Pd(II) complexes with polydentate nitrogen ligands. Molecular recognition and dynamic behavior involving Pd-N bond rupture. X-ray molecular structures of [{Pd(C6HF4)2}(bpzpm)] and [{Pd(η3-C4H7)}2(bpzpm)] (CF3SO3)2 [bpzpm = 4,6-bis(pyrazol-1-yl)pyrimidine]

Article abstract of DOI:10.1021/ic990495x

The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm) and 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Me-bpzpm) were synthesized and their reactions with some palladium derivatives explored. Mononuclear or dinuclear neutral or cationic complexes were obtained by reaction of the ligands with 1 or 2 equiv of Pd(C₆XF₄)₂(cod) (cod = 1,5-cyclooctadiene; X = F, H) or the palladium fragment [Pd(η³-2-Me-C₃H₄)(S)₂]⁺ (S = acetone). The reaction of the dinuclear derivatives with 1 equiv of the respective free ligand immediately led to the regeneration of the mononuclear complexes. Except in the case of the synthesis of [{Pd(C₆HF₄)₂}{Pd(C₆F₅)₂}(bpzpm)], where two similar metallic groups are present, all attempts to obtain dinuclear asymmetric complexes with two different palladium fragments failed. Instead, the dinuclear symmetric complexes were formed. This result could be considered as an example of molecular recognition with the ligand acting as a ditopic receptor. This behavior is comparable to chemical symbiosis but in this case applied to the ligand rather than to the metal center as occurs normally. The polyfluorophenyl rings are situated on average in a perpendicular orientation with respect to the coordination plane. Their restricted rotation results in several atropoisomers for the complexes with m-C₆HF₄. Different cross-reaction experiments were carrieed out, and these showed the mobility of the metallic fragments, with the more difficult process being that involving the more strongly bonded polyfluorophenyl palladium groups. By means of ¹H NMR variable temperature studies, the interconversion of the two isomers of [{Pd(η³-C₄H₇)}₂(bpzpm)]Tf₂ (Tf = CF₃SO₃) was analyzed. In the case of [{Pd(η³-C₄H₇)}(bpzpm)]Tf the existence of two processes, an intramolecular apparent allyl rotation and an intermolecular exchange of the allylpalladium fragments, has been demonstrated. Different ΔG(c)(+) values at the coalescence temperatures have also been determined. An X-ray single-crystal analysis was carried out on [{Pd(η³-C₄H₇)}₂(bpzpm)]Tf₂, which crystallizes in the monoclinic system, space group I2/m, with a = 9.368(2), b = 16.191(3), c = 20.228(6) A, β = 101.26(3), and Z = 4. Compound [{Pd(C₆HF₄)₂}(bpzpm)] crystallized in the triclinic system, space group P1, with a = 8.845(6), b = 12.6609(9), c = 12.826(3) A, α = 88.45(2), β = 74.36(3), γ = 89.32(2), and Z = 2.

Full text of DOI:10.1021/ic990495x

1152
Inorg. Chem. 2000, 39, 1152-1162
Pd(II) Complexes with Polydentate Nitrogen Ligands. Molecular Recognition and Dynamic
Behavior Involving Pd-N Bond Rupture. X-ray Molecular Structures of
[{Pd(C6HF4)2}(bpzpm)] and [{Pd(η3-C4H7)}2(bpzpm)] (CF3SO3)2 [bpzpm )
4,6-Bis(pyrazol-1-yl)pyrimidine]
Felipe Go´mez-de la Torre, Antonio de la Hoz, Fe´lix A. Jalo´n,*,† Blanca R. Manzano,* and
Ana M. Rodr´ıguez
Departamento de Qu´ımica Inorga´nica, Orga´nica y Bioqu´ımica, Universidad de Castilla-La Mancha,
Facultad de Qu´ımicas, Avda. Camilo J. Cela, 10, 13071 Ciudad Real, Spain
Jose´ Elguero
Instituto de Qu´ımica Me´dica, CSIC, Juan de la Cierva, 3, 28006-Madrid, Spain
Mart´ın Mart´ınez-Ripoll
Departamento de Cristalograf´ıa, Instituto Rocasolano, CSIC, Serrano, 119, 28006-Madrid, Spain
ReceiVed May 6, 1999
The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm) and 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Me-bpzpm)
were synthesized and their reactions with some palladium derivatives explored. Mononuclear or dinuclear neutral
or cationic complexes were obtained by reaction of the ligands with 1 or 2 equiv of Pd(C6XF4)2(cod) (cod )
1,5-cyclooctadiene; X ) F, H) or the palladium fragment [Pd(η3-2-Me-C3H4)(S)2]+ (S ) acetone). The reaction
of the dinuclear derivatives with 1 equiv of the respective free ligand immediately led to the regeneration of the
mononuclear complexes. Except in the case of the synthesis of [{Pd(C6HF4)2}{Pd(C6F5)2}(bpzpm)], where two
similar metallic groups are present, all attempts to obtain dinuclear asymmetric complexes with two different
palladium fragments failed. Instead, the dinuclear symmetric complexes were formed. This result could be
considered as an example of molecular recognition with the ligand acting as a ditopic receptor. This behavior is
comparable to chemical symbiosis but in this case applied to the ligand rather than to the metal center as occurs
normally. The polyfluorophenyl rings are situated on average in a perpendicular orientation with respect to the
coordination plane. Their restricted rotation results in several atropoisomers for the complexes with m-C6HF4.
Different cross-reaction experiments were carried out, and these showed the mobility of the metallic fragments,
with the more difficult process being that involving the more strongly bonded polyfluorophenyl palladium groups.
1
By means of H NMR variable temperature studies, the interconversion of the two isomers of [{Pd(η3-C4H7)}2-
(bpzpm)]Tf2 (Tf ) CF3SO3) was analyzed. In the case of [{Pd(η3-C4H7)}(bpzpm)]Tf the existence of two processes,
an intramolecular apparent allyl rotation and an intermolecular exchange of the allylpalladium fragments, has
been demonstrated. Different ∆Gcq values at the coalescence temperatures have also been determined. An X-ray
single-crystal analysis was carried out on [{Pd(η3-C4H7)}2(bpzpm)]Tf2, which crystallizes in the monoclinic system,
space group I2/m, with a ) 9.368(2), b ) 16.191(3), c ) 20.228(6) Å, â ) 101.26(3), and Z ) 4. Compound
[{Pd(C6HF4)2}(bpzpm)] crystallized in the triclinic system, space group P1h, with a ) 8.845(6), b ) 12.6609(9),
c ) 12.826(3) Å, R ) 88.45(2), â ) 74.36(3), γ ) 89.32(2), and Z ) 2.
Introduction
work, other aromatic polydentate N-donor ligands, such as TPT
(2,4,6-tris-2-pyridyl-1,3,5-triazine)17-27 andpyrazolylpyridines,28-38
Polydentate ligands with sp2-hybridized nitrogen atoms have
been frequently used, for instance, polypyrazolylborates1,2 and
polypyridines.2-16 More related to the ligands of the present
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† E-mail: fjalon@qino-cr.uclm.es. Fax: 34 926295318.
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10.1021/ic990495x CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/03/2000

Pd(II) Complexes
Inorganic Chemistry, Vol. 39, No. 6, 2000 1153
have also been the subject of many studies, especially charge-
transfer studies and related properties. On the other hand,
triazines39-42 or pyrimidines43,44 bearing pyrazol-1-yl substituents
have received much less attention.
been proposed. Recently, Orrell et al.,9 in an elegant study with
asymmetric terpyridine ligands coordinated to palladium and
platinum fragments, have shown that the 1,4-metallotopic shift
pursues an associative mechanism where the role of the N atom
in the central pyridine ring is essential.
Orrell et al.45,46 have reported the fluxional behavior of new
palladium and platinum derivatives containing 2,4,6-tris(2-
pyridyl)-1,3,5-triazine and 2,4,6-tris(2-pyridyl)pyrimidine ligands.
An intramolecular mechanism based on a 1,4-metallotropic shift
coupled to the metal hurdling along the coordination positions
of the N-donor ligand has been proposed. There have been some
controversy about the mechanism of the 1,4-metallotropic shift
process, and both associative47 and dissociative48 pathways have
In a previous paper49 we have reported the synthesis and study
of the dynamic behavior of new allylpalladium derivatives
coordinated to pyrazolyltriazine ligands where the metallic group
interchanges between the different coordination positions of the
ligand. As in Orrell’s examples,45,46 but with energy barriers
1
low enough to observe several coalescences in the H NMR
spectra, we have measured two different free activation energies
whose difference lies correctly with the expected strengths of
the Pd-N bonds, which are necessarily broken in each step.
This implies the existence of Pd-N bond rupture in the two
processes. The N5 atom of the triazine ring could assist the
palladium group in the 1,4-metallotropic shift (see Scheme 5
of ref 49), making the process intramolecular.
