Planar chirality in tethered η6:η1-(phosphinophenylenearene-P)ruthenium(II) complexes and their potential use as asymmetric catalysts

Article abstract of DOI:10.1021/om030080q

Reaction of 2-dicyclohexylphosphinobiphenyl with [(η⁶-benzene)RuCl₂]₂ yielded the tethered complex [Ru(η⁶:η¹-dicyclohexylphosphinobiphenyl-P)Cl₂ ], 1, rather than a bridge-splitting product, [(η⁶-benzene)Ru(L)Cl₂], that is often observed. Treatment of [(η⁶-benzene)RuCl₂]₂ with 2-dicyclohexylphosphino-2′-(N,N-dimethylamino)biphenyl yielded the planar chiral, tethered complex [Ru(η⁶:η¹-2-dicyclohexylphosphino-2-′-(N,N-d imethylamino)biphenyl-P)Cl₂], 2. Abstraction of a chloride from 2 with AgSbF₆ and treatment with PPh₃ selectively gave the chiral-at-metal complex [anti-Ru(η⁶:η¹-2-dicyclohexylphosphino-2′-(N ,N-dimethylamino)-biphenyl-P) (PPh₃)Cl]SbF₆, 3a, which underwent spontaneous resolution upon crystallization. The Me₂N group is coplanar with the η⁶-phenyl ring in the cations and directs attack at the metal center, as well as determining the thermodynamic stability of anti versus syn epimers. The dication derived from enantiopure 3a catalyzed the Diels-Alder reaction of methacrolein and cyclopentadiene with modest (19-23%) enantioselectivity. Analogues of 2 and 3a containing 2-(dicyclohexylphosphino)-2′-methylbiphenyl were also prepared. We have found that epimerization at the metal center is slow in these compounds. Averaged NMR spectra at ambient temperatures are observed, however, due to rapid conformational interconversions that can be slowed at low temperature.

Full text of DOI:10.1021/om030080q

Organometallics 2003, 22, 2749-2757
2749
P la n a r Ch ir a lity in Teth er ed
η6:η1-(P h osp h in op h en ylen ea r en e-P )r u th en iu m (II)
Com p lexes a n d Th eir P oten tia l Use a s Asym m etr ic
Ca ta lysts
J . W. Faller* and Darlene G. D’Alliessi
Department of Chemistry, Yale University, New Haven, Connecticut 06520
Received February 3, 2003
Reaction of 2-dicyclohexylphosphinobiphenyl with [(η6-benzene)RuCl2]2 yielded the tethered
complex [Ru(η6:η1-2-dicyclohexylphosphinobiphenyl-P)Cl2], 1, rather than a bridge-splitting
product, [(η6-benzene)Ru(L)Cl2], that is often observed. Treatment of [(η6-benzene)RuCl2]2
with 2-dicyclohexylphosphino-2′-(N,N-dimethylamino)biphenyl yielded the planar chiral,
tethered complex [Ru(η6:η1-2-dicyclohexylphosphino-2′-(N,N-dimethylamino)biphenyl-P)Cl2],
2. Abstraction of a chloride from 2 with AgSbF6 and treatment with PPh3 selectively gave
the chiral-at-metal complex [anti-Ru(η6:η1-2-dicyclohexylphosphino-2′-(N,N-dimethylamino)-
biphenyl-P)(PPh3)Cl]SbF6, 3a , which underwent spontaneous resolution upon crystallization.
The Me2N group is coplanar with the η6-phenyl ring in the cations and directs attack at the
metal center, as well as determining the thermodynamic stability of anti versus syn epimers.
The dication derived from enantiopure 3a catalyzed the Diels-Alder reaction of methacrolein
and cyclopentadiene with modest (19-23%) enantioselectivity. Analogues of 2 and 3a
containing 2-(dicyclohexylphosphino)-2′-methylbiphenyl were also prepared. We have found
that epimerization at the metal center is slow in these compounds. Averaged NMR spectra
at ambient temperatures are observed, however, due to rapid conformational interconversions
that can be slowed at low temperature.
In tr od u ction
2′-(N,N-dimethylamino)biphenyl, LA, which acted as an
arene-tethered ligand instead of an η2-P,N ligand.
Analogues were also prepared from 2-(dicyclohexylphos-
phino)biphenyl, LB, and 2-(dicyclohexylphosphino)-2′-
methylbiphenyl, LC, to yield a series of compounds
based on the parent [Ru(η6:η1-2-dicyclohexylphosphino-
biphenyl-P)Cl2], 1. Tethered ligands are a class of mixed
donor ligands that involve an arene or cyclopentadienyl
(Cp) ring linked to a pendant donor atom. There have
been a moderate number of Cp-tethered (η5:η1) com-
pounds,13-15 but much fewer benzene-derived tethered
(η6:η1) compounds, reported. Most of the (η6:η1) tethers
that are known involve a phosphine as the pendant
donor;16-26 however, examples with pendant S,27 O,28
N, and As29 are also known. The tethered donor can
In the development of effective catalysts for asym-
metric synthesis there has been increasing attention
paid to mixed donor ligands1-3 coordinated to transition
metal centers. We have previously focused on chelated
η2-P,S,4 η2-P,N,5,6 and η2-bisphosphine monoxide7-12
ligand systems in the design of configurationally stable,
chiral ruthenium Lewis acids. Thus far, the successful
application of our ruthenium compounds containing
mixed donor ligands to asymmetric reactions has gener-
ally required the use of ligands that were enantiopure
prior to coordination to Ru.6,9,11,12
In our continuing efforts to utilize ligands that were
not necessarily enantiopure before coordination to the
metal, we have investigated 2-dicyclohexylphosphino-
(13) Butenschon, H. Chem. Rev. 2000, 100, 1527-1564.
(14) Kaulen, C.; Pala, C.; Hu, C. H.; Ganter, C. Organometallics
2001, 20, 1614-1619.
(15) Matsushima, Y.; Onitsuka, K.; Kondo, T.; Mitsudo, T.; Taka-
hashi, S. J . Am. Chem. Soc. 2001, 123, 10405-10406.
(16) Singewald, E. T.; Shi, X. B.; Mirkin, C. A.; Schofer, S. J .; Stern,
C. L. Organometallics 1996, 15, 3062-3069.
(17) Feiken, N.; Pregosin, P. S.; Trabesinger, G. Organometallics
1997, 16, 3735-3736.
(18) Smith, P. D.; Wright, A. H. J . Organomet. Chem. 1998, 559,
141-147.
(19) Therrien, B.; Ward, T. R.; Pilkington, M.; Hoffmann, C.;
Gilardoni, F.; Weber, J . Organometallics 1998, 17, 330-337.
(20) Therrien, B.; Konig, A.; Ward, T. R. Organometallics 1999, 18,
1565-1568.
(21) Therrien, B.; Ward, T. R. Angew. Chem., Int. Ed. 1999, 38, 405-
408.
(22) Abele, A.; Wursche, R.; Klinga, M.; Rieger, B. J . Mol. Catal. A,
Chem. 2000, 160, 23-33.
(23) J an, D.; Delaude, L.; Simal, F.; Demonceau, A.; Noels, A. F. J .
Organomet. Chem. 2000, 606, 55-64.
(1) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27-110.
(2) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233-350.
(3) McCarthy, M.; Guiry, P. J . Tetrahedron 2001, 57, 3809-3844.
(4) Faller, J . W.; Lloret-Fillol, J .; Parr, J . New J . Chem. 2002, 26,
883-888.
(5) Faller, J . W.; Stokes-Huby, H. L.; Albrizzio, M. A. Helv. Chim.
Acta 2001, 84, 3031-3042.
(6) Faller, J . W.; Grimmond, B. J . Organometallics 2001, 20, 2454-
2458.
(7) Faller, J . W.; Patel, B. P.; Albrizzio, M. A.; Curtis, M. Organo-
metallics 1999, 18, 3096-3104.
(8) Faller, J . W.; Parr, J . Organometallics 2000, 19, 3556-3561.
(9) Faller, J . W.; Liu, X.; Parr, J . Chirality 2000, 12, 325-337.
(10) Faller, J . W.; Grimmond, B. J .; Curtis, M. Organometallics
2000, 19, 5174-5181.
(11) Faller, J . W.; Grimmond, B. J .; D’Alliessi, D. G. J . Am. Chem.
Soc. 2001, 123, 2525-2529.
(12) Faller, J . W.; Parr, J . Organometallics 2001, 20, 697-699.
