Directional properties of fluorenylidene moieties in unsymmetrically substituted N-heterocyclic carbenes. Unexpected CH activation of a methylfluorenyl group with palladium. Use in palladium catalysed Suzuki-Miyaura cross coupling of aryl chlorides

Article abstract of DOI:10.1039/c4dt01102c

Benzimidazolium salts having their two nitrogen atoms substituted by different 9-alkylfluorenyl groups (4a-e and 4g, alkyl¹/alkyl ² = Me/Et, Me/Pr, Me/n-Bu, Me/i-Pr, Me/Bn, Me/CH₂SMe have been synthesised in high yields in two or three steps from N,N′-bis(9H- fluoren-9-ylidene)benzene-1,2-diamine (1). The imidazolium salts 4a-e were converted readily into the corresponding PEPPSI-type palladium complexes (PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation), while reaction of the methylthioether-substituted salt 4g with PdCl ₂/K₂CO₃/pyridine afforded the palladacycle 5g resulting from metallation of the methyl group attached to the fluorenylidene moiety. NMR and X-ray diffraction studies revealed that the carbene ligands in 5a-5e behave as clamp-like ligands, the resulting metal confinement arising from a combination of the orientational properties of the fluorenylidene moieties that push the alkyl groups towards the metal centre and attractive anagostic interactions involving CH₂(fluorenyl) groups. Complexes 5a-e were assessed in Suzuki-Miyaura cross-coupling reactions. Like their symmetrical analogues they displayed high activity in the coupling of phenyl boronic acid with p-tolylchloride but their performance remained slightly inferior to that of the related, symmetrical Et/Et complex 5h.

Full text of DOI:10.1039/c4dt01102c

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PAPER
Directional properties of fluorenylidene moieties
in unsymmetrically substituted N-heterocyclic
carbenes. Unexpected CH activation of a
methylfluorenyl group with palladium. Use in
palladium catalysed Suzuki–Miyaura cross
coupling of aryl chlorides†
Cite this: Dalton Trans., 2014, 43,
12251
Matthieu Teci,a Eric Brenner,*a Dominique Matt,*a Christophe Gourlaouenb and
Loïc Toupetc
Benzimidazolium salts having their two nitrogen atoms substituted by different 9-alkylfluorenyl groups
(4a–e and 4g, alkyl1/alkyl2 = Me/Et, Me/Pr, Me/n-Bu, Me/i-Pr, Me/Bn, Me/CH2SMe have been synthesised
in high yields in two or three steps from N,N’-bis(9H-fluoren-9-ylidene)benzene-1,2-diamine (1). The
imidazolium salts 4a–e were converted readily into the corresponding PEPPSI-type palladium complexes
(PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation), while reaction of the
methylthioether-substituted salt 4g with PdCl2/K2CO3/pyridine afforded the palladacycle 5g resulting
from metallation of the methyl group attached to the fluorenylidene moiety. NMR and X-ray diffraction
studies revealed that the carbene ligands in 5a–5e behave as clamp-like ligands, the resulting metal
confinement arising from a combination of the orientational properties of the fluorenylidene moieties
that push the alkyl groups towards the metal centre and attractive anagostic interactions involving
CH2(fluorenyl) groups. Complexes 5a–e were assessed in Suzuki–Miyaura cross-coupling reactions. Like
their symmetrical analogues they displayed high activity in the coupling of phenyl boronic acid with
p-tolylchloride but their performance remained slightly inferior to that of the related, symmetrical
Et/Et complex 5h.
Received 14th April 2014,
Accepted 3rd June 2014
DOI: 10.1039/c4dt01102c
www.rsc.org/dalton
Introduction
A number of palladium complexes with a single N-heterocyclic
carbene (NHC) ligand have proven to be useful catalysts in
cross-coupling reactions of aryl halides (Fig. 1).1–27 Among the
most popular catalysts for such reactions are palladium com-
plexes of the type [PdX2(NHC)L] (X = halide), in which L is an
ancillary ligand that readily dissociates.28–37 Several authors
have identified pertinent criteria that may increase the effec-
tiveness of the NHC ligand. Thus, optimised NHC’s should
aLaboratoire de Chimie Inorganique Moléculaire et Catalyse, Institut de Chimie
(UMR 7177 CNRS), Université de Strasbourg, 1 rue Blaise Pascal, F-67008
Strasbourg Cedex, France. E-mail: dmatt@unistra.fr, eric.brenner@unistra.fr
bLaboratoire de Chimie Quantique, Institut de Chimie (UMR 7177 CNRS),
Université de Strasbourg, 1 rue Blaise Pascal, F-67008 Strasbourg, France
cInstitut de Physique de Rennes, UMR 6251 CNRS, Université de Rennes 1,
Campus de Beaulieu, 35042 Rennes cedex, France
†CCDC 970760–862359. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4dt01102c
Fig. 1 Effective NHCs used as ligands in palladium-catalysed cross-
coupling.
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contain N-substituents that are both bulky and flexible, bulki- (1.2 equiv.) and LiCH2S(O)Me (1.6 equiv.), diamine-sulfoxide
ness favouring the reductive elimination step and stabilisation 3f was obtained in 80% yield. Reduction of the sulfoxide was
of catalytic intermediates, the flexibility enabling an entering carried out with NaBH4 in the presence of iodide, leading to
substrate to approach the metal centre after release of the thioether 3g in 79% yield. In the last step imidazolium salt 4g
product in the last step of the catalytic cycle.
was readily synthesised applying the above HC(OEt)3–HCl pro-
We have recently reported a series of NHC–Pd complexes in cedure. All imidazolium salts are characterised by a methine
which the two nitrogen atoms are substituted by (identical) signal in their 1H NMR spectrum lying in the range
alkylfluorenyl substituents.27 The large fluorenylidene moiety 11.15–11.70 ppm.
was shown to orientate the alkyl groups towards the palladium
centre while its restricted rotational freedom made the ligand
Syntheses of palladium complexes
bulkiness time independent. It is worthy of note that these The PEPPSI-type28–31 palladium complexes 5a–e were obtained
ligands (termed AFB in Fig. 1) do not display hemispherical in medium-to-good yields using the standard procedure
encumbrance such as do, e.g., IPr, IPr*, or SIPr. Instead, the initially developed by Organ (Scheme 2). As already observed
ligands give rise to meridional encumbrance, with two small, for related palladium complexes having two identical alkyl-
apically localised CH2 (or CH3) groups coming in close contact fluorenyl substituents, e.g. 5h (Fig. 2), all the NCCH signals are
to the palladium centre. Despite their rather inflexible form, markedly downfield shifted when compared to their analogues
these NHCs resulted in catalysts that are among the fastest in the corresponding imidazolium precursor (Δδ
=
Suzuki–Miyaura cross-coupling catalysts reported to date. 1.0–1.7 ppm). This reflects anagostic CH interactions between
These results unambiguously establish the key role in cross- these protons and the palladium centre, and means that the
coupling reactions of NHCs that display essentially confining alkyl groups attached to the fluorenylidene moiety are pushed
properties along with very limited flexibility.
towards the metal dz2 orbital, while the fluorenylidene plane
As an extension of these studies, we now report the syn- itself is bent towards the NHC-fused aromatic ring. The parti-
thesis and catalytic performance in Suzuki–Miyaura coupling cular orientation of the fluorenylidene plane is seemingly
of related Pd-complexes containing unsymmetrically substi- persistent in solution, as the only ROESY correlations involving
tuted NHCs. One of the NHCs contains a potentially coordinat- the benzimidazolium unit are seen with aromatic protons of
ing –CH2SMe side group.
the fluorenylidene moieties, but with none of the alkyl
groups.38 A single crystal X-ray diffraction study carried out for
5d confirmed the orientation of the methyl and benzyl moi-
eties towards the metal dz2 orbital, which results in a double
apical encumbrance of the metal centre (Fig. 3). The unit cell
of this structure contains two nearly identical molecules. Short
Results and discussion
Syntheses of benzimidazolium salts
The synthesis of the palladium complexes used for this study CH⋯Pd separations consistent with anagostic interactions
began with that of unsymmetrically substituted imidazolium between CH atoms of the methyl and benzyl groups were
ligand-precursors (4a–e and 4g). These were obtained accord- found in both of them, the shortest CH⋯Pd distances being
ing to one of the routes displayed in Scheme 1. The one-pot 2.457 Å (in molecule 1) and 2.455 Å (in molecule 2). The X-ray
synthesis of 4a–4d was achieved by treatment of rac-1 with one study further allowed evaluation of the percent buried volume
equiv. of MeLi and subsequent addition of a second, distinct of the carbene ligand of 5d as 36.7% (using a M–Ccarbene bond
alkyllithium reagent (2 equiv.). Workup resulted in the corres- fixed at 2.10 Å for the calculation), which actually is close to
ponding diamines (3a–3d) in over 78% yield. Ring closure to that of IMes.39,40 It is worthy of mention here that, as inferred
the imidazolium salts 4a–4d was then performed with triethyl- from ROESY experiments, a “folded-back” orientation of the
orthoformate and HCl. Attempts to prepare an Et/n-Pr ana- fluorenylidene planes as in 5a–5e (as well as 5h, taken as refer-
logue of 3b in a pure form (using EtLi and n-PrLi as reagents) ence compound), can also be seen in the corresponding amine
were unsuccessful, as this product could not be separated and imidazolium precursors. This conclusion was corrobo-
from the Et/Et and n-Pr/n-Pr side products that formed during rated by the observation that the Ha protons belonging to the
its synthesis.
