Chiral olefins as steering ligands: Syntheses of C1-symmetric dibenzo[a,e]cyclooctenes (Rdbcot)

Article abstract of DOI:10.1021/om050093z

A simple three-step synthesis of chiral dibenzo[a,e]cyclooctenes (dbcot) starting from commercially available dibenzosuberenone was developed. These compounds give highly stable and robust rhodium(I) and iridium(I) diene complexes of the type [M(^Rdbcot)(L¹)(L²)] (M = Rh, Ir; L¹, L² = MeCN, Cl, diamine, chloride). The complex [Rh((R)-^Phdbcot)((R)-(+)-1,1′-binaphthyl-2,2′-diamine)] ⁺OTf^- could be obtained in enantiomerically pure form and catalyzes the enantioselective 1,2-addition of PhB(OH)₂ to α,β-unsaturated ketones with good activity and acceptable enantiomeric excess (62%). The iridium complex [Ir(^phdbcot)-(MeCN) ₂]⁺OTf^- catalyzes the hydrogenation of dimethylitaconate with good activity, while the rhodium complexes are almost inactive. Likewise, the complex [Ir(^phdbcot)(H₂NCH ₂-CH₂NH₂)]⁺OTf^- serves as a rather efficient catalyst precursor with an activity 4 orders of magnitude higher than for the analogous rhodium complex. These experiments further establish the use of dienes as steering ligands in catalysis.

Full text of DOI:10.1021/om050093z

Organometallics 2005, 24, 2997-3007
2997
Chiral Olefins as Steering Ligands: Syntheses of
C1-Symmetric Dibenzo[a,e]cyclooctenes (Rdbcot)
Florian La¨ng, Frank Breher, Daniel Stein, and Hansjo¨rg Gru¨tzmacher*
Department of Chemistry and Applied Biosciences, ETH-Ho¨nggerberg,
CH-8093 Zu¨rich, Switzerland
Received February 10, 2005
A simple three-step synthesis of chiral dibenzo[a,e]cyclooctenes (dbcot) starting from
commercially available dibenzosuberenone was developed. These compounds give highly
stable and robust rhodium(I) and iridium(I) diene complexes of the type [M(Rdbcot)(L1)(L2)]
(M ) Rh, Ir; L1, L2 ) MeCN, Cl, diamine, chloride). The complex [Rh((R)-Phdbcot)((R)-(+)-
1,1′-binaphthyl-2,2′-diamine)]+OTf- could be obtained in enantiomerically pure form and
catalyzes the enantioselective 1,2-addition of PhB(OH)2 to R,â-unsaturated ketones with
good activity and acceptable enantiomeric excess (62%). The iridium complex [Ir(Phdbcot)-
(MeCN)2]+OTf- catalyzes the hydrogenation of dimethylitaconate with good activity, while
the rhodium complexes are almost inactive. Likewise, the complex [Ir(Phdbcot)(H2NCH2-
CH2NH2)]+OTf- serves as a rather efficient catalyst precursor with an activity 4 orders of
magnitude higher than for the analogous rhodium complex. These experiments further
establish the use of dienes as steering ligands in catalysis.
Chart 1. Chiral Dienes and Olefin Ligands Used
in Enantioselective Catalyses
Introduction
Many diene complexes described in the literature
contain a η4-1,5-cyclooctadiene (cod) ligand,1 which is
mostly employed as a placeholder for so-called “vacant”
coordination sites. Only recently have dienes became
recognized as valuable steering ligands for homoge-
neously catalyzed reactions. Lemaire et al. found strong
evidence that amide complexes derived from C2-sym-
metric [RhI(cod)(diamine)] complexes are involved in the
catalytic cycle: that is, neither the amine nor the olefin
is displaced in the catalytically active species.2 Likewise,
van Leeuwen et al. proposed chiral aminosulfide or
aminosulfoxide diene complexes [IrI(cod)(RHNnSOR)] as
efficient catalyst precursors in the transferhydrogena-
tion of aryl alkyl ketones.3 Dahlenburg et al. reported
rhodium and iridium cod complexes with â-aminophos-
phanes as further ligands as catalysts for the hydroge-
nation of ketones.4 Several chiral dienes such as C1-
[2.2.2]cod, C2-nbd, and C2-Ph-bnd (Chart 1) have been
introduced recently as steering ligands in enantioselec-
tive catalytic processes5 through the work of Carreira
et al.6 and Hayashi et al.7 In related work, we synthe-
sized chiral C1-tropp ligands (tropp ) tropylidenylphos-
phanes) and used the unsymmetric substitution pattern
at the CdCtrop bond of the central seven-membered ring
for stereochemical induction. Values of up to 86% ee
were achieved in the catalyzed hydrogenation of imines
using [Ir(C1-tropp)] complexes.8
Replacement of the phosphanyl donor function, R2P,
in these tropp-type ligands9 by a CHdCH unit leads to
related dibenzo[a,e]cyclooctenes (dbcot). The parent
hydrocarbon, C16H12, was prepared about 60 years ago,10
and its structure, determined by X-ray diffraction,
shows a boat conformation.11 First coordination com-
pounds with dbcot as ligand contained silver and
palladium as metals,12 followed by reports on complexes
(6) (a) Shintani, R.; Okamoto, K.; Otomaru, Y.; Ueyama, K.; Hayashi,
T. J. Am. Chem. Soc. 2005, 127, 54. (b) Tokunaga, N.; Otomaru, Y.;
Okamoto, K.; Ueyama, K.; Shintani, R.; Hayashi, T. J. Am. Chem. Soc.
2004, 126, 13584. (c) Hayashi, T.; Ueyama, K.; Tokunaga, N.; Yoshida,
K. J. Am. Chem. Soc. 2003, 125, 11508.
* To whom correspondence should be addressed. E-mail:
gruetzmacher@inorg.chem.ethz.ch.
(1) (a) Rhodium cod complexes: Sharp, P. R. Comprehensive Orga-
nometallic Chemistry, 2nd ed.; Abel, E. W., Stone, F. G. A., Wilkinson,
G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 8, pp 245-268. (b) Iridium
cod complexes: Sharp, P. R. Comprehensive Organometallic Chemistry,
2nd ed.; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds., Pergamon:
Oxford, U.K., 1995; Vol. 8, pp 365-270.
(7) (a) Defieber, C.; Paquin, J.-F.; Serna, S.; Carreira, E. M. Org.
Lett. 2004, 6, 3873. (b) Fischer, C.; Defieber, C.; Suzuki, T.; Carreira,
E. M. J. Am. Chem. Soc. 2004, 126, 1628.
(8) (a) Gru¨tzmacher, H.; Deblon, S.; Maire, P.; Scho¨nberg, H. Ger.
Offen. DE 101 59 015.6, 2002. (b) Maire, P.; Deblon, S.; Breher, F.;
Geier, J.; Bo¨hler, C.; Ru¨egger, H.; Gru¨tzmacher, H. Chem. Eur. J. 2004,
10, 4198.
(2) Bernard, M.; Guiral, V.; Delbecq, F.; Fache, F.; Sautet, P.;
Lemaire, M. J. Am. Chem. Soc. 1998, 120, 1441, and literature cited
therein.
(3) Petra, D. G. I.; Kamer, P. C. J.; Spek, A. L.; Schoemaker, H. E.;
van Leeuwen, P. W. N. M. J. Org. Chem. 2000, 65, 3010.
(4) Dahlenburg, L.; Go¨tz, R. Eur. J. Inorg. Chem. 2004, 888. (b)
Dahlenburg, L.; Go¨tz, R. J. Organomet. Chem. 2001, 619, 88.
(5) For a short review see: Glorius, F. Angew. Chem., Int. Ed. 2004,
43, 3364.
(9) Thomaier, J.; Boulmaaˆz, S.; Scho¨nberg, H.; Ru¨egger, H.; Currao,
A.; Gru¨tzmacher, H.; Hillebrecht, H.; Pritzkow, H. New J. Chem. 1998,
21, 947 and literature cited therein.
(10) Fieser, L. F.; Pechet, M. J. Am. Chem. Soc. 1946, 68, 2577.
(11) Irngartinger, H.; Reibel, W. R. K. Acta Crystallogr. 1981, B37,
1724.
10.1021/om050093z CCC: $30.25 © 2005 American Chemical Society
Publication on Web 05/06/2005

2998 Organometallics, Vol. 24, No. 12, 2005
La¨ng et al.
Scheme 1. Syntheses of Chiral
Dibenzo[a,e]cyclooctene (dbcot) Derivatives
With the same procedure, naphthyl and 2-methoxy-
naphthyl groups were introduced, and the alcohols 3a-c
were easily prepared in gram quantities. With the
sterically more demanding 2-methoxynaphthyl group,
the yield of 3c (60%) was lower, and this compound was
always contaminated with small amounts of the ketone
2. However, this impurity did not interfere with the
subsequently performed elimination reaction. Addition
of 20 mol % CF3COOH to CH2Cl2 solutions of 3a-c and
stirring of the reaction mixtures for about 20 h at room
temperature led almost quantitatively (yields >95%) to
racemic mixtures of the desired 5-substituted dibenzo-
[a,e]cyclooctenes (R)-4a and (S)-4a (phdbcot), (R)-4b and
(S)-4b (naphdbcot), and (R)-4c and (S)-4c (2MeO-naphdbcot).
We will denote the racemic mixture as R(S) hereafter;
details concerning the assignment of the stereochemis-
try are given in the Experimental Section. The impurity
2 is easily separated from (R(S))-4c by flash chroma-
tography. The rotation of the 2-methoxynaphthyl group
in (R(S))-4c is hindered at room temperature, causing
a doubling of all NMR resonances.
The syntheses of rhodium(I) and iridium(I) complexes
with Rdbcot as ligands were accomplished in straight-
forward ligand substitution reactions (Scheme 2). [Rh2-
(µ2-Cl)2(CO)4] is a suitable precursor for rhodium com-
plexes and reacts with the racemic mixture of (R(S))-
4a,b to give the chloro-bridged dimeric complexes 5a,b.
These compounds form complex mixtures containing
various stereoisomers which were not isolated or inves-
tigated in detail.
with chromium or molybdenum.13 With chromium,
coordination via the benzo groups was also observed.14
Crabtree et al. demonstrated the remarkable stability
of various molybdenum, rhodium, and iridium com-
plexes,15,16 and the inertness of [MH2(dbcot)L2]+ (M )
Rh, Ir; L ) phosphane) is especially noteworthy; that
is, no hydrogenation of the dbcot ligand is observed.
