Optically active mixed unsymmetric imine platinum(II) complexes - Utilization of the liberated imines for further syntheses of mixed imine-diazadiene complexes and of (E)-cyanoalkenes

Article abstract of DOI:10.1002/ejic.200800343

Treatment of trans-[PtCl₂(NCR)₂] (1) {R = CH ₂CO₂Me (1a), Ph (1b)} with (R*)-camphor oxime (C₉H₁₆)C=NOH (2) gives access to the optically active mixed imine-nitrile complexes trans-(R*)-[PtCl₂{NH=C(R)ON= C(C₉H₁₆)}(NCR)] (4), which, on reaction with ketoximes R¹R²C=NOH (3) {R¹ = R² = Me (3a), C₄H₈ (3b)}, give the chiral unsymmetric bis(imine) complexes trans-(R*)-[PtCl₂{NH=C(R)ON=C(C₉H ₁₆)}{NH=C(R)-ON=CR¹R²}] (6) in moderate yields. An alternative route involves the reaction of the starting complexes 1 with ketoximes 3 to give the mixed imine-nitrile complexes trans-[PtCl ₂{NH=C(R)ON=CR¹R²}(NCR)] (5), followed by reaction of the latter with (R*)-camphor oxime (2) to afford products 6 in similar yields. Treatment of complexes 1 or 4 with two or one equivalent of 2, respectively, gives the symmetrical bis-(imine) complexes trans-[PtCl ₂{NH=C(R)ON=C(C₉H₁₆)}₂] (7). These reactions are accelerated by microwave irradiation to afford, in better yields (71-50%), the same products. The new optically active diimine compounds NH=C(R)ON=C-(C₉H₁₆) (8) are quantitatively liberated upon reaction of complexes 7 with a diphosphane. The chiral diimino ester 8a (R = CH₂CO₂Me) acts as a protic nucleophile and efficiently couples with the coordinated nitrile in 4 to give the new optically active, mixed, unsymmetric imine-1,3-diaza-1,3-diene complexes trans-(R*,R*) -[PtCl₂{NH=C(R)ON=C(C₉H₁₆)}{NH= C(R)N=C(CH ₂CO₂Me)ON=C(C₉H₁₆)}] (9). Diimino ester 8a with an acidic α-methylene group also reacts with acyclic nitrones ^-O⁺N(Me)=C(H)R′ (10) to afford stereoselectively the (E)-cyanoalkenes (N≡C)C(CO₂Me)=C(H) R′ (11) {R′ = 4-MeC₆H₄ (11a), 2,4,6-Me ₃C₆H₂ (11b)}. All of these compounds were characterized by IR and NMR (¹H, ¹³C, and ¹⁹⁵Pt for metal complexes) spectroscopy, ESI-MS or FAB-MS, elemental analysis, and X-ray diffraction analysis (for 5c and 7b). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800343

FULL PAPER
DOI: 10.1002/ejic.200800343
Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes –
Utilization of the Liberated Imines for Further Syntheses of Mixed Imine-
Diazadiene Complexes and of (E)-Cyanoalkenes
Jamal Lasri,*[a] M. Fátima C. Guedes da Silva,[a,b] M. Adília Januário Charmier,[a,b] and
Armando J. L. Pombeiro*[a]
Keywords: (R*)-Camphor oxime / Optically active complexes / (E)-Cyanoalkenes / Platinum / Microwave irradiation
Treatment of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me (1a),
Ph (1b)} with (R*)-camphor oxime (C9H16)C=NOH (2) gives
access to the optically active mixed imine-nitrile complexes
trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4), which,
on reaction with ketoximes R1R2C=NOH (3) {R1 = R2 = Me
(3a), C4H8 (3b)}, give the chiral unsymmetric bis(imine) com-
plexes trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)-
ON=CR1R2}] (6) in moderate yields. An alternative route in-
volves the reaction of the starting complexes 1 with ketox-
imes 3 to give the mixed imine-nitrile complexes trans-
[PtCl2{NH=C(R)ON=CR1R2}(NCR)] (5), followed by reaction
of the latter with (R*)-camphor oxime (2) to afford products 6
in similar yields. Treatment of complexes 1 or 4 with two or
one equivalent of 2, respectively, gives the symmetrical bis-
(imine) complexes trans-[PtCl2{NH=C(R)ON=C(C9H16)}2] (7).
These reactions are accelerated by microwave irradiation to
afford, in better yields (71–50%), the same products. The
new optically active diimine compounds NH=C(R)ON=C-
(C9H16) (8) are quantitatively liberated upon reaction of com-
plexes 7 with a diphosphane. The chiral diimino ester 8a (R
= CH2CO2Me) acts as a protic nucleophile and efficiently
couples with the coordinated nitrile in 4 to give the new op-
tically active, mixed, unsymmetric imine-1,3-diaza-1,3-diene
complexes trans-(R*,R*)-[PtCl2{NH=C(R)ON=C(C9H16)}{NH=
C(R)N=C(CH2CO2Me)ON=C(C9H16)}] (9). Diimino ester 8a
with an acidic α-methylene group also reacts with acyclic
nitrones –O+N(Me)=C(H)RЈ (10) to afford stereoselectively
the (E)-cyanoalkenes (NϵC)C(CO2Me)=C(H)RЈ (11) {RЈ = 4-
MeC6H4 (11a), 2,4,6-Me3C6H2 (11b)}. All of these compounds
were characterized by IR and NMR (1H, 13C, and 195Pt for
metal complexes) spectroscopy, ESI-MS or FAB-MS, elemen-
tal analysis, and X-ray diffraction analysis (for 5c and 7b).
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
and cyclic or acyclic nitrones.[9] These reactions allowed the
selective synthesis of the corresponding achiral, racemic, or
1:1 diastereoisomeric complexes, and these products are
generally stable but not suitable to be applied in asymmetric
chemistry. These observations stimulated our interest to ex-
tend the metal-mediated nitrile-oxime and/or nitrile-imine
reactions to chiral PtII complexes. Further aims of this
study are as follows: (i) To prepare optically active, mixed
unsymmetric trans-PtII complexes by using (R*)-camphor
oxime as a chiral nucleophile towards the nitrile ligand. (ii)
To synthesize bis(imine) platinum(II) complexes and use
them as sources of chiral imines upon ligand liberation. (iii)
To employ the released imines in situ for further syntheses.
