Platinum(II) and palladium(II) compounds containing chiral thioimines

Article abstract of DOI:10.1002/1099-0682(200108)2001:8<2135::AID-EJIC2135>3.0.CO;2-2

A comparative study of the reactivity of the optically pure thioimine: (S_c)-(-)-C₆H₅-CH=N-CH (CO₂Me)-CH₂-CH₂-SMe (1) versus platinum(II) and palladium(II) salts is reported. The reaction of 1 with cis-[PtCl₂(dmso)₂] leads to the cycloplatinated derivative (S_c,R_s)-(+)-[Pt {C₆H₄-CH=N-CH- (CO₂Me)-CH₂-CH₂-SMe}Cl] (3a). The absolute configuration of 3a has been established unambiguously by X-ray diffraction: orthorhombic, with a = 8.979 (4), b = 9.605(9), c = 18.205(6) A, α = β = γ = 90.0°, space group P2₁2₁2₁. Compound 3a contains a [6.5.6] tricyclic system generated by the fusion of a phenyl ring, a five-membered platinacycle and a six-membered chelate ring formed by the coordination of the nitrogen and sulfur to the platinum. When 1 was treated with Na₂[PdCl₄] in methanol at room temperature a (7.9:1) mixture of the two diastereomers {(S_c,R_s)-5a and (S_c,S_s)-5b} of cis-[Pd{C₆H₅-CH=N-CH (CO₂Me)-CH₂-CH₂-SMe}Cl₂] (5) was formed. However, when the reaction was performed in the presence of sodium acetate, the activation of the σ(C_sp²,_phenyl-H) bond took place giving the cyclopalladated complex: (S_c,R_s)-(+)- [Pd{C₆H₄-CH=N-CH (CO₂Me)-CH₂-CH₂-SMe})Cl] (6a). In 6a, the ligand acts as a monoanionic (C,N,S)^- terdentate group. The study of the reactivity of 3a and 6a with PPh₃ is also reported.

Full text of DOI:10.1002/1099-0682(200108)2001:8<2135::AID-EJIC2135>3.0.CO;2-2

FULL PAPER
Platinum(II) and Palladium(II) Compounds Containing Chiral Thioimines
[a]
[a]
[a]
[a]
´
´
Xavier Riera, Concepcion Lopez,* Amparo Caubet,* Virtudes Moreno,
[b]
[b]
`
Xavier Solans, and Merce Font-Bardia
Keywords: Palladium / Platinum / Metallacycles / Chiral metallacycles / Cyclometallation
A comparative study of the reactivity of the optically pure
thioimine: (SC)-(−)-C6H5−CH=N−CH(CO2Me)−CH2−CH2− Na2[PdCl4] in methanol at room temperature a (7.9:1) mix-
SMe (1) versus platinum(II) and palladium(II) salts is re- ture of the two diastereomers {(SC,RS)-5a and (SC,SS)-5b} of
nitrogen and sulfur to the platinum. When 1 was treated with
ported. The reaction of 1 with cis-[PtCl2(dmso)2] leads to the
cycloplatinated derivative (SC,RS)-(+)-[Pt{C6H4−CH=N−CH-
(CO2Me)−CH2−CH2−SMe}Cl] (3a). The absolute configura-
tion of 3a has been established unambiguously by X-ray dif-
cis-[Pd{C6H5−CH=N−CH(CO2Me)−CH2−CH2−SMe}Cl2] (5)
was formed. However, when the reaction was performed in
the presence of sodium acetate, the activation of the σ(
2
Csp ,phenyl−H) bond took place giving the cyclopalladated
fraction: orthorhombic, with a = 8.979 (4), b = 9.605(9), c = complex:
(SC,RS)-(+)-[Pd{C6H4−CH=N−CH(CO2Me)−CH2−
˚
18.205(6) A, α = β = γ = 90.0°, space group P212121. Com- CH2−SMe}}Cl] (6a). In 6a, the ligand acts as a monoanionic
pound 3a contains a [6.5.6] tricyclic system generated by the
fusion of a phenyl ring, a five-membered platinacycle and a
six-membered chelate ring formed by the coordination of the
(C,N,S)− terdentate group. The study of the reactivity of 3a
and 6a with PPh3 is also reported.
Introduction
are uncommon in the literature.[16Ϫ17] Furthermore, optic-
ally pure platina- or palladacycles containing this sort of
environment are very scarce.[18] With these aims we pre-
pared the Schiff base: (SC)-(Ϫ)-C6H5ϪCHϭNϪCH-
(CO2Me)ϪCH2ϪCH2ϪSMe (1) (Scheme 1) and studied its
reactivity towards platinum and palladium(II) salts.
