Synthesis and crystal structures of Ru(II) complexes containing chelating (phosphinomethyl)oxazoline P,N-type ligands and asymmetric catalytic transfer hydrogenation of acetophenone in propan-2-ol

Article abstract of DOI:10.1021/ic0000754

A series of new Ru(II) complexes containing two chelating P,N ligands of the type (2-oxazolin-2-ylmethyl)-diphenylphosphine (PCH₂-oxazoline I), (2-oxazolin-4,4-dimethyl-2-ylmethyl)diphenylphosphine (PCH₂-oxazoline-Me₂ II), and (2-oxazolin-4-(S)-isopropyl-ylmethyl)diphenylphosphine (PCH₂-oxazoline-(i)Pr III) have been prepared and characterized by IR, ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy and by X-ray diffraction studies in the cases of cis, cis,cis-[RuCl₂(PCH₂-oxazoline)₂] (1) and cis, cis, trans-[RuCl₂(PCH₂-oxazoline-Me₂)₂] (3). Four different types of octahedral coordination geometries are found for these complexes depending on the ligand. With I, cis,cis,cis and trans,trans,trans geometries were characterized in complexes 1 and 2, respectively, whereas with ligand II only the cis,cis,trans isomer 3 was formed. Reaction of the enantiomerically pure ligand III with [RuCl₂(COD)(n) afforded a mixture of isomers, and complex trans,cis,cis-[RuCl₂(PCH₂-oxazoline-(i)Pr)₂] 4 was fully characterized. This complex was used for catalytic transfer hydrogenation of acetophenone in propan-2-ol and led to 96% conversion and 72% ee (3 h, 82 °C, [ketone] = 0.1 M, Ru:ketone:base = 1:200:5). For comparison the crude mixture of complexes gave a higher turnover frequency but a lower enantioselectivity than pure 4.

Full text of DOI:10.1021/ic0000754

4468
Inorg. Chem. 2000, 39, 4468-4475
Synthesis and Crystal Structures of Ru(II) Complexes Containing Chelating
(Phosphinomethyl)oxazoline P,N-Type Ligands and Asymmetric Catalytic Transfer
Hydrogenation of Acetophenone in Propan-2-ol†
Pierre Braunstein,*,‡ Claudia Graiff,§ Fre´de´ric Naud,‡ Andreas Pfaltz,| and
Antonio Tiripicchio§
Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Universite´ Louis Pasteur,
4, rue Blaise Pascal, F-67070 Strasbourg Cedex, France, Dipartimento di Chimica Generale ed
Inorganica, Chimica Analitica, Chimica Fisica, Universita` di Parma, Centro di Studio per la
Strutturistica Diffrattometrica del CNR, Parco Area delle Scienze 17A, I-43100 Parma, Italy, and
Department of Chemistry, University of Basel, St. Johanns-Ring 19, H-4056 Basel, Switzerland
ReceiVed January 24, 2000
A series of new Ru(II) complexes containing two chelating P,N ligands of the type (2-oxazolin-2-ylmethyl)-
diphenylphosphine (PCH2-oxazoline I), (2-oxazolin-4,4-dimethyl-2-ylmethyl)diphenylphosphine (PCH2-oxazoline-
Me2 II), and (2-oxazolin-4-(S)-isopropyl-ylmethyl)diphenylphosphine (PCH2-oxazoline-iPr III) have been prepared
1
and characterized by IR, H, 13C{1H}, and 31P{1H} NMR spectroscopy and by X-ray diffraction studies in the
cases of cis,cis,cis-[RuCl2(PCH2-oxazoline)2] (1) and cis,cis,trans-[RuCl2(PCH2-oxazoline-Me2)2] (3). Four different
types of octahedral coordination geometries are found for these complexes depending on the ligand. With I,
cis,cis,cis and trans,trans,trans geometries were characterized in complexes 1 and 2, respectively, whereas with
ligand II only the cis,cis,trans isomer 3 was formed. Reaction of the enantiomerically pure ligand III with [RuCl2-
(COD)]n afforded a mixture of isomers, and complex trans,cis,cis-[RuCl2(PCH2-oxazoline-iPr)2] 4 was fully
characterized. This complex was used for catalytic transfer hydrogenation of acetophenone in propan-2-ol and
led to 96% conversion and 72% ee (3 h, 82 °C, [ketone] ) 0.1 M, Ru:ketone:base ) 1:200:5). For comparison
the crude mixture of complexes gave a higher turnover frequency but a lower enantioselectivity than pure 4.
Introduction
combine the phosphorus donor atom as a soft Lewis base with
the harder nitrogen atom of the oxazoline ring.2 Coordination
through the oxygen donor is less likely, particularly with late
transition metals, because of the unfavorable energy of its
orbitals compared to those of the sp2-hybridized nitrogen atom.
We now extend such studies to the enantiomerically pure ligand
III (PCH2-oxazoline-iPr). Preliminary studies on square planar
Heterotopic ligands have been extensively used in coordina-
tion and organometallic chemistry owing to their structural
features and novel stoeichiometric or catalytic reactivity of their
metal complexes. The interest for such ligands stems from the
fact that the different (stereo)electronic properties of their donor
groups will give rise to selective metal-ligand interactions that
may control the reactivity at the metal site.1-3 In particular, we
and others have investigated the properties of complexes
containing P,O-type ligands, such as phosphinoketones, -esters,
-ethers, or -amides.1,2,4-7 More recently, we have been interested
in the coordination behavior of phosphinooxazoline ligands, such
as I (PCH2-oxazoline) and II (PCH2-oxazoline-Me2), which
* Author to whom correspondence should be addressed. E-mail: braunst@
chimie.u-strasbg.fr.
† Part of the Doctoral Thesis of F.N. Dedicated to Prof. H. Brunner on
the occasion of his 65th birthday, with our best wishes and congratulations.
‡ Universite´ Louis Pasteur, Strasbourg.
Pd(II) complexes of ligands I and II led to the synthesis of
active complexes for alternating ethylene/CO copolymerization.8
We also found it of interest to study their coordination properties
toward metals offering higher coordination numbers. Consider-
ing the rich chemistry of Ru complexes with octahedral
geometry and their proven successful applications in homoge-
neous catalysis (e.g., asymmetric hydrogenation),9-12 we ex-
§ Universita` di Parma.
| University of Basel.
(1) (a) Bader, A.; Lindner, E. Coord. Chem. ReV. 1991, 108, 27. (b) Slone,
C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem. 1999,
48, 233.
(2) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed., review article in press.
(3) Pfaltz, A. Synlett 1999, 835.
(4) Keim, W. New J. Chem. 1994, 18, 93.
(5) Lindner, E.; Pautz, S.; Haustein, M. Coord. Chem. ReV. 1996, 155,
(8) Braunstein, P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig, S.;
Speiser, F. J. Chem. Soc., Dalton Trans. 2000, 1067.
(9) Spencer, A. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford, 1987;
Vol. 6, p 229.
145.
(6) Braunstein, P.; Chauvin, Y.; Na¨hring, J.; DeCian, A.; Fischer, J.;
Tiripicchio, A.; Ugozzoli, F. Organometallics 1996, 15, 5551.
(7) Andrieu, J.; Braunstein, P.; Tiripicchio, A.; Ugozzoli, F. Inorg. Chem.
1996, 35, 5975.
(10) Noyori, R. Acta Chem. Scand. 1996, 50, 380.
10.1021/ic0000754 CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/08/2000

Ru(II) Complexes Containing Chelating P,N-Type Ligands
Inorganic Chemistry, Vol. 39, No. 20, 2000 4469
Scheme 1
amined the coordination behavior of these phosphinooxazoline
ligands toward Ru. In this paper, we report the synthesis of Ru
complexes of general formula [RuCl2(phosphinooxazoline)2],
of which the five possible coordination geometries are shown
in Scheme 1.
