Synthesis and characterization of novel S,N and Se,N homodimetallic Ag(i)-complexes

Article abstract of DOI:10.1039/c2dt30509g

Novel C2-symmetric doubly bidentate Se,N and S,N-ligands based on a readily available Troeger's base backbone were synthesized and fully characterized. Their coordination properties were studied in dinuclear Ag(i)-complexes employing ¹H, ⁷⁷Se and ¹H-¹⁵N HETCOR NMR spectroscopy as well as X-ray diffraction crystallography. In solution, a single ligand can accommodate two silver atoms by coordination to nitrogen and sulfur or selenium. The investigations in the solid state revealed the presence of a pentacoordinated silver atom (NSO₃ and N₃Se ₂ donor sets are influenced by the solvent employed during the crystallization). In the solid state, the Ag(i)-complex with the S,N-ligand 2b forms dimeric structures bridged by the two perchlorate counterions. The analogous Se,N-ligand 2c coordinates to Ag(i) and forms polymeric enantiomerically pure helices, although the crystal is racemic.

Full text of DOI:10.1039/c2dt30509g

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PAPER
Synthesis and characterization of novel S,N and Se,N homodimetallic
Ag(I)-complexes†
Ján Cvengroš,* Elisabeth Maennel and Nico Santschi*
Received 2nd March 2012, Accepted 23rd April 2012
DOI: 10.1039/c2dt30509g
Novel C2-symmetric doubly bidentate Se,N and S,N-ligands based on a readily available Tröger’s base
backbone were synthesized and fully characterized. Their coordination properties were studied in
dinuclear Ag(I)-complexes employing 1H, 77Se and 1H–15N HETCOR NMR spectroscopy as well as
X-ray diffraction crystallography. In solution, a single ligand can accommodate two silver atoms by
coordination to nitrogen and sulfur or selenium. The investigations in the solid state revealed the presence
of a pentacoordinated silver atom (NSO3 and N3Se2 donor sets are influenced by the solvent employed
during the crystallization). In the solid state, the Ag(I)-complex with the S,N-ligand 2b forms dimeric
structures bridged by the two perchlorate counterions. The analogous Se,N-ligand 2c coordinates to Ag(I)
and forms polymeric enantiomerically pure helices, although the crystal is racemic.
Tröger’s base4 and its derivatives are typically mentioned in
Introduction
the context of chiral molecules containing stable stereogenic
nitrogen atoms.5 Numerous Tröger’s base analogues were suc-
Recent tremendous development in the field of catalysis heavily
relies on the application of various established ligands.1 It is a
common practice that one or several representatives of various
cessfully applied in various fields such as molecular recognition,
bioorganic chemistry or supramolecular chemistry.6 The reports
on their use in catalysis are, however, scarce.7 We have contem-
ligand classes are screened upon designing a novel transform-
ation – be it in an asymmetric or non-stereoselective manner.
Regarding the immense arsenal of powerful sophisticated ligands
accessible to researchers, this strategy usually proves successful
and the new reactions can be performed with high efficiencies
and selectivities. The development of new, potent and cheap
ligands remains, however, a challenging task. The ever-increas-
ing pressure of environmental and economic factors calls for the
delivery of efficient ligands in a minimum number of steps start-
ing from cheap materials. There are several strategies for the
development of efficient ligands. Implementation of new back-
bone motifs and application of new elements as coordination
sites certainly belong to the riskier approaches. Despite the fact
that designing ligands from scratch might be a very laborious
and lengthy task, it may also result in new systems with unprece-
dented reactivity. The application of bidentate ligands containing
chalcogens is undoubtedly much less documented compared to
the P,P; P,N or N,N alternatives.2 Several examples of sulfur- and
selenium-based ligands point out that the coordination properties
of these atoms should not be ignored.3
plated using the Tröger’s base scaffold as a skeletal unit for a
new class of ligands.8 Herein we would like to report on our first
efforts in the synthesis, characterization and coordination proper-
ties of novel S,N and Se,N ligands based on Tröger’s base.