(iv) To apply focused microwave irradiation[10] in order to
reduce the reaction time and to increase the yield, selectiv-
ity, and purity in comparison with traditional heating meth-
ods.[6b,8a,11]
Introduction
Organonitrile–platinum complexes are precursors for a
wide variety of N-containing Pt compounds.[1–5] It has been
shown that, when coordinated to a suitable PtII or PtIV cen-
ter, nitrile ligands can undergo coupling with different types
of nucleophiles[6,7] or 1,3-dipoles.[8] The reactions of acyclic
nitrones with cis-[PtCl2(PhMeSO)(PhCN)], containing a
chiral sulfoxide group, could be performed diastereoselec-
tively, and the release of ∆4-1,2,4-oxadiazoline ligands from
the resulting complexes allowed the enantioselective synthe-
sis of this class of heterocycles.[8h]
Recently, we reported the synthesis of new trans- and cis-
mixed, unsymmetric oxadiazoline and/or imine complexes
by treating trans- and cis-bis(methyl cyanoacetate)–PtII
complexes with acetone oxime, N,N-diethylhydroxylamine,
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico, TU Lisbon,
We have synthesized new chiral, trans unsymmetric imine
complexes of the types [PtCl2{(R*)-imine}(nitrile)] and
[PtCl2{(R*)-imine}(imine)], bearing two different ligands,
by undertaking the first examples of coupling an optically
active oxime with a nitrile ligand coordinated to a platinum
center. Further reactions that were also investigated pro-
Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Fax: +351-218464455
E-mail: jamal.lasri@ist.utl.pt
pombeiro@ist.utl.pt
[b] Universidade Lusófona de Humanidades e Tecnologias, ULHT
Lisbon,
Av. Campo Grande 376, 1749-024 Lisboa, Portugal
3668
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3668–3677

Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes
vided a facile metal-mediated route to new free chiral di- clopentanone oxime (3b) as the reacting nucleophiles
imines, which can be used in situ for subsequent coupling (Scheme 1). Complexes 6 were prepared by two different
with a coordinated nitrile to give trans mixed unsymmetric ways: (i) reaction (1) of the starting dinitrile PtII complexes
imine-diazadiene complexes. If the liberated imine bears the 1 with the chiral oxime 2 to give the optically active com-
CH2CO2Me ester group with an acidic α-methylene, its plexes 4, which were further converted to complexes 6 by
reaction with acyclic nitrones affords (E)-cyanoalkenes treatment with oximes 3 [reaction (2)]; (ii) reaction (3) of
stereoselectively.
complexes 1 with oximes 3 leading to complexes 5, which,
upon subsequent reaction (4) with oxime 2, afford the same
final products 6.
All the obtained complexes, whose formation was moni-
tored by TLC, were purified by column chromatography on
silica gel and characterized by IR and NMR (1H, 13C, 195Pt)
spectroscopy, FAB-MS, and elemental analyses.
Treatment of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me
Results and Discussion
Optically Active Imine Complexes
In the first part of this work, we report the selective syn-
thesis of new optically active, mixed unsymmetric platinum (1a), Ph (1b)} with (R*)-camphor oxime (2), in refluxing
complexes of the general types trans-[PtCl2{(R*)- CH2Cl2 at 40 °C for 15 or 60 min (for 1a or 1b, respec-
imine}(nitrile)] 4 and trans-[PtCl2{(R*)-imine}(imine)] 6 by tively), gives access to the corresponding new, optically
using
the
bis(methyl
cyanoacetate)
trans-[PtCl2- active monoimine complexes trans-(R*)-[PtCl2{NH=C(R)-
(NCCH2CO2Me)2] (1a) and the bis(benzonitrile) trans- ON=C(C9H16)}(NCR)] (4) {R = CH2CO2Me (4a), Ph (4b)}
[PtCl2(NCPh)2] (1b) as the starting dinitrile PtII complexes in moderate yields (55–50%). Further reaction of com-
and (R*)-camphor oxime (2), acetone oxime (3a), and cy- plexes 4a or 4b with acetone oxime 3a or cyclopentanone
Scheme 1.
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J. Lasri, M. F. C. Guedes da Silva, M. A. J. Charmier, A. J. L. Pombeiro
FULL PAPER
oxime 3b, under the same experimental conditions, leads to plexes 1, and in their 1H NMR spectra δ(NH) (8.01–
the new, chiral, mixed unsymmetric bis(imine) complexes 8.15 ppm) reflects the hydrogen bond between the imine hy-
trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}{NH=C(R)
drogen and oxime nitrogen atoms, which stabilizes the E
ON=CR1R2}] (6) {R = CH2CO2Me; R1 = R2 = Me (6a), conformation of the iminoacyl ligand. The 13C NMR spec-
C4H8 (6b), R = Ph; R1 = R2 = Me (6c), C4H8(6d)} also in tra show the characteristic signals of the imine and nitrile
moderate yields (52–45%). All these reactions are ac- ligands. The IR spectra of the bis(imine) complexes 6 exhi-
celerated by microwave (M.W.) irradiation (5 or 20 min, for bit ν(N=C) in the 1634–1654 cm–1 range. Both H and 13C
1
1a and 4a or 1b and 4b, respectively), giving the same prod- NMR spectra show that the products contain two different
1
ucts in better yields (70–52%) (Scheme 1).
imine ligands (e.g., two distinct H NMR resonances of the
An alternative route to obtain complexes 6a–6d involves hydrogen-bonded NH protons in the 8.06–8.36 ppm range).
the reverse order of reactions, as follows: Firstly, the start- The single-crystal X-ray diffraction structural analysis
ing dinitrile–PtII complexes 1a or 1b react with acetone ox- of the mono-iminoacylated PtII complex trans-
ime 3a or cyclopentanone oxime 3b to give the monoimine [PtCl2{NH=C(Ph)ON=CMe2}(NCPh)] (5c) confirms the
complexes trans-[PtCl2{NH=C(R)ON=CR1R2}(NCR)] (5) formulation and its trans configuration (the molecular
{R = CH2CO2Me; R1 = R2 = Me (5a), C4H8 (5b), R = structure is depicted in Figure 1, crystal data and selected
Ph; R1 = R2 = Me (5c), C4H8 (5d)} derived from a single bond lengths and angles are given in Table 2 and Table 1,
iminoacylation in moderate yields (51–40%). Secondly, respectively). The values of the bond lengths, Pt–N
monoimine complexes 5a–5d react with (R*)-camphor ox- [1.995(2) and 1.963(2) Å], Pt–Cl [2.2963(7) and
ime (2) to afford the final complexes 6a–6d in comparable 2.2998(8) Å], N1–C1 [1.283(3) Å], N2–C2 [1.137(4) Å], and
yields (52–44%). Also in these cases the reactions are ac-
celerated by M.W. irradiation (5 or 20 min, for 1a and 5a–
5b or 1b and 5c–5d, respectively), leading to the same prod-
ucts in better yields (71–50%) (Scheme 1).
Table 1. Selected bond lengths [Å] and angles [°] for complexes 5c
and 7b.