Pentacoordinated Ru(II) complexes of the type [RuCl2(PPh3)-
(phosphinooxazoline)], which contain a six-membered chelating
phosphinooxazoline ligand, either (phosphinoaryl)oxazoline IV
or (phosphinoferrocenyl)oxazoline V, have very recently been
used successfully in catalytic asymmetric transfer hydrogenation
of ketones in propan-2-ol.13-15
Figure 1. ORTEP view of the structure of the complex 1 together
with the atomic numbering scheme. The ellipsoids for the atoms are
drawn at the 30% probability level.
(PPh3)3] in CH2Cl2 led to a complex of composition [RuCl2-
(PCH2-oxazoline)2], as shown by elemental analysis (eq 1).
Here we also report our preliminary results on the catalytic
asymmetric transfer hydrogenation of acetophenone in propan-
2-ol by a Ru complex bearing the enantiomerically pure ligand
III.
Results
Synthesis and Characterization of the Chiral Ligand III.
The synthesis of (2-oxazolin-4-(S)-isopropyl-ylmethyl)diphen-
ylphosphine III, abreviated PCH2-oxazoline-iPr in the following,
was performed according to a procedure described by Helmchen
et al.16 The 31P{1H} NMR spectrum in CDCl3 exhibits a singlet
The 31P{1H} NMR spectrum of this compound exhibits an
AB spin system with a 2JPP coupling of 32.5 Hz. Thus it appears
that the only possible geometry for 1 is of type A since all the
other structures have a C2 axis of symmetry or a mirror plane
which should give rise to a singlet in the 31P{1H} NMR
1
at δ -17.2. The H NMR spectrum shows two multiplets at δ
1
spectrum. The H NMR spectrum of 1 is in accordance with
3.80 (2 H) and 4.10 (1 H) characteristic for the three oxazoline
protons. The diastereotopic methyl protons of the isopropyl
group appear as two doublets at δ 0.80 and 0.85, coupled to
the isopropyl proton CH(CH3)2 (3JHH ) 8.1 Hz). The PCH2
protons appear only as an AB spin system (2JPH ∼ 0 Hz) at δ
this lack of any symmetry element in the molecule since all
protons are chemically and magnetically different and thus
appear as individual resonances integrating for one proton. The
IR spectrum (KBr pellet) shows two bands at 1647 and 1636
cm-1 assigned to CdN vibrations of two coordinated oxazolines
with different trans donor atoms (ν(CdN) ) 1660 cm-1 for
the uncoordinated ligand). The cis,cis,cis geometry of the
molecule was confirmed by a single-crystal X-ray diffraction
study. The crystals contain two crystallographically independent,
but almost identical, molecules (A and B). A view of the
structure of one of them (A) is shown in the Figure 1 together
with the atomic numbering system; selected bond distances and
angles in them are given in Table 1. The two Ru-N bond
distances in the two octahedral complexes differ slightly; the
longer, 2.113(6) Å [2.137(6) Å, the values in brackets refer to
molecule B], involves the N(2) atom trans to phosphorus, the
2
3.05 and 3.10 with JHH ) 13.5 Hz.
Synthesis of the Ruthenium Complexes. cis,cis,cis-[RuCl2-
(P,N)2] (1). Mixing 2 equiv of ligand I with 1 equiv of [RuCl2-
(11) Cotton, S. A. Chemistry of Precious Metals; Chapman & Hall:
London, 1997.
(12) Schro¨der, M.; Stephenson, T. A. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon: Oxford, 1987; Vol. 4, p 277.
(13) Nishibayashi, Y.; Takei, I.; Uemura, S.; Hidai, M. Organometallics
1999, 18, 2291.
(14) Sammakia, T.; Stangeland, E. L. J. Org. Chem. 1997, 62, 6104.
(15) Langer, T.; Helmchen, G. Tetrahedron Lett. 1996, 37, 1381.
(16) Sprinz, J.; Helmchen, G. Tetrahedron Lett. 1993, 34, 1769.

4470 Inorganic Chemistry, Vol. 39, No. 20, 2000
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1
Braunstein et al.
isomer, compound 1, is soluble in EtOH while the minor one,
2, precipitates in EtOH and was extracted with CH2Cl2 from
unreacted [RuCl2(COD)]n (eq 2, for clarity the front PCH2-
oxazoline ligand is drawn in bold). The elemental analysis of 2
molecule A
molecule B
Bond Distances
2.080(6) Ru(1)-N(1)
Ru(1)-N(1)
2.067(5)
2.137(6)
2.260(2)
2.283(2)
2.451(2)
2.472(2)
1.844(7)
1.871(7)
1.341(8)
1.492(10)
1.359(8)
1.501(10)
1.302(8)
1.469(9)
1.288(9)
1.469(9)
1.505(10)
1.490(10)
Ru(1)-N(2)
Ru(1)-P(2)
Ru(1)-P(1)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
P(1)-C(4)
2.113(6)
2.249(2)
2.292(2)
2.452(2)
2.478(2)
1.873(7)
1.899(8)
1.347(9)
1.485(9)
1.340(9)
Ru(1)-N(2)
Ru(1)-P(2)
Ru(1)-P(1)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
P(1)-C(4)
P(2)-C(20)
O(2)-C(19)
O(2)-C(18)
O(1)-C(3)
P(2)-C(20)
O(1)-C(3)
O(1)-C(2)
O(2)-C(19)
O(2)-C(18)
N(1)-C(3)
N(1)-C(1)
N(2)-C(19)
N(2)-C(17)
C(1)-C(2)
C(3)-C(4)
1.455(10) O(1)-C(2)
1.300(9)
1.471(9)
1.239(9)
1.456(9)
1.532(10) C(1)-C(2)
1.462(11) C(3)-C(4)
N(1)-C(3)
N(1)-C(1)
N(2)-C(19)
N(2)-C(17)
is in agreement with the formulation [RuCl2(PCH2-oxazoline)2],
and the mass spectrum contains an intense peak for the fragment
[RuCl(PCH2-oxazoline)2]+. While there are two P,N ligands in
the molecule, the 31P{1H} NMR spectrum of 2 in CDCl3 exhibits
Bond Angles
N(1)-Ru(1)-N(2) 92.3(2)
N(1)-Ru(1)-Cl(1) 173.07(16)
N(1)-Ru(1)-P(2)
N(2)-Ru(1)-P(2)
N(1)-Ru(1)-P(1)
N(2)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
98.36(18) N(2)-Ru(1)-Cl(1) 83.42(17)
81.11(18) P(2)-Ru(1)-Cl(1) 86.35(9)
78.75(17) P(1)-Ru(1)-Cl(1) 105.23(8)
170.46(17) N(1)-Ru(1)-Cl(2) 86.50(18)
103.16(9) N(2)-Ru(1)-Cl(2) 89.19(18)
1
a singlet at δ 41.3. The H NMR spectrum exhibits only three
resonances for the six methylenic protons. There is therefore a
mirror plane in the molecule which creates three pairs of
enantiotopic protons. The only two possible structures for 3 are
of types D and E, and to distinguish between them, we
