Palladium, iridium and ruthenium complexes with acyclic imino-N-heterocyclic carbenes and their application in aqua-phase Suzuki-Miyaura cross-coupling reaction and transfer hydrogenation

Article abstract of DOI:10.1039/c2dt31989f

Palladium (4a-4c), iridium (5a-5c) and ruthenium (6a-6c) complexes have been prepared by in situ transmetalation from the corresponding silver complexes of acyclic imino-functionalized imidazolium chlorides [1-(Me)-imidazolium-3- {C(p-CH₃-Ph)N(Ar)}]Cl (3) (Ar = 2,4,6-trimethylphenyl (3a), 2,6-diisopropylphenyl (3b) and phenyl (3c)) with [Pd(COD)Cl₂], [Cp*IrCl₂]₂ or [Ru(p-cymene)Cl₂] ₂, respectively. Iridium and ruthenium complexes, 5a[PF ₆]-5c[PF₆], 6a[PF₆]-6c[PF₆], 6c[BF₄], 6c[BPh₄] and 6c[NTf₂], were obtained directly from 5a-5c and 6a-6c through an anion-exchange process with KPF ₆, NaBF₄, NaBPh₄ and LiNTf₂ (bis(trifluoromethylsulfonyl)imide lithium), respectively. All complexes were characterized by FT-IR, ¹H and ¹³C NMR spectroscopy and elemental analysis. Crystal structures of 4a, 5a and 6c[NTf₂] show that five-membered chelate ring is formed in these complexes by the coordination of the carbene carbon and the imino nitrogen atom, and the latter two are cationic compounds with Cl^- and NTf₂^- as counteranion respectively. The catalytic performance of Pd complexes for Suzuki-Miyaura cross-coupling reactions in pure water and Ir and Ru complexes for transfer hydrogenation of ketones and imines was tested in a wide scope of substrates. Pd complex 4b with the largest steric hinder exhibited the best performance to gain moderate to excellent yields on catalyzing Suzuki-Miyaura cross-coupling of aryl chlorides and arylboronic acids in water. While in transfer hydrogenation of various ketones, all the Ir and Ru complexes were effective with good to excellent yields. Among all these complexes, 6c[PF ₆] was found most effective, and moderate yields could be obtained even in the transfer hydrogenation of imines. Moreover, different counteranions of Ru complexes are influential on catalyzing the transfer hydrogenation, with the sequence of PF₆^- ≈ BF₄^- > BPh₄^- > Cl^- > NTf₂ ^-.

Full text of DOI:10.1039/c2dt31989f

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Palladium, iridium and ruthenium complexes with
acyclic imino-N-heterocyclic carbenes and their
application in aqua-phase Suzuki–Miyaura cross-
coupling reaction and transfer hydrogenation†
Cite this: DOI: 10.1039/c2dt31989f
Xu-Qing Guo, Ya-Nong Wang, Dong Wang, Li-Hua Cai, Zhen-Xia Chen and
Xiu-Feng Hou*
Palladium (4a–4c), iridium (5a–5c) and ruthenium (6a–6c) complexes have been prepared by in situ trans-
metalation from the corresponding silver complexes of acyclic imino-functionalized imidazolium
chlorides [1-(Me)-imidazolium-3-{C(p-CH3–Ph)vN(Ar)}]Cl (3) (Ar
= 2,4,6-trimethylphenyl (3a), 2,6-
diisopropylphenyl (3b) and phenyl (3c)) with [Pd(COD)Cl2], [Cp*IrCl2]2 or [Ru(p-cymene)Cl2]2, respectively.
Iridium and ruthenium complexes, 5a[PF6]–5c[PF6], 6a[PF6]–6c[PF6], 6c[BF4], 6c[BPh4] and 6c[NTf2],
were obtained directly from 5a–5c and 6a–6c through an anion-exchange process with KPF6, NaBF4,
NaBPh4 and LiNTf2 (bis(trifluoromethylsulfonyl)imide lithium), respectively. All complexes were character-
ized by FT-IR, 1H and 13C NMR spectroscopy and elemental analysis. Crystal structures of 4a, 5a and 6c-
[NTf2] show that five-membered chelate ring is formed in these complexes by the coordination of the
carbene carbon and the imino nitrogen atom, and the latter two are cationic compounds with Cl− and
−
NTf2 as counteranion respectively. The catalytic performance of Pd complexes for Suzuki–Miyaura cross-
coupling reactions in pure water and Ir and Ru complexes for transfer hydrogenation of ketones and
imines was tested in a wide scope of substrates. Pd complex 4b with the largest steric hinder exhibited
the best performance to gain moderate to excellent yields on catalyzing Suzuki–Miyaura cross-coupling
of aryl chlorides and arylboronic acids in water. While in transfer hydrogenation of various ketones, all
the Ir and Ru complexes were effective with good to excellent yields. Among all these complexes, 6c[PF6]
was found most effective, and moderate yields could be obtained even in the transfer hydrogenation of
Received 30th August 2012,
Accepted 12th October 2012
DOI: 10.1039/c2dt31989f
imines. Moreover, different counteranions of Ru complexes are influential on catalyzing the transfer
−
www.rsc.org/dalton
hydrogenation, with the sequence of PF6− ≈ BF4− > BPh4− > Cl− > NTf2
.
protect the coordination sites by a dynamic “on and off” che-
lating effect.2
Introduction
The N-heterocyclic carbene (NHC) ligands have been proved to
NHC ligands with P,3 O,4 S5 and N6–10 donors have been
be efficient as ancillary ligands because of their strong coordi- developed, among which the design and synthesis of N donor
nation ability and their tunable character of the steric and elec- ligands continue drawing numerous attention. N atom as
tronic properties on the coordinated metal center.1 NHCs chelate has been incorporated to the N-terminated carbene in
functionalized with an additional donor group have become the form of cyclic imines like pyridine6/pyrimidine7 or oxazo-
important ligands due to the potential hemilability of the new line,8 acylic imines, or in the form of amino9/amido.10 They
donor group, which can play a dual role in a catalyst since they bond to carbene nitrogen directly or via one or more CH2
can easily enable coordination sites and, at the same time, linkage through the α carbon. However, the design and appli-
cation of metal complexes bearing pyridine/pyrimidine, oxazo-
line and amino/amido group are restrained in that the
introduction of appropriate substituents on these N-ligands is
inaccessible. We are interested in a kind of acyclic imino-fun-
tionlized N-heterocyclic carbene ligands, where the imino
carbon bonds directly to the carbene nitrogen. These ligands
are prone to form stable five-membered ring complexes when
coordinated to metal, which avoids dynamic behavior in
Department of Chemistry, Fudan University, Han Dan Road 220, Shanghai 200433,
China. E-mail: xfhou@fudan.edu.cn; Fax: +21 6564 1740
†Electronic supplementary information (ESI) available: X-Ray crystallographic
data (CIF) for 4a, 5a and 6c[NTf2], and 1H NMR and 13C NMR spectra of all the
complexes. CCDC 872878 (4a), 872879 (5a) and 872880 (6c[NTf2]). For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c2dt31989f
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Scheme 1 Synthesis of ligands and Pd complexes 4a–4c.
solution such as conformational “ring-flip” of the chelating
ring and solvent-dependent interconversion of chelating and
nonchelating species.11 Furthermore, the synthesis method of
these ligands is rather general and allows systematic variations
of sterics and electronics by introduction of substituents to the
imino carbon and nitrogen atoms and to the other nitrogen
atom of carbene.12 Researches on this kind of ligands mainly
concentrate on the synthesis and characterization of their cor-
responding group 4, 10 and 11 transition metal complexes,13,14
whereas information on their catalytic application is
limited.14,15
Fig. 1 Crystal structure of 4a. Ellipsoids at the 30% probability level. Hydrogen
atoms and solvent molecules have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–C(18) 1.960(2), Pd(1)–N(1) 2.0478(19), Pd(1)–
Cl(2) 2.2929(6), Pd(1)–Cl(1) 2.3335(6); C(18)–Pd(1)–N(1) 79.78(9).
