Pyrrole-based new diphosphines: Pd and Ni complexes bearing the pnp pincer ligand

Article abstract of DOI:10.1021/ic301967r

A new class of diphosphine PNP pincer ligand, 2,5- bis(diphenylphosphinomethyl)pyrrole 2, was synthesized by the reaction between Ph₂PH and 2,5-bis(dimethylaminomethyl)pyrrole in 90% yield. The analogous reaction of Ph₂PH with 1,9-bis(dimethylaminomethyl) diphenyldipyrrolylmethane readily afforded a PNNP type diphosphine ligand, 1,9-bis(diphenylphosphinomethyl)diphenyldipyrrolylmethane 5 in 92% yield. These phosphine compounds were oxidized with H₂O₂ and S ₈ to give the corresponding phosphoryl and thiophosphoryl compounds 6-9 in very good yields. The reaction of the PNP pincer ligand 2 with [PdCl ₂(PhCN)₂] in the presence of Et₃N afforded the mononuclear Pd(II) complex, [PdCl{C₄H₂N-2,5-(CH ₂PPh₂)₂-κ³PNP}] 10 in 87% yield. Conversely, treatment of 2 with [PdCl₂(PhCN)₂] in the absence of Et₃N gave the dinuclear Pd(II) complex [Pd ₂Cl₄{μ-C₄H₃N-2,5-(CH ₂PPh₂)₂-κ²PP}₂], the structure which is proposed based on the spectroscopic data. When 2 was treated with Pd(0) precursor [Pd₂(dba)₃]·CHCl ₃ the dinuclear Pd(I) complex [Pd₂{μ-C ₄H₂N-2,5-(CH₂PPh₂) ₂-κ²PN,κ¹P}₂], 12, was obtained in 23% yield. The formation of complex 12 is solvent dependent, which transforms into complex 10 in CDCl₃ as studied by variable temperature ¹H and ³¹P NMR methods. Treatment of 2 with [Ni(OAc)₂]·4H₂O gave the mononuclear Ni(II) pincer complex [Ni(OAc){C₄H₂N-2,5-(CH₂PPh ₂)₂-κ³PNP}], 13, which upon treatment with an excess of LiCl or LiBr or KI afforded the respective halide ion substituted Ni(II) complexes, [NiX{C₄H₂N-2,5-(CH ₂PPh₂)₂-κ³PNP}] (X = Cl, Br, and I), 14-16, in very good yields. The structures of 5, 2,5- bis(diphenylphosphorylmethyl)pyrrole 6, 10, 12, and 14-16 were determined by the single crystal X-ray diffraction method. In the structure of 12, two short contacts between the diagonally positioned Pd and P atoms are observed. To understand these weak interactions, density functional theory (DFT) calculations were done and an interaction MO diagram is presented.

Full text of DOI:10.1021/ic301967r

Article
pubs.acs.org/IC
Pyrrole-Based New Diphosphines: Pd and Ni Complexes Bearing the
PNP Pincer Ligand
Shanish Kumar, Ganesan Mani,* Sukanta Mondal, and Pratim Kumar Chattaraj
Department of Chemistry, Indian Institute of Technology, Kharagpur, India 721 302
S
* Supporting Information
ABSTRACT: A new class of diphosphine PNP pincer ligand,
2,5-bis(diphenylphosphinomethyl)pyrrole 2, was synthesized by
t h e r e a c t i o n b e t w e e n P h 2 P H a n d 2 , 5 - b i s -
(dimethylaminomethyl)pyrrole in 90% yield. The analogous
reaction of Ph2PH with 1,9-bis(dimethylaminomethyl)-
diphenyldipyrrolylmethane readily afforded a PNNP type
diphosphine ligand, 1,9-bis(diphenylphosphinomethyl)-
diphenyldipyrrolylmethane 5 in 92% yield. These phosphine
compounds were oxidized with H2O2 and S8 to give the
corresponding phosphoryl and thiophosphoryl compounds 6−9
in very good yields. The reaction of the PNP pincer ligand 2
with [PdCl2(PhCN)2] in the presence of Et3N afforded the
mononuclear Pd(II) complex, [PdCl{C4H2N-2,5-(CH2PPh2)2-κ3PNP}] 10 in 87% yield. Conversely, treatment of 2 with
[PdCl2(PhCN)2] in the absence of Et3N gave the dinuclear Pd(II) complex [Pd2Cl4{μ-C4H3N-2,5-(CH2PPh2)2-κ2PP}2], the
structure which is proposed based on the spectroscopic data. When 2 was treated with Pd(0) precursor [Pd2(dba)3]·CHCl3 the
dinuclear Pd(I) complex [Pd2{μ-C4H2N-2,5-(CH2PPh2)2-κ2PN,κ1P}2], 12, was obtained in 23% yield. The formation of complex
1
12 is solvent dependent, which transforms into complex 10 in CDCl3 as studied by variable temperature H and 31P NMR
methods. Treatment of 2 with [Ni(OAc)2]·4H2O gave the mononuclear Ni(II) pincer complex [Ni(OAc){C4H2N-2,5-
(CH2PPh2)2-κ3PNP}], 13, which upon treatment with an excess of LiCl or LiBr or KI afforded the respective halide ion
substituted Ni(II) complexes, [NiX{C4H2N-2,5-(CH2PPh2)2-κ3PNP}] (X = Cl, Br, and I), 14−16, in very good yields. The
structures of 5, 2,5-bis(diphenylphosphorylmethyl)pyrrole 6, 10, 12, and 14−16 were determined by the single crystal X-ray
diffraction method. In the structure of 12, two short contacts between the diagonally positioned Pd and P atoms are observed. To
understand these weak interactions, density functional theory (DFT) calculations were done and an interaction MO diagram is
presented.
PCN,18 PNN,19 and PNP20 have attracted great attention right
INTRODUCTION
■
from the first pincer ligand (PCP) reported in 1976.21
Metal complexes containing a pincer framework ligand
Typically, several of these PCP or other pincer ligands have a
continue to attract attention because of their ability in
six-membered aromatic ring which supplies the central atom. In
providing the required combination of stability and reactivity
with metal complexes.1 The framework of a pincer ligand can
contrast to this, only a few pincer ligands whose central atom
comes from a pyrrole ring have been reported.22 Recently, we
be modified in terms of both steric and electronic factors to
reported the synthesis of a new NNN pincer ligand containing
modulate the property of a metal center, which has led to
development of several types of pincer ligands.2 Pincer ligands
a pyrrole unit which supplies the central atom and its Pd and Li
complexes.23
coordinate in L3, L2X, LX2, and X3 fashions to metal centers.3
Such coordination modes often maintain a rigid planarity with
metal centers.4 Pincer complexes have been shown to be very
active catalysts for various organic transformation reactions
such as alkane dehydrogenation,5 dehydrogenation of alcohols,6
activation of small molecules,7 Suzuki,8 Heck,9 Kumada10 and
olefin polymerization reactions11 among others12 and act as
platforms to understand mechanistic details of very important
reactions such as activation of C−C,13 C−N,14 C−O,15 and C−
H16 bond. Pincer ligands are classified as EZE′ where E and E′
are usually neutral donor atoms and Z is a central monoanionic
or neutral donor atom. Among the known types of pincer
ligands, pincer ligands containing a P donor such as PCP,17
As a continuation of our interests to develop pyrrole-based
pincer ligands, we set to synthesize new pyrrole-based pincer
ligands containing P donors for exploring metal complexes and
their catalytic applications. Herein, we report a simple synthetic
method for the preparation of a new class of pyrrole-based PNP
and the dipyrrolylmethane-based PNNP type diphosphine
ligands, and their oxidized products. In addition, we report the
synthesis and structural characterization of Pd(II), Pd(I), and
Ni(II) complexes containing the PNP pincer ligand together
Received: September 9, 2012
Published: November 8, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of the Pyrrole-Based PNP Pincer (2) and PNNP Type (5) Diphosphines
with density functional theory (DFT) calculations on the Pd(I)
dimer. However, after our work was submitted to this journal, a
paper describing the synthesis of the compounds 2, 14, and 16
was submitted to Dalton Transactions and published online.24
RESULTS AND DISCUSSION
■
Synthesis and Characterization of P(III) and P(V)
Ligands. The reaction between a double Mannich base of
pyrrole, 2,5-bis(dimethylaminomethyl)pyrrole 1, and 2 equiv of
Ph2PH at elevated temperature in the absence of any solvent
cleanly afforded a new PNP pincer diphosphine ligand, 2,5-
bis(diphenylphosphinomethyl)pyrrole 2, in 90% yield. The
a n a l o g o u s r e a c t i o n o f P h 2 P H w i t h 1 , 9 - b i s -
(dimethylaminomethyl)diphenyldipyrrolylmethane in toluene
Figure 1. ORTEP diagram of 1,9-bis(diphenylphosphinomethyl)-
diphenyldipyrrolylmethane, 5 (30% thermal ellipsoids). All hydrogen
atoms except the pyrrollic NH are omitted for clarity. Selected bond
lengths (Å) and angles (deg): P1−C1 1.846(6), C1−C2 1.501(7),
C2−N1 1.368(7), C5−C6 1.521(8), P1−C1−C2 112.6(4), C5−C6−
C7 111.6(5).
under reflux condition readily afforded a new PNNP type
diphosphine ligand, 1,9-bis(diphenylphosphinomethyl)-
diphenyldipyrrolylmethane 5, in 92% yield (Scheme 1).
