A new class of anionic phosphinooxazoline ligands in palladium and ruthenium complexes: Catalytic properties for the transfer hydrogenation of acetophenone

Article abstract of DOI:10.1039/b004786o

The synthesis of the cationic Pd complex [Pd(dmba)(PCH₂-oxazoline)]Cl [PCH₂-oxazoline = 2-oxazoline-2-ylmethyl)diphenylphosphine] (2) has allowed for the first time the observation of hemilabile behaviour for a phosphinooxazoline ligand. This molecular dynamics is stopped upon removal of the chloride anion, by reaction with either NH₄PF₆, which retains the cationic nature of the complex, or Bu^tOK. The latter reaction leads to the formation of the first example of a Pd complex bearing an anionic phosphinooxazoline ligand, [Pd(dmba){Ph₂PCH - -^...C( - -^...N)CH₂CH₂O}], abreviated [Pd(dmba)(PCH-oxazoline)] (7), the anionic charge resulting from the monodeprotonation of the PCH₂ group. Following this methodology, the Ru complex [RuCl(p-cymene){Ph₂PCH - -^...C( - -^...N)CH₂CH₂O}], abreviated [RuCl(η⁶-p-cymene)(PCH-oxazoline)] (8) and containing this four-electron chelating anionic ligand, was prepared and shown to be more reactive for the catalytic transfer hydrogenation of acetophenone in propan-2-ol than the analogous complex bearing the neutral phosphinooxazoline ligand PCH₂-oxazoline. The crystal structure of cis-[Pd{Ph₂PCH - -^...C( - -^...N)CH₂CH₂O}₂], abbreviated cis-[Pd(PCH-oxazoline)₂] (6), was determined by X-ray diffraction.

Full text of DOI:10.1039/b004786o

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A new class of anionic phosphinooxazoline ligands in palladium and
ruthenium complexes: catalytic properties for the transfer
hydrogenation of acetophenone¤
Pierre Braunstein,*a Frederic Nauda and Steven J. Rettigb”
a L aboratoire de Chimie de Coordination (CNRS UMR 7513), Universite L ouis Pasteur, 4 rue
Blaise Pascal, F-67070 Strasbourg cedex, France. E-mail: braunst=chimie.u-strasbg.fr
b Department of Chemistry, University of British Columbia, 2036 Main Mall, V ancouver,
BC V 6T 1Z1, Canada
Received (in Montpellier, France) 13th June 2001, Accepted 12th July 2001
First published as an Advance Article on the web 12th December 2000
The synthesis of the cationic Pd complex [Pd(dmba)(PCH -oxazoline)]Cl [PCH -oxazoline \ 2-oxazoline-2-
2
2
ylmethyl)diphenylphosphine] (2) has allowed for the Ðrst time the observation of hemilabile behaviour for a
phosphinooxazoline ligand. This molecular dynamics is stopped upon removal of the chloride anion, by reaction
with either NH PF , which retains the cationic nature of the complex, or ButOK. The latter reaction leads to the
4
6
formation of the Ðrst example of a Pd complex bearing an anionic phosphinooxazoline ligand,
[Pwd(dmba)MPh PCH}C(}Nz )CH CH ON], abreviated [Pd(dmba)(PCH-oxazoline)] (7), the anionic charge
2
2
2
w
z
resulting from the monodeprotonation of the PCH group. Following this methodology, the Ru complex
2
[RwuCl(p-cymene)MPh PCH}C(}Nz )CH CH ON], abreviated [RuCl(g6-p-cymene)(PCH-oxazoline)] (8) and
2
2
2
w
z
containing this four-electron chelating anionic ligand, was prepared and shown to be more reactive for the catalytic
transfer hydrogenation of acetophenone in propan-2-ol than the analogous complex bearing the neutral
phosphinooxazoline ligand PCH -oxazoline. The crystal structure of cis-[PwdMPh PCH}C(}Nz )CH CH ON ],
2
2
2
2
2
w
z
abbreviated cis-[Pd(PCH-oxazoline) ] (6), was determined by X-ray di†raction.
2
Oxazolines are versatile synthons for ligand design1,2 and
readily available in enantiomerically pure forms, which
accounts for their increasing use in asymmetric reactions
catalysed by transition metal complexes.2h5 Nevertheless,
reports on anionic ligands incorporating an oxazoline ring are
not legion compared to their neutral analogs and such ligands
may be classiÐed according to two main families. In class A
compounds, the anionic charge is carried by an external het-
eroatom (C~, O~, S~) and the nitrogen atom of the oxazoline
remains a neutral donor. This includes ligands such as
bis(oxazolinyl)phenyl,6h8 (hydroxyphenyl)oxazoline,9h15 (hy-
droxyferrocenyl)oxazoline16,17 and (mercaptoaryl)oxazo-
line,17 which upon deprotonation allowed the preparation of
complexes with metals such as Ti, Zr, Hf, V, Mn, Ni, Pd, Pt or
Cu. An oxazoline moiety was recently combined to a pyrrole
for use in copper-catalysed enantioselective cyclopropanation
reactions; the NH group is expected to be deprotonated upon
in situ reaction with Cu(I) triÑate.18 Some of the isolated com-
plexes were found to be catalysts for reactions such as ethyl-
Ðrst deprotonation of the acidic CH of the bis(oxazoline)
ligand at low temperature and subsequent quenching with a
metal salt. This strategy allowed the development of efficient
2
ene
polymerisation,9
epoxydation,11b
alkyl-
and
phenylzincation of aldehydes,16 and conjugate addition to
ketones.17
In the second class of ligands, B, the anionic charge is
largely delocalised onto the nitrogen atom of the oxazoline
but only one such ligand type has been reported, as illustrated
in eqn. (1). The corresponding complexes were obtained by
¤ Part of the Doctoral Thesis of F. N.
” Deceased, October 27th 1998.
32
New J. Chem., 2001, 25, 32È39
DOI: 10.1039/b004786o
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001

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tection and facile generation of reactive sites in the coordi-
nation sphere of their complexes and several of them have
been used in homogeneous catalysis. An additional feature of
these P,O-type ligands is that the acidity of their PCH
protons allows facile deprotonation of this group to form an
2
anionic 4-electron donor phosphino enolate ligand, with loss
of the hemilabile behaviour. These strong chelates confer
special reactivity to their complexes V, as found, for example,
in the reversible CO Ðxation by palladium complexes,38,39
2
the
rhodium-catalysed
transfer
dehydrogenation
of
cyclooctane40 and the highly selective nickel-catalysed conver-
sion of ethylene into linear a-oleÐns.41h47
(1)
Ti,19,20 Cu,21,22 Rh,23 Zn24,25 or Mg26 catalysts for several
asymmetric reactions such as reduction of ketones,20 cyclo-
propanation of oleÐns,21,22 allylzincation,24,25 and hydro-
cyanation of aldehydes.26 The precatalysts are usually
prepared in situ and not isolated (Zn, Mg, Ti) and only three
crystal structures have been determined by X-ray di†raction,
for the Cu,27 Rh23 and Y28 complexes.
