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Craig A Grapperhaus

Publications and source records attributed to Craig A Grapperhaus.

11 recordsLinked to original sources
PubMed2005

Oxygenation of a ruthenium(II) thiolate to a ruthenium(II) sulfinate proceeds via ruthenium(III).

Exposure of acetonitrile/methanol solutions of [PPN][Ru(DPPBT)3] [PPN = bis(triphenylphosphoranylidene); DPPBT = 2-diphenylphosphinobenzene thiolate] to oxygen initiates metal-centered oxidation, yielding the ruthenium(III) thiolate Ru(DPPBT)3. Ru(DPPBT)3 further reacts with oxygen, at sulfur, to give the ruthenium(III) sulfinate complex [Ru(DPPBT-O2)2(DPPBT)], which is reduced under ambient conditions to [PPN][Ru(DPPBT-O2)2(DPPBT)]. Ruthenium(II) sulfinate is the only product isolated from acetonitrile/methanol. Yellow crystals of [PPN][Ru(DPPBT-O2)2(DPPBT)] were obtained. Ruthenium(III) sulfinate was isolated as green prism-shaped crystals upon oxygenation of [PPN][Ru(DPPBT)3] in chlorobenzene/hexane. Electrochemical oxidation of ruthenium(II) sulfinate yields the ruthenium(III) derivative, which is rapidly reduced back to ruthenium(II) upon the addition of hydroxide.

Journal Article↗
PubMed2004

Electrochemical investigations of the [tris(2-(diphenylphosphino)thiaphenolato)ruthenate(II)] monoanion reveal metal- and ligand-centered events: radical, reactivity, and rate.

Electrochemical investigations of [bis(triphenylphosphoranylidene)ammonium)][tris(2-(diphenylphosphino)thiaphenolato)ruthenate(II)], PPN[Ru(DPPBT)(3)] (1), and [(bis(2-(diphenylphosphino)thiaphenolato)methane)(2-(diphenylphosphino)thiaphenolato)ruthenium(II)] chloride, [Ru((DPPBT)(2)CH(2))(DPPBT)]Cl (2) are reported. Complex 1 is oxidized reversibly in a metal-centered event by one electron at a potential of +455 mV (vs Ag/AgCl) to the ruthenium(III) derivative [tris(2-(diphenylphosphino)thiaphenolato)ruthenium(III)], 3. Complex 3 can also be prepared by iodine oxidation of 1 in acetonitrile. Oxidation of 3 in acetonitrile is reversible on a cyclic voltammetry time scale but irreversible upon bulk oxidation yielding Ru-X. Monitoring the oxidation of 3 by UV-visible spectroscopy reveals a proposed metal-coordinated thiyl radical intermediate with a maximum absorbance at 850 nm. This intermediate decays at a temperature of -20 degrees C with a rate constant of (5.82 +/- 0.73) x 10(-)(3) s(-)(1) with a small, positive deltaH and a large, negative deltaS. Ru-X can be oxidized reversibly to Ru-Y at a potential of +806 mV but cannot be reduced. Complex 2 is reversibly oxidized by one electron in a metal-centered event to 4 at a potential of +767 mV.

Journal Article↗
PubMed2004

Synthesis and oxygenation of a nickel(II) and zinc(II) dithiolate: an experimental and theoretical comparison.

The diamino-dithiolato N2S2 ligand N,N'-bis-2-methyl-mercaptopropyl-N,N'-dimethylethylenediamine, H2bmmp-dmed), and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated. Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography, and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur p character in the HOMO of each complex. However, 1 also shows significant metal d character that is pi-antibonding with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.

Journal Article↗
PubMed2004

Structural, spectroscopic, and computational study of an octahedral, non-heme [Fe-NO](6-8) Series: [Fe(NO)(cyclam-ac)]2+/+/0.

