Synthesis, characterization, and application in asymmetric hydrogenation reactions of chiral ruthenium(II) diphosphine complexes

Article abstract of DOI:10.1021/om9506781

Four new complexes of the type [Ru(CF₃CO₂)₂(X)₂(PP)] 7 (X = methanol or ethanol, PP = chiral diphosphine) have been synthesized from the reaction of PP with [Ru₂(CF₃CO₂)₄(H ₂O)-(COD)₂] and characterized by both NMR spectroscopy and single-crystal X-ray diffraction studies. A common feature of these complexes is a pseudooctahedral geometry for ruthenium, an unusual monodentate ligation mode for the mutually trans trifluoroacetate groups, along with two solvent molecules coordinated in mutual cis positions (MeOH for 7a and 7b, EtOH for 7c). 7a (PP = (2S,4S)-BDPP) belongs to the orthorhombic P2₁2₁2₁ space group, Z = 4, a = 9.896(1) ?, b = 19.099(3) ?, and c = 19.689(2) ?. Tb (PP = (4S, 5S)-DIOP) also crystallizes in the orthorhombic P2₁2₁2₁ space group, Z = 4, a = 12.679(1) ?, b = 16.744(2) ?, and c = 18.944(2) ?. 7c (PP = (R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine, abbreviated as PPFCy₂) belongs to the monoclinic P2₁ space group, Z = 4, á= 18.153(2) A, b = 12.364(2) ?, c = 20.431(1) ?, and β = 97.40(1)°. The air-stable [RuCl(p-cymene)(PP)]-PF₆ 9 were synthesized from the reaction of PP with [RuCl₂(p-cymene)]₂ in a refluxing CH₂Cl₂/EtOH mixture, followed by metathesis with KPF₆ in MeOH, in 72-89% yields (PP = (S)-(R) or (R)-(S)-2-(diphenylphosphino or arsino)ferrocenyl]ethylbisphosphine derivative). 9a (PP = (S)-(R)-PPFCy₂ crystallizes in the monoclinic space group P2₁, Z = 2, a = 11.965(2) ?, b = 14.852(3) ?, c = 13.999(2) ?, and β = 111.50(2)°. Complexes 7 were probed for their catalytic behavior in the hydrogenation of methyl acetamidocinnamate 10, acetamidocinnamic acid 11, and dimethyl itaconate 12. Using a typical substrate to catalyst ratio of 50-100:1 and p(H₂) = 50 bar, modest enantiomeric excesses (ee) of up to 75% were achieved. The highest ee's were attained in CH₂Cl₂ or a 5:4 THF/CH₂Cl₂ mixture, whereas higher activities were observed when methanol was employed as solvent. The addition of NEt₃ had a beneficial effect on the ee of the reactions involving 11, whereas with 10 a detrimental effect was observed. The reactions involving 12 gave poor enantioselectivity.

Full text of DOI:10.1021/om9506781

860
Organometallics 1996, 15, 860-866
Syn th esis, Ch a r a cter iza tion , a n d Ap p lica tion in
Asym m etr ic Hyd r ogen a tion Rea ction s of Ch ir a l
Ru th en iu m (II) Dip h osp h in e Com p lexes
Nadia C. Zanetti,† Felix Spindler,*,‡ J ohn Spencer,† Antonio Togni,*,† and
Grety Rihs‡
Central Research Services, FD 6, Ciba-Geigy Ltd., P.O. Box, CH-4002 Basel, Switzerland, and
Laboratory of Inorganic Chemistry, Swiss Federal Institute of Technology,
ETH-Zentrum, CH-8092 Zurich, Switzerland
Received August 30, 1995X
Four new complexes of the type [Ru(CF3CO2)2(X)2(PP)] 7 (X ) methanol or ethanol, PP )
chiral diphosphine) have been synthesized from the reaction of PP with [Ru2(CF3CO2)4(H2O)-
(COD)2] and characterized by both NMR spectroscopy and single-crystal X-ray diffraction
studies. A common feature of these complexes is a pseudooctahedral geometry for ruthenium,
an unusual monodentate ligation mode for the mutually trans trifluoroacetate groups, along
with two solvent molecules coordinated in mutual cis positions (MeOH for 7a and 7b, EtOH
for 7c). 7a (PP ) (2S,4S)-BDPP) belongs to the orthorhombic P212121 space group, Z ) 4,
a ) 9.896(1) Å, b ) 19.099(3) Å, and c ) 19.689(2) Å. 7b (PP ) (4S,5S)-DIOP) also crystallizes
in the orthorhombic P212121 space group, Z ) 4, a ) 12.679(1) Å, b ) 16.744(2) Å, and c )
18.944(2) Å. 7c (PP ) (R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine,
abbreviated as PPFCy2) belongs to the monoclinic P21 space group, Z ) 4, a ) 18.153(2) Å,
b ) 12.364(2) Å, c ) 20.431(1) Å, and â ) 97.40(1)°. The air-stable [RuCl(p-cymene)(PP)]-
PF6 9 were synthesized from the reaction of PP with [RuCl2(p-cymene)]2 in a refluxing
CH2Cl2/EtOH mixture, followed by metathesis with KPF6 in MeOH, in 72-89% yields (PP
) (S)-(R) or (R)-(S)-2-(diphenylphosphino or arsino)ferrocenyl]ethylbisphosphine derivative).
9a (PP ) (S)-(R)-PPFCy2 crystallizes in the monoclinic space group P21, Z ) 2, a )
11.965(2) Å, b ) 14.852(3) Å, c ) 13.999(2) Å, and â ) 111.50(2)°. Complexes 7 were probed
for their catalytic behavior in the hydrogenation of methyl acetamidocinnamate 10,
acetamidocinnamic acid 11, and dimethyl itaconate 12. Using a typical substrate to catalyst
ratio of 50-100:1 and p(H2) ) 50 bar, modest enantiomeric excesses (ee) of up to 75% were
achieved. The highest ee’s were attained in CH2Cl2 or a 5:4 THF/CH2Cl2 mixture, whereas
higher activities were observed when methanol was employed as solvent. The addition of
NEt3 had a beneficial effect on the ee of the reactions involving 11, whereas with 10 a
detrimental effect was observed. The reactions involving 12 gave poor enantioselectivity.
