[PtCL3(C2H4)]-[AmH]+ complexes containing chiral secondary amines: Use as chiral derivatizing agents for the enantiodiscrimination of unsaturated compounds by 195Pt NMR spectroscopy and NMR stereochemical investigation

Article abstract of DOI:10.1021/jo001165t

Ionic complexes [PtCl₃(C₂H₄)]^-[AmH]⁺, containing chiral secondary amines, constitute a versatile class of chiral derivatizing agents (CDAs) for the enantiomeric purity determination of chiral unsaturated compounds via ¹⁹⁵Pt NMR spectroscopy. The NMR conformational analysis allows us to search for the stereochemical basis of their enhanced versatility.

Full text of DOI:10.1021/jo001165t

J . Org. Chem. 2001, 66, 123-129
123
[P tCl3(C2H4)]-[Am H]+ Com p lexes Con ta in in g Ch ir a l Secon d a r y
Am in es: Use a s Ch ir a l Der iva tizin g Agen ts for th e
En a n tiod iscr im in a tion of Un sa tu r a ted Com p ou n d s by 195P t NMR
Sp ectr oscop y a n d NMR Ster eoch em ica l In vestiga tion
Gloria Uccello-Barretta, Raffaella Bernardini, Federica Balzano, and Piero Salvadori*
Centro di Studio del CNR per le Macromolecole Stereordinate ed Otticamente Attive, Dipartimento di
Chimica e Chimica Industriale, via Risorgimento 35, 56126 Pisa, Italy
psalva@dcci.unipi.it
Received J uly 31, 2000
Ionic complexes [PtCl3(C2H4)]-[AmH]+, containing chiral secondary amines, constitute a versatile
class of chiral derivatizing agents (CDAs) for the enantiomeric purity determination of chiral
unsaturated compounds via 195Pt NMR spectroscopy. The NMR conformational analysis allows us
to search for the stereochemical basis of their enhanced versatility.
Ch a r t 1
In tr od u ction
The heightened interest in asymmetric syntheses
raises the need for efficient, versatile and practical
solutions for determining the enantiomeric composition
of the products.
In the area of nonchiroptical techniques, NMR methods
based on the use of a chiral auxiliary to convert the
enantiomeric mixture into diastereoisomeric derivatives
and on the detection of their anisochronous resonances
represent one of the most popular choices.1 Three classes
of chiral auxiliaries for NMR spectroscopy have been
developed, chiral derivating agents (CDAs)1,2 employed
to convert the enantiomeric pair into a diastereoisomeric
mixture by a chemical transformation and chiral solvat-
ing agents (CSAs)1,3 and chiral lanthanide shift reagents
(CLSRs)1,4 which form diastereoisomeric adducts by
noncovalent interactions.
Both organic1,2 and organometallic1,5 CDAs have been
proposed: the former compounds have found extensive
applications in the analyses of chiral substrates endowed
with polar functionalities, the latter compounds have
received more limited attention even if they have inter-
esting potentialities. In fact, their use can involve the
simple coordination of π-moieties of the chiral substrates
to the metal as a derivatization process opening the way
to the analyses of compounds devoid of polar function-
alities, such as the simple olefins or aromatic hydrocar-
bons. The use of organometallic platinum CDAs also gives
the interesting possibility of detecting the diastereotopic
species by the simple analyses of the resonances of their
195Pt nuclei (I ) 1/2, natural abundance 33.8%).
In the past years, we have proposed the use as CDAs
of cis-5f,g (cis-a ) and trans-dichloro(ethylene)(amine)-
platinum(II)5h,i (trans-a ) (Chart 1), containing the chiral
(5) (a) Parker, D.; Taylor, R. J . Tetrahedron 1988, 44, 2241-2248.
(b) Parker, D.; Taylor, R. J . J . Chem. Soc., Chem. Commun. 1987,
1781-1783. (c) Wiesauer, C.; Kratky, C.; Weissensteiner, W. Tetra-
hedron: Asymmetry 1996, 7, 397-398. (d) Chooi, S. Y. M.; Leung, P.-
H.; Lim, C. C.; Mok, K. F.; Quek, G. H.; Sim, K. Y.; Tan, M. K.
Tetrahedron: Asymmetry 1992, 3, 529-532. (e) Buriak, J . M.; Osborn,
J . A. J . Chem. Soc., Chem. Commun. 1995, 689-690. (f) Salvadori, P.;
Uccello-Barretta, G.; Bertozzi, S.; Settambolo, R.; Lazzaroni, R. J . Org.
Chem. 1988, 53, 5768-5770. (g) Uccello-Barretta, G.; Bernardini, R.;
Lazzaroni, R.; Salvadori P. J . Organomet. Chem. 2000, 598, 174-178.
(h) Salvadori, P.; Uccello-Barretta, G.; Lazzaroni, R.; Caporusso, A.
M. J . Chem. Soc., Chem. Commun. 1990, 1121-1123. (i) Uccello-
Barretta, G.; Balzano, F.; Salvadori, P.; Lazzaroni, R.; Caporusso, A.
M.; Menicagli, R. Enantiomer 1996, 1, 365-375. (j) Dunina, V. V.;
Kuz’mina, L. G.; Kazakova, M. Yu.; Grishin, Yu. K.; Veits, Yu. A.;
Kazakova, E. I. Tetrahedron: Asymmetry 1997, 8, 2537-2545. (k)
Staubach, B.; Buddrus, J . Angew. Chem., Int. Ed. Engl. 1996, 35,
1344-1346. (l) Albert, J .; Granell, J .; Muller, G.; Sainz, D.; Font-
Bardia, M.; Solans, X. Tetrahedron: Asymmetry 1995, 6, 325-328. (m)
Klein, J .; Neels, S.; Borsdorf, R. J . Chem. Soc., Perkin Trans. 2 1994,
2523-2524. (n) Chelucci, G.; Bacchi, A.; Fabbri, D.; Saba, A.; Ulgheri,
F. Tetrahedron Lett. 1999, 40, 553-556. (o) Alcock, N. W.; Hulmes, D.
I.; Brown, J . M. J . Chem. Soc., Chem. Commun. 1995, 395-397. (p)
Wu, R.; Odom, J . D.; Dunlap, R. B.; Silks III, L. A. Tetrahedron:
Asymmetry 1999, 10, 1465-1470.
