Photochemical isomerization of Me2Si-bridged zirconocene complexes. Application to stereoselective syntheses of ansa-zirconocene binaphtholate stereoisomers

Article abstract of DOI:10.1021/om961089d

Upon irradiation in toluene solution, meso-racemate mixtures of Me₂Si(2-Me-4-tBu-C₅H₂)₂-ZrCl ₂ or Me₂Si(2-Me-4-phenyl-C₅H₂)₂ZrCl ₂ react with 1 equiv of the dilithium salt of racemic binaphthol quantitatively to the racemic binaphtholate complex. Analogous reactions with 1 equiv of the R(+) enantiomer of dilithium binaphtholate give a near-quantitative yield of the enantiomerically pure ansa-zirconocene binaphtholate complex. The structures of the racemic binaphtholate complex, Me₂Si(2-Me-4-tBu-C₅H₂) ₂Zr(binaphtholate), and of a monodentate binaphtholate complex with a meso configurated zirconocene moiety, Me₂Si(3-tBu-C₅H₃)₂Zr(binaphtholate) chloride, were crystallographically determined.

Full text of DOI:10.1021/om961089d

1724
Organometallics 1997, 16, 1724-1728
P h otoch em ica l Isom er iza tion of Me2Si-Br id ged
Zir con ocen e Com p lexes. Ap p lica tion to Ster eoselective
Syn th eses of a n sa -Zir con ocen e Bin a p h th ola te
Ster eoisom er s†,1
Katrin Schmidt, Annette Reinmuth, Ursula Rief, J osef Diebold, and
Hans H. Brintzinger*
Fakulta¨t fu¨r Chemie, Universita¨t Konstanz, D-78434 Konstanz, Germany
Received December 23, 1996X
Upon irradiation in toluene solution, meso-racemate mixtures of Me2Si(2-Me-4-tBu-C5H2)2-
ZrCl2 or Me2Si(2-Me-4-phenyl-C5H2)2ZrCl2 react with 1 equiv of the dilithium salt of racemic
binaphthol quantitatively to the racemic binaphtholate complex. Analogous reactions with
1 equiv of the R(+) enantiomer of dilithium binaphtholate give a near-quantitative yield of
the enantiomerically pure ansa-zirconocene binaphtholate complex. The structures of the
racemic binaphtholate complex, Me2Si(2-Me-4-tBu-C5H2)2Zr(binaphtholate), and of a mono-
dentate binaphtholate complex with a meso configurated zirconocene moiety, Me2Si(3-tBu-
C5H3)2Zr(binaphtholate) chloride, were crystallographically determined.
In tr od u ction
In an earlier study in our group, ethylenebis(tetra-
hydroindenyl)titanium dichloride had been found to
undergo an efficient photoinduced meso-to-rac isomer-
ization.7 By a combined irradiation/evaporation tech-
nique, meso-racemate mixtures of this complex were
almost completely converted to the pure racemate due
to the much lower solubility of the latter.8 This tech-
nique is not applicable to ansa-metallocene complexes
in general, as solubilities for their meso and racemic
isomers are usually not sufficiently different to drive
their photoisomerization anywhere close to completion.9
In a study on photoisomerizations of ethylene-bridged
bis(cyclopentadienyl)titanium complexes in THF solu-
tions, Collins and co-workers observed that the photo-
stationary rac/meso ratios depend on the substitution
patterns of the cyclopentadienyl rings. Unspectacular
rac/meso ratios of e1 were obtained for complexes
containing only substituents in the â-position; complexes
carrying substituents in the R as well as in the â-posi-
tion, however, yielded rac/meso ratios up to 15:1.10
We now report on a high-yield synthesis of racemic
Me2Si-bridged zirconocene binaphtholate complexes and
their isolated enantiomers, which is based on a com-
bined photoisomerization and complex formation with
1,1′-bi-2-naphthol.
Racemic ansa-metallocene complexes continue to be
of interest as catalysts for the stereospecific polymeri-
zation of R-olefins;2 their separate enantiomers are
presently gaining interest also as precatalysts for enan-
tioselective hydrogenation3 and C-C bond formation
reactions.4 A problem in the synthesis of these com-
plexes is the formation of meso and racemic isomers in
the reaction of a prochiral ligand unit with the ap-
propriate metal halide. While methods have been
devised to minimize the formation of unwanted meso
isomers5 or to eliminate the possibility of their formation
altogether,6 the overall yields of the reaction sequences
required for this purpose are generally relatively low.
† Dedicated to Professor Walter Siebert on the occasion of his 60th
birthday.
X Abstract published in Advance ACS Abstracts, March 15, 1997.
(1) (a) Ansa Metallocene Derivatives. Part 38. For part 37, see:
Dorer, B.; Prosenc, M. H.; Rief, U.; Brintzinger, H. H. Collect. Czech.
