Syntheses, NMR and EPR spectroscopy, electrochemical properties, and structural studies of [5,10,15,20-tetrakis (perfluoroalkyl)porphinato]iron(II) and -iron(III) complexes

Syntheses, structural studies, electrochemistry, and spectroscopy of a numb er of [5,10,15,20-tetrakis(heptafluoropropyl)porphinato]iron derivatives ar e presented. The X-ray crystal structure of 5,10,15,20-tetrakis(heptafluoro propyl)porphinato]iron(II).(pyridine)(2) exhibits a substantial Sq distorti on of the porphyrin macrocycle, with the meso-carbon atoms displaced more t han 0.6 Angstrom above and below the porphyrin mean plane defined by the fo ur central nitrogen atoms; the most notable aspect of this ferrous porphyri n structure is the fact that it exhibits metrical features commonly manifes ted in crystallographically characterized ferric porphyrin complexes. X-ray data are as follows: P2(1)/n with a = 12.772(1) Angstrom, b = 18.895(2) An gstrom, c = 19.756(2) Angstrom, beta = 99.960(6)degrees, V = 4695.7(8) Angs trom(3), Z = 4, and d(calc) = 1.689 g/cm(3). F-19 NMR spectroscopy confirms the sensitivity of the F-19 nucleus as a probe of macrocycle aromaticity a nd electronic structure, while H-1 NMR spectroscopic studies show large iso tropic shifts for the beta-protons of the (porphinato)iron(III) chloride de rivative (delta = 101.5 and 86.4 ppm). Electrochemical data obtained from c yclic voltammetric and spectroelectrochemical experiments reveal that the E -1/2 value for the Fe-II/III redox couple for 5,10,15,20-tetrakis(heptafluo ropropyl)por iron (pyridine)(2) is shifted by 550 mV relative to that obser ved for the corresponding (porphinato)iron(III) chloride complex. The catho dic electrochemistry of [5,10,15,20-tetrakis(heptafuoropropyl)porphinato]-i ron(III).(pyridine)(2) is also unusual in that the first one-electron reduc tion of this complex produces a largely macrocycle-localized radical anion. EPR spectroscopic data shows that 5,10,15,20-tetrakis(heptafluoropropyl)po r iron(III).(pyridine)(2) manifests a pure axial spectrum (Delta/lambda = - 26.4; Sigma g(2) = 12.53) congruent with a (d(xz),d(yz))(4)(d(xy))(1) elect ronic ground state. The extraordinary structural, potentiometric, and spect roscopic properties of these (porphinato)iron species arise from substantia lly reduced metal-centered electron density effected by the macrocycle's no n-pi-conjugating, sigma-electron-withdrawing meso-perfluoroalkyl substituen ts.