Diastereoselectivity in chiral osmium complexes of a bidentate bisphosphine monoxide ligand

Article abstract of DOI:10.1021/om000083s

The chelation of [(η⁶-Cy)OsL] fragments (Cy = cymene; L = monodentate ligand) by bisphosphine monoxide ligands generates chiral-at-metal complexes. If the bisphosphine monoxide backbone contains a chiral center, diastereomeric products are formed. Osmium complexes of this type prepared using rac-Ph₂PCH(Me)P(O)Ph₂ epimerize to form a preferred isomer in which the methyl group is distal to L. This has been observed for the analogous ruthenium complexes, but the interconversion of diastereomers occurs at a greatly reduced rate. The slower interconversion allows spectroscopic characterization of the thermodynamically less favored isomers, as the corresponding ruthenium species are too short-lived for such investigations.

Full text of DOI:10.1021/om000083s

3556
Organometallics 2000, 19, 3556-3561
Dia ster eoselectivity in Ch ir a l Osm iu m Com p lexes of a
Bid en ta te Bisp h osp h in e Mon oxid e Liga n d
J . W. Faller*,† and J onathan Parr‡
Department of Chemistry, Yale University, 225 Prospect Street,
New Haven, Connecticut 06520, and Department of Chemistry, Loughborough University,
Loughborough, Leicestershire LE11 3TU, U.K.
Received February 1, 2000
The chelation of [(η6-Cy)OsL] fragments (Cy ) cymene; L ) monodentate ligand) by
bisphosphine monoxide ligands generates chiral-at-metal complexes. If the bisphosphine
monoxide backbone contains a chiral center, diastereomeric products are formed. Osmium
complexes of this type prepared using rac-Ph2PCH(Me)P(O)Ph2 epimerize to form a preferred
isomer in which the methyl group is distal to L. This has been observed for the analogous
ruthenium complexes, but the interconversion of diastereomers occurs at a greatly reduced
rate. The slower interconversion allows spectroscopic characterization of the thermodynami-
cally less favored isomers, as the corresponding ruthenium species are too short-lived for
such investigations.
In tr od u ction
We have recently reported on the utility of bisphos-
phine monoxide (BPMO) complexes of ruthenium in
asymmetric catalysis1 and on their diastereoselective
isomerization behavior.2 To investigate the behavior of
analogous osmium complexes of BPMOs, we have
prepared a series of compounds using the ligand rac-
(Ph2PCH(Me)P(O)Ph2). Although a number of groups
have prepared complexes with this3 and other BPMO
ligands,4 we believe this to be the first report of fully
characterized osmium(II) BPMO complexes.
F igu r e 1. ORTEP diagram of 1 showing 50% probability
ellipsoids. The compound is racemic, and the (SC)-enanti-
omer is shown. Note that the chirality descriptor at carbon
changes upon binding of the ligand; hence the (RC)-BPMO
free ligand becomes (SC) when the phosphine binds to a
transition metal.
Resu lts
Syn th esis of [(η6-Cy)OsCl2(η1-P h 2P CH(Me)P (O)-
P h 2-P )] (1). The interaction of [CyOsCl2]2 with rac-(Ph2-
PCH(Me)P(O)Ph2) in a mole ratio of 1:2 yields [(η6-
Cy)OsCl2(η1-Ph2PCH(Me)P(O)Ph2-P)], 1, Scheme 1. The
complex exhibits characteristic NMR behavior, the 31P
spectrum showing a distinct downfield coordination shift
for the resonance of the coordinated P(III) of 4.74 ppm
and a reduction in the coupling between the phosphorus
nuclei of 43 Hz. The molecular structure was deter-
mined by single-crystal X-ray diffraction, and the results
are shown in Figure 1, with data collection parameters
given in Table 1 and metrical parameters in Table 2.
Unlike the previously reported ruthenium analogue,2
compound 1 in solution shows no propensity to dissoci-
ate one of the chloro ligands with concomitant chelation
of the phosphine oxide terminus of the ligand, even after
prolonged storage as a solution in a polar solvent.
Syn th esis of [(η6-Cy)OsCl(η2-P h 2P CH(Me)P (O)-
P h 2-P ,O)][SbF 6] (2). Treatment of 1 with 1 equiv of
AgSbF6 in dichloromethane solution leads to chloride
abstraction and chelation of the BPMO by coordination
of the phosphine oxide terminus at the vacant site
generated forming [(η6-Cy)OsCl(η2-Ph2PCH(Me)P(O)-
Ph2-P,O)][SbF6], Scheme 1. The chelation creates a
chiral center at the osmium and, in conjunction with
the chirality of the ligand, the possibility of diastereo-
† Yale University.
‡ Loughborough University.
(1) Faller, J . W.; Parr, J . Organometallics 2000, 19,
(2) Faller, J . W.; Patel, B.; Albrizzio, M. A.; Curtis, M. Organome-
tallics 1999, 18, 3096. This paper gave the configuration of the BPMO
ligand as that of the free phosphine and did not follow the strict
chirality descriptor conventions. Note that the chirality descriptor at
carbon changes upon binding of the ligand; hence the (RC)-BPMO free
ligand becomes (SC) when the phosphine binds to a transition metal.
(3) Grim, S. O.; Satek, L. C.; Tolman, C. A.; J esson, J . P. Inorg.
Chem. 1975, 14, 656.
