Steric and electronic ligand perturbations in catalysis: Asymmetric allylic substitution reactions using C2-symmetrical phosphorus-chiral (Bi)ferrocenyl donors

Article abstract of DOI:10.1021/jo001175u

Three series of P-chiral diphosphines based on ferrocene (1a-f, 2a-c) and biferrocenyl skeletons (3a-c), including novel ligands 1f and 3c, were employed in palladium-catalyzed allylic substitution reactions. Steric effects imposed by the phosphine residues were studied using C₂-symmetrical donors 1 (1 = 1,1′-bis(arylphenylphosphino)ferrocene with aryl groups a = 1-naphthyl, b = 2-naphthyl, c = 2-anisyl, d = 2-biphenylyl, e = 9-phenanthryl, and f = ferrocenyl), whereas paramethoxy- and/or para-trifluoromethyl substitution of the phenyl moieties in 1a enabled investigation of ligand electronic effects applying ferrocenyl diphosphines 2a-c. Ligands 3 (3 = 2,2′-bis-(arylphenylphosphino)-1,1′-biferrocenyls with aryl substituents a,c = 1-naphthyl (diastereomers) and b = 2-biphenylyl) allowed for comparison of backbone structure effects (bite angle variation) in catalysis. Linear and cyclic allylic acetates served as substrates in typical test reactions; upon attack of soft carbon and nitrogen nucleophiles on (E)-1,3-diphenylprop-2-ene-1-yl acetate the respective malonate, amine, or imide products were obtained in enantioselectivities of up to 99% ee. A crystal structure analysis of a palladium 1,3-diphenyl-η³-allyl complex incorporating ligand (S,S)-1a revealed a marked distortion of the allyl fragment, herewith defining the regioselectivity of nucleophile addition.

Full text of DOI:10.1021/jo001175u

J . Org. Chem. 2001, 66, 759-770
759
Ster ic a n d Electr on ic Liga n d P er tu r ba tion s in Ca ta lysis:
Asym m etr ic Allylic Su bstitu tion Rea ction s Usin g C2-Sym m etr ica l
P h osp h or u s-Ch ir a l (Bi)fer r ocen yl Don or s
Ulrike Nettekoven,† Michael Widhalm,*,‡ Hermann Kalchhauser,‡ Paul C. J . Kamer,†
Piet W. N. M. van Leeuwen,*,† Martin Lutz,§ and Anthony L. Spek§
Institute of Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands, Institute of Organic Chemistry, University of Vienna,
Wa¨hringer Strasse 38, 1090 Vienna, Austria, and Bijvoet Center for Biomolecular Research,
Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
pwnm@anorg.chem.uva.nl
Received August 2, 2000
Three series of P-chiral diphosphines based on ferrocene (1a -f, 2a -c) and biferrocenyl skeletons
(3a -c), including novel ligands 1f and 3c, were employed in palladium-catalyzed allylic substitution
reactions. Steric effects imposed by the phosphine residues were studied using C2-symmetrical
donors 1 (1 ) 1,1′-bis(arylphenylphosphino)ferrocene with aryl groups a ) 1-naphthyl, b )
2-naphthyl, c ) 2-anisyl, d ) 2-biphenylyl, e ) 9-phenanthryl, and f ) ferrocenyl), whereas para-
methoxy- and/or para-trifluoromethyl substitution of the phenyl moieties in 1a enabled investigation
of ligand electronic effects applying ferrocenyl diphosphines 2a -c. Ligands 3 (3 ) 2,2′-bis-
(arylphenylphosphino)-1,1′-biferrocenyls with aryl substituents a ,c ) 1-naphthyl (diastereomers)
and b ) 2-biphenylyl) allowed for comparison of backbone structure effects (bite angle variation)
in catalysis. Linear and cyclic allylic acetates served as substrates in typical test reactions; upon
attack of soft carbon and nitrogen nucleophiles on (E)-1,3-diphenylprop-2-ene-1-yl acetate the
respective malonate, amine, or imide products were obtained in enantioselectivities of up to 99%
ee. A crystal structure analysis of a palladium 1,3-diphenyl-η3-allyl complex incorporating ligand
(S,S)-1a revealed a marked distortion of the allyl fragment, herewith defining the regioselectivity
of nucleophile addition.
In tr od u ction
as catalysts.5 Cyclic or linear 1,3-disubstituted acetates
are frequently employed as substrates, which upon
oxidative addition give rise primarily to Cs-symmetrical
allyl units. Among the various possibilities for enantio-
face discrimination, irreversible nucleophilic attack on
equilibrated palladium(II) allyl complexes plays a domi-
nant role. Consequently, steric and electronic ligand
variations were exploited to enhance differentiation
between isomeric allyl species as well as enantiotopic
allyl termini, and this, indeed, afforded substitution
products in high enantiomeric excesses. Prominent ex-
amples of successful ligand structures include P-N
donors such as phosphinooxazolines,6 planar-chiral fer-
rocenyl7 or atropisomeric binaphthyl8 derivatives, as well
Currently, allylic substitution reactions rank among
the most thoroughly and intensively studied catalytic
transformations. Since the first reports by Tsuji,1 Trost,2
and respective co-workers on palladium-mediated C-C
bond formations between allylic substrates and carbon
nucleophiles, this area has seen fast developments in
reaction scope, catalyst structure, nucleophile diversity,
and ligand design.3 Considerable efforts have been de-
voted to asymmetric reaction variants that provide an
access to potentially valuable chiral building blocks.4
With respect to mechanistic features, enantioselective
allylic alkylations and, to some extent, aminations have
been studied in detail, mostly using palladium complexes
* m.widhalm@univie.ac.at.
(5) See for example: (a) Auburn, P. R.; Mackenzie, P. B.; Bosnich,
B. J . Am. Chem. Soc. 1985, 107, 2033. (b) Mackenzie, P. B.; Whelan,
J .; Bosnich, B. J . Am. Chem. Soc. 1985, 107, 2046. (c) Sprinz, J .; Kiefer,
M.; Helmchen, G.; Reggelin, M.; Huttner, G.; Walter, O.; Zsolnai, L.
Tetrahedron Lett. 1994, 35, 1523. (d) von Matt, P.; Lloyd-J ones, G. C.;
Minidis, A. B. E.; Pfaltz, A.; Macko, L.; Neuburger, M.; Zehnder, M.;
Pregosin, P. S. Helv. Chim. Acta 1995, 78, 265. (e) Togni, A.;
Burckhardt, U.; Gramlich, V.; Pregosin, P. S.; Salzmann, R. J . Am.
Chem. Soc. 1996, 118, 1031. (f) Steinhagen, H.; Reggelin, M.; Helm-
chen, G. Angew. Chem., Int. Ed. Engl. 1997, 36, 2108. (g) Lloyd-J ones,
G. C.; Stephen, S. C. Chem. Eur. J . 1998, 4, 2539. (h) Trost, B. M.;
Toste, F. D. J . Am. Chem. Soc. 1999, 121, 4545.
(6) See, for example: (a) Pfaltz, A. Acc. Chem. Res. 1993, 26, 339.
(b) Dawson, G. J .; Frost, C. G.; Williams, J . M. J .; Coote, S. J .
Tetrahedron Lett. 1993, 34, 3149. (c) Helmchen, G.; Kudis, S.; Senn-
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A. Synlett 1999, 835. (e) Yonehara, K.; Hashizume, T.; Mori, K.; Ohe,
K.; Uemura, S. J . Org. Chem. 1999, 64, 9374. (f) Go´mez, M.; J ansat,
S.; Muller, G.; Panyella, D.; van Leeuwen, P. W. N. M.; Kamer, P. C.
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† University of Amsterdam.
‡ University of Vienna.
§ Utrecht University.
(1) (a) Tsuji, J .; Takahashi, H.; Morikawa, M. Tetrahedron Lett.
1965, 49, 4387. (b) Tsuji, J . Acc. Chem. Res. 1969, 2, 144.
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630. (b) Trost, B. M.; Verhoeven, T. R. J . Am. Chem. Soc. 1978, 100,
3435.
(3) (a) Maitlis, P. M.; Espinet, P.; Russell, M. J . H., In Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon: Oxford, 1982; Vol. 8, p 463. (b) Trost, B. M.;
Verhoeven, T. R. In Comprehensive Organometallic Chemistry; Wilkin-
son, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, 1982;
Vol. 8, p 799. (c) Heck, R. F. Palladium Reagents in Organic Synthesis;
Academic Press: New York, 1985. (d) Tsuji, J . Tetrahedron 1986, 42,
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10.1021/jo001175u CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/10/2001