Chem. Commun. 1997 in press. (b) Parts of this work have been
published in German patents No. 195 25 178.4-O.Z. 0050/45999 and
No. 195 25 184.9-O.Z. 0050/46000.
(2) Reviews: Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger,
B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.
Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem. 1994, 479, 1.
Kaminsky, W. Catal. Today 1994, 20, 257. Aulbach, M.; Ku¨ber, F.
Chem. Unserer Zeit 1994, 28, 197.
(3) (a) Waymouth, R.; Pino, P. J . Am. Chem. Soc. 1990, 112, 4911.
(b) Willoughby, C. A.; Buchwald, S. L. J . Am. Chem. Soc. 1992, 114,
7562. Willoughby, C. A.; Buchwald, S. L. J . Am. Chem. Soc. 1994, 116,
11703. Verdaguer, X.; Lange, U. E. W.; Reding, M. T.; Buchwald, S. L.
J . Am. Chem. Soc. 1996, 8, 6784. (c) Conticello, V. P.; Brard, L.;
Giardello, M. A.; Tsuji, Y.; Sabat, M.; Stern, C. L.; Marks, T. J . J . Am.
Chem. Soc. 1992, 114, 2761.
(4) Review: Hoveyda, A. H.; Morken, J . P. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1263. (a) Collins, S.; Koene, B. E.; Ramachandran, R.;
Taylor, N. J . Organometallics 1991, 10, 2092. Hong, Y.; Kuntz, B. A.;
Collins, S. Organometallics 1993, 12, 964. J aquith, J . B.; Guan, J .;
Wang, S.; Collins, S. Organometallics 1995, 14, 1079. (b) Hollis, T. K.;
Robinson, N. P.; Bosnich, B. Organometallics 1992, 11, 2745.
(5) (a) Diamond, G. M.; Rodewald, S.; J ordan, R. F. Organometallics
1995, 14, 5. Diamond, G. M.; J ordan, R. F.; Petersen, J . L. Organo-
metallics 1996, 15, 4045. (b) Erickson, M. S.; Fronczek, F. R.;
McLaughlin, M. L. J . Organomet. Chem. 1991, 415, 75. (c) Chacon, S.
T.; Coughlin, E. B.; Henling, L. M.; Bercaw, J . E. J . Organomet. Chem.
1995, 497, 171. (d) Chen, Y. X.; Rausch, M. D.; Chien, J . C. W.
Organometallics 1994, 13, 748.
(6) (a) Huttenloch, M. E.; Diebold, J .; Rief, U.; Brintzinger, H. H.;
Gilbert, A. M.; Katz, T. J . Organometallics 1992, 11, 3600. Mansel, S.;
Rief, U.; Prosenc, M. H.; Kirsten, R.; Brintzinger, H. H. J . Organomet.
Chem. 1996, 512, 225. (b) Burk, H.; Colletti, S. L.; Haltermann, R. L.
Organometallics 1991, 10, 2998. Ramsey, T. M.; Haltermann, R. L.
Organometallics 1993, 12, 2879. (c) Ellis, W. W.; Hollis, T. K.;
Odenkirk, W.; Whelan, J .; Ostrander, R.; Rheingold, A. L.; Bosnich,
B. Organometallics 1993, 12, 4391. (d) Grossmann, R. B.; Tsai, J .-C.;
Davis, W. M.; Gutierrez, A.; Buchwald, S. L. Organometallics 1994,
13, 3892.
(7) In contrast to ethanediyl-bridged complexes, tetramethyl-
ethanediyl-bridged titanocene and zirconocene complexes are photo-
stable. (a) Burger, P. Dissertation, University of Konstanz, 1991. (b)
Reference 5b.
(8) Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J .
Organomet. Chem. 1982, 232, 233.
(9) Wiesenfeld, H.; Reinmuth, A.; Barsties, E.; Evertz, K.; Brint-
zinger, H. H. J . Organomet. Chem. 1989, 369, 359.
(10) Collins, S.; Hong, Y.; Taylor, N. J . Organometallics 1990, 9,
2695. Collins, S.; Hong, Y.; Ramachandran, R.; Taylor, N. J . Organo-
metallics 1991, 10, 2349.
S0276-7333(96)01089-8 CCC: $14.00 © 1997 American Chemical Society

ansa-Metallocene Derivatives
Ta ble 1. Ir r a d ia tion of th e Com p lexes
Organometallics, Vol. 16, No. 8, 1997 1725
Sch em e 1
Me2Si(1-Cp -3-tBu )2Zr Cl2 (1),
Me2Si(1-Cp -2-Me-4-tBu )2Zr Cl2 (2),
Me2Si(1-Cp -2-Me-4-iP r )2Zr Cl2 (3),
Me2Si(1-Cp -2-Me-4-P h )2Zr Cl2 (4)
time/min
1a
2a
2b
3a
3b
4a
0
15
75:25b
100:0
72:28
100:0
100:0
100:0
64:36
100:0
100:0
0:100
20
45
105
465
1905
61:39
56:44
41:59
56:44
56:44
56:44
90:10
72:82
43:57
42:58
58:42
56:44
96:4
90:10
70:30
56:44
a
b
Rac/meso ratios in benzene-d6 at room temperature. Rac/
meso ratios, in toluene-d8 at -40 °C.