Results and discussion
Synthesis and characterization of the ligands
The synthesis starts with the formation of the 4,10-dibromo-
Tröger’s base 1 by the condensation of 2-bromo-4-methylaniline
with paraformaldehyde in trifluoroacetic acid affording 1 in 98%
yield.9 The subsequent lithium–bromine exchange followed by
quenching with a suitable electrophile led directly to the S,N-
and Se,N-ligands 2a–c (Table 1). The stability of the lithiated
species seems to be rather low resulting in low efficiency of the
nucleophilic substitution on the chalcogen center. The use of
sulfur thus only led to a 19% yield of the S-butylated ligand 2a
whereas butyl bromide originating from the lithium–bromine
exchange acted as an alkylating agent.10 The other by-products
detected in the reaction mixture were the corresponding species
bearing different substituents (BuS and H or BuS and Bu)
arising from the incomplete reaction of the lithiated Tröger’s
base with sulfur. The yield of 2a could only be slightly increased
when butyl iodide was added to the reaction mixture. However,
upon applying more reactive electrophiles such as (PhS)2 and
PhSeCl, the anticipated ligands 2b and 2c were obtained in good
yields.
Department of Chemistry and Applied Biosciences, HCI H230 Swiss
Federal Institute of Technology, ETH Zürich, CH-8093 Zürich,
Switzerland. E-mail: cvengros@inorg.chem.ethz.ch; Fax: +41 44 632
13 10; Tel: +41 44 633 43 31
†Electronic Supplementary Information (ESI) available. CCDC 865870
(S,N-ligand 2a), 865869 (Se,N-ligand 2c), 865871 (Ag-complex 3b)
and 865872 (Ag-complex 3c). For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt30509g
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Table 1 Synthesis of S,N and Se,N-ligands
Entry
Electrophile
Product
R
Yield
1
2
3
4
Sulfur
2a
2a
2b
2c
BuS
BuS
PhS
19%
33%
61%
80%
Sulfur + BuI
PhS–SPh
PhSeCl
PhSe
on the Se,N-ligand 2c and its corresponding silver complex 3c.
The latter was prepared by adding the solution of 2c in d8-THF
to the solution of 2 equivalents of AgClO4 in the same solvent.
1
1
The H, 77Se and H–15N HETCOR spectra recorded at 298 K
indicated the formation of a single species, the disilver complex
3c. The comparison with the corresponding spectra of the free
ligand revealed that the singlet of 77Se shifted upfield from
377 ppm to 267 ppm, hence strongly suggesting the coordination
of the selenium atom to silver (Fig. 2). Unfortunately, we did not
1
observe the J coupling between silver and selenium probably
due to a kinetically labile bond.13 The variable temperature 77Se
NMR studies support this explanation as broadening of the
signal was observed at lower temperatures, however, no coalesc-
ence occurred at temperatures as low as 195 K. Furthermore, the
shift of the cross-peaks on the 15N-axis in 1H–15N HETCOR
from 42.4 ppm to 49 ppm suggests the coordination of silver to
the nitrogen atom. Additionally, significant changes in the
chemical shifts of protons in the vicinity of selenium and nitro-
gen simultaneously corroborate the formation of these coordi-
nation bonds to silver.
Upon concentration, the NMR sample yielded a white solid
which wasn’t soluble in THF anymore. In general, the solubility
of the compound obtained was limited. After significant efforts,
we managed to obtain single crystals suitable for X-ray diffrac-
tion by vapor diffusion of pentane into a 1 : 1 THF–acetonitrile
mixture. The corresponding ORTEP plot is shown in Fig. 3. The
complex crystallizes in enantiomerically pure helices, whereas
the whole crystal is racemic. The polymer consists of repeating
[Ag2(2c)2(ClO4)2] units which ran along the a axis. The dihedral
angle between the aromatic planes is 102.88(14)°.
The oxygen atoms of one of the perchlorate anions (Cl2) are
disordered over two sites with site occupancy factors of 0.87 and
0.13. Each silver atom is pentacoordinated possessing either a
distorted tetragonal pyramidal (Ag1, τ = 0.10) or a distorted tri-
gonal-bipyramidal geometry (Ag2, τ = 0.62).14 Silver(I) typically
prefers a tetrahedral or linear arrangement15 and, although
known, the five coordinate geometry is less common.16 For Ag1
the basal plane is formed by two trans-arranged nitrogen and sel-
enium atoms from two different molecules of ligand 2c. The
apical site is occupied by a nitrogen donor atom of acetonitrile.
The central silver atom lies 0.935 Å out of the N2Se2 plane
towards N5. Ag2 lies in the equatorial plane formed by two sel-
enium atoms from two molecules of 2c and the nitrogen atom of
Fig. 1 ORTEP representation of ligands 2a and 2c. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are drawn at 30% probability.
Selected bond lengths (Å): 2a: S1–C1 1.7652(19), S2–C13 1.7678(18),
N1–C6 1.440(2), N1–C9 1.464(2), N2–C9 1.466(2). 2c: Se1–C2
1.9249(18), Se2–C18 1.9263(19), N1–C17 1.440(2), N2–C1 1.435(2),
N1–C15 1.472(2), N2–C15 1.463(2).