10.1021/om030080q CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/30/2003

2750 Organometallics, Vol. 22, No. 13, 2003
Faller and D’Alliessi
Sch em e 1. Th e F ou r P ossible Dia ster eom er s
Resu ltin g fr om P la n a r Ch ir a lity a n d Meta l
Ch ir a lity If th e Liga n d Is Ch ir a l Non r a cem ic
synthesis of these η6:η1-tethered compounds is more
attractive than those previously reported, in terms of
time (18-72 h for others), temperature (120-140 °C for
others), number of steps performed, and the commercial
availability of reactants.18-21,23,25,26,28,30,31 The analogues
of [Ru(η6:η1-L′-P)Cl2], where L′ ) 2-(dicyclohexylphos-
phino)biphenyl, LB, or 2-(dicyclohexylphosphino)-2′-
methylbiphenyl, LC, were prepared similarly, albeit in
lower yields (31-45%).
F igu r e 1. ORTEP view of [Ru(η6:η1-Me2NC6H4C6H4-
PCy2-P)Cl2]SbF6, 2, with 50% probability ellipsoids.
contribute to the chirality of a catalyst, like other mixed
donor ligands, when two other different ligands are
present, by producing a stereogenic metal center. In
addition, a potential tethered ligand with substitution
on appropriate arene carbon atoms can generate planar
chirality upon coordination to the metal16,17,19-21,29 that
may potentially influence the stereochemical pathway
of asymmetric reactions. In the case of LA and LC, the
ligands are conformationally dynamic and could exist
as a pair of atropisomers if the barrier to biphenyl
rotation were high enough. In a sense, the η6:η1 binding
locks these conformations in place. Perhaps the most
significant feature of tethered ligands is their potential
contribution to the configurational stability at a cata-
lyst’s metal center, a requisite for avoiding low enan-
tioselectivity in the products of asymmetric catalysis.
Herein we present a facile synthesis of tethered
phosphinoarene, planar chiral ruthenium complexes
from commercially available ligands and demonstrate
their preliminary reactivity in an asymmetric carbon-
carbon bond forming reaction.
Attem p ted Resolu tion of En a n tiom er s. The pres-
ence of the 2′-dimethylamino group in [Ru(η6:η1-LA-P)-
Cl2] renders the molecule chiral; however, our attempts
to resolve the planar chiral enantiomers of 2 by a variety
of derivatization and crystallization experiments were
unsuccessful. Owing to the presence of the basic di-
methylamino group, the enantiomeric purity of 2 can
be evaluated by addition of the chiral shift reagent
europium tris[3-(heptafluoropropylhydroxymethylene)-
(+)-camphorate, (+)-Eu(hfc)3, to a CD2Cl2 solution of 2.
Shifts in the 1H and 31P{1H} NMR spectra of rac-2 show
a 1:1 ratio of resonances due to the diastereomeric
interactions. Possible resolutions via the cationic com-
plexes [Ru(η6:η1-LA-P)(L*)Cl]SbF6, where L* ) a chiral
nonracemic ligand, were considered. The abstraction of
a chloride from 2 by AgSbF6 and subsequent replace-
ment by L creates a chiral metal center in addition to
the planar chirality. If L is itself chiral, a maximum of
four diastereomers may form, Scheme 1. If it is achiral
(and not prochiral), a maximum of two diastereomers,
each of which exists as a pair of enantiomers, could be
obtained, Scheme 2. As denoted in Schemes 1 and 2, L
may be situated either anti or syn to the NMe2 sub-
stituent on the η6-coordinated arene. Appropriate steric
or electronic contributions from L could influence the
diastereoselective formation of isomers shown in Schemes
1 and 2, which have the potential of being separated by
classical methods (e.g., crystallization or chromatogra-
phy).
Resu lts a n d Discu ssion
The reaction of commercially available reagents [(ben-
zene)RuCl2]2 and 2-dicyclohexylphosphino-2′-(N,N-di-
methylamino)biphenyl, LA, at 100 °C in DMF for
10-15 min yielded a product resulting from displace-
1
ment of the benzene ligand. The H and 31P{1H} NMR
spectra indicated that the reaction had produced an
η6:η1-tethered compound, [Ru(η6:η1-LA-P)Cl2], 2. Single-
crystal X-ray diffraction verified the η6:η1-tethered
coordination as shown in Figure 1. Removal of DMF by
vacuum distillation and chromatography of the red-
brown residue gave a 94% isolated yield of 2. The
A variety of chiral donor ligands, including amines
(pyridine and (R)-(+)-R-methylbenzylamine) and sul-
foxides ((R)-(+)-methyl-p-tolyl sulfoxide), failed to bind
selectively to the [Ru(η6:η1-LA- P)Cl] moiety and yielded
all possible diastereomers in nearly equal distribu-
tions that resisted separation. The chiral phosphines
(24) den Reijer, C. J .; Worle, M.; Pregosin, P. S. Organometallics
2000, 19, 309-316.
(25) Bennett, M. A.; Edwards, A. J .; Harper, J . R.; Khimyak, T.;
Willis, A. C. J . Organomet. Chem. 2001, 629, 7-18.
(26) J ung, S.; Ilg, K.; Brandt, C. D.; Wolf, J .; Werner, H. J . Chem.
Soc., Dalton Trans. 2002, 318-327.
(27) Dilworth, J . R.; Zheng, Y. F.; Lu, S. F.; Wu, Q. J . Inorg. Chim.
Acta 1992, 194, 99-103.
(28) Miyaki, Y.; Onishi, T.; Kurosawa, H. Inorg. Chim. Acta 2000,
300, 369-377.
(30) Therrien, B.; Ward, T. R. Acta Crystallogr. Sect. C, Cryst. Struct.
Commun. 2000, C56, e561.
(31) Furstner, A.; Liebl, M.; Lehmann, C. W.; Picquet, M.; Kunz,
R.; Bruneau, C.; Touchard, D.; Dixneuf, P. H. Chem., Eur. J . 2000, 6,
1847-1857.
(29) Nelson, J . H.; Ghebreyessus, K. Y.; Cook, V. C.; Edwards, A.
J .; Wielandt, W.; Wild, S. B.; Willis, A. C. Organometallics 2002, 21,
1727-1733.

Planar Chirality in Tethered Ru(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2751
Sch em e 2. Th e P a ir s of En a n tiom er s for th e Tw o
Dia ster eom er s Resu ltin g fr om P la n a r Ch ir a lity
a n d Meta l Ch ir a lity If th e Liga n d Is Ach ir a l
Figu r e 2. ORTEP view of [Ru(η6:η1-Me2NC6H4C6H4PCy2-P)-
(PPh2(S)-1-phenylethyl)Cl]SbF6 with 50% probability el-
lipsoids. A quasi-racemate is formed, and both diastereo-
mers are found in the same unit cell and are related by a
pseudocenter of symmetry.
(S)-(-)-diphenyl(1-phenylethylamino)phosphine, L*D,32
(1R,7R)-9,9-dimethyl-2,2,4,6,6-pentaphenyl-3,5,8,10-
tetraoxa-4-phosphabicyclo[5.3.0]decane, L*E ,33 and
(1R,2S,5R)-5-methyl-2-(1-methylethyl)cyclohexyl ester
of diphenylphosphinous acid, L*F ,34 were prepared by
reacting CH2Cl2 solutions of the appropriate nonracemic
chiral alcohol or chiral amine with Ph2PCl or PhPCl2
in the presence of NEt3 according to literature proce-
dures. Each of these phosphines was stirred with 2 and
1 molar equiv of AgSbF6 to give the cationic bisphos-
phine compounds [Ru(η6:η1-LA-P)(L*)Cl]SbF6, where L*
) L*D, L*E, or L*F . Stirring the monodentate achiral
phosphines, PPh3, PMePh2, PMe2Ph, and PMe3, with
equimolar amounts of 2 and AgSbF6 at room tempera-
ture yielded the cationic bisphosphine compounds [Ru-
(η6:η1-LA-P)(L)Cl]SbF6 (L ) PPh3, PMePh2, PMe2Ph, or
PMe3). Coordination of the new ligand was indicated by
the presence of two doublets arising from phosphorus-
phosphorus coupling in the 31P{1H} NMR spectrum. The
presence of characteristic resonances in the 1H NMR
spectrum indicated that η6-coordination of the arene of
LA was retained in the products.
F igu r e 3. CD spectra of (+)- and (-)-[Ru(η6:η1-Me2NC6H4-
C6H4PCy2-P)(PPh3)Cl]SbF6, 3a , in CH2Cl2.
lize separately. For example, the red-orange crystalline
plates of [Ru(η6:η1-LA-P)(L*D)Cl]SbF6, obtained from
recrystallization (CH2Cl2/hexanes), were quasi-race-
mates (verified by X-ray crystallography, Figure 2)
having the same 1:1 ratio of anti-diastereomers in the
unit cell as in the bulk material.
Of the achiral phosphines, the PPh3 derivative, [Ru-
(η6:η1-LA-P)(PPh3)Cl]SbF6, 3a , yielded a product that
was the easiest to obtain as a pure diastereomer.
