BIPHASE REDUCTION OF HEPTANAL AND CYCLOHEXANONE BY SODIUM FORMATE CATALYZED BY ETHER-PHOSPHINE RUTHENIUM(II) COMPLEXES

Article abstract of DOI:10.1135/cccc19950127

RuCl22 has efficiently catalyzed the reduction of cyclohexanone and heptanal by sodium formate in chlorobenzene-water, using cetylpyridinium bromide as the phase transfer catalyst.In both cases, the reduction was first order both in t

Full text of DOI:10.1135/cccc19950127

Biphase Reduction of Heptanal and Cyclohexanone
127
BIPHASE REDUCTION OF HEPTANAL AND CYCLOHEXANONE
BY SODIUM FORMATE CATALYZED BY ETHER-PHOSPHINE
RUTHENIUM(II) COMPLEXES
Stanislav SABATA, Jaroslav VCELAK and Jiri HETFLEJS
Institute of Chemical Process Fundamentals,
Academy of Sciences of the Czech Republic, 165 02 Prague 6-Suchdol, The Czech Republic
Received July 29, 1994
Accepted December 6, 1994
RuCl2[P(C6H5)2OCH2CH2OCH3]2 has efficiently catalyzed the reduction of cyclohexanone and heptanal
by sodium formate in chlorobenzene–water, using cetylpyridinium bromide as the phase transfer cata-
lyst. In both cases, the reduction was first order both in the substrate and in the initial concentration
of the catalyst. The catalyst activity in the aldehyde reduction could be increased by the addition of
the free ligand while in the ketone reduction the ligand in excess decreased the reaction rate. Several
other phosphines of the type P(C6H5)2L where L = C6H5, C4H9, C2H5OCH2CH2, C4H9OCH2CH2,
1,4-dioxanemethyl, tetrahydrofurfuryl, and P(i-C3H7)3) gave the less efficient catalysts. Kinetic and
activation data for the reduction of both substrates are reported.
In recent years, an increased attention in the chemistry of transition metal-phosphine
complexes has been paid to the ligands containing in addition to the soft phosphorus
also the hard oxygen or nitrogen atom. These were expected to behave as polydentates,
the relatively stable metal–phosphorus coordination being accompanied by a weak
metal–hard base bonding. In the case of ether-phosphines (further denoted as P,O
ligands) their bifunctionality has been observed in complexes of several transition
metals, including tungsten1,2, platinum3,4, palladium3,5,6, iridium7, rhodium3,8,9, and ru-
thenium3,10
.
However, depending on the oxidation state of transition metal and the structure of the
complex, the metal−oxygen bond could undergo cleavage, leaving the phosphine as the
monodentate ligand. The example of such a behaviour has recently been reported for
several platinum complexes4.
It is widely accepted that the hemilability of these ligands could have favourable
effect in transition metal-catalyzed processes where an even weak additional coordina-
tion can stabilize vacant site(s) formed during catalytic cycle. However, when com-
pared to the studies devoted to the chemistry of transition metal complexes containing
ether-phosphines (and other ambivalent ligands – for a recent review see ref.11), much
less attention has been focused on their application as the catalysts. A systematic inves-
tigation has seldom been made, except for methanol carbonylation (cf. ref.8 and refer-
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

