Heterobimetallic Complexes Bridged by Imidazol{[4,5- f][1,10]-phenanthrolin}-2-ylidene: Synthesis and Catalytic Activity in Tandem Reactions

Article abstract of DOI:10.1021/acs.organomet.8b00882

A series of monometallic complexes obtained by metalation of the phenanthrolin donor in 1,3-dibutyl-1H-imidazol[4,5-f][1,10]phenanthrolin}ium hexafluorophospate 1 (M = Pd 2, Ru 3, Ir 4) have been prepared. Subsequently, the imidazolium moiety of complexes 2-4 was metalated with M′, leading to the heterobimetallic phenanthroline/NHC complexes (M/M′ = Pd/Rh 5, Pd/Ir 6, Pd/Ru 7, Ru/Pd 8, Ir/Pd 9) and the homobimetallic complex (M/M′ = Ir/Ir 10). The new complexes were characterized by elemental analysis, FTIR, UV-vis, and NMR spectroscopy. The molecular structures of the heterobimetallic complexes 5 and 6 were determined by X-ray diffraction studies. The catalytic activity of the heterobimetallic complexes 5-9 were tested in selected tandem reactions (dehalogenation/transfer hydrogenation and Suzuki-Miyaura coupling/transfer hydrogenation). It was found that the M/M′ heterobimetallic complexes display higher catalytic activities when compared to equimolar mixtures of the mononuclear complexes M and M′, thus indicating that an increase in the number of metal atoms in one complex leads to an increased activity in the tandem reactions.

Full text of DOI:10.1021/acs.organomet.8b00882

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Heterobimetallic Complexes Bridged by Imidazol{[4,5‑f][1,10]-
phenanthrolin}-2-ylidene: Synthesis and Catalytic Activity in
Tandem Reactions
†
,†
Lutfiye Gok Pezuk, Betul Ş
en,‡ F. Ekkehardt Hahn,§ and Hayati Turkmen*
̈ ̈ ̈ ̈
̈
†Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkey
‡Dokuz Eylu
§Institut fu
r Anorganische and Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstrasse 30, D-48149,
Munster, Germany
̈
l University, Department of Physics, 35160, Buca-Izmir, Turkey
̇
̈
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: A series of monometallic complexes obtained by metalation of the
phenanthrolin donor in 1,3-dibutyl-1H-imidazol[4,5-f ][1,10]phenanthrolin}ium
hexafluorophospate 1 (M = Pd 2, Ru 3, Ir 4) have been prepared. Subsequently,
the imidazolium moiety of complexes 2−4 was metalated with M′, leading to the
heterobimetallic phenanthroline/NHC complexes (M/M′ = Pd/Rh 5, Pd/Ir 6, Pd/
Ru 7, Ru/Pd 8, Ir/Pd 9) and the homobimetallic complex (M/M′ = Ir/Ir 10). The
new complexes were characterized by elemental analysis, FTIR, UV−vis, and NMR
spectroscopy. The molecular structures of the heterobimetallic complexes 5 and 6
were determined by X-ray diffraction studies. The catalytic activity of the
heterobimetallic complexes 5−9 were tested in selected tandem reactions
(dehalogenation/transfer hydrogenation and Suzuki−Miyaura coupling/transfer
hydrogenation). It was found that the M/M′ heterobimetallic complexes display
higher catalytic activities when compared to equimolar mixtures of the mononuclear
complexes M and M′, thus indicating that an increase in the number of metal atoms
in one complex leads to an increased activity in the tandem reactions.
ions potentally allows the utilization of synergistic effects of
INTODUCTION
■
these metals.9
Bimetallic complexes, particularly heterobimetallic ones, have
played a significant role in the development of coordination
chemistry and recently they have emerged as a hot topic as
catalysts in tandem reactions.1−3 They are of interest in areas
as disparate as bioinorganic chemistry, materials science,
photophysics and artificial photosynthetic systems, redox and
photoactive polymers, dendrimer chemistry, nanoscience,
catalysis, and sensors.4 The synthesis of heterobimetallic
complexes requires the use of a ditopic ligand, meaning the
ligand functions as a donor possessing two binding sites for the
coordination to metal atoms. Ditopic ligands capable of
binding metals at two separate sites in principle allow the
creation of well-ordered extended complexes containing
different metal atoms.5 The use of ditopic ligands featuring a
central rigid structure has been demonstrated for diverse
applications.6−8 The interplay of coordination geometry,
thermodynamic, and kinetic properties of the metal ions and
the structural features of the ligands results in one single or a
set of well-defined polynuclear architectures. Most of the
research in this area focused on the coordination chemistry of
easily prepared, heterobifunctional ligands containing a mixed
hard-soft donor set used for discrimination between metal ions.
The design of ligands capable of binding two different metal
Tandem reactions can provide high value organic products
via multiple chemical transformations proceding in a one-pot
reaction.10−13 A significant benefit of such transformations is
the atom economy of the strategy. Research toward improved
activity and selectivity of tandem systems greatly reduces the
amount of waste, costs, energy consumption, and time.14,15
Particularly useful are organic tandem transformations that are
performed in an environmentally friendly medium. These
advantages make tandem reactions particularly attractive.
The catalytic activity of a given dinuclear complex depends
on the appropriate selection of the bridging ligand which
provides electronic and steric stabilization to the metal centers.