(4) (a) Coyle, R. J .; Slovokhotov, Y. L.; Grushin, V. Polyhedron 1998,
17, 3059. (b) Brassat, I.; Englert, U.; Keim, W.; Keitel, D. P.; Killat,
S.; Suranna, G. P.; Wang, R. Inorg. Chim. Acta 1998, 280, 150. (c)
Blagborough, T. C.; Davis, R.; Ivison, P. J . Organomet. Chem. 1994,
467, 85. (d) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. Inorg. Chim.
Acta 1993, 212, 23. (e) Rossi, R.; Marchi, A.; Marvelli, L.; Magon, L.;
Peruzzini, M.; Casellato, U.; Graziani, R. Inorg. Chim. Acta 1993, 204,
63. (f) Katti, K. V.; Barnes, C. L. Inorg. Chem 1992, 31, 4231. (g)
Fontaine, X. L. R.; Fowles, E. H.; Layzell, T. P.; Shaw, B. L.; Thornton-
Pett, M. J . Chem. Soc., Dalton Trans. 1991, 1519. (h) Darensbourg,
D. J .; Zalewski, D. J .; Plepys, C.; Campana, C. Inorg. Chem. 1987, 26,
3727. (i) Higgins, S. J .; Taylor, R.; Shaw, B. L. J . Organomet. Chem.
1987, 325, 285.
10.1021/om000083s CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/01/2000

Diastereoselectivity in Chiral Os Complexes
Organometallics, Vol. 19, No. 18, 2000 3557
Sch em e 1. P r ep a r a tion of 1-6a
a
All reactions performed in dichoromethane at ambient temperature
Ta ble 1. Cr ysta llogr a p h ic Da ta for X-r a y Diffr a ction Stu d ies of CyOsCl2(P h 2P CH(Me)P h 2P O), 1,
[CyOsCl(P h 2P CH(Me)P h 2P O)]SbF 6‚CH2Cl2, 2a , a n d
[CyOs(P h 2P CH(Me)P h 2P O)(P h CHdCHCHO)](SbF 6)2‚CH2Cl2, 4a
1
2a
4a
formula
cryst system
space group
a, Å
b, Å
c, Å
Os Cl2P2OC36H38
monoclinic
C2/c (No. 15)
31.8120(7)
9.6759(2)
21.4873(6)
98.205(1)
6546.3(2)
-90
809.75
1.643 (Z ) 8)
41.83
OsSbCl3P2F6OC37H40
orthorhombic
Pca21 (No. 29)
17.7581(4)
11.4938(3)
19.3382(4)
90
3947.1(3)
-90
1094.97
1.842 (Z ) 4)
42.39
0.24 × 0.24 × 0.35
Nonius KappaCCD
graphite
OsSb2Cl2P2F12O2C46H48
monoclinic
C2/c (No. 15)
40.2616(6)
14.1613(2)
20.1604(4)
117.2093(9)
10222.6(3)
-90
â, deg
V, Å3
temp, °C
fw
1427.42
F
calcd, g/cm3
1.855 (Z ) 8)
37.73
0.48 × 0.19 × 0.07
abs coeff (cm-1
cryst size, mm
diffractometer
)
0.12 × 0.17× 0.24
monochromator
radiatn
max 2θ, deg
Mo KR (0.71073 Å)
54.9
55.0
55.0
refl measrd (unique)
data used, F2 > 3σ(F2)
no. of params refined
p factor
28608 (7956)
5077
379
19973 (5025)
4029
459
55894(12169)
6625 (>5σ)
600
0.01
0.01
0.01
final residuals R, Rw
convergence, largest shift/error
GOF
0.032, 0.029
0.00
1.19
0.042, 0.041
0.00
1.89
0.037, 0.046
0.00
1.42
largest ∆(F), e- Å-3
0.85
2.97
1.93
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 1, 2a , a n d 4a
1
2a
4a
Os(1)-Cl(1)
2.408(1)
2.423(1)
2.372(1)
2.382(3)
Os(1)-Cl(2)
Os(1)-P(1)
2.344(2)
2.136(6)
2.362(2)
2.115(4)
2.125(4)
1.530(5)
Os(1)-O(1)
Os(1)-O(2)
P(2)-O(1)
1.486(3)
86.44(4)
87.26(4)
87.34(4)
1.529(7)
Cl(1)-Os(1)-Cl(2)
Cl(1)-Os(1)-P(1)
Cl(2)-Os(1)-P(1)
Cl(1)-Os(1)-O(1)
P(1)-Os(1)-O(1)
P(1)-Os(1)-O(2)
O(1)-Os(1)-O(2)
Os(1)-O(1)-P(2)
85.75(10)
86.3(2)
81.2(2)
82.6(1)
80.8(1)
81.9(1)
124.2(2)
F igu r e 2. Complexes 2-6. Only one diastereomer of each
enantiomeric pair is shown.
124.7(4)
and 36.5 and 52.8 ppm for the P(V) resonances, respec-
1
mers. In fact, the product exists as two sets of enantio-
meric diastereomers, 2a and 2b (Figure 2). The two sets
of diastereomers have distinct NMR spectra, and so an
accurate ratio of 2a :2b of 3.8:1 is readily obtained. This
value remains constant over extended periods of time
(>72 h), indicating that the rate of epimerization is slow
with respect to that seen for the corresponding ruthe-
nium complexes where one set of enantiomers is seen
to form exclusively. The 31P NMR spectra of 2a and 2b
show characteristic downfield shifts of 23.9 and 28.9
ppm for the P(III) resonances compared to compound 1
tively. In the H NMR, there is a distinct upfield shift
of the resonance of the methine proton on the backbone
of the ligand from δ 5.30 in 1 of 0.86 ppm in 2a and
1.54 ppm in 2b, entirely consistent with chelation.
