The influence of phosphane coligands on the nuclearity of rhodium(I) 4-thiolatobenzoic acid complexes

Article abstract of DOI:10.1021/ic0610684

[RhCl(PR₃)₃] (R = Ph, Et) reacts with the potassium salt of 4-mercaptobenzoic acid to give a mixture of the monomeric and dimeric complexes, [Rh(SC₆H₄COOH)(PR₃)₃] and [{Rh(μ-SC₆H

Full text of DOI:10.1021/ic0610684

Inorg. Chem. 2006, 45, 10300−10308
The Influence of Phosphane Coligands on the Nuclearity of Rhodium(I)
4-Thiolatobenzoic Acid Complexes
Ulrike Helmstedt, Peter Lo1
nnecke,† and Evamarie Hey-Hawkins*
Institut fu¨r Anorganische Chemie der UniVersita¨t Leipzig, Johannisallee 29,
D-04103 Leipzig, Germany
Received June 14, 2006
[RhCl(PR3)3] (R
)
Ph, Et) reacts with the potassium salt of 4-mercaptobenzoic acid to give a mixture of the
Rh( -SC6H4COOH)(PR3)2 2], respectively. With
monomeric and dimeric complexes, [Rh(SC6H4COOH)(PR3)3] and [
{
µ
}
the labile PPh3 coligand, the dimer is the major product, while for the electron-richer coligand PEt3, the equilibrium
is easily shifted to the monomer by the addition of excess PEt3. Phosphane dissociation and dimerization could be
prevented by using the chelating coligand PPh(C2H4PPh2)2. [
(PEt3)3] (3a), and [Rh(SC6H4COOH) PPh(C2H4PPh2)2 ] (4) were fully characterized by nuclear magnetic resonance
{Rh(µ-SC6H4COOH)(PPh3)2}2] (2b), [Rh(SC6H4COOH)-
{
}
and infrared spectroscopy, mass spectrometry, and elemental analysis. The molecular structures of 2b and 4 were
determined by X-ray structure analysis. In solution, the lability of the phosphane ligands leads to the decomposition
of 2b. One of the decomposition products, namely, the mixed-valent complex [
COOH)(SC6H4COOH)(PPh3)3 2] (5), was characterized by X-ray structural analysis. The dinuclear rhodium(III) complex
Rh( -SC6H4COO)(SC6H4COOH)(PEt3)2 2] (6) was shown to be a byproduct in the synthesis of 3a, and this
{ µ-SC6H4COO)(µ-SC6H4-
RhIRhIII(
}
[
{
µ
}
demonstrates the reactivity of the rhodium(I) complexes toward oxidative addition. The structurally characterized
complexes 2b, 4, 5, and 6 show hydrogen bonding of the free carboxyl groups.
Introduction
type [Rh(SR)(PR′3)3] with tertiary phosphane ligands are
especially of interest, because they apparently show higher
reactivity toward electrophiles than the well-investigated
dinuclear thiolato-bridged complexes.5 To date, only a limited
number of stable monomeric rhodium(I) thiolato complexes
is known, that is, [Rh(SC6F5)(PR3)3] for PR3 ) PPh3,
Transition-metal complexes with thiolato ligands have
attracted increasing attention in view of their role in the
desulfurization of organosulfur compounds,1 especially the
hydrodesulfurization of fossil fuel feedstocks,2 metal-
catalyzed C-S bond cleavage and formation in organic
synthesis,3 and in the degradation of the thiolato ligands to
yield transition-metal sulfides.4 Some of these reactions
involve rhodium(I) thiolato phosphane complexes as inter-
mediates. Stable mononuclear rhodium(I) complexes of the
6
PMePh2, PMe2Ph, P(OMe)3, and P(OEt)3 and [Rh(SR)-
(PMe3)3] for SR ) SC6H5, 4-SC6H4Me, and 4-SC6H4OMe.7
Other known phosphane complexes of rhodium(I) thiolates
eliminate one phosphane ligand per rhodium center at room
(4) (a) Osakada, K.; Yamamoto, T. Inorg. Chem. 1991, 30, 2328. (b)
Bochmann, M.; Hawkins, I.; Wilson, L. M. J. Chem. Soc., Chem.
Commun. 1988, 344. (c) Brennan, J. G.; Siegrist, T.; Carroll, R. J.;
Stuczynski, S. M.; Brus, L. E.; Steigerwald, M. E. J. Am. Chem. Soc.
1989, 111, 4141. (d) Nomura, R.; Fujii, S.; Kanaya, K.; Matsuda, H.
Polyhedron 1990, 9, 361.
(5) (a) Carlton, L.; Bulbulia, Z. J. Organomet. Chem. 1990, 389, 139. (b)
Bonnet, J. J.; Kalck, P.; Poilblanc, R. Inorg. Chem. 1977, 16, 1514.
(c) Cruz-Garritz, D.; Garcia-Allejandre, J.; Torrens, H.; Alvarez, C.;
Toscano, R. A.; Poilblanc, R.; Thorez, A. Transition Met. Chem. 1991,
16, 130.
(6) (a) Beck, W.; Tadros, S. Z. Anorg. Allg. Chem. 1970, 375, 231. (b)
Carlton, L. J. Organomet. Chem. 1992, 431, 103.
(7) (a) Osakada, K.; Hataya, K.; Yamamoto, T. Inorg. Chem. 1993, 32,
2360. (b) Osakada, K.; Hataya, K.; Yamamoto, T. Organometallics
1993, 12, 3358.
* To whom correspondence should be addressed. Tel.: +49-(0)341-
9736151. Fax: +49-(0)341-9739319. E-mail: hey@rz.uni-leipzig.de.
† Crystal structure determinations.
(1) (a) Kwart, H.; Schuit, G. C. A.; Gates, B. C. J. Catal. 1980, 61, 128.
(b) Zaera, F.; Kollin, E. B.; Gland, J. L. Surf. Sci. 1987, 184, 75. (c)
Eisch, J. J.; Hallenbeck, L. E.; Han, K. I. J. Org. Chem. 1983, 48,
2963. (d) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259.
(2) (a) Bianchini, C.; Casares, J. A.; Meli, A.; Sernau, V.; Vizza, F.;
Sa´nchez-Delgado, R. A. Polyhedron 1997, 16, 3099. (b) Bianchini,
C.; Herrera, V.; Jimenez, M. V.; Meli, A.; Sa´nchez-Delgado, R. A.;
Vizza, F. J. Am. Chem. Soc. 1995, 117, 8567.
(3) (a) Okamura, H.; Miura, M.; Takei, H. Tetrahedron Lett. 1979, 43.
(b) Wenkert, E.; Ferreira, T. W.; Michelotti, E. L. J. Chem. Soc., Chem.
Commun. 1979, 637. (c) Wenkert, E.; Hanna, J. M.; Leftin, M. H.;
Michelotti, E. L.; Potts, K. T. J. Org. Chem. 1985, 50, 1125.
10300 Inorganic Chemistry, Vol. 45, No. 25, 2006
10.1021/ic0610684 CCC: $33.50
© 2006 American Chemical Society
Published on Web 11/15/2006

Influence of Phosphane Coligands
temperature and dimerize with the formation of [{Rh(µ-SR)-
(PR′3)2}2].5a,8 The tendency to dimerize decreases with
decreasing electron density of the thiolato ligand and with
increasing electron density of the phosphane ligands. Known
syntheses include the oxidative addition of thiols RSH to
[RhH(PPh3)4] followed by H2 elimination,5a,9 salt elimination
reactions of [RhCl(PR3)3] and alkali-metal thiolates,6a,7 and
the reaction of the dimeric complexes with excess phos-
phane.10
Experimental Section
General Remarks. All experiments were carried out under
purified dry nitrogen. Solvents were dried and freshly distilled under
nitrogen. The nuclear magnetic resonance (NMR) spectra were
recorded at 25 °C with a Bruker AVANCE DRX 400 spectrometer
(1H NMR 400.13 MHz, 13C NMR 100.3 MHz, 31P NMR 161.97
MHz); Si(CH3)4 was used as the internal standard in the 1H NMR
spectra. Coupling constants for the AA′BB′ systems of the mba
fragment could not be obtained by simulation because of a high
line width, which probably occurs due to hindered rotation. All
heteronuclei spectra were referenced to Si(CH3)4 with the ¥ scale.18
31P MAS NMR (202.45 MHz) were performed with a Bruker MSL
500 spectrometer. The IR spectra were recorded on a Fourier
transform infrared spectrometer Perkin-Elmer Spektrum 2000 (KBr)
in the range 350-4000 cm-1. The mass spectra were recorded with
a VG ZAB-HSQ [fast atom bombardment (FAB), 3-nitrobenzyl
alcohol matrix] or with a Fourier transform ion cyclotron resonance
mass spectrometer, type APEX II (Bruker-Daltonics). Elemental
composition was determined with a Hereaus CHN-O-S analyzer.
The melting points were determined in sealed capillaries under
nitrogen using a Gallenkamp apparatus and are uncorrected.
4-Mercaptobenzoic acid (H2mba) is commercially available and was
used as received. [RhCl(PPh3)3],19 [RhCl(PEt3)3],20 and [RhCl{PPh-
(C2H4PPh2)2}]21 were prepared according to literature procedures.
We are interested in heterometallic complexes,11 the
synthetic approach being the synthesis of mononuclear
monometallic complexes of bifunctional ligands, which are
then coordinated to the second metal center to form the
heterometallic species. Interest in early/late heterobimetallics
has strongly increased in the past few decades.12 The reasons
for this are mainly the explanation of the strong metal-
support interaction phenomenon in heterogeneous catalysis13
and the applicability of cooperative effects between different
metal centers for catalysts14 and magnetic materials.15 Of
special interest for these applications is the investigation of
metal-metal interactions. These can be achieved either by
direct contact of the metal centers in the compounds16 or
with the help of bridging ligands which allow electronic
interactions via π-conjugated bridges.17 Therefore, rhodium(I)
complexes of the type [Rh(SR)(PR′3)3], where SR is a
thiolato ligand which contains a second donor group in a
conjugated backbone, are intriguing metalloligands for the
synthesis of heterometallic complexes. We therefore inves-
tigated the preparation and characterization of rhodium(I)
complexes with the anion of 4-mercaptobenzoic acid as a
ligand. We present here a study of the influence of the
phosphane coligands on the tendency of the products
[Rh(SC6H4CO2H)(PR3)3] to dimerize. Furthermore, the ten-
dency of these complexes to undergo oxidative addition is
exemplified by the formation of the mixed-valent complex
[{RhIRhIII(µ-SC6H4COO)(µ-SC6H4COOH)(SC6H4COOH)-
(PPh3)3}2] (5) and the dinuclear rhodium(III) complex
[{Rh(µ-SC6H4COO)(SC6H4COOH)(PEt3)2}2] (6). The struc-
turally characterized complexes 2b, 4, 5, and 6 exhibit
interesting structures in the solid state, due to the ability of
free carboxyl groups to associate by hydrogen bonding.
K(Hmba) (1). A solution of KOtBu (1.5 g, 13.4 mmol) in
tetrahydrofuran (THF; 20 mL) was added over 1 h to a solution of
H2mba (2.1 g, 13.6 mmol) in THF (60 mL) at room temperature.
The resulting colorless suspension was stirred for 30 min. The
product was isolated by filtration, washed with THF (3 × 10 mL),
and dried in vacuo (yield: 1.75 g, 67%). K(Hmba) (1) is soluble
in water and slightly soluble in dimethylsulfoxide (DMSO). Elem
anal. calcd (%) for C7H5KO2S (M ) 192.28): C, 43.72; H, 2.62.
1
Found: C, 43.39; H, 2.82. H NMR (DMSO-d6): δ 7.02 (d, 2H,
3JHH ) 8.0 Hz, H2), 7.22 (d, 2H, 3JHH ) 8,0 Hz, H3), 11.6 ppm (s,
br, 1H, H1). IR (KBr): ν˜ 3061 w, 2522 w, 1655 w, 1586 s, 1542
s, 1400 s, 1180 m, 1100 s, 915 w, 855 w, 840 m, 770 s, 725 w,
689 w, 519 m, 474 m cm-1. ESI-MS (high res., neg.) found: m/z
724.8628 {[K3(mba)4]-, 11.7%}, 686.9087 {[K2H(mba)4]-, 21.4%},
648.9522 {[KH2(mba)4]-, 16.5%}, 610.9970 {[H3(mba)4]-, 34.0%},
342.9508 {[K(mba)2]-, 21.0%}, 304.9952 {[H(mba)2]-, 100%}.
The calculated isotopic patterns are in agreement with the observed
ones.
