Facile N-N activation in benzotriazole: Capturing the dimroth azo/triazole intermediate by complexation to iridium

Article abstract of DOI:10.1002/cplu.201300245

The in situ observation of benzotriazole ring and ring-opened isomers, which result from the Dimroth equilibrium for 1-[(nonafluorobutane) sulfonyl]benzotriazole, 1, in solution by ¹⁹F NMR and UV/Vis spectroscopy is reported. Two benzotriazoles

Full text of DOI:10.1002/cplu.201300245

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DOI: 10.1002/cplu.201300245
Facile NÀN Activation in Benzotriazole: Capturing the
Dimroth Azo/Triazole Intermediate by Complexation to
Iridium
D. Scott Bohle,* Zhijie Chua, and Inna Perepichka[a]
The in situ observation of benzotriazole ring and ring-opened
isomers, which result from the Dimroth equilibrium for 1-[(non-
afluorobutane)sulfonyl]benzotriazole, 1, in solution by 19F NMR
and UV/Vis spectroscopy is reported. Two benzotriazoles,
compound 1 and 1,1’-sulfonylbis(benzotriazole) (3), undergo
Dimroth triazole ring opening and coordination to an irid-
ium(I) metal center to give either linear diazo [IrI(h1-
NNPhNSO2C4F9)(Cl)(PPh3)2] (2) or an unusual double bent dia-
zene [IrIII(h3-NNPhNSO2Btz)(Cl)(PPh3)2] (4; Btz=benzotriazole)
complex.
Introduction
Although the azo/triazole equilibrium in Scheme 1 is responsi-
ble for the Dimroth or amidine rearrangement[1] in many polya-
za heterocycles, evidence for its operation in benzotriazoles 1a
tivation of the benzotriazole ring towards oxidative addition,
and 3) two examples of the structures of this Dimroth inter-
mediate bound in two different ways to iridium. Taken togeth-
er, this work opens up new horizons for triazole chemistry
mediated by organometallics.
Results and Discussion
Dimroth rearrangements of benzotriazoles
Physical evidence for the equilibrium of 1a/1b has been diffi-
cult to obtain, although there are indications in the literature
for the presence of 1b for electron-withdrawing substituents
on N1 of a benzotriazole. One early study on 1-cyanobenzotria-
Scheme 1. The Dimroth or amidine rearrangement of triazole and benzotria-
zole.
zole reported a solvent-dependent yellow solution, with lmax
=
435 nm in ethanol.[4] In some of our initial studies with 1, we
too found some surprising deep-yellow solutions that were re-
versibly formed, depending upon the solvent and sample
treatment, and we undertook a more careful experimental and
theoretical characterization of this system. As shown in Table 1,
we find a marked solvent dependence for both the wave-
length and intensity of the low-lying band in 1. Solvents with
larger dielectric constants exhibit a general trend for both an
increase in the energy of the transition and its extinction.
The band at lꢀ400 nm is similar in energy to those found
in arenediazonium species,[5] and for which the isolated salts
often have eꢀ103–104 mÀ1 cmÀ1. The absorbance observed for
1b is weaker owing to the position of the 1a/1b equilibrium
and we have attempted to gauge this by calculating the differ-
ences in the relative energies of the two isomers in these
media (see the right-hand column of Table 1). Although tria-
zole isomer 1a is always theoretically favored, more polar sol-
vents are predicted to better stabilize the zwitterionic polar
isomer; this shift in the equilibrium would rationalize observed
absorption trends. Attempts to confirm the presence of 1b in
these mixtures by IR spectroscopy have been hampered by
overlapping solvent and triazole bands and so another struc-
and 1b is limited. In 1992 Katrizky et al. interpreted several
thermally promoted addition reactions to benzotriazoles in
terms of a Dimroth intermediate[2] and more recently Ziegler
et al. proposed that nucleophiles such as amines, malonoates,
or deprotonated cresols[3] reacted with Dimroth azo isomer 1b
if it was substituted with a perfluoroalkylsulfonyl group at N1.
