Interplay of interactions governing the dynamic conversions of acyclic and macrocyclic helicates

Article abstract of DOI:10.1002/chem.200900693

A rigid, helical macrocycle that contains two copper(I) ions has been synthesized through subcomponent self-assembly. Although it does not obey the "rule of coordinative saturation", this macrocycle could be prepared through subcomponent substitution star

Full text of DOI:10.1002/chem.200900693

DOI: 10.1002/chem.200900693
Interplay of Interactions Governing the Dynamic Conversions of Acyclic and
Macrocyclic Helicates
Victoria E. Campbell,[a] Xavier de Hatten,[b] Nicolas Delsuc,[b] Brice Kauffmann,[b]
Ivan Huc,*[b] and Jonathan R. Nitschke*[a]
Abstract: A rigid, helical macrocycle
that contains two copper(I) ions has
been synthesized through subcompo-
nent self-assembly. Although it does
not obey the “rule of coordinative satu-
ration”, this macrocycle could be pre-
pared through subcomponent substitu-
tion starting from a triACTHNUGTRNEUNG(copper(I)) heli-
cate, in a reaction in which copper(I)
was ejected. The macrocycle was ob-
served to readily participate in a se-
quence of transformations between he-
AHCTUNGTRENNUNG
effects, the conformational preferences
of organic building blocks, and the co-
ordinative preferences of the metal ion.
The thermodynamic parameters gov-
erning the interconversion of an
“open” helicate and the “closed” mac-
rocycle were determined through van ꢀt
Hoff analysis, allowing quantification
of the entropic driving force for macro-
cyclization.
Keywords: dynamic
covalent
chemistry · macrocyclization · self-
assembly · substitution · systems
chemistry
Introduction
covalent bonds), and multicomponent cycles and rotaxanes
(metal coordination + boronate ester formation + imine
bond formation). Herein we build upon these prior exam-
ples by showing how four types of interactions may act to-
gether not only upon a single structure but within a system
of structures.[10] We were able to describe the evolution of
this system following the addition of a subcomponent, allow-
ing multiple sequential transformations to be executed be-
tween acyclic and macrocyclic helicates.
The creation and transformation of complex structures
under thermodynamic control requires a nuanced under-
standing of the rules, or “programming instructions,”[1] gov-
erning the self-assembly processes of interest. Intricate self-
assembled structures have been created using the interplay
of different kinds of interactions, such as circular helicates[2]
and cages[3] (metal coordination + guest templation), Bor-
romean[4] and Solomon[5] links (metal coordination + p-
stacking
+
dynamic covalent[6] imine bond formation),
triply interpenetrated catenanes[7] and functional monolay-
ers[8] (metal coordination + p-stacking), strained grids[9]
(metal coordination + hydrophobic interactions + dynamic
Results and Discussion
The products expressed by our system were observed to
depend upon interactions mediated by 1) the electronic ef-
fects of substituents, 2) entropic effects, 3) the conformation-
al preferences of organic building blocks, and 4) the coordi-
native preferences of copper(I). All of these effects were im-
portant, but none taken alone could allow the prediction of
the product observed from a given set of building blocks.
We have previously described the self-assembly of trinu-
clear double helicates similar to 4, which formed (Scheme 1)
from 2,9-diformyl-1,10-phenanthroline (2 equiv), copper(I)
(3 equiv), and 8-amino-quinoline 3 (4 equiv).[11] We initially
reasoned that introducing bis(aminoquinoline) 1 would give
rise to large architectures containing the trimetallic helicate
motif of 4 as a subunit. However, when subcomponent 1
was incorporated, its preferred geometry imposed the for-
[a] V. E. Campbell, Dr. J. R. Nitschke
Department of Chemistry, University of Cambridge
Lensfield Road, Cambridge, CB2 1EW (UK)
Fax : (+44)1223-336017
E-mail: jrn34@cam.ac.uk
Homepage: http://www-jrn.ch.cam.ac.uk/
[b] Dr. X. de Hatten, Dr. N. Delsuc, Dr. B. Kauffmann, Dr. I. Huc
Institut Europꢁen de Chimie et Biologie, Universitꢁ de Bordeaux-
CNRS UMR5248 and UMS3033, 2 rue Robert Escarpit
33607 Pessac (France)
Fax : (+33)540002215
E-mail: i.huc@iecb.u-bordeaux.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900693.
