Synthesis, Palladium(II) Complexes, and Catalytic Use of a Phosphanylferrocene Ligand Bearing a Guanidinium Pendant

Article abstract of DOI:10.1002/ejic.201601262

A polar phosphanylferrocene donor equipped with a hydrophilic guanidinium pendant, Ph₂PfcCH₂NHC(NH)NH₂·HCl (1·HCl; fc = ferrocene-1,1′-diyl), has been prepared from the corresponding amine hydrochloride, Ph₂PfcCH₂NH₂·HCl (2·HCl), and studied as a ligand for Pd^II. The reactions of 1·HCl with [PdCl₂(MeCN)₂] in 1:1 and 1:2 Pd/ligand ratios led to an unexpected zwitterionic complex, [PdCl₃(1H-κP)] (3), and the expected bis(phosphane) complex, trans-[PdCl₂(1H-κP)₂]Cl₂(4), which were structurally characterized. The defined and air-stable solvated complex 3·Me₂CO and the in situ generated Pd(OAc)₂/1·HCl system were found to be active catalysts for the Suzuki–Miyaura cross-coupling of anionic triolborates with aryl bromides, giving the corresponding biphenyls. These reactions, which do not require the presence of an additional base, were advantageously performed in aqueous ethanol, and the coupling products were isolated in good to excellent yields.

Full text of DOI:10.1002/ejic.201601262

A Journal of
Accepted Article
Title: Synthesis, Palladium(II) Complexes and Catalytic Use of a Phosphanylferroce-
ne Ligand Bearing a Guanidinium Pendant
Authors: Ondrej Barta; Ivana Cisarova; Petr Stepnicka
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201601262
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European Journal of Inorganic Chemistry
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Synthesis, Palladium(II) Complexes and Catalytic Use of
a Phosphanylferrocene Ligand Bearing a Guanidinium Pendant
Ondřej Bárta,[a] Ivana Císařová,[a] Petr Štěpnička*[a]
Abstract: A polar phosphanylferrocene donor equipped with a
hydrophilic guanidinium pendant, Ph2PfcCH2NHC(NH)NH2·HCl
(1·HCl; fc
=
ferrocene-1,1’-diyl), was prepared from the
corresponding amine hydrochloride, Ph2PfcCH2NH2·HCl (2·HCl),
and was studied as a ligand for Pd(II) ions. The reactions of 1·HCl
with [PdCl2(MeCN)2] at 1:1 and 1:2 Pd-to-ligand ratios led to an
unexpected zwitterionic complex, [PdCl3(1H-κP)] (3), and the usual
bis-phosphane complex, trans-[PdCl2(1H-κP)2]Cl2 (4), which were
structurally characterized. The defined and air-stable solvated
complex 3·Me2CO and an in situ generated Pd(OAc)2/1·HCl system
afforded active catalysts for the Suzuki-Miyaura cross-coupling of
anionic triolborates with aryl bromides to give the corresponding
biphenyls. This reaction, which does not require the presence of an
additional base, was advantageously performed in aqueous ethanol,
and the coupling products were isolated in good to excellent yields.
Scheme 1. Examples of phosphanylferrocene donors bearing urea and
guanidinium pendants and the newly designed compound 1·HCl.
In this contribution, we report another polar donor related to the
B-type compounds, the phosphanyl guanidinium salt 1 (Scheme
1), wherein the phosphanylferrocene unit and the hydrophilic
guanidinium moiety are connected by a flexible methylene linker.
Furthermore, we describe Pd(II) complexes prepared with this
new functional phosphane and their use in the Pd-catalyzed
Suzuki-Miyaura cross-coupling of anionic arylborates with aryl
bromides in aqueous solvents.
Introduction
Ferrocene phosphanes are frequently used as supporting
ligands for various metal-mediated organic transformations.[ 1 ]
However, their use in green aqueous reaction media[ 2 ] is
compromised by their generally high hydrophobicity. Few
examples of water-soluble phosphanylferrocene ligands have
appeared in the literature,[3] which prompted us to prepare and
study ferrocene phosphanes modified by hydrophilic polar
substituents. During our investigations, we have mainly focused
Notably, N-(ferrocenylmethyl)guanidines are not unprecedented
but have been studied predominantly with respect to their
10
]
supramolecular complexation ability.[
The application of
guanidinium moieties in the design of hydrophilic ferrocene
donors remains largely unexplored, in contrast with reports
addressing the preparation and catalytic application of water-
soluble phosphane ligands bearing guanidinium substituents on
their organic backbone.[11]
on functional phosphanylamides[
derived from 1’-
4
]
(diphenylphosphanyl)ferrocene-1-carboxylic acid (Hdpf)[ 5 ] and
amines bearing polar terminal substituents.[6] In continuation of
these studies, we recently expanded the palette of polar
modifying groups and prepared ferrocene-based donors with
amide substituents bearing neutral urea[
or cationic
7
, 8 ]
guanidinium[9] moieties in their terminal positions (compounds A-
C in Scheme 1), which were evaluated in Pd-catalyzed reactions
performed in aqueous reaction media.