In tr od u ction
type [Ru(RCO2)2(PP)] (PP ) BINAP (I),1 BIPHEMP
(II)2) have given excellent results, although there would
still appear to be a definite lack of well-characterized,
analogous complexes containing different phosphine
backbones (see Chart 1).3
We recently embarked on a project aimed at preparing
a series of dicarboxylate and η6-aryl-bound ruthenium-
(II) complexes, containing phosphines other than I or
II, for structural characterization and evaluation of
their catalytic properties. Ligands III,4 IV,5 V,6 1,7 and
2,8 as well as a whole host of ferrocenyl bisphosphines
3-5, and one arsenylphosphine 3d , were appropriate
candidates for the attempted synthesis of the required
Recent years have witnessed increasingly impressive
catalytic applications of ruthenium(II) diphosphine
complexes in asymmetric hydrogenation reactions with
notable developments including their successful em-
ployment in the formation of highly enantiomerically
enriched alcohols from ketone, lactone, or ester precur-
sors and their use in olefin hydrogenation.1-3 In this
respect, structurally well-characterized complexes in-
corporating atropisomeric biarylphosphines (PP) of the
† ETH-Zentrum.
‡ Central Research Services, Ciba-Geigy Ltd.
X Abstract published in Advance ACS Abstracts, December 15, 1995.
(1) (a) For an excellent overview, see: Takaya, H.; Ohta, T.; Noyori,
R. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH Publishers:
New York, 1993; pp 1-39, and references cited therein. (b) Noyori, R.;
Takaya, H. Acc. Chem. Res. 1990, 23, 345. (c) Takaya, H.; Ohta, T.;
Mashima, K.; Noyori, R. Pure Appl. Chem. 1990, 1135. (d) Mashima,
K.; Kusano, K.; Sato, N.; Matsumura, Y.; Nozaki, K.; Kumobayashi,
H.; Sayo, N.; Hori, Y.; Ishizaki, T.; Akutagawa, S.; Takaya, H. J . Org.
Chem. 1994, 59, 3064. (e) Ohta, T.; Miyake, T.; Seido, N.; Kumobayashi,
H.; Takaya, H. J . Org. Chem. 1995, 60, 357.
(2) (a) Schmid, R.; Cereghetti, M.; Heiser, B.; Scho¨nholzer, P.;
Hansen, H. J . Helv. Chim. Acta 1988, 71, 897. (b) Heiser, B.; Broger,
E. A.; Crameri, Y. Tetrahedron: Asymmetry 1991, 2, 51. (c) Mezzetti,
A.; Tschumper, A.; Consiglio, G. J . Chem. Soc., Dalton Trans. 1995,
49.
(3) (a) Genet, J . P.; Mallart, S.; Pinel, C.; J uge, S.; Laffitte, J . A.
Tetrahedron: Asymmetry 1991, 2, 43. (b) Alcock, N. W.; Brown, J . M.;
Rose, M.; Wienaud, A. Tetrahedron: Asymmetry 1991, 2, 47. (c) J ames,
B. R.; Dang, D. K. W. Can. J . Chem. 1980, 58, 245. (d) Kawano, H.;
Ikariya, T.; Ishii, Y.; Kodama, T.; Saburi, M.; Yoshikawa, S.; Uchida,
Y.; Akutagawa, S. Bull. Chem. Soc. J pn. 1992, 65, 1595.
(4) (a) Achiwa, K. J . Am. Chem. Soc. 1976, 98, 8265. (b) Ojima, I.;
Yoda, N. Tetrahedron Lett. 1980, 21, 1051.
(5) Fryzuk, M. D.; Bosnich, B. J . Am. Chem. Soc. 1977, 99, 6262.
(6) Brunner, H.; Pieronczyk, W.; Scho¨nhammer, B.; Streng, K.;
Bernal, I.; Korp, J . Chem. Ber. 1981, 114, 1137.
(7) McNeil, P. A:; Roberts, N. K.; Bosnich, B. J . Am. Chem. Soc.
1981, 103, 2280.
(8) Kagan, H. B:; Dang, T. P. J . Am. Chem. Soc. 1972, 94, 6429.
0276-7333/96/2315-0860$12.00/0 © 1996 American Chemical Society

Chiral Ruthenium(II) Diphosphine Complexes
Organometallics, Vol. 15, No. 2, 1996 861
Ch a r t 1
synthetic route to ligands III-V were unfortunately
unsuccessful as were the reactions of the same phos-
phines with [RuCl2(COD)]n in the presence of a base.3d,13a
Ligands 4b, 4c, 5b, and 5c were reacted in situ with 6
in MeOH at rt for 1 h, and after solvent removal in
vacuo, the resulting yellow powders were used directly
in the hydrogenation reactions (vide infra).
The structures of 7 in solution were probed by 31P
NMR spectroscopy. Complexes 7a and 7b, consistent
with the C2 symmetry axis passing through the two
phosphorus atoms, perpendicular to the CF3CO2Ru
bond, gave singlets in their 31P NMR spectrum, the
chemical shift of the homotopic phosphorus atoms being
shifted downfield with respect to the starting ligands.
Despite the two complexes having diarylalkylphosphine
backbones, the 31P chemical shift of 7a (δ ) 62.7 ppm
in CDCl3) is almost 20 ppm downfield from that of 7b
(δ ) 45.4 ppm). As expected, 7c and 7d gave AB
systems due to the nonequivalence of the P atoms. On
complexes (see Chart 2). The choice of ligands such as
3, 4, and 5 was especially desirable given their current
high scope of application in many different catalytic
reactions.9,10 Moreover, the myriad of structural per-
mutations possible by simple chemical transformations
at the stereogenic side arm renders these ferrocenyl
systems very attractive for a study of both steric and
electronic effects in catalysis.10 Compounds 511 have the
added complexity of containing a third, further stereo-
genic center viz. the phosphorus atom.