Resu lts a n d Discu ssion
Irradiation of benzene-d6 or toluene-d8 solutions
containing an arbitrary mixture of the racemic and meso
isomers of the Me2Si-bridged zirconocene dichlorides
Me2Si(3-tBu-C5H3)2ZrCl2 (1),9 Me2Si(2-Me-4-tBu-C5H2)2-
ZrCl2 (2),9 Me2Si(2-Me-4-iPr-C5H2)2ZrCl2 (3),9 or Me2-
Si(2-Me-4-Ph-C5H2)2ZrCl2 (4)11 with a 125 W high-
Sch em e 2
pressure Hg lamp causes
a rather rapid photo-
isomerization. In the course of 1-2 h, one obtains in
each case photostationary reaction mixtures with meso/
racemate ratios close to 1 (Table 1).
Even the presence of R-methyl substituents in the
Me2Si-linked C5 rings, which had been found to lead to
meso/racemate ratios of 1:6 for Me2Si(2-Me-4-iPr-C5H2)2-
ZrCl2 and 1:2 for Me2Si(2-Me-4-tBu-C5H2)2ZrCl29 in the
thermal synthesis of these complexes, does not affect
the photostationary isomer ratios in any comparable
manner. In this regard, the Me2Si-bridged zirconocene
complexes studied here yield results distinctly different
from the C2H4-bridged titanocene complexes studied by
Collins and co-workers.10
In accord with previous studies,12 we assume that this
photoisomerization occurs by way of a homolytic pho-
todissociation of one of the C5 ring ligands, rotation of
the resulting cyclopentadienyl radical about the Si-C(1)
bond, and its reattachment to the Zr(III) center (Scheme
1). Apparently, the extinction coefficients of the two
isomers, the quantum yields for their conversion to the
diradical intermediates and the reaction rates along the
alternative recombination paths are all sufficiently
similar to generate practically identical stationary
concentrations of the two isomers under the conditions
employed.
In an attempt to trap the racemic isomers from each
of these photostationary reaction systems by a selective
reaction with a binaphthol ligand, we have tried to
conduct analogous photoisomerization reactions in tolu-
ene solutions containing the dilithium salt of racemic
1,1′-bi-2-naphthol (Scheme 2).13
of 1 carry only a single substituent, proved fruitless:
Addition of dilithium binaphtholate to this solution
causes the generation of exactly that fraction of the
binaphtholate chelate rac-Me2Si(3-tBu-C5H3)2Zr-
(C20H12O2) (rac-1-BIN) to which rac-1-Cl2 was present
in the initial isomer mixture. The meso isomer, on the
other hand, is quantitatively converted to an asym-
metric binaphtholate complex Me2Si(3-tBu-C5H3)2Zr-
(C20H12O2Li)Cl (meso-1-Cl-BIN-Li). NMR data of this
complex (see Experimental Section) indicate monoden-
tate bonding of the binaphtholate ligand.5b,14 A complex
meso-1-Cl-BINH, derived from meso-1-Cl-BIN-Li by
hydrolysis, was isolated by crystallization. Its molecular
structure, represented in Figure 1 and Table 2, reveals
a monodentate coordination of the binaphtholate ligand
at the unobstructed coordination site of the meso ansa-
zirconocene. The chloride ligand shielded by the two
tert-butyl groups is apparently retained due to its steric
inaccessibility. The torsion angle between the two
naphthyl ring planes (75.8°) is relatively large compared
to bidentate binaphtholate complexes. The Zr-O dis-
tance of 1.98 Å is somewhat shorter, the Zr-O-C angle
(154°) somewhat larger, than the respective parameters
A first experiment of this kind with a meso-racemate
mixture of Me2Si(3-tBu-C5H3)2ZrCl2, where the C5 rings
(11) Burger, P.; Hortmann, K.; Diebold, J .; Brintzinger, H. H. J .
Organomet. Chem. 1991, 417, 9.
(12) Previous mechanistic studies: (a) Harrigan, R. W.; Hammond,
G. S.; Gray, H. B. J . Organomet. Chem. 1974, 81, 79. (b) Tsai, Z. T.;
Brubaker, C. H. J . Organomet. Chem. 1979, 166, 199. (c) Rheingold,
A. L.; Robinson, N. P.; Whelan, J .; Bosnich, B. Organometallics 1992,
11, 1869.
(13) In similar experiments with en(3-t-Bu-C5H3)TiCl2 or en(thind)-
TiCl2 and racemic or enantiomerically pure 1,1′-bi-2-naphthol in THF
solution, Kuntz and Collins obtained the respective binaphtholate
complexes in low yields only. Kuntz, R. A. Ph.D. Thesis, University of
Waterloo, 1991.
