Dinuclear pyridine-4-thiolate-bridged rhodium and iridium complexes as ditopic building blocks in molecular architecture

Article abstract of DOI:10.1021/ic402838y

A series of dinuclear pyridine-4-thiolate (4-Spy)-bridged rhodium and iridium compounds [M(μ-4-Spy)(diolef)]₂ [diolef = 1,5-cyclooctadiene (cod), M = Rh (1), Ir (2); diolef = 2,5-norbornadiene (nbd), M = Rh (3)] were prepared by the reaction of Li(4-Spy) with the appropriate compound [M(μ-Cl)(diolef)]₂ (M = Rh, Ir). The dinuclear compound [Rh(μ-4-Spy)(CO)(PPh₃)]₂ (4) was obtained by the reaction of [Rh(acac)(CO)(PPh₃)] (acac = acetylacetonate) with 4-pySH. Compounds 1-4 were assessed as metalloligands in self-assembly reactions with the cis-blocked acceptors [M(cod)(NCCH₃)₂](BF ₄) [M = Rh (a), Ir (b)] and [M(H₂O)₂(dppp)] (OTf)₂ [M = Pd (c), Pt (d); dppp = 1,3-bis(diphenylphosphino)propane] . The homometallic hexanuclear metallomacrocycles [{M₂(μ-4-Spy) ₂(cod)₂}₂{M(cod)}₂](BF ₄)₂ (M = Rh [(1a)₂], Ir [(2b)₂]) and the heterometallic hexanuclear metallomacrocycles [{Rh₂(μ-4-Spy) ₂(cod)₂}₂{Ir(cod)}₂](BF ₄)₂ [(1b)₂], [{Rh₂(μ-4-Spy) ₂(cod)₂}₂{M′(dppp)}₂](OTf) ₄ (M′ = Pd [(1c)₂], Pt [(1d)₂]), and [{Ir₂(μ-4-Spy)₂(cod)₂}₂{M′ (dppp)}₂](OTf)₄ (M′ = Pd [(2c)₂], Pt [(2d)₂]) were obtained. NMR spectroscopy in combination with electrospray ionization mass spectrometry was used to elucidate the nature of the metalloligands and their respective supramolecular assemblies. Most of the synthesized species were found to be nonrigid in solution, and their fluxional behavior was studied by variable-temperature ¹H NMR spectroscopy. An X-ray diffraction study of the assemblies (1a)₂ and (1d)₂ revealed the formation of rectangular (9.6 A × 6.6 A) hexanuclear metallomacrocycles with alternating dinuclear (Rh₂) and mononuclear (Rh or Pt) corners. The hexanuclear core is supported by four pyridine-4-thiolate linkers, which are bonded through the thiolate moieties to the dinuclear rhodium units, exhibiting a bent-anti arrangement, and through the peripheral pyridinic nitrogen atoms to the mononuclear corners.

Full text of DOI:10.1021/ic402838y

Article
pubs.acs.org/IC
Dinuclear Pyridine-4-thiolate-Bridged Rhodium and Iridium
Complexes as Ditopic Building Blocks in Molecular Architecture
Montserrat Ferrer,*,† Daniel Gomez-Bautista,‡ Albert Gutierrez,† Jose R. Miranda,‡
́
́
́
Guillermo Orduna-Marco,‡ Luis A. Oro,‡ Jesus J. Perez-Torrente,*,‡ Oriol Rossell,† Pilar García-Orduna,‡
́
́
̃
̃
and Fernando J. Lahoz‡
†Departament de Química Inorgan
̀
ica, Universitat de Barcelona, c/Martí i Franques
̀
1-11, 08028 Barcelona, Spain
ea−ISQCH, Facultad de Ciencias,
‡Departamento de Química Inorgan
́
ica, Instituto de Síntesis Química y Catalisis Homogen
́
́
Universidad de Zaragoza−CSIC, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: A series of dinuclear pyridine-4-thiolate (4-
Spy)-bridged rhodium and iridium compounds [M(μ-4-
Spy)(diolef)]2 [diolef = 1,5-cyclooctadiene (cod), M = Rh
(1), Ir (2); diolef = 2,5-norbornadiene (nbd), M = Rh (3)]
were prepared by the reaction of Li(4-Spy) with the
appropriate compound [M(μ-Cl)(diolef)]2 (M = Rh, Ir).
The dinuclear compound [Rh(μ-4-Spy)(CO)(PPh3)]2 (4) was
obtained by the reaction of [Rh(acac)(CO)(PPh3)] (acac =
acetylacetonate) with 4-pySH. Compounds 1−4 were assessed
as metalloligands in self-assembly reactions with the cis-
blocked acceptors [M(cod)(NCCH3)2](BF4) [M = Rh (a), Ir
(b)] and [M(H2O)2(dppp)](OTf)2 [M = Pd (c), Pt (d);
dppp = 1,3-bis(diphenylphosphino)propane]. The homome-
tallic hexanuclear metallomacrocycles [{M2(μ-4-Spy)2(cod)2}2{M(cod)}2](BF4)2 (M = Rh [(1a)2], Ir [(2b)2]) and the
heterometallic hexanuclear metallomacrocycles [{Rh2(μ-4-Spy)2(cod)2}2{Ir(cod)}2](BF4)2 [(1b)2], [{Rh2(μ-4-
Spy)2(cod)2}2{M′(dppp)}2](OTf)4 (M′ = Pd [(1c)2], Pt [(1d)2]), and [{Ir2(μ-4-Spy)2(cod)2}2{M′(dppp)}2](OTf)4 (M′ =
Pd [(2c)2], Pt [(2d)2]) were obtained. NMR spectroscopy in combination with electrospray ionization mass spectrometry was
used to elucidate the nature of the metalloligands and their respective supramolecular assemblies. Most of the synthesized species
1
were found to be nonrigid in solution, and their fluxional behavior was studied by variable-temperature H NMR spectroscopy.
An X-ray diffraction study of the assemblies (1a)2 and (1d)2 revealed the formation of rectangular (9.6 Å × 6.6 Å) hexanuclear
metallomacrocycles with alternating dinuclear (Rh2) and mononuclear (Rh or Pt) corners. The hexanuclear core is supported by
four pyridine-4-thiolate linkers, which are bonded through the thiolate moieties to the dinuclear rhodium units, exhibiting a bent-
anti arrangement, and through the peripheral pyridinic nitrogen atoms to the mononuclear corners.
to be a powerful tool for achieving a remarkable number of
ordered structures,11,12 such an approach depends largely on
the availability of metal-based building blocks suitable for the
assembly.
Lately we have become interested in the design and synthesis
of heterometallic macrocyclic species30−32 since the presence of
different metal moieties can confer cooperative and/or dual
behavior to the final species, particularly in relation with their
participation in catalytic processes.33−35 Although other
methods have been described, the most common strategy to
synthesize heterometallic macrocycles is modular self-assembly.
This methodology requires the initial synthesis of metal-
loligands, that is, coordination complexes with strongly
INTRODUCTION
■
The search for new and complex structures has been a
motivating factor for the intensive study of metalla-supra-
molecular chemistry.1−14 The sustained interest in this area is
driven by the wide range of potential applications of these
species in gas storage,15,16 catalysis,17−20 molecular magnet-
ism,21−23 optical materials,24−26 sensing,27−29 and many other
areas.
In metal-based supramolecules, the metal units play an
important role in controlling the structural geometries and
tuning the chemical and physical properties of the compounds.
In contrast with the synthesis of functionalized organic
compounds, which can be achieved with high specificity by
the use of well-defined reactions and reagents, the creation of
complex metal-based molecules remains highly challenging
because of the dynamic properties and lability of many
coordination bonds. Although self-assembly has been proved
Received: November 13, 2013
Published: January 17, 2014
© 2014 American Chemical Society
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covalently bound ligands that have additional donor sites for
coordination to other acceptor metallic building blocks.
In the general approach, monometallic building blocks are
combined to yield self-assembled architectures. Despite the fact
that the use of bimetallic units in combination with acceptor
metallic complexes opens up new prospects for research in this
area, only a handful number of bimetallic metalloligands have
pyridine-4-thiolato ligands could be prepared, the dangling
pyridine groups would be available for further coordination to
additional d8 transition-metal centers such as those in the
organometallic complexes [M(cod)(CH3CN)2]+ (M = Rh, Ir;
cod = 1,5-cyclooctadiene) or the dppp-chelated complexes
[M(H2O)2(dppp)]2+ [M = Pd, Pt; dppp = 1,3-bis-
(diphenylphosphino)propane] bearing labile acetonitrile and
aqua ligands, respectively. Surprisingly, although the presence
of uncoordinated pyridine groups strongly suggests the
possibility of synthesizing novel supramolecular systems, the
number of reported discrete metallomacrocycles incorporating
this ligand is relatively small. In this regard, the trinuclear
complexes [Cp*MCl(μ-4-Spy)]3 (M = Ir,61,62 Rh62) and
[PdCl(PPh3)(μ-4-Spy)]3,63 the tetranuclear complex [Cp*Ir-
(4-Spy)(μ-4-Spy)]4,61 and the heterotetranuclear complex
[Pt(4,4′-dtbpy)(μ-4-Spy)(ZnCl2)]2 (dtbpy = 4,4′-di-tert-butyl-
2,2′-bipyridine)64 are, to the best of our knowledge, the only
reported examples.
been described to date. In this context, Re2,36−38 Co2,39,40 and
40,41
Mo2
metal−metal-bonded entities bearing either two
terminal pyridine or phosphine groups have been successfully
employed for this purpose (Chart 1). Interestingly, the anionic
Chart 1. Schematic Representations of Reported Bimetallic
Metalloligands
In this paper, we report on the synthesis of dinuclear
rhodium or iridium organometallic ditopic metalloligands
bridged by pyridine-4-thiolato ligands and their successful
application in the construction of rectangular hexanuclear
homo- and heterometallomacrocycles with alternating dinuclear
(Rh2 or Ir2) and mononuclear (Rh, Ir, Pd, or Pt) corners.
EXPERIMENTAL SECTION
■
General Methods. All manipulations were performed under a dry
argon or nitrogen atmosphere using Schlenk-tube techniques. Unless
otherwise stated, reactions were carried out at room temperature.
Liquid or solution transfers between reaction vessels were done via
cannula. Solvents were dried by standard methods and distilled under
argon or nitrogen immediately prior to use, or alternatively, a solvent
purification system (Innovative Technologies) was used. NMR spectra
were recorded at 250, 300, or 400 MHz with Varian or Bruker
spectrometers at variable temperature. Chemical shifts are reported in
parts per million and referenced to SiMe4 using the signals of the
deuterated solvent (1H and 13C) or to 85% H3PO4 as an external
reference (31P). Elemental C, H, and N analyses were performed in a
PerkinElmer 2400 CHNS/O microanalyzer. Electrospray ionization
mass spectrometry (ESI-MS) was performed on a Bruker MicroTof-Q
mass spectrometer at the Universidad de Zaragoza or an LTQ-FT
Ultra mass spectrometer (Thermo Scientific) at the Biomedical
Research Institute (PCB-Universitat de Barcelona). MALDI-TOF
mass spectra were obtained on a Bruker Miocroflex mass spectrometer
using trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]-
malononitrile (DCTB) or dithranol (DIT) as a matrix.
Standard literature procedures were used to prepare the starting
materials [Rh(μ-Cl)(diolef)]2 [diolef = cod,65 norbornadiene
(nbd)66], [Ir(μ-Cl)(cod)]2,67 [Rh(μ-OMe)(cod)]2,68 [Rh(acac)-
(CO)(PPh3)] (acac = acetylacetonate),69 [Pd(H2O)2(dppp)](OTf)2
(c),70 and [Pt(H2O)2(dppp)](OTf)2 (d).70 The cationic complexes
[M(diolef)(NCCH3)2]BF4 (diolef = cod, M = Rh (a), Ir (b); diolef =
nbd, M = Rh) were obtained following a slight modification of the
literature procedure.71 4-pySH was purchased from Aldrich, recrystal-
lized from methanol/diethyl ether, and stored under nitrogen.
Synthesis of [Rh(μ-4-Spy)(cod)]2 (1). Method A. A solution of n-
BuLi (0.6 mL, 0.942 mmol, 1.57 M in hexanes) was slowly added to a
yellow suspension of 4-pySH (0.096 g, 0.864 mmol) in THF (5 mL) at
273 K, and the mixture was stirred for 1 h to give a white suspension of
Li(4-Spy). Solid [Rh(μ-Cl)(cod)]2 (0.213 g, 0.432 mmol) was added
to give an orange-brown suspension that was stirred for 4 h at room
temperature. The solvent was removed under vacuum, and the residue
was washed with cold methanol (2 × 3 mL) to give the compound as a
brown solid that was filtered, washed with cold methanol, and dried
under vacuum. Yield: 0.216 g (78%). Method B. 4-pySH (0.230 g,
2.069 mmol) was added to a solution of [Rh(μ-OMe)(cod)]2 (0.500
mg, 1.032 mmol) in dichloromethane (15 mL) to give an orange
compound [(C6F5)2Pt(μ-PPh2)2Pt(CN)2]2− described by
Fornies and co-workers42 is, to our knowledge, the unique
example of a bimetallic building block lacking metal−metal
bonds that coordinates to additional metal centers through the
terminal cyanide groups that are coordinated to one of the
platinum atoms of the binuclear complex (Chart 1).
In considering the goal of connecting dinuclear and
mononuclear units, and given our experience in the synthesis
and characterization of thiolate-bridged rhodium and iridium
dinuclear complexes43−47 and related hydrosulfide-bridged
counterparts,48 we envisaged the design of angular flexible
dinuclear metalloligands of the type [M(μ-SR)L2]2 (M = Rh,
Ir) as precursors for new inorganic architectures by using
adequately functionalized thiolato ligands. In this context,
dinuclear d8 transition-metal complexes with bridging thiolates
have attracted widespread interest because of their electronic,
structural, and conformational properties45,49−55 and their
catalytic activity in the hydroformylation of olefins under
mild conditions.56−60 Monodentate thiolato bridging ligands
provide flexible structures that support a wide range of bonding
and nonbonding metal distances by modification of the hinge
angle between the rhodium coordination planes. In addition,
the existence of several conformers arising from the relative
disposition of the two thiolato ligands in the dinuclear
framework and their possible interconversion confers to the
complexes an unusual versatility from the point of view of their
potential application as synthons in supramolecular chemistry.
On the other hand, pyridine-4-thiol (4-pySH) is a versatile
ligand since it has the potential to coordinate to transition
metals through either the sulfur atom or the nitrogen atom.
Moreover, the deprotonated pyridine-4-thiolato (4-Spy) ligand
usually coordinates to transition metals through the sulfur atom
while leaving the pyridine moiety free. We thought that if the
bimetallic complexes [M(μ-4-Spy)L2]2 (M = Rh, Ir) based on
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solution that was stirred for 6 h. The solution was concentrated under
vacuum to ca. 2 mL, and then diethyl ether (10 mL) was added to give
a brown suspension. Further concentration and addition of diethyl
ether gave the compound as a brown microcrystalline solid that was
filtered, washed with diethyl ether (2 × 3 mL), and dried under
vacuum. Yield: 0.556 g (84%). Anal. Calcd for C26H32N2Rh2S2 (%): C,
49.22; H, 3.81; N, 4.41; S, 10.10. Found: C, 49.02; H, 4.01; N, 4.35; S,
10.25. 1H NMR (CD2Cl2, 298 K, 300.13 MHz) δ: 8.26 (dd, 4H, JH−H
= 4.7 and 1.4 Hz, Hα), 7.28 (dd, 4H, JH−H = 4.7 and 1.4 Hz, Hβ) (4-
Spy); 4.45 (br s, 8H, CH), 2.46 (br, 8H, >CH2), 2.01 (br, 8H,
>CH2) (cod). 13C NMR (CDCl3, 298 K, 74.46 MHz) δ: 150.0 (CS),
148.9, 128.8 (4-Spy); 81.5 (d, JC−Rh = 11.7 Hz, CH), 31.6 (>CH2)
(cod). MS (ESI+, CH2Cl2) m/z: 853 [Rh3(Spy)2(cod)3]+ (3%), 643
[Rh2(SpyH)(Spy)(cod)2]+ (25%), 433 [Rh(SpyH)2(cod)]+ (100%),
filtered, washed with n-hexane (4 × 3 mL), and dried under vacuum.
Yield: 0.064 g (62%). Anal. Calcd for C68H88B2F8N4Rh6S4 (%): C,
43.43; H, 4.72; N, 2.98; S, 6.82. Found: C, 43.11; H, 4.90; N, 3.05; S,
1
6.90. H NMR (CDCl3, 298 K, 400.16 MHz) δ: 8.30 (d, 8H, JH−H
=
6.6 Hz, Hα), 7.20 (d, 8H, JH−H = 6.6 Hz, Hβ) (4-Spy); 4.79 (br s, 8H,
CH), 4.18 (br s, 8H, CH), 3.97 (br s, 8H, CH), 2.60 (br s,
16H, >CH2), 2.36 (br s, 4H, >CH2), 2.00 (br s, 4H, >CH2), 1.98−1.86
(br s, 24H, >CH2) (cod). 1H NMR (CD2Cl2, 218 K, 300.13 MHz) δ:
8.12 (br s, 4H, Hα), 8.08 (br s, 4H, Hα), 7.52 (br s, 4H, Hβ), 6.64 (br s,
4H, Hβ) (4-Spy); 4.80 (br s, 4H, CH), 4.68 (br s, 4H, CH), 4.37
(br s, 4H, CH), 3.93 (br s, 4H, CH), 3.85 (br s, 8H, CH), 2.47
(br s, 16H, >CH2), 2.28 (br s, 8H, >CH2), 2.10 (br s, 8H, >CH2), 1.85
(br s, 16H, >CH2) (cod). MS (ESI+, CH2Cl2) m/z: 1174
[Rh4(Spy)3(cod)4]+ (15%), 853 [Rh3(Spy)2(cod)3]+ (64%), 643
[Rh2(SpyH)(Spy)(cod)2]+ (100%).
+
322 [Rh(SpyH)(cod)] (60%).
Synthesis of [Ir(μ-4-Spy)(cod)]2 (2). [Ir(μ-Cl)(cod)]2 (0.352 g,
0.524 mmol) and Li(4-Spy), formed in situ by the reaction of 4-pySH
(0.117 g, 1.05 mmol) with n-BuLi (0.72 mL, 1.15 mmol, 1.6 M in
hexanes), were reacted in THF (5 mL) for 10 h. The yellow
suspension was concentrated under vacuum, and then methanol was
added. The yellow solid was filtered, washed with methanol (3 × 4
mL), and dried under vacuum. Yield: 0.310 g (70%). Anal. Calcd for
C26H32N2Ir2S2 (%): C, 38.03; H, 3.93; N, 3.41; S, 7.81. Found: C,
38.15; H, 4.01; N, 3.36; S, 7.67. 1H NMR (C6D6, 298 K, 400.16 MHz)
δ: 8.27 (br d, 4H, JH−H = 6.7 Hz, Hα), 6.99 (br d, 4H, JH−H = 6.9 Hz,
Hβ) (4-Spy); 4.12 (br s, 8H, CH), 2.01 (br, 8H, >CH2), 1.52 (br,
8H, >CH2) (cod). The 1H NMR spectrum was obtained from a freshly
prepared sample. On standing, the compound became insoluble in
most of the usual organic solvents.
Synthesis of [{Ir2(μ-4-Spy)2(cod)2}2{Ir(cod)}2](BF4)2 [(2b)2].
Solid [Ir(cod)(NCCH3)2]BF4 (0.023 g, 0.049 mmol) was added to
a yellow suspension of [Ir(μ-4-Spy)(cod)]2 (2) (0.040 g, 0.049 mmol)
in THF (10 mL), and the mixture was stirred overnight. The solvent
was removed under vacuum, and the residue was washed with a
CH2Cl2/diethyl ether (1:8) mixture (9 mL) to give a deep-red solid
that was filtered, washed with diethyl ether (2 × 3 mL), and vacuum-
dried. Yield: 0.055 g (93%). Anal. Calcd for C68H88B2F8Ir6N4S4 (%):
C, 33.79; H, 3.67; N, 2.32; S, 5.30. Found: C, 33.50; H, 3.51; N, 2.28;
S, 5.25. 1H NMR (CD2Cl2, 298 K, 400.16 MHz) δ: 8.28 (d, 8H, JH−H
= 5.2 Hz, Hα), 7.33 (m, 8H, Hβ) (4-Spy); 4.57 (br s, 8H, CH), 3.95
(br s, 8H, CH), 3.79 (br s, 8H, CH), 2.43 (m, 16H, >CH2), 2.06
(m, 4H, >CH2), 1.81 (m, 4H, >CH2), 1.62 (m, 24H, >CH2) (cod).
MS (MALDI-TOF, DIT matrix, CH2 Cl2 ) m/z: 1121
[Ir3(Spy)2(cod)3]+.
Synthesis of [{Rh2(μ-4-Spy)2(cod)2}2{Ir(cod)}2](BF4)2 [(1b)2].
Solid [Ir(cod)(NCCH3)2]BF4 (0.029 g, 0.062 mmol) was added to
an orange suspension of [Rh(μ-4-Spy)(cod)]2 (1) (0.040 g, 0.062
mmol) in CH2Cl2 (10 mL), and the mixture was stirred for 6 h.
Workup as described above for (1a)2 gave the compound as a red
solid. Yield: 0.045 g (70%). Anal. Calcd for C68H88B2F8Ir2N4Rh4S4
(%): C, 39.66; H, 4.30; N, 2.72; S, 6.23. Found: C, 39.48; H, 4.02; N,
2.65; S, 6.08. 1H NMR (CD2Cl2, 298 K, 400.16 MHz) δ: 8.27 (d, 4H,
JH−H = 5.6 Hz, Hα), 8.20 (d, 4H, JH−H = 5.6 Hz, Hα), 7.20 (br s, 8H,
Hβ) (4-Spy); 4.77 (br s, 4H, CH), 4.54 (br s, 4H, CH) (Rh-cod);
4.27 (br s, 8H, CH), 4.00 (br s, 8H, CH) (Rh-cod and Ir-cod);
2.59 (m, 12H, >CH2), 2.48 (m, 16H, >CH2), 1.97 (m, 12H, >CH2),
1.55 (m, 8H, >CH2) (cod). MS (MALDI-TOF, DIT matrix, CH2Cl2)
m/z: 943 [Rh2Ir(Spy)2(cod)3]+.
Synthesis of [Rh(μ-4-Spy)(nbd)]2 (3). [Rh(μ-Cl)(nbd)]2 (0.200
g, 0.434 mmol) and Li(4-Spy), formed in situ by the reaction of 4-
pySH (0.096 g, 0.868 mmol) with n-BuLi (0.6 mL, 0.942 mmol, 1.57
M in hexanes), were reacted in THF (5 mL) for 15 min at 273 K to
give a brown suspension that was stirred for 4 h. The solvent was
removed under vacuum, and the residue was washed with cold
methanol (2 × 3 mL) to give the compound as a brown solid that was
filtered, washed with cold methanol, and dried under vacuum. Yield:
0.190 g (72%). Anal. Calcd for C24H24N2Rh2S2 (%): C, 47.22; H, 3.96;
1
N, 4.59; S, 10.50. Found: C, 47.13; H, 4.01; N, 4.52; S, 10.35. H
NMR (CDCl3, 298 K, 400.16 MHz) δ: 8.31 (dd, 4H, JH−H = 4.7 and
1.6 Hz, Hα), 6.97 (dd, 4H, JH−H = 4.7 and 1.6 Hz, Hβ) (4-Spy); 3.97
(s, 8H, CH), 3.89 (s, 4H, CH), 1.36 (s, 4H, >CH2) (nbd). MS (ESI
+, CH2Cl2) m/z: 805 [Rh3(Spy)2(nbd)3]+ (15%), 611 [Rh2(SpyH)-
(Spy)(nbd)2]+ (100%), 417 [Rh(SpyH)2(nbd)]+ (65%), 306 [Rh-
+
(SpyH)(nbd)] (70%).
Synthesis of [{Rh2(μ-4-Spy)2(cod)2}2{Pd(dppp)}2](OTf)4 [(1c)2].
Solid [Pd(H2O)2(dppp)](OTf)2 (0.027 g, 0.030 mmol) was added to
a CH2Cl2 solution (5 mL) of [Rh(μ-4-Spy)(cod)]2 (1) (0.020 g, 0.030
mmol). After 2 h of stirring, the reaction mixture was filtered,
concentrated to 5 mL under vacuum, and precipitated with n-hexane.
A yellow solid was obtained. Yield: 0.035 g (78%). Anal. Calcd for
C110H116N4Pd2P4Rh4O12F12S8 (%): C, 45.26; H, 4.01; N, 1.92; S, 8.79.
Synthesis of [Rh(μ-4-Spy)(CO)(PPh3)]2 (4). A solution of 4-pySH
(0.045 g, 0.406 mmol) in CH2Cl2 (10 mL) was slowly added to a
solution of [Rh(acac)(CO)(PPh3)] (0.200 g, 0.406 mmol) in CH2Cl2
(10 mL). The solution was stirred for 1 h to give a cloudy orange
solution. The solvent was removed under vacuum, and the residue was
extracted with a diethyl ether/CH2Cl2 (10:1) mixture (2 × 10 mL).
The orange solution was filtered and concentrated under vacuum to
ca. 1 mL. Slow addition of n-hexane (10 mL) and concentration gave a
yellow solid. The precipitation was completed by the addition of n-
hexane and further concentration under vacuum. The yellow-orange
solid was filtered, washed with n-hexane, and dried under vacuum.
Yield: 0.150 g (73%). Anal. Calcd for C48H38N2O2P2Rh2S2 (%): C,
57.27; H, 3.80; N, 2.78; S, 6.37. Found: C, 57.26; H, 3.78; N, 2.66; S,
6.18. 1H NMR (CDCl3, 298 K, 300.13 MHz) δ: 8.39 (br s, 2H), 7.96
(br s, 2H), 7.85 (br s, 2H) (4-Spy); 7.56 (m, 12H), 7.38 (m, 6H), 7.28
(m, 12H) (Ph); 6.70 (br s, 2H, 4-Spy). 31P{1H} NMR (CDCl3, 298 K,
1
Found: C, 45.43; H, 3.98; N, 1.95; S, 8.70. H NMR (CDCl3, 298 K,
250.13 MHz) δ: 8.33 (br s, 8H, Hα) (4-Spy); 7.57 (m, 16H), 7.32 (m,
24H) (Ph); 6.74 (d, 8H, JH−H = 5.0 Hz, Hβ) (4-Spy); 4.67 (br s, 8H,
CH), 3.98 (br s, 8H, CH) (cod); 3.15 (m, 8H, P−CH2−C)
(dppp); 2.56 (br s, 8H, >CH2), 2.36 (br s, 8H, >CH2) (cod); 2.10 (m,
20H) (>CH2 cod + C−CH2−C dppp). 31P{1H} NMR (CDCl3, 298 K,
101.25 MHz) δ: 6.5 (s). HRMS (ESI+, acetone) m/z: 1311.1
[{Rh2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)2]2+ (90%), 823.7
[{Rh2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)]3+ (8%).
Synthesis of [{Rh2(μ-4-Spy)2(cod)2}2{Pt(dppp)}2](OTf)4 [(1d)2].
Solid [Pt(H2O)2(dppp)](OTf)2 (0.029 g, 0.030 mmol) was added to a
CH2Cl2 solution (5 mL) of [Rh(μ-4-Spy)(cod)]2 (1) (0.020 g, 0.030
mmol), and the mixture was stirred for 2 h. Workup as described
above for (1c)2 gave the compound as an orange solid. Yield: 0.039 g
(80%). Anal. Calcd for C110H116N4Pt2P4Rh4O12F12S8: C, 42.67; H,
121.48 MHz) δ: 38.26 (d, JP−Rh = 157.9 Hz). MS (ESI+, CH2Cl2) m/
+
z: 1007 [Rh2(SpyH)(Spy)(CO)2(PPh3)2]
(60%), 615 [Rh-
(SpyH)2(CO)(PPh3)]+ (100%). IR (CH2Cl2) cm−1: ν(CO), 1983 (s).
Synthesis of [{Rh2(μ-4-Spy)2(cod)2}2{Rh(cod)}2](BF4)2 [(1a)2].
Solid [Rh(cod)(NCCH3)2]BF4 (0.041 g, 0.109 mmol) was added to a
suspension of [Rh(μ-4-Spy)(cod)]2 (1) (0.070 g, 0.109 mmol) in
THF (10 mL) to give an orange solution that was stirred for 2 h.
Concentration of the solution to ca. 1 mL and slow addition of n-
hexane (10 mL) gave the compound as a spongy orange solid that was
1
3.78; N, 1.81; S, 8.28. Found: C, 42.81; H, 3.81; N, 1.76; S, 8.19. H
NMR (CD2Cl2, 298 K, 500.13 MHz) δ: 8.28 (d, 8H, JH−H = 5.0 Hz,
Hα) (4-Spy); 7.59 (m, 16H), 7.35 (m, 24H) (Ph); 6.78 (d, 8H, JH−H
=
5.0 Hz, Hβ) (4-Spy); 4.65 (br s, 8H, CH), 4.05 (br s, 8H, CH)
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(cod); 3.21 (m, 8H, P−CH2−C) (dppp); 2.54 (m, 8H, >CH2), 2.40
(br s, 8H, >CH2) (cod); 2.14 (m, 12H) (>CH2 cod + C−CH2−C
dppp); 2.03 (m, 8H, >CH2) (cod). 31P{1H} NMR (CDCl3, 298 K,
101.25 MHz) δ: −14.5 (s, JP−Pt = 2989 Hz). HRMS (ESI+, acetone)
m/z: 1399.1 [{Rh2(Spy)2(cod)2}2{Pt(dppp)}2(OTf)2]2+ (100%),
882.7 [{Rh2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)]3+ (30%).
with complementary occupancy factors [0.59/0.41(2)] including
geometrical restraints.
In the final steps of both structural refinements, clear evidence of
the existence of large solvent-accessible voids and the presence of
highly disordered solvent was observed. All attempts to model these
molecules were unsuccessful. An analysis of the solvent region was
therefore performed using the SQUEEZE program.84 The contribu-
tion of the estimated solvent content to the total structure factors was
calculated and incorporated in further least-squares refinements. A
summary of the crystal data and structure refinement parameters is
reported in Table 1.
Synthesis of [{Ir2(μ-4-Spy)2(cod)2}2{Pd(dppp)}2](OTf)4 [(2c)2].
Solid [Pd(H2O)2(dppp)](OTf)2 (0.026 g, 0.030 mmol) was added to
a CH2Cl2 suspension (5 mL) of [Ir(μ-4-Spy)(cod)]2 (2) (0.025 g,
0.030 mmol), and the mixture was stirred for 2 h. Workup as described
above for (1c)2 gave the compound as an orange solid. Yield: 0.037 g
(75%). Anal. Calcd for C110H116N4Pd2P4Ir4O12F12S8 (%): C, 40.33; H,
1
3.57; N, 1.71; S, 7.83. Found: C, 40.57; H, 3.54; N, 1.70; S, 7.90. H
Table 1. Crystal Data and Structure Refinement
NMR (CDCl3, 298 K, 250.13 MHz) δ: 8.46 (br s, 8H, Hα) (4-Spy);
7.67 (m, 16H), 7.32 (m, 24H) (Ph); 6.78 (br s, 8H, Hβ) (4-Spy); 4.41
(br s, 8H, CH), 3.65 (br s, 8H, CH) (cod); 3.16 (br s, 8H, P−
CH2−C) (dppp); 2.80−1.90 (m, 36H) (>CH2 cod + C−CH2−C
dppp). 31P{1H} NMR (CDCl3, 298 K, 101.25 MHz) δ: 6.5 (s). HRMS
(ESI+, acetone) m/z: 3127.2 [{Ir2(Spy)2(cod)2}2{Pd-
(dppp)}2(OTf)3]+ (1%); 1489.2 [{Ir2(Spy)2(cod)2}2{Pd-
(dppp)}2(OTf)2]2+ (100%); 943.1 [{Ir2(Spy)2(cod)2}2{Pd-
(dppp)}2(OTf)]3+ (5%).
(1a)2
(1d)2
molecular formula
C69H90N4Rh6S4·
2BF4·CH2Cl2·
1.25C6H14
C106H116N4P4Pt2Rh4S4·
4CF3O3S·4CH2Cl2·
7C4H10O
formula weight
T (K)
2073.39
150
3954.79
100
λ (Å)
0.6934
0.73071
crystal system
space group
a (Å)
monoclinic
C2/c
monoclinic
P21/n
Synthesis of [{Ir2(μ-4-Spy)2(cod)2}2{Pt(dppp)}2](OTf)4 [(2d)2].
Solid [Pt(H2O)2(dppp)](OTf)2 (0.023 g, 0.020 mmol) was added to a
CH2Cl2 suspension (5 mL) of [Ir(μ-4-Spy)(cod)]2 (2) (0.020 g, 0.020
mmol), and the mixture was stirred for 2 h. Workup as described
above for (1c)2 gave the compound as a red solid. Yield: 0.029 mg
(70%). Anal. Calcd for C110H116N4Pt2P4Ir4O12F12S8: C, 38.26; H, 3.38;
39.803(4)
16.5686(16)
28.098(3)
115.516(2)
16723(3)
8
14.4510(9)
18.3763(11)
27.5849(17)
90.8530(10)
7324.5(8)
2
b (Å)
c (Å)
β (deg)
V (Å3)
1
N, 1.62; S, 7.43. Found: C, 37.95; H, 3.34; N, 1.68; S, 7.50. H NMR
(CDCl3, 298 K, 250.13 MHz) δ: 8.50 (d, 8H, JH−H = 2.5 Hz, Hα) (4-
Spy); 7.68−7.34 (m, 40H) (Ph); 6.83 (d, 8H, JH−H = 5.0 Hz, Hβ) (4-
Spy); 4.41 (br, 8H, CH), 3.68 (m, 8H, CH) (cod); 3.27 (m, 8H,
P−CH2−C) (dppp); 2.43 (br, 16H, >CH2) (cod); 2.01 (br m, 20H)
(>CH2 cod + C−CH2−C dppp). 31P{1H} NMR (CDCl3, 298 K,
101.25 MHz) δ: −14.9 (s, JP−Pt = 3054 Hz). HRMS (ESI+, acetone)
m/z: 3303.4 [{Ir2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)3]+ (1%); 1577.7
[{Ir2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)2]2+ (50%); 1002.1
[{Ir2(Spy)2(cod)2}2{Pd(dppp)}2(OTf)]3+ (15%).
Z
μ (mm−1
)
1.174
2.729
Dcalc (g/cm3)
1.647
1.793
F(000)
8356
3988
crystal dimensions (mm)
0.01 × 0.03 ×
0.05 × 0.07 × 0.08
0.08
Tmin/Tmax
0.627/1
0.598/0.746
47211/16801
0.0458
collected/unique reflections 50004/11966
Rint
0.1101
Crystal Structure Determination of (1a)2 and (1d)2. Data for
(1a)2 were collected at 150(1) K using a Bruker SMART APEXII
CCD diffractometer at station 9.8 of the SRS Daresbury Laboratory.
Radiation was monochromatized with a silicon (111) crystal (λ =
0.69340 Å). X-ray diffraction data for (1d)2 were collected at 100(2) K
with graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) on
a Bruker SMART APEX CCD diffractometer. In both cases, ω narrow
rotation (0.3°) scans were used, and the measured intensities were
integrated and corrected for the absorption effect with the programs
SAINT-PLUS72 and SADABS.73 Structures were solved by direct
methods with SHELXS-97.74,75 Refinement was carried out by full-
matrix least-squares on F2 for all data with SHELXL-97.76 All hydrogen
atoms were calculated and refined using a riding model. The PARST
program77,78 was used in the geometrical analysis of the complexes.
Although several crystals were tested, in all cases the data for (1a)2
showed broad reflections with generally low intensity, most probably
because of quick loss of solvent for these samples. The eventual data
collected prevented a proper conventional least-squares refinement but
allowed the appropriate identification of the metallocyclic skeleton of
the molecule. Similar situations have been described for other related
macromolecular complexes where big cavities contain very labile and/
or disordered solvent molecules.79−83 The limited quality of the crystal
data for (1a)2 did not allow a conventional refinement of all non-
hydrogen atoms including anisotropic thermal parameters (ADPs).
