Belinda Van der Westhuizen

Electrochemical illumination of thienyl and ferrocenyl chromium(0) Fischer carbene complexes

A series of ferrocenyl and thienyl mono- and biscarbene chromium(0) complexes 1-6 were synthesised. The complexes were characterised both spectroscopically and electrochemically, and the single crystal X-ray structure of 3 was determined. Electrochemical measurements in CH2Cl2 revealed that the carbene double bond of 1-6 is reduced to an anion radical, (-)Cr-C˙ at formal reduction potentials <-1.7 V vs. FcH/FcH(+). A computational study on 1, 3 and 4 (B3LYP/def2-SVP level) is consistent with electrochemical results in showing that electrochemically generated chromium(I) species may be further electrochemically irreversibly oxidised to chromium(II) at Epa > 0.95 V. The reactivity towards follow-up chemical reactions of the anodically produced Cr(II) species is much higher than the reactivity of the cathodically produced radical anions as the latter was still observably reoxidised to the parent Cr=C species at fast scan rates. The ferrocenyl group is oxidised electrochemically reversibly to ferrocenium at larger potentials than the electrochemically reversible oxidation of the Cr(0) centre to Cr(I). That all redox centres in 1-6 are involved in one-electron transfer steps was confirmed by comparing the ferrocenyl voltammetric wave with those of the other redox centres in linear sweep voltammetric experiments. The ferrocenyl group was electrochemically shown to stabilise the Cr=C centre almost as much as the NHBu, and much more than the ethoxy and thienyl groups.

Trends in the chemistry of mono- to multimetal π-arene complexes of chromium and manganese

The preparation and the features of the ring activation in π-arene metal (chromium, manganese) complexes are discussed. The bottom-up approach to the synthesis of σ, π-bi- and multimetal complexes, and the synthesis of cyclometallated and multicyclic complexes from a variety of selected routes are also reviewed. The stereochemical features of such complexes, and their applications in carbon–carbon coupling reactions and metal insertion reactions are highlighted. The redox reactivities and selected applications of (multi)metal π-arene complexes in catalysis and organic synthesis are included. Finally, the extension of the multimetal π-arene complexes to larger assemblies is shown. The importance of arene ring substituents in the basic mononuclear units and their use as bidentate metalloligands, with bidentate amines as linkers, in the construction of polymers, metal organic frameworks, networks (also on nanoparticles or silica supports), is highlighted.

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.

{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.

1,3-Bis(2,4,6-trimethylphenyl)-3H imidazol-1-ium tetraoxidorhenate(VII)

The title compound, (C21H25N2)[ReO4], was formed as the unexpected product in an attempted synthesis of a rhenium(I)–N-heterocyclic carbene (NHC) complex. The compound has crystallographic mirror symmetry with both the cation and the tetrahedral anion located across a mirror plane. The cation and anion are linked by a C—H⋯O hydrogen bond.