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FULL PAPER
to 2, despite the similarity of their constituent subcompo-
nents.
Single crystals of 2 were grown by diffusion of benzene
into a nitromethane solution. Two views of the X-ray crystal
structure of 2 are presented in Figure 1. NMR spectra of 2
in solution, including NOESY and COSY data, were consis-
tent with the solid-state structure (see the Supporting Infor-
mation).
Figure 1. Two views of the crystal structure of macrocycle 2: C gray, N
violet, O red, Cu orange; hydrogen atoms, iBu groups, counterions, and
molecules of solvent of crystallization are not shown.
Scheme 1. Syntheses of dicopper macrocycle 2 (2·diformylphenanthroline
+ 2·1 + 2·CuI ! 2) and tricopper helicate 4 (2·diformylphenanthroline
+ 4·3 + 3·CuI ! 4), and the transformation of 4 into 2 upon addition of
1 (4 + 2·1 ! 1 + 4·3 + CuI).
Examination of the coordination vectors[16] of the un-
bound nitrogen atoms of 2 revealed that they are not well
situated either to chelate or bridge. The degrees of freedom
available to the system are limited by the rigidity of subcom-
ponent 1 and the preferred trans-orientation of the carbonyl
and N-phenyl vectors of its tertiary amide groups.[17] Operat-
ing within these constraints, we infer that the system of di-
formylphenanthroline, 1, and CuI, minimizes strain and max-
imizes entropy by breaking the rule of coordinative satura-
tion in generating 2.
Bis(aminoquinoline) 1 was observed to react with helicate
5[12] (Scheme 2), with the equilibrium not strongly favoring
either side. This system was thus more amenable to thermo-
dynamic analysis than the transformation of 4 into 2
(Scheme 1), where the equilibrium lay strongly on the side
of 2. Van ꢀt Hoff analysis of the system of Scheme 2 provid-
ed quantitative insight as to the effects of entropy and en-
thalpy on substitution reactions involving 2. The equilibrium
composition of the product mixture of the reaction between
1 and helicate 5 was measured from 373 K to 403 K, and a
linear least-squares fit of ln(K) versus Tꢀ1 (see the Support-
ing Information) yielded the values of DH8=81 kJmolꢀ1
and DS8=0.193 kJmolꢀ1 Kꢀ1. The system of Scheme 2 is thus
balanced between enthalpy, which favors incorporation of
the p-toluidine subcomponent during the formation of 5,
and entropy, which favors the increase in number of parti-
mation of a stable product structure 2 (Scheme 1), wherein
all ligand nitrogen atoms were not bound to metal ions. This
demanding subcomponent could be introduced and removed
quantitatively following selection rules based upon substitu-
ent electronic effects,[12,13] allowing the system to be
switched back and forth between obeying and disobeying
the rule of coordinative saturation. This rule,[14] which postu-
lates that the most stable structure will have all ligand
donor atoms bound to a metal ion and all metal ions coordi-
natively saturated, has been broken in exceptional cases,[15]
but its expression has not previously been switched on and
off within a system.
Even though only four of the six ligand nitrogen atoms of
macrocycle 2 are bound to copper(I) ions, we observed no
tendency for the subcomponents of 2 to form coordinatively
1
saturated structures. No changes to the H NMR spectrum
of 2 were noted following either the addition of excess
copper tetrafluoroborate (4 equiv) or excess 1 (4 equiv) fol-
lowed by heating to 393 K for 12 h. The reaction of helicate
4 (1 equiv) with 1 (2 equiv) resulted in quantitative conver-
sion to 2 with ejection of 3 (4 equiv) and CuI: Remarkably,
coordinative saturation does not render 4 stable with respect
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J. R. Nitschke, I. Huc et al.
the balanced nature of the equilibrium between 5 and 2
would allow 1 to displace electron-poor anilines that p-tolui-
dine (Hammett spara =ꢀ0.17)[18] is able to displace,[12] and
that 1 would in turn be displaced by electron-rich anilines
that displace p-toluidine.
We thus designed the sequence of transformations shown
in Scheme 3. Each step was observed to occur in >95%
yield and the entire sequence could be carried out within
the same reaction flask. The corresponding NMR spectra
are presented in Figure 2. The presence of additional CuI
did not result in the formation of products incorporating 1
that obeyed the rule of coordinative saturation.
