E/Z isomerism in monoalkylated derivatives of [Pt2(μ-S) 2(PPH3)4] containing 2,4-dinitrophenylhydrazone substituents

Article abstract of DOI:10.1080/00958972.2011.606573

Alkylation of [Pt₂(μ-S)₂(PPH₃) ₄] with 2,4-dinitrophenylhydrazone-functionalized alkylating agents XC₆H₄C{=NNHC₆H₃(NO₂) ₂}CH₂Br (X = H

Full text of DOI:10.1080/00958972.2011.606573

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E/Z isomerism in monoalkylated
derivatives of [Pt2(µ-S)2(PPh3)4]
containing 2,4-dinitrophenylhydrazone
substituents
Oguejiofo T. Ujam a , Sarah M. Devoy a , William Henderson a ,
Alistair L. Wilkins a & Brian K. Nicholson a
a Department of Chemistry , University of Waikato , Private Bag
3105, Hamilton, New Zealand
Published online: 09 Aug 2011.
To cite this article: Oguejiofo T. Ujam , Sarah M. Devoy , William Henderson , Alistair L. Wilkins
& Brian K. Nicholson (2011) E/Z isomerism in monoalkylated derivatives of [Pt2(µ-S)2(PPh3)4]
containing 2,4-dinitrophenylhydrazone substituents, Journal of Coordination Chemistry, 64:16,
2782-2790, DOI: 10.1080/00958972.2011.606573
To link to this article: http://dx.doi.org/10.1080/00958972.2011.606573
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Journal of Coordination Chemistry
Vol. 64, No. 16, 20 August 2011, 2782–2790
E/Z isomerism in monoalkylated derivatives of
[Pt2(m-S)2(PPh3)4] containing 2,4-dinitrophenylhydrazone
substituents
OGUEJIOFO T. UJAM, SARAH M. DEVOY, WILLIAM HENDERSON*,
ALISTAIR L. WILKINS and BRIAN K. NICHOLSON
Department of Chemistry, University of Waikato, Private Bag 3105,
Hamilton, New Zealand
(Received 11 May 2011; in final form 6 July 2011)
Alkylation of [Pt2(m-S)2(PPh3)4] with 2,4-dinitrophenylhydrazone-functionalized alkylating
agents XC6H4C{¼NNHC6H3(NO2)2}CH2Br (X ¼ H, Ph) gives monoalkylated cations [Pt2(m-
S){m-SCH2C{¼NNHC6H3(NO2)2}C6H4X}(PPh3)4]þ. An X-ray diffraction study on [Pt2(m-
S){m-SCH2C{¼NNHC6H3(NO2)2}Ph}(PPh3)4]BPh4 shows the crystal to be the Z isomer, with
the phenyl ring and NHC6H3(NO2)2 groups mutually trans. 1H- and 31P{1H} NMR
spectroscopic methods indicate a mixture of Z (major) and E (minor) isomers in solution,
which slowly convert mainly to the E isomer. Reaction of [Pt2(m-S)2(PPh3)4] with the
dinitrophenylhydrazone of chloroacetone [ClCH2C{¼NNH(C6H3(NO2)2}Me] and NaBPh4
gives [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}Me}(PPh3)4]BPh4, which exists as a single (E)
isomer.
Keywords: Platinum complexes; Alkylation reactions; Electrospray ionization mass spectro-
metry; X-ray crystal structure; Dinitrophenylhydrazones
1. Introduction
Alkylation and arylation reactions of the platinum(II) sulfide complex [Pt2(m-
S)2(PPh3)4] (1) [1, 2] are a versatile means of generating thiolate ligands on dinuclear
platinum cores [3, 4]. Using this methodology, a wide range of functionality can be
introduced. Recently, we reported the synthesis and characterization of a range of
monoalkylated complexes [Pt2(m-S)(m-SR)(PPh3)4]þ from alkyl halides RX, where R
contained a wide variety of C¼O and C¼N containing moieties, such as
semicarbazones and oximes [5]. The alkylation chemistry has also been further
extended to an investigation of the factors that promote dialkylation of the {Pt2S2} core
using activated alkylating agents of the type RC(O)CH2X (X ¼ Cl, Br) [6].
In this contribution, we report a detailed study of the monoalkylation chemistry of
some analogous alkylating agents that contain the 2,4-dinitrophenylhydrazone group.
The formation of 2,4-dinitrophenylhydrazone derivatives of aldehydes and ketones is a
*Corresponding author. Email: w.henderson@waikato.ac.nz
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.606573

