Cationic [2,6-Bis(2′-oxazolinyl)phenyl]palladium(II) Complexes: Catalysts for the Asymmetric Michael Reaction

Article abstract of DOI:10.1021/om990710h

Reaction of 1,3-dicyanobenzene with β-amino alcohols (S)-H₂NCHRCH₂OH (R = ⁱPr, ⁱBu, ^tBu, CH₂Cy, CH₂Ph) and (R)-H₂NCHPhCH₂OH gave new 1,3-bis(2′-oxazolinyl)benzenes (30-51%). These, together with 1,3-bis(4′,4′-dimethyl-2′-oxazolinyl)benzene, were treated with LDA/TMEDA followed by the addition of PdBr₂(1,5-COD) to give [2,6-bis(2′-oxazolinyl)phenyl]-palladium(II) bromide complexes (21-41%). In two cases no complexes were obtained (R = Ph, CH₂Ph) due to ring opening of the oxazolines by LDA/TMEDA. Treatment of the palladium complexes with AgBF₄, AgOTf, or AgSbF₆ in wet CH₂Cl₂ provided a series of cationic [2,6-bis(2′-oxazolinyl)phenyl]palladium complexes (28-87%) containing water coordinated to palladium, as established by an X-ray crystal structure analysis of (S,S)-[2,6-bis(4′-isopropyl-2′-oxazolinyl)phenyl]aquopalladium(II) trifluoromethanesulfonate. All of the cationic complexes proved to be efficient catalysts for the Michael reaction between α-cyanocarboxylates and methyl vinyl ketone and between acrylonitrile and activated Michael donors. Selectivities of up to 34% ee were obtained for the formation of (R)-ethyl 2-cyano-2-methyl-5-oxohexanoate.

Full text of DOI:10.1021/om990710h

1282
Organometallics 2000, 19, 1282-1291
Ca tion ic [2,6-Bis(2′-oxa zolin yl)p h en yl]p a lla d iu m (II)
Com p lexes: Ca ta lysts for th e Asym m etr ic Mich a el
Rea ction
Mark A. Stark, Geraint J ones, and Christopher J . Richards*
Department of Chemistry, Cardiff University, P.O. Box 912, Cardiff CF10 3TB, U.K.
Received September 8, 1999
i
Reaction of 1,3-dicyanobenzene with â-amino alcohols (S)-H2NCHRCH2OH (R ) iPr, Bu,
tBu, CH2Cy, CH2Ph) and (R)-H2NCHPhCH2OH gave new 1,3-bis(2′-oxazolinyl)benzenes (30-
51%). These, together with 1,3-bis(4′,4′-dimethyl-2′-oxazolinyl)benzene, were treated with
LDA/TMEDA followed by the addition of PdBr2(1,5-COD) to give [2,6-bis(2′-oxazolinyl)phenyl]-
palladium(II) bromide complexes (21-41%). In two cases no complexes were obtained (R )
Ph, CH2Ph) due to ring opening of the oxazolines by LDA/TMEDA. Treatment of the
palladium complexes with AgBF4, AgOTf, or AgSbF6 in wet CH2Cl2 provided a series of
cationic [2,6-bis(2′-oxazolinyl)phenyl]palladium complexes (28-87%) containing water co-
ordinated to palladium, as established by an X-ray crystal structure analysis of (S,S)-[2,6-
bis(4′-isopropyl-2′-oxazolinyl)phenyl]aquopalladium(II) trifluoromethanesulfonate. All of the
cationic complexes proved to be efficient catalysts for the Michael reaction between
R-cyanocarboxylates and methyl vinyl ketone and between acrylonitrile and activated Michael
donors. Selectivities of up to 34% ee were obtained for the formation of (R)-ethyl 2-cyano-
2-methyl-5-oxohexanoate.
In tr od u ction
complexes 211and proline-derived NCN complexes 3;12a
the former have been applied as catalysts for the
asymmetric aldol reaction between aldehydes and meth-
yl isocyanoacetate11b,d and the latter as catalysts for
Kharasch addition.12a The modest enantioselectivities
observed in these reactions contrast with the neutral
Transition-metal complexes derived from anionic ter-
dentate ligands of general structure 1 (XCX) were first
reported in 1976 with the synthesis of square-planar
platinum group metal containing complexes with X
corresponding to PtBu2.1 More recently, there has been
(2) (a) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259,
C6. (b) Nemeh, S.; J ensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442. (c) Haenel, M. W.; J akubik, D.; Kru¨ger,
C.; Betz, P. Chem. Ber. 1991, 124, 333. (d) Bennett, M. A.; J in, H.;
Willis, A. C. J . Organomet. Chem. 1993, 451, 249. (e) Steffey, B. D.;
Miedaner, A.; Maciejewski-Farmer, M. L.; Bernatis, P. R.; Herring, A.
M.; Allured, V. S.; Carperos, V.; DuBois, D. L. Organometallics 1994,
13, 4844. (f) Cross, R. J .; Kennedy, A. R.; Muir, K. W. J . Organomet.
Chem. 1995, 487, 227. (g) Cross, R. J .; Kennedy, A. R.; Manojlovic-
Muir, L.; Muir, K. W. J . Organomet. Chem. 1995, 493, 243. (h) Karlen,
T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten, G. Organome-
tallics 1996, 15, 5687. (i) J ia, G.; Lee, H. M.; Williams, I. D. J .
Organomet. Chem. 1997, 534, 173. (j) Dani, P.; Karlen, T.; Gossage,
R. A.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Am. Chem. Soc.
1997, 119, 11317. (k) Vigalok, A.; Uzan, O.; Shimon, L. J . W.; Ben-
David, Y.; Martin, J . M. L.; Milstein, D. J . Am. Chem. Soc. 1998, 120,
12539.
(3) (a) Errington, J .; McDonald, W. S.; Shaw, B. L. J . Chem. Soc.,
Dalton Trans. 1980, 2312. (b) Kickham, J . E.; Loeb, S. J . Inorg. Chem.
1994, 33, 4351. (c) Kickham, J . E.; Loeb, S. J . Organometallics 1995,
14, 3584. (d) Kickham, J . E.; Loeb, S. J .; Murphy, S. L. Chem. Eur. J .
1997, 3, 1203.
(4) (a) Mehring, M.; Schu¨mann, M.; J urkschat, K. Organometallics
1998, 17, 1227. (b) Vicente, J .; Arcas, A.; Blasco, M.-A.; Lozano, J .; de
Arellano, M. C. R. Organometallics 1998, 17, 5374.
(5) (a) Grove, D. M.; van Koten, G.; Ubbels, H. J . C.; Spek, A. L. J .
Am. Chem. Soc. 1982, 104, 4285. (b) Grove, D. M.; van Koten, G.;
Louwen, J . N.; Noltes, J . G.; Spek, A. L.; Ubbels, H. J . C. J . Am. Chem.
Soc. 1982, 104, 6609. (c) Grove, D. M.; van Koten, G.; Ubbels, H. J . C.;
Zoet, R. Organometallics 1984, 3, 1003. (d) Terheijden, J .; van Koten,
G.; Groves, D. M.; Vrieze, K.; Spek, A. L. J . Chem. Soc., Dalton Trans.
1987, 1359. (e) Van Koten, G. Pure Appl. Chem. 1989, 61, 1681. (f)
Gossage, R. A.; Ryabov, A. D.; Spek, A. L.; Stufkens, D. J .; van Beek,
J . A. M.; van Eldik, R.; van Koten, G. J . Am. Chem. Soc. 1999, 121,
2488 and references therein.
a spate of interest in related PCP systems2 and also in
complexes containing SCS-,3 OCO-,4 NCN-,5 and even
PCN-based6 ligands. These are finding widespread
application, particularly as catalysts for reactions as
varied as hydrocarbon activation,7 dehydrogenation,8
Kharasch addition,9 and the Heck reaction.10 In con-
trast, chiral variants of 1 are limited to PCP-containing
* To whom correspondence should be addressed. E-mail:
RichardsCJ @cardiff.ac.uk. Fax: +44 1222 874030.
(1) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020.
(6) Gandelman, M.; Vigalok, A.; Shimon, L. J . W.; Milstein, D.
Organometallics 1997, 16, 3981.
10.1021/om990710h CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/04/2000

Pd(II) 2,6-Bis(2′-oxazolinyl)phenyl Complexes
Organometallics, Vol. 19, No. 7, 2000 1283
C2-symmetric tridentate Pybox ligands 4,13 which in
combination with Rh(III),14 Pd(II),)15 and Cu(II)16 have
been successfully applied in a variety of asymmetric
transformations. These results, together with the ease
of oxazoline synthesis, prompted our investigation into
anionic terdentate ligands derived from 1,3-bis(2′-oxa-
zolinyl)benzenes, and we now report in detail on the syn-
thesis and application of the resulting palladium com-
plexes.17During the course of this work two other groups
reported on related palladium,18,19 platinum,20 and rhod-
ium19 complexes and application of the last group as
catalysts for the enantioselective allylation of alde-
hydes.21
Sch em e 1
Resu lts a n d Discu ssion
Syn th esis of [2,6-Bis(2′-oxa zolin yl)p h en yl]p a lla -
d iu m (II) Br om id es. The known 1,3-bis(2′-oxazolinyl)-
(7) (a) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature
1993, 364, 699. (b) Liou, S.-Y.; Gozin, M.; Milstein, D. J . Am. Chem.
Soc. 1995, 117, 9774. (c) Liou, S.-Y.; Gozin, M.; Milstein, D. J . Chem.
Soc., Chem. Commun. 1995, 1965. (d) Rybtchinski, B.; Vigalok, A.; Ben-
David, Y.; Milstein, D. J . Am. Chem. Soc. 1996, 118, 12406. (e) van
der Boom, M. E.; Kraatz, H.-B.; Ben-David, Y.; Milstein, D. Chem.
Commun. 1996, 2167. (f) Liou, S.-Y.; van der Boom, M. E.; Milstein,
D. Chem. Commun. 1998, 687. (g) van der Boom, M. E.; Liou, S.-Y.;
Ben-David, Y.; Gozin, M.; Milstein, D. J . Am. Chem. Soc. 1998, 120,
13415. (h) van der Boom, M. E.; Higgitt, C. L.; Milstein, D. Organo-
metallics 1999, 18, 2413.
(8) (a) Gupta, M.; Hagen, C.; Flesher, R. J .; Kaska, W. C.; J ensen,
C. M. Chem. Commun. 1996, 2083. (b) Gupta, M.; Kaska, W. C.;
J ensen, C. M. Chem. Commun. 1997, 461. (c) Xu, W. W.; Rosini, G. P.;
Gupta, M.; J ensen, C. M.; Kaska, W. C.; Krogh-J espersen, K.; Goldman,
A. S. Chem. Commun. 1997, 2273. (d) Gupta, M.; Hagen, C.; Kaska,
W. C.; Cramer, R. E.; J ensen, C. M. J . Am. Chem. Soc. 1997, 119, 840.
(e) Lee, D. W.; Kaska, W. C.; J ensen, C. M. Organometallics 1998, 17,
1.
