Synthesis and molecular structure of [{Pd2(CH2C6H4P(o-tolyl) 2-κC,F)2(μ3-3,5-dmpz-N,N′,C 4)2Ag(μ-ClO4)}2] (3,5-dmpz = 3,5-dimethylpyrazolato), a silver derivative showing unprecedented η1-azolato coordination

Article abstract of DOI:10.1039/a805938a

The reaction of [Pd₂(CH₂C₆H₄P(o-tolyl) ₂-κC,P)₂(μ-3,5-dmpz)₂] (1) with AgClO₄ renders [{Pd₂(CH₂C₆H₄P(o-tolyl) ₂-κC,P)₂(μ₃-3,5-dmpz-N,N′,C ⁴)₂Ag(η²-μ-ClO₄)} ₂] (2), a palladium-silver derivative displaying an unprecedented dmpz bridging ligand η¹ bonded to the Ag centers, involving only the C⁴ atom of each dmpz ligand.

Full text of DOI:10.1039/a805938a

Synthesis and molecular structure of
[{Pd2(CH2C6H4P(o-tolyl)2-kC,P)2(m3-3,5-dmpz-N,NA,C4)2Ag(m-ClO4)}2]
(3,5-dmpz = 3,5-dimethylpyrazolato), a silver derivative showing
1
unprecedented h -azolato coordination
Larry R. Falvello, Juan Forniés,* Antonio Martín, Rafael Navarro, Violeta Sicilia and Pablo Villarroya
Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-
C. S. I. C., 50009 Zaragoza, Spain. E-mail:forniesj@posta.unizar.es
Received (in Cambridge, UK), 29th July 1998, Accepted 29th September 1998
The reaction of [Pd2(CH2C6H4P(o-tolyl)2-kC,P)2(m-
3,5-dmpz)2] (1) with AgClO4 renders [{Pd2(CH2C6H4P(o-
‘Pd2(C^P)2(m-3,5-dmpz)2’ and a silver atom located in the cleft
1
between the two dmpz groups and h -bonded to the C4 atoms of
2
tolyl)2-kC,P)2(m3-3,5-dmpz-N,NA,C4)2Ag(h -m-ClO4)}2] (2),
the dmpz ligands.
a palladium–silver derivative displaying an unprecedented
The palladium fragment ‘Pd2(C^P)2(m-3,5-dmpz)2’ consists
of a typical head to tail dimer with bridged 3,5-dmpz anions,
with the usual boatlike conformation of the Pd2N4 six-
membered metallocycle. The Pd···Pd distance (3.2297(7) Å) is
slightly longer than those observed in other Pd (or Pt)
complexes with two pyrazolate bridging ligands.3a–c The bond
distances and angles in the metallocycles in compound 2 are
similar to those observed in palladium and platinum compounds
1
dmpz bridging ligand h bonded to the Ag centers, involving
only the C4 atom of each dmpz ligand.
The chemistry of dimetallic compounds containing two m-
azolato bridging groups has been intensively developed in the
last three decades,1 especially in the case of dirhodium and
diiridium derivatives.2 Studies of these systems have included
substitution reactions,2a,b oxidative additions,2c,d kinetics,2e,f
electrochemistry,2g photochemistry,2h hydroformylation re-
actions2i and theoretical studies.2j Pyrazolate ligands have a
proven ability to hold two metal atoms in close proximity, while
permitting a wide range of intermetallic separations. Com-
pounds with two bridging azolato groups show a boat
conformation of the central ‘M2N4’ six membered ring. The p-
electron rich cleft between the two azolato rings in these
molecules offers a potentially interesting site for further
complexation (Fig. 1). To our knowledge there has been no
previous report of a complex in which a dimetallic ‘M2(m-
azolato)2’ moiety uses its p-electron system to accommodate a
transition metal cation.
In view of the paucity of dipalladium and diplatinum
complexes with m-azolato bridging groups3 we decided to
explore the synthesis and reactivity of compounds of the type
[M2(C^P)2(m-L)2] [M = Pd, Pt; C^P = CH2C6H4P(o-tolyl)2;
HL = pyrazole (Hpz), 3,5-dimethylpyrazole (H3,5-dmpz)].
