Five-coordinate [RuCl(P-P *)2]+ complexes containing chiral diphosphines: Application in the asymmetric cyclopropanation and epoxidation of olefins

Article abstract of DOI:10.1021/om990657x

The six-coordinate complexes trans-[RuCl₂(P-P*)₂] (P-P* = (S,S)-1,2-bis(1-naphthylphenylphosphino(ethane (bnpe), 2a; (S,S)-2,3-bis(diphenylphosphino)butane (chiraphos), 2b) have been prepared and structurally characterized. The X-ray

Full text of DOI:10.1021/om990657x

Organometallics 1999, 18, 5691-5700
5691
F ive-Coor d in a te [Ru Cl(P -P *)2]+ Com p lexes Con ta in in g
Ch ir a l Dip h osp h in es: Ap p lica tion in th e Asym m etr ic
Cyclop r op a n a tion a n d Ep oxid a tion of Olefin s
Robert M. Stoop, Christian Bauer, Patrick Setz, Michael Wo¨rle,
Terrance Y. H. Wong, and Antonio Mezzetti*
Laboratorium fu¨r Anorganische Chemie, ETH-Zentrum, CH-8092 Zu¨rich, Switzerland
Received August 16, 1999
The six-coordinate complexes trans-[RuCl2(P-P*)2] (P-P* ) (S,S)-1,2-bis(1-naphthyl-
phenylphosphino)ethane (bnpe), 2a ; (S,S)-2,3-bis(diphenylphosphino)butane (chiraphos), 2b)
have been prepared and structurally characterized. The X-ray studies of 2a ,b show non-
C2-symmetric conformations of the substituents at the PPh2 groups in a highly crowded
octahedral environment. Complexes 2a ,b react with Tl[PF6] in CH2Cl2 to give the corre-
sponding monochloro, cationic derivatives [RuCl(P-P*)2]PF6 (P-P* ) bnpe, 3a ; chiraphos,
3b). The bnpe derivative 3a is five-coordinate both in the solid state (by X-ray investigation)
and in solution (by 31P NMR spectroscopy). The chiraphos analogue 3b apparently dimerizes
in solution, depending on the solvent (CDCl3 or CD2Cl2) and on the concentration. Complexes
3a ,b catalyze the decomposition of ethyl diazoacetate to give, in the presence of styrene, the
corresponding cyclopropanation products with enantioselectivity up to 35% ee and E/ Z ratios
of about 55:45. Complexes 3a ,b also catalyze the epoxidation of unfunctionalized olefins
with iodosyl benzene as the primary oxidant. High olefin conversions and fair selectivity for
the epoxide are observed, but both 3a and 3b give racemic epoxide.
In tr od u ction
than when substrate precoordination leads to dia-
stereomeric complexes.3a,b
In the reactions catalyzed by transition metal com-
plexes, coordinative unsaturation at the metal is gener-
ally considered as condition sine qua non for catalytic
activity. This is a particular issue with the iron group
metals, where six-coordination is the norm. However,
unsaturation can play different roles, depending on the
catalytic system. Thus, in homogeneous hydrogenation
the unsaturated metal center activates the dihydrogen
molecule, either homolytically or heterolytically, and
often also the olefin.1 In other catalytic reactions, such
as cyclopropanation2 and epoxidation,3 the role of the
metal is rather to stabilize a reactive fragment X (a
carbene or oxo ligand) in a coordinatively saturated
complex of the type [M(CR2)L5] or [M(O)L5]. The frag-
ment X () CHR or O) is generally believed to be
transferred to the uncoordinated olefin substrate.2,3 This
poses a problem in asymmetric catalysis, as the interac-
tions involved in enantioface discrimination are weaker
To improve the enantioselectivity, tetradentate ligands
have been used in epoxidation and cyclopropanation
reactions catalyzed by the iron group metals, in par-
ticular porphyrins,4 Schiff bases,5 oxazoline derivatives,6
or hybrid ligands containing imino and phosphino
functionalities.7 Thus, we have recently shown that
ruthenium(II) complexes containing the hybrid phos-
phino imino ligand (S,S)-bis(o-diphenylphosphinoben-
zylidene)diimminocyclohexane efficiently catalyze the
epoxidation of unfunctionalized olefins with hydrogen
peroxide as the primary oxidant.7a
Lately, chiral tridentate ligands have found successful
application in asymmetric cyclopropanation8 and epoxi-
(4) Recent papers: (a) Gross, Z.; Ini, S. Inorg. Chem. 1999, 38, 1446.
(b) Lai, T. S.; Kwong, H. L.; Zhang, R.; Che, C. M. J . Chem. Soc., Dalton
Trans. 1998, 3559. (c) Berkessel A.; Frauenkron, M. J . Chem. Soc.,
Perkin Trans. 1997, 2265. (d) Galardon, E.; Roue, S.; Le Maux, P.;
Simonneaux, G. Tetrahedron Lett. 1998, 36, 2333. (e) Berkessel, A.;
Frauenkron, M. Tetrahedron Lett. 1997, 38, 7175. (f) Lo, W. C.; Cheng,
K. F.; Che, C. M.; Mak, T. C. W. Chem. Commun. 1997, 1205.
(5) Recent papers: (a) Cheng, M. C.; Chan, M. C. W.; Peng, S. M.;
Cheung, K. K.; Che, C. M. J . Chem. Soc., Dalton Trans. 1997, 3479.
(b) Kureshi, R. I.; Khan, N. H.; Abdi, S. H. R.; Iyer, P. J . Mol. Catal.
A-Chem. 1997, 124, 91. (c) Bernardo, K.; Leppard, S.; Robert, A.;
Commenges, G.; Dahan, F.; Meunier, B. Inorg. Chem. 1996, 35, 387.
(6) See, for instance: (a) End, N.; Pfaltz, A. Chem. Commun. 1998,
589. (b) Mizushima, K.; Nakaura, M.; Park, S. B.; Nishiyama, H.;
Monjushiro, H.; Harada, K.; Haga, M. Inorg. Chim. Acta 1997, 261,
175.
(7) Recent papers: (a) Stoop, R. M.; Mezzetti, A. Green Chem. 1999,
39. (b) Song, J .-H.; Cho, D.-J .; J eon, S.-J .; Kim, Y.-H.; Kim, T.-J .; J eong,
J . H. Inorg. Chem. 1999, 38, 893.
(8) Recent papers: (a) Lee, H. M.; Bianchini, C.; J ia, G. C.; Barbaro,
P. Organometallics 1999, 18, 1961. (b) Barbaro, P.; Bianchini, C.; Togni,
A. Organometallics 1997, 16, 3004. (c) Nishiyama, H.; Soeda, N.; Naito,
T.; Motoyama, Y. Tetrahedron: Asymmetry 1998, 9, 2865.
* To whom correspondence should be addressed. Fax: ++41 1 632
13 10. E-mail: mezzetti@inorg.chem.ethz.ch.
(1) For a review, see: Chaloner, P. A.; Esteruelas, M. A.; J oo´, F.;
Oro, L. A. Homogeneous Hydrogenation; Kluwer: Dordrecht, 1994;
Chapter 1.
(2) See, for instance: (a) Cornils, B.; Herrmann, W. A. Applied
Homogeous Catalysis with Organometallic Compounds, 1st ed.; VCH:
New York, 1996; Vols. 1-2. (b) Doyle, M. P.; McKervey, A. M.; Ye, T.
Modern Catalytic Methods for Organic Synthesis with Diazocompounds,
from Cyclopropanes to Ylides, 1st ed.; Wiley: New York, 1998.
(3) See, for instance: (a) J acobsen, E. N. In Catalytic Asymmetric
Synthesis; Ojima, I, Ed.; VCH Publishers: New York, 1993; Chaper
4.2. (b) Ito, Y. N.; Katsuki, T. Bull. Chem. Soc. J pn. 1999, 72, 603. (c)
Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds; Wiley:
New York, 1988. (d) Lin, Z.; Hall, M. B. Coord. Chem. Rev. 1993, 123,
149. (e) Drago, R. S. Coord. Chem. Rev. 1992, 117, 185. (f) J ørgensen,
K. A. Chem. Rev. 1989, 89, 431.
10.1021/om990657x CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/02/1999

5692 Organometallics, Vol. 18, No. 26, 1999
Stoop et al.
Ch a r t 1
Sch em e 1
type [RuCl2(PPh3)(P-P*)] or [RuCl2(P-P)]2.13d,e This is
probably due to the combined effects of increased steric
bulk of the diphosphine and reduced trans effect of
chloride as compared to hydride, as the corresponding
analogues [RuH(P-P)2]+ can be prepared with a general
procedure.14
dation9 catalyzed by ruthenium complexes. By contrast,
bidentate ligands have been rarely used in these reac-
tions,10 and reports involving diphosphino complexes are
rare and restricted to achiral ligands.11 Moreover, we
are not aware of any catalytic transformations that use
ruthenium complexes of chiral diphosphines of the type
[RuCl(P-P*)2]+. This may sound surprising in view of
the large number of chiral diphosphine ligands now
available, but can be probably explained by the fact that
non-hydride ruthenium(II) complexes are difficult to
prepare when the diphosphine is very bulky.