1
the basis of the H NMR spectra it was not possible to
distinguish between a bidentate or monodentate coor-
dination mode of the trifluoroacetate ligand in 7. More-
over, there was no observable difference in chemical
shift between coordinated and free methanol, indicating
a fast exchange process.
This study has resulted in the formation of a series
of complexes of the type [Ru(CF3CO2)2(X)2(PP)] and
[RuCl(p-cymene)(PP)]PF6 where X ) methanol or etha-
nol, and PP a chiral diphosphine (See Chart 2). The
characterization of such complexes by NMR, X-ray
analyses, and preliminary results pertaining to their use
in the catalytic hydrogenation of various olefinic deriva-
tives will be presented hereafter.
Syn th esis of 9. The reaction of 3 or 4 with [RuCl2(p-
cymene)]2 8 in a CH2Cl2/EtOH mixture, followed by
metathesis with KPF6 in MeOH furnished, after work-
up, the cationic, air-stable solids 9 (eq 2). Analysis of
Resu lts a n d Discu ssion
Syn t h esis of 7. The addition of an equimolar
amount of a dichloromethane solution of the phosphines
1, 2, 4a , or 5a to a stirred solution of [Ru2(CF3CO2)4-
(H2O)(COD)2] 612 (COD ) 1,5-cyclooctadiene) in metha-
nol or ethanol at room temperature afforded, after
workup, the yellow or red complexes [Ru(CF3CO2)2-
(ROH)2(PP)] 7 in high yields (eq 1). These solids can be
the 31P NMR spectra of 9 was most informative, and
varying degrees of diastereoselectivity were observed
depending on the phosphine ligand used. Since the
ruthenium atom in complexes 9 is now a new stereo-
genic center, two possible diastereomeric forms arise.
Whereas the 31P NMR spectrum of 9a displayed one
2
major AB system (diastereoselectivity ∼15:1, with a J PP
stored under argon at rt but are rather air-sensitive in
solution, turning green. Attempts at extending this
) 55.8 Hz between the PCy2 and PPh2 groups), that of
9b presented two such AB systems in a ∼5:1 ratio (2J PP
) 58.8 Hz between the two PPh2 groups). This latter
distribution of diastereomers most likely represents the
thermodynamic product ratio of the reaction, since
refluxing a further 16 h under the same reaction
conditions led to no change in this ratio, by 31P NMR.
(9) (a) Hayashi, T. In Ferrocenes; Togni, A., Hayashi, T., Eds.; VCH
Publishers: New York, 1995; Chapter 2, p 105, and references cited
therein. (b) Hayashi, T. Pure Appl. Chem. 1988, 60, 7.
(10) (a) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert,
H. J . Am. Chem. Soc. 1994, 116, 4062. (b) Schnyder, A.; Hintermann,
L.; Togni, A. Angew. Chem. 1995, 34, 931. (c) Abbenhuis, H. C. L.;
Burckhardt, U.; Gramlich, V.; Ko¨llner, C.; Pregosin, P.; Salzmann, R.;
Togni, A. Organometallics 1995, 14, 759.
(11) Togni, A.; Breutel, C.; Soares, M.; Zanetti, N.; Gerfin, T.;
Gramlich, V.; Spindler, F.; Rihs, G. Inorg. Chim. Acta 1994, 222, 213.
(12) Albers, M. O.; Liles, D. C.; Singleton, E.; Yates, J . E. J .
Organomet. Chem. 1984, 272, C62.
(13) (a) Ohta, T.; Takaya, H.; Noyori, R. Inorg. Chem. 1988, 27, 566.
(b) For an overview of bonding modes of carboxylate complexes, see:
Rardin, R. L.; Tolman, W. B.; Lippard, S. J . New. J . Chem. 1991, 15,
417.

862 Organometallics, Vol. 15, No. 2, 1996
Zanetti et al.
Ch a r t 2
may be a contributing factor to this structural differ-
ence. The stability of 7a -c can be attributed to the
formation of two relatively strong hydrogen bonds14
between the carbonyl groups of the trifluoroacetate
ligands and the protons of the coordinated solvent
molecules (O‚‚‚O distances between 2.5 and 2.7 Å), a
feature that is not without precedent in ruthenium
chemistry.15
The structure of 9a was also determined, of crystals
obtained by slow diffusion of diethyl ether into a
dichloromethane solution at room temperature (Fig-
ure 2). The ruthenium atom is part of an overall piano
stool arrangement, comprising the η6-bound cymene
group, the chloride ion, and the two distinct phosphine
atoms of the ferrocenyl ligand. The P-Ru distances
corresponding to the aryl (P1) and alkyl (P2) phosphines
in the six-membered ruthenacycle are slightly differ-
ent, P1-Ru being 2.368(2) Å and P2-Ru 2.390(2) Å.
Other distances, e.g., Ru-Cl (2.400 Å), fall in the
normal range. The bite angle (P-Ru-P) of 92.6(1)° is
slightly larger than that of the related [RuCl(ben-
zene)((S)-BINAP)] complex1c,16 (P-Ru-P ) 91.4(1)°) and
that of 7c (90.5°). The P1-Ru-Cl and P2-Ru-Cl
angles of 85.1(1)° and 85.9°, respectively, emphasize the
distorted fac-octahedral geometry of the complex (see
Table 3).
Hyd r ogen a tion Rea ction s. The catalytic activity
of mainly 7 in the enantioselective hydrogenation of the
olefinic substrates 10-12 was examined, preliminary
results obtained with 9a and 9d being very disappoint-
ing (enantiomeric excesses (ee’s) and conversions of
∼10% with 10 as substrate after ∼17 h) and not pursued
further. Substrate/catalyst ratios of either 50 or 100
were routinely employed, and the results are compiled
in Table 4, including those obtained using the in situ
generated complexes [Ru(CF3CO2)2(MeOH)2(PP)], where
PP ) 4b, 4c, 5b, and 5c.
