Tweaking the Bridge in Metallocene Zr(IV)/W(IV) Bimetallic Hydrides.

Zirconocene cations react with Cp2WH2 affording the bimetallic [Cp2Zr(μ-H)(μ-η1:η5-C5H4)WHCp]+ bridging hydride 1 (Cp = cyclopentadienyl anion, C5H5-) via σ-bond metathesis. Complex 1 features an atypical out of plane Zr(μ-H)W moiety, where no intermetallic interaction is involved, and a fluxional core. Coordination geometry and bond distances of the bridging hydride interaction can be modulated upon reaction with Lewis bases and unsaturated substrates. PMe3, P(p-tol)3, 3,5-dimethylpyridine and THF bind to 1 and shift the hydride bridge on the coordination plane of Zr. Insertion of olefins and alkynes into the Zr-C bond of 1 leads instead to alkyl and vinyl species where the Zr and W coordination planes are perpendicular to each other. Such alterations of the Zr(μ-H)W arrangement are reflected in the average 1H NMR chemical shift values of the hydride, which correlate linearly with computed Zr-H distances. Reactivity experiments with H2 showed that the bridging hydride interaction prevents bimetallic cooperativity and that σ-bond metathesis between Zr-C and H-H bonds is the preferred pathway for all the investigated complexes.