Homochiral Metal−Organic Frameworks for Heterogeneous Asymmetric Catalysis

Poly[[diaqua-bis-(μ-oxalato-κ(4)O(1),O(2):O(1'),O(2'))bis-(μ(3)-5-oxidopyridin-1-ium-3-carboxyl-ato-κ(3)O(3):O(3'):O(5))diholmium(III)] dihydrate]

In the title compound, {[Ho₂(C₆H₄NO₃)₂(C₂O₄)₂(H₂O)₂]·2H₂O}_n, the Ho^III atom is coordinated by three O atoms from three 5-hy­droxy­nicotinate ligands, four O atoms from two oxalate ligands, each lying on an inversion center, and one water mol­ecule in a distorted square-anti­prismatic geometry. The 5-hy­droxy­nicotinate ligand is protonated at the N atom and deprotonated at the hy­droxy group. The Ho^III atoms are bridged by the carboxyl­ate and phenolate O atoms, forming a three-dimensional framework. N—H⋯O and O—H⋯O hydrogen bonds, as well as π–π inter­actions between the pyridine rings [centroid–centroid distance = 3.794 (2) Å], are observed.

Highly dispersed pd catalyst locked in knitting aryl network polymers for Suzuki-Miyaura coupling reactions of aryl chlorides in aqueous media

Highly dispersed palladium chloride catalysts locked in triphenylphosphine-functionalized knitting aryl network polymers (KAPs) are developed and exhibit excellent activity under mild conditions in the Suzuki-Miyaura cross-coupling reactions of aryl chlorides in aqueous media. This work highlights that the microporous polymers not only play the role of support materials, but also protect the Pd species from aggregation and precipitation, hence, positively effect the catalysis activity.

Strategic design and refinement of Lewis acid-base catalysis by rare-earth-metal-containing polyoxometalates

Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-containing POMs (TBA(6)RE-POM, RE = Y(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), or Dy(3+)) were designed and synthesized by reactions of TBA(4)H(4)[γ-SiW(10)O(36)] (TBA = tetra-n-butylammonium) with RE(acac)(3) (acac = acetylacetonato). TBA(6)RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C═O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h(-1)) and the turnover number (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.

Spontaneous resolution through helical association of a Cu-azamacrocyclic complex with Lindqvist-type isopolyanion

Anionic metathesis reaction between the perchlorate salt of a copper-tetraazamacrocycle complex and the tetrabutylammonium salt of Lindqvist-type isopolyoxometalates in acetonitrile leads to the formation of two new inorganic-organic hybrid solids formulated as [Cu(L)(MeCN)][W(6)O(19)] (1) and [Cu(L)(MeCN)][Mo(6)O(19)] (2). Interestingly, both ion-pair complexes crystallize in a chiral space group P2(1)2(1)2(1). Crystallographic analysis of the obtained compounds reveals the occurrence of spontaneous resolution during crystallization. Both the enantiomorphs of compound 1 have been structurally characterized, whereas the resolution of compound 2 is rather poor.

Enantioselective sorption of alcohols in a homochiral metal-organic framework

Single-crystal X-ray diffraction study reveals the host-guest interactions between a homochiral metal-organic framework and two enantiomers of a chiral alcohol providing the key driving force for the enantioselective sorption of alcohols in the framework.

Size-dependent catalysis by DABCO-functionalized Zn-MOF with one-dimensional channels

Lewis basic DABCO-functionalized 3D-like metal-organic framework, Zn-MOF, catalyzes nitroaldol (Henry) reaction of 4-nitrobenzaldehyde with nitroalkanes in a size-dependent manner. Small nitroalkanes give rise to higher conversion than larger ones. This MOF-based heterogeneous catalyst is very robust and can be recycled several times without losing its activity.

Diazido-{(S)-1-phenyl-N,N-bis-[(2-pyrid-yl)meth-yl]ethanamine}-copper(II)

In the title compound, [Cu(N₃)₂(C₂₀H₂₁N₃)], the Cu^II ion is coordinated by the three N atoms of the (S)-1-phenyl-N,N-bis­[(2-pyrid­yl)meth­yl]ethanamine ligand and two N atoms from two azide anions, resulting in a distorted square-pyramidal environment. A weak inter­molecular C—H⋯N hydrogen-bonding inter­action between one pyridine group of the ligand and an azide N atom of an adjacent complex unit gives a one-dimensional chain structure parallel to the c axis.