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To extend our previous work and to evaluate the role of the
triazine central nitrogen atom, we have now synthesized two
similar ligands, 4,6-bis(pyrazol-1-yl)pyrimidine44 (bpzpm) and
4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Me-bpzpm) (see
Scheme 1), that lack the N5 atom, making impossible an
intramolecular 1,4-metallotropic shift of the metal. Because these
ligands still possess two identical asymmetric chelating coor-
dination sites, if the palladium fragments are able to jump from
one position to the other, a different pathway must be involved.
Another goal we have pursued in this work was to explore
the possibility of synthesizing asymmetric dinuclear derivatives
and to study the mutual influence of the two metallic groups
through the ligand core. In this context different reactions have
been performed with the bpzpm and Me-bpzpm ligands, with
the metallic complex Pd(C6F5)2(cod) or Pd(C6HF4)2(cod), and
with the solvato [Pd(η3-2-Me-C3H4)(S)2]Tf.
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V.; Romeo, R. Inorg. Chem. 1998, 37, 2763.
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Experimental Section
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General Comments. All manipulations were carried out under an
atmosphere of dry oxygen-free nitrogen using standard Schlenk
techniques. Solvents were distilled from the appropriate drying agents
and degassed before use. Pyrazole, 4-methylpyrazole, 4,6-dichloro-
pyrimidine, and AgCF3SO3 were purchased from Aldrich. [(η3-2-
MeC3H4)Pd(µ-Cl)]250,51 was prepared as described in the literature. [Pd-
(C6F5)2(cod)] and [Pd(C6HF4)2(cod)] were synthesized as described in
the literature for similar complexes.52 The ligand 4,6-bis(pyrazol-1-
yl)-1,3-pyrimidine (bpzpm) has been previously described.44 Elemental
analyses were performed with a Perkin-Elmer 2400 microanalyzer. 1H,
13C, and 19F NMR spectra were recorded on a Varian Unity 300
spectrometer using, unless specified, acetone-d6 as solvent. Standard
experimental conditions were employed.49 Free energies of activation
were calculated53 from the coalescence temperature (Tc) and the
frequency difference between the coalescing signals (extrapolated at
the coalescence temperature) with the formula ∆Gcq ) aT[9.972 +
log(T/δν)], a ) 1.914 × 10-2. The estimated error in the calculated
(38) Kuang, S. M.; Zhang, Z. Z.; Wang, Q. G.; Mak, T. C. W. J. Chem.
Soc., Dalton Trans. 1998, 1115.
(39) Reimlinger, H.; Noels, A.; Jadot, J.; van Overstraeten, A. Chem. Ber.
1979, 103, 1954.
free energies of activation is 0.5 kJ mol-1
.
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Schultz, G.; Hargittai, I. Struct. Chem. 1994, 5, 255.
(41) Yang, C. Y.; Chen, X.-M.; Zhang, W.-H.; Chen, J.; Yang, Y.-S.; Gong,
M.-L. J. Chem. Soc., Dalton Trans. 1996, 1767.
(47) Abel, E. W.; Orrell, K. G.; Osborne, A. G.; Pain, H. M.; Sˇik, V.;
Hursthouse, M. B.; Malik, K. M. A. J. Chem. Soc., Dalton Trans.
1994, 3441.
(48) Rotondo, E.; Giordano, G.; Minniti, D. J. Chem. Soc., Dalton Trans.
1996, 253.
(49) Go´mez-de la Torre, F.; de la Hoz, A.; Jalo´n, F. A.; Manzano, B. R.;
Otero, A.; Rodr´ıguez, A. M.; Rodr´ıguez-Pe´rez, M. C.; Echevarr´ıa, A.;
Elguero, J. Inorg. Chem. 1998, 37, 6606.
(42) Gelling, A.; Orrell, K. G.; Osborne, A. G.; Sˇik, V. J. Chem. Soc.,
Dalton Trans. 1996, 3371.
(43) Gelling, A.; Noble, D. R.; Orrell, K. G.; Osborne, A. G.; Sˇik, V. J.
Chem. Soc., Dalton Trans. 1996, 3065.
(44) Ikeda, M.; Maruyama, K.; Nobuhara, Y.; Yamada, T.; Okabe, S. Chem.
Pharm. Bull. 1997, 45, 549.
(50) Dent, W. T.; Long, R.; Wilkinson, G. J. Chem. Soc. 1964, 1585.
(51) Tatsuno, Y.; Yoshida, T.; Seiotsuha, Inorg. Synth. 1979, 19, 220.
(52) Espinet, P.; Mart´ınez-de Ilarduya, J. M.; Pe´rez-Briso, C.; Casado, A.
L.; Alonso, M. A. J. Organomet. Chem. 1998, 551, 9.
(53) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: London,
1982.
(45) Gelling, A.; Olsen, M. D.; Orrell, K. G.; Osborne, G.; Sˇik, V. Chem.
Commun. 1997, 587.
(46) Gelling, A.; Olsen, M. D.; Orrell, K. G.; Osborne, A. G.; Sˇik, V. Inorg.
Chim. Acta 1997, 264, 257.

1154 Inorganic Chemistry, Vol. 39, No. 6, 2000
Go´mez-de la Torre et al.
Scheme 1
Preparation of Compounds. (a) 4,6-Bis(4-methylpyrazol-1-yl)-
1,3-pyrimidine (Me-bpzpm). To a solution of 4-methylpyrazole (1.21
g, 14.7 mmol) in 50 mL of THF was added NaNH2 (0.573 g, 14.7
mmol). The solution was stirred at room temperature for 1 h, and
evolution of NH3 was observed. 4,6-Dichloropyrimidine (1.094 g, 7.35
mmol) was then added to the reaction mixture. The pale-brown solution
was left stirring for 10 h, and the mixture was evaporated to dryness.
The product was extracted three times with 30 mL of toluene. The
toluene was removed, and the white solid obtained was dissolved in
dichloromethane. Layering the resulting solution with pentane led to
the precipitation of traces of pyrazole. Me-bpzpm was obtained after
filtration and evaporation to dryness of the resulting solution. The solid
was recrystallized from dichloromethane/pentane. Yield: 67%. Anal.
Calcd for C12H12N6 (240.27): C, 59.99; H, 5.03; N, 34.98. Found: C,
60.16; H, 4.95; N, 35.02.
(e) [{Pd(η3-C4H7)}2(4,6-bis(4-methylpyrazol-1-yl)pyrimidine)]-
(CF3SO3)2 (4). This compound was prepared in a way similar to the
preparation of 3. For method 1, the yield was 75%. For method 2, the
yield was 82%. Anal. Calcd for C22H26F6N6O6Pd2S2 (861.44): C, 30.67;
H, 3.04; N, 9.76. Found: C, 30.17; H, 3.27; N, 9.43.
(f) {Pd(C6F5)2}(4,6-bis(pyrazol-1-yl)pyrimidine) (5). To a solution
of Pd(C6F5)2(cod) (100.0 mg, 0.18 mmol) in 20 mL of acetone was
added bpzpm (38.9 mg, 0.18 mmol). The solution was stirred at room
temperature for 5 h. The colorless solution was evaporated to dryness.
The white solid was recrystallized from dichloromethane/pentane.
Yield: 90%. Anal. Calcd for C22H8F10N6Pd‚2CH2Cl2 (822.62): C,
35.04; H, 1.47; N, 10.22. Found: C, 34.94; H, 1.09; N, 10.61. 19F NMR:
δ -112.25 (m, Fortho), -158.53 (t, JFF ) 20.0, Fpara), -158.92 (t, JFF
20.0, Fpara), -161.09 (m, Fmeta), -161.45 (m, Fmeta) ppm.
)
(g) {Pd(C6HF4)2}(4,6-bis(pyrazol-1-yl)pyrimidine) (6). To a solu-
tion of Pd(C6HF4)2(cod) (124.7 mg, 0.24 mmol) in 20 mL of acetone
was added bpzpm (51.6 mg, 0.24 mmol). The solution was stirred at
room temperature for 4 h. The colorless solution formed was evaporated
to dryness. The product was recrystallized from dichloromethane/
pentane. Crystals suitable for X-ray structure determination were
obtained using these solvents. Yield: 61%. Anal. Calcd for C22H10F8N6-
Pd (616.75): C, 42.84; H, 1.63; N, 13.63. Found: C, 42.85; H, 1.23;
N, 13.76. 19F NMR: δ -92.13 (bs, 3F, F6), -92.21 (bs, 1F, F6), -111.50
(d, JFF ) 27.5, 2F, F2), -111.71 (d, JFF ) 24.4, 1F, F2), -111.80 (d,
JFF ) 21.4, 1F, F2), -143.72 (d, JFF ) 18.3, 1F, F4), -143.76 (d, JFF
(b) [{Pd(η3-C4H7)}(4,6-bis(pyrazol-1-yl)pyrimidine)]CF3SO3 (1).
