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Niobium phosphine macrocyclic complexes Bowdridge, Michael R. 1998

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NIOBIUM PHOSPHINE MACROCYCLIC COMPLEXES by MICHAEL R. BOWDRIDGE B.Sc. (Hon.), Dalhousie University, 1994 A thesis submitted in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES Department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH C O L U M B I A June 1998 © Michael R. Bowdridge, 1998 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, 1 agree that the Library shall make it freely available for reference and study. 1 further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CMB^S T&Y The University of British Columbia Vancouver, Canada Date 6f1* DE-6 (2/88) A B S T R A C T The chemistry of the macrocycle PhP(CH2SiMe2NSiMe2CH2)2PPh (abbreviated as [P2N2] within this thesis) with niobium(III) is explored. The paramagnetic chloride compound NbCl[P2N2] (1) is used as a starting material for other derivatives, such as {[P2N2]Nb}2(u.-N2) (2) , Nb(CH 2 SiMe 3 )[P 2 N2] (6), and Nb(CH 2 Ph)[P 2 N 2 ] (9). Compound 1 forms adducts with small molecules and solvents, including CO which causes the complex to become diamagnetic. NbCl[P2N2] (1) reacts with KCs under 1 atm of N2 to give {[P2N2]Nbh(u-N2) (2). Complex 2, characterized by X-ray crystallography, is found to have an end-on bound dinitrogen ligand with an N - N bond length of 1.272 (5) A . This is only the fourth niobium dinitrogen species to be structurally characterized. Reaction of 2 with 2 equivalents of Me3N-HCl gives the original chloride 1 and 0.31 equivalents of hydrazine. Nb(CH2SiMe3)[P2N2] (6) and Nb(CFJ.2Ph)[P2N2] (9) are synthesized by reaction of chloride 1 with LiCH.2SiMe3 and KCH.2Ph respectively. Reaction of trimethylsilylmethyl 6 with H2 in benzene results in the formation of a cyclohexadienyl ligand complex, Nb(ri5-Cf5H7)[P2N2] (8). Also, reaction of compound 6 with CO results in the CO insertion and rearrangement with the trimethylsilylmethyl ligand to give an enolate complex. Compound 9 is determined to have an T | 5 bound benzyl ligand. Preliminary investigations in the reaction of compound 1 with LiN(SiMe3)2, Mel , and K C 8 while under Ar give Nb{N(SiMe 3) 2}[P2N 2] (4), Nb(MeI)Cl[P 2N 2] (10), and {[P 2 N 2 ]Nb} 2 (3) respectively. Molecular structure information is given for {[P2N2]Nb}2(|i-N2)(u,-Cl) (5); the first characterized side-on bridged dinitrogen niobium complex. Studies into the elemental determinations of {[P2N2]Nbh(u-N2) (2) and Nb(CH2Ph)[P2N2] (9) reveal limitations in microanalysis due to the formation of stable niobium nitrides and carbides. *H N M R spectroscopy is successfully used for identification of all paramagnetic complexes within this thesis. TABLE OF CONTENTS i i i ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES viii LIST OF FIGURES ix LIST OF ABBREVIATIONS xi ACKNOWLEDGEMENTS xiv DEDICATION xv CHAPTER 1 GENERAL INTRODUCTION 1.1 Niobium Chemistry 1 1.2 Transition Metal Dinitrogen Complexes 3 1.3 Phosphine Donor Ligands 6 1.4 The Scope of this Thesis 10 1.5 References 11 CHAPTER 2 NIOBIUM INORGANIC COMPLEXES 2.1 Previous Work from our Laboratory on [P2N2] Complexes 16 iv 2.2 Paramagnetic N M R Spectroscopy 17 2.3 Synthesis and Characterization of a Niobium Halide Complex 19 2;3.1 Paramagnetic lU N M R Spectral Analysis for NbCl[P2N2] 20 2.3.2 Adduct Formation Reactions 22 2.3.3 Magnetic Susceptibility and Evans' Method Calculations 23 2.4 Synthesis and Characterization of a Niobium Dinitrogen Complex 26 2.4.1 Molecular Structure of {[P2N2]Nb}2(H-N2) 28 2.4.2 Reactions with M e 3 N H C l 30 2.5 Synthesis of Other Niobium Complexes 32 2.5.1 Reductive Elimination under Ar using KCs 32 2.5.2 Synthesis of an Amide Ligand Complex 32 2.5.3 Molecular Structure of a Side Product {[P2N2]Nb h ( u - N 2 , u-Cl) 33 2.6 Summary 36 2.7 References ^ 36 CHAPTER 3 NIOBIUM ORGANOMETALLIC COMPLEXES 3.1 Synthesis arid Characterization of a Paramagnetic Niobium Alkyl 3.1.1 Reaction with H2: Evidence for Nb(r)5-C6H7)[P2N2] 39 41 V 3.1.2 Reaction of NbCH 2SiMe3[P 2N2] with CO: 44 3.2 Synthesis and Characterization of a Diamagnetic Niobium Alkyl 47 3.2.1 Evidence for Nb(Ti5-CH2Ph)[P2N2] 48 3.3 Oxidative Addition using Mel 50 3.4 Summary 52 3.5 References 52 CHAPTER 4 EXPERIMENTAL PROCEDURES 4.1 General Procedures 54 4.2 Reagents and Starting Materials 54 4.3 Analytical Methods 55 4.4 Microanalysis Consideration of Reactive Niobium Complexes 55 4.5 Hydrazine Analysis 56 4.6 A Constant Volume Gas Addition Reaction 57 4.7 Synthesis of New Compounds 58 4.7.1 NbCl[PhP(CH 2SiMe 2NSiMe 2CH2)2PPh], (1) 58 4.7.2 {[P2N2]Nb}2(u-N2),(2) 58 4.7.3 {[P 2N 2]Nb} 2 ,(3) 59 vi 4.7.4 Nb (N(S iMe 3 )2 ) [P2N 2 ] , (4) 59 4.7.5 Nb(CH 2 SiMe3)[P 2 N 2 ], (6) 59 4.7.6 N b ( C H 2 C M e 3 ) [ P 2 N 2 ] , (7) 60 4.7.7 Nb(r|5- C6H7)[P 2N 2], (8) 60 4.7.8 Nb(r|5- CH 2 Ph)[P 2 N 2 ] , (9) 61 4.7.9 NbCl(MeI)[P 2N2], (10) 61 4.8 Adduct Formation of N b C l [P2N2 ] Complexes 62 4.8.1 NbCl(PMe 3 ) [P 2 N2], (11) 62 4.8.2 N b C l ( N C 5 H 5 ) [ P 2 N 2 ] , (12) 62 4.8.3 NbCl(THF)[P 2 N 2 ] , (13) : : 62 4.9 C O Addition Reactions 62 4.9.1 Reaction of NbCl[P 2 N 2 ] with CO 62 4.9.2 Reaction of N b ( C H 2 S i M e 3 ) [ P 2 N 2 ] with CO 63 4.9.3 Reaction of {[P 2N 2]Nb } 2(u-N 2) with CO 63 4.10 Reaction of {[P 2N 2]Nb } 2(u-N 2) with Me 3 N-HCl 63 4.10.1 Reaction of {fl^NdNbhCLt-N^ with 2 Equivalents of M e 3 N - H C l 63 4.10.2 Reaction of { [P2N 2 ]Nb }2 (L i -N2) with 1 Equivalent of M e 3 N - H C l 64 4.11 Unsuccessful Reactions 64 vii 4.11.1 Reaction of NbCl[P 2 N 2 ] with MeLi 64 4.11.2 Reactionof {[P2N2]Nb}2(u.-N2) w i t h H 2 64 4.11.3 Reaction of {[P2N.2]Nb} 2 (u-N 2 ) with C2H4 65 4.11.4 Reaction of {[P2N2]Nb}2(u.-N2) with w-BuSiH 3 65 4.11.5 Reaction of {[P2N 2]Nb} 2(u-N 2) with NbCl[P 2 N 2 ] 65 4.11.6 Reaction of NbCIs with Li2(dioxane)[^yn-P2N2] 65 4.12 References 65 FUTURE PROSPECTS 67 APPENDIX A. 1 X-ray Crystallographic Analysis of {[P 2N 2] Nb} 2(p>N2) '. 69 A.2 X-ray Crystallographic Analysis of {[P 2N 2]Nb } 2 (u-N 2 , U.-C1) 74 A.3 Calibration Data for the Determination of Hydrazine 80 LIST OF TABLES viii Table 2.1 [P2N2] Ligand-Metal Complexes 16 Table 2.2 Variable High Temperature *H N M R Data and Least Squares Regression for NbCl[P 2 N 2 ] (1) 22 Table 2.3 Theoretical Spin-Only Magnetic Moments 25 Table 2.4 Selected Bond Lengths for {[P2N2]Nb}2(Lt-N2) 29 Table 2.5 Selected Bond Angles for {[P 2N 2]Nb }2(H-N2) 30 Table 2.6 Compilation of N - N Bond Lengths for Niobium end-on N2 Complexes 30 Table 2.7 Selected Bond Angles for {[P2N2]Nb}2(LI-N2)(LI-C1) 34 Table 2.8 Selected Bond Lengths for {[P2N2]Nb}2(u-N2)(Li-Cl) 35 Table 3.1 Variable High Temperature ] H N M R Data and Least Squares Regression for Nb(CH2SiMe3)[P2N2] (6) 41 Table 3.2 Microanalysis Results for NbBz[P 2 N 2 ] (9) 48 Table A.1 Atomic Coordinates and B e q 71 Table A.2 Atomic Coordinates and B e q 76 Table A.3 Absorbance Data of Standard Hydrazine Concentrations 80 ix LIST OF FIGURES Figure 1.1 Examples of Niobium Complexes 1 Figure 1.2 Dinitrogen-Transition Metal Binding Modes 4 Figure 1.3 Known Dinuclear Niobium Dinitrogen Compounds 5 Figure 1.4 Li2(dioxane)[5yn-PhP(CH2SiMe2NSiMe2CH2)2PPh] 8 Figure 1.5 Synthesis of Li2(THF)[P 2N 2] 9 Figure 1.6 Synthesis of M L X [ P 2 N 2 ] 10 Figure 2.1 Examples of Zirconium [P2N2] Complexes 17 Figure 2.2 400 MHz lH N M R Spectra of NbCl[P 2 N 2 ] (1) in C 6 D 6 21 Figure 2.3 200 M H z ! H and 81 MHz 31p N M R Spectra of NbCl(CO) x [P 2 N 2 ] in C 6 D 6 23 Figure 2.4 400 M H z lH N M R Spectrum of {[P2N2]Nb}2(Li-N2) (2) in C6D 6 27 Figure 2.5 Ball & Stick II® View of Molecular Structure of {[P 2N 2]Nb}2(u-N 2) (2) 28 Figure 2.6 The Molecular Structure of {[P2N2]Nb h0i-N2) (2) 29 Figure 2.7 Reactions with {[P2N2]Nbh(|i-N2) (2) 31 Figure 2.8 Proposed Mechanism for Reaction of {[P2N2]Nb}2(M--N2) (2) with M e 3 N H C l 31 Figure 2.9 400 MHz *H N M R Spectrum of Nb{N(SiMe3)2}[P2N2] (4) in C 6 D 6 33 Figure 2.10 Ball & Stick II® View of Molecular Structure of {[P2N2]Nb}2(Lt-N2)(Ll-Cl)(5) 34 Figure 2.11 The Molecular Structure of {[P 2N 2]Nb } 2(U-N 2)(LI-C1) (5) 35 Figure 3.1 400 M H z ' H N M R Spectrum of Nb(CH 2 SiMe 3 ) [P 2 N 2 ] (6) in C^D6 40 Figure 3.2 400 M H z l H N M R Spectrum of Nb(C 6 H n ) [P 2 N 2 ] (8) in C 6 D 6 42 Figure 3.3 Proposed Reaction Scheme for H 2 Addition to Nb(CH 2 SiMe3)[P 2 N 2 ] (6) 43 Figure 3.4 300 M H z ' H and 121 MHz 3lp N M R Spectra of Nb(CH 2 SiMe 3 ) [P 2 N 2 ] (6) and Excess CO in C6D6 45 Figure 3.5 300 M H z lU and 121 MHz 3 1 P N M R Spectra of Nb(CH 2 SiMe 3 ) [P 2 N 2 ] (6) and Excess CO in C 6 D 6 after 1 month 46 Figure 3.6 Proposed Mechanism for CO Insertion and Rearrangement into Nb(CH 2 SiMe 3 ) [P 2 N 2 ] (6) 47 Figure 3.7 Bonding Arrangements of M(ri x -CH 2 Ph) 48 Figure 3.8 200 MHz lH N M R Spectrum of Nb(CH 2 Ph)[P 2 N 2 ] (9) in C 6 D 6 49 Figure 3.9 Possible Binding Modes for Nb(CH 2 Ph)[P 2 N 2 ] (9) 50 Figure 3.10 200 M H z *H N M R Spectrum of NbCl(MeI)[P 2N 2] (4) in C 6 D 6 51 Figure 3.11 Conversion between Nb(V) and Nb(ffl) species 51 LIST OF ABBREVIATIONS l H proton 1 H { 3 1P} observe proton while decoupling phosphorus 2p£ or D deuterium 31P{ lH} observe phosphorus while decoupling proton A458 absorbance at 458 nm wavelength of light Anal. analysis atm atmosphere Ball & Stick JJ® molecular modeling program for the Macintosh computer B M Bohr magneton br broad Calcd. calculated Chem 3D® molecular modeling program for the Macintosh computer cm*1 wave number Cp cyclopentadienyl group, [C5H5]" Cp' substituted Gp ligand d doublet dioxane 0 ( C 2 H 4 ) 2 0 D M E 1,2-dimethoxyethane, ( C H 3 0 ) 2 C 2 H 4 d n number of d-electrons d of d doublet of doublets coupling pattern E.I. electron impact eq. equivalent(s) g grams HSAB hard-soft-acid-base theory Hz Hertz, seconds"1 I nuclear spin quantum number IR infrared K degrees Kelvin L neutral two-electron donor ligand M central metal atom, or molar m multiplet M ' + parent ion Me methyl group, -CH3 mg milligram(s) M H z megaHertz rriL milliliter mmol millimole mol mole m-Ph meta-hydrogen in phenyl ring m s spin orientation quantum number N M R nuclear magnetic resonance [P2N2] [PhP(CH2SiMe2NSiMe2CH2)2PPh] o-Ph ortho-hydrogen in phenyl ring Ph phenyl group, -C6H5 P-Ph phenyl group of [P2N2] phoshine p-Ph para-hydrogen in phenyl ring ppm parts per million R alkyl substituent RT room temperature S total spin quantum number s singlet or seconds t triplet THF tetrahydrofuran, C4H8O base width at half height A angstrom ( I O 1 0 m) 5 chemical shift 5dia diamagnetic chemical shift value Spara paramagnetic chemical shift value T | n ligand bound to metal by n atoms Ll-X bridging X-ligand M-eff effective magnetic moment Hs.o. spin-only magnetic moment 71 molecular orbital with 1 nodal plane, or math constant a molecular orbital with no nodal planes ° degrees °C degrees Celsius ACKNOWLEDGEMENTS First and foremost, I would like to thank my supervisor, Professor Mike Fryzuk, for his guidance, encouragement, and patience during my course of study. I would like to particularly thank him for his editing and input on the writing of this thesis. Many thanks go to all the past and present members of the Fryzuk group with whom I was fortunate enough to work. Particular thanks goes to Guy Clentsmith, Danny Leznoff, and Dr. Jason Love; their support and supervision during my studies was invaluable. I would also like to thank Paul Duval, Laleh Jafarpour, Sam Johnson, Garth Giesbrecht, Frederic Naud, and Kirsten Lotte for making my experience in the lab exciting and stimulating. Special thanks to Warrick Sze Chung Y u for his assistance in the hydrazine determinations. I greatly appreciate the help of the U B C Department of Chemistry support staff, in particular Dr. Steve Rettig (X-ray crystallography), Steve Rak (glassblowing), Marshall Lapawa (mass spectrometry), Elizabeth Varty (illustrator), Marietta Austria and Liane Darge (NMR spectroscopy). Special thanks goes to Peter Borda (elemental analysis), whose patience and assistance made possible the understanding of these strange niobium systems. I would also like to thank Jennet Taylor for bringing an anthropological outlook to the editing of this thesis, as well as for her continued support. XV To my father CHAPTER 1 GENERAL INTRODUCTION 1.1 Niobium Chemistry Investigation into the chemistry of the heavier Group 5 transition metal elements, namely niobium and tantalum, has lagged behind that of most other transition metals. Before the 1980's, organometallic research of these two metals resulted in just over 300 publications,1 and within the last twenty years, publications in the field have approximately tripled. However, even with the rapid growth in this area, many of these studies have focused on tantalum leaving niobium as one of the least studied transition metals to date. The first well characterized organometallic niobium complex, Cp2NbBr3, was published in 1954,3 and the first isolated alkyl, NbCl2Me3, was found ten years later.4 Other niobium compounds have been discovered since that time, a few examples of which are shown in Figure 1.1. 5 - 1 0 i (ref. 5) i i (ref. 6) i i i (ref. 7) PMe 3 iv (ref. 8) v (ref. 9) vi (ref. 10) Figure 1.1 Examples of Niobium Complexes References begin on page 11 Chapter 1: General Introduction Like many other transition metals, niobium complexes have incorporated a wide range of ligands. Compounds have been synthesized containing typical ligands such as olefins, 1 1 alkyls, 1 2 hydrides, 1 3 carbonyls, 1 4 bridged and terminal halides, 1 5 and metal-metal multiple bonds. 1 6 Dinitrogen niobium compounds (discussed in section 1 . 2 ) , 1 7 - 1 9 and rj 7 -cycloheptatrienyl complexes have also been characterized. A large number of the systems studied have incorporated one or two cyclopentadienyl ligands, many of which have been 21 compiled into a review of their X-ray determined molecular structures. The reactivity patterns in niobium chemistry have been attributed to the Lewis acidity of high valent niobium, the preference for higher oxidation states, and the tendency to form stable niobium oxides. For a few systems, studies have shown that niobium derivatives can be used as 99 catalysts, such as in olefin metathesis, and also as a stoichiometric reagent for carbon-carbon bond formation reactions of unsaturated organic substrates, an example of which is shown in equation 1.1. N ^ R 9 NbCl3(DME) R 2 - M H M R 1 J + R 3 A R 4 K O H * R ? ~ V * Niobium-oxygen bond energies are typically too strong for a catalytic use of the metal in CO reductions (Fischer-Tropsch chemistry). However, niobium has been useful in modeling and understanding the chemistry behind the conversion of CO + H 2 (synthesis gas) to hydrocarbons, particularly in studies looking at the individual steps and intermediates of the process. 