Crystallization of pure 2a , vida infra, provided a defini-
tive structure correlation with NMR, since the diaste-
reomer interconversion is slow. The structure of 2a is
shown in Figure 3. The methyl groups of the isopropyl
substituent of the cymene ring are diastereotopic in 1,
and the differences in chemical shifts become even more
pronounced in both isomers of 2.

3558 Organometallics, Vol. 19, No. 18, 2000
Faller and Parr
F igu r e 3. ORTEP diagram of cation 2a showing 50%
probability ellipsoids. The compound is racemic, and the
(ROs,SC)-enantiomer is shown.
Syn th esis of [(η6-Cy)Os(η2-P h 2P CH(Me)P (O)P h 2-
P ,O)][SbF 6]2 (3). Treatment of 1 with 2 equiv of AgSbF6
leads to removal of both chloro ligands and the chelation
of the BPMO, forming 3a and 3b, Scheme 1 and Figure
2. The complexes are formally coordinatively unsatur-
ated doubly charged 16-electron Lewis acids, but since
again two sets of resonances are seen in the NMR
spectra, it can reasonably be inferred that the cations
are weakly coordinated to either a molecule of solvent
or a counterion or involve a weak agostic interaction. If
this were not the case, the cation would be effectively
“square planar” (or possibly rapidly equilibrating be-
tween two configurations), and therefore there would
only be a single isomer seen.5 The ratio of 3a :3b of 1.4:1
reflects the lower barrier to epimerization accessible via
a “swing” mechanism in the 16-electron intermediate
when the ligand L in Figure 2 is a weakly coordinated
solvent molecule. This contrasts with the case where L
is a nonlabile group, such as the chloro ligand in 2a and
2b.
F igu r e 4. ORTEP diagram of 4a showing 50% probability
ellipsoids. The phenyl groups of the phosphines are omitted
for clarity. The compound is racemic, and the (ROs,SC)-
enantiomer is shown.
largest group on the backbone of the ligand away from
the monodentate ligand.2
The orientation of the coordinated cinnamaldehyde
is controlled by both steric and electronic considerations.
The difference between the P and O donors of the
chelating ligand influences which of the metals d-
orbitals interact with the p-orbitals of the carbonyl
function of the aldehyde. This confers a preferential
alignment of the carbonyl group with respect to the
metal (torsion angle P1-Os-O2-C ) 153.2(5)°), and
the proximity of the phenyl rings on the P(III) force the
phenyl substituent on the aldehyde to adopt a transoid
disposition in order to minimize steric conflict. The only
arrangement that meets these criteria is that seen in
the structure of 4a , Figure 4.
The metrical data shown in Table 2 allow comparison
of the compounds. As might be expected, the P-O bond
lengthens upon coordination. The bite angle of the
BPMO is rather small, 81.2° and 82.6° for 2a and 4a ,
respectively. All of the angles involving the legs of the
“three-legged piano stool” structure are less than 90°.
The angles for P(1)-Os(1)-O(2) of 80.8° and O(1)-Os-
(1)-O(2) of 81.9° found in 4a are relatively small for
donors not constrained by a chelate.
The doubly charged Lewis acids 3 react with alde-
hydes in solution to form complexes of the general
formula [(η6-Cy)Os(η2-Ph2PCH(Me)P(O)Ph2-P,O)(alde-
hyde)][SbF6]2 (aldehyde ) trans-cinnamaldehyde, 4,
methacrolein, 5, and crotonaldehyde, 6). The aldehydes
used here all have the potential to act as ligands
coordinating to the osmium through either π-bonding
interactions, via the carbon-carbon double bond, or
σ-bonding, through the carbonyl oxygen. Simple hard-
soft arguments might predict that in such circumstances
an osmium(II) would preferentially bind an olefinic
double bond, but in fact in all cases the aldehyde co-
ordinates exclusively through the carbonyl oxygen. This
1
is established by comparison of the H NMR spectra of
4-6 with those of the corresponding ruthenium com-
plexes and the crystal structure of the trans-cinnama-
ldehyde complex 4a , Figure 4 and Tables 1 and 2.
Discu ssion
Coordinatively unsaturated 16-electron organometal-
lic complexes are not ordinarily expected to be stere-
ochemically rigid,6 although there are examples in the
literature of chiral species of this type that do not
undergo such racemizations.7,8 Complexes 3 have, if
taken as being only coordinated weakly by a solvent
molecule, the lowest energy pathway to interconversion
amongst the complexes reported here. This could involve
either a dissociation of the solvent to form a [(η6-
The relative configurations are found to be (ROs, SC)
and (SOs, RC) or (R*Os, S*C) for 4a . This configuration
allows the methyl group on the backbone of the ligand
to be oriented away from the coordinated aldehyde to
minimize steric conflict. Structural studies on ruthe-
nium complexes of this and other similarly substituted
BPMOs show similar preferences for orienting the
(5) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Chem. Soc., Chem.