Low-valent organometallic complexes offer the possibility of
trapping azo isomer 1b and potentially promoting the NÀN
activation and ring opening of benzotriazoles. To this end, we
report 1) spectroscopic evidence and supporting density func-
tional calculations for a benzotriazole derivative with Dimroth
ring-open/-closed isomers in equilibrium in solution, 2) the ac-
[a] Prof. D. S. Bohle, Z. Chua, Dr. I. Perepichka
Department of Chemistry
McGill University
801 Sherbrooke St. W., Montreal, H3A 0B8 (Canada)
E-mail: david.bohle@mcgill.ca
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201300245. It contains spectroscopic in-
formation, theoretical calculations, and experimental details.
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Table 1. Visible absorption bands of 1 and related triazoles in different solvents.
Solvent
e [mÀ1 cmÀ1
]
Experimental values[a]
lmax [nm]
Absorption [mÀ1 cmÀ1
Theoretical values[b]
Oscillator strength of 1b
]
lmax of 1b [nm]
Rel. E[c] [kcalmolÀ1] (E1aÀE1b
)
1
gas phase
hexanes
chloroform
ethyl acetate
DMF
acetonitrile
DMSO
propylene carbonate
water
–
–
–
411
403
408
402
406
–
–
–
–
409.08
412.51
409.27
–
0.1450
0.1783
0.1825
–
8.5
6.5
4.7
–
1.88
4.81
6
36.7
37.5
47
64.9
78.39
58.5
17.2
1204
334
2015
482
–
–
–
–
404.64
405.60
–
404.18
–
0.1763
0.1811
–
0.1756
–
3.3
3.3
–
3.2
–
formic acid
396
484
3
DMF
DMSO
36.7
47
411
404
160
452
–
–
–
–
–
–
N-NO2-Btz
DMSO
47
430
0.43 (5)
–
–
–
N-CN-Btz[4]
EtOH
24
435
3.5
–
–
–
[a] The band was only visible from freshly prepared solutions measured at room temperature. This is the absorbance at the lmax. [b] Values for the electron-
ic spectra for 1b were calculated from time-dependent density functional theory at the B3LYP/6-311+ +g** level. Solvent effects were determined by
using a polarized continuum model. [c] Relative energies correspond to the difference in energy between 1a and 1b for each solvent.
tural method was sought to confirm the presence of the 1a/
1b equilibrium.
Theoretical DFT calculations at the B3LYP/6-311+ +G** level
(see the Supporting Information) for 1 give two ground-state
structures for 1a and 1b, which differ by 8.5 kcalmolÀ1 in the
gas phase and 3.3 kcalmolÀ1 in DMSO (Table 1). A stationary
state with an out-of-plane C4F9SO2 group on N1 is 12.9 kcal
molÀ1 above the triazole isomer and internal reaction coordi-
nate calculations indicate that the isomerization of a to
b through this transition state involves lengthening of the
N1ÀN2 bond and shortening and linearization of the N2ÀN3
bond. The transition state is close to the benzotriazole geome-
try. Polar solvents are expected to stabilize both the charges
that develop in ring opening and in isomer 1b. The theoretical
predictions are remarkably close to the experiment for dynam-
ic behavior. For electron-withdrawing substituents on N1, the
Dimroth rearrangement is accessible at low and room temper-
atures for benzotriazole. For other triazoles, those with elec-
tron-donating substituents on the ring, this equilibrium is also
observed under these conditions for less-electron-withdrawing
substituents.[9] The implication is that, with a suitable choice of
triazole substituent, the Dimroth rearrangement represents
a powerful tool to transform triazoles.
