An approach to bimetallic catalysts by ligand design

Article abstract of DOI:10.1039/c0dt00011f

New diphosphines based on benzofurobenzofuran and dibenzodioxocin backbones, forming exclusively bimetallic complexes were designed and synthesized. Depending on the ligand to metal ratio, face-to-face bimetallic complexes or syn-chloride bridged dimeric

Full text of DOI:10.1039/c0dt00011f

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An approach to bimetallic catalysts by ligand design†
Josep M. Lo´pez-Valbuena, Eduardo C. Escudero-Adan, Jordi Benet-Buchholz, Zoraida Freixa* and
Piet W. N. M. van Leeuwen*
Received 20th February 2010, Accepted 16th July 2010
DOI: 10.1039/c0dt00011f
New diphosphines based on benzofurobenzofuran and dibenzodioxocin backbones, forming
exclusively bimetallic complexes were designed and synthesized. Depending on the ligand to metal
ratio, face-to-face bimetallic complexes or syn-chloride bridged dimeric complexes were formed as main
reaction products. The structures of the rhodium complexes of the new ligands 4, 7, 10, 13, 16 were
established in solution by NMR, IR, and MS spectroscopy. The molecular structures of the
syn-chloride bridged dimeric complexes [Rh2(CO)2(m-Cl)2(4)] (22), [Rh2(CO)2(m-Cl)2(10)] (24), and the
face-to-face bimetallic complexes [Rh(CO)Cl(4)]2 (17), [Rh(CO)Cl(10)]2 (19), and [Rh(CO)Cl(13)]2 (20)
were confirmed by X-ray crystallography. Ligands 4, 7, 10, 13, 16, and SPANphos were tested in
rhodium catalyzed methanol carbonylation at 150 ◦C and 22 bar of CO gas, showing high activities
under catalytic conditions.
is cleaved to yield the monomeric adduct.19,30–32 The bimetallic
Introduction
character of those compounds can be maintained by means of
The study of bimetallic compounds fascinates scientists from
ligands able to coordinate to both centres stabilizing the structure
very different areas. The construction of synthetic analogues
and incorporating the donor group intended for catalysis. There
of metallobiomolecules containing bimetallic centres drove its
are several examples on the use of diphosphines as binucleating
initial development. They have been considered as models to
ligands for such complexes. When the ligand-to-metal ratio is 1 : 2,
mimic the coordination environment of metals at biologically
dimers containing one diphosphine and two bridging halogen ions
active sites in an attempt to reproduce their chemical and/or
were characterized (Fig. 1). These complexes can be described
as “edge sharing dimers” as explained elsewhere.33 One can
distinguish four different isomeric forms, taking into account the
coordination mode of the ligand and the bending angle defined by
the two coordination planes of the metals.
physical properties. Both hetero- and homobimetallic species are
known, which may offer new possibilities for activating organic
and inorganic molecules.1–13
Bimetallic species are interesting entities per se due to their
peculiarities. When the two metallic centres are in close proximity
Complexes of this type require binucleating diphosphines with a
large P–P distance. There are complexes consisting of mixed-metal
assemblies where the diphosphine coordinates in the syn-form,34–36
tetranuclear complexes with two units of halide bridged metal
dimers in syn-form,37,38 and dimetallacrown palladium ethers with
the diphosphine chelating in both anti or syn-forms.39,40 There are
few examples of simple diphosphines capable of forming these
kind of structures. They were reported for a phosphine derivative
of 2-diphenylphosphinobenzoic acid,41 for SPANphos42 (giving
anti-dimeric halide bridged complexes) and more recently for a
triptycene based ligand (which forms bent-syn dimers).43 However,
these diphosphines are also able to form mononuclear trans-
chelating complexes in solution.
When two diphosphines are used to stabilize two metals through
a double bridge, a different type of structure is obtained. The
chemistry of those bimetallic compounds was studied extensively,
especially for ligands based on the small diphosphinomethane
skeleton,22,44–52 but also numerous examples containing larger
backbones are known.53–62 One can distinguish basically three
structures. When in addition to the two mutually trans m-ligands a
metal–metal bond exists the structure is called side-by-side.46,48,63–68
If there is neither a metal–metal bond nor another bridging ligand
apart from the m-diphosphine the structures are described as face-
to-face bimetallic complexes.22,46–62,69 The last possibility involves
structures in which a third ligand bridges the two metals: the so
called A-frame compounds (Fig. 2).46,47,51,70–74
˚
(often less than 5 A apart) they exhibit correlated physicochemical
properties, responsible for the often claimed cooperative effect
between the two metallic centres.2,14–18 Clearly, homogeneous
catalysis could benefit enormously of such systems, as catalysts
with improved efficiency and selectivity, able to promote reactions
that are not possible using a single metal centre, can be envisaged.
Several examples have already been reported in the literature.19–29
As concerns applications, the morphological control of the
active site is a requisite, which can be achieved through the use
of the appropriate binucleating ligand. Often these ligands are
tri- and tetradentates. Representative examples are macrocyclic
frameworks derived from Schiff bases and polyketonate precur-
sors, cyclic polyethers or polyamines.1,9
Homo- and heterobimetallic halogen-bridged dimers are among
the most versatile metal precursors for homogeneous catalysis and
organometallic synthesis, due to their high intrinsic reactivity.
Unfortunately, in the presence of an excess of donor ligands
(as phosphines, frequently used in catalysis) the halogen bridge
Institute of Chemical Research of Catalonia (ICIQ), Avgda. Pa¨ısos
Catalans 16, Tarragona, Spain. E-mail: zfreixa@iciq.es; Fax: 34977920221;
Tel: 34977920200
† Electronic supplementary information (ESI) available: Molecular me-
chanic calculations details and crystallographic data. CCDC reference
numbers 762010–762014. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00011f
8560 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©

Fig. 1 Dimeric diphosphine-bridged structures containing M2X2 core.
Results and discussion
Ligand design
Before addressing the synthesis of the new ligands we wanted to
get structural information on the backbones envisaged. Although
it is tempting to consider that CPK models suffice to deduce
main trends, a measure of the backbone strain needed to locate
the phosphorus atoms not only at the correct distance but also
appropriately oriented requires a quantitative methodology.
Looking for objective ligand comparison we considered the
use of molecular mechanics. The limitations of these type of
calculations for structures involving metals are well known.
Accordingly, we limited its use to the evaluation of the energy
of the ligand fragment at different conformations as a measure
of their tendency to form certain structures (namely bimetallic vs.
monometallic). The nuclearity of the products obtained at certain
ligand-to-metal ratios used depends on the backbone structure
and rigidity.
The conformational search was performed introducing metals
to take into account approximate distances and orientation of the
phosphorus lone pairs, but the energy of the ligand fragment only
in the final conformations is considered for comparison.
The energy of the free ligand in its most stable conformation
was calculated as reference value. As models for compounds
having ligand-to-metal ratio 1 : 1, the energy of the ligands on
a monometallic chelate (RhL) and a bimetallic (Rh2L2) fragment
was evaluated. For alower ligand-to-metalratio(1 : 2) werestricted
the studies to model chloro-bridged dimers, (Rh2Cl2L) which were
the structures relevant for our investigation.
Fig. 2 Bimetallic structures containing mutually trans-diphosphines.
In the past, when working with wide bite angle or rigid P–
P ligands, we claimed occasionally the possible involvement of
bimetallic species as responsible for some of the unusual catalytic
events observed.42,75–77 Unfortunately, the capability of the ligands
under study to also form mononuclear species (in which the
ligand coordinates either trans or in a monodentate manner)
did not allow us to attribute the observed activities exclusively
to bimetallic intermediates. The design of ligands that form
exclusively bimetallic complexes (especially the halogen-bridged
ones) is the current challenge. It is not trivial since they should
contain large, rigid and properly designed backbones.
Recently, when studying the homogeneous catalytic carbonyla-
tion of methanol using SPANphos, we encountered an unprece-
dented reactivity which we attributed to SPANphos stabilized
dinuclear complexes.42,75 Although the ligand was originally con-
ceived as a trans-chelator,78 it forms unique dimeric species when
equimolecular quantities of metal and phosphorus are used. A
possible involvement of the oxygen of the backbone, establishing
a metal–oxygen bond could not be discarded with certainty.
That catalytic example, which still intrigues us, triggered this
research. We thought about a new generation of ligands, in which
the backbone design and rigidity ensures that no monomers can
form. Looking for backbones with the same P–C–C–O–C–O–C–
C–P connectivity created by the bischroman backbone of SPAN-
phos, we decided to explore the potential of benzofurobenzofuran
(BFBF) and dibenzodioxocin (DBDOC) skeletons (Fig. 3).
A schematic representation of the different structures used for
the calculations is presented in Fig. 4.
Fig.
backbones.
3
Bischroman, benzofurobenzofuran and dibenzodioxocin
Fig. 4 Structures used for the molecular mechanics calculations.
Here we report, in addition to ligand design and synthesis, a
series of rhodium complexes with two specific types of structures,
face-to-face bimetallic and syn-dimeric halide bridged complexes.
In particular we are interested in [Rh2(m-Cl)2(CO)2(diphosphine)]
complexes and their use in rhodium catalyzed methanol carbony-
lation.
Calculations were performed on CaCheTM using MM2 as Force
Field.79 The results obtained, presented in Table 1, showed that
an important increase in conformational energy of the ligand is
required to form ML chelating structures (DUligand ~ 15–20 kcal
mol-1). The P–P distance needed for the two phosphorus atoms
˚
to coordinate to the same metal (around 4.4 A) is considerably
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Dalton Trans., 2010, 39, 8560–8574 | 8561
©

Table 1 Conformational energy of the ligands and selected structural
parameters. Molecular mechanics calculations were performed on free
ligands (L), rhodium chelate (RhL), rhodium bimetallic (Rh2L2) and
halogen-bridged rhodium dimeric compounds (Rh2Cl2L). See ESI for
details
Ligand synthesis
Scheme 1 summarizes the synthetic pathways to ligands 4, 7, 10,
13 and 16. Ligands 4, 10, 13 and 16 present Cs symmetry. The C2-
symmetric ligand 7, an isomeric form of ligand 4, has been included
due to its availability (2 and 5 were reported as thermodynamic
and kinetic products of the same reaction81,82). It falls outside the
original design and for this reason it is treated as an exception
along the discussion.
Benzofurobenzofuran-based backbones 2 and 5 were both
synthesized by a Claisen rearrangement of diaryloxybutyne 1 using
aluminium trichloride as a Lewis acid catalyst in the case of 2,83,84
and a Brønsted acid in the presence of N,N-diethylaniline in the
case of 5.81,85 They were brominated with N-bromosuccinimide
(NBS) to obtain dibromo derivatives 3 and 6, which were reacted at
-78 ◦C first with n-BuLi and then with chlorodiphenylphosphine
yielding 4 and 7 in 72 and 62% yield respectively.
U/Kcal P–P
Structure mol-1
Backbone ◦ P–M–P
b
˚
Ligand
distance/A “folding”/ angle/◦
BFBFMe2 4
L
RhL
Rh2L2
-27.9
-8.9
7.26
4.36
7.54
6.64
111.6
101.7
112.4
108.0
—
140.1
178.8
—
a
-26.3
Rh2Cl2L -15.1
BFBFH2 10
DBDOC 13
L
RhL
Rh2L2
-27.7
-8.4
7.31
4.28
7.43
6.63
112.9
101.2
112.1
108.4
—
135.0
176.9
—
a
-26.3
Rh2Cl2L -14.7
L
RhL
Rh2L2
-33.1
-18.4
-31.4
6.95
4.31
7.12
6.54
105.6
98.1
105.6
103.5
—
136.9
176.7
—
a
Interestingly, diphosphine derivative 7 is a C2-symmetric chiral
ligand. Isomeric diphosphines 4 and 7 can be easily distinguished
Rh2Cl2L -21.4
1
by H-NMR spectroscopy. Compound 7 shows a single methyl
TRIPTYCENEc
XANTPHOS
L
RhL
Rh2L2
-35.8
-35.8
-32.6
4.53
4.08
4.74
5.39
120.0
117.6
120.4
121.8
—
signal (d 1.58) for the C(CH3) group on the fused furan rings
whereas compound 4 exhibits two distinct resonances (d 1.60
and d 1.41) for the two different C(CH3) methyl groups. In both
molecules the methyl groups on the aromatic rings are equivalent.
Due to the low yields and long reaction times needed for
the synthesis of the diaryloxybutyne 1 (common intermediate
towards 4 and 7) we explored an alternative strategy to obtain
benzofuro[2,3-b]benzofuran backbones. Acid-catalyzed reaction
between p-cresol and glyoxal afforded 8 in overall yield of 40%
in only one step.86 Compound 8 is analogous to 2 but it does not
contain the methyl groups on the fused furan rings. Dibromo
derivative 9 and the desired diphosphine 10 (50% yield) were
prepared as reported above for analogous derivatives of 2.
Dibenzodioxocin-type backbones 11 and 14 were prepared by
a Friedel–Crafts reaction and intramolecular acetalization of p-
cresol or 4-tert-butylphenol and tetramethoxypropane in trifluo-
roacetic acid, which acts as solvent and catalyst.87 Again, the di-
bromo derivatives 12 and 15 and the corresponding diphosphines
13 and 16 were prepared following the same procedures described
above, with 86% and 66% yield, respectively. Diphosphine 16 was
synthesized to increase solubility under catalytic conditions as
some problems were encountered for ligand 13.
123.6
170.2
—
a
Rh2Cl2L -27.0
L
RhL
Rh2L2
-37.4
-35.1
-28.7
4.15
3.80
4.94
5.03
136.8
135.0
136.2
137.2
—
110.4
167.1
—
a
Rh2Cl2L -24.6
To achieve meaningful energy comparison, after calculating the most stable
conformation of the free ligand (L), the monometallic chelate (RhL), the
bimetallic complex (Rh2L2), and the chloride-bridged dimer (Rh2Cl2L),
the energy of only the ligand fragment is evaluated.a Averaged values of
the parameters measured independently for each ligand in the molecule.
b Averaged value of dihedral angles of the central atoms of the backbone.
An exact definition for each ligand can be found in the supplementary
material. c 1,8-Bis(diisopropylphosphino)-triptycene.
˚
shorter than the one encountered in the free ligands (7–8 A). This
short P–P distance can only be achieved by a deformation of the
ligand. The “folding” of the backbone in such a rigid structure
is responsible for the high energy values obtained (Table 1).
Bimetallic M2L2 type complexes instead, can be formed by a
minimal ligand deformation (DUligand ~ 3 kcal mol-1) as they do
not impose large changes in P–P distances.
Such complexes were modeled with a backbone conformation
close to the one of the free ligand (see distances and backbone
“folding” terms in Table 1).
These calculations also showed that all ligands (except 7) are
also suited for the formation of halogen-bridged dimers in a syn
manner when working at a lower ligand-to-metal ratio. BFBF
and DBDOC based ligands suit the structural (P–P distance and
phosphorus lone pair orientation) requirements to form such
constrained structures.
All the compounds and intermediates 1–16 were characterized
by NMR spectroscopy, elemental analysis and exact mass spec-
trometry.
Coordination studies
The coordination ability of the new ligands towards rhodium
was studied by in situ NMR spectroscopy. Additionally, solid
state analysis by X-ray diffraction was performed when crystalline
samples were obtained from these solutions.
According to these data, monometallic complexes with the
ligand acting as a chelate should not be accessible for BFBF and
DBDOC based ligands, but instead they have a marked preference
to form bimetallic species. In contrast, other wide bite angle
ligands (such as Xantphos80 and the triptycene derived ligands
developed by Gelman) form preferentially monometallic species,
which is in agreement with the compounds known.
Ligand-to-metal ratio 1 : 1. Ligands 4, 7, 10, 13 and 16 were
reacted with [Rh2(m-Cl)2(CO)4] in 2 : 1 molar ratio (ligand-to-metal
ratio of 1 : 1) and the nature of the products obtained was inferred
from in situ 31P-NMR spectroscopy.
Three different species were observed in the 31P-NMR spectrum
of mixtures of ligand 4 with [Rh2(m-Cl)2(CO)4] in a ligand-to-
metal ratio of 1 : 1 (CDCl3). Apart from a small doublet due to
8562 | Dalton Trans., 2010, 39, 8560–8574
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©

Scheme 1 Reaction conditions: (a) K2CO3, acetone; (b) AlCl3, DCM; (c) NBS, DMF; (d) n-BuLi, ClPPh2, THF; (e) N,N-diethylaniline, APTS, reflux,
3h; (f) H2SO4, CH3COOH, H2O, 80 ◦C; (g) CF3COOH.
a residual quantity of the tetracarbonyl intermediate 27, (vide
infra) the main signals present ABX patterns; there is a major one
attributed to compound 17a and a less intense one corresponding
to a minor compound 17b (Table 2). Variable temperature
experiments (CD2Cl2, in the range 298–193 K) showed that the
major signal is independent of the temperature, and the minor
one (less intense in this solvent) broadens at lower temperatures.
Surprisingly, two CO bands were found in the IR spectrum of 17,
(one at 1970 cm-1 and one at 1989 cm-1). The latter, at a rather
high frequency is probably due to 22, originating from the residual
quantity of 27 observed in the NMR spectra (as suggested by the
referees). Between different attempts the ratio of the two signals
varied but we never observed the low-frequency signal only, as
expected for 17. Further analysis on isolated samples are required
for a complete characterization of this compound.
compound 19b (dPA = 24.4 ppm, 2JRh–PA = 132 Hz, 1JPB–PA = 359 Hz,
dPB = 21.8 ppm, 2JRh–PB = 128 Hz, 1JPA–PB = 359 Hz). The main signals
present in the low temperature spectra were simulated assuming
two species in 63/37 ratio (Fig. 5). Some minor peaks with
similar spectroscopic patterns were also visible at this temperature
indicating the presence of more isomers in minor proportions.
The 31P-NMR spectrum of a mixture of ligand 10 with half
an equivalent of [Rh2(m-Cl)2(CO)4] in either CD2Cl2 or CDCl3
was too broad to be assigned. Variable temperature experiments
were performed (CD2Cl2). Already at 273 K a sharp signal
corresponding to an ABX pattern was distinguished (dPA 23.9,
2
1
1JRh–PA = 122 Hz, JPB–PA = 371 Hz; dPB 20.9, JRh–PB = 125 Hz,
2JPA–PB = 371 Hz) on top of several minor signals that could not
be identified. When the temperature was lowered to 193 K, the
original signal was still present as the main species 19a, although
Fig. 5 Variable temperature 31P-NMR spectra. Left: species 19 at 298 K,
193 K and simulation. Right: species 18 at different temperatures.
slightly shifted upfield (dPA = 23.1 ppm, 1JRh–PA = 130 Hz, 2JPB–PA
366 Hz, dPB = 20.6 ppm, JRh–PB = 125 Hz, JPA–PB = 366 Hz).
Additionally, a second set of signals with the same pattern could be
distinguished at this temperature and attributed to a closely related
=
1
2
In the 31P-NMR spectra of complexes 20 and 21, (in both
CD2Cl2 and CDCl3) one major species is observed. It appears as
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 8560–8574 | 8563
©

