Further studies on the dialkylation chemistry of [Pt2(μ-S) 2(PPh3)4] with activated alkyl halides RC(O)CH2X (X = Cl, Br)

Article abstract of DOI:10.1016/j.ica.2011.06.023

Further studies have been carried out into the reactivity of [Pt ₂(μ-S)₂(PPh₃)₄] towards a range of activated alkylating agents of the type RC(O)CH₂X (R = organic moiety, e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of both sulfide centers is observed for PhC(O)CH₂Br, 3-(bromoacetyl)coumarin [CouC(O)CH ₂Br], and 1-(bromoacetyl)pyrene [PyrC(O)CH₂Br], giving dications [Pt₂{μ-SCH₂C(O)R}₂(PPh ₃)₄]²⁺, isolated as their PF₆ ^- salts. The X-ray structure of [Pt₂{μ-SCH ₂C(O)Ph}₂(PPh₃)₄](PF ₆)₂ shows the presence of short Pt...O contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH ₂Cl] and imino analogues [e.g. PhC(NOH)CH₂Br] do not dialkylate [Pt₂(μ-S)₂(PPh₃)₄]. The ability of PhC(O)CH₂Br to dialkylate [Pt₂(μ-S) ₂(PPh₃)₄] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt₂{μ-SCH ₂C(O)Ph}(μ-SR)(PPh₃)₄]²⁺ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated compounds [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (from [Pt₂(μ-S)₂(PPh₃)₄] and excess RBr). In these heterodialkylated systems ligand replacement of PPh₃ occurs by the bromide ions in the reaction mixture forming monocations [Pt ₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃) ₃Br]⁺. This ligand substitution can be easily suppressed by addition of PPh₃ to the reaction mixture. The complex [Pt ₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃) ₄]²⁺ was crystallographically characterized. X-ray crystal structures of the bromide-containing complexes [Pt₂{μ-SCH ₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺ (R = Et, Bu) are also reported. In both structures the coordinated bromide is trans to the SCH₂C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt₂{μ-SCH ₂C(O)Ph}₂(PPh₃)₄]²⁺ and [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃) ₄]²⁺ (and many other known analogues) where both alkyl groups adopt axial positions.

Full text of DOI:10.1016/j.ica.2011.06.023

Inorganica Chimica Acta 376 (2011) 255–263
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Inorganica Chimica Acta
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Further studies on the dialkylation chemistry of [Pt2(
l-S)2(PPh3)4]
with activated alkyl halides RC(O)CH2X (X = Cl, Br)
a
b
Oguejiofo T. Ujam a, William Henderson a, , Brian K. Nicholson , T.S. Andy Hor
⇑
a Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
b Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
Further studies have been carried out into the reactivity of [Pt2(l-S)2(PPh3)4] towards a range of activated
alkylating agents of the type RC(O)CH2X (R = organic moiety, e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of
Received 21 April 2011
Accepted 10 June 2011
Available online 21 June 2011
both sulfide centers is observed for PhC(O)CH2Br, 3-(bromoacetyl)coumarin [CouC(O)CH2Br], and 1-
(bromoacetyl)pyrene [PyrC(O)CH2Br], giving dications [Pt2{
l
-SCH2C(O)R}2(PPh3)4]2+, isolated as their
ꢀ
PF6 salts. The X-ray structure of [Pt2{
l-SCH2C(O)Ph}2(PPh3)4](PF6)2 shows the presence of short Ptꢁ ꢁ ꢁO
Keywords:
contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH2Cl] and imino ana-
logues [e.g. PhC(NOH)CH2Br] do not dialkylate [Pt2( -S)2(PPh3)4]. The ability of PhC(O)CH2Br to dialkylate
[Pt2( -S)2(PPh3)4] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt2{
SCH2C(O)Ph}(
-SR)(PPh3)4]2+ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated
compounds [Pt2( -S)( -S)2(PPh3)4] and excess RBr). In these heterodialkylated
-SR)(PPh3)4]+ (from [Pt2(
systems ligand replacement of PPh3 occurs by the bromide ions in the reaction mixture forming
monocations [Pt2{ -SCH2C(O)Ph}(
-SR)(PPh3)3Br]+. This ligand substitution can be easily suppressed
by addition of PPh3 to the reaction mixture. The complex [Pt2{ -SCH2C(O)Ph}(
-SBu)(PPh3)4]2+ was crys-
tallographically characterized. X-ray crystal structures of the bromide-containing complexes [Pt2{
SCH2C(O)Ph}(
-SR)(PPh3)3Br]+ (R = Et, Bu) are also reported. In both structures the coordinated bromide
is trans to the SCH2C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents
adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt2{
SCH2C(O)Ph}2(PPh3)4]2+ and [Pt2{ -SBu)(PPh3)4]2+ (and many other known analogues)
-SCH2C(O)Ph}(
where both alkyl groups adopt axial positions.
Dinuclear platinum complexes
Thiolate complexes
Alkylation reactions
Ligand substitution
Electrospray ionization mass spectrometry
X-ray crystal structures
l
l
l-
l
l
l
l
l
l
l
l
l
-
l
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-
l
l
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
agents produce either monoalkylated, cyclized or bridged products
depending on the alkylating agent and experimental conditions
[24–26], including the use of high-pressure syntheses [27]. Of par-
ticular note is the ability to stepwise introduce two different or-
ganic groups on the {Pt2S2} core, resulting in the formation of
Since the early discoveries of the nucleophilic nature of the plat-
inum(II) sulfide complex [Pt2(l-S)2(PPh3)4] 1 [1–4] there have been
extensive studies into the chemistry of this versatile complex and
analogous complexes with {Pt2S2} [5–7], {Pt2Se2} [8] and {Pd2S2}
[9,10] cores. There is particular interest in the alkylation [11–16]
and arylation [17,18] chemistry of {Pt2S2} complexes, and the
alkylation of {Pt2Se2} complexes [19,20], because of the significant
potential to synthesize novel thiolate (or selenolate) complexes
using suitable organic electrophiles. The products formed with or-
ganic electrophiles are very much dependent on the nature of the
electrophile. For simple monofunctional electrophiles, alkylation of
one sulfide center is most common [21,22], but dialkylation can
also occur, depending on the strength of the alkylating agent and
the ancillary phosphine ligand on the {Pt2S2} core [23]. Dialkylating
dinuclear mixed-thiolate complexes [Pt2(
not easily accessible by other routes [28]. However, the alkylation
of a monocationic [Pt2( -S)(
-SR)(PPh3)4]+ complex requires a
l l
-SR1)( -SR2)(PPh3)4]2+
l
l
powerful alkylating agent (Me2SO4) that generates a non-nucleo-
philic anion (MeSO4ꢀ) due to the susceptibility of the dications
[Pt2(l l
-SR1)( -SR2)(PPh3)4]2+ to nucleophilic attack by anions such
as iodide (generated from alkyl iodide electrophiles) [14]. The
use of diphosphines and high-pressure conditions does allow
heterodialkylation with a range of substrates, but such conditions
are not necessarily convenient [29].
