Catalytic transfer hydrogenation of ketones by the use of ruthenium complexes incorporating the new tridentate ligand, bis(2-oxazolin-2-ylmethyl)phenylphosphine

Article abstract of DOI:10.1039/a808170k

The new heterofunctional phosphine ligand bis(2-oxazolin-2-ylmethyl)phenylphosphine (N,P,N) has been prepared and has allowed the synthesis of the ruthenium complexes fac-[RuCl₂(DMSO)(N,P,N)] 1, fac-[RuCl₂(PPh₃)(N,P,N)] 2, [RuCl(η⁶-C₆H₆)(N,P,N)][O ₃SCF₃] 3 and [Ru(η⁶-C₆H₆)(N,P,N)][O₃SCF ₃]₂ 4. When tridentate, as in 1, 2, and 4, this ligand co-ordinates in a facial-type mode. In complex 3, it acts as a P,N-chelate with a dangling oxazoline ring. The structures of the ligand, 2·CH₂Cl₂·0.25C₆H₁₄ and 3 have been determined by X-ray diffraction. Complexes 1-4 catalyse the transfer hydrogenation reaction between propan-2-ol and ketones. Only small differences in reactivity were observed between 3 and 4, despite the different ligand bonding mode in these complexes. For the best catalyst, 2, yields up to 97% were obtained and turnover frequencies may be as high as 112 000 h^-1.

Full text of DOI:10.1039/a808170k

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Catalytic transfer hydrogenation of ketones by the use of
ruthenium complexes incorporating the new tridentate ligand,
bis(2-oxazolin-2-ylmethyl)phenylphosphine
Pierre Braunstein,*a Michael D. Fryzuk,*b Frédéric Nauda and Steven J. Rettigb
a Université Louis Pasteur, Laboratoire de Chimie de Coordination (UMR 7513 CNRS),
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, Vancouver,
British Columbia, V6T 1Z1, Canada
Received 21st October 1998, Accepted 15th December 1998
The new heterofunctional phosphine ligand bis(2-oxazolin-2-ylmethyl)phenylphosphine (N,P,N) has been prepared
and has allowed the synthesis of the ruthenium complexes fac-[RuCl2(DMSO)(N,P,N)] 1, fac-[RuCl2(PPh3)(N,P,N)]
2, [RuCl(η6-C6H6)(N,P,N)][O3SCF3] 3 and [Ru(η6-C6H6)(N,P,N)][O3SCF3]2 4. When tridentate, as in 1, 2, and 4, this
ligand co-ordinates in a facial-type mode. In complex 3, it acts as a P,N-chelate with a dangling oxazoline ring. The
structures of the ligand, 2ؒCH2Cl2ؒ0.25C6H14 and 3 have been determined by X-ray diffraction. Complexes 1–4
catalyse the transfer hydrogenation reaction between propan-2-ol and ketones. Only small differences in reactivity
were observed between 3 and 4, despite the different ligand bonding mode in these complexes. For the best catalyst,
2, yields up to 97% were obtained and turnover frequencies may be as high as 112 000 hϪ1
.
Improved or novel stoichiometric or catalytic reactivities are
continuously achieved with co-ordination and organometallic
compounds. One major way to control and orient the reactivity
of a metal containing species is by modifying the structure or
the nature of the surrounding ligands. Among the most com-
mon donor atoms, C, N and P play a central role.1,2 In homo-
geneous and asymmetric catalysis homotopic or heterotopic
polydentate ligands have attracted much attention. Thus lig-
ands bearing different donor atoms can induce increased select-
ivity owing to different electronic properties of these atoms
Results and discussion
Synthesis and characterization of the ligand
which is relayed to the reactive metal site.3 In the fast growing
field of asymmetric catalysis high enantioselectivity is usually
obtained by using enantiomerically pure ligands designed with
a rigid platform supporting chiral information. Since the late
eighties advances in this field have been achieved by the use of
the nitrogen based chiral oxazoline heterocycle as the chiral
fragment.4 The fact that the synthesis involves the use of readily
available aminoalcohols allows for a variety of substitution
patterns and most importantly the preparation of enantio-
merically pure oxazolines. Several chiral bidentate or tridentate
oxazoline-containing ligands have been prepared and success-
fully used for asymmetric catalysis. The C2-symmetric tri-
dentate ligands of the type 2,6-bis(2-oxazolin-2-yl)pyridine
(Pybox) I have shown interesting activity and enantioselectivity
in the Rh-catalysed hydrosilylation of ketones and the Ru-
catalysed cyclopropanation of olefins with diazoacetates.5 As
part of a general program to examine the co-ordination proper-
ties of multidentate ligands that contain mixed donors, the
preparation of new ligands that contain both phosphines and
oxazolines in a chelating array has been initiated.
