Structures, reactivity, and catalytic activity of dithiolato-bridged heterobimetallic MRh (M = Pt, Pd) complexes

Article abstract of DOI:10.1021/om020042r

Heterobimetallic complexes [(P-P)Pt(μ-S-S)Rh(cod)]ClO₄ (P-P = (PPh₃)₂, Ph₂P(CH₂)₃-PPh₂ (dppp), and Ph₂P(CH₂)₄PPh₂ (dppb); S-S = ^-

Full text of DOI:10.1021/om020042r

Organometallics 2002, 21, 2609-2618
2609
Str u ctu r es, Rea ctivity, a n d Ca ta lytic Activity of
Dith iola to-Br id ged Heter obim eta llic MRh (M ) P t, P d )
Com p lexes
J orge Fornie´s-Ca´mer, Anna M. Masdeu-Bulto´,* and Carmen Claver
Departament de Quı´mica Fı´sica i Inorga`nica, Universitat Rovira i Virgili,
Pl. Imperial Ta`rraco 1, 43005 Tarragona, Spain
Cristina Tejel* and Miguel Angel Ciriano
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
Christine J . Cardin
Department of Chemistry, The University of Reading, Whiteknights, P.O. Box 224,
Reading RG6 6AD, United Kingdom
Received J anuary 22, 2002
Heterobimetallic complexes [(P-P)Pt(µ-S-S)Rh(cod)]ClO4 (P-P ) (PPh3)2, Ph2P(CH2)3-
PPh2 (dppp), and Ph2P(CH2)4PPh2 (dppb); S-S ) -S(CH2)2S- (EDT), -S(CH2)3S- (PDT),
-S(CH2)4S- (BDT), cod ) 1,5-cyclooctadiene) reacted with CO to form the carbonyl complexes
[(P-P)Pt(µ-S-S)Rh(CO)2]ClO4 and then with PR3 ligands to give [(P-P)Pt(µ-S-S)Rh(CO)-
(PR3)]ClO4. The binuclear framework of these cod complexes was maintained in the reactions
reported. The cod complexes were tested as catalyst precursors in the hydroformylation of
styrene. HPNMR in situ studies showed that mononuclear species formed under catalytic
conditions.
In tr od u ction
and -S(CH2)4S- (BDT); cod ) 1,5-cyclooctadiene) by
direct reaction of the mononuclear complexes [M(S-S)-
(P-P)] with [Rh(cod)2]ClO4.7 We also showed that this
synthetic procedure was very versatile by preparing the
The interest in heterometallic complexes has been
centered on their application as catalyst precursors in
homogeneous catalysis processes,1 as a model for mixed
heterogeneous catalysts,2 and as starting materials for
clusters preparation.3 There are many examples of
heterobimetallic complexes with anionic phosphido bridg-
ing ligands,4 or thiolato bridging ligands (RS-).4a,5 In
contrast, dithiolato (-SRS-)6-bridged heterobimetallic
complexes have been studied considerably less, most of
the examples being of the early-late (ELHB) type.
We recently described the preparation of a series of
complexes [(P-P)M(µ-S-S)Rh(cod)]ClO4 (P-P ) (PPh3)2,
Ph2P(CH2)3PPh2 (dppp), and Ph2P(CH2)4PPh2 (dppb); M
) Pt, Pd; S-S ) -S(CH2)2S- (EDT), -S(CH2)3S- (PDT),
(4) (a) Stephan, D. W. Coord. Chem. Rev. 1989, 95, 41. (b) Fornie´s,
J .; Fortun˜o, C.; Navarro, R.; Mart´ınez, F. J . Organomet. Chem. 1990,
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Chem. 1994, 33, 6242. (d) Braunstein, P.; de J esu´s, E.; Dedieu, A.;
Lanfranchi, M.; Tiripicchio, A. Inorg. Chem. 1992, 31, 399. (e) Braun-
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T. Y.; Wen, Y. S. J . Organomet. Chem. 1993, 460, 229. (g) Shyn, S. G.;
Lin, P. J .; Wen, Y. S. J . Organomet. Chem. 1993, 443, 115. (h) Shyn,
S. G.; Hsiao, S. M.; Lin, K. J .; Gau, H.-M. Organometallics 1995, 14,
4300. (i) Shyn, S. G.; Lin, P. J .; Lin, K. J .; Chang, M. C.; Wen, Y. S.
Organometallics 1995, 14, 2253. (j) Shyn, S. G.; Hsu, J . Y.; Lin, P. J .;
Wu, W. J .; Peng, S. M.; Lea, G. H.; Wen, Y. S. Organometallics 1994,
13, 1699. (k) Hsiao, S. M.; Shyn, S. G. Organometallics 1998, 17, 1151.
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(m) Boni, G.; Lauvageot, P.; Marpeaux, E.; Moise, C. Organometallics
1995, 14, 5652. (n) Brettcher, H.-C.; Graf, M.; Merzweiler, K. J .
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E. Z. Anorg. Allg. Chem. 1997, 623, 1255.
* To whom correspondence should be addressed. (A.M.M.-B.) Fax:
+34 977 559563. E-mail: masdeu@quimica.urv.es. (C.T.) Fax: +34 976
761187. E-mail: ctejel@posta.unizar.es.
(1) (a) Braunstein, P.; Rose, J . In Comprehensive Organometallic
Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Pergamon: Oxford, 1995; Vol. 10, p 351. (b) Farrugia, L. J . Adv.
Organomet. Chem. 1990, 31, 301. (c) The Chemistry of Heteronuclear
Clusters and Multimetallic Catalysts; Adams, R. D., Herrmann, W.
A., Eds.; Polyhedron 1988, 7, 2251. (d) Wheatley, N.; Kalck, P. Chem.
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L., Knozinger, H., Eds.; Elsevier: New York, 1986. (b) Sinfelt, J . H. In
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New York, 1983. (c) Xiao, J .; Puddephat, R. J . Coord. Chem. Rev. 1995,
143, 457. (d) Sachter, W. M. H.; J . Mol. Catal. 1984, 25, 1. (e) Sinfelt,
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S.; Stephan, D. W. Organometallics 1987, 6, 2169. (c) Rousseau, R.;
Stephan, D. W. Organometallics 1991, 10, 3399. (d) Capdevila, M.;
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10.1021/om020042r CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/22/2002

2610 Organometallics, Vol. 21, No. 13, 2002
Fornie´s-Ca´mer et al.
analogous PtIr complexes [(P-P)Ir(µ-S-S)Rh(cod)]BF4.8
Comparison of the crystal structures of the complexes
[(PPh3)2Pt(µ-S-S)Rh(cod)]ClO4 (S-S ) EDT, PDB, BDT),
[(dppb)Pt(µ-BDT)Rh(cod)]ClO4, [(dppp)Pt(µ-BDT)Rh-
(cod)]ClO4, and [(dppb)Pd(µ-BDT)Rh(cod)]ClO4 showed
that simple modifications to the alkyl chain of the
dithiolate moiety or the use of different phosphines and
diphosphines directly affects geometric parameters such
as metal-metal distances and angles between coordina-
tion planes.
In this paper, we study the reactivity and catalytic
activity in the hydroformylation reaction of these com-
plexes. The two main aspects we consider are how
structural differences affect the reactivity and how
strong the heterobimetallic framework is when exposed
to different donor ligands. Thus, we explored the reac-
tion with carbon monoxide and different phosphine and
phosphite ligands at normal pressure and under cata-
lytic conditions. We also used cyclic voltammetry to
study the redox behavior of these complexes.
H, 3.18; S, 5.98. Found: C, 44.56; H, 3.20; S, 5.97. FAB: m/z
970 [M - ClO4]+, 914 [M - (CO)2 - ClO4]+.
[(P P h 3)2P t(µ-P DT)Rh (CO)2]ClO4‚1/2CH2Cl2 (2b): yellow
1
(63% yield). H NMR (300 MHz, CDCl3, 20 °C): δ 2.95 (m, 2
H, -SCH2-, PDT), 2.65 (m, 2 H, -SCH2-, PDT), 1.90 (m, 2
H, -CH2-, PDT), 7.3-7.4 (m, 30 H, Ph, PPh3). Anal. Calcd for
PtRhClS2P2O6C41H36‚1/2CH2 Cl2: C, 44.22; H, 3.28; S, 5.68.
Found: C, 44.13; H, 3.28; S, 5.70. FAB: m/z 984 [M - ClO4]+,
928 [M - (CO)2 - ClO4]+.
[(P P h 3)2P t(µ-BDT)Rh (CO)2]ClO4 (2c): yellow (85% yield).
1H NMR (300 MHz, CDCl3, 20 °C): δ 2.20 (m, 4 H, -SCH2-,
BDT), 1.60 (m, 4 H, -CH2-, BDT), 7.2-7.5 (m, 30 H, Ph,
PPh3). Anal. Calcd for PtRhClS2P2O6C42H38: C, 45.92; H, 3.46;
S, 5.83. Found: C, 45.72; H, 3.44; S, 5.81. FAB: m/z 998 [M -
ClO4]+, 942 [M - (CO)2 - ClO4]+.
