Maleimide-modified phosphonium ionic liquids: A template towards (multi)task-specific ionic liquids

Article abstract of DOI:10.1002/chem.200902610

The synthesis and characterization of several compounds representing a new class of multitask-specific phosphonium ionic liquids that contain a maleimide functionality is reported. The maleimide moiety of the ionic liquid (IL) is shown to undergo Michael-type additions with substrates containing either a thiol or amine moiety, thus, serving as a template to introduce wide structural diversity into the IL. Multitask-specific ILs are accessible by reaction of the maleimide with Michael donors that are capable of serving some function. As a model example to illustrate this concept, a redox active ferrocenyl thiol was incorporated and examined by cyclic voltammetry. Because the maleimide moiety is highly reactive to additions, the task-specific ionic liquids (TSILs) are prepared as the furan-protected Diels-Alder maleimide. The maleimide moiety can then be liberated when required by simple heating.

Full text of DOI:10.1002/chem.200902610

DOI: 10.1002/chem.200902610
Maleimide-Modified Phosphonium Ionic Liquids: A Template Towards
(Multi)Task-Specific Ionic Liquids
Jocelyn J. Tindale,[a] Kurtis D. Hartlen,[a] Abdolhamid Alizadeh,[b]
Mark S. Workentin,*[a] and Paul J. Ragogna*[a]
Abstract: The synthesis and characteri-
zation of several compounds represent-
ing a new class of multitask-specific
phosphonium ionic liquids that contain
a maleimide functionality is reported.
The maleimide moiety of the ionic
liquid (IL) is shown to undergo Mi-
chael-type additions with substrates
introduce wide structural diversity into
the IL. Multitask-specific ILs are acces-
sible by reaction of the maleimide with
Michael donors that are capable of
serving some function. As a model ex-
ample to illustrate this concept, a
redox active ferrocenyl thiol was incor-
porated and examined by cyclic vol-
tammetry. Because the maleimide
moiety is highly reactive to additions,
the task-specific ionic liquids (TSILs)
are prepared as the furan-protected
Diels–Alder maleimide. The maleimide
moiety can then be liberated when re-
quired by simple heating.
Keywords: high-pressure chemistry ·
ionic liquids · maleimide · Michael
addition · phosphonium
containing either
a thiol or amine
moiety, thus, serving as a template to
Introduction
such as ILs that act as ligands for transition-metal cata-
lysts,[2] or capture agents for CO2 and heavy metals.[4]
[3]
Recent advances in the synthesis and development of novel
ionic liquids (ILs) have diverged from their conventional
predecessors, such as N-alkylated imidazolium salts, to focus
on producing task-specific ionic materials. The initial con-
cept and the corresponding definition of a task-specific ionic
liquid (TSIL) was first proposed by J. H. Davis, Jr. who de-
fined TSILs as an organic salt that has a covalently bound
functional group on the cation and/or anion, and behaves
not only as the reaction medium, but serves secondary func-
tion, for example, as a reactant, or a catalyst.[1] The structur-
al design and functionality of the organic salt imposes the
desired property or characteristic for the intended purpose,
Task-specific ionic liquids do not need to be limited to mole-
cules that fit the initial description given by Davis, Jr., but
rather can include any molecule that exhibits the defining
properties of an ionic liquid, such as melting point below
1008C, negligible vapor pressure, large liquid range, and
most importantly, contains a covalently bound substituent,
which performs any function for a target application. Thus,
any ionic liquid synthesized for a specific application may
be deemed a TSIL even though it may not necessarily be
used as the reaction medium or solvent. Examples include
functionalized salts that act as reactive precursors for func-
tional materials, such as thiol-terminated phosphonium ionic
liquids (PILs) for superhydrophobic coatings[5] or disulfide-
tethered imidazolium salts, which are used to form IL-pro-
tected Au nanoparticles.[6]
[a] J. J. Tindale, K. D. Hartlen, Prof. M. S. Workentin, Prof. P. J. Ragogna
Department of Chemistry
In the aforementioned examples, each TSIL was separate-
ly synthesized for the required task, which can often be a
complicated and time consuming process. A more practical
approach is to prepare an ionic liquid that contains a func-
tional group moiety that is reactive towards a broad variety
of substrates, which can then be utilized as a template to in-
troduce task-specific functionality from a single starting ma-
terial.[7] Task-specific ionic liquids that bear a reactive hy-
droxyl functional group, pioneered by Bazureau et al.[8] and
further extended by others,[7,9] exploited this type of concept
and developed TSILs as liquid supports for ionic-liquid-
The University of Western Ontario
1151 Richmond St. London, ON, N6A 5B7 (Canada)
Fax : (+1)519-661-3022
E-mail: mworkent@uwo.ca
pragogna@uwo.ca
[b] Prof. A. Alizadeh
Current address
Department of Chemistry, Razi University
Kermanshah (Iran)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902610.
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FULL PAPER
phase organic synthesis; a methodology that is analogous to
solid-support synthesis.
functionalized phosphonium ionic liquids, which can be uti-
lized as TSIL. Given the maleimide renders the material
available for further reactivity, such as Michael addition re-
action, the maleimide PIL subsequently behaves as a tem-
plate, which enables the synthesis of a library of TSILs.
With a particular focus on the Michael addition reaction, we
demonstrate a facile and an unprecedented method for the
preparation of highly functionalized ionic liquids. Ionic liq-
uids based on the phosphonium cation were used herein for
their higher thermal and chemical stability and to showcase
their potential in alternative applications.
An alternative and versatile reactive moiety that could be
incorporated into the structure of an IL to serve as a tem-
plate TSIL, which is presented in this work, is the N-substi-
tuted maleimide. Maleimide is a cyclic unsaturated imide
and has a symmetrical and activated double bond that can
act as a dienophile in [4+2] cycloaddition reactions, as a di-
polarophile in [3+2] cycloaddition reactions, as well as an
electrophile in Michael-type addition reactions (Scheme 1).
One of the shortcomings of maleimide-modified reagents
is the poor storage capability, given its highly reactive
nature to Michael addition reactions with nucleophiles.
Based on a method by Workentin et al. previously employed
to modify monolayer-protected gold nanoparticles,[12] malei-
mide can be stored as its Diels–Alder-protected furan deriv-
ative, which releases the desired maleimide by simple heat-
ing. Such strategies, taking advantage of the reversibility of
the maleimide–furan Diels–Alder reaction, has been used
for the preparation of thermally responsive polymers and
dendrimers.[13] Here the reversible Diels–Alder reaction is
used simply as a maleimide protecting group. Upon depro-
tection, if the Michael addition reaction utilizes a donor sub-
stituent, which itself can perform a particular function, such
as a ferrocenyl thiol that acts as an electrochemical tag, the
maleimide-modified PIL then functions as a multitask spe-
cific IL as demonstrated herein.
Scheme 1. Schematic representation of
that participates in Michael addition (top) and Diels–Alder (bottom) re-
actions.
a maleimide-functionalized IL
By incorporating the maleimide moiety into the structure of
an IL its wide reactivity allows one to incorporate additional
functionality for specific tasks as required. The reaction of
particular interest here, as proof of concept, is the Michael
addition reaction. Michael additions to maleimides are often
high yielding and versatile because maleimides react with a
variety of nucleophiles (thiols, amines, carbanions) that can
be used to incorporate structural diversity from a single IL
platform, circumventing the tedious synthesis of a unique IL
for each task. The versatility is such that many maleimide-
modified reagents are sold commercially. They are mostly
incorporated as thiol-reactive dyes to prepare fluorescent
peptides, proteins, and oligonucleotides for probing biologi-
cal structure and function. A number of research groups
Results and Discussion
The first approach to prepare the maleimide-tethered phos-
phonium salts 3a and 3b involved the quaternization of tri-
n-butylphosphine with N-(bromobutyl)maleimide. However,
characterization of the resulting product displayed evidence
for the Michael addition of the nBu3P across the C=C of the
maleimide (31P{1H} NMR: d=17 ppm).[14] An alternate pro-
cedure, in which the maleimide moiety was first protected as
its furan Diels–Alder product was selected in order to avoid
these complications.
