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We report the synthesis and characterization of uranium(IV) and thorium(IV) mesoionic carbene complexes [An{N(SiMe

A series of Ni complexes [Ni(Cl)2(PR3)2] with R = Me (1-Me), nPr (1-nPr), and nBu (1-nBu) and nickelocenes [Ni(η5-C5H4R′)2] with R′ = H (2-H), Me (2-Me), and SiMe3 (2-SiMe3) were synthesized and ch...

A systematic quantum chemical study of the bonding in d6 -transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R3 P)2 E, as ligands (E=AlH, BH, CH+ , C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M-E bond is accompanied by weak P-E bonds, and vice versa. Although the Al-M bond is, for example, found to be very strong, the weak Al-P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal-ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal-ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E-H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.

Easy-to-prepare η2 -coordinated phosphine-borane ligands are demonstrated to liberate hydrogen upon treatment with different σ-donor/π-acceptor ligands (CO, tBuNC, CN- ). Depending on the utilized ancillary ligand, different reaction pathways are observed, ranging from simple hydride protonation to iron-boron bond formation and subsequent rearrangement to pincer-type ligands based on a tricoordinate boron centre. The last-named reactivity is in line with a formal umpolung at the boron centre from a Lewis acidic borane to a Lewis basic boron-based donor ligand.

The platform of pincer ligands offers the opportunity to stabilize elusive groups in the coordination sphere of a metal. These groups often exhibit unusual bonding properties and can show unprecedented reactivity patterns, which are potentially useful for (cooperative) catalysis. In the current review, we compare pincer ligands whose central donor group exhibits a sp3-hybridized atom. The primary focus lies on the comparison of reactivity patterns of these formally isoelectronic donor groups. In particular, secondary amine groups, well known to act cooperatively as a proton relay, are compared with recently reported ligands that are based on boron and carbon. In the ABC in pincer chemistry, we will demonstrate that in contrast to Amine donor-groups, ligand-stabilized Borylenes are not acting as a proton source and rather undergo a reversible redox-reaction with the coordinated metal centre. The different types of Carbon-based ligands rather show characteristics of amine reactivity, but there is evidence for some complexes that a reversible redox reaction might be a possible exchange mechanism. Moreover, this review tries to analyze the bonding situation of the aforementioned species and to distinguish them from other related ligand types and their reactivity patterns.

An iron pincer complex containing a hemi-labile (R₃P)₂BH₂-group exhibits temperature-switchable reactivity patterns: a reversible B-H-activation concomitant with a P-B-bond cleavage is observed at room temperature. Below 4 °C intra- and inter-molecular C-H-activation pathways are becoming faster and dominating. Mechanistic investigations reveal that the lability of the (R₃P)₂BH₂-group in combination with the exothermic formation of σ-bonded complexes are responsible for the switchable bond activation. Finally, a protocol for an iron-catalysed C-H-activation in the absence of oxidants has been developed.

Unusual binding properties, enabling the stabilization of elusive species, and beneficial properties for homogeneous catalysts have been predicted and demonstrated for ligand-stabilized main group fragments, such as carbodiphosphoranes and -carbenes. However, the quantification and comparison of their binding properties by experimental means still represent major challenges. In this article, we describe a series of iridium(III) pincer complexes of the type [(PEP)IrCl(CO)(H)] q enabling the quantification of the donor strength of the central donor group E ( q = 0, +1, +2). Our investigations show that phosphine-stabilized boron(I) and carbon(0) compounds are exceptionally strong neutral donor groups in comparison to common spectator ligands in homogeneous catalysis such as carbenes and phosphines. Our experimental and computational results for the first time allow and justify the comparison of the donor strength of cationic, neutral, and anionic ligands. On the basis of quantum chemical investigations, we further demonstrate that the heavier homologues of phosphine-stabilized borylenes and carbon(0) compounds exhibit slightly diminished donor properties.

We report a novel method for the preparation of PBP-pincer complexes from bis(phosphine)boronium salts. The central (R3P)2HB-moiety in a palladium complex is demonstrated to be a L-type ligand, therewith completing a series of pincer-type complexes with Z-, X- and L-type boron-based ligands, respectively.