Various reviews deal with suitable catalysts for tandem
reactions16,17 and water-soluble organometallic complexes.18
We have prepared phenanthroline ligands fused with an N-
alkyl imidazole group. Upon coordination of the phenanthro-
line nitrogen atoms in a chelation fashion, a series of
ruthenium(II) complexes have been prepared. The catalytic
properties of these complexes were investigated in the transfer
hydrogenation of ketones.19 Di- and trinuclear palladium
Received: December 7, 2018
© XXXX American Chemical Society
A
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complexes obtained from the related imidazol{[4,5-f ][1,10]-
phenanthrolin}-2-ylidene were applied in C−C cross-coupling
reactions.20
of palladium N^N-chelate complex 2 with [MCl(COD)]2 (M
= Rh, Ir) in the presence of NaOAc in CH3CN affords
complexes 5 (M = Rh, addition of NaBr necessary) and 6 (M
= Ir) in high yields (Scheme 2, top). The heterobimetallic Ru/
In order to explore the catalytic activity of heterobimetallic
complexes obtained from an N-heterocyclic carbene (NHC)
annulated phenanthroline in selected tandem reactions
(dehalogenation/Suzuki−Miyaura coupling reactions and
transfer hydrogenation/Suzuki−Miyaura coupling reaction),
we have prepared a series of novel Pd/Rh, Pd/Ir, Pd/Ru, Ru/
Pd, and Ir/Pd complexes. The position of the different metals
in the heterobimetallic complexes (N,N-chelate at the
phenanthroline or metalated NHC) has a significant effect
on the reactivity and selectivity in the tandem reactions
studied. The mixed-donor ligand 1,3-dibutylimidazol{[4,5-
f][1,10]-phenanthrolin}-2-ylidene, featuring an extended π-
electron system and the ability to interact with metal centers
via pπ-dπ overlap, exerts a significant effect on the electronic
properties of the bimetallic complexes obtained from this
ligand.
Scheme 2. Synthesis of Heterobimetallic Complexes 5−10
RESULTS AND DISCUSSION
Synthesis and Characterization of Complexes. As
depicted in Scheme 1, the monometallic complexes 2−4 have
■
Scheme 1. Synthesis of Monometallic Complexes 2−4
Pd complex 7 was prepared by metalation of the diamino-
heterocycle of 2 with [RuCl2(p-cymene)Cl2]2 in THF using
NaOAc as base. In addition, reaction of 3 or 4 with an
equimolar amount of [Pd(OAc)2] in the presence of NaOAc,
KCl, and an excess of pyridine affords the heterobimetallic
complexes 8 (Ru/Pd) and 9 (Ir/Pd) featuring a Pd-NHC
moiety (Scheme 2, bottom). The homobimetallic Ir/Ir
complex 10 was prepared by reaction of the dinuclear complex
[IrCp*Cl2]2 with 4. Complexes 5−10 can be handled in air
and were purified by column chromatography on silica gel.
They are rather stable toward air and moisture. The solubility
of the complexes in acetone or halogenated solvents is rather
low.
The heterobimetallic complexes 5−9 were characterized by
spectroscopic methods and elemental analysis, but unfortu-
nately, the 13C NMR spectra of 5 and 6 could not be recorded
due to the low solubility of the complexes. However, single
crystals of 5 and 6 suitable for X-ray diffraction analyses were
obtained by slow evaporation of the solvent from dichloro-
methane solutions of the complexes. These studies confirmed
that 5 and 6 feature a planar three dentate imidazol{[4,5-
been prepared by the reaction of the previously described
imidazolium salt 120 with equimolar amounts of [PdCl2(Me-
CN)2], [RuCl2(p-cymene)]2, and [IrCl2(Cp*)]2, respectively,
in CH2Cl2. In all cases, proligand 1 coordinates with the two
phenanthroline nitrogen atoms to the metal center. The
monometallic complexes 2−4 were obtained in good yields
1
and were characterized by spectroscopic methods. H NMR
spectra of 3 and 4, for example, feature the imidazolium N−
CH−N resonance at δ 10.30 and 10.36 ppm, respectively.
These resonances are slightly downfield shifted in comparison
to the equivalent resonace in imidazolium salt 1 (δ 10.17
ppm). Attempts to prepare monometallic complexes analogous
to 2−4 but featuring an N^N coordinated {M(COD)}
complex fragment (M = Rh or Ir, COD = cyclooctadiene)
failed under various reaction conditions, and only insoluble or
intractable mixtures were obtained.
The monometallic complexes 2−4 were used as a precursors
for the synthesis of heterobimetallic complexes. The reaction
B
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Article
f][1,10]-phenanthrolin}-2-ylidene ligand bridging two metal
Table 1. Selected IR, UV-vis, and NMR Spectroscopic Data
for Compexes 2−10
centers (Pd/Rh or Pd/Ir, Figure 1).
δ(CNHC
(ppm)
)
entry complex
IR (ν, cm−1
)
UV−vis (λ, nm)
1
2
3
4
5
6
7
8
9
2
3
4
5
6
7
8
9
10
3346, 1411, 1352 383, 334, 291, 224
3404, 1716, 1361 385, 305, 220, 205
3366, 1696, 1489 330, 305, 230, 205
3675, 1741, 1364 395, 320, 255, 240
3582, 1631, 1405 398, 330, 240, 215
3597, 1603, 1313 445, 390, 340, 290
3506, 1744, 1482 435, 375, 360, 290
3460, 1522, 1316 410, 351, 304, 268
3469, 1532, 1421 421, 386, 314, 276
not recorded
not recorded
178.6
164.9
154.2
192.2
The electronic absorption spectra of the monometallic
complexes 2−4 and the heterobimetallic complexes 5−9 in
dimethyl sulfoxide at ambient temperature are also summar-
ized in Table 1. The monometallic complexes 2−4 exhibited
intense bands due to ligand centered transitions and metal-to-
ligand charge transfer transitions (MLCT) bands with the
most intense bands recorded in the λ = 383−410 nm range.
With the addition of the second metal by metalation of the
NHC, perceptible changes in the absorption spectra were
observed. For example, the absorption maximum of the
monometallic complex 3 appeared at λ = 385 nm while that
of the bimetallic complex 8, now containing the {NHC−Pd}
complex fragment, exhibited the strongest absorption at λ =
435 nm. Generally, the absorption maxima of the bimetallic
complexes are shifted to higher wavelengths compared to the
monometallic derivatives.
Figure 1. Molecular structures of 5 (top) and 6 (bottom). Hydrogen
atoms have been omitted for clarity, and displacement ellipsoids are
drawn at the 50% probability level.
