Amidines derived from Pt(IV)-mediated nitrile - Amino alcohol coupling and their Zn(II)-catalyzed conversion into oxazolines

Article abstract of DOI:10.1021/ic034070t

The reaction between the platinum(IV) complex trans-[PtCl₄(EtCN)₂] and the amino alcohols NH₂CH₂CH₂OH, NH₂C H₂CH(Me)OH-(R)-(-), NH₂CH(Ph)CH₂OH-(R)-(-), NH₂CH(Et)CH₂OH-(R)-(-), NH₂CH(Et)CH₂OH-(S)-(+), and NH₂CH(Prⁿ)CH₂OH proceeds rapidly at room temperature in CH₂Cl₂ to furnish the amidine complexes [PtCl₄{HN=C(Et)NH-OH}₂] (1-6) in good yield (70-80%). The related reaction between the platinum(II) complex trans-[PtCl₂(EtCN)₂] and monoethanolamine in a molar ratio of 1:2 in CH₂Cl₂ results in the addition of 4 equiv of NH₂-CH₂CH₂OH per mole of complex to give [Pt{HN=C(Et)NHCH₂CH₂OH}₂ (NH₂CH₂CH₂OH)₂]²⁺ (7). Formulation of 1-6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and ¹H, ¹³C{¹H}, ¹⁵N, and ¹⁹⁵Pt NMR spectroscopies, while the structures of trans-[PtCl₄{(Z)-NH=C(Et)NHCH₂CH₂-OH} ₂] (1), trans-[PtCl₄{(Z)-NH=C(Et)NHCH₂CH(Me)OH-(R)-(-)} ₂] (2), and trans-[PtCl₄{(Z)-NH=C(Et)NHCH(Et)- CH₂OH-(R)-(-)}₂] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands is preserved in CDCl₃ solutions as confirmed by gradient-enhanced ¹⁵N,¹H-HMQC spectroscopy and NOE experiments. The amidines, formed upon Pt(IV)-mediated nitrile-amino alcohol coupling, were liberated from their platinum(IV) complexes 1, 3, and 4 by reaction with Ph₂PCH₂CH₂PPh₂ (dppe) giving free NH=C(Et)NHCHRCH₂OH (R = H 8, Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified by ¹³P{¹H} NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same configuration relative to the C=N double bond, i.e., syn-(H,Et)-NH=C(Et)NHCHRCH₂OH. The liberated hydroxo-functionalized amidines 8-10 were converted into oxazolines N=C(Et)OCH₂CH(R) (11-13) in the presence of a catalytic amount of ZnCl₂. A similar catalytic effect has also been reached using anhydrous MSO₄ (M = Cu, Co, Cd), CdCl₂, and AlCl₃.

Full text of DOI:10.1021/ic034070t

Inorg. Chem. 2003, 42, 2805−2813
Amidines Derived from Pt(IV)-Mediated Nitrile−Amino Alcohol Coupling
and Their Zn(II)-Catalyzed Conversion into Oxazolines
,†
Anastassiya V. Makarycheva-Mikhailova,†,‡ Vadim Yu. Kukushkin,* Alexey A. Nazarov,‡
,§
Dmitrii A. Garnovskii,§ Armando J. L. Pombeiro,* Matti Haukka,| Bernhard K. Keppler,‡ and
,‡
Markus Galanski*
Department of Chemistry, St. Petersburg State UniVersity, 198504 Stary Petergof, Russian
Federation, Institute for Inorganic Chemistry, UniVersity of Vienna, Wa¨hringer Strasse 42,
A-1090 Vienna, Austria, Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico,
AV. RoVisco Pais, 1049-001 Lisbon, Portugal, and Department of Chemistry, UniVersity of
Joensuu, P.O. Box 111, FIN-80101, Joensuu, Finland
Received January 22, 2003
The reaction between the platinum(IV) complex trans-[PtCl4(EtCN)2] and the amino alcohols NH CH CH OH,
2
2
2
NH CH CH(Me)OH-(R)-(−), NH CH(Ph)CH OH-(R)-(−), NH CH(Et)CH OH-(R)-(−), NH CH(Et)CH OH-(S)-(+), and
2
2
2
2
2
2
2
2
NH CH(Prn)CH OH proceeds rapidly at room temperature in CH Cl2 to furnish the amidine complexes [PtCl4-
2
2
2
k
{HNdC(Et)NH OH}2] (1−6) in good yield (70−80%). The related reaction between the platinum(II) complex trans-
[PtCl2(EtCN)2] and monoethanolamine in a molar ratio of 1:2 in CH Cl2 results in the addition of 4 equiv of NH -
2
2
CH CH OH per mole of complex to give [Pt{HNdC(Et)NHCH CH OH}2(NH CH CH OH)2]2+ (7). Formulation of
2
2
2
2
2
2
2
1−6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and
1H, 13C{1H}, 15N, and 195Pt NMR spectroscopies, while the structures of trans-[PtCl4{(Z)-NHdC(Et)NHCH CH -
2
2
OH}2] (1), trans-[PtCl4{(Z)-NHdC(Et)NHCH CH(Me)OH-(R)-(−)}2] (2), and trans-[PtCl4{(Z)-NHdC(Et)NHCH(Et)-
2
CH OH-(R)-(−)}2] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands
2
is preserved in CDCl3 solutions as confirmed by gradient-enhanced 15N,1H-HMQC spectroscopy and NOE experiments.
The amidines, formed upon Pt(IV)-mediated nitrile−amino alcohol coupling, were liberated from their platinum(IV)
complexes 1, 3, and 4 by reaction with Ph2PCH CH PPh2 (dppe) giving free NHdC(Et)NHCHRCH OH (R ) H 8,
2
2
2
Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified
by 31P{1H} NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same
configuration relative to the CdN double bond, i.e., syn-(H,Et)-NHdC(Et)NHCHRCH OH. The liberated hydroxo-
2
functionalized amidines 8−10 were converted into oxazolines NdC(Et)OCH CH(R) (11−13) in the presence of a
2
catalytic amount of ZnCl2. A similar catalytic effect has also been reached using anhydrous MSO (M ) Cu, Co,
4
Cd), CdCl2, and AlCl3.
Introduction
naturally occurring (e.g., microbial metal chelators such as
vibriobactin,1 parabactin,2 fluvibactin,3 and agrobactin4) or
Oxazolines (or 4,5-dihydrooxazoles) constitute one of the
most intensely studied classes of heterocycles, a fact
confirmed by the 150 or so references which result when
Chemical Abstracts is searched (from 1964 up until the end
of 2002) for the combination “oxazoline and review”. These
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* To whom correspondence should be addressed. E-mail: kukushkin@
VK2100.spb.edu (V.Yu.K.), pombeiro@ist.utl.pt (A.J.L.P.), and galanski@
ap.univie.ac.at (M.G.).
† St. Petersburg State University.
‡ University of Vienna.
§ Instituto Superior Te´cnico.
| University of Joensuu.
