Promoting effect of ionic liquids on ligand substitution reactions

Article abstract of DOI:10.1016/j.jorganchem.2005.02.018

Ionic liquid solvents N-hexylpyridinium bistrifylimide ([C ₆pyr][Tf₂N]] and 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) promoted the displacement of anionic ligands by pyridine derivatives in trans-(Ph ₃P)₂Rh(CO)NO₃ to a much greater extent than did dichloromethane. Thus, addition of a slight excess of 2-fluoropyridine to trans-(Ph₃P)₂Rh(CO)NO₃ in [C ₄mim][PF₆] gave a 29:71 product mixture of trans-(Ph ₃P)₂Rh(CO)NO₃:[trans-(Ph₃P) ₂Rh(CO)(2-fluoropyridine)][NO₃], while the ratio was 91:9 in dichloromethane.

Full text of DOI:10.1016/j.jorganchem.2005.02.018

Journal of Organometallic Chemistry 690 (2005) 3540–3545
www.elsevier.com/locate/jorganchem
Promoting effect of ionic liquids on ligand substitution reactions
a
a
b
b
Michael D. Sliger , Steven J. PÕPool , Rachel K. Traylor , James McNeill III ,
Sidney H. Young b,z, Norris W. Hoffman , Marc A. Klingshirn ,
b
a
a
Robin D. Rogers , Kevin H. Shaughnessy
a,
*
a
Department of Chemistry and Center for Green Manufacturing, Box 870336, The University of Alabama, Tuscaloosa, AL 35487-0336, USA
b
Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
Received 12 January 2005; accepted 16 February 2005
Available online 19 March 2005
Abstract
Ionic liquid solvents N-hexylpyridinium bistrifylimide ([C6pyr][Tf2N]] and 1-butyl-3-methylimidazolium hexafluorophosphate
([C4mim][PF6]) promoted the displacement of anionic ligands by pyridine derivatives in trans-(Ph3P)2Rh(CO)NO3 to a much greater
extent than did dichloromethane. Thus, addition of a slight excess of 2-fluoropyridine to trans-(Ph3P)2Rh(CO)NO3 in [C4mim][PF6]
gave a 29:71 product mixture of trans-(Ph3P)2Rh(CO)NO3:[trans-(Ph3P)2Rh(CO)(2-fluoropyridine)][NO3], while the ratio was 91:9
in dichloromethane.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ionic liquids; Ligand substitution; Rhodium; Solvent properties
1. Introduction
There have been a number of attempts to quantify
the solvent properties of ILs using solvatochromic
dyes [8–18], linear free energy relationships (LFER)
[19,20], partitioning studies [21], and other approaches
[22,23]. Although a range of solvent properties has
been reported, there is a general consensus that ILs
have polarities comparable to polar aprotic solvents,
such as DMF and acetonitrile, or protic solvents, such
as short-chain alcohols. Despite this apparent high
polarity, 1-butyl-3-methylimidazolium hexafluorophos-
phate ([C4mim][PF6]) has a coordinating ability com-
parable to that of dichloromethane [10,11]. This
combination of properties is unique among potential
solvent media. A polar, weakly coordinating solvent
should promote catalytic processes with key steps
involving charge-separated intermediates or transi-
tion states. Indirect evidence for this sort of acceler-
ation has been noted in some catalytic processes
[10,24–27].
In recent years, the development of air and moisture
stable ionic liquids (ILs) has resulted in a significant
resurgence of interest in their application to a wide
range of fields [1,2]. Ionic liquids have a number of inter-
esting properties, such as low volatility, low flammabil-
ity, large liquid range, variable miscibility with water
and organic solvents, high polarity, and potentially
low coordinating ability, that make them attractive sol-
vents for a range of applications. Based on these proper-
ties, ILs have been suggested as alternatives to organic
solvents in a wide variety of homogeneous metal-
catalyzed processes [3–7].
*
Corresponding author. Tel.: +205 348 4435; fax: +205 348 9104.
E-mail address: kshaughn@bama.ua.edu (K.H. Shaughnessy).