The 31P NMR spectrum of 9d displayed, as expected, a
singlet for the PPh2 group whereas that of 9c was rather
complicated, with a broad multiplet at δ ) ∼35 ppm
and a sharp doublet at δ ) 29 ppm. This can be
explained by a rapid exchange process between the
arene group and the Cl atom on the NMR time scale.
9c proved, moreover, to be rather difficult to obtain in
pure form.
A few pertinent conclusions can be drawn from these
results. First, a strong solvent effect on enantioselec-
tivity is apparent. The enantioselectivity is clearly
higher in aprotic (CH2Cl2 or THF) than in protic
solvents (MeOH) and such an effect is rather pro-
nounced when substrates 10 and 11 are employed.
Thus, 10 was hydrogenated in the presence of 7a as
catalyst with an ee of 69% in CH2Cl2, whereas in MeOH
the ee was significantly lower (24%) (entries 1 and 2,
Table 4). With the same catalyst, 11 was hydrogenated
in a 5:4 mixture of THF/CH2Cl2 with an ee of 47%
whereas in MeOH only a 3% ee was observed (entries 4
and 5). Similarly, again in the hydrogenation of 10,
with the in situ-generated complex obtained from 6 and
5b, the ee dropped in changing from CH2Cl2 (75% ee)
to MeOH (31% ee) (entries 14 and 15). A similar
decrease in enantioselectivity by the same change in
solvent has already been reported for the hydrogenation
of various carbonyl functions,17,18 whereas the opposite
Str u ctu r a l Ch a r a cter iza tion of 7a -c a n d 9a . In
order to elucidate the precise bonding mode of the
trifluoroacetate groups and the overall geometry of the
complexes in the solid state, single-crystal structure
determinations of 7a -c were carried out. Crystals of
7a and 7b suitable for such a determination were
obtained by recrystallization in MeOH and those of 7c
from EtOH. Crystallographic data are given in Table
1. A selection of bond lengths and angles for complexes
7a -c is shown in Table 2.
The Shakal plots given in Figure 1 show, common for
each of these three complexes, a near-octahedral geom-
etry for ruthenium and mutually trans ligated mono-
dentate trifluoroacetate groups, along with two sol-
vent molecules coordinated in mutual cis positions
(MeOH for 7a and 7b, EtOH for 7c). The bite angles
(P-Ru-P) found for 7a and 7b are 92.3 and 94.7°,
respectively (see Table 2), which are somewhat larger
than the 90.6(1)° found for [Ru(OCOt-Bu)2(BINAP)].13a
7c comprised two independent molecules in the unit
cell.
(14) Emsley, J . Chem. Soc. Rev. 1980, 9, 91.
(15) (a) Dobson, A.; Moore, D. S.; Robinson, S. D.; Hursthouse, M.
B:, New, L. Polyhedron 1985, 4, 1119. (b) Albers, M. O.; Liles, D. C.;
Singleton, E. Acta Crystallogr. 1987, C43, 860.
(16) Mashima, K.; Kusano, K.; Ohta, T.; Noyori, R.; Takaya, H. J .
Chem. Soc., Chem. Commun. 1989, 1208.
(17) Genet, J . P.; Pinel, C.; Mallart, S.; J uge, S.; Thorimbert, S.;
Laffitte, J . A. Tetrahedron: Asymmetry 1991, 2, 555.
(18) Mashima, K.; Matsumura, Y.; Kusano, K.; Kumobayashi, H.;
Sayo, N.; Hori, Y.; Ishizaki, T.; Akutagawa, S.; Takaya, H. J . Chem.
Soc., Chem. Commun. 1991, 609.
The most striking feature of these structures is the
monodentate ligation of the trifluoroacetate groups to
ruthenium, which is in sharp contrast to an analogous
BINAP-Ru complex in which this ligand adopts a
bidentate bonding mode.13 The relatively low basicity,
and hence weak trans influence, of the BINAP ligand
as compared to the higher alkylated phosphines in 7a -c

Chiral Ruthenium(II) Diphosphine Complexes
Organometallics, Vol. 15, No. 2, 1996 863
Ta ble 1. Str u ctu r a l P a r a m eter s for 7a -c a n d 9a
compound
formula
mol wt
7a
7b
7c
9a
C
35H38O6F6P2Ru
C37H32D8O8F6P2Ru
897.78
C44H54O6F6P2RuFe
1011.76
C46H58ClF6P3RuFe
1010.2
831.69
crystal dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.70 × 0.45 × 0.36
orthorhombic
P212121
9.896(1)
19.099(3)
19.689(3)
0.76 × 0.60 × 0.30
orthorhombic
P212121
12.679(1)
16.744(2)
0.54 × 0.31 × 0.10
monoclinic
P21
18.153(2)
12.364(2)
20.431(1)
97.40(1)
4547(1)
0.8 × 0.6 × 0.45
monoclinic
P21
11.965(2)
14.852(3)
13.999(2)
111.50(2)
2314.6(7)
2
1.449
8.56
1040
18.944(2)
â(°)
V (Å3)
3721(1)
4
1.484
4.90
1696
4022(1)
4
1.483
5.325
1816
Z
4
F (calcd) (g‚cm-3
)
1.478
7.78
2080
µ (cm-1
F(000)
)
diffractometer
Enraf-Nonius CAD4
Cu KR
6-150
4308
Phillips PW1100
Mo KR
6-60
Phillips PW1100
Mo KR
Syntex P21
radiation (graph. monoch)
2θ range (deg)
no. of unique reflcns
no. of obsd reflcns (no)
refinement methods
hydrogen atoms
no. of params
Mo KR
6-60
3-40
6508
14271
5670
full matrix (in 2 blocks)
not located
1080
2433
4277
4065
2287
full matrix
Riding model; fixed isotr U
517
full matrix
not located
451
full matrix
not located
487
R
Rw
0.069
0.079
0.064
0.076
0.036
0.042
0.027
0.034
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
where PP ) 5b, for the hydrogenation of 10, a yield of
29%, and an ee of 57% was obtained in CH2Cl2 whereas
in MeOH, after only 4 h, quantitative conversion was
achieved, the ee being, however, only 30% (entries 20
and 21, respectively). Here, a substrate/catalyst ratio
of 100:1 was employed. Other in situ-generated cata-
lysts, from 4b and 4c, for example, (entries 22 and 23)
gave poor results, even with a substrate/catalyst ratio
of 50:1.
