Coordination chemistry of the metalloligand [Pt2(μ-S) 2(PPh3)4] with nickel(II) complexes - An electrospray mass spectrometry directed synthetic study

Article abstract of DOI:10.1016/j.ica.2003.03.002

The reactivity of [Pt₂(μ-S)₂(PPh₃) ₄] towards a range of nickel(II) complexes has been probed using electrospray ionisation mass spectrometry coupled with synthesis and characterisation in selected systems. Reaction of [Pt₂(μ-S) ₂(PPh₃)₄] with [Ni(NCS)₂(PPh ₃)₂] gives [Pt₂(μ-S)₂(PPh ₃)₄Ni(NCS)(PPh₃)]⁺, isolated as its BPh₄^- salt; the same product is obtained in the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [NiBr₂(PPh₃)₂] and KNCS. An X-ray structure determination reveals the expected sulfide-bridged structure, with an N-bonded thiocyanate ligand and a square-planar coordination geometry about nickel. A range of nickel(II) complexes NiL₂, containing β-diketonate, 8-hydroxyquinolinate, or salicylaldehyde oximate ligands react similarly, giving [Pt₂(μ-S)₂(PPh₃)₄NiL] ⁺ cations.

Full text of DOI:10.1016/j.ica.2003.03.002

Inorganica Chimica Acta 357 (2004) 1152–1160
www.elsevier.com/locate/ica
Coordination chemistry of the metalloligand [Pt2(l-S)2(PPh3)4]
with nickel(II) complexes – an electrospray mass
spectrometry directed synthetic study
a
a,
a
S.-W. Audi Fong , T.S. Andy Hor *, Jagadese J. Vittal ,
b,
b
William Henderson *, Shelley Cramp
a
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
b
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 2 March 2003; accepted 25 March 2003
Abstract
The reactivity of [Pt2(l-S)2(PPh3)4] towards a range of nickel(II) complexes has been probed using electrospray ionisation mass
spectrometry coupled with synthesis and characterisation in selected systems. Reaction of [Pt2(l-S)2(PPh3)4] with [Ni(NCS)2(PPh3)2]
ꢀ
gives [Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ, isolated as its BPh4 salt; the same product is obtained in the reaction of [Pt2(l-
S)2(PPh3)4] with [NiBr2(PPh3)2] and KNCS. An X-ray structure determination reveals the expected sulfide-bridged structure, with
an N-bonded thiocyanate ligand and a square-planar coordination geometry about nickel. A range of nickel(II) complexes NiL2,
containing b-diketonate, 8-hydroxyquinolinate, or salicylaldehyde oximate ligands react similarly, giving [Pt2(l-S)2(PPh3)4NiL]þ
cations.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Mixed-metal complexes; Sulfide ligands; Electrospray mass spectrometry; Platinum complexes; Nickel complexes
1. Introduction
(PPh3)4] [7–12] towards metal halides and related sub-
strates, and some of these results have been summarised
in a review [13]. The results from these mass spectrom-
etry studies can then be used to direct subsequent
macroscopic syntheses to the more promising reaction
systems, thus providing an efficiency of operation, and
conserving precious metals.
In this paper, we report the application of this meth-
odology to the study of the reactivity of [Pt2(l-S)2
(PPh3)4] (1) towards a range of nickel(II) complexes.
Little work has been done to date in this area; while de-
rivatives of the {Pt2S2} core are known for many metals,
the only nickel species known to date is [Pt2(l-S)2
(PPh3)4Ni(dppe)]2þ [14]. Indeed, all other compounds
containing the Pt–S–Ni–S four-membered ring system are
complexes of thiolate ligands, where each S is alkylated
[15–17]. As will be demonstrated, the {Pt2S2} core sup-
ports nickel substrates bearing a wide range of ancillary
ligands.
The metalloligand [Pt2(l-S)2(PPh3)4] (1) contains
highly nucleophilic sulfur atoms, and has been used to
assemble a wide variety of sulfide-bridged homo- and
hetero-metallic aggregates [1–3]. Complexes containing
other phosphine ligands such as dppe (Ph2PCH2
CH2PPh2) also show similar behaviour, but have been
less studied to date [4,5]. Recently, we have been using
the technique of electrospray ionisation mass spec-
trometry (ESMS) to probe reactions of [Pt2(l-S)2
(PPh3)4] [2,3,6] and the selenium analogue [Pt2(l-Se)2
* Corresponding author. Tel.: +64-7-838 4656; fax: +64-7-838-4219.
E-mailaddresses: andyhor@nus.edu.sg (T.S.A. Hor), w.henderson@
waikato.ac.nz (W. Henderson).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.03.002

S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
1153
2. Results and discussion
2.1. Reactivity with nickel(II) phosphine complexes
isotopic envelopes of these ions, which display the ex-
pected patterns, with a 0.5 m=z separation between ad-
jacent peaks, the characteristic signature of a dication.
For [NiCl2(dppe)] and [NiCl2(dppp)] the ions [Pt2(l-
S)2(PPh3)4NiL]2þ (L ¼ dppe, m=z 980; L ¼ dppp, m=z
987) were observed as major ions, but other species were
also observed with significant intensity, such as
[PtCl(PPh3)(dppe)]þ (m=z 891) and [PtCl(PPh3)(dppp)]þ
(m=z 905), and [Pt(dppe)2]2þ (m=z 495.5).
