F-element metalated dipyrrins: synthesis and characterization of a family of uranyl bis(dipyrrinate) complexes

Article abstract of DOI:10.1039/c7dt00150a

Using an improved, chromatography-free dipyrrin synthesis, the α,β-unsubstituted dipyrrins [RC(C₄H₂N)₂H] (2) (R = tolyl (2^tolyl), p-OMe-C₆H₄ (2^anis), mesityl (2^me

Full text of DOI:10.1039/c7dt00150a

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Efficient extraction of sulfate from water using
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F-element metalated dipyrrins: Synthesis and characterization of
a family of uranyl bis(dipyrrinate) complexes†
Received 00th January 20xx,
Accepted 00th January 20xx
Duer Bolotaulo, Alejandro Metta-Magaña, and Skye Fortier*
DOI: 10.1039/x0xx00000x
Using an improved, chromatography-free dipyrrin synthesis, the α,β-unsubstituted dipyrrins [RC(C4H2N)2H] (2) (R = tolyl
(2tolyl); p-OMe-C6H4 (2anis); mesityl (2mes); ferrocenyl (2Fc)) were isolated in good to excellent yields. Deprotonation of 2 with
Na[N(SiMe3)2] gives the alkali metal salts [Na(DME)n][RC(C4H2N)2] (3) which reacts with UO2Cl2(THF)3 to give the uranyl
bis(dipyrrinates) UO2[RC(C4H2N)2]2(L) (L = THF (4R-THF); DMAP (4 R-DMAP)) (R = tolyl, p-OMe-C6H4, mesityl, ferrocenyl). The
THF adducts, 4R-THF, are unstable in aromatic and nonpolar solvents, rapidly decomposing to 2 and an intractable,
uranium-containing solid. On the other hand, the DMAP adducts, 4R-DMAP, are indefinitely stable in solution. The solid-
state structures of 4R-THF and 4R-DMAP reveal distorted trigonal bipyramidal geometries. In the solid-state, the
dipyrrinate ligands exhibit significant distortions including bowing and, in some instances, out-of-plane equatorial N-atom
coordination, likely as a consequence of steric crowding and interligand repulsion. The complexes, 4R-DMAP, have been
fully characterized by NMR, UV/Vis, and fluorescence spectroscopies and their electrochemical properties investigated
through cyclic voltammetry. The cyclic voltammograms of 4R-DMAP display several redox features but present in all is a
reversible wave at ca. -1.9 V (vs Fc0/+) attributable to a ligand centred reduction. Fluorescence measurements on all
compounds reveal that only the mesityl derivatives 2mes, 3mes, and 4mes fluoresce, with modest Stokes shift that ranges from
ca. 30 – 70 nm, with 4mes displaying the greatest relative emission intensity.
www.rsc.org/
and robust metal complexes upon ligation.8 Owing to the chemical
versatility and photoproperties bestowed by the dipyrrinate ligand,
Introduction
these compounds have been utilized in a variety of applications
such as catalysis,11 as light harvesting arrays,10 and as components
in metal organic frameworks.12, 13
Dipyrrins, also known as dipyrromethenes amongst a host of other
names,1 are a well-studied class of hemiporphyrinoids.1, 2 These
highly conjugated molecules are prized for their novel chemical and
luminescent properties, features which can be finely tuned through
chemical means owing to their high synthetic modularity and ease
of functionalization.1, 2 Accordingly, dipyrrins have received much
attention for their use as intermediates in porphyrin syntheses but
are perhaps best known as precursors to 4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (BODIPY) dyes. Through their dipyrrin core,
BODIPYs exhibit excellent properties such as stability in a wide
range of temperature and pH conditions, absorption and emission
modularity, and high quantum yields.3, 4 As such, BODIPY dyes are
widely used in bioluminescence imaging and labeling,5 as laser
dyes,6 and in photoelectric applications.7
Considering the unique characteristics of the dipyrrin ligand,
especially its utility as
a chromophore for photophysical
applications, there is an apparent paucity of f-element based
dipyrrinate compounds in the literature. This is surprising given the
luminescent properties of the f-elements and the intense study of
lanthanide porphyrins and chromophores for optical materials.14-18
While BODIPY has been used as a light harvesting and sensitizing
substituent in luminescent lanthanide complexes,19 to the best of
our knowledge, only one example of an f-element dipyrrinate
complex is known. Recently, during the course of our study, Love et
al. reported the synthesis and characterization of the uranyl
dipyrrinate UO2Cl(L’) (L’ = {(C6F5)C[C4H2N(CHNtBu)]2}-), featuring a
donor-expanded, tetradentate dipyrrin.20 Notably, the redox non-
innocence of the ligand in UO2Cl(L’) mediates electron transfer to
Not surprisingly, the chemistry of dipyrrins on transition and
main group metals has also been explored to a significant extent.1, 2,
8-10
Upon deprotonation of the pyrrolic N-H proton, dipyrrins form
2+
the metal centre to effect the challenging reduction of the UO2
monoanionic, bidentate ligands which typically generate air-stable
unit.
In an effort to further explore and develop the dipyrrinate
chemistry of the f-block elements, we herein report the synthesis of
a series of uranyl bisdipyrrinates, UO2(dipy)2(L) (L = THF, DMAP). In
contrast to typical dipyrrin metalation procedures, these complexes
have been synthesized using an anhydrous, anaerobic salt-
Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968,
United States. E-mail: asfortier@utep.edu
†
Electronic supplementary information (ESI) available: NMR, IR, UV/vis, and
emission spectra; electrochemical data, solid-state figures and X-ray data. CCDC
1526402-1526405. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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metathesis route between UO2Cl2(THF)3 and Na(dipy) to give the documented by Cohen et al. and can be remedied bVyietwhAertuicsleeOonlfinae
base to trap the acid product generated in the reaction.8 However,
DOI: 10.1039/C7DT00150A
products in good yields. The compounds have been fully
following attempts in the presence of excess NEt3 as base proved
characterized, and their solid-state structures, electrochemical
equally unsuccessful, prompting us to explore better defined, step-
properties, and spectroscopic features are detailed.
wise routes.
Results and discussion
In particular, we envisioned that the targeted uranyl
bis(dipyrrinates) could be accessed through salt metathesis
Ligand Synthesis
To adequately accommodate two dipyrrinate ligands within the
uranyl equatorial plane, α,β-unsubstituted dipyrrins were chosen to
minimize potential steric clashing between the ligands. The
dipyrromethanes [RCH(C4H2NH)2] (1) (R = tolyl (1tolyl); p-OMe-C6H4
(1anis); mesityl (1mes); ferrocenyl (1Fc)) and their dipyrrin derivatives
[RC(C4H2N)2H] (2) (R = tolyl (2tolyl); p-OMe-C6H4 (2anis); mesityl (2mes);
ferrocenyl (2Fc)), substituted only in their meso positions, were
selected to assess the potential electrochemical and luminescent
effects of the backbone substituent on the uranyl complexes.
Initially, the dipyrromethanes 1 were synthesized using standard
between
a uranyl halide and an alkali metal dipyrrinate.
Consequently, this first required the synthesis and isolation of the
free dipyrrins, 2, which can be easily synthesized by the treatment
of a toluene solution of 1 with DDQ in the presence of NEt3.10, 25
Upon work up, this affords a dark red-brown oil which crystallizes
upon standing in cold hexanes. In this manner, we have found
column chromatography is not needed for purification.
Interestingly, free dipyrrins are purported to be difficult to isolate
or unstable compounds;8, 24, 26 however, 2 was readily isolated in
good yields as pure compounds with no decomposition observed
when stored under ambient conditions after several months.
