Matthew T Olsen

University of Illinois, Urbana-Champaign, Urbana, IL, United States

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Publications (9)64.37 Total impact

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    ABSTRACT: Understanding the catalytic process of the heterolytic splitting and formation of molecular hydrogen is one of the key topics for the development of a future hydrogen economy. With an interest in elucidating the enzymatic mechanism of the [Fe(2)(S(2)C(2)H(4)NH)(CN)(2)(CO)(2)(μ-CO)] active center uniquely found in [FeFe]hydrogenases, we present a detailed spectroscopic and theoretical analysis of its inorganic model [Fe(2)(S(2)X)(CO)(3)(dppv)(PMe(3))](+) [dppv = cis-1,2-bis(diphenylphosphino)ethylene] in two forms with S(2)X = ethanedithiolate (1edt) and azadithiolate (1adt). These complexes represent models for the oxidized mixed-valent Fe(I)Fe(II) state analogous to the active oxidized "H(ox)" state of the native H-cluster. For both complexes, the (31)P hyperfine interactions were determined by pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) methods. For 1edt, the (57)Fe parameters were measured by electron spin-echo envelope modulation and Mössbauer spectroscopy, while for 1adt, (14)N and selected (1)H couplings could be obtained by ENDOR and hyperfine sublevel correlation spectroscopy. The spin density was found to be predominantly localized on the Fe(dppv) site. This spin distribution is different from that of the H-cluster, where both the spin and charge densities are delocalized over the two Fe centers. This difference is attributed to the influence of the "native" cubane subcluster that is lacking in the inorganic models. The degree and character of the unpaired spin delocalization was found to vary from 1edt, with an abiological dithiolate, to 1adt, which features the authentic cofactor. For 1adt, we find two (14)N signals, which are indicative for two possible isomers of the azadithiolate, demonstrating its high flexibility. All interaction parameters were also evaluated through density functional theory calculations at various levels.
    Inorganic Chemistry 07/2012; 51(15):8617-28. · 4.59 Impact Factor
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    ABSTRACT: Treatment of Fe(2)(pdt)(CO)(4)(dppv) (1) with aryldiazonium salts affords the 34e(-) adducts [Fe(2)(pdt)(μ-N(2)Ar)(CO)(4)(dppv)](+) (pdt(2-) = 1,3-propanedithiolate, dppv = cis-C(2)H(2)(PPh(2))(2)). Under some conditions, the same reaction gave substantial amounts of [1](+), the product of electron-transfer. Consistent with the influence of electron transfer in the reactions of some electrophiles with Fe(I)Fe(I) dithiolates, the reaction of [Me(3)S(2)](+) and Fe(2)(pdt)(CO)(4)(dppbz) was found to give [Fe(2)(pdt)(CO)(4)(dppbz)](+) as well as Me(2)S and Me(2)S(2) (dppbz = 1,2-bis(diphenylphosphino)benzene).
    Organometallics 04/2012; 31(8):3447-3450. · 4.15 Impact Factor
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    ABSTRACT: Experimental and computational experiments show that the electrophile MeS(+) attacks a single Fe center in Fe(2)(propanedithiolate)(CO)(4)(PMe(3))(2) followed by isomerization of this terminal thiolato complex to the corresponding μ-SMe derivative.
    Chemical Communications 06/2011; 47(23):6554-6. · 6.38 Impact Factor
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    ABSTRACT: This paper summarizes studies on the redox behavior of synthetic models for the [FeFe]-hydrogenases, consisting of diiron dithiolato carbonyl complexes bearing the amine cofactor and its N-benzyl derivative. Of specific interest are the causes of the low reactivity of oxidized models toward H(2), which contrasts with the high activity of these enzymes for H(2) oxidation. The redox and acid-base properties of the model complexes [Fe(2)[(SCH(2))(2)NR](CO)(3)(dppv)(PMe(3))](+) ([2](+) for R = H and [2'](+) for R = CH(2)C(6)H(5), dppv = cis-1,2-bis(diphenylphosphino)ethylene)) indicate that addition of H(2) followed by deprotonation are (i) endothermic for the mixed valence (Fe(II)Fe(I)) state and (ii) exothermic for the diferrous (Fe(II)Fe(II)) state. The diferrous state is shown to be unstable with respect to coordination of the amine to Fe, a derivative of which was characterized crystallographically. The redox and acid-base properties for the mixed valence models differ strongly for those containing the amine cofactor versus those derived from propanedithiolate. Protonation of [2'](+) induces disproportionation to a 1:1 mixture of the ammonium [H2'](+) (Fe(I)Fe(I)) and the dication [2'](2+) (Fe(II)Fe(II)). This effect is consistent with substantial enhancement of the basicity of the amine in the Fe(I)Fe(I) state vs the Fe(II)Fe(I) state. The Fe(I)Fe(I) ammonium compounds are rapid and efficient H-atom donors toward the nitroxyl compound TEMPO. The atom transfer is proposed to proceed via the hydride. Collectively, the results suggest that proton-coupled electron-transfer pathways should be considered for H(2) activation by the [FeFe]-hydrogenases.