Results and Discussion
Synthesis of phosphane 1·HCl
The target phosphanylguanidine hydrochloride 1·HCl was
prepared (Scheme 2) by the direct guanylation of 1’-
(diphenylphosphanyl)-1-(aminomethyl)ferrocene (2), which was
generated in situ from its hydrochloride[7b] and triethylamine, with
1H-pyrazole-1-carboximidamide hydrochloride[12,13] in dry THF.
The compound was obtained as
a yellow-orange, non-
[a]
O. Bárta, Dr. I. Císařová, Prof. Dr. P. Štěpnička
Department of Inorganic Chemistry
Faculty of Science, Charles University
Hlavova 2030, 128 40 Prague
Czech Republic
crystallizing solid in 93% yield after the removal of precipitated
triethylamine hydrochloride and column chromatography.
E-mail: stepnic@natur.cuni.cz
WWW: http://www.natur.cuni.cz/
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
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Scheme 2. Synthesis of 1HCl.
Phosphane 1HCl was characterized by multinuclear NMR
spectroscopy, IR spectroscopy and mass spectrometry. Reliable
microanalytical data were not obtained, presumably due to the
presence of residual solvent in the amorphous material. The 1H,
31P and 13C NMR spectra of 1HCl exhibited signals of the
phosphanylferrocene moiety within the usual ranges. The 13C
NMR signal of the guanidinium unit was observed at δC 156.49,
while the methylene linking group resonated at δH 3.93 (NH-
coupled doublet) and δC 39.56. The electrospray ionization (ESI)
mass spectrum revealed ions attributable to [1H]+ (m/z 442) and
the corresponding phosphane oxide (m/z 458). A further peak in
the ESI MS spectrum at m/z 383 was assigned to the [1-
(diphenylphosphanyl)ferrocenyl]methylium cation, [Ph2PfcCH2]+
(or an isomeric species resulting from a rearrangement), in
accordance with the relatively easy formation of stabilized
ferrocenylmethylium cations.[14 , 15 ] Finally, the IR spectrum of
1HCl showed absorptions typical of the guanidinium moiety,
namely, broad structured bands in the ranges of 2800-3500 cm1
(N-H stretching modes) and 1550-1750 cm1 (N-H bending and
C-N stretching vibrations).[16]
Scheme 3. Preparation of Pd(II) complexes 3 and 4.
The coordination environment of the Pd(II) ion in 3Me2CO is
essentially planar[17] (see Figure 1 and Table 1). However, the
Pd-Cl3 bond located trans to the phosphane donor is
significantly longer that the two remaining Pd-Cl bonds, which
corresponds to a greater trans-influence[18] of the phosphane
donor [P > Cl]. Similarly, the Pd-P bond in 3·Me2CO is shortened
with respect to the Pd-P bond in the bis-phosphane complex 4
(see below).[19]
The ferrocene unit in 3·Me2CO adopts regular geometry with
marginally varying Fe-C distances (2.043(2)-2.053(2) Å). Its
cyclopentadienyls are mutually tilted by 3.6(1)° and assume an
anticlinal eclipsed conformation,[20] which shifts the guanidinium
unit away from the P-bound metal center. The protonated
guanidine moiety is symmetrical and extensively delocalized,
showing similar N-C distances (N.B. the bonds to the terminal
nitrogens are only approximately 0.01 Å shorter than N1-C24)[21]
and N-C-N angles that do not depart much from the ideal 120°.
Pd(II) complexes with 1·HCl as a P-donor
In view of the anticipated catalytic application, compound 1HCl
was studied as a ligand in Pd(II) complexes (Scheme 3). The
reaction of [PdCl2(MeCN)2] with 1HCl at a 1:1 molar ratio
produced a red precipitate, which was insoluble in common
organic solvents and was thus difficult to purify and analyze.
Nonetheless, when the synthesis was performed using
a
reactive diffusion approach (i.e., when a methanol solution of the
ligand was allowed to diffuse into an acetone solution of the
palladium precursor), it produced an orange-red crystalline solid,
which was identified by X-ray diffraction analysis as the relatively
unusual zwitterionic complex 3, in which the protonated
phosphanylguanidine coordinates as a P-donor, whereas its
associated chloride counteranion binds to palladium, forming a
–
negatively charged PdCl3 fragment. The compound separates
in the form of the defined stoichiometric solvate 3Me2CO.