The reactivity of a series of triphenylphosphine–nickel
complexes was then determined. In these experiments the
products formed are influenced by the greater lability of a
triphenylphosphine ligand, compared with a bidentate
ligand. Reactions of [Pt2(l-S)2(PPh3)4] with the com-
plexes [NiX2(PPh3)2] (X ¼ Cl, Br, I) in methanol were
followed by ESMS, and gave very similar spectra. The
common major ions, summarised in Table 1, are [Pt2(l-
S)2(PPh3)4Ni(PPh3)]2þ (m=z 912), [Pt2(l-S)2(PPh3)4-
Ni(PPh3)(MeCN)]2þ (m=z 932.5), [PtX(PPh3)3]þ (the
latter formed by disintegration of the platinum starting
complex), and the monocationic adduct [Pt2(l-S)2-
As an initial entry into the chemistry of the {Pt2S2}
core with nickel(II), complexes containing bidentate
phosphines were investigated, since the only known
nickel adduct of the {Pt2S2} core is of the dppeNi2þ
fragment [14]. Reactions involving a 1:1 molar ratio of
[Pt2(l-S)2(PPh3)4] with the various nickel complexes
were probed by ESMS, as a convenient and established
method for monitoring the coordination chemistry of
the {Pt2S2} system [2,3,6,13]. [NiCl2(dppe)] was studied,
together with related complexes [NiCl2(dppp)] [dppp ¼
Ph2P(CH2)3PPh2] and [NiCl2(dppf)] [dppf ¼ 1,10 -
Fe(C5H4PPh2)2], for comparative purposes. In all cases,
the common ion observed was the dicationic [Pt2(l-
S)2(PPh3)4NiL]2þ ion (L ¼ bidentate ligand). In the case
of the dppf system, the orange [Pt2(l-S)2(PPh3)4Ni
(dppf)]2þ (m=z 1058) ion was the only one observed. The
reaction with [NiCl2(bipy)2] ꢁ MeOH likewise gave solely
yellow-orange [Pt2(l-S)2(PPh3)4Ni(bipy)]2þ (m=z 858.5).
Confirmation was readily achieved by examining the

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S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
Table 1
Electrospray (ES) mass spectrometric data (cone voltage 20 V) for reactions of [Pt2(l-S)2(PPh3)4] with 1.0 equivalent of [NiX2(PPh3)2] (X ¼ Cl, Br, I,
NCS) in methanol
Complex
Ions observed (m=z, %)a
[NiCl2(PPh3)2]
[{Pt2S2}Ni(PPh3)]2þ (912, 54), [{Pt2S2}Ni(PPh3)(MeCN)]2þ (932, 42), [PtCl(PPh3)3]þ (1017, 100),
[{Pt2S2}NiCl(PPh3)]þ (1859, 42)
[NiBr2(PPh3)2]
[NiI2(PPh3)2]
[{Pt2S2}Ni(PPh3)]2þ (912, 100), [{Pt2S2}Ni(PPh3)(MeCN)]2þ (932, 48), [PtBr(PPh3)3]þ (1061, 57),
[{Pt2S2}NiBr(PPh3)]þ (1904, 38)
[{Pt2S2}Ni(PPh3)]2þ (912, 100), [{Pt2S2}Ni(PPh3)(MeCN)]2þ (932, 78), [PtI(PPh3)3]þ (1108, 30),
[{Pt2S2}NiI(PPh3)]þ (1951, 68), plus several minor unidentified ions
[{Pt2S2}Ni(NCS)(PPh3)]þ (1882, 100)
[Ni(NCS)2(PPh3)2]
a {Pt2S2} ¼ [Pt2(l-S)2(PPh3)4].
(PPh3)4NiX(PPh3)]þ common to all three complexes.
Acetonitrile is commonly used as a mobile phase solvent
in the electrospray mass spectrometer used in this study,
and some contamination of the methanol mobile phase
used is possible. The observation of a coordinated ace-
tonitrile ligand clearly indicates an affinity of nickel(II)
for this ligand. It is noteworthy that the relative intensity
of the ion [Pt2(l-S)2(PPh3)4NiI(PPh3)]þ was somewhat
greater than those of [Pt2(l-S)2(PPh3)4NiX(PPh3)]þ
(X ¼ Cl, Br), which were of roughly equal intensity. When
the methanolic solutions were evaporated to dryness and
the products redissolved in acetonitrile, the monocations
[Pt2(l-S)2(PPh3)4NiX(PPh3)]þ disappeared (presumably
due to solvolysis of the halide by MeCN) and the major
ions observed in all three systems were [Pt2(l-
S)2(PPh3)4Ni(PPh3)]2þ and [Pt2(l-S)2(PPh3)4Ni (PPh3)-
(MeCN)]2þ, with the [PtX(PPh3)3]þ ions also observed.
In contrast to the range of species observed in the
halide systems, the reaction of [Ni(NCS)2(PPh3)2] with
[Pt2(l-S)2(PPh3)4] yielded a single product ion at m=z
1882, identified as [Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ.
