Activation of σ(C-H) Bonds in C6H5CH=NCH2CH2SEt Induced by Platinum(II). X-ray Crystal Structure of [Pt{C6H4CH=NCH2CH2SEt}Cl]

Article abstract of DOI:10.1021/om990602v

The study of the reactivity of C₆H₅CH=NCH₂CH₂SEt with platinum(II) salts is reported. These studies have established the relative importance of the factors governing the formation of [Pt{C₆H₄CH=NCH₂CH₂SEt}Cl], in which the ligand acts as a [C,N,S]^- terdentate group.

Full text of DOI:10.1021/om990602v

1384
Organometallics 2000, 19, 1384-1390
Activa tion of σ(C-H) Bon d s in C6H5CHdNCH2CH2SEt
In d u ced by P la tin u m (II). X-r a y Cr ysta l Str u ctu r e of
[P t{C6H4CHdNCH2CH2SEt}Cl]
Xavier Riera,† Amparo Caubet,*,† Concepcio´n Lo´pez,*,† Virtudes Moreno,†
Xavier Solans,‡ and Merce` Font-Bard´ıa‡
Departament de Quı´mica Inorga`nica, Facultat de Quı´mica, Martı´ Franque`s 1-11, Universitat
de Barcelona, 08028-Barcelona, Spain, and Departament de Cristal.lografia, Mineralogia i
Dipo`sits Minerals, Facultat de Geologia, Mart´ı Franque`s s/ n, Universitat de Barcelona,
08028-Barcelona, Spain
Received J uly 30, 1999
The study of the reactivity of C6H5CHdNCH2CH2SEt with platinum(II) salts is reported.
These studies have established the relative importance of the factors governing the formation
of [Pt{C6H4CHdNCH2CH2SEt}Cl], in which the ligand acts as a [C,N,S]- terdentate group.
The study of cyclometalated complexes has attracted
articles focus on platinacycles with terdentate [C,N,S]-
groups. To our knowledge, only three examples of
platinacycles containing [C,N,S]- chelating ligands have
been reported.8-10 Two of them arise from the activation
great interest in the past decade mainly due to their
applications in several areas.1 Among the wide variety
of cyclometalated complexes reported so far, those
containing platinum have attracted additional attention
since some of them have shown outstanding photochemi-
cal, photophysical, and electrochemical properties.2 In
addition, several examples of platinacycles showing
antitumor activity have also been reported.3,4
2
of σ(Csp -H) bonds of benzylthio- or benzosulfinyl-
substituted azobenzenes (Figure 1, 1 and 2 respec-
tively),8,9 and the other involves an N-donor substrate
in which the sulfur atom belongs to a thiophene ring
(Figure 1, 3).10 On this basis we decided to prepare and
characterize the ligand C6H5CHdNCH2CH2SEt (4)
(Figure 1) and to study its reactivity versus plati-
num(II).
A wide variety of cycloplatinated complexes contain-
ing [C,N]- bidentate4-6 and [C,N,N′]- or [N,C,N′]-
terdentate groups7 have been described. However, few
Ligand 4 may produce different sorts of platinum(II)
compounds depending on the mode of coordination of
the ligand. In addition, recent studies on the cycloplati-
nation of 2-methyl-1-phenylbutan-1-one oxime, using
cis-[PtCl2(dmso)2] as metalating agent, report the isola-
tion and structural characterization of the platinum(IV)
derivative [PtCl3(SMe2){C6H4[C(Et)]dNOH}].11 Conse-
quently, the formation of the platinum(IV) derivatives
cannot be ruled out.
† Departament de Qu´ımica Inorga`nica
‡ Departament de Cristal.lografia.
(1) For recent applications of cyclometalated complexes see for
instance: Omae, I. Applications of Organometallic Compounds; J ohn
Wiley: Chichester, U.K., 1998; Chapter 20. Klaus, A. J . Modern
Colorants: Synthesis and Structure; London, U.K., 1995; Vol. 3, pp 1.
Wild, S. B. Coord. Chem. Rev. 1997, 166, 291, and references therein.
Pfeffer, M. Recl. Trav. Chim. Pays-Bas 1990, 109, 567, and references
therein. Ryabov, A. D. Synthesis 1985, 233, and references therein.
Sokolov, V. I. Chirality and Optical Activity in Organometallic
Chemistry; Gordon and Beach: London, United Kingdom, 1991. Buey,
J .; Espinet, P.; Kitzerow, H. S.; Shours, J . Chem. Commun. 1999, 441,
and references therein.
(2) J olliet, P.; Gianini, M.; von Zelewsky, A.; Bernardinelli, G.;
Stoeckli-Evans, H. Inorg. Chem. 1996, 35, 4883. Von Zelewsky, A.;
Suckling, A. D.; Stoeckli-Evans, H. Inorg. Chem. 1996, 35, 4889.
Braterman, P. S.; Song, J . I.; Wimmer, F. M.; Wimmer, S.; Kain, W.;
Klein, A.; Peacock, R. D. Inorg. Chem. 1992, 31, 5084. Maestri, M.;
Deuschel-Cornioley, C.; von Zelewsky, A. Coord. Chem. Rev. 1991, 111,
117, and references therein. Oshawa, Y.; Sprouse, S.; King, K. A.;
DeArmond, M. K.; Hanck, K. W.; Watts, R. J . J . Phys. Chem. 1987,
91, 1047. King, K. A.; Spellane, P. J .; Watts, R. J . J . Am. Chem. Soc.
1985, 107, 1431.
(3) Navarro-Ranninger, C.; Lo´pez-Solera, I.; Gonza´lez, V. M.; Pe´rez,
J . M.; Alvarez-Valde´s, A.; Martin, A.; Raithby, P. R.; Masaguer, J . R.;
Alonso, C. Inorg. Chem. 1996, 35, 5181, and references therein.
(4) Headford, C. E. L.; Mason, R.; Ranatunge-Bandarage, P. R.;
Robinson, B. H.; Simpson, J . J . Chem. Soc., Chem. Commun. 1990,
601. Mdleleni, M. M.; Bridgewater, J . S.; Watts, R. J .; Ford, P. C. Inorg.
Chem. 1995, 34, 2334.
(5) Crespo, M.; Mart´ınez, M.; Sales, J .; Solans, X.; Font-Bard´ıa, M.
