 protons and  2.69 for the CJN protons in the ‘H NMR  spectrum. The reaction that was spiked with the product 4.30 gave a conversion of 86%. This shows that 4.30 does inhibit the hydroamination efficiency, most likely through competitive binding to the yttrium centre. When comparing the different complexes, this effect seems to be more of a problem for the precatalysts that contain the CF 3 groups on the amidate backbone (complexes 4.9 and 4.10). Complexes 4.9 and 4.10 are expected to be more Lewis acidic, and therefore likely bind the product more tightly than the other complexes.  Table 4.5. Hydroamination of 2-allyl-2-methyl-4-pentenylamine (4.29) Entry  Aminoalkene  Product  Cat.  Temp. [°C1  4.8 1  4.29 a  4.9  2 NH  4.30  4.10  110  Timea [hj  Conversion  7  95  5  85  5  77  [%]  Time for conversion value  Overall, complexes 4.9 and 4.10 were deemed the most active catalysts. Since some rareearth catalysts are known to catalyze the intermolecular hydroamination of alkenes and 7072 complex 4.9 was used in a precatalyst screen to see if intermolecular ’ 22 amines, hydroamination was possible with bis(amidate) complexes of yttrium (Figure 4.7).  All  reactions were attempted at 110 °C, since at higher temperatures degradation of catalyst was noted after 24 hours. Attempts at intermolecular hydroamination employed styrene as the alkene source, and aniline, 2,6-dimethylaniline, cyclohexylamine, and benzylamine as the amine sources. Initially the reactions were prepared using a 1:1 stoichiometric ratio between ). When no hydroamination D 6 styrene and amine (10 mol% 4.9, 30 mg styrene, 0.7 g C  140  reaction was seen, as evidenced by no formation of product signals in the ‘H NMR spectrum after a week at 110 °C, the amine stoichiometry was varied from 1.1, 1.5 and 2 equivalents. Polystyrene formation was seen in these conditions as indicated by very broad proton signals between ö 5 and 6 ppm and precipitate forming in the NMR tube. These variations of amine stoichiometry still resulted in no reaction, but previous successful intermolecular alkene hydroamination reactions use 2 equivalents of alkene. 72 Using benzylamine as the amine source, the reactions were attempted again using styrene stoichiometry varied from 5, 2 and 1.5 equivalents. After a week at 110 °C for all experiments, no reaction was observed. This  indicates that the bis(amidate) complexes presented here are not active for intermolecular hydroamination under these conditions. Future work will focus on changing the conditions, as well as catalyst development to obtain a amidate complex that will catalyze intermolecular hydroamination.  +  R  =  HNR  H N  NHR R  or  Phenyl 2,6-Dimethyiphenyl Cyclohexyl Benzyl  Figure 4.7. Intermolecular hydroamination using precatalyst 4.9. The tris(amidate) complex 4.11 was determined to be a highly efficient initiator for the ring-opening polymerization of -caprolactone (Chapter 3) and although the tris(amidate) complex does not have any labile amido ligands, perhaps it can react in situ to give an active catalyst.  Also, the analogous mono(amidate) complexes 4.12 was screened in  hydroamination experiments and the results are shown in Table 4.6. The tris(amidate) complex 4.11 does not catalyze the hydroamination of compound 4.1 (Entry 1, Table 4.6), even at elevated temperatures (65 °C, and 110 °C) for longer than 24  141  hours. The mono(amidate) complex 4.12 had comparable rates and yields to complexes 4.9 and 4.10, as shown in Entries 1-7 (Table 4.6). Although it was shown in Chapter 2 that mono(amidate) complexes will undergo ligand redistribution at 110 °C and at this temperature, it is not known what the reactive species is in solution. For the hydroamination of internal alkene substrate 4.23, mono(amidate) complex 4.12 effected the transformation much quicker than the analgous bis(amidate) complex 4.8, but slightly slower than bis(amidate) complexes 4.9 and 4.10 (Entry 8, Table 4.6). cyclization reaction (Entry  When comparing the tandem  10, Table 4.6) between the amidate complexes, the  mono(amidate) complex 4.12 cyclized the fastest and with the highest conversion to product 4.28.  142  Table 4.6. Hydroamination using complexes 4.11 and 4.12 as precatalysts (10 mol%). Entry  Aminoalkene Ph  2  3  4  Ph  Ph  1  Product  2 NH  Temp. j°C]  4.2  4.12  2 NH  KDc  4.12  4.13  4.14  4.15  4.16  2 NH  >KC  4.17  4.18  4.6  4.7  Ph Ph _-)<NH 2  Ph  Yieldb (isolated)d[%1  25  4.1  2 NH  Time” jhj NRd  4.11  Ph>C  2 NH  6  Cat.  <0.25  94  25  <0.25  89  4.12  25  1.3  92  4.12  25  2.5  83  4.12  110  6.5  >95  4.12  65  0.8  86  4.12  110  16  91  4.12  25  0.8  94 (89)  4.12  65  17  86 (84)  4.12  110  3.5  >95e  Ph  7  4.19  4.20  Ph Ph NH 2  Ph  4.21  Ph  4.22 Ph  8  9  Ph Ph PhXNH 2  Ph Ph’\.._-rJH  4.23  4.24  Ph Ph NH 2  Ph PhH  4.25 10  4.26  4.27 a  Time for >99% conversion. b Yield determined by ‘H NMR spectroscopy using 1,3,5-trimethoxybenzene as an internal standard. C Isolated yield. d No reaction. C Percent conversion.  143  The hydroamination of aminoalkenes produces a chiral centre, and since the amidate backbone in the bis and mono(amidate) complexes is achiral, no enantioselectivity is expected  to  result  from  this  reaction;  however,  these  complexes  can  induce  diastereoselectivity. Using complexes 4.8 and 4.12, for a direct comparison between bis and mono(amidate) complexes, the hydroamination of 1 -methyl-4-pentenylamine (4.31) was carried out and the diastereomeric ratio (dr) determined (Figure 4.8).  The bis(amidate)  complex 4.8 results in a better dr after 99% conversion. Monitoring of the reaction showed that the diastereomeric ratio maintains a constant value throughout both reactions. Furthermore, presumably the bis(amidate) complex is not forming the mono(amidate) complex in situ, or the dr values would be the same as the result using complex 4.12. Complex 4.10 gave the best dr value, and complex 4.9 obtained a slightly better dr value than the mono(amidate) complex 4.12. This indicates that a bis(amidate) complex imparts more stereocontrol over the reaction as compared to the less sterically encumbered mono(amidate). This supports the future use of chiral bis(amidate) complexes for use in asymmetric hydroamination.  yNH2  +  065:0 trans 4.32  4.31 Precatalyst  Yield  4.8 4.9 4.10 4.12  94% 84% 81% 83%  11 7 15 5  cis 4.33  : :  1 1 1  Figure 4.8. Hydroamination of 1-methyl-4-pentenylamine (4.31). Yield determined by ‘H NMR 77 for the ’ 76 spectroscopy using 1,3 ,5-trimethoxybenzene as an internal standard and comparison of known values H1’JCHMe ‘H signal in NMR spectrum of 4.32 and 4.33.  144  4.2.2 Summary Overall the bis(amidate) complexes of yttrium were shown to be good catalysts for the hydroamination of aminoalkenes. The reaction times for multiple substrates indicated that the bis(amidate) complexes that contain the electron-withdrawing group CF 3 on the amidate backbone (complexes 4.9 and 4.10) are more reactive than the bis(amidate) 4.8. One of the more reactive complexes, 4.9, gave no reaction when tested for the ability to catalyze intermolecular hydroamination.  The tris(amidate) complex 4.11 was inactive for the  hydroamination of aminoalkenes, but the mono(amidate) complex 4.12 had comparable reactivity to complexes 4.9 and 4.10. The bis(amidate) complex 4.8 proved to give better diastereoselectivity that related mono(amidate) complex 4.12. It was shown that adding electron-withdrawing groups on the amidate backbone could reduce reaction times.  It is also known for forming bis(amidate) and mono(amidate)  complexes that bulk on the N-substituent on the amidate is necessary for clean synthesis (Chapter 2). By combining these two structural features into the ligand set, the reaction rates and improved selectivity could be further enhanced.  4.3  Conclusions Amidate complexes of group 3 are easily synthesized in high yield and are good  candidates for hydroamination precatalysts. They show moderate activity in comparison to known yttrium precatalysts and adding electron-withdrawing groups onto the amidate backbone has a significant effect on reaction time, resulting in the identification of the most active amidate complexes as 4.9 and 4.10. Mono(amidate) complex 4.12 was found to be a good  precatalyst  for  the  hydroamination  of  aminoalkenes,  but  gave  reduced  145  diastereoselectivity than the analogous bis(amidate) complex (4.8).  Modifications to the  amidate backbone, including more electron-withdrawing groups while maintaining steric protection at the nitrogen, for the synthesis of bis(amidate) complexes increases reactivity rates in the hydroamination of aminoalkenes. Future work will mainly focus on ligand design to increase reaction rates, and attempt to obtain reactivity in intermolecular hydroamination. Since the bis(amidate) complex 4.8 gave better diastereoselectivity than the analogous mono(amidate) complex 4.12, further studies into enantioselective hydroamination will focus on versions of bis(amidate) complexes.  4.4  Experimental  4.4.1 Starting Materials and Reagents All operations were performed under an inert atmosphere of nitrogen using standard Schlenk-line or glovebox techniques. THF, toluene, pentane, and hexanes were all purified by passage through an alumina colun-m and sparged with nitrogen. The compounds 2,262 diphenyl-4-pentenylamine,  78 4-pentenylamine,  1 -methyl-4-pentenylamine, 76  C-( 1-  79 C-( 1 -allyl-cyclopentyl)-methylamine, allylcyclohexyl)-methylamine, 65 2,2-dimethyl-pent° 8 4-enylamine,  2,2-diphenyl-5 -hexenylamine, ’ 8  ’ 8 triphenyl-4-pentenylamine,  2,2-diphenyl-6-septenylamine,  5 -methyl-2,2-diphenyl-4-pentenylamine  and  2,2,5  -  1 -amino-2,2-  82 were made according to previously reported procedures and purified by diallylpropane distillation and storage over molecular sieves. Complexes 4.11, 4.8, 4.9, 4.10, and 4.12 were prepared as stated in Chapter 3. All other chemicals were commercially available and used as received unless otherwise stated.  ‘H and ‘ C NMR spectra were recorded on Bruker 3  AV300, AV400 and AV600 spectrometers.  