Pillarplexes: A Metal–Organic Class of Supramolecular Hosts

Novel octanuclear NHC complexes of gold­(I) and silver­(I) form metallocavitand structures with very defined tubular cavities and are able to selectively host linear molecules, exemplarily demonstrating 1,8‑diaminooctane as a model guest molecule. The solubility of the host-compounds is easily adjusted by simple anion exchange reactions so that the compounds can be made soluble in water wherein they exhibit a high longtime stability. The gold­(I) complex is emissive in aqueous solutions, which enables a determination of the binding constant to the diamine via luminescence quenching. The host–guest interaction was further investigated by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography

Iodine(III)-Catalyzed Cascade Reactions Enabling a Direct Access to β‑Lactams and α‑Hydroxy-β-amino Acids

In the presented method, a one-pot metal-free access to β-lactams is provided. The developed strategy employs a hypervalent iodine­(III)-triggered bromination/rearrangement/cyclization cascade reaction that allows the straightforward synthesis of a broad range of structurally different lactams from cheap and easily available imides. This triple cascade reaction is furthermore extendable by an in situ ring-opening reaction, giving direct access to isoserine derivatives from simple imines in a four-step, one-pot reaction

Iodine(III)-Catalyzed Cascade Reactions Enabling a Direct Access to β‑Lactams and α‑Hydroxy-β-amino Acids

In the presented method, a one-pot metal-free access to β-lactams is provided. The developed strategy employs a hypervalent iodine­(III)-triggered bromination/rearrangement/cyclization cascade reaction that allows the straightforward synthesis of a broad range of structurally different lactams from cheap and easily available imides. This triple cascade reaction is furthermore extendable by an in situ ring-opening reaction, giving direct access to isoserine derivatives from simple imines in a four-step, one-pot reaction

A Pd Halide Cluster from 1964: Pd₆Cl₈ Capped by Ring-Opened C₃Ph₃ Ligands from Oxidative Addition of Cyclopropenium Ions

On the basis of a protocol from 1964 on the reaction of K₂PdCl₄, triphenylcyclopropenium chloride, and ethylene, the product was now identified as a Pd₆Cl₈ cluster capped by μ₃-η¹:η¹:η³-C₃Ph₃ ligands, [C₃Ph₃]₂[Pd₆Cl₈(C₃Ph₃)₂]. The ligand is formed in a two-step reaction involving first the partial reduction of Pd­(II) to Pd(0) by ethylene and second the ring-opening oxidative addition of the cyclopropenium ion, leading to a rare binding mode with one allyl and two alkyl bonds. Although the structure was not recognized at that time, this compound represents the first isolated organometallic Pd cluster compound

Pyrrole as a Directing Group: Regioselective Pd(II)-Catalyzed Alkylation and Benzylation at the Benzene Core of 2‑Phenylpyrroles

Pyrrole has been employed for the first time as a directing group in the Pd­(II)-catalyzed <i>ortho</i>-functionalization of C­(sp²)–H bonds. A variety of substituted 2-phenylpyrroles were successfully methylated, alkylated, or benzylated in the <i>ortho</i>-position of the benzene ring, yielding the respective 2-substituted pyrrol-2-yl benzenes (36 examples, 51–93% yield). Neither additives nor additional ligands were required to perform the reaction, which was routinely conducted with PdBr₂ as the catalyst and Li₂CO₃ as the base. Mechanistically, there is evidence that precoordination of palladium to the pyrrole enables the regioselective <i>ortho</i>-attack

Synthesis of Soai Aldehydes for Asymmetric Autocatalysis by Desulfurative Cross-Coupling

Palladium-catalyzed dehydrosulfurative Liebes­kind–Srogl coupling of terminal alkynes with 2-mercapto-1,3-pyrimidine-5-carbaldehyde under base-free conditions provides 2-(alkynyl)-1,3-pyrimidine-5-carbaldehydes, which are substrates for autocatalytic amplification of chirality according to Soai et al. The mercapto aldehyde acceptor is obtained by condensation of Arnold’s vinamidinium salt with thiourea

NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations

In contrast to Nature that accomplishes polyene cyclizations seemingly with ease, such transformations are difficult to conduct in the lab. In our program dealing with the development of selective halogenations of alkenes, we now asserted that standard X⁺ reagents are perfectly suited for the biomimetic cation-π cyclization of both electron rich and poor linear polyenes in the presence of the Lewis base morpholine and the Lewis acid HFIP. The method stands out due to its broad substrate scope and practicability together with high chemical yields and excellent selectivities, even for highly challenging chloriranium-induced polyene cyclizations

Abnormal N‑Heterocyclic Carbene-Phosphine Ruthenium(II) Complexes as Active Catalysts for Transfer Hydrogenation

The bifunctional phosphine–abnormal N-heterocyclic carbene ruthenium­(II) complex RuBr­(OAc)­(PPh₃)­(P–aNHC) (<b>1</b>) has been synthesized in high yield by reaction of Ru­(OAc)₂(PPh₃)₂ with a phosphine imidazolium bromide (P–NHC × HBr) and characterized by X-ray diffraction. This compound shows high catalytic activity for the transfer hydrogenation of ketones to alcohols in 2-propanol. Rate and efficiency of <b>1</b> can be enhanced by the addition of ethylenediamine or benzylamine, affording TOFs up to 140 000 h^–1. Reaction of <b>1</b> with ethylenediamine leads to the Ru carbene/amine complex [Ru­(OAc)­(PPh₃)­(P–aNHC)­(H₂NCH₂CH₂NH₂)]Br (<b>2</b>), which displays the same activity of the <i>in situ</i> generated species

NXS, Morpholine, and HFIP: The Ideal Combination for Biomimetic Haliranium-Induced Polyene Cyclizations

In contrast to Nature that accomplishes polyene cyclizations seemingly with ease, such transformations are difficult to conduct in the lab. In our program dealing with the development of selective halogenations of alkenes, we now asserted that standard X⁺ reagents are perfectly suited for the biomimetic cation-π cyclization of both electron rich and poor linear polyenes in the presence of the Lewis base morpholine and the Lewis acid HFIP. The method stands out due to its broad substrate scope and practicability together with high chemical yields and excellent selectivities, even for highly challenging chloriranium-induced polyene cyclizations

Toward New Organometallic Architectures: Synthesis of Carbene-Centered Rhodium and Palladium Bisphosphine Complexes. Stability and Reactivity of [PC^BImPRh(L)][PF₆] Pincers

In this article, we report the synthesis of a tridentate carbene-centered bisphosphine ligand precursor and its complexes. The developed four-step synthetic strategy of a new PC^BImP pincer ligand represents the derivatization of benzimidazole in the first and third positions by (diphenylphosphoryl)­methylene synthone, followed by phosphine deprotection and subsequent insertion of a noncoordinating anion. The obtained ligand precursor undergoes complexation, with PdCl₂ and [μ-OCH₃Rh­(COD)]₂ smoothly forming the target organometallics [PC^BImPPdCl]­[PF₆] and [PC^BImPRh­(L)]­[PF₆] under mild hydrogenation conditions. A more detailed study of the rhodium complexes [PC^BImPRh­(L)]­[PF₆] reveals significant thermal stability of the PC^BImPRh moiety in the solid state as well as in solution. The chemical behavior of 1,3-bis­(diphenylphosphinomethylene)­benzimidazol-2-ylrhodium acetonitrile hexafluorophosphate has been screened under decarbonylation, hydrogenation, and hydroboration reaction conditions. Thus, the PC^BImPRh^I complex is a sufficiently stable compound, with the potential to be applied in catalysis