METALLOPORPHYRINS WITH METAL METAL SIGMA-BONDS - SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION, AND ELECTROCHEMISTRY OF (P)MRE(CO)5 WHERE P IS THE DIANION OF OCTAETHYLPORPHYRIN (OEP) OR TETRAPHENYLPORPHYRIN (TPP) AND M = AL, GA, IN OR TL

The synthesis, physicochemical properties, and electrochemistry of a new series of metal-metal sigma-bonded metalloporphyrins are reported. The investigated compounds are represented as (P)MRe(CO)5 where P is the dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP) and M = Al, Ga, In, or Tl. These compounds provide the first examples of Al and Ga metalloporphyrins with covalent metal-metal bonds as well as give the first series of compounds in which the same metalate anion is covalently bonded to four different group 13 metalloprophyrins. Each synthesized complex was characterized by H-1 NMR, IR, and UV-visible spectroscopy as well as by electrochemistry. Graham DELTA-sigma and DELTA-pi parameters, and calculated residual charges on the rhenium atom of (P)MRe(CO)5 demonstrate that the covalency of the metal-metal bond decreases in the order: Tl >> In > Ga > Al. The thallium derivative is stable upon electrooxidation by either one or two electrons. However, the In, Ga, and Al complexes undergo rapid cleavage of the metal-rhenium bond after formation of a [(P)MRe(CO)5]+. cation radical. The chemical reactivity and physical properties, as well as the electrochemistry, of each (P)MRe(CO)5 species were analyzed as a function of the central metal ion or porphyrin ring basicity. The spectroscopic properties and electrochemistry of these metal-metal sigma-bonded species are compared with data for other metal-metal bonded metalloporphyrins of the type (P)MM'(L) as well as with data for related metal-carbon bonded porphyrins of the type (P)M(R).