Palladium complexes of N-heterocyclic carbenes displaying an unsymmetrical: N-alkylfluorenyl/N ′-aryl substitution pattern and their behaviour in Suzuki-Miyaura cross coupling

Article abstract of DOI:10.1039/c9dt02948f

A series of new Pd-PEPPSI complexes containing imidazolylidene ligands with a mixed 9-alkyl-9-fluorenyl/aryl N,N′-substitution pattern have been synthesised. Single crystal X-ray diffraction studies were carried out for four complexes, which revealed that

Full text of DOI:10.1039/c9dt02948f

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Palladium complexes of N-heterocyclic carbenes
displaying an unsymmetrical N-alkylfluorenyl/
N’-aryl substitution pattern and their behaviour in
Suzuki–Miyaura cross coupling†
Cite this: Dalton Trans., 2019, 48,
14516
c
Hamzé Almallah,a,b Eric Brenner, *a Dominique Matt, *a Jack Harrowfield,
Mohamad Jahjahb and Akram Hijazib
A series of new Pd–PEPPSI complexes containing imidazolylidene ligands with a mixed 9-alkyl-9-
fluorenyl/aryl N,N’-substitution pattern have been synthesised. Single crystal X-ray diffraction studies were
carried out for four complexes, which revealed that the N-heterocyclic carbene ligands display a semi-
open, unsymmetrical space occupancy about the metal. Despite their particular unsymmetrical shape,
the new complexes were found to perform as well in Suzuki–Miyaura cross coupling (dioxane, 80 °C) as
previously reported, highly active analogues bearing two sterically protecting 9-alkylfluorenyl substituents.
They were further found to be considerably more active than the standard Pd–PEPPSI complexes
[PdCl2IMes(pyridine)] and [PdCl2IPr(pyridine)]. Surprisingly, unlike the latter, the unsymmetrical complexes
of this study were practically inactive in isopropanol at 80 °C. Under these conditions the complexes
appear to decompose with formation of non-stabilised nanoparticles.
Received 18th July 2019,
Accepted 6th September 2019
DOI: 10.1039/c9dt02948f
rsc.li/dalton
other than organic carbenes.8 In the sole field of inorganic
chemistry, over 3800 studies dealing with NHC-complexes have
Introduction
Transition metal complexes featuring N-heterocyclic carbenes appeared in the literature since 2000. This topic has been
(NHCs) play a central role in contemporary coordination chem- documented in a number of reviews and books.1b,c,9
istry and catalysis.1 Research in this field has led to a variety of
The chemistry of complexes containing bis-N,N′-(9-alkyl-9-
effective, new metal catalysts, striking examples including fluorenyl)-substituted NHCs (noted AF2-NHCs hereafter) has
soluble complexes suitable for C–C bond forming reactions,2 been under investigation in our group for several years.10 NHC
olefin metathesis3 and asymmetric hydrogenation,4 not to ligands of this type constitute valuable monodentate ligands
mention applications in heterogeneous catalysis.5 Although suitable for a meridional confinement of metal ions. Thus, for
NHC-complexes have been known since the late 1960s,6 their example, in PEPPSI-type complexes (PEPPSI stands for pyri-
chemistry really began when organic chemists found that free dine-enhanced precatalyst preparation, stabilisation and
(N-heterocyclic) carbenes can be isolated.7 This discovery, logi- initiation) of general formula [PdCl2(AF2-NHC)(pyridine)]
cally, gave rise to an explosion of interesting experimental and (Fig. 1), the presence of CH groups in the two alkyl side chains
theoretical studies, and paradoxically also stimulated research
aiming at the production of NHC complexes from precursors
aLaboratoire de Chimie Inorganique Moléculaire et Catalyse, Institut de Chimie
(UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal,
67070 Strasbourg Cedex, France. E-mail: eric.brenner@unistra.fr, dmatt@unistra.fr
bInorganic and Organometallic Coordination Chemistry Laboratory,
Faculty of Sciences, Lebanese University, R. Hariri University Campus, Beyrouth,
Hadath, Lebanon
cInstitut de Science et Ingénierie Supramoléculaires (ISIS), UMR 7606 CNRS,
Université de Strasbourg, 8 rue Gaspard Monge, 67083 Strasbourg cedex, France
†Electronic supplementary information (ESI) available: Crystallographic data
and NMR spectra of all new compounds. CCDC 1897856–1897859. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c9dt02948f
Fig. 1 General formula of previously reported [PdCl2(AF2-NHC)(pyri-
dine)] complexes.10
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symmetrically located on the two sides of the metal plane
gives rise to electrostatic C–H⋯Pd interactions, with the conse-
quence that the NHC ligand behaves as a pseudo-tridentate
ligand in which metal binding is ensured by a classical
Results and discussion
Synthesis of Pd–PEPPSI complexes with unsymmetrical (AF,
Ar)-Im ligands
Ccarbene–Pd bond and two anagostic C–H⋯Pd interactions The unsymmetrical complexes described in this study were
(with M⋯H distances in the range 2.3–2.9 Å). The resulting obtained starting either from N-mesitylimidazole (1) or N-2,6-
high steric shielding provided by such ligands was found diisopropyl imidazole (2) (Scheme 1). Both heterocycles were
responsible for the formation of highly stable complexes.
alkylated with 9-bromofluorene to yield quantitatively the
Remarkably, some of these showed higher activities in cross corresponding imidazolium salts 3H and 4H, respectively.
coupling catalysis than those obtained with conventional, bis- Deprotonation of 3H and 4H with LiHMDS (1.2 equiv.), fol-
aryl substituted NHCs (notably IMes and IPr11).
lowed by reaction with appropriate alkyl halides (RX = EtBr,
As a continuation of our studies on 9-alkyl-fluorenyl substi- n-PrBr, ClCH2OEt) and subsequent treatment with NH4BF4
tuted NHCs, we decided to embark on the synthesis of palla- resulted in six new azolium derivatives, namely 3Et, 3Pr, 3EOM
,
dium imidazolylidene (Im) complexes having only one of the 4Et, 4Pr, and 4EOM (EOM standing for CH2OMe). This method-
heterocyclic N atoms substituted by an AF group, with the ology for grafting alkyl side chains on the fluorenylidene unit
other substituted by an o-substituted aryl group. To date, com- was based on a procedure reported recently by César et al. for
plexes of this kind remain unreported. The purpose of this the preparation of an analogous salt. All six compounds were
study was three-fold: (a) to establish a convenient procedure then reacted with PdCl2 in pyridine at 80 °C in the presence of
for the preparation of Pd–PEPPSI complexes containing such K2CO3, affording the expected PEPPSI-type complexes 5Et, 5Pr,
unsymmetrically substituted NHCs, expecting them to possess
5
EOM, 6Et, 6Pr, 6EOM, respectively (Scheme 1). It is noteworthy
a less crowded metal environment than that of their bis-AF that the individual intermediates of the six reaction sequences
substituted versions; (b) to compare the performance of such were all purified chromatographically, the overall yields of
complexes in Suzuki–Miyaura coupling with that of conven- these reactions being close to 50% in each case (see experi-
tional bis-aryl substituted catalysts; and (c) to gain some mental details). The H and 13C{1H} NMR spectra of the com-
1
insight into the stability of the complexes under catalytic con- plexes at ambient temperature are straighforwardly analysed,
ditions with regard to the formation of nanoparticles. The all showing the two different (olefinic) CH groups of the NHC
benefits of mixed alkyl/aryl-substituted NHCs for use in Suzuki ring, as well as the CH protons of the alkyl side chain. For each
1
Miyaura reactions were recently established in a study by complex, the H NMR spectrum reveals that the signal of the
Hashmi et al.12 focussed on NHCs substituted by a flexible methylene unit attached to the fluorenylidene moiety (termed
cycloalkyl group and a di-ortho-substituted aryl ring.
α-CH2 group hereafter) has undergone a significant lowfield
Scheme 1 Synthesis of the Pd–PEPPSI complexes 5R and 6R. The intermediates 3* and 4* have been fully characterised.
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shift (1.78 < Δδ < 1.95 ppm) with respect to that of the corres-
Interestingly, despite their unsymmetrical shape, the
ponding azolium precursor. Similar differences were found in ligands of the four complexes are characterised by a similar
15
previously reported PEPPSI-type complexes based on NHCs steric bulk (36.1 < %VBur < 38.9), which, in fact, does not
bearing two identical AF substituents. The 1J(CH) coupling differ significantly from that of the “symmetrical” ligand EtF2-
constant was determined only for the α-CH2 group of complex Im (%VBur = 38.8).
6Et. As the observed value, 132 Hz, is typical for H atoms
Synthesis of Pd–PEPPSI complexes with symmetrical AF2-Im
bound to sp3-hybridised C atoms, no further 1J(CH) values
ligands
were determined. Overall, these findings are consistent with
the existence of anagostic interactions13 involving the palla- For comparative purposes (vide infra, catalytic study), the three
dium centre and the neighbouring α-CH2 group. Single crystal PEPPSI complexes 9Me, 9Et, 9Pr, in which the NHC ligands bear
X-ray diffraction studies carried out for the complexes 5Et, 5Pr, two identical AF substituents, were also synthesised
6Et, and 6EOM confirmed, in each case, the close proximity of (Scheme 2). Their preparation began with that of 7H, which
the α-CH2 group to the Pd atom (Fig. 2). As expected, the two was obtained by reacting 9-aminofluorene with glyoxal and for-
chlorido ligands are in a relative trans position and the NHC maldehyde in acetic acid in the presence of MgSO4 and ZnCl2.
plane is nearly perpendicular to the metal plane (Fig. 2), The beneficial role of ZnCl2 as additive in condensation reac-
thereby positioning the α-CH2 group near the metal dz2 axis. tions forming imidazolium salts was recently demonstrated by
The bond lengths between the palladium atom and the Mauduit et al.16 To obtain the product as a tetrafluoroborate
four atoms of the first coordination sphere are not unusual salt, the reaction mixture was treated with NH4BF4 after com-
(Table 1).
pletion of the reaction. Chromatographic purification gave 7H
The above four structural studies were useful to establish in 81% yield. The imidazolium salts 8Me, 8Et, 8Pr were then
the topographic steric map14 and buried volume15 (VBur) of the obtained by alkylation of 7H with the appropriate alkyl halide,
corresponding ligands. Owing to the presence of two distinct applying the same methodology as that used above in the syn-
N-substituents, in particular to that of a single alkyl group thesis of the “unsymmetrical” salts 3R and 4R.
pointing to the dz2 axis, the ligand has a markedly unsymme-
trical space occupancy about the metal centre (Fig. 3).
The final products, 9Me, 9Et, and 9Pr, were synthesised from
[PdCl2] applying Organ’s method (Scheme 2). Unsurprisingly,
Fig. 2 Molecular structures of 5Et, 5Pr, 6Et and 6EOM. The CH2Cl2 molecules in 6Et and 6EOM are omitted for clarity. α-CH⋯Pd distances (Å): 2.70,
2.81 (5Et); 2.62, 2.82 (5Pr); 2.68, 2.91 (6Et); 2.61, 2.98 (6EOM). The α-CH2 atoms were positioned geometrically, with C–H = 0.95 (Å). Dihedral angle (°)
between the coordination plane and the NHC ring plane: 87.2 (5Et), 84.5 (5Pr), 86.5 (6Et), 83.9 (6EOM).
