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Investigations Into the Reactivity of an Anionic Gallium(I) TV

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Investigations into the Reactivity of an Anionic Gallium(I) TV- Heterocyclic Carbene Analogue by David P. Mills Thesis presented to the School of Chemistry, Cardiff University, for the degree of Doctor of Philosophy, November 2007 UMI Number: U585026 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U585026 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 Declaration This work has not previously been accepted in substance for any degree and is not concurrently submitted in candidature for any degree. Signed .... Dj .M*/.!?: (candidate) Date . f.! /{?.?................. Statement 1 This thesis is being submitted in partial fulfilment of the requirements for the degree of PhD. Signed ... .^0. .M illh (candidate) Date fl/! (P§................... Statement 2 This thesis is the result of my own independent work/investigation, except where otherwise stated. Other sources are acknowledged by explicit references. Signed ... .bl.. ...................................... (candidate) Date .. .C. Statement 3 I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to outside organisations. Signed .. f h l h (candidate) Date . ................. Summary This thesis is mainly concerned with investigations into the reactivity of the gallium(I) ^-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)] 2 }] (Ar = C6H3PrV 2 ,6 ). Reactions of germanium, tin and lead alkyls, aryls, halides and heterocycles with [K(tmeda)][:Ga{[N(Ar)C(H)] 2 }] afforded complexes such as [K(tmeda)][Sn{CH(SiMe 3)2 }2 {Ga{[N(Ar)C(H)]2 }}], which exhibits the first structurally characterised Ga—Sn bond in a molecular complex. Group 6 , 9 and 11 metal halide complexes were treated with [K(tmeda)][:Ga{[N(Ar)C(H)] 2 }], yielding complexes such as [(IPr)Cu{Ga{[N(Ar)C(H)] 2 }}] and [(IPr)Ag{Ga{[N(Ar)C(H)] 2 }}]. These complexes exhibit the first structurally characterised Ga—Cu and Ga—Ag bonds in molecular complexes. A study of the reactivity of [(lPr)Cu{Ga{[N(Ar)C(H)] 2 }}] with unsaturated organic substrates suggested that the Ga—Cu bond is quite inert. Salt metathesis reactions of group 1 0 metal halide complexes with [K(tmeda)] [:Ga{[N(Ar)C(H)]2 }] afforded complexes such as [(dppe)Pt{Ga{[N(Ar)C(H)] 2 } h ]. An investigation into the further reactivity of this complex towards /er/-butylphosphaalkyne yielded a platinum(II) complex, [(dppe)Pt{Ga{[N(Ar)C(H)] 2 }}{Ga{[PC(Bul)C(H)- (NAr)C(H)N(Ar)]}}], which exhibits a formally anionic P,N-heterocyclic gallium(I) ligand. The kinetics of the formation of this complex were studied. A novel gallium(III) complex, [Gal 2 {C(But)P(H)C(But)=P}]2, was formed by the disproportionation reaction of [:Sn(ri 4-P2C2But2)] with “Gal”. The oxidative insertion reaction of [K(tmeda)] [:Ga{[N(Ar)C(H)] 2 }] with FisoH yielded the gallium(III) hydride, [{N(Ar)C(H)N(Ar)-K}(H)Ga{[N(Ar)C(H)] 2 }]. Reaction of the digallane(4), [Ga{[N(Ar)C(H)]2 }]2, with N 3-SiMe3 afforded the paramagnetic complex, [{p- N(SiMe3)}Ga{[N(Ar)C(H)]2'}]2, which was studied by EPR spectroscopy. A synthetic route to the novel gallium(I) NHC analogue, [K(tmeda)][:Ga{[N(Ar)C(Me)] 2 }], is also described. Work performed in Monash University, involving bulky amidinate and guanidinate ligands, is also discussed. A novel cationic boron heterocycle, [BrB(Giso)]+ (Giso" = [{N(Ar)} 2CNCy2]~), was synthesised from BBr 3 and the gallium(I) guanidinate, [:Ga(Giso)]. The use of [Sm(Giso) 2] as a one-electron reducing agent is exploited in the coupling of two molecules of CS 2 by formation of a C—S bond to yield [{Sm(Giso) 2 }2(p-Tl 2 :ti2-SCSCS2)]. The synthesis of novel r|6-arene rhodium(I) complexes such as [(q 4-COD)Rh(q 6-Giso)], and their thermal conversion into thermodynamically more stable rj2-chelating forms, are also reported. Acknowledgements Thanks go to Cameron for his excellent supervision and getting the most out of me by providing an interesting and rewarding project. 