Compound 3a was purified by column chromatography
and isolated as a single racemic diastereomer in 96%
yield. It crystallized (CH2Cl2/ether) more readily than
the chiral phosphine analogues, and fortunately, the
enantiomers of 3a underwent spontaneous resolution
with a conglomerate forming upon crystallization. Me-
chanical separation of the crystals, determination of the
sign of the optical rotation of individual crystals, and
combination of solutions having similar rotations al-
lowed separation of the pure enantiomers.
The mirror image relationship in the circular dichro-
ism (CD) spectra (Figure 3) and the equivalent molar
ellipticities of isolated (+) and (-)-3a illustrate that
manual separation was an effective means of resolving
this compound. Cutting a large single crystal allowed
the determination of both the optical rotation of the
dissolved crystal and the absolute configuration by
X-ray diffraction study of a single crystal of (-)-3a
(Figure 4). This showed that (-)-3a was the (RRu,R)-
enantiomer. Compound 3a is a rare example of a planar
chiral, tethered, late transition metal compound that
has been isolated in enantiopure form.21,35
For the compounds containing the chiral phosphorus-
donor ligands, L*D, L*E, L*F , two isomers in an ap-
proximate 1:1 ratio rather than the four possible isomers
form at room temperature. The ratio of products did not
change significantly with time (>20 days) or variation
in the stoichiometry of the reactants. For example, when
0.5 molar equiv of L*E or of AgSbF6 was used to prepare
[Ru(η6:η1-LA-P)(L*E)Cl]SbF6, the ratio remained the
same. Also, the reaction of 2 with L*D without AgSbF6
resulted in a 1:1 ratio of isomers for [Ru(η6:η1-LA-P)-
(L*D)Cl]Cl. The 31P{1H} NMR spectra indicated that the
ratio of the diastereomers of [Ru(η6:η1-LA-P)(L*D)Cl]-
SbF6 also remained the same from -80 to 80 °C. We
were unable to find a convenient method for the separa-
tion of these diastereomers. Part of this difficulty can
be traced to the failure of the diastereomers to crystal-
(32) Brunner, H.; Doppelberger, J . Chem. Ber.-Recl. 1978, 111, 673-
691.
(33) Seebach, D.; Hayakawa, M.; Sakaki, J .; Schweizer, W. B.
Tetrahedron 1993, 49, 1711-1724.
(34) Mikolajczyk, M.; Perlikowska, W.; Omelanczuk, J . Synthesis
1987, 1009-1012.
(35) Dodo, N.; Matsushima, Y.; Uno, M.; Onitsuka, K.; Takahashi,
S. J . Chem. Soc., Dalton Trans. 2000, 35-41.

2752 Organometallics, Vol. 22, No. 13, 2003
Faller and D’Alliessi
Figu r e 5. ORTEP view of (RRu,S)-[Ru(η6:η1-Me2NC6H4C6H4-
PCy2-P)(PMe2Ph)Cl]SbF6, 4, with 50% probability ellip-
soids. The descriptor for the metal center is determined
by the priorities arene > Cl > P2 > P1. The descriptor for
the ring chirality is determined by the chirality of the
highest rank carbon atom in the ring, C1. Individual crys-
tals contain both the (RRu, S) and the (SRu, R) enantiomer.
Figu r e 4. ORTEP view of (RRu,R)-[Ru(η6:η1-Me2NC6H4C6H4-
PCy2-P)(PPh3)Cl]SbF6, 3a , with 50% probability ellipsoids.
The descriptor for the metal center is determined by the
priorities arene > Cl > P2 > P1. The descriptor for the
ring chirality is determined by the chirality of the highest
rank carbon atom in the ring, C1. Individual crystals
contain either the (RRu, R) or the (SRu, S) enantiomer.
whereas PPh3 does not have an option for rotating
around the Ru-P bond to reduce the Ph-NMe2 interac-
tions.
Dia ster eom er ic P r efer en ces. The compounds con-
taining the achiral phosphines exhibit a preference for
the initial formation of the anti-diastereomer shown in
Scheme 2, but only in the case of PPh3 is the reaction
essentially completely diastereoselective. The observed
de at room temperature for each [Ru(η6:η1-LA-P)(L)Cl]-
SbF6 is as follows: L ) PPh3 (>96% de); PMePh2 (91%
de); PMe2Ph (86% de); PMe3 (90% de). These diastere-
omeric ratios are unchanged when the compounds are
left in solution over several days. The compounds
containing the achiral phosphines tend to crystallize
(CH2Cl2/ether) more readily than the analogues con-
taining chiral phosphines. The X-ray diffraction study
of a single crystal of [Ru(η6:η1-LA-P)(PPh3)Cl]SbF6, 3a
(Figure 4), which is observed as one diastereomer in
NMR spectra, confirmed the assignment as the anti
isomer, Scheme 2. Repeated recrystallizations from
CH2Cl2/ether allowed isolation of the minor isomer of
[Ru(η6:η1-LA-P)(PMe2Ph)Cl]SbF6, 4. An X-ray crystal
structure determination (Figure 5) confirmed that the
minor isomer had the syn arrangement, Scheme 2.
When syn-4 was dissolved in dichloromethane, no inter-
conversion to the anti isomer was observed over ex-
tended periods.
The observed ratio of the diastereomers containing
achiral phosphines appears to be kinetically controlled
since the ratios remain constant in solution for extended
periods. The diastereomer ratio can, however, be altered
upon repeated crystallization, as observed for 4. The
degree of diastereoselectivity in the formation appar-
ently depends on the steric and electronic influences
exerted on the achiral phosphine by the dimethylamino
group in the η6-ring. PMe2Ph in 4 is a less sterically
demanding and a better donating ligand than PPh3 in
3a . As a result, the syn arrangement in 4 is less ster-
ically disfavored, and some of this diastereomer can
be observed in the product. On the other hand, the
greater bulk of PPh3 prevents the formation of a
significant amount of the syn diastereomer. Comparison
of the crystal structures of syn-4 and anti-3a illustrates
how the PMe2Ph ligand conformation can adjust to
minimize interactions with the dimethylamino group,
It would appear that the principal factor controlling
conformational preferences and diastereomeric prefer-
ences are steric interactions of the ligand with the
dimethylamino group. In this context, it is interesting
to note that the lone pair of the dimethylamino group
has significant donation to the ring in the positively
charged aryl-ruthenium moiety. This should result in
significant double-bond character in the N-aryl bond,
thus making it a relatively rigid structure. The struc-
tures of the cations show that the nitrogen atom in the
dimethylamino group is essentially planar and all of its
atomic constituents are in the same plane as the arene.
This contrasts with the neutral compound (Figure 1),
where the nitrogen atom in the dimethylamino function
is pyramidal and furthermore the methyl groups are
rotated out of the plane of the arene.
Interactions with the dimethylamino group should
direct the initial formation of the diastereomers of
complexes with a particular ligand and then influence
the final thermodynamic equilibrium populations. With
the more basic phosphines that have smaller cone
angles, (i.e., PMe3 and PMe2Ph), the Ru-P bond ap-
pears to be so strong that the thermodynamic equilib-
rium ratio is established so slowly that we were unable
to measure the rate.
Presumably syn-anti interconversion would occur via
loss of a phosphine ligand. This dissociation is slow
with PMe3 and PMe2Ph; however it appears that PPh3
is more labile and should allow more rapid equilibra-
tion. In fact, in the presence of an excess (>5 molar
equiv) of PMe2Ph, interconversion of the single isomer
of 3a to both diastereomers of 4 having a reduced de
(67%) occurs with a half-life of approximately 37 h.
Thus it appears that the >90% de represents a ther-
modynamic equilibrium for 3a , whereas the equilibrium
value for 4 is still uncertain. This diastereomeric prefer-
ence in the formation of anti-3a apparently results from
the incoming PPh3 being directed to a particular coor-
dination site on Ru by steric interaction with the NMe2
substituent on the coordinated arene ring.

Planar Chirality in Tethered Ru(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2753
The single, isolated diastereomer of 3a is apparently
the preferred thermodynamic and kinetic product of the
reaction. A nonequilibrium mixture of syn and anti
isomers of 3a can be prepared by abstraction of chloride
from anti-3a , giving [Ru(η6:η1-LA-P)(PPh3)](SbF6)2, 5,
followed by addition of lithium chloride. A kinetic ratio
of 2:1 (33% de) for anti:syn isomers equilibrates over
150 h to a ratio of 25:1 (92% de) (t1/2 ≈ 25 h). Thus, both
the kinetic and thermodynamic preference in diastere-
omer formation in the reaction of [Ru(η6:η1-LA-P)Cl2]
with PPh3 is determined by interactions with the
dimethylamino group.
