Single-step substitution of all the α, β-positions in pyrrole: Choice of binuclear versus multinuclear complex of the novel polydentate ligand

Article abstract of DOI:10.1021/ic5000974

The α and β-positions of pyrrole were substituted with 3,5-dimethylpyrazolylmethyl groups in a single step that involved the reaction between 2,5-dimethylaminomethylpyrrole and 3,5-dimethylpyrazole-1-carbinol, affording 2,3,4,5-tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole LH in 40% yield. The coordination chemistry of this new polydentate ligand LH was explored by synthesizing several Pd(II), Cu(I), and Ag(I) complexes. When LH was used as a neutral ligand with [Pd(COD)Cl₂], AgBF₄, and CuX (X = Cl and I), compartmental type binuclear Pd(II) and Ag(I) complexes such as [Pd₂Cl₄(μ-C₄HN-2,3,4,5-(CH ₂Me₂pz)₄-N,N,N,N)] and [Ag₂(μ- C₄HN-2,3,4,5-(CH₂Me₂pz)₄-N,N,N,N) (CH₃CN)₂]²⁺[BF₄^-] ₂ and cage-like copper(I) complexes [Cu₂(μ-X)(μ- C₄HN-2,3,4,5-(CH₂Me₂pz)₄-N,N,N,N)] ⁺[CuX₂]^- (X = Cl and I) containing a halide ion bridging in a bent fashion were obtained, respectively. Conversely, when the same metal precursors were treated with LH in the presence of n-BuLi, the multinuclear complexes [Pd₂Cl₃(μ-C₄N-2,3,4, 5-(CH₂Me₂pz)₄-N,N,N,N,N)], [(Cu ₂(μ-I){μ-C₄N-2,3,4,5-(CH₂Me ₂pz)₄-N,N,N,N,N})₂Cu]⁺I ^-, and [Ag₄(μ-C₄N-2,3,4,5-(CH ₂Me₂pz)₄-N,N,N,N)₂] ²⁺[BF₄^-]₂ were obtained. In addition, the treatment of LH with [Pd(OAc)₂] gave the mononuclear complex, [Pd(OAc)(C₄N-2,3,4,5-(CH₂Me₂pz) ₄-N,N,N)]. The chloride analogue of this complex was obtained by the reaction of LH with [Pd(COD)Cl₂] in the presence of triethylamine. The structures of all complexes were determined by single-crystal X-ray diffraction analyses, which revealed interesting structural features, including pyrazole arms adopting different conformations with respect to the pyrrole ring plane and linear two- and three-coordinated copper(I) and silver(I) atoms exhibiting weak interactions between the metal and the pyrrolic carbon atoms and Ag(I)...Ag(I) interactions. The observed shorter metal pyrrolide nitrogen (M-N) bond distances and the elongation of the C-C double and single bond distances of the pyrrole ring in these complexes probably indicates the presence of π-donation/π-back bonding between the metal and the pyrrole ring. These multinuclear complexes are novel, and their formations are favored by the multidentating nature of the ligand LH.

Full text of DOI:10.1021/ic5000974

Article
pubs.acs.org/IC
Single-Step Substitution of all the α, β‑Positions in Pyrrole: Choice of
Binuclear versus Multinuclear Complex of the Novel Polydentate
Ligand
Debasish Ghorai and Ganesan Mani*
Department of Chemistry, Indian Institute of Technology − Kharagpur, Kharagpur, West Bengal India 721 302
S
* Supporting Information
ABSTRACT: The α and β-positions of pyrrole were substituted with 3,5-
dimethylpyrazolylmethyl groups in a single step that involved the reaction between
2,5-dimethylaminomethylpyrrole and 3,5-dimethylpyrazole-1-carbinol, affording
2,3,4,5-tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole LH in 40% yield. The
coordination chemistry of this new polydentate ligand LH was explored by
synthesizing several Pd(II), Cu(I), and Ag(I) complexes. When LH was used as a
neutral ligand with [Pd(COD)Cl2], AgBF4, and CuX (X = Cl and I), compartmental
type binuclear Pd(II) and Ag(I) complexes such as [Pd2Cl4(μ-C4HN-2,3,4,5-
(CH2Me2pz)4-N,N,N,N)] and [Ag2(μ-C4HN-2,3,4,5-(CH2Me2pz)4-N,N,N,N)-
−
(CH3CN)2]2+[BF4 ]2 and cage-like copper(I) complexes [Cu2(μ-X)(μ-C4HN-2,3,4,5-(CH2Me2pz)4-N,N,N,N)]+[CuX2]− (X =
Cl and I) containing a halide ion bridging in a bent fashion were obtained, respectively. Conversely, when the same metal
precursors were treated with LH in the presence of n-BuLi, the multinuclear complexes [Pd2Cl3(μ-C4N-2,3,4,5-(CH2Me2pz)4-
N,N,N,N,N)], [(Cu2(μ-I){μ-C4N-2,3,4,5-(CH2Me2pz)4-N,N,N,N,N})2Cu]+I−, and [Ag4(μ-C4N-2,3,4,5-(CH2Me2pz)4-
N,N,N,N)2]2+[BF4 ]2 were obtained. In addition, the treatment of LH with [Pd(OAc)2] gave the mononuclear complex,
−
[Pd(OAc)(C4N-2,3,4,5-(CH2Me2pz)4-N,N,N)]. The chloride analogue of this complex was obtained by the reaction of LH with
[Pd(COD)Cl2] in the presence of triethylamine. The structures of all complexes were determined by single-crystal X-ray
diffraction analyses, which revealed interesting structural features, including pyrazole arms adopting different conformations with
respect to the pyrrole ring plane and linear two- and three-coordinated copper(I) and silver(I) atoms exhibiting weak interactions
between the metal and the pyrrolic carbon atoms and Ag(I)···Ag(I) interactions. The observed shorter metal pyrrolide nitrogen
(M−N) bond distances and the elongation of the C−C double and single bond distances of the pyrrole ring in these complexes
probably indicates the presence of π-donation/π-back bonding between the metal and the pyrrole ring. These multinuclear
complexes are novel, and their formations are favored by the multidentating nature of the ligand LH.
exhibiting novel electronic and magnetic properties. We
therefore became interested in attaching 3,5-dimethylpyrazolate
groups to the pyrrole ring, which could become a polydentate
ligand for metals. Herein, we report the serendipitous finding
that the first single-step synthesis of α,β-position-substituted
pyrrole, 2,3,4,5-tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole
and the ligating property difference between its neutral and
anionic forms with palladium(II), copper(I) and silver(I)
metals leads to structural characterization of binuclear and
multinuclear palladium(II), copper(I), and silver(I) complexes.
These complexes showed interesting structural features such as
short contacts between metal and pyrrole carbons, Ag(I)···
Ag(I) interactions, and shorter metal pyrrolide nitrogen bond
distances, suggesting π-donation/π-back bonding.
INTRODUCTION
■
The α-positions of pyrrole is more reactive toward electrophiles
than its β-positions. This property has extensively been used for
synthesis of porphyrins and a myriad array of products.1 In fact,
nature also used this property to build its molecules.
Nonetheless, the β-positions are also sufficiently reactive but
remain very difficult for selective substitution over the α-
positions.2 Generally, β-positions or 3,4-disubsituted pyrrole
derivatives have been synthesized by the Piloty−Robinson
pyrrole synthesis with appropriate starting compounds3 and
other methods.4
Metal complexes containing polydentate ligand have been
shown to mimic metallo-enzymes and act cooperatively to
activate small molecules.5 Polydentate ligands increase the
stability of metal complexes because of their chelating bonding
modes. Usually they can be synthesized by tethering ligating
groups to the mainframe of a molecule. The pyrazole molecule
has been shown to coordinate metal atoms in 20 different
modes and has demonstrated its versatile nature of bonding.6
Hence, pyrazole-based polydentate ligands, such as poly-
(pyrazolyl)borates7 and poly(pyrazolyl)alkanes,8 are a fascinat-
ing class of ligand systems as shown by their metal complexes
RESULTS AND DISCUSSION
■
Synthesis of Polydentate Ligand. Earlier, we reported
the α,α′-substituted pyrrole, 2,5-bis(3,5-dimethylpyrazolyl-
Received: January 15, 2014
Published: April 9, 2014
© 2014 American Chemical Society
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Scheme 1. Synthesis of the αα′ββ′-Tetrasubstituted Pyrrole, LH.
methyl)pyrrole, 2 by the reaction between 2,5-bis-
(dimethylaminomethyl)pyrrole and 3,5-dimethylpyrazole at an
elevated temperature.9 Using the same strategy, when the
reaction was carried out with 4 equiv of 3,5-dimethylpyrazole-1-
carbinol, the unprecedented αα′ββ′-tetrasubstituted pyrrole,
2,3,4,5-tetrakis(3,5-dimethylpyrazol-1-ylmethyl)pyrrole (LH),
was isolated in 40% yield along with 2 after workup procedure
(Scheme 1). Attempts to synthesize LH directly from pyrrole
failed and yielded inseparable polymeric products. This suggests
that protection of the more reactive α-positions of pyrrole by
the dimethylaminomethyl groups is important and facilitates
the alkylation of the β-positions. As a result, LH is formed by
replacing not only the dimethylamino groups in 2,5 positions of
1 but also both the β-CH protons, likely resulting in
concomitant formation of water molecules. This reaction is a
new simple method and involves two steps from pyrrole.
