Cationic thiolate and selenolate complexes of platinum(IV)

Article abstract of DOI:10.1139/v01-187

The reaction of the adamantanoid compounds [Hg₄(EPh)₆(L)₄][ClO₄]₂ (E = S or Se, L = PEt₃ or PPh₃) with [PtMe₂(bu₂bpy)] (bu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) occurs easily to give the first examples of cationic thiolate or selenolate derivatives of platinum(IV), [PtMe₂(EPh)L(bu₂bpy)][ClO₄], and the addition is shown to occur with trans stereochemistry. The new complexes are characterized by NMR spectroscopy and when L = PEt₃ by X-ray structure determinations. When L = PPh₃, a competitive reaction leads to methyl group transfer from platinum to mercury to give MeHgEPh (E = S or Se).

Full text of DOI:10.1139/v01-187

41
Cationic thiolate and selenolate complexes of
platinum(IV)
Michael C. Janzen, Michael C. Jennings, and Richard J. Puddephatt
Abstract: The reaction of the adamantanoid compounds [Hg4(EPh)6(L)4][ClO4]2 (E = S or Se, L = PEt3 or PPh3) with
[PtMe2(bu2bpy)] (bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) occurs easily to give the first examples of cationic thiolate
or selenolate derivatives of platinum(IV), [PtMe2(EPh)L(bu2bpy)][ClO4], and the addition is shown to occur with trans
stereochemistry. The new complexes are characterized by NMR spectroscopy and when L = PEt3 by X-ray structure
determinations. When L = PPh3, a competitive reaction leads to methyl group transfer from platinum to mercury to
give MeHgEPh (E = S or Se).
Key words: oxidative-addition, platinum, thiolate, selenolate, mercury.
Résumé : La réaction de composés adamantanoïdes [Hg4(EPh)6(L)4][ClO4]2 (E= S ou Se, L = PEt3 ou PPh3) avec
[PtMe2(bu2bpy)] (bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) se produit facilement pour fournier les premiers exemples
de dérivés thiolates ou sélénolates cationiques du platine(IV), [PtMe2(EPh)L(bu2bpy)][ClO4] et on a observé que
l’addition se produit avec une stéréochimie trans. Les nouveaux complexes ont été caractérisés par spectroscopie RMN
et, lorsque L = PEt3, par diffraction des rayons X. Lorsque L = PPh3, une réaction parallèle conduit à un transfert de
groupe méthyle à partir du platine vers le mercure pour donner le MeHgEPh (E = S ou Se).
Mots clés : addition oxydante, platine, thiolate, sélénolate, mercure.
[Traduit par la Rédaction] Janzen et al. 45
Introduction
Hg(II)—E bonds of the adamantanoid compounds
[Hg4(EPh)6(L)4][ClO4]2 (2a–d) (Chart 1), might give novel
cage complexes containing platinum(IV) centres (4, 5).
It was found that the reactions of 1 with compounds 2a–d
occurred easily but with fragmentation of the adamantanoid
units to give the first cationic thiolato or selenelato com-
plexes of platinum(IV), as described below. The SE– ligand
(E = S or Se) is reducing in nature and tends to form stable
complexes with platinum(II) rather than platinum(IV) (6).
Since cationic platinum(IV) complexes are more easily re-
duced than neutral ones, it is not surprising that the known
thiolate or selenolate derivatives of platinum(IV) are all neu-
tral (7). However, it will be seen that cationic REPt(IV)
complexes can be prepared and that they may have good
thermal stability.
There is a rich chemistry resulting from reactions of
Hg—X bonds from mercury(II) compounds to the organo-
platinum(II) centres in complexes [PtMe2L2] and related
compounds (1, 2). For example, oxidative addition of HgX2 to
[PtMe2(bu2bpy)] (bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine)
(1) gives [PtMe2(HgX)(X)(bu2bpy)] (X = Cl, Br, O2CCF3) (1).