We have undertaken the study of five-coordinate,
cationic complexes of the type [RuCl(P-P*)2]+ (P-P*
) chiral diphosphine) as catalysts for the enantioselec-
tive epoxidation and cyclopropanation of olefins. As
these complexes are the chiral pendant of [RuCl-
(dppp)2]+,12 which has been previously used as epoxi-
dation catalyst,11 we started our investigation with the
enantioselective epoxidation and cyclopropanation of
olefins. In particular, the cationic complexes [RuCl(P-
P)2]+ are expected to be more active catalysts than the
neutral species [RuCl2L3] (L ) phosphine).8a,b We report
here the synthesis and X-ray structures of [RuCl((S,S)-
bnpe)]+ (bnpe ) 1,2-bis(1-naphthylphenylphosphino)-
ethane) and [RuCl((S,S)-chiraphos)]+ (chiraphos ) 2,3-
bis(diphenylphosphino)butane), together with the first
catalytic results.
Enantiomerically pure 1,2-bis(1-naphthylphenylphos-
phino)ethane (bnpe, 1a ) is prepared by deprotonation
and oxidative coupling of the phosphine borane (S)-
P(BH3)(Me)(Ph)(1-Np) (Scheme 1). The latter is obtained
by the procedure published previously,13d which follows
the general method developed by J uge´.15 Deboranation
of the BH3-protected diphosphine 1a ‚(BH3)2 gives enan-
tiomerically pure (S,S)-bnpe (1a ). This is shown by
reprotection of 1a with BH3‚SMe2 and chiral HPLC
analysis of 1a ‚(BH3)2, by comparison with the diaster-
eomeric mixture (l)+(u)-1a ‚(BH3)2 (see Experimental
Section). This is the first stereoselective synthesis of
bnpe. To the best of our knowledge, there is a single
report dealing with bnpe, in which enantiomerically
pure [Rh(COD)(bnpe)]+ (COD ) 1,5-cyclooctadiene) has
been prepared by racemic resolution of the diastereo-
meric camphorsulfonate (Y-) salts [Rh(COD)((l)-
bnpe)]Y.16
[Ru Cl2(P -P *)2]. The complexes [RuCl2(P-P*)2] (P-
P* ) bnpe, 2a ; chiraphos, 2b) are prepared from [RuCl2-
(PPh3)3] by ligand exchange in CH2Cl2 at room temper-
ature.17 In both cases, only the trans isomer is formed,
as indicated by the singlet in the 31P NMR spectrum.
The X-ray structure of both complexes was determined.
The crystals of 2a contain discrete [RuCl2(bnpe)2] units
with the metal in a severely distorted octahedral
environment featuring trans chloro ligands (Figure 1).
The complex is nearly C2-symmetric, with the pseudo-
binary axis bisecting the P(1)-Ru-P(4) angle. The two
P atoms of each bnpe, e.g., P(1) and P(2), are inequiva-
lent (see below). The overall geometry is determined by
the steric crowding due to the large naphthyl groups.
Although the four P atoms are fairly coplanar within
(0.07 Å, the Cl(1)-Ru-Cl(2) angle is closed down to
166.68(5)° due to the short nonbonded contacts between
the Cl atoms and the naphthyl groups on P(1) and P(4)
(Table 1). Accordingly, the Cl-Ru-P angles show that
the naphthyl groups on P(1) and P(4) push the Cl atoms
toward P(3) and P(2), respectively. The Ru-Cl and
Ru-P distances (average 2.453(1) and 2.410(1) Å,
respectively) fall in the upper quartile of the range
Resu lts a n d Discu ssion
Dip h osp h in e Liga n d s. The ligands 1,2-bis(1-naph-
thylphenylphosphino)ethane (bnpe, 1a ) and 2,3-bis-
(diphenylphosphino)butane (chiraphos, 1b) (Chart 1)
were chosen for this study, after chiral ligands forming
six- or seven-membered chelate rings failed to form
complexes of the type [RuCl2(P-P*)2] or [RuCl(P-P*)2]+
from a variety of dichloro-containing precursors. In fact,
binap,13a biphemp,13b J osiphos,13c and C,C′-tetrameth-
ylsilanebis(1-naphthylphenylphosphine)13d react with
[RuCl2(PPh3)3] to give monosubstituted products of the
(9) See, for instance: (a) Nishiyama, H.; Shimada, T.; Ito, H.;
Sugiyama, H.; Motoyama, Y. Chem. Commun. 1997, 1863. (b) Cetinkaya,
B.; Cetinkaya, E.; Brookhart, M.; White, P. S. J . Mol. Catal. A-Chem.
1999, 142, 101.
(10) Recent papers: (a) Barf, G. A.; van den Hoek, D.; Sheldon, R.
A. Tetrahedron 1996, 52, 12971. (b) Boelrijk, A. E. M.; Neenan, T. X.;
Reedijk, J . J . Chem. Soc., Dalton Trans. 1997, 4561. (c) Augier, C.;
Malara. L.; Lazzeri, V.; Waegell, B. Tetrahedron Lett. 1995, 36, 8775.
(11) (a) Bressan, M.; Morvillo, A. Inorg. Chem. 1989, 28, 950. (b)
Morvillo, A.; Bressan, M. J . Mol. Catal. A-Chem. 1997, 125, 119. (c)
Maran, F.; Morvillo, A.; d’Alessandro, N.; Bressan, M. Inorg. Chim.
Acta 1999, 288, 122.
(12) Bressan, M.; Rigo, P. Inorg. Chem. 1975, 14, 2286.
(13) (a) Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345. (b)
Schmid, R.; Cereghetti, M.; Heiser, B.; Scho¨nholzer, P.; Hansen, H.-J .
Helv. Chim. Acta 1988, 71, 897. (c) Togni, A.; Breutel, C.; Schnyder,
A.; Spindler, F.; Landert, H.; Tijani, A. J . Am. Chem. Soc. 1994, 116,
4062. (d) Stoop, R. M.; Mezzetti, A.; Spindler, F. Organometallics 1998,
17, 668. (e) Mezzetti, A.; Tschumper, A.; Consiglio, G. J . Chem. Soc.,
Dalton Trans. 1995, 49.
(14) See for instance: Ogasawara, M.; Saburi, M. Organometallics
1994, 13, 1911.
(15) J uge´, S.; Ste´phan, M.; Laffitte, J . A.; Genet, J . P. Tetrahedron
Lett. 1990, 31, 6357.
(16) Yoshikuni, T.; Bailar, J . C. Inorg. Chem. 1982, 21, 2129.
(17) [RuCl2(chiraphos)2] has been briefly reported previously: (a)
Ikariya, T.; Ishii, Y.; Kawano, H.; Arai, T.; Saburi, M.; Yoshikawa, S.;
Akutagawa, S. J . Chem. Soc., Chem. Commun. 1985, 922. (b) J ames,
B. R.; Fogg, D. E. J . Organomet. Chem. 1993, 462, C21.

Five-Coordinate [RuCl(P-P*)2]+ Complexes
Organometallics, Vol. 18, No. 26, 1999 5693
F igu r e 2. ORTEP view of [RuCl2(bnpe)2] (2a ) along the
RuP4 plane. The second bnpe ligand is omitted for clarity.
F igu r e 1. ORTEP view of [RuCl2(bnpe)2], 2a .
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) in [Ru Cl2(bn p e)2] (2a )
Ru-Cl(1)
2.449(1)
2.415(1)
2.409(1)
3.486(7)
3.222(7)
3.373(6)
Ru-Cl(2)
2.457(1)
2.412(1)
2.406(1)
3.225(6)
3.348(7)
3.401(6)
Ru-P(1)
Ru-P(2)
Ru-P(3)
Ru-P(4)
Cl(1)‚‚‚C(16)
Cl(1)‚‚‚C(48)
Cl(1)‚‚‚C(54)
Cl(2)‚‚‚C(6)
Cl(2)‚‚‚C(36)
Cl(2)‚‚‚C(63)
Cl(1)-Ru-Cl(2)
Cl(1)-Ru-P(1)
Cl(1)-Ru-P(3)
Cl(2)-Ru-P(1)
Cl(2)-Ru-P(3)
P(1)-Ru-P(2)
P(1)-Ru-P(4)
P(2)-Ru-P(4)
166.68(5)
87.51(5)
90.44(5)
102.04(5)
80.46(5)
78.98(5)
96.45(5)
174.08(5)
Cl(1)-Ru-P(2)
Cl(1)-Ru-P(4)
Cl(2)-Ru-P(2)
Cl(2)-Ru-P(4)
P(1)-Ru-P(3)
P(2)-Ru-P(3)
P(3)-Ru-P(4)
83.71(5)
99.94(5)
88.98(5)
88.32(5)
176.47(5)
103.67(5)
81.07(5)
observed for ruthenium complexes,18 which is a further
indication of steric crowding.
F igu r e 3. ORTEP view of [RuCl2(chiraphos)2], 2b.