760 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
as modularly designed, sterically encumbering diphos-
phine donors.9
In the following we describe the synthesis of two new
chiral diphosphine ligands 1f and 3c, as well as the
performance of these and previously reported ligands
1a -e, 2a -c, and 3a ,b14 in typical allylic test reactions.
Excellent results were obtained in some cases, for which
rationalization is attempted by means of a crystal
structure determination of a palladium(II) allyl complex
as well as two-dimensional variable temperature NMR
measurements.
In contrast, the potential of classical C2-symmetrical
diphosphine inducers, devoid of further donor function-
alities such as Binap10 and Chiraphos,11 is assessed low.12
To the best of our knowledge, only one contribution
describes the successful employment of a propeller-
shaped diphospholane ligand in allylic C-C bond forming
reactions, using cyclic as well as linear substrates.13 In
that case, molecular mechanics calculations and crystal
structure analysis did not indicate a preferred site of
nucleophile addition; enantiodiscrimination was therefore
assumed to depend on the ease of clockwise or counter-
clockwise rotation of the allyl moiety upon nucleophilic
attack to form the η2-bonded palladium(0) alkene complex
(late transition state). Thus, the stereogenic elements of
the ligand had to display their efficacy by creating
asymmetric steric congestion in the immediate allyl
termini environments, thereby selectively blocking one
rotation mode. A possible extension and deeper explora-
tion of the given rationale prompted us to investigate the
performance of other P-chiral ligands in allylic substitu-
tion reactions.
Recently, we reported the synthesis of a new class of
P-chiral diphosphine donors based on dppf (1,1′-bis-
(diphenylphosphino)ferrocene).14 Bearing different aryl
substituents on phosphorus, these ligands were found to
induce high enantioselectivities in rhodium-catalyzed
asymmetric hydrogenations of cinnamic acid derivatives.14a
Preliminary results in allylic substitution reactions
seemed also promising14b and set the stage for a detailed
study of the latter reaction employing several substrates
and nucleophiles. Of special interest to us was the
investigation of, on one hand, steric effects imposed by
the nature of the substituents on chiral phosphorus and
the backbone (bite angle variation). On the other hand,
we were intrigued by the impact of ligand electronic
variations on enantiocontrol. These features were studied
by the employment of phosphorus-stereogenic C2-sym-
metrical ferrocenyl and biferrocenyl diphosphines, ex-
hibiting steric and electronic perturbations.
Resu lts a n d Discu ssion
Liga n d Syn th esis. An elegant access to enantio-
enriched borane-protected phosphorus centers was es-
tablished by nucleophilic displacement reactions con-
trolled by the chiral auxiliary ephedrine. First introduced
by J uge´, Geneˆt, and co-workers,15 this approach enabled
the stereoselective attachment of three different bulky
aryl substituents onto phosphorus, which is not easily
achieved by utilizing other auxiliaries or different meth-
ods such as optical resolutions16 and direct asymmetric
synthesis.17 In an extension of this work, it was found
that nucleophilic attack of 1,1′-dilithioferrocene on enan-
tiopure methyl phosphinite boranes resulted in coupling
of two stereogenic phosphorus moieties to the backbone,
after decomplexation of borane giving rise to the first
P-chiral dppf-analogues.14a,b,18 The flexibility of this ap-
proach was evidenced by the synthesis of ligands 1a -e,
bearing sterically demanding aryl moieties on phospho-
rus. Electronically varied diphosphines 2a -c derived
from ligand 1a by introduction of methoxy and trifluo-
romethyl groups in para-positions of the phenyl rings
were synthesized in a similar manner.14d
(7) See, for example: (a) Hayashi, T.; Yamamoto, A.; Ito, Y.;
Nishioka, E.; Miura, H.; Yanagi, K. J . Am. Chem. Soc. 1989, 111, 6301.
(b) Togni, A.; Burckhardt, U.; Gramlich, V.; Pregosin, P. S.; Salzmann,
R. J . Am. Chem. Soc. 1996, 118, 1031. (c) Zhang, W.; Hirao, T.; Ikeda,
I. Tetrahedron Lett. 1996, 37, 4545.
(8) (a) Brown, J . M.; Hulmes, D. I.; Guiry, P. J . Tetrahedron 1994,
50, 4493. (b) Vyskocil, S.; Smrcina, M.; Hanus, V.; Polasˇek, M.;
Kocovsky, P. J . Org. Chem. 1998, 63, 7738.
(9) (a) Trost, B. M.; van Vranken, D. L. Angew. Chem., Int. Ed. Engl.
1992, 31, 228. (b) Trost, B. M.; Breit, B.; Peukert, S.; Zambrano, J .;
Ziller, J . W. Angew. Chem., Int. Ed. Engl. 1995, 34, 2386. (c) Widhalm,
M.; Wimmer, P.; Klintschar, G. J . Organomet. Chem. 1996, 523, 167.
(d) Saitoh, A.; Misawa, M.; Morimoto, T. Tetrahedron: Asymmetry
1999, 10, 1025.
(10) Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345.
(11) (a) Fryzyk, M. D.; Bosnich, B. J . Am. Chem. Soc. 1977, 99, 6262.
(b) Fryzyk, M. D.; Bosnich, B. J . Am. Chem. Soc. 1979, 101, 3043.
(12) (a) Yamaguchi, M.; Shima, T.; Yamagishi, T.; Hida, M. Tetra-
hedron Lett. 1990, 35, 5049. (b) Togni, A. Tetrahedron: Asymmetry
1991, 2, 683. (c) Bovens, M.; Togni, A.; Venanzi, L. M. J . Organomet.
Chem. 1993, 451, C28.
(13) Dierkes, P.; Ramdeehul, S.; Barloy, L.; De Cian, A.; Fischer,
J .; Kamer, P. C. J .; van Leeuwen, P. W. N. M.; Osborn, J . A. Angew.
Chem., Int. Ed. 1998, 37, 3116.
(15) (a) J uge´, S.; Stephan, M.; Laffitte, J . A.; Geneˆt, J . P. Tetrahe-
dron Lett. 1990, 31, 6357. (b) J uge´, S.; Stephan, M.; Merde`s, R.; Geneˆt,
J . P.; Halut-Desportes, S. J . Chem. Soc., Chem. Commun. 1993, 531.
(c) Brown, J . M.; Laing, J . C. P. J . Organomet. Chem. 1997, 529, 435.
(16) (a) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94,
1375.
(17) (a) Muci, A. R.; Campos, K. R.; Evans, D. A. J . Am. Chem. Soc.
1995, 117, 9075. (b) Wolfe, B.; Livinghouse, T. J . Am. Chem. Soc. 1998,
120, 5116.
(14) (a) Nettekoven, U.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.;
Widhalm, M.; Spek, A. L.; Lutz, M. J . Org. Chem. 1999, 64, 3996. (b)
Nettekoven, U.; Widhalm, M.; Kamer, P. C. J .; van Leeuwen, P. W. N.
M. Tetrahedron: Asymmetry 1997, 8, 3185. (c) Nettekoven, U.;
Widhalm, M.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.; Mereiter,
K.; Lutz, M.; Spek, A. L. Organometallics 2000, 19, 2299. (d) Nettek-
oven, U.; Kamer, P. C. J .; Widhalm, M.; van Leeuwen, P. W. N. M.
Organometallics 2000, 19, 4596.

Asymmetric Allylic Substitution Reactions
J . Org. Chem., Vol. 66, No. 3, 2001 761
Sch em e 1
Sch em e 2
angle.20 Its pronounced effect on catalyst performance
was demonstrated in different applications among which
number hydroformylation, hydrocyanation, and allylic
substitution reactions.21 Yet, as a result of their intrinsic
conformational flexibility originating from free rotation
of the cyclopentadienyl rings around or distortion along
the Cp-Fe-Cp axis, calculations of natural bite angles
for ligands based on ferrocenyl skeletons are less reliable
than for other more rigid donor structures. Nevertheless,
we wanted to investigate the steric effects of a backbone
alteration in P-chiral diphosphine ligands. Whereas for
ligands 2a -c electronic modifications were introduced
in para-positions of the phenyl rings in order to prevent
interference with steric conditions, we chose for a back-
bone variation by means of a biferrocenyl entity to keep
the electronic perturbations with respect to the 1,1′-
ferrocenyl skeleton to a minimum.
In a recent contribution we described the multistep
stereoselective approach to enantiopure 2,2′-bis(phenyl-
arylphosphino)biferrocenyls 3a ,b, starting from optically
pure methyl phosphinite boranes.14c The intermediate
1-naphthylphenyl- and 2-biphenylyl-phenylferrocenylphos-
phine oxides were subjected to ortho-magnesiation and
afforded, after quenching with iodine, the substitution
products in 50% and 94% de, respectively. In first in-
stance, only the predominantly formed diastereomer of
compound 7, (RP,Sm)-1-iodo-2-(1-naphthylphenylphosphi-
noxy)ferrocene, was employed in the further course of the
synthesis, which after Ullmann coupling, reduction, and
purification via the bisborane complex gave the (SP,Rm,-
Rm,SP)-configured ligand 3a . To study the effects of
planar chirality, we now also subjected the minor (RP,Rm)-
configured o-iodo ferrocenylphosphine oxide 7 to the
mentioned procedure (Scheme 2). Thus, we finally ob-
tained the diastereomeric biferrocenyl diphosphine prod-
uct 3c, displaying the (SP,Sm,Sm,SP) configuration of the
four adjacent stereogenic elements.
To explore the special aromatic sandwich structure of
ferrocene not only as ligand backbone but also as an
extraordinarily shaped substituent, we set out to prepare
ligand 1f, incorporating three ferrocene units linked via
chiral phosphorus centers. The multistep synthesis was
performed in analogy to described procedures; however,
diastereoselectivities proved to be somewhat lower than
observed during the synthesis of ligands 1a -e (Scheme
1). Nucleophilic attack of monolithioferrocene on (2RP,-
4S,5R)-oxazaphospholidine borane 4 gave rise to the
diastereomeric products (SP,1R,2S)-5 and (RP,1R,2S)-5 in
a ratio of 91:9. Yet, column chromatographic separation
of these phosphorus amide boranes was successful and
enabled continuation of the sequence with diastereomeri-
cally pure starting material.
Similarly, the last substitution reaction using dilithio-
ferrocene showed a reduced degree of stereodiscrimina-
tion, which was evidenced by the formation of ∼10% of
meso-configured diphosphine diborane. Since during the
synthesis of ligands 1a -e as well as 2a -c the amounts
of meso product were considerably smaller, if observed
at all, we ascribe this lower stereoselectivity to the
diminished steric encumbering of the cyclopentadienyl
moieties as compared to the aryl substituents. Again,
chromatographic separation of the isomeric product
mixture and, after deprotection, repeated recrystalliza-
tions finally afforded enantiomerically pure (S,S)-1f.
As previously described, the enantiomeric excess of the
new ligand was checked by NMR measurements of the
derived diphosphine dioxide in the presence of the chiral
solvating agent (S)-N-(3,5-dinitrobenzoyl)-1-phenylethyl-
amine.19 No splitting of signals due to diastereomeric
adduct formation was observed, confirming the enantio-
meric integrity of the bis(ferrocenylphenylphosphino)-
ferrocene 1f.
(20) (a) Casey, C. P.; Whiteker, G. T. Isr. J . Chem. 1990, 30, 299.
(b) Casey, C. P.; Whiteker, G. T.; Melville, M. G.; Petrovich, L. M.;
Gavney, J . A., J r.; Powell, D. R. J . Am. Chem. Soc. 1992, 114, 5535.
(21) (a) Dierkes, P.; van Leeuwen, P. W. N. M. J . Chem. Soc., Dalton
Trans. 1999, 1519 and references therein. (b) Van Leeuwen, P. W. N.
M.; Kamer, P. C. J .; Reek, J . N. H. Pure Appl. Chem. 1999, 71, 1443.
(c) Van Leeuwen, P. W. N. M.; Kamer, P. C. J .; Reek, J . N. H.; Dierkes,
P. Chem. Rev. 2000, 100, 2741.
One ligand parameter that has gained increasing
attention over the past few years is the natural bite
(18) Maienza, F.; Wo¨rle, M.; Steffanut, P.; Mezzetti, A.; Spindler,
F. Organometallics 1999, 18, 1041.
(19) Dunach, E.; Kagan, H. B. Tetrahedron Lett. 1985, 26, 2649.

