Mono-palladium(ii) complexes of diamidopyridine-dipyrromethane hybrid macrocycles

Article abstract of DOI:10.1039/b611946h

The reaction of diamidopyridine-dipyrromethane or dipyrromethene hybrid macrocycles with palladium(ii) affords mono-metalated complexes, wherein the metal centre is coordinated to the macrocycle exclusively through pyrrolic nitrogen donor atoms. The Royal

Full text of DOI:10.1039/b611946h

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Mono-palladium(II) complexes of diamidopyridine–dipyrromethane
hybrid macrocycles{
Evgeny A. Katayev,*ab Yuriy A. Ustynyuk,a Vincent M. Lynchb and Jonathan L. Sessler*b
Received (in Cambridge, UK) 18th August 2006, Accepted 19th September 2006
First published as an Advance Article on the web 4th October 2006
DOI: 10.1039/b611946h
The reaction of diamidopyridine–dipyrromethane or dipyrro-
methene hybrid macrocycles with palladium(II) affords mono-
metalated complexes, wherein the metal centre is coordinated
to the macrocycle exclusively through pyrrolic nitrogen donor
atoms.
In recent years Schiff base oligopyrrolic macrocycles, a special class
of expanded porphyrins, have attracted considerable attention in
part because they display a rich coordination chemistry.1,2 To date,
imine-containing oligopyrrole macrocycles have been used to
stabilize complexes containing high-valent actinide oxo cations,
trivalent lanthanide centers, and several different first-row
transition metals.3 A limited number of binuclear metal complexes
have also been prepared using Schiff base expanded porphyr-
ins.1e,2,3 Recently we described a new class of hybrid diamidopyr-
idine–dipyrromethane macrocycles and showed that the
diiminodipyrromethane fragment could be selectively oxidized to
produce the corresponding conjugated diiminodipyrromethene
system (Scheme 1, structures 1 and 2).4 Both macrocycles proved
effective as anion binding agents. However, their cation complexa-
tion chemistry was not explored. Nonetheless, these two systems
(compounds 1 and 2) are of interest in this latter context because
they contain two potential binding sites for cation coordination,
namely diiminodipyrromethane(methene) and diamidopyridine
fragments. 5,59-Diiminodipyrrole fragments are attractive because
they can provide the same 4N-coordinate metal ligation as
porphyrin, albeit in a very different structural environment; by
contrast, the diamidopyridine subunit is of interest because it can
Scheme 1 Structures of building blocks, diiminodipyrromethane (a) and
potentially stabilize 3N-coordinate complexes with a donor set that
2,6-diamidopyridine (b), showing the coordination environment for Pd(II)
bears little resemblance to porphyrins. To date, complexes of
complexation. Oxidation of
a dipyrromethane fragment 1 to the
palladium(II) have been stabilized using receptors containing both
individual fragments, specifically by Love et al.5 and Hirao et al.,6
respectively. However, to the best of our knowledge no system has
been studied wherein both motifs are contained within a single
macrocycle and thus allowed to ‘‘compete’’ for the same cation. In
this paper we report the cation coordination properties of ligands 1
and 2 with palladium(II) and show that under conditions of
normal metal insertion, the resulting complexes have the metal
corresponding dipyrromethene 2, and the synthesis of two distinct
mono-palladium(II) complexes.
center coordinated to the macrocycles exclusively through pyrrolic
nitrogen donor atoms.
Reaction of
1 or 2 with Pd(OAc)2 in acetonitrile or
dichloromethane using either 1 or 2 equiv. of the metal salt
produces a mixture of mono- and binuclear complexes according
to ESI mass spectrometry. The binuclear complexes appeared to
be unstable and their apparent decomposition made difficult the
separation of the corresponding mononuclear complexes.
