Tungsten Catalyst Metathesis

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.

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].

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. 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.The researchers, led by the Director of the center Jean-Marie Basset, then tested the catalyst by heating it to 150°C with propane for three days.After optimizing the reaction conditions— for example, by allowing the propane to flow continuously over the catalyst—they found that the main products of the reaction were ethane and butane and that each pair of tungsten and titanium atoms could catalyze an average of 10,000 cycles before losing their activity.Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission.The content is provided for information purposes only. [(≡Si–O–Si≡)(≡Si–O–)₂ Al–O–W(≡Ct Bu)(H)₂] was found to be a single‐site catalyst, giving the highest turnover number (TON=800) and the highest reported selectivity for butane (45%) vs. The performance of each of the W‐supported catalysts was assessed for propane metathesis in a flow reactor at 150 °C.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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