762 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
Ta ble 1. Resu lts of Allylic Su bstitu tion Rea ction 1 w ith
Ca ta lysts Com p r isin g Ster ica lly a n d Electr on ica lly
P er tu r bed P -Ch ir a l Dip h osp h in e Liga n d sa
the importance of bulky aryl units, which markedly
contrast with the steric properties of the phenyl group.
As evident from screening runs performed in the presence
of diphosphine 1a , a 1:1 ligand/palladium ratio was
sufficient and, in combination with CH2Cl2 as the solvent
and BSA as the base, identified as the optimum reaction
conditions. For the structurally similar diphosphine
donors 1a and 1e, a temperature dependence was found
that allowed for a small increase of ee values for reactions
run at -10 or -20 °C, respectively. Whereas the slightly
higher value of 77% ee for ligand 1e indicated a beneficial
influence of the larger 9-phenanthryl substituents in
comparison to the 1-naphthyl moieties, the stereodis-
criminating effect of the 2-biphenylyl substituents of
compound 1d was somewhat lower. The best results
within this class of dppf-analogues was obtained employ-
ing diphosphine 1f (81% ee). Interestingly, the combina-
tion of sandwich-type ferrocenyl moieties and phenyl
substituents on phosphorus, if ligated to palladium,
favored nucleophilic attack in a different fashion than
observed for ligands 1a ,d ,e, as evidenced by the forma-
tion of the (R)-configured diester under catalysis by
[(S,S)-1f]Pd.
temp
(°C)
isolated
yield (%)
% eeb
(abs config)
ligand
(R,R)-1a
25
0
88
73
84
91
94
65
91
96
85
82
90
85
80
82
84
88
87
65
87
84
89
93
68 (R)
72 (R)
73 (R)
63 (R)
61 (R)
64 (R)
10 (R)
23 (R)
0
(R,R)-1a
(R,R)-1a
-10
25
25
25
25
-20
25
0
(R,R)-1a c
(R,R)-1a d
(R,R)-1a e
(S,S)-1b
(S,S)-1b
(R,R)-1c
(R,R)-1c
3 (S)
(R,R)-1d
(R,R)-1e
(R,R)-1e
(R,R)-1e
(S,S)-1f
(S,S)-2a
(S,S)-2b
(S,S)-2c
(SP,Rm,Rm,SP)-3a
(SP,Rm,Rm,SP)-3a
(SP,Rm,Rm,SP)-3b
(SP,Sm,Sm,SP)-3c
25
25
0
56 (R)
74 (R)
76 (R)
77 (R)
81 (R)
69 (S)
61 (S)
63 (S)
88 (R)
88 (R)
58 (R)
74 (S)
-20
20
20
20
20
20
-10
20
25
For electronically perturbed ligands 2a -c, the effects
of enhanced or diminished donor basicity on enantio-
selectivities were found to be small. A slightly deleterious
influence may be ascribed to the presence of the trifluo-
romethyl groups, resulting in a decrease of ee values to
61% (2b) and 63% (2c) in comparison to the unsubsti-
tuted diphosphine 1a (68%). Reactivity was not affected,
rendering the reaction profile insensitive to subtle changes
of the electron density.23,24
The best results in this model reaction, however, were
realized employing the biferrocenyl ligand 3a . For this
bulky diphosphine, no further improvement of the 88%
ee values was achieved at lower temperatures. Diphos-
phine 3b delivered a performance similar to the ferro-
cenyl-based ligand 1d ; enantioselectivities scarcely de-
pended on backbone structure in these two cases. The
new biferrocenyl donor 3c effected ee values of 74%,
hereby revealing the all-(S) configuration as the mis-
matched isomer with respect to the more successful
(SP,Rm,Rm,SP)-ligand 3a . Interestingly, the absolute prod-
uct configuration observed on utilizing diphosphines
3a -c depended on metallocene rather than phosphorus
configuration.
a
Reaction conditions: 0.005 mmol of [Pd(η3-C3H5)Cl]2, 0.01
mmol of ligand, 1 mmol of (E)-1,3-diphenylprop-2-en-1-yl acetate,
3 mmol of dimethylmalonate, 3 mmol of BSA, and a catalytic
amount of KOAc in 1 mL of CH2Cl2. Reaction times: 2-48 h (not
optimized). Determined by chiral HPLC (Chiralcel OD-H). c Lig-
b
d
and/palladium ratio ) 2:1. 1,1,3,3-Tetramethylguanidine was
used as the base. e CH3CN was used as the solvent.
Ca ta lysis. The first model reaction we investigated
employing the P-chiral diphosphines 1a -f, 2a -c, and
3a -c was the allylic alkylation of 1,3-diphenylprop-2-
en-1-yl acetate with dimethyl malonate (eq 1). Applying
the Trost protocol22 with BSA (N,O-bis(trimethylsilyl)-
acetamide) as the base, reaction conditions were opti-
mized for catalysts comprising ligand 1a ; the results for
all diphosphine donors are summarized in Table 1.
With reaction times between 2 and 20 h at room
temperature, isolated product yields typically surpassed
80% for most of the catalysts tested. The chemoselectivity
toward the trans-configured propenyl diester proved
excellent in all runs; no isomerized cis-product was
identified in the crude reaction mixture. Within the first
series of ligands 1a -f, differing from each other by the
dissimilar steric demands of the respective aryl substit-
uents on phosphorus, enantiodiscrimination varied con-
siderably. Ligand 1b, bearing 2-naphthyl moieties, showed
a disappointing performance, which might be rationalized
by its resemblance with the achiral dppf chelate. Con-
sequently, substitution in ortho-position of the aryl group
appeared as a necessary, but not sufficient requirement
for good asymmetric induction. This was deduced from
the undiscriminating behavior of ligand 1c, contrasting
with the excellent performance of the o-anisyl substituted
derivative in rhodium-catalyzed hydrogenation reactions.
Ligands 1a ,d ,e,f as catalyst components induced mod-
erate to good enantioselectivities, herewith emphasizing
The good results obtained with 1,3-diphenylpropenyl
acetate could not be repeated with smaller substrates.
As summarized in Table 2, pent-3-en-2-yl acetate was,
in the presence of palladium complexes of ligands 1a -f
as well as 3a -c, converted to the dimethyl malonate
adduct with low enantiomeric excesses (eq 2). A similar
unsatisfactory picture was obtained on utilizing cyclic
substrates, such as cyclohex-2-en-1-yl acetate (eq 3, Table
(23) In contrast, in the hydroformylation of styrene a correlation
between ligand basicity and ee values could be established for
diphosphines 1a and 2a -c: Nettekoven, U.; Kamer, P. C. J .; Widhalm,
M.; van Leeuwen, P. W. N. M. Organometallics 2000, 19, 4596.
(24) Utilizing different ligand systems, electronic effects on reactivity
and enantioselectivity have been reported: (a) Saitoh, A.; Misawa, M.;
Morimoto, T. Synlett 1999, 483. (b) Chelucci, G.; Deriu, S.; Pinna, G.
A.; Saba, A.; Valenti, R. Tetrahedron: Asymmetry 1999, 10, 3803.
(22) Trost, B. M.; Murphy, D. J . Organometallics 1985, 4, 1143.

Asymmetric Allylic Substitution Reactions
J . Org. Chem., Vol. 66, No. 3, 2001 763
Ta ble 2. Resu lts of Allylic Su bstitu tion Rea ction 2 w ith
Ca ta lysts Com p r isin g Ster ica lly P er tu r bed P -Ch ir a l
Dip h osp h in e Liga n d sa
Ta ble 4. Resu lts of Allylic Su bstitu tion Rea ction 4 w ith
Ca ta lysts Com p r isin g Ster ica lly a n d Electr on ica lly
P er tu r bed P -ch ir a l Dip h osp h in e Liga n d sa
temp
(°C)
isolated
yield (%)
% eeb
(abs config)
temp
(°C)
isolated
yield (%)
% eeb
(abs config)
ligand
(R,R)-1a
(R,R)-1a
(S,S)-1b
(R,R)-1c
(R,R)-1d
(R,R)-1e
(S,S)-1f
ligand
(R,R)-1a
25
-10
25
25
25
25
25
20
25
77
76
94
87
85
85
93
63
95
9 (R)
12 (R)
2 (S)
5 (S)
15 (R)
7 (S)
13 (R)
15 (R)
1 (S)
20
20
20
20
20
20
-10
20
20
20
20
20
20
-10
20
83
83
68
89
83
89
90
76
80
68
59
76
92
89
17
53
37 (S)
2 (S)
(S,S)-1b
(R,R)-1c
22 (S)
32 (S)
90 (S)
97 (S)
99 (S)
50 (S)
84 (S)
42 (R)
36 (R)
34 (R)
89 (S)
93 (S)
88 (S)
84 (R)
(R,R)-1d c
(R,R)-1d
(R,R)-1d d
(R,R)-1d
(R,R)-1e
(S,S)-1f
(S,S)-2a
(S,S)-2b
(S,S)-2c
(SP,Rm,Rm,SP)-3a
(SP,Rm,Rm,SP)-3a
(SP,Rm,Rm,SP)-3b
(SP,Sm,Sm,SP)-3c
(SP,Rm,Rm,SP)-3a
(SP,Rm,Rm,SP)-3b
Reaction conditions: 0.005 mmol of [Pd(η3-C3H5)Cl]2, 0.01
mmol of ligand, 1 mmol of (E)-pent-3-en-2-yl acetate, 3 mmol of
dimethylmalonate, 3 mmol of BSA, and a catalytic amount of
KOAc in 1 mL of CH2Cl2. Reaction times: 3-48 h (not optimized).
bDetermined by chiral GC.
a
20
Ta ble 3. Resu lts of Allylic Su bstitu tion Rea ction 3 w ith
Ca ta lysts Com p r isin g Ster ica lly P er tu r bed P -Ch ir a l
Dip h osp h in e Liga n d sa
Reaction conditions: 0.005 mmol of [Pd(η3-C3H5)Cl]2, 0.01
mmol of ligand, 1 mmol of (E)-1,3-diphenylprop-2-en-1-yl acetate,
and 1.2 mmol of benzylamine in 1 mL of CH2Cl2. Reaction times:
a
temp
(°C)
isolated
yield (%)
% eec
(abs config)
b
12-48 h (not optimized). Determined by chiral HPLC. c CH3CN
ligand
d
was used as the solvent. THF was used as the solvent.
(R,R)-1a
(S,S)-1b
(R,R)-1c
(R,R)-1d
(R,R)-1e
(S,S)-1f
25
25
25
25
25
25
77
82
88
84
66
89
26 (R)
1 (R)
4 (R)
29 (S)
17 (R)
11 (S)
(ferrocenyl) ligand 1f. The top result in this model
transformation was due to the biphenylyl-substituted
diphosphine 1d . A value of 97% ee at room temperature
could be increased to a remarkable 99% ee for reactions
run at -10 °C.
Reaction conditions: 0.005 mmol of [Pd(η3-C3H5)Cl]2, 0.01
a
Modification of this successful ligand structure by
means of the biferrocenyl skeleton of ligand 3b, however,
seemed to exceed the permissible degree of steric encum-
bering. Conversions and product yields were found to be
low, and enantiocontrol suffered from a decrease of
approximately 10% compared to 1d . On the contrary, in
the case of the phenyl-1-naphthyl substitution pattern
on phosphorus, exchange of the ferrocenyl for a biferro-
cenyl backbone bearing planar chirality proved advanta-
geous. Up to 93% ee was achieved employing ligand 3a ,
which constituted a remarkable enhancement with re-
spect to the 37% ee obtained for the related diphosphine
1a . Ligand 3c, although giving satisfactory enantiomeric
excesses of 84%, was, in comparison to compound 3a ,
again identified as the configurationally mismatched
derivative. Inductions of absolute product configurations
followed the trend observed for model reaction 1.
Furthermore, phthalimide potassium salt,25 a reagent
creating interesting precursors for unnatural amino
acids,26 was investigated (eq 5). Diminished reactivity of
mmol of ligand, 1 mmol of cyclohex-2-en-1-yl acetate, 3 mmol of
dimethylmalonate, 3 mmol of BSA, and a catalytic amount of
KOAc in 1 mL of CH2Cl2. Reaction times: 20-48 h (not optimized).
b
Determined by optical rotation measurements.
3). With the sense of optical induction caused by ligand
1d differing from the results of other diphosphines,
enantioselectivities were too low to permit decisive
conclusions.
In contrast to substrate variations, alteration of the
nucleophile in reactions employing 1,3-diphenylpropenyl
acetate gave good results. Using benzylamine, diphos-
phine palladium complexes catalyzed conversions to the
secondary amine product in satisfactory yields (eq 4,
Table 4). Enantioselectivities covered a wider range than
in alkylations; a comparable trend for ligand perfor-
mances in model reactions 1 and 4, however, could not
be deduced for all diphosphines. Ligand 1a afforded
modest enantiodifferentiation, which upon employment
of electronically modified derivatives 2a -c did not im-
prove considerably. The sterically more demanding ligand
1e was, again, shown to promote better asymmetric
inductions than the 1-naphthyl containing dppf-analogue
1a . In the same way, a marked structural dissimilarity
of the residues might account for the success of the tris-
this nucleophile, however, prompted good yields only in
the presence of catalysts incorporating ligands 1a ,e,f. In
these cases, excellent enantioselectivities were obtained,
(25) Inoue, Y.; Taguchi, M.; Toyofuku, M.; Hashimoto, H. Bull.
Chem. Soc. J pn. 1984, 57, 3021.
(26) Bower, J . F.; J umnah, R.; Williams, A. C.; Williams, J . M. J . J .
Chem. Soc., Perkin Trans. 1 1997, 1411.

