Hypoelectronic dimetallaheteroboranes of group 6 transition metals containing heavier chalcogen elements

Abstract

We have synthesized and structurally characterized several dimetallaheteroborane clusters, namely, nido-[(Cp*Mo)₂B₄SH₆], 1; nido-[(Cp*Mo ₂B₄SeH₆], 2; nido-[(Cp*Mo)₂B₄TeClH₅], 3; [(Cp*Mo)₂B₅SeH₇], 4; [(Cp*Mo)₂B₆SeH₈], 5; and [(CpW)₂B₅Te₂H₅], 6 (Cp* = η⁵-C₅Me₅, Cp = η⁵-C₅H₅). In parallel to the formation of 1–6, known [(CpM)₂B₅H₉], [(Cp*M)₂B₅H₉], (M = Mo, W) and nido-[(Cp*M)₂B₄E₂H₄] compounds (when M = Mo; E = S, Se, Te; M = W, E = S) were isolated as major products. Cluster 6 is the first example of tungstaborane containing a heavier chalcogen (Te) atom. A combined theoretical and experimental study shows that clusters 1–3 with their open face are excellent precursors for cluster growth reactions. As a result, the reaction of 1 and 2 with [Co₂(CO)₈] yielded clusters [(Cp*Mo₂B₄H₄E(μ³-CO)Co₂(CO)₄], 7–8 (7: E = S, 8: E = Se) and [(Cp*Mo)₂B₃H₃E(μ-CO)₃Co₂(CO) ₃], 9–10 (9: E = S, 10: E = Se). In contrast, compound 3 under the similar reaction conditions yielded a novel 24-valence electron triple-decker sandwich complex, [(Cp*Mo)₂{μ-η⁶:η⁶-B₃H₃TeCo₂(CO)₅}], 11. Cluster 11 represents an unprecedented metal sandwich cluster in which the middle deck is composed of B, Co, and Te. All the new compounds have been characterized by elemental analysis, IR, ¹H, ¹¹B, ¹³C NMR spectroscopy, and the geometric structures were unequivocally established by X-ray diffraction analysis of 1, 2, 4–7, and 9–11. Furthermore, geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state structure determinations. We have analyzed the discrepancy in reactivity of the chalcogenato metallaborane clusters in comparison to their parent metallaboranes with the help of a density functional theory (DFT) study.