These compounds were formed by the nucleophilic sub-
−
stitution of dimethylamide (NMe2 ) by diphenylphosphide
(Ph2P−) group and were obtained in a pure form just by
removing volatiles of the reaction mixture. Earlier we reported a
pyrrole-based NNN pincer ligand, 2,5-bis(3,5-
dimethylpyrazolylmethyl)pyrrole, by this synthetic strategy
which is the reaction between 2,5-bis(dimethylaminomethyl)-
pyrrole and 3,5-dimethylpyrazole.23
which the diphosphine ligands 2 and 5 can be synthesized in
multigram scales, respectively.
The trivalent phosphorus centers in 2 and 5 were converted
to their pentavalent phosphorus centers by the oxidation
reactions shown in Scheme 2. Thus, the treatment of 2 or 5
with an aqueous H2O2 in toluene gave the phosphoryl
compound 6 or 8, respectively. The analogous reaction
between 2 or 5 with the elemental S8 in toluene yielded the
thiophosphoryl compound 7 or 9 in very good yields,
respectively. These compounds were primarily characterized
by spectroscopic methods. One of the interesting features of
The diphosphine compounds 2 and 5 are solid at room
1
temperature and soluble in common organic solvents. The H
NMR spectra of 2 and 5 in CDCl3 feature broad singlets at δ =
7.67 and 7.53 ppm for their NH protons, respectively. The
31P{1H}NMR spectra show a singlet at δ −16.3 ppm for 2 and
at δ −15.5 ppm for 5, suggesting that both phosphorus atoms
of 2 or 5 are in equivalent environments. In addition, the
structure of 5 was further confirmed by the X-ray diffraction
method (Figure 1 and Table 1). The X-ray structure revealed
that the two pyrrolic NH groups are oriented in opposite
directions with the two phosphorus centers pyramidalized in
opposite directions, which thus minimizes steric crowding.
It is noteworthy that these new diphosphine ligands were
synthesized without using an air-sensitive reactant Ph2PLi
which upon reaction with 1 or 4 or their quaternary ammonium
salts could lead to the formation of 2 or 5, respectively. For
example, the reaction between 1 or its quaternary ammonium
salt and 2 equiv of Ph2PLi in tetrahydrofuran (THF) gave a
mixture of products. The 31P NMR spectrum of this reaction
mixture in CDCl3 showed a singlet at −16.3 ppm, which is the
signal of 2, together with the resonance of Ph2PH and other
unidentified products. In view of these, the direct reaction of
Ph2PH with the Mannich bases is a simple and clean method,
and involves two and three steps starting from pyrrole using
1
their H NMR spectra, in contrast to those shown by the
trivalent phosphorus compounds 2 and 5, is the signal due to
the methylene protons, which appears as a doublet, owing to
coupling with the phosphorus atoms, in the deshielded region
as compared to the resonances of the methylene protons in 2
and 5. Similarly, the NH resonances appear as a broad singlet in
the deshielded region. The 31P{1H} spectrum of each
compound 6−9 in CDCl3 gives a singlet in the deshielded
region as compared to the chemical shift value at which the
parent compound resonates. This indicates that P(III) centers
are changed to P(V) centers which are in equivalent
environments. Further, the 31P chemical shift differences (Δδ
= 55.1 ppm for 7 and Δδ = 54.8 ppm for 9) observed for the
thiophosphoryl compounds are larger than those (Δδ = 47.8
ppm for 6 and 47.1 ppm for 8) observed for the phosphoryl
compounds; this is in line with the values of Δδ reported for
Ph3PO and Ph3PS.25
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Table 1. Crystallographic Data for Compounds 5, 6, 10, 12, and 14−16
5
(6·2H2O)2
10
12·0.5(C6H6)
empirical formula
formula weight
wavelength (Å)
temperature (K)
crystal system
color and shape
space group
a/Å
C47H40N2P2
694.75
C60H62N2O8P4
1063.00
C30H26NP2ClPd
604.31
C63H55N2P4Pd2
1176.77
0.71073
0.71073
0.71073
0.71073
295(2)
295(2)
295(2)
295(2)
monoclinic
colorless, needle
C2/c
triclinic
monoclinic
yellow, prism
P2(1)/c
triclinic
colorless, prism
orange, prism
P1
̅
9.873(3)
P1
̅
28.352(3)
10.4594(11)
26.729(3)
90.0
14.438(3)
16.355(3)
11.664(2)
90.0
13.7600(9)
14.2819(9)
16.0506(11)
66.630(2)
69.334(2)
85.481(2)
2702.3(3)
2
b/Å
13.325(4)
22.878(7)
91.246(10)
99.788(11)
109.750(9)
2781.3(16)
2
c/Å
α/deg
β/deg
103.113(3)
90.0
107.914(7)
90.0
γ/deg
volume (Å3)
7719.9(13)
8
2620.9(9)
4
Z
D
calcd, g cm−3
1.169
1.269
1.531
1.446
μ/mm−1
0.148
0.192
0.952
0.826
F(000)
2928
1120
1224
1198
crystal size/mm
θ range (deg)
limiting indices
0.44 × 0.17 × 0.08
1.47 to 20.82
−26 ≤ h ≤ 28,
−10 ≤ k ≤ 10,
−26 ≤ l ≤ 26
30151/4027
0.1313
0.50 × 0.25 × 0.13
0.91 to 25.19
−11 ≤ h ≤ 11
−15 ≤ k ≤ 15
−27 ≤ l ≤ 27
33621/9853
0.0892
0.31 × 0.16 × 0.05
1.48 to 25.00
−17 ≤ h ≤ 17
−19 ≤ k ≤ 19
−13 ≤ l ≤ 13
30979/4603
0.1523
0.27 × 0.19 × 0.14
1.48 to 26.28
−17 ≤ h ≤ 16,
−17 ≤ k ≤ 17,
−19 ≤ l ≤ 19
34841/10698
0.0637
total/unique no. of reflns.
Rint
data/restr./ params.
GOF (F2)
4027/0/468
0.998
9853/4/691
1.000
4603/0/316
1.002
10698/0/631
1.023
R1, wR2
0.0632, 0.1456
0.1284, 0.1809
1.004 and −0.286
0.0608, 0.1408
0.1528, 0.1845
0.413 and −0.280
0.0480, 0.0847
0.1070, 0.1044
0.501 and −0.617
0.0474, 0.0920
0.1007, 0.1133
0.581 and −0.376
16
R indices (all data) R1, wR2
largest different peak and hole (e Å−3
)
14
15
empirical formula
formula weight
wavelength (Å)
temperature (K)
crystal system
color and shape
space group
a/Å
C30H26ClNNiP2
556.62
C30H26BrNNiP2
601.08
C30H26INNiP2
648.07
0.71073
0.71073
0.71073
295(2)
295(2)
295(2)
monoclinic
orange, plate
P2(1)/c
monoclinic
brown, prism
P2(1)/c
monoclinic
purple, plate
P2(1)/c
14.423(3)
16.338(3)
11.552(2)
90.0
14.407(2)
16.410(3)
11.576(18)
90.0
14.436(5)
16.639(5)
11.587(5)
90.0
b/Å
c/Å
α/deg
β/deg
107.125(6)
90.0
107.282(5)
90.0
107.151(5)
90.0
γ/deg
volume (Å3)
2601.3(9)
4
2609.2(7)
4
2659.4(17)
4
Z
D
calcd, g cm−3
1.421
1.530
1.619
μ/mm−1
0.992
2.418
2.031
F(000)
1152
1224
1296
crystal size/mm
θ range (degree)
limiting indices
0.58 × 0.29 × 0.08
1.93 to 24.99
−15 ≤ h ≤ 17,
−19 ≤ k ≤ 19,
−13 ≤ l ≤ 13
30783/4572
0.0642
0.20 × 0.19 × 0.17
1.48 to 24.99
−16 ≤ h ≤ 17,
−19 ≤ k ≤ 19,
−13 ≤ l ≤ 13
30557/4586
0.1084
0.41 × 0.22 × 0.03
1.187 to 25.00
−17 ≤ h ≤ 15
19 ≤ k ≤ 19,
−13 ≤ l ≤ 13
30643/4670
0.0521
total/unique no. of reflns.
Rint
data/restr./ params.
GOF (F2)
4572/0/316
1.036
4586/0/316
1.027
4670/0/316
1.075
R1, wR2
0.0361, 0.0839
0.0620, 0.0955
0.0410, 0.0721
0.0947, 0.0913
0.0304, 0.0641
0.0491, 0.0805
R indices (all data) R1, wR2
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Table 1. continued
14
15
16
0.404 and −0.549
largest different peak and hole (e Å−3
)
0.398 and −0.229
0.371 and −0.412
P1 space group with two molecules in the asymmetric unit
Scheme 2. Synthesis of the Phosphoryl and Thiophosphoryl
Compounds 6−9
̅
along with four water molecules. As shown in Figure 2, two
molecules of 6 are held together primarily via methylene
CH···π interactions involving π electrons of the pyrrole ring.