* To whom correspondence should be addressed. Tel: +39-050-
918203. Fax: +39-050-918409.
(1) Parker, D. Chem. Rev. 1991, 91, 1441-1457.
(2) (a) Yamaguchi, S. In Asymmetric Synthesis; Morrison, J . D., Ed.;
Academic: New York, 1983; Vol. 1, pp 125-152. (b) Hulst, R.; Kellogg,
R. M.; Feringa, B. L. Recl. Trav. Chim. Pays-Bas 1995, 114, 115-138.
(3) (a) Weisman, G. R. In Asymmetric Synthesis; Morrison, J . D.,
Ed.; Academic: New York, 1983; Vol. 1, pp 153-171. (b) Pirkle, W.
H.; Hoover, D. J . Top. Stereochem. 1982, 13, 263-331.
(4) (a) Fraser, R. R. In Asymmetric Synthesis; Morrison, J . D., Ed.;
Academic: New York, 1983; Vol. 1, pp 173-196. (b) Sullivan, G. R.
Top. Stereochem. 1978, 10, 287-329. (c) McCreary, M. D.; Lewis, D.
W.; Wernick, D. L.; Whitesides, G. M. J . Am. Chem. Soc. 1974, 96,
1038-1054.
10.1021/jo001165t CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/09/2000

124 J . Org. Chem., Vol. 66, No. 1, 2001
Uccello-Barretta et al.
Sch em e 1
Ch a r t 2
of the enantiodiscriminating capabilities of these new
ionic and covalent CDAs, their conformation has been
investigated by NMR methods.7
Resu lts a n d Discu ssion
Syn t h esis a n d Ch a r a ct er iza t ion of t h e Am in e
Liga n d s. The employed procedure8 for the diastereose-
lective syntheses of chiral secondary amines b-d , having
two chiral centers directly bound to the same nitrogen,
involves the condensation reaction between an enantio-
merically pure chiral primary amine and a prochiral
ketone to give the syn/anti mixture of the imines, followed
by catalytic hydrogenation (Pd/C 10%) (Scheme 2). The
hydrogenation product is constituted by a mixture of two
diastereoisomeric amines (ca. 90:10), from which the
prevalent species is isolated by simple crystallization of
the hydrochloride derivatives b′-d ′. The crystallized
products b′ and c′ were obtained as optically active (S,S)-
stereoisomers. The absolute configuration of d ′ has been
established by determining the relative stereochemistry
of the two chiral moieties (S)-1-phenylethyl and 1-(1-
naphthyl)ethyl by NOE measurements, to obtain the
spatial proximity constraints between them. The detected
effects (Supporting Information, Figure S1), indicated in
Figure 1 by arrows, demonstrated that the two methine
protons are cis each other, with the methine of the 1-(1-
naphthyl)ethyl moiety mainly directed toward the peri
proton H8 and in spatial proximity of the phenyl group
of the other unit. The methine group of the 1-phenylethyl
fragment is directed toward the H2 proton of the naphthyl
ring. The absolute configuration of the 1-phenylethyl
group is prefixed and S, so the S absolute configuration
must be assigned to the other chiral fragment.
primary amine (S)-1-phenylethylamine (a ), in the analy-
ses of chiral unsaturated compounds. Even though the
cis complex showed a very large applicability to the
analyses of unsaturated ethers, its synthesis is time-
consuming and proceeds with satisfactory yields only in
the case of primary amines. The applicability of the
trans-a was rather limited. Their use5f-i is based on the
fast exchange of the ethylene with the enantiomeric
mixture, the coordination of which occurs by the two
prochiral faces of the double bond (Scheme 1). Therefore,
each enantiomer can originate a maximum number of
two diastereoisomers, the ratio of which reflects the
diastereoselectivity in the complexation. When the dias-
tereoisomers formed by the two enantiomers produce
distinct 195Pt NMR resonances, the comparison between
their integrated areas directly gives the enantiomeric
purity of the complexed substrates.
More recently, we have shown6 the great potentialities
of the ionic organometallic CDA [PtCl3(C2H4)]-[AmH]+
ionic-b (Chart 1), containing the chiral secondary amine
(1S,1′S)-bis(1-phenylethyl)amine (b), which was remark-
ably more versatile than cis-a or trans-a . Indeed, it
discriminates trisubstitued allenes, unsaturated ethers,
and simple olefins also.
Keeping in mind the aforementioned results, we have
prepared the new ionic organometallic complexes ionic-c
and ionic-d (Chart 1), respectively, containing the chiral
secondary amines (1S,1′S)-bis[1-(1-naphthyl)ethyl]amine
(c) and (1S,1′S)-N-[1′-(1-naphthyl)ethyl]-1-phenylethyl-
amine (d ), to investigate the effect of structural changes
in the ammonium cation on the efficiency and versatility
of CDAs for the 195Pt NMR enantiodiscrimination of
several classes of chiral unsaturated compounds 1-9
(Chart 2). Their enantiodiscriminating capabilities have
also been compared to those of the trans-covalent CDAs
trans-b -d , containing the corresponding secondary
amines, as well as the complexes ionic-e and trans-e,
where the primary amine (S)-1-(1-naphthyl)ethylamine
(e) has been employed (Chart 1). Furthermore, with the
aim of having some insight into the stereochemical basis
Syn th esis a n d Ch a r a cter iza tion of th e CDAs. Ionic
and covalent CDAs ionic-b-e and trans-b-e (Chart 1)
have been prepared starting from Zeise’s salt [PtCl3-
(C2H4)]-K+ following the procedures described in ref 6.
The complexes have been employed without further
purification.
The CDAs have been characterized by 1H and 13C NMR
spectroscopy in CDCl3 as solvent: the 1H characterization
in some cases required the comparison between the 2D
NOESY and 2D DQF-COSY maps and the 13C spectra
have been attributed by bidimensional heteronuclear
1
correlation HETCOR. The H NMR spectra of the ionic
complexes ionic-b-d (Supporting Information, Figure S2)
show the signals arising from the amine portion, very
similar to those of the hydrochloride amine. For ionic-
b-c the methyl, methine and aromatic protons of the two
chiral residues are isochronous. The well recognizable
(7) Neuhaus, D.; Williamson, M. P. The Nuclear Overhauser Effect;
WCH Publishers: New York, 1989.