[10]
have also anchored maleimide moieties onto flat SiO2 and
Au self-assembled monolayers (Au/SAMs)[11] to serve as
traps for thiols by the Michael addition reaction. Thiols and
amines are the primary nucleophiles that are used in the for-
mation of biochip assemblies on SiO2 and Au/SAMs. For ex-
ample, biomolecules,[11a,b] carbohydrates,[11c,d] as well as a
number of peptides have been used.[11e]
As far as we are aware, there are no reports for the prep-
aration of maleimide-modified ILs, and incorporating this
versatile and reactive functionality into the ionic framework
is an attractive concept specifically for the formation of
TSILs. In this context, tethering maleimide to a phosphoni-
um salt can alter the solubility properties of the system and
combines the benefits of ionic liquids, such as large electro-
chemical windows, negligible vapor pressures, and high ther-
mal stabilities, with multifaceted functionality. Herein, we
describe the synthesis and characterization of maleimide-
Specifically, and as illustrated in Scheme 2, to encourage
the formation of a phosphonium salt by an SN2 mechanism,
the maleimide was protected with furan through a Diels–
Alder cycloaddition in a sealed tube at 908C. This substrate
was then converted to compounds 1a and 1b by reaction
with the corresponding 1,4-dibromobutane (a) or 1,12-dibro-
mododecane (b) in DMF with potassium carbonate. After
the addition of 1a or 1b to a solution of tri-n-butylphos-
phine the quaternization reaction proceeded, which was
monitored by 31P{1H} NMR spectroscopy. Upon complete
consumption of nBu3P (31P{1H} NMR: d=À32 ppm), the
solvent was removed in vacuo. Characterization of the re-
sulting yellow viscous liquid by multinuclear NMR spectros-
copy displayed the distinctive phosphonium chemical shift
(31P{1H} NMR: d=33 ppm vs. d
(nBu4P+)=32 ppm),[15] which
ACHTUNGTRENNUNG
in conjunction with mass spectrometry and elemental analy-
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M. S. Workentin, P. J. Ragogna et al.
Scheme 2. Synthetic route for the preparation of maleimide-modified
phosphonium ionic liquids.
sis confirmed the presence of the furan-protected phospho-
nium salts 2a and 2b. The salts were isolated in good yields
(81–86%) and no further purification was required. Subse-
quently, 2a and 2b were dissolved in DMF and heated to
1008C in an open vial for ꢀ18 h to deprotect the maleimide
by liberating furan, which easily dissipated, to yield 3a and
3b. Proton NMR spectroscopy of 3a and 3b revealed the
complete disappearance of signals that correspond to those
of alkenyl and bridgehead protons associated with the
furan–maleimide Diels–Alder adduct (1H NMR: d=5.52,
5.21, 2.90 ppm) and the emergence of the alkenyl protons
on the maleimide (1H NMR: d=5.72 ppm), thus, confirming
that the retro-Diels–Alder reaction proceeded quantitatively
yielding the deprotected maleimide phosphonium salts 3a
and 3b.
Table 1. Thermal characteristics of the phosphonium ionic liquids.
Entry
PIL
Tg [8C][a]
Td [8C][b]
TMA [8C][c]
1
2
3
4
5
6
7
8
2a
2b
3a
4a
5a
3b
4b
5b
112[d]
À42
À36
À24
À49
À35
À40
À35
134[e] 365
132[e] 374
365
254
224
194
242
296
216
241
291
395
440
373
426
446
[a] Onset of glass transition. [b] Onset of decomposition. [c] TMA =onset
temperature for the Michael addition. [d] Melting point. [e] Onset tem-
perature for retro-Diels–Alder reaction.
Given that the melting point and other physical properties
of ionic liquids can be tuned by exchanging the cation–anion
pair, several counter anions were incorporated by using met-
athetical routes. Anion exchange of 3a and 3b was carried
out by using LiOTs or LiNTf2 (OTs=p-toluenesulfonate,
NTf2 =bis(trifluoromethanesulfonyl)imide) in acetone or
methanol to afford the corresponding products 4a and 4b
and 5a and 5b. The metathesis of 2a and 2b followed by
the thermal deprotection to yield 4a and 4b or 5a and 5b
was complicated because the high temperatures prompted
the Michael-type addition between the anion and the malei-
mide upon release of the furan. Evidence for this addition
liquids with glass transitions ranging from À24 to À498C.
There were no crystallization or melting points observed for
the viscous liquids indicating that the materials were com-
pletely amorphous. The salt 2a was the only exception. At
room temperature the material is a waxy solid and exhibits
a melting point slightly greater than 1008C. Thermogravi-
metric analysis studies by using heat ramp analysis depicted
decomposition temperatures ranging from 365 to 4468C,
suggesting the ionic liquids have excellent thermal stabilities.
Thermogravimetric analysis is also an exceptional tool to
observe the retro-Diels–Alder deprotection of the phospho-
nium salts 2. A step corresponding to 10–12% mass loss
(calculated: 13.58% (2a), 11.10% (2b); experimental: 12%
(2a), 10% (2b)) correlates to the liberation of furan. The
subsequent step clearly reflects the formation of the malei-
mide PIL and, given the onset temperature, occurs at exact-
ly the same temperature as the decomposition of the malei-
mide PIL 3 (Figure 1a, Table 1). The exchange of anions
does indeed effect the thermal properties of the PILs, espe-
cially in the case of 5 where the thermal stability is in-
creased by 708C (Table 1).
1
was observed by H NMR spectroscopy, which revealed the
loss of the alkenyl protons on the maleimide and the forma-
tion of the characteristic proton splitting pattern imposed by
the generation of the chiral center on the succinimide. Fur-
ther characterization and isolation of this adduct was not
pursued.
The essential thermal characteristics of the phosphonium
ionic liquids 2–5 were determined by differential scanning
calorimetry (DSC) and thermogravimetric analysis (TGA)
(Table 1). In all cases, the phosphonium salts were viscous
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Maleimide-Modified Phosphonium Ionic Liquids
FULL PAPER
Scheme 3. Schematic representation of the Michael addition reactivity of
3 with thiols and an amine (TBAF=tetra-n-butylammonium fluoride).
Figure 1. a) Comparison of TGA thermograms of 2 displaying the libera-
tion of furan followed by subsequent decomposition of the resulting de-
protected phosphonium salt and 3, the synthesized maleimide PILs;
b) DSC thermograms of 2–5 displaying the exotherm for Tg (a), Tm (b),
the Michael-type addition (c),and the decomposition (d).
hexanone (6) was synthesized by a Friedel–Crafts acylation
between ferrocene and 6-bromo-hexanoxyl chloride, which
was then converted to 7 in the presence of hexamethyldisi-
lylthiane. Proton NMR spectroscopy was used to assess the
formation of the ferrocenyl thiol 7, where the most salient
feature was the emergence of a triplet and an overlapping
doublet of triplets (1H NMR: d=1.44 and 2.55 ppm, respec-
tively) indicative of the thiol and the adjacent methylene
protons, thereby, conclusively revealing the generation of 7.