The pyrrolic NH groups are oriented in opposite directions and
hydrogen bonded to the water molecules. One of the
methylene group hydrogen atoms of each molecule is oriented
more toward the center of the pyrrole ring of the adjacent
molecule, resulting in two intermolecular CH···π (pyrrole)
interactions. The observed bond lengths and angles support
this CH···π interaction: C6···Ct2 3.381 Å, H6b··· Ct2 2.501 Å,
C6−H6b···Ct2 150.96° and C31···Ct1 3.542 Å, H31a···Ct1
2.654 Å, C31−H31a···Ct1 152.38° (Ct = the centroid of a
pyrrole ring), which are similar to the reported CH···π
interaction with pyrrole ring.26 These interactions are further
facilitated by the orientation of the two phosphoryl groups
(Ph2PO) of each molecule; the “Ph2PO” groups are bent away
from the plane formed by the pyrrole ring and the two
methylene carbons. The P−O and the P−C (methylene) bond
distances are similar to those reported for other phosphine
oxide compounds.27
The structure of 6 was determined by a X-ray diffraction
study (Figure 2 and Table 1). Compound 6 crystallizes in the
Synthesis and Characterization of Pd Complexes.
Having synthesized the new PNP and PNNP type diphosphine
ligands in high yields, we set out to explore the coordination
chemistry of the PNP pincer ligand by reacting with Pd(II),
Pd(0), and Ni(II) precursors. As shown in Scheme 3, the
reaction between an equimolar quantity of 2 and
[PdCl2(PhCN)2] in the presence of NEt3 afforded the
mononuclear Pd(II) complex 10 in 87% yield after the workup
procedure. The role of NEt3 in this reaction is to facilitate the
removal of HCl. This is in contrast to the reported reduction
reactions giving Pd(I) complexes from Pd(II) precursors in the
presence of NEt3.28 Complex 10 was characterized by both
1
Figure 2. ORTEP diagram of (6·2H2O)2 with 30% probability
ellipsoids. Most H atoms are omitted for clarity. Selected bond lengths
(Å) and angles (deg): O1−P1 1.493(3), O3−P3 1.483(3), O4−P4
1.486(3), C1−P1 1.814(4), C25−P1 1.802(4), C2−N1 1.375(5),
C2−C1−P1 115.2(3), O1−P1−C25 112.11(19), C25−P1−C1
105.26(19), C19−P1−C25 107.92(19), N1−C2−C1 122.4(4),
C6···N2 3.574, H6b···N2 2.674, C6−H6b···N2 154.60; C31···N1
3.684, H31a···N1 2.789, C31−H31a···N1 153.82.
spectroscopic and X-ray diffraction methods. The H NMR
spectrum of 10 in CDCl3 shows a virtual triplet for the
methylene protons, which is the characteristic of the mer-κ3-
PNP coordination mode29 and does not show a NH resonance.
The absence of NH proton is further supported by the IR
spectrum which does not show NH stretching frequency.
Besides, the 31P{1H} NMR spectrum of 10 in CDCl3 shows a
singlet at δ = 33.8 ppm, a downfield shift of 50.1 ppm
Scheme 3. Synthesis of the Mononuclear and Dinuclear Pd Complexes, 10−12, Bearing the PNP Pincer Ligand 2
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compared to that of the free ligand (31P: δ = −16.3 ppm),
indicating that both the phosphorus centers of the ligand are
having equivalent environments. These data indicate the
presence of a monoanionic tridentate (mer-κ3-PNP) coordina-
tion mode of the pincer ligand in the structure of complex 10.
The structure of 10 was confirmed by the X-ray diffraction
method. The ORTEP diagram of the structure and the selected
bond lengths and angles are given in Figure 3 and Table 2,
analogous Pd(II) pyridine-based pincer complex containing
two fused five-membered rings.30 The geometry around the Pd
center is a distorted square planar with the Cl1−Pd1−P1 and
Cl1−Pd1−P2 angles of 99.33° and 98.23°, respectively, which
are larger than the other two angles (P1−Pd1−N1 = 81.53°
and P2−Pd1−N1 = 81.07°). This angle difference is commonly
observed for this type of complexes because of the steric factor
with which the pincer ligand adopts a mer-κ3-PNP coordination
mode. In addition, while the Pd−P bond distances (2.3074(16)
Å and 2.2987(17) Å) and the Pd−Cl bond distance
(2.3136(16) Å) are in the range reported for analogous
mononuclear Pd complexes bearing a PNP pincer ligand,20f,30,31
the Pd−Cl bond distance is shorter than those (2.333 Å,17d
2.395 Å32 and 2.397 Å33) reported for analogous Pd complexes
[(PCP)PdCl] bearing a PCP pincer ligand. This can be because
of a weak trans influence of the pyrrolide nitrogen atom
compared with that of the carbon atom in PCP pincer ligands.
On the contrary, the reaction of 2 with [PdCl2(PhCN)2] in
the absence of a base afforded complex 11 in 95% yield
(Scheme 3). The structure of 11 is proposed based on the
spectroscopic and elemental analysis data. The 1H NMR
spectrum of complex 11 shows a broad singlet at δ = 9.86 ppm
for the pyrrolic NH protons. The presence of NH groups is
further confirmed by the NH stretching frequency at 3344
cm−1 in the IR spectrum. The 31P{1H} NMR spectrum of 11 in
CDCl3 shows a singlet at δ = 14.3 ppm, which is a downfield
shift of 30.6 ppm compared to that of the free ligand and is in
the upfield region as compared to complex 10 (δ = 33.8 ppm)
suggesting that the coordination fashion of the pincer ligand 2
can be different here. Further, the high resolution mass
spectrometry electrospray ionization (HRMS, +ESI) spectrum
of 11 shows peaks m/z at 1173.9480 (calcd 1173.0996) and at
1177.9426 (calcd 1177.0944) corresponding to the [M−
3Cl−]3+ and the [M−4Cl−+K+]5+ ions, respectively. Further-
more, the X-ray structure of an analogous dinuclear Pd(II)
complex bearing the pincer ligand, 2,5-bis(3,5-
dimethylpyrazolylmethyl)pyrrole, has been reported by us.23
These data support the structure proposed for 11 in Scheme 3.
The reaction between 2 equiv of 2 and a Pd(0) precursor,
[Pd2(dba)3]·CHCl3, in toluene afforded a dinuclear Pd(I)
Figure 3. ORTEP diagram of the palladium complex 10 (30% thermal
ellipsoids): (a) top view, and (b) side view, showing the twisted
arrangement of the pincer ligand. All hydrogen atoms are omitted for
clarity.
complex 12 in 23% crystalline yield.34 The H NMR spectrum
1
of 12 in CDCl3 shows two ABX (A = HA and B = HB, X = P)
spin patterns for the PCH2 groups: one in the five-membered
chelate ring and the other in the bridging six-membered ring,
indicating the presence of two different phosphorus centers in
the structure. However, the 31P NMR spectrum which was
recorded immediately after dissolving crystals of 12 in CDCl3
or DMSO-d6 does not show two doublets instead two singlets
at δ = 17.6 and 20.5 ppm are observed. Nonetheless, this
respectively. As shown in Figure 3, the ligand is slightly twisted
and coordinated, and the structure possesses a C2 axis passing
through Pd−N bond. The two methylene carbon atoms are
located above and below the plane defined by the four ligating
atoms around the Pd center. This twisted conformation of the
pincer ligand with the dihedral angle of P1−Pd1−N1−C17 =
2.29° and P2−Pd1−N1−C14 = 15.27° is similar to an
Table 2. Comparison of Bond Lengths (Å) and Angles (deg) for the Mononuclear Pd(II) and Ni(II) Complexes
complex
M−N
M−X
M−P1
M−P2
[PNP]PdCl, 10
[PNP]NiCl, 14
[PNP]NiBr, 15
[PNP]NiI, 16
complex
1.981(4)
1.855(2)
1.856(3)
1.859(3)
2.3136(16)
2.1699(9)
2.3036(7)
2.4844(7)
P1−M−P2
2.3074(16)
2.1990(9)
2.2085(13)
2.1974(14)
2.2987(17)
2.2063(9)
2.1988(13)
2.2088(13)
N−M−P1
N−M−P2
P1−M−X
P2−M−X
N−M−X
[PNP]PdCl, 10
[PNP]NiCl, 14
[PNP]NiBr, 15
[PNP]NiI, 16
81.53(14)
82.94(7)
81.07(14)
83.95(7)
162.28(6)
166.11(3)
166.30(5)
166.43(5)
99.33(6)
96.61(3)
97.20(4)
95.92(4)
98.23(6)
96.80(3)
96.15(4)
97.41(4)
176.82(14)
175.71(8)
175.69(11)
174.85(10)
83.77(11)
83.14(10)
83.15(11)
83.82(10)
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confirms the presence of two different environments for the
phosphorus atoms as suggested by the H NMR spectrum.