Commun. 1988, 278. For amine coordinated examples, see: (a) Gemel,
C.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics 1997, 16,
5601. (b) Mauthner, K.; Slugovc, C.; Mereiter, K.; Schmid, R.; Kirchner,
K. Organometallics 1997, 16, 1956.
(6) (a) Ward, T. R.; Schafer, O.; Daul, C.; Hofmann, P. Organome-
tallics 1997, 16, 3207. (b) 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. (c) Hoffman, P. Angew. Chem., Int.
Ed. Engl. 1977, 16, 536.

Diastereoselectivity in Chiral Os Complexes
Organometallics, Vol. 19, No. 18, 2000 3559
Cy)Os(η2-Ph2PCH(Me)P(O)Ph2-P,O)]2+ ion with a plane
of symmetry, precedent for which in the case of related
ruthenium complexes can be found in the literature,6
or an η2-η1-η2 process of hemidissociation of the BPMO
followed by rechelation in the opposite sense. While it
is difficult to be certain, it seems from the observations
made here that the former mechanism is more likely
because of the relatively rapid rate of epimerization of
the aldehyde complex 4 (half-life 3 h.) compared to the
chloro complex 2 (half-life .72 h.). Coupled with this,
there is no spectroscopic evidence for the formation of
a cationic η1-BPMO complex, even in the presence of a
large excess of aldehydes (>10-fold). It is also more
reasonable to envisage a neutral monodentate ligand
dissociating more readily than one-half of a chelating
ligand.
F igu r e 5. ORTEP diagram of 1 showing 50% probability
ellipsoids illustrating the conformation of the phenyl rings.
The compound is racemic, and the (SC)-enantiomer is
shown. The cymene group has been omitted for clarity.
The low rate of interconversion allows observation,
at least in solution state, of the isomers not seen for
the corresponding ruthenium complexes. The 31P NMR
data for these reveal distinct differences in chemical
1
shift on changing the relative configuration. In the H
The question of the selectivity in the formation of the
original chelated complex of 2a over 2b arises in a way
which it does not for the ruthenium analogue. In that
case, the fast rate of epimerization does not allow the
opportunity to determine whether the initial chelation
occurs with any preference, but for osmium a definite
preference for the loss of one of the two chloro ligands
and subsequent chelation is observed. The activation of
one of these two seemingly equivalent ligands with
respect to the other may be linked to the preferred
disposition of the phenyl groups on the P(III) seen in
the η1 complex 1, which is in turn controlled by the
methyl group on the backbone of the ligand. Comparison
of the structure of 1 with that of the ruthenium
analogue and the hitherto unreported Cp*Rh(Cl)2 com-
plex of the same ligand reveals a definite and coherent
preference for the arrangement of the phenyl groups.
This carries the chiral information on the backbone of
the ligand into the inner coordination sphere of the
complex and may serve to activate one chloro over the
other. Figure 5 shows a view down the P-Os axis in
the structure of (SC)-1. One should note that one phenyl
is nearly parallel to the P-Os vector and the helicity of
the other phenyl is M, and this would appear to be
controlled by the stereochemistry at the bridging carbon.
The Os-Cl distances are significantly different, Os-
Cl1 ) 2.408(1) Å and Os-Cl2 ) 2.423(1) Å, and suggest
that one might be removed more readily than the other.
Some type of anchiomeric assistance could also be
involved from the tethered PO as a silver removes the
chloride. Regardless, the chlorides are diastereotopic
and would be expected to have different chemical
behavior. One might also note that the CyRuCl2(Ph2-
PCH2Ph2PO) crystallizes as a racemate considering the
configuration of the phenyls (which in the absence of a
backbone substituent would not have a preference for
P or M helicity). In this case the Ru-Cl distances are
2.403(1) and 2.423(2) Å.2
NMR spectra, the difference between the two types of
unique proton on the ligand is the most pronounced. The
chemical shifts differ by some 0.8 ppm and exhibit
distinct couplings, indicative of the different spatial
relationships of the spin-active nuclei.
All of the products reported here with the BPMO
chelated are a mixture of the two types of diastereomer,
the thermodynamically favored a and the less favored
b. For the latter group of products, the methyl group is
oriented toward the monodentate ligand L and so
creates steric conflict. This set of products was not
observed for the corresponding ruthenium species and
indicates the relative kinetic stability of the Os-L bond
compared to the Ru-L system, where dissociation of L
must be more readily achieved in order to allow the
faster epimerization. This is also seen in the absence of
the ionization of a chloro ligand from 1 to give the
osmium analogue of [(η6-Cy)RuCl(η2-Ph2PCH(Me)P(O)-
Ph2-P,O)]Cl.
The aldehyde complex 4a can be converted to the
chloro complexes 2 by dissolving it in a methanolic
solution of potassium chloride. The replacement of the
aldehyde is too rapid to follow by NMR, and the
formation of the chloro complex is complete within
minutes at room temperature. The ratio of 2a :2b in a
solution prepared in this way is 7.2:1, substantially
displaced from the 3.8:1 found for the chloro complex
prepared from 1. This suggests that the replacement of
the aldehyde by a chloro ligand occurs largely with
retention of configuration at the metal, since the pro-
portion of the thermodynamically preferred isomer is
enhanced. With the high concentration of 2a obtained
from this reaction, it is possible to obtain pure 2a by
recrystallization. This allowed the preparation of crys-
tals suitable for X-ray diffraction determination.