1 4 ' 2 4 More recent work has shown how useful niobium chemistry is in a number of other reactions, including C-C coupling reactions of alkynes with aldehydes, and the conversion of 9S alkynes to alkenes, as shown in equation 1.2. Insertion chemistry of isonitriles into bridged alkylidyne ligands, and insertion of activated alkynes into hydride ligands have been observed, as shown in equation 1.3. References begin on page 11 Chapter 1: General Introduction R 6 THF + NbCI3(DME) . • (THF) 2CI 3NbC: II > II 1.2 C R R H R .H i>R2 (CpSiMe 3) 2Nb<T + R i c = C R 2 • ^ x k I U J > 1.3 L (CpSiMe3)2Nb < ^ - | _ H In addition, niobium compounds have promoted C - N bond cleavage in ligands, as shown in equation 1.4.28 Recent studies have been done on the a agostic interaction of the metal with alkyls. Also, work has been done on the change in magnetic behaviour of niobium, from 30 paramagnetic to diamagnetic upon ligand modification. H 7 0 °C,lhour (s i lox) 3 Nb=v y ? = \ benzene N = < . N=Nb(silox) 3 \ A 1.2 Transition Metal Dinitrogen Complexes For a number of decades, dinitrogen transition metal compounds have been studied in an attempt to understand the process of dinitrogen fixation and transformation into ammonia. ' The long established Haber process, as shown in equation 1.3, converts mixtures of dinitrogen and dihydrogen to ammonia with the use of an iron heterogeneous catalyst, under extreme pressure and temperature. N 2(g) + 3H2(g) F e C a t " > 2NH 3(g) 1.3 >450°C > 270 atm. The harsh conditions used for the industrial manufacture of ammonia are in sharp contrast to those of dinitrogen fixation within nature. It has been revealed that many plants fix dinitrogen References begin on page 11 Chapter 1: General Introduction using nitrogenase,34 an enzyme that contains such metal centers as Fe, Mo, and the more recently discovered V system. It has long been the focus of many studies to be able to develop a synthetic route that can model the conditions of ambient temperature and pressure used within nature. 3 6 ' 3 7 For a long time, lithium was the only metal known to fix dinitrogen, to form lithium nitride under ambient temperature and pressure.3 8 In 1965, [Ru(NH.3)5N2]2 + was the first dinitrogen compound to be discovered. Since that time, many other transition metal complexes have been synthesized that incorporate a dinitrogen unit. Initial complexation involves a-bond formation through the donation of a lone pair of electrons to the metal center; further stabilization of the M - N bond occurs as a result of the metal center back-donating electron density into the dinitrogen 7C* orbital, as shown in Figure 1.2. It is the importance of this synergistic interaction that will lengthen the N - N bond. 4 0 Frequently, this coordination and lengthening of the N - N bond is considered to be a prerequisite for further transformations of the dinitrogen ligand, 3 1 although cases exist that prove contrary to this generalization 4 1 L x M - * - N = N : L x M - * - N = N - » ^ M L x end-on LvM N - N TC* L X M-side-on -ML, 71" Metal to ligand backbonding TC" Figure 1.2: Dinitrogen-Transition Metal Binding Modes References begin on page 11 Chapter 1: General Introduction Free dinitrogen has a bond length of 1.0976 A, while the average N - N bond lengths for mononuclear and binuclear species are typically 1.10-1.16 A and 1.12-1.36 A, respectively. The longest N - N bond reported is in {[N(SiMe2CH2PPh2)2]ZrCl}2(u-N2), with a value of 1.548 A . 4 3 Recently, dinitrogen derivatives have been reported in which the nitrogen-nitrogen bond has been successfully cleaved, 4 4 including a niobium complex that contains the two nitrido anions 2.598 A apart from one another.1^ Other systems have been observed that actually shorten the N - N bond length upon complexation with a metal center,45 but these examples are suspect. As shown in Figure 1.2, a dinitrogen ligand can bind in an end-on approach4^ or as the less common side-on linkage. 4 7 Figure 1.3: Known Dinuclear Niobium Dinitrogen Compounds References begin on page 11 Chapter 1: General Introduction Only three niobium-dinitrogen complexes have been reported in the literature to date, as shown in Figure 1.3. 1 7 - 1 9 The work on the niobium calix[4]arene complex has also resulted in the previously mentioned niobium-nitrido anion interaction, as also shown in Figure 1.3.19 It is very surprising that so little work has been done on niobium dinitrogen systems considering the evidence for nitrogenase containing V , also a Group 5 element. The studies on V(III) in nitrogenase have demonstrated that low oxidation states of two or less may not be needed for N 2 AO reduction. This has shown that the electron deficient early transition metals can have an important role in dinitrogen activation. Protonation of a coordinated dinitrogen ligand with a strong acid results in one or more of the following products: liberated dinitrogen, hydrazine (N2H4),49 and/or ammonia. 5 0 However, the acid hydrolysis of the complex usually involves the complete decomposition of the transition C 1 I T C O metal species. In a few cases, including niobium and tungsten systems, the protonation of the dinitrogen ligand occurs without decomposition of the compound. This has allowed for some insight into the potential reaction pathways for the conversion of N 2 into NH3. Recent studies on {[P2N2]Zr}2(p>N2) have resulted, for the first time, in the protonation of coordinated dinitrogen directly with dihydrogen. 1.3 Phosphine Donor Ligands Phosphine ancillary ligands have been of great importance in the chemistry of many inorganic 5 4 and organometallic complexes.5 5 These phosphorus donors are rarely involved in the actual transformation of the complex but rather are used to manipulate the steric and electronic properties of the system. Many chelating multi-phosphine ligands have also been used to stabilize reactive transition and main group metal centers over a wide range of oxidation states. An even greater flexibility is achieved when chirality in the backbone of a chelating phosphine is introduced, allowing for the possibility of enantioselective reaction pathways.5 6 References begin on page 11 Chapter 1: General Introduction The diversity in phosphine ligands has made it possible to tailor a system in order to alter the steric and electronic contributions of that complex. The steric bulk of a phosphine is usually measured in terms of the cone angle, and can vary from such angles as 87° for PH3 to 182° for P(tJ3u) 3. 5 7 The cone angle is defined as the angle of a cylindrical cone where the tip is 2.28 A from the phosphorus center and the sides of the cone just touch the van der Waals radii of the outermost atoms of the phosphine substituents. In addition to the effects that sterics have on a system, the phosphorus substituents can be modified in order to alter the electronic properties of the ligand. This can range from such classic cr-donors as P M e 3 to 7i-acceptors like P(OMe 3 ) 3 . In addition to the chemical importance that phosphine ligands have on systems, the phosphorus-31 nuclei (S = 1/2, 100% natural abundance) can be important for the characterization of a complex. 5 9 The wide range of chemical shift resonances in 3 1 P {lH) N M R experiments can provide identification of a particular compound, and indicate multiple products in a reaction when l H N M R spectra are too complex for such determination. In addition, 3 1 P {lH} N M R spectroscopy can provide coupling information with other N M R active nuclei, such as 1 9 5 Pt , as well as potential phosphorus-phosphorus coupling. The hard-soft-acid-base (HSAB) theory 6 0 relates the hardness or softness of an atom to the degree of polarizability of the atom's electron cloud density. Soft ligands have donor atoms that are either from higher than the first row in the Periodic Table (I", PPh 3), or have multiple bonds (C2H4), unlike saturated hard ligands, such as N H 3 and F~. Due to an excess of electron density, soft metals are typically in low oxidation states, whereas higher oxidation states are common for the hard metals. Almost all transition metals can exhibit soft metal character if sufficiently reduced to a low valence state. A hard ligand base will preferentially bind to a hard early transition metal acid, and a soft ligand base to a soft late transition metal acid. Because of this, phosphine ligands have been used more with the late transition metals due to similarities in soft acid-base properties. This is not to say that phosphine ligands wil l not bind to early References begin on page 11 Chapter 1: General Introduction transition metals, as there are many such examples, but the preference of these metal systems to bind to hard ligands makes such phosphine linkages susceptible to displacement. In order to avoid displacement of the phosphine donors from early transition metal compounds, a hybrid hard/soft ligand was designed, as shown in Figure 1.4.61 Previous work on a similar non-cyclic hybrid ligand demonstrated that the phosphines may not bind to metals due to the allowed flexibility in the ligand backbone. The principle behind a macrocyclic ligand design lies in the fact that the amido ligands will form strong bonds with the early transition metals and, by way of the metal bound within the macrocycle, the phosphines would then also be forced to bind. This binding is enhanced by the fact that the two phosphine linkages are within a macrocycle with trans disposed amido groups. Electron deficient early transition metals would bind to the phosphines in order to obtain an increase in electron density around the metal center. In addition, further modification to the substituents on the phosphine wi l l allow for the manipulation of the reactivity at the complex's metal centers, which could not be provided by such hard donors as the amido groups. Figure 1.4: Li2(dioxane)[5yn-PhP(CH2SiMe2NSiMe2CH2)2PPh] The metal template synthesis of this ligand system is shown in Figure 1.5.61 The choice of backbone linkages results from starting materials that are commercially available. Reaction of l,3-bis(chloromethyl)-l,l,3,3-tetramethyldisilazane with 2 equivalents of LiPHPh displaces the chlorides to yield diphosphinodisilazane, HN(SiMe2CH2PHPh)2. The slow addition of BuLi (4 Me 2 .SL Me 2 SL Me 2 Me 2 References begin on page 11 Chapter 1: General Introduction equivalents) to a mixture of this diphosphine and the starting dichlorodisilazane forms the dihthio salt of the macrocycle PhP(CH2SiMe2NSiMe2CH2)2PPh (abbreviated as [P2N2] within this thesis). As shown in Figure 1.5, a 3:1 mixture of the syn and cmft'-[P2N2] dilithio salt is formed when the reaction is done in THF (combined yield of 90%) while only the syn isomer (as the dioxane adduct) is obtained when done in diethyl ether (80% yield). Cl M e 2 M e 2 S k . . ^ S L 1ST I H Cl 2 LiPHPh T H F 0°C P h - P M e 2 M e 2 N I H P—Ph ! H Cl Cl Si M e 2 Ph Si M e 2 M e 2 ,Si 4 BuLi T H F 0°C M e 2 S L Si Me Si Me, Ph S = T H F PIT Si M e 2 Si M e 2 syn-Li 2(THF)[P 2N 2] anf/-Li 2(THF) 2[P 2N 2] •Ph Figure 1.5: Synthesis of Li2(THF)fF>2N2] This ligand starting material has the ability to act as an eight-electron donor to many transition metals by the simple metathesis reaction with a metal dihalide as shown below in Figure 1.6. References begin on page 11 Chapter 1: General Introduction Figure 1.6: Synthesis of ML X[P2N2] 1.4 The Scope of this Thesis The focus of this thesis is to examine the incorporation of the [P2N2] macrocycle onto the Group 5 metal niobium and examine the syntheses and characterization of alkyl and dinitrogen complexes. Research into niobium was initiated because of the success of zirconium with [P2N2], and the interest in observing how changing the metal center to one group over in the periodic table (Group 4 to Group 5) will affect the chemistry of these systems. The work presented in Chapter 2 centers around the inorganic metathesis reactions with a niobium chloride macrocyclic compound. The syntheses and characterization of these derivatives are presented, as well as the molecular structures of new niobium dinitrogen systems. Further investigation into organometallic niobium alkyl systems has been explored, and is discussed in Chapter 3. Much of the syntheses and characterization of these alkyls demonstrate the high reactivity of these compounds. Reactions with small molecules, such as H2 and CO, have been explored, as well as initial investigations into the possible binding modes of certain alkyl ligands. Although further investigation is required on the magnetics of these new systems, preliminary work has shown the feasibility of using N M R spectroscopy for the characterization of paramagnetic niobium complexes. References begin on page 11 Chapter 1: General Introduction References (1) Labinger, J. A . Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, G. A . and Abel, W. E., Ed.; Pergamon, 1982; Vol . 3, p 705. (2) Wigley, D. E.; Gray, S. D. Comprehensive Organometallic Chemistry II; Wilkinson, G. and Stone, G. A. , Ed.; Pergamon, 1995; Vol . 5, p 57. (3) Wilkinson, G.; Birmingham, J. M . J. Am. Chem. Soc. 1954, 76, 4281. (4) Juvinall, G. L . J. Am. Chem. Soc. 1964, 86, 4202. (5) Green, M . L. H. ; Hughes, A. K. ; Mountford, P. J. Chem. Soc, Dalton Trans. 1991, 1407. (6) DeCastro, I.; DeLaMata, J.; Gomez, M . ; Gomez-Sal, P.; Royo, P.; Selas, J. M . Polyhedron 1992, 77,1023. (7) Arnold, J.; Tilley, T. D.; Rheingold, A. L . ; Geib, S. J. Organometallics 1987, 6, 473. (8) Hitchcock, P. B.; Lappert, M . F.; Milne, C. R. C. J. Chem. Soc, Dalton Trans. 1981,180. (9) Green, M . H. ; Mountford, P.; Scott, P.; Mtetwa, V . S. Polyhedron 1991,10, 389. (10) Luethenes, M . L. ; Elcesser, W. L. ; Huffman, J. C.; Sattelberger, A . P. Inorg. Chem. 1984, 23, 1718. (11) Klazinga, A . H.; Teuben, J. H. J. Organomet. Chem. 1980,194, 309. (12) Belmonte, P. A . ; Cloke, F. G. N . ; Theopold, K. H. ; Schrock, R. R. Inorg. Chem. 1984,23,2365. References begin on page 11 Chapter 1: General Introduction 12 (13) Chiu, K. W.; Jones, R. A. ; Wilkinson, G. W.; Galas, A . M . ; Harsthouse, M . B. J. Chem. Soc, Dalton Trans. 