However, the acidic pyrrolic NH group was not alkylated even
in the presence of 6 equiv of 3,5-dimethylpyrazole-1-carbinol,
as shown by the HRMS analysis of the reaction mixture.
The mechanism of formation of LH could involve the steps
shown in Chart 1. It is likely that 3,5-dimethylpyrazole-1-
dimethylpyrazolylmethyl)pyrrole, 2. Subsequently, 2 undergoes
the electrophilic attack by the carbinol in the β-positions to give
the product LH with the formation of two water molecules.
The structure of LH was confirmed by NMR, IR, and HRMS
1
analyses. The H NMR spectrum of LH in CDCl3 shows a
broad signal at δ 8.94 ppm for the pyrrolic NH proton; the two
diastereotopic methylene protons resonate at δ 5.06 and 4.73
ppm as two sharp singlets together with other signals whose
integrated intensities are in accord with the structure.
Synthesis and Characterization of Binuclear Com-
plexes. Having synthesized a new polydentate ligand
containing four nucleophilic nitrogen donors and the pyrrolic
NH group, which can be deprotonated to become an anionic
ligand, we have investigated its coordination chemistry. Besides,
it is interesting to compare its coordination chemistry with that
of the NNN-pincer ligand 2 (see ref 9) and with that of the
t e t r a p y r a z o l y l m e t h y l s u b s t i t u t e d b e n z e n e ,
C6H2(CH2Me2pz)4.10 The compartmental binuclear palladium-
(II) (3) and silver(I) (5) complexes were synthesized by
treating 2 equiv of their respective metal precursors with LH
(Scheme 2). As a result of the relatively smaller copper atom,
the cage-like binuclear copper(I) complex (4) was obtained. In
all these complexes, the pyrrolic NH proton is intact, and all the
pyrazole nitrogens are coordinated. The structures of all these
complexes were determined by single-crystal X-ray diffraction
analyses, which are supported by NMR, HRMS, and elemental
analyses.
Chart 1Proposed mechanism of formation of LH from 2,5-
bis(dimethylaminomethyl)pyrrole at elevated temperature.
The 1H NMR spectrum of 3 in CDCl3 is drastically different
from that of the free LH. Although LH displays two separate
broad resonances for the two methylene groups, 3 gives two AB
pattern resonances with J = 15.2 Hz for its diastereotopic
methylene protons. In addition, the spectrum shows well-
separated resonances for the pyrazolyl methyl groups and a
broad singlet at δ 9.41 ppm for the pyrrolic NH proton. These
contrasting features are attributed to the constraints with which
LH is coordinated; in the free LH, the pyrazolylmethylene
groups are free to move. The 1H NMR spectrum of 4a or 4b in
CDCl3 displays a broad signal for its methylene protons.
Conversely, the same complex in a strongly hydrogen bonding
solvent DMSO-d6 gives well-resolved signals for the methylene
groups. Complex 5 was obtained after crystallization from
acetonitrile/diethyl ether mixture. Although complex 3 and 5
have similar conformations (vide infra), in contrast to the
palladium complex 3, the silver(I) complex 5 in DMSO-d6 gives
broad signals for its methylene groups, probably indicating
dynamic behavior in solution. In addition, this spectrum
showed the presence of coordinated acetonitrile molecules in 5.
The HRMS spectrum of 5 showed a peak m/z at 713.1203
(calcd 713.1274) corresponding to the ion, [M−2MeCN−
2BF4]+.
carbinol is dissociated at this elevated temperature to give its
starting compounds, 3,5-dimethylpyrazole and formaldehyde,
which are in equilibrium. The freed 3,5-dimethylpyrazole could
protonate both the amine groups of 2,5-bis(dimethyl-
aminomethyl)pyrrole, and subsequently, the resulting ammo-
nium salt undergoes the nucleophilic attack by the 3,5-
dimethylpyrazolate anion to give initially 2,5-bis(3,5-
The X-ray structure of 3 (Figure 1 and Table 2) revealed that
the pyrazole arms present on both sides of the pyrrole ring are
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Scheme 2. Synthesis of Binuclear Complexes Using LH as a Neutral Ligand
Figure 1. Molecular structure of the binuclear palladium(II) complex 3 (30% thermal ellipsoids) (a) front view and (b) side view. All hydrogen
atoms except the pyrrolic NH and the solvent of crystallization water molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg):
N3−Pd01 2.033(5), N5−Pd01 2.051(6), Cl03−Pd01 2.278(2), Cl05−Pd01 2.302(2), N7−Pd02 2.030(6), N9−Pd02 2.045(5), Cl04−Pd02
2.297(2), Cl06−Pd02 2.279(2), N3−Pd01−N5 91.7(2), N3−Pd01−Cl03 87.19(17), N5−Pd01−Cl03 177.03(17), N3−Pd01−Cl05 178.69(17),
N5−Pd01−Cl05 89.57(16), Cl03−Pd01−Cl05 91.55(9), N7−Pd02−N9 89.4(2), N7−Pd02−Cl06 175.11(18), N9−Pd02−Cl06 89.44(17), N7−
Pd02−Cl04 91.10(17), N9−Pd02−Cl04 176.15(16), Cl06−Pd02−Cl04 90.42(9), N1···O2 2.845(14), H1n···O2 1.89(7), N1−H1n···O2 158(6),
N1···O2i 2.998(14), H1n···O2i 2.00(7), N1−H1n···O2i 171(6). The symmetry operation used to generate equivalent atoms: −x + 2.5, y, −z + 1.5.
twisted above and below the plane formed by the pyrrole ring
together with its methylene carbon atoms and chelated to two
“PdCl2” units one on each side. It is a neutral binuclear
compartmental type complex. The side view of the structure
shows an “S”-shaped conformation, which minimizes steric
crowding. The geometry around each palladium atom is a
slightly distorted square plane. The Pd−N(pz) and Pd−Cl
bond distances fall within the range reported for the pyrazole-
nitrogen-coordinated palladium complexes.11 The pyrrolic NH
group is hydrogen bonded to the water molecules present in
the lattice.
Cu2 angle of 92.89(5)° in 4a and the acute angle, Cu2−I1−
Cu1 = 75.17(3)°, in 4b are probably the result of steric
constraint of LH with which it bridges the two metal atoms.
However, the Cu···Cu distance in 4a or 4b (3.383(1) Å or
3.127(1) Å, respectively) suggests that there can be no copper−
copper bonding.
Interestingly, the two copper atoms in each structure are
slightly different. For example, in the case of 4b, the summation
of the three angles is 357.8(1)° at Cu1, whereas the sum is
352.5(1)° at Cu2. The slightly pyramidalized copper(I) atom is
in close proximity to two of the pyrrole ring carbon atoms:
Cu1−C7 = 2.704(5) Å and Cu1−C8 = 2.693(4) Å in 4a; Cu2−
C2 = 2.519(5) Å and Cu2−C1 = 2.654(6) Å in 4b. These
distances are shorter than the sum of the van der Waals radii of
the two atoms (1.7 Å (C) + 1.40 Å (Cu) = 3.10 Å) and hence
can represent a weak η2 interaction involving the pyrrolic π-
electrons. Similar close contacts involving arene ring carbons
have been reported for a few Cu(I), Ag(I), and Hg(II)
complexes.12 However, Braunstein and co-workers have
concluded that such close proximities do not correspond to
bonding interactions as shown by DFT calculations.13 Further,
the Cu−N(pz) and Cu−X bond distances are in the range
The structure of copper(I) complex 4 is formulated as
[(LH)Cu2X]+[CuX2]− (X = Cl (4a) and I (4b)) in which the
two copper atoms are bridged by one neutral ligand LH and
one halide ion, forming a cage-like cation whose charge is
−
neutralized by the CuX2 anion (Figure 2 and Figure 3,
respectively). The formation of this product may be due to the
smaller size of the copper atom relative to the palladium atom.
