Mono- and dinuclear tetraphosphabutadiene ferrate anions.

Reduction of [CpArFe(µ-Br)]2 (1, CpAr = C5(C6H4-4-Et)5) by potassium napthalenide, followed by the addition of white phosphorus, affords [K(18-c-6){CpArFe(η4-P4)}] (2, 18-c-6 = [18]crown-6), which features a planar cyclo-P42- ligand. The related diiron complex [Na2(THF)5(CpArFe)2(µ,η4:4-P4)] (3) was obtained by reducing 1 with sodium amalgam in the presence of P4. Protonation of 3 affords [Na(THF)3][(CpArFe)2(µ,η4:4-P4)(H)] (4), while the reaction of 3 with trimethylchlorosilane gives the nortricyclane compound P7(SiMe3)3 as the main product.

Electronic Structure and Magnetic Anisotropy of an Unsaturated Cyclopentadienyl Iron(I) Complex with 15†Valence Electrons.

The 15 valence-electron iron(I) complex [CpAr Fe(IiPr2 Me2 )] (1, CpAr =C5 (C6 H4 -4-Et)5 ; IiPr2 Me2 =1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) was synthesized in high yield from the FeII precursor [CpAr Fe(µ-Br)]2 . 57 Fe Mössbauer and EPR spectroscopic data, magnetic measurements, and ab initio ligand-field calculations indicate an S= 3/2 ground state with a large negative zero-field splitting. As a consequence, 1 features magnetic anisotropy with an effective spin-reversal barrier of Ueff =64 cm-1 . Moreover, 1 catalyzes the dehydrogenation of N,N-dimethylamine-borane, affording tetramethyl-1,3-diaza-2,4-diboretane under mild conditions.

Pentaarylcyclopentadienyl Iron, Cobalt, and Nickel Halides.

The preparation of new stable half-sandwich transition metal complexes, having a bulky cyclopentadienyl ligand C5(C6H4-4-Et)5 (Cp(Ar1)) or C5(C6H4-4-nBu)5 (Cp(Ar2)), is reported. The tetrahydrofuran (THF) adduct [Cp(Ar1)Fe(µ-Br)(THF)]2 (1a) was synthesized by reacting K[Cp(Ar1)] with [FeBr2(THF)2] in THF, and its molecular structure was determined by X-ray crystallography. Complex 1a easily loses its coordinated THF molecules under vacuum to form the solvent-free complex [Cp(Ar1)Fe(µ-Br)]2 (1b). The analogous complexes [Cp(Ar1)Co(µ-Br)]2 (2), [Cp(Ar1)Ni(µ-Br)]2 (3), and [Cp(Ar2)Ni(µ-Br)]2 (4) were synthesized from CoBr2 and [NiBr2(1,2-dimethoxyethane)]. The mononuclear, low-spin cobalt(III) and nickel(III) complexes [Cp(Ar2)MI2] (5, M = Co; 6, M = Ni) were prepared by reacting the radical Cp(Ar2) with NiI2 and CoI2. The complexes were characterized by NMR and UV-vis spectroscopies and by elemental analyses. Single-crystal X-ray structure analyses revealed that the dimeric complexes 1a, 1b, and 3 have a planar M2Br2 core, whereas 2 and 4 feature a puckered M2Br2 ring.

[Cp(Ar)Ni{Ga(nacnac)}]: An Open-Shell Nickel(I) Complex Supported by a Gallium(I) Carbenoid (Cp(Ar) = C5(C6H4-4-Et)5, nacnac = HC[C(Me)N-(C6H3)-2,6-iPr2]2).

The 17 valence electron (VE) open-shell nickel gallanediyl complex [Cp(Ar)Ni{Ga(nacnac)}] (3, Ar = C5(C6H4-4-Et)5, nacnac = HC[C(Me)N(C6H3-2,6-iPr2)]2), having an unsupported Ni-Ga bond, was synthesized from [Cp(Ar)Ni(µ-Br)]2 (1) by reducing the adduct [Cp(Ar)Ni(µ-Br){Ga(nacnac)}] (2) or, alternatively, trapping the "Cp(Ar)Ni(I)" synthon with Ga(nacnac); spectroscopic and DFT studies showed that the single unpaired electron in 3 resides mainly at the Ni center.

Halogenase-Inspired Oxidative Chlorination Using Flavin Photocatalysis.

Chlorine gas or electropositive chlorine reagents are used to prepare chlorinated aromatic compounds, which are found in pharmaceuticals, agrochemicals, and polymers, and serve as synthetic precursors for metal-catalyzed cross-couplings. Nature chlorinates with chloride anions, FAD-dependent halogenases, and O2 as the oxidant. A photocatalytic oxidative chlorination is described based on the organic dye riboflavin tetraacetate mimicking the enzymatic process. The chemical process allows within the suitable arene redox potential window a broader substrate scope compared to the specific activation in the enzymatic binding pocket.

C-H Photooxygenation of Alkyl Benzenes Catalyzed by Riboflavin Tetraacetate and a Non-Heme Iron Catalyst.

A mixture of the photocatalyst riboflavin tetraacetate (RFT) and the biomimetic non-heme iron complex [Fe(TPA)(MeCN)2](ClO4)2 (TPA = tris(2-pyridylmethyl)amine) efficiently catalyzes the visible-light-driven aerobic oxidation of alkyl benzenes to ketones and carboxylic acids. An RFT-catalyzed photocycle and the independent action of the iron complex as a catalyst for H2O2 disproportionation and alkyl benzene oxygenation ensure high yields and selectivities.

Photocatalytic benzylic C-H bond oxidation with a flavin scandium complex.

The enhanced reduction potential of riboflavin tetraacetate coordinating to scandium triflate enables the challenging photocatalytic C-H oxidation of electron-deficient alkylbenzenes and benzyl alcohols.