Nano-sized heterometallic macrocycles based on 4-pyridinylboron-capped iron(II) clathrochelates: Syntheses, structures and properties

Article abstract of DOI:10.1039/c3cc49038f

Ir-Fe heterometallic macrocycles from clathrochelate-based bipyridyl and bis(amidinate) ligands with controllable cavity size have been prepared and characterized. The Royal Society of Chemistry 2014.

Full text of DOI:10.1039/c3cc49038f

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Nano-sized heterometallic macrocycles based on 4-
pyridinylboron-capped iron(II) clathrochelates:
syntheses, structures and properties
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
YingꢀYing Zhang, YueꢀJian Lin and GuoꢀXin Jin*
DOI: 10.1039/x0xx00000x
www.rsc.org/
at room temperature. Macrocycles [(Cp*Ir)4(L1)2(LFe1)2][OTf]4 (3a)
Ir-Fe heterometallic macrocycles from clathrochelate-based
bipyridyl and bis(amidinate) ligands with controllable cavity
size have been prepared and characterized.
and [(Cp*Ir)4(L1)2(LFe2)2][OTf]4 (3b) were obtained simply by
removal of the precipatation. The 1H NMR spectra for 3a and 3b had
similar signals at almost the same chemical shifts except for that of
the substituents in the metallaligands, which suggest that the
structures of 3a and 3b are similar.
The successful applications of wellꢀdefined metalꢀorganic
coordination macrocyles and cages in various areas, such as hostꢀ
guest chemistry, photoꢀ and electrochemical sensing, catalysis and so
on, has driven the development to systematic and rational
approaches for their preparation.1 Most of the macrocyles and cages
synthesized to date are homometallic based on transition metal ions.
The synthesis of multimetallic hybrid materials is of special interest
because the incorporation of two or more kinds of metal ions can add
different functionalities.2 However, much attention has been focused
on the synthesis of homometallic macrocycles, whereas the
chemistry, as well as the synthetic strategy toward discrete
Cy
N
Cy
N
Cy
N
Cy
N
Cl
H
1) nBuLi, THF
2) [Cp*IrCl2
Ir
Ir
]
2
n
n
N
N
N
N
H
R
Cl
Cy
Cy
Cy
Cy
H2L1 (n = 1)
H2L2 (n = 2)
1 (n = 1)
2 (n = 2)
R
4+
+
O
O
O
N
N
N
N
R
N
O
N
Fe
(OTf)ꢀ4
Ir
Ir
N
B
O
B
N
heterometallic frameworks, has received much less attention.3
A
R
N
O
N
N
N
N
Cy
Cy
Cy
Cy
B
useful strategy toward heterometallic macrocycles is to use
metallaligands as building blocks via stepwise formation approach.4
Clathrochelates, cage complexes with an encapsulated metal
ion, were first proposed by Busch.5 Recently, numerous
clathrochelate complexes of different types with the encapsulated
iron(II), ruthenium(II) and cobalt(I, II and III) ions, which display
interesting chemical, physical and physicochemical properties, have
been obtained and characterized.6 One of the main pathways for
functionalization of these clathrochelates is to use various
substituents in both their ribbed chelate αꢀdioximate fragments7 and
the apical capping groups.8 The cage complexes with two apical 4ꢀ
pyridinyl substituents are linear bipyridyl ligands, which has been
widely used as a bridging ditopic N,N′ꢀligand for the preparation of
countless discrete supramolecules,9 as well as coordination
polymers.10 In this paper, we choose 4ꢀpyridinylboronꢀcapped iron
clathrochelates as metallaligands and bis(amidine) as organic ligands
to construct heterometallic macrocycles.
O
N
O
R
R
O
N
R
R
R
N
R
R
AgOTf
CH2Cl2
Fe
R
N
O
N
O
B
N
O
n
n
R
R
Cy
Cy
Cy
Cy
N
N
N
N
O
O
O
N
N
R
N
N
N
R
N
O
Fe
N
B
O
B
N
Ir
Ir
N
O
R
R
LFe1: (R, R) = (CH2)4, FeNx3(B4ꢀPy)2
LFe2: R = CH3, FeDm3(B4ꢀPy)2
Dm2– is dimethylglyoxime dianion
Nx2– is nioxime dianion
3a: n = 1, (R, R) = (CH2)4
3b: n = 1, R = CH3
4a: n = 2, (R, R) = (CH2)4
4b: n = 2, R = CH3
Scheme 1 The syntheses of the heterometallic macrocycles (3a, 3b, 4a and 4b).