1 am sure that I wouldn’t have been as productive if it were not for his David Brent-esque man-management skills. 1 would also like to thank Andreas for performing X-ray crystallography, Shaun for DFT studies, Damien for EPR spectroscopy and Rob for kinetic experiments using NMR spectroscopy. I must acknowledge all of the helpful and friendly technical and support staff in Cardiff and Monash. Thanks go to everyone in team HOMO (Bob, Andreas, Richard, Christian H., Glesni, Ben, Dan, Amim, Timo, Christian S., Shaun, Kai, Graeme, Jade, Jamella and Dennis) for great times during the last three years. I would especially like to thank Bob for teaching me Schlenk techniques. I must thank all of my friends and family for being there whenever 1 need them. Finally, 1 would like to thank Caroline for always being supportive and making me happy. I couldn’t have done this without her. Dedicated to the memory of Harry Bramwell Fowler. Table of Contents Glossary V Chapter 1 General Introduction 1 .1 The Physical and Chemical Properties of the Group 13 Elements 1 1 .2 Subvalent Group 13 Chemistry 5 1.3 Preparation and Chemistry of the Metal Diyls 7 1.4 The Importance of the jV-Heterocyclic Carbene Class of Ligand 11 1.5 Theoretical Studies on Group 13 NHC Analogues 15 1 .6 The Synthesis and Coordination Chemistry of NHC Analogues 23 1 .6 .1 Four-Membered Group 13 Metal(I) Guanidinate Complexes 23 1 .6 . 2 Five-Membered Analogues of 2,3-Dihydro-imidazol-2-ylidenes 27 1.6.3 Six-Membered Group 13 p-Diketiminate Complexes 34 1.7 References 43 Chapter 2 Complexes of an Anionic Gallium(I) TV-Heterocyclic Carbene Analogue with Group 14 Element(II) Fragments 2.1 Introduction 53 2.2 Research Proposal 59 2.3 Results and Discussion 59 2.3.1 Preparation of Ionic Complexes 59 2.3.2 Preparation of Covalent Complexes 76 2.4 Conclusion 80 2.5 Experimental 81 2.6 References 89 Chapter 3 The Synthesis and Reactivity of Transition Metal Gallyl Complexes Stabilised by TV-Heterocyclic Carbene Coordination 3.1 Introduction 93 3.1.1 Transition Metal Gallyl Complexes Incorporating the Heterocycle, 93 [:Ga{[N(Ar)C(H)]2}]- 3.1.2 Transition Metal Boryl Complexes 101 3.2 Research Proposal 103 3.3 Results and Discussion 103 3.3.1 The Preparation of a Group 6 Metal Gallyl Complex 103 3.3.2 The Preparation of a Group 9 Metal Gallyl Complex 107 3.3.3 The Preparation of Group 11 Metal Gallyl Complexes 109 3.3.4 The Reactivity of Group 11 Metal(I) Gallyls with Unsaturated Substrates 121 3.4 Conclusion 130 3.5 Experimental 130 3.6 References 141 Chapter 4 The Preparation of Novel Group 10 Metal Gallyl Complexes 4.1 Introduction 146 4.2 Research Proposal 148 4.3 Results and Discussion 148 4.3.1 The Preparation of Metal Gallyl Complexes with Monodentate 148 Phosphines 4.3.2 The Preparation of Metal Gallyl Complexes with Chelating Ligands 161 4.3.3 The Reactivity of Chelated Metal Gallyl Complexes with Unsaturated 172 Substrates 4.4 Conclusion 183 4.5 Experimental 184 4.6 References 194 Chapter 5 The Preparation of Novel Gallium(I), (II) and (III) Heterocycles 5.1 Introduction 198 5.1.1 The Reactivity of “Gal” 198 5.1.2 The Oxidation Chemistry of the Heterocycle, [:Ga{[N(Ar)C(H)] 2 }]~ 199 5.1.3 Reactivity of the Digallane(4), [Ga{[N(Ar)C(H)] 