When the amount of the phosphane was increased to 2 equiv.,
the reaction afforded the expected bis-phosphane complex 4
(Scheme 3). The coordination of the phosphane moieties and
the structural differences between these complexes were clearly
manifested in the 31P NMR spectra. While the 31P NMR signal of
the free ligand was observed at δP 17.5, those of 3Me2CO and
4 were shifted to δP 24.7 and 17.1, respectively.
Figure 1. PLATON plot of the complex molecule in the structure of 3·Me2CO.
Displacement ellipsoids are scaled to the 30% probability level.
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European Journal of Inorganic Chemistry
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Table 1. Selected geometric parameters for 3·Me2CO.[a,b]
crystallographic inversion centers (space group P–1) and thus
with only the half of the molecule structurally independent. The
guanidinium groups are directed away from the Pd center (see
parameter τ in Table 2), giving rise to hydrophilic layers that
accommodate disordered chloride anions and solvating water
molecules.[22] Solvating methanol also occupies this space but is
fixed in position, serving as a hydrogen bond acceptor to one of
the guanidinium NH groups (N3-H5N···O1S hydrogen bond with
N···O distance of 2.880(3) Å).
Distances
2.3849(6)
Angles
Pd-Cl1
Pd-Cl2
Pd-Cl3
Pd-P
Cl1-Pd-Cl2
Cl1-Pd-Cl3
P-Pd-Cl2
P-Pd-Cl3
N1-C24-N2
N1-C24-N3
N2-C24-N3
C1-C11-N1
tilt
89.03(2)
89.44(2)
92.65(2)
89.13(2)
118.4(2)
121.2(2)
120.4(2)
114.6(2)
3.6(1)
2.3083(5)
2.3170(5)
2.2430(6)
1.335(3)
1.324(3)
1.325(3)
1.457(3)
1.653(1)
1.653(1)
C24-N1
C24-N2
C24-N3
C11-N1
Fe-Cg1
Fe-Cg2
τ
143.3(2)
[a] Definitions: Cg1 and Cg2 are the centroids of the cyclopentadienyl rings
C(1-5) and C(6-10), respectively. Tilt is the dihedral angle subtended by the
least-squares cyclopentadienyl planes, while τ is the torsion angle C1-Cg1-
Cg2-C6. [b] Further data: C1S=O1S = 1.211(4) Å (solvating acetone).
The molecules constituting the structure of 3Me2CO assemble
into compact infinite chains oriented along the crystallographic a
axis by means of N-H···Cl hydrogen bonds (Figure 2). Whereas
the Cl1 and Cl2 atoms form such interactions with only one NH
proton, Cl3 acts as a bifurcate H-bond acceptor (the N···Cl
distances in the range of 3.232(2)-2.320(2) Å). The remaining
NH moiety (N3-H5N) forms a hydrogen bridge toward the
solvating acetone (N3···O1S = 2.882(3) Å).
Figure 3. PLATON plot of the complex molecule in the structure of
4·2MeOH·2H2O. The prime-labeled atoms are generated by crystallographic
inversion. Displacement ellipsoids enclose the 30% probability level.
Overall, the geometry of the complex molecule (Table 2)
resembles that of the analogous compounds resulting from other
1’-functionalized phosphanylferrocene donors, [PdCl2(Ph2PfcX-
κP)2] (fc = ferrocene-1,1’-diyl).[6a-c,23] Because of the imposed
symmetry, the coordination environment of the Pd(II) ion is
ideally planar but the interligand angles differ slightly from the
ideal 90° due to steric reasons. The protonated guanidine units
are planar (within ca. 0.01 Å) and display nearly identical N-C
distances. Similarly to the mono-phosphane complex 3·Me2CO,
the N1-C24-N3 angle in the structure of 4·2MeOH·2H2O is the
most opened among the N-C24-N angles, reflecting the
presence of the connecting methylene group, which is
positioned syn with respect to N3. The guanidine plane is
directed away from the ferrocene unit and subtends a dihedral
angle of 77.15(7)° with the cyclopentadienyl ring C(1-5).
Table 2. Selected geometric parameters for 4·2MeOH·2H2O.[a]
Figure 2. Section of the infinite, one-dimensional hydrogen-bonded array in
the crystal structure of 3·Me2CO. The hydrogen bonds are shown as dashed
lines. For clarity, only the NH hydrogens and pivotal carbons from the phenyl
rings are shown.
