Roger E. Cramer

Enantioselective synthesis of platinum group metal complexes with the chiral PCP pincer ligand R,R-{C6H4-2,6-(CH2P*PhBut)2}. The crystal structure of R,R-PdCl{C6H3-2,6-(CH2P*PhBut)2}

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.

A nitrogenase cluster model [Fe8S6O] with an oxygen unsymmetrically bridging two proto-Fe4S3 cubes: relevancy to the substrate binding mode of the FeMo cofactor.

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.

Magnesium-aluminium alkoxides: The synthesis of Mg[Al(OR)4]2 (R = Busec and Ph), structure of (thf)2Mg[(μ-OPh)2Al(OPh)2]2, and dynamic NMR of Mg[Al(OBusec)4]2

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.

Allyl–palladium compounds with fluorinated benzenethiolate ligands. X-ray crystal structure of [(η3-C3H5)Pd(μ-SC6H4F-4)2Pd(η3-C3H5)]

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.

Formation of a Nitrogenase P-cluster [Fe8S7] Core via Reductive Fusion of Two All-Ferric [Fe4S4] Clusters

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-

Small molecule activation at the uranium carbon multiple bond

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 UCHPMeRPh 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.

Calculation of lanthanide-induced shifts from molecular structure. III. Other lanthanides☆

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.

Nuclear magnetic resonance contact shifts and spin delocalization mechanisms in tris(acetylacetone) nickel(II) perchlorate

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.

Synthesis and Lanthanide Coordination Chemistry of Phosphine Oxide Decorated Dibenzothiophene and Dibenzothiophene Sulfone Platforms

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.

Synthesis and structural characterisation of [RuCl(NO)(η2-O2)(PPh3)2]

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.