Probing the Boundaries between Lewis‐Basic and Redox Behavior of a Parent Borylene

The parent borylene (CAAC)(Me(3)P)BH, 1 (CAAC=cyclic alkyl(amino)carbene), acts both as a Lewis base and one‐electron reducing agent towards group 13 trichlorides (ECl(3), E=B, Al, Ga, In), yielding the adducts 1‐ECl(3) and increasing proportions of the radical cation [1](•+) for the heavier group 13 analogues. With boron trihalides (BX(3), X=F, Cl, Br, I) 1 undergoes sequential adduct formation and halide abstraction reactions to yield borylboronium cations and shows an increasing tendency towards redox processes for the heavier halides. Calculations confirm that 1 acts as a strong Lewis base towards EX(3) and show a marked increase in the B−E bond dissociation energies down both group 13 and the halide group.