Synthesis,structures, and properties of a series of four-, five-, and six-coordinate cobalt(III) triazacorrole complexes: the first examples of transition metal corrolazines

The syntheses of the first transition metal corrolazine complexes, in which the meso carbon atoms of a corrole framework have been replaced by N atoms, are reported. Metalation of the corrolazine (TBP)(8)CzH(3)] (TBP = 4-tert-butylphenyl) (1) with Co(acac)(2) gives (TBP)(8)CzCo(III)] (2) in good yield. Addition of PPh(3) to 2 in pyridine results in the formation of (TBP)(8)CzCo(III)(PPh(3))] (3), which was characterized by X-ray crystallography. Likewise, addition of an excess of pyridine to 2 in CH(2)Cl(2) followed by slow diffusion of MeOH gives (TBP)(8)CzCo(III)(py)(2)] (4) as a crystalline solid, which was also characterized by X-ray crystallography. The crystal structures of 3 and 4 reveal that the corrolazine cavity is significantly smaller ( approximately 0.1 A) than their regular corrole analogues. Characterization of 2-4 by UV-vis spectroscopy reveals some interesting features in the absorption spectra of these compounds, including a dramatic red-shift of the Soret band. In addition, binding of pyridine to 2 was evaluated quantitatively by UV-vis titration, revealing a formation constant of beta(2) = 9.0 x 10(7) M(-)(2), which is larger than any of the regular Co(III) corrole analogues.