Enantiomerically pure C2-symmetric dinuclear silver(I) and copper(I) complexes from a bis(2,2′-bipyridine)-substituted 9,9′-spirobifluorene ligand

Article abstract of DOI:10.1515/znb-2010-0316

We have prepared a new bis(bipyridyl) ligand 1 based on a chiral 9,9′-spirobifluorene core in both enantiomerically pure forms. This ligand was found to undergo diastereoselective self-assembly to optically pure dinuclear coordination compounds upon coordination to copper(I) and silver(I) ions. Surprisingly, however, the resulting diastereomer was not found to be D₂ -symmetric which is usually found for similar bis(bidentate) ligands, but rather C₂ -symmetric with differently configurated metal centers.

Full text of DOI:10.1515/znb-2010-0316

Enantiomerically Pure C2-symmetric Dinuclear Silver(I) and Copper(I)
Complexes from a Bis(2,2ꢀ-bipyridine)-substituted 9,9ꢀ-Spirobifluorene
Ligand
Torsten Piehler and Arne Lu¨tzen
Universita¨t Bonn, Kekule´-Institut fu¨r Organische Chemie und Biochemie, Gerhard-Domagk-Straße 1,
53121 Bonn, Germany
Reprint requests to Prof. Dr. Arne Lu¨tzen. Fax: +49 228 73 9608. E-mail: arne.luetzen@uni-bonn.de
Z. Naturforsch. 2010, 65b, 329 – 336; received December 1, 2009
Dedicated to Professor Rolf Saalfrank on the occasion of his 70th birthday
We have prepared a new bis(bipyridyl) ligand 1 based on a chiral 9,9ꢀ-spirobifluorene core in both
enantiomerically pure forms. This ligand was found to undergo diastereoselective self-assembly to
optically pure dinuclear coordination compounds upon coordination to copper(I) and silver(I) ions.
Surprisingly, however, the resulting diastereomer was not found to be D2-symmetric which is usually
found for similar bis(bidentate) ligands, but rather C2-symmetric with differently configurated metal
centers.
Key words: Self-assembly, Helicates, 2,2ꢀ-Bipyridines, 9,9ꢀ-Spirobifluorene, Diastereoselectivity
Introduction
Nowadays self-assembly is a widely accepted
method to build up sophisticated molecular architec-
tures [1]. Besides the formation of cage-like structures
with cavities of a certain size and a distinct chemical
nature (provided e. g. by functional groups pointing in-
side the cavity) [2, 3], one of the most challenging as-
pects of these efforts is the implementation of chiral in-
formation into the different moieties employed to form
the supramolecular structures. There are quite a num-
ber of beautiful examples where (dia-)stereoselective
self-assembly could indeed be achieved [4]. Helicates
are among the chiral objects that can be used for this
purpose [5]. Such metallosupramolecular aggregates
can be produced in a stereocontrolled manner through
diastereoselective self-assembly from chiral ligands as
demonstrated in many examples in recent years [5 –
10]. However, it is still very difficult to predict the de-
gree of stereoselectivity and the resulting relative con-
figuration of the newly formed stereogenic metal cen-
ters that are programmed in a given ligand structure.
Fig. 1.
we have been able to show that other dissymmetric
building blocks like differently substituted BINOLs
[11], Tro¨ger’s base derivatives [12], or D-isomannit
[13] can also be used in this way. Here, we report
on the synthesis of a new type of enantiomerically
pure bis(bipyridyl) ligand (1, Fig. 1) that bears a 9,9ꢀ-
spirobifluorene, and on its extraordinary self-assembly
to C2-symmetric dinuclear coordination compounds
with differently configurated copper(I) or silver(I) cen-
ters in a completely diastereoselective manner.
