Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

Article abstract of DOI:10.1016/j.ica.2011.07.006

The coordination chemistry of the metalloligand [Pt₂(μ-S) ₂(PPh₃)₄] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology.

Full text of DOI:10.1016/j.ica.2011.07.006

Inorganica Chimica Acta 376 (2011) 446–455
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Extending the coordination chemistry of cobalt with the metalloligand
[Pt2(
l-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives
⇑
Hannah M. Clarke, William Henderson , Brian K. Nicholson
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 April 2011
Received in revised form 7 July 2011
Accepted 7 July 2011
Available online 23 July 2011
The coordination chemistry of the metalloligand [Pt2(l-S)2(PPh3)4] towards cobalt(II) and cobalt(III)
centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed method-
ology. Reaction of [Pt2(
-S)2(PPh3)4] with CoCl2ꢀ6H2O in methanol gave a green-yellow suspension of the
known adduct [Pt2( -S)2(PPh3)4CoCl2], and the CoBr2 adduct could be similarly prepared. When in
situ-generated [Pt2( -S)2(PPh3)4CoCl2] is reacted with 8-hydroxyquinoline (HQ) and base, the initial
product is the cobalt(II) adduct [Pt2(
-S)2(PPh3)4CoQ]+, which is then converted in air to the cobalt(III)
adduct [Pt2(
-S)2(PPh3)4CoQ2]+, isolated as its hexafluorophosphate salt. The corresponding picoli-
nate (Pic) derivative [Pt2(
-S)2(PPh3)4Co(Pic)2]+ was similarly prepared, however reaction of
-S)2(PPh3)4], CoCl2ꢀ6H2O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct
-S)2(PPh3)4CoTQ]+. Reactions of [Pt2(
-S)2(PPh3)4], CoCl2ꢀ6H2O and dithiocarbamates gave cobal-
-S)2(PPh3)4Co(S2CNR2)2]+ [R = Et or R2 = (CH2)4], and proceeded much more rapidly,
l
l
l
l
Keywords:
Platinum complexes
Cobalt complexes
Electrospray ionisation mass spectrometry
X-ray crystal structure
l
l
[Pt2(
[Pt2(
l
l
l
t(III) complexes [Pt2(
l
consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation
states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated
that [Pt2(
be generated by ESI MS analysis of [Pt2(
corresponding indium(III) derivative [Pt2(
[Pt2(
-S)2(PPh3)4Co(S2CN(CH2)4)2]+ are much more reluctant to fragment under analogous conditions,
and the differences are discussed in terms of cobalt(III) redox chemistry.
Ó 2011 Elsevier B.V. All rights reserved.
l l
-S)2(PPh3)4CoQ2]+ fragments to form the radical cation [Pt2( -S)2(PPh3)4]Å+, which could also
l
-S)2(PPh3)4] in methanol–NaOH solution. In contrast, the
l
-S)2(PPh3)4InQ2]+, and the cobalt(III) dithiocarbamate
l
1. Introduction
adducts are the diketonate complexes [Pt2(l
-S)2(PPh3)4CoL]+,
where L = CH3COCHCOCH3 (acac) or (2-thienyl)COCHCOCF3 [5]. In
our current investigations we wished to explore further the chem-
istry of 1 towards cobalt substrates, and in particular address the
question of whether or not cobalt(III) complexes of 1 could be
obtained. Due to the classical kinetic inertness of the low spin d6
cobalt(III) centre, syntheses of substituted cobalt(III) complexes
often conveniently proceed via a more labile cobalt(II) derivative
[6], and the same approach was adopted in this work.
The platinum(II) sulfido complex [Pt2(l-S)2(PPh3)4] 1 (and
related complexes with alternative phosphine or arsine ligands)
has been under investigation for many years. Such complexes
display a rich chemistry on account of the electron-rich bridging
sulfide ligands, which react with a diverse range of organic- and
metal-based electrophiles [1–3].
A common theme in the
chemistry of 1 is the formation of homo- and hetero-metallic
sulfide-bridged aggregates, which are now known for the majority
of main group and transition metals.
2. Results and discussion
As part of ongoing investigations on the coordination chemistry
of 1 we here report on a study of the coordination chemistry
towards cobalt. Few cobalt derivatives of 1 are known, and all
contain cobalt in the II oxidation state. The first example of a cobalt
2.1. Investigation of the cobalt(II) halide adducts
[Pt2(l-S)2(PPh3)4CoX2] (X = Cl or Br)
derivative was [Pt2(l-S)2(PPh3)4CoCl2] 2a formed by reaction of 1
with anhydrous CoCl2 in tetrahydrofuran; carbonylative desulfuri-
sation of this complex eliminated the cobalt, forming
[Pt2(CO)2(PPh3)2(l-S)] [4]. The only other examples of cobalt
In this study, the complex [Pt2(
l
-S)2(PPh3)4] 1 was typically
reacted with CoCl2ꢀ6H2O in methanol giving a green-yellow sus-
pension, which was then reacted in situ with an additional ligand.
In order to identify the green-yellow intermediate, in one
experiment the solid was isolated and found to have properties
⇑
consistent with the neutral cobalt(II) chloride adduct [Pt2(
(PPh3)4CoCl2] 2a. This has been previously synthesised by reaction
l-S)2
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.2011.07.006

H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
447
of [Pt2(
l
-S)2(PPh3)4] with anhydrous CoCl2 in tetrahydrofuran sol-
main features. Fig. 1 shows the structure of the cation, while Table
1 gives selected bond lengths and angles. Refinement of the struc-
ture was complicated by apparent disorder of the two Q ligands
(refer Section 4) and the quality of the data was not sufficient to
resolve the disorder. The disorder in the ligands appears to involve
partial occupancy with the opposite handed-ness about the C2 axis
(Fig. 2), with the O atom positions swapping.
vent, under argon [4]. In this original report it was suggested that
the
use
of
hydrated
CoCl2
would
also
give
[Pt2(l-S)2(PPh3)4CoCl2], but it decomposes on formation. However,
our observations in this work indicate that hydrated CoCl2 can be
used, at least in methanol solvent, without regard for the exclusion
of air and moisture. Using the same method, the corresponding
green bromide [Pt2(l-S)2(PPh3)4CoBr2] 2b was prepared from
[Pt2( -S)2(PPh3)4] and hydrated cobalt(II) bromide. The cobalt–
l
chloride and –bromide adducts are only sparingly soluble in meth-
anol, but quite soluble in dichloromethane. Reaction of cobalt(II)
thiocyanate with 1 resulted in the formation of a bright lime-green
solid that was apparently insoluble in methanol and dichlorometh-
ane, which hampered attempts at characterising the compound.
