Bonding and Reactivity of Gallium and Aluminium Coordination Complexes

<p>This thesis describes the synthesis, structures and reactivities of gallium and aluminium complexes supported by β-diketiminato ligands ([CR{C(R)N(R’)}₂]-, abbrev. [(BDIR’)]-). Chapter 1 gives a general introduction into the trends and properties that distinguish the heavier p-block elements from their lighter counterparts. An introduction into the theory of multiple bond formation, both homonuclear and heteronuclear, in the heavy p-block elements is provided and a summary of the sterically demanding ligands required to stabilise these complexes is introduced. The β-diketiminato ligand framework utilised in this study is introduced and the methods of generation of low valent gallium and aluminium complexes supported by the BDIDIPP ligand are discussed. Chapter 2 discusses the reactivity of the complex BDIDIPPGa with diazo- compounds in the quest to isolate a complex with a formal gallium-carbon double bond. BDIDIPPGa reacts with two equivalents of both trimethylsilyldiazomethane and diazofluorene, presumably through the target gallium-carbon double bond intermediate. No reaction is observed with di-tert-butyldiazomethane, while BDIDIPPGa catalyses the decomposition of diphenyldiazomethane into tetraphenylethene. Three new β-diketiminato gallium(I) complexes were synthesised: ArBDIDIPPGa, BDIAr*Ga and BDIAr’Ga. ArBDIDIPPGa also reacted with two equivalents of trimethylsilyldiazomethane, presumably through the target gallium-carbon double bond intermediate. BDIAr*Ga and BDIAr’Ga both inserted into the C-H bond of trimethylsilyldiazomethane to give BDIAr*Ga(H)C(N2)SiMe₃ and BDIAr’Ga(H)C(N2)SiMe₃ respectively. Upon addition of diazofluorene to BDIAr*Ga, one of the aromatic protons of the BDIAr* ligand was abstracted by the diazofluorene, resulting in coordination of one of the flanking phenyl groups to the gallium centre. Chapter 3 discusses an investigation into the formation of formal double bonds between aluminium and phosphorus, and gallium and phosphorus. The proposed ‘deprotonation/elimination’ method, reacting BDIDIPPM(PHAr)Cl (M = Al, Ga Ar = Ph, Mes) with nBuLi, resulted in the formation of intractable mixtures of products. Direct synthesis by the addition of MesPLi₂ to BDIDIPPMCl₂ (M = Al, Ga) resulted in the formation of BDIDIPPM(PHMes)Cl (M = Al, Ga). Changing the elimination product to TMS-Cl, through the synthesis of BDIDIPPM(P(TMS)Ph)Cl (M = Al, Ga), resulted in the synthesis of BDIDIPPAl(P(TMS)Ph)Cl, which showed no signs of elimination occurring upon heating to 110 °C. BDIDIPPGa(P(TMS)Ph)Cl could not be isolated, potentially as the complex was undergoing the desired elimination of TMS-Cl, but the resulting complex was decomposing. Changing the elimination product to ethane, through the synthesis of BDIDIPPAl(PHMes)Et, resulted in no sign of elimination occurring upon heating to 110 °C. Reduction of BDIDIPPMCl₂ (M = Al, Ga) in the presence of bistrimethylsilylacetylene, as part of the synthesis of BDIDIPPMLi₂ (M = Al, Ga) salts, was unsuccessful, as was the reaction of BDIDIPPGa with bistrimethylsilylacetylene. Reduction of MesPCl₂ with potassium metal in the presence of BDIDIPPGa resulted in an intractable mixture of products, reduction with magnesium resulted in the formation of (MesP)₃ and (MesP)₄. Addition of MesPH₂ to BDIDIPPGa resulted in the formation of BDIDIPPGa(H)P(H)Mes, which did not undergo H₂ elimination at 110 °C. The synthesis of BDIDIPPAl was unsuccessful as the product could not be isolated cleanly. The synthesis of ArBDIDIPPAl resulted in the intramolecular rearrangement of the ligand to give a five-membered aluminium containing ring. The synthesis of BDIAr*Al stalled at the formation of BDIAr*Al(Me)I due to the steric bulk of the ligand blocking the second substitution of iodine from occurring. Chapter 4 discusses the reactivity of the primary phosphanide complexes BDIDIPPAl(PHMes)Cl, BDIDIPPAl(PHMes)Et and BDIDIPPGa(H)P(H)Mes with phenyl acetylene, 4-nitro-phenyl isocyanate, phenyl isothiocyanate, dicyclohexyl carbodiimide, cyclohexene, benzophenone, benzaldehyde, selenium, sulfur, and methyl iodide. Reactivity was not observed for phenyl acetylene, dicyclohexyl carbodiimide or benzophenone with any of the phosphanides. Reactivity with the phosphanides was observed with cyclohexene, however rapid decomposition of the products occurred and they were unable to be identified. BDIDIPPAl(PHMes)Cl and BDIDIPPGa(H)P(H)Mes showed no reactivity with benzaldehyde, however, the ethyl ligand of BDIDIPPAl(PHMes)Et reacted with the aldehyde proton, eliminating ethane and substituting the PhC(O)- ligand onto the aluminium centre. Reactivity with the phosphanides was observed with both sulfur and selenium, however multiple different products were formed, none of which were successfully isolated. Reactivity between the phosphanides and methyl iodide was observed, with the P-M bond appearing to be cleaved and formation of a M-I bond occurring. 4-nitro-phenyl isocyanate and phenyl isothiocyanate underwent insertion reactions into the M-P bond, however only BDIDIPPAl(Cl)N(4-NO₂-Ph)C(O)P(H)Mes was able to be isolated and fully characterised. Finally, chapter 5 summarises the results of this research and provides an outlook at the future direction of this field of research.</p>

