Anionic Platinum Complexes with 2-Pyridylphosphines as Ligands for Rhodium: Synthesis of Zwitterionic Pt-Rh Organometallic Compounds

Article abstract of DOI:10.1021/ic034863f

Bimetallic zwitterionic platinum(II)-rhodium(I) complexes of the type [(C₆F₅)3Pt(μ-PPynPh_3-n)Rh(CO)₂)] and [(C₆F₅)₃-Pt(μ-PPy_nPh _3-n)Rh(diene))] (n = 2, 3; Py = 2-pyridyl) have been prepared. The P end of the bridging ligands (μ-PPy_nPh_3-n) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving metallacycles comparable to pyrazolylborate-Rh complexes. These metallacycles can adopt two conformations, either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically demanding Rh-carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C₆F₅)₃-Pt(μ-PPhPy ₂)Rh(COD)] (COD = 1,5-cyclooctadiene) and (C₆F ₅)₃Pt(μ-PPhPY₂)Rh(CO)₂] are reported.

Full text of DOI:10.1021/ic034863f

Inorg. Chem. 2004, 43, 189−197
Anionic Platinum Complexes with 2-Pyridylphosphines as Ligands for
Rhodium: Synthesis of Zwitterionic Pt−Rh Organometallic Compounds
Juan A. Casares, Pablo Espinet,* Jose´ M. Mart´ın-Alvarez, and Vero´nica Santos
Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid, E-47005 Valladolid, Spain
Received July 21, 2003
Bimetallic zwitterionic platinum(II)−rhodium(I) complexes of the type [(C F ) Pt(µ-PPynPh3-n)Rh(CO)2)] and [(C F ) -
6
5 3
6 5 3
Pt(µ-PPynPh3-n)Rh(diene))] (n ) 2, 3; Py ) 2-pyridyl) have been prepared. The P end of the bridging ligands
(µ-PPynPh3-n) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving
metallacycles comparable to pyrazolylborate−Rh complexes. These metallacycles can adopt two conformations,
either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote
position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically
demanding Rh−carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite
charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C F ) -
6
5 3
Pt(µ-PPhPy2)Rh(COD)] (COD ) 1,5-cyclooctadiene) and [(C F ) Pt(µ-PPhPy2)Rh(CO)2] are reported.
6
5 3
Introduction
As a part of our ongoing research on complexes with
pyridylphosphines and their derivatives,4,5 we have studied
before homobimetallic complexes with PPynPh3-n (n ) 2,
3) as bridging ligands.4,6 PPhPy2 and PPy3 coordinate to the
monoanionic moiety “Pt(C6F5)3” through the P atom giving
[Pt(C6F5)3(PPynPh3-n)]-. The pendant pyridyl groups can then
bind a cationic rhodium center, forming zwitterionic het-
erobimetallic complexes.7 The geometry of these compounds
makes them comparable to bis- and tris(pyrazolyl)borate
complexes (Chart 1),8 although in [Pt(C6F5)3(PPynPh3-n)]-
The coordination chemistry of the 2-pyridylphosphines is
currently a topic of great interest, which has been extensively
reviewed.1 Most studies have been concerned with PPh2Py
(Py ) 2-pyridyl). This is a useful building block for the
synthesis of homo- or heterobimetallic compounds because
the rigidity induced by the small bite angle of the ligand
favors the formation of M-M bonds. On the other hand,
the different electronic properties for P and N donor atoms
facilitate stereoselective bonding of the ligand in molecules
with both hard and soft metal centers. The coordination
chemistry of tridentate and tetradentate ligands PPhPy2 and
PPy3 has been much less studied, but there are a few reports
on their catalytic application as amphiphilic water-soluble
ligands and as proton carriers.2-4
(4) (a) Espinet, P.; Hernando, R.; Iturbe, G.; Villafan˜e, F.; Orpen, A. G.;
Pascual, I. Eur. J. Inorg. Chem. 2000, 5, 1031-1038. (b) Casares, J.
A.; Espinet, P.; Hernando, R.; Iturbe, G.; Villafan˜e, F. Inorg. Chem.
1997, 36, 44-49. (c) Espinet, P.; Go´mez-Elipe, P.; Villafan˜e, F. J.
Organomet. Chem. 1993, 450, 145-150.
(5) (a) Alonso, M. A.; Casares, J. A.; Espinet, P.; Mart´ınez-Ilarduya, J.
M.; Pe´rez-Briso, C. Eur. J. Inorg. Chem. 1998, 1745-1753. (b)
Casares, J. A.; Espinet, P.; Mart´ınez de Ilarduya, J. M.; Lin, Y.-S.
Organometallics 1997, 16, 770-779. (c) Casares, J. C.; Coco, S.;
Espinet, P.; Lin, Y.-S. Organometallics 1995, 14, 3058-3067. (d)
Casares, J. A.; Espinet, P.; Mart´ın-Alvarez, J. M.; Espino, G.; Pe´rez-
Manrique, M.; Vattier, F. Eur. J. Inorg. Chem. 2001, 289-296.
(6) (a) Alonso, M. A.; Casares, J. A.; Espinet, P.; Soulantica, K.; Charmant,
J. P. H.; Orpen, A. G. Inorg. Chem. 2000, 39, 705-711. (b) Casares,
J. A.; Espinet, P.; Soulantica, K.; Pascual, I.; Orpen, A. G. Inorg.
Chem. 1997, 36, 5251.
(7) For recent advances in zwitterionic organometallics, see: (a) Betley,
T. A.; Peters J. C. Angew. Chem., Int. Ed. 2003, 42, 2385-2389. (b)
Betley T. A.; Peters J. C. Inorg. Chem. 2002, 41, 6541-6543 and
references therein. (c) Lu, C.; Peters, J. C. J. Am. Chem. Soc. 2002,
5272-5273. (d) Viau, L.; Lepetit, C.; Commenges, G.; Chauvin, R.
Organometallics 2001, 808-810. (e) Marx, T.; Wesemann, L.;
Dehnen, S. Organometallics 2000, 4653-4656. (f) Chauvin, R. Eur.
J. Inorg. Chem. 2000, 577-591.
* To whom correspondence should be addressed. E-mail: espinet@
qi.uva.es.
(1) (a) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999, 499-556.
(b) Zhang, Z. Z.; Cheng, H. Coord. Chem. ReV. 1996, 147, 1-39. (c)
Newkome, G. R. Chem. ReV. 1993, 93, 2067-2089.
(2) (a) Pruchnik, F. P.; Smolenski, P.; Wajda-Hermanowicz, K. J.
Organomet. Chem. 1998, 570, 63-69. (b) Buhling, A.; Kamer, P. C.
J.; van Leeuwen, P. W. N. M.; Elgersma, J. W. J. Mol. Catal. A:
Chem. 1997, 116, 297-308. (c) Baird, I. R.; Smith, M. B.; James, B.
R. Inorg. Chim. Acta 1995, 235, 291-297. (d) Buhling, A.; Kamer,
P. C. J.; van Leeuwen P. W. N. M. J. Mol. Catal. A: Chem. 1995,
98, 69-80 (e) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J.
Organomet. Chem. 1993, 455, 247. (f) Xie, Y.; Lee, C.-L.; Yang, Y.;
Rettig, S. J.; James, B. R. Can. J. Chem. 1992, 70, 751-756.
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10.1021/ic034863f CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/06/2003
Inorganic Chemistry, Vol. 43, No. 1, 2004 189

Casares et al.
PPhPy2,13 PPy3,14 and (NBu4)[Pt(C6F5)3(tht)]15 (TFB ) 5,6,7,8-
tetrafuoro-1,4-dihydro-1,4-etenonaphthalene, trivial name tetra-
fluorobenzobarrelene; tht ) tetrahydrothiophene) were prepared by
published methods. Combustion CHN analyses were done on a
Perkin-Elmer 2400 CHN microanalyzer. IR spectra were recorded
on a Perkin-Elmer FT 1720 X spectrophotometer.
Chart 1
NMR Spectra. 1H NMR (300.16 MHz), 19F NMR (282.4 MHz),
31P NMR (121.4 MHz), and 195Pt NMR (64.2 MHz) spectra were
recorded on Bruker ARX 300 and AC 300 instruments equipped
with a VT-100 variable-temperature probe. Chemical shifts are
reported in ppm from SiMe4 (1H), CCl3F (19F), H3PO4 (85%) (31P),
or K2[PtCl4] (1M, D2O) (195Pt), with positive shifts downfield, at
ambient probe temperature unless otherwise stated. J values are
given in Hz. The 19F-195Pt correlation experiments were made
operating in inverse mode, with a HMQC sequence with BIRD
selection without decoupling during acquisition (in the F1 projection
(
195Pt) the signals appear as doublets due to coupling to phosphorus).
13C NMR were registered as 1H-13C correlation experiments, which
were made with a HMQC sequence with BIRD selection and GARP
decoupling during acquisition. Chemical shifts of quaternary carbons
are not listed in the experimental data.
Synthesis of the Complexes. (NBu4)[Pt(C6F5)3(PPhPy2)] (1).
To a stirred suspension of (NBu4)[Pt(C6F5)3(tht)] (1.30 g; 1.26
mmol) in EtOH (100 mL) was added PPhPy2 (400.0 mg, 1.52
mmol). The mixture was refluxed for 2 h, the solution was filtered,
and the solvent was removed under reduced pressure. The resulting
oil was washed twice with n-hexane (10 mL) and stirred with EtOH
until crystallization of the product as a white solid, which was
filtered out, washed with n-hexane, and vacuum-dried. Yield: 1.09
g (72%). Anal. Calcd for C50H49F15N3PPt: C, 49.92; H, 4.11; N,
3.49. Found: C, 49.83; H, 4.08; N, 3.33. 1H NMR (25 °C, (CD3)2-
CO, δ): 8.45 (d, 2H); 7.95 (m, 2H); 7.85 (m, 2H); 7.60 (m, 2H);
7.25 (m, 5H); 3.45 (m, 8H); 1.85 (m, 8H); 1.45 (m, 8H); 1.00 (m,
the negative charge is distributed differently from Tp′ ligands
(Tp′: hydridotris(pyrazolyl)borate). Formally, the complexes
with [Pt(C6F5)3(PPynPh3-n)]- have a negative charge at the
Pt and a positive charge at the Rh. Although the negative
charge at the platinum should be in part delocalized into the
perfluoroaryl rings, this charge separation could still influence
the stereochemistry of the complexes.
Complexes MTp′L2 (M ) Rh(I), Ir(I)) show κ2 or κ3
coordination modes depending on the nature of the Tp′
ligand, the metal, and the coligands L. While κ3 coordination
yields 18-electron trigonal-bipyramidal structures (complexes
C in Chart 1), κ2 binding results in 16-electron square-planar
species. In the latter the different substituents at the boron
can be oriented in pseudoequatorial or pseudoaxial positions
in the boat defined by the chelate, giving rise to different
conformers (A or B in Chart 1). These aspects, well studied
in pyrazolylborate chemistry,6,9 are examined here for the
complexes with the ligands [Pt(C6F5)3(PPynPh3-n)]-, where
similar structures (D-F) might appear, but other forces such
as the charge on the metals and the bulk of [Pt(C6F5)3(PPyn-
Ph3-n)]- are involved.
12H). 31P NMR (25 °C, (CD3)2CO, δ): 16.77, (1JPt-P ) 2565). 19
F
NMR (25 °C, (CD3)2CO, δ): -167.5 (m, 2F); -166.5 (m, 6F);
-165.5 (m, 1F); -114.0 (m, 2F); -114.9 (m, 4F). 195Pt NMR (25
°C, (CD3)2CO, δ): - 4369 (1JPt-P ) 2642).
(NBu4)[Pt(C6F5)3(PPy3)] (2). It was prepared as described for
1 but using 401.5 mg of PPy3 (1.52 mmol) instead of PPhPy2.
Yield: 1.20 g (81%). Anal. Calcd for C49H48F15N4PPt: C, 48.88;
H, 4.02; N, 4.65. Found: C, 48.71; H, 3.96; N, 4.49. 1H NMR (25
°C, (CD3)2CO, δ): 8.37 (d, 3H, H-6-Py); 8.20 (m, 3H, H-5-Py);
7.66 (m, 3H, H-4-Py); 7.21 (m, 3H, H-3-Py); 3.46 (m, 8H, NBu4);
1.85 (m, 8H, NBu4); 1.44 (m, 8H, NBu4); 0.97 (m, 12H, NBu4).
31P NMR (25 °C, (CD3)2CO, δ): 19.00 (2JPt-P ) 2658.6). 19F NMR
(25 °C, (CD3)2CO, δ): -167.0 (m, 2F); -166.5 (m, 5F); -165.5
(m, 2F); -115.4 (m, 2F); -114.7 (m, 2F); -114.9 (m, 2F). 195Pt
NMR (25 °C, (CD3)2CO, δ): -4373 (d).
Experimental Section
[(C6F5)3Pt(µ-PPhPy2)Rh(CO)2] (3). To a stirred suspension of
AgNO3 (42.5 mg; 0.250 mmol) in acetone (15 mL) was added [Rh-
(µ-Cl)(CO)2]2 (48.6 mg, 0.125 mmol). After 30 min of stirring,
(NBu4)[Pt(C6F5)3(PPhPy2)] (300.7 mg; 0.250 mmol) was added and
the mixture was stirred for a further 10 min. The AgCl formed
was filtered through Celite, and the yellow solution was evaporated
to dryness. The solid residue was purified by column chromatog-
raphy on silica gel, using CH2Cl2 as eluent. Yield: 45% (126.0
General Methods. All reactions were carried out under N2.
Solvents were distilled using standard methods. The compounds
[Rh2(µ-Cl)2(1,5-COD)2],10 [Rh2(µ-Cl)2(TFB)2],11 [Rh2(µ-Cl)2(CO)4],12
(8) (a) Trofimenko, S. Chem. ReV. 1993, 93, 943-980. (b) Kitajima, N.;
Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 419-531. (c) Slugovc,
C.; Padilla-Mart´ınez, I.; Sirol, S.; Carmona, E. Coord. Chem. ReV.
2001, 213, 129-157.
(9) (a) Bucher, U. E.; Currao, A.; Nesper, R.; Ru¨eger, H.; Venanzi, L.
M.; Younger, E. Inorg. Chem. 1995, 34, 66-74. (b) Sanz, D.; Santa-
Mar´ıa M. D.; Claramunt, R. M.; Cano, M.; Heras, J. V.; Campo, J.
A.; Ru´ız, F. A.; Pinilla, E.; Monge, A. J. Organomet. Chem. 1996,
526, 341-350.
(10) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.
(11) Roe, D. M.; Massey A. G. J. Organomet. Chem. 1971, 28, 273.
(12) Cleverty, M.; Wilkinson, G. Inorg. Synth. 1990, 28, 84.
(13) (a) Newcome, G.; Hagen, D. C. J. Org. Chem. 1978, 43, 947-949.
(b) Xie, Y.; Lee, C.; Yang, Y.; Rettig, S. J.; James, B. R. Can. J.
Chem. 1992, 70, 751.
(14) Kurtev, K.; Ribola, D.; Jones, R. A.; Cole-Hamilton, D. J.; Wilkinson,
G. J. Chem. Soc., Dalton. Trans. 1980, 55-58.
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Soc., Chem. Commun. 1977, 789.
