Complexes [(C₄Me₄)Co(CO)₂{Co(P₂C₂tBu₂)₂}] (1, C₄Me₄ = tetramethylcyclobutadiene) and [CpNi{Co(P₂C₂tBu₂)₂}(PPh₃)] (2, Cp = cyclopentadienyl) were synthesized by transmetalating [Tl(thf)₂{Co(P₂C₂tBu₂)₂}] with [(C₄Me₄)Co(CO)₂I] and [CpNiBr(PPh₃)]. Compounds 1 and 2 were fully characterized by X-ray crystallography, multinuclear NMR, UV/Vis, and IR spectroscopy, and elemental analysis. Their molecular structures show σ-coordination of one phosphorus atom of the [Co(P₂C₂tBu₂)₂]^– anion to the second metal atom (cobalt or nickel). Time-dependent density functional theory (TD-DFT) calculations were applied to gain insight into the electronic structures and the nature of the electronic transitions observed in the UV/Vis spectra. Cyclic voltammetry studies revealed the similar redox behavior of 1 and 2, which are reversibly oxidized to the corresponding monocations 1⁺ and 2⁺ with retention of the dinuclear structures. The cyclic voltammograms furthermore show that 1 and 2 decompose upon reduction with cleavage of the dinuclear structures into the free [Co(P₂C₂tBu₂)₂]^– anion and further uncharacterized products.

Chlorierte Arene sind Bestandteil vieler Pharmazeutika, Agrochemikalien und Polymere sowie wichtige Startmaterialien für übergangsmetallkatalysierte Kreuzkupplungen. Für ihre Herstellung nutzen Chemiker meist Chlorgas oder elektropositive Chlorierungsreagentien. Die Natur hingegen chloriert ausgehend von Chloridionen mithilfe von FAD-abhängigen Halogenasen und O₂ als Oxidationsmittel. Wir beschreiben hier eine diesem enzymatischen Prozess nachempfundene photokatalytische oxidative Chlorierung unter Verwendung des organischen Farbstoffes Riboflavintetraacetat. Dieses chemische Verfahren ermöglicht die Umsetzung von Arenen innerhalb eines definierten Redoxbereichs und hat eine größere Substratbreite als die Aktivierung durch eine substratspezifische Enzymbindungstasche.

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.

Eine Mischung von Riboflavintetraacetat (RFT) mit dem Nicht-Häm-Eisenkomplex [Fe(TPA)(MeCN)₂](ClO₄)₂ (TPA=Tris(2-pyridylmethyl)amin) katalysiert effizient die aerobe Photooxidation von Alkylbenzolen zu Ketonen und Carbonsäuren. Hohe Ausbeuten und Selektivitäten werden durch den flavinkatalysierten Photoredoxzyklus und die davon unabhängige katalytische Wirkung des Eisenkomplexes in der H₂O₂-Disproportionierung und der Alkylbenzol-Oxygenierung erreicht.

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.

1,3-Diphosphacyclobutadiene complexes have previously been employed as metalloligands to a few transition metals such as tungsten, cobalt, rhodium, platinum, and gold. Here, we describe the synthesis and the structural and spectroscopic characterization of novel copper(I) and silver(I) complexes with the sandwich anions [Co(η⁴-P₂C₂R₂)₂]^– (R = tBu or tPent). Reactions of [K(thf)₃{Co(P₂C₂tPent₂)₂}] and [K(thf)₂{Co(P₂C₂tBu₂)₂}] with CuCl(PPh₃)/PPh₃ yielded mononuclear copper(I) complexes [Cu{Co(P₂C₂R₂)₂}(PPh₃)₂] [R = tPent (1), tBu (2)]. The salt [Cu(PMe₃)₄][Co(P₂C₂tPent₂)₂] (3), which consists of a [Cu(PMe₃)₄]⁺ cation and a noncoordinated [Co(P₂C₂tPent₂)₂]^– anion, was obtained when [K(thf)₃{Co(P₂C₂tPent₂)₂}] was treated with CuCl(PPh₃) in the presence of an excess amount of PMe₃. Salt metathesis of [K(thf)₃{Co(P₂C₂tPent₂)₂}] with AgCl and AgSbF₆ in the presence of PMe₃ afforded novel silver(I) complexes [Ag{Co(P₂C₂tPent₂)₂}(PMe₃)₃] (4), [Ag{Co(P₂C₂tPent₂)₂}(PMe₃)₂] (5), and [Ag₂{Co(P₂C₂tPent₂)₂}(PMe₃)₅]SbF₆ (6). The molecular structures of 1, 2, 5, and 6 were determined by X-ray crystallography. The solution behavior of 1–6 was analyzed by variable-temperature ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectroscopy in [D₈]THF. ³¹P solution and solid-state NMR spectra, aided by two-dimensional dipolar and/or J-based correlation spectroscopy, support the proposed structures and allowed the compositions of polycrystalline precipitated products to be analyzed. Furthermore, characteristic ³¹P chemical shifts and indirect spin–spin coupling constants offer a clear distinction between different bonding patterns realized in this class of compounds.