Table 2 Characterization data of rhodium complexes containing ligand-
described should exhibit Cs symmetry. Thus, in the absence of
signals of free phosphine, the existence of inequivalent phosphorus
atoms is indicative of a bimetallic structure. The large value of the
P–P coupling constant observed in all the cases together with the
carbonyl bands observed in the IR spectra at around 1975 cm-1
are indicative of a trans coordination of two diastereotopic
phosphorus atoms at each rhodium centre.61,88–92
to-metal ratio of 1 (CDCl3, 298 K)
31P-NMR
d/ppm 1JP–Rh/Hz 2JP–P/Hz n(CO)/cm-1
IR
Complex
trans,trans-
23.9
16.6
24.9
19.7
25.4
25.0
23.1
20.6
24.4
21.8
25.7
22.6
26.8
22.5
131
131
128
128
128
128
130
125
132
128
130
128
131
129
366
366
368
368
—
[Rh2(Cl)2(CO)2(4)2] (17a)
The situation when using the C2-symmetric ligand 7 should be
analyzed independently. When this ligand was mixed with half an
equivalent of [Rh2(m-Cl)2(CO)4] in CDCl3, two doublets (d 25.4,
J = 128 Hz; d 25.0, J = 128 Hz) were observed in the 31P-NMR
spectra around 25 ppm. These signals cannot be attributed to an
ABX signal as observed for the other ligands, because variable
temperature experiments (in the range 298–193 K) showed that it
corresponds to a more complicated pattern (Fig. 5). The doublet
at 25.4 ppm which slightly broadens at lower temperatures is
probably due to a species in which the two phosphorus nuclei
are equivalent. A C2-symmetric Pd trans-P bimetallic derivative
of ligand 7 has been observed before by X-ray diffraction.93 The
doublet at higher fields splits into two doublets at 273 K, and
broadens at lower temperatures. Most likely it is another isomer
of a trans-P bimetallic, complex in which the P–P coupling is not
observed due to near synchronicity of the phosphorus nuclei.
To better understand the diversity of species observed with some
ligands it is worth highlighting several structural facts: for ideal-
ized face-to-face (trans-P) [Rh2(CO)2Cl2(L)2] bimetallic complexes
(L = diphosphine), two different, syn and anti, conformers can
be envisaged depending on the relative orientation of the CO
and Cl in both rhodium centers (Scheme 2). Additionally, even
though the two metals show parallel coordination planes, (as has
been observed in all the X-ray structures obtained with ligands
4, 10 and 13, vide infra) there are several conformations that
can be obtained by simultaneous rotation of the coordination
plane of each metal around their hypothetical P–Rh–P and/or
Cl–Rh–CO axes (Fig. 6). Most probably, in solution all these
conformations are in a fast exchange, due to the large size of
these macrocyclic assemblies, but different rotation angles (g and
f, Fig. 6) can be encountered in solid state structures. Additionally,
due to the “folded” structure of the backbones, each ligand can
coordinate to the pair of metals exposing its concave or its convex
1970
1970
trans,trans-
[Rh2(Cl)2(CO)2(4)2] (17b)
trans,trans-
[Rh2(Cl)2(CO)2(7)2] (18)
—
trans,trans-
366
366
359
359
362
354
363
363
[Rh2(Cl)2(CO)2(10)2] (19a)a
1973
trans,trans-
[Rh2(Cl)2(CO)2(10)2] (19b)a
trans,trans-
[Rh2(Cl)2(CO)2(13)2] (20)
1958
1968
trans,trans-
[Rh2(Cl)2(CO)2(16)2] (21)
a CD2Cl2, 193 K.
a sharp ABX pattern with chemical shifts and P–Rh coupling
constants similar to those observed for complexes 17 and 19.
Precipitation handicapped low temperature experiments in the
case of complex 20. For the more soluble complex 21, the spectra
did not change with the temperature, which suggests that these
ligands form exclusively one complex in solution, or the several
isomers are in a fast exchange at the temperature range employed.
Applying this stoichiometry to SPANphos, we obtained exclu-
sively the mononuclear complex trans-[Rh(CO)Cl(SPANphos)].42
Monometallic trans-[Rh(CO)Cl(L)] complexes of the ligands
Scheme 2 Schematic representation of the two types of di-rhodium complexes observed for ligands 4, 7, 10, 13, and 16.
8564 | Dalton Trans., 2010, 39, 8560–8574 This journal is The Royal Society of Chemistry 2010
©

Fig. 6 Different conformations obtained by simultaneous rotation of the two metal coordination planes along their P–Rh–P or X–Rh–X axes.
Fig. 7 Isomeric face-to-face (trans-P) bimetallic complexes possible with Cs symmetric ligands 4, 10, 13 and 16; three different conformers of each isomer
A and B have been depicted, depending on the side (concave or convex) exposed toward the metal centers. From all these structures, only B1 and B3
could eventually display magnetically equivalent phosphorus nuclei in trans-[Rh2(CO)2Cl2L2] face-to-face bimetallic compounds due to their symmetry.
Punctual group of symmetry, and the equivalence–non equivalence of the two phosphorus coordinated to the same rhodium on idealized (g = 90◦, j =
90◦) syn and anti derivatives are indicated.
face, not necessarily in a synchronous manner (Fig. 7). With Cs
symmetric ligands 4, 10, 13 and 16, two different isomers (A and
B in Fig. 7) can be encountered. The interconversion between
them requires the cleavage of the two P–Rh bonds of one of the
ligands to permute their positions and thus these isomers should
be distinguished in solution. Additionally, several conformers can
be envisaged for each isomer (A and B) which interconvert through
concerted rotations around the P–Rh axes (as noticed by the
referees). Some representative examples are depicted in Fig. 7.
According to this description, it is reasonable that in the case
of ligands 4 and 10 two different species were observed at 298
and 273 K respectively, with different intensities. They probably
correspond to the two isomeric bimetallic compounds (A and B).
At lower temperatures the existence of more isomers in equilibrium
is evident in both cases. They are probably different rotational
conformers of the minor isomer (either syn–anti or concave–
convex). The fact that the signal of the major isomer (17a, 19a
and 21) remains sharp along the temperature range studied makes
us discard the existence of an equilibrium between isomers A and
B. We consider that the major isomer exists as a unique conformer,
or as a mixture of several of them in a fast exchange on the NMR
time scale.
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Dalton Trans., 2010, 39, 8560–8574 | 8565
©

◦
˚
Table 3 Selected bond distances (A) and angles ( ) for 17, 19 and 20
In the case of ligand 7 the situation is different. Due to its
C2 symmetry when a face-to-face bimetallic is formed, decoor-
dination of one of the ligands and permutation of their P–Rh
bonds renders the same compound. If the ligand were enantiopure
only one isomeric face-to-face bimetallic could be formed (though
concave–convex conformations are still possible). In our studies,
the ligand is obtained and used as a racemate, so the two enan-
tiomeric compounds and a meso bimetallic are possible (Fig. 8).
17
19
20
Rh(1)–P(1)
Rh(1)–P(2)
P(1)–P(2)
2.3161(3)
2.3349(3)
4.625(3)
2.3056(9)
2.3228(8)
4.577(4)
7.939(4)
8.402(3)
2.3764(8)
1.819(3)
3.810(4)
2.3244(5)
2.3305(5)
4.645(3)
P(1)–P(2A)
7.225(3)
6.952(2)
2.3792(3)
1.8114(11)
3.871(3)
7.405(3)
7.469(3)
2.3911(6)
1.810(2)
2.991(3)
Rh(1)–Rh(1A)
Rh(1)–Cl(1)
Rh(1)–C(1)
Rh(1)–O(2)
Rh(1)–O(3)
P(1)–Rh(1)–P(2)
Cl(1)–Rh(1)–C(1)
5.445(3)
6.063(4)
4.737(4)
167.857(10)
176.46(3)
47.13(0.01)
44.24(0.01)
162.88(3)
177.23(10)
72.44(0.03)
48.17(0.03)
172.594(19)
174.90(8)
74.95(0.02)
68.53(0.02)
a
f
g
a
a As described in Fig. 6.
a distorted square planar environment with two approximately
linear and antiparallel Cl–Rh–CO moieties (anti configuration)
bridged by two diphosphines, 4, 10 and 13 respectively, main-
taining a trans-P,P-coordination for each rhodium atom. The
angles P1–Rh1–P2 and Cl1–Rh1–C1(O) and the P–Rh, Cl–Rh
and Rh–C bond lengths lie within the normal range of trans-
diphosphine complexes.41,61,94,95 All complexes contain parallel
metal coordination planes, but very different torsion angles (see
Table 3). It is remarkable that, as observed by the referees, the
three structures can be described as isomer A in Fig. 7. In
compound 17 the two ligands are coordinated through its concave
side (conformer A1, Fig. 7),‡ but convex sides are exposed to the
core in molecular structures of 19 and 20 (conformer A3, Fig. 7).
Dimeric chloro-bridged compounds. 31P-NMR spectroscopic
analysis of 1 : 1 mixtures of ligands 4, 7, 10, 13 and 16 and [Rh2(m-
Cl)2(CO)4] in CDCl3 showed the immediate formation of two
rhodium complexes (two doublets), one at around 40–45 ppm
(1JRh–P ~ 180 Hz) and a second one at higher fields with smaller
Fig. 8 Diastereoisomeric face-to-face (trans-P) bimetallic complexes
possible with the C2 symmetric ligand 7; top and bottom structures are
enantiomers and the middle one is the meso form. Only one conformer of
each isomer has been depicted.
1
Rh–P coupling constants (d ~ 20 ppm, JRh–P ~ 125 Hz). After
half an hour reacting or after the sample was submitted to a
cycle of vacuum, only the doublet at lower fields was observed.
The bimetallic nature of complexes 17, 19 and 20 was confirmed
by X-ray diffraction (Fig. 9). Selected bond lengths and angles are
listed in Table 3. Their molecular structures confirm that they
all are face-to-face bimetallic structures. The two metals are in
‡ Diffraction data to determine molecular structure of 17 corresponds to
the best out of seven different measured crystals. In all of them a structure
type A1 was observed. Structures type A3 have been obtained when other
metals were used.
Fig. 9 ORTEP-plots (thermal ellipsoids shown at 50% probability levels) of complexes 17, 19 and 20. Non-relevant hydrogen atoms have been omitted
for the sake of clarity.
8566 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©