Deceased.
z
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.02.018

M.D. Sliger et al. / Journal of Organometallic Chemistry 690 (2005) 3540–3545
3541
Although ILs have been applied to a wide range of
catalytic reactions, there have been relatively few careful
studies regarding the effects of these solvents on reaction
rate, mechanism, or selectivity [28–32]. Studies of com-
plex multi-step catalytic processes can provide some
information about overall solvent effects, but a more
thorough understanding of these properties requires
looking at solvent effects on individual reaction steps.
Welton [33–35] has studied SN2 substitution reactions
in ILs and found that halide nucleophilicity is dependent
on the hydrogen-bonding properties of the anion and
cation. Examples of similarly detailed studies of funda-
mental organometallic reactions in ILs are limited to a
recent report of the bimolecular rate constant for sol-
vent displacement in (g6-C6H6)Cr(CO)2(solvent) [36].
Ligand substitution is a key step in every homoge-
neous catalytic process. We and others have hypothe-
sized that ILs would promote the displacement of
anionic ligands by neutral molecules leading to charge-
separated species [10,24–27]. This step plays key roles
in important catalytic cycles such as hydrogenation, Zie-
gler–Natta-type polymerization, hydrocarboxylation,
and Heck coupling. Herein we report our initial results
on the effect of IL solvents on the displacement of anio-
nic ligands at a d8 Rh(I) center by pyridine derivatives
[37], which serves as a model for this type of catalytic
step (Eq. (1)). We find that ILs strongly promote the for-
mation of the charge-separated ligand substitution
products, and that the extent of this effect depends on
the nature of the ionic liquid.
after several hours of stirring at room temperature.
Attempts to dissolve 1 in other IL solvents, such as
1-butyl-3-methylimidizolium bistrifylimide, 1-butyl-3-
methylimidizolium triflate, and 1-hexylpyridinium N-(tri-
fluoromethylsulfonyl)nonafluorobutylsulfonimide (MBI)
were unsuccessful.
CH3
HNO3
O
O
OC
OC
OC
PPh3
NO3
2 PPh3
Rh
Rh
(2)
MeOH
Ph3P
CH3
1
IL solutions of 1 were analyzed to determine the car-
bonyl stretching frequencies and molar absorption coef-
ficient (ꢀ) values (Table 1). In all cases, the observed
bands were visibly more broadened in the ILs than those
seen in CH2Cl2 solutions, suggesting a weak interaction
of the IL solvent with the carbonyl ligands of the com-
plexes. The broadening resulted in a 400–500-MÀ1 cmÀ1
drop in ꢀ for both IL solvents and starting complexes.
To determine the spectral properties and ꢀ values of
the ligand substitution products, a small set of
[Rh(CO)(PPh3)2L]+XÀ complexes (2) was prepared.
Addition of AgSbF6 to a toluene or CH2Cl2 solution
of Rh(CO)(PPh3)2Cl in the presence of an excess
amount of the corresponding pyridine gave good yields
of the cationic pyridine complexes (Eq. (3)) [37]. Molar
absorptivity values (ꢀ) for the cationic complexes (2)
were the same within experimental error ( 0.1 ·
103 MÀ1 cmÀ1) independent of the identity of the pyri-
dine ligand. These values also matched those measured
for 1 within experimental error in both dichloromethane
and the ionic liquids. Direct comparisons of absorbance
values should thus be suitable to determine relative con-
centrations of 1 and 2 in ligand substitution reactions
(see Table 2).
PPh3
OC Rh NO3
PPh3
PPh3
OC Rh N
PPh3
N
Rn
(1)
+
NO3
Rn
1
2
Table 1
FTIR spectroscopic data of Rh(CO)(PPh3)2NO3
2. Results and discussion
X
Solvent
k
max (cmÀ1
)
ꢀ (·10À3 MÀ1 cmÀ1
)
Rh(CO)(PPh3)2NO3 (1) was synthesized using previ-
ously reported procedures (Eq. (2)) [38]. Complex 1
was sparingly soluble in the ILs tested. Concentrations
of 1 no larger than 0.01 M in 1-butyl-3-methylimidizo-
lium hexafluorophosphate ([C4mim][PF6]) could be
achieved after stirring for one day at room temperature.