764 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
Ta ble 5. Resu lts of Allylic Su bstitu tion Rea ction 5 w ith
Ca ta lysts Com p r isin g Ster ica lly P er tu r bed P -Ch ir a l
Dip h osp h in e Liga n d sa
temp
(°C)
isolated
yield (%)
% eeb
(abs config)
ligand
(S,S)-1a c
(S,S)-1a
(S,S)-1a
(S,S)-1bc
(R,R)-1cc
(R,R)-1d c
(R,R)-1e
(S,S)-1f
(S,S)-1f
(S,S)-2a
reflux
20
0
reflux
reflux
reflux
0
20
0
25
86
90
86
<20
<20
<20
70
67
<20
91
85 (R)
81 (R)
87 (R)
ndd
nd
nd
92 (S)
93 (S)
nd
84 (R)
a
Reaction conditions: 0.005 mmol of [Pd(η3-C3H5)Cl]2, 0.01
mmol of ligand, 1 mmol of (E)-1,3-diphenylprop-2-en-1-yl acetate,
and 1.2 mmol of phthalimide potassium salt in 2 mL of CH2Cl2.
b
Reaction times: 15-60 h (not optimized). Determined by chiral
d
HPLC (Chiralcel OD-H). c THF was used as the solvent. Not
determined.
with the top result of 93% ee achieved with the 1f-
modified palladium complex (Table 5).
Cr ysta l Str u ctu r e of [(1,3-Dip h en yl-η3-a llyl)(1a )-
P d ]BF 4. Solu tion Str u ctu r es of P a lla d iu m Com -
p lexes [(1,3-d ip h en yl-η3-a llyl)(1a )P d ]BF 4, [(1,3-d i-
p h en yl-η3-a llyl) 1d )P d ]BF 4, a n d [(1,3-d ip h en yl-η3-
a llyl)(3a )P d ]BF 4. As a result of the C2-symmetrical
nature of the diphosphines and the pro-Cs structure of
the allylic acetates employed, enantioface exchange of η3-
allyl complexes should be excluded as stereodiscriminat-
ing features. No enantioselective ionization was found
to be operative, as indicated by the absence of a kinetic
substrate resolution observed for the amination reaction
catalyzed by [(R,R)-1d ]Pd. Thus, in catalytic runs using
1,3-diphenylpropenyl acetate, regioselective nucleophilic
attack on enantiotopic termini of the allyl is assumed as
the enantioselectivity determining process. To investigate
the factors, rendering one carbon atom the preferred site
of nucleophile addition, we performed a crystal structure
analysis on the complex {(1,3-diphenyl-η3-allyl)[(S,S)-1a ]-
Pd}BF4, 9a (Figure 1). This compound was prepared by
reaction of [(1,3-diphenyl-η3-allyl)PdOAc]2 with ligand
(S,S)-1a in the presence of AgBF4. Crystals were grown
from CH2Cl2/benzene with the chiral space group P1. The
BF4 anions are orientationally disordered. The crystals
additionally contain one molecule of benzene per unit cell.
For a summary of selected interatomic distances and
angles see Table 1 in the Supporting Information.
As expected, the solid-state structure showed a syn-
syn configuration of the two phenyl substituents of the
allyl moiety; these are engaged in π-stacking interactions
with the respective neighboring phenyl and 1-naphthyl
groups of the diphosphine ligand.27 Shortest carbon-
carbon nonbonding distances of that kind were identified
between C36‚‚‚C117 (3.256(6) Å) and C31‚‚‚C112 (3.285-
(6) Å), whereas π-π interactions between the two phenyl
rings were found less pronounced (C25‚‚‚C206 ) 3.449-
(6) Å, C30‚‚‚C207 ) 3.453(6) Å). Interestingly, a large
difference in the palladium-allyl carbon bond lengths
(Pd-C22 ) 2.302(4) Å, Pd-C24 ) 2.208(4) Å) and the
respective torsional angles was observed. Whereas the
angle for C32-C31-C24-C23 adopts a value of 34.0(6)°,
the correspondent angle involving the more loosely
F igu r e 1. Displacement ellipsoid plot of {(1,3-diphenyl-η3-
allyl)[(S,S)-1a ]Pd}BF4, 9a , drawn at 50% probability level.
bonded C22 is only 11.4(2)°. Regarding the C2-sym-
metrical nature of the ligand, these distortions seem to
result from purely steric constraints. Yet, these allyl
refinement data are comparable to those of crystal
structures of 1,3-diphenyl-η3-allyl palladium complexes
ligated by P-N, P-S, or electronically dissimilar P-P
donors displaying strong trans influences.28 Less simi-
larities, however, were found to related complexes bear-
ing other C2-symmetrical diphosphine ligands such as
Binap29 or Chiraphos.30 These exhibited approximately
the same palladium-carbon bond lengths for the allylic
termini and, in the latter case, revealed an almost planar
geometry of the allyl ligand, that originated from the
pseudo-Cs conformation adopted by the propeller-shaped
diphosphine.
Thus, the enforced C2-symmetry of P-chiral ligands
such as 1a seemed necessary for repulsive steric forces
that effectively differentiate between the terminal allylic
carbon atoms. The strong π-π stacking effects, extending
toward a favorable offset arrangement of the involved
aryl rings,31 suggested, however, that attractive interac-
tions between ligand and allyl moieties might also
participate in determining the preferred allyl coordina-
tion geometry.
(28) See, for example: (a) Sprinz, J .; Kiefer, M.; Helmchen, G.;
Reggelin, M.; Huttner, G.; Walter, O.; Zsolnai, L. Tetrahedron Lett.
1994, 35, 1523. (b) Togni, A.; Burckhardt, U.; Gramlich, V.; Pregosin,
P. S.; Salzmann, R. J . Am. Chem. Soc. 1996, 118, 1031. (c) Baltzer,
N.; Macko, L.; Schaffner, S.; Zehnder, M. Helv. Chim. Acta 1996, 79,
803. (d) Widhalm, M.; Mereiter, K.; Bourghida, M. Tetrahedron:
Asymmetry 1998, 9, 2983. (e) Albinati, A.; Pregosin, P. S.; Wick, K.
Organometallics 1996, 15, 2419. (f) Abbenhuis, H. C. L.; Burckhardt,
U.; Gramlich, V.; Kollner, C.; Pregosin, P. S.; Salzmann, R.; Togni, A.
Organometallics 1995, 14, 759.
(29) Yamaguchi, M.; Yabuki, M.; Yamagishi, T.; Sakai, K.; Tsubo-
mura, T. Chem. Lett. 1996, 241.
(30) Yamaguchi, M.; Yabuki, M.; Yamagishi, T.; Kondo, M.; Kita-
gawa, S. J . Organomet. Chem. 1997, 538, 199.
(27) No significant π-π interactions involving the benzene solvent
molecules were detected.
(31) Hunter, C. A.; Sanders, J . K. M. J . Am. Chem. Soc. 1990, 112,
5525.

Asymmetric Allylic Substitution Reactions
J . Org. Chem., Vol. 66, No. 3, 2001 765
F igu r e 2. Distortion of the allyl fragment in 9a . The ferrocene
moiety is omitted for clarity.
Assuming the more weakly bonded allyl terminus
C22 as the site of nucleophilic attack, the rotation upon
η3-η2 rearrangement should proceed in a counterclock-
wise fashion with regard to the incoming nucleophile. We
speculate that process to be advantageous in comparison
to a clockwise rotation that would involve movement of
the C24-phenyl moiety toward the sterically demanding
C112-naphthyl group. This hypothesis is further cor-
roborated by the position of the allyl fragment with
regard to the coordination plane. The angle between two
planes defined by atoms C24, Pd, and C22, as well as
P11, Pd, and P21, is 17.3(4)°, whereby the shortest
distances of C22 and C24 with respect to the latter plane
are 0.44(3) and 0.28(5) Å, respectively (Figure 2). Apply-
ing the principle of least motion,32 the C23-C24 bond is
predetermined to move into coplanarity with the phos-
phine coordination plane. Consequently, attack of di-
methyl malonate should preferentially give rise to the
(S)-configured product, which was, indeed, observed as
the reaction outcome.
As evidenced from the crystal structure of 9a , π-π
interactions between one allyl phenyl group and ligand
naphthyl residue exceed those between ligand phenyl and
allyl phenyl moieties. P-chiral bidentate donor structures
bearing aryl phosphino groups of similar effective elec-
tron density (such as, e.g., 1b,c) can be expected to
engage in stacking interactions of the same magnitude,
consequently hampering desymmetrization of the allyl
fragment and reducing the site selectivity of nucleophilic
attack. Assuming the degree of π-π interactions between
allyl phenyl and ligand ferrocenyl moieties to be even
lower than the mentioned phenyl-phenyl interactions,
predominance of the latter is supposed to be accompanied
by a different sense of rotation of the allyl fragment. The
resulting inversion of relative reactivities of the allyl
termini (with respect to complex 9a ) offers rationalization
for the observed (R) configuration of the malonate addi-
tion product upon employing ligand (S,S)-1f (vide supra).
To elucidate specific catalytic performances, we investi-
gated the solution structures of complexes {(1,3-diphenyl-
η3-allyl)[(S,S)-1a ]Pd}BF4, 9a , as well as the analogously
prepared {(1,3-diphenyl-η3-allyl)[(R,R)-1d ]Pd}BF4, 9d ,
and {(1,3-diphenyl-η3-allyl)[(SP,Rm,Rm,SP)-3a]Pd}BF4, 10a.
For all three compounds 400 and 600 MHz 1D and 2D
NMR measurements showed a syn-syn configuration of
the allyl substituents for the predominating isomer, as
F igu r e 3. Schematic representation of π-electronic interac-
tions (1-naphthyl/phenyl > phenyl/phenyl > phenyl/ferrocenyl)
determining allyl desymmetrization and site of nucleophilic
attack (ligand 1b, R2,R3 ) Ph; ligand 1c, R1 ) MeO).
evidenced by NOEs between the terminal allyl protons.
At room temperature, complex 9d existed as mainly one
species in solution (>95%); extensive signal overlap did
not allow complete assignment of all resonances.
In the case of compound 10a , 31P{1H} NMR spectra
revealed the presence of three isomeric complexes in a
ratio of 80:16:4. Using homo- and heteronuclear correla-
tion spectroscopy, the signals for the main isomer could
be fully assigned; NOESY measurements indicated a
pseudoequatorial arrangement of the bulky 1-naphthyl
substituents in the seven-membered chelate ring (Figure
4). A less favorable accommodation of these groups in
pseudoaxial position might give rise to one of the minor
complexes, as could the two possible coordination fash-
ions of a syn-anti configured allyl unit. Yet, marked line
broadening and low concentration, respectively, did not
permit conclusions regarding the precise nature of the
minor isomers.
Complex 9a showed a marked fluxional behavior at
ambient temperature, evidenced by a general broadening
1
(32) See, for example: Hine, J . Adv. Phys. Org. Chem. 1977, 15, 1.
of all signals in H as well as in 31P{1H} NMR. Lowering