Using a single crystal obtained from a solution of 12 in
toluene upon layering with petroleum ether, we determined the
structure of complex 12 by the X-ray diffraction method.
ORTEP diagrams along with selected bond lengths and angles,
and the refinement data are given in Figure 4 and Table 1,
the stronger trans influence of the Pd−Pd bond.35 The
geometry around each metal center is distorted square planar.
For example, around the Pd1 center, while P1 and N2 are
almost linear (N2−Pd1−P1 = 171.32°), P4 and Pd2 deviate
considerably from the linearity (P4−Pd1−Pd2 = 156.85°). The
two Pd square planes are twisted probably owing to the steric
repulsion between the two ligands which forms κ2PN,κ1P
bonding modes with the dihedral angles: N2−Pd1−Pd2−P3 =
−62.64° and N1−Pd2−Pd1−P1 = −59.81°. The Pd−Pd bond
distance of 2.5470 Å indicates a σ-bond between the two Pd(I)
centers. The observed Pd−Pd distance is close to the values
(2.55 to 2.56 Å)35,36 but is longer than the values (2. 41 to 2.50
Å)37 reported for the dinuclear Pd(I) complexes containing
both chelate and bridging modes of pincer ligands. Additionally,
this observed Pd−Pd distance is shorter than those (2.5738 and
2.61 Å39) found in complexes containing an unbridged Pd(I)−
Pd(I) bond. Interestingly, two short contacts are observed
within the two six-membered rings: P3···Pd1 = 2.974 Å and
P1···Pd2 = 3.081 Å. These distances are considerably shorter
than 3.45 Å, the sum of the van der Waals radii of P (1.85 Å)
and Pd (1.60 Å) atoms,40 and hence indicate the existence of
weak bonding interactions between the diagonally positioned P
and Pd atoms in each six-membered ring, which is facilitated by
the twisted square planes of the two Pd centers.
1
Although complex 12 is expected to be relatively more stable
because of the presence of both the chelating and the bridging
modes of the pincer ligand, it readily undergoes a trans-
formation in CDCl3 to give rise to complex 10 as shown by the
1H and 31P NMR spectra. To confirm the transformation of
1
complex 12 to 10, variable temperature H NMR experiments
1
were carried out using crystals of 12 in CDCl3. The VT H
NMR spectra showed the gradual appearance of a triplet at δ =
3.87 ppm, which is the same signal obtained for the PCH2
groups of complex 10, along with the resonances corresponding
to complex 12, upon gradually increasing the temperature of
the sample to 60 °C (see the Supporting Information, Figure
S64). In addition, the 31P NMR spectrum of 12 in CDCl3 also
showed signals corresponding to both the complexes after few
hours (see the Supporting Information, Figure S65), supporting
the transformation of complex 12 to 10. This conversion is
almost over within 2 days at room temperature as shown by the
1H NMR spectrum. Thus, the Pd(I) complex 12 is not stable
and transforms into the mononuclear Pd(II) chloride complex
10 in CDCl3 probably via oxidative addition reactions.
Conversely, 12 does not change to 10 in DMSO-d6 after 24
h as shown by the 31P NMR spectra recorded at different
intervals, suggesting that the complex is stable in this
coordinating solvent. This prompted us to carry out the
reaction in CDCl3 to see if complex 10 is formed or not.
Indeed, the characteristic triplet of the methylene protons of
complex 10 is found as a sole product in the 1H NMR spectrum
recorded for a reaction between 2 and [Pd2(dba)3]·CHCl3 in
CDCl3 carried out in a NMR tube. Besides, this transformation
explains why complex 12 was isolated in low yield (23%) given
the presence of CHCl3 in the starting material Pd(0) complex.
Synthesis and Characterization of Ni Complexes. The
reaction between an equimolar quantity of the PNP pincer
ligand 2 and [Ni(OAc)2]·4H2O gave a mixture of two products
Figure 4. ORTEP diagram of 12·0.5(C6H6) with 30% probability
ellipsoids: view b is showing the existence of the weak interactions
between the diagonally positioned P and Pd atoms. All H atoms, the
lattice benzene molecule, and the phenyl carbon atoms except the ipso
carbons (view b) are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Pd1−Pd2 2.5470(5), N1−Pd2 2.111(4), N2−Pd1
2.090(4), P1−Pd1 2.2395(13), P2−Pd2 2.3504(14), P3−Pd2
2.2329(13), P3−Pd1 2.9744(14), P4−Pd1 2.3559(14), N2−Pd1−P1
171.32(11), N2−Pd1−P4 81.26(11), P1−Pd1−P4 104.09(5), N2−
Pd1−Pd2 92.58(10), P1−Pd1−Pd2 79.84(4), P4−Pd1−Pd2
156.85(4), N2−Pd1−P3 72.26(11), P1−Pd1−P3 104.85(4), P4−
Pd1−P3 146.67(4), Pd2−Pd1−P3 46.92(3), N1−Pd2−P3
169.58(11), N1−Pd2−P2 82.79(12), P3−Pd2−P2 106.38(5), N1−
Pd2−Pd1 93.03(11), P3−Pd2−Pd1 76.65(4), P2−Pd2−Pd1
159.44(4).
respectively. The X-ray structure revealed that the binuclear
complex consists of two Pd(I) centers bridged by two anionic
PNP pincer ligands coordinated in a κ2PN,κ1P bonding modes
in a sort of trans fashion. In the structure, each ligand is twisted
and forms two different rings: a puckered five-membered
chelate ring and a puckered six-membered ring with the two Pd
centers. The six-membered Pd1−P1 and Pd2−P3 bond
distances (2.2395 Å and 2.2329 Å) are shorter than the chelate
five-membered Pd1−P4 and Pd2−P2 bond distances (2.3559 Å
and 2.3504 Å). The short Pd1−P1 and Pd2−P3 bonds which
are trans to the pyrrolide N atoms can be attributed to the
weaker trans influence of the pyrrolide N, while the long Pd−P
bonds which are trans to the Pd−Pd bond can be because of
1
in approximately 4:1 ratio as shown by the 31P NMR and H
spectra in CDCl3. The 31P NMR spectrum shows two singlets:
one at δ 27.0 (major) and the other at δ 30.8 ppm (minor).
The signal at δ 27.0 ppm is assigned to complex 13 (see
Scheme 4) because the other Ni(II) complexes 14−16, which
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Scheme 4. Synthesis of Ni(II) Complexes 13−16 Bearing the PNP Pincer Ligand 2
give singlets in this region, were synthesized in very good yields
without separation of complex 13 from the mixture (see
below). Complex 13 gives the characteristic triplet for the
1
methylene protons in the H spectrum, which is supported by
the 13C NMR spectrum showing a triplet owing to the J(C,P)
coupling for the methylene carbon atoms. The IR spectrum
shows a CO stretching frequency at 1625 cm−1 for the presence
of an acetate group in the structure of 13. In addition, the
HRMS(ESI+) spectrum shows a peak m/z at 561.0298 (calcd
561.0688) corresponding to the [M−OAc+2H++K+]4+ ion.
These data support the structure proposed for the mononuclear
Ni(II) complex 13 containing the monoanionic tridentate
pincer ligand 2 and one acetate group as shown in Scheme 4.
Without separating complex 13, the reaction mixture was
treated with an excess of LiCl or LiBr or KI in acetone/water at
room temperature to give the corresponding halide ion
substituted mononuclear Ni complexes 14−16 in good yields
(80−89%) (see Scheme 4). These products are formed via the
acetate-halide ion exchange reaction in an aqueous−organic
medium. Alternatively, complex 14 was synthesized by the
reaction of [NiCl2(DME)] with 2 in the presence of 1 equiv of
Et3N in 84% yield. All the three Ni halide pincer complexes
were characterized by spectroscopic and single crystal X-ray
1
diffraction studies. While the H NMR spectra of the Ni(II)
pincer complexes 13−16 remain similar to each other; all
displayed a virtual triplet for the methylene protons and a
Figure 5. ORTEP diagram of the nickel chloride complex 14 (30%
thermal ellipsoids): (a) top view, and (b) side view, showing the
twisted arrangement of the pincer ligand. All hydrogen atoms are
omitted for clarity. Selected torsion angles: P1−Ni−N−C14 = 15.85°;
P2−Ni−N−C17 = 2.16°.
singlet for the pyrrole β-CH protons, different singlets at δ =
27.0, 30.6, 35.0, 42.6 ppm for 13, 14, 15, and 16, respectively,
are observed in their 31P NMR spectra. As can be noticed, the
phosphorus chemical shift moves toward the deshielded region
as the electronegativity of the trans group attached to the Ni
center decreases, Cl > Br > I.
are attributed to the tridentate mer-κ3-PNP coordination mode
that is forcefully adopted by the pincer ligand 2.18b,20c,32,41
In the structure of complex 14, the Ni−Cl bond distance is
2.1699(9) Å which is shorter than those (2.232 Å,32 and 2.2167
Å,18b) found in the analogous Ni(II) complexes formed by the
PCP and the PCN pincer ligands, respectively. This is
attributed to the weaker trans influence of pyrrolide N atom
as observed in the Pd complex 10. However, the observed Ni−
N and Ni−P bond distances fall in the range reported for the
analogous Ni(II) complexes bearing the PNP pincer ligand.42,29
In the structure of complex 15, while the Ni−P bond
distances (2.2085(13) Å and 2.1988(13) Å) are close to the
reported Ni−P bond distance (2.183 Å), the Ni−N bond
distance (1.856(3) Å) is shorter than the Ni−N bond distance
(1.912 Å) reported for an analogous “(PNP)NiBr” pincer
complex42 containing an amide bond, indicating that the Ni−N
bond in complex 15 is stronger because of the pyrrolide
nitrogen.