Similarly, the dication [Ru(η6:η1-LA-P)(PMe2Ph)]-
(SbF6)2, 6, is formed by chloride abstraction from 4
using AgSbF6. Addition of excess Cl- in the form of LiCl
to 6 regenerates 4; however this reaction favors for-
mation of the syn isomer (anti:syn ) 10:90, 80% de). This
outcome contrasts with the addition of PMe2Ph to
[Ru(η6:η1-LA-P)Cl]SbF6 that preferentially yields anti-4
(anti:syn ) 93:7, 86% de) and suggests that the kinetic
product in the addition of LiCl to 6 is determined by a
sterically favorable approach for the incoming nucleo-
philic chloride.
With the less bulky methyl substituent in the tethered
complex formed from 2-(dicyclohexylphosphino)-2′-
methylbiphenyl, 3c, reaction with PPh3 yields both
diastereomers in the kinetic product (88% de). Hence,
even a methyl group can significantly influence the
preferred direction of attack of the PPh3.
Con for m a tion s a n d Dia ster eom er ic Con figu r a -
tion s. Brunner36 has pointed out that there have been
a number of errors in interpretation of diastereomeric
ratios based on room-temperature NMR observations.
That is, high diastereoselectivity (100% de) has been
claimed in some cases when only a single set of reso-
nances was observed in the NMR spectra at ambient
temperatures. Careful study at low temperature indi-
cated that both diastereomers were present; however,
an averaged spectrum was observed at higher temper-
atures owing to rapid equilibration between the dia-
stereomers. Since 3a was isolated as a single diastere-
omer, VT NMR spectra were examined to determine if
there were potential problems arising from stereochem-
ical nonrigidity.
The 31P{1H} NMR spectrum of 3a was recorded at
various temperatures in three different solvents: dichlo-
romethane-d2 (Figure 6), acetone-d6, and chloroform-d.
In each solvent only one diastereomer, having a doublet
for each coordinated phosphine, was observed between
60 and -20 °C. At -40 °C the doublets broadened, and
from -60 and -80 °C a major and minor set of doublets
was visible. Although this might have been attributed
to syn-anti interconversion, the slow exchange of phos-
phine in 3a and the extremely slow diastereomeric
interconversions in 4 suggest otherwise. A more likely
alternative is that the two sets of doublets observed at
low temperature were due to the slowing of a confor-
mational interconversion process, such as interconver-
sion of phenyl group conformations on PPh3.37-39 To
evaluate this rationale, the analogues [Ru(η6:η1-L′-P)-
(PPh3)Cl]SbF6, where L′ ) LB or LC, were prepared in
the one-step reaction of [Ru(PPh3)3Cl2], L′, and AgSbF6
in refluxing chlorobenzene. [Ru(η6:η1-LB-P)(PPh3)Cl]-
F igu r e 6. Variable-temperature 31P{1H} NMR spectra of
[Ru(η6:η1-Me2NC6H4C6H4PCy2-P)(PPh3)Cl]SbF6, 3a , in
CD2Cl2.
SbF6, 3b, possesses a chiral metal center and no planar
chirality and exists as a racemate of only one possible
diastereomer. Thus, there is no possibility of syn-anti
interconversion. The variable-temperature 31P{1H} NMR
spectrum of 3b was similar to that of 3a ; a second small
set of doublets was observed at -80 °C. Because the
single possible diastereomer of 3b also exhibited ad-
ditional resonances at low temperature, interconversion
of either phenyl or cyclohexyl conformers is a viable
explanation. The variable-temperature 31P{1H} NMR
spectrum of the methyl-substituted analogue [Ru(η6:η1-
LC-P)(PPh3)Cl]SbF6, 3c, which has planar as well as
central metal chirality like 3a , contributed additional
insight. As a result of the different steric and electronic
influences offered by the methyl- versus the dimethyl-
amino-substituted arene, both diastereomers were ob-
served in the 31P{1H} NMR spectrum from -80 to 80
°C. Nevertheless, an additional pair of doublets was still
observed at lower temperatures associated with the
major diastereomer. The low concentration of the second
diastereomer precluded observation of another set of
doublets associated with the weaker doublet. Presum-
ably, if a greater fraction of the minor diastereomer had
been present, a total of four pairs of doublets attribut-
able to four diastereomers would have been observed
at low temperature.
The VT 31P{1H} NMR spectrum of the PMe2Ph
derivative 4, which shows both diastereomers in sig-
nificant concentrations, shows two pairs of doublets in
the same ratio from -80 to 80 °C but no additional set
of doublets at -80 °C. This further suggests that the
low-temperature interconversions involve conforma-
tional changes. One rationale is that phenyl conformers
on PPh3 are involved and could cause the additional
resonances for 3a , 3b, and 3c, since the only obvious
difference between 4 and 3a is the smaller number of
phenyl groups on PMe2Ph versus PPh3. Alternatively,
the greater steric interactions with PPh3 could affect
the conformational preferences for the cyclohexyl groups
and (cyclohexyl)-C-P bond rotation conformations
(37) Davies, S. G.; Derome, A. E.; McNally, J . P. J . Am. Chem. Soc.
1991, 113, 2854-2861.
(38) Costello, J . F.; Davies, S. G.; McNally, D. J . Chem. Soc., Perkin
Trans. 2 1999, 465-473.
(39) Dance, I.; Scudder, M. J . Chem. Soc., Dalton Trans. 2000, 10,
1579-1585.
(36) Brunner, H.; Zwack, T. Organometallics 2000, 19, 2423-2426.

2754 Organometallics, Vol. 22, No. 13, 2003
Faller and D’Alliessi
could be involved. The important feature is that the low-
temperature phenomenon is associated with a ligand
conformational effect, not an epimerization at the metal
center that interconverts syn and anti isomers.
adventitious water or a substrate would yield a stereo-
genic ruthenium center, the stereochemistry of which
would probably be controlled by steric interactions that
would place the PPh3 anti to the NMe2 group (Scheme
2). Interpretation of the NMR spectra of the adducts of
5 is complicated by multiple equilibria, as well as
conformational interconversions that are temperature
dependent. A future publication will address the com-
plex equilibria in these systems.
P oten tia l Con tr ol of Bid en ta te Liga n d Coor d i-
n a tion . The formation of a particular diastereomer
appears to be controlled by the bulk (cone angle) of a
particular donor. This should thus allow selective
coordination of chelating ligands that have significant
differences in steric bulk at the termini of the chelates.
Two qualitative tests of this aspect were carried out.
Coordination of the chiral bidentate bisphosphine, (R)-
(+)-1,2-bis(diphenylphosphino)propane, (R)-PROPHOS,
to the [Ru(η6:η1-LA-arene, P)] fragment, effected by
abstraction of both chlorides from rac-2 using AgSbF6
at room temperature, did not exhibit differentiation
between the two phosphine termini, as four diastereo-
mers were observed. This system has only modest steric
differences between the termini, but offered potential
as a resolving agent if it had been more selective.
On the other hand, the heterobidentate ligand 1,1′-
bis(diphenylphosphino)methane monoxide, dppmO, has
termini with large differences in steric requirements.
The coordination of both P and O to the metal, which
was established by coupling patterns and characteristi-
cally shifted 31P{1H} NMR resonances,7 gave only one
of the two possible diastereomers. It appears that steric
interactions determine bonding site selectivity, and thus
the phosphine terminus of dppmO presumably occupied
the less congested site anti to NMe2 and allowed the
phosphine oxide to occupy the more hindered site. This
result illustrates the potential of using planar chiral
ligands to control the relative stereochemistry of the
remaining ligands on the metal. We will report on
further studies in this area in the future.
Asym m etr ic Ca ta lysis w ith 3a . The availability of
the enantiopure tethered precatalyst 3a permits testing
its application in an asymmetric Lewis-acid-catalyzed
reaction. The catalytically active dication [Ru(η6:η1-LA-
P)(PPh3)](SbF6)2, 5, is prepared by chloride abstraction
from enantiopure 3a . Few late transition metal catalysts
containing tethers40,41 and, to our knowledge, only one
other containing a planar chiral tether15 have been
applied as catalysts in asymmetric reactions. The
preliminary catalytic reaction in which we applied 5 as
a catalyst was the asymmetric Diels-Alder reaction of
methacrolein with cyclopentadiene. Using 10 mol %
catalyst, the enantioselectivity was modest (19% ee) at
-24 °C, though conversion (95%) and diastereoselectiv-
ity (96% exo) were high. Lowering the temperature to
-78 °C made a modest improvement in the enantiose-
lectivity (23% ee), though the conversion (96%) and
diastereoselectivity (91% exo) remained high. Use of
precatalyst (+)-(SRu,S)-3a generated the (S)-exo Diels-
Alder product predominantly, while (-)-(RRu,R)-3a gen-
erated the (R)-exo product.
Con clu sion s
Commercially available ligands LA, LB, and LC were
found to form η6-arene complexes with tethered donors
when coordinated to ruthenium. Ligands LA and LC
contribute planar chirality upon coordination owing to
the presence of their NMe2 and Me substituents. Chiral-
at-metal 3a spontaneously resolved upon crystallization
and allowed separation of the enantiomers. The dication
derived from enantiopure 3a catalyzed an asymmetric
Diels-Alder reaction, giving products in modest ee.