This dramatic change in reactivity observed when going
from neutral to anionic P,O-type ligands triggered our interest
for new anionic P,N-type ligands derived from I, in which the
We have previously reported the synthesis of Pd and Ru
complexes of type II bearing the neutral P,N-type ligand
acidity of the PCH protons should also allow easy deproton-
2
ation, particularly after coordination to a metal centre. Here
(oxazolinylmethyl)diphenylphosphine
I
(abreviated PCH -
2
we report the synthesis of such complexes containing a phos-
phine moiety covalently linked to an oxazoline, whose nitro-
gen atom formally carries the partly delocalised negative
charge, thus resulting in the formation of a covalent rather
than dative NÈM bond, as depicted in VI. The corresponding
ligand, abreviated PCH-oxazoline, is the Ðrst representative of
a new class of hybrid ligands, which combines some of the
features of B and V type systems. In addition to the synthesis
of palladium(II) complexes, we present a comparison of the
oxazoline) [eqn. (2)] and studied their catalytic properties for
ethylene/CO copolymerization and asymmetric transfer
hydrogenation of ketones, respectively.29,30
(2)
catalytic activity of ruthenium(II) complexes containing PCH -
2
oxazoline (type II) or PCH-oxazoline (type VI) ligands for
transfer hydrogenation of acetophenone in propan-2-ol. A
preliminary communication on related systems where the oxa-
zoline carries two methyl groups on the carbon a to nitrogen
has appeared.48
This provided an extension to work carried out by several
groups, including ours, on bifunctional phosphorus ligands
and more speciÐcally on phosphorus/oxygen P,O-type ligands
III [eqn. (3)].2,31h37
Results and discussion
(3)
Complexes with the neutral PCH -oxazoline ligand I
2
The often encountered hemilabile character of such neutral
ligands in complexes of type IV allows for the temporary pro-
Mixing
2
equiv. of PCH -oxazoline with
1
equiv. of
2
[Pd(NCMe) ](BF ) in CH Cl [eqn. (4)] led to the formation
4
4 2
2
2
Table 1 Selected NMR and IR data
NMRa
IR/cm~1 (CH Cl )
2
2
13CM1HNc
Complex
1Hb
(1J /Hz)
31PM1HNd
l(C2N)
l(CbCbN)
PC
cis-[Pd(PCH -oxazoline) ](BF ) , 1
3.75 (d) PCH e
È
29.7e
32.6e
32.8e
50.5
20.5
24.4
40.5
1633
1660, 1631
1635
1641
È
È
È
È
È
È
È
1538
1537
1546
2
2
4 2
2
[Pd(dmba)Cl(PCH -oxazoline)], 2
3.65 (d) PCH e
31.5 (25.2)
È
30.5 (34.0)
41.2 (78.5)
40.7 (82.5)
37.0 (78.8)
2
2
3.45 (d) PCH e
2
Pd(dmba)(PCH -oxazoline)](PF ), 3
2
6
[RuCl(g6-p-cymene)(PCH -oxazoline)]Cl, 4
3.30 (dd), 3.40 (dd), PCH
2
cis-[Pd(PCH-oxazoline) ], 6
2
2
2.60 (s) PCH
2.82 (s) PCH
3.10 (s) PCH
[Pd(dmba)(PCH-oxazoline)], 7
[RuCl(g6-p-cymene)(PCH-oxazoline)], 8
a In CD Cl , unless otherwise stated. b 300.13 MHz. c 75.4 MHz. d 121.5 MHz. e In CDCl .
2
2
3
New J. Chem., 2001, 25, 32È39
33

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of [Pd(PCH -oxazoline) ](BF ) (1) in high yield (95%).
4 2
2
2
(4)
The spectroscopic data (Table 1) are consistent with the
coordination of the ligand in a static bidentate fashion.29 The
cis arrangement of the P atoms is deduced from the 31PM1HN
NMR chemical shift and from the doublet observed in the 1H
NMR spectrum for the PCH protons. Such an arrangement
2
for two atoms of large trans inÑuence is thermodynamically
favoured.49,50 Moreover, the related Ni complex
[Ni(phosphinoaryloxazoline) ]2` has been recently shown to
2
have a cis structure, both in solution and in the solid state.51
(5)
Scheme 1
The analogous complex, [RuCl(g6-C H )(PCH -oxazo-
6
6
2
Reaction of PCH -oxazoline with [Pd(dmba)(l-Cl)]
line)](O SCF ) (5), was prepared for catalytic purposes
2
2
3
3
a†orded 2 via opening of the chloride bridges [eqn. (5)].
in order to allow comparison with related complexes contain-
ing a tridentate NPN ligand (see below). Its spectroscopic
properties are very similar to those of 4 (see Experimental).
The IR spectrum of 2 in CH Cl shows two bands at 1660
2
2
and 1631 cm~1, assigned to the C2N vibrations of the uncoor-
dinated and coordinated oxazolines, respectively, by analogy
with the values for the free ligand (1660 cm~1)29 and for 1.
These cationic PCH -oxazoline complexes were mainly
2
used as precursors for the synthesis of complexes containing
For comparison, we prepared the PF analogue of 2 by carry-
the anionic PCH-oxazoline ligand (see below).
6
ing out the reaction in the presence of NH PF (see
4
6
Experimental). As expected, its IR spectrum in CH Cl
Complexes with the anionic PCH-oxazoline ligand
2
2
exhibits only one band at 1635 cm~1. Therefore, the existence
of coordinated and uncoordinated oxazolines in solutions of 1
suggests competition between the oxazoline nitrogen and the
chloride for coordination to palladium. Comparison of the
31PM1HN and 1H NMR spectra with those of the free ligand
The deprotonation of the PCH group in complexes 1, 2 and
2
4 in THF was achieved in 78È86% yields, by reaction with
ButOK (Scheme 1).48 This simple and efficient methodology
has been reported before with b-ketophosphines of the type
R1PCH C(O)R2 coordinated to Re,52 Fe,53 Ru,54h56 Rh,40,57
conÐrms that PCH -oxazoline forms a P,N-chelate, but the
broad resonances of the oxazoline protons are again consis-
2
2
2
Pd,58 or Pt,59 using various bases.
In all cases, the typical l(C2N) IR absorption band of the
coordinated oxazoline in the precursor complex is replaced by
a strong absorption in the range 1537È1546 cm~1 (see Table
1). This is consistent with the IR data of a Cu complex
described by Lehn et al., which shows an absorption band at
1530 cm~1.27 The shift towards lower energy by about 100
tent with a hemilabile behaviour of the ligand through
reversible oxazoline nitrogen (de)coordination. For the Ðrst
time, this ligand is shown to display a hemilabile behaviour.2
Reaction of 2 equiv. of PCH -oxazoline with 1 equiv. of
2
[Ru(l-Cl)Cl(g6-p-cymene)] in reÑuxing EtOH [eqn. (6)] led
2
to the isolation of [RuCl(g6-p-cymene)(PCH -oxazoline)]Cl
2
cm~1 on going from PCH -oxazoline to anionic PCH-
(4) in good yield (89%).