Organometallics 1992, 11, 1288. Crespo, M.; Mart´ınez, M.; Sales, J .
Organometallics 1993, 12, 4297.
The ligand was prepared by condensation of equi-
molar amounts of benzaldehyde and (2-ethylthio)ethyl-
amine and characterized by infrared and NMR spec-
troscopy (see Experimental Section). According to NMR
data, only one isomer (E-form) of 4 was present in
solution. When 4 was treated with cis-[PtCl2(dmso)2]
(7) (a) Anderson, C. M.; Crespo, M.; J ennings, M. C.; Lough, A. J .;
Ferguson, G.; Puddephatt, R. J . Organometallics 1991, 10, 2672. (b)
Anderson, C. M.; Crespo, M.; Ferguson, G.; Lough, A. J .; Puddephatt,
R. J . Organometallics 1992, 11, 1177. (c) Crespo, M.; Grande, C.; Klein,
A.; Font-Bard´ıa, M.; Solans, X. J . Organomet. Chem. 1998, 563, 179.
(d) Lo´pez, O.; Crespo, M.; Solans, X.; Font-Bard´ıa, M. Organometallics
1997, 16, 1233. (e) Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca,
A.; Manassero, M. J . Chem. Soc., Dalton Trans. 1995, 777.
(8) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakravorty, A. J .
Organomet. Chem. 1991, 414, 421.
(9) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakravorty, A. Orga-
nometallics 1991, 10, 1135.
(6) (a) Ranatunge-Bandarage, P. R.; Robinson, B. H.; Simpson, J .
Organometallics 1994, 13, 500. (b) Ranatunge-Bandarage, P. R.; Duffy,
N. W.; J ohnston, S. M.; Robinson, B. H.; Simpson, J . Organometallics
1994, 13, 511. (c) Wu, Y. J .; Ding, L.; Wang, H. X.; Liu, Y. H.; Yuan,
H. Z.; Mao, X. A. J . Organomet. Chem. 1997, 535, 49.
(10) Constable, E. C.; Henney, R. P. G.; Tocher, D. A. J . Chem. Soc.,
Dalton Trans. 1992, 2467.
(11) Ryabov, A. D.; Kazankov, G. M.; Payanshkina, I. M.; Grozovsky,
O. V.; Dyachenko, O. G.; Polyakov, V. A.; Kuz’mina, L. G. J . Chem.
Soc., Dalton Trans. 1997, 4385.
10.1021/om990602v CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/08/2000

Activation of σ(C-H) Bonds Induced by Pt(II)
Organometallics, Vol. 19, No. 7, 2000 1385
Sch em e 1a
SEt
a
(i) cis-[PtCl2(dmso)2] in refluxing methanol. (ii) 1 h. (iii)
F igu r e 1. Schematic view of the platinum(II) compounds
containing terdentate [C,N,S]- ligands described so far,
1-3, and of ligand 4.
See text. (iv) In the presence of a stoichiometric amount of
NaCH3COO under reflux (12 h). (v) NaCH3COO in refluxing
methanol (2 h). (vi) PPh3 in CDCl3 at room temperature. (vii)
CH3I in acetone at room temperature (4 h).
{Scheme 1, step (a)} for 1 h in refluxing methanol
complex, cis-[Pt{C6H5CHdNCH2CH2SEt}Cl2] (5) formed.
In 5, the ligand behaves as a neutral [N,S] bidentate
group, and NMR data indicated that the ligand adopts
the Z-form.
et al.8,9 for the cycloplatination of benzylthio- and
benzosulfinyl-substituted azobenzenes (Figure 1, 1 and
2) was also used. When 4 was used as starting material,
a solid formed. Its 1H NMR spectrum revealed the
presence of 5, cis-[Pt{H2NCH2CH2SEt}Cl2] (5′), previ-
ously reported,13 and benzaldehyde, but no evidence for
the formation of any platinacycle was detected. The
formation of 5′ and the aldehyde may be related to
higher proclivity of 4 to hydrolysis.
However, when the reaction time was progressively
increased, the yield of 5 decreased {80% (1 h) and 58%
(3 h)}, and an orange crystalline solid was isolated, by
slow evaporation of the filtrate, in a low yield (ca. 13%)
{Scheme 1, step (b)}. This material was identified (vide
infra) as the cycloplatinated complex [Pt{C6H4CHd
NCH2CH2SEt}Cl] (6), in which the ligand acts as a
[C,N,S]- terdentate group. Compound 6 arises from the
activation of the ortho σ(C-H) bond of the aryl ring,
and its X-ray crystal (see below) revealed an E-form of
the ligand. The ratio of 6 to 5 increased with time, which
suggested that 5 might be an intermediate compound
between the starting material 4 and 6. This finding is
consistent with the results obtained by Ryabov et al.11
on the cyclopalladation of aryl and ferrocenyloximes and
agrees with the mechanism proposed for the cycloplati-
nation of N-donor ligands.12
All the reactions summarized in this section reveal
the advantages of using cis-[PtCl2(dmso)2] or even 5 as
2
starting materials to activate the σ(Csp ,aryl-H) bond in
4. On the other hand, since 4 has a prochiral S-donor
atom, and there is no other source of chiral induction,
6 is expected to consist of an equimolar mixture of the
two enantiomers.
Potentially terdentate chelating ligands [N,C,X]-
{where X ) N, P, or O} or [C,N,N′] may adopt different
bonding modes and hapticities, which is relevant to
catalytic processes. Furthermore, some platinum(II)
metallacycles containing bi- {[C,N]-} or terdentate
{[C,N,N′]- or [N,C,N′]-} ligands undergo oxidative
addition in the presence of alkyl halides or Cl2 in mild
conditions to produce platinum(IV) compounds.14 On
these bases, and in order to explore the bonding abilities
and the proclivity of the platinum(II) to oxidize in 6,
we proceeded to study its reactivity versus PPh3 and
CH3I.
The transformation of 5 to 6 requires the isomeriza-
tion of the ligand {from the Z-form (in 5) to the E-form
(in 6)} and the formation of a σ(Pt-C) bond, in which
the HCl is abstracted. On this basis, we decided to study
if the presence of a base would favor the formation of 6.