Treatment of 2 with NaN(SiMe3)2 cleanly gives the sodium
dipyrrinates [Na(DME)n][RC(C4H2N)2] (R = tolyl (3tolyl), n = 0.3; p-
OMe-C6H4 (3anis), n = 0.75; mesityl (3mes), n = 0; ferrocenyl (3Fc), n =
0) in 76-90% yields after recrystallization. These compounds have
been fully characterized by spectroscopic techniques and elemental
analyses. While alkali metal derivatives of dipyrrinates are
known,27, 28 to the best of our knowledge, compounds 3 are the
first example of α,β-unsubstituted, alkali metallated dipyrrins.
When kept under strictly anhydrous and anaerobic conditions, 3
can be stored indefinitely both as a solid and in solution.
condensation methods by the trifluoroacetic acid catalysed reaction
22
of an aldehyde with 2 equiv of pyrrole.21,
This protocol
necessitates the use of a vast excess of pyrrole, typically as both
reagent and solvent, to disfavour oligomerization and often
requires column chromatography for product purification.
Regardless, in our hands, we found this procedure to be
complicated by the removal of the excess pyrrole and the formation
of tri- and oligopyrrane by-products. Additionally, the α,β-
unsubstituted dipyrromethanes 1 are highly acid sensitive when
dissolved in solution, and the reaction must be carried out quickly
to prevent decomposition (visually indicated by the transformation
of the pale yellow solution to a red/green mixture).
In an effort to avoid these synthetic issues, an alternative
method was sought. Using a modified procedure developed by
Dehaen et al.,23 1 can be synthesized in modest to good yields by
using acidified water (ca. 0.18 M HCl) as the carrier solvent. Under
these conditions, only a slight excess of pyrrole (3 equiv) is required
as the insoluble dipyrromethane product precipitates from solution,
preventing further oligomerization. The crude dipyrromethane is
readily isolated by filtration and can be further purified by
sublimation or recrystallization from toluene, obviating the need for
chromatography.
Uranyl Dipyrrinate Synthesis
The reaction of UO2Cl2(THF)3 with 3 in THF generates a deep red
solution from which the uranyl dipyrrinates UO2[RC(C4H2N)2]2(THF)
(4-THF) (R = tolyl (4tolyl-THF); p-OMe-C6H4 (4anis-THF); mesityl (4mes
-
THF); ferrocenyl (4Fc-THF)) can be isolated as dichroic red-green
microcrystalline solid upon filtration and removal of the solvent
(Scheme 2).
In all cases, slow diffusion of pentane into
concentrated THF/DME solutions of 4-THF kept at -30 °C affords
red-green crystalline material.
Scheme 1. Attempted in-situ synthesis of UO2(dipy)2 and isolation of
dipyrrinium uranyl triacetate.
With 1 in hand, the synthesis of uranyl bis(dipyrrinate) was
attempted using established one-pot procedures for dipyrrin
metalation, namely the in-situ oxidation of 1 to 2 followed by
addition of a metal acetate or halide under ambient conditions.8, 10,
Scheme 2. Synthesis of uranyl bis(dipyrrinates) 4-THF and 4-DMAP via salt
metathesis.
The solid-state structures of 4-THF (vide infra) reveal the
uranium adopts an approximate pentagonal bipyramidal structure
formed by the two axial oxo groups and, in the equatorial plane,
two dipyrrinates with one bound molecule of THF, giving the
complexes an overall C2v symmetry. In solution, however, the 1H
NMR spectra of 4-THF in C6D6/THF-d8 or pyridine-d5 (py-d5) is not
consistent with this geometry as it features a truncated peak set
indicative of higher symmetry. This suggests that the coordinated
THF is labile in solution and exhibits a rapid on/off equilibrium,
providing an averaged D2h symmetry on the NMR time scale, or
completely dissociates to give six-coordinate UO2(dipy)2 (4).
Surprisingly, and in support of the former, 4-THF is only stable in
24
Treatment of a pale yellow, CH2Cl2 solution of 1tol with 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a dark red
mixture consistent with the formation of 2tol Subsequent addition
.
of 0.5 equiv of UO2(CH3COO)2·2H2O gives a complicated product
mixture from which a single crystal was eventually isolated.
Analysis by X-ray crystallography revealed the formation of
[H1tol][UO2(CH3COO)3] (Scheme 1). The dipyrrinium uranyl acetate
salt presumably forms by the protonation of 2tol with CH3COOH,
generated in the reaction, to give [H1tol][CH3COO] which further
complexes with unreacted UO2(CH3COO)2 starting material. The
formation of dipyrrinium salts in this fashion has been previously
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Figure 1. Solid-state structures of 4tolyl-THF·3THF, 4anis-THF·THF·C5H12, 4Fc-THF·C5H12, and 4mes-DMAP·THF·0.5C5H12 (top left, clockwise). Co-crystallized solvent
molecules omitted for clarity. Asterisks denote symmetry generated atoms.
the presence of coordinating solvents as it immediately C6D6/py-d5 displays a persistent set of minor resonances in an
decomposes in aromatics to give 2 and an as of yet unidentified, approximate 3:1 ratio, indicative of the presence of a second
intractable uranium containing precipitate – a transformation isomeric form. Variable temperature 1H NMR spectroscopic
visually marked by a colour change from deep red to brown. measurements were carried out to further elucidate the nature of
Moreover, the 1H NMR spectra of crystalline 4-THF is always the isomeric mixture (Figure S29). Upon cooling a C7D8/py-d5
marked by the appearance of free dipyrrin 2 in varying amounts, solution of 4Fc-DMAP to -30 °C, the isomeric ratio decreases to 2:1.
regardless of the preparation method. The inherent solution-phase At room temperature, the non-Cp resonances of the minor isomer
instability of 4-THF and the ubiquity of 2 in all samples precluded are poorly resolved but sharpen at low temperature, revealing a
further product characterization.
In an attempt to improve the stability of 4 by disfavouring 80 °C, the H NMR spectrum simplifies through coalescence of the
solvent loss through use of superior σ-donor, 4- resonances towards the major isomer. Taken together, this spectral
multitude of peaks consistent with C2v symmetry. Upon warming to
1
a
dimethylaminopyridine (DMAP) was added as a coordinating base data can be explained by an equilibrium shift in which DMAP
in the uranyl dipyrrinate syntheses to give UO2[RC(C4H2N)2]2(DMAP) binding to the uranyl becomes favourable at lower temperatures
(4-DMAP) (R = tolyl (4tolyl-DMAP); p-OMe-C6H4 (4anis-DMAP); mesityl while its lability increases at higher temperatures.
(4mes-DMAP); ferrocenyl (4Fc-DMAP) in excellent yields (Scheme 2).
Attempts to synthesize the solvent-adduct-free form of 4 in the
These DMAP adducts are sparingly soluble in toluene and aliphatics, absence of a coordinating base were unsuccessful, giving 2 as the
partially soluble in benzene and Et2O, and fully soluble in polar only identifiable product.
solvents such as THF or DME. When dissolved, 4-DMAP maintains a
dark red colour in solution that appears solvent independent. More Solid-State Characterization of 4-THF and 4-DMAP
notably, 4-DMAP does not decompose in these solutions.