(7) (a) Dewey, M. A.; Stark, G. A.; Gladysz, J . A. Organometallics
1996, 15, 4798. (b) Fernandez, J . M.; Gladysz, J . A. Organometallics
1989, 8, 207.
(8) Faller, J . W.; Chase, K. J .; Mazzieri, M. R. Inorg. Chim. Acta
1995, 229, 39.
(9) (a) Bye, E.; Schweizer, W. B.; Dunitz, J . D. J . Am. Chem. Soc.
1982, 104, 5893. (b) Mislow, K. Acc. Chem. Res. 1976, 9, 26. (c) Mislow,
K.; Gust, D.; Finocchiaro, P.; Boettcher, R. J . Top. Curr. Chem. 1974,
47, 1. (d) Faller J . W.; J ohnson, B. V. J . Organomet. Chem. 1975, 90,
99.
A further comment on the helicity of the phenyl
groups is in order. When the P,O chelate is formed, it
forces a different orientation of the methyl owing to the
constraints of formation of the five-membered ring. In
this case the methyl group is synclinal to both phenyls,
whereas in the η1-complex the methyl is synclinal to one

3560 Organometallics, Vol. 19, No. 18, 2000
Faller and Parr
Lewis acidity of the osmium(II) center is sufficient to
force preferential coordination of carbonyl oxygen over
an olefinic double bond, a result unexpected for a third-
row transition metal in a low oxidation state.
Exp er im en ta l Section
Gen er a l P r oced u r es. All synthetic manipulations were
carried out under an atmosphere of oxygen-free nitrogen using
standard Schlenk and glovebox techniques. Diethyl ether and
dichloromethane were distilled over sodium benzophenone
ketyl and calcium hydride, respectively. Ethyl acetate, absolute
methanol, and hexanes were reagent grade and used without
3
further purification. The ligand Ph2PCH(Me)P(O)Ph2 and
11
[CyOsCl2]2 were prepared by modifications of published
procedures. trans-Cinnamaldehyde, methacrolein, crotonalde-
hyde, and silver hexafluoroantimonate were commercial (Al-
drich) and used as received. The NMR spectra were recorded
on a GE Omega 500 spectrometer (202.43 MHz for 31P), and
chemical shifts are reported in ppm relative to residual protio
solvent (1H) or external 85% H3PO4 (31P). Elemental analyses
were performed by Atlantic Microlabs.
F igu r e 6. ORTEP view of 2a showing 50% probability
ellipsoids illustrating the conformation of the phenyl rings.
The compound is racemic, and the (SC)-enantiomer is
shown. The cymene group has been omitted for clarity.
P r ep a r a tion of [(η6-Cy)OsCl2(η1-P h 2P CH(Me)P (O)P h 2-
P )] (1). To a solution of [(η6-Cy)OsCl2]2 (50 mg, 0.063 mmol)
in 10 mL of dichloromethane was added Ph2PCH(Me)P(O)Ph2
(52 mg, 0.126 mmol) as a solid. The resultant clear orange-
yellow solution was stirred at room temperature for 2 h before
removal of the solvent under reduced pressure. The pale yellow
solid residue was chromatographed over silica gel using 10%
ethyl acetate in hexanes as eluent. A yellow orange band was
collected and the solvent removed under reduced pressure to
yield a yellow solid, which was recrystallized from dichlo-
romethane/diethyl ether to give 82 mg of microcrystalline 1.
Yield: 80.4%. 1H NMR (CD2Cl2, 293 K, δ): 8.80-7.02 (20H,
m, arom), 5.72 (1H, d, J ) 6.7 Hz, Cy-H), 5.32 (1H, d, J ) 6.7
Hz, Cy-H), 5.30, (1H, qdd, obsc, HCP2) 5.29 (1H, d, J ) 6.7
Hz, Cy-H), 4.32 (1H, d, J ) 6.7 Hz, Cy-H), 2.92 (1H, hept., J
) 7.0 Hz, HC(CH3)2), 1.68 (3H, s, Cy-CH3), 1.31 (3H, d, J )
7.0 Hz, HC(CH3)(CH3)), 1.28 (3H, d, J ) 7.0 Hz, HC(CH3)-
2
2
(CH3)), 0.96 (3H, ddd, J ) 7.5, J H-P ) 13.2, J H-P ) 18.0 Hz,
HCP2(CH3)). 31P{1H} NMR: 33.29 (d, J ) 22 Hz, P(V)), -7.86
(d, J ) 22 Hz, P(III)). IR (KBr disk) ν(PdO): 1194 cm-1. Anal.
Calcd for C36H38OP2Cl2Os: C, 53.40; H, 4.73. Found: C, 52.94;
H, 4.81.
F igu r e 7. ORTEP view of 4a showing 50% probability
ellipsoids illustrating the conformation of the phenyl rings.
The compound is racemic, and the (SC)-enantiomer is
shown. The cymene group has been omitted for clarity.
P r ep a r a tion of [(η6-Cy)OsCl(η2-P h 2P CH(Me)P (O)P h 2-
P ,O)][SbF 6] (2). To a solution of 1 (25 mg, 0.031 mmol) in 3
mL of dichloromethane was added AgSbF6 (11 mg, 0.031 mmol)
in 2 mL of dichloromethane. A white precipitate of AgCl
formed, and after 30 min the mixture was centrifuged. The
supernatant was collected by syringe and the solvent removed
under reduced pressure. The solid yellow residue was recrys-
tallized from dichloromethane/diethyl ether to give 26 mg of
and anticlinal to the other. This induces a different
phenyl to be parallel to the P-Os vector and the other
to assume a P helicity. The orientations in the chloride,
2a , and cinnamaldehyde complex, 4a , are similar as
shown in Figures 6 and 7. The chirality imposed by
phenyl group orientation has been investigated previ-
ously9 and has been found important in explanations
of chiral induction with CHIRAPHOS.10 We anticipate
that it will play an important role in asymmetric
catalysis with BMPO ligands.
