Unusual metalloporphyrin complexes of rhenium and technetium

By reaction of dirhenium decacarbonyl, Re2(CO)10, or ditechnetium decacarbonyl, Tc2(CO)10, with mesoporphyrin IX dimethyl ester, H2MPIXDME, or meso-tetraphenylporphine, H2TPP, monometallic and bimetallic porphyrin complexes of rhenium and technetium were synthesized. The monometallic complex of rhenium can further react with either Re2(CO)10 or Tc2(CO)10 to form the homo- and heterodinuclear metalloporphyrin complexes. Proton magnetic resonance spectrum of (H-TPP)Re(CO)3 gave evidence for the proposed structure of the monometallic porphyrin complexes. In the monometallic complexes, the porphyrin acts as a tridentate instead of a tetradentate ligand, while in the bimetallic complexes the porphyrin acts as a hexadentate ligand; both of these are considered nonclassical coordination numbers for the porphyrin ligand. A fluxional character of both Re and Tc monometallic porphyrin complexes was observed by variable-temperature 1H NMR spectral studies. This fluxional phenomenon is best explained by the intramolecular rearrangement of the metal-carbonyl group among the four ring nitrogen atoms of porphyrin and a concomitant movement of the N--H proton. A novel thermal disproportionation of (H-MP)Tc(CO)3 to MP[Tc(CO)3]2 and H2MPIXDME was also observed. A dissociation and recombination of the metal-carbonyl moieties and the porphyrin ligands between two of the (H-MP)Tc(CO)3 molecules would seem interpretable for this unusual coordination phenomenon. (U.S.)