Analogues of 3a were also prepared for structural
comparison. We are currently considering approaches
to enhance these features of analogous compounds for
application to other catalytic reactions.
Exp er im en ta l Section
All manipulations were carried out under an atmosphere
of nitrogen using standard Schlenk techniques. All solvents
were distilled under nitrogen with standard desiccating agents.
AgSbF6, LA, LB, LC (Strem), PPh3, PMePh2, PMe3, PMe2Ph,
R-PROPHOS, methacrolein, dicyclopentadiene, and (+)-Eu-
(hfc)3 (Aldrich) were used as received. [Ru(benzene)Cl2]2,42,43
L*D,32 L*E,33 L*F ,34 and dppmO44 were prepared according to
literature methods. NMR spectra were recorded at room
temperature, unless otherwise noted, on a GE Omega 300 MHz
(operating at 122 MHz for 31P), Bruker 400 MHz (operating
at 162 MHz for 31P), or Bruker 500 MHz (operating at 202
MHz for 31P) spectrometer. Chemical shifts are reported in
ppm relative to residual solvent peaks (1H, 13C) or an 85%
H3PO4 external standard (31P). Optical rotations were mea-
sured on a Perkin-Elmer model 341 polarimeter at 589 nm
and 25 °C, using a 1 dm path length. CD spectra were recorded
on an AVIV model 202 spectrometer. CD spectra were recorded
in dichloromethane at 25 °C from 600 to 200 nm in 1.0 nm
intervals with a 10 s averaging time, using a 1 mm path length
quartz cell. Elemental analyses were carried out by Atlantic
Microlabs.
P r ep a r a tion of [Ru (η6:η1-LA-P )Cl2], 2. [Ru(benzene)Cl2]2
(171.4 mg, 0.34 mmol) and LA (272.4 mg, 0.69 mmol) were
stirred in DMF (12 mL) at 100 °C for 12-15 min. After cooling
to room temperature, the solvent was removed by reduced
pressure distillation. The dark red-brown residue was purified
by flash chromatography (silica gel, (CH3)2CO), affording 2 in
94% yield (363.8 mg, 0.64 mmol). The product was recrystal-
1
lized from CH2Cl2/ether. H NMR (400 MHz, CDCl3, δ): 7.80
(1 H, m, C6H4P); 7.63 (1 H, m, C6H4P); 7.59 (2 H, m, C6H4P);
6.25 (1 H, m, η6-C6H4N); 5.87 (1 H, d, J ) 6.4 Hz, η6-C6H4N);
5.75 (1 H, t, J ) 5.5 Hz, η6-C6H4N); 4.76 (1 H, d, J ) 5.5 Hz,
η6-C6H4N); 2.70 (1 H, m, C6H11); 2.55 (6 H, s, NCH3); 2.51 (1
H, m, C6H11); 1.98 (1 H, m, C6H11); 1.78 (7 H, m, C6H11); 1.63
(5 H, m, C6H11); 1.25 (5 H, m, C6H11); 1.11 (1 H, m, C6H11);
0.88 (1 H, m, C6H11). 13C NMR (100 MHz, CDCl3, δ): 145.82
A brief comment on the nature of the active catalyst
is appropriate. The unsolvated dication is formally a 16-
electron complex and may effectively yield a planar
[(arene)Ru(P)(PPh3)] metal center. Interaction with
(42) Bennett, M. A.; Smith, A. K. J . Chem. Soc., Dalton Trans. 1974,
233-241.
(43) Scaccianoce, L.; Braga, D.; Calhorda, M. J .; Grepioni, F.;
J ohnson, B. F. G. Organometallics 2000, 19, 790-797.
(44) Grushin, V. V. J . Am. Chem. Soc. 1999, 121, 5831-5832.
(40) Nishibayashi, Y.; Takei, I.; Hidai, M. Organometallics 1997,
16, 3091-3093.
(41) Trost, B. M.; Vidal, B.; Thommen, M. Chem., Eur. J . 1999, 5,
1055-1069.

Planar Chirality in Tethered Ru(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2755
(d, J ) 20 Hz, C6H4P); 142.26 (d, J ) 38 Hz, C6H4P); 131.54
(s, C6H4P); 130.44 (d, J ) 2 Hz, C6H4P); 129.10 (d, J ) 21 Hz,
C6H4P); 129.01 (d, J ) 16 Hz, C6H4P); 116.56 (s, η6-C6H4N);
103.20 (d, J ) 2 Hz, η6-C6H4N); 96.21 (d, J ) 2 Hz, η6-C6H4N);
85.95 (d, J ) 14 Hz, η6-C6H4N); 83.35 (d, J ) 5 Hz, η6-C6H4N);
76.34 (s, η6-C6H4N); 44.00 (s, NCH3); 35.51 (d, J ) 20 Hz,
C6H11); 34.18 (d, J ) 22 Hz, C6H11); 28.10 (s, C6H11); 27.60 (d,
J ) 12 Hz, C6H11); 27.50 (d, J ) 9 Hz, C6H11); 27.41 (d, J ) 9
Hz, C6H11); 27.17 (s, C6H11); 27.09 (d, J ) 11 Hz, C6H11); 26.69
(d, J ) 8 Hz, C6H11); 26.16 (d, J ) 9 Hz, C6H11). 31P{1H} NMR
(122 MHz, CDCl3, δ): 58.79 (s). Anal. Calcd for C26H36Cl2-
NPRu: C, 55.22; H, 6.42; N, 2.48. Found: C, 55.50; H, 6.47;
N, 2.41.
61.48 (br d, J ) 42 Hz, major isomer), 59.99 (br, minor isomer).
The ratio of isomers was 1.1:1.
P r ep a r a tion of [Ru (η6:η1-LB-P )Cl2]. [Ru(benzene)Cl2]2
(96.2 mg, 0.19 mmol) and LB (150 mg, 0.43 mmol) were heated
overnight in 90-100 °C DMF (12 mL), giving a red solution.
The product was washed through a chromatography column
(silica gel) with CH3COOC2H5. Isolated yield: 45% (90.6 mg,
0.17 mmol). Recrystallization involved slow diffusion of ether
1
into a CH2Cl2 solution. H NMR (500 MHz, CD2Cl2, δ): 7.79
(1 H, m, C6H4P); 7.61 (3 H, m, C6H4P); 6.35 (1 H, td, J ) 6 Hz,
2.5 Hz, η6-C6H5); 6.02 (2 H, t, J ) 6 Hz, η6-C6H5); 4.99 (2 H, d,
J ) 5.5 Hz, η6-C6H5); 2.60 (2 H, m, C6H11); 1.82 (6 H, m, C6H11);
1.73 (2 H, m, C6H11); 1.69 (4 H, m, C6H11); 1.40 (2 H, m, C6H11);
1.25 (6 H, m, C6H11). 31P{1H} NMR (202 MHz, CD2Cl2, δ):
62.64 (s). Anal. Calcd for C24H31Cl2PRu: C, 55.17; H, 5.98.
Found: C, 55.24; H, 5.99.
P r ep a r a tion of [Ru (η6:η1-LC-P )Cl2]. [Ru(benzene)Cl2]2
(56.7 mg, 0.113 mmol) and LC (84.2 mg, 0.231 mmol) were
stirred in DMF (6 mL) at 100 °C for 10 min. A bright red
solution resulted. The solvent was removed by vacuum distil-
lation, and the residue was dried in vacuo overnight. The
product was chromatographed (silica gel) with (CH3)2CO.
Isolated yield: 31% (37 mg, 0.069 mmol). Crystals were
obtained by diffusion of hexanes into an ether solution. 1H
NMR (300 MHz, CD2Cl2, δ): 7.78 (1 H, m, C6H4P); 7.62 (2 H,
m, C6H4P); 7.62 (1 H, m, C6H4P); 6.22 (1 H, m, η6-C6H4Me);
5.95 (1 H, d, J ) 6.3 Hz, η6-C6H4Me); 5.73 (1 H, pseudo-t, J )
5.7 Hz, η6-C6H4Me); 4.99 (1 H, d, J ) 6.0 Hz, η6-C6H4Me); 2.70
(1 H, m, C6H11); 2.48 (1 H, m, C6H11); 1.89 (6 H, m, C6H11);
1.75 (3 H, s, CH3); 1.64 (6 H, m, C6H11); 1.22 (7 H, m, C6H11);
0.85 (1 H, m, C6H11). 31P{1H} NMR (162 MHz, CD2Cl2, δ):
61.26 (s).