2
oxazoline is consistent with previous observations made with
P,O-ligands when going from IV to V. The PCH carbon
appears in the 13CM1HN NMR spectrum as a doublet down-
Ðeld shifted (6.5È9 ppm) compared to the corresponding
PCH and exhibits a larger 1J coupling constant, 78.5È82.5
2
PC
Hz vs. 25.2È34.0 Hz, respectively. This increase is attributed to
the change in hybridisation of the carbon atom a to P from
sp3 in the neutral chelate to sp2 in the anionic one. While the
(6)
PCH protons of complexes 1È5 exhibit in the 1H NMR spec-
2
trum a doublet, the PCH proton of 6È8 exhibits only a singlet.
Complexes 6È8 are air-stable and, in contrast to their precur-
In contrast to 2, which also has Cl~ as a counter ion, the IR
spectrum of 4 exhibits only one C2N vibration band at 1641
cm~1, which corresponds to a coordinated oxazoline. The 1H
sors, they react with CDCl to give uncharacterised side pro-
3
ducts. An X-ray di†raction study on single crystals of 6
conÐrmed that the two phosphorus atoms occupy cis posi-
tions (Fig. 1 and Table 2). The coordination around the metal
centre approximates a square planar geometry with a slight
displacement of the PdÈN(2) vector from the plane deÐned by
the two phosphorus, two nitrogen and palladium atoms
[0.150(3) A]. The non-ideal geometry is also reÑected by the
angles P(1)ÈPdÈP(2) and N(1)ÈPd(1)ÈN(2) of 102.16(4)¡ and
NMR spectrum shows that the protons of the PCH -
2
oxazoline ligand appear at six distinct resonances and are thus
diastereotopic. This is consistent with the ruthenium centre
becoming a stereogenic centre upon chelation of PCH -
2
oxazoline. The PCH protons exhibit an ABX spin system
2
with two di†erent 2J coupling constants (8.5 and 13.0 Hz).
PH
34
New J. Chem., 2001, 25, 32È39

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Table 2 Selected bond lengths (A) and angles (¡) for cis-[Pd(PCH-
Catalytic study
oxazoline) ], (6)
2
As part of our interest in the properties of multidentate
ligands that contain both phosphine and oxazoline in a che-
lating array,2 we have tested their ruthenium complexes in the
catalytic transfer hydrogenation of ketones by propan-2-ol
[eqn. (7)].30,48,60,61 There is considerable current research
activity around this reaction in order to both develop new
classes of catalysts and to understand the di†erent steps
involved in the overall catalytic process.62h67
Pd(1)ÈP(1)
Pd(1)ÈP(2)
Pd(1)ÈN(1)
Pd(1)ÈN(2)
2.286(1)
2.293(1)
2.074(3)
2.073(3)
N(1)ÈC(2)
C(2)ÈC(1)
C(1)ÈP(1)
C(2)ÈO(1)
1.335(4)
1.370(5)
1.737(4)
1.380(4)
N(1)ÈPd(1)ÈN(2)
N(2)ÈPd(1)ÈP(2)
P(2)ÈPd(1)ÈP(1)
P(1)ÈPd(1)ÈN(1)
Pd(1)ÈN(1)ÈC(2)
94.40(11)
81.42(8)
102.16(4)
82.20(8)
116.2(2)
N(1)ÈC(2)ÈC(1)
C(2)ÈC(1)ÈP(1)
C(1)ÈP(1)ÈPd(1)
O(1)ÈC(2)ÈC(1)
O(1)ÈC(2)ÈN(1)
125.6(3)
112.1(3)
102.0(1)
121.3(3)
113.1(3)
(7)
We recently described a precursor catalyst for this reaction,
[RuCl(g6-C H )(N,P-NPN)](O SCF ) (9) where NPN is a
6
6
3
3
bis(oxazoline)phosphine that forms a bidentate P,N-chelate.60
It was shown that the dangling oxazoline arm of this ligand
tends to have a detrimental e†ect on the catalytic activity,
possibly owing to the formation of a bis-chelating system of
type 10.60 This is now further supported by the observation
that complex 5 is more active than 9 and 10 (see Table 3).
Fig. 1 ORTEP view of the crystal structure of cis-[Pd(PCH-oxazol-
ine) ] (6).
2
94.40(1)¡, respectively. The two planes deÐning the backbone
of the P,N-chelates, Pd(1), P(1), N(1), C(1), C(2) and Pd(1),
P(2), N(2), C(17), C(18), form a dihedral angle of 1.9¡.
However, the angle between the two planes O(1), N(1), C(2),
C(3), C(4) and O(2), N(2), C(18), C(19), C(20), corresponding to
the two oxazolines, form a dihedral angle of 28.8¡, which
results in a staggered arrangement for the NCH protons. It is
2
interesting to compare the distances and angles of PCHox in 6
with those of the neutral PCH -oxazoline-Me ligand in
2
2
[PdCl (PCH -oxazoline-Me )] where PCH -oxazoline-Me is
In light of our synthetic route to prepare complexes bearing
the anionic ligand, it is likely that under catalytic conditions,
the PriONa base, which is present in a 5-fold excess to Ru,
reacts with the precursor catalyst 4 to form compound 8. To
test this hypothesis we used 8 as the catalyst precursor.
Whereas the conversion obtained after 6 h at reÑux tem-
perature in propan-2-ol was identical to that observed with 4
(94% yield), the turnover frequency (TOF) was higher with
[RuCl(g6-p-cymene)(PCH-oxazoline)] than with [RuCl(g6-p-
2
2
2
2
2
similar to PCH -oxazoline but has two methyl substituents on
the carbon a to the nitrogen atom.29 Of special interest are
2
the bond lengths and angles within the Ðve-membered ring
chelates. The CÈC bond distance decreases on going from the
neutral to the anionic ligand [1.480(4) to 1.370(5) A,
respectively] and this latter value is close to the average
length of a C2C (sp2Èsp2) bond (1.34 A). At the same time, the
CÈN bond length increases from 1.276(4) to 1.335(4) A, which
is in favour of a single CÈN bond [average d(C ÈN) \ 1.36
A]. Even though it is likely that electron delocalisation occurs
cymene)(PCH -oxazoline]Cl during the Ðrst hour (Table 3).
sp2
2
This may correspond to an induction period to form the cata-
within the chelate ring, we prefer to describe the bonding
within the Ðve-membered P,N-chelate as involving a pro-
nounced C2C double bond character. The X-ray crystal struc-
ture of 6 is signiÐcant since there are only three reported
X-ray crystal structures of an anionic oxazoline in a class B
complex (M \ Cu,27 Rh,23 Y28) although this bonding mode
is often invoked, and the only example with a PCH-oxazoline-
type ligand.48
lyst 8. Although it appears that 4 gives 8 under catalytic con-
ditions, we cannot rule out that both 4 and 8 may be
independently active catalysts for transfer hydrogenation.
