Self-assembly of metallosupramolecular rhombi from chiral concave 9,9'-spirobifluorene-derived bis(pyridine) ligands

Article abstract of DOI:10.3762/bjoc.10.40

Two new 9,9'-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands act as concave templates and form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+ ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp)2M2{(R)-L}2](OTf)4, [(dppp)2M2{(S)-L}2](OTf)4, and [(dppp)2M2{(R)-L}{(S)- L}](OTf)4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies could also be characterised by single crystal X-ray diffraction.

Full text of DOI:10.3762/bjoc.10.40

Self-assembly of metallosupramolecular rhombi from
chiral concave 9,9’-spirobifluorene-derived
bis(pyridine) ligands
Rainer Hovorka1, Sophie Hytteballe1, Torsten Piehler1,
Georg Meyer-Eppler1, Filip Topić2, Kari Rissanen2, Marianne Engeser1
and Arne Lützen*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 432–441.
1University of Bonn, Kekulé-Institute of Organic Chemistry and
Biochemistry, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany and
2Department of Chemistry, Nanoscience Center, University of
Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
doi:10.3762/bjoc.10.40
Received: 15 November 2013
Accepted: 24 January 2014
Published: 18 February 2014
Email:
Arne Lützen* - arne.luetzen@uni-bonn.de
This article is part of the Thematic Series "Chemical templates".
Guest Editor: S. Höger
* Corresponding author
Keywords:
© 2014 Hovorka et al; licensee Beilstein-Institut.
License and terms: see end of document.
concave templates; metal complexes; self-assembly; self-sorting;
9,9’-spirobifluorene; supramolecular chemistry
Abstract
Two new 9,9’-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands
act as concave templates and form metallosupramolecular [(dppp)2M2L2] rhombi with cis-protected [(dppp)Pd]2+ and [(dppp)Pt]2+
ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture
of all three possible stereoisomers [(dppp)2M2{(R)-L}2](OTf)4, [(dppp)2M2{(S)-L}2](OTf)4, and [(dppp)2M2{(R)-L}{(S)-
L}](OTf)4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a
factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies
could also be characterised by single crystal X-ray diffraction.
Introduction
Concave templates are versatile tools to achieve self-sorting sorting processes where enantiomers are involved whose shape
behaviour in the self-assembly of defined aggregates from and size does not vary but only their relative spatial orientation.
multicomponent mixtures in a social self-discrimination or a Hence, chiral self-sorting is a truly challenging task and high-
narcissistic self-recognition manner [1-3]. Usually, geometrical fidelity chiral self-sorting processes have been observed in a
size and shape complementarity are employed to ensure such rather limited number of examples for the formation of stereo-
self-sorting. However, these factors do not account in self- chemically defined metallosupramolecular aggregates from
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racemic ligands in a self-recognising [4-18] or a self-discrimi- optically pure ditriflates (R)-2 and (S)-2. (R)-2 was then
nating manner [19-27].
subjected to a two-fold Suzuki reaction to obtain the enan-
tiomerically pure bis(pyridine) ligand (R)-3. (Please note, that
As part of our ongoing programme to develop general guide- the conditions used to elaborate the enantiomerically pure 9,9’-
lines for the diastereoselective self-assembly of metallo- spirobifluorene derivatives were demonstrated not to affect the
supramolecular aggregates, we have recently started a system- optical purity of these compounds in our previous work (see
atic study on the influence of rigid concave building blocks on [35]).)
the outcome of the self-assembly of bis(pyridine) ligands into
dinuclear metallosupramolecular rhombi upon coordination to (S)-1, however, was reacted in a nickel-catalysed Kumada
cis-protected [(dppp)Pd(OTf)2] or [(dppp)Pt(OTf)2] (dppp = cross-coupling reaction to furnish 2,2’-dimethylated spirobi-
1,3-bis(diphenylphosphino)propane) complexes [27,28]. So far fluorene (S)-4 which was then brominated twice to afford tetra-
we have studied templates based on the Tröger’s base [27] and functionalised spirobifluorene (S)-5. Finally, (S)-5 could be
the 2,2’-dihydroxybinaphthyl (BINOL) [28] scaffold and identi- transformed into the second bis(pyridine) ligand (S)-6 in a two-
fied the bend angle of these V-shaped compounds to be a crit- fold Suzuki reaction.
ical factor for the degree of self-sorting that can be achieved
[9,15-18,25-28].
