Chiral Mo-binol complexes: Activity, synthesis, and structure. Efficient enantioselective six-membered ring synthesis through catalytic metathesis

Article abstract of DOI:10.1021/ja991432g

A new class of chiral Mo-based complexes 2a and 2b, bearing functionalized chiral binol ligands, is disclosed. Mo complex 2a promotes the asymmetric ring-closing metathesis (ARCM) of various dienes and trienes to afford six-membered carbo- and heterocycle

Full text of DOI:10.1021/ja991432g

J. Am. Chem. Soc. 1999, 121, 8251-8259
8251
Chiral Mo-Binol Complexes: Activity, Synthesis, and Structure.
Efficient Enantioselective Six-Membered Ring Synthesis through
Catalytic Metathesis
S. Sherry Zhu,† Dustin R. Cefalo,‡ Daniel S. La,‡ Jennifer Y. Jamieson,† William M. Davis,†
Amir H. Hoveyda,*,‡ and Richard R. Schrock*,†
Contribution from the Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, and Department of Chemistry, Merkert Chemistry Center,
Boston College, Chestnut Hill, Massachusetts 02467
ReceiVed May 3, 1999
Abstract: A new class of chiral Mo-based complexes 2a and 2b, bearing functionalized chiral binol ligands,
is disclosed. Mo complex 2a promotes the asymmetric ring-closing metathesis (ARCM) of various dienes and
trienes to afford six-membered carbo- and heterocycles efficiently and in high optical purity. The binol-based
chiral Mo catalysts complement the previously reported biphen-based complexes, which are particularly effective
in the enantioselective synthesis of five-membered rings by ARCM. Studies regarding catalytic kinetic resolutions
and asymmetric desymmetrizations are described. It is possible to obtain optically pure products in high yield
from catalytic reactions without the use of solvent (cf. eq 1). The structural attributes of these complexes are
detailed on the basis of the data available from an X-ray structure and variable-temperature 1H NMR studies.
The results of this investigation indicate the following: (i) The anti-Mo‚THF complex exists as a mixture of
diastereomers, whereas the syn isomer is formed stereoselectively. (ii) The anti-Mo isomers are likely more
Lewis acidic.
Introduction
attention to the preparation of related catalysts that efficiently
promote the enantioselective synthesis of other cyclic structures.
Herein, we report that Mo-based complexes 2a and 2b, bearing
a chiral binol (vs biphen) ligand, deliver chiral cyclohexenes,
dihydropyrans, and 1,7-dienes in high optical purity through
catalytic resolution and desymmetrization processes.5
Structural modularity is one of the most desirable properties
of a catalyst.1 This attribute facilitates access to various sterically
and electronically2 modified systems and provides the chemist
with an opportunity to prepare and screen other potential
candidates. Such considerations are important, since subtle
structural variations within a substrate often render a previously
potent catalyst ineffective.3
The chiral Mo-based catalysts 1a,b, which we reported
recently, benefit from structural modularity.4 These complexes
can be used to initiate asymmetric ring-closing metathesis
(ARCM) of 1,6-dienes to afford five-membered carbo- and
heterocycles in high optical purity. However, 1a,b are signifi-
cantly less effective in promoting the formation of the analogous
unsaturated pyrans and cyclohexenes (lower yields and/or
selectivities). To address this shortcoming, we turned our
† Massachusetts Institute of Technology.
Results and Discussion
‡ Boston College.
1. Chiral Mo-Binaphtholates in Asymmetric Synthesis.
a. Catalytic Kinetic Resolution of Dienes. As depicted in
Scheme 1, we initially examined the ability of complexes 2a
and 2b to catalyze the enantioselective formation of five-
membered rings by the ARCM of 1,6-dienes. The representative
example in Scheme 1 (3 f 4) illustrates that, whereas biphen
complex 1a promotes ring closure with high enantiodifferen-
tiation, 2a does so with significantly reduced selectivity and
(1) (a) Hoveyda, A. H. Chem. Biol. 1998, 5, R187-R191. (b) Shimizu,
K. D.; Snapper, M. L.; Hoveyda, A. H. Chem. Eur. J. 1998, 4, 1885-
1889.
(2) For selected examples of electronic tuning of transition metal-
catalyzed reactions, see: (a) Jacobsen, E. N.; Zhang, W.; Guler, M. L. J.
Am. Chem. Soc. 1991, 113, 6703-6704. (b) Rajanbabu, T. V.; Ayers, T.
A.; Casalnuovo, A. L. J. Am. Chem. Soc. 1994, 116, 4101-4102. (c)
Schnyder, A.; Hintermann, L.; Togni, A. Angew. Chem., Int. Ed. Engl. 1995,
34, 931-933 and references therein.
(3) For a recent example, where structurally related substrates have
different optimum chiral catalysts, see: Shimizu, K. D.; Cole, B. M.;
Krueger, C. A.; Kuntz, K. W.; Snapper, M. L.; Hoveyda, A. H. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1704-1707.
(4) (a) Alexander, J. B.; La, D. S.; Cefalo, D. R.; Hoveyda, A. H.;
Schrock, R. R. J. Am. Chem. Soc. 1998, 120, 4041-4042. (b) La, D. S.;
Alexander, J. B.; Cefalo, D. R.; Graf, D. D.; Hoveyda, A. H.; Schrock, R.
R. J. Am. Chem. Soc. 1998, 120, 9720-9721.
(5) Related Mo complexes have been used in catalyzing ROMP
processes: (a) Totland, K. M.; Boyd, T. J.; Lavoie, G. G.; Davis, W. M.;
Schrock, R. R. Macromolecules 1996, 29, 6114-6125. (b) McConville, D.
H.; Wolf, J. R.; Schrock, R. R. J. Am. Chem. Soc. 1993, 115, 4413-4414.
(c) O’Dell, R.; McConville, D. H.; Hofmeister, G. E.; Schrock, R. R. J.
Am. Chem. Soc. 1994, 116, 3414-3423.
10.1021/ja991432g CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/24/1999

8252 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Zhu et al.
Table 2. Catalytic Enantioselective Heterocycle Synthesis by
Scheme 1
ARCMa
Table 1. Catalytic Enantioselective Carbocycle Synthesis by
ARCMa
T (°C);
entry substrate catalyst reaction time dimer (%)
convb (%);
c,d
krel
17
24
4.3
4.0
>25
>25
2.5
3.3
1
2
3
4
2a
2a
2b
1a
22; 4 h
65; 40 min
22; 1h
66; 34
77; 27
68; 11
58; 11
(()-5a
R ) TES
22; 30 min
5
6
7
8
2a
2a
2b
1a
22; 3 h
65; 35 min
22; 1 h
68; 37
65; 23
59; 23
82; 7
(()-5b
R ) TBS
a-c See Table 1. d Relative rates are based on recovered substrates.
22; 20 min
a Conditions: 5 mol % catalyst, Ar atm, C6H6. b Conversion deter-
Mo catalysts. rac-7 (entry 1, Table 2) is resolved efficiently
within 40 min with 5 mol % 2a (krel > 25) with <5% dimeric
product formed. Catalytic ARCM promoted by biphen complex
1a affords a substantial amount of dimer and negligible
enantiodiscrimination (entry 2, Table 2). With 1b as the catalyst,
resolution efficiency is higher than that observed with 1a but
still substantially lower than that obtained with 2a. Similar
observations were made with silyl ether 9 as the substrate
(entries 4-6, Table 2). It is noteworthy that in resolutions
depicted in Table 2 there is generally less dimer formation than
in reactions depicted in Table 1. This difference may be
attributed to the presence of the sterically bulky dimethylsilyl
unit in the former, inhibiting association of two substrate
molecules with the chiral transition-metal center.
Remarkably, the identity of the optimum catalyst is reversed
in the catalytic resolutions of 11 and 13, where both reactive
sites are terminal olefins (entries 7-9 and 10-12, Table 2).