As noted, crystals of 4-THF can be readily grown from the slow
In the solid-state, the pentagonal bipyramidal UO2(dipy)2(L) diffusion of pentane into concentrated THF/DME solutions. Single
geometry is maintained as represented by the structure of 4mes
-
crystals of 4tolyl-THF, 4anis-THF, and 4Fc-THF were found suitable for
1
DMAP (vide infra). Regardless, the H NMR spectra of 4-DMAP in X-ray crystallographic analysis while single crystals of the mesityl
C6D6 (with a drop of py-d5 for solubility) again shows a set of derivative were isolated as its DMAP adduct, 4mes-DMAP. In all
resonances in line with D2h symmetry. It must be noted, though, cases, the single crystals appear red with a green sheen.
that the 1H NMR spectrum of 4Fc-DMAP at room temperature in
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The complexes crystallize as the solvates 4tolyl-THF·3THF, 4anis
Journal Name
-
(4tolyl-THF); 176.8(2)° and 170.5(2)° (4anis-THF); 177.0(2)° (4Fc-THF);
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THF·THF·C5H12, 4Fc-THF·C5H12, and 4mes-DMAP·THF·0.5C5H12 in the
176.9(2)° (4mes-DMAP)) of 4 are unremarkable for the most part and
DOI: 10.1039/C7DT00150A
2+
̅
̅
triclinic, trigonal, and monoclinic space groups P 1, P 1, P ퟑ1c, and
P21/c, respectively. Both 4tolyl-THF·3THF and 4anis-THF·THF·C5H12
feature two, full independent uranyl molecules in their asymmetric
units with each of the pairs exhibiting similar structural features. In
4Fc-THF·C5H12, the uranyl lies on a crystallographic special position
through which the full molecule is generated by symmetry. The
solid-state structures of 4tolyl-THF·3THF, 4anis-THF·THF·C5H12, 4Fc-
THF·C5H12, and 4mes-DMAP·THF·0.5C5H12 are shown in Figure 1.
within typical UO2 structural parameters (U-O = 1.78 Å, O-U-O =
180°), indicating little perturbation of the uranyl moiety by the
dipyrrinate ligands.36 This is further substantiated by the IR spectra
(KBr pellet) of 4-DMAP which all display an absorption at 963 cm-1
attributable to the asymmetric U=O stretch, similar to that known
for [UO2(H2O)5]2+ (νasym U=O = 962 cm-1).36 Tellingly, this indicates
2+
an electronic insensitivity of the UO2 unit to the dipyrrinate
backbone substituents.
Notably, though, significant distortions are observed in relation
to the dipyrrinate ligands. For instance, the conjugated dipyrrin
core is normally planar but it is noticeably bowed in the case of 4.
This is quantified by the dihedral angles between the pyrrolic rings
in 4tolyl-THF (11.1°, 20.5° and 27.3°, 31.0°), 4anis-THF (8.5°, 20.8° and
29.6°, 29.6), 4Fc-THF (37.2°), and 4mes-DMAP (20.4°, 22.3°); however,
the bond distances within the ligands appear otherwise unaffected.
Additionally, the dipyrrinate ligands bend out from the equatorial
plane in 4tolyl-THF (42.5°, 43.2° and 27.3°, 43.3°), 4anis-THF (43.58°,
44.5° and 41.2°, 24.7°), 4mes-DMAP (44.6°, 40.1°), and 4Fc-THF
(59.9°) as illustrated in Figure 2 (top).
O1
N1
U1
N2
O1*
A further manifestation of the ligand distortion appears in the
form of out of plane, N-atom displacement in some of the solid-
state structures. For example, one of the molecules in 4tolyl
-
THF·3THF (Figure 2, bottom) shows three of the N-atoms sitting out
of the equatorial mean plane at a distance of 0.5 – 0.7 Å. This
deviation is unusual for uranyl, which typically adheres to strictly
bipyramidal geometries, but has been reported in a few instances in
complexes with other N-donor ligands.36-40 While crystal packing
forces may play some role, these structural phenomena are best
explained as a consequence of sterics. Inspection of the spacefilling
models of the uranyl bis(dipyrrinates) clearly show ligand crowding
that necessitates the observed bowing and twisting in order to
avoid intramolecular, interligand clashing with the forward-pointing
α-hydrogen atoms of the dipyrrinates (Figure S37).
O1
N3
N1
U1
N2
N4
O2
Figure 2. Truncated solid-state structures of 4Fc-THF·C5H12 (top) and 4tolyl
-
THF·3THF (bottom) showing out of plane bonding and N-atom
displacement, respectively. Select atoms omitted for clarity. Asterisk
denotes symmetry generated atom.
Electrochemistry
Dipyrrins are well-known to be redox active molecules, capable
of one-electron reduction or oxidation, where the potentials and
In the solid-state, the uranyl bis(dipyrrinates) exhibit a distorted
pentagonal bipyramidal geometry. In order to accommodate the
coordinated THF or DMAP in the fifth equatorial position, the
dipyrrinates are pushed towards one another. Consequently, this
distorts the U-Ndipy bonds giving rise to inequivalent U-N bond
lengths for each ligand, i.e. one short (ca. 2.45 Å) and one long (ca.
2.55 Å). Nonetheless, the U-Ndipy bond distances of 4 (U-N =
2.458(5) – 2.526(6) Å (4tolyl-THF); 2.453(4) – 2.547(5) Å (4anis-THF);
2.457(4) Å, 2.482(4) Å (4Fc-THF); 2.473(6) – 2.555(5) Å (4mes-DMAP))
are similar to that found in the donor-expanded dipyrrinate
28, 41, 42
reversibility is substituent dependent.1,
In the case of
UO2Cl(L’), the dipyrrinate ligand plays an integral part in the
reduction chemistry of the metal centre, facilitating the two-
electron reduction of U(VI) to U(IV).20 As such, the electrochemical
features of the uranyl bis(dipyrrinate) complexes were investigated
by cyclic voltammetric analysis.
The cyclic voltammograms (CVs) of 4-DMAP are feature rich,
exhibiting a varying range of complexity between each complex
(see Supporting Information). Nevertheless, each CV displays a
shared set of three reduction waves that appear from ca. -1.9 to -
2.9 V vs Fc0/+ (cf Figure 3). Of the three reductions, only the first
wave exhibits any reversibility, coming in at E1/2 = -1.91, -1.88, -1.96,
and -1.96 V for 4tolyl-DMAP, 4anis-DMAP, 4Fc-DMAP, and 4mes-DMAP,
respectively. Comparison of this feature to the reversible reduction
wave found in 2anis (E1/2 = -1.96 vs Fc0/+) (Figure 3, top and Figure
UO2Cl(L’) (U-N
=
2.465(5), 2.483(4) Å)20 and other uranyl
porphyrinoids.29-35
The uranium-oxo bonds (U-O = 1.768(5), 1.765(5) Å and 1.755(4),
1.758(5) Å (4tolyl-THF); 1.759(4), 1.764(4) Å and 1.762(4), 1.762(4) Å
(4anis-THF); 1.773(3) Å (4Fc-THF); 1.764(4) and 1.766(4) Å (4mes
-
DMAP)) and the O=U=O angles (O-U-O = 177.4(2)° and 170.9(2)°
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The photophysical properties of the dipyrrin systems 2, 3, and 4
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in benzene were examined by UV-vis spectroscopy. The spectra of
2 are typical for dipyrrins and show maximum absorbances
between 436 to 456 nm (ε = 18,959 – 24,385 L·mol-1·cm-1)
consistent with   * transitions (see Figure 4 and Supporting
Information).13 Interestingly, the deprotonation of 2 to 3 has little
to no significant effect on the electronic absorption spectra of these
compounds (cf Figure 4). Yet, upon complexation to uranyl, a
number of changes are observed. At first glance, the molar
absorptivity is observed to increase in 4-DMAP over those of 2 and
3. Yet, as each uranyl complex features two dipyrrinate ligands, the
molar absorptivity per dipyrrinate in 4-DMAP is actually diminished
in comparison (e.g., 2Fc (ε = 20,412 L·mol-1·cm-1) vs 4Fc-DMAP (ε =
13,789 L·cm-1 per mole dipyrrinate)). Additionally, a new band
appears in 4tolyl-DMAP, 4anis-DMAP, and 4mes-DMAP giving a
different bathochromically shifted maximum absorbance at 462 (ε =
35,416 L·mol-1·cm-1), 467 (ε = 34,826 L·mol-1·cm-1), and 472 nm (ε =
30,214 L·mol-1·cm-1), respectively (cf Figure 4). While sharpening or
splitting of the dipyrrin absorbance bands has been observed upon
metalation,10, 13 the absorption spectra show no appreciable change
in the physiognomy of the dipyrrin peaks in 4-DMAP. This new
Figure 3. Cyclic voltammogram of 2anis (top, blue) and 4anis-DMAP (middle,
red) with its deconvoluted traces (bottom) in THF at a scan rate of 0.25 V s-1
(0.1 M [NBu4][PF6] as supporting electrolyte).
