New rhodium(I) supramolecular structures containing pyridyl and bipyridyl ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.08.014

The use of dimeric [RhCl(CO)₂]₂ as acceptor unit in the construction of mono-, bi- and three-dimensional metallosupramolecular structures is reported. The reaction of the dimer with the alkynylgold complex [Au(C{triple bond, long}CC<

Full text of DOI:10.1016/j.jorganchem.2009.08.014

Journal of Organometallic Chemistry 694 (2009) 3951–3957
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New rhodium(I) supramolecular structures containing pyridyl and bipyridyl ligands
a
a
b
Laura Rodríguez a, , Montserrat Ferrer , Oriol Rossell , Silverio Coco
*
a Departament de Química Inorgànica, Universitat de Barcelona, c/ Martí i Franquès 1-11, 08028 Barcelona, Spain
b IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2009
Received in revised form 7 August 2009
Accepted 10 August 2009
Available online 14 August 2009
The use of dimeric [RhCl(CO)2]2 as acceptor unit in the construction of mono-, bi- and three-dimensional
metallosupramolecular structures is reported.
The reaction of the dimer with the alkynylgold complex [Au(C„CC5H4N)(CNC6H4O(O)CC6H4OC10H21)]
resulted in the mononuclear rhodium complex 1, through an unexpected transfer of the isonitrile ligand
from the gold to the rhodium centres.
The reaction of the linear unit [RhCl(CO)2]2(
phosphino)butane (dppb) yielded the simultaneous formation of both metallomacrocycles [RhCl(CO)
(dppb)]2 (4) and {[RhCl(CO)]2( -dppb)2 (5). The use of a diphosphine with smaller bite
-4,40-bipy)}2(
angle, 1,10-bis-(diphenylphosphino)methane, (dppm) formed the three-dimensional {[RhCl(CO)]2
-4,40-bipy)}2(
-dppm)4 complex (6) that incorporates four diphosphine units connecting two
[RhCl(CO)2]2( -bipy) linear edges. PM3 semi-empirical method has been used to calculate the optimised
geometry of compound 6.
l
-4,40-bipy) (3) with the diphosphine 1,4-bis(diphenyl-
Keywords:
Rhodium(I)
Diphosphine
Supramolecular chemistry
Gold(I)
l
l
(l
l
l
Bipyridine
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
We report herein the synthesis of new mono-, bi- and three-
dimensional rhodium complexes via self-assembly reactions
involving the [RhCl(CO)2]2 dimer. The use of this metallic carbonyl
dimer as acceptor unit in self-assembly reactions is here reported
for the first time.
The self-assembly of finite structures via the application of the
directional bonding approach has become a very topical field of re-
search. The use of transition metal centres and coordination bonds
has been proved to be an efficient method to obtain a great variety
of discrete molecular architectures with different shapes and sizes
that depends on the wide range of the species involved in the
assembly process [1–12].
2. Experimental
2.1. General
Square-planar Pd(II) and Pt(II) complexes have been commonly
used to prepare metallosupramolecules which contain square or
near orthogonal angles in their geometry [13–22]. However, other
metals have also been used in these reactions. In particular, Rh(I)
and Ir(I) units have been explored in the synthesis of bi- [23–27]
and three-dimensional compounds [28,29] and they are of great
interest due to their potential catalytic activity and luminescent
behaviour, that could be very useful in host–guest studies [30–35].
Although diverse donor bridging linkers have been employed in
the construction of supramolecular architectures, the use of bipyr-
idyl-based ligands as organic edges has been proved to be very
convenient due to the ability of N-donating ligands to coordinate
to metal centres. It is interesting to remark that phosphorus donor
linkers, in contrast with nitrogen donor groups, are not very com-
mon and only a limited number of metallomacrocycles and poly-
mers have been reported [22].
All manipulations were performed under prepurified N2 using
standard Schlenk techniques. All solvents were distilled from
appropriate drying agents. Compounds [RhCl(CO)2]2 [35], 1,10-
bis-diphenylphosphinomethane (dppm) [36], 1,4-bis(diphenyl-
phosphino)butane (dppb) [36], CNC6H4O(O)CC6H4OC10H21-p [37],
[AuCl(tht)] [38], 4-ethynylpyridine [39], [Au(C„Cpy)(CNC6H4O
(O)CC6H4OC10H21)] [40] and [PPh4][Au(acac)2] [41] were synthes-
ised as described previously. Compound 4,40-bipyridine (Avocado,
98%) was used as received.
2.2. Measurements
Infrared spectra were recorded on an FT-IR 520 Nicolet spec-
trophotometer. 31P{1H} NMR (d(85% H3PO4) = 0.0 ppm), and 1H
NMR (d(TMS) = 0.0 ppm) spectra were obtained on a Bruker DXR
250, Varian Inova 300 and Varian Mercury 400 spectrometers.
Elemental analyses of C, H and N were carried out at the Serveis
Científico-Tècnics of the Universitat de Barcelona. ESI-MS and FAB
* Corresponding author. Tel.: +34 934031136; fax: +34 934907725.