This product was subsequently synthesised on the mac-
roscopic scale and isolated by addition of either NaBPh4
or NH4PF6 to the reaction solution, giving 2a and 2b,
respectively. The infrared spectrum of the diamagnetic
complex 2a shows a CN stretching frequency at 2092
cmꢀ1, which is consistent with an N-bonded thiocyanate
ligand [18]. The reaction of the related pyridine (py)
complex [Ni(NCS)2(py)4] with [Pt2(l-S)2(PPh3)4] was
also investigated, and gave a brown solution containing
the [Pt2(l-S)2(PPh3)4Ni(NCS)(py)]þ ion (m=z 1699).
The 31P {1H} NMR spectrum of 2a in CDCl3 shows
two inequivalent PPh3 ligands bonded to platinum, at d
17.8 and 15.7 (syn and anti to the NCS ligand on Ni), with
superposition of a singlet at d 17.8 due to the triphenyl-
phosphine on Ni. The two 1J(PtP) coupling constants are
fairly similar, at 3235 and 3190 Hz. When the complex is
dissolved in d6-DMSO, there is a slightchange in chemical
shifts, such that the resonances no longer overlap (d
PPh3–Pt 17.2, 14.8; d PPh3–Ni 15.3). Variable-tempera-
ture 1H NMR in this solvent resulted in coalescence of the
PPh3–Ni resonance with one set of Pt–PPh3 resonances
(at 360 K), followed by coalescence of all resonances at
400 K. On cooling back to 298 K the complex was largely
unchanged, except for a small amount of Ph3PO decom-
position product (d 43) (air was not excluded). Room
temperature fluxional behaviour in a related {Pd3S2} ag-
gregate was reported previously [19]; in this case, the
greater lability of palladium compared to platinum is ex-
pected to be a significant factor. The PPh3 ligand on nickel
does not appear to be labile on the NMR timescale at
room temperature, since addition of free PPh3 to a CDCl3
solution of 2a did not broaden the 31PPh3–Ni resonance,
and a sharp peak for free PPh3 (d )5) was observed.
An attempt was made to find an alternative route to
[Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ, by substitution of a
halide by thiocyanate. Thus, the reaction of [Pt2(l-
S)2(PPh3)4] with one equivalent of [NiBr2(PPh3)2], fol-
lowed by addition of KNCS gives an orange solution in
which the desired cation [Pt2(l-S)2(PPh3)4Ni(NCS)
(PPh3)]þ was identified by ESMS as the base peak, with
a small ion due to [Pt(NCS)(PPh3)3]þ (m=z 1040) also
observed.
Displacement of the thiocyanate ligand of 2a by other
anions can also be readily probed using ESMS. Thus,
addition of excess NaBr to a methanol solution of 2a
yielded (even after standing for 48 h) only a minor ion at
m=z 1904 assigned as the bromide complex [Pt2(l-
S)2(PPh3)4NiBr(PPh3)]þ. Reaction of 2a with NaNO2
also resulted in displacement of the thiocyanate ligand
giving [Pt2(l-S)2(PPh3)4Ni(NO2)(PPh3)]þ (m=z 1870) as a
medium intensity ion. Greater reactivity was shown with
NaN3 which yielded (in addition to the starting material)
the species [Pt2(l-S)2(PPh3)4Ni(N3)(PPh3)]þ (m=z 1866),
as well as an unidentified species at m=z 827. On standing
overnight, the intensity of [Pt2(l-S)2 (PPh3)4Ni(N3)
(PPh3)]þ increased relative to [Pt2(l-S)2 (PPh3)4Ni(NCS)
(PPh3)]þ, though the base peak was now [Pt2(l-S)2
(PPh3)4Ni(N3)]þ (m=z 1603) formed by loss of PPh3
(presumably by reaction with azide ions). Electrospray
mass spectrometry clearly provides a rapid and infor-
mative technique for monitoring such exchange reactions.
2.2. X-ray crystal structure of [Pt2(l-S)2(PPh3)4
Ni(NCS)(PPh3)]PF6 (2b)
Since no crystal structures have been previously car-
ried out on nickel adducts of the {Pt2S2} core, and to

S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
1155
Table 2
Selected bond lengths (A) and angles (°) for [Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)] PF6ꢀ ꢁ 3Me2CO (2b ꢁ 3Me2CO)
þ
ꢀ
Pt(1)–S(1)
Pt(2)–S(1)
Ni(1)–S(1)
Pt(1)–P(1)
Pt(2)–P(3)
Ni(1)–N(1)
2.349(2)
2.333(2)
2.227(2)
2.298(2)
2.293(2)
1.865(6)
Pt(1)–S(2)
Pt(2)–S(2)
Ni(1)–S(2)
Pt(1)–P(2)
Pt(2)–P(4)
Ni(1)–P(5)
2.353(1)
2.356(2)
2.188(2)
2.284(2)
2.280(2)
2.198(2)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(1)–Ni(1)
Pt(2)–S(1)–Ni(1)
S(1)–Pt(1)–S(2)
P(1)–Pt(1)–P(2)
P(1)–Pt(1)–S(1)
P(1)–Pt(1)–S(2)
S(1)–Ni(1)–S(2)
P(5)–Ni(1)–S(1)
P(5)–Ni(1)–S(2)
89.63(5)
80.02(5)
81.08(5)
77.15(5)
98.80(6)
89.37(5)
165.64(5)
83.22(6)
174.77(7)
96.30(7)
Pt(1)–S(2)–Pt(2)
Pt(1)–S(2)–Ni(1)
Pt(2)–S(2)–Ni(1)
S(1)–Pt(2)–S(2)
P(3)–Pt(2)–P(4)
P(3)–Pt(2)–S(1)
P(3)–Pt(2)–S(2)
P(5)–Ni(1)–N(1)
N(1)–Ni(1)–S(1)
N(1)–Ni(1)–S(2)
88.98(5)
80.74(5)
81.37(5)
77.41(5)
98.88(6)
168.52(6)
91.99(5)
89.0(2)
91.9(2)
172.9(2)
ꢀ
2.9440(8), Pt(2). . .Ni(1) 2.9651(8) A] and the Pt(1). . .
