N-(trifluoromethylsulfonyl)aryloxytrifluoromethylsulfoximines [ArO-SO(CF3)=NTf] and N-aryltriflimides Ar-N(Tf)2 by thermal and photolytic dediazoniation of [ArN2][BF4] in [BMIM][Tf2N] ionic liquid: Exploiting the ambident nucleophilic character of a "nonnucleophilic" anion

Article abstract of DOI:10.1021/jo0708801

(Chemical Equation Presented) Arenediazonium tetrafluoroborate salts undergo metathesis on immobilization in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonato)amide [BMIM][Tf₂N]. The "noncoordinating", "nonnucleophilic" [Tf₂N] anion acts as an ambident nucleophile toward the aryl cations, formed via thermal dediazoniation, to give predominantly the oxy anion quenching products [ArO-SO(CF₃)=NTf], with minimal formation of ArN(Tf)₂, irrespective of the nature of the substituent(s) on the ArN₂ ⁺. Strong preference for the formation of oxygen trapping products did not change under photolytic conditions, where dediazoniation occurs at room temperature. A minimal amount of the Schiemann product ArF is also formed in both thermal and photolytic dediazoniation, depending on the substituent(s). Progress of dediazoniation in the IL (both thermal and photolytic) and the evolution of the products were directly monitored by ¹H and ¹⁹F NMR. According to DFT (Density Functional Theory) calculations, PhN(Tf)₂ is more stable than PhO-SO(CF₃)=NTf by 15-17 kcal/mol, depending on the basis set. Inclusion of solvation effects (PCM, with acetone and with CH₂ClCH₂Cl as solvent) did not change this preference. The [ArN₂][BF₄] dediazoniation in [BMIM][Tf₂N] resulted in synthesis and characterization of a series of hitherto unknown [ArO-SO(CF₃)=NTf] compounds. The X-ray structure of MesO-SO(CF₃)=NTf (Mes = mesityl) is reported. On the basis of extraction studies, suitable solvent systems have been identified that remove the products without dissolving [BMIM][NTf₂], thus overcoming product recovery difficulties typically associated with the use of this IL.

Full text of DOI:10.1021/jo0708801

N-(Trifluoromethylsulfonyl)aryloxytrifluoromethylsulfoximines
[ArO-SO(CF3)dNTf] and N-Aryltriflimides Ar-N(Tf)2 by Thermal
and Photolytic Dediazoniation of [ArN2][BF4] in [BMIM][Tf2N]
Ionic Liquid: Exploiting the Ambident Nucleophilic Character of a
“Nonnucleophilic” Anion
Kenneth K. Laali,* Takao Okazaki, and Scott D. Bunge
Department of Chemistry, Kent State UniVersity, Kent, Ohio 44242
klaali@kent.edu
ReceiVed April 26, 2007
Arenediazonium tetrafluoroborate salts undergo metathesis on immobilization in 1-butyl-3-methylimi-
dazolium bis(trifluoromethanesulfonato)amide [BMIM][Tf2N]. The “noncoordinating”, “nonnucleophilic”
[Tf2N] anion acts as an ambident nucleophile toward the aryl cations, formed via thermal dediazoniation,
to give predominantly the oxy anion quenching products [ArO-SO(CF3)dNTf], with minimal formation
+
of ArN(Tf)2, irrespective of the nature of the substituent(s) on the ArN2 . Strong preference for the
formation of oxygen trapping products did not change under photolytic conditions, where dediazoniation
occurs at room temperature. A minimal amount of the Schiemann product ArF is also formed in both
thermal and photolytic dediazoniation, depending on the substituent(s). Progress of dediazoniation in the
IL (both thermal and photolytic) and the evolution of the products were directly monitored by 1H and 19
F
NMR. According to DFT (Density Functional Theory) calculations, PhN(Tf)2 is more stable than PhO-
SO(CF3)dNTf by 15-17 kcal/mol, depending on the basis set. Inclusion of solvation effects (PCM,
with acetone and with CH2ClCH2Cl as solvent) did not change this preference. The [ArN2][BF4]
dediazoniation in [BMIM][Tf2N] resulted in synthesis and characterization of a series of hitherto unknown
[ArO-SO(CF3)dNTf] compounds. The X-ray structure of MesO-SO(CF3)dNTf (Mes ) mesityl) is
reported. On the basis of extraction studies, suitable solvent systems have been identified that remove
the products without dissolving [BMIM][NTf2], thus overcoming product recovery difficulties typically
associated with the use of this IL.