(9) (a) Grove, D. M.; van Koten, G.; Verschuuren, A. H. M. J . Mol.
Catal. 1988, 45, 169. (b) Grove, D. M.; Verschuuren, A. H. M.; van
Koten, G.; van Beek, J . A. M. J . Organomet. Chem. 1989, 372, C1. (c)
Knapen, J . W. J .; van der Made, A. W.; de Wilde, J . C.; van Leeuwan,
P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature 1994,
372, 659. (d) van de Kuil, L. A.; Grove, D. M.; Gossage, R. A.; Zwikker,
J . W.; J enneskens, L. W.; Drenth, W.; van Koten, G. Organometallics
1997, 16, 4985. (e) Gossage, R. A.; van de Kuil, L. A.; van Koten, G.
Acc. Chem. Res. 1998, 31, 423.
(10) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J . Am.
Chem. Soc. 1997, 119, 11687.
(11) (a) Gorla, F.; Venanzi, L. M. Organometallics 1994, 13, 43. (b)
Gorla, F.; Togni, A.; Venanzi, L. M.; Albinati, A.; Lianza, F. Organo-
metallics 1994, 13, 1607. (c) Longmire, J . M.; Zhang, X. Tetrahedron
Lett. 1997, 38, 1725. (d) Longmire, J . M.; Zhang, X.; Shang, M.
Organometallics 1998, 17, 4374.
(12) (a) van de Kuil, L. A.; Veldhuizen, Y. S. J .; Grove, D. M.;
Zwikker, J . W.; J enneskens, L. W.; Drenth, W.; Smeets, W. J . J .; Spek,
A. L.; van Koten, G. Recl. Trav. Chim. Pays-Bas 1994, 113, 267. (b)
See also: Donkervoot, J . G.; Vicario, J . L.; J astrzebski, J . T. B. H.;
Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Organomet. Chem. 1998,
551, 1.
benzenes 5a 22 and 5b were prepared as previously
described, the latter from a zinc chloride promoted
condensation of (S)-valinol with 1,3-dicyanobenzene.23
Using this same technique, the new bisoxazolines 5c-g
were prepared from the appropriate enantiomerically
pure â-amino alcohols in moderate yield (30-51%).
The large amount of literature reporting C-H bond
activation through cyclometalation24 includes the ortho
palladation of 2-phenyl-4,4-dimethyloxazoline by heat-
ing this at reflux with palladium acetate in acetic acid.25
Application of this method to 5a gave a yellow solid
displaying ν(CdN) at 1634 cm-1, indicative of a pal-
ladium-coordinated oxazoline, but without the simple
1
pattern expected in the H NMR spectrum. In addition,
no single compound could be isolated from the resultant
complex mixture. Instead, our attention turned to the
report that 5a undergoes regioselective ortho/ortho
lithiation on treatment with LDA/TMEDA,22 a method
that offered direct access to the desired complexes
following transmetalation with a palladium(II) salt.5b
Accordingly, a solution of lithiated 5a was added to a
solution of dibromo(1,5-cyclooctadiene)palladium in THF
to yield 6a , isolated by column chromatography as an
air- and water-stable pale yellow crystalline solid
(Scheme 1). This structure was verified by the absence
1
from the H NMR spectrum of the proton ortho to both
oxazoline rings, the decrease in ν(CdN) by 33 cm-1 to
1618 cm-1 compared to 5a , and the excellent agreement
between the calculated and observed isotope pattern for
the molecular ion in the EI-derived mass spectrum.
Repetition of this method with the C2-symmetric oxazo-
lines 5b-g successfully led to the isolation of complexes
6b-e but conspicuously failed with the two oxazolines
containing phenyl or benzyl substituents.
(13) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K. Organome-
tallics 1991, 10, 500.
(14) Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K.
J . Am. Chem. Soc. 1994, 116, 2223.
(15) Nesper, R.; Pregosin, P.; Pu¨ntener, K.; Wo¨rle, M.; Albinati, A.
J Organomet. Chem. 1996, 507, 85.
(16) (a) Gupta, A. D.; Bhuniya, D.; Singh, V. K. Tetrahedron 1994,
50, 13725. (b) Evans, D. A.; Murry, J . A.; von Matt, P.; Norcross, R.
D.; Miller, S. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 798. (c) Gupta,
A. D.; Singh, V. K. Tetrahedron Lett. 1996, 37, 2633. (d) Evans, D. A.;
Murry, J . A.; Kozlowski, M. C. J . Am. Chem. Soc. 1996, 118, 5814. (e)
Evans, D. A.; Kozlowski, M. C.; Tedrow, J . S. Tetrahedron Lett. 1996,
37, 7481.
To investigate these anomalous results, 5f was treated
with LDA/TMEDA as before, followed by addition of
(17) Preliminary communications: (a) Stark, M. A.; Richards, C. J .
Tetrahedron Lett. 1997, 38, 5881. (b) Abstracts of Papers, 216th
National Meeting of the American Chemical Society, Boston, MA, 1998;
American Chemical Society: Washington, DC, 1998; ORGN 540.
(18) Denmark, S. E.; Stavenger, R. A.; Faucher, A. M.; Edwards, J .
P. J . Org. Chem. 1997, 62, 3375.
(19) Motoyama, Y.; Makihara, N.; Mikami, Y.; Aoki, K.; Nishiyama,
H. Chem. Lett. 1997, 951.
(20) Motoyama, Y.; Mikami, Y.; Kawakami, H.; Aoki, K.; Nishiyama,
H. Organometallics 1999, 18, 3584.
(21) Motoyama, Y.; Narusawa, H.; Nishiyama, H. Chem. Commun.
1999, 131.
(22) Harris, T. D.; Neuschwander, B.; Boekelheide, V. J . Org. Chem.
1978, 43, 727.
(23) Bolm, C.; Weickhardt, K.; Zehnder, M.; Ranff, T. Chem. Ber.
1991, 124, 1173.
(24) (a) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; Kiefer, G. E.
Chem. Rev. 1986, 86, 451. (b) Ryabov, A. D.; Chem. Rev. 1990, 90, 403.
(25) Izumi, T.; Watabe, H.; Kasahara, A. Bull. Chem. Soc. J pn. 1981,
54, 1711.

1284 Organometallics, Vol. 19, No. 7, 2000
Stark et al.
Sch em e 2
Sch em e 4
of dibromo(1,5-cyclooctadiene)palladium again failed to
yield any trace of the desired complexes, even though
the validity of this approach was demonstrated by
quenching of the reaction with methyl iodide to give 15,
albeit in low yield.27 Methyl iodide has previously been
employed for the methylation of the 2-lithio derivative
of 5a .22 We speculate that the required transmetalations
may have been prevented by arene-lithium interac-
tions, of which there are many documented examples,28
as there would appear to be no steric restriction to
transmetalation (cf. formation of 6d /6e). Since we
carried out this work, Denmark et al. reported on the
insertion of Pd(0) into the carbon-halogen bond of
substrates, including 14g,18 and Nishiyama et al. de-
scribed a Pd(II) transmetalation with 2-(trimethylstan-
nyl)-1,3-bis(oxazolines), obtained from their correspond-
ing 2-bromo derivatives by treatment with BuLi followed
by Me3SnCl.19 Thus, our own work in this area sheds
further light on the relative advantages and disadvan-
tages of all three methods of synthesis.
Sch em e 3
Syn t h esis of Ca t ion ic [2,6-Bis(2′-oxa zolin yl)-
p h en yl]p a lla d iu m (II) Com p lexes. To investigate the
catalytic properties of these complexes required replace-
ment of the bromide ligand and occupation of a more
labile neutral ligand at the exchangeable coordination
site. Addition of 1.2 equiv of AgBF4, AgOTf, or AgSbF6
in wet CH2Cl2 gave the air-stable cationic complexes
16a 1-16e3, for which the yields quoted reflect the
success of reprecipitation in providing analytically pure
material (Scheme 4). Microanalysis revealed all of the
complexes to contain 1 equiv of water, observed in the
1H NMR spectrum as a broad peak between 2 and 3
ppm. That this neutral ligand is coordinated to pal-
ladium, as previously found for cationic palladium
complexes derived from other NCN ligands,5b was
confirmed by an X-ray structure analysis on crystals of
the triflate salt 16b2 formed by slow evaporation of an
acetone solution.
excess methyl iodide to give an excellent yield of
enamide 7 (Scheme 2), most likely as a consequence of
benzylic deprotonation and electrocyclic ring opening of
the oxazoline. Similarly, 5g was found to yield (E)-
cinnamyl alcohol 8 as an elimination product from
benzylic deprotonation, with concomitant formation of
a nitrile. Although the other expected product, 1,3-
dicyanobenzene, was not observed at the end of the
reaction, application of this same procedure to ferro-
cenyloxazoline 9 did result in isolation of a small
quantity of ferrocenyl cyanide 10 in addition to cinnamyl
alcohol. The nitrile functionality produced in this ring
opening appears to be readily consumed by the excess
of LDA/TMEDA employed for the lithiation.
An alternative route to 6f/6g began with 2-bromo-1,3-
dicyanobenzene (11) (Scheme 3). When it was employed
directly in a ZnCl2-promoted cyclization with (S)-2-
amino-3-phenyl-1-propanol, the two oxazoline rings
were formed, though accompanied unsurprisingly by
amino alcohol displacement of the halogen. Instead, the
2-bromo substituent was retained during conversion to
the diacid chloride 12, with subsequent amide formation
and conversion of 13f/13g to their corresponding bis-
oxazolines 14f/14g under Appel conditions.26 Attempts
to effect bromine/lithium exchange followed by addition
The crystal structure consists of two independent
cationic complexes [Pd(C18H23N2O2)(H2O)]+, both situ-
ated on 2-fold axes, and in each a triflate anion is
hydrogen-bonded to water with water-oxygen to triflate-
(27) During the course of this work we also synthesized (S,S)-1,3-
bis[4′-(cyclohexylmethyl)-5′,5′-dimethyl-2′-oxazolinyl]benzene but were
unable to effect the lithiation and/or palladation of this material. Full
details on the synthesis of this and related oxazolines will be reported
elsewhere.
(28) (a) Patterman, S. P.; Karle, I. L.; Stucky, G. D. J . Am. Chem.
Soc. 1970, 92, 1150. (b) Rhine, W. E.; Stucky, G. D. J . Am. Chem. Soc.
1975, 97, 737.
(26) Vorbru¨ggen, H.; Krolikliewicz, K. Tetrahedron Lett. 1981, 22,
4471.