We wished to extend the heterodialkylation methodology more
widely, as well as better understand the factors that promote dial-
kylation, and in this paper we report on further studies on the dial-
kylation chemistry of [Pt2(
the type RC(O)CH2X (X = Cl or Br).
l-S)2(PPh3)4] 1 towards electrophiles of
⇑
Corresponding author. Fax: +64 7 838 4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.023

256
O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
(
l
-SBu)(PPh3)4]2+ (m/z 839, 19%), [Pt2{
(PPh3)3-H]+ (m/z 1415, 90%), [Pt2{
-SCH2C(O)Ph}(
Br]+ 10 (m/z 1497, 40%), and [Pt2( -SBu)(PPh3)4]+ (m/z 1560,
-S)(
100%). The species [Pt2{ -SCH2C(O)Ph}(
-SBu)(PPh3)3-H]+ might
be formed by deprotonation of the C(O)CH2 group. After stirring
l
-SCH2C(O)Ph}(
l-SBu)-
2. Results and discussion
l
l-SBu)(PPh3)3
l
l
Previously it has been found that reaction of [Pt2(l-S)2(PPh3)4]
l
l
1 with PhC(O)CH2Cl yields the monoalkylated complex [Pt2(
l-
S){l
-SCH2C(O)Ph}(PPh3)4]+ 2 [22]. Reaction of 1 with a large excess
for 48 h, the bromide-substituted complex [Pt2{l-SCH2C(O)Ph}(l-
(10 mol equivalents) of PhC(O)CH2Cl in methanol, initially stirred
at room temperature for 48 h and then refluxed for 24 h, did not
result in dialkylation, with the monoalkylated product only being
recovered. However, reaction of 1 with a large excess of the corre-
sponding bromide PhC(O)CH2Br at room temperature proceeded
much more rapidly, giving complete conversion to the monoalky-
lated complex in less than 5 min, followed by a somewhat slower
SBu)(PPh3)3Br]+ was the major species, and was isolated as its
hexafluorophosphate salt 10ꢁPF6 by addition of excess NH4PF6. A
similar result was obtained from the in situ-generated [Pt2(l-
S)(l l-SCH2C(O)Ph}(l-SEt)-
-SEt)(PPh3)4]+, which yielded [Pt2{
(PPh3)3Br]PF6 11ꢁPF6 on reaction with excess PhC(O)CH2Br and
precipitation with NH4PF6. The order of alkylation is important; to
generate the heterodialkylated complexes it is necessary to retain
the strongest alkylating agent for alkylation of the monoalkylated
conversion to the dialkylated complex [Pt2{
(PPh3)4]2+ 3. The rate of alkylation of the free sulfide in monoalky-
lated complexes [Pt2( -S)(
-SR)(PPh3)4]+ is notably slower than
l-SCH2C(O)Ph}2-
intermediate. Thus attempted reaction of [Pt2(
l-S){l-SCH2C(O)Ph}-
l
l
(PPh3)4]+ with EtBr or BuBr gave no reaction.
the alkylation of 1 itself, due to the positive charge on the complex
and steric shielding of the residual free sulfide ligand. Positive ion
ESI mass spectrometry was used as a convenient technique for
monitoring the progress of the alkylation reactions, with the
monoalkylated and dialkylated cations giving distinctive peaks at
m/z 1621 and 870, respectively. The complex was isolated as its
hexafluorophosphate salt 3ꢁ(PF6)2 by addition of excess NH4PF6
to the reaction mixture. It is noteworthy that in the synthesis of
this complex there was no indication of any secondary product
formed by ligand substitution of PPh3 by bromide, as is seen in
other related systems (vide infra). Consistent with its symmetric
nature, complex 3ꢁ(PF6)2 has a single resonance in its 31P{1H}
NMR spectrum at d 20.1 showing 1J(PtP) coupling of 3128 Hz.
Other RC(O)CH2Br compounds also effected dialkylation of 1. 1-
The displacement of PPh3 by bromide is promoted by the dicat-
ionic nature of the thiolate complexes, which makes them suscep-
tible to nucleophilic attack by bromide,
nucleophile with a reasonable affinity for platinum(II). However
it is noteworthy that this secondary reaction occurs for [Pt2{
a moderately good
l-
SCH2C(O)Ph}(l l-SCH2C(O)Ph}2-
-SBu)(PPh3)4]2+ 8, but not for [Pt2{
(PPh3)4]2+ 3, which is probably related to the significantly smaller
size of ethyl and butyl groups which allows the incoming bromide
nucleophile an easier pathway to attack the electrophilic platinum
center. This is supported by X-ray crystal structure determinations
(vide infra).
In order to suppress the loss of triphenylphosphine to enable
isolation of the [Pt2{l-SCH2C(O)Ph}(l
-SR)(PPh3)4]2+ (R = Et, Bu)
cations 8 and 9, the syntheses were repeated with the addition
(Bromoacetyl)pyrene, PyrC(O)CH2Br 4 formed [Pt2{l-SCH2C(O)-
Pyr}2(PPh3)4]2+ 5 (m/z 996) after stirring for 7 days; the reduced
reactivity in this case is expected to be due to the greater steric
bulk of the pyrene group compared to a single phenyl ring. An
additional minor ion at m/z 1748 in this reaction mixture is from
of 1 mol equivalent of PPh3 following formation of the ions
[Pt2{
version to the [Pt2{
l-SCH2C(O)Ph}(l
-SR)(PPh3)3Br]+. This resulted in good con-
l
-SCH2C(O)Ph}(l
-SR)(PPh3)4]2+ ions which
were isolated as hexafluorophosphate salts 8ꢁ(PF6)2 and 9ꢁ(PF6)2.
The reactivityof some related imine-containing alkylating agents
of the type RC(@NR0)CH2X (X = Cl, Br) towards 1 was also studied.
However, these were incapable of dialkylating 1 under the condi-
tions investigated, and therefore contrast markedly with
RC(O)CH2Br, which readily dialkylate 1. For example, under rela-
tively forcing reaction conditions (methanol reflux, 24 h), the oxime
PhC(@NOH)CH2Br only monoalkylated 1, giving the previously re-
the monoalkylated complex [Pt2(
3-(Bromoacetyl)coumarin, CouC(O)CH2Br 6 reacted with 1 to form
predominantly [Pt2{
-SCH2C(O)Cou}2(PPh3)4]2+ 7 (m/z 939) after
7 days at room temperature, together with about 5% of the mono-
alkylated product [Pt2( -S){
-SCH2C(O)Cou}(PPh3)4]+ (m/z 1697).
l-S){l
-SCH2C(O)Pyr}(PPh3)4]+.
l
l
l
Prolonged reaction (to try and drive the reaction to completion) re-
sulted in significant decomposition occurring. Several attempts at
repeating the reaction to obtain a purer product gave similar re-
sults, but with different impurity species, presumably due to vari-
ous secondary reactions. Complexes 5 and 7 were isolated as their
hexafluorophosphate salts 5ꢁ(PF6)2 and 7ꢁ(PF6)2 by addition of ex-
cess NH4PF6 to the reaction mixtures. While 7ꢁ(PF6)2 gave satisfac-
tory elemental microanalyses, the sample was impure, as shown
by ESI MS and 31P NMR.
ported cation [Pt2(l-S){l
-SCH2C(@NOH)Ph}(PPh3)4]+ [22]. In this
case, the lower electron-withdrawing effect of the oxime group
(compared to a carbonyl in PhC(O)CH2Br) makes the CH2 carbon less
electrophilic. Similarly, the semicarbazones PhC{@NNHC(O)NH2}-
CH2Br and p-PhC6H4C{@NNHC(O)NH2}CH2Br also only monoalky-
lated 1, again giving previously reported derivatives [22].