Moreover, dbcot was employed as a catalyst poison. A
tetranuclear copper dbcot complex was also described.17
In this paper we report the facile syntheses of chiral
Rdbcot derivatives as ligands for tetracoordinated 16-
electron rhodium(I) and iridium(I) complexes (R denotes
a substituent in the 5-position). Furthermore, we de-
scribe first results concerning the application of these
complexes in homogeneously catalyzed reactions.
Subsequent reactions with silver salts AgX (X-
)
CF3SO3-, OTf-, SbF6-) in acetonitrile as solvent
give the mononuclear bis(acetonitrile) complexes
[Rh(Rdbcot)(MeCN)2]+X- ((R(S))-6a,b) as orange (X-
)
OTf-) and yellow-brown (X- ) SbF6-) microcrystalline
powders in high yields. Reactions with the sterically
more hindered ligand 2-MeO-naphdbcot (4c) were less suc-
cessful, and no pure compound was obtained. In one ex-
periment, we could however isolate by accident a crys-
talline substance of composition [Rh(2-MeO-naphdbcot)-
(MeCN)(H2O)]OTf ((R(S))-6c) when solutions of [Rh2-
(µ2-Cl2)(CO)4] and (R(S))-4c were kept in presence of
silver triflate for several days in acetonitrile solution.
Results and Discussion
Syntheses. The rather laborious synthesis of dbcot
is the likely reason that the investigation of its coordi-
nation chemistry stopped about 20 years ago. We found
a simple and straightforward synthesis of chiral Rdbcot
derivatives18 which show an unsymmetrical substitution
pattern at the CdC bonds of the central eight-membered
ring. As reported in the literature19 and shown in
Scheme 1, dibenzosuberenone (1) is easily ring-ex-
panded with (trimethylsilyl)diazomethane to give the
ketone 2, having an eight-membered ring in its center.
The reaction of 2 with a phenylcerium reagent prepared
in situ from phenylmagnesium bromide and CeIIICl3 in
thf20 yields the tertiary alcohol 5-phenyl-5,6-dihydro-
dibenzo[a,e]cyclooctene-5-ol (3a) in 88% isolated yield.
The neutral 16-electron iridium complex [IrCl-
(
Phdbcot)(MeCN)] ((R(S))-7a) was obtained as orange
crystals when [Ir2(µ2-Cl)2(cod)2] was reacted with
(R(S))-4a in an acetonitrile/CH2Cl2 mixture at room
temperature. In CD3CN, only one isomer with the chloro
ligand in a position trans to the 5-phenyl substituent
of the Phdbcot ligand is observed. In CDCl3 or CD2Cl2,
several species are observed (some showing exchange
broadened signals), which are tentatively attributed to
the various possible stereoisomers of the chloro-bridged
dinuclear compounds [Ir2(µ2-Cl)2(Phdbcot)2] and a mix-
ture of the mononuclear complexes (R(S))-7a with a cis-
and trans-orientation of the chloro ligand with respect
to PhCdCH unit. Reaction of (R(S))-7a with AgOTf
again gives cleanly the cationic bis(acetonitrile) complex
[Ir(Phdbcot)(MeCN)2]+OTf- ((R(S))-8a) as orange micro-
crystalline powder (X- ) CF3SO3-, SbF6-) in high yield.
In the reaction with the naphthyl-substituted ligand
naphdbcot (4b) in benzene at 80 °C, we used [Ir2(µ2-Cl)2-
(coe)4] as a precursor (coe ) cyclooctene). The chloro-
bridged dinuclear complex 9b precipitates during the
(12) Avram, M.; Dinu, D.; Mateescu, G.; Nenitzescu, C. D. Chem.
Ber. 1960, 93, 1793.
(13) Mu¨ller, J.; Go¨ser, P.; Elian, M. Angew. Chem., Int. Ed. Engl.
1969, 8, 374.
(14) Brown, M.; Zubkowski, J. D.; Valente, E. J.; Yang, G.; Henry,
W. P. J. Organomet. Chem. 2000, 613, 111.
(15) Douglas, A. R.; Crabtree, R. H. Organometallics 1983, 2, 621.
(16) Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 855.
(17) Mak, T. C. W.; Wong, H. N. C.; Sze, K. H.; Book, L. J.
Organomet. Chem. 1983, 255, 123.
(18) La¨ng, F. ETH Dissertation No. 15845, 2004.
(19) Chaffins, S.; Brettreich, M.; Wudl, F. Synthesis 2002, 1191.
(20) Imamoto, T.; Takiyama, N.; Nakamura, K.; Hatajima, T.;
Kamiya, Y. J. Am. Chem. Soc. 1989, 111, 4392.

Chiral Olefins as Steering Ligands
Organometallics, Vol. 24, No. 12, 2005 2999
Scheme 2. Syntheses of Rhodium(I) and Iridium(I) Rdbcot Complexes (R ) Ph, naph)
Table 1. Coordination Shifts, ∆δ ) δligand - δcomplex
,
reaction time (24 h) as a yellow microcrystalline sub-
stance which is only sparingly soluble in common
deuterated solvents. The reaction with AgSbF6 in ac-
etonitrile converts 9b cleanly into the orange crystalline
mononuclear bis(acetonitrile) complex [Ir(naphdbcot)-
Determined for the 13C Chemical Shifts (δ in ppm),
of the Olefinic Carbons C5, C6, C11, and C12a and
the M-ct Distances (Å; ct ) Centroid of the
Coordinated CdC Bond) in the Complexes
(R(S))-7a, (R(S))-8b, and (R)-[(R)-(+)]-11a
(MeCN)2]+SbF6 ((R(S))-8b).
-
In 1H NMR spectra of the complexes [M(Phdbcot)-
(MeCN)2]+X- (M ) Rh, (R(S))-6a; M ) Ir, (R(S))-8a),
the ortho and meta protons of the phenyl group appear
as exchange-broadened signals, indicating hindered
rotation on the NMR time scale. In the corresponding
naphdbcot-substituted complexes (R(S))-6b (M ) Rh) and
(R(S))-8b (M ) Ir), sharp resonances are observed for
all protons of the naphthyl group. Of special diagnostic
value is the resonance of the proton at the 8-position of
the naphthyl substituent, which is shifted to unusually
high frequencies (δ 10.07 ppm (M ) Rh), 9.34 ppm (M
) Ir)). An X-ray diffraction study of [Ir(naphdbcot)-
∆δ(13C)
M
C5
C6
C11
C12 M-ct1 M-ct2
(R(S))-7a
(R(S))-8b
Ir 70.6 72.2 64.3 60.8 2.004(4) 1.997(5)
Ir 57.6 65.3 62.5 64.6 1.990(7) 1.993(8)
(MeCN)2]+SbF6 shows (vide infra) that this proton
-
(R)-[(R)-(+)]-11a Rh 46.0 53.7 53.2b 54.2b 2.016(5) 2.001(5)
(H24) points toward the metal center. We therefore con-
clude that the naphthyl group resides in a frozen posi-
tion which corresponds to that seen in the solid state.
a δligand for 4a: 145.12 (C5), 129.51 (C6), 134.19 (C11), 133.21
(C12). δligand for 4b: 142.97 (C5), 133.85 (C6), 134.87 (C11), 133.50
(C12). b For (R)-[(R)-(+)]-11a the unambiguous assignment of C11
and C12 was impossible.
In Table 1, the coordination shifts, ∆δ ) δligand
-
δcomplex (δligand is the chemical shift in the uncomplexed
Rdbcot molecule; δcomplex is the corresponding chemical
shift in the complex), for the four coordinated carbon
atoms C5, C6, C11, and C12 are listed for selected
compounds. The ∆δ values (46-59 ppm for M ) Rh;
59-72 ppm for M ) Ir) are in the usual range for
rhodium(I) or iridium(I) complexes.21
It is generally assumed that with increasing ∆δ the
interaction energy between the metal and the coordi-
nated olefins increases as well. Remarkably then, these
data indicate in combination with the distances M-ct
from the metal to the centroid of the coordinated CdC
bond (determined by X-ray diffraction; vide supra), that
both CdC units interact almost equally and rather
strongly with the metal center in all [M(Rdbcot)] com-
(21) Mann, B. E.; Taylor, B. E. 13C NMR Data for Organometallic
Compounds; Academic Press: London, 1981; p 16.

3000 Organometallics, Vol. 24, No. 12, 2005
La¨ng et al.
Scheme 3. Synthesis of the Diastereomerically
Pure Complexes (R)-[(R)-(+)]-11a and (R)-6a
2-MeO-naph). Also, analogous reactions with the iri-
dium complexes (R(S))-8a and (R(S))-8b with enantio-
merically pure diamines gave dark brown insoluble
materials only.
The addition of trifluorosulfonic acid, CF3SO3H, to the
diastereomer (R)-[(R)-(+)]-11a in acetonitrile allowed
the displacement of the binaphthyldiamine ligand as
chiral auxiliary, and the bis(acetonitrile) complex
(R)-[Rh(Phdbcot)(MeCN)2]+OTf- ((R)-6a) was obtained
in enantiomerically pure form (determined by adding
(R)-(+)-1,1′-binaphthyl-2,2′-diamine, (R)-(+)-10, which
furnished the single diastereomer (R)-[(R)-(+)]-11a
1
quantitatively within the detection limits of H NMR
spectroscopy).
As discussed above, addition of phosphanes easily
displaces the Rdbcot ligands in the rhodium complexes.
Therefore we hoped that we might obtain the enantio-
merically pure free ligand (R)-Phdbcot ((R)-4a) in the
reaction of (R)-[(R)-(+)-11a or (R)-6a with PPh3. Unfor-
tunately, it turned out that the free ligand (R)-Phdbcot
is not conformationally stable but racemizes completely
in less than 3 h at room temperature.23
Structures. Single crystals of the uncomplexed 5-
phenyldibenzo[a,e]cyclooctene (Phdbcot (R(S))-4a; Figure
1) and the iridium complexes (R(S))-[IrCl(Phdbcot)-
(MeCN)] ((R(S))-7a; Figure 2) and (R(S))-[Ir(naphdbcot)-
(MeCN)2]+SbF6- ((R(S))-8b; Figure 3) were investigated
by X-ray diffraction. The results are displayed as
ORTEP plots for one of the enantiomers in Figures 1-3,
respectively. A crystal of the chiral complex (R)-[(R)-
(+)]-[Rh(Phdbcot)(1,1′-binaphthyl-2,2′-diamine)]+OTf-
((R)-[(R)-(+)]-11a) was also subjected to an X-ray struc-
ture analysis; the result is displayed in Figure 4.