146  4.4.2 Synthesis Typical procedure for hydroamination using amidate complexes. (For Entry 2, Table 4.2) Inside a inert-atmosphere glovebox, complex 4.8 (24.11 mg, 0.025 mmol, 10 mol%), 1,3,5trimethoxybenzene (14.2 mg, 0.084 mmol) and 2,2-diphenyl-4-pentenylamine (4.1) (60.0 mg, 0.253 mmol) were weighed out in separate vials, dissolved and combined in approximately 0.7 g of deuterated benzene inside a J-Young sealable NMR tube. The ‘H NMR spectrum was immediately obtained (approximately 15 minute delay) to monitor conversion (>99%). By comparison of the integration values for the proton signals of 1,3,5trimethoxybenzene (6 6.25 and 3.32 for aryl-H and —O(CH ) protons respectively) to the 3 newly formed CH(CH ) signal (2.47 ppm) in the ‘H NMR spectrum, the NMR yield is 3 obtained (>95%). The reaction was exposed to air and quenched with dichioromethane. The residual material was added to a small fit silica column and initially flushed with 200 mL of 1:1 solution of hexanes and ethyl acetate (to remove residual ligand). The column was then flushed with 200 mL of 10% methanol and 1% isopropylamine in dichloromethane, which was collected and dried in vacuo to give the product 4.2 (57.0 mg, 95% yield). NMR yield is typically larger than isolated yield, due to loss of product during the isolation procedure.  147  4.5  References  (1)  Severin, R.; Doye, S. Chem. Soc. Rev. 2007, 36, 1407.  (2)  Pohiki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104.  (3)  Zhang, Z. B.; Bender, C. F.; Widenhoefer, R. A. I Am. Chem. Soc. 2007, 129, 14148.  (4)  Nishina, N.; Yamamoto, Y. Angew. Chem.,  (5)  Nishina, N.; Yamamoto, Y. Synlett 2007, 1767.  (6)  LaLonde, R. L.; Sherry, B. D.; Kang, F. J.; Toste, F. D. I Am. Chem. Soc. 2007, 129,  mt. Ed.  2006, 45, 3314.  2452. (7)  Ackermann, L.; Bergman, R. G.; Loy, R. N. I Am. Chem. Soc. 2003, 125, 11956.  (8)  Yamamoto, Y.; Radhakrishnan, U. Chem. Soc. Rev. 1999, 28, 199.  (9)  Besson, L.; Gore, J.; Gazes, B. Tetrahedron Lett. 1995, 36, 3857.  (10)  Kinder, R. 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(82)  Quinet, C.; Jourdain, P.; Hermans, C.; Ates, A.; Lucas, I.; Markó, I. E. Tetrahedron  2008, 64, 1077.  151  Chapter 5. Yttrium Amidate Complexes as Irnido Precursors 1 5.1  Introduction Terminal imido (=NR) complexes of group 4 are well known’ and are proposed as  intermediates in multiple catalytic processes such as imine metathesis, 2 transamidation, 3 and hydroamination of alkenes and alkynes. 4 The only amidate supported imido complex has ’ 3 been characterized in the Schafer lab (5.1, Figure 5.1). It was found that in order to generate a terminal imido species, a bulky donor, triphenylphosphine oxide (OPPh ), was required to 3 coordinatively saturate the metal centre. 4 Without an added donor this imido product is not isolable. The imido ligand is formally a dianionic ligand and considered to be a 6-electron donor to the zirconium metal centre. 4  5.1  5.2  Figure 5.1. Examples of imido complexes. 6 ’ 4 Imido complexes of the actinides have also been successfully isolated (5.2, Figure 5.1).569  Isolation of actinide imido complexes is possible without the added bulky base;  however, the imido substituent typically is a bulky group such as diisopropylphenyl (Dipp), 2,4,6-tri-tert-butylphenyl, or tert-butyl. 6 The imido in the uranium compound 5.2, is also ’ 5 considered to be a dianionic ligand and a 6-electron donor. 6 A similarity between the two ’ 5  A version of this chapter will be submitted for publication. Stanlake, L. J. E.; Schafer, L. L. 2009.  152  examples in Figure 5.1, is the ionic radius of the metal centres (Zr 4  =  0.72  A, U 5  =  0.76  7 In contrast to group 4 and actinide imido complexes, isolation of analogous terminal A). 9 Although, it ’ 8 lanthanide or group 3 compounds has proven synthetically impossible to date. has been calculated that a lanthanide imido is possible, 8 although it will most likely involve an optimized coordination environment. 8 In fact, only one example of a terminal imido lanthanide complex (5.4) has been suggested, but is depicted as a Lu-N single bond (2.122(2)  A, Figure 5.2) and is formally a monoanionic  However, DFT studies of complex  5.4 indicate that the bonding in Lu-N is described as 2a,4n-donor (6-electron), like previously mentioned terminal imido complexes. (0.861  3 Interestingly, the ionic radius of Lu  3 (0.90 A). A) is larger than Zr 4 and U , but similar to y 5 7  •0  Dipp  N>Pi  I  H 8 C 2 K  2 Lu(THF)  -KCI, -THF  N NCI 5.3  DIPPNNDIPP 5.4  Figure 5.2. Formation of lanthanide imido complex 5.4.  Typically, lanthanide imido complexes are formed where the imido nitrogen is bridging, or capping.’ ‘‘ An example of a bridging imido is shown in the synthesis of Yb imido complexes 5.5 and 5.6 (Figure 5.3).”  153  -7 iPrf\_—iPr iPr iPr  HN  /  iPr Na—THF  Yb  NH  iPr  2nBuLi  : “  iPr  2 nBuLi  4 nBuLi  Figure 5.3. Synthesis of Yb bridging imido complexes 5.5 and 5.6.  To date, no group 3 terminal imido complex has been characterized. Hessen et al. have proposed that a transition state in the formation of a bridging scandium imido dimer (5.8) is in fact a terminal scandium imido complex (Figure  5•4)•12  Piers et al. propose that with  enough steric support, a terminal group 3 imido complex could indeed be isolable; 13 however, their attempts at deprotonation of a NHR group of a scandium -diketiminato complex have thus far been unsuccessful.’ 3  It should be noted that analogous work on  yttrium has not yet been reported.  154  ______  PhCN  [  1  1/ sN /  _N.sCNN N  Figure 5.4. Postulated scandium imido intermediate.  Although there have been no reports of group 3 terminal imido complex formation, it is plausible that with the right steric support it can occur. It is also calculated to be possible to form a lanthanide imido complex 8 and since yttrium has a comparable size and reactivity to the lanthanides, which display some propensity for imido formation (Figure 5.3), yttrium is therefore thought to be able to form an imido as well. The amidate ligand, with its tunable nature, can incorporate sterically demanding groups easily. Since mono(amidate) complexes of yttrium can be formed in high yield with varying steric properties, they are ideal candidates to explore as imido precursors. This chapter will detail the synthesis of anilido yttrium complex precursors, and deprotonation investigations in an attempt to form yttrium imido compounds.  155  5.2  Anilido Complexes  5.2.1 Introduction Literature precedence for imido formation, whether terminal, bridging or capping, usually involves a bulky substituent as the R group of the NR 2 moiety. The most extensively used substituent is diisopropylphenyl (Dipp). 4 ” 8 ’ 5  Furthermore, the most commonly used  synthetic route to form an imido complex using bulky R groups is deprotonation of previously formed anilido complexes.” 4 Synthesis of anilido yttrium complexes is known in the literature,’ 6 and an anilido phosphinimine (5.9) and amino phosphine (5.10) ” 5 supported yttrium bis(anilido) complexes are shown in Figure  5515  Evans and coworkers  have reported a synthesis of tris(2,6-diisopropylanilido)yttrium, which exists as a dimer in the solid-state, but unfortunately the quality of the structure does not allow discussion of 6 bond lengths and flg5•  Dipp  NHD1pp N/ Y —0  —  p.  \ / 5.9 Mes  =  NHDipp Ph  5.10 2,4,6-trimethyiphenyl Ph = Phenyl  Figure 5.5. Anilido phosphinimine (5.9) and amino phosphine (5.10) supported yttrium bis(anilido) complexes. 15  While anilido complexes of yttrium are known, there has been no success thus far in using them as precursors in the formation of imido complexes. For complex 5.9, this may be due to the Y-N bond not being reactive enough to promote a-H abstraction. With this in mind, aryl yttrium complexes can be used as anilido precursors to exchange the Y-N bond for  156  a more reactive Y-C bond. A useful starting material for yttrium aryl compounds is complex 5.11.17,18  This complex has been used extensively by Hultzsch and coworkers to synthesize  new yttrium complexes.’ ° 82  5.2.2 Results and Discussion A mono(amidate)bis(aryl) yttrium complex was synthesized in 52% yield as shown in Figure 5.6. Yttrium aryl complex 5.11 was dissolved in tetrahydrofuran (THF) and stirred at room temperature. Proligand 5.12 was dissolved in THF and added dropwise slowly to the solution of 5.11. The crude product was redissolved in toluene, heated at 65 °C and then isolated by removal of the solvent in vacuo, and recrystallization from warm pentanes.  +  2h65°2  5.11  5.12  (-3 5.13, 52%  Figure 5.6. Synthesis of aryl/amidate yttrium complex 5.13.  Complex 5.13 is soluble in common hydrocarbon solvents but is resistant to X-ray quality crystal formation.  Compound 5.13 is moisture sensitive, and is thermally sensitive and  decomposes above 65 °C when in solution. This is evidenced by a colour change in solution from a colourless to a dark brown, as well as degradation of proton signals in the ‘H NMR spectrum.  157  The room temperature ‘H NMR spectrum of complex 5.13 is very similar to the analogous mono(amidate)bis(amido) complex introduced in Chapter 2. The diagnostic signal associated with the ortho-naphthyl proton is situated at  8.93 ppm. The proton signals for  the isopropyl substituents are all broadened and no coupling is evident. Unfortunately, due to the thermal sensitivity of this compound high temperature NMR spectra could not be obtained. The proton signals associated with the aryl substituent are very diagnostic at ö 3.69 and 2.40 ppm for the 3 N(CH and ) 2 CH ) 3 N 2 CH (CH , respectively, of the pendant amine donor. Notably, there is no THF donor molecule, unlike the analogous mono(amidate)bis(amido) complexes.  This is most likely due to the pendant amine donor of the aryl substituent  resulting in a potentially 6-coordinate yttrium complex.  The integrations of the proton  signals for the aryl ligands and the amidate ligand are in a 2:1 ratio, matching the proposed structure. A mass spectrum of complex 5.13 was attempted, but due to the decomposition of the compound a spectrum was not obtained. Elemental analysis is consistent with the structure proposed for complex 5.13. With complex 5.13 in hand, preparation of an anilido complex was attempted.  One  equivalent of 2,6-diisopropylaniline (5.15) was diluted in toluene and added dropwise to a stirring solution of 5.13 dissolved in toluene. The reaction mixture turned a bright yellow colour after the full addition of 5.15. The crude product was isolated by concentrating the sample in vacuo to obtain a red oil. The crude 1 H NMR spectrum of the product was very complicated, and did not change when heated at 65 °C overnight. The product was washed with pentanes to hopefully remove the expected amine by-product (N,N-dimethyl- 1phenylmethanamine). An orange sticky solid was obtained after drying by vacuum, which  158  was resistant to recrystallization from various organic solvents (toluene, diethylether). The ‘H NMR spectrum of the orange solid matched that of the crude product. To date, it is unclear whether an anilido complex was formed, and isolation of clean product has not been possible. Furthermore, the synthesis of the mixed aryl/amidate yttrium complex 5.13 is low yielding, and this aryl product is more difficult to work with in comparison to the previously discussed mono(amidate)bis(amido) yttrium complexes. Thus further attempts focused on using mono(amidate)bis(amido) complex 5.14 (same as complex 2.27 from Chapter 2) as a suitable starting material. Mixed  amidate/anilido  diisopropylaniline  (5.15)  complexes and  of  yttrium  mono(amidate) yttrium  were  synthesized  complex  5.14  from  2,6-  (Figure  5.7).  