The synthesis of bis(2-oxazolin-2-ylmethyl)phenylphosphine
(II or N,P,N) was performed in THF at Ϫ78 ЊC via a one-pot
reaction by first deprotonation of the commercially available
2-methyl-2-oxazoline and then addition of Me3SiCl to form the
N-silyl derivative, which was followed by reaction with PPhCl2
[eqn. (1)]. The use of Me3SiCl was found to be crucial as some
uncharacterized side products were formed in its absence. This
is consistent with previous findings on the synthesis of related,
chelating P,N ligands.6
1
The H NMR spectrum of compound II in CDCl3 at room
In this paper we detail the synthesis of the achiral, tridentate
system II which is similar to the Pybox ligand I with the pyrid-
ine moiety replaced by a phosphine donor. Thus changing both
electronic and steric properties of the ligand should modify the
reactivity of the resulting complexes. We first investigated the
co-ordination chemistry of the achiral ligand II and evidenced
two different co-ordination modes. We report the synthesis of
four ruthenium() complexes and describe some preliminary
results on the catalytic transfer hydrogenation of ketones by
propan-2-ol.
temperature reveals a set of 3 complex multiplets for the ali-
1
phatic protons. The PCH2 protons were assigned by H-{31P}
NMR experiments. Considering that there is no symmetry
operation that can interchange these protons and only a mirror
plane in the molecule, the two methylene sets of protons form
an enantiotopic pair of diastereotopic protons. Thus, the
pattern for this spin system was expected to be of the ABX type.
However, selective 1H homonuclear decoupling experiments
5
evidenced the existence of a JHH coupling of 1.2 Hz between
the PCH2 protons and a methylene set of the oxazoline. This
J. Chem. Soc., Dalton Trans., 1999, 589–594
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Table 1 Selected bond distances (Å) and angles (Њ) for compound
N,P,N II
P(1)–C(9)
P(1)–C(1)
P(1)–C(5)
1.827(4)
1.860(4)
1.849(4)
C(2)–O(1)
C(1)–C(2)
C(2)–N(1)
1.301(4)
1.472(5)
1.252(5)
C(9)–P(1)–C(1)
C(1)–P(1)–C(5)
C(5)–P(1)–C(9)
102.5(2)
98.7(2)
98.2(2)
C(1)–C(2)–N(1)
P(1)–C(1)–C(2)
O(1)–C(2)–N(1)
O(1)–C(2)–C(1)
123.3(4)
112.8(3)
117.4(4)
119.2(4)
Fig. 2 An ORTEP view of the structure of fac-[RuCl2(PPh3)(N,P,N)]
in complex 2ؒCH2Cl2ؒ0.25C6H14.
four protons are chemically and magnetically inequivalent
which indicates there is no symmetry element in the molecule.
Furthermore, the far infrared (FIR) spectrum of complex 1
shows absorptions at 297 and 222 cmϪ1 which strongly supports
a cis arrangement of the two chloride ligands. From these data
one can conclude that the N,P,N ligand is co-ordinated in a fac
mode with the phosphorus atom cis to one chloride and one
DMSO ligand.
Fig. 1 An ORTEP7 view of the structure of compound N,P,N II.
long range coupling is responsible for the ABMX spin system
observed. Knowing that long range coupling is likely to occur
where the conjugation is best, we assign the multiplet at δ 3.75
5
to the NCH2 protons. This JHH coupling is observed also for
Reaction of compound II with [RuCl2(PPh3)3] in refluxing
THF yielded complex 2 (85% yield) (Scheme 1). The 1H NMR
resonances of the PCH2 protons were located by 1H-{31P}
experiments and they exhibit two ABX spin systems. Thus the
protons are chemically and magnetically inequivalent which
indicates that there is again no symmetry element in the mole-
cule. The 31P-{1H} NMR spectrum shows the two phosphines
to be in a cis arrangement (2JPP = 31.2 Hz). Furthermore, the
far infrared spectrum shows absorptions at 305 and 243 cmϪ1
which are consistent with a cis arrangement of the two chloride
ligands. From these data one can conclude that the ligand co-
ordinates in a fac mode with its phosphorus atom cis to the
triphenylphosphine and cis to one chloride. Single crystals of
2ؒCH2Cl2ؒ0.25C6H14 were obtained and an X-ray diffraction
study confirmed the stereochemistry of the molecule (Fig. 2).
There are two independent, almost identical molecules and
three solvent regions in the asymmetric unit (see details in the
Experimental section). Selected bond distances and angles are
given in Table 2.
the precursor 2-methyl-2-oxazoline. A single-crystal X-ray dif-
fraction study (Fig. 1) confirmed the structure of II. Selected
bond distances and angles are given in Table 1 and will be used
for comparison with values found for this ligand in ruthenium
complexes (see below).