An important area of organometallic chemistry is that of
cyclopalladated and cycloplatinated compounds.[1] Interest
in such compounds has increased exponentially due to their
applications in several areas.[2Ϫ12]Among the cyclo-
metallated complexes described, those derived from optic-
ally pure N-donor ligands have attracted additional interest,
since they can be used for the resolution of mono- or bi-
dentate ligands[10Ϫ11] as well as in chiral discrimination pro-
cesses.[12] As a part of a project directed towards the design
of new optically pure cyclometallated complexes derived
from Schiff bases of general formula: C6H5ϪCHϭ
NϪCH(R)RЈ or [(η5-C5H5)Fe{(η5-C5H4)ϪCHϭNϪCH-
(R)RЈ}] {R ϭ alkyl, RЈ ϭ phenyl, benzyl, or naphthyl
groups}[11c,12Ϫ14] we attempted to elucidate whether the re-
placement of the RЈ group by a pendant arm containing a
prochiral atom with good donor abilities (i.e. N, O, S, or
P) could determine, not only the diastereoselectivity of the
coordination of the ligand to the palladium(II) or plat-
inum(II), but also the nature of the final product formed in
the cyclometallation process. The incorporation of a sulfur
atom, which according to Pearsons’ concept[15] is a softer
base, in the backbone of the ligand may strengthen the
binding to the palladium or platinum. In addition, the ac-
tivation of the ortho σ(CϪH) bond of the ligand may pro-
duce metallacycles with a (C,N,S)Ϫ terdentate group, which
Scheme 1. R ϭ CO2Me. i) cis-[PtCl2(dmso)2] in refluxing meth-
anol. ii) Na2[PdCl4] in methanol at room temperature. iii)
Na2[PdCl4] and NaAcO in refluxing methanol. iv) NaAcO in re-
fluxing methanol. v) PPh3 in CDCl3 at room temperature
[a]
`
´
Departament de Quimica Inorganica, Facultat de Quımica,
Universitat de Barcelona,
´
`
Martı i Franques 1Ϫ11, 08028-Barcelona, Spain,
Results and Discussion
Fax: (internat.) ϩ 34-93/490-7725
E-mail: conchi.lopez@qi.ub.es
[b]
`
i Diposits
Departament de Cristal·lografia, Mineralogia
Minerals, Facultat de Geologia,
Martı i Franques s/n, 08028-Barcelona, Spain
Ligand 1 was prepared according to the general proced-
ure described for most arylaldimines.[19] The 1H and
´
`
Eur. J. Inorg. Chem. 2001, 2135Ϫ2141
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0808Ϫ2135 $ 17.50ϩ.50/0
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´
X. Riera, C. Lopez, A. Caubet, V. Moreno, X. Solans, M. Font-Bardia
FULL PAPER
13C{1H} NMR spectra of 1 (Exp. Section) suggested that
only one isomer (E-form) was present in solution. When 1
was treated with K2[PtCl4] at room temperature, the reac-
1
tion produced a yellow solid. Its H NMR spectrum was
complex and three signals assigned to the imine proton
were detected at δ ഠ 9.15, 9.26, and 8.30. The 195Pt NMR
spectrum showed three singlets at ca. δ ϭ Ϫ3029, Ϫ3059,
and Ϫ3832 {of relative intensities: 2:0.3:3}. This indicated
that the crude material contained at least three platinum(II)
compounds. The position of signals at δ ϭ Ϫ3029 and
Ϫ3059 was similar to those reported for: [Pt(C6H5ϪCHϭ
NϪCH2ϪCH2ϪSEt)Cl2],[17] [Pt(H2NϪCH2ϪCH2ϪSEt)-
Cl2],[20] and for related compounds containing
‘‘Pt(N,S)Cl2’’ core.[21] This result suggested that two isomers
a
of
cis-[Pt{C6H5ϪCHϭNϪCH(CO2Me)ϪCH2ϪCH2Ϫ
SMe}Cl2] may be present in solution. The chemical shift
of the third signal was similar to that of [Pt{C6H4ϪCHϭ
NϪCH2ϪCH2ϪSMe}Cl] (2),[17] [Pt{(η5-C5H5)Fe[(η5-
C5H3)ϪCH(R)ϪNMe2]}Cl(dmso)],[22] and related com-
pounds.[21,23] Unfortunately, attempts to separate the major
Figure 1. ORTEP diagram of the crystal structure of
(SC,RS)Ϫ(ϩ)Ϫ[Pt{C6H4ϪCHϭNϪCH(CO2Me)ϪCH2ϪCH2Ϫ
˚
SMe}Cl] (3a). Selected bond lengths [in A]: PtϪN, 1.984(11); PtϪS,
2.349(3); PtϪCl, 2.308(4); PtϪC(7), 1.954(14); NϪC(5), 1.954(14).
Selected bond angles [in deg.]: C(7)ϪPtϪCl, 94.0(4); NϪPtϪS,
99.2(3); ClϪPtϪS, 85.84(13); NϪPtϪCl, 174.8(3); PtϪNϪC(5),
components of the mixture by either column chromato- 114.9(11); NϪC(5)ϪC(6) 119.6(16)
graphy or fractional crystallization failed due to the
formation of metallic platinum during these experiments.
More satisfactory results were obtained when the reaction
was carried out using cis-[PtCl2(dmso)2][24] as starting
The structure consists of discrete molecules of
material under refluxing conditions for 12 h. The slow [Pt{C6H4ϪCHϭNϪCH(CO2Me)ϪCH2ϪCH2ϪSMe}] sep-
evaporation of the solvent yielded single crystals suitable arated by van der Waals interactions. The platinum atom is
for X-ray diffraction. Elemental analyses of this material bound to the chloride, the sulfur, the imine nitrogen and
agreed with those expected for [Pt{C6H4ϪCHϭ the ortho-carbon {C(7)} of the phenyl ring in a slightly dis-
NϪCH(CO2Me)ϪCH2ϪCH2ϪSMe}Cl] (3). The two-di- torted square-planar environment. The molecule contains a
mensional heteronuclear {1H-13C} NMR spectrum sug- [6.5.6] tricyclic system derived from the fusion of the six-
2
gested that the activation of the σ(Csp ,phenylϪH) bond had membered chelate ring, formed by the coordination of the
taken place. The position of the signal detected in the 195Pt sulfur and the nitrogen to the platinum(II), a five-mem-
NMR spectrum was similar to that reported for 2[17] and bered platinacycle and the phenyl ring.
