Download or read book Chemical and Redox Non innocence in Iminopyridine and Bis imino pyridine Aluminum III Complexes Including Polar Bond Activation and Catalytic Dehydrogenation by superscript Ph I2P2 Al THF H superscript Ph I2P written by Thomas Winfield Myers and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation discusses the synthesis, reactivity and characterization of iminopyridine and bis(imino)pyridine complexes of aluminum and other electrophilic main group metal ions. It is shown that aluminum complexes of iminopyridine ligands can undergo stoichiometric redox transformations while aluminum complexes of bis(imino)pyridine ligands can facilitate heterolytic substrate activation and catalytic dehydrogenation reactions. In chapter 2, the reaction of disulfides, nitrogen group transfer reagents, and zinc(II) salts with [Na(THF)6][(IP2−)2Al] (2.1c) (IP = 2,6-bis(isopropyl)-N-(2-pyridinyl-methylene)phenylamine) affords aluminum complexes of the form (IP−)2AlX (X = Cl 2.2, [mu]2-SSCN(CH3)2 2.4, SCH3 2.5, NaNTs 2.6, CCPh 2.7, N3 2.8, SPh 2.9, and NHPh 2.10). Additionally, the oxidation of (IP−)2Al(Me) (2.3) by single electron oxidants leads to formation of [(IP−)(IP)Al(Me)]+. When TrBPh4 (Tr = triphenylmethyl) is employed as the oxidant, carbon-carbon coupling between one of the IP ligands and the Tr group is observed to form [(TrIP)(IP)Al(Me)]+ (2.11). This bond formation can be reversed when bulkier anions are added, or can be avoided by using TrB(C6F5)4 and TrBAr[superscript F] as the one electron oxidants. In chapter 3, the formation of Al(III) and Ga(III) oxo intermediates are proposed resulting from the oxidation of [(IP2−)2M]− (M = Al, Ga) with pyO (pyO = pyridine-N-oxide). These reactive intermediates homolytically and heterolytically cleave C-H bonds to form [Na(DME)(THF)][(IP2−)(IP−)Al(OH)] (3.3) and (IP−)2M(OH) (M = Al 3.4, Ga 3.7). The identity of the counter cation directs the reactivity of [(IP2−)2Al]−. When [Na(DME)3][(IP2−)2Al] is employed, C-H activation of solvent is observed, while when [Bu4N][(IP2−)2Al] is employed proton abstraction from Bu4N+ is observed. The oxidation of [(IP2−)2Ga]− by pyO leads to acid base chemistry when either Na+ or Bu4N+ is employed as the counter cation. The reaction of 3.4 and 3.7 with CO2 leads to formation of [(IP−)2M]2([mu][eta]1:[kappa]2-OCO2) (M = Al 3.10, Ga 3.11). Reduction of 3.10 and 3.11 with alkali or alkali earth metals and subsequent oxidation allows for the reformation of 3.4 and 3.7. In chapter 4, the reduction of [superscript Me]IP[subscript Mes] ([superscript Me]IP[subscript Mes] = 2,6-bis(isopropyl)-N-(2-(5-mesityl-pyridinyl)-methylene)phenylamine) with sodium metal followed by metathesis with MCl[subscript n]X[subscript 3-n] (M = Al, Ga, X = Cl, CH3) leads to the formation of ([superscript Me]IP[subscript Mes−)MX2 (M = Al, X = Cl, 4.1a, 4.2a; M = Ga, X = Cl 4.5), ([superscript CH2]IP[subscript Mes]−)AlX2 (X = Cl, 4.1b, 4.2b), ([superscript Me]IP[subscript Mes]2−)MX(OEt2) (M = Al, X = Cl, 4.3, 4.4; M = Ga, X = Cl 4.6) . Unlike the IP ligand system, only one [superscript Me]IP[subscript Mes] ligand coordinates to the metal center in these complexes. Selective deprotonation of the [superscript Me]IP[subscript Mes] ligand is observed in ether solvents, while selective reduction is observed in alkane and aromatic solvents. In chapter 5, complexes of bis(imino)pyridine ligands with aluminum are presented. Reduction of [superscript Ph]I2P ([superscript Ph]I2P = 2,6-(2,6-[superscript i]Pr2-C6H3N=CPh)2C5H3N) by 2 equivalents of sodium metal followed by salt metathesis with AlCl2X (X = Cl, H) affords ([superscript Ph]I2P2−)AlX(THF) (X = Cl 5.1, H 5.2a) and ([superscript Ph]I2P2−)AlH (5.2b). The [superscript Ph]I2P2− ligands in these complexes are shown to be chemically non-innocent. The addition of polar N-H and O-H bonds across the aluminum-amido bonds leads to the formation of ([superscript Ph]HI2P2−)AlH(X) (X = NHDipp 5.3a, NHPh 5.3b, [mu]-O 5.5, OPh 5.8) (Dipp = 2,6-diisopropylphenyl). 5.2b also catalyzes the dehydrogenative coupling of benzylamine with 3.5 turnovers over 24 hours. In chapter 6, complexes of the form ([superscript Ph]I2P2−)AlX(THF) (X = H, Me) are shown to be active catalysts for the selective dehydrogenation of formic acid with an initial TOF of up to 5200 hr−1 and up to 2200 total turnovers observed. The mechanism of the transformation is examined through a series of stoichiometric reactions. In the presence of formic or acetic acid, the [superscrpt Ph]I2P2− ligand is protonated at both the amido nitrogen and at the ipso carbon position effectively hydrogenating one of the imine arms of the ligand. The Al(III) complexes of the [superscript Ph]HI2P− and [superscript Ph]H2I2P