Synthesis and characterization of the [RuCl2(L)(N,P,N)]
(L ؍ DMSO 1 or PPh3 2)
The incorporation of the N,P,N ligand II onto ruthenium was
achieved via ligand substitution processes. Reaction of II with
cis-[RuCl2(DMSO)4] in refluxing toluene resulted in the form-
ation of complex [RuCl2(DMSO)(N,P,N)] 1 (90% yield)
1
(Scheme 1). The H NMR resonances of the PCH2 protons
There are two independent but very similar molecules in the
unit cell. The Ru–P [2.2227(8) and 2.2993(8) Å] and Ru–N dis-
tances [2.085(2) and 2.129(2) Å] in one molecule are compar-
able to literature values.2b The lengthening of the Ru(1)–Cl(1)
distance compared with Ru(1)–Cl(2) may be related to the larger
trans influence of phosphorus compared to nitrogen. The N–
Ru–N [86.72(9)Њ] and P–Ru–P [98.59(3)Њ] angles indicate slight
distortions from ideal octahedral angles. The chelation of the
ligand is characterised by a pinch of the P–C–C angle going
from 112.8(3)Њ in the ‘free’ ligand to 106.0(2)Њ once co-
Scheme 1
were assigned by H-{31P} experiments and they exhibit two
ordinated. The C–O and C᎐N bond distances are not signifi-
1
᎐
ABX spin systems corresponding to two protons each. Thus all
cantly elongated by co-ordination of the oxazoline.
590
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Table 2 Selected bond distances (Å) and angles (Њ) for fac-[RuCl2-
(PPh3)(N,P,N)]ؒCH2Cl2ؒ0.25C6H14 4ؒCH2Cl2ؒ0.25C6H14
Table 3 Selected bond distances (Å) and angles (Њ) for [RuCl(η6-C6H6)-
(N,P,N)][O3SCF3] 3
Molecule 1
Molecule 2
Ru(1)–Cl(1)
Ru(1)–N(1)
Ru(1)–P(1)
P(1)–C(5)
C(5)–C(6)
C(6)–N(2)
C(6)–O(2)
2.403(1)
2.076(3)
2.318(1)
1.818(4)
1.492(6)
1.276(5)
1.318(5)
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–N(1)
Ru(1)–N(2)
C(1)–N(1)
C(1)–C(4)
P(1)–C(4)
P(1)–C(8)
C(8)–C(5)
C(5)–N(2)
O(1)–C(1)
2.4678(7)
2.4255(7)
2.2227(8)
2.2993(8)
2.085(2)
2.129(2)
1.274(4)
1.469(4)
1.848(4)
1.852(4)
1.487(5)
1.255(4)
1.344(3)
Ru(2)–Cl(3)
Ru(2)–Cl(4)
Ru(2)–P(3)
Ru(2)–P(4)
Ru(2)–N(3)
Ru(2)–N(4)
N(3)–C(33)
C(33)–C(36)
P(3)–C(36)
P(3)–C(40)
C(40)–C(37)
C(37)–N(4)
O(3)–C(33)
2.4674(7)
2.4398(7)
2.2219(7)
2.2900(7)
2.077(2)
2.141(2)
1.269(3)
1.488(4)
1.844(3)
1.858(3)
1.469(5)
1.272(4)
1.342(3)
P(1)–C(1)
C(1)–C(2)
C(2)–N(1)
C(2)–O(1)
1.842(4)
1.477(6)
1.263(5)
1.339(5)
Cl(1)–Ru(1)–P(1)
P(1)–Ru(1)–N(1)
P(1)–C(1)–C(2)
Ru(1)–P(1)–C(1)
Cl(1)–Ru(1)–N(1)
Ru(1)–N(1)–C(2)
85.74(4)
79.53(10)
107.4(3)
103.9(1)
84.4(1)
N(1)–C(2)–C(1)
P(1)–C(1)–C(2)
C(1)–C(2)–O(1)
O(1)–C(2)–N(1)
N(2)–C(6)–C(5)
P(1)–C(5)–C(6)
C(5)–C(6)–O(2)
O(2)–C(6)–N(2)
123.5(4)
107.4(3)
119.2(4)
117.3(4)
122.4(4)
116.6(3)
117.9(4)
119.6(4)
124.4(3)
N(1)–Ru(1)–N(2)
P(1)–Ru(1)–P(2)
Cl(1)–Ru(1)–Cl(2)
Cl(1)–Ru(1)–P(1)
Cl(1)–Ru(1)–N(1)
N(1)–C(1)–C(4)
P(1)–C(4)–C(1)
N(1)–C(1)–O(1)
O(1)–C(1)–C(4)
86.72(9)
98.59(3)
91.92(3)
164.41(3)
88.14(6)
123.2(3)
106.0(2)
117.8(3)
119.0(3)
N(3)–Ru(2)–N(4)
P(3)–Ru(2)–P(4)
Cl(3)–Ru(2)–Cl(4)
Cl(3)–Ru(2)–P(3)
Cl(3)–Ru(2)–N(3)
84.23(9)
99.39(3)
93.07(3)
167.06(3)
89.24(7)
N(3)–C(33)–C(36) 123.0(3)
P(3)–C(36)–C(33)
N(3)–C(33)–O(3)
O(3)–C(33)–C(36)
104.4(2)
117.3(3)
119.7(2)
Synthesis and characterization of cationic ruthenium(II)
benzene complexes
Complex [RuCl(η6-C6H6)(N,P,N)][O3SCF3] 3 was obtained in
two steps from the reaction of two equivalents of 2 with one
equivalent of [{Ru(µ-Cl)Cl(η6-C6H6)}2] followed by addition of
two equivalents of AgO3SCF3 (Scheme 2).