The reaction of [Pd2(C^P)2(m-3,5-dmpz)2] (1)† with AgClO4
renders 2‡ [eqn. (1)].
2[Pd2(C^P)2(µ-3,5-dmpz)2] + 2 AgClO4
1
(1)
[{Pd2(C^P)2(µ3-3,5-dmpz-N,N′,C 4)2Ag(η2-µ-ClO4)}2]
2
Compound 2, as has been established by an X-ray study§
(Fig. 2), is formed by two {Pd2(C^P)2(m3-3,5-dmpz-N,NA,-
2
C4)2Ag(h -m-ClO4)} units bridged by two perchlorate groups
and related to each other by a crystallographic center of
symmetry. Each unit contains a dinuclear palladium fragment
C4'
C5'
C4
C5
Fig. 2 Molecular structure for compound 2. Selected bond distances: Pd(1)–
C(7) = 2.034(5), Pd(1)–P(1) = 2.2251(13), Pd(2)–C(28) = 2.042(5),
Pd(2)–P(2) = 2.2268(13), Pd(1)–N(1) = 2.138(4), Pd(1)–N(3) = 2.097(4),
Pd(2)–N(2) = 2.092(4), Pd(2)–N(4) = 2.136(4), Ag–C(44) = 2.410(5),
Ag–C(49) = 2.420(5), Ag–O(1) = 2.431(4), Ag–O(2A) = 2.464(4), N(1)–
C3'
C3
N2' N1'
N1 N2
N(2)
C(44)–C(45) = 1.410(7), N(2)–C(45) = 1.332(6), N(3)–N(4) = 1.375(6),
N(3)–C(48) 1.342(6), C(48)–C(49) 1.405(7), C(49)–C(50)
= 1.371(6), N(1)–C(43) = 1.331(6), C(43)–C(44) = 1.405(7),
M
M'
=
=
=
Fig. 1 Schematic diagram showing a guest atom in the cleft formed by the
two pyrazolate rings of the moiety [Pd2(C^P)2(m-3,5-dmpz)2] .The atom
numbering scheme used in the NMR analyses is shown.
1.405(7), N(4)–C(50) = 1.330(7) Å. Selected bond angles: Ag–C(44)–
C(43) = 94.5(3), Ag–C(44)–C(45) = 89.1(3), Ag–C(49)–C(48) = 86.7(3),
Ag–C(49)–C(50) = 95.7(3)°.
Chem. Commun., 1998, 2429–2430
2429

2
‡ [{Pd2(C^P)2(m3-3,5-dmpz-N,NA,C4)2Ag(h -m-ClO4)}2] (2). To a solution
containing the same C^P group.4 The dmpz groups are planar,
and the angle between them in each ‘Pd2(C^P)2(m-3,5-dmpz)2’
fragment is 44.8°. Bond lengths and angles around the N and C
atoms of the 3,5-dmpz are identical to those observed in other
complexes.3a
of [Pd2(C^P)2(m-3,5-dmpz)2] (1; 0.1136 g, 0.112 mmol) in CH2Cl2–OEt2
(50 : 4 mL) was added AgClO4 (0.0233 g, 0.112 mmol), and the mixture was
stirred for 5 h at room temperature. After filtration through Celites, the
resulting solution was evaporated to dryness. Upon addition of 15 mL of
Et2O and 2 mL of CH2Cl2 a white solid formed immediately, 2 (0.08 g,
58.50%). (Found: C, 51.10; H, 3.96; N, 4.58. Ag2C104Cl2H108N8O8P4Pd4
requires C, 51.31; H, 4.47; N, 4.60%). NMR spectra (RT, CDCl3): dP 39.1
(s); dH 5.52 (s, H4, 3,5-dmpz), 2.43 (s, Me, 3,5-dmpz), 1.91 (s, Me,
3,5-dmpz), 2.53 [d, 2J(H–H) 15.0 Hz, CH2 (C^P)], 3.11 [d, CH2 (C^P)],
2.74 [s, Me (C^P)], 1.88 [s, Me (C^P)]; dC 152.1 (s), 151.7 (s) [C3, C5
(3,5-dmpz)], 86.8 [m, C4 (3,5-dmpz)], 14.6 [s, Me (3,5-dmpz)], 13.2 [s, Me
(3,5-dmpz)], 29.0 [s, CH2 (C^P)], 22.7 [d, 3J(C–P) 7.2 Hz, Me (C^P)], 22.2
[d, 3J(C–P) 12.6 Hz, Me (C^P)].