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Table 1 Important bond lengths in 5Et, 5Pr, 6Et and 6EOM
being, as for 5 and 6, consistent with anagostic CH⋯Pd inter-
actions. Note, the deshielding is less pronounced for the
methylated complex 9Me (Δδα-CH = 1.20) than for 9Et and 9Pr
(Δδα-CH = ca. 2 ppm). This is probably for steric reasons, the
alkyl groups of 9Et and 9Pr favouring conformations in which
the two α-C–H bonds are turned towards the metal rather than
towards the fluorenylidene moiety. In contrast, the three C–H
bonds of the small Me group of 9Me can freely adopt a variety
of orientations (because of unimpeded rotation of the Me
group about the C9-fluorenyl–Me bond), thereby reducing their
time-averaged proximity to the palladium atom and conse-
quently reducing anagostic bonding.
Complex
Pd–Cl
Pd–C (carbene)
Pd–N (pyridine)
5Et
2.303(1); 2.311(2)
2.308(2); 2.316(2)
2.306(2); 2.315(2)
2.306(2); 2.312(2)
1.975(4)
1.970(3)
1.977(4)
1.976(3)
2.112(3)
2.096(3)
2.081(3)
2.101(3)
5Pr
6Et
6EOM
1
all three complexes exhibit a H NMR spectrum in which the
α-CH2 proton signals appear again at considerably lower field
than in the spectra of the corresponding precursors, this
Fig. 3 Topographic steric map of the ligands of 5Et, 5Pr, 6Et, 6EOM and EtF2-Im (9Et) with their %VBur. The numbering below each steric map is that of
the corresponding complex. Views have the carbene axis pointing to the observer; the domain on the left side corresponds to the alkylfluorenyl
group. The distances on the coloured scale indicate the height along the z axis. The calculated buried volumes (%VBur) were obtained applying a
sphere radius of 3.5 Å, and taking into account the H atoms.
Scheme 2 Synthesis of the Pd–PEPPSI complexes 9R.
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Catalytic studies
(Table 2, entry 1). It should be remembered here that nano-
particles and/or clusters can be readily formed from Pd–NHC
complexes (after formation of Pd–C or Pd–H bonds followed by
C-NHC or H-NHC coupling), and that these can result in
azolium-stabilised species which are active in cross coupling.17
The complexes 5R and 6R themselves are stable in isopropanol
at 80 °C. However, in the presence of the reagents, they pro-
vided totally inactive species (at 80 °C). Possibly, under these
conditions the carbene ligand dissociates from the metal and
subsequently undergoes cleavage of the N–C(AF) unit, leading
to a neutral imidazole unable to favour the formation of active
nanoparticles.
The six unsymmetrical complexes 5R and 6R (R = Et, n-Pr,
EtOCH2) were assessed in the coupling of phenylboronic acid
with p-tolyl chloride. Catalysis was performed in dioxane at
80 °C in the presence of 0.5 mol% Pd and 2 equiv. of Cs2CO3.
Under these conditions, all the complexes displayed high
activity (Table 2, entries 3–8), significantly superior to those
obtained with the standard complexes [PdCl2(IMes)(pyridine)]
and [PdCl2(IPr)(pyridine)] (Table 2, entries
1 and 2).
Interestingly, the results obtained with 5R and 6R were quite
similar to those obtained with the symmetrically functiona-
lised complexes 9R (entries 9–11), this showing that a single
alkylfluorenyl group per se provides efficient catalyst stabilis-
ation. Repeating the reactions carried out with 5Et, 6Et, and 9Et
in the presence of added mercury kept the activity high Conclusions
(decrease of activity 7–15%, Table 2), this being a good indi-
We have synthesised the first Pd–PEPPSI complexes featuring
cation that nanoparticle formation was marginal during these
runs, and thus that these catalysts are stable in dioxane. In
contrast, when adding mercury to the catalytic solution con-
taining [PdCl2(IMes)(pyridine)], the yield dropped to ca. 33%.
Further tests were performed in isopropanol at 80 °C. Thus,
the complexes 5Pr and 6Et showed nearly no activity in isopro-
panol (Table 2, entries 4 and 6), this markedly contrasting
with the reference complex [PdCl2(IMes)(pyridine)], which
turned out to be twice as active in isopropanol as in dioxane
despite considerable production of colloids in that case
imidazolylidene ligands characterised by a mixed 9-alkyl-9-
fluorenyl/aryl N,N′-substitution pattern. As revealed by several
X-ray diffraction studies, the bound NHCs display a markedly
unsymmetrical space occupancy about the metal, quite unlike
that of doubly AF-substituted analogues, known to be highly
active in Suzuki–Miyaura cross couplings carried out in
dioxane (80 °C). Significantly, the unsymmetrical form of the
new NHCs is not at all an obstacle to high catalytic activity,
thus showing that the presence of a single AF group ensures
good complex stability. Surprisingly, unlike conventional Pd–
PEPPSI complexes such as [PdCl2IMes(pyridine)] or [PdCl2IPr
(pyridine)], the new unsymmetrical complexes were practically
inactive in isopropanol at 80 °C. This observation, together
with that of the formation of black, colloidal solutions in this
alcohol, suggests that the complexes decompose and result in
organic compounds unable to stabilise concomitantly formed
nanoparticles.
Table 2 Suzuki–Miyaura cross-coupling of PhB(OH)2 with p-tolylchlor-
ide using palladium complexes 5R, 6R, 9R a
Experimental section
General procedures
Yielda (%)
in dioxane
Yielda (%)
in i-PrOH
All commercial reagents were used as supplied. The syntheses
were performed in Schlenk-type flasks under dry nitrogen.
Solvents were dried by conventional methods and distilled
immediately prior to use. Routine 1H and 13C{1H} NMR
spectra were recorded on a FT Bruker Avance 500, 400 or 300
instrument at 25 °C. 1H NMR shifts were referenced to residual
protonated solvent (CHCl3, δ 7.26; [D6]DMSO, δ 2.50), 13C
chemical shifts are reported relative to deuterated solvent
signals (CDCl3, δ 77.16; [D6]DMSO, δ 39.52). In the NMR data
given hereafter, Cq denotes a quaternary carbon atom. Flash
chromatography was performed as described by Still et al.,18
employing Geduran SI (E. Merck, 0.040–0.063 mm) silica.
Routine thin-layer chromatography analyses were carried out
by using plates coated with Merck Kieselgel 60 GF254.
Elemental analyses were performed by the Service de
Microanalyse, Institut de Chimie (UdS-CNRS), Strasbourg.
N-Mesityl imidazole (1) and N-(2,6-diisopropylphenyl)imid-
Entry
[Pd]
with Hgb
with Hgb
1
2
[PdCl2(IMes)(Py)]
[PdCl2(IPr)(Py)]
47
23
32
—
83
81
17
—
3
4
5
5Et
71
83
74
—
70
—
—
5
—
—
—
—
5Pr
5EOM
6
7
8
6Et
81
57
73
75
—
—
3
—
—
—
—
—
6Pr
6EOM
9
10
11
9Me
9Et
9Pr
64
87
76
—
81
—
—
18
—
—
—
—
a p-Tolyl chloride (1 mmol), phenylboronic acid (1.5 mmol), Cs2CO3
(2 mmol), solvent (3 mL). Yields determined by 1H NMR using 1,4-
dimethoxybenzene as internal standard. Averaged over two runs.
b Reaction performed in the presence of 50 μL of Hg (3.38 mmol,
3.4 eq.).
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azole (2) were prepared according to a literature procedure.19 MeOH (1 mL) was added to quench any further reaction. The
9-Fluorenylamine was obtained from commercially available solvent was removed under reduced pressure and the crude
9-fluorenylamine hydrochloride or following a protocol start- product was purified by flash chromatography (SiO2; MeOH/
1
ing from fluorenone.20 [PdCl2(IMes)(Py)]10a and [PdCl2(IPr) CH2Cl2, 2 : 98) to afford 3*Et as a tan solid (0.175 g, 83%). H
3
(Py)]10a were prepared as described in the literature.
NMR (CDCl3, 500 MHz), δ 10.76 (1H, s, NCHN), 7.78 (2H, d, J
= 7.5 Hz, ArH), 7.74 (2H, d, 3J = 7.5 Hz, ArH), 7.51 (2H, dd, 3J =
Synthesis of unsymmetrical imidazolium salts 3R and 4R
3J′ = 7.5 Hz, ArH), 7.41 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.26 (1H,
3
1-(Fluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazolium bromide s, NCH), 7.18 (1H, s, NCH), 6.97 (2H, s, ArH), 3.24 (2H, q, J =
(3H). A mixture of N-mesityl imidazole (1) (0.500 g, 2.68 mmol) 6.9 Hz, CH2), 2.30 (3H, s, CH3), 2.10 (6H, s, CH3), 0.53 (3H, t,
and 9-bromofluorene (0.720 g, 2.95 mmol) in toluene (25 mL) 3J = 6.9 Hz, CH2CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz),
was heated under reflux for 3 days. The mixture was cooled to δ 142.9 (arom. Cq), 141.0 (arom. Cq), 140.3 (arom. Cq), 137.6
room temperature and the solvent removed under reduced (NCHN), 134.1 (arom. Cq), 130.8 (arom. Cq), 130.6 (arom. CH),
pressure. The crude product was purified by flash chromato- 129.7 (arom. CH), 129.2 (arom. CH), 124.2 (arom. CH), 123.7
graphy (SiO2; MeOH/CH2Cl2, 2 : 98) to afford 3H as a pale (NCH), 121.4 (NCH), 120.8 (arom. CH), 75.4 (Cq), 30.4 (CH2),
1
brown solid (1.14 g, 99%). H NMR (CDCl3, 500 MHz), δ 11.30 21.1 (CH3), 17.8 (2CH3), 7.8 (CH2CH3) ppm. Found C, 68.25; H,
(1H, s, NCHN), 7.77 (2H, d, 3J = 7.4 Hz, ArH), 7.76 (1H, s, 6.01; N, 5.91. Calcd for C27H27BrN2·0.21 CH2Cl2 (Mr = 459.43 +
3
3
3
NCH), 7.63 (2H, d, J = 7.4 Hz, ArH), 7.49 (2H, dd, J = J′ = 7.4 17.83): C, 68.48; H, 5.79; N, 5.87%.