Noyori et al. have recently published67 the structure of a pre-
formed catalyst precursor 11, which upon in situ deprotona-
tion of the NH group generates the true catalyst 12 which is
to date among the best catalysts for transfer hydrogenation of
ketones.68,69 These results emphasise the spectacular conse-
New J. Chem., 2001, 25, 32È39
35

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Table 3 Transfer hydrogenation of acetophenone in propan-2-ol
catalyzed by Ru(II) complexesa
were puriÐed and dried under nitrogen by conventional
methods. The 1H, 13C and 31PM1HN NMR spectra were
recorded at 300.13, 75.4 and 121.5 MHz, respectively, on an
FT Bruker AC300 instrument, 1HM31PN NMR at 500.13 MHz
on an FT Bruker ARX500 instrument, chemical shifts are
positive downÐeld from external TMS for 1H and 13C, and
from H PO (85% in H O) for 31P. IR spectra were recorded
Catalyst
Time/h
Yieldb (%)
Turnover/h~1
4
0.25
1
3
6
0.25
1
0.25
1
3
6
8
5
40
68
50
32
184
122
200
98
58
32
34
75
94
23
61
25
49
86
94
16
13.5
54
11
45
3
4
2
in the 4000È400 cm~1 range on a Bruker IFS66 FT spectro-
5
8
meter.
Syntheses
The compounds [Pd(dmba)(l-Cl)] ,72 [Ru(l-Cl)Cl(g6-p-
8c
9d
4
2
cymene)] ,73 and [Pd(NCMe) ](BF ) 74 were prepared
0.25
1
0.25
1
108
108
88
2
4
4 2
according to literature procedures.
10d
90
cis-[Pd(PCH -oxazoline) ](BF ) (1). In a 100 mL Schlenk
a The reactions were carried out in reÑuxing propan-2-ol using a 0.1
M substrate concentration and a 0.1 M solution of PriONa as a base
and a 1 : 200 : 5 RuÈketoneÈbase ratio. b Chemical yields determined
by GC analysis of the crude reaction mixture at the reported time.
c Reaction carried out in propan-2-ol at 30 ¡C. d Taken from ref. 60
with a 1:200:24 RuÈketoneÈbase ratio.
2
2
4 2
Ñask were placed together the ligand PCH -oxazoline (0.715
2
g, 2.660 mmol) and [Pd(NCMe) ](BF ) (0.590 g, 1.330 mmol)
in CH Cl (40 mL). The pale yellow solution was stirred for
12 h and the volume reduced under vacuum to about 5 mL.
Addition of pentane a†orded a white solid, which was further
4
4 2
2
2
washed with Et O (2 ] 10 mL) and dried in vacuo. The
2
product was obtained as a white solid (1.035 g, yield 95%). 1H
quences that ligand deprotonation may have on the catalytic
properties of the metal complex.
NMR (CDCl , 300.13 MHz): d 3.75 (d, 4 H, 2J \ 11.9 Hz,
3
PH
PCH ), 4.40 (t, 4 H, 3J \ 9.5 Hz, NCH ), 4.80 (t, 4 H,
2
HH
2
3J \ 9.5 Hz, OCH ), 7.30È7.65 (m, 20 H, aryl). 31PM1HN
HH
2
NMR (CDCl , 121.5 MHz):
d 29.7. Anal. calc. for
3
2
C
H
B F N O P Pd: C, 46.95; H, 3.94; Found: C, 47.22;
32 32 2 8
H, 3.68%.
2 2
[Pd(dmba)(PCH -oxazoline)]Cl (2). In a 100 mL Schlenk
2
Ñask were placed together the phosphine oxazoline ligand
PCH -oxazoline (1.095 g, 4.070 mmol) and [Pd(dmba)(l-Cl)]
2
2
(1.120 g, 2.03 mmol) in CH Cl (30 mL). The pale yellow solu-
2
2
tion was stirred for 1 h after which the volume was reduced
under vacuum to about 3 mL. Addition of hexane led to the
precipitation of a colourless oil, which was triturated with
Compound [RuCl(g6-p-cymene)(PCH-oxazoline)] (8) is very
similar to 11 with the di†erence that the PCHox ligand in 8
cannot be further deprotonated to form species analogous to
12.67a This could account for the higher reactivity of 11 com-
pared to 8. Nevertheless, our results are encouraging and
complexes analogous to [RuCl(g6-p-cymene)(PCH-oxazoline)]
Et O (2 ] 5 mL); the solid thus obtained was washed with
2
hexane (2 ] 30 mL) and dried under vacuum. The product
was obtained as a white powder (1.995 g, 90%). 1H NMR
(CDCl , 300.13 MHz): d 2.90 [s, 6 H, N(CH ) ], 3.65 (d, 2 H,
with a chiral version of PCH -oxazoline should be synthesised
3
3 2
2
2J \ 8.4 Hz, PCH ), 4.05 [overlapping s and m, 4 H,
in the future. Furthermore, Noyori et al. have shown that the
PH
2
(CH ) NCH and oxazoline NCH ], 4.45 (t, 2 H, 3J \ 9.4
arene ligand has a strong inÑuence on the reactivity and enan-
tioselectivity of the catalysts, suggesting that complexes con-
taining other arene ligands such as benzene or 1,3,5-
trimethylbenzene should also be evaluated.70
3 2
2
2
HH
Hz, OCH ), 6.30È7.00 (m, 4 H, aryl from dmba), 7.40È7.90 (m,
2
10 H, aryl). 13CM1HN NMR (CD Cl , 75.4 MHz): d 31.5 (d,
2
2
1J \ 25.2 Hz, PCH ), 51.0 [s, N(CH ) ], 54.7 (s, NCH ),
PC
2
3 2
2
69.5 [s, (CH ) NCH ], 73.0 (s, OCH ), 123.2È149.5 (m, aryl),
3 2
PC
2
2
167.7 (d, 2J \ 10.9 Hz, C2N). 31PM1HN NMR (CDCl , 121.5
3
Conclusion
MHz): d 32.6. Anal. calc. for C
H
ClN OPPd: C, 55.06; H,
25 28
2
5.18; N, 5.14. Found: C, 55.20; H, 5.17; N, 5.04%.
The versatility of the PCH -oxazoline ligand allows its coor-
2
dination as hemilabile or static neutral P,N- or static anionic
[Pd(dmba)(PCH -oxazoline)](PF ) (3). In
a 100 mL
P,N-type ligand. It was shown that in the latter case its struc-
tural and electronic properties induce higher reactivity in the
catalytic transfer hydrogenation of acetophenone in propan-2-
ol than its neutral analogue. This Ðnding should lead to
further investigations with chiral versions of PCH-oxazoline
in order to study their inÑuence on the enantioselectivity of
this catalytic reaction. Also as an extension to this work, it
would be interesting to evaluate our Ru-phosphinooxazoline
2
6
Schlenk Ñask were placed together [Pd(dmba)(PCH -
2
oxazoline)]Cl (2) (0.400 g, 0.737 mmol) and NH PF (0.122,
4
6
0.740 mmol) in CH Cl (30 mL). The pale yellow solution was
2
2
stirred for 2 h after which the solution was Ðltered through
Celite and its volume reduced under vacuum to about 2 mL.