(d eg) for 7a -c
Bond Distances for 7a
Ru-P2
2.255(4)
2.252(4)
2.16(1)
2.23(1)
O13-O15
Ru-O10
Ru-O14
O11-O14
2.658
Ru-P3
2.11(1)
2.18(1)
2.675
Ru-O12
Ru-O15
Bond Angles for 7a
P2-Ru-P3
P2-Ru-O15
P3-Ru-O12
P3-Ru-O15
92.3(1)
P2-Ru-O10
P3-Ru-O10
P3-Ru-O14
P2-Ru-O14
100.0(3)
91.4(3)
175.2(3)
92.5(3)
173.0(2)
94.7(3)
94.4(2)
In the hydrogenation of 10 and 11, both the enantio-
selectivity and activity of the catalyst were influenced
by the addition of NEt3. The addition of base increased
the optical yield of product for the hydrogenation of 11
in both protic and aprotic solvents (compare entries 6
and 5 and entries 7 and 4), whereas the optical yield
observed for the hydrogenation of 10, in the presence
of 7a or 7c, diminished upon addition of base (entries 1
and 3, where the ee decreases from 69 to 29%). Such a
pronounced effect by the addition of base observed for
11 may be due to an acceleration of the heterolytic hy-
drogen activation and the generation of a carboxylate
group which would be able to coordinate to ruthenium.
This would decrease the number of degrees of freedom
of the system, in terms of coordination geometry, and
thus contribute to achieving a higher enantiodiscrimi-
nation.20
Bond Distances for 7b
Ru-P2
2.248(3)
2.104(8)
2.234(9)
2.62(1)
Ru-P3
2.253(3)
2.107(8)
2.202(9)
2.57(1)
Ru-O14
Ru-O17
O15-O17
Ru-O12
Ru-O16
O13-O16
Bond Angles for 7b
P2-Ru-P3
94.7(1)
P2-Ru-O12
P2-Ru-O16
P3-Ru-O12
P3-Ru-O16
92.4(3)
93.8(3)
90.8(2)
171.4(3)
P2-Ru-O14
P2-Ru-O17
P3-Ru-O14
P3-Ru-O17
87.9(3)
174.6(2)
94.3(3)
90.2(2)
Bond Distances for 7c
Ru-P5
2.296(3)
2.114(7)
2.220(7)
2.63
Ru-P6
2.256(3)
2.133(7)
2.232(7)
2.56
Ru-O21
Ru-O25
O13-O16
Ru-O23
Ru-O26
O15-O17
Bond Angles for 7c
P5-Ru-P6
P5-Ru-O23
P6-Ru-O21
P6-Ru-O25
90.5(1)
94.9(2)
91.6(2)
P5-Ru-O21
P5-Ru-O25
P6-Ru-O23
P6-Ru-O26
88.6(2)
94.5(2)
93.5(2)
90.5(2)
The extra, phosphorus stereogenic center in 5b (P has
the R configuration) and 5c (P has the S configuration)
allows for a study of the effect of chirality at phosphorus
on the enantioselectivity of the hydrogenation process.21
In the hydrogenation of 10, carried out in CH2Cl2, the
in situ-generated complexes [Ru(CF3CO2)2(MeOH)2-
(PP)], where PP ) 5b or 5c, gave significantly different
results, the activity and enantioselectivity of the reac-
tions being higher (74% ee, 85% yield) when complex
5b (entry 14) was employed as opposed to the 57% ee,
and 29% yield, obtained for the complex incorporating
5c (entry 20). Despite the differerent absolute config-
uration at the stereogenic P atom, the reactions cata-
lyzed by 5b and 5c afforded the R-enriched products, a
175.0(2)
trend was observed using [RuBr2((R)-BINAP)] as cata-
lyst for the hydrogenation of 10, the ee increasing in
changing from CH2Cl2 (24% ee) to methanol (85% ee)
as solvent.19
The activity of all catalysts investigated is higher in
MeOH than in CH2Cl2. The hydrogenation of 10,
catalyzed by 7c, was complete within 0.1 h (entry 13),
whereas in CH2Cl2, only 34% conversion was attained
after 18 h (entry 12). The optical yields of these two
reactions were both, however, very low. Using the in
situ-generated complexes [Ru(CF3CO2)2(MeOH)2(PP)]
(19) Noyori, R.; Ikeda, T.; Ohkuma, T.; Widhalm, M.; Kitamura, M.;
Takaya, H.; Akutagawa, S.; Sayo, N.; Saito, T.; Taketomi, T.; Kumoba-
yashi, H. J . Am. Chem. Soc. 1989, 111, 9134.
(20) Ashby, M. T.; Halpern, J . J . Am. Chem. Soc. 1991, 113, 589.
(21) (a) Nagel, U.; Rieger, B. Organometallics 1989, 8, 1534. (b)
Nagel, U.; Bublewitz, A. Chem. Ber. 1992, 125, 1061.

864 Organometallics, Vol. 15, No. 2, 1996
Zanetti et al.
