First examples of bispidine-ferrocene cyclophanes

Article abstract of DOI:10.1016/j.jorganchem.2021.121945

Two approaches for the syntheses of bispidine-ferrocene cyclophanes were reported. Both include the acylation of 1,5-dimethylbispidin-9-one (H₂Bp) or its pendant amino-armed derivative by 1,1’-ferrocenoyl (Fc(CO)₂) dichloride. The first approach allowed to isolate di-, tri- and pentameric cyclic oligomers of composition (BpFc(CO)₂)_n. The second one included the preliminary functionalization of H₂Bp by N-protected glycine followed by deprotection and cyclization with Fc(COCl)₂. The crystal structure of two new bispidine-ferrocene cyclophanes was established by single-crystal X-ray study. This study revealed the anti-conformation of amido-groups attached to the bispidine nitrogen atoms for both molecules. Various NMR techniques were applied to study the solution behavior of the macrocycles; the predominant anti-conformation in solution was also proved. The acyclic model compound Bp(FcCO)₂ also showed only anti-conformer as revealed by VT-NMR and X-ray studies. Cyclic voltammetry study showed the difference in oxidation potentials of the Fc moiety within the row Bp(FcCO)₂ – (BpFc(CO)₂)₂ – (BpFc(CO)₂)₃ with splitting of the oxidation curve in two later cases. The results obtained in this work will find an application in design and study of novel bispidine-ferrocene cyclophanes for the purposes of supramolecular sensing and catalysis.

Full text of DOI:10.1016/j.jorganchem.2021.121945

Journal of Organometallic Chemistry 949 (2021) 121945
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
First examples of bispidine-ferrocene cyclophanes✩
A.V. Medved’koa,∗, D.P. Krut’kob, S.V. Gaisena, A.V. Churakovc, M.E. Minyaeva,
A.A. Moiseevab, D.A. Lemenovskyb, H. Yu d, L. Wang d, S.Z. Vatsadzea
a N.D. Zelinsky Institute of Organic Chemistry RAS, Leninsky Prospect, 47, Moscow 119991, Russian Federation.
b Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory, 1-3, Moscow 119991, Russian Federation.
c N.S. Kurnakov Institute of General and Inorganic Chemistry RAS, Leninsky Prospect, 31, Moscow 119991, Russian Federation.
d State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two approaches for the syntheses of bispidine-ferrocene cyclophanes were reported. Both include the
acylation of 1,5-dimethylbispidin-9-one (H2Bp) or its pendant amino-armed derivative by 1,1’-ferrocenoyl
(Fc(CO)2) dichloride. The first approach allowed to isolate di-, tri- and pentameric cyclic oligomers of
composition (BpFc(CO)2)n. The second one included the preliminary functionalization of H2Bp by N-
protected glycine followed by deprotection and cyclization with Fc(COCl)2. The crystal structure of two
new bispidine-ferrocene cyclophanes was established by single-crystal X-ray study. This study revealed
the anti-conformation of amido-groups attached to the bispidine nitrogen atoms for both molecules. Var-
ious NMR techniques were applied to study the solution behavior of the macrocycles; the predominant
anti-conformation in solution was also proved. The acyclic model compound Bp(FcCO)2 also showed only
anti-conformer as revealed by VT-NMR and X-ray studies. Cyclic voltammetry study showed the differ-
ence in oxidation potentials of the Fc moiety within the row Bp(FcCO)2 – (BpFc(CO)2)2 – (BpFc(CO)2)3
with splitting of the oxidation curve in two later cases. The results obtained in this work will find an ap-
plication in design and study of novel bispidine-ferrocene cyclophanes for the purposes of supramolecular
sensing and catalysis.
Received 16 April 2021
Revised 8 June 2021
Accepted 10 June 2021
Available online 15 June 2021
Keywords:
3,7-diazabicyclo[3.3.1]nonane
Ferrocene
Macroheterocycles
X-ray diffraction study
Conformational analysis
Amide bond rotation
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
tent of unusual, supramolecular properties, i.e. as redox-sensors to
cations [15]In the frames of our general interest in bispidine chem-
The chemistry of macrocycles is in the heart of supramolecular
chemistry [1]. Macrocycles are important because they exhibit var-
ious types of receptor activity, act as selective sensors, components
of supramolecular machines, and versatile models for study the
conformational transitions [2–4]. The incorporation of new build-
ing blocks in the macrocyclic core leads to unexplored types of ac-
tivity, selectivity and, in general sense, widen the habitual frames
of our knowledge about the Nature.
istry [16] and application of bispidine-like molecules to the syn-
thesis of supramolecular architectures [17], we became interested
in making macrocycles combining complexing ability of bispidine
and redox activity of ferrocene.
No more than 10 bispidonophanes, i.e. macrocycles containing
at least one bispidine fragment, are known in literature. Concern-
ing the ferrocenophanes, i.e. macrocycles possessing at least one
ferrocene unit, we may say that this chemistry is much more stud-
ied [2,18-20].
3,7-Diazabicyclo[3.3.1]nonanes (aka bispidines) belong to the
class of widely used diamines because of their unique conforma-
tional, coordination and biological properties [3,5–10]. Ferrocenes
are also important class of organometallic compounds with well-
known electrochemistry, photochemistry and biological properties
[11–14]. It looks promising to conjugate two different valuable
fragments – bispidine and ferrocene – in one macrocyclic molecule,
that would allow one to design and explore novel, with great ex-
In this paper, we describe for the first time the synthesis
and structural study of bispidine-ferrocene cyclophanes (BFC). As
the first synthetic approach, we choose one step acylation of
1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-9-one (1, hereafter bis-
pidine) or its 1,3-diazaadamantane analogue because this reaction
proceeds quickly at room temperature. The second approach to
the bispidine-ferrocene cyclophane uses the acylation of prelim-
inary formed pendant amino-armed bispidine derivative by 1,1’-
ferrocenoyl dichloride. The structural and conformational features
of the amide bond formed during the synthetic stages gave some
additional interesting items to the discussion of the results. Indeed,
✩
This paper is dedicated to the 70th anniversary of Prof. E.S. Shubina.
∗
Corresponding author.
E-mail address: lexeym@gmail.com (A.V. Medved’ko).
https://doi.org/10.1016/j.jorganchem.2021.121945
0022-328X/© 2021 Elsevier B.V. All rights reserved.

