Abnormal-NHC Palladium(II) Complexes: Rational Synthesis, Structural Elucidation, and Catalytic Activity

Article abstract of DOI:10.1021/acs.organomet.6b00662

Reaction of a C2-arylated imidazolium iodide (IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazolium) with PdCl₂ in the presence of Ag₂O affords abnormal N-heterocyclic carbene (aNHC) palladium complexes (aIPr^Ph)PdCl₂ (2) and (aIPr^Ph)₂PdCl₂ (3) (aIPr^Ph = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazol-4-ylidene). Treatment of 2 with a pyridine gives Pd-PEPPSI-type complexes (aIPr^Ph)PdCl₂(L) (L = pyridine (py), 5; L = 3-chloropyridine (3Cl-py), 6). Compounds 5 and 6 are also accessible by a one-pot reaction of 1, PdCl₂, and Ag₂O in a pyridine solvent. While the use of a conventional base K₂CO₃ leads to the formation of mixed halide complexes (aIPr^Ph)Pd(Cl)I(L) (7, L = py; 8, L = 3Cl-py), iodide derivatives (aIPr^Ph)PdI₂(L) (9, L = py; 10, L = 3Cl-py) can be selectively prepared with addition of an excess of KI to the reaction mixture. Albeit in a low yield, a putative transmetalation agent {(aIPr^Ph)₂Ag}AgI₂ (4) has been isolated and characterized. Compounds 2-10 are air stable crystalline solids and have been characterized by elemental analysis, mass spectrometry, and NMR spectroscopic studies. Molecular structures of 2-10 have been established by single crystal X-ray diffraction analyses. Catalytic activity of three representative compounds 2, 5, and 6 has been tested for the Suzuki-Miyaura cross-coupling reactions.

Full text of DOI:10.1021/acs.organomet.6b00662

Article
pubs.acs.org/Organometallics
Abnormal-NHC Palladium(II) Complexes: Rational Synthesis,
Structural Elucidation, and Catalytic Activity
Dennis Rottschafer,† Christian J. Schurmann,‡ Jan-Hendrik Lamm,† Alexander N. Paesch,‡
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Beate Neumann,† and Rajendra S. Ghadwal*,†,§
§
†Anorganische Molekulchemie und Katalyse, Am Lehrstuhl fur Anorganische Chemie und Strukturchemie and Centrum fur
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Molekulare Materialien, Fakultat fur Chemie, Universitat Bielefeld, Universitatsstrasse 25, D-33615, Bielefeld, Germany
‡Institut fur Anorganische Chemie, Georg-August-Universitat Gottingen, Tammannstrasse 4, D-37077 Gottingen, Germany
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S
* Supporting Information
ABSTRACT: Reaction of a C2-arylated imidazolium iodide
(IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-
imidazolium) with PdCl2 in the presence of Ag2O affords
abnormal N-heterocyclic carbene (aNHC) palladium complexes
(aIPrPh)PdCl2 (2) and (aIPrPh)2PdCl2 (3) (aIPrPh = 1,3-bis(2,6-
diisopropylphenyl)-2-phenyl-imidazol-4-ylidene). Treatment of 2
with a pyridine gives Pd-PEPPSI-type complexes (aIPrPh)-
PdCl2(L) (L = pyridine (py), 5; L = 3-chloropyridine (3Cl-py),
6). Compounds 5 and 6 are also accessible by a one-pot reaction
of 1, PdCl2, and Ag2O in a pyridine solvent. While the use of a
conventional base K2CO3 leads to the formation of mixed halide
complexes (aIPrPh)Pd(Cl)I(L) (7, L = py; 8, L = 3Cl-py), iodide
derivatives (aIPrPh)PdI2(L) (9, L = py; 10, L = 3Cl-py) can be
selectively prepared with addition of an excess of KI to the
reaction mixture. Albeit in a low yield, a putative transmetalation agent {(aIPrPh)2Ag}AgI2 (4) has been isolated and
characterized. Compounds 2−10 are air stable crystalline solids and have been characterized by elemental analysis, mass
spectrometry, and NMR spectroscopic studies. Molecular structures of 2−10 have been established by single crystal X-ray
diffraction analyses. Catalytic activity of three representative compounds 2, 5, and 6 has been tested for the Suzuki-Miyaura cross-
coupling reactions.
Chart 1. nNHC− (A) and aNHC− (B) metal complexes, first
aNHC complex (I), and first stable free-aNHC (II)
INTRODUCTION
■
Ligands play an important role in the stability and activity of
metal complexes.1 N-heterocyclic carbenes (NHCs) are
inarguably the most versatile two-electron carbon donor neutral
ligands in transition metal catalysis and organometallic
chemistry.2 The development of highly advanced precatalysts
for olefin metathesis, cross coupling reactions, and other
transformations2h,3 emphasizes the significance of NHCs. The
strong σ-donor ability of NHCs has also been successfully
exploited for stabilizing compounds featuring a low-valent main
group element.4 Easy-to-tune structural features coupled with a
relatively robust nature of the M−C(Carbene) bond (Chart 1; A)
further rationalize the multifarious success of NHCs beyond
catalysis.2a,5 While NHCs are fascinating entities in transition
metal and main group chemistry, research continues toward the
advancement of innovative carbon-donor ligands.2,6 A relatively
new type of NHC-complexes (B) in which the carbene
coordinates to a metal at the C4 (or C5) position have been
developed in the recent years.7 Since normal NHCs (nNHCs)
coordinate to metals at the C2 carbon atoms (A), C4, (or C5)
carbenes (B) are therefore termed abnormal NHCs (aNHCs)
(Chart 1). Experimental and theoretical data5d,8 indicate that
aNHCs are even stronger electron-donating species than
nNHCs as well as CAACs (cyclic alkyl amino carbenes),9
which promises exciting perspectives for their applications in
catalysis and beyond.10 As no canonical resonance form of
aNHCs without the introduction of formal charges can be
drawn, Bertrand described them as mesoionic carbenes
(MICs).11 Albeit as a result of serendipitous discovery, the
first transition metal complex (I) (Chart 1) featuring an aNHC
Received: August 17, 2016
© XXXX American Chemical Society
A
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was reported in 2001 by Crabtree.12 In the past few years,
several other aNHC-complexes have been described.7d
However, the isolation of a stable noncoordinated aNHC
remained a challenge until 2009 when Bertrand reported the
first stable free-aNHC (II).13
Scheme 1. Synthesis of aNHC Complexes 2−4
Despite being exceptionally electron rich ligands, applications
of aNHCs in organometallic chemistry in comparison with
nNHCs are rather limited.2h,14 This is most likely due to the
scarcity of their synthetic methods.7d,10a,15 Therefore, develop-
ing new facile synthetic protocols to aNHC−metal complexes
is highly important. Different synthetic strategies of aNHC−
metal complexes have been developed during the past few
years.7a−d The chelation assistance strategy has found to be
quite useful but is so far limited to a few particular complexes.16
The C2-protecting strategy, particularly with an aryl group,
mostly delivers desired products and has even enabled access to
a free stable aNHC (II).7d,13 Thus, for preparing aNHC-
complexes, C2-arylated imidazolium salts are an appropriate
choice; nevertheless, the synthesis of these salts is rather
demanding. In this context, direct arylation of NHCs is very
appealing as a variety of NHCs can be readily prepared and
some are also commercially available. Very recently, we
reported the catalytic C2-arylation of an NHC using 0.5 mol
% of Pd2(dba)3 (dba = dibenzylideneacetone).17 This high-
yield catalytic route enables access to a variety of C2-arylated
imidazolium salts.17 The palladium-NHC-metal−ligand part-
nership is considered a perfect union in organometallic catalysis
that has particularly recognized enormous significance in many
cross-coupling reactions.2f Therefore, we decided to check the
suitability of our C2-arylated imidazolium salts in the synthesis
of aNHC-palladium complexes and to explore their structure
and catalytic activity.
