Formation of Trinuclear Palladium Orthometalated Complexes with Unprecedented Asymmetrical (μ3-S)(μ3-X) Bridges (X = OH, SR, O2CR) from μ2-Hydroxo Dimeric Complexes and CS2

Article abstract of DOI:10.1021/ic0351085

Complexes [Pd₃(μ₃-S)(μ₃-X)(L) ₃] (L = orthometalated imine), obtained by an unusual reaction of μ₂-OH dimeric complexes and CS₂, are an unprecedented type of asymmetrical bridges between metallatriangles, which force an all-cis arrangement of the three orthometalated ligands relative to the metallatriangle.

Full text of DOI:10.1021/ic0351085

Inorg. Chem. 2004, 43, 843−845
Formation of Trinuclear Palladium Orthometalated Complexes with
Unprecedented Asymmetrical (µ3-S)(µ3-X) Bridges (X ) OH, SR, O CR)
2
from µ2-Hydroxo Dimeric Complexes and CS †
2
Pablo Espinet,* Celia Herna´ndez, Jose´ M. Mart´ın-Alvarez, and Jesu´s A. Miguel
Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Valladolid,
47005 Valladolid, Spain
Received September 19, 2003
Scheme 1
Complexes [Pd3(µ3-S)(µ3-X)(L)3] (L ) orthometalated imine),
obtained by an unusual reaction of µ2-OH dimeric complexes and
CS , are an unprecedented type of asymmetrical bridges between
2
metallatriangles, which force an all-cis arrangement of the three
orthometalated ligands relative to the metallatriangle.
The reactivity of binuclear compounds [Pd(µ-OH)Ln]2 HLn
) p-CnH2n+1O-C6H4-CHdN-C6H4-OCnH2n+1-p (n ) 2,
6, and 10) toward protic substrates such as amines, thiols,
and carboxylic acids provides a versatile entry to mesomor-
phic binuclear complexes (metallomesogens) with other
bridges, and to mesomorphic mononuclear N,N-dialkyl-
dithio-carbamate complexes by reaction with dialkylamines
in the presence of carbon disulfide.1 The change in molecular
shape from dinuclear to mononuclear metallomesogens
produces a noticeable lowering of transition temperatures,
as expected from the less favorable molecular shape of the
latter.2 Pursuing our interest in novel structures to add to
the still limited types of metallomesogenic materials, it was
planned that the reaction of the µ-hydroxo complexes with
alcohols and CS2 might afford mononuclear xanthate com-
plexes.3 The outcome of the study was quite different.
When [Pd(µ-OH)L10]2 (1a, Scheme 1) in CH2Cl2 was
treated with 2 molar equiv of octanol and carbon disulfide
at 35 °C for 7 h, a yellow compound 2a was obtained. The
1H NMR spectrum of 2a showed (a) the absence of
octanyloxy chains; (b) only one set of 1H resonances for the
orthometalated imine ligand; and (c) a singlet at -2.55 ppm
(with intensity 1 for 3 imines) which might be due to the
presence of a µ-OH group. A very weak absorption in the
IR at ca. 3622 cm-1 was in the expected range for ν(OH).
Good quality crystals suitable for a full X-ray analysis could
not be obtained for this complex with long aliphatic chains,
nor for its analogue 2b with L2, but partial resolution of poor
quality crystals for 2b revealed the existence of a Pd3 core
with two bridging ligands which, according to the elemental
1
analysis C,H,N,S and the IR and H NMR spectra, are
assigned one S and one OH group, as shown in Scheme 1.
The structure of 2 is further supported by those found for
two derivatives (3b and 4b). The hydroxo ligand of
complexes 2 is easily replaced when treated with some
Bro¨nsted acids. Thus, treatment of 2b with HSC4H9 (molar
ratio 1:1) afforded the trinuclear complex [Pd3(µ3-S)(µ3-
SC4H9)(L2)3] (3b), with mixed sulfide-thiolato bridges. The
1H NMR resonances of the orthopalladated imine ligand in
3b indicate a cis arrangement of the three imines. The upfield
shift of the methylene groups of the SC4H9 chain is consistent
with the thiolato group being cis to the imine nitrogens.4
The X-ray structure of 3b was determined (Figure 1).5 The
* E-mail: espinet@qi.uva.es.
† Dedicated to Professor J. Vicente on the occasion of his 60th birthday.
(1) D´ıez, L.; Espinet, P.; Miguel, J. A. J. Chem. Soc., Dalton Trans. 2001,
1189.
(4) Buey, J.; D´ıez, L.; Espinet, P.; Kitzerow, H. S.; Miguel, J. A. Chem.
Mater. 1996, 8, 2375.
(2) Baena, M. J.; Espinet, P.; Ros, M. B.; Serrano, J. L. Angew. Chem.,
Int. Ed. Engl. 1991, 30, 711.
(3) Lo´pez, G.; Sa´nchez, G.; Garc´ıa, G.; Garc´ıa, J.; Sanmart´ın, A.; Santana,
M. D. Polyhedron 1991, 10, 2821.
(5) Crystal data for 3b‚2CH2Cl2: C57H67Cl4N3O6Pd3S2, M ) 1415.26,
triclinic, space group P1h, a ) 13.630(10) Å, b ) 14.167(11) Å, c
)16.393(12) Å, R ) 80.885(15)°, â ) 82.382(15)°, γ ) 78.950(14)°,
V ) 3050(4) Å3, Z ) 2, R1 ) 0.0578, wR2 ) 0.1700. CCDC-211688.
10.1021/ic0351085 CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/20/2004
Inorganic Chemistry, Vol. 43, No. 3, 2004 843

