Synthesis of dirhodium(II) complexes with several cyclometalated thienylphosphines

Article abstract of DOI:10.1021/om0605128

The thermal reaction of dirhodium tetraacetate with tris(3-thienyl) phosphine (3TP), diphenyl(3-thienyl)phosphine (3TPPh₂), and diphenyl(2-thienyl)phosphine (2TPPh₂) gives rise to mono-cyclometalated and bis-cyclometalated compounds; the latter can have a head-to-head (H-H) or head-to-tail (H-T) configuration. Bis-cyclometalated compounds with H-T configuration can be prepared in high yield under photochemical conditions or by combining irradiation with subsequent thermal treatment in acetic acid. The reactivity order of aromatic ring C-H activation is phenyl < 2-thienyl ? 3-thienyl, which leads to a selective activation of the thienyl ring. Thus, only one mono-cyclometalated compound is obtained from the thermal reaction with 3TPPh₂, and activation of the thienyl ring competes favorably with activation at the phenyl rings in the case of 2TPPh₂. The reaction of these mono-cyclometalated compounds with d4-acetic acid was monitored by ¹H NMR spectroscopy, which demonstrates that the H/D exchange occurs during the demetalation step. The energy values calculated (DFT) for the different compounds agree with the experimental results.

Full text of DOI:10.1021/om0605128

Organometallics 2006, 25, 5113-5121
5113
Synthesis of Dirhodium(II) Complexes with Several Cyclometalated
Thienylphosphines
Julio Lloret,† Klaus Bieger,† Francisco Estevan,† Pascual Lahuerta,*,† Pipsa Hirva,‡
Julia Pe´rez-Prieto,*,§ and Mercedes Sanau´†
Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, UniVersidad de Valencia, Dr. Moliner 50,
46100 Burjassot, Valencia, Spain, Department of Chemistry, UniVersity of Joensuu, P. O. Box 111,
FIN-80101 Joensuu, Finland, and Departamento de Qu´ımica Orga´nica/Instituto de Ciencia Molecular,
Pol´ıgono La Coma s/n, 46980 Paterna, Valencia, Spain
ReceiVed June 9, 2006
The thermal reaction of dirhodium tetraacetate with tris(3-thienyl)phosphine (3TP), diphenyl(3-thienyl)-
phosphine (3TPPh2), and diphenyl(2-thienyl)phosphine (2TPPh2) gives rise to mono-cyclometalated and
bis-cyclometalated compounds; the latter can have a head-to-head (H-H) or head-to-tail (H-T)
configuration. Bis-cyclometalated compounds with H-T configuration can be prepared in high yield
under photochemical conditions or by combining irradiation with subsequent thermal treatment in acetic
acid. The reactivity order of aromatic ring C-H activation is phenyl < 2-thienyl , 3-thienyl, which
leads to a selective activation of the thienyl ring. Thus, only one mono-cyclometalated compound is
obtained from the thermal reaction with 3TPPh2, and activation of the thienyl ring competes favorably
with activation at the phenyl rings in the case of 2TPPh2. The reaction of these mono-cyclometalated
1
compounds with d4-acetic acid was monitored by H NMR spectroscopy, which demonstrates that the
H/D exchange occurs during the demetalation step. The energy values calculated (DFT) for the different
compounds agree with the experimental results.
Scheme 1. Schematic Drawing of the Thienyl Ring
Arrangement
Introduction
We have recently reported that the reaction of dirhodium
tetraacetate with tris(2-thienyl)phosphine1,2 yields dirhodium-
(II) compounds with the Rh2(O2CCH3)4-x(PC)x‚(CH3CO2H)2
general formula, which results from substituting one or two
acetates for formal thienylphosphine anions that act as P,C
bridging ligands. In this particular cyclometalation reaction, tris-
(2-thienyl)phosphine shows higher reactivity than triarylphos-
phines,3-7 especially when the reaction is photochemically
activated. Interestingly, the metalated rings of these compounds
undergo a selective rearrangement of structure, from type A to
type B, when treated with acetic acid (Scheme 1). However,
the nonmetalated rings retain their original structure.
structure type A to structure type B lowered the energy of the
compound by ca. 15 kJ/mol. In the case of bis-cyclometalated
compounds with H-H or H-T configuration, such rearrange-
ment provides products in which both metalated rings had
structure B, with ca. 30 kJ/mol more stability than the
corresponding products with structure type A. Under thermal
conditions, the H-H compounds transform into their H-T
isomers, which agrees with their calculated relative energy
values.
We are now interested in extending these studies to other
heteroaromatic phosphines, some of them chosen with a mixed
set of aromatic substituents, to provide information about the
relative rate of C-H activation of the aromatic rings. This report
describes the synthesis and characterization of several dirhod-
ium(II) compounds containing cyclometalated phosphines, such
as tris(3-thienyl)phosphine (3TP), diphenyl(3-thienyl)phosphine
(3TPPh2), and diphenyl(2-thienyl)phosphine (2TPPh2) (see
Scheme 2). The compound labeling includes one or two letters
that refer to the structure of the metalated ring(s) in mono- and
bis-cyclometalated compounds, respectively. The energy values
for the dirhodium compounds were calculated by DFT methods,
and labeling experiments with deuterated acetic acid were used
to explore the reactivity of the mono-cyclometalated compounds.
Density functional theoretical (DFT) calculations2 indicated
that the rearrangement of one metalated thienyl ring from
* To whom correspondence should be addressed. (P.L.) Fax: (34)-
963544322. E-mail: pascual.lahuerta@uv.es. E-mail: pipsa.hirva@joensuu.fi.
(J.P.-P.) Fax: (34)963543274. E-mail: julia.perez@uv.es.
† Universidad de Valencia.
‡ University of Joensuu.
§ Instituto de Ciencia Molecular.
(1) Bieger, K.; Estevan, F.; Lahuerta, P.; Lloret, J.; Perez-Prieto, J.; Sanau´,
M.; Siguero, N.; Stiriba, S. E. Organometallics 2003, 22, 1799.
(2) Lloret, J.; Estevan, F.; Lahuerta, P.; Hirva, P.; Perez-Prieto, J.; Sanau´,
M. Organometallics 2006, 25, 3156.
(3) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A.; Tocher, J. H.
Organometallics 1985, 4, 8.
(4) Morrison, E. C.; Tocher, D. A. Inorg. Chim. Acta 1989, 157, 139.
(5) Lahuerta, P.; Paya´, J.; Solans, X.; UÄ beda, M. A. Inorg. Chem. 1992,
31, 385.
(6) Lahuerta, P.; Paya´, J.; Pellinghelli, M. A.; Tiripicchio, A. Inorg. Chem.
1992, 31, 1224.
(7) Estevan, F.; Lahuerta, P.; Peris, E.; UÄ beda, M. A.; Garc´ıa-Granda,
S.; Go´mez-Beltra´n, F.; Pe´rez-Carren˜o, E.; Gonza´lez, G.; Mart´ınez, M. Inorg.
Chim. Acta 1994, 218, 189.
10.1021/om0605128 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/09/2006

5114 Organometallics, Vol. 25, No. 21, 2006
Lloret et al.
compound was isolated by chromatographic methods and
Results
1
identified by H, 31P, COSY, and HMBC NMR spectra as the
Reactions of Dirhodium(II) Tetraacetate with Tris(3-
thienyl)phosphine (3TP). The Rh2(O2CCH3)3[(3-C4H2S)P[(3-
C4H3S)2] mono-cyclometalated compound (1B in Scheme 2)
was obtained as the main product from the thermal reaction of
dirhodium(II) tetraacetate with 3TP (1:0.9 molar ratio) in
refluxing (3:1) toluene/glacial acetic acid solution (Scheme 3a).