Results and Discussion
Synthesis
The synthesis of (R)- and (S)-1 asked for the
preparation of enantiomerically pure 2,2ꢀ-disubstituted
9,9ꢀ-spirobifluorene building blocks and an orthogo-
nally 5-functionalized 2,2ꢀ-bipyridine. The synthesis
of 5-bromo-2,2ꢀ-bipyridine (2) was achieved starting
Some time ago we reported on a BINOL-based
bis(bipyridyl) ligand which undergoes completely di-
astereoselective self-assembly to dinuclear double- and
triple-stranded Dn-symmetric helicates upon coordi-
nation to late transition metal ions [11a]. Since then
c
0932–0776 / 10 / 0300–0329 $ 06.00 ꢀ 2010 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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T. Piehler – A. Lu¨tzen · Diastereoselective Self-assembly of Dinuclear Complexes
from 2-bromopyridine which was transformed into
the corresponding organozinc compound and then re-
acted with 2,5-dibromopyridine using a Negishi cross-
coupling protocol that we were able to develop recently
(Eq. 1) [14].
chiral
resolution
through
clathrate
formation
OH
OH
HO
HO
3
(rac)-
3
(R)- (83%)
+ (S)-3 (96%)
Tf2O, Et3N,
CH2Cl2, –10 °C
1. [Pd(PPh3)2Cl2],
CuI, HCCSiMe3,
DMF, Et3N, 90 °C
2. K2CO3, THF,
MeOH
98%
OTf
(1)
The synthesis of the spirobifluorene building block
started from 2-aminobiphenyl following the estab-
lished procedures of J. M. Tour [15], M. Gomberg [16],
and V. Prelog [17] and led to (rac)-2,2ꢀ-dihydroxy-
9,9ꢀ-spirobifluorene ((rac)-3) in six consecutive steps.
This sequence involved a Sandmeyer-like iodination,
followed by a Grignard reaction with fluorenone to
give the corresponding tertiary alcohol. This was sub-
jected to an acid-mediated condensation reaction to
give the 9,9ꢀ-spirobifluorene. Friedel-Crafts acylation
with acetyl chloride afforded the diketone which was
transformed to a diester using a Baeyer-Villiger oxida-
TfO
(for both steps)
87%
5
(R)-
4
(R)-
Scheme 2. (Tf2O = trifluoromethanesulfonic acid anhydride)
tion. Finally, saponification of the ester function gave
rise to the desired (rac)-3 (Scheme 1).
(rac)-3 was then resolved by clathrate formation
with (R,R)-2,3-dimethoxy-N,N,Nꢀ,Nꢀ-tetracyclohexyl-
succinamide before the enantiomerically pure diols
were transformed into the corresponding optically pure
bistriflates (R)- and (S)-4. These were then reacted
with trimethylsilylacetylene in a Sonogashira cross-
coupling reaction to give the desired diethynylated 9,9-
spirobifluorenes (R)- and (S)-5 after removal of the
silyl protecting group (Scheme 2) [18].
Finally, twofold Sonogashira reaction of 2 and (R)-
and (S)-5 afforded the optically pure bis(bipyridyl) lig-
ands (R)- and (S)-1, respectively (Eq. 2).
(2)
Metal coordination
After the successful synthesis of both enantiomers
of ligand 1 we studied their complexation behavior to-
Scheme 1.
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T. Piehler – A. Lu¨ tzen · Diastereoselective Self-assembly of Dinuclear Complexes
331
wards late transition metal ions. Given the fact that lig-
and 1 has a very rigid V-shaped structure that seems al-
most ideally preorganized for the formation of double-
stranded dinuclear coordination complexes, we chose
copper(I) and silver(I) ions for this purpose because
these diamagnetic ions prefer a tetrahedral coordina-
tion geometry by four N-donor centers of two 2,2ꢀ-
bipyridine ligands and allowed us to investigate the co-
ordination behavior of 1 not only by mass spectrometry
and CD spectroscopy but also by NMR spectroscopy.
In order to prepare the complexes we generated
solutions of the ligands in dichloromethane, and of
[Ag(CH3CN)2](BF4) and [Cu(CH3CN)4](BF4) in ace-
tonitrile. Upon mixing of ligand and salt solutions im-
mediate color changes indicated the successful forma-
tion of bipyridine complexes: pale-yellow for silver(I),
and red-brown for copper(I), typical for these types of
complexes.