2+
band cannot be attributed to the UO2 moiety alone as uranyl,
while photoactive, absorbs at λmax = 414 nm (ε = ca. 11 L·mol-1·cm-1)
with lower intensity.43 Thus, we have tentatively assigned this new
band as arising from a dipyrrin to uranium ligand-to-metal charge
transfer (LMCT).
S60) show this redox event to be ligand based, similar to that found
for other metal dipyrrinates.28
The subsequent irreversible reduction waves for 4-DMAP,
appearing at ca. –2.0 and –2.9 V, share qualitative similarities to the
reduction features in the CV of UO2[N(SiMe3)2]2(THF)2 (Figure S62)
and fall at the lower edge of reduction potentials for uranyl
complexes with N-donor ligands (ca. -1.8V vs Fc0/+).36 However, the
CV of 2anis (Figure S60) also shows two irreversible reduction waves
within this potential window. Thus, the origin of these reductions,
whether ligand or metal based or a combination thereof, is not
readily discernible.
Given the luminescent properties of dipyrrins and their
derivatives, fluorescence measurements were undertaken. The
excitation wavelengths were set to the respective UV/vis
absorption maxima obtained in the same solvent (C6H6) using
comparable concentrations. It should be noted that solvent polarity
can have a profound effect on the fluorescence of metal dipyrrinate
complexes,25 but this phenomenon was not investigated in our
systems. Of the twelve dipyrrin complexes studied, it was found
that only the mesityl derivatives 2mes, 3mes, and 4mes-DMAP
fluoresce and their emission spectra is shown in Figure 5. It is well-
Finally, in the case of 4Fc-DMAP, a reversible oxidation wave is
observed at E1/2 = 0.07 V vs Fc0/+ (Figure S58) assignable to the
Fe(II)/Fe(III) redox couple of the ferrocenyl moiety, similar in
feature to that observed for free ferrocene. As such, the CV of 4Fc-
DMAP shows an electrochemically rich system with promising
ligand and metal based redox chemistry.
Electronic Absorption and Fluorescence Spectroscopy
Figure 5. Emission spectra of 2mes (orange), 3mes (grey),and 4mes-DMAP
(black), as 10 μM solutions in C6H6 at room temperature after excitation at
453, 432, and 472 nm, respectively. The emission wavelengths are 505,
507, and 504 nm for 2mes, 3mes,and 4mes-DMAP, respectively.
Figure 4. Room temperature UV/vis absorption spectra for 2mes (benzene,
25.1 μM, C6H6) (orange), 3mes (9.66 μM, C6H6) (grey), and 4mesDMAP (12.9
μM, C6H6) (black).
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established that aryldipyrrinates with mesityl groups in the meso Xe Arc lamp. For the fluorescence measurements, the excitation
View Article Online
wavelength was set to the absorption maxDimOaI: 1o0f.1e0a3c9h/Cc7oDmT0p0o1u5n0Ad
determined from their UV-vis absorption spectra. All analyte
concentrations were set to 10 μM in benzene. Elemental Analyses
were performed by Robertson Microlit Laboratories, Inc. and
Midwest Microlabs, LLC.
position display enhanced fluorescence due to torsional
constriction, increasing rigidity and thus minimizing competitive
non-radiative decay pathways.1, 2, 25, 44 The spectra in Figure 5 show
a modest Stokes shift that ranges from ca. 30 – 70 nm, in line with
that found for other metalated dipyrrinates.2 Notably, while 2mes
and 3mes exhibit similar emission intensities, the relative
fluorescence of 4mes-DMAP is nearly an order of magnitude greater
in comparison (Figure 5), indicating a marked interaction between
uranyl and the dipyrrinate ligands.
Cyclic Voltammetry.
Cyclic voltammetric measurements were performed using a CH
Instruments 600e potentiostat with a PC unit controlled with CHI
software (version 13.12). Experiments were performed in a
glovebox under an inert N2 atmosphere using platinum disks (2 mm
diameter) embedded in Kel-F thermoplastic as the counter and
working electrodes while the reference electrode consisted of a
platinum wire. Solutions utilized in the electrochemical studies
were approximately 1 mM in complex with [NBu4][PF6] (0.1M, THF)
as supporting electrolyte. All potentials are reported versus the
[Cp2Fe]0/+ couple, referenced as internal standard.
Conclusion
Dipyrrins are popular and versatile chromophores that have
received much attention for their use in BODIPY dyes and
luminescent metal complexes; however, their chemistry with f-
elements has been glaringly underexplored. This may be due to
synthetic challenges as attempts to use standard dipyrrin
metalation procedures failed in our case to generate uranyl
dipyrrinates. Gratifyingly, we have shown that the uranyl
bis(dipyrrinates) UO2[RC(C4H2N)2]2(DMAP) (4-DMAP) can be readily
accessed through an anhydrous, salt metathesis route, opening a
new pathway to lanthanide and actinide dipyrrinate chemistry. The
new compounds were fully characterized and shown to exhibit a
number of salient structural and spectral features. For instance, the
emission spectrum of 4mes-DMAP demonstrates that dipyrrin
fluorescence can be enhanced upon complexation to uranyl.
Efforts to further expand the dipyrrinate chemistry of uranium and
other f-elements are currently underway in our laboratory.
X-ray Crystallography.
Data for 4tolyl-THF·3THF, 4anis-THF·THF·C5H12, 4Fc-THF·C5H12, and
4mes-DMAP·THF·0.5C5H12 were collected on a Bruker 3-axis platform
diffractometer equipped with an APEX I CCD detector using a
graphite monochromator with a Mo Kα X-ray source (λ = 0.71073
Å). The crystals were mounted on a glass fiber or on a Mitigen
Kapton loop, coated in NVH oil, and maintained at 100(2) K under a
flow of nitrogen gas during data collection. A hemisphere of data
was collected using ω and φ scans with 0.5° frame widths. Data
collection and cell parameter determinations were conducted using
the SMART program.47 Integration of the data and final cell
parameter refinement were performed using SAINT48 software with
data absorption correction implemented through SADABS.49
Structure solution, refinement, graphics, and creation of publication
materials were performed using SHELXTL50 or the Olex2
crystallographic package.51 Structures were solved using direct,
charge flipping, or structure expansion methods and difference
Experimental
Fourier techniques. The co-crystallized pentane molecules in 4anis
-
General Considerations.
THF·THF·C5H12, 4Fc-THF·C5H12, and 4mes-DMAP·THF·0.5C5H12 exhibit
positional disorder which was addressed by modeling the
disordered atoms over several orientations. All hydrogen atom
positions were idealized and treated as riding on the parent atom.