Spectroscopic evidence for the Dimroth equilibrium is found
1
in H and 19F variable-temperature NMR spectroscopy for solu-
tions of 1. At room temperature, these solutions are consistent
with the presence of a single species or the high-temperature
limit of an equilibrium under fast exchange. In prior work,
high-temperature NMR spectroscopy was used to examine a so-
lution of 1 in DMF and neither new signals nor significant
broadening of any of the resonances was observed.[6] However,
if these solutions in polar solvents were cooled, the 19F NMR
spectra (Figure 1) exhibited marked temperature dependence
with cooling leading to coalescence at À468C followed by the
emergence of low-temperature-limit spectra with two signals
observed for the a-CF2 fluorines[7] in a 5:1 ratio. These resonan-
ces have a significant difference in the chemical shifts for 1a
and 1b, whereas the remaining three fluorines exhibit limited
broadening or splitting upon cooling (see the Supporting In-
formation). Analysis of these spectra give DG° =11 kcalmolÀ1
.
This low barrier and solvent effect is consistent with the NMR
spectroscopy results previously reported by Regitz and Scherer
for nonannulated triazoles.[8] Under the same conditions,
1H NMR spectra reversibly broaden in DMF upon cooling and
the 19F NMR spectra remain unaltered in CD2Cl2, (see the Sup-
porting Information). Thus, at room temperature, the NMR
spectra of these solutions correspond to the high-temperature
limit at which the observed resonances are the weighted aver-
ages of equilibrated 1a and 1b, and, at low temperatures,
polar solvents are required to stabilize and enrich the popula-
tion of 1b, so the equilibrium in Scheme 1 can be observed.
Coordinative trapping of Dimroth equilibrium
To trap the Dimroth ring-open isomer in Scheme 1, we sought
suitable low-valent organometallic complexes that would stabi-
lize azo isomer 1b and potentially promote NÀN activation
and ring opening of benzotriazoles. The iridium(I) dinitrogen
complex trans-[IrI(Cl)(N2)(PPh3)2] is ideal for these experiments
owing to the general kinetic inertness of iridium(I), the lability
of the nitrogen ligand, its coordinative unsaturation, and its
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Figure 1. 19F NMR spectra of 1a and 1b in [D7]DMF at different temperatures.
known propensity to trap otherwise reactive intermediates. To
this end, if 1 is treated with trans-[IrI(Cl)(N2)(PPh3)2] at room
temperature, there is rapid effervescence of gas and an imme-
diate color change to dark green (Scheme 2). Subsequent isola-
tion of complex 2 gave intensely brackish green crystals. The
molecular structure of 2 shows a ring-opened benzotriazole in
zwitterionic form[10] coordinated to the iridium(I) metal center
through the diazo portion of the benzotriazole ring in a mono-
dentate fashion (Figure 2). Of particular note is the relatively
short diazonium-like N(2)ÀN(3) bond length of 1.165(9) ꢁ and
terionic–diazo ligands, the diazo bond lengths range between
1.163(7) and 1.224(6) ꢁ.[10,11] In all other known cases, the diazo
ligands are N-bound to the metal in a h1 manner with only
a few examples[12] in which the diazo ligand is bound in
a p form.[13] The long Ir(1)ÀN(1) separation of 3.762(7) ꢁ sug-
gests little interaction between the sulfonyl-substituted nitro-
gen and iridium.
In common with many Vaska-type complexes, complex 2 is
relatively stable in the solid state, but exhibits oxygen and
light sensitivity in solution. Upon standing in solution and light
~
close to linear N(3)-N(2)-Ir bond angle of 171.5(7)8. The corre-
exposure, decomposition products show the loss of the n=
À1
À1
sponding new n(NN) band appears at n=1880 cm in the IR
1880 cmÀ1 band and a new band at n=1626 cm is observed.
~
~
spectrum of 2. In contrast, for free non-coordinated 1b, densi-
Further reaction with other nucleophiles, such as phosphines
or p-tolylisocyanide, results in phosphine ligand substitution
and the formation of equilibrium mixtures of iridium(I) com-
plexes that contain 1b’ (possibly a new diazene/azo ligand)
ty function theory predicts an NÀN bond length of 1.11802 ꢁ
À1
~
and a n(NN) band at n=2253.8 cm . Clearly the new diazo
ligand in 2 is an excellent p acid with coordination of iridiu-
m(I), leading to considerable p-backbonding to the ligand. For
transition-metal complexes reported that contain diazo/zwit-
~
and correspond to new bands appearing between n=1600
and 1700 cmÀ1 (Scheme 2). Carbon monoxide addition results
in the loss of 1 and the forma-
tion of trans-[IrI(Cl)(CO)(PPh3)2]
upon extended exposure to CO
gas.
