Organometallics
Article
EXPERIMENTAL SECTION
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All reactions, unless otherwise stated, were carried out under an
atmosphere of dry, oxygen-free nitrogen, using standard Schlenk line
or metal vacuum line techniques or in a nitrogen-purged drybox.
Solvents were distilled under nitrogen from appropriate drying agents
and degassed prior to use.33 [IrF3(CO)3]22 and [RuF2(CO)3]434 were
prepared by the literature routes. The reagents 4-fluoroaniline, 2,4-
difluoroaniline, and 2,4,6-trifluoroaniline were purchased from
Fluorochem and were distilled before use; para-formaldehyde and
glyoxal were purchased from Aldrich Chemical Co. and used without
further purification. All other chemicals were obtained commercially
and used without further purification. 1H, 13C, and 19F NMR
spectroscopies were carried out on a Bruker DRX400 spectrometer
at 400.13, 100.16, and 376.46 MHz, respectively, and were referenced
to external SiMe4 (1H, 13C) and to external CFCl3 (19F). Elemental
analyses were performed at the Science Technical Support Unit,
London Metropolitan University. Mass spectra were recorded on a
Kratos Concept 1H mass spectrometer. IR spectra were recorded as
solid samples on a Perkin-Elmer Spectrum One FT-IR spectrometer.
1,3-Bis(4-fluorophenyl)imidazolium Chloride (1). A solution
of 4-fluoroaniline (15.000 g, 135 mmol) in toluene (15 mL) was added
dropwise to a stirred suspension of para-formaldehyde (2.054 g, 68
mmol) in toluene (50 mL). After addition was complete, the
suspension was heated to 100 °C for 1 h, dissolving all the solids.
The resulting solution was allowed to cool to 40 °C, whereupon a
solution of glyoxal (9.890 g of a 40% aqueous solution, 68 mmol) in
toluene (10 mL) was slowly added. The solution was stirred for an
additional 5 min at this temperature, before HCl (22.6 mL of a 3 M
HCl solution, 68 mmol) was added dropwise. The solution was then
reheated to 100 °C and maintained at this temperature for 8 h. After
cooling to room temperature, all volatiles were removed in vacuo,
giving a dark precipitate. Repeated recrystallization from DMSO/
diethyl ether gave 1 as a hygroscopic white powder (13.530 g, 68%).
Mp: 267−268 °C. Anal. Calcd for C15H11ClF2N2: C, 61.53, H 3.79, N,
9.57. Found: C, 61.58, H, 3.70, N, 9.37. IR: νmax/cm−1 3028br, 1556s,
1508s, 1459w, 1232s, 837br. 1H NMR (DMSO): 10.97 (s, 1H,
NCHN), 8.83 (br s, 2H, NCHCHN), 8.29 (m, 2H, 3-CH), 7.63 (t,
Figure 4. Molecular structure of 6 with 50% displacement ellipsoids
and a partial atom label scheme; H atoms are omitted for clarity. The
fluorine atoms F8/F8′ and F4/F4′ represent the 50:50 disorder
between ortho-sites in two of the aryl rings. Selected bond lengths (Å)
and angles (deg): Ru(1)−C(1), 1.924(3); Ru(1)−C(2), 1.903(3);
Ru(1)−C(3), 2.063(3); Ru(1)−C(18), 2.052(3); Ru(1)−C(7),
2.122(3); Ru(1)−C(22), 2.118(3); C(1)−O(1), 1.132(3); C(2)−
O(2), 1.146(3); C(3)−Ru(1)−C(18), 161.90(10); C(1)−Ru(1)−
C(22), 174.66(10); C(2)−Ru(1)−C(7), 172.14(10); C(3)−Ru(1)−
C(7), 77.35(10); C(18)−Ru(1)−C(22), 77.20(10).
1
3JHH = 8.7 Hz, 2-CH). 13C{1H} NMR (DMSO): 162.5 (d, JCF = 248
complexes 5 and 6 are also statistically invariant. For 4, the
metal−aryl bond lengths are asymmetric, in line with the
different trans-influence of the chloride and carbonyl ligands,
and are shorter than those for the ruthenium complexes as a
consequence of the higher formal oxidation state for iridium.