190 Inorganic Chemistry, Vol. 43, No. 1, 2004

Zwitterionic Pt-Rh Organometallic Compounds
mg). Anal. Calcd for C36H13F15N2O2PPtRh: C, 38.60; H, 1.17; N,
2.50. Found: C, 38.79, H, 1.56; N, 2.47. 1H NMR (25 °C, (CD3)2-
CO, δ): 9.29 (d, 2H); 8.50 (very broad); 8.02 (m, 2H); 7.86 (d,
1H); 7.70 (m, 4H); 7.23 (m, 2H). 31P{1H} NMR (25 °C, (CD3)2-
CO, δ): 20.78 (1JPt-P ) 2513.6 Hz). 19F NMR (25 °C, (CD3)2CO,
δ): -110.53 (m, 2F, 3JPt-F ) 325); -111.66 (m, 2F, 3JPt-F ) 296);
-115.12 (m, 1F, JPt-F ) 361); -116.52 (m, 1F, JPt-F ) 428);
-163.98 (m, 2F); -164.80 (m, 1F); -165.27 (m, 4F); -166.10
(m, 2F). 13C NMR ((CD3)2CO, δ): 156.6; 142.4; 140.6; 135.8;
134.5; 131.4; 129.9; 129.7; 126.9. 195Pt NMR (25 °C, (CD3)2CO,
δ): -4320 (d). IR (Nujol mull, cm-1): 2107 m, ν(CO); 2050 m,
ν(CO); 1591 m, ν(CN). IR (CH2Cl2, cm-1): 2103 s, ν(CO); 2044
s, ν(CO).
129.2 (5D); 129.0 (5D); 128.0 (5E); 126.4 (5E); 126.0 (5D); 90.6
(5D); 89.3 (5E); 87.8 (5D); 85.6 (5E); 31.0 (5D); 30.6 (5D); 30.3
1
(5E); 28.6 (5E). 31P{ H} NMR (25 °C, (CD3)2CO, δ): 40.64 ( JPt-P
1
) 2676, 5E); 23.41 (1JPt-P ) 2523, 5D). 195Pt NMR (δ): -4338
(d, 5D); -4357 (d, 5E).
Caution: AgClO4 is potentially explosiVe and should be handled
with care and in small amounts. AgNO3 can be used instead, as
described for complex 3.
3
3
[(C6F5)3Pt(µ-PPhPy2)Rh(TFB)] (6). This was prepared as
described for 5 but using 80.1 mg of [Rh(µ-Cl)(TFB)]2 (0.109
mmol) instead of [Rh(µ-Cl)(COD)]2. Yield: 145 mg (52%). Anal.
Calcd for C46H19F19N2PPtRh: C, 42.84; H, 1.48; N, 2.17. Found:
C, 42.83; H, 1.67; N, 2.23. NMR: At room temperature the signals
1
[(C6F5)3Pt(µ-PPy3)Rh(CO)2] (4). This was prepared as described
for 3 but using 301 mg of (NBu4)[Pt(C6F5)3(PPy3)] (0.25 mmol)
instead of (NBu4)[Pt(C6F5)3(PPhPy2)]. Yield: 45% (125.1 mg).
Anal. Calcd for C35H12F15N3O2PPtRh: C, 37.50; H, 1.08; N, 3.75.
are in coalescence. H NMR (200 K, (CD3)2CO, mixture of 6D
(64%) and 6E (36%), δ): 9.57 (m, 2H, 6E); 9.34 (m, 2H, 6E);
8.95 (d, 2H, 6E); 8.86 (d, 2H, 6D); 8.31 (m, 2H, 6E); 7.91 (m, 2H,
6E); 7.87 (m, 2H, 6D); 7.80 (m, 1H, 2E); 7.79 (m, 1H, 6D); 7.74
(2H, 6E); 7.51 (m, 2H, 6D); 7.49 (m, 1H, 6D); 7.46 (m, 1H, 6D);
7.26 (t, 1H, 6D); 6.95 (t, 1H, 6D); 6.85 (m, 2H, 6D); 6.38 (broad,
1H, 6D); 6.14 (broad, 1H, 6D); 5.88 (broad 1H, 6E); 4.68 (broad,
2H, 6D); 4.36 (broad 2H, 6E); 4.32 (broad, 2H, 6D) 4.08 (broad,
1H, 6E); 3.52 (broad, 2H, 6E). 13C NMR (193 K, δ): 154.9 (6E);
153.8 (6D); 142.8 (6E); 138.9 (6E + 6E + 6D); 135.8 (6D); 133.8
(6E); 132.5 (6D), 131.4 (two signals, 6D); 129.2 (6E); 128.4 (6E);
126,6 (6D); 67.7 (6D); 65.7 (6D); 63.5 (6E); 41.9 (6D); 41.3 (6D);
40.0 (6E); 39.2 (6E); 64.3 (6E). 19F NMR (δ): -110.19 (m, 3JPt-F
) 323, 2F, 6D); -113.98 (m, 3JPt-F ) 282, 4F, 6E); -115.41 (m,
3JPt-F ) 271, 2F, 6D); -116.21 (m, 3JPt-F ) 240, 2F, 6E); -116.46
1
Found: C, 38.17; H, 1.47; N 3.66. H NMR (25 °C, (CD3)2CO,
δ): 9.58 (t, 1H); 9.28 (d, 2H); 8.87 (d, 1H); 8.40 (m, 1H); 8.00
(m, 2H); 7.85 (m, 2H); 7.67 (m, 2H); 7.12 (m, 2H). 31P{1H} NMR
(25 °C, (CD3)2CO, δ): 20.54 (1JPt-P ) 2467). 13C NMR (25 °C,
(CD3)2CO, δ): 156.3; 151.8; 140.0; 138.8; 137.7; 131.9; 127.8;
126.8. 19F NMR (25 °C, (CD3)2CO, δ): -110.87 (m, 2F, 3JPt-F
)
)
3
3
327); -111.66 (m, 2F, JPt-F ) 282); -115.31 (m, 1F, JPt-F
3
417); -116.48 (m, 1F, JPt-F ) 435); -163.74 (m, 2F); -164.91
(m, 5F); -165.99 (m, 2F). 195Pt NMR (25 °C, (CD3)2CO, δ):
-4314 (d). IR (Nujol mull, cm-1): 1591 m, ν(CN); 1574 m,
ν(CN); 2098 m, ν(CO); 2044 m, ν(CO). IR (CH2Cl2, cm-1): 2102
s, ν(CO); 2044 s, ν(CO).
3
3
(m, JPt-F ) 198, 1F, 6D); -116.70 (m, JPt-F ) 375, 1F, 6D);
-147.47 (broad, 2F TFB, 6D + 6E), -160.32 (broad, 2F TFB,
6D + 6E); -162.8 to -165.9 (m, 9F 6D + 9F 6E). 31P{1H} NMR
(213 K, δ): 36.47 (1JPt-P ) 2672, 6E); 22.79 (1JPt-P ) 2525, 6D).
195Pt NMR (253 K, (CD3)2CO, δ): -4333 (d, 6D); -4423 (d, 6E).
IR (Nujol mull, cm-1): 1588 m, ν(CN).
[(C6F5)3Pt(µ-PPhPy2)Rh(COD)] (5). To a stirred solution of
AgClO4 (45.5 mg; 0.219 mmol) in acetone (15 mL) was added
[Rh(µ-Cl)(COD)]2 (54.1 mg, 0.109 mmol). After 30 min the AgCl
was filtered off, and (NBu4)[Pt(C6F5)3(PPhPy2)] (264.0 mg; 0.219
mmol) was added to the yellow solution. The solution was stirred
for 10 min, the solvent was removed under reduced pressure, and
the residue was dissolved in a mixture of CH2Cl2 and EtOH (20
mL, 1:1). After partial evaporation of the solvent the compound
crystallized as yellow crystals, which were filtered out and vacuum-
dried. The product was further purified by column cromatography
using silica gel and CH2Cl2 as eluent. Yield: 181 mg (78%). Anal.