128
Sabata, Vcelak, Hetflejs:
ences given therein). Briefly mentioned were the two-phase reduction of bromobenzene
with sodium hydride12 and of allyl acetate13, allyl chloride13, and chloronaphthalene5
with sodium formate, hydrogenation of hexyne to hexenes6, all catalyzed by Pd com-
plexes, water gas shift reaction2, hydrogenation of hexene to hexane14, and hydrocarbo-
nylation of methyl acetate8, all catalyzed by Rh complexes, hydrogenation of
phenylacetylene in the presence of Ir catalysts15, and finally hydrogenation of acetalde-
hyde with Ru-P,O complexes16 as the catalysts.
Within the framework of an intended study of poly(oxyalkylene)phosphines as
potential ligands of water soluble catalysts17, we have examined more extensively also
the behaviour of the parent phosphines of the type P(C6H5)2OCH2CH2OR (R = alkyl).
In the present work we report on the two phase hydrogen transfer reduction of the C=O
group by sodium formate18,19 catalyzed by several ruthenium(II) ether-phosphine com-
plexes.
EXPERIMENTAL
Chemicals
Heptanal (purum; Fluka), 1-heptanol (purum; Reakhim, Russia), cyclohexanone, cyclohexanol, and
sodium formate (all analytical grade; Lachema Brno) were commercial products as indicated. Heptanal
and cyclohexanone were redistilled under nitrogen, and the GLC pure medium fraction of both was
used in the experiments. PEG 300 and PEG 1000 (purum; NCHZ Novaky, The Slovak Republic),
methyltrioctylammonium chloride (purum; Fluka), and cetylpyridinium bromide (purum; Lachema
Brno) were used as obtained.
Phosphines
Triphenylphosphine, l,2-bis(diphenylphosphino)ethane (both purum; Fluka), butyldiphenylphosphine
(96%; Aldrich), and triisopropylphosphine (for synthesis; Merck) were used without further purifica-
tion.
2-Methoxyethyl(diphenyl)phosphine was obtained by the reaction of lithium diphenylphosphide
with 2-chloroethyl methyl ether, using the reported procedure20 (yield 26%, b.p. 150 – 156 °C/8 Pa;
for C15H17OP (244.3) calculated: 73.75% C, 7.02% H, 12.68% P; found: 73.50% C, 6.91% H,
12.83% P). The same procedure using the corresponding chloroethyl ethers21, was utilized to prepare
2-ethoxyethyl(diphenyl)phosphine (yield 47%, b.p. 133 – 140 °C/5 Pa; for C16H19OP (258.3) calcu-
lated: 74.39% C, 7.41% H, 11.99% P; found: 74.52% C, 7.49% H, 11.74% P), and 2-butoxyethyl(di-
phenyl)phosphine (yield 53%, b.p. 145 – 152 °C/2 Pa; for C18H23OP (286.3) calculated: 75.49% C,
8.10% H, 10.82% P; found: 75.40% C, 8.16% H, 10.80% P).
Diphenyl(tetrahydrofurfuryl)phosphine22 and 1,4-dioxanemethyl(diphenyl)phosphine23 were ob-
tained by the reaction of lithium diphenylphosphide (prepared by lithiation of triphenylphosphine)
with 2-chloromethyltetrahydrofurane (purum; Merck) and 2-chloromethyl-1,4-dioxane24, respectively.
Physico-chemical data of the products obtained agreed well with those reported.
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

Biphase Reduction of Heptanal and Cyclohexanone
Ruthenium-Phosphine Complexes
129
trans-Dichloro-cis-bis[(2-methoxyethyl)diphenylphosphine-O,P]ruthenium(II) (I) was prepared16 by
the reaction of RuCl3 . 3 H2O (purum; Fluka) with 2-methoxyethyl(diphenyl)phosphine (76% yield of
the red needle-like crystals melting at 145 °C with decomposition (reported16 147 °C). Mass spec-
trum: 660 (M+, 35Cl). For C3OH34Cl2O2P2Ru (660.4) calculated: 10.73% Cl, 9.38% P, l5.30% Ru;
found: 11.23% Cl, 9.72% P, 14.97% Ru. 13C NMR spectra of the complex dissolved in C6D6 agreed
with the proposed structure.
trans-Dichloro-cis-bis[diphenyl(tetrahydro-2-furanylmethyl)diphenylphosphine-O,P]ruthenium(II)
(II) was obtained16 in 70% yield by an analogous reaction from ruthenium trichloride and diphenyl-
(2-tetrahydrofurfuryl)phosphine (dec. temp. 201 °C (reported16 205 °C and 198 °C). Mass spectrum:
712 (M+, 35Cl). For C34H38Cl2O2P2Ru (712.6) calculated: 9.95% Cl, 8.69% P, l4.18% Ru; found:
10.19% Cl, 9.13% P, 14.35% Ru.
trans-Dichloro-cis-bis[(1,4-dioxanemethyl)diphenylphosphine-O,P]ruthenium(II) (III) was obtained in
80% yield by the exchange of the ligand in RuCl2[P(C6H5)3]2 for 1,4-dioxanemethyl(diphenyl)phos-
phine, as reported16 (dec. temp. 199 °C (reported16 197 °C). Mass spectrum: 744 (M+, 35Cl). For
C34H38Cl2O4P2Ru (744.6) calculated: 9.52% Cl, 8.32% P, 13.57% Ru; found: 9.67% Cl, 8.72% P,
13.16% Ru.
Tris(triphenylphosphine)ruthenium(II) chloride (IV) was a commercial product (Aldrich).
RuCl2[P(C6H5)2CH2CH2OCH3]2
RuCl2[P(C6H5)2CH2C4H7O]2
I
II
RuCl2[P(C6H5)2CH2C4H7O2-1,4]2
RuCl2[P(C6H5)3]3
III
IV
Reduction with Ruthenium Catalysts Prepared in situ
A. Ruthenium(III) chloride trihydrate (10.4 mg, 0.045 mmol), phosphine (0.8 – 0.9 mmol), water
(5 ml, degassed in vacuo with ultrasound mixing), organic solvent (0.2 ml), phase transfer catalyst
(0.2 – 0.5 mmol) and 2 M HCOONa solution (2.5 ml) were placed into the reactor and rapidly
warmed up with stirring to the reaction temperature (in 3 min) at which the reaction was started by
the addition of the substrate (1.9 mmol).
B. The organic solvent (2.5 ml), water (5 ml), 2 M HCOONa solution (2.5 ml), phase transfer
catalyst (0.18 mmol), ruthenium-phosphine complex IV (10.4 mg, 0.045 mmol), and a given phos-
phine in excess (P/Ru molar ratio 8 – 12 : 1) were stirred under reaction conditions for a given time,
followed by the substrate addition which started the reduction.
Two Phase Reduction – General Procedure
The reduction was performed in a 25 ml-glass tubular flat-bottom reactor, the side walls of which
were wedge-cut along their axis. The reactor was provided with a silicone-covered septum-inlet
adapter and a magnetic stirrer (250 – 350 min−1). The reactor was flushed with nitrogen and while
maintaining a slow stream of the gas, the reaction components (ca 0.05 mmol of the ruthenium cata-
lyst or its precursor, 0.2 – 0.6 mmol of a phase-transfer catalyst, eventually a phosphine in excess (up
to 0.7 mmol) were introduced. Then the internal standard (undecane or dodecane) was added, fol-
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