Distances
2.3008(4)
Angles
87.66(1)[b]
Pd-Cl1
Pd-P
P-Pd-Cl1
P-Pd-Cl1’
N1-C24-N2
2.3442(4)
1.329(2)
92.34(1)[b]
118.5(2)
The bis-phosphane complex crystallizes in solvated form
C24-N1
4·2MeOH·2H2O (Figure 4) with the Pd atoms residing on the
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European Journal of Inorganic Chemistry
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C24-N2
C24-N3
C11-N1
Fe-Cg1
Fe-Cg2
1.334(2)
1.330(3)
1.473(2)
1.6443(8)
1.6458(8)
N1-C24-N3
N2-C24-N3
C1-C11-N1
tilt
122.1(2)
119.5(2)
111.6(2)
1.8(1)
Table 3. The optimization experiments.[a]
Conversion[b] (Isolated Yield) of 7bc [%]
Solvent
Pd(OAc)2/1HCl
100 (87)
3
ethanol
100 (80)
100 (89)
100 (78)
100 (72)
τ
–142.0(1)
ethanol/water (1:1)
water
100 (87)
100 (79)
[a] The parameters are defined as for 3·Me2CO. See footnote [a] in Table 1.
[b] The angles P-Pd-Cl1 and P-Pd-Cl1’ sum up to 180° due to imposed
symmetry.
toluene/water (1:1)
100 (72)
[a] Borate 5b (1.1 mmol) and aryl bromide 6c (1.0 mmol) were reacted in the
presence of 0.5 mol.% catalyst (generated in situ from Pd(OAc)2 and 1.1
molar equiv. of 1HCl or complex 3) in 5 mL of the solvent at 50 ºC for 24 h.
The quoted conversions and yields are averages of two independent runs.
[b] The conversions were determined by integration of 1H NMR spectra.
Catalytic evaluation
Suzuki-Miyaura cross-coupling, one of the most widely used
cross-coupling reaction, has numerous practical applications in
common laboratory practice and large-scale preparations.[24] As
a part of continuous development, anionic aryltriolborates[25]
—
air-stable boron reagents[26,27] that undergo the coupling reaction
without an added base and can be utilized in aqueous reaction
media—have recently been introduced. With the new hydrophilic
ligand 1·HCl in hands, we decided to use these reagents and
study their reactions mediated by Pd-1 complexes in organic
solvents and their aqueous mixtures.[28]
The initial screening experiments were performed for the
reaction of borate 5b with 4-bromoanisole (6c) to give 4-methyl-
4’-methoxybiphenyl (7bc; Scheme 4) using different solvents
and catalysts. In all cases, a slight excess of the borate was
used (1.1 equiv.) and the concentration of the reaction
components was kept constant (0.2 M for aryl halide). As shown
in Table 3, the reactions performed at 50 ºC and with 0.5 mol.%
of the defined (complex 3·Me2CO) or in situ generated
(Pd(OAc)2/1HCl) pre-catalyst proceeded with complete
conversion within 24 h, irrespective of the solvent used. The
isolated yields of 7bc were satisfactory (above 70%), especially
when ethanol and its 1:1 aqueous mixture were used as the
reaction solvent.
Considering the negligible differences in the reaction yields
achieved with both tested catalysts at 0.5 mol.% Pd loading, the
following experiments were carried out only with the defined and
easy-to-handle solvated complex 3. When the model coupling
reaction was conducted with this pre-catalyst at 80 °C in
aqueous ethanol, complete conversion to 7bc was achieved
within 3 h, and this outcome did not change after decreasing the
catalyst loading to 0.2 mol.% (Note: similar biaryl coupling
reactions described in the original article[25] reporting the use of
anionic triolborates were performed in the presence of 3 mol.%
of Pd(OAc)2 and 6.6 mol.% of supporting phosphine albeit at
20 °C).
In view of the screening results, the following reaction scope
tests (Scheme 5) were performed in the presence of 0.2 mol.%
3·Me2CO in 50% aqueous ethanol at 80 °C for 3 h. The results
given in Table 4 indicate that changing the substituents in the
boronate and aryl bromide has a marginal influence under the
given reaction conditions. Substrates with both electron-donating
and electron-withdrawing substituents reacted efficiently,
affording the coupling products in full or nearly complete
conversion and with good isolated yield. The lowest, but still very
good, conversion of 92%, achieved in the reaction of 4-tolyl
boronate 5b with 1-bromo-4-nitrobenzene (6h), can be
explained by the lower solubility of the aryl halide in the reaction
mixture.