1981, 1892. (14) Fu, P. F.; Rahman, A. K. F.; Nicholas, K. M . Organometallics 1994,13, 418. (15) Canich, J. A . M . ; Cotton, F. A . Inorg. Chem. 1987, 26, 4236. (16) Cotton, F. A . ; Matonic, J. H. ; Murillo, C. A. J. Am. Chem. Soc. 1997,119, 7889. (17) Dilworth, J. R.; Henderson, R. A. ; Hills, A. ; Hughes, D. L. ; Macdonald, C ; Stephens, A . N . ; Walton, D. R. M . J. Chem. Soc, Dalton Trans. 1990, 1077. (18) Berno, P.; Gambarotto, S. Organometallics 1995,14, 2159. (19) Zanotti-Gerosa, A . ; Solari, E.; Giannini, L . ; Floriani, C ; Chiese-Villa, A. ; Rizzoli, C. J. Am. Chem. Soc. 1998,120, 437. (20) Green, M . L . H. ; Mountford, P.; Mtetwa, V . S.; Scott, P.; Simpson, S. J. J. Chem. Soc, Chem. Commun. 1992, 314. (21) Holloway, C. E.; Melnik, M . J. Organomet. Chem. 1986, 303, 1. (22) Rocklage, S . M . ; Fellmann, J. D.; Rupprecht, G. A . ; Messerle, L . W.; Schrock, R. R. J. Am. Chem. Soc. 1981,103, 1440. (23) Roskamp, E. J.; Pedersen, S. F. J. Am. Chem. Soc. 1987,109, 6551. (24) Labinger, J. A . ; Wong, K. S. ACS Sym. Ser. 1981,152, 253. (25) Hartung, J. B. ; Pedersen, S. F. J. Am. Chem. Soc 1989, 111, 5468. (26) Riley, P. N . ; Profilet, R. D.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1996, 75, 5502. References begin on page 11 Chapter 1: General Introduction 13 (27) Antinolo, A . ; Hermosilla, F. C ; Fajardo, M . ; Yuste, S. G.; Lanfranchi, M . ; Otero, A. ; Pellinghelli, M . A. ; Prashar, S.; Villasenor, E. Organometallics 1996,15, 5507. (28) Kleckley, T. S.; Bennett, J. L . ; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem. Soc. 1997, 779,247. (29) Etienne, M . ; Biasotto, F.; Mathieu, R.; Templeton, J. L . Organometallics 1996, 75,1106. (30) Fettinger, J. C.; Keogh, D. W.; Kraatz, H . B. ; Poli, R. Organometallics 1996,15, 5489. (31) Gambarotta, S. J. Organomet. Chem. 1995, 500, 117. (32) Leigh, G. J. Science 1998, 279, 506. (33) Jennings, J. R. Catalytic Ammonia Synthesis: Fundamentals and Practices; Plenum Press, 1991; Vol . 1. (34) Sprent, J. I.; Sprent, P. Nitrogen Fixing Organisms; Chapman and Hall, 1990. (35) Robson, R. L. ; Eady, R. R.; Richardson, T. H. ; Miller, R. W.; Hawkins, M . ; Postgate, J. R. Nature 1986, 322, 388. (36) Leigh, G. L . Science 1995, 268, 827. (37) Sholov, A. E. Metal Complexes in Biomimetic Chemical Reactions; C R C Press, 1997, pCh . 1. (38) Wilkinson, G.; Cotton, F. A. Advanced Inorganic Chemistry; 5 ed.; John Wiley & Sons, 1988, p 126. References begin on page 11 Chapter 1: General Introduction (39) Allen, A . D.; Senoff, C. V . J. Chem. Soc, Chem. Commun. 1965, 621. (40) Hidai, M . ; Mizobe, Y . Chem. Rev. 1995, 95, 1115. (41) Leigh, G. J. Acc. Chem. Res. 1992, 25, 177. (42) Sutton, L . E. Tables of Interatomic and Configurations in Molecules and Ions; Chemical Society Special Publications No. l 1, Chemical Society, 1958. (43) Frzyuk, M . D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990,112, 8185. (44) Laplaza, C. E.; Cummins, C. C. Science 1995, 268, 861. (45) Evans, W. J.; Ulibarri, T. A. ; Ziller, J. W. J. Am. Chem. Soc 1988,110, 6877. (46) Lazarowych, N . J.; Morris, R. H. ; Ressner, J. M . Inorg. Chem. 1986, 25, 3926. (47) Gyname, M . J.; Jeffery, J.; Lappert, M . F. J. Chem. Soc, Chem. Commun. 1978, 34. (48) Arber, J. M . ; Dobson, B. R.; Eady, R. R.; Stevens, P.; Hasmain, S. S.; Garmer, C. D.; Smith, B. E. Nature 1987, 325, 372. (49) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952,24, 2006. (50) Bolleter, W. T.; Bushman, C. J.; Tidwell, P. W. Anal. Chem. 1961, 33, 592. (51) (a) Chow, P.C. M.Sc. Thesis, University of British Columbia, 1993. (b) Haddad, T.S. Ph.D. Thesis, University of British Columbia, 1990. (52) Nishibayashi, Y . ; Iwai, S.; Hidai, M . Science 1998,279, 540. (53) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J.; Young, V . G. Science 1997,275, 1445. References begin on page 11 Chapter 1: General Introduction 15 (54) McAuliffe, C. A . Comprehensive Coordination Chemistry; Wilkinson, G., Gillard, R. D. and McCleverty, J. A. , Ed.; Pergamon Press, 1987; Vol . 2, p 989. (55) Collman, J. P.; Hegedus, L . S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books, 1987. (56) Knowles, W. S. Acc. Chem, Res. 1983,16, 106. (57) Tolman, C. A. Chem. Rev. 1977, 77, 313. (58) Strohmeier, W.; Muller, F. J. Chem. Ber. 1967,100, 2812. (59) Crabtree, R. H . The Organometallic Chemistry of the Transition Metals; 2nd ed.; John Wiley & Sons, 1994, p 243. (60) Pearson, R. G. J. Chem.. Educ. 1968, 45, 581. (61) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J. Chem. Commum. 1996, 2783. (62) Fryzuk, M . D.; MacNeil, P. A. ; Rettig, S. J.; Secco, A. S.; Trotter, J. Organometallics 1982, i , 918. References begin on page 11 16 CHAPTER 2 NIOBIUM INORGANIC COMPLEXES 2.1 Previous work from our Laboratory on [P2N2] Complexes By incorporating both amido and phosphine donors, the [P2N2] ligand 1 has been used in the preparation of many transition metal, rare earth, and main group element complexes. This diversity is shown in the following table: Table 2.1: [P2N2] Ligand-Metal Complexes M [ P 2 N 2 ] MC1[P 2 N 2 ] M C l 2 [ P 2 N 2 l MC1 3[P2N 2] {[P 2 N 2 ]M} 2 (Ll-Cl)2 L i 2 Mo Zr Ta (in situ) Y Co A l Ti Lu Cr Ga Yb Ni In Sc Zn V From these starting compounds many other [P2N2] metal complexes and reactions have been explored and continue to be investigated. The scope of work done in this field has been too vast to allow for a complete overview within this thesis. However, of particular interest for the niobium research presented here are some related studies of zirconium complexes that incorporate the [P2N2] macrocycle. Figure 2.1 outlines some relevant Zr[P2N2] chemistry. References begin on page 36 Chapter 2: Niobium Inorganic Complexes [P 2N 2]Zr Figure 2.1: Examples of Zirconium [P2N2] Complexes The dinuclear zirconium side-on bridged dinitrogen compound, {[P2N2]Zr}2(p>N2), has an N - N bond length of 1.43 A . Remarkably, it reacts with dihydrogen to form the complex {[P2N2]Zr}2(u,-N2H)(p>H); this is the first example where the coordinated N 2 unit undgergoes a transformation upon the addition of H2.3 The zirconium dibenzyl and trimethylsilylmethyl products were determined to have structures with r j^alkyl ligands.4 The reduction of the zirconium dichloride under argon produces a dinuclear complex that is bridged through the n interaction of the phosphorus phenyl rings on the [P2N2] ligand. The reactivities of the [P2N2] niobium compounds presented in this thesis are frequently similar. However, in some cases, reactions done with these complexes have undergone different reaction chemistry from their zirconium analogues. 2.2 Paramagnetic NMR Spectroscopy N M R spectroscopy has become a vital tool in the structural analysis and identification of many diamagnetic transition metal complexes.5 Unlike these diamagnetic compounds, N M R signals from nuclei attached to paramagnetic metal centers are often not observable. However, References begin on page 36 Chapter 2: Niobium Inorganic Complexes occasionally in N M R spectroscopy some resonances can be observed for these complexes. Although these resultant signals are broadened and greatly shifted from their diamagnetic values, it is possible to obtain a significant amount of information from the spectra. The broadening of a signal is related to the relaxation rate of the nucleus of interest. Equation 2.1 shows the relationship between the excited state lifetime of the nucleus, x, and the uncertainty in the energy transition, AE. From this equation it can be shown that when a nucleus is relaxed quickly it leads to a greater uncertainty in the energy transition, or in other words, the signal is observed over a broader field. This relaxation of the nucleus due to a paramagnetic metal center is referred to as spin-lattice relaxation and is the result of unpaired electron-nuclear dipole and through-bond coupling interactions.6 Sometimes 2 H N M R studies are done on paramagnetic 2 H labeled complexes due to the longer intrinsic relaxation time of the deuterium atom over that of the proton. x A E = = 2 ^ 2.1 The shifting of an N M R signal from its typical diamagnetic position is assumed to be the result of two effects: the contact (Fermi) shift and the pseudo-contact shift. Fermi shifts are based on through bond interactions of the nucleus with a paramagnetic center. The change in shift is due to the derealization of the unpaired electron onto the nucleus being studied, resulting in a change in the shielding of that nucleus. These Fermi shifts can be a result of direct derealization or indirect (spin-polarization) derealization. Pseudo-contact shifts are based on a through space interaction in which the magnetic field of the unpaired electron alters the local field around the nucleus being studied. Even with the broad and shifted signals that can result from a paramagnetic complex, a significant amount of information can still be obtained from these spectra. With the paramagnetic compounds discussed in this thesis, all of the lH N M R spectral resonances observed were assigned to particular protons on the complex. However, in all cases, any References begin on page 36 Chapter 2: Niobium Inorganic Complexes information about the coupling between the nuclei was lost due to the resultant broadening. Assignment of the resonances was possible because of the validity of integration for these complexes; in addition, the degree of shifting and broadness of the particular resonance is an indication of the proximity of a proton to the paramagnetic metal center. It is also possible to obtain information about a paramagnetic compound by studying variable temperature N M R experiments. The Curie law states that magnetic susceptibility is inversely proportional to temperature.8 Accordingly, as one increases the temperature, the *H N M R signals should sharpen and shift towards their theoretical diamagnetic values as a result of the decreased influence by the paramagnetic metal center. Thus, a plot of 5 vs. 1/T will give a straight line with a y intercept that corresponds to the theoretical diamagnetic value, 8dia, of a particular resonance. 2.3 Synthesis and Characterization of a Niobium Halide Complex The synthesis of NbCl[P2N2] (1) was accomplished by the reaction of the D M E adduct of niobium(III) trichloride with one equivalent of Li2(dioxane)[.syn-P2N2] in toluene. NbCl[P2N2] was isolated as a paramagnetic red solid in good yield as shown below in equation 2.2. Me Me Me Me \1 \ l toluene RT, 2 days Me Me Me Me M V 2.2 S = dioxane P h — P * • Nb P — Ph Me Me A Me Me 1 References begin on page 36 Chapter 2: Niobium Inorganic Complexes Compound 1 was characterized by *H N M R spectroscopy, E.I. mass spectrometry, magnetic susceptibility measurements, infrared spectroscopy, and microanalysis. Numerous attempts at an X-ray structure determination failed as a result of crystals that were not of good enough quality due to the tendency of the compound forming twinned samples. The C, H , N determinations for 1 were problematic and demonstrated the high reactivity of the new low valent complexes described within this thesis. Initial microanalysis consistently gave incorrect results, but large fluctuations in trial results from the same sample ruled out the possibility of impurities being the problem. A chloride determination was done that was in agreement with the theoretical value. Because of the correct analysis for chloride, changes in the experimental microanalysis procedure were systematically adjusted. From this point it is was possible to determine that the problem occurring was due to the routine additives (such as CuO, NiO, and WO3) that are used on microanalysis samples to ensure complete oxidation. These additives decomposed 1 too quickly preventing accurate readings; however, once the addition of these was excluded, consistent C, H , N determinations were found. 2.3.1 Paramagnetic ! H N M R Spectral Analysis for NbCl[P2N2] As shown in Figure 2.2, even though the niobium chloride complex (1) is paramagnetic, a *H N M R spectrum can be obtained that allows for the characterization of all the proton signals for the compound. No 3 1 P N M R signals were observed, which was not surprising since the phosphines are directly bound to the paramagnetic metal center resulting in a large degree of peak broadening. The results of variable high-temperature N M R spectroscopy for chloride 1 are shown in Table 2.2. The value for 8jia was determined by using a linear least squares fit on the plot of 8 vs. 1/T. These results are also shown in Table 2.2. However, especially for the C H 2 protons on the [P2N2] backbone (with their low field 8^3), reasonable results were not obtained. The theoretical 8<iia values, which in many cases are not within the expected range for a typical proton resonance,9 indicate the presence of a contribution from a temperature independent paramagnetism within the system. In the literature, this independence has been attributed to the References begin on page 36 Chapter 2: Niobium Inorganic Complexes References begin on page 36 Chapter 2: Niobium Inorganic Complexes effects of orbital angular momentum and spin-orbit coupling from the metal center.1 0 Such a consideration is reasonable for second row transition metals where these factors become more important than in the first row metals, and also agrees with the p:eff value as discussed in section 2.3.3. Table 2.2: Variable High Temperature lH N M R Data and Least Squares Regression for NbCl[P 2 N 2 ] (1) 8 at 25 °C 8 a t 4 0 ° C 8 at 60 °C Sdia r2 (ppm, win) (ppm, wi/2) (ppm, wi/ 2 ) (ppm) SiMeMe' 4.8 (0.2) 4.6 (0.2) 4.4 (0.2) 1.0 0.996 SiMeMe' 11.2 (0.5) 10.8 (0.3) 10.4 (0.3) 3.3 0.996 o-Ph 11.9 (br) 11.8 (0.7) 11.7 (0.5) 9.9 0.943 m-Ph 10.2 (0.1) 10.1 (0.1) 10.0 (0.1) 8.5 0.994 p-Ph 8.7 (0.1) 8.7 (0.1) 8.6 (0.1) 7.6 0.998 CHH' 39.6 (2.1) 39.1 (1.9) 38.2 (1.6) 25.5 0.995 CHH' 56.2 (3.1) 55.0 (2.2) 53.0 (1.8) 25.9 0.989 2.3.2 Adduct Formation Reactions It was observed that the electron-deficient five-coordinate niobium chloride complex (1) readily forms adduct complexes with neutral small molecules and solvents. Experiments were done where halide compound 1 was placed under an atmosphere of a small molecule (CO, PMe3), or placed in a coordinating solvent (pyridine, THF). In doing so, it was possible to stabilize the high reactivity and prevent decomposition of this complex to some degree. In addition, adduct complexes using PMe3, pyridine, and THF give different lH N M R chemical shifts for the protons of [P 2 N 2 ] allowing the possibility of analysis of otherwise overlapping peaks due to their broadness. When CO is added to complex 1 the resulting *H N M R spectrum References begin on page 36 Chapter 2: Niobium Inorganic Complexes reveals the new complex to be diamagnetic. The *H spectrum shows an oversimplified pattern and a 3 1 P N M R signal can now be detected for the complex as shown in Figure 2.3. The 3 1 P peak is broadened due to the coupling and relaxation of the quadrupolar nucleus of 9 3 N b (I = 9/2, 100 % abundance).10 Also, it is possible to remove the CO from the complex under vacuum. This allows for the temporary stabilization and further characterization (such as 3 1 P N M R spectroscopy) of halide 1. These initial adduct studies could be applied to other more reactive niobium complexes to better allow characterization, and to possibly improve crystallization of the products. It might also be possible to convert other paramagnetic niobium compounds to diamagnetic adducts with the use of a strong field ligand such as CO. I I I I I I I I ; 1 1 I I | 1 I 1 I | T I I I I i I I I | I I M | I I i | i i i i | I i i i I l I i » | l 1 I 40 20 6 -20 1 0 0 Figure 2.3: 200 M H z lU and 81 MHz 3 1 P N M R Spectra of NbCl(CO) x[P2N 2] in C 6 D 6 2.3.3 Magnetic Susceptibility and Evans' Method Calculations The motion of charged particles in a system causes magnetism to occur; the intrinsic spin and orbital motions of an electron can contribute to paramagnetism in metal complexes, and References begin on page 36 Chapter 2: Niobium Inorganic Complexes diamagnetism is due to the field induced circulation of paired electrons (and is present in any system). 