Preliminary assessment of the Michael addition reactivity
of 3 with hexanethiol at room temperature and atmospheric
pressure in CDCl3 was sluggish and required long reaction
times (60 h) to afford product 9. Increasing the reaction
temperature to 608C reduced the reaction time. Michael ad-
ditions and similar transformations are also known to expe-
rience acceleration at high pressures;[16] thus, hyperbaric
conditions were employed to prepare 8 and 11. Indeed, the
duration of the reaction was shortened significantly for the
ferrocenyl thiol 7 and dibenzylamine when the reactions
were carried out at 11 Katm (the default operating pressure
of our reactor). Evidence for the complete transformation
to the succinimide adducts 8 and 11 was easily revealed by
using 1H NMR spectroscopy, which established the disap-
pearance of the alkenyl protons and the appearance of the
distinctive proton splitting pattern enforced by the genera-
tion of the chiral center on the resulting succinimide. The
isolation of 8 involved the removal of the excess thiol by ex-
traction with hexane and 11 was merely subjected to high
vacuum at elevated temperatures (1008C) to remove the
The DSC experiments included heating the samples past
the decomposition temperatures to determine if any phase
transitions indicative of chemical transformations with zero
mass loss occurred. An exotherm was observed for com-
pounds 3–5 ranging from 200 to 3008C, which is indicative
of a Michael-type addition of the anion to the C=C on the
maleimide (Figure 1b, Table 1). This result, along with the
observations from the attempted anion exchange reactions
of 2, further suggests that Michael addition with the anion
occurs at elevated temperatures. The same type of exotherm
was noted for 2 in the DSC thermogram after the feature
representing the retro-Diels–Alder deprotection. Therefore
the salts 3–5 are only stable at temperatures less than 3008C
in the solid state and approximately 1208C in solution,
which nonetheless, is more than sufficient for most applica-
tions given that the maleimide is reactive, especially towards
Michael addition with sulfhydryl groups.
With the maleimide-tethered phosphonium ionic liquids 3
in hand, as proof of concept, we next investigated their reac-
tivity towards a few model thiol (7, hexanethiol, and ben-
ACHTUNGTRENNUNGzenethiol) and amine (dibenzylamine) nucleophiles to form
the corresponding Michael adducts 8–11 (Scheme 3). The 6-
ferrocene-hexanone-1-thiol (7) was synthesized to act both
as a Michael donor and as a probe on account of the exis-
tence of the electrochemically active center ferrocene. In
order to prepare such a complex, first 6-bromo-1-ferrocene-
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M. S. Workentin, P. J. Ragogna et al.
excess dibenzylamine, affording the viscous liquids in high
yields (80–99%) with no need for further purification.
Therefore, even sluggish nucleophiles were added efficiently
either by gentle heating or at high pressure to eliminate any
competing reactions where the anion acts as a nucleophile
at raised temperatures.
and E8=321 mV versus ferrocene given the lack of the
redox active BrÀ counterion. After each experiment the
system was calibrated against ferrocene/ferrocenium couple
set to 0.0 mV.
As an alternative to the conventional and high-pressure
methodologies employed to afford products, 8, 9, and 11 a
one-pot approach was selected for the synthesis of 10. This
was accomplished simply by heating neat 2a/b at 1008C in
the presence of the nucleophile, benzenethiol, for 30 h to
yield product 10. It should be noted that 2a and 2b are
solids at room temperature and upon heating to 1008C,
which activates the retro Diels–Alder reaction and liberates
furan, the resulting product 3 is a liquid. This ionic liquid is
then used as both the reaction medium, as well as a reagent
in classical TSIL fashion and participates in a Michael-type
addition with the nearby nucleophile. After extraction with
hexane product 10 was isolated in good yield (88%), show-
ing that a one pot approach may be employed as a more
practical way to afford Michael adducts.
The maleimide PIL is task-specific given its propensity to
react as a Michael acceptor. Nucleophiles, which are capable
of performing some function, for example, as an electro-
phore, fluorophore, or acid/base donor/acceptor, facilitate
the formation of multitask-specific ILs. The reaction of 3
with ferrocenyl thiol 7 produces 8 and introduces an electro-
active ferrocenyl group, illustrating this concept. Cyclic vol-
tammetry (CV) of 8 was used to verify the addition of the
ferrocenyl thiol 7 (Figure 2). Cyclic voltammetry of 1 mm
solutions of compound 8a and 8b in dichloromethane that
contain 0.1m tetrabutylammonium perchlorate (TBAP) as
the supporting electrolyte show reversible redox waves with
standard oxidation potentials of E8=255 and 253 mV, re-
spectively, relative to ferrocene (E8=0 mV). In comparison,
compound 3 has no significant redox activity with the excep-
tion of a broad irreversible oxidation due to the bromide
counterion in 3b. The oxidation of the BrÀ counterion gives
rise to the slightly broadened oxidative waves of 8a and 8b.
Comparatively, the CV of a 1 mm solution of the NTf2 salt
of 8b in CH2Cl2/0.1m TBAP has a sharper oxidative wave
Conclusion
The synthesis and characterization of maleimide-modified
phosphonium ionic liquids, which showcase a versatile plat-
form for the preparation of other ILs have been reported.
Subsequent formation of the succinimidyl PILs by Michael
addition with reactive nucleophiles clearly demonstrates the
feasibility of incorporating additional substituents into the
IL framework and reflects their capability to act as a task-
specific ionic liquid. Using the methodology of protecting
the maleimide fragment by employing Diels–Alder chemis-
try allows the storage of the PIL until further reactivity is
required.
A one-pot approach where the deprotection
through liberation of the furan to generate the maleimide in
the presence of a nucleophile to form the corresponding Mi-
chael adduct in a single step was also realized. The flexibili-
ty of the reactivity at the maleimide moiety allows the at-
tachment of fluorophores, electrophores, or biomolecules,
which may lead to further applications of these ILs as func-
tional materials in sensor technology. Such functionalities
and others may also alter the IL in order to improve the sol-
ubility or bioavailability. It is important to note that non-
composite IL sensors are novel commodities that remain
elusive in the literature and our methodology is conducive
to realizing such materials. The strategy employed here of
using a maleimide-tagged ionic liquid as a template for a
TSIL can be extended to other IL platforms easily and sev-
eral methods are currently under investigation, including
studies that explore the reactivity of dienophiles and 1,3-di-
poles with maleimide PILs in Diels–Alder and 1,3-cycload-
dition chemistry.
Experimental Section
The tri-n-butylphosphine was received from Cytec Industries and was dis-
tilled prior to use (0.01 Torr; 808C) and stored in a nitrogen-filled
MBraun Labmaster 130 glove box. The compounds 1,12-dibromodo
ACHTUNGTRENNUNGdec-
AHCTUNGTERGaNNUN ne, 1,4-dibromobutane, furan, silver p-toluenesulfonate (Aldrich), malei-
mide (Alfa Aesar), potassium carbonate, diethyl ether, and N,N-dime-
thylformamide (Caledon) were used as received. Lithium bis(trifluorome-
thanesulfonyl)imide (Fluka) was used as received and stored in the glove
box. The precursors to 2, including 6-endo/exo-tetrahydrophthalimide
and (3,6-endo/exo-tetrahydrophthalimide)bromoalkane, were prepared
by using modified literature procedures.[12b] All manipulations with phos-
phines were carried out in a nitrogen-filled MBraun Labmaster 130 glove
box or by using standard Schlenk techniques. The N,N-dimethylforma-
mide was dried by using an Innovative Technologies Inc. controlled at-
mospheres solvent purification system, which utilize dual-alumina col-
umns, and was collected under vacuum and stored under a nitrogen at-
mosphere in a Strauss flask. Deuterated solvents, [D3]chloroform and
[D6]acetone (Cambridge Isotope Laboratories) were stored over 4 ꢁ
sieves.