Two bis-cyclometalated products with Rh2(O2CCH3)2[(3-
C4H2S)P(3-C4H3S)2]2 formula, presenting metalated phosphines
in a H-T (2BB) or H-H (3BB) configuration (Schemes 2 and
3a), were obtained when a 1:2 molar ratio of dirhodium
tetraacetate to phosphine was used. Multinuclear NMR spec-
troscopy confirmed that the metalated ring had structure type
B in each of the three compounds.
By contrast, irradiation (mercury lamp, Pyrex filter) of a
solution of dirhodium(II) tetraacetate and 3TP (1:2 molar ratio)
in (9:1) CH2Cl2/acetic acid solution led to a ca. 1:1 mixture of
two different H-T bis-cyclometalated products (Schemes 2 and
3a). A similar product distribution was detected when the
photochemical reaction was performed at -30 °C. According
to the 31P NMR spectrum of the reaction crude, one of the
compounds was identified as 2BB, while the second compound
had two different phosphorus environments. After separation
of both compounds by chromatography, multinuclear NMR
spectroscopy confirmed that in the second compound one
metalated thienyl ring presented structure B, while the other
had structure C, which agrees with its assignment as 2BC.
Interestingly, complete rearrangement from 2BC to 2BB was
observed after heating a mixture of both compounds in acetic
acid at 90 °C for 15 h (Scheme 3a). Therefore, the combination
of photochemical and thermal treatments can be used to obtain
thermodynamic product 2BB in high yield and within a
reasonable time scale. All attempts to crystallize these bis-
cyclometalated compounds failed.
Reactions of Dirhodium(II) Tetraacetate with Diphenyl-
(3-thienyl)phosphine (3TPPh2). The reaction of dirhodium-
(II) tetraacetate with 3TPPh2 (1:0.9 molar ratio) in a refluxing
(9:1) toluene/acetic acid mixture gave mono-cyclometalated
compound Rh2(O2CCH3)3[(3-C4H2S)PPh2] (4B) in 75% yield
(Schemes 2 and 3b). In addition, bis-cyclometalated products
with Rh2(O2CCH3)2[(3-C4H2S)PPh2]2 formula, presenting the
metalated phosphines in a H-T (5BB) and H-H (6BB)
configuration, were detected by 31P NMR spectroscopy of the
reaction mixture, although they were formed in low yield
(<10%). However, these bis-cyclometalated compounds were
obtained in higher yield and as a 1:1 mixture when 2 equiv of
phosphine was used. Multinuclear NMR studies on the isolated
products confirmed metalation of phosphines had occurred
through the thienyl ring 3-position (structure type B).
Interestingly, the photochemical reaction gave results very
similar to those already described for 3TP. Thus, a mixture of
two H-T compounds, in approximately equal amount, was
obtained. One compound was identified as 5BB, while the
second, showing two different 31P NMR resonances, was
assigned as 5BC (Schemes 2 and 3b). Isomerization from 5BC
to 5BB was observed after heating the mixture of products at
90 °C in pure acetic acid. All the efforts to obtain single crystals
from pure solutions of 5BB failed, but they were accidentally
obtained from a solution containing a mixture of 5BB and 5BC.
Reactions of Dirhodium(II) Tetraacetate with Diphenyl-
(2-thienyl)phosphine (2TPPh2). The reaction of dirhodium-
(II) tetraacetate with 2TPPh2 (1:0.9 molar ratio) in a refluxing
(9:1) toluene/acetic mixture gave two mono-cyclometalated
compounds in ca. 9:1 ratio (Schemes 2 and 3c). The major
compound with Rh2(O2CCH3)3[(2-C4H2S)PPh2] formula (7A),
resulting from metalation through the thienyl ring (Figures S5
and S6 in SI). X-ray analysis of well-grown crystals from this
compound agreed with this assignment. The minor compound
was formulated as Rh2(O2CCH3)3[(C6H4)P[(2-C4H3S)Ph] (8),
which presented metalation at one of the phosphine phenyl rings.
By contrast, Rh2(O2CCH3)2[(2-C4H2S)PPh2]2 H-T bis-cy-
clometalated compound (9AA) was obtained in 70% yield upon
irradiation of a mixture of dirhodium tetraacetate in the presence
of 2 equiv of 2TPPh2 (Schemes 2 and 3c). Its structure was
assigned on the basis of COSY and HMBC 31P-1H NMR
spectra. Single crystals of Rh2(O2CCF3)2[(2-C4H2S)PPh2]2‚(py)2
[10AA‚(py)2] suitable for X-ray diffraction were obtained after
replacing the acetate groups by trifluoroacetates and using
pyridine as axial ligand (Scheme 2). They presented some
disorder in one of the metalated thienyl rings, but the analysis
confirmed the core structure assigned for 9AA.
No evidence of reorganization of the metalated thienyl ring
from type A to type B structure was observed in acetic acid
media (Scheme 3c). This result contrasts with that found for
the tris(2-thienyl)phosphine derivative.2
Again, though compound 9AA was selectively obtained by
photochemical methods, the thermal reaction of dirhodium(II)
tetraacetate with 2TPPh2 afforded a mixture of 9AA and the
H-H bis-cyclometalated product 11AA (ca. 20%). This species
was isolated as an adduct with water and pyridine molecules
(11AA‚py‚(H2O)0.5), crystallized, and structurally characterized.
Solid State Structures. Complexes 5BB‚CH3CO2H, 7A‚
CH3CO2H, 10AA‚(py)2, and 11AA‚py‚(H2O)0.5 were investi-
gated by X-ray crystallography in order to corroborate the
spectroscopic findings. The molecular structures of all these
compounds together with selected atom distances and bond
angles are depicted in Figures S1-S4 (see SI). The Rh-Rh
bond distances are in the range 2.4361(12) to 2.5980(6) Å, the
mono-cyclometalated compounds showing shorter values than
the bis-cyclometalated compounds. The replacement of acetic
acid by pyridine as axial ligand increases the Rh-Rh bond
distance.
The thienyl ring is essentially flat in all cases, and the C-C
bond distances within the ring retain the short-long-short
sequence with average values of 1.35, 1.42, and 1.35 Å. The
Rh-P and Rh-C bond distances are very similar for the mono-
and bis-cyclometalated compounds, with values in the range
2.21-2.23 and 1.98-2.01 Å, respectively, and the longest ones
correspond to the H-H bis-cyclometalated compound 11AA‚
py‚(H2O)0.5. The Rh-O distances trans to P are slightly shorter
than trans to C, this difference being more significant for 11AA‚
py‚(H2O)0.5 (0.07 Å).
The structures for compounds 7A‚CH3CO2H and 11AA‚py‚
(H2O)0.5 are as anticipated, not only in the ligand configuration
but also in the structure of the metalated thienyl rings. The
location of the sulfur atom in the metalated rings was established
without ambiguity in all the compounds. In 5BB‚CH3CO2H,
whose crystals accidentally grew from a mixture of isomers,
detailed refinement confirmed some disorder in the metalated
rings, with the sulfur atoms in the 3- and 4-positions. The best
refinement was obtained for an 85% of occupation in the
3-position. Compound 10AA‚(py)2 also shows some disorder
in one of the metalated rings, with the sulfur atom in the 2-
and 3-position (Figure S3).
Compound 5BB‚CH3CO2H (Figure S1) contains in the lattice
one molecule of acetic acid per mole of rhodium dimer. All

Synthesis of Dirhodium(II) Complexes
Organometallics, Vol. 25, No. 21, 2006 5115
a
Scheme 2. Mono- and Bis-cyclometalated Compounds Obtained from 3TP, 3TPPh2, and 2TPPPh2
a Structures in frames are determined by X-ray. Compounds between brackets have been spectroscopically detected.
the distances indicate that the lattice molecule of acetic acid is
establishing a hydrogen bond interaction with an oxygen atom
of one bridging carboxylate ligand, with an O6‚‚‚O1 distance
of 2.7 Å. Compound 7A‚CH3CO2H (Figure S2) also has one
molecule of acetic acid in the lattice per rhodium dimer, but in
this case no other interaction with the dirhodium molecule was
found. Instead, two of these molecules are associated, forming
dimers stabilized by hydrogen bonds.