Introduction
situ in the IL, by using nitrosonium salts. Immobilization of
[ArN2][BF4] in [EMIM][CF3COO], [EMIM][OTs], and [EMIM]-
[OTf] resulted in metathesis, and subsequent dediazoniation gave
the corresponding esters (nucleophile trapping products) ArO-
COCF3, ArOTs, and ArOTf, with little or no ArF being
observed.
Ionic liquids (ILs), in particular imidazolium ILs, bearing
[Tf2N] counterion (1) have attracted recent interest due to their
exceptional properties that combine hydrophobicity with low
We have previously reported1 that arenediazonium tetrafluo-
roborates can be dissolved/immobilized in imidazolium ionic
liquids (ILs) [EMIM][BF4] (1-ethyl-3-methylimidazolium tet-
rafluoroborate) and [BMIM][PF6] (1-butyl-3-methylimidazolium
hexafluorophosphate), and subsequently undergo fluorodedia-
zoniation upon heating, to give ArF in very high yield and
selectivity. It is also possible to generate the diazonium salt in
* Address correspondence to this author. Fax: 330-6723816. Phone: 330-
6722988.
(2) Bonhote, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundram, K.;
(1) Laali, K. K.; Gettwert, V. J. J. Fluorine Chem. 2001, 107, 31-34.
Graetzel, M. Inorg. Chem. 1996, 35, 1168-1178.
10.1021/jo0708801 CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/01/2007
6758
J. Org. Chem. 2007, 72, 6758-6762

[ArO-SO(CF3)dNTf] and N-Aryltriflimides Ar-N(Tf)2
melting points, thermal and electrochemical stability, low
viscosity, and high conductivity.2-4
Since HN(Tf)2 is a remarkably strong Brønsted acid with a
pKa (in acetic acid) comparable to that of H2SO4,5 its perflu-
orinated conjugate base is expected to be highly inert, possessing
little or no coordinating and nucleophilic characteristics.
An exception to its noncoordinating nature was the finding
that it coordinates to Yb2+.6 A qualitative sequence of cation/
anion association tendencies was derived recently by Chiappe
and associates7 for a group of ammonium and imidazolium
cations bearing various counterions including [OTf], [PF6], and
[Tf2N] by using ESI-MS, based on MS/MS measurements on
mixed complexes. This work demonstrated that [Tf2N] was the
least interacting anion among the counterions studied. Whereas
dediazoniation of PhN2+ BF4- (1a) in a 1:1 mixture of [BMIM]-
[Br] and [BMIM][PF6] gave only PhBr, the same reaction in
[BMIM][Br] and [BMIM][Tf2N] (1:1) gave the Tf2N trapping
products.8 It was suggested that this stems from differences in
metathesis and pre-association abilities of different anions, which
infer that the following process (eq 1) is highly efficient:
FIGURE 1. Dediazoniation products in [BMIM][Tf2N].
formed via thermal dediazoniation was reported to be variable
depending on solvent, temperature, and reaction time.10
The metathesis approach in imidazolium ILs, as shown in
our earlier work,1 makes it possible to tailor-make diazonium
salts for various studies and eliminates the need for independent
synthesis and isolation of targeted salts.
Parent N-phenyltriflamide and some of its ring-substituted
derivatives have been known in the literature since the early
studies of Hendrickson and Bergeron11a,b and Yagopolskii and
associates11c,d on the synthesis of triflamides via the conjugate
base of amines and Tf2O. Whereas parent PhN(Tf)2 is com-
mercially available, the ring-substituted derivatives are unavail-
able. As for the [ArO-SO(CF3)dNTf] class of compounds, no
published synthetic methods are available. Therefore, access to
these compounds via dediazoniation protocol, starting from
readily available aryldiazonium tetrafluoroborates in [BMIM]-
[Tf2N], represents a useful and remarkably simple approach.
