Metalloradical chemistry of cobalt(II) porphyrins. The syntheses, structure, and reactivity of triphenyltin(II)- and trihalomethylcobalt(III) octaethylporphyrin

摘要

Stannanes R3SnH (R = n-Bu, Ph) reacted with Co-III(OEP)CH3 or Co-II(OEP) to afford Co-III(OEP)SnR3 and CH4 or H-2, respectively. Co-III(OEP)SnR3 was more efficiently prepared by reaction of Co-I(OEP)(-) with R3SnCl. Co-III(OEP)SnPh3, C54H59CoN4Sn, crystallized in the triclinic space group P (1) over bar (Z = 2) with unit cell dimensions a = 12.124(5) Angstrom, b = 14.700(5) Angstrom, c = 15.221(7) Angstrom, alpha = 109.56(4)degrees, beta = 91.44(5)degrees, gamma = 113.27(1)degrees, and V = 2308.4(1.8) Angstrom(3) at 295(2) K. The structure resembled that of five-coordinate alkylcobalt(III) porphyrin complexes with a square-pyramidal Co atom displaced 0.077 Angstrom out of the porphyrin plane toward Sn and a Co-Sn bond length of 2.510(2) Angstrom. The bond dissociation energy of the Co-Sn bond was considerably larger than that of the Co-C bond in alkylcobalt(III) porphyrin complexes. Co-III(OEP)SnPh3 was air stable in solution and decomposed by homolysis slowly at 120 degrees C in toluene. The Co-Sn bond was rapidly cleaved, though, when oxidized by It or by electrochemical means. In contrast, the Co-C bonds in Co-III(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. Co-III(OEP)CX3 complexes were prepared by reaction of Co-I(OEP)(-) with CX4 (X = Cl, Br) or by reaction of Co-II(OEP) with CBrCl3 or CX4 (X = Pr, I). The reaction of Co-I(OEP)- with CX4 (X = Cl, Br, I) also afforded small amounts of Co-III(OEP)CHX2 complexes, which were obtained in greater yield by reaction of Co-I(OEP)(-) with CHX3. The substitution of one hydrogen for a halogen stabilized the Co-III(OEP)CHX2 complexes relative to the corresponding Co-III(OEP)CX3 complexes. [References: 57]