The three-coordinated copper(I) atom exhibits either a
distorted trigonal pyramidal or planar geometry. In addition,
the two copper(I) atoms are bridged by the halide ion
unsymmetrically, as shown by their distances. The Cu1−Cl1−
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and join with the scarcely reported linear16 and bent17
monohalide ion bridged binuclear Cu(I) complexes.
The symmetry-generated [Cu2I4]2− anion has been reported
for several other Cu(I) complexes.18 In locations where there is
a possibility of C−H···I interactions, the observed C···I
distances are higher than the sum of their van der Waals
radii. Hence, there are no significant C−H···I interactions with
which the [Cu2I4]2− anion is held in place with the cation in the
−
asymmetric unit. The same applies to the CuCl2 anion in 4a.
However, in 4a, the pyrrolic NH group is hydrogen bonded to
the lattice THF molecule, N5···O1 = 2.878(6) Å, H···O1 =
2.09(5) Å, ∠N5−H5...O1 = 152(4)°. Each copper atom of the
anion [Cu2I4]2− adopts the trigonal planar geometry, and the
Cu···Cu distance is 2.6128(16) Å, which is similar to the
reported values.19
The X-ray structure of complex 5, given in Figure 4, revealed
a compartmental type binuclear three-coordinate silver(I)
cationic complex formed by a single neutral ligand LH. In
the structure, ligand LH is twisted such that its pyrazole groups
are oriented up and down to the pyrrole ring, in contrast to the
structure of 4 in which these groups are on the same side. As a
result, the molecule adopts an “S”-shaped conformation, which
is similar to the structure of 3. In addition to the chelation
formed by the pyrazole nitrogens conferring a bite angle of
138.1(2)° at Ag1 and 141.0(2)° at Ag2, each silver(I) atom is
coordinated by one acetonitrile molecule. The geometry
Figure 2. Molecular structure of the binuclear copper(I) chloride
complex 4a (30% thermal ellipsoids). All hydrogen atoms except the
pyrrolic NH and one THF solvent molecule are omitted for clarity.
The dotted line indicates short contact. Selected bond lengths (Å) and
angles (deg): N1−Cu1 1.989(4), N3−Cu1 1.957(4), N6−Cu2
1.928(4), N8−Cu2 1.911(4), Cl1−Cu1 2.2793(15), Cl1−Cu2
2.3874(14), Cl2−Cu3 2.081(2), Cl3−Cu3 2.0951(19), Cu1−Cl1−
Cu2 92.89(5), N3−Cu1−N1 126.52(17), N3−Cu1−Cl1 120.52(12),
N1−Cu1−Cl1 109.20(13), N8−Cu2−N6 148.89(16), N8−Cu2−Cl1
107.95(12), N6−Cu2−Cl1 102.83(11), Cl2−Cu3−Cl3 176.05(8).
−
around each metal atom is trigonal planar. Both BF4 anions
are severely disordered; one of them is located in the direction
of the pyrrolic NH group and hydrogen bonded. The Ag−
N(pz) distances range from 2.160(5) to 2.229(6) Å, which are
similar to the values observed in other three-coordinate
silver(I) complexes containing pyrazolate units.20
Synthesis and Characterization of Multinuclear
Complexes. On the contrary, the treatment of LH with the
same metal precursors ([Pd(COD)Cl2], CuI, and AgBF4) in
the presence of n-BuLi in THF afforded interesting multi-
nuclear complexes 6, 7, and 8, respectively (Scheme 3).
Besides, complex 8 was also synthesized by treating LH with
AgBF4 in the presence of triethylamine. As can be noticed in all
complexes, upon deprotonation, LH becomes a pentadentate
ligand which helps form the multinuclear complexes in which
the pyrrolide nitrogen is σ-bonded to the metal atoms.
Complex 6 is formed by a metathesis reaction that involves
the metal-to-ligand mole ratio of 2:1. As a result, all chlorine
atoms are not replaced, and the resulting complex contains
chloride ions bonded to palladium atoms. Complex 8 was
obtained from the reaction involving metal-to-ligand mole ratio
of 2:1, as crystals containing two acetonitrile molecules as a
solvent of crystallization in poor yields. As silver(I) metal
prefers two-coordinate linear geometry and the metal-to-ligand
mole ratio is 2:1, the dicationic linearly coordinated silver(I)
complex 8 containing two anionic ligands was obtained. Instead
of forming a polymeric chain which would be sterically crowded
and unfavorable, the presence of five potential ligating atoms
(four pyrazolyl and one pyrrolic nitrogen atoms per ligand)
force the silver atom to form this tetranuclear complex with
linear coordination, in which all the basic pyrazolyl nitrogen
atoms are involved in bonding. As to the copper(I) complex 7,
the copper metal can form two-, three-, four-, and other
coordinate complexes. Even though the mole ratio is 1:1, which
could replace the iodide ion from CuI, the complex containing
undisplaced iodide ion bonded to copper(I) metal was obtained
in poor yield due to its coordination flexibility. The crystals of
Figure 3. Molecular structure of the binuclear copper(I) iodide
complex 4b (30% thermal ellipsoids) along with the anion Cu2I42−. All
hydrogen atoms except the pyrrolic NH and one THF are omitted for
clarity. The dotted line indicates short contact. Selected bond lengths
(Å) and angles (deg): N3−Cu1 1.973(6), N5−Cu1 1.946(5), N7−
Cu2 1.996(5), N9−Cu2 2.047(5), Cu1−I1 2.6446(10), Cu2−I1
2.4772(9), C2−Cu2 2.520(5), Cu3−I2 2.4885(9), Cu3−I3
2.5615(10), Cu3−I3i 2.6087(10), Cu3−Cu3i 2.6122(16), I3−Cu3i
2.6087(10), N5−Cu1−N3 134.6(2), N5−Cu1−I1 117.78(14), N3−
Cu1−I1 105.44(16), N7−Cu2−N9 104.3(2), N7−Cu2−I1
128.76(14), N9−Cu2−I1 119.43(15), Cu2−I1−Cu1 75.17(3), N7−
Cu2−C2 76.17(18), N9−Cu2−C2 89.29(18), I1−Cu2−C2
126.15(13), I2−Cu3−I3 124.98(4), I2−Cu3−I3i 115.68(4), I3−
Cu3−I3i 119.31(3), I2−Cu3−Cu3i 174.23(6), I3−Cu3−Cui
60.55(3), I3i−Cu3−Cu3i 58.76(3), Cu3−I3−Cu3i 60.69(3). The
symmetry operation used to generate equivalent atoms: −x + 1, −y,
−z + 2.
reported for other copper(I) complexes containing the
pyrazolate ligand.14,15 Furthermore, these complexes are unique
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Figure 4. Molecular structure of the binuclear silver(I) complex 5 (30% thermal ellipsoids) (a) front view and (b) side view. All hydrogen atoms
except the pyrrolic NH and the two disordered BF4− anions are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ag1−N11 2.273(8),
N10−Ag2 2.326(10), N2−Ag1 2.226(7), N4−Ag1 2.182(5), N6−Ag2 2.160(5), N8−Ag2 2.229(6), C30−N10−Ag2 154.4(12), N4−Ag1−N2
138.1(2), N4−Ag1−N11 122.3(3), N2−Ag1−N11 99.5(3), N6−Ag2−N8 141.0(2), N6−Ag2−N10 121.2(3), N8−Ag2−N10 97.7(3).
Scheme 3. Synthesis of Multinuclear Complexes Using LH as an Anionic Ligand
6, 7, and 8 are poorly or not soluble in common organic
solvents and hence they are characterized primarily by CHN,
IR, and X-ray diffraction methods.