When the reaction was performed in the presence of
NaCH3COO {Scheme 1 step (c)}, 6 was isolated in a
higher yield. In addition, when 5 was treated with
NaCH3COO {Scheme 1 step (d)}, a 72% conversion of 5
into 6 was achieved after 2 h, thus confirming that the
presence of the acetate favors the formation of 6.
The addition of a stoichiometric amount of PPh3 to a
solution of 6 in CDCl3 at room temperature produced
(12) Ryabov, A. D. Chem. Rev. 1990, 90, 403.
(13) Riera, X.; Moreno, V.; Font-Bard´ıa, M.; Solans, X. Polyhedron
1998, 18, 65.
To fulfill the study of the reactivity of 4 versus
platinum(II) salts, the method reported by Chakravorty
(14) Rendina, L. M.; Puddephatt, R. J . Chem. Rev. 1997, 17355.

1386 Organometallics, Vol. 19, No. 7, 2000
Riera et al.
[Pt(C6H4CHdNCH2CH2SEt}Cl(PPh3)] (7) {Scheme 1
step (e)}, which results from the cleavage of the Pt-S
bond and the incorporation of a PPh3 in the coordination
sphere of the platinum(II), thus suggesting that in 6 the
Pt-S bond is more labile than the Pt-N bond. This
result is similar to that reported for the related plati-
nacycles with [C,N,N′]- terdentate ligands, such as
[PtMe{(C6RxH(4-x))CHdNCH2CH2NMe2}] {R ) Cl or
F}.7c,d When 7 was treated with an excess of PPh3
{molar ratio 7:PPh3 ) 1:5} in CDCl3, no significant
changes were detected in the NMR spectra in any case,
thus suggesting that the cleavage of the Pt-N bond did
not occur. This finding is consistent with previous
studies on platinacycles containing [C,N]- chelating
groups which have shown that, depending on the nature
of the metallacycle and the basicity of the nitrogen, the
Pt-N bond can be cleaved.15
to the imine proton. In contrast, for complexes contain-
ing the imine in the E-form, the signal due to the proton
of the -CHdN- group is shifted upfield. So, comparison
1
of the H NMR spectra of the platinum(II) compounds
and that of 4 reveals not only the mode of binding of
the ligand but also its conformation (E- or Z-form). The
shift of the signal due to the imine proton in 4 {δ )
8.36 ppm, in dmso-d6} and in 5 {δ ) 9.49 ppm, in dmso-
d6} suggested a Z-form of the imine in 5. This finding
agrees with the results reported for trans-[Pt{(η5-C5H5)-
Fe[(η5-C5H3)C(H)dNR]}Cl2(dmso)] {with R ) CH2CH2-
NMe2, CH2CH2SEt, or CH(COOMe)CH2CH2SMe}.17 In
contrast, the signal of the imine proton in 6 {δ ) 7.84
ppm in CDCl3} appeared at higher fields than in 4 {δ
) 8.29 ppm in CDCl3}, thus suggesting that the imine
is in the E-form. The formation of the platinacycle
requires the appropiate orientation of the σ(C-H) bond
to be activated versus the metal. This is possible only
if the aryl ring and the group bound to the nitrogen are
in trans-arrangement (E-form).
As
a first approach to study proclivity of the
platinum(II) in 6 to oxidize, its reactivity with CH3I was
studied by NMR. Addition of a large excess of CH3I to
an acetone solution of 6 produced [PtMeICl{C6H4CHd
NCH2CH2SEt}] (8), which arises from the oxidative
addition of CH3I to the platinum(II) {Scheme 1, step
(f)}. This result is similar to that obtained in the
reaction of [PtMe{(3-ClC6H3)CHdNCH2CH2NMe2}]
(which contains a [C,N,N′]- terdentate ligand) with
CH3I to produce the platinum(IV) complex [PtMe2I{(3-
ClC6H3)CHdNCH2CH2NMe2}] under mild conditions.7c
All these compounds were characterized by elemental
analyses and infrared and NMR spectroscopy. In all
cases the elemental analyses were consistent with the
proposed formulas (see Experimental Section). The
infrared spectra of 5-8 showed a sharp, intense band
in the range 1500-1650 cm-1, which is ascribed to the
stretching of the >CdN- group. This band appears at
lower frequencies than for 4, indicating the binding of
the nitrogen to the platinum. Similar trends have also
been reported for cyclopalladated16 and cycloplatinated
complexes derived from aldimines and ketimines.6c,17,18
Proton-NMR spectroscopic data for the compounds
under study are summarized in the Experimental
Section. In some cases the spectra were recorded in
different solvents to facilitate the interpretation of the
variations observed in the positions of the signals.
Previous NMR studies of palladium(II) and platinum(II)
compounds containing imines have shown that the
chemical shift of the methinic proton is indicative of the
conformation of the ligand.6c,17-19 For instance, if the
ligand is in the Z-form, the signal of the imine proton
in the complexes is shifted downfield relative to the
corresponding free ligand; this variation is due to the
paramagnetic anisotropy of the metal,20 which is close
The imine proton is strongly coupled with 195Pt in 6
and 7 {3J (Pt-H) ) 134 Hz for 6 and 92 Hz for 7}, and
this coupling is stronger than that observed for the
[PtMe{C6HxR(4-x)CHdNCH2CH2NMe2}] with R ) Cl or
F {3J (Pt-Himine) falls in the range 50-70 Hz}.7c,d In
addition, the formation of the platinacycle produces a
strong high-field shift of the signal due to the proton in
the adjacent position to the metalated carbon, H3. This
trend is in good agreement with the results reported
for platinacycles containing σ(Pt-Csp ,aryl) bonds.7c,d,8,9,11,21
2
Furthermore, the H3 proton is strongly coupled with the
3
platinum. The values of J (Pt-H) are {42 Hz in 6 and
49 Hz in 7} similar to those of [Pt{C6H4-C(R)dNOH}-
Cl(dmso)] with R ) CH3 (51 Hz) or NH2 (52 Hz).11
The signals due to the protons of the “>N-CH2-
CH2-S-” fragment appeared as multiplets in the
platinum compounds due to their diastereotopicity. For
8, the resonance of the methyl group {δ ) 1.27 ppm}
and the value of the coupling constant {2J (Pt-H) ) 98
Hz} are consistent with a trans-arrangement of the CH3
group and the nitrogen {δ(CH3) (in acetone-d6) in the
2
range 1.20-1.50 ppm and J (Pt-H) varying from 59 to
80 Hz}.6c,7c,d Since oxidative additions of methylhalides
to platinum(II) complexes occur with trans-stereochem-
istry, this finding suggests that a rearrangement of
ligands similar to those reported for [PtMe2I{C6H4CHd
NCH2CH2NMe2}I] takes place after the oxidative
addition.7a
Carbon-13 NMR and 2D {1H-13C} heteronuclear
NMR experiments showed a downfield shift of the
resonances due to the imine carbon {ca. 10-18 ppm}
and to the metalated C2 atom upon coordination and
confirmed the mode of binding of the ligand in 5-7.