1 1 The magnetic induction, B, of a sample is related to the magnitude of the induced external magnetic field, H , and the magnetization of the sample, M , as shown in equation 2 .3 . B = H + 4 T C M 2.3 The magnetization of the sample, M , is due to the magnetic dipoles of a complex aligning with the external magnetic field. Instead of measuring the magnetic induction, B , of a sample, the magnetic susceptibility (per unit volume), %v> is normally determined as shown in equation 2.4. The magnetic susceptibility can also be expressed in terms of mass, %g, or molar mass, Xm» by using the conversion factors of density and molecular weight respectively. Xv is normally a small negative value for diamagnetic complexes and a large positive value for paramagnetic ones. _ M * v - H 2.4 Due to the Zeeman splitting effect, the magnetization of a sample can only be observed in 1 9 an applied external magnetic field. This is a result of an unpaired electron, with S = 1/2, having two quantum levels, m s = +1/2 and m s = -1 /2 , that only lose their degeneracy under the influence of an external magnetic field. By considering the energy difference between quantum levels and the Boltzmann distribution for the thermal populations of these levels, equation 2.4 can be rewritten as shown in equation 2.5. Xm = 3 k T S(S+1) 2.5 In the above equation, N A is Avogadro's number, g is a proportionality constant (approximately 2.0 for one unpaired electron with no orbital angular momentum), (5 is the Bohr magneton of an electron, and k is the Boltzmann constant. From this, the effective magnetic moment, ixeff, is determined as shown in equation 2.6. References begin on page 36 Chapter 2: Niobium Inorganic Complexes Assuming no orbital contribution takes place, (j.eff can be related to the spin-only magnetic moment, pLs.o.> shown in equation 2.7, where n is the number of unpaired electrons (examples of which are given in Table 2.3). Hs.o. = g[ S (S+l) ] 1/2 = [ n (n+2) ] ^  2.7 Table 2.3: Theoretical Spin-Only Magnetic Moments number of unpaired electrons S Hs.o. (BM) 1 1/2 1.72 2 1 2.83 3 3/2 3.87 4 2 4.90 5 5/2 5.92 Experimentally, magnetic susceptibility can be determined in solution by using Evans' method.1 3 It has been observed that a paramagnetic complex, through pseudo-contact shifting, will alter the chemical resonances of diamagnetic compounds contained in the same solution. A small amount of a paramagnetic sample (typically 10 to 15 mg in 0.5 mL of solvent) is placed in an N M R tube with a known standard (in these experiments ferrocene was used). A sealed sample of the reference standard is then also placed in the N M R tube. % g for a sample is determined by the following equation: 3At) %g = 2.8 47ro0m References begin on page 36 Chapter 2: Niobium Inorganic Complexes where A D is the absolute Hertz difference between the reference standards, x>0 is the N M R spectrometer frequency in Hertz, and m is the mass of paramagnetic sample in 1 mL of solvent. From equation 2.8, the p:eff for the NhCl[P2N2] complex (1) was found to be 2.7 B M . This corresponds to the value for two unpaired electrons, p:s.o. of 2.83 B M , which has been lowered by a contribution from the orbital angular momentum for a d 2 system. 1 0 2.4 Synthesis and Characterization of a Niobium Dinitrogen Complex The synthesis of {[P2N2]Nb)2(H-N2) (2) was accomplished by the reaction of NbCl[P2N2] with 1.2 eq. of KC% in toluene under 1 atm of dinitrogen, as shown in equation 2.9. The reaction is slow and undergoes completion after a few days, probably due to the insolubility of KC8. The resultant compound is isolated in moderate yield as a paramagnetic brown solid, with low solubility in toluene. toluene, 3 days NbCl[P 2 N 2 ] + 1.2 eq. K C 8 • {[P 2N 2]Nb} 2(p: -N 2 ) 2.9 RT, 1 atm N 2 2 The synthesis of 2 represents only the fourth known niobium dinitrogen compound. 1 4" 1 6 This dinuclear dinitrogen complex was characterized by A H N M R spectroscopy, E.I. mass spectrometry, magnetic susceptibility measurements, microanalysis, and X-ray crystallography. The microanalysis determination was successful for carbon and hydrogen but not nitrogen. However, the stable formation of a niobium nitride complex can be considered to be the end result of the oxidation of the sample's bridging dinitrogen during microanalysis; this allows the theoretical value for the percent nitrogen to match that of the experimental. Stable metal nitrides 17 have been observed for other dinitrogen bridged dimers. Figure 2.4 shows the paramagnetic l H N M R spectrum of dinitrogen complex 2. Evans' method,1 3 used for the determination of magnetic susceptibility, gave a | i e f f value of 2.3 B M , which corresponds to the value for two unpaired electrons (p:s.0. of 2.83 BM) which was lowered by a large contribution from the orbital angular momentum.1 0 This would be in agreement with References begin on page 36 Chapter 2: Niobium Inorganic Complexes equation 2.9 that yields Nb(II) from the reduction of Nb(III), if one considers the two niobium atoms to be in a low spin d 3 configuration. With the potential for ^-conjugation between the metal centers through the dinitrogen unit, it is reasonable to assume that the unpaired electron on each niobium should pair up with each other, causing the structure to become diamagnetic. However, as reported in the literature for other bridged dinitrogen species, it is possible not to 18 have a pairing due to the orbital isolation of the electrons on each metals center. As will be discussed in section 2.4.1, the molecular structure of 2 has bond lengths for the dinitrogen bridge that indicate a Nb(IV) complex with the bridging dinitrogen acting as a N 2 4 " unit. This would give a d 1 system in which the unpaired electrons on the niobium centers still do not pair up. I . SiAfeMe' SiCHtf' I — 1 • 1 i 1 1 1 • i 1 • • • I 1 1 1 1 i • 1 ' i — 1 • i ' • ' • : • ' • 1 : - ' i — i — ' • • • S . t » . 4 7 . 9 ft s « . « s . « , r , . » a.t S . ' i i.t i.i 2.f 1 . S 1 « -•> i . i ••' TVM Figure 2.4: 400 MHz *H N M R Spectrum of {[P2N2]Nb}2(p>N2), 2, in C 6 D 6 (* denotes solvent) References begin on page 36 Chapter 2: Niobium Inorganic Complexes When a solution of {[P2N2]Nb>2(><-N2) (2) is exposed to air, an immediate intense purple-red solution is formed. Within a minute, this solution then forms a light yellow solution, indicating the complete decomposition of the complex. Although this purple-red intermediate has not yet been isolated, it is believed to be the result of a reaction with oxygen rather than water moisture because of its rapid formation. Whether the oxygen has displaced the bridging dinitrogen unit or whether the complex has incorporated both has yet to be investigated. 2.4.1 Molecular Structure of {[P2N2]Nb}2(/**-N2) The molecular structure, determined by X-ray diffraction, of {[P2N2]Nb}2(/<-N2) (2) is shown in Figure 2.5 and 2.6. Selected bond lengths and bond angles are given in Tables 2.4 and 2.5. The coordination geometry of the niobium center is a distorted trigonal bipyramid. The two niobium centers are joined by a near-linear end-on bridging N2 unit. Comparisons of Nb-N and N - N bonds to that of the other three niobium dinitrogen complexes are shown in Table 2.6. Figure 2.5: Ball & Stick II® View of Molecular Structure of {[P 2N 2]Nb}2(^-N2) (2) References begin on page 36 Chapter 2: Niobium Inorganic Complexes Figure 2.6: The Molecular Structure of {[P2N2]Nb}2(p>N2) (2) Table 2.4: Selected Bond Lengths for {[P 2 N 2 ]Nb h(p>N2) Bond Length (A) Bond Length (A) N M - N 5 1.853 (4) N5-N6 1.272 (5) N b l - P l 2.5729 (14) N b l - N l 2.171 (4) NM-P2 2.5799 (14) Nbl-N2 2.157 (4) References begin on page 36 Chapter 2: Niobium Inorganic Complexes Table 2.5: Selected Bond Angles for {[P 2N 2]Nb }2(u.-N2) Bonds Angle (deg) Bonds Angle (deg) P1-NM-P2 161.07 (5) NM-N5-N6 179.5 (3) N1-NM-N2 116.1 (2) N1-NM-N5 123.8 (2) P1-NM-N5 99.22 (12) N2-NM-N5 120.1 (2) P2-Nbl-N5 99.70 (12) Table 2.6: Compilation of N - N Bond Lengths for Niobium end-on N 2 Complexes Complex Bond Length (A) Ref. {[P 2N 2]Nb} 2(Li-N 2) 1.272 (5) this thesis [ {(p-But-calixarene)]^} 2(p>N 2)] 2- 1.390(17) 14 [(Cy 2 N) 3 Nb] 2 (Li-N 2 ) 1.34(1) 15 {(S 2 CNEt 2 ) 3 Nb} 2 (u-N 2 ) 1.25 (2) 16 2.4.2 Reactions with M e 3 N H C l Most reactions attempted with the niobium dinitrogen complex (2) were unsuccessful in causing a chemical change in the complex as summarized below in Figure 2.7. However, when the dinitrogen compound 2 reacted with 2 eq. of M e 3 N H C l the result was the reformation of the starting niobium chloride complex (1). When more than 2 eq. of M e 3 N - H C l were added to complex 2 then l H N M R signals relating to diamagnetic phenyl phosphorus compounds were observed. These signals were caused by the decomposition of the [P 2 N 2 ] macrocycle, because the 3 1 P N M R spectrum showed signals that were not bound to Nb (no quadrupolar broadening) and were not that of free ligand ( H 2 [ P 2 N 2 ] ) . 1 9 Since exactly 2 eq. of M e 3 N H C l did not result in ligand decomposition the question remains of where the protons from the reagent went. The References begin on page 36 Chapter 2: Niobium Inorganic Complexes proposed reaction is summarized in Figure 2.8. A reasonable possibility exists that, since the attacking H C 1 molecule first binds to the niobium dinitrogen dimer, the preferred site of protonation is the lengthened N 2 bond. The resulting H N N H molecule is known to be unstable, and to form half an equivalent of N 2 and N 2 H 4 (hydrazine). The proposed reaction was supported by the successful detection of hydrazine, of which a 62% yield was found. However, the mechanism for the reduction of Nb(IV) to Nb(UI) is still undetermined. NbCl[P 2 N 2 ] 7\ U ^ s i ^ s i 1 Figure 2.7: Reactions with {[P2N2]Nb}2(|i-N2) (2) Nb[P2N2] N N 1 eq. Me,N-HCl —- >• Nb[P2N2] [P2N2] Nb H - N r N / C I \ / / Nb [P2N2] l e q - M C 3 N - H ( i NbCI[P2N2] + N 2 H 2 t N 2 + N 2 H 4 Figure 2.8: Proposed Mechanism for Reaction of {[P2N2]Nb}2(|i-N2) (2) with Me3NHCl References begin on page 36 Chapter 2: Niobium Inorganic Complexes When the niobium dinitrogen complex (2) reacted with 1 eq. of Me3N-HCl, the result was a 2:1 mixture of the starting niobium chloride complex 1 and the dinitrogen complex 2. This indicated that the unknown intermediate, using 1 eq. of Me3N-HCl, was more reactive towards a second Me3N-HCl than the original dinitrogen complex 2. It was hoped that the reaction of one equivalent of Me3NHCl would yield a bridged LI-N2H, Li-Cl dimer. A potentially similar compound will be discussed in section 2.5.3. 2.5 Synthesis of Other Niobium Complexes 2.5.1 Reductive Elimination under Ar using KCg The synthesis of {[P2N2]Nb}2 (3) was accomplished under the same reaction conditions as complex 2, except the reaction was performed under 1 atm of argon or under vacuum. The resultant product, obtained in poor yield, was a diamagnetic brown solid that was not successfully isolated from the reaction byproducts. The *H and 3 1 P N M R spectra indicated that only one Nb[P2N2] product was formed. It is assumed that this complex is the dinuclear {[P2N2]Nb}2 because of the vacancy left by the reductive elimination of chloride and lack of any suitable ligands within the reaction mixture. This also allows compound 3 to be diamagnetic by a direct pairing of the unpaired electrons through the formation of a niobium-niobium multiple 21 bond; cases of multiple bonds for niobium have been established in other systems. In addition, no N M R resonances were observed indicating a phenyl-niobium interaction, as was seen in the zirconium reaction, presented in Figure 2.1, that bound the zirconium to the phenyl of the [P2N2] phosphine. 