Silver-Catalyzed Carboxylative Cyclization of Primary Propargyl Alcohols with CO2.

By using silver complexes with bulky ligands such as DavePhos or N-heterocyclic carbenes, propargylic alcohols are smoothly converted with CO2 into a unique class of unexplored cyclic alkylidene carbonates. These systems, for the first time, also achieve the direct carboxylative cyclization of primary propargylic alcohols. The silver-DavePhos catalyst is further applied for the bis-carboxylative cyclization of primary propargyl derivatives, thereby providing an effective route to a series of previously inaccessible and industrially relevant α-alkylidene cyclic carbonates.

Direct Asymmetric Ruthenium-Catalyzed Reductive Amination of Alkyl-Aryl Ketones with Ammonia and Hydrogen.

The asymmetric ruthenium-catalyzed reductive amination employing ammonia and hydrogen to primary amines is described. Here we demonstrate the capability of our catalyst to perform a chemo- and enantioselective process while using simple ammonia gas as a reagent, one of the most attractive and industrially relevant nitrogen sources. The presence of a catalytic amount of ammonium iodide was essential for obtaining good yields and enantioselectivities. The mechanism of this reaction was investigated by DFT and we found a viable pathway that also explains the trend and magnitude of enantioselectivity through the halide series in good agreement with the experimental data. The in-depth investigation of substrate conformers during the reaction turned out to be crucial in obtaining an accurate prediction of the enantioselectivity. Furthermore, we report the crystallographic data of the chiral [Ru(I)H(CO)((S,S)-f-binaphane)(PPh3)] complex, which we identified as the most efficient catalyst in our investigation.

Synthesis of Mono- and Dinuclear Vanadium Complexes and Their Reactivity toward Dehydroperoxidation of Alkyl Hydroperoxides.

Several vanadium(V) complexes with either dipic-based or Schiff base ligands were synthesized. The complexes were fully characterized by elemental analysis, IR, 1H, 13C, and 51V NMR spectroscopy, as well as mass spectrometry and X-ray diffraction. Furthermore, they were tested toward their catalytic deperoxidation behavior and a significant difference between 4-heptyl hydroperoxide and cyclohexyl hydroperoxide was observed. In the case of 4-heptyl hydroperoxide, the selectivity toward the corresponding ketone was higher than with cyclohexyl hydroperoxide. DFT calculations performed on the vanadium complex showed that selective decomposition of secondary hydroperoxides with vanadium(V) to yield the corresponding ketone and water is indeed energetically feasible. The computed catalytic path, involving cleavage of the O-O bond, hydrogen transfer, release of ketone/water, and finally addition of hydroperoxide, can proceed without the generation of radical species.