In continuation of our studies focusing on onium ion
chemistry and electrophilic aromatic substitution in ionic
liquids,1,12-17 and inspired by recent work of Chiappe,7,8 and
earlier studies by DesMarteau10 and Yagupolskii,9 we have
performed a substituent effect study on dediazoniation to explore
the O- versus N-trapping product dependency, under both
thermal and photolytic conditions, by NMR monitoring. In the
context of this study, we have synthesized and characterized
several hitherto unknown [ArO-SO(CF3)dNTf] compounds (3)
(Figure 1), and have determined the X-ray structure for MesO-
SO(CF3)dNTf (3g). Relative stabilities of the O- versus
N-trapping products were also investigated by the DFT (Density
Functional Theory) method for 2a and 3a (Ar ) Ph).
[ArN2][BF4] + [EMIM][Tf2N] f
[ArN2][Tf2N] + [EMIM][BF4] (1)
Phenyldiazonium bis(trifluoromethylsulfonyl)amide was pre-
viously synthesized and isolated by Yagupolskii et al.9 via the
following reaction (eq 2):
PhN2+ Cl- + XN(SO2CF3)2 f
PhN2+ -N(SO2CF3)2 + XCl (X ) H or Na) (2)
Upon heating, N-(trifluoromethylsulfonyl)phenoxytrifluoro-
methylsulfoximine (3a) and PhN(Tf)2 (2a) were formed in ca.
12:1 ratio. The same approach was used by Zhu and DesMar-
teau,10 who prepared the parent (R ) H) as well as the p-F and
p-OH diazonium salts. The ratio of O versus N trapping products
Whereas the widely utilized [BMIM] and [EMIM] ILs with
TfO and BF4 counterions are insoluble in Et2O, allowing phase
separation and easy workup, the corresponding [Tf2N] ILs are
soluble, not only in ether but also in a host of other organic
solvents, and this creates practical difficulties for product
removal from the IL. This problem has been addressed and
(3) Oldham, W. J., Jr.; Costa, D. A.; Smith, W. H. In Ionic Liquids,
Industrial Applications to Green Chemistry; Rogers, R. D., Seddon, K. R.,
Eds.; ACS Symp. Ser. No. 818; American Chemical Society: Washington,
DC, 2002; Chapter 15.
(4) Anthony, J. L.; Brennecke, J. F.; Holbery, J. D.; Maginn, E. J.; Mantz,
R. A.; Rogers, R. D.; Trulove, P. C.; Visser, A. E.; Welton, T. In Ionic
Liquids in Synthesis; Wasserscheid, P., Welton, T., Eds.; Wiley-VCH:
Weinheim, Germany, 2003; Chapter 3.
(11) (a) Hendrickson, J. B.; Bergeron, R. Tetrahedron Lett. 1973, 4607-
4610. (b) Hendrickson, J. B.; Bergeron, R. Tetrahedron Lett. 1973, 3839-
3842. (c) Gandel’sman, L. Z.; Dronkina, M. I.; Nazaretyan, V. P.;
Yagupol’skii, L. M. Zh. Org. Khim. 1972, 8, 1659-1662; CA 77:139555.
(d) Yagupol’skii, L. M.; Gandel’sman, L. Z.; Nazaretyan, V. P. Zh. Org.
Khim. 1974, 10, 889-890; CA 81:25298. (e) Gandel’sman, L. Z.;
Yagupol’skii, L. M. Ukr. Khim. Zh. 1975, 41, 640-642; CA 83:78784.
(12) Sarca, V. D.; Laali, K. K. Green Chem. 2006, 8, 615-620.
(13) Laali, K. K.; Sarca, V. D.; Okazaki, T.; Brock, A.; Der, P. Org.
Biomol. Chem. 2005, 3, 1034-1042.
(14) Sarca, V. D.; Laali, K. K. Green. Chem. 2004, 6, 245-248.
(15) Laali, K. K.; Borodkin, G. I. J. Chem. Soc., Perkin Trans. 2 2002,
953-957.
(16) Laali, K. K.; Gettwert, V. J. J. Org. Chem. 2001, 66, 35-40.
(17) Laali, K. K. In Ionic Liquids in Organic Synthesis; ACS Symp.
Ser. No. 950; Malhotra, S. V., Ed.; American Chemical Society: Wash-
ington, DC, 2007; pp 16-27.