F igu r e 2. ORTEP view of 9a ′.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 9a ′
Bond Distances
Ru-Cl
2.400(2)
2.368(2)
2.238(8)
2.224(8)
2.321(8)
Ru-P2
2.390(2)
2.270(8)
2.272(8)
2.273(8)
Ru-P1
Ru-C32
Ru-C34
Ru-C36
Ru-C33
Ru-C35
Ru-C37
Bond Angles
Cl-Ru-P1
P1-Ru-C32
P2-Ru-C33
Cl-Ru-P2
85.1(1)
103.3(2)
142.8(2)
85.9(1)
P1-Ru-P2
Cl-Ru-C33
Cl-Ru-C34
P2-Ru-C32
92.6(1)
131.3(2)
163.0(2)
163.8(2)
Con clu sion
A general, facile synthetic route to neutral and
cationic phosphine ligated ruthenium(II) complexes 7
and 9, respectively, has been described. The former
class of complex is particularly interesting from a
structural point of view due to the monodentate ligation
of the trifluoroacetate groups to the metal center and
the complexes were tested as catalysts for the hydro-
genation of olefinic substrates, achieving rather disap-
pointing enantioselectivities. Already described Ru(II)
complexes incorporating axial chiral C2 diphosphine
ligands,1,2 or related Rh(I) derivatives,1a,10a are without
doubt the systems of choice for optimal stereospecificity
and efficiency in such hydrogenation reactions.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions with air- or mois-
ture-sensitive materials were carried out under Ar using
standard Schlenk techniques. Freshly distilled, dry, and
oxygen-free solvents were used throughout. [Ru2(CF3CO2)4-
(H2O)(COD)2],12 [RuCl2(p-cymene)]2,22 [RuCl2(COD)]n,23 3b and
4b (abbreviated as (S,R)- or (R,S)-PPFPh2),24 and the fer-
rocenes of the type (S,R)- or (R,S)-PPFR1R2 were prepared
1
according to literature procedures.10,11,24 Routine H (250.133
MHz) and 31P NMR (101.26 MHz) spectra were recorded with
a Bruker AC 250 spectrometer. Chemical shifts are given in
ppm and coupling constants (J ) are given in hertz. Optical
rotations were measured with a Perkin-Elmer 341 polarimeter
F igu r e 1. Schakal views of the complexes (top) [Ru(CF3-
CO2)2(MeOH)2(2S,4S)-BDPP] (7a ), (middle) [Ru(CF3CO2)2-
(MeOH)2(4S,5S)-DIOP] (7b), and (bottom) [Ru(CF3CO2)2-
(EtOH)2(R)-(S)-PPFCy2] (7c).
(22) Bennet, M. A.; Smith, A. J . Chem. Soc., Dalton Trans. 1974,
233.
(23) Albers, M. O.; Ashworth, T. V.; Oosthuizen, E.; Singleton, E.
Inorg. Synth. 1990, 26, 69.
(24) Hayashi, T.; Mise, T.; Fukushima, M.; Nagashima, M. K. N.;
Hamada, Y.; Matsumoto, A.; Kawakami, S.; Konishi, M.; Yamamoto,
K,; Kumada, M. Bull. Chem. Soc. J pn. 1980, 53, 1151.
result in line with previous observations in analogous
Rh chemistry.15a

Chiral Ruthenium(II) Diphosphine Complexes
Organometallics, Vol. 15, No. 2, 1996 865
3
3J (HH) ) 7.4, Me), 1.21 (t, 3H, J (HH) ) 7.0, CH2Me), 2.37-
Ta ble 4. Hyd r ogen a tion of 10-12 Ca ta lyzed by
0.86 (m, 22H, Cy); 31P{1H} NMR (CDCl3/CD3OH, 298 K) δ 45.4
(s, PCy2). Anal. Calcd for C44H56F6FeO6P2Ru: C, 52.13; H,
5.57. Found: C, 52.35; H, 5.68.
[Ru (CF 3CO2)2S2(P P )] a n d
a
[Ru Cl(p-cym en e)(P P )]P F 6
CO2Me
CO2H
CO2Me
[Ru (CF 3CO2)2(MeOH)2(P P F P h Cy)] (7d ). This was pre-
pared as described above for complex 7a except that 5a (96
mg, 0.16 mmol) and 6 (72 mg, 0.08 mmol) were used: yield 98
mg, 61%; 1H NMR (CDCl3/CD3OH, 298 K) δ 7.87-7.79 (m, 15
H, PPh), 4.62, 4.28, 3.86 (3s, 3H, C5H3), 3.60 (s, 5H, C5H5),
3.35 (m, 1H, PCH), 1.83 (dd, 3H, 3J (HP) ) 11.4, 3J (HH) ) 7.3,
Me), 2.45-1.34 (m, 11H, Cy); 31P{1H} NMR (CDCl3/CD3OH,
298 K) δ 68.61 (d, 2J (PP) ) 50.4, PPh2), 53.67 (d, 2J (PP) )
50.4, PCyPh). Anal. Calcd for C42H46F6FeO6P2Ru: C, 51.49;
H, 4.73. Found: C, 51.97; H, 4.35.
Ph
NHCOMe
Ph
NHCOMe
CO2Me
10
11
12
cat.
