Synthesis of Quinoline-Based Rh–Sb Complexes: Inhibition of Halide Transfer to Access a Rh→Sb Z-Type Interaction

We report the synthesis of Rh-Sb complexes using high valent Sb ligands, Q3SbCl2 (1, Q = 8-quinolinyl) and Q3SbF2 (2), from the low valent Rh precursor [(CO)2Rh-(μ-Cl)]2 to afford the complexes [(κ4-Q3SbCl)-Rh-(CO)-Cl]-[(CO)2RhCl2] (3) and (κ4-Q3SbF2)-Rh-(CO)Cl (4), respectively. The reaction of 1 with [(CO)2Rh-(μ-Cl)]2 results in the transfer of chloride from Sb to Rh to give the ion pair 3 with a Rh-Sb bond for the cation that, according to computational analysis, has some covalent character. Replacing Sb-Cl with Sb-F bonds (i.e., compound 2) inhibited halide transfer and allowed formation of 4 with a Rh→Sb interaction that has more Z-type character than the Rh-Sb bond for complex 3. Molecular orbital and localized orbital bonding analyses are consistent with the proposed Rh→Sb interaction of 4 being more Z-type in character.