In order to investigate possible structural reasons for the ob-
served reactivity towards phosphine substitution, and to fully
characterize the bromide-substituted products, a number of sin-
gle-crystal X-ray structure determinations were carried out. The
The ability of PhC(O)CH2Br to dialkylate [Pt2(
gested that it would provide a complementary alkylating agent to
Me2SO4 for the alkylation of monoalkylated complexes [Pt2( -S)(
SR)(PPh3)4]+, generating a new series of mixed-alkyl dithiolate
complexes [Pt2{ -SC(O)Ph}(
-SR)(PPh3)4]2+. Monoalkylated com-
plexes [Pt2( -S)(
-SR)(PPh3)4]+ (R = Et or n-Bu, hereafter Bu) were
generated in situ by reaction of [Pt2( -S)2(PPh3)4] 1 with an excess
l-S)2(PPh3)4] sug-
l
l-
structure of the cation of [Pt2{l-SCH2C(O)Ph}2(PPh3)4](PF6)2
3ꢁ(PF6)2 is shown in Fig. 1, while selected bond lengths and angles
l
l
are given in Table 1. Attempts at obtaining suitable single crystals
l
l
of the butylthiolate complex [Pt2{l-SCH2C(O)Ph}(l-SBu)(PPh3)4]-
l
(PF6)2 8ꢁ(PF6)2 were unsuccessful, but crystals of the corresponding
tetraphenylborate complex 8ꢁ(BPh4)2 were able to be obtained. The
structure of the cation is shown in Fig. 2, with selected bond
lengths and angles in Table 2. In both structures, the thiolate li-
gands adopt axial positions on the {Pt2S2} butterfly core, an
arrangement which minimizes steric interactions with the bulky
PPh3 ligands (though at the expense of 1,3-diaxial interactions be-
tween the two thiolate ligands. Other dialkylated {Pt2S2} com-
of EtBr or BuBr in methanol, followed by removal of the excess
alkylating agent by evaporation. These complexes were then redis-
solved in methanol and reacted with excess PhC(O)CH2Br, and the
reaction mixtures monitored by ESI MS. The alkylation of the free
sulfide was fast, generating the hetero-dialkylated derivatives
[Pt2{l-SCH2C(O)Ph}(l
-SR)(PPh3)4]2+ (8, R = Bu; 9, R = Et), but their
formation was followed by spontaneous substitution of one of
the PPh3 ligands by a bromide anion. At an intermediate stage in
the reaction (6 h), four major species were observed in the ESI mass
plexes, such as [Pt2(
l l-SMe)(l-
-SMe)2(PPh3)4]2+ [28], [Pt2(
SR)(PPh3)4]2+ (R = CH2Ph, CH2CH@CH2, C5H10CO2Et, C2H4SPh) [28]
spectrum of the butyl system. These were [Pt2{l-SCH2C(O)Ph}-

O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
257
Fig. 2. Molecular structure of the cation of [Pt2{l-SCH2C(O)Ph}(l-
Fig. 1. Molecular structure of the cation of [Pt2{
l
-SCH2C(O)Ph}2(PPh3)4](PF6)2
SBu)(PPh3)4](BPh4)2 8ꢁ(BPh4)2 showing the atom numbering scheme, with thermal
3ꢁ(PF6)2 showing the atom numbering scheme, with thermal ellipsoids at the 50%
ellipsoids at the 50% probability level. Phenyl rings of the PPh3 ligands are omitted
for clarity.
probability level. Phenyl rings of the PPh3 ligands are omitted for clarity.
Table 1
Table 2
Selected bond lengths (Å) and angles (°) for [Pt2{
l-SCH2C(O)Ph}2(PPh3)4](PF6)2
Selected bond lengths (Å) and angles (°) for [Pt2{
l-SCH2C(O)Ph}(l-
3ꢁ(PF6)2 with estimated standard deviations in parentheses.
SBu)(PPh3)4](BPh4)2 8ꢁ(BPh4)2 with estimated standard deviations in parentheses.
Pt(1)–P(2)
Pt(1)–P(1)
Pt(2)–P(3)
Pt(2)–P(4)
C(2)–O(2)
C(10)–O(1)
C(9)–C(10)
2.2902(14)
2.2871(16)
2.2703(19)
2.2901(16)
1.215(8)
Pt(1)–S(1)
Pt(1)–S(2)
Pt(2)–S(1)
Pt(2)–S(2)
S(2)–C(1)
S(1)–C(9)
C(1)–C(2)
2.3917(16)
2.3681(15)
2.3562(15)
2.3843(18)
1.808(8)
Pt(1)–P(2)
Pt(1)–P(1)
Pt(2)–P(3)
Pt(2)–P(4)
S(2)–C(5)
S(1)–C(1)
2.321(3)
2.294(3)
2.303(3)
2.284(3)
1.830(8)
1.829(10)
Pt(1)–S(1)
Pt(1)–S(2)
Pt(2)–S(1)
Pt(2)–S(2)
C(6)–O(1)
2.347(3)
2.383(3)
2.380(3)
2.371(3)
1.250(12)
1.222(9)
1.507(10)
1.817(8)
1.504(10)
S(2)–Pt(1)–S(1)
S(2)–Pt(2)–S(1)
S(1)–C(1)–C(2)
C(6)–C(5)–S(2)
C(5)–S(2)–Pt(2)
C(5)–S(2)–Pt(1)
82.14(11)
81.67(11)
110.8(7)
125.6(3)
107.9(3)
102.7(3)
Pt(1)–S(1)–Pt(2)
Pt(2)–S(2)–Pt(1)
O(1)–C(6)–C(5)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
92.54(11)
91.86(11)
119.9(5)
106.0(3)
112.3(4)
S(2)–Pt(1)–S(1)
S(2)–Pt(2)–S(1)
S(2)–C(1)–C(2)
O(1)–C(10)–C(9)
C(1)–S(2)–Pt(1)
C(1)–S(2)–Pt(2)
82.32(6)
82.72(6)
119.5(5)
123.7(7)
107.5(2)
108.0(3)
Pt(1)–S(1)–Pt(2)
Pt(2)–S(2)–Pt(1)
S(1)–C(9)–C(10)
O(2)–C(2)–C(3)
C(9)–S(1)–Pt(2)
C(9)–S(1)–Pt(1)
94.81(6)
94.69(6)
119.7(5)
120.2(7)
110.4(2)
112.2(3)
S){l
-SCH2C(O)Ph}(PPh3)4]+, as a result of the dipositive charge on
and [Pt2(
have the same arrangement.
l
-SCH2Ph)2(dppp)2]2+ [dppp = Ph2P(CH2)3PPh2] [23] also
the complex which would promote a stronger Ptꢁ ꢁ ꢁO interaction
compared to the monoalkylated complex.