Di-µ(S)-(4-carboxybenzenethiolato)-bis{di(triphenylphos-
phane)}dirhodium(I), [{Rh(µ-SC6H4COOH)(PPh3)2}2] (2b). A
solution of [RhCl(PPh3)3] (390 mg, 0.42 mmol) in THF (80 mL)
was added via cannula to a suspension of K(Hmba) (81 mg, 0.42
mmol) in THF (70 mL). The suspension was heated to 50 °C for
4 h. The resulting orange solution was separated from the solid by
filtration and the volume reduced to ca. 5 mL. At room temperature,
the product was obtained as orange crystals (157 mg), isolated,
washed with cold THF and n-hexane, and dried in vacuo.
Concentrating the mother liquor gave another crop of crystals (100
mg), which had to be recrystallized from THF to remove PPh3.
The product was obtained as orange blocks (yield: 239 mg, 73%)
(8) (a) Carlton, L. Magn. Reson. Chem. 1997, 35, 153. (b) Osakada, K.;
Matsumoto, K.; Yamamoto, T.; Yamamoto, A. Organometallics 1985,
4, 857.
(9) Osakada, K.; Yamamoto, T. Bull. Chem. Soc. Jpn. 1994, 67, 3271.
(10) Carlton, L. J. Organomet. Chem. 1992, 431, 103.
(11) Helmstedt, U.; Lo¨nnecke, P.; Reinhold, J.; Hey-Hawkins, E. Eur. J.
Inorg. Chem. In press.
(12) Stephan, D. W. Coord. Chem. ReV. 1989, 95, 41.
(13) Tauster, S. J. Acc. Chem. Res. 1978, 20, 389.
(14) (a) Rida, M. A.; Smith, A. K. In Modern Coordination ChemistrysA
Legacy to J. Chatt; Leigh, J. J., Winterton, N., Ed.; RSC: London,
2002; pp 154-161. (b) Senocq, F.; Randrianalimanana, C.; Thorez,
A.; Kalck, P.; Choukroun, R.; Gervais, D. J. Chem. Soc., Chem.
Commun. 1984, 1376. (c) Choukroun, R.; Gervais, D.; Jaud, J.; Kalck,
P.; Senocq, F. J. Organomet. Chem. 1986, 5, 67. (d) Partenheimer,
W. Amoco Corp. U.S. Patent 4,992,580, DATE.
(18) Harris, R. H.; Becher, E. D.; Cabral de Menezes, S. M.; Goodfellow,
R.; Granger, P. Concepts Magn. Reson. 2002, 14, 326.
(19) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J. Chem.
Soc. A 1966, 1711.
(15) Kahn, O. AdV. Inorg. Chem. 1995, 43, 179.
(20) Intille, G. M. Inorg. Chem. 1972, 11, 695.
(16) Bullock, R. M.; Casey, C. P. Acc. Chem. Res. 1987, 20, 167.
(17) (a) Back, S.; Stein, T.; Frosch, W.; Wu, I.; Kralik, J.; Bu¨chner, M.;
Huttner, G.; Rheinwald, G.; Lang, H. Inorg. Chim. Acta 2001, 325,
94. (b) Plenio, H.; Burth, D. Organometallics 1996, 15, 4054.
(21) (a) Nappier, T. E.; Meek, D. W. J. Am. Chem. Soc. 1972, 94, 306. (b)
Westcott, S. A.; Stringer, G.; Anderson, S.; Taylor, N. J.; Marder, T.
B. Inorg. Chem. 1994, 33, 4589. (c) King, R. B.; Kapoor, P. N.;
Kapoor, R. N. Inorg. Chem. 1971, 10, 1841.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10301

Helmstedt et al.
1
2
Scheme 1. Numbering Scheme for the Assignment of the Signals in
the NMR Spectra
38.6 Hz, P6), 26.7 (dt, JRhP ) 161.8 Hz, JPP ) 38.3 Hz, P9). IR
(KBr): ν˜ 3059 w, 2962 s, 2935 s (sh), 2877 m, 2649 w, 2544 w
(sh), 1663 s, 1579 s (sh), 1533 m, 1457 m, 1415 s, 1376 m, 1301
m (sh), 1284 s (sh), 1166 m, 1126 m, 1084 s, 1031 s, 999 m, 863
w, 844 w, 805 w, 766 s, 729 m, 704 m, 672 w, 655 w, 616 w, 550
w, 531 w, 477 w, 431 w, 412 w cm-1. FAB-MS found (pos.):
m/z 593.0 {[Rh(SC6H4COOH)(PEt3)3 - H2O + H]+, 10%},
567.0 {[Rh(SC6H4COOH)(PEt3)3 - CO2 + H]+, 7.7%}, 565.0
{[Rh(SC6H4COOH)(PEt3)3 - CO - H2O + H]+, 9.0%}.
4-Carboxybenzenethiolato-bis(diphenylphosphanylethyl)-
phenylphosphan-rhodium(I),
[Rh(SC6H4COOH){PPh-
(C2H4PPh2)2}] (4). A solution of H2mba (76 mg, 0.49 mmol) in
THF (30 mL) was added over 30 min to a solution of [RhCl{PPh-
(C2H4PPh2)2}] (330 mg, 0.49 mmol) and NnBu3 (0.15 mL, 0.49
mmol) in THF (60 mL) at room temperature. The color changed
from bright yellow to pale brown. The solution was stirred
overnight. The solvent was removed in vacuo, and the ochre residue
was washed with toluene (2 × 2.5 mL) and n-hexane (5 mL),
dissolved in THF (20 mL), and precipitated by the addition of
n-hexane (50 mL). The yellow solid was dried in vacuo (yield:
368 mg, 95%). Compound 4 is highly air- and moisture-sensitive.
Single crystals suitable for X-ray analysis were obtained by layering
a concentrated solution of 4 in THF with twice the volume of
n-hexane. Pure 4 is almost insoluble in common organic solvents
(n-hexane, toluene, benzene, THF, CH3CN, and DMSO) and
dissolves in N,N-dimethylformamide (DMF) with decomposition.