the case of 4a, by X-ray crystallography. The CvN stretching
frequency is found at 1617 (4a), 1611 (4b) and 1615 (4c) cm−1
,
significantly lowered compared with that of the ligands (1664
(3a), 1660 (3b), 1666 (3c) cm−1) and quite indicative of coordi-
1
nation of the imino nitrogen to the Pd center. In the H NMR
Our group has been interested in the synthesis and catalytic
performance of well-defined N-heterocyclic carbene metal
complexes for the past few years.16 In this work, we report the
synthesis and characterization of acyclic imino-N-heterocyclic
carbene ligands chelating complexes of Pd, Ir and Ru, and the
catalytic performance of Pd complexes in Suzuki–Miyaura
cross-coupling reactions in pure water and Ir, Ru complexes in
transfer hydrogenation of ketones and imines.
spectra of 4a–4c, the disappearance of downfield-shifted
NCHN resonance indicates the deprotonation of the acidic
proton of 3a–3c. The 13C{1H} NMR spectra provide more evi-
dence for the metalation. Signals at δ 162.5 and 161.5 ppm are
assigned to the Pd–Ccarbene of 4a and 4b, respectively. All these
results prove that the ligands are coordinated to the Pd center
through carbene carbon and imino nitrogen atom. 4c is practi-
cally insoluble in nearly all solvents (only slightly soluble in
acetonitrile and DMSO); the 13C NMR spectrum is thus failed
to record.
Crystals of complex 4a suitable for X-ray crystallography
were grown by the layering of diethyl ether onto a saturated
acetonitrile solution. The molecular structure of 4a is shown
in Fig. 1. The palladium complex 4a has a distorted square-
planar geometry in which the coordinated carbene carbon,
imino nitrogen atom, and one of the chloride ligands are all
approximately coplanar, with the remaining chloride ligand
distorted away from this plane. The dihedral angle of the imi-
dazole ring with the trimethylphenyl ring and that of the imi-
dazole ring with the p-methylphenyl ring are 77.3 and 59.4°,
respectively. The Pd(1)–N(1) bond distance of 2.0478(19) Å,
Pd(1)–C(18) bond distance of 1.960(2) Å and the bite angle
C(18)–Pd(1)–N(1) of 79.78(9)° are similar to those of other palla-
dium(II) NHC complexes.12a The Pd–Cl(1) distance of 2.3335(6)
Å and the Pd–Cl(2) distance of 2.2929(6) Å, with the longer Pd–
Cl bond trans to the carbene, are considered a consequence of
the greater trans influence.
Results and discussion
Synthesis and characterization of Pd complexes 4a–4c
The acyclic imino-functionalized imidazolium chlorides 3 were
prepared according to similar procedures12a reported before by
the reaction of the corresponding imidoyl chlorides ClC-
(p-CH3–Ph)vN(Ar) (Ar = 2,4,6-trimethylphenyl (2a), 2,6-diiso-
propylphenyl (2b) and phenyl (2c)) with 1-methylimidazole (1)
in high yields. (Scheme 1) They were characterized by FT-IR,
elemental analysis, 1H and 13C{1H} NMR spectroscopy.
Metal-NHC complexes are frequently prepared by reaction
of the imidazolium salts with appropriate metal salts, by
in situ carbene generation through treatment of imidazolium
salts with strong bases or transmetalation through silver
carbene complexes. We attempted to treat the imidazolium
salts with Pd(OAc)2 or PdCl2 to prepare Pd iminoylcarbene
complexes, or with NaN[Si(CH3)3]2, tBuOK and nBuLi to obtain
the free carbene, but failed.12a However, Pd complexes 4a–4c
were successfully synthesized by the transfer of the ligands
from the corresponding silver complexes17 to [Pd(COD)Cl2]
Synthesis and characterization of Ir complexes 5a–5c and 5a
[PF6]–5c[PF6]
(Scheme 1) in yields around 60% and characterized by FT-IR, Iridium complexes 5a–5c were prepared by in situ transmetala-
1H and 13C{1H} NMR spectroscopy, elemental analysis and in tion from the silver carbene complexes of ligands 3a–3c with
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Fig. 3 Crystal structure of 6c[NTf2]. Ellipsoids at the 30% probability level.
Hydrogen atoms and solvent molecules have been omitted for clarity. Selected
bond lengths [Å] and angles [°]: Ru(1)–C(2) 2.015(5), Ru(1)–N(3) 2.081(4), Ru
(1)–Cl(1) 2.4011(11), Ru(1)–C(centroid) 1.7086(4); C(2)–Ru(1)–N(3) 76.29(16),
C(2)–Ru(1)–Cl(1) 82.04(11), N(3)–Ru(1)–Cl(1) 86.08(10).
Scheme 2 Synthesis of Ir and Ru complexes.
clarity. 5a is revealed to be a cationic compound with chloride
as counteranion. The Ir center is in a distorted octahedral
environment with Cp* as a three-coordinated ligand, and
other three coordination sites occupied by carbene carbon,
imino nitrogen and chlorine atom, respectively. The five-mem-
bered chelate ring Ir(1)–C(1)–N(5)–C(5)–N(6) is approximately
coplanar with the imidazole ring. The dihedral angle of the
imidazole ring with the trimethylphenyl ring and that of the
imidazole ring with the p-methylphenyl ring are 72.2 and
58.7°, respectively. The Ir–Cl and Ir–Cp*(centroid) distances
are 2.414(3) and 1.8219(8) Å, respectively. The Ir–Ccarbene (1.997
(11) Å) and Ir–N (2.129(7) Å) distances lie in the expected range
for other known Cp*Ir(NHC) complexes.7a The bite angle of
C(1)–Ir(1)–N(6) is 75.8(4)°.
Fig. 2 Crystal structure of 5a. Ellipsoids at the 30% probability level. Hydrogen
atoms and solvent molecules have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Ir(1)–C(1) 1.997(11), Ir(1)–N(6) 2.129(7), Ir(1)–Cl(1)
2.414(3), Ir(1)–Cp*(centroid) 1.8219(8); C(1)–Ir(1)–N(6) 75.8(4), C(1)–Ir(1)–Cl(1)
82.1(3), N(6)–Ir(1)–Cl(1) 91.1(2).
Synthesis and characterization of Ru complexes 6a[PF6]–6c[PF6],
6c[Cl], 6c[BF4], 6c[BPh4], 6c[NTf2]
[Cp*IrCl2]2 in yields of 62%, 59% and 48%, respectively. Com-
plexes 5a[PF6]–5c[PF6] were obtained quantitatively from 5a–5c
through an anion-exchange procedure with KPF6 as anion- The ruthenium complexes 6a[PF6]–6c[PF6] were prepared in an
exchange reagent (Scheme 2). All these complexes were puri-
fied by column chromatography and characterized by FT-IR,
analogous manner with 5a–5c, using [Ru(p-cymene)Cl2]2 as
metalation reagent, followed by an anion-exchange procedure
1H and 13C{1H} NMR spectroscopy, elemental analysis and in with KPF6 and isolated as orange powders. Complex 6c[Cl] was
the case of 5a, by X-ray crystallography. A decrease in the CvN
stretching frequency (around 1610 cm−1 for 5a–5c, and
isolated before anion-exchanging and 6c[BF4], 6c[BPh4] and
6c[NTf2] were prepared by anion-exchange of 6c[Cl] with NaBF4,
1630 cm−1 for 5a[PF6]–5c[PF6]) compared with that of the NaBPh4 and LiNTf2, respectively. (Scheme 2) Similar to the cor-
ligands (around 1660 cm−1) is observed, suggesting coordi-
responding Ir complexes, the CvN stretching frequency of all
the Ru complexes is lower than that of the ligands, indicating
nation of the imino nitrogen to the metal center. The 1H NMR
spectra show the NCHN proton resonance disappeared, indi- the coordination of the imino nitrogen to the Ru center. The
absence of the NCHN proton resonances in 1H NMR spectra
cating the deprotonation of the acidic proton of the ligands.