With two terminal alkenes as reaction partners, it is the biphen-
Mo 1a that is the superior catalyst (krel ) 21 and >25 for 11
and 13, respectively). In both instances, Mo-binaphtholate 2a
and the Mo-biphenolate derivative 1b, bearing a dimethylimido
ligand, are hardly stereodifferentiating (krel <2, entries 7, 9, and
krel <4, entries 10, 12, Table 2). Furthermore, ARCM of 11
underlines the high levels of regiocontrol involved with the
formation of initial Mo-alkylidene and subsequent RCM; there
is <2% product derived from the reaction of the trisubstituted
olefin. It is difficult to offer at the present time a rational
hypothesis as to why 2a is the superior catalyst for reactions
that involve the more substituted alkenes (7 and 9), whereas 1a
is the preferred catalyst when two terminal alkenes are involved
(11 and 13). These results, however, highlight the advantages
inherent in the structural modularity of the present class of Mo
catalysts. In addition, these data caution us against overgener-
alizing the selectivity profiles of various chiral Mo-based
metathesis catalysts.
1
mined by analysis of 400 MHz H NMR of the unpurified mixture.
c Enantioselectivity determined by GLC analysis (CHIRALDEX-GTA
by Alltech) in comparison with authentic racemic material.dRelative
rate determined based on the formation and selectivity of product
(exclusive of dimer amount).
2b effects RCM without any discrimination between the two
diene enantiomers.
As shown in Table 1, in contrast to biphen Mo complexes,
binol Mo systems catalyze the ARCM of 1,7-dienes with excellent
enantioselectiVity.6 In the presence of 5 mol % 2a, rac-5a is
resolved with excellent efficiency, where krel ) 17 and 24, for
reactions at 22 and 65 °C, respectively (entries 1-2, Table 1).7
Although ARCM catalyzed by biphen-Mo complex 1a generates
lower amounts of dimeric products8 (11% with 1a vs >27%
with 2a), these reactions proceed with significantly lower levels
of enantiodifferentiation (entry 4, krel ) 4.0). Similar results,
as observed for 1a, are obtained with the sterically less
demanding 2b (entry 3). Additional data in entries 5-8
demonstrate that the binol-based complex 2a is generally a
superior catalyst for the ARCM of 1,7-dienes.
The Mo-catalyzed kinetic resolutions presented in Table 2
provide an even starker contrast between the selectivity patterns
observed in ARCM reactions promoted by binol- and biphen-
(6) Attempts at Mo-catalyzed ARCM of 1,7-dienes related to 3 at 22 °C
(where one alkene is trisubstituted) resulted in exclusive dimer formation
(by reaction of terminal alkenes).
(7) The krel values are calculated by the equation reported by Kagan.
See: Kagan, H. B.; Fiaud, J. C. Top. Stereochem. 1988, 18, 249-330. This
calculation is only an approximation of the relative rates of reactions of
the two enantiomers, as it is based on a first-order equation, where a
simultaneous process (dimerization) does not occur (see footnote 8 for dimer
definition).
(8) By dimeric product we mean the material obtained by catalytic
intermolecular cross-coupling of two substrate molecules through their
terminal alkenes. The dimeric adduct (mixture of olefin isomers) from diene
5a, shown below, is illustrative.
b. Catalytic Asymmetric Desymmetrization of Trienes.
The ARCM processes presented in Table 3 involve the catalytic
desymmetrization of 1,6- and 1,7-dienes. As depicted in entry
1 (Table 3), 2a is unable to initiate RCM. In this case, it is 2b
that effectively initiates the ARCM of 15. Consistent with the

Chiral Mo-Binol Complexes
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8253
Table 3. Enantioselective Synthesis of Six-Membered Ring
the R isomer). The ligand synthesis utilizes dimethyl ether 21,
which is available from double-alkylation of commercially
available, optically pure binaphthol.9 Subsequent directed
double-deprotonation,10 followed by bromination of the resulting
dianion, delivers dibromide 22. Ni-catalyzed cross-coupling10
with 2,4,6-tri(isopropyl)phenylmagnesium bromide11 and depro-
tection of the resulting methyl ethers affords 23 (42% overall
yield; [R]22D ) 88.0 (c ) 3.0, THF)). Optically pure 2a and 2b
are then prepared in analogy to the previously reported syntheses
of 1a and 1b.4 Both complexes are recrystallized as THF adducts
(from Et2O at -35 °C in the presence of THF).
Heterocycle by Mo-Catalyzed Desymmetrizationa
3. Structure of Mo-Binaphthol Complexes. a. X-ray
Crystallography. Mo complexes 2a and 2b are obtained as
yellow crystals that contain 1 equiv of THF. On the basis of 1H
NMR studies (detailed below) and the previously reported X-ray
structure of the analogous anti-24 (shown in Scheme 3),5a it is
likely that THF is a ligand in the Mo complex.
Crystals of pyridine adduct 25 (bearing (R)-23) were found
to be suitable for X-ray crystallography (Scheme 3; selected
numbering and i-Pr groups omitted for clarity). In this structure,
pyridine is coordinated to one of the two diastereotopic CNO
faces of the Mo complex (complexes shown in Scheme 3
represent coordination from the two CNO faces).12 The resulting
trigonal bipyramid, with the alkylidene and imido ligands
positioned equatorially, is similar to the structures of related
Mo or W complexes.13
Several structural features of syn-25 merit additional discus-
sion. The Mo-C(1) (ModCR) bond distance (1.840(12) Å) and
ModCR-Câ bond angle (149.5(10)°) are typical of the syn
isomers of this class of transition metal complexes (Table 4).4,5
a-c See Table 1. d Isolated yields after silica gel chromatography.
e Reactions in entries 7-9 were performed in n-pentane due to high
product volatility.
aforementioned selectivity trends, the biphen complex 1b proves
to be the best choice for the asymmetric formation of the fiVe-
membered ring (R)-16.
In contrast, 2a readily promotes the conversion of silyl ether
17 to the six-membered ring allyl silane (R)-18; this transforma-
tion occurs within 3 h in >99% ee (chiral GLC) and 98%
isolated yield after silica gel chromatography. Biphen-based
catalysts 1a and 1b are significantly less effective: after 24 h,
there is ∼50% conversion, 18 is formed with substantially lower
levels of enantioselection, and the major product is the derived
dimer. It is particularly noteworthy that, although biphen
complexes 1a and 1b afford substantial amounts of dimer in
the presence of 17, with 2a as catalyst (eq 1), eVen in the
absence of solVent, <2% dimer is obtained; ARCM product
(R)-18 is isolated in 98% yield and >99% ee after distillation.
Table 4. Selected Bond Distances (Å) and Angles (deg) in Mo
Complexes 24 and 25
complex anti-24
complex syn-25
Mo-N(1)
1.732(7) Mo-N(1)
1.715(10)
1.840(12)
1.988(7)
2.018(7)
2.251(10)
Mo-C(33) (Mo-CR)
Mo-O(1)
1.927(9) Mo-C(1) (Mo-CR)
1.988(5) Mo-O(1)
Mo-O(2)
Mo-O(3)
2.012(5) Mo-O(2)
2.195(5) Mo-N(2)
Mo-N(1)-C(101)
Mo-O(2)-C(17)
C(33)-Mo-O(1)
C(33)-Mo-O(2)
N(1)-Mo-C(33)
N(1)-Mo-O(1)
N(1)-Mo-O(2)
O(1)-Mo-O(2)
O(1)-Mo-O(2)
N(1)-Mo-O(3)
O(2)-Mo-O(3)
C(33)-Mo-O(3)
C(1)-C(2)-
166.9(6)
Mo-N(1)-C(11)
158.6(8)
112.8(5)
127.4(3)
92.5(3)
100.3(3)
131.3(3)
100.4(3)
87.8(2)
78.4(2)
88.8(3)
166.2(2)
96.1(3)
65.5a
Mo-O(2)-C(101) 122.3(6)
C(1)-Mo-O(1)
C(1)-Mo-O(2)
N(1)-Mo-C(1)
N(1)-Mo-O(1)
N(1)-Mo-O(2)
O(1)-Mo-O(2)
O(1)-Mo-N(2)
N(1)-Mo-N(2)
O(2)-Mo-N(2)
C(1)-Mo-N(2)
C(201)-C(202)-
C(102)-C(101)
117.8(4)
86.1(4)
110.8(5)
130.6(4)
105.8(3)
86.5(3)
78.5(3)
87.9(4)
164.2(3)
96.5(4)
60.0a
Similar, but less pronounced, trends are observed in the Mo-
catalyzed desymmetrizations of triene 19. Once again, the Mo-
binaphtholate 2a affords optically pure (R)-20 efficiently and
in excellent yield (86% after silica gel chromatography).
