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ABSTRACT: Oxidation and reduction of the bis(imino)pyridine iron dinitrogen compound, ((iPr)PDI)FeN(2) ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N═CMe)(2)C(5)H(3)N) has been examined to determine whether the redox events are metal or ligand based. Treatment of ((iPr)PDI)FeN(2) with [Cp(2)Fe][BAr(F)(4)] (BAr(F)(4) = B(3,5-(CF(3))(2)-C(6)H(3))(4)) in diethyl ether solution resulted in N(2) loss and isolation of [((iPr)PDI)Fe(OEt(2))][BAr(F)(4)]. The electronic structure of the compound was studied by SQUID magnetometry, X-ray diffraction, EPR and zero-field (57)Fe Mössbauer spectroscopy. These data, supported by computational studies, established that the overall quartet ground state arises from a high spin iron(II) center (S(Fe) = 2) antiferromagnetically coupled to a bis(imino)pyridine radical anion (S(PDI) = 1/2). Thus, the oxidation event is principally ligand based. The one electron reduction product, [Na(15-crown-5)][((iPr)PDI)FeN(2)], was isolated following addition of sodium naphthalenide to ((iPr)PDI)FeN(2) in THF followed by treatment with the crown ether. Magnetic, spectroscopic, and computational studies established a doublet ground state with a principally iron-centered SOMO arising from an intermediate spin iron center and a rare example of trianionic bis(imino)pyridine chelate. Reduction of the iron dinitrogen complex where the imine methyl groups have been replaced by phenyl substituents, ((iPr)BPDI)Fe(N(2))(2) resulted in isolation of both the mono- and dianionic iron dinitrogen compounds, [((iPr)BPDI)FeN(2)](-) and [((iPr)BPDI)FeN(2)](2-), highlighting the ability of this class of chelate to serve as an effective electron reservoir to support neutral ligand complexes over four redox states.
Inorganic Chemistry 12/2012; · 4.60 Impact Factor
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ABSTRACT: The oxidation and reduction of a redox-active aryl-substituted bis(imino)pyridine iron dicarbonyl has been explored to determine whether electron-transfer events are ligand- or metal-based or a combination of both. A series of bis(imino)pyridine iron dicarbonyl compounds, [((iPr)PDI)Fe(CO)(2)](-), ((iPr)PDI)Fe(CO)(2), and [((iPr)PDI)Fe(CO)(2)](+) [(iPr)PDI = 2,6-(2,6-(i)Pr(2)C(6)H(3)N═CMe)(2)C(5)H(3)N], which differ by three oxidation states, were prepared and the electronic structures evaluated using a combination of spectroscopic techniques and, in two cases, [((iPr)PDI)Fe(CO)(2)](+) and [((iPr)PDI)Fe(CO)(2)], metrical parameters from X-ray diffraction. The data establish that the cationic iron dicarbonyl complex is best described as a low-spin iron(I) compound (S(Fe) = ½) with a neutral bis(imino)pyridine chelate. The anionic iron dicarbonyl, [((iPr)PDI)Fe(CO)(2)](-), is also best described as an iron(I) compound but with a two-electron-reduced bis(imino)pyridine. The covalency of the neutral compound, ((iPr)PDI)Fe(CO)(2), suggests that both the oxidative and reductive events are not ligand- or metal-localized but a result of the cooperativity of both entities.
Inorganic Chemistry 06/2011; 50(20):9888-95. · 4.60 Impact Factor
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ABSTRACT: A family of cationic, neutral, and anionic bis(imino)pyridine iron alkyl complexes has been prepared, and their electronic and molecular structures have been established by a combination of X-ray diffraction, Mössbauer spectroscopy, magnetochemistry, and open-shell density functional theory. For the cationic complexes, [((iPr)PDI)Fe-R][BPh(4)] ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)N═CMe)(2)C(5)H(3)N; R = CH(2)SiMe(3), CH(2)CMe(3), or CH(3)), which are known single-component ethylene polymerization catalysts, the data establish high spin ferrous compounds (S(Fe) = 2) with neutral, redox-innocent bis(imino)pyridine chelates. One-electron reduction to the corresponding neutral alkyls, ((iPr)PDI)Fe(CH(2)SiMe(3)) or ((iPr)PDI)Fe(CH(2)CMe(3)), is chelate-based, resulting in a bis(imino)pyridine radical anion (S(PDI) = 1/2) antiferromagnetically coupled to a high spin ferrous ion (S(Fe) = 2). The neutral neopentyl derivative was reduced by an additional electron and furnished the corresponding anion, [Li(Et(2)O)(3)][((iPr)PDI)Fe(CH(2)CMe(3))N(2)], with concomitant coordination of dinitrogen. The experimental and computational data establish that this S = 0 compound is best described as a low spin ferrous compound (S(Fe) = 0) with a closed-shell singlet bis(imino)pyridine dianion (S(PDI) = 0), demonstrating that the reduction is ligand-based. The change in field strength of the bis(imino)pyridine coupled with the placement of the alkyl ligand into the apical position of the molecule induced a spin state change at the iron center from high to low spin. The relevance of the compounds and their electronic structures to olefin polymerization catalysis is also presented.
Journal of the American Chemical Society 09/2010; 132(42):15046-59. · 9.91 Impact Factor
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Organometallics. 06/2009; 28:3928-3940.
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ABSTRACT: Sodium amalgam reduction of the aryl-substituted bis(imino)pyridine iron dibromide complex, ((Et)PDI)FeBr2 ((Et)PDI = 2,6-(2,6-Et2-C6H3N=CMe)2C5H3N), under a dinitrogen atmosphere in pentane furnished the bis(chelate)iron compound, ((Et)PDI)2Fe. Characterization by X-ray crystallography established a distorted four-coordinate iron center with two kappa2-bis(imino)pyridine ligands. Reducing the steric demands of the imine substituent to either a less sterically encumbered aryl ring (e.g., C6H4-4-OMe) or an alkyl group (e.g., Cy, iPr, cis-myrtanyl) also yielded bis(chelate) compounds from sodium amalgam reduction of the corresponding dihalide. Characterization of the compounds with smaller imine substituents by X-ray diffraction established six-coordinate, pseudo-octahedral compounds. In one case, a neutral bis(chelate)iron compound was prepared by reduction of the corresponding iron dication, [(PDI)2Fe]2+, providing chemical confirmation of electrochemically generated species that were previously reported as too reducing to isolate. Magnetic measurements, metrical parameters from X-ray structures, Mössbauer spectroscopy, and open-shell, broken symmetry DFT calculations were used to establish the electronic structure of both types (four- and six-coordinate) of neutral bis(chelate) compounds. The experimentally observed S = 1 compounds are best described as having high-spin ferrous (S(Fe) = 2) centers antiferromagnetically coupled to two bis(imino)pyridine radical anions. Thus, the two-electron reduction of the diamagnetic, low-spin complex [(PDI)2Fe]2+ to [(PDI)2Fe] is ligand-based with a concomitant spin change at iron.
Inorganic Chemistry 12/2008; 48(9):4190-200. · 4.60 Impact Factor
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ABSTRACT: Bis(imino)pyridine iron dinitrogen and dialkyl complexes are well-defined precatalysts for the chemo- and regioselective reduction of aldehydes and ketones. Efficient carbonyl hydrosilylation is observed at low (0.1-1.0 mol %) catalyst loadings and with 2 equiv of either PhSiH(3) or Ph(2)SiH(2), representing one of the most active iron-catalyzed carbonyl reductions reported to date.
Organic Letters 08/2008; 10(13):2789-92. · 5.86 Impact Factor
