solvent was removed under vacuum and the solid product 2 washed three
times with 2 ml portions of MeOH; yield, 17.1 mg (50%), mp = 174 °C
(with decomposition). 1H NMR (300 MHz, CDCl3, ppm): d 5.95 (d, 1H, pz-
5-H), 5.98 (d, 1H, pz-4-H), 7.49 (pseudo-t, 1H, Ph p-H), 7.76 (pseudo-t, 2H,
Ph m-H), 8.43 (d, 2H, Ph o-H). 13C NMR (125.77 MHz, CDCl3, ppm): d
104.4 (pz-4-C), 127.1, 128.2, 128.7, 133.5 (Ph), 139.8 (pz-5-C), 150.9 (pz-
3-C).
¶ Crystal data for 2: Bruker-AXS SMART-1000 diffractometer, M =
1178.20, orthorhombic, Pbcn (no. 60), a = 39.095(9), b = 12.364(4), c =
21.697(6) Å, V = 10487(5) Å3, Z = 8, Dc = 1.492 Mg m23, T = 298(2)
K, m = 1.065 mm21, 25417 reflections measured (1.88 < q < 23.27), 7535
independent (Rint = 0.158), R1 = 0.0526 (for 2874 reflections with I >
2s(I)), 0.185 (all data), wR2 = 0.071, for 622 parameters with no restraints.
b201301k/ for crystallographic data in CIF or other electronic format.
so as to avoid steric repulsions between them. In the
centrosymmetric Pbcn space group, the enantiomeric forms of 2
are co-crystallized as a racemic mixture. The coordination of
Pd-atoms approaches square planar, but with Pd(1), Pd(2) and
Pd(3) deviating from the best-fit plane of their four N-atoms and
away of the trimer centre by 0.040, 0.047, and 0.053 Å
respectively. In addition, the short Pd–Pd distances, of
2.997(1)–3.087(1) Å, impose a strain on the Pd–N–N angles,
which average 114.9(8)° for 2. Those angles are more acute than
the ideal 120° angle (for sp2 N-atoms) found in the unrestrained
structure of [Au(m-3,5-Ph2-pz)]3.7b The Pd–Pd distances of 2
are significantly shorter than the distances of L2Pd(m-pz*)2PdL2
complexes (3.115(1)–3.2297(7) Å),11 and the corresponding
MII–MII distances of L2M(m-pz*)2ML2 complexes of metals
with smaller ionic radii than palladium, such as Cu (3.85–3.89
Å), Zn (3.69 Å) and Cd (3.96 Å),9d but only marginally shorter
than the Pt–Pt distances of [Pt(m-pz)2]3, 3.034(1)–3.067(1)
Å.10
The structure of 2 is reminiscent of that of the homoleptic
carboxylate trimers [Pd(m-OCOR)2]3.12 The question of
whether Pd–Pd bonding interactions exist in those trimeric
palladium carboxylates with Pd–Pd distances of 3.131(1) to
3.191(1) Å, was originally raised, and answered negatively, by
Cotton et al. several years ago.12b Recently, however, palladium
acetate with Pd–Pd distances of 3.081(2)–3.203(1) Å, has been
shown to be luminescent.13 States arising from the formally
non-bonding interaction of filled palladium d-orbitals and
modified by d–p mixing have been proposed to be responsible
for the luminescence of [Pd(OCOMe)2]3. This, along with the
discovery of even shorter Pd–Pd distances in 2, bring up again
the question regarding the nature of d8–d8 interactions in
palladium trimers.
1 P. Espinet, K. Soulantica, J. P. H. Charmant and A. G. Orpen, Chem.
Commun., 2000, 917.
2 R.-D. Schnebeck, E. Freisinger, F. Glahé and B. Lippert, J. Am. Chem.
Soc., 2000, 122, 1381; R.-D. Schnebeck, E. Freisinger and B. Lippert, J.
Chem. Soc., Chem. Commun., 1999, 657; R.-D. Schnebeck, L.
Randaccio, E. Zangrando and B. Lippert, Angew. Chem., Int. Ed., 1998,
37, 119.
3 R. F. Carina, A. F. Williams and G. Bernardinelli, Inorg. Chem., 2001,
40, 1826; S. Rüttimann, G. Bernardinelli and A. F. Williams, Angew.
Chem. Int., Ed. Engl., 1993, 32, 392.
4 J. R. Hall, S. J. Loeb, G. K. H. Shimizu and G. P. A. Yap, Angew. Chem.,
Int. Ed., 1998, 37, 121.
5 S. R. Grap, L. G. Kuz’mina, O. Y. Burtseva, M. A. Porai-Koshits, A. P.
Kurbakova and I. A. Efimenko, Russ. J. Inorg. Chem., 1991, 36, 810.
6 G. A. Ardizzoia, S. Cenini, G. La Monica, N. Masciocchi, A. Maspero
and M. Moret, Inorg. Chem., 1998, 37, 4284; M. K. Ehlert, S. J. Rettig,
A. Storr, R. C. Thompson and J. Trotter, Can. J. Chem., 1992, 70, 2161;
M. K. Ehlert, S. J. Rettig, A. Storr, R. C. Thompson and J. Trotter, Can.
J. Chem., 1990, 68, 1444; R. G. Raptis and J. P. Fackler Jr., Inorg.
Chem., 1988, 27, 4179.
7 F. Meyer, A. Jacobi and L. Zsolnai, Chem. Ber./Recueil., 1997, 130,
1441; H. H. Murray, R. G. Raptis and J. P. Fackler Jr., Inorg. Chem.,
1988, 27, 26.
8 B. Bovio, F. Bonati and G. Banditelli, Inorg. Chim. Acta, 1984, 87,
25.
9 M. K. Ehlert, A. Storr, R. C. Thompson, F. W. B. Einstein and R. J.
Batchelor, Can. J. Chem., 1993, 71, 331; M. K. Ehlert, S. J. Rettig, A.
Storr, R. C. Thompson and J. Trotter, Can. J. Chem., 1991, 69, 432; M.
K. Ehlert, S. J. Rettig, A. Storr, R. C. Thompson and J. Trotter, Can. J.
Chem., 1989, 67, 1970; N. Masciocchi, G. A. Ardizzoia, A. Maspero, G.
LaMonica and A. Sironi, Inorg. Chem., 1999, 38, 3657.
10 W. Burger and J. Strähle, Z. Anorg. Allg. Chem., 1985, 529, 111.
11 L. R. Falvello, J. Forniés, A. Martín, R. Navarro, V. Sicilia and P.
Villarroya, Chem. Commun., 1998, 2429; V. K. Jain, S. Kannan and E.
R. T. Tiekink, J. Chem. Soc., Dalton Trans., 1993, 3625; V. K. Jain, S.
Kannan and E. R. T. Tiekink, J. Chem. Soc., Dalton Trans., 1992,
2231.
The structural parallel between carboxylate and pyrazolato
complexes, exemplified here by the comparison of [Pd(m-
OCOR)2]3 and [Pd(m-3-Ph-pz)2]3, is pointing to wide un-
explored areas of pyrazole chemistry. Studies are under way to
explore the implications of the palladium–pyrazolato metal-
lacycle opening/closing reactions in homogeneous catalysis.
This work is supported by the DOD-EPSCoR DAAH04-
96-1-0199 grant.
Notes and references
† cis-PdCl2(3-Ph-pzH)2 is prepared quantitatively from the reaction of
(NH4)2PdCl4 and 10% excess of 3-Ph-pzH in MeOH.
‡ The poor quality of the crystals of 1 have only allowed a preliminary X-
ray structural study. However, the stoichiometry and the heavy atom
coordinates of 1, as depicted in Scheme 1, are established with certainty.
¯
Preliminary crystal data for 1: triclinic, P1, a = 10.441(5), b = 11.228(5),
c = 25.672(11) Å, a = 96.225(9), b = 92.231(8), g = 106.875(9)°, V =
2855(2) Å3, Z = 2, R1 = 0.1526 for 667 parameters and 1610 reflections
with I > 2s(I)).
§ Preparation of 2: to 40.5 mg (0.087 mmol) of cis-PdCl2(3-Ph-pzH)2 in 3
ml CH2Cl2 was added 2.4 ml of a 0.072 M NEt3/CH2Cl2 solution (0.174
mmol). The orange solution changed rapidly to yellow and after 3 h the
12 N. N. Djalina, C. V. Dargina, A. N. Sobolev, T. M. Buslaeva and I. P.
Romm, Koord. Khim., 1993, 19, 57; D. P. Bancroft, F. A. Cotton, L. R.
Falvello and W. Schwotzer, Polyhedron, 1988, 7, 615; F. A. Cotton and
S. Han, Rev. Chim. Miner., 1985, 22, 277; A. C. Skapski and M. L.
Smart, Chem. Commun., 1970, 658.
13 H. Kunkely and A. Vogler, Chem. Phys. Lett., 1999, 308, 169.
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