Tag Archives: MOF

Publication of the week, number 78, 22nd May 2015

Recently Mori etal reported the synthesis of the chiral E-alkene obtained by asymmetric RCM:

sponge01

this interesting twisting compound was obtained in 96 %ee. The absolute configuration of the (+)-isomer of  was assigned as the Sform with the crystalline sponge method (see also here). The details of the x-ray study  have now been reported by Fujita. “The crystalline sponge method is a recently developed technique for single crystal diffraction (SCD) studies that does not require crystallization of the samples. By soaking guests into porous coordination networks (crystalline sponges), the guests are oriented for SCD study. For the practical use of this method, a detailed protocol and experimental guidelines have been reported. When the sponge method is combined with the Bijvoet method, neither heavy-atom incorporation nor crystallization is necessary for absolute structure determination because heavy atoms (zinc and iodine atoms) are already installed in the sponge framework.

The enantiomers of the alkene (prepared as a racemate) were separated by chiral HPLC and using his zinc iodide 2,4,6-tris(4-pyridyl)triazine MOF an x-ray structure was obtained from a <10 μg sample of both enantiomers and confirmed the original assignment of Mori.

The actual method seems to me to have become much simpler “To a microvial containing a single crystal of the zinc MOF and cyclohexane (45 μL), 5 μL of a 1,2-dichloroethane solution of the target compound (1 mg/1 mL) was added. The crystal-containing microvial was then allowed to stand at 45 °C and the solvent was gradually evaporated over 2 days according to the previously reported procedure.” Then expose to x-rays and a computer equipped with the correct software and out pops a structure such as:

sponge02

So yet another application for this great methodology.

I’ll say it again: This methodology represents a major breakthrough in structural determination especially in combination with LC. These sentiments have also been echoed in a recent review (see section 8). So lets see more applications appear, especially in the natural products area.

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