766 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
Ta ble 6. Ter m in a l Allyl 13C Ch em ica l Sh ifts for
1,3-Dip h en yla llyl Dip h osp h in e P a lla d iu m Com p lexes
complex
δ (ppm)
9a
9d
10a
80.9; 103.3
84.5; 127.5
81.9; 98.1
lescence for the minor isomer was reached at a slightly
different temperature (already at 243 K) than for the
main complex.
A further reference to pronounced dissimilar coordina-
tion environments of the terminal allyl carbons was
provided by the large differences in the 13C chemical
shifts of the prevailing isomers in complexes 9a , 9d , and
10a (Table 6). Although these data do not clearly relate
to catalytic performances in general, they suggest dis-
symmetric steric and, possibly, π-electronic influences on
complex geometries to be similarly effective as evidenced
for 9a in the solid state.35
F igu r e 4. Selected NOEs observed for the main complex 10a .
A comparison of our NMR-assignments of complex 9a
with the crystal structure analysis associates the allylic
carbon atoms C22 and C24 with chemical shift values of
80.9 and 103.3 ppm, respectively. As mentioned above,
we expect nucleophilic attack to occur at the more
shielded carbon atom C22, bearing the lower positive
charge distribution. This is in disagreement with litera-
ture results, stating that nucleophile addition takes place
preferentially at the electronically more deshielded car-
bon atom.36 Complex 9a , comprising a C2-symmetrical
ligand system seems, however, less amenable to elec-
tronic preferences commonly observed employing P-N
or related chelates. Our findings are among the first to
experimentally indicate the theoretically anticipated37
predominance of steric influences (including π-stacking
interactions) over electronic effects in determining the
regioselectivity of nucleophilic attack.38
The interference of fluxional processes with catalytic
conversions might be invoked as possible explanation for
the lower ee values obtained with complex 9a in relation
to catalysts incorporating diphosphine (SP,Rm,Rm,SP)-3a .
In this context, effects of the bite angle require consid-
eration. Comparative crystal structure analyses of plati-
num(II) dichloride complexes bearing ligands (S,S)-1a
and (SP,Rm,Rm,SP)-3a displayed a highly distorted system
with a phosphorus-platinum-phosphorus bite angle of
102.97(5)° for the former compound.14c In contrast, the
geometry of complex [3a ]PtCl2 displayed less strain and
a smaller bite angle of only 92.30(5)°. Extrapolation of
these trends onto palladium allyl chemistry might indi-
cate a beneficial effect of a smaller bite angle. Yet, this
conclusion presumably holds only for the phenyl-1-
naphthyl set of substituents on chiral phosphorus as
evidenced by catalysis results. A general trend for the
effect of the bite angle cannot be deduced, since the
F igu r e 5. Selected NOEs observed for the major complex 9a .
the temperature to 223 K, however, gave sufficient
decoalescence to enable identification of the major syn-
syn configured allyl compound and a second isomer in a
ratio of 85:15. For the main compound, unequivocal
assignment of most signals was possible. Interestingly,
allyl phenyl groups as well as phenyl phosphine rings
exhibited hindered rotation, resulting in different signals
for the respective ortho- and meta-protons. 2D-TOCSY
and exchange spectroscopy allowed for determination of
all four connectivity sets. Noteworthy, no NOE contacts
were observed between the phenyl rings B and D (Figure
5), suggesting a similar π-stacking as present in the solid
state33 and indicating the major isomer of compound 9a
to match the spatial arrangements displayed in the
crystal structure.
The signals of the minor isomer showed a syn-syn
configuration of the allyl moiety as well and were
therefore assumed to originate from a different backbone
conformation (pseudoaxial vs. pseudoequatorial arrange-
ment of naphthyl residues). Inspection of the ROESY
spectrum evidenced exchange between major and minor
isomers via chelate ring inversion. Exchange peaks
between the respective ferrocenyl protons were especially
marked, whereas no exchange was observed between the
allyl protons. Dissolution of crystals of complex 9a at 200
K and immediate NMR measurement at 223 K did not
alter the isomeric distribution, showing fast establish-
ment of equilibrium conditions even at low temperatures.
This sort of conformational flexibility might account
for the considerable line broadening observed for com-
pound 9a at room temperature. Yet, (slow) apparent allyl
rotation proceeding via five-coordinate intermediates34
might occur as additional fluxional process, since decoa-
(34) (a) Vrieze, K.; van Leeuwen, P. W. N. M. In Progress in
Inorganic Chemistry; Lippard, S. L., Ed.; J ohn Wiley & Sons: New
York, 1971; Vol. 14, p 1. (b) Hansson, S.; Norrby, P. A.; Sjogren, M. P.
T.; Åkermark, B.; Cucciolito, M. E.; Giordano, F.; Vitagliano, A.
Organometallics 1993, 12, 4940.
(35) (a) Burckhardt, U.; Gramlich, V.; Hofmann, P.; Nesper, R.;
Pregosin, P. S.; Salzmann, R.; Togni, A. Organometallics 1996, 15,
3496. (b) Åkermark, B.; Krakenberger, B.; Hansson, S.; Vitagliano, A.
Organometallics 1987, 6, 620.
(36) (a) Prat, M.; Ribas, J .; Moreno-Man˜as, M. Tetrahedron 1992,
48, 1695. (b) Moreno-Man˜as, M.; Pajuelo, F.; Parella, T.; Pleixats, R.
Organometallics 1997, 16, 205.
(33) See, for example: Pregosin, P. S.; Trabesinger, G. J . Chem. Soc.,
Dalton Trans. 1998, 727.
(37) Blo¨chl, P. E.; Togni, A. Organometallics 1996, 15, 4125.
(38) Trost, B. M.; Oslob, J . D. J . Am. Chem. Soc. 1999, 121, 3057.