Calcd for C42H25F15N2PPtRh: C, 43.05; H, 2.15; N, 2.39. Found:
[(C6F5)3Pt(µ-PPy3)Rh(COD)] (7). To a stirred solution of
AgNO3 (42.5 mg; 0.250 mmol) in acetone (15 mL) was added [Rh-
(µ-Cl)(COD)]2 (61.6 mg, 0.125 mmol). After 30 min, the mixture
was filtered through Celite, and (NBu4)[Pt(C6F5)3(PPhPy3)] (301.0
mg; 0.250 mmol) was added to the solution. The mixture was stirred
for 10 min, the solvent was evaporated, and the residue was
dissolved in a mixture of CH2Cl2 and EtOH (10 mL each). After
partial evaporation of the solvent the compound crystallized as
yellow crystals, which were filtered out and vacuum-dried. The
product was further purified by column chromatography on silica
gel using CH2Cl2 as eluent. Yield: 62% (181.0 mg). Anal. Calcd
for C41H24F15N3PPtRh: C, 41.99; H, 2.06; N, 3.58. Found: C,
41.69; H, 2.09; N, 3.52. 1H NMR (25 °C, (CD3)2CO, δ): 9.91 (m,
2H); 9.05 (d, 2H); 8.85 (m, 3H); 8.45 (d, 2H); 8.30 (m, 2H); 8.10
(m, 3H); 7.75 (m, 2H); 7.60 (m, 4H); 7.50 (m, 2H); 6.60 (m, 2H);
4.30 (m, 4H); 3.75 (m, 4H); 3.00 (m, 2H); 2.21 (d, 4H); 1.85 (m,
6H); 1.66 (d, 4H). 19F NMR (25 °C, (CD3)2CO, δ): -165.41 (m,
16F); -163.84 (m, 2F); -115.98 (d, 4F); -113.92 (d, 6F); -110.79
(d, 2F). 1H NMR (193 K, mixture of 7D (45%) and 7E (55%), δ):
9.80 (m, 1H, 7D); 9.60 (m, 1H, 7E); 9.35 (m, 1H, 7E); 9.15 (m,
1H, 7E); 9.12 (m, 2H, 7D); 9.10 (m, 1H, 7E); 8.50 (m, 1H 7E +
1H 7D); 8.30 (m, 1H 7D + 1H 7E); 8.29 (m, 1H, 7E); 7.80 (m,
2H, 7E); 7.75 (m, 2H, 7D); 7.70 (m, 1H 7D + 1H 7E); 7.50 (m,
2H, 7D); 7.50 (m, 1H, 7E); 7.48 (m, 1H, 7E); 6.60 (m, 2H, 7D);
4.40 (br, 2H, 7D + 1H 7E); 4.15 (s, 1H, 7E); 3.98 (s, 2H, 7D);
3.51 (d, 1H, 7E); 3.41 (m, 1H, 7E); 3.00 (s, 2H 7D + 1H 7E);
2.65 (m, 1H, 7E); 2.63 (m, 2H, 7D); 2.48 (s, 1H, 7E); 2.18 (m,
2H, 7D); 1.92 (s, 1H, 7E); 1.75 (s, 1H, 7E); 1.36 (m, 1H, 7E);
1.32 (m, 2H, 7D) 1.18 (m,1H, 7E); 0.68 (s, 1H, 7E). 13C NMR
1
C, 43.37; H, 2.52; N, 2.60. H NMR (25 °C, (CD3)2CO, δ): 9.91
(broad, 2H); 9.65 (t, 2H); 9.06 (m, 4H); 8.23 (m, 2H); 7.71 (m,
6H); 7.50 (m, 3H); 7.36 (m, 2H); 7.23 (t, 1H); 7.12 (m, 2H); 6.79
(m, 2H); 6.65 (t, 1H); 4.27 (broad, 6H); 3.26 (broad, 2H); 2.84
(broad, 4H); 2.61 (broad, 2H); 2.12 (broad, 2H); 2.04 (2H); 1.86
(broad, 2H); 1.29 (broad, 2H); 0.99 (broad, 2H). 1H NMR (213 K;
mixture of 5D (41%) and 5E (59%), δ): 9.84 (broad, 2H, 5D);
9.55 (m, 2H, 5E); 9.14 (d, 2H, 5E); 9.10 (d, 2H, 5D); 8.31(m, 2H,
5E); 7.81 (m, 1H, 5D); 7.78 (m, 2H, 5E); 7.73 (m, 1H, 5D); 7.67
(m, 1H, 5E); 7.55 (m, 2H, 5E); 7.52 (m, 2H, 5D); 7.35 (m, 2H,
5D); 7.26 (m, 1H, 5D); 7.13 (m, 2H, 5D); 6.85 (m, broad, 2H,
5E); 6.77 (m, broad, 1H, 5D); 4.42 (s, broad, 2H, 5D); 4.27 (broad,
2H, 5E); 4.01 (broad, 2H, 5D); 3.32 (broad, 2H, 5E); 3.06 (broad,
2H, 5D); 2.71 (broad, 2H, 5D); 2.55 (broad, 2H, 5E); 2.16 (broad,
2H, 5D); 2.04 (broad, 2H, 5D) 1.82 (d, 2H, 5E); 1.25 (d, 2H, 5E);
0.89 (broad, 2H, 5E). 19F NMR (193 K, δ): -110.7 (m, 2F, 3JPt-F
3
) 310, 5D); -112.7 (m, 2F, JPt-F ) 282, 5D), -114.4 (m, 4F,
3
3JPt-F ) 424, 5E); -115.8 (m, 2F, JPt-F ) 508, 5E) -115.8 (m,
3
3
1F, JPt-F ) 395, 5D), -116.4 (m, 1F, JPt-F ) 423, 5D) -162.5
to -165.5 (m, 9F 5D + 9F 5E). 13C NMR (213 K, (CD3)2CO, δ):
154.2 (5E); 153.0 (5D); 143.3 (5D); 139.8 (5E); 138.0 (5E); 137.8
(5D); 135.3 (5D); 132.8 (5E); 132.6 (5E); 131.6 (5D); 130.8 (5D);
Inorganic Chemistry, Vol. 43, No. 1, 2004 191

Casares et al.
Table 1. X-ray Data and Data Collection and Refinement Parameters
param
4D‚0.5hex
5E‚2(CD3)2CO
Crystal Data
empirical formula
fw
cryst system
space group
a (Å)
C39H20F15N2O2PPtRh
C48H25D12F15N2O2PPtRh
1162.54
monoclinic
P21/n
9.811(3)
20.149(5)
19.413(5)
93.522(6)
3830.4(18)
4
1299.84
orthorhombic
Pbca
20.766(4)
17.801(3)
25.945(5)
90
9591(3)
8
1.800
b (Å)
c (Å)
â (deg)
V (Å3)
Z
D
calc (g cm-3
)
2.016
4.233
2228
abs coeff (mm-1
F(000)
)
3.391
5024
cryst size (mm)
0.17 × 0.12 × 0.02
0.12 × 0.08 × 0.04
Data Collection
temp (K)
298(2)
298(2)
θ range for data collcn (deg)
1.46-23.29
1.57-23.27
wavelength (Å)
0.710 73 (Mo KR)
-10 h e 10, 0 e k e 22, 0 e l e 21
18 198
0.710 73 (Mo KR)
index ranges
reflcns collcd
0 e h e 23, 0 e k e 19, 0 e l e 28
45 162
indpdt reflcns
obsd reflcns [I > 2σ(I)]
completeness to θ (deg)
5509 (Rint ) 0.0609)
6880 (Rint ) 0.1352)
4240
3948
23.29 (99.8%)
23.27 (99.9%)
Refinement
SADABS
abs corr
SADABS
max and min transm
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.000 000 and 0.648 923
5509/0/551
1.006
R1 ) 0.0354, wR2 ) 0.0743
R1 ) 0.0585, wR2 ) 0.0841
1.428 and -0.460
1.000 000 and 0.852 165
6880/0/688
1.012
R1 ) 0.0411, wR2 ) 0.0761
R1 ) 0.1079, wR2 ) 0.1013
0.605 and -0.543
largest diff peak and hole (e Å-3
)
(193 K, δ): 155.2 (7E); 154.8 (7E); 153.8 (7D); 152.0 (7D); 150.9
(7E); 140.5 (7E); 140.0 (7E); 138.8 (7D); 138.6 (7D); 138.3 (7D);
138.3 (7E); 137.0 (7E); 136.7 (7D); 136.7 (7E); 133.0 (7D); 128.6
(7E); 128.1 (7E); 127.4 (7E); 127.0 (7E); 125.2 (7D); 90.3 (7E);
88.8 (7E); 88.2 (7D); 87.7 (7D); 86.2 (7E); 84.5 (7E); 58.4 (7E);
31.3 (7D); 30.9 (7E); 30.7 (7E); 30.6 (7D); 30.5 (7D); 30.5 (7E);
30.4 (7E); 29.0 (7D); 28.9 (7E); 28.5 (7E); 28.3 (7E). 31P{1H}
NMR (193 K, δ): 40.76 (1JPt-P ) 2652, 7E); 26.62 (1JPt-P ) 2485,
7D). 195Pt NMR (25 °C, (CD3)2CO, δ): -4362 (d, 7D); -4410 (d,
7E). IR (Nujol mull, cm-1): 1590 m, ν(CN); 1572 m, ν(CN).