However, if the platinum(II) centre is less electron rich or the
mercury centre is less electrophilic, the reaction may occur to
give a platinum–mercury donor–acceptor bond. This form of re-
activity is observed with [Pt{CH2C6H4P(o-tolyl)2}(S2CNMe2)]
and HgX2 (X = Br, I) and for the reaction of 1 with
[PtMe2(HgX)(X)(bu2bpy)] (X = Cl, Br, O2CCF3) (2). Further
reactions of these products can occur to give overall alkyl–
halide exchange reactions, with the formation of [PtXMeL2]
and MeHgX (1g). No reactions involving Hg(II)—E (E =
S, Se) bonds with organoplatinum(II) complexes have yet
been reported. It is known that oxidative addition of the
Sn(IV)—E bonds in the ring compounds [(R2SnE)3] (R =
Me, Ph) to complex 1 occurs easily, giving interesting plati-
num(IV) complexes containing PtESnESn rings (3). By anal-
ogy, it was considered possible that oxidative addition of the
Results
The reaction of complex 1 with [Hg4(EPh)6(L)4][ClO4]2
(2) appeared to occur mostly according to eq. [1].
[1]
[PtMe2(bu2bpy)] (1) + 0.5[Hg4(EPh)6L4][ClO4]2 (2)
→ [PtMe2(EPh)L(bu2bpy)][ClO4] (3)
+ Hg(EPh)2L + Hg(0)
Received 10 August 2001. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 10 January 2002.
For example, when L = PEt3, a mixture of products
was formed from which the corresponding complex
[PtMe2(EPh)(PEt3)(bu2bpy)][ClO4] (E = S (3a) or Se (3b))
could be crystallized as an air-stable yellow solid. The other
products from the reaction were not isolated in pure form
and the identity of the proposed product Hg(EPh)2L (eq. [1])
remains uncertain, as discussed below.
M.C. Janzen, M.C. Jennings, and R.J. Puddephatt.1
Department of Chemistry, University of Western Ontario,
London, ON N6A 5B7, Canada.
1Corresponding author (telephone: (519) 661-2111, ext.
86336; fax: (519) 661-3022; e-mail: pudd@uwo.ca).
Can. J. Chem. 80: 41–45 (2002)
DOI: 10.1139/V01-187
© 2002 NRC Canada

42
Can. J. Chem. Vol. 80, 2002
Fig. 1. A view of the molecular structure of complex 3a roughly
down the S—Pt bond, showing the orientation of the phenyl group
with respect to the bu2bpy ligand. Only one component of each of
the disordered ethylphosphorus groups is shown for clarity.
Fig. 2. A view of the molecular structure of complex 3b. Only
one component of each of the disordered ethyl and phenyl
groups is shown for clarity.
1H NMR spectrum due to the EPh protons appear over the
range δ = 6.25–6.52 and are lower in chemical shift than is
normal for aryl protons, probably because they lie in the
shielding region of the aromatic bu2bipy ligand (7). The
NMR data has thus defined a structure with the phosphine
ligand trans to the EPh group at platinum(IV). The spectra
for complex 3b are similar and are listed in the Experimen-
tal section.
Chart 1. NN = bu2bpy.