1
microcrystalline 2. Yield: 83.0%. H NMR (CD2Cl2, 293 K, δ):
2a 8.00-6.92 (20H, m, arom), 5.96 (1H, d, J ) 5.5 Hz, Cy-H),
5.94 (1H, d, J ) 5.5 Hz, Cy-H), 5.90 (1H, d, J ) 5.5 Hz, Cy-H),
5.82 (1H, d, J ) 5.5 Hz, Cy-H), 4.44 (1H, qdd, J ) 5.3 Hz,
2J H-P ) 10.0 Hz, 2J H-P ) 7.5 Hz, HC(CH3)P2), 2.38 (1H, hept.,
J ) 7.0 Hz, HC(CH3)2), 2.21 (3H, s, Cy-CH3), 1.24 (3H, ddd,
obsc, HCP2(CH3)), 1.09 (3H, d, J ) 7.0 Hz, HC(CH3)(CH3)),
0.81 (3H, d, J ) 7.0 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 72.65
(d, J ) 21 Hz, P(V)), 16.00 (d, J ) 21 Hz, P(III)); 2b 8.05-
6.92 (20H, m, arom), 5.60 (1H, d, J ) 5.5 Hz, Cy-H), 5.56 (1H,
d, J ) 5.5 Hz, Cy-H), 5.42 (1H, d, J ) 5.5 Hz, Cy-H), 5.39 (1H,
Con clu sion
We have shown that the osmium BPMO complexes
[(η6-Cy)Os(η2-Ph2PCH(Me)P(O)Ph2-P,O)(L)][SbF6]2 ex-
hibit a greatly reduced rate of epimerization compared
to those seen for the corresponding ruthenium com-
plexes. Further, although the rate is reduced, the
thermodynamically preferred isomer is that in which
the largest group on the backbone of the ligand is
oriented away from the monodentate ligand, the same
as that preferred in the ruthenium complexes. The
2
d, J ) 5.5 Hz, Cy-H), 3.76 (1H, qdd, J ) 5.5 Hz, J H-P ) 9.5
2
Hz, J H-P ) 4.6 Hz, H(CH3)CP2), 2.54 (1H, hept., J ) 7.0 Hz,
HC(CH3)2), 2.24 (3H, s, Cy-CH3), 1.27 (3H, ddd, obsc, HCP2-
(CH3)), 1.02 (3H, d, J ) 7.0 Hz, HC(CH3)(CH3)), 0.90 (3H, d, J
) 7.0 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 88.93 (d, J ) 20.5
Hz, P(V)), 22.38 (d, J ) 20.5 Hz, P(III)). IR (KBr disk) ν(PdO)
:
1120 cm-1 Anal. Calcd for C36H38OF6P2ClSbOs: C, 42.81; H,
3.79. Found: C, 43.26; H, 3.81.
(10) Bosnich, B.; Fryzuk, M. D. Top. Stereochem. 1981, 12, 119.

Diastereoselectivity in Chiral Os Complexes
Organometallics, Vol. 19, No. 18, 2000 3561
P r ep a r a t ion of [(η6-Cy)Os(η2-P h 2P CH (Me)P (O)P h 2-
P ,O)(SLV)][SbF 6]2 (3). To a solution of 1 (25 mg, 0.031 mmol)
in 3 mL of dichloromethane was added AgSbF6 (22 mg, 0.031
mmol) in 2 mL of dichloromethane. A white precipitate of AgCl
formed and after 30 min, and the mixture was centrifuged.
The supernatant was collected by syringe and the solvent
removed under reduced pressure. The yellow product proved
difficult to recrystallize and so was characterized by spectros-
6.5 Hz, Cy-H), 5.89 (1H, d, J ) 6.5 Hz, Cy-H), 5.81 (1H, d, J
) 6.5 Hz, Cy-H), 4.44 (1H, qdd, J ) 5.4, 2J H-P ) 10.0, 2J H-P
)
7.5 Hz, HC(CH3)P2), 2.38 (1H, hept., J ) 6.8 Hz, HC(CH3)2),
2.34 (3H, s, Cy-CH3), 1.84 (3H, s, CHdC(CH3)(CHO)), 1.24 (3H,
ddd, obsc, HCP2(CH3)), 1.08 (3H, d, J ) 6.8 Hz, HC(CH3)(CH3)),
0.86 (3H, d, J ) 6.8 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 73.60
(s, P(V)), 17.63 (s, P(III)). Anal. Calcd for C40H44O2F12P2Sb2-
Os: C, 37.52; H, 3.46. Found: C, 37.42; H, 3.63.