5c
7b
Interestingly,
the
reaction
of
trans-[PtCl2-
Bond lengths
Cl1–Pt1
Cl2–Pt1
N1–Pt1
N2–Pt1
N1–H1
C2–N2
C1–N1
N2–H2
(NCCH2CO2Me)2] (1a) with oximes 2 and 3 leads also to
the formation of small amounts of the bis(imine) complexes
2.2963(7)
2.2998(8)
1.995(2)
1.963(2)
0.85(4)
1.137(4)
1.283(3)
–
2.2994(12)
2.3007(12)
2.004(4)
1.995(3)
0.99(4)
1.280(5)
1.271(6)
0.95(3)
trans-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}2]
(6%
yield) and the known[6b] trans-[PtCl2{NH=C(CH2CO2Me)-
ON=CR1R2}2] {R1 = R2 = Me (15% yield), C4H8 (10%
yield)}, respectively, derived from nucleophilic additions to
both nitrile ligands. Hence, the above-described reactions
show a considerable selectivity towards the mixed ligand
products derived from a single addition, which are the
major ones. The use of M.W. irradiation is a convenient
alternative way to the traditional refluxing method and pro-
vides a synthetic strategy for increasing the selectivity and
the yield with reduction of the reaction time.[6b,8a,10,11]
Complexes 4 and 5 exhibit IR ν(NϵC) values (2339–
2287 cm–1) that are identical to those of the starting com-
Bond angles
Cl1–Pt1–Cl2
N1–Pt1–Cl2
N2–Pt1–Cl2
N1–Pt1–Cl1
N2–Pt1–Cl1
N2–Pt1–N1
Pt1–N1–H1
Pt1–N2–H2
178.33(3)
89.52(6)
90.22(6)
89.43(6)
90.85(6)
179.17(8)
120(3)
179.74(4)
88.53(11)
91.13(13)
91.12 (11)
89.12(11)
179.07(15)
118(2)
–
115.7(18)
Figure 1. Molecular structure of the mono-iminoacylated PtII complex trans-[PtCl2{NH=C(Ph)ON=CMe2}(NCPh)] (5c) with the atomic
numbering scheme (ellipsoids are drawn at 50% probability).
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Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes
N1–H1 [0.85(4) Å], and the bond angles, Cl1–Pt1–N1 CH2CO2Me (7a), Ph (7b)} in moderate yields (50–48%)
[89.43(6)°], Pt1–N1–H1 [120(3)°], and Cl1–Pt1–N2 (Scheme 2, reactions 1 and 2, respectively). All these reac-
[90.85(6)°], as well as those of the N1–H1···N3 hydrogen tions are accelerated by M.W. irradiation (5 or 20 min, for
bond between the imine hydrogen and the oxime nitrogen 1a and 4a or 1b and 4b, respectively), giving the same prod-
atoms [d(H1···N3) is 2.13(4) Å, and the N1–H1···N3 angle ucts, 7a and 7b, in moderate to good yields (65–55%).
1
is 115(3)°], which stabilizes the E conformation of the imi-
Both H and 13C NMR spectra of 7 are consistent with
noacyl ligands, agree with those reported for other imino- two equivalent imine ligands. The single-crystal X-ray dif-
acylated platinum(II) complexes.[6b,6j,9]
fraction structural analysis of trans-[PtCl2{NH=C(Ph)-
ON=C(C9H16)}2] (7b) confirms the formulation and its
trans geometry (the molecular structure is depicted in Fig-
ure 2, crystal data and selected bond lengths and angles are
given in Table 2 and Table 1, respectively). The values of the
bond lengths, Pt–N [2.004(4) and 1.995(3) Å], Pt–Cl
[2.2994(12) and 2.3007(12) Å], N1–C1 [1.271(6) Å], and
N2–C2 [1.280(5) Å], and the bond angles, Cl1–Pt1–N1
[91.23(11)°] and Pt1–N1–H1 [118(2)°], agree with those re-
ported for other bis-iminoacylated platinum(II) complex-
es.[6b,6j] The stabilizing hydrogen bonds between the imine
hydrogen atoms and the oxime nitrogen atoms (see above)
are also confirmed by X-ray analysis [d(H1···N11) and
d(H2···N22) are 1.99(4) and 2.05(3) Å, respectively; the N1–
H1···N11 angle is 115(3)°, and the N2–H2···N22 angle is
114(2)°].
Symmetrical Imine Complexes
In the second part of this work, we report the synthesis
of new symmetrical complexes of the general type trans-
[PtCl2{(R*)-imine}2] 7 by reaction of complexes 1 or 4 with
(R*)-camphor oxime (2) (Scheme 2).
Treatment of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me
(1a), Ph (1b)} or trans-(R*)-[PtCl2{NH=C(R)ON=C-
(C9H16)}(NCR)] (4) {R = CH2CO2Me (4a), Ph (4b)} with
two or one equivalent of (R*)-camphor oxime (2), respec-
tively, in refluxing CH2Cl2 (for 15 or 60 min, for 1a and 4a
or 1b and 4b, respectively), gives the new bis(imine) com-
plexes trans-[PtCl2{NH=C(R)ON=C(C9H16)}2] (7) {R =
Scheme 2.
Eur. J. Inorg. Chem. 2008, 3668–3677
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J. Lasri, M. F. C. Guedes da Silva, M. A. J. Charmier, A. J. L. Pombeiro
FULL PAPER
The liberation of the new optically active diimine ligands
in complexes 7a and 7b was achieved upon addition of the
diphosphane Ph2PCH2CH2PPh2 (dppe) to a CDCl3 solu-
tion of any of those complexes at room temperature
(Scheme 2, reaction 3). The free diimines NH=C(R)-
ON=C(C9H16) (R*-8) {R = CH2CO2Me (R*-8a), Ph (R*-
8b)} are stable for at least one week at room temperature
and were characterized by IR and NMR (1H, 13C) spec-
troscopy and FAB-MS. Their NMR resonances appear at
higher fields than those of the corresponding complex pre-
cursors.
Optically Active Mixed Imine-Diazadiene Complexes
In pursuit of our interest[6g,6h,6k] in the reactivity of
free imines, we have investigated the reaction between the
liberated chiral diimino ester NH=C(CH2CO2Me)-
ON=C(C9H16) (R*-8a) and a Pt-coordinated nitrile. Hence,
in the third part of this work, we found that this diimino
ester efficiently couples with the nitrile ligand in trans-(R*)-
[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4) {R = CH2-
CO2Me (4a), Ph (4b)}, in CH2Cl2 at room temperature, to
give the new optically active, mixed unsymmetric imine-1,3-
diaza-1,3-diene complexes trans-(R*,R*)-[PtCl2{NH=C(R)-
ON=C(C9H16)}{NH=C(R)N=C(CH2CO2Me)ON=C-
(C9H16)}] (9) {R = CH2CO2Me (9a), Ph (9b)} in moderate
to good yields (65–49%) (Scheme 3). In these reactions, the
diimino ester behaves as a protic nucleophile towards the
ligated nitrile.
Figure 2. Molecular structure of the iminoacylated PtII complex
trans-[PtCl2{NH=C(Ph)ON=C(C9H16)}2] (7b) with the atomic
numbering scheme (ellipsoids are drawn at 50% probability).
Scheme 3.
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Eur. J. Inorg. Chem. 2008, 3668–3677

Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes
Scheme 4.
