Oxidative addition of S-S bonds to dimethylplatinum(II) complexes: Evidence for a binuclear mechanism

Article abstract of DOI:10.1021/om800776b

Oxidative addition of the S - S bond of S₂py₂ (py = 2-pyridyl) to [Pt₂Me₄(μ-SMe₂)₂] occurs with displacement of Me₂S to give [PtMe₂(K ²-,S,N-Spy)₂], 1. Oxidative addition of S ₂Ar₂ (Ar = 2-pyridyl or Ph) to [PtMe₂(NN)], NN = 2,2′-bipyridine or 1, 10-phenanthroline, gives initially the binuclear Pt(III) complexes [PtMe₂(k¹-S-SAr)(NN)}₂], which react further with S₂Ar₂ to give [PtMe ₂(K¹-S-SAr)₂(NN)] and then, when Ar = 2-pyridyl, to give an equilibrium with free NN and complex 1. Evidence is presented that the S - S oxidative addition to [Pt₂Me ₄(μ-SMe₂)₂] occurs by a concerted mechanism whereas the reactions with [PtMe₂(NN)] to give the binuclear complexes [{PtMe₂(K¹-S-SAr)(NN)}₂] occur by a polar nonconcerted mechanism, involving a loosely bonded dimer [PtMe ₂(NN)]₂.

Full text of DOI:10.1021/om800776b

Organometallics 2008, 27, 6521–6530
6521
Oxidative Addition of S-S Bonds to Dimethylplatinum(II)
Complexes: Evidence for a Binuclear Mechanism
Kevin J. Bonnington, Michael C. Jennings, and Richard J. Puddephatt*
Department of Chemistry, UniVersity of Western Ontario, London, Canada N6A 5B
ReceiVed August 12, 2008
Oxidative addition of the S-S bond of S2py2 (py ) 2-pyridyl) to [Pt2Me4(µ-SMe2)2] occurs with
displacement of Me2S to give [PtMe2(κ2-S,N-Spy)2], 1. Oxidative addition of S2Ar2 (Ar ) 2-pyridyl or
Ph) to [PtMe2(NN)], NN ) 2,2′-bipyridine or 1,10-phenanthroline, gives initially the binuclear Pt(III)
complexes [{PtMe2(κ1-S-SAr)(NN)}2], which react further with S2Ar2 to give [PtMe2(κ1-S-SAr)2(NN)]
and then, when Ar ) 2-pyridyl, to give an equilibrium with free NN and complex 1. Evidence is presented
that the S-S oxidative addition to [Pt2Me4(µ-SMe2)2] occurs by a concerted mechanism whereas the
reactions with [PtMe2(NN)] to give the binuclear complexes [{PtMe2(κ1-S-SAr)(NN)}2] occur by a polar
nonconcerted mechanism, involving a loosely bonded dimer [PtMe2(NN)]2.
Chart 1. Selected Disulfide Complexes
Introduction
The reversible cleavage of the S-S bond of a disulfide R2S2
by reaction with a transition metal complex or surface may be
important in catalysis,1 in medicinal chemistry involving cis-
platin,2 or in self-assembled monolayers and tribology.3 It is
therefore important to understand how these reactions occur.
In organic chemistry, disulfides can be activated by photolysis
to give thiyl radicals RS· or by electron transfer to give the
radical anion [R2S2]· -, which may then react as the equivalent
of a thiyl radical and a thiolate anion, RS· + RS-.4 The bond
dissociation energy of Ph2S2 has been estimated both experi-
mentally and theoretically.4,5
Disulfide and diselenide ligands usually act as bridging
ligands as illustrated by A-C in Chart 1, but they can also act
as terminal ligands as illustrated by D and E in Chart 1.6 These
complexes exhibit a particularly rich fluxionality, including
migration of metals between chalcogen centers (e.g., E and E′
* To whom correspondence should be addressed. Email: pudd@uwo.ca.
(1) (a) Kuniyasu, H.; Sugoh, K.; Su, M. S.; Kurosawa, H. J. Am. Chem.
Soc. 1997, 119, 4669. (b) Kondo, T.; Mitsudo, T. Chem. ReV. 2000, 100,
3205. (c) Kuniyasu, H.; Yamashita, F.; Terao, J.; Kambe, N. Angew. Chem.,
Int. Ed. 2007, 46, 5929.
(2) (a) Bierbach, U.; Hambley, T. W.; Roberts, J. D.; Farrell, N. Inorg.
Chem. 1996, 35, 4865. (b) Fakih, S.; Munk, V. P.; Shipman, M. A.;
Murdoch, P. D.; Parkinson, J. A.; Sadler, P. J. Eur. J. Inorg. Chem. 2003,
1206. (c) Wei, H.; Wang, X.; Liu, Q.; Lu, Y.; Guo, Z. Inorg. Chem. 2005,
44, 6077.
(3) (a) Schlenoff, J. B.; Li, M.; Ly, H. J. Am. Chem. Soc. 1995, 117,
12528. (b) Wang, X. Y.; Li, X. F.; Wen, X. H.; Tan, Y. Q. J. Theor. Comp.
Chem. 2006, 5, 1.
in Chart 1), inversion at the pyramidal chalcogen center (found
in all complexes) and switching of the ligand between metal
centers (e.g., in complex A).
(4) (a) Scott, T. W.; Liu, S. N. J. Phys. Chem. 1989, 93, 1393. (b)
Armstrong, D. A.; Sun, Q.; Schuler, R. H. J. Phys. Chem. 1996, 100, 9892.
(c) Dvorak, D.; Neugebauerova, E.; Liska, F.; Ludvik, J. Collect. Czech.
Chem. Commun. 1998, 63, 378. (d) Maran, F.; Wayner, D. D. M.;
Workentin, M. S. AdV. Phys. Org. Chem. 2001, 36, 85. (e) Antonello, S.;
Daasbjerg, K.; Jensen, H.; Taddei, F.; Maran, F. J. Am. Chem. Soc. 2003,
125, 14905. (f) Meneses, A. B.; Antonello, S.; Arevolo, M. C.; Gonzalez,
C. C.; Sharma, J.; Wallette, A. N.; Workentin, M. S.; Maran, F. Chem.-
Eur. J. 2007, 13, 7983.
(5) (a) Benassi, R.; Fiandri, G. L.; Taddei, F. THEOCHEM 1997, 418,
127. (b) Kamisuki, T.; Hirose, C. THEOCHEM 2000, 531, 51.
(6) (a) Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog. Inorg. Chem.
1984, 32, 1. (b) Blower, P. J.; Dilworth, J. R. Coord. Chem. ReV. 1987, 76,
121. (c) Atwood, J. L.; Bernal, I.; Calderazzo, F.; Canada, L. G.; Poli, R.;
Rogers, R. D.; Veracini, C. A.; Vitali, D. Inorg. Chem. 1983, 22, 1797. (d)
Baratta, W.; Pregosin, P. S.; Bacchi, A.; Pelizzi, G. Inorg. Chem. 1994,
33, 4494. (e) Kunkely, H.; Vogler, A. Chem. Comm. 1996, 2519.
Disulfides can also take part in redox reactions at metal
centers with reversible formation of thiolate ligands as illustrated
in Scheme 1. Oxidation of thiolate complexes can lead to
formation of free or complexed disulfide.4,6,7
The ligand di-2-pyridyldisulfide can act as an N,N-donor or
N,S-donor chelate (forming 7- or 5-membered rings respectively)
as in complexes F and G (Chart 2), as a bridging ligand, or it
may undergo S-S bond cleavage to give 2-pyridylthiolate
complexes such as H.8
(7) Ludvik, J.; Nygard, B. Electroanal. Chem. 1997, 423, 1.
