ELECTROOXIDATION OF COBALT(II) BETA-BROMINATED-PYRROLE TETRAPHENYLPORPHYRINS IN CH2CL2 UNDER AN N-2 OR A CO ATMOSPHERE

The electrochemical behavior of (TPPBrx)Co (TPPBrx = the dianion of be ta-brominated-pyrrole tetraphenylporphyrin and x = 0-8) is reported un der an N-2 or a CO atmosphere in dichloromethane containing tetra-n-bu tylammonium hexafluorophosphate as supporting electrolyte. Each invest igated compound undergoes three reversible one-electron oxidations wit hin the potential window of the solvent, and this results in the ultim ate formation of a cobalt(III) dication as the final three-electron-ox idation product under both an N-2 and a CO atmosphere. The initial one -electron abstraction from (TPPBrx)Co involves the central metal ion f or derivatives with x less than or equal to 5 and the conjugated porph yrin pi ring system for derivatives with six, seven, or eight Br group s. Thin-layer infrared spectroelectrochemical measurements were perfor med during the first oxidation of (TPPBrx)Co in dichloromethane and in dicate that in situ generated [(TPPBrx)Co](+) forms mono-and bis(carbo n monoxide) adducts for complexes with zero to five Br groups but that no CO molecule binds to the singly oxidized derivatives with six, sev en, or eight Br groups, all of which exist as Co(ll) pi cation radical s.