To a solution of [Pd(η3-C4H7)(µ-Cl)]2 (74.2 mg, 0.19 mmol) in 20 mL
of acetone was added AgCF3SO3 (96.8 mg, 0.38 mmol). The solution
was protected from light and stirred at room temperature for 4 h, and
the resulting suspension was filtered off. The compound bpzpm (80
mg, 0.38 mmol) was added to the filtrate. After the mixture was stirred
for 15 min, the colorless solution formed was evaporated to dryness.
The solid was recrystallized from acetone/diethyl ether. Yield: 82%.
Anal. Calcd for C15H15F3N6O3PdS (522.80): C, 34.46; H, 2.89; N,
16.08. Found: C, 34.33; H, 2.97; N, 15.85. The data for ∆Gcq of
complex 1 at different concentrations were obtained by preparing the
more concentrated solution and diluting consecutively with addition
of 1,1,2,2-tetrachloroethane-d2, and all the data were collected in the
same NMR session.
) 21.4, 1F, F4), -144.19 (d, JFF ) 21.4, 1F, F4), -144.23 (d, JFF
18.3, 1F, F4), -170.91 (m, 2F, F3), -171.18 (m, 2F, F3) ppm.
(h) {Pd(C6F5)2}2(4,6-bis(pyrazol-1-yl)pyrimidine) (7).
)
(h.1) Method 1. To a solution of Pd(C6F5)2(cod) (120.5 mg, 0.22
mmol) in 20 mL of acetone was added bpzpm (23.3 mg, 0.11 mmol).
The solution was stirred at room temperature for 5 h. The colorless
solution was evaporated to dryness. The white solid was recrystallized
from dichloromethane/pentane. Yield: 80%.
(c) [{Pd(η3-C4H7)}(4,6-bis(4-methylpyrazol-1-yl)pyrimidine)]-
CF3SO3 (2). This compound was prepared in a way similar to the
preparation of 1. Yield: 77%. Anal Calcd for C17H19F3N6O3PdS
(550.85): C, 37.07; H, 3.48; N, 15.25. Found: C, 36.92; H, 3.36; N,
14.97.
(h.2) Method 2. To a solution of 5 (120 mg, 0.14 mmol) in acetone
(20 mL), Pd(C6F5)2(cod) (80 mg, 0.14 mmol) was added. Workup
similar to that of method 1 led to 7. Yield: 86%. Anal. Calcd for
C34H8F20N6Pd2‚(1/2)CH2Cl2 (1171.21): C, 36.49; H, 0.80; N, 7.40.
(d) [{Pd(η3-C4H7)}2(4,6-bis(pyrazol-1-yl)pyrimidine)](CF3SO3)2
(3). (d.1) Method 1. To a solution of [Pd(η3-C4H7)(µ-Cl)]2 (148.5 mg,
0.38 mmol) in 20 mL of acetone was added AgCF3SO3 (194.0 mg,
0.76 mmol). The solution was protected from light and stirred at room
temperature for 4 h, and the resulting suspension was filtered off. The
compound bpzpm (80 mg, 0.38 mmol) was added to the filtrate. After
the mixture was stirred for 15 min, the colorless solution was evaporated
to dryness. Yield: 77%.
Found: C, 36.25; H, 0.76; N, 6.92. 19F NMR: δ -117.42 (d, JFF
)
24.3, Fortho), -117.89 (d, JFF ) 24.3, Fortho), -161.55 (t, JFF ) 15.2,
Fpara), -163.53 (t, JFF ) 18.9, Fpara), -165.76 (m, Fmeta), -166.29 (m,
meta) ppm.
F
(i) {Pd(C6HF4)2}2(4,6-bis(pyrazol-1-yl)pyrimidine) (8).
(i.1) Method 1. To a solution of Pd(C6HF4)2(cod) (100.4 mg, 0.20
mmol) in 20 mL of acetone was added bpzpm (20.8 mg, 0.10 mmol).
The solution was stirred at room temperature for 4 h. The colorless
solution was evaporated to dryness, and the resulting solid recrystallized
from acetone/pentane. Yield: 68%.
(d.2) Method 2.To a solution of [Pd(η3-C4H7)(acetone)2]CF3SO3,
prepared from [Pd(η3-C4H7)(µ-Cl)]2 (74.2 mg, 0.19 mmol) as specified
in method 1, a solution of 1 (98 mg, 0.19 mmol) in acetone (10 mL)
was added. Workup identical to that of method 1 led to 3. Yield: 90%.
Anal. Calcd for C20H22F6N6O6Pd2S2 (833.38): C, 28.82; H, 2.66; N,
10.08. Found: C, 28.65; H, 2.73; N, 9.77. Crystals suitable for X-ray
analysis were obtained from acetone/pentane.
(i.2) Method 2. To a solution of 6 (72.5 mg, 0.12 mmol) in acetone
(15 mL), Pd(C6HF4)2(cod) (60.3 mg, 0.12 mmol) was added. A workup

Pd(II) Complexes
Inorganic Chemistry, Vol. 39, No. 6, 2000 1155
similar to that of method 1 led to 8. Yield: 85%. Anal. Calcd for
C34H12F16N6Pd2‚(1/2)(CH3)2CO (1050.36): C, 40.60; H, 1.44; N, 8.00.
Found: C, 40.44; H, 0.97; N, 7.45. 19F NMR: F6, δ -91.80 (bs),
-92.00 (bs), -92.16 (bs), ppm, 2:1:1 ratio; F2, δ -111.0 to -111.35
ppm, complex signal; F4, δ -140.9 to -141.2 (complex signal where
at least three doublets are included), -142.95 to -143.1 (complex signal
where three doublets, -143.00, JFF ) 18.0, -143.01, JFF ) 19.1,
-143.04, JFF ) 19.1, are included) ppm, the ratio of the two complex
signals is 1:1; F3, δ -169.29 to -169.55 (m), -169.78 to -170.04
(m), -170.04 to -170.40 (m), ppm, 1:1:2 ratio.
established. Several spectra were made at different temperatures (183-
323 K), and the ratio was unchanged.
Cross Exchange Experiments. In a procedure similar to that
described for cross reaction type 1, the NMR tube was charged with
equimolecular amounts of 1 and 2, 3 and 4, or 5 and 6 and introduced
in the NMR probe. Spectra were recorded each 5 °C in the studied
temperature range (193-323 K) except when coalescence of signals
were observed. In this case the spectra were recorded each 1 °C in a
range of (10 °C over the coalescence temperatures.
X-ray Structural Determination of 3 and 6. Crystal, data collec-
tion, and refinement parameters are collected in Table 5. Suitable
crystals were selected and mounted on fine glass fibers with epoxy
cement. The unit cell parameters were determined from the angular
setting of a least-squares fit of 25 strong high-angle reflections. The
asymmetric unit for 3 contained a half independent molecule. Reflec-
tions were collected at 25 °C on a Nonius-Mach3 diffractometer
equipped with a graphite monochromated radiation source (λ ) 0.710 73
Å). None of the samples showed any significant intensity decay over
the duration of the data collection.
Data were corrected in the usual fashion for Lorentz and polarization
effects, and empirical absorption correction was not necessary (µ )
14.16 cm-1, 3, and 7.45 cm-1, 6). The space group was determined
from the systematic absence in the diffraction data. The structures were
solved by direct methods,54 and refinements on F2 were carried out by
full-matrix least-squares analysis.55 Anisotropic temperature parameters
were considered for all non-hydrogen atoms, while hydrogen atoms
were included in calculated positions but not refined. For the disordered
F2 and F21 atoms in 6, occupancies were refined initially and then
both fixed at 0.5. Crystallographic data and selected bond parameters
are collected in Tables 5 and 6, respectively.
(j) Reaction of 5 and Pd(C6HF4)2(cod). To a solution of Pd(C6-
HF4)2(cod) (55.9 mg, 0.11 mmol) in acetone (20 mL) complex 5 was
added (71,1 mg, 0.11 mmol). The reaction was stirred at room
temperature for 16 h. The resulting colorless solution was evaporated
1
to dryness. H NMR analyses showed that the reaction product was a
mixture of 7, 8, and 9 in a 1:1:2 ratio. All attempts to purify the mixture
by crystallization failed, and always an identical ratio of products was
obtained. 19F NMR of 9 (although the presence of signals of 9 can be
supposed from a change in integrals, only the signals that appear in
chemical shifts different from those of 7 and 8 are indicated): F2, δ
-110.93 (d, JFF ) 29) ppm; Fortho, δ -117.5 to -117.75 (m) ppm;
F
para, δ -161.41 (t, JFF ) 17.5), -161.47 (t, JFF ) 18.5), -163.63 (t,
JFF ) 19.0) ppm; Fmeta, δ -165.25 (m) ppm.
Cross Reactions in NMR Tube. (a) Cross Reaction Type 1.