Moderate heating aided complex dissolution, but would
often lead to the formation of an uncharacterized side-
NO3
NO3
NO3
CH2Cl2
[C4mim][PF6]
[C6pyr][NTf2]
1983
1987
1986
1.5 0.1
1.0 0.1
1.1 0.1
Table 2
FTIR spectroscopic data of [Rh(CO)(PPh3)2L]+
L
Solvent
kmax
ꢀ
(cmÀ1
)
(·10À3 MÀ1 cmÀ1
)
product possessing an IR-active stretch at 2432 cmÀ1
.
3-Picoline
3-Picoline
CH2Cl2 2009
[C6pyr][NTf2] 2001
1.6
1.1
1.6
1.2
1.2
1.4
1.1
The 0.01 M solutions of 1 provided carbonyl stretch
intensities of up to 0.7 absorption units using a 0.5-mm
FTIR solution cell with CaF2 windows, which
makes them suitable for BeerÕs Law applications. Com-
plex 1 dissolved more readily in 1-hexylpyridinium bis-
trifylimide ([C6pyr][NTf2]) to give 0.01 M solutions
2-Fluoropyridine
2-Fluoropyridine
2-Fluoropyridine
2,6-Difluoropyridinea CH2Cl2
2,6-Difluoropyridinea [C6pyr][NTf2] 2008
CH2Cl2
[C4mim][PF6]
2011
2004
[C6pyr][NTf2] 2005
2012
a
Slightly impure.

3542
M.D. Sliger et al. / Journal of Organometallic Chemistry 690 (2005) 3540–3545
0.35
0.3
0.013 M). The reaction mixtures were stirred overnight
to ensure full equilibration [39] and then were analyzed
by FTIR spectroscopy. In each case, a only a single
maximum was observed, although reactions with inter-
mediate amounts of 2-picoline (0.3–0.8 2-picoline:Rh)
gave broad unsymmetrical peaks. No change was seen
on increasing the 2-picoline:Rh ratio from 0.94 to
1.27, so the reaction goes to completion with as little
as one equivalent of 2-picoline. An overlay of the car-
bonyl stretching region of the FTIR spectra shows an
isosbestic point at 1995 cmÀ1 consistent with clean con-
version of 1–2 (Fig. 1).
0.25
0.2
0.15
0.1
0.05
0
2040
2020
2000
1980
1960
1940
cm-1
A more extensive set of ligand substitution reactions
were performed by adding pyridine derivatives with a
range of coordinating abilities to 0.01 M solutions of 1
in CH2Cl2, [C4mim][PF6], and [C6pyr][Tf2N] (Eq. (1)).
Reaction mixtures were stirred at room temperature
overnight. FTIR spectra were then obtained to deter-
mine the relative concentrations of 1 and 2 (Table 3).
In cases where both the reactant and product were pres-
ent, overlap of the two carbonyl stretches was observed.
This complication was more significant for reactions in
ionic liquids due to broadening of bands and consequent
reduction in the peak separation between the two sig-
nals. Statistical deconvolution techniques based upon a
Gaussian line-shape routine were applied to derive the
actual absorption maxima and to determine absorbance
values for 1 and 2 [40]. The data was corroborated by
Fig. 1. Overlaid FTIR spectra of CO stretching region of 2-picoline/1
with 2-picoline:Rh ratios of 0, 0.27, 0.47, 0.79, 0.94, 1.27, [Rh] = 0.01
M.
