An efficient route to group 6 and 8 metallaborane compounds: synthesis of arachno-[Cp*Fe(CO)B₃H₈] and closo-[(Cp*M)₂B₅H₉] (M = Mo, W)

Abstract

Reaction of [Cp*Fe(CO)₂I] (Cp* = η⁵-C₅Me₅) with an excess amount of BH₃·thf in toluene at 75 °C or with LiBH₄ at –78 °C leads to the isolation of hydrogen-rich ferraborane arachno-[Cp*Fe(CO)B₃H₈] in good yield. In a similar fashion, reaction of [Cp*M(CO) ₃Cl] (M = Mo and W) with an excess amount of BH₃·thf at 80 °C or at –78 °C with LiBH₄ yielded metallaboranes [(Cp*M)₂B₅H₉] (M = Mo, W). Isolated yields of closo-[(Cp*M)₂B₅H₉], (M = Mo and W), both from LiBH₄ and BH₃·thf, are good. All compounds were characterized in solution by IR, ¹H, ¹¹B, and ¹³C NMR spectroscopy and mass spectrometry and the structural types were unequivocally established by crystallographic analysis of arachno-[Cp*Fe(CO)B₃H₈].