Mono(amidate) complex 5.14 was chosen for these studies due to the ease of synthesis and existing structural data for comparison with proposed compounds here. The synthesis of yttrium anilido complex 5.16 is easily achieved by stirring a solution of mono(amidate) complex 5.14 dissolved in 3 mL of tetrahydrofuran (THF), and adding one equivalent of aniline 5.15 dropwise. The reaction mixture turns pale yellow upon addition. The reaction is concentrated in vacuo, and recrystallized from a minimum amount of pentane or hexanes at -30 °C to give a yellow crystalline compound in 85% yield. Compound 5.16 is moisture sensitive, but can be stored in an inert atmosphere glovebox for greater than 4 months at -30 °C. Furthermore, compound 5.16 is thermally sensitive and will decompose above 65 °C when in solution. This is evidenced by a colour change in solution from a bright yellow to a dark brown, as well as degradation of proton signals in the ‘H NMR spectrum.  159  2 NH  Si) N 3 (Me  +  HN(SiMe  O  5.15  5.14  5.16, 85%  Figure 5.7. Synthesis of mixed amidate/anilido complex 5.16.  The ‘H NMR spectrum of complex 5.16 is shown in Figure 5.8. The spectrum is similar to the parent mono(amidate) complex 5.14, but with an new proton signal at ö 5.28 ppm for the N-H proton of the anilido ligand. Interestingly, this proton signal is a doublet, with a small coupling constant of 1.9 Hz, due to the 89 Y coupling. There is no previously reported anilido N-H signal for the ‘H NMR spectrum for the anilido phosphinimine yttrium complex (5.9); however, there is a reported broad singlet for the N-H anilido signal in the amino phosphine yttrium complex (5.10) at ö 4.72 (400 MHz).’ 5 An Y-H agostic interaction in a yttrium complex containing the —N(SiH(CH 2 moeity, was found to have a ) 3  JYH  of 5 Hz.’ 9  Also, the Y-N bond was found to have restricted rotation due to this agostic interaction. 19 Since the 89 Y coupling in complex 5.16 is comparatively small, it is postulated that no Y-H agostic interaction occurs. In compound 5.16 there are also new proton signals associated with the isopropyl groups from the anilido ligand at ö 3.25 (CH(CH 2 and 1.37 ppm (CH(CH ) 3 ). Since there is only 2 ) 3 one methine proton signal, this indicates free rotation about the N-aryl bond. The diagnostic ortho-naphthyl proton signal shifts slightly from complex 5.14, to THF bound  (  9.16 ppm in the parent mono(amidate)  9.13 ppm in complex 5.16. Also, it is evident that there is a molecule of  3.99 and 1.13 ppm) to yttrium. The THF signals are very broad, consistent  160  ___L__J__JL  L 1 __i  with it being a labile donor. The presence of one molecule of THF is also evident in the combustion analysis.  J 1.9 Hz I  1*  5.16 5.35  5.30  5.25520  JL  i 9.0  8 5  8.0  7 5  7.0  6,5  6,0  5.5  5.0 4,5 Chea4cal Shift (ppnl)  40  3,5  3 0  2.5  20  1 5  1 0  05  Figure 5.8. ‘H NMR spectrum (600 MHz, C , 25 °C) of complex 5.16.a D 6 a  Small amounts of toluene (singlet at  2.11 ppm) and pentane (triplet at ppm) are evident in sample.  0.87 ppm, multiplet at ö 1.23  The JR spectrum of complex 5.16 clearly shows an N-H stretch band at 3295 cm 1 for the anilido ligand. The C-O and the C-N stretching frequency do not change compared to the parent mono(amidate) complex 5.14. The mass spectrum of complex 5.16 gives a parent ion for the THF-free complex. X-ray quality crystals of complex 5.16 can be grown at -30 °C from a minimum amount of pentanes and the solid-state molecular structure is shown in Figure 5.9; metrical parameters are in Table 5.1. The C 1 symmetric structure displays a pseudo square-based pyramidal structure, with the -N(SiMe) 2 as the axial group. ) 3  Compared to the  mono(amidate) complex 5.14, the amidate Y-O bond length in complex 5.16 is longer (2.2841(16)  A versus 2.215(2) A) but Y-N bond length is shorter (2.3767(19) A versus  161  2.5 19(3)  A). This indicates that the steric congestion has decreased around the yttrium  centre, allowing a shorter Y-N(amidate) bond.  The amidate metallacycle angles equal  360.0°, indicating the amidate backbone is in the same plane as the yttrium centre. The Y O(THF) is also shorter in complex 5.16 than complex 5.14. The Y-N(anilido) bond length is 2.205(2)  A, with a Y-N-C bond angle of 145.26(19)°. The similar yttrium complex 5.9,  supported by an anilido phosphinimine ligand has similar Y-N(anilido) bond lengths (2.194(5) and 2.242(4)  A) and slightly more linear Y-N-C bond angles (139.5(4) and  139.1 (4)°), 15 likely due to the different steric environment around the yttrium centre.  i1  Figure 5.9. ORTEP diagram of the solid-state molecular structure of 5.16 with the probability ellipsoids drawn at the 50% level. Carbons of the THF, and methyl carbons of the isopropyl and trimethylsilyl groups omitted for clarity. 20  162  Table 5.1. Selected bond length and bond angles for the solid-state molecular structure of 5.16. Bond Length (A) Bond Angle(°) Y 1-01 2.2841(16) Yl -01-Cl 95.41(13) Yl-N1 2.3767(19) 0l-C1-Nl 117.1(2) 01-Cl 1.291(3) C1-N1-Y1 90.80(14) Nl-C1 1.306(3) Ni-Yl-Ol 56.70(6) Y1-02 2.3262(18) Y1-N2-C24 145.26(19) Y1-N2 2.205(2) Y1-N3-Sil 116.84(10) N2-C24 1.386(3) Y1-N3-Si2 117.84(10) Y1-N3 2.225(2) N3-Y1-02 96.20(7) N3-Sil 1.710(2) N2-Y1-N3 112.02(8) N3-Si2 1.708(2) 02-Y1-N2 90.88(7)  Interestingly, if two equivalents of diisopropylaniline are reacted with mono(amidate) complex 5.14, an isolable crystalline compound cannot be obtained. The resultant yellow oil is also thermally sensitive, as is complex 5.16. The ‘H NMR spectrum of the yellow oil does not show any clear diagnostic signals compared to complex 5.16. This is possibly due to dimer or oligomeric species forming in solution and suggests that the steric bulk provided by the —N(SiMe) 2 moiety is necessary to form stable monomeric species. ) 3 In previous work in the group, amidate supported group 4 imido complexes can be formed from anilido precursors simply by adding a bulky donor. 4  In the next section,  attempts to add sterically demanding neutral donors to complex 5.16 to induce cL-H abstraction are discussed.  163  5.3  Attempted a-H Abstraction Routes to Imido Complexes In the Schafer lab, successful isolation of crystalline imido complexes of group 4  generally requires the presence of a neutral donor, such as triphenyiphosphine oxide (TPPO) 4 or pyridine. ’ 2  It is already known that pyridine can displace the THF from yttrium in  tris(amidate) complexes (Chapter 2); however, pyridine is sterically small. It is known that group 3 complexes have a high affinity to bind the bulkier 2,2’-bipyridine (5.17, bipy). 3234 Therefore, one equivalent of bipy dissolved in hexanes was added to a hexanes solution of anilido complex 5.16 (Figure 5.10). Immediately, the solution becomes a deep purple and a red-orange precipitate forms (supematant remains deep purple in colour), which can be isolated by filtration through a fritted funnel and rinsed with hexanes. This solid product can be recrystallized from a minimum amount of toluene and cooled to -30 °C to give complex 5.18 in 76% yield. This red-orange solid is moisture sensitive, and is soluble in toluene or benzene, but not hexanes or pentane. When dissolved in toluene or benzene, a dark purple solution is noted. The compound is also thermally sensitive, and will form a brown-black solid if heated.  /\ Me 3 Si )2 N ArHN>_Ar’  5.16  Th  Ar  —  j  /  5.17 Hexanes ArDipp Ar = Naphthyl  Si) 3 (Me N 2  ii VAr’ ArHNQ  \ /  N  N—  5.18, 76%  Figure 5.10. Synthesis of bipy complex 5.18.  164  The ‘H NMR spectrum of complex 5.18 indicates that the bipy molecule displaces the THF of 5.16, as evidenced by the disappearance of THF proton signals. Also, the chemical shift of bipy proton signals change, for example, there is a doublet signal in free bipy at 8.74 that shifts to ö 9.45 upon formation of complex 5.18. There is still the presence of an N.H proton signal at  4.83  (JYH  =  1.2 Hz), which has shifted upfield compared to the parent  complex 5.16 (ö 5.28 ppm). Another difference in the ‘H NMR spectrum between complex 5.16 and 5.18 is the ortho-naphthyl aryl signal, which has shifted from ö 9.13 ppm to ö 9.32 ppm. The JR spectrum of complex 5.18 also changes from complex 5.16. There is still the presence of an N-H stretching band, but it has shifted from 3295 cm 1 to 3449 cm . 1 Furthermore, the C=O stretching frequency of the amidate has shifted from 1589 cm 1 to 1600 cm . The mass spectrum of complex 5.18 indicates a molecular ion of the complex 1 without bipy; however, there was difficulty in obtaining the mass spectrum due to the thermal stability of the solid. X-ray quality crystals of complex 5.18 were grown at -30 °C from a minimum amount of toluene and the solid-state molecular structure is given in Figure 5.11. The C 1 symmetric structure displays a pseudo-octahedral structure with -N(SiMe 2 and the N-Dipp from the ) 3 amidate backbone as axial ligands and the bipy, NHDipp, and 0-amidate making up the equatorial plane. Compared to complex 5.16, the amidate Y-O and Y-N bond lengths in complex 5.18 are both slightly longer (Y-O 2.3767(19)  =  2.2841(16)  A versus 2.310(3) A, Y-N  =  A versus 2.484(4) A) (Table 5.2). This indicates that the steric congestion has  increased around the yttrium centre, resulting in the slight displacement of the amidate ligand.  The amidate metallacycle angles equal 3 59.9°, indicating the amidate backbone  165  remains in the same plane as the yttrium centre. The Y-N(anilido) bond length is longer (2.275(4)  A) than in complex 5.16 (2.205(2) A) and the Y-N-C bond angle has increased  from 145.26(19)° in complex 5.16 to 154.3(4)° in complex 5.18. This is most likely due to the greater steric congestion around the yttrium centre, when switching from a THF molecule to the bipy ligand.  The bond lengths in the bipy ligand are all very similar  ( 1.37 A)  confirming no loss of aromaticity when bound to yttrium.  Figure 5.11. ORTEP diagram of the solid-state molecular structure of 5.18 with the probability ellipsoids drawn at the 50% level. Methyl carbons of the isopropyl and trimethylsilyl groups omitted for clarity. 