Complex 7 was obtained as crystals containing toluene as a
solvent of crystallization in 28% yield. The H NMR spectrum
1
of 7 in dmso-d6 showed broad signals, and there is no peak
corresponding to a pyrrolic NH proton. The molecular
structure of 7 given in Figure 6 consists of two anionic ligands
bridged by one central copper(I) atom. The four pyrazole
nitrogens of each ligand bridges the two copper(I) atoms of the
moiety “Cu(μ-I)Cu” located on both sides of the molecule, and
the pyrrolic nitrogen of each ligand is σ-bonded to the central
copper(I) atom. The resulting cationic complex [L2Cu5I2]+ is
neutralized by one iodide anion. Interestingly, the central
copper(I) atom is almost linearly coordinated by the pyrrolide
nitrogen atoms with the N1−Cu1−N1i angle of 171.5(4)°,
which is larger than those found for the two-coordinate
copper(I) complexes containing pyrrolides (168.5°)23 or
pyrazolyl rings (167.9(1)°).24 Further, this observed angle is
similar to the angle found in the copper(I) complex containing
3,5-di-tert-butylpyrazolyl ligands (171.2(2)°)25 but is lower
than that (180.0(2)°) reported for [Cu(MeCN)2]+,26 those
The X-ray structure of 6 (Figure 5) revealed that two
palladium(II) atoms are bound to one anionic ligand L, which
adopts the mer κ3-NNN and chelation bonding modes. These
bonding features result in a conformation in which three of the
pyrazole arms are projected above, while the fourth pyrazole
arm is projected below the pyrrole plane. Further, this
conformation is different from that found for the neutral
ligand complex 3 but remains the same as that found in
complex 8 (vide infra). Furthermore, each palladium atom has a
distorted square plane, and their Pd−Cl and Pd−N(pz)
distances are in the range reported.11 The Pd−N(pyrrole)
bond distance is close to the value found in the 2,5-
bis(diphenylphosphinomethyl)pyrrole-coordinated Pd(II)
complex [(PNP)PdCl](1.981(4))21 but is lower than those
found in other pyrrolide nitrogen-bonded Pd(II) complexes.22
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not exhibit any short contact in contrast to a few of the above
two-coordinate copper(I) complexes reported. The bridging
nature of each ligand in this complex is similar to that found in
4 containing the neutral ligand. However, the Cu−I−Cu angle
of 85.44(4)° is larger than that (75.2(1)°) found in 4b.
Accordingly, the nonbonded Cu···Cu distance of 3.545(2) Å in
7 is larger than that (3.127(1) Å) found in 4b. The pyrazolyl
N−Cu bond distances range from 1.956(8) to 1.983(6) Å, and
the Cu−I bond distances are similar to those found in 4b. The
pyrrolic N−Cu bond distance of 1.858(7) Å is slightly shorter
than those (1.865 Å) reported for the two-coordinate copper(I)
complex containing the pyrrolide ring,23 indicating a relatively
stronger bond.
The molecular structure of 8, given in Figure 7, consists of
two anionic ligands coordinated to four silver(I) metal atoms in
Figure 5. Molecular structure of the 6 (30% thermal ellipsoids). All
hydrogen atoms and the solvent of crystallization dichloromethane are
omitted for clarity. Selected bond lengths (Å) and angles (deg): N3−
Pd02 1.971(5), N1−Pd02 2.058(5), N5−Pd02 2.033(5), Cl1−Pd02
2.3169(19), Cl2−Pd01 2.2870(18), Cl3−Pd01 2.286(2), N7−Pd01
2.014(5), N9−Pd01 2.061(6), N3−Pd02−Cl1 179.06(17), N3−
Pd02−N5 86.8(2), N3−Pd02−N1 86.5(2), N5−Pd02−N1 173.3(2),
N5−Pd02−Cl1 93.22(16), N1−Pd02−Cl1 93.41(16), N7−Pd01−N9
89.5(2), N7−Pd01−Cl3 89.12(17), N9−Pd01−Cl3 174.06(17), N7−
Pd01−Cl2 178.77(17), N9−Pd01−Cl2 90.84(17), Cl3−Pd01−Cl2
90.66(7).
Figure 7. Molecular structure of the tetranuclear silver(I) complex 8
(30% thermal ellipsoids). All hydrogen atoms, two acetonitrile
−
molecules as solvent of crystallization and the two disordered BF4
anions are omitted for clarity. The dotted line indicates short contact.
Selected bond lengths (Å) and angles (deg): N1−Ag1 2.117(5), N3−
Ag2 2.205(5), N8−Ag2 2.177(5), N5−Ag2i 2.534(6), N6−Ag1
2.135(5), Ag1−Ag2 3.1151(9), Ag2−N5i 2.534(6), N1−Ag1−N6
172.4(2), N1−Ag1−Ag2 110.40(14), N6−Ag1−Ag2 77.17(15), N8−
Ag2−N3 147.1(2), N8−Ag2−N5i 106.2(2), N3−Ag2−N5i 97.2(2),
N8−Ag2−Ag1 111.35(15), N3−Ag2−Ag1 68.35(14), N5−Ag2−Ag1
128.12(15). The symmetry operation used to generate equivalent
atoms: −x, −y, −z + 1.
Figure 6. Molecular structure of the pentanuclear copper(I) iodide
complex 7 (30% thermal ellipsoids). All hydrogen atoms and one
disordered toluene solvent molecule are omitted for clarity. Selected
bond lengths (Å) and angles (deg): N1−Cu1 1.858(7), N2−Cu2
1.965(8), N4−Cu2 1.983(6), N6−Cu3 1.956(8), N9−Cu3 1.957(7),
Cu2−I1 2.6195(14), Cu3−I1 2.6055(16), Cu1−N1i 1.858(7), N1−
Cu1−N1i 171.5(4), N2−Cu2−N4 128.6(3), N2−Cu2−I1 115.6(2),
N4−Cu2−I1 110.1(2), N6−Cu3−N9 132.7(3), N6−Cu3−I1
110.1(2), N9−Cu3−I1 114.4(2), Cu3−I1−Cu2 85.44(4). The
symmetry operations used to generate equivalent atoms: −x + 1, y,
−z + 0.5; −x + 0.5, −y + 0.5, −z + 1.
a different fashion compared to any of the structures presented
here, which is formulated as the dication [L2Ag4]2+ and
−
neutralized by the two disordered BF4 anions. Three of the
four pyrazole arms of each ligand are twisted to one side of the
pyrrole ring plane, while the fourth arm is twisted to the
opposite direction; one of them remains uncoordinated or as a
spectator ligand. The pyrrolide nitrogen atom of each ligand is
σ-bonded to one silver atom which is bonded to one of the
pyrazole nitrogens of the other ligand with the N1−Ag1−N6
angle of 172.4(2)°. Conversely, the angles around the other
two silver(I) atoms which are coordinated only by the
remaining pyrazole nitrogens are rather bent, for example,
N3−Ag2−N8 = 147.1(2)°. This bent angle could be due to the
short contacts that the Ag2 and Ag2i atoms have with the
nitrogen atoms of the spectator position pyrazole arms (e.g.,
Ag2···N5i = 2.534(7) Å, which is much less than the sum of the
van der Waals radii (3.25 Å) of the nitrogen and silver atoms).
Conversely, the Ag1and Ag1i atoms have close contacts only to
the pyrrole ring carbon atoms C3 and C4 (Ag1···C4i =
2.894(7) Å and Ag1···C3i = 3.080(6) Å), which are also less
(173.8° and 178.2°) reported for [CuL2]+ complexes
containing the ligated 1,3,5-trimethylpyrazole and 1-methyl-
pyrazole, respectively,27 and others.28 In contrast to the nearly
coplanar arrangement of the imidazole- or pyrazole-ring-
coordinated copper(I) complexes,24,27,28a,b the two pyrrole
ring planes are almost perpendicular to each other, which
probably reduces steric hindrance between the two ligands and
can support the presence of π-bonding between the pyrrolide
nitrogen and copper atoms. The central copper(I) atom does
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Scheme 4. Synthesis of Mononuclear Complexes Using LH.