The crystallization of 2a by slow diffusion of hexane into
dichloromethane and of 2c by slow evaporation of its solution in
dichloromethane yielded single crystals suitable for X-ray dif-
fraction. The ORTEP views of the ligand molecules are shown
in Fig. 1. The single crystal analysis did not reveal any abnormal
features and the bond lengths and angles are in the range of
other Tröger’s base-analogues. The most characteristic structural
feature of Tröger’s base, the dihedral angle between the two
aromatic planes, was found to be 96.3(5)° for 2a and 99.1(6)°
for 2c.11,12
Synthesis and characterization of the silver(I) complexes
With the ligands in our hands, we studied their coordination
properties in Ag(I)-complexes. Considering that selenium has an
1
2
NMR-active isotope with spin , it appeared promising to focus
7416 | Dalton Trans., 2012, 41, 7415–7422
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Fig. 2 Comparison of 1H, 77Se and 1H–15N HETCOR spectra of free ligand 2c and its Ag(I)-complex 3c.
acetonitrile. The axial sites are then occupied by nitrogen atoms
N4 and N2 from two molecules of ligand 2c. To the best of our
knowledge, there are no reports on crystal structures of analo-
gous Ag(I) complexes with a N3Se2 donor set. The most similar
structures containing a pentacoordinated Ag(I)-atom describe the
coordination of silver to two nitrogen and two selenium atoms
with a fifth coordination site being occupied by another silver
atom.17 Comparison of the corresponding Ag–Se bond lengths
from the Cambridge Structural Database (5 structures, selenium
bearing phenyl or cyclopentadienyl rings) revealed that all Ag–
Se bonds lie in the range of the reported structures (Fig. 3). The
reported Ag–N distances for silver–tertiary dialkylarylamine
complexes (4 hits in CSD) correspond to the bond lengths
between silver and nitrogen atoms belonging to the ligand 2c,
except for the bond Ag2–N4 (2.735(3) Å) which indicates a
rather labile bond. Finally, the distances between silver and the
nitrogen atom of acetonitrile (2.312(4) Å and 2.237(6) Å) fall in
the middle of the range (from 2.066 Å18 to 3.208 Å19) of 323
reported structures (with a mean value of 2.329 Å) containing
acetonitrile coordinated to a silver atom.
observations made previously for 2c. The exo-benzylic protons
thus shifted from 4.51 ppm to 5.14 ppm, endo-protons from
4.42 ppm to 3.97 ppm and the signal for the methylene bridge
moved from 4.25 ppm to 5.07 ppm upon complexation to silver.
Variations for the carbon signals were also registered, although
to a lesser extent. For example, the methylene carbon shifted
from 67.8 ppm to 68.6 ppm and the benzylic carbons from
55.5 ppm to 57.5 ppm.
To our delight, we were also able to grow a suitable crystal of
3b for X-ray analysis by vapor diffusion of pentane into a
mixture of acetonitrile, tetrahydrofuran and acetone. An ORTEP
plot is shown in Fig. 4. Unfortunately, the necessity of adding
acetone to the crystallization mixture, due to solubility issues,
led also to the incorporation of this solvent into the crystal struc-
ture. The differences in the coordination geometries of the two
Ag(I) complexes 3b and 3c could thus not be easily concluded
as results of the two different donor atoms (Se vs. S). Instead of
polymers, as observed for the complex 3c, dimeric species of
composition [Ag4(2b)2(THF)4(Me2CO)2(ClO4)4] are formed
here. The dihedral angle between the aromatic planes is 109.2(13)°,
a value that approaches the largest dihedral angles reported for
Tröger’s base analogues.12 THF and both of the perchlorate
anions are also coordinating, whereas one of the latter is bridging
two Tröger’s bases and the other is terminally coordinated. Fur-
thermore, the entire terminal perchlorate anion is disordered over
two sites with site occupancy factors of 0.73 and 0.27,
In analogy to the previous complex synthesis, we have carried
out experiments with the sulfur-containing ligand 2b. However,
considering the low sensitivity and usually very broad signals of
1
33S NMR, we have limited our NMR investigations to H and
13C spectra. As expected, chemical shifts were affected upon
coordination and the changes correspond well to the
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Fig. 3 ORTEP representation of complex 3c. Above is the asymmetric unit. Hydrogen atoms and the disordered solvent molecules (THF, CH3CN)
are omitted for clarity. Below is the view of the polymeric structure. Hydrogen atoms, the disordered solvent molecules (THF, CH3CN) and perchlorate
anions are omitted for clarity. Thermal ellipsoids are drawn at 30% probability. Selected bond lengths (Å) and bond angles (°): Ag1–N1 2.514(3),
Ag1–N3 2.649(3), Ag1–N5 2.312(4), Ag1–Se1 2.7539(5), Ag1–Se2 2.6984(6), Ag2–N4 2.735(3), Ag2–N6 2.237(6), Ag2–Se4 2.6165(6), N5–Ag1–
N1 131.75(13), N5–Ag1–N3 86.59(13), N1–Ag1–N3 141.63(11), N5–Ag1–Se2 118.81(11), N1–Ag1–Se2 72.08(8), N3–Ag1–Se2 91.92(7), N5–
Ag1–Se1 100.01(11), N1–Ag1–Se1 98.83(8), N3–Ag1–Se1 68.07(7), Se2–Ag1–Se1 135.45(2), N6–Ag2–Se4 113.44(15), N6–Ag2–N4 91.31(18),
Se4–Ag2–N4 68.63(7), Se3–Ag2–N4 118.64(7), Se3–Ag2–Se4 138.59(2), N6–Ag2–Se3 107.26(15).
