A current trend in porphyrinoid chemistry is the development of ring-contracted macrocycles and the study of their metal complexes. [1] Corroles clearly play a major role in this field, particularly with respect to species containing a porphyrinlike N 4 metal binding site. [2] However, many other noncontracted porphyrinoids, such as the porphyrin isomers and the azaporphyrins, are in fact also characterized by a smaller N 4 cavity. [3] Reports from coordination compounds of such macrocycles clearly prove the importance of the size of the metal binding site for spectacular results in terms of electronic structure, [4] small-molecule binding, [5] and catalysis. [6] Conceptually, the class of 10-heterocorroles can be regarded as intermediate between porphyrins (dianionic ligand) and corroles (ring-contracted ligand; Scheme 1). 10-Heterocorroles with an oxygen, sulfur, or nitrogen atom in the backbone have been known for a long time, [7] and have recently gained renewed interest. [8] However, the literature procedures to synthesize these macrocycles are either long and cumbersome, or yield chelate complexes of Group 10 elements which cannot be demetalated without disintegration of the porphyrinoid ligand.We are interested in free-base 10-heterocorroles with a Group 16 element (O, S, Se) in the backbone, as such ligands may allow a fine-tuning of the electronic properties of the transition metal through the size of the N 4 cavity. For this purpose, a general and efficient entry into this class of porphyrinoids (or better: corrinoids) was needed. We report here the successful syntheses and ligand properties of freebase 10-oxa-, 10-thia-, and 10-selenacorroles.The known synthetic protocols leading to 10-heterocorroles are only of limited use for a general preparative entry into this class of porphyrinoids, as they either require a more than stoichiometric amount of supported palladium as a reagent, or a thioether precursor, the oxygen and selenium homologues of which are unavailable. To overcome these drawbacks we attempted to develop a metal-promoted twostep macrocyclization approach from a,w-dibrominated dipyrrins such as 1 (Scheme 2). These precursors were first coupled to bromine-terminated linear tetrapyrrole copper(II) chelates by using a nBuLi/Cu II protocol, and then cyclized in a second step to the desired copper(II) complexes such as 2-4, by using different nucleophilic O, S, or Se transfer reagents, respectively. During the course of our investigations it Scheme 1. 10-Heterocorroles H 2 (XCor) as hybrid structures from porphyrin and corrole frameworks (with the 18p main conjugation pathways shown in bold).Scheme 2. Syntheses of 10-heterocorroles H 2 L 5-7 via the copper(II) complexes 2-4; a) Cu(OAc) 2 ·H 2 O, wet DMF, 110 8C, 15 min; b) Cu(OAc) 2 ·H 2 O, DMF, 5 min, then Na 2 S·9 H 2 O, 110 8C, 15 min, then TFA, toluene, 110 8C, 3 h; c) Cu(OAc) 2 ·H 2 O, THF, 15 min, then KSeCN, 65 8C, 12 h; d) SnCl 2 ·2 H 2 O, HCl(aq), acetonitrile/dichloromethane, 15 min. TFA = trifluoroacetic acid.

A first systematic study upon the preparation and exploration of a series of iron 10-thiacorroles with simple halogenido (F, Cl, Br, I), pseudo-halogenido (N3 , I3 ) and solvent-derived axial ligands (DMSO, pyridine) is reported. The compounds were prepared from the free-base octaethyl-10-thiacorrole by iron insertion and subsequent ligand-exchange reactions. The small N4 cavity of the ring-contracted porphyrinoid results in an intermediate spin (i.s., S=3/2) state as the ground state for the iron(III) ion. In most of the investigated cases, the i.s. state is found unperturbed and independent of temperature, as determined by a combination of X-ray crystallography and magnetometry with (1) H NMR-, EPR-, and Mössbauer spectroscopy. Two exceptions were found. The fluorido iron(III) complex is inhomogenous in the solid and contains a thermal i.s. (S=3/2)→high spin (h.s., S=5/2) crossover fraction. On the other side, the cationic bis(pyridine) complex resides in the expected low spin (l.s., S=1/2) state. Chemically, the iron 10-thiacorroles differ from the iron porphyrins mainly by weaker axial ligand binding and by a cathodic shift of the redox potentials. These features make the 10-thiacorroles interesting ligands for future research on biomimetic catalysts and model systems for unusual heme protein active sites.

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10-Heterocorrole complexes with oxygen, sulfur, and selenium at position 10 of the macrocycle and with the divalent ions of nickel, copper, and palladium were prepared and investigated. The focus was set on the size adaptation and matching mechanisms of cavity size versus ionic radius in corrole-type macrocycles. A full set of single-crystal X-ray analytical data revealed that in all but one case the N binding site of the ring-contracted tetrapyrrole was larger than necessary to bind the metal ion without deformation. In-plane size adaptation through M-N bond-length elongation by 2.5-3.2 % was effective, as well as pronounced out-of-plane ruffling of the macrocycle for those compounds with a more severe size mismatch. Such ruffling had been excluded for corroles previously, but is apparently the most efficient mechanism to adapt to small central ions.