10.1021/om800776b CCC: $40.75
2008 American Chemical Society
Publication on Web 10/30/2008

6522 Organometallics, Vol. 27, No. 24, 2008
Bonnington et al.
Scheme 1
m(II) with displacement of weakly bound dimethylsulfide
ligands from platinum. Because there are precedents for both
coordination of di-2-pyridyldisulfide to transition metals (F and
G, Chart 2) and undergoing cleavage of the S-S bond to give
2-pyridylthiolate complexes (H, Chart 2), the reaction was
monitored by low temperature NMR spectroscopy in an attempt
to identify reaction intermediates. The reaction occurred over a
period of about one hour at -15 °C, but no reaction intermedi-
ates were detected. As the resonances for [Pt2Me4(µ-SMe2)2]
and S2(2-py)2 decayed, those for complex 1 increased in
intensity. The only complication was that, at intermediate stages,
resonances for cis-[PtMe2(SMe2)2], formed by reaction of
displaced SMe2 with [Pt2Me4(µ-SMe2)2],12 were observed (eq
1). Thus, it seems that the slow step in the reaction is the initial
coordination of di-2-pyridyldisulfide to platinum, and that the
oxidative addition and complete displacement of dimethylsulfide
occur rapidly after that.
Chart 2
Chart 3
The stereochemistry of complex 1 could be deduced from
the 1H NMR spectrum and was confirmed by a structure
determination. The methylplatinum resonance occurred at δ )
1.51 with 2J(PtH) ) 76 Hz, in the range expected for a
methylplatinum(IV) complex with methyl trans to nitrogen.10-13
The H6 proton of the pyridyl group appeared at δ ) 8.11 with
3J(PtH) ) 21 Hz, and the low value of the coupling constant
indicates that the pyridyl group is trans to methyl.10-13 The
structure of complex 1 is shown in Figure 1. It confirms the
predicted structure, with mutually trans sulfur atoms. There are
two independent molecules which have similar chiral structures.
Distortions from regular octahedral geometry at platinum(IV)
arise through the constraints of the 4-membered chelate rings.
Reaction of di-2-pyridyldisulfide with [PtMe2(bipy)], 2a, bipy
) 2,2′-bipyridine, in CD2Cl2 immediately gave a black pre-
cipitate which slowly redissolved to give a yellow solution.
Complex 1 could be crystallized from this solution. A similar
The oxidative addition reactions of disulfides and diselenides
to platinum(0) or platinum(II) have been studied previously.9-11
Cyclic disulfides can give cis-dithiolate complexes, but the
formation of trans-dithiolates is more common, as illustrated
by the examples in Chart 3. In terms of mechanism, the reaction
of anionic [PtMe2(pz3BH)]-, pz ) pyrazolyl, with S2Ph2 is
thought to occur by a 2-electron (SN2) mechanism to give
[PtMe2(SPh)(pz3BH)] and SPh-, while reactions of neutral
complexes [PtR2(NN)], NN ) diimine ligand, are proposed to
occur at least in part by free radical mechanisms.10,11 This paper
describes new mechanistic and structural studies in the reactions
of di-2-pyridyldisulfide and diphenyldisulfide with dimethyl-
platinum(II) complexes.
1
reaction was monitored by H NMR as the solution in CD2Cl2
Results
was warmed from -80 °C to room temperature. Complex 2a
was almost completely consumed at -10 °C and the major
product was identified as the binuclear complex [{PtMe2-
(Spy)(bipy)}2], 3a (Scheme 2). As the mixture was warmed to
room temperature, complex 3a reacted further to give
[PtMe2(Spy)2(bipy)], 4a, and then 4a underwent dissociation
of 2,2′-bipyridine to give the final product [PtMe2(2-Spy)2], 1.
There was an equilibrium between 1 and free 2,2′-bipyridine
and complex 4a (Scheme 2), but the equilibrium strongly
favored 1 and free 2,2′-bipyridine, with only ca. 5% 4a present
at the concentration used. In addition, both [Pt(Spy)Me3(bipy)],
Reactions of Di-2-pyridyldisulfide. The reaction of [Pt2Me4(µ-
SMe2)2]12 with di-2-pyridyldisulfide occurred rapidly at room
temperature to give the platinum(IV) complex [PtMe2(2-Spy)2],
1, py ) pyridyl, according to eq 1. The reaction involves
oxidative addition of the S-S bond of the disulfide to platinu-
(8) (a) Kadooka, M. M.; Warner, L. G.; Seff, K. J. Am. Chem. Soc.
1976, 98, 7569. (b) Kubo, S.; Nishioka, T.; Ishikawa, K.; Kinoshita, I.;
Isobe, K. Chem. Lett. 1998, 1067. (c) Pickardt, J.; von Chrzanowski, L.;
Steudel, R.; Borowski, M.; Beck, S. Z. Naturforsch. B 2005, 60, 373. (d)
Wang, L.-G. Acta Cryst. E 2007, 63, m1826. (e) Wriedt, M.; Jess, I.; Nather,
C. Acta Cryst. E 2007, 64, m83. (f) Pal, P. K.; Drew, M. G. B.; Datta, D.
New J. Chem. 2003, 27, 197. (g) Shi, Y.; Cheng, G.; Lu, S.; Guo, H.; Wu,
Q.; Huang, X.; Hu, N. J. Organomet. Chem. 1993, 455, 115.
2
with δ(1H) ) 0.28 [s, 3H, J(PtH) ) 62 Hz, PtMe trans to S]
(9) (a) Albano, V. G.; Monari, M.; Orabona, I.; Panunzi, A.; Roviello,
G.; Ruffo, F. Organometallics 2003, 22, 1223. (b) Weigand, W.; Brautigam,
S.; Mloston, G. Coord. Chem. ReV. 2003, 245, 167. (c) Shimizu, D.; Takeda,
N.; Tokitoh, N. J. Organomet. Chem. 2007, 692, 2716.
(10) (a) Canty, A. J.; Jin, H.; Skelton, B. W.; White, A. H. Inorg. Chem.
1998, 37, 3975. (b) Panunzi, A.; Roviello, G.; Ruffo, F. Organometallics
2002, 21, 3503. (c) Canty, A. J.; Denney, M. C.; Patel, J.; Sun, H.; Skelton,
B. W.; White, A. H. J. Organomet. Chem. 2004, 689, 672.
(11) Aye, K.-T.; Vittal, J. J.; Puddephatt, R. J. J. Chem. Soc. Dalton
1993, 1835.
(12) (a) Scott, J. D.; Puddephatt, R. J. Organometallics 1983, 2, 1643.
(b) Monaghan, P. K.; Puddephatt, R. J. Organometallics 1984, 3, 444. (c)
Hill, G. S.; Irwin, M. J.; Levy, C. J.; Rendina, L. M.; Puddephatt, R. J.
Inorg. Synth. 1997, 32, 149.
(13) Jenkins, H. A.; Yap, G. P. A.; Puddephatt, R. J. Organometallics
1997, 16, 1946.

OxidatiVe Addition of S-S Bonds
Organometallics, Vol. 27, No. 24, 2008 6523
Figure 2. Structure of complex 4b · H2O. Selected bond parameters:
Pt-C(1) 2.06(1); Pt-C(2) 2.10(1); Pt-N(22) 2.153(9); Pt-N(11)
2.17(1); Pt-S(41) 2.343(3); Pt-S(31) 2.396(3) Å; S(41)-Pt-S(31)
171.3(1); C(32)-S(31)-Pt 105.4(4); C(42)-S(41)-Pt 104.0(4) °.
H-bonding distances: O(51) · · · N(43) 2.87(1); O(51) · · · N(33A)
3.22(2) Å.
