Coinage metal complexes of 2-diphenylphosphino-3-methylindole

Article abstract of DOI:10.1039/c1dt10564g

Coordination of P,N indolyl-phosphine ligands to Au^I, Ag ^I and Cu^I metal ions under weakly basic conditions results in easy deprotonation of the indolyl N-H function and effective formation of a family of homo- and heterob

Full text of DOI:10.1039/c1dt10564g

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PAPER
Coinage metal complexes of 2-diphenylphosphino-3-methylindole†
Igor O. Koshevoy,*a Julia R. Shakirova,b Alexei S. Melnikov,c Matti Haukka,a Sergey P. Tunik*b and
Tapani A. Pakkanena
Received 2nd April 2011, Accepted 13th May 2011
DOI: 10.1039/c1dt10564g
Coordination of P,N indolyl-phosphine ligands to AuI, AgI and CuI metal ions under weakly basic
conditions results in easy deprotonation of the indolyl N–H function and effective formation of a
family of homo- and heterobimetallic complexes MM¢(PPh2C9H7N)2 (M = M¢ = Au (2), Ag (5); M =
Au, M¢ = Cu (3), Ag (4)). The latter (4) exists as an inseparable mixture of four different complexes,
which are in equilibrium driven by slow dynamics. The reaction of silver(I) and copper(I) ions with
PPh2(C9H8N) affords a rare tetranuclear Z-shaped cluster Ag2Cu2(PPh2C9H7N)4 (6), which exhibits red
luminescence in solid state (650 nm) and a weak dual emission in solution with the main component in
the near-IR region (746 nm).
Introduction
Coordination chemistry of d10 coinage metals in general and of
gold(I) in particular, is significantly diversified by the effective
secondary metal–metal interactions which may lead to the forma-
tion of various polymetallic assemblies1 demonstrating attractive
photophysical properties. It has been shown that luminescence of
these compounds often originates or considerably depends on the
metallophilic contacts both in the solid state and in solution.2–4
Therefore different types of bridging ligands, which could bring
two metal ions in close proximity, have been successfully employed
in preparative chemistry of the copper subgroup metal complexes.
As AuI demonstrates much higher affinity toward phosphorus
ligands in comparison to hard donors such as nitrogen and oxygen,
the preference has been given to the bidentate phosphines with a
short bite angle e.g., P,P diphosphine ligands PR2–X–PR2 (X =
Scheme 1 Examples of bidentate phosphine bridging coordination.
CH2, CH-, NR¢, C PMe3, ferrocenyl, various aromatic spacers
etc.),3,5 and some mixed-donor phosphines with P,C- (PR2C6X4 ),6
-
P,S (PhP2CH2SPh),7 or P,N (PPh2-pyridine, 2-PPh2-1-X-imidazole
X = methyl, benzyl etc.)8,9 coordinating functions (Scheme 1).
Additionally, these heterophosphines having N or S donor
atoms allowed for the successful assembly of the mixed-metal
systems,7,9,10 some of which exhibit very intense and tunable
photoluminescence.4,11
However, the chemistry of P,NH heterodentate ligands, where
NH represents pyrrolyl or indolyl groups, to the best of our
knowledge, has never been investigated with respect to the coinage
metal ions and very poorly studied in general. The reason for
this lack of attention probably resides in the rather ineffective
synthetic approach to 2-diphenylphosphino-pyrrole,12 as well as
in the limited ligand stability, manifested by a tendency to break
the P–C bond upon coordination to transition metals.13 Closely
related 2-diphenylphosphino-3-methylindole was reported in 2005
as an easy to make and stable phosphine.14 Subsequent synthesis of
its Pd(II) dinuclear compounds,15 where both P and deprotonated
N donor atoms participate in metal binding, prompted us to
explore the related chemistry of d10 copper subgroup metal
compounds. Herein we report the preparation of a series of the
novel homo- and heterometallic AuI, AgI and CuI complexes with
2-diphenylphosphino-3-methylindole and the study luminescent
properties of the tetranuclear AgI–CuI cluster.
aUniversity of Eastern Finland, Joensuu, 80101, Finland. E-mail: igor.
koshevoy@uef.fi; Fax: +358 13 2513390; Tel: +358 13 2513325
bSt. Petersburg State University, Department of Chemistry, Universitetskii
pr. 26, 198504, St. Petersburg, Russia. E-mail: stunik@inbox.ru; Fax: +7
812 4283969; Tel: +7 812 4284028
cSt. Petersburg State University, Department of Physics, Ulianovskaya Street
3, 198504, St. Petersburg, Russia
† Electronic supplementary information (ESI) available: X-ray crystallo-
graphic data for 3, 5 and 6, selected NMR spectra of 1–6. CCDC reference
numbers 819978, 819979 and 819980. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1dt10564g
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added, followed by NEt3 (1 drop). The pale yellow solution was
stirred for 30 min, evaporated, washed with methanol (2 ¥ 5 cm3)
and diethyl ether (2 ¥ 5 cm3) and recrystallized by gas-phase
diffusion of diethyl ether into the CHCl3–ethanol solution of 3
at +5 ◦C to give very pale yellow crystals (81 mg, 93%).