A summary of relevant crystallographic data is presented in Table
S1.
All air and moisture-sensitive operations were performed in a M.
Braun dry box under an atmosphere of purified nitrogen or using
high vacuum standard Schlenk techniques. Benzene, toluene,
hexanes, pentane, toluene, THF, Et2O, and dimethoxyethane (DME)
were dried using a Pure Process Technology Solvent Purification
System and subsequently stored under a dinitrogen atmosphere
over activated 4 Å molecular sieves. All deuterated solvents were
purchased from Cambridge Isotope Laboratories Inc. and were
degassed by three freeze−pump−thaw cycles and dried over
activated 4 Å molecular sieves for 24 h prior to use. Celite and 4 Å
molecular sieves were heated to 200 °C for at least 24 h and then
cooled under vacuum. Ferrocenecarboxaldehyde and UO2Cl2(THF)3
General procedure for the chromatography-free synthesis of α,β-
unsubstituted aryldipyrromethanes (1)
The following is a modified procedure adapted from published
methods.23 In a 500 mL round bottom flask equipped with a large
magnetic stir bar, deionized water (250 mL) was degassed using
three freeze-pump-thaw cycles. To the water was added HCl(aq)
(3.7 mL, 12 M), to acidify the solution, under an atmosphere of
dinitrogen. Freshly distilled pyrrole (3 equiv) was added and the
solution was vigorously stirred. To this, 1 equiv of arylaldehyde was
added very slowly dropwise at an approximate rate of 0.5 mL/h.
Upon immediate addition of the arylaldehyde, the solution turns
opaque. The subsequent drop was added only after precipitation of
a fine white to pale yellow solid accompanied by a decrease in
turbidity. It is important to note that vigorous stirring and slow
addition of aldehyde are critical for ease of workup and increased
yields and purity. Upon complete addition of the arylaldehyde, a
saturated aqueous solution of NaHCO3 (200 mL) was added. The
supernatant was then decanted and the precipitate was collected
46
were prepared according to literature procedures.45, All other
reagents were purchased from commercial sources and used as
received. NMR spectra were recorded on a JEOL ECA 600 MHz or a
Bruker AVANCE III 400 MHz spectrometer. Resonance assignments
in the 13C NMR spectra were based upon 1H – 13C HMQCGP 2D
correlation spectra. 1H NMR and 13C NMR spectra are referenced to
1
SiMe4 using the residual H solvent peaks as internal standards or
the characteristic 13C resonances of the solvent. IR data were
collected using a Thermo Scientific Nicolet iS5 spectrometer. UV-vis
spectra were recorded on a Shimadzu UV-3101PC UV-vis/NIR
scanning spectrophotometer. All analyte concentrations were set to
10 μM in benzene or as otherwise noted. Fluorescence spectra
were recorded using an Olis DM45 spectrofluorimeter with a 150 W
6 | J. Name., 2012, 00, 1-3
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on a Büchner funnel to give a pale yellow to peach coloured solid. 2tol: 0.55 g (2.3 mmol) of 1tol was treated as described with 0.58 g
The solid was washed copiously with deionized water (5 × 30 mL) (2.6 mmol) of DDQ. The crude product is an oilVietwhaAtrticcleaOnnlibnee
DOI: 10.1039/C7DT00150A
and dried overnight under vacuum. The solid was then sublimated recrystallized from storage of a concentrated hexanes solution at
under reduced pressure at 125 °C to yield white crystals. -10 °C to give red-amber crystals. Yield: 0.50 g (90%).
Alternatively, storage of a concentrated toluene solution of the 2anis: 1.4 g (5.6 mmol) of 1anis was treated with 1.4 g (6.1 mmol) of
aryldipyrromethanes at -10 °C gives the product as a white coloured DDQ as described in the general synthesis with minor modifications.
precipitate. In our hands, the aryldipyrromethanes were observed It was found that foregoing aqueous workup dramatically increases
to be indefinitely stable as solids under ambient conditions. The yield. After removal of triethylamine and toluene, the reaction
products 1tol, 1anis, 1mes, and 1Fc were characterized by 1H and mixture was redissolved in neat toluene (10 mL). This solution was
13C{1H} NMR spectroscopy and their identity confirmed by added dropwise to a stirring solution of hexanes (75 mL), causing
comparison to reported values.21, 52 Note: The dipyrromethanes 1 the formation of a grey precipitate. The precipitate was removed
are highly acid sensitive
by filtration and the solvent evaporated by vacuum to give 2anis as
an oil. The storage of a concentrated hexanes solution at -10°C
1tol: 4.16 mL of pyrrole (4.02 g, 0.06 mol) was treated as described gives the product as pink-orange prismatic needles. Yield: 0.97 g
with 2.36 mL of 4-methylbenzaldehyde (2.40g, 0.02 mol). The (70%).
material was purified by sublimation. Yield: 1.8 g (51%).
2mes: 2.15 g (8.10 mmol) of 1mes was treated as described with 2.0 g
1anis
:
3.70 mL of pyrrole (3.31 g, 49.3mmol) was treated as (8.9 mmol) of DDQ. The crude product is a grey-green solid that can
described with 2 mL of 4-anisaldehyde (2.24 g, 16.4 mmol). The be recrystallized from storage of a concentrated hexanes solution at
peach coloured product was recrystallized from toluene. Yield: 2.1g -10 °C to give dark green crystals. Yield: 1.95 g (91%).
(51%).
2Fc: 1.23 g (3.70 mmol) of 1Fc was treated as described in the
1mes: 2.81 mL of pyrrole (2.72 g, 40.5 mmol) was treated with 2.0 general synthesis with 0.93g (4.1 mmol) of DDQ with minor
mL of mesitaldehyde (2.0 g, 13.5 mmol). The peach coloured modifications. It was found that foregoing aqueous workup
product was recrystallized from toluene. Yield: 2.06 g (60%).
dramatically increases yield. The crude product is a dark solid with a
1Fc: 2.4 mL of pyrrole (2.32 g, 34.6 mmol) was treated with 2.46 g of green luster. Storage of a concentrated hexanes solution at -35° C
ferrocenecarboxaldehyde (11.5 mmol) dissolved in THF (0.5 mL). results in the formation of a lustrous green microcrystalline solid.
1
Upon addition, the solution turns cloudy and red which then fades Yield: 0.86 g (70%). H NMR (25 °C, 400 MHz, C6D6): δ 3.87 (s, 5H,
upon formation of a fine yellow powder. Dissolution in toluene C5H5 Cp-ring), 4.10 (t, 2H, JHH = 1.9 Hz, C-H Cpdipy ring), 4.63 (t, 2H,
afforded an amber solution, and storage at -10°C produced a JHH = 1.9 Hz, C-H Cpdipy ring) 6.35 (dd, 2H, JHH = 4.2, 4JHH = 1.4 Hz, γ-
yellow-orange microcrystalline powder. Yield: 1.2 g (33%).
pyrrole C-H), 7.32 (br m, 2H, α-pyrrole C-H), 7.64 (dd, 2H, JHH = 4.2,
4JHH = 1.4 Hz, β-pyrrole C-H), 13.94 (s, 1H, pyrrole N-H). 13C{1H}NMR
General procedure for the chromatography-free synthesis of α,β- (25 °C, 100 MHz, C6D6): δ 69.9 (Cp), 71.2 (Cp ring), 74.0 (Cp ring),
unsubstituted aryldipyrromethenes (2) 83.0 (Cp ring), 116.9 (γ-pyrrole C-H), 128.6 (β-pyrrole C-H), 141.4,
The following is a modified procedure adapted from published 141.8 (α-pyrrole C-H), 143.9.
