Diazoacetates in coupling reactions: CuI serves as an effective catalyst for coupling terminal alkynes with diazo compounds to generate 3‐alkynoates (see scheme). This method is efficient (1:1 ratio of reactants), mild (room temperature), and simple (no additional ligand), and a range of functional groups are tolerated (e.g., CC double bonds, heteroatoms, and hydroxy groups).

A convenient synthesis of new chiral phosphine-phosphites (P-OP) has been described. The versatility of the synthetic protocol developed has allowed the preparation of ligands with different phosphine fragments and the choice of the stereogenic element location. Analyses of the values of 1 J PSe of the corresponding diselenides are in accord with the expected lower σ-donor ability of the phosphite fragment, with respect to the phosphine group, and with an increase of phosphine basicity after substitution of phenyl substituents by methyl groups. Inspection of υ(CO) values on a series of complexes RhCl(CO)(P-OP) demonstrated a variable π-aceptor ability of the phosphite group, compensating for the change of basicity of the phosphine functionality, as well as having a rather reduced electron density at the metal center compared with diphosphine analogues. The distinct nature of the phosphorus functionalities has also been evidenced in rhodium-catalyzed enantioselective hydrogenation of methyl Z-R-acetamido-cinnamate (MAC). Thus, the coordination mode of the substrate is governed by the chiral ligand, directing the olefinic bond to a cis position with respect to the phosphite group, as demonstrated by NMR studies performed with [Rh(P-OP)(MAC)] + complexes. In consequence, the phosphite group has a greater impact on the enantioselectivity of the product. However, the optical purity of the process also depends on the nature of the phosphine group, and hence, an appropriate election of both phosphorus functionalities is required for the attainment of excellent enantioselectivities (99% ee).

An effective method has been developed for the kinetic resolution of racemic azomethine imines via [3 + 2] cycloadditions with alkynes catalyzed by a chiral copper complex. Efficient kinetic resolution is observed for a variety of N1 and C5 substituents on the dipole, thereby furnishing a wide array of useful enantioenriched azomethine imines, which can readily be transformed into monocyclic and bicyclic pyrazolidinones.

Dedicated to Professor Ernesto Carmona on the occasion of his 65 th birthday.Abstract: In this communication, we report the first synthesis of Pt NPs stabilized with NHC ligands and their investigation as catalysts in the chemoselective hydrogenation of nitroarenes. The results in catalysis show that by a proper choice of the NHC stabilizer and the adjustment of the NHC/metal ratio, these NHC-capped Pt NPs exhibit high levels of activity and selectivity in the hydrogenation reactions. In particular, Pt NPs stabilized with 2 equiv. of IPr carbene (PtIPr 0.2 ) catalyze the chemoselective reduction of a series of functionalized nitroarenes under mild conditions (1 bar H 2 , 308C). This catalyst tolerates the presence of a range of functional groups including hydroxyl, benzyloxy, carbonyl and olefinic moeities as well as halogens.

Rhodium complexes stabilized by modularly designed chiral phosphine−phosphite ligands (P−OP) have been tested in the asymmetric hydroformylation of styrene, vinyl naphthalenes, and allyl cyanide. Based on single-crystal X-ray diffraction analysis and NMR studies, restricted aryl rotation has been found to characterize ligands 1e and 1f. The outcome of the rhodium-catalyzed hydroformylation reactions is highly dependent on the nature of the two coordinating functions of the phosphine−phosphite and of the ligand backbone as well. Among the ligands studied, those with an oxyphenylene backbone and PAr2 ends gave the best results, outperforming those with P-stereogenic phosphine groups. The 1-naphthyl-substituted catalyst brought about the hydroformylation of styrene with a 71% ee, while the xylyl catalyst afforded the best results in the hydroformylation of allyl cyanide, yielding an iso/n ratio of 13 and 53% ee in the branched isomer. Several hydrido(carbonyl) species of the formula RhH(CO)2(P−OP) have been generated by reacting Rh(acac)(CO)2/P−OP with syngas. In situ high-pressure NMR experiments showed the phosphine group to occupy an apical position of the trigonal bipyramidal coordination geometry, which allows an aryl−aryl interaction between the phosphine substituents and the substrate during the hydroformylation of vinyl arenes. In line with this finding, a remarkable enantioselectivity of 89% ee was obtained with the naphthyl catalyst and 1-vinyl naphthalene as substrate.

A family of modularly designed phosphine−phosphites (P−OP), possessing a C−C−O backbone, has been synthesized and evaluated in the iridium-catalyzed asymmetric hydrogenation of N-aryl imines. The enantioselectivity of this reaction is highly dependent on the nature of the ligand, and catalysts bridged by an oxyethylene fragment have produced significantly higher enantiomeric excesses (Δee > 20%) than their o-oxyphenylene counterparts. Structural studies by X-ray crystallography and NMR spectroscopy of complexes with the formulation [Ir(COD)(P−OP)]BF4 and Ir(Cl)(CO)(P−OP), complemented by DFT calculations of model compounds of the chlorocarbonyls, have shown important differences between complexes bridged by an aliphatic or an aromatic bridge, regarding the iridacycle conformation and the location of phosphine substituents. Catalyst optimization has afforded enantioselectivities from 72 to 85% ee in the hydrogenation of several N-aryl imines.

Coordination studies of new lutidine-derived hybrid NHC/phosphine ligands (CNP) to Pd and Ir have been performed. Treatment of the square-planar [Pd(CNP)Cl](AgCl) complex 2a with KHMDS produces the selective deprotonation at the CHP arm of the pincer to yield the pyridine-dearomatised complex 3a. A series of cationic [Ir(CNP)(cod)] complexes 4 has been prepared by reaction of the imidazolium salts 1 with Ir(acac)(cod). These derivatives exhibit in the solid state, and in solution, a distorted trigonal bipyramidal structure in which the CNP ligands adopt an unusual C-N-P coordination mode. Reactions of complexes 4 with CO and H yield the carbonyl species 5a(Cl) and 6a(Cl), and the dihydrido derivatives 7, respectively. Furthermore, upon reaction of complex 4b(Br) with base, selective deprotonation at the methylene CHP arms is observed. The, thus formed, deprotonated Ir complex 8b reacts with H in a ligand-assisted process leading to the trihydrido complex 9b, which can also be obtained by reaction of 7b(Cl) with H in the presence of KOBu. Finally, the catalytic activity of Ir-CNP complexes in the hydrogenation of ketones has been briefly assessed.

Cationic rhodium(I) complexes containing picolyl-NHC (NHC = N-heterocyclic carbene) ligands that differ in the substitution at the 6-position of the pyridine donor serve as efficient E-selective alkyne hydrosilylation catalyst precursors. Particularly, when the steric hindrance of the picolyl fragment is increased, a catalyst precursor exhibiting high catalytic activities (TOF up to 500 h −1 at S/C ratios of 1000) and excellent E selectivities (E/α ratio ≥95/5) in the hydrosilylation of a series of aryl, alkyl, and functionalized terminal alkynes with both carbo-and alkoxysilanes has been obtained. The picolyl-NHC ligands in the Rh complexes exhibit a dynamic behavior in solution due to the hemilabile coordination of the pyridine fragment. Preliminary mechanistic studies support the involvement of Rh silyl hydrido species, which are generated in low concentrations from Rh complexes and the silane, in the hydrosilylation of alkynes in agreement with the assumption of Chalk−Harrod-type mechanisms.