The 195Pt NMR spectra not only provided convincing
evidence for the coordination sphere and structure of
the platinum(II) derivatives but also explained the
variations produced by the different mode of binding of
4 in the platinum(II) complexes. The spectrum of 5
showed one signal at -2927 ppm, the position of which
is consistent with the values reported for related
complexes containing an [N,S,Cl2] environment around
the platinum(II).22 The differences detected in the
(15) Crespo, M.; Solans, X.; Font-Bard´ıa, M. Organometallics 1995,
14, 355.
(16) Albert, J .; Granell, J .; Sales, J .; Font-Bardia, M.; Solans, X.
Organometallics 1995, 14, 1393. Bosque, R.; Lo´pez, C.; Solans, X.; Font-
Bard´ıa, M. Organometallics 1999, 18, 1267, and references therein.
Benito, M.; Lo´pez, C.; Solans, X.; Font-Bard´ıa, M. Tetrahedron:
Asymm. 1998, 9, 4219.
(17) Caubet, A.; Lo´pez, C.; Bosque, R.; Solans, X.; Font-Bardia, M.
J . Organomet. Chem. 1999, 577, 292.
(18) Wu, Y. J .; Cui, X. L.; Du, C. X.; Wang, W. L.; Guo, R. Y.; Chen,
R. F. J . Chem. Soc., Dalton Trans. 1998, 3727.
(19) Albert, J .; Go´mez, M.; Granell, J .; Sales, J .; Solans, X. Orga-
nometallics 1990, 9, 1405. Albert, J .; Ceder, R. M.; Go´mez, M.; Granell,
J .; Sales, J . Organometallics 1992, 11, 1536.
(20) Miller, R. G.; Stauffer, R. D.; Fahey, D. R.; Pernell, D. R. J .
Am. Chem. Soc. 1970, 92, 1511.
(21) Crespo, O.; Gimeno, M. C.; J ones, P. G.; Laguna, A.; Sarroca,
C. Chem. Commun. 1998, 1481.

Activation of σ(C-H) Bonds Induced by Pt(II)
Organometallics, Vol. 19, No. 7, 2000 1387
Ta ble 1. Selected Bon d Len gth s (in Å) a n d An gles
(in d eg) for th e Tw o Molecu les (A a n d B) of
[P t{C6H4CHdNCH2CH2SEt}Cl] (6)a
(a) Bond Lengths
molecule A
Pt(1)-C(1)
Pt(1)-Cl(1)
Pt(1)-S(1)
Pt(1)-N(1)
molecule B
1.994(8)
2.280(3)
2.327(3)
1.948(6)
Pt(2)-C(12)
2.030(7)
2.296(3)
2.341(3)
1.963(7)
Pt(2)-Cl(2)
Pt(2)-S(2)
Pt(2)-N(2)
(b) Bond Angles
molecule A
molecule B
N(1)-Pt(1)-C(1)
C(1)-Pt(1)-Cl(1)
N(1)-Pt(1)-S(1)
Cl(1)-Pt(1)-S(1)
80.8(3)
96.2(3)
86.4(2)
N(2)-Pt(2)-C(12)
C(12)-Pt(2)-Cl(2)
N(2)-Pt(2)-S(2)
82.1(3)
97.0(2)
85.4(2)
95.56(11)
178.3(2)
96.57(10) Cl(2)-Pt(2)-S(2)
N(1)-Pt(1)-C(1) 176.4(2)
N(2)-Pt(2)-Cl(2)
a
Standard deviation parameters are given in parentheses.
and related mono- and bis(cycloplatinated) complexes
with a [C,N,Cl,P] environment around the platinum(II)
and a similar distribution of the N- and P-donor groups.6
The molecular structure of 6 together with the atom-
labeling scheme is depicted in Figure 2, and a selection
of bond lengths and angles is presented in Table 1. The
structure consists of two different and discrete molecules
of [Pt(C6H4CHdNCH2CH2SEt}Cl] (hereinafter referred
to as A and B), separated by van der Waals contacts.
In these two molecules, the platinum {Pt(1) or Pt(2)} is
bound to a chloride {Cl(1) or Cl(2)}, a sulfur {S(1) or
S(2)}, the imine nitrogen {N(1) or N(2)}, and the ortho
carbon of the phenyl ring {C(1) or C(12)} in a slightly
distorted square-planar environment.23 Each molecule
contains a [5,5,6] tricyclic system derived from the
fusion of the five-membered chelate ring formed by the
coordination of the sulfur and nitrogen to the plati-
num(II), a five-membered platinacycle, and the phenyl
ring. This confirms the conclusions reached from NMR
studies, which suggested that the ligand behaves as a
monoanionic [C,N,S]- terdentate ligand in this case.
F igu r e 2. View of the two independent molecules (A and
B) found in the crystal structure of 6 together with the
atom-numbering scheme.
chemical shift of 195Pt of 5 [-2927 ppm] and 5′, in which
the (2-ethylthio)ethylamine acts as an [N,S] bidentate
group [δ ) -2972 ppm],13 can be interpreted on the
basis of the different basicity of the N-donor group
{Namine in 5′ and Nimine in 5}.
The chemical shift of 195Pt in 6 [δ ) -3716 ppm] was
consistent with the range expected for complexes con-
taining a [C,N,S,Cl] environment around the plati-
num(II).6b The comparison of the positions of the signals
in 5 [δ ) -2927 ppm] and 6 [δ ) -3716 ppm] reveals
that the formation of the metallacycle is reflected in an
upfield shift, which is typical of a strong donor interac-
tion with platinum(II). This finding has also been
reported for platinum(II) compounds containing neutral
N-donor ferrocenylamines and their cycloplatinated
derivatives.6a,b
The Pt-S bond lengths [2.327(3) Å in A and 2.341(3)
Å in B] are clearly greater than the value usually
reported for platinum(II)-S(thioether) derivatives [ca.
