Multi-nuclear silver(i) and copper(i) complexes: A novel bonding mode for bispyridylpyrrolides

Article abstract of DOI:10.1039/c3dt52794h

Reaction of deprotonated 2,5-bis(2′-pyridyl)pyrrole (HPDP _H) with AgOTf (where OTf^- = triflato) in THF readily yields a yellow triangular Ag₃ complex [(PDP_H)Ag] ₃ (1), of which the av. Ag...Ag distance is 2.902 A. A mixture of HPDP_H and AgOTf reacts with PPh₃ to afford a linear Ag₃ complex [Ag{(PDP_H)Ag(PPh₃)} ₂](OTf) (2·OTf), whereas it reacts with diethyl phosphite in the presence of Li[N(SiMe₃)₂] to yield a di-nuclear complex Li₂[(PDP_H)Ag₂{P(O)(OEt) ₂}₂](OTf) (Li₂·3·OTf). In 2, the terminal Ag atoms are three coordinate containing one phosphorous atom from PPh₃ and two nitrogen atoms of the PDP_H ligand. The center Ag atom is only two coordinate, binding to the residued pyridyl N atom of the PDP_H ligand. In 3, two silver atoms are bridged by one PDP _H ligand. Treatment of PDP_H with CuCl in the presence of NaH afforded a heterobimetallic copper-sodium complex [Cu(PDP_H) ₂Na(thf)₂] (4). The PDP_H ligand in 1-4 is nonplanar, with torsion angles between pyridine and pyrrole rings in the range of 15.8-38.3°. The argentophilic interactions, π...π stacking, and weak interaction of Ag...C(aromatic) are observed in these complexes. Interestingly, treatment of the analogous 2,5-bis(6′-bromo-2′- pyridyl)pyrrole (HPDP_Br) with AgOTf affords a di-nuclear complex [(HPDP_Br)Ag]₂(OTf)₂ (5·(OTf) ₂). Its HPDP_Br ligands coordinate to Ag atoms in a head-to-head fashion, and two protonated pyrrole linkages reside in the anti-parallel direction and are non-coordinating. Short Ag...Br distances of 3.255-3.390 A are observed.

Full text of DOI:10.1039/c3dt52794h

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Multi-nuclear silver(I) and copper(I) complexes:
a novel bonding mode for bispyridylpyrrolides†
Cite this: Dalton Trans., 2014, 43,
2458
Xiao-Hui Hu, Yan Liang, Chen Li and Xiao-Yi Yi*
Reaction of deprotonated 2,5-bis(2’-pyridyl)pyrrole (HPDPH) with AgOTf (where OTf− = triflato) in THF
readily yields a yellow triangular Ag3 complex [(PDPH)Ag]3 (1), of which the av. Ag⋯Ag distance is 2.902 Å.
A mixture of HPDPH and AgOTf reacts with PPh3 to afford a linear Ag3 complex [Ag{(PDPH)Ag(PPh3)}2]-
(OTf) (2·OTf), whereas it reacts with diethyl phosphite in the presence of Li[N(SiMe3)2] to yield a di-
nuclear complex Li2[(PDPH)Ag2{P(O)(OEt)2}2](OTf) (Li2·3·OTf). In 2, the terminal Ag atoms are three co-
ordinate containing one phosphorous atom from PPh3 and two nitrogen atoms of the PDPH ligand. The
center Ag atom is only two coordinate, binding to the residued pyridyl N atom of the PDPH ligand. In 3,
two silver atoms are bridged by one PDPH ligand. Treatment of PDPH with CuCl in the presence of NaH
afforded a heterobimetallic copper–sodium complex [Cu(PDPH)2Na(thf)2] (4). The PDPH ligand in 1–4 is
nonplanar, with torsion angles between pyridine and pyrrole rings in the range of 15.8–38.3°. The argen-
tophilic interactions, π⋯π stacking, and weak interaction of Ag⋯C(aromatic) are observed in these com-
plexes. Interestingly, treatment of the analogous 2,5-bis(6’-bromo-2’-pyridyl)-pyrrole (HPDPBr) with
AgOTf affords a di-nuclear complex [(HPDPBr)Ag]2(OTf)2 (5·(OTf)2). Its HPDPBr ligands coordinate to Ag
atoms in a head-to-head fashion, and two protonated pyrrole linkages reside in the anti-parallel direction
and are non-coordinating. Short Ag⋯Br distances of 3.255–3.390 Å are observed.
Received 7th October 2013,
Accepted 13th November 2013
DOI: 10.1039/c3dt52794h
www.rsc.org/dalton
Introduction
The pincer-like ligand belongs to a type of tridentate ligand
where the central anionic or neutral donor site is flanked by
two neighboring donor groups.1,2 It can bind tightly to three
adjacent coplanar sites, usually on a transition metal in a meri-
dional configuration. Their metal complexes have attracted
interest due to their high stability and ability to catalyze
various organic reactions.3–5 These include the mono-anionic
dipyridylpyrrolide (PDP) ligand based on a pyrrole backbone
and two pyridine “arms”, shown in Scheme 1.6 The PDP ligand
combines the π-backbonding capability of a 18-π electron N/N/N
ligand with the flexible π-properties of pyrrolate donors that
behave as versatile π-donor and π-acceptor responses to the
metal site π-bonding properties. This ligand has been recog-
nized as an analogue of the neutral terpyridine ligand (tpy). In
recent years its complexes with late transition metals have
received increasing attention. A few opened-shell metals, such
as Co(II), Cu(II), Fe(II), Pt(II) and Pd(II), and closed-shell metal of
Scheme 1 Structure of dipyridylpyrrolide ligand.