confirm the square-planar geometry at nickel, the mo-
lecular structure of the title complex was determined.
Crystals were grown from acetone–hexane, and the
complex crystallises with three molecules of acetone per
cation. Selected bond lengths and angles for the struc-
ture are summarised in Table 2. The molecular struc-
ture, Fig. 1, shows a triangular {NiPt2} core capped on
both sides by symmetrical l3-sulfido ligands. The d8
platinum centres exhibit square-planar coordination
environments, while the nickel(II) centre also adopts a
square-planar geometry, chelated by the two sulfides
and coordinated to a PPh3 ligand and a thiocyanate. No
significant metal–metal interactions occur [Pt(1). . .Ni(1)
ꢀ
Pt(2) distance of 3.300 A lies beyone the expected range
for a metal–metal bond. The dihedral angle that the
{Pt2S2} butterfly makes along the S(1). . .S(2) axis is
128.3°, with the two sulfides chelated to the nickel at an
angle of 83.22(6)°. As might be expected from the
greater steric bulk of a PPh3 ligand compared to NCS,
the P(5)–Ni–S(2) bond angle, 96.30(7)°, is larger than
N(1)–Ni–S(1), 91.9(2)°. The P(5)–Ni–N(1) bond angle in
2b [89.0(2)°] is slightly smaller than that in trans-
[Ni(NCS)2(PPh3)2] [92.1(1)°] [20] probably reflecting the
greater steric bulk in the {Pt2S2} system.
The thiocyanate ligand is N-bonded, as is observed in
all other structures of nickel(II) complexes containing
phosphine and thiocyanate ligands, which, like 2b, also
have square-planar geometries [21]. The Ni–N distance
ꢀ
in 2b [1.865(6) A] is notably longer than in other tri-
phenylphosphine–nickel–thiocyanate complexes, such as
trans-[Ni(NCS)2L2] [L ¼ 10 -(diphenylphosphino)ferro-
ꢀ
cenecarboxylic acid] which has Ni–N 1.819(5) A [22] and
trans-[Ni(NCS)2(PPh3)2] where the Ni–N distance is
ꢀ
ꢀ
1.819(3) A [20]. The Ni–P distance in 2b [2.198(2) A] is
somewhat shorter than in both trans-[Ni(NCS)2L2]
acid]
[L ¼ 10 -(diphenylphosphino)ferrocenecarboxylic
ꢀ
[Ni–P 2.263 A] [22] and trans-[Ni(NCS)2(PPh3)2] [2.245
ꢀ
A] [20]. This is presumably because in 2b the PPh3 on Ni
is trans to a triply-bridging sulfido ligand (with pre-
sumably a lower trans-influence than another PPh3 li-
gand), thus shortening the Ni–P bond in 2b. Likewise, in
2b the NCS ligand is also trans to a sulfido ligand, but
this presumably has a higher trans influence than an-
other NCS ligand present in the trans-[Ni(NCS)2(phos-
phine)2] type complexes compared above, so the Ni–N
bond in 2b is longer.
It is worth commenting on the nature of the product
observed in 2b, i.e., a monocation with one phosphine
and one NCS ligand, and a square-planar nickel(II).
Presumably, the species [{Pt2S2}Ni(PPh3)2]2þ is disfa-
Fig. 1. Molecular structure of the complex [Pt2(l-S)2(PPh3)4
Ni(NCS)(PPh3)]þPF6ꢀ ꢁ 3Me2CO (2b ꢁ 3Me2CO) showing the atom
numbering scheme. Thermal ellipsoids are shown at the 50% proba-
bility level. The phenyl rings of the platinum-bonded triphenylphos-
ꢀ
phine ligands and the PF6 counterion have been omitted for clarity.

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S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
voured because of steric bulk of the PPh3 ligands, and
the relatively short Ni–S and Ni–P bonds which accen-
tuate this. (By comparison, species of the type
[{Pt2S2}Pt(phosphine)2]2þ are well-known, and stable
[14,23].) In addition, due to the much greater lability of
nickel(II) compared with platinum(II), a PPh3 ligand
can be lost from the former metal more easily, thereby
reducing steric congestion.
It might be initially expected that the nickel might
adopt a tetrahedral geometry to minimise steric inter-
actions with the bulky PPh3 ligands. Indeed, nickel(II)
complexes can adopt square-planar, tetrahedral or oc-
tahedral geometries, depending on the ligands. How-
ever, nickel(II) thiocyanate complexes invariably have a
square-planar geometry, and the same electronic effect
also appears to direct the square-planar nickel geometry
in 2a.
square-planar nickel(II). Because sharp NMR spectra
can be obtained on these complexes they are also dia-
magnetic in solution, and so it is possible to rule out a
tetrahedral nickel(II) centre, which would render all
platinum-coordinated phosphines equivalent.