Finally, in compound 11AA‚py‚(H2O)0.5 (Figure S4), there
is one molecule of water showing symmetric hydrogen bond

5116 Organometallics, Vol. 25, No. 21, 2006
Lloret et al.
Scheme 3. Thermal and Photochemical Reactions between
Rh2(O2CCH3)4.(CH3OH)2 and 3TP (a), 3TPPh2 (b), and
2TPPh2 (c)
Scheme 4. H/D Exchange by Thermal Treatment of 1B in
d4-Acetic Acid
and the solid residue was dissolved in CD3CO2D and heated at
70 °C for 12 h, leading to a ca. 50:50 ratio of 7A/8 (point 4 in
Figure S11). However, after longer reaction time the 7A/8 molar
ratio increased, reaching a 76:26 value after 135 h (point 5 in
Figure S11), similar to the equilibrium mixture upon treatment
in acetic acid. For comparison, 7A led to a 55:45 molar ratio
of 7A/8 when heated at 70 °C in d4-acetic acid (point 1 in Figure
S11). These observations can be attributed to isotopic effects
(see below).
The isomerization mixtures were analyzed by 1H NMR, taking
into account the signals belonging to 7A, which had been
previously isolated, and assigning the additional resonances to
8 (Figures S5-S10). From the analysis of the evolution from
7A to 8 in d4-acetic acid, it can be concluded that complete
H/D exchange occurred at the thienyl ring C-3 of 8 (Figure
S10 in SI). However, the H/D exchange at the phenyl ring ortho-
position of both compounds increased from only about 30%
after 12 h to 80% after 135 h of heating.
No evidence of reorganization of the metalated thienyl ring
from type A to type B structure was observed in these
experiments. This result contrasts with that found for the tris-
(2-thienyl)phosphine derivative.2
Computational Results. Theoretical (DFT) calculations were
performed in order to clarify the reactivity of the thienylphos-
phines and the stability of the corresponding rhodium complexes.
As a preliminary approach, the energy of 2TP and 3TP, as
well as the phosphines containing a mixed set of thienyl
substituents, 2,2,3TP and 2,3,3TP, were calculated. No signifi-
cant differences were observed in the values for these four
ligands (2TP: 0.0 kJ/mol, 2,2,3TP: -1.3 kJ/mol, 2,3,3TP: 0.5
kJ/mol, and 3TP: 3.0 kJ/mol).
The energy values for the mono-cyclometalated dirhodium-
(II) compounds with symmetrical thienyl phosphines, 2TP and
3TP, as well as with the phosphines having a mixed set of
thienyl substituents were also calculated (Table 1).
We observed that metalated compounds with structure type
B are the least energetic. Thus, compound 1B is found 23.7
kJ/mol more stable than the related compound 3TP-C, whose
metalated ring has structure C. In agreement with that, the latter
isomer was not detected in any of the metalation reactions
performed with 3TP.
interactions with two rhodium dimers, in particular with two O
atoms of two carboxylate groups (O5‚‚‚O1 distance of 2.73 Å).
Treatment of Mono-cyclometalated Compounds with
Acetic Acid. As part of the comparative studies of reactivity
for these compounds, we treated compounds 1B, 4B, and 7A
with d4-acetic acid at 70 °C. The chemical evolution was
1
followed by H NMR spectroscopy.
Compound 1B. Complete and selective H/D exchange was
observed at the C-4 of the cyclometataled ring after 2 h, and
compound 1B(d1) was selectively formed (Scheme 4). This
exchange can be explained by rhodium-carbon bond cleavage
following ring protonation/deuteration at the metalated position.
Such a process is relatively fast and selective, as no activation
of the other thienyl rings was observed. Under these conditions,
the introduction of deuterium at the nonmetalated thienyl rings
required considerably longer reaction time (>50 h). This
observation could indicate that rotation around the Rh-P bond
is considerably slower than around the P-C bond. Only species
1B, with different levels of H/D exchange, were spectroscop-
ically observed in solution during all the process. The isomeric
compound with structure C was not detected, in good agreement
with the lower stability calculated for species with structure C
(see below calculated data for 3TP-C).
Compound 4B. Only H/D exchange at the metalated thienyl
ring was detected when compound 4B was treated under the
same conditions as 1B. No evidence of incorporation of
deuterium into the phenyl rings or formation of isomeric species
metalated through the phenyl rings was observed.
Compound 7A. Partial isomerization of compound 7A to 8
(up to 78:22 ratio of 7A/8) was observed when 7A was dissolved
in acetic acid and heated at 70 °C, reaching equilibrium after
10 h (point 2 in Figure S11). No changes were detected after
extending the heating for 10 additional hours (point 3 in Figure
S11). The solvent of this sample was removed under vacuum,
We have recently reported that mono-cyclometalated com-
pounds derived from 2TP undergo selective rearrangement of
the metalated ring in the presence of acetic acid and adopt
structure B.2 This unusual ring rearrangement from structure
type A to B is driven by the higher stability (15.8 kJ/mol) of
the resulting species (see data for 2TP-B and 2TP-A in Table
1). On the other hand, substitution of 2-thienyl by 3-thienyl
groups in the nonmetalated substituents of the phosphine also
yields more stable mono-cyclometalated compounds, though the
effect is relatively small (compare data for 3TP-B with those
for 2,3TP-B and 2TP-B in Table 1).

Synthesis of Dirhodium(II) Complexes
Organometallics, Vol. 25, No. 21, 2006 5117
Table 1. Calculated Energy Values (kJ/mol) for
Rh2(O2CCH3)3(PC)‚(H2O)2 Mono-cyclometalated Compounds
with Tris-thienylphosphines as Ligands
Table 3. Calculated Energy (kJ/mol) for
Rh2(O2CCH3)2(PC)2‚(H2O)2 Bis-cyclometalated Compounds
with Tris-thienylphosphines as Ligands
E
E
configuration
HT
∆G(323)
∆G(298)
2TP-AAa
2TP-ABa
2TP-BBa
2TP-AA
0.0
0.0
-16.9
3TP-CC
0.0
0.0
3TP-BC (2BC)
3TP-BB (2BB)
3TP-BB (3BB)
-23.2
-21.9
-46.2
-45.2
-29.5
-21.4
-32.6
-29.6
25.0
HH
27.7
a In ref 2.
Interestingly, in contrast with the case of the tris(2-thienyl)-
phosphine mono-cyclometalated compound,2 no rearrangement
from structure A to B was observed upon thermal treatment of
7A in acid media, despite the higher stability (ca. 15 kJ/mol)
of 4B compared to Ph2TP-A.
Similar trends are observed for the energies of the bis-
cyclometalated derivatives. Compounds with metalated 3-thienyl
rings and with structure type B are energetically favored
compared to other structures (Table 3).
Although calculations indicated that H-T bis-cyclometalated
compounds with thienyl phosphines are more stable than the
H-H isomers, both types of compounds formed from the
thermal reactions of dirhodium tetraacetate and thienyl phos-
phines. Slow isomerization from H-H to H-T structure upon
prolonged heating in acetic acid has been observed only for
compounds derived from 2TP.2
a In ref 2.
Table 2. Calculated Energy Values (kJ/mol) for
Rh2(O2CCH3)3(PC)‚(H2O)2 Mono-cyclometalated Compounds
with Diphenylthienylphosphines as Ligands
Discussion
In general, the thienylphosphines show higher reactivity than
the aryl phosphines previously described. This increasing
reactivity is especially remarkable under photochemical condi-
tions; the thienyl phosphines readily yield the bis-cyclometalated
compounds under conditions where the aryl phosphines only
give mixtures of metalated compounds.8 One additional detail
is the higher tendency of the thienyl phosphines to form, under
thermal conditions, bis-cyclometalated compounds with H-H
arrangement of the phosphines. Fortunately, the H-T com-
pounds can be selectively obtained, in moderate to high yield,
when the reactions are performed under photochemical condi-
tions. The DFT calculations confirm that bis-cyclometalated
compounds with H-H structure have much higher energy value
than the corresponding H-T isomers.