Figure 1. Structure of complex 1. Selected bond parameters for
molecule 1, which are similar for molecule 2: Pt(1)-C(1) 2.045(13);
Pt(1)-C(2) 2.057(11); Pt(1)-N(23) 2.160(8); Pt(1)-N(13) 2.168(9);
Pt(1)-S(21) 2.362(3); Pt(1)-S(11) 2.364(3) Å; N(23)-Pt(1)-S(21)
68.3(2); N(13)-Pt(1)-S(11) 68.0(2); S(21)-Pt(1)-S(11) 164.6(1)°.
room temperature. There were several byproducts formed during
this period, among which the complexes [Pt(Spy)Me3(phen)]
and [PtClMe3(phen)] were identified by their 1H NMR spectra.
Complex 4b only partly decomposed to give 1 over a period of
a week at room temperature. Because complex 3b was longlived
in solution, many attempts were made to crystallize it, but only
4b could be crystallized from this and similar reaction mixtures.
Scheme 2
The structure of 4b, which crystallized as a water solvate, is
shown in Figure 2. It confirms the trans orientation of the two
2-pyridylthiolate ligands, as found in related complexes.10,11 The
C-S-Pt angles are less than the tetrahedral angle, which allows
π-stacking of the pyridyl and phenanthroline rings. Individual
molecules are self-assembled into polymeric chains through
hydrogen bonding between pyridyl groups and the water
molecules, N · · · HOH · · · N, as shown in Figure 2.
The characterization of the binuclear complexes 3a and 3b
depends in large part on the 1H NMR spectra. Consider the case
of formation of 3a from 2a. If the reaction with di-2-
pyridyldisulfide is carried out in a 1:1 ratio, only half of the
disulfide is consumed in forming 3a, and the stoichiometry of
the product is readily confirmed by integration of the 1H NMR
spectrum. Complex 3a is much longer lived when formed in
the absence of excess di-2-pyridyldisulfide. The complex gives
a single methylplatinum resonance and the coupling constant
2J(PtH) ) 75 Hz is in the range expected for 6-coordinate
platinum and considerably less than in 2a, which gives 2J(PtH)
) 86 Hz. The resonance for the ortho hydrogen, NdCH6, of
the bipy ligand occurs at δ ) 9.28 in 2a but at 8.70 and 8.04
in 4a and 3a respectively. Similarly, the ortho-hydrogen of the
2-pyridylthiol unit, SdCH3, is at δ ) 7.62 in the parent ligand
S2py2 but at δ ) 6.78 and 6.22 in 4a and 3a respectively. These
shifts must arise primarily through ring shielding effects, and
indicate more extensive π-stacking of the aromatic rings in 3a
than in 4a. The shielding effects are even more pronounced in
the 1,10-phenanthroline complex 3b as illustrated in Figure 3.
The spectra indicate apparent C2V symmetry of the
[Pt2Me4(NN)2] units in 3a and 3b, indicating easy rotation of
the 2-pyridylsulfide groups as well as easy libration about the
Pt-Pt bond at room temperature. Both the methylplatinum peaks
and the 1,10-phenanthroline peaks in 3b (except the H5
resonance) are broadened at low temperature, indicating the
slowing of rotation about the Pt-Pt bond but not about the Pt-S
bond, under these conditions.
2
and δ(1H) ) 1.28 [s, 6H, J(PtH) ) 70 Hz, PtMe trans to N],
and [PtClMe3(bipy)], with δ(1H) ) 0.39 [s, 3H, J(PtH) ) 75
2
Hz, PtMe trans to Cl] and δ(1H) ) 1.22 [s, 6H, J(PtH) ) 70
2
Hz, PtMe trans to N], were identified in ca. 2% yield from
14
1
their characteristic H NMR spectra. Remarkably, a similar
reaction of 2a with S2py2 in CDCl3 solution was very much
slower, with only about 10% decay of resonances for 2a in one
hour at room temperature. The product mixture was complex,
with some products arising from reaction with solvent.15
The loss of 2,2′-bipyridine (bipy) from 4a to give 1 under
mild conditions was not expected, so the reaction was also
studied for the 1,10-phenanthroline (phen) complex 2b. The
greater rigidity of the phen ligand compared to bipy makes its
displacement much more difficult. The reaction in CD2Cl2
solution also occurred according to Scheme 2, but there were
significant differences. The initial reaction was very similar and
led to formation of the black binuclear complex 3b in high yield.
This step was complete in a few minutes at 0 °C. The next step
to give 4b (Scheme 2) was slower than in the similar reaction
with 2a and decay of 3b was complete in about one day at
(14) (a) Hux, J. E.; Puddephatt, R. J. Inorg. Chim. Acta 1985, 100, 1.
(b) Hux, J. E.; Puddephatt, R. J. Organomet. Chem. 1992, 437, 251.
(15) (a) Kuyper, J. Inorg. Chem. 1978, 17, 77. (b) Monaghan, P. K.;
Puddephatt, R. J. J. Chem. Soc. Dalton 1988, 595.

6524 Organometallics, Vol. 27, No. 24, 2008
Bonnington et al.
Scheme 3
by π-stacking of the aromatic groups. For example, in Ph2S2,
6b and 5b, the ortho-hydrogen atoms of the PhS groups
appeared at δ ) 7.48, 6.18 and 5.35 respectively as π-stacking
increased. Similarly, in 2b, 6b, and 5b, the ortho-hydrogen
atoms of the phen groups appeared at δ ) 9.51, 8.89 and 7.99
respectively, confirming mutual shielding of aromatic protons
of both the phenylthiolate and 1,10-phenanthroline groups with
increasing π-stacking. Complex 5b gives a single methylplati-
Figure 3. 1H NMR spectra in CD2Cl2 solution of (a) [PtMe2(phen)],
2b (400 MHz, 20 °C); (b) [Pt2Me4(Spy)2(phen)2], 3b (600 MHz,
-20 °C); (c) S2py2 (400 MHz, 20 °C). The correlation lines show
the chemical shift changes in 3b compared to the reagent molecules
primarily as a result of the π-stacking. The peak marked * is due
to CHDCl2, while that marked # in (b) is due to impurity of complex
4b.
2
num resonance at δ ) 1.32 with J(PtH) ) 76 Hz.
Further evidence for the proposed binuclear structure of 3a
and 3b was obtained by ESI-MS of reaction mixtures in
dichloromethane solution. The first step of the reaction of
[PtMe2(bipy)], 2a, with S2py2 was complete in ten minutes and
the base peak was at m/z
) 491, corresponding to
[PtMe2(bipy)(Spy)]+. Lower intensity peaks were observed at
m/z ) 981 [(3a-H)+], 825 [(3a-bipy-H)+] and also at m/z )
1092 [(3a+Spy)+]. Over a period of one hour, the peak at m/z
) 1092 decayed and a peak at m/z ) 505 [(PtMe3(bipy)(Spy)-
H)+] grew in intensity. Analogous results were obtained for the
reaction with [PtMe2(phen)], 2b, in which the ESI-MS gave a
base peak was at m/z
)
515, corresponding to
Figure 4. Structure of complex 6a. Selected bond parameters:
Pt-C(1) 2.055(6); Pt-N(11) 2.163(4); Pt-S(21) 2.366(2); Pt-S(31)
2.381(2) Å; C(1)-Pt-S(21) 87.2(2); N(11)-Pt-S(21) 92.91(11);
C(1)-Pt-S(31)87.7(2);N(11)-Pt-S(31)92.56(11);S(21)-Pt-S(31)
173.06(9); C(22)-S(21)-Pt 105.6(3) °. Symmetry equivalent
atoms: A, x, -y+1/2, z.
[PtMe2(phen)(Spy)]+, with lower intensity peaks at m/z ) 1029
[(3b-H)+], 849 [(3b-phen-H)+], 1140 [(3b+Spy)+] and 529
[(PtMe3(phen)(Spy)-H)+].