The structures of 3a and 3b were determined crystallo-
graphically and are shown in Figs. 1 and 2, respectively,
with relevant bond parameters listed in Table 1. The two
compounds are isomorphous and have similar structures,
with the EPh and PEt3 ligands mutually trans at plati-
num(IV). In each complex, the phenyl substituent of the EPh
ligand is oriented above the bipyridyl ligand. This leads to
π-stacking (11) with intercentroid distances between the
phenyl and N(1) pyridyl ring of 3.81 Å for 3a and 3.64 Å
for 3b and between the phenyl and N(12) pyridyl ring of
4.04 Å for 3a and 4.45 Å for 3b. The Pt—P bond lengths are
2.315(5) and 2.291(4) Å for complexes 3a and 3b, respec-
tively; comparison with other phosphine complexes of plati-
num(IV) (12) suggests that these distances are relatively
short and, therefore, the EPh ligand has only a moderate
trans influence. The slightly longer Pt—P bond in 3a as
compared to 3b may indicate that the SPh ligand has a mar-
ginally higher trans-influence than SePh. In 3a, the Pt—S
bond distance of 2.398(5) Å and the Pt-S-C angle of
108.9(8)° are unexceptional. The only other structurally char-
acterized arylthiolate complex of platinum(IV) with a two-
coordinate sulfur atom is [(η5-C5Me5)PtMe2(S-p-C6H4Me)],
which has Pt—S = 2.344(1) Å and Pt-S-C = 108.4(2)° (13),
very similar to the corresponding values in 3a. The cubane
complex [{PtMe3(µ3-SPh)}4], which contains four-
coordinate sulfur atoms with sulfur trans to methyl, has a
longer Pt—S = 2.506(5) Å and a more open angle Pt-S-C =
118.1(7)° (14). Several arylthiolate complexes of plati-
num(II) with two-coordinate sulfur atoms have been struc-
turally characterized, and the bond parameters for the Pt-S-C
units are similar to those for complex 3a (15). In complex
Complexes 3a and 3b were characterized spectroscopi-
cally and crystallographically. The H NMR spectrum of 3a
1
contained a single methylplatinum resonance, with the cou-
pling constant (2JPt,Me = 66 Hz) in the range expected for
methylplatinum(IV) complexes with methyl trans to nitro-
gen (8). The presence of a single methylplatinum resonance
indicates that the product is formed by trans oxidative addi-
tion and so supports the structure shown in Chart 1. The mir-
ror symmetry (Cs) of 3a is also shown by the presence of
only three aromatic bu2bpy peaks and one tert-butyl peak in
the 1H NMR spectrum. The presence of the triethyl-
phosphine ligand is shown in the 31P NMR spectrum of 3a
by the presence of a singlet resonance at δ = 0.29, with satel-
1
lites due to the coupling (1JPt,P = 1895 Hz) and in the H
NMR spectrum by the observation of coupling to the
methylplatinum protons with 3JP,Pt,Me = 5 Hz. The magnitude
of the coupling constant (1JPt,P = 1895 Hz) is consistent with
the phosphine being trans to EPh, but is too high for a phos-
phine trans to a methyl group (9, 10). The resonances in the
© 2002 NRC Canada

Janzen et al.
Table 1. Selected bond distances (Å) and an-
43
Table 2. Crystal data and experimental details.
gles (°) for complexes 3a and 3b.
Complex
3a·CH2Cl2
3b·CH2Cl2
3a (E = S)
3b (E = Se)
Empirical formula
FW
C33H52Cl3N2O4PSPt
890.12
C33H52Cl3N2O4SePt
952.14
Bond distances (Å)
Pt—P
Pt—E
2.315(5)
2.398(5)
2.14(1)
2.16(1)
2.13(2)
2.05(2)
2.291(4)
2.512(2)
2.13(1)
2.12(1)
2.10(2)
2.10(1)
T (K)
λ (Å)
Space group
a (Å)
b (Å)
c (Å)
β (°)
V (Å3)
200
0.71073
P21
13.4447(6)
8.0461(4)
18.9052(9)
109.443(3)
1928.5(2)
2
1.533
3.977
882
0.1054
200
0.71073
P21
13.3754(4)
8.1982(3)
18.9704(6)
109.970(1)
1955.1(1)
2
1.617
4.801
948
0.0442
Pt—N(1)
Pt—N(12)
Pt—C(21)
Pt—C(22)
Bond angles (°)
P-Pt-E
176.7(2)
108.9(8)
174.9(1)
106.1(8)
C-E-Pt
Z
Dcalcd. (g cm–3)
µ (mm–1)
F(000)
Scheme 1. NN = bu2bpy.
R1 [I > 2σ (I)]a
wR2 [I > 2σ (I)]a
0.2691
0.1125
aR1 = Σ||Fo| – |Fc||)/Σ|Fo|; wR2 = [Σw(Fo2 – Fo2)2/ΣwFo4]1/2
.
identified as the major product, but several mercury(II)
phosphine complexes appeared to be formed as indicated by
several singlet resonances in the range δ = 5–24 in the 31P
NMR spectrum.