The extraordinary structural feature of this compound is the
unprecedented coordination mode of the 3,5-dmpz groups to
Ag+. The silver cation is located in the cleft between, and
approximately equidistant from, the two 3,5-dmpz rings at a
distance of 2.410(5) Å and 2.420(5) Å from C(44) and C(49)
respectively, the C4 atom of each dmpz ring (Fig. 1). The Ag–
C(49) and Ag–C(44) vectors are nearly perpendicular to the
corresponding dmpz rings, the angles between the perpendicu-
lar to the corresponding rings and the Ag–C4 bonds being 5.9°
[Ag–C(49)] and 4.0° [Ag–C(44)] respectively. The long Ag–
C(48) (2.728 Å), Ag–C(50) (2.917 Å), Ag–C(43) (2.883 Å) and
Ag–C(45) (2.773 Å) distances seem to exclude any bond
interaction between Ag and these atoms. So, both 3,5-dmpz
§
Crystal
data
for
2·CH2Cl2·C5H12
:
C52H54AgCl-
¯
N4O4P2Pd2·CH2Cl2·C5H12, M = 1374.12; triclinic, space group P1 (no. 2),
a = 12.686(2), b = 15.050(2), c = 17.349(3) Å, a = 112.190(15), b =
108.53(2), g = 90.996(15)°, U = 2872.2(7) Å3, Z = 1, T = 150 K, m =
1.201 mm21, graphite monochromated Mo-Ka radiation, l = 0.71073 Å,
yellowish prism with dimensions 0.45 3 0.22 3 0.20 mm, Nonius CAD4
diffractometer, w scans, data collection range 4 < 2q < 50°, semiempirical
absorption correction based on Y scans, transmission factors 0.891–0.861,
653 refined parameters with 10049 unique (Rint = 0.015) reflections (10547
measured). Full-matrix least-squares refinement of this model against F2
(program SHELXL-937) converged to final residual indices R1 = 0.043,
wR2 = 0.111. (R factors defined in ref. 7), g.o.f. 1.03. Final difference
electron density maps showed six peaks above 1 e Å23 (from 2.68 to 1.35;
largest diff. hole 21.45) lying close to the solvent molecules. CCDC
182/1038.
1
rings seem to be h -coordinated [C(44) and C(49)] to the silver
atom. The Ag–C bond lengths (ca. 2.415 Å) are similar to the
1
shortest values found in Ag–h -arene complexes such as
[AgB11CH12·2C6H6] [2.400(7) Å],5a [Ag(deltaphane)-
(O3SCF3)] (2.41–2.48 Å),5b [Ag{(Z)-2,2,5,5-tetramethyl-
3,4-diphenylhex-3-ene}(O3SCF3)] [2.579(4) Å],5c and [in-
dene·AgClO4]2 [2.47(2) Å],5d and are clearly shorter than the
2
Ag–C distances observed in Ag–h -arene complexes, such
as [Ag(25,26,27,28-tetramethoxycalix(4)arene)(NO3-O,OA)]
1 (a) S. Trofimenko, Prog. Inorg. Chem., 1986, 34, 115; (b) A. P.
Sadimenko and S. S. Basson, Coord. Chem. Rev., 1996, 147, 247; (c) G.
La Monica and G. A. Ardizzoia, Prog. Inorg. Chem., 1997, 46, 151; (d)
J. E. Cosgriff and G. B. Deacon, Angew. Chem., Int. Ed. Engl., 1998, 37,
286.