The positive-ion ESI mass spectrum of [Pt2(
l-S)2(PPh3)4CoCl2] in
acetonitrile–methanol solution shows [Pt2(
l
-S)2(PPh3)4CoCl]+ at m/
z 1597.120 (calculated 1597.140) resulting from ionisation by loss of
a chloride ligand. Similar behaviour was shown by the bromide com-
plex [Pt2(
(m/z 1642.082, calculated m/z 1642.089). Neutral [Pt2(
l-S)2(PPh3)4CoBr2] which gave [Pt2(l
-S)2(PPh3)4CoBr]+
l-S)2
(PPh3)4CoCl2] would be expected to be invisible to ESI MS analysis,
and ionisation by chloride loss is the expected ionisation pathway
based on the ESI MS behaviour of other neutral metal chloride coor-
dination complexes [7]. Under soft fragmentation conditions (capil-
lary exit voltage 50 V) additional minor peaks of a dication at m/z
1597.617 overlap with the isotope pattern for [Pt2(
l
-S)2(PPh3)4
-S)2(PPh3)4
CoCl]+, and are assigned to the dimeric species [{Pt2(
l
CoCl}2]2+ (calculated m/z 1597.640) which presumably contains
chloride bridges and four-coordinate cobalt centres; a possible
structure is given by 3. Examination of the supernatant solution in
a [Pt2(
species: [Pt2(
Co2Cl3]+ (m/z 1727) in addition to [Pt2(
l
-S)2(PPh3)4]-CoCl2 reaction mixture showed some related
-S)2(PPh3)4Co2Cl2]2+ (m/z 846) and [Pt2(
-S)2(PPh3)4
-S)2(PPh3)4CoCl]+.
l
l
Fig. 1. Structure of the cation of [Pt2(l-S)2(PPh3)4CoQ2]PF6 showing the atom
numbering scheme. Only the ipso carbons of the PPh3 ligands are shown as arbitrary
small spheres.
l
2.2. Synthesis of cobalt(III) adducts with N,N and N,O chelating ligands
The reactivity of [Pt2(
hydroxyquinoline (HQ) was initially investigated. Reaction of
[Pt2(
-S)2(PPh3)4] 1 with one molar equivalent of CoCl2ꢀ6H2O in
methanol quickly gave greenish suspension of [Pt2( -S)2
l-S)2(PPh3)4] 1 towards CoCl2ꢀ6H2O and 8-
l
a
l
(PPh3)4CoCl2] (vide supra). Upon addition of 2 mol equivalents of
8-hydroxyquinoline and excess trimethylamine base the solid dis-
solved to give an orange solution. This solution gradually darkened
on stirring in air, giving (after several hours) a dark orange-brown
solution that was shown to contain the cobalt(III) derivative
[Pt2(
1850.283, calculated 1850.262]. Precipitation of the product with
excess NH4PF6 yielded [Pt2(
l
-S)2(PPh3)4CoQ2]+ 4 by positive-ion ESI MS [observed m/z
l
-S)2(PPh3)4CoQ2]PF6 (4ꢀPF6) as
a
brown solid in 57% yield. It is worth noting that the use of a smaller
amount of HQ (around 1.14 mol equivalents based on 1) still leads
to the isolation of pure [Pt2(l-S)2(PPh3)4CoQ2]PF6 in 86% yield
based on HQ used.
Monitoring of the above reaction on a smaller scale by ESI MS
showed the initial orange solution to contain predominantly the
cobalt(II) complex [Pt2(
lated m/z 1706.217), with only a low intensity ion [Pt2(
(PPh3)4CoQ2]+. Over a period of several hours stirring in air
[Pt2(
-S)2(PPh3)4CoQ]+ slowly decreased in intensity and was re-
placed by [Pt2(
-S)2(PPh3)4CoQ2]+ with concomitant darkening of
l
-S)2(PPh3)4CoQ]+ at m/z 1706.250 (calcu-
l
-S)2
l
l
the solution to a deep orange-brown; no other significant intensity
species were observed. After stirring for 24 h, the formation of the
cobalt(III) product was complete.
Crystallisation of 4ꢀPF6 by vapour diffusion of diethyl ether into
a dichloromethane solution yielded very dark brown, almost black,
crystals suitable for an X-ray diffraction study. The crystals were of
relatively poor quality but did provide a data set which reveals the
Fig. 2. A view of the core of the [Pt2(l
-S)2(PPh3)4CoQ2]+ cation looking down the
approximate C2 axis.

448
H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
.
[Pt2(µ-S)2(PPh3)4InQ2]+
+
[Pt2(µ-S)2(PPh3)4]
(b)
(a)
[Pt2(µ-S)2(PPh3)4CoQ]+ [Pt2(µ-S)2(PPh3)2(Ph2PC6H4)InQ]+
.
+
[Pt2(µ-S)2(PPh3)4]
[Pt2(µ-S)2(PPh3)4CoQ2]+
1400
1600
1800
1400
1200
1600
1800
2000
m/z
m/z
Fig. 3. Positive-ion ESI mass spectra of (a) [Pt2(
l
-S)2(PPh3)4CoQ2]PF6 and (b) [Pt2(
l
-S)2(PPh3)4InQ2]PF6 recorded using a capillary exit voltage of 210 V, showing the different
fragmentation behaviour of the complexes.
The complex contains a bidentate [Pt2(
l
-S)2(PPh3)4] metalloli-
gand coordinated to the CoQ2 moiety giving the archetypal octa-
hedral coordination at cobalt(III). Of the derivatives [Pt2( -S)2
fore represents the first structurally characterised example of a
[Pt2(l-S)2(PPh3)4] metalloligand complex with a true six-coordi-
nate metal adduct.
+
l
(PPh3)4MLn] that have been structurally characterised, the vast
majority have M coordination numbers of ꢁ5, with most being
four-coordinate or less. We are only aware of one structurally-
characterised related complex with a pseudo six-coordinate metal
The N donor atoms are trans to the sulfide ligands, which places
the O donors mutually trans to each other, and above the platinum
centres, which is sterically the most favourable arrangement, and
is shown in Fig. 2. Although there are few known structures of co-
balt(III) complexes containing two Q ligands and two additional
hetero-ligands for comparison, [CoQ2(Ph2PNPPh2NPPh2)] (YIBSOR)
adduct, being [{Pt2(l-S)2(PPh3)3Cl}Re(O)(g
5-C5Me4Et)]+, where
the cycopentadienyl ligand is considered to occupy three
coordination positions [8]. The only adducts with sixfold
[10] and the mixed cobalt(II)–cobalt(III) complex [CoQ2(
l-N3)2Co
or greater coordination are [Pt2(
Re(CO)3] (six-coordinate Re) and [Pt2(
l
-S)2(PPh3)4Re(CO)3(
l
-OMe)2
(H2O)2( -N3)2CoQ2] (CIHQOA) [11] have trans Q oxygens, while
[CoQ2(NH2CH2COO)] (LOBYAD) [12] has Q oxygens that are mutu-
l
l
-S)2(PPh3)4MI(CO)4]+
(M = seven-coordinate Mo or W), though none have been
ally cis.
structurally characterised [9]. Complex 4 reported herein there-
The Co–S bond distances of 4 [Co(1)–S(1) 2.285(5), Co(1)–S(2)
2.288(5) Å] are shorter than those in the cobalt(II) adducts
[Pt2(l-S)2(PPh3)4CoCl2] [2.359(4) Å] [4] and [Pt2(l-S)2(PPh3)4
Co(CH3COCHCOCH3)]+ [2.3063(12) and 2.3139(12) Å] [5], but long-
er than in cobalt(III) complexes with thiolate ligands bridging the
Table 1
Selected bond lengths (Å) and angles (°) for [Pt2(l-S)2(PPh3)4CoQ2]PF6.
two metals [i.e. CoIII( -SR)PtII], such as in [{Co(SCH2CH2NH2)3}
l
Pt(1)–P(1)
Pt(1)–S(2)
Pt(1)–Pt(2)
Pt(2)–P(3)
Pt(2)–S(2)
Co(1)–O(21)
Co(1)–N(21)
Co(1)–S(2)
O(21)–C(21)
2.299(4)
2.355(4)
3.2347(9)
2.299(4)
2.361(5)
1.932(15)
1.948(19)
2.288(5)
1.17(2)
Pt(1)–P(2)
Pt(1)–S(1)
Pt(2)–P(4)
Pt(2)–S(1)
Co(1)–O(11)
Co(1)–N(11)
Co(1)–S(1)
O(11)–C(11)
2.301(4)
2.366(4)
2.293(4)
2.354(4)
1.930(11)
1.938(12)
2.285(5)
1.33(3)
(l
-Pt)Co{(SCH2CH2NH2)3}]2+ [GAJSUG, average 2.255(3) Å] [13].
This reflects the steric effect of a bulky [Pt2( -S)2(PPh3)4] metallo-
l
ligand, which also effects a bending in the O(11)–Co(1)–O(21)
angle to 167.8(6)°, compared to 173.0(2)° in [CoQ2(Ph2PNPPh2
NPPh2)] [10]. The bite angle of the {Pt2S2} metalloligand [defined
by the angle S(1)–Co(1)–S(2)] is (as expected) more acute
[76.31(17)°] compared to the corresponding angles of 80.1(1)°
P(1)–Pt(1)–P(2)
P(2)–Pt(1)–S(1)
P(4)–Pt(2)–P(3)
P(3)–Pt(2)–S(2)
102.27(14)
91.18(13)
102.24(15)
91.08(16)
167.8(6)
86.6(6)
85.6(8)
92.2(4)
170.2(5)
97.2(4)
94.7(5)
P(1)–Pt(1)–S(2)
S(2)–Pt(1)–S(1)
P(4)–Pt(2)–S(1)
S(1)–Pt(2)–S(2)
93.57(14)
73.52(14)
93.77(14)
73.63(15)
85.1(5)
86.4(7)
96.0(7)
97.4(5)
93.3(6)
and 84.67(4)° in the cobalt(II) adducts [Pt2(
l-S)2(PPh3)4CoCl2]
and [Pt2(
l
-S)2(PPh3)4Co(CH3COCHCOCH3)]+ respectively.
The steric crowding also results in a very acute dihedral angle be-
tween the two PtS2 planes of 117.8°; increased folding of the {Pt2S2}
butterfly reduces steric congestion around the cobalt centre from
the four PPh3 ligands. By contrast, dihedral angles between the
PtS2 planes in the sterically non-congested cobalt(II) adducts
O(11)–Co(1)–O(21)
O(21)–Co(1)–N(11)
O(21)–Co(1)–N(21)
O(11)–Co(1)–S(1)
N(11)–Co(1)–S(1)
O(11)–Co(1)–S(2)
N(11)–Co(1)–S(2)
S(1)–Co(1)–S(2)
Co(1)–S(1)–Pt(1)
Co(1)–S(2)–Pt(1)
Pt(1)–S(2)–Pt(2)
O(11)–Co(1)–N(11)
O(11)–Co(1)–N(21)
N(11)–Co(1)–N(21)
O(21)–Co(1)–S(1)
N(21)–Co(1)–S(1)
O(21)–Co(1)–S(2)
N(21)–Co(1)–S(2)
Co(1)–S(1)-Pt(2)
Pt(2)–S(1)–Pt(1)
Co(1)–S(2)–Pt(2)
[Pt2(
are 126.3° and 129.8° respectively. Although there is some expected
variability, dihedral angles in complexes of [Pt2( -S)2(PPh3)4] acting
as a bidentate metalloligand are typically around 130–135° [2]. A
noteworthy exception however is [{Pt2( -S)2(PPh3)3Cl}Re(O)
5-C5Me4Et)]+, which has a dihedral angle between the two PtS2
l-S)2(PPh3)4CoCl2] and [Pt2(l
-S)2(PPh3)4Co(CH3COCHCOCH3)]+
92.3(5)
169.0(6)
87.41(15)
86.51(13)
87.18(16)
76.31(17)
87.50(16)
87.72(16)
86.62(15)
l
l
(g

H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
449
1503
1502
1504
1504
1503
1503
.
[1 + H]+
.
+
+
[1 + H]+ / [1]
[1]
(a)
(b)
(c)
m/z
1515
1515
1495
1500
1510
1515
1495
1500
1510
1505
1510
1505
1505
1495
1500
Fig. 4. Positive-ion ESI mass spectra of [Pt2(l-S)2(PPh3)4] 1 in methanol solution, recorded on a Bruker MicrOTOF instrument using a capillary exit voltage of 150 V: (a) with
addition of aqueous HCl, (b) with addition of aqueous NaOH, and (c) original methanol solution.
planes of 114.14°, most likely due to the steric bulk of the Re(O)
(
g
5-C5Me4Et)]+ moiety. Another example of an adduct with a more
8-(tosylamino)quinoline and Me3N in refluxing methanol, followed
by precipitation of the salmon-coloured product 8ꢀBPh4 by addi-
tion of excess NaBPh4. The complex shows the expected two dou-
blets in its 31P{1H} NMR spectrum, with two different 1J(PtP)
couplings of 3168 and 3872 Hz.
highly folded {Pt2S2} core and smaller dihedral angle is [{Pt2
(l
-S)2(Ph2PCH2CH2PPh2)2}2Cu]2+ (118.4° and 121.1°) [14]; in this
complex the two bulky [Pt2(l-S)2(PPh3)4] metalloligands coordinate
to a Cu2+ ion such that steric interactions between them are
minimised by increased folding of the {Pt2S2} cores.
The propensity for other N,O ligands to effect conversion
2.3. Dithiocarbamate system
of [Pt2(
l
-S)2(PPh3)4]
1
to {Pt2S2}CoIII derivatives was then
explored. Reaction of
1
with CoCl2ꢀ6H2O and picolinic acid
The dithiocarbamate ligand, R2NCS2ꢂ, is known to stabilize
transition metal complexes in their higher oxidation states. For
example, cobalt(II) dithiocarbamates Co(S2CNR2)2 are readily oxi-
dised [15] whereas cobalt(III) dithiocarbamates Co(S2CNR2)3 are
stable compounds, that can even be oxidised to the higher
oxidation state cobalt(IV) cations [Co(S2CNR2)3]+ [16,17]. This sug-
gested that reactions of cobalt(II)–dithiocarbamate mixtures with
(pyridine-2-carboxylic acid, PicH) proceeded in a similar manner,
forming a dark brown solution that contains the cobalt(III) adduct
[Pt2(l
-ꢂS)2(PPh3)4Co(Pic)2]+ 5. The cation was similarly isolated as
its PF6 salt 5ꢀPF6. The 31P{1H} NMR spectra of complexes 4ꢀPF6
and 5ꢀPF6 showed two inequivalent PPh3 resonances, each appear-
ing as a complex multiplet, showing very similar couplings to 195Pt
(e.g. 3261 and 3225 Hz for 4).