Zn(II) complexes stabilized by dipyridylpyrrolide have been
reported.6–8 All of these complexes display a coplanar mono-
nuclear geometry (mode I, Scheme 2), where dipyridylpyrrolide
acts as a chelating tridentate ligand binding to the metal
center in a meridional configuration. It is noted that the ana-
logous tpy ligand not only acts as a pincer-like ligand to bind
to the metal center, but also is capable of aggregating metal
ions to form novel multi-nuclear metal complexes. Numerous
examples of silver(I) and copper(I) complexes with tpy have
been well documented.9–15 However, the chemistry of a closed-
shell d10 coinage metal complex containing a bispyridylpyrro-
lide ligand is still unknown. It inspires us to take more interest
in studies aimed at the investigation of silver(I) and copper(I)
complexes with PDP ligands and their structural variation.
In this paper, we report the syntheses and characterizations
of a family of silver(I) and copper(I) complexes stabilized
by 2,5-bis(2-pyridyl)pyrrolate (HPDPH) or 2,5-bis(6-bromo-
2-pyridyl)pyrrolate (HPDPBr) ligands. Complexes 1–4 feature
Key Laboratory of Resources Chemistry of Nonferrous Metals, Ministry of Education,
School of Chemistry and Chemical Engineering, Central South University, Changsha,
Hunan 410083, P. R. China. E-mail: xyyi@csu.edu.cn; Fax: +86 731 88879616;
Tel: +86 731 88879616
†CCDC 963075–963079 for complex 1, 2·OTf, Li2·3·OTf, 4 and 5·(OTf)2, respect-
ively. For crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt52794h
2458 | Dalton Trans., 2014, 43, 2458–2464
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
[Ag{(PDPH)Ag(PPh3)}2](OTf) (2·OTf)
To a mixture of HPDPH (33.0 mg, 0.15 mmol) and AgOTf
(38.4 mg, 0.15 mmol) in THF (3 mL) was added PPh3 (39.3 mg,
0.15 mmol). The reaction mixture became clear quickly and
was continued to be stirred for 3 h. The filtrate was layered
with hexane to give yellow crystals which was suitable for X-ray
1
diffraction study. Yield: 29.5 mg (33.5%). H NMR (d6-DMSO):
δ 8.553 (d, J = 2.4 Hz, 4H), 7.888 (d, J = 3.6 Hz, 4H), 7.792 (t, J =
7.6 Hz, 4H), 7.569–7.423 (m, 30H), 7.203 (d, J = 6.0 Hz, 4H),
6.927 (d, J = 0.8 Hz, 4H); 31P NMR (CDCl3): δ 18.30, 14.61 (s,
PPh3). IR (KBr, cm−1): 3446(s), 3257(s), 3048(w), 3003(w), 1590(s),
1557(m), 1516(m), 1476(s), 1460(s), 1437(s), 1260(vs), 1151(s),
1056(s), 1031(vs), 989(m), 948(w), 892(w), 799(m), 774(vs),
714(w), 679(w), 637(s), 617(s), 575(w), 518(m). MS(ESI): m/z
644.52 (M+ − OTf + H+). Anal. Calcd for C65H50Ag3F3N6O3P2S:
C, 54.30; H, 3.51; N, 5.85. Found: C, 53.21; H, 3.68; N, 5.48.
Scheme 2 Coordination modes of bispyridylpyrrolides. κ3-N,N’N’’ (I);
μ2-κ2(N,N’),κ2(N’,N’’) (II); μ2-κ2(N,N’),N’’ (III); μ2-N’,N’’ (IV).
multi-nuclear metal ions bridged by the twisted PDPH ligand,
and complex 5 displays a novel head-to-head coordination
mode of the PDPBr ligand. A novel bonding mode of bispyridyl-
pyrrolide in 1–5 was found.
Li2[(PDPH)Ag2{P(O)(OEt)2}2](OTf) (Li2·3·OTf)
To a mixture of HPDPH (33.0 mg, 0.15 mmol) and AgOTf
(38.4 mg, 0.15 mmol) in THF (3 mL) was added diethyl phos-
phite (20.7 mg, 0.15 mmol) and LiN(SiMe3)2 (0.025 mg,
0.15 mmol). The resulting solution was stirred overnight and
filtered. The filtrate was layered with hexane to give yellow crys-
tals which were suitable for X-ray diffraction study. Yield:
Experimental
1
21.3 mg (64.5%). H NMR (CDCl3): δ 8.599 (d, J = 2.4 Hz, 2H),
General considerations
7.683–7.674 (m, 4H), 7.104 (d, J = 6.4 Hz, 2H), 6.885 (s, 2H),
3.661 (q, J = 10.0 Hz, 8H), 0.993 (t, J = 6.8 Hz, 12H); 31P NMR
(CDCl3): δ 115.17, 108.87 (s, –P(O)(OEt)2). IR (KBr, cm−1): 3444
(br, w), 3068(w), 1588(s), 1556(m), 1502(s), 1449(m), 1426(s),
1326(s), 1252(m), 1148(m), 1042(m), 998(w), 946(w), 922(w),
870(w), 778(m), 746(s), 715(w), 691(w). MS(ESI): m/z 790.67
(M − LiOTf + H+). Anal. Calcd for C23H30Ag2N3O9P2SF3Li2·
5H2O: C, 28.68; H, 4.19; N, 4.36. Found: C, 27.51; H, 3.83;
N, 4.28.