Both 1H and 13C NMR spectra of 9 confirm the presence
The association of those reactions with the subsequent
of the two different ligands. To the best of our knowledge, ligand liberation from the metal provides a facile metal-me-
these reactions represent the first examples of coupling a diated route to the syntheses of previously unknown op-
chiral imine with a nitrile ligand coordinated to a platinum tically active diimine compounds 8, which are inaccessible
center to give complexes bearing mixed chiral ligands of the directly by pure organic chemistry. They can thus be gener-
general type [PtCl2{(R*)-imine}{(R*)-diazadiene}].
ated and used in situ,[6a,6g] namely for further coupling with
the coordinated nitrile in 4 to give the new optically active,
mixed unsymmetric imine-diazadiene complexes [PtCl2-
{(R*)-imine}{(R*)-diazadiene}] 9. In the case of the gener-
ated free diimino ester 8a (bearing an acidic α-methylene
group), its reaction with acyclic nitrones affords (E)-cyano-
alkenes stereoselectively. Imino esters are useful intermedi-
ates in organic synthesis, and their coordination to a metal
can stabilize them, allowing their storage for a prolonged
time. When required, their liberation can be easily under-
taken and used in situ.
Synthesis of (E)-Cyanoalkenes
Apart from the protic nucleophile moiety, the chiral di-
imino ester 8a also bears an acidic α-methylene group, and
we investigated its reactivity towards acyclic nitrones
–O+N(Me)=C(H)RЈ (10). The corresponding (E)-cyanoal-
kenes (NϵC)C(CO2Me)=C(H)(RЈ) (11) {RЈ = 4-MeC6H4
(11a), 2,4,6-Me3C6H2 (11b)} were obtained in moderate
yields (ca. 52%) (Scheme 4).
Further potential interests of these studies include the
eventual use of the chiral imines as precursors of lactam
heterocycles[12] (which could be applied in enantioselective
catalysis[13]) and the possible pharmacological significance
of the Pt complexes, since enantiomerically pure platinum
compounds with N-ligands can display enhanced antitumor
activity.[14] Further reactions are under study in our labora-
tory towards the synthesis of chiral heterocyclic com-
pounds.
The formation of products 11 involves the overall and
formal removal of the two α-acidic methylene protons of
the imino ester 8a by the {NOMe}2– fragment of the
nitrone –O+N(Me)=C(H)RЈ which thus undergoes N=C
bond cleavage, with coupling of the remaining imine- and
oxime-derived fragments to afford (NϵC)C(CO2-
Me)=C(H)(RЈ) and (R*)-camphor oxime. This oxime could
be isolated at the end of the reaction and characterized by
1H and 13C NMR spectroscopy. The final step conceivably
is the C–O bond cleavage of the HN=C[ON=C(C9H16)]-
C(CO2Me)=C(H)(RЈ) species, affording products 11. We re-
cently reported a similar mechanism involving the synthesis
of (E)-cyanoalkenes starting from free nitriles.[8a]
Experimental Section
Materials and Instrumentation
Reagents and solvents were purchased from Aldrich and dried
by usual procedures. Complexes trans-[PtCl2(NCCH2CO2Me)2]
(1a),[6b] trans-[PtCl2(NCPh)2] (1b),[15] and acyclic nitrones
–O+N(Me)=C(H)RЈ (10)[16] were prepared according to published
methods. C, H, and N elemental analyses were carried out by the
Concluding Remarks
The results of this work show that bis(nitrile)–PtII com-
plexes of the type trans-[PtCl2(nitrile)2] (nitrile
NCCH2CO2Me or NCPh) can act as convenient starting
materials for the syntheses of a variety of optically active
mixed-ligand complexes of the types trans-[PtCl2{(R*)-
imine}(nitrile)] 4 and trans-[PtCl2{(R*)-imine}(imine)] 6,
=
1
Microanalytical Service of the Instituto Superior Técnico. H, 13C,
and 195Pt NMR spectra (in CDCl3) were measured with a Varian
Unity 300 spectrometer at ambient temperature. Positive-ion FAB
mass spectra were obtained with a Trio 2000 instrument by bom-
barding the samples in 3-nitrobenzyl alcohol (NBA) matrixes with
and the reactions represent the first examples of coupling a 8 keV (ca. 1.28ϫ1015 J) Xe atoms. Electrospray mass spectra were
recorded with an ion-trap instrument (Varian 500-MS LC Ion Trap
Mass Spectrometer) equipped with an electrospray (ESI) ion
source. 1H and 13C chemical shifts (δ) are expressed in ppm relative
to Si(Me)4, and 195Pt chemical shifts are relative to Na2[PtCl6] (by
using aqueous K2[PtCl4], δ = –1630 ppm, as a standard) with half-
height line width in parentheses. J values are in Hz. Infrared spec-
tra (4000–400 cm–1) were recorded with a Bio-Rad FTS 3000MX
and a Jasco FT/IR-430 instrument by using KBr pellets, and the
wavenumbers are in cm–1. Optical rotations were measured with a
Perkin–Elmer 241 polarimeter by using a 0.5-dm cell. Concentra-
tions (c) are given in mgmL–1. The microwave irradiation experi-
chiral oxime with a nitrile ligand coordinated to a platinum
center. This methodology could also introduce optical ac-
tivity into achiral mixed-ligand complexes of the type trans-
[PtCl2(imine)(nitrile)] 5 by nucleophilic addition of (R*)-
camphor oxime to the nitrile ligand.
Microwave irradiation generally enhances the reaction
rates and yields, and also the selectivity of the reaction of
the starting complex with (R*)-camphor oxime, because the
first nucleophilic addition appears to be accelerated to a
higher extent than the second one.
Eur. J. Inorg. Chem. 2008, 3668–3677
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3673

J. Lasri, M. F. C. Guedes da Silva, M. A. J. Charmier, A. J. L. Pombeiro
FULL PAPER
ments were undertaken in a focused microwave CEM Discover re-
actor (10 mL, 13-mm diameter, 300 W) which was fitted with a
rotational system and an IR detector of temperature.
yield). All the spectroscopic, FAB-MS, and elemental analytical
data are in agreement with those reported earlier.[9]
trans-[PtCl2{NH=C(CH2CO2Me)ON=C(C4H8)}(NCCH2CO2Me)]
(5b): Method (i) (30.4 mg, 50% yield), method (ii) (39.5 mg, 65%
Heating Methods
yield). IR: ν = 3444 (NH), 2338 (NϵC), 1743 (CO Me), 1648
˜
2
(i) The Conventional Method: The reactions were carried out in re-
fluxing CH2Cl2 with stirring, and their progress was monitored by
TLC (CH2Cl2/Et2O as eluent). After concentration of the solution
in vacuo to dryness, the crude residue was purified by column
chromatography on silica (CH2Cl2 or CH2Cl2/Et2O as eluent) fol-
lowed by evaporation of the solvent in vacuo to give the final prod-
ucts.
(C=N) cm–1 1 H NMR: δ = 1.81 (m, 4 H), 2.53 (m, 4 H)
.