130
Sabata, Vcelak, Hetflejs:
lowed by the solvents (2.5 ml of chlorobenzene or o-xylene and 5 ml of water) and an aqueous 2 M
HCOONa solution (2.5 ml). The last component added was the compound to be reduced (1 – 2.5
mmol). The mixture was heated to the reaction temperature (40 – 80 °C) with vigorous stirring. At
fixed time intervals the samples of the reaction mixture were withdrawn ( max. 0.3 ml) and immedi-
ately diluted with the same volume of diethyl ether.
Analysis and Data Treatment
The samples worked up as mentioned above were analyzed by gas chromatography on the content of
the starting carbonyl compound and its reduction product, the corresponding alcohol, using internal
standards (undecane for heptanal reduction and dodecane for the reduction of cyclohexanone) under
the following conditions: Chrom 5a Chromatograph (Laboratorni pristroje, Prague) equipped with a
flame ionization detector and a 3.6 m-long column (3 mm i.d.) packed with 10% silicone elastomer
OV-17 on Chromosorb W-DMCS. Temperature program was run from 110 to 200 °C with the gra-
dient 6 °C per min, nitrogen as a carrier gas. The contents of the above compounds in the samples
were obtained with the use of calibration graphs relating chromatographic responses of the compo-
nents to those of the internal standard.
Data obtained in the form of time–concentration dependence were treated using a simple model of
the first-order reaction in both the catalyst and the substrate. The rate constants so obtained were
taken as a measure of the efficiency of the catalyst in dependence on its type, method of its forma-
tion and reaction conditions. A set of time and concentration data was solved numerically as a
pseudo-first-order reaction (Eq. (1)), [S] denotes substrate concentration). The constant k′ was fur-
ther divided by the initial catalyst concentration (Eq. (2)) to eliminate the influence of this term.
− d[S]/dt = k′ [S]
(1)
(2)
− d[S]/dt = k [cat0] [S]
The so obtained k values are presented in Tables I – III. The above kinetic scheme was obeyed in the
case of optimum reaction conditions to substrate conversions exceeding 90 per cent. The k values
were determined with the relative error 7 to 13 per cent. In two cases (catalyst I and IV), the tem-
perature dependence of rate data was measured with cyclohexanone and used to estimate activation
parameters of the reduction (see Table II).
RESULTS AND DISCUSSION
Reduction Catalyzed by Ruthenium Complexes I – IV
It is well known that reactions between reactants present each in one of the two immis-
cible phases are besides chemical factors (i.e. the structure of reactants and catalysts,
reaction conditions) affected also by mass transport between these phases. In the case
of the hydrogen transfer reduction under study, these factors were already thoroughly
examined by other authors19 and demonstrated on an example of the reduction of
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