than the sum of the van der Waals radii, 3.40 Å,29 and are
similar to complex 4 and to other silver complexes reported.30
The pyrrolide N−Ag distance (2.117(5) Å) is shorter than any
of the pyrazole N−Ag distances in the structure. Furthermore,
the structure showed a metal−metal contact; the Ag1···Ag2
distance of 3.1150(9) Å is less than the sum of the van der
Waals radii of silver atoms, 3.40 Å, but is longer than that found
in silver metal, 2.884 Å,31 and closer to other reported silver
complexes.32
Synthesis and Characterization of Mononuclear
Complexes. The ligating property of LH was also explored
with metal precursors containing a leaving group that can
abstract a proton from the ligand. Thus, the reaction of LH
with 1 equiv of [Pd(OAc)2] afforded the mononuclear
cyclopalladated complex 9 containing the η1-coordinated
acetate group and two spectator position pyrazole arms in
84% yield (Scheme 4). The chloride analogue complex 10 was
obtained when LH was treated with 1 equiv of [Pd(COD)Cl2]
in the presence of triethylamine. The structure of 10 was
confirmed by comparing its 13C NMR spectrum, which
displayed 14 peaks with that of 9 in CDCl3. In addition, the
(+)ESI-MS spectra of 9 and 10 showed the same molecular ion
peak m/z at 604.2151, which corresponds to the [M − OAc]+
and [M − Cl]+ ions, respectively. In addition, complex 9 was
transformed to 10 by treating 9 with lithium chloride in
Figure 8. Molecular structure of the mononuclear palladium(II)
complex 9 (30% thermal ellipsoids). All hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): N1−Pd1
1.963(5), N3−Pd1 2.038(5), N4−Pd1 2.048(5), O1−Pd1 2.022(4),
C29−O2 1.224(8), C29−O1 1.266(9), C29−C30 1.513(9), N1−
Pd1−O1 178.43(18), N1−Pd1−N3 87.27(19), O1−Pd1−N3
91.56(19), N1−Pd1−N4 87.42(19), O1−Pd1−N4 93.72(19), N3−
Pd1−N4 174.3(2), C29−O1−Pd1 116.8(4).
acetate groups, respectively. All the pyrazolyl and pyrrole N−
Pd bond distances are within the reported range.33
1
acetone/water. The H NMR spectrum of 9 or 10 in CDCl3
gives overlapped multiplets for the methylene protons
belonging to the coordinated and uncoordinated arms,
indicating dynamic behavior involving movement of pyrazole
groups in solution that could be similar to the dynamic
property shown by the palladium complex formed by 2,5-
bis(3,5-dimethylpyrazolylmethyl)pyrrole 2 (see ref 9) and
other complexes.10
Structure Comparison. A considerable amount of
theoretical work has been done to understand the nature of
the metal pyrrolide nitrogen (M−N) bond in metal complexes,
which showed the existence of π-donation/π-back bonding
synergism.34 In several X-ray structures, the pyrrolide nitrogen
metal bond distance is shorter than the value expected if there
is only σ bonding, indicating some π-bonding character.35 This
interaction also affects the pyrrole ring C−C double and single
bond distances.34c In view of these studies (see Table 1), it is
conceivable that the observed pyrrolide nitrogen metal bond
distances are considerably shorter than the neutral pyrazolyl
nitrogen metal bond distances. In 6, 9, 7, and 8, the difference
in distance between the average M−N(pyrazolyl) and the M−
N(pyrrolide) bonds is 0.074, 0.070, 0.107, and 0.046 Å,
respectively. This could be because of π-back bonding from the
metal to empty MO of the pyrrole ring, as reported for other
pyrrolide nitrogen-bonded metal complexes.34b,c The copper(I)
complex 7 showed the highest difference. Further, the presence
of π-back bonding can also be inferred from the elongation of
both the C−C double and single bonds of the pyrrole ring in
comparison with uncoordinated ligand. Because an X-ray
structure of LH is not available, the pyrrole ring bond distances
are compared with the closely related free ligand 2, for which a
crystal structure has been reported.9 For example, the average
pyrrole ring C−C double bond distance in 6 or 9, which
contains the anionic ligand, is 1.382(9) or 1.386(8) Å,
The structure of complex 9 was confirmed by the X-ray
diffraction method (Figure 8 and Table 2). In this structure, the
ligand LH adopts the monoanionic mer κ3-NNN coordination
mode to coordinate to the palladium atom and left the other
two pyrazole arms in a spectator position. Further, each
pyrazole arm is twisted alternatively up and down to the pyrrole
plane; that is, pyrazolyl groups of every pair attached to any two
adjacent positions on the pyrrole ring are oriented opposite to
each other. This configuration could be an effort to reduce the
steric crowding, which is probably not retained in solution as
shown by the overlapped multiplets for the methylene protons
1
in its H NMR spectrum at room temperature. The twist
angles, C1−N1−Pd1−N3 = 37.4(5)° and C4−N1−Pd1−N4 =
36.0(5)° are almost the same as those in the structure of
[Pd(OAc){C4H2N-2,5-(CH2Me2pz)2-N,N,N}].9 The palladium
atom adopts a distorted square planar geometry defined by the
two neutral pyrazolyl nitrogen atoms, lying trans to each other
with the “pincer bite” angle of 174.3°, and the two anionic
donorsnitrogen and oxygen atoms of the pyrrole and the
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Table 1. Comparison of the Metal Nitrogen (M−N) and the Pyrrole Ring C−C Bond Distances (Å) Observed in 3−9 with the
Free Ligand 2
pyrrole ring distances
ave. M−N
M−N (pyrrolide)
(pyrazolyl)
CC
CC
C−C
N−C
free ligand 2
C9−C10 1.360(6) C7−C8 1.359(6)
C8−C9 1.415(7) N3−C7 1.354(5) N3−C10 1.365(6)
C2−C3 1.408(9) N1−C1 1.369(8) N1−C4 1.359(9)
3
2.039(5)
1.946(4)
1.990(5)
2.199(6)
2.045(5)
1.965(7)
C1−C2 1.377(9)
C7−C8 1.380(6)
C1−C2 1.377(7)
C7−C8 1.394(8)
C7−C8 1.387(9)
C3−C4 1.369(9)
4a
4b
5
C21−C22 1.383(6) C8−C22 1.430(6) N5−C7 1.359(6) N5−C21 1.355(5)
C3−C4 1.376(8) C2−C3 1.432(7) N1−C1 1.369(7) N1−C4 1.350(7)
C21−C22 1.387(8) C8−C21 1.412(8) N1−C7 1.360(8) N1−C22 1.364(8)
C15−C22 1.378(9) C8−C15 1.422(9) N3−C22 1.340(8) N3−C7 1.373(8)
6
N3−Pd02 1.971(5)
N1−Cu1 1.858(7)
7
C1−C2 1.404(12) C3−C4 1.396(12) C2−C3 1.420(12) N1−C1 1.371(10) N1−C4
1.358(10)
8
9
N1−Ag1 2.117(5)
N6−Ag1 2.135(5)
N1−Pd1 1.963(5)
2.172(5)
2.043(5)
C1−C2 1.391(8)
C1−C2 1.382(8)
C3−C4 1.393(8)
C3−C4 1.391(8)
C2−C3 1.416(8) N1−C1 1.375(7) N1−C4 1.365(7)
C2−C3 1.419(8) N1−C4 1.341(7) N1−C1 1.373(7)
respectively, which are longer than those found in the free
ligand 2. Similarly, the C−C single bond distance in the same
complexes is slightly longer than that shown by 2. A similar
trend, with even greater elongation, was also observed for the
copper(I) (7) and silver(I) (8) complexes, as shown in Table 1.
spectrometer. Chemical shifts are referenced with respect to
the chemical shift of the residual protons present in the
deuterated solvents. FTIR spectra were recorded using
PerkinElmer Spectrum Rx. High-resolution mass spectra
(ESI) were recorded using the Xevo G2 Tof mass spectrometer
(Waters). Elemental analyses were carried out using a Perkin−
Elmer 2400 CHN analyzer. Melting points were determined in
open capillaries and are corrected using benzophenone as a
reference.
CONCLUSION
■
A single-step synthesis of the αα′ββ′-tetrasubstituted pyrrole
was developed starting from the Mannich base. As a
polydentate ligand, the ligating property of LH depends on
the size of metal atom and what form of LH is usedneutral or
anionic. When LH was used as a neutral ligand, the
compartmental type binuclear palladium(II) and silver(I)
complexes were isolated; with the relatively smaller size copper
atom, it afforded cage-like binuclear copper(I) complexes.
Conversely, when LH was used as an anionic ligand, the
multinuclear copper(I) and silver(I) complexes were isolated
and structurally characterized. Thus, it gives us the option of
choosing either binuclear or multinuclear complexes, and their
structures were established by X-ray diffraction. Although two-
coordinate copper(I) complexes have been reported,36 these
multinuclear complexes exhibit interesting structural features
including short contacts, and their formations are strongly
favored by the multidentating nature of the ligand LH.
Consequently, for example in 7, the copper(I) atom possesses
two different geometrieslinear and trigonal. Upon compar-
ison of the M−N and the pyrrole ring C−C bond distances
with the free ligand 2, within the group 11 metals studied, the
relatively shorter M−N bond distance in the copper(I) complex
7 probably indicates the presence of more pronounced π-
donation and back bonding than that in the silver(I) complex 8.