Scheme 3 Schematic representation of the preparation for rhodium chloride bridge diphosphine dimers.
Table 4 Characterization data of rhodium complexes containing ligand-
This signal, consistent with those published for halogen-bridged
dimeric complexes,35,42,43 was attributed to the dimeric species
[Rh2(m-Cl)2(CO)2(L)] (L = 4, 7, 10, 13, 16). These complexes
show a single band in the carbonyl region of the IR spectra at
~1993 cm-1, in agreement with the values reported for similar
compounds.37,38,42 The doublet initially observed was assigned to
an intermediate species in which the halide bridges are cleaved, but
both rhodium atoms are still coordinated to two carbonyl ligands,
a chloride, and a phosphorus atom of a bridging diphosphine,
[Rh2(Cl)2(CO)4(L)] (L = 4, 7, 10, 13, 16). Indirect evidence on
the nature of these species was obtained through their reactivity
and alternative synthetic pathway. Complexes 27–31 could be
characterized by NMR as unique compounds in solution when
CO was bubbled through a CDCl3 solution of the corresponding
dimers 22–26 for 10 min. Additionally, 27–31 could also be
observed by bubbling CO for 10 min through solutions containing
[Rh2(m-Cl)2(cod)2] (cod = 1,5-cyclooctadiene) and the ligands (via
intermediates 32–36) in a ligand-to-metal ratio of 1 : 2 (Scheme 3).
Compounds 27–31 are only stable in solutions saturated in CO.
Compounds 27–31 were occasionally observed as intermediates
towards compounds 17–21, together with free phosphine. When
the CO atmosphere is substituted by argon they evolve to the
corresponding halogen-bridged dimers 22–26 mentioned before
(Table 4). The presence of a doublet as a unique signal in the
31P-NMR spectra in all the cases except for 23, suggests a syn-
arrangement for all the compounds (Cs symmetry). In the latter,
the equivalence of the two phosphorus nuclei is indicative of
an anti form similar to the one described for SPANphos due
to the C2 symmetry of the ligand.42 (see Scheme 2). 31P-NMR
spectra of an equimolar mixture of ligand 7 and [Rh2(m-Cl)2(CO)4]
shows a much broader signal at around 40 ppm than the other
derivatives. Perhaps in this case “supramolecular” oligomers are
also present due to the large P–P distance of ligand 7. Additionally,
the spectra shows two doublets at 24.9 (1JRh–P = 129.6 Hz), and
to-metal ratio of 0.5
31P-NMR (CDCl3)
Complex
d/ppm 1JP–Rh/Hz IR n (CO)/cm-1
syn-[Rh2(m-Cl)2(CO)2(4)] (22)
[Rh2(m-Cl)2(CO)2(7)] (23)
44.6
40.4
180
179
179
182
180
126
127
125
126
127
149
151
149
146
145
1992
1988
1993
1991
syn-[Rh2(m-Cl)2(CO)2(10)] (24) 44.1
syn-[Rh2(m-Cl)2(CO)2(13)] (25) 45.7
syn-[Rh2(m-Cl)2(CO)2(16)] (26) 46.6
1991
[Rh2(Cl)2(CO)4(4)] (27)a
[Rh2(Cl)2(CO)4(7)] (28)
[Rh2(Cl)2(CO)4(10)] (29)a
[Rh2(Cl)2(CO)4(13)] (30)
[Rh2(Cl)2(CO)4(16)] (31)
[Rh2(Cl)2(cod)2(4)] (32)
[Rh2(Cl)2(cod)2(7)] (33)
[Rh2(Cl)2(cod)2(10)] (34)
[Rh2(Cl)2(cod)2(13)] (35)
[Rh2(Cl)2(cod)2(16)] (36)
20.5
19.2
21.0
20.1
21.0
25.2
26.1
26.7
24.6
26.3
2092, 2010
2092, 2012
2092, 2010
2092, 2010
2092, 2010
—
—
—
—
—
a CD2Cl2.
25.3 (1JRh–P = 139.3 Hz), probably due to compound 18 formed as
by-product.
The molecular structures of complexes 22 and 24 were deter-
mined by X-ray diffraction and they are depicted in Fig. 10.
Selected bond lengths and angles are listed in Table 5. Both
complexes can be described as bent-syn structures, similar to the
one published by Gelman for the analogous compound derived
from a 1,8-bis(diisopropylphosphino)-triptycene ligand.43 This is
in contrast with complexes observed for SPANphos (presumably
responsible for the activities observed in methanol carbonylation),
which form the bent-anti isomer.42 A direct consequence of the syn
structures observed is that the oxygen atoms of the backbone are
further away from the metal centres than those in the SPANphos
analogues. Whether this structural detail has consequences for the
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 8560–8574 | 8567
©

Fig. 10 ORTEP-plots (thermal ellipsoids shown at 50% probability levels) of complexes 22 and 24. Non-relevant hydrogen atoms have been omitted for
the sake of clarity.
◦
˚
Table 5 Selected bond distances (A) and angles ( ) for 22 and 24
22
24
Rh(1)–P(1)
Rh(2)–P(2)
P(1)–P(2)
2.2391(9)
2.2402(8)
6.576(3)
2.2476(9)
2.2411(9)
6.354(4)
Rh(1)–Rh(2)
Rh(1)–Cl(1)
Rh(1)–Cl(2)
Rh(2)–Cl(1)
3.375(2)
3.245(3)
2.3977(8)
2.4145(9)
2.3920(8)
2.4173(8)
1.805(3)
1.806(3)
3.675(4)
2.4037(8)
2.4154(9)
2.4017(8)
2.4024(9)
1.810(3)
1.813(4)
4.037(5)
Rh(2)–Cl(2)
Rh(1)–C(43/41)b
Rh(2)–C(44/42)b
Rh(1)–O(1)
Fig. 11 Triptycene-based syn-rhodium chloride bridged dimer.
Rh(2)–O(2)
3.614(4)
3.998(5)
◦
was carried out at 150 C under a CO pressure of 22 bar. After
P(1)–Rh(1)–Cl(2)
Cl(1)–Rh(1)–C(43/41)b
P(2)–Rh(2)–Cl(2)
Cl(1)–Rh(2)–C(44/42)b
Interplanar anglea
174.89(3)
175.00(12)
178.90(2)
171.68(11)
138.0(2)
178.20(4)
173.63(12)
174.86(3)
173.09(11)
127.3(2)
90 min the reaction was stopped and the solution was analyzed by
NMR spectroscopy to determine the selectivity. The conversion
was calculated from gas consumption of a pressurized reservoir.
These highly diluted conditions were chosen, as described in our
previous publication with SPANphos42 to demonstrate that the
observed activities could not be attributed to a medium effect
caused by phosphine quaternization.
The results obtained (Table 6) showed that the new ligands
show similar or better activities to those obtained with SPANphos
(diphenyl phosphine derivative).
a Rh(1)–Cl(1)–Cl(2) and Rh(2)–Cl(1)–Cl(2) interplanar angle. b C(43) and
C(44) for complex 22; C(41) and C(42) for complex 24.
reactivity or not remains a key-question in our research, which
hopefully the study of these systems will help to elucidate.
The interplanar angle measured at the Rh2Cl2 core was esti-
mated at 138◦ and 127◦ for complexes 22 and 24 respectively.
The bending is not as large as that reported for triptycene-diphos
(Fig. 11),38,43 possibly due to the larger P–P distance that our
ligands exhibit.
This interplanar angle is even larger than the one encountered
for analogous SPANphos complexes which accounts for the large
Rh–Rh distances observed (3.37 and 3.24 A for 22 and 24
Table 6 Methanol carbonylation with Rh catalyst and diphosphine
ligandsa
Entry
Ligand
Conv. (%)b
TONc
TOFd
1
2
3
4
5
6e
4b
6.4
4.9
13.8
13.8
9.6
679
527
1470
1468
1030
888
453
351
980
979
687
592
˚
7b
10b
respectively).42 Eachrhodium atom is inaplanar environment. The
terminal carbonyl ligands adopt, as expected, a syn conformation
with Rh–C, Rh–Cl and Rh–P distances within the normal range.
As mentioned before, there is no bonding interaction between
rhodium and the oxygen atom of the backbone.
13b
16b
SPANphos
8.9
a Conditions: T = 150 ◦C, P (at 22 ◦C) = 22 bar of CO, 700 rpm, [Rh(m-
Cl)(CO)2]2 57 mmol, 1.5 h, MeOH/MeI/H2O/Rh = 9670/1000/6820/2.
b The conversion was calculated from gas consumption of the reservoir
autoclave. The solution was analyzed by NMR spectroscopy to determine
the selectivity. c TON = turnover number (in mol conversion per mol
Rh2). d TOF = turnover frequency (in mol conversion per mol Rh2 per
h). e SPANphos diphenylphosphine used.
Carbonylation of methanol
In situ generated chloro-bridged dimeric complexes derived from
ligands 4, 7, 10, 13, 16 and SPANphos (diphenylphosphine deriva-
tive) were tested in the carbonylation of methanol. The reaction
8568 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©