The {Pt2S2} core of 3ꢁ(PF6)2 has a dihedral angle (h, between the
The mixed-thiolate complex 8ꢁ(BPh4)2 shows overall similar fea-
tures; again the carbonyl oxygen sits above the Pt center with a fairly
short Ptꢁ ꢁ ꢁO distance of 2.981 Å. The butyl group however takes up a
position pointing away from the platinum atoms. The Pt–P bonds
trans to the SBu ligand [Pt(1)–P(2) 2.321(3), Pt(2)–P(3) 2.303(3) Å]
are longer than those trans to the phenacylthiolate ligand [Pt(1)–
P(1) 2.294(3), Pt(2)–P(4) 2.284(3) Å], indicating that the SBu ligand
has a higher trans influence [31]. This is in accord with 31P{1H}
NMRspectroscopicmeasurements; the 1J(PtP) valuesof PPh3 ligands
two PtS2 planes) of 156.36°, very similar to the corresponding an-
gle in [Pt2(l
-SMe)2(PPh3)4]2+ (156.87°) [28]. The corresponding an-
gle in 8ꢁ(BPh4)2 is 145.11°. These dialkylated derivatives have
considerably flatter {Pt2S2} butterfly cores (with larger h values)
when compared to monoalkylated derivatives such as [Pt2(
l-
S){
l
-SCH2C(O)Ph}(PPh3)4]+ (134.71°) [22]. The Pt–P bond distances
of complex 3ꢁ(PF6)2 range from 2.2703(19) to 2.2902(14) Å. The
carbonyl oxygen atoms reside above the Pt centers [Pt(1)ꢁ ꢁ ꢁO(2)
2.711, Pt(2)ꢁ ꢁ ꢁO(1) 2.901 Å, though there is some disorder in the
Pt(2) position so this value may be less reliable]. This may repre-
sent an interaction, since the sum of the van der Waals radii for
trans to SBu and SCH2COPh ligands in complexes [Pt2(l-S)(l-
SR)(PPh3)4]+ [22,32] are 3235 and 3386 Hz, respectively.
The structures of 3ꢁ(PF6)2 and 8ꢁ(BPh4)2 provide an explanation
as to why bromide-substituted products are not formed when both
thiolate ligands are SCH2C(O)Ph. The presence of the carbonyl
groups in close proximity to both Pt centers in 3 sterically protects
them towards attack by bromide ions. However in 8, while one of
Pt and O is 3.24 Å [30]. In monoalkylated [Pt2(l-S){l-SCH2C(O)Ph}-
(PPh3)4]+ the C@O group also resides approximately above the Pt
center, but the Ptꢁ ꢁ ꢁO distance is a lot longer (3.604 Å). The Pt cen-
ters in 3ꢁ(PF6)2 are expected to be more electrophilic than in [Pt2(
l-

258
O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
in Figs. 3 and 4, respectively. Selected bond lengths and angles
are given in Tables 3 and 4. The two structures are isomorphous,
despite the different alkyl substituents. There are some significant
differences between the bromide-containing complexes and their
‘parent’ triphenylphosphine analogues 3 and 8, as can be seen in
the figures and Table 5, which shows a comparison of selected
parameters of the {Pt2S2} cores of complexes 3, 8, 10 and 11.
Complexes 10 and 11 have a significantly more folded {Pt2S2}
butterfly core, with dihedral angles between the two PtS2 planes
[10 124.66°, 11 123.84°] that are substantially smaller than in
the corresponding non-bromide complexes 3 and 8 (vide supra).
This results in a marked shortening of the transannular distances.
For example the Ptꢁ ꢁ ꢁPt and Sꢁ ꢁ ꢁS separations in 10 [3.2197(4)
and 2.979(3) Å, respectively] are significantly less than the corre-
sponding values in 8 [3.4159(4) and 3.107(4) Å]. The Pt–S–Pt an-
gles are also decreased in 10 and 11 (Table 5). In 10 and 11 the
phenacylthiolate ligands adopt axial positions, but, significantly,
the butyl and ethyl substituents both adopt equatorial positions.
Most likely this is due to the presence of the smaller bromide li-
gand, which opens up a pocket of space in the equatorial plane,
in which the ethyl or butyl substituent can reside, with concomi-
Table 3
Selected bond lengths (Å) and angles (°) for [Pt2{
l
-SCH2C(O)Ph}(
l
-SBu)(PPh3)3Br]PF6
10ꢁPF6 with estimated standard deviations in parentheses.
Fig. 3. Molecular structure of the cation of [Pt2{l-SCH2C(O)Ph}(l-
Pt(2)–P(2)
Pt(1)–P(1)
Pt(2)–P(3)
Pt(1)–S(2)
C(2)–C(3)
C(1)–C(2)
C(2)–O(1)
2.270(2)
2.268(2)
2.302(2)
2.375(2)
1.497(11)
1.507(11)
1.220(10)
Pt(2)–S(1)
Pt(2)–S(2)
Pt(1)–S(1)
Pt(1)–Br(1)
S(1)–C(1)
S(2)–C(9)
2.3637(19)
2.3823(19)
2.2795(18)
2.4641(9)
1.824(8)
SBu)(PPh3)3Br]PF6 10ꢁPF6 showing the atom numbering scheme, with thermal
ellipsoids at the 50% probability level. Phenyl rings of the PPh3 ligands are omitted
for clarity.
1.830(8)
S(2)–Pt(1)–S(1)
S(2)–Pt(2)–S(1)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
S(1)–Pt(1)–P(1)
P(1)–Pt(1)–Br(1)
P(2)–Pt(2)–S(1)
S(1)–C(1)–C(2)
79.55(7)
77.74(7)
109.2(3)
104.0(3)
93.63(7)
90.47(5)
88.00(7)
110.8(6)
Pt(1)–S(1)–Pt(2)
Pt(2)–S(2)–Pt(1)
C(9)–S(2)–Pt(2)
C(9)–S(2)–Pt(1)
S(2)–Pt(1)–Br(1)
P(2)–Pt(2)–P(3)
P(3)–Pt(2)–S(2)
S(2)–C(9)–C(10)
87.78(6)
85.19(7)
120.8(3)
114.8(3)
96.22(5)
98.04(7)
98.20(7)
109.0(6)
Table 4
Selected bond lengths (Å) and angles (°) for [Pt2{
11ꢁPF6 with estimated standard deviations in parentheses.
l-SCH2C(O)Ph}(
l
-SEt)(PPh3)3Br]PF6
Pt(1)–P(2)
Pt(1)–P(1)
Pt(2)–P(3)
Pt(2)–Br(1)
C(1)–C(2)
C(2)–O(1)
2.2729(11)
2.2992(11)
2.2669(11)
2.4657(5)
1.508(6)
Pt(1)–S(1)
Pt(1)–S(2)
Pt(2)–S(1)
Pt(2)–S(2)
C(2)–C(3)
S(1)–C(1)
2.3655(10)
2.3725(11)
2.2799(11)
2.3702(11)
1.492(6)
1.198(6)
1.821(4)
S(2)–Pt(1)–S(1)
S(2)–Pt(2)–S(1)
S(1)–C(1)–C(2)
C(1)–S(1)–Pt(1)
C(1)–S(1)–Pt(2)
77.36(4)
79.08(4)
111.6(3)
105.24(15)
108.24(16)
S(1)–Pt(2)–P(3)
Pt(1)–S(1)–Pt(2)
Pt(2)–S(2)–Pt(1)
O(1)–C(2)–C(3)
S(2)–Pt(2)–Br(1)
93.45(4)
87.52(4)
85.30(3)
121.7(4)
96.16(3)
Fig. 4. Molecular structure of the cation of [Pt2{l-SCH2C(O)Ph}(l-SEt)(PPh3)3Br]PF6
Table 5
A comparison of selected structural parameters of the dialkylated derivatives [Pt2{
SCH2C(O)Ph}2(PPh3)4](PF6)2 [Pt2{ -SCH2C(O)Ph}( -SBu)(PPh3)4](BPh4)2
10ꢁPF6 and [Pt2{
11ꢁPF6 showing the atom numbering scheme, with thermal ellipsoids at the 50%
l
-
probability level. Phenyl rings of the PPh3 ligands are omitted for clarity.
