Atroposelective Ir-Catalyzed C–H Borylation of Phthalazine Heterobiaryls

The atroposelective iridium-catalyzed borylation of menthyloxy-substituted phthalazine heterobiaryls with diborons is reported. Utilizing [Ir(OMe)(COD)]2/2-aminopyridine as a rarely used efficient catalyst system, the heterobiaryls were selectively borylated in the 2-position of the carbocycle, exclusively yielding only one of the atropisomers, depending on the substitution of the phthalazine with (+)-menthyl or (−)-menthyl moieties. Exemplary further functionalization of a borylated atropisomer demonstrated that nickel-catalyzed Suzuki-Miyaura cross-coupling with an aryl halide was able to provide stereoretention to a certain degree (up to 75% de)

CoCl(PPh₃)₃ as Cyclotrimerization Catalyst for Functionalized Triynes under Mild Conditions

The ubiquitary Co­(I) complex CoCl­(PPh₃)₃ was found to be a convenient catalyst for the [2 + 2 + 2] cycloaddition of functionalized triynes under mild reaction conditions and devoid of any additional additive, yielding the substituted arene compounds. Successful development of synthetic routes to various triynes and the subsequent cyclotrimerization key step gave systematic access to a variety of different bi- and triaryls with good to excellent yields for the cyclization

Formation and Reactivity of a Co₄‑μ-Alkyne Cluster from a Co(I)-Alkene Complex

Highly reactive Co­(I) complex [CpCo­(H₂CCHSiMe₃)₂] (<b>1</b>) easily forms a tetranuclear Co₄ cluster in hydrocarbon solvents under mild conditions, possessing a bridging alkyne ligand stemming from an unusual C–H activation of the H₂CCHSiMe₃ ligand. The cluster was structurally characterized, and the catalytic reactivity in [2+2+2] cycloaddition, hydroformylation, and hydrogenation reactions investigated. Interesting differences were found and compared to the mononuclear complex <b>1</b>, which could be relevant for the real catalytically active species

Synthesis and Catalytic Activity of [Cp′Co(COD)] Complexes Bearing Pendant N‑Containing Groups

The novel Co­(I)-complex [Cp^CNCo­(COD)] (Cp^CN = η⁵-(C₅H₄CMe₂CH₂CN), COD = 1,5-cyclooctadiene; <b>3</b>) with a substituted cyclopentadienyl ligand containing a pendant nitrile moiety has been synthesized and characterized by X-ray diffraction. The reactivity of the nitrile group in <b>3</b> has been investigated regarding its behavior in cyclization reactions with alkynes, leading to three new complexes containing pendant 2-pyridyl groups. All synthesized complexes have been evaluated as catalysts in the [2 + 2 + 2] cycloaddition reaction of 1,6-heptadiyne and benzonitrile

Synthesis of Naphthylpyridines from Unsymmetrical Naphthylheptadiynes and the Configurational Stability of the Biaryl Axis

A series of different unsymmetrically substituted naphthyl-based diynes were synthesized. These substrates formed the foundation for the assembly of novel biaryls containing pyridine moieties with differently substituted five-membered rings in the backbone of the newly formed heterobiaryl system. The key step for their efficient construction was the photo- and cobalt-catalyzed [2 + 2 + 2] cycloaddition reaction between the corresponding naphthyldiyne and aceto- or benzonitrile. The heterobiaryl products have been isolated and investigated with respect to the configurational stability of their biaryl axis using dynamic chiral HPLC; subtle effects of the substitution pattern on the stability of the axis were observed. For several compounds the activation barriers (Δ<i>G</i>^‡) of racemization were determined. Suitable substitution of the five-membered ring backbone exemplarily allowed the Co-catalyzed enantioselective cyclization to yield the enantiomerically enriched heterobiaryl