Metal coordination
After the successful synthesis we mixed solutions of ligands 3
The 9,9’-spirobifluorene scaffold is another very interesting and 6 and [(dppp)Pd(OTf)2] or [(dppp)Pt(OTf)2] and charac-
concave structure that offers the possibility to orient functional terised the resulting complexes by 1H, 31P, 1H 2D-DOSY
groups in a defined manner [29]. Hence, we were wondering NMR, ESI-MS, and single crystal X-ray diffraction to investi-
how V-shaped bis(pyridine) ligands based on this chiral gate if the desired rhomboid complexes are formed and whether
skeleton would behave upon coordination to [(dppp)Pd(OTf)2] we can observe any degree of self-sorting in the self-assembly
or [(dppp)Pt(OTf)2] in order to learn more about the underlying processes of the racemic samples.
principles of chiral self-sorting in metallosupramolecular chem-
istry.
The ESI-MS spectra recorded from the complex solutions
showed the successful formation of the expected dinuclear
[(dppp)2M2(L)2] aggregates with different numbers of counter
ions both from the enantiomerically pure (R)-3 and the racemic
Results and Discussion
Synthesis
The synthesis of the spirobifluorene-based templates is shown ligand (rac)-3 and the enantiomerically pure template (S)-6, and
in Scheme 1. It started from 2-aminobiphenyl following the hence, proved the selectivity of the self-assembly processes in
established procedures of J. M. Tour [30], M. Gomberg [31], terms of aggregate stoichiometry (Figure 1 and Supporting
and V. Prelog [32,33] leading to (rac)-2,2’-dihydroxy-9,9’- Information File 1). (Please note, that we investigated our
spirobifluorene ((rac)-1) in six consecutive steps. This sequence complexes in a number of different solvents (acetone, acetoni-
involved a Sandmeyer-like iodination, followed by a Grignard trile, mixtures of dichloromethane and acetonitrile) and in all
reaction with fluorenone to furnish the corresponding tertiary cases we observed the expected dinuclear [(dppp)2M2(L)2]-
alcohol. This alcohol was subjected to an acid-mediated con- complexes as the dominating species.)
densation to give the 9,9’-spirobifluorene. Friedel–Crafts acyla-
tion with acetyl chloride gave rise to the racemic 2,2’-diketone Next we measured 1H NMR spectra of the aggregates and the
which was transformed to the racemic diester in a free ligands. All complexes of the enantiomerically pure ligands
Baeyer–Villiger oxidation. Saponification of the ester functions gave rise to NMR spectra with sharp but significantly shifted
then afforded (rac)-1. One part of the racemic material was signals compared to the ones of the free ligands, which supports
transformed into the corresponding racemic ditriflate (rac)-2 the formation of discrete metallosupramolecular species
which was reacted with a 4-pyridylboronic acid ester in a (Figure 2b,c). This could be further confirmed by 2D 1H DOSY
Suzuki cross-coupling to afford the desired racemic bis(pyri- NMR spectra (see Supporting Information File 1) of the aggre-
dine) ligand (rac)-3. (Please note that (rac)-3 has been prepared gates as well as of the free ligands. In all cases the relative size
before, however, on a different way [34].)
of the aggregates was a little more than twice as large as that of
the respective concave template. (Please note, that we could
The other part of the racemic diol (rac)-1 was resolved via only determine relative sizes or ratios of sizes from the DOSY
clathrate formation with (R,R)-2,3-dimethoxy-N,N,N',N'-tetra- experiments because the spectra were recorded in a 3:1 mixture
cyclohexylsuccindiamide to obtain enantiomerically pure (R)-1 of dichloromethane and acetonitrile of unknown viscosity
and (S)-1 [35,36] which were subsequently converted into the which does not allowed us to calculate hydrodynamic radii.)
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Beilstein J. Org. Chem. 2014, 10, 432–441.
Scheme 1: Synthesis of ligands 3 and 6.
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Figure 1: ESI mass spectrum (positive mode) of an 1:1 mixture of (R)-3 and [(dppp)Pd(OTf)2] in acetone.