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Figure 2. Molecular structure of 4b with thermal ellipsoids (30%
probability). Selected bond lengths (Å): S(1)-Pd(2) 2.254(2), S(1)-Pd(1)
2.286(2), S(1)-Pd(3) 2.296(2), O(1)-Pd(1) 2.215(5), O(1)-Pd(2) 2.237(5),
O(2)-Pd(3) 2.195(5).
Figure 1. Molecular structure of 3b with thermal ellipsoids (30%
probability). Selected bond lengths (Å): S(1)-Pd(1) 2.304(2), S(1)-Pd(3)
2.307(3), S(1)-Pd(2) 2.314(3), S(2)-Pd(3) 2.385(2), S(2)-Pd(1) 2.407(3),
S(2)-Pd(2) 2.430(3).
Scheme 2 Proposed Mechanism for the Synthesis of 2
molecule consists of three Pd(C-N) moieties linked by one
µ3-sulfide and one µ3-thiolate ligand. The triangle formed
by the three Pd atoms in the Pd3S2 core of the molecule is
not equilateral due to the distortion forced by the alkyl tail
of the thiolato, which is oriented between the imines
coordinated to Pd(1) and Pd(3). The Pd(1)-S(1)-Pd(3) angle
(96.32°) is larger than the other two (Pd(1)-S(1)-Pd(2),
82.43°; Pd(2)-S(1)-Pd(3), 84.99°). The Pd(1)‚‚‚Pd(3) dis-
tance (3.387 Å) is longer than the other two (Pd(1)‚‚‚Pd(2),
3.091 Å; Pd(2)‚‚‚Pd(3), 3.047 Å). None is suggestive of Pd‚
‚‚Pd interactions.
Propionic acid also displaces the hydroxo ligand of 2b to
give the corresponding trinuclear complex [Pd3(µ3-S)-
(µ-O2CC2H5)(L2)3] 4b. Its X-ray structure was determined
(Figure 2).6 The oxygen atom O(1) of the bridging carbox-
ylato is coordinated to Pd(1) and Pd(2), while O(2) is bonded
to Pd(3). This distorts the triangular Pd3 core, and the
Pd(2)‚‚‚Pd(3) distance (3.500 Å) is longer than the other two
(Pd(1)‚‚‚Pd(2), 3.196 Å; Pd(2)‚‚‚Pd(3), 3.145 Å).
The formation of 2 can be rationalized as shown in Scheme
2.
The formal insertion of CS2 into the Pd-OH bond should
produce a hydrosulfide intermediate, which will react with
a new molecule of the starting dimer affording 2. Insertion
reactions of CS2 into M-X bonds,7 including M-OR bonds,8
have been reported. The formation of M-SH (M ) Mo,
Re) from M-OH and CS2 has also been reported very
recently.9 Dimeric hydrosulfide-bridged palladium complexes
can be formed by reaction of hydroxo-bridged complexes
and SH2.10,11 However, in our case the use of SH2 led to
uncontrolled reactions producing decomposition of 1 to
(8) (a) Simpson, R. D.; Bergman, R. Organometallics 1992, 11, 4306.
(b) Hevia, E.; Pe´rez, J.; Riera, L.; Riera, V.; del R´ıo, I.; Garc´ıa-Granda,
S.; Miguel, D. Chem. Eur. J. 2002, 8, 4510.
(6) Crystal data for 4b: C54H59N3O8Pd3S, M ) 1229.30, triclinic, space
group P1h, a ) 13.041(5) Å, b ) 13.205(6) Å, c )15.361(6) Å, R )
94.995(10)°, â ) 91.463(9)°, γ ) 95.415(10)°, V ) 2622.0(19) Å3, Z
) 2, R1 ) 0.0465, wR2 ) 0.1139. CCDC-211687.
(9) Gerbino, D. C.; Hevia, E.; Morales, D.; Navarro Clemente, M. E.;
Pe´rez, J.; Riera, L.; Riera, V.; Miguel, D. Chem. Commun. 2003, 328.
(10) Kuwata, S.; Hidai, M. Coord. Chem. ReV. 2001, 213, 211.
(11) Ruiz, J.; Rodr´ıguez, V.; Vicente, C.; Mart´ı, J. M.; Lo´pez, G. Inorg.
Chem. 2001, 40, 5354.
(7) For a review see: Pandy, K. K. Coord. Chem. ReV. 1995, 140, 37.
844 Inorganic Chemistry, Vol. 43, No. 3, 2004