Furthermore, we investigated (R(S))-6c. However, the
asymmetric unit contains several solvent molecules
(that is, n-hexane and CH2Cl2) on special positions of
2-fold symmetry. Due to strong disorder, the quality of
the data set is insufficient to allow for a detailed
discussion (a graphical presentation of the complex is
given in the Supporting Information).
Selected structural parameters for each compound are
given in the corresponding figure caption, and details
concerning the data collections and refinements are
given in Table 3 in the Experimental Section. In the
uncomplexed Phdbcot ((R(S))-4a) the central olefinic
C5-C6 (1.332(4) Å) and C12-C11 (1.323(5) Å) double
bonds have the usual lengths. For the description of
the boat conformation in Phdbcot, we use the average
of the four torsion angles defined by the central ole-
finic bonds and the adjacent CdCbenzo bonds (for in-
stance, C5-C6-C15-C16) which amounts to 62.9° in
(R(S))-4a. This value is similar to that for the parent
dbcot (59.7°).11 All structures of the metal complexes
plexes, despite the fact that trisubstituted olefins are
usually considered to be significantly more weakly
bound ligands. The coordination shifts ∆δ are, as
expected, somewhat larger in the iridium complexes
than in the rhodium complexes, indicating a higher
degree of metal-to-ligand back-bonding. Therefore, the
Rdbcot ligand should be more tightly bound in the
iridium complexes, which is confirmed by the following
experiments. When the rhodium complex [Rh(Phdbcot)-
(MeCN)2]+OTf- ((R(S))-6a) is reacted with 4 equiv of
PPh3 in acetonitrile solution at room temperature, a
quantitative displacement of the Phdbcot ligand and
the formation of [Rh(PPh3)3(MeCN)]+ is observed.22 On
the other hand, the complete displacement of the
Rdbcot ligands from the iridium complexes by PPh3 or
even chelating diphosphanes such as dppe requires
temperatures above 70 °C and prolonged reaction times
(∼24 h).
All complexes described so far were obtained as
racemic mixtures containing both enantiomers of the
Rdbcot ligands. Our attempts to find conditions allowing
R
a separation of either the free dbcot or the complexes
failed. However, the reaction of the rhodium complex
[Rh(Phdbcot)(MeCN)2]+OTf ((R(S))-6a) with (R)-(+)-1,1′-
binaphthyl-2,2′-diamine ((R)-(+)-10) gave the diaster-
eomeric diamine rhodium complexes (R)-[(R)-(+)]-11a
and (S)-[(R)-(+)]-11a (Scheme 3) as pure compounds,
which show clearly separated signals for each diaste-
1
reomer in the H NMR spectrum. Also, the reaction of
racemic (R(S))-6a with a the R,R-configured enantiomer
of 1,2-diaminocyclohexane ((R,R)-dach) gave a mixture
of diastereomeric diamine complexes which show clearly
separated sets of NMR resonances; however, these could
not be separated by fractional crystallization. On the
other hand, recrystallization of the mixture of (R)-[(R)-
(+)]-11a and (S)-[(R)-(+)]-11a from ethanol/n-hexane
gave one diastereomer in 32% isolated yield, as deter-
(23) The inversion barrier of cyclooctatetraene (C8H8, cod) is lower
than 14 kcal mol-1, and the resolution of the enantiomers of mono-
substituted cod derivatives could not be achieved: (a) Anet, F. A. L.;
Bourn, A. J. R.; Lin, Y. S. J. Am. Chem. Soc. 1964, 86, 3576. (b) Cope,
A. C.; Meili, J. E. J. Am. Chem. Soc. 1967, 89, 1883. Also, the inversion
barrier of other chiral dibenzo[a,e]cyclooctenes (dbcot’s) with substit-
uents attached to one of the benzo groups is too low to allow isolation
in nonracemic form: (c) Senkler, G. H.; Gust, D.; Riccobono, P. X.;
Mislow, K. J. Am. Chem. Soc. 1972, 94, 8626. However, chiral dbcot’s
showing multiple substitution at the olefinic CdC bonds have inversion
barriers >25 kcal mol-1, which is sufficient to allow their isolation in
enantiomerically pure form: (d) Mislow, K.; Perlmutter, H. D. J. Am.
Chem. Soc. 1962, 84, 3591. (e) Salisbury, L. E. J. Org. Chem. 1978,
43, 26.
1
mined by H NMR spectroscopy. The absolute configu-
ration of this compound was determined by X-ray
analysis as the (R)-[(R)-(+)]-11a isomer (vide infra). No
further diastereomerically pure complex could be iso-
lated from the mother liquor. All attempts to use this
method with the other Rdbcot ligands failed (R ) naph,
(22) Pimblett, G.; Garner, C. D.; Clegg, W. J. Chem. Soc., Dalton
Trans. 1985, 1977.

Chiral Olefins as Steering Ligands
Organometallics, Vol. 24, No. 12, 2005 3001
Figure 2. Molecular structure of [IrCl(Phdbcot)(MeCN)]
7a. Only the R-configured isomer is shown. Thermal
ellipsoids are drawn at the 50% probability level; hydrogen
atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ir1-C5 ) 2.148(4), Ir1-C6 ) 2.107(4),
Ir1-ct1 ) 2.004(4), Ir1-C11 ) 2.110(4), Ir1-C12 ) 2.134-
(5), Ir1-ct2 ) 1.997(5), Ir1-N1 ) 2.059(5), Ir1-Cl1 )
2.344(1), C5-C6 ) 1.431(6), C11-C12 ) 1.432(6); N1-Ir1-
Cl1 ) 88.7(1), N1-Ir1-Ct1 ) 91.4(2), Cl1-Ir1-Ct2 ) 92.1-
(2), Ct1-Ir1-Ct2 ) 88.4(2). ct ) centroids of the coordi-
nated CdC units); æ ) 8.8° is the intersection angle of the
ct1-Ir1-ct2 plane and the Cl1-Ir1-N1 plane. Torsion
angles (deg): C5-C6-C15-C16 ) 75.8(5), C15-C16-
C11-C12 ) -69.2(5), C11-C12-C13-C14 ) 66.1(6),
C13-C14-C5-C6 ) -71.7(5); average 70.6°.
Figure 1. Molecular structure of Phdbcot (4a). Only the
R-configured isomer is shown. Thermal ellipsoids are
drawn at the 50% probability level; hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles
(deg): C5-C6 ) 1.332(4), C11-C12 ) 1.323(5), C5-C17
) 1.499(4), C5-C14 ) 1.484(4), C12-C13 ) 1.485(5), C11-
C16 ) 1.473(5), C6-C15 ) 1.481(4), C13-C14 ) 1.403(4),
C15-C16 ) 1.404(5); C15-C6-C5 ) 127.4(3), C6-C5-
C14 ) 122.4(3), C13-C12-C11 ) 124.6(3), C12-C11-C16
) 126.6(3). Torsion angles (deg): C5-C6-C15-C16 )
62.2(5), C15-C16-C11-C12 ) -60.6(5), C11-C12-C13-
C14 ) 62.2(5), C13-C14-C5-C6 ) -65.4(4); average
62.9°.
1
cant high-frequency shifts in the H NMR spectra, as
we also see in (R(S))-8b (vide supra).24,25
show only minor distortions from a planar coordination
sphere (the intersection angles æ of the ct1-M-ct2
plane with the L1-M-L2 plane (L1, L2 ) donor atoms
of the other two ligands) are smaller than 12°). The
olefinic bonds of the Rdbcot ligands are elongated in the
complexes to about 1.41-1.43 Å, which is normal for
diene complexes of this type. The bond lengthening in
the iridium complexes is slightly more pronounced,
which is in accord with the higher degree of metal-to-
ligand bonding and back-bonding and with the stability
of these complexes. The curvature of the boat form of
the central eight-membered ring is in all complexes
more pronounced (by about 10°) than in the uncom-
plexed Phdbcot molecule ((R(S))-7a, 70.6°; (R(S))-8b,
70.8°; (R)-[(R)-(+)]-11a, 71.2°). However, the differences
are rather small and we believe that the preorganization
in the uncomplexed Rdbcot molecules is the decisive
factor for the very high stability of these complexes (an
extreme example is complex 9b, which decomposes only
above 300 °C).
Noteworthy is the orientation of the naphthyl groups
in the complex [Ir(naphdbcot)(MeCN)2]+SbF6- ((R(S))-8b).
While in [Rh(2-MeO-naphdbcot)(MeCN)(H2O)]OTf ((R(S))-
6c, not shown here; see the Supporting Information) the
naphthyl substituent is oriented away from the rhodium
center which shows a weak interaction (∼3 Å) with the
oxygen center of the methoxy group, the naphthyl group
in (R(S))-8b points toward the iridium center. This
brings the hydrogen atom H24 at the 8-position into
contact with the metal center at 2.83 Å. Similar weak
interactions at 2.3-2.9 Å have been detected in Pt
compounds, for instance, and are noticeable by signifi-
Catalyses. Crabtree et al. observed that the addition
of dibenzo[a,e]cyclooctene (dbcot) to solutions containing
ruthenium, rhodium, or iridium phosphane complexes
impedes or even blocks their catalytic activity in hy-
drogenation reactions.16,17 Presumably, the formation of
highly inert [M(dbcot)(PR3)2] complexes is responsible
for this finding. We tested the complexes [M(Phdbcot)-
(MeCN)2]+X- ((R(S))-6a (M ) Rh), (R(S))-8a (M ) Ir))
and [M(naphdbcot)(MeCN)2]+X- ((R(S))-6b (M ) Rh),
(R(S))-8b (M ) Ir)) as catalyst precursors. Because the
complex (R)-6a is enantiomerically pure, reactions
aimed at achieving enantioselective transformations
were of special interest. All complexes are phosphane-
R
free and contain a firmly bound dbcot ligand and two
labile acetonitrile ligands. Homogeneously catalyzed (i)
hydrogenations with H2, (ii) transfer hydrogenations
with 2-propanol, (iii) additions of arylboronic acids to
R,â-unsaturated ketones, (iv) hydroborations, and (v)
hydrosilylations were investigated (Scheme 4). Dimeth-
ylitaconate (12) is a frequently used substrate in enan-
tioselective hydrogenations.26 However, attempts to
hydrogenate 12 under 4 bar of H2 using 1 mol % of
[Rh(Phdbcot)(MeCN)2]+OTf- ((R)-6a) as catalyst precur-
sor yielded only 3-4% of 13 after 20 h (stereochemistry
not determined). With the analogous iridium complex
(24) Albinati, A.; Arz, C.; Pregosin, P. S. Inorg. Chem. 1987, 26, 508.
