A series of isoreticular chiral metal–organic frameworks as a tunable platform for asymmetric catalysis

Abstract

Metal-organic frameworks, built by bridging metal ions with organic linkers, represent a new class of porous hybrid materials with attractive tunability in compositions, structures and functions. In particular, the mild conditions typically employed for their synthesis allow for the functionalization of their building blocks, and thus the rational design of novel materials. Here we demonstrate the systematic design of eight mesoporous chiral metal-organic frameworks, with the framework formula [LCu2(solvent)2] (where L is a chiral tetracarboxylate ligand derived from 1,1'-bi-2-naphthol), that have the same structures but channels of different sizes. Chiral Lewis acid catalysts were generated by postsynthesis functionalization with Ti(OiPr)4, and the resulting materials proved to be highly active asymmetric catalysts for diethylzinc and alkynylzinc additions, which converted aromatic aldehydes into chiral secondary alcohols. The enantioselectivities of these reactions can be modified by tuning the size of the channels, which alters the diffusion rates of the organic substrates.

Heterogeneous catalytic properties of unprecedented μ-O-[FeTCPP]2dimers (H2TCPP = meso-tetra(4-carboxyphenyl)porphyrin): an unusual superhyperfine EPR structure

“…As occurs with other similar compounds that exhibit strong antiferromagnetic couplings through two high-spin iron(III) centres, 97 we did not expect to obtain EPR signal for this 15 compound. However, the X-band EPR spectral measurements carried out for µ-O-[FeTCPP] 2 ·16DMF at room temperature in solid state show an axially symmetric spectra with g ┴ and g ║ values close to 6 and 2 , respectively; unequivocal evidence of high spin Fe III (S = 5/2) ions ( Figure 7).…”

“…Afterwards, a second mass loss occurs from 360 ºC to 400 ºC, assigned to both porphyrin units (51.5% weight loss) ( Figure S5, ESI †). The 15 calcination product has been identified by powder X-ray diffraction analysis, and it consists of Fe 2 O 3 [space group R-3c, a = 5.0142 Å, c = 13.6733 Å and γ = 120º]. 95 …”

“…As shown in Figure S6, ESI † the characteristic vibrations of the porphyrin macrocycle are present, including the Fe-TCPP and Fe-O-Fe vibrations at 1000 cm -1 , 870 cm -1 and 824 cm -1 . 15 A heterogeneity test was carried out for the oxidation of benzyl alcohol over µ-oxo-FeTCPP sample. For rigorous proof of heterogeneity, the test 102 was carried out by filtering the catalyst from the reaction mixture at 70 ºC after 25 min, when a conversion rate of 34 % had been reached.…”

“…Hydrogen bonds produce a 2D array, and interlayer π-π 15 interactions give rise to the 3D network. The compound has been exhaustively characterised by means of X-ray diffraction, IR, Raman, UV-Vis, Mössbauer and EPR (Electron Paramagnetic Resonance) spectroscopies, thermogravimetric analysis, magnetic susceptibility measurements and catalytic activity tests.…”

Porous materials with pre-designed single-molecule traps for CO2 selective adsorption

“…These materials possess unique properties and vast application potential [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . The hallmark of these new materials is their modular design, which is far beyond the scope of other porous materials 22,[25][26][27][28][29][30][31][32][33][34][35][36] and allows for facile structure and property tuning. This therefore enables precise control of functions by accurate design of structures at the molecular level.…”