E-mail address: laura.rodriguez@qi.ub.es (L. Rodríguez).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.014

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L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
mass spectra were recorded on a LC/MSD-TOF spectrometer and
on a Fisons VG Quattro spectrometer at the Universitat de Barce-
lona. Microscopy studies were carried out using a Leica DMRB
microscope provided with a Mettler FP82HT hot stage and a Met-
1H NMR (298 K, CDCl3): 8.94 (d, J(H–H) = 6.8 Hz, 4H, H -pyr),
a
7.71 (d, 4H, Hb-pyr). FAB(+) m/z: 547.3 (M+H+, Calc.: 547.1), 369.0
(M–Rh(CO)2Cl + H2O, Calc.: 369.0), 157.1 (4,40-bipy + H+, Calc.:
157.1). IR (KBr, cmꢀ1): 2098 vs, 2013 vs,
m(C„O); 1612 s,
tler FP90 central processor, at a heating rate of 10 °C minꢀ1
.
m(C„N). Anal. Calc.: C, 30.84; H, 1.47; N, 5.14. Found: C, 30.86;
H, 1.50; N, 5.17.
2.2.1. Molecular modelling and semi-empirical calculations
3.4. Synthesis of [RhCl(CO)]2(l l-dppb)2 (5)
-4,40-bipy)(
Electronic structure was calculated with PM3 semi-empirical
methods in structures previously optimised with MM+ molecular
mechanics method, both methods included in the software pack-
age Spartan’04 V1.0.0.
A dichloromethane solution (15 ml) of dppb (31 mg, 0.08 mmol)
was added to a solution (20 ml) of [RhCl(CO)2]( -bipy) (40 mg,
l
0.08 mmol) in the same solvent. After 1 h of stirring the orange
solution turned orange. The solution was concentrated to ca. 4 ml
and hexane (10 ml) was added. The obtained red solid was filtered,
washed with hexane and vacuum dried. Yield: 10%.
3. Synthesis and characterisation
3.1. Synthesis of [RhCl(CO)2(CNC6H4O(O)CC6H4OC10H21)] (1)
31P NMR (298 K, CDCl3): 38.6 ppm (1J(Rh–P) = 158 Hz). 1H NMR
(298 K, CDCl3): 9.14 (s, br, 8H, H -pyr), 7.74–7.28 (m, 48H, Ph+H -pyr),
a
a
2.57–2.42 (m, br, 8H, P-CH2–CH2–), 1.77–1.63 (m, br, 8H, P-CH2–
CH2). ESI-MS(+) m/z: 1803.2 (M–CO + H+, Calc.: 1803.0), 1747.2
(M–3CO + H+, Calc.: 1746.9) and 1719.1 (M–4CO + H+, Calc.:
1719.0). Anal. Calc.: C, 52.37; H, 4.18; N, 3.05. Found: C, 52.39; H,
4.19; N, 3.08.
3.1.1. Method A
A dichloromethane solution (8 ml) of [Au(C„CC5H4N)(CNC6H4-
O(O)CC6H4OC10H21)] (40 mg, 0.06 mmol) was added to a solution
(8 ml) of [RhCl(CO)2]2 (12 mg, 0.03 mmol) in the same solvent.
After 1 h of stirring the dark orange suspension was concentrated
to dryness and the violet solid residue was dissolved in the mini-
mum quantity of acetone and kept at ꢀ10 °C for 2 h. A dark purple
solid was obtained in 45% yield.
3.5. Synthesis of ([RhCl(CO)]2(l l-dppm)4 (6)
-4,40-bipy))2(
A dichloromethane solution (15 ml) of dppm (28 mg, 0.08
mmol) was added to a solution (20 ml) of [RhCl(CO)2]( -bipy)
l
3.1.2. Method B
(40 mg, 0.08 mmol) in the same solvent. After 1 h of stirring the or-
ange solution turned bright yellow. The solution was concentrated
to ca. 4 ml and hexane (10 ml) was added. The obtained pale or-
ange solid was filtered, washed with hexane and vacuum dried.
Yield: 80%.
A dichloromethane solution (8 ml) of CNC6H4O(O)CC6H4OC10
-
H21-p (78 mg, 0.21 mmol) was added to a solution (10 ml) of
[RhCl(CO)2]2 (40 mg, 0.10 mmol) in the same solvent. After
30 min of stirring the yellow solution became dark orange. The
solution was concentrated to dryness and the solid residue was
dissolved in the minimum quantity of acetone and kept at
ꢀ10 °C for 2 h. A dark purple solid was obtained in 40% yield.
1H NMR (298 K, CDCl3): 8.11 (d, J(H–H) = 9.0 Hz, 2H, (O)C–
C6H4–O), 7.57 (d, J(H–H) = 8.9 Hz, 2H, CN–C6H4–O), 7.33 (d, 2H,
CN–C6H4–O), 6.97 (d, 2H, (O)C–C6H4–O), 4.04 (t, 2H, J(H–
H) = 6.4 Hz, 2H, CH2–O–C6H4), 1.86–0.87 (m, 19H, C9H19). FAB(+)
m/z: 576.0 (M+H+, Calc.: 575.9), 477.0 (M–C7H15, Calc.: 476.9). IR
31P NMR (298K, CDCl3): 19.5 ppm (1J(Rh–P) = 121 Hz). 1H NMR
(298 K, CDCl3): 8.83 (d, J(H–H) = 8.4 Hz, 8H, H -pyr), 7.63–7.38 (m,
a
88H, Ph+Hb-pyr), 3.95–3.91 (m, br, 8H, P-CH2-P). ESI-MS(+) m/z:
2131.1 (M-dppm + H+, Calc.: 2131.1), 1047.0 ([RhCl(CO)(4,40-bi-
py)]2(
IR (KBr, cmꢀ1): 2093 s, 2062 s, 1982 vs,
(C„N). Anal. Calc.: C, 59.20; H, 4.14; N, 2.23. Found: C, 59.25;
l
-dppm) + H2O, Calc.: 1047.1), 803.5 (M–3Clꢀ, Calc.: 803.5).
m
(C„O); 1635 s, 1616 s,
m
(KBr, cmꢀ1): 2959 s, 2922 s, 2852 s
2012 m, 1999 s, 1967 s, (Rh–C„O), 1735 s
m
(C–H); 2168 s,
m(C„N);
H, 4.17; N, 2.26.
m
m(O–C„O). Anal. Calc.
C, 54.23; H, 5.43; N, 2.43. Found: C, 54.28; H, 5.48; N, 2.48.
4. Results and discussion
4.1. Use of [RhCl(CO)2]2 as building block in self-assembly reactions
3.2. Synthesis of [RhCl(CO)2(NC5H4C„CH)] (2)
In order to obtain a Rh/Au heterometallic compound (Fig. 1),
[RhCl(CO)2]2 was reacted with the [Au(C„CC5H4N)(CNC6H4O(O)C-
C6H4OC10H21)] gold complex, in a 1:2 molar ratio in CH2Cl2
solution.
The resulting violet compound was spectroscopically character-
ised. The IR spectrum shows the presence of a strong C„N band
and the bands corresponding to the carbonyl ligands coordinated
to the rhodium metal atom and those of the carboxylic group of
A dichloromethane solution (5 ml) of 4-ethynylpyridine (53 mg,
0.52 mmol) was added to a solution (5 ml) of [RhCl(CO)2]2 (100 mg,
0.26 mmol) in the same solvent. After 1 h of stirring at room tem-
perature the resulting orange solution was concentrated to ca. 2 ml
and hexane (8 ml) was added. An orange solid was obtained, fil-
tered, washed with hexane, and vacuum dried. Yield: 90%.
1H NMR (298 K, CDCl3): 8.65 (d, J(H–H) = 6.5 Hz, 2H, H -pyr),
a
7.43 (d, 2H, Hb-pyr), 3.45 (s, 1H, C„CH). FAB(+) m/z: 301.0 (M+H+,
Calc.: 300.5), 243.6 (M–2 CO, Calc.: 243.5). IR (KBr, cmꢀ1): 3217
the isonitrile ligand. The expected m(C„C) and m(C„N) vibration
bands were not observed by this technique.
m,
m(C–H); 2112 m, m(C„C); 2088 vs, 2074 s, 2017 vs, 1995 s,
The recorded 1H NMR spectrum of the compound shows four
distorted doublets attributed to the aromatic hydrogens of the
isonitrile rings in the range 8.11–6.97 ppm. The first methylene
m(C„O). Anal. Calc. C, 36.44; H, 1.68; N, 4.72. Found: C, 36.49; H,
1.69; N, 4.70.
3.3. Synthesis of [RhCl(CO)2]2(l
-4,40-bipy) (3)
O
C
Cl
Solid 4,40-bipyridine (40 mg, 0.26 mmol) was added to a dichlo-
romethane solution (10 ml) of [RhCl(CO)2]2 (100 mg, 0.26 mmol).
After 1 h of stirring at room temperature a red solid was obtained
that was filtered, washed with hexane and vacuum dried. Yield:
85%.
OC Rh
N
Au
CN
O
O
C10H21
CO
Fig. 1. Drawing of the attempted Rh/Au heterometallic compound.

L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
3953
proton of the alkoxy chain of the isonitrile group appears as a trip-
let at 4.04 ppm and the remaining alkoxy chain hydrogens appear
in the range 1.86–0.87 ppm. The peaks corresponding to the pyri-
dine protons were not displayed by this technique.
These results are indicative of the lack of the alkynylpyridine
group in the obtained compound and agree with the formation of
a rhodium complex containing only the corresponding isonitrile li-
gand directly coordinated to the rhodium metal atom (compound
1). The IR spectrum of the residue of the reaction shows a C„C
stretch band at 2126 cmꢀ1 that evidences the presence of the
[Au(C„CC5H4N)]n gold polymer as secondary product (see Scheme
1, method A).
complex, the process is clean, since no traces of metallic gold were
deposited in this reaction.
It is interesting to notice that to our knowledge, there is no
precedent in the literature for the reaction where an isonitrile li-
gand is transferred from a gold(I) to a rhodium(I) metal atom.
The mesogenic behaviour of the free isonitrile ligand has been
previously studied and has been seen to display smectic A and
nematic mesophases [37]. The isonitrile gold(I) derivative also pre-
sents liquid crystalline properties (SmA mesophase) [40]. For this
reason the potential properties of compound 1 as a liquid crystal
were carefully investigated. Unfortunately, the rhodium isonitrile
complex decomposes upon heating at 355 °C without melting
The FAB(+)-MS spectrum detected peaks at m/z 576.0 (M+H+)
and 477.0 (M–C7H15) that are also indicative of the formation of 1.
In order to check this hypothesis, the isonitrile CNC6H4O(O)C-
C6H4OC10H21-p was allowed to react with the [RhCl(CO)2]2 dimer
in CH2Cl2 solution at room temperature and the formation of com-
pound 1 was observed (Scheme 1, method B).
The results show that the obtention of 1 following method A
takes place by means of an unexpected isonitrile transfer reaction
where the organic ligand is transferred from the gold compound to
the rhodium(I) derivative. This reaction seems to be favoured by
the formation of the [Au(C„CC5H4N)]n polymer as secondary
product.
Similar processes involving alkynyl ligands and gold(I) metal
atoms are known but still scarce [42–45]. In particular, the trans-
metallation reaction where an ethynylpyridine group is transferred
from a gold(I) metal centre to a rhenium (I) complex, has been pre-
viously reported by us and being favoured by the formation of the
same [Au(C„CC5H4N)]n polymer [45]. As observed for the rhenium
and consequently compound
1 does not exhibit mesogenic
behaviour.
This high decomposition temperature suggests very strong
intermolecular interactions in the solid state, which is not compat-
ible with formation of liquid crystalline assemblies. A similar
behaviour is found in some cis-[RhCl(CO)2(L)] (L = 40-alkoxy-4-stil-
bazole)] [46]. In contrast, the structurally related cyanobyphenyl
complex cis-[RhCl(CO)2(NC-C6H4C6H4OC9H19)] that exhibits rela-
tively low melting temperatures and consequently lower intermo-
lecular interactions than 1, displays a nematic mesophase at 79 °C
[47].
A second attempt of using the [RhCl(CO)2]2 unit in self-assem-
bly processes was explored by means of its reaction with 4-ethyn-
ylpyridine in a 1:2 ratio, in order to obtain 2 (Scheme 2) which was
thought to be an excellent precursor for the synthesis of heterome-
tallic supramolecular complexes.
A red solid was obtained after addition of hexane to the previ-
ously concentrated dichloromethane solution. Evidence for the
Method A
Cl
Cl
O
OC
OC
CO
CO
Rh
Rh
N
Au
C
+
2
CN
O
O
C10H21
Cl
O
C
OC Rh CN
CO
O
N
Au
O
C10H21
+
n
1
Method B
Cl
Cl
O
C
OC
OC
CO
Rh
Rh
+
2
CN
O
O
C10H21
CO
O
Cl
C
OC Rh CN
CO
O
O
C10H21
1
Scheme 1.

3954
L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
CI
Cl
Cl
CO
CO
The great stability of the [Au(C„CC5H4N)]n polymer could be
considered as a possible driving force for the formation of this
insoluble compound in front of the pre-designed heterobimetallic
supramolecular squares.
OC
OC
Rh
Rh
N
H
N
H
+
2
OC Rh
CO
2
Our third attempt to use [RhCl(CO)2]2 as precursor for metallo-
supramolecular species involved its reaction with the 4,40-bipyri-
dine ligand (Scheme 3) to give 3, which was thought to be an
interesting metallosupramolecular edge in self-assembly
processes.
Scheme 2.
proposed structure was obtained from IR, and 1H NMR spectrosco-
pies, FAB-MS spectrometry and elemental analysis. The IR spec-
trum of 2 shows a band at 3217 cmꢀ1 that corresponds to the
presence of a terminal acetylenic proton. There is also observed a
C„C vibration band at 2112 cmꢀ1 that is shifted about 15 cmꢀ1
to higher frequencies with respect to the corresponding free 4-eth-
The 1H NMR spectrum of the obtained dark red solid shows the
H
a
and Hb signals due to the coordinated 4,40-bipyridine ligand
that have shifted 0.2 ppm downfield with respect to the free organ-
ic ligand. IR spectroscopy and FAB-MS(+) spectrometry also con-
firm the formation of the product.
ynylpyridine ligand and the
m(C„O) stretching vibrations from the
Compound 3 was reacted with the diphosphine dppb in an at-
tempt to obtain a bidimensional supramolecular rectangle consti-
tuted by two units of 3 as edges linked by two dppb groups
(compound 5, scheme 4). Both reactants were mixed in dichloro-
methane at room temperature. After 1h of stirring the red reaction
solution turned orange. After concentration under vacuum, hexane
was added to precipitate a solid whose characterisation shows the
presence of a mixture of two different macrocyclic compounds
carbonyl ligands bonded to rhodium are observed between 2088
and 1995 cmꢀ1. The presence of two only
m(C„O) stretching bands
in dichloromethane solution (at 2088 and 2014 cmꢀ1), lead us to
attribute a cis-geometry for 2, according to literature [46].