(25) Albinati, A.; Pregosin, P. S.; Wombacher, F. Inorg. Chem. 1989,
29, 1812.
(26) Selected examples: (a) Tappe, K.; Knochel, P. Tetrahedron:
Asymmetry 2004, 15, 91 and literature cited therein. (b) Reetz, M. T.;
Mehler, G. Angew. Chem., Int. Ed. 2000, 39, 3889, and literature cited
therein. (c) Burk, M. J.; Gross, M. F. Tetrahedron Lett. 1994, 35, 9363.

3002 Organometallics, Vol. 24, No. 12, 2005
La¨ng et al.
a ligand in the iridium catalyst or when (R(S))-4a is
added as substrate instead of 12.
η4-1,5-Cyclooctadiene complexes such as [Rh(cod)-
(RHN∩*NHR)]+ and [Ir(cod)(RHN∩*SOR)]+ with chiral
chelating diamine2 or â-amino sulfoxide ligands3 (∩*
denotes a chiral ligand backbone) are rather effective
catalyst precursors for the transfer hydrogenation of
acetophenone 14 with 2-propanol to 1-phenylethanol
(15) and ee’s >90% can be achieved for one of the
enantiomers. We explored the combination of a chiral
diene with an achiral diamine in the ligand sphere of
the catalyst precursor. The complex (R(S))-[Rh(Phdbcot)-
(MeCN)2]+OTf- ((R(S))-6a) was reacted with various
simple ethylenediamines RHNCH2CH2NHR (R ) H,
Me, Et) to give the complexes (R(S))-[Rh(Phdbcot)(di-
amine)]+OTf-. The iridium complex (R(S))-[Ir(Phdbcot)-
(H2NCH2CH2NH2)]+OTf- was prepared in an analogous
way. Furthermore, the enantiomerically pure com-
plex (R)-[Rh(Phdbcot)(EtHNCH2CH2NHEt)]+OTf- was
synthesized. All these diamine complexes give yellow
powders after evaporation of the solvent and were used
without further purification or characterization as crude
reaction products. In addition, the complex [Rh(Phdbcot)-
(1,1′-binap-2,2′-NH2)]+OTf- ((R)-[(R)-(+)]-11a) was in-
vestigated as catalyst precursor. The results are com-
piled in Table 2.
Unfortunately, the rhodium complexes, the only ones
we had at hand enantiomerically pure, showed low
activity again. The best result was obtained with N,N-
diethylethylenediamine (entry 3), and this diamine was
therefore tested in an enantioselective hydrogenation
with (R)-[Rh(Phdbcot)(EtHNCH2CH2NHEt)]+OTf-. The
enantiomeric excess (ee) was reproducible within 10%
but was disappointingly low. Even worse is the perfor-
mance of (R)-[(R)-(+)]-11a, which shows both low activ-
ity and selectivity (entry 4). That sterically more
demanding diamines perform better in transfer hydro-
genations has been observed before.27 Remarkably, the
iridium complex (R(S))-[Ir(Phdbcot)(H2NCH2CH2NH2)]+-
OTf- serves as a rather efficient catalyst precursor
(entry 5), with an activity 4 orders of magnitude higher
than that of the analogous rhodium complex (entry 1).
Future work will therefore concentrate on the isolation
of enantiomerically pure iridium complexes.
Figure 3. Structure of the cation [Ir(Naphdbcot)(MeCN)2]+
in 8b. Only the R-configured isomer is shown. Thermal
ellipsoids are drawn at the 50% probability level; hydrogen
atoms, the SbF6- anion, and a MeCN solvent molecule are
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ir1-C5 ) 2.131(6), Ir1-C6 ) 2.102(7), Ir1-ct1 )
1.990(7), Ir1-C11 ) 2.126(8), Ir1-C12 ) 2.103(8), Ir1-
ct2 ) 1.993(8), Ir1-N1 ) 2.030(6), Ir1-N2 ) 2.041(6),
C5-C6 ) 1.443(9), C11-C12 ) 1.41(1); N1-Ir1-N2 )
90.3(3), N2-Ir1-Ct1 ) 90.2(3), Ct1-Ir1-Ct2 ) 88.6(3),
Ct2-Ir1-N1(3) ) 91.3. ct ) centroids of the coordinated
CdC units; æ ) 6.7° is the intersection angle of the
ct1-Ir1-ct2 plane with the N1-Ir1-N2 plane. Torsion
angles (deg): C5-C6-C15-C16 ) 71.1(9), C15-C16-
C11-C12
) -69(1), C11-C12-C13-C14 ) 74(1),
C13-C14-C5-C6 ) -68.8(9); average 70.8°.
The catalytic addition of aryl- and alkenylboronic
acids to R,â-unsaturated ketones has been developed by
Miyaura and Hayashi,28 giving examples for the ap-
plication of chiral dienes as steering ligands in catalysis.6c
We used (R)-[Rh(Phdbcot)(MeCN)2]+OTf- ((R)-6a) as a
catalyst precursor for the 1,2-addition of PhB(OH)2 to
cyclohexen-2-one (16) under the reported conditions6c
and obtained (3R)-phenylcyclohexanone ((R)-17) in 92%
yield and 62% ee (the configuration of the major isomer
was determined by comparison with the reported optical
rotation for (R)-1729). While the activity of (R)-6a is
comparable to that of the Hayashi catalyst, the ee is
lower (99% is given in ref 6c). As previously proposed
for the preferred formation of (R)-17, we likewise
assume that the R-re face of cyclohexen-2-one (16) is
Figure 4. Structure of the cation [Rh((R)-Phdbcot)((R)-(+)-
1,1′-binaphthyl-2,2′-diamine)]+ in (R)-[(R)-(+)]-11a. Ther-
mal ellipsoids are drawn at the 50% probability level;
-
hydrogen atoms and the CF3SO3 anion are omitted for
clarity. Selected bond lengths (Å) and angles (deg):
Rh1-C5 ) 2.148(4), Rh1-C5 ) 2.123(5), Rh1-ct1 ) 2.016-
(5), Rh1-C11 ) 2.121(4), Rh1-C12 ) 2.121(5), Rh1-ct2
) 2.001(5), Rh1-N1 ) 2.138(4), Rh1-N2 ) 2.193(4),
C5-C6 ) 1.407(7), C11-C12 ) 1.403(7); N1-Rh1-N2 )
87.7(1), N2-Rh1-Ct1 ) 92.7(2), Ct1-Rh1-Ct2 ) 88.0(2),
Ct2-Rh1-N1 ) 92.6(2) ct ) centroids of the coordinated
CdC units; æ ) 11.5° is the intersection angle of the
ct1-Rh1-ct2 plane with the N1-Rh1-N2 plane. Torsion
angles (deg): C5-C6-C15-C16 ) 74.9(6), C15-C16-
C11-C12 ) -69.3(6), C11-C12-C13-C14 ) 72.2(6),
C13-C14-C5-C6 ) -68.4(6): average 71.2°.
(27) Gamez, P.; Fache, F.; Lemaire, M. Tetrahedron: Asymmetry
1995, 6, 705.
(28) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura,
N. J. Am. Chem. Soc. 1998, 120, 5579.
(R(S))-8a complete conversion was achieved under the
same conditions. Note that we have no indications that
the Phdbcot ligand ((R(S))-4a) is hydrogenated either as
(29) Schultz, A. G.; Harrington, R. E. J. Am. Chem. Soc. 1991, 113,
4926.

Chiral Olefins as Steering Ligands
Organometallics, Vol. 24, No. 12, 2005 3003
Scheme 4. Catalytic Transformation with [M(Rdbcot)] Complexes
Table 2. Results in Transfer Hydrogenations of
Acetophenone with Isopropyl Alcohol with 1 mol
% [M(Phdbcot)(diamine)]+OTf- as Catalyst
6a as catalyst precursor, we find less than 5% conver-
sion, however.
Precursor and 5 Mol % KOH as Base (T ) 80 °C)
Conclusions
t
conversn TOF ee
M/diamine
(h)
(%)
(h-1
)
(%)
A simple synthesis of unsymmetrically chiral dibenzo-
[a,e]cyclooctenes, Rdbcot, has been developed. Remark-
ably, this protocol includes fewer reaction steps (only
three) and gives higher yields than the best synthesis
of the parent dibenzo[a,e]cyclooctene reported so
far.19 With these dienes, tetracoordinated 16-electron
rhodium(I) and, especially, iridium(I) complexes could
be prepared. Importantly, the NMR and X-ray data
show that these complexes are very stable, despite
the high degree of substitution of the coordinated
CdC double bonds. Unfortunately, only one complex,
(R)-[Rh(Phdbcot)(MeCN)2]+OTf- ((R)-6a), could be ob-
tained in enantiomerically pure form. The first in-
vestigations of [M(Rdbcot)(MeCN)2]+ and [M(Rdbcot)-
(RHNnNHR)]+complexes show, especially for M ) Ir,
promising properties as catalyst precursors in hydro-
genations with H2 and in transfer hydrogenations. The
enantiomerically pure rhodium complex (R)-6a catalyses
the enantioselective 1,2-addition of PhB(OH)2 to R,â-
unsaturated ketones with good activity and acceptable
enantiomeric excess. Thereby, the use of dienes as
steering ligands for a wide range of reactions, including
even catalyzed hydrogenations of unsaturated function-
alities, is firmly established.8 Clearly, these first experi-
1
2
3
4
5
Rh/H2NCH2CH2NH2
Rh/MeHNCH2CH2NHMe
Rh/EtHNCH2CH2NHEt
Rh/(R)-(+)-1,1′-binap-2,2′-NH2 24
Ir/H2NCH2CH2NH2 0.3
20
22
4
4
42
71
80
92
0.2
1.9
17.7 10
3.3
307
4
coordinated to the metal center, leading to a sterically
less encumbered transition state for the insertion of 16
into Rh-Ph bond (see Scheme 4). The relatively low
steric demand of the phenyl substituent may then
explain the rather low ee.