PPh3
OC Rh Cl
PPh3
PPh3
OC Rh N
PPh3
Rn
N
AgSbF6
(3)
SbF6
+
toluene
-AgCl
Rn
2
To determine if ligand substitution occurred cleanly
in IL solvents, a 0.01-M solution of 1 in [C6pyr][Tf2N]
was treated with varying amounts of 2-picoline (0–
Table 3
Degree of ligand substitution in the reaction of Rh(CO)(PPh3)2NO3 with L
Entry
L (pKa)a
Solvent
kmax (1)
kmax (2)
% of 2b
1
2
4-Dimethylaminopyridine (9.7)c
2,4-Lutidine (6.99)d
CH2Cl2
CH2Cl2
2002
2009
2006
2009
2010
2010
2010
2012
>95
81
1985
1984
1985
1985
1985
1983
1984
1984
3
2,6-Lutidine (6.60)d
CH2Cl2
CH2Cl2
80
80
4
2-Picoline (5.97)d
5
3-Picoline (5.66)d
CH2Cl2
CH2Cl2
73
63
6
Quinoline (4.90)d
7
2-Bromopyridine (0.90)d
2-Fluoropyridine (À0.44)d
2,6-Difluoropyridine (À5.32)e
4-Dimethylaminopyridine (9.7)c
2,4,6-Collidine(7.43)d
2-Picoline (5.97)d
CH2Cl2
CH2Cl2
CH2Cl2
20
8
9
<5
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
a
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C4mim][PF6]
[C6pyr][NTf2]
[C6pyr][NTf2]
[C6pyr][NTf2]
[C6pyr][NTf2]
[C6pyr][NTf2]
[C6pyr][NTf2]
1998
1999
2002
2003
2003
2002
2004
2004
1997
2001
2003
2004
2006
>95
>95
>95
>95
>95
>95
71
3-Picoline(5.66)d
Pyridine (5.23)d
2-Bromopyridine (0.90)d
2-Fluoropyridine (À0.44)d
2,6-Difluoropyridine (À5.32)e
4-Dimethylaminopyridine (9.7)c
2,6-Lutidine (6.60)d
1986
1986
12
>95
>95
>95
>95
67
2-Picoline (5.97)d
Quinoline (4.90)d
2-Fluoropyridine (À0.44)d
1988
1986
2,6-Difluoropyridine (À5.32)e
<5
pKa of the pyridinium conjugate acid.
Percent conversion to 2 as determined by IR. Values >95% or <5% indicate that the minor component was not observed.
b
c
pKa value taken from [41a].
pKa value taken from [41b].
pKa value taken from [41c].
d
e

M.D. Sliger et al. / Journal of Organometallic Chemistry 690 (2005) 3540–3545
3543
subtracting a height adjusted standard spectrum of 1
from the reaction solution spectrum. Comparisons of
the 2 peak heights of the extrapolated spectra to those
from the statistically generated data typically showed
deviations of 62% unless the relative concentration of
either component fell to about 5%, the limit for detec-
tion by deconvolution due to the broad nature of these
bands. In those cases, the overall equilibrium levels
show variations of 5% or less. Examples of deconvo-
luted spectra for the reaction of 2-fluoropyridine and 1
in [C4mim][PF6] and [C6pyr][Tf2N] are shown in Figs.
2 and 3, respectively.
Alkylated pyridine derivatives gave 70–80% conver-
sion of 1 to complex 2 in dichloromethane (Table 3,
entries 2–5). Only a strongly basic pyridine, 4-dimeth-
ylaminopyridine, resulted in 2 being the only species
detectable in dichloromethane solution. The amount of
2 generated in dichloromethane was significantly de-
creased with less basic halogenated pyridine derivatives,
however. Thus, 2-bromopyridine addition led to only
20% conversion to 2 (entry 7), while 2-fluoropyridine
gave only a small amount of 2 in dichloromethane (entry
8). No ligand substitution product (2) was observed
when was treated with 2,6-difluoropyridine in
dichloromethane.
1
In contrast, interactions of alkylated pyridine deriva-
tives and 1 in ionic liquid solvents led to complete con-
version to 2 (<5% 1, entries 11–14). Even weakly basic
2-bromopyridine gave >95% conversion when reacted
with 1 in [C4mim][PF6] (entry 15). Weakly coordinating
fluorinated pyridines did not give complete nitrate dis-
placement in the ILs, however. Addition of 2-fluoropyri-
dine addition led to 71% and 67% conversion to 2 when
reacted with 1 in [C4mim][PF6] and [C6pyr][NTf2],
respectively (entries 16 and 22), significantly higher lev-
els of substitution than occurred with 2-fluoropyridine
in dichloromethane (Fig. 4). 2,6-Difluoropyridine, how-
ever, gave little or no ligand substitution product in the
ionic liquid solvents (entries 17 and 23). For both fluori-
nated pyridine derivatives, [C4mim][PF6] gave higher
conversions to 2 than did [C6pyr][NTf2].
