Among hindered dialkylboranes is disiamylborane, abbreviated SiaBH.  It also is a dimer. Owing to its steric bulk, it selectively hydroborates less hindered, usually terminal alkenes in the presence of more substituted alkenes. Disiamylborane must be freshly prepared as its solutions can only be stored at 0 °C for a few hours. Dicyclohexylborane ChxBH exhibits improved thermal stability than SiaBH.