The reaction of 1 and the triphenylphosphine derivatives
[Hg4(EPh)6L4][ClO4]2 (L = PPh3; E = S (2c) or Se (2d)) were
somewhat more complex. Again, the complexes
[PtMe2(EPh)L(bu2bpy)][ClO4] (E = S (3c) or Se (3d)) were
isolated as yellow solids. They were readily characterized by
1
comparison of their H and 31P NMR spectra with those of
the structurally characterized complexes 3a and 3b. When the
reaction of 1 with 2c was monitored by NMR spectroscopy,
complex 3c was identified as one major product. In addition,
the 31P spectrum contained a resonance at δ = 26.2 (1JP,Hg
=
1
3215 Hz) tentatively assigned to Hg(SPh)2(PPh3). In the H
NMR spectrum, the known methylmercury(II) compound
MeHgSPh was readily identified (17), present at about half
the concentration of 3c. A similar reaction of 1 with 2d gave
3b, the distance Pt—Se = 2.512(2) Å and angle Pt-Se-C =
106.1(9)° are similar to those in the known neutral Pt(IV)–
SePh complexes. For example, corresponding parameters are
[PtMe2(SePh)2(phen)] (2.4896(9) Å, 103.7(2)°) (7) and
[PtMe2(SePh)2(bpy)] (2.478(1) Å, 2.498(1) Å, 103.4(4)°,
103.1(3)°) (7).
complex 3d and a compound having δ (31P) = 29.2 (1JP,Hg
=
3177 Hz), tentatively identified as Hg(SePh)2(PPh3), while
MeHgSePh was identified by its H NMR spectrum (18).
1
The stoichiometry of these reactions can be understood by
considering that the adamantanoid mercury(II) complexes
(2) react as if they were comprised of two components:
[Hg4(EPh)6L4][ClO4]2 = 2[PhEHgL][ClO4] + 2[Hg(EPh)2L]
(Scheme 1). The major product 3 is formed by oxidative ad-
dition of the fragment [PhEHgL][ClO4] to 1 with loss of
mercury metal. It is not known at which stage the mercury
atom is extruded, or even at what stage the adamantane de-
rivative fragments, but Scheme 1 shows one possible route.
The oxidative addition probably occurs by a polar mecha-
nism initiated by nucleophilic attack of the electron-rich
platinum(II) centre of complex 1 to the electrophilic mer-
cury(II), leading to the observed trans addition in the prod-
uct complex 3. There are several precedent-setting examples
for the loss of mercury(0) from Pt–Hg bonded compounds,
such as the reaction of trans-[(2-Me2NCH2C6H4)2Pt] with
Hg(O2CMe)2 to yield [(2-Me2NCH2C6H4)2Pt(O2CMe)2] and
Hg(0) (19).
The reaction of complex 1 with [Hg4(SPh)6(PEt3)4][ClO4]2
1
(2a) was monitored by H and 31P NMR spectroscopy in an
attempt to identify the other products of eq. [1]. Complex 3a
was readily identified as a major product (ca. 75% based on
1), and it was shown that one equivalent of 2a consumed at
least 2 equivalents of 1 as required by eq. [1]. A second ma-
jor product was identified by a resonance in the 31P NMR
spectrum at δ = 16.7, with satellites due to the coupling
(1JP,Hg = 2817 Hz). It is tentatively suggested that this com-
plex is Hg(SPh)2(PEt3) (eq. [1]), but it was not possible to
isolate it in pure form to carry out further characterization. If
the formulation is correct, it is likely to form a dimer or
oligomer by forming Hg2(µ-SR) bridges (4, 16). The forma-
tion of trace amounts of metallic mercury was visually evi-
dent. In a similar reaction of 1 with 2b, complex 3b was
© 2002 NRC Canada

44
Can. J. Chem. Vol. 80, 2002
The minor product MeHgEPh formed in the reactions of 1
7 Hz, JP,H = 7 Hz, 6H, -CH2), 0.81 (m, JH,H = 7 Hz, JP,H =
with 2c and 2d is likely to be formed by the competing oxi-
dative-addition reaction of complex 1 with the fragment
[Hg(EPh)2L] to give intermediate 4 (Scheme 1), which can
undergo reductive elimination to yield MeHgEPh and
[PtMe(EPh)(bu2bpy)] (5). Complex 5 would then react with
more 2 to give additional MeHgEPh. The formed complexes
(3) are thermally stable, and therefore, cannot be the source
of formation of MeHgEPh.