All manipulations were carried out under nitrogen by standard
Schlenk techniques unless otherwise stated. Solvents were puri-
fied, distilled and degassed prior to use. H NMR spectra were
1
recorded on a Bruker AV 400 spectrometer operating at
400 MHz, and chemical shifts (δ, ppm) were reported with
reference to SiMe4. Infrared spectra (KBr) were recorded on a
AVATR360 FT-IR spectrophotometer. The starting 2,5-bis(2′-
pyridyl)pyrrolide (HPDPH)16,17 and 2,5-bis(6′-bromo-2′-pyridyl)-
pyrrolide (HPDPBr)18,19 were prepared according to literature
methods. All of other chemicals were obtained from J&K Scien-
tific Ltd and used as received.
[Cu(PDPH)2Na(thf)2] (4)
To a stirred mixture of HPDPH (132.0 mg, 0.60 mmol) and
NaH (14.4 mg, 0.60 mmol) in THF (10 mL) was added CuCl
(59.4 mg, 0.6 mmol). The color of the solution changed from
yellow to orange immediately. After stirring for 4 h, the suspen-
sion solution was filtered. The filtrate was layered by hexane to
give darkish red crystals which were suitable for X-ray diffrac-
tion study. Yield: 30.5 mg (15% based on PDP ligand).
1H NMR (CDCl3): δ 8.527 (s, 2H), 7.650–7.627 (m, 2H), 7.582
(d, J = 3.6 Hz, 2H), 7.073 (s, 2H), 6.773 (s, 2H), 3.75 (m, 8H),
1.92 (m, 8H); IR (KBr, cm−1): 3435(br, w), 3079(w), 2846(w),
1598(vs), 1556(m), 1509(s), 1455(m), 1432(s), 1335(s), 1260(w),
1154(m), 1057(m), 1012(w), 959(w), 924(w), 790(w), 755(s),
717(w), 644(w). MS(ESI): m/z 528.00 (M − 2thf + H+). Anal.
Calcd for C36H36CuN6NaO2: C, 64.42; H, 5.41; N, 12.52. Found:
C, 64.25; H, 5.38; N, 12.37.
[(PDPH)Ag]3 (1)
To a mixture of HPDPH (33.0 mg, 0.15 mmol) and AgOTf
(38.4 mg, 0.15 mmol) in THF (3 mL) was added Et3N (15.2 mg,
0.15 mmol). The yellow suspension reaction mixture was con-
tinued to be stirred for 2 h and filtered. The filtrate was slowly
evaporated to give yellow block crystals which were suitable for
X-ray diffraction study. The residue yellow solid of 1 was col-
lected, and washed with water, ethanol and Et2O. Yield:
25.1 mg (51.2%). 1H NMR (d6-DMSO): δ 8.544 (d, J = 1.2 Hz,
2H), 7.885 (d, J = 3.2 Hz, 2H), 7.802–7.771 (m, 2H), 7.209–7.185
(m, 2H), 6.920 (s, 2H); IR (KBr, cm−1): 3455(w), 3257(m),
1594(s), 1557(m), 1504(m), 1474(s), 1437(s), 1261(vs), 1158(s),
1094(w), 1031(vs), 775(s), 715(w), 636(s), 575(w), 517(m).
[(HPDPBr)Ag]2(OTf)2 (5·(OTf)2)
MS(ESI): m/z 763.25 (M+
−
PDPH). Anal. Calcd for
C42H30Ag3N9: C, 51.25; H, 3.07; N, 12.81. Found: C, 51.36; A reaction mixture of HPDPBr (38.0 mg, 0.1 mmol) and AgOTf
H, 3.35; N, 12.91.
(25.6 mg, 0.1 mmol) in THF (3 mL) was stirred for 12 h. The
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 2458–2464 | 2459

View Article Online
Paper
Dalton Transactions
yellow suspension solution was formed and filtered. The fil-
trate was slowly evaporated to give yellow block crystals which
were suitable for X-ray diffraction study. The residue yellow
solid of 5·(OTf)2 was collected and washed with Et2O. Yield:
1
34.2 mg (53.5%). H NMR (CDCl3): δ 11.364 (s, 2H), 7.956 (d,
J = 3.2 Hz, 4H), 7.752 (t, J = 6.4 Hz, 4H), 7.438 (d, J = 3.2 Hz,
4H), 6.964 (d, J = 0.4 Hz, 4H). IR (KBr, cm−1): 3440(br, w), 3340(w),
3241(w), 3107(w), 1587(s), 1541(s), 1432(vs), 1389(w), 1252(vs),
1163(vs), 1129(m), 1109(m), 1081(m), 1056(w), 998(m),
787(s), 754(m), 633(s), 573(m), 516(m). MS(ESI): m/z 487.08
(M2+ − 2OTf). Anal. Calcd for C15H9AgBr2F3N3O3S·2H2O:
C, 26.81; H, 1.95; N, 6.25. Found: C, 26.51; H, 1.92; N, 6.10.