[(d p p p )P t(µ-EDT)Rh (CO)2]ClO4‚CH2Cl2 (2d ): red (68%
yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ 3.00 (m, 2 H,
-SCH2-, EDT), 2.80 (m, 2 H, -SCH2-, EDT), 7.4-7.7 (m, 20
H, Ph, dppp), 2.56 (m, 4 H, -PCH2-, dppp), 1.60 (m, 2 H,
-CH2-, dppp). Anal. Calcd for PtRhClS2P2O6C31H30‚CH2Cl2:
C, 36.83; H, 3.07; S, 6.14. Found: C, 36.96; H, 3.11; S, 6.17.
FAB: m/z 858 [M - ClO4]+, 802 [M - (CO)2 - ClO4]+.
[(dppp)P t(µ-BDT)Rh (CO)2]ClO4‚CH2Cl2 (2e): yellow (75%
yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ 3.20 (m, 4 H,
-SCH2-, BDT), 1.2-2.8 (a, 4 H, -CH2-, BDT), 7.3-7.4 (m,
20 H, Ph, dppp), 1.2-2.8 (a, 4 H, -PCH2-, dppp), 1.2-2.8 (m,
2 H, -CH2-, dppp). Anal. Calcd for PtRhClS2P2O6C33H34‚CH2-
Cl2: C, 38.11; H, 3.36; S, 5.97. Found: C, 37.83; H, 3.15; S,
5.86. FAB: m/z 886 [M - ClO4]+, 830 [M - (CO)2 - ClO4]+.
[(d p p b)P t(µ-EDT)Rh (CO)2]ClO4‚CH2Cl2 (2f): red (73%
yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ 2.98 (m, 2 H,
-CH2-, EDT), 2.50 (m, 2 H, -CH2-, EDT), 7.4-7.8 (m, 20 H,
Ph, dppb), 2.87 (m, 4 H, -PCH2-, dppb), 1.90 (m, 4 H, -CH2-,
dppb). Anal. Calcd for PtRhClS2P2O6C32H32‚CH2Cl2: C, 37.48;
H, 3.22; S, 6.06. Found: C, 37.23; H, 3.25; S, 6.10. FAB: m/z
872 [M - ClO4]+, 816 [M - (CO)2 - ClO4]+.
Exp er im en ta l Section
Gen er a l Meth od s. All rhodium complexes were synthe-
sized using standard Schlenk techniques under a nitrogen
atmosphere. Solvents were distilled and deoxygenated before
use. The complex [Rh(cod)2]ClO4 and diene complexes 1a -i7
9
were prepared using methods described in the literature. All
other reagents were used as commercially supplied. Elemental
analyses were performed on a Carlo-Erba microanalyzer. The
IR spectra were obtained using a Nicolet 5ZDX-FT spectro-
photometer. 1H NMR spectra were recorded on a Varian
Gemini 300 MHz spectrophotometer, and chemical shifts are
quoted in ppm downfield from internal SiMe4. FAB mass
spectrometry was performed on a VG Autospect in a nitroben-
zyl alcohol matrix. Catalytic experiments were performed as
previously described.10 Gas chromatography analyses were
performed in a Hewlet-Packard Model 5890 gas chromato-
graph with flame ionization detector using a 25 m × 0.2 mm
Ø capillary column (Ultra 2).
Cyclic voltammetry experiments were performed with an
EG&G PARC model 273 potentiostat/galvanostat. The three-
electrode glass cell that we used consisted of a platinum-disk
working electrode, a platinum-wire auxiliary electrode, and a
standard calomel reference electrode (SCE). Tetra-n-butylam-
monium hexafluorophosphate (TBAH) was used as supporting
electrolyte. Electrochemical experiments were carried out
under nitrogen in ∼5 × 10-4 M dichloromethane or MeCN
solutions of the complexes and 0.1 M in TBAH. The [Fe-
(C5H5)2]+/[Fe(C5H5)2] couple was observed at + 0.47 V under
these experimental conditions.
[(dppb)P t(µ-BDT)Rh (CO)2]ClO4‚CH2Cl2 (2g): yellow (76%
yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ 3.40 (m, 2 H,
-SCH2-, BDT), 2.92 (m, 2 H, -SCH2-, BDT), 2.23 (m, 4 H,
-CH2-, BDT), 7.4-7.8 (m, 20 H, Ph, dppb), 2.80 (m, 4 H,
-PCH2-, dppb), 1.80 (m, 4 H, -CH2-, dppb). Anal. Calcd for
PtRhClS2P2O6C34H36‚CH2Cl2: C, 38.73; H, 3.50; S, 5.90.
Found: C, 38.60; H, 3.47; S, 6.01. FAB: m/z 900 [M - ClO4]+,
844 [M - (CO)2 - ClO4]+.
P r ep a r a tion of Com p lexes [(P -P )P t(µ-S-S)Rh (CO)-
(P R3)]ClO4 (S-S ) EDT, P DT, BDT; (P -P ) ) (P P h 3)2,
d p p p , a n d d p p b; P R3 ) P P h 3, P Cy3, P (OtBu P h )3). Gen er a l
P r oced u r e. Carbon monoxide was bubbled for 10 min through
a
dichloromethane solution of the corresponding diolefin
complexes 1a -g (0.05 mmol in 5 mL of solvent) to form the
corresponding carbonyl complex. The corresponding PR3 ligand
(0.10 mmol) was added, and the solution was stirred for 10
min. The solution was concentrated to 2 mL, and hexane was
added to crystallize the products. The solid was filtered,
washed with hexane, and vacuum-dried.
[(P P h 3)2P t(µ-EDT)Rh (CO)(P P h 3)]ClO4‚1/2CH2Cl2 (3a ):
yellow solid (65% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
3.19 (m, 1 H, -CH2-, EDT), 3.08 (m, 1 H, -CH2-, EDT), 2.75
(m, 1 H, -CH2-, EDT), 2.25 (m, 1 H, -CH2-, EDT), 7.1-7.5
(m, 45 H, Ph, PPh3). IR (KBr, cm-1): ν(CO), 1992 (vs). Anal.
Calcd for PtRhClS2P3O5C57H49‚1/2CH2Cl2: C, 51.26; H, 3.64;
S, 4.75. Found: C, 51.25; H, 3.73; S, 4.68. FAB: m/z 1205 [MH
- ClO4]+, 914 [M - (CO) - PPh3 - ClO4]+.
[(P P h 3)2P t(µ-P DT)Rh (CO)(P P h 3)]ClO4‚1/2CH2Cl2 (3b):
yellow solid (60% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
2.60 (m, 2 H, -SCH2-, PDT), 2.43 (m, 2 H, -SCH2-, PDT),
2.00 (m, 1 H, -CH2-, PDT), 1.84 (m, 1 H, -CH2-, PDT), 7.2-
7.6 (m, 45 H, Ph, PPh3). IR (KBr, cm-1): ν(CO), 1961 (vs). Anal.
Calcd for PtRhClS2P3O5C58H51‚1/2CH2Cl2: C, 51.62; H, 3.82;
S, 4.70. Found: C, 51.33; H, 3.81; S, 4.78. FAB: m/z 1219 [MH
- ClO4]+.
P r ep a r a tion of Ca r bon yl Com p lexes [(P -P )P t(µ-S-S)-
Rh (CO)2]ClO4 (S-S ) EDT, P DT, BDT; (P -P ) ) (P P h 3)2,
d p p p , a n d d p p b). Gen er a l P r oced u r e. Carbon monoxide
was bubbled for 10 min through dichloromethane solutions of
complexes 1a -g (0.05 mmol in ca. 5 mL of solvent). The
resulting solution was concentrated to ca. 2 mL. The solid
formed by adding hexane was filtered, washed with hexane,
and vacuum-dried.
[(P P h 3)2P t(µ-EDT)Rh (CO)2]ClO4 (2a ): purple crystals
1
(68% yield). H NMR (300 MHz, CDCl3, 20 °C): δ 3.32 (m, 2
H, -CH2-, EDT), 2.50 (m, 2 H, -CH2-, EDT), 7.2-7.5 (m, 30
H, Ph, PPh3). Anal. Calcd for PtRhClS2P2O6C40H34: C, 44.88;
(8) Fornie´s-Ca´mer, J .; Masdeu-Bulto´, A. M.; Claver, C. Inorg. Chem.
Commun. 1999, 2/ 3, 89.
(9) Uso´n, R.; Oro, L. A.; Iba´n˜ez, F. Rev. Acad. Cienc. Zaragoza 1975,
169.
(10) Masdeu, A. M.; Orejo´n, A.; Ruiz, A.; Castillo´n, S.; Claver, C. J .
Mol. Catal. 1994, 94, 149.

