Metalloradical Chemistry of Cobalt(II) Porphyrins. The Syntheses, Structure, and Reactivity of Triphenyltin(II)- and Trihalomethylcobalt(III) Octaethylporphyrin
datasetposted on 10.09.1998, 00:00 by Yang Cao, Jeffrey L. Petersen, Alan M. Stolzenberg
Stannanes R3SnH (R = n-Bu, Ph) reacted with CoIII(OEP)CH3 or CoII(OEP) to afford CoIII(OEP)SnR3 and CH4 or H2, respectively. CoIII(OEP)SnR3 was more efficiently prepared by reaction of CoI(OEP)- with R3SnCl. CoIII(OEP)SnPh3, C54H59CoN4Sn, crystallized in the triclinic space group P1̄ (Z = 2) with unit cell dimensions a = 12.124(5) Å, b = 14.700(5) Å, c = 15.221(7) Å, α = 109.56(4)°, β = 91.44(5)°, γ = 113.27(1)°, and V = 2308.4(1.8) Å3 at 295(2) K. The structure resembled that of five-coordinate alkylcobalt(III) porphyrin complexes with a square-pyramidal Co atom displaced 0.077 Å out of the porphyrin plane toward Sn and a Co−Sn bond length of 2.510(2) Å. The bond dissociation energy of the Co−Sn bond was considerably larger than that of the Co−C bond in alkylcobalt(III) porphyrin complexes. CoIII(OEP)SnPh3 was air stable in solution and decomposed by homolysis slowly at 120 °C in toluene. The Co−Sn bond was rapidly cleaved, though, when oxidized by I2 or by electrochemical means. In contrast, the Co−C bonds in CoIII(OEP)CX3 (X = Cl, Br, I) were substantially weaker than in the Co−C bond in alkylcobalt(III) porphyrin complexes and weakened progressively with heavier halogens. CoIII(OEP)CX3 complexes were prepared by reaction of CoI(OEP)- with CX4 (X = Cl, Br) or by reaction of CoII(OEP) with CBrCl3 or CX4 (X = Br, I). The reaction of CoI(OEP)- with CX4 (X = Cl, Br, I) also afforded small amounts of CoIII(OEP)CHX2 complexes, which were obtained in greater yield by reaction of CoI(OEP)- with CHX3. The substitution of one hydrogen for a halogen stabilized the CoIII(OEP)CHX2 complexes relative to the corresponding CoIII(OEP)CX3 complexes.