Other NiL2 complexes also gave clean reactions with
[Pt2(l-S)2(PPh3)4]. Reaction with [Ni(hq)2] ꢁ 2H2O
(hq ¼ anion of 8-hydroxyquinoline) gave yellow [Pt2(l-
S)2(PPh3)4Ni(hq)]þ (m=z 1706). The complex was iso-
lated as a yellow solid 6 by addition of NaBPh4 to the
reaction mixture. When excess nickel complex is used,
there is a small ion due to [Pt(hq)(PPh3)2]þ at m=z 863,
which is removed when the [Pt2(l-S)2(PPh3)4Ni(hq)]þ
ion is precipitated with BPh4ꢀ. The 31P {1H} NMR
spectrum shows two sets of inequivalent PPh3 ligands
[1J(PtP) coupling constants 3163, 3245 Hz], as a result of
the different (N,O) donor atoms at the nickel centre. In a
similar fashion, reaction of [Pt2(l-S)2(PPh3)4] with the
nickel(II) complex of salicylaldehyde oximate
[Ni(salox)2] gave the corresponding monocation [Pt2(l-
S)2(PPh3)4Ni(salox)]þ, which was also isolated and
2.3. Reactivity with nickel(II) complexes containing
bidentate monoanionic nitrogen/oxygen donor ligands
ꢀ
With the success in the nickel-thiocyanate system
discussed in the preceding Sections, other nickel(II)
complexes containing chelating monoanionic ligands (L)
were trialed, with the expectation of obtaining stable,
monocationic NiLþ adducts of the {Pt2S2} core. We
recently described ESMS-monitored reactions of
[Pt2(l-S)2(PPh3)4] with various transition metal acetyl-
acetonate complexes, though nickel(II) was not investi-
gated [2,3,6]. Reaction of [Pt2(l-S)2(PPh3)4] with
[Ni(acac)2(H2O)2] (acac ¼ CH3COCHCOCH3) gave a
brown solution for which ESMS showed only the [Pt2(l-
S)2(PPh3)4Ni(acac)]þ ion (m=z 1660). In analogous
fashion, the related nickel(II) b-diketonate complexes
derived from thenoyltrifluoroacetone [Ni(tta)2(H2O)2]
and ethyl benzoylacetate [Ni(PhCOCHCOOEt)2(H2O)2]
gave solely [Pt2(l-S)2(PPh3)4Ni(diketonate)]þ ions.
The attempted Ôone-potÕ synthesis of [Pt2(l-S)2(PPh3)4-
Ni(acac)]þ starting from [Pt2(l-S)2(PPh3)4], one equiv-
alent of NiCl2 ꢁ 6H2O and excess Hacac in methanol was
unsuccessful, with the major species being [Pt(acac)
(PPh3)2]þ(m=z 818) in addition to a small amount of
[Pt2(l-S)2(PPh3)4Ni(acac)]þ, as shown by ESMS.
characterised as its BPh4 salt 7. Complexes 6 and 7
were found to be diamagnetic, indicating the presence of
square-planar nickel(II) centres.
In contrast to the reactivity of [Pt2(l-S)2(PPh3)4] with
the nickel(II) complexes described above, no reaction
was observed with the dimethylglyoximate complex
[Ni(dmg)2]; this highly insoluble nickel complex is used
in gravimetric determinations of nickel [24], and this,
together with its pronounced stability are the most likely
reasons for its lack of reactivity.
The possibility of exchange reactions on the {Pt2S2}
core can easily be demonstrated by ESMS. When 2a was
stirred for 24 h with an excess of [Ni(acac)2(H2O)2] in
MeOH–CH2Cl2, the ESMS spectrum revealed that the
complex [Pt2(l-S)2(PPh3)4Ni(acac)]þ (m=z 1661) is lar-
gely formed, with a small amount of residual [Pt2(l-
S)2(PPh3)4Ni(NCS) (PPh3)]þ (m=z 1882).
2.4. Reactivity with nickel(II) complexes containing
bidentate monoanionic sulfur donor ligands
The nickel(II)–diketonate complexes 3–5 were sub-
sequently isolated on the macroscopic scale by addition
of NaBPh4 to the filtered reaction solutions, and fully
characterised. The 31P {1H} NMR spectra show single
31P environments. This is as expected for the acac
complex, and in the case of the unsymmetrical com-
plexes (viz. 4 and 5) the different substituents on the
diketonate ligand are presumably too distant from the
PPh3 ligands on platinum to effect any inequivalence
between them (or, less likely, the system is fluxional at
room temperature). Magnetic susceptibility measure-
ments on complexes 3 and 5 indicate that they are dia-
magnetic in the solid state, and therefore contain
Nickel(II) forms NiL2 complexes with chelating
sulfur donor ligands L, such as dithiophosphinate
(R2PS2ꢀ) and dithiocarbamate (R2NCS2ꢀ). Complexes
[Ni(S2PR2)2] and [Ni(S2CNR2)2] have been investigated
with [Pt2(l-S)2(PPh3)4], since it is of interest to see if ꢀa
simple reactiꢀon occurs in this case. The liberated R2PS2
or R2NCS2 ions are good ligands towards plati-
num(II), and might effect fragmentation of the
{Pt2S2Ni} aggregate, ligand substitution (of the triphe-
nylphosphine ligands), or the formation of more
complex products.
Reaction of [Pt2(l-S)2(PPh3)4] with [Ni(S2CNEt2)2]
results in dissolution of the starting materials and

S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
1157
formation of a brown solution which contains mainly
[Pt(S2CNEt2)(PPh3)2]þ (m=z 868) together with a small
amount of the desired [Pt2(l-S)2(PPh3)4Ni(S2CNEt2)]þ
(m=z 1710). Likewise, reaction with [Ni(S2PBui2)2] gave
mainly [Pt(S2PBu2i )(PPh3)2]þ (m=z 929) plus some
[Pt2(l-S)2(PPh3)4Ni(S2PBui2)]þ (m=z 1771). No attempt
was made to isolate the {Pt2S2} adducts in these cases.
analytical data were obtained from the Campbell Mi-
croanalytical Laboratory, University of Otago, New
Zealand, or the Microanalytical Laboratory, Depart-
ment of Chemistry, National University of Singapore.
Magnetic susceptibility measurements were carried out
using a Gouy balance.
The complexes [Pt2(l-S)2(PPh3)4] (1) [26], [Ni(acac)2
(H2O)2] [27], [Ni(tta)2(H2O)2] [28], [Ni(PhCOCHCO
OEt)2(H2O)2] [29], [Ni(hq)2] ꢁ 2H2O [30], [Ni(salox)2] [31],
[NiCl2(PPh3)2] [32], [NiBr2(PPh3)2] [32], [NiI2(PPh3)2]
[32], [Ni(NCS)2(PPh3)2] [20], [Ni(NCS)2(py)4] [33],
[NiCl2(dppe)] [34], [NiCl2(dppp)] [34], [NiCl2(dppf)]
[35], [NiCl2(bipy)2] ꢁ MeOH [36], and [Ni(S2PBui2)2] [37]
were prepared by minor modifications of the literature
procedures. NaBPh4, KNCS, nickel(II) chloride hexa-
hydrate and acetylacetone were used as supplied from
BDH, and NH4PF6 was used as supplied by Aldrich.
2.5. Conclusions
We have successfully used electrospray mass spec-
trometry to probe the reactivity of [Pt2(l-S)2(PPh3)4]
with a wide range of nickel(II) complexes. This mass
spectrometry-directed approach allows identification of
those reaction systems which give single products wor-
thy of macroscopic isolation and characterisation. The
dominant theme in this area is the formation of mono-
cationic products, either through use of a monoanionic
chelating ligand (e.g., acetylacetonate or 8-hydroxyqui-
nolinate anions, and related ligands) or, in the case of
triphenylphosphine complexes, through retention of a
coordinated monodentate anion (such as thiocyanate).
Dicationic products [Pt2(l-S)2(PPh3)4NiL]2þ are con-
firmed [14] when L is a neutral bidentate phosphine li-
gand (such as dppf) or 2,20 -bipyridine. In these cases, the
reduced lability results in retention of this ligand in
preference to an anion.
3.2. Mass spectrometry experiments
[Pt2(l-S)2(PPh3)4] (1) (25 mg) and the nickel substrate
(e.g., NiX2(PPh3)2, X ¼ Cl, Br, I, NCS; 1 mole equiva-
lent) were suspended in ca. 20 mL methanol, and stirred
for 24 h. A small sample (ca. 5 drops) of the reaction
solution was withdrawn, diluted with methanol (2 mL),
centrifuged (to remove any traces of insoluble matter)
and injected directly into the mass spectrometer.
3.3. Synthesis of [Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ
BPh4 (2a)
3. Experimental
ꢀ
3.1. General procedures
The complex [Pt2(l-S)2(PPh3)4] (301 mg, 0.200 mmol)
and [Ni(NCS)2(PPh3)2] (88 mg, 0.126 mmol) were sus-
pended in methanol (20 mL) and stirred for 24 h, giving
a red-brown solution. After filtration, NaBPh4 (80 mg,
0.234 mmol) in methanol (5 mL) was added with stir-
ring, immediately giving a light brown precipitate. This
was filtered, washed with water (5 mL), methanol (5
mL), diethyl ether (5 mL) and dried under vacuum to
give 2a (225 mg, 81%). IR, m(CN) 2092 cmꢀ1 (s). A
sample for elemental analysis was recrystallised as red-
orange needles by vapour diffusion of diethyl ether into
a dichloromethane solution of the complex. Found: C,
62.2; H, 4.4; N, 0.9. C115H95NBNiP5Pt2S3 requires C,
62.7; H, 4.4; N, 0.6%. 31P {1H} NMR, d 17.8 [d, 1J(PtP)
Reactions were carried out in LR grade methanol,
with no precautions taken to exclude air or moisture.
Products were recrystallised from dichloromethane and
diethyl ether that were dried and distilled (from CaH2
and sodium benzophenone ketyl, respectively) under a
nitrogen atmosphere prior to use. Water was double
distilled prior to use.