However, using one equivalent of dichlorobis(acetonitrile)
palladium(II) salt as the Pd(II) source and carrying out the
insertion in the presence of triethylamine led to the formation of
the mono-palladium(II) complex 3 in 81% yield. In contrast, the
metallation of ligand 2 could only be effected readily in the absence
of base, yielding the mono-palladium(II) complex 4 in 60% yield.
aDepartment of Chemistry M.V. Lomonosov Moscow State University,
Leninskie gory 1/3, Moscow, 119992, Russian Federation.
E-mail: kataev@nmr.chem.msu.ru; Fax: +7 495 9392677;
Tel: +7 495 1359273
bDepartment of Chemistry and Biochemistry, 1 University Station,
A5300, University of Texas at Austin, Texas, 78712-0165, USA.
E-mail: sessler@mail.utexas.edu; Fax: +1 512 4717550;
Tel: +1 512 4715009
{ Electronic supplementary information (ESI) available: additional experi-
mental and crystal data. See DOI: 10.1039/b611946h
4682 | Chem. Commun., 2006, 4682–4684
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Based on an analysis of the spectroscopic and crystallographic
data,{ the palladium(II) cation is coordinated selectively within the
diiminodipyrrole environment in the case of both complexes 3
and 4.
In the 1H NMR spectrum (CD2Cl2, room temperature) of
complex 3, all the signals are broadened except the AA9BB9
pattern ascribed to the tolyl group. At 250 uC, the signals are
sharp and correspond to an unsymmetrical structure, wherein the
two characteristic signals of the amido 1H protons appear as a
broad peak at 10.9 ppm and a sharp signal at 8.4 ppm, as inferred
from an 1H-13C HSQC NMR experiment. These signals disappear
upon treatment with D2O. All NMR spectroscopic data are
consistent with the suggestion that 3 undergoes self-association to
produce aggregates containing several molecules of the complex in
dichloromethane solution and that this aggregation process is
substantially enhanced when the solution is cooled to 250 uC. In
contrast, the peaks ascribed to aggregation are absent from the
corresponding 1H NMR spectrum recorded in DMSO-d6 at room
temperature. In fact, sharp signals are observed, supporting the
notion that no appreciable self-association takes place in this
highly polar solvent. The self-association inferred from the 1H
NMR analyses in CD2Cl2, was explicitly confirmed in the solid
state via a single crystal X-ray diffraction analysis. In particular,
the complex is seen to form a dimer through a hydrogen bond
network involving the amido groups from two different molecules
within independent unit cells (Fig. 1).
Fig. 2 Single crystal X-ray diffraction structure of complex 4 showing
the hydrogen bond between chloride Cl(1) and the amido N(3)H hydrogen
atoms (50% probability ellipsoids, solvent molecules are omitted for
clarity).
and N(2)–Pd–N(7) angles: namely 80 and 86 in 3 vs. 90, 90u in
porphyrin complexes.7
According to the crystallographic data, complex 4 has an L-like
conformation, with the two NH amido groups directed into the
macrocycle cavity (Fig. 2). The palladium cation is in a square
coordination environment, with the following palladium-to-nitro-
gen bond lengths and angles: Pd–N(7), N(1), N(2) = 2.042(5),
The complexation of palladium locks the conformation of the
ligand, such that the two amide NH protons are oriented in the
same direction. One of the amide NH signals seen in the NMR
spectrum recorded in CD2Cl2 resonates at lower field and is
thought to participate in the hydrogen bonding interactions that
stabilize the self-association process both in dichloromethane
solution and in the solid state. According to the crystallographic
data, two molecules of complex 3 are bound via a hydrogen bond
˚
1.950(5), 2.073(5) A, respectively, and N(7)–Pd–N(2) and N(2)–
Pd–N(1) = 87 and 80u, respectively. The hydrogen bond between
the amido group and the chloride anion is within normal limits,
˚
namely Cl(1)–N(3) = 3.099(5) A. The presence of the metal cation
presumably stabilizes the unsymmetrical ligand, an effect that is
reflected in the NMR spectrum in solution. No evidence of
association events is seen for complex 4, either in solution or in the
solid state.