(8) (a) Overberger, C. G.; Marullo, N. P.; Hiskey, R. G. J . Am. Chem.
Soc. 1961, 83, 1374-1378. (b) Eleveld, M. B.; Hogeveen, H.; Schudde,
E. P. J . Org. Chem. 1986, 51, 3635-3642.
(6) Uccello-Barretta, G.; Bernardini, R.; Lazzaroni, R.; Salvadori P.
Org. Lett. 2000, 2, 1795-1798.

[PtCl3(C2H4)]-[AmH]+ Complexes
J . Org. Chem., Vol. 66, No. 1, 2001 125
Sch em e 2
F igu r e 1. Representation of the ammonium cation of b′-d ′.
ethylene resonance is a sharp singlet accompanied by the
satellites which result from the coupling with 195Pt. For
all ionic complexes ethylene protons behave as a simple
A4 system, indicating the free rotation of the coordinated
ethylene.9 Very different spectral patterns have been
observed for the covalent complexes trans-b-d : in
trans-b or trans-c the coordination of the nitrogen makes
anisochronous the two amine methyl, methine and
aromatic groups. However, the coordinated ethylene
maintains the A4 pattern in trans-b (Figure 2a) and
produces a symmetrical multiplet corresponding to an
AA′BB′ system in trans-c (Figure 2b), to indicate that
ethylene is freely rotating in the former and its rotation
is restricted (at room temperature) in the latter. In both
cases the amine proton shows coupling to platinum. A
very complicated spectrum is obtained for trans-d , show-
ing simultaneous presence of two main species in a ratio
80:20, the prevailing one having the ethylene in free
rotation (A4 system) and the minor one having it in
hindered rotation (AA′BB′) (Figure 2c). These two species
reasonably are due to the fact that, in this case, the
nitrogen is chiral and its coordination generates two
diastereoisomers corresponding to the two sets of signals.
Accordingly, the platinum spectrum of each ionic complex
ionic-b-d , and covalent trans-b-c shows a single ab-
sorption, whereas the complex trans-d shows two signals
at -2909.6 ppm and -2916.6 ppm, corresponding to the
two diastereoisomers.
F igu r e 2. 1H NMR spectral regions (300 MHz, CDCl3, 25 °C)
corresponding to the ethylene resonances of trans-covalent
complexes: (a) trans-b, (b) trans-c, and (c) trans-d .
deuterated solvent (C6D6). By using a small excess of the
CDA (CDA/substrate ) 1:0.8) the fast exchange reaction
occurs without detectable kinetic resolution phenomena.
The diastereoisomeric mixtures are directly analyzed by
195Pt NMR spectroscopy and the magnitudes of un-
equivalences (∆δ, differences between the chemical shifts
of the diastereoisomers containing the two enantiomers)
measured in the spectra reflect the enantiodiscriminating
capabilities of the CDAs used. Due to the possibility to
have four or two signals in the spectra, two unequiva-
lences values must be defined, calculated as differences
between the 195Pt NMR chemical shifts of the more (∆δ1)
and less (∆δ2) abundant diastereoisomers formed by the
two enantiomers (Table 1). The data reported in Table 1
summarize the results obtained in the use of the com-
plexes ionic-b-d as CDAs for the unsaturated chiral
substrates 1-9 (Chart 2) and demonstrate that the
nature of the amine hydrochloride strongly affects the
unequivalences.
The diastereoisomeric mixtures originated by complex-
ation of the trisubstituted allene 1 always produce two
signals, each due to one enantiomer and the unequiva-
lence is 376 Hz by using ionic-b and remarkably in-
creases to 496 Hz in the presence of the analogous cation
having the 1-(1-naphthyl)ethyl moiety (ionic-c) (Figure
3) and to 440 Hz for CDA ionic-d , where the mixed amine
derivative is employed. Also for the diastereoisomeric
mixtures arising from the complexation of the allene 2,
producing two signals for each complexed enantiomer,
Use of CDAs. The enantiodiscrimination experiments
involve the displacement of the coordinated ethylene in
the CDAs by the unsaturated chiral substrates (Scheme
1). This reaction can be very easily performed by dissolv-
ing a mixture of the CDA and of the substrate in the
(9) (a) Lazzaroni, R.; Uccello-Barretta, G.; Bertozzi, S.; Salvadori,
P. J . Organomet. Chem. 1984, 275, 145-152. (b) Lazzaroni, R.; Uccello-
Barretta, G.; Bertozzi, S.; Salvadori, P. J . Organomet. Chem. 1985,
297, 117-129.

126 J . Org. Chem., Vol. 66, No. 1, 2001
Uccello-Barretta et al.
Ta ble 1. 195P t NMR (64.3 MHz, C6D6, 25 °C)
Un equ iva len ces (Hz) Mea su r ed by Usin g ion ic-b-d a s
CDAs, Given a s Differ en ces betw een th e Ch em ica l Sh ifts
of th e Mor e (∆δ1) a n d Less (∆δ2) Abu n d a n t
Dia ster eoisom er s in th e Com p lexes F or m ed w ith
Com p ou n d s 1-9
ionic complex ionic-b.6 For all other unsaturated sub-
strates, trans-b did not allow to measure significant
unequivalences. In the use of trans-c as CDA, the 195Pt
NMR spectra of the diastereoisomeric mixtures reveal the
presence of a great number of complexed species (see the
Supporting Information, Figure S3, as an example),
which can be explained taking into account that also
complexed ethylene is not freely rotating in the CDA and,
hence, in the complexation of nonsymmetrical unsatur-
ated chiral compounds, simultaneous presence of differ-
ent rotamers must be expected for each diastereoisomer.
The situation is more complicated in the use of CDA
trans-d , which, due to the chirality of nitrogen, is present
as a mixture of two diastereoisomers one having the
ethylene in free rotation and the other slowly rotating.
Therefore, trans-b has a limited enantiodiscriminating
capability and trans-c and trans-d cannot be employed
at all as CDAs.
ionic-b
ionic-c
ionic-d
substrate
∆δ1
∆δ2
∆δ1
∆δ2
∆δ1
∆δ2
1
2
3
4
5
6
7
8
9
376a
420a
118a
134
99
496
515
145
243
187
373
132
180
153
440
437
109
182
71
224
84
116
0
372a
148a
284
270
0
473
189
343
240
473
292
93
391
147
361
148
355
182
0
0
120a
141
114a
196a
48
0a
0
0
a
Data reported in ref 6.