Biphase Reduction of Heptanal and Cyclohexanone
131
p-tolualdehyde (Eq. (A)) in the presence of a methyltrioctylammonium salt (preferen-
tially X = HCOO(−)) as a phase transfer catalyst.
CH3(C8H15)3N(+)X(−)
p-CH3C6H5CHO(org) + HCOONa(aq)
p-CH3C6H5CH2OH(org) + NaHCO3(aq)
Ru cat., H2O/C6H5Cl
(A)
TABLE I
Reduction of carbonyl compounds with aqueous sodium formate catalyzed by Ru(II) complexes I – IV
(1.8 mmol substrate, 0.045 mmol Ru catalyst, 2.5 ml chlorobenzene, 2.5 ml aqueous 2 M HCOONa
solution, 5 ml water, 0.18 cetylpyridinium bromide, 0.15 ml internal chromatographic standard)
k . 102, l mol−1 s−1
Ru complex
Free ligand, mmol
cyclohexanonea
heptanalb
I
0
1.4
0.8
0.4
0.7
9.4
9.8
13
0.85
0
48
IIc
IIIc
0.6
0.8
3.1
13
0
IV
0
0.85
a
c
At: 50 °C; b 60 °; 70 °C.
TABLE II
Temperature dependence of the rate constants k of reduction of cyclohexanone with HCOONa cata-
lyzed by ruthenium complexes I and IV (for reaction conditions see Table I)
k a, l mol−1 s−1
t, °C
I
IV
60
70
80
1.6
4.4
9.8
9.4
18.5
33.2
Eact, kJ mol−1
96.3
61.9
a
Equation (2).
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

132
Sabata, Vcelak, Hetflejs:
Starting from reported data19, several reaction parameters were maintained constant to
ensure good reproducibility of experimental results: one and the same reactor in all
experiments, the same magnetic stirring bar and stirring speed (320 – 350 min−1, above
the critical mixing speed19), the same volume of the reaction mixture (10 ml) with a
constant ratio of both phases (the aqueous to organic phase 3 : 1 v/v).
As the study was aimed at comparison of the catalytic properties of a series of ruthe-
nium(II)-phosphine complexes and interpretation of the results in terms of structure
differences, the type of the phase transfer agent (cetylpyridinium bromide was chosen
on the basis of preliminary experiments as the most suitable of the compounds tested –
TABLE III
Activity of ruthenium catalysts prepared in situ in two phase reduction of heptanal (1.8 mmol heptanal,
0.045 mmol Ru compound, 0.85 mmol free phosphine, the other conditions as in Table I)
k . 102
Heptanal
Entry
Phosphine added
l mol−1 s−1,a
conversion, %b
RuCl3 . 3 H2O (method A, Experimental)
1
2
3
4
5
6
7
8
9
none
0
0
P(C6H5)3
0c
0c
P(C6H5)3
0.7
0.2c
20.4
0.9
9.2
2.8
95.5
11.8
15.5
5.7
3.0
P(C6H5)2CH2CH2OCH3
P(C6H5)2CH2CH2OCH3
P(C6H5)2CH2CH2OC2H5
P(C6H5)2CH2CH2OC4H7
P(C6H5)2CH2CH2CH2CH3
P(i-C3H7)3
1.1
0.4
0.2
RuCl2[P(C6H5)3]3 (method B, Experimental)
10
11
12
13
none
0.8c
8.5c
10c
P(C6H5)3
0.9c
P(C6H5)3
13
1.7c
80.7
22c
P(C6H5)2CH2CH2OCH3
RuCl2[P(C6H5)2CH2CH2OCH3]2 (method B, Experimental)
14
15
16
17
none
1.1c
13.3
1.8c
48
11.5
93.5
30.3c
99.8
none
P(C6H5)2CH2CH2OCH3
P(C6H5)2CH2CH2OCH3
a
b
Equation (2). The reaction time 1 h, determined by gas chromatography (see Analysis and Data
c
Treatment in Experimental). Other products than heptanol were not detected. The reaction was car-
ried out in the absence of the phase transfer catalyst (cetylpyridinium bromide).
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

