Roger E. Cramer
University of Hawaii
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Featured researches published by Roger E. Cramer.
Journal of Organometallic Chemistry | 2002
David Morales-Morales; Roger E. Cramer; Craig M. Jensen
The novel PCP chiral ligand R , R -{C 6 H 4 -2,6-(CH 2 P *PhBu t ) 2 } and its platinum metal complexes have been easily synthesized in enantiomeric pure form. The palladium compound R , R -PdCl{C 6 H 3 -2,6-(CH 2 P *PhBu t ) 2 } has been characterized by X-ray crystal structure analysis thus confirming the absolute configuration of the complexated ligand. Preliminary catalytic experiments with the iridium and palladium complexes R , R -IrH 4 {C 6 H 3 -2,6-(CH 2 P *PhBu t ) 2 } and R , R -PdCl{C 6 H 3 -2,6-(CH 2 P *PhBu t ) 2 } in the dehydrogenation of cycloalkanes and in the hydrosilylation of styrene, allylic alkylation and Heck coupling reactions, respectively have been carried out.
Inorganic Chemistry | 2012
Shun Ohta; Yasuhiro Ohki; Takayoshi Hashimoto; Roger E. Cramer; Kazuyuki Tatsumi
An oxygen-encapsulated iron sulfido cluster, [(DmpS)Fe(4)S(3)O][(DmpS)Fe(4)S(3)](μ-SDmp)(2)(μ-OCPh(3)) (2; Dmp = 2,6-(mesityl)(2)C(6)H(3)), has been synthesized by the reaction of the preformed dinuclear iron thiolate/alkoxide [(Ph(3)CO)Fe](2)(μ-SDmp)(2) (1) with (1/8)S(8) and (1/4)H(2)O in toluene. In the [Fe(8)S(6)O] core, the oxygen atom bridges unsymmetrically two incomplete Fe(4)S(3) cubes, and two coordinatively unsaturated iron atoms are weakly bound to mesityl rings. Relevance of the cluster structure of 2 to the nitrogenase FeMo cofactor and its substrate binding mode is discussed.
Polyhedron | 1994
Juliane A. Meese-Marktscheffel; Roger E. Cramer; John W. Gilje
Abstract Magnesium reacts with 2 equivalents of Al(OR)3 and 2 equivalents of HOR, R = Busec or Ph, yielding Mg[Al(OBusec4]2, a liquid which can be distilled under reduced pressure, or (thf)2Mg[(μ-OPh)2Al(OPh)2]2, a crystalline solid. An X-ray structure for (thf)2Mg[(μ-OPh)2Al(OPh)2]2 shows a distorted octahedral magnesium which is attached to two thf ligands and two Al(OPh)4− chelates via double OPh bridges. Mass spectra indicate that the molecule oligomerizes upon loss of the thf solvate molecules. Variable temperature NMR spectra of Mg[Al(OBusec)4]2 can be interpreted in terms of a structure in which each Al(OBusec)4 moiety is coordinated to the magnesium via double OBusec bridges. At low temperature the exchange of bridging and terminal OBusec groups slows on the NMR time scale with a barrier to exchange of 43 kJ mol−1.
Polyhedron | 2001
Rocío Redón; Roger E. Cramer; Sylvain Bernès; David I. Morales; Hugo Torrens
Abstract Treatment of the di-μ-chloride allyl–palladium complex [(η3-C3H5)Pd(μ-Cl)2Pd(η3-C3H5)] with Pb(SR)2 in acetone affords dinuclear fluorothiolate bridged complexes of the type [(η3-C3H5)Pd(μ-SR)2Pd(η3-C3H5)] (R=C6F5, 1; C6HF4-4, 2; C6H4F-2, 3; C6H4F-3, 4 and C6H4F-4, 5). Complex 1 reacts with para-substituted phosphines P(C6H4X-4)3 to give the mononuclear perfluorobenzenethiolate complexes [Pd(SC6F5)(η3-C3H5)(P(C6H4X-4)3)] (X=F, 6; CF3, 7; OCH3, 8 and CH3, 9). The single crystal X-ray diffraction structure of [(η3-C3H5)Pd(μ-SC6H4F-4)2Pd(η3-C3H5)] (5) has been resolved.