[Pt2(ꢀ-S)2(PPh3)4]
2783
classical derivatization strategy for their qualitative and quantitative determination,
despite the fact that the outcome is usually quantitatively complicated by the formation
of E and Z isomers [7, 8]. We previously reported a scoping study of alkylation
chemistry of [Pt2(m-S)2(PPh3)4] monitored using the technique of electrospray ionization
mass spectrometry (ESI–MS) [9], which included a very preliminary study of some of
the dinitrophenylhydrazones investigated herein [10]. However, these complexes were
not isolated and characterized, and their initial identification was based solely on MS
evidence; this article now reports the detailed synthesis and characterization of these
new dinitrophenylhydrazone derivatives together with an investigation of
isomerization.
2. Results and discussion
[Pt2(m-S)2(PPh3)4] (1) reacts smoothly in methanol with the 2,4-dinitrophenylhydrazone
derivative of BrCH2C(O)Ph [i.e. BrCH2C{¼NNHC6H3(NO2)2}Ph] in an analogous
manner to reactions with other related monofunctional alkylating agents [5]. The
progress of the reaction was indicated by the dissolution of the sparingly soluble 1 and
replacement of the [1 þ H]þ ion by the molecular cation of the product in the ESI mass
spectrum. From the resulting solution, the product was isolated as its tetraphenylborate
salt [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}Ph}(PPh3)4]BPh4 (2aꢀBPh4), by the addi-
tion of excess NaBPh4 to the reaction mixture. Similarly, the reaction of [Pt2(m-
S)2(PPh3)4] with the dinitrophenylhydrazone of BrCH2C(O)C6H4Ph-4 gave
[Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}C6H4Ph}(PPh3)4]PF6 (2bꢀPF6), by precipita-
tion with excess NH4PF6.
Crystals of 2aꢀBPh4 suitable for a single-crystal X-ray diffraction study were obtained
by recrystallization from dichloromethane–diethyl ether, and a structure determination
was carried out to fully characterize the compound. The molecular structure of the
cation is given in figure 1 together with the atom numbering scheme, while selected
bond lengths and angles are summarized in table 1. The structure determination
confirms the product as a monoalkylated derivative of [Pt2(m-S)2(PPh3)4] with structural
features very similar to those of the corresponding phenacyl compound [Pt2(m-S){m-
SCH2C(O)Ph}(PPh3)4]þ [5]. The complex has the typically folded butterfly {Pt2S2} core
showing a dihedral angle between the two PtS2 coordination planes of 129.22ꢁ, which
compares well with 133.8ꢁ in [Pt2(m-S){m-SCH2C(O)Ph}(PPh3)2]þ. As normal in
complexes of this type, the Pt(1)–P(4) and Pt(2)–P(2) bonds are longer than Pt(1)–
P(3) and Pt(2)–P(1), due to P(2) and P(4) being trans to the higher trans-influence [11]
sulfide. Pt-S(sulfide) bond distances are notably shorter [Pt(1)–S(1) 2.3319(7), Pt(2)–
˚
S(1) 2.3379(7) A] compared to Pt–S(thiolate) bond distances [Pt(1)–S(2) 2.3843(7),
˚
Pt(2)–S(2) 2.3541(7) A].
The alkyl substituent on S(2) adopts the typical axial position, analogous to [Pt2(m-
S){m-SCH2C(O)Ph}(PPh3)2]þ [5]. The hydrazone has the NHC6H3(NO2)2 group and
phenyl substituents mutually trans, formally making it the Z isomer on the basis of the
Cahn–Ingold–Prelog priority rules [12]. The hydrazone N–N bond is positioned directly
above Pt(2). The phenyl ring on C(2) is directed away from the {Pt2S2} core, while the
NNHC6H3(NO2)2 group is positioned to one side of the core.

