Issue 97, 2015

Different acidity and additive effects of zirconium metal–organic frameworks as catalysts for cyanosilylation

Abstract

The Zr(IV) metal–organic framework with 1,4-benzenedicarboxylate (UiO-66) in different forms was studied as a solid catalyst for carbonyl cyanosilylation. The anhydrous material (UiO-66-A) obtained after calcination has open Lewis-acid sites and acts as a heterogeneous and size selective catalyst for the reaction of aldehydes and trimethylsilylcyanide (TMSCN). Notably, it was found that the as-synthesized hydrous form (UiO-66-H) shows comparable activity to UiO-66-A, so UiO-66 can be used as a catalyst for cyanosilylation with no need of high-temperature activation. With a number of intentionally designed control experiments, we demonstrated that the acetic acid enclosed in UiO-66-H during synthesis serves as a Brønsted acid to promote the reaction, though acetic acid is inactive by itself. The different acidity between UiO-66-H and UiO-66-A was confirmed by using the isomerization of α-pinene oxide as a probe reaction. Both UiO-66-H and UiO-66-A are recyclable without significant degradation in framework integrity and catalytic activity. In addition, it was unexpectedly found that pyridine, which is inactive alone, acts as co-catalyst, rather than a Lewis acid poison, to dramatically accelerate the catalytic reaction over UiO-66-H or UiO-66-A. A synergistic mechanism was suggested, in which the Lewis or Brønsted acid activates the aldehyde substrate while pyridine acts as a Lewis base to activate TMSCN.

Graphical abstract: Different acidity and additive effects of zirconium metal–organic frameworks as catalysts for cyanosilylation

Article information

Article type
Paper
Submitted
06 Jul 2015
Accepted
11 Sep 2015
First published
11 Sep 2015

RSC Adv., 2015,5, 79216-79223

Author version available

Different acidity and additive effects of zirconium metal–organic frameworks as catalysts for cyanosilylation

F. Xi, Y. Yang, H. Liu, H. Yao and E. Gao, RSC Adv., 2015, 5, 79216 DOI: 10.1039/C5RA13149A

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