Metal Switcheroo Tunes Selectivity | Chemical & Engineering News
Volume 93 Issue 16 | p. 25 | Concentrates
Issue Date: April 20, 2015

Metal Switcheroo Tunes Selectivity

Catalysis: Tuning metal concentrations in multimetal frameworks tailors reaction rates and product selectivities
Department: Science & Technology
News Channels: Materials SCENE, Nano SCENE, JACS In C&EN
Keywords: MOF, metal-organic framework, catalyst, selectivity, porous crystals

Changing the ratio of metal ions in multi­metal catalytic framework compounds can be an effective strategy for steering multicomponent reactions toward a desired product, according to researchers in Spain (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b02313). To demonstrate the principle, which can be used to reduce waste and bypass purification steps, M. Ángeles Monge and coworkers at the Materials Science Institute of Madrid prepared three isostructural metal-organic framework (MOF) compounds, each containing one type of metal—aluminum, gallium, or indium. They used the MOFs individually to catalyze a one-pot Strecker reaction between benzaldehyde, trimethylsilyl cyanide, and aniline. The aluminum MOF generated an α-aminonitrile, the gallium MOF formed a cyanosilyl derivative, and the indium MOF yielded an imine. The team also prepared mixed indium-gallium MOFs in which the metals, located at equivalent lattice positions, were present in various ratios. They found that tuning the indium-to-gallium ratio altered the reaction rates and product selectivities. For example, a gallium-rich MOF functioned similarly to the aluminum compound and catalyzed formation of the α-aminonitrile in 96% yield in 30 minutes. In contrast, an indium-rich MOF led to just 64% yield after four days.

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Tuning the metal ion ratio in multimetal catalytic MOFs affects the outcome of these multicomponent reactions.
Credit: J. Am. Chem. Soc.
Graphic and structures show how tuning the metal ion ratio in MOFs affects product selectivity in multicomponent catalytic reactions.
 
Tuning the metal ion ratio in multimetal catalytic MOFs affects the outcome of these multicomponent reactions.
Credit: J. Am. Chem. Soc.
 
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