Method B. 2 (50 mg, 0.049 mmol) was dissolved in CH2Cl2
(15 cm3) and a solution of [Cu(NCMe)4]PF6 (37.0 mg, 0.099 mmol)
and PPh2(C9H8N) (31 mg, 0.098 mmol) in CH2Cl2 (5 cm3) was
added, followed by NEt3 (2 drop). The pale yellow solution was
treated as above (method A) to give pale yellow crystals of 3 (81 mg,
93%).
Experimental
General comments
Au(tht)Cl (tht = tetrahydrothiophene),16 2-diphenylphosphino-3-
methylindole14 were obtained according to the literature methods.
Other reagents and solvents were used as received. The solution 1D
1H, 31P NMR and 1H–1H COSY spectra were recorded on Bruker
Avance 400 and Bruker DPX 300 spectrometers. Microanalyses
were carried out in the analytical laboratory of the University of
Eastern Finland.
1
31P{ H} NMR (CDCl3; d): 28.5 (s). 1H NMR (CDCl3; d): 1.93
[Au(PPh2C9H8N)2]PF6 (1). Au(tht)Cl (100 mg, 0.312 mmol)
was dissolved in CH2Cl2 (7 cm3) and crystalline PPh2(C9H8N)
(200 mg, 0.635 mmol) was added. The colorless transparent
mixture was stirred for 15 min and then treated with a solu-
tion of AgPF6 (79 mg, 0.312 mmol) in acetone (3 cm3). The
stirring was continued for an additional 15 min, the precipitate
of AgCl was removed by filtration and the colorless filtrate
was evaporated. The amorphous solid was washed with diethyl
ether (3 ¥ 5 cm3) and recrystallized by gas-phase diffusion of
diethyl ether into a CH2Cl2 solution of 1 at 5 ◦C to give
(s, 6H, CH3 of indole), 7.05 (dd, 2H, aromatic H of indole, J(HH)
ca. 8.0, 6.8 Hz), 7.25 (dd, 2H, aromatic H of indole, J(HH) 8.3,
6.8 Hz), 7.42–7.51 (m, 12H, phenyl H), 7.57–7.63 (m, 8H, phenyl
H), 7.59 (d, 2H, aromatic H of indole, J(HH) ca. 8.0 Hz), 7.97
(d, 2H, aromatic H of indole, J(HH) 8.3 Hz). Anal. Calc. for
AuC42CuH34N2P2: C, 56.73; H, 3.85; N, 3.15. Found: C, 56.47; H
4.09; N 3.17.
{AuAg(PPh2C9H7N)2} (4). Method A. 1 (50 mg, 0.051 mmol)
was dissolved in CH2Cl2 (10 cm3) and a solution of AgCF3SO3
(13.5 mg, 0.053 mmol) in methanol (2 cm3) was added, followed
by NEt3 (1 drop). The reaction mixture was treated analogously
to that of 2 to give colorless crystalline material (44 mg, 91%).
Method B. AgCF3SO3 (51 mg, 0.198 mmol) was dissolved
in methanol (2 cm3) and a solution of PPh2(C9H8N) (62 mg,
0.197 mmol) in CH2Cl2 (3 cm3) was added. This mixture was
added to a solution of 2 (100 mg, 0.098 mmol) in CH2Cl2 (15 cm3),
followed by NEt3 (5 drops). The colorless solution darkened to
brownish and was stirred for 1.5 h. Then it was treated analogously
to 2 to give 168 mg (92%) of white crystalline material.
a colorless crystalline material (279 mg, 92%). 31P{ H} NMR
1
(CDCl3; d): 24.6 (s, 2P), -143 (sept, 1P). 1H NMR (CDCl3;
d): 2.33 (s, 6H, CH3 of indole), 7.17 (dd, 2H, aromatic H of
indole, J(HH) 8.4, 7.1 Hz), 7.30 (dd, 2H, aromatic H of indole,
J(HH) ca. 8, 7.1 Hz), 7.52 (d, 2H, aromatic H of indole, J(HH)
8.4 Hz), 7.59 (d, 2H, aromatic H of indole, J(HH) ca. 8 Hz), 7.55–
7.66 (m, 20H, phenyl H), 8.61 (s, 2H, NH of indole). Anal. Calc.
for AuC42H36F6N2P3: C, 51.87; H, 3.73; N, 2.88. Found: C, 51.58;
H 3.98; N 2.89.