Synthesis of other ligands using this method and metal
complexes across the periodic table is under progress.
Synthesis of 2,3,4,5-Tetrakis(3,5-dimethylpyrazol-1-
ylmethyl)pyrrole, LH. A xylene (20 mL) solution of 3,5-
dimethylpyrazole-1-carbinol (5.57 g, 44.2 mmol) and 2,5-
bis(dimethylaminomethyl)pyrrole (2.00 g, 11.05 mmol) was
refluxed for about 12 h. The solution was cooled to room
temperature and then concentrated to ∼7 mL. Addition of
petroleum ether (50 mL) to this solution gave LH as a crude
dark brown precipitate. The precipitate was separated and
washed with petroleum ether (3 × 25 mL). The precipitate was
loaded onto a silica gel column chromatography. Elution using
ethyl acetate/methanol (50:1, v/v) gave the first fraction from
which the solvent was removed under vacuum to give LH as a
colorless solid (2.20 g, 4.41 mmol, 40%), mp 174 °C. 1H NMR
(CDCl3, 200 MHz, 25 °C): δ = 8.94 (br s, 1H, NH), 5.78 (s,
2H, pyrazole CH), 5.73 (s, 2H, pyrazole CH), 5.06 (s, 4H,
CH2), 4.73 (s, 4H, CH2), 2.19(s, 12H, CH3), 2.06 (s, 6H,
CH3), 2.04 (s, 6H, CH3). 13C NMR (CDCl3, 50.3 MHz, 25
°C): δ = 148.1, 147.1, 139.3, 139.1, 124.8, 113.7, 105.7, 105.4,
44.5, 43.3, 13.6, 11.2, 10.9. FT-IR (KBr, cm−1): ν = 3402 (m),
2923 (m), 1652 (w), 1550 (s), 1458 (s), 1427 (s), 1382 (m),
1283 (m), 1225 (w), 1028 (w), 985 (w), 855 (w), 775 (m),
685 (w), 620 (w), 550 (w). HRMS (−ESI) m/z: [M − H+]−
calcd for C28H36N9, 498.3094; found, 498.3089.
Synthesis of [Pd2Cl4(μ-C4HN-2,3,4,5-(CH2Me2pz)4-
N,N,N,N)], 3. To a solution of [Pd(COD)Cl2] (0.1 g, 0.35
mmol) in dichloromethane (15 mL) was added LH (0.09 g,
0.175 mmol). The solution was stirred for 16 h at room
temperature. The solvent was removed under vacuum and the
residue was washed with diethyl ether (3 × 10 mL) and then
dried under vacuum to give 3 as red solid (0.12 g, 0.135 mmol,
77% based on Pd). A saturated solution of 3 in toluene/
dichloromethane mixture was allowed to stand for slow
evaporation at room temperature to give 3 as red-colored
needle-shaped crystals. 1H NMR (CDCl3, 400 MHz, 25 °C): δ
= 9.41 (br s, 1H, NH), 5.92 (s, 2H, pyrazole CH), 5.88 (s, 2H,
pyrazole CH), 5.41 (d, J(HAHB) = 15.2 Hz, 2H, CH2), 5.29 (d,
EXPERIMENTAL SECTION
■
All reactions and manipulations were carried out under a
nitrogen atmosphere using standard Schlenk-line techniques.
Petroleum ether (bp 40−60 °C) and other solvents were
distilled according to the standard procedures. 2,5-Bis-
[(dimethylamino)methyl]pyrrole,37 3,5-dimethylpyrazole-1-car-
binol,38 and [Pd(COD)Cl2]39 were prepared according to the
literature procedures. Other chemicals were obtained from
1
commercial sources and used without further purification. H
NMR (200 and 400 MHz) and 13C NMR (50.3 and 100.6
MHz) spectra were recorded on a Bruker ACF200
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J(HAHB) = 15.2 Hz, 2H, CH2), 4.48 (overlapped doublets,
J(HAHB) = 15.2 Hz, 4H, CH2), 2.73 (s, 6H, CH3), 2.59 (s, 6H,
CH3), 2.32 (s, 6H, CH3), 2.28 (s, 6H, CH3). FT-IR (KBr,
cm−1): ν = 3245 (m), 3128 (w), 2926 (m), 1627 (w), 1554 (s),
1459 (s), 1422 (s), 1263 (m), 1155 (w), 1056 (w), 991 (w),
793 (m), 657 (w), 621 (w). HRMS (+ESI) m/z: [M − 2Cl]+
calcd for C28H37Cl2N9Pd2, 781.0619; found, 781.0622. Anal.
Calcd for C28H40Cl4N9O1.5Pd2: C, 38.16; H, 4.57; N, 14.30.
Found: C, 38.11; H, 4.59; N, 13.79.
Synthesis of [Cu2(μ-X)(μ-C4HN-2,3,4,5-(CH2Me2pz)4-
N,N,N,N)]+[CuX2]− (X = Cl for 4a and I for 4b). To a
solution of CuX (X = Cl or I) in THF (∼50 mL) was added
LH. The solution was stirred for 12 h at room temperature.
The solvent was removed under vacuum, and the residue was
dissolved in THF. The THF solution was layered with
petroleum ether to give 4a or 4b as colorless crystals after 3
days.
crystals of 5 over a period of 7 days (0.06 g, 0.06 mmol, 48%
based on Ag). H NMR (DMSO-d6, 200 MHz, 25 °C): δ =
1
11.39 (br s, 1H, NH), 6.08 (s, 2H, pyrazole CH), 6.02 (s, 2H,
pyrazole CH), 5.15 (s, 4H, CH2), 4.84 (s, 4H, CH2), 2.37 (s,
6H, CH3), 2.21 (s, 12H, CH3), 2.07 (s, 6H, CH3), 2.05 (s, 6H,
CH3). 13C NMR (DMSO-d6, 50.3 MHz, 25 °C): δ = 148.4,
148.0, 142.2, 141.7, 127.3, 114.9, 105.8, 105.7, 99.5, 42.0, 41.8,
14.2, 11.2, 10.6. FT-IR (KBr, cm−1): ν = 3402 (m), 3324 (m),
2922 (m), 1633 (w), 1552 (s), 1462 (s), 1426 (s), 1387 (m),
1273 (m), 1229 (w), 1080 (vs), 1032 (vs), 890 (w), 807 (m),
774 (m), 689 (w), 617 (w), 524 (w), 467 (w). HRMS (+ESI)
m/z: [M − 2MeCN − 2BF4]+ calcd for C28H37Ag2N9,
713.1274; found, 713.1203.
Synthesis of [Pd2Cl3(μ-C4N-2,3,4,5-(CH2Me2pz)4-
N,N,N,N,N)], 6. To a toluene solution of LH (0.25 g, 0.50
mmol) was added n-BuLi (1.6 M in hexanes, 0.5 mL, 0.75
mmol) at −78 °C. The solution was allowed to warm to room
temperature and stirred for an additional 1 h. Then this
solution was added to the tetrahydrofuran solution of
[Pd(COD)Cl2] (0.285 g, 1.00 mmol) at room temperature.
After stirring for 12 h, all volatiles were evaporated, and the
residue was dissolved in dichloromethane (∼100 mL). The
solution was layered with petroleum ether, and orange crystals
of 6 were formed over a period of 1 week (∼0.09 g, 0.10 mmol,
20% yield). FT-IR (KBr, cm−1): ν = 3121 (w), 2954 (w), 2922
(m), 1626 (w), 1554 (s), 1464 (s), 1424 (s), 1390 (s), 1263
(m), 1228 (m), 1058 (w), 1002 (w), 887 (w), 833 (w), 793
(m), 735 (w), 623 (w). Anal. Calcd for C29H38Cl5N9Pd2: C,
38.58; H, 4.24; N, 13.96. Found: C, 38.15; H, 4.23; N, 13.67.
