Tungsten Catalyst Metathesis

Tungsten Catalyst Metathesis-8
At the heart of the catalyst are compounds of two metals, titanium and tungsten, which are anchored to a silica surface via oxygen atoms. Previous studies showed that monometallic catalysts were engaged in two functions: alkane to olefin and then olefin metathesis.Titanium was chosen because of its ability to activate the C-H bond of paraffins to transform them to olefins, and tungsten was chosen for its high activity for olefin metathesis.

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To create the catalyst, the team heated silica to remove as much water as possible and then added hexamethyl tungsten and tetraneopentyl titanium, forming a light-yellow powder.

The researchers studied the catalyst using nuclear magnetic resonance (NMR) spectroscopy to show that the tungsten and titanium atoms lie extremely close together on the silica surfaces, perhaps as close as ≈0.5 nanometres.

The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review.

Keywords: C–C bond formation is one of the most important types of reaction in organic synthesis.

Transformations employing organometallic compounds as catalysts have achieved a significant role because of their advantages such as simplicity (fewer reaction steps) and efficiency (higher yields) in comparison with traditional synthetic strategies.

Nowadays, a plethora of methods is known, which can be used for the formation of C–C single and double bonds, whereas simple ways to create C–C triple bonds are less common, despite the importance and ubiquity of C–C triple bonds in research areas such as natural product synthesis and advanced material science [1]. A further reaction with hydrogen under mild conditions afforded the tungsten carbyne bis‐hydride [(≡Si–O–Si≡)(≡Si‐O–)₂Al–O–W(H)₂(≡C‐t Bu)]. This acidic support was used to create a well‐defined surface organo‐tungsten fragment [(≡Si–O–Si≡)(≡Si–O–)₂Al–O–W(≡Ct Bu)(CH₂t Bu)2] by reacting 3 with W(≡Ct‐Bu)(CH2‐t Bu)3.Alkyne metathesis, which deals with the breaking and making of C–C triple bonds, has only relatively recently become part of the tool box of organic and polymer chemists for the preparation of their target molecules [2-11].Catalyzed by organotransition metal complexes, this reaction type creates new C–C triple bonds very simply via the Katz mechanism (Scheme 1) [12], based on which a series of different reaction types such as alkyne cross metathesis (ACM), ring-closing alkyne metathesis (RCAM), ring-opening alkyne metathesis polymerization (ROAMP) and acyclic diyne metathesis polymerization (ADIMET) are known (Scheme 2). Under the applied reaction conditions, 1-butene metathesis yields with a relatively large selectivity iso-butene in addition to the expected metathesis products.The isobutene selectivity is high for catalysts with a relative low activity and decreases with increasing metathesis activity. Basset Chem Cat Chem, Volume11, Issue1, Special Issue: 10th Anniversary Issue of Chem Cat Chem, January 9, 2019, Pages 614-620, (2019) Surface organometallic chemistry, Aluminium tetra-coordinated, Lewis acid site, Propane metathesis, silica ​A well‐defined aluminium‐bound hydroxyl group on the surface of mesoporous SBA‐15, [(≡Si–O–Si≡) (≡Si–O)₂ Al–OH], 3 was obtained by reacting di‐isopropyl aluminium hydride with SBA‐15 treated at 700 °C.A highly efficient catalyst that converts propane gas into heavier hydrocarbons has been developed by Saudi Arabia's King Abdullah University of Science and Technology. It significantly speeds up a chemical reaction known as alkane metathesis, which could be used to produce liquid fuels.First, a titanium atom removes hydrogen atoms from propane to form propene and then a neighboring tungsten atom breaks open propene at its carbon-carbon double bond, creating fragments that can recombine into other hydrocarbons.The researchers also found that catalyst powders containing only tungsten or titanium performed very poorly; even when these two powders were physically mixed together, their performance did not match the cooperative catalyst.

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