Chemistry-an Asian Journal | 2012
Yasuhiro Ohki; Kazuki Tanifuji; Norihiro Yamada; Roger E. Cramer; Kazuyuki Tatsumi
Iron–sulfur clusters are ubiquitous in electron-transfer proteins, and the cuboidal [Fe4S4] core is thermodynamically robust, exhibiting multiple oxidation states with only minor geometry change. Although the removal of an iron or sulfur atom from an [Fe4S4] core is chemically difficult, [2–4] the reversible transformation between [Fe4S4] and [Fe3S4] clusters has been suggested to occur under physiological conditions. Further, the nitrogenase P-cluster core [Fe8S7] (Figure 1), which plays an important role in the electron-
Inorganica Chimica Acta | 1987
John W. Gilje; Roger E. Cramer
Abstract One strategy for the activation of CO involves the formation of bimetallic compounds where one metal is bonded to a carbonyl carbon atom while the second coordinates oxygen. Insertion of CO, coordinated to transition metals, into the uranium—carbon multiple bond in Cp 3 UCHPMeRPh produces such complexes. The resulting phosphonium-metallaenolate complexes have been shown to undergo further reactions which include CO coupling to produce an allyl moiety, a novel isomerization, and carbon-oxygen bond cleavage to form phosphonium acetylide zwitterions.
Journal of Magnetic Resonance | 1978
Roger E. Cramer; Richard B. Maynard
Abstract The NMR spectra of Ln(thd)3(sub)2 (where Ln = Pr, Sm, Dy, Ho, Er, Yb, and sub = 3-pic and 3,5-lut) in CS2 were observed at 30°C and the lanthanide-induced shifts for all protons, including those of the chelate, were calculated using the complete dipolar shift equation. The values for the magnetic anisotropy parameters D1 and D2 and the location of the x magnetic axis were obtained by a least-squares fit of the observed data. The calculated magnetic anisotropies were found to be in fair to good agreement with the single-crystal anisotropy data. It was found that the location of the x magnetic axis was the parameter most sensitive to errors in the procedure.
Journal of Magnetic Resonance | 1973
Roger E. Cramer; Mary Ann Chudyk
Abstract The NMR contact shifts for the complex tris(acetylacetone) Ni(II) perchlorate have been found to be +4.7 ppm for the methyl group and +35.6 for the methylene group. INDO molecular orbital calculations are used to show that the major spin delocalization is into the highest filled ligand orbital which is of sigma symmetry, with a minor contribution from delocalization into the lowest empty pi orbital. In the case of Ni(acac)3− and Ni(acac)2(py)2 the major spin delocalization is into the highest filled ligand orbital, of π symmetry, with a minor contribution from the next highest filled orbital, which is a sigma type. For Co(acac)2(py)2 an additional mechanism, which places spin in the third highest filled orbital, also sigma, is found to be consistent with the contact shift results. The implications of these results on the “ratio method” of separating contact and dipolar shifts in complexes of the type M(acac)2L2, M Co, Ni, is discussed and the donor properties of the acetylacetone and acetylacetonate ligands are compared.
Inorganic Chemistry | 2014
Daniel Rosario-Amorin; Sabrina Ouizem; Diane A. Dickie; Robert T. Paine; Roger E. Cramer; Benjamin P. Hay; Julien Podair; Lætitia H. Delmau
Syntheses for new ligands based upon dibenzothiophene and dibenzothiophene sulfone platforms, decorated with phosphine oxide and methylphosphine oxide donor groups, are described. Coordination chemistry of 4,6-bis(diphenylphosphinoylmethyl)dibenzothiophene (8), 4,6-bis(diphenylphosphinoylmethyl)dibenzothiophene-5,5-dioxide (9) and 4,6-bis(diphenylphosphinoyl)dibenzothiophene-5,5-dioxide (10) with lanthanide nitrates, Ln(NO3)3·(H2O)n is outlined, and crystal structure determinations reveal a range of chelation interactions on Ln(III) ions. The nitric acid dependence of the solvent extraction performance of 9 and 10 in 1,2-dichloroethane for Eu(III) and Am(III) is described and compared against the extraction behavior of related dibenzofuran ligands (2, 3; R = Ph) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (4) measured under identical conditions.
Inorganica Chimica Acta | 2001
David Morales-Morales; Rocı́o Redón; Roger E. Cramer
Abstract The extremely reactive and air-sensitive nitrosyl-ruthenium(0) species trans-[RuCl(NO)(PPh3)2] (2) oxidatively adds HCl to give the octahedral ruthenium(II) complex [RuHCl2(NO)(PPh3)2] (3). On treatment of 2 with O2, the five-coordinate 1:1 adduct [RuCl(NO)(η2-O2)(PPh3)2] (4) is formed. The dioxygen complex has been characterised by X-ray structural analysis.