C6H4-ring have significantly higher-field shifts (ca. 0.8 ppm)
For the preparation of 4e, the first alkylation was arbitrarily with respect to their analogues in o-phenylenediamine. This is
performed with a Grignard reagent, namely i-PrMgBr, this a consequence of the fact that the Ha protons lie in the shield-
leading after hydrolysis to the mixed imine–amine 2e in 73% ing region of the neighbouring fluorenylidene moieties.
yield. Alkylation of 2e with MeLi and subsequent hydrolysis
gave 3e in 90% yield. Finally, diamine 3e was reacted with HC complex 5h, which has two ethyl substituents oriented towards
(OEt)3–HCl to yield the imidazolium salt 4e in 79%.
the dz2 orbital, indicate a rotational barrier of ca. 30 kcal mol−1
Preliminary DFT calculations carried out on the reference
The preparation of thioether-imidazolium salt 4g, which we for a 180° rotation of the alkylfluorenylidene groups about the
considered as a potential precursor (vide infra) of a chelating N–C(fluorenylidene) bond. In the following, an alkyl orien-
carbene-thioether ligand is basically similar to that of 4a–4d, tation as in 5h will be termed an exo-orientation, while the
although this synthesis required an additional step to generate opposite one will be called an endo-orientation. The theoretical
the thioether function. Thus, after sequential addition of MeLi study revealed that 5h is more stable by about 16.4 kcal mol−1
12252 | Dalton Trans., 2014, 43, 12251–12262
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Scheme 1 Synthesis of benzimidazolium salts 4a–e.
than a hypothetical endo/endo rotamer, that is the one with the
fluorenylidene plane inclined towards the metal ion. Interest-
ingly, the calculated rotational barrier for an endo–exo alkyl
orientational change was found to be lower by ca. 15 kcal
mol−1 than the exo–endo conversion discussed above. This
obviously reflects the presence of anagostic interactions in the
exo/exo conformer, which significantly increase the stability of
this rotamer vs. the opposite one. Overall these calculations
lead us to refine somewhat our previous description of the
clamp-like behaviour of the carbene ligand of complex 5h and
related ones. Clearly, the encumbrance of the dz2 orbital in all
the PEPPSI complexes discussed in this study is due to a com-
bination of the orientational properties of the pre-oriented
fluorenylidene plane and the attractive anagostic interactions
that contribute to maintain the steric encumbrance on both
sides of the coordination plane.
Scheme 2 Synthesis of palladium complexes 5a–e.
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Fig. 4 Molecular structure of 5g (top view, left: side view, right).
Fig. 2 Diamine 3h and palladium complexes 5h and 5i.
alkyl side group (It is noteworthy that CH activation of
propane with NHC–Pd complexes has been reported
recently).41 As K2CO3 and pyridine are both relatively weak
bases, metalation probably occurred through CH activation by
the palladium centre after coordination of the thioether group.
Molecular models clearly show that owing to the orientational
properties of the fluorenyl moieties, C,S-chelation of an
hypothetical thioether-carbene ligand positions the Me group
of the methylfluorenyl substituent trans to the sulfur atom,
thereby strongly facilitating a CH activation process.
Comparison with symmetrically-substituted carbenes
In our previous publication on clamp-like carbene ligands, we
had assessed symmetrically substituted analogues of the above
complexes in Suzuki–Miyaura cross coupling reactions. Thus
for example, the meridionally encumbered complexes 5h and
5i were found to behave as fast catalytic systems in the coup-
Fig. 3 Solid state structure of complex 5d (only one of the two similar
molecules in the unit cell is shown).
Attempts to form an analogue of 5a–5e starting from the
thioether imidazolium salt 4g failed. Instead, the cyclometal-
lated pincer-type complex 5g formed quantitatively (Scheme 3),
the structure of which was determined by a single crystal X-ray
1
diffraction study (Fig. 4). In the H NMR spectrum, the meta-
lated CH2 group appears as a sharp singlet at 3.70 ppm
(cf. 2.31 ppm for the methyl group of precursor 4g). In contrast,
the CH2S signal is broad, this reflecting some dynamics within
the puckered Pd,Ccarbene,S ring. Complex 5g is the only known
example of a palladium–NHC complex containing a metallated
Fig. 5 Product yields in Suzuki–Miyaura cross-coupling of PhB(OH)2
with p-Cl-C6H4Me using palladium complexes 5a–e and 5h,i. Reaction
conditions: p-tolyl chloride (1 mmol), phenylboronic acid (1.5 mmol),
Cs2CO3 (2 mmol), [Pd] (1 mol%), dioxane (3 mL). Yields were determined
by 1H NMR.
Scheme 3 High yield synthesis of the cyclometalated carbene complex 5g.
12254 | Dalton Trans., 2014, 43, 12251–12262
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ling of phenylboronic acid with p-tolyl chloride, their activities Hertz (Hz), integration and assignment. In the NMR data
being equal or superior to those of the fastest systems reported given hereafter, Cq denotes a quaternary carbon atom. Flash
to date (IMes/Pd, IPr/Pd).27 To answer the question whether an chromatography was performed as described by Still et al.,42
unsymmetrical ligand structure in a related complex would employing Geduran SI (E. Merck, 0.040–0.063 mm) silica.
modify the catalytic outcome, tests were performed with 5a–5e Routine thin-layer chromatography analyses were carried out
under conditions identical to those previously applied for 5h by using plates coated with Merck Kieselgel 60 GF254. Mass
and 5i, namely by operating with 1 mol% of palladium spectra were recorded either with a Bruker MicroTOF spectro-
complex and 2 equiv. of Cs2CO3 in dioxane at 80 °C. The reac- meter (ESI-TOF) using CH2Cl2 or CH3CN as solvent, or with a
tion rates observed for the unsymmetrical complexes were of Bruker MaldiTOF spectrometer (MALDI-TOF) using dithranol
the same order of magnitude as those of 5h and 5i, although as matrix. Elemental analyses were performed by the Service
slightly inferior (see Fig. 5). The sole complex leading to a de Microanalyse, Institut de Chimie (CNRS), Strasbourg.
somewhat disappointing performance was the Me/Bn complex Melting points were determined with a Büchi 535 capillary
5d, this probably reflecting the bulkiness of the benzyl group melting-point apparatus and are uncorrected. Diimine 1a and
that hinders substrate approach. A similar effect had pre- complexes 5h and 5i were prepared following procedures
viously been observed for the corresponding Bn/Bn complex.
described in the literature.27
Syntheses of amines
N-(2-((9H-Fluoren-9-ylidene)amino)phenyl)-9-isopropyl-9H-
fluoren-9-amine (2e). A solution of i-PrBr (0.598 g, 4.86 mmol)
Conclusions
We have described synthetic methodology that enables prepa- in Et2O (5 mL) was added dropwise to a suspension of Mg
ration in three or four steps of benzimidazolium salts having (0.118 g, 4.86 mmol) in Et2O (5 mL), at a rate to maintain a
their two nitrogen atoms substituted by different alkylfluorenyl steady reflux (about 30 min). The suspension was maintained
groups. With the exception of the thioether derivative 4g, these at reflux for 3 h and then allowed to reach room temperature.
salts readily form PEPPSI-type palladium complexes in which The i-PrMgBr solution (C ≈ 0.48 M, 6 mL, 2.90 mmol) was
both fluorenylidene moieties orientate the corresponding alkyl added dropwise at 0 °C to a stirred solution of diimine 1
group towards the dz2 orbital of the palladium ion. Owing to a (1.05 g, 2.43 mmol) in CH2Cl2 (10 mL). The dark solution was
high rotational barrier about the N–C(fluorenyl) bond, time heated at refluxed for 4 h and then allowed to reach room
independent crowding is created about the metal in the most temperature. Water was slowly added (40 mL) and the product
stable conformer, in which anagostic interactions significantly was extracted with AcOEt (3 × 40 mL). The combined organic
contribute to maintain the observed apical encumbrance. layers were dried with Na2SO4, and the solvent was removed
With imidazolium salt 4g, and by applying conditions that nor- under reduced pressure. The crude product was purified by
mally lead to PEPPSI complexes, the cyclometallated pincer flash chromatography (SiO2; AcOEt–petroleum ether, 10 : 90) to
complex 5g was obtained quantitatively. Its formation is likely afford 2e as a red solid (0.845 g, 73%). 1H NMR (CDCl3,
to involve CH activation by the palladium centre after for- 300 MHz), δ 8.11 (1H, d, 3J = 7.4 Hz, ArH), 7.74 (2H, d, 3J =
3
3
mation of a carbene ligand and binding of the thioether 7.5 Hz, ArH), 7.67 (2H, d, J = 7.5 Hz, ArH), 7.53 (1H, dd, J =
group. Like their symmetrical analogues, the complexes dis- 7.5 Hz, 4J = 1.2 Hz, ArH), 7.47–7.32 (4H, m, ArH), 7.31–7.24
played high activities in the cross coupling of phenyl boronic (2H, m, ArH), 7.22–7.10 (3H, m, ArH), 7.01 (1H, dd, 3J = 7.6 Hz,
acid with p-tolylchloride, but their performance did not 4J = 1.0 Hz, ArH), 6.82–6.76 (1H, m, ArH), 6.53–6.44 (2H, m,
surpass that of the symmetrical Et/Et complex 5h.