…
˚
involving O(1) N(3) (separation: 2.792(6) A). The palladium(II)
cation is in square coordination environment with distances
Pd–N(1), N(2), N(6), N(7)
˚
= 1.934(6), 2.108(6), 2.115(6),
Both mono-palladium complexes appeared to be rather stable in
air. The UV-vis spectrum of complex 3 has two characteristic
1.943(6) A, respectively. These bond lengths are similar to those
in palladium porphyrin complexes but differs in N(1)–Pd–N(2)
Fig. 1 Structure of the dimer of complex 3 showing the formation of two hydrogen bonds between the molecules (50% probability ellipsoids; solvent
molecules are omitted; carbon atoms are shown in grey, nitrogen in blue, hydrogen bonds in orange and hydrogen atoms in pink). O(1*)—symbol indicates
an atom at equivalent position (2x,2y,1 2 z).
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bands at 327 and 433 nm, with shoulders at 358 and 455 nm,
respectively. Complex 4, which contains a conjugated diiminodi-
pyrromethene moiety gives rise to bands at 319 and 445 nm; it also
displays bands in the visible region at 615 and 655 nm.
Notes and references
{ Crystal data. 3: C46.57H46.24Cl3.24N7O2Pd, M = 957.24, yellow lathes,
0.35 6 0.10 6 0.03 mm3, triclinic, space group P1, a = 10.3506(4), b =
˚
15.7321(5), c = 15.8708(6) A, a= 60.823(2), b = 87.392(2), c = 86.802(2)u,
V = 2252.43(14) A , Z = 2, rc = 1.411 mg m23, m = 0.650 mm21, F(000) =
3
˚
Since the macrocycles have two potential binding sites for
metal cations, we attempted to study the complexation of a
second metal cation to the diamidopyridine moiety. Using
both mild metal insertion conditions (acetate or chloride salts
of metal cations in the presence of an organic base) with the
range of transition metal cations, including Pd(II), as well as
deprotonation with strong base followed by reaction with metal
salts, failed to produce bimetallic complex. Only polymeric
products and products of decomposition were seen in the
case of complexes 3 and 4. The inaccessibility of bimetallic
complexes leads us to suggest that complex 3 is unable to adopt
a conformation appropriate for coordinating a second metal
cation, a suggestion that is in accord with solution and solid
state studies. In contrast, the inability of complex 4 to stabilize
the complexation of a second cation is ascribed to its smaller
size; the cavity simply cannot accommodate readily two
metal cations without undue steric distortion or electrostatic
repulsion.
983, T = 153(2) K, Nonius Kappa CCD diffractometer, graphite
monochromator with MoKa radiation, R1 = 0.0722, wR2 = 0.1279,
7817 independent reflections and 601 parameters. 4: C55H63ClN8O3Pd M =
1025.98, long dark-green needles, 0.42 6 0.08 6 0.07 mm3, monoclinic,
˚
space group C2/c, a = 35.3431(8), b = 16.0453(6), c = 21.7368(7) A, a = 90,
3
b = 127.270(2), c = 90u, V = 9809.5(5) A , Z = 8, rc = 1.389 mg m23, m =
˚
0.486 mm21, F(000) = 4288, T = 153(2) K, Nonius Kappa CCD
diffractometer, graphite monochromator with MoKa radiation, R1 =
0.0688, wR2 = 0.1421, 8607 independent reflections and 514 parameters.