2.5.2 Synthesis of an Amide Ligand Complex The synthesis of Nb{N(SiMe3)2}[P2N2] (4) was accomplished by the reaction of NbCl[P2N2l with 1 eq. of LiN(SiMe3)2 in toluene. The resultant paramagnetic dark green solid was characterized by N M R spectroscopy and E.I. mass spectrometry, which indicated that the new complex was the expected niobium amide 4. Figure 2.9 shows the *H N M R spectrum of References begin on page 36 Chapter 2: Niobium Inorganic Complexes this complex. Similarities between the synthetic route and physical properties of the amide, and those of the paramagnetic alkyls, discussed in Chapter 3, were observed. Importantly, this niobium amide complex was the most "relatively" stable niobium complex synthesized in this thesis. In the glovebox, the stability of the complex while in solution for over a period of weeks has been attributed to the steric bulk of the amide used. SiMeMe" N(SiMe3)2 SiMeMe' SiCHFf m-Ph I B , a 15.0 n . « i . i . o i i a i 3 . i i a . n a . a ? . a fi.d 5 . a « . a ri>M Figure 2.9: 400 M H z lU N M R Spectrum of Nb{N(SiMe 3 ) 2 }[P2N2] (4) in C 6 D 6 (* denotes solvent) 2.5.3 Molecular Structure of a Side Product {[P2N 2]Nb}2(|i-N2)(u-Cl) Numerous attempts to crystallize the niobium chloride complex (1) resulted once in the molecular structure determination of {[P2N2]Nb}2(M-N2)(p>Cl) (5) by X-ray diffraction. The crystals were obtained by the slow evaporation of a toluene solution of NbCl [P2N2] . This compound, which has yet to be synthesized in a known reaction, is presented here because of its relevance to the intermediate product, discussed in section 2.4.2, that has resisted isolation. The References begin on page 36 Chapter 2: Niobium Inorganic Complexes information presented here may allow for more insight into the bonding arrangements in these new niobium macrocyclic complexes. The X-ray crystal structure of {[P2N2]Nb>2(/<-N2)(/<-Cl) is shown in Figure 2.10 and 2.11. Selected bond lengths and bond angles are given in Tables 2.7 and 2.8. The niobium centers consist of a seven coordinate geometry, and are joined by a side-on bridging N2 unit and a bridging chloride unit. This is the first example of a niobium compound containing a side-on bridged dinitrogen ligand. The N - N bond in 5 is slightly longer than that for the other dinitrogen complex 2 and also has longer Nb-N2 bond lengths. Figure 2.10: Ball & Stick II® View of Molecular Structure of {[P2N2]Nb}2(/<-N2)(/<-Cl) (5) Table 2.7: Selected Bond Angles for {[P2N2]Nb}2(/<-N2)(/<-Cl) Bonds Angle (deg) Bonds Angle (deg) Nbl-Cl l -Nb2 81.26 (7) Nbl-N5-Nb2 113.9 (3) N1-NM-N2 98.19(14) Nbl-N6-Nb2 114.8 (3) P1-NM-P2 153.52 (5) References begin on page 36 Chapter 2: Niobium Inorganic Complexes Figure 2.11: The Molecular Structure of {[P2N2]Nb}2(u:-N2Xu-Cl) (5) Table 2.8: Selected Bond Lengths for {[P2N2]Nb}2(M-N2)(u>Cl) Bond Length (A) Bond Length (A) N M - N 5 2.061 (6) Nb2-N5 2.094 (6) N M - N 6 2.046 (6) Nb2-N6 2.088 (6) N b l - C l l 2.674 (2) Nb2-Cll 2.676 (2) N5-N6 1.326(9) N b l - N l 2.170 (4) N b l - P l 2.5723 (13) N M - N 2 2.138 (4) NM-P2 2.5977 (12) References begin on page 36 Chapter 2: Niobium Inorganic Complexes 2.6 Summary The new niobium complexes presented here have shown a rich diversity for the chemistry of niobium chloride complex 1. As little previous research on niobium phosphines has been presented in the literature, this study has greatly broadened the understanding of the potential within this area of mixed phosphine and amido donors. The crystal structures presented here give insight into the coordination around the niobium metal centers, and the ability of phosphine ligands to bind to hard metal centers. NbCl[P2N2] (1) has demonstrated the ability to undergo reduction reactions, and to engage in a metathesis reaction with LiNR2- A lky l metathesis reactions wil l be discussed in Chapter 3. In addition, a new example of a niobium dinitrogen complex 2 has been isolated and characterized, adding to the few known niobium dinitrogen species in the literature. The reactivity of these new systems is significant. While the dinitrogen complex 2 does not show a wide range of reactivity, the starting chloride complex 1 has successfully undergone reaction with every reagent presented to it thus far. This high reactivity has also made isolation and stabilization challenging. The use of bulky ligands, as in the case of the amide complex 4, has demonstrated the increased stability that steric bulk provides to the electron deficient niobium complexes. This work has shown the ability to isolate materials with an alternate ligand system to that of Cp compounds commonly used within niobium chemistry. 2.7 References (1) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J. Chem. Commun. 1996, 2783. (2) Research was carried out by G. Giesbrecht (Al, Ga, In, V , Ti), L . Jafarpour (Lu, Yb), D. Leznoff (Co, Cr, Mo), J. Love (Li, N i , Zr, Sc, Y) , and S. Johnson (Zn, Ta) (3) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J.; Young, V . G. Science 1997,275, 1445. (4) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J. Organometallics 1998,17, 846. References begin on page 36 Chapter 2: Niobium Inorganic Complexes 37 (5) Ebsworth, E. A. ; Rankin, D. W. H. ; Cradock, S. Structural Methods in Inorganic Chemistry; 2nd ed.; Blackwell Scientif Publications, 1991. (6) Murthy, N . N . ; Karlin, K. D.; Bertini, I.; Luchinat, C. / . Am. Chem. Soc. 1997, 779,2156. (7) Lamar, G. N . ; Horrocks, W. D.; Holm, R. H. NMR of Paramagnetic Molecules; Academic Press, 1973. (8) Cotton, F. A . ; Wilkinson, G. Advanced Inorganic Chemistry; 3rd ed.; Interscience Publishers, 1972, p 541. (9) Williams, D. H. ; Fleming, I. Spectroscopic methods in organic chemistry; 4th ed.; McGraw-Hill Book Company, 1989. (10) Drago, R. S. Physical Methods in Chemistry; W. B. Saunders Company, 1977. (11) Earnshaw, A. Introduction to Magnetochemistry; Academic Press, 1968. (12) Hollas, J. M . Modern Spectroscopy; 2nd ed.; John Wiley & Sons Ltd., 1987, p 190. (13) Evans, D. J. J. Chem. Soc. 1959, 2003. (14) Zanotti-Gerosa, A . ; Solari, E.; Giannini, L . ; Floriani, C ; Chiese-Villa, A. ; Rizzoli, C. J. Am. Chem. Soc. 1998, 720, 437. (15) Berno, P.; Gambarotto, S. Organometallics 1995,14, 2159. (16) Dilworth, J. R.; Henderson, R. A. ; Hills, A . ; Hughes, D. L. ; Macdonald, C ; Stephens, A . N . ; Walton, D. R. M . J. Chem. Soc, Dalton Trans. 1990, 1077. (17) Personal communication with Mr. P. Borda, microanalysis technician. References begin on page 36 Chapter 2: Niobium Inorganic Complexes 38 (18) Ferguson, R.; Solari, E.; Floriani, C ; Osella, D.; Ravera, M . ; Re, N . ; Chiesi-Villa, A . ; Rizzoli, C. J. Am. Chem. Soc. 1997,119, 10104. (19) 3 1 P { !H} resonance for FJ.2[P2N2] appears as a singlet at -36.8 ppm (20) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952,24, 2006. (21) Cotton, F. A . ; Matonic, J. H . ; Murillo, C. A . / . Am. Chem. Soc. 1997,119, 7889. (22) Wigley, D. E.; Gray, S. D. Comprehensive Organometallic Chemistry IT, Wilkinson, G. and Stone, G. A. , Ed.; Pergamon, 1995; Vol . 5, p 57. (23) Halloway, C. E.; Melnik, M . J. Organomet. Chem. 1986, 303, 1. References begin on page 36 39 CHAPTER 3 NIOBIUM ORGANOMETALLIC COMPLEXES 3.1 Synthesis and Characterization of a Paramagnetic Niobium Alkyl The synthesis of Nb(CH2SiMe 3 )[P 2 N 2 ] (6) was accomplished by the reaction of NbCl[P2N2] with 1 eq. of the trimethylsilylmethyl reagent, LiCH.2SiMe3, as shown in equation 3.1. Nb(CH2SiMe3)[P2N2] was isolated, in high yield, as a paramagnetic blue solid. toluene, RT NbCl[P 2 N 2 ] + L i C H 2 S i M e 3 • Nb(CH 2SiMe3)[P 2N 2] 3.1 Complex 6 was characterized by '•H N M R spectroscopy (as shown in Figure 3.1), E.I. mass spectrometry, and microanalysis determination. The high solubility of the complex, even in hexanes, and the oiling out from solution upon concentration has made it difficult to obtain X -ray quality crystals thus far. With most of the alkyls discussed in this chapter, the difficulty of obtaining molecular structure determinations by X-ray diffraction, due to the high solubility of the compounds, has left an important gap in the understanding of these new complexes. Variable high temperature N M R studies were performed on niobium alkyl 6 and are summarized in Table 3.1. The results of plotting 8 vs. 1/T, following the Curie law, 1 and a linear least squares fit to determine the value for 8<jia are also shown in Table 3.1. As was the case for the original niobium chloride, 1, the theoretical 8di a values (especially for the CH2 protons on the [P2N2] backbone, with their low field 8 p a r a ) did not give straightforward results. This again demonstrates a temperature independent-paramagnetic behaviour, indicating a contribution by orbital angular momentum and spin-orbit coupling, as discussed in section 2.3.1 for chloride 1. References begin on page 52 Chapter 3: Niobium Organometallic Complexes Chapter 3: Niobium Organometallic Complexes Table 3.1: Variable High Temperature lH N M R Data and Least Squares Regression for Nb(CH2SiMe3)[P 2N2] (6) 8 at 25 °C 8 a t 4 0 ° C 8 at 60 °C Sdia r 2 (ppm, win) (ppm, wi/ 2) (ppm, w\ii) (ppm) SiMeMe' 4.7 (0.2) 4.6 (0.2) 4.3 (0.2) 0.9 0.991 SiMeMe' 10.5 (0.3) 10.2 (0.3) 9.7 (0.2) 2.7 0.994 o-Ph 13.8 (0.7) 13.6 (0.7) 13.3 (0.6) 9.3 0.996 m-Ph 10.8 (0.1) 10.7(0.1) 10.6(0.1) 8.5 0.991 p-Ph 8.9(0.1) 8.8(0.1) 8.8(0.1) 7.6 0.999 C H 2 S i M e 5 7.6 (0.3) 7.1 (br) 6.6(0.3) -1.8 0.997 CHH' 48.6(1.9) 47.4 (1.5) 45.6 (1.5) 20.3 0.995 CHH' 85.0 (3.6) 82.7 (3.4) 78.8 (2.90) 25.4 0.991 A similar synthesis was performed using L i C H 2 C M e 3 to form the complex Nb(CH 2 CMe3)[P 2 N 2 ] (7). This was done to try to slightly modify the compound to allow better crystallization of the product; however, complex 7 showed the same solubility behaviour as the other niobium alkyl (6). Bulkier alkyl reagents, such as LiCH(SiMe3) 2 , were not examined because of the possible reduction in reactivity as a result of steric crowding of the metal center. However, it may become necessary to use them to provide a crystal structure of these alkyls. 3.1.1 Reaction with H 2 : Evidence for Nb(rj5-C6H7)[P2N2] When Nb(CH 2 SiMe3)[P 2 N 2 ] (6) was placed under 1 atm of H 2 in benzene, a dark yellow solution was formed after 12 hours. A single diamagnetic product was formed upon workup which had a TC coordinated arene ring, as indicated by the *H N M R spectrum shown in Figure 3.2. The microanalysis determination obtained was in agreement to that of a compound with a general formula of Nb(C6H n )[P 2 N 2 ] (8) where n = 6 or 7. References begin on page 52 Chapter 3: Niobium Organome tallic Complexes SiMe I • • i • ! I I } • ' • i I • • i i i ' i i i • i i i i i i i i i i ; i 7.% 7.9 S . S R.'D S .S S.a ' . 0 ».9 i . ' i 3.0 2.5 2.3 ! . S 1.8 S 3 .0 PPM Figure 3.2: 400 M H z *H N M R Spectrum of Nb(C 6 H n )[P 2 N2] (8) in C 6 D 6 (* denotes solvent and trace impurities) To rationalize the transformation of the alkyl 6 to 8 by addition of H 2 , the following mechanism is proposed in Figure 3.3. The oxidative addition of H 2 to the niobium (Til) alkyl (6) will generate a dihydride species. The reductive elimination between a hydride ligand and the alkyl would then allow the formation of the stable tetramethyl silane (TMS) molecule. The resultant metal complex would be sterically uncrowded and the Lewis acidity would cause a solvent molecule to bind to the compound forming the proposed unstable intermediate References begin on page 52 Chapter 3: Niobium Organometallic Complexes Nb(C6H6)H[P2N2] (8a) as shown in Figure 3.3. Upon examination of the *H N M R spectrum shown in Figure 3.2, which has three resonances for bound arene protons of an integration of 1:2:2, it was believed that the remaining hydride was added into the arene ring to form the complex Nb( r | 5 -C6H7) [P2N2] (8). Reaction of 6 with deuterium gas under the same conditions allowed for better insight into the proposed structure of complex 8. Coupling was removed in the r ) 5 - C / / H ' and r | 5 - o - H resonances due to the labeled hydrogen, indicating a hydride-arene bond formation. The T | 5 - C H J ¥ ' peak was confirmed to be buried under the multiple SiCF»2 peaks at 1.3 ppm by homonuclear decoupling experiments at this resonance and observing the loss of coupling in the r\5-CHH' and r|5-o-H peaks. .H' Nb(CH 2SiMe 3)[P 2N 2] + H 2 (g)-6 [P2N2]Nb^ \ CH 2 SiMe 3 NbH[P 2N 2] + SiMe 4 I • H' [P 2N 2]Nb-8a Figure 3.3: Proposed Reaction Scheme for H2 Addition to Nb(CH2SiMe3)[P2N2] (6) Previous work in our laboratory on the Y(CH2SiMe3)[P2N2] system indicates a different reaction chemistry than the niobium analog (6) presented in this thesis. Equation 3.2 shows the reaction of Y(CFJ.2SiMe3)[P2N2] with benzene to form a biphenyl dimer. The cyclohexadienyl complex (8) is not believed to be a biphenyl dimer as a result of carbon-carbon bond formation as seen in this system. This is considered to be the case for a number of reasons; the first reason is that the chemical shifts for the bound arene ring are in a reverse pattern than what is observed for the yttrium compound. The second, and more important reason, is that when this reaction is done in toluene, although a mixture of two products forms, the major product has identical References begin on page 52 Chapter 3: Niobium Organometallic Complexes and 3 1 P N M R chemical shifts as niobium cyclohexadienyl complex 8. What this suggests is that an insignificant N M R coupling is observed between the arene protons and the tolyl methyl protons, and therefore results in the same spectral appearance as for the benzene case. This is more reasonable than considering the formation of a biphenyl dimer, which would now involve carbon-carbon bond breaking preferentially over carbon-hydrogen bond breaking in order to give similar *H and 3 1 P N M R spectra. Also, the yttrium reaction, when done in toluene, selectively gives the para-tolyl biphenyl complex; this is in contrast with the mixture of products seen in the analogous niobium system. 