2. Synthesis of Mo-Binaphthol Complexes. Binaphthol 23
was prepared as depicted in Scheme 2 (sequence shown is for
C(22)-C(17)
Scheme 2a
a The dihedral angle between the two naphthyl rings in the binaph-
tholate ligands.
Overall, the structure of syn-25 (Table 1) is comparable to that
of the closely related anti-24 (Scheme 4). It is, however,
important to note two structural variations between these two
metal systems. (i) Mo complex anti-24 contains a smaller Mod
(9) Both antipodes of binaphthol are commercially available (Aldrich
Co. and Kankyo Kagaku Center Co., Japan).
(10) (a) Lingenfelter, D. S.; Helgeson, R. C.; Cram, D. J. J. Org. Chem.
1981, 46, 393-406. (b) Hu, Q. S.; Vitharana, D.; Ou, L. Tetrahedron:
Asymmetry 1995, 6, 2123-2126.
(11) 1-Bromo-2,4,6-triisopropylbenzene is commercially available (Alfa/
Aesar).
a Key: (a) TMEDA, n-BuLi, Et2O, 22 °C, 4 h; Br2, Et2O, -40 f
+22 °C, 8 h (71% overall); (b) 1.0 mol % (PPh3)2NiCl2, 2,4,6-
tri(isopropyl)phenylmagnesium bromide, Et2O, 45 °C, 24 h, 70%; (c)
BBr3, CH2Cl2, 22 °C, 12 h, 83%; (d) benzylpotassium, THF, 10 min;
Mo(CHCMe2Ph)(NAr)(OTf)2‚dme, THF, 22 °C, 15 min, 64% (Ar )
2,6-diisopropylPh).
(12) Wu, Y.-D.; Peng, Z.-H. J. Am. Chem. Soc. 1997, 119, 8043-8049.
(13) Feldman, J.; Schrock, R. R. Prog. Inorg. Chem. 1991, 39, 1-74.

8254 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Zhu et al.
Scheme 3
CR-Câ bond angle (128.1(6)°) than syn-25 (149.5 (10)°). (ii)
anti-24 has a longer Mo-C(33) bond (1.927(9) Å) than syn-25
(1.840 (12) Å). These differences can be rationalized in the
following manner:
(a) ModCR-Câ bond angles in syn complexes (e.g., 25) are
larger than those in anti isomers, due (in part) to the steric
interaction between the alkylidene unit pointing toward the ortho
substituents of the phenylimido ligand (Scheme 4).
H-CR and the s character of the ModCR bond, giving the latter
partial triple bond character.
b. NMR Studies. A 13C NMR spectrum (22 °C) of 25 shows
an alkylidene peak (ModC) at 309 ppm that we ascribe to the
1
more abundant syn adduct.5,17 The H NMR spectrum of 25
(Figure 2, 20 °C, C6D6) exhibits one sharp resonance at 13.110
ppm and two (∼1:1) signals at 14.290 and 14.371 ppm in a
1
ratio of 88:12 (syn peak: both anti peaks). A high-intensity H
NMR spectrum reveals 13C satellites on the alkylidene reso-
nances. The high-field HR resonance (ModCH) exhibits JCRHR
) 114 Hz and is assigned to the syn isomer.16b The two lower
field HR resonances are attributed to anti alkylidenes, based on
the larger coupling constant (JCRHR ) 147 Hz). Two anti isomers
likely arise from coordination of pyridine to the two CNO faces
of the Mo complex (see below for further discussion).
Scheme 4a
a The steric interaction shown above causes the following: (i) larger
N-Mo-CR angle; (ii) bending of Mo-N-C11 bond; (iii) twisting of
the imido ligand.
In syn-25, steric interaction between the alkylidene unit and
the imido ligand o-i-Pr substituent (Scheme 4) causes the Mo-
N-C(11) bond system to bend from its preferred linear
orientation (158.6 (8)° and 166.9 (6)° in syn-25 and anti-24,
respectively).14 Such interactions cause the twisting of the 2,6-
diisopropylphenyl ring. The 2,6-Me2C6H3 ring in anti-24 can
lie in the N-Mo-CR-Câ plane because of the lesser steric
interaction between the imido and alkylidene groups.
(b) As illustrated in Figure 1, and as supported by various
theoretical studies,15 an agostic interaction16 between the H-CR
bond and the transition metal might be partially responsible for
Figure 2. Alkylidene region (ModCH) from variable-temperature 1H
NNR experiments with 7.
The chemical shifts of signals corresponding to both the syn
and anti HR nuclei appear to be somewhat temperature-
dependent. The resonance corresponding to the syn isomer shifts
upfield upon heating. When the sample is heated to 70 °C, the
ratio of the HR resonances for the anti adduct relative to those
for the syn adduct becomes 43:57 (from 12:88). It is plausible
that the syn/anti ratio changes as a consequence of pyridine
dissociation, followed by equilibration by rotation about the
Figure 1. Agostic interaction between alkylidene CH and σ* Mo-N
leads to shortening of the ModC bond.
the shorter ModCR bond of the syn isomer. Thus, hypercon-
jugation (σC-H f σ*Μï-Ν) increases the p character of the
(15) (a) Reference 12. (b) Folga, E.; Ziegler, T. Organometallics 1993,
12, 325. (c) Monteyne, K.; Ziegler, T. Organometallics 1998, 17, 5901-
5907. (d) Cundari, T. R.; Gordon, M. S. Organometallics 1992, 11, 55-
63. (e) Fox, H. H.; Schofield, M. H.; Schrock, R. R. Organometallics 1994,
13, 2804-2815.
(16) (a) Schrock, R. R. In Reactions of Coordinated Ligands; Braterman,
P. R., Ed.; Plenum: New York, 1986; pp 221-283. (b) Brookhart, M.;
Green, M. L. H.; Wong, L. Prog. Inorg. Chem. 1988, 36, 1-124.
(17) Schrock, R. R.; Crowe, W. E.; Bazan, G. C.; DiMare, M.; O’Regan,
M. B.; Schofield, M. H. Organometallics 1991, 10, 1832-1843.
(14) The bending caused by steric strain is reinforced by lowering of
the overlap between the imido N nonbonding electrons into a Mo d orbital,
reducing the triple bond character of the Mo-N bond. Thus, the Mo-N
bond regains some of its double bond character to cause the observed change
in bond angles. For a review on orbital ineractions involved in the syn-
anti isomerization of this class of Mo complexes, see: Schrock, R. R. In
Alkene Metathesis in Organic Synthesis; Furstner, A., Ed.; Springer: Berlin
1998; pp 1-37.

Chiral Mo-Binol Complexes
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8255
Figure 4. Alkylidene region (ModCH) from the variable-temperature
1H NMR experiments involving 2a from which THF has been partially
removed.
Figure 3. Alkylidene region (ModCH) from the variable-temperature
1H NMR experiments with 2a (excess THF, toluene-d8).
ModCR bond.18 It must be noted that two resonances for each
alkylidene isomer would have been observed if pyridine were
to bind indiscriminately to the two diastereotopic CNO faces
in each isomer. Several explanations may be put forth as to
why only one syn HR resonance is observed:19 (i) pyridine binds
to only one CNO face of the syn isomer; (ii) both syn
diastereomers are present in solution, but the HR resonances
happen to have the same chemical shift; and (iii) pyridine rapidly
dissociates from and reassociates with the complex, allowing
two diastereomeric syn complexes to equilibrate rapidly on the
NMR time scale without the base free complex being observed.
It is not likely that there is rapid equilibration between 25 and
the corresponding base-free complex, a pathway that is probably
required for interconversion of the derived diastereomers.20 This
contention is supported by the following observations: (i) The
1H NMR resonances are sharp. (ii) Heating of the NMR sample
to 70 °C and subsequent recooling does not result in regeneration
of the initial syn/anti isomer ratios observed at 22 °C (pyridine
does not readily dissociate at ambient temperature).
complex 25, this is likely the result of THF dissociation to afford
the free syn complex, with which the syn THF adduct exchanges
rapidly. In contrast there is little change in the average chemical
shift of the anti isomer upon heating. These obserVations imply
that the anti isomer is more Lewis acidic than the syn isomer,
since the latter more readily loses its THF ligand (additional
supporting data is provided below).20 This hypothesis is
consistent with, inter alia, the suggested agostic interaction in
this class of syn Mo complexes (cf. electron donation from C-H
to Mo in Figure 1).