(14) A related complex Me4C2(3-tBu-C5H3)2TiCl-BINH has been
described by McLaughlin et al.5b

1726 Organometallics, Vol. 16, No. 8, 1997
Schmidt et al.
F igu r e 2. Molecular structure of rac-2-BIN (30% prob-
F igu r e 1. Molecular structure of meso-1-Cl-BINH (30%
ability thermal ellipsoids).
probability thermal ellipsoids).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for
Me2Si(2-Me-4-tBu -C5H2)2Zr -Bin a p h th ola te (2-BIN)
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Me2Si(3-tBu -C5H3)2Zr Cl-Bin a p h th ola te
(1-Cl-BINH)
Zr(1)-O(1)
Zr(1)-C(1)
Zr(1)-C(3)
Zr(1)-C(5)
Zr(1)-C(7)
Zr(1)-C(9)
Zr(1)-Cp(1)a
Si(1)-C(1)
Si(1)-C(31)
2.010 (2)
2.502 (3)
2.603 (3)
2.544 (3)
2.511 (3)
2.681 (4)
2.264
Zr(1)-O(2)
Zr(1)-C(2)
Zr(1)-C(4)
Zr(1)-C(6)
Zr(1)-C(8)
Zr(1)-C(10)
Zr-Cp(2)a
Si(1)-C(6)
Si(1)-C(32)
2.019 (2)
2.514 (3)
2.668 (3)
2.489 (4)
2.606 (3)
2.540 (4)
2.265
Zr(1)-O(1)
Zr(1)-C(1)
Zr(1)-C(3)
Zr(1)-C(5)
Zr(1)-C(7)
Zr(1)-C(9)
Zr(1)-Cp(1)a
Si(1)-C(1)
Si(1)-C(31)
1.967 (2)
2.481 (3)
2.668 (4)
2.452 (4)
2.531 (3)
2.592 (4)
2.248
Zr(1)-Cl(1)
Zr(1)-C(2)
Zr(1)-C(4)
Zr(1)-C(6)
Zr(1)-C(8)
Zr(1)-C(10)
Zr(1)-Cp(2)a
Si(1)-C(6)
Si(1)-C(12)
2.446 (2)
2.556 (4)
2.583 (4)
2.486 (4)
2.640 (4)
2.476 (4)
2.243
1.872 (4)
1.857 (3)
1.873 (3)
1.852 (4)
1.876 (3)
1.845 (4)
1.859 (3)
1.852 (4)
C(1)-Si(1)-C(6)
95.8
64.9
Zr(1)-O(1)-C(12)
Zr(1)-O(2)-C(22)
120.8 (2)
120.5 (2)
C(1)-Si(1)-C(6)
95.0 (1)
75.8
O(1)-Zr(1)-Cl(1)
Zr(1)-O(1)-C(12)
97.8 (1)
154.6 (2)
Naph(1)-Naph(2)b
Naph(1)-Naph(2)b
a
a
Cp(1) and Cp(2) are the centroids of the C(1)-C(5) and C(6)-
C(10) cyclopentadienyl rings. b Naph(1) and Naph(2) are the planes
of C(11)-C(20) and C(21)-C(30) binaphtolate rings.
Cp(1) and Cp(2) are the centroids of the C(1)-C(5) and C(6)-
C(10) cyclopentadienyl rings. b Naph(1) and Naph(2) are the planes
of C(11)-C(20) and C(21)-C(30) binaphtholate rings.
in chlorine-free, bidentate binaphtholate complexes.
meso-1-Cl-BINH as well as its unprotonated precursor
meso-1-Cl-BIN-Li are totally insensitive to irradiation.
Apparently, the lowest-lying ligand-to-metal charge-
transfer absorption, which appears to be antibonding
with respect to the Zr-C5 ring bond in the dichloride
complexes 1-Cl2, 2-Cl2, 3-Cl2, and 4-Cl2, is replaced by
an even lower-lying binaphtholate-to-metal charge trans-
fer which is expected to leave the Zr-C5 ring bond
unaffected.
These observations suggest that a successful sequence
of photoisomerization and complex formation reactions
requires that the meso isomer is protected from forma-
tion of a monodentate binaphtholate complex, e.g., by
steric restraints. The Me2Si-bridged zirconocene com-
plexes 2-Cl2 and 4-Cl2, which carry an R-methyl sub-
stituent at each C5 ring ligand, do indeed conform to
this expectation. Upon irradiation of a mixture of meso
and racemic isomers of one of these complexes (or even
of the pure meso isomer) in the presence of 1 equiv of
dilithium binaphtholate, we observe the formation of the
corresponding racemic zirconocene binaphtholate com-
plexes, rac-2-BIN and rac-4-BIN. Although the reaction
mixtures are not homogeneous, due to the low solubility
of Li2BIN in toluene, the zirconocene binaphtholate
complexes can be isolated, after removal of the LiCl
precipitate, in near-quantitative yields by crystallization
from hexane (rac-2-BIN) or diethyl ether (rac-4-BIN)
solutions.