for related platinum(II) compounds with a ‘‘Pt(C,N,S,Cl)’’
The metallacycle, which is formed by the atoms: Pt, N,
C(5), C(6), and C(7), is practically planar and contains the
ϾCϭNϪ functional group. The ϾCϭNϪ bond length is in
core.[21]
Recent studies have shown that for optically pure organic the range described for related five-membered platinacycles
imines or amines, such as: R1ϪCHϭNϪCH(Me)ϪR2 derived from imines.[27] The ligand adopts the anti-con-
{R1 ϭ phenyl or ferrocenyl groups and R2ϭ phenyl or formation [(E)-form] and the phenyl ring forms an angle of
naphthyl groups} or C10H7ϪCH(R1)ϪNR2R3 {R1, R2, 6.27° with the plane of the platinacycle.
R3 ϭ alkyl groups} the formation of the metallacycle
The six-membered chelate ring formed by the platinum
2
through the activation of the σ(Csp ,arylϪH) bond does not and the ‘‘NϪCH(CO2Me)ϪCH2ϪCH2ϪSϪ’’ moiety ex-
modify the absolute configuration of the stereogenic centre hibits a chair-conformation in which the atoms C(3) and Pt
of the ligand.[11a,11c,25] Consequently, since 1 contains a ste- deviate from the mean plane Ϫ0.6148 and ϩ0.0928 A, re-
˚
reogenic carbon and a prochiral sulfur atom, 3 may consist spectively.
of a mixture of two diastereomers: {(SC,RS) or (SC,SS) here-
The comparison of the bond lengths and angles involving
inafter referred to as 3a and 3b}. The use of molecular the platinum(II) atom in 3a and in 2,[17] which contains a
models and the SPARTAN 4.0 computer program[26] indic- [6.5.5] tricyclic system, shows that in 3a the PtϪC(7) bond
ated that in 3a, where the ϪCO2Me and the Me group length [1.954(14) A] is clearly shorter than in 2 [2.012(8)
bound to the sulfur are on opposite sides of the coordina- A]. However, this variation does not significantly affect the
tion plane, the steric hindrance is clearly smaller than in the length of the PtϪS bond in a trans position [2.349(3) A in
˚
˚
˚
˚
(SC,SS) isomer (3b). Thus, the formation of 3a is expected 3a and 2.334(10) A in 2]. In contrast, an increase in the size
1
to be strongly preferred to that of 3b. H and 13C NMR of the chelate ring [a five-membered ring in 2 and a six-
spectra indicated that only one of the diastereomers of 3 membered ring in 3a] introduces significant differences in
was present in solution and its absolute configuration was the angles involving the pair of atoms Pt and Cl. For in-
determined by X-ray diffraction. An ORTEP diagram of 3a stance, in 2, the angles: CϪPtϪCl and ClϪPtϪS are bigger
is shown in Figure 1.
than in 3a. This finding, together with the higher value of
2136
Eur. J. Inorg. Chem. 2001, 2135Ϫ2141

Platinum(II) and Palladium(II) Compounds Containing Chiral Thioimines
FULL PAPER
the PtϪCl bond length in 3a compared with 2, suggests that flux in the presence of NaAcO, which yielded a bright yel-
the environment of the chlorine is more crowded in 3a.
low solid. Its elemental analyses agreed with those expected
The absolute configuration of the molecule is determined for
the complex [Pd{C6H4ϪCHϭNϪCH(CO2-
1
by the chirality of the carbon atom (SC) and the relative Me)ϪCH2ϪCH2ϪSMe}Cl] (6). Its H, 13C{1H}, and the
arrangement of the Me bound to the sulfur towards the two dimensional heteronuclear {1H-13C} NMR spectra
ϪCO2Me group. In 3a, these groups face opposite sides of suggested the formation of a palladacycle with a σ(PdϪ
2
the coordination plane of the palladium [the torsion angle
Csp ,phenylϪH) bond and the presence of only one of the
C(1)ϪSϪC(4)ϪC(12) is 166.81°]. As mentioned above, if two diastereomers of 6 in solution. In the view of the results
these substituents were on the same side a strong steric obtained from the SPARTAN 4.0 program[26] and from the
hindrance would arise. This arrangement of groups on the X-ray crystal structure of the platinum(II) analogue (see
stereogenic centres of 3a is formally identical to that above) we assume that the absolute configuration of the
found in [Pd2{(C4H3S)ϪCHϭNϪC(CO2Me)ϪCH2ϪCH2Ϫ isolated material is (SC,RS).
SMe}2Cl2] (4).[18]
The comparison of the results obtained in the reaction of with the stoichiometric amount of NaOAc in refluxing
Compound 6a could also be isolated by treatment of 5
cis-[PtCl2(dmso)2] with
1
or C6H5ϪCHϭNϪCH2Ϫ methanol. The transformation of 5 to 6a requires the iso-
CH2ϪSEt[17] shows that cycloplatination of 1 occurs easily, merization (Z) Ǟ (E) of the ligand and the formation of
2
leading to one of the two diastereomers. These differences the σ(PdϪCsp ,aryl) bond.
may be attributed to the presence of a bulky group[28] in the
proximity of the imine nitrogen.