Molecular squares are among the most common supramolecular architectures, but phospha-organometallic complexes have not been used as building blocks for this type of structure. Herein we describe the formation of the molecular square [Au{Co(P₂C₂tBu₂)₂}]₄ (1) by the self-assembly of anionic 1,3-diphosphacyclobutadiene cobalt complexes and gold(I) cations. The X-ray crystallographic determination of the molecular structure of 1 is complemented by solid-state ³¹P and ¹³C NMR investigations. High-level DFT calculations confirm the assignment of the ³¹P and ¹³C NMR resonances.

75 years after the discovery of hydroformylation, cobalt catalysts are now undergoing a renaissance in hydrogenation reactions. We have evaluated arene metalates in which the low-valent metal species is—conceptually different from heteroatom-based ligands—stabilized by π coordination to hydrocarbons. Potassium bis(anthracene)cobaltate 1 and -ferrate 2 can be viewed as synthetic precursors of quasi-“naked” anionic metal species; their aggregation is effectively impeded by (labile) coordination to the various π acceptors present in the hydrogenation reactions of unsaturated molecules (alkenes, arenes, carbonyl compounds). Kinetic studies, NMR spectroscopy, and poisoning studies of alkene hydrogenations support the formation of a homogeneous catalyst derived from 1 which is stabilized by the coordination of alkenes. This catalyst concept complements the use of complexes with heteroatom donor ligands for reductive processes.

Molekulare Quadrate gehören zu den bekanntesten Typen von supramolekularen Architekturen. Phosphorhaltige metallorganische Baueinheiten fanden in derartigen Strukturen bisher allerdings keine Verwendung. Hier beschreiben wir die Synthese eines molekularen Quadrats aus vier Gold- und vier Cobaltatomen, das durch Selbstorganisation von anionischen 1,3-Diphosphacyclobutadien-Komplexen und Gold(I)-Kationen gebildet wird. Die röntgenkristallographische Bestimmung der Molekülstruktur der Verbindung [Au{Co(P₂C₂tBu₂)₂}]₄ (1) wird durch ³¹P- und ¹³C-NMR-spektroskopische Untersuchungen im Festkörper komplementiert. DFT-Rechnungen bestätigen die Zuordnung der ³¹P- und ¹³C-NMR-Signale.

75 Jahre nach der Entdeckung der Hydroformylierung erleben Cobalt-Katalysatoren eine Renaissance in Hydrierungen. Wir haben Arenmetallate untersucht, in denen die niedervalente Metallspezies nicht durch Heteroatom-Liganden, sondern durch einfache π-Kohlenwasserstoffe stabilisiert ist. Kaliumbis(anthracen)cobaltat 1 und -ferrat 2 sind synthetische Vorstufen für quasi-“nackte” anionische Metallspezies. Eine Aggregation wird durch (labile) Koordination der in Hydrierungen vorhandenen π-Akzeptoren (Olefine, Arene, Carbonylverbindungen) effektiv unterdrückt. Kinetische Studien, NMR-Spektroskopie und Vergiftungsexperimente in Alkenhydrierungen bestätigen die Bildung eines homogenen Katalysators aus 1, der durch Ligandenaustausch gebildet und durch Koordination an Alkene stabilisiert wird. Das zugrundeliegende Katalysatorkonzept ist komplementär zur Verwendung von Komplexen mit Heteroatom-Donorliganden in reduktiven Prozessen.