Addition of pentane led to the precipitation of a pale yellow
solid, which was further washed with Et O (2 ] 10 mL) and
2
dried in vacuo. The product was obtained as a pale yellow
complexes in DielsÈAlder reactions, since a [Ru(H O)(g6-p-
2
solid (0.438 g, 91%). 1H NMR (CDCl , 300.13 MHz): d 2.90
cymene)-phosphinoaryloxazoline]2` complex has been recent-
3
[s, 6 H, N(CH ) ], 3.45 (d, 2 H, 2J \ 10.5 Hz, PCH ), 4.00
ly reported to be a good catalyst for such reactions.71
3 2
PH
2
[s, 2 H, (CH ) NCH ], 4.05 (t, 2 H, 3J \ 11.1 Hz, oxazoline
3 2
NCH ), 4.60 (t, 2 H, 3J \ 11.1 Hz, OCH ), 6.40È7.00 (m, 4
HH
2
HH
Experimental
2
2
H, aryl from dmba), 7.40È7.90 (m, 10 H, aryl). 31PM1HN NMR
(CDCl , 121.5 MHz):
d
32.8. Anal. calc. for
General procedures
3
C
H
N OP Pd: C, 45.85; H, 4.31. Found: C, 45.61; H,
25 28
2
2
All reactions were performed under puriÐed nitrogen. Solvents
4.22%.
36
New J. Chem., 2001, 25, 32È39

View Article Online
Table 4 Selected crystallographic data for complex cis-[Pd(PCH-
reduced under vacuum to ca. 2 mL. Addition of Et O a†orded
a yellow solid, which was further washed with 10 mL of
2
oxazoline) ], 6
2
hexane and Et O. Pure 5 was obtained by crystallisation from
2
Formula
FW
C
642.95
Monoclinic
P21/n (no. 14)
180(1)
17.293(2)
9.7528(13)
17.6784(6)
115.2840
2695.9(4)
4
8.42
24477
6934
352
H
N O P Pd
2 2
1 : 3 CH Cl Èhexane (0.375 g, 75%). 1H NMR (CDCl ,
32 30
2
2
2
3
300.13 MHz): ABX spin system d 3.25 (dd, 1 H, 2J \ 17.5
Crystal system
Space group
T /K
A
HH
Hz, 2J \ 8.5 Hz, PCH H), d 3.40 (dd, 1 H, 2J \ 17.5 Hz,
PH HH
2J \ 12.5 Hz, PCHH ), 4.15 (m with appearance of overlap-
PH
A
B
B
a/A
ping dt, 1 H, J \ 10.2 Hz, J \ 10.5 Hz, OCHH), 4.75 (m,
HH
HH
b/A
1 H, NCHH), 4.90 (m, NCHH), 5.20 (m with appearance of
overlapping dt, 1 H, J \ 8.5 Hz, J \ 9.6 Hz, OCHH),
c/A
b/¡
HH
HH
5.80 (s, 6 H, g6-benzene), 7.30 (m, 2 H, aryl), 7.50È7.80 (m, 8 H,
U/A
Ž
3
aryl H). 31PM1HN NMR (CDCl , 121.5 MHz): d 48.4. Anal.
Z
3
k/mm~1
calc. for C
H
ClF NO PSRu: C, 44.38; H, 4.04; N, 2.16.
24 26
3
4
No. of reÑections collected
No. of unique reÑections
No. of variable parameters
No. of reÑections [I [ 3p(I)]
Found: C, 44.49; H, 3.95; N, 2.27%.
cis-[Pd(PCH-oxazoline) ] (6). In a 100 mL Schlenk Ñask
4082
0.037, 0.031
2
Residuals (R, R )a
were placed together cis-[Pd(PCH -oxazoline) ](BF ) (1.005
w
2
2
4 2
g, 1.228 mmol) and ButOK (0.305 g, 2.700 mmol) in THF (30
mL). The colourless suspension turned redÈorange within 15
min with formation of a white precipitate; the reaction
mixture was then stirred for 12 h. The solvent was removed
under reduced pressure and CH Cl (30 mL) was added. The
a R \ & ( p F o [ o F p )/& o F o ;
hkl
obs
calc
hkl obs
R \ [& w( o F o [ o F o )2/& wF2 ]1@2, w \ 1/p2(F ).
w
hkl
obs
calc
hkl obs
obs
2
2
[RuCl(g6-p-cymene)(PCH -oxazoline)]Cl (4). In a 100 mL
white precipitate was Ðltered o† by means of a canula Ðtted
with glass Ðber Ðlter paper. The volume of the solution was
2
Schlenk Ñask Ðtted with a reÑux condenser were placed
together the ligand PCH -oxazoline (0.138 g, 0.513 mmol) and
reduced under vacuum to about 4 mL; addition of Et O
2
2
a†orded an orange solid, which was further washed with Et O
2
[Ru(l-Cl)Cl(g6-p-cymene)] (0.157 g, 0.256 mmol) in EtOH
2
(15 mL). The yellow solution was heated to reÑux temperature
(2 ] 20 ml) and dried in vacuo. The product was obtained as
for 1.5 h, then cooled to room temperature and the solvent
was removed under vacuum. The solid was partially dissolved
in THF (2 mL) and precipitated by addition of pentane (15
mL). This procedure was repeated twice and a†orded the
product as a yellow powder (0.260 g, yield: 89%). 1H NMR
(CD Cl , 300.13 MHz): d 1.15 [d, 3 H, 2J \ 6.8 Hz,
an orange powder (0.616 g, yield 78%). 1H NMR (CD Cl ,
2
2
300.13 MHz): d 2.60 (s, 1 H, PCH), 3.90 (t, 2 H, 3J \ 7.9
HH
Hz, NCH ), 4.35 (t, 2 H, 3J \ 7.9 Hz, OCH ), 7.00È7.40 (m,
2
HH
2
20 H, aryl). 13CM1HN NMR (CD Cl , 75.4 MHz): d 41.2 (d,
2
2
2
1J \ 78.5 Hz, PCH), 52.7 (s, NCH ), 70.1 (s, OCH ), 126.5È
PC
2
135.0 (m, aryl), 180.5 (d, C2N). 31PM1HN NMR (CD Cl , 121.5
2
2
HH
2 2
CH(CH )(CH )], 1.25 [d,
3
H, 2J \ 6.8 Hz,
MHz): d 20.5. Anal. calc. for C
H
N O P Pd: C, 59.78; H,
3
3
3
HH
32 30
2 2 2
CH(CH )(CH )], 1.50 (s, 3 H, p-CH ), 2.50 [sept, 1 H, 2J
6.8 Hz, CH(CH ) ], ABX spin system d 3.30 (dd, 1 H,
\
4.70; N, 4.36. Found: C, 60.04; H, 4.62; N, 4.18%.