For the analysis of the stoichiometric composition
of the complexes we performed ESI MS measure-
ments. These did indeed show the expected peaks
at m/z = 735.2 and 781.1 with matching isotope
patterns for the doubly-charged dinuclear complexes
[Cu2(1)2]2+ and [Ag2(1)2]2+, and also peaks at m/z =
1559.4 and 1648.3 with matching isotope patterns that
could be assigned to the singly charged complexes
+
still carrying one counterion {[Cu2(1)2](BF4)} and
+
{[Ag2(1)2](BF4)} , respectively [19], thus, confirm-
ing the formation of discrete dinuclear complexes
rather than oligo- or polymeric species (Fig. 2).
MS studies can help to elucidate the selectivity
Fig. 3. PM3-TM-minimized structures of the three possi-
of self-assembly processes in terms of stoichiometry
ble diastereomeric dinuclear copper(I) complexes (∆,∆)-
[Cu2{(R)-1}2]2+
,
(Λ,Λ)-[Cu2{(R)-1}2]2+
, and (Λ,∆)-
[Cu2{(R)-1}2]2+ formed upon self-assembly of (R)-1 and
[Cu(CH3CN)4](BF4)2.
but provide no information about the stereoselectiv-
ity of these processes. NMR spectroscopy, however,
can address this problem. A simple 1H-NMR spectrum
can already give information about the selectivity and
also the symmetry of the dinuclear coordination com-
pounds with newly formed stereogenic metal centers
generated from enantiomerically pure C2-symmetric
ligands: in principle three diastereomeric complexes
can form in such cases, one where both metal cen-
ters are (∆)-configurated, one where both are (Λ)-
configurated, and one where one is (∆)- and the other
one (Λ)-configurated, as illustrated in Fig. 3. The first
two would be D2-symmetric. Thus, the two halves of
each of the ligands remain magnetically equivalent.
Fig. 2. Pos. ESI MS of a 1 : 1 mixture of [Ag(CH3CN)2]BF4
and (R)-1 in CH2Cl2/CH3CN 3 : 1.
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T. Piehler – A. Lu¨tzen · Diastereoselective Self-assembly of Dinuclear Complexes
Although the third one represents a “meso”-form with
respect to the coordination geometry at the two metal
centers it is, however, still chiral and even less symmet-
ric (C2-symmetric) due to the fact that we use enan-
tiomerically pure ligands. Thus, in this case the two
halves of the ligands are no longer magnetically equiv-
alent because they are bound to differently configu-
rated metal centers, which makes their relative orien-
tation to the stereogenic center of the spirobifluorene
different from each other.
Fig. 4 shows the spectra that were obtained for
ligand 1 and its silver(I) and copper(I) complexes.
Like with all other chiral ligands that we have inves-
tigated so far [11 – 13], we indeed arrived at a com-
pletely diastereoselective self-assembly of dinuclear
double-stranded coordination compounds as we ob-
served only a single set of signals which all belong
to a single species. However, in view of our previ-
ous results these spectra were really surprising because
they clearly reveal that the two halves of the ligand are
no longer magnetically equivalent in the dinuclear ag-
gregates since now the number of signals is doubled
compared to the free ligand. Thus the presence of the
Fig. 5. CD spectra (5 × 10−5 M solutions in CH2Cl2/
CH3CN) of (R)-1 (grey) and (∆,Λ)-[Ag2{(R)-1}2](BF4)2
(black).
therefore the dinuclear complexes must be the (∆,Λ)-
configurated C2-symmetric aggregate.
This was further corroborated by electron circular
dichroism (ECD) spectroscopy [20]. As shown exem-
plarily in Fig. 5 for the silver complex of (R)-1, the
two D2-symmetric diastereomers can be ruled out, and CD spectra obtained for the complexed ligands are
very similar to the spectra of the free ligands because
the signals arising from the differently configurated
bis(bipyridyl) metal complexes cancel each other out.