The use of these exclusively binucleating ligands confirms the
high activity of dimeric-rhodium complexes as precatalysts in
rhodium catalyzed methanol carbonylation. If the actual catalyst is
the halo-bridged dimer or the CO-cleaved species (27–31), formed
under CO pressure is currently under study by means of these
binucleating ligands.96
shifts of 31P NMR spectra are referred to H3PO4 as external
standard. Signals are quoted as s (singlet), d (doublet), t (triplet),
m (multiplet), br (broad)). Mass spectra were run by ESI-TOF
on a Waters LCT Premier spectrometer. ATR measurements were
carried out in a FT-IR Bruker Tensor 27 with DTGS detector,
with a resolution of 4 cm-1 and 32 scans, using an ATR Specac
Golden Gate accessory with diamond crystal.
Conclusions
Syntheses
A new class of diphosphines able to stabilize dimeric complexes
were designed and synthesized. Complexation studies undertaken
confirmed the binucleating nature of the ligands. In accordance
with molecular mechanics studies, monometallic species with
the ligand acting as a chelator were never observed. The out-
come of the reaction of these ligands with [Rh2(m-Cl)2(CO)4] or
[Rh2(m-Cl)2(cod)2] is determined by the stoichiometry used. When
a ligand-to-metal ratio of 1 : 1 was employed, (a ratio suited to form
monometallic chelates for most bidentates) bimetallic face-to-face
complexes with two ligands acting as a double bridge between
the two metals occupying mutually trans positions were obtained
(as a mixture of different isomers in some cases). When the
ligand-to-metal ratio was lowered to 1 : 2, halide-bridged dimers
were formed. The molecular structure of these compounds was
elucidated by NMR spectroscopy as well as X-ray crystallography.
The new ligands, when tested in rhodium catalyzed methanol
carbonylation, showed activities comparable to the ones obtained
with SPANphos, which confirms that bimetallic halogen-bridged
complexes lead to the most active catalysts for this reaction. The
application of these ligands to reactions that may benefit from
the cooperative effect of two metal centres in close proximity is
currently under study.
4,7-Dibromo-5a,10b-dihydro-5a,10b-dimethyl-2,9-dimethylben-
zofuro[2,3-b]benzofuran (3). To a stirred solution of 5a,10b-
dihydro-5a,10b-dimethyl-2,9-dimethylbenzofuro[2,3-b]benzofuran
2 (10.08 g, 37.8 mmol) in DMF (400 ml), NBS (40.89 g, 230 mmol)
was added. The reaction was monitored by GC chromatography.
When there was no signal of starting compound, DMF was
removed by evaporation. The residue dissolved in H2O and
extracted with dichloromethane. The combined organic layers
were dried over MgSO4, and the solvent was evaporated to obtain
3 as a white solid (11.05 g, 69%). (Found: C, 51.58; H, 3.96.
1
C18H16Br2O2 requires C, 50.97; H, 3.80%). H NMR (400 MHz,
CDCl3): d 1.63 (3H, s, CH3), 1.81 (3H, s, CH3), 2.28 (6H, s, CH3),
4
4
6.95 (2H, d, JH–H = 0.88 Hz), 7.10 (2H, d, JH–H = 0.84 Hz); 13C
NMR (100 MHz, CDCl3): d 20.4 (s), 20.8 (s), 21.2 (s), 58.8 (s),
102.6 (s), 122.3 (s), 125.1 (s), 132.3 (s), 133.2 (s), 133.5 (s), 152.2
(s). m/z (ESI+): 424 [M]+.
4,7-Bis(diphenylphosphino)-5a,10b-dihydro-5a,10b-dimethyl-2,
9-dimethylbenzofuro[2,3-b]benzofuran (4). At -78 ◦C n-
butyllithium (7 ml, 2.5 M in hexanes, 17.5 mmol) was added
dropwise to a stirred solution of 3 (3.44 g, 8.1 mmol) in dry
THF (350 ml). The reaction mixture was stirred for 1 h and
then was allowed to warm to -40 ◦C. At this temperature
chlorodiphenylphosphine (3.1 ml, 17.3 mmol) was added and
the reaction mixture was allowed to warm to room temperature
overnight. The solvent was removed in vacuo and the resulting
solid was dissolved in dry CH2Cl2 and the solution was washed
with deoxygenated water. The organic layer was removed in
vacuo and recrystallized from deoxygenated methanol to afford
4 (3.72 g, 72%) as an air-stable white solid. (Found: C, 78.77;
H, 6.25. C42H36O2P2 requires C, 79.48; H, 5.72%). 1H NMR
(400 MHz, CDCl3): d 1.41 (3H, s, CH3), 1.60 (3H, s, CH3), 2.17
Experimental
Materials and methods
All reactions were performed using standard vacuum-line and
Schlenk techniques under argon atmosphere. Solvents were
purchased from Sigma-Aldrich as HPLC grade and dried with an
SPS system of ITC-inc. Methyl iodide and deuterated chloroform
were purchased from Sigma-Aldrich, distilled over CaH2 and
stored under argon atmosphere. p-Cresol, 1,4-dichlorobutyne,
glyoxal, n-Butyllithium and chlorodiphenylphosphine were
purchased from Sigma-Aldrich. 1,1,3,3-Tetramethoxypropane,
trifluoroacetic acid, tetracarbonyldi-m-chlorodirhodium(I) and
chloro(1,5-cyclooctadiene)rhodium(I) dimer were purchased from
Acros. N-Bromosuccinimide was purchased from Alfa Aesar. 1,4-
Bis(p-methylphenoxy)-2-butyne (1),83,84 5a,10b-dihydro-5a,10b-
dimethyl-2,9-dimethylbenzofuro[2,3-b]benzofuran (2),83,84 4b,9b-
dihydro-4b,9b-dimethyl-3,8-dimethylbenzofuro[3,2-b]benzofuran
(5),81,85 5a,10b-dihydro-2,9-dimethylbenzofuro[2,3-b]benzofuran
(8)86 and 2,10-dimethyl-6,12-methano-12H-dibenzo[2,1-d:l¢,2¢¢-g]
[l,3]dioxocin (11),87 were synthesized according to the published
procedures or slight modifications thereof. NMR spectra unless
otherwise stated were recorded at the following frequencies:
400.13 MHz (1H), 100.63 MHz (13C), 161.98 MHz (31P). 13C and
31P NMR spectra were recorded using broad band decoupling.
Chemical shifts of 1H and 13C NMR spectra are reported in
ppm downfield from TMS, used as internal standard. Chemical
3
4
(6H, s, CH3), 6.48 (2H, dd, JH–P = 6.0 and JH–H = 1.0 Hz, Ar),
7.06 (2H, d, JH–H = 1.3 Hz), 7.23–7.34 (20H, m, Ar); 31P { H}
4
1
NMR (162 MHz, CDCl3): d –13.7 (s); 13C NMR (100 MHz,
CDCl3): d 19.8 (s), 21.1 (s), 21.1 (s), 56.4 (s), 118.0 (d, JC–P
16.1 Hz), 124.4 (s), 125.1 (s), 128.4 (d, JC–P = 6.2 Hz), 128.5 (d,
JC–P = 5.4 Hz), 128.7 (s), 131.3 (d, JC–P = 2.2 Hz), 132.5 (d, JC–P
2.2 Hz), 133.5 (d, JC–P = 6.6 Hz), 133.7 (d, JC–P = 19.7 Hz), 134.1
=
=
(d, JC–P = 20.1 Hz), 136.4 (d, JC–P = 3.6 Hz), 136.5 (d, JC–P
=
4.1 Hz), 157.4 (d, JC–P = 13.9 Hz). m/z (ESI+): 635 [M + H]+, 657
[M + Na]+. HR-MS: (ESI+) m/z calcd for C42H36O2NaP2 ([M +
Na]+) 657.2088, found 657.2092.
1,6-Dibromo-4b,9b-dihydro-4b,9b-dimethyl-3,8-dimethylbenzo-
furo [3,2-b]benzofuran (6). Compound 6 was prepared using
the same procedure described above for compound 3, but
using 4b,9b-dihydro-4b,9b-dimethyl-3,8-dimethylbenzofuro[3,2-
b]benzofuran 5 as substrate to brominate. Yield: 99% (Found:
C, 50.71; H, 3.49. C18H16Br2O2 requires C, 50.97; H, 3.80%).
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 8560–8574 | 8569
©