[Pt2(l-S)2(PPh3)4] were likely to generate cobalt(III) adducts. In-
The reaction of [Pt2(
slightly more than one molar equivalent of 8-(tosylamino)quino-
line (HTQ) 6 with added Me3N base gave an orange solution, from
l
-S)2(PPh3)4]
1
with CoCl2ꢀ6H2O and
deed, when Na[S2CNEt2] was added to a stirred mixture of
[Pt2(l-S)2(PPh3)4] and CoCl2ꢀ6H2O in methanol, the initial solid of
[Pt2(l-S)2(PPh3)4CoCl2] rapidly dissolved, giving a deep orange-
which the cobalt(II) adduct [Pt2(
l
-S)2(PPh3)4Co(TQ)]PF6 7ꢀPF6 was
brown solution, and positive-ion ESI MS after several minutes
showed a dominant peak due to [Pt2(
-S)2(PPh3)4Co(S2CNEt2)2]+
at m/z 1858.237 (calculated 1858.223), with relatively small ion
isolated by addition of excess NH4PF6 to the filtered reaction solu-
tion. The positive-ion ESI mass spectrum of this compound showed
the expected cation at m/z 1859.168 (calculated 1859.242), with no
l
signals at m/z 1710.210 due to the cobalt(II) adduct [Pt2(l-S)2
evidence for the cobalt(III) adduct [Pt2(
l
-S)2(PPh3)4Co(TQ)2]+.
(PPh3)4Co(S2CNEt2)]+ (calculated m/z 1710.197) and the decompo-
sition product [Pt(S2CNEt2)(PPh3)2]+ at m/z 867.186 (calculated m/z
867.172). The dithiocarbamate NH4[S2CN(CH2)4] behaved in an
identical manner. Reactions were fully complete after several
When the synthesis reaction was repeated using 2 mol equivalents
of 8-(tosylamino)quinoline and a ca. 60 h reaction time, in air, ESI
MS analysis of the reaction mixture again showed 7 as the base
peak, with a small amount of the mononuclear platinum complex
[Pt(TQ)(PPh3)2]+ (m/z 1016.201, calculated m/z 1016.217) and some
very minor unidentified side products. Unlike the 8-hydroxyquin-
oline system, 8-(tosylamino)quinoline does not form a correspond-
ing cobalt(III) derivative under the conditions investigated. This
may be due to steric crowding from the bulky 8-(tosylamino)quin-
oline ligand around the cobalt which prevents formation of a
six-coordinate cobalt(III) derivative.
hours, and the adducts [Pt2(
l
-S)2(PPh3)4Co(S2CNR2)2]+PF6ꢂ [9aꢀPF6,
R = Et and 9bꢀPF6, R2 = (CH2)4] were readily isolated in a fairly pure
form by addition of excess NH4PF6 to the filtered reaction
solutions. Reaction of [Pt2(
[O(CH2CH2)2NH2][O(CH2CH2)2NCS2] likewise yielded [Pt2(
l
-S)2(PPh3)4] with CoCl2ꢀ6H2O and
l
-S)2
(PPh3)4Co{S2CN(CH2CH2)2O}2]PF6 (9cꢀPF6) but this reaction was
slower than for the other dithiocarbamates, probably because of
the lower solubility of the morpholine-derived dithiocarbamate
salt in MeOH. The dithiocarbamate–cobalt(III) adducts are brown
or orange-brown solids, readily soluble in dichloromethane but
The complex [Pt(TQ)(PPh3)2]+ has not been previously reported,
but can be easily synthesised by reaction of cis-[PtCl2(PPh3)2] with

450
H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
insoluble in methanol. The dithiocarbamate complexes all show
very similar 31P{1H} NMR spectra, with two multiplets due to
two inequivalent sets of PPh3 ligands (that arise from the asymme-
try in the Co(S2CNR2)2 moiety), showing similar couplings to 195Pt
(e.g. 3215 and 2983 Hz for 9a).
of aqueous HCl had been added yielded
Fig. 4(a), which showed solely [Pt2(
-S)2(PPh3)4H]+, with excellent
agreement between the experimental and calculated isotope
patterns. However, analysis of a methanolic solution of [Pt2( -S)2
(PPh3)4] to which some NaOH is added results in the observation
of the oxidised ion [Pt2(
-S)2(PPh3)4]Å+ in the ESI mass spectrum,
a mass spectrum,
l
l
l
2.4. Electrospray mass spectrometric investigation of cobalt(III)
adducts
Fig. 4(b). Again, inspection of the isotope pattern shows good
agreement with the calculated pattern. Under these conditions,
the concentration of H+ ions in the alkaline solution is obviously
The behaviour of 4ꢀPF6 under variable fragmentation conditions
in ESI MS was investigated, and revealed some interesting results.
Under gentle conditions (capillary exit voltage 60 V), the ion
very low, such that electrochemical oxidation of [Pt2(l-S)2
(PPh3)4] in the steel ESI capillary (a well-known electrospray ioni-
sation pathway for relatively easily oxidised analytes [23–25]) now
becomes competitive, and ionisation by protonation is suppressed.
Such behaviour has been observed previously, for example for
FcCH2P(O)(OPh)2, which gives oxidised [M]+ or protonated [MH]+
ions, depending on the pH of the analyte solution [26]. Osmocene,
[Pt2(l
-S)2(PPh3)4CoQ2]+ was the only one observed, consistent
with the formation of a pure product. However, at high capillary
exit voltages >150 V, fragmentation to two major ions was ob-
served; the most intense of these (at all voltages) was an ion at
m/z 1503.271, while the minor ion at m/z 1706.248 is assigned to
(g
5-C5H5)2Os, behaves similarly [27]. Finally, when a methanol
solution of [Pt2( -S)2(PPh3)4] was analysed (with no acid or base
the cobalt(II) ion observed previously, viz. [Pt2(
l
-S)2(PPh3)4CoQ]+
l
(calculated m/z 1706.217). Examination of the high resolution iso-
tope pattern of the ion at m/z 1503 indicated that this ion is due to
addition), the mass spectrum, Fig. 4(c), shows a somewhat differ-
ent isotope pattern, indicative of contributions from both the
oxidised [Pt2(
l
-S)2(PPh3)4], viz. [Pt2(
l
-S)2(PPh3)4]Å+ (vide infra).
protonated [Pt2(l l
-S)2(PPh3)4H]+ and oxidised [Pt2( -S)2(PPh3)4]Å+
Thus, the two most intense peaks in the isotope pattern were ob-
served at m/z 1502.270 and 1503.271 and the calculated m/z values
for these same two isotopomers are at m/z 1502.237 and 1503.239.
In contrast, the most intense two peaks in the isotopic envelope of
ions. It can be estimated (from peak intensities) that the
protonated ion is the major component (around 70%).
Further experiments were carried out in order to investigate the
MS fragmentation processes in the cobalt adducts; the analogous
protonated [Pt2(
l
-S)2(PPh3)4], i.e. [Pt2(
l
-S)2(PPh3)4H]+, are at m/z
indium complex [Pt2(
l
-S)2(PPh3)4InQ2]+PF6 has recently been
ꢂ
1503.245 and 1504.247. At even greater capillary exit voltages
prepared [28] and because indium(III) is not readily reduced to
lower oxidation states, its fragmentation behaviour was
investigated in more detail in order to ascertain the effect of metal
redox activity. Even at high capillary exit voltages, the parent ion
(e.g. 210 V), another minor ion at m/z 1240.184 was observed in
the spectrum of 4, and is assigned as [Pt2(l
-S)2(PPh3)3]Å+ (calcu-
lated m/z 1240.146) formed by dissociation of a PPh3 ligand. The
ESI mass spectrum of 4ꢀPF6 at a capillary exit voltage of 210 V is
shown in Fig. 3a. The picolinate complex 5ꢀPF6 behaved in a very
similar manner, though with some differences; at a capillary exit
[Pt2(l
-S)2(PPh3)4InQ2]+ was the base peak in the spectrum, as
illustrated in Fig. 3b at a capillary exit voltage of 210 V; this
Figure dramatically illustrates the very different behaviour shown
by the Co and In complexes under highly fragmenting conditions.