A sample of 2a, from which THF is partially removed by
subjection of the sample to vacuum, was examined by 1H NMR
spectroscopy. Partial removal of THF was effected so as to allow
the detection of the THF-bound as well as any derived THF-
free Mo complex (temperature range is different than that used
in Figure 2). Indeed, as illustrated in Figure 4, at -60 °C, the
1H NMR spectrum of 2a exhibits an HR resonance at 10.98 ppm
for the THF-free syn isomer and one for the THF-bound syn
adduct (12.810 ppm). In addition, there are two signals for the
diastereotopic anti-THF complexes (14.520 and 14.416 ppm);
however, there are no signals corresponding to the THF-free
anti-2a. The spectrum obtained at -60 °C therefore suggests
that the THF complex deriVed from the syn isomer is formed
diastereoselectiVely.21
As the sample temperature is raised (-40 °C f 20 °C, Figure
4), the HR signal for the THF-free syn-2a broadens and coalesces
with that for the THF-bound syn adduct, an observation that
again points to the higher lability of a THF ligand in the
corresponding syn complex compared to the more Lewis acidic
anti isomer. In accord with the proposal that the anti isomer is
more Lewis acidic, the rate and degree of THF dissociation at
20 °C is sufficiently small that it does not lead to a significant
variation in the chemical shift of the HR resonances of anti-2a
(∼14.5-14.4 ppm) or rapid interconversion of diastereomers.
The above data imply that the average resonance for the
interconverting syn-THF adduct and its parent base-free complex
can be used to estimate the concentration of these entities in
solution. These measurements are based on the assumption that
the Mo-alkylidene HR resonances for the THF-bound and free
complex are not significantly temperature dependent (compared
to the chemical shift difference between the THF-bound and
THF-free syn complex, cf. Figure 4). Accordingly, based on
1
The related H NMR spectra of 2a (500 MHz, toluene-d8)
are more complex than those of 25; this can be ascribed to the
higher lability (lower Lewis basicity) of THF. Accordingly, for
the sake of simplicity, we decided to examine the spectra derived
from samples of 2a in the presence of excess THF, so as to
minimize the presence of any THF-free Mo complex. As shown
1
in Figure 3, the H NMR spectrum of 2a (-20 °C) in the
presence of excess THF reveals two anti alkylidene HR signals
and one syn alkylidene HR resonance. As the temperature is
raised, the HR signals for the two diastereomeric anti THF
adducts (14.5-14.3 ppm) broaden and coalesce at ∼33 °C. The
broadening and coalescence of the two anti HR resonances may
be ascribed to the rapid interconversion of the two anti THF
diastereomers.
As illustrated in Figure 3, the signal from the syn isomer
begins to shift upfield when the sample temperature is above
40 °C. As mentioned before in connection to the pyridine-bound
(18) Alexander, J. B.; Hoveyda, A. H.; Schrock, R. R. Unpublished
results. The assumption that pyridine (or THF) dissociation is required before
syn: anti isomerization occurs, is supported by previous studies on the effect
of added PMe3 on the syn and anti forms of Mo(NAr)(CHCMe2Ph)[OCMe-
(CF3)2]2; see ref 17.
(19) These mechanistic possibilities are based on the theoretically
supported assumption that an approaching Lewis base binds to the metal
complex through one of the CNO faces (see ref 17).
(20) Oskam, J. H.; Schrock, R. R. J. Am. Chem. Soc. 1993, 115, 11831-
11845.
(21) The identity of the major syn THF-bound diastereomer has not yet
been determined.

8256 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Zhu et al.
rationale for the selectivity trends exhibited by the two classes
of catalysts (complexes 1 vs 2); future mechanistic and modeling
work will hopefully lead to the formulation of an effective
model. Nonetheless, the findings detailed here offer a compelling
case for the continued development of chiral metathesis
catalysts.23
Several structural features of these complexes emerge through
examination of X-ray data and various NMR studies. Notewor-
thy is the apparent higher Lewis acidity of the anti Mo isomers
and the diastereoselective coordination of THF to the syn, but
not anti, complex.
The synthesis and development of additional classes of chiral
Mo catalysts and investigation of their ability to promote ARCM
and other metathesis-based processes are in progress. The results
of these studies will be revealed shortly.
Figure 5. Alkylidene region (ModCH) from the variable-temperature
1H NMR experiments involving 2a (toluene-d8).
Experimental Section
the average resonance for the THF-bound and THF-free syn
complex, Keq = 2 at 20 °C for the syn-THF complex and its
corresponding THF-free isomer.
General Information. Infrared (IR) spectra were recorded on Perkin-
Elmer 781 and 1608 spectrophotometers, νmax in cm-1. Bands are
characterized as broad (br), strong (s), medium (m), and weak (w). 1H
NMR spectra were recorded on Varian GN-400 (400 MHz), Unity 300
(300 MHz), and Varian VXR 500 (500 MHz) spectrometers. Chemical
shifts are reported in ppm from tetramethylsilane with the solvent
resonance as the internal standard (CHCl3: δ 7.26). Data are reported
as follows: chemical shift, multiplicity (s ) singlet, d ) doublet, t )
triplet, q ) quartet, br ) broad, m ) multiplet), coupling constants
(Hz), integration, and assignment. 13C NMR spectra were recorded on
a Varian GN-400 (100 MHz), Unity 300 (75 MHz), and Varian VXR
500 (125 MHz) spectrometers with complete proton decoupling.
Chemical shifts are reported in ppm from tetramethylsilane with the
solvent as the internal reference (CDCl3: δ 77.7 ppm). Conversions
were determined by 1H NMR of the unpurified reaction mixtures.
Enantiomer ratios were determined by chiral GLC analysis (Alltech
Associates Chiraldex GTA column (30m × 0.25 mm)) or Betadex 120
column (30m × 0.25 mm) in comparison with authentic materials.
Microanalyses were performed by Robertson Microlit Laboratories
(Madison, NJ) and Microlytics Analytical Laboratories (Deerfield, MA).
High-resolution mass spectrometry was performed by the University
of Illinois and Massachusetts Institute of Technology Mass Spectrom-
etry Laboratories.
All reactions were conducted in oven (135 °C) and flame-dried
glassware under an inert atmosphere of dry argon. Benzene, toluene,
and n-pentane were distilled from sodium metal/benzophenone ketyl.
n-Pentane was stirred over concentrated H2SO4 for 5 days and then
distilled over Na. Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OTf)2‚DME and
Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(OTf)2‚DME were synthesized ac-
cording to a published procedure.24 Mo(N-2,6-iPr2C6H3)(CHCMe2Ph)-
((S)-(-)-t-Bu2Me4(biphen))4b and Mo(N-2,6-Me2C6H3)(CHCMe2Ph)-
((S)-(-)-t-Bu2Me4(biphen))4b were synthesized on the basis of previously
reported procedures.
With the above information in hand, we turned our attention
to variable-temperature 1H NMR experiments with a sample of
Mo complex 2a (no excess THF added nor any removed). As
illustrated in Figure 5, the significant shift of the syn ModCH
signal (20 f 40 °C, Figure 5) is due to the rapid loss of THF
from the syn isomer and a rapid equilibrium between the THF-
bound and free complexes (cf. Figure 5). At 40 °C, the signal
for the alkylidene CH of the THF-bound and more Lewis acidic
anti complex begins to broaden and shift, as it too begins to
lose its THF ligand.22
On the basis of studies with analogous THF-free biphenoxide
complexes,18 it is likely that further broadening of both syn and
anti alkylidene HR signals between 60 and 80 °C arises from
interconversion of THF-free syn-2a and anti-2a. Thus, as
depicted in Figure 5, when the sample is heated to 100 °C, the
sharpening signal likely represents the average of all possible
THF-free and THF-bound complexes. Moreover, consistent with
the relative Lewis acidity of syn- vs anti-2a, while syn-2a
releases a THF ligand readily at 40 °C, anti-2a is relatively
resistant to the loss of THF. It is nonetheless important to note
the following: (i) There are as yet no direct data concerning
the relative reactivity of the syn and anti isomers of binol-based
chiral Mo complex 2a. The relative reactivity of syn and anti
isomers may vary among different Mo complexes (from
variations in imido, diolate, and alkylidene ligands). (ii) The
relative reactivity of syn and anti isomers may further depend
on the electronic and steric nature of the approaching olefin.17
(R)-(+)-Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(3,3′-bis(2,4,6-triisopro-
pylphenyl)-2,2′-dihydroxy-1,1′-dinaphthyl)(THF) (2a). To a stirred
solution of (R)-3,3′-bis(2,4,6-triisopropylphenyl)-2,2′-dihydroxy-1,1′-
dinaphthyl (23) (3.4 g in 250 mL of THF, 4.9 mmol) was added
benzylpotassium (1.34 g, 10.3 mmol) slowly at 22 °C. The resulting
solution turned from colorless to yellow over the course of 10 min. At
this point, Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(OTf)2‚DME (3.5 g, 4.4
mmol) was added in a single portion. After the mixture was allowed
to stir at 22 °C for 15 min, volatile solvents were removed in vacuo
from the resulting red solution to yield a dark red solid. This residue
was washed with 20 mL of benzene and filtered through Celite.