Reactions of Diphenyldisulfide. The reaction of
[PtMe2(phen)], 2b, with diphenyldisulfide was studied previ-
ously but, with the instrumentation available at that time, it was
not possible to obtain satisfactory NMR data on the initial
product.11 A reinvestigation with both 2a and 2b has now shown
that the reactions occur according to Scheme 3.
The course of the reaction is similar to the first steps in the
reaction with di-2-pyridyldisulfide (Scheme 2). If the reactions
are carried out with a 1:1 ratio of 2a or 2b: Ph2S2, the reaction
mixture becomes black on mixing and much of this black
product (5a or 5b) precipitates. On stirring, the black material
slowly redissolves to give 6a or 6b, which can be isolated as
yellow crystalline solids. If the reaction is carried out in a 2:1
ratio of 2a or 2b: Ph2S2, the black products 5a or 5b are more
persistent, but it has not been possible to crystallize them. The
structures of 6a and 6b are shown in Figures 4 and 5. They
confirm the overall product of trans oxidative addition of
diphenyldisulfide to 2a or 2b, with π-stacking of the phenyl
groups with the bipy or phen units.10,11
Figure 5. Structure of complex 6b. Selected bond parameters:
Pt-C(2) 2.050(7); Pt-C(1) 2.059(8); Pt-N(11) 2.161(5); Pt-N(22)
2.174(6); Pt-S(31) 2.364(2); Pt-S(41) 2.374(2) Å; C(32)-S(31)-Pt
106.5(2); C(42)-S(41)-Pt 106.3(1) °.
The 1H NMR spectra of complexes 5a and 5b were, like those
of the 2-pyridylthiolate analogs 3a and 3b, greatly influenced

OxidatiVe Addition of S-S Bonds
Scheme 4
Organometallics, Vol. 27, No. 24, 2008 6525
platinum(IV) complex and which is calculated to be 72 kJ mol-1
more stable than 11) is faster than the pyridine coordination
step. The activation enthalpy is calculated to be 130 kJ mol-1.
In the reaction of S2py2 or S2Ph2 with 2a, the bipy ligand
cannot be displaced by the neutral disulfide ligand so the above
mechanism is not possible. A search for a concerted mechanism
of oxidative addition in this system was unsuccessful, so
calculations were carried out with a model system of S2H2 with
cis-[PtMe2(NH3)2] in order to gain insight into this problem.
The results are shown in Scheme 6. The disulfide first adds to
give the square pyramidal disulfide complex 14.16 As the second
sulfur atom approaches the platinum atom the SS bond is
weakened and, near the transition state, 15, one of the ammine
ligands is essentially dissociated and then recoordinates in the
product of cis oxidative addition 16. The situation is reminiscent
of the oxidative addition of nonpolar C-H or C-C bonds to
platinum(II) in which coordinative unsaturation is needed17,18
but, of course, the disulfide case differs in that the sulfur atoms
carry lone pairs of electrons and so 15 would be a 20-electron
complex intermediate if the ligand dissociation did not occur.
There is another route, with slightly lower activation energy,
which involves intermediate ligand displacement (Scheme 6).
One ammine ligand is displaced from 14 by way of a trigonal
bipyramidal transition state 17 to give the κ1-disulfide complex
18.16 The concerted cis oxidative addition from 18 through 19
to give the dithiolate complex 20 occurs easily as the Pt-S-S
angle distorts to allow a second Pt · · · S interaction, and there is
then an easy route to the trans isomer 21 and then to product
of trans oxidative addition 22. The ease of reaction of 18 to
give 20 and 21, suggests an alternative route to 1 from di-2-
pyridyldisulfide and [Pt2Me4(µ-SMe2)2] by direct rearrangement
of [PtMe2(SMe2)(κ1-S-S2py2)] to give [PtMe2(SMe2)(Spy)2],
followed by displacement of dimethylsulfide to give 1. Calcula-
tions indicate a similar activation energy as for the oxidative
addition step in Scheme 5. What is clear from these calculations
is that a concerted mechanism of oxidative addition is possible
provided that a disulfide complex of platinum(II) with a square
planar 16-electron configuration can be formed as an intermedi-
ate. However, a concerted mechanism of reaction is not favored
with complexes such as 2a and 2b which have no easily
displaced ligand.18
When the reaction of 2b with diphenyldisulfide was carried
out in acetone solution, a trace product formed along with 6b
was identified as the product of cis oxidative addition, cis,cis-
[PtMe2(SPh)2(phen)].11 This product is not formed in the
reaction in dichloromethane solution, but a minor product was
identified as [PtClMe3(phen)].14 It was formed in only about
2% yield, and was identified near the end of the slower step of
the overall reaction to form 6b from 5b and Ph2S2 in dichlo-
romethane solution.
Discussion
There are several potential mechanisms of oxidative addition
of S-S bonds to transition metal complexes as outlined in
Scheme 4. A concerted mechanism is expected to give the
product of cis oxidative addition, but this stereochemistry is
observed only when there are geometrical constraints (for
example I, Chart 3), and is clearly impossible for formation of
the binuclear complexes 3 and 5.9-11 The polar mechanism,
forming the intermediate [LnMSR]+SR-, has precedents in
oxidative addition of halogens and finds support in oxidative
addition to anionic complexes.10 However, disulfides rarely act
as simple electrophiles as required in this mechanism.4,5 Free
radical nonchain or chain mechanisms have more precedents
in disulfide chemistry,4 and there is some evidence for these in
oxidative addition of disulfides or diselenides to platinum(II),
including complex kinetics and enhancement by photons.10,11
However, attempts to detect radical intermediates by EPR or
CIDNP have not been successful. Any of the polar or radical
mechanisms can give trans oxidative addition (Scheme 4). A
major complication in the reactions studied here is the kinetic
preference for formation of the binuclear complexes 3 and 5.
To gain insight into the mechanism of S-S bond activation,
calculations have been carried out using density functional
theory (DFT).
Concerted Mechanism of S-S Bond Cleavage. The sim-
plest reaction is the reaction of [Pt2Me4(µ-SMe2)2] with S2py2
to give complex 1 and the calculated energies of some potential
intermediates are shown in Scheme 5. There are several ways
in which S2py2 may chelate to a dimethylplatinum(II) unit after
displacement of dimethylsulfide. The calculations indicate, as
do the precedents in Chart 2,8 that the N,N or N,S chelate, 7 or
8, is preferred. The 5-membered chelate ring in 8 is favored
over the 4-membered chelate ring in 8′. Coordination of both
sulfur atoms in 9 or 10 leads to considerable weakening of the
S-S bond and then concerted oxidative addition leads to the
cis 5-coordinate platinum(IV) complex 11. Complex 11 has an
essentially barrier-free route to the trans 5-coordinate isomer
12 and then coordination of the free pyridyl group gives 1. It is
also possible for 11 to give the product of cis oxidative addition
13, and 13 is calculated to lie only about 10 kJ mol-1 higher in
energy than 1 (Scheme 5). Complex 13 is not observed because
the rearrangement of 11 to 12 (in which both sulfur π-donors
are cis to the vacant coordination site in the 16-electron
Nonconcerted Mechanisms of S-S Bond Cleavage.
Schemes 7 shows potential mechanisms of oxidative addition
of diphenyldisulfide to complex 2a to give [Pt(SPh)2Me2(bipy)],
6a, a reaction which does not occur in practice. Calculations
suggest a weak bonding between 2a and S2Ph2 to give 23 which
might then undergo S-S bond homolysis or heterolysis to give
24 and PhS· or 25 and PhS-, respectively.16 Recombination of
the radicals or ions would then give 6a. In the radical chain
mechanism, a phenylthiyl radical is formed in an initiation step,
then reacts with 2a to give 24, which reacts with S2Ph2 to give
6a and PhS· , to continue the chain.
