Mono- and di-borylated [3]ferrocenophanes

Treatment of [3]ferrocenophane (1) with 0.7 eq. or 3 eq. of BBr3 in hexane at reflux temperature gives the corresponding dibromoboryl (2) or 1,1′-bis(dibromoboryl) derivative (3) in good yields. Compounds 2 and 3 can be transformed into the corresponding di(tert-butoxy)boryl (4, 5) and pinacolboryl [3]ferrocenophanes (6, 7). Reaction of 6 and 7 with aqueous CuBr2 in MeOH/iPrOH at reflux temperature leads to the formation of the mono- and 1,1′-di-brominated [3]ferrocenophanes 8 and 9; subsequent Stille-type C–C-coupling reactions with nBu3SnPh yield mono- and 1,1′-di-phenylated [3]ferrocenophanes. Treatment of 6 with Li[AlH4] in Et2O at −78 °C provides access to the monotopic lithium trihydridoborate 12.