1H and 13C {1H} NMR spectra were recorded on a
Bruker DRX400 instrument (1H 400.13 MHz; 13C
100.62 MHz) and 31P {1H} NMR spectra were recorded
on a Bruker AC300P instrument at 121.51 MHz. NMR
spectra were typically recorded in CDCl3 solution, and
referenced relative to residual CHCl3 or (for 31P spectra)
external H3PO4. Electrospray mass spectra were re-
corded in positive-ion mode, in MeCN–H2O (1:1 v/v) or
methanol solvent, and cone voltages were varied be-
tween 20 and 50 V to explore fragmentation of the
various ions. Assignment of ions was assisted by com-
parison of experimental and calculated isotope patterns,
the latter obtained by means of the Isotope program [25].
Melting points were recorded on a Reichert Thermopan
apparatus and are uncorrected. Infrared spectra were
recorded on a Bio-Rad FTS-40 Spectrometer. Micro-
2
1
2
3235, J(PP) 11], 15.7 [d, J(PtP) 3190, J(PP) 11] and
15.8 [s, PPh3–Ni]. The complex was found to be dia-
magnetic by Gouy balance measurements.
3.4. Alternative synthesis of [Pt2(l-S)2(PPh3)4Ni
ꢀ
(NCS) (PPh3)]þBPh4 (2a)
[Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol) and
[NiBr2(PPh3)2] (99 mg, 0.133 mmol) in methanol (30
mL) were stirred for 1 h, giving a slightly cloudy brown

1158
S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
solution. A solution of KNCS (20 mg, 0.206 mmol) in
methanol (3 mL) was added, resulting in a colour
change to a bright orange solution. The reaction mixture
was stirred for 48 h, and analysis by ESMS showed
[Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ (m=z 1882, 100%)
and [Pt(NCS)(PPh3)3]þ (m=z 1039, 30%). The solution
was filtered, and solid NaBPh4 (100 mg, 0.292 mmol)
added to the clear orange filtrate with stirring, giving an
orange precipitate which was filtered off, washed with
water (10 mL), methanol (5 mL) and diethyl ether (5
mL), and dried under vacuum to give an orange-brown
solid (155 mg) which was identified as pure 2a by ESMS
and 31P {1H} NMR spectroscopy.
(8 mg, 0.033 mmol) and acetylacetone (3 drops, excess)
and the mixture stirred for 45 h. The resulting cloudy
light green solution was analysed by ESMS which re-
vealed [Pt(acac)(PPh3)2]þ (m=z 818) as the major species,
together with a trace of the desired [Pt2(l-S)2(PPh3)4-
Ni(acac)]þ (m=z 1660).
ꢀ
3.8. Synthesis of [Pt2(l-S)2(PPh3)4Ni(tta)]þBPh4
(4)
Following the method for 3, [Pt2(l-S)2 (PPh3)4] (201
mg, 0.134 mmol) with [Ni(tta)2(H2O)2] (72 mg, 0.142
mmol) and NaBPh4 (46 mg, 0.135 mmol) gave a light
brown powder of 4 (109 mg, 39%). A sample for ele-
mental analysis was recrystallised as deep red rosettes by
vapour diffusion of diethyl ether into a dichloromethane
solution of the complex. Found: C, 59.7; H, 3.9.
3.5. Synthesis of [Pt2(l-S)2(PPh3)4Ni(NCS)(PPh3)]þ
PFꢀ6 (2b)
[Pt2(l-S)2(PPh3)4] (71 mg, 0.0472 mmol) and
[Ni(NCS)2(PPh3)2] (33 mg, 0.0472 mmol) were sus-
pended in methanol (20 mL) and stirred for 24 h, giving
a red-brown solution. After filtration, and washing of
the filter with additional methanol (2 ꢂ 5 mL) excess
NH4PF6 (10 mg, 0.0613 mmol) was added. After stirring
for a further 1 h, a red solid precipitated. Distilled water
(10 mL) was added to complete precipitation. The red
solid was filtered, and washed with water (2 ꢂ 10 mL),
ethanol (5 mL), diethyl ether (5 mL) and dried under
vacuum giving a red powder of 2b (82 mg, 79%). Found:
C, 53.9; H, 3.7; P, 9.2; S, 4.7. C91H75F6NNiP6Pt2S3
requires C, 53.9; H, 3.7; P, 9.2; S, 4.7%.
C
107H91BNNiO3P4Pt2S2 requires C, 59.4; H, 4.0%. 31P
1
1
{1H} NMR, d 19.4 [s, J(PtP) 3200]. H NMR, d 7.49–
6.89 (m, 83H, PPh3, BPh4 and thienyl H) and 6.20 (s,
CH).
ꢀ
3.9. Synthesis ꢀ of [Pt2(l-S)2(PPh3)4Ni(PhCOCH-
COOEt)]þBPh4 (5)
Following the method for 3, [Pt2(l-S)2 (PPh3)4] (200
mg, 0.133 mmol) with [Ni(PhCOCHCOOEt)2(H2O)2]
(65 mg, 0.136 mmol) and NaBPh4 (130 mg, 0.380 mmol)
gave an light brown powder of 5 (150 mg, 54%). Found:
C, 61.8; H, 4.4. C107H91BNNiO3P4Pt2S2 requires C,
62.0; H, 4.4%. ESMS [M]þ m=z 1753, 100%. 31P {1H}
ꢀ
1
1
3.6. Synthesis of [Pt2(l-S)2(PPh3)4Ni(acac)]þBPh4
(3)
NMR, d 18.5, [s, J(PtP) 3190]. H NMR, d 7.50–6.90
(m, 85H, Ph), 5.50 (s, 1H, CH), 3.64 [q, CH2, J(HH)
3
3
5.3] and 1.13 [t, CH3, J(HH) 5.3].