respectively. In the case of the bridging perchlorate anion, only
the oxygen atoms are disordered over two sites (0.54 and 0.46).
Finally, also the C56 and C57 of the tetrahydrofuran coordinated
to silver are doubly disordered (0.60 and 0.40).
coordination of an additional perchlorate anion instead of
acetone. The τ value of 0.55 suggests that the geometry around
these silver atoms should have more trigonal-bipyramidal charac-
ter than in the previous case. Ag2(I), however, lies 0.648 Å out
of the plane formed by the equatorial ligands O11, O12 and S2
towards O20. The comparison with 12 similar silver(I) com-
plexes bridged by two perchlorate anions from CSD shows that
the distances between silver and oxygen of the perchlorate
anions (2.543(5) Å and 2.440(10) Å) in 3b belong to the lower
half of the reported values (from 2.353 Å20 to 2.904 Å21 with a
mean value of 2.581 Å). Only one of these 12 structures contains
a five coordinate Ag(I) atom.22 Compared to the situation around
the terminal silver atoms, the Ag2–S2 bond length is slightly
shorter than the Ag1–S1 one (2.5702(13) Å vs. 2.6514(14) Å).
On the other hand, Ag2–N2 is longer than Ag1–N1 (2.597(4) Å
vs. 2.488(4) Å). The direct comparison of the bond lengths
Within one dimer, two distinct silver atoms with different
coordination environments are observed. The terminal ones co-
ordinate to sulfur and nitrogen atoms of the ligand 2b and the
coordination sphere is completed with one molecule of each of
acetone, tetrahydrofuran and perchlorate resulting in a severely
distorted trigonal bipyramidal geometry around silver (τ = 0.40).
Silver lies in the equatorial plane formed by the O1, O13 and S1
atoms. The axial positions are occupied by the N1 and O14
atoms. The axis is slightly bent as the N1–Ag1–O14 angle is
160.38(14)°.
The coordination environment around the central silver atoms
differs only slightly from that of the terminal ones by the
7418 | Dalton Trans., 2012, 41, 7415–7422
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Fig. 4 ORTEP representation of complex 3b. Above is the monomeric structure of 3b containing all solvent molecules coordinated to the silver
atom. Hydrogen atoms, the disordered THF molecules and perchlorate anions are omitted for clarity. Below is the dimeric structure of 3b showing the
bridging via two disordered perchlorate anions. Solvent molecules are partially omitted. Thermal ellipsoids are drawn at 30% probability. Selected
bond lengths (Å) and bond angles (°): Ag1–S1 2.6514(14), Ag1–N1 2.488(4), Ag1–O14 2.495(4), Ag1–O1b 2.361(19), Ag1–O13 2.339(5), Ag2–S2
2.5702(13), Ag2–N2 2.597(4), Ag2–O12 2.543(5), Ag2–O11 2.425(5), Ag2–O20a 2.440(10), O13–Ag1–O1b 114.5(5), O13–Ag1–N1 100.62(17),
O1b–Ag1–N1 103.7(5), O13–Ag1–O14 90.43(17), O1b–Ag1–O14 86.0(5), N1–Ag1–O14 160.38(14), O13–Ag1–S1 136.37(14), O1b–Ag1–S1
109.0(5), N1–Ag1–S1 71.13(9), O14–Ag1–S1 89.67(11), O11–Ag2–O20a 75.4(3), O11–Ag2–O12 103.25(17), O11–Ag2–S2 115.78(12), O20a–
Ag2–S2 127.8(2), O12–Ag2–S2 121.46(12), O11–Ag2–N2 79.79(14), O20a–Ag2–N2 154.6(2), O12–Ag2–N2 77.59(13), S2–Ag2–N2 69.06(8).