Removal of solvents in vacuo afforded a red solid, which was washed
with cold Et2O (5 mL) and again filtered through Celite. The Et2O
solution was cooled to -35 °C to afford 2.0 g (36% yield) of 2a as a
Conclusions
We disclose a class of chiral Mo-based catalysts that effect
the enantioselective formation of a range of six-membered
carbo- and heterocycles. Catalysts 2a,b are complementary to
the previously reported biphen-based systems;4 they significantly
enhance the synthetic utility of catalytic metathesis in asym-
metric synthesis. Although binol complexes are typically more
effective in the asymmetric synthesis of six-membered rings
by ARCM, one cannot always predict which class of catalysts
is the best choice. Catalytic ARCM of a 1,6-diene is likely most
efficiently promoted by a Mo-biphen complex and that of a
1,7-diene by a Mo-binol catalyst, but subtle substrate structural
variations can cause such roles to be reversed (e.g., entries 7-12,
Table 2). At the present time it is difficult to provide a plausible
1
yellow solid. H NMR (300 MHz, toluene-d8): δ 14.45 (s (br), 23%
(23) For a related study in this area, see: Fujimura, O.; Grubbs, R. H.
J. Am. Chem. Soc. 1996, 118, 2499-2500.
(24) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare,
M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875-3886.
(22) The HR resonance in free anti-2a is likely to be upfield of that for
THF-bound anti-2a on the basis of studies involving other complexes in
this general family. See ref 5.

Chiral Mo-Binol Complexes
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8257
of 1H, anti-CHCMe2Ph), 14.30 (s (br), 24% of 1H, anti-CHCMe2Ph),
12.26 (s (br), 53% of 1H, syn-CHCMe2Ph), 7.75 (s, 2H, ArH), 7.65-
7.60 (m, 4H, ArH), 7.18-6.90 (s (br), ArH), 6.81 (s, 4H, Me2CHC6H2),
3.26 (s (br), THF), 3.08 (s (br), THF), 3.96-2.72 (s (br), 8H, Me2CH),
1.48 (s, 3H, CHC(CH3)2Ph), 1.45 (s, 3H, CHC(CH3)2Ph), 1.28-0.71
(s (br), CH(CH3)2 and THF), 0.70 (d, J ) 6.0 Hz, 14H, (CH3)2CH).
13C NMR (125 MHz, toluene-d8): δ 321.8, 154.7, 150.7, 148.6, 148.2,
147.8, 147.2, 137.6, 137.2, 136.6, 136.1, 132.4, 132.0, 130.3, 130.2,
129.6, 128.9, 128.6, 127.9, 127.4, 126.9, 126.6, 126.5, 126.2, 125.8,
124.1, 123.6, 121.4, 121.2, 120.9, 73.1, 66.3, 54.5, 35.4, 35.1, 32.4,
31.7, 31.5, 30.4, 29.4, 28.7, 27.2, 26.6, 25.7, 25.3, 25.1, 24.9, 24.7,
24.6, 24.2, 23.4, 21.3, 21.1, 20.5, 20.4, 16.0, 2.4. Anal. Calcd for C76H93-
NO3Mo: C, 78.39; H, 8.05; N, 1.20. Found: C, 78.46; H, 8.12; N,
1.24.
(R)-(+)-Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(3,3′-bis(2,4,6-triisopro-
pylphenyl)-2,2′-dihydroxy-1,1′-dinaphthyl)(THF) (2b). Complex 2b
was synthesized according to the above procedures, except that Mo-
(N-2,6-Me2C6H3)(CHCMe2Ph)(OTf)2‚DME was used as the starting
material. 1H NMR (300 MHz, CDCl3): δ 14.24 (s, 27% of 1H,
CHCMe2Ph), 11.90 (s (br), 73% of 1H, CHCMe2Ph), 7.82 (s, 1H, ArH),
7.74-6.59 (m, 19H, ArH), 6.54 (s, 2H, ArH), 3.50-2.78 (m, 9H, THF,
(CH3)2CH), 2.40 (s, 1H, (CH3)2CH), 1.83-1.53 (s (br), 3H, ModCH-
(CH3)), 1.37-0.61 (m, 49 H, ModCH(CH3), CH(CH3)2, Ar(CH3)2,
THF). 13C NMR (125 MHz, C6D6): δ 287.3, 156.7, 151.6, 150.5, 149.9,
149.4, 148.8, 148.0, 147.6, 136.3, 135.3, 134.7, 134.2, 133.6, 132.7,
131.4, 130.7, 130.1, 128.9, 127.6, 126.9, 126.5, 125.5, 125.1, 124.6,
123.8, 123.4, 114.4, 75.3, 72.0, 66.3, 54.8, 53.1, 36.0, 35.6, 35.0, 32.6,
31.6, 31.2, 29.5, 29.1, 26.9, 26.4, 25.7, 24.6, 23.1, 19.6, 15.9, 14.6.
Anal. Calcd for C72H85NO3Mo: C, 78.02; H, 7.73; N, 1.26. Found: C,
77.88; H, 7.84; N, 1.32.
1.68 (s (br), 3H, CHdCCH3), 1.53-1.46 (m, 2H, CH2CHOSi), 0.90 (s
(br), 9H, (CH3)3CSi), 0.09 (s, 6H, CH3SiCH3). 13C NMR (75 MHz,
CDCl3): δ 124.7, 114.2, 69.7, 33.2, 26.2, 25.7, 21.2, 19.3, -4.1, -4.5.
Anal. Calcd for C13H26OSi: C, 68.96; H, 11.57. Found: C, 68.71; H,
11.39.
(R)-1-Oxa-6-pentyl-2-sila-2,2,5-trimethyl-cyclohex-4-ene (8). IR
(NaCl): 2962 (s), 2936 (s), 2867 (m), 1457 (m), 1376 (w), 1262 (s),
1224 (w), 1105 (m) cm-1. 1H NMR (400 MHz, CDCl3): δ 5.61-5.57
(m, 1H, CdCH), 4.21 (s (br), 1H, OCH), 1.61 (s, 3H, CH3CdCH),
1.59-1.13 (m, 10H, CH2CH2CH2CH2CH3, SiCH2CH), 0.88 (t, J ) 6.8
Hz, 3H, CH2CH2CH2CH3), 0.17 (s, 3H, SiCH3), 0.09 (s, 3H, SiCH3).
13C NMR (100 MHz, CDCl3): δ 139.0, 120.0, 77.1, 36.7, 32.6, 25.3,
23.4, 22.8, 14.8, 13.0, 1.5, 0.2. HRMS (EI+): calcd for C12H24OSi
212.1596, found 212.1603. Anal. Calcd for C12H24OSi: C, 67.86; H,
11.39. Found: C, 67.90; H, 11.15.
Determination of the Stereochemical Identity of Mo-Catalyzed
Kinetic Resolution Products. A sample of optically enriched (R)-7
was prepared through silylation of a sample of optically enriched allylic
alcohol, prepared by the method of Sharpless.25 The product obtained
from the Mo-catalyzed ARCM was correlated with this authentic
material.
(R)-1-Oxa-6-cyclohexyl-2-sila-2,2,5-trimethyl-cyclohex-4-ene (10).
IR (NaCl): 2930 (s), 2861 (m), 1464 (w), 1256 (m), 1111 (m) cm-1
.
