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Unearthing a Well-Defined Highly Active Bimetallic W/Ti Precatalyst Anchored on a Single Silica Surface for Metathesis of Propane
journal contribution
posted on 2017-02-10, 00:00 authored by Manoja K. Samantaray, Santosh Kavitake, Natalia Morlanés, Edy Abou-Hamad, Ali Hamieh, Raju Dey, Jean-Marie BassetTwo 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.