3ꢁ(PF6)2,
l
l
8ꢁ(BPh4)2,
[Pt2{
l
l
-SCH2C(O)Ph}(
l
-SBu)(PPh3)3Br]PF6
l-
the Pt centers [Pt(2)] is similarly protected by a C(O)Ph group, the
other platinum Pt(1) is more exposed, offering a pathway to
bromide attack, consistent with the observed formation of
SCH2C(O)Ph}(
-SEt)(PPh3)3Br]PF6 11ꢁPF6.
Parameter
3ꢁ(PF6)2
8ꢁ(BPh4)2
10ꢁPF6
11ꢁPF6
bromide-substituted products in the case of [Pt2{
-SR)(PPh3)4]2+ (R = Bu or Et).
The structures of the bromide-substituted complexes [Pt2{
SCH2C(O)Ph}( -SCH2C(O)Ph}
-SBu)(PPh3)3Br]PF6 10ꢁPF6 and [Pt2{
-SEt)(PPh3)3Br]PF6 11ꢁPF6 were also determined, and are shown
l-SCH2C(O)Ph}-
Ptꢁ ꢁ ꢁPt (Å)
Sꢁ ꢁ ꢁS (Å)
3.4952(5)
3.133(2)
94.75(6)
156.36
3.4159(4)
3.107(4)
92.20(11)
145.11
3.2197(4)
2.979(3)
86.49(7)
124.66
3.2134(2)
2.961(1)
86.41(4)
123.84
(
l
Pt–S–Pt (average, °)
Dihedral angle (°)a
l
-
l
l
a
Angle between the Pt(1)S2 and Pt(2)S2 planes.
(l

O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
259
tant increased puckering of the {Pt2S2} core to accommodate the
steric bulk of the remaining groups.
Examination of the Cambridge Structural Database (version 5.32,
February 2011 update) for complexes of the type P2Pt(l-SR)2PtP2
the type 12 [4,34–36]. In these, the SR group on the phosphine side
of the {Pt2S2} core adopts an axial position, while the other (on the
side of the smaller anionic ligand, e.g. halide) is in an equatorial posi-
tion, similar to the arrangement in 10 and 11. The complex
(P = phosphine ligand, R = organic substituent) reveals that, of those
complexes with puckered {Pt2S2} cores, in all cases the thiolate
ligandsbothadoptaxial (syn)positions[somestructures, havingpla-
(Ph3P)BrPt(l-SMe)2PtBr(PPh3) 12d [36] provides the closest com-
parison to 10 and 11; in this complex the {Pt2S2} core is also signifi-
cantly puckered (h = 129.19°), though less puckered than 10 and 11
(which have dihedral angles ca. 124° Table 5). Concomitantly, the
Ptꢁ ꢁ ꢁPt separation in 12d [3.247 Å] is larger than 10 and 11. A de-
tailed theoretical study on dinuclear Pt complexes with thiolate
bridges has found that energy differences between different
arrangements in these systems is small [37].
nar {Pt2S2} cores, e.g. [dpppPt(l-SCH2CH2NHC(O)NHPh)2Pt(dppp)]-
(CF3SO3)2 [33] have an anti arrangement of the thiolate ligands
across the core]. Although there are no known structures of deriva-
tives with a single halide (X) replacing a phosphine ligand (P), viz.
P2Pt(
l-SR)2PtXP, there are several structures containing cations of
+
CH C(O)Ph
2
S
S
S
S
Pt
Pt
Ph P
3
PPh
3
Pt
Pt
PPh
Ph P
3
Ph P
3
PPh
3
3
PPh
Ph P
3
3
1
2
2+
O
O
O
RC(O) CH
2
CH C(O)R
2
Br
Br
S
S
Pt
Pt
O
Ph P
PPh
3
3
PPh
Ph P
3
3
CouC(O)CH Br, 6
PyrC(O)CH Br, 4
2
2
3, R = Ph
5, R = Pyr
7, R = Cou
+
2+
RC(O) CH
Pt
CH C(O)Ph
2
2
R
S
S
S
S
Pt
Pt
Pt
Ph P
3
PPh
3
Br
Ph P
3
PPh
3
PPh
Ph P
3
Ph P
3
3
R
10, R = n-Bu
11, R = Et
8, R = n-Bu
9, R = Et
R
S
1
S
Pt
Pt
R P
3
PR
3
X
X
R
1
12a, R P = PPh , R = Me, X = NO
2
3
3
1
12b, R P = PMe Ph, R = CH Ph, X = SCH Ph
3
3
2
1
2
2
12c, R P= PPr , R = Et, X = Cl
3
1
12d, R P = PPh , R = Me, X = Br
3
3
1

260
O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
In complex 10, and especially in the ethylthiolate 11, the C(O)Ph
out in LR grade methanol, without precautions to exclude light, air
or moisture. Water was singly distilled prior to use.
group is not located directly above a platinum center; these com-
plexes are monocationic, the Pt centers are presumably less elec-
trophilic, and there is no Ptꢁ ꢁ ꢁO interaction, as is the case for
1H NMR spectra were recorded on Bruker DRX spectrometers
operating either at 300 or 400 MHz. 31P{1H} NMR spectra were re-
corded on a Bruker DRX spectrometer operating at 121.49 MHz.
Spectra were recorded in CD2Cl2 solution; all dialkylated com-
plexes had relatively poor solubility in CDCl3. ESI mass spectra
were recorded on a VG Platform II instrument; samples were pre-
pared by dissolving a small quantity (<1 mg) of sample in a few
drops of CH2Cl2 and diluting with methanol. Cone voltages were
typically 20 V. High resolution mass spectra were recorded on a
Bruker MicrOTOF instrument. Assignment of ions was achieved
by use of a simulation program [39,40]. Melting points were re-
corded on a Reichert Thermovar hotstage apparatus and are
uncorrected. Infrared spectra were recorded as KBr discs on a
Perkin–Elmer spectrum 100 FT-IR spectrometer and microelemen-
tal analyses were carried out at the Campbell Microanalytical
Laboratory at the University of Otago.
[Pt2(l-S){l
-SCH2C(O)Ph}(PPh3)4]+. Both 10 and 11 have the coordi-
nated bromide ligand trans to the SCH2C(O)Ph ligand. In complex
10 the Pt–P bond distances for the phosphines trans to the SBu li-
gand are similar [Pt(1)–P(1) 2.268(2) and Pt(2)–P(2) 2.270(2) Å],
both being shorter than the Pt(2)–P(3) bond trans to SCH2C(O)Ph,
the opposite trend to that observed in the non-bromide complex
8. The same effect is observed in 11. The lower trans influence of
bromide compared to PPh3 can be seen in complexes 10 and 11,
with the Pt(2)–S(1) bond length (of e.g. 11) [2.2799(11) Å] shorter
than Pt(1)–S(1) [2.3655(10) Å].