[(C6F5)3Pt(µ-PPy3)Rh(TFB)] (8). This compound was prepared
as described for 7 but using 91.2 mg of [Rh(µ-Cl)(TFB)]2 (0.125
mmol) instead of [Rh(µ-Cl)(COD)]2. Yield: 40% (129 mg). Anal.
Calcd for C45H18F19N3PPtRh: C, 41.88; H, 1.41; N, 3.26. Found:
Experimental Procedure for X-ray Crystallography. Suitable
single crystals were mounted in glass fibers, and diffraction
measurements were made using a Bruker SMART CCD area-
detector diffractometer with Mo KR radiation (λ ) 0.710 73 Å).16
Intensities were integrated from several series of exposures, each
exposure covering 0.3° in ω, the total data set being a hemisphere.17
Absorption corrections were applied, based on multiple and
symmetry-equivalent measurements.18 The structure was solved by
direct methods and refined by least squares on weighted F2 values
for all reflections (see Table 1).19 All non-hydrogen atoms were
assigned anisotropic displacement parameters and refined without
positional constraints. Hydrogen atoms were taken into account at
calculated positions, and their positional parameters were refined.
Refinement proceeded smoothly to give R1 ) 0.0354 for 4D‚0.5hex
(hex ) hexane) and R1 ) 0.0411 for 5E‚2(CD3)2CO on the basis
of the reflections with I > 2σ(I). Complex neutral-atom scattering
factors were used.20 Crystallographic data (excluding structure
factors) for the structures 4D‚0.5hex and 5E‚2(CD3)2CO reported
in this paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publications CCDC-200983
and CCDC-202042, respectively. Copies of the data can be obtained
free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. [fax (internat.) + 44-1223/336-033;
E-mail deposit@ccdc.cam.ac.uk].
1
C, 41.81; H, 1.67; N, 3.11. H NMR (25 °C, (CD3)2CO): At this
temperature the signals are in coalescence. 1H NMR (213 K, mixture
of 8D (65%) and 8E (35%), δ): 9.64 (broad, 1H, 8D); 8.82 (m,
1H 8D + 1H 8E); 8.69 (d, 1H, 8D); 8.65 (broad, 3H, 8E); 8.40
(m, 2H, 8D); 8.20 (t, 3H, 8E); 7.78 (m, 2H, 8D + 1H, 8E); 7.51
(m, 2H, 8D); 6.71 (broad, 2H, 8D); 6.41 (s, 1H 8D); 6.14 (s, 1H,
8D); 5.05 (broad, 2H, 8E); 4.67 (s, 2H, 8D); 4.37 (s, 2H, 8D) 3.94
(s, 4H, 8E). 13C NMR (193 K, (CD3)2CO, δ): 153.8 (8D); 153,5
(8E); 152.3 (8D); 152.1 (8E); 138.9 (8E); 138.7 (8D); 138.6 (8D);
137.6 (8D); 132.2 (8D); 127.9 (8D); 127.5 (8E); 126.9 (8D); 67.5
(8D); 66.0 (8D); 64.9 (8E); 42.0 (8D); 41.4 (8D). 40.3 (8E). 19F
NMR (223 K, (CD3)2CO, δ): -110.32 (m, 2F, 8D); -113.64 (m,
4F, 8E); -115.49 (m, 2F 8D); -116.46 (m, 2F 8D + 2F, 8E);
-146.79 (m, 2F-TFB, 8E); -147.09 (m, 2F-TFB 8D); -159.64
(m, 2F-TFB, 8E); -159.78 (m, 2F-TFB 8D); -163 to -165 (m,
9F 8D + 9F 8E). 31P{1H} NMR (223 K, δ): 37.24 (1JPt-P ) 2642,
8E); 25.47 (1JPt-P ) 2487, 8D). 195Pt NMR: δ -4340 (d, 8D);
-4428 (d, 8E). IR (Nujol mull, cm-1): 1589 m, ν(CN); 1574 m,
ν(CN).
(16) SMART V5.051 Diffractometer Control Software; Bruker Analytical
X-ray Instruments Inc.: Madison, WI, 1998.
(17) SAINT V6.02 Integration Software; Bruker Analytical X-ray Instru-
ments Inc.: Madison, WI, 1999.
(18) Sheldrick, G. M. SADABS: A program for absorption correction with
the Siemens SMART system; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(19) SHELXTL program system Version 5.1; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.
192 Inorganic Chemistry, Vol. 43, No. 1, 2004

Zwitterionic Pt-Rh Organometallic Compounds
Table 2. Selected Spectroscopic Data
compd
isomer (%)
δ(31P)
δ(13C)
89.3, 85.6
90.6, 87.8
65.7, 67.7
63.5, 64.3
δ(195Pt)
(NBu4)[Pt(C6F5)3(PPhPy2)] (1)
[Pt(C6F5)3](µ-PPhPy2)[Rh(COD)] (5)
16.7
22.7
40.2
22.9
36.5
20.8
19.0
26.6
40.8
25.90
37.93
20.59
-4368
-4338
-4357
-4333
-4423
-4320
-4373
-4362
-4410
-4340
-4428
-4314
D (41)
E (59)
D (64)
E (36)
D (100)
[Pt(C6F5)3](µ-PPhPy2)[Rh(TFB)] (6)
[Pt(C6F5)3](µ-PPhPy2)[Rh(CO)2] (3)
(NBu4)[Pt(C6F5)3(PPhPy2)] (2)
[Pt(C6F5)3](µ-PPy3)[Rh(COD)] (7)
D (45)
E (55)
D (65)
E (35)
D (100)
88.2, 87.7
90.3, 88.8, 86.2, 84.5
67.3, 65.8
[Pt(C6F5)3](µ-PPy3)[Rh(TFB)] (8)
[Pt(C6F5)3](µ-Ppy3)[Rh(CO)2] (4)
64.8
Results
Complexes 1 and 2 were prepared according to eq 1, by
substitution of tht by PPhPy2 or PPy3 on the precursor
(NBu4)[Pt(C6F5)3(tht)]. The resulting compounds, 1 and 2
were used as anionic N,N ligands for cationic [Rh(diolefin)-
(solv)2]+ (solv ) solvent) or [Rh(CO)2(solv)2]+ complexes
prepared in situ (eqs 2 and 3), affording zwitterionic Pt/Rh
complexes 3-8.
