Zinc-Catalyzed Hydroalkoxylation/Cyclization of Alkynyl Alcohols

Despite the great interest in zinc catalysis for hydroelementation reactions, the use of zinc complexes as catalysts for the hydroalkoxylation of alkynyl alcohols has not been reported to date. Scorpionate zinc complexes have been successfully designed as precatalysts for the hydroalkoxylation reaction of alkynyl alcohols under mild reaction conditions. Zinc amide complex 8 has been shown to be an excellent precatalyst for the highly selective intramolecular hydroalkoxylation process to yield the corresponding exocyclic enol ethers. Kinetic studies have been performed and confirmed that reactions are first-order in [catalyst] and zero-order in [alkynyl alcohol]. NMR spectroscopy and X-ray diffraction analysis provided evidence for the formation of an alkynyl zinc compound which has been shown to be a key intermediate in the hydroalkoxylation process. On the basis of the experimental results, a catalytic cycle is proposed.

Design, scope and mechanism of highly active and selective chiral NHC-iridium catalysts for the intramolecular hydroamination of a variety of unactivated aminoalkenes

Chiral, cationic NHC-iridium complexes are introduced as catalysts for the intramolecular hydroamination reaction of unactivated aminoalkenes. The catalysts show high activity in the construction of a range of 5- and 6-membered N-heterocycles, which are accessed in excellent optical purity, with various functional groups being tolerated with this system. A major deactivation pathway is presented and eliminated by using alternative reaction conditions. A detailed experimental and computational study on the reaction mechanism is performed providing valuable insights into the mode of action of the catalytic system and pointing to future modifications to be made for this catalytic platform.

Multiple coordination modes of a new ditopic bis(pyrazolyl)methane-based ligand

A new ditopic ligand, N-(2,2-bis(pyrazolyl)ethyl)-2,2-bis(pyrazolyl)acetamide ((pz)₂CH-C(O)-NH-CH₂-CH(pz)₂, L4Pz, pz = pyrazolyl ring), comprising two bis(pyrazolyl)methane donor groups linked via an amide bridge, has been prepared from the reaction of HOOCCH(pz)₂ and H₂NCH₂CH(pz)₂. The ligand coordinates to various metallic salts (i.e. AgO₃SCF₃, PdCl₂, Re(CO)₅Br, and Fe(BF₄)₂), in either a κ²-μ-κ² or a κ³-μ-κ² fashion, depending on the coordination preferences of the metallic center. These compounds were characterized by NMR, UV-Vis and IR spectroscopy, and in solid state by single crystal X-ray diffraction. In the case of silver(i), a mono-dimensional coordination polymer was obtained, while the others were found to be discrete complexes. The synthesis and characterization of a heterobimetallic complex is also described. In solid state, all compounds are associated into supramolecular architectures via hydrogen bonding and pyrazolyl embrace interactions.

An Efficient and Versatile Lanthanum Heteroscorpionate Catalyst for Carbon Dioxide Fixation into Cyclic Carbonates

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.

Rigid NON-donor pincer ligand complexes of lutetium and lanthanum: synthesis and hydroamination catalysis

A rigid NON-donor pincer ligand was employed for the synthesis of neutral lutetium and anionic lanthanum alkyl complexes; the former is highly active for both intra- and inter-molecular hydroamination.

Rare-earth metal diisopropylamide-catalyzed intramolecular hydroamination

Well-defined rare-earth metal diisopropylamide complexes provide an exemplary case study to investigate the effect of donor solvent, alkali metal, chloro co-ligands, and in situ catalyst formation.