[=C(C4H8)], 3.76 and 3.83 (two s, 3 H each, MeO), 4.01 and 4.13
(two s, 2 H each, CH2), 8.05 (br. s, 1 H, NH) ppm. 13C{1H} NMR:
δ = 24.9, 25.6, 30.5, 32.1 [=C(C4H8)], 26.9 and 40.0 (CH2), 53.4
and 54.7 (MeO), 112.6 (NϵC), 162.1 and 166.6 (CO2Me), 168.7
[N=C(C4H8)], 178.5 [C(O)=N] ppm. 195Pt NMR: δ = –2230 (J =
805 Hz) ppm. FAB+-MS: m/z = 563 [M]+. C13H19Cl2N3O5Pt
(563.29): calcd. C 27.72, H 3.40, N 7.46; found C 27.67, H 3.50, N
7.60.
(ii) Focused Microwave Irradiation: The reagents and solvent
(CH2Cl2) were added to a cylindrical Pyrex tube, which was then
placed in a focused microwave reactor. After the reaction, the mix-
ture was cooled down, the solvent was removed in vacuo, and the
crude residue was purified as indicated in (i).
trans-[PtCl2{NH=C(Ph)ON=CMe2}(NCPh)] (5c): Method (i)
(28.2 mg, 48% yield), method (ii) (32.3 mg, 55% yield). IR: ν =
˜
3436 (NH), 2288 (NϵC), 1646 (C=N) cm–1. 1H NMR: δ = 2.11
and 2.12 (two s, 3 H each, =CMe2), 7.49–7.73 (m, 8 H), 8.29 (br.
s, 1 H, NH), 8.67 (d, JHH = 8.0 Hz, 2 H) ppm. 13C{1H} NMR: δ
= 17.5 and 21.9 (Me groups), 109.9 (Cipso, NϵCPh), 116.3 (NϵC),
128.2, 128.6, 129.2, 129.6, 132.9, 133.4, and 134.6 (Caromatic), 165.5
(=CMe2), 168.1 [C(O)=N] ppm. 195Pt NMR: δ = –2186 (J =
806 Hz) ppm. FAB+-MS: m/z = 545 [M]+. C17H17Cl2N3OPt
(545.32): calcd. C 37.44, H 3.14, N 7.71; found C 37.74, H 3.25, N
7.33.
Reactions of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me (1a), Ph
(1b)} with (R*)-Camphor Oxime (2), Acetone Oxime (3a), or Cyclo-
pentanone Oxime (3b)
(i) By the Conventional Method: A solution of 1a (50.0 mg,
0.108 mmol) or 1b (51.0 mg, 0.108 mmol) in dry CH2Cl2 (3 mL)
was added at room temperature to the appropriate oxime 2 or 3
(0.108 mmol), and the mixture was heated with stirring at 40 °C
for 15 or 60 min (for 1a or 1b, respectively).
trans-[PtCl2{NH=C(Ph)ON=C(C4H8)}(NCPh)] (5d): Method (i)
(ii) By Focused Microwave Irradiation: A CH2Cl2 solution of the
reagents in the above amounts was subjected to focused microwave
irradiation at 40 °C for 5 or 20 min (for 1a or 1b, respectively). In
both cases, the corresponding mono-iminoacylated products 4 or 5
were isolated and purified as indicated above.
(24.7 mg, 40% yield), method (ii) (30.8 mg, 50% yield). IR: ν =
˜
1
3448 (NH), 2289 (NϵC), 1638 (C=N) cm–1. H NMR: δ = 1.85–
1.87 (m, 4 H) and 2.55–2.66 (m, 4 H) [=C(C4H8)], 7.47–7.79 (m, 8
H), 8.22 (br. s, 1 H, NH), 8.66 (d, JHH = 7.1 Hz, 2 H) ppm.
13C{1H} NMR: δ = 24.4, 25.0, 29.9, and 31.5 (C4H8), 109.8 (Cipso
,
NϵCPh), 116.2 (NϵC), 128.1, 128.5, 129.1, 129.4, 132.7, 133.3,
and 134.5 (Caromatic), 168.2 [=C(C4H8)], 176.9 [C(O)=N] ppm. 195Pt
NMR: δ = –2181 (J = 876 Hz) ppm. FAB+-MS: m/z = 571 [M]+.
C19H19Cl2N3OPt (571.36): calcd. C 39.94, H 3.35, N 7.35; found
C 39.90, H 3.40, N 7.42.
Reactions of Mono-Iminoacylated PtII Complexes trans-(R*)-
[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4) {R = CH2CO2Me
(4a), Ph (4b)} or trans-[PtCl2{NH=C(R)ON=CR1R2}(NCR)] (5) {R
= CH2CO2Me; R1 = R2 = Me (5a), C4H8 (5b), R = Ph; R1 = R2 =
Me (5c), C4H8 (5d)} with (R*)-Camphor Oxime (2), Acetone Oxime
(3a), or Cyclopentanone Oxime (3b)
trans-(R*)-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}(NCCH2-
CO2Me)] (4a): Method (i) (37.5 mg, 55 % yield), method (ii)
(47.7 mg, 70% yield). [α]2D0 = –7.1 (c = 0.59 in CHCl ). IR: ν =
˜
3
3479 (NH), 2339 (NϵC), 1749 (CO2Me), 1656 (C=N) cm–1. 1H
NMR: δ = 0.76, 0.90, and 1.01 (three s, 3 H each, Me groups),
1.19–1.27 (m, 1 H), 1.41–1.50 (m, 1 H), 1.65–2.09 (m, 4 H), 2.51–
2.60 (m, 1 H), 3.74 and 3.82 (two s, 3 H each, MeO), 4.00 and 4.13
(two s, 2 H each, CH2), 8.01 (br. s, 1 H, NH) ppm. 13C{1H} NMR:
δ = 11.4, 18.9, 20.0 (Me), 26.8, 27.3, 32.7, 35.6, 40.2 (CH2), 43.8
(CH), 49.6 (CMe), 53.3 (CMe2), 53.4 and 54.4 (MeO), 112.6
(NϵC), 162.1 and 166.6 (CO2Me), 168.9 [C(O)=N], 180.5 [(O)-
N=CCH2] ppm. 195Pt NMR: δ = –2228 (J = 812 Hz) ppm. FAB+-
MS: m/z = 631 [M]+. C18H27Cl2N3O5Pt (631.41): calcd. C 34.24, H
4.31, N 6.66; found C 34.12, H 4.37, N 6.55.
(i) By the Conventional Method: A solution of 4a (58.7 mg,
0.093 mmol), 4b (59.5 mg, 0.093 mmol), 5a (50.0 mg, 0.093 mmol),
5b (52.4 mg, 0.093 mmol), 5c (50.7 mg, 0.093 mmol), or 5d
(53.1 mg, 0.093 mmol) in dry CH2Cl2 (3 mL) was added at room
temperature to the appropriate oxime 2 or 3 (0.093 mmol). The
mixture was heated with stirring at 40 °C for 15 or 60 min (for 4a
and 5a–b or 4b and 5c–d, respectively).
trans-(R*)-[PtCl2{NH=C(Ph)ON=C(C9H16)}(NCPh)] (4b):
Method (i) (34.5 mg, 50% yield), method (ii) (46.2 mg, 67% yield).