(NBu4)[Pt(C6F5)3(tht)] + PPynPh3-n f
(NBu4)[Pt(C6F5)3(PPynPh3-n)] (1)
n ) 2, 1; n ) 3, 2
(NBu4)[Pt(C6F5)3(PPynPh3-n)] + [Rh(CO)2(solv)2]NO3 f
[Pt(C6F5)3(µ-PPynPh3-n)Rh(CO)2] + (NBu4)NO3 (2)
n ) 2, 3; n ) 3, 4
Figure 1. Structure and 19F NMR spectrum (only Fortho) of complex 3
showing the inequivalence of the fluorine atoms of the C6F5 ligands and
the protons of the phenyl ring. For clarity only one C6F5 group is shown.
F2 and F6 signals correspond to the C6F5 group trans to phosphorus, while
F2c and F6c signals correspond to the two equivalent C6F5 groups cis to
phosphorus.
(NBu4)[Pt(C6F5)3(PPynPh3-n)] + [Rh(diolefin)
(solv)2]ClO4 f [Pt(C6F5)3(µ-PPynPh3-n)Rh(diolefin)] +
(NBu4)ClO4 (3)
diolefin ) COD, n ) 2, 5, and n ) 3, 7;
diolefin ) TFB, n ) 2, 6, and n ) 3, 8
a further consequence of this location is that the noncoor-
dinated Py group is unable to undergo fast exchange with
those coordinated to rhodium, and distinct and sharp signals
for the pendant and the coordinated Py groups are observed
in the H NMR spectrum at 25 °C. The exchange between
coordinated and noncoordinated Py groups is slow on the
NMR time scale.
In the cases of carbonyl compounds, the CO stretching
can be used as an additional indicator of the coordination
mode. It is known that pentacoordinated [MTp′(CO)2]
complexes show the two stretching vibrations (symmetrical
and asymmetrical) at lower energy compared to their four-
coordinated isomers.9 Since the values obtained for the CO
stretching in complexes 3 and 4 are very close, both of them
are assigned a square-planar coordination (the only one
possible for 3). This eliminates structure F for 4.
Compounds with Geometries D and E Coexisting:
Complexes 5, 6 and 7, 8. Complexes of the type [(C6F5)3-
Pt(µ-PPynPh3-n)Rh(diolefin)] give in solution a mixture of
isomers D and E (Chart 1) which do not interconvert on the
NMR time scale. The major isomer is E for diolefin ) COD
but D for diolefin ) TFB (Table 2). The spectroscopic
Compounds with Only Geometry D: Complexes 3 and
4. The compounds [Pt(C6F5)3(µ-PPynPh3-n)Rh(CO)2] (n )
2, 3; n ) 3, 4) have a structure D in solution, as evidenced
by their NMR spectra (selected NMR data given in Table
2). The rotation of the C6F5 groups around the M-Cipso bond
is hindered, as it is often found in other fluoroaryl complexes
of square-planar Pd and Pt species.5 In complexes 3 and 4
also the rotation around the PsPt bond is restricted, probably
due to the proximity of the coordination planes of Pt and
Rh. Hence, the F2 and F6 atoms of each C6F5 are nonequiva-
lent and give rise to four signals (2:2:1:1) in the 19F NMR
spectrum, two of double intensity for the two C6F5 cis to
phosphorus and two for the C6F5 trans to phosphorus (Figure
1). On the other hand, the pendant ring of the PPynPh3-n
ligand (Ph in PPhPy2 or the noncoordinated Py in PPy3) is
sandwiched between the two coordinated Py rings. Accord-
1
1
ingly the H and 13C NMR spectra of 3 show five signals
for the five inequivalent C-H groups of the Ph ring. For 4
(20) International Tables for Crystallography; Kluwer: Dordrecht, The
Netherlands, 1992; Vol. C.
Inorganic Chemistry, Vol. 43, No. 1, 2004 193

Casares et al.
Figure 2. 19F-195Pt correlation experiment of 5 at room temperature. The
cross-peaks correlate each signal of 195Pt with the satellites of the signals
on the 19F spectrum: (a) ) 3J
Pt; (b) ) 1J
19F-195
31P-195
Pt. Only the Fortho signals
(F2 and F6) have been recorded.
properties (19F and H NMR) of isomers D are similar to
those described above for compounds 3 and 4 and are not
further discussed here. The isomers E give in the 19F NMR
at room temperature only two signals (2:1) due to the Fortho
atoms because in this geometry there is fast rotation about
the PsPt bond, which makes equivalent the four Fortho nuclei
of the two C6F5 groups cis to phosphorus as well as the F2
and F6 nuclei on the C6F5 group trans to phosphorus. In all
the complexes studied these signals appear partially over-
lapped with the signals of Fortho nuclei of the D isomer and
with their satellites due to 19F-195Pt coupling. However all
the signals are easily identified in 19F-195Pt correlation
experiments (see for instance Figure 2 for complex 5).
Due to the symmetry of the complexes, in the isomers 5E
1
Figure 3. Two ORTEP plots of 4D‚0.5hex with thermal ellipsoids drawn
at the 30% probability level.
1
and 6E four of the five H nuclei of the phenyl ring are
complexes with PPy3 do not show any relevant shift with
respect to those with PPhPy2. Hence, although the 1H
spectrum of 8D could be misinterpreted as being the result
of a pentacoordinated complex, the 13C spectrum clearly
supports a square planar coordination (Table 2). Thus, the
spectroscopic data show no evidence for structures of the
type F in the complexes with the ligand [(C6F5)3Pt(µ-PPy3)]-.
This is in contrast with the usual behavior of [RBpz3]-
ligands.
X-ray Structures of Complexes 4D‚0.5hex and 5E‚
2(CD3)2CO. The two structural types proposed from spec-
troscopic studies have been confirmed in the solid state for
representative complexes.
The X-ray diffraction structure of 4D.0.5hex is shown in
Figure 3. Distances and angles at the coordination planes of
the two metals are gathered in Table 3. The structure strongly
suggests that the molecule is distorted to bring close the
rhodium and the platinum coordination planes in a D-type
geometry. The angles C(61)-Pt(1)-P(1) and Pt(1)-P(1)-
C(21) have values of 94.2 and 119.4°, respectively, and the
equivalent by pairs, and only three cross-peaks are obtained
1
in the H-13C experiment. With PPy3 (complexes 7E and
8E) the asymmetry of the noncoordinated Py group, which
lies above the coordination plane (see Figure 2), lowers the
symmetry of the complex leading, in the slow-exchange limit,
to chemical nonequivalence of the two coordinated Py groups
and the four olefinic hydrogens. In fact this is the spectrum
obtained for 7E at 193 K. At higher temperatures the fast
exchange of the coordinated Py groups with the pendant one
renders the three rings equivalent and also the four olefinic
hydrogens. For 8E the exchange of Py groups is very fast
and the coalescence temperature is below the 193 K limit
reached in our study.
It is known for Tp′Rh-olefin complexes that κ3-Tp′
compounds display the olefinic carbon signal at higher field
than their κ2-Tp′ analogues.9b,21 A similar effect should be
expected here, but the olefinic carbon signals of the
(21) Del Ministro, E.; Renn, O.; Ru¨egger, H.; Venanzi, L. M.; Burckhardt,
U.; Gramlich, V. Inorg. Chim. Acta 1995, 240, 631.