2784
O.T. Ujam et al.
Figure 1. ORTEP diagram of the cation of [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}Ph}(PPh3)4]BPh4
(2aꢀBPh4). Thermal ellipsoids are at the 50% probability level. Phenyl rings of the triphenylphosphine ligands
and the BPhꢂ4 counterions have been omitted for clarity.
ꢁ
˚
Table 1.
(PPh3)4]BPh4 (2aꢀBPh4); estimated standard deviations are in parentheses.
Selected bond lengths (A) and angles ( ) for [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}Ph}
Pt(1)–S(1)
Pt(1)–S(2)
Pt(1)–P(3)
Pt(1)–P(4)
S(2)–C(1)
C(2)–N(1)
Pt(1) ꢀ ꢀ ꢀ Pt(2)
S(1)–Pt(1)–S(2)
P(3)–Pt(1)–S(1)
P(3)–Pt(1)–P(4)
P(4)–Pt(1)–S(2)
P(1)–Pt(2)–P(2)
C(1)–S(2)–Pt(1)
C(2)–C(1)–S(2)
N(1)–C(2)–C(11)
2.3319(7)
2.3843(7)
2.2657(7)
2.3060(7)
1.854(3)
1.301(4)
3.2162(2)
81.37(2)
91.12(3)
97.46(3)
90.07(2)
98.62(3)
98.56(10)
114.7(2)
116.0(3)
Pt(2)–S(1)
Pt(2)–S(2)
Pt(2)–P(1)
Pt(2)–P(2)
C(1)–C(2)
N(1)–N(2)
S(1) ꢀ ꢀ ꢀ S(2)
2.3379(7)
2.3541(7)
2.2880(7)
2.2940(7)
1.502(4)
1.379(4)
3.075(1)
81.89(2)
84.66(3)
94.87(2)
87.06(2)
85.49(2)
107.37(10)
124.4(3)
117.8(3)
S(1)–Pt(2)–S(2)
P(1)–Pt(2)–S(1)
P(2)–Pt(2)–S(2)
Pt(1)–S(1)–Pt(2)
Pt(1)–S(2)–Pt(2)
C(1)–S(2)–Pt(2)
N(1)–C(2)–C(1)
C(2)–N(1)–N(2)
The hydrazone NH interacts with an oxygen of the ortho nitro group forming a six-
membered hydrogen-bonded ring. Such hydrogen–bond interactions in dinitrophenyl-
˚
hydrazones are well-known [13]. The H ꢀ ꢀ ꢀ O distance of 2.095(3) A and the N ꢀ ꢀ ꢀ O
˚
separation of 2.672(4) A fall well within the suggested ranges for N–H ꢀ ꢀ ꢀ O and N ꢀ ꢀ ꢀ O