1
copy and used for further reactions in situ. H NMR (CD2Cl2,
6a : 9.27 (1H, d, J ) 8.8 Hz, CHO) 7.95-7.08 (20H, m, arom),
7.06 (1H, m, (CH3)CHCH(CHO), 6.10 (1H, m, (CH3)CHCH-
(CHO), 5.96 (1H, d, J ) 5.5 Hz, Cy-H), 5.94 (1H, d, J ) 5.5
Hz, Cy-H), 5.88 (1H, d, J ) 5.5 Hz, Cy-H), 5.81 (1H, d, J ) 5.5
Hz, Cy-H), 3.64 (1H, qdd, J ) 5.5, 2J H-P ) 9.5, 2J H-P ) 4.5 Hz,
HC(CH3)P2), 2.38 (1H, hept., J ) 7.0 Hz, HC(CH3)2), 2.26 (3H,
s, Cy-CH3), 2.05 (3H, dd, J ) 5.0, 1.6 Hz, (CH3)CHCH(CHO))
1.27 (3H, ddd, obsc, HCP2(CH3)), 1.16 (3H, d, J ) 7.0 Hz, HC-
(CH3)(CH3)), 0.84 (3H, d, J ) 7.0 Hz, HC(CH3)(CH3)). 31P{1H}
NMR: 73.65 (s, P(V)), 17.48 (s, P(III)); 6b 9.27 (1H, d, J ) 8.8
Hz, CHO) 7.95-7.08 (20H, m, arom), 7.10 (1H, m, (CH3)-
CHCH(CHO), 6.32 (1H, d, J ) 5.5 Hz, Cy-H), 6.20 (1H, d, J )
5.5 Hz, Cy-H), 6.15 (1H, d, J ) 5.5 Hz, Cy-H), 6.10 (1H, m,
(CH3)CHCH(CHO), 6.08 (1H, d, J ) 5.5 Hz, Cy-H), 4.46 (1H,
293 K, δ): 3a 8.10-7.22 (20H, m, arom), 6.32 (1H, d, J ) 6.5
Hz, Cy-H), 6.14 (1H, d, J ) 6.5 Hz, Cy-H), 5.96 (1H, d, J ) 6.5
Hz, Cy-H), 5.84 (1H, d, J ) 6.5 Hz, Cy-H), 3.57 (1H, qdd, J )
5.8 Hz, 2J H-P ) 9.6 Hz, 2J H-P ) 4.6 Hz, HC(CH3)P2), 2.39 (1H,
hept., J ) 7.2 Hz, HC(CH3)2), 2.09 (3H, s, Cy-CH3), 1.21 (3H,
ddd, obsc, HCP2(CH3)), 1.18 (3H, d, J ) 7.2 Hz, HC(CH3)(CH3)),
0.86 (3H, d, J ) 7.2 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 79.68
(s, P(V)), 23.53 (s, P(III)); 3b 8.10-7.22 (20H, m, arom), 6.39
(1H, d, J ) 6.5 Hz, Cy-H), 6.04 (1H, d, J ) 6.5 Hz, Cy-H), 5.94
(1H, d, J ) 6.5 Hz, Cy-H), 5.88 (1H, d, J ) 6.5 Hz, Cy-H), 4.41
2
2
(1H, qdd, J ) 5.4 Hz, J H-P ) 11.0 Hz, J H-P ) 7.2 Hz, HC-
(CH3)P2), 2.68 (1H, hept., J ) 7.0 Hz, HC(CH3)2), 2.11 (3H, s,
Cy-CH3), 1.38 (3H, ddd, obsc, HCP2(CH3)), 1.15 (3H, d, J )
7.0 Hz, HC(CH3)(CH3)), 0.91 (3H, d, J ) 7.0 Hz, HC(CH3)-
(CH3)). 31P{1H} NMR: 74.06 (s, P(V)), 18.14 (s, P(III)).
P r ep a r a t ion of [(η6-Cy)Os(η2-P h 2P CH (Me)P (O)P h 2-
P ,O)(a ld eh yd e)][SbF 6]2 (4-6). These complexes were pre-
pared in situ by the addition of the appropriate aldehyde to a
solution of 3 prepared as given above and were characterized
by NMR. Crystals of 4a were obtained by the vapor diffusion
of diethyl ether into a methanolic solution of 4a using a closed
2
2
qdd, J ) 5.3, J H-P ) 10.0, J H-P ) 7.5 Hz, HC(CH3)P2), 2.38
(1H, hept., J ) 6.8 Hz, HC(CH3)2), 2.26 (3H, s, Cy-CH3), 2.02
(3H, dd, J ) 5.0, 1.6 Hz, (CH3)CHCH(CHO)) 1.27 (3H, ddd,
obsc, HCP2(CH3)), 1.16 (3H, d, J ) 6.8 Hz, HC(CH3)(CH3)),
0.84 (3H, d, J ) 6.8 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 78.79
(s, P(V)), 26.29 (s, P(III)). The sample for analysis was
recrystallized from methylene chloride/diethyl ether. Anal.
Calcd for C40H44O2F12P2Sb2Os. C2H5O0.5: C, 38.29; H, 3.75.
Found: C, 38.48; H, 3.76.