ArH), 5.54–5.47 (1H, m, ArH), 5.08 (1H, s, NH), 2.37–2.20 (1H,
3
m, CH), 0.67 (6H, d, J = 6.7 Hz, CH3). 13C{1H} NMR (CDCl3,
75 MHz), δ 163.9 (CvN), 147.6 (2 overlapped arom. Cq), 143.8
(arom. Cq), 141.9 (arom. Cq), 140.8 (2 overlapped arom. Cq),
138.1 (arom. Cq), 137.8 (arom. Cq), 136.9 (arom. Cq), 132.1
(arom. CH), 131.9 (arom. CH), 131.5 (arom. Cq), 128.6 (arom.
Experimental section
General procedures
All commercial reagents were used as supplied. The syntheses CH), 128.0 (3 overlapped arom. CH), 127.3 (2 overlapped arom.
were performed in Schlenk-type flasks under dry nitrogen. Sol- CH), 127.1 (arom. CH), 125.9 (arom. CH), 124.2 (2 overlapped
vents were dried by conventional methods and distilled arom. CH), 123.3 (arom. CH), 120.3 (arom. CH), 119.9 (2 over-
immediately prior to use. Routine 1H and 13C{1H} NMR lapped arom. CH), 119.8 (arom. CH), 118.1 (arom. CH), 116.8
spectra were recorded on
a FT Bruker AVANCE 300 (arom. CH), 113.4 (arom. CH), 71.4 (Cq), 65.5 (Cq), 39.1 (CH),
1
(1H: 300.1 MHz, 13C: 75.5 MHz) instrument at 25 °C. H NMR 17.7 (CH3). Found C, 87.85; H, 6.02; N, 6.12. Calc. for C35H28N2
spectral data were referenced to residual protonated solvents (Mr = 476.62): C, 88.20; H, 5.92; N, 5.88%.
(CHCl3, δ 7.26; [D6]DMSO, δ 2.50), 13C chemical shifts are
N-(9-Ethyl-9H-fluoren-9-yl)-N′-(9-methyl-9H-fluoren-9-yl)-
reported relative to deuterated solvents (CDCl3, δ 77.16; benzene-1,2-diamine (3a). A solution of ethyl bromide (1.04 g,
[D6]DMSO, δ 39.52). Data are represented as follows: Chemical 9.72 mmol) in pentane (10 mL) was added to a suspension of
shift, multiplicity (s = singlet, d = doublet, t = triplet, q = lithium powder (25 wt% in mineral oil 0.551 g, 19.7 mmol)
quartet, m = multiplet, br = broad), coupling constant (J) in in pentane (9 mL) at a rate to maintain a steady reflux
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(about 1 h). The suspension was maintained at reflux for 3 h Cq), 135.5 (arom. Cq), 128.1 (arom. CH), 128.1 (arom. CH),
and then allowed to reach room temperature. The EtLi solution 127.8 (arom. CH), 127.7 (arom. CH), 123.5 (arom. CH), 123.2
(C ≈ 0.5 M) was used without further purification. To a stirred (arom. CH), 120.4 (arom. CH), 120.2 (arom. CH), 120.1 (arom.
solution of diimine 1 (1.06 g, 2.45 mmol) in THF (10 mL) CH), 117.4 (arom. CH), 117.6 (arom. CH), 116.9 (arom. CH),
cooled to −78 °C, was added dropwise MeLi (1.6 M in Et2O, 68.7 (Cq), 65.5 (Cq), 45.9 (CqCH2) 30.6 (CH3), 17.1 (CH2CH3),
1.8 mL, 2.88 mmol). The dark solution obtained was allowed 14.3 (CH2CH3). Found C, 87.62; H, 6.66; N, 5.51. Calc. for
to reach room temperature and was stirred for 1 h. The C36H32N2 (Mr = 492.67): C, 87.77; H, 6.55; N, 5.69%.
mixture was then cooled to −78 °C and the EtLi solution pre-
N-(9-Butyl-9H-fluoren-9-yl)-N′-(9-methyl-9H-fluoren-9-yl)-
viously prepared (10 mL, 5 mmol), was added dropwise. The benzene-1,2-diamine (3c). To a stirred solution of diimine 1
mixture was allowed to reach room temperature and was (1.04 g, 2.40 mmol) in THF (8 mL) cooled to −78 °C, was
stirred 1 h. Water was slowly added (30 mL) and the product added dropwise MeLi (1.6 M in Et2O, 1.7 mL, 2.72 mmol). The
was extracted with AcOEt (3 × 30 mL). The combined organic dark solution obtained was allowed to reach room temperature
layers were dried with Na2SO4, and the solvent was removed and was stirred for 1 h. The mixture was then cooled to −78 °C
under reduced pressure. The crude product was purified by and n-BuLi, (1.6 M in hexanes, 2 mL, 3.20 mmol) was added
flash chromatography (SiO2; AcOEt–petroleum ether, 0.5 : 99.5) dropwise. The mixture was allowed to reach room temperature
to afford 3a as a pale red solid (0.962 g, 82%); mp 164 °C. and was stirred 1 h. Water was slowly added (30 mL) and the
1H NMR (CDCl3, 300 MHz), δ 7.77–7.72 (4H, m, ArH), product was extracted with AcOEt (3 × 30 mL). The combined
7.41–7.34 (8H, m, ArH), 7.30–7.24 (4H, m, ArH), 6.11–6.08 (2H, organic layers were dried with Na2SO4, and the solvent was
m, ArH), 5.68–5.65 (1H, m, ArH), 5.63–5.60 (1H, m, ArH), 4.39 removed under reduced pressure. The crude product was puri-
(2H, br s, NH), 2.20 (2H, q, 3J = 7.4 Hz, CH2), 1.76 (3H, s, CH3), fied by flash chromatography (SiO2; AcOEt–petroleum ether,
0.57 (3H, t, 3J = 7.4 Hz, CH2CH3). 13C{1H} NMR (CDCl3, 0.5 : 99.5) to afford 3c as a pale red solid (0.947 g, 78%);
75 MHz), δ 149.9 (arom. Cq), 148.26 (arom. Cq), 140.12 (arom. mp 90 °C. 1H NMR (CDCl3, 300 MHz), δ 7.78–7.74 (4H, m, ArH),
Cq), 139.1 (arom. Cq), 136.3 (arom. Cq), 135.3 (arom. Cq), 7.42–7.34 (8H, m, ArH), 7.31–7.24 (4H, m, ArH), 6.14–6.09 (2H,
128.1 (arom. CH), 128.0 (arom. CH), 127.7 (arom. CH), 127.6 m, ArH), 5.72–5.69 (1H, m, ArH), 5.63–5.60 (1H, m, ArH),
(arom. CH), 123.4 (arom. CH), 123.2 (arom. CH), 120.3 (arom. 4.39 (2H, br s, NH), 2.18–2.11 (2H, m, CqCH2), 1.78 (3H, s, CH3),
CH), 120.1 (arom. CH), 119.3 (arom. CH), 117.7 (arom. CH), 1.22 (2H, tq, 3J = 3J′ = 7.5 Hz, CH2CH3), 0.95–0.86 (2H, m,
116.8 (arom. CH), 68.8 (Cq), 65.4 (Cq), 36.4 (CH2) 30.4 (CH3), CqCH2CH2), 0.80 (3H, t, 3J = 7.5 Hz, CH2CH3). 13C{1H} NMR
8.31 (CH2CH3). Found C, 87.52; H, 6.46; N, 5.96. Calc. for (CDCl3, 75 MHz), δ 150.0 (arom. Cq), 148.7 (arom. Cq), 140.0
C35H30N2 (Mr = 478.63): C, 87.83; H, 6.32; N, 5.85%.
(arom. Cq), 139.1 (arom. Cq), 136.3 (arom. Cq), 135.4 (arom.
