Convergent Synthesis of a Metal–Organic Framework Supported Olefin Metathesis Catalyst

Synthesis of a metal–organic framework (MOF)-supported olefin metathesis catalyst has been accomplished for the first time following a new, convergent approach where an aldehyde-functionalized derivative of Hoveyda’s recently reported ruthenium catecholate olefin metathesis catalyst is condensed with an amine-functionalized IRMOF-74-III. The resulting material, denoted MOF-Ru, has well-defined, catalytically active ruthenium centers confined within channels having a ca. 20 Å diameter. MOF-Ru is a recyclable, single-site catalyst for self-cross-metathesis and ring-closing metathesis of terminal olefins. Comparison of this heterogeneous catalyst with a homogeneous analogue shows different responses to substrate size and shape suggestive of confinement effects. The MOF-Ru catalyst also displays greater resistance to double-bond migration that can be attributed to greater catalyst stability. For the preparation of well-defined, single-site heterogeneous catalysts where catalyst purity is essential, the convergent approach employed here, where the catalytic center is prepared ex situ and covalently linked to an intact MOF, offers an attractive alternative to in situ catalyst preparation as currently practiced in MOF chemistry

Superacidity in Sulfated Metal–Organic Framework-808

Superacids, defined as acids with a Hammett acidity function <i>H</i>₀ ≤ −12, are useful materials, but a need exists for new, designable solid state systems. Here, we report superacidity in a sulfated metal–organic framework (MOF) obtained by treating the microcrystalline form of MOF-808 [MOF-808-P: Zr₆O₅­(OH)₃­(BTC)₂­(HCOO)₅(H₂O)₂, BTC = 1,3,5-benzene­tricar­box­ylate] with aqueous sulfuric acid to generate its sulfated analogue, MOF-808-2.5SO₄ [Zr₆O₅­(OH)₃­(BTC)₂­(SO₄)_2.5(H₂O)_2.5]. This material has a Hammett acidity function <i>H</i>₀ ≤ −14.5 and is thus identified as a superacid, providing the first evidence for superacidity in MOFs. The superacidity is attributed to the presence of zirconium-bound sulfate groups structurally characterized using single-crystal X-ray diffraction analysis

Synthesis and Characterization of the Platinum-Substituted Keggin Anion α‑H₂SiPt­W₁₁O₄₀^4–

Acidification of an aqueous solution of K₈SiW₁₁O₃₉ and K₂Pt­(OH)₆ to pH 4 followed by addition of excess tetramethylammonium (TMA) chloride yielded a solid mixture of TMA salts of H₂SiPt­W₁₁O₄₀^4– (<b>1</b>) and SiW₁₂O₄₀^4– (<b>2</b>). The former was separated from the latter by extraction into an aqueous solution and converted into tetra-<i>n</i>-butylammonium (TBA) and potassium salts <b>TBA-1</b> and <b>K-1</b>. The α-H₂SiPtW₁₁O₄₀^4– was identified as a monosubstituted Keggin anion using elemental analysis, IR spectroscopy, X-ray crystallography, electrospray ionization mass spectrometry, ¹⁹⁵Pt NMR spectroscopy, ¹⁸³W NMR spectroscopy, and ¹⁸³W–¹⁸³W 2D INADEQUATE NMR spectroscopy. Both <b>TBA-1</b> and <b>K-1</b> readily cocrystallized with their unsubstituted Keggin anion salts, <b>TBA-2</b> and <b>K-2</b>, respectively, providing an explanation for the historical difficulty of isolating certain platinum-substituted heteropolyanions in pure form