Formation of the heterobimetallic complexes 7−9 and the
homobimetallic complex 10 was confirmed by 1H NMR
spectroscopy where the downfield resonance for the N−CH−
N protons of the monometallic complexes 2−4 was not
observed anymore. The 13C NMR spectra showed the
characteristic CNHC resonance at δ 178.6 (7), 164.9 (8),
154.2 (9), and 192.2 ppm (10).
Molecular Structures of 5 and 6. The coordination
geometry around the rhodium atom (in 5) or the iridium atom
(in 6) is distorted square-planar with two coordination sites
occupied by the midpoints of the double bonds of the
cycloocta-1,5-diene (COD) ligand while the remaining two
sites are occupied by the CNHC atom and a halogeno ligand
(Figure 1). The parameter τ4 has been used to describe the
coordination geometry of ML4 complexes.25,26 For a square-
planar complex, τ4 is zero, while it becomes one for a
tetrahedral complex. For the iridium atom of the hetero-
bimetallic complex 6, the τ4 value of 0.07 confirms the square-
planar coordination geometry, while a τ4 value of 0.04 was
calculated for the rhodium atom in heterobimetallic complex 5.
In complex 6, the NHC ligand and the halogeno ligand are
bound cis to each other and in trans positions to the centroids
of the COD double bonds. This leads to two short Ir−Colefin
(trans to chloride) and two longer Ir−Colefin (trans to NHC)
bond distances due to the differences in trans influence of the
halogeno and the NHC ligands. The Ir−CCOD distances range
from 2.087(9) to 2.197(6) Å, and these values fall in the range
reported for related IR-cod complexes.27−29 The Ir−Cl1 bond
length is also close to values reported for this separation in the
literature.30,31 (Table 2). The two chloride ligands and the two
nitrogen atoms from the phenanthroline (phen) donor form an
approximately square-planar polyhedron around the palladium
atom of 6, which lies 0.008(2) Å out of the least-squares plane
defined by the atoms N3, N4, Cl2, and Cl3. The bond lengths
and angles in the coordinated phen ligand of complexes 5 and
6 are slightly different from those found in the free phen
ligand.32 In the both complexes, the two nitrogen atoms are
arranged closer to each other (2.639 Å in 5, 2.620 Å in 6, 2.720
In geneal, NHC ligands display good σ-donor and weak π-
acceptor properties.21 For an approximate evaluation of the
electronic situation at a given metal center, metal bound
carbonyl ligands have proved useful. Measuring of the carbonyl
stretching frequencies of {M(CO)(NHC)} complexes allows
an evaluation of the donor properties of NHC ligands, which is
an important factor for homogeneous catalysis.22−24 In order
to evaluate the donor properties of the NHC ligand in 6, for
example, CO was bubbled through a solution of the complex in
dichloromethane at ambient temperature to give complex 11 in
good yield (Scheme 3). The reaction resulted in a quantitative
Scheme 3. Synthesis of Complex 11
substitution of the COD ligand by two CO ligands. The
wavenumbers of the CO stretching modes were recorded at ν
= 2067 and 1987 cm−1, and these values are consistent with
known [IrCl(CO)2(NHC)]-type complexes.13
The IR data of the complexes 2−10 are summarized in
Table 1. The spectra showed bands of varying intensities in the
range of 4000−400 cm−1 clearly indicating the presence of the
diaminoheterocycle with ν(C−N) vibrations between ν = 1411
and 1744 cm−1.
C
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i
haloacetophenone in the presence of PrOH and KOH at 80
Table 2. Selected Bond Lengths [Å] and Angles [deg] for
Complexes 5 and 6
°C (Table 3, entries 1−5). In a related study, Peris and co-
5 (M = Rh, X = Br)
6 (M = Ir, X = Cl)
Table 3. Dehalogenation/Transfer Hydrogenation of 4-
Haloacetophenone
a
M−X1
M−C1
M−C2
M−C5
M−C6
M−C9
2.512 (8)
2.101 (6)
2.105 (6)
2.197 (6)
2.202 (6)
2.016 (5)
2.404 (8)
2.392 (8)
2.041 (4)
2.047 (4)
89.1 (1)
91.1 (2)
176.2 (2)
177.0 (2)
92.8(2)
2.374 (2)
2.104 (9)
2.087 (9)
2.196 (8)
2.160 (9)
2.025 (8)
2.281(2)
2.286(2)
2.014(7)
2.017(7)
90.2 (2)
89.8 (2)
175.2 (2)
174.9 (2)
95.3 (2)
86.9 (3)
90.7 (8)
175.1 (2)
94.1(2)
Pd1−X2
Pd1−X3
Pd1−N3
Pd1−N4
X1−M1−C9
X1−M1−D1
X1−M1−D2
C9−M1−D1
C9−M1−D2
D1−M1−D2
X2−Pd1−X3
X2−Pd1−N3
X2−Pd1−N4
X3−Pd1−N3
N3−Pd1−N4
yield (%)
entry
catalyst
X
base
A
B
C
1
2
3
4
5
6
7
8
9
5
6
7
8
9
8
9
8
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Br
Br
KOH
KOH
KOH
KOH
20
10
18
0
14
18
26
0
10
5
66
72
56
>99
88
66
58
0
a
KOH
0
Cs2CO3
Cs2CO3
KOtBu
KOH
KOH
KOH
28
33
0
0
34
0
9
87.1 (2)
90.4 (3)
175.1 (1)
97.4(1)
94.5 (1)
80.4(2)
>99
87
10
0
8
13
56
92
10
11
10 + 12
8
b
94.1 (2)
81.0(3)
a
Reaction conditions: 4-haloacetophenone (0.36 mmol), base (1.08
mmol), catalyst (1 mol %), 2-propanol (2.0 mL), 80 °C, 2 h. Yields
a
b
D1 and D2 are the midpoints of the C5C6 and C1C2 double
determined by gas chromatography. The reaction was carried out in
bonds.
the presence of a drop of Hg0.
workers used heterobimetallic complexes and Cs2CO3 as a
base.16 As can be seen from the data in Table 3, the best results
regarding formation of the desired compound C were obtained
by using complexes 8 and 9 (entries 4 and 5). Complexes 5−7
gave product mixtures containing larger amounts of A and B.