The molecular structure of complex rac-2-BIN (Figure
2 and Table 3) documents the tight fit of the binaph-
tholate ligand into the helical groove of the chiral ansa-
zirconocene framework. The torsion angle between the
naphthyl ring planes (64.5°) and the Zr-C-O angles
(120-121°) are comparable to other bidentate binaph-
tholate complexes.8
Analogous procedures, in which racemic 1,1′-bi-2-
naphthol is replaced by its R enantiomer, give enantio-
merically pure (S)-2-(R)-binaphtholate and (S)-4-(R)-
binaphtholate. Optical rotation values of these
binaphtholates indicate a substantial enantiomeric
excess. Independent control experiments show that the
binaphtholate auxiliary is configurationally stable under
the conditions of the procedure employed.
The conversion of the racemic zirconocene binaph-
tholate complexes thus obtained, either to a dihalide or
to a dimethyl derivative, proved unexpectedly difficult.
Reacting Me2Si(2-Me-4-Ph-C5H2)2Zr-BIN (4-BIN) with
acids HX, with Lewis acidic metal halides such as BX3,
AlX3, or ZrX4 (X ) Cl, Br), and with methyl-transferring
nucleophiles such as CH3Li or CH3MgX produced vary-
ing amounts of the meso configurated products along
with the expected R and/or S compounds from the
racemic zirconocene binaphtholates (Table 4). Appar-
ently, the Zr-C5 ring bonding is sufficiently labile in
comparison to the Zr-O bonds to be cleaved at least to
some degree when the Zr-O bonds in these complexes
are attacked by nucleophilic or electrophilic reagents.

ansa-Metallocene Derivatives
Organometallics, Vol. 16, No. 8, 1997 1727
Ta ble 4. Ra cem a te Meso Ra tios for Rea ction
P r od u cts Obta in ed fr om r a c-4-BIN w ith Va r iou s
Nu cleop h iles or Electr op h iles
metric binaphtholate complex (1-Cl-BIN-Li), formed from the
meso isomer. Complex (1-Cl-BINH) was isolated after several
recrystallizations from diethyl ether, yielding 42 mg (9% based
on meso-1) of light yellow crystals, of which a crystal structure
was obtained. 1H NMR of 1-Cl-BINH (C6D6, 250 MHz, δ in
ppm): 0.1 (s, 3H, Si(CH3)2), 0.27 (s, 3H, Si(CH3)2,), 1.37 (s, 9H,
C(CH3)3), 1.47 (s, 9H, C(CH3)3), 4.49 (br s, 1H, OH), 4.41, 5.29,
5.56, 5.72 (each dd, 1H, R-C5H2H and â-C5H2H), 6.8-7.8 (m,
BBr3
BCl3
AlCl3
ZrCl4
9:1a
5:1b
4:1b
3:1b
HCl
MeLi
MgCl2
MeMgCl
3:1b
9:1c
3:1b
3:1c
4-Br2. 4-Cl2. c 4-Me2.
a
b
C
20H12O2). Complex 1-BIN was enriched in the mother liquor
but could not be isolated in pure form. 1H NMR of 1-BIN
(C6D6, 250 MHz, δ in ppm): 0.49 (s, 6H, Si(CH3)2), 0.74 (s, 18H,
C(CH3)3), 5.65 (dd, 2H, R-C5H2H), 5.80 (dd, 2H, R-C5H2H), 6.11
(dd, 2H, â-C5H2H), 6.8-7.8 (m, C20H12O2).
Racemic Me2Si(2-Me-4-tBu-C5H2)2Zr-BIN (2-BIN), on
the other hand, reacts with methyllithium to produce
only the racemic dimethyl complex 2-Me2 in a clean
reaction. We conclude, therefore, that the phenyl sub-
stituent in complex 4-BIN is responsible for the partial
isomerization to the unwanted meso complex, possibly
by stabilizing a negative charge of the Cp ring in the
transition state of the side reaction, which does not
occur with tert-butyl-substituted cyclopentadienyl rings.
The same observations were made with the enantio-
merically pure complexes (S)-2-(R)-BIN and (S)-4-(R)-
BIN. While methylation of (S)-4-(R)-BIN gave a mix-
ture of the 4-Me2 isomers, only (S)-2-Me2 is obtained
when (S)-2-(R)-BIN is reacted with methyllithium.
