Chemistry of early and late transition metallaboranes: synthesis and structural characterization of periodinated dimolybdaborane [(Cp*Mo)₂B₄H₃I₅]

Abstract

Thermolysis of an in situ generated intermediate [(Cp*Ta)₂(BH₃)₂Cl₂], 1 generated from the reaction of [Cp*TaCl₄], (Cp* = η⁵-C₅Me₅) and [LiBH₄·thf], in presence of [Ru₃(CO)₁₂] yielded pileo-[Cp*TaCl(μ-Cl)-B₂H₄Ru₃(CO)₈], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)₂(B₂H₆)(B₂H₄Cl₂)], 3 as a by-product. In addition, the reaction of [Cp*MoCl₄] (Cp* = η⁵-C₅Me₅) with [LiBH₄.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)₂B₄H₃I₅], 4 that hints a possible existence of [(Cp*Mo)₂B₄H₈]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)₃B₄H₄], 5 using [PtBr₂] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)₃(BH)-(BBr)₃], 6 and [(Cp*Rh)₃(BH)₃(BBr)], 7. All the compounds were characterized by IR and ¹H, ¹¹B and ¹³C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis.