New isoindoline aminoxyl based polyradicals for spin probes and molecular magnetic materials

Article abstract of DOI:10.1039/b109485h

The synthesis of a range of aminoxyl polyradicals based on the isoindoline aminoxyl moiety is described. FriedelCrafts alkylation reactions between 1,1,3,3-tetramethylisoindolin-2-yloxyl (1) and suitable haloalkanes were used to prepare three new biradicals and one new triradical. Standard methods ¹¹ for the synthesis of nitronyl aminoxyls and iminyl aminoxyls were employed to prepare two novel tridentate biradical derivatives of 1. Also a novel isoindolinelike fused biradical was prepared. The room temperature solution EPR spectra of all radicals are reported and reveal a wide range of exchange coupling constants. The crystal structure determinations of two of these compounds, 1,1-bis(1',1',3',3'-tetramethylisoindolin-2'-yloxyl-5'-yl)ethane (3) and 1,2,3,5,6,-hexahydro-1,1,3,3,5,5,7,7octamethylbenzo[1,2-c:4,5-c']dipyrrol-2,6-di yloxyl (15), are reported.

Full text of DOI:10.1039/b109485h

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New isoindoline aminoxyl based polyradicals for spin probes and
molecular magnetic materials
Craig D. Smith, Raymond C. Bott, Steven E. Bottle,* Aaron S. Micallef and Graham Smith
2
CIDC, School of Physical and Chemical Sciences, Queensland University of Technology,
GPO Box 2434, Brisbane, Q4001, Australia
Received (in Cambridge, UK) 17th October 2001, Accepted 7th January 2002
First published as an Advance Article on the web 31st January 2002
The synthesis of a range of aminoxyl polyradicals based on the isoindoline aminoxyl moiety is described. Friedel–
Crafts alkylation reactions between 1,1,3,3-tetramethylisoindolin-2-yloxyl (1) and suitable haloalkanes were used to
prepare three new biradicals and one new triradical. Standard methods11 for the synthesis of nitronyl aminoxyls and
iminyl aminoxyls were employed to prepare two novel tridentate biradical derivatives of 1. Also a novel isoindoline-
like fused biradical was prepared. The room temperature solution EPR spectra of all radicals are reported and reveal
a wide range of exchange coupling constants. The crystal structure determinations of two of these compounds,
1,1-bis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)ethane (3) and 1,2,3,5,6,7-hexahydro-1,1,3,3,5,5,7,7-
octamethylbenzo[1,2-c:4,5-cЈ]dipyrrol-2,6-diyloxyl (15), are reported.
1). This type of Friedel–Crafts alkylation is known, how-
ever yields are typically higher. In this case low yields can be
attributed to acid mediated oxidation of the aminoxyl 1 to the
corresponding oxoammonium ion 6, evident by the deep red
colouration of the reaction solution. The aromatic ring of 6
would be less reactive towards electrophilic substitution due to
the influence of the cationic oxoammonium group.
Introduction
1,1,3,3-Tetramethylisoindolin-2-yloxyl (1) aminoxyls exhibit
superior EPR linewidths as well as excellent thermal and chem-
ical stability compared to commercially available aminoxyls.1
Their stability, relative ease of synthesis and functionalis-
ation make them ideal candidates for use in many biological,
chemical and materials science applications.
The solution EPR spectrum of 2 in toluene-d8 (Fig. 1)
A broad range of aminoxyls has received attention in the
exhibits five resolved resonances characteristic of an aminoxyl
biradical system where |J0| ≈ aN.10 In systems where |J0| ≈ aN, |J0|
field of molecular magnetism with encouraging results arising
from many structural variations of the aminoxyl radical.
can be accurately determined by spectral simulation due to the
Isoindoline aminoxyls have provided the basis for much
sensitivity of the spectrum to changes in J0. The ability to
accurately determine J0 presents possibilities for spin labelling
research in the area of radical trapping2–5 and spin probes,6–8
however their application to the field of molecular magnetism
applications where changes in J0 may relate to variations in
has been largely overlooked. The use of aminoxyl polyradicals
certain environmental conditions. An investigation of the vari-
as coupling units for magnetic metal ions has received much
able temperature EPR behaviour of biradical 2 with analysis of
J0 values that support this will appear in a later publication.
attention and represents a promising approach for the prepar-
ation of functional molecular magnetic materials.9
We have successfully synthesised a range of isoindoline
aminoxyl polyradicals which may find use in a range of fields
applicable to aminoxyl radicals. Of primary interest is the field
of molecular magnetism, although the polyradicals prepared
1,1-Bis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)ethane
(3)
The Friedel–Crafts alkylation reaction between 1 and 1,2-
dichloroethane affords the 1,1-substituted dimer in 15% yield
may also prove to be useful as spin probes. Recent spin probe
(45% based on consumed starting material). The observed
studies have mainly focused on monoradicals. However, the
substitution is expected to arise from rapid rearrangement of
advantages of using biradicals as spin probes have previously
been outlined.10 Notably the presence of exchange interactions
the initial carbocation adduct to give the more stable benzylic
carbocation.
contributing to the EPR spectrum of biradicals may represent
Crystals suitable for X-ray crystallography were obtained by
another method for obtaining environmental information from
slow evaporation from a cyclohexane–dichloromethane (1 : 1)
spin probes.
solution of 3.
The solution EPR spectrum of 3 in toluene-d8 (Fig. 1)
exhibits five resolved resonances, again characteristic of an
aminoxyl biradical system where |J0| ≈ aN.
The crystal structure analysis confirmed in the first instance
the presence of the 1,1-aminoxyl disubstitution rather than the
expected 1,2-disubstitution (Fig. 2). The presence of two mole-
cules of the compound in the orthorhombic unit cell (space
Results and discussion
Bis(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (2)
The Friedel–Crafts alkylation reaction between 1 and dichloro-
methane gave biradical 2 as the sole isolated reaction product in
16% yield (45% based on consumed starting material, Scheme
DOI: 10.1039/b109485h
J. Chem. Soc., Perkin Trans. 2, 2002, 533–537
This journal is © The Royal Society of Chemistry 2002
533

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Fig. 2 Molecular configuration and atom numbering scheme for 3
viewed down the approximate 2-fold rotational axis. Only one site of
the disordered atom (C62) is shown. Non-hydrogen atoms are shown as
30% probability ellipsoids.
despite the reaction being less selective. Biradical 5 was also
isolated in 3.6% yield.
The synthesis of triradical 4 was of particular interest since it
represents a potential precursor for a triphenylmethyl type
carbon centred radical. Our attempts at preparing tetraradical
7 have so far proven unsuccessful.
The solution EPR spectrum of 4 in toluene-d8 (Fig. 1)
exhibits seven resolved resonances as expected for an aminoxyl
triradical where |J0| ≈ aN.
The solution EPR spectrum of 5 in toluene-d8 (Fig. 1)
exhibits five resolved resonances characteristic of an aminoxyl
biradical system where |J0| ≈ aN.
5-(4Ј,4Ј,5Ј,5Ј-Tetramethyl-1Ј-oxido-3Ј-oxylimidazolin-2Ј-yl)-
1,1,3,3-tetramethylisoindolin-2-yloxyl (9) and
5-(4Ј,4Ј,5Ј,5Ј-tetramethyl-1Ј-oxylimidazolin-2Ј-yl)-1,1,3,3-
tetramethylisoindolin-2-yloxyl (10)
The nitronyl aminoxyl (9) and iminyl aminoxyl (10) derivatives
of 1 were prepared by an Ullmann nitronyl aminoxyl syn-
thesis.11 The aldehyde precursor 8 was prepared according to
our previously reported method.12 The oxidation reaction yields
both 9 and 10 (Scheme 2), the relative proportions of which are
dependent on reaction temperature. The observed yields are
typical for nitronyl aminoxyl syntheses.11
The solution EPR spectrum of nitronyl aminoxyl 9 in
toluene-d8 (Fig. 1) exhibits nine resonances indicative of a
system containing three nitrogen nuclei with two different aN
values, where aN(1) ≈ 2 × aN(2), and |J0| ӷ aN. One aN value arises
from the nitronyl aminoxyl group (aN = 7.2 G) and the other
from the isoindoline aminoxyl group (aN = 14.4 G). The
solution EPR spectrum of iminyl aminoxyl 10 in toluene-d8
(Fig. 1) exhibits 13 resonances which arise from three different
aN values, where aN(1) ≈ 2 × aN(2) ≈ 3 × aN(3), and |J0| ӷ aN. Two
of the aN values (9.4 and 4.7 G) are associated with the iminyl
aminoxyl while the third (14.1 G) is associated with the iso-
indoline aminoxyl. It is difficult to obtain values for J0 from the
EPR spectrum when |J0| ӷ aN since the spectra in this regime
are relatively insensitive to changes in J0.
Fig. 1 X-Band EPR spectra of radicals 2–5, 9, 10 and 15 in toluene
(298 K).
group Pnn2) means that the two aminoxyl substituents are
related by 2-fold rotational symmetry, with the central linking
carbon (C61) constrained to this axis. To achieve this, the
second ethane carbon (C62) must be disordered over two sites
(S.O.F. = 0.5) related by 2-fold symmetry. Fig. 2 shows only one
of the disordered sites for this second carbon. Also as a con-
sequence of this disorder, not all of the protons on the chain
could be located by difference methods.
Tris(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (4) and
chlorobis(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (5)
The preparation of the triradical 4, using chloroform as the
Friedel–Crafts haloalkane, was analogous to that for the
biradicals 2 and 3. The yield for the preparation was 26%
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J. Chem. Soc., Perkin Trans. 2, 2002, 533–537

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Scheme 1
Scheme 2
1,2,3,5,6,7-Hexahydro-1,1,3,3,5,5,7,7-octamethylbenzo-
[1,2-c:4,5-cЈ]dipyrrole-2,6-diyloxyl (15)
The novel fused biradical was prepared using methods similar
to those used for the preparation of the related monoradical
TMIO (1).13 Benzylation of pyromellitic dianhydride (11) was
achieved by treatment with benzylamine in glacial AcOH to
give 12 in 90% yield (Scheme 3). The octamethyl species 13 was
prepared by the exhaustive methylation of 12 with MeMgI in
boiling toluene and was isolated and purified in 4.6% yield. The
low yield for 13 reflects both the difficult nature of this type of
methylation procedure and the limited solubility of the prod-
ucts. The analogous step involving the addition of four methyl
groups in the synthesis of TMIO (1) affords yields of <40%.13
Hydrogenation of 13 at 50 psig over 5% Pd/C in glacial
AcOH afforded diamine 14 in 90% yield. The material was used
as is without further purification for the next step. Oxidation of
diamine 14 with mCPBA in THF afforded biradical 15 in 63%
yield. Biradical 15 has only limited solubility in most common
organic solvents. Recrystallisation could be achieved from
several solvents including MeCN, toluene and DMF. However
to obtain crystals suitable for X-ray crystallography a solution
of 15 in boiling DMF was cooled extremely slowly (>16 h) in an
oil bath, yielding small yellow needles.
Scheme 3
The crystal structure of 15 shows the biradical aminoxyl
which is centrosymmetric and planar and lies on a crystallo-
graphic inversion centre (Fig. 3). The poor refinement residual is
The solution EPR spectrum of 15 in toluene-d8 (Fig. 1)
exhibits five resonances (1 : 2 : 3 : 2 : 1) characteristic of an
aminoxyl biradical system where |J0| ӷ aN. Systems such as
these are of interest in the field of molecular magnetism where
high exchange interactions are desired.
Fig. 3 Molecular configuration and atom numbering scheme for 15
(30% probability ellipsoids).
J. Chem. Soc., Perkin Trans. 2, 2002, 533–537
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due to a combination of poor crystal quality and considerable
thermal motion, particularly in the methyl substituents.
Triradical 4: Slow evaporation from a 1 : 1 DCM–n-hexane
mixture gave yellow prisms, mp >180 ЊC (slow decomp.); EI MS
Mϩ 580.35497 (1.82 ppm from mass calc. for C37H46N3O3);
g = 2.00582, aN = 14.1 G (toluene-d8, 293 K).
Experimental
5-(4Ј,4Ј,5Ј,5Ј-Tetramethyl-1Ј-oxido-3Ј-oxylimidazolin-2Ј-yl)-
1,1,3,3-tetramethylisoindolin-2-yloxyl (9) and
5-(4Ј,4Ј,5Ј,5Ј-tetramethyl-1Ј-oxylimidazolin-2Ј-yl)-
1,1,3,3-tetramethylisoindolin-2-yloxyl (10)
NMR Spectra were recorded on a Varian Unity 300 spectro-
meter. EPR spectra were recorded on a Brüker ESP 300E EPR
spectrometer (X-band, ∼9.2 GHz) using an EIP 548B micro-
wave frequency counter and a Brüker O35M gaussmeter for
microfrequency calibration.
To a solution of 5-formyl-1,1,3,3-tetramethylisoindolin-2-yl-
oxyl (8, 90 mg, 412 µmol, 1 equiv.) in MeOH (2 cm3) was added
2,3-bis(hydroxyamino)-2,3-dimethylbutane (85 mg, 574 µmol,
1.4 equiv.). The mixture was stirred at room temperature for
22 h whereupon the solvent was removed under vacuum. The
residue was taken up in CHCl3 (3 cm3), cooled to 0 ЊC then
NaIO4 (180 mg, 842 µmol) in H2O (2 cm3) was added with
stirring over 5 min. The solution was stirred at 0 ЊC for a further
15 min. The mixture was diluted with H2O (3 cm3) and
extracted with CHCl3 (3 × 10 cm3). The combined organic
extracts were washed with sat. NaCl (2 × 15 cm3), dried over
anhydrous Na2SO4, filtered, and evaporated to dryness. Chrom-
atography (SiO2; 40 : 60 : 0.2 EtOAc–n-hexane–MeOH) gave
iminyl aminoxyl 10 (32 mg, 97 µmol, 24%) followed by nitronyl
aminoxyl 9 (18 mg, 52 µmol, 13%).
Nitronyl aminoxyl 9: Slow evaporation from a 1 : 1 DCM–n-
hexane mixture gave dark blue prisms, mp 209 ЊC (decomp.); EI
MS Mϩ 345.205330 (Ϫ0.3 ppm from calc. for C19H27N3O3); g =
2.00677, aN(1) = 14.4 G, aN(2) = 7.2 G, aN(3) = 7.2 G (toluene-d8,
293 K).
Iminyl aminoxyl 10: Recrystallisation from n-hexane gave
orange–red clusters, mp 199–201 ЊC (Found: C, 69.1; H, 8.4; N,
12.8. C19H27N3O2 requires C, 69.3; H, 8.3; N, 12.8%); g =
2.00516, aN(1) = 14.1 G, aN(2) = 9.4 G, aN(3) = 4.7 G (toluene-d8,
293 K).
Bis(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (2)
To a solution of 1 (1.00 g, 5.26 mmol, 1 equiv.) in CH2Cl2
(10 cm3) was added AlCl3 (2.80 g, 21.0 mmol, 4 equiv.). The
mixture was stirred at room temperature under an atmosphere
of argon for 24 h. The dark red mixture was poured slowly onto
ice with stirring. The layers were separated and the aqueous
portion was extracted with CHCl3 (3 × 5 cm3). The combined
organics were washed with sat. NaCl (10 cm3), dried over
anhydrous Na2SO4, filtered, and evaporated to dryness. Chrom-
atography (SiO2; 40 : 60 : 0.5 EtOAc–n-hexane–MeOH) gave
starting material 1 (662 mg, 3.48 mmol) followed by biradical 2,
which was recrystallised as fine yellow crystals from hexane
(163 mg, 0.416 mmol, 16%), mp 156 ЊC (decomp.) (Found:
C, 76.3; H, 8.5; N, 6.4. C25H32N2O2 requires C, 76.5; H, 8.2;
N, 7.1%); m/z 392 (100%), 377 (75%), 362 (40%), 347 (71%),
332 (34%), 317 (12%) (fused ring N-containing compounds
frequently give poor combustion analysis and so high reso-
lution EI MS was also run); EI MS found Mϩ 392.245929
(1.1 ppm from calc. mass for C25H32N2O2); g = 2.00580, aN
14.0 G (toluene-d8, 293 K).
=
1,1-Bis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)ethane
(3)
To a solution of 1 (1.00 g, 5.26 mmol, 1 equiv.) in 1,2-
dichloroethane (10 cm3) was added AlCl3 (2.80 g, 21.0 mmol, 4
equiv.). The mixture was stirred at room temperature under an
atmosphere of argon for 24 h. The dark red mixture was poured
slowly onto ice with stirring. The layers were separated and the
aqueous portion was extracted with CHCl3 (3 × 5 cm3). The
combined organics were washed with sat. NaCl (10 cm3), dried
over anhydrous Na2SO4, filtered, and evaporated to dryness.
Chromatography (SiO2; 40 : 60 : 0.5 EtOAc–hexane–MeOH)
gave starting material 1 (550 mg, 2.89 mmol) followed by the
biradical 3, which was recrystallised as yellow hexagonal prisms
by slow evaporation from a cyclohexane–dichloromethane
(1 : 1) solution (155 mg, 0.382 mmol, 15%), mp 218 ЊC (dec.);
EI MS Mϩ 406.262124 (Ϫ0.2 ppm from calc. mass for
C26H34N2O2); g = 2.00582, aN = 14.0 G (toluene-d8, 293 K).
N,NЈ-Dibenzylpyromellitimide (12)
To a stirred solution of pyromellitic dianhydride (11, 9.6 g,
0.044 mol, 1 equiv.) in glacial AcOH (50 mL) was added drop-
wise benzylamine (14.6 mL, 0.134 mol, 1.5 equiv.). A white
precipitate rapidly formed and the mixture was stirred for a
further 30 min at room temperature. The white precipitate was
collected by vacuum filtration to yield N,NЈ-dibenzyl-
pyromellitimide (12, 15.7 g, 0.0396 mol, 90%). Recrystallisation
from toluene gave colourless needles, mp 301–302 ЊC (Found:
C, 72.6; H, 4.1; N, 7.1. C24H16N2O4 requires C, 72.7; H, 4.1;
1
N, 7.1%); H NMR (CDCl3) δ 4.85 (s, 4H, CH2), 7.32–7.43
(m, 10H, ArH), 8.25 (s, 2H, ArH).
2,6-Dibenzyl-1,2,3,5,6,7-hexahydro-1,1,3,3,5,5,7,7-
octamethylbenzo[1,2-c:4,5-cЈ]dipyrrole (13)
Tris(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (4) and
chlorobis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)-
methane (5)
Magnesium turnings (19.6 g, 0.81 mol, 16 equiv.) and a few
crystals of iodine were placed in a flame dried Grignard appar-
atus under a positive pressure of Ar. Anhydrous Et2O (∼300
mL) and a few drops of iodomethane were added to initiate the
reaction. The remaining iodomethane (51.0 mL, 0.81 mol, 16
equiv. total) and anhydrous Et2O (1.5 L total) were added to
maintain a constant rate of reaction. When addition of the
reagents was complete the mixture was stirred until all activity
subsided. Ether was removed by distillation until the temper-
ature of the mixture reached 80 ЊC. A solution of N,NЈ-
dibenzylpyromellitimide (12, 20.0 g, 0.050 mmol, 1 equiv.) in
anhydrous toluene (1 L) was added to the methyl Grignard
solution (∼60 ЊC) at a rate which maintained a constant tem-
perature. When addition was complete, solvent was distilled
until the temperature of the reaction mixture reached 110 ЊC.
The reaction mixture was refluxed for two hours, then concen-
trated by distillation. After cooling, the reaction was diluted
with hexane fraction (1.5 L) and mixed thoroughly. The result-
ant purple slurry was vacuum filtered through Celite and the
To a solution of 1 (2.00 g, 10.5 mmol, 1 equiv.) in CHCl3
(20 cm3) was added AlCl3 (4.63 g, 34.7 mmol, 3.3 equiv.). The
mixture was stirred at room temperature under an atmosphere
of argon for 24 h. The dark green mixture was poured slowly
onto ice with stirring. The layers were separated and the
aqueous portion was extracted with CHCl3 (3 × 20 cm3). The
combined organics were washed with sat. NaCl (50 cm3), dried
over anhydrous Na2SO4, filtered, and evaporated to dryness.