Synthesis of [(Cu2(μ-I){μ-C4N-2,3,4,5-(CH2Me2pz)4-
N,N,N,N,N})2Cu]+I−, 7. To a toluene solution of LH (0.25 g,
0.50 mmol) was added n-BuLi (1.6 M in hexanes, 0.5 mL, 0.75
mmol) at −78 °C. The solution was allowed to warm to room
temperature and stirred for an additional 1 h. This solution was
added to the THF solution of CuI (0.10 g, 0.5 mmol) at room
temperature. After stirring for 12 h, the solution was layered
with petroleum ether to give colorless crystal of 7 over a period
For 4a (X = Cl). CuCl (0.1 g, 1.01 mmol), LH (0.25 g, 0.50
1
mmol). Yield: 0.15 g, 0.17 mmol, 51% based on Cu. H NMR
(CDCl3, 400 MHz, 25 °C): δ = 11.79 (br s, 1H, NH), 5.82 (s,
2H, pyrazole CH), 5.64 (s, 2H, pyrazole CH), 4.95 (br s, 8H,
CH2), 2.43 (s, 6H, CH3), 2.28 (s, 6H, CH3), 2.25 (s, 6H, CH3),
2.21 (s, 6H, CH3). 1H NMR (DMSO-d6, 400 MHz, 25 °C): δ =
11.95 (br s, 1H, NH), 6.06 (s, 2H, pyrazole CH), 5.71 (s, 2H,
pyrazole CH), 5.34 (d, J(HAHB) = 14.0 Hz, 2H, CH2), 5.19 (s,
4H, CH2), 4.96 (d, J(HAHB) = 14.0 Hz, 2H, CH2), 2.38 (s, 6H,
CH3), 2.28 (s, 6H, CH3), 2.19 (s, 6H, CH3), 2.12 (s, 6H, CH3).
13C NMR (DMSO-d6, 100.6 MHz, 25 °C): δ = 146.7, 145.5,
140.1, 138.7, 127.2, 116.4, 105.7, 104.8, 66.8, 41.4, 40.8, 24.9,
13.6, 13.6, 10.8. FT-IR (KBr, cm−1): ν = 3116 (m), 3018 (m),
2924 (m), 2734 (w), 1620 (w), 1552 (s), 1460 (s), 1425 (s),
1266 (m), 1093 (w), 1048 (m), 788 (m), 680 (w), 620 (w).
HRMS (+ESI) m/z: [M − CuCl2]+ calcd for C28H37ClCu2N9,
660.1647; found, 660.1434.
For 4b (X = I). CuI (0.10 g, 0.52 mmol), LH (0.13 g, 0.30
1
mmol). Yield: 0.10 g, 0.08 mmol, 47% based on Cu. H NMR
(CDCl3, 200 MHz, 25 °C): δ = 9.33 (br s, 1H, NH), 5.86 (s,
2H, pyrazole CH), 5.80 (s, 2H, pyrazole CH), 5.21 (br s, 4H,
CH2), 4.67 (br s, 4H, CH2), 2.36 (s, 6H, CH3), 2.32 (s, 6H,
CH3), 2.30 (s, 6H, CH3), 2.11 (s, 6H, CH3). 1H NMR
(DMSO-d6, 400 MHz, 25 °C): δ = 12.10 (br s, 1H, NH), 6.05
(s, 2H, pyrazole CH), 5.76 (s, 2H, pyrazole CH), 5.18 (br s,
8H, CH2), 2.39 (s, 6H, CH3), 2.26 (s, 6H, CH3), 2.19 (s, 6H,
CH3), 2.16 (s, 6H, CH3). 13C NMR (DMSO-d6, 100.6 MHz,
25 °C): δ = 146.7, 145.8, 140.2, 138.9, 126.9, 116.4, 106.1,
105.2, 66.9, 41.5, 41.2, 25.0, 14.4, 14.1, 10.8. FT-IR (KBr,
cm−1): ν = 3239 (w), 2928 (m), 2868 (m), 1650 (w), 1625
(w), 1553 (s), 1458 (s), 1422 (s), 1387 (m), 1265 (m), 1115
(w), 1045 (w), 920 (w), 888 (w), 788 (w), 682 (w). HRMS
(+ESI) m/z: [M − CuI2]+ calcd for C28H37Cu2IN9, 752.1009;
found, 752.0784. Anal. Calcd for C32H45Cu3I3N9O: C, 33.62;
H, 3.97; N, 11.03. Found: C, 33.41; H, 3.75; N, 11.26.
1
of 7 days (0.05 g, 0.03 mmol, 28% based on Cu). H NMR
(DMSO-d6, 400 MHz, 25 °C): δ = 5.86 (s, 2H, pyrazole CH),
5.70 (s, 2H, pyrazole CH), 5.23−4.77 (m, 8H, CH2), 2.30 (s,
12H, CH3), 2.26 (s, 12H, CH3), 2.17 (s, 12H, CH3), 2.13 (s,
12H, CH3). 13C NMR (DMSO-d6, 100.6 MHz, 25 °C): δ =
146.4, 145.2, 139.7, 134.8, 125.3, 114.3, 105.7, 105.0, 45.7, 42.3,
14.5, 14.3, 11.4, 10.9. FT-IR (KBr, cm−1): ν = 2921 (m), 2868
(w), 1551 (s), 1457 (s), 1423 (s), 1385 (w), 1266 (m), 1228
(m), 1046 (m), 985 (w), 954 (w), 881 (w), 780 (m), 682 (w),
621 (w), 509 (w). Anal. Calcd for C63H80Cu5I3N18: C, 42.32;
H, 4.51; N, 14.10. Found: C, 41.82; H, 4.45; N, 14.23.
Synthesis of [Ag4(μ-C4N-2,3,4,5-(CH2Me2pz)4-
−
N,N,N,N)2]2+ [BF4 ]2, 8. Method A. To a toluene solution of
LH (0.25 g, 0.50 mmol) was added n-BuLi (1.6 M in hexanes,
0.5 mL, 0.75 mmol) at −78 °C. The solution was allowed to
warm to room temperature and stirred for an additional 1 h.
This solution was added to a THF solution of AgBF4 (0.20 g,
1.00 mmol) at room temperature. After stirring for 12 h in the
dark, all volatiles were evaporated under vacuum, and the
residue was dissolved in acetonitrile (∼20 mL). The solution
was filtered and layered with diethyl ether (∼50 mL), which
was allowed to stand for slow evaporation to give a few
colorless crystals of 8.
Synthesis of [Ag2(μ-C4HN-2,3,4,5-(CH2Me2pz)4-
N,N,N,N)(CH3CN)2]2+[BF4 ]2, 5. To a tetrahydrofuran (∼50
−
mL) solution of AgBF4 (0.05 g, 0.26 mmol) was added LH
(0.06 g, 0.13 mmol). The solution was stirred for 12 h at room
temperature in the dark, resulting in the formation of colorless
precipitate. The solution was filtered to remove the precipitate.
The solvent was removed from the filtrate under vacuum, and
the residue was washed with THF (10 mL) followed by
petroleum ether twice (2 × 20 mL) and then dried under
vacuum, giving a colorless solid. This solid was dissolved in
acetonitrile and then layered with diethyl ether to give colorless
Method B. To an acetonitrile (∼40 mL) solution of LH
(0.25 g, 0.50 mmol) and triethylamine (0.278 mL, 2.00 mmol)
was added AgBF4 (0.195 g, 1.00 mmol). The solution was
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stirred for 12 h at room temperature in dark, resulting in the
formation of suspension. The solution was filtered, and the
filtrate was evaporated under vacuum. The residue was washed
with diethyl ether (3 × 10 mL) and extracted with acetonitrile
(∼50 mL). The acetonitrile solution was layered with diethyl
stirred at room temperature for 48 h to give a pale yellow
precipitate. The solution was filtered, and the precipitate was
washed with water twice (3 mL). The precipitate was dissolved
in dichloromethane, and the solution was dried over anhydrous
Na2SO4 and then filtered. The filtrate was evaporated under
vacuum to give complex 10 as a brown solid (0.03 g, 0.05
1
ether (∼100 mL) to give tiny colorless crystals of 8. H NMR
1
(CDCl3, 400 MHz, 25 °C): δ = 6.02 (s, 2H, pyrazole CH), 5.90
(s, 2H, pyrazole CH), 5.31 (s, 4H, CH2), 5.21 (s, 4H, CH2),
2.46 (s, 12H, CH3), 2.32 (s, 12H, CH3), 2.30 (s, 12H, CH3),
2.23 (s, 12H, CH3). FT-IR (KBr, cm−1): ν = 2927 (m), 1626
(w), 1552 (s), 1460 (s), 1424 (s), 1383 (m), 1336 (w), 1269
(w), 1226 (w), 1056 (vs), 949 (w), 884 (w), 831 (w), 779 (w),
731 (w), 680 (w), 626 (w). Anal. Calcd for C60H78Ag4B2F8N20:
C, 42.78; H, 4.67; N, 16.63. Found: C, 42.52; H, 4.68; N, 16.32.