Fig. 3 An ORTEP view of the structure of [RuCl(η6-C6H6)(N,P,N)]-
[O3SCF3] 3.
strongly bound to the metal since one equivalent of 4-methyl-
pyridine does not displace the oxazoline. This structure of
3 was confirmed by a single crystal X-ray diffraction study
(Fig. 3, Table 3). The complex adopts a piano-stool type of
geometry with a P–Ru–N bite angle of 79.53(10)Њ. For the
chelated arm of the ligand the P–C–C angle of 107.4(3)Њ is
much smaller than the related P–C–C of the dangling oxazoline
116.6(3)Њ. In a smaller range the O–C–N angle from the oxazo-
line increases from co-ordinated [117.4(4)] to unco-ordinated
[119.6(4)Њ].
Scheme 2
1
The H resonances for the two PCH2 protons were located
Complex 4 was isolated in 60% yield in two steps from the
reaction of two equivalents of II with one equivalent of
[{RuCl2(η6-C6H6)}2] followed by the addition of four equiv-
by 1H-{31P} NMR experiments and they exhibit two ABX spin
systems corresponding to two protons each. Both signals are
shifted downfield when compared to those of the ‘free’ ligand,
one by 0.7 ppm the other by 0.35 ppm. The most deshielded
methylenic protons are assigned to the chelate ring. It is note-
worthy that PCH2 protons of the unco-ordinated arm of the
ligand are diastereotopic, thus indicating restricted flexibility
owing to steric hindrance around the phosphorus atom. The IR
spectrum in a KBr pellet shows two bands at 1666 and 1645
1
alents of Ag(O3SCF3). The H NMR spectrum shows a ABX
spin system for the four PCH2 protons of the tridentate ligand
since a mirror plane makes the two pairs of diastereotopic
methylene protons enantiotopic. The IR spectrum in KBr
shows only one band at 1648 cmϪ1
.
Catalytic transfer hydrogenation of ketones
cmϪ1 assigned to the C᎐N vibrations of the unco-ordinated and
᎐
co-ordinated oxazoline, respectively. This is in agreement with
the data found for the ‘free’ ligand and for II as a chelating
ligand in complex 1 or 2. The structure is static on the NMR
timescale and there is no exchange between the co-ordinated
and unco-ordinated arms of the ligand. The P,N chelate is
Preliminary catalytic studies with the complexes 1 and 2 have
been performed for the transfer hydrogenation of ketones by
propan-2-ol, a reaction of current interest.8 For comparative
purposes, the experiments were performed using the reaction
conditions described by Chowdhury and Bäckvall8c with [RuCl2-
J. Chem. Soc., Dalton Trans., 1999, 589–594
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Table 4 Transfer hydrogenation of ketones catalysed by the ruthenium(II) complexes 1–4a
Substrate
Catalyst
Ketone:Ru:base
1000:1:24a
Yield (%)
t/min
Turnover hϪ1
Cyclohexanone
1
7
0.5
60
8400
990
99 (89)b
2
1000:1:24a
94 (99)c
99.5
0.5
15
112800 (118800)c
3980
Acetophenone
1
2
2
3
4
1000:1:24a
1000:1:24a
200:1:24d
200:1:24d
200:1:24d
4
0.5
60
0.5
15
0.5
15
15
60
15
60
4800
58 (48)b
58.5 (50)c
88 (88)c
61
580
70200 (60000)c
3520
14600
776
108
108
88
97
13.5
54
11
45
90
a Reactions were carried out in refluxing propan-2-ol using 1 M substrate concentration and NaOH as a base, unless otherwise specified. b Values in
parentheses refer to results from ref. 8(c) under similar conditions. c Values in parentheses refer to results from ref. 8(d) under similar conditions.
d Using a 0.1 M substrate concentration and KOH as a base.
(PPh3)3] as a catalyst precursor. The use of the DMSO complex
Experimental
1 as catalyst precursor indicates that it has a reactivity only
All reactions were performed under purified nitrogen. Solvents
slightly higher than that of [RuCl2(PPh3)3] in terms of conver-
were purified and dried under nitrogen by conventional
sion and turnover frequency (TOF) for cyclohexanone and
acetophenone. However, the use of precursor 2 leads to higher
yields than for 1 for the same substrates and to a TOF more
than 10 times larger. The activity of catalyst 2 is comparable to
that of [RuCl2(PPh3)(P,N,O)] [P,N,O = 1-(diphenylphosphino)-
2-ethoxy-1-(2-pyridyl)ethane] which appears to show the
methods. The 1H and 31P-{1H} NMR spectra were recorded at
300.13 and 121.5 MHz, respectively, on a FT Bruker AC300
instrument, 13C NMR spectra at 50.32 MHz on a FT Bruker
AC200 instrument, H-{31P} NMR at 500.13 MHz on a FT
1
Bruker AMX500 instrument, IR spectra in the 4000–400 cmϪ1
range on a Bruker IFS66 FT spectrometer and FIR spectra in
highest activity reported for the ruthenium-catalysed transfer
the 500–90 cmϪ1 range on a Bruker ATS 83 spectrometer.
hydrogenation of ketones by propan-2-ol.8c,d No activity was
observed in the absence of NaOH. The difference in activity
between complexes 1 and 2 is therefore related to the change in
Syntheses
The compounds [RuCl2(PPh3)3],12 cis-[RuCl2(DMSO)4],13 and
the ancillary ligand. We have noticed that one equivalent of
[{Ru(µ-Cl)Cl(η6-C6H6)}2]14 were prepared according to liter-
ature procedures. The 2-methyl-2-oxazoline was purchased
from Aldrich.
