Extension of Surface Organometallic Chemistry to Metal–Organic Frameworks: Development of a Well-Defined Single Site [(≡Zr–O−)W(═O)(CH₂^tBu)₃] Olefin Metathesis Catalyst

Abstract

We report here the first step by step anchoring of a W(≡C t Bu)(CH 2 t Bu) 3 complex on a highly crystalline and mesoporous MOF, namely Zr-NU-1000, using Surface organometallic Chemistry (SOMC) concept and methodology. SOMC allowed us to selectively graft the complex on the Zr 6 clusters and characterize the obtained single site material by using state of the art experimental methods including extensive solid-state NMR techniques and HAADF-STEM imaging. Further FT-IR spectroscopy revealed the presence of a W=O moiety arising from the in situ reaction of the W≡C t Bu functionality with the coordinated water coming from the 8-connected hexanuclear Zr 6 clusters. All the steps leading to the final grafted molecular complex have been identified by DFT. The obtained material was tested for gas phase and liquid phase olefin metathesis and exhibited higher catalytic activity than the corresponding catalysts synthesized by different grafting methods. This contribution establishes the importance of applying SOMC to MOF chemistry to get well defined single site catalyst on MOF inorganic secondary building units, in particular the in situ synthesis of W=O alkyl complexes from their W carbyne analogues.

Synthesis, characterization and application of defective metal–organic frameworks: current status and perspectives

“…In addition to the introduction of NPs into the pores of defective MOFs, the organic linkers or metal nodes can also be used to anchor some species as active sites. 115,116,[125][126][127] Yaghi et al 39 synthesized a single-atom catalyst, Cu/UiO-66, through a covalent attachment of Cu atoms to the defect sites at zirconium oxide clusters (Fig. 11d).…”

Unexpected “Spontaneous” Evolution of Catalytic, MOF-Supported Single Cu(II) Cations to Catalytic, MOF-Supported Cu(0) Nanoparticles

“…23−28 The exposed portions of these nodes, and related hafnium-and cerium-containing nodes, 29−32 can be viewed as structurally well-defined analogues of conventional metal− oxide supports, lending themselves well to interrogation of the structure and connectivity of grafted catalysts by single-crystal X-ray diffraction and other spectroscopic methods. Indeed, we and others have successfully introduced and structurally resolved various mononuclear metal species, 33,34 metal−oxide and metal−sulfide clusters, 35−37 in zirconiumbased MOFs via vapor-phase or condensed-phase postsynthetic treatments. These materials have been further applied as heterogeneous catalysts in hydrogenation, 38,39 oligomerization, 40,41 oxidative dehydrogenation, 42 and selective partial oxygenation reactions 43,44 as well as electrocatalytic 36,45 and photocatalytic water-splitting reactions.…”

“…Highly crystalline and porous metal–organic frameworks (MOFs), composed of inorganic nodes and organic linkers, − are increasingly regarded as promising model supports for single-site catalysts due to their uniform structure and well-defined pore environment. − In particular, MOFs featuring hexa-Zr­(IV)-oxy nodes have attracted attention because (1) many of them have catalyst binding sites in the form of −OH and −OH 2 groups regularly arranged on the nodes and (2) their exceptional chemical and thermal stability ensures that the MOF network and, in many cases, the installed catalyst remain structurally intact during catalysis. , Shown in Figure (upper left) is an idealized representation of the node of the eight-connected Zr-MOF, NU-1000 , and its congener, NU-901 , as well as PCN-222/MOF-545 and its congener, NU-902 , and various reticular expansions of these compounds. − The exposed portions of these nodes, and related hafnium- and cerium-containing nodes, − can be viewed as structurally well-defined analogues of conventional metal–oxide supports, lending themselves well to interrogation of the structure and connectivity of grafted catalysts by single-crystal X-ray diffraction and other spectroscopic methods. Indeed, we and others have successfully introduced and structurally resolved various mononuclear metal species, , as well as metal–oxide and metal–sulfide clusters, − in zirconium-based MOFs via vapor-phase or condensed-phase postsynthetic treatments. These materials have been further applied as heterogeneous catalysts in hydrogenation, , oligomerization, , oxidative dehydrogenation, and selective partial oxygenation reactions , as well as electrocatalytic , and photocatalytic water-splitting reactions. , …”

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

“…As it is often cited as a conceptual starting point in studies involving MOFs, the pioneering work of Basset should be noted, 127,128 along with his emphasis on gaining predictive mechanistic understanding by ''enter(ing) the catalytic cycle of a given reaction by a suitable predefined Surface Organometallic Fragment.'' 129 Most readily grafted are molecular catalysts that feature ancillary oxo or hydroxo ligands that can be shared with nodes, or that present pendant carboxylates, phosphonates, or similar species that have affinity for metal-oxy nodes (or other functionalities for non-oxy nodes). 130,131 By way of illustration (Fig.…”