Au2(PPh2C9H7N)2 (2). Method A. 1 (50 mg, 0.051 mmol) was
dissolved in CH2Cl2 (10 cm3) and a solution of Au(tht)Cl (17.0
mg, 0.053 mmol) in CH2Cl2 (3 cm3) was added, followed by NEt3
(1 drop). The colorless solution was stirred for 30 min, evaporated,
washed with methanol (2 ¥ 5 cm3), diethyl ether (2 ¥ 5 cm3) and
recrystallized by slow evaporation of the CHCl3–heptane solution
of 2 at room temperature to give a colorless crystalline material
(48 mg, 92%).
1
31P{ H} NMR (CDCl3; d): the spectrum corresponds to the
mixture of 4 complexes, see discussion; 4.5 (two d, J(107Ag–P)
555 Hz and J(109Ag–P) 641 Hz, 3J(PP) 4.6 Hz), 8.3 (two d, J(107Ag–
P) 543 Hz and J(109Ag–P) 629 Hz), 15.8 (s), 19.9 (d, 3J(PP) 4.6 Hz),
28.8 (s). Anal. Calc. for AgAuC42H34N2P2: C, 54.04; H, 3.67; N,
3.00. Found: C, 53.71; H 3.86; N 3.02.
Ag2(PPh2C9H7N)2 (5). AgCF3SO3 (40 mg, 0.156 mmol) was
dissolved in methanol (3 cm3) and added to a solution of
PPh2(C9H8N) (50 mg, 0.159 mmol) in CH2Cl2 (20 cm3), followed by
NEt3 (2 drops). The colorless solution was filtered and placed into
a refrigerator at 5 ◦C. Small block colorless crystals formed within
2–3 days, washed with methanol (3 ¥ 5 cm3) and diethyl ether
(2 ¥ 5 cm3), and vacuum dried (60 mg, 91%). The crystalline
samples are very poorly soluble in common organic solvents.
Method B. Au(tht)Cl (100 mg, 0.312 mmol) was dissolved
in CH2Cl2 (10 cm3) and crystalline PPh2(C9H8N) (100 mg,
0.317 mmol) was added. The colorless transparent mixture was
stirred for 15 min and then treated with NEt3 (8 drops, slight
excess). The stirring was continued for an additional 30 min, then
the colorless solution was filtered and evaporated. The white solid
was washed with methanol (2 ¥ 5 cm3) and diethyl ether (2 ¥ 5 cm3),
and then recrystallized by slow evaporation of the CHCl3–heptane
solution of 2 at room temperature to give a colorless crystalline
1
31P{ H} NMR (CDCl3; d): 8.3 (two d, J(107Ag–P) 545 Hz and
1
J(109Ag–P) 629 Hz). H NMR (CDCl3; d): 1.94 (s, 6H, CH3 of
material (150 mg, 94%). 31P{ H} NMR (CDCl3; d): 15.8 (s). H
NMR (CDCl3; d): 1.89 (d, 6H, CH3 of indole, J(HP) 1.4 Hz),
7.02 (dd, 2H, aromatic H of indole, J(HH) 8.0, 7.0 Hz), 7.16 (dd,
2H, aromatic H of indole, J(HH) 8.1, 7.0 Hz), 7.41–7.49 (m, 12H,
phenyl H), 7.58 (d, 2H, aromatic H of indole, J(HH) 8.0 Hz),
7.62–7.69 (m, 8H, phenyl H), 7.76 (d, 2H, aromatic H of indole,
J(HH) 8.1 Hz). Anal. Calc. for Au2C42H34N2P2: C, 49.33; H, 3.35;
N, 2.74. Found: C, 49.16; H 3.34; N 2.74.
1
1
indole), 7.01 (dd, 2H, aromatic H of indole, J(HH) 8.2, 7.8 Hz),
7.13 (dd, 2H, aromatic H of indole, J(HH) ca. 8.0, 7.8 Hz), 7.40–
7.48 (m, 12H, phenyl H), 7.52 (d, 2H, aromatic H of indole, J(HH)
8.2 Hz), 7.55–7.61 (m, 10H, phenyl H and aromatic H of indole).
Anal. Calc. for Ag2C42H34N2P2: C, 59.74; H, 4.06; N, 3.32. Found:
C, 59.32; H 4.19; N 3.27.
Ag2Cu2(PPh2C9H7N)4 (6). AgCF3SO3 (50 mg, 0.195 mmol)
was dissolved in methanol (3 cm3) and added to a solution of
PPh2(C9H8N) (125 mg, 0.397 mmol) and Cu(NCMe)4PF6 (73 mg,
0.196 mmol) in CH2Cl2 (20 cm3), followed by NEt3 (2 drops).
