Reactions of 1,3,2‐Diselenaphospholanes with Lewis Acids: Borane and (Pentamethylcyclopentadienyl)rhodium and ‐iridium Dichloride

2-R-1,3,2-Diselenaphospholanes (R = iPr, Ph) with an annelated 1,2-dicarba-closo-dodecaborane(12) unit were treated with Lewis acids such as borane reagents (BH3 in THF, and BH3–SMe2) as well as Cp*-rhodium and -iridium dichloride (Cp* = pentamethylcyclopentadienyl). In all cases, the adduct formation in the beginning was followed by ring expansion through insertion of the borane or Cp*MCl2 into one of the P–Se bonds accompanied by transfer of a hydrido or chlorido ligand to phosphorus. Finally, the P–R unit was displaced from the ring to give the exchange products, in which the boron or the metal had become part of the five-membered rings. The reactions were monitored by NMR spectroscopy (1H, 11B, 13C, 31P, and 77Se). The proposed reaction sequences were found to be in agreement with calculated [B3LYP/6-311+G(d,p), LANL2DZ (Rh, Ir) level of theory] relative energies of optimized gas-phase structures of the various products. The novel molecular structure of the preferred insertion product with M = Ir, R = iPr was determined by X-ray analysis.