[α]2D0 = –9.4 (c = 0.65 in CHCl ). IR: ν = 3464 (NH), 2287 (NϵC),
˜
3
1641 (C=N) cm–1. H NMR: δ = 0.81, 0.94, and 1.01 (three s, 3 H
1
each, Me groups), 1.23–1.27 (m, 1 H), 1.47–1.54 (m, 1 H), 1.76–
1.97 (m, 3 H), 2.16–2.22 (m, 1 H), 2.66–2.72 (m, 1 H), 7.48–7.69
(m, 8 H), 8.15 (br. s, 1 H, NH), 8.64 (d, JHH = 7.2 Hz, 2 H) ppm.
13C{1H} NMR: δ = 11.5, 18.9, 20.1 (Me), 27.5, 32.8, 35.9 (CH2),
43.9 (CH), 49.6 (CMe), 54.5 (CMe2), 110.5 (Cq, NϵCPh),
116.8 (NϵC), 128.7, 129.5, 130.1, 130.2, 133.4, 133.9, and 135.2
(Caromatic), 169.0 [C(O)=N], 179.9 [(O)N=CCH2] ppm. 195Pt NMR:
δ = –2176 (J = 886 Hz) ppm. FAB+-MS: m/z = 639 [M]+.
C24H27Cl2N3OPt (639.47): calcd. C 45.08, H 4.26, N 6.57; found
C 45.30, H 4.30, N 6.50.
(ii) By Focused Microwave Irradiation: A CH2Cl2 solution of the
reagents in the above amounts was subjected to focused microwave
irradiation at 40 °C for 5 or 20 min (for 4a and 5a–b or 4b and 5c–
d, respectively). In both cases, the corresponding products 6 were
isolated and purified as indicated above.
trans-(R*)-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}{NH=C-
(CH2CO2Me)ON=CMe2}] (6a): Method (i) (34.1 mg, 52% yield),
method (ii) (39.3 mg, 60% yield). [α]2D0 = –1.4 (c = 0.40 in CHCl3).
1
IR: ν = 3448 (NH), 1749 (CO Me), 1654 (C=N) cm–1. H NMR:
˜
2
δ = 0.79, 0.94, and 1.06 (three s, 3 H each, Me groups), 1.21–1.27
trans-[PtCl2{NH=C(CH2CO2Me)ON=CMe2}(NCCH2CO2Me)] (m, 2 H), 1.46–1.52 (m, 2 H), 1.91–1.95 (m, 1 H), 2.02 and 2.04
(5a): Method (i) (29.6 mg, 51% yield), method (ii) (41.2 mg, 71% (two s, 3 H each, =CMe2), 2.53–2.65 (m, 2 H), 3.79 (s, 6 H, MeO),
3674
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3668–3677

Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes
4.20 (s, 4 H, CH2CO2Me), 8.06 and 8.19 (two s, br, 2 H, NH) ppm.
13C{1H} NMR: δ = 11.5, 19.0, 20.1 (Me), 17.9 and 22.4 (=CMe2),
1.43–1.54 (m, 1 H), 1.64–2.13 (m, 4 H), 2.59–2.65 (m, 1 H), 3.79
(s, 3 H, MeO), 4.17 and 4.21 (two s, 2 H, CH2), 8.06 (br. s, 1 H,
27.5, 32.8, 35.7 (CH2), 39.9 and 40.2 (CH2CO2Me), 44.0 (CH), 49.7 NH) ppm. 13C{1H} NMR: δ = 11.5, 19.0, 20.1 (Me), 27.5, 32.8,
(CMe), 53.3 (CMe2), 54.4 (MeO), 166.2 (CO2Me), 167.1 (=CMe2),
167.7 and 168.1 [C(O)=N], 179.9 [(O)N=CCH2] ppm. 195Pt NMR:
δ = –2058 (J = 886 Hz) ppm. FAB+-MS: m/z = 704 [M]+.
35.7 (CH2), 40.1 (CH2CO2Me), 44.0 (CH), 49.6 (CMe), 53.3
(CMe2), 54.4 (MeO), 167.2 (CO2Me), 168.0 [C(O)=N], 179.8 [(O)-
N=CCH2] ppm. 195Pt NMR: δ = –2060 (J = 846 Hz) ppm. FAB+-
C21H34Cl2N4O6Pt (704.50): calcd. C 35.80, H 4.86, N 7.95; found MS: m/z = 798 [M]+. C28H44Cl2N4O6Pt (798.66): calcd. C 42.11, H
C 35.75, H 4.80, N 7.86.
5.55, N 7.02; found C 42.54, H 5.77, N 6.95.
trans-(R*)-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}{NH=C-
trans-[PtCl2{NH=C(Ph)ON=C(C9H16)}2] (7b): Method (i)
(CH2CO2Me)ON=C(C4H8)}] (6b): Method (i) (33.3 mg, 49 % (43.5 mg, 50% yield), method (ii) (47.8 mg, 55% yield). IR: ν =
˜
1
yield), method (ii) (37.3 mg, 55% yield). [α]2D0 = –36.8 (c = 0.49 in
3463 (NH), 1637 (C=N) cm–1. H NMR: δ = 0.82, 0.95, and 1.11
CHCl ). IR: ν = 3432 (NH), 1749 (CO Me), 1652 (C=N) cm–1. 1H (three s, 3 H each, Me groups), 1.18–1.27 (m, 1 H), 1.49–1.61 (m,
˜
3
2
NMR: δ = 0.81, 0.95, and 1.07 (three s, 3 H each, Me groups),
1.26–2.55 (m, 15 H) [CH2, CH, and =C(C4H8)], 3.80 (s, 6 H, MeO),
4.19 and 4.20 (two s, 2 H each, CH2CO2Me), 8.07 and 8.14 (two s,
br, 2 H, NH) ppm. 13C{1H} NMR: δ = 11.5, 19.0, 20.1 (Me), 25.1,
25.7, 30.4, 32.1 [=C(C4H8)], 27.5, 32.9, 35.7 (CH2), 40.0 and 40.2
1 H), 1.76–1.96 (m, 3 H), 2.14–2.20 (m, 1 H), 2.64–2.71 (m, 1 H),
7.46–7.63 (m, 3 H), 8.24 (br. s, 1 H, NH), 8.64 (d, JHH = 7.2 Hz,
2 H) ppm. 13C{1H} NMR: δ = 10.9, 18.3, 19.4 (Me), 26.8, 32.2,
35.1 (CH2), 43.3 (CH), 48.9 (CMe), 53.6 (CMe2), 127.9, 129.2,
129.4, 132.1 (Caromatic), 167.2 [C(O)=N], 178.4 [(O)N=CCH2] ppm.