[2.504(5),
2.643(5),
2.527(5),
2.549(5)
Å],5e
4
[{AuAg(C6F5)2(C6H6)n}] [2.48, 2.50 Å]5f and [catena(m-h -
rac(2)(1,5-naphthalino(2)paracyclophane)(m-perchlorato-
O,OA,OAA)silver(
)] [2.365, 2.607 Å].5g
I
Finally, the Ag coordination is completed by two Ag–O
bonds [Ag–O(1) = 2.431(4), Ag–O(2A) = 2.464(4) Å], one
from each of the two bridging ClO4 groups, in such a way that
Ag shows a distorted tetrahedral coordination environment. The
Ag–O bond distances are in the range found in complexes with
triflate,5b nitrate5e or for m-ClO4 bonded to silver.6
2 (a) R. Usón, L. A. Oro, M. A. Ciriano, D. Carmona, A. Tiripicchio and
M. Tiripicchio-Camellini, J. Organomet. Chem., 1982, 224, 69; (b) C.
Tejel, J. M. Villoro, M. A. Ciriano, J. A. López, E. Eguizabal, F. J. Lahoz,
V. I. Bakhmutov and L. A. Oro, Organometallics, 1996, 15, 2967; (c)
D. O. K. Fjeldsted, S. R. Stobart and M. J. Zaworotko, J. Am. Chem. Soc.,
1985, 107, 8258; (d) A. Tiripicchio, F. J. Lahoz, L. A. Oro and M. T.
Pinillos, J. Chem. Soc., Chem. Commun., 1984, 936; (e) R. D. Brost and
S. R. Stobart, Inorg. Chem., 1989, 24, 4308; (f) R. D. Brost, D. O. K.
Fjeldsted and S. R. Stobart, J. Chem. Soc., Chem. Commun., 1989, 488;
(g) D. C. Boyd, G. S. Rodman and K. R. Mann, J. Am. Chem. Soc., 1986,
108, 1779; (h) J. L. Marshall, S. R. Stobart and H. B. Gray, J. Am. Chem.
Soc., 1984, 106, 3027; (i) C. Claver, P. Kalck, M. Ridmy, A. Thorez,
L. A. Oro, M. T. Pinillos, M. C. Apreda, F. H. Cano and C. Foces-Foces,
J. Chem. Soc., Dalton Trans., 1988, 1523; (j) D. L. Lichtenberger, A. S.
Copenhaver, H. B. Gray, J. L. Marshall and M. D. Hopkins, Inorg. Chem.,
1988, 27, 4488.
3 (a) V. K. Jain, S. Kannan and E. R. T. Tiekink, J. Chem. Soc., Dalton
Trans., 1992, 2231; (b) V. K. Jain, S. Kannan and E. R. T. Tiekink,
J. Chem. Soc., Dalton Trans., 1993, 3625; (c) V. Y. Kukushkin, E. A.
Aleksandrova, V. M. Leovac, E. Z. Iveges, V. K. Belsky and V. E.
Konovalov, Polyhedron, 1992, 11, 2691; (d) V. K. Jain and S. Kannan,
Polyhedron, 1992, 11, 27; (e) A. Singhal, V. K. Jain and S. Kannan,
J. Organomet. Chem., 1993, 447, 317; (f) G. López, J. Ruiz, G. García,
J. M. Martí, G. Sánchez and J. García, J. Organomet. Chem., 1991, 412,
435; (g) G. López, J. Ruiz, G. García, C. Vicente, J. Casabó, E. Molins
and C. Miravitlles, Inorg. Chem., 1991, 30, 2605.