    Journal of the American Chemical Society 12/2010; 132(50):17733-40. · 10.68 Impact Factor
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    ABSTRACT: Decades of biophysical study on the hydrogenase (H(2)ase) enzymes have yielded sufficient information to guide the synthesis of analogs of their active sites. Three families of enzymes serve as inspiration for this work: the [FeFe]-H(2)ases, [NiFe]-H(2)ases, and [Fe]-H(2)ases, all of which feature iron centers bound to both CO and thiolate. Artificial H(2)ases affect the oxidation of H(2) and the reverse reaction, the reduction of protons. These reactions occur via the intermediacy of metal hydrides. The inclusion of amine bases within the catalysts is an important design feature that is emulated in related bioinspired catalysts. Continuing challenges are the low reactivity of H(2) toward biomimetic H(2)ases.
    Current Opinion in Biotechnology 03/2010; 21(3):292-7. · 8.04 Impact Factor
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    ABSTRACT: Using the thermally stable salts of [Fe(2)(SR)(2)(CO)(3)(PMe(3))(dppv)]BAr(F)(4), we found that the azadithiolates [Fe(2)(adtR)(CO)(3)(PMe(3))(dppv)](+) react with high pressures of H(2) to give the hydride [Fe(2)(mu-H)(adtR)(CO)(3)(dppv)(PMe(3))]BAr(F)(4). The related oxadithiolate and propanedithiolate complexes are unreactive toward H(2). Molecular hydrogen is proposed to undergo heterolysis assisted by the amine followed by isomerization of an initially formed terminal hydride. Use of H(2) and D(2)O gave the deuteride as well as the hydride, implicating protic intermediates.
    Inorganic Chemistry 08/2009; 48(16):7507-9. · 4.59 Impact Factor
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    ABSTRACT: Nitrosyl derivatives of diiron dithiolato carbonyls have been prepared starting from the precursor Fe(2)(S(2)C(n)H(2n))(dppv)(CO)(4) (dppv = cis-1,2-bis(diphenylphosphinoethylene). These studies expand the range of substituted diiron(I) dithiolato carbonyl complexes. From [Fe(2)(S(2)C(2)H(4))(CO)(3)(dppv)(NO)]BF(4) ([1(CO)(3)]BF(4)), the following compounds were prepared: [1(CO)(2)(PMe(3))]BF(4), [1(CO)(dppv)]BF(4), NEt(4)[1(CO)(CN)(2)], and 1(CO)(CN)(PMe(3)). Some of these substitution reactions occur via the addition of 2 equiv of the nucleophile followed by the dissociation of one nucleophile and decarbonylation. Such a double adduct was characterized crystallographically in the case of [Fe(2)(S(2)C(2)H(4))(CO)(3)(dppv)(NO)(PMe(3))(2)]BF(4). This result shows that the addition of two ligands causes scission of the Fe-Fe bond and one Fe-S bond. When cyanide is the nucleophile, nitrosyl migrates away from the Fe(dppv) site, yielding a Fe(CN)(2)(NO) derivative. Compounds [1(CO)(3)]BF(4), [1(CO)(2)(PMe(3))]BF(4), and [1(CO)(dppv)]BF(4) were also prepared by the addition of NO(+) to the di-, tri-, and tetrasubstituted precursors. In these cases, the NO(+) appears to form an initial 36e(-) adduct containing terminal Fe-NO, followed by decarbonylation. Several complexes were prepared by the addition of NO to the mixed-valence Fe(I)Fe(II) derivatives. The diiron nitrosyl complexes reduce at mild potentials and in certain cases form weak adducts with CO. IR and EPR spectra of 1(CO)(dppv), generated by low-temperature reduction of [1(CO)(dppv)]BF(4) with Co(C(5)Me(5))(2), indicates that the SOMO is located on the FeNO subunit.