The covalent complex trans-e containing the primary
amine (S)-1-(1-naphthyl)ethylamine does not discrimi-
nate the enantiomers of allene 2 and the corresponding
ionic complex ionic-e only produces very small unequiva-
lences (Supporting Information, Figure S4).
Ster eoch em ica l An a lysis of CDAs. As already dis-
cussed, the stereochemistry of the asymmetrical amine
d as well as of its hydrochloride salt d ′ has been
determined by NOE measurements. The intrinsic equiva-
lence of corresponding nuclei of the two chiral units of
b′ unabled us to define its conformation. In c′, a highly
diagnostic NOE between the methine protons and the
naphthalene proton H7 was detected, indicating that the
C-H bond of one 1-(1-naphthyl)ethyl group points at the
H7 aromatic proton of the other chiral residue (Figure
1). Thus, the two methines must be cis and internal to
the structure of the amine, and, being (S,S), the absolute
configuration of the two chiral carbon atoms, the two
naphthalene rings must be trans as well as the methyl
groups. Hence, the conformation of c′ is similar to that
of d ′, and it can be reasonably extended to b′ (Figure 1).
In the ionic complexes ionic-b-d , the ammonium
cations show the same NOEs patterns detected in the
free state and the ethylene produces an A4 resonance
system in the 1H NMR spectra, indicating that it is freely
rotating around the coordination axis. This last one
produces NOEs (Supporting Information, Figure S5) only
on the methyl and aromatic protons of the amine (mainly
H2 and H3 in the case of ionic-c and both H2-H3 and
phenyl protons for ionic-d ), and no dipolar interaction is
detected with the methine protons. Therefore, in the
hypothesis that the ammonium cation interacts, via
formation of an hydrogen bond, with the chlorine atom
trans to ethylene, the two chiral units lie on opposite
sides with respect to the coordination plane with the
aromatic ring of one unit and the methyl group of the
other one pointing at the metal and hence at the ethylene
as in Figure 5. In the complex ionic-d , containing the
mixed secondary ammonium cation d ′, the NOEs pro-
duced by the ethylene on both naphthalene and phenyl
protons and on the methyl groups indicate that the CDA
is present in solution as a mixture, fast exchanging on
NMR time scale, of the two possible structures repre-
sented in Figure 5.
F igu r e 3. 195Pt NMR spectrum (64.3 MHz, C6D6, 25 °C, Na2-
PtCl6 as external standard) of the diastereoisomeric mixtures
formed from rac-1 and ionic-c.
F igu r e 4. 195Pt NMR spectrum (64.3 MHz, C6D6, 25 °C, Na2-
PtCl6 as external standard) of the diastereoisomeric mixtures
formed from (S)-2 (ee 18%) and ionic-c.
the unequivalences measured are markedly superior by
using ionic-c (∆δ1 515 Hz and ∆δ2 473 Hz) (Figure 4) than
they are for ionic-b (∆δ1 420 Hz and ∆δ2 372 Hz) or
ionic-d (∆δ1 437 Hz and ∆δ2 391 Hz). In the complexation
of open-chain vinyl ethers 3-5, the superior perfor-
mances of CDA ionic-c with respect to ionic-b and ionic-d
are evidenced once again at least for the ∆δ1 value. In
the case of cyclic allyl ether 6 only by using ionic-c and
ionic-d enantiodiscrimination is observed. The complex
ionic-c is also the more efficient CDA for the analyses of
simple olefins 7-8. For the chiral olefin 9, having the
chiral carbon atom in beta position to the double bond,
unequivalences are measured only for the more abundant
diastereoisomers produced by ionic-c and ionic-b, but this
fact does not prevent us from determining the enantio-
meric composition as this can be also based on the
comparison between the areas of the signals originated
by two corresponding species (the more or less abundant
diastereoisomers). This is exact as a consequence of the
fact that the same diastereoselectivity for the complex-
ation of the two enantiomers of each substrate is ob-
served.
By extending the analysis to the corresponding trans-
covalent complexes trans-b-d , we can observe that only
in the case of trisubstituted allene 2 the complex trans-b
has efficiency comparable to that of the corresponding
In the formation of trans-covalent complexes trans-b
and trans-c, corresponding nuclei of the two chiral
residues become unequivalent as a consequence of the
complexation of the nitrogen. As obtained from NOE

[PtCl3(C2H4)]-[AmH]+ Complexes
J . Org. Chem., Vol. 66, No. 1, 2001 127
and the methyl group of the amine has been detected to
indicate that the aromatic group is far away from the
coordinated olefin.
Con clu sion s
The efficiency of the new ionic platinum(II) complexes,
containing secondary amines, is strongly dependent on
the nature of aromatic group present in the amine, the
highest unequivalences for the complex containing the
more hindered (1S,1′S)-bis[1-(1-naphthyl)ethyl]amine be-
ing measured. In fact, this last one allows us to detect
unequivalences in the 195Pt NMR spectra of the diaste-
reoisomeric mixtures arising from the complexation to
the metal of trisubstituted allenes, simple olefins having
the stereogenic centers R or â to the double bond, vinyl
ethers, and allyl ethers. Therefore, it represents one of
the most versatile organometallic CDAs for the analyses
of chiral unsaturated compounds. This is an important
result, taking into account that, overall in the case of
simple olefins, no alternative methods are available.
By contrast, the corresponding trans-covalent CDAs
containing secondary amines have remarkable limita-
tions: their applicability is limited as only symmetrical
secondary amines having reduced steric hindrance can
be employed. In fact, the diastereoisomeric mixtures
obtained from trans-c produce very complicated 195Pt
NMR spectra due to the presence of several slow-
exchanging rotamers for each complexed species. The
trans-covalent CDA containing (1S,1′S)-N-[1′-(1-naphth-
yl)ethyl]-1-phenylethylamine also adds the problem of
being present in solution as a diastereoisomeric mixture
due to the stereogenicity of the nitrogen.
F igu r e 5. Representation of the ionic complexes ionic-b-d .