[Pt2(ꢀ-S)2(PPh3)4]
2785
˚
˚
distances of 1.60–2.40 A [14] and 2.57–3.22 A [15], respectively. The N–H bond also
appears to be directed toward the free sulfide, S(1), raising the possibility of an N–
H ꢀ ꢀ ꢀ S hydrogen bond [16, 17]. The sulfide centers of [Pt2(m-S)2(PPh3)4] have been
recently shown to form O–H ꢀ ꢀ ꢀ S hydrogen-bonded adducts with alcohols [18], while
[(Ph3P)4Pt2(m-S){m-SCH2C(O)NHC6H4NHC(O)CH2S}(m-S)Pt2(PPh3)4]2þ (containing
an ortho-phenylenediamide group) was also recently proposed to have an N–H ꢀ ꢀ ꢀ S
˚
interaction based on an N ꢀ ꢀ ꢀ S separation of 3.297 A [19]. N ꢀ ꢀ ꢀ S distances in hydrogen-
˚
bonded systems are normally in the range 3.3–3.5 A [20, 21]. However, the N ꢀ ꢀ ꢀ S
˚
separation in 2aꢀBPh4 is long [3.570(3) A], and any N–H ꢀ ꢀ ꢀ S interaction will therefore
be very weak.
The positive ion ESI mass spectra of the phenyl-substituted dinitrophenylhydrazones
2aꢀBPh4 and 2bꢀPF6 gave single ions at m/z 1802 and 1876, respectively, suggesting the
formation of pure products. However, the 31P{1H} NMR spectra of freshly prepared
solutions of the compounds in CDCl3 gave almost identical spectra that showed the
presence of two different isomers, as illustrated in figure 2(a) for 2bꢀPF6. These were
subsequently shown (vide infra) to be the E and Z geometric isomers at the C¼N bond
(scheme 1). For 2b, the major Z isomer shows two overlapping multiplets for two
inequivalent PPh3 ligands, showing 1J(PtP) values of 3344 Hz (for PPh3 trans to
thiolate) and 2602 Hz (for PPh3 trans to sulfide). The initially minor E isomer of 2b gave
better separated multiplets for the two PPh3 environments with similar 1J(PtP) coupling
1
constants to the Z isomer [3411 and 2639 Hz]. The J(PtP) coupling constants for 2a
and 2b are similar to those previously reported for the ketone compound [Pt2(m-S)
{m-SCH2C(O)Ph}(PPh3)2]BPh4 (3386 and 2630 Hz) [5].
1
The H-NMR spectrum of the initially prepared solution of 2bꢀPF6 confirmed the
presence of two isomers. In order to determine that the crystallographically charac-
1
terized Z isomer was the major isomer in the initially prepared solution, further H-
NMR studies were carried out. The hydrazone NH protons are easily identified in the
1H-NMR spectrum of the initial solution for the major and minor isomers at ꢁ 10.68
and 11.19, by comparison with other dinitrophenylhydrazones, e.g. CH3C{¼
NNHC6H3(NO2)2}CH3 (ꢁ NH 11.3) [22]. The spectrum also showed signals due to
the SCH2 protons at ꢁ 4.40 and 3.65 for the major and minor isomers, respectively.
Assignment of the NH and SCH2 signals to the individual E and Z isomers was made
on the basis of ROESY NMR data. Thus the SCH2 resonance at ꢁ 4.40 and the NH
resonance at ꢁ 10.68 (for the initial major isomer) exhibited mutual ROESY correla-
tions, consistent with the close proximity of these protons in the Z isomer (scheme 1).
However, the SCH2 proton resonance in the initial minor isomer (at ꢁ 3.65) showed a
ROESY correlation to a nearby aromatic proton at ꢁ 6.79 and not to the NH proton at
ꢁ 11.19. Similarly, this NH proton showed a ROESY correlation to an aromatic proton
at ꢁ 6.79 and not to the SCH2 protons at ꢁ 3.65. These correlations are consistent with
the relationship between the NH and SCH2 protons as given in the E isomer (scheme 1).
Analysis of the starting alkylating agent BrCH2C{¼NNHC6H3(NO2)2}C6H4Ph by
1H-NMR indicated that the major component had the same spatial arrangement as
observed in the initially major Z isomer of 2b.
When the solution of 2bꢀPF6 used for NMR analysis was stored at ꢂ18ꢁC for
6 months, there was reversal of the relative amounts of the two isomers in both the
31P{1H}- and 1H-NMR spectra, with the initially minor E isomer now being the major
species (figure 2b). After a longer period (9 months) complete conversion had still not
occurred. The conversion of the initial Z isomer to the E isomer in solution is

2786
O.T. Ujam et al.
Figure 2. 31P{1H} NMR spectra of 2bꢀPF6 in CDCl3: (a) freshly prepared solution; peaks due to the initially
dominant Z isomer are indicated by stars, while those for the E isomer are indicated by circles; (b) after
storage at ꢂ18ꢁC for 6 months.
NO
+
2
NO
+
2
O N
2
H
N
NO
2
N
N
N
H
X
C
X
C
H
H
H
H
C
C
S
S
S
S
Pt
Pt
Pt
Pt
Ph P
PPh
3
3
Ph P
3
Ph P
3
PPh
3
3
3
PPh
PPh
Ph P
3
Z isomer
E isomer
Scheme 1. Structures of the
Z
and
E
isomers of the cations [Pt2(m-S){m-SCH2C{¼NNHC6H3
(NO2)2}C6H4X}(PPh3)4]þ (X ¼ H 2a or Ph 2b), showing the spatial relationship between the NH and
SCH2 protons.