The enantiomeric purity of (S)-2-Me2 was determined
by reaction with D-(-)-acetylmandelic acid.15 Although
a clean reaction to the bisacetylmandelate complex was
not feasiblesprobably because of steric hindrance
between the tert-butyl groups and the acetylmandelate
ligandsswe were able to generate a monomethyl-
monoacetylmandelate species, which gave rise to well-
R ea ct ion of Com p lex
1 w it h Dilit h iu m 1,1′-Bi-2-
n a p h th ol u p on Ir r a d ia tion . A reaction was set up as
described above, and 1 mL of the well-mixed suspension was
transferred into an NMR tube, evaporated to dryness, and
suspended in benzene-d6. The tube was irradiated with the
high-pressure mercury lamp. The same two products, 1-BIN
and 1-Cl-BINLi, were formed in a ratio identical to the original
rac/meso ratio. This result documents that the irradiation
does not affect the product distribution in this case.
Me2Si(2-Me-4-tBu -C5H 2)2Zr -BIN (r a c-2-BIN). In
a
Schlenk tube, 248 mg (0.51 mmol) of complex 2 (rac/meso 1:1)
and 160 mg (0.51 mmol) dilithium 1,1′-bi-2-naphtholate were
suspended in 60 mL of toluene. The tube was stirred and
irradiated at 80 °C for 24 h. The reaction mixture was
evaporated to dryness and the resulting residue taken up in
toluene again, salts were removed by filtration, the solvent
was evaporated, and the residue recrystallized from 5 mL of
pentane to yield 316 mg (0.45 mmol, 88%) of complex rac-2-
BIN as a clean yellow powder. Crystals were obtained from
toluene or hexane. 1H NMR (C6D6, 600 MHz, δ in ppm):16 0.59
(s, 6H, Si(CH3)2), 0.76 (s, 18H, C(CH3)3), 2.11 (s, 6H, C5H2CH3),
5.59 (2H, d, J ) 2.17 Hz, R-C5HH), 5.96 (2H, d, J ) 1.99 Hz,
â-C5HH), 6.91 (2H, t, HC(17,27)), 7.09 (2H, t, HC(16,26)), 7.20
(2H, d, J ) 8.75 Hz, HC(13,23)), 7.27 (2H, d, J ) 8.59,
HC(18,28)), 7.73 (2H, d, J ) 7.99 Hz, HC(15,25)), 7.80 (2H, d,
J ) 8.75 Hz, HC(14,24)). 13C NMR (C6D6, 600 MHz, δ in
ppm): -1.85 (Si(CH3)2), 16.07 (C5H2CH3), 29.44 (C(CH3)3),
33.08 (C(CH3)3), 106.08 (C(1,6)), 108.96 (C(5,10)), 118.72
(C(11,21)), 119.06 (C(3,8)), 122.08 (C(13,23)), 122.77 (C(16,26)),
126.06 (C(17,27)), 126.29 (C(2,7)), 127.72 (C(18,28)),
127.84(C(15,25)), 129.43 (C(19,29)), 129.7 (C(14,24)), 136.33
(C(20,30)), 154.01 (C(4,9)), 160.14 (C(12,22)). Anal. Calcd for
1
separated H-NMR signals for the two possible diaster-
eomers in the case of racemic 2-BIN as starting material.
With (S)-2-Me2 derived from enantiomerically pure (S)-
2-(R)-BIN we did indeed detect only resonances of a
single diastereomer after reaction with acetylmandelic
acid.
These results show that photoassisted complex for-
mation with binaphtholate converts ansa-metallocene
complexes, which are susceptible to photoisomerization,7
to any desired chiral stereoisomer in practically quan-
titative yields.
C
42H46O2SiZr: C, 71.85; H, 6.60. Found: C, 71.68; H, 6.63.
In an analogous experiment with enantiomerically pure
Exp er im en ta l Section
R(+)-dilithium 1,1′-bi-2-naphtholate the reaction time had to
All reactions were carried out under Ar or N2 atmosphere
using standard Schlenk and glovebox techniques. NMR
spectra were recorded on Bruker WM 250 MHz, Bruker DRX
600 MHz, and J eol FX 90Q spectrometers with residual C6HD5
(7.15 ppm) and CHCl3 (7.24 ppm) as internal standards.
Ir r a d ia tion of Com p lexes 1-4. A sample of 5 mg of each
of these complexes was dissolved in 0.4 mL of benzene-d6 or
toluene-d8 in an NMR tube. The tube was sealed and placed
adjacent to the cooling jacket of a high-pressure mercury lamp
(125 W). For low-temperature reactions, the lamp and the
tube were placed into a cooling bath. The photoreaction was
monitored by 1H NMR; the rac/meso ratios were calculated
from the integrals of the appropriate Me2Si, tert-butyl, and
R-methyl signals. The results are summarized in Table 1.