forms of the ligand favor [beta]-hydride abstraction from formate, while the Al(III) complexes of the [superscript Ph]I2P2− form of the ligand favors the reverse reaction: insertion of CO2 into the Al-H bond. The liberation of CO2 from formate is investigated through a series of deuterium labeling studies which show [beta]-hydride transfer from formate to the aluminum center. Finally, in chapter 7, the variety of electronic states adopted by complexes of methyl-substituted bis(imino)pyridine ligands is discussed. Reduction of [superscript Me]I2P ([superscript Me]I2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine) with sodium metal leads to the formation of ([superscript Me]I2P−)Na(OEt2) (7.1). Reduction of [superscript Me]I2P by sodium metal followed by salt metathesis with MgCl2, Mg(OTf)2, AlCl3, and AlCl2H affords [([superscript Me]I2P2−)Mg(THF)](MgCl2) (7.2), ([superscript Me]I2P2−)Mg(THF)2 (7.3), ([superscript Me]I2P−)AlCl2 (7.4), ([superscript Me]I2P2−)AlCl(THF) (7.5) and ([superscript Me]I2P2−)AlH(THF) (7.6), respectively. The electronic states of 7.1 to 7.6 are shown to be dependent on the reaction conditions used to synthesize the complexes with certain conditions leading to dimer formation. Initial reactivity studies with 7.5 and 7.6 are discussed.

Download or read book Synthesis and Reactivity of Redox active Bis imino pyridine I2P Aluminum Complexes written by Emily Jordan Thompson and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation discusses the synthesis and characterization of bis(imino)pyridine (I2P) complexes of Lewis acidic aluminum(III) (Al3+), and presents how these redox-active complexes can catalyze small molecule reduction. It is shown that Al3+ complexes can electrocatalytically reduce protons to hydrogen through ligand-mediated proton and electron-transfer. This work also exhibits an Al3+ complex with unique square planar geometry that binds Lewis bases. In chapter 2 the synthesis of two four-coordinate and square planar complexes of Al3+ is presented. Reaction of a phenyl-substituted bis(imino)pyridine ligand that is reduced by two electrons, Na2([superscript Ph]I2P2−), with AlCl afforded five-coordinate ([superscript Ph]I2P2−)Al(THF)Cl (2.1). Square-planar ([superscript Ph]I2P2−)AlCl (2.2) was obtained by performing the same reaction in diethyl ether followed by lyophilization of ([superscript Ph]I2P2−)Al(Et2O)Cl from benzene. Its four-coordinate geometry index, [tau]4, is 0.22, where on a 0-1 scale, 0 would be a perfectly square planar molecule. The analogous aluminum hydride complex, ([superscript Ph]I2P2−)AlH (2.3), is also square-planar, and has [tau]4 = 0.13. Both molecules are highly Lewis acidic and bind weak bases. In chapter 3 ([superscript Ph]I2P2−)Al(THF)Cl (3.1) is shown to catalyze the hydrogen evolution reaction. Environmentally sustainable hydrogen-evolving electrocatalysts are key in a renewable fuel economy, and ligand-based proton and electron transfer could circumvent the need for precious metal ions in electrocatalytic H2 production. 3.1 reduces protons at -1.16 V vs. SCE with 500 mV of overpotential in organic solvent. The mechanism was probed using electrochemical methods and stoichiometric reactions that were observed using 1H NMR spectrometry and gas chromatography. These investiagtions show that the H2 generation proceeds through a ligand-mediated proton and electron-transfer mechanism. In chapter 4 the research in the previous chapter towards H2 evolution is as expanded upon to design a new ligand that provides increased stability and faster reactivity. The methoxy-substituted bis(imino)pyridine ligand ([subscript OMe]I2P) was designed and synthesized. [subscript OMe]I2P coordinates twice to Al3+ to form a coordinately-saturated, redox-active catalyst that is stable to H2O. Mixed-valent ([subscript OMe]I2P−)([subscript OMe]I2P2−)Al (4.1) electrocatalytically reduces protons to hydrogen at -1.2 V vs. SCE with 450 mV of overpotential, and 96% Faradaic efficiency in MeCN. In chapter 5 low energy routes to NH3 formation from N2 were explored using ([superscript Ph]I2P2−)Al(THF)Cl. Chemical and electrochemical reactions demonstrate that the ligand backbone is twice protonated forming [H2I2PAlCl(DMAP)2]2+ when reacted with two equivalents of moderate strength acid, 4-dimethylaminopyridinium (DMAPH+), under a N2 atmosphere at room temperature and pressure. Upon electrochemical reduction of [H2I2PAlCl(DMAP)2]2+ under N2, NH3 is formed in sub-stoichiometric yields and the complex decomposes. Labeling studies have shown that the source of nitrogen in NH3 is from N2. Ongoing studies are focused on pinpointing the exact source of the protons for NH3 and identifying the complex decomposition product.