10.1021/ic034070t CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/27/2003
Inorganic Chemistry, Vol. 42, No. 8, 2003 2805

Makarycheva-Mikhailova et al.
synthetic5-10 compounds have a broad application in both
organic5-10 and coordination chemistries11 as useful synthons
(for preparation of more complex fragments) and in polymer
chemistry (in step-growth12 and ring-opening polymeriza-
tions,13 as amphiphilic block copolymers for micellar ca-
talysis,14 and as reactive modifiers in the compatibilization
of polymer blends15), and they also have intrinsic practical
applications as insecticides and acaricides.16 However, the
basic idea that drives the overwhelming majority of the recent
achievements in the chemistry of these heterocycles is that
chiral oxazolines, bis(oxazolines), and oxazoline-based metal
complexes can be employed as highly efficient inducers of
asymmetry in many kinds of organic reactions. The synthesis,
properties, and valuable applications of chiral oxazolines and
their metal complexes in the asymmetric synthesis and
catalysis were repeatedly surveyed along the past two
decades, e.g., see recent books17 and reviews.18-24
Scheme 1
Synthesis of oxazolines7-10 and oxazoline type monomers
for further polymerization10 has been reviewed. The most
developed synthetic approaches to furnish these heterocycles
include dehydration and cyclization of some carboxamides
(e.g., hydroxyamides), reaction between halocarboxamides
and strong bases, additions of oxiranes to nitriles and amino
alcohols to carboxylic acids or imino esters, and, eventually,
two routes involving metal centers: (i) addition of halo
alcohols/base or oxirane/Cl- systems to Pt(II)-bound nitriles25
and (ii) reactions between nitriles and amino alcohols which
are catalyzed by zinc(II),26-29 cadmium(II),28 nickel(II),30 and
aluminum(III)29 ions (Scheme 1, route A) or mediated by
cobalt(II) and copper(II)31 centers (Scheme 1, route B). The
metal-catalyzed reaction between nitriles and amino alcohols
(Scheme 1, route A) is one of the most advantageous
synthetic methods leading to the oxazolines owing to its
superior simplicity and the commercial availability of (or
the easy synthetic access to) the starting materials; some of
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2806 Inorganic Chemistry, Vol. 42, No. 8, 2003

Amidines DeriWed from Nitrile-Amino Alcohol Coupling
recently reviewed by two of us34 and also by others35-37),
we observed that the platinum(IV) nitrile complexes [PtCl4-
(RCN)2] are very reactive toward various protic nucleophiles
(HNuc)38-43 achieving imino complexes [PtCl4{HNdC(R)-
Nuc}2] which exhibit substantial inertness toward substitution
and hydrolysis, and the latter fact gave the hope that some
intermediates in the reaction between nitriles and amino
alcohols could be trapped at the Pt(IV) center and stored in
the form of the imino complexes.
We decided to extend our research in the chemistry of
nitrile-based systems to amino alcohols, and the scenario of
the current work was the following: (i) to perform the
addition of amino alcohols to Pt(IV)-bound nitrile species
and to establish, by both X-ray solid and NMR solution
structural studies, the mode of addition of the amino alcohols
to complexed nitriles; (ii) to liberate the ligands formed in
the course of the metal-mediated reaction; and (iii) to perform
their conversion into oxazolines. In this work, we succeeded
in isolating (amidine)Pt(IV) complexes, establishing their fine
structure both in the solid state and in solution, liberating
the hydroxo-functionalized amidines, and performing their
Zn(II)-catalyzed conversion to oxazolines, and all these
results are presented in the article.
Scheme 2
the reaction is yet unknown, a few nonsystematic approaches
allowed the assumption that the reaction between RCN and
k
NH2 OH proceeds via the intermediate formation of the
amidine HNdC(R)NHkOH rather than the imino ester
HNdC(R)OkNH2. Thus, the Cu(II)-32 or Ni(II)-mediated33
reactions between o-(NtC)C5H4N and amino alcohols led
to amidine complexes, but liberation of the hydroxo-func-
tionalized amidines followed by their conversion into oxa-
zolinessthus unambiguously proving that the amidines are
intermediates in the reactionswas not attempted.32,33 In
organic chemistry, it is anticipated that the second step of
the Pinner synthesis44 should give the amidines (which are
then converted to oxazolines), but formulation of the ami-
1
dines is only weakly supported by H NMR study. Hence,
until now there were no reports where (i) the intermedi-
ates in the oxazoline synthesis were generated and identified
and (ii) the Zn(II)-catalyzed conversion of the amidines
HNdC(R)NHkOH into oxazolines was conducted. We
endeavored to fill these gaps in the current work.
Results and Discussion
Although amino alcohols, as ambidentate nucleophiles, can
be added to nitriles by either N or O atoms, it is reasonable
to assume that the addition would occur via the more
nucleophilic N center. Indeed, although the mechanism of
Pt(IV)-Mediated Nitrile-Amino Alcohol Coupling. As
a source of coordinated nitrile for this study we addressed
the rather soluble (in organic solvents) platinum(IV) complex
trans-[PtCl4(EtCN)2] because it has been demonstrated by
our previous work that nitrile ligands in compounds of such
type are highly activated toward the addition of nucleophiles
such as oximes,39 dione monoximes,40 Vic-dioximes,41 hy-
droxamic acids,42 and imines and sulfimides43 and they are
also quite reactive in 1,3-dipolar cycloaddition of nitrones45,46
and nitrile oxides.47 In the context of the current work, one
should mention that the nitrile platinum(IV) complexes easily
react with both ammonia48 and alcohols38 to form amidine
and imino ester complexes, respectively (Scheme 2) but their
reaction with amino alcohols bearing both functionalities has
not yet been studied.
(32) Miklos, D.; Segl’a, P.; Glowiak, T. Inorg. Chem. Commun. 2001, 4,
66.
(33) Segl’a, P.; Miklos, D.; Jamnicky, M.; Sima, J. J. Coord. Chem. 1999,
48, 15.
(34) Kukushkin, V. Yu.; Pombeiro, A. J. L. Chem. ReV. 2002, 102, 1771
and references therein. Pombeiro, A. J. L.; Kukushkin, V. Yu. In
ComprehensiVe Coordination Chemistry, 2nd ed.; Lever, A. B. P.,
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addition of monoethanolamine to the nitrile,49 but available
data are insufficient to determine whether the amino alcohol
adds via either the N or O nucleophilic center.
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(43) (a) Makarycheva-Mikhailova, A. V.; Bokach, N. A.; Kukushkin, V.
Yu.; Kelly, P. F.; Gilby, L. M.; Kuznetsov, M. L.; Holmes, K. E.;
Haukka, M.; Parr, J.; Stonehouse, J. M.; Elsegood, M. R. J.; Pombeiro,
A. J. L. Inorg. Chem. 2003, 42, 301. (b) Garnovskii, D. A.; Kukushkin,
V. Yu.; Haukka, M.; Wagner, G.; Pombeiro, A. J. L. J. Chem. Soc.,
Dalton Trans. 2001, 560.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2807

Makarycheva-Mikhailova et al.
Scheme 3
The reaction between trans-[PtCl4(EtCN)2] and the amino
Moreover, NMR data favor the addition of monoethanol-
amine via the N atom thus forming the metal-bound amidine.
In general, the addition of asymmetrical bifunctional
nucleophiles to metal-activated nitriles is only poorly ex-
plored,32,33,49 albeit the reactions with symmetric bifunctional
nucleophiles, e.g., ethylenediamine,50,51 has been much more
broadly investigated.
X-ray Structure Determinations of Amidine Pt(IV)
Complexes. The structures of compounds trans-[PtCl4{(Z)-
NHdC(Et)NHCH2CH2OH}2] (1), trans-[PtCl4{(Z)-NHd
C(Et)NHCH2CH(Me)OH-(R)-(-)}2] (2), and trans-[PtCl4-
{(Z)-NHdC(Et)NHCH(Et)CH2OH-(R)-(-)}2] (4) were de-
termined by X-ray single-crystal diffraction. The coordination
geometry of the three complexes is slightly distorted
octahedral (Figures 1-3).
