A new cofacial binucleating macropolycycle: Segregated versus encapsulated complexation

Article abstract of DOI:10.1039/b108549m

A new cofacial binucleating macropolycycle combining, for the first time, the distinctive coordination properties of [9]aneN₃ (1,4,7-triazacyclononane) with those of phenol-based compartmental macrocycles is reported together with binuclear Cd<

Full text of DOI:10.1039/b108549m

A new cofacial binucleating macropolycycle: segregated versus
encapsulated complexation†
Lorenzo Tei,a Alexander J. Blake,a Francesco A. Devillanova,b Alessandra Garau,b Vito Lippolis,*b
Claire Wilsona and Martin Schröder*a
a School of Chemistry, The University of Nottingham, University Park, Nottingham, UK NG7 2RD.
E-mail: m.schroder@nottingham.ac.uk
b Dipartimento di Chimica Inorganica ed Analitica, University of Cagliari, Complesso Universitario di
Monserrato, S.S. 554 Bivio per Sestu 09042. Monserrato (Ca), Italy
Received (in Cambridge, UK) 20th September 2001, Accepted 29th October 2001
First published as an Advance Article on the web 14th November 2001
A new cofacial binucleating macropolycycle combining, for
the first time, the distinctive coordination properties of
[9]aneN3 (1,4,7-triazacyclononane) with those of phenol-
based compartmental macrocycles is reported together with
binuclear CdII and YIII complexes, which show segregated
and encapsulated complexation, respectively.
bringing together two metal ions in close proximity, or as a
segregated system leaving the metal ions separated within two
independent N5O-donating sites.
Reaction of H2L with two mol equivalents of both
Cd(NO3)2·4H2O and Me4NOH in MeOH–CHCl3 (2+1 v/v)
under reflux gives yellow plate crystals on partial removal of
solvent and diffusion of Et2O vapour into the remaining
solution. The single crystal X-ray structure of [Cd2(L)](NO3)2·
2MeOH confirms‡ the formation of a binuclear complex lying
on a two-fold rotation axis with each six coordinate CdII ion
bound to an N5O donor set within a distorted octahedral
environment (Fig. 1). Each CdII is coordinated to three N-
donors of the triaza ring [Cd–N 2.342(3)–2.511(3) Å], to two
imine nitrogen atoms [Cd–N(13) 2.293(3) and Cd–N(43)
2.313(3) Å] and to one phenolate oxygen [Cd–O(17) 2.283(2)
Å]. The two N5O-donating chambers of the macropolycycle act,
therefore, as isolated donor sets and the phenolate oxygens do
not bridge the metal ions. However, the phenolate O-donors are
involved in a strong hydrogen-bond with a methanol molecule
[H(1M)…O(17) 1.70 Å, O(1M)–H(1M)…O(17) 172°] which is
also hydrogen-bonded to the secondary N–H of the triazacyclo-
nonane ring [H(7)…O(1M) 2.34 Å, N(7)–H(7)…O(1M) 139°]
to form a six-membered ring including the CdII ion. Sig-
nificantly, the two aromatic rings of the macropolycycle are
stacked with a perpendicular distance of 3.342(4) Å between the
mean planes of the rings and a distance of 3.428(4) Å between
the centres of the rings (Fig. 1). This face-to-face p–p
interaction and additional hydrogen-bonding force the donor
atoms of the anionic ligand L22 to assume a peculiar disposition
with the phenolate oxygens twisted in opposite directions [twist
angle 81.1(3)°] and each pointing towards an individual metal
ion. As a result, the phenolate O-donors cannot bridge the CdII
The design and synthesis of phenol-based binucleating com-
partmental macrocycles and the preparation of their homo- and
hetero-dinuclear complexes incorporating bridging phenolate
donors have important applications in several fields of chemical
research.1 In particular, binuclear complexes with transition
metal ions in close proximity can show fascinating magnetic
properties2 and can serve as synthetic analogues of bimetallic
biosites.3 Furthermore, homo- and hetero-dinuclear lanthanide
complexes with phenol-based compartmental macrocycles have
proved to be useful models in studying the nature and
applications of such compounds in lasers,4 phosphors,5 tunable
photonic devices,6 and in molecular recognition processes
which govern LnIII cation pairing events.7 Variation of the
building blocks1,8 has afforded compartmental ligands incorpo-
rating lateral chains such as 2,2A-bipyridyl,9 triethylenete-
traamine10 or 1,8-diamino-3,6-dioxaoctane.11 Interestingly,
there are no reports of pre-formed macrocycles being in-
troduced as part of the lateral chains bridging the two phenolic
units to give binucleating compartmental or cofacial macro-
polycycles.
We report herein the synthesis of H2L and its coordination to
CdII and YIII. H2L represents a new cofacial binucleating
macropolycycle in which, for the first time, the particular
coordination properties of [9]aneN3 are combined with those of
phenol-based compartmental macrocycles. Thus, direct [2 + 2]
Schiff-base condensation of one mol equivalent of 1,4-bis(2-
aminoethyl)-1,4,7-triazacyclononane, 3, with one mol equiva-
lent of 2,6-diformyl-4-methylphenol in MeOH gives, after
partial removal of the solvent and addition of light petroleum,
the cofacial macropolycycle H2L in 78% yield as confirmed by
1H, 13C NMR spectroscopy, FAB mass spectrometry and
analytical data† (Scheme 1). 3 was synthesised in overall 88%
yield by reaction of 1-(p-tolylsulfonyl)-1,4,7-triazacyclononane
1 with two equivalents of N-tosylaziridine and subsequent
detosylation of 2 with concentrated sulfuric acid. The ligand 3
has been reported previously,12 but only as a by-product of the
synthesis of the tris-pendant arm-species 1,4,7-tris(2-aminoe-
thyl)-1,4,7-triazacyclononane. Our synthesis of 3 represents a
selective and efficient methodology to the synthesis of asym-
metric amine-functionalised [9]aneN3 derivatives.
H2L is characterised by two large adjacent chambers each
with potential N5O2 donacity capable of accommodating metal
ions with large ionic radii. We sought to determine whether H2L
behaves as a compartmental macrocycle encapsulating and
Scheme 1 Reagents and conditions: i, TsN(CH2)2, CH3CN, reflux 3 h, 96%
yield, ii, conc. H2SO4, 110 °C, 72 h; iii, Amberlite IRA-416, 93% overall
yield from 2; iv, 4-methyl-2,6-diformylphenol, MeOH, reflux 2 h, 78%
yield.
† Electronic supplementary information (ESI) available: spectroscopic and
crystallographic data. See http://www.rsc.org/suppdata/cc/b1/b108549m/
2582
Chem. Commun., 2001, 2582–2583
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b108549m