Figure 2: 1H NMR spectra (500.1 MHz, in CD2Cl2/CD3CN 3:1 at 298 K) of a) a 1:1 mixture of [Pd(dppp)]OTf2 and (rac)-3, b) a 1:1 mixture of
[Pd(dppp)]OTf2 and (R)-3, and c) (R)-3.
Therefore, these NMR-spectroscopic results nicely comple- Comparison of the 1H NMR spectra of the homochiral
ment the results from mass spectrometry with regard to the complexes of (R)-3 with the spectra of the complexes obtained
assemblies’ composition.
from the racemic ligand (rac)-3 then allowed us to obtain infor-
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Beilstein J. Org. Chem. 2014, 10, 432–441.
mation about the stereoselectivity of the self-assembly complexes for both palladium (Figure 2a,b) and platinum ions
processes (Figure 2a,b). In principle, three stereoisomers of since the intensity of the signals of the homochiral assemblies is
the dinuclear metallosupramolecular rhombi can form from larger than expected from statistics. However, both diastereo-
racemic ligands upon coordination to [(dppp)Pd(OTf)2] or mers were found to give very similar NMR spectra resulting in
[(dppp)Pt(OTf)2] – a racemic mixture of two enantiomeric strong signal overlap. Hence, we wanted to obtain further proof
homochiral assemblies and an achiral heterochiral complex. by recording 31P NMR spectra in which signal overlap should
These are expected to form in a 1:1:2 ratio if the assembly be considerably less problematic due to the much broader spec-
would occur in a completely non-selective purely statistical tral width.
manner. Any deviation from this ratio would either mean an
amplification of the racemic homochiral assemblies in the sense As shown in Figure 3 the 31P NMR spectra indeed confirm the
of self-recognition or an amplification of the heterochiral conclusions drawn from the 1H NMR spectra. Two individual
assembly in the sense of self-discrimination.
peaks for the two diastereomers can be detected when (rac)-3 is
employed for complexation and the intensities of the signals of
Analysis of the 1H NMR spectra provides versatile information: the racemic homochiral diastereomer are approximately three
first, the self-assembly is not completely diastereoselective, times as large as those of the signals of the heterochiral one in
since a number of additional signals are visible in the spectrum both cases – the palladium and the platinum complexes and
of the aggregates obtained from (rac)-3. Second, the self- independent of the solvents we used. This corresponds to an
assembly does not happen in a completely statistical fashion but amplification of the homochiral stereoisomers via self-recogni-
rather proceeds with a preference for forming homochiral tion by a factor of approximately three.
Figure 3: 31P NMR spectra of a) a 1:1 mixture of [Pd(dppp)]OTf2 and (R)-3, b) a 1:1 mixture of [Pd(dppp)]OTf2 and (rac)-3 (both recorded at
162.0 MHz in CD2Cl2/CD3CN 3:1 at 293 K), and c) of a 1:1 mixture of [Pt(dppp)]OTf2 and (rac)-3 (202.5 MHz, in CD2Cl2 at 298 K).
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Beilstein J. Org. Chem. 2014, 10, 432–441.
Although these NMR spectra already provide a very good proof relative quantification of different components compared to the
for the stereoselectivity of the self-assembly process we wanted ratios obtained by other techniques, e.g. NMR spectroscopy, as
to get additional independent evidence by another analytical we have recently reported [28].