The values of the Pt-Cl bond distances are in the range
from 2.322 to 2.329 Å, and these distances agree well with
those in the previously characterized platinum(IV) chloride
compounds.40-43,52 Although the X-ray crystallography, in
some instances, has certain restrictions in a reliable localiza-
tion of N and O atoms, e.g., in 1, the availability of the
substituents in the methylene chain of 2 and 3 allowed the
conclusion that amino alcohols were added by their N ends.
The two amidine ligands in 1-3 are mutually trans, which
is the thermodynamically stable form for complexes having
metal centers in a high oxidation state.53 In the amidine
ligands, the values of the C(1)-N(1) bond lengths (1.304-
1.318 Å) are similar within the 3σ range, while the bonds
alcohols with different degrees of substitution in the meth-
ylene groups, i.e., NH2CH2CH2OH, NH2CH2CH(Me)OH-(R)-
(-), NH2CH(Ph)CH2OH-(R)-(-), NH2CH(Et)CH2OH-(R)-
(-), NH2CH(Et)CH2OH-(S)-(+), and NH2CH(Prn)CH2OH,
proceeds rapidly at room temperature in CH2Cl2 to furnish
the platinum complexes [PtCl4{HNdC(Et)NHkOH}2]
(1-6) in good yield (70-80%). Electrospray mass spec-
trometry was performed using ca. 2 × 10-6 mol/L solutions
of the complexes in acetone, and the spectra obtained, in all
cases, display the fragment [M - H]- (where M denotes
the molecular ion of a product of the addition of 2 equiv of
k
the NH2 OH per 1 equiv of the starting platinum complex)
having isotopic patterns which agree well with the calculated
ones. The 2:1 stoichiometry of the addition was additionally
confirmed by satisfactory C, H, and N analyses. The IR
spectra show no band due to ν(CtN) but very strong bands
of the imino ν(CdN) [1623-1637 cm-1] along with less
specific weak-to-medium ν(O-H) and ν(N-H) stretching
vibrations. The combined data of NMR study (in solution)
and X-ray determinations (in the solid state) presented later
led to the conclusion on the formation of the amidine
structure of 1-6, i.e., [PtCl4{HNdC(Et)NHkOH}2], and,
consequently, on the N-addition of the N,O-bifunctional
nucleophile (Scheme 3, route A). The process is metal-
mediated because 1H NMR experimentation shows that EtCN
does not react with the amino alcohols under the reaction or
even more harsh (70 °C, 12 h) conditions. Complexes are
presumably formed by nucleophilic attack of the nitrogen
on the highly electrophilically activated carbon atom of the
organonitrile.
(50) (a) Kukushkin, Yu. N.; Kiseleva, N. P.; Zangrando, E.; Kukushkin,
V. Yu. Inorg. Chim. Acta 1999, 285, 203. (b) Syamala, A.; Chakra-
varty, A. R. Inorg. Chem. 1991, 30, 4699. (c) Maresca, L.; Natile, G.;
Intini, F. P.; Gasparrini, F.; Tiripicchio, A.; Tiripicchio-Camellini, M.
J. Am. Chem. Soc. 1986, 108, 1180.
(51) (a) Nolan, K. B.; Hay R. W. J. Chem. Soc., Dalton Trans. 1974, 914.
(b) Buckingham, D. A.; Foxman, B. M.; Sargeson, A. M.; Zanella,
A. J. Am. Chem. Soc. 1972, 94, 1007. (c) Rousselet, G.; Capdevielle,
P.; Maumy, M. Tetrahedron Lett. 1993, 34, 6395.
(52) Ryabov, A. D.; Kazankov, G. M.; Panyashkina, I. M.; Grozovsky, O.
V.; Dyachenko, O. G.; Polyakov, V. A.; Kuzmina, L. G. J. Chem.
Soc., Dalton Trans. 1997, 4385.
(53) Kukushkin, V. Yu. Russ. J. Inorg. Chem. (Engl. Transl.) 1988, 33,
1085.
We have also studied, for comparativity reasons, the
reaction between the platinum(II) complex trans-[PtCl2-
(EtCN)2] and monoethanolamine in a molar ratio 1:2 in
CH2Cl2 (Scheme 3, route B) and observed, in accord with
the previous study on the related benzonitrile complex,49 the
addition of 4 equiv of NH2CH2CH2OH per 1 mol of the
complex. The IR and NMR spectra clearly show that 2 equiv
of monoethanolamine adds to the coordinated nitriles.
2808 Inorganic Chemistry, Vol. 42, No. 8, 2003

Amidines DeriWed from Nitrile-Amino Alcohol Coupling
Figure 1. Molecular structure of trans-[PtCl4{(Z)-NHdC(Et)NHCH2CH2-
OH}2] 1. The thermal ellipsoids are drawn at the 50% probability level.
The shortest intramolecular hydrogen interactions: N(2)-H 0.94 Å,
N(2)‚‚‚Cl(1A) 3.151(5) Å, H‚‚‚Cl(1A) 2.29 Å, N(2)-H‚‚‚Cl(1A) 153.1°;
O(1)-H 1.04 Å, O(1)‚‚‚Cl(2) 3.346(4) Å, H‚‚‚Cl(2) 2.31 Å, O(1)-
H‚‚‚Cl(2) 174.2°.
Figure 3. Molecular structure of trans-[PtCl4{(Z)-NHdC(Et)NHCH(Et)-
CH2OH-(R)-(-)}2] 4. The thermal ellipsoids are drawn at the 50%
probability level. The shortest intramolecular hydrogen interactions: N(2)-H
0.88 Å, N(2)‚‚‚Cl(3) 3.334(3) Å, H‚‚‚Cl(3) 2.55 Å, N(2)-H‚‚‚‚Cl(1)
149.3°; N(4)-H 0.88 Å, N(4)‚‚‚Cl(4) 3.236(3) Å, H‚‚‚Cl(4) 2.47 Å,
N(2)-H‚‚‚Cl(2) 146°.
concludedsafter careful inspection of the X-ray datasthat
the Z-configuration of N(H)dC(NHMe)Me species is de-
termined by the formation of strong intramolecular hydrogen
bonds between each chlorine atom and the amino proton of
the NHMe moiety to give a six-membered ring.54 In our
cases, the hydrogen bonding is not particularly strong, the
shortest donor-acceptor distances (N‚‚‚Cl or O‚‚‚Cl) being
between 3.151(5) and 3.346(4) Å. Therefore, it is hardly
solely responsible for the configuration of the coordinated
amidines.
NMR Solution Structural Study of the Amidine Pt(IV)
Complexes. The addition of the amino alcohols to the nitrile
complex trans-[PtCl4(EtCN)2] can be conveniently monitored
Figure 2. Molecular structure of trans-[PtCl4{(Z)-NHdC(Et)NHCH2CH-
(Me)OH-(R)-(-)}2] 2. The thermal ellipsoids are drawn at the 50%
probability level. The shortest intramolecular hydrogen interactions: N(2)-H
0.94(5) Å, N(2)‚‚‚Cl(1) 3.325(3) Å, H‚‚‚Cl(1) 2.72(5) Å, N(2)-H‚‚‚Cl(1)
123(4)°; N(2)-H 0.94(5) Å, N(2)‚‚‚Cl(2A) 3.210(3) Å, H‚‚‚Cl(2A)
2.47(5) Å, N(2)-H‚‚‚Cl(2) 145.7°.