N-(9-Propyl-9H-fluoren-9-yl)-N′-(9-methyl-9H-fluoren-9-yl)- Cq), 128.1 (arom. CH), 128.0 (arom. CH), 127.8 (arom. CH),
benzene-1,2-diamine (3b). A solution of n-propyl bromide 127.6 (arom. CH), 123.5 (arom. CH), 123.2 (arom. CH), 120.4
(0.950 g, 7.72 mmol) in pentane (10 mL) was added to a sus- (arom. CH), 120.2 (arom. CH), 120.1 (arom. CH), 119.3 (arom.
pension of lithium powder (25 wt% in mineral oil 0.514 g, CH), 117.7 (arom. CH), 116.9 (arom. CH), 68.6 (Cq), 65.5 (Cq),
18.3 mmol) in pentane (9 mL) at a rate to maintain a steady 43.4 (CqCH2), 30.5 (CH3), 25.9 (CqCH2CH2), 23.0 (CH2CH3),
reflux (about 1 h). The suspension was maintained at reflux for 14.1 (CH2CH3). Found C, 87.30; H, 6.83; N, 5.68. Calc. for
3 h and then allowed to reach room temperature. The n-PrLi C37H34N2 (Mr = 506.69): C, 87.71; H, 6.76; N, 5.53%.
solution (C ≈ 0.4 M) was used without further purification. To
N-(9-Benzyl-9H-fluoren-9-yl)-N′-(9-methyl-9H-fluoren-9-yl)-
a stirred solution of diimine 1 (0.950 g, 2.20 mmol) in THF benzene (3d). n-BuLi (1.6 M in hexanes, 3.80 mL, 6.10 mmol)
(10 mL) cooled to −78 °C, was added dropwise MeLi (1.6 M in was added dropwise at −78 °C to a suspension of toluene
Et2O, 1.7 mL, 2.72 mmol). The dark solution obtained was (0.645 mL, 6.10 mmol) and t-BuOK (0.685 g, 6.10 mmol) in
allowed to reach room temperature and was stirred for 1 h. THF (5 mL). The red solution was allowed to reach room temp-
The mixture was then cooled to −78 °C and the n-PrLi solution erature and was stirred 1 h. The benzyl lithium solution
previously prepared (11 mL, 4.40 mmol), was added dropwise. obtained (C ≈ 0.7 M) was used without further purification. To
Water was slowly added (30 mL) and the product was extracted a stirred solution of diimine 1 (1.30 g, 3.00 mmol) in THF
with AcOEt (3 × 30 mL). The combined organic layers were (12 mL) cooled to −78 °C, was added dropwise MeLi (1.6 M in
dried with Na2SO4, and the solvent was removed under Et2O, 2.0 mL, 3.20 mmol). The dark solution obtained was
reduced pressure. The crude product was purified by flash allowed to reach room temperature and was stirred for 1 h.
chromatography (SiO2; AcOEt–petroleum ether, 0.5 : 99.5) to The mixture was then cooled to −78 °C and the benzyl lithium
afford 3b as a pale red solid (0.864 g, 80%); mp 148 °C. solution previously prepared (9 mL, 6.10 mmol), was added
1H NMR (CDCl3, 300 MHz), δ 7.67–7.61 (4H, m, ArH), dropwise. The mixture was allowed to reach room temperature
7.45–7.34 (8H, m, ArH), 7.34–7.24 (4H, m, ArH), 6.14–6.11 (2H, and stirred 1 h. Water was slowly added (30 mL) and the
m, ArH), 5.71–5.69 (1H, m, ArH), 5.65–5.62 (1H, m, ArH), 4.42 product was extracted with AcOEt (3 × 30 mL). The combined
(2H, br s, NH), 2.18–2.13 (2H, m, CqCH2), 1.79 (3H, s, CH3), organic layers were dried with Na2SO4, and the solvent was
3
0.99–0.89 (2H, m, CH2CH3), 0.82 (3H, t, J = 7.3 Hz, CH2CH3). removed under reduced pressure. The crude product was puri-
13C{1H} NMR (CDCl3, 75 MHz), δ 150.0 (arom. Cq), 148.7 fied by flash chromatography (SiO2; AcOEt–petroleum ether,
(arom. Cq), 140.1 (arom. Cq), 139.1 (arom. Cq), 136.2 (arom. 0.5 : 99.5) to afford 3d as a pale orange solid (1.36 g, 84%);
12256 | Dalton Trans., 2014, 43, 12251–12262
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mp 110 °C. 1H NMR (CDCl3, 300 MHz), δ 7.80 (2H, d, 3J = was extracted with AcOEt (3 × 30 mL). The combined organic
3
7.5 Hz, ArH), 7.73 (2H, d, J = 7.5 Hz ArH), 7.44–7.20 (15H, m, layers were dried with Na2SO4, and the solvent was removed
ArH), 7.05 (2H, dd, 3J = 7.6 Hz, 4J = 1.8 Hz, ArH), 6.05–6.01 under reduced pressure. The crude product was purified by
(2H, m, ArH), 5.65–5.62 (1H, m, ArH), 5.48–5.45 (1H, m, ArH), flash chromatography (SiO2; AcOEt–petroleum ether, 70 : 30) to
1
4.92–4.11 (2H, overlapped br s, NH), 3.30 (2H, s, CH2C6H5), afford 3f as a pale red solid (1.99 g, 80%); mp 185 °C. H NMR
1.86 (3H, s, CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 150.0 (CDCl3, 300 MHz), δ 7.87–7.78 (5H, m, ArH), 7.67–7.59 (3H, m,
3
3
(arom. Cq), 148.2 (arom. Cq), 139.6 (arom. Cq), 139.2 (arom. ArH), 7.54–7.29 (8H, m, ArH), 5.99 (1H, ddd, J = J′ = 7.6 Hz,
3
3
4
Cq), 136.1 (arom. Cq), 135.7 (arom. Cq), 135.2 (arom. Cq), 4J = 1.3 Hz, ArH), 5.90 (1H, ddd, J = J′ = 7.6 Hz, J = 1.3 Hz,
3
131.2 (arom. CH), 128.2 (arom. CH), 128.1 (arom. CH), 128.0 ArH), 5.59 (1H, br s, NH), 5.40 (2H, d, J = 7.6 Hz, ArH), 5.23
(arom. CH), 127.9 (arom. CH), 127.2 (arom. CH), 127.1 (arom. (1H, br s, NH), 3.76 (1H, d, J = 13.5 Hz, CH2SCH3), 2.66 (1H,
2
2
CH), 124.3 (arom. CH), 123.0 (arom. CH), 120.4 (arom. CH), d, J = 13.5 Hz, CH2SCH3), 2.63 (3H, s, CH2SCH3), 1.95 (3H, s,
120.3 (arom. CH), 119.8 (arom. CH), 119.1 (arom. CH), 116.7 CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 150.32 (arom. Cq),
(arom. CH), 115.8 (arom. CH), 68.5 (Cq), 65.3 (Cq), 45.9 150.19 (arom. Cq), 148.17 (arom. Cq), 146.03 (arom. Cq),
(CH2C6H5) 31.1 (CH3). Found C, 88.46; H, 5.99; N, 4.99. Calc. 139.46 (arom. Cq), 139.14 (arom. Cq), 138.89 (arom. Cq),
for C40H32N2 (Mr = 540.71): C, 88.85; H, 5.97; N, 5.18%.
138.49 (arom. Cq), 135.69 (arom. Cq), 132.71 (arom. Cq),
N-(9-Isopropyl-9H-fluoren-9-yl)-N′-(9-methyl-9H-fluoren-9-yl)- 129.07 (2 overlapped arom. CH), 128.40 (arom. CH), 127.92
benzene-1,2-diamine (3e). To a stirred solution of amine 2e (arom. CH), 127.85 (arom. CH), 127.81 (3 arom. CH), 125.03
(0.829 g, 1.54 mmol) in THF (10 mL) cooled to −78 °C, was (arom. CH), 123.29 (arom. CH), 123.17 (arom. CH), 122.82
added MeLi (1.6 M in Et2O, 2.1 mL, 3.40 mmol). The dark (arom. CH), 120.80 (arom. CH), 120.69 (arom. CH), 120.33
solution obtained was allowed to reach room temperature and (arom. CH), 120.29 (arom. CH), 119.40 (arom. CH), 117.40
was stirred for 1 h. Water was slowly added (30 mL) and the (arom. CH), 114.51 (arom. CH), 113.37 (arom. CH), 68.11 (Cq),
product was extracted with AcOEt (3 × 30 mL). The combined 66.84 (CH2SCH3), 65.06 (Cq), 39.67 (CH2SCH3), 31.51 (CH3).
organic layers were dried with Na2SO4, and the solvent was Found C, 79.57; H, 5.92; N, 5.11. Calc. for C35H30N2OS (Mr =
removed under reduced pressure. The crude product was puri- 526.70): C, 79.82; H, 5.74; N, 5.32%.