(5) (a) Vij, A.; Kirchmeier, R. L.; Shreeve, J. M.; Verma, R. D. Coord.
Chem. ReV. 1997, 158, 413-432. (b) Foropoulos, J., Jr.; DesMarteau, D.
D. Inorg. Chem. 1984, 23, 3720-3723.
(6) Mudring, A.-V.; Babai, A.; Arenz, S.; Giernoth, R. Angew. Chem.,
Int. Ed. 2005, 44, 5485-5488.
(7) Bini, R.; Bortolini, O.; Chiappe, C.; Pieraccini, D.; Siciliano, T. J.
Phys. Chem. B 2007, 111, 598-604.
(8) Bini, R.; Chiappe, C.; Marmugi, E.; Pieraccini, D. Chem. Commun.
2006, 897-899.
(9) Haas, A.; Yagupol’skii, Y. L.; Klare, C. MendeleeV Commun. 1992,
70.
(10) Zhu, S.-Z.; DesMarteau, D. D. Inorg. Chem. 1993, 32, 223-226.
J. Org. Chem, Vol. 72, No. 18, 2007 6759

Laali et al.
TABLE 1. Dediazoniation Outcomes, Product Ratios, and Yields for Thermal Decomposition of Diazonium Salts in [BMIM][NTf2]a
products distribution
2:3:4 (%)b
diazonium
salt 1
temp
(°C)
reaction
time
conversion
of 1 (%)
after recovery
from ILd
yields
(%)c
in IL
a: R ) H
rt
2 days
13 min
1 h
2.5 h
13 h
2 days
2 h
13 h
22.5 h
1 day
1 day
12 h
27 h
14 min
13 min
32
100
85
100
100
0
7:93:-
6:84:19
8:70:22
7:74:19
5:66:29
90
90
90
90
rt
50
90
90
70
80
90
4:96:-e
36
36
b: R ) p-Clf
10:90:-g
c: R ) p-Br
0
100
100
0
31
84
100
100
100
5:72:23
6:80:14
8:92:-e
61
29
d: R ) m-NO2
e: R ) p-CH3O
14:86:-e
-:-:trace
-:-:trace
-:-:trace
4:84:12
f: R ) p-t-Bu
g: R ) 2,4,6-trimethyl
90
90
3:97:-e
1:99:-h
64
56
2:72:26
a Reaction condition: 0.12 mmol of 1; 0.60 mmol of IL. b By NMR. c Amount of crude mixture of products after recovery from IL. d Extraction with
hexane-ether (19:1) and evaporation at rt under reduced pressure. e Colorless oil. f Reaction condition: 0.24 mmol of 1; 1.20 mmol of IL. g Pale-yellow oil.
h Pale-pink crystals.
resolved in the framework of this study, by identifying solvents
that selectively extract the products without dissolving the IL.
Information show the proton and fluorine NMR spectra,
following the completion of dediazoniation and prior to extrac-
tion (with signals due to the products 2b and 3b marked on the
spectrum and on the inset; traces of 4b are also detectable).
Product recovery tests (for a more complete list and outcomes
see Table S1 in the Supporting Information) were performed
with CS2, and with hexane-ether mixtures (in 1:1, 8:2, and
19:1 ratios) (2 × 1 mL). It was confirmed that CS2 could extract
the products with negligible contamination with the IL. Simi-
larly, the NMR spectrum of the IL phase following product
extraction with hexane-ether (19:1) showed no detectable peaks
due to products.
Figures S4 and S5 (Supporting Information) illustrate the
proton and fluorine NMR spectra of the reaction mixture
following extraction with hexane/ether (19:1), and after solvent
removal under reduced pressure. It is noted that a trace of 4b,
observed in the reaction mixture prior to extraction, is no longer
present after extraction and solvent removal. Loss of the volatile
4b was also corroborated based on material balance, and from
relative NMR integrals before and after dediazoniation, which
also implied partial decomposition of 2b/3b under thermal
dediazoniation.
Results and Discussion
NMR Monitoring of Dediazoniation in [BMIM][Tf2N]. (a)
Initial Studies and Search for Suitable Solvents for Product
Recovery from IL. Parent 1a underwent slow dediazoniation
at room temperature to give 2a and 3a in 1:13 ratio, with 68%
of 1a remaining unreacted after 2 days. Dediazoniation pro-
ceeded to completion when the sample was briefly heated to
ca. 70 °C (for just 15 min), at which point the 2a:3a ratio was
1:14.