The single main fragment ion observed at m/z 1498.093 is 1 mass
voltage of 180 V, less fragmentation of [Pt2(
to [Pt2(
-S)2(PPh3)4]Å+ occurred, and fragmentation to the cobalt(II)
adduct [Pt2(
-S)2(PPh3)4CoII(Pic)]+ was negligible by comparison to
the Q system.
Complexes with oxidised {Pt2(
investigated. In a detailed electrochemical and theoretical study on
the redox properties of the complexes [Pt2( -S)2L2] [L = Ph2
l
-S)2(PPh3)4Co(Pic)2]+
l
l
unit less than expected for [Pt2(l
-S)2(PPh3)3InQ]+, and is thus ten-
tatively assigned to a species which contains a cyclometallated
PPh3 ligand on Pt (calculated m/z 1498.087).
l
-S)2} cores have been previously
Based on the above observations, the proposed fragmentation
l
pathway for [Pt2(l
-S)2(PPh3)4CoQ2]+ proceeds via an internal
P(CH2)nPPh2; n = 2 (dppe) or n = 3 (dppp)] it was found that the
complexes undergo two consecutive one-electron oxidations [18].
electron transfer process in which inert, low-spin d6 cobalt(III) is
reduced to cobalt(II) by electron transfer from a sulfide ligand. Loss
of CoIIQ2 (promoted by the substantially greater lability of the
newly-generated d7 cobalt(II) centre [6]) can lead to the major
The arsine complex [Pt2(l-S)2(Ph2As(CH2)2AsPh2)2] behaves in a
similar manner [19]. The mono-oxidised species [Pt2(l
-S)2L2]Å+
are direct analogues of [Pt2(
[Pt2(
The monocations [Pt2(
not isolable, evolving instead to give the trimetallic complexes
[Pt3( chemical oxidation of [Pt2( -S)2(Ph2As(CH2)2
-S)2L3]2+
AsPh2)2] with 4-nitrobenzenediazonium tetrafluoroborate (a one-
l
-S)2(PPh3)4]Å+ while the dications
fragment ion [Pt2(
of Q from [Pt2(
-S)2(PPh3)4CoIIQ2]+ can lead to the observed cobal-
t(II)-Q adduct [Pt2(
-S)2(PPh3)4CoQ]+ (m/z 1706), observed as a
lower intensity fragment ion, Fig. 3(b). The corresponding indium
complex [Pt2(
-S)2(PPh3)4InQ2]+ shows no such redox behaviour,
l
-S)2(PPh3)4]Å+ at m/z 1502. Alternatively, loss
2ꢂ
l
-S)2L2]2+ are considered to contain the disulfide S2 ligand.
l
l
-S)2L2]Å+ were found to be unstable and
l
l
;
l
l
and is substantially resistant towards fragmentation.
electron oxidant) resulted in the formation of [Pt3(
good yield.
l
-S)2L3]2+ in
2.5. Other cobalt(II) adducts with 2,20-bipyridine, 1,10-phenanthroline
and ethyl maltolate ligands
Positive-ion ESI MS of [Pt2(
has been reported to give the protonated ion [Pt2(
[20]. As far as we are aware, ESI MS investigations on
[Pt2( -S)2(PPh3)4] and analogues thereof have only detected the
l
-S)2(PPh3)4] 1 in methanol solution
l
-S)2(PPh3)4H]+
The reaction of [Pt2(
l
-S)2(PPh3)4] 1 with CoCl2ꢀ6H2O and either
l
2,20-bipyridine (bipy) or 1,10-phenathroline (phen) does not lead
to cobalt(III) adducts. Instead, fairly rapid dissolution of the initial
protonated ion in solution. The observation of protonated analytes
in positive ion mode ESI MS is well understood in terms of a de-
crease in pH upon droplet evaporation [21], which has been probed
using a pH-sensitive fluorescent dye [22]. The suggestion that the
high nucleophilicity of the sulfide ligands in complexes with
{Pt2S2} cores is in accord with the observed redox behaviour [18]
solid [Pt2(l-S)2(PPh3)4CoCl2] occurs with the formation of deep or-
ange-brown solutions, from which red-brown solids were isolated
by addition of excess NH4PF6. Analysis of the products by ESI MS
and microelemental analysis suggests that they are mixtures of
the chloride-free four-coordinate adducts 10 and the five-coordi-
nate chloride-containing adducts 11. For example, in the bipy
system, experimental CHN microanalytical data (C 50.84; H 3.50;
suggested that the [Pt2(
by ESI MS. The ESI MS behaviour of [Pt2(
been investigated under different pH conditions. Analysis of a
methanol solution of [Pt2( -S)2(PPh3)4] to which a small quantity
l
-S)2(PPh3)4]Å+ ion might be observable
-S)2(PPh3)4] has therefore
l
N 1.33%) are intermediate between those calculated for [Pt2(
l
-S)2
-S)2
l
(PPh3)4Co(bipy)](PF6)2 (C 49.02; H 3.41; N 1.40%) and for [Pt2(
l

H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
451
(PPh3)4CoCl(bipy)]PF6 (C 51.85; H 3.61; N 1.48%). ESI MS analysis
showed the ions [Pt2(
-S)2(PPh3)4Co(bipy)]2+ (m/z 859.110, calcu-
lated m/z 859.120) and [Pt2(
-S)2(PPh3)4CoCl(bipy)]+ (m/z
1753.193, calculated m/z 1753.209).
Reaction of 1 with CoCl2ꢀ6H2O and ethyl maltol with added
Me3N base also proceeds smoothly to give the cobalt(II) adduct
12, isolated as its hexafluorophosphate salt 12ꢀPF6 as a greenish-
brown solid. This complex is similar to the known diketonate
cobalt(II) adducts, in that the maltolate ligand is also an
O,O0-bidentate chelating ligand. No evidence for cobalt(III) adducts
was observed in this system.
considerably extending the range of known cobalt derivatives.
The oxidation of cobalt(II) precursors was a successful strategy
l
l
for the synthesis of these complexes. The radical cation [Pt2(l-
S)2(PPh3)4]Å+ is a key fragment ion formed by cobalt(III)–{Pt2S2} ad-
ducts in ESI mass spectrometry, attributable to the redox activity of
the cobalt(III) centre. This cation can be readily generated mass
spectrometrically by electrochemical (capillary) oxidation of
[Pt2(l-S)2(PPh3)4] in alkaline solution. We are currently investigat-
ing the extension of the synthetic methodology to the coordination
chemistry of [Pt2(l-S)2(PPh3)4] with other previously uncoordi-
nated metals.
An attempt at the synthesis of a cobalt(III) acetylacetonate
(acac) derivative was unsuccessful; reaction of [Pt2(
l-S)2(PPh3)4]
1 with Co(acac)2(H2O)2 yielded [Pt2(
l
-S)2(PPh3)4Co(acac)]+ (as pre-
4. Experimental
viously reported [5]) but we were unsuccessful in oxidising this
cation using hydrogen peroxide.
ESI mass spectra were recorded on (low resolution) VG Platform
II or (high resolution) Bruker MicrOTOF instruments. Samples were
analysed as solutions (ca. 0.1 mg mLꢂ1), prepared by dissolving a
small quantity of sample in a few drops of either dichloromethane
or acetonitrile, followed by dilution to ca. 1.5 mL with methanol.