Both chelate rings adopt an envelope conformation
with the two flaps, P(2) and P(3), lying above and below
the RuP4 plane. In the first one, Ru, P(1), C(1), and C(2)
are coplanar within (0.05 Å, and P(2) is displaced from
their mean plane by 1.00 Å (Figure 2). In the second
one, Ru, P(4), C(3), and C(4) are coplanar within (0.12
Å, and P(3) is displaced by 0.87 Å. As a consequence,
the naphthyl and phenyl groups on P(2) and P(3) occupy
the equatorial and axial positions, respectively. The
flattening at P(1) and P(4) makes the equatorial and
axial positions nearly equivalent: Figure 2 shows that
the orientation of the 1-naphthyl and phenyl substitu-
ents on P(1) is nearly the same, although their steric
requirements largely differ. Eventually, the substituents
at the P atoms of each bnpe ligand assume a syn-
diaxial,syn-diequatorial conformation. Similar confor-
mations are found in trans-[RuCl2(Ph2PCH2CH2PPh2)2]19
and in trans-[RuCl2(chiraphos)2] (see below), whereas
in trans-[RuCl2((S,S)-MePhPCH2CH2PMePh)2] both che-
late rings assume a half-chair conformation with the
phenyls in the less hindered equatorial positions.20
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) in [Ru Cl2(ch ir a p h os)2] (2b)
Ru(1)-Cl(1)
Ru(1)-P(1)
Ru(1)-P(3)
Cl(1)‚‚‚C(12)
Cl(1)‚‚‚C(24)
2.435(2)
2.431(2)
2.385(2)
3.454(7)
3.299(7)
Ru(1)-Cl(2)
Ru(1)-P(2)
Ru(1)-P(4)
Cl(2)‚‚‚C(30)
Cl(2)‚‚‚C(42)
2.451(2)
2.368(2)
2.367(2)
3.523(7)
3.326(7)
Cl(1)-Ru(1)-Cl(2) 178.75(6)
Cl(1)-Ru(1)-P(1)
Cl(1)-Ru(1)-P(3)
Cl(2)-Ru(1)-P(1)
Cl(2)-Ru(1)-P(3)
P(1)-Ru(1)-P(2)
P(1)-Ru(1)-P(4)
P(2)-Ru(1)-P(4)
82.95(7) Cl(1)-Ru(1)-P(2)
99.36(7) Cl(1)-Ru(1)-P(4)
97.33(7) Cl(2)-Ru(1)-P(2)
80.37(7) Cl(2)-Ru(1)-P(4)
81.00(6) P(1)-Ru(1)-P(3)
99.25(6) P(2)-Ru(1)-P(3)
176.73(7) P(3)-Ru(1)-P(4)
86.45(6)
90.34(7)
94.80(6)
88.41(6)
177.68(8)
98.86(6)
81.03(6)
The crystal of the chiraphos derivative trans-[RuCl2-
(chiraphos)2] (2b) contains two independent molecules
in the unit cell, with approximately the same distorted
octahedral coordination. As most structural parameters
of the two molecules are very similar, only one is
described below. As in 2a , a pseudo-C2 axis bisects the
P(1)-Ru-P(4) angle (Figure 3). Although the Cl(1)-
Ru-Cl(2) angle of 178.75(6)° is nearly ideal (Table 2),
the Cl(1)-Ru-Cl(2) vector is tilted away by ca. 8° from
the normal to the RuP4 plane along the P(1)-P(3)
vector. Both chelate rings have an envelope conforma-
(18) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.
(19) Polam, J . R.; Porter, L. C. J . Coord. Chem. 1993, 29, 109.
(20) Wartchow, R.; Berthold, H. J Z. Kristallogr. 1977, 145, 240.

5694 Organometallics, Vol. 18, No. 26, 1999
Stoop et al.
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) in [Ru Cl(bn p e)2]P F 2O2 (2b)
Ru(1)-Cl(1)
Ru(1)-P(1)
Ru(1)-P(3)
Ru(1)‚‚‚C(22)
Ru‚‚‚H-C(22)
2.400(4)
2.391(4)
2.468(4)
3.61(1)
3.00
Ru(1)-P(2)
Ru(1)-P(4)
Ru(1)‚‚‚C(54)
Ru‚‚‚H-C(54)
2.283(4)
2.315(4)
3.13(2)
2.40
Cl(1)-Ru(1)-P(1)
Cl(1)-Ru(1)-P(3)
P(1)-Ru(1)-P(2)
P(1)-Ru(1)-P(4)
P(2)-Ru(1)-P(4)
Ru(1)-P(1)-C(5)
Ru(1)-P(3)-C(37)
89.7(1)
86.6(1)
82.6(1)
99.3(1)
94.8(1)
122.8(5)
121.4(5)
Cl(1)-Ru(1)-P(2)
Cl(1)-Ru(1)-P(4)
P(1)-Ru(1)-P(3)
P(2)-Ru(1)-P(3)
P(3)-Ru(1)-P(4)
Ru(1)-P(2)-C(21)
Ru(1)-P(4)-C(53)
112.9(2)
151.8(2)
174.4(2)
102.6(1)
82.2(2)
115.6(5)
103.5(5)
by 31P NMR. As the two cations are very similar, only
one will be discussed here. As expected for a π-stabi-
lized, 16-electron complex, [RuCl(bnpe)2]+ has a dis-
torted trigonal bipyramidal geometry (Y-shaped).22 Other
typical features are the shorter Ru-Cl bond (2.400(4)
Å) than in the 18-electron complex 2a (2.449(1) and
2.457(1) Å) and the characteristically narrow P(2)-Ru-
P(4) angle of 94.8(1)°. The conformation at ruthenium
is Λ in both independent molecules. Each chelate ring
has an envelope conformation, but, at difference with
2a ,b, the flap is located on a C atom.23 However, the
conformation of the substituents at the P atoms is
virtually the same as observed in the six-coordinate 2a ,
i.e., approximately syn-diaxial,syn-diequatorial.
F igu r e 4. ORTEP view of [RuCl2(chiraphos)2] (2b) along
the RuP4 plane. The second chiraphos ligand is omitted for
clarity.
The Y-shaped equatorial plane is distorted, with
largely different Cl-Ru-P angles (112.9(2)° and
151.8(2)°), as already observed in analogous systems.24-26
The latter feature is coupled with a short nonbonded
contact of 3.13(2) Å between Ru and C(54). This is the
C2 atom of the naphthyl group approaching the metal
on the sixth coordination site left open by the large Cl-
Ru-P(1) angle.27 The resulting calculated Ru‚‚‚H-C
contact (2.40 Å, Ψ ) 129.4°) suggests a weak to medium
γ-agostic interaction,28 which stabilizes the electron-
deficient complex together with steric effects,29 as
observed in other 16- or 14-electron complexes of ru-
thenium(II).30 The Ru-P-C(naphthyl) angles suggest
that there is an attractive interaction between Ru and
C(54). The smallest Ru-P-C angle is the one involved
in the agostic interaction, Ru(1)-P(4)-C(53) (103.5(5)°).
F igu r e 5. ORTEP view of [RuCl(bnpe)2][PF2O2], 3a .
tion with the four methyl groups in pseudo-equatorial
positions. The two flaps are on P(2) and P(3), which are
displaced on opposite sides of the RuP4 plane. In the
first chelate, Ru, P(1), C(49), and C(50) are coplanar
within (0.11 Å, and P(2) is displaced from their mean
plane by 0.85 Å (Figure 4). In the second one, Ru, P(4),
C(53), and C(54) are coplanar within (0.09 Å, and P(3)
is displaced by 0.82 Å. This results in an proximate syn-
diaxial,syn-diequatorial conformation for the four phen-
yls in both chiraphos ligands. Thus, despite the stereo-
centers on the diphosphine backbone, the molecule is
nearly centrosymmetric, and the phenyl groups are
arranged with a pseudo-C2h symmetry (2/m). Finally,
the axial phenyl groups on P(1) and P(3) point toward
the Cl atoms and open the corresponding Cl-Ru-P
angles to about 98°, as indicated by the short Cl‚‚‚C
contacts (Table 2). As observed for 2a , the Ru-Cl and
Ru-P distances are long due to steric crowding.18
[Ru Cl(bn p e)2]P F 6. The reaction of 2a with Tl[PF6]
in CH2Cl2 gives the five-coordinate, cationic complex
[RuCl(bnpe)2]PF6 (3a ), as confirmed by an X-ray study
(Figure 5, Table 3). The unit cell contains two crystal-
lographically independent [RuCl(bnpe)2]+ cations, one
[PF2O2]- anion, one (µ-H)-bridged [PF2O2H‚‚‚O2F2P]-
unit, one (µ-H)2-bridged [PF2O2H]2 dimer, and two
CH2Cl2 molecules. The presence of the [PF2O2]- anion,
possibly formed by hydrolysis of [PF6]-,21 is confirmed
(21) J effery, J . C.; J elliss, P. A.; Lebedev, V. N.; Stone, F. G. A.
Organometallics 1996, 15, 4737.
(22) (a) Caulton, K. G. New J . Chem. 1994, 18, 25. (b) Riehl, J .-F.;
J ean, Y.; Eisenstein, O.; Pe´lissier, M. Organometallics 1992, 11, 729.
(c) J ohnson, T. J .; Folting, K.; Streib, W. E.; Martin, J . D.; Huffman,
J . C.; J ackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995,
34, 488, and references therein.
(23) In the first molecule, Ru, P(3), P(4), and C(3) are perfectly
coplanar, with C(4) at 0.74 Å from their plane, whereas Ru, P(1), P(2),
and C(2) are coplanar within (0.09 Å, and C(1) is displaced by 0.70 Å
from the mean plane.
(24) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Bresciani Pahor, N. J .
Chem. Soc., Dalton Trans. 1989, 1045.
(25) Batista, A. A.; Centeno Cordeiro, L. A.; Oliva, G. Inorg. Chim.
Acta 1993, 203, 185.
(26) Chin, B.; Lough, A. J .; Morris, R. H.; Schweitzer C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(27) The next closest contact is Ru‚‚‚C(22) (3.61(1) Å).
(28) (a) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg.
Chem. 1988, 36, 1. (b) Crabtree, R. H.; Holt, E. M.; Lavin, M.;
Morehouse, S. M. Inorg. Chem. 1985, 24, 1986. (c) Crabtree, R. H.
Angew. Chem., Int. Ed. Engl. 1993, 32, 789. (d) Yao, W.; Eisenstein,
O.; Crabtree, R. Inorg. Chim. Acta 1997, 254, 105.