The structure of 3a was confirmed by Xꢀray crystallography at
193 K. As shown in Fig. 1, the cation of complex 3a adopts a
slightly distorted rectangular structure based on the [4Ir + 2Fe]
nuclear core with a nanoꢀscaled cavity of 18.7 × 10.9 Å, which
accommodates several solvent molecules (CH2Cl2) and a part of
triflate anions. The three coordination sites of the halfꢀsandwich Ir
fragment are occupied by pyridyl donor LFe1 and chelating group L1.
The coordination geometry of Fe(II) center is intermediate between a
trigonal prism (TP, distortion angle φ = 0°) and a trigonal antiprism
(TAP, distortion angle φ = 60°); the distortion angle φ values are
equal to 22.1, 22.0 and 21.7°, respectively. The heights h of their
As shown in Scheme 1, [Cp*IrCl2]2 was first treated with
dilithium salt (formed by the addition of 2 equiv. of nBuLi at ꢀ78 °C)
of the bis(amidine) ligand H2L1 in THF at 0 oC to afford the
bis(amidinate) bridged dinuclear complex [Cp*IrCl]2(L1) (1), to
which 4ꢀpyridinylboronꢀcapped clathrochelates LFe1/LFe2 was added
o
in the presence of 2 equiv. AgOTf at ꢀ78 C. After the mixture was
stirred at low temperature for 2 h and kept stirring for additional 6 h
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TPꢀTAP coordination polyhedra are approximately 2.3 Å. The several solvent molecucles found as guests are contained in the
average IrꢀN and FeꢀN distances (Table S1) are equal to 2.126 and rectangular framework. A remarkable feature of the structure is that
1.904 Å, which are similar to the observed sixꢀcoordinated iridium both of the metallaligands and the organic ligands are almost in the
complexes11 and iron(II) clathrochelates, respectively.12
normal configuration compared with the twisted ones in complex 3a.
The IrꢀN and FeꢀN distances are in the range of 2.084(15) to
2.198(12) Å and 1.872(13) to 1.936(13) Å (Table S2), respectively,
which are close to the values of 3a.
R
R
O
N
N
R
N
N
N
R
N
O
Cl
Cl
Fe
Ir
Ir
N
B
O
O
B
N
+
Cl
Cl
O
O
R
R
CH2Cl2
R
R
Cl
O
N
N
N
N
O
Cl
Fe
Ir
N
B
O
O
B
N
Ir
R
N
R
N
Cl
Cl
O
O
R
R
5a: (R, R) = (CH2)4
5b: R = CH3
Scheme 2 Formation of complexes 5a and 5b.
Fig. 1 (a) Molecular structure of 3a. All hydrogen atoms and guest molecules were
omitted for clarity. (b) The dimensions of cavity for 3a. (c) Top view of 3a and (d)
side view of 3a in spaceꢀfilling mode. Triflate anions and solvent molecules
outside the framework, as well as hydrogen atoms are omitted for clarity. Color
We attempted to use the reported synthetic methodology4 to
obtain the same matallarectangles, but the crude products are
code: N, blue; O, red; B, yellow; C, gray; Cl, light green; F, green; S, violet; Fe, complicate and difficult to purify so that only the heterometallic
orange; Ir, pink.
dinuclear complexes were obtained. A stoichiometric (1:1) mixture
of [Cp*IrCl2]2 and the corresponding clathrochelateꢀbased bipyridyl
ligands LFe1/LFe2 in CH2Cl2 at room temperature gave the dinucler
With the intent of exploring the scope of our synthetic approach
and improving the cavity size of the rectangles, xenylꢀlinked
complexes 5a and 5b in almost quantitative yields (Scheme 2). The
1H NMR spectra of 5a and 5b display a similar signal pattern of the
bis(amidine) ligand H2L2 was introduced to these reactions.
Complexes [(Cp*Ir)4(L2)2(LFe1)2][OTf]4 (4a) and [(Cp*Ir)4(L2)2
Cp* protons and pyridyl protons (Hα and Hβ). However, with respect
to the macrocycles above, in 5a and 5b, the Hα signal is shifted to
higher frequencies (δ = 8.85 ppm for 5a and 8.88 ppm for 5b),
whereas both of the Cp* signal and Hβ signal are shifted to lower
(LFe2)2][OTf]4 (4b) were obtained by treatment of [Cp*IrCl]2(L2) (2)
with iron(II) clathrochelates LFe1/LFe2 used the previously conditions
in 88% and 85% yields, respectively.
frequencies (δ = 1.56, 7.57 ppm for 5a and 1.57, 7.58 ppm for 5b)
(Fig. S1).
Fig. 3 Molecular structures of complex 5a (a) and 5b (b). All hydrogen atoms and
guest molecules were omitted for clarity. Color code: N, blue; O, red; B, yellow; C,
gray; Cl, light green; Fe, orange; Ir, pink.