X-Ray crystallography
Diffraction data of 1, 2·OTf, Li2·3·OTf, 4·2(thf), 5·(OTf)2 were
recorded on a Bruker CCD diffractometer with monochro-
matized MoK radiation (λ = 0.71073 Å). Data collection and
reduction were carried out using SAINT and CrysAlisPro
program. SADABS was used for the absorption correction.20
Structures were solved by direct methods and refined by full-
matrix least-squares on F2 using the SHELXTL software
package.21 Atomic positions of non-hydrogen atoms were
refined with anisotropic parameters. All hydrogen atoms were
introduced at their geometric positions and refined as riding
Scheme 3 Syntheses of complexes 1, 2·OTf, Li2·3·OTf, 4 and 5·(OTf)2.
atoms. In anionic 3, C21, C22 atoms on diethyl phosphite are synthesized by the treatment of AgOTf with one equivalent of
disordered with 65/35 occupancy. The co-crystallized THF HPDPBr in THF.
solvent is found to be disordered, and has been refined with
an occupancy of 53/47.
Complexes 1, 2·OTf, Li2·3·OTf, 4 and 5·(OTf)2 are characteri-
zed by IR, NMR spectra and X-ray diffraction study. The IR
spectra are recorded in the region 4000–450 cm−1 on KBr
disks. The PDPH ligand has several distinctive signals, includ-
ing the weak aromatic C–H stretching at 2976–3107 cm−1. A
region from 1420 to 1590 cm−1 consists of three or four quite
intense signals, corresponding to the in-plane vibrations of
the CvC bonds. All of the above are presented in these five
complexes. In addition, 2·OTf, Li2·3·OTf, and 5·(OTf)2 show a
strong stretching band at 1253–1278 cm−1 due to the triflato
Results and discussion
Synthesis and characterization
Treatment of AgOTf with one equivalent of HPDPH in the pres-
ence of a base, such as Et3N, affords yellow precipitate in
medium yield (Scheme 3). This reaction becomes completed
within less than 1 h at room temperature. The isolated solid is
identified as tri-nuclear [(PDPH)Ag]3 (1) by NMR spectrum. 1 is
insoluble in common organic solvent, but soluble in the polar
solvent such as DMF and DMSO. Upon reaction of a mixture of
AgOTf and HPDPH with phosphine, the silver phosphine com-
plexes are formed. As illustrated in Scheme 3, the suspension
mixture of AgOTf and HPDPH reacts with one equivalent of
PPh3 to produce yellow tri-nuclear [Ag{(PDPH)Ag(PPh3)}2](OTf)
(2·OTf), whereas it reacts with one equivalent of diethyl phos-
phite in the presence of LiN(SiMe3)2 to afford yellow di-nuclear
Li2[(PDPH)Ag2{P(O)(OEt)2}2](OTf) (Li2·3·OTf). Complexes of
2·OTf and Li2·3·OTf are soluble in THF, CH2Cl2, while insolu-
ble in Et2O and hexane. Attempts to produce other phosphine
complexes by treatment of the mixture of AgOTf and HPDPH
with 1,2-bis(diphenylphosphino), 1,10-dilhydro-9-oxa-10-phos-
phaphenanthrene 10-oxide have failed. Treatment of CuCl
with HPDPH in the presence of Et3N gives a red intractable oily
product. NaH instead of Et3N used to deprotonate the HPDPH,
1
group. The H NMR spectrum of 1 in d6-DMSO clearly reveals
the formation of the Ag–N(pyrrolate) bond, which is indicated
by the absence of the imino N–H resonance. Of the four
chemical shifts (δ = 8.55, 7.88, 7.78 and 7.20 ppm) for the
pyridyl ring hydrogens, the most downfield resonance (δ =
8.55 ppm) is routinely assigned to the H ortho to the nitrogen.
The proton resonances of the pyrrole ring appear at 6.92 ppm
as a doublet. The 1H NMR spectrum of pyridine and pyrrole
protons in 2·OTf, Li2·3·OTf and 4 in CDCl3 closely resemble
those in 1. The 31P{1H} NMR spectra of 2·OTf and Li2·3·OTf
display multiple peaks of 18.3, 14.6 ppm and 115.2, 108.9 ppm
attributable to PPh3 and P(O)(OEt)2 ligands, respectively. In
the 1H NMR spectrum of 5·(OTf)2, a resonance of 11.36 ppm is
observed, tentatively assigned to the imino proton on the
pyrrole ring, which is consistent with the solid state structure.
Description of structure
copper–sodium heterobimetallic complex [Cu(PDPH)2Na(thf)2] A summary of the crystallographic data and experimental
(4) is isolated. Di-nuclear [(HPDPBr)Ag]2(OTf)2 (5·(OTf)2) is details for these five complexes are selected in Table 1.