Potentially terdentate chelating ligands [N,C,X]Ϫ {where
X ϭ N, P, O, or S} may adopt different binding modes and
When 1 was treated with Na2[PdCl4] in methanol at hapticities which is relevant to catalytic processes. As a first
ca. 20 °C cis-[Pd{C6H5ϪCHϭNϪCH(CO2Me)ϪCH2Ϫ approach to explore whether the mode of binding or the
1
CH2ϪSMe}Cl2] (5) was obtained. The H NMR spectrum hapticity of 1 could be modified under mild experimental
of 5 showed two superimposed sets of signals of relative conditions, the reactions of 3a and 6a with PPh3 were
intensities 7.9:1.0, which suggested the presence of two spe- studied in solution. When PPh3 was added to a solution of
cies in solution. 13C{1H} NMR spectroscopic studies also 3a {Pt:PPh3 molar ratio equals to 1:2} in CDCl3 at 20 °C,
1
confirmed these results. Complex 5 could also consist of a pale yellow solution was obtained. Its H and 13C{1H}
different isomers which may differ in a) the conformation NMR spectra suggested the formation of [Pt{C6H4ϪCHϭ
of the ligand (E- or Z-forms) and/or b) the chirality of the NϪCH(CO2Me)ϪCH2ϪCH2ϪSMe}Cl(PPh3)2] (7a). Its
sulfur atom in the complex (RS or SS). Previous NMR spec- 195Pt NMR spectroscopic data is consistent with the values
troscopic studies of palladium(II) and platinum(II) com- reported for platinum(II) compounds having a trans-
pounds containing imines have shown that the chemical ‘‘Pt(C,Cl,P2)’’ core.[31]
shift of the methinic proton indicates the conformation of
This result is in sharp contrast with that reported for 2,
the ligand.[13,17,29,30] The H NMR spectrum of 5 showed for which the addition of large excesses of PPh3 did not
two singlets assigned to the imine protons at lower fields produce the cleavage of the PtϪN bond[17] and suggests a
(δ ϭ 8.41 and 8.38) than in 1, thus suggesting that in the higher lability of the PtϪN bond in complex 3a. The use of
two species the imine had the (Z) form. Consequently, the the SPARTAN 4.0 computer program[26] for the diastere-
two isomers may have a different origin, which might be omer (SC)-[Pt{C6H4ϪCHϭNϪCH(CO2Me)ϪCH2ϪCH2Ϫ
related to the presence of the prochiral sulfur atom in 1. SMe}Cl(PPh3)] (8a) reveals that the environment around
The formation of the six-membered chelate ring by coor- the metal is very crowded and at least one of the phenyl
dination of the N and S atoms to the palladium(II) may rings of the PPh3 ligand is very close to the atoms of the
produce two diastereomers [(SC,RS) and (SC,SS)]. On this ϪCO2Me group. This would increase the steric hindrance
1
1
basis we assumed that the complexity of the H and 13C and reduce the stability of the molecule which may be re-
NMR spectra of 5 could be due to the presence of the two lated to the higher proclivity of 3a {compared with 2} to
diastereomers [(SC,RS), 5a and (SC,SS), 5b]. Attempts to undergo a ring-opening process. The cleavage of the PtϪN
separate them by crystallization or SiO2-column chromato- bond would permit the free rotation around the NϪC*
graphy failed due to the low solubility of 5.
bond, leading to a larger separation between the aryl rings
The use of molecular models and the SPARTAN 4.0 and the ‘‘CO2Me’’ fragment.
computer program[26] also suggested that the less hindered
When the reaction was performed in identical experi-
isomer corresponds to the (SC,RS) diastereomer (5a). Thus, mental conditions, but using 6a and PPh3, [Pd-
we assume that the absolute configuration of the main com- {C6H4ϪCHϭNϪCH(CO2Me)ϪCH2ϪCH2ϪSMe}Cl-
ponent is (SC,RS).
(PPh3)2] (9a) was formed in solution and its 31P NMR spec-
In order to examine whether the activation of the trum suggested a trans- arrangement of the PPh3 ligands.
2
σ(Csp ,phenylϪH) bond of 1 could be promoted by palla-
Since the formation of 7a and 9a involves the cleavage of
dium(II) salts, more drastic reaction conditions were used the MϪS bond (in 3a and 6a, respectively), the absolute
(i.e. refluxing methanol and reaction periods of up to 7 configuration of these derivatives is expected to be SC.
days). However, no evidence of the formation of any pallad-
To sum up, the results reported in this work show the
acycle was detected by NMR spectroscopy. Better results importance of the presence of a bulky and electron-with-
were obtained when the reaction was carried out under re- drawing group on the stereogenic carbon atom of 1 in the
Eur. J. Inorg. Chem. 2001, 2135Ϫ2141
2137

´
X. Riera, C. Lopez, A. Caubet, V. Moreno, X. Solans, M. Font-Bardia
FULL PAPER
chemical shifts (δ) are given in ppm and the coupling constants (J)
in Hz. Ϫ The optical rotations were determined in CH2Cl2 using
a PerkinϪElmer 241MC-polarimeter. Ϫ FABϩ mass spectra were
obtained with a VG-Quatro Fisions instrument using 3-nitrobenzyl
alcohol as matrix.