Hz, ArH), 7.34 (2H, dd, 3J = 3J′ = 7.4 Hz, ArH), 7.07 (1H, s,
1-(9-Ethylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazolium
NCH), 7.03 (2H, s, ArH), 6.85 (1H, s, aliph. CH), 2.35 (3H, s, tetrafluoroborate (3Et). To a solution of imidazolium bromide
CH3), 2.14 (6H, s, CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz), 3*Et (0.400 g, 0.87 mmol) in CH2Cl2 (20 mL) was added a solu-
δ 141.6 (arom. Cq), 141.0 (arom. Cq), 140.1 (arom. Cq), 139.4 tion of ammonium tetrafluoroborate (0.110 g, 1.04 mmol) in
(NCHN), 134.2 (arom. Cq), 130.7 (arom. Cq), 130.6 (arom. CH), water (20 mL). The mixture was vigorously stirred at room
130.1 (arom. CH), 128.8 (arom. CH), 125.7 (arom. CH), 123.4 temperature for 1 h. The organic layer was separated and the
(NCH), 120.8 (arom. CH), 120.2 (NCH), 63.2 (aliph. CH), 21.2 aqueous phase was extracted with CH2Cl2 (2 × 10 mL). The
(CH3), 17.8 (2CH3) ppm. Found C, 67.17; H, 5.44; N, 6.14. combined organic layers were dried with Na2SO4, and the
Calcd for C25H23BrN2·0.25 CH2Cl2 (Mr = 431.38 + 21.23): C, solvent was removed under reduced pressure. The imidazo-
67.01; H, 5.23; N, 6.19%. NMR spectroscopic data are consist- lium tetrafluoroborate 3Et (0.401 g, 99%) was obtained as a tan
1
ent with those in the literature.21
solid. H NMR (CDCl3, 500 MHz), δ 9.16 (1H, s, NCHN), 7.79
3
1-(Fluoren-9-yl)-3-(2,6-diisopropylphenyl)imidazolium bromide (2H, d, J = 7.5 Hz, ArH), 7.57–7.49 (4H, m, ArH), 7.40 (2H, dd,
(4H).
A
mixture of N-(2,6-diisopropylphenyl)imidazole (2) 3J = 3J′ = 7.5 Hz, ArH), 7.24 (1H, s, NCH), 7.19 (1H, s, NCH),
3
(3.00 g, 13.1 mmol) and 9-bromofluorene (3.50 g, 14.3 mmol) 6.96 (2H, s, ArH), 2.95 (2H, q, J = 7.2 Hz, CH2), 2.29 (3H, s,
in toluene (50 mL) was heated under reflux for 3 days. The CH3), 2.02 (6H, s, CH3), 0.52 (3H, t, J = 7.2 Hz, CH3) ppm. 13
C
3
mixture was cooled to room temperature and the solvent {1H} NMR (CDCl3, 125 MHz), δ 142.9 (arom. Cq), 141.2 (arom.
removed under reduced pressure. The crude product was Cq), 140.3 (arom. Cq), 135.4 (NCHN), 134.2 (arom. Cq), 130.8
washed with diethyl ether (40 mL) and then dried to afford 4H (overlapped signals, arom. Cq and arom. CH), 129.8 (arom.
as a pale grey solid (6.06 g, 98%). 1H NMR ([D6]DMSO, CH), 129.4 (arom. CH), 124.4 (NCH), 123.7 (arom. CH), 121.8
500 MHz), δ 10.15 (1H, s, NCHN), 8.18 (1H, s, NCH), 8.05 (2H, (NCH), 121.0 (arom. CH), 75.1 (Cq), 29.3 (CH2), 21.1 (CH3),
d, 3J = 7.5 Hz, ArH), 7.85 (1H, s, NCH), 7.68–7.57 (5H, m, ArH), 17.2 (2CH3), 7.8 (CH2CH3) ppm. 19F NMR (CDCl3, 282 MHz), δ
1
7.49–7.44 (4H, m, ArH), 7.07 (1H, s, aliph. CH), 2.29 (2H, qq, 3J −152.77 (br s, 19F–10B), −152.83 (q, J(19F–11B) = 1.1 Hz) ppm.
3
= 3J′ = 6.8 Hz, CHMe2), 1.19 (6H, d, J = 6.8 Hz, CH3), 1.14 (6H, Found C, 69.30; H, 5.93; N, 6.12. Calcd for C27H27BF4N2 (Mr =
3
d, J = 6.8 Hz, CH3) ppm. 13C{1H} NMR ([D6]DMSO, 125 MHz), 466.33): C, 69.54; H, 5.84; N, 6.01%.
δ 145.0 (arom. Cq), 140.5 (arom. Cq), 140.1 (arom. Cq), 138.7
1-(9-Ethylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imidazolium
(NCHN), 131.5 (para arom. CH dipp), 130.5 (arom. Cq), 130.4 bromide (4*Et). LiHMDS (2.53 mL, 2.53 mmol, 1 M in THF)
(arom. CH), 128.5 (arom. CH), 125.9 (NCH), 125.1 (arom. CH), was added dropwise to a stirred suspension of 1-(fluoren-9-yl)-
124.4 (arom. CH), 121.6 (NCH), 121.2 (arom. CH), 62.7 (aliph. 3-(2,6-diisopropylphenyl)imidazolium bromide (4H) (1.00 g,
CH), 28.2 (CHMe2), 23.8 (CH3), 23.7 (CH3) ppm. Found C, 2.11 mmol) in THF (40 mL) cooled at −50 °C. After 1 h, the
70.79; H, 6.16; N, 5.98. Calcd for C28H29BrN2 (Mr = 473.47): C, reaction mixture was allowed to reach room temperature and
71.03; H, 6.17; N, 5.92%.
ethyl bromide (0.70 g, 6.4 mmol) was added. The mixture
1-(9-Ethylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazolium was stirred overnight at room temperature and MeOH (2 mL)
bromide (3*Et). LiHMDS (0.55 mL, 0.55 mmol, 1 M in THF) was added to quench any further reaction. The solvent was
was added dropwise to a stirred suspension of 1-(fluoren-9-yl)- removed under reduced pressure and the crude product was
3-(2,4,6-trimethylphenyl)imidazolium bromide (3H) (0.200 g, purified by flash chromatography (SiO2; MeOH/CH2Cl2, 4 : 96)
1
0.46 mmol) in THF (6 mL) cooled to −50 °C. After 1 h (at to afford 4*Et as a white solid (0.64 g, 60%). H NMR (CDCl3,
−50 °C), the reaction mixture was allowed to reach room tem- 500 MHz), δ 10.25 (1H, s, NCHN), 7.86 (1H, s, NCH), 7.78 (2H,
perature and ethyl bromide (0.150 g, 1.37 mmol) was added. d, 3J = 7.5 Hz, ArH), 7.76 (2H, d, 3J = 7.5 Hz, ArH), 7.52 (2H, dd,
3
3
The mixture was stirred overnight at room temperature and 3J = J′ = 7.5 Hz, ArH), 7.48 (1H, t, J = 7.8 Hz, ArH), 7.42 (2H,
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dd, J = J′ = 7.5 Hz, ArH), 7.34 (1H, s, NCH), 7.26 (2H, d, J = (CDCl3, 125 MHz), δ 143.3 (arom. Cq), 141.0 (arom. Cq), 140.1
3
3
7.8 Hz, ArH), 3.25 (2H, q, J = 7.2 Hz, CH2), 2.18 (2H, qq, J = (arom. Cq), 137.5 (NCHN), 134.0 (arom. Cq), 130.7 (arom. Cq),
3J′ = 6.9 Hz, CHMe2), 1.19 (6H, d, 3J = 6.9 Hz, CH3), 1.11 (6H, d, 130.5 (arom. CH), 129.7 (arom. CH), 129.2 (arom. CH), 124.1
3J = 6.9 Hz, CH3), 0.57 (3H, t, J = 7.2 Hz, CH2CH3) ppm. 13C (arom. CH), 123.8 (NCH), 121.3 (NCH), 120.8 (arom. CH), 74.8
3
{1H} NMR (CDCl3, 125 MHz), δ 145.0 (arom. Cq), 142.8 (arom. (Cq), 38.8 (CqCH2), 21.1 (CH3), 17.8 (2CH3), 17.0 (CH2CH3),
Cq), 140.2 (arom. Cq), 137.3 (NCHN), 131.8 (para arom. CH 13.6 (CH2CH3) ppm. Found C, 69.99; H, 6.13; N, 5.86. Calcd
dipp), 130.7 (arom. CH), 130.2 (arom. Cq), 129.3 (arom. CH), for C28H29BrN2 (Mr = 473.46): C, 71.03; H, 6.17; N, 5.92%.
124.8 (NCH), 124.6 (arom. CH), 124.1 (arom. CH), 122.3
1-(9-Propylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazolium
(NCH), 121.0 (arom. CH), 75.5 (Cq), 30.4 (CH2), 28.8 (CHMe2), tetrafluoroborate (3Pr). To a solution of imidazolium bromide
24.4 (CH3), 23.9 (CH3), 7.9 (CH2CH3) ppm. Found C, 71.83; H, 3*Pr (0.556 g, 1.17 mmol) in CH2Cl2 (20 mL) was added water
6.61; N, 5.70. Calcd for C30H33BrN2 (Mr = 501.51): C, 71.85; H, (20 mL) and ammonium tetrafluoroborate (0.148 g,
6.63; N, 5.59%.
1.40 mmol). The mixture was stirred vigorously at room temp-
1-(9-Ethylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imidazolium erature for 1 h. The organic layer was separated and the
tetrafluoroborate (4Et). To a solution of imidazolium bromide aqueous phase was extracted with CH2Cl2 (2 × 10 mL). The
4*Et (0.508 g, 1.01 mmol) in CH2Cl2 (20 mL) was added a solu- combined organic layers were dried with Na2SO4, and the
tion of ammonium tetrafluoroborate (0.127 g, 1.21 mmol) in solvent was removed under reduced pressure. The imidazo-
water (20 mL). The mixture was stirred vigorously at room lium tetrafluoroborate 3Pr (0.502 g, 89%) was obtained as a tan
1
temperature for 1 h. The organic layer was separated and the solid. H NMR (CDCl3, 500 MHz), δ 9.09 (1H, s, NCHN), 7.79
3
3
aqueous phase was extracted with CH2Cl2 (2 × 10 mL). The (2H, d, J = 7.5 Hz, ArH), 7.56 (2H, d, J = 7.5 Hz, ArH), 7.52
3
3
3
3
combined organic layers were dried with Na2SO4, and the (2H, dd, J = J′ = 7.5 Hz, ArH), 7.40 (2H, dd, J = J′ = 7.5 Hz,
solvent was removed under reduced pressure. The imidazo- ArH), 7.26 (1H, s, NCH), 7.19 (1H, s, NCH), 6.97 (2H, s, ArH),
lium tetrafluoroborate 4Et (0.510 g, 99%) was obtained as a 2.90–2.84 (2H, m, CqCH2), 2.29 (3H, s, CH3), 2.02 (6H, s, CH3),
light pink solid. 1H NMR (CDCl3, 500 MHz), δ 8.96 (1H, s, 0.83–0.77 (5H, m, CH2CH3 and CH2CH3) ppm. 13C{1H} NMR
3
NCHN), 7.80 (2H, d, J = 7.5 Hz, ArH), 7.57–7.46 (6H, m, ArH), (CDCl3, 125 MHz), δ 143.2 (arom. Cq), 141.1 (arom. Cq), 140.1
7.42 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.33 (1H, s, NCH), 7.26 (arom. Cq), 135.1 (NCHN), 134.2 (arom. Cq), 130.7 (over-
3
3
(2H, d, J = 7.7 Hz, ArH), 2.95 (2H, q, J = 7.2 Hz, CH2), 2.17 lapped signals, arom. Cq and arom. CH), 129.7 (arom. CH),
(2H, qq, 3J = 3J′ = 6.8 Hz, CHMe2), 1.12 (6H, d, 3J = 6.9 Hz, CH3) 129.4 (arom. CH), 124.4 (NCH), 123.7 (arom. CH), 121.7
1.11 (6H, d, 3J = 6.9 Hz, CH3), 0.55 (3H, t, 3J = 7.2 Hz, CH2CH3) (NCH), 121.0 (arom. CH), 74.4 (Cq), 37.8 (CqCH2), 21.3 (CH3),
ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 145.1 (arom. Cq), 17.2 (2CH3), 16.9 (CH2CH3), 13.4 (CH2CH3) ppm. 19F NMR
142.7 (arom. Cq), 140.3 (arom. Cq), 135.6 (NCHN), 131.9 (para (CDCl3, 282 MHz), δ −152.43 (br s, 19F–10B), −152.49 (q,
arom. CH dipp), 130.9 (arom. CH), 130.2 (arom. Cq), 129.4 1J(19F–11B) = 1.1 Hz) ppm. Found C, 70.09; H, 6.16; N, 5.82.