1H NMR (400 MHz, CDCl3): d 1.77 (6H, s, CH3), 2.30 (6H, s,
CH3), 7.20 (2H, s, Ar), 7.22 (2H, s, Ar). 13C NMR (100 MHz,
CDCl3): d 20.6 (s), 20.7 (s), 97.5 (s), 103.0 (s), 124.4 (s), 129.8
(s), 132.5 (s), 134.4 (s), 153.8 (s). m/z (ESI+): 425 [M + H]+,
447 [M + Na]+.
(6H, s, CH3), 3.88–3.90 (1H, m, CH), 6.33–6.34 (1H, m, CH),
4
4
6.93 (2H, d, JH–H = 1.72 Hz, Ar), 7.17 (2H, d, JH–H = 1.52 Hz,
Ar); 13C NMR (100 MHz, CDCl3): d 20.4 (s), 25.4 (s), 32.2 (s),
92.9 (s), 110.3 (s), 127.2 (s), 127.3 (s), 132.2 (s), 132.5 (s), 145.8 (s).
m/z (ESI+): 432.9 [M + Na]+.
1,6-Bis(diphenylphosphino)-5a,10b-dihydro-5a,10b-dimethyl-3,
8-dimethylbenzofuro[3,2-b]benzofuran (7). Ligand 7 was pre-
pared following the same synthetical procedure described above
for compound 4, but using compound 6 as dibrominated precur-
sor. Yield: 62%. (Found: C, 78.00; H, 6.48. C42H36 O2P2 requires
C, 79.48; H, 5.72%). 1H NMR (400 MHz, CDCl3): d 1.58 (6H, s,
2,10-Dimethyl-4,8-diphenylphosphino-6,12-methano-12H-di-
benzo[2,1-d:l¢,2¢¢-g][l,3]dioxocin (13). Ligand 13 was prepared
following the same synthetical procedure described above for
compound 4, but using compound 12 as dibrominated precursor.
Yield: 86%. (Found: C, 79.15; H, 5.57. C41H34O2P2 requires C,
1
79.34; H, 5.52%). H NMR (400 MHz, CDCl3): d 2.09 (2H, t,
3JH–H = 2.48 Hz, CH2), 2.11 (6H, s, CH3), 3.89–3.92 (1H, m, CH),
3
4
CH3), 2.10 (6H, s, CH3), 6.50 (2H, dd, JH–P = 6.2 and JH–H
=
4
3
4
1.3 Hz, Ar), 6.80 (2H, d, JH–H = 1.32 Hz), 7.15–7.33 (20H, m,
5.88–5.90 (1H, m, CH), 6.32 (2H, dd, JH–P = 4.8 and JH–H =
Ar); 31P { H} NMR (162 MHz, CDCl3): d -12.9 (s); 13C NMR
1.9 Hz, Ar), 7.02 (2H, d, 4JH–H = 1.72 Hz, Ar), 7.19–7.35 (20H, m,
1
1
(100 MHz, CDCl3): d 20.7 (s), 21.0 (s), 95.9 (d, JC–P = 1.5 Hz),
118.2 (d, JC–P = 13.9 Hz), 126.5 (s), 128.2 (d, JC–P = 6.6 Hz), 128.4
(d, JC–P = 6.6 Hz), 128.5 (s), 128.7 (s), 129.1 (d, JC–P = 2.2 Hz),
Ar); 31P { H} NMR (162 MHz, CDCl3): d -12.8 (s); 13C NMR
(100 MHz, CDCl3): d 20.8 (s), 25.7 (s), 32.2 (s), 92.2 (s), 124.6 (d,
JC–P = 15.4 Hz), 126.1 (d, JC–P = 2.2 Hz), 128.4 (d, JC–P = 4.9 Hz),
128.5 (d, JC–P = 3.6 Hz), 128.6 (s), 129.0 (s), 130.6 (d, JC–P = 1.5 Hz),
130.6 (d, JC–P = 2.2 Hz), 133.6 (d, JC–P = 19.7 Hz), 134.1 (d, JC–P
=
20.5 Hz), 135.0 (d, JC–P = 7.3 Hz), 136.2 (d, JC–P = 8.1 Hz), 136.3
(d, JC–P = 7.3 Hz), 158.2 (d, JC–P = 13.2 Hz). m/z (ESI+): 635 [M +
H]+, 657 [M + Na]+. HR-MS: (ESI+) m/z for C42H36O2P2Na ([M +
Na]+) 657.2088; found 657.2112.
133.0 (d, JC–P = 1.5 Hz), 133.8 (d, JC–P = 19.8 Hz), 134.1 (d, JC–P =
20.5 Hz), 136.8 (d, JC–P = 11.3 Hz), 137.1 (d, JC–P = 11.4 Hz), 150.9
(d, JC–P = 15.0 Hz). m/z (ESI+): 621 [M + H]+, 643 [M + Na]+.
HR-MS: (ESI+) m/z for C41H34O2P2Na ([M + Na]+) 643.1932;
found 643.1935.
4,7-Dibromo-5a,10b-dihydro-2,9-dimethylbenzofuro[2,3-b]-
benzofuran (9). Compound 9 was prepared using the same
procedure described above for compound 3, but using 5a,10b-
dihydro-2,9-dimethylbenzofuro[2,3-b]benzofuran 8 as substrate to
brominate. Yield: 69%. (Found: C, 48.47; H, 3.09. C16H12Br2O2
2,10-Di-tert-butyl-6,12-methano-12H-dibenzo[2,1-d:l¢,2¢¢-g]-
[l,3]dioxocin (14). To a stirred solution of 4-tert-butylphenol
(20.48 g, 136.3 mmol) in trifluoroacetic acid (42 ml), was added
1,1,3,3-tetramethoxypropane (11.5 ml, 69.5 mmol) and left stirring
overnight at r.t. After addition of acetic acid (80 ml), the crude
product was collected by filtration, washed with methanol and
finally boiled with water to afford after filtration 14 (8.6 g, 37%) as
a white-pink solid. (Found: C, 77.44; H, 8.11. C17H14Br2O2 requires
C, 82.10; H, 8.39%). 1H NMR (400 MHz, CDCl3): d 1.28 (18H, m,
tBu, 2.25 (2H, m, CH2), 3.90–3.96 (1H, m, CH), 6.10–6.15 (1H,
1
requires C, 48.52; H, 3.05%). H NMR (400 MHz, CDCl3): d
2.29 (6H, s, CH3), 5.09 (1H, d, 3JH–H = 6.7 Hz, CH), 6.95 (1H, d,
3JH–H = 6.7 Hz, CH), 7.07 (2H, s, Ar), 7.14 (2H, s, Ar); 13C NMR
(100 MHz, CDCl3): d 20.6 (s), 52.1 (s), 102.6 (s), 112.2 (s), 123.4
(s), 127.8 (s), 132.6 (s), 133.4 (s), 153.3 (s). m/z (ESI+): 419 [M +
Na]+.
3
3
m, CH), 6.82 (2H, d, JH–H = 8.5 Hz, Ar), 7.11 (2H, d, JH–H
=
4,7-Bis(diphenylphosphino)-5a,10b-dihydro-2,9-dimethylbenzo-
furo[2,3-b]benzofuran (10). Ligand 10 was prepared following the
same synthetical procedure described above for compound 4, but
using compound 9 as dibrominated precursor. Yield: 50%. (Found:
8.5 Hz, Ar), 7.20 (2H, s, Ar); 13C NMR (100 MHz, CDCl3): d 25.9
(s), 31.7 (s), 32.5 (s), 34.3 (s), 92.4 (s), 116.0 (s), 124.3 (s), 125.0 (s),
126.3 (s), 144.2 (s), 148.9 (s). m/z (ESI+): 359.2 [M + Na]+.
1
C, 78.58; H, 5.57. C40H32O2P2 requires C, 79.20; H, 5.32%). H
4,8-Dibromo-2,10-di-tert-butyl-6,12-methano-12H -dibenzo-
[2,1-d:l¢,2¢¢-g][l,3]dioxocin (15). Compound 15 was prepared us-
ing the same procedure described above for compound 3, but using
compound 14 as substrate to brominate. Yield: 90%. (Found: C,
55.56; H, 5.42. C23H26Br2O2 requires C, 55.89; H, 5.30%). 1H NMR
(400 MHz, CDCl3): d 1.26 (18H, s, tBu), 2.26 (2H, t, 3JH–H = 2.5 Hz,
CH2), 3.95–3.98 (1H, m, CH), 6.33–6.36 (1H, m, CH), 7.12 (2H,
NMR (400 MHz, CDCl3): d 2.18 (6H, s, CH3), 4.91 (1H, d,
3JH–H = 6.7 Hz, CH), 6.52 (2H, d, 3JH–P = 5.6 Hz, Ar), 6.74 (1H, d,
3JH–H = 6.7 Hz, CH), 7.17 (2H, s, Ar), 7.26–7.34 (20H, m, Ar); 31
P
1
{ H} NMR (162 MHz, CDCl3): d -14.4 (s); 13C NMR (100 MHz,
CDCl3): d 21.1 (s), 50.2 (s), 112.7 (s), 118.3 (d, JC–P = 16.9 Hz),
125.5 (s), 127.0 (d, JC–P = 2.6 Hz), 128.4 (d, JC–P = 4.3 Hz), 128.5
4
4
(d, JC–P = 4.4 Hz), 128.7 (d, JC–P = 18.4 Hz), 131.7 (d, JC–P
1.9 Hz), 133.7 (d, JC–P = 20.1 Hz), 133.8 (s), 134.0 (d, JC–P
=
=
d, JH–H = 2.04 Hz, Ar), 7.35 (2H, d, JH–H = 2.04 Hz, Ar); 13C
NMR (100 MHz, CDCl3): d 25.4 (s), 31.4 (s), 31.5 (s), 32.8 (s),
34.4 (s), 93.0 (s), 110.2 (s), 123.6 (s), 127.2 (s), 129.2 (s), 145.7 (s),
145.8 (s). m/z (ESI+): 517 [M + Na]+.
20.5 Hz), 136.2 (d, JC–P = 4.4 Hz), 136.3 (d, JC–P = 4.4 Hz), 158.6 (d,
JC–P = 14.9 Hz). m/z (ESI+): 607 [M + H]+, 629 [M + Na]+. HR-
MS: (ESI+) m/z for C40H32O2NaP2 ([M + Na]+) 629.1775, found
629.1776.
2,10-Di-tert-butyl-4,8-diphenylphosphino-6,12-methano-12H-
dibenzo[2,1-d:l¢,2¢¢-g][l,3]dioxocin (16). Ligand 16 was prepared
following the same synthetical procedure described above for
compound 4, but using compound 15 as dibrominated precursor.
Yield: 66%. (Found: C, 77.69; H, 6.81. C47H46O2P2 requires C,
4,8-Dibromo-2,10-dimethyl-6,12-methano-12H-dibenzo[2,1-d:
l¢,2¢¢-g][l,3]dioxocin (12). Compound 12 was prepared using the
same procedure described above for compound 3, but using
2,10-dimethyl-6,12-methano-12H-dibenzo[2,1-d:l¢,2¢¢-g][l,3] diox-
ocin 11 as substrate to brominate. Yield: 87%. (Found: C, 49.91;
H, 3.18. C17H14Br2O2 requires C, 49.79; H, 3.44%). 1H NMR
1
80.09; H, 6.58%). H NMR (400 MHz, CDCl3): d 1.08 (18H, s,
tBu), 2.10 (2H, t, 3JH–H = 2.46 Hz, CH2), 3.93–3.97 (1H, m, CH),
5.87–5.90 (1H, m, CH), 6.53 (2H, dd, 3JH–P = 5.4 and 4JH–H = 2.4 Hz,
3
4
(400 MHz, CDCl3): d 2.22 (2H, t, JH–H = 2.64 Hz, CH2), 2.24
Ar), 7.19 (2H, d, JH–H = 2.3 Hz, Ar), 7.26–7.34 (20H, m, Ar);
8570 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©