2}]2 2 0 0 5.2 Research Proposal 2 0 0 5.3 Results and Discussion 2 0 1 5.3.1 The Reactivity of “Gal” 2 0 1 iii 5.3.2 Investigations into the Oxidation of the Heterocycle, 204 [:Ga{[N(Ar)C(H)]2}]- 5.3.3 The Reactivity of the Digallane(4), [Ga{[N(Ar)C(H)] 2}]2 209 5.3.4 Investigations into the Preparation of Novel Gallium(I) 216 Heterocyclic Compounds 5.4 Conclusion 225 5.5 Experimental 226 5.6 References 232 Chapter 6 The Preparation and Reactivity of Novel Amidinate and Guanidinate Complexes 6.1 Introduction 235 6.2 Research Proposal 242 6.3 Results and Discussion 243 6.3.1 The Reactivity of the Heterocycle, [:Ga{ [N( Ar)] 2CNCy2 } ] 243 6.3.2 The Reactivity of the Samarium(II) Complex, [Sm(Giso) 2] 246 6.3.3 Preparation of Rhodium(I) Amidinate and Guanidinate Complexes 250 6.4 Conclusion 266 6.5 Experimental 266 6 . 6 References 273 Appendix 1 General Experimental Procedures 276 Appendix 2 Publications in Support of this Thesis 277 Glossary 18-crown-6 1,4,7,10,13,16-hexaoxacyclooctadecane A Angstrom, 1 x 10 ' 10 m do Hyperfine coupling value ab initio A quantum chemistry method Ar, Ar\ Ar", Ar*, Ar* A general aryl substituent ArF, ArF\ ArF", ArF'" A general fluorinated aryl substituent Ar-DAB WV-Bis(diisopropylphenyl)diazabutadiene br.
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  • Gallium Nitride Phosphide Absorber for Silicon-Based Solar Power Researchers Achieve 3X Efficiency of Best Gallium Phosphide Solar Cell to Date

    Gallium Nitride Phosphide Absorber for Silicon-Based Solar Power Researchers Achieve 3X Efficiency of Best Gallium Phosphide Solar Cell to Date

    Technology focus: Photovoltaics 71 Gallium nitride phosphide absorber for silicon-based solar power Researchers achieve 3x efficiency of best gallium phosphide solar cell to date. esearchers in the USA have been working on that conversion efficiencies up to 45% could be gallium nitride phosphide (GaNP) as an absorb- achieved from an AM1.5G solar spectrum with a III-V Ring material for solar power [S. Sukrittanon et material on silicon. al, Appl. Phys. Lett., vol107, p153901, 2015]. The aim Gallium phosphide is one contender for such a top cell of the team from University of California San Diego since it is near lattice matched (0.37% mismatch) and (UCSD) and Sandia National Laboratories is to create a has a suitable bandgap of 2.26eV. Unfortunately GaP suitable sub-cell to boost the performance of silicon- has an indirect bandgap, which makes for inefficient based photovoltaic power conversion. Theory suggests photon conversion to electric power. Figure 1. Cross-sections of GaP control and GaNP solar cells. Inset: x-ray diffraction (XRD) spectra. www.semiconductor-today.com semiconductorTODAY Compounds&AdvancedSilicon • Vol. 10 • Issue 10 • December 2015/January 2016 72 Technology focus: Photovoltaics With the addition of only 0.4% of nitrogen into GaP, giving GaNP, the bandgap becomes direct, shifting absorption coefficients from 102–103/cm towards 104/cm. Further, at a nitro- gen concentration of 2%, GaNP becomes lattice matched with silicon. The UCSD/Sandia researchers achieved effi- ciencies up to 7.9% without a window layer. The team comments: “This GaNP solar cell’s efficiency is 3x higher than the most effi- cient GaP solar cell to date and higher than other solar cells with similar direct bandgap (InGaP, GaAsP).” They add: “These perform- ance gains are expected to motivate further investiga- tion into the integration of GaNP into future dual- junction solar cells on sili- con substrate.” The solar cells were grown on GaP substrates by molecular beam epitaxy (MBE) at 570°C (Figure 1).