(arom. CH), 125.3 (NCH), 124.6 (arom. CH), 123.6 (arom. CH), Calcd for C28H29BF4N2 (Mr = 480.36): C, 70.01; H, 6.09; N,
121.9 (NCH), 121.1 (arom. CH), 75.2 (Cq), 29.3 (CH2), 28.8 5.83%.
(CHMe2), 24.0 (CH3), 23.9 (CH3), 7.8 (CH2CH3) ppm. 19F NMR
1-(9-Propylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imidazolium
(CDCl3, 282 MHz), δ −152.70 (br s, 19F–10B), −152.76 (q, bromide (4*Pr). LiHMDS (2.53 mL, 2.53 mmol, 1 M in THF)
1J(19F–11B) = 1.1 Hz) ppm. Found C, 70.98; H, 6.62; N, 5.58. was added dropwise to a stirred suspension of 1-(fluoren-9-yl)-
Calcd for C30H33BF4N2 (Mr = 508.41): C, 70.87; H, 6.54; N, 3-(2,6-diisopropylphenyl)imidazolium bromide (4H) (1.00 g,
5.51%.
2.11 mmol) in THF (40 mL) cooled at −50 °C. After stirring for
1-(9-Propylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazolium 1 h, the reaction mixture was allowed to reach room tempera-
bromide (3*Pr). LiHMDS (1.70 mL, 1.70 mmol, 1 M in THF) ture and n-propyl bromide (0.78 g, 6.30 mmol) was added.
was added dropwise to a stirred suspension of 1-(fluoren-9-yl)- The mixture was stirred overnight at room temperature and
3-(2,4,6-trimethylphenyl)imidazolium bromide (3H) (0.600 g, MeOH (2 mL) was added. The solvent was removed under
1.40 mmol) in THF (20 mL) cooled at −50 °C. After stirring for reduced pressure and the crude product was purified by flash
1 h (temperature being maintained at −50 °C), the reaction chromatography (SiO2; MeOH/CH2Cl2, 3 : 97) to afford 4*Pr as a
mixture was allowed to reach room temperature and n-propyl light pink solid (0.82 g, 76%). 1H NMR (CDCl3, 400 MHz),
bromide (0.52 g, 4.22 mmol) was added. The mixture was δ 10.22 (1H, s, NCHN), 7.83–7.73 (5H, m, ArH), 7.55–7.38 (6H,
stirred overnight at room temperature, then MeOH (2 mL) was m, ArH), 7.25 (2H, d, 3J = 7.7 Hz, ArH), 3.21–3.14 (2H, m,
3
added. The solvent was removed under reduced pressure and CqCH2), 2.19 (2H, qq, 3J = J′ = 6.9 Hz, CHMe2), 1.18 (6H, d,
3
the crude product was purified by flash chromatography (SiO2; 3J = 6.9 Hz, CH3), 1.11 (6H, d, J = 6.9 Hz, CH3), 0.93–0.82 (5H,
MeOH/CH2Cl2, 3 : 97) to afford 3*Pr as a tan solid (0.64 g, m, CH2CH3 and CH2CH3) ppm. 13C{1H} NMR (CDCl3,
1
96%). H NMR (CDCl3, 500 MHz), δ 10.74 (1H, s, NCHN), 7.77 125 MHz), δ 144.8 (arom. Cq), 143.0 (arom. Cq), 139.9 (arom.
3
3
(2H, d, J = 7.6 Hz, ArH), 7.75 (2H, d, J = 7.6 Hz, ArH), 7.50 Cq), 136.9 (NCHN), 131.6 (para arom. CH dipp), 130.6 (arom.
3
3
3
3
(2H, dd, J = J′ = 7.6 Hz, ArH), 7.40 (2H, dd, J = J′ = 7.6 Hz, CH), 130.1 (arom. Cq), 129.1 (arom. CH), 124.9 (NCH), 124.4
ArH), 7.28 (1H, s, NCH), 7.15 (1H, s, NCH), 6.97 (2H, s, ArH), (arom. CH), 124.0 (arom. CH), 122.0 (NCH), 120.9 (arom. CH),
3.20–3.15 (2H, m, CqCH2), 2.29 (3H, s, CH3), 2.10 (6H, s, CH3), 74.5 (Cq), 38.6 (CqCH2), 28.6 (CHMe2), 24.3 (CH3), 23.7 (CH3),
0.86–0.80 (5H, m, CH2CH3 and CH2CH3) ppm. 13C{1H} NMR 16.9 (CH2CH3), 13.5 (CH2CH3) ppm. Found C, 72.33; H, 6.79;
14522 | Dalton Trans., 2019, 48, 14516–14529
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N, 5.53. Calcd for C31H35BrN2 (Mr = 515.54): C, 72.22; H, 6.84; 4.25 (2H, s, CqCH2), 3.64 (2H, q, J = 6.9 Hz, OCH2CH3), 2.29
N, 5.43%.
(3H, s, CH3), 2.07 (6H, s, CH3), 1.19 (3H, t, 3J = 6.9 Hz,
1-(9-Propylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imidazolium OCH2CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 141.7
tetrafluoroborate (4Pr). To a solution of imidazolium bromide (arom. Cq), 141.1 (arom. Cq), 139.8 (arom. Cq), 137.3 (NCHN),
4*Pr (0.778 g, 1.50 mmol) in CH2Cl2 (30 mL) was added water 134.3 (arom. Cq), 131.0 (arom. CH), 130.8 (arom. Cq), 129.8
(30 mL) and ammonium tetrafluoroborate (0.189 g, (arom. CH), 129.1 (arom. CH), 125.6 (arom. CH), 123.7 (NCH),
1.80 mmol). The mixture was vigorously stirred at room temp- 121.7 (NCH), 120.9 (arom. CH), 73.1 (Cq), 71.5 (CqCH2), 66.9
erature for 1 h. The organic layer was separated and the (OCH2CH3), 21.1 (CH3), 17.2 (2CH3), 15.1 (OCH2CH3) ppm. 19
F
aqueous phase was extracted with CH2Cl2 (2 × 15 mL). The NMR (CDCl3, 282 MHz), δ −152.49 (br s, 19F–10B), −152.54 (br
combined organic layers were dried with Na2SO4, and the s, 19F–11B) ppm. Found C, 67.33; H, 5.84; N, 5.67. Calcd for
solvent was removed under reduced pressure. The imidazo- C28H29BF4N2O·0.04 CH2Cl2 (Mr = 496.36 + 3.40): C, 67.39; H,
lium tetrafluoroborate 4Pr (0.770 g, 98%) was obtained as a 5.87; N, 5.61%.
light pink solid. 1H NMR (CDCl3, 500 MHz), δ 8.93 (1H, s,
1-(9-(Ethoxymethyl)fluoren-9-yl)-3-(2,6-diisopropylphenyl)
NCHN), 7.79 (2H, d, J = 7.5 Hz, ArH), 7.57 (2H, d, J = 7.5 Hz, imidazolium tetrafluoroborate (4EOM). LiHMDS (2.55 mL,
ArH), 7.53 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.50–7.46 (2H, m, 2.55 mmol, 1 M in THF) was added dropwise to a stirred sus-
ArH and NCH), 7.41 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.36 (1H, s, pension of 1-(fluoren-9-yl)-3-(2,6-diisopropylphenyl)imida
NCH), 7.26 (2H, d, 3J = 7.8 Hz, ArH), 2.92–2.84 (2H, m, zolium bromide (4H) (1.00 g, 2.11 mmol) in THF (40 mL)
3
3
3
CqCH2), 2.17 (2H, qq, 3J = J′ = 6.8 Hz, CHMe2), 1.12 (6H, d, cooled at −50 °C. After stirring the cold solution for 1 h, the
3
3J = 6.8 Hz, CH3), 1.11 (6H, d, J = 6.8 Hz, CH3), 0.87–0.79 (5H, reaction mixture was allowed to reach room temperature and
m, CH2CH3 and CH2CH3) ppm. 13C{1H} NMR (CDCl3, chlormethyl ethyl ether (0.600 g, 6.33 mmol) was added. The
125 MHz), δ 145.1 (arom. Cq), 143.1 (arom. Cq), 140.1 (arom. mixture was stirred overnight at room temperature and MeOH
Cq), 135.4 (NCHN), 131.9 (para arom. CH dipp), 130.9 (arom. (2 mL) was added. The solvent was removed under reduced
CH), 130.2 (arom. Cq), 129.3 (arom. CH), 125.4 (NCH), 125.5 pressure and water (20 mL) was added. The product was
(arom. CH), 123.6 (arom. CH), 121.8 (NCH), 121.1 (arom. CH), extracted with CH2Cl2 (3 × 20 mL), the organic layers were com-
74.5 (Cq), 37.8 (CqCH2), 28.7 (CHMe2), 24.0 (overlapped bined and the solvent was removed under reduced pressure.
signals 2CH3), 16.9 (CH2CH3), 13.4 (CH2CH3) ppm. 19F NMR To the crude mixture dissolved in CH2Cl2 (30 mL) was added
(CDCl3, 282 MHz), δ −152.45 (br s, 19F–10B), −152.50 (q, water (30 mL) and ammonium tetrafluoroborate (0.265 g,
1J(19F–11B) = 1.1 Hz) ppm. Found C, 71.36; H, 6.87; N, 5.38. 2.53 mmol). The mixture was vigorously stirred at room temp-
Calcd for C31H35BF4N2 (Mr = 522.44): C, 71.27; H, 6.75; N, erature for 1 h. The organic layer was separated and the
5.36%.
aqueous phase was extracted with CH2Cl2 (2 × 15 mL). The
1-(9-(Ethoxymethyl)fluoren-9-yl)-3-(2,4,6-trimethylphenyl) combined organic layers were dried with Na2SO4, and the
imidazolium tetrafluoroborate (3EOM). LiHMDS (2.78 mL, solvent was removed under reduced pressure. The crude
2.78 mmol, 1 M in THF) was added dropwise to a stirred sus- product was purified by flash chromatography (SiO2; EtOAc/
pension of 1-(fluoren-9-yl)-3-(2,4,6-trimethylphenyl)imidazo- CH2Cl2, 3 : 97) to afford 4EOM as a pale brown solid (0.810 g,
1
lium bromide (3H) (1.00 g, 2.32 mmol) in THF (30 mL) cooled 71%). H NMR (CDCl3, 500 MHz), δ 9.20 (1H, s, NCHN), 7.82
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3
at −50 °C. After stirring the cold solution for 1 h, the reaction (2H, d, J = 7.6 Hz, ArH), 7.74 (2H, d, J = 7.6 Hz, ArH), 7.56
3
3
3
mixture was allowed to reach room temperature and chlor- (2H, dd, J = J′ = 7.6 Hz, ArH), 7.51 (1H, t, J = 7.8 Hz, ArH),
methyl ethyl ether (0.660 g, 6.96 mmol) was added. The 7.40 (2H, dd, J = J′ = 7.6 Hz, ArH), 7.29 (2H, d, J = 7.8 Hz,
3
3
3
mixture was stirred overnight at room temperature and MeOH ArH), 7.28 (1H, s, NCH), 7.12 (1H, s, NCH), 4.28 (2H, s,
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(2 mL) was added. The solvent was removed under reduced CqCH2), 3.65 (2H, q, J = 7.0 Hz, OCH2CH3), 2.31 (2H, qq, J =
pressure and water (20 mL) was added. The product was 3J′ = 6.8 Hz, CHMe2), 1.22 (6H, d, 3J = 6.8 Hz, CH3), 1.19 (3H, t,
3
extracted with CH2Cl2 (3 × 20 mL), the organic layers were com- 3J = 7.0 Hz, OCH2CH3), 1.14 (6H, d, J = 6.8 Hz, CH3) ppm. 13C
bined and the solvent was removed under reduced pressure. {1H} NMR (CDCl3, 125 MHz), δ 145.3 (arom. Cq), 141.6 (arom.