An interesting observation is the affinity of the rhodium atoms
to sulfur atoms. Thus, in the absence of other donor molecules,
some sort of aggregation is observed by NMR for the H-H
product 3BB. In these conditions, the two phosphorus atoms
become nonequivalent. The addition of acetic acid produces
again a symmetrical spectrum, and this is a reversible process.
These observations suggest that an intermolecular interaction
between the rhodium center of one molecule and a sulfur atom
belonging to a thienyl group of other one occurs. All the efforts
to obtain single crystals of 3BB to confirm this association have
failed.
The calculated energy values for the mono-cylometalated
compounds with diphenylthienylphosphine ligands are shown
in Table 2. In a qualitative sense, there is agreement between
the experimental results for the isolated compounds and their
calculated energies in the gas phase. Compound 7A is only 10.6
kJ/mol more stable than 8. We observed that the thermal reaction
of dirhodium tetraacetate with 2TPPh2 gave a mixture of both
compounds, though 7A was the major product. However, no
mono-cyclometalated compound metalated at one phenyl ring
was detected when using 3TPPh2, in good agreement with the
higher stability of 4B than Ph,3TP-Ph (ca. 25 kJ/mol). The
same applies to the compound metalated through the 3-thienyl
ring and with structure type C (Ph2TP-C), which was not
detected in solution, in good agreement with the higher stability
of 4B (ca. 24 kJ/mol).
The reactivity order of aromatic ring C-H activation (phenyl
< 2-thienyl , 3-thienyl) is in agreement with the relative energy
values calculated for the dirhodium derivatives. Thus, only one
mono-cyclometalated compound, 4B, is obtained from the
(8) Unpublished results.

5118 Organometallics, Vol. 25, No. 21, 2006
Lloret et al.
Scheme 5. Evolution from 7A to 8 in (i) Acetic Acid and
(ii) d4-Acetic Acid
reaction of 3TPPh2, and two mono-cyclometalated compounds,
7A and 8, are obtained in a 9:1 ratio from the reaction with
2TPPh2.
For 3TP and 3TPPh2, two carbon atoms from the 3-thienyl
ring are accessible for C-H activation, giving rise to two types
of structure, B or C. Calculations assign lower energy for the
first type of structure, and in agreement with that, only
compounds with two metalated ligands having structure B, 2BB
and 5BB, can be obtained by a combination of photochemical
and thermal reactions. Thus, irradiation of 3TP with dirhodium
tetraacetate gives a mixture of two products, the more stable
2BB and the intermediate 2BC. By thermal treatment, this
intermediate rearranged to give 2BB as the only product. The
same applies to the reaction with 3TPPh2. A mixture of 5BB
and 5BC is formed after irradiation, and again rearrangement
of 5BC to 5BB is observed by thermal treatment of that mixture.
However, if these reactions are thermally performed, mixtures
of H-T (2BB and 5BB) and H-H compounds (3BB and 6BB)
are obtained. In these cases, rearrangement from a H-H to a
H-T structure is not detected, although such a process,
according to the calculations, should be thermodynamically
favored.
The treatment of mono-cyclometalated compounds with CD3-
CO2D provides interesting information on different processes
occurring in solution. Evidence of reversible Rh-C bond
cleavage and C-H bond activation is obtained in all the cases,
but a detailed analysis was possible only for the more simple
compounds, the mono-cyclometalated ones. In the case of
compound 1B, results indicate that all the processes yielding
1B(d1), shown in Scheme 4, must be considerably faster than
the rotation around the Rh-P bond, which would extend the
H/D exchange to all the thienyl rings. Therefore, it is not
surprising that complete and selective H/D exchange is obtained
at the metalated thienyl ring for compound 4B. The higher
reactivity of the 3-thienyl rings toward the metalation reaction,
compared to the phenyl rings, and the restricted rotation around
the Rh-P bond prevent the incorporation of deuterium into the
phenyl rings.
agreement with these calculations, as the 7A:8 molar ratio is
ca. 3:1 at equilibrium, demonstrating that C-H activation at
the thienyl ring is favored compared to the C-H activation at
phenyls.
However, the fact that the final product distribution is
different for acetic acid and d4-acetic acid requires some
comments. Assuming that the slowest process is the Rh-C bond
cleavage and that differences in acid strength would produce
only differences in the time required to reach the equilibrium,
we propose that the higher 7A/8 is due to an isotopic effect.
Treatment of 7A in d4-acetic acid after 12 h yields a 7A:8
ratio of ca. 50:50. In this case, the formation of 7A from the
intermediate species requires C-D activation, while formation
of 8 involves C-H activation. Therefore, the higher strength
of the C-D bond compared to the C-H bond makes metalation
at the phenyl ring more competitive and justifies the result.
However, after longer reaction times, both phenyl groups
become deuterated and, consequently, the molar ratio of products
slowly evolves to the 3:1 initial value.
The selective deuteration at the C-4 position of the metalated
thienyl ring in 1B and 4B can be easily explained. These two
compounds undergo Rh-C bond cleavage when heated in acetic
acid to form species with one equatorial ligand, 3TP or 3TPPh2,
respectively. Such species, which are considered intermediates
in the metalation reaction, can undergo cyclometalation reaction
via activation of any of the two available C-H bonds in the
3-thienyl ring, yielding finally metalated rings with structure B
or C. The observation of deuterium incorporation at the C-4
position of the thienyl ring confirms that metalation takes places
at both C-2 and C-4 carbon atoms. The fact that the mono-
cyclometalated compound with structure type C is not observed
in solution is in agreement with the lower stability calculated
for this type of coordination, compared to structure type B.
Additionally, it has been observed that bis-cyclometalated
compounds having a metalated thienyl ring with structure type
C, for example 2BC or 5BC, thermally rearrange to form the
isomeric compounds with structure type BB.
Conclusions
The thermal reaction of dirhodium tetraacetate with tris-(3-
thienyl)phosphine (3TP), diphenyl(3-thienyl)phosphine (3TP-
Ph2), and diphenyl(2-thienyl)phosphine (2TPPh2) gives rise to
mono-cyclometalated compounds or bis-cyclometalated com-
pounds (with head-to-tail (H-T) and head-to-head (H-H)
configuration) depending on the Rh2(O2CCH3)4/phosphine molar
ratio. The reactivity order of aromatic ring C-H activation is
phenyl < 2-thienyl , 3-thienyl, which leads to a selective
activation of the thienyl ring. Bis-cyclometalated compounds,
with symmetric H-T configuration, can be prepared in 63-
77% yield under photochemical conditions or upon combination
of photochemical and thermal treatment in acetic acid.
The observed isomerization from 7A to 8, when the first
compound is reacted with acid, is an additional evidence of
activation of phenyl rings in 2TPPh2. In all the conditions used,
compound 7A is always the major product in this equilibrium.
Calculations indicate that for phosphines with a mixed set of
substituents, such as 2TPPh2, metalation at the thienyl ring
yields a more stable isomer (7A) than metalation at the phenyl
ring (8). The results after treatment of 7A in acetic acid are in
The available results confirm that the structure of type B is
the most stable one for the metalated thienyl ligands. Under

Synthesis of Dirhodium(II) Complexes
Organometallics, Vol. 25, No. 21, 2006 5119
tography was performed on silica gel (35-70 mesh) on hexane.
Elution solvents used were volume/volume mixtures, unless speci-
fied otherwise. All reactions were carried out in oven-dried
glassware under an argon atmosphere, although the isolated solids
are air-stable.
photochemical conditions, species with metalated thienyl moi-
eties having structure type C have been detected as intermedi-
ates. Rearrangement from structure type C to type B takes place
under thermal treatment. Additionally, the formation in acid
media of intermediate species with structure type C, not
spectroscopically detected, from complex 1B or 4B must be
invoked in order to explain the observed incorporation of
deuterium at the C-4 of the metalated ring in isotopic labeling
experiments performed at 70 °C.