In contrast with the relatively
simple substitution of dinitrogen
for the diazo ligand in 2, it is
possible that coordination could
lead to complete formal two-
electron transfer to the new
ligand to give rise to an iridium-
(III) chelate complex; in part, this
happens when trans-[IrI(Cl)(N2)-
Scheme 2. Synthesis of 2 from 1.
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Figure 2. Molecular structure of 2. Selected bond lengths [ꢁ]: Ir(1)À
N(1)=1.791(6), N(2)ÀN(3)=1.165(9), S(1)ÀN(1)=1.536(8), S(1)À
C(7)=1.861(11), N(1)ÀC(6)=1.420(13), N(3)ÀC(1)=1.410(11). Selected bond
angles [8]: N(3)-N(2)-Ir(1)=171.5(7), N(2)-N(3)-C(1)=139.2(8).
Figure 3. Molecular structure of 4. Selected bond lengths [ꢁ]: Ir(1)À
N(2)=1.991(4), Ir(1)ÀN(1)=2.075(4), Ir(1)ÀN(3)=2.107(4), S(1)À
N(1)=1.600(4), S(1)ÀN(4)=1.713(5), N(1)ÀC(6)=1.407(6), N(2)À
N(3)=1.244(7), N(3)ÀC(1)=1.444(8). Selected bond angles [8]: N(3)-N(2)-
Ir(1)=124.9(4), N(2)-N(3)-C(1)=127.4(5).
(PPh3)2] is treated with 1,1’-sulfonylbis(benzotriazole) (3). As
with 1, this triazole is able to undergo nucleophilic ring open-
ing,[2b] and it exhibits some solvatochromism in polar solvents
to give a new band at about 411 nm (Table 1). When 3 was
added to trans-[IrI(Cl)(N2)(PPh3)2] at 08C, a vigorous evolution
of gas was coupled with an immediate color change to dark
green. The reaction mixture slowly turned wine red over the
course of 3 h at room temperature (Scheme 3). The ultimate
red product isolated, 4, contained an opened triazole, which
was bound as a chelate, and included an unusual cis doubly
bent diazene. The second heterocycle is a coordinated but un-
modified benzotriazole. From X-ray crystallography, all nitrogen
atoms are bound in a meridional geometry (Figure 3). The
N(2)ÀN(3) bond lengths and N(2)-N(3)-Ir(1) bond angles reveal
that the ring-opened triazole fragment is similar to a doubly
bent diazene ligand.[14] Unlike complex 2, complex 4 does not
react with CO and PR3.
À1
~
bands at n=1887 and 567 cm . Over 2.5 h, these bands of
the intermediate depicted in Scheme 3 disappear and lead to
À1
~
new bands at n=1602 and 593 cm (Figure 4), which corre-
spond to final product 4.
This strategy of trapping the ring-opened Dimroth inter-
mediate has been applied before in the reaction 1,2,3-thiadia-
zole, which is not a triazole, with iron carbonyls.[15] In this case,
the Dimroth equilibrium is generally more favored[16] for the
ring-opened form and resulting dinuclear product has a bridg-
ing diazo ligand. Most recently, non-benzannulated triazoles
have been used as substrates for the putative catalytic genera-
tion of rhodium(II) carbene-like intermediates. These intermedi-
ates arise from facile Dimroth ring opening followed by dini-
trogen extrusion and proposed metallocarbene formation of
the {LnRh=C(R)CR(=NSO2R’)} fragment.[17] The 1-sulfonyltriazoles
employed in these catalytic studies are of the type demon-
strated to undergo facile Dimroth ring opening at room tem-
perature by Regitz and Scherer.[8] In the catalytic system, there
are no reports of either isolated intermediates in these systems
or of the benzotriazoles engaging in this chemistry. The stabili-
zation of these types of intermediates by iridium described
herein provides an important
The identity of the diazo-green intermediate in Scheme 3 is
supported by the solution IR spectra shown in Figure 4. The in-
À1
~
tense dinitrogen stretch at n=2105 cm from the starting
material dinitrogen disappears immediately upon addition of 3
and is correlated with the appearance of new diazonium
insight into possible catalytic in-
termediates in these systems.