1
31P { H} NMR (162 MHz, CDCl3): d = -11.54 (s); 13C NMR
[Rh2(CO)2(l-Cl)2(L)] dimeric complexes 22–26
(100 MHz, CDCl3): d 25.9 (s), 31.1 (s), 31.4 (s), 31.7 (s), 32.8 (s),
34.3 (s), 92.2 (s), 123.9 (d, JC–P = 15.4 Hz), 125.3 (d, JC–P = 2.9 Hz),
125.7 (d, JC–P = 1.5 Hz), 128.4 (br), 128.5 (br), 128.6 (s), 130.0 (s),
General synthesis. [Rh2(m-Cl)2(CO)4] (8 mmol) and corre-
sponding ligand (8 mmol) were dissolved in 1–2 ml of CH2Cl2.
After 5 min the solvent was removed by vacuum and the residue
dissolved in 0.8 ml of CDCl3 or CD2Cl2.
Alternatively, identical compounds (according to their 31P NMR
pattern) can be obtained when [Rh2(m-Cl)2(cod)2] (8 mmol) and
corresponding ligand (8 mmol) were dissolved in 1–2 ml of CH2Cl2.
Then CO was bubbled through the solution for 5 min, the solvent
was removed by vacuum and the residue dissolved in 0.8 ml of
CDCl3 or CD2Cl2.
133.9 (br), 134.1 (br), 137.0 (d, JC–P = 11.3 Hz), 137.2 (d, JC–P
=
11.7 Hz), 143.8 (s), 150.8 (d, JC–P = 15.4 Hz). m/z (ESI+): 705 [M +
H]+, 727 [M + Na]+. HR-MS: (ESI+) m/z for C47H47O2P2 ([M]+)
calcd. 705.3051, found 705.3074.
[Rh2(CO)2Cl2(L)2] bimetallic complexes 17–21
General synthesis. [Rh2(m-Cl)2(CO)4] (8 mmol) and corre-
sponding ligand (16 mmol) were dissolved in 0.8 ml of dry CDCl3
or CD2Cl2, and the solution was subjected to one cycle of vacuum
and stored under argon.
Alternatively, identical compounds (according to their 31P NMR
pattern) can be obtained when [Rh2(m-Cl)2(cod)2] (8 mmol) and
corresponding ligand (16 mmol) were dissolved in 0.8 ml of dry
CDCl3 or CD2Cl2. Then CO was bubbled through the solution for
5 min.
[Rh2(CO)2(l-Cl)2(4)] (22). 1H NMR (400 MHz, CDCl3): d
1.26 (3H, s, CH3), 1.69 (3H, s, CH3), 2.08 (6H, s, CH3), 6.10
(2H, d, 3JH–P = 10.8 Hz, Ar), 6.96 (2H, s, Ar), 7.37–7.48 (12H, m,
1
Ar), 7.76–7.84 (8H, m, Ar); 31P { H} NMR (162 MHz, CDCl3): d
1
44.6 (d, JRh–P = 180.3 Hz). MALDI+ve: m/z: 931 [M - Cl]+. IR
(ATR mode, liquid, carbonyl region, cm-1): n = 1992.
[Rh2(CO)2(l-Cl)2(7)] (23). 1H NMR (400 MHz, CDCl3): d
1.26–1.64 (6H, br, CH3), 2.09–2.34 (6H,br, CH3), 6.61–7.86 (24H,
[Rh(CO)Cl(4)]2 (17). 1H NMR (400 MHz, CDCl3): d 1.21–
1.40 (6H, m, CH3), 2.08–2.15 (6H, m, CH3), 6.00–6.52 (2H, m,
1
1
br, Ar); 31P { H} NMR (162 MHz, CDCl3): d 40.4 (d, JRh–P
=
179.5 Hz), 24.9 (18 as by-product, d, 1JRh–P = 129.6 Hz), 25.3 (18 as
by-product, d, 1JRh–P = 139.3 Hz). IR (ATR mode, liquid, carbonyl
region, cm-1): n = 1988.
Ar), 7.00–8.2 (22H, m, Ar); 31P { H} NMR (162 MHz, CDCl3):
1
1
2
1
d 16.6 (dd, JRh–P = 131 Hz, JP–P = 366 Hz), 23.9 (dd, JRh–P
=
=
2
1
131 Hz, JP–P = 366 Hz) (major compound); 19.7 (dd, JRh–P
128 Hz, 2JP–P = 368 Hz), 24.9 (dd, 1JRh–P = 128 Hz, 2JP–P = 368 Hz)
(minor compound). IR (ATR mode, solid, carbonyl region, cm-1):
n = 1970, 1989 (22).
[Rh2(CO)2(l-Cl)2(10)] (24). 1H NMR (400 MHz, CDCl3): d
3
2.08 (6H, s, CH3), 4.96 (1H, d, JH–H = 6.2 Hz, Ar), 6.14 (2H, d,
3JH–P = 10.8, Ar), 6.64 (1H, d, 3JH–H = 6.2 Hz, CH), 7.08 (2H, s, Ar),
7.37–7.48 (12H, m, Ar), 7.74–7.82 (8H, m, Ar); 31P { H} NMR
1
[Rh(CO)Cl(7)]2 (18). 1H NMR (400 MHz, CDCl3): d 2.07–
2.14 (6H, br, CH3), 2.16–2.19 (6H, br, CH3), 6.66–6.72 (2H, br,
1
(162 MHz, CDCl3): d 44.1 (d, JRh–P = 179 Hz); IR (ATR mode,
liquid, carbonyl region, cm-1): n = 1993.
Ar), 7.11–7.80 (22H, m, Ar); 31P { H} NMR (162 MHz, CDCl3,
1
1
1
[Rh2(CO)2(l-Cl)2(13)] (25). 1H NMR (400 MHz, CDCl3): d
1.99–2.02 (2H, m, CH2), 2.05 (6H, s, CH3), 3.79–3.83 (1H, m,
CH), 5.54–5.58 (1H, m, CH), 6.14 (2H, d, 3JH–P = 11.2, Ar), 6.92
298 K): d 25.0 (d, JRh–P = 128 Hz), 25.4 (d, JRh–P = 128 Hz). IR
(ATR mode, solid, carbonyl region, cm-1): n = 1970.
[Rh(CO)Cl(10)]2 (19). 1H NMR (500 MHz, CD2Cl2, 273 K):
d 2.13 (6H, s, CH3), 2.18 (6H, s, CH3), 4.48 (1H, m, CH), 4.66
(1H, m, CH), 6.20 (1H, m, CH), 6.29 (1H, m, CH), 6.53–8.76
(48H, m, Ar); 31P {1H} NMR (202 MHz, CD2Cl2, 193 K): d 20.6
1
(2H, s, Ar), 7.35–7.80 (20H, m, Ar); 31P { H} NMR (162 MHz,
1
CDCl3): d 45.7 (d, JRh–P = 182 Hz). IR (ATR mode, liquid,
carbonyl region, cm-1): n = 1991.
1
2
1
[Rh2(CO)2(l-Cl)2(16)] (26). 1H NMR (400 MHz, CDCl3): 1H
NMR (400 MHz, CDCl3): d 1.0 (18H, s, tBu), 2.07–2.11 (2H, m,
(dd, JRh–P = 125 Hz, JP–P = 366 Hz), 23.1 (dd, JRh–P = 130 Hz,
2JP–P = 366 Hz) (major compound); 21.8 (dd, JRh–P = 128 Hz,
1
2JP–P = 359 Hz), 24.4 (dd, 1JRh–P = 132 Hz, 2JP–P = 359 Hz) (minor
compound). IR (ATR mode, solid, carbonyl region, cm-1): n =
1973
3
CH2), 3.90 (1H, m, CH), 5.64(1H, m, CH), 6.27 (2H, d, JH–P
=
4
4
12.1 and JH–H = 2.1 Hz, Ar), 7.09 (2H, d, JH–H = 2.1 Hz, Ar),
7.3–7.8 (20H, m, Ar); 31P { H} NMR (162 MHz, CDCl3): d 46.6
1
(d, 1JRh–P = 180 Hz). IR (ATR mode, liquid, carbonyl region, cm-1):
n = 1991.
[Rh(CO)Cl(13)]2 (20). 1H NMR (400 MHz, CDCl3): d 2.03–
2.07 (12H, br, CH3), 2.11–2.15 (4H, br, CH2), 3.67–3.97 (2H, br,
CH), 6.31–6.37 (4H, br, Ar), 6.40–6.50 (2H, br, CH), 6.55–6.61
(2H, br, Ar), 6.74–7.91 (42H, br, Ar); 31P { H} NMR (162 MHz,
1
[Rh2(CO)4Cl2(L)] bimetallic complexes 27–31
1
2
CDCl3): d 22.6 (dd, JRh–P = 128 Hz and JP–P = 354 Hz), 25.7
General method. [Rh2Cl2(CO)4] (8 mmol) and corresponding
ligand (8 mmol) were dissolved in 0.8 ml of dry CDCl3. Then CO
was bubbled through the solution for 10 min.
1
2
(dd, JRh–P = 130 Hz and JP–P = 362 Hz). IR (ATR mode, solid,
carbonyl region, cm-1): n = 1958.
[Rh(CO)Cl(16)]2 (21). 1H NMR (400 MHz, CDCl3): d 0.98–
1.05 (18H, s, tBu), 1.05–1.12 (18H, s, tBu), 1.16–1.32 (2H, m,
CH2), 1.40–1.48 (2H, m, CH2), 3.71–3.76 (2H, m, CH), 6.33–6.51
(2H, m, CH), 6.74–6.85 (4H, m, Ar), 7.20–7.28 (4H, m, Ar), 7.30–
[Rh2(CO)4(Cl)2(4)] (27). 1H NMR (500 MHz, CD2Cl2): d 1.30
(3H, s, CH3), 1.50 (3H, s, CH3), 2.21 (6H, s, CH3), 6.76 (2H,
3
1
d, JH–P = 11.7 Hz, Ar), 7.24–7.76 (22H, m, Ar); 31P { H} NMR
(202 MHz, CD2Cl2): d = 20.5 (d, JRh–P = 125.7 Hz). IR (ATR mode,
liquid, carbonyl region, cm-1): n = 2092, 2010.
1
7.94 (40H, m, Ar); 31P { H} NMR (162 MHz, CDCl3): d = 22.5
1
2
1
(dd, JRh–P = 129 Hz, JP–P = 363 Hz), 26.8 (dd, JRh–P = 131 Hz,
2JP–P = 363 Hz). IR (ATR mode, solid, carbonyl region, cm-1): n =
1968.
[Rh2(CO)4(Cl)2(7)] (28). 1H NMR (400 MHz, CDCl3): d 1.60
3
(6H, s, CH3), 2.2 (6H, s, CH3), 6.7 (2H, d, JH,P = 11.6 Hz,
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 8560–8574 | 8571
©