Scheme 4. The coupling reaction used to screen the reaction conditions.
Scheme 5. Reaction scope tests [X/Y = H (a), Me (b), MeO (c), Ph (d), CF3
(e), F (f), Cl (g), NO2 (h), and CN (i)].
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The NMR spectra were measured at 25 ºC with a Varian INOVA 400
spectrometer operating at 399.95, 100.58, 376.29 and 161.90 MHz for 1H,
13C, 19F and 31P, respectively. The chemical shifts (δ in ppm) are given
relative to an internal tetramethylsilane (1H and 13C), external neat CFCl3
(19F) and external 85% aqueous H3PO4 (31P). In addition to the usual
description of signal multiplicity, vt and vq are used to denote virtual
multiplets due to the magnetically non-equivalent protons at the
cyclopentadienyl rings (spin systems AA’BB’ and AA’BB’X for the
methylene- and phosphanyl-substituted rings, respectively, where A, B =
1H, and X = 31P). IR spectra were recorded in Nujol mulls on a Nicolet
6700 FTIR spectrometer over the range of 400-4000 cm1. ESI+ MS
spectra were obtained with a Bruker Esquire 3000 spectrometer for
samples dissolved in HPLC-grade methanol. ESI– MS spectra including
the high-resolution (HR) measurements were performed with a LTQ
Orbitrap XL (Thermo Fisher Scientific) instrument. Elemental analyses
were determined with a Perkin-Elmer 2400 Series II CHNS/O analyzer.
The presence of residual solvent (if any) was confirmed by NMR analysis.
Table 4. Summary of the reaction scope tests.[a]
Boronate 5
Bromide 6
Product 7
Conversion (Yield)[b] [%]
5b (4-Me)
5b (4-Me)
5b (4-Me)
5b (4-Me)
5b (4-Me)
5b (4-Me)
5a (4-H)
6b (4-Me)
6c (4-MeO)
6e (4-CF3)
6g (4-Cl)
7bb
7bc
7be
7bg
7bh
7bi
100 (90)
100 (90)
100 (83)
100 (89)
92 (85)
6h (4-NO2)
6i (4-CN)
100 (88)
98 (89)
6c (4-MeO)
6c (4-MeO)
6c (4-MeO)
7ac
7cd
7cf
Synthesis of 1HCl. Compound 2HCl (871 mg, 2.0 mmol) and
commercial 1H-pyrazole-1-carboxamidine hydrochloride (322 mg,
2.2 mmol) were mixed in dry THF (30 mL). Anhydrous triethylamine (0.59
mL, 4.2 mmol) was added, and the reaction mixture was stirred at room
temperature overnight. The resulting mixture was filtered to remove
precipitated triethylammonium chloride, and the orange filtrate was
evaporated under vacuum. The crude orange oily product was purified by
column chromatography using silica gel and dichloromethane-methanol
(10:1) as the eluent. The first minor band was discarded. The following
(major) band was collected, evaporated and the residue was
chromatographed again over a short silica gel column with ethyl acetate-
methanol (4:1). Following evaporation, hydrochloride 1HCl was isolated
as a yellow-orange glassy solid. Yield: 893 mg (93%).
5d (4-Ph)
5f (4-F)
94 (71)
100 (89)
[a] The corresponding borate 5 (1.1 mmol) and aryl bromide 6 (1.0 mmol)
were reacted in the presence of 0.2 mol.% of complex 3 in 5 mL of ethanol-
water (1:1 v/v) at 80 ºC for 3 h. The quoted data are averages of two
independent runs. [b] The conversions were determined by integration of 1H
NMR spectra.
1H NMR (DMSO-d6): δ = 3.93 (d, JHH = 5.6 Hz, 2 H, CH2), 3.98 (vt,
3
Conclusions
J′ = 1.8 Hz, 2 H, fc), 4.12 (vq, J′ = 1.9 Hz, 2 H, fc), 4.17 (vt, J′ = 1.9 Hz, 2
H, fc), 4.51 (vt, J′ = 1.7 Hz, 2 H, fc), 7.28-7.41 (m, 10 H, Ph), 7.81 (t, 3JHH
= 5.6 Hz, 1 H, CH2NH) ppm. 13C{1H} NMR (DMSO-d6): δ = 39.56 (s, CH2),
68.84 (s, CH of fc), 69.05 (s, CH of fc), 71.73 (d, JPC = 4 Hz, CH of fc),
A new polar phosphanylferrocene donor bearing a cationic
guanidinium substituent at the other cyclopentadienyl ring
connected through a methylene spacer can be easily prepared
from the corresponding amine and isolated as the stable
chloride salt 1·HCl. This compound coordinates Pd(II) ions as a
simple phosphane, affording the zwitterionic complex [PdCl3(1H-
κP)] (3) or the usual bis-phosphane complex trans-[PdCl2(1H-
κP)2]Cl2 (4), depending on the Pd-to-ligand ratio. Both the
defined complex 3 and a simple catalyst generated in situ from
palladium(II) acetate and 1·HCl efficiently mediate the “base-free”
coupling of aryl boronate reagents with aryl bromides to afford
biphenyls in aqueous solvents.