Melting point: 205-208 °C (decomp.). Elem anal. calcd (%) for
C41H38O2P3RhS (M ) 790.63): C, 62.28; H, 4.84. Found: C, 62.31;
H, 4.76. Because of the low solubility of pure 4, 1H and 31P NMR
spectroscopic characterizations were carried out with the solid
containing traces of impurities (grease, solvent, and NnBu3). Only
and is soluble in THF. Compound 2b is air-stable for several weeks
as a solid but air- and moisture-sensitive in solution. Melting
point: 220 °C (decomp.). Elem anal. calcd (%) for C86H70O4P4-
Rh2S2 (Mm ) 1561.31): C, 66.21; H, 4.58. Found: C, 66.04; H,
4.48. Compound 2 slowly decomposes in solution; therefore, the
NMR spectra could only be obtained in the presence of 1 equiv of
PPh3 to stabilize 2b in solution. Only signals of 2b are given (see
Scheme 1 for the numbering scheme assignments of the signals in
1
the NMR spectra). H NMR (THF-d8): δ 6.68 (m, 4H, A part of
the AA′BB′ spin system, H4), 6.77 (d, 4H, B part of the AA′BB′
spin system, H3), 6.92 (m, 24H, H7), 7.04 (t, 12H, 3JHH ) 7.6 Hz,
H9), 7.54 ppm (m, 24H, H8), OH not observed. 13C{1H} NMR
(THF-d8): δ 126.4 (s, C4), 126.7 (m, C7)†, 127.9 (s, C9), 128.0 (s,
C5), 131.8 (m, C6)†, 134.4 (s, C3), 134.6 (m, C8)†, 151.6 (s, C2),
172.7 ppm (s, C1) (†coupling constants JA-X, JA′-X, and JM-X could
not be obtained by simulation because of a high line width and
low signal-to-noise ratio). 31P{1H} NMR (THF-d8): δ 41.9 ppm
1
(d, JRhP ) 168.9 Hz, PPh3). IR (KBr): ν˜ 3052 m, 2960 w, 1682
1
the signals of 4 are given. H NMR (THF-d8): δ 1.6-1.8 (2m,
s, 1586 s, 1552 m, 1480 m, 1434 s, 1416 s, 1305 s, 1171 m, 1120
m, 1091 s, 1027 m, 1016 m, 846 m, 805 m, 741 s, 722 m, 694 s,
534 s, 521 s, 493 m, 432 m cm-1. FAB-MS found (pos.): m/z
766.1 {[Rh(SC6H4COH)(PPh3)2 + 2H]+, 0.4%}, 627.1 {[Rh-
(PPh3)2]+, 1%}, 613.1 {[Rh(SC6H4COH)(PPh3)2 - 2Ph + 2H]+,
2%}, 154.0 {[HOOCC6H4SH]+, 95%}, 136.0 {[OCC6H4S + 2H]+,
100%}. The calculated isotopic patterns are in agreement with the
observed ones.
4H, H8), 2.5-2.9 (3m, 4H, H7), 7.07-8.08 ppm (m, 29H, H3,
H4, H6, H9), OH not observed. 31P{1H} NMR (THF-d8): δ 47.6
1
2
1
(dd, JRhP ) 150.9 Hz, JPP ) 32.0 Hz, P6), 106.9 (dt, JRhP
)
138.2 Hz, 2JPP ) 31.9 Hz, P9). IR (KBr): ν˜ 3051 m, 2958 w (sh),
1671 m (sh), 1580 s, 1482 w, 1435 s, 1411 m, 1306 w, 1265 w,
1168 m, 1098 s (sh), 1027 m, 890 w, 866 w, 808 w, 744 m, 696
s, 518 m, 485 w cm-1. FAB-MS found (pos.): m/z 789.1 ([M -
H]+, 51%), 672.1 ([Rh(SH){PPh(C2H4PPh2)2} + 2H]+, 22%), 637.1
([Rh{PPh(C2H4PPh2)2}]+, 72%). The calculated isotopic patterns
are in agreement with the observed ones.
4-Carboxybenzenethiolato-tris(triethylphosphane)-rhod-
ium(I), [Rh(SC6H4COOH)(PEt3)3] (3a). A solution of [RhCl-
(PEt3)3] (162 mg, 0.33 mmol) and PEt3 (1 mL) in THF (7 mL)
was added to a suspension of K(Hmba) (67 mg, 0.35 mmol) in
THF (7 mL) at 0 °C. The suspension was allowed to warm to room
temperature and was stirred for 16 h. The red solution was filtered
[this was performed under argon, as the filtration takes about 8 h
(very fine solid) and the product is very air-sensitive], and the
solvent was removed in vacuo. The dark orange solid was washed
with cold THF (1 mL) and n-hexane (2 × 5 mL) and dried in vacuo
(yield: 147 mg, 73%). Compound 3a is soluble in THF and slightly
soluble in toluene. At room temperature, an orange solid precipitates
from solution, which is almost insoluble in all common solvents,
but shows the same elemental analyses and IR spectroscopic data
as 3a. Melting point: 201-205 °C (decomp.). Elem anal. calcd
(%) for C25H50O2P3RhS (M ) 610.56): C, 49.18; H, 8.25. Found:
C, 49.11; H, 8.18. For the stabilization of 3a in solution, 10 equiv
of PEt3 were added to the NMR tube. Only the signals of 3a are
given. 1H NMR (THF-d8): δ 1.00-1.90 (m, 45H, PEt3), 7.48 (m,
2H, A part of the AA′BB′ spin system, H4), 7.90 ppm (m, 2H, B
part of the AA′BB′ spin system, H3), OH not observed. 13C{1H}
NMR (THF-d8): δ 8.3 (C8), 8.7 (C11), 17.3 (C7), 21.3 (C10), 122.3
(C5), 127.3 (2s, C4), 131.1 (C3), 162.4 (C2), 163.0 ppm (C1).
Data Collection and Structure Determination. X-ray data
(Table 1) were collected with a Siemens CCD-Smart diffractometer
for 4 and with a Stoe IPDS1 for 2b, 5, and 6 using graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). Absorption
correction was performed with the program SADABS22 for 4 and
numerically for 2b, 5, and 6. Structure solution and refinement were
performed with WinGX,23 SHELXS-97, and SHELXL-97.24 All
non-hydrogen atoms were refined anisotropically; most hydrogen
atoms were refined in calculated positions. Visualization was carried
out with the program DIAMOND. CCDC-609913 (2b‚6THF),
CCDC-609911 (4‚THF), CCDC-609912 (5‚10THF), and CCDC-
609914 (6‚2THF) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(22) Sheldrick, G. M. SADABSsA Program for Empirical Absorption
Correction; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1998.
(23) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(24) Sheldrick, G. M. SHELXS97, SHELXL97sPrograms for Crystal
Structure Analysis, release 97-2; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1998.
