Synthesis and Electrochemistry of Tin(IV) Octaethylcorroles, (OEC)Sn(C6H5) and (OEC)SnCl

Abstract
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 σ-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 π-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, P21/n, with a = 13.235(4) Å, b = 14.502(4) Å, c = 18.387(5) Å, β = 95.45(2)°, Z = 4, R = 0.0619.

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