Synthesis of [Pd(OAc)(C4N-2,3,4,5-(CH2Me2pz)4-
N,N,N)], 9. To a solution of [Pd(OAc)2] (0.20 g, 0.90
mmol) in dichloromethane (30 mL) was added LH (0.44 g,
0.90 mmol). The solution was stirred for 16 h at room
temperature. The solvent was removed under vacuum, and the
residue was dissolved in a minimum quantity (∼5−10 mL) of
dichloromethane. Addition of hexanes (∼150 mL) results in
the precipitate of some solid, which was separated by filtration.
The solvent was removed from the filtrate under vacuum to
give 9 as a pale yellow solid (0.50 g, 0.75 mmol, 84% based on
Pd). Suitable single crystals of 9 for X-ray diffraction study were
grown from a dichloromethane/hexane (1/15, v/v) solution
upon slow evaporation at room temperature. 1H NMR (CDCl3,
200 MHz, 25 °C): δ = 5.75 (s, 4H, pyrazole CH), 5.08−4.91
(m, 8H, CH2), 2.30 (s, 6H, CH3), 2.18 (s, 12H, CH3), 2.03 (s,
6H, CH3), 1.93 (s, 3H, acetate-CH3). 13C NMR (CDCl3, 50.3
MHz, 25 °C): δ = 177.8, 151.0, 146.8, 141.2, 138.9, 126.1,
112.0, 107.1, 105.7, 45.2, 44.9, 23.3, 13.7, 13.6, 11.7, 11.3. FT-
IR (KBr, cm−1): ν = 2925 (m), 2863 (w), 2574 (w), 1715 (m),
1623 (m), 1554 (s), 1460 (s), 1423 (s), 1387 (s), 1327 (m),
1259 (s), 1060 (w), 1034 (w), 876 (w), 797 (m), 680 (w), 615
(w). HRMS (+ESI) m/z: [M − OAc]+ calcd for C28H36N9Pd,
604.2128; found, 604.2151.
mmol, 62% yield based on Pd). The H NMR spectrum of 10
obtained from this procedure is the same as that obtained for
10 synthesized from the above method.
X-ray Crystallography. Suitable single crystals of 3−9
were obtained from solvents mentioned in their respective
synthetic procedures. Single crystal X-ray diffraction data
collections for these crystals were performed using a Bruker-
APEX-II CCD diffractometer with graphite monochromated
molybdenum Kα radiation (λ = 0.71073 Å). The structures
were solved by SIR-9240 available in the WinGX program which
successfully located most of the non-hydrogen atoms.
Subsequently, least-squares refinements were carried out on
F2 using SHELXL-9741 (WinGX version) to locate the
remaining non-hydrogen atoms. Typically for all the structures,
hydrogen atoms attached to carbon atoms were fixed in
calculated positions. The pyrrolic NH hydrogen atoms were
located from the difference Fourier map and freely refined
isotropically with their thermal parameters set as equivalent to
1.2 times that of their parent atoms.
Complex 3 crystallizes in the monoclinic P2/n space group,
and the asymmetric unit contains one molecule of 3 and three
water molecules, two of which have half occupancy. Hydrogen
atoms attached to these water molecules are neither fixed nor
located, as they have not appeared, which results in the
discrepancy between the calculated and reported values in its cif
file. Complex 4a crystallizes in the monoclinic space group P21/
c, and the asymmetric unit contains both the cation and anion
represented together with one THF molecule; however,
complex 4b crystallizes in the triclinic space group P1 , and
̅
the asymmetric unit contains units similar to 4a. Complex 5
crystallizes in the orthorhombic space group Pna2(1) with the
whole molecule of 5 in the asymmetric unit. The pyrrolic NH
Synthesis of [Pd(Cl)(C4N-2,3,4,5-(CH2Me2pz)4-N,N,N)],
10. To a solution of [Pd(COD)Cl2] (0.10 g, 0.35 mmol) and
LH (0.175 g, 0.35 mmol) in dichloromethane (10 mL) was
added dropwise triethylamine (0.20 mL, 1.40 mmol) at room
temperature. The solution was stirred for 12 h and then washed
with water three times. The organic layer was separated and
dried over anhydrous Na2SO4. The solution was filtered, and
the filtrate was concentrated to a minimum amount. Addition
of hexanes (200 mL) results in the formation of a light brown
precipitate. The solution was again filtered, and the precipitate
was washed with diethyl ether two times. The precipitate was
dried under vacuum to give 10 as brown solid (0.10 g, 0.16
−
hydrogen atom could not be located but was fixed. Its BF4
ions are severely disordered and were handled successfully
using SIMU and SADI. Complex 6 crystallizes in the
monoclinic space group P21/c with all angle values equal to
90° and the asymmetric unit contains one molecule of 6
together with one dichloromethane molecule in the lattice.
Complex 7 crystallizes in the monoclinic centrosymmetric
space group C2/c, and the asymmetric unit contains one-half of
the molecule, in which the central copper(I) atom is located on
the inversion center, together with one iodine atom and one
toluene molecule as a solvent of crystallization. The whole
molecule was generated by the symmetry operation. The
toluene molecule is highly disordered and could not be
modeled. As a result, there is a discrepancy between the
calculated and reported number of hydrogen atoms. Complex 8
crystallizes in the monoclinic P21/n space group and the
1
mmol, 44% yield based on Pd). H NMR (CDCl3, 200 MHz,
25 °C): δ = 5.82 (s, 2H, pyrazole CH), 5.78 (s, 2H, pyrazole
CH), 5.30−4.90 (m, 8H, CH2), 2.58 (s, 6H, CH3), 2.24 (s, 6H,
CH3), 2.22 (s, 6H, CH3), 2.07 (s, 6H, CH3). 13C NMR
(CDCl3, 50.3 MHz, 25 °C): δ = 153.1, 147.0, 141.6, 139.0,
126.0, 111.8, 107.6, 105.8, 45.6, 44.9, 16.3, 13.7, 11.9, 11.5. FT-
IR (KBr, cm−1): ν = 2956 (w), 2923 (m), 2857 (w), 1653 (w),
1552 (s), 1458 (s), 1426 (s), 1384 (s), 1336 (w), 1295 (w),
1260 (s), 1220 (w), 1094 (m), 1029 (m), 874 (w), 800 (s), 678
(w), 626 (w). HRMS (+ESI) m/z: [M − Cl]+ calcd for
C28H36N9Pd, 604.2128; found, 604.2151.
−
asymmetric unit contains one-half of the molecule, one BF4
and one acetonitrile solvent. The whole molecule was
generated by the symmetry operation and has an inversion
−
center. The two BF4 ions are severely disordered and were
handled successfully using EADP and SADI. Complex 9
crystallizes in the monoclinic space group C2/c with one
molecule in the asymmetric unit. The refinement data for all
the structures are summarized in Table 2.
Synthesis of 10 from 9. Solid LiCl (0.02 g, 0.375 mmol)
was added to a solution of complex 9 (0.05 g, 0.075 mmol) in
acetone/water (v/v 3/2, 5 mL). The resultant suspension was
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(13) Liu, X.; Pattacini, R.; Deglmann, P.; Braunstein, P. Organo-
metallics 2011, 30, 3302−3310.
ASSOCIATED CONTENT
* Supporting Information
NMR, IR spectra, and crystallographic data (CIF). This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
(14) Muller, H.; Bauer-Siebenlist, B.; Csapo, E.; Dechert, S.; Farkas,
̈
E.; Meyer, F. Inorg. Chem. 2008, 47, 5278−5292.
(15) (a) Neo, S. P.; Zhou, Z.-Y.; Mak, T. C. W.; Hor, T. S. A. J.
Chem. Soc., Dalton Trans. 1994, 3451−3458. (b) Bowmaker, G. A.;
Hart, R. D.; Jones, B. E.; Skelton, B. W.; White, A. H. J. Chem. Soc.,
Dalton Trans. 1995, 3063−3070.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gmani@chem.iitkgp.ernet.in. Fax: +91 3222 282252.
Notes
■
(16) (a) Duggan, D. M.; Jungst, R. G.; Mann, K. R.; Stucky, G. D.;
Hendrickson, D. N. J. Am. Chem. Soc. 1974, 96, 3443−3450.
(b) Reger, D. L.; Pascui, A. E.; Smith, M. D.; Jezierska, J.;
Ozarowski, A. Inorg. Chem. 2012, 51, 11820−11836.
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Trans. 1984, 2581−2583. (b) Stamp, L.; Dieck, H. T. Inorg. Chim. Acta
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the CSIR and DST (New Delhi, India) for financial
support and for the X-ray and NMR facilities.
■
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