22  166  Table 5.2. Selected bond length and bond angles for the solid-state molecular structure of 5.18. Bond Length (A) Bond Angle(°) Yl-Ol 2.310(3) Yl-Ol-Ci 99.2(2) Yl-Ni 2.484(4) 01-Cl-Ni 115.5(4) 1.294(5) 01-Cl Ci-Nl-Yi 90.6(3) Ni-Cl 1.312(5) Ni-Yl-Ol 54.61(11) Yi-N2 2.275(4) Yi-N2-C24 154.3(4) Yi-N3 2.263(3) Yl-N3-Sii 125.31(17) Yi-N4 2.482(3) Yi-N3-5i2 111.98(17) 2.496(3) Yi-N5 N3-Sil 1.715(4) N3-Si2 1.712(3)  Interestingly, the bis(anilido) yttrium complex 5.19 can be made directly from mono(amidate) complex 5.14 (Figure 5.12).  As mentioned previously, the intermediate  (presumably a bis(anilido) yttrium oligomer or dimer) could not be isolated as a solid. However, if one equivalent of bipy is added to the proposed bis(anilido) yellow oil redissolved in hexanes, complex 5.19 is obtained in 83% yield.  As in the case of  synthesizing complex 5.18, the reaction mixture turns a dark red colour upon addition of bipy, and simultaneously complex 5.19 precipitates out of solution as a red solid. The solid can be isolated by filtration through a fitted filter, and rinsed with hexanes or pentane. Complex 5.19 can be recrystallized at -30 °C from a minimum amount of toluene; however, an X-ray crystallographic structural determination has not been successful. This compound has similar solubility properties as complex 5.18; it is soluble in toluene or benzene, but not hexanes or pentane. It is also thermally sensitive, and will decompose above 100 °C to give a brownlblack solid.  It is for this reason that an ElMS analysis was unattainable.  Interestingly, if complex 5.18 is synthesized in the same manner (by not isolating complex  167  5.16 first) clean formation does not occur, as evidenced by the ‘H NMR spectrum that  indicates there is free bipy (doublet at  2 S 3 (Me N i) N Y 7 SO 3 (Me N 2  /=\  ))— /)  8.76 ppm).  1. 2 equiv. H NDipp 2 THE, rt 2. 1 equiv. bipy hexanes, rt  5.14  5.19, 83%  Figure 5.12. Synthesis of bis(anilido) yttrium complex 5.19.  The ‘H NMR spectrum of complex 5.19 is very indicative of two bound anilido ligands (Figure 5.13). The diagnostic N-H signal at of 1.4 Hz.  5.42 ppm integrates to 2 protons, and has  aJYH  This chemical shift is more downfield than compared to the mono(anilido)  complex 5.18 (N-H signal at  4.83 ppm). Furthermore, the methine signal at  the isopropyl substituents on the anilido ligands integrates to 4 protons.  3.15 ppm for  An interesting  feature of this ‘H NMR spectrum is the drastic shift in the ortho-naphthyl proton signal. In complex 5.18 this signal is at ö 9.32 ppm, and for all other amidate complexes this signal is between ö 9.10 and 9.30 ppm. However, for complex 5.19 the ortho-naphthyl proton signal has shifted upfield to  7.53 ppm, indicating a different chemical environment. There still is  a proton signal associated with the bipy ligand at 6 9.15 ppm, which is shifted upfield compared to complex 5.18 (6 9.45 ppm). The JR spectrum of complex 5.19 is very similar to that of complex 5.18, and also has a broad N-H stretch band at 3449 cmi.  168  ( 5.19  Chrical Shift (ppm)  Figure 5.13. ‘H NMR spectrum (600 MHz, C , 25 °C) of complex 5.19. D 6  Both complexes 5.18 and 5.19 are intensely coloured in the solid-state as well as in solution. Complexes 5.18 dissolved in toluene gives an intense purple  max 2 (  whereas complex 5.19 dissolved in toluene results in red solution  =  max 2 (  calculated molar absorptivity values at the maximum wavelengths are cm for 5.18 and 1  E54  =  262 dm mol’cm’ for 5.19. 3  6544  544 urn),  514 nm). The =  292 dm moF 3  Presumably these highly coloured  solutions are from charge-transfer bands associated with a ligand to metal charge-transfer (LMCT) or a ligand to ligand charge-transfer (LLCT). The yttrium centre is formally d°, so a metal-ligand charge transfer (MLCT) band is not probable.  169  Bipy was found to have great donor ability to mixed amidate/anilido yttrium complexes. The initial hope was that binding bipy would induce a a-H abstraction from the anilido ligands to form a yttrium imido. So far, this strategy has been unsuccessful. Regardless, these are novel compounds that show interesting characteristics, such as intense colour. Successful ventures into group 3 or lanthanide imido formation have typically used deprotonation of an anilido N-H with a strong base. Complexes 5.18 and 5.19 can be formed in high yield and with high purity, and are ideal precursors for deprotonation attempts to form a yttrium imido complex.  5.4  Attempted Deprotonation Routes Literature precedence for group 3 or lanthanide imido formation (where the imido is  bridging or capping) have been formed by deprotonation of an anilido complex.” 4 It has been shown that mixed amidate/anilido complexes of group 3 can be formed easily. These yttrium complexes can be coordinated readily by one molecule of bipy, which will create some steric protection around the yttrium centre as opposed to one molecule of THF (such as in complex 5.16). Since the bipy yttrium complex 5.19 can be formed in high-yield in a onepot synthesis, it was chosen for deprotonation studies. Three bases were chosen to initially test the deprotonation of complex 5.19, n butyllithium (n-BuLi), sodium bis(trimethylsilyl)amide (Na(N(SiMe ), and potassium 2 ) 3 xylide (KXy). All these bases, once reacted, will form volatile products that can be removed in vacuo. Also, using a range of metal counterions (Li, Na, and K), will give an indication of  the best counterion size for forming proposed deprotonated yttrium species. Unfortunately,  170  formation of single crystals is necessary in fully determining whether an imido is formed, and this can be counterion dependant. The deprotonation studies have been carried out in the same manner for all bases, so a direct comparison can be obtained. Complex 5.19 can be dissolved in 5 mL toluene and stirred at room temperature. An equimolar amount of base is dissolved in 2 mL of toluene, was added dropwise to the stirring solution of complex 5.19 at room temperature. These reactions are performed with approximately 60 mg of complex 5.19. In all cases, the reaction mixture changes colour from red to dark brown. The solvent is removed in vacuo to give a crude brown oil when using n-BuLi and Na(N((SiMe) , but a brown solid when using KXy 2 ) 3 as the base. The ‘H NMR spectrum of the crude compound in all cases shows multiple N-H signals from ö 4.50 to 5.50 ppm and evidence of 2,6-diisopropylaniline formation (septet at ö 2.67 ppm, and doublet at  1.15 ppm). All the ‘H NMR spectra were complicated and  contained multiple signals in the aryl and alkyl region that were not identifiable. Recrystallization of the products was only successful in forming amorphous solids. Since a solid was initially obtained from the reaction of complex 5.19 and KXy (instead of an oil) this reaction was further studied. 1 8-Crown-6 is known to coordinate potassium molecules, and also aid in crystallization of compOuflds. 3133  With this in mind, KXy was reacted with 18-crown-6, and then  subsequently added to a solution of complex 5.19. After removing the solvent in vacuo, a dark brown solid was obtained. The ‘H NMR spectrum of this compound was similar to analogous reaction without the crown ether. The crown ether is thought to be coordinated since the proton signal for 18-crown-6 has shifted from ö 3.52 ppm (for free 18-crown-6) to ö 2.90 ppm. Again, diisopropylaniline was evident in the sample (septet at  2.67 ppm, and  171  doublet at ö 1.15 ppm) and there were multiple N-H signals between  5.00 ppm and 5.50  ppm. Presumably, the diisopropylaniline is formed by a-H abstraction of the anilido ligand of complex 5.19. The multiple N-H signals could arise from a mix of different compounds (oligomers or dimers) that have bridging or capping imido ligands, and bridging anilido ligands. The deprotonation is most likely not going to completion. Heating the solution of the product to above 65 °C to force deprotonation causes solid to precipitate and the ‘H NMR spectrum becomes very complicated.  Most likely, the compound obtained is a dimer or  oligomer with bridging imido and/or amido compounds. Unfortunately, only amorphous solid has been obtained after recrystallization attempts. Scaling up the reaction (above 60 mg of 5.19) also proved difficult, and only resulted in dark brown oils, with very complicated ‘H NMR spectra.  Also, other characterization techniques, such as JR spectroscopy, mass  spectrometry have been inconclusive. The JR spectroscopy still indicates an N-H stretch band at 3449 cm , and the mass spectrometry analysis was unable to be performed due to 1 decomposition of the sample on the instrument probe. To test if there is an imido present, an insertion reaction with 2,6-dimethyiphenyl isocyanate (5.20) was attempted. The insertion reaction with 5.20 would produce yttrium oxide species 5.21 (which are very insoluble) and carbodiimide 5.22 (Figure 5.14). Ideally, the yttrium oxide species would precipitate out of solution and the carbodiimide would be confirmed in the ‘ C NMR spectrum by the diagnostic N=CN signal. Since only small 3 amounts of the proposed imido complex can be obtained at a time, this insertion reaction consequently was performed on small (NMR) scale. Upon addition of 5.20 to the proposed imido complex, the reaction mixture turned a darker brown colour and subsequently a solid precipitated out of solution.  Unfortunately, due to the small scale of the reaction, the  172  experimental results were inconclusive. However, a precipitate did form, possibly indicating that yttrium oxide species are indeed forming.  NCO  5.20  fYN—) 2 L  Proposed  / FJ 5.21  +  5.22  Figure 5.14. Insertion reaction into proposed imido complex.  Although a solid-state molecular structure of an yttrium imido species was not obtained, possibly a-H abstraction by a strong base may result in an imido-containing yttrium species. The complex formed is most likely not fully deprotonated (to form a monomeric terminal imido), but possibly an oligomer where there are bridging or capping imido groups mixed with bridging or terminal anilido ligands (as indicated by N-H proton signal and stretch band present in the ‘H NMR and JR spectrum) is formed. With the right chemical environment, and the correct choice of base, ideally a crystalline yttrium amidate/imido species can be formed.  