The difference in intensity is merely a result of the fact
that all samples were measured at the same concentra-
tion which means that there is the double amount of
the spirobifluorene ligand in the solutions of the com-
plexes.
Conclusion
We have synthesized a new bis(bipyridyl) ligand
1 based on a chiral 9,9ꢀ-spirobifluorene core in both
enantiomerically pure forms in an effective manner
via a 12-step reaction sequence. The self-assembly of
dinuclear metal coordination compounds from 1 and
copper(I) and silver(I) ions was studied by ESI mass
spectrometry, and NMR and ECD spectroscopy. These
experiments have clearly demonstrated that the self-
assembly processes are not only selective in terms of
the formation of discrete dinuclear complexes, but they
were also found to occur in a completely diastere-
Fig. 4. 1H-NMR spectra (500.1 MHz, 298 K, in CD2Cl2/
oselective manner. Surprisingly, however, the result-
CD3CN 3 : 1) of a) (∆,Λ)-[Cu2{(R)-1}2](BF4)2, b) (R)-1,
ing diastereomer was not found to be D2-symmetric
and c) (∆,Λ)-[Ag2{(R)-1}2](BF4)2. Arrows indicate shifts
but rather C2-symmetric with metal centers of differ-
nuclear complexes (dotted arrows 25-H, dashed arrows 1-H, ent configuration. Such a behavior has never been ob-
normal arrow 20-H; for the numbering see Fig. 6).
served before for this type of ligands.
and splitting of some of the ligands’ proton signals in the di-
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T. Piehler – A. Lu¨ tzen · Diastereoselective Self-assembly of Dinuclear Complexes
333
Experimental Section
added via syringe. The mixture was heated to 60 ◦C for 48 h.
After that time TLC monitoring (eluent toluene/THF 20 : 1 +
5 % Et3N) revealed the complete consumption of the start-
ing material. The reaction was quenched by adding 5 mL of
brine, and the mixture was filtered through Celite. The filtrate
was collected and washed with sat. aq. NaHCO3 solution.
After drying the organic phase with Na2SO4 the solvents
were evaporated in vacuo, and the residue was subjected to
column chromatography on silica gel (eluent: toluene/THF
20 : 1 + 5 % Et3N) to give the desired product as a yellow
solid. Yield: 85 mg (71 %). [α]2D7.6 ((R)-1) = +740◦ (c = 0.73;
CHCl3), [α]2D8.8 ((S)-1) = −675◦ (c = 0.74; CHCl3). – CD (λ
(∆ε), CH2Cl2/CH3CN 1 : 1, c = 5 × 10−5 mol/L): (R)-1 =
315 (−5.2), 362 (19.7), (S)-1 = 315 (5.3), 362 (−19.6). –
Rf: 0.20 (toluene/THF 20 : 1 + 5 % Et3N, silica gel). – MS
(EI): m/z (%) = 673.1 (100) [M]+•. – HRMS (EI) m/z =
673.2362 (calcd. 673.2314 for [C49H28N4]+•, [M]+•). – 1H
NMR (CDCl3, 298.0 K, 500.1 MHz): δ = 6.78 (d, J = 7.7 Hz,
2 H, 8-H), 6.97 (d, J = 1.1 Hz, 2 H, 1-H), 7.16 (ddd, J =
7.1 Hz, J = 7.7 Hz, J = 1.1 Hz, 2 H, 7-H), 7.26 – 7.29 (2 H,
24-H), 7.41 (ddd, J = 7.1 Hz, J = 7.7 Hz, J =1.1 Hz, 2 H,
6-H), 7.60 (dd, J = 7.7 Hz, J = 1.1 Hz, 2 H, 3-H), 7.77 – 7.79
(m, 2 H, 23-H), 7.81 (dd, J = 8.2 Hz, J = 1.7 Hz, 2 H, 17-H),
7.86 (d, J = 7.7 Hz, 2 H, 4-H), 7.87 (d, J = 7.7 Hz, 2 H, 5-H),
8.34 (d, J = 8.2 Hz, 2 H, 18-H), 8.37 (d, J = 8.2 Hz, 2 H, 22-
H), 8.65 (d, J = 4.4 Hz, 2 H, 25-H), 8.69 (m, 2 H, 20-H). –
13C NMR (CDCl3, 298.0 K, 125.8 MHz): δ = 65.6 (C-9),
86.8 (C-15), 93.8 (C-14), 120.2 (C-4), 120.3 (C-18), 120.5
(C-5), 121.3 (C-22), 121.8 (C-16), 123.8 (C-24), 124.1 (C-
8), 127.3 (C-1), 128.1 (C-6), 128.6 (C-7), 131.7 (C-3), 136.8
(C-17), 139.2 (C-23), 140.9 (C-12), 142.4 (C-11), 148.4 (C-
10∗), 148.5 (C-13∗), 149.2 (C-25), 151.4 (C-20), 154.7 (C-
19), 155.4 (C-21) (assignment might be interchanged).