To the crude mixture dissolved in CH2Cl2 (30 mL) was added Cq), 139.9 (arom. Cq), 137.3 (NCHN), 131.8 (para arom. CH
water (30 mL) and ammonium tetrafluoroborate (0.295 g, dipp), 131.1 (arom. CH), 130.3 (arom. Cq), 129.1 (arom. CH),
2.81 mmol). The mixture was vigorously stirred at room temp- 125.5 (arom. CH), 124.7 (NCH), 124.6 (arom. CH), 121.8
erature for 1 h. The organic layer was separated and the (NCH), 121.0 (arom. CH), 73.2 (Cq), 71.5 (CqCH2), 67.0
aqueous phase was extracted with CH2Cl2 (2 × 15 mL). The (OCH2CH3), 28.7 (CHMe2), 24.1 (CH3), 24.0 (CH3), 15.0
combined organic layers were dried with Na2SO4, and the (OCH2CH3) ppm. 19F NMR (CDCl3, 282 MHz), δ −152.30 (br s,
solvent was removed under reduced pressure. The crude 19F–10B), −152.35 (q, 1J(19F–11B) = 1.1 Hz) ppm. Found C,
product was purified by flash chromatography (SiO2; EtOAc/ 69.24; H, 6.60; N, 5.24. Calcd for C31H35BF4N2O (Mr = 538.44):
petroleum ether, 70 : 30) to afford 3EOM as a tan solid (0.760 g, C, 69.15; H, 6.55; N, 5.20%.
1
66%). H NMR (CDCl3, 500 MHz), δ 9.22 (1H, s, NCHN), 7.81
(2H, d, J = 7.5 Hz, ArH), 7.73 (2H, d, J = 7.5 Hz, ArH), 7.54
3
3
Synthesis of palladium complexes 5R and 6R
3
3
3
3
(2H, dd, J = J′ = 7.5 Hz, ArH), 7.38 (2H, dd, J = J′ = 7.5 Hz,
trans-[1-(9-Ethylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imida-
ArH), 7.20 (1H, s, NCH), 6.98 (2H, s, ArH), 6.96 (1H, s, NCH), zol-2-ylidene](pyridine)palladium(II) dichloride (5Et). A suspen-
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sion of imidazolium salt 3Et (0.350 g, 0.750 mmol), finely crushed K2CO3 (0.575 g, 4.15 mmol), and PdCl2 (0.176 g,
crushed K2CO3 (0.520 g, 3.75 mmol), and PdCl2 (0.159 g, 0.996 mmol) in pyridine (7 mL) was heated at 80 °C for 18 h
0.90 mmol) in pyridine (6 mL) was heated at 80 °C for 18 h under vigorous stirring. The mixture was cooled to room temp-
under vigorous stirring. The mixture was cooled to room temp- erature, filtered through Celite and the collected solid washed
erature, filtered through Celite and the retained solid washed with CH2Cl2 (ca. 20 mL). The filtrate was evaporated to dryness
with CH2Cl2 (ca. 20 mL). The filtrate was evaporated to dryness and the residue purified by flash chromatography (SiO2;
and the residue purified by flash chromatography (SiO2; CH2Cl2/petroleum ether, 50 : 50) to afford 5Pr as a yellow solid
CH2Cl2/petroleum ether, 50 : 50) to afford 5Et as a yellow solid (0.443 g, 82%). 1H NMR (CDCl3, 500 MHz), δ 8.76–8.71 (2H, m,
(0.377 g, 79%). 1H NMR (CDCl3, 500 MHz), δ 8.77–8.73 (2H, m, o-NC5H5), 7.80 (2H, d, 3J = 7.5 Hz, ArH), 7.75 (2H, d, 3J =
3
4
o-NC5H5), 7.77 (2H, d, 3J = 7.5 Hz, ArH), 7.74 (2H, d, 3J = 7.5 Hz, ArH), 7.68 (1H, tt, J = 7.7 Hz, J = 1.6 Hz, p-NC5H5),
7.5 Hz, ArH), 7.68 (1H, tt, J = 7.7 Hz, J = 1.6 Hz, p-NC5H5), 7.45 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.37 (2H, dd, 3J = 3J′ =
3
4
7.44 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.37 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.28–7.23 (2H, m, m-NC5H5), 7.07 (2H, s, ArH),
3
3
7.5 Hz, ArH), 7.27–7.23 (2H, m, m-NC5H5), 7.05 (2H, s, ArH), 6.66 (1H, d, J = 2.2 Hz, NCH), 6.26 (1H, d, J = 2.2 Hz, NCH),
6.67 (1H, d, J = 2.1 Hz, NCH), 6.27 (1H, d, J = 2.1 Hz, NCH), 4.83–4.75 (2H, m, CqCH2), 2.39 (3H, s, CH3), 2.30 (6H, s, CH3),
3
3
3
3
4.73 (2H, q, J = 7.3 Hz, CH2), 2.34 (3H, s, CH3), 2.29 (6H, s, 0.95 (3H, t, J = 7.3 Hz, CH2CH3), 0.75–0.66 (2H, m, CH2CH3)
CH3), 0.46 (3H, t, 3J = 7.3 Hz, CH2CH3) ppm. 13C{1H} NMR ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 151.6 (arom. CH o-Py),
(CDCl3, 125 MHz), δ 151.7 (arom. CH o-Py), 148.7 (NCN), 147.4 148.9 (NCN), 147.8 (arom. Cq), 139.9 (arom. Cq), 139.1 (arom.
(arom. Cq), 140.2 (arom. Cq), 139.2 (arom. Cq), 137.8 (arom. Cq), 137.7 (arom. CH p-Py), 136.9 (arom. Cq), 136.0 (arom. Cq),
CH p-Py), 137.0 (arom. Cq), 136.0 (arom. Cq), 129.4 (arom. 129.3 (arom. CH), 129.2 (arom. CH), 129.1 (arom. CH), 124.7
CH), 129.3 (arom. CH), 129.1 (arom. CH), 124.8 (arom. CH), (arom. CH), 124.4 (arom. CH), 123.8 (NCH Imid.), 122.9 (NCH
124.4 (arom. CH), 123.9 (NCH Imid.), 123.2 (NCH Imid.), 120.1 Imid.), 120.1 (arom. CH), 74.9 (Cq), 42.3 (CqCH2), 21.3 (CH3),
(arom. CH), 75.7 (Cq), 32.8 (CH2), 21.3 (CH3), 19.3 (2CH3), 8.7 19.3 (2CH3), 17.6 (CH2CH3), 14.4 (CH2CH3) ppm. Found C,
(CH2CH3) ppm. Found C, 58.10; H, 4.72; N, 6.32. Calcd for 61.03; H, 5.11; N, 6.49. Calcd for C33H33Cl2N3Pd (Mr = 648.97):
C32H31Cl2N3Pd·0.4 CH2Cl2 (Mr = 634.94 + 33.97): C, 58.18; H, C, 61.08; H, 5.15; N, 6.48%.
4.79; N, 6.28%.
trans-[1-(9-Propylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imida-
trans-[1-(9-Ethylfluoren-9-yl)-3-(2,6-diisopropylphenyl)imida- zol-2-ylidene](pyridine)palladium(II) dichloride (6Pr). A suspen-
zol-2-ylidene](pyridine)palladium(II) dichloride (6Et). A suspen- sion of imidazolium salt 4Pr (0.639 g, 1.22 mmol), finely
sion of imidazolium salt 4Et (0.500 g, 0.983 mmol), finely crushed K2CO3 (0.850 g, 6.15 mmol), and PdCl2 (0.259 g,
crushed K2CO3 (0.700 g, 5.06 mmol), and PdCl2 (0.208 g, 1.46 mmol) in pyridine (18 mL) was heated at 80 °C for 18 h
1.17 mmol) in pyridine (14 mL) was heated at 80 °C for 18 h under vigorous stirring. The mixture was cooled to room temp-
under vigorous stirring. The mixture was cooled to room temp- erature, filtered through Celite and the retained solid washed
erature, filtered through Celite and the retained solid washed with CH2Cl2 (ca. 25 mL). The filtrate was evaporated to dryness
with CH2Cl2 (ca. 25 mL). The filtrate was evaporated to dryness and the residue purified by flash chromatography (SiO2;
and the residue purified by flash chromatography (SiO2; CH2Cl2/petroleum ether, 50 : 50) to afford 6Pr as a yellow solid
CH2Cl2/petroleum ether, 50 : 50) to afford 6Et as a yellow solid (0.673 g, 80%). 1H NMR (CDCl3, 400 MHz), δ 8.77–8.73 (2H, m,
(0.495 g, 74%). 1H NMR (CDCl3, 500 MHz), δ 8.79–8.74 (2H, m, o-NC5H5), 7.85 (2H, d, 3J = 7.5 Hz, ArH), 7.77 (2H, d, 3J =
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o-NC5H5), 7.83 (2H, d, 3J = 7.5 Hz, ArH), 7.77 (2H, d, 3J = 7.5 Hz, ArH), 7.67 (1H, tt, J = 7.6 Hz, J = 1.6 Hz, p-NC5H5),
7.5 Hz, ArH), 7.67 (1H, tt, J = 7.7 Hz, J = 1.6 Hz, p-NC5H5), 7.53 (1H, t, 3J = 7.8 Hz, ArH), 7.47 (2H, dd, 3J = 3J′ = 7.5 Hz,
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7.52 (1H, t, 3J = 7.7 Hz, ArH), 7.47 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.43–7.36 (4H, m, ArH), 7.27–7.22 (2H, m, m-NC5H5),
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ArH), 7.43–7.35 (4H, m, ArH), 7.27–7.22 (2H, m, m-NC5H5), 6.75 (1H, d, J = 1.9 Hz, NCH), 6.27 (1H, d, J = 1.9 Hz, NCH),
6.76 (1H, d, J = 2.0 Hz, NCH), 6.28 (1H, d, J = 2.0 Hz, NCH), 4.88–4.79 (2H, m, CqCH2), 3.02 (2H, qq, 3J = 3J′ = 6.8 Hz,
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4.78 (2H, q, J = 7.3 Hz, CH2), 3.00 (2H, qq, J = J′ = 6.8 Hz, CHMe2), 1.50 (6H, d, 3J = 6.8 Hz, CH3), 0.98 (6H, d, 3J = 6.8 Hz,
CHMe2), 1.49 (6H, d, 3J = 6.8 Hz, CH3), 0.97 (6H, d, 3J = 6.8 Hz, CH3), 0.96 (3H, t, 3J = 7.3 Hz, CH2CH3), 0.78–0.66 (2H, m,
CH3), 0.47 (3H, t, 3J = 7.3 Hz, CH2CH3) ppm. 13C{1H} NMR CH2CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 151.4 (arom.