By using Et2O (the most commonly employed solvent for
preparative chemistry in ILs), the products were completely
extracted, but the ether layer contained significant amounts of
the IL. Product extraction with hexane (a solvent that does not
dissolve the IL) was only effective/acceptable when several
extractions were performed and the extracts were combined.
These initial tests underscored the need for finding suitable
solvents for extraction and product recovery, without dissolving/
removing the IL.
Diazonium salt 1c was immobilized in [BMIM][NTf2] and
heated by ca. 70 °C for 2 h. At this point, dediazoniation was
complete and the 2c to 3c ratio was 1:22. Suitability of tert-
butyl methyl ether, benzene, nitromethane, and CS2 as potential
solvents for extraction was tested. With t-BuOMe the organic
extract contained significant amounts of the IL. Benzene
appeared more suitable, but still removed some of the IL.
MeNO2 was miscible with the IL and gave just one phase, but
CS2, on the other hand, was able to extract the products with
no contamination from the IL.
(b) Larger Scale Dediazoniations and Product Recovery.
Following the above-mentioned exploratory experiments (on
3-5 mg scale), dediazoniation of 1b in [BMIM][NTf2] was
carried out on a larger scale (500 mg) (with 1b: IL molar ratio
of 1:5). Figure S1 in the Supporting Information shows the 1H
NMR spectrum at the onset, prior to dediazoniation (signals
due to the IL and the diazonium ion are marked on the spectrum
and on the inset). The immobilized diazonium salt was heated
at 90 °C for 2.5 h. Figures S2 and S3 in the Supporting
Based on a number of test studies, hexane/ether (19:1) was
selected as the optimal solvent system for workup, and the
method was used for product isolation in subsequent runs.
Table 1 summarizes the product ratios at various intervals
(in the IL before extraction and after extraction and product
recovery) for the thermal dediazoniation of diazonium tetrafluo-
roborate salts 1a through 1g, immobilized in [BMIM][Tf2N].
Isolated product yields were typically in the 30-60% range,
depending on the diazonium salt. NMR monitoring of the
progress of dediazoniation in the IL, and product analysis before
and after extraction, indicated that all dediazoniations were
heterolytic (absence of any detectable ArH),18 and that aryl
cation trapping by [Tf2N] anion was very predominant relative
to Schiemann product (ArF) formation, irrespective of the
substituent on the diazonium ion. These findings are in concert
with earlier dediazoniation studies in ILs.1
(18) Zollinger, H. In Diazo Chemistry I; VCH: Weinheim, Germany,
1994; Chapter 8.
6760 J. Org. Chem., Vol. 72, No. 18, 2007

[ArO-SO(CF3)dNTf] and N-Aryltriflimides Ar-N(Tf)2
TABLE 2. Dediazoniation Outcomes, Product Ratios, and Yields for Photolytic Decomposition of Selected Diazonium Salts in [BMIM][NTf2]a
products distribution
2:3:4 (%)c
diazonium
salt 1
temp
(°C)
reaction
timeb
conversion
of 1 (%)
after recovery
from ILe
yields
(%)d
in IL
b: R ) p-Cl
rt
rt
rt
rt
rt
10 df
100
100
100
100
87
6:77:17
4:86:10
3:64:33
2:86:12
8:64:28
7:93:-g
38
12
<5
32
d: R ) m-NO2
e: R ) p-OMe
f: R ) p-t-Bu
1.5 dh
18:82:-g
4 df + 4 hh
9.5 hh
18:82:-g
8:92:-g
3 hh
41
a Reaction condition: 0.12 mmol of 1; 0.60 mmol of IL. b d (day); h (hour). c By NMR. d Amount of crude mixture of products after recovery from IL.
e Extraction with hexane-ether (19:1) and evaporation at rt under reduced pressure. f 0.2 W low-pressure mercury lamp. g Pale-yellow oil. h 15 W low-
pressure mercury lamp.