Pd(II) 2,6-Bis(2′-oxazolinyl)phenyl Complexes
Organometallics, Vol. 19, No. 7, 2000 1285
Sch em e 6
F igu r e 1. One of the two independent crystal structures
of 16b2. Selected bond distances (Å) and angles (deg) are
as follows (corresponding values for the unshown second
structure are given in brackets): C(3)-Pd(1) ) 1.85(3)
[1.96(2)], C(1)-N(1) ) 1.31(2) [1.298(14)], N(1)-Pd(1) )
2.060(10) [2.059], O(1)-Pd(1) ) 2.16(2) [2.11(2)]; N(1)-
Pd(1)-N(1′) ) 160.4 (6) [158.6 (5)], C(1)-N(1)-Pd(1) )
112.1(9) [112.5(7)].
cyanoacetate.31 Use of 1 mol % of 16b3 with 10 mol %
of Hunig’s base resulted in only a small increase in the
rate of formation of the resulting oxazolines (trans:cis
) 4:1), unlike related palladium-containing PCP cationic
complexes, which are efficient catalysts for this
reaction.11b,d Instead we examined the possibilities
offered by nitrogen-metal coordination by swapping an
isonitrile for a nitrile.32-34 Thus, in the presence of 1
mol % of 16a 3 and 10 mol % of Hunig’s base, ethyl
cyanoacetate and methyl vinyl ketone cleanly gave the
double Michael adduct 19 in 95% yield within 5 h in a
reaction carried out at room temperature in CH2Cl2
(Scheme 6, reaction A: Table 1, entry 1). Significantly,
in the absence of 16a 3, essentially no reaction could be
detected under the same conditions after 23 h (entry
2). To provide for the formation of a new stereogenic
center, ethyl R-cyanopropionate was next employed as
the Michael donor. When catalyzed by 16b1, again in
the presence of 10 mol % of Hunig’s base, the adduct
20a was cleanly formed, albeit in a very modest 8% ee
(reaction B, entry 3). Changing the counterion from
BF4- to SbF6- resulted in little change in enantioselec-
tivity (entry 4), although under the conditions and
reaction times employed the competitive noncatalyzed
background reaction is very slow (entry 5). A significant
jump in selectivity was observed, however, on changing
the solvent to toluene (entry 6), the ee of the product
being essentially maintained on decreasing the amount
of Hunig’s base to just 1 mol % (entry 7). Further
increases in ee were observed with increases in the size
of the substituents attached to the oxazoline rings of
the catalysts (entries 8 and 9), the best result of 34%
ee being obtained with the cyclohexylmethyl substitu-
ents of catalyst 16e3 (entry 10). This enantioselectivity
was essentially unchanged when the reaction was
Sch em e 5
oxygen distances of 2.702 and 2.673 Å. The rigid
geometry of the terdentate ligand dictates a distorted-
square-planar arrangement about palladium with
C-Pd-N bond angles of 80.2 and 79.3° and, thus,
N-Pd-N bond angles of 160.4 and 158.6°. The C-Pd
bond distances of 1.85 and 1.96 Å are similar to that of
the corresponding neutral complex (the chloride ana-
logue of 6b) determined at 1.928 Å,19 other bond lengths
and angles being also very similar. The isopropyl groups
lie in neither a pronounced pseudoaxial nor a pseudo-
equatorial position, due to the relatively small deviation
from planarity of the oxazoline rings. An ORTEP
representation of 16b2 and selected data are given in
Figure 1.
The anions BF4- and SbF6- are reported to be weaker
metal coordinators than triflate due to the presence of
less basic sites on the periphery of the anion (F vs O),29
and on this basis the other cationic complexes also
contain coordinated water molecules. That a number of
peaks arise in their IR spectra due to B-F and Sb-F
stretching, indicating a loss of Td and Oh symmetry,
respectively, is a consequence of hydrogen bonding
between these ions and coordinated H2O.30 The pos-
sibility of generating other neutral ligand adducts from
16 was briefly investigated by addition of either excess
acetonitrile or excess ethyl cyanoacetate to 16b3 followed
by precipitation of complexes 17 and 18, respectively
(Scheme 5)
(31) Hayashi, T.; Sawamura, M.; Ito, Y. Tetrahedron 1992, 48, 1999.
(32) (a) Naota, T.; Taki, H.; Mizuno, M.; Murahashi, S.-I. J . Am.
Chem. Soc. 1989, 111, 5954. (b) Murahashi, S.-I.; Naota, T.; Taki, H.;
Mizuno, M.; Takaya, H.; Komiya, S.; Mizuho, Y.; Oyasato, N.; Hiraoka,
M.; Hiranao, M.; Fukuoka, A. J . Am. Chem. Soc. 1995, 117, 12436.
(33) Paganelli, S.; Schionato, A.; Botteghi, C. Tetrahedron Lett. 1991,
32, 2807.
(34) (a) Sawamura, M.; Hamashima, H.; Ito, Y. J . Am. Chem. Soc.
1992, 114, 8295. (b) Sawamura, M.; Hamashima, H.; Ito, Y. Tetrahe-
dron 1994, 50, 4439. (c) Sawamura, M.; Hamashima, H.; Shinoto, H.;
Ito, Y. Tetrahedron Lett. 1995, 36, 6479. (d) Sawamura, M.; Sudoh,
M.; Ito, Y. J . Am. Chem. Soc. 1996, 118, 3309. (e) Inagaki, K.; Nozaki,
K.; Takaya, H. Synlett 1997, 119. (f) Kuwano, R.; Miyazaki, H.; Ito, Y.
Chem. Commun. 1998, 71. (g) Blacker, A. J .; Clarke, M. L.; Loft, M.
S.; Mahon, M. F.; Williams, J . M. J . Organometallics 1999, 18, 2867.
Asym m etr ic Ca ta lysis w ith Ca tion ic [2,6-Bis(2′-
oxa zolin yl)p h en yl]p a lla d iu m (II) Com p lexes. In a
preliminary investigation of the catalytic potential of
these complexes, we investigated their activity in the
aldol reaction between benzaldehyde and methyl iso-
(29) Strauss, S. H. Chem. Rev. 1993, 93, 927.
(30) Olgemo¨ller, B.; Olgemo¨ller, L.; Beck, W. Chem. Ber. 1981, 114,
2971.

1286 Organometallics, Vol. 19, No. 7, 2000
Stark et al.
Ta ble 1. Resu lts of th e Ca ta lysis of Mich a el Rea ction s w ith Ca tion ic
[2,6-Bis(2′-oxa zolin yl)p h en yl]p a lla d iu m (II) Com p lexes
entrya
reacn/prod.
cat.b
solvent
time (h)
% yieldc (% conversnd)
% eee (confignf)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
22
22
A/19g
A/19g
B/20a
B/20a
B/20a
B/20a
B/20a h
B/20a h
B/20a h
B/20a h
B/20a h,i
B/20a h
B/20b
B/20b
B/20b
B/20a
B/20bh
C/21
16a 3
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
CH2Cl2
PhMe
PhMe
5
23
3.5
95
(<5)
67
16b1
16b3
8 (R)
6 (R)
4
86
4-50-95
4
7
(3)-(50)-(76)
73
73
78
80
86
66
16b3
16b3
16c3
16d 3
16e3
16e3
22 (R)
20 (R)
29 (R)
27 (R)
34 (R)
33 (R)
143
97
120
143
23-143-335
1
5
70
5
5
(7)-(29)-(38)
90
16b3
16b3
16e3
17
17
16b3
17 (R)
15 (R)
28 (R)
15 (R)
18 (R)
84
70j
PhMe
71
66
79
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
PhMe
3
C/21
D/22
D/22
D/22
5-70-148
90
4-70-144
46
(0)-(23)-(42)
90
(0)-(11)-(21)
74
16e3
16e3
16e3
2k
8k
a
Reactions were performed with 1.6 mmol of Michael acceptor, 2.4 mmol of activated esters, and 0.16 mmol of Hunig’s base in 4 mL
of solvent at room temperature. b 1 mol %. c After workup and bulb-to-bulb distillation. Determined by 1H NMR spectroscopy. e Determined
d
by GC with CP-Chirasil-Dex CB. f Determined by optical rotation.31b From 4.8 mmol of MVK. 1 mol % Hunig’s base. 0 °C. On the
g
h
i
j
k
basis of 50% conversion, the reaction had ceased after 70 h. Absolute configuration not determined.
carried out at 0 °C (entry 11). The bulkier oxazoline
substituents also resulted in an increase in the time
required for the reaction to complete, allowing some
leakage in the potential selectivity due to a competitive
noncatalyzed reaction (entry 12).
reaction takes place, nor is any product observed when
diethyl malonate is substituted for the R-cyanopropi-
onates. These observations suggest the presence of a
nitrogen-coordinated intermediate carrying a nitrile/
palladium and ester-stabilized carbanion generated by
Hunig’s base. This subsequently undergoes partially
selective addition of methyl vinyl ketone followed by
protonation of the resulting enolate and regeneration
of Hunig’s base. This process differs slightly from the
previous use of low-valent ruthenium32 and rhod-
ium33,34a-f complexes as catalysts for this reaction. These
are rationalized by the oxidative addition of the metal
into the R-C-H bond of the nitrile, leading via isomer-
ization to an intermediate hydrido complex containing
a nitrile-coordinated enolate. This is supported by the
isolation and characterization by X-ray crystal structure
analysis of the oxidative addition product of alkyl
cyanoacetates to Ru(0) as mer-RuH(NCCHCO2R)(NCCH2-
CO2R)(PPh3)3.32b,35 For the Pd(II) systems described in
this work, a similar mechanism not requiring a base
would involve an intermediate cationic Pd(IV) interme-
diate. That reaction is only observed with Hunig’s base
present instead suggests a fixed Pd(II) oxidation level
and activation of the R-C-H to deprotonation and/or
enolate activation through nitrile-metal coordination.
A fixed oxidation level is also consistent with activation
of acrylonitrile, the palladium complex acting as a Lewis
acid to this Michael acceptor. The kinetic lability of the
palladium-nitrile bond, aided by the relatively high
trans effect of the coordinated phenyl group, allows for
the use of low catalyst loadings, as no significant level
of product inhibition was observed. As the new stereo-
genic center is formed three bonds distant from pal-
ladium, the size and length of the oxazoline substituents
are clearly important in determining the outcome of the
reaction. In this context the rather open cleft defined
The influence of the size of the ester substituent was
investigated with tert-butyl R-cyanopropionate, which
on addition to methyl vinyl ketone resulted in the
formation of 20b. When the reaction was carried out in
CH2Cl2, the product was formed with a higher ee than
was observed with the corresponding ethyl ester (entry
13; compare to entry 4), but in this case a jump in
selectivity was not observed on changing the solvent to
toluene (entry 14). Neither did use of the cyclohexyl-
methyl-substituted catalyst 16e3 promote a higher
selectivity than previously observed in the ethyl ester
series (entry 15). The two reactions leading to 20a and
20b were also efficiently catalyzed by the nitrile-
containing complex 17, confirming the lability of this
functionality when attached to the exchangeable coor-
dination site of these complexes (entries 16 and 17).