(29) (a) Cooper, A. C.; Streib, W. E.; Eisenstein, O.; Caulton, K. G.
J . Am. Chem. Soc. 1997, 119, 9069. (b) Ujaque, G.; Cooper, A. C.;
Maseras, F.; Eisenstein, O.; Caulton, K. G. J . Am. Chem. Soc. 1998,
120, 361.

Five-Coordinate [RuCl(P-P*)2]+ Complexes
Organometallics, Vol. 18, No. 26, 1999 5695
A low-temperature NMR investigation of 3a in CD2Cl2
was directed to assess the agostic interaction in solution.
The room-temperature 31P NMR spectrum shows a
static spectrum with two pseudo-triplets at δ 65.4 (Peq
)
and 46.6 (Pax). This indicates that one conformation of
the chelate rings is preferred (the Λ one is observed in
the solid state). Alternatively, the exchange between Pax
and Peq, which switches the ∆ and Λ configurations,
must be slow on the NMR time scale. Also, there is fast
exchange between C(54) and C(22), as the four P atoms
are equivalent in pairs at room temperature. Broaden-
ing of the Peq triplet occurs upon cooling below -50 °C,
suggesting that this exchange process slows down. The
signals of the H atoms at the 2-position of the equatorial
naphthyl groups (C(54) and C(22) in the X-ray structure)
were attributed by NOESY and P-H correlation 2D
spectroscopy at -70°. However, they exchange rapidly
with each other even at -70 °C. Thus, the corresponding
J C,H value (158 Hz) has little significance, but disfavors
a strong agostic interaction.
F igu r e 6. Ball-and-stick view of the D2-symmetric dimer
[Ru2Cl2(chiraphos)4]2+ (Cerius2 molecular modeling calcula-
tions).
Finally, the conformational features of the diphos-
phines in 2a ,b and 3a deserve a comment. Examining
the CSD database, Seebach and co-workers have found
that a number of complexes containing chiral bidentate
phosphines exhibit pseudo-Cs-symmetry due to the
flattened conformation of one of the PPh2 groups,31
similarly to our findings in 2a ,b and 3a . They also
discussed the relationship between the symmetry of the
chelate ring and that of the conformation of the PPh2
groups and proposed a distinction between C2- and C1-
symmetric ligands. Chiraphos has been long considered
a conformationally rigid ligand, with the chelate ring
in a twist conformation that forces the PPh2 groups in
a C2-symmetric “edge-on/face-on” conformation.32 Also
in disubstituted complexes, such as cis-[IrH2((S,S)-
chiraphos)2]+, both chiraphos ligands assume a twist (δ)
conformation.33 However, recent investigations have
shown that the alternative envelope conformation also
occurs, at least in the solid state, as in the π-allyl
complex [Pd(η3-PhCHCHCHPh)(chiraphos)]PF6.34 The
flexibility of the chiraphos backbone is illustrated also
by [Ru(L)(chiraphos)(C5H5)]+. Changing the ligand L
from (chiral) S(Me)(O)(Ph) to (achiral) SMe2 switches
the conformation of the phenyl rings from C1- to C2-
symmetric.35 Thus, rather than an intrinsic property of
the ligand,31,32 the conformation of the substituents at
the P atoms in coordinated diphosphines appears to
depend on the coordination environment as a whole. We
suggest that the configuration and steric crowding of
Ch a r t 2
the complex play an important role and discuss the
effects of this conformational flexibility of chiraphos on
catalysis below.
[Ru Cl(ch ir a p h os)2]2[P F 6]2. Similarly to 2a , [RuCl2-
(chiraphos)2] (2b) reacts with Tl[PF6] in CH2Cl2 giving
a product analyzing as [RuCl(chiraphos)2]PF6 (3b).
However, the 31P NMR spectrum in CD2Cl2 solution (in
the concentration range 5-20 mM) shows signals that
are better attributed to the dimers [(chiraphos)2Ru(µ-
Cl)2(chiraphos)2]2+ (4a ,b) rather than to five-coordinate
3b. The major species present in solution (95% inte-
grated intensity) shows two pseudo-triplets (AA′XX′, δ
51.9, 38.6, J P,P′ ) 22.6 Hz). A minor component (ca. 5%)
exhibits two apparent AA′XX′ systems (δ 52.6, 47.1, J P,P′
) 27.8 Hz; δ 40.8, 38.1, J P,P′ ) 21.4 Hz). The chemical
shifts of both species are indicative of a six-coordinate
structure rather than a five-coordinate one.24,26 As two
diastereomers are possible for the binuclear species
[Ru2Cl2(chiraphos)4]2+, we suggest that the major sig-
nals are those of the D2-symmetric isomer 4a , whereas
the low-intensity ones are those of the C2-symmetric 4b
(Chart 2). Molecular modeling suggests that two five-
coordinate fragments 3b can form µ-dichloro-bridged
dimers [(P-P*)2Ru(µ-Cl)2Ru(P-P*)2]2+ (4a ,b) (P-P* )
chiraphos). UFF calculations based on the Cerius2
program36 give energy values that are in qualitative
agreement with the observed isomer distribution, with
4b at higher energy than 4a (Chart 2). The minimized
structure of the D2-symmetric dimer 4a is shown in
Figure 6.
(30) For recent examples, see: (a) Martelletti, A.; Gramlich, V.;
Zu¨rcher, F.; Mezzetti, A. New J . Chem. 1999, 199. (b) Baratta, W.;
Herdtweck, E.; Rigo, P. Angew. Chem. 1999, 111, 1733. (c) Huang, D.;
Huffman, J . C.; Bollinger, J . C.; Eisenstein, O.; Caulton, K. G. J . Am.
Chem. Soc. 1997, 119, 7398. (d) Huang, D.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. Angew. Chem., Int. Ed. Engl. 1997, 36, 2004. (e)
Ogasawara, M.; Saburi, M. Organometallics 1994, 13, 1911.
(31) Seebach, D.; Devaquet, E.; Ernst, A.; Hayakawa, M.; Ku¨hnle,
F. N. M.; Schweizer, W. B.; Weber, B. Helv. Chim. Acta 1995, 78, 1636.
(32) (a) Orpen, A. G. Chem. Soc. Rev. 1993, 22, 191. (b) Halpern, J .
Science 1982, 217, 401. (c) Of notice, (R,S)-2,3-bis(diphenylphosphino)-
butane mantains the C2-conformation in [RhCl((R)-P(Men)Ph2)((R,S)-
chiraphos)]: Gugger, P.; Limmer, S. O.; Watson, A. A.; Willis, A. C.;
Wild, S. B. Inorg. Chem. 1993, 32, 5692.
(33) Brown, J . M.; Evans, P. L.; Maddox, P. J .; Sutton, K. H. J .
Organomet. Chem. 1989, 359, 115.
(34) Yamaguchi, M.; Yabuki, M.; Yamagishi, T.; Kondo, M.; Kita-
gawa, S. J . Organomet. Chem. 1997, 538, 199.
Complexes 4a ,b partially dissociate to the five-
coordinate cation [RuCl(chiraphos)2]+ in CDCl3 solution
(35) Schenk, W. A.; Frisch, J .; Du¨rr, M.; Burzlaff, N.; Stalke, D.;
Fleischer, R.; Adam, W.; Prechtl, F.; Smerz, A. K. Inorg. Chem. 1997,
36, 2372.
(36) (a) Rappe´, A. K.; Casewit, C. J .; Colwell, K. S.; Goddard, W. A.,
III; Skiff, W. M. J . Am. Chem. Soc. 1992, 114, 10024. (b) Rappe´, A. K.;
Colwell, K. S.; Casewit, C. J . Inorg. Chem. 1993, 32, 3438.

5696 Organometallics, Vol. 18, No. 26, 1999
Stoop et al.
(eq 1). The 31P NMR spectrum in CDCl3 (8 × 10-3 mol
Sch em e 2
(1)
Ta ble 4. Ca ta lytic Cyclop r op a n a tion of Styr en ea
selectivity (ee) (%)
L-1) shows two broad triplets at δ 63.2 and 58.6 (J P,P′
= 25 Hz), downfield of the signals of dimers 4a ,b. The
chemical shifts of the former are similar to those of 4a
and other [RuCl(P-P)2]+ complexes with diphosphines
forming five-membered rings.24,26 Integration of the
spectrum indicates that 47% of the complex is present
as the monomer [RuCl(chiraphos)2]+ at room tempera-
ture and the remaining part as dimer 4. Upon raising
the temperature to 50 °C, the equilibrium shifts toward
the monomer (68%), whose signals coalesce in a broad
hump at δ 62, as expected for a fluxional five-coordinate
complex. The occurrence of equilibrium 1 is further
supported by spectrophotometric measurements. The
electronic spectrum of 4 in 4.5 × 10-3 mol L-1 CHCl3
solution shows the features of six-coordinate ruthe-
nium(II) complexes, with a shoulder at 350 nm and a
band at 450 nm (ꢀ ) 380 L mol-1 cm-1). However, the
extinction coefficient ꢀ of the latter band increases as
the concentration is lowered (ꢀ ) 720 mol-1 cm-1 at C
) 1.8 × 10-4 mol L-1), and two shoulders appear at 555
and 630 nm, in the region observed for five-coordinate
3a . This suggests that the solution contains a five-
coordinate complex,12,24 whose concentration increases
by lowering the concentration. The different tendency
of 3a and 3b toward dimerization can be rationalized
in terms of the larger steric bulk of bnpe as compared
to chiraphos.
run
1
cat.