When Ph and 3-thienyl moieties are competing, 3TPPh2,
selective activation of the thienyl ring is always observed. These
results are in good agreement with the difference in the energy
values (∆G° 27 kJ/mol) calculated for the corresponding
compounds resulting from activation (Table 2). However,
competition of Ph and 2-thienyl rings gives a mixture of
compounds resulting from activation of the 2-thienyl (7A) and
phenyl rings (8). The equilibrium between these two species
was also studied in some detail.
Synthesis of Rh2(O2CCH3)3[(3-C4H2S)P(3-C4H3S)2] (1B).
Rh2(O2CCH3)4‚(CH3OH)2 (100 mg, 0.20 mmol) was dissolved in
toluene/acetic acid (20 mL, 3:1), and 3TP (50 mg, 0.18 mmol)
was added. The color changed nearly immediately to purple, and
the mixture was heated for 2 h under reflux. The solvent was
evaporated under reduced pressure and the product purified by
column chromatography using 100:20:0.5 toluene/AcOEt/AcOH
mixtures. The desired product was collected from a dark gray band
and obtained pure after evaporation of the solvents, crystallization
from CH2Cl2/hexanes, and washing with Et2O/hexanes. 1B was
obtained as a gray solid poorly soluble in the absence of acetic
1
acid (yield 74 mg, 55%). H NMR (400 MHz, CDCl3, 298 K): δ
1.43 (s, cis-CH3CO2, 6H), 2.34 (s, trans-CH3CO2, 3H), 7.26 (dd, J
) 5.1 Hz, J ) 2.2 Hz, 1H), 7.33 (m, 2H), 7.48 (m, 3H), 7.63 (m,
2H). 13C{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 23.51 (s), 23.80
(s), 126.21 (d, J ) 12.5 Hz), 128.03 (b), 130.25 (d, J ) 14.1 Hz),
132.04 (d, J ) 12.6 Hz), 146.62 (d, J ) 55.4 Hz), 183.10 (s), 190.12
ppm (s). 31P{1H} NMR (121.4 MHz, CDCl3/acetic acid, 298 K):
Finally, the energy values calculated (DFT) for the different
compounds are in good agreement with the experimental results.
Experimental Section
1
δ -5.23 ppm (bd, JP,Rh ) 150 Hz). Anal. Calcd for 1B‚
Computational Details. All calculations were carried out with
the Gaussian98 program package.9 The DFT level of theory with
the nonlocal density functional B3PW9110 was selected for the
quantum chemical studies. The basis set comprised the Stuttgart-
Dresden effective small core potential11 augmented with an extra
p-polarization function for rhodium (SDD(p)) and a standard all-
electron basis set 6-31G* for other atoms. Frequency analysis with
no scaling was performed to ensure ground state optimization.
General Comments. Rh2(O2CCH3)4‚(CH3OH)2 was purchased
from Pressure Chemical Co. P(3-SC4H3)3, P(3-SC4H3)Ph2, and P(2-
SC4H3)Ph2 were prepared by standard methods using nucleophilic
displacement on PCl3 or PClPh2.12
(CH3CO2H)2, C20H21O8PRh2S3 (722.4): C 33.25, H 2.93. Found:
C 33.54, H 2.90.
Synthesis of (H-T) Rh2(O2CCH3)2[(3-C4H2S)P(3-C4H3S)2]2
(2BB). Rh2(O2CCH3)4‚(CH3OH)2 (100 mg, 0.2 mmol) and 3TP (120
mg, 0.43 mmol) were dissolved in a mixture of CH2Cl2 and AcOH
(100 mL, 9:1). The resulting solution was irradiated for 6 h. The
solvent was evaporated under reduced pressure, and the residue,
dissolved in acetic acid, was heated at 90 °C for 15 h. After
evaporation of the solvent and filtration through silica (CH2Cl2/
Et2O, 9:1), 2BB was crystallized as a violet solid (yield, 110 mg,
1
63%). H NMR (400 MHz, CDCl3, 298 K): δ 1.53 (s, 6H), 6.86
(m, 2H), 6.88 (m, 2H), 6.98 (m, 2H), 7.12 (m, 2H), 7.19 (m, 2H),
7.36 (m, 2H), 7.40 (m, 2H), 7.52 ppm (m, 2H). 13C{1H} NMR
(100.5 MHz, CDCl3, 298 K): δ 22.87 (s), 125.67 (d, J ) 12.8
Hz), 126.82 (d, J ) 12.4 Hz), 128.35 (d, J ) 10.0 Hz), 129.70 (d,
J ) 10.7 Hz), 130.13 (d, J ) 14.6 Hz), 130.72 (d, J ) 7.8 Hz);
130.80 (d, J ) 4 Hz), 182.16 ppm (s). 31P{1H} NMR (161.9 MHz,
CDCl3, 298 K): δ -1.70 ppm (AA′XX′ system). Anal. Calcd for
2BB‚(H2O)2, C28H26O6P2Rh2S6 (918.7): C 36.60, H 2.85. Found:
C 36.57, H 3.23.
All solvents were of analytical grade. All the irradiations were
1
made with a 125 W mercury lamp with Pyrex filter. H, 13C, and
31P NMR spectra were recorded on a Bruker Avance 400 MHz
spectrometer at 25 °C in CDCl3 unless otherwise indicated. 1H and
13C NMR spectra were referenced to residual solvent peaks. 31P
spectra were referenced to an external H3PO4 sample. Chemical
shifts are reported in ppm and coupling constants (J) in hertz (Hz).
Elemental analyses were provided by Centro de Microana´lisis
Elemental, Universidad Complutense de Madrid. Column chroma-
Synthesis of (H-T) Rh2(O2CCH3)2[(3-C4H2S)P(3-C4H3S)2]-
[(3′-C4H2S)P(3-C4H3S)2] (2BC). Rh2(O2CCH3)4‚(CH3OH)2 (100
mg, 0.2 mmol) and 3TP (120 mg, 0.43 mmol) were dissolved in a
mixture of CH2Cl2 and AcOH (100 mL, 9:1). The resulting solution
was irradiated for 6 h. The solvent was evaporated under reduced
pressure, and the residue was transferred to a chromatography
column. First elution with a 80:20:0.5 toluene/AcOEt/AcOH
mixture eliminated decomposition compounds and phosphine
oxides. The remaining violet fraction was collected and was
submitted to a second chromatography. Starting the elution with a
100:6:0.5 CH2Cl2/Et2O/AcOH mixture and increasing polarity
different fractions were collected and were analyzed by phosphorus
NMR spectroscopy. The first fractions contained compound 2BB
(yield, 71 mg, 35%), while the last fractions that contained 2BC
were evaporated and the residue was crystallized from dichlo-
romethane/hexanes/AcOH (yield, 60 mg, 29%). 1H NMR (400
MHz, CDCl3, 298 K): δ 1.28 (s, 3H), 1.56 (s, 3H), 6.75 (m, 1H),
6.86 (m, 2H), 6.88 (m, 1H), 7.00 (m, 1H), 7.14 (b, 1H), 7.21 (b,
1H), 7.43-7.36 (m, 3H), 7.55 ppm (m, 1H). 13C{1H} NMR (100.5
MHz, CDCl3, 298 K): δ 22.60 (dd, J ) 6.5 Hz, J ) 2.6 Hz), 119.82
(d, 19.9 Hz), 132-124 (overlapping multiplets), 133.53 (d, J )
58.1 Hz), 133.91 (d, J ) 27.2 Hz), 134.85 (d, J ) 63.8 Hz), 137.94
(d, J ) 76.4 Hz), 141.96 (d, J ) 75.8 Hz), 145.42 (m), 167.48 (m,
(9) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M.
W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon,
M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.7; Gaussian,
Inc.: Pittsburgh, PA, 1998.