PPh3 does not displace the ligand DMSO from complex 1 in
chloroform at room temperature. This would tend to support
the idea that dissociation of a neutral ligand is necessary during
the catalytic cycle; given that PPh3 is bulkier than DMSO, its
ease of dissociation is perhaps not surprising.9 Further work to
confirm this is in progress. Since the conversion rate is depend-
ent on substrate concentration,8 e.g.,10 we performed the trans-
fer hydrogenation reaction of acetophenone with our most
active catalyst 2 using a 0.1 M substrate concentration and
obtained a yield of 97%.
Following the optimized procedure for complex 2 we tested
the catalytic activity of 3 and 4 (Table 4). Both complexes were
less efficient than 2 under similar conditions. Their similar
activity suggests that replacing a terminal chloride (in 3) with a
chelating oxazoline (in 5) does not significantly affect the rate-
determining step in the catalysis. Compared with the mono-
cationic 3, the expected increased efficiency of the dicationic
complex 4 appears to be counterbalanced by the formation of a
bis-chelating system.8f
Bis(2-oxazolin-2-ylmethyl)phenylphosphine II. A THF solu-
tion of degassed 2-methyl-2-oxazoline (5.00 g, 58.7 mmol) was
added dropwise over a 10 min period to a LiBu solution (58.7
mmol, 1.6 M hexane) cooled at Ϫ78 ЊC in 100 mL of THF.
After the pale yellow mixture was stirred for 1 h at Ϫ78 ЊC, 7.45
mL (58.7 mmol) of degassed chlorotrimethylsilane in 5 mL of
THF were injected into the solution, and stirring was continued
for 2 h. The compound PPhCl2 (5.250 g, 29.3 mmol) was rapidly
added to the cloudy solution at Ϫ78 ЊC. A white powder pre-
cipitated and the mixture was allowed to reach room temper-
ature overnight. The solvents were evaporated under reduced
pressure until a beige solid was obtained. The powder was then
treated with 50 mL of degassed water containing 0.80 g of
NaOH. The product was extracted with 4 × 50 mL of Et2O and
the extract dried over MgSO4. The pale yellow oil thus obtained
was dissolved in the minimum of Et2O and 80 mL of hexane
were added, the solution was then heated for a few minutes
under stirring and then placed overnight at Ϫ28 ЊC. This
afforded the pure ligand as a pale yellow powder (3.630 g, 45%),
mp 56 ЊC (Found: C, 60.43; H, 6.00; N, 9.84. C14H17N2O2P
requires C, 60.86; H, 6.20; N, 10.14%). IR (KBr): νmax/cmϪ1
During the course of our work, Zhang and co-workers11
reported another N,P,N-type ligand with a C2H4 spacer
between the oxazoline rings and the phosphorus atom.
Although a benzene ruthenium complex was used as catalyst
for transfer hydrogenation of ketones, the precursor complex
was prepared in situ and not isolated. Their best result with
acetophenone (0.2 M) as a substrate was 72% with ratio
ketone:Ru:base = 200:1:30 at 80 ЊC.
Further work from our laboratories will expand the results
here to chiral systems since the chiral versions of compound II
are readily available. Of particular interest is the comparison of
tridentate ligands such as II that prefer a facial co-ordination
mode to Pybox systems that are known to bind in a meridional
fashion.
(C᎐N) 1661. δH (CDCl3, 300 MHz): ABMX spin system (A, B,
᎐
M = H, X = P) 2.82 (m with appearance of dq, 2 H, JAB = 14.4,
5
2JXB = 3.3, JMB = 1.2), 2.95 (m with appearance of dt, 2 H,
2
5
JAB = 14.4, JXA = 1.2, JMA = 1.2 Hz), 3.75 (m, 4 H, NCH2),
4.10 (m, 4 H, OCH2), 7.30–7.40 (m, 3 H, aromatic H) and
7.50–7.60 (m, 2 H, aromatic H). 31P-{1H} NMR (CDCl3, 121.5
MHz): δ Ϫ27 (s). 13C-{1H} NMR (CDCl3, 50 MHz): δ 26.7
(d, JPC = 21.3, PCH2), 54.6 (s, NCH2), 67.4 (s, OCH2), 128.4
592
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(d, JPC = 6.7, o-C of aryl), 129.4 (s, p-C of aryl), 132.0 (d,
JPC = 20.7, m-C of aryl), 135.70 (d, JPC = 17.2, o-C of aryl) and
C21H23ClF3N2O5PRuS requires C, 39.41; H, 3.62%); IR (KBr):
1
νmax/cmϪ1 (C᎐N non co-ordinated) 1666 and 1645. H NMR
᎐
164.9 (d, JPC = 5.7 Hz, C᎐N).