Figure 2. Cyclic voltammograms of the maleimide PIL 3b (blue) and the
ferrocenyl thiol Michael adducts 8a (orange), 8b (red) and the NTf2 salt
of 8b (green).
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Maleimide-Modified Phosphonium Ionic Liquids
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1
Solution H, 13C{1H} and 31P{1H} NMR spectra were recorded on a Varian
33.4 ppm (s); MS (ESI): m/z+ (%): 534.4 ([M+], 100), 1147.7 ([M2Br+],
17); m/zÀ (%): 699.9 ([MBr2À], 70).
INOVA 400 MHz spectrometer unless otherwise noted (1H: 400.09 MHz;
13C: 100.52 MHz; 31P: 161.82 MHz). All samples for 1H NMR and
13C{1H} NMR spectroscopy were referenced to the residual protons or
13C nuclei in the NMR solvent relative to (CH3)4Si (d [ppm]); 1H:
Preparation of 3a: The 4-(3,6-endoxo-D4-tetrahydrophthalimide)butyl-
tri-n-butylphosphonium bromide (2a) (0.667 g, 1.331 mmol) was dis-
solved in DMF (7 mL) and heated in an open vial at 1008C for 20 h to
liberate furan. 1H NMR spectroscopy confirmed the reaction was quanti-
tative. The DMF was removed in vacuo, the resulting mixture was dis-
solved in CH2Cl2 (2 mL) and Et2O (20 mL) was added. The emulsion was
cooled to À308C and upon separation of product, the solvent was deca-
nted and the extraction procedure was repeated. The residual solvent
was removed in vacuo to afford 4-(maleimidyl)butyl-tri-n-butylphospho-
nium bromide (3a) as a clear brown viscous liquid (0.437 g, 1.009 mmol,
76%). Tg =À368C; Td =3658C; 1H NMR (400 MHz, CDCl3): d=5.72 (s,
2H), 3.60 (t, 3J=4 Hz, 2H), 2.64 (m, 2H), 2.44 (m, 6H), 1.83 (quintet,
3J=8 Hz, 2H), 1.53 (m, 14H), 0.98 ppm (t, 3J=8 Hz, 9H); 13C{1H} NMR
[D3]chloroform
d=7.26,
[D6]acetone
d=2.05 ppm;
13C{1H}:
[D3]chloroform d=77.0 ppm). 31P chemical shifts were reported relative
to an external standard (85% H3PO4: d=0.00 ppm). The high-pressure
reactions were carried out on a LECOTempres High-Pressure chemical
reactor at 11000 atm, which is the default pressure under normal operat-
ing conditions. (CAUTION: Working with high-pressure reactors can be
dangerous. Follow manufacturer guidelines for safe operation.) Mass
spectrometry measurements were recorded in positive and negative ion
modes by using an electrospray ionization Micromass LCT spectrometer
and exact masses were recorded on a MAT 8200 Finnigan High Resolu-
tion Mass Spectrometer. Elemental analyses were performed by Guelph
Chemical Laboratories Ltd., Guelph, Ontario, Canada. The decomposi-
tion temperatures were determined by using Thermoravimetric analysis
(TGA) on a TGA/SDTA 851e Mettler Toledo instrument. A 0.005–
0.010g sample was loaded in an Al2O3 crucible (70 mL) and heated at a
rate of 108CminÀ1 over a temperature range of 25–6008C under a flow of
N2 (100 mLminÀ1). Melting and glass transition points were determined
by using differential scanning calorimetry (DSC) on a DSC 822e Mettler
Toledo instrument. A 0.005–0.010 g sample was loaded in a sealed,
pierced aluminum pan (40 mL) and cooled to À708C where the tempera-
ture was sustained for 15 min, followed by heating to 5008C with
108CminÀ1. Cyclic voltammetry was preformed by using a Perkin–Elmer
Par 263A potentiostat interfaced to a computer equipped with PAR 270
electrochemistry software. The working electrode was a 1 mm diameter
glassy carbon rod, Tokai, GC-20, sealed in glass tubing. The counter elec-
trode was a Pt wire. The reference electrode was a silver wire immersed
in a glass tube with a sintered end containing 0.1m tetrabutylammonium
perchlorate (TBAP) in dichloromethane. After each experiment, the
system was calibrated against the ferrocene/ferricinium couple at 0.5 V
versus saturated calomel electrode (SCE).
(100 MHz, CDCl3): d=170.6, 134.0, 35.9, 29.2 (d, 3J
(d, 3J(C,P)=15.3 Hz), 23.5 (d, 2J(C,P)=4.7 Hz), 18.8 (d, 1J
47.0 Hz), 18.6 (d, 1J(C,P)=47.7 Hz), 18.7 (d, 2J
(C,P)=4.1 Hz), 13.2 ppm;
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
31P{1H} NMR (162 MHz, CDCl3): d=33.7 ppm (s); MS (ESI): m/z+ (%):
353.9 ([M+], 100), 787.5 ([M2Br+], 30), 1222.5 ([M3Br2+], 1); m/zÀ (%):
514.1 ([MBr2À], 25), 947.3 ([M2Br3À], 1).
Preparation of 3b: The 12-(3,6-endoxo-D4-tetrahydrophthalimide)dodec-
yl-tri-n-butylphosphonium bromide (2b) (0.627 g, 1.022 mmol) was dis-
solved in DMF (7 mL) and heated in an open vial at 1008C for 15 h to
remove furan. 1H NMR spectroscopy confirmed the reaction was quanti-
tative. A workup procedure analogous to 3a afforded 12-(maleimidyl)do-
decyl-tri-n-butylphosphonium bromide (3b) as a clear brown viscous
liquid (0.355 g, 0.650 mmol, 64%). Tg =À358C; Td =3738C; 1H NMR
(400 MHz, CDCl3): d=5.68 (s, 2H), 3.50 (t, 3J=7.2 Hz, 2H), 2.47 (m,
8H), 1.54 (m, 18H), 0.98 ppm (t, 3J=8 Hz, 9H); 13C{1H} NMR
3
(100 MHz, CDCl3): d=170.1, 133.4, 37.0, 32.0, 30.0 (d, J
(C,P)=14.5 Hz),
28.6, 28.5, 28.4, 28.2 (d, 4J
(C,P)=9.7 Hz), 27.7, 25.9, 25.1, 23.1 (d, 3J-
2
2
(C,P)=15.2 Hz), 23.0 (d, J
(C,P)=4.7 Hz), 21.0 (d, J
(C,P)=4.5 Hz), 18.5
(d, 1J(C,P)=47 Hz), 18.3 (d, 1J(C,P)=47.1 Hz), 12.7 ppm; 31P{1H} NMR
ACTHNUTRGENNUG CAHTUNGTRENNUGN
(162 MHz, CDCl3): d=33.5 ppm (s); MS (ESI): m/z+ (%): 463 ([M+],
100), 1013.7 ([M2Br+], 5); m/zÀ (%): 631.2 ([MBr2À], 100).