Reaction of 3 and bpzpm. The dinuclear compounds 3, 4, 7, and 8
react with the corresponding free ligands to afford the mononuclear 1,
2, 5, and 6, respectively, in an apparent quantitative yield. The reactions
were monitored by 1H NMR. An example of the experimental procedure
is the following. A solid sample of 3 (20 mg, 0.024 mmol) was solved
in acetone-d6 (0.7 mL). This solution was frozen with an external bath
of liquid N2, and then bpzpm was added (5.1 mg, 0.024 mmol). The
tube was sealed and introduced into the NMR probe previously at 183
Results and Discussion
1
K. A H NMR spectrum of pure 1 (compared with a pure sample of
Synthesis of Ligands and Complexes. Compounds bpzpm44
and Me-bpzpm were prepared from the corresponding pyra-
zolate anion and 4,6-dichloropyrimidine. Reaction of 1 equiv
of [Pd(η3-2-Me-C3H4)(S)2]CF3SO3 (S ) acetone), prepared by
reaction of [Pd(η3-2-Me-C3H4)(µ-Cl)]2 with AgCF3SO3 in
acetone solution, with bpzpm or Me-bpzpm generated the
mononuclear complexes [{Pd(η3-C4H7)}(bpzpm)]CF3SO3 (1)
and [{Pd(η3-C4H7)}(Me-bpzpm)]CF3SO3 (2), respectively
(Scheme 1). The homologous complexes with two coordinated
allylpalladium fragments, [{Pd(η3-C4H7)}2(bpzpm)](CF3SO3)2
(3) and [{Pd(η3-C4H7)}2(Me-bpzpm)](CF3SO3)2 (4), were
prepared when a 2:1 molar ratio was used. Under similar
conditions the reaction of Pd(C6F5)2(cod) (cod ) 1,5-cyclo-
octadiene) or Pd(2,3,4,6-C6HF4)2(cod) with bpzpm in a 1:1
molar ratio led to the complex [{Pd(C6F5)2}(bpzpm)] (5) or
[{Pd(C6HF4)2}(bpzpm)] (6), whereas when a 2:1 molar ratio
was used, the homologous complex [{Pd(C6F5)2}2(bpzpm)] (7)
or [{Pd(C6HF4)2}2(bpzpm)] (8) was the corresponding reaction
product.
The reaction of the mononuclear complexes 1, 2, 5, or 6 with
the corresponding Pd precursors led to the respective symmetric
dinuclear complexes 3, 4, 7, or 8. The reaction of 3 or 4, even
at 183 K, with 1 equiv of the respective free ligand led
instantaneously to the mononuclear complexes. Identical reac-
tions with 7 or 8, bearing the bis(polyfluorophenyl)palladium
fragments, with bpzpm regenerated the mononuclear compounds
only at higher temperatures (258 K).
this compound at this temperature) was observed at 183 K. In a similar
way 2 was also formed from the corresponding reactants (4 and Me-
bpzpm). Compounds 5 and 6 were also formed as pure products in the
NMR tube at higher temperature (258 K) from the mixture of the
corresponding reactants when the temperature was slowly raised. NMR
spectra were recorded at intervals of 10 °C up to that for the complete
reaction.
(b) Cross Reaction Type 2. Reaction of 1 and Pd(C6F5)2(cod),
1:1 Ratio. Reactions of 1 with Pd(C6F5)2(cod) or Pd(C6HF4)2(cod)
afforded equimolecular mixtures of the homodinuclear compounds 3
and 7 or 3 and 8. An example of the experimental procedure is the
following. A mixture of 1 (5.4 mg, 0.01 mmol) and Pd(C6F5)2(cod)
(5.7 mg, 0.01 mmol) was introduced in an NMR tube. Acetone-d6 (0.7
1
mL) was added. When the reaction was monitored by H NMR, the
formation of an equimolecular mixture of 3 and 7 was observed, even
at 183 K.
(c) Cross Reaction Type 3. Reaction of 1 and Pd(C6F5)2(cod),
1:2 Ratio. Compound 1 (2.70 mg, 0.005 mmol) and 2 equiv of Pd-
(C6F5)2(cod) (5.7 mg, 0.01 mmol) were introduced in a NMR tube,
and they were made to react at room temperature in 0.7 mL of acetone-
d6. Formation of a mixture of 7 together with [Pd(η3-C4H7)(cod)]CF3-
SO3 and free cod in a 1:1:1 ratio was observed. The 1H NMR resonances
of the products were compared with those of the corresponding free
samples.
(d) Cross Reaction Type 4. Reaction of 1 and Me-bpzpm. In a
procedure similar to that described for cross reaction type 1, Me-
bpzpm and 1 where made to react. An equimolecular mixture of the
1
starting materials, 2 and bpzpm, was observed at 183 K by H NMR
(comparison with pure samples of these products at this temperature
was made). The mixture ratio was unaltered in the studied range of
temperatures (183-323 K).
(e) Cross Reaction Type 5. Reaction of 7 and 8. In an NMR tube,
7 (0.45 mg, 0.38 mmol) and 8 (0.40 mg, 0.38 mmol) were made to
react at room temperature in 0.7 mL of acetone-d6. A new complex, 9,
appeared until finally a mixture of 7, 8, and 9 in a 1:1:2 ratio was
When compound 5 was made to react with 1 equiv of Pd-
(C6HF4)2(cod) in acetone solution, a 1:1:2 mixture (determined
by NMR) of the symmetric complexes 7 and 8 and the
asymmetric derivative [{Pd(C6F5)2}{Pd(C6HF4)2}(bpzpm)] (9)
(55) Sheldrick, G. M. Program for the Refinement of Crystal Structures
from Diffraction Data; University of Go¨ttingen: Go¨ttingen, Germany,
1993.
(54) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Cryst. 1994, 435.

1156 Inorganic Chemistry, Vol. 39, No. 6, 2000
Go´mez-de la Torre et al.
Table 1. 1H NMR Data for bpzpm, Me-bpzpm Ligands, and Complexes 1-9a
2-Me-allylc
compoundb
bpzpm
H2
H5
H3′
H4′
H5′
H3′′
H4′′
H5′′
CH3
Ha
Hs
8.89 d
J25 ) 1.0
8.41
7.92 dd
6.65 dd
8.69 dd
J34 ) 1.5 J45 ) 2.9 J53 ) 0.7
7.74
Me-bpzpm 8.82 d
8.30
2.18d
8.44
J25 ) 1.0
9.35 bs
9.41 d
J25 ) 1.0
9.19 bs
9.29
1
8.52 bs 8.52 bs
8.48 8.61 d
7.12 bs
7.23 dd
9.48 bs
9.66 d
8.06 bs
8.20 d
J34 ) 1.5 J45 ) 2.7
7.90 bs
7.98
6.76 bs
6.84 dd
8.74 bs 2.26 3.46 bs
8.81 d
4.62 bs
1 (193 K)
2.24 3.39(a)
4.57(s)
4.64(s′)
4.58 bs
4.54(s)
4.62(s′)
4.71
J34 ) 2.0 J45 ) 3.1
3.49(a′)
2
8.34 bs 8.34 bs
8.41
2.29d
2.23d
9.27 bs
9.29
2.19d
2.12d
8.48 bs 2.26 3.44 bs
8.51
2 (193 K)
8.17
2.20 3.35(a)
3.45(a′)
2.27 3.52
3
9.83
9.15
8.60 d
7.18 dd
9.28 d
J34 ) 2.0 J45 ) 3.1
3a (183 K)
3b (183 K)
4
10.0
10.0
9.73 d
J25 ) 1.0
9.90
9.92
8.40
9.22
9.22
8.92
8.72 d
8.72 d
8.46
7.30 d
7.30 d
2.29d
9.18 d
9.18 d
9.04
2.16 3.42, 3.44(a)
2.18 3.48(2H,a′)
2.26 3.49
4.61(2H,s)
4.74, 4.79(s′)
4.67
4a (183 K)
4b (183 K)
5
8.56
8.56
8.55
8.74 bs
8.74 bs
8.06 d
2.22d
8.77 bs
8.77 bs
9.50 d
2.18 3.45, 3.50(a)
2.22 3.42, 3.49(a′)
4.62, 4.75(s)
4.61, 4.65(s′)
2.22d
7.02 dd
7.84 d
6.73 dd
8.67 d
8.69 d
J34 ) 2.2 J45 ) 3.2
8.05 d 6.99 dd
J34 ) 1.9 J45 ) 3.1
7.98 d 7.14 dd
J34 ) 2.1 J45 ) 3.1
7.85 d 7.10 dd
J34 ) 2.0 J45 ) 3.2
J34 ) 1.5 J45 ) 2.9
7.74 d 6.73 dd
J34 ) 1.7 J45 ) 2.9
6
7
8
8.33 d
J25 ) 1.0
7.75
8.54
9.26
9.20
9.46 d
9.19 d
9.16 d
C6HF4
6.67(bs)
7.80
C6HF4
6.46, 6.53,
6.63 (2H), (bs)
[6.50 (2H) (bs)]
[6.63 (2H) (bs)]
9e
7.77
9.23
7.95 d
J34 ) 2.0
[7.14]
[9.19]
7.86
JHH ) 2.0
[7.10]
[9.16]
a T ) 293 K if not indicated; δ, ppm; J, Hz; solvent ) acetone-d6. See Scheme 1 for numbering scheme. Unless specified the signals are singlets;
d ) doublet, bs ) broad singlet. b a and b denote the two different stereoisomers (meso and dl pair). c Ha ) Hanti, Hs ) Hsyn (a, s, or s′, a′; see
Scheme 1). d Me group on the C4′ or C4′′ positions of the pyrazole. e The values in square brackets correspond to signals overlapping with those of
complexes 7 and 8. Hn′′ corresponds to the protons of the pyrazol group coordinated to the fragment [Pd(C6HF4)2].