Scheme 2. Equilibrium between helicate 5 and macrocycle 2 (2·1 + 5 Ð
4·p-toluidine + 2).
cles during the formation of macrocycle 2 (three species
going to five). Similar effects presumably govern the forma-
tion of 2 from 4 (Scheme 1), although this system is more
complicated to analyze because the equilibrium lay strongly
on the side of 2 and because of potential interactions be-
tween liberated CuI and the solvent and with liberated 3.
In prior work[12] we had investigated how substituent ef-
fects can generate an enthalpic driving force for imine ex-
change. The Hammett equation[18] was observed to quantita-
tively predict the degree to which a less electron-rich amine
residue was displaced by a more electron-rich amine within
the imine ligands of a metal complex. Although the Ham-
mett equation appears an unsuitable tool to quantify the be-
havior of the systems incorporating diamines because of the
importance of entropy in these equilibria, we reasoned that
Figure 2. 1H NMR spectra of four-stage transformation shown in
Scheme 3: *=helicate 6, o=p-chloroaniline, &=macrocycle 2, &=dia-
minoquinoline 1, !=helicate 7, !=p-methoxyaniline, *=macrocycle 8.
Scheme 3. Four-stage subcomponent substitution sequence incorporating 2 (6 + 2·1 ! 2 + 4·p-chloroaniline; 2 + 4·p-methoxyaniline ! 7 + 2·1; 7 +
2·(ethylenedioxy)bis(ethylamine) ! 8 + 4·p-methoxyaniline).
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Dynamic Conversions of Acyclic and Macrocyclic Helicates
FULL PAPER
8.32 Hz, 2H, f’), 7.07 (s, 2H, h), 6.99 (t, J=7.89 Hz, 2H, f), 6.88 (s, 2H,
h’), 6.73 (s, 2H, d’), 6.39 (dd, J=8.72 Hz, J2’ =1.94 Hz, 2H, Ph1), 6.19 (dd,
J=8.72 Hz, J2’ =1.94 Hz, 2H, Ph2), 6.08 (dd, J=8.72 Hz, J2’ =1.94 Hz,
2H, Ph3), 4.98 (dd, J=8.72 Hz, J2’ =1.94 Hz, 2H, Ph4), 3.87 (m, 8H,
The substantial geometrical changes required during the
conversion of 6 to 2 and 2 to 7 are reflected in the slower ki-
netics of these transformations (t1/2 =ca. 12 h at 393 K) than
in the transformation of 7 to 8 (t1/2 =ca. 5 min at 393 K). We
attribute this difference in activation energy to the extensive
rearrangement necessary—involving the breakage and re-
forming of six nitrogen-copper linkages—to convert the co-
ordination environments of 6 to 2 or 2 to 7.
With the exception of 2, all of the products shown in
Schemes 1–3 obey the rule of coordinative saturation,
having four ligand nitrogen atoms per copper ion. The pres-
ence of subcomponent 1 thus causes this “rule” to be
broken upon its incorporation, only to be reinstated follow-
ing this subcomponentꢃs ejection. Thus, to determine wheth-
er the system will follow this rule, it is necessary to know
not only whether 1 is present, but also whether another sub-
component is present with a greater affinity for complex for-
mation (such as 4-methoxyaniline). The first condition must
be true, and the second false, for the system to exist in the
state of coordinative unsaturation exemplified by 2.
OCH2CH
N
ACHTUNGTRENNUNG(CH3)2),
1.08 ppm (m, 24H, OCH2CHAHCTUNTGRENNUNG
CD2Cl2): d=168.51, 166.28, 164.19, 163.27, 162.48, 156.56, 155.84, 154.66,
151.66, 151.09, 149.00, 143.77, 141.66, 141.33, 140.91, 140.05, 138.94,
138.62, 138.29, 137.76, 139.98, 129.94, 128.45, 128.23, 126.67, 126.31,
124.74, 123.86, 122.84, 122.43, 120.83, 120.78, 120.53, 118.90, 103.24,
101.97, 76.38, 75.41, 67.95, 38.91, 36.19, 29.92, 28.44, 28.23, 25.84, 19.13,
19.05, 18.95, 18.84 ppm; ESI-MS: m/z: 884.24 (22+).