(CDCl3, 125 MHz), δ 151.5 (arom. CH o-Py), 149.7 (NCN), 147.5 CH o-Py), 150.1 (NCN), 147.8 (arom. Cq), 147.5 (arom. Cq),
(arom. Cq), 147.4 (arom. Cq), 140.1 (arom. Cq), 137.7 (arom. 139.9 (arom. Cq), 137.7 (arom. CH p-Py), 135.7 (arom. Cq),
CH p-Py), 135.7 (arom. Cq), 130.3 (arom. CH), 129.3 (arom. 130.3 (arom. CH), 129.3 (arom. CH), 129.0 (arom. CH), 125.7
CH), 129.0 (arom. CH), 125.7 (arom. CH), 124.8 (arom. CH), (arom. CH), 124.8 (arom. CH), 124.4 (arom. CH), 123.9 (arom.
124.4 (arom. CH), 123.9 (arom. CH), 122.2 (arom. CH), 120.0 CH), 121.9 (arom. CH), 120.0 (arom. CH), 75.0 (Cq), 42.2
(arom. CH), 75.8 (Cq), 32.7 (CH2), 28.7 (CHMe2), 26.8 (CH3), (CqCH2), 28.7 (CHMe2), 26.7 (CH3), 23.2 (CH3), 17.5 (CH2CH3),
23.2 (CH3), 8.7 (CH2CH3) ppm. Found C, 62.24; H, 5.49; N, 14.4 (CH2CH3) ppm. Found C, 62.84; H, 5.73; N, 6.00. Calcd
6.18. Calcd for C35H37Cl2N3Pd (Mr = 677.02): C, 62.09; H, 5.51; for C36H39Cl2N3Pd (Mr = 691.05): C, 62.57; H, 5.69; N, 6.08%.
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N, 6.21%.
trans-[1-(9-Ethoxymethylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)
trans-[1-(9-Propylfluoren-9-yl)-3-(2,4,6-trimethylphenyl)imida- imidazol-2-ylidene](pyridine)palladium(II) dichloride (5EOM). A
zol-2-ylidene](pyridine)palladium(II) dichloride (5Pr). A suspen- suspension of imidazolium salt 3EOM (0.641 g, 1.29 mmol),
sion of imidazolium salt 3Pr (0.400 g, 0.830 mmol), finely finely crushed K2CO3 (0.900 g, 6.51 mmol), and PdCl2 (0.276 g,
14524 | Dalton Trans., 2019, 48, 14516–14529
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1.56 mmol) in pyridine (20 mL) was heated at 80 °C for 18 h of 9-fluorenylamine (1.66 g, 9.16 mmol) and acetic acid
under vigorous stirring. The mixture was cooled to room temp- (1.18 mL, 1.24 g, 20.6 mmol) was heated at 60 °C for 5 min,
erature, filtered through Celite and the retained solid washed then MgSO4 (1.10 g, 9.16 mmol) was added. This gave mixture
with CH2Cl2 (ca. 30 mL). The filtrate was evaporated to dryness A. In another flask, a mixture of glyoxal (0.525 mL, 0.664 g,
and the residue purified by flash chromatography (SiO2; 4.58 mmol, 40 wt% in water), formaldehyde (0.343 mL,
EtOAc/CH2Cl2, 1.5 : 98.5) to afford 5EOM as a yellow solid 0.371 g, 4.58 mmol, 37 wt% in water) and acetic acid (1.18 mL,
(0.521 g, 61%). 1H NMR (CDCl3, 400 MHz), δ 8.64–8.60 (2H, m, 1.24 g, 20.6 mmol) was heated at 60 °C for 5 min, then ZnCl2
o-NC5H5), 7.83 (2H, d, 3J = 7.5 Hz, ArH), 7.74 (2H, d, 3J = (0.750 g, 5.50 mmol) was added. This gave mixture B. Mixture
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7.5 Hz, ArH), 7.63 (1H, tt, J = 7.8 Hz, J = 1.6 Hz, p-NC5H5), B was then added to mixture A at 60 °C. After stirring for
7.44 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.35 (2H, dd, 3J = 3J′ = 25 min, the solution was cooled to room temperature. CH2Cl2
7.5 Hz, ArH), 7.23–7.16 (2H, m, m-NC5H5), 7.03 (2H, s, ArH), (50 mL) and a 3 M aqueous solution of HCl (90 mL) were
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6.72 (1H, d, J = 1.9 Hz, NCH), 6.64 (1H, d, J = 1.9 Hz, NCH), added and the resulting mixture was stirred for 1 h at room
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6.05 (2H, s, CqCH2), 3.42 (2H, q, J = 7.0 Hz, OCH2CH3), 2.36 temperature. The organic layer was separated, water (40 mL)
(3H, s, CH3), 2.27 (6H, s, CH3), 0.95 (3H, t, 3J = 7.0 Hz, and ammonium tetrafluoroborate (1.92 g, 18.3 mmol) were
OCH2CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 151.4 added and the mixture was vigorously stirred at room tempera-
(arom. CH o-Py), 149.4 (NCN), 146.3 (arom. Cq), 140.7 (arom. ture for 1 h. The organic layer was separated and the aqueous
Cq), 139.1 (arom. Cq), 137.7 (arom. CH p-Py), 136.8 (arom. Cq), layer treated with CH2Cl2 (2 × 25 mL). The combined organic
135.7 (arom. Cq), 129.4 (arom. CH), 129.2 (arom. CH), 128.4 layers were dried with Na2SO4, and the solvent was removed
(arom. CH), 125.2 (arom. CH), 124.3 (arom. CH), 123.7 (NCH under reduced pressure. The crude product was washed with
Imid.), 123.0 (NCH Imid.), 120.1 (arom. CH), 74.9 (CqCH2), EtOAc (25 mL) then with diethyl ether (25 mL). After drying,
73.5 (Cq), 67.7 (OCH2CH3), 21.2 (CH3), 19.2 (2CH3), 14.9 product 7H was obtained as a white solid (1.79 g, 81%). 1H
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(OCH2CH3) ppm. Found C, 58.59; H, 4.82; N, 6.19. Calcd for NMR ([D6]DMSO, 500 MHz), δ 9.73 (1H, t, J = 1.5 Hz, NCHN),
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C33H33Cl2N3OPd (Mr = 664.97): C, 59.61; H, 5.00; N, 6.32%.
8.03 (4H, d, J = 7.5 Hz, ArH), 7.65 (4H, d, J = 7.5 Hz, ArH),
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trans-[1-(9-Ethoxymethylfluoren-9-yl)-3-(2,6-diisopropylphenyl) 7.59 (4H, dd, J = J′ = 7.5 Hz, ArH), 7.53 (2H, d, J = 1.5 Hz,
imidazol-2-ylidene](pyridine)palladium(II) dichloride (6EOM). A NCH), 7.45 (4H, dd, J = J′ = 7.5 Hz, ArH), 6.83 (2H, s, aliph.
suspension of imidazolium salt 4EOM (0.500 g, 0.928 mmol), CH) ppm. 13C{1H} NMR ([D6]DMSO, 125 MHz), δ 140.4 (arom.
finely crushed K2CO3 (0.642 g, 4.64 mmol), and PdCl2 (0.197 g, Cq), 140.0 (arom. Cq), 137.1 (NCHN), 130.3 (arom. CH), 128.5
1.11 mmol) in pyridine (15 mL) was heated at 80 °C for 18 h (arom. CH), 125.5 (arom. CH), 121.9 (NCH), 121.0 (arom. CH),
under vigorous stirring. The mixture was cooled to room temp- 62.7 (aliph. CH) ppm. 19F NMR ([D6]DMSO, 282 MHz), −148.19
erature, filtered through Celite and the retained solid washed (br s, 19F–10B), −148.24 (q, 1J(19F–11B) = 1.1 Hz) ppm. Found C,
with CH2Cl2 (ca. 20 mL). The filtrate was evaporated to dryness 71.42; H, 4.43; N, 5.90. Calcd for C29H21BF4N2·0.05 CH2Cl2 (Mr
and the residue purified by flash chromatography (SiO2; = 484.30 + 4.25): C, 71.42; H, 4.35; N, 5.73%.
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CH2Cl2) to afford 6EOM as a yellow solid (0.444 g, 68%). 1H
NMR (CDCl3, 500 MHz), δ 8.68–8.64 (2H, m, o-NC5H5), 7.90 (8Me). LiHMDS (4.43 mL, 4.43 mmol, 1 M in THF) was added
1,3-Bis(9-methylfluoren-9-yl)imidazolium tetrafluoroborate
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(2H, d, J = 7.5 Hz, ArH), 7.78 (2H, d, J = 7.5 Hz, ArH), 7.65 dropwise to a stirred suspension of imidazolium tetrafluoro-
(1H, tt, 3J = 7.6 Hz, 4J = 1.6 Hz, p-NC5H5), 7.53 (1H, t, 3J = borate 7H (0.895 g, 1.85 mmol) in THF (25 mL) cooled at
7.7 Hz, ArH), 7.48 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.43–7.35 −50 °C. After stirring for 1 h, the reaction mixture was allowed
(4H, m, ArH), 7.25–7.19 (2H, m, m-NC5H5), 6.83 (1H, d, 3J = to reach room temperature, then CH3I (0.700 mL, 1.57 g,
1.9 Hz, NCH), 6.62 (1H, d, 3J = 1.9 Hz, NCH), 6.18 (2H, s, 11.1 mmol) was added. The mixture was stirred overnight at
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CqCH2), 3.43 (2H, q, J = 7.0 Hz, OCH2CH3), 2.98 (2H, qq, J = room temperature and MeOH (2 mL) was added. The solvent
3J′ = 6.7 Hz, CHMe2), 1.47 (6H, d, 3J = 6.7 Hz, CH3), 0.99 (6H, d, was removed under reduced pressure and water (20 mL) was
3J = 6.7 Hz, CH3), 0.97 (3H, t, J = 7.0 Hz, OCH2CH3) ppm. 13C added. The product was extracted with CH2Cl2 (3 × 20 mL), the
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{1H} NMR (CDCl3, 125 MHz), δ 151.3 (arom. CH o-Py), 150.5 organic layers were combined and the solvent was removed
(NCN), 147.4 (arom. Cq), 146.4 (arom. Cq), 140.8 (arom. Cq), under reduced pressure. To the crude mixture dissolved in
137.7 (arom. CH p-Py), 135.4 (arom. Cq), 130.3 (arom. CH), CH2Cl2 (30 mL) was added water (30 mL) and ammonium
129.4 (arom. CH), 128.4 (arom. CH), 125.6 (arom. CH), 125.3 tetrafluoroborate (1.16 g, 11.1 mmol). The mixture was vigor-
(arom. CH), 124.3 (arom. CH), 123.9 (arom. CH), 122.1 (arom. ously stirred at room temperature for 1 h. The organic layer
CH), 120.1 (arom. CH), 74.9 (CqCH2), 73.7 (Cq), 67.7 was separated and the aqueous phase was treated with CH2Cl2
(OCH2CH3), 28.6 (CHMe2), 26.7 (CH3), 23.1 (CH3), 14.8 (2 × 20 mL). The combined organic layers were dried with
(OCH2CH3) ppm. Found C, 61.19; H, 5.52; N, 5.90. Calcd for Na2SO4, and the solvent was removed under reduced pressure.