In the presence of a strong base such as KOtBu, complex 8
catalyzed only the transfer hydrogenation to give B and no
dehalogenation was observed (entry 8). For the chlorinated
acetophenone, this type of reaction was also observed with
complex 8 and KOH as the base (entry 9). When two
homodimetallic complexes (Ir/Ir complex 10, Scheme 2, and
known Pd/Pd complex 12;20 see Figure 2) were used in
Å in the free ligand), most likely a consequence of the
chelating coordination to the palladium atom.
In complex 5, the angle between the NHC plane and the
coordination plane Br1/D1/D2 (D1, D2 are the midpoints of
the COD double bonds) measures 86.1(3)°, which is slightly
smaller than dihedral angles reported for related com-
plexes.33,34 The COD ring adopts a boat conformation, with
the Rh−CCOD distances in the range 2.101(6)−2.202(6) Å.
These distances agree well with the values reported in the
literature for related complexes.34−37 Similarly to complex 6,
the Rh−C1 and Rh−C2 bond distances in 5 (trans to Br1) are
shorter than Rh−C5 and Rh−C6 distances (trans to CNHC).
The Rh−Br1 separation is close to the values reported in the
literature for related complexes.34−37
Catalytic Studies. Transition metal catalyzed processes
have enabled various transformations in modern organic
synthesis. The power and efficiency of such methods is limited
by the conventional focus on chemical reactions as discrete
events. Peris and co-workers, however, studied polydentate N-
heterocyclic carbene ligands and triazoldiylidene bridged
heterobimetallic complexes of palladium, rhodium, iridium,
and ruthenium as catalysts for tandem reactions, such as the
dehalogenation/transfer hydrogenation and the Suzuki cou-
pling/transfer hydrogenation.12,13,16
We have developed the heterobimetallic complexes 5−9 as
catalysts for selected tandem reactions. These complexes,
containing two different metal centers, were investigated in
tandem reactions such as the dehalogenation/transfer hydro-
genation and the Suzuki−Miyaura coupling/transfer hydro-
genation. We also compared the catalytic properties of the
dinuclear complexes to the activity of mixtures of related
mononuclear complexes.
Figure 2. Known homobimetallic complex 12 and monometallic
complexes 13−16 used in catalytic studies.19,20,38
equimolar ratio (base KOH), the yield of C decreassed (entry
10) relative to the heterobimetallic Ir/Pd complex 9 (entry 5).
In order to establish the homogeneous character of the
catalytic transformation, a Hg0 poisoning test was performed
(entry 11). No change of the catalytic activity was observed in
the presence of mercury for complex 8, indicative for a
homogeneous catalytic reaction.
In order to obtain some basic information on the catalytic
activity of the heterobimetallic complexes, we first studied their
use in the dehalogenation/transfer hydrogenation of 4-
D
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Table 4 shows representative data for the Suzuki coupling of
4-haloacetophenone with phenylboronic acid using various of
be a consequence of the higher local concentration of metal
centers in the heterobimetallc complexes. In addition, subtle
differences in the coordination of the bridging ligand may
produce important differences in its electron-donating and
steric properties. However, the data in Table 4 clearly show
that the bridging ligand plays an essential role in the tandem
reaction.
Table 4. Suzuki Coupling/Transfer Hydrogenation of 4-
a
Haloacetophenone
Using the most active catalyst 8, the scope of the catalytic
Suzuki coupling/transfer hydrogenation was studied with 4-
bromobenzophenone and various boronic acids, affording the
corresponding biphenyl alcohols in excellent yields (88−99%)
(Table 5). The reaction tolerated a variety of functional
yield (%)
entry
catalyst
X
base
D
E
Table 5. Tandem Suzuki−Miyaura/Transfer Hydrogenation
1
2
3
4
5
6
7
8
9
5
6
7
8
9
8
8
8
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Br
Br
Br
KOH
KOH
KOH
KOH
KOH
Cs2CO3
KOtBu
NaOH
KOH
KOH
KOH
KOH
26
12
24
1
12
44
8
21
86
33
85
97
14
19
5
a
of 4-Bromoacetophenone Derivatives
99
88
56
30
79
14
48
8
8
10
11
12
10 + 12
13 + 14
15 + 16
2
a
Reaction conditions: 4-bromoacetophenone (0.36 mmol), KOH
(0.72 mmol), phenylboronic acid (0.55 mmol), 2-propanol (2.0 mL),
80 °C, 2 h. Yields were determined by gas chromatography.
the prepared catalysts. Several bases (KOH, Cs2CO3, KOtBu,
and NaOH) were employed. The best results were obtained in
iPrOH at 80 °C. As can be seen from Table 4, the C−C
coupling/transfer hydrogenation is best catalyzed by com-
plexes 8 and 9 where it is completed within 2 h if formation of
E is considered. The best results were obtained with complex 8
(entry 4). In contrast, the analogues of 8 and 9, complexes 6
and 7, containing the same metals, but at opposite
coordination sites, give lower yields of E (entries 2 and 3).
These results indicate that the coordination of an identical set
of metals, but differing sites (N^N chelate or NHC), influences
the catalytic performance of the complexes. The highest yields
of E were always obtained when the palladium atom was
bound to the NHC donor and the second metal (Ru or Ir) by
the N^N chelate site.
Interestingly, when 4-chloroacetophenone was used as
substrate, C−C coupling and formation of compound D was
observed as the major reaction product (catalyst 8, entry 9).
The mixture of two homobimetallic complexes (10 + 12) also
gave a lower yield of E when compared to 9 (entry 10). Under
the reaction conditions used, no dehalogenation products were
observed, indicating that the coupling reaction is faster than
the reduction of the 4-haloacetophenones.