3
3
HH
3 2
A
B
2J \ 17 Hz, 2J \ 8.5 Hz, PCH H), d 3.40 (dd, 1 H,
HH PH
2J \ 17 Hz, 2J \ 13.0 Hz, PCHH ), 4.10 (dd, 1 H,
HH PH
2J \ 21.0 Hz, 3J \ 10.4 Hz, OCHH), 4.75 (dd, 1 H,
HH HH
2J \ 14.2 Hz, 3J \ 7.5 Hz, NCHH), 5.10 (dd, 1 H,
HH HH
A
[Pd(dmba)(PCH-oxazoline)] (7). In a 100 mL Schlenk Ñask
B
were placed together complex [Pd(dmba)Cl(PCH -oxazoline)]
2
(1.020 g, 1.875 mmol) and ButOK (0.220 g, 1.970 mmol) in
THF (20 mL). The colourless suspension turned yellow within
5 min with formation of a white precipitate; the reaction
mixture was stirred then for 12 h. The solvent was removed
under reduced pressure and CH Cl (30 mL) was added. The
2J \ 21.0 Hz, 3J \ 10.4 Hz, OCHH), 5.20 (m, 1 H,
HH
HH
NCHH), 5.60 (d, 1 H, 3J \ 5.8 Hz, p-cymene), 5.70 (d, 1 H,
HH
3J \ 5.8 Hz, p-cymene), 6.15 (d, 1 H, 3J \ 6.0 Hz, p-
HH
HH
cymene), 6.25 (d, 1 H, 3J \ 6.0 Hz, p-cymene), 7.30 (m, 2 H,
2
2
HH
white precipitate was Ðltered o† by means of a canula Ðtted
with glass Ðber Ðlter paper. The volume of the solution was
reduced under vacuum to about 4 mL; addition of pentane
a†orded a yellow solid, which was further washed with hexane
(2 ] 20 mL) and dried in vacuo. The product was obtained as
a yellow powder (0.800 g, yield 84%). 1H NMR (CD Cl ,
aryl), 7.40È7.70 (m, 8 H, aryl H). 13CM1HN NMR (CD Cl ,
2
2
75.4 MHz): d 17.4 (s, p-CH ), 21.8 [s, CH(CH )(CH )], 22.8 [s,
3
3
3
CH(CH )(CH )], 30.5 (d, 1J \ 34 Hz, PCH ), 31.2 [s,
PC
CH(CH ) ], 58.6 (s, NCH ), 73.5 (s, OCH ), 84.7 (s, aromatic
3
3 2
3
2
2
2
p-cymene), 87.3 (d, J \ 6.6 Hz, aromatic p-cymene), 89.3 (d,
PC
2J \ 6.9 Hz, aromatic p-cymene), 101.4 (s, aromatic p-
2
2
PC
300.13 MHz): d 2.80 [s, 6 H, N(CH ) ], 2.82 (s, 1 H, PCH),
cymene), 117.1 (d, J \ 4.7 Hz, aromatic p-cymene), 126.2È
3 2
PC
3.70 (t, 2 H, 3J \ 7.9 Hz, oxazoline NCH ), 3.95 [s, 2 H,
135.5 (m, aryl), 175.6 (d, 2J \ 16.9 Hz, C2N). 31PM1HN NMR
HH
2
PC
(CH ) NCH ], 4.30 (t, 2 H, 3J \ 7.9 Hz, OCH ), 6.55È7.00
(CD Cl , 121.5 MHz):
d
50.5. Anal. calc. for
3 2
2
HH
2
2
2
(m, 4 H, aryl from dmba), 7.40È7.70 (m, 10 H, aryl). 13CM1HN
(CD Cl , 75.4 MHz): d 40.7 (d, 1J \ 82.5 Hz, PCH), 50.9 [s,
C
H
NOPCl Ru: C, 54.20; H, 5.21; N, 2.43. Found: C,
26 30
2
54.17; H, 5.31; N, 2.27%.
2
2
PC
N(CH ) ], 52.2 (s, oxazoline NCH ), 69.3 [s, (CH ) NCH ],
3 2
2
3 2
2
3
73.3 (s, OCH ), 122.8È149.5 (m, aryl). 31PM1HN NMR (CDCl ,
[RuCl(g6-benzene)(PCH -oxazoline)](O SCF ) (5). In
a
2
2
3
3
121.5 MHz): d 24.4. Anal. calc. for C
H, 5.35; N, 5.50. Found: C, 58.79; H, 5.22; N, 5.46%.
H
N OPPd: C, 59.01;
100 mL Schlenk Ñask were placed together the ligand PCH -
25 27
2
2
oxazoline (0.210 g, 0.78 mmol) and [Ru(l-Cl)Cl(g6-benzene)]
2
(0.195 g, 0.39 mmol) in CH Cl (15 mL). The dark orange
2
2
solution obtained was stirred for 1 h at room temperature and
then Ðltered through a canula Ðtted with glass Ðber paper.
The resulting orange solution was evaporated to about 1 mL
and an orange precipitate was obtained by addition of hexane.
The orange solid was further washed with 2 ] 10 mL of
hexane. After drying under vacuum for 2 h, solid Ag(O SCF )
[RuCl(g6-p-cymene)(PCH-oxazoline)] (8). In a 100 mL
Schlenk Ñask were placed together [RuCl(g6-p-cymene)-
(PCH -oxazoline)]Cl (0.440 g, 0.765 mmol) and ButOK (0.090
2
g, 0.800 mmol) in THF (20 mL). The yellow solution turned
orange within 5 min with formation of a white precipitate; the
reaction mixture was then stirred for 12 h. The solvent was
removed under reduced pressure and CH Cl (30 mL) was
3
3
(0.200 g, 0.78 mmol) and 20 mL of CH Cl were added. After
2
2
2 2
a few minutes, a pale yellow suspension appeared and the
reaction mixture was stirred for 1 h. The suspension was Ðl-
tered over Celite and the volume of the orange Ðltrate was
added. The white precipitate was Ðltered o† by means of a
canula Ðtted with glass Ðber Ðlter paper. The volume of the
deep orange solution was reduced under vacuum to about 4
New J. Chem., 2001, 25, 32È39
37

View Article Online
9
P. G. Cozzi, E. Gallo, C. Floriani, A. ChiesiÈVilla and C. Rizzoli,
Organometallics, 1995, 14, 4994.
mL; addition of Et O a†orded a brownÈorange solid, which
2
was further washed with Et O (2 ] 20 ml) and dried in vacuo.
2
10 P. G. Cozzi, C. Floriani, A. ChiesiÈVilla and C. Rizzoli, Inorg.
Chem., 1995, 34, 2921.
The product was isolated as a brownÈorange powder (0.355 g,
yield: 86%). 1H NMR (CD Cl , 500.13 MHz): d 0.95 [d, 3 H,
11 (a) C. Bolm, K. Weickhardt, M. Zehnder and D. Glasmacher,
Helv. Chim. Acta, 1991, 74, 717; (b) C. Bolm, G. Schlinglo† and
K. Weickhardt, Angew. Chem., Int. Ed. Engl., 1994, 33, 1848; (c)
C. Bolm and G. Schlinglo†, J. Chem. Soc., Chem. Commun., 1995,
1247; (d) C. Bolm, T. K. K. Luong and K. Harms, Chem. Ber.
Recueil, 1997, 130, 887.