entry or PP substrate
time yield
ee (%)
solvent
CH2Cl2
(h)
(%)
(config)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
7a
7a
7a b
7a
7a
7a c
7a c
7a
7b
7b
7b
7c
7c
5b
5b
5b
5b
5b
5b
5c
5c
4b
4c
10
10
10
11
11
11
11
12
10
10
12
10
10
10
10
12
12
10
11
10
10
10
10
21
75 69 (S)
100 24 (S)
100 29 (S)
100 47 (S)
MeOH
20
28
20
20
CH2Cl2
THF/CH2Cl2
MeOH
d
d
[Ru Cl{(S)-(R)-P P F Cy2}(p-cym en e)]P F 6 (9a ). 3a (317
mg, 0.53 mmol) and [RuCl2(p-cymene)]2 (161 mg, 0.26 mmol)
were heated in a 3:1 suspension of EtOH/CH2Cl2 (15 mL:5 mL)
at 60 °C for 1.75 h. After cooling and filtration over Celite to
remove some decomposition products, the orange suspension
was evaporated to dryness. Metathesis with excess KPF6 (210
mg, 1.14 mmol) in MeOH (20 mL) for 2 h at room temperature
was followed by solvent evaporation. The orange residue was
extracted with CH2Cl2 (50 mL) and the organic phase washed
with water (10 mL) and then dried over MgSO4. Removal of
the latter by filtration followed by evaporation of the filtrate
afforded an orange solid: yield 478 mg, 89%; [R]20D ) 271 (c )
0.16, CH2Cl2); 1H NMR (CDCl3, 298 K) δ 8.25-7.00 (m, 10 H,
100
3 (S)
MeOH
0.5 100 40 (S)
THF/CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
MeOH
CH2Cl2
MeOH
CH2Cl2
MeOH
CH2Cl2
CH2Cl2
CH2Cl2
MeOH
CH2Cl2
CH2Cl2
45
100 63 (S)
100 32 (R)
100
27 13 (S)
100 22 (S)
34 11.3 (S)
17
90
15
20
18
2 (S)
0.1 100
7 (R)
85 75 (R)
100 31 (R)
100 42 (R)
19
19
19
18
16
20
21
4
100
0
100 65 (R)
100 21 (R)
29 57 (R)
100 30 (R)
67
100
3
PPh2), 6.21 (m, 2H, Hcym), 6.08 (d, 1H, J (HH) ) 6.0, Hcym),
5.78 (m, 1H, Hcym), 4.97 (dq, 1H, 3J (HH) ) 5.4, PCHMe), 4.59,
4.42, 4.35 (3m, 3H, C5H3), 4.00 (s, C5H5 of minor diastereomer),
3.59 (s, 5H, C5H5), 2.77, 2.51, 2.30 (3m, 3H, Me2CH, 2CH
cyclohex), 2.20-0.84 (m, 29H, Cy, MeCHP, CHMe2), 0.55 (s,
3H, Me); 31P NMR δ 53.4 (d, 2J (PP) ) 55.8, PCy2), 25.8 (d,
2J (PP) ) 55.8, PPh2), -144.8 (sept, 1J (PF) ) 713, PF6). Traces
of a second diastereomer at δ ) 35 and 54 ppm were detected.
MS (FAB) 865 (M+, 15). Anal. Calcd for C46H58ClF6FeP3Ru:
C, 54.69; H, 5.79. Found: C, 54.97; H, 6.04.
19
66
5.6 (R)
5.9 (S)
a
Reaction conditions: p(H2) 50 bar; Substrate/Ru ) 50 (entries
1-13, 22, and 23); substrate/Ru ) 100 (entries 14-21). For all
b
reactions, [substrate] ) 1.5-2.5 mmol; room temperature. NEt3/
Ru, 10 equiv. c NEt3/Ru, 50 equiv. 5:4 ratio.
d
using 10 cm cells. Elemental analyses were performed by the
Mikroelementar-analytisches Laboratorium der ETH and by
the Analytical Research Services at Ciba-Geigy. Mass spectra
were carried out at the Mass Spectroscopy Service of the ETH.
Catalytic experiments and analyses of reaction products were
carried out as previously described.10
[Ru Cl{(R)-(S)-P P F Cy2}(p-cym en e)]P F 6 (9a ′). This was
made in a fashion analogous to its (S)-(R) derivative: [R]20
-233 (c ) 0.25, CH2Cl2).
)
D
[Ru Cl{(S)-(R)-P P F P h 2}(p-cym en e)]P F 6 (9b). This was
made in a fashion analogous to 9a using 3b (118 mg, 0.20
mmol) and [RuCl2(p-cymene)]2 (60 mg, 0.10 mmol), followed
by metathesis with KPF6 (74 mg, 0.40 mmol) in MeOH, and
[Ru (CF 3CO2)2(MeOH)2(2S,4S-BDP P )] (7a ). A solution of
1 (254 mg, 0.57 mmol), in CH2Cl2 (3 mL), was slowly added to
an orange MeOH solution (6 mL) of [Ru2(CF3CO2)4(H2O)-
(COD)2] (6; 252 mg, 0.28 mmol) at room temperature. After 4
h stirring, the resulting red solution was concentrated in vacuo
to 2 mL, affording 7a as a yellow powder. Washing with cold
MeOH, followed by drying in vacuo, gave analytically pure 7a
(yield 359 mg, 75%), which was used as such for the ensuing
obtained as an orange solid: yield 144 mg, 72%; [R]20 ) 213
D
1
(c ) 0.45, CH2Cl2); H NMR (CDCl3, 298 K) δ 8.28-6.90 (m,
20H, 2 PPh2), 6.03, 5.81, 5.57, 4.55 (4m, 4H, Hcym), 5.22 (dq,
3
1H, J (HH) ) 5.4, PCHMe), 4.48, 4.33, 4.30 (3m, 3H, C5H3),
4.04 (s, C5H5 of minor diastereomer), 3.68 (s, 5H, C5H5), 2.64
3
3
(q, 1H, J (HH) ) 5.6, CHMe2), 1.45 (ABX, 3H, J (HH) ) 6.9,
3J (HP) ) 13.4, PCHMe), 1.25, 0.77 (2d, 6H, 3J (HH) ) 6.5,
hydrogenation reactions: [R]20 ) 90.3 (c ) 0.6, MeOH); 1H
D
CHMe2), 0.63 (s, 3H, Me); 31P NMR δ 48.3 and 27.4 (d, J (PP)
2
NMR (CDCl3, 298 K) δ 7.70-6.70 (m, 20 H, 2 PPh2), 3.12 (s,
6H, MeOH), 2.94 (m, 1H, PCH), 2.00 (tt, 2H, 3J (HH) ) 5.4,
3J (HP) ) 20.5, CH2), 0.94 (dd, 6H, 3J (HH) ) 7.0, 3J (HP) )
13.3, 2 Me); 31P{1H} NMR (CDCl3, 298 K) δ 62.7 (s, PPh2).