The Caryl−M−Ccarbene angles within the metallocycles are very
similar and comparable to that seen for other orthometalated
arylcarbene metal complexes.28−32 The Ccarbene−M−Ccarbene
angles display marked distortions from linearity, being more
pronounced for the ruthenium complexes than the iridium
complex, presumably due to the steric constraints of metallo-
cycle formation.
Hz, 4-C), 135.3 (s, NCHN), 131.4 (d, 4JCF = 3 Hz, 1-C), 124.8 (d, 3JCF
2
= 9 Hz, 2-C), 122.4 (s, NCHCHN), 117.2 (d, JCF = 24 Hz, 3-C).
19F{1H} NMR (DMSO): −111.0 (s, 4-CF). MS m/z (FAB): 257 ([M
− Cl]+, 72%). Acc. Mass: C15H11F2N2 ([M − Cl]+), requires
257.08903, found 257.08905.
1,3-Bis(2,4-difluorophenyl)imidazolium Chloride (2). This
was prepared as a hygroscopic white powder in a similar manner
(13.405 g, 60%). Mp: 293−295 °C. Anal. Calcd for C15H9ClF4N2: C,
54.79, H 2.76, N, 8.52. Found: C, 54.62, H, 2.84, N, 8.63. IR: νmax
/
cm−1 2995w, 1554s, 1498s, 1274w, 1155s, 1068s, 974s, 803s, 652s. 1H
NMR (DMSO): 10.43 (s, 1H, NCHN), 8.50 (br s, 2H, NCHCHN),
8.18 (m, 2H, ArH), 7.82 (m, 2H, ArH), 7.49 (m, 2H, ArH). 19F{1H}
4
NMR (DMSO): −105.5 (d, 2F, JFF = 8.8 Hz, 4-CF), −118.5 (d, 2F,
4JFF = 8.8 Hz, 2-CF). MS m/z (FAB): 293 ([M − Cl]+, 100%). Acc.
Mass: C15H9F4N2 ([M − Cl]+), requires 293.07013, found 293.07019.
1,3-Bis(2,4,6-trifluorophenyl)imidazolium Chloride (3). This
was prepared as a hygroscopic white powder in a similar manner
(14.892 g, 60%). Mp: 325−328 °C (dec). Anal. Calcd for
C15H7ClF6N2: C, 49.38, H 1.94, N, 7.68. Found: C, 49.48, H, 1.87,
N, 7.59. IR: νmax/cm−1 3060br, 1616s, 1562s, 1495s, 1457s, 1258w,
1190w, 1133s, 996s, 897br. 1H NMR (DMSO): 10.38 (s, 1H,
NCHN), 8.51 (br s, 2H, NCHCHN), 7.78 (br s, 4H, 3-CH). 19F{1H}
NMR (DMSO): −101.8 (br s, 2F, 4-CF), −117.1 (br s, 4F, 2-CF). MS
m/z (FAB): 329 ([M − Cl]+, 100%). Acc. Mass: C15H7F6N2 ([M −
Cl]+), requires 329.05134, found 329.05131
CONCLUSIONS
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Prolonged heating and reaction times allows the formation of
fluoroaryl-imidazolium salts from a one-pot condensation of
glyoxal, formaldehyde, and the respective fluorinated aniline.
Various experimental observations, including the inability to
isolate the related free NHCs, indicate that the fluorine
substituents do influence the chemistry of these systems.
Attempts to react the N,N′-bis(2,4,6-trifluorophenylimidazo-
lium) salt with ruthenium and iridium carbonyl fluoride
reagents failed. However, coordination of the related 4-
fluorophenyl- and 2,4-difluorophenylcarbenes, with concom-
itant aryl C−H bond activation, to both iridium and ruthenium
afforded new bis-cyclometalated metal carbene derivatives.
Bis(η2-1,3-bis(4-fluorophenyl)imidazol-2-ylidene)-
carbonyliridium Chloride (4). 1,3-Bis(4-fluorophenyl)imidazolium
chloride (0.680 g, 2.32 mmol) (1), potassium tert-butoxide (0.260 g,
2.32 mmol), and fac-[IrF3(CO)3] (0.091 g, 0.27 mmol) were stirred in
dry tetrahydrofuran (50 mL) under nitrogen for 16 h. After removal of
all volatiles in vacuo, the dark solid was recrystallized from
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dx.doi.org/10.1021/om2009809 | Organometallics 2012, 31, 1518−1523