fied by flash chromatography (SiO2; AcOEt–petroleum ether,
N-(9-Methyl-9H-fluoren-9-yl)-N′-(9-methylthiomethyl-9H-
0.5 : 99.5) to afford 3e as a pale brown solid (0.777 g, 90%); fluoren-9-yl)benzene-1,2-diamine (3g). NaBH4 (0.224 g,
mp 80 °C. 1HNMR (CDCl3, 300 MHz), δ 7.76 (2H, d, 3J = 7.4 Hz, 5.92 mmol) was added under vigorous stirring at 0 °C to a
3
ArH), 7.73 (2H, d, J = 7.4 Hz, ArH), 7.41–7.21 (12H, m, ArH), solution of diamine 3f (1.29 g, 2.45 mmol) and I2 (1.50 g,
6.08–6.06 (2H, m, ArH), 5.74–5.72 (1H, m, ArH), 5.51–5.48 (1H, 5.90 mmol) in THF (40 mL). Gas emission was observed. The
m, ArH), 4.72 (1H, br s, NH), 4.20 (1H, br s, NH), 2.44 (1H, reaction mixture was allowed to reach room temperature and
hept, 3J = 6.8 Hz, CH(CH3)2), 1.78 (3H, s, CH3), 0.84 (6H, d, 3J = was stirred 1 h. A 10% aqueous sodium hydroxide solution
6.8 Hz, CH(CH3)2). 13C{1H} NMR (CDCl3, 75 MHz), δ 150.0 was slowly added (80 mL) and the product was extracted with
(arom. Cq), 147.6 (arom. Cq), 140.8 (arom. Cq), 139.2 (arom. AcOEt (3 × 60 mL). The combined organic layers were washed
Cq), 137.1 (arom. Cq), 134.8 (arom. Cq), 128.1 (arom. CH), with a 10% aqueous sodium thiosulfate solution (2 × 80 mL),
128.0 (arom. CH), 127.8 (arom. CH), 127.3 (arom. CH), 124.0 water (80 mL) and dried with Na2SO4. The solvent was
(arom. CH), 123.2 (arom. CH), 120.6 (arom. CH), 120.4 (arom. removed under reduced pressure. The crude product was puri-
CH), 119.9 (arom. CH), 118.7 (arom. CH), 118.2 (arom. CH), fied by flash chromatography (SiO2; AcOEt–petroleum ether,
115.7 (arom. CH), 71.4 (Cq), 65.5 (Cq), 39.7 (CH(CH3)2), 30.4 10 : 90) to afford 3g as a white solid (0.988 g, 79%); mp 84 °C.
(CH3), 17.7 (CH(CH3)2). Found C, 87.72; H, 6.65; N, 6.00. Calc. 1H NMR (CDCl3, 300 MHz), δ 7.83 (4H, d, 3J = 7.5 Hz, ArH),
3
3
for C36H32N2 (Mr = 492.67): C, 87.77; H, 6.55; N, 5.69%.
7.61 (2H, d, J = 7.5 Hz, ArH), 7.54 (2H, d, J = 7.3 Hz, ArH),
N-(9-Methyl-9H-fluoren-9-yl)-N′-(9-methylsulfinylmethyl-9H- 7.49–7.40 (4H, m, ArH), 7.40–7.30 (4H, m, ArH), 6.19–6.05 (2H,
fluoren-9-yl)benzene-1,2-diamine (3f). A solution of n-BuLi m, ArH), 5.17–5.60 (2H, m, ArH), 5.29–4.30 (2H, overlapped
(1.6 M in hexanes, 4.6 mL, 7.40 mmol) was added dropwise at br s, NH), 3.21 (2H, s, CH2SCH3), 2.21 (3H, s, CH2SCH3), 1.88
−78 °C to a solution of dimethylsulfoxide (DMSO, 526 μL, (3H, s, CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 149.9 (arom. Cq),
0.578 g, 7.40 mmol) in THF (10 mL). The white suspension 147.8 (arom. Cq), 139.6 (arom. Cq), 139.1 (arom. Cq), 135.9
was allowed to reach room temperature and was stirred 1 h. (arom. Cq), 135.2 (arom. Cq), 128.6 (arom. CH), 128.1 (arom.
The dimsyl lithium (LiDMSO) suspension (C ≈ 0.5 M) was CH), 127.8 (arom. CH), 127.6 (arom. CH), 124.0 (arom. CH),
used without further purification. To a stirred solution of 123.1 (arom. CH), 120.4 (arom. CH), 120.3 (arom. CH), 119.8
diimine 1 (2.05 g, 4.73 mmol) in THF (10 mL) cooled to (arom. CH), 119.4 (arom. CH), 116.6 (arom. CH), 116.4 (arom.
−78 °C, was added a solution of MeLi (1.6 M in Et2O, 3.5 mL, CH), 68.0 (Cq), 65.3(Cq), 49.6 (CH2SCH3), 30.8 (CH2SCH3), 18.4
5.67 mmol). The dark solution obtained was allowed to reach (CH3). Found C, 82.60; H, 5.82; N, 5.23. Calc. for C35H30N2S
room temperature and was stirred for 1 h. The mixture was (Mr = 510.70): C, 82.32; H, 5.92; N, 5.49%.
then cooled to −78 °C and the LiDMSO solution previously
prepared (15 mL, 7.40 mmol), was then added dropwise. The
Syntheses of benzimidazolium salts
mixture was allowed to reach room temperature and was
1-(9-Ethyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-9-yl)-1H-
stirred 1 h. Water was slowly added (30 mL) and the product benzimidazolium chloride (4a). Diamine 3a (0.512 g,
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1.07 mmol) was dissolved under magnetic stirring in HC m, ArH), 6.80–6.73 (2H, m, ArH), 6.25–6.19 (2H, m, ArH),
3
(OEt)3. HCl (12 M, 116 μL, 1.39 mmol) was added, and the 3.71–3.66 (2H, m, CqCH2), 2.94 (3H, s, CH3), 1.38 (2H, tq, J =
mixture was heated at 80 °C for 15 h. The mixture was then 3J′ = 7.5 Hz, CH2CH3), 0.79–0.67 (5H, m, overlapped signals,
cooled to room temperature and petroleum ether was added CqCH2CH2 and CH2CH3). 13C{1H} NMR (CDCl3, 75 MHz),
(ca. 20 mL). The precipitate was collected by filtration and δ 145.1 (arom. Cq), 143.5 (arom. Cq), 142.2 (NCHN), 140.3
washed with petroleum ether (3 × 15 mL). Compound 4a (arom. Cq), 139.0 (arom. Cq), 131.0 (arom. Cq), 130.8 (arom.
(0.507 g, 90%) was obtained as a hygroscopic white solid; mp Cq), 130.2 (2 overlapped arom. CH), 129.4 (arom. CH), 129.4
192 °C. 1H NMR (CDCl3, 300 MHz), δ 11.16 (1H, s, NCHN), (arom. CH), 126.2 (arom. CH), 126.2 (arom. CH), 125.0 (arom.
7.86–7.78 (8H, m, ArH), 7.51–7.43 (4H, m, ArH), 7.38–7.29 (4H, CH), 124.9 (arom. CH), 120.8 (arom. CH), 120.5 (arom. CH),
m, ArH), 6.78–6.72 (2H, m, ArH), 6.26–6.16 (2H, m, ArH), 3.70 115.0 (arom. CH), 114.7 (arom. CH), 74.8 (Cq), 71.4 (Cq), 37.7
(2H, q, 3J = 7.0 Hz, CH2CH3), 2.91 (3H, s, CH3), 0.51 (3H, t, 3J = (CqCH2), 27.3 (CH3), 25.2 (CqCH2CH2), 22.5 (CH2CH3), 14.2
7.0 Hz, CH2CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 145.1 (CH2CH3). Found C, 80.80; H, 6.03; N, 5.10. Calc. for
(arom. Cq), 143.1 (arom. Cq), 142.4 (NCHN), 140.4 (arom. Cq), C38H33ClN2·0.5H2O (Mr = 553.15 + 9.01): C, 81.19; H, 6.10;
139.0 (arom. Cq), 131.1 (arom. Cq), 130.7 (arom. Cq), 130.2 N, 4.98%.
(2 overlapped arom. CH), 129.4 (2 overlapped arom. CH), 126.1
1-(9-Benzyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-9-yl)-1H-
(2 overlapped arom. CH), 125.0 (arom. CH), 124.9 (arom. CH), benzimidazolium chloride (4d). Diamine 3d (0.612 g,
120.8 (arom. CH), 120.5 (arom. CH), 114.9 (arom. CH), 114.7 1.13 mmol) was dissolved under magnetic stirring in HC(OEt)3
(arom. CH), 75.3 (Cq), 71.4 (Cq), 31.4 (CH2CH3), 27.3 (CH3), (4 mL) and then HCl 12 M (122 μL, 1.47 mmol) was added.