Confirmation of species was facilitated by comparison of observed
and calculated isotope distribution patterns, the latter obtained
3. Conclusions
The first examples of cobalt(III) derivatives of [Pt2(l-S)2(PPh3)4]
have been synthesised along with some new cobalt(II) adducts,
2+
Ph P
3
PPh
3
3
X
X
Ph P
PPh
3
Pt
Cl
Pt
Pt
S
S
Co
S
S
Co
S
S
Pt
Pt
Pt
Pt
Ph P
3
Ph P
3
PPh
3
Ph P
3
Ph P
3
PPh
3
3
3
Cl
PPh
PPh
Co
2a, X = Cl
2b, X = Br
1
S
S
2c, X = NCS
Pt
Ph P
3
Ph P
3
PPh
3
PPh
3
3
+
+
O
N
N
S
O
O
2
2
Co
Co
S
S
S
Pt
Pt
Pt
Pt
Ph P
3
PPh
3
3
Ph P
PPh
3
PPh
3
3
PPh
Ph P
Ph P
3
3
4
5
+
CH
3
N
N
S
N
N
S
H
S
CH
3
Co
O
O
O
O
S
Pt
Pt
Ph P
PPh
3
3
3
PPh
Ph P
3
6
7

452
H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
from the Isotope programme [29], or from instrument-based
software. M/z values are of the most abundant isotopomer in the
isotope envelope of the ion. Elemental analyses were obtained by
the Campbell Microanalytical Laboratory at the University of Otag-
o, Dunedin, New Zealand. NMR spectra were recorded at 162 MHz
in CDCl3 solution on a Bruker AVIII 400 under Topspin 3.0 software,
or an AVII 300 under Topspin 2.1 software.
4.1. Synthesis of [Pt2(
l
-S)2(PPh3)4CoCl2] 2a
A mixture of [Pt2(
l-S)2(PPh3)4] 1 (188 mg, 0.125 mmol) and
CoCl2ꢀ6H2O (40 mg, 0.168 mmol) in methanol (10 mL) was stirred
for 30 min., giving a greenish suspension. The product was filtered,
washed with cold methanol (2 ꢃ 3 mL) and dried under vacuum to
give 2a (156 mg, 76%) as a yellowish-green solid. Anal. Calc.
The platinum complexes [Pt2(
l
-S)2(PPh3)4]
1
[30,31] and
C
72H60Cl2CoP4Pt2S2 (Mr 1632.31): C, 52.93; H, 3.70. Found: C,
52.70; H, 3.56%. ESI MS (MeCN–MeOH): m/z 1597.121 (calculated
m/z 1597.140) [Pt2(
-S)2(PPh3)4CoCl]+ (100%).
[Pt2( -S)2(PPh3)4InQ2]PF6 [28] were prepared by the literature pro-
l
cedures. The dithiocarbamate [O(CH2CH2)2NH2]+[O(CH2CH2)2
NCS2]ꢂ [32] and [Co(acac)2(H2O)2] [33] were prepared by the liter-
ature procedures. Cobalt(II) chloride hexahydrate (BDH), cobalt(II)
thiocyanate (BDH), hydrated cobalt(II) bromide (BDH), ammonium
hexafluorophosphate (Aldrich), aqueous trimethylamine solution
(25–30% w/v, BDH), sodium diethyldithiocarbamate (BDH), ammo-
nium pyrollidinedithiocarbamate (BDH), 8-(tosylamino)quinoline
(Aldrich), ethyl maltol (2-ethyl-3-hydroxy-4H-pyran-4-one, Al-
drich), picolinic acid (BDH) and 8-hydroxyquinoline (Riedel de
Haën) were used as supplied from commercial sources. Reactions
were carried out in methanol (LR grade) in air.
l
4.2. Synthesis of [Pt2(
l-S)2(PPh3)4CoBr2] 2b
Following the procedure for 2a, a mixture of [Pt2(l-S)2(PPh3)4] 1
(178 mg, 0.118 mmol) and hydrated cobalt(II) bromide (62 mg) in
methanol (20 mL) for 1.5 h gave 2b (157 mg, 77%) as a yellowish-
green solid. Anal. Calc. C72H60Br2CoP4Pt2S2 (Mr 1721.21): C, 50.20;
H, 3.51. Found: C, 50.43; H, 3.43%. ESI MS (MeCN–MeOH): m/z
1642.082 (calculated m/z 1642.089) [Pt2(l
-S)2(PPh3)4CoBr]+ (100%).
NR
2
+
+
S
S
CH
3
2
Co
N
N
S
S
Pt
S
O
O
Pt
Pt
Ph P
3
PPh
3
Ph P
3
PPh
Ph P
3
3
PPh
3
8
9a, R = Et
9b, R = (CH )
2
2 4
9c, R = (CH CH ) O
2
2
2 2
2+
+
N
N
N
Cl
N
Co
Co
S
S
S
S
Pt
Pt
Pt
Pt
Ph P
3
PPh
3
Ph P
3
PPh
3
PPh
Ph P
3
3
PPh
Ph P
3
3
10a, N-N = 2,2'-bipyridine
10b, N-N = 1,10-phenanthroline
11a, N-N = 2,2'-bipyridine
11b, N-N = 1,10-phenanthroline
O
+
O
O
Co
S
S
Pt
Pt
Ph P
3
PPh
3
PPh
Ph P
3
3
12

H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
453
4.3. Synthesis of [Pt2(
l
-S)2(PPh3)4Co(NCS)2] 2c
trimethylamine (10 drops), whereupon the suspension began to
dissolve giving a brownish solution. After stirring for 1.5 h, the
resulting orange solution was filtered to remove some insoluble
matter, and NH4PF6 (300 mg, 1.84 mmol) added to the filtrate, giv-
ing an orange precipitate. The product was filtered, washed with
water (2 ꢃ 5 mL) and dried under vacuum to give 7ꢀPF6 (207 mg,
73%) as an orange solid. Anal. Calc. C88H73CoF6N2O2P5Pt2S2 (Mr
2003.43): C, 52.71; H, 3.67; N, 1.40. Found: C, 52.61; H, 3.57; N,
1.37%. ESI MS (CH2Cl2–MeOH): m/z 1859.168 (calculated m/z
Following the procedure for 2a, a mixture of [Pt2(
l-S)2(PPh3)4] 1
(233 mg, 0.155 mmol) and hydrated cobalt(II) thiocyanate (78 mg)
in methanol (25 mL) for 1.5 h gave 2c (212 mg, 82%) as a bright
lime-green solid. Anal. Calc. C74H60CoN2P4Pt2S4 (Mr 1677.35): C,
52.94; H, 3.60; N, 1.67. Found: C, 51.94; H, 3.53; N, 1.43%. The com-
pound is insoluble in dichloromethane and methanol; ESI mass
spectra could not be recorded.
1859.242) [Pt2(l
-S)2(PPh3)4Co(TQ)]+ (100%). 31P NMR data could
4.4. Synthesis of [Pt2(
l
-S)2(PPh3)4CoQ2]PF6 (4ꢀPF6)
not be acquired for this complex.
