Metal fragment exchange from a molybdaborane to a tungstaborane

Reaction of the molybdaborane arachno-2-[Mo(η-C5H5)(η5:η1-C5H4)B4H7] (I) with the electron-rich molecule [W(PMe3)3H6] at 60 °C for 12 h in toluene gives the novel tungstaborane nido-2-W(PMe3)3H2B4H7[Mo(η-C5H5)(η5:η1-C5H4)H2] (II) in 60% yield. The reaction is almost quantitative when followed by NMR. This is a rare example of metal fragment exchange within a metallaborane cage. The molybdenum atom is retained in the molecule via a σ-bond between the substituted cyclopentadienyl ring and a basal boron atom in the metallaborane cluster.