From the 13C{1H} NMR spectra, signals at δ 167–170 ppm are
associated with the presence of the Ru–Ccarbene carbon signals
attributed to Ir–Ccarbene, implying the metalation of Ir with the (around 190 ppm) in 13C{1H} NMR spectra proves that the
carbene carbon of the ligands.
coordination also occurs at the carbene carbon atom. Besides,
Crystals of complex 5a suitable for X-ray crystallography
we notice that the νCvN frequency of 6c[PF6], 6c[BF4] and
were grown by slow diffusion of diethyl ether to a nearly satu- 6c[BPh4] (around 1630 cm−1) is higher than that of 6c[Cl] and
6c[NTf2] (around 1610 cm−1), suggesting a weaker CvN double
rated dichloromethane solution. The molecular structure of 5a
is illustrated in Fig. 2. It is found that there are two molecules
in one unit cell, and one of them has been eliminated for teranion. The carbene N–CH3 resonance of 6c[BPh4] is found
bond, which might be attributed to the influence of the coun-
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Table 1 Optimization of the Suzuki–Miyaura coupling reaction conditions in
pure watera
Table 2 Suzuki–Miyaura coupling reactions with various substratesa
Entry
1
Aryl halide
Arylboronic acid
Yieldb (%)
99 (97c)
2
3
4
93c
90
62
Entry
Cat.
Base
Yieldb (%)
1
4a
4b
4c
4b
4b
4b
4b
KOH
64
2
KOH
99
3
KOH
17
4
K2CO3
Cs2CO3
KOH
22
5
46
5
6
54
51
6c
7d
67
KOH
Trace
a Reaction conditions: 4-chloroacetophenone (1.0 mmol),
phenylboronic acid (1.5 mmol), catalyst (1 mol%), KOH
(2.0 mmol), water (6 mL), 100 °C, 24 h. b Yields determined by H
1
NMR spectroscopy. c 0.5 mol% of catalyst loading. d Temperature
reduced to 25 °C.
7
8
9
48
74
70
upfield shifted than the others, which is possibly due to the
ring current effect of BPh4− anion.18
Crystals of complex 6c[NTf2] suitable for X-ray crystallogra-
phy were grown by slow diffusion of diethyl ether to a nearly
saturated dichloromethane solution. The molecular structure
of 6c[NTf2] is shown in Fig. 3. It is found a cationic compound
10
11
12
Trace
69
−
−
with a NTf2 as anion. The NTf2 anion of 6c[NTf2] is highly
disordered and divided into two parts.19 The center metal Ru
displays a distorted octahedral geometry in which the p-
cymene group occupies three coordination sites, and the
carbene carbon, imino nitrogen and chlorine atom occupy
others. The chloride ligand is found to adopt the opposite
orientation to the iPr substituent of the p-cymene ligand,
which is probably due to steric repulsion. The five-membered
chelate ring Ru(1)–C(2)–N(2)–C(5)–N(3) is approximately copla-
nar with the imidazole ring. The dihedral angle of the imida-
zole ring with the phenyl ring and that of the imidazole ring
with the p-methylphenyl ring are 80.5 and 60.0°, respectively.
The Ru–Ccarbene distance and Ru–N distance are 2.015(5) and
2.081(4), respectively, similar to those of analogous
complexes.6c
99
a Reaction conditions: aryl halide (1.0 mmol), arylboronic acid
(1.5 mmol), 4b (1 mol%), KOH (2.0 mmol), water (6 mL), 100 °C,
24 h. b Yields determined by 1H NMR spectroscopy. c Isolated
yield.
Initially the cross-coupling of 4-chloroacetophenone with
phenylboronic acid was used as a representative reaction, and
the reaction conditions were briefly optimized (Table 1).
Complex 4b with 2,6-diisopropylphenyl as substituent in the
imine moiety was more effective than 4a and 4c under the
same conditions, showing quantitative yield (entry 2). This be-
havior demonstrates that steric effects may be playing an
important role in the catalytic activity.21 Several bases were
also employed in this reaction, and KOH was found most
effective (entries 4 and 5). Then we attempted to decrease the
loading of catalyst and moderate yield (67%) was obtained
when the catalyst loading was 0.5 mol% (entry 6). An attempt
at room temperature gave a depressed result (entry 7).
Several aryl halides and arylboronic acids were then chosen
to explore the activity of 4b, with KOH as the base at 100 °C in
water. The results are summarized in Table 2. Aryl chlorides
containing either electron-withdrawing group (–CN, entry 2) or
electron-donating group (–OMe, entry 3) obtained yield above
90%. Then the cross-coupling reactions of 4-chloroacetophe-
none or 4-chloroanisole with different arylboronic acids were
tested to obtain moderate to good yield (entries 4–9). It was
interesting to observe that 4-chloroacetophenone obtained
Suzuki–Miyaura coupling reactions catalyzed by Pd complexes
in water
Well-defined Pd(NHC) complexes with nitrogen donors as
ancillary ligands have attracted much attention for Suzuki–
Miyaura cross-coupling reactions.20 Analogous Pd complexes
have also been employed in Suzuki–Miyaura reactions with
aryl bromides as substrates in organic solvents to attain good
yields,12a and solvent with higher polarity may benefit the acti-
vity.12b On the basis of these precious results, catalytic per-
formance of 4a–4c in Suzuki–Miyaura cross-coupling reactions
is tested in pure water as an environmental benign solvent.
Surprisingly, catalyst 4b exhibited excellent activity on catalyz-
ing cross-coupling of deactivated aryl chlorides and arylboro-
nic acids.
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higher yield than 4-chloroanisole when reacted with 4-(trifluoro- catalyst in the presence of 1.0 mmol of potassium tert-butoxide
methyl)phenylboronic acid (entries 4 and 7), however, when (tBuOK) as the base. All the complexes exhibited excellent cata-
reacted with 4-methylphenylboronic acid or 1-naphthalene- lytic activity (above 80% isolated yield), as shown in Table 3.
boronic acid, 4-chloroanisole, on contrary, exhibited higher Among which, Ru complex 6c[PF6] with the smallest steric
yield (entries 5–6 and 8–9). No product was observed when hinder proved to be most effective with yield up to 96%
thiophen-2-ylboronic acid was reacted with 4-chloroacetophe- (entries 1–7). The decrease of tBuOK or loading of 6c[PF6], or
none, however, it underwent smoothly reaction to get yield of the replacement of tBuOK by KOH lowered the yield (entries
69% when 4-chloroacetophenone was replaced by higher acti- 8–11). From an environmental as well as from an economic
vated 4-bromoacetophenone (entries 10 and 11), providing a point of view, the following reactions were performed with
useful way for the synthesis of aryl-substituted sulfur hetero- 10 mol% of tBuOK as the base and 1 mol% of 6c[PF6] as the
cycles. Summarily, palladium complex 4b with the largest catalyst in iPrOH.
steric hinder proves to be most effective to gain moderate to
excellent yields for the coupling of various aryl chlorides and ketones as well as imines were selected to investigate the
arylboronic acids in pure water. activity of 6c[PF6], as shown in Table 4. It is obviously observed
Under optimal conditions, several aromatic and aliphatic
In order to clarify the possibility of Pd nanoparticle acting that p-substituted acetophenones with both electron-withdraw-
as catalytic species during the cross-coupling process, the ing halo groups (entries 2 and 3) and electron-donating methyl
mercury tests22 were performed under optimal conditions with group (entry 5) obtained good to excellent yields. However, 4-
4-chloroacetophenone and phenylboronic acid in pure water.
One drop of Hg (excess amount with respect to the palladium
resource) was added to the reaction mixture after 0 and
Table 4 Transfer hydrogenation of different substratesa
12 hours resulting in 83% and 90% yields respectively, demon-
strating that the reaction may not follow the Pd nanoparticle
catalytic route.
Entry
1
Substrate
Time (h)
5
Yieldb (%)
91
Transfer hydrogenation catalyzed by Ir and Ru complexes
2
3
4
5
>99
94
Transfer hydrogenation of CvO and CvNR groups have
drawn great attention, providing environmentally friendly and
simple processes for the production of alcohols and amines23
which play a significant role in organic synthesis. Several NHC
complexes of iridium24 and ruthenium25 have been developed
as catalysts for the transfer hydrogenation of ketones. Herein,
acyclic imino-N-heterocyclic carbene Ir and Ru complexes were
tested for these transformations.