25
methods.10,
aryldipyrromethane 1 was dissolved in toluene with vigorous General
stirring. Approximately 50 mL of toluene was used per gram of 1 to aryldipyrromethenates (3)
In a 250 mL round bottom flask, 1 equiv of
procedure
for
the
synthesis
of
sodium
completely dissolve the material. A solution of 2,3-dichloro-5,6- In a 100 mL round bottom flask, 1 equiv of aryldipyrromethene 2
dicyano-1,4-benzoquinone (DDQ) (1.1 equiv) in toluene (50 mL) was was dissolved in hexanes (50 mL). In a separate vial, 0.95
added all at once to the aryldipyrromethane. Upon addition, a equivalents of sodium hexamethyldisilazide (NaHMDS) was
brown precipitate is formed. The progress of the reaction was dissolved in toluene (9 mL). The NaHDMS solution was added slowly
monitored by TLC (silica, Et2OAc:Hexanes, 25:75), showing full dropwise to the vigorously stirring solution of 2, resulting in the
consumption of the dipyrromethane after 3 h. Excess triethylamine formation of a fine, insoluble solid. After 1 h, the solid was collected
(5 equiv) was added to the stirring solution to dissolve the brown on a medium porosity glass frit, washed with hexanes (20 mL), and
precipitate. After 30 minutes, the volatiles were removed in vacuo. dried in vacuo to afford pure, orange powders.
The product mixture was dissolved in CH2Cl2, and the solution was
washed with saturated NaHCO3 solution (1 × 50 mL), brine (1 × 50 3tol: 1.58 g (6.7 mmol) of 2tol was treated as described with 1.18 g
mL), and deionized water (1 × 50 mL). The CH2Cl2 fraction was (6.4 mmol) of NaHMDS. The product can be recrystallized from a
dried over anhydrous MgSO4 and the solution was concentrated concentrated DME solution layered with hexanes stored at -35 °C to
under reduced pressure, leaving the minimum amount of solvent generate orange crystals. The product crystallizes as the DME
1
necessary to keep the product dissolved. The brown solution was solvate 3tol-0.3DME. Yield: 1.55 g (80%). H NMR (25 °C, 400 MHz,
added dropwise to a stirring solution of hexanes (75 mL) which C6D6/py-d5): δ 2.17 (s, 3H, tolyl Me), 3.07 (s, DME), 3.24 (s, DME),
4
caused the precipitation of a fine, grey-brown precipitate. The solid 6.64 (dd, 2H, JHH = 3.7 Hz, JHH = 0.9 Hz, γ-pyrrole C-H), 6.98 (d, 2H,
4
was removed via filtration through Celite supported on a medium JHH = 8.1 Hz, tolyl C-H), 7.01 (dd, 2H, JHH = 3.9 Hz, JHH = 1.0 Hz, β-
porosity glass frit. Concentration of the filtrate and storage of the pyrrole C-H), 7.44 (d, 2H, JHH = 7.9 Hz, tolyl C-H), 8.00 (br, 2H, α-
solution at -10 °C for 24 h produces the dipyrromethene as a pure pyrrole C-H). 13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ 21.3
material. The α,β-unsubstituted aryldipyrromethenes were stored (tolyl Me), 58.7 (DME), 71.9 (DME), 116.8 (γ-pyrrole C-H), 127.5
under ambient conditions and observed to be unchanged after (tolyl), 131.8 (tolyl), 132.5 (β-pyrroleC-H), 137.2, 140.5, 144.4,
several months.
The products 2tol 2anis and 2mes were 150.2, 151.3 (α-pyrrole C-H). Anal. Calcd. for C16H13N2Na-0.3DME: C,
, ,
characterized by 1H and 13C{1H} NMR spectroscopy and their 72.70; H, 5.76; N, 9.78. Found: C, 72.17; H, 5.85; N, 9.62.
identity confirmed by comparison to reported values.10, 23
3anis: 0.94 g (3.7 mmol) of 2anis was treated as described with 0.65 g
(3.5 mmol) of NaHMDS. The crude pink-orange product can be
recrystallized from a concentrated DME solution layered with
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hexanes. Storage of this solution at -35°C yields orange crystals as 4mes-THF: 1H NMR (25 °C, 400 MHz, py-d5): δ 1.62 (THF), 2.25 (s,
the solvated product 3anis-0.75DME. Yield: 0.92 g (77%). H NMR 12H, o-Me), 2.36 (s, 6H, p-Me), 3.66 (THF), 6D.5O3I:(1s0,.410H3V)9,ie/6wC.97ADr7tiTc(l0de0,O14n5Hl0in)Ae,
1
(25 °C, 400 MHz, C6D6/py-d5): δ 3.08 (s, 3H, p-OMe), 3.27 (s, DME), 7.00 (s, 4H, mesityl C-H), 7.76 (br s, 4H).
4
3.36 (s, DME), 6.63 (dd, 2H, JHH = 3.9, JHH = 1.0 Hz, γ-pyrrole C-H), 4Fc-THF: 1H NMR (25 °C, 400 MHz, py-d5): δ 1.42 (THF), 3.56 (THF),
4
6.76 (d, 2H, JHH = 8.6 Hz, anisole C-H), 7.02 (dd, JHH = 3.9, JHH = 1.1 3.96 (s, 10H, C5H5 Cp ring), 4.21 (s, 4H, C-H Cpdipy ring), 4.88 (s, 4H,
Hz, β-pyrrole C-H), 7.45 (d, JHH = 8.7 Hz, , anisole C-H), 7.98 (br m, C-H Cpdipy ring), 6.43 (s, 4H), 7.34 (s, 4H), 7.73 (s, 4H).
2H, α-pyrrole C-H). 13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ
54.9 (p-OMe), 58.7 (DME), 72.0 (DME), 112.4 (anisole), 116.8 (γ- General
procedure
for
the
synthesis
of
uranyl
pyrrole C-H), 132.2 (β-pyrrole C-H), 133.11 (anisole), 135.69, 144.60, bis(aryldipyrromethenates) (4-DMAP)
150.80 (α-pyrrole C-H), 160.07, one carbon resonance not In a 20 mL scintillation vial, UO2Cl2(THF)3 was suspended in Et2O (3
observed. Anal. Calcd. for C16H13N2ONa-0.75DME: C, 67.14; H, 6.09; mL) with 5 equiv of 4-dimethylaminopyridine (DMAP). After 10 min,
N, 8.24. Found: C, 66.96; H, 5.82; N, 8.75.
the yellow suspension transformed into a red-orange mixture. The
3mes 1.0 g (3.8 mmol) of 2mes was treated as described in the Et2O was decanted and the powder resuspended in benzene (6 mL),
:
general synthesis with 0.66 g (3.6 mmol) of NaHMDS. The yellow- and this was added to a stirring suspension of 3 (2 equiv) in
lime product can be recrystallized from a concentrated Et2O benzene (10 mL). The reaction colour turned deep red and it was
solution at room temperature. Storage of this solution at -35 °C left to stir for 2 h. The product mixture was then filtered through
affords a second crop of crystals. Yield: 0.78 g (76%). 1H NMR (25 °C, Celite supported on a medium porosity frit to give a dark red
400 MHz, C6D6/py-d5): δ 2.11 (s, 3H, p-Me), 2.24 (s, 6H, o-Me), 6.55 filtrate. The Celite filter cake was triturated with benzene to
4
(dd, 2H, JHH = 3.9, JHH = 0.9 Hz, γ-pyrrole C-H), 6.85 (s, 2H, mesityl dissolve any remaining product. The solvent was removed under
4
C-H), 6.89 (dd, 2H, JHH = 3.9, JHH = 1.1 Hz, β-pyrrole C-H), 8.06 (br vacuum to give a dichroic, green-red microcrystalline solid. The
m, 2H, α-pyrrole C-H). 13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ solid was then washed with cold (-30 °C) Et2O on a medium porosity
20.3 (o-Me), 21.2 (p-Me), 117.2 (γ-pyrrole C-H), 131.0 (β-pyrrole C- glass frit to remove the excess DMAP. X-ray quality single crystals
H), 136.2, 136.9, 139.5, 143.4, 149.0, 151.1 (α-pyrrole C-H), two were obtained by slow diffusion of pentane into a saturated THF
carbon resonances not observed. Anal. Calcd. for C18H17N2Na: C, solution of 4-DMAP stored at -30 °C.
