Synthesis of Complexes of Rhodium(I) and Iridium(I) with 3,5-Pyrazoledicarboxylic Acid and Their Mixed-Valence Oxidation Products

The ability of the trianion of 3,5-pyrazoledicarboxylic acid (H3Dcbp) to form dinuclear complexes has been utilized in the preparation of a family of anionic complexes of rhodium(I) and iridium(I) using 1,5-cyclooctadiene, CO, and PPh3 as ancillary ligands. The complex (NBu4)[Rh2(CO)4Dcbp] crystallizes in the [formula omitted] space group with a = 13.043 (5) Å, b = 13.543 (3) Å, c = 10.702 (3) Å, α = 109.91 (2)°, β = 112.06 (2)°, γ = 95.56 (2)°, V = 1591.5 (8), and Z = 2. The complex anion is nearly planar and has a short intermolecular distance between the rhodium atoms. Stacking interactions in some of the rhodium and iridium anionic carbonyl complexes in the solid state can be inferred from the dramatic change of color with changes in the countercation. The electrochemical oxidation of (NR4)[Ir2(CO)4Dcbp] (R = Bu, Pr) produced dark materials growing on the anode surface of the electrode. The solid analyzed as (NR4)0.5[Ir2(CO)4Dcbp]. Pressed-pellet conductivities of these materials are in the range 10−5 Ω−1 cm−1, which are 1000 times higher than the unoxidized precursor. X-ray photoelectron spectroscopy corroborates the stoichiometry of these compounds and indicates that both iridium atoms in the dinuclear unit are involved in the formation of stacks with delocalized mixed valence. © 1991, American Chemical Society. All rights reserved.