7.4 (CH2CH3). Found C, 80.30; H, 5.70; N, 5.34. Calc. for The mixture was heated at 120 °C for 15 h. After cooling to
C36H29ClN2·0.6H2O (Mr = 525.09 + 10.81): C, 80.69; H, 5.68; room temperature petroleum ether was added (ca. 20 mL). The
N, 5.23%.
precipitate was collected by filtration and washed with petro-
1-(9-Methyl-9H-fluoren-9-yl)-3-(9-propyl-9H-fluoren-9-yl)-1H- leum ether (3 × 15 mL). Compound 4d (0.510 g, 77%) was
benzimidazolium chloride (4b). Diamine 3b (0.271 g, obtained as a hygroscopic white solid; mp 209 °C. 1H NMR
0.550 mmol) was dissolved under magnetic stirring in HC ([D6]DMSO, 300 MHz), δ 10.70 (1H, s, NCHN), 8.12 (4H, dd,
3
3
(OEt)3 (2 mL) and then HCl 12 M (58 μL, 0.70 mmol) was 3J = J′ = 8.8 Hz, ArH), 7.99 (2H, d, J = 7.4 Hz, ArH), 7.72 (2H,
added. The mixture was heated at 80 °C for 15 h. The mixture d, 3J = 7.2 Hz, ArH), 7.56 (2H, dd, 3J = 3J′ = 7.4 Hz, ArH),
was then cooled to room temperature and petroleum ether was 7.46–7.35 (6H, m, ArH), 7.00–6.80 (5H, m, ArH), 6.45 (2H, d,
added (ca. 20 mL). The precipitate was collected by filtration 3J = 7.4 Hz, ArH), 6.14–6.05 (2H, m, ArH), 4.88 (2H, CH2(C6H5),
and washed with petroleum ether (3 × 15 mL). Compound 4b 2.70 (3H, s, CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 145.2
(0.274 g, 93%) was obtained as a hygroscopic white solid; mp (arom. Cq), 143.6 (NCHN), 142.6 (arom. Cq), 140.0 (arom. Cq),
192 °C. 1H NMR (CDCl3, 300 MHz), δ 11.15 (1H, s, NCHN), 138.6 (arom. Cq), 132.5 (arom. Cq), 130.3 (arom. CH), 130.2
7.87–7.81 (8H, m, ArH), 7.48 (4H, t, 3J = 7.5 Hz, ArH), 7.38–7.31 (arom. CH), 130.1 (arom. CH), 130.0 (arom. Cq), 129.8 (arom.
(4H, m, ArH), 6.79–6.73 (2H, m, ArH), 6.24–6.19 (2H, m, ArH), Cq), 129.0 (arom. CH), 128.4 (arom. CH), 127.1 (arom. CH),
3
3.67–3.62 (2H, m, CqCH2), 2.93 (3H, s, CH3), 0.91 (3H, t, J = 126.6 (arom. CH), 126.3 (arom. CH), 126.2 (arom. CH), 125.3
7.5 Hz, CH2CH3), 0.85–0.75 (2H, m, CH2CH3). 13C{1H} NMR (arom. CH), 124.6 (arom. CH), 121.5 (arom. CH), 120.8 (arom.
(CDCl3, 75 MHz), δ 145.1 (arom. Cq), 143.6 (arom. Cq), 142.3 CH), 114.2 (arom. CH), 113.9 (arom. CH), 73.9 (Cq), 70.3 (Cq),
(NCHN), 140.3 (arom. Cq), 139.0 (arom. Cq), 131.0 (arom. Cq), 42.4 (CH2(C6H5)), 26.2 (CH3). Found C, 79.72; H, 5.50; N, 4.20.
130.8 (arom. Cq), 130.3 (2 overlapped arom. CH), 129.5 (arom. Calc. for C41H31ClN2·1.7H2O (Mr = 587.16 + 30.63): C, 79.71;
CH), 129.4 (arom. CH), 126.2 (arom. CH), 126.2 (arom. CH), H, 5.61; N, 4.53%.
125.0 (arom. CH), 124.9 (arom. CH), 120.8 (arom. CH), 120.5
1-(9-Methyl-9H-fluoren-9-yl)-3-(9-iso-propyl-9H-fluoren-9-yl)-
(arom. CH), 115.0 (arom. CH), 114.7 (arom. CH), 74.8 (Cq), 1H-benzimidazolium chloride (4e). Diamine 3e (0.455 g,
71.4 (Cq), 39.9 (CqCH2) 27.3 (CH3), 16.5 (CH2CH3), 13.9 0.92 mmol) was dissolved under magnetic stirring in HC(OEt)3
(CH2CH3). Found C, 79.73; H, 5.90; N, 4.80. Calc. for (3 mL) and then HCl 12 M (110 μL, 1.32 mmol) was added.
C37H31ClN2·0.9H2O (Mr = 539.12 + 16.21): C, 80.03; H, 5.95; N, The mixture was heated at 80 °C for 15 h. The solution was
5.04%.
then cooled to room temperature and petroleum ether was
1-(9-Butyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-9-yl)-1H- added (ca. 20 mL). The precipitate was collected by filtration
benzimidazolium chloride (4c). Diamine 3c (0.902 g, and washed with petroleum ether (3 × 15 mL). Compound 4e
1.78 mmol) was dissolved under magnetic stirring in HC(OEt)3 (0.391 g, 79%) was obtained as a hygroscopic white solid; mp
(8 mL) and then HCl 12 M (195 μL, 2.34 mmol) was added. 175 °C. 1H NMR (CDCl3, 300 MHz), δ 11.67 (1H, s, NCHN),
3
3
3
The mixture was heated at 80 °C for 15 h. The mixture was 7.90 (2H, d, J = 7.5 Hz, ArH), 7.82 (4H, dd, J = J′ = 7.3 Hz,
then cooled to room temperature and petroleum ether was ArH), 7.77 (2H, d, 3J = 7.5 Hz, ArH), 7.49 (4H, dd, 3J = 3J′ =
added (ca. 20 mL). The precipitate was collected by filtration and 7.5 Hz, ArH), 7.34 (4H, dd, 3J = 3J′ = 7.3 Hz, ArH), 6.79–6.71
washed with petroleum ether (3 × 25 mL). Compound 4c (0.865 g, (2H, m, ArH), 6.19–6.13 (1H, m, ArH), 5.99–5.93 (1H, m, ArH),
88%) was obtained as a hygroscopic white solid; mp 163 °C.
4.88 (1H, hept, 3J = 6.5 Hz, CH(CH3)2), 2.97 (3H, s, CH3),
1H NMR (CDCl3, 300 MHz), δ 11.15 (1H, s, NCHN), 1.05 (6H, d, 3J = 6.5 Hz, CH(CH3)2). 13C{1H} NMR (CDCl3,
7.89–7.82 (8H, m, ArH), 7.52–7.41 (4H, m, ArH), 7.38–7.30 (4H, 75 MHz), δ 145.0 (arom. Cq), 144.2 (NCHN), 142.8 (arom. Cq),
12258 | Dalton Trans., 2014, 43, 12251–12262
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140.6 (arom. Cq), 139.1 (arom. Cq), 131.4 (arom. Cq), 130.7 (arom. CH), 113.1 (arom. CH), 76.7 (Cq), 72.3 (Cq), 36.7
(arom. Cq), 130.4 (arom. CH), 130.3 (arom. CH), 129.4 (arom. (CH2CH3) 33.9 (CH3), 6.7 (CH2CH3). Found C, 65.91; H, 4.80;
CH), 129.0 (arom. CH), 126.2 (arom. CH), 126.2 (arom. CH), N, 5.51. Calc. for C41H33Cl2N3Pd (Mr = 745.06): C, 66.10;
126.1 (arom. CH), 124.7 (arom. CH), 120.9 (arom. CH), 120.5 H, 4.46; N, 5.64%.
(arom. CH), 115.4 (arom. CH), 114.8 (arom. CH), 78.8 (Cq),
trans-[1-(9-Methyl-9H-fluoren-9-yl)-3-(9-propyl-9H-fluoren-
71.7 (Cq), 33.7 (CH(CH3)2) 27.8 (CH3), 17.9 (CH(CH3)2). Found 9-yl)-1H-benzimidazol-2-ylidene](pyridine)palladium(II) dichloride
C, 79.46; H, 6.15; N, 4.77. Calc. for C37H31ClN2·1.2H2O (5b). A suspension of benzimidazolium salt 4b (0.307 g,
(Mr = 539.12 + 21.62): C, 79.25; H, 6.00; N, 5.00%.