T (°C)
t (h)
conv. (%)
E
Z
3b
3b
3b
3b
3b
3a
3a
3c
20
20
20
0
1
6
6
1
6
1
6
6
37
55
38
29
40
24
37
38
54 (25)
56 (14)
56 (10)
58 (25)
56 (21)
54 (5)
46 (6)
44 (16)
44 (35)
42 (14)
44 (7)
2b
3
0
4
20
20
20
46 (6)
55 (<5)
56 (-)
45 (11)
44 (-)
5b
a
Reaction conditions: ethyl diazoacetate (1 mmol) in CH2Cl2
(1 mL) was added dropwise to a CH2Cl2 solution (5 mL) of styrene
(20 mmol), the catalyst (0.01 mmol), and decane (1 mmol) as
b
internal GC standard. In 20 mL of CH2Cl2.
ation of styrene. For comparison’s sake, the achiral
[RuCl(dppp)2]PF6 (3c)12 was also tested. The complexes
3a -c (1 mol %) catalyze the cyclopropanation of styrene
by ethyl diazoacetate to give the corresponding 2-phen-
ylcyclopropane carboxylates (Scheme 2). All catalysts
give both E- and Z-isomers with approximately the same
ratio (ca. 55:45, Table 4), which lies in the range of
diastereoselectivity generally obtained with ethyl diazo-
acetate.39 The reaction is highly chemoselective, as
neither dimerization (fumarate and maleate) nor ho-
1
mologation products are observed with 3a -c. The H
NMR spectrum of the reaction mixture shows unreacted
diazoacetate after the reaction has stopped (6 h reaction
time). The conversions obtained (∼40% based on the
diazoacetate) are similar to those obtained with other
phosphino complexes of ruthenium.38
Rea ctivity of [Ru Cl(P -P )2]+. The five-coordinate
species 3a ,b react with carbon monoxide to give the
carbonyl complexes trans-[RuCl(CO)(P-P*)2]+. In line
with the presence of five-coordinate [RuCl(chiraphos)2]+
in CDCl3 solution, 3b reacts instantaneously with CO
in CDCl3 to give [RuCl(CO)(chiraphos)2]+ (5b). This also
indicates that equilibrium 1 is rapidly established. The
bnpe analogue 3a reacts reluctantly. No reaction is
observed between 3a and CO at room temperature in
CDCl3 during 24 h. The carbonyl derivative trans-[RuCl-
(CO)(bnpe)2]+ (5a ) is formed by reacting 3a with CO at
50 °C in CDCl3 for 12 h. As 16-electron complexes
usually react very rapidly with CO, this unusual
behavior is further evidence that the sixth coordination
position of 3a is shielded by a naphthyl group, as
observed in the solid state. Accordingly, the relatively
crowded five-coordinate species [RuCl(dppp)2]+ does not
react with CO at temperatures lower than -40 °C.37
Asym m etr ic Cyclop r op a n a tion . Recently, ruthe-
nium-catalyzed cyclopropanation has attracted growing
interest.2 Although catalytic systems based on N- and
P,N-donor ligands have been reported,7b,8 the applica-
tion of bis(diphosphine) complexes is new.38 Unsatur-
ated cationic ruthenium complexes are expected to be
more reactive than neutral ones.8a Thus, we tested 3a ,b
as catalyst precursors in the asymmetric cyclopropan-
The chiraphos derivative 3b induces moderate enan-
tioselectivity, giving up to 35% ee for the Z-product (run
2) and to 25% for the E-isomer (run 1, after 1 h).
Monitoring by chiral GC shows that the ee values of
both diastereomers are not constant throughout the
reaction. With 3b, the enantiomeric excess of the
E-product drops from 25% after 1 h to 14% after 6 h
reaction time, whereas that of the Z-product increases
from nearly racemic to 16% (run 1). As most of the
substrate is converted within 1 h, we suspect that the
enantioselectivity drops due to catalyst degradation.40
Lowering the temperature does not change either activ-
ity or selectivity (run 3). The bnpe derivative 3a gives
racemic products (run 4). As only few ruthenium car-
bene complexes have been isolated,4f,1 some effort was
spent attempting to trap the putative carbene interme-
diate [RuCl(CH2COOEt)(chiraphos)2]+. The reaction of
ethyl diazoacetate with 3b gave an unstable complex
(39) (a) The cis-trans ratio is usually increased with increasing
bulkiness of the ester group of the diazoacetates within a row: Me <
Et < t-Bu = Men, according to diastereotopic face discrimination during
the approach of the olefin on the Ru-carbene intermediate.39b (b)
Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K. J . Am.
Chem. Soc. 1994, 116, 2223.
(40) However, the use of 5 mol % of the catalyst did not improve
either conversion or ee.
(37) Mezzetti, A.; Rigo, P. Unpublished results.
(41) See, for instance: (a) Galardon, E.; Le Maux, P.; Toupet, L.;
Simmoneaux, G. Organometallics 1998, 17, 565. (b) Nishiyama, H.;
Aoki, K.; Itoh, H.; Iwamura, T.; Sakata, N.; Kurihara, O.; Motoyama,
Y. Chem. Lett. 1996, 1071.
(38) For selected papers on ruthenium catalysts with monodentate
phosphines, see: Demonceau, A.; Simal, F.; J an, D.; Noels, A. F.
Tetrahedron Lett. 1999, 40, 1653, and references therein.

Five-Coordinate [RuCl(P-P*)2]+ Complexes
Organometallics, Vol. 18, No. 26, 1999 5697
Ta ble 5. Ca ta lytic Ep oxid a tion a
Ch a r t 3
selectivity (%)
run
cat.
olefin
conv. (%)
epoxide
PhCHO
1
2
3
4
5
6
7
8
9
3a
3b
3c
3a
3b
3c
3a
3b
3c
3a
3b
3c
6
6
6
7
7
7
8
8
8
9
9
9
100
74
93
64
74
92
76
84
87
35
3
30
51
3
41
13b
33c
27d
4
24
33
30
38
33
35
<1
<1
<1
Sch em e 3
10
11
12
100
100
97
2
42
a
Reaction conditions: PhIO (440 mg, 2.0 mmol) was added
batchwise to a CH2Cl2 solution (5 mL) of the olefin (1.0 mmol),
the catalyst (0.01 mmol), and decane as internal GC standard.
Chiral GC analysis showed that racemic products are invariably
that decomposed in solution within 3 h, giving the
fumarate and maleate esters, as detected by GC analy-
sis. The low stability of this species precluded 13C NMR
and MS studies.
b
formed with 3a ,b. 4% of trans isomer is formed (based on
d
converted olefin). c 0.3% of trans isomer is formed. 3% of trans
We suggest two explanations for the low (or lack of)
asymmetric induction observed with 3a ,b. First, inef-
ficient enantioface selection can result from a six-
coordinate carbene intermediate8a,c having a pseudo-Cs-
symmety similar to that observed in 2a ,b.2,39b An
analogous explanation holds also for [RuCl2(P)3] (P3 )
chiral triphosphine).8a Second, as we observe a signifi-
cant blank reaction in the absence of the catalyst (ca.
20% conversion), the low enantioselectivity might be
explained by a concurrent, non-metal-catalyzed path-
way. In conclusion, the systems based on P4 (and P3
donor sets)8a,b are less efficient that those based on N4
and P2N2 donors.7b,8c Improved ligand design and en-
hancement of the catalytic activity are clearly required.
Asym m etr ic Ep oxid a tion . Complexes 3a ,b were
tested as catalyst precursors in the epoxidation of
unfunctionalized alkenes with iodosyl benzene (PhIO)
as primary oxidant. Styrene (6), trans-â-methylstyrene
(7), cis-â-methylstyrene (8), and 1,2-dihydronaphthalene
(9) were chosen as model substrates (Chart 3). The
overall reaction is shown in Scheme 3. The main
products are the epoxide, PhCHO (and other aldehydes)
from the oxidative cleavage of the CdC bond, and the
polymer of the olefin. In general, good to excellent olefin
conversions are achieved with all substrates, but neither
the bnpe nor the chiraphos complexes 3a ,b give any
chiral induction. The reaction conditions were optimized
using [RuCl(dppp)2]PF6 (3c) as catalyst precursor on
the lines of Bressan’s work.11 We found that adding the
primary oxidant PhIO in batches dramatically increases
both the olefin conversion (60-100%) and the selectivity
for the epoxide (up to 51%) (Table 5). In the optimized
catalytic run, solid PhIO was added in portions (13 ×
0.15 mmol) to a CH2Cl2 solution of the olefin (1.0 mmol)
and catalyst (10 µmol, 1 mol %) under argon over a time
of 6 h. The course of the reaction was monitored by GC
for 7 h. Control experiments show that the epoxidation
proceeds only in the presence of both the oxidant and
the catalyst.
isomer is formed.
1
benzaldehyde (and formaldehyde, detected by H NMR
spectroscopy) (run 2). The missing mass in runs 1-3 is
attributed to the formation of polystyrene, which was
isolated according to the mass balance by addition of
1
CH3OH to the reaction solution, and identified by H
NMR spectroscopy. Similarly, the chiraphos and dppp
complexes 3a and 3c epoxidize trans-â-methylstyrene
(7) with high chemoselectivity (runs 4, 6). In the
epoxidation of cis-â-methylstyrene (8), 3b and 3c give
the best chemoselectivity (runs 7-9). As oxidative
cleavage is negligible with all three catalysts, the
missing mass is attributed to polymer formation. In-
terestingly, the reactions catalyzed by 3a -c are stereo-
specific to a large extent: the major epoxidation product
is cis-â-methylstyrene oxide (13-33% of the converted
olefin), and trans-â-methylstyrene oxide is formed in
minor amounts (0.3-4% of the converted olefin). This
supports a concerted oxene transfer to the olefin,
whereas Mn-based catalysts generally give a large
amount of the trans-epoxide due to stepwise C-O bond
formation.3a,b,43 Finally, 1,2-dihydronaphthalene (9) gives
quantitative conversion, but the epoxide is not stable
under the reaction conditions (runs 10-12). GC moni-
toring showed that, as the reaction proceeds, the epoxide
is converted to other products that were not identified.
