Dimeric and Cyclotrimeric Piano-Stool Vanadium(III) Dihalides with Unusual Differences in V−V Distance and Magnetochemistry. Syntheses, Structures, and Reactivities of (η-C₅Me₄R)₂V₂(μ-Br)₄ and the Trivanadium Cluster (η-C₅Me₄R)₃V₃(μ-Cl)₆, New Mid-Valent Organovanadium Synthons

Abstract

Reductive oligomerization of (C5Me4R)VX3 or addition of (C5Me4R)SnBu3 to VX3L3 (L = thf, tht) yields the (peralkylcyclopentadienyl)vanadium(III) halides (η5-C5Me4R)2V2(μ-Br)4 and (η5-C5Me4R)3V3(μ-Cl)6 (R = Me, Et), which can be halogenated to afford (C5Me4R)VX3. Paramagnetic (C5Me4Et)2V2(μ-Br)4 is a four-legged piano-stool dimer in the solid state with a nominal V−V bond (2.565(1) Å), while the spin-frustrated, antiferromagnetic (C5Me4Et)3V3(μ-Cl)6 is a piano-stool cyclotrimer with two μ-chlorines per nonbonded V···V edge (3.3732[63] Å).