[Pt2(ꢀ-S)2(PPh3)4]
2787
presumably driven by steric interactions, as found in previous studies of the E–Z
isomerization of dinitrophenylhydrazones derived from substituted acetophenones [23].
In the E isomer, the steric bulk of the 2,4-dinitrophenyl group projects further away
from the {Pt2S2} core. The observation of this isomerization process suggests that any
N–H ꢀ ꢀ ꢀ S hydrogen bond interaction (only possible in the Z isomer) must indeed be
very weak.
Finally, observation of both E/Z isomers appears to be confined to aryl ketone
derivatives. Thus, reaction of 1 with dinitrophenylhydrazone of chloroacetone
[ClCH2C{¼NNH(C6H3(NO2)2}Me] proceeded rapidly, giving a bright yellow-orange
solution from which the salt [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}Me}
(PPh3)4]BPh4, 3ꢀBPh4 was isolated by the addition of NaBPh4. The product showed a
single ion in its ESI mass spectrum, at m/z 1740, due to the product cation. The NMR
spectra of this product also showed only a single isomer, in contrast to the aromatic-
substituted dinitrophenylhydrazones described above. Thus, two 31P resonances were
observed for the two inequivalent types of PPh3, showing coupling constants of 3342
and 2613 Hz. The 1H-NMR spectrum showed a single NH resonance at ꢁ 10.56, as well
1
as single CH2 and CH3 resonances at ꢁ 3.73 and 0.47, respectively. H-ROESY NMR
data showed enhancement of the CH3 but not the NH proton on irradiation of the CH2
protons, while irradiation of the NH proton produced an enhancement only in the
methyl protons. This places the NH and CH3 groups mutually cis, making the complex
the E isomer (scheme 2).
In conclusion, this study has further extended the alkylation chemistry of [Pt2(m-
S)2(PPh3)4] to include alkylating agents containing 2,4-dinitrophenylhydrazone groups
and demonstrated the occurrence of hydrazone E–Z isomerization in some derivatives.
3. Experimental
[Pt2(m-S)2(PPh3)4] (1) was prepared by the literature procedure [18, 24]. The
dinitrophenylhydrazone alkylating agents BrCH2C{¼NNHC6H3(NO2)2}C6H4Ph,
BrCH2C{¼NNHC6H3(NO2)2}Ph, and ClCH2C{¼NNHC6H3(NO2)2}Me were pre-
pared by the standard procedure for the conversion of ketones into their
2,4-dinitrophenylhydrazones [25], by the reaction of BrCH2C(O)C6H4Ph (2-bromo-40-
phenylacetophenone, Aldrich), BrCH2C(O)Ph (phenacyl bromide, BDH), or
ClCH2C(O)CH3 (chloroacetone, BDH) with 2,4-dinitrophenylhydrazine (BDH) in
acidified ethanol solution.
ESI mass spectra were recorded on a VG Platform II instrument. Solutions of
approximate concentration ca. 0.1 mg mLꢂ1 were 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
from the Isotope program [26]. 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 Otago, Dunedin, New Zealand. NMR
spectra were recorded in CDCl3 solution on a Bruker Avance DRX300 spectrometer
using XWIN-NMR software version 3.0. IR spectra were recorded as KBr discs using a

2788
O.T. Ujam et al.
NO
+
2
O N
2
H
N
N
H C
3
C
H
H
C
S
S
Pt
Pt
Ph P
3
Ph P
3
PPh
3
3
PPh
Scheme 2. Structure of the cation [Pt2(m-S){m-SCH2C{¼NNHC6H3(NO2)2}CH3}(PPh3)4]þ 3 as the E isomer
observed by 1H-NMR studies.
Digilab FTS2000 Scimitar Series FT-IR with Digilab Merlin Version 3.4 software.
Melting points were recorded on a Reichert Thermovar apparatus, and are uncorrected.
3.1. Synthesis of [Pt2(l-S){l-SCH2C{^NNHC6H3(NO2)2}Ph}(PPh3)4]BPh4
(2aꢀBPh4)
[Pt2(m-S)2(PPh3)4] (149 mg, 0.099 mmol) and BrCH2C{¼NNHC6H3(NO2)2}Ph (76 mg,
0.201 mmol) in methanol (40 mL) were stirred for 1 h giving a cloudy yellow-orange
solution. The solution was filtered and NaBPh4 (73 mg, 0.214 mmol) added to the
filtrate to give a yellow-orange precipitate. The product was filtered, washed
successively with water (10 mL), methanol (10 mL), and diethyl ether (10 mL) and
dried to give 2aꢀBPh4 (121 mg, 58%). Found: C, 61.4; H, 4.3; N, 2.6.
C
110H91N4BO4P4Pt2S2 requires C, 62.2; H, 4.3; N, 2.6%. M.p. 168–172ꢁC. IR ꢂ(NH)
3285; ꢂ(C¼N) 1614; ꢂ(NO2) 1512, 1335 cmꢂ1. ESI–MS (cone voltage 20 V) m/z 1802
([M]þ, 100%). 31P{1H} NMR: Z isomer, ꢁ 24.4 [m, J(PtP) 3341 and 2602]; E isomer,
ꢁ 23.3 [m, J(PtP) 2648] and 22.6 [m, J(PtP) 3424]. Selected H-NMR data: Z isomer,
ꢁ 10.5 (s, NH), 4.45 (s, br, SCH2); E isomer, ꢁ 11.1 (s, NH), 3.60 (s, br, SCH2).
1
1
1
1
3.2. Synthesis of [Pt2(l-S){l-SCH2C{^NNHC6H3(NO2)2}C6H4Ph}(PPh3)4]PF6
(2bꢀPF6)
[Pt2(m-S)2(PPh3)4] (100 mg, 0.067 mmol) and BrCH2C{¼NNHC6H3(NO2)2}C6H4Ph
(36.4 mg, 0.080 mmol) in methanol (25 mL) were stirred for 1 h giving a clear, deep
yellow-orange solution. After filtration to remove a small amount of insoluble matter,
NH4PF6 (80 mg, 0.491 mmol) was added to the filtrate. Water (10 mL) was added to
assist precipitation, the product was filtered, washed with diethyl ether (40 mL), and
dried to give 2bꢀPF6 (91.5 mg, 68%). The product was recrystallized by vapor diffusion
of diethyl ether into a dichloromethane solution of the complex. Found: C, 54.2; H, 3.7;
N, 2.7. C92H75N4F6O4P5Pt2S2 requires C, 54.6; H, 3.7; N, 2.8%. IR ꢂ(C¼N) 1613;