The possibility of activating the Michael acceptor
through metal coordination was investigated by com-
bining diethyl nitromalonate and acrylonitrile in the
presence of Hunig’s base. When 16b3 was also present,
the adduct 21 was readily formed (reaction C, entry 18),
in contrast to its slow formation in the absence of this
complex (entry 19). This result led us to investigate the
addition of ethyl R-cyanopropionate to acrylonitrile
catalyzed by 16e3, a reaction which offered the possibil-
ity of double asymmetric induction. Although these
reactions produced adduct 22 in high yields (reaction
D, entries 20 and 22) with comparatively little competi-
tive noncatalyzed reaction (entry 21), only very low
selectivities were observed. If this reaction proceeds via
coordination of both nitriles to different palladium
complexes, the interaction of the ligand frameworks in
this instance is clearly not cooperative.
(35) (a) Mizuho, Y.; Kasuga, N.; Komiya, S. Chem. Lett. 1991, 2127.
(b) Hirano, M.; Takenaka, A.; Mizuho, Y.; Hiraoka, M.; Komiya, S. J .
Chem. Soc., Dalton Trans. 1999, 3209.
It is of note that in the absence of Hunig’s base no

Pd(II) 2,6-Bis(2′-oxazolinyl)phenyl Complexes
Organometallics, Vol. 19, No. 7, 2000 1287
zene (1.81 g, 14.1 mmol), and (S)-(+)-2-amino-3,3-dimethyl-
butanol (5.00 g, 42.7 mmol) were used. Column chromatogra-
phy (CH2Cl2-EtOAc (95:5)) gave 5d as a colorless crystalline
solid (1.40 g, 30%). Mp: 121-122 °C. Anal. Found: C, 73.18;
H, 8.88; N, 8.58. Calcd for C20H28N2O2: C, 73.14; H, 8.59; N,
by the N-Pd-N bond angle of 160.4° is a disadvantage,
as it accentuates the distance between the oxazoline
substituents and the newly forming stereogenic center.
Con clu sion
20
8.53. [R]D ) -168 (c 0.1, EtOH). IR (νmax; Nujol): 1651
(CdN) cm-1. 1H NMR (δ; CDCl3): 0.89 (18 H, s, -C(CH3)), 3.99
(2 H, dd, J ) 10.1, 7.8 Hz, -OCHH-), 4.18 (2 H, t, J ) 8.0,
-CHN-), 4.29 (2 H, t, J ) 9.9, -OCHH-), 7.38 (1 H, t, J )
7.8, 5-H), 7.99 (2 H, d, J ) 7.8, 4- & 6-H), 8.44 (1 H, s, 2-H).
13C{1H} NMR (δ; CDCl3): 26.3 (-CH3), 34.5 (-C(CH3)3), 69.2
(-CHN-), 76.7 (-OCH2-), 128.4 (Ph, 5-C), 128.6 (Ph, 4- &
6-C), 128.7 (Ph, 1- & 3-C), 131.3 (Ph, 2-C), 163.0 (CdN). MS
(m/z; EI): 329 (M+, 9%), 313 (10), 271 (94), 214 (11), 144 (41),
74 (5), 57 (100).
In this work we have described the rapid synthesis
of a series of enantiomerically pure 2,6-bis(2′-oxazolin-
yl)phenylpalladium(II) bromides, obtained directly from
1,3-bis(2′-oxazolinyl)benzenes, which are themselves
easily synthesized from commercially available â-amino
alcohols. The limitations of this approach have also been
defined by both discovering the fate of bis(oxazolines)
containing phenyl and benzyl substituents and attempt-
ing the lithiation/transmetalation sequence on a steri-
cally congested bis(oxazoline) containing additional 5,5-
dimethyl substituents. The palladium complexes are
readily activated on treatment with a variety of silver
salts to give analytically pure cationic complexes con-
taining water in the exchangeable coordination site. The
lability of ligands in this site was demonstrated by the
low (1 mol %) loading required for the cationic complexes
to efficiently catalyze the addition of R-cyanocarboxy-
lates to Michael acceptors. Although the enantioselec-
tivities described are modest, the efficiency of catalysis
in these clean reactions and the potential for attachment
of the catalysts to a solid support have maintained our
interest in the design of related cationic palladium
complexes.
(S,S)-1,3-Bis(4′-cycloh exylm et h yl-2′-oxa zolin yl)b en -
zen e (5e). Anhydrous zinc dichloride (0.087 g, 0.64 mmol), 1,3-
dicyanobenzene (0.82 g, 6.4 mmol), and (S)-(+)-2-amino-3-
cyclohexyl-1-propanol (3.02 g, 19.2 mmol). Column chromatog-
raphy (CH2Cl2-EtOAc (9:1)) gave 5e as a colorless oil which
solidified on standing (1.20 g, 46%). Mp: 57-58 °C Anal.
Found: C, 76.71; H, 9.07; N, 7.04. Calcd for C26H36N2O2: C,
20
76.43; H, 8.89; N, 6.86. [R]D ) +144 (c 0.1, EtOH). IR (νmax
;
Nujol): 1652 (CdN) cm-1. 1H NMR (δ; CDCl3): 0.97-1.83 (26
H, m, -CH2Cy), 4.01 (2 H, t, J ) 7.9 Hz, -OCHH-), 4.35-
4.43 (2 H, m, -CHN-), 4.53 (2 H, t, J ) 8.2, -OCHH-), 7.46
(1 H, t, J ) 7.8, 5-H), 8.07 (2 H, d, J ) 7.8, 4- & 6-H), 8.49 (1
H, s, 2-H). 13C{1H} NMR (δ; CDCl3): 26.6 (-CH2- × 2), 26.9
(-CH2-), 33.8 (-CH2-), 34.0 (-CH2-), 35.3 (-CH2CH-), 44.7
(-CH2Cy), 65.1 (-CHN-), 73.7 (-OCH2-), 128.4 (Ph, 5-C),
128.7 (Ph, 4- & 6-C), 128.7 (Ph, 1- & 3-C), 131.2 (Ph, 2-C), 163.1
(CdN). MS (m/z; EI): 407 (M+, 91), 310 (71), 213 (19), 143
(100).
Exp er im en ta l Section
(R,R)-1,3-Bis(4′-p h en yl-2′-oxa zolin yl)ben zen e (5f). An-
hydrous zinc dichloride (0.20 g, 1.5 mmol), 1,3-dicyanobenzene
(1.56 g, 12.2 mmol), and (R)-(-)-2-amino-2-phenylethanol
(5.00 g, 36.5 mmol) were used Column chromatography (CH2-
Cl2-EtOAc (95:5)) gave 5f as a colorless crystalline solid (2.29
g, 51%). Mp: 129-130 °C Anal. Found: C, 78.46; H, 5.49; N,
Tetrahydofuran was distilled from sodium benzophenone
ketyl, and toluene, dichloromethane, chloroform, and TMEDA
were distilled from calcium hydride. Methanol was distilled
from activated 4 Å molecular sieves, and diisopropylamine was
distilled from sodium hydroxide. Chlorobenzene was stored
before use over activated 4 Å molecular sieves. Petroleum ether
refers to that fraction boiling in the range 40-60 °C and
hexane to the fraction boiling in the range 65.5-70 °C. Column
chromatography was performed on SiO2 (40-63 µm). Enan-
tiomeric excesses were determined by GC using a CP-Chirasil-
Dex CB column (25 m × 0.25 mm). Compound 5a was prepared
as previously described.22 Chiral amino alcohols were obtained
from Sigma-Aldrich Co. Ltd.
20
7.43. Calcd for C24H20N2O2: C, 78.24; H, 5.47; N, 7.60. [R]D
) +100 (c 0.1, EtOH). IR (νmax; Nujol): 1652 (CdN) cm-1; H
1
NMR (δ; CDCl3): 4.32 (2 H, t, J ) 8.4 Hz, -OCHH-), 4.83 (2
H, dd, J ) 10.0, 8.5, -OCHH-), 5.42 (2 H, dd, J ) 10.0, 8.3,
-CHN-), 7.26-7.39 (10 H, m, Ph), 7.54 (1 H, t, J ) 7.8, 5-H),
8.22 (2 H, d, J ) 7.8, 4- & 6-H), 8.71 (1 H, s, 2-H). 13C{1H}
NMR (δ; CDCl3): 70.2 (-CHN-), 75.0 (-OCH2-), 126.7 (Ph),
127.7 (Ph), 128.0 (Ph), 128.5 (Ph), 128.6 (Ph), 128.8 (Ph), 131.4
(Ph, 2-C), 142.2 (Ph, 1- & 3-C), 164.1 (CdN). MS (m/z; EI):
368 (M+, 22%), 291 (5), 218 (11), 104 (24), 91 (68), 90 (97), 89
(100).
(S,S)-1,3-Bis(4′-ben zyl-2′-oxa zolin yl)ben zen e (5g). An-
hydrous zinc dichloride (0.30 g, 2.2 mmol), 1,3-dicyanobenzene
(2.82 g, 22.0 mmol), and (S)-(+)-2-amino-3-phenyl-1-propanol
(10.00 g, 66.1 mmol). Column chromatography (CH2Cl2-EtOAc
(9:1)) gave 5g as a colorless crystalline solid (3.32 g, 38%).
Mp: 107-109 °C Anal. Found: C, 78.55; H, 6.25; N, 7.31.
Calcd for C26H24N2O2: C, 78.76; H, 6.10; N, 7.07. [R]D20 ) +52
(c 0.1, EtOH). IR (νmax; Nujol): 1649 (CdN) cm-1. 1H NMR (δ;
CDCl3): 2.88 (2 H, dd, J ) 13.8, 8.2 Hz, -CHHPh-), 3.40 (2
H, dd, J ) 13.8, 5.4, -CHHPh), 4.31 (2 H, t, J 7.9, -OCHH-),
4.52 (2 H, t, J ) 8.0, -OCHH-), 4.71-4.78 (2 H, m, -CHN-),
7.26-7.41 (10 H, m, Ph), 7.63 (1 H, t, J ) 7.8, 5-H), 8.23 (2 H,
d, J ) 7.8, 4- & 6-H), 8.64 (1 H, s, 2-H). 13C{1H} NMR (δ;
CDCl3): 42.2 (-CH2Ph), 68.4 (-CHN-), 72.4 (-OCH2-), 127.0
(Ph), 128.6 (Ph), 128.9 (Ph), 129.0 (Ph), 129.7 (Ph), 131.4 (2-
C), 138.3 (1- & 3-C), 163.7 (CdN). MS (m/z; EI): 397 (M+, 9%),
305 (87), 213 (3), 143 (31), 90 (100).
P r ep a r a t ion of 1,3-Bis(2′-oxa zolin yl)b en zen es 5c-g.
The previously reported procedure for the synthesis of 5b23
was employed for the synthesis of the following new bis-
(oxazolines).