The catalytic reaction was monitored by 31P and H
1
NMR spectroscopy in order to determine the fate of the
catalyst. Solid PhIO (0.68 equiv vs styrene) was added
to a CD2Cl2 solution containing styrene and 3a (50:1
mol ratio). The formation of styrene oxide, PhCHO, and
HCHO was observed by 1H NMR. After ca. 2 h, catalytic
activity ceases due to oxidant consumption, and the
31P{1H} NMR spectrum shows the Ru complex and bnpe
oxide (29% of starting 3a ). Catalytic activity resumes
after addition of PhIO, and quantitative substrate
conversion is achieved. NMR spectroscopic analyses ∼2
h after each addition of oxidant reveal further decom-
position of the Ru complex to give bnpe dioxide, but ca.
16% of starting 3a is present after complete substrate
conversion, showing that the catalyst survives (at least
in part) during the reaction. On the basis of this
In contrast with what is generally observed with
ruthenium-based catalysts,42 epoxidation effectively
competes with oxidative cleavage (Table 5). Thus, 3a
and 3c yield styrene oxide with 30-35% selectivity
(runs 1, 3), whereas the bnpe derivative 3a gives mainly
(42) Barf, G. A.; Sheldon, R. A. J . Mol. Catal. A-Chem. 1995, 102,
23.
(43) Chang, S.; Galvin, J . M.; J acobsen, E. N. J . Am. Chem. Soc.
1994, 116, 6937.

5698 Organometallics, Vol. 18, No. 26, 1999
Stoop et al.
or OB-H columns (0.46 cm × 25 cm). Optical rotations were
measured using a Perkin-Elmer 341 polarimeter with a 1 dm
cell. Elemental analyses were carried out by the Laboratory
of Microelemental Analysis (ETH Zu¨rich). [RuCl2(PPh3)3],47
trans-â-methylstyrene oxide, iodosyl benzene, 1,2-dihydronaph-
thalene oxide, cis-â-Me-styrene, and cis-â-Me-styrene oxide
were prepared according to published methods (see Supporting
Information). (S)-P(1-Np)(Ph)(Me)(BH3) was prepared as pre-
viously described.13d
observation, and precedents of asymmetric epoxidation
of terminal olefins catalyzed by platinum complexes
containing chiral diphosphines,44 we suspect that the
lack of chiral induction with 3a ,b is due to the pseudo-
Cs-symmetry in the oxo intermediate [RuCl(O)(P-
P*)2]+. The latter species is the putative oxene-transfer
reagent based on previous mechanistic studies11a and
on the isolation of the osmium analogue trans-[OsCl-
(O)(dcpe)2]+ (dcpe ) 1,2-bis(dicyclohexylphosphino)-
ethane).45,46 However, as partial oxidative degradation
of the P-P* ligand occurs, the lack of asymmetric
induction could also be due to the formation of an achiral
complex.
Con clu sion . In the bis(diphosphino) complexes [RuCln-
(P-P*)2](2-n)+ (n ) 1, 2; P-P* ) chiraphos or bnpe), the
aryl substituents at the P atoms assume a pseudo-Cs-
symmetric conformation due to the envelope conforma-
tion of the five-membered chelate ring. This is appar-
ently independent of whether the stereogenic centers
are C or P atoms and of the nature of the aryl group
(either phenyl or 1-naphthyl). Our results confirm that
chiraphos can assume different conformations, depend-
ing on the coordination environment. The results of the
catalytic reactions reported herein, the first ones using
chiral bis(diphosphino) complexes of the type [RuCl(P-
P*)2]+, suggest that a pseudo-Cs-symmetric conforma-
tion of the diphosphine correlates with low enantio-
selectivity also in reactions occurring at an octahedral
complex without precoordination of the substrate. We
are addressing this problem with an improved design
of the ligands R1R2P-PR1R2 using R1 and R2 substitu-
ents having largely different steric bulks, and studying
other catalytic applications of the [RuX(P-P*)2]+ com-
plexes.
(S,S)-[(BH3)(P h )(1-Np)P CH2CH2P (BH3)(P h )(1-Np)], (S,S)-
1a ‚(BH3)2. A hexane solution (6.25 mL, 1.1 M) of sec-BuLi (6.87
mmol) was added dropwise to a THF solution (60 mL) of (S)-
P(BH3)(Me)(Ph)(1-Np) (1.5 g, 5.67 mmol) at -78 °C. After the
solution was stirred for 2.5 h, a suspension of anhydrous
[Cu(O2C(CH3)3)2] (4.51 g, 17.0 mmol) in THF (100 mL), cooled
to -78 °C, was added by cannula. The resulting solution was
allowed to reach room temperature overnight. The reaction
was quenched with 1 M HCl (10 mL). The organic layer was
diluted with ethyl acetate, washed twice with 1 M HCl, and
neutralized with 1 M NaOH. The organic phase was extracted,
and the product was separated by chromatography (silica gel,
toluene/hexane, 1:1) from unreacted (S)-P(BH3)(Me)(Ph)(1-Np)
(343 mg). The latter exhibits the same enantiomeric purity as
before the reaction and can be recycled. Chiral HPLC: (S,S):
(S,R):(R,R) ) 99.5:0.4:0.1 (OD-H, hexane/PriOH/AcOEt) 98:
1.5:0.5, Rt(R,R)-1a ‚(BH3)2 ) 25.80 min, Rt(R,S)-1a ‚(BH3)2
)
29.18 min, Rt(S,S)-1a ‚(BH3)2 ) 32.64 min). Recrystallization
from CH2Cl2/hexane (or AcOEt) gave 1a ‚(BH3)2 as white
microcrystals. Yield: 0.98 g (66%). Enantiomeric purity:
>99%, only one enantiomer detected by HPLC. [R]20D ) -32.1
1
( 0.12 (C ) 1, CHCl3). H NMR (CDCl3) δ 7.95-7.09 (m, 24
H, arom), 2.60 (multiplet, 4 H, CH2P). 31P NMR (CDCl3): 18.3
(br s, 2 P). MS (EI): m/z 511.2 (M+ - BH4, 5%), 498.2 (M+
-
2BH3, 59%), 362.1 (M+ - 2BH3 - (Ph)PC2H4, 59%), 312.1 (M+
- 2BH3 - (1-Np)PC2H4, 34%), 235.1 (M+ - 2BH3 - (1-Np)-
(Ph)PC2H4, 41%) 233.1 (M+ - 2BH3 - (1-Np)(Ph)PC2H4 - 2H,
100%). Anal. Calcd for C34H34B2P2‚1/2AcOEt: C, 75.82; H, 6.72.
Found: C, 75,75; H, 6.92.
(S,S)-[(P h )(1-Np )P CH2CH2P (P h )(1-Np )], (S,S)-1a . (S,S)-
1a ‚(BH3)2 (0.52 g, 1 mmol) was dissolved in morpholine (30
mL), and the colorless solution was stirred overnight at room
temperature. The yellowish solution was evaporated to dry-
ness. Flash chromatography (alumina, toluene as eluent)
yielded 1a as a colorless oil. Yield: 0.46 g (94%). Enantiomeric
purity: >99%, measured by reprotection with Me2S‚BH3. The
HPLC trace of resulting 1a shows only one enantiomer under
the above conditions. 1H NMR (CDCl3): δ 7.95-7.09 (m, 24
H, arom), 2.4-2.1 (m, 4 H, CH2P). 31P NMR (CDCl3): -24.22
(s, 2 P). MS (EI): m/z 498.2 (M+, 30%), 265.1 (M+ - P(1-Np)-
(Ph) + 2H, 45%), 249.1 (M+ - (Ph)(1-Np)PCH2, 31%), 233.1
(M+ - (Ph)(1-Np)PC2H4 - 2H, 91%), 149.1 (P(Ph)(C3H5)+,
100%). Anal. Calcd for C34H28P2‚0.2CH2Cl2: C, 79.68; H, 5.86.
Found: C, 79.86; H, 5.55.
(l)+(u )-[(BH 3)(P h )(1-Np )P CH 2CH 2P (BH 3)(P h )(1-Np )],
(l)+(u )-1a ‚(BH3)2. The diastereomeric mixture was prepared
as described for (S,S)-(bnpe)(BH3)2, but starting from (rac)-
P(BH3)(Me)(Ph)(1-Np) (210 mg). Yield: 138 mg (66%). 1H NMR
(CDCl3): (u)-isomer (50%): 2.76 (br, 2 H, PCHH′), 2.42 (br, 2
H, PCHH′); (l)-isomer (50%): δ 2.60 (s, 4 H, PCHH′). 31P NMR
(CDCl3): δ 18.31 (br, 2P, (l)- and (u)-isomers not resolved).