5
22
64
The reduction of acetophenone to 1-phenylethanol was
initially used as a model reaction with Ir or Ru complexes as
5
6
7
17
22
17
88
Table 3 Optimization of reaction conditions of transfer hydrogenationa
89
>99
Entry
Cat.
Base
Time (h)
Yieldb (%)
8
9
17
22
92
45
1
5a
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (1.0 mmol)
tBuOK (0.1 mmol)
tBuOK (0.1 mmol)
KOH (1.0 mmol)
KOH (0.5 mmol)
12
10
9
82
2
5a[PF6]
5b[PF6]
5c[PF6]
6a[PF6]
6b[PF6]
6c[PF6]
6c[PF6]
6c[PF6]
6c[PF6]
6c[PF6]
83
3
85
4
9
85
5
12
9
82
6
82
10
11
22
22
59
58
7
9
5
96
8
91
9c
10
11
24
9
Trace
76
9
69
a Reaction conditions: acetophenone (1.0 mmol), base, catalyst
(1 mol%), iPrOH (5 mL), 82 °C. b Isolated yield. c 0.1 mol% of a Reaction conditions: substrate (1.0 mmol), tBuOK (0.1 mmol), 6c
catalyst loading.
[PF6] (1 mol%), iPrOH (5 mL), 82 °C. b Isolated yield.
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carbon bonds directly to the carbene nitrogen, were syn-
thesized and characterized. The crystal structures of 4a, 5a and
6c[NTf2] indicate that N atom of the imino moiety and C atom
of the NHC moiety of the ligand are coordinated to the metal
(Pd, Ir or Ru) center and a five-membered chelate ring is
formed. 5a and 6c[NTf2] are found cationic complexes with Cl−
Table 5 Influence of counterions on the transfer hydrogenation of 4-iodo-
acetophenonea
Entry
Cat.
Yieldb (%)
1
2
3
4
5
6c[PF6]
6c[Cl]
6c[BF4]
6c[BPh4]
6c[NTf2]
64
31
62
49
23
−
and NTf2 as counteranion, respectively. Pd complex 4b with
the largest steric hinder proves to be most effective to gain
moderate to excellent yields for the cross-coupling of various
aryl chlorides and arylboronic acids in pure water. All Ir and
Ru complexes work well for the transfer hydrogenation of
ketones with iPrOH as a hydrogen source and tBuOK as an
activator, and especially Ru complex 6c[PF6] with the smallest
steric hinder exhibits excellent performance in a wide range of
substrates. Noticeably, moderate yields were obtained in the
transfer hydrogenation of imines, providing potential appli-
cation in the construction of C–N bond. Besides, we found
that different counteranions in those Ru complexes had an
obvious influence on the yield of the transfer hydrogenation of
less-activated 4-iodoacetophenone, with 6c[PF6] and 6c[BF4]
displaying the best catalytic reactivity. These results demon-
strate the high versatility and application potential of acylic
imino-N-heterocyclic carbene ligands in the design of effective
homogeneous catalysts.
a Reaction conditions: 4-iodoacetophenone (1.0 mmol), tBuOK
(0.1 mmol), catalyst (1 mol%), iPrOH (5 mL), 82 °C, 22 h.
b Isolated yield.
iodoacetophenone showed lower yield even with an increased
reaction time (entry 4). Besides, 2-acetylnaphthalene and
benzophenone were hydrogenated to corresponding alcohols
with excellent yields (entries 6 and 7). On the other hand,
6c[PF6] was also demonstrated to be active for the reduction of
aliphatic 2-decanone (entry 8).
Imines are harder to reduce by transfer hydrogenation cata-
lysis than ketones mainly because of the drawbacks such as
the coordination of the imine nitrogen lone pair to the metal
center, which inhibits the η2-(CvN) coordination required for
the insertion into metal-hydride bonds, or the poisoning effect
of the resultant amines on the catalyst.26 We have found
6c[PF6] works effectively in the transfer hydrogenation of
imines with both electron-drawing and electron-donating
groups in moderate yields (entries 9–11). All these results
demonstrate the versatility of 6c[PF6] towards the transfer
hydrogenation of both ketones and imines.
Experimental
General
All manipulations were carried out under a nitrogen atmos-
phere using standard Schlenk techniques unless otherwise
stated. Solvents were distilled under nitrogen from sodium
benzophenone (n-hexane, diethyl ether, toluene) or calcium
hydride (dichloromethane), methanol and i-propanol was dis-
tilled over Mg/I2. The starting materials [Pd(COD)Cl2],33
The properties of counteranions may play an important role
in catalytic process,27 and the counteranion effects on catalytic
reactions have been researched.28 In order to give some infor-
mation on counteranion effect in transfer hydrogenation, less-
activated 4-iodoacetophenone was selected as substrate to
explore the activity of complexes 6c with various countera-
35
[Cp*IrCl2]2,34 [Ru(p-cymene)Cl2]2 and imines36 were syn-
−
−
nions. As shown in Table 5, 6c with PF6 or BF4 as countera-
nion display better reactivity than others. This outcome may
result from their weak interaction with the cation, which
benefit the generation of catalytically active species.29 More-
over, their weakly coordinating ability will hinder them from
coordinating to the Ru intermediate to block the catalytic
thesized according to the literature procedures. The imidoyl
chloride was prepared by refluxing the corresponding amide
with SOCl2 in the absence of solvent.37 Other chemical
reagents were obtained from commercial sources and used
without further purification. NMR spectra were recorded using
Bruker spectrometers operating at 400 or 500 (1H) and 100 or
125 MHz (13C{1H}), respectively. NMR spectra were recorded at
room temperature in CDCl3 or [D6]DMSO, unless otherwise
stated. FT-IR spectra were recorded on a Nicolet AVATAR-360 IR
−
cycle.30 BPh4 is also a weakly coordinating anion, but it has
the ability to ligate to metal through one of its phenyl ring to
exhibit η6-coordinating structure.31 The poor activity of 6c[Cl]
is probably due to its poor stability in solution so that the
dehalogenation process of the catalyst by base might be
restrained by the high concentration of Cl− in the solvent. The
fact that 6c[NTf2] displays the worst catalytic performance
perhaps result from the special coordination property of the
NTf2− anion to Ru intermediate through N or O atom.32
spectrometer using KBr disc in the range of 4000–400 cm−1
;
only characteristic frequency of each product was listed.
Elemental analysis was performed using an Elementar Vario
EL III analyzer.
SYNTHESIS OF 3A–3C. 3a–3c were synthesized by similar pro-
cedures reported before.12a 1-methylimidazole (12 mmol) was
added dropwise to a solution of corresponding imidoyl chlor-
ides (10 mmol) in 10 mL of dry THF with constant stirring at
room temperature. The mixture was stirred under nitrogen at
Conclusions
In this article, Pd, Ir and Ru complexes bearing acylic imino- room temperature for 12–48 h, during which time the product
funtionlized N-heterocyclic carbene ligands where the imino precipitated. After removal of the solvent by filtration, the
Dalton Trans.
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precipitate was washed with dry THF for three times and dried light under nitrogen. After having been stirred at room temp-
under vacuum to obtain the products. erature for 2–4 h, the suspension was filtered and the filtrate
3a. Yellow solid, yield: 80%. 1H NMR (Z-isomer) (CDCl3, was added dropwise at −78 °C to a solution of [Pd(COD)Cl2] in
400 MHz, ppm): δ 10.22 (s, 1H, NCHN), 8.14 (s, 1H, NCHCHN 10 mL of CH2Cl2 over a period of 15 min. The mixture was
near imine), 7.46 (s, 1H, NCHCHN near N–CH3), 7.18 (m, 4H, slowly warmed to room temperature and stirred overnight. All
C–Ph), 6.74 (s, 2H, N–Ph), 4.33 (s, 3H, N–CH3), 2.32 (s, 3H, the volatiles were removed under vacuum and the crude
CH3–Ph), 2.20 (s, 3H, p-CH3–Ph), 1.96 (s, 6H, o-CH3–Ph). 13C product was dissolved in acetonitrile (15 mL) and filtered to
{1H} NMR (CDCl3, 100 MHz, ppm): δ 147.9 (CvN), 143.2 (N– remove precipitated silver chloride. The solvent was removed
Ph–C), 140.8 (C–Ph–C), 137.5 (NCN), 135.3 (Ph), 133.9 (Ph), in vacuo and the crude product was purified by column chrom-
130.0 (Ph), 128.7 (CH3–Ph–C), 127.2 (Ph), 126.0 (Ph) 124.6 atography or recrystallization.