3.1.2 Reaction of Nb(CH 2 SiMe 3 ) [P2N 2 ] with C O When excess CO is added to niobium alkyl complex 6, the lH and 3 1 P N M R spectra show resonances due to three diamagnetic complexes. Two major products and one minor product have been identified, but not completely assigned. Over the course of a month, one of the major products slowly converted over to the other major product, as shown in the N M R spectra in Figures 3.4 and 3.5. For product A , it was possible to identify the CFJ.2 protons associated with the alkyl ligand because of the slight broadening of the peak caused by the proximity to the quadrupolar Nb nucleus. Such a resonance was not found for product B, but an assignment was made to a doublet signal resulting from one allene CH2 proton. On the basis of previous studies done on the CO addition4 and rearrangement into a metal-ligand CFJ.2SiMe3 bond, 5 a tentative reaction mechanism is proposed in Figure 3.6. The insertion of C O into the niobium-alkyl bond accounts for product A , which still has the CH2 protons of the ligand relatively close to the metal center. Over time, the CO inserted ligand rearranges to give the enolate complex, product B, as shown in Figure 3.6, which has been demonstrated in the literature.5 RT, 2 days 3.2 Y[P2N2] References begin on page 52 References begin on page 52 Chapter 3: Niobium Organometallic Complexes References begin on page 52 Chapter 3: Niobium Organometallic Complexes Nb(CH2SiMe3)[P2N2] CO B [P2N2]Nb ,0 SiMe 3 [P 2 N 2 ] (CO)Nb^ C H 2 CH 2 SiMe 3 CO CO [P 2N 2 ] (CO)Nb^ CH 2 SiMe 3 A O c : ,S iMe 3 [ P 2 N 2 ] ( C O ) N b ^ ^ > C H 2 , C ' ^ S i M e 3 [P 2N 2 ](CO)Nb^ C H 2 Figure 3.6: Proposed Mechanism for CO Insertion and Rearrangement into Nb(CH 2SiMe3)[P 2N2] (6) 3.2 Synthesis and Characterization of a Diamagnetic Niobium Alkyl The synthesis of Nb(CH 2 Ph)[P 2 N 2 ] (9) was accomplished by the reaction of NbCl[P 2 N 2 ] with 1 eq. of potassium benzyl as shown in equation 3.3. Nb(CH 2 Ph)[P 2 N 2 ] was isolated from THF as a diamagnetic dark yellow solid. NbCl[P 2 N 2 ] + K C H 2 P h THF, -78 °C 12 hours Nb(CH 2Ph)[P 2N 2] 3.3 Microanalysis for benzyl complex 9 consistently gave low carbon results, as shown in Table 3.2. Even though the carbon value does not agree with the theoretical value, it is very unusual to have the hydrogen and nitrogen in such close agreement under these circumstances. Since microanalysis determinations depend on all of the carbon being given off as free C 0 2 , it is References begin on page 52 Chapter 3: Niobium Organometallic Complexes reasonable to assume that this was not occurring in the metal-alkyl system (9). Because of this, it is also reasonable to assume that the large error in carbon might have been due to the formation of a stable niobium carbide. NbC is resistive to oxidization up to temperatures of 1000 °C; 6 this is also the temperature at which the microanalysis samples undergo combustion. Recently, similar results were obtained for another benzyl system. Table 3.2: Microanalysis Results for NbBz[P 2 N 2 ] (9) C H N Theoretical 51.93 6.89 3.91 Found 50.04 6.84 4.00 "NbC" 50.26 6.89 3.91 3.2.1 Evidence for Nb(ri 5-CH2Ph)[P2N2] Over the past few years, the different coordination modes that the benzyl ligand, CH 2 Ph, can adopt have been explored.8 Examples ranging from the classical r\l-o bound down through to an T|5-7t interaction are shown in Figure 3.7, which have been confirmed by X-ray crystallography. The large flexibility in binding modes enables the benzyl ligand to be suitable for electron deficient early transition metal complexes. T| T | r\ r\ T) ref: 9 10 11 12 13 Figure 3.7: Bonding Arrangements of M(n x -CH 2 Ph) References begin on page 52 Chapter 3: Niobium Organometallic Complexes * SiMe 2 Nb[P 2N 2] ! I I I i I I I I \ I I i I I I 1 I I I J I I I J I I I J I I I i I Figure 3.8: 200 M H z ! H N M R Spectrum of Nb(CH 2 Ph)[P 2 N 2 ] (9) in C 6 D 6 (* denotes solvent) The niobium benzyl complex (9) was characterized by ^H N M R spectroscopy, as shown in Figure 3.8, and 3 1 P N M R spectroscopy, which gave a single peak at 27.7 ppm that was broadened as a result of the relaxation from the quadrupolar Nb nucleus.2 From the *H N M R spectrum, it is possible to propose that the benzyl ligand is it bound in some fashion to the metal center. This is due to the proton resonances that are attributed to the benzyl ring shifting upfield between the range of 3 and 5.5 ppm as a result of the interaction with the niobium. The similarity of the patterns of these proton resonances and those of the cyclohexadienyl complex 8 References begin on page 52 Chapter 3: Niobium Organometallic Complexes indicate a similar environment for the nuclei, which contributes to the idea that the entire arene ring may be bound to the niobium in an r | 5 mode. This is also supported by the fact that an r | 5 -benzyl ligand would allow for a greater donation of electron density to give a 16 e" niobium (III) species. Because of the ability for further electron donation, the possibility remains that an T | 7 -benzyl ligand is bound to the niobium center. However, an increase in electron density around the metal may also be attributed to a bridged T^-r^-pi-benzyl dimer, as shown in Figure 3.9. These speculations demonstrate the need for molecular structure determination, by X-ray diffraction, to confirm the correct binding mode. Figure 3.9: Possible Binding Modes for Nb(CH 2 Ph)[P 2 N 2 ] (9) 3.3 Oxidative Addition using M e l The synthesis of NbCl(MeI)[P 2N 2] (10) was accomplished by reacting NbCl[P 2 N 2 ] with 1 eq. of M e l in toluene. E.I. mass spectrometry revealed a parent ion consistent with NbClMeI[P 2 N 2 ] and a fragmentation pattern indicating each ligand was bound to the metal center. Figure 3.10 shows the A H N M R spectrum for a single paramagnetic complex with all resonances assigned, including that for the methyl ligand. There was a significant difference between the resonances of complex 10 and those of all the other niobium complexes discussed in this thesis. This included the observation that all proton signals demonstrated only a small shift from their expected diamagnetic values, which was especially true for the C H 2 protons on the backbone of the [P 2 N 2 ] ligand. 1 4 The fact that the methyl resonance was seen was surprising if considering that the ligand was directly bound to the r | 5 bound r) bound bridged dimer References begin on page 52 Chapter 3: Niobium Organometallic Complexes paramagnetic niobium center. In addition, this species should have an oxidation state of +5, meaning that it has no unpaired electrons that could cause the complex to be paramagnetic. Tentatively, it is proposed that a Nb(V) compound in a rapid equilibrium with a Nb(III)-MeI adduct species, as shown in Figure 3.11, accounted for the paramagnetic contribution to the *H N M R spectra. SiCHH' NbMe I—•—•—•—I—•—i • I ' 10.0 e.o 6.o PPM SiMeMe' | I I I I | I l l I | l l l l | l l l l | l—l—l—i—|—i—i i i—|—I—T—I—•—[—I—I—r—l—|—l i i—i—|—i—•—i—i—I—i 10.0 9.0 S.O 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 PPM Figure 3.10: 200 MHz lH N M R Spectrum of NbCl(MeI)[P2N 2] (10) in C 6 D 6 (* denotes solvent) Cl [P 2 N 2 ]Nb^—Me ^ 1 Nb(V) [P2N2]Nb Cl I Me Nb(III) Figure 3.11: Conversion between Nb(V) and Nb(III) species References begin on page 52 Chapter 3: Niobium Organometallic Complexes 3.4 Summary Initial investigations into the synthesis of stable niobium [P2N2] alkyl complexes have proved successful. Both paramagnetic and diamagnetic niobium alkyl derivatives have been isolated and characterized. For the paramagnetic compound Nb(CH2SiMe3)[P2N2] (6) reactions have been observed with small molecules, namely H 2 and CO. In both cases, the reactions that followed were not simple ligand additions to the niobium systems, but demonstrated more complex rearrangement and insertion chemistry. It was observed that the diamagnetic complex Nb(r|5-CH2Ph)[P2N2] (9) gave some insight into how this conjugated alkyl ligand might undergo structural changes that would provide better stabilization to the electron deficient niobium center. Although these bulky alkyls have proven stable enough to be isolated, their high reactivity makes their handling and characterization challenging. Because the high solubility of the compounds meant that X-ray quality crystals could not be grown, the details of their molecular structures remain undetermined. 3.5 References (1) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; 3rd ed.; Interscience Publishers, 1972, p 541. (2) Drago, R. S. Physical Methods in Chemistry; W. B. Saunders Company, 1977. (3) Fryzuk, M . D.; Love, J. B.; Rettig, S. J. J. Am. Chem. Soc. 1997,119, 9071. (4) Sonnenberger, D. C ; Mintz, E. A. ; Marks, T. J. J. Am. Chem. Soc. 1984,106, 3484. (5) Lee, L.; Berg, D. J.; Einstein, F. W.; Batchelor, R. J. Organometallics 1997,16, 1819. References begin on page 52 Chapter 3: Niobium Organometallic Complexes 53 (6) Marmer, E. N . ; Gurvich, O. S.; Mal'tseva, L . F. High Temperature Materials; Freund Publishing House, 1971, p 179. (7) Unpublished results of Cp*W(NO)(CH2C6H4R), where R is either ortho or meta, by P. Legzdins, E. Tran. (8) Carmona, E.; Marin, J. M . ; Paneque, M . ; Poveda, M . L . Organometallics 1987, 6, 1757. (9) Chappell, S. D.; Cole-Hamilton, D. J. J. Chem. Soc, Dalton Trans. 1983, 1051. (10) Legzdins, P.; Jones, R. H. ; Phillips, E. C ; Yee, V . C ; Trotter, J.; Einstein, F. W. Organometallics 1991,70, 986. (11) Cotton, F. A . ; LaPrade, M . D. J. Am. Chem. Soc. 1968, 90, 5418. (12) Mintz, E. A . ; Molay, K. G.; Marks, T. J.; Day, V . W. J. Am. Chem. Soc 1982, 104, 4692. (13) Hamon, J. R.; Astruc, D.; Roman, E.; Batail, P.; Mayerle, J. J. J. Am. Chem. Soc. 1981,703, 2431. (14) Resonances for the C H 2 protons of all other paramagnetic complexes presented in this thesis fell in the range from 31 to 86 ppm. References begin on page 52 CHAPTER 4 EXPERIMENTAL PROCEDURES 4.1 General Procedures Unless otherwise stated, all manipulations were performed under a dry and dioxygen free atmosphere of dinitrogen or argon. The glovebox used was a Vacuum Atmospheres HE-533-2 device equipped with an MO-40-2H purification system and a -40 °C freezer. The Schlenk techniques were performed on a vacuum line with standard Schlenk-type glassware. Unless otherwise stated, all products were dried under full vacuum, and microanalysis samples were dried under a high vacuum for 12 hours using a mercury diffusion pump. 4.2 Reagents and Starting Materials Toluene, hexanes, and THF were pre-dried over C a H 2 for 24 hours, and then dried by refluxing over sodium benzophenone ketyl, followed by distillation under argon. Benzene and diethyl ether were treated in a similar manner except that these solvents were not pre-dried. Deuterated benzene (C6D6) and deuterated THF (C4D8O) were refluxed under vacuum with potassium metal, vacuum transferred, and "freeze-pump-thawed" three times prior to use. The following compounds were prepared by published procedures: NbCbCDME), 1 Li 2(dioxane)[sy/7-P 2N 2], 2 K C 8 , 3 L i C H 2 S i M e 3 , 4 and K B z . 5 L i C H 2 C M e 3 , and L i N ( S i M e 3 ) 2 were prepared in a similar manner as L i C H 2 S i M e 3 . Me 3 N-HCl was re-crystallized from ethanol and dried under vacuum.6 CO and H 2 were used as received. M e l was distilled, degassed, and stored under N 2 with a Cu wire prior to use.6 References begin on page 65 Chapter 4: Experimental Procedures Diatomaceous earth (Celite) was dried overnight at 170 °C before being taken inside the glovebox for use. 4.3 Analytical Methods 1 H and 3 1 P { 1 H } N M R spectroscopy were performed on a Varian XL-300 instrument (300 M H z and 121.4 MHz), routine spectra were run on a Bruker AC-200 (200.1 M H z and 81.1 MHz), and variable high temperature J H N M R experiments on a Bruker WH-400 (400 MHz). i H p i P } N M R spectroscopy was performed on a Bruker AMX-500 instrument (500 MHz). *H N M R spectra were referenced to internal C 6 D 5 H (7.15 ppm) and 3 l P { ! H } N M R spectra were referenced to external P (OMe3 )3 (141.0 ppm, with respect to 85% H 3 P O 4 at 0.00 ppm). Magnetic susceptibility measurements were performed on the Bruker AC-200 instrument using Evans' method. A ferrocene reference was sealed in a capillary tube (in C6D6) and loaded into an N M R tube along with the sample and ferrocene (in CgDg). C, H , N , and halogen microanalyses were performed by Mr. P. Borda of this department. Mr. M . Lapawa, also of this department, acquired all the electron ionization (E.I.) mass spectra. The X-ray crystal structures were determined at the U B C Crystallographic Services in this department by Dr. S. Rettig. The crystals were loaded in 0.3 or 0.5 mm glass capillaries in the glovebox, and then sealed under dinitrogen. Details of the structure determinations are given in the Appendix A. 1 and A.2. 4.4 Microanalysis Consideration of Reactive Niobium Complexes The niobium alkyls and related products presented in Chapter 3 are among the most reactive compounds synthesized and isolated in this thesis. Although thermally stable, their ability to react with many reagents (including trace amounts of air and water) make the storage of these new complexes challenging. Even with the use of a glovebox, these complexes, while in solution, will show decomposition products from trial to trial, References begin on page 65 Chapter 4: Experimental Procedures which usually coincides with the quality of the box atmosphere. Most samples can be kept for a reasonable duration of time, provided that the samples are kept dry and capped within the glovebox. The greatest problem that occurred with these samples was in the microanalysis determinations of C, H , and N . The glove bag and unfiltered N 2 used in the preparation of microanalysis samples within this department did not provide a clean enough atmosphere to prevent these compounds from partially decomposing. Color changes were observed in some complexes before weighing was completed, and as a result the values from the microanalysis did not match theoretical values. Although some samples in the past from this department have shown too high a reactivity for proper microanalysis determination, this is the first case reported that demonstrates an entire Q series of complexes that fall under this category. The observed color changes and differences in trials from the same sample confirm that these errors are not a result of impurities or mixtures of products. For several of the products presented in Chapter 3, almost reasonable C, H , and N determinations were possible. In these cases, both carbon and hydrogen were just outside the general acceptable limits of error of 0.4% and 0.2% respectively. Taking into consideration the high reactivity of these complexes, such values are reasonable for these determinations. In other cases, however, the values were too far off from the theoretical values to make comment, although the fluctuations between trials from the same sample indicates that a similar problem occurred. 4.5 Hydrazine Analysis Hydrazine was analyzed according to a published procedure.9 The resultant solution from the reaction of {[P2N2]Nb}2(p>N2) (250 mg, 0.20 mmol, in 30 mL of toluene) with 2 eq. of M e 3 N H C l (37 mg, 39 mmol) was placed into a Schlenk flask and References begin on page 65 Chapter 4: Experimental Procedures attached to a vacuum line. The atmosphere of dinitrogen was removed and replaced with 1 atm of anhydrous HC1, resulting in the immediate formation of a dark green suspension. The sample was evaporated to dryness, exposed to air, extracted into distilled water, and filtered into a 250 mL volumetric flask. A 1.0 mL aliquot of the solution was added to 20 mL of a color developer (p-dimethylaminobenzaldehyde, 4.0 g; ethanol, 200 mL; concentrated HC1, 20 mL) and diluted to 25 mL with 1M HC1. Absorbance readings of the sample were taken within 10 minutes. The spectrometer was set to 100% transmittance using a blank solution consisting of 10 mL of color developer diluted to 25 mL with 1M HC1. Absorbance readings were converted to hydrazine concentrations by the linear regression equation 4.1 (refer to Appendix A.3 for calibration data). A458 = 0.0023329+ 2.1716[hydrazine] 4.1 4.6 A Constant Volume Gas Addition Reaction M e l was added to the reaction mixture by means of a constant volume gas addition apparatus, which consisted of a Schlenk style cell with two valves, 1 0 one of which was connected to the reaction flask and the other to the vacuum line and Mel flask. Both the reaction flask and the cell were evacuated, and then the cell was backfilled with M e l vapor. By using the Ideal Gas Law, rearranged as shown in Equation 4.2, it was possible to determine a very accurate and small amount of a volatile compound. The filled cell was opened to the evacuated reaction flask at -169 °C, and the vapor then condensed into the flask. When the solution was allowed to warm to room temperature, the Mel reacted with the metal complex. This technique was very useful when the sample sizes for the reagent were small enough to make weighing difficult, References begin on page 65 Chapter 4: Experimental Procedures which was especially true when small molecules were added to large transition metal complexes. 