Xꢀray analysis indicated that all of the Cp*Ir fragments in
complexes 5a and 5b are coordinated to two chlorine atoms and one
nitrogen atom from the pyridine ligand. Despite the fact that these
two complexes in some respects are alike, the details of their crystal
structures are significantly different. Obviously, the Cp* groups in
Fig. 2 (a) Molecular structure of 4a. All hydrogen atoms and guest molecules were
omitted for clarity. (b) The dimensions of cavity for 4a. (c) Top view of 4a and (d)
side view of 4a in spaceꢀfilling mode. Triflate anions and solvent molecules
outside the framework, as well as hydrogen atoms are omitted for clarity.
5a are positioned trans to each other while neither trans nor cis in 5b.
The UVꢀvis spectra of the complexes containing 4ꢀ
pyridinylboronꢀcapped iron(II) clathrochelates obtained contain one
metalꢀtoꢀligand Fed → Lπ* charge transfer (MLCT) band in the
visible region with maxima at about 450 nm (Fig. S2), which is
characteristic of the macrobicyclic iron(II) trisꢀdioximates.
The structure of 4a, which contains four iridium and two iron
metal centers, was established by Xꢀray structure analysis (Fig. 2).
The complex cation of 4a is quite similar to that of 3a and has a
rectangular cavity with dimensions of 19.1 × 15.2 Å according to
Ir…Ir nonꢀbonding distances, which is much larger than that of 3a,
as well as the known molecular rectangles.13 Two triflate anions and
2 | Chem. Commun., 2013, 00, 1-3
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Meanwhile, the bands of the intraligand πꢀπ* transitions are
observed in the UV region from 227 to 283 nm.
4
S.ꢀL. Huang, Y.ꢀJ. Lin, T. S. A. Hor and G.ꢀX. Jin, J. Am. Chem.
Soc., 2013, 135, 8125.
The electrochemical characteristics of the dichloromethane
solutions of the heterometallic complexes obtained were studied by
cyclic voltammetry (CV) using a glassy carbon (GC) working
electrode. All of the CVs have similar shapes and exhibit one redox
pair and one oxidation wave in the potential range from ꢀ1.5 to +1.7
V (Fig. S3 and Table S3). The CVs for all of the complexes in their
cathodic ranges contain only one peak of the oxidation, which is
apparently irreversible and may correspond to the oneꢀelectron
process of Fe2+/+. However, the anodic ranges of these CVs contain
quasiꢀreversible oneꢀelectron waves assigned to the Fe2+/3+
oxidations. The ꢁE values for complexes 5a and 5b are higher than
those of the macrocycles (3a, 3b, 4a and 4b) (170ꢀ230 mV), which
might be because of the slight effect of the electronꢀwithdrawing
chloride ions.
5
6
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Conclusions
In summary, we have reported a series of iridium(III)ꢀ
iron(II) heterometallic complexes with clathrochelateꢀbased
bipyridyl and bis(amidine) ligands. Singleꢀcrystal Xꢀray
diffraction indicated that they have rectangular structures with
different nanoꢀsized cavities, in which some small molecules
and anions were found, such as dichloromethane molecules,
triflate anions, and so on. The cyclic voltammograms exhibits
one redox pair and one oxidation wave. Our results further
confirmed that 4ꢀpyridinylboronꢀcapped iron(II) clathrochelates
can be used as building blocks to construct the nanoꢀsized
multicentered hybrid systems.
7
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This work was supported by the National Science
Foundation of China (91122017, 21374019), the Shanghai
Science and Technology Committee (13JC1400600,
13DZ2275200) and the Program for Changjiang Scholars and
Innovative Research Team in University (IRT1117).
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Notes and references
Shanghai Key Laboratory of Molecular Catalysis and Innovative
Material, Department of Chemistry, Fudan University, Shanghai 200433,
P. R. China; Fax: +86ꢀ21ꢀ65641740; Tel: +86ꢀ21ꢀ65643776; Eꢀmail:
gxjin@fudan.edu.cn
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†
Electronic supplementary information (ESI) available: Experimental
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CCDC 973498 (3a), CCDC 973499 (4a), CCDC 973500 (5a), and CCDC
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DOI: 10.1039/C3CC49038F
Toc Graphic
:
Text:
A series of nanoꢀscaled IrꢀFe heterometallic rectangles were prepared
from 4ꢀpyridinylboronꢀcapped iron(II) clathrochelates and bis(amidine)
ligands. The cavity size could be controlled easily by the length of the
organic ligand.
4 | Chem. Commun., 2013, 00, 1-3
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