In order to evaluate the effect of the heterobimetallic
complexes compared to equimolar mixtures of homometallic
ones, the known monometallic complexes 13 (Ru-N^N-
chelate), 14 (Pd-NHC), 15 (Ru-N^N-chelate), and 16 (Pd-
NHC) were prepared (Figure 2). As shown in Table 4, a
significant decrease in catalytic activity of mixtures of two
monometallic complexes 13 + 14 (entry 11) and 15 + 16
(entry 12) regarding the production of compound E was
observed in comparison to the heterobimetallic Ru-N^N-
chelate/Pd-NHC complex 8 (entry 4). While the reasons for
this observation are not fully understood at this time, this may
a
Reaction conditions: ketone (0.36 mmol), KOH (0.72 mmol),
arylboronic acid (0.55 mmol), 2-propanol (2.0 mL), 80 °C, 2 h.
Yields were determined by gas chromatography.
groups, including OMe, Me, and COOH, CN, OCF3, and Ph,
in varying substitution patterns, enabling a benign and efficient
two-step synthesis of various organic compounds.
CONCLUSION
■
We have prepared a series of heterobimetallic complexes (Pd/
Rh 5, Pd/Ir 6, Pd/Ru 7, Ru/Pd 8, and Ir/Pd 9) bridged by the
mixed donor set 1,3-dibutylimidazol{[4,5-f ][1,10]-phenan-
throlin}-2-ylidene ligand in which the metals coordinated to
different donors of the ligand. The heterobimetallic complexes
5−9 were synthesized in a stepwise procedure and were used
E
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Synthesis of Complex 6. A mixture of 2 (100 mg, 0.15 mmol),
[IrCl(COD)]2 (50 mg, 0.075 mmol), and NaOAc (38 mg, 0.45
mmol) in CH3CN (5 mL) was stirred for 2 h at ambient temperature.
The resulting yellow colored precipitate was isolated by filtration. The
crude solid product was washed with diethyl ether (3 × 5 mL). The
orange residue was recrystallized from CH2Cl2. Yield: 96 mg (0.11
as catalysts in the tandem reactions (dehalogenation/transfer
hydrogenation and Suzuki−Miyaura coupling/transfer hydro-
genation). It was observed that the heterobimetallic complex 8
is the most active catalyst for the preparation of biphenyl
alcohols. However, the analogue with an inverted coordination
of the metals (complex 7) only catalyzed cross-coupling
reactions.
1
mmol, 76%). H NMR (400 MHz, CDCl3): δ 9.02 (d, J = 5.2 Hz, 2
H, phen-H), 8.86 (d, J = 5.2 Hz, 2 H, phen-H), 7.80 (m, 2 H, phen-
H), 5.76 (t, J = 6.8 Hz, 2 H, butyl-CH2), 5.03 (t, J = 5.2 Hz, 2 H,
butyl-CH2), 4.87 (br, 2 H, COD-CH), 3.29 (br, 2 H, COD-CH), 2.34
(m, 8 H, COD-CH2, butyl-CH2), 1.81 (m, 8 H, COD-CH2, butyl-
CH2), 1.17 (t, J = 8.0 Hz, 6 H, butyl-CH3). The 13C NMR spectrum
could not be recorded due to the low solubility of the complex. Anal.
Calcd for C29H36N4Cl3IrPd (M = 845.59): C, 41.19; H, 4.29; N, 6.62.
Found: C, 41.01; H, 4.38; N, 6.51.
EXPERIMENTAL SECTION
■
All reactions were performed under air. The solvents were used as
received, and the reagents were purchased from Sigma-Aldrich,
Merck, Alfa Aesar, and Acros Organics. When required, solvents were
dried by standard techniques. Compounds 1, 2, 12,20 15,19 and 1338
1
were synthesized according to published procedures. H NMR (400
Synthesis of Complex 7. A mixture of 2 (100 mg, 0.15 mmol),
[RuCl2(p-cymene)]2 (46 mg, 0.075 mmol), and NaOAc (38 mg, 0.45
mmol) in THF (10 mL) was stirred for 2 h at ambient temperature.
The resulting yellow colored precipitate was isolated by filtration. The
crude solid product was washed with diethyl ether (3 × 5 mL). Yield:
MHz) and 13C NMR (100 MHz) spectra were recorded with a Varian
AS 400 Mercury instrument, and tetramethylsilane (TMS) was used
as the internal standard. Chemical shifts (δ) are given in ppm and
coupling constants (J) in Hz. FT-IR spectra were obtained on a
PerkinElmer Spectrum 100 series spectrometer, and UV spectra were
recorded on a PG T60 UV−vis spectrophotometer. Elemental
analyses were performed with a PerkinElmer PE 2400 elemental
analyzer.
1
64 mg (0.07 mmol, 52%). H NMR (400 MHz, DMSO-d6): δ 9.11
(d, J = 8.4 Hz, 1 H, phen-H), 9.06 (d, J = 8.4 Hz, 1 H, phen-H), 8.52
(d, J = 8.4 Hz, 1 H, phen-H), 8.25 (d, J = 8.4 Hz, 1 H, phen-H), 7.94
(t, J = 8.4 Hz, 1 H, phen-H), 7.76 (t, J = 8.4 Hz, 1 H, phen-H), 5.72
(m, 2 H, butyl-CH2), 5.23 (d, J = 6.0 Hz, 1 H, cymene-H), 5.10 (d, J
= 6.0 Hz, 1 H, cymene-H), 5.04 (m, 2 H, cymene-H), 4.59 (m, 2 H,
butyl-CH2), 2.76 (m, 1 H, cymene-H), 2.35 (s, 3 H, cymene-H), 2.08
(m, 8 H, butyl-CH2), 1.68 (d, J = 7.6 Hz, 6 H, cymene-H), 1.07 (t, J =
7.2 Hz, 6 H, butyl-CH3). 13C NMR (100 MHz, DMSO-d6): δ 178.6,
151.3, 144.9, 134.6, 127.8, 126.3, 120.6, 106.3, 104.7, 88.3, 83.7, 50.8,
31.7, 30.2, 22.7, 19.8, 18.4, 12.8. Anal. Calcd for C31H38N4Cl4PdRu
(M = 815.92): C, 45.63; H, 4.69; N, 6.87. Found: C, 45.13; H, 4.68;
N, 4.59.
