Optically Active Transition Metal Complexes. 128 [1]
Synthesis, Characterization and Molecular Structures of Cycloheptatrienyl-
Iminphos-Molybdenum Complexes Differing Only in the Metal Configuration
Henri Brunner*, Jürgen Klankermayer, and Manfred Zabel
1)
Institut für Anorganische Chemie, Universität Regensburg
Received February 27th, 2002.
Dedicated to Professor Dieter Fenske on the Occasion of his 60th Birthday
Abstract. The chiral-at-metal cycloheptatrienyl-molybdenum
complexes (R
Mo
,S
C
)-[(η
7
-C
7
H
7
)Mo(iminphos)(CO)]BF
4
(2a) and
(S
Mo
,S
C
)-[(η
7
-C
7
H
7
)Mo(iminphos)(CO)]BF
4
(2b) (iminphos ⫽ 2-[N-
(S)-1-phenylethylcarbaldimino]phenyl(diphenyl)phosphane), which
only differ in the molybdenum configuration, were prepared and
separated by fractional crystallization. The absolute configuration
Optisch aktive Übergangsmetall-Komplexe. 128 [1]
Synthese, Charakterisierung und Molekülstrukturen von chiralen Cycloheptatrienyl-
Iminphos-Molybdän-Komplexen mit unterschiedlicher Metallkonfiguration
Inhaltsübersicht. Die am Metall chiralen Cycloheptatrienyl-Molyb-
dän-Komplexe (R
Mo
,S
C
)-[(η
7
-C
7
H
7
)Mo(iminphos)(CO)]BF
4
(2a)
und (S
Mo
,S
C
)-[(η
7
-C
7
H
7
)Mo(iminphos)(CO)]BF
4
(2b) (iminphos ⫽
2-[N-(S)-1-Phenylethylcarbaldimino]phenyl(diphenyl)phosphan),
die sich nur in der Konfiguration am Molybdänatom unterschei-
Introduction
Three-legged “piano stool” complexes of the type [(η
n
-
C
n
H
n
)MLL⬘L⬙] are well known examples of chiral-at-metal
compounds [2, 3, 4]. Provided, one of the ligands, e.g. an
unsymmetrical chelate ligand L⫺L⬘, is enantiomerically
pure, a pair of diastereomers arises, differing only in the
metal configuration. Usually, such diastereomers can be
distinguished on the basis of their NMR spectra. Then, the
diastereomer ratio can be determined by the integration of
suitable signals.
Generally, the diastereomer, which is the less soluble or
present in excess, can be separated from a diastereomer
mixture on crystallization [2, 3, 4]. This is the basis of dia-
stereomer separation by fractional crystallization. Interest-
ingly, for configurationally labile compounds, frequently en-
countered among half-sandwich complexes, asymmetric
* Prof. Dr. Henri Brunner
Institut für Anorganische Chemie, Universität Regensburg
D-93040 Regensburg, Germany
Fax: (internat.) ⫹49-(0)941/943-4439
E-mail: henri.brunner@chemie.uni-regensburg.de
1)
X-ray structure analyses
2264 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044⫺2313/02/628/2264⫺2268 $ 20.00⫹.50/0 Z. Anorg. Allg. Chem. 2002, 628, 2264⫺2268
for both diastereomers was determined by X-ray analysis.
1
H NMR
studies demonstrated the configurational lability at the molyb-
denum centre in solution.
Keywords: Chirality; Molybdenum; Half-sandwich complexes; Me-
tal configuration
den, wurden dargestellt und durch fraktionierende Kristallisation
getrennt. Die absolute Konfiguration wurde für beide Diastereo-
mere durch Kristallstrukturanalyse bestimmt. Durch
1
H-NMR-
spektroskopische Untersuchungen konnte die Konfigurationslabili-
tät des Metallzentrums nachgewiesen werden.
transformations may be involved [4, 5]. To the best of our
knowledge, there are so far only two examples of chiral-at-
metal compounds, for which the molecular structures of
both diastereomers could be determined by X-ray crystal-
lography [6, 7]. In the present paper we describe another
example: the synthesis, separation and characterization of
diastereomeric cycloheptatrienyl-molybdenum half-sand-
wich complexes of the type [(η
7
-C
7
H
7
)Mo(iminphos)-
(CO)]BF
4
and the determination of the molecular structures
of both diastereomers [8].
Results and Discussion
Synthesis of the compounds 1 and 2
Treatment of the reactive complex [(η
7
-C
7
H
7
)Mo(η
6
-
C
6
H
5
CH
3
)]BF
4
[9] with the chiral phosphaneimine 2-[N-
(S)-1-phenylethylcarbaldimino]phenyl(diphenyl)phosphane,
(S)-iminphos [10, 11], in CH
3
CN resulted in the formation
of a diastereomer mixture of [(η
7
-C
7
H
7
)Mo(imin-
phos)(NCMe)]BF
4
(1) (Scheme 1). The diastereomer ratio
could be determined by
1
H NMR spectroscopy as 55:45
in [D
6
]acetone.