(10) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Perdew, J. P.;
Wang, Y. Phys. ReV. B: Condens. Matter Mater. Phys. 1992, 45, 13244.
(11) The basis set was obtained from the Extensible Computational
Chemistry Environment Basis Set Database, Version 9/12/01, as developed
and distributed by the Molecular Science Computing Facility, Environmental
and Molecular Sciences Laboratory, which is part of the Pacific Northwest
Laboratory, P.O. Box 999, Richland, WA 99352, and funded by the U.S.
Department of Energy. The Pacific Northwest Laboratory is a multiprogram
laboratory operated by Battelle Memorial Institue for the U.S. Department
of Energy under contract DE-AC06-76RLO 1830. Contact David Feller or
Karen Schuchardt for further information.
(12) (a) Isslieb, K.; Krech, F. Z. Anorg. Allg. Chem. 1964, 328, 21. (b)
Lahuerta, P.; Peris, E.; Sanau´, M.; UÄ beda, M. A.; Garc´ıa-Granda, S. J.
Organomet. Chem. 1993, 445, C10.

5120 Organometallics, Vol. 25, No. 21, 2006
Lloret et al.
metalated), 181.95 (d, J ) 2,1 Hz; CO2), 182.45 ppm (d, J ) 2.1
Hz, CO2). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ 4.08 (dd,
1J(P,Rh) ) 169.0 Hz, 2JP,Rh ) 6.1 Hz), -0.4 ppm (dd, 1JP,Rh ) 169.4
Hz, 2JP,Rh ) 6.5 Hz). The solid products obtained by crystallization
from solutions containing acetic acid did not provide reproducible
elemental analysis.
) 9.9 Hz), 134.56 (d, J ) 72.0 Hz), 166.08 (m, metalated), 183.28
(s) 190.12 (s). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ 11.23
ppm (dd, 1JP,Rh ) 148.5 Hz, 2JP,Rh ) 4.7 Hz). Anal. Calcd for 4B‚
CH3CO2H, C24H25O8PRh2S (710.3): C 40.58, H 3.54. Found: C
40.57, H 3.65.
Synthesis of (H-T) Rh2(O2CCH3)2[(3-C4H2S)PPh2]2 (5BB).
Rh2(O2CCH3)4‚(CH3OH)2 (150 mg, 0.3 mmol) and 3TPPh2 (175
mg, 0.65 mmol) were dissolved in a mixture of CH2Cl2 and AcOH
(100 mL, 9:1). The resulting solution was irradiated for 6 h, the
solvent was evaporated under reduced pressure, and the residue,
dissolved in acetic acid, was heated at 90 °C for 15 h. After
evaporation of the solvent and filtration through silica (CH2Cl2/
Et2O, 9:1) compound 5BB was crystallized as a violet solid (yield,
Synthesis of (H-H) Rh2 (O2CCH3)2[(3-C4H2S)P(3-C4H3S)2]2
(3BB). Rh2(O2CCH3)4‚(CH3OH)2 (113 mg, 0.22 mmol) was dis-
solved in toluene/acetic acid (20 mL, 3:1). 3TP (225 mg, 80 mmol)
was added to the hot (ca. 100 °C) solution, which immediately
changed to red-violet color. After refluxing for 3 h the solvent was
evaporated and the residue was passed to a chromatography column,
eluted using a 100:20:0.5 toluene/AcOEt/AcOH mixture. The main
colored fraction was collected and evaporated, and the residue was
transferred again to a chromatography column that was eluted using
a 50:3 CH2Cl2/Et2O mixture. A first fraction containing 3BB was
eluted followed by a second one, which contained compound 2BB.
From the first band, 3BB was obtained as a red crystalline solid
(yield, 47 mg, 21%). 1H NMR (400 MHz, CDCl3, 298 K): δ 1.30
(s, 3H, CH3CO2, trans to PB), 1.91 (s, 3H, CH3CO2, 3H, trans to
PA), 6.03 (m, 1H, PB), 6.26 (d, J ) 4.83 Hz, 1H, PB), 6.64 (m, 1H
PB), 6.69 (dd, J ) 2.32 Hz, J ) 5.2 Hz, 1H, PB), 6.81 (m, 1H, PA),
7.04 (d, J ) 4.4 Hz, 1H, PA), 7.14 (b, 1H, PA), 7.20 (m, 1H, PA),
7.25 (m, 1H, PA), 7.32 (d, J ) 5.0 Hz, 1H, PB), 7.44 (m, 1H, PB),
7.51 (m, 2H, PB + PA), 7.75 (d, J ) 5.3 Hz, 1H, PA), 7.92 ppm (d,
J ) 5.6 Hz, 1H, PA) 8.18 (d, J ) 5.0 Hz, 1H, PB). 13C{1H} NMR
(100.5 MHz, CDCl3, 298 K): δ 22.41 (s, CH3CO2, trans to PB),
24.40 (s,CH3CO2, trans to PA), 123.3 (d, J ) 12.0 Hz, PB), 124.6-
125.1 (overlapping multiplets), 125.82 (d, J ) 11.5 Hz, PA), 126.91
(d, J ) 12.6 Hz, PB), 129.04 (d, J ) 10.5 Hz, PB), 129.52 (d, J )
11.5 Hz, PA), 130.0-132.4 (overlapping multiplets), 133.00 (d, J
) 31.9 Hz), 133.74 (d, J ) 14.1 Hz), 134.63 (d, J ) 56.0 Hz),
136.68 (d, J ) 51.7 Hz), 138.42 (d, J ) 74.8 Hz), 139.27 (dd, J )
2.9 Hz; J ) 74.0 Hz), 162.40 (dd, J ) 35.6 Hz, J ) 41.8 Hz,
RhCCPB), 173.11 (dd, J ) 36.6 Hz; J ) 43.9 Hz, RhCCPA), 181.82
(d, J ) 2.6 Hz, trans-CH3CO2(equatorial), PA), 181.90 ppm (d, J
) 2.1 Hz, trans-CH3CO2(equatorial), PB). 31P{1H} NMR (161.9
MHz, CDCl3, 298 K): δ 2.8 (ddd, 1JP,Rh ) 150.7 Hz, 2JP,P ) 43.5
1
230 mg, 70%). H NMR (400 MHz, CDCl3, 298 K): δ 1.46 (s,
6H), 6.81 (dd, J ) 5.1 Hz, J ) 1.7 Hz, 2H), 7.08 (dd, J ) 5.1 Hz,
J ) 1.2 Hz, 2H), 7.22 (m, 8H), 7.29 (m, 2H), 7.33 (m, 6H), 7.80
ppm (m, 4H). 13C{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 22.7
(d, J ) 2.6 Hz), 126.3 (d, J ) 11.6 Hz), 127.5 (d, J ) 6.1 Hz),
127.6 (d, J ) 5.8 Hz), 128.7 (d, J ) 2.5 Hz), 129.1 (d, J ) 2.3
Hz), 129.4 (d, J ) 9.3 Hz), 132.0 (d, J ) 9.1 Hz), 133.2 (d, J )
9.4 Hz), 133.8 (d, J ) 53.8 Hz), 134.2 (d, J ) 47.6 Hz), 135.2 (d,
J ) 77.0 Hz), 167.7 (m, metalated), 182.4 ppm (s). 31P{1H} NMR
(161.9 MHz, CDCl3, 298 K): δ 10.6 ppm (AA′XX′ system). Anal.
Calcd for 5BB‚CH3CO2H, C38H34O6P2Rh2S2 (918.6): C 49.68, H
3.73. Found: C 49.40, H 3.98.
Synthesis of (H-H) Rh2(O2CCH3)2[(3-C4H2S)PPh2]2 (6BB).