173  5.5  Conclusions Simple reactions with mono(amidate) yttrium complex 5.14 proved to be a route into  yttrium imido precursors. The mono(anilido) complex 5.16 could be isolated in high-yield by addition of one equivalent of diisopropylaniline to complex 5.14. Increasing the amount of diisopropylaniline to two equivalents resulted in a non-isolable species, presumably a bis(anilido) yttrium dimer or oligomer. Bipy was found to be an excellent donor for yttrium, but does not induce a-H abstraction of an anilido ligand to form an yttrium imido complex under these particular experimental conditions. Bipy mono(anilido) yttrium complex 5.18 can be formed in high yield from the reaction of mono(anilido) complex 5.16, but can not be formed in one-pot from mono(amidate) complex 5.14. In contrast, bis(anilido) bipy yttrium complex 5.19 can be formed in high yield in one-pot from mono(amidate) 5.14.  Both  complexes are highly coloured, and thermally sensitive. Deprotonation of complex 5.19 with a strong base to form an yttrium imido complex proved to be very difficult. This is not surprising since the target yttrium imido complex is a long-standing goal in group 3 chemistry. Reaction of complex 5.19 with the base KXy gave a solid as opposed to a dark oil (as is the case when using n-BuLi or Na(N(SiMe )), which 2 ) 3 seems promising as suggested by spectroscopic studies and preliminary insertion reactions. A crystalline yttrium imido complex, whether formed by a-H abstraction or by deprotonation methods, would be a remarkable discovery.  Many more conditions, bipy  derivatives, supporting ligands and deprotonating bases can be tested in the synthesis of the elusive yttrium imido complex. The efforts described in this Chapter are promising, but are just a starting point for further research in the Schafer group and the broader chemistry community.  174  5.6  Experimental  5.6.1 Starting Materials and Reagents All operations were performed under an inert atmosphere of nitrogen using standard Schienk-line or glovebox techniques. THF, toluene, pentane, and hexanes were all purified by passage through an alumina column and sparged with nitrogen.  ] was 2 ) 3 Y[N(SiMe  synthesized as described in literature, 23 or purchased from Aldrich and recrystallized from hexanes before use. 2,6-Diisopropylaniline was purchased from Aldrich and distilled from 2 before use. 1 8-crown-6 was purchased from Aldrich and sublimed under vacuum at Call 140 °C before use. All other chemicals were commercially available and used as received unless otherwise stated. ‘H and ‘ C NMR spectra were recorded on Bruker AV300, AV400 3 and AV600 spectrometers.  Shifts are reported in parts per million (ppm) relative to  tetramethylsilane (TMS) and calibrated against residual solvent signal, coupling constants J are given in Hertz (Hz) (all couplings are 3 J unless otherwise stated). Infrared spectra were measured on a Nicolet 4700 spectrometer using KBr pellets and JR bands v are reported in Elemental analyses and mass spectra were performed by the microanalytical laboratory of the Department of Chemistry at the University of British Columbia.  Some elemental  analyses gave low carbon content for yttrium complexes, possibly due to carbide formation. 24 X-ray crystallography was conducted at the University of British Columbia by Dr. Brian Patrick, Dr. Rob Thomson, or Neal Yonson.  175  5.6.2 Synthesis Synthesis  of  mono(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate)bis(2-  methyldimethylaminophenyl) yttrium (5.13) Inside a glovebox, a 20 mL glass vial was charged with  I  yttrium aryl complex 5.11 (0.297 g, 0.604 mmol), 5 mL of  0 Nc  ( —  tetrahydrofuran and a stirbar. The reaction mixture was stirred until  all  solid  was  dissolved  and  N 2  —  /  N  N-2’,6’-  diisopropylphenyl(naphthyl) amide 5.12 (0.202 g, 0.605 mmol) was dissolved in 5 mL of tetrahydrofuran was added very slowly to the stirring reaction mixture at room temperature. The solution was stirred within the glovebox for 2 hours filtered through a pipette plug of CeliteTM and then concentrated under reduced pressure to a pale yellow solid.  The product  was washed with 3 x 5 mL of pentanes to remove residual amine. The solid was redissolved in 5 mL toluene, heated to 65 °C for 2 hours and then concentrated in vacuo. The white solid was recrystallized by dissolving in minimum amount of warm pentane, with a few drops of toluene and then cooled to -30 °C to give a white solid. Yield: 0.2 16 g, 52%. 1 H NMR (600 MHz, C ) ö 8.93 (d, J D 6  12 Hz, 1H, ortho-naphthyl-I]), 8.14 (d, J  (d, J= 12 Hz, 1H, aryl-I]), 7.46 (t, J  6 Hz, 2H, aryl-If), 7.51  6 Hz, 1H, aryl-I]), 7.37 (m, 3H, aryl-H), 7.28 (t, J  6  Hz, 2H, aryl-If), 7.23 (t, J = 6 Hz, 1H, aryl-I]), 7.03 (t, J = 6 Hz, 3H, aryl-I]), 6.94 (s, 3H, aryl-I]), 6.69 (t, J  6 Hz, 1H, aryl-I]), 3.69 (broad s, 4H, 3 N(CH -CH ) 2 ) , 3.25 (broad s, 2H,  ), 2.40 (s, 12H, 3 2 ) 3 CH(CH N(CH -CH ) 2 ) , 1.05 (broad s, 6H, CH(CH ), 0.45 (broad s, 6H, 2 ) 3 ). ‘ 2 ) 3 CH(CH C NMR (150.9 MHz, C 3 ) ö 184.0 (C=O), 183.7, 179.8, 146.5, 141.0, 140.8, D 6 137.1, 133.9, 131.6, 131.3, 129.6, 127.9, 126.5, 126.3, 125.6, 125.5, 125.3, 124.5, 124.4, 124.3, 123.3, 123.2 (aryl-C’s), 68.5 3 N(CH (-CH ) 2 ) , 44.5 3 N(CH (-CH ) 2 ) , 28.0 (CH(CH ), 2 ) 3  176  23.8 (CH(CH ), 22.7 (CH(CH 2 ) 3 ). 2 ) 3  Anal. found (calcd for N 3 C 4 H 0 3 Y): 9 4  C 71.40°/b  (71.01%), N 6.00% (6.37%), H 6.8 1% (6.72%).  Synthesis  of  mono(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate)mono(trimethylsilyl  amido)mono(2,6-diisopropylanilido)mono(tetrahydrofuran)yttrium (5.16) Inside a glovebox, a 20 mL glass vial was charged with mono(amidate) complex 5.14 (0.203 g, 0.249 mmol), 5 mL of tetrahydrofuran and a stirbar. The reaction mixture was stirred  until  all  solid  was  dissolved  and  2,6-  diisopropylaniline (44.1 mg, 0.248 mmol) diluted in 2 mL of tetrahydrofuran was added very slowly to the stirring reaction mixture at room temperature. The solution was stirred within the glovebox for 2 hours and then concentrated under reduced pressure to a yellow oil.  The product was recrystallized by dissolving in minimum amount  of pentane and then cooled to -30 °C to give yellow crystals. Yield: 0.175 g, 85%. Refer to Figure 5.9, Table 5.1 and Appendix II for crystallographic data. ‘H NMR (600 MHz, C ) D 6 9.13 (d, J  9 Hz, 1H, aryl-H), 7.55 (m, 2H, aryl-I]), 7.33 (t, J= 9 Hz, 2H, aryl-R), 7.25 (t,  J= 9 Hz, 2H, aryl-I]), 7.18 (s, 2H, aryl-H), 6.93 (s, 2H, aryl-R), 6.89 (t, J= 6 Hz, 1H, aryl H), 6.76 (t, J= 6 Hz, 1H, aryl-H), 5.28 (d, J 1.9 Hz, 1H, N-H), 3.99 (broad s, 4H, O-CH ), 2  3.48 (broad septet, J— 6 Hz, 2H, CH(CH ), 3.25 (septet, J 2 ) 3 J  =  6 Hz, 12H, CH(CH ), 1.17 (d, J 2 ) 3  =  ), 1.37 (d, 2 ) 3 6 Hz, 2H, CH(CH  ), 1.13 (broad s, 4H, 02 ) 3 6 Hz, 12H, CH(CH  CH CH ) 2 , 0.44 (s, 18H, N(Si(CH ). ‘ 2 ) 3 ) 6 180.8 (C0), 151.9, D 6 C NMR (150.9 MHz, C 3  142.1, 141.7, 134.9, 133.6, 132.3, 131.7, 131.0, 129.3, 128.7, 127.2, 127.0, 126.7, 126.3, 125.6, 125.4, 124.5, 123.4, 116.5 (aryl-C’s), 71.8 (0-CR ), 30.6 (CH(CH 2 ), 28.4 2 ) 3  177  ), 25.9 2 2 ) 3 (CH(CH CH (O-CH ) , 25.5 (CH(CH ), 24.4 (CH(CH 2 ) 3 ), 5.9 (N(Si(CH 2 ) 3 ). JR 2 ) 3 (KBr, cm’): 3295 (s), 3264 (w), 2958 (s), 1589 (w), 1517 (s), 1497 (s), 1422 (w), 1399 (s), 1379 (w), 1255 (s), 984 (s), 838 (s), 763 (w), 744 (w), 670 (w) cm . MS (El): 755 (M), 1 579 (M  -  NHDipp).  Anal. found (calcd for 2 38 C 6 H S O 3 N Y 9 ): i  C 65.60% (65.27%), N  4.78% (5.07%), H 8.41% (8.28%).  Synthesis of mono(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate) mono(trimethylsilyl amido) mono(2,6-diisopropylanilido)mono(2,2 ‘-bipyridine)yttrium (5.18)  Inside a glovebox, a 20 mL glass vial was charged with complex 5.16 (0.240 g, 0.290 mmol), 5 mL of hexanes and  /  N  Si) 3 (Me N 2  a stirbar. The reaction mixture was stirred until all solid  was dissolved and bipyridine (45.4 mg, 0.290 mmol) diluted in 2 mL of hexanes was added very slowly to the  /  N  \ /  \ /  stirring reaction mixture at room temperature. Immediately the reaction mixture turns a dark purple colour and an orange solid precipitates out of solution. The product was isolated by filtration through a fritted funnel and rinsed with hexanes. The product was recrystallized by dissolving in minimum amount of toluene and then cooled to -30 °C to give red-orange crystals.  Yield: 0.199 g, 76%.  Refer to Figure 5.11, Table 5.2 and Appendix II for  crystallographic data. ‘H NMR (400 MHz, C ) D 6  9.45 (d, J = 4.4 Hz, 2H, aryl-H (bipy)),  9.32 (d, J = 9 Hz, 1H, ortho-naphthyl-II), 7.53 (m, 2H, aryl-I]), 7.40 (m, 1H, aryl-I]), 7.25 (m, 4H, aryl-H), 7.13-7.0 1 (m, 8H, aryl-H), 6.94 (m, 4H, aryl-I]), 6.89-6.80 (m, 4H, aryl-H), 6.73 (t, J  8 Hz, 2H, aryl-IJ), 6.39 (t, J  8 Hz, 2H, aryl-I]), 4.83 (d, J= 1.2 Hz, 1H, N-I]),  3.52 (broad s, 1H, CH(CH ), 3.33 (septet, J 2 ) 3  6 Hz, 2H, CH(CH ), 2.90 (broad s, 1H, 2 ) 3  ), 1.22 (overlapping d and broad s, J = 6 Hz, 1 8H, amidate CH(CH 2 ) 3 CH(CH 2 and anilido ) 3  178  ), 1.17 (broad s, 6H, CH(CH 2 ) 3 CH(CH ), 0.49 (s, 18H, N(Si(CH 2 ) 3 ). ‘ 2 ) 3 C NMR (150.9 3 MHz, C ) D 6  178.2 (C0), 153.7, 153.6, 152.6, 143.7, 140.2, 137.0, 135.1, 134.6, 133.2,  132.9, 130.6, 128.9, 127.8, 127.2, 126.5, 126.0, 124.5, 124.1, 124.0, 121.5, 115.2 (aryl-C’s), 28.8 (CH(CH ), 26.1 (CH(CH 2 ) 3 ), 24.8 (CH(CH 2 ) 3 ), 24.1 (CH(CH 2 ) 3 ). 2 ) 3 ), 6.3 (N(Si(CH 2 ) 3 JR (KBr, cm’): 3449 (broad, s), 2960 (s), 1600 (w), 1576 (w), 1513 (s), 1461 (s), 1424 (w), 1258 (s), 1013 (w), 975 (w), 811 (s), 779 (w), 666 (w) cm . MS (El): 755 (M 1  -  bipy).  Anal. found (calcd for 2 5Si C 6 H O 5 N Y 1 8 ): C 66.02% (67.15%), N 7.22% (7.68%), H 7.23% (7.5 1%).  Synthesis  of  mono(N-2 ‘,6 ‘-diisopropylphenyl(naphthyl)amidate)bis(2,6-  diisopropylanilido)mono(2,2 ‘-bipyridine)yttrium (5.19) Inside a glovebox, a 20 mL glass vial was charged with mono(amidate) complex 5.14 (0.294 g, 0.361 mmol), 5 mL of THF and a stirbar. The reaction mixture was stirred  until  all  solid  was  dissolved  and  2,6-  diisopropylaniline (0.1286 g, 0.725 mmol) diluted in 2 mL of tetrahydrofuran was added very slowly to the stirring reaction mixture at room temperature. The reaction mixture turned a bright pale yellow colour and was stirred for 10 minutes. The solvent was then removed under vacuum, and the product was redissolved in 5 mL of hexanes. 