diastereoselectivity of the reactions under study. The prefer-
ential formation of 5a versus 5b (d.e. ϭ 77.5%) may be at-
tributed to steric effects. In 5a, where the ϪCO2Me group
and the Me bound to the sulfur are pointing towards op-
posite sides of the coordination plane of the metal, the
steric hindrance is clearly smaller than in 5b. A similar argu- Preparation of (SC)-(؊)-C6H5؊CH؍N؊CH(CO2Me)؊CH2؊
CH2؊SMe (1): Benzaldehyde (304 mg, 2.86·10Ϫ3 mol) was added
ment can be used to explain the formation of the metalla-
cycles 3a and 6a. These findings suggest that the absolute
configuration of the stereogenic carbon in 1 induces a high
degree of diastereoselectivity in the coordination of the pro-
to a solution of H2NϪCH(CO2Me)ϪCH2ϪCH2ϪSMe (467 mg,
2.86·10Ϫ3 mol) in 15 mL of methanol. The mixture was refluxed
for 3 h. Then, the solution was concentrated to dryness giving a
whitish oil. (Yield 601 mg, 82%). Ϫ IR: ν(ϪCO): 1736 and ν(ϾCϭ
chiral sulfur.
NϪ): 1644 cmϪ1. Ϫ 1H NMR (in CDCl3):[33] δ ϭ 2.09 (s, 3 H,
Several authors have postulated that the presence of an
ϪSMe), 2.18Ϫ2.35 (m, 2 H, ϪCH2Ϫ), 2.46Ϫ2.60 (m, 2 H,
electron-withdrawing group favours the metallation of ali-
ϪSCH2Ϫ), 3.75 (s, 3 H, ϪOMe), 4.22 (m, 1 H, ϾCHϪ), 7.43 (m,
phatic carbon atoms.[1,18,32] On this basis, for 1, which con-
1 H, H4), 7.45 (m, 2 H, H3 and H5), 7.80 (d, 2 H, H2 and H6), 8.33
tains an electron-withdrawing group[28] at the stereogenic
(s, 1 H, ϪCHϭNϪ). Ϫ 13C{1H} NMR (in CDCl3):[33] δ ϭ 16.2
2
3
carbon, the activation of a (Csp ,phenylϪH) or a (C*sp ϪH) (ϪSMe), 30.2 (ϪSCH2Ϫ), 31.9 (ϪCH2Ϫ), 52.3 (ϪOMe), 71.2
(ϾCHϪ), 135.4 (C1), 128.5 (C2 and C6), 128.5 (C3 and C5), 131.2
bond, in principal, could be expected. However, for 1, the
metallation of the phenyl ring is strongly preferred and no
evidence of the presence of the metallacycles with a
(C4), 164.3 (ϪCHϭNϪ), 172.1 (ϾCO2). [α]24
100 mL) ϭ Ϫ24.12.
(c ϭ 0.05 g/
°C
3
σ(MϪC*sp ) bond was detected by NMR spectroscopy.
Preparation of (SC,RS)-(؉)-[Pt{C6H4؊CH؍N؊CH(CO2Me)؊
CH2؊CH2؊SMe}Cl] (3a): To a hot solution formed by cis-
These findings are in sharp contrast with those obtained in
the cyclopalladation of [(C4H3S)ϪCHϭNϪCH(CO2Me)Ϫ [PtCl2(dmso)2] (100 mg, 2.36·10Ϫ4 mol) and 20 mL of methanol, 1
(59 mg, 2.35·10Ϫ4 mol) was added. The suspension was refluxed for
12 h and filtered out. Then, the filtrate was concentrated to ca.
5 mL on a rotary evaporator. The slow evaporation of the solvent
at ca. 20 °C produced golden crystals, which were collected and
air-dried. (Yield 92 mg, 81.0%). Ϫ C13H16ClNO2SPt: calcd. (found)
C 32.5 (32.5), H 3.3 (3.3), N 2.9 (3.0), S 6.7 (6.7). Ϫ IR: ν(ϪCO):
CH2ϪCH2ϪSMe}][18] which produced: [Pd2{(C4H3S)Ϫ
CHϭNϪC(CO2Me)ϪCH2ϪCH2ϪSMe}2Cl2] (4) through
[18]
3
activation of the σ(C*sp ϪH) bond.
results presented here reveal the importance of the group
bound to the imine carbon in determining the type
Consequently, the
2
of the σ(MϪC) bond to be formed [σ(MϪCsp ,aryl) or
1739 cmϪ1 and ν(ϾCϭNϪ): 1594 cmϪ1
. Ϫ
1H NMR (in
3
σ(MϪC*sp )] in the cyclometallation process. Besides that,
CDCl3):[33] δ ϭ 2.55 [s, 3 H, ϪSMe, 3J(PtϪH) ϭ 20], 2.62 and 2.79
(m, 2 H, ϪSCH2Ϫ), 2.30 and 2.60 (m, 2 H, ϪCH2Ϫ), 3.74 (s, 3 H,
compounds 3a and 6a have an additional interest since they
ϪOMe), 4.52 [m, 2 H, ϾCHϪ, 3J(PtϪH) ϭ 52], 7.31 (d, 1 H, H3),
may be potentially useful in a wide variety of processes, i.e.
as chiral recognition compounds or discriminators, or as 7.09 (t, 1 H, H4), 7.28 (t, 1 H, H5), 7.95 [d, 1 H, H6, J(PtϪH) ϭ
4
3
39], 8.27 [s, 1 H, ϪCHϭNϪ, J(PtϪH) ϭ 133]. Ϫ 13C{1H} NMR
precursors for the asymmetrical synthesis of novel organic
or organometallic derivatives.
