Hydroboration of Alkenes and Alkynes with Aza‐nido‐decaboranes

The 6‐aza‐nido‐decaboranes RNB₉H₁₁ ( 1a—d ; R = H, Ph, 4‐C₆H₄Me, 4‐C₆H₄Cl) act as 1, 2‐hydroboration agents via their 9‐BH vertex, giving products RNB₉H₁₀R′. The boranes 1a, b and 3‐hexyne yield the 9‐(1‐ethyl‐1‐butenyl)‐6‐aza‐nido‐decaboranes 2a, b (R′ = CEt = CHEt). 2, 3‐Dimethyl‐2‐butene is hydroborated by 1a—d under formation of the 9‐(1, 1, 2‐trimethylpropyl)‐6‐aza‐nido‐decaboranes 3a—d (R′ = —CMe₂ —CHMe₂). With the boranes 1a—c and (trimethylsilyl)ethene, a 85:15 mixture of the products (RNB₉H₁₀)CH₂CH₂(SiMe₃)( 4a—c ) and their chiral isomers (RNB₉H₁₀)CH(SiMe₃)CH₃ ( 5a—c ) is obtained. The action of BH₃(SMe₂) on the mixtures 4b/5b or 4c/5c results in a closure of the nido‐NB₉ skeleton of 4b or 4c , respectively, with a closo‐NB₁₁ skeleton of the products RNB₁₁H₁₀R′ ( 6b or 6c;R′ = CH₂CH₂(SiMe₃)); R′ is found in position 7 of 6b, c . All products of the type 2—6 are characterised by NMR.