Marilé Landman

Consequences of Electron-Density Manipulations on the X-ray Photoelectron Spectroscopic Properties of Ferrocenyl-β-diketonato Complexes of Manganese(III). Structure of [Mn(FcCOCHCOCH3)3]

Reaction of [Mn3(OAc)6O·3H2O](+) (1) with ferrocenyl β-diketones of the type FcCOCH2COR with R = CF3 (2a) and CH3 (2b), Ph = C6H5 (2c), and Fc = Fe(II)(η(5)-C5H4)(η(5)-C5H5) (2d) yielded a series of ferrocene-functionalized β-diketonato manganese(III) complexes 3a-3d, respectively, of general formula [Mn(FcCOCHCOR)3]. The mixed-ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)] (4) was obtained by reacting mixtures of diketones 2b and 2d with 1. A single-crystal X-ray structure determination of 3b (Z = 2, triclinic, space group P1̅) highlighted a weak axial elongating Jahn-Teller effect and a high degree of bond conjugation. An X-ray photoelectron spectroscopic study, by virtue of linear relationships between group electronegativities of ligand R groups, χR, or ∑χR, and binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines, confirmed communication between molecular fragments of 2a-2d as well as 3a-3d. This unprecedented observation allows prediction of binding energies from known β-diketonato side group χR values.

Fischer aminocarbene conformers containing a 2-thienyl or 2-furyl ring: a crystallographic, NMR, and DFT study

Fischer aminocarbene complexes [(CO)5M=C(NHR)Y] (M=Cr or W; R=H, Cy or C2H4NH2; Y=2-thienyl or 2-furyl) containing an amino group exist as two isomers in solution, the E and Z isomers. The two isomers arise from restricted rotation about the N–Ccarbene bond, that exhibits double bond character due to π-donation from nitrogen to the carbene carbon. Each isomer exists as two conformers in fast equilibrium with each other. The conformers arise from the rotation of the aryl ring around the Ccarbene–Caryl single bond with a DFT calculated rotation barrier of 0.1–0.5 eV. The main isomer, isolated in the solid state, generally exhibits a syn orientation of the aryl ring relative to the amino substituent and a Z configuration of the amino substituent relative to the metal. Graphical abstract

Rhenium ethoxy- and hydroxycarbene complexes with thiophene substituents

Reaction of mono- and dilithiated thiophene (a), bithiophene (b) and 2,5-dibromothiophene (c) with [Re(2)(CO)(10)] afforded, after subsequent alkylation with triethyloxonium tetrafluoroborate, tetra- and binuclear Fischer carbene complexes, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)X}], n = 1, X = H (1a); n = 2, X = H (1b); n = 1, X = Br (1c); n = 1, X = C(OEt)Re(2)(CO)(9), (2a); n = 2, X = C(OEt)Re(2)(CO)(9) (2b), as major products. The dirhenium acylate intermediates from this reaction not only gave the expected novel ethoxycarbene complexes with alkylation but after rhenium-rhenium bond breaking afforded a number of minor products. The (1)H NMR spectrum of the crude reaction mixture revealed the formation of four metal hydride complexes and aldehydes. Protonation with HBF(4) instead of alkylation with Et(3)OBF(4) significantly increased the yields of the hydride complexes, which enabled the positive identification of three of these complexes. In addition to the known compounds [Re(CO)(5)H] and [Re(3)(CO)(14)H] (3), a unique complex displaying a hydroxycarbene fragment connected to an acyl fragment via an O-H···O hydrogen bond and a Re···H···Re bond linking the two Re centers, [(μ-H){Re(CO)(4)C(OH){C(4)H(2)S}(n)H}{Re(CO)(4)C(O){C(4)H(2)S}(n)H}], n = 1 (4a) or n = 2 (4b), were isolated. The formation of thiophene aldehydes, H{C(O)}(m){C(4)H(2)S}(n)C(O)H (m = 0 or 1 and n = 1 or 2), were observed and the novel monocarbene complexes with terminal aldehyde groups, [Re(2)(CO)(9){C(OEt){C(4)H(2)S}(n)C(O)H}], n = 1 (5a) and n = 2 (5b) could be isolated. A higher yield of 5b was obtained after stirring crystals of 2b in wet THF. The crystal structures of 1a, 2a, 4a and 5b are reported.