(in CDCl3):[33] δ ϭ 21.2 (Me), 27.7 (ϪSCH2), 31.4 (ϪCH2Ϫ), 53.3
(ϪOMe), 66.3 (ϾCHϪ), 143.0 (C1), 152.1 (C2), 128.2 (C3), 124.3
(C4), 133.4 (C5), 132.2 (C6), 181.9 (ϪCHϭNϪ), 170.0 (ϪCO2). Ϫ
195Pt NMR (in CDCl3): Ϫ3832. [α]24 °C (c ϭ 0.1 g/100 mL) ϭ
ϩ73.9. FABϩ(selected data): 481 [M ϩ H]ϩ, 445 [M Ϫ Cl]ϩ.
Experimental Section
Preparation
of
cis-[Pd{C6H5؊CH؍N؊CH(CO2Me)؊CH2؊
CH2؊SMe}Cl2] (5): Ligand 1 (157 mg, 6.25·10Ϫ4 mol) was dis-
solved in 15 mL of methanol. A solution formed by Na2[PdCl4]
(184 mg, 6.25·10Ϫ4 mol) and 10 mL of methanol was then added.
The mixture was stirred at ca. 20 ° C for 3 h. The solid formed
was collected, washed with methanol (3·2 mL) and air-dried. (Yield
143 mg, 53.3%). Ϫ C13H17Cl2NO2SPd: calcd. (found) C 36.5 (36.3),
Materials and Synthesis: Benzaldehyde was obtained from standard
sources and purified by vacuum distillation before use. (SC)-Me-
thionine methyl ester hydrochloride was obtained from Janssen
Chimica and transformed into the free amine before use. cis-
[PtCl2(dmso)2] was prepared as previously described.[24] All the
solvents used in this study were HPLC grade.
H 4.0 (4.0), N 3.3 (3.1), S 7.5 (7.45). Ϫ IR: ν(ϪCO): 1740 cmϪ1
1
Elemental analyses (C, H, N, and S) were carried out at the Serveis and ν(ϾCϭNϪ) ϭ 1624 cmϪ1. Ϫ H NMR spectroscopic data (in
´
`
Cientıfico Tecnics de la Universitat de Barcelona and at the Serveis
CDCl3):[33] Major isomer, 5a {(SC,RS)}: δ ϭ 2.63 (s, 3 H, ϪSMe),
2.50 and 2.55 (m, 2 H, ϪSCH2Ϫ), 3.40 and 3.90 (m, 2 H, ϪCH2Ϫ),
3.88 (s, 3 H, ϪOMe), 4.22 (m, 1 H, ϾCHϪ), 7.69Ϫ7.82 (m, 3 H,
´
de Recursos Cientıfics (Universitat Rovira i Virgili, Tarragona). Ϫ
Infrared spectra were obtained with a Nicolet Impact 400 instru-
ment using NaCl discs for 1 and KBr pellets for the solid samples. H3, H4 and H5), 8.38 (s, 1 H, ϪCHϭNϪ) and 9.23 (d, 2 H, H2
Ϫ H and the two dimensional {1H-13C} heteronuclear NMR ex-
and H6). Minor isomer, 5b {(SC,SS)}: δ ϭ 2.52 (s, 3 H, SMe), 2.60
1
periments were run using a Varian VXR-500 or a Bruker Avance and 2.45 (m, 2 H, ϪSCH2Ϫ), 3.40 and 3.90 (m, 2 H, ϪCH2Ϫ),
500DMX instrument. The solvents and references used are speci-
fied in the characterization section of each compound. 13C{1H}-
and 195Pt NMR spectra were recorded with a Bruker-250DXR in-
3.81 (s, 3 H, ϪOMe), 4.02 (m, 1 H, ϾCHϪ), 7.69 (m, 3 H, H3, H4
and H5), 8.41 (s, 1 H, ϪCHϭNϪ), 9.05 (d, 2 H, H2 and H6). Ϫ
1H NMR spectroscopic data (in [D6]DMSO):[33] Major isomer, 5a
strument. The 195Pt chemical shifts are referred to a Na2[PtCl6] {(SC,RS)}: δ ϭ 2.88 (s, 3 H, ϪSMe), 2.96Ϫ3.11 (m, 2 H,ϪSCH2Ϫ),
solution in D2O as external reference. 31P{1H} NMR spectra were
obtained with a Bruker-250DXR instrument using CDCl3 as solv-
3.40Ϫ3.90 (m, 2 H, ϪCH2Ϫ), 4.07 (s, 3 H, ϪOMe), 4.96 (m, 1 H,
ϾCHϪ), 7.69Ϫ7.82 (m, 3 H, H3, H4, and H5), 8.38 (s, 1 H, ϪCHϭ
ent and P(OMe)3 as reference {δ31P[P(OMe)3] ϭ 140.17}. The NϪ), 9.23 (d, 2 H, H2 and H6). Ϫ 13C{1H} NMR spectroscopic
2138
Eur. J. Inorg. Chem. 2001, 2135Ϫ2141

Platinum(II) and Palladium(II) Compounds Containing Chiral Thioimines
FULL PAPER
data (in [D6]DMSO):[33] Major isomer, 5a {(SC,RS)}: δ ϭ 21.1 (m, 1 H, ϾCHϪ), 8.06 (s, 1 H, ϪCHϭNϪ), 7.33 (d, 1 H, H3), 7.09
(ϪSMe), 29.3 (ϪSCH2Ϫ), 30.7 (ϪCH2Ϫ), 53.2 (OMe), 70.5
(t, 1 H, H4), 7.21 (t, 1 H, H5), 7.94 (t, 1 H, H6). Ϫ 13C{1H} NMR
19.9 (ϪSMe), 27.6
(ϾCHϪ), 132.0 (C1), 132.3 (C2 and C4), 129.2 (C3 and C5), 134.7 spectroscopic data (in CDCl3):[33]
δ ϭ
(C4), 168.4 (ϪCO2), 178.3 (ϪCHϭNϪ).
