Linked and fused tungstaborane clusters: synthesis, characterization, and electronic structures of bis-{(η⁵-C₅Me₅W)₂B₅H₈}₂ and (η⁵-C₅Me₅W)₂{Fe(CO)₃}nB_6-nH_10-n,n= 0, 1

Abstract

In addition to (η ⁵-C₅Me₅W)₂B₅H₉, (η ⁵-C₅Me₅W)₃(μ-H)B₈H₈, and (η ⁵-C₅Me₅W)₂B₇H₉ reported earlier, thermolysis of {η⁵-C₅Me₅W}H₃B₄H₈ (1) with BH₃·THF leads to the formation of bicapped closo-{η⁵-C₅Me₅W}₂B₆H₁₀ (2) in parallel with a B−B linked dimer of {η⁵-C₅Me₅W}₂B₅H₉ (4) and bis-{(η⁵-C₅Me₅W)₂B₅H₈}₂ (3). Reaction of 4 with a 3-fold excess of Fe₂(CO)₉ in hexane generates an iron analogue of 2, (η⁵-C₅Me₅W)₂B₅H₉Fe(CO)₃ (5) in 46% yield. All the metallaboranes, 2, 3, and 5, have been characterized by ¹H, ¹¹B NMR spectra and crystal structure determinations. The structures of 2 and 5 appear to follow the regular electron counting rules as they possess seven skeletal electron pairs (sep) appropriate for bicapped octahedral structures. However, their electronic structures revealed by a molecular orbital analysis is more closely related to that of [{η⁵-C₅Me₅Re}₂B₇H₇], a cluster that does not obey the classical electron counting rules. Clusters 2 and 5 are notable examples of closo clusters containing four bridging hydrogens. 3 is a coupled-cage structure in which two bicapped trigonal bipyramidal frameworks, W₂B₅, are joined by an exopolyhedral boron−boron bond.