+
between silver and the nitrogen of the synthesized ligands in 3c
and 3b shows similar values in the range from 2.488(4) Å to
2.735(3) Å.
2c, Ag(2c)+ (m/z 668.9477, found: 668.9571) and Ag(2c)2 (m/z
1228.9912, found: 1229.0072), hence further substantiating the
polymeric nature found by X-ray diffractometry.
The mass spectrometric investigations corroborated the above
mentioned observations. Uncalibrated matrix-assisted laser de-
sorption/ionization (MALDI) mass spectrometry of material
obtained through concentration of an NMR sample of 2b (1.0
equiv.) and AgClO4 (2.0 equiv.) in d8-THF indicated the pres-
ence of free ligand 2b, Ag(2b)+ (m/z 573.0588, found:
Conclusions
We have designed and readily synthesized a new class of
Tröger’s base inspired Se,N- and S,N-ligands. The complexation
studies revealed that these structures can coordinate silver(I)
atoms in a doubly bidentate fashion. In the solid state, polymeric
one-dimensional structures are formed in the case of 3c, whereas
3b crystallizes as dimeric perchlorate-bridged species. This,
however, is proposed to stem from the method of crystallization
and not from the donor atom (S vs. Se) employed. In both cases,
+
573.0666) and Ag(2b)2 (m/z 1039.2126, found: 1039.2258).
These findings hint towards a dimeric or polymeric structure in
solution and in the absence of additional donors such as aceto-
nitrile or acetone.23 Application of the same method to 3c crys-
tallized from a THF–MeCN solution showed the same species:
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a rather uncommon, five coordinate geometry around the silver
atom is observed. Although the incorporation of acetone into the
crystal structure of 3b hampered the direct comparison with 3c,
it suggests that this type of complex could be applied as Lewis
acids for the activation of carbonyl compounds. Furthermore,
since both sulfenyl and selenenyl groups usually act as good
π-acceptors, their combination with a nitrogen atom (being a
good donor) bodes well for an interesting catalytic performance
of such structures. Applications of these systems in supramolecu-
lar architectures as well as their catalytic activity are currently
being studied in our laboratory.
successive interpretation of the difference Fourier maps, fol-
lowed by full-matrix least-squares refinement (against F2).
Crystal data and details of data collection and structure refine-
ment for 3b and 3c are given in Table 2. CCDC 865870 (S,N-
ligand 2a), CCDC 865869 (Se,N-ligand 2c), CCDC 865871
(Ag-complex 3b) and CCDC 865872 (Ag-complex 3c) contain
the supplementary crystallographic data for this paper and are
also available in the ESI† for this article.
4,10-Bis(butylthio)-2,8-dimethyl-6,12-dihydro-5,11-
methanodibenzo[b,f][1,5]diazocine (2a)
4,10-Dibromo-TB 1 (0.52 g, 1.27 mmol) was placed in a
Schlenk flask under argon and dry THF (15 mL) was added.
Then it was cooled down to −78 °C and n-BuLi (1.6 M in
hexane, 1.7 mL, 2.67 mmol, 2.1 equiv.) was added dropwise to
form a pale-yellow suspension. After 5 min, sulfur (0.11 g,
3.43 mmol, 2.7 equiv.) was added in one portion and the result-
ing yellow thick mixture was stirred overnight at ambient temp-
erature. A clear orange solution had formed. Butyl iodide
(0.39 mL, 3.43 mmol, 2.7 equiv.) was added and stirring was
continued for 4 h at RT. The reaction was quenched with a satu-
rated aqueous solution of NH4Cl (10 mL) and the mixture was
extracted with EtOAc (3 × 10 mL). The combined organic layers
were dried over MgSO4 and concentrated under reduced
pressure. The crude mixture was purified by flash chromato-
graphy (SiO2 (100 g), Hex–EA = 30 : 1) to give a white solid.
Yield: 176 mg (0.41 mmol, 33%). M.p. = 104–107 °C.
