Hydroboration. LXXXIX: Preparation of DIBborane, a sterically hindered monoalkylborane. Comparison with thexylborane

DIBborane (DibBH 2 ) is prepared in quantitative yield by the reaction of BH 3 .THF or BH 3 .SMe 2 with 2,4,4-trimethyl-2-pentene (diisobutylene-2 ≡ Dib-2) at 0 or 25 o C, respectively. DIBborane exists as a symmetrically bridged dimer in THF, as seen by IR and 11 B NMR, and reacts with water or methanol to liberate hydrogen quantitatively to form the corresponding boronic acid or dimethylboronate ester. Both DIBborane and thexylborane react with a variety of bases, S(CH 3 ) 2 , pyridine, N(CH 3 ) 3 , TMED, and NEt 3 , to give the corresponding addition compounds. The stability of the adducts was investigated spectroscopically (IR, 11 B NMR) and the rate of reaction with olefins (1-octene,α-pinene) and methanol