corresponding signals for the aIPrPh moiety in the expected
regions.
Organ et al. incorporated pyridine (py) as a secondary
ancillary (throwaway) ligand and coined the term “PEPPSI”
(Pyridine-Enhanced-Precatalyst-Preparation-Stabilization-In-
duction) for (NHC)PdCl2(py) type complexes.18 Pd-PEPPSI
complexes have been a considerable success and are therefore
regarded as universal precatalysts for numerous cross-coupling
reactions,19 which further prompted interest in developing their
more atom-economic synthetic methods.20 Similarly, backbone
functionalized21 NHCs as well as NHCs with more specialized
substituents at the imidazole nitrogen atoms19b,e,22 have been
developed to further improve the activity of Pd-PEPPSI
complexes. However, Pd-PEPPSI complexes featuring a 1,3-
imidazol-derived aNHC that have been structurally fully
characterized are very scarce.23 Addition of a small amount of
pyridine to a dichloromethane solution of 2 cleanly yields Pd-
PEPPSI type complex (aIPrPh)PdCl2(L) (L = pyridine (py), 5;
L = 3-chloropyridine (3Cl-py), 6) (Scheme 2). Compounds 5
and 6 can also be prepared in a one-pot reaction by using the
silver-transmetalation strategy. Reaction of 1 and PdCl2 in the
presence of Ag2O leads to the clean formation of compounds 5
and 6 in a good yield. K2CO3 can also be used to deprotonate 1
in a pyridine solvent, however this leads to the formation of
mixed halide compounds (aIPrPh)PdCl(I)(L) (L = py, 7; L =
3Cl-py, 8) (Scheme 2). Solution and solid-state analyses clearly
support the consumption of 1 and formation of 7 and 8.
Nevertheless, complexes 7 and 8 exhibit somewhat complex
NMR spectra due to diminished molecular symmetry and
uncertain halide composition.24 This can be avoided by the
addition of an excess of KI to the reaction mixture, which
exclusively affords iodo-derivatives (aIPrPh)PdI2(L) (L = py, 9;
L = 3Cl-py, 10) under similar experimental conditions.
Compounds 5−10 are air stable yellow to pale-yellow solids.
Herein, we report on a very facile rational synthetic route to a
series of aNHC-palladium(II) complexes featuring a (aIPrPh)-
PdX2 (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imida-
zol-4-ylidene; X = Cl or I) scaffold. All the complexes have
been characterized by elemental analysis, NMR spectroscopy,
and mass spectrometry. The molecular structures have been
established by single crystal X-ray diffraction studies. Moreover,
preliminary results of their catalytic activity for the Suzuki-
Miyaura cross-coupling reactions are presented.
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Reaction of (IPrPh)I
(1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazo-
lium) with PdCl2 in the presence of Ag2O leads to the
formation of palladium complexes (aIPrPh)PdCl2 (2) and
(aIPrPh)2PdCl2 (3) as pale yellow crystalline solids (Scheme 1).
Albeit in a low yield, a putative transmetalation agent
{(aIPrPh)2Ag}AgI2 (4) has been isolated and characterized
(Scheme 1). Each of 2 and 3 exhibits corresponding peaks in
the ESI-mass spectrum. Similarly, the ESI-mass spectrum of 4
shows a molecular ion peak for the cationic {(aIPrPh)2Ag} part.
1H NMR spectra of compounds 2 and 3 exhibit four doublets
for methyl protons of HCMe2 groups, whereas methine protons
(HCMe2) appear as two multiplets, which is consistent with the
asymmetrically substituted imidazol-backbone (C4/C5) posi-
tions. The signal due to the imidazolium backbone protons (for
1 at δ 8.38 ppm in CDCl3) has completely disappeared and a
new signal arises at 6.97 ppm for the remaining C5−H moiety.
In addition, C6H3 protons show two sets of 1H NMR
resonances. 13C NMR spectra of compounds 2 and 3 exhibit
1
Except for 7 and 8, 5−10 exhibit well-resolved H and 13C
NMR resonances for the aIPrPh and respective pyridine unit.
B
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Scheme 2. Synthesis of aNHC−Palladium Complexes 5−10
13C NMR spectra of 5−10 reveal corresponding signals for
(aIPrPh) and pyridine ligands. Each of complexes 5−10 exhibits
the corresponding peak for the [M−X] moiety (X = Cl or I) in
the ESI mass spectrum.