Biphase Reduction of Heptanal and Cyclohexanone
133
see Experimental) and its narrow concentration range (given by its constant ratio with
respect to the Ru catalyst – see Procedure in Experimental) were maintained the same
through all the experiments. Chlorobenzene was chosen as the solvent based on pre-
paratory cyclohexanone reduction in the presence of the ruthenium ether-phosphine
complex I. In nonchlorinated aromatic hydrocarbons such as xylene or toluene the re-
action proceeded at distinctly slower rate. The same situation was already reported19 for
the reaction (A) and ascribed to the higher dielectric constant of the former solvent.
To characterize the activity of the catalysts quantitatively, we determined first the
kinetics of the reaction (for procedure and treatment of data see Experimental). We
have found that the reduction is first order in the catalyst, as documented by the following
dependence of k (Eq. (1)) on [I]0 for cyclohexanone (1.8 mmol) (chlorobenzene (2.5 ml),
water (5 ml), 2 M HCOONa (2 ml), cetylpyridinium bromide (0.18 mmol), 50 °C).
k . 103, min−1
[I]0, mmol l−1
3.2
9.7
5.2
7.3
15.3
19.5
As shown in Fig. 1, the reaction followed well the first-order kinetics in the substrate
for at least two half times and that both for the aldehyde (curve 1) and the ketone
(curve 2). These results confirmed Eq. (1) and allowed to describe the efficiency of the
catalyst by the rate constant k (Eq. (2), cf. Experimental).
The k values obtained under comparable conditions for the ruthenium(II) complexes
I – IV presented in Table I show that of the three ether-phosphine complexes tested,
only that having aliphatic straight chain P,O group (I) exerts activity comparable to the
Ru-phosphine complex IV. However, by contrast to RuCl2[P(C6H5)3]3 which does not
differentiate much between both reduced substrates (especially in the presence of the
excess free ligand, cf. the last row of Table I), the Ru-ether phosphine complex I shows
at least by one order of magnitude greater activity (measured by k values, cf. the first
0
ln (1−x)
−2
1
FIG.1
2
Plot of ln (1 − x) vs time for the biphase re-
duction of heptanal (50 °C, curve 1) and cy-
clohexanone (60 °C, curve 2) with sodium
formate catalyzed by RuCl2[P(C6H5)2CH2CH2OCH3]2
(for conditions see Table I)
−4
0
50
100
150
t, min
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

134
Sabata, Vcelak, Hetflejs:
row in Table I) in the aldehyde than ketone reduction. At the same time, in the former
reduction it is also distinctly more efficient than the ruthenium-triphenylphosphine
complex IV (compare k = 48 . 10−2 and 13 . 10−2 for I and IV, respectively, Table I).
The favourable effect of the added free phosphine on both catalysts I and IV is spe-
cific and limited to the aldehyde reduction. Although it has not so far been noticed for
the ruthenium catalysts, it was found18 in an analogous reduction of p-tolualdehyde
catalyzed with some rhodium-triphenylphosphine complexes (Wilkinson catalyst and
RhCl(CO)[P(C6H5)3]2). It was attributed to stabilization of the complexes towards their
reduction to the inactive free metal by added phosphines. However, such an effect
cannot be the only reason of the enhanced activity of both ruthenium complexes men-
tioned as neither of them was visibly reduced to the metal at the beginning or during
the reaction. According to our opinion it reflects rather an increased concentration of
the catalytically active species or their structure difference leading to the rate enhanc-
ing effect. In any case, these processes should take place fast at the beginning of the
reaction as they do not change its kinetics (do not cause any significant deviation from
the first-order reaction).
The first-order kinetics followed to the late stages of the reduction of both substrates
further indicates that its rate is not product-dependent. Furthermore, within the region
of the initial substrate concentrations chosen (1 – 2.5 . 10−2 mol l−1, see Procedure in
Experimental) the concentration effect was that predicted by the first-order kinetics (for
the rate retarding effect of the substrate when used in greater amounts cf. ref.19).
Nevertheless, as the rate constants k used here to characterize the efficiency of the
studied catalysts include in the phase transfer processes also the mass transfer contribu-
tion (for detailed discussion see ref.19), it was of interest to compare the behaviour of
the above catalysts I and IV on the basis of activation data. The temperature depend-
ence of k′s for the reduction of cyclohexanone (Table II) gave the following activation
energies: Eact 96.3 kJ mol−1 (23.0 kcal mol−1) for ruthenium ether-phosphine complex I
and 61.9 kJ mol−1 (14.8 kcal mol−1) for ruthenium-triphenylphosphine complex IV. In
both cases their magnitude speaks for the chemical control of the reduction (chemically
controlled hydrogen transfer hydrogenations are reported25 to have activation energies
20 – 25 kcal mol−1 while typical diffusion controlled processes 4 – 5 kcal mol−1, as
reported in ref.19).
The Effect of Other Phosphine Ligands
The encouranging results obtained with the ruthenium ether-phosphine complex I in the
reduction of heptanal led us to examine the behaviour of the two other linear chain P,O
ligands such as P(C6H5)2CH2CH2OC2H5 and P(C6H5)2CH2CH2OC4H7. However, by
contrast to the above complex obtained in high preparative yield16, all our attempts at
preparing analogous Ru(II) complexes containing the above ligands starting from
RuCl3 . 3 H2O have failed to give well defined products (instead, red viscous liquids of
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

