Syntheses, NMR and EPR spectroscopy, electrochemical properties, and structural studies of [5,10,15,20-tetrakis (perfluoroalkyl)porphinato]iron(II) and -iron(III) complexes
Kt. Moore et al., Syntheses, NMR and EPR spectroscopy, electrochemical properties, and structural studies of [5,10,15,20-tetrakis (perfluoroalkyl)porphinato]iron(II) and -iron(III) complexes, J AM CHEM S, 121(22), 1999, pp. 5196-5209
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.