The 1H NMR spectrum confirms the coordination of the ligand
since the H of the pyridine ring shifted 0.4 ppm downfield relative
a
to the same signals of the free organic ligand. Furthermore, the ter-
minal acetylene protons shifted ca. 0.5 ppm upfield with respect to
the non-coordinated ligand. The incorporation of only one 4-eth-
ynylpyridine group was confirmed by elemental analysis and
FAB-MS mass spectrometry that displays the protonated molecular
peak at m/z 301.0 and the signal corresponding to the loss of the
two carbonyl ligands at m/z 243.6.
This compound is particularly interesting due to the presence of
a potentially removable acetylene proton located at terminal
position that makes compound 2 a good candidate to behave as a
building block for the construction of more complex metallosupra-
molecular structures. Specifically, 2 was assumed to be able to
react with the gold complex (PPh4)[Au(acac)2], according to the
‘‘acac method” [48], yielding heterobimetallic structures where
the gold centre should coordinate to two equivalents of 2 by means
of the formation of Au–C„C bonds. Unfortunately, the latter reac-
tion gave intractable solids that we were not able to characterise.
[RhCl(CO)(dppb)]2 (4) and {[RhCl(CO)]2(l l-dppb)2
-4,40-bipy)}2(
(5) in a 2:1 molar ratio (scheme 4). 31P NMR spectrum in deuter-
ated chloroform displays two doublets centred at 38.5 and
22.5 ppm with Rh–P coupling constants of 158 and 123 Hz attrib-
uted to 4 and 5, respectively. 1H NMR is in agreement with the for-
mation of a mixture of different compounds since two different
sets of signals are obtained for both bipyridine protons and meth-
ylene groups of the diphosphine. One of the bipyridine sets are
attributed to the free 4,40-bipyridine ligand, what is indicative that
this compound precipitates together with both macrocycles. The
H
a
protons of the bipyridine unit of 5 are displayed at 9.14,
0.2 ppm downfield shifted with respect to the precursor 3, whilst
the Hb protons are observed in the same region of the phenyl pro-
tons (7.74–7.28 ppm).
ESI-MS(+) mass spectrometry was very helpful in the identifica-
tion of the resulting compounds of the reaction. Peaks at m/z
1149.1 and 557.4 corresponding to ([RhCl(CO)(dppb)]2–Cl) and
([RhCl(CO)(dppb)]2–2 Cl) evidence the formation of a small macro-
cycle constituted by two RhCl(CO) units connected by two dppb li-
gands as major product (Scheme 4, compound 4). Moreover, peaks
at m/z 1803.2, 1747.2 and 1719.1 are attributable to
Cl
Cl
Cl
Cl
OC
OC
CO
CO
Rh
Rh
+
N
OC Rh
N
N
N
Rh CO
CO
CO
{[RhCl(CO)]2(l l-dppb)2 (5) with the loss of one, three
-4,40-bipy)}2(
3
and four carbonyl ligands. Compound 4 was previously reported in
the literature [49] and recently investigated by Lamb et al. [30,50].
Scheme 3.
CO
Rh
Cl
Cl
+
dppb
OC Rh
CO
N
N
CO
Ph
P
Ph
P
CO
Rh
Cl
CO
Rh
Cl
Ph
Ph
P
CO
Ph
Ph
Ph
Ph
N
N
N
N
P
Rh
Cl
+
+
N
N
+ ...
(CH2)4
(CH2)4
(CH2)4
(CH2)4
CO
Rh
Cl
Cl
Rh
CO
Cl
P
P
P
Rh
CO
Ph
P
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4
5
Scheme 4.

L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
3955
CO
Rh
Cl
Cl
OC Rh
CO
2
+ 4 dppm
N
N
CO
3
Ph
Ph
Ph
Cl
Cl
Ph
P
P
Rh
N
N
Rh
Ph
Ph
CO
P
CO
P
P
Ph
Ph
+
4
CO
CH2
CH2
CH2
CH2
Ph
Ph
Ph
P
CO
CO
Rh
Cl
Ph
N
N
Rh
Cl
Ph
P
P
Ph
Ph
Ph
6
Scheme 5.
The authors demonstrated that this compound presents a high
thermodynamic stability that could be the reason for the favoured
formation of this macrocycle compared with that of 5. The great
stability of this compound made difficult the formation of the de-
sired compound 5 in pure form in the reaction medium and it was
only obtained after several recrystallisation processes.
Hβ,pyr + Ph
In order to test the effect of the bite angle of the diphosphine,
the same reaction was investigated by using dppm instead of dppb
and a more soluble pale orange solid was obtained. Surprisingly,
the characterisation of the solid indicated the formation of the
Hα,pyr
298 K
P-CH2-P
unexpected
(compound 6, scheme 5) with three-dimensional structure which
incorporates four dppm units connecting two [RhCl(CO)]2(
-4,40-
compound
{[RhCl(CO)]2(l l-dppm)4
-4,40-bipy)}2(
l
bipy) edges. In spite of numerous attempts, we were not able to
grow single crystals of 6. However, its proposed structure is
strongly supported spectroscopically. Thus, 1H NMR spectrum re-
corded in deuterated chloroform at 298 K shows only one signal
220 K
for the H of the bipyridine at 8.83, 0.1 ppm upfield shifted with re-
a
9
8
7
6
5
4
3
spect to the precursor 3 (Fig. 2, top). Hb resonance together with
the corresponding to the phenyl protons and are displayed in the
range 7.63–7.38 ppm. 1H NMR integration confirms the incorpora-
δ (ppm)
Fig. 2. 1H NMR spectrum of compound 6 in CDCl3 recorded at 298 K (up) and at
220 K (down).
tion of four dppm in the structure of the compound since the H
a
and the CH2 groups of the diphosphine are observed to be in a
1:1 ratio instead of expected 2:1 for the rectangular bidimensional
complex.
The signal corresponding to the methylene protons of the
diphosphine is unexpectedly broad (298 K) and could be indicative
of a dynamic process that involves the diphosphine ligand.
Interestingly, the 1H NMR spectrum recorded at 220 K shows
the splitting of the broad CH2 signal into two broad peaks centred
at 4.15 and 3.40 ppm (Fig. 2, below) that coalesce into a single band
at ca. 3.90 ppm at room temperature. All these facts are indicative
of the unequivalence of the methylene protons of the carbon
chains. gCOSY-NMR spectroscopy shows cross peaks, that confirm
the vicinity of both unequivalent CH2 protons.
constant is in the same range than the corresponding to two phos-
phorus atoms bonded to a rhodium centre, as the obtained for 4.
The 31P NMR broad doublet recorded at room temperature be-
comes sharp and perfectly defined (1J(Rh–P) = 114 Hz) when the
spectrum is registered at 220 K (Fig. 3). From these results we sug-
gest that the observed broad signals are due to a dynamic process
that involves the coordination of the diphosphines in 6.
Characterisation by IR spectroscopy shows the presence of a un-
ique
lower wavenumbers with respect to the two IR bands recorded
for the [RhCl(CO)2]2(
-4,40-bipy) precursor. This shift is in agree-
ment with a higher retrodonation effect from the rhodium centre
m
(C„O) vibration at 1982 cmꢀ1, shifted 30 and 115 cmꢀ1 to
31P NMR spectrum shows one broad doublet centred at ca.
20 ppm with a Rh–P coupling constant of ca. 120 Hz. This coupling
l

3956
L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
T = 298 K
T = 220 K
Fig. 5. Space filling model of the optimised equilibrium geometry of compound 6.
24
22
20
18
16
14
δ ( ppm)
The symmetry plane delimited by the four rhodium centres
makes equivalent the protons of the methylene units from differ-
ent dppm ligands. This graphical model has been very useful to
understand the unequivalence of the CH2 protons observed in the
1H NMR spectrum since it could be observed that one of the pro-
tons is located outside the cavity and the other one inside.
As could be observed in the space filling model representation
(Fig. 5), compound 6 presents an empty inner cavity that makes
the compound potentially active in molecular recognition pro-
cesses and catalysis. The size of the cavity (5.2 ꢁ 13.9 Å) has been
calculated by means of distances between the opposite atoms of
both edges.
Fig. 3. 31P NMR spectrum of compound 6 in CDCl3 at 298 K (top) and 220 K (down).
to the antibonding molecular orbital of the carbonyl ligand as a
consequence of the loss of one of these ligands when the phospho-
rus coordination occurs.
ESI-MS spectrum was also recorded and peaks at m/z 2131.1
and 803.5 corresponding to {([RhCl(CO)]2(
l-bipy)}2(l-dppm)4–
dppm) and {([RhCl(CO)]2( -bipy)}2( -dppm)4–3Cl), respectively
l
l
were detected. The assignation of these peaks clearly evidences
the formation of 6 (Scheme 5) as the resulting product of the
process.
Preliminary luminescence and molecular calculations studies of
the compound seem to indicate that compound 6 is a good candi-
date to be used as a sensor in host/guest processes.
All these results encourage us to extend our investigations to
other diphosphines or bipyridine bridging units in order to con-
struct new three-dimensional supramolecular assemblies with dif-
ferent inner cavity sizes. The effect of the different bridging ligands
on the nature of the corresponding empty inner cavity should be
studied in order to develop new supramolecular systems that
could be potentially used in luminescence and molecular recogni-
tion applications.