P(2)-Ru(1)-Cl(2) 169.27(8) N(1)-Ru(1)-Cl(1) 171.90(16)
P(1)-Ru(1)-Cl(2) 87.13(9)
Cl(1)-Ru(1)-Cl(2) 88.02(9)
N(2)-Ru(1)-Cl(1) 84.23(16)
P(2)-Ru(1)-Cl(1) 90.34(9)
P(1)-Ru(1)-Cl(1) 104.95(7)
N(1)-Ru(1)-Cl(2) 86.16(18)
N(2)-Ru(1)-Cl(2) 89.39(17)
P(2)-Ru(1)-Cl(2) 170.23(7)
P(1)-Ru(1)-Cl(2) 86.07(8)
Cl(1)-Ru(1)-Cl(2) 87.75(9)
1
performed a 500 MHz H ROESY NMR experiment in CD2-
C(4)-P(1)-Ru(1)
99.7(2)
C(3)-N(1)-Ru(1) 119.6(5)
Cl2. There are two key cross peaks: the first one is between
the oxazoline NCH2 protons at δ 3.90 and aryl protons, and the
second is between the OCH2 protons and aryl protons. This is
not consistent with a cis arrangement of the P,N chelates, and
only structure E can account for the existence of these cross
peaks. Complex 2 should therefore be formulated as trans,trans,-
trans-[RuCl2(PCH2-oxazoline)2]. Furthermore, the 13C{1H} and
1H NMR spectra of 2 exhibit a broad virtual triplet for the PCH2
carbon and protons, respectively, and the ipso carbon atoms of
C(19)-N(2)-Ru(1) 122.1(5)
N(1)-C(3)-C(4)
O(1)-C(3)-C(4)
C(3)-C(4)-P(1)
123.2(7)
120.4(7)
104.6(5)
N(2)-C(19)-C(20) 121.8(7)
O(2)-C(19)-C(20) 118.4(7)
N(1)-Ru(1)-N(2) 90.4(2)
N(1)-Ru(1)-P(2)
N(2)-Ru(1)-P(2)
N(1)-Ru(1)-P(1)
N(2)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
C(4)-P(1)-Ru(1)
100.6(2)
C(3)-N(1)-Ru(1) 120.4(5)
C(19)-N(2)-Ru(1) 119.7(5)
94.76(18) N(1)-C(3)-C(4) 122.2(7)
80.88(17) O(1)-C(3)-C(4)
79.97(16) C(3)-C(4)-P(1)
120.0(6)
105.2(5)
the four P-phenyl groups give rise to a well-resolved virtual
169.57(17) N(2)-C(19)-C(20) 122.9(7)
103.67(9) O(2)-C(19)-C(20) 119.4(7)
1+3
triplet (|
J
| ) 37.4 Hz).20-24 This is consistent with the
PC
pattern of an AXX′ (A ) C; X ) X′ ) P) spin system where
the JXX′ coupling constant is large. These data confirm that the
phosphorus atoms occupy mutually trans positions.
shorter 2.080(6) Å [2.067(5) Å] the N(1) atom trans to chlorine.
The longer Ru-P bond distance, 2.292(2) Å [2.283(2) Å], is
trans to nitrogen, and the shorter, 2.249(2) Å [2.2602) Å], is
trans to chlorine. The Ru(1)-Cl(2) bond distance, 2.472(2) Å
[2.472(2) Å], with Cl(2) trans to phosphorus is slightly longer
than the Ru-Cl(1) distance, 2.452(2) Å [2.451(2) Å], with Cl-
(1) trans to nitrogen. This is consistent with the larger trans
influence of phosphorus compared to nitrogen.17,18 The three
angles involving the coordinated atoms trans to one another,
ranging from 169.27(8)° to 173.07(16)° [169.57(17)° to 171.90-
(16)°], indicate slight distortions from ideal octahedral geometry.
The P,N bite angles of 78.75(17)° and 81.11(18)° [79.97(16)°
and 80.88(17)°] are in accordance with other five-membered
phosphorus, nitrogen chelates.19 The double-bond character of
N(1)-C(3) and N(2)-C(19) bonds is reflected in their lengths
1.300(9) and 1.239(9) Å [1.302(8) and 1.288(9) Å].
cis,cis,trans-[RuCl2(PCH2-oxazoline-Me2)2] (3). In order to
study the influence of the substituents R to the nitrogen atom
of the oxazoline ring on the coordination properties of such
ligands, we extended the procedure described for 2 to the ligand
PCH2-oxazoline-Me2, and complex 3 was isolated in 55% yield
after refluxing the reaction mixture for 3 h.
While with the PCH2-oxazoline ligand two complexes were
detected and isolated, the same procedure using PCH2-oxazoline-
Me2 led to the formation of only complex 3, of which the
elemental analysis data indicate a composition [RuCl2(PCH2-
oxazoline-Me2)2]. Its 31P{1H} NMR spectrum in CDCl3 exhibits
a singlet at δ 40.9, indicative of a mirror plane or a C2 axis for
1
the molecule in solution. The H NMR spectrum exhibits two
singlets for the NC(CH3)2 protons and an AB spin system for
trans,trans,trans-[RuCl2(PCH2-oxazoline)2] (2). The reaction
of 2 equiv of ligand I with 1 equiv of [RuCl2(COD)]n in
refluxing EtOH afforded two isomeric products. The major
(20) Verstuyft, A. W.; Redfield, D. A.; Cary, L. W.; Nelson, J. H. Inorg.
Chem. 1977, 16, 2776.
(21) Krassowski, D. W.; Nelson, J. H.; Brower, K. R.; Hauenstein, D.;
Jacobson, R. A. Inorg. Chem. 1988, 27, 4294.
(17) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335.
(18) Hartley, F. R. Chem. Soc. ReV. 1973, 2, 163.
(19) Mudalige, D. C.; Rettig, S. J.; James, B. R.; Cullen, W. R. J. Chem.
Soc., Chem. Commun. 1993, 830.
(22) Redfield, D. A.; Nelson, J. H. Inorg. Chem. 1973, 12, 15.
(23) Redfield, D. A.; Cary, L. W.; Nelson, J. H. Inorg. Chem. 1975, 14,
51.
(24) Costella, L.; Del Zotto, A.; Mezzetti, A.; Zangrando, E.; Rigo, P. J.
Chem. Soc., Dalton Trans. 1993, 3001.

Ru(II) Complexes Containing Chelating P,N-Type Ligands
Inorganic Chemistry, Vol. 39, No. 20, 2000 4471
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
3‚CH2Cl2
Bond Distances
Ru(1)-N(2)
Ru(1)-P(2)
Ru(1)-Cl(2)
P(1)-C(5)
O(1)-C(3)
O(2)-C(19)
N(1)-C(1)
N(2)-C(17)
C(1)-C(33)
C(3)-C(4)
C(17)-C(35)
C(19)-C(20)
2.133(6)
2.267(3)
2.466(3)
1.813(8)
1.347(9)
1.332(9)
1.496(9)
1.515(10)
1.517(11)
1.501(11)
1.567(11)
1.486(11)
Ru(1)-N(1)
Ru(1)-P(1)
Ru(1)-Cl(1)
P(2)-C(20)
O(1)-C(2)
O(2)-C(18)
N(2)-C(19)
C(1)-C(34)
C(1)-C(2)
C(17)-C(36)
C(17)-C(18)
2.122(6)
2.290(2)
2.466(2)
1.877(8)
1.438(9)
1.458(10)
1.288(10)
1.519(11)
1.544(11)
1.554(11)
1.553(11)
Bond Angles
N(2)-Ru(1)-N(1) 179.3(3)
N(2)-Ru(1)-P(2)
81.3(2)
N(1)-Ru(1)-P(2)
N(1)-Ru(1)-P(1)
N(2)-Ru(1)-Cl(2)
98.07(19) N(2)-Ru(1)-P(1)
82.09(18) P(2)-Ru(1)-P(1)
98.31(19)
93.78(9)
85.09(19)
89.43(9)
94.61(18)
Figure 2. ORTEP view of the structure of the complex 3 together
with the atomic numbering scheme. The ellipsoids for the atoms are
drawn at the 30% probability level.
