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A well-defined, silica-supported bimetallic precatalyst ≡Si-O-W(Me)5≡Si-O-Zr(Np)3 (4) has been synthesized for the first time by successively grafting two organometallic complexes W(Me)6 (1) followed by ZrNp4 (2) on a single silica support. Surprisingly, multiple-quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of zirconium hydride, probably facilitated by tungsten hydride which was formed at this temperature. This bimetallic W/Zr hydride precatalyst proved to be more efficient (TON = 1436) than the monometallic W hydride (TON = 650) in the metathesis of n-decane at 150 °C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C-H bond activation that occurs on Zr. The produced olefin resulting from a β-H elimination undergoes easy metathesis on W.
Samantaray et al. (Thu,) studied this question.
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