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unidentified solids. The smooth generation of hydrosulfide
from CS2 seems crucial for the success of the synthesis.
Homobridged Pd3(µ3-S)2 cores are known,12 but these
heterobridged cores reported here were unknown. They are
interesting because they force an all-cis arrangement (relative
to the metallatriangle) of the three orthometalated imine
ligands. The preference for a cis arrangement of C and
S(sulfide) observed is probably associated with the desta-
bilization inherent to isomers placing in mutually trans
positions ligands with a high trans influence.13 Cis arrange-
ment in molecules containing a repeated unit (in our case
the imine group) is interesting in the fields of NLO14,15 and
liquid crystals,1,14,16 because it favors a larger molecular
hyperpolarizability.
In summary, an unusual reaction leads to the formation
of a novel structural type of trimetallic complexes, which
arranges the substituents in an all-cis parallel alignment. This
kind of alignment should produce a reinforcement of the
contributions of the molecular fragments to the molecular
hyperpolarizability. The use of imines (or related ligands)
with suitable donor and acceptor groups should produce
interesting materials. Further studies on these systems are
under way.
Acknowledgment. We gratefully acknowledge financial
support by the Spanish Comisio´n Interministerial de Ciencia
y Tecnolog´ıa (Project MAT2002-00562) and the Junta de
Castilla y Leo´n (Project VA050/02).
(12) (a) Yeo, J. S. L.; Li, G.; Yip, W. H.; Mak, T. C. W.; Hor, T. S. A. J.
Chem. Soc., Dalton Trans. 1999, 435. (b) Capdevila, M.; Clegg, W.;
Coxall, R. A.; Gonza´lez-Duarte, P.; Hamidi, M.; Lledo´s, A.; Ujaque,
G. Inorg. Chem. Commun. 1998, 1, 466. (c) Matsumoto, K.; Takahashi,
K.; Nakao, Y. Polyhedron 1999, 18, 1811. (d) Wirth, S.; Fenske, D.
Z. Anorg. Allg. Chem. 1999, 625, 2064. (e) Cowan, R. L.; Pourreau,
D. B.; Rheingold, A. L.; Geib, S. J.; Trogler, W. C. Inorg. Chem.
1987, 26, 259. (f) Werner, H.; Bertleff, W.; Schubert, U. Inorg. Chim.
Acta 1980, 43, 199. (g) Narayan, S.; Jain, V. K.; Butcher, R. J.
Polyhedron 1998, 17, 2037. (h) Fenske, D.; Fleischer, H.; Krautscheid,
H.; Magull, J. Z. Naturforsch., B 1990, 45, 127.
Supporting Information Available: Synthetic procedures,
NMR, IR, and elemental analysis data, and two crystallographics
files in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
(13) For examples of the concepts antisymbiotic behavior and transphobia
see references in: (a) Pearson, R. G. Inorg. Chem. 1973, 12, 712. (b)
Vicente, J.; Abad, J. A.; Martinez-Viviente, E.; Jones, P. G. Orga-
nometallics 2002, 21, 4454.
(14) Buey, J.; Coco, S.; D´ıez, L.; Espinet, P.; Mart´ın-Alvarez, J. M.; Miguel,
J. A.; Garc´ıa-Granda, S.; Tesouro, A.; Ledoux, I.; Zyss, J. Organo-
metallics 1998, 17, 1750.
IC0351085
(15) Fave, C.; Hissler, M.; Se´ne´chal, K.; Ledoux, I.; Zyss, J.; Re´au, R.
Chem. Commun. 2002, 1674.
(16) Buey, J.; D´ıez, G. A.; Espinet, P.; Garc´ıa-Granda, S.; Pe´rez-Carren˜o,
E. Eur. J. Inorg. Chem. 1988, 1235.
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