All solvents were distilled and thoroughly dried prior to
use according to standard procedures. All syntheses with
air- and moisture-sensitive compounds were performed un-
der Schlenk conditions, with argon as the inert gas. For pu-
rification purposes column chromatography on silica gel was
applied. Solvents for mobile phases were distilled prior to
use. Detection was done under UV light (254 and 366 nm).
1H- and 13C-NMR spectra were recorded at 298 K and at
500.1 and 125.8 MHz, or at 400.1 and 100.6 MHz, respec-
1
tively. H-NMR chemical shifts are reported on the δ scale
(ppm) relative to residual non-deuterated solvent as the in-
ternal standard. 13C-NMR chemical shifts are given in δ
values (ppm) relative to the deuterated solvent as the in-
ternal standard. Signals were assigned on the basis of 1H-,
13C-, HMQC-, and HMBC-NMR experiments. Numbering
of the 1H and 13C nuclei is according to Fig. 6. Melt-
ing points are not corrected. Chemicals and reagents (ex-
cept for the solvents) obtained from commercial sources
were used as received. The following compounds were pre-
pared according to published procedures: 5-bromo-2,2ꢀ-bi-
pyridine (2) [14c], 2-iodobiphenyl [15], 9,9ꢀ-spirobifluor-
ene [16], (rac)-2,2ꢀ-diacetyl-9,9ꢀ-spirobifluorene [17], (rac)-
2,2ꢀ-diacetoxy-9,9ꢀ-spirobifluorene [17], (rac)-2,2ꢀ-dihydr-
oxy-9,9ꢀ-spirobifluorene (rac)-3) [17], (R)-2,2ꢀ-dihydroxy-
9,9ꢀ-spirobifluorene ((R)-3) [18], (S)-2,2ꢀ-dihydroxy-9,9ꢀ-
spirobifluorene ((S)-3) [18], (R)-2,2ꢀ-bis(trifluoromethylsulf-
onyloxy)-9,9ꢀ-spirobifluorene ((R)-4) [18], (S)-2,2ꢀ-bis(tri-
fluoromethylsulfonyloxy)-9,9ꢀ-spirobifluorene ((S)-4) [18],
(R)-2,2ꢀ-diethynyl-9,9ꢀ-spirobifluorene ((R)-5) [18], and (S)-
2,2ꢀ-diethynyl-9,9ꢀ-spirobifluorene ((S)-5) [18].
(R)- and (S)-2,2ꢀ-Bis(5-ethynyl-2,2ꢀ-bipyridyl)-9,9ꢀ-spirobi-
fluorene ((R)- and (S)-1)
(∆,Λ)-[Ag {(R)-1}2](BF ) /(∆,Λ)-[Ag {(S)-1}2](BF )
4 2
2
4 2
2
6.00 mg (8.92 mmol) of (R)-1 was dissolved in 0.6 mL
of CD2Cl2. 2.81 mg (8.92 mmol) of [Ag(CH3CN)2](BF4)
was dissolved in 0.2 mL CD3CN. The two solutions were
combined and mixed. The resulting light-yellow solution was
transferred into an NMR tube. Likewise, solutions for mea-
surement of ESI and CD spectra were generated. For ESI-MS
and CD studies a 5 × 10−5 mol L−1 solution was prepared
(CH2Cl2/CH3CN 1 : 1). The complexes of (S)-1 were pre-
pared and characterized likewise.
