Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane

M. Samantaray, S. Kavitake, N. Morlanés, E. Hamad, A. Hamieh, R. Dey, J. Basset
Journal of the American Chemical Society, 139 (9), pp. 3522-3527, (2017)

Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane

Keywords

Bimetallic, W/Ti precatalyst

Abstract

​Two compatible organometallic complexes, W(Me)6 (1) and TiNp4 (2), were successively anchored on a highly dehydroxylated single silica support (SiO2−700) to synthesize the well-defined bimetallic precatalyst [(≡Si–O−)W(Me)5(≡Si–O−)Ti(Np)3] (4). Precatalyst 4 was characterized at the molecular level using advanced surface organometallic chemistry (SOMC) characterization techniques. The strong autocorrelation observed between methyl of W and Ti in 1H–1H multiple-quantum NMR spectra demonstrates that W and Ti species are in close proximity to each other. The bimetallic precatalyst 4, with a turnover number (TON) of 9784, proved to be significantly more efficient than the silica-supported monometallic catalyst [(≡Si–O−)W(Me)5] (3), with a TON of 98, for propane metathesis at 150 °C in a flow reactor. The dramatic improvement in the activity signifies the cooperativity between Ti and W and indicates that the key step of alkane metathesis (C–H bond activation followed by β-H elimination) occurs on Ti, followed by olefin metathesis, which occurs on W. We have demonstrated the influence and importance of proximity of Ti to W for achieving such a significantly high activity. This is the first report demonstrating the considerably high activity (TON = 9784) in propane metathesis at moderate temperature (150 °C) using a well-defined bimetallic system prepared via the SOMC approach.

Code

DOI: 10.1021/jacs.6b12970

Sources

Website PDF

See all publications 2017