95.5(2)
N(1)-Ru(1)-Cl(2)
P(2)-Ru(1)-Cl(2) 175.77(9) P(1)-Ru(1)-Cl(2)
N(2)-Ru(1)-Cl(1)
P(2)-Ru(1)-Cl(1)
85.02(19) N(1)-Ru(1)-Cl(1)
88.55(9) P(1)-Ru(1)-Cl(1) 176.19(9)
102.6(3)
C(3)-N(1)-Ru(1) 120.1(5)
N(1)-C(3)-C(4) 123.9(7)
107.7(5) N(2)-C(19)-C(20) 123.4(7)
Cl(2)-Ru(1)-Cl(1) 88.39(8) C(4)-P(1)-Ru(1)
C(20)-P(2)-Ru(1) 103.0(3)
C(19)-N(2)-Ru(1) 120.6(5)
C(3)-C(4)-P(1)
C(19)-C(20)-P(2) 106.7(6)
trans,cis,cis-[RuCl2(PCH2-oxazoline-iPr)2] (4). The reaction
of 2 equiv of enantiomerically pure ligand III with 1 equiv of
[RuCl2(COD)]n could lead to a maximum of eight stereoisomers
(two diastereomers for each of structures A-C plus D and E
in Scheme 1). The presence of at least four complexes was
detected by 31P{1H} NMR spectroscopy where they exhibit
singlets and AB spin systems in the range 40-54.5 ppm.
Complex 4 was isolated by column chromatography in 27%
yield (eq 4). The other products could not be isolated pure and
the methylenic OCH2 protons, indicating their diastereotopic
nature. There is therefore no mirror plane in the molecule, and
the geometry of 3 cannot be described by structures of type D
or E. At this stage, we are left with possibilities B or C. The
1
PCH2 protons exhibit in the H NMR spectrum an ABX spin
system of the “filled-in” type, consistent with a small cis JPP′
2
1
coupling.20,22 The JHH coupling was determined from the H-
{31P} NMR spectrum. Similarly, the PCH2 carbons show in the
13C{1H} NMR spectrum a multiplet which has the appearance
2
of a “filled-in” doublet. From this pattern, the JPP′ coupling
constant was extracted and found to be 31.3 Hz, which is in
the expected range for two phosphorus atoms in cis position.
The formulation of 3 as cis,cis,trans-[RuCl2(PCH2-oxazoline-
Me2)2] has been also confirmed by an X-ray diffraction study
on the crystals of its dichloromethane solvate. A view of the
structure of 3 is shown in Figure 2 together with the atomic
numbering system; selected bond distances and angles are given
in Table 2. As expected from the mutual trans arrangement of
the two nitrogen atoms, the Ru-N bond distances are similar,
2.122(6) and 2.133(6) Å. Although this molecule has no
crystallographically imposed symmetry in the solid state, it
shows an approximate C2 symmetry with the pseudo-2-fold axis
bisecting the Cl-Ru-Cl and P-Ru-P angles. The Ru-P bond
distances, 2.267(3) and 2.290(2) Å, are similar whereas the Ru-
Cl distances, 2.466(2) and 2.466(3) Å, involving chlorine atoms
trans to phosphorus are identical. The three angles involving
the coordinated atoms trans to one another, 175.77(9)°, 176.19-
(9)°, and 179.3(3)° indicate smaller distortions from ideal
octahedral geometry than in complex 1. The P,N bite angles
are similar, 82.09(18)° and 81.3(2)°, and in accordance with
those found in 1. The double-bond character of the N(1)-C(3)
and N(2)-C(19) bonds is reflected in their length, 1.283(10)
and 1.288(10) Å, respectively.
were retained on either alumina or silica gel. The 31P{1H} NMR
spectrum of 4 in CDCl3 exhibits a singlet at δ 54.5 indicative
of a mirror plane or a C2 axis in the molecule. All protons were
assigned using H homonuclear decoupling and H{31P} and
2D 1H NMR experiments. As in the case of the free ligand, the
methyl protons of the iPr group appear in the 1H NMR spectrum
as a pair of doublets at similar chemical shifts. The PCH2 protons
were located at δ 3.20 and 3.85. Proton NCHb
1
1
could be easily
distinguished by virtue of its complexity: it couples to Ha
(3JH H cis ) 10.3 Hz), Hc (3JH H trans ) 6.0 Hz), Hd (3JH H ) 2.6
Hz), and one proton of the PCH2 moiety (5JHH ) 1.5 Hz) (see
III).
a
b
c
b
d b

4472 Inorganic Chemistry, Vol. 39, No. 20, 2000
Braunstein et al.
Table 3. Enantioselective Transfer Hydrogenation of Acetophenone
temperature led to the formation of a mixture of at least five
in Propan-2-ol Catalyzed by Chiral Ru(II) Complexesa
complexes which gave rise in 31P{1H} NMR spectroscopy to
A
B
doublets of doublets with cis JP P coupling constants. Upon
addition of a second equivalent of P,N the orange solution turned
yellow and a major complex formed at the expense of the others.
When this reaction was repeated starting from a 2:1 ligand/Ru
ratio, it led selectively to the formation of complex 1 in 90%
isolated yield. The poor selectivity of the reaction when a 1:1
ligand/Ru ratio was used is surprising when compared to studies
with other P,N-type ligands. For example, complexes 5 and 6
were prepared following similar procedures and gave high yields
of a pentacoordinated complex with one bidentate P,N
ligand.13,15,19 Electronic and steric effects always play a crucial
turnover
d
catalyst time (min) yield (%)b ee (%)/(confign)c freq (h-1
)
4
15
60
180
15
63
90
96
97
98
74 (R)
73 (R)
72 (R)
68 (R)
61 (R)
504
180
64
776
196
in situe
60
a Reactions were carried out in refluxing propan-2-ol using a 0.1 M
substrate concentration, a 0.1 M solution of i-PrONa as a base, and a
1:200:5 Ru/ketone/base ratio. b Chemical yields determined by GC
analysis on the crude reaction mixture at the reported time. c Determined
by GC analysis (Lipodex A 25 m × 0.25 mm), absolute configurations
were determined by comparing optical rotations of isolated 1-phenyl-
ethanol with literature data. d Given as a time-average. e See text for
details.
This 5JHH coupling was also observed in related systems with
phosphinooxazoline-type ligands.8,25 The OCH2 protons could
be distinguished on the basis of the different magnitudes of their
vicinal scalar couplings to Hb. In planar five-membered rings
cis-vicinal couplings are greater than trans-vicinal couplings.26
The 13C{1H} NMR spectrum of 4 is very helpful in the
determination of the geometry of the molecule: the PCH2
carbons exhibit an AXX′ spin system “filled-in” doublet at δ
role in coordination chemistry, and the latter govern the behavior
of diphosphine ligands such as Ph2P(CH2)nPPh2 toward [RuCl2-
(PPh3)3].28 This could account for the difference in reactivity
between the six-membered-ring (phosphinoferrocenyl)oxazoline
ligand in 5 and ligand I. Nevertheless the phosphinoamine ligand
in 6 has a P-Ru-N bite angle (81.88(8)°) almost identical to
that observed in the X-ray crystal structure of 1 (80.88(17)°
and 79.97(16)° molecule B). It is likely that the electronic
contribution of the tertiary phosphine is important to stabilize
the 16-electron pentacoordinated complex 6 and that P(p-tolyl)3
should be preferred to PPh3. Using [RuCl2(COD)]n as a metal
precursor and a 1:1 P,N/Ru ratio led to the formation of
complexes 1 and 2 which both have the chemical composition
[RuCl2(PCH2-oxazoline)2]. These experiments suggested that
there is a thermodynamic preference for the formation of bis-
(chelate) compounds of the type [RuCl2(PCH2-oxazoline)2]. As
expected, an increased yield was observed for the reaction
between P,N and [RuCl2(COD)]n when a 2:1 ligand/Ru ratio
was used. In complex 2 the trans arrangement of the phosphorus
atoms is surprising since two donor atoms of high trans
influence usually tend to occupy cis positions17 as observed in
the stable complexes cis-[Pd(PCH2-oxazoline)2](BF4)2.30 and
trans,cis,cis-[RuCl2(P,O)2] (P,O ) Ph2PCH2C(O)Ph).31 The low
(ideally zero) dipolar moment of trans,trans,trans-[RuCl2(PCH2-
oxazoline)2] most likely explains the precipitation of the product
in a polar solvent such as EtOH. This represents an obvious
driving force for its formation. In a recent study, Otero et al.
have succeeded in isolating complexes of the formula [RuCl2-
(COD)(N,N)] (N,N ) bis(pyrazol-1-yl)methane or bis(5-trimeth-
ylsilylpyrazol-1-yl)methane) upon reaction of [RuCl2(COD)]n
with N,N in a 1:1 molar ratio.32 Interestingly, the subsequent
addition of a second equivalent of ligand N,N led to trans-
[RuCl2(N,N)2] only in the case of bis(5-trimethylsilylpyrazol-
1-yl)methane. No conclusive explanation was provided for this
contrasting behavior. Obviously, subtle effects are at work, and,
2
33.5 of which the analysis allows the determination of JPP′
)
38.9 Hz. This coupling constant is in the range found for two
phosphorus atoms in cis position. Therefore among the possible
structures of 4, types C and E can be ruled out. To distinguish
between B and D we recorded the 600 MHz 1H NOESY
spectrum in CD2Cl2. There are no cross peaks, neither between
the NCH protons at 4.35 ppm and aryl protons nor between the
OCH2 protons at 4.45 and 4.55 ppm and aryl protons. Therefore
complex 4 belongs to type D and is formulated as trans,cis,cis.
Furthermore, this assignment is in agreement with the 31P{1H}
NMR chemical shift of 54.5 ppm, downfield with respect to
the expected chemical shift for a phosphorus trans to chloride,
as would be the case for type B complex and as found in 3 (δ
40.9).17,27,28 By comparison with the 31P{1H} NMR data
collected in this study we conclude that the reaction mixture
contains, among other products, the two possible diastereomeric
structures of the type A observed by 31P{1H} NMR when we
used the chiral PCH2-oxazoline-iPr ligand. Another, chiral at
phosphorus P,N ligand has recently been found to lead to a
similar structure for its Ru(II) complex.29
Catalytic Transfer Hydrogenation of Acetophenone. As
part of our interest in the reactivity of Ru complexes with
multidentate heterotopic ligands that contain oxazoline unit(s)
and a phosphorus donor atom,25 we undertook a preliminary
study on the asymmetric transfer hydrogenation of acetophenone
in propan-2-ol catalyzed by 4 (see Discussion and Table 3 for
results and details).
Discussion
Synthesis of the Ru Complexes. Reaction of 1 equiv of I
with 1 equiv of [RuCl2(PPh3)3] in CH2Cl2 or toluene at room
(25) (a) Braunstein, P.; Fryzuk, M. D.; Naud, F.; Rettig, S. J. J. Chem.
Soc., Dalton Trans. 1999, 589. (b) Braunstein, P.; Naud, F.; Pfalz,
A.; Rettig, S. J. Organometallics 2000, 19, 2676.
(26) Abraham, R. J.; Fisher, J.; Loftus, P. Introduction to NMR Spectros-
copy; Wiley: New York, 1988.
(27) Barbaro, P.; Bianchini, C.; Togni, A. Organometallics 1997, 16, 3004.
(28) Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg.
Chem. 1984, 23, 726.
(30) Braunstein, P.; Naud, F.; Rettig, S. J. New J. Chem., in press.
(31) Braunstein, P.; Chauvin, Y.; Na¨hring, J.; Dusausoy, Y.; Bayeul, D.;
Tiripicchio, A.; Ugozzoli, F. J. Chem. Soc., Dalton Trans. 1995, 851.
(32) Fajardo, M.; de la Hoz, A.; Die´z-Barra, E.; Jalo´n, F. A.; Otero, A.;
Rodriguez, A.; Tejeda, J.; Belletti, D.; Lanfranchi, M.; Pellinghelli,
M. A. J. Chem. Soc., Dalton Trans. 1993, 1935.
(29) Yang, H.; Lugan, N.; Mathieu, R. C. R. Acad. Sci., Ser. IIc 1999,
251.

Ru(II) Complexes Containing Chelating P,N-Type Ligands
Inorganic Chemistry, Vol. 39, No. 20, 2000 4473
Table 4. Crystal Data and Structure Refinement for 1 and
3‚CH2Cl2
in order to evaluate the influence of the oxazoline substituents
on the geometry of the complexes, we investigated the ligands
PCH2-oxazoline-Me2 and PCH2-oxazoline-iPr. All experiments
were performed under similar conditions (1:2 Ru/ligand ratio,
refluxing EtOH, 3 h).
1
3‚CH2Cl2
formula
C32H32Cl2N2O2P2Ru C36H40Cl2N2O2P2Ru‚
CH2Cl2
The most selective reaction was obtained with PCH2-
oxazoline-Me2 where only one complex, cis,cis,trans-[RuCl2-
(PCH2-oxazoline-Me2)2], was detected. Despite their similar
mode of preparation, the differences between the compounds
obtained from I and II are surprising. They must be related to
the nature of the substituents on each oxazoline. If two
phosphinooxazoline ligands II were to coordinate in the
equatorial plane, each pair of methyls would point toward
another pair of methyls (as in structure D) or toward a pair of
phenyls (as in structure E) and thus create in both cases an
unfavorable steric clash. This is not the case with the smaller
corresponding protons of I. Note that with PCH2-oxazoline-
Me2 we failed to obtain a compound analogous to cis-[Pd(PCH2-
oxazoline)2](BF4)2. Among the three possible structures A-C
which avoid two coplanar PCH2-oxazoline-Me2 ligands, B is
the only one where the two nitrogen atoms are in trans position,
thus keeping further away the methyl substituents of the
oxazolines.
fw
710.51
293(2)
851.54
293(2)
0.71073
triclinic
P1h
15.757(5)
12.212(4)
11.390(3)
68.47(5)
73.75(6)
67.25(5)
1856(1)
2
1.524
0.833
R1 ) 0.0493,
wR2 ) 0.1392
R1 ) 0.1274,
wR2 ) 0.1639
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.71073
monoclinic
P21/c
18.427(4)
17.487(3)
22.422(5)
R (deg)
â (deg)
γ (deg)
vol (Å3)
Z
113.44(6)
6629(2)
8
density (calcd) (Mg/m3) 1.424
abs coeff (cm-1
final R indices
[I > 2σ(I)]a
)
0.761
R1 ) 0.0673,
wR2 ) 0.1910
R1 ) 0.1599,
wR2 ) 0.2142
R indices (all data)
a R1 ) Σ|Fo - Fc|/|Σ(Fo). wR2 ) [Σ[w(Fo - Fc2)2]/Σ[w(Fo )2]]1/2
.