Equally significant is the ability
of iridium(I) to activate and trap
a ring-opened benzotriazole.
Benzotriazoles are also now
widely used as auxiliaries in or-
ganic syntheses[18] and any reac-
tion or methodology that leads
to NÀN activation of benzotria-
zole will allow many new appli-
Scheme 3. Synthesis of 4 from 3.
cations of this fundamental or-
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Figure 4. Solution IR spectra for the reaction of trans-[IrI(Cl)(N2)(PPh3)2] with 3. Reaction performed at À108C in CHCl3 over 2.5 h. Aliquots were taken at the
following time intervals: red: initial trans-[IrI(Cl)(N2)(PPh3)2] complex; blue: immediately after the addition of 3; brown: after 45 min; green: after 1.5 h; black:
after 2.5 h.
ganic building block, as well as for the triazole class as
Experimental Section
a whole. Diazo–metal complexes are often important inter-
mediates in transformations.[19] Our observation that a mononu-
General
clear iridium(I) complex is able to activate the obdurate benzo-
triazole suggests that this reaction may be quite general. A
preliminary screen of other benzotriazoles with N1 electron-
withdrawing substituents, such as CN, NO2, and p-nitrophenyl-
SO2, suggest common, rapid coordination to trans-[IrI(Cl)(N2)-
(PPh3)2], as in Scheme 2, which is then followed by subsequent
reactions that lead to complex product mixtures.
All solvents were degassed thoroughly with nitrogen and reactions
were performed under a nitrogen atmosphere. 1,2-Dimethoxy-
ethane was dried with Na/benzophenone, CH2Cl2 and CH3CN were
distilled from CaH2, and pentanes were distilled from sodium ben-
1
zophenone ketyl. H, 13C, 19F, and 31P NMR spectra were measured
on Varian Mercury 200, 300, 400, or 500 MHz spectrometers. Varia-
ble-temperature NMR spectroscopy was performed on a Varian
Mercury 500 MHz spectrometer. Melting points were measured by
using a 2010 differential scanning calorimeter. The IR spectra were
measured as KBr disks by using an ABB Bomem MB Series spec-
trometer with a spectral resolution of 4 cmÀ1. UV/Vis spectra were
measured by using an HP 8453 Diode Array spectrophotometer.
Mass spectra analyses were performed on a Finnigan LCQ-Duo
spectrometer operating at 70 eV.
Conclusion
Spectroscopic evidence of the coexistence of the ring-
opened/-closed isomers of benzotriazole derivatives in solution
indicated that the Dimroth equilibrium was rapidly established
for triazoles with electron-withdrawing substituents on nitro-
gen. These intermediates could be trapped by coordination to
a suitable organometallic complex, and two new adducts were
prepared with this strategy. Preliminary experiments suggested
these rearrangements were general for other triazoles and pos-
sibly for other transitions metals. This new method of stabiliz-
ing the ring-opened forms of triazole ring allows further organ-
ic transformations either through catalysis with other metal
systems or other organic reagents.
Crystal structure determination
Crystals were mounted on Mitegen mounts by using Paratone-N
from Hampton Research and X-ray data were collected on a Bruker
AXS APEX2 CCD diffractometer by using graphite-monochromated
MoKa radiation (l=071073 ꢁ). The program APEX2 was used to col-
lect the intensity data, indexing, and determination of lattice pa-
rameters; SAINT was used for integration of the intensity reflec-
tions and scaling; SADABS was used for absorption correction;
SHELXTL was used for space group and structure determination
and least-squares refinements against F2. The structures were
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solved by means of the Patterson method to locate the heavy
atoms, followed by difference maps for light, non-hydrogen atoms.
The hydrogen atoms were placed in calculated positions.
