2 research outputs found
Reactions of Grignard Reagents with Tin-Corrole Complexes: Demetalation Strategy and σ‑Methyl/Phenyl Complexes
An efficient, mild, and one-step
methodology for the conversion
of tin-corroles to the corresponding free base corroles has been developed. The Grignard reagent, namely, methylmagnesium chloride, is responsible
for the facile demetalation of tin-corroles. In an optimized reaction,
almost complete destannation is observed using methylmagnesium chloride
in a representative corrolato-Sn(IV)-chloride complex. This particular
protocol has also been proven to be versatile on a wide variety of
corrolato-Sn(IV)-chloride substrates. Similar Grignard reagents, namely,
methyl/phenylmagnesium bromides, however, failed to perform the desired
demetalation reaction and rather resulted in the usual σ-methyl/phenyl
complexes in good yields. In addition to two novel σ-phenyl complexes and three novel
σ-methyl complexes, one new A<sub>3</sub>-corrole and one new
corrolato Sn(IV)chloride have also been synthesized. All the complexes
have been thoroughly characterized by various spectroscopic techniques,
including single-crystal X-ray structural analysis of the representative
complexes. In the single-crystal X-ray data analyses, it was observed
that the Sn–N and Sn–C bond distances are shorter than
those in the similar tin porphyrin analogues. The <sup>1</sup>H NMR
spectrum of a representative σ-methyl complex exhibits peaks
corresponding to σ-bonded methyl groups in the high field regions
at −3.39 ppm
Synthesis, Spectral Characterization, Structures, and Oxidation State Distributions in [(corrolato)Fe<sup>III</sup>(NO)]<sup><i>n</i></sup> (<i>n</i> = 0, +1, −1) Complexes
Two
novel <i>trans</i>-A<sub>2</sub>B-corroles and three
[(corrolato){FeNO}<sup>6</sup>] complexes have been prepared
and characterized by various spectroscopic techniques. In the native
state, all these [(corrolato){FeNO}<sup>6</sup>] species are
diamagnetic and display “normal” chemical shifts in
the <sup>1</sup>H NMR spectra. For two of the structurally characterized
[(corrolato){FeNO}<sup>6</sup>] derivatives, the Fe–N–O
bond angles are 175.0(4)° and 171.70(3)° (DFT: 179.94°),
respectively, and are designated as linear nitrosyls. The Fe–N
(NO) bond distances are 1.656(4) Å and 1.650(3) Å (DFT:
1.597 Å), which point toward a significant Fe<sup>III</sup> →
NO back bonding. The NO bond lengths are 1.159(5) Å and 1.162(3)
Å (DFT: 1.162 Å) and depict their elongated character. These
structural data are typical for low-spin Fe(III). Electrochemical
measurements show the presence of a one-electron oxidation and a one-electron
reduction process for all the complexes. The one-electron oxidized
species of a representative [(corrolato){FeNO}<sup>6</sup>]
complex exhibits ligand to ligand charge transfer (LLCT) transitions
(cor(π) → cor(π*)) at 399 and 637 nm, and the one-electron
reduced species shows metal to ligand charge transfer (MLCT) transition
(Fe(dπ) → cor(π*)) in the UV region at 330 nm.
The shift of the ν<sub>NO</sub> stretching frequency of a representative
[(corrolato){FeNO}<sup>6</sup>] complex on one-electron oxidation
occurs from 1782 cm<sup>–1</sup> to 1820 cm<sup>–1</sup>, which corresponds to 38 cm<sup>–1</sup>, and on one-electron
reduction occurs from 1782 cm<sup>–1</sup> to 1605 cm<sup>–1</sup>, which corresponds to 177 cm<sup>–1</sup>. The X-band electron
paramagnetic resonance (EPR) spectrum of one-electron oxidation at
295 K in CH<sub>2</sub>Cl<sub>2</sub>/0.1 M Bu<sub>4</sub>NPF<sub>6</sub> displays an isotropic signal centered at <i>g</i> = 2.005 with a peak-to-peak separation of about 15 G. The in situ
generated one-electron reduced species in CH<sub>2</sub>Cl<sub>2</sub>/0.1 M Bu<sub>4</sub>NPF<sub>6</sub> at 295 K shows an isotropic
signal centered at <i>g</i> = 2.029. The 99% contribution
of corrole to the HOMO of native species indicates that oxidation
occurs from the corrole moiety. The results of the electrochemical
and spectroelectrochemical measurements and density functional theory
calculations clearly display a preference of the {FeNO}<sup>6</sup> unit to get reduced during the reduction step and the corrolato
unit to get oxidized during the anodic process. Comparisons are presented
with the structural, electrochemical, and spectroelectrochemical data
of related compounds reported in the literature, with a particular
focus on the interpretation of the EPR spectrum of the one-electron
oxidized form