Synthesis of Complex 3. A mixture of [RuCl2(p-cymene)]2 (26
mg, 0.1 mmol) and proligand 1 (48 mg, 0.1 mmol) in THF (5 mL)
was stirred for 2 h at ambient temperature. The resulting cream
colored precipitate was isolated by filtration. The crude solid product
was washed with diethyl ether (2 × 5 mL) and dried in vacuo. Yield:
1
69 mg (0.08 mmol, 89%). H NMR (400 MHz, DMSO-d6): δ 10.30
(s, 1 H, N-CH-N), 10.11 (d, J = 4.8 Hz, 2 H, phen-H), 9.32 (d, J =
4.8 Hz, 2 H, phen-H), 8.32 (m, 2 H, phen-H), 6.41 (d, J = 5.2 Hz, 2
H, cymene-H), 6.16 (d, J = 6.0 Hz, 2 H, cymene-H), 4.99 (t, J = 6.8
Hz, 4 H, butyl-CH2), 2.65 (m, 1 H, cymene-H), 2.18 (s, 3 H, cymene-
H), 2.01 (m, 4 H, butyl-CH2), 1.48 (m, 4 H, butyl-CH2), 0.95 (m, 12
H, cymene-H, butyl-CH3). 13C NMR (100 MHz, DMSO-d6): δ 156.9,
144.9, 143.9, 133.9, 127.7, 125.8, 120.4, 105.6, 104.0, 86.8, 85.0, 50.4,
31.0, 30.4, 22.2, 19.2, 18.5, 13.9. Anal. Calcd for C31H39N4Cl2F6PRu
(M = 784.61): C, 47.45; H, 5.01; N, 7.14. Found: C, 47.41; H, 5.09;
N, 7.11.
Synthesis of Complex 4. A mixture of [IrCl2Cp*]2 (26 mg, 0.1
mmol) and proligand 1 (48 mg, 0.1 mmol) in CH3CN (5 mL) was
stirred for 2 h at ambient temperature. The resulting yellow colored
precipitate was isolated by filtration. The crude solid product was
washed with diethyl ether (2 × 5 mL) and dried in vacuo. Yield: 79
mg (0.09 mmol, 90%). 1H NMR (400 MHz, DMSO-d6): δ 10.36 (s, 1
H, N-CH-N), 9.52 (d, J = 4.8 Hz, 2 H, phen-H), 9.38 (d, J = 4.8 Hz, 2
H, phen-H), 8.41 (m, 2 H, phen-H), 5.02 (t, J = 7.2 Hz, 4 H, butyl-
CH2), 2.01 (m, 4 H, butyl-CH2), 1.73 (s, 15 H, Cp*-CH3), 1.49 (m, 4
H, butyl-CH2), 0.96 (t, J = 7.6 Hz, 6 H, butyl-CH3). 13C NMR (100
MHz, DMSO-d6): δ 153.4, 144.4, 134.4, 128.5, 125.8, 120.4, 97.9,
50.9, 30.7, 19.3, 13.9, 8.9. Anal. Calcd for C31H40N4Cl2F6IrPIr (M =
876.76): C, 42.47; H, 4.60; N, 6.39. Found: C, 42.36; H, 4.43; N,
6.21.
Synthesis of Complex 5. A mixture of complex 2 (100 mg, 0.15
mmol), [Rh(COD)Cl]2 (36 mg, 0.075 mmol), NaOAc (38 mg, 0.45
mmol), and NaBr (46 mg, 0.45 mmol) in MeCN (5 mL) was stirred
for 2 h at ambient temperature. The resulting yellow colored
precipitate was isolated by filtration. The crude solid product was
washed with diethyl ether (3 × 5 mL). The orange residue was
recrystallized from CH2Cl2. Yield: 96 mg (0.10 mmol, 72%). 1H
NMR (400 MHz, CDCl3): δ 8.72 (d, J = 5.2 Hz, 2 H, phen-H), 8.56
(d, J = 5.2 Hz, 2 H, phen-H), 7.69 (m, 2 H, phen-H), 5.78 (m, 2 H,
butyl-CH2), 5.23 (br, 2 H, COD-CH), 5.18 (m, 2 H, butyl-CH2),
3.77 (br, 2 H, COD-CH), 2.46 (m, 6 H, COD-CH2), 2.11 (m, 4 H,
butyl-CH2), 1.91 (m, 2 H, COD-CH2), 1.78 (m, 4 H, butyl-CH2),
1.22 (t, J = 8.4 Hz, 6 H, butyl-CH3). The 13C NMR spectrum could
not be recorded due to the low solubility of the complex. Anal. Calcd
for C29H36N4Br3PdRh (M = 887.79): C, 39.23; H, 4.09; N, 6.31.
Found: C, 39.18; H, 4.23; N, 6.21%.
Synthesis of Complex 8. A mixture of 3 (100 mg, 0.13 mmol),
Pd(OAc)2 (29 mg, 0,13 mmol), KCl (38 mg, 0.52 mmol), pyridine
(1.0 mL), and NaOAc (38 mg, 0.45 mmol) in CH3CN (5 mL) was
stirred for 2 h at ambient temperature. The resulting yellow colored
precipitate was isolated by filtration. The crude solid product was
purified by column choromatography (eluent: CH2Cl2/MeOH).
