Synthesis and Characterization of Rhodium(I) Boryl and Rhodium(III) Tris(Boryl) Compounds: Molecular Structures of [(PMe3)4Rh(B(cat))] and fac-[(PMe3)3Rh(B(cat))3] (cat = 1,2-O2C6H4)

The complex [(PMe3)4RhMe] (2) reacts with 1 equiv of B2cat2 (1) (cat = 1,2-O2C6H4) yielding the rhodium(I) boryl complex [(PMe3)4Rh(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-[(PMe3)3Rh(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 PMe3 gives 2 equiv of 3 and 1 equiv of 4.