(CDCl3, 500.13 MHz): δ 3.25 [AB part of ABX spin system
᎐
2
2
(X = P), dd, 1 H, JHH = 18.7, JPH = 9.5, PCH2], 3.31 [AB part
2
2
Ruthenium complexes. All the complexes are air-stable for a
short period of time but should be better kept under an inert
atmosphere.
of ABX spin system (X = P), dd, 1 H, JHH = 18.7, JPH = 9.5,
PCH2], 3.60 [AB part of ABX spin system (X = P), dd, 1 H,
2JHH = 16.5, JPH = 7.6, PCH2], 3.68 [AB part of ABX spin
2
2
2
[RuCl2(DMSO)(N,P,N)] 1. In a 150 mL Schlenk tube fitted
with a reflux condenser were placed together 0.430 g (1.56
mmol) of compound II and 0.756 g (1.56 mmol) of cis-
[RuCl2(DMSO)4] in 50 mL of toluene. The suspension was
heated under reflux for 4 h. The volume of toluene was reduced
to about 10 mL and the yellow precipitate obtained filtered off
and washed with 2 × 30 mL portions of Et2O. Drying in vacuo
yielded complex 1 as a yellow solid (0.740 g, 90%) (Found: C,
36.62; H, 4.20; N, 5.10. C16H23Cl2N2O3PRuS requires C, 36.51;
system (X = P), dd, 1 H, JHH = 18.7, JPH = 9.5 Hz, PCH2],
3.75 (m, 2 H, CH2 from unco-ordinated oxazoline), 4.10 (m,
1 H, CH2 co-ordinated oxazoline), 4.15 (m, 2 H, CH2 unco-
ordinated oxazoline), 4.70 (m, 2 H, CH2 co-ordinated oxazo-
line) and 5.05 (m, 1 H, CH2 co-ordinated oxazoline). 31P-{1H}
NMR (CDCl3, 121.5 MHz): δ 40.7.
[Ru(η6-C6H6)(N,P,N)][O3SCF3 ]2 4. In a Schlenk tube were
placed together the ligand II (0.260 g, 0.944 mmol) and [{Ru-
(µ-Cl)Cl(η6-C6H6)}2] (0.236 g, 0.472 mmol) in CH2Cl2 (10 mL).
The dark orange solution obtained was stirred for 1 h at room
temperature and then filtered through a cannula fitted with
glass fiber 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(O3SCF3) (0.485 g, 1.888 mmol) and 30 mL of CH2Cl2 were
added. After a few minutes a pale yellow suspension appeared
and the reaction mixture was stirred for 2 h. The solvent was
evaporated and 20 mL of acetone were added. The suspension
was filtered twice over Celite and the orange solution obtained
reduced under vacuum to about 2 mL. Addition of Et2O
afforded a yellow-brown solid which was further washed with
10 mL of hexane and Et2O (0.416 g, 60%) (Found: C, 34.50; H,
2.97. C22H23F6N2O8PRuS2 requires C, 35.06; H, 3.08%). IR
(KBr): νmax/cmϪ1 (C᎐N) 1648. δ (acetone-d6, 300 MHz): 3.93
H, 4.40; N, 5.32%). IR: νmax/cmϪ1 (C᎐N) 1650 (KBr), (Ru–Cl)
᎐
297, 222 (polyethylene). 1H NMR (CDCl3, 500.13 MHz): δ 2.85
[s, 3 H, S(O)(CH3)2], 3.08 [AB part of ABX spin system (X = P),
2
2
dd, 1 H, JHH = 18.5, JPH = 8, PCH2], 3.12 [AB part of ABX
spin system (X = P), dd, 1 H, 2JHH = 18.5, 2JPH = 8, PCH2], 3.17
2
[AB part of ABX spin system (X = P), dd, 1 H, JHH = 19,
2JPH = 8, PCH2], 3.30 [s, 3 H, S(O)(CH3)2], 3.50 [AB part of
2
2
ABX spin system (X = P), dd, 1 H, JHH = 19, JPH = 8 Hz,
PCH2], 2.85 [s, 3 H, CH3S(O)CH3], 3.85 (m, 1 H), 3.95 (m, 1 H),
4.15 (m, 1 H), 4.30 (m, 1 H), 4.50–4.70 (m, 4 H), 7.35–7.55 (m, 3
H) and 8.05 (m, 2 H). 31P-{1H} NMR (CDCl3, 121.5 MHz):
δ 56.8 (s).
