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)

Calcium-Based Catalytic System for the Synthesis of Bio-Derived Cyclic Carbonates under Mild Conditions

Recently, bio-derived cyclic carbonates have gained significant importance: e.g., as building blocks in non-isocyanate polyurethanes (NIPUs). Herein we report the development of a calcium-based catalyst system for the synthesis of challenging internal and trisubstituted cyclic carbonates from bio-derived epoxides and CO₂ under mild reaction conditions. Several crown ethers were tested as ligands in combination with various cocatalysts for the possible activation of CO₂. The most active system consists of a dicyclohexyl-functionalized 18-crown-6 ether and triphenylphosphane in addition to calcium iodide. The in situ complexation of Ca²⁺ by the crown ether was detected by ¹H NMR spectroscopy. Interestingly, the addition of triphenylphosphane as a cocatalyst leads to a significant increase in activity, which is similar to or even higher than that of organic superbases such as DBU and TBD. The catalytic system was employed in the conversion of 16 different bio-derived epoxides, including fatty acid esters, oils, and terpenes with CO₂, and is able to facilitate the reaction under mild conditions. Various internal epoxides were converted at only 45 °C, 0.5 MPa CO₂ pressure, a catalyst loading of 5 mol %, and a reaction time of 24 h with isolated yields up to 98% of the respective carbonate. The challenging terpene-based carbonates were isolated in yields up to 81%, although harsher reaction conditions were necessary

Selective Hydrogenation of Ruthenium Acylphosphine Complexes

Hydrogenation of a benzene ruthenium chloride dimer in the presence of novel acyl­phosphine (phosphomide) ligands resulted in the formation of corresponding ruthenium­(II)–benzyl phosphine complexes. Here, selective reduction of the carbonyl group to a methylene unit takes place with molecular hydrogen under mild conditions in good yield. This approach provides an alternative synthesis of ruthenium phosphine complexes of benzyl and heterobenzyl phosphine ligands

Calcium-Based Catalytic System for the Synthesis of Bio-Derived Cyclic Carbonates under Mild Conditions

Recently, bio-derived cyclic carbonates have gained significant importance: e.g., as building blocks in non-isocyanate polyurethanes (NIPUs). Herein we report the development of a calcium-based catalyst system for the synthesis of challenging internal and trisubstituted cyclic carbonates from bio-derived epoxides and CO₂ under mild reaction conditions. Several crown ethers were tested as ligands in combination with various cocatalysts for the possible activation of CO₂. The most active system consists of a dicyclohexyl-functionalized 18-crown-6 ether and triphenylphosphane in addition to calcium iodide. The in situ complexation of Ca²⁺ by the crown ether was detected by ¹H NMR spectroscopy. Interestingly, the addition of triphenylphosphane as a cocatalyst leads to a significant increase in activity, which is similar to or even higher than that of organic superbases such as DBU and TBD. The catalytic system was employed in the conversion of 16 different bio-derived epoxides, including fatty acid esters, oils, and terpenes with CO₂, and is able to facilitate the reaction under mild conditions. Various internal epoxides were converted at only 45 °C, 0.5 MPa CO₂ pressure, a catalyst loading of 5 mol %, and a reaction time of 24 h with isolated yields up to 98% of the respective carbonate. The challenging terpene-based carbonates were isolated in yields up to 81%, although harsher reaction conditions were necessary

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

Selective Hydrogenation of Ruthenium Acylphosphine Complexes

Hydrogenation of a benzene ruthenium chloride dimer in the presence of novel acyl­phosphine (phosphomide) ligands resulted in the formation of corresponding ruthenium­(II)–benzyl phosphine complexes. Here, selective reduction of the carbonyl group to a methylene unit takes place with molecular hydrogen under mild conditions in good yield. This approach provides an alternative synthesis of ruthenium phosphine complexes of benzyl and heterobenzyl phosphine ligands

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

<i>P</i>‑Chirogenic Xantphos Ligands and Related Ether Diphosphines: Synthesis and Application in Rhodium-Catalyzed Asymmetric Hydrogenation

A series of <i>P</i>-chirogenic Xantphos ligands and related diaryl ether diphosphines have been synthesized by a modification of the well-established Jugé method. The approach consists of the in situ deboranation of the chiral ephedrine-based phosphinite before the P–C coupling takes place. The stereochemical integrity of the stereocenters of the diphosphines during synthesis, long-time storage, and catalytic application was evaluated. In the rhodium-catalyzed asymmetric hydrogenation of isophorone as a model substrate for industrially relevant prostereogenic enones with some of the diphosphines, almost complete conversion, high chemoselectivity, and 96% ee were achieved

Hydrogenation of Esters Catalyzed by Bis(<i>N</i>‑Heterocyclic Carbene) Molybdenum Complexes

A series of Mo complexes bearing inexpensive bidentate bis­(NHC) ligands have been synthesized and characterized by NMR and IR spectroscopy as well as single crystal XRD analysis. These complexes proved to be efficient for the catalytic hydrogenation of aliphatic and aromatic esters (>35 examples) operating at low catalyst loadings (0.5–2 mol %) and temperatures (80–120 °C). Various functional groups, e.g., CC double bonds, nitriles, alcohols, tertiary amines, halides, and acetals, as well as heteroaromatic substrates, lactones, and diesters, are tolerated by the optimal catalyst system. Based on NMR spectroscopic investigations, control experiments and DFT computations a non-bifunctional outer-sphere hydrogenation mechanism is proposed

Hydrogenation of Esters Catalyzed by Bis(<i>N</i>‑Heterocyclic Carbene) Molybdenum Complexes

A series of Mo complexes bearing inexpensive bidentate bis­(NHC) ligands have been synthesized and characterized by NMR and IR spectroscopy as well as single crystal XRD analysis. These complexes proved to be efficient for the catalytic hydrogenation of aliphatic and aromatic esters (>35 examples) operating at low catalyst loadings (0.5–2 mol %) and temperatures (80–120 °C). Various functional groups, e.g., CC double bonds, nitriles, alcohols, tertiary amines, halides, and acetals, as well as heteroaromatic substrates, lactones, and diesters, are tolerated by the optimal catalyst system. Based on NMR spectroscopic investigations, control experiments and DFT computations a non-bifunctional outer-sphere hydrogenation mechanism is proposed