Preparation of 2a: Neat tri-n-butylphosphine (0.351 g, 1.732 mmol) was
added dropwise to a solution of 4-(3,6-endoxo-D4-tetrahydrophthalim-
Preparation of 4a: A vial wrapped in aluminum foil was charged with
silver p-toluenesulfonate (0.367 g, 1.315 mmol) and a solution of 4-(male-
imidyl)butyl-tri-n-butylphosphonium bromide (3a) (0.380 g, 0.876 mmol)
in MeOH (5 mL) was added. The mixture stirred for 72 h and centri-
fuged, the supernatant was decanted and the AgBr was washed with
MeOH (5 mL) and then CH2Cl2 (5 mL). The combined supernatant was
filtered through a Celite column (0.5ꢂ4 cm) and the solvent was re-
moved in vacuo at 358C for 1 h. The liquid was redissolved in CH2Cl2
(5 mL), filtered through a Celite column, and the solvent was removed in
vacuo at 358C for 1 h, then the filtration procedure was repeated one
more time. The residual solvent was removed in vacuo at 358C for 13 h
and then at RT for 14 h to afford 4-(maleimidyl)butyl-tri-n-butylphospho-
nium p-toluenesulfonate (4a) as a clear brown viscous liquid (0.415 g,
0.789 mmol, 90%). Tg =À248C; Td =3958C; 1H NMR (400 MHz,
CDCl3): d=7.55 (d, 3J=7.6 Hz, 2H), 6.95 (d, 3J=8.0 Hz, 2H), 5.57 (s,
2H), 3.36 (t, 3J=8 Hz, 2H), 2.18 (m, 5H), 2.04 (m, 6H), 1.55 (quintet,
3J=8 Hz, 2H), 1.28 (m, 14H), 0.76 ppm (t, 3J=8 Hz, 9H); 13C{1H} NMR
(100 MHz, CDCl3): d=170.5, 144.3, 138.3, 133.9, 128.0, 125.5, 35.7, 28.9
ACHTUNGTRENNUNGide)bromobutane (0.518 g, 1.732 mmol) in dry DMF (5 mL) in the glove
box and was subsequently heated to 508C for 17 h under a flow of nitro-
gen. The DMF was removed by oil pump vacuum. The viscous oil was
dissolved in CH2Cl2 (2 mL) and titrated with Et2O (20 mL). The resulting
emulsion was cooled to À308C and upon separation of product, the sol-
vent was decanted and the extraction procedure was repeated. The resid-
ual solvent was removed in vacuo, yielding the 4-(3,6-endoxo-D4-tetrahy-
drophthalimide)butyl-tri-n-butylphosphonium bromide (2a) as a viscous
yellow oil (0.705 g, 1.406 mmol, 81%). Tm =1128C; Td =1348C (12%
mass loss), 3658C; 1H NMR (400 MHz, CDCl3): d=5.52 (s, 2H), 5.21 (s,
2H), 3.56 (t, 3J=4 Hz, 2H), 2.93 (s, 2H), 2.54 (m, 2H), 2.41 (m, 6H),
1.83 (quintet, 3J=4 Hz, 2H), 1.52 (m, 14H), 0.97 ppm (t, 3J=8 Hz, 9H);
3
13C{1H} NMR (100 MHz, CDCl3): d=173, 131, 80.7, 47.3, 37.0, 28.0 (d, J-
ACHTUNGTRENNUNG ACHTUNGTRENNUNG ACTUHNGTRENNUGN
(C,P)=15.7 Hz), 23.7 (d, 3J(C,P)=15.2 Hz), 23.4 (d, 2J
18.7 (d, 1J
N
G
ACHTUNGTRENNUNG
(d, 3J
4.7 Hz), 20.8, 18.3 (d, 2J
ACTHNUGTRNENUG
(d, 1J(C,P)=47.6 Hz), 13.0 ppm; 31P{1H} NMR (162 MHz, CDCl3): d=
A
R
ACHTUNGTRENNUNG(C,P)=
A
ACHTUNGTRENNUNG
Preparation of 2b: Tri-n-butylphosphine (0.216 g, 1.067 mmol) was added
dropwise to a solution of 12-(3,6-endoxo-D4-tetrahydrophthalimide)bro-
mododecane (0.400 g, 0.973 mmol) in dry DMF (10 mL) and heated to
508C for 17 h under a flow of nitrogen. A workup procedure analogous
to 2a yielded 2b as a viscous yellow oil (0.456 g, 0.743 mmol, 86%). Tg =
33.7 ppm (s); MS (ESI): m/z+ (%): 354.6 ([M+], 100), 879.1 ([M2OTs+],
40), 1403.4 ([M3OTs2+], 1); m/zÀ (%): 692 ([MOTs2À], 80).
Preparation of 4b: A vial wrapped in aluminum foil was charged with
silver p-toluenesulfonate (0.119 g, 0.426 mmol) and a solution of 12-(mal-
1
À428C; Td =1328C (10% mass loss, Àfuran), 3748C; H NMR (400 MHz,
CDCl3): d=5.51 (s, 2H), 5.26 (s, 2H), 3.46 (t, 3J=7.6 Hz, 2H), 2.83 (s,
2H), 2.48 (m, 8H), 1.53 (m, 20H), 1.24 (m, 12H), 0.98 ppm (t, 3J=
7.2 Hz, 9H); 13C{1H} NMR (151 MHz, CDCl3): d=176.0, 133, 80.6, 47.1,
eimidyl)dodecyl-tri-n-butylphosphonium
bromide
(3b)
(0.155 g,
0.284 mmol) in MeOH (3 mL) was added. The mixture was stirred for
72 h. A workup procedure analogous to 4a gave 12-(maleimidyl)dodecyl-
tri-n-butylphosphonium p-toluenesulfonate (4b) as a clear brown viscous
liquid (0.129 g, 0.202 mmol, 71%). Tg =À408C; Td =4268C; 1H NMR
38.7, 32.5, 30.5 (d, 3J
(C,P)=11.5 Hz), 27.3, 23, 25.5, 23.7 (d, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
2
1
3
3
E
E
A
(400 MHz, CDCl3): d=7.77 (d, J=8.0 Hz, 2H), 7.10 (d, J=7.6 Hz, 2H),
3
N
5.68 (s, 2H), 3.50 (t, J=7.6 Hz, 2H), 2.32 (m, 11H), 1.49 (m, 18H), 1.24
Chem. Eur. J. 2010, 16, 9068 – 9075
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9073

M. S. Workentin, P. J. Ragogna et al.
(m, 14H), 0.96 ppm (t, 3J=8 Hz, 9H); 13C{1H} NMR (100 MHz, CDCl3):
d=170.7, 144.4, 138.3, 133.9, 128.1, 125.8, 37.6, 32.6, 30.5 (d, 3J
(C,P)=
14.6 Hz), 29.19, 29.16, 29.05, 28.6 (d, 4J
(C,P)=10.8 Hz), 28.3, 25, 25.6,
23.7 (d, 3J(C,P)=15.2 Hz), 23.5 (d, 2J(C,P)=4.8 Hz), 21.5 (d, 2J
(C,P)=
4.5 Hz), 21.0, 18.6 (d, 1J(C,P)=48 Hz), 18.4 (d, 1J
(C,P)=47.2 Hz),
3J=7.0 Hz, 2H), 1.93 (m, 2H), 1.74 (m, 2H), 1.53 ppm (m, 2H);
13C NMR (100 MHz, CDCl3): d=204.3, 79.2, 72.4, 69.9, 69.5, 39.6, 34.0,
32.8, 28.3, 23.8 ppm; FTIR (dropcast on NaCl): 3094, 2935, 2861, 1667,
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
G
R
A
1455, 1411, 1378, 1258, 1232, 1105, 1054, 1026, 1002, 824, 533, 482 cmÀ1
;
R
G
HRMS: m/z: calcd for C16H19OBrFe: 361.9969; found: 361.9973.