Data reduction were performed using DENZO-SMN. The structure was
solved by direct methods using SIR97 and refined by full-matrix least-
squares on F2 with anisotropic displacement parameters for the non-H
atoms using SHELXL-97. SQUEEZE in PLATON98 was used to remove
the contribution of the solvent to the structure factors. CCDC 615936 and
615937 for 3 and 4, respectively. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b611946h
1 For recent publications reporting expanded porphyrin metal complexes,
see: (a) J. L. Sessler and D. Seidel, Angew. Chem., Int. Ed., 2003, 42, 5134;
(b) E. Burri, M. Onm, C. Daguenet and K. Severin, Chem.–Eur. J., 2005,
11, 5055; (c) S. Shimizu and A. Osuka, Eur. J. Inorg. Chem., 2006, 1319;
(d) P. L. Arnold, A. J. Blake, C. Wilson and J. B. Love, Inorg. Chem.,
2004, 43, 8206; (e) P. L. Arnold, D. Patel, A. J. Blake, C. Wilson and
J. B. Love, J. Am. Chem. Soc., 2006, 128, 9610; (f) S. D. Reid, A. J. Blake,
C. Wilson and J. B. Love, Inorg. Chem., 2006, 45, 636.
2 For recent Schiff base mono- and polynuclear complexes, see: (a)
P. A. Vigato and S. Tamburini, Coord. Chem. Rev., 2004, 248, 1717; (b)
R. Li, D. S. Larsen and S. Brooker, New J. Chem., 2003, 27, 1353; (c)
D. Mulhern, Y. Lan, S. Brooker, J. F. Gallagher, H. Gorls, S. Rau and
J. G. Vos, Inorg. Chim. Acta, 2006, 359, 736; (d) J. R. Price, Y. Lan,
G. B. Jameson and S. Brooker, Dalton Trans., 2006, 1491.
3 J. L. Sessler, A. E. Vivian, D. Seidel, A. K. Burrell, M. Hoehner,
T. D. Mody, A. Gebauer, S. J. Weghorn and V. Lynch, Coord. Chem.
Rev., 2001, 216–217, 411.
4 J. L. Sessler, E. A. Katayev, G. D. Pantos and Y. A. Ustynyuk, Chem.
Commun., 2004, 1276; E. A. Katayev, G. D. Pantos, V. M. Lynch,
J. L. Sessler, M. D. Reshetova and Yu. A. Ustynyuk, Russ. Chem. Bull.,
2005, 54, 165; J. L. Sessler, E. A. Katayev, G. D. Pantos, P. Scherbakov,
M. D. Reshetova, V. N. Khrustalev, V. M. Lynch and Y. A. Ustynyuk,
J. Am. Chem. Soc., 2005, 127(32), 11442.
During the course of these studies, we found that 3 can be
oxidized to 4 quantitatively by treatment with VOCl3 in THF.
Moreover, we also found that complex 4 can be reduced to
produce 3 by stirring a dichloromethane solution in the presence of
triethylamine. This ligand-based redox chemistry of this complex
resembles the behaviour seen for palladium(II) complexes bearing
phosphine ligands, with the exception that the ligand (not
palladium) is subject to two electron oxidation or reduction.
This finding could make diiminodipyrrole–Pd type complexes of
interest in catalytic studies. At present we are investigating the
chemical reactivity of acyclic diiminodipyrrole palladium com-
plexes. We are also targeting the preparation of more flexible
analogous of ligands 1 and 2 with the goal of exploring further the
metal coordination properties of this potentially generalizable class
of hybrid macrocycles.
5 G. Givaja, A. J. Blake, C. Wilson, M. Schroder and J. B. Love, Chem.
Commun., 2003, 2508.
6 (a) T. Moriuchi, S. Bandoh, Y. Miyaji and T. Hirao, J. Organomet.
Chem., 2000, 599, 135; (b) T. Moriuchi, S. Bandoh, M. Miyaishi and
T. Hirao, Eur. J. Inorg. Chem., 2001, 651.
We thank the U.S. Department of Energy (grant no. DE-FG02-
01ER15186 to J.L.S.) and the Russian Foundation for Basic
Research (Yu.A.U. and E.A.K. grants no. 05-03-32684 and 05-03-
08017) for support of this work.
7 S. J. Silvers and A. Tulinsky, J. Am. Chem. Soc., 1967, 89, 3331.
4684 | Chem. Commun., 2006, 4682–4684
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