1
(24H, m, Ar); 31P { H} NMR (162 MHz, CDCl3): d = 26.32 (d,
Ar), 6.9 (2H, s, Ar), 7.33–7.50 (10H, m, Ar), 7.56–7.67 (10H,
1
m, Ar); 31P { H} NMR (162 MHz, CDCl3): d 19.2 (d, JRh–P
=
JRh–P = 145 Hz).
127.0 Hz). IR (ATR mode, liquid, carbonyl region, cm-1): n = 2092,
2012.
Catalysis. In a typical experiment 29.4 mL of a mixture
MeOH–H2O was placed in a 100 mL Hastelloy autoclave. The
autoclave was then pressurized to 10 bar of carbon monoxide
and heated to 150 ◦C with vigorous stirring (700 rpm). When the
reaction temperature was reached and had stabilized, a solution
of [Rh2(m-Cl)2(CO)4] and the appropriate quantity of the corre-
sponding ligand in 3.55 mL of MeI were added through a liquid
injection port and the autoclave was pressurized to the desired
reaction pressure. Pressure was maintained constant during the
reaction by feeding gas from a 300 mL autoclave pressurized with
over 60 bar of carbon monoxide. After the required reaction time,
the autoclave was cooled to room temperature. The solution was
analyzed by NMR spectroscopy to determine the selectivity. The
conversion was calculated from gas consumption of the reservoir
autoclave.
[Rh2(CO)4(Cl)2(10)] (29). 1H NMR (500 MHz, CD2Cl2): d
2.24 (6H, s, CH3), 4.89 (1H, d, JH–H = 6.7 Hz, CH), 6.72–
3
6.76 (2H, m, Ar), 6.77–6.82 (1H, m, CH), 7.28–7.82 (22H, m,
Ar); 31P { H} NMR (202 MHz, CD2Cl2): d 21.0 (d, JRh–P
=
1
125.5 Hz). IR (ATR mode, liquid, carbonyl region, cm-1): n = 2092,
2010.
[Rh2(CO)4(Cl)2(13)] (30). 1H NMR (400 MHz, CDCl3): d 2.07
(2H, m, CH2), 2.18 (6H, s, CH3), 3.97 (1H, m, CH), 6.13 (1H, m,
CH), 6.60 (2H, d, 3JH–P 11.1 Hz, Ar), 7.24–7.77 (22H, m, Ar); 31
P
1
{ H} NMR (162 MHz, CDCl3): d = 20.1 (d, JRh–P = 126.1 Hz). IR
(ATR mode, liquid, carbonyl region, cm-1): n = 2092, 2010.
[Rh2(CO)4(Cl)2(16)] (31). 1H NMR (400 MHz, CDCl3): d 1.13
(18H, s, tBu), 2.06 (2H, m, CH2), 4.0 (1H, m, CH), 6.06 (1H, m,
CH), 6.84 (2H, d, 3JH–P 11.8 Hz, Ar), 7.27–7.75 (22H, m, Ar); 31
P
1
X-Ray structure determinations†
{ H} NMR (162 MHz, CDCl3): d = 21.0 (d, JRh–P = 126.8 Hz). IR
(ATR mode, liquid, carbonyl region, cm-1): n = 2092, 2010.
Crystals of complexes 17, 19, and 22 were obtained by slow
diffusion of Et2O into a CDCl3 solution. Crystals of complex
20 and 24 were obtained by slow diffusion of Et2O into CD2Cl2
solution. Measured crystals were prepared under inert conditions
immersed in perfluoropolyether as protecting oil for manipulation.
[Rh2(cod)2Cl2(L)] bimetallic complexes 32–36.
General method. [Rh2Cl2(cod)2] (8 mmol) and corresponding
ligand (8 mmol) were dissolved in 0.8 ml of dry CDCl3.
[Rh2(cod)2(Cl)2(4)] (32). 1H NMR (400 MHz, CDCl3): d 1.56
(3H, s, CH3), 1.68 (3H, s, CH3), 2.23 (6H, s, CH3),1.60–2.50 (16H,
m, CH2 (cod)), 3.14 (2H, m, CH (cod)), 3.36 (2H, m, CH (cod)),
5.36 (2H, m, CH (cod)), 5.57 (2H, m, CH (cod)), 6.06–6.50 (20H,
Data collection. Measurements were made on a Bruker-
Nonius diffractometer equipped with a APPEX 2 4 K CCD area
detector, a FR591 rotating anode with Mo-Ka radiation, Montel
mirrors as monochromator and a Kryoflex low temperature device
1
m, Ar), 8.10–8.15 (4H, m, Ar); 31P { H} NMR (162 MHz, CDCl3):
◦
(T = -173 C). Full-sphere data collection was used with w and
d = 25.2 (d, JRh–P = 149 Hz).
j scans. Programs used: Data collection Apex2 V. 1.0-22 (Bruker-
Nonius 2004), data reduction Saint + Version 6.22 (Bruker-Nonius
2001) and absorption correction SADABS V. 2.10 (2003).
[Rh2(cod)2(Cl)2(7)] (33). 1H NMR (400 MHz, CDCl3): d 1.42
(6H, s, CH3), 1.50–2.06 (8H, m, CH2 (cod)), 2.21 (6H, s, CH3),
2.30 (8H, m, CH2 (cod)), 3.02 (2H, m, CH (cod)), 3.23 (2H, m, CH
(cod)), 5.47 (4H, m, CH (cod)), 6.95–6.98 (4H, m, Ar), 7.27–7.89
Structure solution and refinement. SHELXTL Version 6.14
(Sheldrick, 2008) was used.97
1
(20H, m, Ar); 31P { H} NMR (162 MHz, CDCl3): d = 26.06 (d,
JRh–P = 150.6 Hz).
Comments to the structures. See Table 7 for full details. Com-
pounds 17, 19 and 20 crystallize with a half molecule in the asym-
metric unit showing a similar Ci-symmetry. Compound 19: several
crystals were attempted for the structure determination. The
measured sample was a twin with domains ratio 64 : 36. Structure
determination was possible after integration of two crystals. The
absorption correction was done with the program TWINABS.98,99
The asymmetric unit contains fourteen disordered positions of
water molecules which correspond to a total of six water molecules
for each half molecule of complex. Water occupancies were freely
refined. The best data completeness obtained reached 90.2% since
overlapping reflections of the two different crystals were omitted.
Compound 20: the asymmetric unit contains half molecule of the
complex and two molecules of dichloromethane, disordered in
two positions with occupation ratio 61 : 39. Compound 22: due
to the formation of ice no better data completeness could be
obtained (91%). Compound 24: the asymmetric unit contains 0.25
molecules of dichloromethane disordered in two orientations and
centered on an inversion axis (-4). The measured data correspond
to a racemic twin with a ratio of 51 : 49.
[Rh2(cod)2(Cl)2(10)] (34). 1H NMR (400 MHz, CDCl3): d
1.64–2.52 (16H, m, CH2 (cod)), 2.26 (6H, s, CH3), 3.17 (2H, m,
CH (cod)), 3.40 (2H, m, CH (cod)), 4.97 (1H, d, 3JH–H = 6.8 Hz,
3
CH), 5.37–5.55 (4H, m, CH (cod)), 6.93 (1H, d, JH–H = 6.7 Hz,
1
CH), 7.09–7.44 (20H, m, Ar), 7.04–8.12 (4H, m, Ar); 31P { H}
NMR (162 MHz, CDCl3): d = 26.75 (d, JRh–P = 148.6 Hz).
[Rh2(cod)2(Cl)2(13)] (35). 1H NMR (400 MHz, CDCl3): d
1.62–2.51 (16H, m, CH2 (cod)), 2.11 (2H, m, CH2), 2.19 (6H, s,
CH3), 3.21 (2H, m, CH (cod)), 3.54 (2H, m, CH (cod)), 3.96 (1H,
m, CH), 5.20 (2H, m, CH (cod)), 5.50 (2H, m, CH (cod)), 6.47
(1H, m, CH), 7.02 (2H, d, 3JH–P = 10.8 Hz, Ar), 7.09–7.47 (18H, m,
1
Ar), 8.08–8.17 (4H, m, Ar); 31P { H} NMR (162 MHz, CDCl3):
d = 24.58 (d, JRh–P = 146.5 Hz).
[Rh2(cod)2(Cl)2(16)] complex 36. 1H NMR (400 MHz, CDCl3):
d 1.19–1.24 (18H, br, tBu), 1.60–1.95 (8H, m, CH2 (cod)), 2.02
(2H, m, CH2), 2.09–2.52 (8H, m, CH2 (cod)), 3.20 (2H, m, CH
(cod)), 3.40 (2H, m, CH (cod)), 3.98 (1H, m, CH), 5.20 (2H, m,
CH (cod)), 5.47 (2H, m, CH (cod)), 6.19 (1H, m, CH), 7.19–8.16
8572 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©

Table 7 Crystal data for compounds 17, 19, 20, 22 and 24
Compound
Formula
17
19
20
22
24
C90H76Cl14O6P4Rh2
C82H88Cl2O18P4Rh2
3 H2O
1654.03
0.2 ¥ 0.2 ¥ 0.3
100(2)
Monoclinic
P21/c
18.1626(9)
17.4391(9)
13.3646(6)
90
108.713(2)
90
4009.3(3)
2
C88H76Cl10O6P4Rh2
2 Dichloromethane
1913.69
0.20 ¥ 0.10 ¥ 0.05
100(2)
Monoclinic
P21/c
12.7468(5)
18.3066(7)
19.1337(8)
90
105.1580(10)
90
4309.5(3)
2
C45H37Cl5O4P2Rh2
1 Chloroform
1086.76
0.4 ¥ 0.3 ¥ 0.3
100(2)
C42.25H33.5Cl2.5O4P2Rh2
1/4 Dichloromethane
961.58
0.02 ¥ 0.03 ¥ 0.3
100(2)
Solvent in asymmetric unit 4 Chloroform
Formula weight
Crystal size/mm
T/K
2079.51
0.10 ¥ 0.10 ¥ 0.05
100(2)
Monoclinic
P21/c
16.6357 (4)
18.7449(5)
14.8117(4)
90
100.5780(10)
90
4540.3(2)
2
1.521
Crystal system
Triclinic
Tetragonal
¯
¯
Space group
P1
I4
˚
A/A
11.2602(16)
14.114(4)
14.469(2)
87.046(10)
76.892(8)
79.328(9)
2200.8(8)
2
28.7585(6)
˚
B/A
28.7585(6)
9.2270(2)
90
90
90
7631.2(3)
8
˚
C/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
r/Mg m-3
1.370
1.475
1.640
1.674
m/mm-1
0.898
0.616
0.819
1.169
1.167
Completeness to q (%)
Number of all reflections
Unique reflections
F(000)
Absorption correction
Max., min transmission
96.0 (q = 39.65◦)
90 973
90.2 (q = 36.54◦)
49 393
95.7 (q = 37.50◦)
65 761
91.0 (q = 32.50◦)
30 226
94.0 (q = 33.17◦)
41 695
26 435 [Rint = 0.0223] 17 840 [Rint = 0.0674]
2104 1816
Empirical (SADABS) Empirical (TWINABS) Empirical (SADABS) Empirical (SADABS) Empirical (SADABS)
0.96 and 0.92
21 725 [Rint = 0.0224]
1944
14 497 [Rint = 0.0274]
1088
12 617 [Rint = 0.0597]
3852
0.98 and 0.81
17 840/124/546
0.0728/0.1971
0.0999/0.2213
1.074
0.96 and 0.85
21 725/57/538
0.0456/0.1284
0.0558/0.1385
1.075
1.00 and 0.82
14 497/0/527
0.0499/0.1327
0.0609/0.1473
1.049
0.99 and 0.89
12 617/7/491
0.0411/0.921
0.0539/0.0989
1.033
Data/restraints/parameters 26 435/0/527
R1, wR2 [I > 2s(I)]
0.0349/0.0955
0.0435/0.1021
1.029
R1, wR2 [all data]
Goodness-of-fit (F2)
3
˚
Peak/hole (e/A )
2.153/-1.885
3.597/-1.773
1.854/-2.204
2.896/-2.848
2.473/-0.644
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8574 | Dalton Trans., 2010, 39, 8560–8574
This journal is
The Royal Society of Chemistry 2010
©