method. Standard mass spectrometry, however, cannot distin-
guish between different stereoisomers. In order to employ this Finally, we were able to grow single crystals of the dinuclear
technique for this purpose, we therefore used a 1:1 mixture of palladium complexes derived from the racemic ligands from a
ligands (R)-3 and (S)-6 as a pseudo-racemate in which the two 3:1 mixture of dichloromethane and acetonitrile using ethyl
methyl groups of 6 in the outer periphery of the ligand structure acetate as anti-solvent and characterise them by X-ray diffrac-
serve as a kind of mass label. These labels then allowed us to tion. Interestingly, we only obtained single crystals of the
identify the three possible different complexes due to their racemic mixture of homochiral complexes although the solu-
different number of methyl groups, and hence, different m/z tion obviously contains both diastereomers. Figure 5 shows
values. Equimolar amounts of the enantiomerically pure ligands both of the homochiral complexes {[(dppp)2Pd2{(R)-3}2](OTf)4
(R)-3 and (S)-6 and two equivalents of the respective metal and {[(dppp)2Pd2{(S)-3}2](OTf)4 as they were found in the
corner were mixed. The ESI mass spectrum of the diluted solu- crystal structure. Again, this indicates the preferred formation of
tion (Figure 4) nicely corroborates the results obtained by the the homochiral complexes in the sense of a self-recognition
NMR experiments as it shows the presence of ions derived because in most of the cases where both the achiral heterochiral
from all three complexes [(dppp)2M2{(R)-3}2](OTf)4, and the chiral homochiral assemblies are present in solution the
[(dppp)2M2{(R)-3}{(S)-6}](OTf)4, and [(dppp)2M2{(S)- heterochiral aggregates tend to crystallise more readily. (The
6}2](OTf)4. Furthermore the peak ratios of the signals of these reason for the usually preferred crystallization of the achiral
ions differ from the statistically expected 1:2:1 ratio. Although assembly (compared to the corresponding diastereomeric
these peak ratios suggest a slightly lower amplification of the homochiral assembly) is not yet completely clear. It might be
homochiral assemblies by a factor of only two to three, this still due to the fact that nature often tries to achieve the highest
reinforces our analysis – especially, if one takes into account possible symmetry in crystalline matter. There is also some evi-
that mass labelling in the periphery might cause differences in dence that in most cases the achiral assemblies can pack more
the ESI response factors that can cause slight deviations in the efficiently in the solid state than the chiral ones.) Hence, selec-
Figure 4: ESI mass spectrum (positive mode) of an 1:1:2 mixture of (R)-3, (S)-6, and [(dppp)Pt(OTf)2] in acetonitrile.
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Figure 5: Single crystal X-ray structure analysis of [(dppp)2Pd2{(R)-3}2][(dppp)2Pd2{(S)-3}2](OTf)8 obtained from a 1:1 mixture of (rac)-3 and
[(dppp)Pd(OTf)2]. (Counterions and solvent molecules within the crystal packing, and hydrogen atoms are omitted, colour code: petrol – palladium,
grey – carbon, blue – nitrogen, orange – phosphorous).
tive crystallisation of the homochiral aggregate can be inter- 6 provides further evidence that angles at the lower end of this
preted as another hint for its thermodynamic more favourable range do lead to a preferred self-recognition.
formation. It is important to note, however, that dissolving the
crystals again very quickly led to a mixture of homo- and Experimental
heterochiral assemblies in the same ratio as observed before. Reactions under inert gas atmosphere were performed under
argon using standard Schlenk techniques and oven-dried glass-
Conclusion
ware prior to use. Thin-layer chromatography was performed on
In summary, we were able to synthesise dissymmetric bis(4- aluminum TLC plates silica gel 60F254 from Merck. Detection
pyridyl) ligands (R)- and (rac)-3 based on the 9,9'-spirobi- was carried out under UV light (254 and 366 nm). Products
fluorene scaffold in racemic and optically pure form and a were purified by column chromatography on silica gel 60
closely related mass-labelled dimethylated derivative (S)-6. (70–230 mesh) from Merck. The 1H and 13C NMR spectra were
These ligands self-assemble into dinuclear metallosupramolec- recorded on a Bruker Avance 500 spectrometer at 298 K, at
ular [(dppp)2M2(L)2](OTf)4 rhombi upon coordination to 500.1 and 125.8 MHz, or a Bruker AM 400 at 293 K, at
[(dppp)Pt(OTf)2] or [(dppp)Pd(OTf)2], respectively. Interest- 400.1 MHz and 100.6 MHz, respectively. 31P NMR spectra
ingly, these self-assembly processes proceed with significant were recorded at 293 K at 162.0 MHz or at 298 K at
diastereoselective self-sorting via preferred narcissistic self- 202.0 MHz. The 1H NMR chemical shifts are reported on the δ
recognition amplifying the formation of the homochiral assem- scale (ppm) relative to residual non-deuterated solvent as the
blies by a factor of approximately three. Together with the internal standard. The 13C NMR chemical shifts are reported on
results obtained for further bis(pyridine) ligands derived from the δ scale (ppm) relative to deuterated solvent as the internal
other rigid scaffolds such as Tröger's bases or 2,2'-dihydroxy- standard. 31P NMR chemical shifts are reported on the δ scale
1,1'-binaphthyls this suggests that the bend angle of the (ppm) relative to 85% H3PO4 as the external standard. Signals
V-shaped ligands seems to be a crucial general factor that has to were assigned on the basis of 1H, 13C, HMQC, and HMBC
be adjusted carefully to obtain (high-fidelity) self-sorting. NMR experiments (for the numbering of the individual nuclei
Angles of more than 105° cause an unfavourable preorganisa- see Supporting Information). Mass spectra were recorded at a
tion of the ligands’ structure thus leading to non-selective self- microOTOF-Q or an Apex IV FT-ICR from Bruker. Most
assembly processes whereas smaller angles of about 90–105° solvents were dried, distilled, and stored under argon according
lead to chiral self-sorting. The current study of the ligands 3 and to standard procedures. 4-Pyridylboronic acid pinacol ester and
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Beilstein J. Org. Chem. 2014, 10, 432–441.
