Differentiation of Epoxide Enantiomers in the Confined Spaces of an Homochiral Cu(II) Metal-Organic Framework by Kinetic Resolution.

TAMOF-1, a homochiral metal-organic framework (MOF) constructed from an amino acid derivative and Cu(II), was investigated as a heterogeneous catalyst in kinetic resolutions involving the ring opening of styrene oxide with a set of anilines. The branched products generated from the ring opening of styrene oxide with anilines and the unreacted epoxide were obtained with moderately high enantiomeric excesses. The linear product arising from the attack on the non-benzylic position of styrene oxide underwent a second kinetic resolution by reacting with the epoxide, resulting in an amplification of its final enantiomeric excess and a concomitant formation of an array of isomeric aminodiols. Computational studies confirmed the experimental results, providing a deep understanding of the whole process involving the two successive kinetic resolutions. Furthermore, TAMOF-1 activity was conserved after several catalytic cycles. The ring opening of a meso-epoxide with aniline catalyzed by TAMOF-1 was also studied and moderate enantioselectivities were obtained.

Homochiral Metal-Organic Frameworks for Enantioselective Separations in Liquid Chromatography.

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification due to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture, and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here, we disclose a porous, robust homochiral metal-organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural l-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale.

TAMOF-1 as a Versatile and Predictable Chiral Stationary Phase for the Resolution of Racemic Mixtures.

Metal-organic frameworks (MOFs) have become promising materials for multiple applications due to their controlled dimensionality and tunable properties. The incorporation of chirality into their frameworks opens new strategies for chiral separation, a key technology in the pharmaceutical industry as each enantiomer of a racemic drug must be isolated. Here, we describe the use of a combination of computational modeling and experiments to demonstrate that high-performance liquid chromatography (HPLC) columns packed with TAMOF-1 as the chiral stationary phase are efficient, versatile, robust, and reusable with a wide array of mobile phases (polar and non-polar). As proof of concept, in this article, we report the resolution with TAMOF-1 HPLC columns of nine racemic mixtures with different molecular sizes, geometries, and functional groups. Initial in silico studies allowed us to predict plausible separations in chiral compounds from different families, including terpenes, calcium channel blockers, or P-stereogenic compounds. The experimental data confirmed the validity of the models and the robust performance of TAMOF-1 columns. The added value of in silico screening is an unprecedented achievement in chiral chromatography.

Ni and Pd mediate asymmetric organoboron synthesis with ester functionality at the beta-position.

Catalytic systems based on Ni and Pd complexes modified with chiral P-P ligands can be used in a convenient strategy for enantioselectively adding a boron unit to the beta-position of alpha,beta-unsaturated esters.

The selective catalytic formation of beta-boryl aldehydes through a base-free approach.

(NHC)Cu(I) complexes are key in a new strategy to selectively add a boron unit at the beta-position of alpha,beta-unsaturated aldehydes in the absence of a base.

Axially chiral P-N ligands for the copper catalyzed beta-borylation of alpha,beta-unsaturated esters.

The synthesis and resolution of a new axially chiral Quinazolinap ligand are reported. The application of this and other related P-N ligands to the copper catalyzed beta-borylation of alpha,beta-unsaturated esters resulted in conversions of up to 100% and ee values of up to 79%. A diastereomerically pure palladacycle of the new ligand was characterised by X-ray crystallography.

Multifaceted palladium catalysts towards the tandem diboration-arylation reactions of alkenes.

Novel Pd(2) (6+) compounds have been synthesized in high yield. These compounds and their Pd(2) (4+) counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemoselectivities. The presence of bis(catecholato)diboron (B(2)cat(2)) favours the reduction of Pd(III) to Pd(II), while the catalytic precursor of Pd(II) is transformed into Pd(0)-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the carbohydroxylated adduct. Eventually, the same catalyst performs both sequences with total conversion from the alkene.

The active role of NHC ligands in platinum-mediated tandem hydroboration-cross coupling reactions.

Stable N-heterocyclic platinum-carbene complexes are the first example of platinum-mediated regioselective H-B addition to vinylarenes and alkynes, allowing consecutive cross coupling reactions with the same catalytic system.

Palladium-NHC complexes do catalyse the diboration of alkenes: mechanistic insights.

Novel catalytic activation of the B-B bond by palladium(II)-NHC complexes in presence of a mild base (NaOAc) and an excess of diboron reagent enables chemoselective 1,2-diboration of alkenes, suggesting the heterolytic cleavage of diboron rather than oxidative addition of a B-B bond to the metal.

Transition metal complexes with oligopeptides: single crystals and crystal structures.

The coordination chemistry of short chain peptides with transition metals is described in terms of the available crystal structures. Despite their high interest as synthetic models for metalloproteins and as building blocks for molecular materials based on the tuneable properties of oligopeptides, single crystal X-ray diffraction studies are scarce. A perusal of the most relevant results in this field allows us to define the main characteristics of oligopeptide-metal interactions, the fundamental problems for the crystallization of these complexes, and some hints to identify future promising approaches to advance the development of metallopeptide chemistry.

Aqueous synthesis of sulfonate-functionalized 1,2,4-triazole ligands and their 2D Cd2+ coordination networks: crystal structure and photoluminescent properties.

We have developed a water-based synthesis for the preparation of 4-substituted 1,2,4-triazole ligands with highly polar functional groups. This general synthetic approach has allowed us to prepare two sulfonate functionalized 4-substituted 1,2,4-triazole anions ( L1(-)= 4-(1,2,4-triazol-4-yl)benzenesulfonate; L2(-)= 4-(1,2,4-triazol-4-yl)ethanesulfonate). Reaction of these ligands with cadmium(II) salts leads to the formation of two novel two-dimensional coordination networks of formula [Cd(L)Cl]n (1, L1; and 2, L2), which were structurally characterized by X-ray diffraction. In both compounds, the cadmium ions are bridged by chloride ions and the triazole ligands in a bis-bidentate coordination mode using the N1, N2 atoms from the triazole and two oxygen atoms from the -SO3 group. The photoluminescence studies indicate that the ligand photoemission is retained in these networks.

Asymmetric induction on beta-boration of alpha,beta-unsaturated compounds: an inexpensive approach.

Transition metal complexes mediate beta-boration of alpha,beta-unsaturated carbonyl compounds highlighting the advantages of using inexpensive catalytic systems, (Cu, Ni), both in the catalytic activity and selectivity. The new C(beta)-B bond can be accomplished in a stereoselective manner by modifying the metal complex with chiral ligands. Alternative mechanistic studies support the enantioselectivity observed, and large-scale applications of this reaction are currently being developed.

A valuable, inexpensive Cui/n-heterocyclic carbene catalyst for the selective diboration of styrene.

The complexes [Cu(NHC)(NCMe)]BF4 (NHC=N-heterocyclic ligand), with bis(catecholato)diboron (B2(cat)2) as the boron source, efficiently catalyze the diboration of styrene with very high degrees of conversion. With the appropriate NHC ligand, the reaction proceeds quantitatively toward the diborated derivative PhCH(Bcat)--CH2(Bcat). The [styrene]/[B2(cat)2] ratio also has a strong effect on the selectivity: the use of an excess of styrene allows modification of the selectivity toward the formation solely of the monoborated derivative, PhCH2--CH2(Bcat). DFT calculations suggest that no oxidative addition processes take place at copper, but that intermediates containing coordinated sigma-bonds are involved in the catalytic cycle.