1
73.10 (d, JPC = 15 Hz, CH of fc), 75.70 (d, JPC = 7 Hz, C-PPh2 of fc),
84.10 (s, C-CH2 of fc), 128.18 (d, 2JPC = 7 Hz, CHortho of PPh2), 128.50 (s,
3
CHpara of PPh2), 132.91 (d, JPC = 20 Hz, CHmeta of PPh2), 138.61 (d,
1JPC = 10 Hz, Cipso of PPh2), 156.49 (s, guanidinium Cipso) ppm. 31P{1H}
NMR (DMSO-d6): δ = –17.5 (s) ppm. IR (Nujol): ν = 3296 s, 3238 s, 3133
s, 3057 s, 2725 w, 2670 w, 1648 s, 1609 s, 1560 w, 1433 m, 1414 w,
1338 m, 1304 w, 1238 w, 1197 w, 1159 m, 1088 w, 1039 w, 1026 m, 844
w, 832 m, 746 s, 696 s, 580 m, 511 w, 496 s, 487 sh, 451 m cm–1. ESI+
MS: m/z
=
383 (dominant, [Ph2PfcCH2]+), 442 ([1H]+), 458
([Ph2P(O)fcCH2NHC(NH2)2]+). ESI– MS: m/z = 476 ([1 + Cl]–), 512
([1·HCl + Cl]–). HR MS calc. for C24H24ClFeN3P ([1 + Cl]–): 476.0751,
found: 476.0743.
Preparation of 3Me2CO. [PdCl2(CH3CN)2] (25.9 mg, 0.10 mmol) was
dissolved in dry acetone (5 mL), and the solution was filtered through a
PTFE syringe filter (pore size 0.45 μm) into a test tube. A solution of 1
(47.8 mg, 0.10 mmol) in anhydrous methanol (5 mL) was carefully added
as a top layer, and the sealed test tube was set aside for crystallization
by liquid-phase diffusion. The red crystals that separated during 2 d (the
solution was nearly colorless) were filtered off, washed with cold acetone
and pentane, and dried under vacuum to give analytically pure 3Me2CO
as a deep red crystalline solid. Yield: 52.1 mg (79%).
Experimental Section
Materials and methods. All syntheses were performed under argon
using standard Schlenk techniques and with the protection from the
direct daylight. Compound 2HCl was prepared according to the
literature.[7b] Tetrahydrofuran and methanol were dried by PureSolv MD5
(Innovative Technology, USA) solvent purification system. Acetone was
dried with anhydrous potassium carbonate and then distilled under argon.
Toluene and triethylamine were dried by standing over sodium metal and
distilled. Other chemicals and solvents (Lach-Ner, Czech Republic) were
used without additional purification.
3
1H NMR (DMSO-d6): δ = 2.09 (s, 6 H, Me2CO), 4.51 (d, JHH = 5.7 Hz, 2
H, CH2), 4.55 (vq, J′ = 1.9 Hz, 2 H, fc), 4.61 (vt, J′ = 1.8 Hz, 2 H, fc), 4.64
(vq, J′ = 1.6 Hz, 2 H, fc), 4.80 (vt, J′ = 1.8 Hz, 2 H, fc), 7.40-7.52 (m, 10 H,
Ph), 7.60 (t, 3JHH = 6.0 Hz, 1 H, CH2NH) ppm. 31P{1H} NMR (DMSO-d6): δ
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= 24.7 (s). IR (Nujol): ν = 3368 s, 3301 s, 3261 s, 3191 s, 3079 m, 2725
w, 1702 s, 1670 s, 1648 s, 1617 s, 1589 m, 1435 m, 1404 w, 1366 m,
1327 m, 1305 w, 1233 m, 1193 w, 1170 m, 1095 m, 1041 w, 1032 m,
1024 sh, 846 w, 828 w, 750 s, 710 m, 690 s, 635 w, 620 w, 549 m, 525 s,
Bruker D8 VENTURE Kappa Duo diffractometer with a PHOTON100
detector (4·2MeOH·2H2O) at 150(2) K. The data were corrected for
absorption using methods included in the diffractometer software.