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
Fig. 1. The stereochemistry of bispidine bis-amides: the dl-pair, where two carbonyl
oxygens are in anti-position (left); the meso-form, where those two atoms are in
syn-position (plane of symmetry, right).
Scheme 3. Bispidine macrocycle with asymmetric linkers by acylation-alkylation
sequence [33].
it is well-known in bispidine’s bis-amide chemistry that at room
temperature both anti- and syn-stereoisomers (Fig. 1) could be ob-
served using NMR spectroscopy in some solvents [3,21,22].
2. Results and discussion
2.1. Known ways to bispidinophanes
There are three general approaches to bispidine-containing
macrocycles.
(i) Mannich condensation with appropriate diamines [23-
25] (Scheme 1) typically leads to macrocycles in one step
but with very low yield.
Scheme 4. Bispidine macrocycles by RCM [35].
(ii) Sequential acylation and alkylation potentially lead to asym-
metric macrocycles with different bispidines or diamines
(Scheme 2) but the linkers are always polyalkyl chains.
(iii) Also, a modular approach can be applied to make the bis-
pidine macrocycles with different linking groups [33,34]
(Scheme 3).
(iv) Ring-Closing Metathesis (RCM) reaction is used for macro-
cycle closure when two alkene terminal groups are present
[35] (Scheme 4) in the precursor. This method typically gives
up to 36-80% yields.
Only one paper reports on the acyclic conjugates of bispidine
and ferrocene [36]. To the best of our knowledge, no ways to bis-
pidinophanes based on the simultaneous formation of two bonds
in one reaction step are present in literature. Thus, we attempted
to use the amidation of bispidine building blocks by ferrocenoyl
dichloride.
2.2. Synthesis
To compare the stereochemistry and to study the effect of
macrocyclic structure, we synthesized model acyclic compounds 2
and 3 (Scheme 5).
As the first attempt for cyclophanes making, we tried simply
looking methylene bridge-splitting reaction of 5,7-dimethyl-1,3-
diazaadamantan-6-one (4) with 1,1’-bis(chlorocarbamoyl)ferrocene
to make the smallest possible macrocycle of this series (Scheme 6).
But the product was insoluble in any solvent making it impossi-
ble to analyze it thoroughly. Presumably, the bispidine-ferrocene
containing polymeric product(s) were formed in this reaction in-
stead of the desired monocycle which seems to be highly strained
molecule (Scheme 6).
Scheme 1. Azacrown bispidine synthesis based in Mannich condensation [23].
Taking in consideration the failure in the reaction with diaza-
adamantane 4, in another attempt we applied high dilution condi-
tions and slow addition of diamine 1 to the solution of chloroan-
hydride and triethylamine in toluene, and this way was success-
ful. Three compounds were separated with column chromatogra-
phy, dimer 5c2, trimer 5c3 and pentamer 5c5 (scheme 7). The size
of macrocycles were confirmed by HRMS-ESI (see SI), while their
1H-NMR spectra were almost identical.
Scheme 2. Tetrazabispidine macrocycles by acylation-alkylation-reduction se-
quence. X = H2, O, CHCO2Et, R = H, CH3, Ph [26-32].
2