To a suspension of [Pt2( -S)2(PPh3)4] 1 (210 mg, 0.140 mmol) in
l
4.8. Synthesis of [Pt(TQ)(PPh3)2]BPh4 (8ꢀBPh4)
methanol (40 mL) was added CoCl2ꢀ6H2O (34 mg, 0.143 mmol) and
the mixture stirred for 10 min. to give a greenish suspension. 8-
Hydroxyquinoline (41 mg, 0.282 mmol) was added, followed by
aqueous trimethylamine (5 drops), whereupon the solid quickly
dissolved giving an orange solution. The mixture was stirred in
air, darkening in colour to deep orange-brown after several hours.
After stirring for 24 h, the solution was filtered to remove a trace of
insoluble matter. Ammonium hexafluorophosphate (300 mg,
1.84 mmol) was added to the stirred filtrate, giving an orange-
brown precipitate. After 20 min., water (10 mL) was added to assist
precipitation. The product was filtered, washed with water
(2 ꢃ 5 mL) and dried under vacuum to give an orange-brown pow-
A mixture of cis-[PtCl2(PPh3)2] (237 mg, 0.300 mmol), 8-(tosyla-
mino)quinoline (95 mg, 0.318 mmol) and aqueous trimethylamine
(10 drops) in methanol (40 mL) was refluxed for 2 h, giving a clou-
dy orange solution. After filtration, NaBPh4 (300 mg, 0.877 mmol)
was added to the warm filtrate, giving a pinkish precipitate. The
product was filtered, washed with methanol–water (1:1, 5 mL)
and dried under vacuum to give 8ꢀBPh4 (210 mg, 52%). Anal. Calc.
C
76H63BN2O2P2PtS (Mr 1335.49): C, 68.29; H, 4.75; N, 2.10. Found:
C, 67.98; H, 4.73; N, 1.84%. ESI MS (CH2Cl2–MeOH): m/z 1016.079
(calculated m/z 1016.217) [Pt(TQ)(PPh3)2]+ (100%). 31P{1H} NMR,
d 12.4 [d, 1J(PtP) 3168, 2J(PP) 25.8] and 8.4 [d, 1J(PtP) 3872, 2J(PP)
25.8].
der (159 mg, 57%). Anal. Calc.
C90H72CoF6N2O2P5Pt2S2 (Mr
1994.45): C, 54.15; H, 3.64; N, 1.40. Found: C, 53.44; H, 3.50; N,
1.20%. ESI MS (CH2Cl2–MeOH): m/z 1850.170 (calculated m/z
4.9. Synthesis of [Pt2(
l
-S)2(PPh3)4Co(S2CNEt2)2]PF6 (9aꢀPF6)
1850.262) [Pt2(
l
-S)2(PPh3)4CoQ2]+ (100%). 31P{1H} NMR, d 15.9
[m, 1J(PtP) 3261] and 14.5 [m, 1J(PtP) 3225].
A mixture of [Pt2( -S)2(PPh3)4] 1 (363 mg, 0.242 mmol) and
l
CoCl2ꢀ6H2O (59 mg, 0.248 mmol), in methanol (40 mL) was stirred
for 10 min. to give a greenish suspension. Solid NaS2CNEt2ꢀ3H2O
(110 mg, 0.488 mmol) was added in several portions, rapidly form-
ing a brown solution. After stirring for several minutes, ESI MS
4.5. Reaction monitoring of [Pt2(l
-S)2(PPh3)4CoQ2]+ synthesis
Following the general procedure used in the synthesis of 4ꢀPF6, a
reaction mixture comprising [Pt2( -S)2(PPh3)4] (55 mg),
l
1
showed predominantly [Pt2(l
-S)2(PPh3)4Co(S2CNEt2)2]+. After stir-
CoCl2ꢀ6H2O (10 mg), 8-hydroxyquinoline (11.6 mg) and aqueous
trimethylamine solution (4 drops) in methanol (30 mL) was stirred
and aliquots monitored periodically by positive-ion ESI MS.
ring for 2 h the reaction mixture was filtered to remove a trace of
insoluble material. NH4PF6 (300 mg, 1.84 mmol) was added to the
stirred filtrate, giving a brown precipitate. The product was iso-
lated by filtration, washed with methanol (5 mL) and then water
(5 mL) and dried under vacuum to give 9aꢀPF6 (450 mg, 93%). A
sample for microelemental analysis was recrystallised from dichlo-
romethane-diethyl ether giving black crystals. Anal. Calc.
4.6. Synthesis of [Pt2(
l
-S)2(PPh3)4Co(Pic)2]PF6 (5ꢀPF6)
To
a
stirred mixture of [Pt2( -S)2(PPh3)4]
l
1
(143 mg,
0.095 mmol) and CoCl2ꢀ6H2O (22.6 mg, 0.095 mmol) in methanol
(30 mL) was added 2-picolinic acid (24 mg, 0.195 mmol), followed
by trimethylamine solution (0.5 mL, excess), giving a cloudy or-
ange solution. On stirring, the mixture quickly converted to a
red-orange suspension. After stirring for 3.5 h, dichloromethane
(ca. 5 mL) was added to the red-orange suspension, resulting in a
clear solution. Solid NH4PF6 (300 mg, 1.84 mmol) was added, and
the volume of the mixture reduced to around 25 mL, to remove
most of the dichloromethane. The resulting brown precipitate
was filtered, washed with 1:1 methanol–water (5 mL) and dried
under vacuum to give 5ꢀPF6 (128 mg, 69%). A sample for microele-
mental analysis was recrystallised from dichloromethane–diethyl
ether giving black crystals. Anal. Calc. C84H68CoF6N2O4P5Pt2S2 (Mr
1950.41): C, 51.68; H, 3.51; N, 1.44. Found: C, 50.63; H, 3.68; N,
1.37%. ESI MS (CH2Cl2–MeOH): m/z 1806.188 (calculated m/z
C
82H80CoF6N2P5Pt2S6 (Mr 2002.42): C, 49.14; H, 4.03; N, 1.40.
Found: C, 49.21; H, 4.07; N, 1.31%. ESI MS (CH2Cl2–MeOH): m/z
1858.392 (calculated m/z 1858.223) [Pt2(l-S)2(PPh3)4Co(S2C-
NEt2)2]+ (100%). 31P{1H} NMR, d 19.1 [m, 1J(PtP) 3215] and 13.6
[m, 1J(PtP) 2983].
4.10. Synthesis of [Pt2(
l
-S)2(PPh3)4Co{S2CN(CH2)4}2]PF6 (9bꢀPF6)
-S)2(PPh3)4] 1 (383 mg,
Following the method for 9aꢀPF6 [Pt2(
l
0.255 mmol) with CoCl2ꢀ6H2O (61 mg, 0.256 mmol), NH4[S2CN
(CH2)4] (85 mg, 0.517 mmol) and NH4PF6 (300 mg, 1.84 mmol)
gave 9bꢀPF6 (274 mg, 54%) as an orange-brown powder. A sample
for microelemental analysis was recrystallised from dichlorometh-
ane-diethyl ether giving black crystals. Anal. Calc.
F6N2P5Pt2S6 (Mr 1998.39): C, 49.24; H, 3.83; N, 1.40. Found: C,
C82H76Co
1806.221) [Pt2(
l
-S)2(PPh3)4Co(Pic)2]+ (100%). 31P{1H} NMR, d 14.5
48.18; H, 3.65; N, 1.35%. ESI MS (CH2Cl2–MeOH): m/z 1854.188
[m, 1J(PtP) 3242] and 13.8 [m, 1J(PtP) 3237].