2.25 Å].24 This variation can be explained in terms of
the strong trans-influence of the metalated carbon.25
The remaining Pt-ligand bond distances are similar to
those found in five-membered platinacycles containing
a σ(Pt-Csp ,aryl) bond derived from arylimines.26
2
The metallacycles that are formed by the atoms Pt(1),
C(1), C(6), C(7), and N(1) in A and Pt(2), C(12), C(17),
The 195Pt NMR spectra of 7 showed a doublet {1J (P-
Pt) ) 3806 Hz} centered at -4485 ppm. The position
and multiplicity of the signal are consistent with a
[C,N,P,Cl] environment around the platinum(II)6a,b such
as [Pt{(η5-C5H5)Fe[(η5-C5H3)CH2NMe2}Cl(PPh3)] (7′) [δ
) -4173 ppm].6a According to the literature, an upfield
shift in 195Pt NMR is related to a strong donor interac-
tion, and since 7 and 7′ differ only in the nature of their
chelating [C,N]- ligand, the variations observed in their
195Pt NMR spectra can be ascribed to the different donor
abilities of the metalated group.
(22) Pregosin, P. S. Coord. Chem. Rev. 1982, 44, 247.
(23) The least-squares equation of the planes defined by the sets of
atoms Pt(1), Cl(1), N(1), S(1), and C(1) (in A) and Pt(2), Cl(2), N(2),
S(2), and C(12) (in B) are (0.1639)XO + (0.9322)YO + (-0.3226)ZO )
-0.3687 and (-0.1740)XO + (0.9760)YO + (0.1312)ZO ) 6.1251,
respectively. The deviations from the main planes are in A Pt(1),
-0.013; S(1), -0.015; N(1), +0.027; Cl(1), +0.019; and C(1), -0.019 Å,
and in B Pt(2), -0.062; Cl(2), -0.025; S(2), +0.059; N(2), -0.041; and
C(12), +0.069 Å.
(24) Wehman, E.; van Koten, G.; Knaap, C. T.; Ossor, H.; Pfeffer,
M.; Spek, A. L. Inorg. Chem. 1988, 27, 4409. Orpen, A. G.; Brammer,
L.; Allen, F. H.; Kennard, O.; Watson, D. G.; Taylor, R. J . Chem. Soc.,
Dalton Trans. 1989, S1.
1
The 31P chemical shift of 7 [δ ) 19.15 ppm, J (Pt-P)
(25) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335. Elder, R. C.; Curea, R. D. P.; Morrison, R. F. Inorg.
Chem. 1976, 15, 5, 1623.
(26) Allen, T. H.; Kennard, O. Chem. Des. Autom. News 1993, 8,
146.
) 3801 Hz] suggested a trans-arrangement of the PPh3
and the imine nitrogen. Similar values have been
1
reported for 7′ [δ ) 17.21 ppm, J (Pt-P) ) 4291 Hz]6a

1388 Organometallics, Vol. 19, No. 7, 2000
Riera et al.
C(18) and N(2) in B are practically planar27 and contain
the >CdN- functional group (endocyclic). The >CdN-
bond lengths [1.249(10) Å (in A) and 1.304(10) Å (in B)]
lie in the range described in the literature for related
five-membered platinacycles derived from imines.26 The
ligand has an anti-conformation {E-form}, as reflected
in the torsion angles C(6)-C(7)-N(1)-C(8) ) 168.17(7)°
(in A) and C(17), C(18), N(2), and C(19) ) 168.17(7)°
(in B). The phenyl rings are planar, and they form an
angle of 4.7° or 3.8° (A and B, respectively) with the
plane of the corresponding platinacycle.
The five-membered chelate rings formed by the
platinum and the “{dN-CH2-CH2-S-}” moiety ex-
hibit an envelope-like conformation. In A the atoms
Pt(1), S(1), N(1), and C(8) are nearly coplanar,28 and the
C(9) deviates by 0.5855 Å toward the C(10) atom; in B
the C(20) is {-0.8278 Å} out of the plane29 defined by
the remaining atoms, in the opposite direction of C(21).
tance of the presence of NaCH3COO in the cycloplati-
nation process.
On the other hand, it has been recently reported
that platinum(II) complexes of general formula cis-
[PtCl2{[4-RC6H4]CH2CHdNNHC(S)NH2}] {with R ) H
or CHMe}30 (formally analogous to 5) show higher
cytotoxic activity versus cisplatin-resistant tumor cells
than that of other antitumor drugs (i.e., etoposide and
andriamycin) and have a greater capacity to form DNA
interstrand cross-links than cisplatin. Furthermore, the
antitumor properties of cyclometalated platinum(II) and
even platinum(IV) complexes containing bi- and terden-
tate ligands have also been reported.3,4,31 Thus, the
compounds reported here (especially 5 and 6) appear
to be excellent candidates to study their interaction with
DNA as well as their cytotoxic activity. Further work
on this area is currently under way.
Exp er im en ta l Section
To elucidate whether the different nature of the
terdentate group [C,N,S]- could affect the structures of
the platinacycles, a comparison of bond lengths and
angles involving the platinum(II) in 6 (Table 1) and in
1a 9 was carried out. In the two independent molecules
of 6, the Pt-C, Pt-N, and Pt-Cl bond distances are
similar to those of 1a {Pt-C 1.999(8) Å, Pt-N 1.946(8)
Å, and Pt-Cl 2.293(3) Å}, while the Pt-S bond is
slightly shorter [Pt-S in 1a 2.359(3) Å] (if significant,
since the differences hardly exceed 3σ). The main
structural differences are found in N-Pt-C and Cl-
Pt-S bond angles. In 1a , the N-Pt-C bond angle
[79.1(3)°] is smaller than in 6, while the opposite trend
is found for the Cl-Pt-S bond angle [in 1a 92.2(1)° and
in 6 96.57(10)° (in A) and 95.56(11)° (in B)]. The
normalized (S,N) bite, b(S,N) {1.36}, for 1a and 6 does
not differ significantly from that reported for the 2-(eth-
ylthio)ethylamine {b(S,N) ) 1.38(1)}.13,26
The high values obtained for the intermolecular
Pt(1)‚‚‚Pt(2) (5.5803(2) Å) and S(1)‚‚‚S(2) (5.3329(4) Å)
distances preclude any direct interaction between the
two pairs of atoms. The crystal structure also confirms
that 6 consists of a 1:1 mixture of the two enantiomers
{R and S isomers}, which is consistent with the lack of
chiral induction during the cycloplatination process.