The reaction of low-spin [FeIICl(cyclam-ac)] with NO in CH3CN yields the octahedral, non-heme (nitrosyl)iron complex [Fe(NO)(cyclam-ac)](PF6) (2), S = 1/2, which can be one-electron oxidized with (tris(4-bromophenyl)ammoniumyl)hexachloroantimonate to the complex [Fe(NO)(cyclam-ac)](PF6)2 (1'), S = 0, or complex [Fe(NO)(cyclam-ac)]Cl(ClO4).H2O (1); (cyclam-ac)- represents the pentadentate monoanion of 1,4,8,11-tetraazacyclotetradecane-1-acetic acid. Similarly, in CH3CN solution 2 can be electrochemically or chemically reduced by one-electron to the neutral complex [Fe(NO)(cyclam-ac)]0 (3), S = 0. 1-3 represent members of the [FeNO]6-8 series, respectively. The electronic structure of these three species have been spectroscopically elucidated by EPR, UV-vis, Mössbauer, and IR spectroscopy. The crystal structures of 1 and 2 have been determined by X-ray crystallography. In addition, detailed density functional calculations have been performed for all three species taking into account the possibility that 3 is actually a protonated HNO or NOH species. For all complexes structures, energetics, IR parameters, and Mössbauer parameters as well as EPR parameters (g-values and hyperfine couplings) have been calculated using state-of-the art DFT methods which are compared to experiment. The results establish unequivocally that 3 is indeed the elusive [FeNO]8 species. Furthermore a detailed picture of the bonding in the low-spin non-heme iron nitrosyl series [FeNO]6, [FeNO]7, and [FeNO]8 has been developed. This allows a description of 1 as a low-spin ferrous complex containing an N-coordinated NO+, whereas 2 is a low-spin ferrous species with a NO* ligand and 3 is a low-spin ferrous complex with a coordinated NO-. On the basis of this description, all spectroscopic and geometric observables find a satisfactory interpretation.

Journal Article↗
PubMed2003

Synthesis and characterization of N2S3X-Fe models of iron-containing nitrile hydratase.

A series of iron complexes based on the pentadentate ligand 4,7-bis(2'-methyl-2'-mercaptopropyl)-1-thia-4,7-diazacyclononane), (bmmp-TASN)(2)(-), have been synthesized and characterized as models of iron-containing nitrile hydratase (NHase). The chloro derivative [(bmmp-TASN)Fe(III)Cl].0.5EtOH (1) contains a labile chloride which facilitates synthesis of related complexes via substitution reactions. Complex 1 is high-spin, g = 4.28. Addition of NEt(4)CN with 1 in CH(2)Cl(2) results in the cyanide ligated complex [(bmmp-TASN)Fe(III)CN] x 0.5EtOH (2), which shows a single intense nu(CN) band at 2083 cm(-)(1) in the IR region. Complex 2 is low-spin, g(1) = 2.31, g(2) = 2.16, and g(3) = 1.96. Under basic conditions complex 1 affords a mu-oxo bridged dimeric Fe(III) complex [(bmmp-TASN)Fe(III)](2)O (3), which shows an intense band at 799 cm(-)(1). Complex 3 was recrystallized from CH(2)Cl(2)/hexane solution in the triclinic space group P1, with a = 10.5486(15) A, b = 13.0612(19) A, c = 8.1852(12) A, alpha = 96.923(2) degrees, beta = 112.729(2) degrees, gamma = 81.048(2) degrees, and Z = 1. Density functional theory (DFT) calculations of the previously communicated iron-nitrosyl complex [(bmmp-TASN)Fe(III)(NO)][BPh(4)] (4) (Inorg. Chem. 2002, 41, 1039-1041) reveal that the HOMO region is dominated by Fe-S bonding. Complexes 1-4 display irreversible or quasi-reversible reductions in the cyclic voltammograms. All of the iron complexes and the zinc derivative, (bmmp-TASN)Zn (5), display an irreversible oxidation. Complex 5 was crystallized in the monoclinic space group P2(1)/n with a = 9.5759(6) A, b = 20.9790(13) A, c = 10.7113(7) A, beta = 91.283(1) degrees, and Z = 4.

Crystallography, X-Ray↗
PubMed2002

Dichloromethane alkylates a trithiolato-ruthenium complex to yield a methylene-bridged thioether core. Synthesis and structural comparison to the thiolato-ruthenium precursor.

The previously reported triphosphino/trithiolato-ruthenium anion, [tris-(2-diphenylphosphinothia-phenolato)ruthenium(II)](-), [Ru(DPPBT)(3)](-), has been isolated as the PPN salt (PPN = bis(triphenylphosphoranylidene) ammonium), 1, from chlorobenzene/ether as light-orange crystalline plates, and the X-ray crystal structure has been determined. In dichloromethane, the cis positioned thiolates are alkylated by solvent yielding the methylene-bridged triphosphino/dithioether/thiolato complex [(bis-(2-diphenylphosphinothiaphenolato)methane)(2-diphenyl-phosphinothiaphenolato)ruthenium(II)]chloride, [Ru((DPPBT)(2)CH(2))(DPPBT)]Cl (2). Dichloromethane solutions of 1 layered with hexanes yield 2 as orange cubes. The ruthenium-sulfur bond distances in the alkylated, thioether product are slightly shorter than in the thiolate precursor. Within 2, the iron-thioether bond distances are comparable to the iron-thiolate distances.

Journal Article↗
PubMed2002

Unique reactivity of a tetradentate N(2)S(2) complex of nickel: intermediates in the production of sulfur oxygenates.