The results obtained explain the enhanced efficiency
of ionic complexes containing secondary amines with
respect to those containing primary amines: in the
former ones the unsaturated ligand simultaneously
interacts with the alkyl and aromatic substituents of the
amine lying on opposite sides of the coordination plane,
in the latter ones the complexed olefin is only affected
by the amine on one side of the coordination plane. In
ionic-c, which is the more efficient CDA, the interaction
with the complexed olefin involves the naphthalene ring
of the amine instead of a phenyl as in ionic-b.
F igu r e 6. Representation of the trans-covalent complexes
trans-b-d .
measurements (Supporting Information, Figure S6), the
complexed amines of trans-b and trans-c have a confor-
mation different with respect to that observed for the
corresponding ammonium salts in the ionic complexes:
the aromatic moieties are nearly perpendicular and one
methyl group is between them, whereas the other one is
external to the structure of the amine and only close to
the aromatic ring of its own residue (Figure 6). The
ethylene produces NOEs only on this last methyl group
(that one external to the structure of the amine) and on
the aromatic ring of the other chiral residue. In the case
of the complex trans-b, the resonance of the coordinated
ethylene holds the A4 pattern found for the ionic com-
plexes (Figure 2a), i.e., it is freely rotating, whereas in
trans-c, the rotation of the olefin is not free (AA′BB′
system in Figure 2b) as a consequence of the spatial
proximity to the naphthalene ring. In trans-d , the
simultaneous presence of the signals corresponding to the
two diastereoisomers in a 80:20 ratio did not allow us to
define their stereochemical features, but it is reasonable
to suppose that the major diastereoisomer, the one having
the ethylene freely rotating, has the phenyl ring bent at
the ethylene as in Figure 6, and the minor species, where
the rotation of ethylene is slow, has the naphthalene ring
in spatial proximity of it.
Exp er im en ta l Section
Gen er a l Meth od s. All spectra were recorded using a
spectrometer operating at 300, 75, and 64.3 MHz for 1H, 13C
and 195Pt, respectively and the temperature was controlled to
1
(0.1 °C. All H and 13C NMR chemical shifts are referred to
TMS as external standard. 195Pt NMR spectra were recorded
in CDCl3 or C6D6 and all 195Pt NMR chemical shifts are
referred to Na2PtCl6 as external standard. Standard pulse
sequences have been employed for 195Pt NMR measurements
by using a spectral width of 50 000 Hz and an acquisition time
of 0.3 s. No relaxation delays have been inserted between
pulses. The 2D NMR spectra were obtained by using standard
sequences. The DQF-COSY (double-quantum filter correlated
spectroscopy) experiments were recorded with the minimum
spectral width required; 512 increments of 8 scans and 2K data
points were acquired. The relaxation delay was 10 s. The data
were zero-filled to 2K × 1K, and a Gaussian function was
applied for processing in both dimensions. The NOESY
(nuclear Overhauser and exchange spectroscopy) spectra were
recorded in the phase-sensitive mode, by employing a mixing
time of 0.6 s. The spectral width used was the minimum
required in both ω1 and ω2 dimensions. The pulse delay was
maintained at 10 s; 512 hypercomplex increments of 8 scans
In the complexes containing the primary amine (ionic-e
and trans-e) only a NOE between the ethylene protons

128 J . Org. Chem., Vol. 66, No. 1, 2001
Uccello-Barretta et al.
and 2K data points each were collected. The data matrix was
zero-filled at 2K × 1K and a Gaussian function was applied
for processing in both dimensions. The HETCOR (hetero-
nuclear chemical shift-correlation) spectra were acquired with
a spectral width of 11 000 Hz in F2 and 3500 Hz in F1 in 2K
data points using 32 scans of the 256 increments. The
relaxation delay was 2 s. The data were zero-filled to 2K ×
1K, and a Gaussian function was applied for processing in both
dimensions.
The 1H{1H}-NOE experiments were performed in the dif-
ference mode. The decoupler power used was the minimum
required to saturate the spin of interest. A waiting time of
5-10 s was used to allow the system to reach the equilibrium.
Each NOE experiment was repeated at least four times. All
the solutions were accurately degassed by freeze-pump-thaw
cycles for 1D and 2D NOE experiments.
Hyd r och lor id e sa lt of (1S,1′S)-N-[1′-(1-n a p h th yl)eth yl]-
1-p h en yleth yla m in e (d ′): mp 258-260 °C; [R]22 ) +99.2°
D
(c 1.00, CHCl3); 1H NMR (300 MHz, CDCl3, 25 °C) δ 1.99 (3H,
Me′, d, J ) 6.8 Hz), 2.00 (3H, Me, d, J ) 6.8 Hz), 4.03 (1H,
CH′, m), 4.83 (1H, CH, m), 6.99 (1H, H8, bs), 7.17-7.34 (5H,
Ph, m), 7.25 (1H, H7, dd, J ) 8.1, 6.9 Hz), 7.44 (1H, H6, dd, J
) 8.1, 6.9 Hz), 7.69 (1H, H3, dd, J ) 8.0, 6.9 Hz), 7.86 (1H, H4,
d, J ) 8.0 Hz), 7.88 (1H, H5, d, J ) 8.1 Hz), 8.59 (1H, H2, bs),
10.80 (2H, NH2+, m); 13C NMR (75 MHz, CDCl3, 25 °C) δ 21.1
and 21.9 (Me′ and Me); 51.4 (chiral CH), 57.2 (chiral CH′);
121.6 (C8); 125.5 (C2); 125.9 (C6); 126.1 (C3); 126.4 (C7); 128.3,
128.9, 129.0 (phenyl CH); 128.9 (C4); 129.0 (C5); 130.2, 132.7,
133.7, 136.0 (quaternary C). Anal. Calcd for C20H22NCl: C,
77.03; H, 7.11; N, 4.49. Found: C, 77.28; H, 7.05; N, 4.35.