Chromatography (SiO2; 20 : 20 : 60 : 0.5 DCM–EtOAc–n-
hexane–MeOH) gave starting material 1 (444 mg, 2.34 mmol)
followed by biradical 5 (82 mg, 0.190 mmol, 3.6%) then triradical
4 (533 mg, 0.918 mmol, 26%).
Biradical 5: Recrystallisation from n-hexane gave yellow
needles, mp 180–182 ЊC; EI MS Mϩ 426.20835 (2.22 ppm from
mass calc. for C25H31N2O2Cl); g = 2.00582, aN = 13.9 G
(toluene-d8, 293 K).
536
J. Chem. Soc., Perkin Trans. 2, 2002, 533–537

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residue was washed with hexane fraction (∼500 mL). Residues
were deactivated with i-PrOH and air was bubbled through the
filtrate overnight. The filtrate was passed through a column of
basic alumina and solvent was removed under vacuum to yield
crude 13. Recrystallisation from MeCN gave 13 (1.06 g, 2.34
mmol, 4.6%) as colourless prisms, mp 213–215 ЊC (Found:
C, 76.3; H, 8.5; N, 6.4. C25H32N2O2 requires C, 76.5; H, 8.2;
0.202 (F 2) [509 observed with I > 2.0 σ(I )]; S = 1.17. Crystal
size 0.30 by 0.20 by 0.10 mm.
Data collection, structure solution and refinement
X-ray diffraction data for both compounds were measured on
a Rigaku AFC7R diffractometer by using crystal mono-
chromatized Mo Kα X-radiation (λ = 0.71073 Å) from a 12 kW
rotating anode source. Negligible change in the intensities of
three standards monitored throughout the data collection
periods for both compounds (1.5% for 3 and 0.1% for 15) indi-
cated no significant crystal decomposition. Data were corrected
for Lorentz and polarization effects and extinction but not for
absorption The structures were solved by direct methods and
refined by full-matrix least-squares (on F 2) using SHELXL-
9714 within TeXsan.15 Figures were drawn using PLATON
for Windows.16 Anisotropic thermal parameters were used
for all non-hydrogen atoms. Hydrogen atoms were included at
calculated positions in the refinements as riding models.
Full crystallographic details, excluding structure factor
tables, have been deposited at the Cambridge Crystallographic
Data Centre (CCDC). For details of the deposition scheme,
see ‘Instructions for Authors’, J. Chem. Soc., Perkin Trans. 2,
available via the RSC web page (http://www.rsc.org/authors).
Any request to the CCDC for this material should quote the
full literature citation and the reference numbers 176995 and
176996.
1
N, 6.1%); H NMR (CDCl3) δ 1.30 (s, 24H, CH3), 4.00 (s, 4H,
CH2), 6.8 (s, 2H, ArH), 7.3–7.50 (m, 10H, ArH) ppm; 13C NMR
(CDCl3) δ 28.5 (CH3), 46.0 (CH2), 65.2 (quat. C), 126–129
(ArC), 143–148 (ArC) ppm.
1,2,3,5,6,7-Hexahydro-1,1,3,3,5,5,7,7-octamethylbenzo-
[1,2-c:4,5-cЈ]dipyrrole (14)
A solution of diamine 13 (0.530 g, 1.17 mmol) in glac. AcOH
was hydrogenated (50 psig) over a 5% Pd/C catalyst for 6 h. The
solution was evaporated to dryness then taken up in 1 M HCl.
The solution was filtered to remove residual catalyst then was
made basic (pH 14) with 5 M NaOH. The solution was
extracted with CHCl3 (4 × 25 mL), evaporation of which gave
14 (0.287 g, 1.05 mmol, 90%) as a white solid. Recrystallisation
from MeCN gave 14 as fine white crystals which sublimed at
200 ЊC. 1H NMR (CDCl3) δ 1.45 (s, 24H, CH3), 1.8 (s, 2H, NH),
6.8 (s, 2H, ArH) ppm; 13C NMR (CDCl3) δ 27.0 (CH3), 65.0
(quat. C), 126.0 (ArC), 128–129 (ArC), 143–149 (ArC) ppm.