The phosphine complexes [Pt2{l-SCH2C(O)Ph}(l-SR)(PPh3)4]-
(PF6)2 3 and 8 show a single resonance in their 31P{1H} NMR spec-
tra due to almost coincidental phosphine chemical shifts (which
could not be resolved by the use of other solvents, e.g. d6-DMSO),
but two sets of 195Pt satellites are observed for the phosphines
trans to the two different thiolate ligands, with coupling constants
of 3107 and 2934 Hz in 8. The behavior shown by the bromide
4.1. Synthesis of [Pt2{
l
-SCH2C(O)Ph}2(PPh3)4](PF6)2 3ꢁ(PF6)2
complexes [Pt2{
l-SCH2C(O)Ph}(l-SR)(PPh3)3Br]PF6 10 and 11 was
To a suspension of [Pt2( -S)2(PPh3)4] (100 mg, 0.067 mmol) in
l
more complicated. If the structures observed in the solid state were
maintained in solution, three different PPh3 environments, and
hence a relatively simple spectrum would be observed. The 31P
methanol (30 mL) was added PhC(O)CH2Br (132.4 mg, 0.67 mmol)
and the mixture stirred at room temperature. After 1 h a clear pale
yellow solution had formed. After 24 h the nearly colorless solution
NMR spectrum of [Pt2{
l
-SCH2C(O)Ph}(
l
-SBu)(PPh3)3Br]PF6 10ꢁPF6
was analyzed by ESI MS and found to contain solely [Pt2{l-
showed several (>4, possibly 6) overlapping multiplets with their
corresponding 195Pt satellites, which may arise from the presence
of isomers in solution. This may be due to axial/equatorial conver-
sion of the SBu group, or alternatively it is possible that geometric
isomers are formed, with the bromide trans to either SBu or
SCH2COPh, and that the crystal selected for X-ray crystallographic
study is one of these isomers.
SCH2C(O)Ph}2(PPh3)4]2+. After filtration to remove a trace amount
of insoluble matter, solid NH4PF6 (80 mg, 0.49 mmol) was added,
followed by water (30 mL) to induce precipitation. The solid was
filtered and washed successively with water (10 mL), methanol
(10 mL) and diethyl ether (10 mL) and dried under vacuum to give
3ꢁ(PF6)2 as an off-white powder (90.5 mg, 67%). Anal. Calc. for
C
88H74F12O2P6Pt2S2 (Mr 2030.49): C, 52.01; H, 3.67. Found: C,
51.77; H, 3.69%. M.p. 221–223 °C. IR mmax 1673 cmꢀ1. ESI MS m/z
870 (100%), [Pt2{l .
-SCH2C(O)Ph}2(PPh3)4]2+ 31P{1H} NMR, d 20.1
3. Conclusions
[s, 1J(PtP) 3128]. 1H NMR (300 MHz), d 2.11 (br s, 4H, CH2), 7.06–
7.79 (m, 70H, Ph).
In this work we have demonstrated that phenacyl bromide
[PhC(O)CH2Br] (but not imine derivatives thereof), and other com-
pounds of the type RC(O)CH2Br [3-(bromoacetyl)coumarin and 1-
4.2. Synthesis of [Pt2{
l
-SCH2C(O)Pyr}2(PPh3)4](PF6)2 5ꢁ(PF6)2
-S)2(PPh3)4] (100 mg, 0.067 mmol) and 1-
(bromoacetyl)pyrene] successfully dialkylate [Pt2(
l
-S)2(PPh3)4] 1
A mixture of [Pt2(l
(bromoacetyl)pyrene
and monoalkylated derivatives [Pt2( -S)(
l
l
-SR)(PPh3)4]+, leading
4
(129 mg, 0.399 mmol) in methanol
to new hetero-dithiolate platinum complexes. X-ray structure
(25 mL) was stirred for 7 days. Complete formation of the product
cation was shown by ESI MS. The solution was filtered to remove
traces of insoluble impurities and excess NH4PF6 (40 mg,
0.245 mmol) added to the filtrate, giving a bright yellow precipi-
tate. Distilled water (10 mL) was added to assist precipitation.
The product was filtered, washed with water (40 mL), diethyl ether
(40 mL) and dried under vacuum to give a yellowish-orange pow-
der of 5ꢁ(PF6)2 (98 mg, 65%). Anal. Calc. for C108H82F12O2P6Pt2S2 (Mr
2278.56): C, 56.88; H, 3.63. Found: C, 56.69; H, 3.92%. M.p. 222–
determinations suggest a Ptꢁ ꢁ ꢁO@C interaction in the dicationic,
dialkylated complexes [Pt2{
l
-SCH2C(O)Ph}2(PPh3)4](PF6)2 3ꢁ(PF6)2
and [Pt2{
l
-SCH2C(O)Ph}(
l
-SBu)(PPh3)4](BPh4)2 8ꢁ(BPh4)2. When
one of the thiolate ligands contains ethyl or n-butyl, attack of the
liberated bromide anion results in phosphine substitution giving
mono-cationic
complexes
[Pt2{l-SC(O)Ph}(l
-SR)(PPh3)3Br]+
(R = Et or Bu). This process can be successfully suppressed by sim-
ply adding PPh3 to the reaction mixture at the completion of the
alkylation reactions. With these results, we now have a greater
understanding of factors that influence the dialkylation of 1, and
the products that are formed.
224 °C. IR mmax 1638 cmꢀ1
. ESI MS m/z 996 (100%), [Pt2{l-
SCH2C(O)Pyr}2(PPh3)4]2+ 31P{1H} NMR, d 22.4 [s, 1J(PtP) 3136]. 1H
.
NMR (300 MHz), d 2.47 (br s, 4H, SCH2) and 6.68–8.45 (m, aromatic
CH).
4. Experimental
4.3. Synthesis of [Pt2{
l
-SCH2C(O)Cou}2(PPh3)4](PF6)2 7ꢁ(PF6)2
The complex [Pt2(l-S)2(PPh3)4] 1 was prepared by the literature
A mixture of [Pt2( -S)2(PPh3)4] (100 mg, 0.067 mmol) and 3-
l
procedure from cis-[PtCl2(PPh3)2] and Na2Sꢁ9H2O in benzene
[2,38]. The following compounds were used as supplied from
commercial sources: phenacyl chloride (BDH), phenacyl bromide
(Aldrich), 1-bromobutane (BDH), bromoethane (BDH), 1-(bromo-
acetyl)pyrene (Aldrich), 3-(bromoacetyl)coumarin (Aldrich), so-
dium tetraphenylborate (Aldrich), triphenylphosphine (BDH) and
ammonium hexafluorophosphate (Aldrich). Reactions were carried
(bromoacetyl)coumarin (107 mg, 0.401 mmol) in methanol
6
(25 mL) was stirred for 7 days. After filtration to remove traces of
insoluble matter excess NH4PF6 (40 mg, 0.245 mmol) was added,
giving a white precipitate. Water (10 mL) was added to assist pre-
cipitation. The product was filtered, washed with water (40 mL),
diethyl ether (40 mL) and dried under vacuum to give crude
7ꢁ(PF6)2 (92 mg, 64%). Anal. Calc. for C94H74F12O6P6Pt2S2 (Mr

O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
261
2166.47): C, 52.08; H, 3.44. Found: C, 51.77; H, 3.59%. M.p. 178–
47.35; H, 3.84%. M.p. 216–218 °C. IR mmax 1681 cmꢀ1. ESI MS m/z
1497 (100%), [Pt2{ -SCH2C(O)Ph}(
-SBu)(PPh3)3Br]+.
Crystals suitable for an X-ray diffraction study were obtained by
vapor diffusion of diethyl ether into a dichloromethane solution of
the complex at room temperature.