4.2. PM3. and MM+ geometry optimisation
Due to the lack of crystal structure of 6, PM3 and MM+ calcula-
tions were undertaken to optimise the minimum energy geometry
of this complex and visualise its expected shape. The calculated
molecule is shown in Fig. 4.
It is clearly shown that both dppm ligands coordinate to two
rhodium metals forming a three-dimensional structure with one
diphosphine above and the other below the plane determined by
the four rhodium atoms.
5. Conclusions
Carbonyl and chloride ligands and some of the phenyl rings are
expected to be located outside the cavity. Furthermore, the two
pyridine rings of both bipyridines are observed to be twisted
approximately 35°.
The [RhCl(CO)2]2 compound has been used as acceptor in self-
assembly reactions with different pyridine derivatives for the
construction of mono-, bi- and three-dimensional novel rhodium(I)
Fig. 4. Minimum energy geometry calculated for compound 6 (hydrogens are omitted for clarity). Green: rhodium; orange: phosphorous; grey: carbon; blue: nitrogen and
red: oxygen. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

L. Rodríguez et al. / Journal of Organometallic Chemistry 694 (2009) 3951–3957
3957
[16] M. Ferrer, L. Rodríguez, O. Rossell, J. Organomet. Chem. 681 (2003) 158.
[17] K. Suzuki, M. Kawano, M. Fujita, Angew. Chem., Int. Ed. 46 (2007) 2819.
[18] M. Fujita, J. Yazaki, K. Ogura, J. Am. Chem. Soc. 112 (1990) 5645.
[19] M. Fujita, S. Nagao, M. Iida, K. Ogura, J. Am. Chem. Soc. 115 (1993) 1574.
[20] J. Manna, C.J. Kuehl, J.A. Whiteford, P.J. Stang, D.C. Muddiman, S.A. Hofstadler,
R.D. Smith, J. Am. Chem. Soc. 119 (1997) 11611.
[21] K. Onitsuka, S. Yamamoto, S. Takahashi, Angew. Chem., Int. Ed. 38 (1999) 174.
[22] S. Ghosh, P.S. Mukherjee, Organometallics 26 (2007) 3362.
[23] J. Forniés, J. Gómez, E. Lalinde, M.T. Moreno, Chem. Eur. J. 10 (2004) 888.
[24] T. Tonase, H. Takenaka, E. Goto, J. Organomet. Chem. 692 (2007) 175.
[25] S. Liu, G.-L. Wang, G.-X. Jin, Dalton Trans. (2008) 425.
[26] M.C. Álvarez-Vergara, M.A. Casado, M.L. Martín, F.J. Lahoz, L.A. Oro, J.J. Pérez-
Torrente, Organometallics 24 (2005) 5929.
[27] M.A. Casado, J.J. Pérez-Torrente, M.A. Ciriano, F.J. Lahoz, L.A. Oro, Inorg. Chem.
43 (2004) 1558.
[28] J.C. Garrison, M.J. Panzner, P.D. Custer, D. Venkat Reddy, P.L. Rinaldi, C.A.
Tessier, W.J. Youngs, Chem. Commun. (2006) 4644.
[29] Y.-F. Han, W.-G. Jia, Y.-J. Lin, G.-X. Jin, J. Organomet. Chem. 693 (2008) 546.
[30] G. Lamb, M. Clarke, A.M.Z. Slawin, B. Williams, L. Key, Dalton Trans. (2007)
5582.
[31] L.I. Rodríguez, O. Rossell, M. Seco, G. Muller, J. Organomet. Chem. 692 (2007)
851.
derivatives. Attempts to obtain
[RhCl(CO)2(NC5H4C„C)Au(CNC6H4O(O)CC6H4OC10H21)]
a
Rh/Au heterobimetallic
com-
pound, lead to an unexpected isonitrile transfer process of the iso-
nitrile organic ligand from the gold(I) precursor to the rhodium(I)
metal complex giving the unexpected homometallic rhodium
derivative [RhCl(CO)2(CNC6H4O(O)CC6H4OC10H21)] (1). The study
of the mesogenic behaviour of 1 shows that the compound decom-
poses upon heating at 355 °C.
Whilst the reaction of [RhCl(CO)2]2(
allowed the obtention of the three-dimensional derivative
{[RhCl(CO)]2( -bipy)}2( -dppm)4 (6), the reaction with the larger
l-bipy) (3) and dppm has
l
l
dppb conduces to a bi-dimensional rectangular structure, fact that
clearly indicates the influence of the bite angle of the diphosphine
on the structure of the final product of the reaction.
The calculated optimised geometry of 6 has been shown to
present an empty inner cavity that makes the compound poten-
tially useful in molecular recognition and catalytic processes.
[32] I. Angurell, G. Muller, M. Rocamora, O. Rossell, M. Seco, Dalton Trans. (2004)
2450.
[33] N.T. Tran, J.R. Stork, D. Pham, C.J. Chancellor, M.M. Olmstead, J.C. Fettinger, A.L.
Balch, Inorg. Chem. 48 (2007) 7998.