The promoting effect of ILs on the ligand substitution
reaction can be seen more clearly by comparing the ba-
sicity of the pyridine ligands, based on the pKa of the
conjugate pyridinium acid [41], versus the mole fraction
of 2 in the ligand substitution reactions (Fig. 5). For
dichloromethane, a linear dependence of the equilibrium
mole fraction of 2 on the basicity of the pyridine ligand
was found. Since most pyridines tested in the ILs gave
complete conversion, there were not enough data points
to fully evaluate the linearity in IL solvents. The y-inter-
cept for the dichloromethane data was À1.19, while
intercepts of À5.32 and À6.02 were found for [C6pyr]
[NTf2] and [C4mim][PF6], respectively. Thus, the basi-
city of the pyridine ligand required to give a particular
degree of ligand substitution was significantly lower
for the IL solvents than for dichloromethane. The lower
y-intercept of [C4mim][PF6] compared with [C6pyr]
[NTf2] suggests that it is better able to promote the li-
gand dissociation reaction; however, the reason for this
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
1960
2040
2020
2000
1980
1940
cm-1
Fig. 2. Deconvoluted FTIR spectra for 2-fluoropyridine/1 in
[C4mim][PF6]. kmax (1) = 1987 cmÀ1, kmax (2) = 2005 cmÀ1, 1:2 = 29:71.
0. 8
0. 7
0. 6
0. 5
0. 4
0. 3
0. 2
0. 1
0
0.6
0.5
0.4
0.3
0.2
0.1
0
2040
2020
2000
1980
1960
1940
2040
2020
2000
1980
1960
1940
cm-1
cm-1
Fig. 3. Deconvoluted FTIR spectra for 2-fluoropyridine/1 in
[C6pyr][Tf2N]. 1:2 = 29:71. kmax (1) = 1986 cmÀ1
2006 cmÀ1, 1:2 = 33:67.
Fig. 4. FTIR spectra of the carbonyl stretching region of reaction
mixtures of 1 with 2-fluoropyridine in CH2Cl2 (—) and [C6pyr][NTf2]
(Á Á Á).
,
kmax (2) =

3544
M.D. Sliger et al. / Journal of Organometallic Chemistry 690 (2005) 3540–3545
8
6
NMR spectra were obtained on either a Bruker
¨
1
AX360 or a Bruker AX500 spectrometer. H and 13C
¨
NMR spectra are reported as positive parts per million
(ppm) downfield from a tetramethylsilane (TMS) stan-
dard. 31P NMR spectra are referenced from an external
H3PO4 standard. All FTIR spectra were obtained on a
BIO-RAD FTS-40 spectrometer.
4
2
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
All ionic liquids were prepared by standard proce-
dures [8,43]. Ionic liquids were dried in vacuo overnight
at 70 ꢁC prior to use. Water contents determined by
Karl-Fischer titration were typically <200 ppm. Halide
contents were measured using halide-selective electrodes
and were determined to be <100 ppm. Rh(CO)(PPh3)2-
NO3 (1) was synthesized using previously reported pro-
cedures [38]. Rh(CO)2(acac) and Rh(CO)(PPh3)2Cl were
acquired from Strem Chemicals. All other ligands,
reagents and solvents were purchased from Aldrich
Chemicals, Acros Organics, or Fisher Scientific.
-2
-4
-6
-8
K
mole fraction 2
Fig. 5. Conjugate acid pKa of substituted pyridines vs. mole fraction 2
for substitution reactions in CH2Cl2 (r, y = 9.59x À 1.19, R2 = 0.9895),
[C6pyr][NTf2] (m, y = 7.34x À 5.32), and [C4mim][PF6] (j, y = 7.26x À
6.02).
difference is not clear. The imidazolium cation in
[C4mim][PF6] would be expected to be a better H-bond
donor than the pyridinium cation, so it may better sta-
bilize the nitrate anion, thus promoting nitrate displace-
ment. The poor solubility of 1 in ILs precluded a more
systematic comparison of cation and anion effects on
the equilibrium for this complex.