Clearly these reactions are more complex than was envis-
aged and they did not yield the anticipated platinum–mer-
cury-bonded cage complexes. Nevertheless, they do give a
simple route to the first cationic thiolate and selenolate com-
plexes of platinum(IV), and it is shown that these com-
pounds are both air-stable and thermally stable.
8 Hz, 9H, -CH3). 31P NMR δ: –5.83 (s, 1JPt,P = 1966 Hz, P-Pt).
Anal. calcd. for C32H50ClN2O4PSePt·CH2Cl2: C 41.68,
H 5.50, N 2.94; found: C 41.55, H 5.41, N 2.84. Crystals
were grown as described for 3a.
[(PtMe2(SPh)(PPh3)(bu2bpy)][ClO4] (3c)
This was prepared similarly except that 2c was used in-
stead of 2a. Yield: 43%. 1H NMR (CD2Cl2) δ: 7.88 (d,
3
3
4J3,5 = 2 Hz, 2H, H3), 7.85 (d, J6,5 = 6 Hz, JPt,H6 = 15 Hz,
2H, H6), 7.46–7.00 (m, 15H, C6H5), 6.61–6.30 (m, 5H,
SC6H5), 1.71 (d, 3JP,Me = 5 Hz, 2JPt,H = 65 Hz, 6H, Pt-Me), 1.43
1
(s, 18H, t-Bu). 31P NMR δ: –0.2 (s, JPt,P = 1802 Hz, P-Pt).
Anal. calcd. for C44H50ClN2O4PSPt: C 54.80, H 5.23,
N 2.90; found: C 54.71, H 5.19, N 2.80.
[(PtMe2(SePh)(PPh3)(bu2bpy)][ClO4] (3d)
This was prepared similarly except that 2d was used in-
Experimental
stead of 2a. Yield: 39%. 1H NMR (CD2Cl2) δ: 7.93 (d,
3
3
4J3,5 = 2 Hz, 2H, H3), 7.81 (d, J6,5 = 6 Hz, JPt,H6 = 14 Hz,
General
NMR spectra were recorded by using a Varian 300 MHz
spectrometer. Chemical shifts are reported with respect to
TMS (1H) or external H3PO4 (31P) references. Solvents were
dried and freshly distilled prior to use. Complexes 2 (4) and
[PtMe2(bu2bpy)] (20) were prepared according to the litera-
ture procedures. CAUTION: toxic methylmercury com-
pounds are formed in some reactions; appropriate
precautions should be taken.
2H, H6), 7.50–6.95 (m, 15H, C6H5), 6.53–6.20 (m, 5H,
3
2
SeC6H5), 1.75 (d, JP,Me = 5 Hz, JPt,H = 66 Hz, 6H, Pt-Me),
1.44 (s, 18H, t-Bu). 31P NMR δ: –3.6 (s, 1JPt,P = 1860 Hz, P-Pt).
Anal. calcd. for C44H50ClN2O4PSePt: C 52.25, H 4.98,
N 2.77; found: C 52.07, H 4.79, N 2.69.