A two-neck flask equipped with a condenser was charged
with 64 mg (178 mmol) of (R)-2,2ꢀ-diethinyl-9,9ꢀ-spiro-
bifluorene ((R)-5), 2 mg (0.01 mmol) of CuI, 105 mg
(446 mmol, 2.5 equiv.) of 5-bromo-2,2ꢀ-bipyridine, 6 mg
(6 mol-%) of 1,1ꢀ-bis(diphenylphosphino) ferrocene (dppf),
and 6 mg (3 mol-%) of tris(dibenzylideneacetone)dipallad-
ium(0) chloroform adduct (Pd2(dba)3·CHCl3). The flask vol-
ume was evacuated and flushed with argon twice. 5 mL of
abs. THF and 0.06 mL (2.4 equiv.) diisopropylamine were
CD (λ (∆ε)): (∆,Λ,R) = 315 (−10.7), 351 (20.0),
362 (35.4); (∆,Λ,S) = 315 (10.8), 351 (−19.9), 362
(−35.4). – MS ((+)-ESI, CD2Cl2/CD3CN): m/z = 781.1
([Ag212]2+, [Ag1]+), 1648.3 {[Ag212](BF4)} ). – 1H
+
NMR (CD2Cl2/CD3CN 2 : 1, 298.0 K, 500.1 MHz): δ = 5.87
(s, 1 H, H-1ꢀ), 5.98 (d, J = 7.2 Hz, 1 H, 8ꢀ-H), 6.11 (s, 1 H,
1-H), 6.24 (d, J = 7,7 Hz, 1 H, 8-H), 6.37 (dd, J = 7.2 Hz,
J = 7.2 Hz, 1 H, 7ꢀ-H), 6.66 (d, J = 8.2 Hz, 1 H, 3ꢀ-H), 6.72
(dd, J = 7.3 Hz, J = 7.7 Hz, 1 H, 6ꢀ-H), 6.81 (m, 1 H, 24-H),
Fig. 6. Labeling of the carbon nuclei in ligand 1 (the mag-
netically non-equivalent nuclei in the complexes are labeled
C-1, C-1ꢀ etc.).
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T. Piehler – A. Lu¨tzen · Diastereoselective Self-assembly of Dinuclear Complexes
6.88 (m, 1 H, 7-H), 6.90 (s, 1 H, 20-H), 7.03 (d, J = 7,7 Hz, 298.0 K, 500.1 MHz): δ = 5.85 (s, 1 H, 1ꢀ-H), 5.98 (s, 1 H,
1 H, 3-H), 7.22 (m, 1 H, 6-H), 7.23 (d, J = 7.7 Hz, 1 H, 4-H), 1-H), 6.06 (d, J = 7.7 Hz, 1 H, 8ꢀ-H), 6.30 (d, J = 7.5 Hz,
7.29 (d, J = 7.7 Hz, 1 H, 17ꢀ-H), 7.37 (d, J = 8.2 Hz, 1 H, 1 H, 8-H), 6.40 (dd, J = 7.0 Hz, J = 7.7 Hz, 2 H, 7ꢀ-H), 6.62
4ꢀ-H), 7.50 (d, J = 7.7 Hz, 1 H, 5ꢀ-H), 7.59 (m, 1 H, 24ꢀ-H), (s, 1 H, 20-H), 6.65 (m, 1 H, 24-H), 6.70 (d, J = 7.9 Hz, 1 H,
7.62 (d, J = 7.7 Hz, 1 H, 5-H), 7.82 (s, 1 H, 25-H), 7.98 (d, 3ꢀ-H), 6.71 (m, 1 H, 6ꢀ-H), 6.91 (m, 1 H, 7-H), 6.93 (d, J =
J = 8.2 Hz, 1 H, 17-H), 8.06 (d, J = 7.7 Hz, 1 H, 18ꢀ-H), 8.13 8.2 Hz, 1 H, 3-H), 7.22 (dd, J = 7.7 Hz, J = 7.7 Hz, 2 H,
(m, 1 H, 23-H), 8.13 (s, 1 H, 20ꢀ-H), 8.17 (m, 1 H, 23ꢀ-H), 6-H), 7.33 (d, J = 8.2 Hz, 1 H, 4-H), 7.56 (dd, J = 8.4 Hz,
8.32 (d, J = 7.7 Hz, 1 H, 22ꢀ-H), 8.41 (d, J = 8.2 Hz, 1 H, J = 1.7 Hz, 17ꢀ-H), 7.42 (d, J = 8.2 Hz, 1 H, 4ꢀ-H), 7.51 (d,
18-H), 8.47 (d, J = 8.2 Hz, 1 H, 22-H), 8.72 (d, J = 4.4 Hz, 1 J = 8.0 Hz, 1 H, 5ꢀ-H), 7.53 (m, 1 H, 24ꢀ-H), 7.67 (d, J =