Anal. Calcd for C35H38O6F6P2Ru: C, 50.55; H, 4.61. Found:
C, 50.50; H, 4.50.
1
) 58, PPh2), -144.8 (sept, J (PF) ) 713, PF6); second isomer
(∼16%) at δ 54.8, 37.2 (2d, 2J (PP) ) 58, PPh2). MS (FAB) 853
(M+, 100). Anal. Calcd for C46H46ClF6FeP3Ru: C, 55.35; H,
4.65. Found: C, 55.23; H, 4.56.
[Ru Cl{(S)-(R)-P P F P h obyl}(p-cym en e)]P F 6 (9c). This
was made in a fashion analogous to 9a using 3c (139 mg, 0.26
mmol) and [RuCl2(p-cymene)]2 (79 mg, 0.13 mmol), followed
by metathesis with KPF6 (92 mg, 0.5 mmol) in MeOH, and
[Ru (CF3CO2)2(MeOH)2(4S,5S-DIOP )] (7b). This was pre-
pared as described above for complex 7a except that 2 (396
mg, 0.79 mmol) and 6 (348 mg, 0.39 mmol) were used: yield
obtained as a pale brown solid: yield 191 mg, 77%; [R]20
)
521 mg, 75%; [R]20 ) 16.3 (c ) 0.3, CHCl3); 1H NMR (CDCl3,
D
D
77 (c ) 0.1, CH2Cl2); 1H NMR (CDCl3, 298 K) δ 7.70-7.25 (m,
10 H, PPh2), 6.22, 5.81, 5.42, 5.24 (4m, 4H, Hcym), 4.52, 4.40,
4.07 (3m, 3H, C5H3), 4.01 (s, 5H, C5H5 of minor diastereomer),
3.87 (s, 5H, C5H5), 3.73 (m, 1H, PCHMe), 2.78 (m, 1H, CHMe2),
298 K) δ 7.50-7.30 (m, 20 H, 2 PPh2), 3.86 (m, 1H, CH), 2.97
(s, 6H, 2 MeOH), 2.93 (m, 1H, PCH), 2.50 (m, 1H, PCH), 1.29
(s, 6H, 2 Me); 31P{1H} NMR (CDCl3, 298 K) δ 45.4 (s, PPh2).
Anal. Calcd for C37H40O8F6P2Ru: C, 49.95; H, 4.53. Found:
C, 49.80; H, 4.44.
[Ru (CF 3CO2)2(EtOH)2-(R)-(S)-P P F Cy2)] (7c). This was
prepared as described above for complex 7a except that 4a
(196 mg, 0.33 mmol) and 6 (146 mg, 0.165 mmol) were used
and that ethanol was employed as solvent: yield 135 mg, 80%;
1H NMR (CDCl3/CD3OH, 298 K) δ 7.78-7.70 (m, 10 H, PPh2),
4.62, 4.54, 4.40 (3s, 3H, C5H3), 3.65 (q, 2H, 3J (HH) ) 7.0, CH2),
3.35 (m, 1H, PCH), 3.54 (s, C5H5), 1.76 (dd, 3H, 3J (HP) ) 10.2,
3
2.40-0.80 (m, 17H, Hphob, Me), 1.08, 1.00 (2d, 6H, J (HH) )
2
6.1, Me2CH); 31P NMR δ 35.4 (m), 29.0 (d, J (PP) ) 57, PPh2),
-144.8 (sept, 1J (PF) ) 713, PF6). MS (FAB) 809 (M+, 11).
Anal. Calcd for
C42H50ClF6FeP3Ru: C, 52.87; H, 5.28.
Found: C, 51.78; H, 5.62.
[Ru Cl{(S)-(R)-P AsF Cy2}(p-cym en e)]P F 6 (9d ). This was
made in a fashion analogous to 9a except using 3d (125 mg,
0.20 mmol) and [RuCl2(p-cymene)]2 (56 mg, 0.09 mmol),

866 Organometallics, Vol. 15, No. 2, 1996
Zanetti et al.
followed by metathesis with KPF6 (97 mg, 0.53 mmol) in
MeOH, and obtained as an orange solid: yield 170 mg, 82%;
[R]20D ) 169 (c ) 0.4, CH2Cl2); 1H NMR (CDCl3, 298 K) δ 8.04-
is gratefully acknowledged (by J .S.) for financial support
of this project. V. Gramlich is thanked for solving the
structure of 9a .
3
7.10 (m, 10 H, PPh2), 6.22 (d, 1H, J (HH) ) 5.1, Hcym), 6.07,
5.72 (2d, 2H, Hcym), 4.68 (dq, 1H, 3J (HH) ) 6.5, PCHMe), 4.59,
4.44, 4.37 (3m, 3H, C5H3), 3.99 (s, 5H, C5H5 of minor diaste-
reomer), 3.63 (s, 5H, C5H5), 2.75-0.83 (m, 31H, Cy, MeCHP,
CHMe2), 0.74 (s, 3H, Me); 31P NMR δ 48.8 (s, PCy2), -144.8
(sept, 1J (PF) ) 713, PF6). MS (FAB) 909 (M+, 22). Anal.
Calcd for C46H58AsClF6FeP2Ru: C, 52.41; H, 5.55. Found: C,
51.81; H, 5.40.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and refinement details, atomic coordinates, complete
listing of bond distances and angles, torsion angles, tables of
anisotropic displacement coefficients, and positional param-
eters for 7a , 7b, 7c, and 9a ′ (51 pages). Ordering information
is given on any current masthead page. Tables of calculated
and observed structure factors for all four compounds (167
pages) may be obtained from the authors upon request.
Ack n ow led gm en t. The Swiss National Science
Foundation (CHiral2 program, Grant 2127-41′203.94)
OM9506781