Heterobimetallic MRh (M ) Pt, Pd) Complexes
Organometallics, Vol. 21, No. 13, 2002 2611
[(P P h 3)2P t(µ-BDT)Rh (CO)(P P h 3)]ClO4 (3c): yellow solid
(83% yield). H NMR (300 Hz, CDCl3, 20 °C): δ 2.40 (m, 1 H,
-CH2-, EDT), 6.8-7.4 (m, 60 H, Ph, PPh3, and P(OPh)3). Anal.
Calcd for PtRhClS2P4O10C74H64‚1/2CH2Cl2: C, 53.34; H, 3.87;
S, 3.81. Found: C, 53.09; H, 3.87; S, 3.77. FAB: m/z 1535 [MH
- ClO4]+, 914 [M - 2P(OPh)3 - ClO4]+.
Cr ysta l Da ta for Com p lexes [(P P h 3)2P t(µ-EDT)Rh -
(CO)2]BF 4 (2a ′) a n d 3a . Suitable crystals of complexes 2a ′
and 3a were grown by diffusing n-hexane into a solution of
the complex in dichloromethane and mounted on a glass fiber.
The data were collected and processed at room temperature
on a Mar Research image plate scanner. Graphite-monochro-
mated Mo KR radiation was used to measure 95/2 frames, 180
s per frame in both cases.
1
-SCH2-, BDT), 2.18 (m, 3 H, -SCH2-, BDT), 1.98 (m, 2 H,
-CH2-, BDT), 1.38 (m, 1 H, -CH2-, BDT), 1.17 (m, 1 H,
-CH2-, BDT), 7.1-7.6 (m, 45 H, Ph, PPh3). IR (KBr, cm-1):
ν(CO), 1979 (vs). Anal. Calcd for PtRhClS2P3O5C59H53
: C,
51.52; H, 3.93; S, 4.65. Found: C, 51.39; H, 3.87; S, 4.64.
FAB: m/z 1233 [MH - ClO4]+.
[(d p p p )P t (µ-E DT)R h (CO)(P P h 3)]ClO4‚1/2CH 2Cl2 (3d ):
yellow solid (72% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
3.00 (m, 1 H, -SCH2-, EDT), 2.85 (m, 1 H, -SCH2-, EDT),
2.38 (m, 1 H, -SCH2-, EDT), 2.15 (m, 1 H, -SCH2-, EDT),
6.8-7.8 (m, 35 H, Ph, dppp, PPh3), 2.7-2.8 (m, 4 H, -PCH2-,
dppp), 2.10 (m, 2 H, -CH2-, dppp). IR (KBr, cm-1): ν(CO),
1980 (vs). Anal. Calcd for PtRhClS2P3O5C48H45‚1/2CH2Cl2: C,
47.16; H, 3.72; S, 5.18. Found: C, 46.98; H, 3.69; S, 5.16.
FAB: m/z 1092 [M - ClO4]+.
[(d p p p )P t (µ-BDT)R h (CO)(P P h 3)]ClO4‚1/2CH 2Cl2 (3e):
yellow solid (84% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
2.6-3.2 (a, 4 H, -SCH2-, BDT), 1.80 (m, 2 H, -CH2-, BDT),
1.65 (m, 2 H, -CH2-, BDT), 7.2-8.1 (m, 35 H, Ph, dppp, PPh3),
2.45 (m, 4 H, -PCH2-, dppp), 2.00 (m, 2 H, -CH2-, dppp).
IR (KBr, cm-1): ν(CO), 1988 (vs). Anal. Calcd for
PtRhClS2P3O5C50H49‚1/2CH2Cl2: C, 48.02; H, 3.88; S, 5.07.
Found: C, 47.92; H, 3.86; S, 4.82. FAB: m/z 1120 [M - ClO4]+.
[(dppb)P t(µ-EDT)Rh (CO)(P P h 3)]ClO4‚1/2CH2Cl2 (3f): yel-
low solid (68% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
2.5-3.0 (m, 2 H, -CH2-, EDT), 1.6-2.0 (m, 2 H, -CH2-,
EDT), 7.0-7.8 (m, 35 H, Ph, dppb, PPh3), 2.5-3.0 (m, 4 H,
-PCH2-, dppb), 1.9-2.3 (m, 4 H, -CH2-, dppb). IR (KBr,
cm-1): ν(CO), 1984 (vs). Anal. Calcd for PtRhClS2P3O5C49H47‚1/
2CH2Cl2: C, 47.59; H, 3.84; S, 5.07. Found: C, 47.71; H, 3.83;
S, 5.11. FAB: m/z 1106 [M - ClO4]+.
[(d p p b )P t (µ-BDT)R h (CO)(P P h 3)]ClO4‚1/2CH 2Cl2 (3g):
yellow solid (70% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
3.30 (m, 1 H, -SCH2-, BDT), 3.12 (m, 1 H, -SCH2-, BDT),
2.80 (m, 1 H, -SCH2-, BDT), 2.38 (m, 1 H, -SCH2-, BDT),
1.90 (m, 1 H, -CH2-, BDT), 1.60 (m, 1 H, -CH2-, BDT), 1.37
(m, 1 H, -CH2-, BDT), 1.10 (m, 1 H, -CH2-, BDT), 7.2-8.3
(m, 35 H, Ph, dppb and PPh3), 2.80 (m, 4 H, -PCH2-, dppb),
1.70 (m, 4 H, -CH2-, dppb). IR (KBr, cm-1): ν(CO), 1982 (vs).
Anal. Calcd for PtRhClS2P3O5C51H51‚1/2CH2Cl2: C, 48.43; H,
4.07; S, 5.01. Found: C, 48.63; H, 4.10; S, 4.93. FAB: m/z 1134
[M - ClO4]+.
Com p ou n d 2a ′: PtRhS2P2O2C40H34BF4‚1/2CH2Cl2, M )
1098.9, monoclinic, a ) 18.407 Å, R ) 90°, b ) 14.162 Å, â )
100.56°, c ) 32.693 Å, γ ) 90°, V ) 8378.2 Å3, space group
P21/c (14), Z ) 4, Dc ) 1.743 Mg/m3, F(000) ) 4288, purple,
crystal dimensions 0.22 × 0.15 × 0.18 mm, µ(Mo KR) ) 19.85
cm-1
.
Com p ou n d 3a : PtRhClS2P3O6C57H49‚CH2Cl2, M ) 1403.35,
triclinic, a ) 14.246 Å, R ) 81.75°, b ) 14.439 Å, â ) 81.06°,
c ) 14.519 Å, γ ) 83.15°, V ) 2905.4 Å3, space group P1h, Z )
2, Dc ) 1.604 Mg/m3, F(000) ) 1392, yellow, crystal dimensions
0.12 × 0.23 × 0.15 mm, µ(Mo KR) ) 14.67 cm-1
.
The XDS11 package was used to give the following: 7664
unique reflections [merging R ) 0.0266] (2a ′) and 5710 unique
reflections [merging R ) 0.0317] (3a ). The heavy atoms were
found from the Patterson map using the SHELX8612 program
and refined subsequently from successive difference Fourier
maps using SHELXL9313 by full-matrix least squares of 528
(2a ′) and 713 (3a ) variables, to a final R-factor of 0.0619 (2a ′)
and 0.0428 (3a ) for 7659 (2a ′) and 5705 (3a ) reflections with
[Fo] > 4σ(Fo). All atoms were revealed by the Fourier map
difference. Non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed geometrically and then refined
with fixed isotropic atomic displacement parameters. The
weighting scheme w ) 1/[σ2(Fo2) + (aP)2 + bP], where P ) max-
((Fo2, 0) + 2Fc2)/3, a ) 0.0846 (2a ′), 0.0523 (3a ) and b ) 115.82
(2a ′), 20.68 (3a ) with σ(Fo) from counting statistics, gave
satisfactory agreement analyses. The final parameters R1 ([Fo]
> 4σ(Fo)) were 0.0619 (2a ′) and 0.0428 (3a ), and wR2 (all data)
were 0.0777 (2a ′) and 0.0590 (3a ) for R1 ) ∑||Fo| - |Fc||/∑|Fo|
and wR2 ) [∑w(Fo - Fc2)/∑w(Fo2)2)]1/2. The ORTEP diagrams
2
for 2a ′ and 3a were generated using ORTEP-3.14
[(P P h 3)2P t(µ-EDT)Rh (CO)(P Cy3)]ClO4‚1/2CH2Cl2 (3h ):
yellow solid (79% yield). 1H NMR (300 MHz, CDCl3, 20 °C): δ
3.35 (m, 2 H, -CH2-, EDT), 2.88 (m, 1 H, -CH2-, EDT), 2.51
(m, 1 H, -CH2-, EDT), 7.2-7.6 (m, 30 H, Ph, PPh3), 1.1-1.9
(m, 33 H, -CH2-, PCy3). IR (KBr, cm-1): ν(CO), 1966 (vs).
Anal. Calcd for PtRhClS2P3O5C57H67‚1/2CH2Cl2: C, 50.58; H,
4.98; S, 4.69. Found: C, 50.48; H, 5.01; S, 4.09.FAB: m/z 1223
[MH - ClO4]+.