C25H34N2S2 requires 70.37% C; 8.03% H; 6.57% N. Found:
Experimental
The reactions were carried out in dried glassware under argon
using Schlenk techniques. All solvents were freshly distilled
under argon from an appropriate drying agent before use. Flash
chromatography was performed with Fluka silica gel 60. NMR
spectra were measured on Bruker Avance 300, 400 and 500 spec-
trometers. The chemical shifts are referenced to TMS (1H and
13C) and Me2Se (77Se) as external standards. High-resolution
mass spectra were measured by the MS-Service of the “Labora-
torium für Organische Chemie der ETH”. Elemental analyses
were carried out by the Laboratory of Microelemental Analysis
(ETH Zürich). X-ray structures were measured on a Bruker
APEX2 CCD area detector diffractometer with Mo-Kα radiation.
Single crystals were coated at room temperature with perfluoro-
alkylether oil and mounted on a 0.1 mm glass capillary. The
structures were solved by direct methods in SHELXTL and
Table 2 Details of crystal data and structure refinement for complexes 3b and 3c
Compound
3b
3c
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions: a (Å)
b (Å)
C
80H96Ag4Cl4N4O22S4
C62H58Ag2N6Se4,2(ClO4),0.38(C4H8O), 0.62(CH3CN)
1670.45
100(2)
0.71073
Monoclinic
P21/c
13.9683(3)
21.6538(4)
2167.13
100(2)
0.71073
Triclinic
P1
10.6111(3)
ˉ
11.8157(3)
18.9074(5)
c (Å)
21.3918(4)
α (°)
β (°)
86.053(2)
89.515(2)
90
94.7900(10)
γ (°)
64.611(2)
2135.95(10)
1
1.685
1.201
1100
90
6447.7(2)
4
1.721
3.016
3524
Volume (Å3)
Z
Density (Mg m−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
Crystal habit
0.20 × 0.19 × 0.10
Prism
0.24 × 0.16 × 0.10
Prism
Θ range for data collection
Limiting indices
1.08 to 27.10°
−13 ≤ h ≤ 13, −15 ≤ k ≤15, −24 ≤ l ≤ 24
23 087
9403 [R(int) = 0.0500]
99.7%
0.8883 and 0.7934
9403/0/538
1.34 to 28.70°
−17 ≤h ≤18, −29≤ k ≤29, −28 ≤ l ≤ 28
77 242
16 635 [R(int) = 0.0436]
99.9%
0.7504 and 0.5326
16 635/24/947
Reflections collected
Independent reflections
Completeness to θ = 27.10
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
1.021
1.017
R1 = 0.0497, wR2 = 0.1080
R1 = 0.0831, wR2 = 0.1261
1.207 and −0.851
R1 = 0.0452, wR2 = 0.0988
R1 = 0.0803, wR2 = 0.1165
2.881 and −2.155
Largest diff. peak and hole (e Å−3
)
7420 | Dalton Trans., 2012, 41, 7415–7422
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1
Ag2(2b)(ClO4)2 (3b)
69.51% C; 8.13% H; 6.11% N. H-NMR (400 MHz, CDCl3): δ
3
[ppm] 1.00 (t, J = 7.3 Hz, 6H, CH3), 1.56 (m, 4H, CH2), 1.77
Ligand 2b (20.7 mg, 44 μmol) and AgClO4 (18.2 mg, 88 μmol,
2 equiv.) were weighed into a NMR tube, then dissolved in d8-
THF (0.8 mL) to yield a colorless solution. It was shaken for
10 min. After recording the NMR-spectra, the solvent was
removed affording a white solid (38 mg, 43 μmol, 97%).
1H-NMR (400 MHz, d8-THF): δ [ppm] = 2.05 (s, 6H, CH3),
(m, 4H, CH2), 2.25 (s, 6H, CH3), 2.97 (m, 4H, CH2), 4.30 (d, 2J
= 17.1 Hz, 2H, ArCHendoN), 4.36 (s, 2H, NCH2N), 4.51 (d, 2J =
17.1 Hz, 2H, ArCHexoN), 6.56 (s, 2H, Ar-H), 6.83 (s, 2H, Ar-
H). 13C-NMR (100 MHz, CDCl3): δ [ppm] 14.1, 21.5, 22.7,
31.1, 31.3, 54.8 (CH2N), 68.1 (NCH2N), 124.0, 124.4, 128.8,
133.5, 134.4, 141.8. HRMS (ESI): calcd m/z for C25H35N2S2:
427.2236 ([MH]+), found: 427.2237 ([MH]+).