4.1. [Rh(CO)(PPh3)2L][SbF6] (2)
Rh(CO)(PPh3)2Cl (91.3 mg, 0.13 mmol) was mixed
with AgSbF6 (62.7 mg, 0.18 mmol) in a Schlenk flask.
Dry, deoxygenated toluene (15 mL) was added via syr-
inge, yielding a yellow solution and a yellow paste. After
stirring for 1.5 h, the supernatant was transferred by syr-
inge to another flask. The paste was washed with an-
other 8 mL of toluene. The supernatant samples were
combined and treated with the appropriate substituted
pyridine (0.6 mmol) to precipitate the desired product.
Decantation of the supernatant was followed by vacuum
drying at 40–45 ꢁC for several hours to yield a yellow
powder. [Rh(CO)(PPh3)2(3-picoline)][SbF6] (2a): 1H
NMR (360 MHz, CD2Cl2): d 7.52 (m, 18H, Ph), 7.41
(m, 12H, Ph), 7.13 (br, 2 H, pyr-H), 6.62 (m, 1H, pyr-
H), 1.68 (s, 3H, pyr-Me). [Rh(CO)(PPh3)2(2-fluoropyri-
3. Conclusions
This work provides the first measurement of the pro-
moting effect of ionic liquid solvents on the displacement
of anionic ligands by neutral ligands. Equilibrium ratios
have been measured for the displacement of nitrate from
1 by pyridine derivatives in dichloromethane and ILs.
The IL solvents stabilize the charge-separated Rh-pyri-
dine complex to a much greater extent than dichloro-
methane, resulting in higher equilibrium concentrations
of complex 2. As a result, even weakly basic pyridine li-
gands can displace the nitrate ligand. These results are
relevant to catalytic processes in which displacement of
an anionic ligand by a neutral reactant (i.e., an olefin
or CO) converts a catalytically inactive species into an
active species. Therefore, ionic liquids should be ex-
pected to promote catalytic processes in which anionic li-
gands compete for coordination to the active site. Unlike
polar organic solvents, however, weakly coordinating
ILs should not compete for coordination to the catalyti-
cally active species.
1
dine)][SbF6] (2b): H NMR (360 MHz, CD3OD): d 7.82
(br, 2H, pyr), 7.59 (m, 12H, Ph), 7.43 (m, 18H, Ph), 6.82
(br, 1H, pyr), 6.62 (br, 1H, pyr). [Rh(CO)(PPh3)2(2,6-
difluoropyridine)][SbF6] (2c): 1H NMR (360 MHz,
CD2Cl2): d 7.58 ppm (m, 18H, Ph), 7.42 (m, 12H, Ph),
6.33 (d, J = 8.63 Hz, pyr).
4.2. General procedure for equilibration studies
A stock solution was prepared by dissolving Rh(CO)-
(PPh3)2NO3 (53.2 lmol) in 5 mL of solvent (dichloro-
methane, [C4mim][PF6], or [C6pyr][NTf2]) in a volumetric
flask in the drybox to give a 0.01-M solution. A stan-
dard amount (0.60 mL, 6.4 lmol Rh) of this solution
was added to a septum sealed vial under nitrogen. The
pyridine (8–10 lmol) was added to the Rh solution
and stirred overnight. A portion of the solution was then
transferred under nitrogen to an IR solution cell (0.5
mm) with CaF2 windows and analyzed by IR spectros-
copy. In cases where overlapping peaks were observed,
4. Experimental
Standard Schlenk and drybox techniques were used
for all reactions unless noted. All solvents used were
purified and dried before use following procedures
1
found in Perrin and Armarego [42]. H, 13C and 31P

M.D. Sliger et al. / Journal of Organometallic Chemistry 690 (2005) 3540–3545
3545
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Funding for this work was provided by the National
Science Foundation (KHS, CHE-0124255), Research
Corporation (KHS and NWH), the donors of the Petro-
leum Research Fund administered by the American
Chemical Society (KHS), and the US Environmental
Protection AgencyÕs STAR program (RDR, RD
83143201-0). (Although the research described in this
article has been funded in part by EPA, it has not been
subjected to the AgencyÕs required peer and policy review
and therefore does not necessarily reflect the views of the
Agency and no official endorsement should be inferred.).
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