Resu lts a n d Discu ssion
cis-Dica r bon yl Com p lexes. The reaction of the
diolefin complexes [(P-P)Pt(µ-S-S)Rh(cod)]ClO4 (1a -
g) (P-P ) (PPh3)2, Ph2P(CH2)3PPh2 (dppp), and Ph2P-
(CH2)4PPh2 (dppb); S-S ) -S(CH2)2S- (EDT), -S(CH2)3S-
(PDT), -S(CH2)4S- (BDT), cod ) 1,5-cyclooctadiene,
Scheme 1) with carbon monoxide under atmospheric
pressure yielded the dicarbonyl complexes [(P-P)Pt(µ-
S-S)Rh(CO)2]ClO4 (2a -g, Scheme 1), which were iso-
lated in good yields.
The dinuclear framework was maintained in these
reactions as deduced from the spectroscopic data, which
confirmed the proposed formulations and revealed the
lack of bridge cleavage and ligand redistribution pro-
cesses. The m/z peaks of the cations were observed in
the FAB+ mass spectra, while the IR spectra showed
two ν(CO) bands separated by ca. 60 cm-1 as expected
[(P P h 3)2P t (µ-E DT)R h (CO)(P (Ot Bu P h )3)]ClO4‚1/2CH 2-
1
Cl2 (3i): yellow solid (88% yield). H NMR (300 MHz, CDCl3,
20 °C): δ 3.40 (m, 2 H, -CH2-, EDT), 2.97 (m, 1 H, -CH2-,
EDT), 2.51 (m, 1 H, -CH2-, EDT), 6.8-7.7 (m, 42 H, Ph, PPh3,
and P(OtBuPh)3), 1.30 (s, 27 H, -CH3, P(OtBuPh)3). IR (KBr,
cm-1): ν(CO), 2016 (vs). Anal. Calcd for PtRhClS2P3O8C69H73‚1/
2CH2Cl2: C, 53.39; H, 4.73; S, 4.09. Found: C, 53.12; H, 4.75;
S, 4.12. FAB: m/z 1421 [MH - ClO4]+, 915 [MH - (CO) -
P(OtBuPh)3 - ClO4]+.
P r ep a r a t ion
of Com p lex [(P P h 3)2P t (µ-E DT)R h -
(P (OP h )3)2]ClO4‚1/2CH2Cl2 (4). Carbon monoxide was bubbled
for 10 min through a dichloromethane solution of the corre-
sponding diene complex 1a (0.05 mmol in 5 mL of solvent) to
form the corresponding carbonyl complex. Then, P(OPh)3 (0.10
mmol) was added and the solution was stirred for 10 min. The
solution was concentrated to 2 mL, and hexane was added to
give a yellow precipitate (79% yield). The solid was filtered,
(11) Kabsch, W. J . Appl. Crystallogr. 1993, 26, 795.
(12) Sheldrick, G. M. SHELXS-86: Program for Crystal Structure
Solutions; University of Go¨ttingen: Germany, 1986.
(13) Sheldrick, G. M. SHELXS-93: Program for Crystal Structure
Solutions; University of Go¨ttingen: Germany, 1993.
(14) Farrugia, L. J . ORTEP-3 for Windows. J . Appl. Crystallogr.
1997, 30, 565.
1
washed with hexane, and vacuum-dried. H NMR (300 MHz,
CDCl3, 20 °C): δ 2.68 (m, 2 H, -CH2-, EDT), 1.40 (m, 2 H,

2612 Organometallics, Vol. 21, No. 13, 2002
Fornie´s-Ca´mer et al.
1J Pt-P (Hz)
Ta ble 1. In fr a r ed (cm -1
)
a n d 31P {1H} NMRb (δ) Da ta for Com p lexes 2a -g
a
complex
ν(CO)
δ(31P)
[(PPh3)2Pt(µ-EDT)Rh(CO)2]ClO4 (2a )
[(PPh3)2Pt(µ-PDT)Rh(CO)2]ClO4 (2b)
[(PPh3)2Pt(µ-BDT)Rh(CO)2]ClO4 (2c)
[(dppp)Pt(µ-EDT)Rh(CO)2]ClO4 (2d )
[(dppp)Pt(µ-BDT)Rh(CO)2]ClO4 (2e)
[(dppb)Pt(µ-EDT)Rh(CO)2]ClO4 (2f)
[(dppb)Pt(µ-BDT)Rh(CO)2]ClO4 (2g)
2075 vs, 2023 vs
2089 vs, 2012 vs
2076 vs, 2018 vs
2060 vs, 2011 vs
2088 vs, 2024 vs
2064 vs, 2015 vs
2087 vs, 2013 vs
14.73
17.32
18.51
-2.89
0.01
3265
3155
2955
3004
2765
3142
2917
14.03
17.50
a
b
Spectra recorded in CH2Cl2. Spectra recorded in CDCl3. Chemical shifts are referenced to H3PO4 (δ ) 0 ppm). vs ) very strong.
Sch em e 1
F igu r e 1. X-ray structure of the cation [(PPh3)2Pt(µ-EDT)-
Rh(CO)2]+ of complex 2a ′ showing thermal ellipsoids at 50%
probability.
for rhodium cis-dicarbonyl compounds (Table 1).15 In
addition, the two equivalent phosphorus nuclei bonded
to platinum produced a singlet with the corresponding
195Pt satellites in the 31P{1H} NMR spectra (Table 1).
The P-Pt coupling constants were in the normal range
for Pt(II) complexes16 and slightly larger than those of
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 2a ′
Pt(1)-Rh(2)
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-S(1)
Pt(1)-S(2)
Rh(2)-C(3)
Rh(2)-C(4)
Rh(2)-S(1)
Rh(2)-S(2)
2.9826(9)
2.296(2)
2.281(2)
2.369(3)
2.377(3)
1.856(12)
1.89(2)
P(2)-Pt(1)-Rh(2) 120.83(7)
P(1)-Pt(1)-Rh(2) 120.28(6)
S(1)-Pt(1)-Rh(2) 51.00(7)
S(2)-Pt(1)-Rh(2) 50.98(6)
1
the corresponding cod complexes (1a -g). The H NMR
spectra of complexes with an EDT ligand (2a , 2d , 2f)
C(3)-Rh(2)-C(4)
C(3)-Rh(2)-S(1)
C(4)-Rh(2)-S(1)
C(3)-Rh(2)-S(2)
C(4)-Rh(2)-S(2)
S(1)-Rh(2)-S(2)
90.9(7)
showed the methylenic protons as two signals in the
95.7(5)
1
2.5-3.5 ppm region, which were identified by H,1H-
172.8(4)
173.9(5)
94.8(5)
2.370(3)
2.370(3)
COSY experiments. The signals attributed to the pro-
tons oriented toward the platinum center were more
deshielded (ca. 3.5 ppm) than those oriented toward
rhodium (ca. 2.5 ppm), as previously reported.7 The
complexes with the BDT ligand (2c, 2e, 2g) showed a
wide nonresolved signal in this region.
P(2)-Pt(1)-P(1) 101.34(9)
78.51(10)
P(2)-Pt(1)-S(1) 166.06(10) S(1)-Rh(2)-Pt(1) 50.99(7)
P(1)-Pt(1)-S(1) 92.52(10)
P(2)-Pt(1)-S(2) 87.87(9)
P(1)-Pt(1)-S(2) 170.27(9)
S(2)-Rh(2)-Pt(1) 51.19(6)
Pt(1)-S(1)-Rh(2) 78.01(9)
Rh(2)-S(2)-Pt(1) 77.84(8)
S(1)-Pt(1)-S(2)
78.39(10)
106.4
Θ(PtS2Rh)
108.5
X-r a y Str u ctu r e of th e Com p lex [(P P h 3)2P t(µ-
EDT)Rh (CO)2]BF 4 (2a ′). Crystals suitable for X-ray
analysis of the tetrafluoroborate analogues of complex
2a (2a ′) were grown by diffusing n-hexane into a
solution of the complex in dichloromethane. The bi-
nuclear cation [(PPh3)2Pt(µ-EDT)Rh(CO)2]+ represented
in Figure 1 has a bent structure in which the dithiolate
is bonded as a bridge ligand to both metal atoms, each
of which has a square-planar environment. Selected
bond distances and angles are given in Table 2.
æ
propose a weak rhodium-rhodium interaction since the
distances reported for complexes with unidirectional
packing as a result of intermetallic interactions are
somewhat shorter. Some examples are [Rh(acac)(CO)2],
which has a Rh‚‚‚Rh distance of 3.26 Å,18 or the
dinuclear complex [Rh(µ-Cl)(CO)2]2 with a Rh‚‚‚Rh
distance of 3.31 Å.19
The metal-ligand bond distances are in the range
observed for related heterobimetallic PtRh complexes
with dithiolate bridge ligands.7 The Pt-P bond dis-
tances (average 2.288 Å) are similar to the ones for diene
complex 1a (average 2.276 Å) and mononuclear complex
The distance Rh-Pt (2.9826(9) Å) is longer than the
value considered for the Pt-Rh metal-metal bond (2.6
Å). Nevertheless, it is shorter than the distance for the
analogous diene complex [(PPh3)2Pt(µ-EDT)Rh(cod)]-
ClO4 (3.0096(6) Å)7 and one of the shortest reported in
the literature for nonbonded Rh-Pt atoms.17
(17) (a) Guimerans, R. R.; Wood, F. E.; Balch, A. L. Inorg. Chem.