AuCu(PPh2C9H7N)2 (3). Method A. 1 (50 mg, 0.051 mmol)
was dissolved in CH2Cl2 (10 cm3) and
a solution of
[Cu(NCMe)4]PF6 (19.5 mg, 0.054 mmol) in CH2Cl2 (3 cm3) was
7928 | Dalton Trans., 2011, 40, 7927–7933
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˚
The resulting orange solution was stirred for 30 min, filtered
and evaporated. The orange solid was washed with methanol
(2 ¥ 5 cm3) and diethyl ether (2 ¥ 5 cm3) and recrystallized by
slow evaporation of the CHCl3–heptane solution of 4 at room
temperature to give an orange-red crystalline material (136 mg,
87%). 31P{ H} NMR (CDCl3; -50 C d): 3.0 (two d, 1P (J(107Ag–P)
441 Hz and J(109Ag–P) 509 Hz)); 2.6 (two d, 1P (J(107Ag–P)
479 Hz and J(109Ag–P) 551 Hz)). Anal. Calc. for
Ag2C84Cu2H68N4P4: C, 63.05; H, 4.28; N, 3.50. Found: C,
62.90; H 4.24; N 3.52.
0.99 A, and Uiso = 1.2–1.5 Ueq (parent atom). The crystallographic
details are summarized in the corresponding footnote.‡
Results and discussion
◦
1
Synthesis and characterization
The reaction of Au(tht)Cl with PPh2(C9H8N) in a 2 : 1 stoichiomet-
ric ratio and consequent treatment with AgPF6 resulted in nearly
quantitative formation of the complex [Au(PPh2C9H8N)2]PF6 (1),
Scheme 2. The composition of 1 has been established on the basis
of H, 31P NMR spectroscopic studies and elemental analysis.
1
Thus, its 31P spectrum displays a singlet resonance at 24.6 ppm
Photophysical measurements
-
along with septet of PF6 counterions (-143 ppm), indicating the
equivalence of the phosphine ligands. The 1H spectrum consists of
a set of resonances of aromatic protons together with the high-field
singlet of the methyl group and a broad low-field resonance of the
N–H proton of the indolyl moiety, relative intensity and multiplic-
ity of the signals are also completely compatible with equivalence
of the phosphine ligands. (Experimental and Fig. S1, ESI†).
Addition of 1 equivalent of Au(tht)Cl to 1 in the presence
of base (NEt3, to deprotonate indolyl nitrogen atoms) gave a
dimeric digold complex formulated as Au2(PPh2C9H7N)2 (2).
Alternatively, 2 can be obtained in the one-step reaction of
Au(tht)Cl with PPh2(C9H8N) (1 : 1 ratio) upon treatment with
NEt3. Dimer 2 didn’t give crystals suitable for X-ray diffraction
studies and was characterized by 1H, 31P NMR spectroscopy. The
31P{ H} spectrum displays a singlet at 15.8 ppm, while the H
NMR data fit well the structure shown in Scheme 2 (Experimental
and Fig. S1, ESI†). The position of the 31P signal is considerably
shifted into high field in comparison with that of 1, which points to
the head-to-tail coordination of the phosphines in 2. Analysis of
the spectral patterns of other complexes (see below) also confirms
this hypothesis.
The photophysical measurements for 6 were carried out in solid
state and in CH2Cl2, which was distilled immediately prior to
use. The solutions were carefully degassed before taking life-
time measurements. The light-emitting diodes (LEDs, maximum
emission at 390 and 532 nm) were used to pump luminescence.
The LEDs were used in the continuous and pulse modes (pulse
width, 1–20 ms; duty of edge, ~90 ns; repetition rate, 100 Hz to
10 kHz). A digital oscilloscope Tektronix TDS3014B (Tektronix,
bandwidth 100 MHz), monochromator MUM (LOMO, interval
of wavelengths 10 nm) and photomultiplier tube Hamamatsu were
used for life-time measurements. Emission spectra were recorded
using an HR2000 spectrometer (Ocean Optics). A halogen lamp,
LS-1-CAL (Ocean Optics), and deuterium lamp, DH2000 (Ocean
Optics), were used to calibrate the absolute spectral response of
the spectral system in the 200–1100 nm range. Excitation spectra
were measured on a Varian Cary Eclipse spectrofluorimeter.
1
1
X-ray structure determinations
The crystals of 3, 5 and 6 were immersed in cryo-oil, mounted
in a Nylon loop, and measured at a temperature of 100 K. The
X-ray diffraction data were collected on a Bruker AXS Smart
Similar to the synthesis of 2, the reaction of 1 with
[Cu(NCMe)4]PF6 and NEt3 led to high yield formation of the
heterometallic dimer AuCu(PPh2C9H7N)2 (3). Treatment of 2
with 2 equivalents of [Cu(NCMe)4]PF6, PPh2(C9H8N) and NEt3
allowed for the selective preparation of 3. The crystal structure
˚
ApexII diffractometer using Mo-Ka radiation (l = 0.710 73 A).