A DFT-Elucidated Comparison of the Solution-Phase and SAM Electrochemical Properties of Short-Chain Mercaptoalkylferrocenes: Synthetic and Spectroscopic Aspects, and the Structure of Fc-CH2CH2-S-S-CH2CH2-Fc.

Facile synthetic procedures to synthesize a series of difficult-to-obtain mercaptoalkylferrocenes, namely, Fc(CH2)nSH, where n = 1 (1), 2 (2), 3 (3), or 4 (4) and Fc = Fe(η(5)-C5H5)(η(5)-C5H4), are reported. Dimerization of 1-4 to the corresponding disulfides 19-22 was observed in air. Dimer 20 (Z = 2) crystallized in the triclinic space group P1̅. Dimers 20-22 could be reduced back to the original Fc(CH2)nSH derivatives with LiAlH4 in refluxing tetrahydrofuran. Density functional theory (DFT) calculations showed that the highest occupied molecular orbital of 1-4 lies exclusively on the ferrocenyl group implying that the electrochemical oxidation observed at ca. -15 < Epa < 76 mV versus FcH/FcH(+) involves exclusively an Fe(II) to Fe(III) process. Further DFT calculations showed this one-electron oxidation is followed by proton loss on the thiol group to generate a radical, Fc(CH2)nS(•), with spin density mainly located on the sulfur. Rapid exothermic dimerization leads to the observed dimers, Fc(CH2)n-S-S-(CH 2)nFc. Reduction of the ferrocenium groups on the dimer occurs at potentials that still showed the ferrocenyl group ΔE = Epa,monomer - Epc,dimer ≤ 78 mV, indicating that the redox properties of the ferrocenyl group on the mercaptans are very similar to those of the dimer. (1)H NMR measurements showed that, like ferrocenyl oxidation, the resonance position of the sulfhydryl proton, SH, and others, are dependent on -(CH2)n- chain length. Self-assembled monolayers (SAMs) on gold were generated to investigate the electrochemical behavior of 1-4 in the absence of diffusion. Under these conditions, ΔE approached 0 mV for the longer chain derivatives at slow scan rates. The surface-bound ferrocenyl group of the metal-thioether, Fc(CH2)n -S-Au, is oxidized at approximately equal potentials as the equivalent CH2Cl2-dissolved ferrocenyl species 1-4. Surface coverage by the SAMs is dependent on alkyl chain length with the largest coverage obtained for 4, while the rate of heterogeneous electron transfer between SAM substrate and electrode was the fastest for the shortest chain derivative, Fc-CH2-S-Au.

N-(2,4,6-Trimethyl-phen-yl)formamide.

The title compound, C10H13NO, was obtained as the unexpected, almost exclusive, product in the attempted synthesis of a manganese(I)–N-heterocyclic carbene (NHC) complex. The dihedral angle between the planes of the formamide moiety and the aryl ring is 68.06 (10)°. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming infinite chains along the c axis.

Synthesis and structure of dithizonato complexes of antimony(III), copper(II) and tin(IV)

Abstract In view of the important role of dithizone in trace metal analyses, new structural aspects and approaches used to probe metal complexes of dithizone are of interest. Three X-ray diffraction structures are reported, dichloridobis(dithizonato)tin(IV), dichlorido(dithizonato)antimony(III), and bis(dithizonato)copper(II). During synthesis of the tin complex, auto-oxidation of SnIICl2 to SnIV occurred without chloride liberation. The SbIII complex revealed a unique distorted see-saw geometry which is, as for the other complexes, predicted by DFT molecular orbital calculations. The computed products of the lowest energy reactions are in agreement with experimentally obtained reaction products, which, together with molecular orbital renderings serve as a tool toward prediction of modes of coordination in these complexes. The S–M–N bond angle in the five-membered coordination ring shows a linear relationship with the corresponding metal ionic radii.