Rh2(O2CCH3)4‚(CH3OH)2 (150 mg, 0.3 mmol) and 3TPPh2 (175
mg, 0.65 mmol) were dissolved in a mixture of toluene/glacial acetic
acid (100 mL, 90:10), and the solution was refluxed for 8 h. After
evaporation, the residue was submitted to standard column chro-
matography, eluting with 100:10:0.5 CH2Cl2/Et2O/AcOH. The first
violet band collected contained compound 6BB (yield, 55 mg, 19%)
followed by a second violet band due to compound 5BB (yield,
1
121 mg, 42%). H NMR (400 MHz, CDCl3, 298 K): δ 1.39 (s,
6H), 6.69 (m, 4H), 6.86 (m, 8H), 7.32 (m, 4H), 7.40 (m, 2H), 7.53
(d, J ) 6.4 Hz, 2H), 7.73 (m, 4H). 13C{1H} NMR (100.5 MHz,
CDCl3, 298 K): δ 23.44 (s), 124.20 (s), 127.03 (m), 127.43 (m),
128.48 (s), 128.89 (s), 129.32 (s), 132.68 (m), 133.52 (m) 135.25
(s) 136.15 (s), 164.55 (m, metalated), 181.30 ppm (s). 31P{1H} NMR
(161.8 MHz, CDCl3, 298 K): δ 24.88 (dd, 1JP-Rh ) 153.8 Hz, J )
5.0 Hz). The solid products obtained by crystallization from
solutions containing acetic acid did not provide reproducible
elemental analysis.
2
1
2
Hz, JP,Rh ) 5.8 Hz, PA), -7.4 ppm (ddd, JP,Rh ) 152.3 Hz, JP,P
) 43.3 Hz, 2JP,Rh ) 5.8 Hz, PB). Anal. Calcd for 3BB‚(CH3CO2H)2,
C32H30O8P2Rh2S6 (1002.7): C 38.32, H 3.01. Found: C 38.65, H
3.10.
NMR data of 3BB in CDCl3 with traces of CH3CO2H mixtures:
1H NMR (400 MHz, CDCl3/CH3CO2H, 298 K): δ 1.60 (s, CH3-
CO2, 6H), 6.59 (d, J ) 3.7 Hz, 2H), 6.84-6.81 (m, 4H), 6.95 (m,
2H), 7.11 (m, 2H), 7.20 (d, J ) 5.2 Hz, 2H), 7.25 (m, 2H), 7.32
ppm (m, 2H). 13C{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 19.85
(s), 123.73 (m), 124.33 (m), 127.47 (m), 128.58 (m), 129.43 (m),
130.27 (m), 136.82 (m), 167.40 (m, metalated), 176.62 (s), 182.00
ppm (s). 31P{1H} NMR (161.9 MHz, CDCl3/CH3CO2H, 298 K):
Synthesis of Rh2(O2CCH3)3[(2-C4H2S)PPh2] and Rh2(O2CCH3)3-
[(C6H4)P(2-C4H2S)Ph] (7A and 8). 2TPPh2 (60 mg, 0.22 mmol)
and Rh2(O2CCH3)4‚(CH3OH)2 (118 mg, 0.23 mmol) were dissolved
in a mixture of toluene/acetic acid (55 mL, 9:1), and the solution
was heated under reflux for 3 h. After cooling, the solvent was
evaporated under reduced pressure and the resulting brown solid
was dissolved in CH2Cl2/AcOH (2 mL, 10:0.1), transferred to a
chromatography column, and eluted with the same mixture of
solvents. The eluted green-gray band was collected in two separate
fractions. The first fraction was evaporated and the residue
crystallized from CH2Cl2/hexanes/AcOH (5%), giving 7A as a
green-gray crystalline solid (yield, 72 mg, 50%). Single crystals of
7A suitable for X-ray diffraction were obtained from the same
mixture of solvents by slow evaporation. 1H NMR (400 MHz,
CDCl3, 298 K): δ 1.43 (s, 6H, cis-CH3CO2), 2.15 (s, 3H, trans-
CH3CO2), 7.46 (m, 4H), 7.51 (m, 2H), 7.75 (m, 4H), 7.88 (dd, J )
5.0 Hz, J ) 2.6 Hz, 1H), 8.05 ppm (dd, J ) 4.8 Hz, J ) 2.4 Hz,
1H). 13C{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 21.64 (s), 23.69
(s), 127.93 (d, J ) 10.8 Hz), 128.51 (d, J ) 3.2 Hz), 129.93 (d, J
) 2.7 Hz), 132.86 (d, J ) 10.3 Hz), 133.74 (s), 134.66 (dd, J )
18.1 Hz, J ) 1.3 Hz), 164.91 (m), 179.44 (b), 182.74 (s), 182.77
(s). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ 14.74 ppm (dd,
1
2
δ -3.1 ppm (dd, JP-Rh ) 152.9 Hz, JP-Rh ) 7.2 Hz).
Synthesis of Rh2(O2CCH3)3[(3-C4H2S)PPh2] (4B). Rh2(O2-
CCH3)4‚(CH3OH)2 (100 mg, 0.2 mmol) and 3TPPh2 (50 mg, 0.18
mmol) were dissolved in toluene/AcOH (50 mL, 9:1), giving a dark
gray-purple solution, which was refluxed for 2 h, yielding a dark
green-gray solution. After evaporation of the solvent under reduced
pressure the residue was purified by column chromatography. Using
a mixture of toluene/AcOEt/AcOH (100:20:0.5) a reddish fraction
of double-metalated product came off. Then elution with a 60:20:
0.5 toluene/AcOEt/AcOH mixture afforded a gray fraction, which
1
after crystallization gave 4B (yield, 94 mg, 75%). H NMR (400
MHz, CDCl3, 298 K): δ 1.38 (s, cis-CH3CO2, 6H), 2.35 (s, trans-
CH3CO2, 3H), 7.13 (dd, J ) 5 Hz, J ) 2 Hz, 5-CH2S, 1H), 7.31
(m, Ph, 4H), 7.38 (m, 2H), 7.45 (m, 1H), 7.61 ppm (m, 4H). 13C-
{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 19.50 (s), 20.81 (s),
127.70 (b), 127.97 (d, J ) 10 Hz), 128.50 (bd, J ) 8.4 Hz), 129.81
(d, J ) 2.5 Hz), 132.5 (s), 132.83 (d, J ) 53.0 Hz), 132.85 (d, J
2
1JP-Rh ) 153.4 Hz, JP-Rh ) 5.2 Hz). Anal. Calcd for 7A‚

Synthesis of Dirhodium(II) Complexes
Organometallics, Vol. 25, No. 21, 2006 5121
CH3CO2H, C24H25O8PRh2S (710.3): C 40.58, H 3.54. Found: C
40.34, H 3.73.
Slow evaporation of the solvents from a CH2Cl2/hexanes solution
of the pyridine adduct afforded single crystals of 10AA‚(py)2,
suitable for X-ray diffraction.
The second fraction contained a mixture of 7A and 8 in a 4:1
ratio. Additional chromatographic enrichment provided solutions
with a 1:1 ratio of both compounds that allowed the spectroscopic
characterization of 8. 1H NMR (400 MHz, CDCl3, 298 K): δ 1.29
(s, 3H, cis-CH3CO2(equatorial)), 1.36 (s, 3H, cis-CH3CO2-
(equatorial)), 2.36 (s, 3H, cis-CH3CO2(trans)), 6.98 (m, 1H), 7.10
(m, 2H), 7.26 (m, 1H), 7.32 (m, 2H), 7.38 (m, 1H), 7.43 (m, 1H),
Synthesis of H-H Rh2(O2CCH3)2[(2-C4H2S)PPh2]2 (11AA).
To a well-stirred solution of Rh2(O2CCH3)4‚(CH3OH)2 (250 mg,
0.5 mmol) in toluene/AcOH (30 mL, 2:1) at 100 °C was slowly
added 2TPPh2 (295 mg, 1.1 mmol) in 10 mL toluene. After
refluxing the mixture for 2.5 h the solvent was removed under
reduced pressure. The residue was transferred to a chromatography
column eluted with hexanes/AcOEt (2:1 to 1:3 ratio), separating
two bands. The second violet fraction corresponds to the already
described H-T compound 10AA (198 mg, 41%). The first fraction,
corresponding to 11AA, was evaporated under reduced pressure,
and the residue was precipitated with hexanes (yield, 75 mg, 17%).