16.8 mmol) in anhydrous CH3CN (15 mL). The mixture was stirred
for 2 h followed by dropwise addition of sulfuryl chloride at 08C.
The reaction mixture was stirred overnight at room temperature.
After removal of the solvent, the mixture was subjected to short
column chromatography (CHCl3) to give pure 3 (1.60 g, 62%). M.p.
The structural data has been deposited with the Cambridge Crys-
tallographic Data Centre. CCDC 894670 (2) and 894671 (4) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
1
1588C (DSC); H NMR (400 MHz, CDCl3): d=7.55 (t, 2H, J=7.8 Hz),
7.77 (t, 2H, J=7.8 Hz), 8.08 (d, 2H, J=8.4 Hz), 8.24 ppm (d, 2H, J=
~
8.8 Hz); IR (KBr): n=3070w, 1595s, 1590s, 1483s, 1441s, 1370m,
1324m, 1308m, 1266m, 1203m, 1151m, 1124m, 1006m, 926s, 905s,
660s, 600s, 537s, 485m cmÀ1
.
[IrIII(h3-NNPhNSO2Btz)(Cl)(PPh3)2] (4): A solution of trans-[IrI(Cl)(N2)-
(PPh3)2] (0.050 g, 0.064 mmol) in degassed CHCl3 (10 mL) was
cooled to 08C under nitrogen. While stirring, a solution of 3
(0.019 g, 0.064 mmol) in degassed CHCl3 (1 mL) was added with
a syringe. After an additional 3 h of stirring at ambient tempera-
ture, the solvent was evaporated to give a quantitative yield of the
product. Deep-red crystals of 4 were obtained from recrystalliza-
Theoretical calculations
DFT calculations were performed with the Gaussian 03 program by
using the B3LYP functional and 6-311+ +g** basis sets. The two
ground-state structures corresponded to local minima with all-pos-
itive vibrational modes; the transition state was located by the
quadratic synchronous transit algorithm, which was then checked
with an internal reaction coordinate calculation to ensure that the
transition state led to the triazole and Dimroth products. The time-
dependent calculations were performed for the optimized ground-
state geometries.
1
tion in CH2Cl2/CH3OH. H NMR (200 MHz, CDCl3): d=6.66 (t, 1H, J=
7.5 Hz), 7.03 (m, 1H+PPh3), 7.34 (t, 2H, J=7.3 Hz), 7.52 (m, 2H+
PPh3), 7.75 ppm (q, 2H, J=9 Hz); 31P NMR (81 MHz, CDCl3) : d=
À13.08 ppm (s); IR (KBr): 3057w, 2960w, 2915w, 2855w, 1591w,
1484m, 1459m, 1435s, 1320m, 1272w, 1233w, 1158s, 1093s, 927m,
915m, 863w, 793w, 743s, 707m, 694s, 593w, 560w, 522s cmÀ1; MS
(ESI+): m/z (%): 790.69 (95) [MÀ[PPh3]+H]+, 1052.62 (50) [M+H]+;
elemental analysis calcd (%) for C48H38N6O2SP2ClIr·CH3OH: C 54.21,
H 3.87, N 7.74, S 2.95; found: C 54.17, H 3.92, N 7.58, S 2.54; UV
(CHCl3, lmax, e): 270 (31000), 490 nm (1100mÀ1 cmÀ1).
