CpRh(η5-C4H4BPh) shows fast exchange at the α-position to the boron at 0°C, thus providing the first evidence of an electrophilic substitution of an (η5-borole)metal complex. Protonation of V gives RhHL2 (VII) as the first (η5-borole)metal hydrides. Various neutral nucleophiles effect a valence disproportionation of IIIb (R = Ph) with formation of the compounds [LRhY3][RhL2] (VIII) (Y = PMe3), IX (Y = P(OMe)3)