Norcorrole and Dihydronorcorrole: A Predictive Quantum Chemical Study

DFT calculations indicate norcorrole (NCH2), a 16π‐electron doubly contracted porphyrin, to be a promising synthetic target, especially when complexed to a small cation such as NiII. The relative stability of norcorrole derivatives appears to reflect the fact that they are not antiaromatic, but should rather be viewed as bis(dipyrrins). However, norcorrole (NC) complexes are expected to be prone to reduction and we predict that high‐valent transition metal dihydronorcorrole (DHNC) derivatives should exist as reasonably stable substances. Our calculations further predict that both NC and DHNC complexes should exhibit short metal–nitrogen distances and moderate to strong doming of the macrocycle. Overall, a number of calculated results suggest that NC and DHNC derivatives should be of unique electronic‐structural interest, as conceptual links between aromatic tetrapyrroles such as porphyrin and corrole on the one hand and open‐chain pyrrole‐based ligands such as dipyrrins and biliverdines on the other. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)