Cationic I·6-coordinated BINAP rhodium complexes with benzene and toluene

Article abstract of DOI:10.1002/zaac.201200016

Two novel BINAP rhodium complexes containing I·⁶- coordinated arenes have been disclosed. Both have been characterized by X-ray analysis and NMR spectroscopy. Copyright

Full text of DOI:10.1002/zaac.201200016

SHORT COMMUNICATION
DOI: 10.1002/zaac.201200016
Cationic η6-Coordinated BINAP Rhodium Complexes with Benzene and
Toluene
Christian Fischer,[a] Carmen Selle,[a] Hans-Joachim Drexler,[a] and Detlef Heller*[a]
Keywords: η6-Arene complexes; Rhodium; Binap; Homogeneous catalysis; Catalyst inhibition
Abstract. Two novel BINAP rhodium complexes containing η6-coor-
dinated arenes have been disclosed. Both have been characterized by
X-ray analysis and NMR spectroscopy.
Introduction
Results and Discussion
The chelating diphosphine ligand BINAP was introduced
into homogeneous catalysis by Noyori et al.[1] in 1980 and
since then has proved to be a very successful chiral modifier.[2]
An up-to-date compilation of results concerning its application
in asymmetric hydrogenation promoted by cationic rhodium
complexes can be found in Reference [3]. Recently very active
cationic solvate complexes of the type [Rh(BINAP)(solvent)2]-
Anion have been characterized by X-ray analysis with the sol-
vent being either methanol, tetrahydrofurane or acetone.[4]
Such complexes were prepared by hydrogenation of the diole-
fin precatalysts [Rh(BINAP)(cod)]BF4 (cod = 1,5-cyclooc-
tadiene) or [Rh(BINAP)(nbd)]BF4 (nbd = norbornadiene) in
the corresponding solvents.[3] When hydrogenation of the same
catalyst precursors was carried out in non-coordinating sol-
vents, e.g. dichloromethane or dichloroethane, dimers resulted
in which each BINAP acts as a bridging ligand through one of
its phenyl moieties. The dimers have been characterized by X-
ray analysis as well.[4]
When a tenfold excess of benzene was added to a solution
of [Rh(BINAP)(MeOH)2]BF4 (0.01 mmol) in methanol
(10 mL), a color change from yellow to light red occurred. By
layering the solution with diethyl ether red crystals suitable for
X-ray analysis were grown (Figure 1). The 31P NMR spectrum
of these crystals in deuterated dichloromethane shows that be-
side the known arene bridged dimer, a second species is pres-
ent in solution[4] (31P NMR in CD2Cl2, δ = 42.5 ppm; JRh–P
=
203.4 Hz; see spectrum in Supporting Information). The X-ray
analysis documents the coordination of rhodium to the benzene
ring.
BINAP is a classical seven-membered ring chelating ligand
whose rhodium-substrate complexes are significant less stable
than those containing typical five-membered ring chelating li-
gands like DPPE, Me-DuPhos and Et-DuPhos.[3] Rhodium
complexes with the latter ligands may also coordinate arenes
such as benzene or toluene in a η6-fashion.[5] The apparent
high stability of these rhodium-arene complexes might lead to
deactivation phenomena in catalysis.[5–7]
This paper reports the preparation and full characterization
of analogous rhodium-benzene and rhodium-toluene com-
plexes containing the BINAP ligand.
* Prof. Dr. D. Heller
Fax: +49-381-1281-50183
E-Mail: detlef.heller@catalysis.de
[a] Leibniz-Institut für Katalyse e.V.
an der Universität Rostock
Albert-Einstein Straße 29a
Figure 1. Molecular structure of the cation of [Rh(BINAP)(η6-benz-
ene)]BF4; ORTEP, 30% probability ellipsoids. Hydrogen atoms are
omitted for clarity. Selected distances and bond angles are summarized
in Table 1. CCDC-861327.
18059 Rostock, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200016 or from the au-
thor.
Z. Anorg. Allg. Chem. 2012, 638, (᭿), 1–3
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

C. Fischer, C. Selle, H.-J. Drexler, D. Heller
SHORT COMMUNICATION
Analogue results were obtained by using toluene instead. the literature.[8] To what extent catalyst deactivation has to be
The appropriate molecular structure is presented in Figure 2. considered depends on either the ratio of the stability constants
The corresponding 31P NMR spectrum (31P NMR in CD2Cl2, of arene complexes and active catalyst complexes or, other-
δ = 42.6 ppm; JRh–P = 203.2 Hz) is presented in the Supporting wise, on the ratio of the concentrations of arene and substrate.
Information.
The data in Table 1 show that the relevant distances and
angles in the two complexes are very similar.
Conclusions
In summary it has been shown that, despite their less sta-
bility compared to analogues complexes bearing five-mem-
bered chiral chelating diphosphines, arene complexes [Rh(BI-
Although rhodium arene complexes may be responsible for
lower activity, asymmetric hydrogenations with cationic rho-
dium complexes in aromatic solvents have been described in
NAP)(benzene)]BF4
and
[Rh(BINAP)(methyl-η6-benz-
ene)]BF4 were successfully prepared, isolated and charac-
terized by X-ray analysis.
Supporting Information (see footnote on the first page of
this article): 31P NMR spectra of the title compounds.
References
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[4] A. Preetz, C. Fischer, C. Kohrt, H.-J. Drexler, W. Baumann, D.
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Figure 2. Molecular structure of the cation of [Rh(BINAP)(methyl-η6-
benzene)]BF4; ORTEP, 30% probability ellipsoids. Hydrogen atoms
are omitted for clarity. Selected distances and bond angles are summa-
rized in Table 1. CCDC-861326.
[7] M. J. Burk, C. S. Kalberg, A. Pizzano, J. Am. Chem. Soc. 1998,
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Table 1. Selected distances /Å and bond angles /° of the isolated arene
complexes.
Arene
distance /Å
Rh–P
distance /Å
angle /°
P–Rh–P
Rh–η6C
Benzene
Toluene
2,231–2,241 (1)
2,226–2,234 (2)
2,288–2,367 (3)
2,296–2,361 (4)
89,86 (2)
89,64 (4)
Received: January 13, 2012
Published Online: ᭿
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 1–3

Cationic η6-Coordinated BINAP Rh Complexes with Benzene and Toluene
C. Fischer, C. Selle, H.-J. Drexler, D. Heller* ................ 1–3
Cationic η6-Coordinated BINAP Rhodium Complexes with
Benzene and Toluene
Z. Anorg. Allg. Chem. 2012, 1–3
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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