was obtained, which corresponds to a statistical distribution of
the similar metallic fragments. All attemps to isolate 9 as a pure
product failed, and always the thermodynamic mixture of 7, 8,
and 9 was obtained. However, attempts to prepare asymmetric
dinuclear complexes with both allyl and bispolyfluoroaryl
fragments attached to the same ligand by reaction of the
mononuclear complexes with a different Pd precursor failed as
it was monitored by NMR. Equimolecular amounts of the
corresponding symmetric dinuclear complexes were obtained
in these reactions. Furthermore, reaction of complex 1 with 2
equiv of Pd(C6F5)2(cod) (acetone-d6, NMR tube) led to a
complete and instantaneous displacement of the allylpalladium
fragment with the formation of complex 7 and [Pd(η3-C4H7)-
(cod)]+ (see eq 1).
fragments are very similar (i.e., Pd(C6F5)2 and Pd(C6HF4)2) is
the asymmetric compound observed.
This last conclusion opens the possibility of considering the
ligand as a ditopic receptor56 that, after the coordination of the
first metallic center, induces the bonding in the second
coordination position of a near-identical metallic fragment.
Consequently, homotopic (autotopic) cosystems56 with identical
subunits are formed against a statistical distribution of the
fragments. This behavior is comparable to the chemical
symbiosis57 very often used in metallic complexes.58 In our case,
this phenomenon is driven by the ligand instead of being directed
by the metal center.
Characterization of 1-9. Complexes 1-8 were character-
ized by NMR and IR spectroscopy and elemental analysis (9
only by NMR). 1H and 13C NMR data of the complexes at room
and low temperature, along with those of the starting ligands,
are compiled in Tables 1 and 2. Although some 1H NMR values
of complex 9 are tentative because of overlapping with signals
of 7 and 8, some of these resonances have been seen separately
at temperatures different from room temperature. The pyrazole
protons H3′ and H5′ were assigned according to their different
coupling constants with H4′ (J45 > J34).59,60 The assignment of
the pyrazole carbons was made on the basis of the general order
in chemical shifts59-61 δ3 > δ5 > δ4, which was confirmed in
[{Pd(η3-C4H7)}(bpzpm)]Tf (1) + 2Pd(C6F5)2(cod) f
[{Pd(C6F5)2}2(bpzpm)] (7) + [Pd(η3-C4H7)(cod)]Tf + cod
(1)
The following conclusions may be drawn from these results:
(i) The bis(polyfluorophenyl)palladium groups are more strongly
bonded than the allylpalladium cations. (ii) The bonds between
the palladium fragments and the ligands are stronger in the
mononuclear than in the dinuclear complexes as a consequence
of the partial deactivation of the second coordination position
of the ligand when the first one is implicated in the coordination.
(iii) The asymmetric dinuclear complexes are less stable than
the symmetric dinuclear species, and only when the two metallic
1
complex 7 by a H-13C shift-correlated spectrum.
(57) Jo¨rgensen, C. K. Inorg. Chem. 1964, 3, 1201.
(58) Pearson, R. G. Inorg. Chem. 1973, 12, 712.
(59) Oro, L. A.; Esteban, M.; Claramunt, R. M.; Elguero, J.; Foces-Foces,
C.; Cano, F. H. J. Organomet. Chem. 1984, 276, 79.
(60) Esteruelas, M. A.; Oro, L. A.; Apreda, M. C.; Foces-Foces, C.; Cano,
F. H.; Claramunt, R. M.; Lo´pez, C.; Elguero, J.; Begtrup, M. J.
Organomet. Chem. 1988, 344, 93.
(56) Lehn, J.-M. Supramolecular Chemistry, Concepts and PerspectiVes;
VCH: Weinhein, 1995.

Pd(II) Complexes
Inorganic Chemistry, Vol. 39, No. 6, 2000 1157
2-Me-allyl
Table 2. 13C {1H} NMR Data for bpzpm, Me-bpzpm Ligands, and Complexes 1-9a
compound
bpzpm
C2
C4
C5
C6
C3′
C4′
C5′
C3′′
C4′′
C5′′
CH3
CH2
C
CH3
159.3 159.7 95.7 159.7
145.0 110.1 128.4
146.0 120.7 126.6 8.9
Me-bpzpm 159.1 159.2 94.6 159.2
1
2
3
4
162.2 156.6 96.3 160.2 148.6 113.7 133.2 146.8 112.1 130.0
161.9 156.3 95.0 159.8 148.2 127.7 130.6 146.0 124.1 127.2 8.9
164.6 157.2 97.4 157.2 150.3 114.6 133.9
62.3
136.2
23.4
23.3
23.1
23.1
61.8
63.2
63.1
135.6
136.6
136.6
164.7 157.0 96.2 157.0 151.3 125.9 131.4
9.0
Co
Cm
136.6 bd
Cp
138.5 bd
5
6
7
160.0 157.0 96.0 159.2 146.0 112.8 132.9 146.2 111.6 129.7 148.5 bd
1JCF ) 240 1JCF ) 240 1JCF ) 240
C6HF4(CH) ) 99.0-100.0
Co
158.9 157.0 95.9 159.9 146.5 112.8 132.8 146.0 111.6 129.8
156.5 159.1 96.8 159.1 148.0 114.5 133.3
Cm
136.6 bd
Cp
138.4 bd
148.4 bd
1JCF ) 240 1JCF )240 1JCF ) 240
C6HF4(CH) ) 98.7-100.0
8
157.3 159.0 96.7 159.0 147.5 114.2 132.9
157.5 159.0 96.8 159.0 147.6 114.3 133.0 147.9 114.3 133.2
9b
C6HF4(CH) ) [98.7-100.0]
a T ) 295 K; δ, ppm; solvent ) acetone-d6. See Scheme 1 for numbering scheme. Unless specified, the signals are singlets. bd ) broad doublet.
bThe values in square brackets correspond to signals overlapping with those of complexes 7 and 8.
Scheme 2. Schematic View of the Possible Rotamers for
Complexes 6 (a) and 8 (b) Considering an Averaged
Perpendicular Orientation of the C6HF4 Groups
The symmetrical binuclear complexes 3, 4, and 7 show a
symmetrical pattern with one set of signals for the pyrazole
protons and carbons and for the pyrimidine C4 and C6. In
contrast, the asymmetrical mononuclear complexes 1, 2, 5, and
6 and the binuclear complex 9 show two sets of signals for
each of the above nuclei. Compound 8, although it bears four
identical ligands, is not strictly symmetrical owing to the
presence of several atropoisomers (see later on), but the effect
on the resonances, even that associated with C2 and C3′, is too
small to observe any splitting of these signals (Tables 1 and 2).
The 1H and 13C NMR resonances of the coordinated pyrazole
and pyrimidine rings are generally shifted to higher frequency
as a consequence of their coordination to the palladium center.
However, in complexes with bispolyfluorophenyl fragments (5-
9) the pyrazole and especially the pyrimidine protons adjacent
to the coordinated nitrogens (H3′ of pyrazole and H2 of
pyrimidine) are shifted to lower frequency with respect to the
free ligands as a consequence of the ring current anisotropy of
the polyfluorophenyl groups,62 as has been found in several
complexes with other aromatic rings.63,64 This strong effect (up
to -2 ppm) produces the inversion of the signals corresponding
to H2 and H5.
We have observed for these complexes that, although
asymmetric allylic groups are expected, the Hanti, Hsyn protons
and the terminal allylic carbons appear as unique signals in each
case at room temperature. These observations point to a fluxional
behavior similar to that observed for other allylpalladium
complexes with N-donor ligands.49,65
The 19F NMR spectra (see Experimental Section) of 5 and 7
clearly show the existence of two different C6F5- groups (cis
to pyrazole or pyrimidine) with the two Fortho or Fmeta atoms
equivalent in each ring. This may be indicative of free rotation
of the C6F5 groups, but taking into account the plane of
symmetry existing in the (bpzpm)Pd moiety, a static and
perpendicular disposition of these rings could also account for
the 19F NMR observations. The first possibility is less likely
considering the steric hindrance in the coordination environment
of the Pd center.66-72
To distinguish between these two alternatives, the analogous
derivatives 6 and 8 were synthesized, and these contain the
nonsymmetrically substituted tetrafluorophenyl groups (the H
atom is in one of the meta positions). If the phenyl rings were
freely rotating, two types of tetrafluoro groups would also be
observed for each complex. However, in an averaged perpen-
dicular situation with restricted rotation several atropoisomers66
would be expected depending on the relative orientation of the
C6HF4 groups. This situation is represented in Scheme 2, where
H represents the orientation of this atom of the phenyl ring with
respect to the molecular plane. For complex 6 two dl pairs (syn-
H,H and anti-H,H) are expected, whereas for 8, with two Pd-
(C6HF4)2 fragments, up to four dl pairs and two meso forms
could be formed. 19F NMR spectroscopy has been useful for
studying this problem, and the assignment of the different
fluorine resonances has been made on the basis of 19F-19F
(66) Albe´niz, A. C.; Casado, A. L.; Espinet, P. Organometallics 1997, 16,
5416.