1
(NCCN, near N–CH3), 119.5 (NCCN, near imine), 37.6 (N–CH3),
4a. Yellow solid, yield: 56%. H NMR ([D6]DMSO, 400 MHz,
1
21.6 (CH3–Ph), 20.6 (p-CH3–Ph), 18.2 (o-CH3–Ph). H NMR (E- ppm): δ 7.49 (s, 1H, Ph), 7.28 (m, 5H, Ph), 6.70 (s, 2H, Ph), 4.17
isomer) (CDCl3, 400 MHz, ppm): δ 9.49 (s, 1H, NCHN), 7.74 (s, (s, 3H, N–CH3), 2.29 (s, 3H, CH3–Ph), 2.16 (s, 6H, o-CH3–Ph),
1H, NCHCHN near imine), 7.31 (s, 1H, NCHCHN near N–CH3), 2.12 (s, 3H, p-CH3–Ph). 13C{1H} NMR ([D6]DMSO, 100 MHz,
7.18 (m, 4H, C–Ph), 6.74 (s, 2H, N–Ph), 4.08 (s, 3H, N–CH3), ppm): δ 162.5 (C–Pd), 156.9 (CvN), 142.4 (Ph), 139.1 (Ph),
2.32 (s, 3H, CH3–Ph), 2.20 (s, 3H, p-CH3–Ph), 1.96 (s, 6H, 135.4 (Ph), 131.1 (Ph), 129.1 (Ph), 128.1 (Ph), 127.9 (Ph), 125.0
o-CH3–Ph). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 166.1 (NCCN), 122.4 (Ph), 119.5 (NCCN), 37.7 (N–CH3), 30.6 (CH3–
(CvN), 141.5 (N–Ph–C), 136.1 (C–Ph–C), 135.3 (NCN), 134.8 Ph), 20.9, 20.4 (o-CH3), 18.5 (p-CH3). FT-IR (KBr) νCvN
(Ph), 131.7 (Ph), 130.9 (Ph), 128.7 (CH3–Ph–C), 128.4 (Ph), 1617 cm−1. Anal. Calcd for C21H23N3Cl2Pd: C, 50.98; H, 4.69;
124.3 (Ph), 122.0 (NCCN, near N–CH3), 119.3 (NCCN, near N, 8.49. Found: C, 50.95; H, 4.71; N 8.47.
imine), 35.6 (N–CH3), 21.0 (CH3–Ph), 20.5 (p-CH3–Ph), 18.0 (o-
4b. Yellow solid, yield: 63%. 1H NMR (CDCl3, 500 MHz,
CH3–Ph). FT-IR (KBr) νCvN 1664 cm−1. Anal. Calcd for ppm): δ 7.48 (m, 4H, Ph), 7.20 (m, 1H, NCHCHN near imine),
C21H24N3Cl: C, 71.27; H, 6.84; N, 11.87. Found: C, 71.25; H, 7.19 (m, 1H, Hp, DIPP), 7.17 (d, 1H, NCHCHN near N–Me),
6.85; N, 11.88.
7.09 (m, 2H, Hm, DiPP), 4.38 (s, 3H, N–CH3), 3.12 (m, 2H, CH-
3b. White solid, yield: 75%. 1H NMR (Z-isomer) (CDCl3, (CH3)2), 2.35 (s, 3H, CH3–Ph), 1.44 (d, J = 8.5 Hz, 6H, CH3),
400 MHz, ppm): δ 10.04 (s, 1H, NCHN), 8.17 (s, 1H, NCHCHN 0.89 (d, J = 8.5 Hz, 6H, CH3). 13C{1H} NMR (CDCl3, 100 MHz,
near imine), 7.89 (s, 1H, NCHCHN near N–CH3), 7.16 (m, 4H, ppm): δ 161.5 (C–Pd), 158.9 (CvN), 143.7 (Ph), 141.3 (Ph),
C–Ph), 7.05 (m, 3H, N–Ph), 4.20 (s, 3H, N–CH3), 2.74 (m, 2H, 138.4 (Ph), 129.5 (Ph), 129.0 (Ph), 128.3 (Ph), 125.8 (NCCN),
CH(CH3)2), 2.29 (s, 3H, CH3–Ph), 1.14 (d, J = 6.4 Hz, 6H, CH 123.3 (Ph), 121.8 (NCCN), 118.7 (Ph), 38.8 (N–CH3), 28.6 (CH-
1
(CH3)2), 1.09 (d, J = 6.4 Hz, 6H, CH(CH3)2). H NMR (E-isomer) (CH3)2), 24.2, 23.1 (o-CH3), 21.5 (CH3–Ph). FT-IR (KBr) νCvN
(CDCl3, 400 MHz, ppm): δ 9.12 (s, 1H, NCHN), 7.79 (s, 1H, 1611 cm−1. Anal. Calcd for C24H29N3Cl2Pd: C, 53.70; H, 5.44;
NCHCHN near imine), 7.44 (s, 1H, NCHCHN near N–CH3), N, 7.83. Found: C, 53.69; H, 5.42; N, 7.80.
1
7.16 (m, 4H, C–Ph), 7.05 (m, 3H, N–Ph), 3.97 (s, 3H, N–CH3),
4c. Yellow solid, yield: 58%. H NMR ([D6]DMSO, 400 MHz,
3.16 (m, 2H, CH(CH3)2), 2.38 (s, 3H, CH3–Ph), 1.14 (d, J = ppm): δ 7.43 (s, 1H, Ph), 7.30 (d, 2H, imi), 7.16 (m, 5H, Ph),
6.4 Hz, 6H, CH(CH3)2), 0.89 (d, J = 6.4 Hz, 6H, CH(CH3)2). 13C 6.99 (m, 3H, Ph), 4.11 (s, 3H, N–CH3), 2.27 (s, 3H, CH3–Ph).
{1H} NMR (CDCl3, 100 MHz, ppm): δ 146.5 (CvN), 142.5 (N– FT-IR (KBr) νCvN 1615 cm−1. Anal. Calcd for C18H17N3Cl2Pd:
Ph–C), 140.1 (C–Ph–C), 136.8 (NCN), 135.8 (Ph), 129.4 (Ph), C, 47.76; H, 3.79; N, 9.28. Found: C, 47.78; H, 3.76; N, 9.30.
128.7 (CH3–Ph–C), 124.8 (Ph), 124.7 (Ph), 123.5 (NCCN, near
SYNTHESIS OF IR COMPLEXES 5A–5C AND 5A[PF6]–5C[PF6]. Ag2O
N–CH3), 122.8 (Ph), 119.0 (NCCN, near imine), 37.1 (N–CH3), (0.1 mmol, 0.5 equiv) was added to a solution of ligand 3a, 3b
27.9 (CH(CH3)2), 23.5 (CH(CH3)2), 21.4 (CH(CH3)2), 21.0 (CH3– or 3c (0.2 mmol) in 15 mL of dry CH2Cl2 with constant stirring
Ph). FT-IR (KBr) νCvN 1660 cm−1. Anal. Calcd for C24H30N3Cl: in the absence of light under nitrogen, and the suspension
C, 72.80; H, 7.64; N, 10.61. Found: C, 72.83; H, 7.61; N, 10.62.
was stirred at room temperature for 2–4 h. After the addition
3c. White solid, yield: 83%. 1H NMR (CDCl3, 400 MHz, of [Cp*IrCl2]2 (0.1 mmol, 0.5 equiv), the mixture was stirred for
ppm): δ 9.93 (s, 1H, NCHN), 8.05 (s, 1H, NCHCHN near imine), another 12 h at room temperature in the dark. The precipitate
7.66 (s, 1H, NCHCHN, near N–CH3), 7.23 (m, 7H, Ph), 6.76 (d, was filtered off and the residue was purified by column chrom-
2H, Ph), 4.28 (s, 3H, N–CH3), 2.34 (s, 3H, CH3–Ph). 13C{1H} atography to obtain 5a–5c. 5a[PF6]–5c[PF6] were produced
NMR (CDCl3, 100 MHz, ppm): δ 148.7 (CvN), 145.1 (N–Ph–C), through anion-exchange procedure by addition of potassium
142.6 (C–Ph–C), 137.1 (NCN), 129.9 (Ph), 129.5 (Ph), 128.8 (Ph), hexafluorophosphate (0.24 mmol, 1.2 equiv) to the unpurified
125.2 (CH3–Ph–C), 124.7 (NCCN, near N–CH3), 123.7 (Ph), residue, and purified by column chromatography.