(16) For a discussion, from a theoretical perspective, of 5-coordinate
intermediates in substitution reactions of platinum(II): Cooper, J.; Ziegler,
T. Inorg. Chem. 2002, 41, 6614.
(17) (a) Bartlett, K. L.; Goldberg, K. I.; Borden, W. T. J. Am. Chem.
Soc. 2000, 122, 1456. (b) Gilbert, T. M.; Hristov, I.; Ziegler, T. Organo-
metallics 2001, 20, 2669. (c) Hoover, J. M.; Freudenthal, J.; Michael, F. E.;
Mayer, J. M. Organometallics 2008, 27, 2238.
(18) Arguments have been made for either concerted or polar (SN2)
mechanisms for oxidative addition of the O-O bond of peroxides to
dimethylplatinum(II) complexes: (a) Taylor, R. A.; Law, D. J.; Sunley, G. J.;
White, A. J. P.; Britovsek, G. J. P. Chem. Commun. 2008, 2800. (b)
Thorshaug, K.; Fjeldahl, I.; Romming, C.; Tilset, M. J. Chem. Soc., Dalton
Trans. 2003, 4051. (c) Rashidi, M.; Nabavizadeh, M.; Hakimelahi, R.;
Jamali, S. J. Chem. Soc., Dalton Trans. 2001, 3430. (d) Rostovtsev, V. V.;
Henling, L. M.; Labinger, J. A.; Bercaw, J. E. Inorg. Chem. 2002, 41, 3608.

6526 Organometallics, Vol. 27, No. 24, 2008
Bonnington et al.
Scheme 5. Calculated S-S Distances are 7 ) 2.35, 8 ) 2.42, 8′ ) 2.49, 9 ) 3.03, 10 (Transition State) ) 3.31, 11 ) 3.70, 12 )
4.90, 13 ) 4.08, 1 ) 4.99 Å
Scheme 6. Calculated S-S Distances: 14, 2.56; 15, 2.89; 17, 2.41; 18, 2.53; 19, 2.76 Å
Coordination of S2Ph2 to give 23 is calculated to lead to
lengthening of the S-S distance from 2.42 to 2.57 Å, arising
from backbonding from filled d-orbitals on platinum into the
S-S σ*-orbital of the disulfide. Nevertheless, either homolysis
to give PhS· and 24 or heterolysis to give PhS- and 25 in the
gas phase requires a high activation energy (Scheme 8).
Solvation effects in solution will certainly stabilize the polar
intermediates but probably not by enough to favor the polar
mechanism.19 Once the intermediates are formed, collapse to
give 6a is highly favorable. Hence the fact that 6a is not a
primary product must be associated with the high barrier to the
activation of 23. If free phenylthiyl radicals can be formed, the
addition to 2a to give 24, followed by further reaction to
give 6a, should be easy in a chain reaction (Scheme 7, 8), but
there may be no easy source of the initiating radicals under the
mild reaction conditions used.
It is well-known that square planar platinum(II) complexes
with 2,2′-bipyridine or 1,10-phenanthroline can form π-stacked
dimers, which involve attractions between aromatic groups
sometimes enhanced by secondary Pt · · · Pt bonding, in solution
or solid states.20,21 In the solid state structure of [PtMe2(bipy)],
2a, neighboring pairs of molecules are separated by 3.48 Å.21
We therefore explored the potential involvement of the dimer
[PMe2(bipy)]2, 26, in the reaction with diphenyldisulfide. The
results should be treated with caution because DFT is not the
(20) (a) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1989, 28,
1529. (b) Connick, W. B.; Henling, L. M.; Marsh, R. E.; Gray, H. B. Inorg.
Chem. 1996, 35, 6261. (c) Connick, W. B.; Marsh, R. E.; Schaefer, W. P.;
Gray, H. B. Inorg. Chem. 1997, 36, 913. (d) Kato, M.; Kosuge, C.; Morii,
K.; Ahn, J. S.; Kitagawa, H.; Mitani, T.; Matsushita, M.; Kato, T.; Yano,
S.; Kimura, M. Inorg. Chem. 1999, 38, 1638. (e) Momeni, B. Z.; Hamzeh,
S.; Hosseini, S. S.; Rominger, F. Inorg. Chim. Acta 2007, 360, 2661.
(21) Achar, S.; Catalano, V. J. Polyhedron 1997, 16, 1555.
(19) For a detailed theoretical study of solvation effects during the model
reaction of oxidative addition of methyl iodide to cis-[PtMe2(NH3)2] by
the SN2 mechanism, see: (a) Hayaki, S.; Yokogawa, D.; Sato, H.; Sakaki,
S. Chem. Phys. Lett. 2008, 458, 329.

OxidatiVe Addition of S-S Bonds
Organometallics, Vol. 27, No. 24, 2008 6527
Scheme 7. Possible Mechanisms of Oxidative Addition
Scheme 9. Possible Mechanisms of Formation of Complex
5a
Scheme 8. Calculated Activation Enthalpies (kJ mol-1) for
Gas Phase Reaction of 2a to Give Ionic or Radical
Intermediates En Route to 6a
Scheme 10. Calculated Energies (kJ mol-1
) for the
Complexes and Intermediates Defined In Scheme 8
best theory for modeling weak interactions, but the overall
picture obtained is useful.
23 (Scheme 8), 30 from 27 and 2 × 24 from 28 (Scheme 10)
are 181, 127, and 83 kJ mol-1, respectively, and these values
correlate well with the calculated S-S distances in 23, 27, and
28 of 2.57, 2.67, and 2.71 Å, respectively. The calculated
activation energy for gas phase heterolysis of the S-S bond of
27 (292 kJ mol-1) is similarly much lower than in 23 (416 kJ
mol-1). As the S-S bond of the intermediate 27 is cleaved to
give 29 or 30, the calculations indicate that both the Pt-Pt and
Pt-S bonds are strengthened [Pt-Pt ) 3.35, 2.94, 2.95 Å; Pt-S
) 2.81, 2.57, 2.55 Å in 27, 29, and 30 respectively]. Similarly,
cleavage of the S-S bond in 28 to give two molecules of the
radical 24 is accompanied by strengthening of both Pt-S bonds
[Pt-S ) 2.72, 2.58 Å in 28 and 24, respectively]. These
calculations correspond to formation of ions or radicals separated
at infinity in the gas phase. Calculations of units 29 + PhS- or
The calculated energies of the intermediates defined in
Schemes 9 are shown in Scheme 10. The enthalpy change for
formation of 26 is similar to that for addition of S2Ph2 to 2a to
give 23. The addition of S2Ph2 to 26, or the addition of
[PtMe2(bipy)] to 23, can then give 27, and this is also calculated
to be favorable (Scheme 10). Alternatively, complex 23 can
react with [PtMe2(bipy)] to give the bridging diphenyldisulfide
complex 28, and this is also easy and favorable. There are then
three possible routes to 5a, involving heterolysis or homolysis
of the S-S bond to give 29 or 30, followed by recombination
of the ions 29 and PhS- or the radicals 30 and PhS · ,
respectively, to give 5a, or involving homolysis of the S-S
bond of 28 to give two radicals [PtMe2(SPh)(bipy)] · , 24, which
then recombine to form 5a (Scheme 9 and 10). For the homolytic
cleavage mechanisms, the activation energies to form 24 from

6528 Organometallics, Vol. 27, No. 24, 2008
Bonnington et al.
30 + PhS· in geometries corresponding to gas phase tight ion
pairs or radical pairs give lower energies, the most favorable
of which studied corresponds to the ion pair 29 + PhS- in which
the thiolate ion is π-stacked with the bipyridyl ligand on the
platinum cation (i.e., close to the product). In geometries closer
to the initial transition state, the radical pair structure is favored.