(67) Casares, J. A.; Coco, S.; Espinet, P.; Lin, Y. S. Organometallics 1995,
14, 3058.
(61) Fajardo, M.; de la Hoz, A.; D´ıez-Barra, E.; Jalo´n, F. A.; Otero, A.;
Rodr´ıguez, A.; Tejeda, J.; Belletti, D.; Lanfranchi, M.; Pellinghelli,
M. A. J. Chem. Soc., Dalton Trans 1993, 1935.
(62) Alkorta, I.; Elguero, J. New J. Chem. 1998, 381.
(63) Orellana, G.; Alvarez-Ibarra, C.; Santoro, J. Inorg. Chem. 1988, 27,
1025.
(68) Deacon, G. B.; Lawrenz, E. T.; Hambley, T. W.; Rainone, S.; Webster,
L. K. J. Organomet. Chem. 1995, 493, 205.
(69) Sarsfield, M. J.; Ewart, S. W.; Tremblay, T. L.; Roszak, A. W.; Baird,
M. C. J. Chem. Soc., Dalton Trans. 1997, 3097.
(70) Casares, J. A.; Espinet, P.; Martinez de Ilarduya, J. M.; Lin, Y. S.
Organometallics 1997, 16, 770.
(64) Steel, P. J.; Constable, E. C. J. Chem. Soc., Dalton Trans. 1990, 1389.
(65) Elguero, J.; Fruchier, A.; de la Hoz, A.; Jalo´n, F. A.; Manzano, B. R.;
Otero, A.; Go´mez-de la Torre, F. Chem. Ber. 1996, 129, 589.
(71) Casares, J. A.; Espinet, P. Inorg. Chem. 1997, 36, 5428.
(72) Brown, J. M.; Pe´rez-Torrente, J. J.; Alcock, N. W. Organometallics
1995, 14, 1195.

1158 Inorganic Chemistry, Vol. 39, No. 6, 2000
Go´mez-de la Torre et al.
correlation spectroscopy (COSY) experiments and the expected
chemical shifts according to literature.66 The resonances that
most effectively indicate the presence of atropoisomers are those
of F4. Four different doublets in a 1:1:1:1 ratio are observed
for this fluorine in the spectrum of complex 6, which indicates
the existence of the four different C6HF4 groups expected for
the two dl pairs of 6 (1:1 ratio). Although in some casual
coincidence of chemical shifts, the appearance of three doublets
(2:1:1 ratio) for F2 and two complex signals (3:1 ratio) for F6
are in accordance with the restricted rotation of the two
polyfluorophenyl groups. F3 only gives rise to two multiplets
of both complexes coalesced, and the same phenomenon was
observed for the Hanti signals. This is clearly a consequence of
the exchange of the allyl-Pd fragments between the two ligands.
q
The ∆Gc values at the coalescence temperatures were calcu-
lated: ∆Gc 303 ) 63.4 and ∆Gc 307 ) 65.7 kJ mol-1 for Hanti
and Hsyn, respectively.
q
q
A similar experiment was carried out for the dinuclear
complexes 3 and 4 (which have the second coordination position
blocked by an allylpalladium unit), and these compounds
showed an unchanged spectrum over the temperature range
studied (183-323 K). According to these data, the allylpalla-
dium fragment must be weakly coordinated in complexes 1-4,
but contrary to the relative residual charge of the complexes,
the barrier for the exchange of these Pd groups is higher (in
fact, unattainable in our experiment) in the dinuclear complexes
3 and 4 than in the mononuclear derivatives 1 and 2. This result
points to the participation of the second coordination position
in the process of interchange. This hypothesis is in accordance
with the results of the study of the fluxional behavior of complex
1 (see below).
A mixture of equimolecular amounts of the mononuclear
complexes 5 and 6 showed no changes over the temperature
range studied (183-323 K), and this is consistent with the
polyfluorophenylpalladium groups being more strongly bonded
to the ligands.
The reaction of 7 with 8 at room temperature and monitored
by NMR led to the progressive formation of 9. Finally, a
statistical distribution of the polyfluorophenyl groups with the
establishment of the equilibrium ratio 7/8/9 ) 1:1:2 took place.
The corresponding resonances are separated in the NMR
spectrum over the temperature range studied (183-323 K), and
no coalescences were observed. The equilibrium 7 + 8 h 9
must be established by thermodynamic control, but the energy
barrier for the exchange is too high to observe the process by
means of NMR coalescences.
1
with identical integrals. The H and 13C NMR spectroscopies
are not able to show the existence of atropoisomers in this
compound probably because of very small differences in
chemical shifts. The C6HF4 signal is very broad and complex,
and in the C6HF4 (CH) resonance, although several lines are
observed, the existence of C-F coupling constants prevents an
unequivocal elucidation of the signal. For complex 8, although
it is not possible to observe separately the 16 signals theoretically
expected for the whole set of isomers, at least 6 resonances are
seen for F4. (Probably only the local symmetry has a noticeable
effect on the chemical shifts.) This is also in accordance with
the existence of several atropoisomers considering that only two
signals would be expected if the fluorophenyl rings were in a
fast rotation regime. The rest of the fluorine atoms F2, F3, and
F6 also show patterns more complicated than those expected
for a nonrestricted rotation of the fluorophenyl rings. Besides,
in the 1H NMR spectrum a set of three broad signals in a 2:1:1
ratio is observed for C6HF4 while two signals would be expected
if the polyfluorophenyl groups were freely rotating. Therefore,
we can conclude that in complexes 6 and 8, and by extrapolation
also in 5 and 7, there is a restricted rotation of the polyfluo-
rophenyl groups and they are situated in an averaged perpen-
dicular position with respect to the coordination plane. Neither
close nor distant interannular Fortho-Fortho couplings were
observed in the COSY experiment for 8, a situation that is in
contrast with the observation of other authors66 for this type of
through-space contact in comparable polyfluorophenyl groups
with restricted rotation.
For complex 9, a situation similar to that previously described
for 6 would be expected, but unfortunately, 9 is always in a
thermodynamic mixture with 7 and 8, which precludes a clear
identification of its 19F resonances. Only the signals unambigu-
ously discerned have been indicated in the Experimental Section,
and unfortunately, the existence of atropoisomerism cannot be
conclusively stated, although the presence of three different
resonances for Fpara of the C6F5 groups could be estimated as a
valuable indication.
Cross Reaction Experiments. Several cross reaction experi-
ments were envisaged to confirm the ease of mobility of the
Pd organometallic fragments on the R-bpzpm ligands and to
show the role of the free coordination position of the ligand in
the case of the mononuclear complexes.
From the results described in this section it can be concluded
that the exchange between the polyfluorophenylpalladium
fragments must occur at higher energies than with allylpalladium
groups, but in any case, the dissociation of the metallic moieties
from the N-donor ligands is possible. The exchange is favored
by the existence of a free coordination position in the ligand.
Fluxional Behavior of Complexes 1 and 3. (a) Complex
3. In the 1H NMR spectra, the methyl, Hsyn, and Hanti signals of
the allyl groups are single at room temperature while they are
split at 183 K (see Table 1). Assignment of Hsyn and Hanti
resonances was performed by nuclear Overhauser effect (NOE)
experiments and H,H correlations. (For example, irradiation at
the frequency of H2 of the pyrimidine ring shows an NOE in
the Hsyn and Hanti close to this ring; see Hs′ and Ha′ in Table 1,
and see also Scheme 1.) Some coalescences have been measured
and the corresponding free activation energies at the coalescence
q
temperature (∆Gc ) calculated (see Table 3).
All these data correspond to the existence of two intercon-
verting compounds: a meso form and a dl pair of enantiomers
(see Scheme 3), similar to what we have found for complexes
with related ligands.49 The molecular structure of the meso form
has been determined by an X-ray diffraction study (see below).
The existence at room temperature of a unique signal for the
Hsyn and the Hanti protons implies that at this temperature not
In the first experiment equimolecular amounts of 1 and the
free ligand Me-bpzpm in acetone-d6 solution were mixed. A
fast reaction led to a statistical distribution of ligands with
formation of compound 2 and free bpzpm according to the
equilibrium
1 + Me-bpzpm h 2 + bpzpm
(2)
(73) Crociani, B.; Di Bianca, F.; Giovenco, A.; Boschi, T. Inorg. Chim.