1
by NMR spectroscopy because the changes in the H, 13C,
and 15N NMR spectrasupon addition of the corresponding
amino alcohols through the amino group along the CtN
bondsare very indicative for the investigated reaction. After
the addition, the proton signals of the products show high
field shifts of the ethyl group in comparison with the starting
complex trans-[PtCl4(EtCN)2]. In the latter compound, the
resonances at 1.55 (CH3CH2) and 3.20 (CH3CH2) ppm were
found, whereas in the products the corresponding groups
resonate at 1.3 and 2.6 ppm, respectively. In the 13C NMR
spectra, the carbon of the imino group of the amidine
complexes was detected at ca. 171 ppm, in comparison to
the resonance at 119 ppm for the nitrile carbon of the starting
platinum complex. The chemical shifts of both nitrogen
atoms of the HNdC(NHR) moiety were obtained using
gradient-enhanced 15N,1H-HMQC spectroscopy. The coor-
dinated NH groups show shift correlation signals between
84.4 and 97.3 ppm (15N) and 5.40 and 5.61 ppm (1H). Typical
coupling constants of 333-360 Hz (1JN,Pt) and 25-27 Hz
(2JH,Pt) were observed. Addition of the potentially ambiden-
tate amino alcohols through the N atom is reflected by a
significant shift of the 15N resonance, which is detected at
62 ppm in the amidines in comparison to ca. -10 ppm of
the free amines. In the 1H NMR spectra, the HNdC
resonance was found in the range 7.39-8.11 ppm, and these
C(1)-N(2) are slightly longer (1.324-1.328 Å), thus indi-
cating that the N(2)H group is of the amido type, although
some degree of the electron delocalization within the amidine
moiety should be taken into account as in the previously
observed (amidine)Pt(II) system.54a Similar values of the
C-N bonds have been earlier found in the (amidine)Pt(IV)
complex [1.305(7)/1.315(7) Å43a]. The complexed amidines
in 1-3 are in the Z-configuration, and in all three structures
the amido hydrogens are involved in intramolecular H-
bonding with the chloride ligands as depicted in Figures 1-3.
In 1, an additional hydrogen bonding is observed between
the OH tails and Cl atoms.
Recently, the reaction between trans-[PtCl2(NCMe)2] and
MeNH2 to give the bis-amidine complex trans-[PtCl2{(Z)-
N(H)dC(NHMe)Me}2] has been studied, and it was
(54) (a) Bertani, R.; Catanese, D.; Michelin, R. A.; Mozzon, M.; Bandoli,
G.; Dolmella, A. Inorg. Chem. Commun. 2000, 3, 16. (b) Belluco,
U.; Benetollo, F.; Bertani, R.; Bombieri, G.; Michelin, R. A.; Mozzon,
M.; Tonon, O.; Pombeiro, A. J. L.; Guedes da Silva, F. C. Inorg.
Chim. Acta 2002, 334, 437. (c) Belluco, U.; Benetollo, F.; Bertani,
R.; Bombieri, G.; Michelin, R. A.; Mozzon, M.; Pombeiro, A. J. L.;
Guedes da Silva, F. C. Inorg. Chim. Acta 2002, 330, 229. (d) Michelin,
R. A.; Bertani, R.; Mozzon, M.; Sassi, A.; Benetollo, F.; Bombieri,
G.; Pombeiro, A. J. L. Inorg. Chem. Commun. 2001, 4, 275.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2809

Makarycheva-Mikhailova et al.
Scheme 4
Liberation of the amidines was monitored by NMR and
IR spectroscopies and also by electrospray mass spectrometry
([M + H]+ ions were detected for 8-10). It was shown,
using NOESY spectroscopy, that the liberated hydroxo-
functionalized amidines retained the same configuration
relative to the CdN double bond, i.e., syn-(H,Et)-NHd
C(Et)NHCHRCH2OH. Indeed, NOE shift correlation signals
between the imino proton HNdC(CH2CH3) and the meth-
ylene protons HNdC(CH2CH3) were found for all the
amidines.
Zn(II)-Catalyzed Conversion of the Amidines into
Oxazolines. The liberated amidines 8-10 were converted
into oxazolines 11-13, respectively, upon reflux in ni-
tromethane for 3 days. The formation of the heterocycles is
much faster in the presence of a catalytic amount of ZnCl2
(0.024 mol per 1 mol of the amidine; Scheme 4) when the
conversion is complete after 4 h. A similar catalytic effect
has also been reached using anhydrous MSO4 (M ) Cu, Co,
Cd), CdCl2, and AlCl3.
rather high values indicate the involvement of the imino
proton in the hydrogen bonding. 195Pt resonances were
observed between -101 and -75 ppm, which is in accord
with the ligand sphere around the platinum(IV) center of the
amidine complexes.
Previously, NOE experiments have been effectively used
by us for observation of the E-Z forms in Pt(IV)-bound
imino esters,38 and it was proved that this method allows
the determination of the configuration even when only one
form is available. The NOE experiment for studying the E-Z
isomerism has now been applied to the amidine complexes,
and NOE shift correlation signals between the imino proton
[Pt]-HNdC(CH2CH3) and the methylene protons [Pt]-
HNdC(CH2CH3) were found in the NOESY spectra. The
latter gives explicit evidence that the platinum amidine
compounds in solution retain the Z-configuration observed
in the solid state by the X-ray diffraction (see above).
Liberation of the Hydroxo-Functionalized Amidines.
The amidine Pt(IV) complexes exhibit substantial inertness
(characteristic for Pt(IV) complexes55) toward substitution
with such strong chelating ligands as 2,2′-bipyridyl, ethyl-
enediamine, EDTA, and 1,5,9-triazacyclododecane. How-
ever, the amidine has been displaced from 1 by reaction with
pyridine in CH2Cl2 (2 days, reflux) giving NHdC(Et)-
NHCH2CH2OH and the well-known [PtCl4(py)2];56 the very
poor solubility of the latter is the apparent driving force for
the reaction. However, the substitution for pyridine of the
other amidines (from 2-6) failed and only the starting
platinum complexes were detected in the mass spectra.
The most general and facile method for the liberation of
the hydroxo-functionalized amidines we found so far is based
on the reaction of the amidine complexes with 1,2-bis-
(diphenylphosphine)ethane (dppe), which acts as both replac-
ing and reduction agent (Scheme 4), giving the amidine along
with the platinum(II) complex [Pt(dppe)2]Cl2 and the dppe
oxides; the P-containing species were identified by 31P{1H}
NMR. This reaction was illustrated by use of complexes 1,
3, and 4. The treatment of these complexes with dppe
followed by subsequent workup allowed the isolation of the
amidines NHdC(Et)NHCHRCH2OH (R ) H 8, Et 9, Ph
10) with the substituents R of different type.
Although the synthesis of oxazolines from amino alcohols
and nitriles is known, the metal-catalyzed synthesis of
oxazolines from the amidines HNdC(R)NHkOH has never
been reported in the past. We anticipate that, in general, the
role of metal ions in the metal-catalyzed synthesis of
oxazolines is at least dual. First, metal centers activate nitriles
toward the nucleophilic addition of amino alcohols, and,
second, they provide conditions for the facile cyclization of
the amidines HNdC(R)NHkOH formed in the first step of
the reaction.