Gen er a l P r oced u r e. tr a n s-Dich lor o(b-e)(eth ylen e)-
p la tin u m (II) Com p lexes (tr a n s-b-e). To a solution of
Zeise’s salt [PtCl3(C2H4)]-K+ (1.58 mmol) in H2O/CH3OH (2:
1, 20 mL) was added, at 0 °C, a methanol solution of the
appropriate amine (1.58 mmol). Trans-b-e were filtered off
and recovered as pale yellow solids.
tr a n s-Dich lor o(b)(eth ylen e)p la tin u m (II) (tr a n s-b): mp
166-168 °C; 1H NMR (300 MHz, CDCl3, 25 °C) δ 1.33 (3H,
Me′, d, J ) 7.1 Hz), 2.03 (3H, Me, d, J ) 7.1 Hz), 4.25 (4H,
C2H4, s), 4.54 and 4.57 (2H, CH, m), 5.29 (1H, NH, bt), 7.27-
7.49 (10H, Ph, m);13C NMR (75 MHz, CDCl3, 25 °C) δ 22.1
(Me′), 24.3 (Me), 61.5, 62.5 (chiral CH′ and CH), 71.4 (C2H4),
127.0, 127.1, 128.1, 128.5, 129.2, 129.4 (phenyl CH), 140.0,
142.2 (quaternary C); 195Pt NMR (64.3 MHz, C6D6, 25 °C) δ
-2916.5. Anal. Calcd for C18H23NCl2Pt: C, 41.63; H, 4.46; N,
2.70. Found: C, 42.06; H, 4.61; N, 2.52.
Melting points were determined using a Kofler hot-stage
apparatus.
Ma ter ia ls. Tetrahydrofuran (THF) was distilled from Na/K
alloy. Acetophenone, 1-acetonaphthone (S)-1-phenylethyl-
amine, (S)-1-(1-naphthyl)ethylamine, 3-methyl-1-pentene, and
Zeise’s salt were purchased from Aldrich. Unless noted, all the
other reagents were used without purification.
1-Phenyl-3,4,4-trimethyl-1,2-pentadiene (1),10 1-phenyl-3-
methyl-1,2-pentadiene (2),10 and 2-vinyltetrahydropyran (6)11
were prepared as described elsewhere. Literature methods
were used to prepare 1,2,2-trimethylpropyl vinyl ether (3),12
2,2-dimethyl-1-phenylpropyl vinyl ether (4),12 1-phenylethyl
vinyl ether (5),12 3-phenyl-1-butene (7),13 and 5,5-dimethyl-4-
phenyl-1-hexene (9).13
Gen er a l P r oced u r e. Ch ir a l Secon d a r y Am in e (S,S)-b-
d .8 According to the literature procedure reported in ref 8, (S)-
1-phenylethylamine and (S)-1-(1-naphthyl)ethylamine were
converted into the corresponding imines ((S)-N-(1-phenyleth-
ylidene)-1-phenylethylamine, (S)-N-[(1-naphthyl)ethylidene]-
1-phenylethylamine, and (S)-N-[(1-naphthyl)ethylidene]-1-(1-
naphthyl)ethylamine) by reacting the former with acetophenone
and 1-acetonaphthone and the latter with 1-acetonaphthone.
The resulting isomeric mixtures of syn and anti imines was
hydrogenated in the presence of 10% Pd/C and the correspond-
ing amine b-d were recovered as diastereoisomeric mixtures
((S,S)/(S,R) 88:12, 94:6 and 90:10 for b, c, and d respectively,
tr a n s-Dich lor o(c)(eth ylen e)p la tin u m (II) (tr a n s-c): mp
218-220 °C; 1H NMR (300 MHz, CDCl3, 25 °C) δ 1.24 (3H,
Me′, d, J ) 6.4 Hz), 2.23 (3H, Me, d, J ) 6.4 Hz), 4.04 (4H,
C2H4, m), 5.59 (2H, CH and CH′, m), 5.93 (1H, NH, bs), 7.48
(2H, H6′ and H7′, m), 7.52 (1H, H3′, dd, J ) 8.2, 7.4 Hz), 7.58
(1H, H6, dd, J ) 8.2, 7.2 Hz), 7.61 (1H, H3, dd, J ) 8.2, 7.4
Hz), 7.68 (1H, H7, dd, J ) 8.2, 7.2 Hz), 7.74 (1H, H2′, d, J )
7.4 Hz), 7.84 (1H, H4′, d, J ) 8.2 Hz), 7.86 (1H, H5′, d, J ) 8.2
Hz), 7.87 (1H, H2, d, J ) 7.4 Hz), 7.89 (1H, H4, d, J ) 8.2 Hz),
7.95 (1H, H5, d, J ) 8.2 Hz), 8.08 (1H, H8′, d, J ) 8.2 Hz), 8.23
(1H, H8, d, J ) 8.2 Hz); 13C NMR (75 MHz, CDCl3, 25 °C) δ
23.2 (Me′), 25.1 (Me), 56.4, 57.6 (chiral CH and CH′), 70.9
(C2H4), 121.8 (C8), 123.1 (C2), 123.8 (C8′), 124.9 (C3′), 125.4 (C6),
125.8 (C6′ and C7′), 126.0 (C3), 126.3 (C2′), 127.2 (C7), 128.8 (C5′
and C4′), 129.0 (C4), 129.4 (C5), 130.3, 133.8, 134.2, 137.4, 139.4,
141.2 (quaternary C); 195Pt NMR (64.3 MHz, C6D6, 25 °C) δ
-2916.5. Anal. Calcd for C26H27NCl2Pt: C, 50.41; H, 4.39; N,
2.26. Found: C, 50.66; H, 4.46; N, 2.11.
tr a n s-Dich lor o(d )(eth ylen e)p la tin u m (II) (tr a n s-d ): mp
204-206 °C; 1H NMR (300 MHz, CDCl3, 25 °C) (* denotes the
minor species) δ 1.23 (3H, Me′, d, J ) 6.8 Hz), 1.35 (3H, Me′*,
d, J ) 6.8 Hz), 2.12 (3H, Me*, d, J ) 6.8 Hz), 2.17 (3H, Me, d,
J ) 6.8 Hz), 4.01 (4H, C2H4*, m), 4.28 (4H, C2H4, s), 4.64 (1H,
CH* and CH′, m), 5.51 (1H, CH and CH′*, m), 5.64 (1H, NH*
and NH, m), 7.05-8.30 (12H, Np*, Np and Ph*, Ph, m); 13C
NMR (75 MHz, CDCl3, 25 °C) δ 21.8, 23.8, 24.5, 24.9 (Me, Me′,
Me* and Me′*); 55.5, 62.8 (CH, CH′, CH* and CH′*); 70.7
(C2H4*); 71.3 (C2H4); 121.7, 122.7, 123.3, 123.7, 124.8, 125.4,
125.7, 125.8, 126.0, 126.2, 126.8, 127.0, 127.2, 127.3, 127.6,
128.2, 128.5, 128.8, 128.9, 129.3, 129.4, 130.6, 131.1, 133.9,
134.1, 137.6, 138.9, 139.9 (aromatic CH and quaternary C);
195Pt NMR (64.3 MHz, C6D6, 25 °C) δ -2909.6, -2916.6. Anal.