1984, 23, 1307. (b) Balch, A. L.; Guimerans, R. R.; Linehan, J .; Wood,
F. E. Inorg. Chem. 1985, 24, 2021. (c) Hutton, A. T.; Langrick, C. R.;
McEwan, D. M.; Pringle, P. G.; Shaw, B. L. J . Chem. Soc., Dalton
Trans. 1985, 2121. (d) Balch, A. L.; Catalano, V. J . Inorg. Chem. 1992,
31, 3934.
(18) Bailey, N. A.; Coates, E.; Robertson, G. B.; Bonati, F.; Ugo, R.
J . J . Chem. Soc., Dalton Trans. 1967, 1041.
(19) Dahl, L. F.; Martell, C.; Wampler, D. L. J . Am. Chem. Soc. 1961,
83, 1761.
The intercationic rhodium-rhodium distances found
in the packed structure are quite long (4.481 Å) to
(15) Nakamoto, K. In Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 5th ed.; Wiley: New York, 1997.
(16) Verkade, V. G.; Quin, L. D. In Phosphorus-31 NMR Spectroscopy
in Stereochemical Analysis Organic Compounds and Metal Complexes;
VCH Publishers: Deerfield, 1987.

Heterobimetallic MRh (M ) Pt, Pd) Complexes
Organometallics, Vol. 21, No. 13, 2002 2613
Ta ble 3. 31P {1H} NMRa (δ) Da ta for Com p lexes 3a -i a n d 4
b
b
complex
Pa
Pb
Pc
1J Pa-Rh
1J Pb-Pt
1J Pc-Pt
4J Pa-Pb
4J Pa-Pc
2J Pb-Pc
3J Pb-Rh
3J Pc-Rh
3a
3b
3c
3d
3e
3f
3g
3h
3i
36.3
39.1
41.8
36.8
42.8
36.7
43.4
51.2
114.7
116.9
16.2
20.4
20.7
-3.9
0.6
17.3
17.8
17.3
14.8
15.2
14.4
16.5
17.8
-4.9
-0.9
7.9
15.1
13.8
13.7
156
153
148
156
146
157
148
150
269
284
3240
3149
2946
2989
2708
3165
2838
3226
3308
3119
3104
2957
2816
2922
2707
2970
2853
3070
3052
4.6
4.1
5.6
3.3
5.5
3.6
5.6
4.1
6.4
8.2
18.0
22.2
6.9
20.0
7.3
19.3
6.5
11.4
17.9
18.0
14.7
29.4
23.8
23.0
17.4
18.5
17.8
1.4
1.8
1.4
1.3
1.3
1.0
1.3
4
a
a
b
Spectra recorded in CDCl3. Chemical shifts are referenced to H3PO4 (δ ) 0 ppm). Assignation for Pb and Pc may be the opposite.
Sch em e 2
cis-[Pt(EDT)(PPh3)2] (average 2.2885 Å).20 This distance,
however, is longer than the one for the dichloro analogue
cis-[PtCl2(PPh3)2] (average 2.258 Å).21
The Rh-S distances in complex 2a ′ (average 2.370
Å) are longer than in diene complex 1a (average 2.359
Å), which is attributed to the fact that the trans
influence of the carbonyl ligand is greater than that of
the cod ligand. Pt-S bond distances are also slightly
longer in complex 2a ′ than in the cod complex.
The torsion angle Θ (RhS2Pt) of the bent structure of
2a ′ (108.5°) is smaller than that of the diene complex
1a (111.27°). This may be because the steric repulsion
between the terminal ligands in the dicarbonylic com-
plex is lower. By comparing 2a ′ with the related homo-
binuclear complexes [Rh2(µ-EDT)(cod)2] or [Rh2(µ-PDT)-
(cod)2], which have torsion angles of 104°,22 we can
conclude that the triphenylphosphino terminal ligands
produce a repulsion that opens the bent structure.
The angle between the coordination planes without
the metal atoms (æ) in 2a ′ is 106.4°, which is ca. 2°
difference with respect to Θ. This small difference
between æ and Θ indicates that the metal atom is only
slightly separated from the coordination plane. In diene
complex 1a the differences between æ and Θ were
greater (111.27° and 96.02°, respectively) and were
attributed to intermetallic repulsion due to the short
metal-metal distance.22
Rea ction s of Com p lexes 2a -g w ith P h osp h in es,
P h osp h ites, a n d th e Dip h osp h in e d p p p . The addi-
tion of 1 molar equiv of PPh3 to the dicarbonyl com-
plexes [(P-P)Pt(µ-S-S)Rh(CO)2]ClO4 (2a -g) produced
the replacement of one carbonyl group with formation
of the complexes [(P-P)Pt(µ-S-S)Rh(CO)(PPh3)]ClO4
(3a -g, Scheme 2). In a similar way, complex 2a reacted
with the bulky PCy3 and P(O-o-tBuPh)3 ligands to give
[(PPh3)2Pt(µ-EDT)Rh(CO)(PR3)]ClO4 (R ) Cy (3h ), O-o-
tBuPh (3i)). No reaction was observed between the cod
compounds 1a -g and PPh3. Complexes 3a -i were
isolated in good yields, and the IR spectra showed only
one absorption in the ν(CO) region, which confirmed
their formulation. The ν(CO) frequencies of the EDT
complexes with different PR3 ligands were in the order
3h < 3a < 3i. This was the expected order because of
the basicity of the PR3 ligands PCy3 > PPh3 > P(O-o-
tBuPh)3.
Sch em e 3
The 31P{1H} NMR spectra of complexes 3a -i (Table
3) displayed three signals, one of which showed a
103Rh-P coupling (Pa, Scheme 2) and the other two
showed the characteristic satellites of a 195Pt-P coup-
ling (Pb and Pc, Scheme 2). The signals corresponding
to Pb and Pc were assigned on the basis of the structural
data of complex 3a , assuming that the signal with the
largest Pt-P coupling constant is the one with the
shortest Pt-P distance. As the shortest Pt-P distance
in the X-ray structure of complex 3a (discussed in the
next section) corresponds to the phosphorus cis to the
Rh-P bond, the signal at δ 16.2 ppm was attributed to
Pb and the signal at 14.4 ppm was assigned to Pc.
The reaction between 2a and 1 molar equiv of the less
bulky phosphite, P(OPh)3, produced mixtures of the
species [(PPh3)2Pt(µ-EDT)Rh(CO){P(OPh3)}]ClO4 and
[(PPh3)2Pt(µ-EDT)Rh{P(OPh3)}2]ClO4 (4), which evolved
to 4 when the second molar equivalent of P(OPh)3 was
1
added (Scheme 3). The H NMR spectrum of 4 showed
two signals corresponding to the two different methyl-
enic environments of the EDT ligand (see Experimental
Section). These methylenic signals are shielded consid-
erably more than those of parent complex 2a , which may
be because the π-acceptor ability of the phosphite is less
than that of the carbonyl ligand.
(20) Bryan, S. A.; Roundhill, D. M. Acta Crystallogr., C: Cryst.
Struct. Commun. 1983, 39, 184.
Since diphosphines have shown interesting applica-
tions in homogeneous catalysis due to their ability to
control the selectivity,23 we studied the reactivity of the
carbonyl complexes toward the diphosphine dppp. The
(21) Fergusson, G.; Anderson, G. K.; Clark, H. C.; Davies, J . A.;
Parvez, M. J . Cryst. Spectrosc. Res. 1982, 12, 449.
(22) Masdeu, A..M.; Ruiz, A.; Castillo´n, S.; Claver, C.; Hitchcock,
P. B.; Chaloner, P.; Bo, C.; Poblet, J . M.; Sarasa, P. J . Chem. Soc.,
Dalton Trans. 1993, 268.

2614 Organometallics, Vol. 21, No. 13, 2002
Fornie´s-Ca´mer et al.