It is likely that solvation effects would favor the ion pair
structure in these cases but calculation of these effects is difficult
in such a complex system.19
Scheme 11. Proposed Mechanism of Binuclear Oxidative
Addition of S-S Bonds
Related Reactions and a Proposed Mechanism. Binuclear
oxidative addition reactions are well-known in ligand-bridged
binuclear precursor complexes,22-24 but they are rare in
unbridged complexes.25 Some examples with platinum(II)
precursors are shown in eqs 2 and 3. Equation 2 shows an
example with bridging ligands to anchor the binuclear unit, and
the oxidation exhibits easy electrochemical reversibility.22 The
formation of complex O from N (eq 3) can involve oxidation
by [AuCl(SMe2)] or N-chlorosuccinimide, and the reaction is
thought to occur by a 1-electron mechanism involving sequen-
tially the intermediates [ClPt(C6H4py)2]· and [ClPt(C6H4py)2-
Pt(C6H4py)2]· .25 However, oxidation of complex N with PhICl2
gives simple oxidation to [PtCl2(C6H4py)2], evidently by a polar
mechanism.23
observe CIDNP effects in NMR spectra, there are no byproduct
of the type expected from platinum radical intermediates, there
are no induction periods, and the reactions are not retarded by
traces of free radical scavengers. Although none of this
constitutes a definitive proof, the combination is strongly
indicative.14 Evidence for an ionic mechanism was obtained by
ESI-MS of reaction mixtures, in which compounds
[Pt2Me4(NN)2(Spy)(S2py2)]+, NN ) bipy or phen, were observed
in reactions leading to 3a or 3b. These are likely to be formed
by trapping of the corresponding intermediates [Pt2Me4-
(NN)2(Spy)]+ by the reagent S2py2. The ion [Pt2Me4(NN)2-
(Spy)]+ was not observed, but the most abundant ion was
[PtMe2(NN)(Spy)]+ which would be formed by cleavage of its
Pt-Pt bond. A general mechanism which is consistent with the
data is shown in Scheme 11. It is suggested, based on the data
in Schemes 8 and 10, that the activation energy for direct
reaction of [PtMe2(NN)], NN ) bipy or phen, with R2S2 is too
high to allow easy reaction.26 However, the weakly bonded
dimer [Pt2Me4(NN)2] is in easy equilibrium with [PtMe2(NN)],
and then a neighboring group effect leading to acceleration of
the reaction is possible. A similar effect has been proposed
previously for bridged binuclear complexes, but this appears to
be the first evidence for such an effect in simple mononuclear
complexes.22-25 The puzzling solvent effect on the reaction rate,
in which the reaction of 2a or 2b with S2Ph2 or S2py2 was much
faster in CD2Cl2 than in CDCl3, can be understood in terms of
this mechanism. Thus, it has been shown that electron rich
dimethylplatinum(II) complexes can interact with chloroform
through Pt · · · HCCl3 bonding and this is likely to prevent the
association between units of 2a or 2b in CDCl3 solution.27
The mechanism of reaction of the binuclear platinum(III)
complexes 3 or 5 with a disulfide to give 4 or 6 is likely to
involve radical intermediates. These reactions are faster in the
light than in the dark, and they occur with formation of
byproducts including [PtMe3(SR)(NN)] and [PtClMe3(NN)]. The
platinum centers in 3 and 5 are sterically inaccessible, so radical
attack at platinum is not possible. In the light it is possible that
homolysis of the Pt-Pt bond might occur. Otherwise, thiol
radical attack at a thiolate ligand followed by loss of disulfide
might generate the reactive intermediate [PtMe2(SR)(NN)]· and
[PtMe2(NN)]. In either case, the reactive intermediate
[PtMe2(SR)(NN)] · can abstract an RS group to give 4 or 6, or
abstract a methyl group to give [PtMe3(SR)(NN)].
There are several pieces of evidence against a free radical
mechanism in formation of the binuclear complexes 3 (Scheme
2) and 5 (Scheme 3) in dichloromethane or acetone solution at
concentrations used in monitoring by NMR. We have failed to
(22) (a) Elduque, A.; Aguilera, F.; Lahoz, F. J.; Oro, L. A.; Pinillos,
M. T. Inorg. Chim. Acta 1998, 274, 15. (b) Kirss, R. U.; Forsyth, D. A.;
Plante, M. A. J. Organomet. Chem. 2003, 688, 206. (c) Abdou, H. E.;
Mohamed, A. A.; Fackler, J. P., Jr. Inorg. Chem. 2007, 48, 9692. (d) Fackler,
J. P., Jr. Polyhedron 1997, 16, 1. (e) Fisher, J. R.; Mills, A. J.; Sumner, S.;
Brown, M. P.; Thomson, M. A.; Puddephatt, R. J.; Frew, A. A.; Monojlovic-
Muir, Lj.; Muir, K. W. Organometallics 1982, 1, 1421. (f) Azam, K. A.;
Brown, M. P.; Hill, R. H.; Puddephatt, R. J.; Yavari, A. Organometallics
1984, 3, 697.
(23) (a) Koshiyama, T.; Omura, A.; Kato, M. Chem. Lett. 2004, 33,
1386. (b) Koshiyama, T.; Kato, M. Acta Cryst. C 2005, C61, m173.
(24) The bridging must allow face-to-face orientation of the two square
planar units in order to see binuclear oxidative addition: (a) Jain, V. K.;
Jain, L. Coord. Chem. ReV. 2005, 249, 3075. (b) Scott, J. D.; Puddephatt,
R. J. Organometallics 1986, 5, 1538. (c) Scott, J. D.; Puddephatt, R. J.
Organometallics 1986, 5, 2522.
(26) The low reactivity of disulfides in oxidative addition to Vaska’s
complex has long been known: Lam, C. T.; Senoff, C. V. J. Organomet.
Chem. 1973, 57, 207.
(27) Zhang, F.; Jennings, M. C.; Puddephatt, R. J. Organometallics 2004,
23, 1396.
(25) (a) Yamaguchi, T.; Kubota, O.; Ito, T. Chem. Lett. 2004, 33, 190.
(b) Whitfield, S. R.; Sanford, M. S. Organometallics 2008, 27, 1683. (c)
Dick, A. S.; Kampf, J. W.; Sanford, M. S. Organometallics 2005, 24, 482.

OxidatiVe Addition of S-S Bonds
Organometallics, Vol. 27, No. 24, 2008 6529
Table 1. Crystal Data and Structure Refinements
complex 4b · H2O 6a
formula C12H14N2PtS2 C24H24N4OPtS2 C24H24N2PtS2 C26H24N2PtS2
1
6b
fw
T/ K
λ/Å
cryst. syst.
445.46
150(2)
643.68
150(2)
0.71073
monoclinic
Pn
599.66
300(2)
0.71073
orthorhombic monoclinic
Pnma P21/n
623.68
150(2)
0.71073
0.71073
Triclinic
j
Space gp.