The APEX217 program package was used for cell refinements and
data reductions. The structures were solved by direct methods
using the SHELXS-9718 program with the WinGX19 graphical user
interface. Multi-scan absorption corrections based on equivalent
reflections (SADABS)20 were applied to all data. Structural refine-
ments were carried out using SHELXL-97.18 In 3 a chlorine atom
in one of the chloroform of crystallization was disordered over
three sites with occupancies of 0.4/0.4/0.2. One of the disordered
chlorines was restrained so that its Uij components approximate
to isotropic behavior. Furthermore, the hydrogen atom of CHCl3
‡ Crystal data for 3: C44H36AuCl6CuN2P2, M = 1127.89, colourless block,
3
¯
0.28 ¥ 0.16 ¥ 0.14 mm , triclinic, space group P1, a = 10.8076(3),
˚
b = 13.5369(4), c = 16.5304(5) A, a = 68.8140(10), b = 82.764(2), g =
◦
3
-3
˚
72.5220(10) , V = 2150.45(11) A , Z = 2, Dc = 1.742 g cm , F000 = 1108,
Mo-Ka radiation, l = 0.71073 A, T = 100(2)K, 2qmax = 72.9◦, 76139
˚
reflections collected, 20526 unique (Rint = 0.0560). Final GooF = 1.022, R1 =
0.0315, wR2 = 0.0652, R indices based on 20526 reflections with I > 2s(I)
(refinement on F2), 529 parameters, 7 restraints; wR2 = 0.0691 (all data).
Crystal data for 5: C44H38Ag2Cl4N2P2, M = 1014.24, colourless needle,
0.14 ¥ 0.08 ¥ 0.06 mm3, monoclinic, space group C2/c, a = 26.223(2),
˚
was refined with a fixed C–H distance (1.00(4) A) and Uiso = 1.2 Ueq
◦
˚
b = 8.9783(8), c = 18.0291(16) A, a = 90, b = 107.870(5), g = 90 , V =
(parent carbon atom). In 5 the solvent of crystallization (CH2Cl2)
was disordered over two sites with equal occupancies. The carbon
and chlorine atoms of the solvent molecules were restrained so
that their Uij components approximate to isotropic behavior. In
6 the chlorine atoms in one of the CHCl3 solvent molecules were
disordered over two sites with occupancies of 0.74 and 0.26. Also,
the carbon atom C85 of the second CHCl3 solvent molecule was
disordered over two sites with occupancies 0.63 and 0.37. The C–Cl
and Cl–Cl distances in both chloroform molecules were restrained
to be similar. The hydrogen atoms were positioned geometrically
and constrained to ride on their parent atoms, with C–H = 0.95–
3
-3
˚
4040.0(6) A , Z = 4, Dc = 1.668 g cm , F000 = 2032, Mo-Ka radiation, l =
0.71073 A, T = 100(2)K, 2qmax = 52.0◦, 15701 reflections collected, 3935
˚
unique (Rint = 0.0480). Final GooF = 1.052, R1 = 0.0454, wR2 = 0.1119,
R indices based on 3935 reflections with I > 2s(I) (refinement on F2),
269 parameters, 36 restraints; wR2 = 0.1193 (all data). Crystal data for 6:
C86H70Ag2Cl6Cu2N4P4, M = 1838.86, orange block, 0.20 ¥ 0.10 ¥ 0.07 mm3,
¯
˚
triclinic, space group P1, a = 12.8508(5), b = 16.2521(6), c = 18.9675(7) A,
◦
3
˚
a = 98.284(2), b = 92.794(2), g = 95.373(2) , V = 3895.1(3) A , Z = 2,
Dc = 1.568 g cm-3, F000 = 1856, Mo-Ka radiation, l = 0.71073 A, T =
˚
100(2)K, 2qmax = 55.3◦, 61774 reflections collected, 17947 unique (Rint
=
0.0639). Final GooF = 1.005, R1 = 0.0510, wR2 = 0.1058, R indices based
on 17947 reflections with I > 2s(I) (refinement on F2), 979 parameters,
58 restraints; wR2 = 0.1231 (all data).
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group of indolyl substituent (Experimental and Fig. S1, ESI†).
The number of signals and their relative intensities confirm the
equivalence of the phosphine ligands.