Molecular Structures. Molecular structures of compounds
2, 3 (Figure 1), 4 (Figure S3), 5, 6 (Figure 2), 7 (Figure S6), 8
(Figure S7), 9, and 10 (Figure 2) have been determined by
single crystal X-ray diffraction studies. Compound 2 crystallizes
as orange-yellow crystals upon storage of a solution (1:4
mixture of CH2Cl2 and Et2O) at −30 °C for 1 week. Each of
complexes 2, 3, and 5−10 features a 4-fold coordinated
palladium atom with a distorted square planar geometry (Table
1). The Pd−C(carbene) bond length of 1.979 Å (average) of 2, 3,
and 5−8 is in line with those of the NHC-Pd-PEPPSI
complexes.19e,25 The C−Pd−N bond angle of complexes 5−10
ranges from 173.20° to 175.02°. The Pd−N bond lengths
(2.106−2.131 Å) in 5−10 are comparable with those of
(NHC)PdCl2(py) complexes, where steric hindrance imposed
by the imidazole nitrogen substituents also plays a crucial role
on the bond elongation. This may be attributed as an increased
trans-effect of the aNHC ligand in 5−10. The C−C(carbene)−N
(C5−C4−N3, Table 1) bond angle of the imidazole ring of
complexes 5−10 is smaller by 3° when compared with that of
the compound 1 (107.2°). This indicates increased s-character
(carbene nature) of the C4 carbon atom that coordinates to the
palladium. As expected, the N−C−N bond angle of the
imidazole ring of 5−10 is comparable to that of the 1.17 The
average Pd−Cl bond length of 2.30 Å of 5 and 6 is consistent
with those of other four coordinated palladium complexes.19e
Catalytic Study. Catalytic activity of three representative
palladium compounds 2, 5, and 6 was tested for the Suzuki-
Miyaura cross-coupling reactions. All compounds were found
to be active catalysts and afforded biaryls at room temperature.
In a general procedure, a mixture of aryl halide (1 mmol) and
phenylboronic acid (1.2 mmol) was treated with KOBut (1.5
mmol) in the presence of a palladium precatalyst (2, 5, or 6).
Analytic grade isopropanol was used as a solvent. In all cases
(Table 2), 3 mol % of precatalyst was used. The progress of the
Figure 1. Solid-state molecular structures of compounds 2 and 3.
Anisotropic displacement parameters are depicted at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths and bond angles are given in Table 1.
reactions was monitored by GC/MS analysis (entries 1−13) or
19F NMR spectroscopy (entry 14). The results are listed in
Table 2. In all cases the dimeric Pd-complex 2 was found to be
more active than 5 and 6, leading to good to excellent yields for
coupling bromo- and iodoaryls (up to 100% conversion after
0.5 h in the case of p-iodonitrobenzene, entry 13). While
moderate to good conversion of 4-chlorotoluoene (55% after
24 h, entry 1) or 1-chloro-2-fluorobenzene (69% after 24 h,
entry 14) was observed with 2, only 12−31% conversion was
achieved with 5 or 6 under similar experimental conditions. For
coupling 4-bromotoluene with phenylboronic acid (entries 4−
6), PEPPSI-complexes 5 and 6 were found to be somewhat
slower than compound 2. However, the 3-chloropyridine
derivative (6) was found to be slightly more active catalyst
than its pyridine analogue 5.
EXPERIMENTAL SECTION
■
General. All syntheses and manipulations, unless otherwise stated,
were performed under an inert gas (N2 or Ar) atmosphere using an
MBraun glovebox or Schlenk techniques. Dichloromethane, CD2Cl2,
CDCl3 (CaH2), 1,4-dioxane, THF, and toluene (Na/K-benzophe-
none) were dried by refluxing over an appropriate drying agent and
stored under N2. Other analytic grade solvents and reagents were used
as received without further purification. 1H and 13C NMR spectra were
recorded using a Bruker Avance III 500 or a Bruker Avance III 300 or
a Bruker Avance DRX 500 spectrometer. Chemical shifts are given in δ
1
ppm and are referenced to the solvent residual peak(s). CDCl3: H,
1
7.26 and 13C, 77.16; CD2Cl2: H, 5.32 and 13C, 54.00; C6D6: 7.16 for
C
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Figure 2. Solid-state molecular structures of compounds 5, 6, 9, and 10. Anisotropic displacement parameters are depicted at the 50% probability
level. Hydrogen atoms are omitted for clarity. Selected bond lengths and bond angles are given in Table 1.
1H, 13C, 128.06. ESI mass spectra were recorded with a Bruker Esquire
3000 spectrometer. Melting points were measured with an Electro-
thermal Melting Point apparatus. Elemental analyses were performed
(d, 6H, J = 6.76 Hz, HCMe2); 1.72 (d, 6H, J = 6.60 Hz, HCMe2); 2.44
(sept, 2H, J = 6.75 Hz, HCMe2); 2.78 (sept, 2H, J = 6.65 Hz,
HCMe2); 6.80 (d, J = 7.41 Hz, 2H, o-C6H5); 6.97 (s, 1H, NCH); 7.05
(t, J = 7.00 Hz, 2H, m-C6H5); 7.21 (m, 3H, p-C6H5, m-C6H3), 7.29 (d,
J = 7.74 Hz, 2H, m-C6H3), 7.52 (m, 2H, p-C6H3), ppm. 13C{1H} NMR
(75 MHz, CD2Cl2, 25 °C): δ 22.66, 24.20, 25.97, 26.50 (HCMe2);
29.29, 29.41 (HCMe2); 123.67, 125.13, 125.24, 125.48 ((NCCN,
C6H5, C6H3); 126.81 (NCCN), 128.88, 130.09, 130.88, 131.24, 131.50,
132.32, 134.24, (C6H5, C6H3); 144.89 (NCN), 145.52, 146.13 (ipso-
C6H5, C6H3) ppm.
at the Institute for Inorganic Chemistry, Universitat Bielefeld. PdCl ,
̈
2
pyridine (py), 3-chloropydine (3Cl-py), KI, K2CO3, Cs2CO3, and
Ag2O were used as received. (IPrPh)I (1) was prepared by employing
the reported method.17
Synthesis of [(aIPrPh)PdCl2]2 Compound (2). To a Schlenk flask
containing 1 (2.00 g, 3.44 mmol), PdCl2 (0.61 g, 3.44 mmol), and
Ag2O (0.39 g, 1.69 mmol) were added 30 mL of 1,4-dioxane and 20
mL of CH3CN. The resulting reaction mixture was refluxed for 10 h
with constant stirring. The volatiles were removed under reduced
pressure and the residue was extracted with 20 mL dichloromethane.