1,2,3,5,6,7-Hexahydro-1,1,3,3,5,5,7,7-octamethylbenzo-
[1,2-c:4,5-cЈ]dipyrrole-2,6-diyloxyl (15)
Acknowledgements
3-Chloroperoxybenzoic acid (2.01 g, 11.6 mmol, 6 equiv.) was
slowly added to a solution of diamine 14 (0.530 g, 1.95 mmol,
1 equiv.) in THF (100 mL) at 0 ЊC. The reaction mixture was
stirred at 0 ЊC for 1 h then was allowed to warm to room
temperature. The mixture was stirred at room temperature for
a further 24 h. H2O (50 mL) was added to the solution which
was then acidified with 1 M HCl and extracted with CHCl3 (4 ×
20 mL). The combined organic extracts were washed with 2 M
NaOH (3 × 20 mL). The organic extracts were evaporated to
dryness to yield biradical 15 (0.370 g, 1.22 mol, 63%) as a
yellow crystalline material. Recrystallisation from DMF gave
15 as small yellow needles, mp 230 ЊC (dec.); g = 2.006076,
aN = 14.0 G (toluene).
Dr Peter Healy is thanked for collection of X-ray diffraction
data.
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Crystallography†
Crystal data for (3). C26H34N2O2, M = 406.55, orthorhombic,
space group Pnn2, (No. 34), a = 12.611(2), b = 16.164(2), c =
5.895(2) Å, V = 1201.7(3) Å3, F(000) = 440, Z = 2, Dc = 1.124 g
cmϪ3, µ(Mo Kα) = 0.71 cmϪ1, temperature 293(2) K; 1174
unique reflections measured [2θmax 50Њ: h, 0 to 14; k, 0 to 19;
l, 0 to 7]. Final R1‡ 0.057 (F); wR2‡ 0.172 (F 2) [899 observed
with I > 2.0 σ(I ); 142 refined parameters]; S = 1.42. Crystal size
0.50 by 0.25 by 0.15 mm.
10 G. R. Luckhurst, in Spin Labeling: Theory and Applications, ed.
L. J. Berliner, Academic Press, New York, 1976, pp. 133–181.
11 E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. Darcy, J. Am.
Chem. Soc., 1972, 94, 7049.
Crystal data for (15). C18H26N2O2, M = 302.41, monoclinic,
space group P21/n, (No. 14), a = 6.332(2), b = 13.403(2), c =
11.209(2) Å, β = 92.01(2)Њ, V = 950.7(4) Å3, F(000) = 328, Z = 2,
Dc 1.063 g cmϪ3, µ(Mo Kα) = 0.69 cmϪ1, temperature 293(2) K;
1833 reflections measured, 1676 unique (Rint = 0.035) [2θmax 50Њ:
h, 0 to 7; k, 0 to 15; l, Ϫ13 to 13]. Final R1* 0.073 (F); wR2*
12 S. E. Bottle, D. G. Gillies, D. L. Hughes, A. M. Micallef, A. I.
Smirnov and L. H. Sutcliffe, J. Chem. Soc., Perkin Trans. 2, 2000,
1285.
13 P. G. Griffiths, G. Moad, E. Rizzardo and D. H. Solomon, Aust. J.
Chem., 1983, 36, 397.
14 G. M. Sheldrick, SHELXL-97. Program for Crystal Structure
Determination, University of Göttingen, Federal Republic of
Germany, 1997.
15 TeXsan for Windows. Version 1.06, Molecular Structure
Corporation, 9009 New Trails Drive, The Woodlands, TX 77381,
USA, 1999.
16 A. L. Spek, PLATON for Windows. September 1999 version,
University of Utrecht, The Netherlands, 1999.
† CCDC reference numbers 176995 and 176996. See http://
www.rsc.org/suppdata/p2/b1/b109485h/ for crystallographic files in .cif
or other electronic format.
2
‡ R1 = (Σ Fo Ϫ Fc)/(Σ Fo); wR2 = [Σ w(Fo2 Ϫ Fc2)2/Σ w(Fo )2]1/2
.
J. Chem. Soc., Perkin Trans. 2, 2002, 533–537
537