1
Yield: 72 mg (0.08 mmol, 62%). H NMR (400 MHz, DMSO-d6):
δ 9.97 (d, J = 4.8 Hz, 2 H, phen-H),), 9.21 (t, J = 4.8 Hz, 2 H, phen-
H), 8.91 (d, J = 5.2 Hz, 2 H, py-H), 8.28 (m, 2 H, phen-H), 8.02 (t, J
= 5.2 Hz, 1 H, py-H), 7.62 (t, J = 5.2 Hz, 2 H, py-H), 6.33 (d, J = 6.8
Hz, 1 H, cymene-H), 6.30 (d, J = 6.8 Hz, 1 H, cymene-H), 6.09 (m, 2
H, cymene-H), 5.50 (br, 4 H, butyl-CH2), 2.65 (m, 1 H, cymene-H),
2.17 (m, 4 H, butyl-CH2, 3 H, cymene-H), 1.75 (m, 4 H, butyl-CH2),
1.12 (d, J = 7.6 Hz, 6 H, cymene-H), 0.95 (t, 6 H, J = 8.4 Hz, butyl-
CH3). 13C NMR (100 MHz, DMSO-d6): δ 164.9, 152.5, 150.9, 144.8,
139.4, 134.0, 127.7, 127.0, 125.8, 120.4, 105.5, 104.0, 87.0, 84.9, 50.4,
30.9, 30.6, 22.2, 19.3, 18.7, 13.9. Anal. Calcd for C36H43N5Cl4PdRu
(M = 895.02): C, 48.31; H,4.84; N, 7.83. Found: C, 48.36; H, 5.04;
N, 7.91.
Synthesis of Complex 9. A mixture of 4 (100 mg, 0.11 mmol),
Pd(OAc)2 (25 mg, 0,11 mmol), KCl (38 mg, 0.52 mmol), pyridine
(1.0 mL), and NaOAc (38 mg, 0.45 mmol) in CH3CN (5 mL) was
stirred for 2 h at ambient temperature. The resulting yellow colored
precipitate was isolated by filtration. The crude solid product was
purified by column choromatography (eluent: CH2Cl2/MeOH).
1
Yield: 56 mg (0.05 mmol, 52%). H NMR (400 MHz, DMSO-d6):
δ 9.41 (d, J = 8.8 Hz, 2 H, phen-H), 9.21 (d, J = 8.8 Hz, 2 H, phen-
H), 8.87 (d, J = 7.6 Hz, 2 H, py-H), 8.34 (m, 2 H, phen-H), 8.02 (t, J
= 7.6 Hz, 1 H, py-H), 7.64 (t, J = 7.6 Hz, 2 H, py-H), 5.55 (br, 4 H,
butyl-CH2), 2.15 (m, 4 H, butyl-CH2,), 1.75 (m, 4 H, butyl-CH2),
1.52 (m, 15 H, Cp*-CH3), 1.10 (t, J = 7.6 Hz, 6 H, butyl-CH3). 13C
NMR (100 MHz, DMSO-d6): δ 154.2, 153.1, 151.4, 145.3, 145.2,
145.1, 135.2, 134.9, 129.4, 128.0, 127.7, 126.7, 126.5, 121.3, 120.1,
98.8, 51.3, 31.5, 20.2, 14.8, 9.9. Anal. Calcd for C36H44N5Cl4IrPd (M
= 987.17): C, 43.80; H, 4.49; N, 7.10. Found: C, 43.82; H, 4.62; N
7.13.
F
DOI: 10.1021/acs.organomet.8b00882
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Synthesis of Complex 10. A mixture of 4 (100 mg, 0.11 mmol),
[IrCp*Cl2]2 (45 mg, 0.05 mmol), and NaOAc (38 mg, 0.45 mmol) in
THF (10 mL) was stirred under argon for 2 h at ambient
temperature. The mixture was then heated to reflux for 24 h. The
solvent was removed under reduced pressure. The orange solid
product was recrystallized from CH2Cl2. Yield: 114 mg (0.10 mmol,
mmol, internal standard), and 2 mL of 2-propanol. The reaction
mixture was stirred at 80 °C for 2 h. Yields were determined by GC
chromatography and NMR spectroscopy.
X-ray Diffraction Studies. Single-crystal data were collected at
293(2) K for 5 and at 100 K for 6 using the ω-scan technique on a
Rigaku-Oxford Xcalibur diffractometer with an Eos CCD area
detector using graphite-monochromated MoKα radiation (λ =
0.71073 Å). The data collection, cell refinement, and data reduction
were performed using the CrysAlisPro program.39 Analysis of the
structures was performed using the OLEX2 programs,40,41 and the
structure models were refined by the full-matrix least-squares method
based on F2 against all reflections using the SHELXL.42 All non-
hydrogen atoms were refined anisotropically. The carbon-bound
hydrogen atoms were included on idealized positions and were
refined riding on their parent carbon atoms with C−H = 0.93, 0.96,
0.97, and 0.98 Å for aryl, methyl, methylene, and methine hydrogen
atoms, respectively, with Uiso(H) = 1.5Ueq(methyl carbon) and
1.2Ueq(nonmethyl carbon). Geometrical calculations were performed
1
92%). H NMR (600 MHz, DMSO-d6): δ 9.36 (d, 2 H, J = 5.6 Hz,
phen-H), 9.13 (d, J = 8.0 Hz, 2 H, phen-H), 8.33 (dd, 1J = 6.4 Hz, 1J
1
2
= 5.6 Hz, 2 H, phen-H), 5.61 (td, J = 12.9 Hz, J = 4.8 Hz, 1 H,
butyl-CH2), 5.15 (td, 1J = 12.9 Hz, 2J = 4.8 Hz, 1 H, butyl-CH2), 4.62
(s, br, 1 H, butyl-CH2), 3.08 (s, br, 1 H, butyl-CH2), 2.27 (s, br, 2 H,
butyl-CH2), 2.01 (m, 2 H, butyl-CH2), 1.93−1.57 (m, 34 H, butyl-
CH2, Cp*-CH3), 1.07 (t, J = 7.2 Hz, 6 H, butyl-CH3). 13C NMR (100
MHz, DMSO-d6): δ 192.2, 151.5, 144.1, 133.5, 128.3, 127.3, 119.9,
89.9, 85.4, 65.4, 53.0, 50.5, 33.6, 31.1, 29.6, 19.7, 15.7, 14.0, 8.6. Anal.
Calcd for C41H54N4Cl4Ir2 (M = 1129.12): C, 43.61; H, 4.96; N, 4.96.