(CH2CO2Me), 44.0 (CH), 49.6 (CMe), 53.4 (CMe2), 54.4 (MeO), 195Pt NMR: δ = –1947 (J = 750 Hz) ppm. FAB+-MS: m/z = 806
167.2 (CO2Me), 167.9 [N=C(C4H8)], 168.1 and 177.8 [C(O)=N],
[M]+. C34H44Cl2N4O2Pt (806.72): calcd. C 50.62, H 5.50, N 6.95;
179.9 [(O)N=CCH2] ppm. 195Pt NMR: δ = –2059 (J = 874 Hz) found C 50.94, H 5.25, N 6.56.
ppm. FAB+-MS: m/z = 730 [M]+. C23H36Cl2N4O6Pt (730.54): calcd.
Liberation of the Iminoacylated Oxime 8: The ligand dppe (39.5 mg,
C 37.81, H 4.97, N 7.67; found C 37.90, H 4.80, N 7.77.
0.099 mmol) was added to a solution of trans-[PtCl2{NH=C(R)-
ON=C(C9H16)}2] (7) {R = CH2CO2Me (7a), Ph (7b)} (0.049 mmol)
in CDCl3 (1 mL, 99.8% D), and the mixture was left to stand for
30 min, with the release of a colorless precipitate of [Pt(dppe)2]Cl2.
This solid was removed by filtration, and the filtrate was charac-
terized by NMR and, after being taken to dryness, by IR and FAB-
trans-(R*)-[PtCl2{NH=C(Ph)ON=C(C9H16)}{NH=C(Ph)-
ON=CMe2}] (6c): Method (i) (29.8 mg, 45 % yield), method (ii)
(34.4 mg, 52% yield). [α]2D0 = –8.8 (c = 0.25 in CHCl ). IR: ν =
˜
3
1634 (C=N) cm–1. H NMR: δ = 0.82, 0.96, and 1.12 (three s, 3 H
1
each, Me groups), 1.20–1.28 (m, 2 H), 1.50–1.56 (m, 2 H), 1.86–
1.96 (m, 1 H), 2.07 and 2.08 (two s, 3 H each, =CMe2), 2.57–2.71 MS.
(m, 2 H), 7.46–7.64 (m, 6 H), 8.22 and 8.36 (two s, br, 2 H, NH),
NH=C(CH2CO2Me)ON=C(C9H16) (R*-8a): [α]2D0 = –32.7 (c = 0.40
in CHCl ). IR: ν = 1749 (CO Me), 1611 and 1672 (C=N) cm–1. 1H
8.66 (t, JHH = 8.1 Hz, 4 H) ppm. 13C{1H} NMR: δ = 10.9, 18.3,
19.4 (Me), 17.3 and 21.8 (=CMe2), 26.8, 32.2, 35.2 (CH2), 43.4
(CH), 49.0 (CMe), 53.6 (CMe2), 127.9, 128.1, 129.1, 129.2, 129.4,
132.1, 133.4, and 134.5 (Caromatic), 164.6 (=CMe2), 167.3 and 168.4
[C(O)=N], 179.3 [(O)N=CCH2] ppm. 195Pt NMR: δ = –2177 (J =
876 Hz) ppm. FAB+-MS: m/z = 712 [M]+. C27H34Cl2N4O2Pt
(712.57): calcd. C 45.51, H 4.81, N 7.86; found C 45.72, H 5.01, N
8.21.
˜
3
2
NMR: δ = 0.81, 0.92, and 1.05 (three s, 3 H each, Me groups),
1.21–1.26 (m, 1 H), 1.44–1.47 (m, 1 H), 1.75–1.94 (m, 3 H), 2.10–
2.18 (m, 1 H), 2.59–2.65 (m, 1 H), 3.65 (s, 3 H, MeO), 3.72 and
4.38 (two s, 2 H, CH2), 7.67 (br. s, 1 H, NH) ppm. 13C{1H} NMR:
δ = 10.9, 18.4, 19.4 (Me), 27.0, 32.5, 34.6 (CH2), 43.5 (CH), 48.6
(CMe), 50.2 (MeO), 53.0 (CMe2), 64.3 (CH2CO2Me), 168.8
[C(O)=N], 171.8 (CO2Me), 175.2 [(O)N=CCH2] ppm. FAB+-MS:
m/z = 266 [M]+.
trans-(R*)-[PtCl2{NH=C(Ph)ON=C(C9H16)}{NH=C(Ph)ON=C-
(C4H8)}] (6d): Upon evaporation of the solvent, the initially yellow
solution transformed into a dark oil, with product decomposition,
precluding the possibility of recording reliable characterization
data.
NH=C(Ph)ON=C(C9H16) (R*-8b): [α]2D0 = –15.2 (c = 0.37 in
1
CHCl ). IR: ν = 1650 (C=N) cm–1. H NMR: δ = 0.85, 0.97, and
˜
3
1.14 (three s, 3 H each, Me groups), 1.27–1.34 (m, 1 H), 1.48–1.62
(m, 1 H), 1.77–2.00 (m, 3 H), 2.24–2.30 (m, 1 H), 2.71–2.79 (m, 1
Reaction of trans-[PtCl2(NCR)2] (1) {R = CH2CO2Me (1a), Ph H), 7.30 (d, JHH = 6.0 Hz, 2 H), 7.38–7.48 (m, 2 H), 7.69 (br. s, 1
(1b)} or trans-(R*)-[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4) {R H, NH), 8.01 (d, JHH = 6.0 Hz, 1 H) ppm. 13C{1H} NMR: δ = 11.0,
= CH2CO2Me (4a), Ph (4b)} with (R*)-Camphor Oxime (2)
18.5, 19.5 (Me), 27.1, 32.6, 34.8 (CH2), 43.6 (CH), 48.6 (CMe),
53.0 (CMe2), 127.6, 128.1, 129.1, 131.9 (Caromatic), 162.7 [C(O)=N],
176.0 [(O)N=CCH2] ppm. FAB+-MS: m/z = 270 [M]+.
Reactions of the Mono-Iminoacylated PtII Complexes trans-(R*)-
[PtCl2{NH=C(R)ON=C(C9H16)}(NCR)] (4) {R = CH2CO2Me
(4a), Ph (4b)} with the Diimino Ester NH=C(CH2CO2Me)ON=C-
(C9H16) (R*-8a)
(i) By the Conventional Method: A solution of 1a (50.0 mg,
0.108 mmol), 1b (51.0 mg, 0.108 mmol), 4a (58.7 mg, 0.093 mmol),
or 4b (59.5 mg, 0.093 mmol) in dry CH2Cl2 (3 mL) was added at
room temperature to (R*)-camphor oxime (2) (2 equiv. for 1a–b or
1 equiv. for 4a–b). The mixture was heated with stirring at 40 °C
for 15 or 60 min (for 1a and 4a or 1b and 4b, respectively).
(ii) By Focused Microwave Irradiation: A CH2Cl2 solution of the
reagents in the above amounts was subjected to focused microwave
irradiation at 40 °C for 5 or 20 min (for 1a and 4a or 1b and 4b,
respectively). In both cases, the corresponding symmetric bis-imi-
noacylated products 7 were isolated and purified as indicated
above.