Drying under vacuum afforded an orange solid, which was washed with
n-hexane. The residue was dissolved in 10 mL of dichloromethane,
combined with 10 mL Et2O, and stored at −30 °C for 20 h to obtained
orange crystals of 2 (1.83 g, 85%). Elemental analysis for
C66H80N4Cl4Pd2 (1284): calcd. C, 61.74; H, 6.28; N, 4.36; found C
Synthesis of (aIPrPh)2PdCl2 Compound (3). Compound 3 was
prepared by employing a similar method as described for 2 using 1
(1.00 g, 1.69 mmol), PdCl2 (0.15 g, 0.85 mmol), and Ag2O (0.20 g,
0.84 mmol) as an orange solid (0.60 g, 65%). Elemental analysis for
C66H80N4Cl2Pd (1106): calcd. C, 71.63; H, 7.29; N, 5.06; found C
1
71.74, H 7.32, N 4.89. MS (ESI, m/z [M]): 1069.4 [M−Cl]+. H
NMR (300 MHz, CD2Cl2, 25 °C): δ 0.68 (d, 6H, J = 6.72 Hz,
HCMe2); 0.93 (d, 6H, J = 6.85 Hz, HCMe2); 1.22 (d, 6H, J = 6.74 Hz,
HCMe2); 1.72 (d, 6H, J = 6.57 Hz, HCMe2); 2.44 (sept, 2H, J = 6.82
Hz, HCMe2); 2.78 (sept, 2H, J = 6.65 Hz, HCMe2); 6.80 (d, J = 7.44
Hz, 2H, o-C6H5); 6.97 (s, 1H, NCH); 7.04 (t, J = 7.55 Hz, 2H, m-
1
61.61, H 6.29, N 4.28. H NMR (300 MHz, CD2Cl2, 25 °C): δ 0.68
(d, 6H, J = 6.75 Hz, HCMe2); 0.93 (d, 6H, J = 6.86 Hz, HCMe2); 1.22
D
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Table 1. Selected Bond Lengths (Å) and Angles (deg) of Complexes 2, 3, and 5−10 (X = I/Cl)
a
b
The asymmetric unit contains one-half of the molecule; 52:48 population disordered structure (Figure S1). Two molecules in the asymmetric unit
(Figure S5).
C6H5); 7.20 (m, 3H, p-C6H5, m-C6H3); 7.29 (d, J = 7.78 Hz, 2H, m-
C6H3); 7.52 (m, 2H, p-C6H3), ppm. 13C{1H} NMR (75 MHz, CD2Cl2,
25 °C): δ 22.67, 24.20, 25.97, 26.50 (HCMe2), 29.30, 29.42 (HCMe2),
123.71, 125.16, 125.26, 125.50 ((NCCN, C6H5, C6H3), 126.84
(NCCN), 128.89, 130.11, 130.90, 131.25, 131.52, 132.36, 134.28,
(C6H5, C6H3), 144.91 (NCN), 145.56, 146.17 (ipso-C6H5, C6H3) ppm.
Synthesis of [(aIPrPh)2Ag]AgI2 Compound (4). A 50 mL toluene
suspension of 1 (1.00 g, 1.69 mmol) and Ag2O (0.39 g, 1.69 mmol)
was refluxed for 8 h in the dark. Filtration afforded a solution, which
was concentrated to 20 mL and stored at −30 °C. The crystalline solid
was washed with cold toluene (2 × 20 mL) and dried under vacuum to
yield 4 as a light brown solid (0.16 g, 13%). MS (ESI, m/z [M]): 1035
chloropyridine and the resulting reaction mixture was stirred at room
temperature for 1 h. The volatiles were removed under vacuum and
the residue was washed with n-hexane (2 × 10 mL). Drying under
vacuum afforded compound 5 as a yellow solid (0.21 g, 89%). Mp.:
178 °C (dec.). MS (ESI, m/z [M]): 720.2 [M−Cl]+. Elemental
analysis for C38H44N3Cl3Pd (755): calcd. C 60.41, H 5.87, N 5.56;
found C 60.68, H 6.05, N 5.45. 1H NMR (500 MHz, CDCl3, 25 °C): δ
0.75 (d, 6H, J = 6.79 Hz, HCMe2); 0.97 (d, 6H, J = 6.88 Hz, HCMe2);
1.30 (d, 6H, J = 6.77 Hz, HCMe2); 1.73 (d, 6H, J = 6.58 Hz, HCMe2);
2.58 (sept, 2H, J = 6.84 Hz, HCMe2); 3.06 (sept, 2H, J = 6.67 Hz,
HCMe2); 6.85 (d, 2H, o-C6H5), 7.07 (t, 2H, m-C6H5), 7.15 (s, 1H,
NCH), 7.20 (m, 2H, p-C6H5, 3Cl−C5H4N); 7.24 (d, 2H, m-C6H3),
7.29 (d, 2H, m-C6H3) 7.48 (m, 2H, p-C6H3); 7.67 (d, 1H, 3Cl−
C5H4N); 8.88 (d, 1H, 3Cl−C5H4N); 8.99 (d, 1H, 3Cl−C5H4N) ppm.
13C{1H} NMR (125 MHz, CDCl3, 25 °C): δ 22.63, 23.93, 25.92,
1
[M−AgI2]+. H NMR (300 MHz, C6D6, 25 °C): δ 0.83 (pseudo t,
12H, HCMe2); 0.99 (d, 6H, J = 6.91 Hz, HCMe2); 1.41 (d, 6H, J =
6.61 Hz, HCMe2); 2.52 (sept, 2H, J = 6.74 Hz, HCMe2); 2.67 (sept,
2H, J = 6.78 Hz, HCMe2); 6.53 (m, 3H, C6H5); 6.88 (br, 1H, NCH);
6.85 (d, J = 7.56 Hz, 2H, m-C6H3); 6.95 (d, 2H, m-C6H3); 7.03 (t, J =
7.84 Hz, 1H, p-C6H3); 7.12 (t, J = 7.84 Hz, 1H, p-C6H3); 7.16 (br, 2H,
C6H5) ppm.
26.10 (HCMe2), 28.76, 28.96 (HCMe2); 123.63, 124.50, 124.76,
124.94, 125.40 (p-C6H5, 3Cl-C5H4N), 128.26 (NCH), 128.39, 128.43
(m-C6H5), 129.56 (o-C6H5), 130.42, 130.45 (p-C6H5), 130.95, 132.15,
132.24 (p-C6H3), 134.47, 135.95, 137.33 (3Cl-C5H4N), 144.13, 14.91,
145.21, 145.66, 147.70, 149.06, 149.69, 150.76 (ipso-C6H5, ipso-C6H3,
ipso-3Cl-C5NH4) ppm.