1
2
31P{1H} NMR (THF-d8): δ 12.1 (dd, JRhP ) 136.4 Hz, JPP
)
10302 Inorganic Chemistry, Vol. 45, No. 25, 2006

Influence of Phosphane Coligands
Table 1. Crystallographic Data for 2b‚6THF, 4‚THF, 5‚10THF, and 6·2THF
compound
empirical formula
mol wt
2b‚6THF
110H118O10P4Rh2S2
1993.86
4‚THF
C45H46O3P3RhS
862.70
5‚10THF
C190H198O22P6Rh4S6
3623.30
6‚2THF
C60H94O10P4Rh2S4
1433.29
C
T [K]
207(2)
213(2)
180(2)
213(2)
λ [pm]
71.073
monoclinic
P21/n
1846.2(3)
2613.8(3)
2170.4(3)
90
102.46(2)
90
10.23(1)
4
1.295
0.483
4160
71.073
monoclinic
C2/c
3626.5(2)
1256.85(7)
2022.6(1)
90
115.048(2)
90
8.3516(8)
8
1.372
0.613
3568
71.073
triclinic
P1h
71.073
monoclinic
P21/n
1566.4(1)
1066.50(7)
2040.7(2)
90
96.08(1)
90
3.3900(5)
2
1.404
cryst syst
space group
a [pm]
1496.0(1)
1911.4(1)
2051.8(2)
113.635(5)
106.230(6)
94.296(6)
5.0427(6)
1
b [pm]
c [pm]
R [deg]
â [deg]
γ [deg]
V [nm3]
Z
F
calcd [g‚cm3]
1.193
0.489
1880
µ [mm-1
F(000)
]
0.756
1496
cryst size [mm]
Θ range [deg]
h, k, l collected
0.40 × 0.30 × 0.25
2.04-26.04
-22 e h e 22
-32 e k e 32
-24 e l e 26
68 058
0.60 × 0.40 × 0.20
1.91-28.29
-48 e h e 47
-16 e k e 16
-26 e l e 26
37 002
0.40 × 0.20 × 0.20
3.11-23.25
-16 e h e 16
-20 e k e 21
-22 e l e 22
47 746
0.45 × 0.20 × 0.05
2.01-25.92
-19 e h e 19
-11 e k e 12
-24 e l e 24
20 733
reflns measd
unique reflns
19 707
9971
14 452
6466
restraints/params
GOF (all data)
150/1005
0.881
47/530
1.030
1106/1178
0.928
10/368
0.704
final R indices [I > 2σ(I)]
R1 ) 0.0429
wR2 ) 0.1139
R1 ) 0.0645
wR2 ) 0.1192
1.367/-0.514
R1 ) 0.0279
wR2 ) 0.0701
R1 ) 0.0439
wR2 ) 0.0751
0.788/-0.418
R1 ) 0.0776
wR2 ) 0.2057
R1 ) 0.1299
wR2 ) 0.2305
1.217/-0.650
R1 ) 0.0346
wR2 ) 0.0732
R1 ) 0.0758
wR2 ) 0.0776
0.571/-0.312
R indices
all data
∆F (max/min) [e‚Å-3
]
Discussion
material, heating to 50 °C for 4 h is necessary. Very small
amounts of the monomer [Rh(SC6H4COOH)(PPh3)3] are
observed in the 31P NMR spectrum of highly concentrated
solutions of 2b when a large excess of PPh3 (15-fold) is
present (Scheme 2).
Because of the pronounced tendency of rhodium(I)
complexes to undergo oxidative addition, salt elimination
was preferred over base-mediated HCl elimination for the
synthesis of the rhodium(I) thiolato complexes. For this
purpose, the potassium salt of H2mba was prepared by
deprotonation with 1 equiv of KOtBu. The resulting product,
K(Hmba) (1), is a colorless solid. As the pKa values of
benzoic acid and thiophenol in nonprotic solvents are very
similar (e.g., 11.125a and 10.325b in DMSO, respectively), it
was impossible to predict the deprotonation site. Unfortu-
nately, the spectroscopic data of K(Hmba) (1) are not
To prevent dimerization, two strategies were employed:
(1) utilization of the electron-richer triethylphosphane and
(2) exploitation of the chelate effect by using PPh(C2H4PPh2)2
as a coligand. The reaction of K(Hmba) with [RhCl(PEt3)3]
(1:1) proceeds at room temperature and yields a mixture of
the monomeric and dimeric rhodium(I) complexes. The
equilibrium is fully shifted toward the monomer [Rh(SC6H4-
COOH)(PEt3)3] (3a) when an excess of PEt3 is present. No
dimeric complex is formed when PPh(C2H4PPh2)2 is used,
[Rh(SC6H4COOH){PPh(C2H4PPh2)2}] (4) being the only
product. Because of the low solubility of 4, separation from
KCl proved difficult. Therefore, base-mediated HCl elimina-
tion with NnBu3 was the preferred synthetic approach here,
as the ammonium salt [NHnBu3]Cl is soluble in toluene and
can thus be easily removed (Scheme 2).
1
unambiguous. Thus, in the H NMR spectrum (in DMSO),
a signal at 11.6 ppm seems to indicate the presence of the
protonated carboxyl group in solution, while the IR spectrum
of solid 1 seems to indicate deprotonation of the carboxyl
group, as the typical absorptions for the asymmetric and
symmetric stretching vibrations of a COO group in carbox-
ylates are observed at 1542 and 1400 cm-1, respectively,
while the CdO vibration of the starting material H2mba
(1678 cm-1) is no longer observed. However, different
structures in the solid state and in solution cannot be
excluded.
Syntheses of the Rhodium(I) Complexes. The reaction
of K(Hmba) (1) with 1 equiv of [RhCl(PPh3)3] yields
exclusively the dimer [{Rh(µ-SC6H4COOH)(PPh3)2}2] (2b),
which forms with the elimination of one phosphane ligand
per rhodium atom. To achieve full conversion of the starting
The composition of the rhodium(I) complexes was verified
by elemental analysis and mass spectrometry. FAB mass
spectrometry proved to be suitable for investigating 2b and
4, while the investigation of 3a was rather difficult. Neither
ionization with electron impact, electrospray ionization, or
matrix-assisted laser desorption ionization nor that with laser
desorption ionization resulted in informative spectra. In the
FAB mass spectrum, only three fragments of very low
intensity could be identified, [M + H - 18]+ (cleavage of
H2O), [M + H - 44]+ (cleavage of CO2), and [M + H -
46]+ (cleavage of formic acid or CO and H2O, respectively).
(25) (a) Piljugin, V. S.; Kusnetzova, S. L.; Schkunova, N. A. Zh. Obshch.
Khim. 1986, 56, 425. (b) Bordwell, F. G.; Cheung, J.-P.; Ji, G.-Z.;
Satish, A. V.; Zhang, X. J. Am. Chem. Soc. 1991, 113, 9790.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10303

Helmstedt et al.
Scheme 2. Syntheses of 2, 3, and 4
Table 2. Selected Bond Lengths [pm] and Angles [deg] for 2b‚6THF
and 4‚THF
Solid-State Structures of the Rhodium(I) Complexes.