2
2
2J \ 6.9 Hz, CH(CH )(CH )], 1.10 [d, 3 H, 2J \ 6.9 Hz,
HH
3
3
HH
CH(CH )(CH )], 2.10 (s, 3 H, p-CH ), 2.20 [sept, 1 H, 2J
6.9 Hz, CH(CH ) ], 3.10 (s, 1 H, PCH), 3.70 (m with appear-
ance of t of d, 2J \ 9.0 Hz, 3J
Hz, OCHH), 3.85 (m with appearance of overlapping dt, 1 H,
\
3
3
3
HH
3 2
\ 9.0 Hz, 3J
\ 3.6
HH
HHcis
HHtrans
12 (a) H. Brunner and J. Berghofer, J. Organomet. Chem., 1995, 501,
161; (b) H. Brunner and B. Hassler, Z. Naturforsch. B, 1998, 53,
126.
J
\ 10.2 Hz, J \ 9.0 Hz, NCHH), 4.25 (m with appear-
HH
HH
ance of overlapping dt, 1 H, J \ 10.2 Hz, J \ 7.8 Hz,
HH
HH
OCHH), 4.25 (overlapping m, 1 H, J \ 1.2 Hz, p-cymene),
13 H. R. Hoveyda, V. Karunaratne, S. J. Rettig and C. Orvig, Inorg.
HH
Chem., 1992, 31, 5408.
4.35 (m with appearance of t of d of d, 2J \ 7.8 Hz,
HH
14 H. Yang, M. A. Khan and K. M. Nicholas, Organometallics, 1993,
12, 3485.
15 M. GomezÈSimon, S. Jansat, G. Muller, D. Panyella, M. Font-
Bard•a and X. Solans, J. Chem. Soc., Dalton T rans., 1997, 3755.
16 (a) C. Bolm, K. MunizÈFernandez, A. Seger, G. Raabe and K.
Gunther, J. Org. Chem., 1998, 63, 7860; (b) C. Bolm and K.
Muniz, Chem. Commun., 1999, 1295.
17 Q.-L. Zhou and A. Pfaltz, T etrahedron, 1994, 50, 4467.
18 H. Brunner and B. Hassler, Z. Naturforsch. B, 1998, 53, 476.
19 R. P. Singh, Synth. React. Inorg. Met.-Org. Chem., 1997, 27, 155.
20 M. Bandini, P. G. Cozzi, L. Negro and A. UmaniÈRonchi, Chem.
Commun., 1999, 39.
21 R. E. Lowenthal, A. Abiko and S. Masamune, T etrahedron L ett.,
1990, 31, 6005.
22 D. A. Evans, K. A. Woerpel, M. M. Hinman and M. M. Faul, J.
Am. Chem. Soc., 1991, 113, 726.
23 J. M. Brown, P. J. Guiry, D. W. Price, M. B. Hursthouse and S.
Karalulov, T etrahedron: Asymmetry, 1994, 5, 561.
24 M. Nakamura, M. Arai and E. Nakamura, J. Am. Chem. Soc.,
1995, 117, 1179.
25 M. Nakamura, A. Hirai and E. Nakamura, J. Am. Chem. Soc.,
1996, 118, 8489.
26 E. J. Corey and Z. Wang, T etrahedron L ett., 1993, 34, 4001.
27 J. Hall, J.-M. Lehn, A. DeCian and J. Fischer, Helv. Chim. Acta,
1991, 74, 1.
28 H. W. Gorlitzer, M. Spiegler and R. Anwander, J. Chem. Soc.,
Dalton T rans., 1999, 4287.
29 P. Braunstein, M. D. Fryzuk, M. Le Dall, F. Naud, S. J. Rettig
and F. Speiser, J. Chem. Soc., Dalton T rans., 2000, 1067.
30 P. Braunstein, C. Grai†, F. Naud, A. Pfaltz and A. Tiripicchio,
Inorg. Chem., 2000, 39, 4468.
31 A. Bader and E. Lindner, Coord. Chem. Rev., 1991, 108, 27.
32 S.-E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D.
Nobel, Inorg. Chem., 1986, 25, 3765.
33 J. Andrieu, P. Braunstein and A. D. Burrows, J. Chem. Res.,
Synop., 1993, 380.
34 W. Keim, H. Maas and S. Mecking, Z. Naturforsch. B, 1995, 50,
3J
\ 7.8 Hz, 3J
\ 3.6 Hz, 5J \ 1.2 Hz, NCHH),
HHcis
HHtrans
HH
5.20 (d, 1 H, 3J \ 6.2 Hz, p-cymene), 5.40 (d, 1 H, 3J
\
HH
HH
5.7 Hz, p-cymene), 5.70 (d, 1 H, 3J \ 6.2 Hz, p-cymene),
HH
7.30È7.40 (m, 6 H, aryl), 7.50È7.70 (m, 4 H, aryl H). 13CM1HN
NMR (CD Cl , 75.4 MHz):
d
18.4 (s, CH ), 22.0 [s,
2
2
3
CH(CH )(CH )], 23.0 [s, CH(CH )(CH )], 31.4 [s,
3
3 2
3
3
3
CH(CH ) ], 37.0 (d, 1J \ 78.8 Hz, PCH), 55.4 (s, NCH ),
PC
2
69.3 (s, OCH ), 83.5 (s, PriÈCÉ É ÉCH from p-cymene), 84.5 (s,
2
MeÈCÉ É ÉCH from p-cymene), 88.6 (d, J \ 5.9 Hz, PriÈ
PC
CÉ É ÉCH from p-cymene), 93.3 (d, J \ 5.9 Hz, MeÈCÉ É ÉCH
PC
from p-cymene), 97.4 (s, quat C p-cymene), 103.1 (s, quat C
p-cymene), 126.8È142.2 (m, aryl), 179.3 (d, 2J \ 43.4 Hz,
PC
C2N). 31PM1HN NMR (CD Cl , 121.5 MHz): d 40.5. Anal.
2
2
calc. for C
H
NOPRuCl: C, 57.88; H, 5.38; N, 2.59.
26 29
Found: C, 57.65; H, 5.29; N, 2.56%.
X-Ray structural analysis75
The intensity data were collected on a Rigaku/ADSC CCD
di†ractometer at 180(1) K in 0.50¡ oscillations with 35.0 s
exposures. The structure was solved by heavy-atom Patterson
methods and expanded using Fourier techniques. The non-
hydrogen atoms were reÐned anisotropically. Hydrogen atoms
were Ðxed in calculated positions with CÈH \ 0.98 A. Selected
data are given in Table 4.
CCDC reference number 440/211. See http://www.rsc.org/
suppdata/nj/b0/b004786o/ for crystallographic Ðles in cif
format.
430.
35 G. J. P. Britovsek, W. Keim, S. Mecking, D. Sainz and T.
Wagner, J. Chem. Soc., Chem. Commun., 1993, 1632.
36 C. S. Slone, D. A. Weinberger and C. A. Mirkin, Prog. Inorg.
Chem., 1999, 48, 233.