194 Inorganic Chemistry, Vol. 43, No. 1, 2004

Zwitterionic Pt-Rh Organometallic Compounds
Table 3. X-ray Structural Data: Selected Distances (Å) and Angles
(deg)
4D‚0.5hex
Rh(1)-N(1)
Rh(1)-N(2)
Rh(1)-C(1)
Rh(1)-C(2)
Rh(1)-Pt(1)
P(1)-Pt(1)
P(1)-Rh(1)
Pt(1)-C(41)
Pt(1)-C(61)
Pt(1)-C(51)
5E‚2(CD3)2CO
Rh(1)-N(1)
Rh(1)-N(2)
Rh(1)-M(1)a
Rh(1)-M(2)a
Rh(1)-Pt(1)
P(1)-Pt(1)
P(1)-Rh(1)
Pt(1)-C(41)
Pt(1)-C(61)
Pt(1)-C(51)
2.095(5)
2.082(6)
1.875(9)
1.848(10)
3.590(2)
2.254(2)
3.197(2)
2.082(6)
2.082(7)
2.056(7)
2.108(8)
2.121(8)
2.027(17)
2.021(16)
5.687(2)
2.281(3)
3.432(3)
2.069(10)
2.053(11)
2.069(9)
N(1)-Rh(1)-N(2)
C(41)-Pt(1)-C(51)
C(61)-Pt(1)-C(51)
C(41)-Pt(1)-P(1)
C(61)-Pt(1)-P(1)
86.0(2)
87.6(3)
88.6(3)
89.5(2)
94.2(2)
N(1)-Rh(1)-N(2)
C(41)-Pt(1)-C(61)
C(61)-Pt(1)-C(51)
C(41)-Pt(1)-P(1)
C(51)-Pt(1)-P(1)
88.4(2)
85.8(4)
87.3(4)
95.5(3)
91.3(3)
a M(1) and M(2) are the C(1)-C(2) and C(3)-C(4) centroids.
Figure 4. ORTEP plot of 5E‚2(CD3)2CO with thermal ellipsoids drawn
at the 30% probability level.
P(1) atom is situated 0.333 Å above the plane defined by
the other three donor atoms (C(41), C(51), and C(61)) and
the Pt(1) atom. The Pt atom is not on the normal to the
rhodium coordination plane passing through the Rh center
but displaced to one side. At the same time the fluoroaryl
rings are tilted with respect to the coordination plane at the
Pt atom, with angles in the range 60-76°. One of them
(C(61)-C(66)) makes an angle of only 18.8° with the
rhodium coordination plane, which allows the rhodium to
reduce the steric hindrance by approaching this pentafluo-
rophenyl ring (the shortest nonbonding distance to the atoms
of this ring is Rh(1)‚‚‚F(62) of 3.561 Å) and moving away
from the opposed fluoroaryl ring C(41)-C(46) (the shortest
nonbonding distance to the atoms of this ring is Rh(1)‚‚‚
F(42) of 3.538 Å). Therefore, the shortest distances between
the rhodium atom and the platinum frame are Rh(1)‚‚‚F(42)
and Rh(1)‚‚‚F(62). There is also a tetrahedral distortion in
the rhodium frame, being the angle between the planes N(1)-
Rh(1)N(2) and C(1)Rh(1)C(2) of 9.8°, to avoid a contact
distance between the carbonyl group C(1)O(1) and the closest
fluoroaryl ring. These features lead to a Pt(1)-Rh(1) distance
of 3.590 Å, still too large to consider a interaction between
the metal centers but lower than in an undistorted geometry.
Scheme 1
imposed by the steric hindrance between the PPhPy2 ligand
and the fluoroaryl ring. In the Rh center the PPhPy2 ligand
behaves as an N,N donor ligand, with the phenyl ring
oriented toward the Rh in an E-type geometry. The Pt and
Rh centers are separated by more than 5 Å. This configu-
ration of the chelate ring is also found in some X-ray
structures of Pd, Pt, and Rh complexes with 2-pyridylphos-
phine oxides as ligands.5 Geometry E is also found in the
solid state for Tp′Rh derivatives.6,9,22
Discussion
Pyridylphosphine ligands allow the easy and controlled
synthesis of bimetallic complexes. The phosphorus is first
coordinated to Pt affording a metal-containing N,N donor
chelate, which is then coordinated to a Rh(I) center. Although
the P,N-chelating coordination of other P,N ligands to
transition metal centers (including Rh) is well documented,1,14
apparently the P,N chelation on rhodium does not compete
with the observed N,N chelation in complexes 5 and 4
(Scheme 1). In other words, the regiochemistry is mostly
controlled by the ring size of the resulting metalacycle. A
four-membered P,N chelate should be unfavorable versus a
six-membered N,N chelate. The other possible structure
shown in Scheme 1, which involves transmetalation of a C6F5
group, is not observed either.
Finally, the phenyl ring C(31)-C(36) bisects the angle
formed by the pyridyl rings. This situation hinders its rotation
about the C-P bond, in agreement with the NMR observa-
tion discussed above.
The X-ray diffraction structure of 5E‚2(CD3)2CO is shown
in Figure 4, with distances and angles at the coordination
planes of the two metals collected in Table 3. The structure
shows that the coordination about each metal is slightly
distorted square planar, with both coordination planes roughly
perpendicular (with an angle between them of 119°). The
aryl ring on the P atom is lying over the Rh coordination
plane and is almost parallel to the nearest fluorophenyl ring.
All the bond lengths and angles are within the normal values,
and the fluoroaryl rings are tilted with respect to the Pt
coordination plane with angles in the range 67-77°.
Stereochemistry at the Phosphorus: Isomer D vs
Isomer E. As described above, complexes 4 and 5 are square
planar in solution. Two geometries are possible depending
(22) See for instance: (a) Akita, M.; Ohta, K.; Takahasi, Y.; Hikichi, S.;
Moro-Oka, Y. Organometallics 1997, 16, 4121. (b) Cocivera, M.;
Desmond, T. J.; Ferguson, G.; Kaitner, B.; Lalor, F. J.; O’Sullivan D.
J. Organometallics 1982, 1, 1125-1132.
The main deviation from the ideal geometry in the Pt is
due to the value of the C(41)-Pt(1)-P(1) angle (95.5°)
Inorganic Chemistry, Vol. 43, No. 1, 2004 195

Casares et al.
Chart 2
account that the anionic charge on the platinum moiety
(probably distributed mostly between the Pt-C and the C-F
bonds) can introduce a term of attractive electrostatic
interaction with the rhodium (positive) fragment in favor of
conformation D. The experimental results suggest that the
preferred conformation depends much on the steric require-
ments of the ligands on the rhodium center above the
coordination plane. For small size ligands lying in the
coordination plane, such CO in 3 and 4, conformation D is
preferred since the [Pt(C6F5)3]- plane can be located over
the Rh plane, bringing regions with opposite electrostatic
charge closer to each other. In this geometry, the rotation
around the P-Pt bond is very hindered. In fact, a putative
rotation intermediate, in which both coordination planes are
perpendicular, would push the platinum group to an equato-
rial location, which means close to conformation E, produc-
ing an exchange between D and E. The fact that this is not
observed suggests a noticeable difference in stability in favor
of D in this case.
Conformational Exchange. This conformational ex-
change, although slow, is observed on the NMR time scale
for complexes with COD, as a result of the destabilization
of D when the ligands on Rh invade the space above its
coordination plane. The exchange is faster for the complexes
with TFB, 6 and 8, which show the coalescence of the P
signals assigned to both conformers at room temperature.
This dependence of the rate of conformational exchange on
the olefin coordinated to the rhodium must be the result of
two factors associated with the geometry of the TFB
ligand: (i) a larger destabilization of the ground state due
to the bigger steric repulsion of the TFB with the P axial
subtituents; (ii) a stabilization of the transition state for the
TFB complex with respect to the COD complexes, due to
the smaller bite angle of the former and therefore the smaller
interaction between the olefinic bond and the H6 of the Py
coordinated to the rhodium in a putative planar transition
state.
on the relative distribution of the substituents on the
phosphorus: D if the third aryl ring is in a “pseudoequatorial”
position (toward the rhodium center) or E if the noncoor-
dinated aryl is in a “pseudoaxial” position (away from the
rhodium center, Chart 1).