1H NMR (400 MHz, CDCl3): δ 5.64 (d, J ) 8.4 Hz, 1H, SiCH2CH),
4.04 (s, 1H, SiOCH), 1.77-1.72 (m, 2H, Cy-H), 1.63-1.34 (m, 9H,
CH3CdCH, Cy-H), 1.28-1.02 (m, 5H, SiCH2CH, Cy-H), 0.17 (s, 3H,
SiCH3), 0.07 (s, 3H, SiCH3). 13C NMR (100 MHz, CDCl3): δ 137.9,
120.6, 81.7, 43.5, 31.0, 27.5, 27.2, 27.2, 26.7, 23.3, 13.2, 0.9, 0.2. Anal.
Calcd for C13H24OSi: C, 69.58; H, 10.78. Found: C, 69.64; H, 10.62.
(R)-2,2-Dimethyl-6-(2(E)-ethenyl)-1-oxa-2-silacyclohex-4-ene (12).
IR (NaCl): 3018 (m), 2968 (m), 2917 (w), 1652 (m), 1564 (m), 1249
Representative Procedure for Mo-Catalyzed Kinetic Resolution
(at 22 °C). 2-Methyl-3-tert-butyldimethylsiloxy-1,7-octadiene (5b)
(0.15 g, 0.59 mmol) was dissolved in benzene (5.9 mL) in a capped
vial (to allow for the release of ethylene). Optically pure catalyst (2a)
(0.034 g, 0.029 mmol, 5 mol %) was then added. The resulting mixture
was allowed to stir at 22 °C for ∼3.5 h. At this point, the reaction
mixture was exposed to air; subsequently, methanol (1 mL) was added.
Removal of the volatiles in vacuo afforded a dark red oil. Percent
1
(s), 1180 (s), 1080 (m) cm-1. H NMR (400 MHz, CDCl3): δ 5.93-
5.87 (m, 1Η, CH3CH)C) 5.53-5.44 (m, 2H, SiCH2CH)CH), 4.74
(dd, J ) 2.4, 2.4 Hz, 1H, OCH), 1.61 (d, J ) 7.6 Hz, 3H, CH3CH),
1.58 (d, J ) 1.2 Hz, 3H, CH3C) 1.37-1.14 (m, 2H, SiCH2CH), 0.19
(s, 3H, SiCH3), 0.17 (s, 3H, SiCH3). 13C NMR (100 MHz, CDCl3): δ
138.1, 132.2, 125.2, 121.6, 79.4, 13.9, 12.7, 11.7, 0.9, 0.0. HRMS (EI+)
calcd for C10H18OSi 182.1127, found 182.1125.
1
conversion was calculated by analysis of the H NMR spectrum (500
(R)-6-Cyclohexyl-2,2-dimethyl-1-oxa-2-silacyclohex-4-ene (14). IR
(NaCl): 3018 (w), 2936 (s), 2848 (s), 1646 (w), 1457 (m), 1394 (w),
MHz, CDCl3). The starting material, metathesis product, and dimeric
products were isolated by silica gel chromatography (hexanes). In the
case of highly volatile products, percent conversion was determined
1
1256 (s), 1168 (s), 1111 (s) cm-1. H NMR (400 MHz, CDCl3): δ
5.90-5.85 (m, 1Η, OCHCHdCH), 5.57-5.54 (m, 1H, OCHCH)CH),
4.18 (dd, J ) 2.0, 0.8 Hz, 1H, SiOCH), 1.72 (d, J ) 9.6 Hz, 2H, SiCH2),
1.67-1.62 (m, 2H, Cy-H), 1.43-1.37(m, 2H, Cy-H), 1.27-0.96 (m,
7H, Cy-H), 0.16 (s, 3H, SiCH3), 0.13 (s, 3H, SiCH3). 13C NMR (100
MHz, CDCl3): δ 131.9, 125.0, 77.3, 45.8, 29.3, 28.5, 27.3, 27.1, 27.0,
13.2, 1.0, 0.0. HRMS (EI+): calcd for C12H22OSi 210.1440, found
210.1440.
1
by the analysis of the H NMR spectrum of the unpurified reaction
mixture (C6D6).
Representative Procedure for Mo-Catalyzed Kinetic Resolution
(Temperatures above 22 °C). 2-Methyl-3-tert-butyldimethylsiloxy-
1,7-octadiene (5b) (0.15 g, 0.59 mmol) was dissolved in benzene (5.9
mL) in a tightly capped vial (to prevent solvent loss). Optically pure
catalyst (2a) (0.034 g, 0.029 mmol, 5 mol %) was added to this solution
as a solid. The resulting orange solution was placed into a heated bath
(equilibrated to 60 °C) for ∼35 min. At this time, the reaction mixture
was exposed to air and methanol (1 mL) was added. In analogy to the
purification procedure mentioned above, the percent conversion was
determined, and starting material, metathesis product, and dimeric
product were isolated. In the case of highly volatile products, percent
conversion was determined by analysis of the 1H NMR of the unpurified
reaction mixture (C6D6).
(R)-2-Methyl-1-triethylsiloxy-2-cyclohexene (6a). IR (NaCl): 2962
(s), 2873 (s), 1457 (m), 1243 (m), 1086 (m), 1004 (s) cm-1. 1H NMR
(400 MHz, CDCl3): δ 5.50 (s, 1H, CH2CHdC), 4.04 (s (br), 1H,
CHOSi), 2.01 (d, J ) 18.4 Hz, 1H, CHHCHdC), 1.88 (d, J ) 18.4
Hz, 1H, CHHCHdC) 1.78-1.47 (m, 4H, CH2CH2), 1.71 (s, 3H, CHd
CCH3), 0.98 (t, J ) 8.0 Hz, 9H, (CH3CH2)3SiO), 0.64 (q, J ) 8.0 Hz,
6H, (CH3CH2)3SiO). 13C NMR (100 MHz, CDCl3): δ 136.6, 125.5,
69.9, 33.7, 26.2, 21.5, 19.6, 7.6, 5.7. Anal. Calcd for C13H26OSi: C,
68.96; H, 11.57. Found: C, 68.76; H, 11.43.
(R)-2-(2(E)-sec-Butenyl)-3-methyl-2,5-dihydrofuran (16). IR
(NaCl): 2976 (s), 2917 (s), 2845 (s), 1762 (m), 1430 (m), 1380 (m),
1
1297 (w), 1250 (w), 1184 (w), 1054 (s) cm-1. H NMR (500 MHz,
CDCl3): δ 5.60 (dq, J ) 3.0, 1.0 Hz, 1H, OCH(CdC)2), 5.55 (m, 1H,
CH3HCdCCH3), 5.25-5.19 (m, 1H, OCH2CH)C), 4.64 (m, 2H, OCH2-
CHdC), 1.66 (dq, J ) 7.0, 1.0 Hz, 3H, CH3HCdCCH3), 1.60 (s (br),
3H, CH3HCdCCH3), 1.50 (dq, J ) 3.0, 1.0 Hz, 3H, OCH2HCdCCH3).
13C NMR (125 MHz, CDCl3): δ 137.3, 135.7, 123.9, 121.6, 95.1, 75.7,
13.6, 12.6, 10.2. HRMS (EI+): calcd for C9H14O 138.1045, found
138.1045.
(R)-1-Oxa-6-(2-propenyl)-2-sila-2,2,5-trimethylcyclohex-4-ene (18).
IR (NaCl): 2974 (m), 2924 (m), 2836 (w), 1464 (w), 1275 (s), 1099
1
(s), 1055 (s) cm-1. H NMR (400 MHz, CDCl3): δ 5.72-5.70 (m,
1H, HCdCCH3), 4.92 (dd, J ) 1.2, 1.2 Hz, 1H, HHCdCCH3), 4.85
(t, J ) 1.2 Hz, 1H, HHCdCCH3), 4.62 (s (br), 1H, OCH), 1.66 (t, J )
0.8 Hz, 3H, HCdCCH3), 1.55 (dd, J ) 1.2, 1.2 Hz, 3H, CH2dCCH3),
1.35-1.14 (m, 2H, SiCH2CH), 0.19 (s, 3H, SiCH3), 0.12 (s, 3H, SiCH3).