P1
cell dimens.
a/Å
b/Å
c/Å
9.4800(5)
12.3371(6) 11.2501(6)
13.5806(6) 10.5571(6)
9.6789(5)
14.1299(3) 7.6899(2)
12.5587(2) 15.7816(5)
12.6883(3) 18.7901(6)
R/°
78.662(3)
70.699(3)
74.273(3)
1432.9(1)
4
2.065
10.064
17835
90
91.340(3)
90
1149.2(1)
2
1.860
6.311
13428
90
90
90
2251.6(1)
4
1.769
6.430
28275
90
96.913(2)
90
2263.8(1)
4
1.830
6.399
19085
ꢀ/°
γ/°
V/Å3
Z
dc/Mg m-3
Abs. coeff./ mm
Reflns
-1
Data/restr./param. 5044/0/311 5107/267/297 2406/0/144 3943/0/259
R1[I > 2σ(I)]
wR2[all data]
0.0474
0.1159
0.0538
0.1355
0.0345
0.0901
0.0467
0.1343
In conclusion, the oxidative addition reactions of disulfides
to platinum(II) are surprisingly complex. Most oxidative addition
reactions to dimethylplatinum(II) complexes of the type
[PtMe2(NN)], with NN ) bipy or phen, give mononuclear
platinum(IV) products, whether they occur by polar or free
radical mechanisms.9-15,28 This includes reactions of E-E
bonds with E ) O, S, Se.9-11,18 The formation of the
diplatinum(III) complexes 3 and 5 by reaction of [PtMe2(NN)]
with disulfides is therefore unusual,25,28 and most precedents
for binuclear oxidative addition involve reactions to bridged
binuclear complexes.22-25,28,29 The combination of experimental
and computational work described above suggests that the
unusual reactivity arises for the following combination of
reasons.
Figure 6. Calculated structures of complex 5a and potential
intermediates 27, 29 · PhS-, and 30 · PhS· .
addition with complexes [PtMe2(NN)] will be favored in
stepwise reactions with substrates which have intrinsically low
reactivity.
1. A concerted mechanism of oxidative addition to 16-electron
platinum(II) complexes is generally unfavorable and has a high
activation energy, unless an easy ligand dissociation or displace-
ment step can occur easily (see Scheme 6). This conclusion
applies to reactions involving many nonpolar bonds, including
H-H, C-H, C-C, N-N, O-O, and S-S bonds.17,18,28 Hence
a simple concerted oxidative addition of an S-S bond to
[PtMe2(NN)] is not favored.
Experimental Section
All reactions were carried out under nitrogen using standard
Schlenk techniques, unless otherwise specified. NMR spectra were
recorded using Varian Mercury 400 or Varian Inova 400 or 600
spectrometers. ESI mass spectra were recorded using a Micromass
LCT spectrometer, with an injection flow rate of 20 µL/min, and
were calibrated with NaI at a concentration of 2 µg/µL in 50:50
propan-2-ol/water. The injection flow rate at 20.0 µL/min was used
throughout all experiments. The complexes [Pt2Me4(µ-SMe2)2],
[PtMe2(bipy)], and [PtMe2(phen)] were prepared by the literature
methods.12
2. The activation energy for a polar (SN2) or free radical
reaction mechanism of reaction is too high to allow easy
reaction, owing to the low reactivity of disulfides in oxidative
addition (Schemes 7 and 8).26 If the first step in Scheme 7 were
possible, a simple oxidative addition would be expected, as is
observed with the more reactive diselenide reagents.9-11
[PtMe2(2-SC5H4N)2], 1. A mixture of [Pt2Me4(µ-SMe2)2] (26.1
mg, 0.045 mmol) and di-2-pyridyldisulfide (20 mg, 0.091 mmol)
3. Easy association between dimethylplatinum(II) complexes
can occur, and a neighboring group effect of the second platinum
atom leads to a much lower activation energy for oxidative
addition (Schemes 9 and 10). The bond activation step leads to
strengthening of the PtPt bond and so this bond remains intact
through to formation of the products 3 or 5. The effect of weak
association of platinum(II) complexes on spectral properties is
well-known,20 but the effect on chemical reactivity is not well
documented. This work suggests that binuclear oxidative
1
in CD2Cl2 (1 mL) was allowed to react for 10 min. The H NMR
spectrum showed formation of 1 and free SMe2 [δ(1H) ) 2.10]
only. Evaporation of the solution gave complex 1, as a yellow-
orange solid, which was crystallized from CH2Cl2/pentane. Anal.
Calc. for C12H14N2PtS2: C, 32.36; H, 3.17; N, 6.29. Found: C, 32.01;
H, 3.05; N, 6.28%. NMR in CD2Cl2: δ(1H) ) 1.51 [s, 6H, 2J(PtH)
) 76 Hz, PtMe]; 6.87 [m, 2H, H5]; 6.91 [m, 2H, H3]; 7.43 [m, 2H,
3
H4]; 8.11 [m, 2H, J(PtH) ) 21 Hz, H6]. A similar reaction was
monitored from -15 to 0 °C and showed formation of 1, SMe2
and cis-[PtMe2(SMe2)2],12 identified by resonances at δ(1H) ) 0.68
2
3
[s, 6H, J(PtH) ) 81 Hz, PtMe] and 2.39 [s, 12H, J(PtH) ) 23
Hz, SMe], at intermediate stages.
(28) (a) Rendina, L. M.; Puddephatt, R. J. Chem. ReV. 1997, 97, 1735.
(b) Hill, R. H.; Puddephatt, R. J. J. Am. Chem. Soc. 1985, 107, 1218. (c)
Jamali, S.; Nabavizadeh, S. M.; Rashidi, M. Inorg. Chem. 2005, 44, 8594.
(d) Aye, K.-T.; Canty, A. J.; Crespo, M.; Puddephatt, R. J.; Scott, J. D.;
Watson, A. A. Organometallics 1989, 8, 1518.
(29) Brown, M. P.; Fisher, J. R.; Franklin, S. J.; Puddephatt, R. J.;
Seddon, K. R. Chem. Commun. 1978, 749.
[{PtMe2(Spy)(bipy)}2], 3a, and [PtMe2(Spy)2(bipy)], 4a. To a
solution of [PtMe2(bipy)], 2a (10 mg, 0.026 mmol) in CD2Cl2 (0.5
mL) was added a solution of di-2-pyridyldisulfide (5.8 mg, 0.026
mmol) in CD2Cl2 (0.5 mL). The solution became black and a black

6530 Organometallics, Vol. 27, No. 24, 2008
Bonnington et al.
precipitate formed, which redissolved to give a yellow solution after
2 h. This solution was shown to contain a mixture of 1, free 2,2′-
bipyridine and 4a. A similar reaction was carried out at low
temperature and was monitored by 1H NMR as it warmed to room
temperature. At -10 °C, complex 2a was almost completely
consumed and the major product was 3a. After 1 h at 20 °C, the
major product was 4a, but 1 and 3a were also major products along
with free 2,2′-bipyridine. After 1 day, complex 1 and free 2,2′-
bipyridine were the major products, with only ca. 5% 4a. Both
[Pt(Spy)Me3(bipy)] and [PtClMe3(bipy)] were identified in ca. 2%
71 Hz]; 6.18 [m, 4H, SPh, Ho]; 6.19 [m, 4H, SPh, Hm]; 6.43 [m,
2H, SPh, Hp]; 7.70 [s, 2H, H5]; 7.75 [m, 2H, H3]; 8.28 [m, 2H,
H4]; 8.89 [m, 2H, 3J(PtH) ) 19 Hz, H2]. The reaction was monitored
by dissolving [PtMe2(phen)], 2b (10.7 mg, 0.026 mmol) and
PhSSPh (3.0 mg, 0.014 mmol) in CD2Cl2 (1 mL) at -60 °C, then
recording 1H NMR spectra as the solution was warmed to room
temperature. At 0 °C, the product was very largely 5b: NMR in
2
CD2Cl2: δ(1H) ) 1.32 [s, 6H, J(PtH) ) 76 Hz, PtMe]; 5.35 [m,
2H, SPh, Ho]; 5.74 [m, 2H, SPh, Hm]; 6.18 [m, 1H, SPh, Hp]; 7.07
[m, 2H, H3]; 7.34 [s, 2H, H5]; 7.76 [m, 2H, H4]; 7.99 [m, 2H, H2].
An analytical sample was prepared as above, followed by precipita-
tion with n-pentane at 0 °C. Anal. calcd for C40H38N4Pt2S2: C, 46.69;
H, 3.72; N, 5.44. Found: C, 47.04; H, 3.78; N, 5.09%.