2
3.93 (d, J = 17.1 Hz, 2H, ArCHendoN), 5.02 (s, 2H, NCH2N),
2
5.10 (d, J = 17.1 Hz, 2H, ArCHexoN), 6.69 (s, 2H, Ar-H), 6.70
(s, 2H, Ar-H), 7.37–7.46 (m, 6H, Ar-H), 7.60–7.62 (m, 4H, Ar-
H). 13C-NMR (100 MHz, d8-THF): δ [ppm] = 20.8 (CH3), 58.5
(CH2N), 69.6 (NCH2N), 127.8, 129.2, 129.5, 130.4, 130.5,
130.8, 131.9, 134.8, 136.6, 141.3. HRMS (ESI): calcd m/z
for C29H26AgN2S2: 573.0588 ([Ag(2b)]+), found: 573.0666
([Ag(2b)]+).
2,8-Dimethyl-4,10-bis(phenylthio)-6,12-dihydro-5,11-
methanodibenzo[b,f][1,5]diazocine (2b)
4,10-Dibromo-TB 1 (0.50 g, 1.23 mmol) was placed in a
Schlenk flask under argon and dry THF (20 mL) was added. The
solution was then cooled to −78 °C and n-BuLi (1.6 M in
hexane, 1.95 mL, 3.12 mmol, 2.54 equiv.) was added dropwise
to form a pale-yellow suspension. After 5 min, diphenyl
disulfide (0.80 g, 3.66 mmol, 2.98 equiv.) was added under an
argon counterflow and the resulting mixture was allowed to
slowly warm to RT over 20 h. The reaction mixture was poured
onto 50% NH4Cl solution (100 mL). The organic layer was sep-
arated and the aqueous one was extracted once with additional
EtOAc (50 mL). The combined organic layers were dried over
Na2SO4 and finally concentrated under reduced pressure to give
a yellow oil. The product (350 mg, 0.75 mmol, 61%) was preci-
pitated as a white solid upon treatment with hexane (100 mL).
M.p. = 174–176 °C. C29H26N2S2 requires 74.64% C; 5.62% H;
6.00% N. Found: 74.58% C; 5.77% H; 5.98% N. 1H-NMR
Ag2(2c)(ClO4)2 (3c)
Ligand 2c (25 mg, 45 μmol) and silver perchlorate (20.1 mg,
97 μmol, 2 equiv.) were weighed into a NMR-tube and d8-THF
(0.8 mL) was added. It was shaken for 10 min. After recording
the NMR-spectra, the solvent was removed affording a white
1
solid (43 mg, 44 μmol, 98%). H-NMR (400 MHz, d8-THF): δ
[ppm] 2.06 (s, 6H, CH3), 3.76 (d, 2J = 17.0 Hz, 2H,
2
ArCHendoN), 4.97 (s, 2H, NCHN), 5.09 (d, J = 17.0 Hz, 2H,
ArCHexoN), 6.72 (s, 2H, Ar-H), 6.91 (s, 2H, Ar-H), 7.37 (t, 3J =
7.3 Hz, 4H, Ar-H), 7.44 (t, 3J = 7.3 Hz, 2H, Ar-H), 7.72 (d, 3J =
7.1 Hz, 2H, Ar-H). 13C-NMR (100 MHz, d8-THF): δ [ppm] =
20.5 (CH3), 59.0 (CH2N), 69.1 (NCH2N), 128.3, 128.5, 129.0,
129.3, 130.0, 130.6, 131.8, 135.6, 136.6, 142.8. HRMS (ESI):
calcd m/z for C29H26AgN2Se2: 668.9477 ([Ag(2c)]+), found:
668.9571 ([Ag(2c)]+).
2
(400 MHz, CDCl3): δ [ppm] 2.09 (s, 6H, CH3), 4.38 (d, J =
16.9 Hz, 2H, ArCHendoN), 4.39 (s, 2H, NCH2N), 4.58 (d, J =
2
17.4 Hz, 2H, ArCHexoN), 6.56 (s, 2H, Ar-H), 6.61 (s, 2H, Ar-
H), 7.32–7.41 (m, 6H, Ar-H), 7.47–7.49 (m, 4H, Ar-H).
13C-NMR (100 MHz, CDCl3): δ [ppm] 21.1, 55.2 (CH2N), 67.9
(NCH2N), 125.4, 127.7, 128.1, 128.8, 129.6, 132.9, 133.5,
133.7, 134.6, 142.2. HRMS (ESI): calcd m/z for C29H27N2S2:
467.1610 ([MH]+), found: 467.1619 ([MH]+).
Notes and references
1 (a) T. P. Yoon and E. N. Jacobsen, Science, 2003, 299, 1691–1693;
(b) Privileged Chiral Ligands and Catalysts, ed. Q.-L. Zhou, Wiley-
VCH, Weinheim, 2011.