76.04; H, 6.03; N, 9.85. Found: C, 74.04; H, 6.30; N, 9.39.
Combustion analyses of 3mes consistently tested low in carbon.
4tol-DMAP: 0.255 g (0.457 mmol) of UO2Cl2(THF)3 was treated as
3Fc: 0.45 g (1.4 mmol) of 2Fc was treated with 0.24 g (1.3 mmol) of described with 0.279 g (2.28 mmol) of DMAP and 0.400 g (0.917
NaHMDS. The brown product can be recrystallized from a mmol) of 3tol. Yield: 0.40 g, (88%). H NMR (25 °C, 400 MHz, C6D6
1
concentrated THF solution layered wtih hexanes. Storage of this /py-d5): δ 2.13 (s, 6H, tolyl Me), 2.21 (s, 6H, DMAP), 6.08 (d, 2H, JHH
solution at -35 °C affords dark, brown-red crystals. Yield: 0.41 g = 6.4 Hz, DMAP), 6.45 (dd, 4H, JHH = 4.1, γ-pyrrole C-H), 6.95 (d, 4H,
(90%). 1H NMR (25 °C, 400 MHz, C6D6/py-d5): δ 3.96 (s, 5H, C5H5 Cp- JHH = 7.8 Hz, tolyl C-H), 7.10 (d, 4H, JHH = 4.8 Hz, β-pyrrole C-H), 7.48
ring), 4.18 (t, 2H JHH = 1.9 Hz, C-H Cpdipy ring), 4.94 (t, 2H, JHH = 1.9 (d, 4H, JHH = 8.0 Hz, tolyl C-H), 7.95 (br s, 4H, α-pyrrole C-H), 8.73 (br
Hz, C-H Cpdipy ring), 6.71 (dd, 2H, JHH = 3.9, 4JHH = 1.0 Hz, γ-pyrrole C- s, 2H, DMAP). 13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ 21.2
H), 7.87 (br m, 2H, α-pyrrole C-H), 8.09 (dd, 2H, JHH = 3.8, 4JHH = 1.0 (tolyl Me), 38.3 (DMAP), 107.2 (DMAP), 116.8 (γ-pyrrole C-H), 127.7
Hz, β-pyrrole C-H). 13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ 69.5 (tolyl), 131.3 (tolyl]), 132.7, 133.8 (β-pyrrole C-H), 137.5, 138.1,
(Cp ring), 70.9 (Cp ring), 76.1 (Cp ring), 86.2, 116.4 (γ-pyrrole C-H), 144.5, 151.3, 152.8 (α-pyrrole C-H), one carbon resonance not
130.1 (β-pyrrole C-H) , 144.1, 149.0 (α-pyrrole C-H), 152.1. Anal. observed. IR (KBr Pellet, cm-1): 531 (w), 578 (w), 283 (w), 620 (w),
Calcd. for C19H15FeN2Na: C, 65.17; H, 4.32 ; N, 8.00. Found: C, 65.03; 647 (w), 653 (w), 713 (w), 730 (m), 770 (m), 797 (m), 848 (w), 873
H, 4.73, N, 7.66.
(w), 883 (m), 897 (w), 920 (m), 937 (w), 963 (m, νasym U=O), 989 (m),
1007 (m), 1029 (s), 1060 (w), 1069 (w), 1095 (w), 1113 (w), 1166
uranyl (m), 1183 (w), 1197 (m), 1227 (m), 1264 (w), 1328 (m), 1373 (s),
1399 (m), 1436 (w), 1537 (s), 1615 (s), 2328 (w), 2365 (w), 2871 (w),
General
procedure
for
the
synthesis
of
bis(aryldipyrromethenates) (4-THF)
In a 20 mL scintillation vial, UO2Cl2(THF)3 was dissolved in THF (3 2923 (w), 2965 (w), 3029 (w), 3103 (w). Anal. Calcd. for
mL). The clear yellow solution was added dropwise to a stirring C32H26N4O2U-DMAP: C, 54.54; H, 4.23; N, 9.79. Anal. Calcd. for
solution of 3 (2 equiv) in THF (3 mL). The reaction colour turned C32H26N4O2U-1.2DMAP: C, 53.98; H, 4.35; N, 10.15. Found: C, 53.61;
deep red and was left to stir for 2 h. The product mixture was then H, 4.13; N, 9.51.
filtered through Celite supported on a medium porosity glass frit to 4anis-DMAP: 0.282 g (0.506 mmol) of UO2Cl2(THF)3 was treated as
give a dark red filtrate. The solvent was removed under vacuum to described with 0.310 g (2.54 mmol) of DMAP and 0.368 g (1 mmol)
give 4-THF as a dichroic, green-red microcrystalline solid. The solid of 3anis. Yield: 0.400 g (88%). 1H NMR (25 °C, 400 MHz, C6D6/py-d5):
was washed with hexanes (3 × 3 mL) and dried under reduced δ 2.20 (s, 6H, DMAP), 3.24 (s, 6H, p-OMe), 6.09 (d, 2H, JHH = 6.1 Hz,
pressure. Crystals of 4-THF were obtained by slow diffusion of DMAP), 6.49 (d, 4H, JHH = 3.2 Hz, γ-pyrrole C-H), 6.75 (d, 4H, JHH
=
pentane into a saturated THF:DME (2:1) solution of 4-THF stored at 8.4 Hz, anisole C-H), 7.14 (d, 4H, JHH = 3.7 Hz, β-pyrrole C-H), 7.50 (d,
-30 °C. The instability of these compounds in solution, attributed to 4H, JHH = 8.4 Hz, anisole C-H), 8.00 (br s, 4H, α-pyrrole C-H), 8.79 (br
the lability of the coordinated THF, precluded full characterization.
s, 2H, DMAP). 13C{1H} NMR (25 °C, 100 MHz): δ 38.3 (DMAP), 54.9
4tol-THF: 1H NMR (25 °C, 400 MHz, C6D6/THF-d8): δ 1.43 (THF), 2.12 (p-OMe), 107.3 (DMAP), 112.9 (anisole), 116.9 (γ-pyrrole C-H),
(s, 6H, Me), 3.68 (THF) 6.43 (br s, 4H), 6.97 (m, 8H, tolyl C-H), 7.40 132.8 (anisole), 133.8 (β-pyrrole C-H), 144.53, 150.22, 151.12
(br s, 4H), 8.05 (br s, 4H).