2
2
Somewhat disappointingly, the reaction with the chiral ligand
PCH2-oxazoline-iPr was the least selective. From the reaction
mixture, only compound trans,cis,cis-[RuCl2(PCH2-oxazoline-
iPr)2] 4 could be isolated pure. Its structure is different from
those obtained with the ligands PCH2-oxazoline and PCH2-
oxazoline-Me2 and exhibits two phosphinooxazoline ligands
coordinated to the metal in the equatorial plane, with the two
phosphorus donor atoms in a cis arrangement. The bulky i-Pr
substituents are not causing any steric clash when the two
oxazoline rings are in close proximity since they point in
opposite directions. The structure of 4 is to be compared with
a recently reported X-ray crystallographic structure of a square-
planar complex [Ni(P,N)2](O3SCF3)2 (P,N ) (S)-iBu-phosphi-
noaryloxazoline) where the stereogenic carbons of the two
oxazolines ring are in a pseudoaxial position relative to the
P-Ni-N plane.33 This study also showed that the cis arrange-
ment of the phosphorus atoms is preferred to the trans.
Catalysis. The compound trans,cis,cis-[RuCl2(PCH2-oxazo-
line-iPr)2] 4 exhibits a C2 axis of symmetry and a structure
related to those of 7 and 8. Noyori et al. have shown that, despite
their apparent similarity, complexes 7 and 8 exhibit very
different reactivity for the catalytic transfer hydrogenation of
acetophenone in propan-2-ol (5, 7% yield, 5% ee at 82 °C for
4 h; 8, 93% yield, 97% ee at 45 °C for 7 h), a reaction of current
interest.34-39
which is thought to be responsible for the stabilization of a six-
membered transition state involving the Ru-H and the CdO
fragment of the ketonic substrate.35,40
Although complex 4 does not have any NH function, we
obtained under standard reaction conditions a conversion up to
96% with 72% ee for this reaction (see Table 4). Reducing the
amount of base from 24 to 5 equiv per Ru did not have any
significant effect on either conversion or enantioselectivity.
Whereas, in asymmetric transfer hydrogenation, long reaction
times usually deteriorate the enantiomeric purity of the product,
we found in our case that the enantioselectivity remains almost
constant during the course of the reaction (up to 3 h). Since
different isomeric complexes were formed with ligand III that
could not be isolated pure, we decided to explore their catalytic
potential in situ in order to examine the importance of different
geometries on the catalysis. In a first experiment, the ruthenium
complexes were prepared according to eq 4 but using propan-
2-ol as a solvent for both their synthesis and catalysis. In a
second set of experiments, the complex mixture of ruthenium
complexes prepared according to eq 4 (in refluxing EtOH, 3 h)
was taken to dryness and redissolved in propan-2-ol. In both
cases, the catalytic results were identical: the conversion was
97% with 68% ee after 15 min. It is interesting that the crude
mixture gives higher turnover frequency (TOF) than 4 alone
with, however, a lower enantioselectivity. This indicates that
This difference between the diimine and the diamine complexes
is due to the presence of the NH moiety in the diamine ligand,
(33) Bray, K. L.; Butts, C. P.; Lloyd-Jones, G. C.; Murray, M. J. Chem.
Soc., Dalton Trans. 1998, 1421.
(34) Gao, J.-X.; Ikariya, T.; Noyori, R. Organometallics 1996, 15, 1087.
(35) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97.
(36) Zassinovich, G.; Mestroni, G.; Gladiali, S. Chem. ReV. 1992, 92, 1051.
(37) Palmer, M. J.; Willis, M. Tetrahedron: Asymmetry 1999, 10, 2045.
(38) Aranyos, A.; Csjernyik, G.; Szabo´, K. J.; Ba¨ckvall, J.-E. Chem.
Commun. 1999, 351.
(40) (a) Jiang, Y.; Jiang, Q.; Zhang, X. J. Am. Chem. Soc. 1998, 120, 3817.
(b) Alonso, D. A.; Brandt, P.; Nordin, S. J. M.; Andersson, P. G. J.
Am. Chem. Soc. 1999, 121, 9580. (c) Yamakawa, M.; Ito, H.; Noyori,
R. J. Am. Chem. Soc. 2000, 122, 1466. (d) Petra, D. G. I.; Reek, J. N.
H.; Handgraaf, J.-W.; Meijer, E. J.; Dierkes, P.; Kamer, P. C. J.;
Brussee, J.; Schoemaker, H. E.; van Leeuwen, P. W. N. M. Chem.
Eur. J. 2000, 6, 2818.
(39) Ohkuma, T.; Doucet, H.; Pham, T.; Mikami, K.; Korenaga, T.; Terada,
M.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 1086.

4474 Inorganic Chemistry, Vol. 39, No. 20, 2000
Braunstein et al.
cis,cis,cis-[RuCl2(PCH2-oxazoline)2] (1). In a 100 mL Schlenk flask
were reacted ligand PCH2-oxazoline (0.200 g, 0.745 mmol) and [RuCl2-
(PPh3)3] (0.340 g, 0.355 mmol) in CH2Cl2 (20 mL) The deep reddish
solution quickly turned yellow and was stirred for 15 min. The solvent
was removed under reduced pressure to afford a yellow solid, which
was washed twice with a 1:3 mixture of toluene/hexane (2 × 15 mL)
and Et2O (2 × 10 mL). Compound 1 was obtained as a yellow powder
the mixture contains other catalyst precursors than 4 and that
the trans,cis,cis ligand arrangement may not be the optimum
for catalysis. One can expect that a Ru-Cl bond trans to a P
atom would be more reactive than a Ru-Cl bond trans to a
chloride. It is difficult to comment on the slight decrease of
enantioselectivity when starting from a mixture of two or more
catalyst precursors. Nevertheless, the decrease of the enantio-
meric purity with time when using the in situ catalyst mixture
suggests that the reverse reaction becomes more significant, and
this represents a clear disadvantage over the use of pure 4. It is
interesting to compare the activity of 4 with literature values
for catalysts bearing only one chelating six-membered phos-
phinooxazoline, such as [RuCl2(PPh3)(phosphinooxazoline)].
Comparisons are not straightforward since reactions with the
latter catalysts have not always been carried out under compa-
rable conditions.13,15,41 In transfer hydrogenation of ketones in
propan-2-ol, a higher concentration of ketone gives a lower yield
of alcohol,42,43 while an increase of the amount of base can
accelerate the reaction rate but may also deteriorate the enan-
tioselectivity.40 The best results were obtained with the complex
[RuCl2(PPh3){(phosphinoaryl)oxazoline-iPr}] (80% yield, 78%
ee, 3 min, 82 °C, [ketone] ) 0.1 M, Ru:ketone:base ) 1:1000:
25),15 [RuCl2(PPh3){(phosphinoferrocenyl)oxazoline-iPr}] (94%
yield, >99% ee, 2 h, room temperature, [ketone] ) 0.02 M,
Ru:ketone:base ) 1:200:413 and 77% yield, 48% ee, 5 min, 82
°C, [ketone] ) 1 M, Ru:ketone:base ) 1:1000:2541). Our
preliminary results on complex 4 are encouraging and deserve
further investigations on the optimization of the catalytic
conditions. Further studies on the structure-reactivity relation-
ship with metal complexes containing chiral ligands such as
III are needed.