(calculated m/z 1854.191) [Pt2(l
-S)2(PPh3)4Co{S2CN(CH2)4}2]+
(100%). 31P{1H} NMR, d 19.2 [m, 1J(PtP) 3204] and 13.5 [m, 1J(PtP)
4.7. Synthesis of [Pt2(
l
-S)2(PPh3)4Co(TQ)]PF6 (7ꢀPF6)
3010].
A mixture of [Pt2( -S)2(PPh3)4] 1 (213 mg, 0.142 mmol) in
l
4.11. Synthesis of [Pt2(
l
-S)2(PPh3)4Co{S2CN(CH2)2O}2]PF6 (9cꢀPF6)
methanol (40 mL) with CoCl2ꢀ6H2O (36 mg, 0.151 mmol) was stir-
red for 10 min. giving a greenish suspension. 8-(Tosylamino)quin-
oline 6 (48 mg, 0.161 mmol) was added, followed by aqueous
Following the method for 9aꢀPF6 [Pt2( -S)2(PPh3)4] 1 (367 mg,
l
0.244 mmol) with CoCl2ꢀ6H2O (59 mg, 0.248 mmol), [O(CH2CH2)2

454
H.M. Clarke et al. / Inorganica Chimica Acta 376 (2011) 446–455
NH2][O(CH2CH2)2NCS2] (124 mg, 0.496 mmol) and NH4PF6
(300 mg, 1.84 mmol) gave 9cꢀPF6 (295 mg, 59%) as an orange-
brown powder. Anal. Calc. C82H76CoF6N2O2P5Pt2S6: C, 48.46; H,
3.77; N, 1.38. Found: C, 48.06; H, 3.64; N, 1.33%. ESI MS (CH2Cl2–
stirring overnight, ESI MS showed [Pt2(
a small amount of [Pt(acac)(PPh3)2]+ (m/z 818.216).
l
-S)2(PPh3)4Co(acac)]+ with
5. X-ray structure determination of [Pt2(l-S)2(PPh3)4CoQ2]PF6
MeOH): m/z 1886.238 (calculated m/z 1886.182) [Pt2(
l
-S)2
(PPh3)4Co{S2CN(CH2)2O}2]+ (100%). 31P{1H} NMR,
d 19.9 [m,
Crystals were obtained from dichloromethane-diethyl ether. X-
ray data were collected on a Bruker Apex II CCD diffractometer at
the University of Auckland and were corrected for absorption by
a multi-scan method (SADABS) [34]. The structure was solved and re-
fined with SHELX97 [35].
1J(PtP) 3222] and 12.7 [m, 1J(PtP) 2998].
4.12. Attempted synthesis of [Pt2(l-S)2(PPh3)4Co(bipy)](PF6)2
10aꢀ(PF6)2 using CoCl2ꢀ6H2O
Refinement was complicated by apparent disorder of the two Q
ligands whereby there was partial occupancy of each in the oppo-
site sense, i.e. where the N(11) ligand has O(11) in the O(21) posi-
tion and vice versa. The quality of the data was not sufficient to
resolve the disorder so the second component was not included
in the model, so led to the unrealistically enlarged ellipsoids for
the outer C atoms of the rings. The PF6 anion was disordered
equally over two sites, but this could be modelled reasonably
successfully.
To a suspension of [Pt2(l-S)2(PPh3)4] 1 (200 mg, 0.133 mmol) in
methanol (40 mL) was added CoCl2ꢀ6H2O (34 mg, 0.143 mmol),
and the mixture stirred for 10 min. to give a greenish suspension.
2,20-Bipyridine (24 mg, 0.154 mmol) was added and the mixture
stirred for 1 h, giving a clear deep orange-brown solution. After fil-
tration to remove a trace of insoluble matter NH4PF6 (200 mg,
1.23 mmol) was added to the filtrate, giving a red-brown precipi-
tate. Water (10 mL) was added dropwise, the product filtered,
washed with water (10 mL) and dried under vacuum to give the
ꢂ
Crystal data for C90H72CoF6N2O2P5Pt2S2: Mr = 1995.58; mono-
clinic; space group P21/c; a = 14.2924(5) Å; b = 22.6951(8) Å;
product (169 mg). Anal. Calc. [Pt2(
(C82H68CoF12N2P6Pt2S2): C, 49.02; H, 3.41; N, 1.40. Found: C,
50.84; H, 3.50; N, 1.33% and Anal. Calc. [Pt2( -S)2(PPh3)4CoCl(bi-
l-S)2(PPh3)4Co(bipy)](PF6)2
c = 25.7042(10) Å;
T = 93(2) K; k(Mo
b = 91.021(2)°;
) = 0.71073 Å;
V = 8336.3(5) Å3;
(Mo
Z = 2;
) = 3.753 mmꢂ1
;
l
Ka
l
K
a
dcalc = 1.590 g cmꢂ3; reflections collected 74457; unique 18199
(Rint = 0.1174); giving R1 = 0.1023, wR2 = 0.2094 for data with
py)]PF6 (C82H68ClCoF6N2P5Pt2S2): C, 51.85; H, 3.61; N, 1.48. Found:
C, 50.84; H, 3.50; N, 1.33%. ESI MS (MeCN–MeOH): m/z 859.110
(calculated m/z 859.120) [Pt2(l
-S)2(PPh3)4Co(bipy)]2+ 10a and m/
[I > 2r(I)] and R1 = 0.1700, wR2 = 0.2350 for all data. Residual elec-
z 1753.193 (calculated m/z 1753.209) [Pt2(
l
-S)2(PPh3)4CoCl(bipy)]+
tron density (e Åꢂ3) maximum/minimum: 2.370/ꢂ5.791.
11a.
Acknowledgements
4.13. Attempted synthesis of [Pt2(l-S)2(PPh3)4Co(phen)](PF6)2
10bꢀ(PF6)2
We thank the University of Waikato for financial support of this
work and Dr. Tania Groutso (University of Auckland) for collection
of the X-ray data set. Pat Gread is thanked for assistance with mass
spectrometry instrumentation and Oguejiofo Ujam is thanked for
recording the NMR spectra.
Following the procedure for the preceding synthesis, and
replacing the bipyridine with 1,10-phenanthrolineꢀH2O (35 mg,
0.177 mmol), gave the product as a red-brown solid (198 mg). Anal.
Calc. [Pt2(
49.62; H, 3.37; N, 1.38. Found: C, 51.03; H, 3.41; N, 1.95% and Anal.
Calc. [Pt2( -S)2(PPh3)4CoCl(phen)]PF6 (C84H68ClCoF6N2P5Pt2S2): C,
52.45; H, 3.57; N, 1.46. Found: C, 51.03; H, 3.41; N, 1.95%. ESI MS
(MeCN–MeOH): m/z 871.123 (calculated m/z 871.120) [Pt2(
S)2(PPh3)4Co(phen)]2+ 10b and m/z 1777.195 (calculated m/z
1777.209) [Pt2(
-S)2(PPh3)4CoCl(phen)]+ 11b.
l-S)2(PPh3)4Co(phen)](PF6)2 (C84H68CoF12N2P6Pt2S2): C,
Appendix A. Supplementary material
l
CCDC 817416 contains the supplementary crystallographic data
for complex [Pt2(l-S)2(PPh3)4]. 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 associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.07.006.
l
-
l
4.14. Synthesis of [Pt2(
l-S)2(PPh3)4Co(ethyl maltolate)]PF6 (12ꢀPF6)
To
a
stirred mixture of [Pt2( -S)2(PPh3)4] (256 mg,
l
1
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