13C NMR (100 MHz, CDCl3): δ 146.5, 136.0, 121.1, 113.8, 82.1, 22.4,
17.2, 13.0, 0.8, 0.0. HRMS (EI+): calcd for C10H18OSi 182.1127, found
(R)-2-Methyl-1-tert-butyldimethylsiloxy-2-cyclohexene (6b). IR
(NaCl): 2929 (w), 2857 (s), 1603 (w), 1462 (m), 1375 (m), 1250 (s),
1073 (m), 1038 (s), 1019 (s), 1004 (s) cm-1 1H NMR (300 MHz,
.
(25) Gao, Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.; Masamune, H.;
Sharpless, K. B. J. Am. Chem. Soc. 1987, 109, 5767-5780 and references
therein.
CDCl3): δ 5.48 (s, 1H, CH2CHdCCH3), 4.03 (s, 1H, CHOSi), 2.05-
1.80 (m, 2H, CH2CHdCCH3), 1.78-1.59 (m, 2H, CH2CH2CHCdC),

8258 J. Am. Chem. Soc., Vol. 121, No. 36, 1999
Zhu et al.
The reaction was then allowed to chill to 0 °C and quenched slowly
by the addition of 50 mL of a 1.0 M solution of HCl. The resulting
aqueous layer was separated from the Et2O layer and washed three
times with excess Et2O (50 mL). The resulting organic layers were
then dried over MgSO4; volatile solvents were removed in vacuo to
afford the unpurified residue as a white solid that was then recrystallized
from CH2Cl2/hexanes to afford (R)-3,3′-bis(2,4,6-triisopropylphenyl)-
2,2′-dimethoxy-1,1′-dinaphthyl as a white solid (4.7 g, 77% yield). 1H
NMR (500 MHz, CDCl3): δ 7.82 (d, J ) 8.5 Hz, 2H, ArH), 7.71 (s,
2H, ArH), 7.39 (t, J ) 6.0 Hz, 2H, ArH), 7.35-7.31 (m, 4H, ArH),
7.07 (d, J ) 9.0 Hz, 4H, ArH), 3.04 (s, 6H, OCH3), 2.99-2.93 (m,
2H, CH(CH3)2), 2.88-2.85 (m, 2H, CH(CH3)2), 2.82-2.76 (m, 2H,
CH(CH3)2), 1.54 (s, 12H, CH(CH3)2), 1.29 (d, J ) 7.0 Hz, 6H, CH-
(CH3)2), 1.13 (d, J ) 8.0 Hz, 6H, CH(CH3)2), 1.09 (d, J ) 6.5 Hz, 6H,
CH(CH3)2), 1.04 (d, J ) 6.0 Hz, 6H, CH(CH3)2). 13C NMR (125 MHz,
CDCl3): δ 155.4, 148.4, 147.3, 147.0, 134.4, 134.2, 133.5, 131.4, 131.2,
130.5, 128.2, 126.2, 126.1, 125.0, 124.8, 120.9, 60.1, 34.6, 31.3, 31.2,
25.8, 25.6, 24.5, 24.4, 23.7, 23.7. HRMS (FAB) calcd for C52H62O2
718.4750, found (M+) 718.4750. Anal. Calcd for C52H62O2: C, 86.86;
H, 8.69. Found: C, 86.62; H, 8.77.
Scheme 5
182.1129. Anal. Calcd for C10H18OSi: C, 65.87; H, 9.95. Found: C,
65.80; H, 10.00.
Determination of the Stereochemical Identity of Catalytic De-
symmetrization Products. As illustrated in Scheme 5, Ti-catalyzed
kinetic resolution of allylic alcohol 27, followed by the installment of
the requisite allylsilyl chloride, led to the formation of optically enriched
(R)-28. Subsequent catalytic RCM with 2 mol % (Mo(N-2,6-i-
Pr2C6H3)(CHCMe2Ph)(OCCH3(CF3)2)2)24 resulted in the formation of
an authentic sample of (R)-26. This material was compared by chiral
GLC (BETADEX chiral column) with a sample of optically pure (R)-
26, obtained from the site-selective Rh-catalyzed hydrogenation of (R)-
18 (derived from Mo-catalyzed desymmetrization of 17).
rac- and (R)-3,3′-Bis(2,4,6-triisopropylphenyl)-2,2′-dihydroxy-
1,1′-dinaphthyl (23). A solution of 3,3′-bis(2,4,6-triisopropylphenyl)-
2,2′-dimethoxy-1,1′-dinaphthyl (4.0 g, 5.60 mmol) in 150 mL of CH2Cl2
was charged with 39.0 mL of a 1.0 M BBr3 solution in CH2Cl2 (38.9
mmol) slowly at 0 °C. The resulting mixture was allowed to warm to
22 °C and stirred for 12 h. The mixture was then cooled to 0 °C, and
the reaction was quenched by the slow addition of 50 mL water.
Aqueous extraction with CH2Cl2 (3 × 50 mL), followed by drying of
the organic layers over MgSO4 and removal of the solvents in vacuo
to afford an off-white solid, which was washed with hexanes, filtered,
and dried in vacuo to afford 3.76 g of a white powder (5.44 mmol,
97% yield). Crystals of (R)-3,3′-bis(2,4,6-triisopropylphenyl)-2,2′-
dihydroxy-1,1′-dinaphthyl (23) were obtained through slow evaporation
2-iso-Propenyl-3-methyl-5,6-dihydro-2H-pyran (20). 1H NMR
(400 MHz, CDCl3): δ 5.67 (s (br), 1H, CdCHCH2), 4.99 (t, J ) 1.2
Hz, 1H, CdCHH), 4.96 (s, 1H, CdCHH), 4.36 (s, 1H, CCHO), 3.90
(ddd, J ) 10.8, 4.8, 3.2 Hz, 1H, CH2CHHO), 3.58 (ddd, J ) 12.8, 8.8,
4.0 Hz, 1H, CH2CHHO), 2.26-2.17 (m, 1H, CHCHHCH2), 1.97-1.92
(m, 1H, CHCHHCH2), 1.67 (s (br), 3H, CH3CdCH2), 1.51 (d, J ) 1.2
Hz, 3H, CH3CdCH). 13C NMR (100 MHz, CDCl3): δ 144.5, 134.3,
122.0, 116.1, 82.6, 63.0, 26.2, 20.2, 18.1. HRMS (EI+): calcd for
C9H14O 138.1045, found 138.1045.
(R)-3,3′-Dibromo-2,2′-dimethoxy-1,1′-dinaphthyl (22). A solution
of n-BuLi (28 mL, 2.5 M in hexanes, 70 mmol) and tetramethyleth-
ylenediamine (TMEDA; 7.80 g, 67.0 mmol) was added to Et2O (500
mL) and allowed to stir for 15 min. To this solution was added solid
(R)-2,2′-dimethoxy-1,1′-dinaphthyl (10.0 g, 31.8 mmol). After 4 h, the
brown dilithium salt precipitateed from solution. The reaction mixture
was then cooled to -35 °C, and Br2 (8.0 mL, 65.3 mmol) was added
over a period of 0.5 h. The resulting white suspension was allowed to
warm to 22 °C and stirred for 2 h. At this point, the mixture was cooled
to 0 °C, and 50 mL of water was added. Aqueous extraction with Et2O
(3 × 50 mL) was followed by drying of the organic layers over
anhydrous MgSO4 and removal of the volatiles in vacuo. At this point,
(R)-3,3′-dibromo-2,2′-dimethoxy-1,1′-dinaphthyl (22) precipitated from
1
of solvent from a CH2Cl2 solution. H NMR (500 MHz, CDCl3): δ
7.85 (d, J ) 8.0 Hz, 2H, ArH), 7.75 (s, 2H, ArH), 7.36 (t, J ) 8.0 Hz,
2H, ArH), 7.32-7.26 (m, 4H, ArH), 7.12 (s, 2H, ArH), 7.10 (s, 2H,
ArH), 4.90 (s, 2H, OH), 2.95-2.93 (m, 2H, CH(CH3)2), 2.85-2.81
(m, 2H, CH(CH3)2), 2.69-2.65 (m, 2H, CH(CH3)2), 1.29 (d, J ) 7.0
Hz, 12H, CH(CH3)2), 1.18 (d, J ) 6.5 Hz, 6H, CH(CH3)2), 1.10-1.06
(m, 12H, CH(CH3)2), 1.01 (d, J ) 6.5 Hz, 6H, CH(CH3)2). 13C NMR
(125 MHz, CDCl3): δ 150.9, 149.4, 148.1, 148.0, 133.7, 131.0, 130.7,
129.4, 129.3, 128.5, 126.9, 124.8, 124.1, 121.5, 121.5, 113.4, 34.7,
31.2, 31.2, 24.6, 24.6, 24.4, 24.3, 24.2, 24.0. HRMS (FAB): calcd for
C50H58O2 690.4437, found (M+) 690.4435. Anal. Calcd for C50H58O2:
C, 86.91; H, 8.46. Found: C, 87.05; H, 8.72. [R]589 ) 88.0 (c ) 3.0,
THF).