P r ep a r a tion of [Ru (η6:η1-LA-P )(P P h 3)Cl]SbF 6, 3a . [Ru-
(η6:η1-LA-P)Cl2] (50.8 mg, 0.090 mmol), AgSbF6 (31 mg, 0.090
mmol), and PPh3 (24.4 mg, 0.093 mmol) were stirred in
CH2Cl2 (5 mL) for 2 h. The solvent was then removed under
reduced pressure, giving an orange residue. After purification
by flash chromatography (silica gel, CH2Cl2/(CH3)2CO (1:1)),
3a was isolated in 96% yield (88.2 mg, 0.086 mmol). Crystals
suitable for X-ray diffraction were obtained by slow diffusion
of ether into a dichloromethane solution. anti-3a : 1H NMR
(400 MHz, CD2Cl2, δ): 7.71 (1 H, m, C6H4P); 7.65 (1 H, m,
C6H4P); 7.61 (2 H, m, C6H4P); 7.46 (15 H, m, C6H5P); 6.00 (1
H, d, J ) 6.8 Hz, η6-C6H4N); 5.82 (1 H, m, η6-C6H4N); 5.08 (1
H, m, η6-C6H4N); 3.89 (1 H, m, η6-C6H4N); 3.095 (3 H, s, NCH3);
3.091 (3 H, s, NCH3); 2.61 (1 H, m, C6H11); 2.14 (1 H, m, C6H11);
1.81 (3 H, m, C6H11); 1.67 (3 H, m, C6H11); 1.56 (3 H, m, C6H11);
1.44 (2 H, m, C6H11); 1.22 (3 H, m, C6H11); 1.11 (3 H, m, C6H11);
0.85 (1 H, m, C6H11); 0.77 (2 H, m, C6H11). 31P{1H} NMR (162
MHz, CDCl3, δ): 53.79 (d, J ) 40 Hz); 29.65 (d, J ) 40 Hz).
One diastereomer (anti) was isolated. Anal. Calcd for C44H51
-
P r ep a r a tion of [Ru (η6:η1-LB-P )(P P h 3)Cl]SbF 6, 3b. To
[Ru(PPh3)3Cl2] (53.6 mg, 0.056 mmol) in chlorobenzene (5 mL)
was added AgSbF6 (19 mg, 0.055 mmol) and LB (20 mg, 0.057
mmol). There was a color change in the solution from dark
red-brown to yellow-orange as the mixture was refluxed. After
2 h, the solvent was removed by vacuum distillation. The
residue was stirred in ether to remove excess PPh3, then
washed through a chromatography column (silica gel) with
ClF6NP2RuSb: C, 51.40; H, 5.00, N, 1.36. Found: C, 51.46;
H, 5.01; N, 1.40.
A sample with an enrichment of the syn isomer was obtained
in situ by treating anti-3a with AgSbF6 and quenching with 5
equiv of LiCl (vide infra preparation of 5). This showed an
initial anti:syn ratio of ∼2:1. syn-3a : 31P{1H} NMR (162
MHz, CDCl3, δ): 58.98 (d, J PP ) 44 Hz); 28.86 (d, J PP ) 44
Hz). The ratio decayed from a 33% de after 1 h to 92% de after
150 h.
1
(CH3)2CO. Yield was 75% (41 mg, 0.041 mmol). H NMR (400
P r ep a r a tion of [Ru (η6:η1-LA-P )(L*D)Cl]SbF 6. [Ru(η6:η1-
LA-arene, P)Cl2] (11.2 mg, 0.020 mmol) and AgSbF6 (7 mg,
0.020 mmol) were stirred in CD2Cl2 (0.9 mL). Ligand L*D (66
mg, 0.22 mmol) was added, and the solution was stirred for
1.5 h. The compound was purified by column chromatography
(silica gel, CH2Cl2/CH3COOC2H5 (1:1)). Orange crystalline
plates of quasi-racemates were obtained by diffusion of hex-
anes into a dichloromethane solution. 31P{1H} NMR (162 MHz,
CD2Cl2, δ): 69.96 (d, J ) 44 Hz, minor isomer); 66.93 (d, J )
44 Hz, major isomer); 57.81 (pseudo-t, J ) 44 Hz, overlapped
major and minor isomers). The ratio of isomers was 1.1:1.
P r ep a r a tion of [Ru (η6:η1-LA-P )(L*E)Cl]SbF 6. [Ru(η6:η1-
LA-P)Cl2] (17.2 mg, 0.030 mmol) was stirred with AgSbF6 (10
mg, 0.029 mmol) in CD2Cl2 (0.85 mL). As L*E (17.6 mg, 0.031
mmol) was stirred into the purple solution for 2 h, the color
changed to red-orange. Purification was achieved by column
chromatography (silica gel, CH2Cl2/(CH3)2CO (1:1)). 31P{1H}
NMR (122 MHz, CD2Cl2, δ): 151.50 (d, J ) 51 Hz, major
isomer); 150.29 (d, J ) 46 Hz, minor isomer); 59.95 (br, major
isomer); 57.04 (d, J ) 46 Hz, minor isomer). The ratio of
isomers was 1.4:1.
P r ep a r a tion of [Ru (η6:η1-LA-P )(L*F )Cl]SbF 6. [Ru(η6:η1-
LA-P)Cl2] (17.4 mg, 0.031 mmol), AgSbF6 (11 mg, 0.032 mmol),
and L*F (11.9 mg, 0.035 mmol) were stirred in CH2Cl2 (2.5
mL), giving an orange solution with a white suspension within
4 h. The mixture was then filtered through Celite, the solvent
was removed, and the orange residue was dried in vacuo. The
compound was purified by column chromatography (silica gel,
CH2Cl2/CH3COOC2H5 (2:1)). 31P{1H} NMR (162 MHz, CD2Cl2,
δ): 122.74 (d, J ) 44 Hz, overlapped major and minor isomers),
MHz, CD2Cl2, δ): 7.71-7.38 (19 H, m, C6H5P and C6H4P); 6.36
(1 H, m, η6-C6H5); 5.94 (1 H, d, J ) 5.6 Hz, η6-C6H5); 5.85 (1
H, m, η6-C6H5); 5.76 (2 H, m, η6-C6H5); 2.67 (1 H, m, C6H11);
2.04 (2 H, m, C6H11); 1.69 (5 H, m, C6H11); 1.42 (6 H, m, C6H11);
1.24 (4 H, m, C6H11); 0.86 (1 H, m, C6H11); 0.72 (1 H, m, C6H11);
0.51 (2 H, m, C6H11). 31P{1H} NMR (162 MHz, CD2Cl2, δ):
61.05 (d, J ) 45 Hz); 28.53 (d, J ) 45 Hz).
P r ep a r a tion of [Ru (η6:η1-LC-P )(P P h 3)Cl]SbF 6, 3c. To
[Ru(PPh3)3Cl2] (26.6 mg, 0.028 mmol) in chlorobenzene (5 mL)
was added AgSbF6 (9 mg, 0.026 mmol) and LC (16.5 mg, 0.045
mmol). There was a color change in the solution from red-
brown to yellow as the mixture was refluxed. After 3 h, the
solvent was removed by vacuum distillation, then the residue
was stirred in ether and dried in vacuo. Yield was 78% (20
mg, 0.020 mmol). 1H NMR (400 MHz, CD2Cl2, δ): anti isomer:
7.60 (19 H, m, C6H5P and C6H4P); 6.35 (1 H, d, J ) 5.5 Hz,
η6-C6H4Me); 5.97 (1 H, m, η6-C6H4Me); 5.41 (1 H, d, J ) 5.5
Hz, η6-C6H4Me); 4.60 (1 H, m, η6-C6H4Me); 2.64 (1 H, m, C6H11);
2.11 (3 H, d, J ) 3.0 Hz, CH3); 1.87 (1 H, m, C6H11); 1.65 (12
H, m, C6H11); 1.13 (6 H, m, C6H11); 0.96 (1 H, m, C6H11); 0.82
(1 H, m, C6H11); syn isomer: not distinguishable. 31P{1H} NMR
(162 MHz, CD2Cl2, δ): 57.99 (d, J ) 42 Hz, syn isomer); 55.46
(d, J ) 42 Hz, anti isomer); 27.05 (d, J ) 42 Hz, major anti
isomer); 25.42 (d, J ) 42 Hz, syn isomer). At room temperature,
there were two isomers present in a 16:1 (anti:syn) ratio.
