Synthesis and Structural Characterization of Mixed-Sandwich Complexes of Rhodium(III) and Iridium(III) with Cyclopentadienyl and Hydrotris(pyrazolyl)borate Ligands

MCp*(Tp')Cl (M = Rh or Ir, Cp* = pentamethyleyclopentadienyl, Tp' = hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*)) complexes have been synthesized by reaction of the appropriate [(CP*)MCl2](2) with KTp'. Reaction between MCp*(Tp)Cl and AgNO3 in acetonitrile affords ionic [M(Cp*)Tp]NO3 species, whereas with MCp*(Tp*)Cl B-N bond cleavage within the Tp* ligand occurs. B-N bond scission is also detected during the interaction of [MCP*Cl-2](2) complexes with KTp' salts when the reactions are carried out in air for extended periods of time, providing pyrazole derivatives, e.g., RhCp*Cl-2(pz*H), (pz*H) = 3,5-dimethylpyrazole) (8). Two different compounds have been obtained from the reaction of KBp (Bp = dihydrobis(pyrazolyl)borate) and [IrCp*Cl-2](2), namely, monomeric IrCp*Cl-2(pzH) and the binuclear [IrCp*Cl](2)(mu-Cl)(mu-pz) (10), which contains bridging chloride and pyrazolategroups. In contrast, the analogous reaction of [RhCp*Cl-2](2) with KBp produces RhCp*(Bp)Cl. Crystal structure determinations have been performed for some of the complexes. IR data indicate kappa(3)-Tp binding for [MCp*Tp]NO3; moreover, the expected correlation between nu(B-H) and the Tp' hapticity is found for MCp*Tp' systems.