The atoms of the counterions (found to be disordered) were refined
with isotropic thermal parameters, and a common thermal parameter
was used for the fluorine atoms; geometrical restraints for both the B−
F bond lengths and F−B−F angles were also applied. Moreover, some
additional restraints in ADPs were defined for some bonds of cod
ligands to ensure fulfillment of the Hirshfeld test. Finally, one of the
pyridine rings was found to be disordered; atoms of this group were
included in the model in two sets of positions and isotropically refined
data/restraints/parameters
11966/188/783
0.1028
16801/2/755
0.0480
a
R1 [I > 2σ(I)]
b
wR2 (all data)
0.3229
0.1336
a
b
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {[∑w(Fo2 − Fc2)2]/[∑w(Fo )2]}1/2
2
RESULTS AND DISCUSSION
Synthesis of the Dinuclear Rhodium and Iridium
■
Ditopic Metalloligands [M(μ-4-Spy)(diolef)]2. The syn-
thesis of bimetallic metalloligands containing pyridine-4-
thiolato ligands was readily accomplished following two
procedures described in the literature by our group. The first
one43 makes use of the lithium salt Li(4-Spy), which was
prepared in situ by reaction of 4-pySH with n-BuLi in THF
(method A). As shown in Scheme 1, the reaction of Li(4-Spy)
with the compounds [M(μ-Cl)(cod)]2 in a 2:1 molar ratio led
to the formation of the thiolate-bridged complexes [M(μ-4-
Spy)(cod)]2 [M = Rh (1), Ir (2)], which were isolated as air-
sensitive orange-brown (1) and yellow-brown (2) solids in
good yields. While compound 1 is soluble in most of the
common organic solvents, the iridium derivative 2 shows
limited solubility in all of them. Compound 1 was obtained in
similar yield by an alternative method45 involving direct
protonation of the methoxide bridging ligands in the complex
[Rh(μ-OMe)(cod)]2 by 4-pySH in dichloromethane (method
B).
The binuclear compounds 1 and 2 were characterized by
elemental analysis, mass spectrometry (ESI+), and NMR
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1H NMR spectrum was not resolved even at 193 K, which
points to a low-energy ring inversion process.
Scheme 1. Preparation of Dinuclear Thiolate-Bridged
Rhodium and Iridium Metalloligands
A dirhodium compound analogous to 1 but containing 2,5-
norbornadiene ligands was also synthesized. [Rh(μ-Spy)-
(nbd)]2 (3) was obtained from [Rh(μ-Cl)(nbd)]2 and Li(4-
Spy) as a brown solid in good yield (Scheme 1). Its
characterization by elemental analysis, NMR spectroscopy,
and mass spectrometry confirmed its analogy with compound
1
1. In fact, its H NMR spectrum also evidenced a fluxional
behavior that renders equivalent the CH and CH protons of
the two nbd ligands.
Treatment of the mononuclear complex [Rh(acac)(CO)-
(PPh3)] with 1 equiv of 4-pySH in dichloromethane gave a
deep-orange solution from which the dinuclear compound
[Rh(μ-4-Spy)(CO)(PPh3)]2 (4) was isolated as a yellow-
orange solid in good yield. Complex 4 was characterized by
elemental analysis, mass spectrometry, and IR and NMR
spectroscopies. The dinuclear formulation of compound 4
relies on the ESI+ mass spectrum, which showed a peak at m/z
1007 corresponding to the protonated molecular cation
[Rh2(SpyH)(Spy)(CO)2(PPh3)2]+.
1
The H NMR spectrum of 4 in CDCl3 also featured broad
resonances, although in this case the pyridine-4-thiolato ligands
were not equivalent and showed four resonances at 8.39, 7.96,
7.85, and 6.70 ppm. The 31P{1H} NMR spectrum was in
accordance with the equivalence of the two triphenylphosphine
ligands because only a doublet due to the coupling with the
rhodium nucleus was observed (1JP−Rh = 158 Hz). The
inequivalence of the bridging ligands suggests a dinuclear
structure with a cis disposition of the bulky triphenylphosphine
ligands. Most probably, the thiolato ligands display an anti
conformation with the endo substituent at the side of the
molecule with the small carbonyl ligands, as is usually found in
related complexes.45
General Strategy for Self-Assembly Reactions. Once
prepared and fully characterized, the bimetallic metalloligands
described above were used to design self-assembled metal-
lomacrocycles. The thiolate-bridged dinuclear compounds
feature two peripheral pyridine nitrogen donor atoms that are
available for coordination to suitable metal fragments. However,
in view of the lack of conformational rigidity of this family of
compounds, different possibilities of self-assembly could be
envisaged depending on the relative disposition of the pyridine
rings (Figure 1). This feature provides highly flexible linkages
for the design of supramolecular assemblies.
While the syn-exo isomer could yield discrete metallomacro-
cycles as a result of its combination with metal building blocks
having two available coordination sites at 180°, acceptor units
having two coordination positions at 90° should be necessary in
order to get a discrete assembly in the case of the syn-endo
isomer, which displays an almost linear orientation of the
pyridine fragments. The anti isomer, however, has the
possibility of forming discrete species either by combination
with 90° or 180° acidic metal fragments. Nevertheless, it has to
be considered that the disposition of the donor moieties in
these metalloligands does not rule out the formation of self-
assembled polymeric species such as infinite chains or
networks.
spectroscopy. The MS (ESI+) spectrum of 1 in CH2Cl2
displayed a peak at m/z 643 corresponding to the dinuclear
protonated species [Rh2(SpyH)(Spy)(cod)2]+ that supports
the formation of the desired compound. In spite of numerous
attempts [ESI(+), FAB(+), and MALDI-TOF in different
solvents], mass spectrometry did not provide confirmation of
the nuclearity of compound 2. However, satisfactory mass
spectra were obtained when the dinuclear iridium compound
was a constituent of the supramolecular assemblies that will be
described later on.
1
The room-temperature H NMR spectra of both 1 and
freshly prepared 2 (in CD2Cl2 and C6D6, respectively) showed
the expected signals for the α and β protons of the pyridine
rings as well as those attributable to the CH and >CH2
protons of the 1,5-cyclooctadiene ligand, which were observed
as a set of broad resonances. The CH protons were observed
as single resonances at 4.45 and 4.12 ppm for 1 and 2,
respectively. The two resonances at 2.46 and 2.01 for 1 and
2.01 and 1.52 for 2 were assigned to the nonequivalent protons
within each of the >CH2 groups (exo and endo protons). The
straightforward pattern is indicative of the high symmetry of the
obtained species. This simplicity could be also found in the
13C{1H} NMR spectrum of 1 (the spectrum of 2 could not be
registered because of its low solubility), where apart from the
three resonances assigned to the pyridine carbons, only one
doublet for the olefinic CH groups (81.5 ppm, JC−Rh = 11.7
Hz) and a single resonance for the >CH2 carbons (31.6 ppm)
were observed for the 1,5-cyclooctadiene ligands. The features
1
of the H NMR spectrum suggest a fluxional behavior derived
from an open-book structure resulting from the μ-(1:2-κ2S)
coordination mode of the two pyridine-4-thiolato ligands with a
syn disposition. In fact, inversion of the nonplanar Rh2S2 ring
accounts for the equivalence of all the olefinic CH protons
and carbons at room temperature.43,45,85−87 Interestingly, a
number of thiolate-bridged dinuclear rhodium and iridium
complexes containing cyclooctadiene ligands display a syn-endo
conformation in the solid state and exhibit dynamic behavior
similar to that found for complex 1.45,86−89 Unfortunately, the
Although the choice of a metal-containing acceptor with an
adequate angle between the vacant positions may be decisive
for the control of the reactivity at the metal site, the nature of
the final products will depend on their thermodynamic
stabilities, since it is known that self-assembly is a
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Scheme 2. Self-Assembly of Hexanuclear Rhodium and
Iridium Metallomacrocycles
Figure 1. Different isomers arising from the relative disposition of the
pyridine rings in the thiolate-bridged dinuclear metalloligands.
thermodynamically controlled process. As we have pointed out
above, we chose two different types of acceptor building blocks,
namely, [M(diolef)(CH3CN)2]+ (diolef = cod; M = Rh, Ir) and
[M(H2O)2(dppp)]2+ (M = Pd, Pt), where two adjacent
coordination positions are blocked by bidentate ligands in
order to ensure an angle of 90° between the acidic sites.
Self-Assembly Reactions Involving [M(μ-Spy)(cod)]2
[M = Rh (1), Ir (2)] Metalloligands and [M(diolef)-
(CH3CN)2]+ [diolef = cod, nbd; M = Rh (a), Ir (b)]
Acceptor Units. The bimetallic pyridine-4-thiolate-bridged
compounds [M(μ-Spy)(cod)]2 [M = Rh (1), Ir (2)] were
found to undergo self-assembly with both of the solvent-
stabilized species [M(cod)(NCCH3)2]+ [M = Rh (a), Ir (b)] in
dichloromethane at room temperature to give exclusively the
rectangular hexanuclear metallomacrocycles (1a)2, (1b)2, and
(2b)2, as shown in Scheme 2. After completion of the reactions
[2 h for (1a)2 and (1b)2 and 12 h for (2b)2], the species were
obtained as solids in moderate to good yields (60−90%) and
characterized by elemental analysis, mass spectrometry (ESI+
or MALDI), and NMR spectroscopy. In addition, single crystals
of compound (1a)2 were grown by slow diffusion of hexane
into a dichloromethane solution of the complex at 258 K and
were further characterized by X-ray diffraction analysis.