Me2Si(3-tBu -C5H3)2Zr Cl-Bin aph th olate (1-Cl-BINH). To
a mixture of 488 mg (1.2 mmol) of complex 1 with a rac/meso
ratio of 1:1.3 and 410 mg (1.4 mmol) dilithium 1,1′-bi-2-
naphtholate was added 20 mL of CH2Cl2. This suspension was
stirred overnight at room temperature and filtered, and the
filtrate evaporated to dryness. According to its 1H-NMR
spectrum, the residue is a 1:1.3 mixture of the racemic complex
Me2Si(3-tBu-C5H3)2Zr-binaphtholate (1-BIN) and of an asym-
be extended to six days to obtain the enantiomerically pure
complex (S)-2-(R)-BIN in 87% yield. [R]D ) -780°; [R]436
-2620° (c ) 1 g/100 mL, toluene).
)
Me2Si(2-Me-4-tBu -C5H2)2Zr -Me2 (2-Me2). A 120 mg (0.171
mmol) sample of 2-BIN was dissolved in 20 mL of diethyl
ether, and 0.22 mL of a 1.6 M solution of methyllithium in
diethyl ether (0.342 mmol) was added via syringe. After 1 h,
during which Li2BIN precipitated and the yellow color of the
solution had disappeared, the solvent was evaporated and the
residue taken up in pentane. Li2BIN was removed by filtration
and the filtrate evaporated to dryness. The white residue
1
consistedsaccording to its H-NMR spectrumsonly of racemic
2-Me2. Enantiomerically pure (S)-2-(R)-BIN was converted to
(S)-2-Me2 following the same procedure. In both cases, 2-Me2
was not further purified before reaction with D-(-)-acetyl-
mandelic acid to avoid enrichment of one enantiomer. 1H
NMR (CDCl3, 250 MHz, δ in ppm): -0.26 (s, 6H, Zr(CH3)2),
0.56 (s, 6H, Si(CH3)2), 1.31 (s, 18H, C(CH3)3), 1.96 (s, 6H,
C5H2CH3), 5.28 (2H, d, J ) 2.35 Hz, C5HH), 6.48 (2H, d, J )
2.28 Hz,C5HH).
Rea ction of 2-Me2 w ith D-(-)-Acetylm a n d elic Acid . A
solution of complex rac-2-Me2 (10.7 mg, 0.024 mmol) in CDCl3
was treated in one portion with 1 equiv of D-(-)-acetylmandelic
acid (4.6 mg, 0.024 mmol) at room temperature. After gas
(15) Scha¨fer, A.; Eberhard, K.; Zsolnai, L.; Huttner, G.; Brintzinger,
H. H. J . Organomet. Chem. 1987, 328, 87.

1728 Organometallics, Vol. 16, No. 8, 1997
Schmidt et al.
mg (0.93 mmol, 93%) rac-4-BIN as a yellow powder. 1H NMR
(C6D6, 600 MHz, δ in ppm):16 0.66 (s, 6H, Si(CH3)2), 2.07 (s,
6H, C5H2CH3), 5.92 (2H, d, J ) 2.3 Hz, R-C5HH), 6.22 (2H, d,
J ) 2.06 Hz, â-C5HH), 6.48 (4H, m, o-C6H3H2), 6.49 (4H, m,
m-C6H3H2), 6.68 (2H, t, p-C6H4H), 6.92 (2H, t, HC(17,27)), 6.97
(2H, d, J ) 8.08 Hz, HC(13,23)), 7.11 (2H, m, HC(18,28)), 7.12
(2H, m, HC(16,26)), 7.65 (2H, d, J ) 8.8 Hz, HC(14,24)), 7.7
(2H, d, J ) 8.81 Hz, HC(15,25)). 13C NMR (C6D6, 600 MHz, δ
in ppm): -1.73 (Si(CH3)2), 16.05 (C5H2CH3), 107.41 (C(1,6)),
108.95 (C(5,10)), 118.44 (C(11,21)), 120.48 (C(3,8)), 122.18
(C(13,23)), 122.8 (C(16,26)), 126.07 (C(17,27)), 126.75(o-CC5H5),
126.86 (C(2,7)),127.24 (p-CC5H5) 127.68 (C(18,28)), 128.08-
(C(15,25)), 128.16 (m-CC5H5), 129.22 (C(19,29)), 129.37
(C(14,24)), 133.592 (Cp-CC5H5), 136.06 (C(20,30)), 141.77
(C(4,9)), 160.14 (C(12,22)). Anal. Calcd for C46H38O2SiZr: C,
74.45; H, 5.16. Found: C, 74.41; H, 5.64.