X-ray structure determinations
Crystals of 3a and 3b, as perchlorate salts, were mounted
on glass fibres. Data were collected using a Nonius Kappa-
CCD diffractometer using COLLECT software (21a). Crys-
tal cell refinement and data reduction were carried out using
the Nonius DENZO package (21a). The data were scaled us-
ing SCALEPACK (21a) and no other absorption corrections
were applied. The SHEXTL 5.1 program was used to solve
the structure by direct methods, followed by successive dif-
ference Fouriers (21b). Crystallographic details are listed in
Table 2.2 The two compounds are isomorphous, each crystal-
lizing in space group P21 with one molecule of CH2Cl2 of
solvation. For complex 3a, two of the ethyl groups on the
phosphorus atom were modeled as isotropic, half occupancy
moieties. Only one of each disordered ethyl group is shown
in Fig. 1 for clarity. The third ethyl group was also kept iso-
tropic. For complex 3b, the phenyl ring attached to the sele-
nium atom was modeled as two half-occupancy rings with
isotropic carbon atoms. Two of the ethyl groups on the phos-
phorus atom were also modeled as isotropic, half-occupancy
moieties. In Fig. 2 only one of each disordered group is
shown for clarity. In both compounds, there was disorder of
the CH2Cl2 molecule and of the ClO−4 anion, and they were
modeled with geometrical constraints.
[(PtMe2(SPh)(PEt3)(bu2bpy)][ClO4] (3a)
A mixture of [PtMe2(bu2bpy)] (80 mg, 0.162 mmol) and
2a (133 mg, 0.162 mmol) was dissolved in CH2Cl2 (5 mL)
and the mixture was stirred for 10 min. The yellow solution
was filtered through dry Celite, and pentane (40 mL) was
added to the filtrate to precipitate the product as a yellow
microcrystalline solid, which was isolated by filtration,
1
washed with pentane, and dried in vacuo. Yield: 58%. H
3
3
NMR (CD2Cl2) δ: 8.56 (d, J6,5 = 6 Hz, JPt,H6 = 14 Hz, 2H,
4
3
H6), 7.95 (d, J3,5 = 2 Hz, 2H, H3), 7.70 (dd, J5,6 = 6 Hz,
3J5,3 = 2 Hz, 2H, H5), 6.52–6.25 (m, 5H, C6H5), 1.42 (d,
3JP,Me = 5 Hz, 2JPt,H = 66 Hz, 6H, Pt-Me), 1.46 (s, 18H, t-Bu),
1.38 (m, JH,H = 8 Hz, JP,H = 8 Hz, 6H, CH2), 0.81 (m, JH,H
=
=
1
8 Hz, JP,H = 8 Hz, 9H, CH3). 31P NMR δ: –2.7 (s, JPt,P
1976 Hz, P-Pt). Anal. calcd. for C32H50ClN2O4PSPt·CH2Cl2:
C 43.78, H 5.79, N 3.09; found: C 43.88, H 5.83, N 2.99.
Crystals suitable for X-ray crystallographic study were
grown over a period of several days by slow diffusion of
pentane into a CH2Cl2 solution at 22°C.
[(PtMe2(SePh)(PEt3)(bu2bpy)][ClO4] (3b)
This complex was prepared similarly, except that 2b was
1
used instead of 2a. Yield: 52%. H NMR (CD2Cl2) δ: 8.52
Acknowledgments
3
3
4
(d, J6,5 = 6 Hz, JPt,H6 = 14 Hz, 2H, H6), 8.05 (d, J3,5
=
3
3
2 Hz, 2H, H3), 7.59 (dd, J5,6 = 6 Hz, J5,3 = 2 Hz, 2H, H5),
6.85–6.42 (m, 5H, C6H5), 1.52 (d, JP,Me = 5 Hz, JPt,H
65 Hz, 6H, Pt-Me), 1.46 (s, 18H, t-Bu), 1.38 (m, JH,H
We thank the NSERC (Canada) for financial support and
for a scholarship to MCJ. RJP thanks the Government of
Canada for a Canada Research Chair. Thanks are given to
3
2
=
=
2 Supplementary material may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada. For information on obtaining material electronically go to http://www.nrc.ca/cisti/irm/unpub_e.shtml.
Crystallographic information has also been deposited with the Cambridge Crystallographic Data Centre (CCDC Nos. 168359–168360).
Copies of the data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk)
© 2002 NRC Canada

Janzen et al.
45
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Prof. P.A.W. Dean for a generous gift of samples of com-
plexes 2 and for helpful discussions.
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