H. 25ꢀ-H).
7.7 Hz, 1 H, 5-H), 7.74 (d, J = 4.8 Hz, 1 H, 25-H), 7.86 (dd,
J = 8.6 Hz, J = 1.7 Hz, 1 H, 17-H), 7.93 (s, 1 H, 20ꢀ-H), 8.04
(m, 1 H, 23-H), 8.08 (m, 1 H, 23ꢀ-H), 8.10 (d, J = 8.4 Hz,
(∆,Λ)-[Cu {(R)-1}2](BF ) /(∆,Λ)-[Cu {(S)-1}2](BF )
4 2
2
4 2
2
3
1 H, 18ꢀ-H), 8.31 (d, J = 8.4 Hz, 1 H, 22ꢀ-H), 8.42 (d, J =
6.00 mg (8.92 mmol) of (R)-1 was dissolved in 0.6 mL
of CD2Cl2. 2.81 mg (8.92 mmol) of [Cu(CH3CN)4](BF4)
was dissolved in 0.2 mL CD3CN. The two solutions were
combined and mixed. The resulting light-yellow solution was
transferred into an NMR tube. Likewise, solutions for mea-
surement of ESI and CD spectra were generated. For ESI-MS
and CD studies a 5 × 10−5 mol L−1 solution was prepared
(CH2Cl2/CH3CN 1 : 1). The complexes of (S)-1 were pre-
pared and characterized likewise.
8.6 Hz, 1 H, 18-H), 8.46 (m, J = 8.3 Hz, 2 H, 22-H), 8.48 (d,
J = 5.0 Hz, 1 H, 25ꢀ-H). – 13C NMR (CD2Cl2/CD3CN 2 : 1,
298.0 K, 125.8 MHz): δ = 64.5, 84.8, 85.0, 95.3, 95.9, 119.0
(2 C), 119.1, 120.1 (2C), 120.3, 120.5, 121.1, 121.6, 121.9,
122.4, 122.8, 123.5 (3 C), 125.4 (2 C), 125.7, 126.7, 127.6,
128.1, 128.4, 131.1, 131.3, 138.2, 138.4, 139.1, 140,4, 140.6,
141.5, 142.6, 146.4, 147.5, 147.6 (2 C), 147.7, 147.8, 148.3,
148.4, 148.9, 149.3, 149.8, 151.1, 151.3.
CD (λ (∆ε)): (∆Λ,R) = 297 (−5.2), 364 (11.7);
(∆,Λ,S) = 297 (5.2), 364 (−11.6). – MS ((+)-ESI, pos.,
CD2Cl2/CD3CN): m/z = 735.2 ([Cu212]2+, [Cu1]+), 1559.4
Acknowledgement
We are grateful to the Deutsche Forschungsgemeinschaft
(SFB 624) for financial support.
+
({[Cu212](BF4)} ). – 1H NMR (CD2Cl2/CD3CN 2 : 1,
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