Diimino ester 8a (35.6 mg, 0.134 mmol) was added to a solution of
4a (50.0 mg, 0.079 mmol) or 4b (50.0 mg, 0.078 mmol) in dry
CH2Cl2 at room temperature, and the reaction solution was stirred
for 2 h. The progress of the reaction was monitored by TLC
(CH2Cl2 as eluent). After concentration of the solution in vacuo to
dryness, the crude residue was purified by column chromatography
on silica (CH2Cl2 as eluent) followed by evaporation of the solvent
in vacuo to give the corresponding complexes 9.
trans-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}2] (7a): Method
(i) (41.4 mg, 48% yield), method (ii) (56.0 mg, 65% yield). IR: ν =
˜
3437 (NH), 1755 (CO2Me), 1651 (C=N) cm–1. 1H NMR: δ = 0.79, trans-(R*,R*)-[PtCl2{NH=C(CH2CO2Me)ON=C(C9H16)}{NH=C-
0.94, and 1.06 (three s, 3 H each, Me groups), 1.21–1.29 (m, 1 H), (CH2CO2Me)N=C(CH2CO2Me)ON=C(C9H16)}] (9a): 46.0 mg,
Eur. J. Inorg. Chem. 2008, 3668–3677
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3675

J. Lasri, M. F. C. Guedes da Silva, M. A. J. Charmier, A. J. L. Pombeiro
FULL PAPER
65% yield. [α]2D0 = –20.3 (c = 0.40 in CHCl ). IR: ν = 3443 (NH),
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
˜
3
1749 (CO2Me), 1655 (C=N) cm–1. H NMR: δ = 0.78–1.04 (m, 18
1
H, Me groups), 1.19–2.60 (m, 14 H), 3.77 (s, 9 H, MeO), 4.10–4.23
(m, 6 H, CH2CO2), 8.04 (br. s, 1 H, NH), 8.40 (br. s, 1 H, NH)
ppm. 13C{1H} NMR: δ = 10.8, 11.0, 18.3, 18.4, 19.3, 19.4 (Me),
26.8, 27.2, 32.1, 32.6, 32.9, 34.9 (CH2), 39.4 (CH2CO2Me), 43.3,
43.6 (CH), 48.1, 48.9 (CMe), 51.7, 52.6 (MeO), 53.7 (CMe2), 166.4
[C(O)=N], 167.3 (CO2Me), 169.9 [C(N)=N], 179.1 [(O)N=CCH2]
ppm. 195Pt NMR: δ = –2011 (J = 850 Hz) ppm. ESI-MS: m/z =
896 [M]+. C32H49Cl2N5O8Pt (896.26): calcd. C 42.81, H 5.50, N
7.80; found C 42.94, H 5.27, N 7.96.
Table 2. Relevant crystal data for trans-[PtCl2{NH=C(Ph)-
ON=CMe2}(NCPh)] (5c) and trans-[PtCl2{NH=C(Ph)ON=C-
(C9H16)}2] (7b).
5c
7b
Empirical formula
Formula weight
Crystal system
Space group
T [K]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C17H17Cl2N3OPt C34H44Cl2N4O2Pt
545.32
806.71
orthorhombic
P212121
150(2)
11.7513(4)
14.2981(4)
20.7949(7)
90
triclinic
¯
P1
trans-(R*,R*)-[PtCl2{NH=C(Ph)ON=C(C9H16)}{NH=C(Ph)-
N=C(CH2CO2Me)ON=C(C9H16)}] (9b): 34.6 mg, 49% yield. [α]2D0
150(2)
9.2541(10)
9.8917(11)
11.3966(13)
109.041(6)
91.674(6)
110.700(5)
910.08(18)
2
= –25.4 (c = 0.37 in CHCl ). IR: ν = 3437 (NH), 1725 (CO Me),
˜
3
2
1638 (C=N) cm–1. 1H NMR: δ = 0.83–1.12 (m, 18 H, Me groups),
1.61–2.40 (m, 14 H), 3.78 (s, 3 H, MeO), 4.62 (s, 2 H, CH2CO2),
7.47–7.61 (m, 8 H), 8.25 (br. s, 1 H, NH), 8.65 (d, JHH = 6.0 Hz,
2 H) ppm. 13C{1H} NMR: δ = 10.9, 12.5, 17.9, 18.0, 18.3, 19.5
(Me), 25.6, 26.9, 32.2, 35.2, 35.4 (CH2), 39.5 (CH2CO2), 43.4 (CH),
46.0, 46.8 (CMe), 48.9 (MeO), 53.7 (CMe2), 119.7, 120.9, 128.0,
129.3, 129.5, 132.2, 147.7 (Caromatic), 167.2 [C(O)=N], 168.9
[C(N)=N], 171.7 (CO2Me), 178.5 [(O)N=CCH2] ppm. 195Pt NMR:
δ = –2013 (J = 825 Hz) ppm. ESI-MS: m/z = 905 [M]+.
C38H49Cl2N5O4Pt (905.81): calcd. C 50.39, H 5.45, N 7.73; found
C 50.55, H 5.85, N 7.82.
90
90
γ [°]
V [Å3]
3493.99(19)
4
Z
ρcalcd. [gcm–3]
F(000)
1.990
520
1.534
1616
RInt.
0.0412
0.0163
0.0375
1.051
0.0404
0.0285
0.0515
0.965
R1[a] (I Ն 2σ)
wR2[b] (I Ն 2σ)
GoF
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc2)2]/Σ[w(Fo ) ]}1/2
.
Reactions of the Diimino Ester (R*-8a) with the Acyclic Nitrones
–O+N(Me)=C(H)RЈ (10) {RЈ = 4-MeC6H4 (10a), 2,4,6-Me3C6H4
(10b)}
Acknowledgments
A solution of 8a (30.0 mg, 0.113 mmol) in dry CH2Cl2 (3.0 mL)
was added at room temperature to the appropriate nitrone 10
(1.2 equiv.), and the mixture was heated in a sealed stainless steel
tube (20 mL) at 80 °C for 2 h. The progress of the reaction was
monitored by TLC (CH2Cl2 as eluent). After concentration of the
solution in vacuo to dryness, the crude residue was purified by
column chromatography on silica (CH2Cl2 as eluent) followed by
evaporation of the solvent in vacuo to give the corresponding (E)-
cyanoalkenes 11.
This work has been partially supported by the Fundação para a
Ciência e a Tecnologia (FCT) and its POCI 2010 program (FEDER
funded) (Portugal). J. L. expresses gratitude to FCT for a postdoc
fellowship (grant SFRH/BPD/20927/2004) and to the FCT and the
Instituto Superior Técnico (IST) for a research contract (Ciência
2007 program).
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(NϵC)C(CO2Me)=C(H)(4-MeC6H4) (11a): 11.6 mg, 51% yield.
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X-ray Crystal Structure Determinations for 5c and 7b: Single crys-
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Published Online: July 7, 2008
Eur. J. Inorg. Chem. 2008, 3668–3677
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