The X-ray structures of 14, 15, and 16 are depicted in
Figures 5, 6, and 7, respectively, and their selected bond lengths
and angles are given in Table 2. Complexes 14, 15, and 16
exhibit very similar unit cell parameters and have the same
space group P21/c (Table 1). The structures of these complexes
resemble the structure of the Pd(II) complex 10. In each
structure, the pincer ligand is slightly twisted and adopts the
mer-κ3-PNP coordination mode resulting in two fused five-
membered chelate rings with the Ni(II) center with the
dihedral angles given below each diagram. A distorted square
planar geometry was observed in each Ni(II) complex as
indicated by their bond angles. As can be observed from Table
2, both the N−Ni−P1 and N−Ni−P2 bond angles are lower
than the other two angles, P1−Ni−X and P2−Ni−X (X = Cl,
Br, and I). In addition, the P1−Ni−P2 angles (∼166°), a
considerably lower value compared to the expected 180°, are
lower than the N−Ni−X angles (∼175°). These are typically
observed values for a distorted square planar Ni(II) pincer
complex containing two fused five-membered chelate rings and
In the structure of complex 16, the Ni−N and Ni−P bond
distances are very similar to those found in the structures of 14
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Figure 7. ORTEP diagram of the nickel iodide complex 16 (30%
thermal ellipsoids): (a) top view, and (b) side view, showing the
twisted arrangement of the pincer ligand. All hydrogen atoms are
omitted for clarity. Selected torsion angles: P1−Ni−N−C2 = 14.90°;
P2−Ni−N−C5 = 4.80°.
Figure 6. ORTEP diagram of the nickel bromide complex 15 (30%
thermal ellipsoids): (a) top view, and (b) side view, showing the
twisted arrangement of the pincer ligand. All hydrogen atoms are
omitted for clarity. Selected torsion angles: P1−Ni−N−C5 = 3.09°;
P2−Ni−N−C2 = 15.24°.
formation of Pd(I) dimer complex 12 is solvent dependent.
The bonding modes of the pincer ligand in these complexes,
bridging and chelating, were established by the X-ray diffraction
method, which demonstrated the versatile nature of the pincer
ligand. The conversion of the dimeric Pd(I) complex to the
and 15. However, as observed in the chloride and bromide
complexes, the Ni−I bond distance of 2.4844(7) Å is shorter
than the distance of 2.5229(9) Å found in the structure of
[NiI{2,6-(CH2PiPr2)2-C6H3}] in which the iodide atom is trans
to the more trans influencing carbon atom.43
mononuclear Pd(II) complex was demonstrated by 1H and 31
P
NMR methods. The weak interactions present in the crystal
structure of the Pd(I) dimer were analyzed by DFT
calculations. Synthesis of other phosphine ligands using this
method, and synthesis and catalysis studies of other metal
complexes are in progress in our laboratory.
DFT Study. DFT calculations are performed to understand
the nature of the weak interaction between the diagonally
oriented Pd and P atoms in the structure of complex 12. From
the DFT calculations, this interaction is shown to be through
the responsible donor and acceptor molecular orbitals (see the
Supporting Information, Table 3). The HOMO-15 and
HOMO-16 (Figure 8) are involved in the electron delocaliza-
tion for these interactions, as shown in the simplified MO
interaction diagram (Figure 9). Wiberg bond indices for these
weak interactions are 0.2507 and 0.2275 which are considerably
lower than those (0.5575 and 0.4869) obtained for the normal
bonds existing between the Pd and P atoms in the same
structure. This supports the weak bonding interactions as
observed in the crystal structure of complex 12.
EXPERIMENTAL SECTION
■
General Procedure. 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-
( d i m e t h y l a m i n o m e t h y l ) p y r r o l e 1 , 4 4 1 , 9 - b i s ( N , N -
dimethylaminomethyl)diphenyldipyrrolylmethane 4,4 5
[Pd2(dba)3]·CHCl3,46 [Pd(COD)Cl2],47 [Pd(PhCN)2Cl2],48
[NiCl2(DME)],49 and Ph2PH50 were prepared as reported. Other
chemicals were obtained from commercial sources and were used
without further purification. 1H NMR (200 and 400 MHz), 13C NMR
(50.3 and 100.6 MHz), and 31P (161.9 MHz) spectra were recorded
on Bruker ACF200 and AV400 spectrometers at room temperature.
1H NMR chemical shifts are referenced with respect to the chemical
shift of the residual protons present in the deuterated solvents. For 31P
NMR measurements 85% H3PO4 as an external standard was used.
FTIR spectra were recorded using Perkin−Elmer Spectrum Rx.
Elemental analyses were carried out using a Perkin−Elmer 2400 CHN
analyzer. High Resolution Mass Spectra (ESI) were recorded using an
LCT Orthogonal Acceleration TOF Electrospray Mass Spectrometer.
CONCLUSION
■
In conclusion, a new synthetic method was developed for the
preparation of a novel class of pyrrole-based PNP pincer and
dipyrrolylmethane-based PNNP type ligands from the double
Mannich bases of the corresponding pyrrole systems in high
yields. The coordination chemistry of the PNP pincer ligand
was explored with the synthesis of a series of mononuclear
Ni(II) and Pd(II), and dinuclear Pd(I) complexes. The
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Figure 8. Selected occupied molecular orbitals for the weak interactions in the structure of complex 12.
Synthesis of 2,5-Bis(diphenylphosphinomethyl)pyrrole, 2. A
mixture of 2,5-bis(dimethylaminomethyl)pyrrole (6.0 g, 33.09 mmol)
and Ph2PH (12.32 g, 66.17 mmol) was heated to 150 °C with stirring
for 22 h. The reaction mixture was cooled to room temperature, giving
a sticky precipitate which was dissolved in 40 mL of toluene. To this
solution was added petroleum ether (120 mL) and then cooled to −10
°C to give a colorless precipitate of 2 after 3 days. The precipitate was
separated and dried under vacuum (13.8 g, 29.7 mmol, 90% yield). 1H
NMR (CDCl3, 400 MHz, ppm): δ = 3.30 (s, 4H, CH2), 5.66 and
5.67(s, 2H, pyrrole β-CH), 7.33(br m, 20H, phenyl CH), 7.67 (br s,
1H, NH). 31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = −16.3(s).
13C NMR (CDCl3, 50.3 MHz, ppm): δ = 28.2 (d, J(C,P) = 15.1 Hz,
CH2), 107.6 (d, J(C,P) = 5 Hz, pyrrole β-CH), 126.2 (d, J(C,P) = 10
Hz, pyrrole α-C), 128.5, 128.6, 128.7, 128.9, 132.7, 133.1, 138.2, 138.5
(phenyl C). FT-IR(KBr, cm−1): ν = 3364 (w), 3050 (w), 2867 (w),
1645 (w), 1580 (w), 1480 (w), 1430 (m), 1400 (w), 1306 (w), 1269
(w), 1205 (w), 1096 (w), 1028 (w), 975 (w), 834 (w), 808 (w), 775
(w), 740 (s), 694 (s), 638 (w), 503 (m), 475 (w), 446 (w). Anal.
Calcd. for C30H27NP2: C, 77.74; H, 5.87; N, 3.02. Found: C, 77.17; H,
5.95; N, 2.98.