In an attempt to synthesize the silver analogue of 3, we
investigated the reaction of 1 with AgCF3SO3 and NEt3. Instead
of the expected dinuclear complex AuAg(PPh2C9H7N)2, a mixture
of compounds 4 were generated according to 31P{H} NMR
spectrum (Fig. 2). Numerous attempts to recrystallize the mixture
in order to separate the constituents were not successful and
even didn’t change the relative intensities of the 31P{H} NMR
signals. Moreover, variation of the synthetic method (Scheme
2(f,g) and Experimental) also led to the formation of the mixture of
exactly the same composition that points to a dynamic equilibrium
of the molecular species presented in solution. The VT NMR
experiments in the -50 – +45 ◦C temperature interval (Figure
S2, ESI†) showed only slight broadening of the minor signal
(8.3 ppm) at +50 ◦C and small variations in relative intensities
of all resonances. This is an indication of a relatively slow (in the
NMR time scale) intermolecular dynamics which start to affect the
spectroscopic pattern only at the temperature close to the solvent
boiling point. Comparative analysis of the room temperature
spectrum, which can be considered as a low temperature dynamics
limit, allowed for a tentative assignment of the observed signals
to the species shown in Fig. 2. Thus, the signal at 15.8 ppm
exactly matches that of complex 2 (species c). The low field
singlet at 28.8 ppm very probably originates from the head-to-
head AuAg(PPh2C9H7N)2 complex, with the phosphorus atom
coordinated to gold (species a), as its position is very close to the
resonance of the Au–Cu relative 3 (28.5 ppm). The multiplicity
and the coupling constants of the dominant signals at 19.9 (d,
3J(PP) 4.6 Hz) and 4.5 (dm, J(107Ag– P) 555 Hz and J(109Ag–
Scheme 2 Reaction conditions: (a) 0.5 Au(tht)Cl, 0.5 AgPF6; (b)
Au(tht)Cl, NEt3; (c) Au(tht)Cl, NEt3; (d) [Cu(NCMe)4]PF6, NEt3; (e)
2 [Cu(NCMe)4]PF6, 2 PPh2(C9H8N), NEt3; (f ) AgCF3SO3, NEt3; (g) 2
AgCF3SO3, 2 PPh2(C9H8N), NEt3.
3
P) 641 Hz, J(PP) 4.6 Hz) ppm indicate that the corresponding
phosphorus atoms are bound to the AuI and AgI ions, respectively.
This spectral pattern most probably stems from the nonsymmetric
head-to-tail AuAg(PPh2C9H7N)2 complex (Fig. 2, b). A typical
“silver” multiplet-two doublets at 8.3 ppm (J(107Ag–P) 543 Hz and
J(109Ag–P) 629 Hz) is indicative of the phosphorus coordination
to the silver(I) ions, very probably in the head-to-tail mode of
the phosphine ligands in the homometallic Ag2(PPh2C9H7N)2
complex (species d).
Fig. 1 Structural plot of AuCu(PPh2C9H7N)2 (3). Selected bond dis-
tances (A): Au(1)–P(2) 2.3061(5), Au(1)–P(1) 2.3132(5), Au(1)–Cu(1)
˚
2.7054(2), Cu(1)–N(1) 1.8594(17), Cu(1)–N(2) 1.8660(17); angles (deg):
P(2)–Au(1)–P(1) 166.989(18), N(1)–Cu(1)–N(2) 173.87(7).
of 3 is shown in Fig. 1. Complex 3 adopts a head-to-head
coordination mode of the heterodentate PN phosphines, where
the gold and copper ions are bound to phosphorus and nitrogen
atoms, respectively. Hard-to-hard and soft-to-soft metal–ligand
interaction is evidently the driving force in the formation of
the structural pattern found in 3. A visible distortion of the
linear geometry at gold(I) center (167◦) is probably determined
˚
by a rather short intermetallic distance (2.7054(2) A) that is
considerably less than the sum of Au and Cu van der Waals radii
I
I
˚
(3.06 A) and falls in the range found for other Au –Cu bonds
reported in the literature.10,21 The solution NMR spectral data for
3 are consistent with the solid-state structure. The 31P spectrum
displays one singlet at 28.5 ppm and the proton NMR pattern
consists of the resolved set of signals, which correspond to the
aromatic protons together with a high field singlet of the CH3
◦
1
Fig. 2 31P{ H} NMR spectrum of the mixture 4, 400 MHz, CDCl3, 25 C.
The relative molar ratio of the forms a:b:c:d is ca. 1 : 7.5 : 1.8 : 1.4.
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In order to prove this structural hypothesis we have probed a
direct reaction of AgCF3SO3 with the diphosphine under study.
Indeed, mixing the stoichiometric amounts of the reagents and
the addition of NEt3 (Scheme 3a) led to fast crystallization of
colorless Ag2(PPh2C9H7N)2 (5), which was characterized by an
X-ray diffraction study (Fig. 3) and by NMR spectroscopy.
also did not show selective crystallization of the isomers to give a
broad unresolved set of signals in the area, which encompass the
0–25 ppm area that is very similar to the spectral range observed
1
in the 31P{ H} solution NMR spectra of 4.
The synthetic approach, which gave the homometallic AuI, AgI
complexes 2 and 5, respectively (see Scheme 2c, Scheme 3a), did
not allow for isolation of any stable product in the case of CuI
ions, though some interaction occurred judging by the appearance
of yellow color upon adding NEt3 to the solution containing
1
[Cu(NCMe)4]PF6 and PPh2(C9H8N). The 1H and 31P{ H} NMR
spectra of the reaction mixture showed non-informative patterns
of broad signals. However, when two metal ions, CuI and AgI, were
combined together followed by treatment with 2 equivalents of the
PN ligand and NEt3, a bright orange solution was formed, from
which a red-orange crystalline sample of the tetranuclear cluster
Ag2Cu2(PPh2C9H7N)4 (6) was obtained in high yield (Scheme 3b).
