Oxidative addition of functional disulfides to platinum(II): Formation of chelating and bridging thiolate-carboxylate complexes of platinum(IV)

Article abstract of DOI:10.1016/j.inoche.2010.10.024

An unusual type of oxidative addition of disulfides containing a carboxylic acid group to platinum(II) is established, giving the first thiolate-carboxylate complexes of platinum(IV). The disulfide R ₂S₂ with R = CH₂CH₂CO₂H reacts with [PtMe₂(2,2′-bipyridine)] to give RSH and the chelating thiolate-carboxylate complex [PtMe₂(κ²-S, O-SCH₂CH₂CO₂)(bipy)]. However, the disulfide R₂S₂ with R = C₆H₃-4-NO ₂-3-CO₂H reacts to give first the product of trans oxidative addition [PtMe₂(SR)₂(bipy)], which slowly reacts further to give RSH and the bridging thiolate-carboxylate complex [Pt ₂Me₄(κ²-S,O-SC₆H ₃-4-NO₂-3-CO₂)₂(bipy)₂].

Full text of DOI:10.1016/j.inoche.2010.10.024

Inorganic Chemistry Communications 14 (2011) 210–212
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Oxidative addition of functional disulfides to platinum(II): Formation of chelating
and bridging thiolate–carboxylate complexes of platinum(IV)
⁎
Matthew S. McCready, Richard J. Puddephatt
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
a r t i c l e i n f o
a b s t r a c t
Article history:
An unusual type of oxidative addition of disulfides containing a carboxylic acid group to platinum(II) is
established, giving the first thiolate–carboxylate complexes of platinum(IV). The disulfide R2S2 with
R=CH2CH2CO2H reacts with [PtMe2(2,2′-bipyridine)] to give RSH and the chelating thiolate–carboxylate
complex [PtMe2(κ2-S,O–SCH2CH2CO2)(bipy)]. However, the disulfide R2S2 with R=C6H3–4–NO2–3–CO2H
reacts to give first the product of trans oxidative addition [PtMe2(SR)2(bipy)], which slowly reacts further to
give RSH and the bridging thiolate–carboxylate complex [Pt2Me4(κ2–S,O–SC6H3–4–NO2–3–CO2)2(bipy)2].
© 2010 Elsevier B.V. All rights reserved.
Received 1 October 2010
Accepted 25 October 2010
Available online 30 October 2010
Keywords:
Platinum
Oxidative Addition
Disulfide
Thiolate
Carboxylate
The reversible cleavage of the S–S bond of a disulfide R2S2 by
reaction with a transition metal complex, cluster, nanoparticle or
surface can have significance in areas ranging from self-assembled
monolayers and tribology to catalysis and medicinal chemistry [1–5].
The oxidative addition of the S–S bond to transition metal complexes
is one route for activation of disulfides and there have been several
studies of such reactions with either platinum(0) or platinum(II)
complexes [6–11]. In particular, in an earlier study it was shown that
the reaction of [PtMe2(2,2′-bipyridine)], 1, with diphenyl disulfide
occurred according to Scheme 1, with initial formation of a diplatinum
(III) complex [Pt2(SPh)2Me2(bipy)2], 2a, which finally gave the
dithiolatoplatinum(IV) complex [Pt(SPh)2Me2(bipy)], 3a [9]. This
article shows that the disulfides R2S2 with R=CH2CH2CO2H or C6H3–
4–NO2–3–CO2H can give the first examples of thiolate–carboxylate
complexes of platinum(IV) [12,13].
easily monitored by 1 H NMR spectroscopy. Fig. 1 shows that as
complex 1 reacts slowly, only the peaks assigned to 4 are observed,
with no evidence for formation of 2b or 3b, Scheme 1, the expected
products of oxidative addition of the S–S bond. If the primary reaction
was with the carboxylic acid group, cleavage of a methylplatinum
bond would be expected to occur [15,16], so it is likely that the
reaction occurs by an SN2 mechanism at the S–S bond to give an
intermediate [PtMe2(SCH2CH2CO2H)(bipy)]+[SCH2CH2CO2H]−
,
which then undergoes proton transfer to give HSCH2CH2CO2H and
complex 4 (Scheme 2) rather than simple coordination of the thiolate
anion to give 3b.
The reaction of complex 1 with the disulfide R2S2, R=C6H3–4–
NO2–3–CO2H, occurred much more rapidly and gave complex 3c as
the major product. Fig. 2 shows the NMR spectrum of a 2:1 mixture of
The reaction of complex 1 [9,14] with the disulfide R2S2, R=CH2-
CH2CO2H, in either acetone or dimethylsulfoxide occurred according
to Scheme 2 to give the 3-thiolatopropionate complex [PtMe2(SCH2-
CH2CO2)(bipy)], 4, which was isolated as a red-brown solid. Complex
4 was characterized in the 1 H NMR by the presence of two
methylplatinum resonances at δ=0.43 [s, 3 H, 2 J(PtH)=73 Hz,
MePt trans to O] and 1.56 [s, 3 H, 2 J(PtH)=69 Hz, MePt trans to N]
and by four overlapping multiplet resonances, integrating to a total of
four protons, for the CH2CH2 protons in the range δ=2.3–2.6. The
MALDI MS gave a peak at m/z=486 (4+H+). The reaction occurred
slowly over a period of several days at room temperature, so it was
⁎
Corresponding author.
E-mail address: pudd@uwo.ca (R.J. Puddephatt).
Scheme 1.
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.10.024