Synthesis of 1,9-Bis(diphenylphosphinomethyl)-
diphenyldipyrrolylmethane, 5. A solution of 1,9-bis(N,N-
dimethylaminomethyl)diphenyldipyrrolylmethane, 4 (6.0 g, 14.55
mmol) and Ph2PH (5.69 g, 30.55 mmol) in toluene (15 mL) was
heated to 110 °C with stirring for 20 h. The reaction mixture was
cooled to room temperature and then the solvent was removed under
vacuum. The resultant sticky precipitate was dissolved in 40 mL of
toluene to which petroleum ether (120 mL) was added and cooled to
−10 °C to give colorless precipitate of 5 after 3 days. The colorless
precipitate was separated and dried under vacuum (9.3 g, 13.4 mmol,
92% yield). Suitable single crystals of 5 were obtained from CH2Cl2
and petroleum ether mixture (1:2). 1H NMR (CDCl3, 400 MHz,
ppm): δ = 3.38 (s, 4H, CH2), 5.66 (t, 2H, pyrrole β-CH), 5.85 (t, 2H,
pyrrole β-CH), 6.92−6.97 (m, 4H, phenyl CH), 7.23−7.45(m, 26H,
phenyl CH), δ 7.53 (br s, 2H, NH). 31P{1H}NMR (161.9 MHz,
CDCl3, ppm): δ = −15.5(s). 13C NMR (CDCl3, 100.6 MHz, ppm): δ
= 28.1 (d, J(C,P) = 14.6 Hz, CH2), 55.9 (s, meso C), 107.1 (d, J(C,P)
= 5.7 Hz, pyrrole β-CH), 110.0 (s, pyrrole β-CH), 126.8 (t, J(C,P) =
7.4 Hz, pyrrole α-C), 127.9 (s, pyrrole α-C), 128.7, 128.7, 128.9, 128.9,
129.0, 129.2, 129.4, 129.5, 131.1, 131.2, 132.9, 133.0, 134.4, 134.4,
138.2, 138.4, 146.1 (phenyl C). FT-IR (KBr, cm−1): ν = 3415 (m),
3049 (w), 1955 (w), 1880 (w), 1818 (w), 1574 (w), 1483 (w), 1433
(m), 1410 (w), 1263 (w), 1178 (w), 1097 (m), 1042 (m), 825 (w),
776 (m), 738 (s), 697 (s), 625 (w), 509 (w), 474 (w), 429 (w). Anal.
Calcd. for C47H40N2P2: C, 81.25; H, 5.80; N, 4.03. Found: C, 80.90;
H, 6.00; N, 3.88.
Figure 9. Simplified interaction MO diagram showing the selected
energy levels and their interactions including the weak interactions in
the structure of complex 12.
Computational Details. Geometry optimization (B3LYP/
LANL2DZ) and frequency calculation are performed using Gaussian
09 program package.51 The Wiberg bond indices of complex 12 are
calculated by NBO at the B3LYP/LANL2DZ level. The molecular
orbitals are generated by using GaussView, Version 3.0.52 The
interaction MO diagram was generated by using the ADF program53
following the work of Vega et al.54 Calculation is carried out using
local density approximation with gradient corrections for exchange
(Becke88)55 and correlation (Perdew).56 The standard ADF basis set
is used for all the atoms in the complex along with the ZORA scalar
Hamiltonian.57 Fragment interaction analysis between L2 and Pd2
2−
2+
is done through a single point calculation using the method proposed
by Ziegler to generate the interaction diagram.58 Using this approach,
the orbital interaction energies are decomposed into components
related to various irreducible representations. As the system is too
large it is difficult to generate the exact nature of the irreducible
representations. The geometrical parameters, comparison of selected
bond lengths and bond angles with those obtained by the X-ray
diffraction method, and Wiberg bond indices are given in the
Supporting Information.
Synthesis of 2,5-Bis(diphenylphosphorylmethyl)pyrrole, 6.
To a toluene (10 mL) solution of 2 (0.10 g, 0.215 mmol) was added
aqueous H2O2 (0.2 mL, 1.72 mmol, 30%). The solution was stirred for
overnight to give colorless precipitate of compound 6 which was
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separated and dried under vacuum (0.093 g, 0.17 mmol, 80% yield).
Suitable single crystals were obtained by slow evaporation of a solution
Synthesis of [PdCl{C4H2N-2,5-(CH2PPh2)2-κ3PNP}], 10. To a
mixture of [PdCl2(PhCN)2] (0.100 g, 0.260 mmol) and 2 (0.121 g,
0.260 mmol) in acetonitrile (15 mL) was added dropwise triethyl-
amine (0.080 mL, 0.573 mmol) with stirring at room temperature.
After 24 h stirring, the solvent was removed under vacuum, and the
residue was dissolved in dichloromethane. The dichloromethane
solution was washed with water (3 × 30 mL) and dried over
anhydrous Na2SO4. The solution was filtered, and the solvent was
removed under vacuum to give a light brown precipitate of 10 (0.137
g, 0.23 mmol, 87% yield). Suitable single crystals were obtained from a
1
of 6 in CH2Cl2/petroleum ether (v/v 1:3). H NMR (CDCl3, 200
2
MHz, ppm): δ = 3.63 (d, 4H, J(P,H) = 11.4 Hz, CH2), 5.55 (s, 2H,
pyrrole β-CH), 7.37−7.69 (m, 20H, phenyl CH), 10.15 (s, 1H, NH).
31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = 31.5(s). 13C NMR
(CDCl3, 50.3 MHz, ppm): δ = 30.7 (d, J(C,P) = 69.4 Hz, CH2), 108.9
(s, pyrrole β-CH), 121.2 (s, pyrrole α-C), 128.7, 128.8, 128.9, 130.4,
131.2, 131.3, 131.3, 132.3 (phenyl C). FT-IR (KBr, cm−1): ν = 3475
(s), 3373 (s), 3204 (m), 2902 (w), 1644 (w), 1586 (w), 1486 (w),
1435 (m), 1390 (w), 1312 (w), 1171 (s), 1121 (m), 1029 (w), 990
(w), 827 (m), 744(m), 730 (m), 696 (s), 531 (s). HRMS (+ESI):
Calcd m/z for [M + H+]+ C30H28NP2O2: 496.1595, Found: 496.1647.
Synthesis of 2,5-Bis(diphenylthiophosphorylmethyl)pyrrole,
7. To a toluene (10 mL) solution of 2 (0.10 g, 0.215 mmol) was added
elemental sulfur (0.0172 g, 0.537 mmol). The solution was stirred for
overnight and then the solvent was removed under vacuum. The
resultant residue was washed with petroleum ether (2 × 50 mL) and
then dried under vacuum to give 7 (0.095 g, 0.18 mmol, 84% yield).
1
solution of 10 in toluene at −18 °C. H NMR (CDCl3, 200 MHz,
ppm): δ = 3.87 (t, 8H, 2J(P,H) = 5 Hz, CH2), 6.09 (s, 4H, pyrrole β-
CH), 7.40−7.46 (m, 24H, phenyl CH), 7.81−7.91 (m, 16H, phenyl
CH). 31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = 33.8(s). 13C
NMR (CDCl3, 100.6 MHz, ppm): δ = 34.0 (t, J(C,P) = 13.5 Hz,
CH2), 104.8 (t, J(C,P) = 7 Hz, pyrrole β-CH), 129.1, 129.2, 129.2
(phenyl C), 130.4 (s, pyrrole α-C), 130.9, 131.1, 131.2, 131.3, 133.0,
133.1, 133.1, 136.1, 136.2 (phenyl C). FT-IR (KBr, cm−1): ν = 3052
(w), 1616 (w), 1482 (w), 1433 (s), 1374 (w), 1311 (w), 1262 (w),
1103 (s), 998 (w), 832 (w), 740 (s), 691 (s), 516 (s), 478 (m). HRMS
(+ESI): Calcd m/z for [M−Cl−+K+]2+ C30H26NP2PdK: 607.0212,
Found: 607.0836.
2
1H NMR (CDCl3, 200 MHz, ppm): δ = 3.79 (d, 4H, J(P,H) = 11.4
Hz, CH2), 5.62 (s, 2H, pyrrole β-CH), 7.36−7.51 (m, 12H, phenyl
CH), 7.67−7.77 (m, 8H, phenyl CH), 9.44 (s, 1H, NH). 31P{1H}-
NMR (161.9 MHz, CDCl3, ppm): δ = 38.8(s). 13C NMR (CDCl3,
50.3 MHz, ppm): δ = 34.5 (d, J(C,P) = 55.3 Hz, CH2), 109.6 (s,
pyrrole β-CH), 121.7(s, pyrrole α-C), 128.5, 128.6, 128.7, 128.8, 131.4,
131.5, 131.6, 131.7, 131.8, 133.0 (phenyl C). FT-IR (KBr, cm−1): ν =
3354 (w), 3048 (w), 2891 (w), 1644 (w), 1580 (w), 1485 (w), 1434
(m), 1387 (w), 1306 (w), 1264 (w), 1172 (w), 1102 (s), 1035 (w),
996 (w), 814 (w), 778 (w), 743 (m), 693 (s), 601 (m), 506 (m).
HRMS (+ESI): Calcd m/z for [M+2H+]2+ C30H29NP2S2: 529.1217,
Found: 529.1201.
Synthesis of 1,9-Bis(diphenylphosphorylmethyl)-
diphenyldipyrrolylmethane, 8. To a toluene (10 mL) solution of
5 (0.150 g, 0.216 mmol) was added aqueous H2O2 (0.2 mL, 1.72
mmol, 30%). The solution was stirred for overnight. After separating
the toluene layer from the aqueous layer, toluene was removed under
vacuum. The resultant residue was washed with petroleum ether (2 ×
50 mL) and dried under vacuum to give 8 (0.117 g, 0.16 mmol, 74%
yield). 1H NMR (CDCl3, 200 MHz, ppm): δ = 3.68 (d, 4H, 2J(P,H) =
12.4 Hz, CH2), 5.62 (s, 2H, pyrrole β-CH), 5.71 (s, 2H, pyrrole β-
CH), 6.91−7.70 (m, 30H, phenyl CH), 8.93 (br s, 2H, NH).