Con clu sion s. Although several authors have re-
ported the syntheses of cycloplatinated(II) complexes,
in most of the cases the isolation of these complexes
proceeds in low yield. The results presented here provide
(a) a useful method to prepare platinum(II) compounds
in which 4 can act not only as a neutral [S,N] donor (in
5) and as monoanionic bidentate [C,N]- ligand (in 7)
but also as a [C,N,S]- terdentate group (in 6 and 8), in
good yields and (b) conclusive evidence for the impor-
Gen er a l Com m en ts. The benzaldehyde was obtained from
standard sources and purified by distillation before use. The
2-(ethylthio)ethylamine hydrochloride was obtained from Al-
drich and transformed to the free amine before use. cis-[PtCl2-
(dmso)2] was prepared as described before.32 All the solvents
used in this study were HPLC grade. Elemental analyses (C,
H, N, and S) were carried out at the Serveis Cient´ıfico-
Te`cnics(Universitat de Barcelona). Infrared spectra were
1
obtained with a NICOLET-Impact 400 instrument. H NMR
and the 2D-heteronuclear {1H-13C} NMR experiments were
run at 500 MHz either in a Varian VXR-500 or in a Bruker
Avance 500DMX-500 instrument. The solvents and references
used are specified in the characterization section of each
compound. 13C NMR spectra and 195Pt NMR spectra of 5-7
were recorded with a Bruker-250 DRX instrument. The 195Pt
chemical shifts given are referred to a Na2[PtCl6] solution in
D2O as the external reference. 31P NMR spectrum of 7 was
obtained with a Bruker-250-DRX instrument using CDCl3 as
solvent and P(OMe)3 as reference [δ31P{P(OMe)3} ) 140.17
ppm]. In all cases the chemical shifts (δ) are given in ppm and
the coupling constants (J ) in Hz. The conductivity of the 10-3
M solutions of 5-8 were determined with a CRISON microCM
2200 conductimeter.
P r ep a r a tion of 4. Benzaldehyde (390 mg, 3.68 × 10-3 mol)
was added to a solution formed by the amine H2NCH2CH2-
SEt (284 mg, 3.66 × 10-3 mol) and 15 cm3 of ethanol. The
mixture was refluxed for 3 h. After this period the resulting
solution was concentrated to dryness on a rotary evaporator
to give a pale yellow oil (yield: 0.674 g, 95.4%). Characteriza-
tion data: IR (NaCl disks): ν(>CdN-): 1644 cm-1. H NMR
1
(in CDCl3):33 1.25 [t, 3H, -CH3, 3J (H-H) ) 7], 2.57 [q, 2H,
-S-CH2-CH3, 3J (H-H) ) 7], 2.86 [t, 2H, -CH2-, 3J (H-H) )
3
7], 3.81 [t, 2H, N-CH2-, J (H-H) ) 7], 7.42 [m, 3H, H3, H4,
and H5], 7.72 [d, 2H, H2 and H6, 3J (H-H) ) 8], 8.29 [s, 1H,
-CHdN-]. In dmso-d6:33 1.18 [t, 3H, -CH3, 3J (H-H) ) 7],
2.57 [q, 2H, -S-CH2-CH3, 3J (H-H) ) 7], 2.80 [t, 2H, -CH2-,
3
3J (H-H) ) 7], 3.75 [t, 2H, N-CH2-, J (H-H) ) 7], 7.46 [m,
3H, H3, H4, and H5], 7.76 [d, 2H, H2and H6, 3J (H-H) ) 8],
8.36 [s, 1H, -CHdN-]. 13C NMR (in CDCl3):33 15.46 [-CH3],
25.87 [-S-CH2-CH3], 32.40 [-CH2-], 61.24 [N-CH2-],
135.56 [C1], 129.20 [C2 and C6], 128.46 [C3 and C5], 131.23 [C4]
(27) The least-squares equation of the planes defined by the sets of
atoms Pt(1), N(1), C(1), C(6), and C(7) in A and Pt(2), N(2), C(12), C(17),
and C(18) in B are (0.1927)XO + (0.9068)YO + (-0.3750)ZO ) -0.6516
and (-0.2085)XO + (0.9711)YO + (0.1161)ZO ) 6.1197. The deviations
from the main plane are Pt(1), 0.352; N(1), -0.042; C(1), -0.034; C(6),
0.021; and C(7), 0.023 Å (in A) and Pt(2), 0.032; N(2), -0.031; C(12),
0.041; C(17), -0.033; and C(18), -0.006 Å in B.
(28) The least-squares equation of the plane defined by the atoms
Pt(1), S(1), N(1), and C(8) is (0.0991)XO + (0.9425)YO + (-0.3192)ZO.
The deviations from the main plane are Pt(1), -0.057; S(1), 0.037; N(1),
0.086; and C(8), -0.066 Å.
(30) Quiroga, A. G.; Pe´rez, J . M.; Lo´pez Solera, I.; Montero, E. I.;
Masaguer, J . R.; Alonso, C.; Navarro-Ranninger, C. J . Inorg. Biochem.
1998, 69, 275.
(31) Hambley, T. Coord. Chem. Rev 1997, 166, 1181. Lippert, B.
Coord. Chem. Rev. 1992, 92, 263.
(32) Price, J . H.; Williamson, A. N.; Schramm, R. F.; Wayland, B.
B. Inorg. Chem. 1972, 11, 1280.
(33) Numbering of the atoms corresponds to that shown in Scheme
1.
(29) The least-squares equation of the plane defined by the atoms
Pt(2), S(2), N(2), and C(19) is (-0.1352)XO + (0.9763)YO + (0.1688)ZO
) 6.0908. The deviations from the main plane are Pt(2), 0.0005; S(2),
-0.0003; N(2), -0.0008; and C(19), 0.0006 Å.