0.57 mmol), finely crushed K2CO3 (0.407 g, 2.95 mmol), and
1-(9-Methyl-9H-fluoren-9-yl)-3-(9-methylthiomethyl-9H-fluoren- PdCl2 (0.120 g, 0.67 mmol) in pyridine (2 mL) was heated at
9-yl)-1H-benzimidazolium chloride (4g). Diamine 3g (0.292 g, 80 °C for 15 h under vigorous stirring. The mixture was cooled
0.57 mmol) was dissolved under magnetic stirring in HC(OEt)3 to room temperature, filtered through Celite and the filtered
(2 mL) and then HCl 12 M (65 μL, 0.78 mmol) was added. The solid was washed with CH2Cl2 (ca. 20 mL). The combined
mixture was heated at 80 °C for 15 h. The solution was then washings and the filtrate were evaporated to dryness. The
cooled to room temperature and petroleum ether was added residue was then purified by flash chromatography (SiO2;
(ca. 20 mL). The precipitate was collected by filtration and CH2Cl2–petroleum ether, 50 : 50) to afford 5b as a yellow solid
washed with petroleum ether (3 × 15 mL). Compound 4g (0.412 g, 95%); mp > 240 °C. 1H NMR (CDCl3, 300 MHz),
(0.235 g, 73%) was obtained as a hygroscopic white solid; mp δ 9.19–9.14 (2H, m, o-NC5H5), 7.88–7.76 (9H, m, 8H ArH and
178 °C. 1H NMR (CDCl3, 300 MHz), δ 11.61 (1H, s, NCHN), 1H p-NC5H5), 7.48–7.37 (6H, m, 4H ArH and 2H m-NC5H5),
3
3
8.03 (2H, d, J = 7.7 Hz, ArH), 7.84 (6H, d, J = 7.7 Hz, ArH), 7.35–7.27 (4H, m, ArH), 6.41–6.35 (2H, m, ArH), 6.21–6.14 (1H,
7.55–7.46 (4H, m, ArH), 7.39–7.31 (4H, m, ArH), 6.80–6.76 (2H, m, ArH), 6.11–6.05 (1H, m, ArH), 5.47–5.41 (2H, m, CqCH2),
3
m, ArH), 6.21–6.17 (1H, m, ArH), 6.10–6.06 (1H, m, ArH), 4.74 4.07 (3H, s, CH3), 0.95 (3H, t, J = 7.1 Hz, CH2CH3), 0.76–0.50
(2H, s, CH2SCH3), 2.94 (3H, s, CH2SCH3), 2.31 (3H, s, CH3). (2H, m, CH2CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 161.1
13C{1H} NMR (CDCl3, 75 MHz), δ 145.0 (arom. Cq), 144.4 (NCN), 151.8 (arom. CH), 149.3 (arom. Cq), 146.9 (arom. Cq),
(NCHN), 143.2 (arom. Cq), 139.9 (arom. Cq), 139.0 (arom. Cq), 140.1 (arom. Cq), 138.3 (arom. Cq), 138.2 (arom. CH), 134.5
130.8 (arom. Cq), 130.6 (arom. CH), 130.5 (arom. Cq), 130.3 (arom. Cq), 134.3 (arom. Cq), 129.1 (arom. CH), 129.0 (arom.
(arom. CH), 129.4 (arom. CH), 129.1 (arom. CH), 126.2 (arom. CH), 124.8 (arom. CH), 124.7 (arom. CH), 124.6 (arom. CH),
CH), 126.1 (2 overlapped arom. CH), 124.9 (arom. CH), 120.8 122.4 (arom. CH), 120.7 (arom. CH), 120.0 (arom. CH), 113.4
(arom. CH), 120.7 (arom. CH), 114.8 (arom. CH), 114.7 (arom. (arom. CH), 113.1 (arom. CH), 75.9 (Cq), 72.3 (Cq), 46.0
CH), 73.7 (Cq), 71.3 (Cq), 42.6 (CH2SCH3), 27.2 (CH2SCH3), (CqCH2) 33.9 (CH3), 17.5 (CH2CH3), 14.5 (CH2CH3). Found C,
17.4 (CH3). Found C, 77.86; H, 5.30; N, 4.78. Calc. for 66.17; H, 4.86; N, 5.17. Calc. for C42H35Cl2N3Pd (Mr = 759.08):
C36H29ClN2S (Mr = 557.15): C, 77.61; H, 5.25; N, 5.03%.
C, 66.46; H, 4.65; N, 5.54%.
trans-[1-(9-Butyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-9-yl)-
1H-benzimidazol-2-ylidene](pyridine)palladium(II) dichloride
Palladium complexes
trans-[1-(9-Ethyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-9-yl)- (5c). A suspension of benzimidazolium salt 4c (0.498 g,
1H-benzimidazol-2-ylidene](pyridine)palladium(II) dichloride 0.90 mmol), finely crushed K2CO3 (0.622 g, 4.50 mmol), and
(5a). A suspension of benzimidazolium salt 4a (0.310 g, PdCl2 (0.191 g, 1.08 mmol) in pyridine (2 mL) was heated at
0.59 mmol), finely crushed K2CO3 (0.407 g, 2.95 mmol), and 80 °C for 15 h under vigorous stirring. The mixture was cooled
PdCl2 (0.126 g, 0.71 mmol) in pyridine (2 mL) was heated at to room temperature, filtered through Celite and the filtered
80 °C for 15 h under vigorous stirring. The mixture was cooled solid was washed with CH2Cl2 (ca. 20 mL). The combined
to room temperature, filtered through Celite and the filtered washings and the filtrate were evaporated to dryness. The
solid was washed with CH2Cl2 (ca. 20 mL). The combined residue was then purified by flash chromatography (SiO2;
washings and the filtrate were evaporated to dryness. The CH2Cl2–petroleum ether, 50 : 50) to afford 5c as a yellow solid
residue was then purified by flash chromatography (SiO2; (0.330 g, 47%); mp > 240 °C. 1H NMR (CDCl3, 300 MHz),
CH2Cl2–petroleum ether, 50 : 50) to afford 5a as a yellow solid δ 9.19–9.14 (2H, m, o-NC5H5), 7.87–7.70 (9H, m, 8H ArH and
(0.373 g, 85%); mp > 240 °C. 1H NMR (CDCl3, 300 MHz), 1H p-NC5H5), 7.46–7.36 (6H, m, 4H ArH and 2H m-NC5H5),
δ 9.17–9.12 (2H, m, o-NC5H5), 7.89–7.73 (9H, m, 8H ArH and 7.33–7.24 (4H, m, ArH), 6.39–6.33 (2H, m, ArH), 6.18–6.12 (1H,
1H p-NC5H5), 7.48–7.37 (6H, m, 4H ArH and 2H m-NC5H5), m, ArH), 6.09–6.03 (1H, m, ArH), 5.45–5.39 (2H, m, CqCH2),
3
3
7.35–7.26 (4H, m, ArH), 6.41–6.35 (2H, m, ArH), 6.22–6.17 (1H, 4.04 (3H, s, CH3), 1.37 (2H, tq, J = J′ = 7.4 Hz, CH2CH3), 0.71
m, ArH), 6.11–6.05 (1H, m, ArH), 5.45 (2H, q, 3J = 7.1 Hz, (3H, t, 3J = 7.4 Hz, CH2CH3), 0.64–0.51 (2H, m, CqCH2CH2).
3
CH2CH3), 4.06 (3H, s, CH3), 0.46 (3H, t, J = 7.1 Hz, CH2CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 161.0 (NCN), 151.8 (arom.
13C{1H} NMR (CDCl3, 75 MHz), δ 161.0 (NCN), 151.7 (arom. CH), 149.4 (arom. Cq), 146.9 (arom. Cq), 140.2 (arom. Cq),
CH), 149.3 (arom. Cq), 146.3 (arom. Cq), 140.3 (arom. Cq), 138.3 (arom. Cq), 138.2 (arom. CH), 134.6 (arom. Cq), 134.3
138.3 (arom. Cq), 138.2 (arom. CH), 134.6 (arom. Cq), 134.2 (arom. Cq), 129.1 (arom. CH), 129.0 (arom. CH), 128.6 (arom.
(arom. Cq), 129.2 (arom. CH), 129.1 (arom. CH), 129.0 (arom. CH), 124.8 (arom. CH), 124.7 (arom. CH), 122.4 (arom. CH),
CH), 124.9 (arom. CH), 124.8 (arom. CH), 124.7 (arom. CH), 120.7 (arom. CH), 120.1 (arom. CH), 113.4 (arom. CH), 113.1
122.5 (arom. CH), 120.7 (arom. CH), 120.0 (arom. CH), 113.4 (arom. CH), 75.9 (Cq), 72.3 (Cq), 43.6 (CqCH2) 34.0 (CH3), 26.1
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(CqCH2CH2), 23.0 (CH2CH3), 15.1 (CH2CH3). Found C, 65.51; (CH(CH3)2). Found C, 66.13; H, 4.85; N, 5.17. Calc. for
H, 4.93; N, 5.42. Calc. for C43H37Cl2N3Pd (Mr = 773.11): C42H35Cl2N3Pd (Mr = 759.02): C, 66.46; H, 4.65; N, 5.54%.
C, 66.80; H, 4.82; N, 5.44%.