Analytic and MS properties are as given for (S,S)-1a ‚(BH3)2.
tr a n s-[Ru Cl2(bn p e)2], 2a . [RuCl2(PPh3)3] (240 mg, 0.25
mol) and (S,S)-bnpe (250 mg, 0.5 mmol, 2 equiv) were placed
in a Schlenk tube, and CH2Cl2 (5 mL) was added. The resulting
solution was then stirred at room temperature for 6 h before
it was reduced in volume to ∼1 mL. Upon addition of diethyl
ether (10 mL) and partial evaporation of the solvents, a light
brown precipitate was formed, which was filtered off, washed
Exp er im en ta l Section
Gen er a l Com m en ts. Reactions with air- or moisture-
sensitive materials were carried out under an argon atmo-
sphere using standard Schlenk techniques. Olefins and sol-
vents were purified according to standard procedures. Yields
1
of complexes are based on ruthenium. H, 31P, and 13C NMR
spectra were measured on a Bruker DPX 250 spectrometer.
1H (and 13C) and 31P positive chemical shifts in ppm are
downfield from tetramethylsilane and external 85% H3PO4,
respectively. The 1H and 31P NMR spectra of the PfBH3
borane adducts P(BH3)(Me)(Ph)(1-Np) and 1a ‚(BH3)2 are par-
tially relaxed, non-binomial 1:1:1:1 quartets due to coupling
to 11B (80.1% natural abundance). The J B,H and J P,B coupling
constants were measured between the central peaks. Mass
spectra were measured by the MS service of the Laboratorium
fu¨r Organische Chemie (ETH Zu¨rich) using a ZAB VSEQ mass
spectrometer. A 3-NOBA (3-nitrobenzyl alcohol) matrix and a
Xe atom beam with a translation energy of 8 keV were used
for FAB+ MS. Gas chromatographic analyses were performed
using a Carlo Erba 6000 Vega Series gas chromatograph and
a Fisons Instruments GC 8000 Series gas chromatograph, both
equipped with an FID detector. Species identification was
made by comparison with authentic samples. HPLC was
performed on a Hewlett-Packard 1050 chromatograph equipped
with a variable wavelength detector and Daicel Chiralcel OD-H
(44) Sinigalia, R.; Michelin, R. A.; Pinna, F.; Strukul, G. Organo-
metallics 1987, 6, 728.
(45) Barthazy, P.; Wo¨rle, M.; Mezzetti, A. J . Am. Chem. Soc. 1999,
121, 480.
(46) However, metal-PhIO adducts have been suggested to react
with olefins without the intermediacy of a metal-oxo species: Yang,
Y.; Diederich, F.; Valentine, J . S. J . Am. Chem. Soc. 1991, 113, 7195.
(47) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.

Five-Coordinate [RuCl(P-P*)2]+ Complexes
Organometallics, Vol. 18, No. 26, 1999 5699
with hexane, and dried in a vacuum. Yield: 203 mg (69%). 1H
NMR (CDCl3): δ 8.5-6.5 m (48 H, Ph and 1-Np), 3.12 d (br)
(4 H, PCHH′), 2.53 d (br) (4 H, PCHH′). 31P{1H} NMR
(CDCl3): δ 38.4 (s). MS (FAB+): m/z 1168.2 (M+, 12%), 1133.2
(M+ - Cl + H, 68%), 1097.2 (M+ - 2Cl - H, 100%), 861.2 (M+
- P(1-Np)(Ph)H, 25%), 634.0 (M+ - Cl + H - bnpe, 40%),
599.1 (M+ - 2Cl + H - bnpe, 74%). Crystals contain one mole
equatorial Ph, p-CH), 2.6-2.2 (br m, 6 H, PCHH′); -70 °C: δ
9.17 (d, 2 H, Np-CH, J H,H ) 8.6 Hz), 7.37 (br, 2 H, equatorial
Ph, C8H), 7.3-6.6 (m, 40 H, arom), 6.30 (br, 2 H, equatorial
Np, C2H), 5.90 (t, 2 H, equatorial Ph, p-CH), 2.6-2.2 (br m, 6
H, CHH′), 2.0-1.7 (br m, 2 H, CHH′). 31P{1H} NMR (CD2Cl2):
δ 65.37 (t, AA′ part of AA′XX′, 2P, J P,P′ ) 17.5 Hz), 46.6 (t, XX′
part of AA′XX′, 2P, J P,P′ ) 17.5 Hz), δ -144.6 (septet, PF6, J P,F
) 713 Hz). UV-visible (CH2Cl2), λ (nm) (ꢀmax (mol-1 cm-1)):
350 (sh), 450 (1920), 555 (910), 630 (sh). MS (FAB+): m/z
1
of H2O per mole of complex, as confirmed by H NMR. Anal.
Calcd for C68H56Cl2P4Ru‚H2O: C, 68.80; H, 4.92. Found: C,
68.86; H, 4.83.
1133.2 (M+, 91%), 1097.2 (M+ - Cl - H, 100%), 599.1 (M+
-
2Cl - H - bnpe, 16%). Anal. Calcd for C68H56ClF6P5Ru‚H2O:
C, 62.99; H, 4.51. Found: C, 63.13; H, 4.46.
X-r a y of [Ru Cl(bn p e)2][P F 2O2], 3a . Red crystals were
obtained by diffusion of hexane into a CDCl3 solution of 3a .
X-r a y of [Ru Cl2(bn p e)2], 2a . Crystals of 2a were obtained
by diffusion of hexane into a CDCl3 solution of 2a at room
temperature. Crystal data: C58H56Cl2P4Ru orange platelet, M
)1168.98, T ) 293 K, orthorhombic, P212121, a ) 11.5658(4)
Å, b ) 22.6250(9) Å, c ) 22.8667(9) Å, V ) 5983.7(4) Å3, F(000)
Crystal data:
C138H119Cl6F10O10P13Ru2, red platelet, M )
) 2408, Z ) 4, Dc ) 1.298 Mg m-3, µ(Mo KR) ) 0.498 mm-1
,
2944.78, T ) 293 K, tetragonal, P41, a ) 17.3249(5) Å, b )
crystal size 0.70 × 0.60 × 0.32 mm3, Siemens SMART platform
with CCD detector, normal focus molybdenum-target X-ray
tube, graphite monochromator, ω-scans, h, -14 to 14, k, 0 to
28, l, 0 to 28; 37 098 reflections for 1.27° < θ < 26.37° (12 239
unique). Unit cell dimensions determination and data reduc-
tion were performed by standard procedures, and an empirical
absorption correction (SADABS) was applied. The structure
was solved with SHELXS-96 using direct methods and refined
by full-matrix least-squares on F2 with anisotropic displace-
ment parameters for all non-H atoms. Hydrogen atoms were
introduced at calculated positions on nondisordered C atoms
of the cation and refined with the riding model and individual
isotropic thermal parameters. R1 ) 0.0468 and wR2 ) 0.1363
(9871 unique reflections with I > 2σ(I)), R1 ) 0.0671, and wR2
) 0.1498 (all data), GOF ) 1.162. Max. and min. difference
peaks 1.189 and -0.398 e Å-3, largest and mean ∆/σ were
0.230 and 0.007. Selected bond lengths and angles are given
in Table 1.
[Ru Cl2(ch ir a p h os)2], 2b. [RuCl2(PPh3)3] (224 mg, 0.23
mmol) and (S,S)-chiraphos (200 mg, 0.45 mmol) were dissolved
in CH2Cl2 (5 mL). After stirring the red-brown solution for 4
h, hexane (10 mL) was added, and CH2Cl2 was evaporated in
a vacuum. The resulting light yellow precipitate was filtered
off, washed with hexane, and dried in a vacuum. 1H NMR
spectroscopy shows that the solid contains 1 mol CH2Cl2 per
mole of complex. Yield: 230 mg (90%). 1H NMR (CDCl3): 7.8-
6.7 (m, 40 H, arom), 2.9-2.7 (br m, 4 H, PCH), 0.65 (br m, 12
H, CH3). 31P{1H} NMR (CDCl3): δ 47.0 (s, 4P). Anal. Calcd
for C56H56Cl2P4Ru‚CH2Cl2: C, 61.69; H, 5.27. Found: C, 61.42;
H, 5.35.
X-r a y of [Ru Cl2(ch ir a p h os)2], 2b. Crystals of 2b were
obtained by diffusion of Et2O into a CDCl3 solution of 2b.
Crystal data: C112H112Cl4P8Ru2, orange platelet, M ) 2049.72,
T ) 293 K, monoclinic, P21, a ) 13.3497(5) Å, b ) 17.9236(7)
Å, c ) 20.3450(7) Å, V ) 4 858.9(3) Å3, F(000) ) 2120, Z ) 4,
Dc ) 1.401 Mg m-3, µ(Mo KR) ) 0.602 mm-1, crystal size 0.64
× 0.28 × 0.22 mm3, Siemens SMART platform with CCD
detector, normal focus molybdenum-target X-ray tube, graph-
ite monochromator, ω-scans, h, -17 to 16, k, -24 to 22, l, -25
to 26; 35 285 reflections for 1.00° < θ < 29.98° (20 542 unique).
Data reduction and structure solution and refinement were
as described above for 2a . R1 ) 0.0388 and wR2 ) 0.0688
(11 643 unique reflections with I > 2σ(I)), R1 ) 0.0989, and
wR2 ) 0.0848 (all data), GOF ) 0.921 Max. and min. difference
peaks 0.584 and -0.571 e Å-3, largest and mean ∆/σ were
0.184 and 0.008. Selected bond lengths and angles are given
in Table 2.