(R)-(+)-Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(3,3′-bis(2,4,6-triisopro-
pylphenyl)-2,2′-dihydroxy-1,1′-dinaphthyl)(Py) (25). Complex (R)-
(+)-Mo(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(3,3′-bis(2,4,6-triisopropylphenyl)-
2,2′-dihydroxy-1,1′-dinaphthyl)(THF) (2a) (0.5 g, 0.4 mmol) was
dissolved in toluene (5 mL), and 0.5 mL pyridine (6.1 mmol) was added
to this solution. The mixture was allowed to stir at 22 °C for 1 h. At
this point, solvent was removed in vacuo, and the resulting yellow solid
(25) was recrystallized from Et2O. The single crystal was formed after
2 days at -30 °C. 1H NMR (500 MHz, C6D6): δ 14.37 (s,
anti-CHCMe2Ph), 14.29 (s, anti-CHCMe2Ph), 13.11 (s, 90% of 1H,
syn-CHCMe2Ph), 8.53 (d, J ) 5.0 Hz, 90% of 1H, syn-ArH), 8.09 (d,
J ) 5.0 Hz, 10% of 1H, anti-ArH), 7.88-7.87 (m, 2H, ArH), 7.78-
7.65 (m, 2H, ArH), 7.55, (s, 1H, ArH), 7.53-7.47 (m, 1H, ArH), 7.39
(d, J ) 8.5 Hz, 2H, ArH), 7.32-7.31 (m, 1H, ArH), 7.23 (d, J ) 1.5
Hz, 1H, ArH), 7.15-6.90 (m, 8H, ArH), 6.82-6.72 (m, 4H, ArH),
6.66 (t, J ) 6.0 Hz, 1H, ArH), 6.54 (t, J ) 7.5 Hz, 1H, ArH), 6.04 (t,
J ) 7.0 Hz, 90% of 2H, syn-ArH), 5.91 (t, J ) 7.0 Hz, 90% of 2H,
anti-ArH), 3.98-3.94 (m, 90% of 1H, anti-Me2CH), 4.12-4.07 (m,
10% of 1H, anti-Me2CH), 3.78-3.72 (m, 10% of 1H, anti-Me2CH),
3.61-3.57 (m, 10% of 1H, anti-Me2CH), 3.48-3.43 (m, 90% of 1H,
anti-Me2CH), 3.28-3.18 (m, 2H, Me2CH), 3.12-3.07 (m, 90% of 1H,
syn-Me2CH), 2.98-2.91 (m, 90% of 1H, syn-Me2CH), 2.88-2.82 (m,
10% of 1H, anti-Me2CH), 2.80-2.76 (m, 10% of 1H, anti-Me2CH),
1
the ether solution as a white solid (9.90 g, 66% yield). The H NMR
spectrum proved to be identical to that reported in the literature.10a [R]589
) +71.4 (c ) 1.4, THF).
(2,4,6-Triisopropylphenyl)magnesium Bromide. A three-neck
round-bottom flask containing Mg (3.00 g, 125 mmol) was equipped
with a condenser and an addition funnel. A 10.0 mL portion of a 1.4
M solution of 2,4,6-triisopropylphenyl bromide (20.0 g in 50 mL of
Et2O, 70.6 mmol) was added to the flask through the addition funnel.
After 5 min, 0.20 mL (0.002 mmol) of 1,2-dibromoethane was added
to the mixture. Once the solution began to reflux, the remaining 2,4,6-
triisopropylphenyl bromide solution was slowly added over 1 h. After
the addition was complete, the reaction was allowed to reflux for 12 h.
The resulting Grignard reagent was then titrated and stored in a drybox.
rac- and (R)-3,3′-Bis(2,4,6-triisopropylphenyl)-2,2′-dimethoxy-
1,1′-dinaphthyl. (R)-3,3′-Dibromo-2,2′-dimethoxy-1,1′-dinaphthyl (4.0
g, 8.5 mmol) and Ni(PPh3)2Cl2 (0.60 g, 11 mol %, 0.90 mmol) were
suspended in 100 mL of Et2O. To this suspension was added (2,4,6-
triisopropylphenyl)magnesium bromide (0.8 M, 31.7 mL, 25.4 mmol)
slowly at 22 °C. The mixture was allowed to stir at 22 °C for 10 min;
at this point, the resulting dark green solution was refluxed for 24 h.

Chiral Mo-Binol Complexes
J. Am. Chem. Soc., Vol. 121, No. 36, 1999 8259
2.70-2.65 (m, 90% of 1H, syn-Me2CH), 2.59-2.54 (m, 90% of 1H,
syn-Me2CH), 2.50-2.45 (m, 10% of 1H, anti-Me2CH), 1.76 (s, 3H,
CHC(CH3)2Ph), 1.45-0.63 (m, 45H, CH(CH3)2 and CHC(CH3)2Ph),
0.45 (d, J ) 7.0 Hz, 6H, (CH3)2CH). 13C NMR (125 MHz, C6D6): δ
309.4, 167.3, 166.1, 165.7, 161.9, 161.3, 160.8, 154.6, 153.5, 152.1,
151.7, 151.6, 150.7, 149.9, 148.8, 148.5, 148.4, 148.2, 148.0, 147.6,
147.6, 147.5, 147.5, 147.4, 147.3, 147.2, 147.1, 147.0, 146.2, 143.7,
141.0, 138.5, 138.4, 138.2, 137.3, 137.2, 137.0, 136.9, 136.9, 136.8,
136.1, 135.9, 135.5, 133.6, 133.3, 133.0, 132.7, 132.0, 131.3, 131.2,
130.9, 130.4, 130.3, 130.1, 130.0, 129.7, 129.6, 129.0, 128.9, 128.8,
128.7, 128.0, 127.7, 127.5, 127.2, 127.1, 127.0, 126.8, 126.7, 126.5,
126.4, 126.2, 125.9, 125.9, 125.8, 125.7, 124.2, 124.1, 123.8, 123.7,
123.6, 123.4, 123.3, 123.2, 123.2, 123.1, 122.9, 122.8, 121.6, 121.4,
121.3, 121.3, 121.1, 121.1, 120.9, 120.8, 120.7, 120.6, 120.6, 120.5,
66.3, 54.3, 53.6, 52.8, 35.4, 35.2, 35.0, 34.8, 34.6, 32.8, 32.3, 32.2,
32.1, 31.8, 31.7, 31.4, 31.3, 31.2, 31.1, 31.0, 30.8, 30.6, 29.9, 29.6,
29.5, 29.2, 28.6, 28.2, 27.8, 27.5, 27.4, 27.0, 26.6, 26.5, 26.4, 26.2,
25.9, 25.8, 25.7, 25.6, 25.6, 25.4, 25.4, 25.3, 25.1, 25.1, 25.0, 24.9,
24.9, 24.8, 24.7, 24.7, 24.7. Anal. Calcd for C77H90N2O2Mo: C, 78.94;
H, 7.74; N, 2.39. Found: C, 79.06; H, 7.79; N, 2.29.
Acknowledgment. This work was supported by the NIH
(GM-47480 to A.H.H.), the NSF (CHE-9905806 to A.H.H. and
CHE-9700736 to R.R.S.), the American Chemical Society
(graduate fellowship in organic chemistry to D.S.L., sponsored
by Boehringer-Ingelheim), and the Natural Sciences and Engi-
neering Research Council of Canada (predoctoral fellowship
to J.Y.J.). We thank J. B. Alexander for experimental assistance
and helpful discussions.
Supporting Information Available: Spectral and analytical
data for recovered starting materials and reaction products.
Tables of crystallographic experimental details, atomic coordi-
nates and isotropic displacement parameters, interatomic bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates for Mo complex 25. This material is
available free of charge via the Internet at http://pubs.acs.org.
JA991432G