1
concentric vial arrangement. H NMR (CD2Cl2, 293 K, δ): 4a
9.46 (1H, d, J ) 9.0 Hz, CHO) 7.90-7.18 (25H, m, arom), 6.54
(1H, d, J ) 9.0 Hz, CH(CHO)), 6.51 (1H, d, J ) 9.0 Hz, CH(Ph))
6.41 (1H, d, J ) 5.5 Hz, Cy-H), 6.24 (1H, d, J ) 5.5 Hz, Cy-H),
6.14 (1H, d, J ) 5.5 Hz, Cy-H), 5.92 (1H, d, J ) 5.5 Hz, Cy-H),
X-r a y Cr ysta llogr a p h y. Single crystals suitable for X-ray
analysis were formed by vapor diffusion of diethyl ether into
a chloroform solution of 1 or diethyl ether and methylene
chloride for 2a and 4a . Crystallographic data are summarized
in Table 1. The structures were determined from data collected
with a Nonius KappaCCD at -90 °C. Lorentz and polarization
corrections were applied to all data. An empirical absorption
correction was applied using SORTAV.12 Intensities of equiva-
lent reflections were averaged. The structures were solved by
direct methods (SIR9213) using the teXan crystal structure
analysis package, and the function minimized was ∑w(|Fo| -
|Fc|)2 in all cases. Hydrogen atoms were placed at calculated
positions before each refinement and were included in the
refinement, but were not refined.
2
2
3.77 (1H, qdd, J ) 5.5, J H-P ) 9.5, J H-P ) 4.5 Hz, HC(CH3)-
P2), 2.45 (3H, s, Cy-CH3), 2.32 (1H, hept., J ) 6.5 Hz, HC-
2
2
(CH3)2), 1.27 (3H, ddd, J ) 5.5, J H-P ) 11.1, J H-P )12.8 Hz,
HCP2(CH3)), 1.06 (3H, d, J ) 6.5 Hz, HC(CH3)(CH3)), 0.78 (3H,
d, J ) 6.5 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 78.65 (s, P(V)),
25.89 (s, P(III)); 4b 9.46 (1H, d, J ) 9.0 Hz, CHO) 7.90-7.18
(25H, m, arom), 6.54 (1H, d, J ) 9.0 Hz, CH(CHO)), 6.51 (1H,
d, J ) 9.0 Hz, CH(Ph)) 6.20 (1H, d, J ) 5.5 Hz, Cy-H), 5.98
(1H, d, J ) 5.5 Hz, Cy-H), 5.88 (1H, d, J ) 5.5 Hz, Cy-H), 5.80
2
(1H, d, J ) 5.5 Hz, Cy-H), 4.45 (1H, qdd, J ) 5.8, J H-P ) 9.7,
2J H-P ) 7.6 Hz, HCP2), 2.20 (3H, s, Cy-CH3), 2.44 (1H, hept.,
The correct polarity for 2a was determined by refining the
inverted structure, which gave R ) 0.050 and Rw ) 0.050,
2
J ) 6.5 Hz, HC(CH3)2), 1.23 (3H, ddd, J ) 5.8, J H-P ) 11.2,
2J H-P )13.0 Hz, HCP2(CH3)), 1.09 (3H, d, J ) 6.5 Hz, HC-
(CH3)(CH3)), 0.82 (3H, d, J ) 6.5 Hz, HC(CH3)(CH3)). 31P{1H}
NMR: 73.95 (s, P(V)), 18.34 (s, P(III)). The crystal lattice
contained methylene chloride, which was slowly lost on stand-
ing. The sample for elemental analysis was dried overnight
under vacuum, and the solvent was completely removed in the
process. Anal. Calcd for C45H46O2F12P2Sb2Os: C, 40.26; H, 3.45.
Found: C, 40.11; H, 3.43.
whereas the reported coordinates gave R ) 0.042 and Rw
0.041.
)
Ack n ow led gm en t . This research was supported
by a grant from the National Science Foundation
(CHE9726423).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and bond lengths
and angles for 1, 2a , and 4a . This material is available free of
charge via the Internet at http://pubs.acs.org.
5a : 9.46 (1H, s, CHO) 7.95-7.12 (20H, m, arom), 6.35 (1H,
s, CH)C(CH3)(CHO)), 6.06 (1H, d, J ) 6.5 Hz, Cy-H), 6.00
(1H, s, CH)C(CH3)(CHO)), 5.91 (1H, d, J ) 6.5 Hz, Cy-H),
5.86 (1H, d, J ) 6.5 Hz, Cy-H), 5.75 (1H, d, J ) 6.5 Hz, Cy-H),
2
2
3.68 (1H, qdd, J ) 5.2, J H-P ) 9.2, J H-P ) 4.4 Hz, HC(CH3)-
P2), 2.61 (1H, hept., J ) 7.2 Hz, HC(CH3)2), 2.21 (3H, s, Cy-
CH3), 1.86 (3H, s, CHdC(CH3)(CHO)), 1.24 (3H, ddd, obsc,
HCP2(CH3)), 1.28 (3H, d, J ) 7.2 Hz, HC(CH3)(CH3)), 0.94 (3H,
d, J ) 7.2 Hz, HC(CH3)(CH3)). 31P{1H} NMR: 80.95 (s, P(V)),
29.43 (s, P(III)); 5b 9.46 (1H, s, CHO) 7.95-7.12 (20H, m,
arom), 6.35 (1H, s, CH)C(CH3)(CHO)), 6.00 (1H, s, CH)C-
(CH3)(CHO)), 5.96 (1H, d, J ) 6.5 Hz, Cy-H), 5.94 (1H, d, J )
OM000083S
(11) Bennett, M. A.; Matheson, T. W.; Robertson, G. B.; Smith, A.
K.; Tucker, P. A. Inorg. Chem 1980, 19, 1014.
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R. H. J . Appl. Crystallogr. 1997, 30, 421-426.
(13) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
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