31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = 31.6(s). 13C NMR
(CDCl3, 50.3 MHz, ppm): δ = 30.4 (d, J(C,P) = 69.9 Hz, CH2), 56.0
(s, meso C) 108.3 (s, pyrrole β-CH), 110.1(s, pyrrole β-CH), 120.4 (s,
pyrrole α-C), 120.6 (s, pyrrole α-C), 127.7, 128.2, 128.4, 128.6, 128.8,
129.6, 130.2, 130.9, 131.1, 131.3, 131.5, 132.0, 132.6, 132.9, 136.2,
145.8 (phenyl C). FT-IR (KBr, cm−1): ν = 3282 (m), 3053 (m), 2946
(w), 2889 (w), 1710 (m), 1639 (w), 1592 (w), 1488 (w), 1436 (s),
1315 (w), 1172 (s), 1123 (s), 1028 (w), 823 (w), 793 (m), 732 (s),
695 (s), 632 (w), 537 (s). HRMS (+ESI): Calcd m/z for [M+H+]+
C47H41N2P2O2: 727.2643, Found: 727.3982.
Synthesis of 1,9-Bis(diphenylthiophosphorylmethyl)-
diphenyldipyrrolylmethane, 9. To a toluene (10 mL) solution of
5 (0.150 g, 0.216 mmol) was added elemental sulfur (0.0172 g, 0.537
mmol). The solution was stirred overnight. The solvent was removed
under vacuum to give a residue which was washed with petroleum
ether and dried under vacuum to give 9 (0.120 g, 0.16 mmol, 73%
yield). 1H NMR (CDCl3, 200 MHz, ppm): δ = 3.89 (d, 4H, 2J(P,H) =
12.4 Hz, CH2), 5.73 (br s, 2H, pyrrole β-CH), 5.78 (br s, 2H, pyrrole
β-CH), 7.05−7.85 (m, 30H, phenyl CH), 8.84 (br s, 2H, NH).
31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = 39.3(s). 13C NMR
Synthesis of [Pd2Cl4{μ-C4H3N-2,5-(CH2PPh2)2-κ2PP}2], 11. To a
toluene (10 mL) solution of [PdCl2(PhCN)2] (0.05 g, 0.130 mmol)
was added 2 (0.06 g, 0.130 mmol). The solution was stirred for
overnight at room temperature. The solvent was removed under
vacuum to give a residue which was washed with petroleum ether and
dried under vacuum to give 11 as a yellow precipitate (0.079 g, 0.06
mmol, 95% yield). 1H NMR (CDCl3, 400 MHz, ppm): δ = 3.83 (br s,
8H, CH2), 5.06 (s, 4H, pyrrole β-CH), 7.24−7.64 (m, 40H, phenyl
CH), 9.86 (br s, 2H, NH). 31P{1H}NMR (161.9 MHz, CDCl3, ppm):
δ = 14.3(s). 13C NMR (CDCl3, 100.6 MHz, ppm): 26.8 (s, CH2),
109.1 (s, pyrrole β-CH), 122.2 (s, pyrrole α-C), 128.4, 129.8, 130.0,
130.3, 130.8, 131.0, 133.9, 134.3 (phenyl C). FT-IR (KBr, cm−1): ν =
3344(m), 3048 (m), 1583 (w), 1480 (m), 1434(s), 1390 (m), 1309
(w), 1273 (w), 1178 (m), 1102 (s), 1035 (m), 996 (w), 812 (m), 772
(m), 743 (s), 692 (s), 641 (w), 504 (m). Anal. Calcd. for
C60H54Cl4N2P4Pd2: C, 56.23; H, 4.25; N, 2.19. Found: C, 55.83; H,
4.39; N, 2.13. HRMS (+ESI): Calcd m/z for [M−3Cl−]3+
C60H54ClN2P4Pd2: 1173.0996, Found: 1173.9480 and Calcd m/z for
[M−4Cl−+K+]5+ C60H54KN2P4Pd2: 1177.0944, Found: 1177.9426.
Synthesis of [Pd2{μ-C4H2N-2,5-(CH2PPh2)2-κ2PN,κ1P}2], 12. To
a toluene (15 mL) solution of [Pd2(dba)3]·CHCl3 (0.15 g, 0.145
mmol) was added 2 (0.154 g, 0.330 mmol). The solution was stirred
for 16 h at room temperature. The solvent was removed under
vacuum. The resultant residue was washed with petroleum ether (2 ×
10 mL) followed by washing with diethyl ether (1 × 10 mL). The
residue was dissolved in 20 mL of toluene on top of which petroleum
ether was added slowly to form a layer. Red crystals of compound 12
were formed after 3 weeks. The crystals were separated, washed with
petroleum ether and then dried under vacuum (0.04 g, 0.034 mmol,
1
23.5% yield). H NMR (CDCl3, 400 MHz, ppm): δ = 4.05 and 3.53
(ABX spin system, 4H, 2J(HA,HB) = 16.6 Hz, 2J(P,HA) and 2J(P,HB) =
2
7.2 Hz, PCH2), 3.72 and 3.46 (ABX spin system, 4H, J(H,H) = 15.2
Hz, 2J(P,H) = 7.0 Hz, PCH2), 6.02 (s, 2H, pyrrole β-CH), 6.15 (s, 2H,
pyrrole β-CH), 6.81−7.42 (m, 40H, phenyl CH). 31P{1H}NMR
(161.9 MHz, CDCl3, ppm): δ = 20.5(s) and 17.6(s). 13C NMR
(CDCl3, 100.6 MHz, ppm): δ = 30.6 (d, J(C,P) = 33.3 Hz, CH2), 35.9
(t, J(C,P) = 10.4 Hz, CH2), 104.8 (d, J(C,P) = 230.5 Hz, pyrrole β-
CH), 106.0 (d, J(C,P) = 7.7 Hz, pyrrole β-CH), 125.3 (d, J(C,P) =
12.8 Hz, pyrrole α-C), 127.4, 127.5, 127.6, 127.7, 127.9, 127.9, 128.0,
128.0, 128.1, 128.2, 128.3, 128.6, 128.7, 128.8, 128.9, 129.0, 129.7,
130.5, 130.9,131.0, 131.1, 131.1, 131.2, 131.8, 131.9, 132.6, 132.8,
132.9, 133.1, 133.2, 133.3, 133.4, 133.5, 133.6, 133.7, 133.8, 135.9,
136.0, 136.0, 139.5, 139.6, 139.9, 140.0, 140.9, 141.0, 141.4, 141.5,
143.3 (phenyl C). FT-IR (KBr, cm−1): ν = 3050 (m), 2869 (w), 1952
(w), 1886 (w), 1584 (w), 1572 (w), 1538 (w), 1481 (m), 1433 (s),
1375 (m), 1309 (w), 1267 (w), 1183 (w), 1155 (w), 1129 (w), 1098
(m), 1046 (m), 1027 (w), 998 (w), 835 (m), 736 (s), 693 (s), 513 (s),
470 (m), 408 (w). Anal. Calcd. for C63H55N2P4Pd2: C, 64.30; H, 4.71;
(CDCl3, 50.3 MHz, ppm): δ = 34.2 (d, J(C,P) = 54.3 Hz, CH2), 56.0
(s, meso C), 109.1 (d, J(C,P) = 7 Hz, pyrrole β-CH), 109.8 (s, pyrrole
β-CH), 120.7 (d, J(C,P) = 8 Hz, pyrrole α-C), 126.7(s, pyrrole α-C),
127.9, 128.4, 128.6, 128.8, 129.2, 129.6, 131.5, 131.7, 133.0, 135.9,
145.9 (phenyl CH). FT-IR (KBr, cm−1): ν = 3417 (w), 3348 (w),
3052 (w), 2880 (w), 1813 (w), 1574 (w), 1484 (m), 1435 (s), 1387
(w), 1261 (w), 1180 (m), 1103 (s), 1042 (m), 821 (m), 779 (m), 744
(s), 696 (s), 638 (w), 602 (m), 506 (s). HRMS (+ESI): Calcd m/z for
[M+H+]+ C47H41N2P2S2: 759.2186, Found: 759.2631.
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Inorganic Chemistry
Article
N, 2.38. Found: C, 64.47; H, 4.62; N, 2.24. HRMS (+ESI): Calcd m/z
for [M+2H+]2+ C60H54N2P4Pd2: 1138.1307, Found: 1138.1362.
Synthesis of [Ni(OAc){C4H2N-2,5-(CH2PPh2)2-κ3PNP}], 13. A
solution of 2 (0.374 g, 0.805 mmol) and [Ni(OAc)2]·4H2O (0.2 g,
0.803 mmol) in acetonitrile (30 mL) was stirred for 24 h at room
temperature. The solvent was removed under vacuum to give a red
colored residue which was washed with petroleum ether and dried
under vacuum to give a red colored solid (0.430 g). This solid is
Synthesis of [NiI{C4H2N-2,5-(CH2PPh2)2-κ3PNP}], 16. This
complex was synthesized using KI (0.667 g, 4.01 mmol) by following
the above procedure (Method a) for complex 14. To a solution of 16
in benzene (10 mL) was added slowly petroleum ether to form a layer.