Finally, we tested in preliminary experiments the
rhodium complex (R(S))-[Rh(Phdbcot)(MeCN)2]+OTf-
((R(S))-6a) as a catalyst precursor (1 mol %) for hy-
droborations and hydrosilylations. When styrene is used
as substrate and catecholborane (catBH) as borane, no
hydroboration is observed but polymerization of styrene
occurred instead. With 1-hexene (18) as the more
reactive substrate, complete conversion is achieved and
1-hexanol (19) and 2-hexanol (20) are obtained after the
usual workup30 with H2O2 in a 6:1 ratio. Since the
internal alcohol is the minor product in this reaction,
we employed the enantiomerically pure catalyst precur-
sor (R)-6a.
The enantioselectively catalyzed hydrosilylation of
norborene with HSiCl3 has been reported by Togni et
al.31 Under the same conditions using 1 mol % of (R)-
(30) Evans, D. A.; Fu, G. C.; Hoveyda, A. H. J. Am. Chem. Soc. 1992,
114, 6671.
(31) Pioda, G.; Togni, A. Tetrahedron: Asymmetry 1998, 9, 3903.

3004 Organometallics, Vol. 24, No. 12, 2005
La¨ng et al.
with 30 mL of 0.1 M HCl and extracted three times with 30
mL of tert-butyl methyl ether (tbme). The organic phase was
dried over MgSO4 and concentrated under reduced pressure
to yield a sticky, slightly yellow solid. Recrystallization from
hexane afforded the pure product as a colorless solid (1.20 g,
Chart 2. Description of the Stereochemical
Assignment in Rdbcot Molecules
1
88%). Mp: 97-98 °C. H NMR (300 MHz, CDCl3): δ 2.85 (s,
1H, OH), 3.09 (d, JHH ) 13.6, 1H, CH2), 4.08 (d, JHH ) 13.6,
1H, CH2), 6.86 (d, JHH ) 12.2, 1H, CHalkene), 7.04-7.36 (m, 10H,
CHar, CHalkene), 7.40-7.53 (m, 3H, CHar), 7.60-7.66 (m, 1H,
CHar). 13C NMR (75.5 MHz, CDCl3): δ 48.70 (CH2), 80.04
(C(OH)), 124.96 (2C, CHphenyl), 126.45 (CH), 126.65 (CH),
126.83 (CH), 127.33 (CH), 127.38 (CH), 128.05 (2C, CHphenyl),
128.06 (CH), 130.03 (CH), 130.53 (CH), 130.84 (CH), 131.11
(CH), 133.57 (CH), 133.97 (Cquat), 136.46 (Cquat), 138.10 (Cquat),
143.82 (Cquat), 149.42 (Cquat). MS (70 eV, m/z, %): 298.1 (100)
[M+], 280.1 (24) [M+ - H2O], 207.1 (37), 178.0 (44), 165.0(39),
77.1 (61).
ments show that chiral dibenzo[a,e]cyclooctenes and
related cyclooctatetraenes have a high potential for the
development of robust phosphane-free catalyst precur-
sors.
5-Phenyldibenzo[a,e]cyclooctene (4a). A mixture of the
alcohol 3a (0.88 g, 2.95 mmol) and CF3COOH (0.07 mL) in 40
mL of CH2Cl2 was stirred at room temperature for 22 h. The
reaction solution was washed with 20 mL of water and then
two times with 20 mL of saturated Na2CO3 solution. The
organic phase was dried over MgSO4 and concentrated under
reduced pressure to give a colorless, foamy solid. Recrystalli-
zation from hexane yielded the pure product as a colorless,
Experimental Section
General Remarks. All syntheses were performed in flame-
dried glassware under an atmosphere of argon using standard
Schlenk techniques. Solvents were freshly distilled from
sodium/benzophenone (THF), from sodium/tetraglyme/ben-
zophenone (hexane, toluene), or calcium hydride (dichlo-
romethane) prior to use. Air-sensitive compounds were stored
and weighed in an argon-filled glovebox (Braun MB 150 B-G
system), and reactions on a small scale were performed directly
in the glovebox. (Z)-6H-Dibenzo[a,e]cycloocten-5-one (2) was
prepared from dibenzosuberenone (1) by a literature method.19
CeCl3‚7H2O was dried by the procedure of Dimitrov et al.32
NMR spectra were taken at room temperature on an AMX-
500, Avance DRX-400, Avance DPX-300, or Avance DPX-250
system. The chemical shifts are given as dimensionless δ
values and were referenced against tetramethylsilane (tms)
for 1H and 13C, 85% H3PO4 for 31P, and CFCl3 for 19F NMR
spectra. Coupling constants J are given in hertz (Hz) as
positive values, regardless of their absolute signs. The mul-
tiplicity of the signals is indicated as s, d, t, q, or m for singlets,
doublets, triplets, quartets, or multiplets, respectively. Qua-
ternary carbons are indicated as Cquat and aromatic carbons
as Car, when not noted otherwise. Broadened signals are
indicated as “br”. The assignments of C11 and C12 in free
ligands 4a-c as well as in complexes 6a,b, 7a, 8b, and 11a
are established by CH-COSY and CH-long-range experiments.
Mass spectra were taken on a Finnigan MAT SSQ 7000 in the
EI (70 eV) mode.
Assignment of the Stereochemistry. The stereochemis-
try of the Rdbcot ligands was assigned according to the rules
for molecules showing “planar chirality” given by Chan, Ingold,
and Prelog in ref 33. In our case, the element of planar
chirality is defined by the carbon atoms of the unsymmetrically
substituted CdC bond and the atoms directly attached to it.
The “pilot atom” is then the atom of highest priority next to
these atoms sticking out of the plane. In our case, this is the
quaternary carbon atom of one benzo group, as indicated in
Chart 2. Looking from this atom onto the plane and ranking
the atoms in the element of planar chirality according to their
priority leads to an S conformation for the molecule on the
left and a R conformation for the molecule on the right side in
Chart 2.
1
crystalline solid (0.77 g, 93%). Mp: 91-92 °C. H NMR (500
MHz, CDCl3): δ 6.90 (d, JHH ) 11.8, 1H, C(11)Halkene), 6.97 (d,
JHH ) 11.8, 1H, C(12)Halkene), 6.99 (dm, JHH ) 7.9, C(4)Hbenzo),
7.12-7.27 (m, 8H, CHbenzo, C(6)Halkene), 7.28-7.38 (m, 5H,
CHphenyl). 13C NMR (125.7 MHz, CDCl3): δ 126.97 (CHbenzo),
127.17 (CHbenzo), 127.20 (CHbenzo), 127.34 (CHbenzo), 127.76 (s,
1C, CHphenyl), 128.13 (2C, CHphenyl), 128.53 (CHbenzo), 128.63 (2C,
CHphenyl), 128.86 (CHbenzo), 128.98 (CHbenzo), 129.51 (C(6)Halkene),
133.21 (C(12)Halkene), 134.19 (C(11)Halkene), 137.84 (s, 1C, Cquat
benzo), 138.55 (Cquat benzo), 138.56 (Cquat benzo), 140.00 (Cquat benzo),
143.42 (Cquat phenyl), 145.12 (C(5)quat alkene). MS (70 eV, m/z, %):
280.0 (100) [M+], 202.0 (76) [M+ - Ph], 177.9 (59). Anal. Calcd
for C22H16: C, 94.24; H, 5.75. Found: C, 93.99; H, 5.69.
5-Naphthalen-1-yl-5,6-dihydrodibenzo[a,e]cycloocten-
5-ol (3b). The preparation was performed as described for 3a
by reacting CeCl3 (0.61 g, 2.5 mmol) with NaphMgBr (5 mL of
a 0.5 M solution, 2.5 mmol) and 2 (0.40 g, 1.81 mmol) in 17
mL of THF for 17 h at room temperature. The crude product
was contaminated with naphthalene, which was removed by
sublimation (40 °C, 0.05 mbar). After recrystallization from
hexane the pure product was obtained as a colorless powder
(0.52 g, 82%). Mp: 165-169 °C dec. 1H NMR (250 MHz,
CDCl3): δ 2.88 (s, 1H, OH), 3.42 (d, JHH ) 13.7, 1H, CH2),
4.37 (d, JHH ) 13.7, 1H, CH2), 6.90-7.64 (m, 13H, Car, CHalkene),
7.73-7.92 (m, 3H, CHar), 8.57 (m, br, 1H, CHar). 13C NMR (62.9
MHz, CDCl3): δ 45.60 (CH2), 80.75 (C(OH)), 123.90 (CH),
124.90 (CH), 125.15 (CH), 125.20 (CH), 126.37 (CH), 126.89
(CH), 127.26 (CH), 127.32 (CH), 128.33 (CH), 129.07 (CH),
130.21 (Cquat), 131.12 (CH), 131.21 (CH), 132.01 (CH), 132.34
(CH), 132.75 (CH), 133.92 (Cquat), 134.64 (Cquat), 136.51 (Cquat),
137.92 (Cquat), 144.13 (Cquat), 144.88 (Cquat). MS (70 eV, m/z,
%): 348.2 (100) [M+], 330.2 (44) [M+ - H2O], 207.1 (56), 128.1
(69) [naphH+].
5-Naphthalen-1-yldibenzo[a,e]cyclooctene (4b). The
preparation was as described for 4a by reacting alcohol 3b
(0.52 g, 1.49 mmol) with CF3COOH (0.05 mL) in 10 mL of
CH2Cl2 for 20 h at room temperature. The pure product is
obtained after recrystallization from n-hexane as colorless
5-Phenyl-5,6-dihydrodibenzo[a,e]cycloocten-5-ol (3a).
A suspension of dry CeCl3 (1.57 g, 6.36 mmol) in 20 mL of THF
was treated dropwise with a solution of PhMgBr (5.6 mL of a
1.13 M solution in Et2O, 6.36 mmol) at 0 °C. The mixture was
stirred at 0 °C for 1 h, and then a solution of (Z)-6H-dibenzo-
[a,e]cycloocten-5-one (2; 1.00 g, 4.54 mmol) was added. After
3 h of stirring at room temperature, the mixture was quenched
1
crystals (0.45 g, 91%). Mp: 138-139 °C. H NMR (500 MHz,
CDCl3): δ 6.94-7.01 (m, 2H, CHbenzo), 7.04 (s, 1H, C(6)Halkene),
7.05 (d, JHH ) 11.3, 1H, C(11)Halkene), 7.11-7.32 (m, 7H,
CHbenzo, C(12)Halkene), 7.47-7.61 (m, 4H, CHnaphthyl), 7.83-7.90
(m, 2H, CHnaphthyl), 8.25-8.30 (m, 1H, C(24)Hnaphthyl). 13C NMR
(125.7 MHz, CDCl3): δ 127.75 (CHnaphthyl), 126.06 (CHbenzo),
126.46 (CHnaphthyl), 126.61 (CHnaphthyl), 127.19 (CHbenzo), 127.21
(CHbenzo), 127.28 (CHbenzo), 127.36 (CHbenzo), 127.88 (CHnaphthyl),
(32) Dimitrov, V.; Kostova, K.; Genov, M. Tetrahedron Lett. 1996,
37, 6787.