X-ray crystal structure of 2: A thin needle-shaped crystal of compound 2
was mounted on a cryoloop using Paratone-N oil as cryoprotectant. Data
were collected at 213 K on a R-axis Rapid-S goniometer equiped with a
Rigaku MM07 CuKa rotating anode (l=1.54178 ꢄ). The IP camera on
this setup is of size 460 mm ꢅ 256 mm with an angle range of ꢀ60 to
+144 degrees. The camera length is fixed at 127.4 mm. The crystal be-
¯
longs to the triclinic P1 space group with unit cell parameters a=17.19,
b=19.63, c=21.21 ꢄ with angles a=93.13, b=100.15, and g=105.478.
V=6751.3(4) A3, 1calcd =1.272 gcmꢀ3, m=1.033 mmꢀ1, Z=2, reflections
collected: 89919, independent reflections: 23046 (Rint =0.1735), final R
indices [I> 2s(I)]: R1=0.1653, wR2=0.3776, R indices (all data) R1=
0.3250, wR2=0.4646. The structure was solved by direct methods using
SHELXD and refined with SHELXL-97.[20] Seven benzene molecules
ꢀ
and two BF4 ions were located in the density map. The poor quality of
the refinement and data collection statistics are a consequence of the
large number of disordered solvent molecules, the relatively large size of
the complex and the very small size of the crystal collected (0.1ꢅ0.1ꢅ
0.025 mm3). CCDC-718066 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Conclusions
The system encompassing helicates 2, 4, 5, 6, 7, and 8 is thus
governed by substituent and entropic effects, acting together
to determine which subcomponent will be incorporated into
the favored product. The rule of coordinative saturation[14]
dictates the structure of this product, except when this prod-
uct incorporates 1: the preferred geometry of this subcom-
ponent then favors the structure of 2. We are currently in-
vestigating new structures built around the novel dicopper
double-helicate core of 2, as well as developing new ways to
use linear free energy relationships to quantitatively predict
the outcome of reassembly reactions involving diamines and
higher-order multitopic amines.
Four-step transformation of Scheme 3: Into a Teflon-capped NMR tube,
6 (2.32 mg, 2.23 mmol), 1 (2.77 mg, 4.47 mmol), CD3CN (0.1 mL), and
[D6]DMSO (0.4 mL) were added. The tube was sealed and the solution
was purged of dioxygen by three vacuum/argon-fill cycles, and heated for
12 h at 393 K, after which 2 and p-chloroaniline were the only species ob-
served in solution by 1H NMR spectroscopy. p-Methoxyaniline (1.10 mg,
8.94 mmol) was added to this solution and the tube was purged of dioxy-
gen by three vacuum/argon fill cycles. The solution was heated to 393 K
for five days, after which 7 and 1 were the only products observed by
NMR spectroscopy. To this solution 2,2’-(ethylenedioxy)bis(ethylamine)
(1.32 mg, 8.94 mmol) was added. The tube was sealed and the solution
was purged of dioxygen by three vacuum/argon-fill cycles, and heated for
5 min at 393 K, to afford 8, p-methoxyaniline and 1 as the unique prod-
1
ucts sobserved by H NMR spectroscopy.
Experimental Section
Synthesis of 4: Into a Teflon-capped NMR tube, 2,9-diformyl-1,10-phe-
nanthroline (1.87 mg, 7.94 mmol),
AHCTUNGTRENNUNG
3
(5.55 mg, 15.9 mmol), [Cu-
General: All reactions were carried out in dry glassware with an argon
overpressure. Unless otherwise noted, all reagents were purchased from
Aldrich or Acros and used without further purification; 1,10-phenanthro-
line-2,9-dicarbaldehyde[19] was prepared according to the literature. NMR
spectra were recorded on Bruker Aspect 300, Bruker DRX-400, Bruker
Avance 500 Cryo, and Bruker 500 TCI-ATM Cryo Spectrometers.