X-ray structure determinations were carried out on single
crystals of 2b and 4. [{Rh(µ-SC6H4COOH)(PPh3)2}2] (2b)
crystallizes in the monoclinic space group P21/n with one
molecule per asymmetric unit and six molecules of THF per
molecule of 2b. The central structural motif is a puckered
Rh2S2 ring (dihedral angle Rh1-S1-S2/Rh2-S1-S2 )
139°). With the exception of [{Rh(µ-SC6H5)(dippe)2}2]
(dippe ) iPr2PCH2CH2PiPr2),26 which exhibits a planar Rh2S2
ring, all other structurally characterized complexes of the
type [{Rh(µ-SR)(PR3)2}2] show a puckered ring. The prefer-
ence for the bent structure despite a small energy difference,
as shown by theoretical calculations,27 is explained by the
pronounced tendency of sulfur to undergo sp3 hybridization
and of rhodium to form d8-d8 contacts. In 2b, each rhodium
atom is coordinated in a distorted square-planar fashion by
two phosphane and two bridging thiolato ligands (Figure 1).
The sum of bond angles at S1 and S2 are 304.23 and 305.90°,
respectively, and the Rh1‚‚‚Rh2 distance is 338 pm (Table
2).
2b‚6 THF
239.27(4)
4‚THF
Rh1-S1
Rh1-S1
Rh1-P1
Rh1-P2
Rh1-P3
C41-O1
C41-O2
O1-H1O
240.61(5)
228.78(6)
219.02(5)
228.42(6)
124.7(3)
130.6(3)
82.02(2)
97.14(2)
83.65(2)
83.81(2)
95.15(2)
159.19(2)
178.73(2)
120.9(2)
116.0(2)
123.1(2)
123.7(4)
Rh2-S1
240.35(3)
226.82(2)
225.06(2)
223.59(3)
226.09(3)
237.78(3)
239.02(2)
82.223(7)
97.762(7)
86.72(3)
Rh1-P1
Rh2-P3
Rh1-P2
Rh2-P4
Rh1-S2
Rh2-S2
S1-Rh1-P1
P1-Rh1-P2
P2-Rh1-P3
P3-Rh1-S1
P1-Rh1-P3
S1-Rh1-P2
C38-C41-O1
C38-C41-O2
O1-C41-O2
C41-O1-H1O
S1-Rh1-S2
P1-Rh1-P2
S1-Rh1-P1
S2-Rh1-P2
S1-Rh2-S2
P3-Rh2-P4
S2-Rh2-P3
S1-Rh2-P4
S1-Rh2-S2
93.27(3)
81.739(7)
97.550(7)
176.35(4)
166.32(3)
81.739(7)
between two neighboring carbon atoms is 358 pm; the
longest distance is 375 pm), in which the aromatic rings of
the Hmba ligands exhibit a “face-to-face” arrangement.28
Hydrogen bonds between the carboxyl groups of two of these
molecules result in a centrosymmetric tetranuclear unit which
is located on a crystallographic inversion center (Figure 2).
Accordingly, in the IR spectrum, 2b exhibits the CdO
vibration at 1682 cm-1 and the “out-of-plane” deformation
δ(-OH‚‚‚O) at 913 cm-1, as expected for hydrogen-bonded
dimers.29
For 2b, the syn-exo conformer is present in the solid state,
which is stabilized by π-π stacking of the aromatic rings
of the 4-carboxyphenylthiolato ligands (average distance
[Rh(SC6H4COOH){PPh(C2H4PPh2)2}] (4) crystallizes in
the monoclinic space group C2/c with one molecule of 4
and one highly disordered THF molecule in the asymmetric
unit cell. The rhodium atom is coordinated in a distorted
square-planar fashion by the three phosphorus atoms of the
triphos ligand and a terminal thiolato ligand (Figure 3 and
Table 2). The P1-Rh1-P2 and P2-Rh1-P3 bond angles
deviate from 90° by 6° and P1-Rh1-P3 from 180° by 21°,
which shows the strain in the Rh-P-C-C-P five-
membered rings. As was observed for 2b, two molecules of
(26) Oster, S. S.; Jones, W. D. Inorg. Chim. Acta 2004, 357, 1836.
(27) Aullo´n, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S. Chem.sEur. J. 1999,
5, 1391.
(28) Roesky, H. W.; Andruh, M. Coord. Chem. ReV. 2003, 236, 91.
(29) Gu¨nzler, H.; Gremlich, H.-U. In IR Spectroscopy: An Introduction;
Wiley-VCH: New York, 2002.
Figure 1. View of the molecular structure of [{Rh(µ-SC6H4COOH)-
(PPh3)2}2] (2b). Hydrogen atoms (other than H1O and H3O) and solvent
molecules have been omitted for clarity. Thermal ellipsoid level: 30%.
10304 Inorganic Chemistry, Vol. 45, No. 25, 2006

Influence of Phosphane Coligands
Figure 2. Association of 2b in the solid state. Thermal ellipsoid level: 30%.
equivalent, as expected for 3a. However, in the IR spectrum
of the insoluble solid, the CdO vibration is observed at 1682
cm-1 (H2mba: ν˜CO ) 1678 cm-1), while for 3a, this appears
at 1663 cm-1. This indicates that different modes of
association of the carboxyl groups are possible in the solid
state and apparently result in different solubility.
Structures in Solution. 2b undergoes dissociation of PPh3
in solution and exists in equilibrium with unknown species
which show a very broad signal at 40 ppm in the 31P{1H}
NMR spectrum. As could be shown by exchange experiments
with PPh2(p-tolyl), the free phosphane ligands exchange with
the coordinated ones, indicating fluxional behavior in solu-
tion. However, 2b is stable when an excess of 1 equiv of
PPh3 is present and shows a doublet at 41.9 ppm (1JPRh
)
168.9 Hz) in the 31P{1H} NMR spectrum. As in similar
3
compounds,8-10 no JPRh coupling is observed; that is, it is
Figure 3. View of the molecular structure of [Rh(SC6H4COOH){PPh-
(C2H4PPh2)2}] (4). Hydrogen atoms (other than H1O) and solvent molecules
have been omitted for clarity. Thermal ellipsoid level: 30%.
clearly smaller than the line width of the signals (9 Hz).
In solution, complexes of general formula [{Rh(µ-SR)-
(PR′3)2}2] with a puckered Rh2S2 ring can exist as different
stereoisomers, in which the thiolates occupy different posi-
tions, that is, the syn or anti conformation. In the syn
arrangement, the thiolates can occupy the exo or endo
position30 (Figure 5).
