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Abstract

The aza-closo-decaborane RNB₉H₉ (4a; R = 4-ClC₆H₄) is opened to give the nido-cluster RNB₉H₉(tmeda) (7a) by the addition of Me₂N(CH₂)₂NMe₂ (tmeda). The cluster 7a contains the same type of asymmetric hydrogen bridge as is present in the isoelectronic nido-anion [RNB₉H₁₀]^- (10b, 10c; R = Ph, PhCH₂), obtained by the action of KBHEt₃ on the corresponding arachno-cluster RNB₉H₁₁(NH₂t-Bu) (9b, 9c). Secondary amines HNR¹R² yield the azaboranes RNB₉H₁₀(NR¹R²) (11a-11c; R¹/R² = H/t-Bu, Et/Et, i-Pr/i-Pr). From 2D-¹H/¹¹B NMR correlations, concerning the two non-terminal H atoms, and from the ¹¹B NMR shifts, a nido/arachno hybrid structure is deduced for 11a-11c, governed by the contribution of pi-bonding between the lone pair of the amino group and the neighbouring B atom. Amines, like nucleophiles generally, attack the closo-boranes RNB₉H₉ at one of the B atoms adjacent to the N atom, as expected.

Keywords: Azadecaboranes; Cluster opening; nido/arachno Hybrids.