2,2’-bipyridine (56.5 mg, 0.362 mmol) diluted in 2 mL of hexanes was added very slowly to the stirring reaction mixture at room temperature. Immediately the reaction mixture turns a dark purple colour and an red solid precipitates out of solution. The product was isolated by filtration through a fitted funnel and rinsed with hexanes. The product was recrystallized by dissolving in minimum amount  179  of toluene and then cooled to -30 °C to give red crystals. Yield: 0.2784 g, 83%. ‘H NMR (300 MHz, C ) D 6  9.15 (d, J = 4.4 Hz, 2H, aryl-H (bipy)), 7.53 (d, J  naphthyl-R), 7.44 (d, J= 9 Hz, 1H, aryl-I]), 7.33 (d, J  =  9 Hz, 1H, ortho 9 Hz,  9 Hz, 1H, aryl-H), 7.26 (d, J  1H, aryl-H), 7.18-7.15 (m, 1H, aryl-I]), 7.05 (m, 6H, aryl-H), 6.95 (t of d, 3 J= 9 Hz, 4 J Hz, 4H, aryl-H), 6.87 (t, J= 8 Hz, 4H, aryl-I]), 6.71 (t, J= 8 Hz, 1H, aryl-I]), 6.45 (t, J Hz, 2H, aryl-I]), 5.42 (d, J= 1.4 Hz, 2H, N-H), 3.64 (septet, J  1.2 8  6 Hz, 2H, 3 CH(CH ) 2 ) , 3.15  (septet, J= 6 Hz, 4H, 3 CH(CH ) 2 ) , 1.39 (d, J= 6 Hz, 6H, 3 CH(CH ) 2 ) ), 1.25 (d, J= 6Hz, 12H, CH(CH ) 2 ) 3 ), 1.15 (d, J  6 Hz, 12H, 3 CH(CH ) 2 ) ), 0.55 (d, J 6 Hz, 6H, CH(CH )). ‘ 2 ) 3 C 3  NMR (150.9 MHz, C ) ö 179.7 (C=O), 153.4, 153.3, 152.2, 142.1, 141.8, 139.9, 134.9, D 6 133.5, 133.3, 133.1, 132.6, 132.0, 130.1, 129.1, 127.5, 126.7, 125.9, 125.5, 125.1, 125.0, 124.7, 123.5, 121.5, 115.0 (aryl-C’s), 30.4 3 (CH(CH ) 2 ) ), 25.8 3 2 ) 3 , 28.7 (CH(CH (CH(CH ) 2 ) , 24.4 3 (CH(CH ) 2 ) , 24.3 3 (CH(CH ) 2 ) ). JR (KBr, cm’): 3449 (broad, s), 2960 2 ) 3 , 24.1 (CH(CH  (s), 1641 (w), 1591 (w), 1513 (s), 1422 (w), 1259 (s), 781 (w), 622 (w) cm . Anal. found 1 (calcd for 5 N 5 C 6 H 0 Y): 7 C 72.30% (73.77%), N 7.55% (7.47%), H 7.50% (7.39%). 8  180  5.7  References  (1)  Hazari, N.; Mountford, P. Ace. Chem. Res. 2005, 38, 839.  (2)  Zuckerman, R. L.; Krska, S. W.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 751.  (3)  Eldred, S. E.; Stone, D. A.; Geliman, S. H.; Stahl, S. S. I Am. Chem. Soc. 2003, 125,  3422. (4)  Thomson, R. K.; Bexrud, J. A.; Schafer, L. L. Organometallics 2006, 25, 4069.  (5)  Hayton, T. W.; Boncella, J. M.; Scott, B. L.; Palmer, P. D.; Batista, E. R.; Hay, P. J.  Science 2005, 310, 1941. (6)  Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc. 2007,  129, 11914. (7)  Shannon, R. D. Acta Crystallogr., Sect. A: Cryst. Phys., Dzffr., Theor. Gen. Cryst.  1976, 32, 751. (8)  Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387.  (9)  Masuda, J. D.; Jantunen, K. C.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008,  27, 803.  (10)  Panda, T. K.; Randoll, S.; Hrib, C. G.; Jones, P. G.; Bannenberg, T.; Tamm, M.  Chem. Commun. 2007, 5007. (11)  Chan, H. S.; Li, H. W.; Xie, Z. W. Chem. Commun. 2002, 652.  (12)  Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2003, 22,  4372. (13)  Knight, L. K.; Piers, W. E.; McDonald, R. Organometallics 2006, 25, 3289.  (14)  Gordon, J. C.; Giesbrecht, G. R.; Clark, D. L.; Hay, P. J.; Keogh, D. W.; Poli, R.;  Scott, B. L.; Watkin, J. G. Organometallics 2002, 21, 4726. (15)  Liu, B.; Cui, D.; Ma, J.; Chen, X. S.; Jing, X. B. Chem. Eur. 1 2007, 13, 834.  (16)  Evans, W. J.; Ansari, M. A.; Ziller, J. W. Inorg. Chem. 1996, 35, 5435.  (17)  Booij, M.; Kiers, N. H.; Heeres, H. J.; Teuben, J. H. I Organomet. Chem. 1989, 364,  79. (18)  Gribkov, D. V.; Hultzsch, K. C. Chem. Commun. 2004, 730.  (19)  Eppinger, J.; Spiegler, M.; Hieringer, W.; Herrmann, W. A.; Anwander, R. I Am.  Chem. Soc. 2000, 122, 3080.  181  (20)  Data was processed using the SQUEEZE function of the PLATON software to  remove disordered pentane. Speck, A. L. I Appi. Cryst. 2003, 36, 7. (21)  Zhang, Z.; Leitch, D. C.; Lu, M.; Patrick, B. 0.; Schafer, L. L. Chem. Eur. 1 2007,  13, 2012. (22)  Data was processed using the SQUEEZE function of the PLATON software to  remove residual THF. Speck, A. L. I Appl. Cryst. 2003, 36, 7. (23)  Bradley, D. C.; Ghotra, J. S.; Hart, F. A. I Chem. Soc., Dalton Trans. 1973, 1021.  (24)  Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. Dalton Trans. 2005, 1565.  182  Chapter 6. Conclusions and Future Work 6.1  Summary and Conclusions The research in this thesis explores the chemistry involved with novel yttrium amidate  complexes. These complexes can be synthesized in high yield from amide proligands and yttrium tris(bis(trimethylsilyl)amide).  By changing the stoichiometry and reaction  conditions, tris, bis and mono(amidate) yttrium complexes can be formed.  A library of  complexes with varied electronic and steric properties was prepared and their reactivity investigated. All the yttrium complexes were found to be highly active initiators for the ring-opening polymerization of -caprolactone. The tris(amidate) complexes were the more controlled initiators to give poly(-capro1actone) in high yield with the narrowest polydispersity values. The amidate backbone did have an effect on initiation properties; complexes with ligands containing electron-withdrawing groups were not as efficient. The mechanism of initiation was studied and is proposed to go through a coordination-insertion mechanism. In addition, a detrimental side-reaction was postulated where -caprolactone may react with the yttrium amidate compound to form an enolate complex. Another reaction explored was the hydroamination of aminoalkenes. The yttrium mono and bis(amidate) complexes were moderate catalysts for this transformation, whereas the tris(amidate) complexes did not catalyze the reaction at all. Electron-withdrawing groups on the amidate backbone had a large effect on reaction time, and complexes that contained an amidate ligand with one or more trifluoromethyl groups had the fastest reaction times.  183  A mono(amidate) yttrium complex was used in stoichiometric reactions to form anilido complexes. The anilido complexes were further reacted with large bulky donors, and bases in the hopes of forming a terminal yttrium imido complex.  To date, attempts at c’s-H  abstraction, and deprotonation have not proved successful in forming an isolable imido complex; however, these investigations are on-going in the hands of another doctoral student. This thesis discusses an extension of amidate chemistry to group 3, a new area of research for the Schafer group.  There is much more to discover using yttrium amidate  complexes, and these compounds provide an important benchmark for lanthanide chemistry. Some suggestions that are extensions of this research or new research directions are recommended here.  6.2  Future Work  6.2.1 Yttrium Amidates as Polymerization Initiators for other Oxygencontaining Monomers The mechanistic proposal in Chapter 3 suggests that to improve initiation for tris(amidate) complex 6.1 (3.19 in Chapter 3), or any other amidate complex, the side reaction to give an enolate complex needs to be minimized. The polymerization studies in Chapter 3 have also indicated that the substituents on the amidate backbone did have an effect on initiator ability. Taking advantage of the modularity that can be achieved in the amidate ligand, new complexes can be designed for ROP of -capro1actone.  184  6.1  Figure 6.1. Tris(amidate) yttrium complex 6.1.  It has been shown that adding electron-withdrawing groups to the amidate backbone is detrimental to polymerization.  Perhaps, adding more electron-donating groups to the  amidate backbone (such as OCR ) could result in a more controlled polymerization. Another 3 method could be to install more bulk on the amidate backbone, possibly by adding 2,6-ditert-butyl groups on the nitrogen phenyl substituent. Future work will also involve utilizing the monomer lactide (6.2, Figure 6.2). Enolate formation may be sterically disfavoured in this case, due to the neighbouring CR 3 group.  0  6.2  Figure 6.2. Structure of rac-lactide (6.2).  6.2.2 Intermolecular Hydroamination In Chapter 4, yttrium bis and mono(amidate) complexes were found to be good precatalysts for hydroamination of aminoalkenes. Furthermore, by changing the electronic 3 group) the activity of the yttrium properties of the amidate ligand (such as adding a CF 185  precatalyst was enhanced. Although intermolecular hydroamination was not seen using the conditions presented in Chapter 4, it is an on-going research goal. The modular nature of the amide synthesis allows for further ligand design, in the hopes of creating a more reactive yttrium amidate complex.  For example, the proposed proligand shown in Figure 6.3  combines steric properties at the nitrogen with an enhanced electron-withdrawing effect. The steric properties are necessary in order to obtain crystalline bis and mono(amidate) complexes, as mentioned in Chapter 2.  CF CF 5 C F 3  Figure 6.3. Potential new amide proligand.  Potentially, amide 6.3 will result in a highly active yttrium amidate complex that will catalyze intermolecular hydroamination under the conditions presented in Chapter 4. However, other reaction conditions for intermolecular hydroamination should also be attempted with all active yttrium amidate complexes.  Examples of intermolecular  hydroamination by Marks and coworkers have used n-propylamine with 1 -butene and trimethyl(vinyl)silane.’  Also, substituted styrene molecules have been effective for  2 Screening both identity and concentration of reagents is key intermolecular hydroamination. to discovering a working catalytic system.  186  Si 3 Me 0 R R= F, CF , NMe 3 , OMe 2  Figure 6.4. Possible alkene sources for intermolecular hydroamination.  6.2.3 Amidate Complexes as Imido Precursors Chapter 5 explored preliminary reactivity into imido precursors starting with a mono(amidate) bis(amido) yttrium complex. Multiple avenues can be further investigated in the synthesis of the elusive terminal yttrium imido. Initial experiments using 2,2’-bipyridine (bipy), could be complemented with modifications to the bipy molecule, such as 4,4’-di-tertbutyl-2,2’-bipyridine or 2,2’:6’,2”-terpyridine. 4 These bulkier groups may be able to induce ’ 3 a-H abstraction on their own, or may be able to stabilize the complex during deprotonation with strong bases. In Chapter 5, an yttrium aryl complex was used in the synthesis of an yttrium amidate complex. The further synthesis of the yttrium anilido complex proved to be difficult, likely due to the difficult separation of product and aryl amine by-product. A suggestion for future work would be to use a different starting material, such as the yttrium alkyl complex S Y(CH ( ) 3 5 . 2 THF) iMe The removal of the tetramethylsilane by-product would be more facile; furthermore, the Y-C bond is more reactive than a Y-N bond and may be more successful for forming an yttrium imido complex by a-H abstraction or by deprotonation. Another option in group 3 imido research is to change the metal centre entirely. 3+ Scandium has a similar ionic radius (Sc  6 A).  =  0.745  i)  to that of Zr  4+  (0.72  i)  and U  5+  (0.76  Both zirconium and uranium terminal imido complexes have been successfully  187  79 the similar size of scandium makes it a good candidate for imido precursor synthesized; synthesis.  