Synthesis
1-[(nonafluorobutane)sulfonyl]-1H-benzotriazolesulfonylbis(ben-
zotriazole) (1): Compound 1 was prepared by following a previous-
ly published procedure.[6] 1H NMR (400 MHz, CDCl3): d=8.23 (d, 1H,
J=12 Hz), 7.98 (d, 1H, J=8.0 Hz), 7.77–7.81 (m, 1H), 7.62–
7.66 ppm (m, 1H); 1H NMR (400 MHz, [D6]DMSO): d=8.63 (d, 1H,
J=8.5 Hz), 8.18–8.24 (m, 2H), 7.86–7.9 ppm (m, 1H); 19F (470 MHz,
[D7]DMF):[7] d=À(81.09–81.07) (m, CF3), À110.78 (s, SO2-CF2),
À121.17 (s, CF2), À(126.00–126.06) ppm (m, CF2); 13C NMR
(126 MHz, CDCl3): d=145.3, 132.1, 131.9, 127.3, 121.5, 111.8 ppm;
IR monitoring of the formation of 4 in solution
A solution of trans-[IrI(Cl)(N2)(PPh3)2] (0.010 g, 0.013 mmol) in de-
gassed CHCl3 (3 mL) was cooled to À108C under nitrogen. Com-
pound 3 (0.004 g, 0.013 mmol) in cold degassed CHCl3 (0.5 mL)
was added by means of a syringe with stirring. Aliquots of the re-
action mixture were removed, placed in a solution IR cell, recorded
and recovered, at intervals over a period of 3 h.
~
IR (KBr): n=3108w, 3084w, 1599m, 1484m, 1436s, 1356m, 1331w,
1271s, 1238s, 1193s, 1139s, 1072m, 1027s, 1007m, 883s, 809m,
771s, 747s, 665s, 588s, 555s, 532s cmÀ1; Raman: 1596, 1437, 1389,
1306, 1282, 1272, 1224, 1196, 1008, 774, 741, 704, 664, 555,
535 cmÀ1
.
Acknowledgements
[IrI(h1-NNPhNSO2C4F9)(Cl)(PPh3)2]
(2):
trans-[IrI(Cl)(N2)(PPh3)2]
(0.195 g, 0.25 mmol) and 1 (0.100 g, 0.25 mmol) were dissolved in
degassed CHCl3 (10 mL). The solution turned dark green rapidly
with vigorous effervescence. The reaction mixture was allowed to
stir for 1 h and the solvent was removed in vacuo. The dark-green
residue was recrystallized from dry CH2Cl2/pentanes to give dark
We gratefully acknowledge NSERC and the CRC for support of
this research. We thank Dr. Chuck Campana for assistance with
the structural refinement of 2 and Dr. Fred Morin for assistance
with NMR spectroscopy measurements.
1
green crystals of 2 (0.225 g, 0.195 mmol, 78%). H NMR (200 MHz,
CDCl3): d=6.11 (dd, 1H, J=8.0, 1.6 Hz), 6.35, (td, 1H, J=7.7,
1.2 Hz), 6.97 (td, 1H, J=7.8, 1.4 Hz), 7.14 (m, 1H), 7.36 (m, PPh3),
7.84 ppm (m, PPh3); 19F NMR (470 MHz, CDCl3): d=À80.86 (t, 3F,
J=9.4 Hz), À112.70 (tq, 2F, J=14.1, 4.7 Hz), À121.32 (m, 2F),
À125.95 ppm (m, 2F); 31P NMR (81 MHz, CDCl3): d=16.26 ppm (s);
Keywords: azo compounds
addition reactions rearrangement
vibrational spectroscopy
·
benzotriazoles
· oxidative
·
·
transition metals ·
~
IR (KBr): n=3057w, 2960w, 2923w, 2856w, 1880m, 1482m, 1464m,
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1436m, 1321m, 1297m, 1234s, 1190m, 1149s, 1097s, 1028m,
1010m, 982m, 825w, 746s, 709m, 693s, 582m, 573m, 520s cmÀ1; el-
emental analysis calcd (%) for C46H34N3O2F9SP2ClIr: C 47.85, H 2.95,
N 3.64, S 2.77; found: C 47.87, H 3.01, N 3.53, S 2.63; UV (CHCl3,
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lmax
, e): 242 (60000), 290sh (34000), 405 (5400), 600 nm
(266mÀ1 cmÀ1).
1,1’-sulfonylbis(benzotriazole) (3): Compound 3 was prepared by
following a previously published procedure[3c] with some modifica-
tions. Under nitrogen at room temperature, NEt3 (1.82 g,
18.0 mmol) was added to a stirred solution of benzotriazole (2.0 g,
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Received: March 26, 2013
Published online on July 31, 2013
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ChemPlusChem 2013, 78, 1304 – 1310 1310