121.0 (Ph), 119.3 (NCCN, near imine), 37.4 (N–CH3), 21.4
5a. Yellow solid, yield: 62%. 1H NMR (CDCl3, 400 MHz,
(CH3–Ph). FT-IR (KBr) νCvN 1666 cm−1. Anal. Calcd for ppm): δ 4.19 (s, 3H, N–CH3), 2.41 (s, 3H, o-CH3–Ph), 2.35 (s,
C18H18N3Cl: C, 69.34; H, 5.82; N, 13.48. Found: C, 69.36; H, 3H, o-CH3–Ph), 2.25 (s, 3H, CH3–Ph), 1.74 (s, 3H, p-CH3–Ph),
5.79; N, 13.46.
1.55 (s, 15H, Cp*). 13C{1H} NMR (CDCl3, 125 MHz, ppm): δ
SYNTHESIS OF PD COMPLEXES 4A–4C. To a solution of ligand 3a, 168.4 (C–Ir), 164.4 (CvN), 143.8 (Ph), 141.3 (Ph), 137.4 (Ph),
3b or 3c (0.2 mmol) in 15 mL of dry CH2Cl2 with constant stir- 133.4 (Ph), 129.9 (Ph), 129.6 (Ph), 129.2 (Ph), 127.2 (NCCN
ring, Ag2O (0.1 mmol, 0.5 equiv) was added in the absence of near imine), 123.0 (Ph), 119.4 (NCCN near N–CH3), 93.6 (Cp*),
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37.9 (N–CH3), 21.6 (CH3–Ph), 20.4, 20.6 (o-CH3), 19.4 (p-CH3), Cp*). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 170.8 (C–Ir),
9.2 (Cp*, CH3). FT-IR (KBr) νCvN 1612 cm−1. Anal. Calcd for 164.4 (CvN), 145.9 (Ph), 142.7 (Ph), 129.8 (Ph), 124.9 (Ph),
C31H38N3Cl2Ir: C, 52.02; H, 5.35; N, 5.87. Found: C, 52.04; H, 123.9 (Ph), 123.8 (Ph), 122.1 (NCCN near imine), 119.7 (NCCN
5.34; N, 5.85.
near N–CH3), 93.4 (Cp*), 37.6 (N–CH3), 21.5 (CH3–Ph), 8.8
5a[PF6]. Yellow solid, yield: 60%. 1H NMR (CDCl3, 400 MHz, (Cp*, CH3). FT-IR (KBr) νCvN 1633 cm−1. Anal. Calcd for
ppm): δ 4.04 (s, 3H, N–CH3), 2.41 (s, 3H, o-CH3–Ph), 2.34 (s, C28H32N3ClF6PIr: C, 42.94; H, 4.12; N, 5.37. Found: C, 42.98;
3H, o-CH3–Ph), 2.24 (s, 3H, CH3–Ph), 1.78 (s, 3H, p-CH3–Ph), H, 4.15; N, 5.34.
1.55 (s, 15H, Cp*). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ
SYNTHESIS OF RU COMPLEXES 6A[PF6]–6C[PF6], 6C[CL], 6C[BF4], 6C
169.0 (C–Ir), 164.4 (CvN), 143.7 (Ph), 141.3 (Ph), 137.4 (Ph), [BPH ] AND 6C[NTF ]. Ag2O (0.11 mmol, 0.55 equiv) was added
4
2
133.3 (Ph), 130.1 (Ph), 129.8 (Ph), 129.3 (Ph), 125.8 (NCCN to a solution of ligand 3a, 3b or 3c (0.2 mmol) in 15 mL of dry
near imine), 123.1 (Ph), 119.5 (NCCN near N–CH3), 93.7 (Cp*), CH2Cl2 with constant stirring in the absence of light under
37.5 (N–CH3), 21.6 (CH3–Ph), 20.4, 20.6 (o-CH3), 19.1 (p-CH3), nitrogen, and the suspension was stirred at room temperature
8.9 (Cp*, CH3). FT-IR (KBr) νCvN 1633 cm−1. Anal. Calcd for for 2–4 h. After the addition of [Ru(p-cymene)Cl2]2 (0.1 mmol,
C31H38N3ClF6PIr: C, 45.12; H, 4.64; N, 5.09. Found: C, 45.15; 0.5 equiv), the mixture was stirred for another 12 h at room
H, 4.72; N, 5.06.
temperature in the dark. The precipitate was filtered off and
5b. Yellow solid, yield: 59%. 1H NMR (CDCl3, 400 MHz, the residue was purified by column chromatography to obtain
ppm): δ 8.01 (s, 1H, Ph), 7.32 (d, J = 8.0 Hz, 2H, Ph), 7.20 (m, 6c[Cl]. 6a[PF6]–6c[PF6] were produced through anion-exchange
2H, Ph), 7.14 (d, J = 8.0 Hz, 2H, Ph), 7.08 (d, J = 7.6 Hz, 2H, procedure by addition of potassium hexafluorophosphate
imi), δ 4.22 (s, 3H, N–CH3), 3.45 (m, 1H, CH(CH3)2), 2.61 (m, (0.24 mmol, 1.2 equiv) to the unpurified residue, and purified
1H, CH(CH3)2), 2.34 (s, 3H, CH3), 1.60 (s, 15H, Cp*), 1.37 (d, by column chromatography. 6c[BF4], 6c[BPh4] and 6c[NTf2]
J = 6.0 Hz, 3H, iPr–CH3), 1.12 (d, J = 6.0 Hz, 3H, iPr–CH3), 0.64 were synthesized by addition of 1.2 equiv of sodium tetra-
(d, J = 6.0 Hz, 3H, iPr–CH3), 0.52 (d, J = 6.0 Hz, 3H, iPr–CH3). fluoroborate, sodium tetraphenylborate and bis (trifluoro-
13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 167.2 (C–Ir), 164.3 methylsulfonyl)imide lithium to the unpurified residue and
(CvN), 143.7 (Ph), 142.8 (Ph), 142.1 (Ph), 139.4 (Ph), 130.6 purified by column chromatography, respectively.
(Ph), 129.3 (Ph), 128.8 (Ph), 126.8 (Ph), 125.5 (Ph), 124.2
6a[PF6]. Orange solid, yield: 76%. 1H NMR (CDCl3,
(NCCN near imine), 122.8 (Ph), 119.8 (NCCN near N–CH3), 400 MHz, ppm): δ 5.78 (d, J = 6.0 Hz, 1H, Cy), 5.36 (d, J =
93.7 (Cp*), 38.3 (N–CH3), 27.3 (CH(CH3)2), 25.6, 25.5 (CH 6.0 Hz, 1H, Cy), 4.98 (d, J = 6.0 Hz, 1H, Cy), 4.83 (d, J = 6.0 Hz,
(CH3)2), 24.7 (CH(CH3)2), 23.5 (CH(CH3)2), 21.3 (CH3–Ph), 9.2 1H, Cy), 4.19 (s, 3H, N–CH3), 2.61 (m, 1H, CH(CH3)2), 2.58 (s,
(Cp*, CH3). FT-IR (KBr) νCvN 1610 cm−1. Anal. Calcd for 3H, CH3), 2.35 (s, 3H, p-CH3), 2.29 (d, 6H, o-CH3), 1.76 (s, 3H,
C34H44N3Cl2Ir: C, 53.88; H, 5.85; N, 5.54. Found: C, 53.92; H, Cymene p-CH3), 1.23 (dd, 6H, CH(CH3)2). 13C{1H} NMR
5.89; N, 5.51.