The utility of the fac-[RuH₃(PR₃)₃]^– anion (R = Ph, C₆H₄-4-Me) for the preparation of new oligonuclear transition metal polyhydrides has been examined. The lithium salts [Li(thf)_x{Ru(μ-H)₃(PPh₃)₃}] {1: R = Ph, x = 3; 1′: R = C₆H₄-4-Me (Tol), x = 2.5} react with [Cp*RuCl]₄ (Cp* = C₅Me₅), ZnCl₂, and CuCl(SMe₂) to form new oligonuclear polyhydrido complexes. The compounds [Cp*Ru(μ-H)₃Ru(PR₃)₃] (2: R = Ph, 2′: R = Tol), [Zn{Ru(μ-H)₃(PPh₃)₃}₂] (3), and [Cu₂{Ru(μ-H)₃(PPh₃)₃}₂] (4) were synthesized and characterized by multinuclear NMR and IR spectroscopy, and microanalysis. The molecular structures were determined by X-ray crystallography. Density functional theory calculations at the PBE-D3/def2-TZVP level support the proposed structures of the new polyhydride complexes. The impact of intramolecular London dispersion interactions on the optimized geometries is discussed.

The synthesis and structural characterization of the first coordination compounds of bis(diphosphacyclobutadiene) cobaltate anions [M(P₂C₂R₂)₂]⁻ is described. Reactions of the new potassium salts [K(thf)₃{Co(η⁴-P₂C₂tPent₂)₂}] (1) and [K(thf)₄{Co(η⁴-P₂C₂Ad₂)₂}] (2) with [AuCl(tht)] (tht=tetrahydrothiophene), [AuCl(PPh₃)] and Ag[SbF₆] afforded the complexes [Au{Co(P₂C₂tPent₂)₂}(PMe₃)₂] (3), [Au{Co(P₂C₂Ad₂)₂}]_x (4), [Ag{Co(P₂C₂Ad₂)₂}]_x (5), [Au(PMe₃)₄][Au{Co(P₂C₂Ad₂)₂}₂] (6), [K([18]crown-6)(thf)₂][Au{Co(P₂C₂Ad₂)₂}₂] (7), and [K([18]crown-6)(thf)₂][M{Co(P₂C₂Ad₂)₂}₂] (8: M=Au 9: M=Ag) in moderate yields. The molecular structures of 2 and 3, and 6–9 were elucidated by X-ray crystallography. Complexes 4–9 were thoroughly characterized by ³¹P and ¹³C solid state NMR spectroscopy. The complexes [Au{Co(P₂C₂Ad₂)₂}]_x (4) and [Ag{Co(P₂C₂Ad₂)₂}]_x (5) exist as coordination polymers in the solid state. The linking mode between the monomeric units in the polymers is deduced. The soluble complexes 1–3, 6, and 7 were studied by multinuclear ¹H-, ³¹P{¹H}-, and ¹³C{¹H} NMR spectroscopy in solution. Variable temperature NMR measurements of 3 and 6 in deuterated THF reveal the formation of equilibria between the ionic species [Au(PMe₃)₄]⁺, [Au(PMe₃)₂]⁺, [Co(P₂C₂R₂)₂]⁻, and [Au{Co(P₂C₂R₂)₂}₂]⁻ (R=tPent and Ad).

Although there has been much interest in the chemistry of bimetallic transition metal complexes, compounds with naphthalene or anthracene as bridging ligands are still rare. In this article, we describe the synthesis of the homodinuclear iron complexes [Cp*Fe(μ-η⁴:η⁴-L)FeCp*] (1: L = C₁₀H₈, 2: L = C₁₄H₁₀; Cp* = η⁵-C₅Me₅). The complexes were characterized by ¹H and ¹³C{¹H} NMR, UV/Vis, and ⁵⁷Fe Mössbauer spectroscopy, and their molecular structures were determined by X-ray crystallography. Both complexes are diamagnetic as a result of the strong magnetic coupling of the 17e Fe^I centers mediated by the polyarene bridge. An analysisof the redox behavior of 1 and 2 by cyclic voltammetry andUV/Vis spectroelectrochemistry shows that the complexes can be oxidized reversibly in two well-separated one-electron steps to the monocation [Cp*Fe(μ-L)FeCp*]⁺ and the dication [Cp*Fe(μ-L)FeCp*]²⁺. The reduction to the monoanion [Cp*Fe(μ-L)FeCp*]^– was also observed.