Ni^II and Cu^II Complexes of 5-Oxa-, 5-Sulfa-, 5-Selena-, and 5-Telluracorroles

Cyclization of α,α'-dibromo tetrapyrrolic Ni^II complex 4Ni with K₂S, Na₂Se, and Na₂Te gave Ni^II 5-sulfacorrole, Ni^II 5-selenacorrole, and Ni^II 5-telluracorrole, respectively, as the first example of 5-heterocorrole. The corresponding Cu^II 5-heterocorroles were similarly synthesized from Cu^II complex 4Cu, while Ni^II 5-oxacorrole was synthesized by reaction of 4Ni with Ni(cod)₂ and 2,2'-bipyridine and subsequent oxygen-insertion reaction of molecular oxygen, and Cu^II 5-oxacorrole was obtained from reaction of 4Cu with Cu^I thiophene-2-carboxylate (CuTC) and tetrabutylammonium hydroxide. Moderate aromatic characters of the Ni^II 5-heterocorroles are evinced by the ¹H NMR chemical shifts, the absorption spectra, and DFT calculations. ESR measurement and simulation studies on the Cu^II 5-heterocorroles revealed that spins are largely centered on the Cu^II but a reduced spin density at the Cu^II is indicated for the Cu^II 5-telluracorrole.