Triple-decker complex CpCo(μ-C3B2Me5)Rh(C2H4)2: Synthesis, structure and bonding

The reaction of the thallium derivative [CpCo(μ-C3B2Me5)]Tl with [Rh(C2H4)2Cl]2 affords the μ-diborolyl bis(ethylene) triple-decker complex CpCo(μ-C3B2Me5)Rh(C2H4)2 (4). Structure of 4 was determined by X-ray diffraction. According to DFT calculations, the ethylene dissociation energies for the triple-decker complexes CpCo(μ-C3B2R5)Rh(C2H4)2 (R = H, Me) are ca. 6 kcal mol−1 lower than for cyclopentadienyl analogs (C5R5)Rh(C2H4)2. Energy decomposition analysis revealed that the bonding of anions [CpCo(C3B2R5)]− with [Rh(C2H4)2]+ is also weaker than that of [C5R5]−; the attractive interactions in both cases are 60–63% electrostatic and 37–40% covalent. The electrostatic potentials at the Rh nuclei suggest that the donor ability of the anions increases in the following order: Cp < [CpCo(C3B2H5)] ⩽ [CpCo(C3B2Me5)] < Cp∗.