A molecular representation of the cation of (1a)2 is depicted
in Figure 2, and selected structural parameters are summarized
in Table 2. The rhodium atoms of both bimetallic [Rh(μ-4-
SPy)(cod)]2 fragments display a slightly distorted square-planar
geometry resulting from the coordination of sulfur atoms of
two pyridine-4-thiolato ligands and a cod molecule chelated
through the two olefinic bonds. Similar acute S−Rh−S angles
[in the range 79.49(17)−80.68(15)°] and trans angles S−Rh−
G (where G is the centroid of an olefinic CC bond) close to
180° [167.4(6)−177.0(6)°] are observed. The rhodium atoms
are slightly displaced out of their coordination mean plane
[Rh(1), 0.111(1); Rh(2), 0.074(1); Rh(3), 0.008(2); Rh(4),
0.114(2) Å], evidencing the distortion from an ideal square-
planar conformation, as previously observed in related thiolate-
bridged Rh(I) complexes.47 The central Rh2S2 cores are folded,
as indicated by the hinge angles between the two rhodium
coordination planes [78.1(2) and 75.4(3)° for the Rh(1)−
S(2)−Rh(2)−S(4) and Rh(3)−S(1)−Rh(4)−S(3) bimetallic
fragments, respectively]. Long intermetallic distances of
2.924(3) and 2.965(3) Å are found, excluding metal−metal
Figure 2. Molecular structure of the cation of (1a)2 drawn at the 40%
probability level. For clarity, hydrogen atoms and the minor
component of the disordered pyridine ring have been omitted.
interactions. Both the dihedral angles and interatomic distances
nicely agree with values reported for the related compounds
[Rh(μ-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzenethiolato)-
(cod)]2 [73.85° and 2.9595(3) Å],90 [{Rh(cod)}2(μ-S,S-
EtSNS)]OTf [EtSNS = EtNC(S)Ph2PNPPh2C(S)NEt]
(77.56° and 2.942 Å),91 and [Rh(μ2-methylthiolato)(cod)]2
(75.86° and 2.947 Å).89
The bimetallic metalloligands with a bent (anti) arrangement
coordinate to the Rh(cod) fragments, giving rise to hexanuclear
metallomacrocycles exhibiting an unusual alternating disposi-
tion of bi- and monometallic corners. The anti disposition of
the thiolato ligands in the dinuclear rhodium corners contrasts
with the syn disposition observed in the parent dinuclear
thiolate-bridged building block (see above). As the syn−anti
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a
Table 2. Selected Bond Lengths and Angles for (1a)2
bond
length (Å)
angle
size (deg)
angle
size (deg)
Rh(1)−S(2)
Rh(1)−S(4)
Rh(2)−S(2)
Rh(2)−S(4)
Rh(3)−S(1)
Rh(3)−S(3)
Rh(4)−S(1)
Rh(4)−S(3)
Rh(5)−N(1)
Rh(5)−N(2)
Rh(6)−N(3)
Rh(6)−N(4)
mean Rh−G
2.380(5)
2.366(5)
2.387(5)
2.366(4)
2.377(6)
2.384(5)
2.383(5)
2.366(5)
2.105(13)
2.151(10)
2.094(12)
2.047(13)
2.017(6)
S(2)−Rh(1)−S(4)
S(2)−Rh(1)−G(1)
S(2)−Rh(1)−G(2)
S(4)−Rh(1)−G(1)
S(4)−Rh(1)−G(2)
G(1)−Rh(1)−G(2)
S(2)−Rh(2)−S(4)
S(2)−Rh(2)−G(3)
S(2)−Rh(2)−G(4)
S(4)−Rh(2)−G(3)
S(4)−Rh(2)−G(4)
G(3)−Rh(2)−G(4)
N(1)−Rh(5)−N(2)
N(1)−Rh(5)−G(5)
N(1)−Rh(5)−G(6)
N(2)−Rh(5)−G(5)
N(2)−Rh(5)−G(6)
G(5)−Rh(5)−G(6)
80.68(15)
167.4(6)
101.7(7)
88.7(5)
S(1)−Rh(3)−S(3)
S(1)−Rh(3)−G(7)
S(1)−Rh(3)−G(8)
S(3)−Rh(3)−G(7)
S(3)−Rh(3)−G(8)
G(7)−Rh(3)−G(8)
S(1)−Rh(4)−S(3)
S(1)−Rh(4)−G(9)
S(1)−Rh(4)−G(10)
S(3)−Rh(4)−G(9)
S(3)−Rh(4)−G(10)
G(9)−Rh(4)−G(10)
N(3)−Rh(6)−N(4)
N(3)−Rh(6)−G(11)
N(3)−Rh(6)−G(12)
N(4)−Rh(6)−G(11)
N(4)−Rh(6)−G(12)
G(11)−Rh(6)−G(12)
79.49(17)
176.6(7)
92.7(7)
102.0(9)
172.0(8)
85.9(11)
79.71(15)
92.9(8)
174.8(6)
88.3(8)
80.55(15)
101.1(5)
170.1(5)
177.0(6)
91.1(6)
167.6(7)
172.6(6)
98.9(6)
86.9(8)
88.5(9)
88.4(4)
88.3(4)
177.2(5)
90.6(6)
178.0(5)
91.9(5)
93.5(5)
91.8(6)
176.8(6)
87.6(7)
178.1(6)
88.1(6)
a
G(n) represents the centroid of the nth olefinic bond among the cod ligands.
interconversion cannot be explained by inversion of the
nonplanar Rh2S2 ring, the formation of the metallomacrocycles
should involve a sulfur inversion. This can occur either by
breaking of a Rh−S bond (dissociative mechanism) or through
a planar transition state in which the S atom is sp2-hybridized
(nondissociative mechanism).52
The Rh(5) and Rh(6) metal centers at the mononuclear
corners also display square-planar coordination that is less
distorted than for the metal atoms of the bimetallic fragments
[out-of-plane distances of 0.008(1) and 0.001(2) Å for Rh(5)
and Rh(6), respectively]. The N(1)−Rh(5)−N(2) and N(3)−
Rh(6)−N(4) angles, which are very close to 90°, generate a
rectangular molecule core whose dimensions can be roughly
estimated from the Rh(5)···S(1)···Rh(6)···S(4) distances as
6.641(3) Å × 9.613(4) Å (Figure 3). The mean plane of the
metallomacrocycle, defined by Rh(5), Rh(6), sulfur, and
nitrogen atoms, is almost parallel to the bc crystallographic
plane.
The conformational geometry, with pyridine-4-thiolato
ligands as intermetallic linkers, causes the rhodium atoms of
the bimetallic fragments to be placed above and below this
mean plane, with the bulkiest cod ligands being located in the
outer part of the metallomacrocycle. Apparently, no steric
impediment seems to hinder the accessibility to the metal-
lomacrocyclic cavity. Along the a axis, the structure shows the
presence of pairs of molecules with the metallomacrocycles in a
parallel disposition but twisted 90° with respect to each other
(Figure 4). The minimal distances between Rh atoms within a
pair and between pairs are 7.668(2) and 7.212(2) Å,
respectively.
Interestingly, the coordination chemistry of the complexes
[M(μ-4-Spy)(cod)]2 that results in the formation of the
macrocyclic species contrasts with that of the related dinuclear
thiophenolato (SPh)-bridged complexes [M(μ-SPh)(cod)]2
(M = Rh, Ir). The latter reacted with solvent-stabilized cationic
[M(cod)L2]+ fragments to give cationic trinuclear aggregates
[M3(μ-SPh)2(cod)3]+ that are formed by a triangular arrange-
ment of metal atoms capped on each side by two triply bridging
phenylthio ligands.43 These species showed outstanding
stability, and in fact, related trinuclear ions corresponding to
halves of the self-assembled species were observed in the mass
spectra of the three macrocyclic compounds (1a)2, (1b)2, and
(2b)2, namely, [Rh3(Spy)2(cod)3]+ (m/z 853), [Rh2Ir-
(Spy)2(cod)3]+ (m/z 943) and [Ir3(Spy)2(cod)3]+ (m/z
1221), respectively.
1
On the other hand, the room-temperature H NMR spectra
of the obtained compounds (Figures S1−S6 in the Supporting
Information) were in agreement with the existence of a single
species that undergoes a dynamic process in solution. Indeed,
the metallomacrocycles [{M2(μ-4-Spy)2(cod)2}2{M′(cod)}2]2+
(M = M′= Rh [(1a)2]; M = Rh, M′ = Ir [(1b)2]; M = M′ = Ir
[(2b)2]) are fluxional as evidenced by a variable-temperature
1
(VT) NMR study. The H NMR spectrum of (1a)2 at 218 K
(Figure 5 bottom) is in agreement with the C2h symmetry of
the structure found in the solid state. Thus, the two sets of
resonances at 8.12/6.64 and 8.08/7.52 ppm correspond to the
two types of 4-Spy ligands in the metallomacrocycle having exo
and endo dispositions in the dinuclear rhodium subunit. The
Figure 3. Schematic view of the rectangular molecular core of (1a)2.
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Figure 4. Molecular packing of (1a)2 along the crystallographic a and b axes. To properly show the cavity, counterions and solvent have been
omitted. Different colors are used to identify pairs of molecules with overlapping metallomacrocycles.
1
Figure 5. Low-field region of the H NMR spectra (CD2Cl2) of metallomacrocycle (1a)2 at 298 K (top) and 218 K (bottom).
olefinic protons of the cod ligands show five resonances, one of
them with double the intensity of the others, which were
unambiguously identified by means of the 1H−1H COSY
spectrum at 218 K (Figure S5 in the Supporting Information).