Bonding and Reactivity of Gallium and Aluminium Coordination Complexes

<p>This thesis describes the synthesis, structures and reactivities of gallium and aluminium complexes supported by β-diketiminato ligands ([CR{C(R)N(R’)}₂]-, abbrev. [(BDIR’)]-). Chapter 1 gives a general introduction into the trends and properties that distinguish the heavier p-block elements from their lighter counterparts. An introduction into the theory of multiple bond formation, both homonuclear and heteronuclear, in the heavy p-block elements is provided and a summary of the sterically demanding ligands required to stabilise these complexes is introduced. The β-diketiminato ligand framework utilised in this study is introduced and the methods of generation of low valent gallium and aluminium complexes supported by the BDIDIPP ligand are discussed. Chapter 2 discusses the reactivity of the complex BDIDIPPGa with diazo- compounds in the quest to isolate a complex with a formal gallium-carbon double bond. BDIDIPPGa reacts with two equivalents of both trimethylsilyldiazomethane and diazofluorene, presumably through the target gallium-carbon double bond intermediate. No reaction is observed with di-tert-butyldiazomethane, while BDIDIPPGa catalyses the decomposition of diphenyldiazomethane into tetraphenylethene. Three new β-diketiminato gallium(I) complexes were synthesised: ArBDIDIPPGa, BDIAr*Ga and BDIAr’Ga. ArBDIDIPPGa also reacted with two equivalents of trimethylsilyldiazomethane, presumably through the target gallium-carbon double bond intermediate. BDIAr*Ga and BDIAr’Ga both inserted into the C-H bond of trimethylsilyldiazomethane to give BDIAr*Ga(H)C(N2)SiMe₃ and BDIAr’Ga(H)C(N2)SiMe₃ respectively. Upon addition of diazofluorene to BDIAr*Ga, one of the aromatic protons of the BDIAr* ligand was abstracted by the diazofluorene, resulting in coordination of one of the flanking phenyl groups to the gallium centre. Chapter 3 discusses an investigation into the formation of formal double bonds between aluminium and phosphorus, and gallium and phosphorus. The proposed ‘deprotonation/elimination’ method, reacting BDIDIPPM(PHAr)Cl (M = Al, Ga Ar = Ph, Mes) with nBuLi, resulted in the formation of intractable mixtures of products. Direct synthesis by the addition of MesPLi₂ to BDIDIPPMCl₂ (M = Al, Ga) resulted in the formation of BDIDIPPM(PHMes)Cl (M = Al, Ga). Changing the elimination product to TMS-Cl, through the synthesis of BDIDIPPM(P(TMS)Ph)Cl (M = Al, Ga), resulted in the synthesis of BDIDIPPAl(P(TMS)Ph)Cl, which showed no signs of elimination occurring upon heating to 110 °C. BDIDIPPGa(P(TMS)Ph)Cl could not be isolated, potentially as the complex was undergoing the desired elimination of TMS-Cl, but the resulting complex was decomposing. Changing the elimination product to ethane, through the synthesis of BDIDIPPAl(PHMes)Et, resulted in no sign of elimination occurring upon heating to 110 °C. Reduction of BDIDIPPMCl₂ (M = Al, Ga) in the presence of bistrimethylsilylacetylene, as part of the synthesis of BDIDIPPMLi₂ (M = Al, Ga) salts, was unsuccessful, as was the reaction of BDIDIPPGa with bistrimethylsilylacetylene. Reduction of MesPCl₂ with potassium metal in the presence of BDIDIPPGa resulted in an intractable mixture of products, reduction with magnesium resulted in the formation of (MesP)₃ and (MesP)₄. Addition of MesPH₂ to BDIDIPPGa resulted in the formation of BDIDIPPGa(H)P(H)Mes, which did not undergo H₂ elimination at 110 °C. The synthesis of BDIDIPPAl was unsuccessful as the product could not be isolated cleanly. The synthesis of ArBDIDIPPAl resulted in the intramolecular rearrangement of the ligand to give a five-membered aluminium containing ring. The synthesis of BDIAr*Al stalled at the formation of BDIAr*Al(Me)I due to the steric bulk of the ligand blocking the second substitution of iodine from occurring. Chapter 4 discusses the reactivity of the primary phosphanide complexes BDIDIPPAl(PHMes)Cl, BDIDIPPAl(PHMes)Et and BDIDIPPGa(H)P(H)Mes with phenyl acetylene, 4-nitro-phenyl isocyanate, phenyl isothiocyanate, dicyclohexyl carbodiimide, cyclohexene, benzophenone, benzaldehyde, selenium, sulfur, and methyl iodide. Reactivity was not observed for phenyl acetylene, dicyclohexyl carbodiimide or benzophenone with any of the phosphanides. Reactivity with the phosphanides was observed with cyclohexene, however rapid decomposition of the products occurred and they were unable to be identified. BDIDIPPAl(PHMes)Cl and BDIDIPPGa(H)P(H)Mes showed no reactivity with benzaldehyde, however, the ethyl ligand of BDIDIPPAl(PHMes)Et reacted with the aldehyde proton, eliminating ethane and substituting the PhC(O)- ligand onto the aluminium centre. Reactivity with the phosphanides was observed with both sulfur and selenium, however multiple different products were formed, none of which were successfully isolated. Reactivity between the phosphanides and methyl iodide was observed, with the P-M bond appearing to be cleaved and formation of a M-I bond occurring. 4-nitro-phenyl isocyanate and phenyl isothiocyanate underwent insertion reactions into the M-P bond, however only BDIDIPPAl(Cl)N(4-NO₂-Ph)C(O)P(H)Mes was able to be isolated and fully characterised. Finally, chapter 5 summarises the results of this research and provides an outlook at the future direction of this field of research.</p>