[RuCl2(PPh3)(N,P,N )] 2. In a 150 mL Schlenk tube fitted
with a reflux condenser were placed together (0.420 g, 1.52
mmol) of compound II and 1.460
g (1.52 mmol) of
[RuCl2(PPh3)3] in 50 mL of THF. After the THF was added a
cloudy yellow solution was rapidly obtained and after a few
minutes upon reflux a yellow precipitate formed. The suspen-
sion was heated under reflux for 2.5 h. The solvent was then
evaporated to about 10 mL. The yellow precipitate was filtered
off and washed with 2 × 10 mL of Et2O. The solid was then
dissolved in the minimum of CH2Cl2 and precipitated by add-
ition of hexane. This procedure repeated twice afforded 0.915 g
(85% yield) of the pure complex (Found: C, 53.61; H, 4.75; N,
3.83. C32H32Cl2N2O2P2Ru requires C, 54.09; H, 4.54; N, 3.94%);
᎐
H
[AB part of ABX spin system (X = P), dd, 2 H, JAB = 18.6,
2JAX = 13.6, PCH2], 3.98 [AB part of ABX spin system (X = P),
2
dd, 2 H, JAB = 18.6, JBX = 10.2 Hz, PCH2], 4.40 (m, 4H,
NCH2), 4.85 (m, 4 H, OCH2), 6.20 (s, 6 H, benzene), 7.70–7.80
(m, 3 H, aromatic H) and 8.20–8.30 (m, 2 H, aromatic H).
Catalytic experiments
Typical procedure for catalytic transfer hydrogenation of
ketones: in a Schlenk round bottom flask were added together
the ruthenium complex (0.01 mmol) and 5 mL of degassed
propan-2-ol and the solution was heated at 82 ЊC for 5–10 min
under N2. Acetophenone (1.201 g, 10.0 mmol) dissolved in
degassed propan-2-ol (3 mL) was added dropwise to the reflux-
ing mixture. The resulting yellow solution was stirred for 10 min
and then a solution of NaOH (0.0095 g, 0.237 mmol) in
propan-2-ol (2 mL) was added dropwise. The yellow solution
turned slightly orange after the addition of base. The extent of
conversion was determined by gas chromatography using a
CPWAX58CB column (50 m × 0.25 mm).
IR: νmax/cmϪ1 (C᎐N) 1649 (KBr), (Ru–Cl) 305, 243 (poly-
᎐
ethylene). 1H NMR (CDCl3, 500.13 MHz): δ 2.35 (m, 1 H), 2.83
2
[AB part of ABX spin system (X = P), dd, 1 H, JHH = 18.5,
2JPH = 11.5, PCH2], 2.85 [AB part of ABX spin system (X = P),
overlapping dd, 1 H, 2JHH = 19, 2JPH = 6.5, PCH2], 2.91 [AB part
2
2
of ABX spin system (X = P), dd, 1 H, JHH = 18.5, JPH = 11.5,
PCH2], 3.22 [AB part of ABX spin system (X = P), dd, 1 H,
2JHH = 19, 2JPH = 6.5, PCH2], 3.15 (m, 1 H), 3.62 (m, 1 H), 4.16
(m, 1 H), 4.22 (m, 1 H), 4.45 (m, 1 H), 4.55 (m, 1 H) and 4.70
(m, 1 H). 31P-{1H} NMR (CDCl3, 121.5 MHz): δ 46.2 (AB spin
2
system d, 1 P, JPP = 31.2) and 52.3 (AB spin system d, 1 P,
2JPP = 31.2 Hz).
X-Ray crystallographic analyses
[RuCl(η6-C6H6)(N,P,N)][O3SCF3] 3. In a Schlenk tube were
placed together the ligand II (0.147 g, 0.53 mmol) and [{Ru(µ-
Cl)Cl(η6-C6H6)}2] (0.133 g, 0.265 mmol) in CH2Cl2 (10 mL).
The dark orange solution obtained was stirred for 1 h at room
temperature and then filtered through a cannula fitted with
glass fiber paper. The resulting orange solution was evaporated
to about 1 mL and an orange precipitate 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(O3-
SCF3) (0.121 g, 0.47 mmol) and 20 mL of CH2Cl2 were added.
After a few minutes a pale yellow suspension appeared and the
reaction mixture was stirred for 1 h. The suspension was filtered
over Celite and the orange solution obtained reduced under
vacuum to about 2 mL. Addition of Et2O afforded a yellow
solid which was further washed with 10 mL of hexane and
Et2O. Pure complex 3 was obtained by crystallization from 1:3
CH2Cl2–hexane (0.203 g, 60%) (Found: C, 39.87; H, 3.80.
Bis(2-oxazolin-2-ylmethyl)phenylphosphine II. Crystal data.
C14H17N2O2P, M = 276.27, monoclinic, space group P21/a
(no. 14), a = 7.0634(6), b = 17.961(1), c = 11.688(1) Å, β =
103.89(1)Њ, U = 1439.4(2) Å3 (by least-squares refinement on the
setting angles for 25 reflections with 55 < 2θ < 72Њ, λ = 1.541 78
Å, T = 21 ЊC), Z = 4, Dc = 1.275 g cmϪ3, F(000) = 584. Colorless
prisms. Crystal dimensions 0.20 × 0.25 × 0.40 mm, µ(Cu-Kα) =
16.98 cmϪ1
.
