Synthesis and electrochemistry of tin(IV) octaethylcorroles, (OEC)Sn(C6H5) and (OEC)SnCl

Two Sn(IV) corroles were synthesized and electrochemically examined. The investigated compounds are represented as (OEC)Sn(C6H5) and (OEC)SnCl, where OEC = trianion of 2,3,7,8,12,13,17, 18-octaethylcorrole. (OEC)Sn(C6H5) represents the first example of a sigma-bonded metallocorrole which does not undergo a metal-centered electrode reaction. Both compounds undergo three reversible one-electron oxidations, all of which occur at the conjugated macrocycle. The reduction of (OEC)SnCl involves an overall two electrons, with the product being spectroscopically identified as a Sn(II) corrole after bulk electrolysis of the starting compound. (OEC)Sn(C6H5) is reversibly reduced by a single electron to give a Sn(IV) corrole pi-anion radical. The electrochemically measured HOMO-LUMO gap (defined as the absolute potential difference between the first-ring centered reduction and first ring-centered oxidation) is equal to 2.25 V in benzonitrile, a value which closely approximates what is observed for porphyrins containing octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP) macrocycles. An X-ray crystallographic analysis for the molecular structure of (OEC)Sn(C6H5) is also presented: monoclinic, P2(1)/n, with a = 13.235(4) Angstrom, b = 14.502(4) Angstrom, c = 18.387(5) Angstrom, beta = 95.45(2)degrees, Z= 4, R = 0.0619.