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 3a
Pt(1)-P(2)
Pt(1)-P(1)
Pt(1)-S(1)
Pt(1)-S(2)
Pt(1)-Rh(1)
Rh(1)-C(1)
Rh(1)-P(3)
Rh(1)-S(2)
Rh(1)-S(1)
C(1)-O(1)
2.278(3)
2.301(2)
2.357(3)
2.362(2)
3.0217(8) P(3)-Rh(1)-S(2)
1.836(14) C(1)-Rh(1)-S(1)
2.275(3)
2.375(3)
2.406(3)
S(1)-Pt(1)-Rh(1) 51.34(6)
S(2)-Pt(1)-Rh(1) 50.55(7)
C(1)-Rh(1)-P(3)
C(1)-Rh(1)-S(2)
89.4(4)
168.6(4)
97.53(9)
96.6(4)
P(3)-Rh(1)-S(1)
S(2)-Rh(1)-S(1)
172.00(10)
77.40(9)
Pt(1)-S(1)-Rh(1) 78.74(8)
1.138(14) Pt(1)-S(2)-Rh(1) 79.28(8)
P(2)-Pt(1)-P(1) 99.11(9)
P(2)-Pt(1)-S(1) 169.40(9)
P(1)-Pt(1)-S(1) 88.66(9)
P(2)-Pt(1)-S(2) 94.10(9)
P(1)-Pt(1)-S(2) 166.50(9)
Θ(PtS2Rh)
æ
109.9
103.7
F igu r e 2. X-ray structure of the cation [(PPh3)2Pt(µ-EDT)-
Rh(CO)(PPh3)]+ of complex 3a showing thermal ellipsoids
at 50% probability for the two enantiomers.
S(1)-Pt(1)-S(2)
78.61(9)
The Rh-S(1) bond distance trans to the Rh-PPh3
bond (2.406(3) Å) is longer than the Rh-S(2) distance
(2.375(3) Å) trans to the carbonyl ligand. This is because
the PPh3 ligand has a greater trans influence than the
carbonyl ligand.26 This was also observed in related
mixed complexes such as cis-[Ir(µ-StBu)(CO)(P(OMe)3)]2,
where the Ir-S trans to P(OMe)3 is 2.393 Å while the
distance Ir-S trans to CO is 2.386 Å.27
The different trans influence of PPh3 and CO is
reflected in the Pt-P distances. The longest Pt-P
distance is Pt-P(2), which is trans to Pt-S(1) and
experiences the greater trans influence of the PPh3
ligand. This can be considered a long-range trans
influence: it acts through two trans bonds and finally,
because of the binuclear structure of the complex, it is
also detected in a position cis to the original ligand.
Taking into account that the shorter Pt-P distance
should correspond to the greater 195Pt-31P coupling, we
assigned the P(2) that is cis to P(3) to the 31P{1H} NMR
signal named Pb.
The difference between the angles æ and Θ (109.9°
and 103.7°, respectively) is in this case greater than for
complex 2a ′. The whole hinge structure is twisted due
to the repulsion between the terminal triphenylphos-
phine ligands. The angles between the ligands are far
from the theoretical 90°: in fact they range between
97.53(9)° for P(3)-Rh(1)-S(2) and 77.40(9)° for S(1)-
Rh(1)-S(2). The deviation in the planarity can also be
observed in the trans angles such as C(1)-Rh(1)-S(2)
with a value of 168.6(4)° or P(1)-Pt(1)-S(2) with a value
of 166.50(9)°.
31P{1H} NMR spectrum of a solution of 2a with 2 molar
equiv of dppp in CDCl3 indicated that a mixture of
complexes formed as a result of a bridge-cleavage
reaction. These products were the mononuclear complex
[Pt(EDT)(PPh3)2], which showed a singlet with Pt-P
satellites at 21.0 ppm, as previously described,24 and
the pentacoordinated species [Rh(dppp)2(CO)]+, which
showed broad signals at 15.6 and -10.3 ppm, resolved
at -65 °C as two double triplets with J PP ) 45 Hz, J PaxRh
) 86.3 Hz, J PeqRh ) 113.6 Hz,25 and free ligand. Two
small signals at -2 and -4 ppm were also detected.
To sum up, the heterobimetallic cod complexes 1a -g
reacted with PR3 donor ligands in the presence of carbon
monoxide and maintained the heterobimetallic struc-
ture, while 1a reacted with the diphosphine dppp in the
presence of carbon monoxide and led to the rupture of
the dinuclear framework.
X-r a y Str u ctu r e of Com p lex 3a . The crystal struc-
ture of complex 3a (Figure 2) was determined by X-ray
diffraction of a suitable crystal that had been obtained
by diffusing n-hexane through a solution of the complex
in dichloromethane. Complex 3a is an example of a
chiral complex in which none of the ligands are chiral.
The X-ray structure was obtained from the racemic
sample, so both enantiomers were observed in the unit
cell. The structure of the cation complex of 3a is bent,
analogous to the related dithiolate bridge complex 2a ′.
Selected bond distances and angles are given in Table
4.
There is no metal-metal bond since the PtRh dis-
tance is 3.022(2) Å. The PtRh distance of 3a is longer
than that of 2a ′, presumably because of the steric
repulsion between the triphenylphosphine terminal
ligands bonded to the different metals.
The Rh-C bond distance (1.836(14) Å) is shorter in
complex 3a than in complex 2a ′ (average 1.873 Å),
which indicates that there is an increase in the back-
bonding nature of the Rh-CO bond. This is because a
strong π-acceptor ligand such as CO is replaced by a
better donor and less acceptor ligand such as triphenyl-
phosphine. The variation in the bond distances agrees
with the variation in the stretching ν(CO) bands in the
IR spectrum.
Cyclic Volt a m m et r y a n d Ch em ica l Oxid a t ion
Stu d ies. We used cyclic voltammetry (CV) to study the
electrochemical behavior of some selected complexes.
The complexes [(PPh3)2Pt(µ-S-S)Rh(cod)] (S-S ) EDT
(1a ), PDT (1b), BDT (1c)), whose environments are
identical at the metal centers, were chosen as the most
appropriate ones to show how the dithiolate bridge
affects the redox properties of these heterobimetallic
complexes. Compounds 1a and 1c showed a wave with
(Ep + Ep )/2 values of 0.97 and 0.95 V at 0.2 V s-1
,
a
c
respectively. In both cases, the ipc/ipa ratio was below
1.00 and decreased as the scan rate was reduced, which
is indicative of a coupled irreversible chemical reaction.
(23) Pignolet, L. H. In Homogeneous Catalysis with Metal Phosphine
Complexes; Plenum Press: New York, 1983.
(24) Rauchfuss, T. B.; Shu, J . S.; Roundhill, D. M. Inorg. Chem. 1976,
15, 2096.
(26) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1977, 77, 313.
(27) Bonnet, J . J .; Thorez, A.; Maisonnat, A.; Galy, J .; Poilblanc, R.
J . Am. Chem. Soc. 1979, 101, 5940.
(25) J ames, B. R.; Mahajan, D. Can. J . Chem. 1980, 58, 996.

Heterobimetallic MRh (M ) Pt, Pd) Complexes
Organometallics, Vol. 21, No. 13, 2002 2615
Ta ble 5. Hyd r ofor m yla tion of Styr en e Usin g th e
[(P -P )M(µ-BDT)Rh (cod )]ClO4/P -P System s (P -P )
(P P h 3)2 a n d M ) P t (1c), d p p p a n d M ) P t (1e),
P -P ) d p p p a n d M ) P d (1h ), P -P ) d p p b a n d M
) P t (1g), P -P ) d p p b a n d M ) P d (1i)) a n d
[Rh (cod )2]ClO4 (5) a s Ca ta lyst P r ecu r sor sa
For complex 1b the oxidation process was irreversible,
while the CV showed only the anodic peak at 1.1 (at
0.2 V s-1), and the reverse scan showed no cathodic peak
even at scan rates around 1 V s-1. Modifications to the
phosphorus ligands at the platinum center produced no
a
c
significant variation in the (Ep + Ep )/2 values or wave
features. Thus, the CVs of the compounds [(P-P)Pt(µ-
EDT)Rh(cod)]] (P-P ) dppp (1d ), dppb (1f)) were
entry
prec
% convb
% 2-PPc/3-PPd
1
2
3
4
5
6
7
8
9
1c/PPh3
1c
96
2
96
2
17
51
4
56
8
91/9
81/19
91/9
77/23
93/7
70/30
96/4
a
c
similar to those of 1a with (Ep + Ep )/2 values of 0.94
V at 0.2 V s-1 for both complexes. On the other hand,
modifications to the ancillary ligands at the rhodium
center produced important differences. The complex
[(PPh3)2Pt(µ-EDT)Rh(CO)2] (2a ) was found to give no
voltammetric wave in the 0-1.4 V region, but the
related [(PPh3)2Pt(µ-EDT)Rh(CO)(PPh3)] (3a ) showed an
irreversible oxidation peak at 1.21 V (at 0.2 V s-1). In
addition, the electrogenerated species showed an ir-
reversible reduction wave at 0.70 V (at 0.2 V s-1). These
results indicate that the oxidation process of these
complexes produces unstable species that undergo
further chemical reactions. Moreover, attempts to iso-
late the oxidation products on a preparative scale led
to only mixtures of unidentified compounds. As the
oxidation process depends essentially on the chemical
environment of the rhodium atoms, electrons are prob-
ably removed at this center. However, the dithiolate
ligands may undergo associated chemical reactions
leading to the formation of dithiolate radicals or disul-
fides. In fact, the oxidation of thiols with metal ions can
easily lead to the formation of disulfides, as is well
documented in the literature.28
5/PPh3
1e/dppp
1h /dppp
5/dppp
1g/dppb
1i/dppb
5/dppb
91/9
83/17
a
Reaction conditions: styrene (4 mmol), complex (0.01 mmol),
tetrahydrofurane (10 mL), P/Rh ) 4, pressure ) 10 bar, CO/H2
)
b
1, T ) 50 °C, t ) 24 h. Aldehyde conversion measured by
d
chromatography integral ratio. c 2-phenylpropanal. 3-phenylpro-
panal.
showed that results were best at 10 atm, 50 °C, and a
P/Rh ratio of 4 (96% aldehyde conversion) and 91% of
2-phenylpropanal (entry 1, Table 5). The conversion was
very low in the absence of PPh3 (entry 2, Table 5).
