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Polyhedron 19 (2000) 1829 – 1835
Studies of dirhodium(II) tetrakis(trifluoroacetate).
Part 8. One-dimensional polymers of Rh
2
(O
2
CCF
3
)
4
with aromatic
ligands: benzene, p -xylene and naphthalene
F. Albert Cotton *, Evgeny V. Dikarev, Marina A. Petrukhina, Salah-Eddine Stiriba
Laboratory for Molecular Structure and Bonding, Department of Chemistry, PO Box 30012, Texas A&M Uniersity, College Station,
TX 77842 -3012, USA
Received 30 May 2000; accepted 7 June 2000
Abstract
The interaction of benzene, p -xylene, and naphthalene with a strong two-ended Lewis acid, Rh
2
(O
2
CCF
3
)
4
, led to one-dimen-
sional linear polymers of 1:1 composition, [Rh
2
(O
2
CCF
3
)
4
·L]
, where L =C
6
H
6
(1), p -(CH
3
)
2
C
6
H
4
(2), and C
10
H
8
(3). Compounds
1 – 3 have been characterized by elemental analysis and IR spectroscopy and their structures have been determined by X-ray
diffraction. In the crystal structures of the compounds the alternating arrangement of the dirhodium(II) tetrakis(tri-
fluoroacetate) units with the aromatic ligands coordinated to their axial positions forms infinite chains extended along one direction
of the unit cell. The rare bridging off-centered,
2
:
2
coordination of arene groups by the Rh(II) centers was found to be preferred
in all three cases with the two closest RhC
arene
distances averaged to 2.662(6) A in the benzene complex (1), to 2.684(7) A in the
p -xylene analogue (2), and to 2.588(9) A in the naphthalene product (3). © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Dirhodium(II) compounds; Trifluoroacetate; One-dimensional polymers; Arene coordination; -Complexes; Crystal structures
1. Introduction
Dirhodium(II) tetrakis(trifluoroacetate) exhibits an
extensive axial coordination chemistry with a variety of
strong N, O, P-containing bases [1]. Our research inter-
est has been recently focused on studies of weak axial
interactions by the powerful two-ended Lewis acid,
Rh
2
(O
2
CCF
3
)
4
[2]. We introduced a solid state deposi-
tion technique (‘solventless’ synthesis) [2] as an efficient
way to study these interactions and to avoid competi-
tive coordination of solvents in solutions. Our recent
results have included the first structurally characterized
-complex with an aromatic ligand (hexamethylbenz-
ene), [Rh
2
(O
2
CCF
3
)
4
·(C
6
Me
6
)]
[2a] and a compound
[Rh
2
(O
2
CCF
3
)
4
·(C
2
Ph
2
)]
[2e] with both a triple car-
boncarbon bond and an arene system from the bifunc-
tional diphenylacetylene ligand involved in coordin-
ation (Scheme 1). A rare off-centered orientation of the
aromatic ligands at the Rh(II) centers has been found
in both dirhodium trifluoroacetate chain compounds,
with the C
6
Me
6
and the Ph
2
C
2
ligands. We believe
systematic research is needed in order to get more
insight into complexation of arenes by the electron-defi-
cient dirhodium(II) carboxylate molecules, as these in-
teractions have an important role in some catalytic and
aromatic substitution reactions [3]. Therefore, we have
extended the number of arene ligands to benzene, p -xy-
lene and naphthalene and report here on their interac-
tions with Rh
2
(O
2
CCF
3
)
4
. The first two ligands are
commonly used as non-coordinating solvents for study-
ing weak interactions in the Lewis acid–Lewis base
systems. Naphthalene is the first conjugated arene
molecule used for such reactions with the dirhodium
moiety. With all three ligands the products are
analogous one-dimensional linear polymers of 1:1 com-
position, namely [Rh
2
(O
2
CCF
3
)
4
·C
6
H
6
]
(1), [Rh
2
-
(O
2
CCF
3
)
4
·(p -(CH
3
)
2
C
6
H
4
)]
(2) and [Rh
2
(O
2
CCF
3
)
4
·
C
10
H
8
]
(3). They have been crystallographically char-
acterized and their structures have been compared.
* Corresponding author. Tel.: +1-979-845-4432; fax: +1-979-845-
9351.
E-mail address: cotton@tamu.edu (F.A. Cotton).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00472-1