2460 | Dalton Trans., 2014, 43, 2458–2464
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 1 Crystallographic data and experimental details for 1, 2·OTf and Li2·3·OTf, 4 and 5·(OTf)2
Complexes
1
2·OTf
Li2·3·OTf
4
5·(OTf)2
Formula
Fw
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C42H30Ag3N9
984.36
Monoclinic
C65H50Ag3F3N6O3P2S
1437.72
Monoclinic
C2/c
19.8842(3)
17.3938(3)
17.4070(2)
90
108.2390(10)
90
5717.94(15)
4
C54H76Ag4F6Li4N6O20P4S2
1890.45
Triclinic
ˉ
P1
12.4463(2)
12.9013(2)
14.0856(2)
66.1580(10)
69.5560(10)
74.9330(10)
1919.76(5)
1
C36H36CuN6NaO2
671.24
Orthorhombic
Fdd2
11.6882(3)
30.6434(8)
18.0484(5)
90
90
90
6464.3(3)
8
1.379
C30H18Ag2Br4F6N6O6S2
1272
Triclinic
ˉ
P1
7.8073(16)
15.310(3)
16.630(3)
110.57(3)
98.30(3)
96.19(3)
1814.4(6)
2
Cc
15.055(3)
19.328(4)
12.632(2)
90
104.687(2)
90
3555.6(11)
4
1.839
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalc (g cm−3
T (K)
)
1.670
120(2)
1.174
1.635
296(2)
1.224
2.328
120(2)
5.684
296(2)
1.683
120(2)
0.732
μ (mm−1
)
No. of refln.
No. of indep. refln.
9592
4730
29 949
6557
22 224
7469
7241
2976
15 452
8113
Rint
GoF
0.0561
0.975
0.0180
1.024
0.0163
1.010
0.0137
1.049
0.0211
1.059
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0506, 0.1118
0.0644, 0.1212
0.0205, 0.0671
0.0257, 0.0793
0.0361, 0.1047
0.0459, 0.1141
0.0178, 0.0530
0.0180, 0.0532
0.0266, 0.0585
0.0355, 0.0679
and Cu3 monopyridylpyrrole complex.24,25 Short Ag–Ag dis-
tances in 1 (Ag1–Ag2 2.9370(12) Å, Ag1–Ag3 2.8732(13) Å, Ag2–
Ag3 2.8937(13) Å) due to the silver–silver interaction are
slightly longer than av. 2.784 Å observed in Ag3 N-heterocyclic
carbene complexes.22 The Ag–N distances in 1 range from
2.281(9) to 2.659(3) Å. To be noticeable, the Ag1–N2(pyridine)
bond (2.659(3) Å) is significantly longer than other Ag–N
bonds in 1, indicating that there may be no or only a weak
interaction between Ag1 and N2. This is consistent with the
non-centrosymmetric structure of complex 1. Thus, the Ag1
atom is three coordinate, while Ag2 and Ag3 atoms are four
coordinate in distorted tetrahedron geometry.
Complex 2·OTf crystallizes in the monoclinic space group
C2/c. The structure of 2 is shown in Fig. 2. A trisilver helicate is
present with the Ag⋯Ag distance of 3.12827(14) Å; the μ2-(κ2-
N,N′),N″ (III) bonding mode of the PDPH ligand occurs. The
terminal Ag1 and Ag1A atoms are three coordinate and bond
to two nitrogen donors of the ligand and one triphenylpho-
sphine; the coordination geometry is Y-shape with larger N1–
Ag1–P1 (132.85(4)°), N2–Ag1–P1 (148.77(4)°) and smaller N1–
Ag1–N2 (74.28(6)°) bond angles. The central Ag2 silver atom is
only two coordinate with short Ag–N bonds (2.1275(16) Å) to
terminal pyridine rings of each of two ligands and two longer
Ag⋯N contacts to the central pyrrole ring (2.89 Å).
Fig. 1 ORTEP diagram of trinuclear Ag(I) complex 1 with ellipsoids
shown at the 50% probability level. The hydrogen atoms are omitted for
clarity. Selected bond distances (Å): Ag1–Ag2 2.9370(12), Ag1–Ag3
2.8732(13), Ag2–Ag3 2.8937(13), Ag1–N1 2.281(9), Ag1–N2 2.659(9),
Ag1–N4 2.333(11), Ag1–N5 2.468(10), Ag2–N1 2.494(9), Ag2–N3
2.310(9), Ag2–N7 2.455(10), Ag2–N8 2.283(10), Ag3–N4 2.464(11), Ag3–
N6 2.361(9), Ag3–N7 2.369(11), Ag3–N9 2.368(9); selected bond angles
(°): Ag2–Ag1–Ag3 59.73(3), Ag1–Ag2–Ag3 59.04(3), Ag1–Ag3–Ag2
61.23(3), Ag1–N1–Ag2 75.8(2), Ag1–N4–Ag3 73.5(3), Ag2–N7–Ag3
73.7(3), N1–Ag1–N4 169.4(4), N1–Ag1–N5 115.3(3), N4–Ag1–N5 71.2(3),
N8–Ag2–N3 163.8(4), N8–Ag2–N7 71.9(3), N3–Ag2–N1 71.3(3), N7–
Ag2–N1 159.4(3), N6–Ag3–N9 161.3(3), N6–Ag3–N4 70.6(3), N9–Ag3–
N7 71.4(3), N7–Ag3–N4 166.2(3).