Complex 1 [(N,N'-dimethyl-N,N'-bis(2-sulfanylethyl)ethylenediamine)nickel(II)], previously shown to react with H(2)O(2) to produce the fully oxygenated disulfonate 5 [diaqua(N,N'-dimethyl-N,N'-bis(2-sulfonatoethyl)ethylenediamine)nickel(II)], has been explored in detail to explain the observed reactivity of this compound and to discern intermediates in the oxygenation reaction. Reaction of 1 with 1 equiv of methyl iodide results in the monomethylated square-planar nickel complex 2 [[(N,N'-dimethyl-N-(2-sulfanylethyl)-N'-(2-methylthioethyl)(ethylenediamine)nickel(II)] iodide], while a slight excess of methyl iodide results in the dimethylated complex 3 [diiodo(N,N'-dimethyl-N,N'-bis(2-methylthioethyl)ethylenediamine)nickel(II)], an X-ray structure of which has shown that the nickel ion is in an octahedral N(2)S(2)I(2) environment. Crystal data of 3: monoclinic, a = 8.865(3) A, b = 14.419(4) A, c = 14.389(6) A, beta = 100.19(3) degrees, V = 1810.2(12) A(3), space group P2(1)/n, Z = 4. The equatorial positions are occupied by the two cis-amine N-atoms and the coordinated iodides, while the axial positions are occupied by the thioether sulfur atoms. In organic solvents, the dithiolate complex 1 reacts with molecular oxygen or H(2)O(2) to produce the mixed sulfinato/thiolato complex 4 [(N,N'-dimethyl-N-(2-sulfanylethyl)-N'-(2-sulfinatoethyl)(ethylenediamine)nickel(II)], and the fully oxidized product 5. X-ray analysis of complex 4 reveals a square-planar geometry in which the nickel ion is coordinated by two cis-amine nitrogens, one thiolate sulfur donor, and one sulfinato sulfur donor. Crystal data of 4: orthorhombic, a = 11.659(2) A, b = 13.119(3) A, c = 16.869(3) A, V = 2580.2(9) A(3), space group Pbca, Z = 8. This complex is the only intermediate in the oxygenation reaction that could be isolated, and it is shown to be further reactive toward O(2) to yield the fully oxidized product 5. For a better understanding of the reactivity observed for 4, DFT calculations have been undertaken, which show a possible reaction path toward the fully oxidized product 5.

Journal Article↗
PubMed2002

cis-Dioxocyclam.

Molecules of 1,4,8,11-tetraazacyclotetradecane-5,7-dione, or cis-dioxocyclam, C(10)H(20)N(4)O(2), lie across mirror planes in space group Cmca; the crystal structure reveals interleaved columns of cis-dioxocyclam molecules along the 2(1) screw axis parallel to the crystallographic b axis. The columns are interconnected in a chain-like arrangement by an amido hydrogen-bonding network (N* * *O = 2.816 A) and an amino hydrogen-bonding network (N* * *N = 3.193 A). The intracolumn spacing is 9.02 A.

Journal Article↗
PubMed2002

First [Fe-NO](6) complex with an N(2)S(3)Fe-NO core as a model of NO-inactivated iron-containing nitrile hydratase. Are thiolates and thioethers equivalent donors in low-spin iron complexes?

The spectroscopic and structural properties of [(bmmp-TASN)FeNO]BPh(4) (1) (bmmp-TASN = 4,7-bis(2'-methyl-2'-mercaptopropyl)-1-thia-4,7-diazacyclononane) have been determined and are compared with the nitric oxide inactivated form of iron-containing nitrile hydratase, NHase(dark). [(bmmp-TASN)FeNO]BPh(4) is prepared from the addition of NO to (bmmp-TASN)FeCl followed by addition of sodium tetraphenylborate. [(bmmp-TASN)FeNO]BPh(4) crystallizes from acetonitrile-methanol solutions upon ether vapor diffusion as dark blue plates in the monoclinic space group P2(1)/c with a = 11.9521(14) A, b = 11.3238(13) A, c = 26.624(3) A, beta = 98.280(2), and Z = 4. The nu(NO) stretching frequency of 1856 cm(-)(1) and the Mössbauer parameters, delta = 0.06 mm/s and DeltaE(q) = 1.75 mm/s, compare favorably with those of NHase(dark). The similarities of the iron-sulfur bond distances to the thiolate, 2.284(2) A and 2.291(2) A, versus thioether, 2.285(2) A, are attributed to the low-spin configuration of the iron. The relationship between this structural observation and the spectroscopic properties of the complex are discussed.

Binding Sites↗