17.3249(5) Å, c ) 45.528(2) Å, V ) 13665.4(8) Å3, F(000) )
6008, Z ) 4, Dc ) 1.431 Mg m-3, µ(Mo KR) ) 0.561 mm-1
,
crystal size 0.38 × 0.20 × 0.04 mm3, Siemens SMART platform
with CCD detector, normal focus molybdenum-target X-ray
tube, graphite monochromator, ω-scans, h, -11 to 12, k, 0 to
17, l, -45 to 34; 11 094 reflections for 2.53° < θ < 20.81°
(11 094 unique). Data reduction and structure solution and
refinement were as described above for 2a . R1 ) 0.0764 and
wR2 ) 0.1826 (8788 unique reflections with I > 2σ(I)), R1 )
0.0991 and wR2 ) 0.1970 (all data), GOF ) 1.094. Max. and
min. difference peaks 0.725 and -0.624 e Å-3, largest and
mean ∆/σ were 0.007 and 0.062. Selected bond lengths and
angles are given in Table 2.
[Ru Cl(ch ir a p h os)2]P F 6, 3b. trans-[RuCl2(chiraphos)2] (2b)
(130 g, 0.126 mmol) and Tl[PF6] (82 mg, 0.192 mmol) were
stirred in CH2Cl2 (5 mL) for 12 h. The resulting dark brown
solution was filtered to remove TlCl, and hexane (10 mL) was
added. Partial evaporation of the solvents yielded a brown
1
solid, which was filtered off and dried in a vacuum. H NMR
spectroscopy shows that the solid contains CH2Cl2 (1 mol) and
hexane (1 mol, per mole of complex). Yield: 103 mg (62%). 1H
NMR (CD2Cl2): D2-symmetric dimer 4a (95%), δ 7.8-6.7 (m,
80 H, aromatic), 3.2 (br m, 4 H, PCH), 2.5 (br m, 4 H, PCH′),
0.95-0.75 (br m, 24 H, CH3). 31P{1H} NMR (CD2Cl2): D2-
symmetric dimer 4a (95%), δ 51.9 (t, 2P, J P,P′ ) 22.6 Hz), 38.6
(t, 2P, J P,P′ ) 22.6 Hz); C2-symmetric dimer 4b (5%), δ 52.6 (t,
2P, J P,P′ ) 27.8 Hz), 47.1 (t, 2P, J P,P′ ) 27.8 Hz), 40.8 (t, 2P,
J P,P′ ) 21.4 Hz), 38.1 (t, 2P, J P,P′ ) 21.4 Hz); -144.6 (septet,
1P, J P,F ) 713 Hz, PF6). 31P{1H} NMR (CDCl3): monomer 3b
(47%): δ 63.2 (br, 2P), 58.6 (br, 2P); D2-symmetric dimer 4a
(48%), δ 51.9 (t, 2P, J P,P′ ) 22.6 Hz), 38.6 (t, 2P, J P,P′ ) 22.6
Hz); C2-symmetric dimer 4b (5%), 52.6 (t, 2P, J P,P′ ) 27.8 Hz),
47.1 (t, 2P, J P,P′ ) 27.8 Hz), 40.8 (t, 2P, J P,P′ ) 21.4 Hz), 38.1
(t, 2P, J P,P′ ) 21.4 Hz); -144.6 (septet, 1P, J P,F ) 713 Hz, PF6).
MS (FAB+): m/z 1025.9 (M+ + HCl, 6%), 989.0 (M+, 54%),
952.9 (M+ - HCl, 100%). MS (ESI, CH2Cl2): m/z 953.4 (M+
-
HCl, 100%). Anal. Calcd for C56H56ClF6P5Ru‚C6H14‚CH2Cl2: C,
57.96; H, 5.56. Found: C, 57.44; H, 5.35.
[Ru Cl(CO)(bn p e)2]P F 6, 5a . A CDCl3 solution of 3a (23 mg,
18 µmol) was saturated with CO gas. The solution color turned
from brown to pale yellow after 12 h at 50 °C. Evaporation of
1
the solvent gave a pale yellow solid in quantitative yield. H
NMR (CDCl3): δ 8.3-6.5 (m, 48 H, arom), 3.40 (br, 2 H,
PCHH′), 3.03 (br, 2 H, PCHH′) 2.70 (br, 2 H, PCHH′), 2.02
(br, 2 H, PCHH). 31P{1H} NMR (CDCl3): δ 48.08 (t, AA′ part
of AA′XX′, 2P, J P,P′ ) 19.2 Hz), 32.1 (t, XX′ part of AA′XX′, 2P,
J P,P′ ) 19.2 Hz), δ -144.6 (septet, PF6, J P,F ) 713 Hz). 13C{1H}
NMR (CDCl3): δ 201.3 (br, 1C, CO). MS (FAB+): m/z 1161.1
(M+, 100%), 1098.0 (M+ - Cl - CO, 6%), 599.0 (M+ - Cl -
CO-bnpe, 64%).
[Ru Cl(bn p e)2]P F 6, 3a . trans-[RuCl2(bnpe)2] (2a ) (200 mg,
0.17 mol) and Tl[PF6] (110 mg, 0.192 mmol) were stirred in
CH2Cl2 (5 mL) for 12 h. The resulting dark brown solution
was filtered to remove the white precipitate TlCl, and to the
filtrate was added Et2O (10 mL). Evaporation of the solvents
in a vacuum gave a brown solid, which was subsequently dried
[Ru Cl(CO)(ch ir a p h os)2]P F 6, 5b. A CDCl3 solution of 3b
(22 mg, 19 µmol) was saturated with CO gas. The solution color
turned instantaneously from brown to yellow. Evaporation of
1
1
in a vacuum. Yield: 170 mg (88%). H NMR (CD2Cl2, 20 °C):
the solvent gave a pale yellow solid in quantitative yield. H
δ 9.17 (d, 2 H, arom), 8.4-6.5 (m, 44 H, arom), 5.90 (t, 2 H,
NMR (CDCl3): δ 8.0-6.5 (m, 40 H, arom), 3.2 (br s, 2 H, PCH),

5700 Organometallics, Vol. 18, No. 26, 1999
Stoop et al.
2.4 (br s, 2 H, PCH′), 0.8 (br m, 12 H, CH3). 31P{1H} NMR
(CDCl3): δ 56.2 (t, AA′ part of AA′XX′, 2P, J P,P′ ) 22.4 Hz),
34.4 (t, XX′ part of AA′XX′, 2P, J P,P′ ) 22.4 Hz), δ -144.6
(septet, PF6, J P,F ) 713 Hz). 13C{1H} NMR (CDCl3): δ 199.8
(br, 1C, CO). MS (FAB+): m/z 1017.2 (M+, 100%), 953.2 (M+
- CO - H - Cl, 65%), 591.0 (M+ - chiraphos, 14%), 527.0
(M+ - CO - H - Cl - chiraphos, 34%).
stirring the solution for 5 min, PhIO (440 mg, 2.0 mmol) was
added in portions (13 × 34 mg) during 6 h. The reaction
solution was analyzed over 7 h reaction time by GC. Achiral
GC: fused silica capillary column (Supelco Optima δ-3). Chiral
GC: R-cyclodextrin capillary column (Supelco Alpha Dex).
Results are reported in Table 5. Olefin conversion is defined
as the percentage of converted olefin, and the percent selectiv-
ity to product a is calculated as (mol(a)/mol(converted olefin))
× 100. The GC peaks of the enantiomeric epoxides were
attributed by comparison with authentic samples of the
racemates. Details of GC analyses are given in the Supporting
Information. Monitoring of styrene epoxidation by NMR
spectroscopy was as follows. A CDCl3 solution (1 mL) contain-
ing 3a (2 µmol) and styrene (100 µmol) was placed in an NMR
tube under argon, and PhIO (15 mg, 68 µmol) was added
thereto. The resulting slurry was shaken at room temperature,
and the reaction was periodically checked by 1H and 31P NMR
spectroscopy.
Ca ta lytic Cyclop r op a n a tion . A standard procedure was
as follows. A CH2Cl2 solution (1 mL) of ethyl diazoacetate (114
mg, 1 mmol) was added dropwise over 4 h to a CH2Cl2 solution
(5 mL) containing styrene (2.08 g, 20 mmol), the catalyst (0.01
mmol), and decane (1 mmol) as internal GC standard. The
reaction solutions were kept under argon and at the desired
temperature by means of a thermostatic bath. The evolution
of N2 gas was observed during the reaction. The reaction
solutions were analyzed periodically by GC up to a total
reaction time of 6 h. Achiral GC: fused silica capillary column
(Macherey Nagel SE 54). Chiral GC: â-cyclodextrin capillary
column (Supelco Beta Dex). Details of GC analyses are given
in the Supporting Information. Results are reported in Table
4. Conversion is based on ethyl diazoacetate. The percent
selectivity to product a is defined as (mol(a)/mol(converted
diazoacetate)) × 100. The GC peak of trans-2-phenylcyclopro-
panecarboxylate ethyl ester was attributed by comparison with
an authentic sample with a E/ Z ratio of 99:1 (Lancaster). The
latter was also used as authentic sample for chiral GC
analysis. The absolute configuration of the cyclopropanation
product was not determined.
Ack n ow led gm en t. R.M.S. and T.Y.H.W. acknowl-
edge the Swiss National Science Foundation for finan-
cial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement parameters, atomic coordinates,
bond lengths and angles, anisotropic displacement parameters,
and hydrogen coordinates of 2a ,b and 3a , and details of
catalytic reactions. This material is available free of charge
via the Internet at http://pubs.acs.org.
Ca ta lytic Ep oxid a tion . A typical procedure was as follows.
The olefin (freshly filtered over alumina, 1.0 mmol), decane
(as internal GC standard, 35 mg), and 3a -c (0.01 mmol, 1
mol %) were dissolved in CH2Cl2 (5 mL) under argon. After
OM990657X