Palladium complex 5g
trans-[1-(9-Benzyl-9H-fluoren-9-yl)-3-(9-methyl-9H-fluoren-
9-yl)-1H-benzimidazol-2-ylidene](pyridine)palladium(II) dichloride A suspension of benzimidazolium salt 4g (0.234 g, 0.42 mmol,
(5d). A suspension of benzimidazolium salt 4d (0.211 g, finely crushed K2CO3 (0.291 g, 2.10 mmol), and PdCl2 (0.089 g,
0.39 mmol), finely crushed K2CO3 (0.282 g, 2.04 mmol), and 0.50 mmol) in pyridine (3 mL) was heated at 80 °C for 15 h
PdCl2 (0.085 g, 0.48 mmol) in pyridine (2 mL) was heated at under vigorous stirring. The mixture was cooled to room temp-
80 °C for 15 h under vigorous stirring. The mixture was cooled erature, filtered through Celite and the filtered solid was
to room temperature, filtered through Celite and the filtered washed with CH2Cl2 (ca. 20 mL). The combined washings and
solid was washed with CH2Cl2 (ca. 20 mL). The combined the filtrate were evaporated to dryness. The residue was then
washings and the filtrate were evaporated to dryness. The purified by flash chromatography (SiO2; CH2Cl2–MeOH ether,
residue was then purified by flash chromatography (SiO2; 92 : 8) to afford 5g as a yellow solid (0.260 g, 93%); mp >
1
3
CH2Cl2–petroleum ether, 50 : 50) to afford 5d as a yellow solid 240 °C. H NMR (CDCl3, 300 MHz), δ 7.90 (2H, d, J = 7.5 Hz,
(0.205 g, 65%); mp > 212 °C. 1H NMR (CDCl3, 300 MHz), ArH), 7.78 (2H, d, J = 7.5 Hz, ArH), 7.72 (2H, d, 3J = 7.5 Hz,
3
δ 9.11–9.05 (2H, m, o-NC5H5), 7.97–7.93 (2H, m, ArH), 7.87 ArH), 7.60–7.52 (4H, m, ArH), 7.45–7.24 (6H, m, ArH),
3
(4H, d, J = 7.9 Hz, ArH), 7.73 (1H, m, 8H, p-NC5H5), 7.51–7.26 6.65–6.42 (2H, m, ArH), 5.96–5.90 (1H, m, ArH), 5.77–5.71 (1H,
3
(12H, m, 10H ArH and 2H m-NC5H5), 6.94 (1H, t, J = 7.5 Hz, m, ArH), 3.70 (2H, s, CH2Pd), 3.33 (2H, br s, CH2SCH3), 2.70
ArH), 6.80 (2H, dd, 3J = 3J′ = 7.5 Hz, ArH), 6.73 (2H, s, (3H, s, CH2SCH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 176.5
CH2C6H5), 6.43–6.33 (4H, m, ArH), 6.14–6.09 (2H, m, ArH), (NCN), 147.3 (arom. CH), 144.2 (arom. Cq), 139.2 (arom. Cq),
4.09 (3H, s, CH3). 13C{1H} NMR (CDCl3, 75 MHz), δ 161.5 138.9 (arom. Cq), 132.0 (arom. Cq), 131.7 (arom. Cq), 130.6
(NCN), 151.6 (arom. CH), 149.3 (arom. Cq), 146.2 (arom. Cq), (arom. CH), 129.1 (arom. Cq), 128.7 (arom. CH), 128.5 (arom.
140.1 (arom. Cq), 138.4 (arom. Cq), 138.1 (arom. CH), 134.6 CH), 124.8 (arom. CH), 123.8 (2 overlapped arom. CH), 123.2
(arom. Cq), 134.5 (arom. Cq), 134.3 (arom. Cq), 131.1 (arom. (arom. CH), 121.3 (arom. CH), 120.4 (arom. CH), 113.4 (arom.
CH), 129.2 (arom. CH), 129.1 (arom. CH), 129.0 (2 overlapped CH), 111.3 (arom. CH), 77.3 (Cq), 72.1 (Cq), 47.4 (CH2Pd) 38.8
arom. CH), 128.5 (arom. CH), 126.6 (arom. CH), 125.9 (arom. (CH2SCH3), 19.4 (CH2SCH3). Found C, 65.61; H, 4.32; N, 4.51.
CH), 125.3 (arom. CH), 125.0 (arom. CH), 124.7 (arom. CH), Calc. for C36H27ClN2PdS (Mr = 661.56): C, 65.36; H, 4.11;
122.5 (arom. CH), 120.7 (arom. CH), 120.0 (arom. CH), 113.7 N, 4.23%.
(arom. CH), 113.2 (arom. CH), 76.0 (Cq), 72.4 (Cq), 49.9
General procedure for palladium-catalysed Suzuki–Miyaura
(CH2C6H5), 34.0 (CH3). Found C, 68.33; H, 4.59; N, 4.89. Calc.
cross-coupling reactions
for C46H35Cl2N3Pd (Mr = 807.13): C, 68.45; H, 4.37; N, 5.21%.
trans-[1-(9-Methyl-9H-fluoren-9-yl)-3-(9-iso-propyl-9H-fluoren- A mixture of the palladium complex (0.01 mmol), phenylboro-
9-yl)-1H-benzimidazol-2-ylidene](pyridine)palladium(II) dichloride nic acid (0.183 g, 1.50 mmol) and Cs2CO3 (0.652 g, 2 mmol)
(5e). A suspension of benzimidazolium salt 4e (0.518 g, was suspended in dioxane (3 mL). After the addition of p-tolyl
0.96 mmol), finely crushed K2CO3 (0.656 g, 4.75 mmol), and chloride (0.126 g, 1 mmol), the mixture was vigorously stirred
PdCl2 (0.199 g, 1.12 mmol) in pyridine (3 mL) was heated at at 80 °C for a given period of time. The hot mixture was filtered
80 °C for 15 h under vigorous stirring. The mixture was cooled through Celite. 1,4-Dimethoxybenzene (0.069 g, 0.5 mmol;
to room temperature, filtered through Celite and the filtered internal standard) was then added to the filtrate. The solvent
solid was washed with CH2Cl2 (ca. 20 mL). The combined was removed under reduced pressure, and the crude mixture
1
washings and the filtrate were evaporated to dryness. The was analysed by H NMR spectroscopy. The yields were deter-
residue was then purified by flash chromatography (SiO2; mined by comparing the intensity of the methyl signal of the
CH2Cl2–petroleum ether, 50 : 50) to afford 5e as a yellow solid product [δ(Me) = 2.41 ppm] with that of the internal reference
(0.539 g, 74%); mp > 203 °C. 1H NMR (CDCl3, 300 MHz), [δ(Me) = 3.78 ppm]. In some experiments the product was iso-
δ 9.14–9.09 (2H, m, o-NC5H5), 7.86–7.76 (9H, m, 8H ArH and lated chromatographically. The isolated yield turned out to be
1H p-NC5H5), 7.46–7.38 (6H, m, 4H ArH and 2H m-NC5H5), very close (deviation less than 5%) to that determined by using
3
7.32–7.22 (4H, m, ArH), 7.00 (1H, hept, J = 6.6 Hz, CH(CH3)2), the internal reference.
6.39–6.23 (2H, m, ArH), 6.11–6.05 (1H, m, ArH), 5.86–5.80 (1H,
3
X-ray crystallography
m, ArH), 4.13 (3H, s, CH3), 1.32 (6H, d, J = 7.1 Hz, CH(CH3)2).
13C{1H} NMR (CDCl3, 75 MHz), δ 161.7 (NCN), 151.7 (arom.
Crystal data for complex 5d. Crystals suitable for X-ray diffr-
CH), 149.7 (arom. Cq), 146.1 (arom. Cq), 140.2 (arom. Cq), action were obtained by slow diffusion of pentane into a
138.2 (overlapped arom. CH and arom. Cq), 135.8 (arom. Cq), dichloromethane solution of the complex: C98H75Cl9N6Pd2,
134.6 (arom. Cq), 129.1 (2 overlapped arom. CH), 128.9 (arom. M = 1868.49, monoclinic, space group P21/c, a = 20.5938(5), b =
CH), 128.0 (arom. CH), 126.4 (arom. CH), 125.0 (arom. CH), 18.5018(4), c = 24.0322(7) Å, β = 103.048(3), V = 8920.4(4) Å3,
124.7 (arom. CH), 122.5 (arom. CH), 122.3 (arom. CH), 120.7 Z = 4, μ = 0.723 mm−1, F(000) = 3800. Crystals of the compound
(arom. CH), 120.0 (arom. CH), 113.9 (arom. CH), 113.3 (arom. were mounted on a Oxford Diffraction CCD Saphire 3 Xcalibur
CH), 82.1 (Cq), 73.1 (Cq), 34.2 (CH(CH3)2) 33.7 (CH3), 22.4 diffractometer. Data collection with Mo-Kα radiation
12260 | Dalton Trans., 2014, 43, 12251–12262
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(λ = 0.71073 Å) was carried out at 150 K. 67 669 reflections were
collected (2.60 < θ< 27.00°), 19 447 were found to be unique
and 9064 were observed (merging R = 0.0689). The structure
was solved with SHELXS-97.43 Final results: R2, R1, wR2, wR1,
Goof; 0.1384, 0.0673, 0.2091, 0.1883, 0.717. Residual electron
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.
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