496 s, 473
m . ESI+ MS: m/z =
cm–1 383 ([Ph2PfcCH2]+), 546
Both structures were solved by direct methods and were refined by full-
matrix least-squares based on F2 (SHELXL97 and SHELX-2014).[29] All
non-hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms residing on the N and O atoms were
identified on the difference electron density maps and were refined as
riding atoms with Uiso(H) assigned to 1.2Ueq of their bonding N/O atom.
Hydrogen atoms bonded to carbon atoms were placed in their calculated
positions and similarly refined. The solvating water molecules and
chloride anions in the structure of 4·2MeOH·2H2O were disordered within
([Pd{Ph2PfcCH2(CH3N3)}]+), 582 ([PdCl{Ph2PfcCH2NHC(NH)NH2}]+).
ESI– MS: m/z = 654 ([3 – H]–). HRMS calc. for C24H24Cl3FeNPPd ([3 –
H]–):
651.9163,
found:
651.9148
(monoisotopic).
C24H25Cl3FeN3PPdMe2CO (713.15): C 45.47, H 4.38, N 5.89%; found: C
45.20, H 4.73, N 5.70%.
Preparation of trans-[PdCl2(1-κP)2]2HCl (4). [PdCl2(CH3CN)2] (13.0 mg,
0.050 mmol) and 1HCl (47.8 mg, 0.10 mmol) were dissolved in dry
methanol (5 mL) to give a red solution, which was stirred for 1 h and
partially evaporated on a rotary evaporator. Methyl tert-butyl ether was
added (ca. 8 mL), causing the product to separate as a red solid. The
precipitate was filtered off, washed with methyl tert-butyl ether, and dried
under vacuum to afford solvated complex 5 as a red-brown solid. Yield:
52.3 mg (91%).
channels
defined
by
the
bulky
complex
cations
[PdCl2{Ph2PfcCH2NHC(NH2)2}2]2+ and were refined over two equally
populated positions (50:50). The water molecules were modelled only as
isolated oxygen atoms because the OH hydrogens could not be
unequivocally located on the difference electron density maps. Selected
crystallographic data and refinement parameters are given in Table 5.
3
1H NMR (DMSO-d6): δ = 4.08 (d, JHH = 5.9 Hz, 2 H, CH2), 4.47 (vt, J′ =
A recent version of the PLATON program[30] was used for the graphical
representation of the structures and all geometric calculations. The
numeric values are rounded with respect to their estimated deviations
(ESDs) given to one decimal place. Parameters pertaining to atoms in
constrained positions are given without ESDs.
1.8 Hz, 2 H, fc), 4.50 (br s, 2 H, fc), 4.54 (vt, J′ = 1.8 Hz, 2 H, fc), 4.64 (vt,
3
J′ = 1.8 Hz, 2 H, fc), 7.40-7.59 (m, 10 H, Ph), 7.85 (t, JHH = 5.8 Hz, 1 H,
CH2NH) ppm. 31P{1H} NMR (DMSO-d6): δ = 17.1 (s) ppm. IR (Nujol): ν =
3308 s, 3132 s, 3049 s, 2725 w, 2671 w, 1663 s, 1648 s, 1620 s, 1436 m,
1341 w, 1303 w, 1266 w, 1195 w, 1164 m, 1098 m, 1072 w, 1029 m, 999
w, 838 m, 746 m, 709 w, 694 s, 570 w, 539 m, 516 m, 498 s, 474 m cm–1
.
ESI+
MS:
m/z
=
546
([Pd{Ph2PfcCH2(CH3N3)}]+),
582
([PdCl{Ph2PfcCH2NHC(NH)NH2}]+), 987 ([4 – 3HCl – Cl]+), 1023 ([4 –
2HCl – Cl]+). ESI– MS: m/z = 1131 ([4 – H]–), 1167 ([4 + Cl]–). HR MS
calc. for C48H49Cl4Fe2N6P2Pd ([4 – H]–): 1128.9987, found: 1128.9978
(monoisotopic). C48H50Cl4Fe2N6P2PdMeOH·2H2O (1200.9): C 49.01,
H 4.87, N 7.00%; found: C 49.10, H 4.56, N 6.95%.
Table 5. Crystal data and refinement parameters for the crystal structures of
3·Me2CO and 4·2MeOH·2H2O.