In thermal dediazoniations described, nucleophilic trapping
by the [Tf2N] anion resulted in predominant formation of [ArO-
SO(CF3)dNTf] over the alternative ArN(Tf)2, and preference
for trapping at oxygen over trapping at nitrogen remained
+
unchanged by changing the nature of the substitutents on PhN2
(electron withdrawing or donating).
(c) Tf2N-Derived Product Ratios Under Photolytic De-
diazoniation. To determine whether preference for trapping at
oxygen could change if dediazoniations were effected at room
temperature under photolytic conditions19 (by UV irradiation),
diazonium salts 1b, 1d, 1e, and 1f were immobilized in [BMIM]-
[Tf2N] and subjected to UV irradiation in quartz NMR tubes.
As in earlier cases, dediazoniation progress was monitored
directly by NMR. Product ratios were determined in each case
after specified intervals, both prior to extraction (directly in the
IL) and after product recovery (data summarized in Table 2).
The corresponding [ArO-SO(CF3)dNTf] compounds were
found to be the major product in every case, whereas ArN(Tf)2
compounds were consistently present in minor amounts. As
FIGURE 2. Thermal ellipsoid plot of 3g (ellipsoids are drawn at the
observed in the thermal reactions, the corresponding ArF was
also formed in minor amounts (detected in the reaction mixtures
prior to workup). The use of very low power UV source (a 0.2
W low-pressure mercury lamp used in the laboratory to visualize
spots in TLC) in the case of 1b (a diazonium salt whose thermal
dediazoniation was relatively slow) resulted in very slow
dediazoniation. After 10 days 1b had fully reacted. The [Tf2N]-
derived products were obtained in 38% isolated yield (in 93:7
ratio). Dediazoniation rates were accelerated when a higher
power UV lamp was employed. For example, in the case of 1f
(R ) t-Bu) NMR monitoring indicated that after 3 h, only 13%
unreacted diazonium salt was present in the reaction mixture.
Under photolytic conditions, and with the more powerful UV
lamp, shorter reaction times resulted in higher isolated yields
as compared to longer reactions, suggesting that prolonged
irradiation resulted in product degradation. This problem was
especially significant in the case of 1e (p-OMe).
Strong preference for trapping at oxygen versus nitrogen was
therefore also established in photolytic dediazoniations in the
IL. The presence of the corresponding Schiemann products
(ArF) and absence of the protio-dediazoniation products (ArH)
(at the NMR detection limit) argue in favor of heterolytic
dediazoniation for both thermal and photolytic dediazoniation
reactions in the IL.
50% level).
products 4a-g1,21 agree with the reported data in the literature.
NMR data for 2d11c and 2e11d,e are also included. As can be
seen in the representative NMR spectra (Supporting Informa-
tion), 19F NMR provides the simplest and most direct assay for
monitoring the evolution of Tf2N-derived products upon de-
diazoniation, with [ArO-SO(CF3)dNTf] exhibiting two well-
resolved singlets (1:1 ratio) and ArN(Tf)2 a slightly more
deshielded singlet (see Figure S5, Supporting Information).
(d) X-ray Structure of 3g. The novel MesO-SO(CF3)dNTf
product 3g, formed via thermal dediazoniation of diazonium
salt 1g in the IL, was isolated as pale pink crystals, and its X-ray
structure was determined. The thermal ellipsoid plot is shown
in Figure 2 (for detailed structural data see the Supporting
Information). The two N-S bonds are noticeably short [1.493-
(7) Å] and long [1.625(6) Å]. The Ar-O-SO angle is 120.7-
(4)°. Bond angles for N-SO2-CF3, NdSO2-CF3, and the
S-N-S moieties are 100.9(3)°, 105.8(4)°, and 127.9(4)°
respectively.
(e) DFT Calculations. To get a handle on relative product
stabilities, the Tf2N-derived products 2a and 3a were calculated
(20) (a) Shainyan, B. A.; Tolstikov, L. L.; Zhinkin, A. R. Russ. J. Org.
Chem. 2003, 39, 1180-1182. (b) Dantzig, A. H.; Grese, T. A.; Norman,
B. H.; Palkowitz, A. D.; Sluka, J. P.; Starling, J. J.; Winter, M. A. EP
773217; CA 127:50535.