Data collection and processing.15 Rigaku AFC6S diffract-
ometer, graphite–monochromated Cu-Kα radiation; 3074
unique reflections measured (1 < θ < 77.5Њ, h,k, l), 1674 having
I ≥ 3σ(I). Absorption correction: azimuthal scans for three
reflections (relative transmission factors 0.933–1.000). The
intensities of three standard reflections, measured each 200
reflections, decayed linearly by 2.3% (correction applied).
Structure analysis and refinement. Direct methods followed
J. Chem. Soc., Dalton Trans., 1999, 589–594
593

View Article Online
by Fourier synthesis. Full-matrix least squares with all non-
hydrogen atoms anisotropic and hydrogen atoms in calculated
positions [C–H 0.98 Å, Biso = 1.2B(parent atom)]. Unit weights =
1.15 Final R = 0.053, RЈ = 0.048 for 1674 reflections with
I у 3σ(I). Computer programs and source of scattering factors
are given in ref. 15.
CCDC reference number 186/1286.
See http://www.rsc.org/suppdata/dt/1999/589/ for crystallo-
graphic files in cif. format.
Acknowledgements
We are grateful to Mrs Libs for the GC measurements,
Dr Graff for NMR experiments, the Centre National de la
Recherche Scientifique (Paris) and the Natural Sciences and
Engineering Council of Canada for support, the Université
Louis Pasteur for a Visiting-Professor position for M. D. F. and
the Ministère de l’Enseignement Supérieur et de la Recherche
(Paris) for a PhD grant to F. N.
fac-[RuCl2(PPh3)(N,P,N)]ؒCH2Cl2ؒ0.25C6H14
2ؒCH2Cl2ؒ
0.25C6H14. Crystal Data. C34.5H37.5Cl4N2O2P2Ru, space group
C2/c (no. 15), M = 817.01, monoclinic, a = 38.3173(3), b =
18.2006(2), c = 20.5863(1) Å, β = 106.818(1)Њ, U = 13742.8(2) Å3
(by least-squares refinement on setting angles for 19556 reflec-
tions with 2 < θ < 31Њ, λ = 0.710 69 Å, T = 25 ЊC), Z = 16,
Dc = 1.577 g cmϪ3, F(000) = 6648. Pale yellow prism. Crystal
dimensions 0.20 × 0.25 × 0.30 mm, µ(Mo-Kα) = 0.896 mmϪ1
.
References
Data collection and processing.16 Rigaku/ADSC CCD dif-
fractometer, graphite-monochromated Mo-Kα radiation; 56084
reflections, 18843 unique (1 < θ < 30.9Њ, h, k, l), 10897
having I у 3σ(I). Absorption correction: analysis of symmetry-
equivalent data (decay/absorption correction factors: 0.890–
1.000).
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Structure analysis and refinement. Direct methods followed
by Fourier synthesis. There are two independent molecules and
three solvent regions in the asymmetric unit. The first solvent
region was modeled as a dichloromethane molecule 1:1 dis-
ordered about a twofold axis. The second region is complex and
was modeled by anisotropic carbon atoms of varying occu-
pancy [C(66–74)]. This region is probably overlapping CH2Cl2
and hexane molecules. The third solvent region consists of a
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[RuCl(ç6-C6H6)(N,P,N)][O3SCF3] 3. Crystal Data. C21H23-
ClF3N2O5PRuS, M = 639.98, monoclinic, space group P21/a
(no. 14), a = 10.526(2), b = 20.611(2), c = 11.592(1) Å, β =
90.36(1)Њ, U = 2514.9(6) Å3 (by least-squares refinement on
setting angles for 25 reflections with 17 < 2θ < 28Њ, λ = 0.710 69
Å, T = 21 ЊC), Z = 4, Dc = 1.690 g cmϪ3, F(000) = 1288. Orange
prism. Crystal dimension: 0.20 × 0.25 × 0.55 mm, µ(Mo-Kα) =
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9.34 cmϪ1
.
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ometer, graphite-monochromated Mo-Kα radiation; 5954
unique reflections measured (1 < θ < 27.5Њ, h,k, l), 3088 having
I у 3σ(I). Absorption correction: azimuthal scans for three
reflections (relative transmission factors 0.918–1.000). The
intensities of three standard reflections, measured each hour of
X-ray exposure time, showed only small random fluctuations.
Structure analysis and refinement. Patterson method followed
by Fourier synthesis. There is a possibility of O/N disorder in
the unco-ordinated ring of the ligand. Full-matrix least squares
with all non-hydrogen atoms anisotropic and hydrogen atoms
in calculated positions [C–H 0.98 Å, Biso = 1.2B(parent atom)].
Final R = 0.035, RЈ = 0.032 for 3088 reflections with I у 3σ(I).
Computer programs and source of scattering factors are given
in ref. 15.
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Paper 8/08170K
594
J. Chem. Soc., Dalton Trans., 1999, 589–594