(CDCl3, 100 MHz, ppm): δ 189.8 (C–Ru), 163.4 (CvN), 146.0
5b[PF6]. Yellow solid, yield: 58%. 1H NMR (CDCl3, (Ph), 144.0 (Ph), 137.5 (Ph), 133.0 (Ph), 130.2 (Ph), 129.8 (Ph),
400 MHz, ppm): δ 4.05 (s, 3H, N–CH3), 3.53 (m, 1H, CH(CH3)2), 129.3 (Ph), 129.0 (Ph), 127.8 (Ph), 126.2 (Ph), 123.1 (NCCN
2.63 (m, 1H, CH(CH3)2), 2.33 (s, 3H, CH3), 1.58 (s, 15H, Cp*), near imine), 119.3 (NCCN near N–CH3), 112.6 (Ph), 107.7 (Ph),
1.35 (d, J = 6.0 Hz, 3H, iPr–CH3), 1.15 (d, J = 6.0 Hz, 3H, iPr– 85.0 (Cy, CH), 85.6 (Cy, CH), 87.0 (Cy, CH), 92.1 (Cy, CH), 38.7
CH3), 0.65 (d, J = 6.0 Hz, 3H, iPr–CH3), 0.52 (d, J = 6.0 Hz, 3H, (N–CH3), 31.7 (Cy, CH(CH3)2), 22.0, 24.0 (Cy, CH(CH3)2), 21.6
iPr–CH3). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 168.4 (C–Ir), (CH3–Ph), 20.6, 20.8 (o-CH3), 19.2 (p-CH3–Ph), 18.6 (Cy,
164.3 (CvN), 143.7 (Ph), 142.9 (Ph), 142.3 (Ph), 139.7 (Ph), p-CH3). FT-IR (KBr) νCvN 1637 cm−1
. Anal. Calcd for
130.8 (Ph), 129.4 (Ph), 128.8 (Ph), 126.8 (Ph), 125.5 (Ph), 125.3 C31H37N3ClF6PRu: C, 50.79; H, 5.09; N, 5.73. Found: C, 50.82;
(Ph), 124.5 (NCCN near imine), 122.9 (Ph), 120.2 (NCCN near H, 5.12; N, 5.75.
N–CH3), 93.8 (Cp*), 37.8 (N–CH3), 27.5, 27.2 (CH(CH3)2), 25.7,
6b[PF6]. Orange solid, yield: 65%. 1H NMR (CDCl3,
25.6 (CH(CH3)2), 24.7 (CH(CH3)2), 23.9 (CH(CH3)2), 21.4 (CH3– 500 MHz, ppm): δ 6.21 (d, J = 6.0 Hz, 1H, Cy), 5.20 (d, J = 6.0
Ph), 9.2 (Cp*, CH3). FT-IR (KBr) νCvN 1636 cm−1. Anal. Calcd Hz, 1H, Cy), 5.07 (d, J = 6.0 Hz, 1H, Cy), 5.04 (d, J = 6.0 Hz, 1H,
for C34H44N3ClF6PIr: C, 47.08; H, 5.11; N, 4.84. Found: C, Cy), 4.20 (s, 3H, N–CH3), 3.85 (m, 1H, CH(CH3)2), 2.50 (m, 1H,
47.12; H, 5.14; N, 4.87.
CH(CH3)2), 2.35 (m, 1H, CH(CH3)2), 2.33 (s, 3H, CH3), 2.29 (s,
5c. Yellow solid, yield: 48%. 1H NMR (CDCl3, 400 MHz, 3H, p-CH3), 1.36 (d, J = 6.5 Hz, 3H, iPr–CH3), 1.34 (d, J = 6.5
ppm): δ 4.19 (s, 3H, N–CH3), 2.34 (s, 3H, CH3), 1.63 (s, 15H, Hz, 3H, iPr–CH3), 1.21 (dd, 6H, CH(CH3)2), 1.09 (d, J = 6.5 Hz,
Cp*). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 170.3 (C–Ir), 3H, iPr–CH3), 0.21 (d, J = 6.5 Hz, 3H, iPr–CH3). 13C{1H} NMR
164.1 (CvN), 145.8 (Ph), 142.8 (Ph), 129.7 (Ph), 127.7 (Ph), (CDCl3, 125 MHz, ppm): δ 189.9 (C–Ru), 162.9 (CvN), 144.7
126.2 (Ph), 123.8 (Ph), 121.9 (NCCN near imine), 119.4 (NCCN (Ph), 144.2 (Ph), 143.8 (Ph), 138.8 (Ph), 130.7 (Ph), 129.7 (Ph),
near N–CH3), 93.2 (Cp*), 37.9 (N–CH3), 21.5 (CH3–Ph), 9.0 128.8 (Ph), 126.0 (Ph), 125.6 (Ph), 124.9 (Ph), 122.6 (NCCN
(Cp*, CH3). FT-IR (KBr) νCvN 1610 cm−1. Anal. Calcd for near imine), 120.4 (NCCN near N–CH3), 113.9 (Ph), 108.3 (Ph),
C28H32N3Cl2Ir: C, 49.92; H, 4.79; N, 6.24. Found: C, 49.94; H, 91.8 (Cy, CH), 86.1 (Cy, CH), 85.9 (Cy, CH), 82.0 (Cy, CH), 38.8
4.76; N, 6.27.
(N–CH3), 30.9 (CH(CH3)2), 28.1, 27.4 (CH(CH3)2), 26.1 (CH
5c[PF6]. Yellow solid, yield: 45%. 1H NMR (CDCl3, 400 MHz, (CH3)2), 25.2, 24.9 (CH(CH3)2), 24.6, 24.2 (CH(CH3)2), 22.2 (CH
ppm): δ 4.09 (s, 3H, N–CH3), 2.33 (s, 3H, CH3), 1.57 (s, 15H, (CH3)2), 21.5 (CH3–Ph), 19.0 (CH3–Cy). FT-IR (KBr) νCvN
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Table 6 Crystal data and structure refinement for 4a, 5a·0.5(CH2Cl2)·1.5(H2O) and 6c[NTf2]
4a
5a·0.5(CH2Cl2)·1.5(H2O)
6c[NTf2]
Formula
Mr
C21H23Cl2N3 Pd
494.72
Orthorhombic
Pbca
16.9571(17)
14.9440(15)
19.461(2)
90
(C31H38N3Cl2Ir)·0.5(CH2Cl2)·1.5(H2O)
C30H31ClF6N4O4RuS2
826.23
785.23
Crystal system
Space group
a [Å]
Monoclinic
C2/c
41.54(3)
11.423(5)
32.26(2)
90
Triclinic
ˉ
P1
8.8397(12)
11.0339(15)
17.918(2)
91.615(2)
102.572(2)
96.477(2)
1692.4(4)
2
b [Å]
c [Å]
α [°]
β [°]
90
90
113.60(4)
90
γ [°]
V [Å3]
Z
4931.6(9)
8
14 025(14)
16
μ [mm−1
]
0.978
4.065
0.740
ρcalcd [mg m−3
F [000]
]
1.333
1.488
1.621
2000
6272
836
T [K]
θ range [°]
173(2)
293(2)
173(2)
2.09 to 27.58
34 264/5681
0.0229
1.38 to 25.01
24 896/12 350
0.0627
2.14 to 25.50
10 193/6170
0.0183
Reflns collected/indep reflns
R(int)
Data/restraints/params
5681/0/249
1.122
0.0313
0.0842
12 350/12/765
0.991
0.0596
0.1544
6170/6/539
1.055
0.0501
0.1263
GOF
R1 (I > 2σ(I))
wR2
1638 cm−1. Anal. Calcd for C34H43N3ClF6PRu: C, 52.68; H, 3H, p-CH3), 2.21 (s, 3H, Cymene p-CH3), 1.13 (dd, 6H, CH
5.59; N, 5.42. Found: C, 52.65; H, 5.56; N, 5.38.