2 (a) Phosphorus Ligands in Asymmetric Catalysis, ed. A. Börner, Wiley-
VCH, Weinheim, 2008, vol. I–III; (b) F. Fache, E. Schulz, M.
L. Tommasino and M. Lemaire, Chem. Rev., 2000, 100, 2159–2232;
(c) C. A. Caputo and N. D. Jones, Dalton Trans., 2007, 4627–4640;
(d) A. A. Mohamed, Coord. Chem. Rev., 2010, 254, 1918–1947.
3 (a) K. Hiroi and T. Sone, Curr. Org. Synth., 2008, 5, 305–320;
(b) K. Hiroi, in Handbook of Organopalladium Chemistry for Organic
Synthesis, ed. E.-i. Negishi, John Wiley & Sons, Inc., 2002, vol. 1, pp.
67–79.
2,8-Dimethyl-4,10-bis(phenylselanyl)-6,12-dihydro-5,11-
methanodibenzo[b,f][1,5]diazocine (2c)
The title compound was synthesized in analogy to 2b. Phenyl-
selenyl chloride (0.70 g, 3.66 mmol, 2.98 equiv.) was used
instead of diphenyl disulfide. The crude product was treated
repeatedly with hexane until the washings were colorless. The
title compound was obtained as an off-white microcrystalline
solid (550 mg, 0.98 mmol, 80%). M.p. = 228–230 °C.
C29H27N2Se2 requires C 62.15%; H 4.68%; N 5.00%. Found: C
4 J. Tröger, J. Prakt. Chem., 1887, 36, 225–245.
5 (a) B. G. Bag, Curr. Sci., 1995, 68, 279–288; (b) M. Demeunynck and
A. Tatibouet, in Progress in Heterocyclic Chemistry, ed. G. W. Gribble
and T. L. Gilchrist, Elsevier Science Ltd., Oxford, 1999, vol. 11, p. 1;
(c) M. Valík, R. M. Strongin and V. Král, Supramol. Chem., 2005, 17,
347–367; (d) B. Dolenský, J. Elguero, V. Král, C. Pardo and M. Valík,
Adv. Heterocycl. Chem., 2007, 93, 1–56; (e) S. Sergeyev, Helv. Chim.
Acta, 2009, 92, 415–444.
6 Additional examples of recent applications not covered by the reviews in
5: (a) S. Sergeyev, D. Didier, V. Boitsov, A. Teshome, I. Asselberghs,
K. Clays, C. M. L. V. Velde, A. Plaquet and B. Champagne, Chem.–Eur.
J., 2010, 16, 8181–8190; (b) Y.-M. Jeon, G. S. Armatas, D. Kim, M.
G. Kanatzidis and C. A. Mirkin, Small, 2009, 5, 46–50; (c) P.
R. Brotherhood, I. J. Luck and M. J. Crossley, Magn. Reson. Chem.,
2009, 47, 257–262; (d) C. Michon, M.-H. Goncalves-Farbos and
J. Lacour, Chirality, 2009, 21, 809–817; (e) E. B. Veale, D.
O. Frimannsson, M. Lawler and T. Gunnlaugsson, Org. Lett., 2009, 11,
1
61.98%; H 4.77%; N 5.00%. H-NMR (400 MHz, CDCl3): δ
2
[ppm] 2.07 (s, 6H, CH3), 4.37 (d, J = 17.7 Hz, 2H, ArCHen-
2
doN), 4.39 (s, 2H, NCH2N), 4.56 (d, J = 17.1 Hz, 2H, ArCHe-
xoN), 6.56 (s, 2H, Ar-H), 6.61 (s, 2H, Ar-H), 7.35–7.43 (m, 6H,
Ar-H), 7.62–7.67 (m, 4H, Ar-H). 13C-NMR (100 MHz, CDCl3):
δ [ppm] 21.1, 55.3 (CH2N), 67.8 (NCH2N), 125.4, 128.4, 128.6,
128.8, 129.7, 130.7, 135.1, 136.3, 142.5 (one aromatic carbon
was not found). HRMS (ESI): calcd m/z for C29H27N2Se2:
563.0504 ([MH]+), found: 563.0498 ([MH]+).
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7415–7422 | 7421

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23 An alternative explanation for the observed MS-spectrum is that the Ag
(2b)+ species are in equilibrium with Ag(2b)2+, free ligand 2b and sol-
vated cations Ag+.
7422 | Dalton Trans., 2012, 41, 7415–7422
This journal is © The Royal Society of Chemistry 2012