6.2.4 Yttrium Amidates as Atomic Layer Deposition Precursors The computer industry has led a large increase in research involving metal-oxide semiconductor field-effect transistors (MOSFET). The size of these transistors is becoming smaller with the improvements in technology. Traditionally, Si0 2 is used as a gate oxide in MOSFET, but shrinking the thickness of the Si0 2 layer has led to tunneling, and high leakage currents in the transistors. 10 Lanthanide oxides (typically Ln ) have a higher 3 0 2 , which allows for gate oxide layers with less tunneling and 2 dielectric constant than Si0 current leakage.  The most common method of forming these lanthanide oxide layer, is  atomic layer deposition (ALD) of lanthanide complexes.’° Many lanthanide complexes have been used as ALD precursors, and amidinate and acetoacetonate complexes are the most successful.’ 114 The key features of these complexes is that they are volatile, and typically contain alkyl groups on the ligand backbone. The amidate ligand is very similar to these ligand sets, as shown in Chapter 1, and could be used in the formation of lanthanide complexes for ALD precursors. The alkyl amide proligands introduced in Chapter 2 were used in preliminary reactions with yttrium, which were found to be inconclusive (Figure 6.5). Dimers or oligomers of yttrium were likely forming due to the lack of steric bulk at nitrogen, compared to the 2,6-dimethyiphenyl or 2,6-diisopropylphenyl substituents.  Dimer  compounds of lutetium have shown to be volatile, so oligomers of yttrium may still be 4 These reactions were not optimized, and yttrium amidate complexes applicable in ALD.’ could be isolable and used as ALD precursors if research was continued.  188  (2.14)  (2.15)  (2.16)  Figure 6.5. Amide proligands introduced in Chapter 2.  6.2.5 Imidates (O,N,O chelate) as a Ligand Set for Rare Earths In Chapter 1 many different ligand sets for yttrium complexes were introduced. Many of 8 ’ 15 these binding motifs formed a six-membered ring upon chelation, such as acetoacetonate, and j3-diketiminate ligands. 19-26 A similar binding motif to these ligand sets as well as the amidate ligand, is the imidate ligand.  The only crystallographically determined O,N,O  27 binding mode on yttrium results from isocyanate insertion into a yttrium caprolactamate. The imidate ligand can be formed from the imide proligand, which has a similar synthesis to the amidate ligand set (Figure 6.6). One difference is that a primary amide is first formed by reaction of an acid chloride and ammonium hydroxide, and then further reacted with another acid chloride to obtain the imide proligand.  Two examples, 6.10 and 6.11, have been  synthesized and fully characterized.  o  2 ONH OH 4 NH  cc  cc  6.7  6.8  RACI 6.9 6.10 R 6.11 R  = =  tBu Ph  Figure 6.6. Synthesis of imide proligands 6.10 and 6.11.  189  Initial experiments into preparation of an yttrium imidate complex followed the general procedure used for yttrium amidate formation. The reaction conditions were not optimized, and only a few attempts at synthesizing complex 6.12 were performed.  Y(N(SiMe 2 ) 3 THF 60 °C  3 equiv. 6.10  6.12  Figure 6.7. Synthesis of imidate complex 6.12.  ‘H NMR and IR spectra of complex 6.12 were obtained. Each possess similar features to amidate complexes. The ‘H NMR spectrum contained other very minor products that even after recrystallization were not removed. However, the spectrum did contain major peaks that correspond to complex 6.12. Just as in the yttrium amidate synthesis, one molecule of THF is bound by the metal centre as evidenced by the THF signals in the ‘H NMR spectrum  ( 3.63 and 1.21), which are shifted slightly from unbound THF (3 3.57 and  1.40).28  The ‘H  NMR spectrum contains the diagnostic ortho-naphthyl proton at 3 9.67, which is a large downfield shift from the proligand (ortho-naphthyl proton for 6.10 is at 6 8.18). Complex formation was confirmed by the lack of the N-H proton signal (6 8.43 in 6.10). X-ray quality crystals were formed by dissolving 6.12 in a minimum amount of toluene and cooling to -30 °C. The solid-state molecular structure of complex 6.12 has a pseudo mono-capped octahedral geometry, with 02 and 06 as the axial ligands, and 05 as the  190  capping ligand (Figure 6.8, Table 6.1). imidate backbone are 1.345  The average C-N and C-U bond lengths in the  A and 1.259 A, respectively, indicating delocalization through  the chelate. The average Y-0 bond for the imidate ligand is 2.264  A, which is very similar to  the yttrium amidate complexes. The average imidate bite angle (0-Y-0) is 72.44°, which is much larger than the 4-membered metallacycle for the yttrium amidate complexes.  03  Figure 6.8. Solid-state molecular structure of complex 6.12. THF methylene and tert-butyl methyl carbons have been removed for clarity. Table 6.1 Selected bond lengths (A) and angles (°) for complex 6.12. Bond Length (A) Bond Angle(°) 2.268(4) Yl-Ol-Ci 136.3(4) Yl-Ul 01-Cl-Ni 115.0(6) 01-Cl 1.267(6) Cl-Ni 1.332(7) C1-Ni-C2 120.6(5) Nl-C2-02 126.3(6) Ni-C2 1.339(7) 132.6(4) C2-02 1.264(6) C2-02-Yi 0l-Yi-02 71.19(14) 02-Yl 2.288(4) 2.286(4) 03-Y1-04 73.40(14) Y1-03 05-Y1-06 72.73(14) Y1-04 2.230(4) Yl-05 2.264(4) Yl-06 2.250(4) Y1-07 2.349(4)  191  There is still much to learn of this new class of yttrium compounds.  The reaction  conditions have not been optimized, and full characterization was not obtained. Synthesis of an yttrium imidate complex using imide 6.11 was also not optimized.  Presumably imidate  complex 6.12 can also initiate -caprolactone ring-opening polymerization (ROP), which has yet to be investigated.  Furthermore, the synthesis of mono and bis(imidinate) yttrium  complexes has not been attempted. Since these are a new class of yttrium compounds, the chemistry involved could extend to the range of reactivities explored in this thesis. The same investigations, such as -caprolactone ROP, hydroamination of aminoalkenes, and yttrium imido precursor synthesis could be performed with the analogous mono, bis and tris(imidate) yttrium complexes.  6.3  Summary The research presented in this thesis is a new avenue in amidate chemistry for the Schafer  group. It is merely the beginning of research into these group 3 amidate compounds, and already some continuing research into lactide polymerization has been initiated. The other research proposed in this section would extend the work in this thesis. Yttrium complexes are generally under-exploited in catalysis in spite of their low cost and promising reactivity trends in a range of transformations. The work presented here and subsequent proposed new directions take advantage of the modular amidate family of complexes.  There are many  accomplishments in this thesis and there are many more endeavors that can be explored from the foundations presented herein.  192  6.4  Experimental  6.4.1 Starting Materials and Reagents All operations were performed under an inert atmosphere of nitrogen using standard Schlenk line or glovebox techniques.  THF, toluene, pentane, and hexanes were all purified by  passage through an alumina column and sparged with nitrogen.  2 was ) 3 Y(N(SiMe  29 or purchased from Aldrich and recrystallized from synthesized as described in literature, hexanes before use. All other chemicals were commercially available and used as received H and ‘ C NMR spectra were recorded on Bruker AV300, AV400 3 unless otherwise stated. 1 and AV600 spectrometers.  Shifts are reported in parts per million (ppm) relative to  tetramethylsilane (TMS) and calibrated against residual solvent signal, coupling constants J J unless otherwise stated). Infrared spectra were are given in Hertz (Hz) (all couplings are 3 measured on a Nicolet 4700 spectrometer using KBr pellets and JR bands v are reported in . Elemental analyses and mass spectra were performed by the microanalytical laboratory 1 cm of the Department of Chemistry at the University of British Columbia. X-ray crystallography was conducted at the University of British Columbia by Dr. Brian Patrick, Dr. Rob Thomson, or Neal Yonson.  6.4.2 Synthesis Synthesis of tert-butyl(naphthyl) imide (6.10) Under a flow of nitrogen, 1-Naphthoic chloride (6.00 mL, 40.0 mol) was added to a dry round bottom flask, equipped with a stir bar. An excess of ammonium hydroxide (100 mL) was added to the crude solid, in which a white gas was produced. The resultant mixture was stirred overnight and then filtered to  193  isolate a beige solid. The solid, 1-naphthoyl amide (6.8), was washed with water and then hexanes before use (Yield  =  4.68 g, 68%). Lithium diisopropylamide (LDA) was prepared  by adding n-butyllithium (22.7 mL, 1.60 M, 36.0 mmol) dropwise to a cooled (-78 °C) solution of diisopropylamine (5.10 mL, 36.0 mmol) in tetrahydrofuran (THF). The LDA solution was canula transferred to a solution of 6.8 (3.40 g, 20.0 mmol) in dry THF. The reaction mixture was stirred for 30 mm at -78 °C, before trimethylacetyl chloride (2.45 mL, 20.0 mmol) was added via syringe. The colourless reaction mixture was warmed to room temperature and stirred overnight. The THF was removed in vacuo and the crude solid was redissolved in dichloromethane (DCM) and extracted with 1 x 30 mL 1 H aqueous HC1, 1 x 30 mL of 1 M aqueous NaOH, and 1 x 30 mL of brine. The DCM layer was then dried over , filtered and dried in vacuo to give a white solid. The solid was recrystallized by 4 MgSO dissolving in minimum amount of DCM and adding hexanes until a white solid precipitated ) 3 out of solution. Yield: 3.95 g, 78%. ‘H NMR (300 MHz, CDC1  8.43 (broad s, 1H, N-H),  8.18 (d, J= 9 Hz, 1H, ortho-naphthyl-H), 7.96 (d, J= 9 Hz, 1H, aryl-H), 7.86 (m, 1H, aryl ). ‘ ) 3 C NMR (CDC1 3 , 75 MHz, 293K) 3 1]), 7.61-7.46 (m, 4H, aryl-H), 1.27 (s, 9H, C(CH  176.1 (C=O), 169.0 (C=O), 133.8, 133.1, 131.8, 129.9, 128.8, 127.7, 126.8, 125.7, 124.8, 40.5 (C(CH ), 27.2 (C(CH ) 3 ). IR data (KBr, cm’): 3284 (s), 2971(s), 1733 (s), 1680 (w), ) 3 1511 (s), 1490 (s), 1248 (m), 1141 (w), 781 (w). ElMS (m/z): 255 [Mf. Anal. found (calcd for N0 C 1 H ) 2 6 7 : C 75.64% (75.27%), N 5.76% (5.49%), H 6.80% (6.71%).  194  Synthesis of phenyl(naphthyl) imide (6.11)  The experimental method described for 6.10 was used in the preparation of 6.11 using n-butyllithium (7.50 mL, 1.53 M, 11.5 mmol), diisopropylamine (1.30 mL, 9.30 mmol), 6.8 (1.31 g, 7.66 mmol), and benzoyl chloride (1.07 mL, 9.23 mmol). Yield: 1.23 g, 58%. ‘H NMR (300 MHz, CDC1 ) ö 9.12 (broad s, 1H, N-I]), 8.27 (d, J= 9 Hz, 1H, ortho-naphthyl-H), 7.97 (d, J 3 =  9 Hz, 1H, aryl-I]), 7.88 (m, 3H, aryl-I]), 7.71 (d, J= 9 Hz, 1H, aryl-I]), 7.60-7.42 (m, 6H,  aryl-H).  