(S,S)-1,3-Bis(4′-isobu tyl-2′-oxa zolin yl)ben zen e (5c). An-
hydrous zinc dichloride (0.15 g, 1.1 mmol), 1,3-dicyanobenzene
(1.81 g, 14.1 mmol), and (S)-(+)-2-amino-4-methyl-1-pentanol
(5.00 g, 42.7 mmol) were used. Column chromatography (CH2-
Cl2-EtOAc (95:5)) gave 5c as a colorless crystalline solid (1.62
g, 35%). Mp: 48-49 °C. Anal. Found: C, 73.06; H, 8.35; N,
20
8.30. Calcd for C20H28N2O2: C, 73.14; H, 8.59; N, 8.53. [R]D
) -96 (c 0.1, EtOH). IR (νmax; Nujol): 1652 (CdN) cm-1 1H
.
NMR (δ; CDCl3): 0.98 (12 H, d, J ) 6.8 Hz, 4 × -CH3), 1.36-
1.41 (2 H, m, -CH(CH3)2), 1.68-1.74 (2 H, m, -CHH-), 1.81-
1.87 (2 H, m, 2 × -CHH-), 3.99 (2 H, t, J ) 8.0, -OCHH-),
4.30-4.38 (2 H, m, -CHN-), 4.51 (2 H, dd, J ) 8.8, 7.6,
-OCHH-), 7.44 (1 H, t, J ) 7.8, 5-H), 8.05 (2 H, d, J ) 7.6, 4-
& 6-H), 8.47 (1 H, s, 2-H). 13C{1H} NMR (δ; CDCl3): 22.7
(-CH3), 22.8 (-CH3), 25.4 (-CH(CH3)2), 45.6 (-CH2-), 65.2
(-CHN-), 73.2 (-OCH2-), 128.0 (Ph, 5-C), 128.2 (Ph, 4- &
6-C), 128.3 (Ph, 1- & 3-C), 130.7 (Ph, 2-C), 162.6 (CdN). MS
(m/z; EI): 329 (M+, 10%), 271 (100), 215 (20), 145 (12), 75 (12).
(S,S)-1,3-Bis(4′-ter t-b u t yl-2′-oxa zolin yl)b en zen e (5d ).
Anhydrous zinc dichloride (0.15 g, 1.1 mmol), 1,3-dicyanoben-
Gen er a l P r oced u r e for th e P r ep a r a tion of 2,6-Bis(2′-
oxa zolin yl)p h en ylp a lla d iu m (II) Br om id es 6a -e. A solu-
tion of diisopropylamine (3 equiv) in THF (3 mL/1 mL amine)
was cooled under a nitrogen atmosphere to -78 °C. Butyl-

1288 Organometallics, Vol. 19, No. 7, 2000
Stark et al.
lithium (3.3 equiv) was added and the mixture stirred for 20
min at this temperature. The cooling bath was then removed
and the solution warmed to room temperature for 30 min
before replacing the cooling bath. This solution was transferred
via a cannula into a flask containing a solution of the relevant
1,3-bis(2′-oxazolinyl)benzene (1 equiv) and N,N,N′,N′-tetra-
methylethylenediamine (TMEDA) (3 equiv) in THF (20 mL/g
of oxazoline) under a nitrogen atmosphere at -78 °C. After
the addition was complete, the cooling bath was removed and
the resulting deep red solution was stirred at room tempera-
ture for 5-7 h. This was then added by cannula in small
fractions to a stirred suspension of dibromo(1,5-cycloocta-
diene)palladium(II) (1.5 equiv) in THF (20 mL/g) at 0 °C. After
the addition was completed, the ice bath was removed and the
reaction mixture stirred overnight at room temperature. The
resulting black solution was filtered through Celite 520 and
purified by column chromatography.
(S,S)-[2,6-Bis(4′-ter t-bu tyl-2′-oxa zolin yl)p h en yl]p a lla -
d iu m (II) Br om id e (6d ). LDA (9.1 mmol), 5d (1.00 g, 3.0
mmol), TMEDA (1.06 g, 9.1 mmol) in THF (20 mL), and [PdBr2-
(1,5-COD)] (1.71 g, 4.6 mmol) in THF (30 mL) followed by
column chromatography (CH2Cl2-light petroleum (4:1)) gave
6d as an orange solid (0.38 g, 24%). Mp: 258-260 °C. Anal.
Found: C, 46.53; H, 5.77; N, 5.13. Calcd for C20H27BrN2O2Pd:
C, 46.76; H, 5.30; N, 5.45. [R]D20 ) +600 (c 0.1, EtOH). IR (νmax
;
Nujol): 1610 (CdN) cm-1. H NMR (δ; CDCl3): 1.10 (18 H, s,
-C(CH3)3), 4.05 (2 H, dd, J ) 8.4, 2.1 Hz, -OCHH-), 4.50 (2
H, t, J ) 8.8, -CHN-), 4.76 (2 H, dd, J ) 9.1, 2.2, -OCHH-),
7.12 (1 H, t, J ) 7.8, 4-H), 7.24 (2 H, d, J ) 7.5, 3- & 5-H).
13C{1H} NMR (δ; CDCl3): 27.0 (-CH3), 35.8 (-C(CH3)3), 70.8
(-CHN-), 74.1 (-OCH2-), 124.5 (Ph, 4-C), 127.3 (Ph, 3- &
5-C), 129.7 (Ph, 2- & 6-C), 167.0 (Ph, 1-C), 175.1 (CdN). MS
(m/z; EI): 514 (M+, 2%), 438 (8), 437 (43), 435 (86), 433 (93),
432 (73), 431 (34) [all M - Br], 375 (8), 271 (32), 249 (7), 213
(8), 185 (6), 144 (13), 130 (7), 116 (15), 103 (7), 89 (12), 80 (8),
57 (100).
1
[2,6-Bis(4′,4′-d im eth yl-2′-oxa zolin yl)p h en yl]p a lla d iu m -
(II) Br om id e (6a ). LDA (3.3 mmol), 5a (0.300 g, 1.10 mmol),
TMEDA (0.385 g, 3.31 mmol) in THF (8 mL), and [PdBr2(1,5-
COD)] (0.45 g, 1.2 mmol) in THF (10 mL) followed by column
chromatography [CH2Cl2-EtOAc (9:1)] gave 6a as a pale yellow
solid (0.176 g, 35%). Mp: 295-297 °C. Anal. Found: C, 42.28;
H, 4.28; N, 6.27. Calcd for C16H19BrN2O2Pd: C, 41.99; H, 4.18;
(S,S)-[2,6-Bis(4′-cycloh exylm eth yl-2′-oxazolin yl)ph en yl]-
p a lla d iu m (II) Br om id e (6e). LDA (7.4 mmol), 5e (1.00 g,
2.5 mmol), TMEDA (0.85 g, 7.3 mmol) in THF (20 mL), and
[PdBr2(1,5-COD)] (1.50 g, 4.0 mmol) in THF (30 mL) followed
by column chromatography (CH2Cl2-light petroleum (4:1))
gave 6e as a pale yellow solid (0.60 g, 41%). Mp: 264-266 °C.
N, 6.12. IR (νmax; Nujol): 1618 (CdN) cm-1 1H NMR (δ;
.
CDCl3): 1.68 (12 H, s, -CH3), 4.46 (4 H, s, -OCH2-), 7.17 (1
H, t, J ) 7.8 Hz, 4-H), 7.30 (2 H, d, J ) 7.8, 3- & 5-H). 13C{1H}
NMR (δ; CDCl3): 28.1 (-CH3), 66.2 (-C(CH3)2-), 82.8
(-OCH2-), 124.0 (Ph, 4-C), 126.8 (Ph, 3- & 5-C), 130.0 (Ph, 2-
& 6-C), 167.5 (Ph, 1-C), 172.6 (CdN). MS (m/z; EI): 462 (2%),
460 (7), 458 (10), 457 (5), 456 (7), 455 (4), 454 (2) [all M+], 381
(34), 379 (75), 377 (88), 376 (67), 375 (32) [all M - Br], 41 (100).
(S,S)-[2,6-Bis(4′-isop r op yl-2′-oxa zolin yl)p h en yl]p a lla -
d iu m (II) Br om id e (6b). LDA (5 mmol), 5b (0.500 g, 1.66
mmol), TMEDA (0.590 g, 5.08 mmol) in THF (10 mL), and
[PdBr2(1,5-COD)] (0.94 g, 2.5 mmol) in THF (20 mL) followed
by column chromatography (CH2Cl2) and further purification
by precipitation from CHCl3/hexane gave 6a as a pale yellow
solid (0.331 g, 41%). Mp: >290 °C. Anal. Found: C, 44.15; H,
4.77; N, 5.50. Calcd for C18H23BrN2O2Pd: C, 44.51; H, 4.78;
Anal. Found: C, 52.71; H, 5.83; N, 4.63. Calcd for C26H35-
20
BrN2O2Pd: C, 52.58; H, 5.94; N, 4.72. [R]D ) +68 (c 0.1,
EtOH). IR (νmax; Nujol): 1612 (CdN) cm-1 1H NMR (δ;
.
CDCl3): 1.00-1.73 (24 H, m, -CHHCy), 2.46 (2 H, brt, J )
8.3 Hz, -CHHCy), 4.29-4.35 (2 H, m, -CHN-), 4.46 (2 H,
dd, J ) 8.5, 6.0, -OCHH-), 4.72 (2 H, t, J ) 8.9, -OCHH-),
7.08 (1 H, t, J ) 7.8, 4-H), 7.22 (2 H, d, J ) 7.6, 3- & 5-H).
13C{1H} NMR (δ; CDCl3): 26.6 (-CH2-), 32.5 (-CH2-), 34.6
(-CH2-), 35.3 (-CH2CH-), 43.0 (-CH2-), 61.6 (-CHN-),
76.9 (-OCH2-), 124.3 (Ph, 4-C), 127.0 (Ph, 3- & 5-C), 130.0
(Ph, 2- & 6-C), 168.7 (Ph, 1-C), 174.2 (CdN). MS (m/z; EI):
519 (5%), 518 (18), 516 (37), 514 (40), 513 (29), 512 (13) [all M
- Br], 408 (5), 81 (14), 79 (18), 55 (100).
Rea ction of (R,R)-1,3-Bis(4′-p h en yl-2′-oxa zolin yl)ben -
zen e (5f) w it h LDA/TME DA. (R,R)-1,3-Bis(4′-phenyl-2′-
oxazolinyl)benzene (5f; 0.50 g, 1.4 mmol) was lithiated as
described for the formation of 6a -e (LDA, 4.1 mmol; TMEDA,
0.47 g, 4.0 mmol; THF, 20 mL) except that after stirring at
room temperature for 5 h the reaction was quenched by the
addition of MeI (1.93 g, 13.6 mmol). The resultant precipitate
was removed by filtration and the filtrate diluted with EtOAc
(25 mL), washed with water (2 × 20 mL), dried (MgSO4), and
filtered and the solvent removed in vacuo. Recrystallization
from EtOAc/hexane gave enamide 7 (0.522 g, 97%) as a brown
solid. Mp: 117-121 °C. IR (νmax; Nujol): 1650 (CdO), 1635
20
N, 5.77. [R]D ) +128 (c 0.1, EtOH). IR (νmax; Nujol): 1620
(CdN) cm-1 1H NMR (δ; CDCl3): 0.81 (6 H, d, J ) 6.9 Hz,
.