Final Remarks. Besides the contribution to the chemistry
of oxazolines, this work adds more on the synthetic routes
to amidines and their complexes, and the importance of the
latter is manifested in the following: (i) In accord with the
recent data, some amidine complexes of platinum exhibit
substantial antitumor activity,57 and the bioinorganic chem-
istry of amidine compounds will certainly be further inves-
tigated. (ii) Despite the intrinsic pharmacological signifi-
cance, high synthetic utility, and number of industrial appli-
cations of amidines,58-60 information on synthetic pathways
to their alcohol HNdC(R)NHkOH derivatives is scarce and
limited to only the reactions between amidines and 2-halo-
ethanol or ethylene oxide,61 monoethanolamine with 3-cyano-
4,5-dialkyl-2-butenolides or 3-cyano-4,5-dialkylbutyrolac-
(57) (a) Michelin, R. A.; Mozzon, M.; Belluco, U.; Bertani, R.; Baccichetti,
F.; Bordin, F.; Marzano, C. Synthesis and Biological Activity of
Amidine Complexes of Platinum(II). In XXXVth Int. Conf. Coord.
Chem., Heidelberg, 2002, Book of Abstracts, P1.008. (b) Michelin,
R. A. Private communication, 2003.
(58) (a) Oshovsky, G. V.; Pinchuk, A. M. Russ. Chem. ReV. 2000, 69, 845.
Raczynska, E. D.; Gawinecki, R. Trends Org. Chem. 1998, 7, 85. (b)
Liu, Y.; Zhang, J. Huaxue Tongbao 1996, 11, 1; Chem. Abstr. 126,
89091. (c) Boyd, G. V. In Chemistry of Amidines and Imidates; Patai,
S., Rappoport, Z., Eds.; Wiley: Chichester, 1991; Vol. 2, p 339. (d)
Neilson, D. G. In Chem. Amidines and Imidates; Patai, S., Ed.;
Wiley: New York, 1975; p 385. (e) Granik, V. G. Russ. Chem. ReV.
(Engl. Transl.) 1983, 52, 377.
(59) For reviews on the medicinal chemistry of amidines see: (a) Greenhill,
J. V.; Lue, P. Prog. Med. Chem. 1993, 30, 203. (b) Richter, P. H.;
Wunderlich, I.; Schleuder, H.; Keckeis, A. Pharmazie 1993, 48, 163.
(60) For reviews on the coordination chemistry of amidines see: (a) Baker,
J.; Kilner, M. Coord. Chem. ReV. 1994, 133, 219. (b) Wang, H.-X.;
Ding, L.; Wu, Y.-J. Youji Huaxue 2000, 20, 44; Chem. Abstr. 2000,
132, 166256.
(55) (a) Hall, M. D.; Hambley, T. W. Coord. Chem. ReV. 2002, 232, 49.
(b) Mason, W. R. Coord. Chem. ReV. 1972, 7, 241.
(56) Jørgensen, S. M. J. Prakt. Chem. 1886, 33, 489.
2810 Inorganic Chemistry, Vol. 42, No. 8, 2003

Amidines DeriWed from Nitrile-Amino Alcohol Coupling
tones,62 L-arginine and monoethanolamine (giving 2-guanidino-
ethanol),63 and imidates with amino alcohols.44 In addition,
it has recently been reported that the platinum(II) complex
[(Me2PO‚‚‚H‚‚‚OPMe2)PtH(PMe2OH)] efficiently catalyzes
the direct conversion of propionitrile and monoethanolamine
into NHdC(Et)NHCH2CH2OH; the latter was characterized
only by GCMS.64 The current work is the first one where a
general pathway to this type of hydroxo-functionalized ami-
dines is developed and the compounds HNdC(R)NHkOH
have been fully characterized both in solution and in the solid
state. The synthetic significance of such compounds toward
the formation of oxazolines was also clearly recognized in
this work. The only handicap to achieve a great variety of
such amidines is the extreme kinetic inertness of the
platinum(IV) complexes making difficult the substitution of
the HNdC(R)NHkOH formed in the metal-mediated reac-
tion. However, the metal enhancement of the activation of
the ligated nitriles is expected to promote other amino alcohol
reactions, and we anticipate the discovery of much more
labile metal systems to furnish those organic compounds;
work in this direction is underway in our group.
Table 1. Crystal Data for Complexes 1, 2, and 4
1
2
4
emp formula
fw
C10H24Cl4N4O2Pt C12H28Cl4N4O2Pt C14H30Cl4N4O2Pt
569.22
597.27
623.31
100(2)
0.71073
orthorhombic
P212121
8.89200(10)
11.0774(2)
22.7956(3)
90
temp, K
λ, Å
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
120(2)
150(2)
0.71073
monoclinic
P21/n
7.8130(4)
13.1622(8)
8.7544(5)
0.71073
triclinic
P1h
7.9911(2)
8.5378(2)
9.0101(3)
104.2530(10)
98.8570(10)
116.112(2)
510.11(2)
1
1.944
7.412
0.0203
0.0493
97.909(3)
90
90
891.71(9)
2
2.120
2245.37(6)
4
Z
F
calcd, g/cm3
1.850
6.740
0.0175
0.0406
µ(Mo KR), mm-1 8.475
R1a (I g 2σ)
0.0267
0.0543
wR2b (I g 2σ)
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
correction based on equivalent reflections69 was applied to all data.
The structures were refined with the SHELXL-9770 program and
the WinGX graphical user interface.71 In 2, the OH group was
disordered in two positions with approximately equal occupation
parameters. OH and NH hydrogens were located from the difference
Fourier map. In the case of 4, NH hydrogens were refined
isotropically. All other hydrogens either were not refined or were
constrained to ride on their parent atom. Crystallographic data are
summarized in Table 1, and selected bond lengths and angles, in
Table 2 and the figure captions.
Experimental Section
Materials and Instrumentation. Solvents were obtained from
commercial sources and used as received. trans-[PtCln(EtCN)2] (n
) 2, 4) were prepared accordingly to the published methods.65
Amino alcohols were purchased from Fluka and Aldrich. C, H,
and N elemental analyses were carried out by the laboratory for
elemental analyses of the Institute of Physical Chemistry, University
of Vienna, with a Perkin-Elmer 2400 CHN elemental analyzer.
Melting points were determined on a Bu¨chi B-540 melting point
apparatus and are uncorrected. For TLC, Merck 60 F254 SiO2-plates
have been used. Mass spectra were obtained on a Bruker esquire3000
(ESI) instrument. Infrared spectra (4000-400 cm-1) were recorded
on a Perkin-Elmer FTIR instrument in KBr pellets.
NMR Measurements. 1H, 13C{1H}, 31P{1H}, 195Pt, and 15N
NMR spectra were measured on a Bruker DPX 400 spectrometer
(Ultrashield Magnet) at 400.13 MHz (1H), 100.63 MHz (13C), 162.0
MHz (31P), 85.99 MHz (195Pt), and 40.55 MHz (15N), correspond-
ingly, at ambient temperature. 195Pt chemical shifts are given relative
to Na2[PtCl6] (by using K2[PtCl4], δ ) -1630 ppm, as a standard),
and the half-height line width is given in parentheses. Peak
attribution is based on gradient-enhanced 1H,1H-DQF-COSY,
13C,1H-HMQC, 13C,1H-HMBC, 15N,1H-HMQC, and NOESY spec-
troscopy using standard pulse programs.
Synthetic Work and Characterization. Addition of Amino
Alcohols to EtCN Ligands in trans-[PtCl4(EtCN)2]. Monoetha-
nolamine (5.5 mg, 0.095 mmol) was added to a suspension of trans-
[PtCl4(EtCN)2] (20.0 mg, 0.0447 mmol) in CH2Cl2 (2 mL) at room
temperature. After ca. 2 min the orange crystalline precipitate was
formed; it was filtered off, washed with three 3-mL portions of
CH2Cl2, two 3-mL portions of Et2O, and one 3-mL portion of EtOH,
and dried in vacuo for 1 day at 20-25 °C. The yield is 82%, based
on Pt.