13.2 ppm; 31P{1H} NMR (162 MHz, CDCl3): d=33.5 ppm (s); MS (ESI):
m/z+ (%): 466 ([M+], 100), 1102.8 ([M2OTs+], 45); m/zÀ (%):808.4
([MOTs2À], 10), 1445.8 ([M2OTs3À], 1).
Preparation of 7: Compound 6 (1.08 g, 3.0 mmol) and hexamethyldisila-
thiane (0.64 g, 0.75 mL, 3.59 mmol) were dissolved in dry THF (6 mL)
and cooled to À15–À208C in an ice/NaCl bath. A solution of TBAF in
THF (1m, 3.30 mL, 3.30 mmol) was added. The mixture was allowed to
warm to room temperature over 45 min. The reaction was quenched by
adding the solution to ice cold water (15 mL). The organic layer was then
diluted with Et2O and washed with water (5ꢂ30 mL). The organic layer
was collected and dried with MgSO4 and the solvent was removed in by
rotary evaporation to yield a reddish-orange oil. The 6-ferrocene-hexa-
none-1-thiol was then purified by liquid column chromatography
Preparation of 5a: A solution of 4-(maleimidyl)butyl-tri-n-butylphospho-
nium bromide (3a) (0.282 g, 0.650 mmol) in acetone (5 mL) was added to
lithium bis(trifluoromethanesulfonyl)imide (0.280 g, 0.976 mmol) and
stirred for 72 h. The solvent was removed in vacuo, CH2Cl2 (5 mL) was
added and the mixture was filtered twice through a Celite column (0.5ꢂ
4 cm). The solvent was concentrated to 2 mL and was extracted with
H2O (2ꢂ18 mL). The aqueous layers were tested with an aqueous solu-
tion of AgNO3 (10% ) to confirm the complete removal of LiBr. The or-
ganic fraction was dried with MgSO4 and the residual solvent was re-
moved in vacuo to afford 4-(maleimidyl)butyl-tri-n-butylphosphonium
bis(trifluoromethanesulfonyl)imide (5a) as a clear brown viscous liquid
(0.362 g, 0.413 mmol, 88%). Tg =À498C; Td =4408C; 1H NMR
1
(hexane/ethyl acetate, 1:1) to afford 7 (0.66 g, 2.10 mmol, 70%). H NMR
(600 MHz, CDCl3): d=4.78 (t, 3J=2.0 Hz, 2H), 4.49 (t, 3J=2.0 Hz, 2H),
4.18 (s, 5H), 2.70 (t, 3J=7.4 Hz, 2H) 2.55 (dt, 3J=7.8, 7.2 Hz, 2H) 1.69
(m, 4H) 1.48 (m, 2H), 1.44 ppm (t, 3J=7.8, 1H); 13C NMR (100 MHz,
CDCl3): d=204.6, 79.3, 72.4, 69.9, 69.5, 39.7, 39.0, 34.1, 29.3, 28.6, 28.4,
24.7, 24.3, 24.1 ppm; FTIR (dropcast on NaCl): 3096, 2932, 2857, 1667,
3
(400 MHz, CDCl3): d=5.71 (s, 2H), 3.59 (t, J=6 Hz, 2H), 2.25 (m, 2H),
2.12 (m, 6H), 1.80 (quintet, 3J=6 Hz, 2H), 1.51 (m, 14H), 0.98 ppm (t,
3J=6 Hz, 9H); 13C{1H} NMR (151 MHz, CDCl3): d=170.8, 134.0, 119.6
1454, 1410, 1378, 1264, 1238, 1105, 1055, 1026, 1002, 824, 533, 483 cmÀ1
;
HRMS: m/z: calcd for C16H20OSFe: 316.0584; found: 316.0577.
(quartet, 1J
(C,P)=15.3 Hz), 23.0 (d, 2J
18.2 (d, 3J(C,P)=4.2 Hz), 17.7 (d, 1J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(C,F)=320.0 Hz), 35.5, 28.9 (d, 3J
Preparation of 8a: Compound 3a (0.015 g, 0.034 mmol) was dissolved in
CDCl3 (3 mL) and (0.032 g, 0.101 mmol) was dissolved in CDCl3
A
(C,P)=4.7 Hz), 18.0 (d, 1J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
7
T
(3 mL) and several drops of anhydrous MeOH. Each solution was de-
gassed with nitrogen until the volume was reduced by half. The solutions
were then transferred to a brass-clamp sealed PTFE tube and placed in
the LECO Tempres high-pressure reactor at 11000 atm for 16 h. The sol-
vent was removed in vacuo and the residue was redissolved in CH2Cl2
(0.5 mL). The solution was extracted with hexane (4ꢂ10 mL) to remove
excess 6-ferrocene-hexanone-1-thiol. The residual solvent was removed
31P{1H} NMR (162 MHz, CDCl3): d=33.9 ppm (s); FTIR (dropcast on
KBr, ranked intensity): 659 (10), 695 (5), 750 (4), 832 (6), 918 (9), 968
(16), 1099 (13), 1140 (7), 1242 (11), 1382 (12), 1408 (2), 1442 (8), 1463
(18), 1636 (20), 1705 (1), 1769 (17), 2456 (19), 2873 (14), 2933 (15),
2960 cmÀ1 (3); MS (ESI): m/z+ (%): 354.2 ([M+], 100), 988.4 ([M2-
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(NTf2)+], 27); m/zÀ (%): 279.9 ([(NTf2)À], 100), 914.0 ([M(NTf2)2À], 1).
Preparation of 5b: A solution of 12-(maleimidyl)dodecyl-tri-n-butylphos-
phonium bromide (3b) (0.166 g, 0.304 mmol) in acetone (5 mL) was
in vacuo yielding 8a as
a viscous red-brown, clear liquid (0.025 g,
0.033 mmol, 99%). 1H NMR (400 MHz, CDCl3): d=4.75 (dd, 3J=1.6,
3
3
added
to
lithium
bis(trifluoromethanesulfonyl)imide
(0.131 g,
2.0 Hz, 2H), 4.48 (dd, J=1.6, 2.0 Hz, 2H), 4.17 (s, 5H), 3.92 (dd, J=3.2,
8.4 Hz, 1H), 3.56 (t, 3J=6.0 Hz, 2H), 3.34 (dd, 3J=9.2, 18.8 Hz, 1H),
2.93–2.74 (m, 2H), 2.70 (t, 3J=7.2 Hz, 2H), 2.54–2.35 (m, 9H), 1.80
(quintet, 3J=5.6 Hz, 2H), 1.74–1.58 (m, 6H), 1.55–1.45 (m, 14H),
0.456 mmol) and stirred for 72 h. A workup procedure analogous to 5a
yielded 12-(maleimidyl)dodecyl-tri-n-butylphosphonium bis(trifluorome-
thanesulfonyl)imide (5b) as
a clear brown viscous liquid (0.172 g,
0.230 mmol, 76%). Tg =À538C; Td =4468C; 1H NMR (400 MHz,
CDCl3): d=5.68 (s, 2H), 3.50 (t, 3J=7.2 Hz, 2H), 2.14 (m, 8H), 1.52 (m,
20H), 1.26 (m, 12H), 0.99 ppm (t, 3J=5.6 Hz, 9H); 13C{1H} NMR
0.96 ppm (t, J=6.0 Hz, 9H); 13C{1H} NMR (100 MHz, CDCl3): d=204.2,
3
177.1, 175.3, 79.0, 72.1, 69.7, 69.2, 39.3, 39.2, 37.0, 34, 31.7, 28.9, 28.5, 28.3
(d, 3J(C,P)=11 Hz), 23.91 (d, 3J(C,P)=15.3 Hz), 23.88, 23.7 (d, 2J
ACHTUNGTRNEUNNG ACHUTNGTENRNUG ACHTUNGTRENNUNG
(100 MHz, CDCl3): d=170.8, 134.0, 119.8 (quartet, 1J
37.8, 32.7, 30.4 (d, 3J
13.6 Hz), 28.7, 28.4, 26, 25.6, 23.6 (d, J
4.6 Hz), 21.4 (d, 2J(C,P)=4.6 Hz), 18.6 (d, 1J
(C,P)=47.3 Hz), 13.1 ppm; 31P{1H} NMR (162 MHz, CDCl3): d=
R
5.3 Hz), 18.9 (d, 1J
1J
(C,P)=47.3 Hz), 18.85 (d, 2J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
A
N
ACHTUNGTRENNUNG
3
2
N
(C,P)=
34.0 ppm (s); FTIR (dropcast on KBr, ranked intensity): 639 (12), 729
(4), 825 (10), 923 (5), 1026 (17), 1053 (19), 1098 (15), 1146 (7), 1236 (16),
1312 (20), 1383 (13), 1401 (2), 1439 (18), 1456 (6), 1664 (14), 1702 (1),
1773 (9), 2176 (11), 2873 (8), 2933 cmÀ1 (3); MS (ESI): m/z+ (%): 670.3
([M+], 100), 1421.6 ([M2Br+], 2).