1
(0.475 g, yield 90%). IR (KBr): ν (cm-1) 1647, 1636 vs (CdN). H
NMR (CDCl3, 300.16 MHz): δ 2.15 (m, 1 H), 3.05 (m, 1 H), 3.45,
3.45 (overlapping m, 2 H, PCH2), 3.55 (overlapping m, 3 H), 4.00 (m,
1 H), 4.25 (m, 1 H), 4.45 (m, 1 H), 4.70 (m, 1 H), 4.80 (m, 1 H),
6.90-7.50 (m, 16 H), 8.20 (m, 4 H). 31P{1H} NMR (CDCl3, 121.5
2
MHz): δ AB spin system δΑ 52.4 (d, JPP ) 30.5 Hz), δΒ 50.2 (δ,
2JPP ) 30.5 Hz). Anal. Calcd for C32H32Cl2N2O2P2Ru: C, 54.09; H,
4.54. Found: C, 54.45; H, 4.84.
trans, trans, trans-[RuCl2(PCH2-oxazoline)2] (2). In a 100 mL
Schlenk flask fitted with a reflux condenser were reacted the ligand
PCH2-oxazoline (0.210 g, 0.780 mmol) and [RuCl2(COD)]n (0.105 g,
0.390 mmol) in EtOH (20 mL). The brown suspension was heated under
reflux for 3 h and then cooled to room temperature. The yellow solution
containing pure cis,cis,cis-[RuCl2(PCH2-oxazoline)2] 1 was separated
from the brown suspension by means of a cannula fitted with a glass-
fiber filter paper. The brown residue was treated with CH2Cl2 (20 mL),
which extracted a yellow-orange solution, which was separated from
the remaining solid with a cannula. This solution was concentrated to
ca. 2 mL, and addition of pentane afforded a precipitate, which was
further washed with pentane (2 × 10 mL). The product was obtained
as a yellow-orange powder (0.055 g, yield 20%). IR (KBr): ν (cm-1
)
1631 vs (CdN). far-IR (polyethylene): ν (cm-1) 391 s, 357 m, 271 m,
213 w. 1H NMR (CDCl3, 300.16 MHz): δ 3.70 (m with appearance of
3
t, 4 H, PCH2), 3.78 (t, 4 H, JHH ) 9.5 Hz, NCH2), 4.45 (t, 4 H,
3JHH ) 9.5 Hz, OCH2), 7.30-7.40 (m, 12 H, aryl), 7.70-7.80 (m, 8
H, aryl). 13C{1H} (CDCl3, 125.7 MHz): δ 30.3 (m with appearance of
t, PCH2), 57.5 (s, NCH2), 69.6 (s, OCH2), 128.0 (m, o-aryl), 129.7 (s,
p-aryl), 133.0 (virtual t, 1+3JPC ) 37.4 Hz, ipso-aryl), 133.5 (m, m-aryl),
172.2 (br s, CdN). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 41.3 (s).
Anal. Calcd for C32H32Cl2N2O2P2Ru: C, 54.09; H, 4.54; N, 3.94.
Found: C, 54.13; H, 4.44; N, 3.90.
Experimental Section
All reactions were performed under purified nitrogen. Solvents were
1
purified and dried under nitrogen by conventional methods. The H
cis,cis,trans-[RuCl2(PCH2-oxazoline-Me2)2] (3). In a 100 mL
Schlenk flask fitted with a reflux condenser were reacted ligand II
(0.855 g, 2.88 mmol) and [RuCl2(COD)]n (0.405 g, 1.44 mmol) in EtOH
(40 mL). The brown suspension was heated under reflux for 3 h and
then cooled to room temperature. The yellow solution was separated
from the brown suspension (unreacted [RuCl2(COD)]n) by means of a
cannula fitted with a glass-fiber filter paper. The suspension was further
washed with 15 mL of EtOH, the filtrates were collected together, and
the solvent was evaporated under reduced pressure to approximately 5
mL. Addition of pentane (20 mL) afforded a yellow precipitate. This
procedure was repeated to collect a second crop, and the solid fractions
were washed with Et2O (2 × 15 mL) to remove II and dried in vacuo.
The product was isolated as a yellow powder (0.615 g, 55% yield). IR
(KBr): ν (cm-1) 1631 vs (CdN). far-IR (polyethylene): ν (cm-1) 390
NMR spectra were recorded at 300.13 MHz, 31P{1H} NMR spectra at
81.0 or 121.5 MHz, 13C{1H} NMR spectra at 75.4 MHz on a FT Bruker
AC200 or AC300 instrument, IR spectra in the 4000-400 cm-1 range
on a Bruker IFS66 FT spectrometer, far-IR spectra in the 500-90 cm-1
range on a Bruker ATS 83 spectrometer. The ligands PCH2-oxazoline
and PCH2-oxazoline-Me2 were prepared following a method described
elsewhere.8
(2-Oxazolin-4-(S)-isopropyl-ylmethyl)diphenylphosphine (PCH2-
oxazoline-iPr, III). IR (CH2Cl2): ν(cm-1) 1663 (CdN). 1H NMR
(CDCl3, 200.13 MHz): δ 0.80 (d, 3 H, 3JHH ) 8.1 Hz, CH(CH3)(CH3)),
0.85 (d, 3 H, 3JHH ) 8.1 Hz, CH(CH3)(CH3)), 1.60 (sept, 1 H, 3JHH
)
8.1 Hz, CH(CH3)2), AB spin system (A ) B ) H) δΑ 3.05 (1 H,
2
2JHH ) 13.5 Hz, PCHH) and δΒ 3.10 (1 H, JHH ) 13.5 Hz, PCHH),
3.80 (overlapping m, 2 H, NCH and OCHH), 4.10 (m, 1 H, OCHH),
7.10-7.40 (m, 10 H, aryl). 13C{1H} (CDCl3, 75.5 MHz): δ 17.9 (s,
CH(CH3)(CH3)), 18.5 (s, CH(CH3)(CH3)), 32.4 (s, CH(CH3)2), 28.3 (d,
1JPC ) 18.5 Hz, PCH2), 70.2 (s, NCH), 72.1 (s, OCH2), 127.4 (d,
1
m, 366 w, 295 s, 267 w, 235 vs. H NMR (CD2Cl2, 500.13 MHz): δ
1.25 (s, 6 H, NC(CH3)(CH3)), 1.75 (s, 6 H, NC(CH3)(CH3)2), ABXX′
spin system (A ) B ) H; X ) X′ ) P) δA 3.15 (“filled-in d”, 2 H,
2JHH ) 18.1 Hz, 2+4JPH ) 11.1 Hz, PCHH), δB 3.25 (“filled-in d”, 2 H,
2JHH ) 18.1 Hz, 2+4JPH ) 8.5 Hz, PCHH), AB spin system δA 4.25 (d,
2 H, 2JHH ) 8.1 Hz, OCHH), δB 4.30 (d, 2 H,2JHH ) 8.1 Hz, OCHH),
6.90 (m, 4 H, aryl), 7.15-7.30 (m, 14 H, aryl H), 7.50 (m, 2 H, aryl
H). 13C{1H} (CDCl3, 75.4 MHz): δ 28.0 (s, NC(CH3)(CH3)), 28.5 (s,
2
m-aryl), 127.0-138.0 (m, aryl), 163.8 (d, JPC ) 7.3 Hz, CdN). 31P-
{1H} NMR (CDCl3, 121.5 MHz): δ -17.2.
Ru(II) Complexes. All the complexes are air-stable for a short period
of time but should be best kept under inert atmosphere. Yields of Ru
complexes are given based on the phosphinooxazoline ligand. The
compound [RuCl2(PPh3)3] and [RuCl2(COD)]n were prepared according
to literature procedures.44,45
2
1
NC(CH3)(CH3)2), 32.0 (“filled-in d”, JXX′ ) 31.3 Hz, JAX ) 27.8
cis
Hz, 3JAX ) 1.2 Hz, PCH2), 71.7 (s, NC(CH3)2), 83.5 (s, OCH2), 126.8-
133.5 (m, aryl H), 134.6 (“filled-in d”,
1+3
J
) 43.2 Hz, ipso-aryl),
PC
1+3
136.7 (“filled-in d”,
J
) 41.3 Hz, ipso-aryl), 171.0 (m, CdN).
PC
(41) Arikawa, Y.; Ueoka, M.; Matoba, K.; Nishibayashi, Y.; Hidai, M.;
Uemura, S. J. Organomet. Chem. 1999, 572, 163.
(42) de Graauw, C. F.; Peters, J. A.; van Bekkum, H.; Huskens, J. Synthesis
1994, 1007.