Activation of σ(C-H) Bonds Induced by Pt(II)
Organometallics, Vol. 19, No. 7, 2000 1389
and 162.19 [-CHdN-]. In dmso-d6:33 14.93 [-CH3], 26.38
[-S-CH2-CH3], 32.44 [-CH2-], 61.65 [N-CH2-], 135.86 [C1],
128.83 [C2 and C6], 128.10 [C3 and C4], 130.68 [C4] and 162.03
[-CHdN-].
Ta ble 2. Cr ysta llogr a p h ic Da ta for
[P t{C6H4CHdNCH2CH2SEt}Cl] (6)
formula
M
C11H14ClNPtS
422.844
P r ep a r a tion of 5. cis-[PtCl2(dmso)2]32 (219 mg, 5.2 × 10-4
mol) was suspended in 40 cm3 of methanol and refluxed until
complete dissolution. Then 4 (100 mg, 5.2 × 10-4 mol) was
added, and the mixture was refluxed for 1 h. The yellow solid
formed was collected by filtration, washed in small amounts
of methanol, air-dried, and finally dried on a silica desiccator
(yield: 195 mg, 80%). Characterization data: Anal. (%) Calcd
for C11H15NCl2PtS (found): C, 28.77 (28.85); H, 3.29 (3.25);
N, 3.05 (2.9); and S, 6.98 (6.70). IR (KBr pellets): ν(>CdN-):
T (K)
293(2)
cryst dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.1 × 0.1 × 0.1
monoclinic
P21/n
8.270(7)
14.917(6)
19.610(14)
90.0
92.04(7)
90.0
2418(3)
8
2.329
11.967
R (deg)
â (deg)
γ (deg)
1
3
V (Å3)
1625 cm-1. H NMR (in dmso-d6):33 1.40 [t, 3H, -CH3, J (H-
H) ) 7], 2.70-3.00 [m, 2H, -S-CH2-CH3], 3.00-3.20 [m, 2H,
-CH2-], 4.00-4.30 [m, 2H, N-CH2-], 7.00-7.40 [m, 5H, H2,
H3, H4 H5, and H6], 9.49 [s, 1H, -CHdN-, 3J (Pt-H) ) 52].
13C NMR (in dmso-d6):33 12.98 [-CH3], 31.80 [-S-CH2-CH3],
36.26 [-CH2-], 60.64 [N-CH2-], 130.57 [C1], 129.57 [C2 and
C6], 129.44 [C3 and C4], 132.26 [C5], and 170.41 [-CHdN-].
195Pt NMR (in dmso-d6): δ ) -2927.
Z
Fcalcd (g cm-3
)
µ (mm-1
F(000)
)
1592
θ range for data collection (deg)
h, k, l ranges
2.08-29.96
-11 e h e 11; 0 e k e 20;
0 e l e 27
5551
5368 [R(int) ) 0.0337]
5318/0/272
0.904
0.0382
0.0862
0.858 and -0.754
no. of collected reflns
no. of ind reflns
P r ep a r a tion of 6. A stoichiometric amount of 4 (45 mg,
2.33 × 10-4 mol) and NaCH3COO (20 mg, 2.4 × 10-4 mol) were
added to a hot solution formed by cis-[PtCl2(dmso)2] (100 mg,
2.36 × 10-4 mol) and 20 cm3 of methanol. The resulting
suspension was refluxed for 12 h and filtered out to remove
the unreacted 5. The orange filtrate was then concentrated to
ca. 10 cm3 on a rotary evaporator. The slow evaporation of the
solvent at ca. 20 °C produced bright orange crystals, which
were collected by filtration and air-dried (yield: 82 mg, 82%).
Characterization data: Anal. (%) Calcd for C11H14NClPtS
(found): C, 31.25 (31.3); H, 3.34 (3.3); N, 3.31 (3.1); S, 7.58
no. of data/restrains/params
goodness of fit on F2
R1 [Fo > 2σ(Fo2)]a
wR2b
largest diff peak and hole (e Å-3
)
a
b
2
2
2
R1 ) ∑(|Fo| - |Fc|)/∑|Fo|. wR2 ) ∑w(|Fo| - |Fc| )/∑w(|Fo| ).
NMR (in CDCl3):33 14.11 [-CH3, J (Pt-C) ) 18], 29.31 [-S-
3
2
CH2-CH3], 36.96 [-CH2-], 58.06 [N-CH2-, J (Pt-C) ) 44],
141.76 [C1], 150.74 [C2, 1J (C-Pt) ) 85], 128.50 [C3], 125.24
[C4], 129.46 [C5], 136.70 [C6] and 179.65 [-CHdN-, 2J (C-
Pt) ) 73] and four additional doublets centered at 134.49,
131.95, 131.22, and 128.91 due to the carbons of the PPh3
ligand. 31P NMR (in CDCl3): δ ) 19.15 [1J (Pt-P) ) 3801]. 195Pt
(7.7). IR (KBr pellets): ν(>CdN-): 1596 cm-1 1H NMR (in
.
CDCl3):33 1.42 [t, 3H, -CH3, J (H-H) ) 15, J (Pt-H) ) 26],
3.10 [br m, 4H, -S-CH2-CH3 and -CH2-], 3.90 [m, 2H,
N-CH2-], 7.02 [t, 1H, H5, 3J (H-H) ) 8, 4J (Pt-H) ) 26], 7.12
[d, 1H, H3, 3J (H-H) ) 8, 3J (Pt-H) ) 42], 7.29 [t, 1H, H4,
2
4
NMR (in CDCl3): δ ) -4485 [d, 1J (P-Pt) ) 3806]. ΛM (10-3
M
-1
in acetone): 50 Ω
cm2 mol-1
.