The other amino alcohols (0.095 mmol) were added to a suspen-
sion of trans-[PtCl4(EtCN)2] (20.0 mg, 0.0447 mmol) in CH2Cl2
(2 mL) at room temperature to give an orange solution, which, after
2 h, was evaporated to dryness at 20-25 °C under reduced pressure;
the orange oily residue formed was washed with three 3-mL
portions of Et2O, whereupon it was dried in vacuo at room
temperature to give crystalline material. The yields were 70-80%,
based on Pt.
trans-[PtCl4{(Z)-NHdC(Et)NHCH2CH2OH}2] (1). Anal. Calcd
for C10H24N4Cl4O2Pt: C, 21.10; H, 4.25; N, 9.84. Found: C, 21.26;
H, 4.46; N, 9.47. ESI-MS (acetone), m/z: 567 [M - H]-. Mp )
145-146 °C. TLC: Rf ) 0.51 (eluent CH2Cl2:acetone ) 1:1). IR,
X-ray Structure Determinations of 1, 2, and 4. The X-ray
diffraction data were collected on a Nonius Kappa CCD diffrac-
tometer using Mo KR radiation (λ) 0.71073 Å. The Denzo-
Scalepack66 program package was used for cell refinements and
data reduction. Structures were solved by direct methods using the
SIR97 or SHELXS-97 programs.67,68 An empirical absorption
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(67) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Deter-
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(68) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
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R. J. Appl. Crystallogr. 1999, 32, 115.
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Systems, Bruker AXS, Inc.: Madison, WI, 1998.
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ment; University of Go¨ttingen: Go¨ttingen, 1997.
(71) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
Inorganic Chemistry, Vol. 42, No. 8, 2003 2811

Makarycheva-Mikhailova et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg)
trans-[PtCl4{(Z)-NHdC(Et)NHCH(CH2CH3)CH2OH-(R)-
(-)}2] (4). Anal. Calcd for C14H32N4Cl4O2Pt: C, 26.92; H, 4.48;
N, 8.97. Found: C, 26.87; H, 4.70; N, 8.75. ESI-MS (acetone),
m/z: 623 [M - H]-. Mp ) 140 °C. TLC: Rf ) 0.63 (eluent
MeCOOEt). IR, cm-1: 3499 m-w ν(O-H), 3407 and 3334 m-w
ν(N-H), 1632 vs ν(CdN). 1H NMR spectrum in CDCl3, δ: 7.39
(d, 1H, -NH-), 5.42 (t, 1H, -NHd), 3.72 and 3.60 (two m, 2 H,
CH2OH), 3.49 (m, 1H, CH), 2.60 (two q, 2H, CH2 from Et), 1.63
and 1.53 (two m, 2H, CH(CH2)CH3), 1.31 (t, 3H, CH3 from Et),
1.03 (t, 3H, CH3). 13C{1H} NMR spectrum in CDCl3, δ: 170.85
(CdN), 65.68 (CH2OH), 58.23 (CH), 27.17 (CH2 from Et), 24.77
(CH(CH2)CH3), 10.93 (CH3 from Et), 10.86 (CH3). 195Pt NMR
spectrum in CDCl3, δ: -75.5 (450 Hz). 15N NMR spectrum in
1
2
4
Pt(1)-Cl(1)
Pt(1)-Cl(2)
Pt(1)-Cl(3)
Pt(1)-Cl(4)
Pt(1)-N(1)
N(1)-C(1)
C(1)-N(2)
N(2)-C(4)
C(4)-C(5)
C(5)-O(1)
Pt(1)-N(3)
N(3)-C(8)
C(8)-N(4)
N(4)-C(11)
C(11)-C(12)
C(12)-O(2)
2.3270(14)
2.3271(14)
2.3216(8)
2.3207(8)
2.3288(8)
2.3251(7)
2.3194(7)
2.3142(8)
2.034(3)
1.304(4)
1.328(4)
1.462(4)
1.564(5)
1.389(4)
2.026(2)
1.308(4)
1.339(4)
1.466(4)
1.527(5)
1.423(4)
2.039(4)
1.315(7)
1.324(7)
1.474(7)
1.517(8)
1.407(7)
2.033(3)
1.318(4)
1.327(4)
1.462(4)
1.475(5)
1.337(7)/1.304(7)a
2
CDCl3, δ: 96.7, 61.4 (1JN,Pt ) 333 Hz, JH,Pt ) 27 Hz).
trans-[PtCl4{(Z)-NHdC(Et)NHCH(CH2CH3)CH2OH-
(S)-(+)}2] (5). Anal. Calcd for C14H32N4Cl4O2Pt: C, 26.92; H, 4.48;
N, 8.97. Found: C, 26.67; H, 4.78; N, 8.68. ESI-MS (acetone),
m/z: 623 [M - H]-. Mp ) 142 °C. TLC: Rf ) 0.35 (eluent
Me2CO: CHCl3 ) 1:5). IR, cm-1: 3501 m-w ν(O-H), 3403 and
3356 m-w ν(N-H), 1629 vs ν(CdN). 1H NMR spectrum in
CDCl3, δ: 7.40 (d, 1H, -NH-), 5.42 (t, 1H, -NHd), 3.72 and
3.60 (two m, 2 H, CH2OH), 3.49 (m, 1H, CH), 2.60 (q, 2H, CH2
from Et), 1.63 and 1.53 (two m, 2H, CH(CH2)CH3), 1.31 (t, 3H,
CH3 from Et), 1.03 (t, 3H, CH3). 13C{1H} NMR spectrum in CDCl3,
δ: 170.84 (CdN), 65.66 (CH2OH), 58.22 (CH), 27.17 (CH2 from
Et), 24.78 (CH(CH2)CH2), 10.93 (CH3 from Et), 10.86 (CH3).
195Pt NMR spectrum in CDCl3, δ: -76.0 (450 Hz). 15N NMR
Cl(1)-Pt(1)-Cl(2)
Cl(1)-Pt(1)-Cl(3)
Cl(2)-Pt(1)-Cl(4)
N(1)-Pt(1)-N(3)
Cl(1)-Pt(1)-N(1)
Cl(2)-Pt(1)-N(1)
Pt(1)-N(1)-C(1)
C(4)-C(5)-O(1)
Pt(1)-N(3)-C(8)
C(11)-C(12)-O(2)
90.13(3)
89.33(3)
178.81(3)
179.57(3)
177.82(11)
84.59(8)
92.56(8)
134.5(2)
113.3(3)
131.6(2)
113.1(3)
92.99(8)
86.13(8)
133.8(2)
118.3(4)/116.1(4)a
a Oxygen is disordered in two positions.
cm-1: 3504 m-w ν(O-H), 3298 and 3253 m-w ν(N-H), 1636
vs ν(CdN). 1H NMR spectrum in CDCl3, δ: 7.54 (t, 1H,
-NH-), 5.48 (t, 1H, -NHd), 3.81 (s, br, 2H, CH2OH), 3.45 (q,
2H, CH2NH), 2.59 (q, 2H, CH2 from Et), 1.32 (t, 3H, CH3).
13C{1H} NMR spectrum in CDCl3, δ: 170.69 (CdN), 61.90
(CH2OH), 45.88 (CH2NH), 27.17 (CH2 from Et), 10.61 (CH3 from
Et). This complex exhibits poor solubility in CDCl3 to measure its
195Pt NMR spectra even at high acquisition time; the solubility is
higher in (CD3)2SO, but the complex is decomposed in this solvent.