Synthesis of (aIPrPh)PdCl2(py) Compound (5). To a 5 mL DCM
solution of 2 (0.20 g, 0.16 mmol) was added 0.2 mL of pyridine and
the resulting reaction mixture was stirred at room temperature for 1 h.
The volatiles were removed under vacuum and the residue was washed
with n-hexane (2 × 10 mL). Drying under vacuum afforded compound
5 as a yellow solid (0.20 g, 90%). Mp.: 193 °C (dec.) MS (ESI, m/z
[M]): 684.3 [M−Cl]+. Elemental analysis for C38H45N3Cl2Pd (721):
Alternative One-Pot Synthesis of (aIPrPh)PdCl2(py) (5) and
(aIPrPh)PdCl2(3Cl-py) (6). To a pyridine suspension of 1 (1.82 g,
3.07 mmol) and PdCl2 (0.55 g, 3.10 mmol) was added Ag2O (0.40 g,
1.72 mmol) in one portion and the resulting reaction mixture was
stirred at 85 °C for 12 h. Removal of the volatiles under vacuum
afforded a pale yellow residue, which was dissolved in 20 mL of DCM
and filtered. The residue obtained after the removal of the volatiles
under vacuum was washed with n-hexane and dried to obtain
compound 5 as a yellow solid. Recrystallization (4 °C, 2 days) from a
mixture of DCM and n-hexane (1:1) solution yielded yellow crystals of
5 (1.70 g, 76%).
1
calcd. C 63.29, H 6.29, N 5.83; found C 62.41, H 6.29, N 5.71. H
NMR (500 MHz, CDCl3, 25 °C): δ 0.74 (d, 6H, J = 6.78 Hz,
HCMe2); 0.97 (d, 6H, J = 6.85 Hz, HCMe2); 1.30 (d, 6H, J = 6.74 Hz,
HCMe2); 1.74 (d, 6H, J = 6.58 Hz, HCMe2); 2.59 (sept, 2H, J = 6.80
Hz, HCMe2); 3.08 (sept, 2H, J = 6.69 Hz, HCMe2); 6.85 (d, J = 7.64
Hz, 2H, o-C6H5); 7.06 (t, J = 7.91 Hz, 2H, m-C6H5); 7.16 (s, 1H,
NCH); 7.19 (t, J = 7.50 Hz, 1H, p-C6H5); 7.21 (m, 4H, m-C6H3, p-
C6H3); 7.28 (d, J = 8.52 Hz, 2H, m-C6H3); 7.47; 7.49 (dt, J = 7.75,
13.04 Hz, 2H, m-C5NH5); 7.66 (tt, J = 1.67, 7.64 Hz, 1H, p-C5NH5);
8.92; 8.93 (dd, J = 1.62, 4.97 Hz, 2H, o-C5NH5) ppm. 13C{1H} NMR
(125 MHz, CDCl3, 25 °C): δ 22.56, 23.94, 25.92, 26.10 (HCMe2),
28.76, 28.87 (HCMe2), 123.71, 124.08 124.72, 124.89 (C6H5, C6H3),
128.30 (NCPd), 128.35 (NCH), 129.55, 129.89 (m-C5NH5), 130.32,
130.35, 130.88, 132.30, 134.55 (C6H5, C6H3), 137.22 (p-C5NH5);
143.98; 145.21, 145.67 (ipso-C6H5, C6H3); 151.69 (o-C5NH5) ppm.
Synthesis of (aIPrPh)PdCl2(3Cl-py) Compound (6). To a 5 mL
DCM solution of 2 (0.20 g, 0.16 mmol) was added 0.2 mL of 3-
Similarly, compound 6 was prepared as a yellow solid in 85% (2.0 g)
yield by using 1 (1.83 g, 3.08 mmol), PdCl2 (0.56 g, 3.23 mmol), and
Ag2O (0.50 g, 2.15 mmol) in 10 mL of 3Cl-py.
Synthesis of (aIPrPh)PdCl(I) (py) (7). To a flask containing a mixture
of 1 (1.00 g, 1.69 mmol), PdCl2 (0.30 g, 1.69 mmol), and K2CO3 (1.5
g) was added 6 mL of pyridine. NMR analysis after 16 h stirring at 85
°C indicated the presence of 20% of the starting material 1. The
resulting mixture was further stirred at 85 °C for 8 h to obtain a yellow
suspension. All the volatiles were removed under vacuum at 50 °C to
yield a pale yellow residue. The residue was extracted with DCM (20
mL). Drying under vacuum afforded a yellow solid, which was washed
E
DOI: 10.1021/acs.organomet.6b00662
Organometallics XXXX, XXX, XXX−XXX

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Table 2. Catalytic Activity of Compounds 2, 5, and 6 in the Suzuki-Miyaura Cross-Coupling Reactions
a
b
3 mol % loading. Conversions were determined by GC/MS analysis (entries 1−13) and 19F NMR spectroscopy (entry 14).
with n-hexane (2 × 20 mL) and dried to obtain compound 7 (91%,
1.25 g) yield. Mp.: 186 °C (dec.). MS (ESI, m/z [M]): 776.2 [M−
Cl]+, 684.3 [M−I]+. Elemental analysis for C38H45N3ClIPd (812):
1H, 3Cl−C5NH4); 7.35−7.44 (m, 2H, C6H3); 7.50−7.55 (m, 1H,
3Cl−C5NH4); 7.88 (d, 1H, 3Cl−C5NH4); 8.87−8.89 (m, 1H, 3Cl−
C5NH4) ppm. 13C{1H} NMR (125 MHz, CDCl3, 25 °C): δ 22.57,
23.95, 25.88, 26.74 (HCMe2), 27.07, 28.82, 28.90 (HCMe2), 123.56,
124.80, 125.14, 125.47, 129.56, 130.41, 130.95, 132.35, 133.32, 134.74,
137.17, 144.89, 145.63, 145.23, 145.68, 149.66, 150.73, 151.26, 152.16,
152.85 (NCHCN, C6H5, C6H3, 3Cl-C5NH4) ppm.