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
33.7 ppm (s); FTIR (dropcast on KBr ranked intensity): 660 (8), 696 (6),
752 (4), 827 (5), 917 (12), 969 (15), 1006 (17), 1099 (10), 1115 (20), 1243
(9), 1381 (3), 1407 (11), 1442 (14), 1464 (7), 1627 (19), 1706 (1), 1769
(18), 2455 (16), 2857 (13), 2929 cmÀ1 (2); MS (ESI): m/z+ (%): 463 ([M+
Preparation of 8b: Compound 3b (0.032 g, 0.058 mmol) was dissolved in
CDCl3 (4 mL) and
7 (0.055 g, 0.174 mmol) was dissolved in CDCl3
], 100), 1212.6 ([M
([M
(NTf2)2À], 1).
2ACHTUNGTRENNUNG
(NTf2)+], 25); m/zÀ (%): 279.9 ([(NTf2)À], 100), 1022
(4 mL) and several drops of anhydrous MeOH. Each solution was de-
gassed with nitrogen until the volume was reduced by half. The solutions
were then transferred to a brass-clamp sealed PTFE tube and placed in
the LECO Tempres high-pressure reactor at 11000 atm for 16 h. A
workup procedure analogous to 8a yielded 8b as a viscous red-brown,
ACHTUNGTRENNUNG
Preparation of 6: Ferrocene (5.54 g, 35.2 mmol) was dissolved in CH2Cl2
(15 mL) and cooled to À15–À208C in an ice/NaCl bath. Aluminum tri-
chloride (2.19 g, 14 mmol) was added immediately. A solution of 6-
bromo-hexanoxyl chloride (2.71 g, 12.7 mmol) in CH2Cl2 (5 mL) was
added while the solution was kept in the ice/NaCl bath. The solution was
then stirred for 2 h while warming to room temperature. The reaction
was quenched by adding the solution to ice cold water (15 mL). The con-
tents were transferred to a separation funnel and the organic layer was
isolated. The aqueous layer was washed with CH2Cl2 (2ꢂ10 mL) and the
combined organic layers were washed with distilled water until the aque-
ous layer became clear colorless. The organic fraction was dried with
MgSO4 and the solvent was removed by rotary evaporation to reveal an
orange oil. 6-Bromo-1-ferrocene-hexanone was then purified by liquid
column chromatography (ethyl acetate/hexane, 3:1) to yield 6 (3.78 g,
10.4 mmol, 82%). 1H NMR (600 MHz, CDCl3): d=4.78 (t, 3J=2.0 Hz,
1
clear liquid (0.040 g, 0.046 mmol, 80%). H NMR (400 MHz, CDCl3): d=
4.77 (s, 2H), 4.50 (s, 2H), 4.19 (s, 5H), 3.71 (dd, 3J=3.6, 9.2 Hz, 1H),
3.49 (t, 3J=7.2 Hz, 2H), 3.12 (dd, 3J=9.2, 18.8 Hz, 1H), 2.92–2.72 (m,
2H), 2.71 (t, 3J=7.2 Hz, 2H), 2.49–2.34 (m, 9H), 1.73–1.64 (m, 4H),
1.58–1.41 (m, 20H), 1.32–1.17 (m, 14H), 0.97 ppm (brs, 9H);
13C{1H} NMR (100 MHz, CDCl3): d=204.1, 175, 174.7, 78.9, 72.1, 69.6,
69.1, 39.2, 38.91, 38.87, 36.0, 31.4, 30.7 (d, 3J
29.1, 28.9, 28.8 (d, 4J(C,P)=9.5 Hz), 28.4, 27.4, 25, 23.9 (d, 3J
15.4 Hz), 23.8 (d, 2J(C,P)=4.5 Hz), 21.8 (d, 2J(C,P)=4.6 Hz), 19.4 (d, 1J-
(C,P)=47.6 Hz), 19.2 (d, 1J(C,P)=47.5 Hz), 13.4 ppm; 31P{1H} NMR
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
T
ACHTUNGTRENNUNG
T
ACHTUNGTRENNUNG
(162 MHz, CDCl3): d=33.7 ppm (s); FTIR (dropcast on KBr, ranked in-
tensity): 483 (13), 659 (15), 751 (4), 825 (7), 923 (6), 1003 (18), 1026 (17),
1054 (20), 1099 (14), 1135 (9), 1240 (12), 1382 (16), 1399 (3), 1456 (5),
3
3
2H), 4.49 (t, J=2.0 Hz, 2H), 4.18 (s, 5H), 3.44 (t, J=6 Hz, 2H), 2.73 (t,
9074
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 9068 – 9075

Maleimide-Modified Phosphonium Ionic Liquids
FULL PAPER
1665 (8), 1703 (1), 1774 (11), 2174 (19), 2857 (10), 2929 cmÀ1 (2); MS
Acknowledgements
(ESI): m/z+ (%): 782.4 ([M+], 100), 1645.8 ([M2Br+], 2).
We would like to thank The Natural Sciences and Engineering Research
Council of Canada (NSERC), The Canada Foundation for Innovation
(CFI), the Ontario Ministry of Research and Innovation and The Univer-
sity of Western Ontario for funding, Cytec Industries for the generous
gift of nBu3P and Dr. K. M. Baines for the use of her TGA and DSC.
Preparation of 9b: Compound 3b (0.052 g, 0.097 mmol) was combined
with hexanethiol (0.034 g, 0.291 mmol) in CDCl3 (3 mL) and the solution
was divided and transferred to two NMR tubes. One tube was left at at-
mospheric pressure and 258C, while the other was kept at atmospheric
pressure and 608C. The progress of the reactions was monitored by
1H NMR spectroscopy. After each reaction was deemed to have gone to
completion (ca. 64 h at 258C and 30 h at 608C) a similar workup proce-
dure analogous to 8 was used to give product 9b, a viscous orange-red
clear liquid. 1H NMR (400 MHz, CDCl3): d=3.63 (dd, 1J=3.67, 2J=
9.08 Hz, 1H), 3.43 (t, J=7.4 Hz, 2H), 3.05 (dd, 1J=9.09, 2J=18.68 Hz,
1H), 2.84–2.78 (m, 1H), 2.71–2.64 (m, 1H), 2.47 (d, 3J=3.53 Hz, 1H),
[1] a) P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis, Vol. 1, 2nd
ed., Wiley-VCH, Weinheim, 2008; b) J. H. Davis, Jr., Chem. Lett.