2-aminobiphenyl were used as received from commercial tion of Na2CO3 and the aqueous phase was repeatedly extracted
sources. 2-Iodobiphenyl [30], 9,9'-spirobifluorene [31], (rac)- with dichloromethane. The collected organic phases were
2,2'-diacetyl-9,9'-spirobifluorene [32], (rac)-2,2'-diacetoxy-9,9'- washed with a diluted hydrochloric acid (5%) and the resulting
spirobifluorene [33], (rac)-, (S)-, and (R)-2,2'-dihydroxy-9,9'- aqueous phase was extracted thoroughly with CH2Cl2. The
spirobifluorene {(rac)-, (S)-, and (R)-1} [33,36], (rac)-, (S)-, aqueous phase was brought to pH 14 with 2 N NaOH and
and (R)-2,2'-bis(trifluoromethylsulfonyloxy)-9,9'-spirobi- extracted thoroughly with CH2Cl2. The collected organic
fluorene {(rac)-, (S)-, and (R)-2} [36], (S)-2,2'-dimethyl-9,9'- phases were washed with water and brine and subsequently
spirobifluorene {(S)-4} [36], (S)-2,2'-dibromo-7,7'-dimethyl- dried with MgSO4. The solvents were removed in vacuo. The
9,9'-spirobifluorene {(S)-5} [36], and (dppp)M(OTf)2 (M = crude product was purified by column chromatography on silica
PdII, PtII) [37,38] were prepared according to literature known gel using petrol ether/ethyl acetate/triethylamine (5:1:1) as
procedures.
eluent resulting in a yellow solid (207 mg, 69%). 1H NMR
(500.1 MHz, CDCl3) δ 8.50 (d, J15,16 = 5.6 Hz, 4H, H-16), 7.91
(R)-2,2’-Bis(4-pyridyl)-9,9’-spirobifluorene ((R)-3): (R)-2 (d, J3,4 = 7.9 Hz, 2H, H-4), 7.78 (d, J6,5 = 7.8 Hz, 2H, H-6),
(339 mg, 0.55 mmol), K3PO4 (476 mg, 2.24 mmol), 4-pyridyl- 7.67 (dd, J3,4 = 7.9 Hz, J1,3 = 1.6 Hz, 2H, H-3), 7.33 (m, 4H,
boronic acid pinacol ester (551 mg, 2.69 mmol), [Pd(dppf)Cl2] H-15), 7.22 (d, J5,6 = 7.8 Hz, 2H, H-6), 6.99–6.98 (d, J1,3 = 1.6
(25 mg, 0.031 mmol), and dppf (22 mg, 0.040 mmol) were Hz, 2H, H-1), 6.56 (s, 2H, H-8), 2.23 (s, 6H, H-17) ppm; 13C
added to a round-bottomed flask. Dry THF (10 mL) was added NMR (125.8 MHz, CDCl3) δ 149.7 (C-16)*, 149.5 (C-10)*,
and the mixture was heated to 65 °C and stirred overnight 149.2 (C-13), 147.9 (C-14), 143.0 (C-11), 138.6 (C-7), 138.2
resulting in a brown solution. After that the reaction mixture (C-12), 137.1 (C-2), 129.0 (C-6), 126.9 (C-3), 124.7 (C-8),
was cooled to rt and quenched with a sat. solution of NaHCO3. 122.4 (C-1), 121.3 (C-15), 120.3 (C-5)*, 120.2 (C-4)*, 65.7
The aqueous phase was extracted three times with dichloro- (C-9), 24.8 (C-17) ppm (* signal assignment might be inter-
methane and the collected organic phase was washed with water changed); HRMS-ESI (m/z): [M + H]+ calcd for [C37H27N2]+,
and brine and dried with MgSO4. The solvent was removed in 499.2169; found, 499.2160. [α]D24 −128.1° (c 0.39, CHCl3).