Variable-temperature 31P{1H} NMR spectroscopic inves-
tigations in THF-d8 showed splitting of the signal for 2b
into two broad signals below 185 K. Unfortunately, no
resolution of the fine splitting could be achieved because of
solvent restrictions. Theoretical calculations31 and experi-
mental studies on [{Rh(µ-SR)(dippe)}2] (dippe ) iPr2PCH2-
CH2PiPr2; R ) H, Me, Cy, o-biphenyl, Ph)30 showed that
the conversion from the syn to the anti isomer (inversion at
the sulfur center) has a higher free reaction enthalpy (ca. 40
kJ/mol) than ring inversion between the exo and endo forms
(<35 kJ/mol). Therefore, it seems likely that the two signals
can be assigned to the syn and anti isomers.
Figure 4. Association of 4 in the solid state.
4 dimerize via hydrogen bonds and the dimer is located on
a crystallographic inversion center (Figure 4).
No single crystals could be obtained of 3a, probably
because of the monomer-dimer equilibrium. If a THF
solution of 3a is treated with toluene or n-hexane, or if the
synthesis is performed in a THF/toluene mixture, a red solid
precipitates which is insoluble in common organic solvents
(n-hexane, toluene, THF, acetonitrile, DMF, and DMSO).
The solid-state 31P{1H} NMR spectrum of this solid shows
two signals at 20 and 75 ppm, in a ratio of 2:1, indicating
three phosphorus nuclei, of which two are magnetically
For the monomer of 3a and for 4, a doublet of doublets
and a doublet of triplets are observed in the 31P{1H} NMR
spectrum. Phosphorus-rhodium coupling constants of 136.4
(30) Oster, S. S.; Jones, W. D. Inorg. Chim. Acta 2004, 357, 1836.
(31) Duran, N.; Gonza´lez-Duarte, P.; Lledo´s, A.; Parella, T.; Sola, J.;
Ujaque, G.; Clegg, W.; Fraser, K. A. Inorg. Chim. Acta 1997, 265,
89.
Inorganic Chemistry, Vol. 45, No. 25, 2006 10305

Helmstedt et al.
Figure 5. Equilibrium between the different conformers in a solution of 2b.
Hz (P trans to thiolate) and 161.8 Hz (2P cis to thiolate) for
3a and 138.2 Hz (P trans to thiolate) and 150.9 Hz (2P cis
to thiolate) for 4 are typical for rhodium(I) complexes.32
While no dissociation of a phosphane ligand is observed for
4, for 3a, a singlet for free PEt3 and a doublet for the dimeric
form are observed, as was also found for 2b. With an excess
of PEt3, the equilibrium can be shifted to the monomeric
form (Scheme 2).
After purification, 4 is insoluble in common organic
solvents (n-hexane, toluene, THF, acetonitrile, and DMSO)
and dissolves in DMF with decomposition. Low solubility
was also observed for the starting material, [RhCl{PPh(C2H4-
PPh2)2}], for which bridging bonding modes of the tripodal
phosphane ligand were suggested to account for this unex-
pected behavior.21a However, X-ray analysis later showed
this complex to be monomeric in the solid state;21b thus, there
is still no rational explanation for the low solubility.
Therefore, NMR spectroscopic characterization of 4 was
carried out on the slightly impure, but still soluble, com-
pound, and no 13C NMR spectroscopic characterization was
1
performed. In the H NMR spectrum, the signals for the
Figure 6. View of the molecular structure of [{Rh(µ-SC6H4COO)(SC6H4-
COOH)(PEt3)2}2] (6). Hydrogen atoms (other than H1) and solvent
molecules have been omitted for clarity. Thermal ellipsoid level: 30%.
AA′BB′ spin system for the aromatic ring of the 4-thiolato-
benzoate ligand in 2-4 were broader than the other signals;
this indicates hindered rotation of the SC6H4COOH group,
which prevents simulation of the spectra to determine the
coupling constants.
Reactivity of the Rhodium(I) Complexes. Interesting
insight into the reactivity of the rhodium(I) complexes 2b
and 3a is given by two compounds which were isolated
during the experiments, [{RhIRhIII(µ-SC6H4COO)(µ-SC6H4-
COOH)(SC6H4COOH)(PPh3)3}2] (5) and [{Rh(µ-SC6H4-
COO)(SC6H4COOH) (PEt3)2}2] (6), and, because of low
solubility and low yield (a few crystals), were only charac-
terized by X-ray crystallography.
formed via the oxidative addition of additional K(Hmba), a
reaction already known for other rhodium(I) complexes,7a
which is employed in slight excess in the reaction to facilitate
the full conversion of [RhCl(PEt3)3]. The spectrum of the
reaction solution showed the additional signal for 6 at 34.9
ppm with a Rh-P coupling constant of 123.9 Hz, which is
typical for rhodium(III) complexes. The same spectrum is
observed when 1 equiv of K(Hmba) is added to a THF
solution of 3 at room temperature. Unfortunately, isolation
of pure 6 from this reaction fails because of the low solubility
of 6 in common organic solvents. A better solubility would
be necessary to separate it from residual K(Hmba).
When a solution of 2b in THF was layered with n-hexane
to obtain single crystals, the color of the solution surprisingly
changed from deep orange to brown, and dark brown crystals
of the mixed-valent complex [{RhIRhIII(µ-SC6H4COO)(µ-
SC6H4COOH)(SC6H4COOH)(PPh3)3}2] (5) (Figure 7, top)
The dimeric rhodium(III) complex [{Rh(µ-SC6H4COO)-
(SC6H4COOH)(PEt3)2}2] (6) (Figure 6, top) was isolated as
a side product in the synthesis of 3a and crystallized on the
vapor diffusion of diethyl ether into a concentrated solution
of the reaction mixture. Compound 6 might have been
(32) Brown, T. H.; Green, P. J. J. Am. Chem. Soc. 1970, 92, 2359.