Thus, the expected four resonances for the two olefinic bonds
of the cod ligands in the dinuclear subunit were observed at
4.80/3.85 and 4.68/4.37 ppm. In addition, the signals at 3.93
and 3.85 ppm, which showed no coupling, correspond to the
cod ligands of the Rh(cod) units bonded to the pyridine
fragments.
allowed the identification of the CH resonances of the cod
ligand in the dinuclear subunit at 4.79 and 4.18 ppm through
the observation of proximity cross-peaks with the signal at 7.20
ppm that corresponds to the β protons of the 4-Spy ligands. In
addition, exchange cross-peaks between the two CH
resonances were observed, which indicates that the fluxional
process makes the two protons of the same olefinic bond
equivalent. This process also renders equivalent the olefinic
protons of the cod ligands in the Rh(cod) units bonded to
pyridine, which were observed at 3.97 ppm.
In contrast, the spectrum at 298 K (Figure 5 top) is
deceptively simple and shows equivalent 4-Spy ligands and only
three resonances (8H each) for the CH protons of the cod
ligands. The 1H−1H NOESY spectrum (Figure S6 in the
Supporting Information) was particularly informative because it
As has been pointed out above, inversion of the nonplanar
Rh2S2 ring in dinuclear complexes having thiolato ligands as
bridges is a common phenomenon that is responsible for their
fluxional behavior. In this case, this process would account for
the pattern of resonances observed at room temperature.
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However, the ring-flipping process results not only in the
exchange of the thiolato ligands with exo and endo disposition
but also in the movement of the bulky cod ligands toward the
inner part of the metallomacrocycle. Thus, this process requires
the concerted motion of the metallomacrocycle in order to
allow the rotation about the C−S bonds just for relocating the
cod ligands in the outside part of the metallomacrocycle. For
that reason, breaking of the Rh−N bonds in order to assist this
process should not be ruled out. Interestingly then, the
existence of an equilibrium between the supramolecular species
and their corresponding building blocks seems to be
responsible for this dynamic behavior.
Scheme 3. Self-Assembly of Hexanuclear [M4M′2]
Metallomacrocycles (M = Rh, Ir; M′ = Pd, Pt)
The 1H NMR spectrum of the compound [{Ir2(μ-4-
Spy)2(cod)2}2{Ir(cod)}2]2+ [(2b)2] at room temperature is
very similar to that described for the [Rh6] species, which
suggests a similar fluxional behavior for this compound.
However, in this case the fluxional process could not be frozen
at low temperature, precluding further investigation.
The synthesis of metallomacrocycles containing different
diolefin ligands, as for example [{Rh2(μ-4-Spy)2(cod)2}2{Rh-
(nbd)}2]2+, was unsuccessful. Thus, even though the reaction of
[Rh(μ-4-Spy)(cod)]2 (1) with the metal fragment [Rh(nbd)-
(NCCH3)2]+ resulted in the formation of [Rh6] metallomacro-
cycles, the self-assembly took place in a nonselective way
because at least four different species were observed in the
aromatic region of the 1H NMR spectrum, probably as a
consequence of scrambling of metal fragments having different
diolefin ligands (cod and nbd) between the different sites of the
metallomacrocyclic framework. In fact, in addition to the
species [Rh3(Spy)2(cod)2(nbd)]+ at m/z 837, the ESI+ mass
spectrum showed the cationic fragment [Rh2(SpyH)(Spy)-
(cod)(nbd)]+ at m/z 627, which supports the scrambling
process.
Self-Assembly Reactions Involving [M(μ-Spy)(cod)]2
[M = Rh (1), Ir (2)] Metalloligands and [M(H2O)2(dppp)]2+
[M = Pd (c), Pt (d)] Acceptor Units. Interestingly, our
attempts to synthesize heterometallic metallomacrocycles using
cis-chelated palladium(II) or platinum(II) complexes as
acceptor building blocks allowed us to obtain the targeted
species. As shown in Scheme 3, treatment of [M(μ-4-
Spy)(cod)]2 [M = Rh (1), Ir (2)] with the square-planar
compounds [M(H2O)2(dppp)](OTf)2 [M = Pd (c), Pt (d)] in
a 1:1 molar ratio in dichloromethane at room temperature
allowed the preparation of the series of hexanuclear [Rh4Pd2],
[Rh4Pt2], [Ir4Pd2], and [Ir4Pt2] metallocycles (1c)2, (1d)2,
(2c)2, and (2d)2, respectively, which were isolated as yellow-
orange solids in good yields.
1
Figure 6. H NMR spectrum (298 K, CD2Cl2) of the metallomacro-
cycle [{Rh2(μ-4-Spy)2(cod)2}2{Pt(dppp)}2](OTf)4 [(1d)2].
Because of the presence of a diphosphine in the acceptor
fragment, monitoring of the reaction solution by 31P{1H} NMR
spectrometry was very helpful to confirm the formation of the
targeted heteronuclear assembly in each case. After completion
of the reaction (ca. 2 h), the 31P{1H} NMR spectra displayed a
singlet for the palladium macrocycles (1c)2 and (2c)2 and a
singlet, with its concomitant satellites, for the platinum species
(1d)2 and (2d)2. The upfield shift of the 31P signals together
displayed only one signal each for the α and β protons of the
pyridine groups and two broad resonances (8H each) for the
CH protons of the cod ligands. The observed pattern is
indicative of fluxional behavior similar to that described for the
rhodium and iridium metallomacrocycles. However, in this
particular case, the spectra registered in CD2Cl2 down to 208 K
showed a large number of resonances that could not be safely
interpreted.
1
with the significant decrease in the value of the JP−Pt coupling
constant evidenced the coordination of the pyridine rings to
either the palladium or platinum centers.
The formation of [{M2(μ-4-Spy)2(cod)2}2{M′(dppp)}2]-
(OTf)4 supramolecules was further supported by high-
resolution ESI+ mass spectrometry. The acetone mass spectra
of the compounds showed peaks due to successive loss of
triflate anions, in contrast with the assemblies described above,
where the hexanuclear metallomacrocycles remained intact. For
Analogously to the [{M2(μ-4-Spy)2(cod)2}2{M′(cod)}2]2+
1
(M, M′ = Rh, Ir) species described above, the H NMR
spectra at 298 K for the assemblies containing palladium or
platinum were deceptively simple. As can be seen in Figure 6
for compound (1d)2 as a representative example, the spectrum
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example, the mass spectrum of the compound [{Ir2(μ-4-
Spy)2(cod)2}2{Pd(dppp)}2](OTf)4 [(2c)2] (Figure 7) displays
Figure 8. Molecular structure of the cation of (1d)2. For clarity, only
the ipso carbon atoms of the phenyl groups are represented. Primed
atoms are related to the nonprimed ones through the symmetry
operation 1 − x, −y, −z.
a
Table 3. Selected Bond Lengths and Angles for (1d)2
Bond Lengths (Å)
Rh(1)−S(1′)
Rh(1)−S(2)
Rh(1)−G(1)
Rh(1)−G(2)
Pt(1)−P(1)
Pt(1)−P(2)
2.3707(17) Rh(2)−S(1′)
2.3781(14) Rh(2)−S(2)
2.3474(16)
2.3688(17)
2.013(7)
2.027(7)
2.088(4)
2.109(4)
2.018(6)
Rh(2)−G(3)
Rh(2)−G(4)
Figure 7. ESI-MS spectrum of [{Ir2(μ-4-Spy)2(cod)2}2{Pd(dppp)}2]-
(OTf)4 [(2c)2].
2.030(7)
2.2631(14) Pt(1)−N(1)
2.2628(15) Pt(1)−N(2)
Bond Angles (deg)
peaks at m/z 1489.2 and 943.1 that correspond to [(2c)2 −
2OTf]2+ and [(2c)2 − 3OTf]3+, respectively. The doubly
charged fragment [(2c)2 − 2OTf]2+ (Figure 7) and its
analogues with (1c)2, (1d)2, and (2d)2 (Figures S8−S10 in
the Supporting Information) gave rise to the most intense
signals, and no superimposition of smaller species with the
same value of m/z was observed after the analysis of the isotope
patterns. In addition, it is worth pointing out that the
satisfactory mass spectra of the iridium metallomacrocycles
(2c)2 and (2d)2 confirm the dinuclear formulation of the
iridium metalloligand [Ir(μ-4-Spy)(cod)]2 (2), whose limited
solubility had precluded a complete characterization.
Furthermore, the characterization of this family of com-
pounds was complemented with an X-ray diffraction study of a
single crystal of (1d)2 grown by slow diffusion of diethyl ether
into a dichloromethane solution of the compound at 253 K. As
featured in Figure 8, the crystal structure shows a square-shaped
macrocyclic assembly containing [Rh(μ-4-Spy)(cod)]2 binu-
clear ligands and Pt(dppp) groups located at alternating corners
of the cationic hexametallic unit. The whole molecule
resembles the molecular structure observed for (1a)2, where
the two “Rh(cod)” corners in (1a)2 have been substituted by
the “Pt(dppp)” groups (Figure S7 in the Supporting
Information). The asymmetric unit of (1a)2 contains half of
the molecule, which can be expanded via the inversion
symmetry operation.