    Inorganic Chemistry 12/2008; 47(24):11816-24. · 4.59 Impact Factor
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    ABSTRACT: The dithiolate cofactor for the [FeFe]-hydrogenase models, Fe(2)(xdt)(CO)(2)(dppv)(2) (where xdt = 1,3-propanedithiolate (pdt), azadithiolate (adt), (SCH(2))(2)NH, and oxadithiolate (odt), (SCH(2))(2)O; dppv = cis-1,2-bis(diphenylphosphino)ethylene) have been probed for their functionality as proton relays enabling formation and deprotonation of terminal hydrides. Compared to the propanedithiolate derivative, the azadithiolate and oxaditiholate show enhanced rates of proton transfer between solution and the terminal site on one Fe center. The results are consistent with the heteroatom of the dithiolate serving a gating role for both protonation and deprotonation. The pK(a) of the transiently formed ammonium (pK(CD(2))(Cl(2)) 5.7-8.2) or oxonium (pK(CD(2))(Cl(2)) -4.7-1.6) regulates the proton transfer. As a consequence, only the azadithiolate is capable of yielding the terminal hydride from weak acids. The aza- and oxadithiolates manifested the advantages of proton relays: the odt derivative proved to be a faster catalyst for hydrogen evolution than the pdt derivative as indicated from cyclic voltammetry plots of i(c)/i(p) vs [H(+)]. The adt derivative was capable of proton reduction from the weak acid [HPMe(2)Ph]BF(4) (pK(CD(2))(Cl(2)) = 5.7). The proton relay function does not apply to the isomeric bridged-hydrides [Fe(2)(xdt)(mu-H)(CO)(2)(dppv)(2)](+), where the hydride is too distant and too basic to interact to be affected by the heteroatomic relay site. None of these mu-H species can be deprotonated.
    Journal of the American Chemical Society 12/2008; 130(50):16834-5. · 10.68 Impact Factor
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    ABSTRACT: This study probes the impact of electronic asymmetry of diiron(I) dithiolato carbonyls. Treatment of Fe2(S2C(n)H(2n))(CO)(6-x)(PMe3)x compounds (n = 2, 3; x = 1, 2, 3) with NOBF4 gave the derivatives [Fe2(S2C(n)H(2n))(CO)(5-x)(PMe3)x(NO)]BF4, which are electronically unsymmetrical because of the presence of a single NO(+) ligand. Whereas the monophosphine derivative is largely undistorted, the bis(PMe3) derivatives are distorted such that the CO ligand on the Fe(CO)(PMe3)(NO)(+) subunit is semibridging. Two isomers of [Fe2(S2C3H6)(CO)3(PMe3)2(NO)]BF4 were characterized spectroscopically and crystallographically. Each isomer features electron-rich Fe(CO)2PMe3 and electrophilic Fe(CO)(PMe3)(NO)(+) subunits. These species are in equilibrium with an unobserved isomer that reversibly binds CO (DeltaH = -35 kJ/mol, DeltaS = -139 J mol(-1) K(-1)) to give the symmetrical adduct [Fe2(S2C3H6)(mu-NO)(CO)4(PMe3)2]BF4. In contrast to Fe2(S2C3H6)(CO)4(PMe3)2, the bis(PMe3) nitrosyl complexes readily undergo CO substitution to give the (PMe3)3 derivatives. The nitrosyl complexes reduce at potentials that are approximately 1 V milder than their carbonyl counterparts. Results of density functional theory calculations, specifically natural bond orbital analysis, reinforce the electronic resemblance of the nitrosyl complexes to the corresponding mixed-valence diiron complexes. Unlike other diiron dithiolato carbonyls, these species undergo reversible reductions at mild potentials. The results show that the novel structural and chemical features associated with mixed-valence diiron dithiolates (the so-called H(ox) models) can be replicated in the absence of mixed-valency by the introduction of electronic asymmetry.
    Journal of the American Chemical Society 10/2008; 130(36):12021-30. · 10.68 Impact Factor