180 °C. IR mmax 1608, 1725 cmꢀ1. ESI MS m/z 938.151 (100%),
l
l
[Pt2{
l
-SCH2C(O)Cou}2(PPh3)4]2+
.
31P{1H} NMR, d 18.9 [s, 1J(PtP)
3110]. 1H NMR (400 MHz), d 3.52 [t, 4H, SCH2, J(PH) 5.2, J(PtH)
ca. 30] and 7.05–7.91 (m, aromatic CH).
4.7. Synthesis of [Pt2{
l
-SCH2C(O)Ph}(l-SEt)(PPh3)3Br]PF6 11ꢁPF6
4.4. Synthesis of [Pt2{
l-SCH2C(O)Ph}(l-SBu)(PPh3)4](PF6)2 8ꢁ(PF6)2
Following the procedure for 10ꢁPF6, [Pt2( -S)2(PPh3)4]
l
1
[Pt2(
l-S)2(PPh3)4] (100 mg, 0.067 mmol) was reacted with ex-
(100 mg, 0.067 mmol) in methanol (25 mL) with bromoethane
(1 mL, large excess) and PhC(O)CH2Br (66 mg, 0.34 mmol), fol-
lowed by precipitation with NH4PF6 (40 mg, 0.245 mmol) gave
11ꢁPF6 as a light brown precipitate (67 mg, 62%). Anal. Calc. for
C64H57BrF6OP4Pt2S2 (Mr 1613.33): C, 47.60; H, 3.56. Found: C,
46.51; H, 3.38%. M.p. 191–194 °C. IR mmax 1689 cmꢀ1. ESI MS m/z
cess 1-bromobutane (1 mL, large excess) in methanol (25 mL),
and the mixture stirred for 1 h to give a yellow solution. ESI MS
indicated complete formation of [Pt2(l-S)(l
-SBu)(PPh3)4]+. The
volatiles were removed by rotary evaporation, and the residue
redissolved in methanol (25 mL). PhC(O)CH2Br (66 mg, 0.34 mmol)
was then added and the reaction mixture stirred overnight. Tri-
phenylphosphine (17.5 mg, 0.067 mmol) was added, and the reac-
tion mixture stirred an additional 12 h. The solution was filtered to
remove traces of insoluble matter and excess NH4PF6 (40 mg,
0.245 mmol) added, giving an off-white precipitate. Water
(10 mL) was added to assist precipitation. The product was filtered,
washed with water (40 mL) and diethyl ether (40 mL) and dried
under vacuum to give 8ꢁ(PF6)2 (69.5 mg, 53%). Anal. Calc. for
1469 (100%), [Pt2{l-SCH2C(O)Ph}(l
-SEt)(PPh3)3Br]+.
Crystals suitable for an X-ray diffraction study were obtained by
vapor diffusion of diethyl ether into a dichloromethane solution of
the complex at room temperature.
4.8. X-ray crystal structure determinations
Data for 3ꢁ(PF6)2, 8ꢁ(BPh4)2 and 10ꢁPF6 were collected on a Bru-
C
84H76F12OP6Pt2S2 (Mr 1968.52): C, 51.22; H, 3.89. Found: C,
51.08; H, 3.89%. M.p. 188–191 °C. IR mmax 1637 cmꢀ1. ESI MS m/z
ker Apex II diffractometer equipped with a CCD area detector,
839 (100%), [Pt2{l-SCH2C(O)Ph}(l .
-SBu)(PPh3)4]2+ 31P{1H} NMR, d
using Mo K
a radiation (k = 0.71073 Å). SADABS [41] was used for
19.6 [br s, 1J(PtP) 3107 and 2934]. 1H NMR (400 MHz), d 0.36 m,
2H, CH3), 0.55 (m, 2H, CH2), ꢀ0.4 (m, 2H, CH2), 2.06 (m, br, 2H,
SCH2), 2.7 (m, br, 2H, SCH2), 7.08–7.77 (m, 65H, Ph).
empirical absorption correction. Structures were solved by the di-
rect methods option of SHELXS-97 [42] and the Pt, S and P atoms
were located. All other non-hydrogen atoms were located from a
series of difference maps. Full-matrix least-squares refinement
Attempts at obtaining single crystals of this compound suitable
for an X-ꢀray diffraction study were unsuccessful. The correspond-
ing BPh4 salt was prepared in an analogous manner (replacing
NH4PF6 by NaBPh4) and yielded suitable crystals by vapor diffusion
of diethyl ether into a dichloromethane solution of the complex.
2
was based on Fo with all non-hydrogen atoms anisotropic and
hydrogen atoms in calculated positions. All calculations were car-
ried out using the SHELX-97 suite of programs. A summary of crys-
tallographic parameters and refinement details is given in Table 6.
Most of the details of the structure of 3ꢁ(PF6)2 evolved normally
on refinement. The asymmetric unit of the refined structure con-
tained the dication [Pt2{l
-SCH2C(O)Ph}2(PPh3)4]2+, two PF6ꢀ anions
4.5. Synthesis of [Pt2{
l-SCH2C(O)Ph}(l-SEt)(PPh3)4](PF6)2 9ꢁ(PF6)2
and CH2Cl2. There was a significant residual peak adjacent to Pt(2)
which was modeled as a partially disordered occupancy of the
Pt(2) site. This refined to 7% occupancy. One molecule of CH2Cl2
was well resolved, and residual electron density suggested a less
well-defined one. This was included in the refinement with con-
strained C–Cl bond lengths and refined to 83% occupancy. A final
difference map revealed more electron density (ca. 3–4 e Åꢀ3) in
a region with solvent-accessible voids of ca. 160 Å3 which was pre-
sumably more solvent molecules (possibly a diethyl ether). This
could not be successfully modeled, so was not included in the final
model. All non-hydrogen atoms were refined anisotropically ex-
cept for the minor Pt(2) component, and hydrogen atoms were in-
cluded in calculated positions.
Crystal data for 8ꢁ(BPh4)2 were acquired and solved by direct
methods in space group Cc. The Pt, S and P atoms evolved, followed
by all other atoms on refinement. All non-hydrogen atoms were re-
fined anisotropically except C(4) which was very floppy. A disor-
dered solvent molecule was treated as a disordered chlorine
atom of CH2Cl2 and included in the final refinement.
Following the procedure for 8ꢁ(PF6)2, [Pt2( -S)2(PPh3)4]
l
(100 mg, 0.067 mmol) in methanol (25 mL) with bromoethane
(1 mL, large excess) formed the monoalkylated complex [Pt2(
S)(
-SEt)(PPh3)4]+. The resulting yellow solution was reacted with
l
-
l
PhC(O)CH2Br (66 mg, 0.34 mmol) and then PPh3 (17.5 mg,
0.067 mmol), followed by precipitation of the product with NH4PF6
(40 mg, 0.245 mmol). The product was filtered, washed with water
(2 ꢂ 20 mL) and diethyl ether (2 ꢂ 20 mL) and dried under vacuum
to give 9ꢁ(PF6)2 (74 mg, 57%) as a white powder. Anal. Calc. for
C
82H72F12OP6Pt2S2 (Mr 1940.48): C, 50.73; H, 3.74. Found: C,
50.53; H, 3.65%. M.p. 211–213 °C. IR mmax 836, 1096, 1436, 1481,
1674 cmꢀ1
ESI MS m/z 826 (100%), [Pt2{ -SCH2C(O)Ph}(
SEt)(PPh3)4]2+ 31P{1H} NMR, d 19.7 [br m, 1J(PtP) 3050 and 2942].