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
Scheme 5. Synthesis of model acyclic ferrocenoyl diamines: (a) bispidinone 1 for 2 or piperazine for 3, Et3N, toluene, 20°С.
Scheme 6. Bridge-splitting reaction. (a) NaHCO3, C6H6, H2O, 20°С, 2 h.
˚
The second approach to BFC was to combine the N,N’-
A). No short intermolecular contacts were observed in the studied
functionalized bispidine S4 with ferrocenoyl moiety (Scheme 8).
crystals.
BFC
6 was synthetized by the same reaction (compare
The asymmetric unit of the crystal of 6 (Fig. 5) contains a
chloroform molecule and the macrocycle, which has almost a
regular ferrocene structure with two short linkers to the bispi-
dine fragment, formally forming a 16-membered macrocycle. The
Cp planes are parallel: the Cp..Cp folding angle is 0.75(13)°, and
the centroid(C13..C17)-Fe-centroid(C21..C25) angle is 178.3°. The
Fe atom is entirely symmetrically bounded to the Cp ligands,
since the Fe-Cpcentroid distances and normals from Fe to the Cp
Schemes 7 and 8) but in somewhat different conditions, however,
the yield was also low because of flexibility of molecule S4. The
attempt to use the opposite reagent design, i.e., amidation of bis-
pidine with bis-alanine-functionalized ferrocene failed, presumably
due to flexibility of ferrocenic component of the reaction.
2.3. X-Ray diffraction study
˚
plane are equal within the ESDs: 1.649(2)A for Fe-Cp(C13..C17) and
˚
1.647(2)A for Fe-Cp(C21..C25). Due to rather short (four-membered)
chains from ferrocene to rigid bispidine, the CCp1-centroidCp1
The structure of 2 contains one crystallographycally indepen-
dent molecule lying on general position (Fig. 2). The asymmet-
ric unit of formally 20-membered metallocycle 5c2 comprises of
two independent molecules with very close geometrical parame-
ters (Figs. 3, 4), one solvate ether molecule, and one solvent chlo-
roform molecule disordered over three proximal positions.
-
centroidCp2-CCp2 torsion angles for the closest carbon atoms of
two different Cp ligands lie in the range of 16.1° to 16.3°, and
the C13-centroid(C13..C17)-centroid(C21..C25)-C21 torsion angle is
56.2°. Therefore, the Cp carbon atoms adopt a conformation some-
where between staggered and eclipsed. The short linkers between
ferrocenyl and bispidine moieties, which additionally contain π-
π (Cp-CO-NH) and p-π (>N-CO) conjugated fragments, sterically
induce short range of non-covalent intramolecular interactions,
In all structures, bispidinone skeleton adopts chair-chair con-
˚
formation with N…N separations ranging within 2.856 – 2.887 A.
Both molecules adopt in crystal state the anticonformation in re-
spect to both carbonyl fragments attached to the bispidine’s ni-
trogen atoms. The main geometrical parameters of bicyclic core in
studied compounds are close to the values reported and discussed
for several bispidine derivatives in [37, 38] and references cited
therein. All amide fragments (CH2)2N-C(=O)-C are planar within
˚
e.g., the N1..N2 distance is 2.832(6)A, the C10..C18 bond length
˚
is 3.300(6)A. In order to reduce intramolecular repulsion between
the linkers and to partly relax the steric strain of the macrocycle,
one of the linkers (atoms C12, O2, N3, C11, C10 and O1) is signif-
icantly bent, whereas the other linker (C20, O4, N4, C19, C18 and
O3) is approximately flat and is located almost within the Cp plane
(C21..C25). The following geometrical parameters support this idea:
the (C1, N1, C4, C10, O1)-(C3, C6, N2, C18, O3) dihedral angle de-
viates significantly from 0°, being equal to 21.05(12)°; atoms C20,
O4 and N4 lie nearly within the Cp plane (C21..C25), but atoms O2
and N3 deviates significantly from the other Cp plane (C13..C17)
˚
0.16 A. In all cases two amide substituents at each bispidine frame-
work adopt mutual anti-conformation. Both molecules 2 and 5c2
contain sandwich ferrocenyl fragments with typical Fe-C distances
(CSD ver 5.39, [39]). In both 2 and 5c2, all ferrocenyl fragments
adopt staggered conformation with m=3 [40, 41]. Both macrocyclic
molecules of 5c2 contain central holes. Unfortunately, the size of
these holes is too small to accept any guest molecules (the sep-
arations of some opposite carbonyl oxygen atoms are less than 4
˚
˚
by 0.308(9)A and 0.28(1)A, correspondingly; the dihedral angle
3