The discrimination of the solution structures D and E is
straightforward considering the differences in their dynamic
behavior. Complexes with the D structure are quite static in
solution. At 25 °C they do not undergo fast rotation about
the Pt-P or Pt-C bonds and each pentafluorophenyl ring
gives five signals in their 19F NMR spectra. The rotation
about the P-C(phenyl) bond in complexes with PPhPy2 is
also hindered, due to the location of the phenyl ring between
the coordinated pyridyl groups, and five signals are obtained
in the 1H-13C HMQC spectrum. On the contrary, in
complexes E, the rotations about Pt-P and P-C(phenyl)
are not hindered and only three 19F signals from the C6F5
trans to P plus three more 19F signals from the two equivalent
C6F5 groups cis to P are observed. Also, only three signals
arising from C(phenyl)-H are obtained in the HMQC
spectrum of complexes with PPhPy2.
In previous works we have studied the behavior of
P-blocked EPPhPy2 and EPPy3 derivatives (E ) O, S) in
which the phosphorus atom has been oxidized and the two
Py rings behave as a chelate in square-planar complexes.5
The geometry found was always E. On the other hand, the
stereochemistry in “boatlike” metallacycles has been ana-
lyzed for complexes with pyrazolylborates (Chart 2). Bulky
R5 substituents produce steric repulsion between these and
the free Pz ring in conformation A, favoring conformation
B. A coordination environment crowded out of the coordina-
tion plane of the metal repels the noncoordinated Pz ring in
B, favoring conformation A.9,10,23
In 2-pyridylphosphine complexes with the phosphorus
coordinated to [Pt(C6F5)3]- the biggest steric interactions of
the Rh ligands are with the platinum complex, more than
with the other phosphorus substituent (Ph or Py). Considering
other intramolecular interactions it was, however, difficult
to decide a priori whether the overall steric hindrance was
bigger in conformation D or in E. It must also be taken into
Py Exchange. Complexes 6E and 8E have a structure
similar to that of 5 in the solid state (Figure 2), with an
uncoordinated pyridyl group in place of the phenyl ring. This
orientation facilitates the substitution of coordinated Py by
pendant Py groups. For 8E this exchange is fast at 193 K,
rendering spectroscopically equivalent the three Py rings and
the four olefinic protons. For 6E the exchange of Py and
also the rotation of the Py ring about the P-C bond are slow
at 193 K. Both processes share their coalescence in the NMR
spectra, suggesting a common transition state with the
incoming Py plane lying perpendicular to the rhodium
coordination plane. For analogous complexes of Pd(II) and
Rh(I) with Py3PO, the rotation of the uncoordinated Py is
too fast to be detected by NMR.5,17 An important conse-
quence of conformation D is the inability of the third Py
ring to substitute the coordinated Py groups in the rhodium
center. In fact this chemical exchange is very slow for 4D
and does not affect the shape of their NMR spectra at 25
°C.
In summary, the Py exchange is very fast in complexes E
and is controlled by the conformational exchange in com-
(23) Akita, M.; Hashimoto, M.; Hikichi, S.; Moro-oka, Y. Organometallics
2000, 19, 3744-3747.
196 Inorganic Chemistry, Vol. 43, No. 1, 2004

Zwitterionic Pt-Rh Organometallic Compounds
Table 4. CO Stretching Frequencies for Neutral and Cationic
Square-Planar Dicarbonylrhodium(I) Complexes
ν(CO) values for representative cationic and neutral com-
plexes with N,N chelated ligands. Only values for square-
planar isomers are collected, and complexes with donor
groups very different from Py or Pz have been excluded.
Complexes 3 and 4 show ν(CO) wavenumbers in the range
found for cationic complexes with neutral ligands, tipically
νsym about 2100 cm-1 and νass about 2040 cm-1. Neutral
complexes show νsym about 2085 cm-1 and νass about 2025
cm-1. This suggests that the electron density of the negative
charge is mostly delocalized in the (C6F5)3Pt fragment for
[(C6F5)3Pt(µ-PPynPh3-n)]- ligands, as proposed above in the
structure discussion) while it is more delocalized in the
pyrazolate rings for [HBPz3]-. Consequently the latter are
much better N,N donors.
complex
ν(CO) (cm-1
)
solvent
ref
[Pt(C6F5)(µ-PPhPy2)Rh(CO)2] (3)
[Pt(C6F5)(µ-PPy3)Rh(CO)2] (4)
2103, 2044 CH2Cl2
2102, 2044 CH2Cl2
this work
this work
24b
[RhTpPh,Me(CO)2] (two conformers) 2089, 2022 CHCl3
2077, 2008
[RhTpMe(CO)2]
2085, 2019 CHCl3
25
25
[RhTpiPr,4Br(CO)2] (two conformers) 2089, 2026 CHCl3
2077, 2020
[Rh(Pz4B)(CO)2]
2088, 2022 hexane
2104, 2047 CH2Cl2
2102, 2042 CH3CN
2101, 2042 CH3CN
2100, 2039 CH3CN
26
5d
27
27
27
[Rh(OPPy2Ph)(CO)2]+
[Rh(PMI)(CO)2]+ a
[Rh(PEI)(CO)2]+ b
[Rh(PiPI)(CO)2]+ c
[Rh(bipy)2(CO)2]+
2108, 2050 Nujol mull 28
2100, 2035 Nujol mull 24c
[{(3,5-Me2Pz)2CH2)}Rh(CO)2]+
a PMI ) 2-pyridinalmethylimine. b PEI ) 2-pyridinalethylimine. c PiPI
) 2-pyridinalisopropylimine.
Conclusion
In conclusion, the conformational and dynamic behavior
of anionic [(C6F5)3Pt(µ-PPynPh3-n)]- ligands is comparable
to that of Tp′, but conformation D is more favorable in the
former due to the bulkiness of the (C6F5)3Pt moiety and its
negative charge. On the other hand, the Tp′ ligands are much
better N,N donors than [(C6F5)3Pt(µ-PPynPh3-n)]-. These
features disfavor the κ3 coordination mode, which has not
been found for [(C6F5)3Pt(µ-PPy3)]- ligands although it is
frequent for Tp′ rhodium complexes.
plexes D, a behavior comparable to that of analogous
compounds with pyrazolylborate ligands.8,9
Differences of the N-Donor Ends in [HBPz3]- and in
[(C6F5)3Pt(µ-PPynPh3-n)]- Ligands. The stretching CO
band in the IR spectra shows no observable effect of the
negative charge of the [(C6F5)3Pt(µ-PPynPh3-n)]- ligands on
the rhodium center, since the observed values are similar to
those obtained for cationic dicarbonyl complexes such as
[Rh(CO)2(ÃPPynPh3-n)]+ and much higher than for com-
plexes with anionic [HBPz3]- ligands.9,24 Table 4 gathers
Acknowledgment. Financial support by the Ministerio
de Ciencia y Tecnolog´ıa (Project BQU2001-2015) and the
Junta de Castilla y Leo´n (Project No. VA120-01) is very
gratefully acknowledged.
(24) (a) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000,
19, 87-90. (b) Moszner, M.; Woloviec, S.; Tro¨sch, A.; Heinrich, V.
J. Organomet. Chem. 2000, 595, 178-185. (c) Oro, L. A.; Esteban,
M.; Claramunt, R. M.; Elguero, J.; Foces-Foces, C.; Cano, F. H.; J.
Organomet. Chem. 1984, 276, 79-97.
(25) Bucher, U. E.; Currao, A.; Nesper, R.; Ru¨egger, H.; Venanzi, L. M.;
Younger, E. Inorg. Chem. 1995, 34, 66-74.
(26) King, R. B.; Bond, A. J. Organomet. Chem. 1974, 73, 115.
(27) Zassinovich, G.; Camus, A.; Mestroni, G. J. Organomet. Chem. 1977,
133, 377-384.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC034863F
(28) Reddy, G.; Susheelemma, L. Chem. Commun. 1970, 54.
Inorganic Chemistry, Vol. 43, No. 1, 2004 197