4
3
3J (H-H) ) 7, J (Pt-H) ) 46], 7.76 [d, 1H, H6, J (H-H) ) 8,
P r ep a r a tion of 8. This complex was prepared at NMR
scale as follows: 6 (6 mg, 1.4 × 10-6 mol) was dissolved in 2
cm3 of acetone, and CH3I (0.5 cm3, 1.5 × 10-3 mol) was then
added. The mixture was stirred at ca. 20 °C for 4 h. The
solution was then filtered out, and the yellow filtrate was
concentrated to dryness in a vacuum. Characterization data:
IR (KBr pellets): ν(>CdN-): 1607 cm-1. 1H NMR (in acetone-
4J (Pt-H) ) 35], 7.84 [t, 1H, -CHdN-, J (H-H) ) 2, J (Pt-
3
3
H) ) 134]. In acetone-d6:33 1.42 [t, 3H, -CH3, J (H-H) ) 7],
3
4J (Pt-H) ) 21], 3.10 [br m, 2H, -S-CH2-CH3], 3.15 [t, 2H,
-CH2-, 3J (H-H) ) 7, 3J (Pt-H) ) 54], 4.20 [br m, 2H,
N-CH2-], 7.02 [d, 1H, H5, 3J (H-H) ) 7, 4J (Pt-H) ) 30], 7.26
[d, 1H, H3, 3J (H-H) ) 7, 4J (Pt-H) ) 40], 7.28 [t, 1H, H4,
4
3
3J (H-H) ) 6, J (Pt-H) ) 55], 7.65 [d, 1H, H6, J (H-H) ) 7,
d6):33 1.27 [t, 3H, Pt-CH3, J (Pt-H) ) 98], 1.42 [t, 3H, -CH3,
2
4J (Pt-H) ) 43], 8.61 [s, 1H, -CHdN-, J (H-H) ) 2, J (Pt-
H) ) 133]. 13C NMR (in CDCl3):33 13.37 [-CH3, 3J (Pt-C) )
41], 30.59 [-S-CH2-CH3, 2J (Pt-C) ) 49], 37.87 [-CH2-,
3J (Pt-C) ) 45], 57.60 [N-CH2-, 2J (Pt-C) ) 69], 152.24 [C2],
127.75 [C3, 3J (Pt-C) ) 33], 123.97 [C4, 3J (Pt-C) ) 29], 131.84
[C5], 131.71 [C6, 3J (Pt-C) ) 41], and 174.02 [-CHdN-, 2J (Pt-
4
3
3J (H-H) ) 7], 2.98 [m, 2H, -S-CH2-CH3], 3.35 [m, 2H,
-CH2-], 3.50 [br, m, 2H, N-CH2-], 7.18 [d, 1H, H3,3J (H-H)
) 7], 7.66 [t, 1H, H4, J (H-H) ) 7], 7.38 [br, 1H, H5], 7.76 [d,
3
1H, H6, 3J (H-H) ) 7], 8.76 [s, 1H, -CHdN-, 3J (H-Pt) ) 112].
Cr ysta llogr a p h y. A bright orange prismatic crystal of 6
was selected and mounted on an Enraf-Nonius CAD4 four-
circle diffractometer. Unit cell parameters (Table 2) were
calculated from accurate settings of 25 automatically centered
reflections in the range 12° e θ e 21° and refined by the least-
squares method. Intensities were collected with graphite-
monochromated Mo KR radiation using the ω-2θ scan tech-
nique. The numbers of collected reflections were in the range
2.08° e θ e 29.96°, and those assumed as observed [I > 2σ(I)]
are presented in Table 2. Three reflections were measured
every 2 h as orientation and intensity control, and no signifi-
cant intensity decay was observed. Lorentz-polarization cor-
rections but not for absorption were made. The structure was
solved by direct methods using the SHELXS computer pro-
gram34 and refined by full-matrix least-squares method with
the SHELX93 computer program35 using 5318 reflections (very
C) ) 102]. 195Pt NMR (in CDCl3): δ ) -3716. ΛM (10-3M in
-1
CHCl3): 32 Ω
cm2 mol-1
.
P r ep a r a tion of 7. PPh3 (17.6 mg, 6.7 × 10-5 mol) was
added to a solution formed by 28.6 mg (6.7 × 10-5 mol) of 6
and 0.5 cm3 of CDCl3. During the addition of the PPh3, the
color of the mixture changed from orange to bright yellow. The
resulting solution was shaken vigorously for 5 min, and the
solvent was then allowed to evaporate at ca. 20 °C. The pale
yellow residue was treated with 5 cm3 of n-hexane, and the
solid was collected by filtration, washed in n-hexane, and air-
dried (yield: 34 mg, 74%). Characterization data: Anal. (%)
Calcd for C29H29NClPPtS (found): C, 50.84 (50.5); H, 4.27 (4.4);
N, 2.04 (2.05); S, 4.68 (4.2). IR (KBr pellets): ν(>CdN-): 1615
cm-1. 1H NMR (in CDCl3):33 0.92 [t, 3H, -CH3, 3J (H-H) ) 7],
2.30 [br m, 2H, -S-CH2-CH3], 3.30 [br m, 2H, -CH2-], 4.65
3
[br m, 2H, N-CH2-], 6.94 [t, 1H, H5, J (H-H) ) 7], 6.66 [t,
(34) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467.
(35) Sheldrick, G. M. SHELX93, A computer program for determi-
nation of crystal structures; University Go¨ttingen: Germany, 1994.
(36) International Tables of X-ray Crystallography; Kynoch Press:
1974; Vol. IV, pp 99, 100, and 149.
3
4
3
1H, H4, J (H-H) ) 7, J (Pt-H) ) 30], 6.36 [d, 1H, H3, J (H-
H) ) 7, 3J (Pt-H) ) 48], 7.41-7.61 [m, 16H, H6 and PPh3],
9.01 [d, 1H, -CHdN-, 3J (Pt-H) ) 92, 4J (P-H) ) 10]. 13C

1390 Organometallics, Vol. 19, No. 7, 2000
Riera et al.
negative intensities were not assumed). The function mini-
PB94-0922-C02-01 and PB97-0164).
2
2
mized was ∑w||Fo| - |Fc| |, where w ) [σ2(I) + (0.0536P)2]-1
Su p p or tin g In for m a tion Ava ila ble: Tables containing
final atomic coordinates for non-hydrogen atoms and equiva-
lent isotropic temperature displacement parameters, a com-
plete list of bond lengths and angles, anisotropic displacement
parameters, hydrogen coordinates, and hydrogen bond lengths
and angles for 6 have been deposited as a CIF file. This
material is available free of charge via the Internet at
http://pubs.acs.org.
2
2
and P ) (|Fo| + 2|Fc| )/3. f, f ′, and f ′′ were obtained from the
literature.36 All hydrogen atoms were computed and refined
with an overall isotropic temperature factor using a riding
model. Further details concerning the resolution and refine-
ment of the structure are presented in Table 2.
Ack n ow led gm en t. We are grateful to the Ministe-
rio de Educacio´n of Spain for financial support (projects
OM990602V