Acta 1987, 127, 169.
(74) Hansson, S.; Norrby, P. O.; Sjo¨gren, M. P. T.; A° kermark, B.;
Cucciolito, M. E.; Giordano, F.; Vitagliano, A. Organometallics 1993,
12, 4940.
In a different experiment, equimolecular amounts of com-
plexes 1 and 2 were dissolved in acetone-d6, and separated allyl
resonances for each compound were observed at room temper-
ature. As the temperature was increased, the two Hsyn resonances

Pd(II) Complexes
Inorganic Chemistry, Vol. 39, No. 6, 2000 1159
Table 3. Observed Coalescences and Calculated Free Activation
allylpalladium group. Such an intermolecular process could also
explain the equivalence of the two halves of the allyl group.
1
Energies from the Variable Temperature H NMR Spectra of 1 and
3 in Acetone-d6 Solutiona
To determine if an intermolecular process induces the
equivalence of the two pyrazolyl rings and if this process is
also the origin of the syn-syn, anti-anti allylic interconversion,
we decided to determine the coalescence temperatures of the
allyl and pyrazolyl protons at different concentrations using
1,1,2,2-tetrachloroethane-d2 as the solvent. In Table 4 the
coalescence temperatures and the calculated free energies of
activation for Hsyn, Hanti, and also H3, H4, and H5 of pyrazol at
various concentrations are given, and Figure 3 represents the
variation of ∆Gcq as a function of the coalescence temperature
for each proton and concentration.
complex
coalescenceb
Tc (K)c
∆Gcq (kJ/mol)d
3
Ha + Ha
Hs′ + Hs′
209
214
233
240
255
263
46.3
45.8
50.0
49.1
53.9
54.2
(Ha + Ha) + Ha′
(Hs′ + Hs′) + Hs
Hs + Hs′
1
Ha + Ha′
a See Figures 1 and 2a. b See Scheme 1 for assignment. c Coalescence
temperatures. d Free activation energies at the coalescence temperatures
calculated by ∆Gcq ) aT[9.972 + log(T/δν)] (a ) 1.914 × 10-2).
Scheme 3
From Table 4 and Figure 3 the following is evident. (i) The
free activation energy for the interchange of the pyrazolyl
protons is always markedly higher than for the interchange of
the allyl protons, indicating the existence of two different
processes. (ii) There is a clear tendency in the variation of the
free activation energy with concentration in the pyrazolyl protons
with ∆Gcq values that increase when the concentration decreases,
and this corresponds to an intermolecular process. This effect
is negligible in the allyl protons, since this corresponds to an
intramolecular mechanism. (iii) A negative activation entropy
has been found for the process that interchanges the two
pyrazolyl fragments, and this would be expected for an
associative process. Although the sign of the activation entropy
cannot be unequivocally deduced for the syn-syn, anti-anti
allyl interchange, the values obtained for ∆Gcq point to a positive
sign for this parameter. (iv) The free activation energy values
found for the allyl interchange in acetone are smaller than those
determined in the less coordinating solvent 1,1,2,2-tetrachlo-
roethane-d2, a phenomenon that could be due to the participation
of the solvent molecules in the process.
only does an isomer interconversion take place but also a syn-
syn, anti-anti interchange in each allylic group. For a similar
complex with a central triazine ring,49 we have found that the
apparent allyl rotation implying Pd-N bond rupture65,73-81 is
the origin of both types of interconversion. For a more detailed
explanation about the mechanism, see refs 49 and 65.
1
(b) Complex 1. Low-Temperature Study. The H NMR
spectrum of 1 at room temperature in acetone-d6 solution
exhibits the signals for Hsyn and Hanti of the allyl group as one
singlet each. Because both Hsyn and Hanti protons are situated
in different environments, this equivalence could be indicative
of an apparent allyl rotation similar to that observed for complex
3.
From the data reported, we propose that two different
mechanisms are operating in complex 1. The process of
palladium coordination site exchange that interconverts the two
pyrazolyl groups must be associative in nature, possibly with
the participation of the free coordination site of another molecule
of the ligand, as shown in Scheme 4. This is in accordance with
the different barriers observed in the cross reaction experiments
between mononuclear and dinuclear allylic derivatives. An
apparent allyl rotation with a smaller energy barrier must also
be operating in the complex. Because of the negligible effect
of the concentration and the possible positive activation entropy,
we propose a dissociative mechanism as the most likely
alternative. Stabilization of the three-coordinate intermediate
could be achieved by the coordination of the acetone molecules
or even the counterion.
X-ray Structure of 3. To support our studies, we determined
the molecular structure of 3 (meso form) by X-ray diffraction.
The crystal structure consists of a dinuclear Pd cation and two
triflate counterions, one of which is disordered. An ORTEP plot
of the cation is shown in Figure 4, and a selected list of bond
lengths and angles is given in Table 6.
The cation lies on a crystallographic mirror plane perpen-
dicular to the molecular plane, which contains the atoms C(10)
and C(8), so that only half of the molecule is crystallographically
independent. The geometry around the Pd(1) atom is ap-
proximately square planar, and the five-membered chelate ring,
including the Pd atom, shows only very small deviations from
planarity. The dihedral angle between the pyrazole and the
pyrimidine fragments is only 6.0(1)°. The Pd(1)-N(2) and Pd-
(1)-N(9) bonds form the basis of the five-membered chelate
ring, and the distances are only slightly different [Pd(1)-N(2),
At 183 K two signals for both Hsyn (4.57 and 4.64) and Hanti
(3.39 and 3.48) are observed. The assignment of these protons
was performed by NOE experiments similar to those carried
out for complex 3. When the temperature is increased, coales-
cence of Hsyn (Tc ) 255 K) and Hanti (Tc ) 263 K) is achieved
q
(see Figure 2a). The calculated free activation energies (∆Gc )
are given in Table 3, and they are comparable to the corre-
sponding values for the same process in 3.
(c) Complex 1. High-Temperature Study. Increasing the
temperature to 323 K leads to a clear broadening of the pyrazole
signals, although the boiling point of the solvent prevents the
determination of the coalescence temperatures. These coales-
cences have been clearly observed using 1,1,2,2-tetrachloro-
ethane-d2 as solvent (see Figure 2b). Because of the lack of a
nitrogen atom in the 5-position of the central ring to assist the
palladium fragment in its migration between the two coordina-
tion sites of the ligand, the equivalence of the pyrazole nucleus
should be explained by an intermolecular exchange of the
(75) Crociani, B.; Antonaroli, S.; Paci, M.; Di Bianca, F.; Canovese L.
Organometallics 1997, 16, 384.
(76) Albinati, A.; Kunz, R. W.; Amman, C. J.; Pregosin, P. S. Organo-
metallics 1991, 10, 1800.
(77) Gogoll, A.; O¨ rnebro, J.; Grennberg, H.; Ba¨ckvall, J. E. J. Am. Chem.
Soc. 1994, 116, 3631.
(78) Gogoll, A.; Grennberg, H.; Axe´n, A. Organometallics 1997, 16, 1167.
(79) Jalo´n, F. A.; Manzano, B. R.; Otero, A.; Rodr´ıguez-Pe´rez, M. C. J.
Organomet. Chem. 1995, 494, 179.
(80) Ferna´ndez-Gala´n, R.; Jalo´n, F. A.; Manzano, B. R.; Rodr´ıguez-de la
Fuente, J.; Vrahami, M.; Jedlicka, B.; Weissensteiner, W.; Jogl, G.
Organometallics 1997, 16, 3758.
(81) Go´mez-de la Torre, F.; Jalo´n, F. A.; Lo´pez-Agenjo, A.; Manzano, B.
R.; Rodr´ıguez, A.; Sturm, T.; Weissensteiner, W. Organometallics
1998, 17, 4634.

1160 Inorganic Chemistry, Vol. 39, No. 6, 2000
Go´mez-de la Torre et al.
1
Figure 1. Variable-temperature H NMR study (acetone-d6) of complex 3 in the allylic region. See Table 1 for assignments. A simultaneous
syn-syn, anti-anti, and meso ) dl isomer exchange of these two isomers is observed (see Scheme 3).
Figure 2. Variable-temperature 1H NMR study of complex 1 in the allylic (a) (acetone-d6) and the aromatic (b) (1,1,2,2-tetrachloroethane-d2, 2.87
× 10-2 mol/L) regions. Temperatures are in kelvin. In the allylic region an apparent rotation of the allyl unit is observed. In the aromatic region
the coordination site exchange of the allyl-Pd group on the ligand is observed.