vacuo. The crude product was purified by column chromato-
graphy on silica gel using MeOH/ethyl acetate (1:1) as eluent. Preparation and characterisation of the metal complexes:
The solvents were evaporated and the residue extracted with di- Approximately 10 µmol of a ligand and an equimolar amount of
chloromethane to get rid of previously dissolved silica gel. [(dppp)Pt(OTf)2] or [(dppp)Pd(OTf)2], respectively, were
After evaporation of the dichloromethane the product was dissolved in 0.6 mL of CD2Cl2 and 0.2 mL of CD3CN. The
obtained as a brown oil (262 mg, 100%). 1H NMR (500.1 MHz, resulting solution was characterised by NMR. For the ESI-MS
CDCl3) δ 8.50 (d, J15,16 = 5.4 Hz, 4H, H-16), 7.97 (d, J3,4 = 7.9 studies ca. 10 µmol of a ligand and an equimolar amount of
Hz, 2H, H-4), 7.91 (d, J5,6 = 7.5 Hz, 2H, H-5), 7.68 (dd, J3,4 = [(dppp)Pt(OTf)2] or [(dppp)Pd(OTf)2], respectively, were
7.9 Hz, J1,3 = 1.0 Hz, 2H, H-3), 7.41 (dd, J5,6 = 7.5 Hz, J6,7 = dissolved in 1 mL of solvent (acetone, acetonitrile, mixtures of
7.3 Hz, 2H, H-6), 7.33 (d, J15,16 = 5.4 Hz, 4H, H-15), 7.15 (dd, dichloromethane and acetonitrile). An aliquot of this solution
J6,7 = 7.3 Hz, J7,8 = 7.5 Hz, 2H, H-7), 7.00 (s, 2H, H-1), 6.77 was then diluted with the same solvent to give 1 mL of a
(d, J7,8 = 7.5 Hz, 2H, H-8) ppm; 13C NMR (125.8 MHz, 300 µmolar solution of the complex.
CDCl3) δ 150.0 (C-16), 149.4 (C-10), 148.9 (C-13), 148.0
(C-14), 142.9 (C-11), 140.9 (C-12), 137.8 (C-2), 128.6 (C-7), [(dppp)2Pd2{(R)-3}2](OTf)4: 1H NMR (500 MHz, CD3CN/
128.2 (C-6), 127.1 (C-3), 124.2 (C-8), 122.5 (C-1), 121.5 CD2Cl2 1:1) δ 8.48 (d, J15,16 = 5.8 Hz, 4H, H-16), 7.94 (d, J5,6
(C-14), 120.8 (C-4), 120.5 (C-5), 66.0 (C-9) ppm; HRMS-ESI = 7.7 Hz, 2H, H-5), 7.92 (d, J3,4 = 8.0 Hz, 2H, H-4), 7.53–7.46
(m/z): [M + H]+ calcd for [C35H23N2]+, 471.1856; found, (m, 8H, H-dppp), 7.44 (dd, J5,6 = 7.7 Hz, J6,7 = 7.7 Hz, 2H,
471.1861; [α]D25 +280.7° (c 0.385, CHCl3).