Its crystal structure is shown in Fig. 4.
Fig. 3 Structural plot of Ag2(PPh2C9H7N)2 (5). Selected bond distances
˚
(A): Ag(1)–N(1) 2.101(4), Ag(1)–P(1) 2.3507(13), Ag(1)–Ag(1¢) 2.8577(7);
angles (deg): N(1)–Ag(1)–P(1) 174.86(12).
Scheme 3 Reaction conditions: (a) AgCF3SO3, NEt3; (b) 0.5 AgCF3SO3,
0.5 [Cu(NCMe)4]PF6, NEt3.
Fig.
4
Structural plot of Ag2Cu2(PPh2C9H7N)4 (6). Selected
˚
bond distances (A): Ag(1)–P(4) 2.3953(12), Ag(1)–P(1) 2.4263(13),
Ag(1)–Cu(1) 2.7335(7), Ag(1)–Ag(2) 3.0745(5), Ag(2)–P(2) 2.4071(12),
Ag(2)–P(3) 2.4327(12), Ag(2)–Cu(2) 2.7492(7), Cu(1)–N(1) 1.838(4),
Cu(1)–N(2) 1.845(4), Cu(2)–N(3) 1.842(4), Cu(2)–N(4) 1.847(4);
Complex 5 expectedly shows the symmetrical head-to-tail
bonding mode of the PN ligands. Both silver(I) ions have the
linear two-coordinate environment. The intermetallic distance is
angles
(deg):
P(4)–Ag(1)–P(1)
140.72(4),
Cu(1)–Ag(1)–Ag(2)
˚
2.8577(7) A, which is much less than the sum of van der Waals
74.665(17), P(2)–Ag(2)–P(3) 140.22(4), Cu(2)–Ag(2)–Ag(1) 69.427(16),
N(1)–Cu(1)–N(2) 174.09(18), N(3)–Cu(2)–N(4) 172.58(17).
˚
radii (3.44 A) and is consistent with the previously reported values
for Ag–Ag separations in phosphine-containing compounds,9,22
testifying to a presence of the metal–metal interaction. The
The metal core of complex 6 has a rare Z-shaped planar
geometry, in which the spatially separated copper ions are bound
to the central di-silver unit in an asymmetric way. This structural
pattern gives only two effective Ag–Cu contacts (Ag(1)–Cu(1)
1
31P{ H} NMR spectrum displays two doublets centered at 8.3
ppm which is characteristic for P–Ag coordination. The values
of the chemical shift and coupling constants for the 107Ag and
109Ag containing isotopomers (J(107Ag–P) 545 Hz and J(109Ag–P)
629 Hz) are exactly the same as the corresponding parameters of
the d species revealed in the mixture 4 (Fig. 2, d). The proton
NMR data of dimer 5 are in complete agreement with the solid
state structure.
˚
2.7335(7) and Ag(2)–Cu(2) 2.7492(7) A), which fits well the
literature data,23,24 while two other silver–copper distances are
˚
considerably elongated (3.327 and 3.533 A) and exceed the sum
˚
of Ag and Cu van der Waals radii (3.12 A). The non-bridged Ag–
˚
˚
Ag bond (3.0745(5) A) is longer than that in 5 (2.8577(7) A) but
is still within the reported range of this type of contacts.9,22 The
phosphine ligands are coordinated in a bridging mode providing
N,N and P,P environment for the copper and silver centers,
respectively. The geometry at the copper ions is almost linear,
while the P–Ag–P angles are only ca. 140 ◦C. To the best of
our knowledge the tetranuclear AgI2CuI2 metal core has been
previously found only in one structurally characterized complex,
The observed non-selective formation of different homo- and
heterometallic species in the presence of gold(I) and silver(I) ions
is most probably a consequence of similar “softness” of these
coordination centers in contrast to the formation a single isomer
in the case of related gold–copper chemistry with essentially
different properties of the coordinating metal ions. Solid state
1
31P{ H} CP-MAS NMR spectrum of the crystalline bulk sample
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Table 1 Absorption, excitation and emission data of 6
(PPh3)2Ag2Cu2(C3H4NS2)4, which has a “butterfly” arrangement
of the metal ions.23
l
abs , nm
l
em, nm lex, nm t, ms
Uem
The 31P and 1H NMR spectra of 6 display intramolecular
dynamics in the temperature range above -30 ◦C, Fig. 5 and S2–
a
Solution (CH2Cl2) 294, 450 746 w
520 vvw
650
452
(8 2)·10-4
1
S4, ESI.† However, the limiting low temperature 31P{ H} spectrum
was obtained at -50◦ C.
Solid state
0.76 0.05
a Lifetime in solution couldn’t be accurately determined due to low
intensity of emission.