Biphase Reduction of Heptanal and Cyclohexanone
135
variable composition were obtained). Similarly also an alternative way found to be
successful16 in preparing the ruthenium-dioxanylphosphine complex III and based on
the exchange of triphenylphosphine in RuCl2[P(C6H5)3]3 have not met with success in
any of its modifications used.
However, both precursors can be used to form catalysts in situ, using procedures
described in detail in Experimental. The results obtained with these systems are sum-
marized in Table III. Several comments can be made concerning these data: (i) the
reduction does not proceed with RhCl3 precursor in the absence of phosphine even with
the phase transfer catalyst added (entry 1, Table III). (ii) On the other hand, the reduc-
tion does not take place when the phosphine is added but without the phase transfer
catalyst (entries 2 and 4). When the complexes I and IV are separately prepared and
used as precursors, the reaction pathway not including the phase transfer catalyst
becomes appreciable (entries 10 and 14), the more so when the catalyst system is stabi-
lized by the free ligand addition (entries 13 and 16). This effect is less pronounced in
the case of the less efficient catalyst (compare entries 10 and 11 for complex IV). (iii)
Except for the RuCl3 + P(C6H5)2CH2CH2OCH3 system, the other ether-phosphines (en-
tries 5 and 6) were much less efficient, which could be ascribed to their low stability
observed also in their separate preparation, as already mentioned. The favourable effect
of the O-donor atom in 2-methoxyethyl(diphenyl)phosphine (entry 5) is well illustrated
by comparison with the C-analogue of the phosphine, butyl(diphenyl)phosphine (entry 8)
which yields the system with markedly lower catalytic activity. (iv) The rather high
sensitivity to relatively small structure changes of the ether-phosphines follows from
comparison of data for methoxy (entry 5), ethoxy (entry 6, and butoxy (entry 7) deriva-
tive. (v) The fact that the system prepared in situ from ruthenium trichloride and the
methoxyethylphosphine (entry 5) shows activity higher than the ruthenium-triphenyl-
phosphine complex IV (entry 12) offers advantage in avoiding the separate synthesis of
the catalyst.
CONCLUSIONS
As documented by the results obtained with two model carbonyl compounds, the ruthe-
nium ether-phosphine complex RuCl2[P(C6H5)2CH2CH2OCH3]2 (I) is an efficient cata-
lyst of the hydrogen transfer reduction of aliphatic saturated aldehydes and ketones by
sodium formate. In the aldehyde reduction its activity exceeds significantly that of the
so far best catalyst18, RuCl2[P(C6H5)3]3. The reduction proceeds as the first-order reac-
tion in the catalyst and in the substrate. Based on energetic data, the ketone reduction
is an example of chemically controlled phase transfer reaction. The reduction of the
aldehyde catalyzed by the ether-phosphine complex proceeds to a significant extent
also by the way which does not include participation of the phase transfer catalyst. Of
synthetic importance could be the fact that the efficient catalytic system is formed also
Collect. Czech. Chem. Commun. (Vol. 60) (1995)

136
Sabata, Vcelak, Hetflejs:
under reaction conditions from the metal precursor, RuCl3 . 3 H2O, and the phosphine,
by which the separate synthesis of the ruthenium ether-phosphine complex is avoided.
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