Parameter
Formula
3·Me2CO
C27H31Cl3FeN3OPPd
713.12
4·2MeOH·2H2O
C50H58Cl4Fe2N6O4P2Pd
1228.86
General procedure for the catalytic experiments. An oven-dried
Schlenk tube was charged with the respective aryl bromide (1.0 mmol),
borate (1.1 mmol) and catalyst (0.2 or 0.5 mol.% Pd(OAc)2/1HCl (1.1
equiv.) or complex 3). A stirring bar was inserted, and the reaction flask
was flushed with argon and sealed with a rubber septum. Then, the
solvent was introduced (5 mL), and the reaction vessel was transferred to
an oil bath maintained at 50 or 80 ºC and stirred for 3 or 24 h. The
reaction mixture was diluted with water (5 mL) and extracted with diethyl
ether (4 5 mL). The organic extracts were dried over anhydrous MgSO4
and evaporated with silica gel. The crude pre-adsorbed product was
transferred to a silica gel column. Elution with hexane-ethyl acetate
(30:1) and evaporation under vacuum afforded pure coupling product.
M [g mol–1
Crystal system
Space group
a [Å]
]
triclinic
triclinic
P–1 (no. 2)
10.0157(2)
10.0774(2)
14.5935(3)
95.4051(9)
94.0863(9)
108.2048(8)
1385.09(5)
2
P–1 (no. 2)
9.2204(4)
9.5490(4)
17.0889(6)
73.965(1)
76.393(1)
69.922(1)
1341.64(9)
1
b [Å]
c [Å]
α [°]
This procedure was modified in the case of 7cd due to the low solubility
of this compound. Thus, following the quenching by the addition of water,
the reaction mixture was extracted with toluene (ca. 100 mL). The
toluene solution was washed with water (3 25 mL), and the aqueous
washings were back-extracted with toluene (2  25 mL). The combined
toluene layers were washed with brine (25 mL), dried over MgSO4, and
evaporated to afford a white residue, which was crystallized from boiling
methanol. The product, which separated upon cooling, was filtered off,
washed with cold methanol and dried under vacuum.
β [°]
γ [°]
V [Å3]
Z
Dcalc [g cm–3
]
1.710
1.521
F(000)
720
628
X-ray crystallography. Crystals suitable for X-ray diffraction analysis
were selected directly from the preparative batch (3·Me2CO) or were
grown by layering a solution of complex 4 in wet methanol with methyl
tert-butyl ether and crystallization by liquid-phase diffusion over several
days (4·2MeOH·2H2O). Full set diffraction data (hkl, θ ≤ 27.5°, data
Diffractions collected
Independent diffractions
Rint [%][a]
17448
50551
6351
6158
2.29
1.46
completeness 99.9%) were recorded with
a Nonius Kappa CCD
diffractometer equipped with a Bruker Apex II detector (3·Me2CO) or a
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European Journal of Inorganic Chemistry
10.1002/ejic.201601262
FULL PAPER
Observed diffractions[b]
No. of parameters
5361
5656
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2.57, 5.36
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2
[a] Rint = Fo  Fo2(mean)/Fo2, where Fo2(mean) stands for the average
intensity of symmetry-equivalent diffractions. [b] Diffractions with Io ≥ 2σ(Io). [c]
R(F) = Σ(|Fo| – |Fc|)/Σ|Fo|, wR = {Σ[w(Fo2 – Fc2)2]/Σw(Fo2)2}1/2, where w = [σ2Fo
2
+ (w1P)2 + w2P]–1 and P = (Fo2 + 2Fc2)/3.
CCDC 1508804 (for 3·Me2CO) and 1508805 (for 4·2MeOH·2H2O)
contain the supplementary crystallographic data for this paper. These
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[17] Palladium and its four ligating atoms in the structure of 3·Me2CO are
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The research reported in this article received support from the
Czech Science Foundation (project no. 13-08890S).
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European Journal of Inorganic Chemistry
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European Journal of Inorganic Chemistry
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Entry for the Table of Contents
FULL PAPER
A phosphanylferrocene donor with a
hydrophilic guanidinium substituent,
Ph2PfcCH2NHC(NH)NH2·HCl (fc =
ferrocene-1,1’-diyl), was synthesized
and utilized as a ligand for Pd(II)
complexes. Both the defined
Ferrocene phosphanes*
Ondřej Bárta, Ivana Císařová, Petr
Štěpnička*
Page No. – Page No.
Synthesis, Palladium(II) Complexes
and Catalytic Use of
a Phosphanylferrocene Ligand
Bearing a Guanidinium Pendant
complexes and their in situ generated
analogues were evaluated as pre-
catalysts for the Suzuki-Miyaura
cross-coupling of aryl boronates with
aryl bromides in polar reaction
solvents.
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