Photophysical characteristics of the Ag2Cu2(PPh2C9H7N)4 cluster
(6)
None of the bimetallic complexes 1–5 show appreciable pho-
toemission in the solid state or fluid medium at room temper-
ature, while the tetrametallic cluster 6 is moderately emissive in
the solid state and exhibits a weak luminescence in degassed
dichloromethane solution. The characteristics of absorption,
emission and excitation spectra are given in Table 1 below.
The solid state emission band (Fig. S5, ESI†) is centered at
650 nm to show substantial Stokes shift, single exponential decay
and excited state lifetime in microsecond domain that is indicative
of triplet origin of the emission. The previous works on the
Ag–Cu heterometallic cluster complexes25 showed that the metal
cluster-centered orbitals make a considerable contribution to both
the ground and emissive excited states of these compounds. The
emission in this case is very probably associated with the MLCT
or (d → s) excitations modified by metal–metal contacts, which is
characteristic of the polynuclear d10 complexes with metallophilic
interactions in the coordination core.26
1
Fig. 5 VT 31P{ H} NMR spectra of the complex 6, CDCl3, 300 MHz.
In dichloromethane solution, complex 6 displays weak dual
emission at 746 and 520 nm, the latter being too weak to determine
its parameters. Substantial differences in emission characteristics
of the solid sample and solution is probably determined by
“dissociative” equilibria in fluid media which were detected
by the NMR measurements. Relatively weak metallophilic Ag–
Ag bonding in the Z-shaped Ag2Cu2 cluster may be broken
upon transfer of the tetranuclear aggregate in solution, which
in turn results in changes in the nature of emission responsible
excited state, making it similar to those of non-emissive binuclear
heterometallic complexes 3 and 4.
The structure of 6, revealed in the solid state, belongs to the
C2 symmetry group with the two-fold axis through (perpendicular
to) the center Ag(1)–Ag(2) bond. In this symmetry group, four
phosphine ligands are grouped into two couples: P(1)↔P(3) and
P(2)↔P(4), bound to each other by the symmetry element. In
1
accord with this structural pattern, the 31P{ H} NMR spectrum
displays two slightly different pairs of doublets at 2.6 ppm
(J(107Ag–P) 479 Hz, J(109Ag–P) 551 Hz) and 3.0 ppm (J(107Ag–
P) 441 Hz, J(109Ag–P) 509 Hz), respectively (Fig. 5, top spectrum).
Analysis of the spectroscopic variations observed in the 31P
spectrum upon warming the CDCl3 solution of 6 shows that the
high-field resonance starts to broaden first, which is evidently
related to local dynamics of the organic substituents at this
phosphorus center. This low temperature dynamics eventually
results in the fast symmetry exchange of the phosphine ligands,
causing the signal to split into a broad doublet due to the coupling
to the silver nuclei. The proton VT NMR spectra (Fig. S3, ESI†)
show more complicated behavior to reveal the presence of major
and minor conformations of the organic environment around the
phosphorus centers at -40 ◦C. The proton signals corresponding
to these conformations can be distinguished in the 1H–1H COSY
spectrum of 6, Fig. S4, ESI†, but they are particularly visible in
the high field part of the 1D spectrum where two major singlets
of the methyl groups at 1.71 and 1.89 ppm, associated with the
different phosphorus ligands, are in dynamic equilibrium with
the minor signals of conformationally different indole fragments.
Thus the spectroscopic data obtained are compatible with the
structure shown in Fig. 4 and also point to its fluxionality in
solution.
Conclusions
We have investigated coordination chemistry of the heterobiden-
tate P,N indolyl-phosphine ligand with respect to CuI, AgI
and AuI metal ions. The phosphine demonstrated an ability
to serve as bridging P,N- group upon deprotonation of the
indolyl nitrogen atom under mild conditions. The homometallic
complexes of Ag and Au were found in dimeric head-to-tail forms
M2(PPh2C9H7N)2 (M = Au (2), Ag (5)). The heterobimetallic
compound AuCu(PPh2C9H7N)2 (3) demonstrated a head-to-head
ligand arrangement and preferential binding of P and N donor
atoms to Au and Cu, respectively. Interestingly, its Au–Ag
analogue 4 doesn’t exist in a single molecular form, but appears to
be an inseparable mixture of four different bimetallic complexes,
which present in slow dynamic equilibrium. Coupling of the AgI
and CuI metal ions in the presence of the indolyl-functionalized
phosphine unexpectedly gave a tetranuclear Z-shaped cluster
Ag2Cu2(PPh2C9H7N)4 (6), which exhibits red luminescence in solid
7932 | Dalton Trans., 2011, 40, 7927–7933
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and dual emission in solution with main component in near-IR
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We thank European Union/European Regional Development
Fund (grant 70026/08, I.O.K.), Russian Foundation for Basic Re-
search (grant 11-03-00541-a) and St. Petersburg State University
(grant 12.37.132.2011) for financial support.
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