Purple crystals of 16 were formed after 3 days (0.421 g, 0.65 mmol,
1
81% yield). H NMR (CDCl3, 200 MHz, ppm): δ = 3.69 (t, 4H,
2J(P,H) = 4.9 Hz, CH2), 6.06 (s, 2H, pyrrole β-CH), 7.37−7.47 (m,
12H, phenyl CH), 7.79−7.88 (m, 8H, phenyl CH). 31P{1H}NMR
(161.9 MHz, CDCl3, ppm): δ = 42.6(s). 13C NMR (CDCl3, 50.3
MHz, ppm): δ = 34.5 (d, J(C,P) = 13.1 Hz, CH2), 105.5(d, J(C,P) = 6
Hz, pyrrole β-CH), 128.5, 128.7, 128.8, 128.9, 130.8, 131.0, 131.3,
131.7, 133.6, 133.7, 133.8, 137.3, 137.5 (phenyl C). FT-IR (KBr,
cm−1): ν = 3050 (m), 2924 (m), 1710 (w), 1585 (w), 1482 (m),
1433(s), 1369 (m), 1251 (m), 1185 (w), 1100 (s), 1065 (w), 998 (w),
836 (m), 739 (s), 691 (s), 517 (s), 481 (m). HRMS (+ESI): Calcd m/
z for [M−I+2H++K+]4+ C30H28KNNiP2: 561.07, Found: 561.17.
X-ray Crystallography. Single crystal X-ray diffraction data
collections for all the compounds were performed using Bruker-
APEX-II CCD diffractometer with graphite monochromated MoKα
radiation (λ = 0.71073 Å). The structures were solved by SIR-9259
available in WinGX, which successfully located most of the non-
hydrogen atoms. Subsequently, least-squares refinements were carried
out on F2 using SHELXL-97 (WinGX version)60 to locate the
remaining non-hydrogen atoms. All non-hydrogen atoms were refined
anisotropically, and the most of the hydrogen atoms were refined
isotropically on calculated positions using a riding model. In the
structure of 5 and 6, the NH and all water hydrogen atoms except the
hydrogen atoms of O6 water were located and refined isotropically
with restraints, SADI and their thermal parameters were set equivalent
to 1.2 times the thermal parameter value of the atom to which the
hydrogen atoms are bonded. The O6 water hydrogen atoms in 6 could
not be located. A severely disordered one-half of the benzene molecule
was found in the crystal lattice of 12.
1
predominantly consisting of 13 as shown by the H and 31P NMR
data. 1H NMR (CDCl3, 200 MHz, ppm): δ = 1.51 (s, 3H, OAc), 3.50
(t, 4H, 2J(P,H) = 4.8 Hz, CH2), 5.90 (s, 2H, pyrrole β-CH), 7.41−7.48
(m, 12H, phenyl CH), 7.80−7.86 (m, 8H, phenyl CH). 31P{1H}NMR
(161.9 MHz, CDCl3, ppm): δ = 27.0(s). 13C NMR (CDCl3, 100.6
MHz, ppm): δ = 23.4 (s, CH3COO), 31.8 (m, J(C,P) = 13.8 Hz,
CH2), 106.2 (t, J(C,P) = 5.3 Hz, pyrrole β-CH), 128.9, 129.0, 129.0,
130.6, 130.9, 131.0, 131.1, 131.3, 132.1, 132.9, 133.0, 133.0, 133.1,
133.2, 133.2, 133.4, 136.6, 136.7 (phenyl C), 177.3 (s, CH3COO). FT-
IR (KBr, cm−1): ν = 3412 (m), 3052(m), 1625(s), 1483 (m), 1434
(s), 1367 (s), 1317(s), 1250 (w), 1184 (w), 1103 (m), 1066 (w), 1000
(w), 838 (w), 741 (s), 694 (s), 520 (s), 477 (m). HRMS (+ESI):
Calcd m/z for [M−OAc+2H++K+]4+ C30H28KNNiP2: 561.0688,
Found: 561.0298.
Synthesis of [NiCl{C4H2N-2,5-(CH2PPh2)2-κ3PNP}], 14. Method
a. A solution of 2 (0.374 g, 0.805 mmol) and [Ni(OAc)2]·4H2O (0.2
g, 0.803 mmol) in acetonitrile (30 mL) was stirred for 24 h at room
temperature. The solvent was removed under vacuum to give a red
colored solid. The solid was dissolved in acetone (12 mL) to which a
solution of LiCl (0.172 g, 4.01 mmol) in water (8 mL) was added. The
suspension was stirred at room temperature for 48 h to give precipitate
of complex 14. The solution was filtered, and the precipitate was
washed with water three times (10 mL) and dried under vacuum (0.40
g, 0.72 mmol 89% yield). Suitable single crystals were obtained from a
solution of 14 in benzene upon layering with petroleum ether at room
temperature.
ASSOCIATED CONTENT
* Supporting Information
Method b. To a mixture of [NiCl2(DME)] (0.100 g, 0.460 mmol)
and 2 (0.214 g, 0.461 mmol) in acetonitrile (15 mL) was added
dropwise triethylamine (0.065 mL, 0.461 mmol) with stirring at room
temperature. After 24 h stirring, the solvent was removed under
vacuum, and the residue was dissolved in dichloromethane. The
dichloromethane solution was washed with water (3 × 30 mL) and
dried over anhydrous Na2SO4 and then filtered. The solvent was
removed under vacuum to give a dark brown precipitate of 14 (0.210
■
S
NMR, IR, HRMS spectra, crystallographic data (CIF), and
packing diagrams. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gmani@chem.iitkgp.ernet.in (G.M.).
■
1
g, 0.377 mmol, 84% yield). H NMR (CDCl3, 400 MHz, ppm): δ =
2
3.59 (t, 4H, J(P,H) = 4.8 Hz, CH2), 5.99 (s, 2H, pyrrole β-CH),
7.37−7.50 (m, 12H, phenyl CH), 7.86−7.91(m, 8H, phenyl CH).
31P{1H}NMR (161.9 MHz, CDCl3, ppm): δ = 30.6(s). 13C NMR
(CDCl3, 100.6 MHz, ppm): δ = 32.0 (t, J(C,P) = 13.5 Hz, CH2), 106.1
(t, J(C,P) = 5.6 Hz, pyrrole β-CH), 129.0, 129.1, 129.1, 133.0, 133.1,
133.2, 137.1(phenyl C). FT-IR (KBr, cm−1): ν = 2923(s), 2853 (m),
1586 (w), 1465 (w), 1432 (m), 1370 (w), 1303 (w), 1250 (w), 1178
(w), 1101 (m), 1066 (w), 997 (w), 833 (w), 740 (m), 690 (m), 518
(m), 479 (m). HRMS (+ESI): Calcd m/z for [M−Cl+2H++K+]4+
C30H28KNNiP2: 561.07, Found: 561.20.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the DST and CSIR for support and for the X-ray and
NMR facilities. We thank Dr. Carola Schulzke, Trinity College,
Dublin for HRMS.
Synthesis of [NiBr{C4H2N-2,5-(CH2PPh2)2-κ3PNP}], 15. Com-
plex 15 was synthesized using LiBr (0.349 g, 4.01 mmol) by following
the above procedure (Method a) for complex 14. To a solution of 15
in benzene (10 mL) was added slowly petroleum ether to form a layer.
Brown crystals of 15 were formed after 24 h (0.390 g, 0.65 mmol, 80%
yield). 1H NMR (CDCl3, 400 MHz, ppm): δ = 3.62 (t, 4H, 2J(P,H) =
4.8 Hz, CH2), 6.02 (s, 2H, pyrrole β-CH), 7.37−7.50 (m, 12H, phenyl
CH), 7.85−7.90 (m, 8H, phenyl CH). 31P{1H}NMR (161.9 MHz,
CDCl3, ppm): δ = 35.0(s). 13C NMR (CDCl3, 100.6 MHz, ppm): δ =
32.7 (t, J(C,P) = 13.2 Hz, CH2), 105.7(t, J(C,P) = 5.7 Hz, pyrrole β-
CH), 128.7, 128.7, 128.8, 130.4, 130.6, 130.7, 133.1, 133.1, 133.2,
137.0 (phenyl C). FT-IR (KBr, cm−1): ν = 3052, (m), 1661 (w), 1585
(w), 1482 (m), 1433 (s), 1369 (m), 1309 (w), 1252 (m), 1184 (w),
1101 (s), 1065 (m), 1026 (w), 998 (w) 835 (m), 739 (s), 691 (s), 518
(s), 481 (m), 445 (w). HRMS (+ESI): Calcd m/z for [M−Br
+2H++K+]4+ C30H28KNNiP2: 561.07, Found: 561.16.
DEDICATION
■
Dedicated to Professor S. S. Krishnamurthy on the occasion of
his 73rd birthday.
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