2004, 33, 1072–1077; c) S.-g. Lee, Chem. Commun. 2006, 1049–
1063; d) Z. Fei, T. J. Geldbach, D. Zhao, P. J. Dyson, Chem. Eur. J.
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3
2.40 (m, 8H), 1.49–1.44 (m, 20H), 1.26–1.18 (m, 20H), 0.91 (t, J=92 Hz,
9H), 0.82 ppm (t, 3J=93 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): d=
177.2, 177, 83.4, 79.0, 49.4, 49.3, 45.5, 37.9, 37.4, 35.7, 32.5, 31.3, 29.4, 28.6,
28.1 (d, 3J(C,P)=16.0 Hz), 24.0 (d, 3J(C,P)=15.2 Hz), 23.7 (d, 2J
ACHTUNGTRENNUNG ACHTUNGTENRNUG ACTUHNGTRENNUGN
4.5 Hz), 22.5, 18.94 (d, 1J
18.5 (d, 2J
(C,P)=47.3 Hz), 18.85 (d, 1J
ACHUTGTNRENNUG CAHTUNGTRENNUNG
ACHTUNGTRENNUNG
CDCl3): d=34.0 ppm (s); FTIR (dropcast on NaCl): 3751, 3675, 3628,
2927, 2856, 1736, 1714, 1651, 1559, 1541, 1521, 1458, 1401, 1082,
1059 cmÀ1; HRMS: m/z: calcd for C34H67NO2NPS+: 584.4625; found
584.4622.
Preparation of 11a: A brass-clamp sealed PTFE tube was charged with
3a (0.030 g, 0.069 mmol) in CDCl3 (3 mL), dibenzylamine (0.041 g,
0.208 mmol) and anhydrous MeOH (2 drops). The tube was placed in the
LECOTempres high-pressure reactor at 11000 atm for 3 h. The solvent
and excess dibenzylamine was removed in vacuo at 1008C for 19 h yield-
ing 11a as a viscous orange clear liquid (0.043 g, 0.068 mmol, 98%).
1H NMR (400 MHz, CDCl3): d=7.37 (d, 3J=7.2 Hz, 4H), 7.31 (t, 3J=
7.8 Hz, 4H), 7.24 (t, 3J=7.2 Hz, 2H), 3.98 (dd 3J=4.8, 9.2 Hz, 1H), 3.70
(dd, 3J=13.2, 64.4 Hz, 4H), 3.53 (t, 3J=6 Hz, 2H), 2.78 (dd, 2J=18.6,
3J=9.6 Hz, 1H), 2.64–2.55 (m, 3H), 2.42–2.37 (m, 6H), 1.77 (quintet,3J=
7.2 Hz, 2H), 1.58–1.45 (m, 14H), 0.95 ppm (t, 3J=7.2 Hz, 9H);
13C{1H} NMR (100 MHz, CDCl3): d=177.4, 175.3, 137.9, 128.7, 128.4,
127.5, 57.6, 54.7, 37, 31.8, 28.7 (d, 3J
15.3 Hz), 23.7 (d, 2J(C,P)=5.3 Hz), 18.9 (d, 1J
(C,P)=4.5 Hz), 18.8 (d, 1J(C,P)=52.6 Hz), 13.4 ppm; 31P{1H} NMR
A
ACHTUNGTRNE(NUNG C,P)=
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
(162 MHz, CDCl3): d=33.7 ppm (s); FTIR (dropcast on KBr, ranked in-
tensity): 639 (15), 700 (9), 732 (4), 825 (16), 924 (19), 973 (19), 1028 (17),
1099 (20), 1144 (6), 1382 (14), 1400 (2), 1455 (7), 1494 (11), 1701 (1),
1773 (12), 2174 (13), 2873 (8), 2933 (10), 2960 (3), 3029 cmÀ1 (18); MS
(ESI): m/z+ (%): 551.3 ([M+], 100), 1183.6 ([M2Br+], 8).
Preparation of 11b: A brass-clamp sealed PTFE tube was charged with
3b (0.038 g, 0.069 mmol) in CDCl3 (3 mL), dibenzylamine (0.041 g,
0.208 mmol) and anhydrous MeOH (2 drops). The tube was placed in the
LECO Tempres high-pressure reactor at 11000 atm for 3 h. A workup
procedure analogous to 11a gave 11b as a viscous orange clear liquid
1
3
(0.046 g, 0.062 mmol, 89%). H NMR (400 MHz, CDCl3): d=7.39 (d, J=
8.0 Hz, 4H), 7.32 (t, 3J=8.0 Hz, 4H), 7.25 (t, 3J=4 Hz, 2H), 3.91 (dd,
3J=5.6, 9.2 Hz, 1H), 3.72 (dd, 3J=13.2, 73.2 Hz, 4H), 3.47 (t, 3J=7.2 Hz,
2H), 2.75 (dd, 2J=18.4, 3J=9.2 Hz, 1H), 2.60 (dd, 2J=18.4, 3J=4.8 Hz,
1H), 2.50–2.40 (m, 8H), 1.59–1.46 (m, 18H), 1.35–1.19 (m, 14H),
0.97 ppm (t, 3J=8 Hz, 9H); 13C{1H} NMR (100 MHz, CDCl3): d=177.3,
175.2, 138.2, 128.7, 128.4, 127.4, 57.3, 54.5, 38.5, 32.1, 30.7 (d, 3J
14.4 Hz), 29.4, 29.3, 29.3, 29.2, 29.0, 28.9, 27.7, 28, 23.9 (d, 3J
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
15.3 Hz), 23.8 (d, 2J
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(C,P)=3.8 Hz), 21.9 (d, 2J(C,P)=4.6 Hz), 19.3 (d, 1J-
[13] a) J. R. McElhanon, D. R. Wheeler, Org. Lett. 2001, 3, 2681–2683;
b) X. Chen, M. A. Dam, K. Ono, A. Mal, H. Shen, S. R. Nutt, K.
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[14] E. Hedaya, S. Theodoropulos, Tetrahedron 1968, 24, 2241–2254.
[15] G. M. Kosolapoff, L. Maier, Organic Phosphorus Compounds,
Vol. 2, Wiley, New York, 1972.
A
ACTHNGUTERNNUG
(162 MHz, CDCl3): d=33.5 ppm (s); FTIR (dropcast on KBr, ranked in-
tensity): 639 (15), 700 (9), 732 (4), 825 (14), 924 (7),1028 (16), 1133 (8),
1383 (13), 1399 (3), 1456(5),1494 (11), 1702 (1), 1773 (10), 2170 (12),
2856 (6), 2928 cmÀ1 (2); MS (ESI): m/z+ (%): 663.5 ([M+], 100), 1407.9
([M2Br+], 5).
[16] a) G. Jenner, J. Phys. Org. Chem. 1999, 12, 619–625; b) G. Jenner,
New J. Chem. 1999, 23, 525–529.
Received: September 22, 2009
Revised: March 22, 2010
Published online: June 22, 2010
Chem. Eur. J. 2010, 16, 9068 – 9075
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9075