Diethyl phosphite instead of PPh3 is added into a mixture
of HPDPH and AgOTf in the presence of Li[N(SiMe3)2] to
produce binuclear Li2·3·OTf. As shown in Fig. 3, PDPH ligand
Complex 1 is non-centrosymmetric and crystallizes in the adopts mode II to coordinate two silver atoms. Each silver
monoclinic space group Cc. As shown in Fig. 1, a nearly equi- atom is tri-coordinated by two N atoms from PDPH ligand and
lateral triangle Ag3 core (Ag2–Ag1–Ag3 59.73(3)°, Ag1–Ag2–Ag3 one P atom from diethyl phosphite. Here, the Ag–N(pyrrole)
59.04(3)°, Ag1–Ag3–Ag2 61.23(3)°) is supported by three PDPH distance (av. 2.437 Å) is longer than that of Ag–N(pyridine) (av.
ligands in the μ2-(κ2-N,N’),(κ2-N,N″) (II) bonding mode 2.231 Å). The two silver atoms have a distance of 2.8282(9) Å
(Scheme 2). This core structure is quite similar to those of Ag3 indicating a strong Ag⋯Ag interaction, which is comparable
N-heterocyclic carbene complexes, [Ag3(CH3im(CH2py))3- with the Ag–Ag distance found previously. Lithium triflate is
(NCCH3)2]3−, [Ag3(im(CH2py)2)3]3− and [Ag3(im(CH2Mepy)2)3]3− 22,23
,
cocrystallized in Li2·3·OTf. Its lithium cations are surrounded
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 2458–2464 | 2461

View Article Online
Paper
Dalton Transactions
Fig. 2 ORTEP diagram of trinuclear Ag(I) cationic 2 with ellipsoids
shown at the 50% probability level. The hydrogen atoms are omitted for
clarity. Selected bond distances (Å): Ag1–N1 2.3645(16), Ag1–N2
2.2163(15), Ag1–P1 2.3503(5), Ag2–N3 2.1275(16), Ag1–Ag2 3.12827(14);
selected bond angles (°): N1–Ag1–P1 132.85(4), N2–Ag1–P1 148.77(4),
N1–Ag1–N2 74.28(6), N3–Ag2–N3A 180.00(6), Ag1–Ag2–Ag1A
180.000(3). Symmetry transformations used to generate equivalent
atoms: A −x + 1, −y + 1, –z.
Fig. 4 Coordination geometry of lithium cationic in Li2·3·OTf. Selected
bond distances (Å): Li1–O4 1.961(8), Li1–O8A 1.943(8), Li1–O1S
1.935(18), Li1–O1A 2.395(7), Li1–O2A 2.299(8), Li2–O1 1.954(7), Li2–O4
1.933(6), Li2–O9 1.948(6), Li2–O1A 1.939(6).
Fig. 3 ORTEP diagram of dinuclear Ag(I) anionic
3 with ellipsoids
shown at the 50% probability level. The hydrogen atoms are omitted for
clarity. Selected bond distances (Å): Ag1–N1 2.402(7), Ag1–N2 2.226(8),
Ag1–P1 2.325(2), Ag2–N1 2.471(7), Ag2–N3 2.235(8), Ag2–P2 2.316(3),
Ag1–Ag2 2.8181(9); selected bond angles (°): N2–Ag1–P1 146.18(19),
N2–Ag1–N1 74.1(3), P1–Ag1–N1 139.28(18), N3–Ag2–P2 149.0(2), N3–
Ag2–N1 74.3(3), P2–Ag2–N1 135.78(18).
Fig. 5 ORTEP diagram of copper(I) complex 4 with ellipsoids shown at
the 50% probability level. The hydrogen atoms are omitted for clarity.
Selected bond distances (Å): Cu(1)–N(1) 2.0581(12), Cu(1)–N(2)
2.0041(12), Na(1)–N(1) 2.6745(13), Na(1)–N(3) 2.4365(12), Na(1)–O(1)
2.3736(13), Cu(1)–Na(1) 2.8927(9). Selected bond angles (°): N1–Cu1–N2
82.61(5), N1–Cu1–N2A, 116.04(5), N1–Cu1–N1A 125.52(7), N2–Cu1–
N2A 140.35(7).
by oxygen atoms from tetrahydrofunan, diethylphosphite and/
or the triflato ligand (Fig. 4), resulting in the formation of a
tetranuclear ladder-like structure. Li2 and Li2A atoms are
four coordinate in tetrahedron geometry with an average Li–O
bond distance of 1.943 Å. Li1 and Li1A atoms are coordinated
by five oxygen atoms to form a distorted bipyramidal geometry,
if longer Li–O bond (Li1–O1A 2.395(7) Å, Li1–O2A 2.299(8) Å)
could not be ignored.
In complex 4, a helical arrangement around the copper(I)
and sodium ions is displayed in Fig. 5. Copper(I) atom is
chelate-bound by both PDPH ligands with two nitrogen atoms,
while sodium rises to hexa-coordination, additionally bound
to two tetrahydrofuran solvent molecules. Within this struc-
tural arrangement, the central pyrrole nitrogen atoms N1 and
N1A are μ-bridged Cu1 and Na1 with Cu1–N1 and Na1–N1 dis-
tances of 2.0581(12) and 2.6745(13) Å, respectively. The Na1–N
(pyridine) and Na1–O(thf) bond distances are 2.4365(12) and
2.3736(13) Å, respectively (Fig. 5).