(43) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R. J. Am.
Chem. Soc. 1995, 117, 7562.
(44) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945.
(45) Albers, M. O.; Singleton, E.; Yates, J. E. Inorg. Synth. 1989, 26, 253.
31P{1H} NMR (CDCl3, 121.5 MHz): δ 40.9 (s). Anal. Calcd for C36H40-
Cl2N2O2P2Ru: C, 56.40; H, 5.26; N, 3.65. Found: C, 56.20; H, 5.27;
N, 3.45.
trans, cis, cis-[RuCl2(PCH2-oxazoline-iPr)2] (4). Following the
procedure described for 3, but starting from PCH2-oxazoline-iPr (0.257
g, 0.825 mmol) and [RuCl2(COD)]n (0.115 g, 0.412 mmol), the orange
solid obtained was purified by filtration over silica (10 cm × 1 cm,

Ru(II) Complexes Containing Chelating P,N-Type Ligands
Inorganic Chemistry, Vol. 39, No. 20, 2000 4475
THF). The first orange fraction was collected and the solvent removed
under reduced pressure. The solid was dried in vacuo and isolated as
an orange powder (0.090 g, 27% yield). IR (KBr): ν (cm-1) 1637 vs
(CdN). far-IR (polyethylene): ν (cm-1) 398 s, broad absorptions in
Siemens AED (1) and on a Philips PW 1100 (3‚CH2Cl2) single-crystal
diffractometer using graphite-monochromated Mo KR radiation and the
θ/2θ scan technique. Crystallographic and experimental details for both
structures are summarized in Table 4.
1
the range 340-280 w. H NMR (CDCl3, 600.22 MHz): δ 0.75 (d, 6
A correction for absorption was made for both complexes [maximum
and minimum values for the transmission coefficient were 1.000 and
0.692 (1), 1.000 and 0.875 (3).46,47 The structures were solved by
Patterson and Fourier methods and refined by full-matrix least-squares
3
3
H, JHH ) 6.6 Hz, CH(CH3)(CH3)), 0.90 (d, 6 H, JHH ) 6.6 Hz, CH-
3
3
d
b
(CH3)(CH3)), 2.85 (sept. of d, 2 H, JHH ) 6.6 Hz, JH H ) 2.6 Hz,
CHd(CH3)2), ABXX′ spin system (A ) B ) H, X ) X′ ) P) δA 3.20
(“filled-in d”, 2 H, 2JHH ) 17.0 Hz, 2+4JPH ) 11.2 Hz, PCHH), δB 3.85
2
procedures (based on Fo ) with anisotropic thermal parameters in the
2
2+4
5
(“filled-in d”, 2 H, JHH ) 17.0 Hz,
J
) 9.1 Hz, JHH ) 1.5 Hz,
3
b c
PH
last cycles of refinement for all the non-hydrogen atoms.
3
b
a
PCHH), 4.35 (m, 2 H, JH H
) 10.2 Hz, JH H
) 6.0 Hz,
2
c a
cis
trans
In both structures the hydrogen atoms were introduced into the
geometrically calculated positions and refined riding on the corre-
sponding parent atoms. In the final cycles of refinement a weighting
scheme w ) 1/[σ2Fo2 + (0.0916P)2] (1) and w ) 1/[σ2Fo2 + (0.0677P)2]
JH H ) 2.6 Hz, JHH ) 1.5 Hz, NCHb), 4.45 (dd, 2 H, JH H ) 8.8
3
5
b
d
3
3
c
b
a b
Hz, JH H
) 6.0 Hz, OCHcH), 4.55 (dd, 2H, JH H
) 10.2 Hz,
trans
cis
JH H ) 8.8 Hz, OCHH ), 7.00-7.55 (m, 20 H, aryl). 13C{1H} (CDCl3,
2
a
a
c
150.9 MHz): δ 14.6 (s, CH(CH3)(CH3)), 19.8 (s, CH(CH3)(CH3)), 28.5
2
(3•CH2Cl2) where P ) (Fo + 2Fc2)/3 was used.
(s, CH(CH3)2), 33.5 (“filled-in d”, 2JXX′cis ) 38.9 Hz, 1JAX ) 23.2 Hz,
3JAX ) 4.3 Hz, PCH2), 70.0 (s, NCH), 71.4 (s, OCH2), 127.39 and
All calculations were carried out on the DIGITAL AlphaStation 255
computers of the “Centro di Studio per la Strutturistica Diffrattometrica”
del CNR, Parma, using the SHELX-97 systems of crystallographic
computer programs.47
3+5
127.43 (two overlapping “filled-in d” with appearance of q,
J
)
PC
10 Hz determined by a 13C{31P,1H} experiment, m-aryl), 129.2 (s,
p-aryl), 129.4 (s, p-aryl), 133.3 (AXX′ spin system with appearance of
2+4
triplet,
J
) 9.0 Hz, o-aryl), 133.8 (AXX′ spin system with
PC
2+4
Acknowledgment. We are grateful to Prof. M. D. Fryzuk
(Vancouver) for stimulating discussions and hospitality toward
F.N. and to Dr. Graff (Strasbourg) for NMR experiments. The
Centre National de la Recherche Scientifique (Paris) and the
Max-Planck-Institut fu¨r Kohlenforschung (Mu¨lheim an der
Ruhr) are gratefully acknowledged for a visiting grant to F.N.
and the Ministe`re de l’Enseignement Supe´rieur et de la
Recherche (Paris) for a Ph.D. grant to F.N.
appearance of triplet,
J
) 10.0 Hz, o-aryl), 135.1 (“filled-in d”,
PC
2JXX′cis ) 38.9 Hz, JAX ) 41.7 Hz, JAX′ ) 5.6 Hz, ipso-aryl), 136.7
(“filled-in d”, 2JXX′cis ) 38.9 Hz, 1JAX ) 34.9 Hz, 3JAX′ ) 3.6 Hz, ipso-
aryl), 171.5 (AXX′ spin system with appearance of triplet, JPC ) 17.0
Hz, CdN). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 54.5. Anal. Calcd
for C38H44Cl2N2O2P2Ru: C, 57.43; H, 5.53; N, 3.53 Found: C, 57.22;
H, 5.52; N, 3.46.
1
3
Catalytic Transfer Hydrogenation. Typical procedure for catalytic
transfer hydrogenation of acetophenone: 4 (0.0079 g, 0.01 mmol) was
i
dissolved in 19.5 mL of PrOH in a 50 mL two-neck round-bottom
Supporting Information Available: X-ray crystallographic files
in CIF format of the structures of cis,cis,cis-[RuCl2(PCH2-oxazoline)2]
and cis,cis,trans-[RuCl2(PCH2-oxazoline-Me2)2]‚CH2Cl2. This material
is available free of charge via the Internet at http://pubs.acs.org.
flask fitted with a reflux condenser. Acetophenone (0.234 mL, 2.0
mmol) was added, and the yellow solution was brought to the desired
temperature. The solution was stirred for 10 min, and 0.5 mL (0.05
mmol) of a solution of iPrONa in iPrOH (0.1 M) was added. The volume
i
of PrOH was adjusted so that all catalytic runs were performed with
IC0000754
an initial concentration in acetophenone of 0.1 M. The addition of
iPrONa was considered as the starting time of the reaction. The extent
of conversion was determined by gas chromatography using a Lipodex
A 25 m × 0.25 mm column.
(46) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
Ugozzoli, F. Comput. Chem. 1987, 11, 109.
(47) Sheldrick, G. M. SHELX-97: Program for the solution and refinement
of crystal structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
X-ray Structure Determination of 1 and 3•CH2Cl2. The intensity
data of both complexes were collected at room temperature on a