Rhenium Biscorrole Sandwich Compounds: XAS Evidence for a New Coordination Motif

The interaction of three free-base meso-tris(p-X-phenyl)corroles H₃[TpXPC] (X = H, CH₃, OCH₃) with Re₂(CO)₁₀ at 235 °C in the presence of K₂CO₃ in o-dichlorobenzene has led to putative rhenium biscorrole sandwich compounds with the formula ReH[TpXPC]₂. Density functional theory calculations and Re L₃-edge extended X-ray absorption fine structure measurements suggest a seven-coordinate metal center, with the "extra" hydrogen located on one of the corrole nitrogens. The complexes can be deprotonated by a base such as 1,8-diazabicyclo[5.4.0]undec-7-ene, resulting in a substantial sharpening of the UV-vis spectra and split Soret bands, consistent with the generation of C₂-symmetric anions. Both the seven-coordinate neutral and eight-coordinate anionic forms of the complexes represent a new coordination motif in the field of rhenium-porphyrinoid interactions.