Asymmetric Allylic Substitution Reactions
J . Org. Chem., Vol. 66, No. 3, 2001 767
on a J EOL J MS SX/SX102A four sector mass spectrometer;
for FAB-MS 3-nitrobenzyl alcohol was used as matrix. Ele-
mental analyses were obtained using an Elementar Vario EL
apparatus. With exception of the compounds given below, all
reagents were purchased from commercial suppliers and used
without further purification. Diethylamine was distilled from
KOH under argon. The following compounds were synthesized
according to published procedures: (2RP,4S,5R)-3,4-dimethyl-
2,5-diphenyl-1,3,2-oxazaphospholidine borane 4,15a 1,1′-dilithio-
ferrocene,40 (RP,Rm)-1-iodo-2-(1-naphthylphenylphosphinoxy)-
ferrocene 7,14c (E)-1,3-diphenylprop-2-en-1-yl acetate,5a (E)-
pent-3-en-2-yl acetate,41 cyclohex-2-en-1-yl acetate,42 and [(1,3-
diphenyl-η3-allyl)PdOAc]2.7a In the nomenclature of ligands
3a -c and their precursor compounds, indices P and m denote
absolute configurations of phosphorus and metallocene ele-
ments of chirality, respectively.
structural diversity of 2-biphenylyl and 1-naphthyl groups
is too complex to neglect or unify their behavior upon
backbone alteration.
Con clu sion s
Our investigations of allylic substitution reactions
using P-chiral diphosphine ligands revealed some inter-
esting trends. Devoid of dissymmetric electronic model-
ing, the employed C2-symmetrical ligands (with exception
of diphosphine 2c) were found capable of inducing
enantioselectivities of up to 99% ee. Yet, this efficiency
depended on several factors, such as substrate structure,
type of nucleophile, backbone constitution, and substitu-
tion pattern of the chiral phosphorus donors. The small-
est effects were observed on varying ligand electronic
properties by para-methoxy and para-trifluoromethyl
substitution of the phenyl rings of the phosphines; the
latter resulted in a slight decrease of ee values.
In contrast, steric aspects concerning the substituents
on phosphorus were found eminently important; a marked
difference in spatial requirements, exhibited in proximity
to the metal center achieved good asymmetric modeling
of the coordination environment. In this context, bulky
9-phenanthryl, 2-biphenylyl, or ferrocenyl moieties were,
in combination with phenyl groups, identified as the most
efficient substitution arrays. Catalysis results did not
show a clear effect of the bite angle; a change of the latter
presumably resulted in extensive repositioning of the
phosphine residues. NMR spectra indicated, however,
that the choice of substituents is crucial to establish a
rigid, well-defined chiral pocket.
The crystal structure analysis revealed that marked
distortion of the η3-allyl fragment in complex 9a and,
consequently, determination of the site of nucleophilic
attack is imposed by a combination of steric constraints
and π-π interactions. These require the engagement of
bulky allyl as well as ligand substituents to induce useful
levels of enantiodiscrimination. Thus, purely steric mod-
eling by P-chiral residues could surpass the efficiency of
other propeller-shaped ligands bearing carbon or axial
chiral elements. In certain cases it even paralleled the
good results of P-N or dissymmetric P-P donors, that
rely on the exploitation of (stereo)electronic effects39 in
catalysis. Yet, few similarities were established between
the ferrocenyl ligands used in this study and the diphos-
pholane donors mentioned in the introductory part.
Summarizing, the interesting performance of P-chiral
diphosphines in allylic substitutions reactions will prompt
further exploration in other catalytic applications soon.
Syn th esis of F er r ocen yl Dip h osp h in e 1f. (SP ,1R,2S)-
(-)-N-Meth yl-N-(1-h yd r oxy-1-p h en yl)p r op -2-yl-P -(fer r o-
cen yl)-P -(p h en yl)-p h osp h in a m id e bor a n e, 5. Ferrocene
(72 mmol) was dissolved in 80 mL of THF, degassed, and cooled
to 0 °C. t-BuLi (60 mmol of a 1.7 M solution in pentane) was
slowly added via a syringe and the resulting monolithiofer-
rocene suspension was kept at that temperature for 20 min.
Then it was added via a Teflon cannula to a precooled (-78
°C) solution of (2RP,4S,5R)-oxazaphospholidine borane 4 (35
mmol) in 50 mL of THF. The reaction mixture was allowed to
reach room temperature over a period of 12 h and quenched
with water. THF was evaporated, and the residue was
extracted twice with CH2Cl2. The combined organic layers were
dried over MgSO4 and filtered, and the solvent was removed
in vacuo. The crude product was subjected to column chroma-
tography (SiO2, toluene/ethyl acetate ) 96:4), at which the
diastereomeric (RP)-byproduct (<10%) was eluted first, fol-
lowed by (SP)-configured phosphine amide borane. Yield: 81%.
1
Mp: 94 °C. H NMR (400.13 MHz): δ 0.85-1.33 (m, br, 3H);
1.10 (d, 3H, J ) 6.5 Hz); 1.80 (s, 1H); 2.23 (d, 3H, J HP ) 8.6
Hz); 4.07 (m, 1H); 4.09 (m, 1H); 4.14 (s, 5H); 4.33 (m, 1H);
4.37 (m 1H); 4.45 (m, 1H); 4.73 (d, br, 1H, J ) 5.0 Hz); 7.12-
7.31 (m, 10H) ppm. 13C NMR (100.62 MHz): δ 13.40 (CH3);
30.94 (d, CH3, J CP ) 3.1 Hz); 58.11 (d, CH, J CP ) 9.2 Hz); 70.07
(5CH); 70.94 (d, CH, J CP ) 6.9 Hz); 71.08 (d, CH, J CP ) 8.2
Hz); 71.80 (d, C, J CP ) 68.7 Hz); 72.07 (d, CH, J CP ) 13.0 Hz);
72.37 (d, CH, J CP ) 7.6 Hz); 78.80 (d, CH, J CP ) 5.4 Hz); 126.54
(CH); 127.61 (CH); 128.10 (d, CH, J CP ) 10.7 Hz); 128.37 (CH);
130.36 (d, CH, J CP ) 1.5 Hz); 131.41 (d, CH, J CP ) 10.7 Hz);
132.86 (d, C, J CP ) 70.4 Hz); 142.58 (C) ppm. 31P NMR (121.50
MHz): δ 70.05 (q, br, J PB ) 80.1 Hz) ppm. [R]20 ) -118.7
D
(c ) 0.59; CH2Cl2). HRMS (FAB+): m/z calcd for C26H31
BFeNOP 471.1586, obsd 471.1598. Anal. Calcd for C26H31
-
-
BFeNOP: C, 66.28; H, 6.63; N, 2.97. Found: C, 66.24; H, 6.60;
N, 2.82.
(R)-(+)-Met h yl (F er r ocen ylp h en yl)p h osp h in it e Bo-
r a n e, 6. Phosphinamide borane 5 (27 mmol) was dissolved in
220 mL of degassed methanol. At 0 °C, concentrated sulfuric
acid (28.35 mmol, 1.05 equiv) was added dropwise, and the
solution was stirred for 15 h at room temperature. The
progress of the reaction was monitored by TLC; however,
complete conversion could not be obtained. Addition of up to
1.5 equiv of sulfuric acid gave no improvement but, instead,
resulted in extensive decomposition. The reaction mixture was
concentrated and the residue directly subjected to column
chromatography (SiO2, hexane/ethyl acetate ) 95:5). The
desired product was eluted first; after a change of the eluent
composition (hexane/ethyl acetate ) 1:1) unreacted starting
material (∼30%) was recovered. Yield: 31%. Mp: 98-100 °C.
1H NMR (400.13 MHz): δ 0.62-1.37 (m, br, 3H); 3.62 (d, 3H,
J HP ) 12.5 Hz); 4.13 (s, 5H); 4.26 (m, 1H); 4.42 (m, 1H); 4.48
(m, 1H); 4.64 (m, 1H); 7.45-7.56 (m, 3H); 7.83-7.91 (m, 2H)
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out under
an atmosphere of argon using standard Schlenk techniques.
THF and Et2O were distilled from sodium/benzophenone ketyl,
CH2Cl2 and acetonitrile from CaH2, and toluene and methanol
from sodium wire under nitrogen. Melting points are uncor-
rected. 1D and 2D NMR spectra were recorded on 250, 300,
400, 500, and 600 MHz instruments; CDCl3 was used as
solvent, if not mentioned otherwise. Phosphorus-carbon cou-
pling constants (J CP) were identified by comparison of J -
modulated 13C (APT) spectra measured at different magnetic
field strengths. Optical rotations were measured in a thermo-
stated polarimeter with l ) 1 dm. Mass spectra were recorded
(40) Bishop, J . J .; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.;
Merrill, R. E.; Smart, J . C. J . Organomet. Chem. 1971, 27, 241.
(41) von Matt, P.; Loiseleur, O.; Koch, G.; Pfaltz, A.; Lefeber, C.;
Feucht, T.; Helmchen, G. Tetrahedron: Asymmetry 1994, 5, 573.
(42) Heumann, A.; Åkermark, B.; Hansson, S. Org. Synth. 1990, 68,
109.
(39) RajanBabu, T. V.; Casalnuovo, A. L. J . Am. Chem. Soc. 1996,
118, 6325.