(ϪSCH2Ϫ), 30.4 (ϪCH2Ϫ), 53.1 (ϪOMe), 66.6 (ϾCHϪ), 179.8
(ϪCHϭNϪ), 169.2 (ϪCO2), 144.0 (C1), 160.1 (C2), 128.2 (C3),
124.9 (C4), 131.6 (C5), 134.7 (C6). Ϫ [α]24 °C (c ϭ 0.05 g/100 mL) ϭ
Ϫ51.6. Ϫ FABϩ(selected data): 391 [M ϩ H]ϩ, 357 [M Ϫ Cl]ϩ.
Preparation of (SC,RS)-(؉)-[Pd{C6H4؊CH؍N؊CH(CO2Me)؊
CH2؊CH2؊SMe}Cl] (6a): This complex was isolated by two dif-
ferent procedures using either compounds 1 or 5 [methods (a) and
(b), respectively] as starting materials.
Preparation of (SC)-[Pt{C6H4؊CH؍N؊CH(CO2Me)؊CH2؊
CH2؊SMe}Cl(PPh3)2] (7a): This complex was prepared on an
NMR spectroscopic scale. A 10 mg (2.05·10Ϫ5 mol) amount of 3a
was dissolved in 0.7 mL of CDCl3, then PPh3 (11 mg, 4.16·10Ϫ5
mol) was added. The mixture was stirred vigorously for 5 min. at
ca. 20 ° C and the pale solution was characterized by NMR spec-
Method A: A 100 mg amount (3.98·10Ϫ4 mol) of 1 was dissolved
in 10 mL of methanol. Na2[PdCl4] (117 mg, 3.98·10Ϫ4 mol) and
NaOAc (33 mg, 4.0·10Ϫ4 mol) were then added and the mixture
was refluxed for 2 h. The solid formed was removed by filtration
and discarded. Slow evaporation of the filtrate produced the precip-
itation of a yellow solid, which was filtered out and air-dried. (Yield
87 mg, 56).
1
troscopies. Ϫ H NMR spectroscopic data (in CDCl3):[33] δ ϭ 2.59
(s, 3 H, ϪSMe), 2.54 and 2.72 (m, 2 H, ϪSCH2Ϫ), 2.61 and 2.75
(m, 2 H, ϪCH2Ϫ), 3.75 (s, 3 H, ϪOMe), 5.72 [br., 1 H, ϾCH-],
6.45 [d, 1 H, H3], 6.90 [t, 1 H, H4], 6.58 (t, 1 H, H5), 8.68 (s, 1 H,
ϪCHϭNϪ) and 7.10Ϫ7.80 (m, 31 H, H6 and protons of PPh3).
Method B: Compound 5 (98 mg, 2.28·10Ϫ4 mol) was suspended in
methanol (15 mL), and a solution of NaOAc (19 mg, 2.31·10Ϫ4
mol) and 10 mL of methanol was added. The mixture was refluxed
for 2 h and filtered out. The filtrate was allowed to evaporate at ca.
20 °C and the solid formed was collected by filtration and air-
dried. (Yield 58 mg, 68%). C13H16ClNO2PdS: calcd. (found) C 39.8
(39.8), H 4.1 (4.2), N 3.6 (3.6), S 8.2 (8.3). Ϫ IR: ν(ϪCO): 1736
cmϪ1 and ν(ϾCϭNϪ): 1601 cmϪ1. Ϫ 1H NMR spectroscopic data
(in CDCl3):[33] δ ϭ 2.51 (s, 3 H, ϪSMe), 2.22Ϫ2.70 (m, 2 H,
ϪSCH2Ϫ), 2.58Ϫ2.72 (m, 2 H, CH2Ϫ), 3.80 (s, 3 H, ϪOMe), 4.42
Ϫ
13C{1H} NMR spectroscopic data (in CDCl3):[33Ϫ35] δ ϭ 16.6
(ϪSMe), 29.9 (ϪSCH2Ϫ), 30.0 (ϪCH2Ϫ), 57.7 (ϪOMe), 68.3
(ϾCHϪ), 171.4 (ϪCO2), 168.6 (ϪCHϭNϪ), 131.8 (C3), 123.4
(C4), 132.6 (C5), 138.1 (C6). Ϫ 195Pt NMR (in CDCl3): δ ϭ Ϫ4439,
1J(195Pt-31P)ϭ 3637. Ϫ 31P NMR spectroscopic data (in CDCl3):
1
δ ϭ 13.69, J(31P-195Pt)ϭ 3635.