Analysis of the samples at consecutive reaction times
in experiment 1 showed that the regioselectivity in
2-phenylpropanal evolves slowly from 84% after 1 h
reaction (at 1% conversion) to 91% after 24 h.
To determine whether mononuclear Rh phosphine-
carbonyl complexes were responsible for the catalytic
activity, the related cationic mononuclear complex [Rh-
(cod)2]ClO4 5 was used as catalyst precursor adding
PPh3 with the same P/Rh ratio (entry 3, Table 5). In
this case, the conversion and regioselectivity in 2-phen-
ylpropanal are identical to those observed for the
precursor 1c/PPh3. Therefore, these results suggest that
mononuclear species are formed under reaction condi-
tions in both cases and no particular advantage is
observed using the heterobimetallic precursors.
In general, the heterobimetallic-diphosphine cata-
lytic systems showed lower conversions than the PPh3
systems. Since the final catalytic solutions showed no
decomposition, the lower conversions could be attributed
to lower catalytic activity. On the other hand, the
catalytic behavior observed for the diphosphine plati-
num (1e and 1g) and palladium (1h and 1i) precursor
systems was different, as shown in Table 5 (entries
4-9).
In general, the PdRh-diphosphine systems provide
higher conversions at the same reaction times, and the
regioselectivities of the reaction were also different
depending on the second metal (see for example entry
5 (PdRh) compared to entry 4 (PtRh) in Table 5).
Under the same conditions, the results obtained with
the mononuclear species 5 with diphosphines (entries
6 and 9, Table 5) are different from the ones obtained
with the heterobimetallic systems.
Hyd r ofor m yla tion Stu d ies. The use of homodi-
nuclear rhodium complexes as catalyst precursors in the
hydroformylation of alkenes had been extensively stud-
ied,29 although, posterior high-pressure IR studies in
situ have shown that mononuclear species are formed
under catalytic conditions in the case of monothiolate
dinuclear rhodium systems with monophosphines or
monophosphites.30 Nevertheless, for the dithiolate sys-
tems no mononuclear species were observed by HPIR
under catalytic conditions, although there was indirect
evidence of bridge cleavage. To determine whether
heterodinuclear complexes would behave differently, we
studied the catalytic activity of heterobimetallic PtRh
complexes with the dithiolate BDT2- 1c, 1e, 1g for the
hydroformylation of styrene (eq 1). The effect of the
second metal was studied using the palladium com-
plexes [(dppp)Pd(µ-BDT)Rh(cod)]ClO4 (1h ) and [(dppb)-
Pd(µ-BDT)Rh(cod)]ClO4 (1i) as catalyst precursors. The
results obtained with these systems are summarized in
Table 5. Hydrogenation of styrene was not observed in
any case.
Ph-CH2dCH2 + CO + H2 [catal]8
Ph-CH(CHO)-CH3 + Ph-CH2-CH2CHO (1)
The reaction conditions optimized for catalyst precur-
sor 1c, which contains the BDT dithiolate ligand,
Although [M(dithiolate)(diphosphine)] (M ) Pt, Pd)
species may form under catalytic conditions, it is
important to note that they do not participate in the
catalytic activity since [Pt(dithiolate)(P-P)] (dithiolate
) EDT, PDT, and BDT; P-P ) (PPh3)2, dppp, and dppb)
complexes are not active unless SnCl2 is not added.31
Likewise, when [Pd(BDT)(dppb)]/dppb was used as
catalyst precursor under the same conditions, no alde-
(28) Uemura, S. In Comprehensive Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon: Oxford: U.K., 1991; Vol. 7, Chapter 6.2.
(29) Bayo´n, J . C.; Claver, C.; Masdeu-Bulto´, A. M. Coord. Chem.
Rev. 1999, 193, 73.
(30) Die´guez, M.; Claver, C.; Masdeu-Bulto´, A. M.; Ruiz, A.; van
Leeuwen, P. W. N. M.; Schoemaker, G. C. Organometallics 1999, 18,
2107.

2616 Organometallics, Vol. 21, No. 13, 2002
Fornie´s-Ca´mer et al.
ium complex [Rh2(µ-BDT)(PPh3)2(CO)2]32 (δ 38.8 ppm
(d, 1J P-Rh ) 158 Hz)), while the P-Pt coupling constant
is smaller than that reported for [Pt(BDT)(dppp)],31
which is consistent with a decrease in the trans influ-
ence of the dithiolate bridge with respect to the dithi-
olate chelated in the mononuclear complex.
When carbon monoxide is added to a total pressure
of 10 bar (Figure 3b), the signal corresponding to the
mononuclear species [Pt(BDT)(dppp)] increases. Two
new double triplets at δ 17.8 ppm (1J P-Rh ) 86.7 Hz,
2J P-P ) 45.8 Hz) and δ -9.9 ppm (1J P-Rh ) 114.7 Hz)
were attributed to [Rh(CO)(dppp)2]+ (9).25 A new doublet
at δ 30.1 ppm (1J P-Rh ) 116.5 Hz) in the 31P{1H} NMR
spectrum together with a double triplet in the hydride
1
region of the H NMR spectrum at δ -9.1 ppm (2J H-P
2
) 54 Hz, J H-Rh ) 11 Hz) are characteristic of the
pentacoordinated mononuclear species [RhH(CO)2(dppp)]
(10), in which the diphosphine occupies the apical and
equatorial position of a trigonal bipyramidal structure.33
At room temperature there is a fluxional process that
interchanges equatorial and apical phosphorus, so the
observed coupling constants are an average between
both situations. For instance, the related complex [RhH-
(CO)2(bdpp)] (bdpp ) 2,4-bis(diphenyl)phosphinopen-
tane)) presents a doublet at δ 29.8 ppm (1J P-Rh ) 112
Hz) and the hydride signal at δ -8.8 ppm (2J H-P ) 57
F igu r e 3. 31P{1H} NMR spectrum of 1e/2dppp in THF:
(a) under 5 atm of H2, (b) under total 10 atm (5 atm of H2
and 5 atm of CO).
hydes were detected. Thus, in this case the active center
is the rhodium.
In conclusion, the results obtained in the hydroformyl-
ation of styrene with heterobimetallic complexes with
triphenylphosphine as catalyst precursors indicate that
mononuclear carbonyl-phosphine species are presum-
ably responsible for the catalytic activity.
In the case of heterobimetallic complexes with diphos-
phines there is a clear difference between the results
obtained with the platinum-rhodium and the pal-
ladium-rhodium systems. This may be an indication
that the active species are not the same as in the case
of mononuclear rhodium systems.
High -P r essu r e 31P {1H} a n d 1H NMR Stu d ies. To
determine the origin of the different catalytic behavior
of the heterometallic complexes with diphosphines, we
decided to study the dppp systems 1e and 1h by
HPNMR spectroscopy.
The experiments were performed in two steps: (a) a
solution of the complex and excess of the diphosphine
was pressurized under 5 bar of H2 and shaken for 1 h
at 50 °C, and the spectra were recorded at different
temperatures; (b) the above solution was pressurized
with CO up to 10 bar (CO/H2 ) 1:1) and shaken for 1 h
at 50 °C, and the spectra were recorded at different
temperatures.
2
Hz, J H-Rh ) 11 Hz).34 For some diphosphines it has
been proposed that the [RhH(CO)2(diphosphine)] species
exists as a mixture of the species with the diphosphine
in the equatorial-equatorial positions (ee) and in the
equatorial-apical positions (ea ).33
The variable-temperature 31P{1H} NMR spectra con-
firmed the existence of a fluxional process, since the
coupling constant of the doublet signal of 10 changed
with the temperature. The different values are 116.5
Hz (rt), 127.4 Hz (-20 °C), 145.1 Hz (-40 °C), and 157.4
(-65 °C). The high value of the P-Rh coupling constant
at -65 °C is characteristic of phosphorus in an equato-
rial position. These data suggest that there may be
equilibrium between ea and ee isomers and it will be
displaced to the ee species at low temperatures. Unfor-
1
tunately, the 31P{1H} or H NMR spectra could not be
further resolved. Small signals at -2 and -4 ppm were
not assigned.