Table S2 in the Supporting Information summarizes the
multinuclear NMR data (1H, 13C, and 19F) as well as IR data
for the Tf2N-derived products synthesized in this study. Spectral
data for 2a,10,20a 3a,9,10 2c,20b and the corresponding ArF
(21) (a) Pouchert, C. J.; Behnke, J. The Aldrich library of 13C and H
1
FT NMR spectra; Aldrich Chemical Co.: Milwaukee, WI, 1993. (b) Stavber,
S.; Zupan, M. J. Org. Chem. 1985, 50, 3609-3612. (c) Stavber, S.; Zupan,
M. J. Org. Chem. 1983, 48, 2223-2226. (d) Laali, K. K.; Borodkin, G. L.
J. Chem. Soc., Perkin Trans. 2 2002, 953-957.
(19) See Chapter 10 in ref 18.
J. Org. Chem, Vol. 72, No. 18, 2007 6761

Laali et al.
cation via dediazoniation, which is opposite to the relative
thermodynamic stabilities of the two types of products.
Summary
Immobilization of the readily available diazonium tetrafluo-
roborates in [BMIM][Tf2N] and subsequent dediazoniation
provided a simple and practical one-pot approach for the
synthesis of the Tf2N-derived products. Despite the “nonnu-
cleophilic” and “noncoordinating” nature of the [Tf2N] anion,
nucleophilic quenching products were predominantly formed,
with relatively minor formation of the Schiemann product.
Oxygen-trapping product was greatly favored over N-trapping
product, irrespective of the substituents, and this preference was
observed in both thermal and photolytic dediazoniation reactions.
The 19F NMR provided the most convenient tool for monitoring
the dediazoniation progress and the evolution of the products.
DFT calculations at various basis sets showed that PhO-SO-
(CF3)dNTf is consistently less stable than ArN(Tf)2. The X-ray
structure of MesO-SO(CF3)dNTf provided the first glance into
the structure of this class of molecules. Compound 1g and
related compounds, bearing other carbocation stabilizing groups
on the aryl ring, represent intriguing probes for solvolytic
studies, especially in ILs. Studies focusing on these aspects are
ongoing in our laboratory.
FIGURE 3. Optimized structures for 2a and 3a by B3LYP/6-31G(d).
by DFT at various basis sets and the data are gathered in Table
S5 (Supporting Information). Compound 2a is 16.0 kcal/mol
more stable than 3a at the B3LYP/6-31G(d) level. The computed
lowest energy structure for 3a has a different conformation as
compared to the X-ray geometry, which was calculated to be
slightly less stable. The order of stability is similar at B3LYP/
6-31++G(d,p) and B3LYP/6-311++G(d,p) levels. The opti-
mized structures are shown in Figure 3.
The dielectric constant (ꢀ ) 11.6) has been measured for
[BMIM][NTf2].22 Since the dielectric constants for CH2ClCH2-
Cl and acetone are 10.36 and 20.7, respectively, and these
solvents are available for PCM (polarizable continuum models)
calculations in the Gaussian 03 program, solvation effects in
the two solvents were estimated by PCM. The dielectric constant
of acetone is larger than that of [BMIM][NTf2], and it was
anticipated that it could result in overestimation of the solvation
effect. Nevertheless, relative stability differences between 2a
and 3a were not affected by this test.
Supporting Information Available: Experimental section, 1H
and 19F NMR spectra of reaction mixtures and products (Figures
S1-S15), results of product recovery studies from the ionic liquid
(Table S1), multinuclear NMR and IR data (Table S2), data
collection parameters (Table S3), selected bond distances and angles
for 3g from X-ray analysis (Table S4), computed energies (Table
S5), and Cartesian coordinates for optimized structures by the DFT
calculations (Tables S6-S11); the X-ray crystallographic file in
CIF format for 3g, also available from the Cambridge Data Base
under CCDC 645183. This material is available free of charge via
the Internet at http://pubs.acs.org.
Clearly, the observed strong preference for oxy-anion trapping
is related to the kinetics of nucleophilic quenching of the aryl
(22) Krossing, I.; Slattery, J. M.; Daguenet, C.; Dyson, P. J.; Oleinikova,
A.; Weinga¨rter, H. J. Am. Chem. Soc. 2006, 128, 13427-13434.
JO0708801
6762 J. Org. Chem., Vol. 72, No. 18, 2007