P r ep a r a tion of [Ru (η6:η1-LA-P )(P MeP h 2)Cl]SbF 6. To
[Ru(η6:η1-LA)Cl2] (29.4 mg, 0.052 mmol) in CH2Cl2 (2 mL) was
added AgSbF6 (18 mg, 0.052 mmol). The solution darkened in
color. Centrifugation removed the precipitated AgCl. PMePh2
(0.012 mL, 0.064 mmol) was then added, slowly turning the

2756 Organometallics, Vol. 22, No. 13, 2003
Faller and D’Alliessi
solution orange. After ∼3 h, the solvent was removed and the
orange residue was washed with ether to remove excess
PMePh2. Small red crystals were obtained by diffusion of ether
and AgSbF6 (30 mg, 0.087 mmol) were stirred in CD2Cl2 (0.9
mL) for 3.5 h, giving an orange solution. Yield was 92% (54
mg, 0.040 mmol). Orange-yellow crystals were obtained by slow
ether diffusion into a CH2Cl2/MeOH solution. 1H NMR (400
MHz, CD2Cl2, δ): 7.96-6.65 (24 H, m, C6H5P and C6H4P); 6.12
(1 H, m, η6-C6H4N); 5.61 (1 H, d, J ) 7.2 Hz, η6-C6H4N); 4.98
(1 H, m, η6-C6H4N); 4.48 (1 H, m, η6-C6H4N); 4.25 (1 H, m,
CH); 3.53 (1 H, ddd, J ) 16, 16, 10 Hz, CH); 2.96 (6H, s, NCH3);
2.85 (1 H, m, C6H11); 2.41 (1 H, m, C6H11); 1.66 (16 H, m,
C6H11); 0.76 (2 H, m, C6H11); 0.41 (1 H, m, C6H11); 0.13 (1 H,
m, C6H11). 31P{1H} NMR (162 MHz, CD2Cl2, δ): 72.39 (d, J )
27 Hz, P(O)Ph2); 52.57 (dd, J ) 27, 43 Hz, PPh2); 49.78 (d, J
) 43 Hz, PCy2). One diastereomer was isolated.
In Situ P r ep a r a tion of [Ru (η6:η1-LA-P )(P P h 3)](SbF 6)2,
5. [Ru(η:6η1-LA-P)(PPh3)Cl]SbF6 (19.7 mg, 0.0192 mmol) and
AgSbF6 (6 mg, 0.02 mmol) were stirred in CD2Cl2 (0.9 mL) for
1 h 20 min. After centrifuging to remove precipitated AgCl,
the supernatant was transferred to an NMR tube. 31P{1H}
NMR (162 MHz, CD2Cl2, δ): +60 °C: 58.54 (d, J PP ) 36 Hz);
35.53 (d, J PP ) 36 Hz). 20 °C: 58.17 (br); 35.58 (br). -40 °C:
57.66 (d, J PP ) 36 Hz); 34.46 (d, J PP ) 36 Hz).
1
into a CH2Cl2 solution. H NMR (400 MHz, CD2Cl2, δ): anti
isomer: 7.76-7.34 (14 H, m, C6H5P and C6H4P); 5.93 (1 H, d,
J ) 6.8 Hz, η6-C6H4N); 5.55 (1 H, br, C6H5P and η6-C6H4N);
5.19 (1 H, br, C6H5P and η6-C6H4N); 4.98 (1 H, br, C6H5P and
η6-C6H4N); 3.04 (6 H, s, NCH3); 2.21 (3 H, d, J ) 9.2 Hz, PCH3);
2.67 (1 H, m, C6H11); 2.04 (1 H, m, C6H11); 1.85 (4 H, m, C6H11);
1.51 (12 H, m, C6H11); 0.88 (3 H, m, C6H11); 0.65 (1 H, m,
C6H11); syn isomer: not distinguishable. 31P{1H} NMR (162
MHz, CD2Cl2, δ): 61.35 (d, J ) 46 Hz, syn isomer); 59.13 (d,
J ) 45 Hz, anti isomer); 14.49 (d, J ) 45 Hz, anti isomer);
13.24 (d, J ) 46 Hz, syn isomer). The observed ratio of the
anti to syn isomer was 22:1.
P r ep a r a tion of [Ru (η6:η1-LA-P )(P Me3)Cl]SbF 6, 7. [Ru-
(η6:η1-LA-P)Cl2] (22.6 mg, 0.040 mmol), AgSbF6 (14 mg, 0.040
mmol), and PMe3 (1.0 M in toluene, 0.04 mL, 0.040 mmol) were
stirred in CD2Cl2 (0.9 mL) for 3 h. The purple color of the
dicationic solution slowly turned more orange-brown as the
reaction proceeded. After centrifugation to remove AgCl, the
NMR spectra were recorded. Small red crystals were obtained
by diffusion of ether into a CH2Cl2 solution. 1H NMR (400 MHz,
CD2Cl2, δ): anti isomer: 7.76 (2 H, m, C6H4P); 7.67 (2 H, m,
C6H4P); 6.01 (1 H, m, η6-C6H4N); 5.97 (1 H, m, η6-C6H4N); 5.66
(1 H, m, η6-C6H4N); 4.79 (1 H, m, η6-C6H4N); 2.84 (6 H, s,
NCH3); 2.19 (1 H, m, C6H11); 1.71 (9 H, d, J ) 10 Hz, PCH3);
1.65 (20 H, m, C6H11); 0.52 (1 H, m, C6H11); syn isomer: not
distinguishable. 31P{1H} NMR (162 MHz, CD2Cl2, δ): 64.46
(d, J ) 51 Hz, syn isomer); 62.84 (d, J ) 47 Hz, anti isomer);
2.09 (d, J ) 47 Hz, anti isomer); -0.24 (d, J ) 51 Hz, syn
isomer). The initial ratio of the anti to syn isomer was 18:1.
P r ep a r a tion of [Ru (η6:η1-LA-P )(P Me2P h )Cl]SbF6, 4. [Ru-
(η6:η1-LA-P)Cl2] (21.0 mg, 0.037 mmol) and AgSbF6 (13 mg,
0.038 mmol) were stirred in CD2Cl2 (0.9 mL) for 20 min. PMe2-
Ph (0.007 mL, 0.049 mmol) was added, and the color of the
solution turned red-orange. After stirring for 3 h, the solution
was centrifuged, dried, and washed with ether. Yield was 89%
(30 mg, 0.033 mmol). Small red crystals were obtained by
In Situ P r epar ation of [Ru (η6:η1-LA-P )(P Me2P h )](SbF6)2,
6. [Ru(η6:η1-LA-P)(PMe2Ph)Cl]SbF6 (17 mg, 0.019 mmol) and
AgSbF6 (6 mg, 0.02 mmol) were stirred in CD2Cl2 (0.9 mL) for
1 h. After centrifuging to remove precipitated AgCl, the
supernatant was transferred to an NMR tube. 31P{1H} NMR
(122 MHz, CD2Cl2, δ): 62.26 (br, minor isomer); 56.71 (br,
major isomer); 5.09 (br, major isomer); 0.23 (br, minor isomer).
The ratio of the isomers was 4:1.
Gen er a l P r oced u r e for t h e Ca t a lyzed Diels-Ald er
Rea ction .11 To enantiopure (-)-(RRu,R)-[Ru(η6:η1-LA-P)(PPh3)-
Cl]SbF6 (9.8 mg, 0.0095 mmol) in CH2Cl2 (2 mL) was added
AgSbF6 (3 mg, 0.0087 mmol). Additional CH2Cl2 (1 mL) washed
any AgSbF6 from the walls of the centrifuge tube into the
mixture. After stirring for 35 min, the solution was centrifuged.
The orange supernatant was transferred to a precooled -20
°C vial. Methacrolein (8 µL, 0.097 mmol) was added, and the
mixture was allowed to cool to -78 °C for 40 min. An aliquot
of freshly distilled CpH (0.08 mL, 0.97 mmol) was then added
by syringe to the reaction mixture. After 17 h at -78 °C, the
solution was transferred to a flask, where the solvent was
removed under reduced pressure to give an orange residue.
Conversion of methacrolein (96%) and diastereomeric excess
1
diffusion of ether into a CH2Cl2 solution. H NMR (300 MHz,
CD2Cl2, δ): anti isomer: 7.64 (9 H, m, C6H4P and C6H5P); 5.83
(1 H, d, J ) 7.2 Hz, η6-C6H4N); 5.39 (1 H, m, η6-C6H4N); 5.24
(1 H, m, η6-C6H4N); 4.80 (1 H, d, J ) 5.2 Hz, η6-C6H4N); 2.903
(3 H, s, NCH3); 2.901 (3 H, s, NCH3); 2.79 (1 H, m, C6H11);
2.19 (1 H, m, C6H11); 2.00 (3 H, d, J ) 10 Hz, PCH3); 1.95 (3
H, d, J ) 10 Hz, PCH3); 1.52 (19 H, m, C6H11); 0.67 (1 H, m,
C6H11); syn isomer (partial): 5.86 (1 H, obstructed m, η6-
C6H4N); 5.56 (1 H, d, J ) 6.0 Hz, η6-C6H4N); 5.37 (1 H,
obstructed m, η6-C6H4N); 5.20 (1 H, obstructed m, η6-C6H4N);
2.50 (6 H, s, NCH3); 2.10 (3 H, d, J ) 10 Hz, PCH3); 2.07 (3 H,
d, J ) 10 Hz, PCH3). 31P{1H} NMR (122 MHz, CD2Cl2, δ):
61.79 (d, J ) 49 Hz, syn isomer); 60.42 (d, J ) 46 Hz, anti
isomer); 2.01 (d, J ) 46 Hz, anti isomer); -0.79 (d, J ) 49 Hz,
syn isomer). The initial ratio of anti to syn isomer was 13:1.