Acknowledgements
We are grateful to Prof. M. D. Fryzuk (Vancouver) for his
hospitality toward F.N. and to the Centre National de la
Recherche ScientiÐque (Paris) and the Ministere de
lÏEnseignement Superieur de la Recherche et de la Technol-
ogie (Paris) for Ðnancial support and a PhD grant to F.N.
37 J. Andrieu, P. Braunstein, F. Naud and R. D. Adams, J.
Organomet. Chem., 2000, 601, 43.
38 P. Braunstein, D. Matt, Y. Dusausoy, J. Fischer, A. Mitschler and
L. Ricard, J. Am. Chem. Soc., 1981, 103, 5115.
39 P. Braunstein, D. Matt and D. Nobel, J. Am. Chem. Soc., 1988,
110, 3207.
40 P. Braunstein, Y. Chauvin, J. Nahring, A. DeCian, J. Fischer, A.
Tiripicchio and F. Ugozzoli, Organometallics, 1996, 15, 5551.
41 W. Keim, Angew. Chem., Int. Ed. Engl., 1990, 29, 235.
42 W. Keim, New J. Chem., 1994, 18, 93.
References
43 U. Klabunde, T. H. Tulip, D. C. Roe and S. D. Ittel, J.
Organomet. Chem., 1987, 334, 141.
1
2
T. G. Gant and A. I. Meyers, T etrahedron, 1994, 50, 2297.
P. Braunstein and F. Naud, Angew. Chem., Int. Ed., 2001, 40, in
press.
44 P. Braunstein, Y. Chauvin, S. Mercier, L. Saussine, A. DeCian
and J. Fischer, J. Chem. Soc., Chem. Commun., 1994, 2203.
45 D. Matt, M. Huhn, M. Bonnet, I. Tkatchenko, U. Englert and W.
Klaui, Inorg. Chem., 1995, 34, 1288.
3
4
C. Bolm, Angew. Chem., Int. Ed. Engl., 1991, 30, 542.
A. K. Ghosh, P. Mathivanan and J. Cappiello, T etrahedron:
Asymmetry, 1998, 9, 1.
46 X. Gao, M. D. Fryzuk and S. J. Rettig, Can. J. Chem., 1995, 73,
1175.
5
6
A. Pfaltz, Synlett, 1999, 835.
47 J. Pietsch, P. Braunstein and Y. Chauvin, New J. Chem., 1998,
221, 467.
48 P. Braunstein, C. Graif, F. Naud and A. Tiripicchio, Chem.
Commun., 2000, 897.
49 T. G. Appleton, H. C. Clark and L. E. Manzer, Coord. Chem.
Rev., 1973, 10, 335.
S. E. Denmark, R. A. Stavenger, A.-M. Faucher and J. P.
Edwards, J. Org. Chem., 1997, 62, 3375.
Y. Motoyama, N. Makihara, Y. Mikami, K. Aoki and H. Nishiy-
ama, Chem. L ett., 1997, 951.
Y. Motoyama, Y. Mikami, H. Kawakami, K. Aoki and H.
Nishiyama, Organometallics, 1999, 18, 3584.
7
8
38
New J. Chem., 2001, 25, 32È39

View Article Online
50 F. R. Hartley, Chem. Soc. Rev., 1973, 2, 163.
51 K. L. Bray, C. P. Butts, G. C. LloydÈJones and M. Murray, J.
Chem. Soc., Dalton T rans., 1998, 1421.
52 P. Braunstein, L. Douce, F. Balegroune, D. Grandjean, D.
Bayeul, Y. Dusausoy and P. Zanello, New J. Chem., 1992, 16,
925.
63 R. Noyori and S. Hashiguchi, Acc. Chem. Res., 1997, 30, 97.
64 M. J. Palmer and M. Willis, T etrahedron: Asymmetry, 1999, 10,
2045.
65 A. Aranyos, G. Csjernyik, K. J. Szabo and J.-E. Backvall, Chem.
Commun., 1999, 351.
66 D. A. Alonso, P. Brandt, S. J. M. Nordin and P. G. Andersson, J.
Am. Chem. Soc., 1999, 121, 9580.
53 P. Braunstein, S. Coco Cea, A. DeCian and J. Fischer, Inorg.
Chem., 1992, 31, 4203.
67 (a) K.-J. Haack, S. Hashiguchi, A. Fujii, T. Ikariya and R.
Noyori, Angew. Chem., Int. Ed. Engl., 1997, 36, 285; (b) M. Yama-
kawa, H. Ito and R. Noyori, J. Am. Chem. Soc., 2000, 122, 1466.
68 Y. Jiang, Q. Jiang and X. Zhang, J. Am. Chem. Soc., 1998, 120,
3817.
54 J. Bank, P. Steinert, B. Windmuller, W. Wolfsberger and H.
Werner, J. Chem. Soc., Dalton T rans., 1996, 1153.
55 G. Henig, M. Schulz and H. Werner, Chem. Commun., 1997, 2349.
56 P. Braunstein, Y. Chauvin, J. Nahring, Y. Dusausoy, D. Bayeul,
A. Tiripicchio and F. Ugozzoli, J. Chem. Soc., Dalton T rans.,
1995, 851.
69 Y. Nishibayashi, I. Takei, S. Uemura and M. Hidai,
Organometallics, 1999, 18, 2291.
70 J. Takehara, S. Hashiguchi, A. Fujii, S.-I. Inoue, T. Ikariya and R.
Noyori, Chem. Commun., 1996, 233.
57 P. Braunstein, Y. Chauvin, J. Nahring, A. DeCian and J. Fischer,
J. Chem. Soc., Dalton T rans., 1995, 863.
58 J. Andrieu, P. Braunstein and F. Naud, J. Chem. Soc., Dalton
T rans., 1996, 2903.
59 P. Braunstein, T. Stahrfeldt and J. Fischer, C. R. Seances Acad.
Sci., t. 2, Ser. IIc, 1999, 273.
60 P. Braunstein, M. D. Fryzuk, F. Naud and S. J. Rettig, J. Chem.
Soc., Dalton T rans., 1999, 589.
61 P. Braunstein, F. Naud, A. Pfaltz and S. J. Rettig,
Organometallics, 2000, 19, 2676.
62 G. Zassinovich, G. Mestroni and S. Gladiali, Chem. Rev., 1992,
92, 1051.
71 D. Carmona, C. Cativiela, S. Elipe, F. J. Lahoz, M.-P. Lamata,
M.-P. LopezÈRam de V•u, L. A. Oro, C. Vega and F. Viguri,
Chem. Commun., 1997, 2351.
72 A. C. Cope and E. C. Friedrich, J. Am. Chem. Soc., 1968, 90, 909.
73 M. A. Bennett, T.-N. Huang, T. W. Matheson and A. K. Smith,
Inorg. Synth., 1982, 21, 74.
74 A. Sen and T.-W. Lai, Inorg. Chem., 1984, 23, 3257.
75 T. Y. Fu, Z. Liu, S. J. Rettig, J. R. Sche†er and J. Trotter, Acta
Crystallogr., Sect. C, 1997, 53, 1577.
New J. Chem., 2001, 25, 32È39
39