Ta ble 5. Cr ysta llogr a p h ic a n d Exp er im en ta l Da ta
for Me2Si(3-tBu -C5H3)2Zr Cl-Bin a p h th ola te
(m eso-1-Cl-BINH) a n d
Me2Si(2-Me-4-tBu -C5H2)2Zr -Bin a p h th ola te
(r a c-2-BIN)
compound
formula
fw
meso-1-Cl-BINH
44H53ClO3SiZr
784.6
rac-2-BIN
C42H46O2SiZr
702.1
C
color, habit
crystal size
crystal system
space group
unit cell dimensions
a, Å
yellow rhombohedron yellow cube
0.2 × 0.2 × 0.3
triclinic
P1h
0.3 × 0.3 × 0.3
triclinic
P1h
10.061(8)
10.501(7)
19.901(14)
99.39(5)
92.96(6)
92.71(6)
2068(3)
2
10.019(4)
10.407(5)
19.719(8)
78.25(3)
75.35(3)
67.94(3)
1830(1.4)
2
b, Å
c, Å
R, deg
â, deg
Reacting 37 mg (0.125 mmol) of R(+)-dilithium 1,1′-bi-2-
naphtholate with 53 mg (0.1 mmol) of meso-4 yields 65 mg
γ, deg
volume
(0.088 mmol, 88%) of (S)-4-(R)-BIN. [R]D ) -750°; [R]436
-2100° (c ) 0.05 g/100 mL, toluene).
)
Z
density (calcd), g/cm3
abs coeff (µ), mm-1
temp, K
1.260
1.274
Cr ysta l Str u ctu r es of Com p lexes 2-BIN a n d 1-Cl-
BINH. Crystals were obtained by slow crystallization from
hexane (2-BIN) or diethyl ether (1-Cl-BINH). Intensity data
were measured on a Syntex/Siemens-P3 four-circle diffractom-
eter with graphite-monochromated Mo KR radiation (0.71073
pm). Crystallographic and experimental data are summarized
in Table 5. Both structures were solved by direct methods and
refined by least-squares methods using the SHELXTL (VMS)
program. All non-H-atoms were refined anisotropically. Hy-
drogen atom positions were calculated and refined with fixed
isotropic U using riding model techniques. The resulting
structures are represented in Figures 1 and 2 and Tables 2
and 3.
0.389
0.359
233
296
2θ range, deg
no. of rflns collected
4.0-54
8038
4.0-54
8462
no. of independent rflns 7512
7994
no. of obsd rflns
soln
weighting scheme
RF, %
6145 (F > 4σ(F))
6325 (F > 5σ(F))
direct methods
σ2(F) + 0.0004F2
3.89
4.50
1.29
direct methods
σ2(F) + 0.0004F2
3.68
4.36
1.34
R
wF, %
goodness of fit
residual density, e Å-3 0.69
0.38
evolution had ceased (10 min), a 1H-NMR sprectrum (250
MHz) was recorded. With 2-Me2 derived from racemic 2-BIN
as starting material, we observed eight doublets in the
cyclopentadienyl region (δ in ppm: 5.1, 5.3, 5.67, 5.75, 5.99,
6.0, 6.14, and 6.33), which are assignable to two diastereomers
of a monomethylmonoacetylmandelate complex. Only four
doublets were observed when (S)-2-Me2, derived from enan-
tiomerically pure (S)-2-(R)-BIN as starting material, was
reacted with 1 equiv of D(-)-acetylmandelic acid (δ in ppm:
5.1, 5.67, 5.99, 6.33); signals of the other diastereomer were
not detectable here. This corresponds to an optical purity of
ee > 95% for the dimethyl complex (S)-2-Me2.
Me2Si(2-Me-4-P h -C5H 2)2Zr -BIN (4-BIN). 4-BIN was
obtained by a procedure similar to that described above for
2-BIN. A 528 mg (1 mmol) sample of meso-4 was reacted
under irradiation with 328 mg (1.2 mmol) of racemic dilithium
1,1′-bi-2-naphtholate in 60 mL of toluene. In contrast to the
procedure described above, this reaction was already complete
after 4-6 h at 40 °C. The toluene suspension was evaporated
to dryness and redissolved in toluene; precipitated LiCl was
removed by filtration and the residue evaporated again. The
resulting yellow powder was suspended in diethyl ether, where
impurities were dissolved; the racemic complex 4-BIN was
collected by filtration and washed with pentane to yield 690
Ack n ow led gm en t. We thank Dr. Armin Geyer and
Monika Cavegn for measurements of two-dimensional
NMR spectra and Professor S. Collins (University of
Waterloo) for valuable comments and information.
Financial support of this work by BMBF, BASF AG,
Fonds der Chemischen Industrie and by funds of the
University of Konstanz is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of additional
crystallographic data for complexes 1-Cl-BINH and 2-BIN,
final positional parameters, bond distances, and bond angles
(18 pages). Ordering information is given on any current
masthead page. This information is also available on request
from Fachinformationszentrum Karlsruhe, D-76344 Eggen-
stein-Leopoldshafen 2, upon quotation of the depository num-
bers 406317 and 406318, the authors, and the journal reference
for this article.
OM961089D
(16) Assignments are based on DEPT, COSY, ROESY, HMQC, and
HMBC spectra. Labels of the binaphtholate carbons in complexes
2-BIN and 4-BIN are analogous to those of complex 2-BIN in Figure
2.