(0.4 mL) were added. The tube was sealed and the solution was purged
from dioxygen by three vacuum/argon-fill cycles. The dark brown solu-
tion was left at 323 K overnight, resulting in the formation of 3 in quanti-
tative yield, as observed by 1H NMR spectroscopy. 1H NMR (400 MHz,
300 K, CD2Cl2/CD3CN, referenced to CHDCl2 at 5.32 ppm): d=9.29 (s,
4H, imine), 8.05 (br s, 4H, phenanthroline), 7.93 (br s, 4H, phenanthro-
line), 7.31 (br s, 4H, phenanthroline), 7.19 (br m, 4H, AQ), 7.13–7.09 (br
m, 12H AQ), 6.85 (br s, 12H, AQ), 6.73 (br s, 8H, Ph), 6.53 (br s, 8H,
Macrocycle 2: Into a Teflon-capped NMR tube, 2,9-diformyl-1,10-phe-
nanthroline (1.07 mg, 4.78 mmol),
1
(2.97 mg, 4.78 mmol), [Cu-
ACHTUNGTRENNUNG
(0.4 mL) were added. The tube was sealed and the solution was purged
of dioxygen by three vacuum/argon-fill cycles. The dark brown solution
was left at 323 K overnight, following which 2 was observed as the
unique product by 1H NMR spectroscopy. 1H NMR (500 MHz, 243 K,
CD2Cl2/CD3CN, referenced to CHDCl2 at 5.32 ppm, a-h and a’-h’ refer to
resonances that have been assigned to protons in the structure of 2; see
the Supporting Information for assignments): d=9.09 (s, 2H, d), 8.69 (d,
J=8.05 Hz, 2H, b’), 8.42 (d, J=8.36 Hz, 2H, c’), 8.18 (d, J=8.05 Hz, 2H,
b), 7.96 (d, J=8.36 Hz, 2H, c), 7.92 (d, J=9.26 Hz, 2H, a’), 7.75 (d, J=
9.32 Hz, 2H, a), 7.72 (d, J=8.43 Hz, 2H, g’) 7.68 (d, J=7.55 Hz, 2H, g),
7.50 (d, J=6.52 Hz, 2H, e), 7.47 (d, J=8.89 Hz, 2H, e’), 7.37 (t, J=
Ph), 5.94 (br s, 4H, Ph), 3.91 (d, 4H, ROCH2CH
ROCH2CH(CH3)2), 1.18 ppm (br s, 24H, ROCH2CH
m/z: 662.8 (43+).
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Synthesis of 2 from 4: Into a Teflon-capped NMR tube, 2,9-diformyl-
1,10-phenanthroline (1.87 mg, 7.94 mmol), 3 (5.55 mg, 15.9 mmol), [Cu-
ACHNUTTGERNNG(UN CH3CN)4]BF4 (3.75 mg, 11.9 mmol), CD3CN (0.1 mL), and CD2Cl2
(0.4 mL) were added. The tube was sealed and the solution was purged
from dioxygen by three vacuum/argon-fill cycles. The dark brown solu-
tion was left at 323 K overnight, resulting in the formation of 4 in quanti-
tative yield, as observed by 1H NMR spectroscopy. Compound
1
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J. R. Nitschke, I. Huc et al.
(4.01 mg, 6.61 mmol) was added into the NMR tube. The solution was
purged of dioxygen again, then heated at 323 K for 2.5 h, after which all
volatiles were removed under dynamic vacuum and CD3CN (0.2 mL) and
[D6]DMSO (0.2 mL) were added. The reaction was heated at 353 K for
five days, then at 393 K for seven days, after which the reaction came to
completion. The reaction was monitored by 1H NMR spectroscopy and
ESI-MS. 1H NMR (400 MHz, 300 K, CD3CN/[D6]DMSO, referenced to
CD2HCN at 1.94 ppm): d=9.54 (s, 2H, d), 8.88 (d, J=7.18 Hz, 2H, b’),
8.57 (d, J=8.38 Hz, 2H, c’), 8.36 (d, J=7.18 Hz, 2H, b), 8.11 (d, J=
8.38 Hz, 2H, c), 7.88 (d, J=8.38 Hz, 2H, a’), 7.79 (d, J=7.18 Hz, 2H, a),
7.75 (d, J=7.18 Hz, 2H, g’), 7.65 (d, broad, 2H, g), 7.63 (d, broad, 2H,
e), 7.45 (m, 6H, e’, f’, h), 7.24–7.07 (m, 3 and 2), 6.77 (broad, 8H,
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phenyl), 3.92 (m, 8H, OCH2CH
OCH2CH(CH3)2), 1.00 ppm (m, 24H, OCH2CH
350.19 (3+), 411.09 (3·Cu+), 884.24 (22+).
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ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
5
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acknowledges financial support from the Walters-Kundert Charitable
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Received: March 17, 2009
Published online: May 14, 2009
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