4.7 Syntheses of New Compounds 4.7.1 NbCl[PhP(CH2SiMe2NSiMe2CH2)2PPh], (1) NbCl3(DME) (547 mg, 1.89 mmol) was added to a solution of Li2(dioxane)[*yn-P2N2] (1.0 g, 1.57 mmol) in toluene (30 mL), at room temperature. The resultant red suspension reacted over 12 hours yielding an intense green solution. After a further 2 days, to ensure complete reaction, the solution was concentrated down to a minimal amount of toluene, and then filtered through Celite. The solution was evaporated to dryness and the resulting solid was rinsed with a minimal amount of hexanes and dried, yielding a dark red product (729 mg, 70% yield). The product was crystallized by the slow evaporation of a toluene solution. J H N M R (8, 400 MHz, C6D6): 4.78 (yv\l2 84 Hz, 12H, S iC/ /3CH 3 ' ) ; 8.70 (28 Hz, 2H, p-Ph); 10.22 (48 Hz, 4H, m-Ph); 11.19 (208 Hz, 12H, S i C H 3 C / / 5 ' ) ; 11.95 (140 Hz, 4H, o-Ph); 39.65 (856 Hz, 4H, PC/ /H ' ) ; 56.16 (1244 Hz, 4H, PCH/ / ' ) . jieff (Evans method) = 2.7 B M . mass spec. (E.I.): M + 660. IR (cm-1, nujol): 1256, 1074, 930, 833, 798, 740. Anal. Calcd for C 2 4H42P2N 2 Si4NbCl: C, 43.59; H , 6.40; N , 4.24; C l , 5.36. Found: C, 43.34; H , 6.32; N , 4.19; C l , 5.49. 4.7.2 {[P2N2]Nb}2(n-N2),(2) KCg (61 mg, 0.45 mmol) was added to a solution of NbCl[P2N 2] (250 mg, 0.38 mmol) in toluene (20 mL), at room temperature and 1 atm of dinitrogen. After 3 days, the resultant brown solution was filtered through Celite and evaporated to dryness. The resulting solid was rinsed with a minimal amount of hexanes and dried, yielding a dark brown product (121 mg, 50% yield). The product was crystallized from a slow evaporating toluene solution. lH N M R (8,400 MHz, C 6 D 6 ) : -11.52 (w\/2 768 Hz, 4H, o-Ph); 0.82 (88 Hz, 12H, S i C f / j C ^ ' ) ; 5.44 (216 Hz, 12H, SiCH^CHf); 6.60 (120 Hz, 4H, References begin on page 65 Chapter 4: Experimental Procedures m-Ph); 7.67 (32 Hz, 2H p-Ph); 32.39 (2720 Hz, 4H, PC/ /H ' ) . p: e f f (Evans method) = 2.3 B M . mass spec. (E.I.): M'+ 1278. Anal. Calcd for C ^ H ^ N e S i g N t ^ : C, 45.05; H , 6.62; N , 6.57 (4.38 for a non-volatile niobium nitride). Found: C, 44.86; H , 6.47; N , 4.13. 4.7.3 {[P 2N 2]Nb} 2,(3) K C 8 (61 mg, 0.45 mmol) was added to a solution of NbCl [P 2 N 2 ] (250 mg, 0.38 mmol) in toluene (20 mL), at room temperature and 1 atm of argon. After 2 days, the resultant brown solution was filtered through Celite and evaporated to dryness. The resulting solid was rinsed with a minimal amount of hexanes and dried, yielding a minimal quantity of dark brown product (95 mg). *H N M R (8, 200 MHz, C6D6): 0.05, 0.10, 0.23, 0.38 (s, 6H, SiCtfj); 0.89, 1.25 (m, 4H, PCH2); 7.25, 7.44, 7.61 (m, P C ^ ) . 31p N M R (8, 81.1 MHz, C 6 D 6 ) : 32.0 (wi/ 2 405.5 Hz). 4.7.4 Nb{N(SiMe 3)2}[P 2N 2], (4) LiN(SiMe3) 2 (25 mg, 15 mmol) was added to a solution of NbCl[P 2 N 2 ] (100 mg, 0.15 mmol) in toluene (20 mL), at room temperature. Over the next 2 hours, the solution changed from an intense green color to a dark green. The solution was filtered through Celite, evaporated to dryness, and rinsed with hexanes yielding a dark green product (84 mg). l H N M R (8, 400 MHz, C 6 D 6 ) : 5.18 (wi / 2 56 Hz, 12H, SiC#3CH 3 ' ) ; 7.83 (24 Hz, 2H,p-Ph); 9.51 (76 Hz, 12H, S i C H 3 C / / / ) ; 12.09 (40 Hz, 4H, m-Ph); 13.36 (120 Hz, 18H, N(SiMe3)2); 14.91 (280 Hz, 4H, o-Ph); 37.06 (516 Hz, 4H, PC/ /H ' ) ; 44.25 (664 Hz, 4H, PCH/ / ' ) . mass spec. (E.I.): M + 785. 4.7.5 Nb(CH 2 SiMe 3 ) [P 2 N 2 ] , (6) A solution of L i C H 2 S i M e 3 (35 mg, 0.38 mmol) in toluene (5 mL) was added dropwise to a solution of NbCl[P 2 N 2 ] (250 mg, 0.38 mmol) in toluene (20 mL), at room References begin on page 65 Chapter 4: Experimental Procedures temperature. The resultant solution slowly lost its dark green color and, within the hour, became an intense blue. The solution was evaporated to dryness, and the product was extracted into hexanes and filtered through Celite. The solution was evaporated yielding a dark blue product (234 mg, 87% yield). *H N M R (5, 400 MHz, C 6 D 6 ) : 4.74 (wy2 76 Hz, 12H, S iC/ /3CH 3 ' ) ; 7.55 (120 Hz, 9H, Si(C//j) 3); 8.91 (24 Hz, 2H,p-Ph); 10.49 (108 Hz, 12H, S i C H 3 C / / i ' ) ; 10.81 (52 Hz, 4H, m-Ph); 13.77 (288 Hz, 4H, o-Ph); 48.61 (748 Hz, 4H, P C / / H ' ) ; 85.02 (1420 Hz, 4H, PCHH') . mass spec. (E.I.): M + 712. Anal. Calcd. for C 2 8 H 3 3 P 2 N 2 S i 5 : C, 47.17; H , 7.49; N , 3.93. Found: C, 46.49; H , 7.29; N , 3.99. 4.7.6 Nb(CH 2 CMe 3 ) [P2N 2 ] , (7) The same procedure that was used previously for the preparation of 6 was followed. The reaction of a toluene solution (20 mL) of NbCl [P 2 N 2 ] (200 mg, 0.30 mmol) and a toluene solution (5 mL) of L i C H 2 C M e 3 (24 mg, 0.30 mmol) gave a purple-red solution. The resultant product was obtained in good yield (176 mg). *H N M R (8, 200 MHz, C6D 6 ) : 4.40 (wi/ 2 60 Hz, 12H, SiCT/jCH^); 7.85 (br, 9H, C(CH3)3); 8.69 (24 Hz, 2H, p-Ph); 10.62 (70 Hz, 12H, S i C H ^ H j ' ) ; 10.92 (40 Hz, 4H, m-Ph). Attempts to obtain C, H , N failed because samples decomposed during microanalysis preparation. 4.7.7 Nb(r|5-C6H7)[P2N2],(8) A solution of Nb(CH 2 SiMe 3 ) [P 2 N 2 ] (200 mg, 0.28 mmol) in benzene (25 mL) was placed under one atm of H 2 . Overnight the solution went from intense purple to a clear dark yellow color. The solution was filtered through Celite and evaporated to dryness yielding a gray powder (181 mg, 92% yield). J H N M R (8, 500 M H z , C6D 6 ) : 0.00,0.18,0.43,0.51 (s, 6H, SiCffj); 0.85, 1.28, 1.36,1.85 (d of d, 2H, PCH2); 1.58 (d of d, 1H, r\5-CHH'); 2.52 (m, 2H, r|5-o-H); 4.30 (d of d, 2H, r i5- m -H); 5.51 (d of t of t, 1H, r|5-p-H); 7.42 (d of d, 2H, P-o-Ph); 7.72 (d of d, 2H, P-o-Ph). 31p{lH.} N M R (8, 81.1 References begin on page 65 Chapter 4: Experimental Procedures MHz, C6D 6 ) : 28.4 (br). Anal. Calcd. for C 3oH49P 2N2Si4Nb: C, 51.12; H, 7.01; N , 3.97. Found: C, 51.74; H , 6.67; N , 4.03. When the reaction was done in toluene, a minor second product was observed with a broad 3 1 P{ *H} N M R signal at -35.4 ppm. 4.7.8 Nb(Ti5- C H 2 C 6 H 5 ) [ P 2 N 2 ] , (9) A mixture of NbCl[P2N 2] (300 mg, 0.45 mmol) and K C H 2 P h (60 mg, 0.45 mmol) was placed in a solution of THF (30 mL) at -78 °C. The resultant suspension was stirred for 30 min. before being slowly brought back up to room temperature. Overnight the solution turned a dark yellow color. The solution was evaporated to dryness, and the product was extracted into hexanes and filtered through Celite. The solution was evaporated under vacuum, yielding a dark yellow powder (170 mg). ! H N M R (8, 200 M H z , C6D 6 ) : -0.04, 0.19, 0.43, 0.50 (s, 6H, SiCtfj); 1.28 (m, 8H, PCH2); 2.95 (s, 2H, NbCi7 2Ph); 3.49 (m, 2H, CH 2 ^ -Ph ) ; 4.25 (m, 2H, CH 2-m-Ph); 5.02 (m, 1H, CH 2-p-Ph); 7.35 (d of d, 2H, P-o-Ph); 7.63 (d of d, 2H, P-o-Ph). 31p{lH} N M R (8, 81.1 M H z , C6D 6 ) : 27.7 (w\/2 446 Hz), mass spec. (E.I.): M + -4H 712 (90% Int.). Attempts to obtain C, H , N are discussed in section 3.2. 4.7.9 NbCl(MeI)[P 2 N 2 ] , (10) A solution of NbCl[P2N2] (75 mg, 0.11 mmol) in toluene (20 mL) was placed under vacuum and cooled to -169 °C. Volatile Mel (0.11 mmol) was added by a constant volume gas apparatus (230 mmHg in a 9.1 mL cell at RT). When slowly warmed to room temperature, the solution turned a light yellow-orange color. The solution was evaporated to dryness, yielding a light yellow product (59 mg). lH N M R (8, 200 M H z , C 6 D 6 ) : 1.63 (wi/2 22 Hz, 12H, S i C / / j C H 3 ' ) ; 1.91 (22 Hz, 12H, S i C H 3 C # / ) ; 5.65 (44 Hz, 3H, NbCJ/j); 7.61 (22 Hz, 2H, p-Ph); 7.90 (26 Hz, 4H, m-Ph); 8.36 (26 Hz, 4H, o-Ph); 8.69 (br, 4H, PCtfH'); 8.95 (br, 4H, PCHJ/ ') . mass spec. (E.I.): M + 802. References begin on page 65 Chapter 4: Experimental Procedures 4.8 Adduct Formation of NbCl[P2N2] Complexes 4.8.1 NbCI(PMe3)[P2N2], (11) Excess P M e 3 was added via vacuum transfer to a solution of NbCl[P2N2] (100 i mg, 0.15 mmol) in toluene (20 mL), at -169 °C. When allowed to warm to room temperature, the solution went from an intense green color to a dark yellow. N M R (8, 200 MHz, C 6 D 6 ) : 3.78 (wy2 172 Hz, 12H, S iC/ / jCH 3 ' ) ; 8.82 (22 Hz, 2H, p-Ph); 9.61 (36 Hz, 4H, m-Ph); 10.38 (132 Hz, 12H, S i C H 3 C / / 5 ' ) . mass spec. (EL) : M + 735. 4.8.2 NbCl(NC5H5)[P2N2], (12) The same procedure that was used for the preparation of 11 was followed. The reaction of a toluene solution (20 mL) of NbCl[P2N2] (100 mg, 0.15 mmol) and excess pyridine gave a dark blood-red solution. lH N M R (8, 200 M H z , C6D6): 4.00 (wi/2 80 Hz, 12H, SiC//3CH 3 ' ) ; 5.96 (88 Hz, 12H, S i C H 3 C / / j ) ; 8.25 (26 Hz, 2H,p-Ph); 10.62 (44 Hz, 4H, m-Ph). 4.8.3 NbCI(THF)[P2N2], (13) A 10 mg sample of NbCl[P 2 N 2 ] was loaded into a N M R tube with dg-THF. lH N M R (8, 200 MHz, C4D 8 0) : 4.20 (wi / 2 56 Hz, 12H, SiC/ /3CH 3 ' ) ; 5.58 (72 Hz, 12H, S i C H 3 C / / j ) ; 8.85 (22 Hz, 2H,p-Ph); 10.80 (46 Hz, 4H, m-Ph). 4.9 CO Addition Reactions 4.9.1 Reaction of NbCl[P2N2] with CO A 10 mg sample of NbCl[P2N2] was loaded into a Teflon screw cap N M R tube containing CgD^ The N M R tube was frozen to -169 °C, evacuated, and backfilled with 1 atm of CO. When allowed to warm to room temperature, the solution turned a very dark yellow color. The product gave an oversimplified *H N M R spectrum. lH N M R (8, 300 References begin on page 65 Chapter 4: Experimental Procedures MHz, C6D 6 ) : 0.24 (br m, 24H, S iC/ / 5 ) ; 1.74 (br m, 8H, PC/ / 2 ) ; 7.23, 8.19 (br m, P C ^ ) -31p N M R (8, 121.4 MHz, C 6 D 6 ) : 10.7 (wi/2 852.5 Hz). The adduct lost CO when it was placed under vacuum, to give the original paramagnetic NbCl[P2N2] complex. 4.9.2 Reaction of Nb(CH2SiMe3)[P2N2] with CO The same procedure used in section 4.9.1 was followed for a 10 mg sample of Nb(CH2SiMe3)[P2N2]. When allowed to warm to room temperature, the sample went from the initial blue color to a red, before quickly converting to a yellow solution. *H and 3 l P N M R spectra indicate two major products and one minor. Product 1 is converted to Product 2 over one month. Product A : lH N M R (8, 300 MHz, C 6 D 6 ) : -0.16 (s, 9H, CH 2 Si(C#j) 3 ) ; 0.04, 0.26, 0.34, 0.44 (s, 6H, SiC#j); 2.58 (br, 2H, C / / 2 SiMe 3 ) ; 7.25 (d oft, 4H, m-Ph); 8.02 (d of t, 4H, o-Ph). 31p N M R (8, 121.4 MHz, C 6 D 6 ) : 12.8, 28.5 (br). Product B: l H NMR: 0.02 (s, 9H, CH 2 Si(C#i ) 3 ) ; 0.10, 0.27, 0.43, 0.68 (s, 6H, SiCH3); 1.85 (d, 1H, CCHW); 7.39 (d of t, 4H, m-Ph); 8.18 (d of t, 4H, o-Ph). 31p N M R : 27.6, 29.7 (br). Product C: 31p NMR: 18.4 (br). 4.9.3 Reaction of {[P2N2]Nb}2(p:-N2) with CO The same procedure used in section 4.9.1 was also followed for a 10 mg sample of {Nb[P2N2]}2(!t-N2). When allowed to warm to room temperature, the solution turned a dark yellow color. The A H N M R spectrum showed a large degree of decomposition but indicated a major product with shifts of 7.5 ppm and 7.9 ppm for the phenyl protons. 31p N M R (8, 81.1 MHz, C 6 D 6 ) : 18.4, 39.0 (br). 4.10 Reaction of {[P2N2jNb}2(p>N2) with Me 3 NHCl 4.10.1 Reaction of {[P2N2]Nb}2(u.-N2) with 2 Equivalents of Me 3 NHCl M e 3 N H C l (37 mg, 39 mmol) was added to a solution of {[P 2N2]Nb} 2(fi-N 2) (250 mg, 0.20 mmol) in toluene (30 mL), at room temperature. The solution was stirred References begin on page 65 Chapter 4: Experimental Procedures overnight, during which time the dark brown color changed to an intense green. The solution was filtered through Celite and evaporated to dryness yielding a red solid. The 1 H N M R spectrum (in C^Ps) showed the product to be NbCl[P2N2]. Any excess M e 3 N H C l reacted with the P2N2 ligand to give multiple diamagnetic PPh proton resonances, with 3 1 P signals at -22.0 and -5.0 ppm. 4.10.2 Reaction of {[P 2 N2 ]Nb} 2 (Ll-N2) with 1 Equivalent of Me 3 NHCl The same procedure used in section 4.10.1 was followed. The reaction of a toluene solution (30 mL) of {[P2N2]Nb}2(p:-N2) (250 mg, 0.20 mmol) and M e 3 N H C l (19 mg, 0.20 mmol) gave a dark green solution. The *H N M R spectrum (in C^D^) showed a mixture of NbCl[P2N2] and {[P2N2]Nb}2(|i-N2) of approximately 2:1. 4.11 Unsuccessful Reactions 4.11.1 Reaction of NbCI[P 2 N 2 ] with MeLi M e L i (0.1 mL of 1.6 M stock in hexanes diluted to 5 mL, 0.16 mmol) was added dropwise to a solution of NbCl[P2N2] (100 mg, 0.15 mmol) in toluene (20 mL), at -78 °C. The solution was allowed to warm to room temperature, then filtered and evaporated to dryness. The N M R spectrum showed complete decomposition of starting material. 4.11.2 Reaction of {[P2N 2]Nb} 2(p>N 2) with H 2 A solution of {[P2N2]Nb}2(M--N2) (100 mg, 0.08 mmol) in toluene (30 mL) was placed under 1 atm of H2 at room temperature. No change in the N M R spectrum was observed after 3 weeks. References begin on page 65 Chapter 4: Experimental Procedures 4.11.3 Reaction of {[P2N2]Nb}2(p>N2) with C 2 H 4 A solution of {[P2N2]Nb}2(u-N2) (100 mg, 0.08 mmol) in toluene (30 mL) was placed under 1 atm of ethylene at room temperature. After 2 days, the lH N M R spectrum showed only decomposition products, believed to be caused by the purity of the ethylene. 4.11.4 Reaction of {[P2N2]Nb}2(p>N2) with n-BuSiH3 A solution of {[P2N2]Nb}2(p>N2) (50 mg, 0.04 mmol) in toluene (20 mL) was cooled to -169 °C and placed under vacuum. Volatile n-BuSiFJ.3 (0.04 mmol) was added by a constant volume gas apparatus (80 mmHg in a 9.1 mL cell at RT). No change in the i H N M R spectrum was observed after 3 weeks. Addition of excess n-BuSiH3 (>10 eq.) gave no reaction. 4.11.5 Reaction of {[P2N2]Nb}2(u-N2) with NbCl[P 2N 2] A mixture of NbCl[P2N 2 ] (100 mg, 0.15 mmol) and {[P2N2]Nb}2(u.-N2) (97 mg, 0.08 mmol) was placed in a solution of toluene (30 mL), at room temperature. No change in the l H N M R spectrum was observed after 3 weeks. 4.11.6 Reaction of NbCls with Li2(dioxane)[syn-P2N2] NbCIs (47 mg, 0.17 mmol) was added to a solution of Li2(dioxane)[.syn-P2N2] (100 mg, 0.16 mmol) in toluene (30 mL), at room temperature. No change in the JjH N M R spectrum was observed after 3 weeks. 