As has been mentioned, the bond distances and angles in the
dmpz groups in 2 are very similar to those observed in
uncomplexed ‘M2L2(m-pz)2’ compounds, indicating that in
1
spite of the h interaction to the silver centre, the pyrazolato
rings maintain their aromaticity. The mass spectrum (FAB+) of
2 shows the molecular peak for the cation [Pd2(C^P)2(m3-
1
3,5-dmpz-N,NA,C4)2Ag]+ (1119). The sharp 31P, H and 13C
NMR signals of 2 at room temperature and their observed shifts
with respect to those in the starting material, 1, indicate that the
1
silver–h -dmpz bonds are present in solution. Especially
significant are the changes observed in the 13C NMR spectrum
of 2 with respect to that of 1, mainly in the signal due to the C
1
atoms h -bonded to silver, the C4 atom of each dmpz group. For
compound 2 it appears at 86.8 ppm, i.e., shifted upfield by 16.34
ppm, and which becomes a multiplet, probably as a con-
sequence of the coupling of the C4 atoms to the P, 107Ag, and
109Ag nuclei. Due to the poor resolution of this spectrum, no
individual values for the coupling constants could be ex-
tracted.
4 (a) W. A. Herrmann, Ch. Brossmer, K. Öfele, C.-P. Reisinger, T.
Priermeier, M. Beller and H. Fischer, Angew. Chem., Int. Ed. Engl., 1995,
34, 1844; (b) L. R. Falvello, J. Forniés, A. Martín, R. Navarro, V. Sicilia
and P. Villarroya, Inorg. Chem., 1997, 36, 6166.
Studies of the reactivity of other palladium and platinum
pyrazolate complexes towards other Lewis acid metal com-
plexes are in progress.
The authors thank the Dirección General de Enseñanza
Superior (Spain) for financial support (Projects PB95-
0003-C02-01 and PB95-0792).
5 (a) K. Shelly, D. C. Finster, Y. J. Lee, W. R. Scheidt and C. A. Reed,
J. Am. Chem. Soc., 1985, 107, 5955; (b) H. C. Kang, A. W. Hanson, B.
Eaton and V. Boekelheide, J. Am. Chem. Soc., 1985, 107, 1979; (c) J. E.
Gano, G. Subramaniam and R. Birnbaum, J. Org. Chem., 1990, 55, 4760;
(d) P. F. Rodesiler, E. A. Hall Griffith and B. L. Amma, J. Am. Chem.
Soc., 1972, 761; (e) W. Xu, R. J. Puddephatt, K. W. Muir and A. A.
Torabi, Organometallics, 1994, 13, 3054; (f) R. Usón, A. Laguna, M.
Laguna and B. R. Manzano, J. Chem. Soc., Dalton Trans., 1984, 285;
(g) H. Schmidbaur, W. Bublack, M. W. Haenel, B. Huber and G. Muller,
Z. Naturforsch. Teil B, 1988, 43, 702.
Notes and references
† [Pd2(C^P)2(m-3,5-dmpz)2] (1): NMR spectra (RT, CD2Cl2) were recorded
on either a Varian Unity-300 or a Bruker ARX-300 spectrometer using the
standard references: dP 35.6 (s); dH 5.57 (s, 2H, H4 3,5-dmpz) 1.68 (s, 6H,
3,5-dmpz), 2.32 (s, 6H, 3,5-dmpz), 2.28 [s, 2H, CH2 (C^P)], 2.83 [s, 2H,
CH2 (C^P)], 2.87 [s, 6H, Me (C^P)], 1.61 [s, 6H, Me (C^P)]; dC 145.7 [d,
3J(C–P) 3.0 Hz], 147.2 [d, 3J(C–P) 2.3 Hz, C3,C5 (3,5-dmpz)], 103.1 [d, C4,
4J(C–P) 3.2 Hz], 14.3 (s, Me, 3,5-dmpz), 12.6 (s, Me, 3,5-dmpz), 28.6 (s,
CH2, C^P), 22.3 [d, 3J(C–P) 13.8 Hz, Me (C^P)], 21.6 [d, 3J(C–P) 8.6 Hz,
Me (C^P)].
6 (a) S. Kitagawa, M. Kondo, S Kawata, S. Wada, M. Maekawa and M.
Munakata, Inorg. Chem., 1995, 34, 1455.
7 G. M. Sheldrick, SHELXL-93,
a Program for Crystal Structure
Refinement, University of Go¨ttingen, Germany, 1993.
Communication 8/05938A
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Chem Commun., 1998, 2429–2430