768 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
ppm. 13C NMR (100.58 MHz): δ 53.71 (d, CH3, J CP ) 3.1 Hz);
(0.2 mmol) was introduced in a glass tube and toluene (3 mL),
trichlorosilane (10 mmol), and triethylamine (15 mmol) were
added consecutively. The tube was sealed under vacuum,
placed in an autoclave, and heated at 140 °C for 60 h. After
treatment, the tube was cooled in liquid nitrogen and opened.
NaOH solution (15 M) was carefully added to the crude product
mixture, and the resulting solution was extracted with CH2-
Cl2. The combined organic layers were washed with water,
dried (MgSO4), and the solvent was evaporated. For separation
of isomerized byproducts, the residue was dissolved in 5 mL
of degassed THF, and BH3‚THF (0.5 mL of a 1 M solution in
THF) was added dropwise. After TLC indicated complexation
to be complete, the solvent was evaporated and the crude
borane complexes were chromatographed (SiO2, CH2Cl2/hexane
) 1:1.). The desired C2-symmetrical diphosphine was eluted
first, followed by not further separated epimerized C1-sym-
metrical and doubly phosphorus-isomerized byproducts (∼30%).
For deprotection, the thus obtained diborane complex of 3c
was dissolved in degassed diethylamine (1 mL) and stirred
overnight at room temperature. The solvent was removed in
vacuo, and the residual diphosphine was subjected to column
chromatography (SiO2, CH2Cl2/hexane ) 1:1) to give the
enantiopure ligand as orange crystals. Yield: 38%. Mp: 228-
69.96 (5CH); 71.15 (d, C, J CP ) 70.4 Hz); 71.57 (d, CH, J CP
)
10.7 Hz); 71.82 (d, CH, J CP ) 9.1 Hz); 71.98 (d, CH, J CP ) 13.1
Hz); 72.00 (d, CH, J CP ) 7.9 Hz); 128.44 (d, CH, J CP ) 9.9 Hz);
131.10 (d, CH, J CP ) 11.5 Hz); 131.81 (d, CH, J CP ) 2.3 Hz);
131.94 (d, C, J CP ) 63.5 Hz) ppm. 31P NMR (121.44 MHz): δ
108.45 (q, br, J PB ) 75 Hz) ppm. [R]20D ) +30.5 (c ) 0.62; CH2-
Cl2). HRMS (EI+): m/z calcd for C17H20BFeOP 338.0694, obsd
338.0703. Anal. Calcd for C17H20BFeOP: C, 60.41; H, 5.96.
Found: C, 60.46; H, 5.78.
(S,S)-(+)-1,1′-Bis(fer r ocen ylp h en ylp h osp h in o)fer r o-
cen e, 1f. Phosphinite borane (R)-6 (8 mmol) was dissolved in
10 mL of THF and cooled to -40 °C. A suspension of
1,1′-dilithioferrocene (4 mmol) in 7 mL of THF and 35 mL of
Et2O was cooled and added slowly via a Teflon cannula to the
phosphinite solution. The reaction mixture was warmed to
ambient temperature over a period of 15 h and then quenched
with water. The solvent was removed in vacuo and the residue
was extracted with CH2Cl2. The combined organic layers were
dried (MgSO4), filtered, and concentrated. The residue was
chromatographed (SiO2, hexane/CH2Cl2 ) 1:1) to remove small
amounts of monosubstituted and meso-configured byproducts.
The diastereomerically pure diphosphine diborane complex
was then subjected to deprotection using an excess of degassed
diethylamine (20 mL). After stirring for 15 h at room temper-
ature, the solvent was evaporated and the crude product was
chromatographically purified (SiO2, hexane/CH2Cl2 ) 1:1).
Repeated recrystallizations from CH2Cl2/hexane (diffusion
method) removed small amounts of isomerized meso-diphos-
phine and left the enantiopure ligand (S,S)-1f. Yield: 54%.
1
230 °C (dec). H NMR (400.13 MHz): δ 3.86 (m, 2H); 4.12 (s,
10H); 4.49 (m, 2H); 4.95 (m, 2H); 5.93 (t, br, 2H, J ) 7.6 Hz);
6.43 (m 2H); 7.06 (d, 2H, J ) 8.1 Hz); 7.19-7.32 (m, 10H);
7.41-7.45 (m, 4H); 7.61 (d, 2H, J ) 7.8 Hz); 8.02 (dd, 2H, J )
3.0; 8.1 Hz) ppm. 13C NMR (100.62 MHz): δ 70.06 (d, CH,
J CP ) 4.0 Hz); 70.14 (5CH); 72.22 (d, CH, J CP ) 4.6 Hz); 77.00
(d, CH, J CP ) 11.5 Hz); 77.93 (d, C, J CP ) 9.2 Hz); 91.05 (d, C,
J CP ) 31.2 Hz); 124.66 (CH); 125.02 (CH); 125.10 (d, CH,
J CP ) 2.3 Hz); 126.15 (d, CH, J CP ) 24.5 Hz); 127.94 (CH);
127.98 (d, CH, J CP ) 8.0 Hz); 128.17 (d, CH, J CP ) 1.5 Hz);
128.83 (CH); 130.84 (CH); 133.02 (d, C, J CP ) 3.8 Hz); 133.61
(d, C, J CP ) 19.9 Hz); 134.68 (d, CH, J CP ) 22.1 Hz); 135.79
(d, C, J CP ) 13.0 Hz); 138.12 (d, C, J CP ) 7.7 Hz) ppm. 31P
1
Mp: 75 °C. H NMR (400.13 MHz): δ 3.75 (m, 2H); 3.91 (m,
2H); 4.00 (s, 10H); 4.05 (m, 2H); 4.08 (m, 2H); 4.12 (m, 2H);
4.18 (m, 4H); 4.22 (m, 2H); 7.27-7.31 (m, 6H); 7.44-7.50 (m,
4H) ppm. 13C NMR (100.62 MHz): δ 69.00 (5CH); 69.83 (d,
CH, J CP ) 3.8 Hz); 70.52 (d, CH, J CP ) 3.8 Hz); 71.60 (m, CH);
71.95 (d, CH, J CP ) 13.7 Hz); 72.16 (m, CH); 72.54 (d, CH,
J CP ) 10.6 Hz); 72.58 (d, CH, J CP ) 15.3 Hz); 73.61 (d, CH,
NMR (121.50 MHz): δ -30.72 (s) ppm. [R]20 ) +181.1 (c )
D
J CP ) 16.8 Hz); 77.80 (d, C, J CP ) 4.6 Hz); 78.37 (d, C, J CP
)
0.13; CH2Cl2). HRMS (FAB+): m/z calcd for C52H41Fe2P2 (MH+)
839.1382; obsd 839.1351. Anal. Calcd for C52H40Fe2P2: C,
74.48; H, 4.81. Found: C, 74.62; H, 4.67.
5.4 Hz); 127.84 (d, CH, J CP ) 7.6 Hz); 128.77 (CH); 133.83
(d, CH, J CP ) 20.7 Hz); 138.98 (d, C, J CP ) 9.2 Hz) ppm. 31P
NMR (121.50 MHz): δ -29.54 (s) ppm. [R]20 ) +36.3 (c )
Asym m etr ic Allylic Alk yla tion Rea ction s 1, 2, a n d 3
(Typ ica l P r oced u r e). In a Schlenk tube [Pd(η3-C3H5)Cl]2
(0.005 mmol) and the respective ligand (0.01 mmol) were
dissolved in 1 mL of CH2Cl2 and degassed. (E)-1,3-Diphenyl-
prop-2-en-1-yl acetate, (E)-pent-3-en-2-yl acetate, or cyclohex-
2-en-1-yl acetate (1 mmol) was added as the substrate, and
after 20 min of stirring at room temperature, dimethyl
malonate (3 mmol), BSA (3 mmol), and a catalytic amount of
KOAc were added consecutively. The reaction mixture was
degassed again and stirred at the given temperature. If TLC
indicated no further conversion, the reaction was quenched
by dilution with Et2O (15 mL); the organic layer was washed
twice with saturated NH4Cl solution and dried over Na2SO4.
Filtration and removal of solvent left a red oil which was
chromatographed (SiO2; petroleum ether/CH2Cl2 ) 1:1 (reac-
tion 1), petroleum ether/Et2O ) 3:1 (reactions 2 and 3)) to give
analytically pure products.43 Determination of ee values was
performed by chiral HPLC (Chiralcel OD-H, n-hexane/2-
propanol ) 98:2, 0.5 mL‚min-1, tR (R) ) 15.4 min, tR (S) )
16.8 min; reaction 1), chiral GC (50% octakis(6-O-methyl-2,3-
di-O-pentyl)-γ-cyclodextrin, isothermal, T ) 55 °C, tR (S) ) 95
min, tR (R) ) 98 min; reaction 2) and by optical rotation
D
0.30; CH2Cl2). HRMS (FAB+): m/z calcd for C42H37Fe3P2
771.0419, obsd 771.0413. Anal. Calcd for C42H36Fe3P2: C,
65.49; H, 4.71. Found: C, 65.94; H, 4.50.
Syn th esis of Bifer r ocen yl Dip h osp h in e 3c. (RP ,Sm ,Sm ,-
RP )-(+)-2,2′-Bis(1-n a p h t h ylp h en ylp h osp h in oxy)-1,1′-b i-
fer r ocen yl, 8. The (RP,Rm)-o-iodophosphine oxide 7 (2 mmol)
was dissolved in 2 mL of CH2Cl2, and activated copper powder
(10 mmol) was added under stirring. The solvent was removed
in vacuo and the brown residue was heated at 135 °C for 48
h. After this treatment, the crude product was agitated with
CH2Cl2, filtered over Celite, and concentrated. Column chro-
matography (SiO2, CH2Cl2/ethyl acetate ) 4:1) eluted unre-
acted starting material first, followed by enantiopure (RP,Sm,-
1
Sm,RP)-8. Yield: 35% Mp: 180 °C. H NMR (400.13 MHz): δ
4.10 (s, 10H); 4.17 (m, 2H); 4.33 (m, 2H); 4.95 (m, 2H); 7.02
(dt, br, 4H, J ) 3.0; 8.1 Hz); 7.19-7.24 (m, 2H); 7.29 (ddd,
2H, J ) 2.2; 7.2; 8.3 Hz); 7.37-7.48 (m, 8H); 7.82 (dd, br, 2H,
J ) 6.8; 14.2 Hz); 7.85 (d, br, 2H, J ) 7.8 Hz); 7.90 (d, br, 2H,
J ) 8.1 Hz); 8.68 (d, br, 2H, J ) 8.6 Hz) ppm. 13C NMR (100.61
MHz): δ 70.13 (d, CH, J CP ) 10.7 Hz); 70.56 (5CH); 73.50 (d,
CH, J CP ) 13.8 Hz); 74.17 (d, C, J CP ) 114.0 Hz); 79.15 (d,
CH, J CP ) 9.2 Hz); 88.65 (d, C, J CP ) 10.7 Hz); 124.40 (d, CH,
J CP ) 13.8 Hz); 126.04 (CH); 126.50 (CH); 127.72 (d, CH,
J CP ) 4.6 Hz); 127.91 (d, CH, J CP ) 12.2 Hz); 128.71 (d, CH,
J CP ) 0.9 Hz); 130.92 (d, CH, J CP ) 2.3 Hz); 131.01 (d, C,
J CP ) 102.5 Hz); 131.70 (d, CH, J CP ) 10.7 Hz); 132.34 (d, CH,
measurements ([R]20 ) -46.1 for (S)-dimethyl 2-(cyclohex-2-
D
en-1-yl)malonate,44 reaction 3).
Asym m etr ic Allylic Am in a tion /Im id a tion Rea ction s 4
a n d 5 (Typ ica l P r oced u r e). In a Schlenk tube [Pd(η3-C3H5)-
Cl]2 (0.005 mmol) and the respective ligand (0.01 mmol) were
J CP ) 3.1 Hz); 133.63 (d, C, J CP ) 3.1 Hz); 133.71 (d, C, J CP
2.3 Hz); 133.90 (d, CH, J CP ) 9.9 Hz); 136.01 (d, C, J CP ) 105.5
Hz) ppm. 31P NMR (161.98 MHz): δ 33.12 (s) ppm. [R]20
)
(43) Product characterization data were found in agreement with
the reported literature; see, for example: Brown, J . M.; Hulmes, D. I.;
Guiry, P. J . Tetrahedron 1994, 50, 4493. Vyskocil, S.; Smrcina, M.;
Hanus, V.; Polasˇek, M.; Kocovsky, P. J . Org. Chem. 1998, 63, 7738.
Widhalm, M.; Wimmer, P.; Klintschar, G. J . Organomet. Chem. 1996,
523, 167.
)
D
+473.9 (c ) 0.30; CH2Cl2). HRMS (FAB+): m/z calcd for C52H41
-
Fe2O2P2 (MH+) 871.1281; obsd 871.1303. Anal. Calcd for
C
52H40Fe2O2P2: C, 71.75; H, 4.63. Found: C, 71.98; H, 4.82.
(SP ,Sm ,Sm ,SP )-(+)-2,2′-Bis(1-n aph th ylph en ylph osph in o)-
1,1′-bifer r ocen yl, 3c. Diphosphine dioxide (RP,Sm,Sm,RP)-8
(44) Sennhenn, P.; Gabler, B.; Helmchen, G. Tetrahedron Lett. 1994,
35, 8595.

