metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
observed the crystals of form (II) to be in the majority in a
ratio of about 3:1 between the two forms. The crystal struc-
tures of both modi®cations were determined and are reported
and compared in this paper.
ISSN 0108-2701
trans-(2-Methylthiobenzoato-O)-
phenylbis(triphenylphosphine)-
palladium(II), two conformational
isomers
It was expected that, since the SÐO ligands are potentially
bidentate, the structures would differ in the way in which the
ligands bind to the metal centres. However, they were found to
be mono-coordinated in both cases. The molecular con®g-
urations are the same in the two forms, i.e. a square-planar
substitution of the Pd atom by the four ligands, with deviations
Gert J. Kruger,a* Catharine Thompson,a Wolfgang H.
Meyer,b Robert Brullb and Helgard G. Raubenheimerb
È
aDepartment of Chemistry and Biochemistry, Rand Afrikaans University, PO Box
524, Auckland Park, Johannesburg 2006, South Africa, and bDepartment of
Chemistry, Stellenbosch University, Private Bag X1, Matieland 7600, South Africa
Correspondence e-mail: gjk@na.rau.ac.za
Ê
from the best plane of less than 0.13 A. The phenyl group and
the SÐO ligand are trans to each other and the SÐO ligand
bonds through the carboxylate-O rather than the S atom.
The difference between the two modi®cations lies in the
orientation of the SÐO ligands. In form (I), the S of the
carboxylate ligand is adjacent to the O atom bonded to the Pd
atom (O41 in Fig. 1). In form (II), the ligand is rotated around
the C(carboxylate)ÐC(phenyl) bond to bring the S atom in
close proximity to the carbonyl O atom (O42 in Fig. 2). The
phenyl ligands are oriented perpendicular to the square plane,
whereas the SÐO ligands tilt at angles of 63.86 (7) and
42.40 (5)ꢀ to the molecular plane in forms (I) and (II),
respectively. The orientations of the triphenylphosphines are
very similar for both forms, as can be seen in the ®gures and
from the torsion angles listed in Tables 1 and 2.
Received 19 July 1999
Accepted 29 November 1999
The title compound, trans-[Pd(C6H5)(C8H7O2S)(C18H15P)2],
crystallizes in two modi®cations differing only in the
orientation of the 2-methylthiobenzoato ligand. In both cases,
this ligand binds to the metal centre via one O atom in a
monodentate fashion. The only signi®cant difference is a
rotation about the C(Ph)ÐCOO bond, with OÐCÐCÐC
torsion angles having values of 6.3 (7) and 157.3 (3)ꢀ in the two
isomeric forms.
Comment
Organometallic catalysts often incorporate hemilabile ligands,
i.e. ligands that could bind either in a monodentate or a
bidentate fashion, so as to facilitate the liberation of one
coordination site of the metal centre under the conditions of
the catalytic reaction. The title compound is an example of a
phenylpalladium compound containing such a hemilabile
ligand, namely a methylthioethercarboxylate SÐO ligand.
Due to their importance in industrial catalytic processes, Pd
compounds containing hemilabile PÐO ligands have been
investigated extensively (Bader & Lindner, 1991). Examples
of compounds with hemilabile SÐO ligands are, however,
quite rare (Britovsek et al., 1996).
We have recently described (Meyer et al., 1998) the synth-
esis of a series of compounds containing this type of ligand,
namely trans-[Pd(OOC±C6H4±2-SR-ꢀO)(C6H5){P(C6H5)3}2]
with R = Me, Et, iPr and tBu. The crystal structure of one of the
compounds in this series, i.e. where R = Et, was reported and it
i
was shown that the last two complexes, i.e. with R = Pr and
tBu, are hemilabile in solution.
The title compound (with R = Me) forms two distinct
polymorphs, co-crystallizing from the same solution and easily
distinguishable by their dissimilar crystal shapes. Their habits
are monoclinic prismatic for the form we called isomer (I) and
spindle-shaped monoclinic prismatic for our isomer (II). We
Figure 1
The molecular conformation of form (I) of the title compound, with
anisotropic displacement ellipsoids shown at 50% probability level.
ꢁ
Acta Cryst. (2000). C56, 329±331
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved 329
Kruger, Gert J.