1
Table 4. Observed Coalescences and Calculated Free Activation Energies from the Variable Temperature H NMR Spectra at Different
Concentrations of 1 in 1,1,2,2-Tetrachloroethane-d2 Solutiona
∆Gcq
∆Gcq
[1]b (mol/L)
2.87 × 10-2
coalescence
Tc (K)c
(kJ/mol)d
[1]b (mol/L)
1.21 × 10-2
coalescence
Tc (K)c
(kJ/mol)d
Ha + Ha′
Hs + Hs′
H4′ + H4′′
H3′ + H3′′
279
270
355
345
330
279
271
362
350
334
58.9
59.7
72.1
71.7
71.0
58.9
59.7
73.6
72.7
72.4
Ha + Ha′
Hs + Hs′
H4′ + H4′′
H3′ + H3′′
H5′ + H5′′
Ha + Ha′
Hs + Hs′
H4′ + H4′′
H3′ + H3′′
H5′ + H5′′
280
272
371
360
339.3
280
273
371
360
339
59.3
60.2
75.4
74.9
73.4
59.1
60.3
77.1
75.5
74.0
H5 + H5 ′′
1
1.76 × 10-2
Ha + Ha
9.56 × 10-3
Hs + Hs′
H4′ + H4′′
H3′ + H3′′
H5′ + H5′′
a See Figure 2b. b Concentration of 1. c Coalescence temperatures. d Free activation energies at the coalescence temperatures calculated by ∆Gcq
) aT[9.972 + log(T/δν)] (a ) 1.914 × 10-2).
2.089(4) Å; Pd(1)-N(9), 2.132(4) Å] in accordance with the
expected difference in basicity of the respective heterocycles.
The Pd-η3-allyl distances are as follows: Pd(1)-C(11) )
2.100(6) Å; Pd(1)-C(12) ) 2.141(5) Å; Pd(1)-C(13) ) 2.119-
(6) Å. These latter values are in the range expected for a Pd-
(II)-allyl bond with nitrogen ligands in trans positions. The

Pd(II) Complexes
Inorganic Chemistry, Vol. 39, No. 6, 2000 1161
Table 5. Crystallographic Data for 3 and 6
3
6
empirical formula
fw
space group
a, Å
b, Å
C20H22F6N6O6Pd2S2
833.36
I2/m
9.368(2)
16.191(3)
20.228(6)
90
101.26(3)
90
C22H10F8N6Pd
616.76
P1h
8.845(6)
12.6609(9)
12.826(3)
88.45(2)
74.36(3)
89.32(2)
1382.6(10)
2
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
3009.1(12)
4
Τ, °C
25
0.710 70
1.840
14.16
0.0361
0.0875
25
0.710 70
1.481
7.45
0.0631
0.2061
λ, Å
F
calcd, g/cm3
Figure 3. Linear plot of ∆Gcq (kJ/mol) versus Tc (K) for complex 1
(see Table 4): (9) 2.87 × 10-2 mol/L; ([) 1.76 × 10-2 mol/L; (b)
1.21 × 10-2 mol/L; (2) 9.56 × 10-3 mol/L.
µ, cm-1
R1 [I > 2σ(I)]a
wR2 [I > 2σ(I)]b
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}0.5.
Table 6. Crystal Data and Structure Refinement for 6 and 3
bond length (Å)
bond angle (deg)
6
Pd(1)-C(11) 1.984(8)
Pd(1)-C(21) 1.999(7)
C(11)-Pd(1)-C(21)
C(11)-Pd(1)-N(6)
C(21)-Pd(1)-N(6)
C(11)-Pd(1)-N(1)
C(21)-Pd(1)-N(1)
N(6)-Pd(1)-N(1)
C(4)-N(1)-Pd(1)
N(6)-N(5)-C(4)
N(5)-N(6)-Pd(1)
85.9(3)
175.5(3)
98.7(3)
97.7(3)
175.5(3)
77.8(2)
115.2(5)
117.2(5)
113.9(4)
Pd(1)-N(6)
Pd(1)-N(1)
N(1)-C(4)
N(3)-C(2)
N(5)-N(6)
N(5)-C(4)
2.062(6)
2.101(6)
1.326(9)
1.387(9)
1.374(7)
1.411(8)
Figure 4. ORTEP view with atomic numbering of the cation of 3
(meso form) (30% probability ellipsoids).
3
Pd(1)-N(2)
2.089(4)
Pd(1)-C(11) 2.100(5)
N(2)-Pd(1)-C(11)
N(2)-Pd(1)-C(13)
C(11)-Pd(1)-C(13)
N(2)-Pd(1)-N(9)
C(11)-Pd(1)-N(9)
C(13)-Pd(1)-N(9)
N(2)-Pd(1)-C(12)
N(6)-N(2)-Pd(1)
N(2)-N(6)-C(7)
N(9)-C(7)-N(6)
C(7)-N(9)-Pd(1)
105.7(2)
172.8(2)
68.2(2)
Scheme 4
Pd(1)-C(13) 2.119(5)
Pd(1)-N(9)
2.132(4)
76.80(14)
175.6(2)
109.1(2)
138.1(2)
114.0(3)
119.1(3)
115.0(3)
115.1(3)
Pd(1)-C(12) 2.141(4)
N(2)-N(6)
N(6)-C(7)
C(7)-N(9)
C(7)-C(8)
N(9)-C(10)
1.371(5)
1.379(5)
1.361(5)
1.370(5)
1.329(4)
C(13)-C(12)-C(11) 115.2(5)
C(13)-C(12)-C(14) 122.3(6)
C(11)-C(12)-C(14) 121.0(6)
coordination plane defined by the Pd(1)-N(2)-N(9) atoms is
approximately perpendicular to the allyl ligand plane (defined
by the C(11)-C(12)-C(13) atoms) with a dihedral angle of
116.4(4)°. In the allyl ligand the C(12)-CH3 vector points away
from the metal. C(14) is 0.306(8) Å away from the allylic plane.
X-ray Structure of 6. An ORTEP plot of the structure of
complex 6 is shown in Figure 5, and a selected list of bond
lengths and angles is given in Table 6. The palladium atom is
in an approximately square plane geometry with the bpzpm
ligand coordinated in a bidentate fashion with distances Pd-
(1)-N(1) of 2.101(6) and Pd(1)-N(6) of 2.062(6) Å. As in
complex 3, the difference found in the Pd-N distances is in
accordance with the basicities of the respective heterocycles.
Two tetrafluorophenyl groups complete the coordination sphere
around the metal. The bpzm ligand is approximately planar.
The dihedral angle between the coordinated pyrazolyl and the
pyrimidine ring is 5.4(3)°, and that formed between pyrimidine
and the free pyrazolyl group is 5.1(3)°. The five-membered
metallacycle (Pd(1), N(6), N(5), C(4), N(1)) is also nearly planar.
The two tetrafluorophenyl groups are bound to the square-planar
unit (C21, N6, N1, C11, Pd1) with dihedral angles of 78.3(2)°
Figure 5. ORTEP view with atomic numbering of 6 (30% probability
ellipsoids).
and 105.9(3)°, the dihedral angle between the two rings being
93.8(3)°. In each unit cell a dl pair is present, with the two
enantiomers being related by an inversion center. Because the

1162 Inorganic Chemistry, Vol. 39, No. 6, 2000
Go´mez-de la Torre et al.
F(2) atom is disordered over the two meta positions (occupancy
factors of 0.5), the two dl pairs are present along the crystal.
These occupancy factors are in accordance with the presence
of the two atropoisomers in a 1:1 ratio, as has been deduced by
NMR.
The fluxional behavior of complexes 1 and 3 has been studied,
and the free energies of activation have been calculated from
the coalescence temperatures determined by NMR spectroscopy.
Two processes have been detected in complex 1: an intramo-
lecular apparent allyl rotation and an intermolecular process of
interconversion of the two pyrazolyl groups, with negative
activation entropy, for which an associative mechanism is
proposed. The existence of this latter process indicates that the
presence of a nitrogen atom is not necessary in the 5-position
of the central heterocycle of the ligands in order for an
interconversion of the two pyrazolyl groups to take place.
However, participation of a nitrogen atom in the 5-position
cannot be excluded when it is present.
Conclusions
We have described and characterized new mono- and di-
nuclear palladium complexes with the bpzpm and Me-bpzpm
ligands. Coordination of the first metallic center induces the
bonding in the second position in a kind of chemical symbiosis
driven by the ligand rather than the metal center, as is usually
the case. This behavior can also be considered as an expression
of molecular recognition, the ligand being a ditopic receptor.
The study of the exchange of the metallic fragments allows the
conclusion to be drawn that the strength of the Pd-N bonds
depends on the ancillary ligands and, in dinuclear complexes,
on the presence of identical or very similar metallic fragments.
The polyfluorophenyl groups have a restricted rotation around
the Pd-C bond and are situated on average in a perpendicular
orientation with respect to the coordination plane. Several
atropoisomers for the complexes 6 and 8, with m-C6HF4, have
been detected.
Acknowledgment. We gratefully acknowledge financial
support from the Direccio´n General de Investigacio´n Cient´ıfica
y Te´cnica (DGICYT) (Grant No. PB98-0315) of Spain.
Supporting Information Available: Two X-ray crystallographic
files, in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC990495X