Acknowledgements
[34] J. Poulin, C. Stern, R. Guilard, P.D. Harvey, Photochem. Photobiol. 82 (2006)
171.
[35] S. Rojas, S. Murcia-Mascarós, P. Terreros, J.L. García Fierro, New J. Chem. 25
(2001) 1430.
[36] W. Hewertso, H.R. Watson, J. Chem. Soc. (1962) 1490.
[37] T. Kaharu, R. Ishii, T. Adachi, T. Yoshida, S. Takahashi, J. Mater. Chem. 5 (1995)
687.
[38] R. Usón, A. Laguna, Organomet. Synth. 3 (1986) 324.
[39] L.D. Ciana, A. Haim, J. Heterocycl. Chem. 21 (1984) 607.
[40] M. Ferrer, M. Mounir, L. Rodríguez, O. Rossell, S. Coco, P. Gómez-Sal, A. Martín,
J. Organomet. Chem. 690 (2005) 2200.
We are indebted to the Ministerio de Educación y Ciencia
(Spain) for financial support (Project CTQ2006-02362/BQU). S.C.
thanks the Junta de Castilla y León for support (Project GR169).
Authors also would like to thank Dr. I. Angurell, Dr. R. Bosque
and Prof. G. Muller from the Inorganic Department of the Universi-
tat de Barcelona for fruitful discussions.
References
[41] J. Vicente, M.T. Chicote, Inorg. Synth. 32 (1998) 141.
[42] W.M. Khairul, M.A. Fox, N.N. Zaitseva, M. Gaudio, D.S. Yufit, B.W. Skelton, A.H.
White, J.A.K. Howard, M.I. Bruce, P.J. Low, Dalton Trans. (2009) 610.
[43] M.I. Bruce, M.E. Smith, N.N. Zaitseva, B.W. Skelton, A.H. White, J. Organomet.
Chem. 670 (2003) 170.
[44] A.B. Antonova, M.I. Bruce, B.G. Ellis, M. Gaudio, P.A. Humphrey, M. Jevric, G.
Melino, B.K. Nicholson, G.J. Perkins, B.W. Skelton, B. Stapleton, A.H. White, N.N.
Zaitseva, Chem. Commun. (2004) 960.
[1] C.-L. Chen, J.Y. Zhang, C.-Y. Su, Eur. J. Inorg. Chem. (2007) 2997.
[2] C.J. Jones, Chem. Soc. Rev. 27 (1998) 289.
[3] M. Fujita, Chem. Soc. Rev. 27 (1998) 417.
[4] S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 27 (2000) 853.
[5] B.J. Holliday, C.A. Mirkin, Angew. Chem., Int. Ed. 40 (2001) 2022.
[6] C.A. Schalley, A. Lutzen, M. Albrecht, Chem.- Eur. J. 10 (2004) 1072.
[7] F. Wurthner, C.C. You, C.R. Saha-Moller, Chem. Soc. Rev. 33 (2004) 133.
[8] P. Thanasekaran, R.T. Liao, Y.H. Liu, T. Rajendran, S. Rajagopal, K.L. Lu, Coord.
Chem. Rev. 249 (2005) 1085.
[45] M. Ferrer, L. Rodríguez, O. Rossell, J.C. Lima, P. Gómez-Sal, A. Martín,
Organometallics 23 (2004) 5096.
[9] S. Ghosh, S.R. Batten, D.R. Turner, P.S. Mukherjee, Organometallics 26 (2007) 3252.
[10] B.H. Northrop, D. Chercka, P.J. Stang, Tetrahedron 64 (2008) 11495.
[11] L. Rodríguez, C. Lodeiro, J.C. Lima, R. Crehuet, Inorg. Chem. 47 (2008) 4952.
[12] B.H. Northrop, H.-B. Yang, P.J. Stang, Chem. Commun. (2008) 5896.
[13] M. Fujita, M. Tominaga, A. Hori, B. Therren, Acc. Chem. Res. 38 (2005) 371.
[14] M. Ferrer, A. Gutiérrez, M. Mounir, O. Rossell, E. Ruiz, A. Rang, M. Engeser,
Inorg. Chem. 46 (2007) 3395.
[46] M.A. Esteruelas, E. Sola, L.A. Oro, M.B. Ros, M. Marcos, J.L. Serrano, J.
Organomet. Chem. 387 (1990) 103.
[47] D.W. Bruce, E. Lalinde, P. Styring, D.A. Dunmur, P.M. Maitlis, J. Chem. Soc.,
Chem. Commun. (1986) 581.
[48] J. Vicente, M.T. Chicote, Coord. Chem. Rev. 195 (1999) 1143.
[49] A.R. Sanger, J. Chem. Soc., Chem. Commun. (1975) 893.
[50] G.W. Lamb, M.L. Clarke, A.M.Z. Slawin, B. Williams, Dalton Trans. (2008)
4946.
[15] M. Ferrer, M. Mounir, O. Rossell, E. Ruiz, M.A. Maestro, Inorg. Chem. 42 (2003)
5890.