M.S. McCready, R.J. Puddephatt / Inorganic Chemistry Communications 14 (2011) 210–212
211
Scheme 2. R=CH2CH2CO2H.
Fig. 2. 1H NMR spectra (400 MHz, dmso-d6) in the methylplatinum area during the
reaction of complex 1 with R2S2, R=C6H3–4–NO2–3–CO2H, to give complex 3c, with 2c
as minor product.
1 and R2S2 in dmso-d6 a few minutes after mixing. Complex 3c is
identified by the single methylplatinum resonance at δ=1.45, 2 J
(PtH)=69 Hz, by comparison to the known complex 3a [δ(MePt)
=1.50, 2 J(PtH)=71 Hz] [9]. Almost half of complex 1 remained and a
minor product was tentatively identified as 2c [δ(MePt)=1.56, 2 J
(PtH)=66 Hz]. Under similar conditions, complex 1 reacts with Ph2S2
to give mostly 2a, so the selectivity is greatly affected by the nature of
the aryl group. The reaction was also examined in acetone and in
dimethylformamide (dmf) and gave similar results, though the
product 3c is insoluble in acetone.
When the reaction of complex 1 with R2S2, R=C6H3–4–NO2–3–
CO2H, was carried out in dmf, or in a mixture of dmf and
chlorobenzene, the initial product 3c slowly decomposed with
precipitation of a yellow crystalline solid which was characterized
as the binuclear complex [Pt2Me4(C6H3–4–NO2–3–CO2)2(bipy)2], 5,
according to Scheme 3. Once formed, this complex was insoluble in all
common organic solvents so NMR data could not be obtained.
The structure of complex 5 is shown in Fig. 3 [17]. The complex is
binuclear and centrosymmetric. The complex contains two thiolate–
carboxylate ligands which bridge between octahedral dimethylplati-
num(IV) centers. The low solubility of complex 5 appears to result from
a 3-dimensional network structure involving many weak CH..O and CH..
S interactions using the oxygen atoms of the nitro and carbonyl groups
and the sulphur atoms of the thiolate groups. There are channels in the
structure which are occupied by highly disordered dmf molecules,
whose electron density was treated by using SQUEEZE.
Fig. 1. 1H NMR spectra (400 MHz, dmso-d6) in the methylplatinum area during the
reaction of complex 1 with R2S2, R=CH2CH2CO2H to give complex 4: top, after 10 min.;
center, after 5 h.; bottom, after 4 d.
Scheme 3. R=C6H3–4–NO2–3–CO2H. The decomposition of complex 3c to give
complex 5.

212
M.S. McCready, R.J. Puddephatt / Inorganic Chemistry Communications 14 (2011) 210–212
Appendix A. Supplementary material
CCDC 795154 contains the crystallographic data for complex 5.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via http://www.ccdc.cam.uk.data_re-
quest.cif.
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Fig. 3. A view of the structure of complex 5. Selected bond parameters: Pt(1)–S(1)
2.287(4); Pt(1)–O(4) 2.127(9); Pt(1)–N(1) 2.14(1); Pt(1)–N(2) 2.08(1); Pt(1)–C(11)
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[17] Crystal data for 5: formula C38H34N6O8Pt2S2, fw=1157.01, triclinic, space
group P-1, a=9.5670(4), b=10.5794(5), c=11.7181(6) Å, α=95.393(3),
β = 95.400(3), γ = 93.415(3) o, V = 1172.73(10) Å3, Z = 1, R1 = 0.075,
wR2=0.157. The crystals were prepared by slow diffusion of a solution of
S2R2, R=C6H3–4–NO2–3–CO2H, in N, N-dimethylformamide into a solution of
complex 1 in chlorobenzene. Analytical data: Calcd. for C38H34N6O8Pt2S2: C
39.45, H 2.96, N 7.26. Found: C 39.02, H 2.76, N 7.10%.
The differences in chemistry between the two disulfides studied
evidently arises from the much higher reactivity to oxidative addition
of the diaryldisulfide compared to the dialkyldisulfide, and from
ability of the ligand [SCH2CH2CO2]2− to chelate in forming complex 4
compared to inability of the rigid ligand [SC6H3–4–NO2–3–CO2]2− to
chelate, thus leading to slow formation of the binuclear complex 5.
Acknowledgements
We thank the NSERC (Canada) for financial support and Dr. G.
Popov for the structure determination.