-CH3), 0.94 (6 H, d, J ) 6.9, -CH3), 2.85-2.94 (2 H, m,
-CH(CH3)2), 4.34-4.39 (2 H, m, -CHN-), 4.60-4.69 (4 H,
m, -OCH2-), 7.18 (1 H, t, J ) 7.6, 4-H), 7.32 (2 H, d, J ) 7.4,
3- & 5-H). 13C{1H} NMR (δ; CDCl3): 14.4 (-CH3), 19.3 (-CH3),
29.6 (-C(CH3)2), 67.5 (-CHN-), 71.5 (-OCH2-), 124.5 (Ph,
4-C), 127.4 (Ph, 3- & 5-C), 129.7 (Ph, 2- & 6-C), 168.4 (Ph, 1-C),
174.4 (CdN). MS (m/z; EI): 490 (1%), 488 (5), 486 (8), 485 (5),
483 (2), 482 (1) [all M+], 411 (5), 409 (21), 407 (14), 405 (47),
403 (53), 402 (56) [all M - Br], 361 (7), 257 (12), 43 (100).
(S,S)-[2,6-Bis(4′-isob u t yl-2′-oxa zolin yl)p h en yl]p a lla -
d iu m (II) Br om id e (6c). LDA (4.6 mmol), 5c (0.50 g, 1.5
mmol), TMEDA (0.53 g, 4.6 mmol) in THF (10 mL), and [PdBr2-
(1,5-COD)] (0.85 g, 2.3 mmol) in THF (15 mL) followed by
column chromatography (CH2Cl2) gave 6c as a pale yellow solid
(0.16 g, 21%). Mp: >270 °C. Anal. Found: C, 46.75; H, 5.33;
N, 5.21. Calcd for C20H27BrN2O2Pd: C, 46.76; H, 5.30; N, 5.45.
1
(CdC) cm-1. H NMR (δ; CDCl3): 3.13 (6 H, s, -CH3), 4.69 (2
H, s, -CdCHH), 5.23 (2 H, s, -CdCHH), 6.93 (2 H, d, J ) 7.5
Hz, 4- & 6-H), 7.19-7.30 (11 H, m, Ph and 5-H), 7.62 (1 H, s,
2-H). 13C{1H} NMR (δ; CDCl3): 37.1 (-CH3), 112.9 (-CdCH2),
126.4 (4- & 6-C), 127.6 (-Ph), 127.8 (-Ph), 129.2 (-Ph), 129.4
(-Ph), 129.4 (-Ph), 136.2 (-Ph), 136.5 (1- & 3-C), 149.4
(-CdCH2), 171.2 (CdO). MS (m/z; EI): 396 (M+, 73%), 381 (12),
366 (80), 292 (45), 277 (10), 263 (68), 249 (32), 235 (91), 220
(20), 207 (40), 198 (44), 178 (100), 172 (58), 165 (42), 145 (70),
134 (64), 118 (88), 103 (90), 90 (69), 75 (68), 65 (81) High-
resolution MS (m/z; EI): found for M+, 396.1837; calcd for
[R]D20 ) +146 (c 0.1, EtOH). IR (νmax; Nujol): 1616 (CdN) cm-1
.
1H NMR (δ; CDCl3): 0.98 (6 H, d, J ) 6.6 Hz, -CH3), 1.01 (6
H, d, J ) 6.6, -CH3), 1.36-1.44 (2 H, m, -CH(CH3)2), 1.65-
1.70 (2 H, m, -CHH-), 2.44-2.51 (2 H, m, -CHH-), 4.33-
4.40 (2 H, m, -CHN-), 4.54 (2 H, dd, J ) 8.6, 6.0, -OCHH-),
4.80 (2 H, t, J ) 9.0, -OCHH-), 7.16 (1 H, t, J ) 7.4, 4-H),
7.30 (2 H, d, J ) 7.4, 3- & 5-H). 13C{1H} NMR (δ; CDCl3): 21.7
(-CH3), 23.7 (-CH3), 25.5 (-CH(CH3)2), 43.8 (-CH2-), 61.6
(-CHN-), 76.4 (-OCH2-), 123.9 (Ph, 4-C), 126.7 (Ph, 3- &
5-C), 129.6 (Ph, 2- & 6-C), 168.3 (Ph, 1-C), 173.8 (CdN). MS
(m/z; EI): 514 (M+, 1%), 437 (42), 435 (83), 433 (100), 432 (77),
431 (37) [all M - Br], 376 (5), 327 (2), 271 (10), 57 (36), 55
(39).
C
26H24N2O2, 396.1838.
Rea ction of (S,S)-1,3-Bis(4′-ben zyl-2′-oxa zolin yl)ben -
zen e (5g) w ith LDA/TMEDA. (S,S)-1,3-Bis(4′-benzyl-2′-ox-
azolinyl)benzene (5g; 0.54 g, 1.4 mmol) was lithiated and
quenched as described for the formation of 7 (LDA, 4.08 mmol;
TMEDA, 0.47 g, 4.0 mmol; THF, 20 mL; MeI, 1.93 g, 13.6
mmol). Identical workup and removal of the solvent in vacuo
gave cinnamyl alcohol 8 (0.147 g, 40%) as a yellow oil which
solidified on cooling, Mp: 35-36 °C (lit. mp 34 °C). IR (νmax
;
1
Nujol): 3334 (O-H) cm-1. H NMR (δ; CDCl3): 4.17 (2 H, d,

Pd(II) 2,6-Bis(2′-oxazolinyl)phenyl Complexes
Organometallics, Vol. 19, No. 7, 2000 1289
J ) 5.4 Hz, -CH2-), 6.21 (1 H, dt, J ) 15.8, 5.9, -CHd
CHCH2-), 6.46 (1 H, d, J ) 16.0, -CHdCHCH2-), 7.14-7.23
(5 H, m, Ph).
(-OCH2-), 125.8 (Ph), 127.0 (Ph), 127.2 (Ph), 128.0 (Ph), 129.2
(Ph), 129.6 (Ph), 132.8 (Ph), 142.7 (Ph, 1- & 3-C), 165.8
(CdN); MS (m/z; EI): 382 (M+, 30), 235 (88), 220 (10), 89 (100)
High-resolution MS (m/z): found for M+, 382.1681; calcd for
Rea ction of F er r ocen yloxa zolin e 9 w ith LDA/TMEDA.
(S)-2-Ferrocenyl-4-benzyloxazoline 936 (0.250 g, 0.72 mmol) was
lithiated as described for the formation of 7 (LDA, 1.09 mmol;
TMEDA 0.126 g, 1.08 mmol; THF, 2.5 mL) except that the
reaction mixture was stirred at room temperature for only 30
min and then quenched with 1 M HCl(aq) (5 mL). After
extraction with Et2O (50 mL), the organic phase was dried
(MgSO4), filtered, and concentrated in vacuo and the residue
chromatographed (EtOAc/petroleum ether) to give 1037 (0.01
g, 7%) and 8 (0.07 g, 72%).
C
25H22N2O2, 382.1681.
Gen er a l P r oced u r e for th e P r ep a r a tion of Ca tion ic
[2,6-Bis(2′-oxa zolin yl)p h en yl]a q u op a lla d iu m (II) Sa lt s
16a -e. To a stirred solution of [1,3-bis(2′-oxazolinyl)phenyl]-
palladium(II) bromide (1 equiv) in CH2Cl2/H2O (9.9:0.1 mL per
0.10 g of complexsa corresponding ratio of acetone to H2O was
used for the synthesis of the tetrafluoroborate complexes) in
a foil-covered flask was added the appropriate silver salt (1.2
equiv) as a single portion. The reaction mixture was stirred
for 3 h, and the resultant gray silver bromide precipitate was
removed by filtration through Celite 520 and washed with
additional CH2Cl2 (20 mL). The combined filtrate and washings
were evaporated in vacuo to give a pale gray solid that was
purified by repeated precipitation from CH2Cl2/hexane (acetone/
Et2O for the tetrafluoroborate complexes).
(R,R)-Bis(2-h yd r oxy-1-p h en ylet h yl)-2-b r om o-1,3-ben -
zen ed ia m id e (13f). To a solution of (R)-(-)-2-amino-2-
phenylethanol (1.95 g, 14.2 mmol) in dry chloroform (100 mL)
cooled in an ice/water bath was added a solution of 2-bromo-
1,3-benzene dichloride (1.00 g, 3.6 mmol) in dry chloroform
(30 mL). The reaction mixture was removed from the cooling
bath and stirred at room temperature for 24 h. The resultant
colorless solid was collected by filtration, washed with Et2O
(3 × 100 mL), and recrystallized from hot methanol to give
13f as a colorless crystalline solid (1.56 g, 91%). Mp: 257-
[2,6-Bis(4′,4′-d im eth yl-2′-oxa zolin yl)p h en yl]a qu op a lla -
d iu m (II) Tetr a flu or obor a te (16a 1). 6a (0.15 g, 0.3 mmol)
in acetone/H2O (14.85/0.15 mL) and silver tetrafluoroborate
(0.07 g, 0.4 mmol) gave (0.13 g, 82%) of 16a 1 as a colorless
solid. Mp: 267-270 °C Anal. Found: C, 39.84; H, 4.41; N, 5.91.
Calcd for C16H21BF4N2O3Pd: C, 39.83; H, 4.39; N, 5.81. IR
(νmax; Nujol): 3464 (OH), 1618 (CdN), 1109, 1058, 1007 (BF)
259 °C. Anal. Found: C, 59.52; H, 4.96; N, 6.11. Calcd for
21
C
24H23BrN2O4: C, 59.61; H, 4.79; N, 5.80. [R]D ) -28 (c 0.1,
EtOH). IR (νmax; Nujol): 3278 (NH), 1652 (CdO) cm-1. 1H NMR
(δ; d6-DMSO): 3.59-3.67 (4 H, m, -OCH2-), 4.90-4 95 (2 H,
m, -OH), 5.00-5.05 (2 H, m, -CHN-), 7.20-7.50 (13 H, m,
Ph), 8.85 (2 H, d, J ) 8.2 Hz, -NH). 13C{1H} NMR (δ;
d6-DMSO): 55.5 (-CHN-), 64.5 (-OCH2-), 116.0 (Ph), 126.7
(Ph), 127.0 (Ph), 127.4 (Ph), 127.9 (Ph), 128.7 (Ph), 140.1 (Ph),
140.7 (Ph, 1- & 3-C), 166.7 (CdO). MS (m/z; CI): 485/483 (M+,
2%), 405 (7), 120 (100).