1
calcd. C 56.17, H 5.58, N 5.17; found C 56.17, H 6.04, N 5.21. H
NMR (500 MHz, CDCl3, 25 °C): δ 0.70−0.72 (m, 6H, HCMe2);
0.88−0.96 (m, 6H, HCMe2); 1.26−1.30 (m, 6H, HCMe2); 1.70−1.73
(m, 6H, HCMe2); 2.51−2.59 (m, 2H, HCMe2); 3.02−3.29 (m, 2H,
HCMe2); 6.82−6.85 (m, 2H, C6H5); 7.00−7.04 (m, 2H, C6H5); 7.11−
7.28 (m, 8H, C6H5, C6H3, NCH); 7.42−7.50 (m, 2H, m-C5NH5);
7.58−7.65 (m, 1H, p-C5NH5); 8.85−8.96 (m, 2H, o-C5NH5) ppm.
13C{1H} NMR (75 MHz, CD2Cl2, 25 °C): δ 23.10, 23.14, 24.51, 26.41
(HCMe2), 27.36, 29.58, 29.61, 29.69 (HCMe2), 124.54, 124.82,
124.87, 124.90, 125.60, 125.64, 125.89, 129.10, 129.16, 130.38, 130.43,
130.94, 131.28, 131.73, 133.05, 138.13, 146.03, 146.68, 150.75, 152.33,
153.89, 154.63 (NCHCN, C6H5, C6H3, C5NH5) ppm.
Synthesis of (aIPrPh)PdI2(py) (9). To a flask containing a mixture of
1 (0.67 g, 1.13 mmol), PdCl2 (0.20 g, 1.13 mmol), KI (0.63 g, 3.80
mmol) and K2CO3 (1 g) was added 10 mL of pyridine. The resulting
mixture was stirred at 85−90 °C for 16 h. After usual workup,
compound 9 was isolated as yellow solid in 60% yield. Mp.: 185 °C
(dec.). MS (ESI, m/z [M]): 904.0 [M]+, 776.2 [M−I]+. Elemental
analysis for C38H45N3I2Pd (904): calcd. C 50.46, H 5.02, N 4.65;
found C 50.71, H 5.20, N 4.69. 1H NMR (500 MHz, CDCl3, 25 °C): δ
0.70 (d, J = 6.75 Hz, 6H, HCMe2); 0.87 (d, J = 6.90 Hz, 6H, HCMe2);
1.28 (d, J = 6.78 Hz, 6H, HCMe2); 1.71 (d, J = 6.62 Hz, 6H, HCMe2);
2.54 (sept, J = 6.89 Hz, 2H, HCMe2); 3.25 (sept, J = 6.89 Hz, 2H,
HCMe2); 6.83−7.26 (m, 12H, NCH, C6H5, C6H3); 7.45 (m, 2H, m-
C5NH5); 7.57 (tt, J = 1.69, 7.68 Hz, 1H, p-C5NH5); 8.91 (dt, J = 1.61,
5.02 Hz, 2H, o-C5NH5) ppm. 13C{1H} NMR (125 MHz, CDCl3, 25
°C): δ 22.53, 24.05, 25.82, 26.99 (HCMe2), 28.70, 28.78 (HCMe2),
123.71, 124.02, 124.74, 124.94, 125.35, 128.23, 129.37, 130.29 (C6H5,
C6H3 NCH), 130.36 (m-C5NH5),130.86, 132.03, 133.31 (C6H5,
C6H3), 136.91 (p-C5NH5), 144.73, 145.15, 145.54, 153.81 (o-
C5NH5) ppm.
Synthesis of (aIPrPh)PdCl(I)(3Cl-py) (8). Compound 8 was prepared
as a yellow solid by adopting a similar method as described for 7 using
1 (1.00 g, 1.69 mmol), PdCl2 (0.30 g, 1.69 mmol) and K2CO3 (1.3 g)
in 5 mL of 3-chloropyridine (3Cl-py). Yield found: 1.33 g, 93%. MS
(ESI, m/z [M]): 810.2 [M−Cl]+, 720.2 [M−I]+. Elemental analysis for
C38H44Cl2IN3Pd (847): calcd. C 53.89, H 5.24, N 4.96; found C 53.60,
1
H 5.44, N 4.78. H NMR (500 MHz, CDCl3, 25 °C): δ 0.65 (d, 6H,
HCMe2); 0.81−0.86 (m, 6H, HCMe2); 1.18−1.23 (m, 6H, HCMe2);
1.62−1.66 (m, 6H, HCMe2); 2.48 (q, 2H, HCMe2); 3.03−3.21 (m,
2H, HCMe2); 6.74−6.77 (m, 2H, C6H5); 6.92−7.6.97 (m, 2H, C6H5);
7.05−7.10 (m, 2H, C6H5, NCH); 7.16−7.21 (m, 4H, C6H3), 7.29 (m,
F
DOI: 10.1021/acs.organomet.6b00662
Organometallics XXXX, XXX, XXX−XXX

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Table 3. Crystal Data and Collection Parameters of Compounds 2−4
Compound
CCDC Number
2
3
4
1487623
1494820
1498255
Empirical formula
C68H84Cl8N4Pd2
1453.79
C94H112Cl2N4Pd
1475.17
C40H48AgIN2
791.57
Formula weight [g/mol]
Temperature [K]
100(2)
100(2)
100(2)
Wavelength [Å]
0.71073
0.71073
0.71073
Space group
P1
̅
P21/n
P1
̅
Unit cell dimensions [Å] a
10.282(2)
11.538(2)
15.223(3)
80.14(2)
16.581(2)
12.031(2)
20.983(3)
90
15.240(2)
16.277(2)
17.354(3)
67.82(2)
72.16(2)
89.60(3)
3765.7(11)
4
b
c
α [°]
β [°]
γ [°]
Volume [Å3]
78.85(2)
99.25(2)
83.87(3)
90
1740.6(6)
1
4131.4(11)
2
Z
Absorption coefficient [mm−1
]
0.865
0.336
1.383
F(000)
748
1568
1608
Crystal size [mm3]
0.274 × 0.096 × 0.078
1.380 to 28.255
60420/8524
0.0288
0.190 × 0.140 × 0.090
1.457 to 25.380
108043/7593
0.0707
0.190 × 0.160 × 0.110
1.341 to 25.430
191628/13765
0.0630
Theta range for data collection [°]
Reflections collected/unique
Rint
Completeness
100%
100%
100%
Max. and min transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
0.7457 and 0.7005
8524/1084/582
1.126
0.4288 and 0.3755
7593/918/593
1.041
0.4287/0.3819
13769/729/877
1.095
R1 = 0.0280
wR2 = 0.0591
R1 = 0.0346
wR2 = 0.0624
0.676 and −1.232
R1 = 0.0436