A Computational Study of the Succinimide Derivative Surfactant

Density functional theory of calculations was used to optimize the molecular structures of a succinimide surfactant at B3LYP/6-311 level. The interaction of the surfactant with water molecules was investigated. The hydration shell was formed in the form of H-bonds between the hydrophilic group on the surfactant and water molecules. The binding energy of the system increases due to hydrogen bond formation with the water molecules.

Triphenylstibine-substituted Fischer carbene complexes of tungsten(0): synthesis, structure, DFT and electrochemistry

The synthesis, solid-state structure, and electrochemical behaviour of triphenylstibine-containing Fischer carbene complexes of tungsten(0) of the type [(SbPh3)(CO)4WC(OEt)(Ar)] with Ar = 2-thienyl (1), 2-furyl (2), 2-(N-methyl)pyrrolyl (3) or 2,2′-bithienyl (4) are reported. A density functional theory study of all the possible conformations and isomers of the various moieties in these complexes show that while the 2-furyl group adopts an anti-orientation relative to the ethoxy group, the thienyl and 2-(N-methyl)pyrrolyl adopt a cis-orientation. The preferred orientation of the aryl groups was confirmed by the solid-state structures. An electrochemical study of the complexes reveals that the decreasing order of the metal-centred oxidation and the carbene–carbon reduction of the [(SbPh3)(CO)4WC(OEt)(Ar)] complexes is: Ar = C4H3S > C4H3O > C4H3NMe. The electrochemical study further reveals substitution of a CO group in [(CO)5WC(OEt)(Ar)] with SbPh3, leads to a lowering of the metal-centred oxidation and the carbene–carbon reduction potential of ca. 0.27 and 0.13 V, respectively.

Base-free glucose dehydration catalysed by NHC-stabilised heterohalo cyclopentadienyl Cr(III) complexes

A range of five air-stable heterohalo Cr(III)–NHC complexes (1–5) have been synthesised from chromocene and the corresponding imidazolium salts. Employment of an N-4-NO2-benzyl imidazolium salt led to a side reaction where C–N bond cleavage occurred to form an imidazolium Cr(III) complex salt (6). The electrochemical processes of all six complexes were studied by means of cyclic voltammetry and a detailed conformational DFT analysis, which showed metal-centred redox behaviour. Furthermore, the Cr(III) complex salt (6) was electrochemically oxidised to Cr(IV) and electrochemically reduced to Cr(II) more readily than the related Cr(III)–NHC complexes (1–5). All complexes (1–6) were active (up to 81% conversion) as catalysts in the dehydration of glucose to form 5-hydroxymethylfurfural in moderate yields (up to 76%). This homogeneous system does not require oxidants or stoichiometric amounts of strong bases such as KOtBu, as often required in related catalytic systems, which is important for the development of greener catalytic processes employing naturally abundant precursors.

{μ-5-[1,3-Bis(2,4,6-trimethyl­phen­yl)-3H-imidazolium-2-yl]-2-(2-oxoethenyl-1κC1)furan-3-yl-2κC3}-μ-hydrido-bis(tetra­carbonyl­rhenium) tetra­hydro­furan 0.67-solvate

The title complex, [Re2(C27H25N2O2)H(CO)8]·0.67C4H8O, was formed as a product in the reaction of a rhenium(I)–Fischer carbene complex with a free NHC carbene. The coordination environment about the two Re atoms is slightly distorted octahedral, including a bridging H atom. The imidazolium and furan groups are almost coplanar, whereas the mesityl substituents show an almost perpendicular arrangement with respect to both heterocyclic units. Molecules of the complex pack in such a way as to form channels parallel with the bc unit-cell face diagonal running through the unit face diagonal. These channels are partially occupied by tetrahydrofuran solvent molecules.