The complex [Pt2(l-S)2(PPh3)4] (300 mg, 0.200 mmol)
and [Ni(acac)2(H2O)2] (58 mg, 0.198 mmol) were sus-
pended in methanol (20 mL) and stirred for 24 h, giving
a brownish solution. After filtration, NaBPh4 (80 mg,
0.234 mmol) in methanol (5 mL) was added to the fil-
trate with stirring, giving a light brown precipitate. This
was filtered, washed with water (5 mL), methanol (5
mL), ether (5 mL) and dried under vacuum to give 3
(207 mg, 53%). A sample for elemental analysis was
recrystallised as deep red rosettes by vapour diffusion of
diethyl ether into a dichloromethane solution of the
complex. Found: C, 60.8; H, 4.6. C101H87BNiO2P4Pt2S2
requires C, 61.3; H, 4.4%. ESMS [M]þ, m=z 1660
(100%). 31P {1H} NMR, d 21.1 [s, 1J(PtP) 3180]. 1H
NMR, d 7.50–6.89 (m, 80H, PPh3 and BPh4ꢀ), 5.12 (s,
CH) and 1.72 (s, 6H, CH3).
3.10. Synthesis of [Pt2(l- S)2(PPh3)4Ni(hq)]þBPh4ꢀ (6)
Following the method for 3, [Pt2(l-S)2(PPh3)4] (200
mg, 0.133 mmol) with [Ni(hq)2].2H2O (46 mg, 0.120
mmol) gave a cloudy, bright yellow solution. Filtration
followed by addition of NaBPh4 (120 mg, 0.351 mmol)
to the filtrate gave yellow-orange 6 (150 mg, 62%).
Found: C, 61.7; H, 4.2; N, 0.5. C105H86BNNiOP4Pt2S2
requires C, 62.3; H, 4.3; N, 0.7%. ESMS [M]þ m=z 1706,
1
100%. 31P {1H} NMR, d 17.6 [s, br, J(PtP) ca. 3163,
1
2J(PP) not discernible] and 17.3 [s, br, J(PtP) ca. 3245,
2J(PP) not discernible].
ꢀ
3.11. Synthesis of [Pt2(l-S)2(PPh3)4Ni(salox)]þBPh4
(7)
3.7. Attempted alternative synthesis of [Pt2(l-S)2
[Pt2(l-S)2(PPh3)4] (200 mg, 0.133 mmol) with
[Ni(salox)2] (44 mg, 0.133 mmol) in methanol (30 mL)
was stirred for 22.5 h giving a slightly cloudy brown
solution. After filtration to remove a small amount of
insoluble green material, NaBPh4 (120 mg, 0.351 mmol)
ꢀ
(PPh3)4Ni(acac)]þBPh4 (3)
To a suspension of [Pt2(l-S)2(PPh3)4] (50 mg, 0.033
mmol) in methanol (10 mL) was added NiCl2 ꢁ 6H2O

S.-W. Audi Fong et al. / Inorganica Chimica Acta 357 (2004) 1152–1160
1159
was added with stirring to the clear orange-brown fil-
trate. The resulting orange-brown precipitate was fil-
tered off, washed with methanol (10 mL) and diethyl
ether (10 mL) and dried under vacuum to give 138 mg
(51%) of 7. Found: C, 61.1; H, 4.3; N, 0.6.
Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk).
C
103H86BNNiO2P4Pt2S2 requires C, 61.3; H, 4.3; N,
Acknowledgements
0.7%. ESMS [M]þ m=z 1698, 100%. 31P {1H} NMR, d
17.8, [s, J(PtP) 3211].
1
We thank the University of Waikato (UW) and the
National University of Singapore (NUS) for financial
support of this work, including a visiting attachment for
S-WAF to visit UW. W.H. thanks the New Zealand
Lottery Grants Board for a grant-in-aid towards the
mass spectrometer, the Royal Society of Chemistry for a
Journals Grant for International Authors to visit NUS,
and Johnson Matthey plc for a generous loan of plati-
num. Pat Gread and Dr. Ralph Thomson (UW) are
thanked for recording mass and NMR spectra, respec-
tively, and Sarah Devoy for technical assistance.
3.12. X-ray structure determꢀination of [Pt2(l-S)2
(PPh3)4Ni(NCS)(PPh3)]þPF6 (2b ꢁ 3Me2CO)
Red single crystals were grown by layering n-hexane
over a red acetone solution at 4 °C. The crystals were
quickly transferred from the sample vial onto a micro-
scope containing Paratone N oil. Under the microscope,
a red block (0.40 ꢂ 0.18 ꢂ 0.14 mm) was selected and
quickly mounted on a glass fibre using wax.
A Bruker AXS SMART diffractometer equipped with
a CCD detector was used, and Mo Ka radiation
ꢀ
(k ¼ 0:71073 A). A total of 46 826 reflections were col-
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