1
cm-1. H NMR (δ; d6-acetone): 1.40 (12 H, s, -CH3), 2.90 (2
H, brs, -OH2), 4.74 (4 H, s, -OCH2-), 7.42 (1 H, t, J ) 6.6
Hz, 4-H), 7.51 (2 H, d, J ) 6.9, 3- & 5-H). 13C{1H} NMR (δ;
d6-acetone): 26.5 (-CH3), 64.9 (-C(CH3)2), 82.5 (-OCH2-),
125.8 (Ph, 4-C), 127.8 (Ph, 3- & 5-C), 130.1 (Ph, 2- & 6-C), 161.9
(Ph, 1-C), 172.8 (CdN).
(S,S)-[2,6-Bis(4′-isop r op yl-2′-oxa zolin yl)p h en yl]a qu o-
p a lla d iu m (II) Tr iflu or om eth a n esu lfon a te (16b2). 6b (0.10
g, 0.2 mmol) in CH2Cl2/H2O (9:1 mL) and AgOSO2CF3 (0.063
g, 0.25 mmol) gave 0.067 g (57%) of 16b2 as a colorless solid.
Mp: 208-210 °C. Anal. Found: C, 39.99; H, 4.29; N, 4.59.
(R ,R )-2-Br om o-1,3-b is(4′-p h e n yl-2′-oxa zolin yl)b e n -
zen e (14f). To a suspension of 13f (0.70 g, 1.4 mmol) in
acetonitrile (30 mL) containing triethylamine (1.02 g, 10.15
mmol) and carbon tetrachloride (1.56 g, 10.1 mmol) was added
dropwise a solution of triphenylphosphine (2.66 g, 10.1 mmol)
in pyridine (40 mL) and acetonitrile (40 mL). The resulting
yellow solution was stirred at room temperature overnight,
concentrated in vacuo, diluted with EtOAc (100 mL), and
washed with water (2 × 75 mL). The organic phase was dried
(MgSO4) and evaporated and the residue column-chromato-
graphed (CH2Cl2-EtOAc (3:2)) to give 14f as a pale yellow oil
20
Calcd for C19H25F3N2O6PdS: C, 39.84; H, 4.40; N, 4.89. [R]D
) +116 (c 0.1, EtOH). IR (νmax; Nujol): 3490 (OH), 1620 (Cd
N), 1289 and 1033 (SO3), 1242, 1161 (CF3) cm-1. H NMR (δ;
1
d6-acetone): 0.88 (6 H, d, J ) 6.9 Hz, -CH3), 0.95 (6 H, d, J )
6.8, -CH3), 2.14-2.21 (2 H, m, -CH(CH3)2), 3.13 (2 H, brs,
-OH2), 4.34-4.40 (2 H, m, -CHN-), 4.87-4.96 (4 H, m,
-OCH2-), 7.40 (1 H, t, J ) 6.7, 4-H), 7.48 (2 H, d, J ) 7.0, 3-
& 5-H). 13C{1H} NMR (δ; d6-DMSO): 14.7 (-CH3), 18.6
(-CH3), 29.9 (-CH(CH3)2), 66.4 (-CHN-), 72.2 (-OCH2-),
125.9 (Ph, 4-C), 128.3 (Ph, 3- & 5-C), 129.5 (Ph, 2- & 6-C), 162.1
(Ph, 1-C), 173.7 (CdN), 202.0 (-CF3).
(S,S)-[2,6-Bis(4′-isop r op yl-2′-oxa zolin yl]p h en yla q u o-
p a lla d iu m (II) Hexa flu or oa n tim on a te (16b3). 6b (0.070 g,
0.14 mmol) in CH2Cl2/H2O (9:1 mL) and AgSbF6 (0.072 g, 0.21
mmol) gave 0.083 g (87%) of 16b3 as a colorless solid. Mp:
20
(0.31 g, 48%). [R]D ) +116 (c 0.1, EtOH). IR (νmax; liquid
1
film): 1657 (CdN) cm-1. H NMR (δ; CDCl3): 4.24 (2 H, t, J
) 8.5 Hz, -OCHH-), 4.75 (2 H, dd, J ) 10.1, 8.5, -OCHH-),
5.33 (2 H, dd, J ) 10.2, 8.5, -CHN-), 7.22-7.32 (10 H, m,
Ph), 7.34 (1 H, t, J ) 7.7, 5-H), 7.71 (2 H, d, J ) 7.9, 4- &
6-H). 13C{1H} NMR (δ; CDCl3): 70.8 (-CHN-), 75.7 (-OCH2-),
126.5 (Ph, 2-C), 127.2 (Ph), 127.6 (Ph), 128.1 (Ph), 129.2 (Ph),
132.4 (Ph), 133.5 (Ph), 142.3 (Ph, 1- & 3-C), 164.8 (CdN). MS
(m/z; EI): 448 (M+, 20%), 446 (5), 368 (3), 89 (100). High-
resolution MS (m/z; EI): found for M+, 446.0630; calcd for
176-179 °C. Anal. Found: C, 32.91; H, 3.71; N, 4.25. Calcd
20
for C18H25F6N2O3PdSb: C, 32.78; H, 3.82; N, 4.25. [R]D
)
+248 (c 0.1, EtOH). IR (νmax; Nujol): 3493 (OH), 1620 (CdN)
C
24H19BrN2O2, 446.0630.
cm-1 1H NMR (δ; CDCl3): 0.87 (6 H, d, J ) 6.8 Hz, -CH3),
.
(R ,R )-2-Me t h yl-1,3-b is(4′-p h e n yl-2′-oxa zolin yl)b e n -
0.98 (6 H, d, J ) 6.8, -CH3), 2.20-2.30 (2 H, m, -CH(CH3)2),
2.37 (2 H, br s, -OH2), 4.36-4.41 (2 H, m, -CHN-), 4.64-
4.73 (4 H, m, -OCH2-), 7.23 (1 H, t, J ) 6.6, 4-H), 7.31 (2 H,
d, J ) 6.9, 3- & 5-H). 13C{1H} NMR (δ; d6-acetone): 14.2
(-CH3), 17.5 (-CH3), 30.2 (-CH(CH3)2), 66.7 (-CHN-), 72.4
(-OCH2-), 125.9 (Ph, 4-C), 128.0 (Ph, 3- & 5-C), 129.6 (Ph, 2-
& 6-C), 162.5 (Ph, 1-C), 174.1 (CdN).
zen e (15). To a solution of 14f (0.059 g, 0.132 mmol) in THF
(5 mL) at -78 °C under nitrogen was added butyllithium (2.5
M, 0.05 mL, 0.13 mmol); the resulting mixture was stirred at
-78 °C for 2 h and quenched with MeI (0.19 g, 1.3 mmol). After
the mixture was warmed to room temperature, workup as
described for 7 and column chromatography (CH2Cl2-EtOAc
(7:3)) gave 15 as a colorless oil (0.01 g, 20%). IR (νmax; liquid
film): 1651 (CdN) cm-1 1H NMR (δ; CDCl3): 2.78 (3 H, s,
.
(S,S)-[2,6-Bis(4′-isob u t yl-2′-oxa zolin yl)p h en yl]a q u o-
p a lla d iu m (II) Hexa flu or oa n tim on a te (16c3). 6c (0.06 g, 0.1
mmol) in CH2Cl2/H2O (4.9:0.1 mL) and silver hexafluoroanti-
monate (0.06 g, 0.2 mmol) gave 16c3 as a colorless solid (0.048
g, 60%). Mp: 154-158 °C. Anal. Found: C, 35.85; H, 4.57; N,
3.97. Calcd for C20H29F6N2O3PdSb: C, 34.94; H, 4.25; N, 4.07.
[R]D20 ) +132 (c 0.1, EtOH). IR (νmax; Nujol): 3501 (OH), 1620
-CH3), 4.21 (2 H, t, J ) 8.4 Hz, -OCHH-), 4.74 (2 H, dd, J
) 10.2, 8.5, -OCHH-), 5.38 (2 H, dd, J ) 10.2, 8.4, -CHN-),
7.20-7.30 (11 H, m, Ph), 7.83 (2 H, d, J ) 7.8, 4- & 6-H). 13C-
{1H} NMR (δ; CDCl3): 19.4 (-CH3), 70.9 (-CHN-), 74.9
(36) Sammakia, T.; Latham, H. A.; Schaad, D. R. J . Org. Chem.
1995, 60, 10.
1
(CdN) cm-1. H NMR (δ; CDCl3): 0.90 (12 H, d, J ) 6.4 Hz,

1290 Organometallics, Vol. 19, No. 7, 2000
Stark et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta for Com p lex 16b2
-CH3), 1.30-1.40 (2 H, m, -CH(CH3)2), 1.61-1.64 (2 H, m,
-CHH-), 1.90-2.00 (2 H, m, -CHH-), 2.06 (2 H, brs, -OH2),
4.30-4.40 (2 H, m, -CHN-), 4.47 (2 H, dd, J ) 8.5, 6.3,
-OCHH-), 4.80 (2 H, t, J ) 9.0, -OCHH-), 7.14 (1 H, t, J )
6.7, 4-H), 7.23 (2 H, d, J ) 7.6, 3- & 5-H). 13C{1H} NMR (δ;
CDCl3): 22.1 (-CH3), 23.9 (-CH3), 25.5 (-C(CH3)2), 44.2
(-CH2-), 61.4 (-CHN-), 76.9 (-OCH2-), 125.5 (Ph, 4-C),
128.0 (Ph, 3- & 5-C), 130.1 (Ph, 2- & 6-C), 171.0 (Ph, 1-C), 173.9
(CdN).
formula
fw
C19H25F3N2O6PdS
572.87
temp, K
wavelength, Å
cryst syst
space group
a, Å
150(2)
0.71069
monoclinic
I2 (No. 5)
11.932(3)
b, Å
12.755(4)
c, Å
15.422(3)
(S,S)-[2,6-Bis(4′-ter t-bu tyl-2′-oxa zolin yl)p h en yl]a qu o-
p a lla d iu m (II) Hexa flu or oa n tim on a te (16d 3). 6d (0.10 g,
0.2 mmol) in CH2Cl2/H2O (9.9:0.1 mL) and silver hexafluoro-
antimonate (0.08 g, 0.2 mmol) gave 16d 3 as a colorless solid
(0.039 g, 29%). Mp: 238-240 °C. Anal. Found: C, 35.19; H,
4.36; N, 3.95. Calcd for C20H29F6N2O3PdSb: C, 34.94; H, 4.25;
â, deg
98.42(2)
2321.8(10)
4
1.639
0.893
V, Å3
Z
d
calcd, g cm-3
µ, mm-1
F(000)
1160
cryst size, mm
θ range, deg
no. of rflns coll
no. of indep rflns
no. of data/restraints/params
GOF on F2
0.25 × 0.20 × 0.15
2.02-25.11
5152
3225 (Rint ) 0.0691)
3225/67/297
0.998
20
N, 4.07. [R]D ) +204 (c 0.1, EtOH). IR (νmax; Nujol): 3504
1
(OH) 1614 (CdN) cm-1. H NMR (δ; d6-acetone): 0.98 (18 H,
s, -CH3), 2.93 (2 H, brs, -OH2), 4.05 (2 H, dd, J ) 9.0, 3.0
Hz, -CHN-), 4.90 (2 H, t, J ) 9.3, -OCHH-), 5.13 (2 H, dd,
J ) 9.6, 3.0, -OCHH-), 7.44 (1 H, t, J ) 6.8, 4-H), 7.52 (2 H,
d, J ) 7.2, 3- & 5-H). 13C{1H} NMR (δ; d6-acetone): 25.8
(-CH3), 35.7 (-C(CH3)3), 71.7 (-CHN-), 74.5 (-OCH2-),
126.8 (Ph, 4-C), 128.9 (Ph, 3- & 5-C), 130.4 (Ph, 2- & 6-C), 162.5
(Ph, 1-C), 176 (CdN).
final R indices (I > 2σ(I))
R indices (all data)
R1 ) 0.0522, wR2 ) 0.1281
R1 ) 0.0647, wR2 ) 0.1308
(Na2SO4), the solvent was removed in vacuo, and the resultant
oil obtained was purified by Kugelrohr distillation.