S(1′)−Rh(1)−
79.52(5)
S(1′)−Rh(2)−
80.18(5)
90.1(2)
S(2)
S(2)
S(1′)−Rh(1)−
90.9(2)
S(1′)−Rh(2)−
G(1)
G(3)
S(1′)−Rh(1)−
175.8(2)
S(1′)−Rh(2)−
169.7(2)
G(2)
G(4)
S(2)−Rh(1)−G(1) 170.3(2)
S(2)−Rh(1)−G(2) 102.3(2)
S(2)−Rh(2)−G(3) 170.2(2)
S(2)−Rh(2)−G(4) 101.7(2)
G(1)−Rh(1)−
87.3(3)
G(3)−Rh(2)−
87.5(3)
G(2)
G(4)
P(1)−Pt(1)−P(2)
P(1)−Pt(1)−N(1)
P(1)−Pt(1)−N(2)
93.22(5)
89.46(12)
174.85(13)
P(2)−Pt(1)−N(1)
P(2)−Pt(1)−N(2)
N(1)−Pt(1)−N(2)
176.82(13)
91.92(13)
85.40(17)
a
G(1), G(2), G(3), and G(4) represent the centroids of the C(11)−
C(12), C(15)−C(16), C(19)−C(20), and C(23)−C(24) olefinic
bonds, respectively.
ability of this nonsymmetric bimetallic unit as a rigid building
block to control self-assembly.
In fact, coordination of two “Pt(dppp)” fragments through
the nitrogen atoms of the 4-Spy moieties gives rise to a
heterometallomacrocycle with alternating Rh2 and Pt corners.
The observed Pt−N bond lengths agree with those reported for
the related complexes [(4,4′-bipyridyl)4{Pt(dppp)}4](OTf)8,70
[(dipyridyldibenzotetraaza[14]annulene)2{Pt(dppp)}2]-
(OTf)4,92 [L14{Pt(dppp)}4](OTf)8 [L1 = 2-(3′-(1-methox-
ycarbonylethylcarbamoyl)-(4,4′)-bipyridinyl-3-carbonyl)-
aminopropionic acid methyl ester],83 [(N,N′-bis(3,5-dimethyl-
4-pyridinyl)-4-ethoxy-2,6-pyridinedicarboxamide)2{Pt-
(dppp)}2](OTf)4,93 [L22{Pt(dppp)}2](OTf)4 [L2 = bis(μ2-
3,11-dimethyl-5,13-bis((pyridin-4-yl)-1,9-diazatetracyclo-
[7.7.1.02,7.010,15]heptadeca-2,4,6,10,12,14-hexene],94 and [{Pd-
(η3-2-Me-C3H4)(PPh2py)2}2{Pt(dppp)}2](OTf)6.31 The
An analysis of the geometrical parameters of the binuclear
ligand revealed interatomic bond distances and angles
(summarized in Table 3), a dihedral angle between the mean
rhodium coordination planes [74.01(11)°], and a Rh···Rh
interatomic distance [2.9871(8) Å] very similar to those
previously observed in (1a)2. This fact points out the potential
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square-planar configuration of the platinum atoms is achieved
by the coordination of two nitrogen atoms of pyridine-4-
thiolate units and the phosphorus atoms of a chelating dppp
ligand, with P(1)−Pt(1)−N(2) and P(2)−Pt(1)−N(2) angles
of 89.46(12) and 91.92(13)°, respectively, which are very close
to the ideal cis angle value of 90°. Substitution of cod with
dppp seems to hardly affect to the macrocyclic core dimensions,
which are 6.6354(16) Å × 9.6200(15) Å for this compound.
On the other hand, the bite angle of the bidentate chelate
dppp is close to those reported in the literature for M(dppp)
fragments. The six-membered Pt(1)−P(1)−C(27)−C(28)−
1
C(29)−P(2) metallocycle adopts a C4 chair conformation [Q
= 0.640(5) Å, Θ = 13.8(4)°, φ = −173(2)°].95 Within this
arrangement, π···π interactions between the equatorial phenyl
rings of the diphosphine and the pyridine rings are observed
(Figure 9 and Table S1 in the Supporting Information).
Figure 10. Packing diagram for (1d)2. For simplicity, hydrogen atoms,
counterions, and solvent molecules have been omitted.
A potential catalytic application of the diolefin-based
metallomacrocycles is olefin hydroformylation.47,96 However,
under syngas (H2/CO) pressure and an excess of phosphine
ligand, the diolefin rhodium catalyst precursors are readily
transformed into the corresponding CO/PPh3 derivatives. In
order to explore the stability of the metallocycles based on
“Rh(CO)(PPh3)” metal fragments, self-assembly reactions
involving the metalloligand [Rh(μ-4-Spy)(CO)(PPh3)]2 (4)
were carried out. The reaction of 4 with [Rh(cod)(NCCH3)2]-
BF4 (a) in a 1:1 molar ratio in CH2Cl2 gave an orange-brown
crude product that was isolated after the addition of diethyl
ether. Interestingly, in contrast to what was observed for the
previously described metallomacrocycles, the NMR spectra of
this material indicated the presence of a mixture of self-
assembled species with a clear predominance of one of them.
Figure 9. Schematic representation of the π··· π interactions in (1d)2.
For clarity, carbon atoms of the cod fragments have been omitted.
Primed atoms are related to the nonprimed ones through the
symmetry operation 1 − x, −y, −z.
1
Thus, the H NMR spectrum (Figure S11 in the Supporting
Information) showed four intense sharp doublets that indicated
the equivalence of pyridines into pairs, while the 31P{1H} NMR
spectrum (Figure S12 in the Supporting Information) displayed
as the most intense resonance a doublet (1JP−Rh = 129 Hz), in
accordance with the equivalence of the four phosphorus nuclei.
The packing arrangement of (1d)2 is very different than that
observed in (1a)2, as it shows columnar stacking along the a
axis with perfect overlay of the metallomacrocycles (Figure 10).
Self-Assembly Reactions Involving [Rh(μ-4-Spy)-
(nbd)]2 (3) and [Rh(μ-4-Spy)(CO)(PPh3)]2 (4). In contrast
with [Rh(μ-4-Spy)(cod)]2, the dinuclear compound [Rh(μ-4-
Spy)(nbd)]2 (3) was not an effective building block.
Monitoring of the reaction of 3 with [Rh(nbd)(NCCH3)2]+
in CD2Cl2 evidenced the formation of the metallomacrocycle
[{Rh2(μ-4-Spy)2(nbd)2}2{Rh(nbd)}2]2+ which was identified
by the set of characteristic resonances for the α and β protons
of the pyridine-4-thiolato ligands: four doublets at 8.22, 8.18,
7.08, and 6.90 ppm (1JH−H ≈ 6 Hz). However, we could not
isolate a well-defined product in the solid state, and after several
attempts, we were able to obtain only orange solids with poorly
defined NMR spectra. Most probably, this fact could be a
consequence of the lability of the formed assembly, which is in
agreement with the stronger π-acceptor character of the 2,5-
norbornadiene ligands compared with 1,5-cyclooctadiene,
which in turn reduces the electron density on the peripheral
nitrogen donor atoms, thereby decreasing their coordinating
ability.
1
In addition, the H−1H NOESY spectrum showed proximity
cross-peaks between one of the pyridine β-protons and a
phenyl group of triphenylphosphine. Since metalloligand 4 can
adopt different structures depending on the relative disposition
of the PPh3 and CO ligands, four different isomeric
metallocycles can be envisaged, including two cis−cis ones
(C2h and Cs symmetry) and two trans−trans ones (C1 and C2
symmetry). The NMR data strongly suggest that the major
species from the 4 + a self-assembly should be the cis−cis
isomer with C2h symmetry (represented in Figure 11), which
reinforces the proposed cis disposition of the PPh3/CO ligands
in compound 4.
CONCLUSIONS
■
The dinuclear complexes [M(4-Spy)(cod)]2 (M = Rh, Ir)
supported by bridging pyridine-4-thiolato ligands have been
proved to be effective ditopic building blocks for the
construction of new supramolecular architectures. The two
nucleophilic nitrogen atoms of the terminal pyridine groups
allow these compounds to self-assemble with suitable acceptor
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ACKNOWLEDGMENTS
■
Financial support for this work was provided by the Ministerio
́
de Economia y Competitividad (MINECO/FEDER) of Spain
(Projects CTQ2010-15221 and CTQ2012-31335), Diputacion
General de Aragon (Group E07), and Fondo Social Europeo.
́
́
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The related dinuclear complexes [Rh(4-Spy)(nbd)]2 and
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[M(4-Spy)(cod)]2 (M = Rh, Ir). The metallomacrocycles
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could be related to the stronger π-acceptor character of ndb
compared to cod, which reduces the coordination ability of the
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ASSOCIATED CONTENT
* Supporting Information
■
S
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X-ray crystallographic files in CIF format for the structure
determination of metallomacrocycles (1a)2 and (1d)2; NMR
spectra of (1a)2 and (4a)2; ESI-MS spectra of (1c)2, (1d)2, and
(2d)2; and geometrical parameters of the π···π interactions in
(1d)2. This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: montse.ferrer@qi.ub.es (M.F.).
*E-mail: perez@unizar.es (J.J.P.-T.).
■
(29) Yao, L. Y.; Qin, L.; Xie, T. Z.; Li, Y. Z.; Yu, S. Y. Inorg. Chem.
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Notes
The authors declare no competing financial interest.
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