2
spectrum in CDCl3, δ: 96.7, 61.6 (1JN,Pt ) 355 Hz, JH,Pt ) 26
Hz).
trans-[PtCl4{(Z)-NHdC(Et)NHCH(CH2CH2CH3)CH2OH}2]
(6). Anal. Calcd for C16H36N4Cl4O2Pt: C, 29.40; H, 5.51; N, 8.57.
Found: C, 29.11; H, 5.24; N, 8.27. ESI-MS (acetone), m/z: 651
[M - H]-. Mp ) 131 °C (dec). TLC: Rf ) 0.63 (eluent Me2CO:
CHCl3 ) 1:5). IR, cm-1: 3507 m-w ν(O-H), 3345 and 3294
m-w ν(N-H), 1628 vs ν(CdN). 1H NMR spectrum in CDCl3, δ:
7.40 (d, 1H, -NH-), 5.40 (t, 1H, -NHd), 3.70 (m, 1H, CH),
3.58 (m, 2H, -CH2OH), 2.59 (q, 2H, CH2 from Et), 1.51 (m, 4H,
2CH2), 1.30 (t, 3H, CH3 from Et), 0.95 (t, 3H, CH3). 13C{1H}
NMR spectrum in CDCl3, δ: 170.75 (CdN), 65.98 (-CH2OH),
56.64 (CH), 33.75 (CH(CH2)CH2), 27.07 (CH2 from Et), 19.52
(CH2(CH2)CH3), 14.39 (CH3), 10.87 (CH3 from Et). 195Pt NMR
spectrum in CDCl3, δ: -76.7 (450 Hz). 15N NMR spectrum in
trans-[PtCl4{(Z)-NHdC(Et)NHCH2CH(Me)OH-(R)-(-)}2] (2).
Anal. Calcd for C12H28N4Cl4O2Pt: C, 24.12; H, 4.69; N, 9.38.
Found: C, 24.23; H, 4.63; N, 9.24. ESI-MS (acetone), m/z: 595
[M - H]-. Mp ) 128 °C. TLC: Rf ) 0.47 (eluent Me2CO:
MeCOOEt ) 1:2). IR, cm-1: 3561 m-w ν(O-H), 3403 and 3343
m-w ν(N-H), 1623 vs ν(CdN). 1H NMR spectrum in CDCl3, δ:
7.70 (t, 1H, -NH-), 5.48 (t, 1H, -NHd), 4.00 (m, 1H, CH), 3.33
and 3.21 (two m, 2H, CH2NH-), 2.56 (q, 2H, CH2 from Et), 1.29
and 1.27 (two t, 6H, CH3 from Et and Me). 13C{1H} NMR spectrum
in CDCl3, δ: 170.61 (CdN), 67.18 (CH), 50.66 (CH2NH), 27.16
(CH2 from Et), 20.66 (CH(CH3)OH), 10.56 (CH3 from Et). 195Pt
NMR spectrum in CDCl3, δ: -83.0 (450 Hz). 15N NMR spectrum
2
CDCl3, δ: 97.3, 61.2 (1JN,Pt ) 356 Hz, JH,Pt ) 25 Hz).
Reaction between NH2CH2CH2OH and the Platinum(II)
Complex trans-[PtCl2(EtCN)2]. Monoethanolamine (L) (6.5 mg,
0.106 mmol) was added to a solution of trans-[PtCl2(EtCN)2] (20.0
mg, 0.053 mmol) in CH2Cl2 (2 mL) at room temperature, and the
reaction mixture was kept for 1 h (during this time the oily residue
was released), whereupon the yellow solution was decanted and
the oily residue was subject to ESI-MS, TLC, IR, and NMR and
monitoring.
2
in CDCl3, δ: 84.4, 62.0 (1JN,Pt ) 354 Hz, JH,Pt ) 26 Hz).
trans-[PtCl4{(Z)-NHdC(Et)NHCH(Ph)CH2OH-(R)-(-)}2] (3).
Anal. Calcd for C22H32N4Cl4O2Pt: C, 36.61; H, 4.38; N, 7.77.
Found: C, 36.44; H, 4.40; N, 7.50. ESI-MS (acetone), m/z: 719
[M - H]-. Mp ) 161 °C. TLC: Rf ) 0.46 (eluent MeCOOEt).
IR, cm-1: 3492 m-w ν(O-H), 3402 and 3342 m-w ν(N-H),
[Pt{NHdC(Et)NHCH2CH2OH}2L2]Cl2 (7). ESI-MS (acetone),
m/z: 585 [M - Cl]+, 524 [M - L - Cl]+, 463 [M - 2L - Cl]+.
TLC: Rf ) 0.56 (eluent CH2Cl2:acetone ) 1:2). IR, cm-1: 3299
m-w ν(N-H), 1628 vs ν(CdN). 1H NMR spectrum in CDCl3, δ:
7.36 (s, br, 1H, -NH-), 5.32 (s, br, 1H, -NHd), 3.78 (m,
2H, CH2OH), 3.37 (m, 2H, CH2NH), 2.41 (q, 2H, CH2 from Et),
1.20 (t, 3H, CH3). 13C{1H} NMR spectrum in CDCl3, δ: 170.69
(CdN), 61.90 (CH2OH), 45.88 (CH2NH), 27.17 (CH2 from Et),
1
1637 vs ν(CdN). H NMR spectrum in CDCl3, δ: 8.11 (d, 1H,
-NH-), 7.50-7.30 (m, 5H, Ph), 5.61 (t, 1H, -NHd), 4.68 (m,
1H, CH), 3.92 and 3.84 (two m, 1H, CH2NH-), 2.57 (two m, 2H,
CH2 from Et), 1.23 (t, 3H, CH3 from Et). 13C{1H} NMR spectrum
in CDCl3, δ: 170.68 (CdN), 137.90 (Cipso), 129.57 (p-Ph), 128.79
and 126.91 (o-Ph and m-Ph), 67.54 (CH2NH), 60.81 (CH), 26.97
(CH2 from Et), 10.56 (CH3). 195Pt NMR spectrum in CDCl3, δ:
-101.0 (400 Hz). 15N NMR spectrum in CDCl3, δ: 94.2, 63.0 (1JN,Pt
1
10.61 (CH3 from Et). The H and 13C signals for ethanolamine
coordinated to platinum could not be unequivocally assigned.
Liberation of the Amidines from the Platinum(IV) Com-
plexes. Method I. In a preparative experiment, dppe (0.125 mmol)
2
) 360 Hz, JH,Pt ) 26 Hz).