wR2 = 0.1093
R1 = 0.0557
wR2 = 0.1184
1.428 and −0.587
R1 = 0.0411
wR2 = 0.0853
R1 = 0.0557
wR2 = 0.0912
0.936 and −1.132
R indices (all data)
Largest diff. peak and hole (e.Å−3
)
Synthesis of (aIPrPh)PdI2(3Cl-py) (10). Compound 10 was prepared
by employing a similar method as described for 9 using 1 (0.33 g, 0.56
mmol), PdCl2 (0.10 g, 0.56 mmol), KI (0.31 g, 1.87 mmol), and
K2CO3 (1 g) in 5 mL of pyridine. Yield: 0.35 g, 66%. Mp.: 193 °C
(dec.). MS (ESI, m/z [M]): 937.0 [M]+, 812.1 [M−I]+. Elemental
analysis for C38H44N3ClI2Pd (938): calcd. C 48.63, H 4.73, N 4.48;
found C 48.90, H 4.81, N 4.60. 1H NMR (500 MHz, CDCl3, 25 °C): δ
0.72 (d, 6H, J = 6.72 Hz, HCMe2); 0.89 (d, 6H, J = 6.87 Hz, HCMe2);
1.30 (d, 6H, J = 6.73 Hz, HCMe2); 1.72 (d, 6H, J = 6.55 Hz, HCMe2);
2.55 (sept, 2H, J = 6.78 Hz, HCMe2); 3.24 (sept, 2H, J = 6.64 Hz,
HCMe2); 6.83−6.86 (m, 2H, o-C6H5); 7.02 (t, J = 7.95 Hz, 2H, m-
C6H5); 7.13−7.17 (m, 2H, 3Cl−C5NH4); 7.22 (s, 1H, NCH); 7.27 (d,
J = 8.09 Hz, 3H, p-C6H5, m-C6H3); 7.47 (dt, J = 7.75, 10.89 Hz, 2H, p-
C6H3); 7.59 (dd, J = 1.30, 2.31, 8.22 Hz, 1H, 3Cl−C5NH4); 8.86 (dd, J
= 1.36, 5.46 Hz, 1H, 3Cl−C5NH4); 8.95 (d, J = 2.29 Hz, 1H, 3Cl−
C5NH4) ppm. 13C{1H} NMR (125 MHz, CDCl3, 25 °C): δ 22.60,
24.13, 25.90, 27.08 (HCMe2), 28.82, 28.88 (HCMe2), 123.61, 123.76,
124.32 (C6H5), 124.84, 125.48 (C6H3), 128.33 (C6H5), 129.49 (C6H5),
130.41 (p-C6H3), 130.51 (3Cl-C5NH4), 130.97 (p-C6H3), 131.81
(C6H5), 132.07 (C6H3), 133.33 (NCH), 135.73 (NCPd), 137.11 (3Cl-
C5NH4), 144.95 (C6H5), 145.26 (ipso-C6H5), 145.62 (ipso-C6H3);
151.88, 152.85 (3Cl-C5NH4) ppm.
resulting brownish mixture was stirred at room temperature (22 °C).
An aliquot (0.5 mL) of the reaction mixture was removed via a syringe
after 0.5, 2, and 24 h intervals and quenched with 1 mL of water.
Organic contents were extracted with dichloromethane (2 mL), dried
over anhydrous MgSO4, and GC-MS analyzed. The conversion was
determined by GC analysis or NMR spectroscopy.
Single Crystal X-ray Analysis of Compounds 2, 5, 6, 7, and 8.
Suitable single crystals were selected from the mother liquor and
covered with perfluorinated polyether oil on a microscope slide, which
was cooled with a nitrogen gas flow using the X-Temp2 device.26 The
diffraction data of compounds 2, 6, 7, and 8 were collected at 100 K on
a Bruker D8 three circle diffractometer, equipped with a SMART
APEX II CCD detector and an INCOATEC microfocus source (Mo
Kα radiation) with INCOATEC Quazar mirror optics (Tables 3 and
4). The diffraction data of compound 5 were collected at 100 K on a
Bruker D8 three-circle diffractometer, equipped with a SMART APEX
II CCD detector and an INCOATEC microfocus source (Ag Kα
radiation) with INCOATEC Quazar mirror optics. The data were
integrated with SAINT.27 For compound 6, a multiscan absorption
correction with TWINABS28 was applied. For compounds 2, 5, 7, and
8, a multiscan absorption correction with SADABS29 was applied. In
addition, a 3λ-correction in SADABS29 was applied to compounds 2,
7, and 8. The structure solutions were performed with Bruker Intrinsic
Phasing - SHELXT30 and the structure refinement was performed with
SHELXL,31 using the graphical user interface SHELXLE.32 All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were assigned to ideal positions and
refined using a riding model. Their Uiso values were constrained to 1.5
Ueq of their pivot atoms for terminal sp3 carbon atoms and 1.2 times
for all other carbon atoms.
Catalytic Activity. Phenyl boronic acid (Fluka Chemicals), KOtBu
(Merck), 4-chlorotoluene (Merck), 4-bromotoluene (J. T. Baker
Chemicals), 4-iodotoluene (Fluka Chemicals), 2-bromo-1,3-dimethyl-
benzene (Sigma-Aldrich), 1-bromonaphthalene (Sigma-Aldrich), 4-
iodoanisole (Acros Organics), 1-iodo-4-nitrobenzene (Sigma-Aldrich),
and 1-chloro-2-fluorobenzene (TCI Chemicals) were used without
further purification. 2-Propanol (analytical grade, VWR Chemicals)
was degassed by three freeze−pump−thaw cycles prior to use.
