The complex [(PMe(3))(4)RhMe] (2) reacts with 1 equiv of B(2)cat(2) (1) (cat = 1,2-O2C6H4) yielding the rhodium(I) boryl complex [(PMe(3))(4)Rh(B(cat))] (3) and MeB(cat) (4) while reaction with 2 equiv of 1 or reaction of 3 with 1 equiv of 1 gives the triboryl complex fac-[(PMe(3))(3)Rh(B(cat))(3)] (5). Both 3 and 5 have been characterized by X-ray diffraction. The second B-B oxidative addition (i.e. 3 + 1 --> 5) is apparently reversible as reaction of 2 with 5 in the presence of PMe(3) gives 2 equiv of 3 and 1 equiv of 4.