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
Scheme 7. BFC’s by bispidinone acylation. (a) bispidinone 1, Et3N, toluene, 20°С.
between planes defined by the atom sets C12, C13, O2, N3 and
C13..C17 is 14.9(2)°, but the (C20, C21, O4, N4)-(C21..C25) dihedral
angle is 2.25(14)°; the folding angles (C1, C2, C4, C5)–(C1, N1, C4,
C10, O1) and (C2, C3, C5, C6)–(C3, N2, C6, C18, O3) are 39.3(2)° and
51.3(2)°, correspondingly.
see Table S2 for details); no noticeable intermolecular interactions
have been detected for the crystal.
This part of work shows that in all crystal structures the amide
carbonyl groups attached to bispidine nitrogen atoms adopts the
anti-conformation.
Therefore, the short linkers exhibiting π-π and p-π conjuga-
tion, ferrocenyl and bispidinone moieties forms a rather strained
and non-flexible macrocycle, which is partly relaxed by distorting
one of the linkers.
2.4. NMR studies
In CDCl3 and DMSO solutions, acyclic compound 2 exist as a
single anti-isomer because in the 1H and 13C NMR spectra two
C1,5 bridgehead atoms as well as two methyl groups each exhibit
It might be also noted that compound 6 exhibits only two in-
tramolecular hydrogen bonds, forming 5-membered rings (Fig. 5,
4

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
Scheme 8. Cyclophane synthesis. (a) Fc(COCl)2, DIPEA, DCM, 20°С. The synthesis of
compound S4 is described in SI.
a single peak, which indicates that they are chemically equiva-
lent (C2 axis of symmetry). At the same time, the signals of NCH2
ꢀ
and CH2ꢀ,5 ferrocene protons and carbons are strongly broadened
at room temperature. We studied the dynamic behavior of 2 in
CDCl3 solution in the temperature range from 255 K to 323 K
to estimate the rotation barrier of C-N amide bond (see SI). The
slow exchange limit for 1H and 13C spectra is achieved at 255 K,
the sets of narrow signals in both spectra strictly correspond to
C2 symmetry of anti-isomer. The barrier of amide rotation in 2
(ꢀG= = 60.8
0.9 kJ/mol (14.5
0.2 kcal/mol), (see SI) is in a
good agreement with known values (ꢀG= = 13.4 – 15.4 kcal/mol)
Fig. 2. Molecular structure of 2. Thermal ellipsoids are shown at 50% probability
level. Hydrogen atoms are omitted for clarity.
for 1,1’-ferrocene-bis-amides [42].
Fig. 3. Molecular structure of 5c2. Thermal ellipsoids are shown at 50% probability level. Hydrogen atoms are omitted for clarity.
5