The silver(I) complex supported by the bromo-substituted
PDPBr ligand is also studied. Complex 5·(OTf)2 crystallizes in
ˉ
the triclinic space group P1 with an asymmetric unit contain-
ing two one-half of cationic 5 and two OTf− anions (Fig. 6). X-ray
dif-fraction studies reveal that the PDPBr ligands coordinate to
2462 | Dalton Trans., 2014, 43, 2458–2464
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Fig. 6 ORTEP diagram of dinuclear Ag(I) cationic 5 with ellipsoids
shown at the 50% probability level. The hydrogen atoms are omitted for
clarity except of the pyrrole proton on the nitrogen atom. Selected bond
distances (Å): Ag1–N2 2.282(3), Ag1–N3A 2.276(3), Ag3–N23 2.260(3),
Ag3–N22B 2.246(3); selected bond angles (°): N3A–Ag1–N2 177.30(9),
N22B–Ag3–N23 173.72(9). Symmetry transformations used to generate
equivalent atoms: A −x + 1, −y, −z; B −x, −y, −z + 1.
Scheme 4 (a) Ag⋯C contact in 2·OTf; (b) Ag⋯C contact in Li2·3·OTf;
(c) Ag⋯Br contact in 5·(OTf)2.
could be a cause of the ligand twisting and forming a large
torsion angle of 38.3° between the pyrrole and sideways pyri-
dine rings. The intermolecular contact is perpendicular to the
coordination plane of NNP, possibly causing the Ag to be out
of this plane by 0.21 Å. The similar intermolecular contact
(3.090 Å, 3.055 Å) in Li2·3·OTf is observed, which is in the
opposite direction of Ag⋯Ag contact. In the case of 5·(OTf)2,
the strong affinity of the “soft” bromine toward silver atom
proves to be very effective in adjusting the coordination frame-
work.27 The distances between silver and the adjacent Br atom
within one molecule, such as Ag1⋯Br3 (3.390 Å), Ag1⋯Br4
(3.248 Å), Ag2⋯Br1 (3.253 Å), Ag2⋯Br2 (3.239 Å), are shorter
than their van der Waals radius, which is analogous to that
in the silver complex of N-4-bromophenyl-N-4-pyridylurea
(3.261 Å).27a PDPBr could hinder the aggregation of silver
atoms, perhaps due to the weak steric effect of the ortho-
bromine atom. Thus, the combination of Ag⋯Br contacts and
steric hindrance of Br in 5 may lead PDPBr in the formation
of mode IV, although the PDP ligand favorable for forming
other chelating bonding modes, such as I, II and III.
Ag atoms only with pyridine nitrogen in a head-to-head
fashion (mode IV). The central pyrrole is protonated and non-
coordinated, residing in the anti-parallel direction. To our
knowledge, this is the first report of such a coordination mode
of the bispyridylpyrrolide ligand. The Ag–N bond distances
(2.246(3)–2.282(3) Å) are comparable with those for the Ag–N-
(pyridine) complexes. The N–Ag–N bond angles are almost
linear (N3A–Ag1–N2 177.30(9) and N22B–Ag3–N23 173.72(9)°).
All known bispyridylpyrrolide metal complexes, such as
[Co(PDPH)2], [M(PDPH)Cl] (M = Pd, Pt),7,8 are mononuclear
and rigorously planar, including the coplanarity of the three
rings of the bispyridylpyrrolides. In comparison, the most
noteworthy feature of the structures in this paper is the aggre-
gation of the coinage metal by nonplanar bispyridylpyrrolides.
The two side rings and the pyrrole ring of the ligand have
twisted to form three interplanar angles with the central ring,
which are in the range of 15.8–38.3°, well comparable with
those found in the coinage metal terpyridine complexes.10–15
Potential weak interactions, such as π–π stacking, Ag⋯C-
(aromatic) and/or Ag⋯Br interactions are extensively observed
in 1–5. Weak intermolecular face-to-face π–π stacking is found
within the two pendant pyridyls (centroid–centroid distance
3.7957 and 3.8587 Å for 1, 3.7985, 3.7760 Å for 2·OTf and
3.901 Å for Li2·3·OTf, 3.734 Å for 5).
Conclusion
Silver is known to have a remarkable high affinity for some
aromatic π-donor system. As shown in Scheme 4, the aromatics
in 2·OTf and Li2·3·OTf are found η2-interacting with the silver
ions. The separations vary in the range of 3.01–3.13 Å, and the
next closest contacts between Ag and C/N are all over 3.3 Å,
which is well comparable with those for polycyclic aromatic
silver(I) compounds.26 In the case of 2·OTf, only terminal Ag is
involved in the Ag⋯C contacts. The contact between Ag and N
on the sideway pyridine ring is short (3.080 and 3.014 Å). That
In summary, we have successfully designed and synthesized
silver(I) and copper(I)-bispyridylpyrrolide complexes with
different nuclearity. Structural investigation reveals that the
bispyridylpyrrolide ligand has analogous chemistry to terpyri-
dine, being capable of aggregating metal ions to form novel
multi-nuclear metal complexes. PDPH in 1–4 acts as a bridging
ligand to coordinate two metal atoms in bonding modes II
and III, while PDPBr in 5 binds to silver atoms in a face-to-face
fashion (bonding mode IV). It seems likely that the bonding
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 2458–2464 | 2463

View Article Online
Paper
Dalton Transactions
flexibility of the central pyrrole nitrogen and the range of 13 Effendy, F. Marchetti, C. Pettinari, R. Pettinari,
potential molecular interactions, such as π–π stacking, Ag⋯Br,
Ag⋯C interactions, directly lead the bispyridylpyrrolide ligand
B. W. Skelton and A. H. White, Inorg. Chim. Acta, 2007, 360,
1414–1423.
to change its bonding mode, and to rotate away from planarity 14 (a) H. Feng, X.-P. Zhou, T. Wu, D. Li, Y.-G. Yin and
to accommodate a bridging structural role.