H-6), 7.41 (dd, J3,4 = 8.1 Hz, J1,3 = 1.5 Hz, 2H, H-3), 7.36 (dd,
J = 7.5 Hz, J = 7.5 Hz, 2H, H-dppp), 7.24 (dd, J = 7.4 Hz, 4H,
(S)-2,2'-Bis(4-pyridyl)-7,7'-dimethyl-9,9'-spirobifluorene H-dppp), 7.21–7.14 (m, 6H, H-7, H-dppp), 7.09 (dd, J = 7.3 Hz,
((S)-6): CsF (602 mg, 3.96 mmol) was dried under vacuum. J = 7.3 Hz, 2H, H-dppp), 6.90 (s, 6H, H15), 6.69 (dd, J7,8 = 7.5
After flushing with argon (S)-5 (300 mg, 0.60 mmol), 4-pyridyl- Hz, 2H, H-8), 6.52 (d, J1,3 = 1.5 Hz, 2H, H-1), 3.10–3.00 (m,
boronic acid pinacol ester (148 mg, 0.72 mmol), and 4H, H-dppp), 2.23–2.06 (m, 2H, H-dppp); 13C NMR (125.8
[Pd(Pt-Bu3)2] (15 mg, 5 mol %) were added and the reaction MHz, CD3CN/CD2Cl2 1:1) δ 150.1, 149.9, 149.5, 148.4, 144.1,
flask was evacuated twice. Next dry THF (10 mL) was added 140.8, 134.8, 133.1, 132.9, 132.3, 132.0, 129.4, 129.1, 128.5,
and the reaction was heated to 65 °C overnight. After that the 127.1, 125.9, 125.4, 125.4, 125.0, 123.9, 123.3, 122.4, 122.1,
reaction mixture was cooled to rt and diluted with dichloro- 121.3, 121.2, 119.9, 65.7, 21.4, 17.5; MS (ESI, positive mode,
methane. The organic phase was washed with a saturated solu- acetone) m/z: 667. 0 {(dppp)Pd(OTf)}+ , 709. 2
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Beilstein J. Org. Chem. 2014, 10, 432–441.
{[(dppp)2Pd2{(R)-3}2](OTf)}3+, 1138.2 {[(dppp)2Pd2{(R)- www.ccdc.cam.ac.uk/data_request/cif, or by emailing
3}2](OTf)2}2+, 1567.6 {[(dppp)4Pd4{(R)-3}4](OTf)5}3+, 2426.4 data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
{[(dppp)2Pd2{(R)-3}2](OTf)3}+ and {[(dppp)4Pd4{(R)- Crystallographic Data Centre, 12, Union Road, Cambridge CB2
3}4](OTf)6}2+.
1EZ, UK; fax: +44 1223 336033.
[(dppp)2Pd2{(S)-6}2](OTf)4: 1H NMR (500.1 MHz, CD3CN/
CD2Cl2 1:1) δ 8.47 (d, J15,16 = 5.5 Hz, 4H, H-16), 7.86 (d, J3,4
= 7.9 Hz, 2H, H-4), 7.82 (d, J5,6 = 7.9 Hz, 2H, H-5), 7.54–7.45
(m, 9H, H-dppp), 7.39 (dd, J3,4 = 7.9 Hz, J1,3 = 1.6 Hz, 2H,
H-3), 7.36 (d, J = 7.5 Hz, 2H, H-dppp), 7.28–7.21 (m, 6H, H-6,
H-dppp), 7.16 (dd, J = 7.1 Hz, J = 7.1 Hz, 4H, H-dppp), 7.08
(dd, J = 7.3 Hz, J = 7.3 Hz, 2H, H-dppp), 6.89 (s, 3H, H-15),
6.52 (s, 2H, H-8), 6.49 (d, J1,3 =1.6 Hz, 2H, H-1), 3.09–3.01
(m, 4H, H-dppp), 2.19 (s, 6H, H-17); 13C NMR (125.8 MHz,
CD3CN/CD2Cl2 1:1) δ 150.1, 149.9, 149.6, 148.8, 144.3, 139.4,
138.1, 134.2, 133.2, 133.0, 132.3, 131.9, 129.4, 126.0, 125.9,
125.5, 125.4, 125.0, 124.5, 123.3, 122.4, 122.1, 120.9, 119.9,
65.4, 21.5, 21.1, 17.5; MS (ESI, positive mode, acetone) m/z:
667.0 {(dppp)Pd(OTf)}+, 1166.3 {[(dppp)2Pd2{(S)-
6}2](OTf)2}2+, 2482.5 {[(dppp)2Pd2{(S)-6}2](OTf)3}+ and
{[(dppp)4Pd4{(S)-6}4](OTf)6}2+.
Supporting Information
Supporting Information File 1
NMR and ESI mass spectra of ligands 3 and 6 and their
metal complexes.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-10-40-S1.pdf]
Acknowledgements
Financial support from the DFG (SFB 624) and the Academy of
Finland (KR. grant no. 265328 and 263256) and the NGS-
NANO (FT) is gratefully acknowledged.
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