(33) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem. 1966, 78,
413.

Chiral Olefins as Steering Ligands
Organometallics, Vol. 24, No. 12, 2005 3005
128.33 (CHnaphthyl), 128.68 (CHnaphthyl), 129.07 (CHbenzo), 129.14
2C, CHphenyl(meta)), 129.47 (2C, CHphenyl(ortho)), 142.90 (Cquat benzo),
142.93 (Cquat benzo), 142.99 (Cquat benzo), 143.78 (Cquat phenyl), 145.13
(Cquat benzo). 19F NMR (188.3 MHz, CDCl3): δ -77.9 (s). 103Rh
NMR (12.7 MHz, CDCl3): δ 1530 (m). MS (70 eV, m/z, %):
532.0 (13) [Rh(4a) (OTf)]+, 382.1 (12) [Rh(4a)]+, 280.1 (100)
(4a)+. Anal. Calcd for C27H22F3N2O3RhS: C, 52.78; H, 3.61;
N, 4.56. Found: C, 53.04; H, 3.82; N, 4.24.
(CHbenzo), 129.39 (CHbenzo), 129.62 (CHbenzo), 131.99 (Cquat naph
-
th ), 133.50 (C(12)Halkene), 133.85 (C(6)Halkene), 134.32 (s, 1C,
yl
C
quat naphthyl), 134.87 (C(11)Halkene), 137.42 (Cquat benzo), 137.60
(Cquat benzo), 138.07 (Cquat benzo), 140.96 (Cquat benzo), 142.97
(C(5)alkene). MS (70 eV, m/z, %): 330.0 (M+, 100%), 202.0 (M+
- naph), 177.9. Anal. Calcd for C26H18: C, 94.51; H, 5.49.
Found: C, 94.43; H, 5.20.
-
[Rh(Naphdbcot)(MeCN)2]+SbF6 (6b). A solution of [Rh2-
5-(2-Methoxynaphthalen-1-yl)-5,6-dihydrodibenzo[a,e]-
cycloocten-5-ol (3c). The preparation was as described for
3a from CeCl3 (1.20 g, 4.9 mmol), (2-methoxynaphthyl)MgBr
(15 mL of a 0.32 M solution in THF, 4.9 mmol), and 2 (0.75 g,
3.4 mmol) in 15 mL of THF. The mixture was stirred at room
temperature for 24 h and then heated under reflux for 6 h.
The crude product was purified by flash chromatography (FC)
on silica gel with n-hexane/AcOEt (4:1) as eluent to give the
product (1.41 g, ca. 55%) together with about 40 mol %
(determination by NMR) of the starting ketone. The two
products could not be separated, and the mixture was directly
applied in the following transformation.
(µ2-Cl)2(CO)4] (28 mg, 72 µmol) and ligand 4b (47 mg, 244 µmol)
in 2 mL of CH2Cl2 and 2 mL of MeCN was stirred at room
temperature for 16 h. AgSbF6 (49 mg, 142 µmol) was then
added, and the reaction mixture was stirred for 1 h. The
precipitate was removed by filtration through Celite, and the
filtrate was concentrated under vacuum to give a dark yellow
solid. Recrystallization from CH2Cl2/hexane yields the product
as yellow-brown, thin needles (62 mg, 57%). Mp: >235 °C dec.
1H NMR (300 MHZ, CD3CN): δ 2.07 (s, 6H, CH3), 5.65 (d, JHH
) 8.4, 1H, C(12)Halkene), 5.73 (dd, JHH ) 8.4, JRhH ) 1.7, 1H,
C(11)Halkene), 5.90 (s, br, 1H, C(6)Halkene), 6.48 (d, J ) 7.7, 1H,
CHbenzo), 6.69 (d, J ) 7.7, 1H, CHbenzo), 7.02 (dt, J ) 7.6, J )
1.1, 1H, CHbenzo), 7.06-7.17 (m, 4H, CHbenzo), 7.23 (m, 1H,
CHbenzo), 7.45-7.57 (m, 2H, CHnaph), 7.60-7.68 (m, 2H, CHnaph),
7.93 (d, J ) 8.3, 1H, CHnaph), 7.96 (d, J ) 8.4, 1H, CHnaph),
10.07 (d, J ) 8.4, 1H, CHnaph). 13C NMR (75.5 MHz, CD3CN):
δ 0.93 (2C, CH3), 80.5 (br, C(6)Halkene), 81.1 (br, C(12)Halkene),
85.5 (br, C(11)Halkene), 124.98 (CHnaph), 126.24 (CHnaph), 126.5
(2C, CHnaph), 126.53 (CHbenzo), 126.82 (CHbenzo), 127.08 (CHbenzo),
127.23 (CHbenzo), 127.26 (CHbenzo), 127.29 (CHbenzo), 127.33
(CHbenzo), 127.44 (CHbenzo), 127.84 (CHnaph), 128.90 (CHnaph),
130.38 (CHnaph), 132.66 (Cquat naph), 134.39 (Cquat naph) 140.09
(C(17)quat naph), 141.3 (C(13)quat benzo), 142.23 (C(15)quat benzo),
142.44 (C(16)quat benzo), 146.0 (C(14)quat benzo). 19F NMR (188.3
MHz, CD3CN): δ -125 (sext, br, JSbF ) 1950). MS (ESI, m/z,
%): 465.2 (15), 451.2 (14), 433.2 (100) [Rh(4b)]+. Anal. Calcd
for C30H24N2F6RhSb: C, 47.97; H, 3.22; N, 3.73; Found: C,
48.03; H, 3.33; N, 3.49.
5-(2-Methoxynaphthalen-1-yl)dibenzo[a,e]cyclo-
octene (4c). To a solution of the mixture 3c/2 (0.30 g, con-
taining ca. 0.4 mmol of alcohol 3c) in 10 mL of CH2Cl2 was
added CF3COOH (0.02 mL). The reaction mixture was stirred
at room temperature for 20 h. After workup in a way analogous
to that described for 4a, the crude product (a slightly pink oil)
containing the unreacted ketone was purified by FC (silica gel,
hexane/AcOEt (10:1)) to yield the pure product as a color-
less solid (0.13 g, 90%). Due to hindered rotation around the
C5-C17 bond, the compound 4c consists of solution of two
rotational isomers (ratio 1:2.5) which exchange at room tem-
perature. The NMR signals are therefore doubled and broad-
ened. Signals of the minor isomer are given and assigned only
1
where possible. Mp: 165-166 °C. H NMR (400 MHz, C6D6):
δ 3.69 (s, 3H, OCH3(maj)), 4.16 (s, 3H, OCH3(min)), 6.82-7.01
(m, 3H, CHalkene(min,maj)), 7.03-7.51 (m, 11H, CHar), 7.41 (m,
1H, CHnaphthyl(min)), 7.47 (m, 1H, CHnaphthyl(maj,min)), 7.67 [m,
1H, CHnaphthyl(maj)), 7.77 (m, br, 1H, Cnaphthyl(min)), 7.85 (m,
br, 1H, CHnaphthyl(maj)], 7.88 (m, br, 1H, CHnaphthyl(min)), 8.20
(m, br, 1H, CHnaphthyl(min)), 8.56 (m, br, 1H, CHnaphthyl(maj)).
13C NMR (100.6 MHz, C6D6): δ 57.29 (OCH3(maj)), 57.42
(OCH3(min)), 114.86 (CHnaphthyl), 124.07 (CHnaphthyl), 125.47
(CHnaphthyl), 126.74 (CHbenzo), 127.13 (CHbenzo), 127.17 (CHbenzo),
127.34 (CHbenzo), 128.42 (CHnaphthyl), 128.55 (CHbenzo), 128.56
(CHbenzo), 128.93 (Cquat naphthyl), 129.03(CHbenzo), 129.17 (CHbenzo),
129.48 (CHnaphthyl), 129.95 (Cquat naphthyl), 133.09 (C(12)Halkene),
133.95 (Cquat naphthyl), 134.27 (C(11)Halkene), 134.31 (C(6)Halkene),
137.83 (Cquat), 138.22 (Cquat), 139.76 (C5quat alkene), 141.09 (Cquat),
153.24 (COCH3(min)), 154.24 (COCH3(maj)). MS (70 eV, m/z,
%): 360.0 (100) [M+], 328.9 (33), 202.0 (81), 178.0 (94).
[Rh(Phdbcot)(MeCN)2]+OTf- (6a). A mixture of [Rh2(µ2-
Cl)2(CO)4] (0.20 mg, 0.56 mmol) and ligand 4a (0.288 g, 1.02
mmol) in 10 mL of CH2Cl2 and 5 mL of MeCN was stirred at
room temperature for 16 h. To the orange solution was added
AgOTf (0.26 g, 1.02 mmol), and the suspension was stirred
for 1 h at room temperature. The precipitated silver chloride
was removed by filtration through a pad of Celite, and the
filtrate was concentrated under high vacuum to give an orange,
foamy solid. Precipitation from CH2Cl2 and hexane afforded
the product as an orange powder (0.45 g, 73%). Mp: >175 °C
dec. 1H NMR (400 MHz, CDCl3): δ 2.12 (s, 6H, CH3), 5.37 (d,
JHH ) 8.3, 1H, C(12)Halkene), 5.56 (dd, JHH ) 8.3, JRhH ) 1.6,
[IrCl(Phdboct)(MeCN)] (7a). To a solution of [Ir2(µ2-Cl)2-
(cod)2] (0.170 g, 0.25 mmol) in 2 mL of CH2Cl2 and 2 mL of
MeCN was added a solution of ligand 4a (0.142 g, 0.51 mmol)
in 2 mL of CH2Cl2. The solution was stirred for 18 h at room
temperature and was then concentrated to a volume of 2 mL.