(S ,S )-[2,6-Bis(4′-(cycloh e xylm e t h yl)-2′-oxa zolin yl)-
p h en yl]a qu op a lla d iu m (II) Hexa flu or oa n tim on a te (16e3).
6e (0.25 g, 0.4 mmol) in CH2Cl2/H2O (19:1 mL) and silver
hexafluoroantimonate (0.174 g, 0.51 mmol) gave 16e3 as a
colorless solid (0.090 g, 28%). Mp: 150-152 °C Anal. Found:
5-Cya n o-5-(ca r boeth oxy)n on a n e-2,8-d ion e (19).34b Col-
orless oil. IR (νmax; liquid film): 2244 (CdN), 1745 (CdO), 1719
(CdO) cm-1 1H NMR (δ; CDCl3): 1.31 (3 H, t, J ) 7.1 Hz,
.
-CH3), 2.05-2.22 (4 H, m, -CH2-), 2.15 (6 H, s, -COCH3),
2.54-2.69 (4 H, m, -CH2CO-), 4.24 (2 H, J ) 7.1, q,
-OCH2-).
C, 40.84; H, 4.76; N, 3.67. Calcd for C26H37F6N2O3PdSb: C,
20
40.68; H, 4.86; N, 3.65. [R]D ) +176 (c 0.1, EtOH). IR (νmax
;
Eth yl 2-Cya n o-2-m eth yl-5-oxoh exa n oa te (20a ).34b Color-
less oil. IR (νmax; liquid film): 2244 (CdN), 1744 (CdO), 1727
Nujol): 3498 (OH), 1620 (CdN) cm-1 1H NMR (δ; d6-
.
acetone): 0.95-1.98 (28 H, m, -CH2Cy and -OH2), 4.30-4.37
(2 H, m, -CHN-), 4.47 (2 H, dd, J ) 8.5 Hz, 6.4, -OCHH-),
4.79 (2 H, t, J ) 9.0, -OCHH-), 7.14 (1 H, t, J ) 7.2, 4-H),
7.23 (2 H, d, J ) 7.5, 3- & 5-H). 13C{1H} NMR (δ; d6-acetone):
26.2 (-CH2-), 26.4 (-CH2-), 32.8 (-CH2-), 34.3 (-CH2-),
34.6 (-CH2CH-),42.9 (-CH2-),61.0 (-CHN-),77.4 (-OCH2-),
126.2 (Ph, 4-C), 128.2 (Ph, 3- & 5-C), 130.3 (Ph, 2- & 6-C), 168.0
(Ph, 1-C), 174.3 (CdN).
(CdO) cm-1 1H NMR (δ; CDCl3): 1.29 (3 H, t, J ) 7.1 Hz,
.
-CH3), 1.58 (3 H, s, -C(CN)CH3), 1.96-2.21 (2 H, m, -CH2-),
2.12 (3 H, s, -COCH3), 2.54-2.64 (2 H, m, -CH2-), 4.22 (2
H, q, J ) 7.1, -OCH2-).
ter t-Bu tyl 2-Cya n o-2-m eth yl-5-oxoh exa n oa te (20b).34b
Colorless oil. IR (νmax; liquid film): 2243 (CdN), 1741 (CdO),
1727 (CdO) cm-1. 1H NMR (δ; CDCl3): 1.49 (9 H, s, -C(CH3)3),
1.55 (3 H, s, -C(CN)CH3), 1.99-2.21 (2 H, m, -CH2-), 2.17
(3 H, s, -COCH3), 2.56-2.68 (2 H, m, -CH2-).
(S,S)-[2,6-Bis(4′-isop r op yl-2′-oxa zolin yl)p h en yl](a ceto-
n itr ile)p a lla d iu m (II)Hexa flu or oa n tim on a te (17). Com-
plex 16b3 (0.030 g, 0.05 mmol) was dissolved in acetone (4 mL)
and the solution degassed and placed under nitrogen. Aceto-
nitrile (24 µL, 0.46 mmol) was added dropwise to the homo-
geneous solution and the mixture stirred overnight. The
solution was concentrated in vacuo to ca. 1 mL, and addition
of diethyl ether (20 mL) caused precipitation of an off-white
solid (0.0185 g, 60%). Mp: 100-104 °C. Anal. Found: C, 35.37;
H, 4.04; N, 5.89. Calcd for C20H26F6N3O2PdSb: C, 35.19; H,
4,4-Bis(ca r boeth oxy)-4-n itr obu ta n on itr ile (21). Color-
less oil. Anal. Found: C, 46.74; H, 5.70; N, 10.87. Calcd for
C
10H14N2O6: C, 46.51; H, 5.46; N, 10.85. IR (νmax; liquid film):
2253 (CdN), 1753 (CdO), 1571 (NO2) cm-1 1H NMR (δ;
.
CDCl3): 1.31 (6 H, t, J ) 7 Hz, -CH3), 2.72-2.75 (2 H, m,
-CH2-), 2.78-2.83 (2 H, m, -CH2-), 4.36 (4 H, q, J ) 7,
-OCH2-). 13C{1H} NMR (δ; CDCl3): 12.99 (-CH2-), 13.64
(-CH3), 29.78 (-CH2-), 64.38 (-OCH2-), 95.11 (-C(NO2)-),
117.56 (-CdN), 161.59 (CdO). MS (m/z; EI): 259 (M+, 5%),
213 (7), 185 (5), 112 (100).
20
3.84; N, 6.16. [R]D ) +120 (c 0.1, EtOH). IR (νmax; Nujol):
2320, 2292 (CdN), 1616 (CdN) cm-1. 1H NMR (δ; CDCl3): 0.89
(6 H, d, J ) 7 Hz, -CH3), 1.00 (6 H, d, J ) 7, -CH3), 2.10-
2.20 (2 H, m, -CH(CH3)2), 2.40 (3 H, br s, -CH3), 4.30-4.36
(2 H, m, -CHN-), 4.64-4.76 (4 H, m, -OCH2-), 7.23 (1 H, t,
J ) 8, 4-H), 7.31 (2 H, d, J ) 8, 3- & 5-H). 13C{1H} NMR (δ;
CDCl3): 12.5 (-CH3), 14.9 (-CH3), 18.4 (-CH3), 30.4 (-CH-
(CH3)2), 66.8 (-CHN-), 72.0 (-OCH2-), 125.5 (Ph, 4-C), 127.8
(Ph, 3- & 5-C), 129.6 (Ph, 2- & 6-C), 142.5 (-CdN), 163.1 (Ph,
1-C), 174.4 (CdN).
2-(Ca r boeth oxy)-2-m eth ylp en ta n ed in itr ile (22).32b Col-
orless oil. IR (νmax; liquid film): 2241 (CdN), 1745 (CdO) cm-1
.
1H NMR (δ; CDCl3): 1.38 (3 H, t, J ) 7 Hz, -CH3), 1.70 (3 H,
s, -C(CN)CH3), 2.15 (1 H, ddd, J ) 14, 9, 6, -CHHCN), 2.35-
2.70 (3 H, m, -CH2CHHCN), 4.30 (2 H, q, J ) 7, -OCH2-).
Cr ysta l Str u ctu r e Deter m in a tion . The method employed
for the crystal structure determination of 16b2 was performed
as previously described.38 The noncentrosymmetric space group
I2 (a nonstandard setting of C2) was confirmed by the
successful solution and refinement of the structure. It is also
consistent with only one-handed cationic complex species being
present in the crystal. Initial attempts to solve the structure
in the centrosymmetric space group I2/m were unsuccessful.
Crystal data, details of data collection, and refinement are
given in Table 2.
Gen er a l P r oced u r e for P a lla d iu m -Ca ta lyzed Mich a el
Rea ction s. Under a nitrogen atmosphere, the catalyst (0.012
g, 0.01 equiv) was dissolved in either dry CH2Cl2 or dry toluene
(4 mL). The cyano or nitro ester (1 equiv) was added dropwise
via a syringe, followed by the neat Michael acceptor (1.5 equiv)
and finally N-ethyldiisopropylamine (0.1 equiv. or 0.01 equiv).
The homogeneous reaction mixture was stirred and monitored
1
by H NMR spectroscopy. After the ester had been consumed,
(37) Broadhead, G. D.; Osgerby, J . M.; Pauson, P. L. Chem. Ind.
1957, 209
(38) Locke, A. J .; Richards, C. J . Organometallics 1999, 18, 3750.
the reaction mixture was diluted with CH2Cl2 (30 mL) and
washed with 1 M HCl (20 mL). The organic layer was dried

Pd(II) 2,6-Bis(2′-oxazolinyl)phenyl Complexes
Organometallics, Vol. 19, No. 7, 2000 1291
Ack n ow led gm en t. This work was supported by the
Link Asymmetric Synthesis Core Program, and we wish
to thank the participating companies and the EPSRC
for a studentship to M.A.S. In addition, we wish to
thank Dr. J . Whittall (Lancaster Synthesis), Dr. J . Paul
(Chiroscience), and Dr. G. Potter for their contribution
to this program. G.J . also acknowledges the EPSRC for
support, and we all thank the EPSRC Mass Spectrom-
etry Service (Swansea, U.K.) for their speedy turn-
around. In addition, we also thank D. E. Hibbs, K. M.
A. Malik, and M. B. Hursthouse for the crystal structure
determination.
Su p p or tin g In for m a tion Ava ila ble: Text giving full
characterization data for 16a 2, 16a 3, 16b1, 13g, 14g, 18, and
12 and details of the X-ray structure determination of 16b2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM990710H