Stabilized borylenes (L2 BH:) with weakly π-accepting substituents L, such as phosphines, were previously believed to be unstable. In the current manuscript, we describe a series of complexes formally containing a phosphine-stabilized borylene or boryl anion. In contrast to common trivalent boron compounds, the boron-based ligands in this study act as electron-donating ligands. The reported iron hydride complexes exhibit a unique reactivity pattern, undergoing a reversible B-H reductive elimination concomitant with oxidation of the boron(I) center.

Stabilisierte Borylene (L2BH:) mit schwach π-akzeptierenden Substituenten L, wie Phosphanen, galten bisher als instabil. Hier beschreiben wir eine Serie von Komplexen, die formal ein Phosphan-stabilisiertes Borylen oder Boryl-Anion als Liganden enthalten. Im Unterschied zu gangigen dreibindigen Bor-Verbindungen agieren die hier beschriebenen Liganden als elektronendonierende Liganden. Die erhaltenen Eisen-Hydrid-Komplexe weisen eine ungewohnliche Reaktivitat auf und reagieren reversibel unter reduktiver B-H-Eliminierung, die formal mit einer Oxidation der Bor(I)-Donorgruppe einhergeht.

Two missing compounds within the binary K-Se system have been synthesized and structurally characterized by means of single-crystal diffraction. β-K2Se2 comprises cell parameters that are in line with predictions made from the series α/β-A2Chx. K2Se4, in contrast, incorporates “Se5 2–” chains with 50% occupation of the terminal selenium atoms, and has been synthesized on a rather unconventional solvothermal pathway employing successively mercury and ethylene dithiol as solvents.

Quantum theoretical studies show that the extremely high proton affinity at the metal center of the unusual T-shaped (LXL)AuI -pincer complex, consisting of a carbazole framework and two mesoionic carbenes, is caused by relativistic effects. This brings the basicity of the AuI center in line with the electron-rich nitrogen atom of the carbazole ring system, resulting in one of the highest proton affinities for a neutral molecule.

An iron pincer complex containing a hemi-labile (R

A series of iron(II) dihalogenide complexes with two different bisphosphinoethane ligands is reported. In the case of 1,2-bis(diphenylphosphanyl)ethane (dppe), depending on the stoichiometry, the tetrahedral [(μ-dppe)FeCl2]n and octahedral trans-[(dppe)2FeCl2] complexes are formed. The polymeric complex [(μ-dppe)FeCl2]n, with iron in a tetrahedral environment, preferentially reacts with chelating amines to give the octahedral diphosphine complex, trans-[(dppe)2FeCl2], and different octahedral amine complexes. With the sterically more demanding 1,2-bis(diisopropylphosphanyl)ethane (dippe), the monomeric and tetrahedral halogen complexes [(dippe)FeX2] are exclusively obtained (X = Cl, Br). These complexes react with chelating amines in a similar manner, to give free ligand and the corresponding octahedral amine complex. The present results suggest that the diphosphines in the investigated iron(II) complexes are bound too weakly to form productive catalyst precursors.

Reduction of chalcogen-rich Pb:Ch (1:2) phases in ethane-1,2-diamine (en) by elemental alkali metals results in the formation of solutions of [Pb2Ch3]2– of high purity and abundance. In contrast, application of the same reaction conditions to a binary Bi:Te (1:2) phase yields the mononuclear [BiTe3]3– anion. Instead of the expected [Tl2Te3]4– or [Tl2Te2]2– anions, analogous reactions with a Tl:Te (1:1) phase end up with a C–C-bond cleavage of the solvent en with formation of a salt of the telluridocyanate (N≡C–Te)– anion. Side reactions of en and elemental cesium are presented and metalate solutions are investigated with NMR spectroscopy.

Reduction of chalcogen-rich Pb:Ch (1:2) phases in ethane-1,2-diamine (en) by elemental alkali metals results in the formation of solutions of [Pb2Ch3]2– of high purity and abundance. In contrast, application of the same reaction conditions to a binary Bi:Te (1:2) phase yields the mononuclear [BiTe3]3– anion. Instead of the expected [Tl2Te3]4– or [Tl2Te2]2– anions, analogous reactions with a Tl:Te (1:1) phase end up with a C–C-bond cleavage of the solvent en with formation of a salt of the telluridocyanate (N≡C–Te)– anion. Side reactions of en and elemental cesium are presented and metalate solutions are investigated with NMR spectroscopy.