When the orange-brown solution was layered with hexane, the
product precipitated as orange crystals suitable for X-ray
analysis (0.21 g, 76%). Mp: 215-220 °C. 1H NMR (500 MHz,
CD3CN): δ 1.96 (s, 3H, CH3), 5.43 (d, JHH ) 8.0, 1H, C(12)-
Halkene), 5.54 (s, 1H, C(6)Halkene), 5.58 (d, JHH ) 8.0, 1H, C(11)-
Halkene), 6.53 (dm, JHH ) 7.70, 1H, CHbenzo), 6.77 (tm, JHH
)
7.70, 1H, CHbenzo), 6.85-6.95 (m, 3H, CHbenzo), 7.00-7.07 (m,
2H, CHbenzo), 7.11-7.17 (m, 1H, CHbenzo), 7.25-7.34 (m, br, 3H,
CHphenyl), 7.55 (s, br, 1H, CHphenyl), 7.72 (s, br, 1H, CHphenyl).
13C NMR (125.7 MHz, CD3CN): δ 2.19 (CH3), 57.33 (br,
C(6)Halkene), 69.85 (br, C(12)Halkene), 72.39 (br, C(11)Halkene),
74.55 (br, C(5)quat alkene), 117.00 (Cquat, CN), 125.91 (CHbenzo),
125.92 (CHbenzo), 125.99 (CHbenzo), 126.2 (br, CHphenyl(ortho)),
126.21 (CHbenzo), 126.28 (CHbenzo), 126.43 (CHbenzo), 126.45
(CHbenzo), 127.37 (CHphenyl(para)), 127.88 (br, CHphenyl(meta)), 127.93
(CHbenzo), 129.18 (br, CHphenyl(para)), 133.93 (br, CHphenyl(ortho)),
145.53 (Cquat benzo), 145.82 (Cquat benzo), 146.62 (Cquat benzo), 147.21
(Cquat phenyl), 149.22 (Cquat benzo). Anal. Calcd for C24H19ClNIr:
C, 52.50; H, 3.49; N, 2.55. Found: C, 52.63; H, 3.58; N, 2.61.
[Ir2(µ2-Cl)2(Naphdbcot)2] (9b). A mixture of [Ir2(µ2-Cl)2(coe)4]
(90 mg, 0.10 mmol) and ligand 4b (49 mg, 0.15 mmol) in 3 mL
of benzene was kept at 80 °C for 24 h. The yellow, crystalline
precipitate 9b was filtered, washed with 2 mL of benzene und
dried under high vacuum. It is only sparingly soluble in
common deuterated solvents. The crystals contain 0.5 equiv
of benzene, which could not be removed upon prolonged drying
under high vacuum (80 mg, 90% with respect to 4b). Mp: >
1H, C(11)Halkene), 5.69 (s, br, 1H, C(6)Halkene), 6.60 (dm, JHH
)
7.7 Hz, 1H, C(4)Hbenzo), 6.88-6.94 (m, 1H, CHbenzo), 6.99-7.10
(m, 6H, CHbenzo), 7.39 (m, br, 3H, CHphenyl), 7.8 (s, br, 2H,
CHphenyl). 13C NMR (100.6 MHz, CDCl3): δ 3.03 (2C, CH3),
74.43 (d, JRhC ) 13.5, 1C, C(6)Halkene), 81.17 (d, JRhC ) 12.3,
C(12)Halkene), 84.50 (d, JRhC ) 14.1, C(11)Halkene), 97.72 (d, JRhC
) 12.9, C(5)quat alkene), 121.82 (2C, Cquat, CN), 126.32 (2C,
CHbenzo), 126.38 (CHbenzo), 127.26 (CHbenzo), 127.35 (CHbenzo),
127.38 (CHbenzo), 127.74 (CHbenzo), 128.54 (CHbenzo), 129.0 (br,
1
310 °C dec. H NMR (300 MHz, CD3CN): δ 5.62 (d, br, J )
7.2, 1H, CHalkene), 5.68 (d, br, J ) 7.2, 1H, CHalkene), 5.76 (s,
br, 1H, C(6)Halkene), 6.30 (d, J ) 7.8, 1H, CHbenzo), 6.51 (dt, J1

3006 Organometallics, Vol. 24, No. 12, 2005
La¨ng et al.
) 7.8, J2 ) 1.0, 1H, CHbenzo), 6.77 (dt, J1 ) 7.8, J2 ) 1.2, 1H,
CHbenzo), 6.82-6.89 (m, 2H, CHbenzo), 7.00-7.06 (m, 2H,
CHbenzo), 7.20 (m, 1H, CHbenzo), 7.30-7.40 (m, 3H, CHnaph),
7.73-7.88 (m, 3H, CHnaph), 9.42 (m, 1H, CHnaph). MS (70 eV,
m/z, %): 1116.0 (16) [M+], 518.1 (29), 330.1 (25) [M+ (4b)]
(100%), 191.0 (22), 149.0 (44). Anal. Calcd for C52H36Cl2Ir2 ×
0.5 C6H6: C, 57.18; H, 3.40. Found: C, 57.13; H, 3.28.
3 mL of CH2Cl2 and the solution filtered through Celite.
Precipitation of the crude material from CH2Cl2/hexane gave
the enantiomerically pure complex (R)-6a (19 mg, 95%). The
analytical data are identical with those for the racemic mixture
of 6a. Optical rotation [R]20 ) -93.0° (c ) 0.55, CHCl3).
D
Displacement of Phdbcot from (R)-6a. A mixture of (R)-
6a (47 mg, 58 µmol) and PPh3 (67 mg, 230 µmol) in 2 mL of
CH2Cl2 and 1 mL of MeCN was stirred at room temperature
for 1 h. The solvent was removed under high vacuum. To the
solid residue was added 5 mL of hexane, and the mixture was
treated with ultrasonic radiation for 15 min and then filtered
through Celite. The clear solution was concentrated under high
vacuum and dissolved in 2 mL of toluene, and 3 drops of H2O2
(30%) were added in order to oxidize the remaining PPh3.
Subsequently, the mixture was stirred for 1.5 h and then
filtered through MgSO4 and silica gel. After removal of the
solvent, the pure ligand 4a was obtained (14 mg, 86%).
Immediate treatment of this ligand with [Rh2(µ2-Cl)2(CO)4],
AgOTf, and (R)-(+)-1,1′-binaphthyl-2,2′-diamine (10) gave a
1:1 mixture of the two diastereomeric complexes (R)-[(R)-(+)]-
11a and (S)-[(R)-(+)]-11a.
Catalyses: Hydrogenations. A Schlenk tube containing
a solution of dimethylitaconate (12; 1.8 mmol) and catalyst
(0.018 mmol) in 3 mL of CH2Cl2 was frozen in liquid nitrogen,
evacuated, and purged with 1 bar of hydrogen. The closed
vessel was brought to room temperature and stirred for 20 h.
The reaction mixture was analyzed by GC.
Transfer Hydrogenation of Acetophenone. (a) Prepa-
ration of the Catalysts. For [Rh((R)-Phdbcot)(EtHNCH2CH2-
NHEt)]+OTf-, a mixture of enantiomerically pure (R)-6a and
1 equiv of N,N′-diethylethane-1,2-diamine was stirred in
CH2Cl2 for 3 h. The solvent was evaporated, and the product
was precipitated from CH2Cl2/hexane as a yellow powder. In
the same manner the racemic complexes [Rh((R,S)-Phdbcot)-
(NH2CH2CH2NH2)]+OTf- and [Rh((R,S)-Phdbcot)(MeHNCH2-
CH2NHMe)]+OTf- were prepared from (R,S)-6a and the
corresponding diamine. For, [Ir((R,S)-Phdbcot)(NH2CH2CH2-
NH2)]+OTf-, a mixture of 7a and ethylene-1,2-diamine in
CH2Cl2 was reacted with AgOTf and stirred for 1 h at room
temperature. The solvent was removed under high vacuum,
which left the product as a yellow solid.
[Ir(Naphdbcot)(MeCN)2]+SbF6- (8b). A suspension of com-
pound 9b (35 mg, 31 µmol) in 2 mL of MeCN and 1 mL of
CH2Cl2 was treated with AgSbF6 (22 mg, 64 µmol) and stirred
at room temperature for 2 h. Filtration of the reaction mixture
through Celite and removal of the solvent left an orange solid.
Precipitation from CH2Cl2/hexane yielded the pure product as
an orange, microcrystalline solid (45 mg, 89%). Mp: > 185 °C
dec. 1H NMR (300 MHz, CD3CN): δ 1.99 (s, 6H, CH3), 5.60 (d,
J ) 7.8, 1H, C(12)Halkene), 5.68 (d, J ) 7.8, 1H, C(11)Halkene),
5.93 (s, 1H, C(6)Halkene), 6.41 (d, J ) 7.5, 1H, CH(4)benzo), 6.63
(td, J ) 7.5, J ) 0.9, 1H, CH(3)benzo), 6.87 (td, J ) 7.5, J ) 1.1,
1H, CH(2)benzo), 6.91-7.00 (m, 2H, CHbenzo), 7.08 (m, 2H,
CHbenzo), 7.17 (m, 1H, CHbenzo), 7.35-7.52 (m, 3H, CHnaph), 7.65
(d, J ) 7.2, 1H, CHnaph), 7.82 (d, J ) 8.2, 1H, CHnaph), 7.87 (d,
J ) 8.2, 1H, CHnaph), 9.34 (d, J ) 8.3, 1H, C(24) Hnaph). 13C
NMR (75.5 MHz, CD3CN): δ 1.56 (2C, CH3), 68.56 (C(6)Halkene),
68.61 (C(12)Halkene), 72.37 (C(11)Halkene), 85.34 (C(5)quat alkene),
116.85 (2C, CN), 124.78 (CHnaphthyl), 125.50 (CHbenzo), 125.7-
126.2 (6C, 2 × CHnaphthyl, 4 × CHbenzo), 126.31 (CH(4)benzo),
126.32 (CHnaphthyl), 126.57 (CH(3)benzo), 126.74 (CHbenzo), 128.27
(CHnaphthyl), 128.43 (CHnaphthyl), 129.70 (CHnaphthyl), 132.73
(C(25)quat naphthyl), 134.48 (C(26)quat naphthyl), 140.50 (C(17)quat naphthyl),
142.49 (C(13)quat benzo), 143.53 (C(15)quat benzo), 143.69
(C(16)quat benzo), 147.44 (C(14)quat benzo). MS (ESI, m/z, %): 647.4
(69), 619.4 (94), 548.0 (100) [Ir(4b)]+, 521.0 (30), 437.2 (44).
Anal. Calcd for C30H24F6N2IrSb: C, 42.87; H, 2.88; N, 3.33.
