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Journal of Organometallic Chemistry 621 (2001) 218 – 223
Chelating behaviour of a phosphinoalcohol leading to a stable
alcohol palladium complex
Chris Mattheis, Pierre Braunstein *
Laboratoire de Chimie de Coordination, UMR CNRS 7513, Uniersite ´ Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France
Received 4 September 2000; accepted 13 September 2000
Dedicated to Professor H. Brunner on the occasion of his 65th birthday, with our best wishes and most sincere congratulations
Abstract
Using the enantiopure phosphinoalcohol ligand (P,OH) (1) [(P,OH) =[(1S ),(2S ),(4R )-1-OH-1-Me-2-PPh
2
-4-C(Me)CH
2
-c -
C
6
H
7
], the stable Pd(II) complexes [(dmba)Pd(P,OH)Cl] (2) (dmba =o -C
6
H
4
CH
2
NMe
2
), [(dmba)Pd(P,OH)]PF
6
(3) and
[(dmba)Pd(P,O)] (4) have been prepared. Conductivity and NMR measurements showed that complex 2 gives rise to a
solvent-dependent equilibrium in solution between the neutral and the cationic species [(dmba)Pd(P,OH)Cl] (2a) and
[(dmba)Pd(P,OH)]Cl (2b), respectively. The crystal structures of 2b and [(dmba)Pd(P,OH)]PF
6
(3) have been determined by X-ray
diffraction. In the solid state, both cationic complexes display chelating behaviour for the P,OH ligand. © 2001 Elsevier Science
B.V. All rights reserved.
Keywords: Synthesis; Chiral ligands; Ditopic ligands; Functional phosphines; Palladium; X-ray structures
1. Introduction
Palladium and platinum alkoxide complexes have
aroused special interest because they offer a rich chem-
istry with versatile reactivity [1]. They undergo for
instance insertion reactions of carbon monoxide, car-
bon dioxide and olefins into the metal–oxygen bond
and are assumed to be intermediates in several catalytic
and stoichiometric reactions [2]. The difficulties often
encountered in isolating them are mainly due to their
sensitivity towards -hydride elimination reactions [1].
However, an appropriate choice of ligands has recently
allowed the preparation of several palladium and plat-
inum alkoxide complexes [1]. One possible approach in
this context is the use of chelating P, O ligands [3].
In the course of current studies with phosphinoalco-
hols, we discovered the advantages of the easily accessi-
ble limonene-based ligand 1 [4]. The tertiary character
of its alcohol function prevents -hydride elimination
and enabled us to obtain the stable palladium alkoxide
4. It was prepared in a stepwise approach: first the
phosphinoalcohol ligand 1 was introduced by coordina-
tion of the phosphine moiety to the metal centre, then
the Pd–O bond is created by reaction with a base
[3c – f]. The intermediate phosphinoalcohol palladium
complex 2 could also be isolated. An interesting feature
of this complex is the strong tendency for chelation
displayed by the ligand which leads after dissociation of
the chloride ion to the formation of a cationic complex
in the solid state. This structure is partly retained in
solution.
2. Results and discussion
2.1. Synthesis
Using a modified literature method we prepared the
phosphinoalcohol ligand (1S )-trans -( +)-1-hydroxy-1-
methyl-2-diphenylphosphino-4-isopropene-cyclohexane
(1), (abbreviated P,OH in the following), which is
derived from trans -( +)-limonene oxide [4]. Reaction of
1 with [(dmba)Pd(-Cl)]
2
(dmba =o -C
6
H
4
CH
2
NMe
2
) in
the ratio 2:1 in dichloromethane at room temperature
led to the formation of an air-stable complex 2a in 93%
yield (see Scheme 1).
* Corresponding author. Tel. and fax: +33-388-416030.
E-mail address: braunst@chimie.u-strasbg.fr (P. Braunstein).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
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