C36H39Cl2N3OPd (Mr = 707.05): C, 61.16; H, 5.56; N, 5.94%.
The crude product was purified by flash chromatography
(SiO2; EtOAc/CH2Cl2, 5 : 95) to afford 8Me as a white solid
Synthesis of symmetrical imidazolium salts 7R and 8R
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(0.740 g, 78%). H NMR (CDCl3, 400 MHz), δ 9.87 (1H, t, J =
1,3-Bis(fluoren-9-yl)imidazolium tetrafluoroborate (7H). The 1.3 Hz, NCHN), 7.69 (4H, d, J = 7.5 Hz, ArH), 7.72 (4H, d, J =
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following procedure follows that applied by Mauduit et al. for 7.5 Hz, ArH), 7.44 (4H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.38 (4H, dd,
the synthesis of unsymmetrical imidazolium salts.16 A mixture 3J = 3J′ = 7.5 Hz, ArH), 6.38 (2H, d, J = 1.3 Hz, NCH), 2.51 (6H,
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s, CH3) ppm. 13C{1H} NMR (CDCl3, 125 MHz), δ 145.3 (arom. with CH2Cl2 (2 × 20 mL). The combined organic layers were
Cq), 139.0 (arom. Cq), 134.6 (NCHN), 130.4 (arom. CH), 129.4 dried with Na2SO4, and the solvent was removed under
(arom. CH), 124.4 (arom. CH), 120.8 (arom. CH), 120.6 (arom. reduced pressure. The crude product was purified by flash
CH), 71.6 (Cq), 23.4 (CH3) ppm. 19F NMR (CDCl3, 470 MHz), chromatography (SiO2; EtOAc/CH2Cl2, 5 : 95) to afford 8Pr as a
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δ −149.15 (br s, 19F–10B), −149.20 (br s, 19F–11B) ppm. Found white solid (0.888 g, 76%). H NMR (CDCl3, 500 MHz), δ 9.65
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C, 72.14; H, 5.12; N, 5.23. Calcd for C31H25BF4N2·0.15 H2O (1H, t, J = 1.4 Hz, NCHN), 7.70 (4H, d, J = 7.5 Hz, ArH), 7.61
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(Mr = 512.36 + 2.70): C, 72.29; H, 4.95; N, 5.44%.
(4H, d, J = 7.5 Hz, ArH), 7.45 (4H, dd, J = J′ = 7.5 Hz, ArH),
1,3-Bis(9-ethylfluoren-9-yl)imidazolium tetrafluoroborate (8Et). 7.37 (4H, dd, J = J′ = 7.5 Hz, ArH), 6.59 (2H, d, J = 1.4 Hz,
LiHMDS (7.92 mL, 7.92 mmol, 1 M in THF) was added drop- NCH), 3.03–2.97 (4H, m, CqCH2), 0.85 (6H, t, 3J = 7.1 Hz, CH3),
wise to a stirred suspension of imidazolium tetrafluoroborate 0.80–0.71 (4H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3,
7H (1.59 g, 3.30 mmol) in THF (50 mL) cooled at −50 °C. After 125 MHz), δ 140.2 (arom. Cq), 140.3 (arom. Cq), 133.4 (NCHN),
stirring for 1 h (with the temperature maintained at −50 °C), 130.5 (arom. CH), 129.3 (arom. CH), 124.1 (arom. CH), 120.8
the reaction mixture was allowed to reach room temperature, (arom. CH), 120.7 (arom. CH), 74.6 (Cq), 37.7 (CqCH2), 16.9
then EtBr (1.50 mL, 2.15 g, 19.8 mmol) was added. The (CH2CH3), 13.5 (CH2CH3) ppm. 19F NMR (CDCl3, 282 MHz),
mixture was stirred overnight at room temperature, then −151.95 (br s, 19F–10B), −150.98 to −151.02 (m, 19F–11B) ppm.
MeOH (3 mL) was added to quench any further reaction. The Found C, 73.73; H, 5.91; N, 4.86. Calcd for C35H33BF4N2 (Mr =
solvent was removed under reduced pressure and water 568.47): C, 73.95; H, 5.85; N, 4.93%.
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(30 mL) was added. The product was extracted with CH2Cl2
(3 × 30 mL), the organic layers were combined and the solvent
Synthesis of palladium complexes 9
was removed under reduced pressure. To the crude mixture
trans-[1,3-Bis(9-methylfluoren-9-yl)imidazol-2-ylidene](pyr-
dissolved in CH2Cl2 (30 mL) was added water (30 mL) and idine)palladium(II) dichloride (9Me). A suspension of imidazo-
ammonium tetrafluoroborate (2.07 g, 19.8 mmol). The mixture lium salt 8Me (0.367 g, 0.716 mmol), finely crushed K2CO3
was vigorously stirred at room temperature for 1 h. The (0.500 g, 3.61 mmol), and PdCl2 (0.153 g, 0.862 mmol) in pyri-
organic layer was separated and the aqueous phase was treated dine (10 mL) was heated at 80 °C for 18 h under vigorous stir-
with CH2Cl2 (2 × 30 mL). The combined organic layers were ring. The mixture was cooled to room temperature, filtered
dried with Na2SO4, and the solvent was removed under through Celite and the retained solid washed with CH2Cl2 (ca.
reduced pressure. The crude product was purified by flash 25 mL). The filtrate was evaporated to dryness and the residue
chromatography (SiO2; EtOAc/CH2Cl2, 7 : 93) to afford 8Et as a purified by flash chromatography (SiO2; CH2Cl2/petroleum
1
white solid (1.38 g, 77%). 1H NMR (CDCl3, 500 MHz), δ 9.60 ether, 50 : 50) to afford 9Me as a yellow solid (0.393 g, 81%). H
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(1H, s, NCHN), 7.70 (4H, d, J = 7.5 Hz, ArH), 7.60 (4H, d, J = NMR (CDCl3, 500 MHz), δ 9.15 (2H, d, J = 5.2 Hz, o-NC5H5),
7.5 Hz, ArH), 7.46 (4H, dd, 3J = 3J′ = 7.5 Hz, ArH), 7.38 (4H, dd, 7.88–7.79 (5H, m, 4ArH and p-NC5H5), 7.70 (4H, d, J = 7.5 Hz,
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3J = 3J′ = 7.5 Hz, ArH), 6.61 (2H, s, NCH), 3.08 (4H, q, 3J = ArH), 7.44–7.36 (6H, m, 4ArH and m-NC5H5), 7.33 (4H, dd, 3J =
7.2 Hz, CH2), 0.49 (6H, t, J = 7.2 Hz, CH3) ppm. 13C{1H} NMR 3J′ = 7.5 Hz, ArH), 5.85 (2H, s, NCH), 3.71 (6H, s, CH3) ppm.
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(CDCl3, 125 MHz), δ 142.9 (arom. Cq), 140.3 (arom. Cq), 133.5 13C{1H} NMR (CDCl3, 125 MHz), δ 151.7 (arom. CH o-Py), 149.7
(NCHN), 130.6 (arom. CH), 129.4 (arom. CH), 124.2 (arom. (NCN), 144.9 (arom. Cq), 138.4 (arom. Cq), 138.1 (arom. CH),
CH), 120.9 (arom. CH), 120.7 (arom. CH), 75.3 (Cq), 29.1 129.1 (arom. CH), 128.9 (arom. CH), 124.9 (arom. CH), 124.8
(CH2), 7.9 (CH3) ppm. 19F NMR (CDCl3, 282 MHz), δ −151.54 (arom. CH), 122.5 (arom. CH), 120.2 (arom. CH), 71.0 (Cq),
(br s, 19F–10B), −151.56 to −151.62 (m, 19F–11B) ppm. Found C, 28.8 (CH3) ppm. Found C, 63.56; H, 4.26; N, 6.14. Calcd for
73.28; H, 5.43; N, 5.26. Calcd for C33H29BF4N2 (Mr = 540.41): C, C33H29Cl2N3Pd (Mr = 680.97): C, 63.50; H, 4.29; N, 6.17%.
73.34; H, 5.41; N, 5.18%.
trans-[1,3-Bis(9-methylfluoren-9-yl)imidazol-2-ylidene](pyr-
1,3-Bis(9-propylfluoren-9-yl)imidazolium tetrafluoroborate (8Pr). idine)palladium(II) dichloride (9Et). A suspension of imidazo-
LiHMDS (4.90 mL, 4.90 mmol, 1 M in THF) was added drop- lium salt 8Et (0.600 g, 1.11 mmol), finely crushed K2CO3
wise to a stirred suspension of imidazolium tetrafluoroborate (0.767 g, 5.54 mmol), and PdCl2 (0.236 g, 1.33 mmol) in pyri-
7H (0.987 g, 2.04 mmol) in THF (25 mL) cooled at −50 °C. dine (18 mL) was heated at 80 °C for 18 h under vigorous stir-
After stirring the cold solution for 1 h, the reaction mixture ring. The mixture was cooled to room temperature, filtered
was allowed to reach room temperature and n-PrBr (1.10 mL, through Celite and the retained solid washed with CH2Cl2 (ca.