Preparation
of
(SC)-[Pd{C6H4؊CH؍N؊CH(CO2Me)؊
CH2؊CH2؊SMe}Cl(PPh3)2] (9a): This complex was prepared ac-
cording to the procedure described for 7a but using 6a (40 mg,
5.1·10Ϫ5 mol) and PPh3 (54 mg, 2.06·10Ϫ5 mol). Ϫ H NMR spec-
1
troscopic data (in CDCl3):[33] δ ϭ 2.09 (s, 3 H, ϪSMe), 2.38 and
2.48 (m, 2 H, ϪSCH2Ϫ), 2.60 and 2.65 (m, 2 H, ϪCH2Ϫ), 3.74 (s,
3 H, ϪOMe), 5.46 (m, 1 H, ϾCHϪ), 6.39 (d, 1 H, H3), 6.90 (t, 1
H, H4), 6.56 (t, 1 H, H5), 8.42 (s, 1 H, ϪCHϭNϪ), 7.30Ϫ8.60 (m,
31 H, H6 and protons of PPh3). Ϫ 13C{1H} NMR spectroscopic
data (in CDCl3):[33Ϫ34] δ ϭ 15.3 (ϪSMe), 30.5 (ϪSCH2Ϫ), 31.8
(ϪCH2Ϫ), 52.4 (ϪOMe), 65.0 (ϾCHϪ), 171.7 (ϪCO2), 177.3
(ϪCHϭNϪ), 158.8 (C1), 147.90 (C2), 130.8 (C3), 124.0 (C4), 128.9
(C5), 138.1 (C6). Ϫ 31P NMR spectroscopic data (in CDCl3): δ ϭ
28.86.
Table 1. Crystal data and details of the refinement of the crystal
structure of 3a
Empirical formula
Mr
C13H16ClNO2PtS
480.88
Crystal size [mm ϫ mm ϫ mm]
0.1 ϫ 0.1 ϫ 0.2
8.797(4)
9.605(9)
18.205(6)
90.0
1538.2(17)
Orthorhombic
P212121
˚
a [A]
˚
b [A]
˚
c [A]
Crystallography: A prismatic crystal of 3a was selected and
mounted on an Enraf CAD4 four-circle diffractometer. Unit cell
parameters were determined from automatic centering of 25
reflections in the range 12° Ͻ Θ Ͻ 21° and refined by least-squares
method. Intensities were collected with graphite monochromated
Mo-Kα radiation, using ω/2Θ scan technique. Three reflections
were measured every 2 h as orientation and intensity control, and
no significant intensity decay was observed. Lorentz-polarization
and absorption corrections were made. The structure was solved
by Direct methods using the SHELXS97 computer program[36] and
refined by full-matrix least-squares method with the SHELXL97
computer program[37] using 2526 reflections (very negative intensit-
ies were not assumed). The function minimized was Σ||Fo|2 Ϫ |Fc|2|2,
where w ϭ [σ2(I) ϩ (0.0795 P)2]Ϫ1 and P ϭ (|Fo|2 ϩ 2 |Fc|2)/3. f, fЈ,
and f’’ were obtained from the literature.[38] The chirality of the
structure was defined from the Flack coefficient.[39] All the hydro-
gen atoms were computed and refined with an overall isotropic
temperature factor using a riding model. The final R(on F) factor
was 0.048 and wR(on F) ϭ 0.112. Further details concerning the
resolution and refinement of the crystal structure of 3a are pre-
sented in Table 1. Crystallographic data (excluding structure fac-
tors) for the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplement-
ary publication no. CCDC-152831. Copies of the data can be ob-
α, β, γ [deg.]
3
˚
V [A ]
Crystal System
Space group
Ζ
4
˚
λ [A]
0.71069
T [K]
293(2)
2.081
9.891
Dcalcd. [Mg·m3]
Absorption coefficient [mmϪ1
]
F(000)
912
Θ range for data collection [deg.]
Refinement method
from 2.57 to 29.94
Full-matrix
least-squares on F2
2571
Number of collected
reflections
Number of independent
reflections
Number of data
2552 [R(int) ϭ 0.0107]
2526
Number of parameters
Goodness of fit on F2
Final R indices [I Ն 2σ(I)]
R indices (all data)
173
0.994
R1 ϭ 0.0484, wR2 ϭ 0.1124
R1 ϭ 0.0709, wR2 ϭ 0.1205
0.00(2)
Absolute structure parameter
Largest difference peak and hole
0.835 and Ϫ0.894
Ϫ3
˚
[eA
]
Eur. J. Inorg. Chem. 2001, 2135Ϫ2141
2139

´
X. Riera, C. Lopez, A. Caubet, V. Moreno, X. Solans, M. Font-Bardia
FULL PAPER
[13c]
´
R. Bosque, M. Font-Bardıa, C.
Trans. 1994, 735Ϫ747. Ϫ
Lopez, J. Sales, J. Silver, X. Solans, J. Chem. Soc., Dalton Trans.
tained free of charge on applications to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat) ϩ44Ϫ1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
´
[13d]
´
C. Lopez, R. Bosque, X. Solans, M.
1994, 747Ϫ752. Ϫ
[13e]
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Font-Bardıa, J. Organomet. Chem. 1997, 539, 99Ϫ107. Ϫ
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C. Lopez, R. Bosque, X. Solans, M. Font-Bardıa, Tetrahedron:
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