C NMR (CDC1 3 ‘ , 75 MHz, 293K) ö 168.7 (C=O), 165.5 (C=O), 133.6, 133.1, 3  132.8, 132.4, 131.9, 129.9, 128.8, 128.5, 127.8, 127.7, 126.6, 125.9, 124.7, 124.5. JR data (KBr, cm’): 3482 (br), 3235 (s), 1716 (s), 1671 (w), 1509 (s), 1499 (s), 1233 (m), 1198 (w), 780 (w). ElMS (m/z): 275 [Mf. Anal. found (calcd for NO C 1 H ) 2 8 3 : C 78.14% (78.53%), N 5.00% (5.09%), H 4.80% (4.76%).  Synthesis of tris(tert-butyl(naphthyl)imidate)mono(tetrahydrofuran)yttrium (6.12)  Inside a nitrogen filled glovebox, a vial was charged yttrium tris(bis(trimethylsilyl)amide) (77.0 mg, 0.135 mmol) and a stirbar. To this, 5 mL of tetrahydrofuran (THF) was transferred to the reaction vessel at room temperature. Imide 6.10 (0.101 g, 0.3 96 mmol) was dissolved in 5 mE THF and transferred dropwise to the stirring solution of yttrium tris(bis(trimethylsilyl)amide in THF. The solution was stirred within the glovebox for 2 hours at 60 °C, and then filtered through CeliteTM and concentrated under reduced pressure to a beige powder. The product was recrystallized by dissolving in a minimum amount of toluene and then left at -30 °C to yield colorless crystals. Yield: 0.102 g, 84%. X  195  ray quality crystals were grown from cold toluene. Appendix III for crystallographic data.  Refer to Figure 6.8, Table 6.1 and  ‘H NMR (300 MHz, C ) D 6  9.67 (broad s, 3H,  ortho-naphthyl-I]), 8.81 (d, J= 8 Hz, 3H, aryl-If), 7.64 (d, J= 8 Hz, 3H, aryl-H), 7.59 (d, J= 8 Hz, 3H, aryl-If), 7.23 (m, 6H, aryl-H), 7.02 (m, 3H, aryl-I]), 3.63 (m, 4H, 2 O-CH ) , 1.46 (s, 27H, 3 C(CH ) ) , 1.21 (m, 4H, ) CH 2 O-CH . JR data (KBr, cm’): 3283 (w), 2956 (s), 1650 (s), 1558 (vs), 1408 (vs), 1376 (w), 1024 (w), 932 (s), 868 (w), 799 (s) cm . 1  196  6.5  References  (1)  Ryu, J. S.; Li, G. Y.; Marks, T. J. J Am. Chem. Soc. 2003, 125, 12584.  (2)  Ryu, J. S.; Marks, T. J.; McDonald, F. E. Abstr. Pap. Am. Chem. Soc. 2001, 222,  U567. (3)  Masuda, J. D.; Jantunen, K. C.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008,  27, 1299.  (4)  Jantunen, K. C.; Scott, B. L.; Hay, P. J.; Gordon, J. C.; Kiplinger, J. L. I Am. Chem.  Soc. 2006, 128, 6322. (5)  Arndt, S.; Voth, P.; Spaniol, T. P.; Okuda, J. Organometallics 2000, 19, 4690.  (6)  Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.  (7)  Thomson, R. K.; Bexrud, J. A.; Schafer, L. L. Organometallics 2006, 25, 4069.  (8)  Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. I Am. Chem. Soc. 2007,  129, 11914. (9)  Hayton, T. W.; Boncella, J. M.; Scott, B. L.; Palmer, P. D.; Batista, E. R.; Hay, P. 1.  Science 2005, 310, 1941. (10)  Jones, A. C.; Aspinall, H. C.; Chalker, P. R.; Potter, R. J.; Kukli, K.; Rahtu, A.;  Ritala, M.; Leskelä, M. Mater. Sci. Eng., B 2005, 118, 97. (11)  Aspinall, H. C.; Bickley, J. F.; Gaskell, J. M.; Jones, A. C.; Labat, G.; Chalker, P.R.;  Williams, P. A. Inorg. Chem. 2007, 46, 5852. (12)  Kukli, K.; Ritala, M.; Pilvi, T.; Sajavaara, T.; Leskelae, M.; Jones, A. C.; Aspinall, H.  C.; Gilmer, D. C.; Tobin, P. J. Chem. Mat. 2004, 16, 5162. (13)  Paeivaesaari, J.; Dezelah, C. L. I. V.; Back, D.; El-Kaderi, H. M.; Heeg, M. J.;  Putkonen, M.; Niinistoe, L.; Winter, C. H. I Mater. Chem. 2005, 15, 4224. (14)  Anwander, R.; Munck, F. C.; Priermeier, T.; Scherer, W.; Runte, 0.; Herrmann, W.  A. Inorg. Chem. 1997, 36, 3545. (15)  Barash, E. H.; Coan, P. S.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. Inorg.  Chem. 1993, 32, 497. (16)  Liu, W.; Zhu, Y.; Tan, M. I Coord. Chem. 1991, 24, 107.  (17)  Plaziak, A. S.; Zeng, C. H.; Costello, C. E.; Lis, S.; Elbanowski, M. Inorg. Chim.  Acta 1991, 184, 229. (18)  Wang, R.; Song, D.; Seward, C.; Tao, Y.; Wang, S. Inorg. Chem. 2002, 41, 5187.  197  (19)  Avent, A. G.; Caro, C. F.; Hitchcock, P. B.; Lappert, M. F.; Li, Z.; Wei, X.-H. Dalton  Trans. 2004, 1567. (20)  Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers, W. E.; Parvez, M.  Organometallics 2003, 22, 1577. (21)  Liddle, S. T.; Arnold, P. L. Dalton Trans. 2007, 3305.  (22)  Sanchez.-Barba, L. F.; Hughes, D. L.; Humphrey,  S. M.; Bochmann, M.  Organometallics 2005, 24, 3792. (23)  Sanchez-Barba, L. F.; Hughes, D. L.; Humphrey, S. M.; Bochmann, M.  Organometallics 2006, 25, 1012. (24)  Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. Dalton Trans. 2005, 1565.  (25)  Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. I Organomet. Chem. 2005, 690, 5182.  (26)  Wei, X.; Cheng, Y.; Hitchcock, P. B.; Lappert, M. F. Dalton Trans. 2008, 5235.  (27)  Evans, W. J.; Fujimoto, C. H.; Ziller, J. W. Organometallics 2001, 20, 4529.  (28)  Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. I Org. Chem. 1997, 62, 7512.  (29)  Bradley, D. C.; Ghotra, J. S.; Hart, F. A. I Chem. Soc., Dalton Trans. 1973, 1021.  198  Appendix I Crystallographic details for complexes 2.18, 2.24, 2.25, 2.27 and 2.28 from Chapter 2. 2.18 N 7 C 8 H Y 4 0 3 3 0 1152.31 Chip, colorless 173(2) 0.71073 Monoclinic, /c 1 P2 13.7820(11), 33 .598(3), 16.0575(12)  2.24 (2 molecules tol) 70 C 9 H S O 3 N Y 2 i 1166.54 Prism, colourless 173(2) 0.7 1073 Monoclinic,  2.25  cL,13,y(°)  90, 98.762(3), 90  90, 101.524(2), 90  Volume (A ), Z 3 Calcd. Density (g/cm ) 3 Abs. coeff (mm’) F(000) Cryst. size (mm) Data collection 6 range (°)  7348.7(10), 4 1.042 0.837 2440 0.25 x 0.20 x 0.20  6484.4(7), 4 1.195 0.983 2488 0.30 x 0.25 x 0.20  2 5 C 6 H S O 3 N 6 F Y 0 8 i 1018.16 Plate, colourless 173(2) 0.7 1073 Triclinic, P-i 13.5055(5), 14.0512(4), 16.4069(6) 71.270(2), 73.207(2), 66.732(2) 2661.40(16), 2 1.27 1 1.203 1068 0.50 x 0.20 x 0.070  1.77—22.77  1.63 -22.50  1.62—22.75  -12h 14,-36 k36,-17l16 43713 9816 [R(int) 0.07351  -14h 13,-21 k21,-26l26 37610 0.0636]  -14h 13,-15k 15, -17 1 17 18825 6783 [R(int) = 0.0837]  98.8  99.8  94.3  Semi-empirical from equivalents 0.846 and 0.5 15 Full-matrix least squares on F 2 9816/0/744 0.976 Ri = 0.0614, wR2 = 0.1492 Ri = 0.1040, wR2 = 0.1649  Semi-empirical from equivalents 0.8215 and 0.3382 Full-matrix least squares on F 2 8456/0/728 1.026 Ri = 0.0492, wR2 = 0.0980 Ri = 0.0844, wR2 = 0.1124  Semi-empirical from equivalents 0.9 192 and 0.6497 Full-matrix least 2 squares on F 6783/0/595 0.95 1 Ri = 0.0475, wR2 = 0.0867 Ri 0.1011,wR2 0.0969  0.590 and -1.863  0.648 and -0.508  0.4 17 and -0.345  Emperical Formula Morphology, colour, Temperature (K) Wavelength (A) Cryst. syst., space group Unit cell dimensions a, b, c (A)  Limiting indices Reflections collected Indep. reflections Completeness to max 0 (%) Abs. correction Max and mm transmn Refinement method Data/restraints/param GOF on F 2 Final R indices [I> 2a(1)1 R indices (all data) Largest diff. peak and  hole (e/A ) 3  199  /n 1 P2 13.2111(8), 20.1020(14), 24.9192(17)  8456 [R(int)  =  Complex Emperical Formula  2.27 38 C 6 H S 2 O 3 N Y 4 9 i 812.23 Plate, colourless 173(2) 0.71073 Orthorhombic, 1 22 P2 11.6377(14), 19.076(2), 20.423(2)  cL,13,y(°)  90, 90, 90  Volume (A ), Z 3 Calcd. Density (g/cm ) 3 Abs. coeff (mm’) F(000) Cryst. size (mm) Data collection 0 range (°)  4534.1(9), 4 1.190 1.425 1736 0.35 x 0.20 x 0.08  2.28 30 C 7 H S 2 O 3 N Y 4 3 i 742.19 Prism, colourless 173(2) 0.71073 Monoclinic, C 2/c 30.5629(9), 19.4095(4), 15.8674(4) 90, 115.7900(10), 90 8475.2(4), 8 1.163 1.519 3200 0.20 x 0.20 x 0.10  1.99—28.12  1.48—25.43  -15h 14,-22 k25,-26l 14 34857 10974 [R(int) = 0.06 16]  -36h36,-15 k23,-19119 37105 7770 [R(int) 0.0447]  99.3  99.2  Semi-empirical from equivalents 0.8945 and 0.63 54 Full-matrix least squares on F 2 10974/0/488 0.998 Ri = 0.0466, wR2 = 0.0787 Ri = 0.0877, wR2 = 0.0890  Semi-empirical from equivalents 0.8642 and 0.6766 Full-matrix least squares on 7770/0/503 1.014 Ri = 0.0669, wR2 = 0.1581 Ri = 0.1082, wR2 = 0.1935  0.33 5 and -0.294  1.067 and -1.160  Morphology, colour, Temperature (K) Wavelength (A) Cryst. syst., space group  Unit cell dimensions a, b, c (A)  Limiting indices Reflections collected Indep. reflections Completeness to max 0 (%) Abs. correction Max and mm transmn Refinement method Data/restraints/param GOF on F 2 Final R indices [I> 2c(1)j R indices (all data) Largest diff. peak and hole (eIA ) 3  200  Appendix II Crystallographic details for complexes 5.16, and 5.18 from Chapter 5.  Emperical Formula Morphology, colour, Temperature (K) Wavelength (A) Cryst. syst., space  group Unit cell dimensions a, b, c (A)  Volume (A ), Z 3 Calcd. Density (g/cm ) 3 Abs. coeff (mm’) F(000) Cryst. size (mm) Data collection 0 range (°) Limiting indices Reflections collected Indep. reflections  5.16 48 C 6 H 3 N 52 Si O Y 828.11 Prism, yellow 173(2) 0.7 1073 Triclinic, P-l 12.3 86 1(7), 12.4287(7), 17.5 174(10) 73.689(3), 72.55 1(3), 77.253(3) 2441.5(2), 2 1.126 1.278 884 0.25 x 0.20 x 0.15 1.73  Max and mm transmn Refinement method Data/restraints/param GOF on F 2 Final R indices [I> 2a(I)] R indices (all data) Largest diff. peak and hole (e/A ) 3  28.37  90, 100.624(4), 90 6364.6(12), 4 0.952 0.985 1936 0.40 x 0.15 x 0.06 1.71 -22.60  -16h 16,-16 k 15,-23 l21 48561 11827 [R(int) = 0.0444]  -17h 16,-25 k25,-15l18 38602 8359 [R(int) = 0. 1049]  96.6  99.1  Semi-empirical from equivalents 0.8256 and 0.6967 Full-matrix least squares on 11827/0/491 1.048 Ri = 0.0424, wR2 = 0.1056 Ri = 0.0590, wR2 = 0.1100  Semi-empirical from equivalents 0.9432and0.6939 Full-matrix least squares on 8359/0/559 0.905 Ri = 0.0497, wR2 = 0.1002 Ri = 0.1068, wR2 = 0.1116  0.582 and -0.49 1  0.333 and -0.502  Completeness to max 0 (%) Abs. correction  —  5.18 5Si C 6 H O 5 N Y 2 1 8 912.19 Prism, red 173(2) 0.7 1073 Monoclinic, P 1 2/n 1 16.2277(17), 23.826(3), 16.7482(18)  201  Appendix III Crystallographic details for complex 6.12 from Chapter 6.  Emperical Formula  Morphology, colour, Temperature (K)  Wavelength (A) Cryst. syst., space group Unit cell dimensions a, b, c (A) ct, f3, y (°) Volume (A ), Z 3 Calcd. Density (glcm ) 3 Abs. coeff (mm’) F(000) Cryst. size (mm)  Data collection 0 range (°) Limiting indices Reflections collected Indep. reflections Completeness to max 0 (%) Abs. correction Max and mm transmn Refinement method Data/restraints/param GOF on F 2 Final R indices jI> 2cy(1)] R indices (all data) Largest diff. peak and hole ) 3 (eIA  202  6.12 C 5 H Y 7 0 3 N 2 6 923.91 Prism, yellow 173(2) 0.7 1073 Monoclinic, /c 1 P2 22.593(3), 9.1237(10), 23.576(2) 90, 101.846(4), 90 4756.2(9), 4 1.290 1.280 1936 0.30 x 0.20 x 0.20 1.82 22.56 -24h24,-9k9,-25 1 24 27337 6210 [R(int) = 0.12391 99.2 Semi-empirical from equivalents 0.774 and 0.6 17 Full-matrix 1 east squares on —  Ri Ri  = =  6210/0/577 0.999 0.0543, wR2 = 0.1022 0.1286, wR2 0.1256 0.548 and -0.3 07  

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