Found: C, 42.62; H, 3.04; N, 3.35.
(R)-[Rh(Phdbcot)(R-(+)-1,1′-binaphthyl-2,2′-di-
amine)]+OTf- ((R)-[(R)-(+)]-11a). A racemic mixture of the
complex (R,S)-6a (0.185 mg, 0.30 mmol) and (R)-(+)-1,1′-
binaphthyl-2,2′-diamine (10; 0.086 g, 0.30 mmol) in 5 mL of
CH2Cl2 was stirred at room temperature for 3 h. The solvent
was removed under high vacuum to give the product as a
mixture of diastereomers in the form of an orange powder. The
product was dissolved in 2.5 mL of EtOH and layered with 5
mL of hexane. After 1 week at 4 °C, the product (R)-[(R)-(+)]-
11a was obtained as orange crystals which were suitable for
X-ray analysis (0.080 mg, 32%). The compound is only slightly
soluble in common nonpolar solvents. In polar solvents (that
is, d3-acetonitrile or d6-acetone) exchange with the diamine
ligand is observed. Additionally, the 13C NMR signals are
strongly broadened. It was therefore not possible to detect and
assign all 13C signals. Mp: > 250 °C dec. 1H NMR (500 MHz,
CD2Cl2): δ 2.1 (m, br, 2H, NH), 3.7 (m, br, 2H, NH), 5.43 (d,
(b) Typical Procedure Employed in Catalyses. In a
closed Schlenk tube, a mixture of acetophenone 14 (96 mg,
800 µmol), KOtBu (5 mg, 40 µmol), and catalyst (8 µmol) in
i
2.5 mL of PrOH was heated to 80 °C. The progress of the
reaction was monitored by GC analysis, taking aliquots of the
reaction solution. The enantiomeric excess (ee) was determined
by GC on a chiral capillary (Machery-Nagel Lipodex-E).
Asymmetric 1,4-Addition. The procedure was adapted
from ref 34. A mixture of 2-cyclohexenone (16; 158 mg, 1.62
mmol), phenylboronic acid (397 mg, 3.25 mmol), KOH (0.54
mL, 1.5 M in H2O, 0.88 mmol), and catalyst (R)-6a was stirred
for 2 h at room temperature (20 °C). The reaction was
quenched with saturated NaHCO3, and the mixture was
extracted with 3 × 10 mL of tbme. The organic phase was dried
over MgSO4 and concentrated under reduced pressure. The
crude product was purified with flash chromatography (silica
gel, hexane/AcOEt (2:1)) to give the product 3-phenylcyclo-
hexanone (17) as a slightly yellow oil (250 mg, 92%). The
enantiomeric excess was determined with chiral HPLC (Chiracel
OD-H, n-hexane/iPrOH (98:2)), being 62%. The absolute con-
figuration of the stereogenic center of the major enantiomer
is R (by comparison with the reported optical rotation of (3R)-
JHH ) 8.3, CHalkene), 5.52 (s, 1H, C(6)Halkene), 5.81 (d, JHH
)
8.3, 1H, CHalkene), 6.38 (t, br, JHH ) 7.0, 1H, CHbenzo), 6.57 (d,
br, JHH ) 7.7, 1H, CHbenzo), 6.75-7.71 (m, 18 H, CHar), 7.87-
8.37 (m, br, 5H, CHar). 13C NMR (125.7 MHz, CD2Cl2): δ 75.8
(C(6)Halkene), 79.0 (CHalkene), 81.0 (CHalkene), 99.1 (Cquat alkene),
119.7 (CHar), 120.6 (CHar), 124.8 (CHar), 125.3 (CHar), 125.4
(CHar), 126.5 (2C, CHar), 126.6 (CHar), 126.9 (CHar), 127.0-
127.1 (m, br, 3C, CHar), 127.7 (CHar), 127.8 (CHar), 128.1 (CHar),
128.8 (CHar), 128.9 (CHar), 129.0 (CHar), 129.2 (CHar), 129.3
(CHar), 131.8 (br, 2C, CHar), 132.3 (CHar), 132.7 (Cquat), 142.4
(Cquat), 142.6 (Cquat), 143.5 (Cquat), 143.7 (Cquat), 145.1 (Cquat).
19F NMR (188.3 MHz, CD2Cl2): δ -78.7 (s). 103Rh NMR (15.7
MHz, CD2Cl2): δ 1517. Anal. Calcd for C42H32F3N2O3SRh: C,
62.69; H, 4.01; N, 3.48. Found: C, 62.97; H, 4.28; N, 3.55.
(R)-[Rh(Phdbcot)(MeCN)2]+OTf- ((R)-6a). To a solution
of (R)-[(R)-(+)]-11a (20 mg, 24 µmol) in 1.5 mL of MeCN was
added CF3SO3H (0.05 mL of a 1 M solution in MeCN, 50 µmol).
The mixture was stirred at room temperature for 3 h, and then
the solvent was removed under high vacuum. The oily residue
was dried under high vacuum for 12 h and then dissolved in
3-phenyl-cyclohexanone:29 [R]20 ) +11.8° (c ) 0.55, CHCl3).
D
Crystal Data and Structure Determination of (R(S))-
4a, (R(S))-8b, (R(S))-7a, and (R)-[(R)-(+)]-11a. Data collec-
tion for the X-ray structure determinations were performed
on a Bruker SMART Apex ((R(S))-4a, (R(S))-8b, (R)-[(R)-(+)]-
(34) Hayashi, T.; Ueyama, K.; Tokunaga, N.; Yoshida, K. J. Am.
Chem. Soc. 2003, 125, 11508.

Chiral Olefins as Steering Ligands
Organometallics, Vol. 24, No. 12, 2005 3007
Table 3. Details Concerning the Data Collection and Refinement of the Structures of (R(S))-4a, (R(S))-7a,
(R(S))-8b, and (R)-[(R)-(+)]-11a
(R(S))-4a
(R(S))-7a
(R(S))-8b‚CH3CN
(R)-[(R)-(+)]-11a
empirical formula
C
22H16
C
24H19NClIr
C30H24Cl6IrN2Sb‚CH3CN
980.22
monoclinic
P21/c (No. 14)
13.904(4)
9.393(2)
C43H32F3N2O3SRh
816.68
orthorhombic
P212121 (No. 19)
10.758(1)
14.537(1)
22.981(1)
Mr
280.35
549.05
cryst syst
monoclinic
P21/n (No. 14)
13.392(1)
7.869(1)
15.579(2)
113.685(2)
1503.5(3)
0.070
monoclinic
Cc (No. 9)
17.941(1)
8.959(1)
12.430(1)
103.128(1)
1945.7(2)
7.008
space group
a/Å
b/Å
c/Å
23.682(6)
96.004(5)
3075.9(1)
5.752
â/deg
V/Å3
3594.0(3)
0.593
1.509
µ/mm-1
Dcalcd/g cm-3
1.239
1.874
2.117
cryst dimens/mm
Z
0.60 × 0.39 × 0.39
0.42 × 0.20 × 0.20
0.65 × 0.22 × 0.14
0.13 × 0.11 × 0.11
4
4
4
4
T/K
2θmax/deg
250
room temp
52.70
200
250
46.50
56.56
49.42
no. of rflns measd
no. of unique rflns
no. of params/restraints
R1 (I g 2σ(I))
wR2 (all data)
max/min resid electron dens/e Å-3
9730
5312
21 899
28 511
2152 (Rint ) 0.0462)
199/0
3360
7625 (Rint ) 0.0423)
391/0
6131 (Rint ) 0.0597)
478/1
245/2
0.0768
0.1771
0.240/-0.211
0.0169
0.0483
0.1420
3.381/-1.959
0.0424
0.0952
1.396/-0.712
0.0381
0.305/-0.929
11a) or Siemens CCD1k ((R(S))-7a) diffractometer system with
CCD area detector by using graphite-monochromated Mo KR
(0.710 73 Å) radiation and a low-temperature device if avail-
able (Table 3).
atom of the triflate counteranion (∼1.00 Å) or the heavy atom
rhodium (∼1.00 Å); for (R(S))-8b residual electron density was
found around the [SbCl6]- counteranion (∼0.80 Å) or the heavy
atom iridium (∼0.80 Å) even when an absorption correction
was applied.
Crystals suitable for X-ray diffraction of (R(S))-4a were
obtained by crystallization of a concentrated n-hexane solution
at room temperature; those of (R(S))-7a and (R(S))-8b were
obtained from a methylene chloride/acetonitrile solution lay-
ered with n-hexane at 0 °C. Crystals of (R)-[(R)-(+)]-11a were
grown at 0 °C from a ethanol solution layered with n-hexane.
The asymmetric unit of (R(S))-8b contains one acetonitrile
solvent molecule. To avoid quality degradation, most single
crystals were mounted in perfluoropolyalkyl ether oil on top
of a glass fiber and then brought into the cold nitrogen stream
of a low-temperature device so that the oil solidified. All
calculations were performed by using the programs SHELXTL
(version 6.12) and SHELXL-97. The structures were solved by
direct methods and successive interpretation of the difference
Fourier maps, followed by full matrix least-squares refinement
(against F2). Moreover, an empirical absorption correction
using SADABS (version 2.03) was applied to all structures,
except for (R)-[(R)-(+)]-11a. All non-hydrogen atoms were
refined anisotropically. The contribution of the hydrogen
atoms, in their calculated positions, was included in the
refinement using a riding model. Upon convergence, the final
Fourier difference map of the X-ray structures of (R(S))-4a and
(R(S))-7a showed no significant peaks. For (R)-[(R)-(+)]-11a,
some residual electron density was located close to the sulfur
Relevant data concerning crystallographic data, data col-
lection, and refinement details are summarized in Table 3.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as Supplementary
Publication Nos. CCDC 267929 (4a), CCDC 267930 (7a),
CCDC 267931 (8b), and CCDC 267932 ((R)-[(R)-(+)]-11a).
Copies of the data can be obtained free of charge on application
to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax,
(+44) 1223-336-033; e-mail, deposit@ccdc.cam.ac.uk).
Acknowledgment. This work was supported by the
Swiss Science Foundation and the ETH Zu¨rich. We
thank our colleague Antonio Togni for helpful discus-
sions.
Supporting Information Available: Cell constants and
a structure plot of the complex [Rh(2-MeO-naphdbcot)(MeCN)-
(H2O)]OTf ((R(S))-6c). This material is available free of charge
via the Internet at http://pubs.acs.org.
OM050093Z