.
l
l-
.
4.6. Synthesis of [Pt2{
l-SCH2C(O)Ph}(l-SBu)(PPh3)3Br]PF6 10ꢁPF6
1-Bromobutane (1 mL, large excess) was added to a stirred sus-
pension of [Pt2( -S)2(PPh3)4] 1 (100 mg, 0.067 mmol) in methanol
(25 mL), and the mixture stirred for 1 h to give a yellow solution.
ESI MS indicated complete formation of [Pt2( -S)(
-SBu)(PPh3)4]+.
l
The structure of 10ꢁPF6 was solved by direct methods and al-
most all details evolved normally. All atoms except hydrogen
atoms were refined anisotropically. At the end of the first refine-
ment, two residual peaks of about 4 e Åꢀ3 revealed in solvent-
accessible spaces. In the final refinement they were treated and re-
fined as the oxygen atoms of partial water molecules taking into
account the hydrogen-bonding distances.
l
l
The volatiles were removed by rotary evaporation, the residue
redissolved in methanol (25 mL) and PhC(O)CH2Br (66 mg,
0.33 mmol) added. After stirring for 48 h the solution was filtered
to remove traces of insoluble matter and excess NH4PF6 (40 mg,
0.245 mmol) added to the filtrate, followed by water (10 mL) to as-
sist precipitation. The product was filtered, washed with water
(40 mL) and diethyl ether (40 mL) and dried under vacuum to give
Crystallographic data for 11ꢁPF6 were obtained on a Bruker AXS
SMART APEX diffractometer equipped with a CCD area detector
10ꢁPF6 as
a
brownish powder (61 mg, 56%). Anal. Calc. for
using Mo K
a radiation. The SMART program [43] was used for the
C
66H61BrF6OP4Pt2S2 (Mr 1641.36): C, 48.25; H, 3.75. Found: C,
collection of data frames, indexing reflections, and to determine

262
O.T. Ujam et al. / Inorganica Chimica Acta 376 (2011) 255–263
Table 6
Crystal data and structure refinement details for the complexes [Pt2{
l
-SCH2C(O)Ph}2(PPh3)4](PF6)2 3ꢁ(PF6)2, [Pt2{
l
-SCH2C(O)Ph}(
l
-SBu)(PPh3)4](PF6)2 8ꢁ(BPh4)2, [Pt2{
11ꢁPF6ꢁCH2Cl2
l-
SCH2C(O)Ph}(
l
-SBu)(PPh3)3Br]PF6 10ꢁPF6, and [Pt2{
l
-SCH2C(O)Ph}(
l
-SEt)(PPh3)3Br]PF6 11ꢁPF6.
3ꢁ(PF6)2ꢁ2CH2Cl2
8ꢁ(BPh4)2ꢁCH2Cl2
10ꢁPF6ꢁ2H2O
Formula
Formula weight
T (K)
C90H78Cl4F12O2P6Pt2S2
2201.44
93(2)
C133H118B2Cl2OP4Pt2S2
2402.97
89(2)
C66H63BrF6O2P4Pt2S2
1660.25
89(2)
C65H59BrCl2F6OP4Pt2S2
1699.11
223(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
13.9856(5)
17.5866(6)
18.9340(6)
91.906(2)
monoclinic
Cc
monoclinic
P21/c
13.8278(4)
22.7551(7)
19.8603(6)
90
monoclinic
P21/c
13.9445(6)
22.6725(11)
20.0422(9)
90
ꢀ
31.9776(4)
14.7512(2)
27.7611(4)
90
a
(°)
b (°)
101.551(2)
93.392(2)
4549.8(3)
115.730(1)
90
11796.7(3)
4
1.353
2.554
92.221(2)
90
6244.4(3)
4
1.766
5.347
90.415(1)
90
6336.3(5)
4
1.781
5.352
c
(°)
V (Å3)
Z
2
Calculated density (g cmꢀ3
)
1.607
3.411
2176
Absorption coefficient (mmꢀ1
F(0 0 0)
)
4864
3248
3312
Crystal size (mm3)
0.29 ꢂ 0.27 ꢂ 0.15
106 616/21 940 (0.0448)
semi-empirical from
equivalents
0.6286 and 0.4379
0.25 ꢂ 0.22 ꢂ 0.20
73 575/25 367 (0.0305)
semi-empirical from
equivalents
0.6292 and 0.5677
0.28 ꢂ 0.22 ꢂ 0.20
74 187/14 958 (0.0680)
semi-empirical from
equivalents
0.4144 and 0.3159
0.46 ꢂ 0.26 ꢂ 0.10
44 741/14 543 (0.0435)
semi-empirical from
equivalents
0.6166 and 0.1921
Reflections collected/unique (Rint
Absorption correction
)
Maximum and minimum
transmission
Data/restraints/parameters
21 940/20/1069
1.110
25 367/301/1306
1.055
14 958/0/748
1.199
14 543/2/744
1.004
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0500, wR2 = 0.1252
R1 = 0.0709, wR2 = 0.1403
3.562 and ꢀ1.439
R1 = 0.0439, wR2 = 0.1362
R1 = 0.0538, wR2 = 0.1450
3.279 and ꢀ0.997
R1 = 0.0505, wR2 = 0.0960
R1 = 0.0914, wR2 = 0.1090
1.812 and ꢀ2.637
R1 = 0.0351, wR2 = 0.0792
R1 = 0.0474, wR2 = 0.0835
1.575 and ꢀ0.583
Largest difference in peak and hole
(e Åꢀ3
)
[6] T.S.A. Hor, J. Cluster Sci. 7 (1996) 263.
lattice parameters. SAINT [43] was used for integration of the inten-
sity of reflections and for scaling, and SHELXTL [44] was used for
space group and structure determination, refinements, graphics
and structure reporting. The structure was refined by full-matrix
least-squares on F2 with anisotropic thermal parameters for non-
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Dalton Trans. (2005) 2742.
hydrogen atoms. The asymmetric unitꢀcontains a cation [Pt2{
l-
SCH2C(O)Ph}(
l
-SEt)(PPh3)3Br]+, one PF6 anion and one molecule
of CH2Cl2. The ethyl group attached to S(2) has large thermal mo-
tion; in final refinement cycles it was treated as disordered over
two positions.
Acknowledgments
[16] R. Mas-Ballesté, M. Capdevila, P.A. Champkin, W. Clegg, R.A. Coxall, A. Lledós,
C. Mégret, P. González-Duarte, Inorg. Chem. 41 (2002) 3218.
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[22] O.T. Ujam, S.M. Devoy, W. Henderson, B.K. Nicholson, T.S.A. Hor, Inorg. Chim.
Acta 363 (2010) 3558.
We thank the University of Waikato and the National University
of Singapore (NUS) for financial support of this work. We also
thank Dr. Tania Groutso (University of Auckland) for collection of
the X-ray data sets of 3ꢁ(PF6)2, 8ꢁ(BPh4)2 and 10ꢁPF6 and Lip Lin
Koh, Geok Kheng Tan and Yimain Hong (NUS) for the data set of
11ꢁPF6.
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(2008) 1908.
Appendix A. Supplementary material
CCDC 822270, 822271, 822272, and 822269 contain the supple-
mentary crystallographic data for [3ꢁ(PF6)2], [8ꢁ(BPh4)2], [10ꢁPF6],
and [11ꢁPF6]. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
06.023.
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