1.50 g, 12.2 mmol) was added. The mixture was stirred over- 25 mL). The filtrate was evaporated to dryness and the residue
night at room temperature and MeOH (2 mL) was added. The purified by flash chromatography (SiO2; CH2Cl2/petroleum
1
solvent was removed under reduced pressure before water ether, 50 : 50) to afford 9Et as a yellow solid (0.623 g, 79%). H
(20 mL) was added. The product was extracted with CH2Cl2 NMR (CDCl3, 400 MHz), δ 9.15–9.11 (2H, m, o-NC5H5), 7.82
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(3 × 20 mL), the organic layers were combined and the solvent (1H, tt, J = 7.6 Hz, J = 1.6 Hz, p-NC5H5), 7.76 (4H, d, J = 7.5
was removed under reduced pressure. To the crude mixture Hz, ArH), 7.66 (4H, d, 3J = 7.5 Hz, ArH), 7.45–7.40 (2H, m,
3
3
dissolved in CH2Cl2 (30 mL) was added water (30 mL) and m-NC5H5), 7.37 (4H, dd, J = J′ = 7.5 Hz, ArH), 7.32 (4H, dd,
ammonium tetrafluoroborate (1.28 g, 12.2 mmol). The mixture 3J = 3J′ = 7.5 Hz, ArH), 5.85 (2H, s, NCH), 4.99 (4H, q, 3J =
was vigorously stirred at room temperature for 1 h. The 7.3 Hz, CH2), 0.47 (6H, t, 3J = 7.3 Hz, CH3) ppm. NMR data are
organic layer was separated and the aqueous phase was treated consistent with those given in the literature.10e
14526 | Dalton Trans., 2019, 48, 14516–14529
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trans-[1,3-Bis(9-propylfluoren-9-yl)imidazol-2-ylidene](pyr- rotation and 30 s per frame, range hkl: h – 15,9 k – 20,20 l –
idine)palladium(II) dichloride (9Pr). A suspension of imidazo- 25,25) gave 65 424 reflections. The structure was solved using
lium salt 8Pr (0.542 g, 0.953 mmol), finely crushed K2CO3 SHELXS-2013,22 which revealed the non-hydrogen atoms of the
(0.656 g, 4.75 mmol), and PdCl2 (0.202 g, 1.14 mmol) in pyri- molecule. After anisotropic refinement, all of the hydrogen
dine (15 mL) was heated at 80 °C for 18 h under vigorous atoms were found using a Fourier difference map. The struc-
stirring. The mixture was cooled to room temperature, fil- ture was refined using SHELXL-201323 by the full-matrix least-
tered through Celite and the retained solid washed with squares technique (use of F2 magnitude; x, y, z, βij for C, Cl, N
CH2Cl2 (ca. 25 mL). The filtrate was evaporated to dryness and Pd atoms; x, y, z in riding mode for H atoms); 347 vari-
and the residue purified by flash chromatography (SiO2; ables and 7970 observations with I > 2.0σ(I); calcd w = 1/
2
2
2
CH2Cl2/petroleum ether, 50 : 50) to afford 9Pr as a yellow [σ2(Fo ) + (0.0098P)2 + 3.8829P] where P = (Fo + 2Fc )/3, with
1
solid (0.611 g, 87%). H NMR (CDCl3, 500 MHz), δ 9.12 (2H, the resulting R = 0.0326, RW = 0.0703 and SW = 1.172, Δρ <
d, 3J = 5.3 Hz, o-NC5H5), 7.82 (1H, t, 3J = 7.6 Hz, p-NC5H5), 1.317 e Å−3. CCDC 1897858.†
3
3
7.78 (4H, d, J = 7.5 Hz, ArH), 7.66 (4H, d, J = 7.5 Hz, ArH),
7.44–7.40 (2H, m, m-NC5H5), 7.37 (4H, dd, 3J = 3J′ = 7.5 Hz, action were obtained by slow diffusion of pentane into a di-
Crystal data for complex 6Et. Crystals suitable for X-ray diffr-
3
3
ArH), 7.32 (4H, dd, J = J′ = 7.5 Hz, ArH), 5.81 (2H, s, NCH), chloromethane solution of the complex. Crystal data:
5.08–4.98 (4H, m, CqCH2), 0.98 (6H, t, 3J = 7.3 Hz, CH3), C35H37Cl2N3Pd·CH2Cl2, Mr = 761.90 g mol−1, monoclinic,
0.75–0.65 (4H, m, CH2CH3) ppm. 13C{1H} NMR (CDCl3, space group P21/c, a = 22.6496(4) Å, b = 10.2717(2) Å, c =
125 MHz), δ 151.7 (arom. CH o-Py), 144.3 (NCN), 144.9 16.0422(2) Å, α = 90°, β = 104.4740(10)°, γ = 90°, V = 3613.76
(arom. Cq), 139.8 (arom. Cq), 138.0 (arom. CH), 129.1 (arom. (11) Å3, Z = 4, D = 1.400 g cm−3, μ = 0.838 mm−1, F(000) = 1560,
CH), 128.9 (arom. CH), 124.9 (arom. CH), 124.8 (arom. CH), T = 173(2) K. The sample was studied on a Kappa CCD diffract-
122.4 (arom. CH), 119.9 (arom. CH), 74.9 (Cq), 42.5 (CqCH2), ometer (graphite monochromated Mo-Kα radiation,
λ =
17.7 (CH2CH3), 14.5 (CH2CH3) ppm. Found C, 65.13; H, 4.97; 0.71073 Å). The data collection (2θmax = 55.0°, omega scan
N, 5.67. Calcd for C40H37Cl2N3Pd (Mr = 737.08): C, 65.18; H, frames by using 0.7° omega rotation and 30 s per frame, range
5.06; N, 5.70%.
hkl: h – 29,29 k – 13,13 l – 20,20) gave 59 152 reflections. The
structure was solved using SIR-92,24 which revealed the non-
hydrogen atoms of the molecule. After anisotropic refinement,
all of the hydrogen atoms were found using a Fourier
General procedure for palladium-catalysed Suzuki–Miyaura
cross-coupling reactions
A mixture of palladium complex (0.01 mmol), phenylboronic difference map. The structure was refined using
acid (0.183 g, 1.50 mmol), Cs2CO3 (0.652 g, 2.00 mmol) and, SHELXL-201423 by the full-matrix least-squares technique
for the specific runs carried out in the presence of mercury, (use of F2 magnitude; x, y, z, βij for C, Cl, N and Pd atoms; x, y,
Hg (50 μl, 0.677 g, 3.38 mol), was suspended in dioxane z in riding mode for H atoms); 402 variables and 6731
2
(3 mL). After addition of p-tolyl chloride (0.126 g, 1.00 mmol), observations with I > 2.0σ(I); calcd w = 1/[σ2(Fo ) + (0.0705P)2 +
2
the mixture was vigorously stirred at 80 °C for a given period of 8.7427P] where P = (Fo2 + 2Fc )/3, with the resulting R = 0.0551,
time. The hot mixture was filtered through Celite. 1,4- RW = 0.1507 and SW = 1.102, Δρ < 3.267 e Å−3. CCDC 1897859.†
Dimethoxybenzene (0.069 g, 0.5 mmol; internal standard) was
Crystal data for complex 5Pr. Crystals suitable for X-ray diffr-
then added to the filtrate. The solvent was removed under action were obtained by slow diffusion of pentane into a di-
reduced pressure, and the crude mixture was analysed by 1H chloromethane solution of the complex. Crystal data:
NMR spectroscopy. The yields were determined by comparing C33H33Cl2N3Pd, Mr = 648.92 g mol−1, monoclinic, space group
the intensity of the methyl signal of the product [δ(Me) = P21/n, a = 10.7502(2) Å, b = 24.8309(5) Å, c = 11.05370(10) Å, α =
2.41 ppm] with that of the internal reference [δ(Me) = 90°, β = 93.3620(10), γ = 90°, V = 2945.57(9) Å3, Z = 4, D =
3.78 ppm]. In some experiments the product was isolated chro- 1.463 g cm−3, μ = 0.839 mm−1, F(000) = 1328, T = 173(2) K. The
matographically. The isolated yield turned out to be very close sample was studied on a Kappa CCD diffractometer (graphite
(deviation less than 5%) to that determined by using the monochromated Mo-Kα radiation, λ = 0.71073 Å). The data col-
internal reference.
lection (2θmax = 54.9°, omega scan frames by using 0.7° omega
rotation and 30 s per frame, range hkl: h – 13,13 k – 31,32 l –
14,14) gave 45 352 reflections. The structure was solved using
X-ray crystallography
Crystal data for complex 5Et. Crystals suitable for X-ray diffr- SIR-92,24 which revealed the non-hydrogen atoms of the mole-
action were obtained by slow diffusion of pentane into a di- cule. After anisotropic refinement, all of the hydrogen atoms
chloromethane solution of the complex. Crystal data: were found using a Fourier difference map. The structure was
C32H31Cl2N3Pd, Mr = 634.90 g mol−1, orthorhombic, space refined using SHELXL-201423 by the full-matrix least-squares
group P212121, a = 10.7007(4) Å, b = 14.7879(7) Å, c = 17.9151(7) technique (use of F2 magnitude; x, y, z, βij for C, Cl, N and Pd
Å, α = β = γ = 90°, V = 2834.9(2) Å3, Z = 4, D = 1.488 g cm−3, μ = atoms; x, y, z in riding mode for H atoms); 356 variables and
0.869 mm−1, F(000) = 1296, T = 173(2) K. The sample was 5502 observations with I > 2.0σ(I); calcd w = 1/[σ2(Fo ) +
2
studied on a Kappa APEX II diffractometer (graphite mono- (0.0260P)2 + 5.9879P] where P = (Fo + 2Fc )/3, with the result-
2
2
chromated Mo-Kα radiation, λ = 0.71073 Å). The data collection ing R = 0.0468, RW = 0.1028 and SW = 1.085, Δρ < 0.576 e Å−3
(2θmax = 60.4°, omega scan frames by using 0.7° omega CCDC 1897856.†
.
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Dalton Transactions
Crystal data for complex 6EOM. Crystals suitable for X-ray
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diffraction were obtained by slow diffusion of pentane into a
dichloromethane solution of the complex. Crystal data:
C36H39Cl2N3OPd.CH2Cl2, Mr = 791.93 g mol−1, monoclinic,
space group P21/c, a = 12.1594(2) Å, b = 19.9702(3) Å, c =
15.1796(3) Å, α = 90°, β = 99.3060(10)°, γ = 90°, V = 3637.48(11)
Å3, Z = 4, D = 1.446 g cm−3, μ = 0.837 mm−1, F(000) = 1624, T =
173(2) K. The sample was studied on a Kappa CCD diffract-
ometer (graphite monochromated Mo-Kα radiation,
λ =
0.71073 Å). The data collection (2θmax = 54.9.0°, omega scan
frames by using 0.7° omega rotation and 30 s per frame, range
hkl: h – 15,15 k – 25,25 l – 19,19) gave 59 394 reflections. The
structure was solved using SHELXS-2014,22 which revealed the
non-hydrogen atoms of the molecule. After anisotropic
refinement, all of the hydrogen atoms were found using a
Fourier difference map. The structure was refined using
SHELXL-201423 by the full-matrix least-squares technique (use
of F2 magnitude; x, y, z, βij for C, Cl, N, O and Pd atoms; x, y, z
7 A. J. Arduengo, R. L. Harlow and M. Kline, J. Am. Chem.
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in riding mode for H atoms); 427 variables and 6730 obser-
vations with I > 2.0σ(I); calcd w = 1/[σ2(Fo ) + (0.0589P)2
+
2
2.0747P] where P = (Fo2 + 2Fc )/3, with the resulting R = 0.0426,
RW = 0.1218 and SW = 1.161, Δρ < 0.736 e Å−3. CCDC 1897857.†
2
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
H. A. gratefully acknowledges the “Association de 10 (a) M. Teci, E. Brenner, D. Matt and L. Toupet,
spécialisation et d’orientation scientifique” (Lebanon) for
financial support. We thank Mr Vincent Bruno (Unistra) for
assistance in obtaining NMR data.
Eur. J. Inorg. Chem., 2013, 2841–2848; (b) M. Teci,
E. Brenner, D. Matt and L. Toupet, Z. Kristallogr. – New
Cryst. Struct., 2014, 229, 169–171; (c) M. Teci, E. Brenner,
D. Matt, C. Gourlaouen and L. Toupet, Dalton Trans.,
2014, 43, 12251–12262; (d) M. Teci, E. Brenner, D. Matt,
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Z. Kristallogr. – New Cryst. Struct., 2016, 231, 733–735;
(g) M. Teci, D. Hueber, P. Pale, L. Toupet, A. Blanc,
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