4.12 References (1) Roskamp, E. J.; Pederson, S. F. J. Am. Chem. Soc. 1987,109, 6551. (2) Fryzuk, M . D.; Love, J. B. ; Rettig, S. J. Chem. Commum. 1996, 2783. (3) Bergbreiter, D. E.; Killough, J. M . J. Am. Chem. Soc. 1978,100, 2126. References begin on page 65 Chapter 4: Experimental Procedures 66 (4) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978,100, 3359. (5) Schlosser, M . ; Hartmann, J. Angew. Chem. Int. Ed. Engl. 1973,12, 508. (6) Perrin, D. D.; Armarego, W. L . F. Purification of Laboratory Chemicals; 3rd ed.; Butterworth-Heinemann Ltd., 1988. (7) Evans, D. F. J. Chem. Soc. 1959, 2003. (8) Personal communication with Mr. P. Borda, microanalysis technician. (9) Watt, G. W.; Chrisp, J. D. Anal. Chem. 1952, 24, 2006. (10) The cells used in our lab were 9.1,4.2, and 1.2 mL volumes References begin on page 65 FUTURE PROSPECTS The studies presented in this thesis have demonstrated the wide range of reaction chemistry possible for these new niobium [P2N2] compounds. This diversity of Nb(L)[P2N2] complexes stresses the need for further research within this area. Two general areas of focus are the continued physical characterization of these systems, and the further development of new reactions and products.. NbCl[P2N2] (1) has proven to be a useful starting material in many other compound syntheses. However, only a few alkyl systems have been looked at, leaving a wide range of other alkyls to be made. In addition, unsaturated ligands, such as olefins and alkynes, can be used to yield new complexes of niobium [P2N2]. Further work should be done on the protonation hydrolysis of {[P2N2]Nb}2(p>N2) (2), with an emphasis on obtaining information about the reaction mechanism. This must include a firm understanding of the intermediate structure formed by the addition of 1 equivalent of M e 3 N H C l to complex 2, as well as determining how the niobium species is reduced from a +4 to a +3 oxidation state. The rich chemistry of Nb(CH2SiMe3)[P2N2] (6) requires a continuation of in-depth work. This should include potential reactions with more small molecules, such as olefins and other unsaturated ligands. Since complex 6 has already been demonstrated to undergo oxidative addition, reductive elimination, and insertion chemistry, a complete study of this system could yield many possible reaction pathways. The importance of obtaining X-ray crystallographic molecular structures can not be stressed enough. The solid state structures will be able to show the correct binding Future Prospects arrangement for many of the complexes, such as Nb(r|5-C6H7)[P2N2] (8) and Nb(r)5-CH2Ph)[P2N2] (9). Structures of the paramagnetic compounds of NbCl[P2N2] (1) and Nb(CFJ.2SiMe3)[P2N2] (6) should be resolved in order to complete the characterization of these starting materials for future reactions. Although initial studies into the magnetics of NbCl[P2N2] (.1) and {[P2N2]Nb}2(|-t-N2) (2) were preformed, in-depth work is still needed on these systems, including detailed low temperature and solid state magnetic determinations. Further research may provide some insight into the temperature independent components of these complexes as well as the change in magnetism, from paramagnetic to diamagnetic, when particular ligands are modified. Further characterization of the new highly colored complexes presented in this thesis should include UV/Vis spectroscopy. In addition, infrared spectroscopy should be used in order to determine the v(CO) stretching frequencies during the reaction of Nb(CH2SiMe3)[P2N2] (6) with CO, as well as for the CO adduct of chloride 1. APPENDIX A.1 X-ray Crystallographic Analysis of {[P2N2]Nb}2(|-i-N2) A.1.1 Crystal Data Emperical Formula Formula Weight Crystal Color, Habit Crystal Dimensions Crystal System Lattice Type Lattice Parameters Space Group Z Value FOOO Li(MoKa) C48H84N6Nb2P4Si8 1279.62 brown, prism 0.35 X 0.40 X 0.45 mm monoclinic Primitive a = 16.1151 (11) A b = 15.887 (2) A c = 26.0621 (7) A (3=92.8130(4)° V = 6664.6 (7) A P2i/n (#14) 4 1.275 g/cm 3 2672.00 6.18 cm- 1 A. 1.2 Intensity Measurements Diffractometer Rigaku / ADSC C C D Appendix A.l: X-ray Crystallographic Analysis of{[P2N2]Nb)2(fJ--N2) Radiation Detector Aperture Data Images <|> oscillation Range (%=-90) co oscillation Range (%=-90.0) Detector Position Detector Swing Angle No. of Reflections Measured Corrections A.1.3 Structure Solution and Refinement Structure Solution Refinement Function Minimized Least Squares Weights p-factor Anomalous Dispersion No. Observations (to 26 = 60°) MoKoc (X = 0.71069 A) graphite monochromated 94 mm x 94 mm 920 exposures at 60.0 seconds 0.0 - 190.0° -22.0-18.0° 39.13(2) mm -10.00° 63.7° Total: 59032 Unique: 18134 ( R i n t = 0.047) Lorentz-polarization Absorption (trans, factors: 0.8322 - 1.0071) Patterson Methods ( D I R D I F 9 2 PATTY) Full-matrix least-squares Zco(IFo2l - IFc2/)2 CO = 1/[CT 2(FO 2)] 0.0000 A l l non-hydrogen atoms 16286 No. Variables 613 Appendix A. 1: X-ray Crystallographic Analysis of {[PiNjlNb]2(11-^2) Reflections / Parameter Ratio 26.57 Residuals (on F 2 ) : R: Rw 0.114; 0.124 Goodness of Fit Indicator 2.59 Max Shift / Error in Final Cycle 0.001 No. Observations (I>3q(I)) 8438 Residuals (on F, I>3cr(i)): R; Rw 0.073; 0.069 Maximum peak in Final Diff. Map 2.13 eVA 3 (near Nb) Minimum peak in Final Diff. Map -1.77 e-/A3 (nearNb) Table A . l : Atomic Coordinates and Beq atom X V z Nb(l) 0.48470(3) 0.25846(3) 0.37608(2) 2.341(10) Nb(2) 0.51783(3) 0.26330(3) 0.18735(2) 2.338(10) P(l) 0.53049(10) 0.40999(9) 0.39782(6) 3.41(4) P(2) 0.43243(10) 0.10621(9) 0.38641(6) 3.53(4) P(3) 0.36719(9) 0.22589(9) 0.15921(6) 3.19(5) P(4) 0.67279(9) 0.30132(10) 0.18547(6) 3:70(4) Si(D 0.35098(11) 0.39714(10) 0.41361(7) 4.04(4) Si(2) 0.63778(12) 0.29605(12) 0.46714(7) 4.73(5) Si(3) 0.60435(12) 0.11665(11) 0.43047(8) 4.63(5) Si(4) 0.31174(11) 0.21612(11) 0.44177(7) 4.28(5) Si(5) 0.39747(11) 0.40614(11) 0.13169(7) 4.02(4) Si(6) 0.47730(12) 0.10780(12) 0.10075(7) 5.11(5) Si(7) 0.65138(11) 0.12530(11) 0.14865(7) 4.44(5) Si(8) 0.58108(12) 0.42736(11) 0.11560(7) 4.77(5) Appendix A.l: X-ray Crystallographic Analysis of'{[F'2/V2/M>j'2(^-^2) N(l) 0.3698(3) 0.2908(3) 0.4115(2) 3.27(11) N(2) 0.5874(3) 0.2233(3) 0.4279(2) 3.44(11) N(3) 0.4996(3) 0.3769(3) 0.1429(2) 3.30(11) N(4) 0.5481(3) 0.1538(3) 0.1436(2) 3.48(11) N(5) 0.4977(2) 0.2600(2) 0.30584(14) 2.40(9) N(6) 0.5065(2) 0.2617(2) 0.25762(14) 2.41(9) C( l ) 0.4507(4) 0.4481(4) 0.4393(2) 4.7(2) C(2) 0.6276(4) 0.4027(4) ; 0.4351(2) 4.9(2) C(3) 0.5018(4) 0.0631(4) 0.4381(3) 5.1(2) C(4) 0.3277(4) 0.1125(3) 0.4099(2) 4.3(2) C(5) 0.3221(4) 0.4389(4) 0.3480(3) 5.9(2) C(6) 0.2692(4) 0.4327(4) 0.4581(3) 6.8(2) C(7) 0.5922(5) 0.3005(5) 0.5321(3) 7.8(3) C(8) 0.7550(5) 0.2818(5) 0.4777(3) 7-5(2) C(9) 0.6515(5) 0.0755(4) 0.3720(3) 6-7(2) C(10) 0.6714(5) 0.0796(5) 0.4860(4) 9.5(3) C ( l l ) 0.3452(6) 0.2068(5) 0.5116(3) 8.1(3) C(12) 0.1956(4) 0.2336(4) 0.4371(3) 6.8(2) C(13) 0.5447(4) 0.4931(3) 0.3513(3) 3.9(2) C(14) 0.5487(4) 0.4727(4) 0.3011(3) 4.8(2) C(15) 0.5638(5) 0.5337(5) 0.2636(3) 6.6(2) C(16) 0.5751(4) 0.6165(5) 0.2790(4) 6.8(2) C(17) 0.5707(4) 0.6373(4) 0.3298(4) 5.8(2) C(18) 0.5556(4) 0.5768(4) 0.3662(3) 4.9(2) C(19) 0.4270(4) 0.0279(4) 0.3344(3) 4.4(2) C(20) 0.4477(5) 0.0505(4) 0.2868(3) 7.0(2) C(21) 0.4401(6) -0.0066(5) 0.2456(3) 8.0(3) Appendix A.l: X-ray Crystallographic Analysis of {[P2N2WD) 2(11-^2) C(22) 0.4101(6) -0.0854(6) 0.2547(5) 9.8(4) C(23) 0.3912(7) -0.0516(6) 0.3024(5) 11.8(4) C(24) 0.3993(6) -0.0516(5) 0.3426(4) 9.2(3) C(25) 0.3352(4) 0.3090(4) 0.1147(2) 4.3(2) C(26) 0.3695(4) 0.1266(4) 0.1239(3) 4.8(2) C(27) 0.7154(4) 0.2248(4) 0.1421(2) 5.1(2) C(28) 0.6796(4) 0.4050(4) 0.1549(3) 5.2(2) C(29) 0.3548(4) 0.4548(4) 0.1894(3) 6.8(2) C(30) 0.3777(4) 0.4786(4) 0.0758(3) 7.3(2) C(31) 0.4823(5) 0.1564(6) 0.0345(3) 9.5(3) C(32) 0.4855(5) -0.0096(5) 0.0948(4) 9.0(3) C(33) 0.6795(4) 0.0778(4) 0.2128(3) 6.3(2) C(34) 0.6880(5) 0.0499(5) 0.0998(3) 7.6(3) C(35) 0.5971(5) 0.3891(5) 0.0491(3) 8.0(3) C(36) 0.5733(5) 0.5450(4) 0.1125(3) 7.2(2) C(37) 0.2844(3) 0.2140(3) 0.2031(2) 3.29(14) C(38) 0.2939(3) 0.2397(4) 0.2536(2) 4.4(2) C(39) 0.2342(4) 0.2309(4) 0.2888(2) 4.8(2) ' C(40) 0.1615(5) 0.1911(4) 0.2731(3) 6.0(2) C(41) 0.1497(4) 0.1633(4) 0.2241(4) 6.3(2) C(42) 0.2099(4) 0.1751(4) 0.1877(3) 53(2) C(43) 0.7447(4) 0,3033(3) 0.2412(3) 4.0(2). C(44) 0.7191(4) 0.2775(5) 0.2870(3) 5.7(2) C(45) 0.7724(5) 0.2776(6) 0.3311(3) 7.7(3) C(46) 0.8531(6) 0.3052(6) 0.3270(5) 8.0(3) C(47) 0.8790(5) 0.3316(5) 0.2819(4) 7.4(3) C(48) 0.8249(4) 0.3311(4) 0.2392(3) 6.1(2) APPENDIX A.2 X-ray Crystallographic Analysis of {[P2N2]Nb}2((i-N2)(ix-Cl) A.2.1 Crystal Data Emperical Formula Formula Weight Crystal Color, Habit Crystal Dimensions Crystal System Lattice Type Lattice Parameters Space Group Z Value FOOO }l(MoKa) C48H.84ClN6Nb2P4Si8 1315.08 red, needle 0 .10X0.15X0.45 mm monoclinic Primitive a = 12.1835 (9) A b = 39.764 (3) A c = 13.6941 (3) A p = 105.5604 (4) ° V = 6391.2 (6) A P2i/n (#14) 1.367g/cm3 2740.00 6.87 cm" 1 A.2.2 Intensity Measurements Diffractometer Rigaku / A D S C C C D Appendix A.2: X-ray Crystallographic Analysis of {[P2N2]Nb}2(lL-N2)(li-Cl) Radiation M o K a (k = 0.71069 A) graphite monochromated 94 mm x 94 mm 766 exposures at 120.0 seconds -22.0-18.0° 0.0 - 190.0° 39.13 (2) mm -10° 55.8° Total: 52874 Unique: 14255 (R;„, = 0.072) Lorentz-polarization Absorption (trans, factors: 0.8315 - 1.0041) Detector Aperture Data Images <|> oscillation Range (%=-90) co oscillation Range (%=-90.0) Detector Position Detector Swing Angle 2 Qmax No. of Reflections Measured Corrections A.2.3 Structure Solution and Refinement Structure Solution Refinement Function Minimized Least Squares Weights p-factor Anomalous Dispersion No. Observations (to 26 = 60°) Patterson Methods (DIRDIF92 PATTY) Full-matrix least-squares Eco(IFo2l - IFc2/)2 co = l/[a 2(Fo 2)] 0.0100 A l l non-hydrogen atoms 14255 No. Variables 650 Appendix A.2: X-ray Crystallographic Analysis of {[P2N2]Nb}2(H-N2)([i-Cl) Reflections / Parameter Ratio Residuals (on F 2 ) : R: Rw Goodness of Fit Indicator Max Shift / Error in Final Cycle No. Observations (I>3a(I)) Residuals (on F, I>3G(I)): R; Rw Maximum peak in Final Diff. Map Minimum peak in Final Diff. Map Table A.2: Atomic Coordinates and B, 21.93 0.137; 0.115 1.68 0.008 6087 0.058; 0.050 1.98 e-/A3 (nearNb) -2.28 e7A3 (near Nb) eq atom X V z Nb(l) 0.24921(4) 0.169761(11) 0.28323(3) 2.337(10) Nb(2) 0.24803(4) 0.082452(12) 0.26210(3) 2.623(11) Cl( l ) 0.1362(2) 0.12309(5) 0.3581(2) 2.34(5) Cl(la) 0.3626(3) 0.12765(9) 0.1921(3) 2.60(9) P(l) 0.09896(12) 0.18748(4) 0.12067(10) 2.88(3) P(2) 0.40204(11) 0.18175(3) 0.45243(9) 2.44(3) P(3) 0.41645(11) 0.06471(3) 0.41277(10) 2.71(3) P(4) 0.07889(12) 0.07011(4) 0.10576(10) 3.09(3) Si(l) -0.00308(13) 0.20423(4) 0.28857(11) 3.62(4) Si(2) 0.29869(13) 0.23735(4) 0.15182(11) 3.17(4) Si(3) 0.50225(12) 0.20260(4) 0.28495(10) 3.14(4) Si(4) 0.20026(13) 0.22570(4) 0.45257(11) 3.12(4) Si(5) 0.20832(14) 0.03888(5) 0.46202(12) 4.00(4) Si(6) 0.43398(14) 0.02406(4) 0.22555(13) 3.99(4) Si(7) 0.28956(15) 0.05903(6) 0.04163(13) 5.41(5) occ 0.637 0.363 Appendix A.2: X-ray Crystallographic Analysis off[P2N2]Nb)2(H-N2)(H-Cl) 77 Si(8) 0.06826(14) 0.01698(4) 0.25972(12) 3.66(4) N(l) 0.1434(3) 0.20427(9) 0.3407(3) 2.55(10) N(2) 0.3556(3) 0.20606(9) 0.2383(3) 2.42(9) N(3) 0.1732(3) 0.04316(10) 0.3316(3) 2.91(10) N(4) 0.3255(3) 0.05194(10) 0.1717(3) 3.17(11) N(5) 0.3428(5) 0.12700(15) 0.2775(7) 3.3(2) N(5a) 0.1537(9) 0.1257(3) 0.2655(10) 3.4(3) N(6) 0.2572(6) 0.1290(2) 0.1941(4) 2.9(2) N(6a) 0.2390(10) 0.1226(3) 0.3513(7) 2.2(3) C( l ) -0.0339(4) 0.18977(13) 0.1522(4) 3.50(13) C(2) 0.1402(4) 0.23101(12) 0.1051(3) 2.74(12) C(3) 0.5350(4) 0.18501(12) 0.4189(3) 2.80(12) C(4) 0.3606(4) 0.22396(11) 0.4797(3) 2.66(12) C(5) -0.0718(5) 0.2463(2) 0.2819(4) 5.3(2) C(6) -0.0816(5) 0.1766(2) 0.3581(4) 6.1(2) C(7) 0.3177(5) 0.28032(14) 0.2077(5) 5.3(2) C(8) 0.3606(5) 0.2384(2) 0.0415(4) •5.0(2) C(9) 0.5657(5) 0.1746(2) 0.2064(4) 6.1(2) C(10) 0.5787(4) 0.2438(2) 0.2966(4) 4.9(2) C ( l l ) 0.1668(5) 0.27159(15) 0.4488(5) 6.0(2) C(12) 0.1554(5) 0.2072(2) 0.5617(4) 4-6(2) C(13) 0.0800(5) 0.16976(13) -0.0046(4) 3.59(14) C(14) -0.0279(5) 0.16133(14) -0.0663(4) 4.4(2) G(15) -0.0385(7) 0.1492(2) -0.1655(5) 5.9(2) C(16) 0.0546(9) 0.1462(2) -0.2010(5) 6.6(2) C(17) 0.1617(8) 0.1543(2) -0.1402(5) 6.7(2) C(18) 0.1741(6) 0.1661(2) -0.0419(4) 5.2(2) 0.637 0.363 0.637 0.363 Appendix A.2: X-ray Crystallographic Analysis of{[P2N2]Nb}2(fJ--N2)(li-Cl) C(19) 0.4309(4) 0.16152(12) 0.5765(3) 2.69(12) C(20) 0.3503(5) 0.14062(14) 0.5989(4) 3.39(14) C(21) 0.3702(5) 0.12645(14) 0.6958(4) 4.05(15) C(22) 0^4683(5) 0.13344(15) 0.7684(4) 4.2(2) C(23) 0.5492(5) 0.15416(15) 0.7471(4) 4.06(15) C(24) 0.5305(4) 0.16789(13) 0.6514(4) 3.50(13) C(25) 0.3574(5) 0.05540(13) 0.5164(4) 3.65(14) C(26) 0.4548(4) 0.02429(12) 0.3674(4) 3.51(14) C(27) 0.1362(5) 0.07386(15) -0.0015(4) 4.28(15) C(28) 0.0559(4) 0.02620(13) 0.1226(4) 3.41(13) C(29) 0.2108(6) -0.0058(2) 0.5080(5) 6.5(2) C(30) 0.1122(5) 0.0622(2) 0.5235(5) 7.2(2) C(31) 0.4015(7) -0.02111(15) 0.1892(5) 6.6(2) C(32) 0.5702(5) 0,0341(2) 0.1944(5) 6:0(2) C(33) 0.2965(6) 0.0202(2) -0.0327(5) 9.4(3) G(34) 0.3825(6) 0.0913(3) 0.0013(6) 10,9(3) C(35) 0.0976(6) -0.02967(15) 0.2730(5) . 6.4(2) C(36) -0.0716(5) 0.0235(2) 0.2863(4) 5.9(2) C(37) 0.5538(4) 0.08531(12) 0.4613(4) 3.13(13) C(38) 0.6141(5) 0.09595(14) 0.3953(4) 4.05(15) C(39) 0.7234(6) 0.10860(15) 0.4292(6) 5.2(2) C(40) 0.7717(5) 0.1114(2) 0.5312(6) 5.5(2) C(41) 0.7150(6) 0.1016(2) 0.5992(5) 5-5(2) C(42) 0.6060(5) 0.08799(14) 0.5649(4) 4.15(15) C(43) -0.0664(4) 0.08698(13) 0.0718(4) 3.26(13) C(44) -0.1103(5) 0.10144(15) 0.1452(4) 4.14(15) C(45) -0.2210(5) 0.1132(2) 0.1232(5) 4.9(2) Appendix A.2: X-ray Crystallographic Analysis of {[P2N2lNb}2(lA-N2)(fL~Cl) C(46) -0.2891(5) 0.11022(15) 0.0250(5) 4.7(2) C(47) -0.2475(5) 0.0961(2) -0.0490(5) 4.8(2) C(48) -0.1356(5) 0.08458(14) -0.0265(4) 4.3(2) Beq = (8/3)TC2{Uii(aa*)2+U22(^*)2+U33(cc*)2+ 2Ui2aa*^&*cosY+2Ui3aa*cc*cosP+2U23&fo*cc*cosa} APPENDIX A.3 Calibration Data for the Determination of Hydrazine Table A.3 Absorbance Data of Standard Hydrazine Concentrations Hydrazine Concentration (ppm) (± 0.00002) A458 (± 0.0005) 0.03139 0.0701 0.06278 0.1366 0.09418 0.2088 0.12557 0.2712 0.15696 0.3419 0.18835 0.4127 0.21974 0.4806 0.25114 0.5512 0.28253 0.6180 0.31392 0.6831 0.34531 0.7528 0.37670 0.8217 0.40810 0.8867 0.43949 0.9585 0.47088 1.0253 0.50227 1.0900 0.53366 1.1604 Linear Least Squares Regression Equation: A45g = 0.0023329 + 2.1716[hydrazine] 

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