The analysis of the spectra of the PtRh complex 1e
with dppp shows that under H2 pressure some binuclear
species are present, but under H2/CO only the mono-
nuclear rhodium-dppp and Pt-BDT-dppp species are
formed (see Scheme 4).
HP NMR Sp ectr a of 1h /d p p p . The 31P{1H} NMR
spectrum of the PdRh 1h /dppp system under H2 pres-
sure is more complex than in the case of 1e (Figure 4a).
The double triplet at δ 20.1 ppm and the broad signal
at δ 8.0 ppm indicated the presence of the mononuclear
rhodium dihydrido species 7. The singlet at δ 5.8 ppm
matches with the value reported for [Pd(BDT)(dppp)]
(11).31 Two singlets at δ 12.5 and -0.8 ppm may
HP NMR Sp ectr a of 1e/d p p p . The 31P{1H} NMR
spectrum obtained for 1e/dppp (P/Rh ) 4) under 5 bar
of H2 in THF-d8 (Figure 3a) shows a signal at δ 4.5 ppm
with the characteristic satellites (1J P-Pt ) 2663.6 Hz),
which corresponds to the mononuclear species [Pt(BDT)-
(dppp)] (6).31 A double triplet at δ 21.2 ppm (1J P-Rh
)
2
100 Hz, J P-Rh ) 30 Hz) and a broad signal at δ 8.2
ppm were assigned to the dihydrido complex [RhH2-
(dppp)2]+ (7) by comparison with published data.25 The
signal at δ 3.2 ppm (1J P-Pt ) 2598 Hz) along with a
doublet at δ 31.3 ppm (1J P-Rh ) 149 Hz) may be
attributed to the dinuclear species [(dppp)Pt(µ-BDT)-
Rh(dppp)]+ (8). These features are similar to those
reported for the related homodinuclear dithiolate rhod-
(32) Aaliti, A.; Masdeu, A. M.; Ruiz, A.; Claver, C. J . Organomet.
Chem. 1995, 489, 101.
(33) (a) Casey, C. P.; Paulsen, E. L.; Beuttenmueller, E. W.; Proft,
B. R.; Petrovich, L. M.; Matter, B. A.; Powell, D. R. J . Am. Chem. Soc.
1997, 119, 11817. (b) van der Veen, Boele, M. D. K.; Bregman, F. R.;
Kamer, P. C. J .; van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J .;
Schenk, H.; Bo, C. J . Am. Chem. Soc. 1998, 120, 11616.
(34) Castellanos-Pa´ez, A.; Castillo´n, S.; Claver, C.; van Leeuwen,
P. W. N. M.; de Lange, W. G. J . Organometallics 1998, 17, 2523.
(31) Fornie´s-Ca´mer, J .; Aaliti, A.; Ruiz, N.; Masdeu-Bulto´, A. M.;
Claver, C.; Cardin, C. J . Organomet. Chem. 1997, 530, 199.

Heterobimetallic MRh (M ) Pt, Pd) Complexes
Organometallics, Vol. 21, No. 13, 2002 2617
Sch em e 5
F igu r e 4. 31P{1H} NMR spectrum of 1h /2dppp in THF:
(a) under 5 atm of H2, (b) under total 10 atm (5 atm of H2
and 5 atm of CO).
Sch em e 4
[Pd(dppp)2] is δ 3.95 ppm in tetrahydrofuran.39 It has
been reported that Pd(0) species form from Pd(II) species
through phosphine oxidation.39 The unreacted binuclear
complex 1h and signals at -2 and -4 ppm were also
observed.
Carbon monoxide was introduced to the above solu-
tion up to 10 atm CO/H2; the solution was shaken for 1
h at 50 °C and cooled at room temperature to record
the spectra. At room temperature, the 31P{1H} NMR
spectrum (Figure 4b) shows the signals corresponding
to the rhodium monocarbonyl species 9, the pentacoor-
dinated hydride 10, the palladium dithiolate 11, and the
palladium(II) diphosphines 12. Free dppp and the
signals at -2 and -4 ppm were also observed. The
species formed for this system are summarized in
Scheme 5.
To sum up, the above HPNMR spectroscopic data
indicated that the PtRh 1e/dppp and PdRh 1h /dppp
heterobimetallic systems split under catalytic hydro-
formylation conditions into identical mononuclear rhod-
ium species and the corresponding platinum or palla-
dium fragments. Since the platinum and palladium
species are not active in the hydroformylation reaction,
the activity of the heterobimetallic systems is due to the
hydride rhodium complex 10. The differences in the
catalytic behavior of these two systems can only be
explained by the differences in the formation of 10. Since
several equilibria act to form the different species, the
concentration of active complex 10 will depend on the
stability of the precursor complex. Therefore, the con-
centrations of complex 10 will determine the activity.
In both cases, there was evidence of dinuclear species
under H2, but under CO/H2 only mononuclear species
were detected by 31P{1H} NMR.
correspond to palladium-dppp species. The signal at δ
12.5 ppm may correspond to a Pd(II) complex, since
related Pd(II) complexes such as [Pd(OAc)2(dppp)], [Pd-
(OTf)2(dppp)], and [Pd(OTf)2(dppp)] were reported to
give singlets in the 31P{1H} NMR spectrum at δ 11.1,35
11.6,36 and 12.9 ppm,37 respectively. More deshielded
signals have been reported for the ditosilate [Pd(OTs)2-
(dppp)] (δ 17.5 ppm in CD3C(O)CD3)35 and for the
cationic bis(diphosphine) complex [Pd(dppp)2](OTs)2.38
So, the signal at 12.5 could be attributed to [Pd(S)2-
(dppp)]2+ (12) (S ) solvent). The singlet at δ -0.8 ppm
may be attributed to a Pd(0) species (13). For instance,
the 31P chemical shift reported for the Pd(0) complex
Concerning the regioselectivity, similar behavior was
reported for related thiolate bridging complexes [Rh(µ-
S(CH2)2NMe2)(cod)]2/PPh3.40 The HPIR experiments for
this system showed that the species 10 was present,30
(35) Drent. E.; van Broekhoven, J . A. M.; Doyle, M. J . J . Organomet.
Chem. 1991, 417, 235.
(36) Makhaev, V. D.; Shul’ga, Y. M.; Dzhabieva, Z. M.; Belov, G. P.;
Chernushevich, I. V.; Kozlovskii, V. I.; Donodov, A. F. Russ. J . Coord.
Chem. 1994, 20, 360.
(37) Sanger, A. R. J . Chem. Soc., Dalton Trans. 1977, 1971.
(38) Benetollo, F.; Bertani, R.; Bombieri, G.; Toniolo, L. Inorg. Chim.
Acta 1995, 233, 5.
(39) Amatore, C.; Broeker, G.; J utand, A.; Khalil F. J . Am. Chem.
Soc. 1997, 119, 5176.
(40) Balue´ i Parad´ıs, J . Doctoral Thesis, Universitat Auto`noma de
Barcelona, 2000.

2618 Organometallics, Vol. 21, No. 13, 2002
Fornie´s-Ca´mer et al.
but the regioselectivities in the hydroformylation of
different substrates were different from those obtained
with a mononuclear rhodium complex under identical
conditions. Since the P/Rh ratio affects the regioselec-
tivity, the degree of dissociation of the starting thiolate
complex will affect the P/Rh ratios and, subsequently,
the regioselectivity. In our case, since the rhodium
species observed were identical for both precursors 1e
and 1h , the differences in regioselectivity could also be
attributed to the different composition of the catalytic
solution.
processes, but the species formed could not be identified.
Heterobimetallic diene complexes were used as catalyst
precursors for the hydroformylation of styrene. The
comparison of selectivity data for different catalyst
precursors gives no conclusive evidence of the active
species, but spectroscopic studies under pressure condi-
tions provide further information. Thus, HPNMR ex-
periments show that mononuclear species are formed
under pressure conditions, and therefore, the catalytic
activity can be attributed to these mononuclear rhodium
species.
It should also be taken into account that mononuclear
platinum and palladium complexes 6 and 11 may act
as metalloligands, which may also interfere in the
activity and selectivity of the systems coordinating to
the active species when the substrate is present.
Ack n ow led gm en t. We thank Ministerio de Educa-
cio´n y Cultura (PB97-0407-C05-01 and PB98-0641) for
financial support.
Su p p or tin g In for m a tion Ava ila ble: Crystal data and
structure refinement, atom coordinates, complete list of bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates for complexes 2a ′ and 3a are available
as Supporting Information. This material is available free of
charge via the Internet at http://pubs.acs.org.
Con clu sion
The reactivity of heterobimetallic PtRh complexes
with dithiolate bridges [(P-P)Pt(µ-S-S)Rh(cod)]ClO4
toward carbon monoxide and phosphines produces het-
erobimetallic structures with no cleavage of the bridges
in most cases. CV studies showed irreversible oxidation
OM020042R