Found: C, 43.62; H, 4.96; N, 4.91.
Synthesis of Complex 11. Complex 6 (0.1 mmol) was dissolved
in MeOH (5 mL), and CO gas was bubbled through the solution for
1 h. The color of the solution changed from bright yellow to pale
yellow. The solution was concentrated to 1 mL and pentane (5 mL)
was added. A pale yellow solid precipitated and was isolated by
filtration and was washed with pentane. Yield: 71 mg (0.08 mmol,
89%). 1H NMR (400 MHz, CDCl3): δ 8.62 (d, J = 8.4 Hz, 2 H, phen-
H), 8.44 (d, J = 8.4 Hz, 2 H, phen-H), 7.76 (m, 2 H, phen-H), 5.26
(m, 2 H, butyl-CH2), 4.83 (m, 2 H, butyl-CH2), 2.09 (m, 2 H, butyl-
CH2), 1.88 (m, 2 H, butyl-CH2), 1.63 (m, 4 H, butyl-CH2), 1.10 (t, J
= 6.8 Hz, 6 H, butyl-CH3). 13C NMR (100 MHz, CDCl3): δ 185.1,
180.3, 167.3, 148.5, 144.0, 133.3, 127.0, 126.2, 119.9, 51.9, 31.2, 19.9,
13.6. Anal. Calcd for C23H24N4Cl3IrO2Pd (M = 793.43): C, 34.81; H,
3.05; N, 7.06. Found: C, 34.58, H, 3.41, N, 6.96.
using PLATON.43 The figures were made using ORTEP.44
A
summary of the crystal data, experimental details, and refinement
results for complexes 5 and 6 is presented (see the Supporting
Information, Table S1).
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00882.
NMR spectra of all compounds (PDF)
General Procedure for the Preparation of Complexes 14
and 16. The appropriate azolium salt (0.5 mmol) and Pd(OAc)2 (0.5
mmol) were suspended in anhydrous pyridine (10 mL), and the
mixture was stirred at 65 °C for 4 h. The residual pyridine was then
removed in vacuo at room temperature. The complexes were purified
by column chromatography on silica gel. Removal of the solvent and
crystallization from CH2Cl2/diethyl ether afforded 14 and 16.
Accession Codes
CCDC 1584349 and 1584351 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
Complex 14. Yield: 200 mg (0.34 mmol, 70%). H NMR (400
MHz, CDCl3): δ 9.05 (dd, J = 8.0 Hz, 2 H, py-H), 8.71 (t, J = 8.0 Hz,
1 H, py-H), 7.79 (m, 2 H, py-H), 7.37 (m, 2H, Ar-H), 7.24 (t, J =
16.0 Hz, 2 H, Ar-H), 4.71 (t, J = 16.0 Hz, 4 H, butyl-CH2), 2.22 (m, 4
H, butyl-CH2), 1.59 (m, 4 H, butyl-CH2), 1.08 (t, J = 8.0 Hz, 6 H,
butyl-CH3). 13C NMR (100.6 Hz, CDCl3): δ 178.2, 159.5, 153.8,
134.8, 122.6, 110.3, 49.3, 30.3, 20.4, 13.8. Anal. Calcd for
C20H27N3Br2Pd (M = 575.64): C, 41.73; H, 4.73; N, 7.30. Found:
C, 41.84; H, 4.68; N, 7.21.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hayatiturkmen@hotmail.com.
ORCID
F. Ekkehardt Hahn: 0000-0002-2807-7232
Hayati Turkmen: 0000-0001-7411-2652
̈
Notes
■
1
Complex 16. Yield: 162 mg (0.03 mmol, 62%). H NMR (400
MHz, CDCl3): δ 9.04 (d, J = 8.0 Hz, 2 H, py-H), 8.89 (d, J = 8.0 Hz,
1 H, py-H), 7.76 (t, J = 8.0 Hz, 2 H, py-H), 7.33 (t, J = 8.0 Hz, 2 H,
im-CH), 4.51 (t, J = 16.0 Hz, 4 H, butyl-CH2), 2.07 (m, 4 H, butyl-
CH2), 1.47 (m, 4 H, butyl-CH2), 1.03 (t, J = 16.0 Hz, 6 H, butyl-
CH3). 13C NMR (100.6 Hz, CDCl3): δ 160.6, 154.3, 138.3, 124.9,
120.9, 51.1, 32.2, 20.0, 13.8. Anal. Calcd for C16H25N3Br2Pd (M =
525.59): C, 36.56; H, 4.79; N, 7.99; Found: C, 36.60; H, 4.82; N,
8.03%.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
̇
Financial support from Ege University (Project 2012-BIL-042;
̈
2013 FEN 062) and TUBITAK (111T398) is gratefully
acknowledged. The authors acknowledge Dokuz Eylul
̈
University for the use of the Oxford Rigaku Xcalibur Eos
Diffractometer (purchased under University Research Grant
No 2010.KB.FEN.13). F.E.H. thanks the Deutsche For-
schungsgemeinschaft (SFB 858 and IRTG 2027).
General Procedure for the Tandem Dehalogenation/Trans-
fer Hydrogenation of Haloacetophenones. In a typical run, a
reaction vessel containing a stirring bar was charged with the 4-
haloacetophenone (0.36 mmol), base (1.08 mmol), catalyst (1 mol
%), phenylboronic acid (0.55 mmol), diethylene glycol-di-n-
butylether (0.6 mmol, internal standard), and 2 mL of 2-propanol.
The reaction mixture was stirred at 80 °C for the 2 h. For reaction
monitoring, a small amount of sample was periodically withdrawn by
syringe and conversion was analyzed by GC chromatography.
General Procedure for the Tandem Suzuki Coupling/
Transfer Hydrogenation of Haloacetophenones. In a typical
run, a capped vessel containing a stirring bar was charged with the
ketone (0.36 mmol), base (0.72 mmol), catalyst (1 mol %),
arylboronic acid (0.55 mmol), diethylene glycol-di-n-butylether (0.6
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