S. W. Ng, Inorg. Chim. Acta, 2006, 359, 4027–4035;
(b) Z. Ma, Y.-P. Xing, M. Yang, M. Hu, B.-Q. Liu, M. F. C.
G. da Silva and A. J. L. Pombeiro, Inorg. Chim. Acta, 2009,
362, 2921–2926.
Acknowledgements
15 M. J. Hannon, C. L. Painting, E. A. Plummer, L. J. Childs
and N. W. Alcock, Chem.–Eur. J., 2002, 8, 2225–2238.
16 H. Schindlbauer, Monatsh. Chem., 1968, 99, 1799–
1807.
17 R. A. Jones, M. Karatza, T. N. Voro, P. U. Civcir, A. Franck,
O. Ozturk, J. P. Seaman, A. P. Whitmore and
D. J. Williamson, Tetrahedron, 1996, 52, 8707–8724.
18 D. C. Owsley, J. M. Nelke and J. J. Bloomfield, J. Org. Chem.,
1973, 38, 901–903.
This work was supported by the National Natural Science
Foundation of China (project 21001118), China Postdoctoral
Science Foundation (2011M500129) and the Postdoctoral
Science Foundation of Central South University. This material
is available free of charge via the Internet at http://pubs.acs.
org.
Notes and references
19 Z. Zhang, J. M. Lim, M. Ishida, V. V. Roznyatovskiy,
V. M. Lynch, H.-Y. Gong, X. Yang, D. Kim and J. L. Sessler,
J. Am. Chem. Soc., 2012, 134, 4076–4079.
1 C. J. Moulton and B. L. Shaw, J. Chem. Soc., Dalton Trans.,
1976, 1020–1024.
2 J. Dehand and M. Pfeffer, Coord. Chem. Rev., 1976, 18, 327– 20 G. M. Sheldrick, SADABS, University of Göttingen,
352. Germany, 1997.
3 M. E. van der Boom and D. Milstein, Chem. Rev., 2003, 103, 21 G. M. Sheldrick, SHELXTL-Plus V5.1 Software Reference
1759–1792.
Manual, Bruker AXS Inc., Madison, Wisconsin, USA,
4 M. G. Scheibel, B. Askevold, F. W. Heinemann,
1997.
E. J. Reijerse, B. de Bruin and S. Schneider, Nat. Chem., 22 (a) V. J. Catalano and S. J. Horner, Inorg. Chem., 2003, 42,
2012, 4, 552–558.
5 N. Selander and K. J. Szabó, Chem. Rev., 2011, 111, 2048–
2076.
8430–8438; (b) V. J. Catalano and M. A. Malwitz, Inorg.
Chem., 2003, 42, 5483–5485; (c) V. J. Catalano and
A. L. Moore, Inorg. Chem., 2005, 44, 6558–6566.
6 J. W. Ciszek, Z. K. Keane, L. Cheng, M. P. Stewart, L. H. Yu, 23 (a) P. A. Leach, S. J. Geib and N. J. Cooper, Organometallics,
D. Natelson and J. M. Tour, J. Am. Chem. Soc., 2006, 128,
3179–3189.
1992, 11, 4367–4370; (b) J. C. Garrison, C. A. Tessier and
W. J. Youngs, J. Organomet. Chem., 2005, 690, 6008–6020.
7 G. H. Imler, Z. Lu, K. A. Kistler, P. J. Carroll, B. B. Wayland 24 V. J. Catalano, L. B. Munro, C. E. Strasser and A. F. Samin,
and M. J. Zdilla, Inorg. Chem., 2012, 51, 10122–10128. Inorg. Chem., 2011, 50, 8465–8476.
8 F. Hein and U. Beierlein, Pharm. Zentralhalle Dtschl., 1957, 25 J. G. Andino, J. A. Flores, J. A. Karty, J. P. Massa, H. Park,
96, 401–421.
N. P. Tsvetkov, R. J. Wolfe and K. G. Caulton, Inorg. Chem.,
2010, 49, 7626–7628.
26 M. Munakata, L.-P. Wu, G.-L. Ning, T. Kuroda-Sowa,
M. Maekawa, Y. Suenaga and N. Maeno, J. Am. Chem. Soc.,
1999, 121, 4968–4976.
9 M. Al-Anber, B. Walfort, S. Vatsadze and H. Lang, Inorg.
Chem. Commun., 2004, 7, 799–802.
10 Y. Cui and C. He, J. Am. Chem. Soc., 2003, 125, 16202–
16203.
11 G. Baum, E. C. Constable, D. Fenske, C. E. Housecroft and 27 (a) S. K. Chandran, R. Thakuria and A. Nangia, CrystEng-
T. Kulke, Chem. Commun., 1998, 2659–2660.
12 E. C. Constable, T. Kulke, M. Neuburger and M. Zehnder,
Chem. Commun., 1997, 489–490.
Comm, 2008, 10, 1891–1898; (b) M. D. Ward,
S. M. Couchman and J. C. Jeffery, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1998, 54, 1820–1823.
2464 | Dalton Trans., 2014, 43, 2458–2464
This journal is © The Royal Society of Chemistry 2014