10306 Inorganic Chemistry, Vol. 45, No. 25, 2006

Influence of Phosphane Coligands
Figure 7. Schematic drawing (top) and view of the molecular structure (bottom) of [{RhIRhIII(µ-SC6H4COO)(µ-SC6H4COOH)(SC6H4COOH)(PPh3)3}2]
(5). Hydrogen atoms (other than H4O and H6O) and solvent molecules have been omitted for clarity. Thermal ellipsoid level: 30%.
formed besides a brown insoluble precipitate. The mechanism
for the formation of 5 is less straightforward, because there
is no excess K(Hmba) present in solution. As mentioned
above, 2b eliminates PPh3 with the formation of unknown
species in solution. Therefore, the removal of free PPh3 by
the addition of n-hexane (PPh3 is not very soluble in
n-hexane) could result in the decomposition of 2b. The
formation of an insoluble brown precipitate, which does not
show any CdO vibration in the IR spectrum, besides 5
indicates that the decomposition takes place with cleavage
of the rhodium-thiolate bond, and thus, 4-thiolatobenzoic
acid is present as a monoanion or neutral thiol, which can
oxidatively add to residual 2b to yield 5. All known mixed-
valent rhodium(I)-rhodium(III) complexes were synthesized
by the selective oxidative addition of one rhodium center in
dinuclear rhodium(I) complexes.33
Table 3. Selected Bond Lengths [pm] and Angles [deg] for 5‚10THF
and 6‚2THF
5‚10THF
6‚2THF
Rh1-O1
Rh1-O2
Rh1-P1
Rh1-S1
Rh1-S2
Rh1-S3
Rh2-S1
Rh2-S2
Rh2-P2
Rh2-P3
S1-Rh1-P1
S2-Rh1-S3
O1-Rh1-O2
S2-Rh1-O2
S3-Rh1-O1
S1-Rh2-S2
S2-Rh2-P3
S1-Rh2-P2
P2-Rh2-P3
221.2(5)
211.4(5)
233.2(2)
239.1(2)
231.6(2)
232.4(2)
237.7(2)
236.0(2)
219(2)
224.1(5)
173.79(8)
81.40(8)
60.8(2)
103.7(2)
113.7(2)
81.87(8)
91.7(1)
86.7(5)
100.9(5)
Rh1-O3
Rh1-O4
Rh1-P1
Rh1-P2
Rh1-O3
Rh1-S1
Rh1-S2
O3-Rh1-O4
O3-Rh1-P1
O4-Rh1-P2
S1-Rh1-S2
219.4(3)
218.4(3)
226.7(1)
226.0(1)
219.4(3)
240.0(1)
239.6(1)
60.4(1)
100.46(8)
101.70(9)
178.99(5)
Because of solvent loss during the preparation of single
crystals of 5 for X-ray measurement, the quality of the data
is rather low and only a structural motif was obtained.
Compound 5 crystallizes in the triclinic space group P1h with
one half molecule of 5 (Figure 7, Table 3) in the asymmetric
unit and 10 THF molecules per unit cell. Some of the phenyl
rings and the bridging ligands are highly disordered. The
Inorganic Chemistry, Vol. 45, No. 25, 2006 10307

Helmstedt et al.
central Rh2S2 ring as the structural motif of 2b still exists,
but one of the rhodium centers, rhodium(III) (Rh1), is now
coordinated octahedrally by two thiolates and one S-
coordinated thiolatobenzoato ligand (mba2-) in a facial
geometry, one bidentate carboxylato group, and one phos-
phane ligand. The rhodium(I) group, Rh(PPh3)2 (Rh2), and
rhodium(III) are bridged by one of the three thiolato ligands
and the S-coordinated thiolatobenzoato ligand. Rh2 has a
distorted square-planar environment. The Rh2S2 ring is nearly
planar (dihedral angle Rh1-S1-S2/Rh2-S1-S2 ) 174.1°).
The deviation from planarity is possibly due to packing
effects. Two dimeric RhI-RhIII units are bridged by two
mba2- dianions to give a centrosymmetric tetranuclear
complex. As in 2b, “π-π stacking” stabilizes the molecule,
but geometry restraints force the two aromatic rings into an
“offset” or “slipped” arrangement. The distance of the ipso-
carbon atom C58 to the plane of the opposite aromatic
ring (C55′-C60′) is 331 pm.28 In the solid state, 5 forms
one-dimensional zigzag chains via hydrogen bonds of the
free carboxyl groups of the terminal thiolato ligands (S3,
C75, O5, and O6, see Figure 1 in the Supporting Informa-
tion).
Table 3), but in contrast to 5, there is no additional four-
membered Rh2S2 ring. The rhodium(III) center is coordinated
octahedrally by two phosphane ligands in cis positions, two
thiolato ligands in trans positions, and one bidentate car-
boxylato group of the bridging 4-thiolatobenzoato ligand
(mba2-). As in 5, the free carboxyl groups associate via
hydrogen bonds to give zigzag chains of 6 (see Figure 2 in
the Supporting Information).
Conclusion
Variation of the phosphane ligands L in rhodium(I)
complexes of the type [Rh(SC6H4COOH)L] influences their
tendency to dimerize with the dissociation of phosphane. For
L ) (PPh3)3, mainly the dimer is observed. An equilibrium
between the monomeric and dimeric form is observed for
the electron-richer triethylphosphane [L ) (PEt3)3], which
is shifted to the monomer by excess free PEt3 in solution.
The chelate effect of the PPh(C2H4PPh2)2 ligand completely
inhibits dissociation and stabilizes the monomeric form. As
was shown by the isolation and structural characterization
of a side product and a decomposition product, the rhod-
ium(I) complexes are susceptible to the oxidative addition
of (Hmba) to form rhodium(III) complexes.
[{Rh(µ-SC6H4COO)(SC6H4COOH)(PEt3)2}2] (6) crystal-
lizes in the monoclinic space group P21/n with one half
molecule of 6 in the asymmetric unit and four molecules of
THF in the unit cell. Like 5, 6 has a 16-membered
RhIII2(SC6H4COO)2 ring, which is located on a crystal-
lographic inversion center, as the central motif (Figure 6,
Acknowledgment. U.H. thanks the Studienstiftung des
Deutschen Volkes for a Ph. D. grant. Financial support from
the Graduiertenkolleg 378 and a generous donation of RhCl3
from Umicore AG & Co KG are gratefully acknowledged.
(33) (a) Tejel, C.; Ciriano, M. A.; Edwards, A. J.; Lahoz, F. J.; Oro, L. A.
Organometallics 1997, 16, 45. (b) Tejel, C.; Ciriano, M. A.; Edwards,
A. J.; Lahoz, F. J.; Oro, L. A. Organometallics 2000, 19, 4968. (c)
Pinillos, M. T.; Elduque, A.; Oro, L. A. Polyhedron 1992, 11, 1007.
(d) Ho, D. G.; Ismail, R.; Franco, N.; Gao, R.; Leverich, E. P.; Tsyba,
I.; Ho, N. N.; Bau, R.; Selke, M. Chem. Commun. 2002, 570.
Supporting Information Available: Figures of the associations
of 5 and 6 in the solid state. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC0610684
10308 Inorganic Chemistry, Vol. 45, No. 25, 2006