Fig. 3 View of the coordination polyhedra in [Y2(L)(OH)]3+
.
3.4295(19) Å, which is considerably shorter than distances
reported for binuclear lanthanide complexes.13 The three
bridging oxygen atoms in [Y2(L)(OH)]3+ form an almost
Fig. 1 Structure of [Cd2(L)](NO3)2·2MeOH with numbering scheme
adopted. Nitrate anions and hydrogen atoms on carbon atoms have been
omitted for clarity. Hydrogen bonds and the face to face p–p interaction are
drawn as single and double dashed lines, respectively. Displacement
ellipsoids are drawn at 50% probability. Symmetry operation: i = 2x + 1,
y, 2z + 1/2.
equilateral triangle [O(21)…O(21i) 2.747(13)
Å
and
O(21)…O(1) 2.721(12) Å, O(1)–O(21)–O(21i) 59.7(2)° and
O(21)–O(1)–O(21i) 60.6(4)°], and the two YIII ions lie 1.716(5)
Å out of this O3 plane. Therefore, the coordination polyhedron
at each metal ion can best be described as monocapped distorted
dodecahedral (Fig. 3).
The work described herein represents the first example of a
phenol-based compartmental system incorporating [9]aneN3 to
afford a large cofacial macropolycycle capable of forming
binuclear complexes in which the two metal centres can be
segregated or encapsulated. Furthermore, since H2L can be
synthesised directly without using templating metal ions,
heterodinuclear complexes may be targeted, and this is
currently under investigation.
centres, which are, therefore, segregated each within its own
N5O-donor chamber [Cd…Cd distance 7.017(1) Å].
Reaction of H2L with Y(NO3)3·6H2O in a 1+2 molar ratio
under the same conditions as above afforded yellow crystals.
The single crystal X-ray structure of [Y2(L)(OH)][Y(NO3)4-
(MeOH)2](NO3)2·2MeOH shows‡ the complex cation lying
across a two-fold rotation axis with [Y(NO3)4(MeOH)2]2 and
two nitrate counter-anions (Fig. 2). The two YIII centres in the
cation lie within the two N5O donating chambers of L22 and are
bridged not only by the phenolate oxygen atoms but also by a
hydroxy group. To our knowledge the cation [Y2(L)(OH)]3+
represents one of the few structurally characterised homo-
binuclear lanthanide complexes with phenol-based compart-
mental macrocycles.9,10 Each YIII ion in [Y2(L)(OH)]3+ is eight
coordinate and bound to three N-donors from the triazacyclono-
none framework [Y(1)–N 2.436(9)–2.655(7) Å], two azome-
thine nitrogen atoms [Y(1)–N(13) 2.418(8) and Y(1)–N(24)
2.472(8) Å], two phenolate oxygens [Y(1)–O(21) 2.391(6) and
Y(1)–O(21i) 2.322(6) Å] and a hydroxy O-donor [Y(1)–O(1)
2.277(7) Å]. This coordination mode is similar to that observed
for the binuclear LuIII and DyIII complexes with the iminophe-
nolate cryptate obtained by the template Schiff-base condensa-
tion of tris(2-aminoethyl)amine and 4-methyl-2,6-diformylphe-
nol, where three phenolate oxygens bridge a pair of adjacent
lanthanide ions [Lu…Lu 3.447(1) Å, Dy…Dy 3.4840(4) Å].13
In the case of the binuclear PrIII, GdIII and LaIII complexes of
phenol-based compartmental macrocycles with 1,8-diamino-
3,6-dioxaoctane11 and 2,2A-bipyridine9 as lateral chains, the two
metal centres are bridged only by the two phenolate oxygen
atoms, with nitrate and acetate anions completing the coordina-
tion sphere. The Pr…Pr, Gd…Gd and La…La distances are
4.05, 3.97 and 4.135(12) Å, respectively, whereas in
[Y2(L)(OH)]3+ the Y…Y distance is significantly shorter at
We thank the EPSRC and University of Nottingham for
support.
Notes and references
‡ CCDC reference numbers 171456 and 171457. See http://www.rsc.org/
suppdata/cc/b1/b108549m/ for crystallographic data in cif or other
electronic format.
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Fig. 2 Structure of [Y2(L)(OH)]3+ with numbering scheme adopted.
Hydrogen atoms have been omitted for clarity. Symmetry operation: i = 2x
+ 1, y, 2z + 3/2.
Chem. Commun., 2001, 2582–2583
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