1
yield from their characteristic H NMR spectra. 3a: δ(1H) ) 1.15
[s, 12H, 2J(PtH) ) 75 Hz, PtMe]; 6.22 [m, 2H, H3′]; 6.45 [m, 2H,
H4′]; 6.62 [m, 2H, H5′]; 7.38 [m, 2H, H6′]; 7.39 [m, 4H, H3]; 7.63
[ m, 8H, H4,5]; 8.04 [m, 4H, H6]. 4a: δ(1H) ) 1.56 [s, 6H, 2J(PtH)
) 70 Hz, PtMe]; 6.58 [m, 2H, H4′]; 6.78 [m, 2H, H3′]; 6.92 [m,
2H, H5′]; 7.62 [m, 2H, H6′]; 7.45 [m, 2H, H3]; 7.83, 7.88 [ m, each
2H, H4,5]; 8.70 [m, 2H, H6]. A similar reaction in CDCl3 was
complete in about 7 days to give 1, free 2,2′-bipyridine and several
unidentified minor products. Only complex 1 could be isolated in
pure form from this reaction.
[{PtMe2(SPh)(bipy)}2], 5a, and [PtMe2(SPh)2(bipy)], 6a
Were Prepared Similarly from Complex 2a. Complex 5a: Anal.
calcd for C36H38N4Pt2S2: C, 44.08; H, 3.90; N, 5.71. Found: C,
44.47; H, 3.80; N, 5.43%. NMR in CD2Cl2: δ(1H) ) 1.09 [s, 12H,
2J(PtH) ) 76 Hz, PtMe]; 5.87 [m, 4H, Ho]; 6.49 [m, 4H, Hm]; 6.50
[m, 2H, Hp]; 7.2-7.5 [m, 12H, H3,4,5]; 8.01 [m, 4H, H6]. Complex
6a: Anal. calcd for C24H24N2PtS2: C, 48.07; H, 4.03; N, 4.67. Found:
C, 47.81; H, 3.79; N, 4.52%.NMR in CD2Cl2: δ(1H) ) 1.50 [s,
6H, 2J(PtH) ) 71 Hz, PtMe]; 6.41 [m, 2H, SPh, Ho]; 6.50 [m, 2H,
SPh, Hm]; 6.74 [m, 1H, SPh, Hp]; 7.43 [m, 2H, H5]; 7.58 [s, 2H,
[{PtMe2(Spy)(phen)}2], 3b, and [PtMe2(Spy)2(phen)], 4b. To
a solution of [PtMe2(phen)], 2b (10.7 mg, 0.026 mmol) in CD2Cl2
(0.5 mL) was added di-2-pyridyldisulfide (5.8 mg, 0.026 mmol) in
1
3
H3]; 7.81 [m, 2H, H4]; 8.61 [m, 2H, J(PtH) ) 19 Hz, H6].
CD2Cl2 (0.5 mL) at -78 °C and H NMR spectra were recorded
as the mixture warmed to room temperature. At 0 °C complex 2b
was almost completely consumed and the major product was 3b.
After several hours at 20 °C, the major product was 4b, but 3b,
[Pt(Spy)Me3(phen)] and [PtClMe3(phen)] were also major products
along with a minor amount of 1 and free 1,10-phenanthroline. After
1 day, the solution was allowed to evaporate slowly to give 4b as
a yellow crystalline solid. Anal. calcd for C24H22N4PtS2: C, 46.07;
H, 3.54; N, 8.95. Found: C, 45.74; H, 3.32; N, 8.68%. NMR in
Structure Determinations. Data were collected using a Nonius
Kappa-CCD area detector diffractometer with COLLECT (Nonius
B.V., 1997-2002). The unit cell parameters were calculated and
refined from the full data set. Crystal cell refinement and data
reduction were carried out using HKL2000 DENZO-SMN (Otwi-
nowski and Minor, 1997). The absorption correction was applied
using HKL2000 DENZO-SMN (SCALEPACK). The SHELXTL/
PC V6.14 for Windows NT (Sheldrick, G.M., 2001) suite of
programs was used to solve the structure by direct methods.
Subsequent difference Fourier syntheses allowed the remaining
atoms to be located. All of the non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atom positions
were calculated geometrically and were included as riding on their
respective carbon atoms. The crystal data and refinement parameters
are listed in Table 1.
2
CD2Cl2: 3b: δ(1H) ) 1.40 [s, 12H, J(PtH) ) 75 Hz, PtMe]; 5.51
[m, 2H, H3′]; 6.04, 6.09 [m, each 2H, H4′,5′]; 6.84 [m, 2H, H6′];
7.12 [m, 4H, H3]; 7.40 [ s, 4H, H5]; 7.86 [m, 4H, H4]; 8.05 [m, 4H,
2
H2]. 4b: δ(1H) ) 1.72 [s, 6H, J(PtH) ) 70 Hz, PtMe]; 6.31 [m,
2H, H5′]; 6.45 [m, 2H, H3′]; 6.57 [m, 2H, H4′]; 7.22 [m, 2H, H6′];
7.63 [m, 2H, H5]; 7.65 [ m, 2H, H3]; 8.12 [m, 2H, H4]; 8.62 [m,
2
2H, H2]. [Pt(Spy)Me3(phen)]: δ(1H) ) 0.41 [s, 3H, J(PtH) ) 62
Hz, PtMe trans S]; δ(1H) ) 1.46 [s, 6H, 2J(PtH) ) 70 Hz, PtMe].
DFT Calculations. Calculations were made using the Amster-
dam Density Functional program based on the Becke-Perdew
functional, with first-order scalar relativistic corrections.30 Transition
state structures were located using a linear transit scan.17b
2
[PtClMe3(phen)]: δ(1H) ) 0.73 [s, 3H, J(PtH) ) 73 Hz, PtMe
trans Cl]; 1.44 [s, 6H, 2J(PtH) ) 70 Hz, PtMe]. In a similar reaction
in CDCl3, very little reaction occurred in 1 h at 20 °C. For a typical
ESI-MS experiment, a mixture of [PtMe2(bipy)], 2a (10 mg, 0.026
mmol) and pySSpy (5.8 mg, 0.026 mmol) were dissolved in CH2Cl2
(1 mL). Samples of the solution were injected into the ESI-MS at
ten minute intervals over a period of 100 min.
Acknowledgment. We thank NSERC (Canada) for finan-
cial support.
Supporting Information Available: X-ray data for the com-
plexes 1, 4b, 6a, and 6b. This material is available free of charge
via the Internet at http://pubs.acs.org.
[{PtMe2(SPh)(phen)}2], 5b, and [PtMe2(SPh)2(phen)], 6b. The
complex [PtMe2(phen)], 2b (100 mg, 0.247 mmol) and PhSSPh
(53.9 mg, 0.247 mmol) were dissolved in CH2Cl2 (4 mL) and stirred
overnight. The mixture became black in color with formation of a
black precipitate, which slowly redissolved to give an orange/yellow
solution. After 1 day, the solution was allowed to evaporate slowly
to give 6b as a yellow crystalline solid, which was washed with
pentane and dried under vacuum. Yield: 86.3 mg, 56%. Anal. calcd
for C26H24N2PtS2: C, 50.07; H, 3.88; N, 4.49. Found: C, 49.80; H,
3.76; N, 4.33%. NMR in CD2Cl2: δ(1H) ) 1.63 [s, 6H, 2J(PtH) )
OM800776B
(30) (a) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; van Gisbergen,
S.; Guerra, C. F.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22,
931. (b) Becke, A. Phys. ReV. A 1988, 38, 3098. (c) Ziegler, T.; Tschinke,
V.; Baerends, E. J.; Snijders, J. G.; Ravenek, W. J. Phys. Chem. 1989, 93,
3050.