Calcd for C22H25NCl2Pt: C, 46.40; H, 4.43; N, 2.46. Found: C,
46.61; H, 4.54; N, 2.36.
1
as determined by H NMR analysis). The pure (S,S)-diastere-
isomers of amines were obtained by crystallization of their
hydrocloride salt b′-d ′ from H2O for b′ and from CHCl3/
pentane (1:2) for c′ and d ′. The free amine was then regener-
ated by treating the corresponding salt with KOH (10%).
H yd r och lor id e sa lt of (1S,1′S)-b is(1-p h en ylet h yl)-
a m in e (b′): mp 192-194 °C; [R]22 ) -74.9° (c 4.0, EtOH);
D
1H NMR (300 MHz, CDCl3, 25 °C) δ 1.90 (6H, Me, d, J ) 6.7
Hz), 3.84 (2H, CH, q, J ) 6.7 Hz), 7.33-7.46 (6H, Ph, m), 7.52
(4H, Ph, d, J ) 7.9 Hz), 10.48 (2H, NH2+, bs); 13C NMR (75
MHz, CDCl3, 25 °C) δ 21.5 (Me), 57.2 (chiral CH), 128.2, 129.0,
129.2 (phenyl CH); 136.3 (quaternary C). Anal. Calcd for
C
16H20NCl: C, 73.41; H, 7.70; N, 5.35. Found: C, 73.68; H,
8.53; N, 5.20.
Hyd r och lor id e sa lt of (1S,1′S)-bis[1-(1-n a p h th yl)eth yl]-
a m in e (c′): mp 231-233 °C; [R]22D ) +317.19° (c 0.89, CHCl3);
1H NMR (300 MHz, CDCl3, 25 °C) δ 2.09 (6H, Me, d, J ) 6.8
Hz), 4.96 (2H, CH, q, J ) 6.8 Hz), 6.33 (2H, H8, bs), 6.56 (2H,
H7, dd, J ) 8.1, 6.8 Hz), 7.06 (2H, H6, dd, J ) 8.1, 6.8 Hz),
7.61 (2H, H5, d, J ) 8.1 Hz), 7.73 (2H, H3, dd, J ) 7.9, 6.8 Hz),
+
7.82 (2H, H4, d, J ) 7.9 Hz), 8.70 (2H, H2, bs), 10.96 (2H, NH2
,
bs); 13C NMR (75 MHz, CDCl3, 25 °C) δ 21.7 (Me), 51.0 (chiral
CH), 120.4 (C8), 125.3 (C6), 125.5 (C2), 125.8 (C3 and C7), 128.3
(C5), 129.0 (C4), 130.3, 132.7, 133.5 (quatenary C). Anal. Calcd
for C24H24NCl: C, 79.65; H, 6.68; N, 3.87. Found: C, 79.92;
H, 6.61; N, 3.76.
tr a n s-Dich lor o(e)(eth ylen e)p la tin u m (II) (tr a n s-e): mp
113-114 °C; 1H NMR (300 MHz, CDCl3, 25 °C) δ 2.01 (3H,
Me, d, J ) 6.8 Hz), 4.30 (2H, NH2, bs), 4.70 (4H, C2H4, m),
5.55 (1H, CH, q, J ) 6.8 Hz), 7.47 (1H, H3, dd, J ) 8.0, 7.8
Hz), 7.52 (1H, H6, dd, J ) 8.2, 7.2 Hz), 7.54 (1H, H2, d, J ) 7.8
Hz), 7.61 (1H, H7, dd, J ) 8.5, 7.2 Hz), 7.84 (1H, H4, d, J ) 8.0
Hz), 7.89 (1H, H5, d, J ) 8.2 Hz), 8.29 (1H, H8, d, J ) 8.5 Hz);
13C NMR (75 MHz, CDCl3, 25 °C) δ 21.7 (Me); 50.7 (CH); 75.1
(C2H4); 122.2, 122.5, 125.3, 126.3, 127.4, 129.2, 129.4 (naphthyl
CH); 130.3, 130.7, 134.0 (quaternary C); 195Pt NMR (64.3 MHz,
(10) Caporusso, A. M.; Polizzi, C.; Lardicci, L. J . Org. Chem. 1987,
52, 3920-3923.
(11) Ficini, J . Bull. Chem. Soc. Fr. 1956, 119-124.
(12) Reppe, W. Ann. 1956, 601, 84-111.
(13) Crowell, T. I. In The Chemistry of Alkenes; Patai, S., Ed.;
Interscience: New York, 1964; pp 241-270.

[PtCl3(C2H4)]-[AmH]+ Complexes
J . Org. Chem., Vol. 66, No. 1, 2001 129
C6D6, 25 °C) δ -3068.7. Anal. Calcd for C14H17NCl2Pt: C,
36.14; H, 3.68; N, 3.01. Found: C, 36.49; H, 3.58; N, 2.92.
Gen er a l P r oced u r e. Ion ic [P tCl3(C2H4)]-(b′-e′)+ Com -
p lexes (ion ic-b-e). To a suspension of Zeise’s salt [PtCl3-
(C2H4)]-K+ (1.58 mmol) in CHCl3 was added b′-e′ (1.58 mmol).
As a consequence of the rapid exchange of the two cations, a
white fine powder of KCl was formed and filtered off. ionic-
b-e were recovered as yellow solids by removal of the solvent
in vacuo.
127.8 (C2′), 129.2 (C4′), 129.4 (C3′), 129.8 (C5), 129.9 (C4), 131.4,
133.0, 133.8, 134.6 (quaternary C); 195Pt NMR (64.3 MHz, C6D6,
25 °C) δ -2825.6. Anal. Calcd for C22H26NCl3Pt: C, 43.61; H,
4.33; N, 2.31. Found: C, 43.72; H, 4.38; N, 2.25.