Src activates retrograde membrane traffic through phosphorylation of GBF1

The Src tyrosine kinase controls cancer-critical protein glycosylation through Golgi to ER relocation of GALNTs enzymes. How Src induces this trafficking event is unknown. Golgi to ER transport depends on the GTP Exchange factor (GEF) GBF1 and small GTPase Arf1. Here we show that Src induces the formation of tubular transport carriers containing GALNTs. The kinase phosphorylates GBF1 on 10 tyrosine residues; two of them, Y876 and Y898 are located near the C-terminus of the Sec7 GEF domain. Their phosphorylation promotes GBF1 binding to the GTPase; molecular modeling suggests partial melting of the Sec7 domain and intramolecular rearrangement. GBF1 mutants defective for these rearrangements prevent binding, carrier formation and GALNTs relocation, while phosphomimetic GBF1 mutants induce tubules. In sum, Src promotes GALNTs relocation by promoting GBF1 binding to Arf1. Based on residue conservation, similar regulation of GEF-Arf complexes by tyrosine phosphorylation could be a conserved and wide-spread mechanism.

Molecular basis of enzymatic nitrogen-nitrogen formation by a family of zinc-binding cupin enzymes

Molecules with a nitrogen-nitrogen (N-N) bond in their structures exhibit various biological activities and other unique properties. A few microbial proteins are recently emerging as dedicated N-N bond forming enzymes in natural product biosynthesis. However, the details of these biochemical processes remain largely unknown. Here, through in vitro biochemical characterization and computational studies, we report the molecular basis of hydrazine bond formation by a family of di-domain enzymes. These enzymes are widespread in bacteria and sometimes naturally exist as two standalone enzymes. We reveal that the methionyl-tRNA synthase-like domain/protein catalyzes ATP-dependent condensation of two amino acids substrates to form a highly unstable ester intermediate, which is subsequently captured by the zinc-binding cupin domain/protein and undergoes redox-neutral intramolecular rearrangement to give the N-N bond containing product. These results provide important mechanistic insights into enzymatic N-N bond formation and should facilitate future development of novel N-N forming biocatalyst.

Electrosynthesis of 1,4-bis(diphenylphosphanyl) tetrasulfide via sulfur radical addition as cathode material for rechargeable lithium battery

Organic electrodes are promising as next generation energy storage materials originating from their enormous chemical diversity and electrochemical specificity. Although organic synthesis methods have been extended to a broad range, facile and selective methods are still needed to expose the corners of chemical space. Herein, we report the organopolysulfide, 1,4-bis(diphenylphosphanyl)tetrasulfide, which is synthesized by electrochemical oxidation of diphenyl dithiophosphinic acid featuring the cleavage of a P–S single bond and a sulfur radical addition reaction. Density functional theory proves that the external electric field triggers the intramolecular rearrangement of diphenyl dithiophosphinic acid through dehydrogenation and sulfur migration along the P–S bond axis. Impressively, the Li/bis(diphenylphosphanyl)tetrasulfide cell exhibits the high discharge voltage of 2.9 V and stable cycling performance of 500 cycles with the capacity retention of 74.8%. Detailed characterizations confirm the reversible lithiation/delithiation process. This work demonstrates that electrochemical synthesis offers the approach for the preparation of advanced functional materials.

Cascade intramolecular rearrangement/cycloaddition of nitrocyclopropane carboxylates with alkynes/alkenes: access to uncommon bi(hetero)cyclic systems

A straightforward approach for the one-pot synthesis of fused bi(hetero)cyclic systems via cascade intramolecular rearrangement/cycloaddition reaction of nitrocyclopropane carboxylates with substituted alkynes/alkenes has been demonstrated.