Asymmetric Allylic Substitution Reactions
J . Org. Chem., Vol. 66, No. 3, 2001 769
dissolved in 1 mL (reaction 4) or 2 mL (reaction 5) of CH2Cl2
and degassed. (E)-1,3-Diphenylprop-2-en-1-yl acetate (1 mmol)
was added, and the solution was stirred for 20 min at ambient
temperature. Subsequently, benzylamine (1.2 mmol) or N-
phthalimide potassium salt (1.2 mmol) was added, and the
reaction was kept at the given temperature until TLC indi-
cated no further progress. The solvent was removed in vacuo,
and the residue was purified by column chromatography (SiO2;
petroleum ether/ethyl acetate ) 95:5 for reaction 4 or petro-
leum ether/Et2O ) 4:1 for reaction 5) to give pure products.45
Determination of ee values was performed by chiral HPLC
(Chiralcel-OD; n-hexane/2-propanol/diethylamine ) 99.55:0.25:
0.2, 0.5 mL‚min-1, tR (R) ) 37.8 min, tR (S) ) 41.0 min for
reaction 4 and n-hexane/2-propanol ) 98:2, 0.5 mL‚min-1, tR
(R) ) 26.2 min, tR (S) ) 22.8 min for reaction 5).
3.76 (m, 1H, fc); 3.90 (m, 1H, fc); 4.08 (m, 1H, fc); 4.18 (m, 1H,
fc); 4.36 (t, 1H, anti-allyl, J ) 11.5 Hz); 4.96 (m, 1H, fc); 5.30
(m, br, 1H, fc); 6.42 (t, 1H, syn-allyl, J ) 13.0 Hz); 6.53 (m,
1H, anti-allyl), 6.54-6.59 (m, 5H); 6.63-6.67 (m, 2H); 6.68-
6.85 (m, 12H); 7.01 (t, 2H, J ) 7.4 Hz); 7.03-7.09 (m, 3H);
7.14-7.18 (m, 3H); 7.19-7.25 (m, 6H); 7.43-7.47 (m, 3H);
7.57-7.60 (m, 2H) ppm. 31P NMR (161.98 MHz): δ 28.86 (d,
J ) 72.0 Hz); 31.02 (d, J ) 73.2 Hz) ppm. Anal. Calcd for
C
61H49BF4Fe2P2Pd‚1/2CH2Cl2: C, 65.05; H, 4.44. Found: C,
64.87; H, 4.53.
{(1,3-Dip h en yl-η3-a llyl)[(SP ,Rm ,Rm ,SP )-3a ]P d }BF 4, 10a
1
(Ma in Isom er ). Yield: 81%. H NMR (600.13 MHz, CD2Cl2):
δ 3.11 (m, H3); 3.47 (m, H6); 3.59 (t, J ) 11.8 Hz, H33); 4.00
(s, 10H, fc); 4.01 (m, H2); 4.15 (m, H5); 4.69 (m, H1); 4.78 (m,
H4); 4.92 (t, J ) 10.2 Hz, H31); 5.78 (t, J ) 12.8 Hz, H32);
5.91 (m, H39/43); 6.16 (m, br, H34/38); 6.48 (t, br, J ) 8.0 Hz,
H35/37); 6.87 (m, H36); 6.88 (t, J ) 7.7 Hz, H40/42); 7.06 (t,
br, J ) 7.2 Hz, H41); 7.11 (d, J ) 7.1 Hz, H7*); 7.12 (d, J )
7.4 Hz, H19*); 7.20 (t, br, J ) 7.1 Hz, H8); 7.25 (m, H27/29);
7.26 (m, H12); 7.37 (m, H26/30); 7.39 (m, H20); 7.44 (t, br,
J ) 8.2 Hz, H28); 7.47 (t, br, J ) 7.2 Hz, H24); 7.59 (m, H11);
7.62 (m, H15/17); 7.65 (m, H16); 7.67 (m, H23); 7.80 (d, J )
8.5 Hz, H9); 7.86 (d, J ) 8.8 Hz, H10); 8.06 (dd, J ) 7.1; 12.2
Hz, H14/18); 8.09 (d, J ) 8.5 Hz, H22); 8.12 (d, J ) 8.7 Hz,
H21); 8.19 (dd, J ) 2.8; 8.2 Hz, H13); 8.39 (d, br, J ) 8.7 Hz,
H25) ppm. 13C NMR (150.91 MHz, coupling constants not
determined): δ 69.0 (C2); 69.2 (C5); 70.7 (10C, fc); 75.4 (C3);
75.5 (C6); 76.0 (C45); 76.4 (C47); 77.4 (C1); 77.7 (C4); 81.9
(C33); 86.8 (C46); 87.0 (C44); 98.1 (C31); 108.7 (C32); 120.1
(C48); 124.3 (C13); 124.5 (C52); 124.7 (C20); 125.7 (C8); 126.3
(C12); 126.4 (C39/43); 126.5 (C34/38); 126.5 (C11); 126.6 (C25);
126.8 (C24); 127.2 (C23); 127.5 (C41); 127.8 (C35/37); 128.1
(C27/29); 128.4 (C36); 128.5 (C40/42); 128.7 (C15/17); 129.8
(C10); 130.1 (C22); 131.3 (C28); 131.5 (C16); 131.7 (C7); 132.1
(C9); 132.2 (C56); 132.2 (C21); 133.2 (C19); 133.4 (C55); 133.5
(C49); 133.6 (C53); 133.9 (C26/30); 134.1 (C14/18); 134.1 (C51);
134.3 (C50); 134.4 (C54); 135.9 (C57) ppm. 31P NMR (161.97
MHz): δ 10.59 (d, J ) 74.4 Hz); 11.96 (d, J ) 73.2 Hz) ppm.
MS (FAB+): m/z ) 1137.2 (M+); 945.1; 709.1; 603.1. Anal.
Syn th esis of Allyl P a lla d iu m Com p lexes 9a , 9d , a n d
10a (Typ ica l P r oced u r e). In a Schlenk tube, [(1,3-diphenyl-
η3-allyl)PdOAc]2 (0.025 mmol) was dissolved in 2 mL of
degassed acetone. After addition of AgBF4 (0.05 mmol), the
suspension was stirred for 20 min at ambient temperature and
then filtered through Celite into a second Schlenk tube
containing a solution of the respective ligand (0.05 mmol) in 1
mL of CH2Cl2. After stirring for another 20 min, the reaction
mixture was concentrated, and the product precipitated by
addition of 3 mL of Et2O. It was collected on a glass filter,
washed with hexane, and dried under vacuum.
{(1,3-Dip h en yl-η3-a llyl)[(S,S)-1a ]P d }BF 4, 9a (Ma jor Iso-
1
m er ). Yield: 86%. H NMR (600.13 MHz; CD2Cl2, 223 K): δ
3.38 (m, H8); 4.03 (m, H7); 4.14 (m, H5); 4.14 (m, H1); 4.24 (m
H6); 4.44 (m, H2); 4.58 (t, J ) 11.3 Hz, H33); 4.70 (m H4);
4.96 (m, H3); 5.75 (t, J ) 8.7 Hz, H32); 6.08 (t, J ) 12.3 Hz,
H34); 6.28 (m, H35); 6.42 (m, H9); 6.43 (m, br, H45); 6.53 (m,
br, H42); 6.60 (t, J ) 7.4 Hz, H31); 6.81 (m, br, H44); 6.89 (t,
J ) 7.2 Hz, H10); 6.91 (m, br, H16); 6.98 (m, H26); 6.99 (m,
H37); 7.00 (m, H43); 7.07 (m, H27); 7.09 (m, H19*); 7.10 (m,
H17*); 7.11 (m, H38); 7.28 (m, br, H41); 7.30 (m, H39); 7.31
(m, H18); 7.33 (m, H36); 7.40 (m, H25); 7.40 (m, H30); 7.56
(m, H13); 7.57 (m, H14); 7.64 (m, H40); 7.76 (t, J ) 7.2 Hz,
H29); 7.80 (d, J ) 8.2 Hz, H11); 7.93 (m, H12); 8.01 (d, J )
8.2 Hz, H24); 8.04 (d, br, J ) 7.4 Hz, H15); 8.18 (m, H28);
8.24 (t, J ) 7.4 Hz, H22); 8.36 (d, J ) 8.2 Hz, H23); 8.74 (dd,
br, J ) 6.9; 15.3 Hz, H20); 9.19 (dd, J ) 6.7; 20.5 Hz, H21)
ppm. 31P NMR (121.50 MHz, CD2Cl2, 230K): δ 24.53 (d, J )
57.5 Hz); 27.82 (d, J ) 57.3 Hz) ppm. HRMS (FAB+): m/z calcd
for C57H46FeP2Pd (MH+) 954.1427, obsd 954.1401. *Assign-
ment exchangeable.
Calcd for
C67H53BF4Fe2P2Pd‚CH2Cl2: C, 62.35; H, 4.23.
Found: C, 62.56; H, 4.04. *Assignment exchangeable.
1
Min or Isom er 9a . H NMR (600.13 MHz; CD2Cl2, 223 K)
(selected signals, numbering refers to exchange with major
isomer): δ 3.46 (m, H5′); 3.74 (m, H1′); 4.09 (m, H6′); 4.16 (m,
H2′); 4.28 (m, H7′); 4.28 (m, H8′); 4.48 (m, H3′); 4.86 (m, H4′);
4.91 (t, J ) 13.1 Hz, anti-allyl-H); 6.06 (m, syn-allyl-H); 6.38
(m, anti-allyl-H) ppm. 31P NMR (121.50 MHz; CD2Cl2, 230K):
δ 18.86 (d, J ) 59.6 Hz); 26.43 (d, J ) 59.7 Hz) ppm.
Min or Isom er 10a (16%). 31P NMR (161.97 MHz, CD2Cl2):
δ -12.93 (m, br); -8.35 (m, br) ppm.
Min or Isom er 10a (4%). 31P NMR (161.97 MHz, CD2Cl2):
δ 7.81 (d, J ) 68.2 Hz); 9.97 (d, J ) 67.0 Hz) ppm.
Exp er im en ta l Deta ils for Cr ysta l Str u ctu r e Deter m i-
n a t ion of {(1,3-Dip h en yl-η3-a llyl)[(S,S)-1a ]P d }BF 4, 9a .
C
57H45FeP2Pd‚C6H6‚BF4, fw ) 1119.04, colorless needle,
0.63 × 0.13 × 0.13 mm3, triclinic, P1 (No. 1), a ) 9.7082(1),
b ) 10.2737(2), c ) 13.2188(3) Å, R ) 96.039(1)°, â ) 95.557-
(1)°, γ ) 99.533(1)°, V ) 1284.15(4) Å3, Z ) 1, F ) 1.447 g
cm-3, 22845 measured reflections, 11540 unique reflections
(Rint ) 0.0441). An absorption correction was not considered
necessary (µ ) 0.751 mm-1); 647 refined parameters, 108
restraints. R (I > 2σ(I)): R1 ) 0.0357, wR2 ) 0.0905. R (all
data): R1 ) 0.0366, wR2 ) 0.0913. S ) 1.184. Intensities were
measured on Nonius Kappa CCD diffractometer with rotating
anode (Mo KR, λ ) 0.71073 Å) at a temperature of 150 K up
{(1,3-Diph en yl-η3-allyl)[(R,R)-1d]P d}BF4, 9d. Yield: 73%.
1H NMR (600.13 MHz): δ 2.57 (m, 1H, fc); 3.38 (m, 1H, fc);
(45) Product characterization data were found in agreement with
the reported literature; see, for example: Bower, J . F.; J umnah, R.;
Williams, A. C.; Williams, J . M. J . J . Chem. Soc., Perkin Trans. 1 1997,
1411. Bower, J . F.; J umnah, R.; Williams, A. C.; Williams, J . M. J . J .
Chem. Soc., Perkin Trans. 1 1997, 1411.

770 J . Org. Chem., Vol. 66, No. 3, 2001
Nettekoven et al.
to a resolution of (sin ϑ/λ)max ) 0.65 Å-1. The structure was
interactions, as well as to J . A. J . Geenevasen and A.
M. van den Burg for 500 MHz NMR measurements.
Financial support by The Netherlands Ministry of
Economic Affairs (project IKA 94081) is gratefully
acknowledged, as is a special grant to U.N. Part of this
work (M.L. and A.L.S.) was financially supported by the
Council for Chemical Sciences of The Netherlands
Organization for Scientific Research (CW-NWO).
solved with automated Patterson methods (DIRDIF-97)46 and
47
refined with the program SHELXL97
against F2 of all
reflections. Non-hydrogen atoms were refined freely with
anisotropic displacement parameters. Hydrogen atoms were
refined as rigid groups. The drawing, structure calculations,
and checking for higher symmetry was performed with the
program PLATON.48
Ack n ow led gm en t. We are indebted to Dr. J . N. H.
Reek for valuable discussions concerning π-electronic
Su p p or tin g In for m a tion Ava ila ble: Crystal structure
refinement data for compound 9a including atomic coordinates,
isotropic and anisotropic displacement parameters and a
complete listing of bond angles and bond distances. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(46) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF 97 Program System, Technical Report of the Crystallography
Laboratory; University of Nijmegen: Nijmegen, The Netherlands, 1997.
(47) Sheldrick, G. M. SHELXL-97. Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(48) Spek, A. L. PLATON. A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2000.
J O001175U