2812 Inorganic Chemistry, Vol. 42, No. 8, 2003

Amidines DeriWed from Nitrile-Amino Alcohol Coupling
is added to a solution of the amidine complex (0.050 mmol) in
nondried CH2Cl2 (2 mL) at 20-25 °C, the color turns from yellow
to colorless for 10 min, and a colorless precipitate of [Pt(dppe)2]-
Cl2 is released. The solvent is decanted and evaporated until half
of the initial volume and Et2O (1 mL) is added, whereupon the
mixture is left to stand at ca. -5 °C for 2-3 min. The precipitate
of [Pt(dppe)2]Cl2 formed in almost quantitative yield (31P{1H} NMR
in CDCl3, δ, 45.7, JPt-P 2360.5 Hz; lit.72); it is separated by filtration,
the filtrate is evaporated until dryness, and the residue is washed
with Et2O (1 mL) [31P{1H} NMR of the ether washings in CDCl3,
δ: Ph2P(dO)(CH2)2PPh2 (31.2, d, JP-P 48.5 Hz for Ph2P(dO)-
(CH2)2PPh2 and -13.5, d, JP-P 48.5 Hz for Ph2P(dO)(CH2)2PPh2;
lit.73-75), Ph2P(dO)(CH2)2P(dO)Ph2 (31.2 s; lit.76), and Ph2P(CH2)2-
PPh2 (-14.1 s)] and dried in a vacuum. Yield: ca. 70%. Method
II. In a preparative experiment, pyridine (0.40 mmol) is added to
a solution of the amidine complex 1 (0.05 mmol) in CH2Cl2 (1
mL) and, upon reflux, the color turns from deep orange to orange
for 2 days and a yellow precipitate of [PtCl4(py)2]56 is quantitatively
released. The precipitate is separated by filtration, the filtrate is
evaporated until dryness, and the residue of amidine is dried in a
vacuum; the yield is almost quantitative. The attempts to liberate
other amidines apart from NHdC(Et)NHCH2CH2OH with pyridine
failed, and only the starting platinum complexes were detected in
mass spectra.
Conversion of the Amidines into the Appropriate Oxazolines.
In a preparative experiment, zinc chloride (1 mg, 0.006 mmol) was
added to a solution of the amidine (0.25 mmol) in MeNO2 (2 mL)
and the solution was refluxed for 4 h, whereupon the complete
conversion (NMR yield of oxazolines is almost quantitative) of the
amidine into the oxazoline was observed. A similar catalytic effect
has been reached using anhydrous MSO4 (M ) Cu, Co, Cd), CdCl2,
and AlCl3. In the blank experiment, i.e., without the added metal
salt, no traces of the oxazoline were detected after 4 h, but the
slow conversion is complete after 3 days of refluxing.
NdC(Et)OCH2CH2 (11). ESI-MS (MeOH), m/z: 100 [M +
H]+. TLC: Rf ) 0.42 [eluent is MeC(dO)OEt] which correspond
to the Rf value of NdC(Et)OCH2CH2 purchased from Aldrich. 1H
NMR spectrum in CDCl3 (MeNO2) δ: 3.82 (s, br, 2H, CH2O),
2.69 (q, 2H, CH2 from Et), 2.66 (m, 2H, CH2N), 1.28 (t, 3H, CH3).
13C{1H} NMR spectrum in CDCl3 (MeNO2) δ: 173.28 (CdN),
44.85 (CH2O) 35.02 (CH2N), 20.69 (CH2 from Et), 11.01 (CH3).
NdC(Et)OCH2CH2 (12). ESI-MS (MeOH), m/z: 128 [M +
H]+. 1H NMR spectrum in CDCl3 (MeNO2) δ: 3.98-3.51 (m, 2H,
CH2O), 2.64 (q, 2H, CH2Cd), 1.59 (m, 2H, CH3CH2CHN), 1.20
(t, 3H, CH3CH2Cd), 0.87 (t, 3H, CH3CH2CH); the signal for CHN
could not unequivocally be assigned. 13C{1H} NMR spectrum in
CDCl3 (MeNO2) δ: 172.30 (CdN), 49.9 (CH2O), 28.05 (CHCH2-
CH3), 21.26 (CH2Cd), 10.70 (CH3), 9.29 (CHCH2CH3); the signal
for CHN could not be unequivocally assigned.
NHdC(Et)NHCH2CH2OH (8). ESI-MS (MeOH), m/z: 117 [M
+ H]+. IR, cm-1: 3425 m-w ν(O-H) and ν(N-H), 1635 s
1
ν(CdN). H NMR spectrum in CDCl3, δ: 8.47 (t, 1H, -NH-),
6.64 (t, 1H, -NHd), 3.71 (s, br, 1H, CH2OH), 2.84 (q, 1H,
CH2NH), 1.88 (s, br, 2H, CH2 from Et), 0.35 (t, 3H, CH3).
13C{1H} NMR spectrum in CDCl3, δ: 171.1 (CdN), 61.0
(CH2OH), 45.7 (CH), 26.2 (CH2 from Et), 10.9 (CH3).
NdC(Et)OCH2CH2 (13). ESI-MS (MeOH), m/z: 176 [M +
H]+. 1H NMR spectrum in CDCl3 (MeNO2) δ: 3.83-3.64 (m, 2H,
CH2O), 2.69 (q, 2H, CH2Cd), 1.22 (t, 3H, CH3CH2Cd); the CHN
resonance overlaps with CH2 signals from dppe and dppe oxides.
NHdC(Et)NHCH(CH2CH3)CH2OH (9). ESI-MS (MeOH),
m/z: 145 [M + H]+. IR, cm-1: 3390 m-w ν(O-H) and ν(N-H),
Acknowledgment. A.V.M.-M. is indebted to the Gov-
ernor of St. Petersburg for a fellowship (Grant M01-2.5D-
446). M.G. and B.K.K. gratefully acknowledge the support
of the FWF (Fonds zur Foerderung der wissenschaftlichen
Forschung). V.Yu.K. thanks the Russian Fund for Basic
Research for the grant. A.V.M.-M. and V.Yu.K. express
gratitude to the International Science Foundation (Soros
Foundation) for the Soros Fellowship and Soros Professor-
ship, correspondingly. D.A.G. is very much obliged to the
PRAXIS XXI and POCTI programs (Portugal) for Grant
BCC16428/98. A.J.L.P. and V.Yu.K. are grateful to the FCT
(Foundation for Science and Technology) (Portugal) and the
POCTI program (POCTI/QUI/43415/2001) for financial
support of these studies.
1
1633 s ν(CdN). H NMR spectrum in CDCl3, δ: 8.46 (t, 1H,
-NH-), 6.68 (t, 1H, -NHd), 3.73 (m, 2H) and 2.94 (m, 1H) (CH
and CH2OH), 1.93 (q, 2H, CH2 from Et), 1.36 (m, 2H, CH3CH2),
0.72 (t, 3H, CH3), 0.37 (t, 3H, CH3 from Et). 13C{1H} NMR
spectrum in CDCl3, δ: 171.16 (CdN), 64.15 (CH2OH), 61.01
(CH2), 58.83 (CH), 26.49 (CH2 from Et), 12.02 (CH3CH2), 10.98
(CH3), 10.88 (CH3 from Et).
NHdC(Et)NHCH(Ph)CH2OH (10). ESI-MS (MeOH), m/z:
193 [M + H]+. IR in KBr, selected bands, cm-1: 3416 m-w
ν(O-H) and ν(N-H), 1633 s ν(CdN). 1H NMR spectrum in
CDCl3, δ, 9.95 (s, br, 1H, -NH-), 7.90-7.45 (m, 5H, Ph, NHd),
4.96 (m, 1H, CH), 4.07-3.94 (m, 2H, CH2NH-), 2.77-2.71 (m,
2H, CH2 from Et), 1.21 (t, 3H, CH3 from Et). 13C{1H} NMR
spectrum in CDCl3, δ: 171.77 (CdN), 136.80 (Cipso), 129.32 (p-
Ph), 129.13 and 126.39 (o-Ph and m-Ph), 68.57 (CH2NH), 64.07
(CH), 27.01 (CH2 from Et), 10.56 (CH3).
Supporting Information Available: Tables S1-S21 listing
crystallographic data, atomic coordinates, bond lengths and bond
angles, anisotropic displacement parameters, hydrogen coordinates,
isotropic displacement parameters, and hydrogen bonds for all
structures. X-ray crystallographic files in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
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IC034070T
Inorganic Chemistry, Vol. 42, No. 8, 2003 2813