[P tCl3(C2H4)]-(e′)+ (ion ic-e): mp 183-185 °C; 1H NMR
(300 MHz, CDCl3, 25 °C) δ 1.90 (3H, Me, d, J ) 6.8 Hz), 4.30
(4H, C2H4, m), 5.60 (1H, CH, m), 7.41 (3H, NH3+, bs), 7.49 (1H,
H6, dd, J ) 8.2, 6.9 Hz), 7.52 (1H, H3, dd, J ) 8.2, 7.2 Hz),
7.58 (1H, H7, dd, J ) 8.5, 6.9 Hz), 7.77 (1H, H2, d, J ) 7.2 Hz),
7.84 (1H, H4, d, J ) 8.2 Hz), 7.86 (1H, H5, d, J ) 8.2 Hz), 8.07
(1H, H8, d, J ) 8.5 Hz); 13C NMR (75 MHz, CDCl3, 25 °C) δ
21.0 (Me), 48.3 (chiral CH), 70.2 (C2H4), 122.2, 123.8, 125.6,
126.4, 127.5, 129.2, 129.8 (naphthyl CH), 129.9, 132.8, 133.9
(quaternary C); 195Pt NMR (64.3 MHz, C6D6, 25 °C) δ -2842.5.
Anal. Calcd for C14H18NCl3Pt: C, 33.51; H, 3.62; N, 2.79.
Found: C, 33.66; H, 3.57; N, 2.61.
[P tCl3(C2H4)]-(b′)+ (ion ic-b): mp 145-148 °C; 1H NMR
(300 MHz, CDCl3, 25 °C) δ 1.83 (6H, Me, d, J ) 7.0 Hz), 3.94
(2H, CH, q, J ) 7.0 Hz), 4.61 (4H, C2H4, s), 7.33-7.48 (10H,
Ph, m), 8.66 (2H, NH2, bs); 13C NMR (75 MHz, CDCl3, 25 °C)
δ 21.7 (Me), 57.8 (chiral CH), 69.5 (C2H4), 127.7, 129.6, 129.7
(phenyl CH), 135.2 (quaternary C); 195Pt NMR (64.3 MHz,
C6D6, 25 °C) δ -2825.4. Anal. Calcd for C18H24NCl3Pt: C,
38.90; H, 4.35; N, 2.52. Found: C, 39.08; H, 4.42; N, 2.19.
[P tCl3(C2H4)]-(c′)+ (ion ic-c): mp 162-164 °C; 1H NMR
(300 MHz, CDCl3, 25 °C) δ 1.99 (6H, Me, d, J ) 6.9 Hz), 4.70
(4H, C2H4, s), 4.94 (2H, CH, q, J ) 6.9 Hz), 6.68 (2H, H8, bs),
6.82 (2H, H7, dd, J ) 8.2, 6.8 Hz), 7.26 (2H, H6, dd, J ) 8.2,
6.8 Hz), 7.63 (2H, H3, dd, J ) 8.2, 6.8 Hz), 7.75 (2H, H5, d, J
) 8.2 Hz), 7.88 (2H, H4, d, J ) 8.2 Hz), 7.99 (2H, H2, bs), 8.71
(2H, NH2+, bs); 13C NMR (75 MHz, CDCl3, 25 °C) δ 22.2 (Me),
52.7 (chiral CH), 69.7 (C2H4), 120.8 (C8), 124.4 (C2), 125.8 (C3),
126.1 (C6), 126.7 (C7), 128.8 (C5), 130.0 (C4), 130.2, 131.3, 133.7
(quaternary C); 195Pt NMR (64.3 MHz, C6D6, 25 °C) δ - 2827.4.
Anal. Calcd for C26H28NCl3Pt: C, 47.61; H, 4.30; N, 2.14.
Found: C, 47.73; H, 4.35; N, 2.01.
Gen er a l P r oced u r e In volved in th e Use of th e CDAs
for th e En a n tiod iscr im a tion Mea su r em en ts. The chiral
substrate (1-9) was added (substrate/CDA 0.8:1) to a solution
containing 50-100 mg of CDA in 0.5 mL of C6D6 and the 195Pt
NMR spectra of the reaction mixtures were analyzed. The 195Pt
resonances of the small excess of trans-b-e (from -2909.6 to
-3068.7 ppm) and ionic-b-e (from-2825.4 to -2842.5 ppm)
are at low frequencies with respect to the absorptions due to
complexes containing the substrate 1-9.
Ack n ow led gm en t. This work was supported by the
Ministero della Ricerca Scientifica
(MURST) and CNR, Italy.
e Tecnologica
[P tCl3(C2H4)]-(d ′)+ (ion ic-d ): mp 158-159 °C; 1H NMR
(300 MHz, CDCl3, 25 °C) δ 1.88 (3H, Me′, d, J ) 6.8 Hz), 1.94
(3H, Me, d, J ) 6.8 Hz), 3.98 (1H, CH′, m), 4.66 (4H, C2H4, s),
4.89 (1H, CH, m), 7.13 (2H, H2′, d, J ) 7.5 Hz), 7.33 (2H, H3′,
dd, J ) 7.5, 7.5 Hz), 7.34 (1H, H8, d, J ) 8.2 Hz), 7.38 (1H,
H4′, t, J ) 7.5 Hz), 7.42 (1H, H7, dd, J ) 8.2, 7.0 Hz), 7.54 (1H,
H6, dd, J ) 8.2, 7.0 Hz), 7.66 (1H, H3, dd, J ) 8.0, 7.6 Hz),
7.92 (1H, H5, d, J ) 8.2 Hz), 7.94 (1H, H4, d, J ) 8.0 Hz), 7.97
(1H, H2, d, J ) 7.6 Hz); 13C NMR (75 MHz, CDCl3, 25 °C) δ
21.6 (Me′), 22.4 (Me), 52.7 (chiral CH), 58.3 (chiral CH′), 69.5
(C2H4), 121.4 (C8), 124.5 (C2), 126.0 (C3), 126.4 (C6), 127.0 (C7),
Su p p or tin g In for m a tion Ava ila ble: 1H{1H}-NOE dif-
ference spectra of d ′ in CDCl3. 1H NMR spectra of ionic
complexes. 195Pt NMR spectra of the diastereoisomeric mix-
tures obtained for 2 by using CDAs trans-c, trans-e and ionic-
1
e. H{1H}-NOE difference spectra corresponding to the satu-
ration of the ethylene protons of ionic complexes. 1H{1H}-NOE
difference spectra of trans-c. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O001165T