(DMAP), 152.71 (α-pyrrole C-H), 160.36, two carbon resonances
1
4anis-THF: H NMR (25 °C, 400 MHz, py-d5): δ 1.75 (THF), 3.80 (p- not observed. IR (KBr Pellet, cm-1): 421 (w), 463 (w), 470 (w), 532
OMe, overlapped with THF resonance), 3.83 (THF), 6.22 (s, 4H), 7.15 (w), 583 (w), 616 (w), 645 (w), 667 (w), 716 (w), 734 (w), 757 (w),
(d, 4H, anisole C-H), 7.34 (s, 4H), 7.78 (d, 4H, anisole C-H), 8.12 (s, 774 (w), 808 (m), 837 (w), 874 (w), 882 (w), 897 (w), 916 (m), 935
4H).
(w), 963 (w, νasym U=O), 988 (m), 1007 (s), 1031 (s), 1060 (w), 1095
(m), 1101 (w), 1165 (m), 1169 (m), 1199 (w), 1247 (m), 1291 (w),
8 | J. Name., 2012, 00, 1-3
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1327 (m), 1354 (w), 1374 (s), 1396 (m), 1440 (w), 1458 (w), 1535 (w). Anal. Calcd. for C45H40Fe2N6O2U: C, 51.64; H, 3.85; N, 8.03.
View Article Online
(s), 1563 (m), 1605 (s), 1614 (s), 2336 (w), 2355 (w), 2833 (w), 2849 Found: C, 49.07; H, 4.03; N, 7.88. Combustion analyses of 4FcDMAP
DOI: 10.1039/C7DT00150A
(w), 2863 (w), 2921 (w), 2957 (w), 3028 (w), 3057 (w), 3093 (w), consistently tested low in carbon.
3421 (w) Anal. Calcd. for C39H36N6O4U-DMAP: C, 52.58; H, 4.08; N,
9.44. Found: C, 51.99; H, 4.20; N, 8.86.
Acknowledgements
4mes-DMAP: 0.291 g (0.522 mmol) of UO2Cl2(THF)3 was treated as
We are grateful to the University of Texas at El Paso, NSF PREM
described with 0.319 g (2.6 mmol) of DMAP and 0.293 g (1.04
Program (DMR-1205302), and the UT STARS award for support of
this work.
mmol) of 3mes. Yield: 0.406 g (85%). 1H NMR (25 °C, 400 MHz,
C6D6/py-d5): δ 2.19 (s, 6H, p-Me), 2.22 (s, 6H, DMAP), 2.28 (s, 12H,
o-Me), 6.04 (d, 2H, JHH = 5.7 Hz, DMAP), 6.41 (d, 4H, JHH = 4.9 Hz, γ-
pyrrole C-H), 6.84 (s, 4H, mesityl C-H), 6.98 (d, 4H, JHH = 4.7 Hz, β-
Notes and references
pyrrole C-H), 7.83 (br s, 4H, α-pyrrole C-H), 8.69(br s, 2H, DMAP).
13C{1H} NMR (25 °C, 100 MHz, C6D6/py-d5): δ 20.2 (o-Me), 21.2 (p-
Me), 38.3 (DMAP), 107.2 (DMAP), 117.1 (γ-pyrrole C-H), 128.2
(mesityl), 128.6, 131.9 (β-pyrrole C-H), 136.8, 137.1, 143.6, 150.4,
152.6 (α-pyrrole C-H), two carbon resonances not observed. IR (KBr
Pellet, cm-1): 487 (w), 536 (w), 566 (w), 591 (w), 598 (w), 606 (w),
644 (w), 668 (w), 679 (w), 723 (m), 736 (m), 758 (w), 777 (m), 817
(m), 837 (m), 863 (w), 882 (w), 917 (m), 947 (w), 963 (m, νasym
U=O), 987 (m), 1006 (m), 1030 (s), 1063 (w), 1093 (w), 1115 (w),
1165 (m), 1201 (w), 1222 (m), 1234 (m), 1272 (w), 1326 (m),
1337 (w), 1372 (s), 1397 (m), 1439 (w), 1476 (w), 1540 (s), 1567
(w), 1616 (s), 2339 (w), 2357 (w), 2853 (w), 2913 (w), 2943 (w),
3024 (w), 3059 (w), 3084 (w), 3100 (w). Anal. Calcd. for
C43H44N6O2U: C, 56.45; H, 4.85; N, 9.19. Found: C, 56.34; H, 4.92; N,
8.91.
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4FcDMAP: 0.250 g (0.489 mmol) of UO2Cl2(THF)3 was treated as
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mmol) of 3Fc. Yield: 0.235 g (50%). 1H NMR (-30 °C, 600 MHz,
C7D8/py-d5) δ 2.05 (s, minor isomer), 2.12 (s, minor isomer DMAP),
2.23 (br s, DMAP), 3.84 (s, 5H, minor isomer C5H5 Cp ring), 3.98 (s,
5H, minor isomer C5H5 Cp ring), 4.00 (s, 10H, major isomer C5H5 Cp
ring) , 4.11 (s, 2H, minor isomer C-H Cpdipy ring), 4.15 (s, 2H, minor
isomer C-H Cpdipy ring), 4.18 (s, 4H, major isomer C-H Cpdipy ring),
4.58 (s, 2H, minor isomer C-H Cpdipy ring), 4.78 (s, 2H, minor isomer
C-H Cpdipy ring), 4.85 (s, 4H, major isomer C-H Cpdipy ring), 5.88 (d,
2H, minor isomer JHH = 6.7 Hz, DMAP), 6.03 (br s, DMAP), 6.36,
6.48, 6.66, 7.30 (s, minor isomer), 7.60 (s, minor isomer), 7.79 (s,
minor isomer), 7.87 (s, minor isomer), 7.96 (s, major isomer), 8.70
(minor isomer DMAP).1H NMR (30 °C, 600 MHz, C7D8/py-d5): δ 2.12
(s, minor isomer DMAP), 2.28 (br s, DMAP), 3.88 (s, 5H, minor
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3.97(s, 10H, major isomer C5H5 Cp ring), 4.16 (s, 2H, minor isomer C-
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major isomer C-H Cpdipy ring), 4.61 (s, 2H, minor isomer C-H Cpdipy
ring), 4.80 (s, 2H, minor isomer C-H Cpdipy ring), 4.88 (s, 4H, major
isomer C-H Cpdipy ring), 6.06(s, DMAP), 6.33, 6.35, 6.48, 6.73, 7.06,
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major isomer C5H5 Cp ring), 4.26(s, 4H, major isomer C-H Cpdipy
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(s, minor isomer) , 6.41 (s, 4H, major isomer (γ-pyrrole C-H)), 7.10
(s, 4H, major isomer (β -pyrrole C-H)), 7.74(s, minor isomer), 7.75 (s,
4H, major isomer (α -pyrrole C-H)). IR (KBr Pellet, cm-1): 413 (w), 425
(w), 481 (m), 499 (m), 529 (w), 571 (w), 597 (m), 610 (m), 655 (m),
656 (m), 664 (w), 677 (m), 730 (m), 769 (m), 806 (m), 831 (m), 883
(m), 914 (m), 950 (w), 963 (m, νasym U=O), 958 (m), 1004 (s), 1030
(s), 1038 (s), 1047 (m), 1087 (w), 1096 (w), 1105 (w), 1127 (w), 1159
(m), 1200 (m), 1227 (m), 1267 (w), 1311 (m), 1321 (m), 1372 (s),
1392 (s), 1417 (w), 1442 (w), 1459 (w), 1520 (s), 1613 (s) 2331 (w),
2357 (w), 2553 (w), 2852 (w), 2911 (w), 3023 (w), 3083 (w), 3095
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10 | J. Name., 2012, 00, 1-3
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View Article Online
DOI: 10.1039/C7DT00150A
Using an improved, chromatography-free dipyrrin synthesis, a new family of actinide dipyrrinate
complexes has been synthesized.