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
Fig. 6. CV curves of compounds 2 (red), 3 (blue), 5c2 (green) and 5c3 (black). DMF
–1
in presence 0.1 M Bu4NClO4 at a GC electrode; potential scan rate 100 mV s
.
Fig. 4. Orthogonal fitting of two independent molecules in the structure 5c2.
2.5. Electrochemistry
Compounds 2, 3, 5c2 and 5c3 were investigated with cyclic
voltammometry (CV) on rotating disk electrode, glassy carbon (GC)
and gold electrodes. Redox properties slightly depended on mate-
rials of electrode. Electrochemical potentials were shown on Table
S3 and CV curves on Fig. 6.
Investigated compounds didn’t show any electrochemical activ-
ity in cathodic region (no reduction peaks were observed up to
-2500 mV for all compounds). In anodic region, only peaks cor-
responding to oxidation of ferrocene fragments presented. As ex-
pected, electron-withdrawing amide groups shifted potentials of
these peaks up to 140-170 mV as compared to unsubstituted fer-
rocene. It is interesting to note that in noncyclic compounds 2 and
3 both ferrocene fragments oxidized independently but simultane-
ously thus giving two-electron wave (Fig. 6). However, in cyclic 5c2
and 5c3 we observed splitting of oxidation peaks that can prove
their sequential reduction. Probably, the first ferrocenium cation
approximates to the second electron-donating non-oxidized iron
atom that reduces its capability to oxidize. Of interest, this effect
is stronger manifested in the case of trimeric molecule compared
to the dimeric one.
Fig. 5. Molecular structure of 6. Thermal ellipsoids are shown at 50% probability
level. NH…O hydrogen bonds are shown as dotted lines.
1H and 13C NMR spectra of 3 in CDCl3 are consistent with its
pseudo-C2v symmetry (see Figs. S13 and S14). At ambient tem-
perature the signals of protons and especialy carbon atoms of the
piperazine cycle are markedlly broadened, which is likely due to
chair-chair interconvertion.
3. Conclusion
NMR data for macrocycle 5c2 in both solvents are in excelent
agreement with its X-ray diffraction structure (Figs. S15-S18). Its
spectral patterns (with the exception of C5H5 singlets) at room
temperature are similar to those of 2 at 255 K. The signals in
DMSO-d6 are somewhat broadened as compared to the solution in
CDCl3. (see Fig. S15 and Fig. S17) The spectral data unumbigously
confirmed the presence of only anti-conformer in respect to mu-
tual amide carbonyl group orientation.
In this work we have demonstrated that bispidine-ferrocene cy-
clophanes could be obtained using simple amidation reaction be-
tween 1,1’-bisferrocenoyl dichloride and bispidine-based diamines.
Two new types of macrocycles have been designed, synthesized,
isolated, and thoroughly studied. The X-ray and NMR have shown
the predominance of anti-conformers for all compounds in the
crystal state and in the solution. The further development of the
BFC chemistry for the purposes of supramolecular sensing and
catalysis is a subject of current study in our laboratories.
NMR data for 6 are also consistent with its crystal structure
(Fig. 5). The single signals of C 1,5 carbon atoms and methyl groups
in both spectra are convincingly confirmed the anti-conformation
of amide carbonyl groups at the bispidine framework. Therefore,
from the NMR experiment we can conclude that the solution con-
formation for acyclic as well as cyclic compounds 2, 5c2 and 6 is
anti, so the rigid solid-state structures retains also in the solution.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
6

A.V. Medved’ko, D.P. Krut’ko, S.V. Gaisen et al.
Journal of Organometallic Chemistry 949 (2021) 121945
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