31P{1H} NMR (121.4 MHz, CDCl3, 298 K): δ 18.5 ppm (dd, 1JP-Rh
1
7.54 (m, 2H), 7.65 (m, 1H), 8.62 ppm (m, 1H). H NMR (400
MHz, CD3CO2D, 298 K): δ 6.98 (m, 1H), 7.11 (m, 1H), 7.17 (m,
1H), 7.27 (m, 1H), 7.36 (m, 2H), 7.43 (m, 1H), 7.50 (m, 1H), 7.57
(m, 2H), 7.73 (m, 1H), 8.48 ppm (m, 1H). 31P{1H} NMR (161.9
MHz, CDCl3, 298 K): δ 11.5 ppm (dd 1J(P,Rh) ) 151.8 Hz, 2J(P,-
Rh) ) 6.2 Hz). The isolation of compound 8 in a pure state was
not achieved. Additional spectroscopic data concerning its structural
assignment are included in the SI.
2
) 154.7 Hz, JP-Rh ) 7.2 Hz). The solid was dissolved in
dichloromethane, and three drops of pyridine were added. Addition
Synthesis of H-T Rh2(O2CCH3)2[(2-C4H2S)PPh2]2 (9AA).
Rh2(O2CCH3)4‚(CH3OH)2 (100 mg, 0.2 mmol) and 2TPPh2 (120
mg, 0.44 mmol) were dissolved in a mixture of CH2Cl2/AcOH (100
mL, 9:1 ratio). The mixture was irradiated for 5-6 h, and the
solvent was evaporated under reduced pressure. The resulting
product was purified by standard column chromatography (SiO2,
hexanes/AcOEt (3:1 to 2:1 ratio)), giving 9AA (yield 118 mg, 70%).
1H NMR (400 MHz, CDCl3, 298 K): δ 1.43 (s, 6H), 6.36 (dd, J )
6.4, J ) 3.2 Hz, 2H), 7.14 (m, 8H), 7.19 (dd, J ) 6.4, J ) 2.4 Hz,
2H), 7.25 (m, 2H), 7.36 (m, 6H), 7.84 (m, 4H). 13C{1H} NMR
(100.5 MHz, CDCl3, 298 K): δ 23.01 (d, J ) 4 Hz), 127.29 (d, J
) 13.8 Hz), 127.49 (d, J ) 13.5 Hz); 128.83 (d, J ) 3.5 Hz),
128.96 (s), 129.17 (d, J ) 3.5 Hz), 132.28 (d, J ) 12.6 Hz), 133.31
(d, J ) 13.5 Hz), 134.99 (d, J ) 23.6 Hz), 134.68 (d, J ) 32.9
Hz), 134.96 (d, J ) 22.6 Hz), 164.96 (m, metalated), 181.72 ppm
(d, J ) 2.3 Hz). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ
16.82 ppm (AA′XX′ system). Anal. Calcd for 9AA‚(CH3CO2H)2,
C40H38O8P2Rh2S2 (978.7): C 49.09, H 3.91. Found: C 48.84, H
4.01.
Synthesis of H-T Rh2(O2CCF3)2[(2-C4H2S)PPh2]2 (10AA). To
a solution of 9AA (150 mg, 0.23 mmol) in chloroform (5 mL) was
added CF3CO2H (0.1 mL). After 5 min stirring, the solvents were
removed under vacuum at RT. This procedure was repeated five
times. The resulting product was purified by column chromatog-
raphy on SiO2 with CH2Cl2/Et2O (9:1 ratio). The collected fraction
was concentrated and precipitated with hexanes as a violet powder.
The solid was dissolved in dichloromethane (3 mL), and pyridine
(0.1 mL) was added. Addition of hexanes and slow evaporation
gave 10AA‚(py)2 (yield, 130 mg, 77%). 1H NMR (400 MHz,
CDCl3, 298 K): δ 6.63 (m, 2H), 6.95 (m, 4H), 7.15 (m, 10H);
7.51 (m, 12H), 7.80 (m, 2H), 8.65 ppm (d, J ) 8,7 Hz, 4H). 13C-
{1H} NMR (100.5 MHz, CDCl3, 298 K): δ 116.0 (q 1JC-F ) 288
Hz), 124.4 (s, NCC), 127.8-126.7 (overlapping multiplets), 129.4
(s), 129.7 (s), 132.8-133.5 (overlapping multiplets), 133.6 (d, J )
21.4 Hz), 135.2 (d, J ) 17.8 Hz), 137.1 (s), 151.7 (s, CN), 161.6
(m, metalated), 166.8 ppm (q, 2JC-F ) 38 Hz). 31P{1H} NMR (121.4
MHz, CDCl3, 298 K): δ 15.09 ppm (dd, 1JP-Rh ) 169.6 Hz, 2JP-Rh
) 5.9 Hz). Anal. Calcd (%) for 10AA‚(py)2, C46H34F6O4P2Rh2S2
(1124.7): C 49.12, H 3.04. Found: C 48.92, H 3.08.
of hexanes and slow evaporation gave single crystals of 11AA‚
py‚(H2O)0.5, suitable for X-ray diffraction. H NMR (400 MHz,
1
CDCl3, 298 K): δ 1.41 (s, 6H), 2.14 (s, 2H), 6.73 (m, 6H), 6.90
(m, 8H), 7.34 (m, 6H), 7.42 (m, 2H), 7.55 (d, J ) 4.9 Hz, 2H),
7.76 (m, 2H), 7.86 (m, 1H), 8.94 ppm (m, 2H). 31C{1H} NMR
(100.5 MHz, CDCl3, 298 K): δ 21.95 (s), 23.17 (s), 125.32 (s),
127.05 (d, J ) 5.4 Hz), 127.12 (d, J ) 5.2 Hz), 127.38 (d, J ) 5.2
Hz), 127.38 (d, J ) 5.2 Hz), 127.45 (d, J ) 5.2 Hz), 128.75 (d, J
) 10.8 Hz), 128.90 (d, J ) 10.8 Hz), 132.63 (d, J ) 5.3 Hz),
132.70 (d, J ) 5.3 Hz), 133.00 (d, J ) 5.0 Hz), 133.07 (d, J ) 5.0
Hz), 133.84 (d, J ) 9.2 Hz), 133.96 (d, J ) 9.4 Hz), 134.57 (s),
152.25 (s), 164.60 (m, metalated), 179.37 (b), 181.30 ppm (s). 31P-
{1H} NMR (161.9 MHz, CDCl3, 298 K): δ 22.61 ppm (dd, 1JP-Rh
2
) 155.0 Hz, JP-Rh ) 3.7 Hz). Anal. Calcd for (11AA.py)2‚H2O,
C82H72N2O9P4Rh4S4 (1893.3): C 52.02, H 3.83. Found: C 51.88,
H 3.95.
Experiments of Chemical Evolution in Acid Media. In a
standard experiment 7A (5 mg, 6.5 × 10-3 mmol) was dissolved
1
in acetic acid (0.45 mL), and the solution was monitored by H
and/or 31P NMR spectroscopy at 70 °C, recording a new spectrum
every 15 min.
Crystal structure data for 5BB‚CH3CO2H, 7A‚CH3CO2H, 2B,
10AA‚(py)2, and 11AA‚py‚(H2O)0.5 can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccd-
c.cam. ac.uk/data_request/cif.
Acknowledgment. Financial support by the Spanish Gov-
ernment (Project MAT2002-0442-1-C02-02 and J. Lloret fel-
lowship) is gratefully acknowledged.
1
Supporting Information Available: COSY and HMBC H-
31P spectra for compound 7A, as well as spectra of the evolution
1
from 7A to 8 (31P{1H} and H NMR and COSY spectra of 7A/8
mixtures) are included. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM0605128