Anal. Calcd for C34H47ClF6NP2RuSb: C, 45.18; H, 5.24; N, 1.55.
Found: C, 45.14; H, 5.28; N, 1.53. (Note that the X-ray
structure was from a sample obtained by fractional crystal-
lization from CH2Cl2/ether that gave only the syn isomer.)
[R u (η6:η1-LA -P )(η2-(R)-P R OP H OS-P ,P )](Sb F 6)2. [Ru-
(η6:η1-LA-P)Cl2] (30.9 mg, 0.055 mmol), (R)-PROPHOS (23.6
mg, 0.057 mmol), and AgSbF6 (38 mg, 0.11 mmol) were stirred
in CD2Cl2 (0.9 mL) for 3 h. After centrifuging to remove the
AgCl precipitate, an NMR spectrum was recorded of the red
supernatant. 31P{1H} NMR (122 MHz, CD2Cl2, δ): 76.95
(pseudo-t, J ) 30 Hz); 73.74 (pseudo-t, J ) 27 Hz); 73.06
(pseudo-t, J ) 31 Hz); 64.83 (pseudo-t, J ) 29 Hz); 58.44 (m);
54.90 (pseudo-t, J ) 30 Hz); 53.11 (m); 44.98 (pseudo-t, J )
31 Hz); 39.63 (pseudo-t, J ) 27 Hz). Four diastereomers in
nearly equal ratios were formed.
1
(de, 91% exo) were determined by H NMR spectroscopy. The
shift reagent (+)-Eu(hfc)3 was used to determine an enantio-
meric excess of 23% (R).
When (+)-(SRu,S)-[Ru(η6:η1-LA-P)(PPh3)Cl]SbF6 was used as
the precatalyst at -20 °C, the conversion of methacrolein was
95% and the diastereomeric excess was 96% (exo), as deter-
mined by 1H NMR spectroscopy. The shift reagent (+)-Eu(hfc)3
was used to determine an enantiomeric excess of 19% (S).
Str u ctu r e Deter m in a tion a n d Refin em en t of 2, 3a , 4,
a n d 7. Data were collected on a Nonius KappaCCD (Mo KR
radiation) and corrected for absorption (SORTAV).45 The
structures were solved by direct methods (SIR92)46 and refined
on F for all reflections. Non-hydrogen atoms were refined with
anisotropic displacement parameters. Hydrogen atoms were
included at calculated positions. Relevant crystal and data
parameters are presented in Table 1. A sample was cut from
a large crystal of 3a , and the absolute configuration of that
portion was determined by inverting coordinates and noting
a difference in R and Rw of 0.0373 and 0.0389 compared to
0.0343 and 0.0355 of the correct configuration. The remainder
of the crystal was dissolved, and the optical rotation and CD
spectrum were recorded to correlate chiroptical properties with
absolute configuration. ORTEP views are shown in Figures 1,
(45) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. (b) Blessing,
R. H. J . Appl. Crystallogr. 1997, 30, 421.
(46) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J .
Appl. Crystallogr. 1993, 26, 343.
[Ru (η6:η1-LA-P )(η2-d p p m O-P ,O)](SbF 6)2. [Ru(η6:η1-LA-P)-
Cl2] (24.3 mg, 0.043 mmol), dppmO (20.3 mg, 0.049 mmol),

Planar Chirality in Tethered Ru(II) Complexes
Organometallics, Vol. 22, No. 13, 2003 2757
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p lexes Con ta in in g a Teth er ed P h osp h in e Moiety
[Ru (η6:η1-Me2NC6H4C6H4P Cy2-P )(L)Cl]
2 (L ) Cl)
anti-3a (L ) PPh3)
anti-7 (L ) PMe3)
syn-4 (L ) PPhMe2)
color, shape
empirical formula
fw
red-orange plate
C26H36Cl2NPRu
565.53
orange block
C44H51ClF6NP2RuSb
1028.10
yellow plate
C29H45ClF6NP2RuSb
841.89
orange needle
C35H49Cl3F6NP2RuSb
988.90
radiation/Å
T/K
Mo K R (monochr.) 0.71073
183
183
296
183
cryst syst
space group
monoclinic
P21/n (No. 14)
orthorhombic
P212121 (No. 19)
monoclinic
P21/n (No. 14)
orthorhombic
Pca21(No. 29)
unit cell dimens
a/Å
b/Å
c/Å
11.7759(5)
10.7780(5)
20.5862(10)
103.178(3)
2544.0(2)
4
1.476
9.03
0.05 × 0.12 × 0.14
19583, 6077
0.117
10.9480(3)
14.1398(5)
27.1255(9)
90
4199.1(2)
4
1.626
12.02
0.07 × 0.07 × 0.010
16673, 9974
0.048
14.0169(5)
16.2724(6)
15.2783(6)
100.333(2)
3428.3(2)
4
1.631
14.51
0.05 × 0.12 × 0.17
19048, 6870
0.099
15.1594(5)
14.1727(5)
18.2768(5)
90
3926.8(2)
4
1.673
14.12
0.05 × 0.05 × 0.12
22071, 11213
0.066
â/deg
V/Å3
Z
D
calc/g cm-3
µ/cm-1 (Mo KR )
cryst size/mm
total reflns, unique reflns
Rint
no. obsd (I > nσ (I)
transmn range
params, constrnts
R,a Rw,b GOF
2556, 2
0.917-0.963
280, 0
0.040, 0.035, 0.67
-0.49 < 0.51
3302, 3
0.865-0.919
505, 0
0.034, 0.036, 0.90
-0.47 < 0.54
2449, 3
0.794-1.000
370, 0
0.042, 0.048, 1.09
-0.67 < 0.63
3228, 2
0.847-0.935
441, 0
0.042, 0.040, 0.084
-0.62 < 0.068
resid density/e Å-3
a
b
R1 ) ∑||Fo| - |Fc||/∑|Fo|, for all I > n(I). Rw ) [∑[w(|Fo| - |Fc|)2]/∑[w(Fo)2]]1/2
.
4, and 5 for 2, 3a , and 4, respectively. An ORTEP view of 7 is
similar to that of 3a and is included in the Supporting
Information.
There was also a ∼4:1 disorder in one of the SbF6 ions. Heavy
atoms (Sb, Ru, Cl, P, F) were refined with anisotropic displace-
ment parameters, and the remaining non-hydrogen atoms
were refined with isotropic parameters. Since the heavy atoms
are related by a pseudocenter, there are not sufficient anoma-
lous dispersion differences to determine the polarity using the
Flack parameter or differences in R upon inversion. The
polarity was fixed by using the known S-configuration of the
amine. For data > 3σ(I), and 6239 observations with 566
variables, the final residuals were R ) 0.052 and Rw ) 0.063.
St r u ct u r e Det er m in a t ion a n d R efin em en t of [R u -
(η6:η1-Me2NC6H4C6H4P Cy2-P )(P P h 2(S)-1-p h en yleth yla m i-
n o)Cl]SbF 6, 8. An orange plate suitable for analysis was
obtained by diffusion of hexane into a methylene chloride
solution of a 1:1 mixture of diastereomers. Data were collected
on a Nonius KappaCCD (Mo KR radiation) and corrected for
absorption (SORTAV).45 A triclinic cell with Z ) 2 was found
with cell constants of a ) 10.7371(3) Å; b ) 11.7416(3) Å; c )
19.5736(5) Å; R ) 86.531(2)°; â ) 75.512(2)°; γ ) 77.1560(13)°;
V ) 2329.38(11) Å3. The structure was solved by direct meth-
ods (SIR92)46 and refined on F for all reflections. A solution
could be found for either centrosymmetric P1h or noncen-
trosymmetric P1. In the P1h solution, there was a disorder in
the phenethylamine moiety corresponding to both chiralities
being present. Since the phenethylamine was not racemic, it
followed that the two ruthenium moieties were epimeric and
the appropriate space group was P1 with two independent
cations and anions. Owing to the pseudosymmetry, the move-
ments of the two independent molecules were correlated and
the atom movements during refinement had to be dampened.
Ack n ow led gm en t. D.G.D. would like to thank Dr.
J onathan Parr and Dr. J ohn F. Hartwig for helpful
suggestions. This work was supported by the National
Science Foundation Grant CHE0092222.
Su p p or tin g In for m a tion Ava ila ble: A listing of atomic
positions, thermal parameters, and bond distances and angles
for 2, 3a , 4, 7, and 8, as well as an ORTEP view of 4. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM030080Q