Phenyl boronic acid (1.2 mmol), KOtBu (1.5 mmol), and the
precatalyst (2, 5, or 6) were added into a reaction vessel and evacuated
for at least 45 min and then filled with N2. 2-Propanol (6 mL) and 1.0
mmol of the aryl halide were added to the reaction vessel. The
Single Crystal X-ray Analysis of Compounds 9 and 10. Single
crystals suitable for X-ray diffraction measurement were picked,
suspended in a Paratone-N/paraffin oil mixture, mounted on a glass
fiber and transferred onto the goniometer of the diffractometer. The
G
DOI: 10.1021/acs.organomet.6b00662
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Crystal Data and Collection Parameters of Compounds 5−10
Compound
5
6
7
8
9
10
1446057
CCDC Number
1445486
1445487
1445484
1445485
1446056
Empirical formula
C38H45Cl2N3Pd
721.07
C38H44Cl3N3Pd
755.51
C38H45Cl1.06I0.94N3Pd
807.46
C38H44Cl1.74I1.26N3Pd
871.06
C38H45Cl0.15I1.85N3Pd
890.61
C38H44Cl1I2N3Pd
938.41
Formula weight
[g/mol]
Temperature [K]
Wavelength [Å]
Space group
100(2)
0.56086
P21/n
100(2)
100(2)
0.71073
P21/n
100(2)
100.0 (1)
0.71073
100.0 (1)
1.54184
0.71073
0.71073
P1
̅
P1
̅
P1
̅
P1
̅
Unit cell dimensions
[Å] a
9.437(2)
9.537(2)
9.151(3)
9.2685(3)
9.2753(3)
9.630(2)
b
25.014(3)
15.126(2)
90
15.348(2)
24.812(3)
91.36(2)
91.14(2)
99.93(3)
3610.2(10)
4
24.824(3)
15.418(2)
90
11.811(3)
18.420(6)
103.33(2)
96.42(3)
103.24(2)
1857.0(10)
2
11.7625(4)
18.2798(8)
101.143(4)
96.316(4)
102.930(3)
1881.08(14)
2
11.7753(3)
18.6313(5)
102.384(2)
97.461(2)
103.547(2)
1897.19(9)
2
c
α [°]
β [°]
γ [°]
Volume [Å3]
100.00(2)
90
100.47(2)
90
3516.4(10)
4
3589.4(10)
4
Z
Absorption coefficient
0.379
0.766
1.438
1.705
2.053
17.584
[mm−1
]
F(000)
Crystal size [mm3]
1496
1560
1632
871
881.5
924
0.193 × 0.126 × 0.217 × 0.213 ×
0.057
0.280 × 0.079 × 0.068 0.278 × 0.082 × 0.077 0.222 × 0.162 × 0.126 0.24 × 0.033 ×
0.117
0.02
Theta range for data
1.256 to 20.556
1.347 to 28.307
1.574 to 29.044
187613/9067
1.154 to 26.664
54131/7826
1.823 to 29.999
110480/10943
2.473 to 71.996
68190/7465
collection [°]
Reflections collected/
unique
75942/7228
−/17928 (2 twin
domains)
Rint
0.0834
100.0%
− (merged)
100.0%
0.0323
0.0401
0.0359
0.0522
Completeness
100.0%
100.0%
99.8%
100.0%
Max. and min
transmission
0.4254 and
0.3871
0.4311 and
0.34956
0.7458 and 0.6777
0.7454 and 0.6573
0.859 and 0.709
0.726 and 0.136
Data/restraints/
parameters
Goodness-of-fit on F2
7228/0/406
17928/0/828
9067/7/413
7826/6/422
10943/1/409
7465/0/414
1.022
1.195
1.199
1.102
1.106
1.036
Final R indices [I >
R1 = 0.0385,
wR2 = 0.0839.
R1 = 0.0596,
wR2 = 0.0913
R1 = 0.0507
wR2 = 0.1319
R1 = 0.0543,
wR2 = 0.1335
R1 = 0.0227
wR2 = 0.0508
R1 = 0.0247
wR2 = 0.0514
R1 = 0.0280,
wR2 = 0.0614
R1 = 0.0343
wR2 = 0.0641
0.765 and −0.549
R1 = 0.0279
wR2 = 0.0706
R1 = 0.0307
wR2 = 0.0720
2.945 and −0.868
R1 = 0.0295
wR2 = 0.0776
R1 = 0.0327
wR2 = 0.0800
1.387 and −0.607
2sigma(I)]
R indices (all data)
Largest diff. peak and
1.783 and
−0.793
2.051 and −1.110 0.568 and −0.506
hole (e.Å−3
)
crystals were kept at 100 K during data collection. The measurement
of 9 was carried out with Mo Kα radiation (λ = 0.71073 Å) on a
SuperNova, single source at offset, Eos diffractometer. The data
collection of 10 was carried out with Cu Kα radiation (λ = 1.5418 Å)
on a SuperNova, Dual, Cu at zero, Atlas diffractometer (Table 4).
Using Olex233 the structures were solved by direct methods and
refined by full-matrix least-squares cycles with SHELXL.31 Hydrogen
atoms were refined using a riding model with U(H) = 1.5 Ueq for CH3
groups and U(H) = 1.2 Ueq for all others.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00662.
■
S
NMR plots of compounds 2−10 and Structure reports
for 2−10 (PDF)
Crystallographic data for 2 (CIF)
Crystallographic data for 3 (CIF)
Crystallographic data for 4 (CIF)
Crystallographic data for 5 (CIF)
Crystallographic data for 6 (CIF)
Crystallographic data for 7 (CIF)
Crystallographic data for 8 (CIF)
Crystallographic data for 9 (CIF)
Crystallographic data for 10 (CIF)
CONCLUSION
■
In conclusion, high-yield rational synthesis routes to palladium-
(II) complexes 2, 3, and 5−10 featuring an 1,3-imidazole
derived aNHC ligand have been described. All complexes have
been fully characterized by NMR spectroscopy and mass
spectrometry studies. Molecular structures of 2−10 have been
determined by single crystal X-ray diffraction analyses.
Preliminary investigations on the catalytic activity of three
representative compounds 2, 5, and 6 for the Suzuki-Miyaura
cross-coupling reactions are presented. Compounds 2 and 6 are
highly active catalysts and afford biaryls in a good to excellent
yield at room temperature.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rghadwal@uni-bielefeld.de. Tel: +49-521-106-6167.
Fax: +49-521-106-6026.
■
Notes
The authors declare no competing financial interest.
H
DOI: 10.1021/acs.organomet.6b00662
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ACKNOWLEDGMENTS
■
Funding from the Deutsche Forschungsgemeinschaft (DFG) is
gratefully acknowledged (GH 129/4-1). We are thankful to
Professor Norbert W. Mitzel for his generous support.
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DOI: 10.1021/acs.organomet.6b00662
Organometallics XXXX, XXX, XXX−XXX