(CH3)2). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 190.4 (C–Ru),
6c[PF6]. Orange solid, yield: 70%. 1H NMR (CDCl3, 162.8 (CvN), 150.2 (Ph), 143.0 (Ph), 129.9 (Ph), 129.3 (Ph),
400 MHz, ppm): δ 5.87 (d, J = 6.0 Hz, 1H, Cy), 5.54 (d, J = 6.0 127.9 (Ph), 125.9 (NCCN near imine), 122.5 (Ph), 119.0 (NCCN
Hz, 1H, Cy), 5.27 (d, J = 6.0 Hz, 1H, Cy), 5.23 (d, J = 6.0 Hz, 1H, near N–CH3), 110.0 (Ph), 106.3 (Ph), 91.2 (Cy, CH), 89.6 (Cy,
Cy), 4.22 (s, 3H, N–CH3), 2.66 (m, 1H, CH(CH3)2), 2.34 (s, 3H, CH), 87.7 (Cy, CH), 85.6 (Cy, CH), 38.9 (N–CH3), 31.4 (Cy, CH
p-CH3), 2.19 (s, 3H, Cymene p-CH3), 1.13 (dd, 6H, CH(CH3)2). (CH3)2), 22.6, 22.4 (Cy, CH(CH3)2), 21.7 (CH3–Ph), 19.1 (Cy, p-
13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 190.5 (C–Ru), 162.7 CH3). FT-IR (KBr) νCvN 1634 cm−1
. Anal. Calcd for
(CvN), 150.1 (Ph), 143.1 (Ph), 130.0 (Ph), 129.4 (Ph), 127.9 C28H31N3BClF4Ru: C, 53.14; H, 4.94; N, 6.64. Found: C, 53.17;
(Ph), 125.7 (NCCN near imine), 122.3 (Ph), 119.0 (NCCN near H, 4.98; N, 6.63.
N–CH3), 109.7 (Ph), 106.8 (Ph), 91.4 (Cy, CH), 89.3 (Cy, CH),
6c[BPh4]. Orange solid, yield: 65%. 1H NMR (CDCl3,
87.8 (Cy, CH), 85.5 (Cy, CH), 38.7 (N–CH3), 31.0 (Cy, CH 400 MHz, ppm): δ 5.37 (d, J = 6.0 Hz, 1H, Cy), 5.02 (d, J =
(CH3)2), 22.6, 22.4 (Cy, CH(CH3)2), 21.7 (CH3–Ph), 19.0 (Cy, 6.0 Hz, 1H, Cy), 4.89 (d, J = 6.0 Hz, 1H, Cy), 4.78 (d, J = 6.0 Hz,
p-CH3). FT-IR (KBr) νCvN 1637 cm−1
.
Anal. Calcd for 1H, Cy), 3.37 (s, 3H, N–CH3), 2.38 (m, 1H, CH(CH3)2), 2.32 (s,
C28H31N3ClF6PRu: C, 48.66; H, 4.52; N, 6.08. Found: C, 48.63; 3H, p-CH3), 2.00 (s, 3H, Cymene p-CH3), 0.99 (dd, 6H, CH
H, 4.55; N, 6.07.
(CH3)2). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 189.7 (C–Ru),
6c[Cl]. Orange solid, yield: 72%. 1H NMR (CDCl3, 400 MHz, 164.9 (Ph), 164.4 (Ph), 163.9 (Ph), 163.4 (Ph), 162.5 (CvN),
ppm): δ 6.30 (d, J = 6.0 Hz, 1H, Cy), 5.66 (d, J = 6.0 Hz, 1H, Cy), 149.9 (Ph), 143.4 (Ph), 130.4 (Ph), 130.2 (Ph), 129.4 (Ph), 128.1
5.49 (d, J = 6.0 Hz, 1H, Cy), 5.24 (d, J = 6.0 Hz, 1H, Cy), 4.45 (s, (Ph), 125.7 (NCCN near imine), 122.0 (Ph), 118.8 (NCCN near
3H, N–CH3), 2.67 (m, 1H, CH(CH3)2), 2.35 (s, 3H, p-CH3), 2.25 N–CH3), 108.2 (Ph), 92.3 (Cy, CH), 88.2 (Cy, CH), 87.9 (Cy, CH),
(s, 3H, Cymene p-CH3), 1.11 (dd, 6H, CH(CH3)2). 13C{1H} NMR 84.5 (Cy, CH), 38.3 (N–CH3), 31.5 (Cy, CH(CH3)2), 22.8, 22.5
(CDCl3, 100 MHz, ppm): δ 190.2 (C–Ru), 162.3 (CvN), 149.9 (Cy, CH(CH3)2), 21.7 (CH3–Ph), 19.2 (Cy, p-CH3). FT-IR (KBr)
(Ph), 142.9 (Ph), 129.8 (Ph), 129.1 (Ph), 127.7 (Ph), 126.2 νCvN 1635 cm−1. Anal. Calcd for C52H51N3BClRu: C, 72.18; H,
(NCCN near imine), 122.2 (Ph), 118.5 (NCCN near N–CH3), 5.94; N, 4.86. Found: C, 72.16; H, 5.89; N, 4.83.
108.7 (Ph), 107.0 (Ph), 91.7 (Cy, CH), 89.3 (Cy, CH), 88.0 (Cy,
6c[NTf2]. Orange solid, yield: 68%. 1H NMR (CDCl3,
CH), 85.1 (Cy, CH), 39.4 (N–CH3), 31.2 (Cy, CH(CH3)2), 22.5, 400 MHz, ppm): δ 5.93 (d, J = 6.0 Hz, 1H, Cy), 5.46 (d, J =
22.4 (Cy, CH(CH3)2), 21.4 (CH3–Ph), 19.1 (Cy, p-CH3). FT-IR 6.0 Hz, 1H, Cy), 5.25 (d, J = 6.0 Hz, 1H, Cy), 5.21 (d, J = 6.0 Hz,
(KBr) νCvN 1615 cm−1. Anal. Calcd for C28H31N3Cl2Ru: C, 1H, Cy), 4.21 (s, 3H, N–CH3), 2.62 (m, 1H, CH(CH3)2), 2.34 (s,
57.83; H, 5.37; N, 7.23. Found: C, 57.85; H, 5.34; N, 7.26.
3H, p-CH3), 2.20 (s, 3H, Cymene p-CH3), 1.10 (dd, 6H, CH
6c[BF4]. Orange solid, yield: 60%. 1H NMR (CDCl3, (CH3)2). 13C{1H} NMR (CDCl3, 100 MHz, ppm): δ 190.4 (C–Ru),
400 MHz, ppm): δ 5.92 (d, J = 6.0 Hz, 1H, Cy), 5.56 (d, J = 162.7 (CvN), 150.1 (Ph), 143.3 (Ph), 130.1 (Ph), 129.4 (Ph),
6.0 Hz, 1H, Cy), 5.33 (d, J = 6.0 Hz, 1H, Cy), 5.24 (d, J = 6.0 Hz, 128.1 (Ph), 125.8 (NCCN near imine), 122.2 (Ph), 119.1 (NCCN
1H, Cy), 4.26 (s, 3H, N–CH3), 2.65 (m, 1H, CH(CH3)2), 2.33 (s, near N–CH3), 109.2 (Ph), 107.4 (Ph), 91.9 (Cy, CH), 88.9 (Cy,
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CH), 87.7 (Cy, CH), 85.6 (Cy, CH), 38.8 (N–CH3), 31.5 (Cy,
CH(CH3)2), 22.6, 22.3 (Cy, CH(CH3)2), 21.7 (CH3–Ph), 19.1 (Cy,
Notes and references
p-CH3). FT-IR (KBr) νCvN 1616 cm−1
.
Anal. Calcd for
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General procedure for Suzuki–Miyaura cross-coupling reaction
in pure water
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X-ray crystallography
Intensity data for the compounds were collected on Bruker
Smart APEX (at 293 K) (5a) and Bruker APEX DUO diffract-
ometers (at 173 K) (4a and 6c[NTf2]), respectively. Both are
equipped with 2.4 kW sealed tube X-ray source (Mo-Kα radi-
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−
isotropically with fixed thermal factors. The NTf2 anion of 6c
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Acknowledgements
Financial support from the National Science Foundation of
China (Grant No. 20871032, 20971026 and 21271047) and
Shanghai Leading Academic Discipline Project, Project
Number: B108, is gratefully acknowledged.
Dalton Trans.
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