[Pt2(ꢀ-S)2(PPh3)4]
2789
ꢂ(NO2) 1501, 1333 cmꢂ1. ESI–MS (cone voltage 20 V) m/z 1876 ([M]þ, 100%). 31P{1H}
1
NMR: Z isomer, ꢁ 24.5 [m, J(PtP) 3344 and 2602]; E isomer, ꢁ 23.1 [m, J(PtP) 2639]
1
1
1
and 22.5 [m, J(PtP) 3411]. Selected H-NMR data: Z isomer, ꢁ 10.68 (s, NH), 4.40
(s, br, SCH2); E isomer, ꢁ 11.19 (s, NH), 3.65 (s, br, SCH2).
3.3. Synthesis of [Pt2(l-S){l-SCH2C{^NNHC6H3(NO2)2}Me}(PPh3)4]BPh4
(3ꢀBPh4)
[Pt2(m-S)2(PPh3)4] (150 mg, 0.100 mmol) and ClCH2C{¼NNH(C6H3(NO2)2}Me (54 mg,
0.198 mmol) in methanol (40 mL) were stirred at room temperature for 30 min giving a
clear, bright yellow-orange solution. NaBPh4 (70 mg, 0.205 mmol) was added to give a
bright yellow precipitate. The product was filtered, washed successively with water
(10 mL), methanol (10 mL), and petroleum spirits (10 mL), and dried to give 3ꢀBPh4 as a
bright yellow solid (139 mg, 68%). Found: C, 61.1; H, 4.4; N, 2.8. C105H89N4
BO4P4Pt2S2 requires C, 61.2; H, 4.4; N, 2.7%. M.p. decomposition 4152ꢁC. IR ꢂ(NH)
3287; ꢂ(C¼N) 1616; ꢂ(NO2) 1509, 1335 cmꢂ1. ESI–MS (cone voltage 20 V) m/z 1740
1
1
([M]þ, 100%). 31P{1H} NMR, ꢁ 24.9 [m, J(PtP) 3342] and 23.6 [m, J(PtP) 2613].
1
Selected H-NMR data, ꢁ 10.56 (s, NH), 3.73 [s, br, 2H, SCH2, J(PtH) 33] and 0.47
3
(s, 3H, CH3).
3.4. X-ray crystal structure determination of [Pt2(l-S)
{l-SCH2C{^NNHC6H3(NO2)2}Ph}(PPh3)4]BPh4 (2aꢀBPh4)
Crystals (orange blocks) were grown by vapor diffusion of diethyl ether into a
dichloromethane solution of the complex at room temperature. Intensity data and unit
cell dimensions were obtained on a Bruker SMART CCD diffractometer at the
University of Auckland.
The structure was solved for the positions of the Pt atoms using the Patterson
methods option of SHELXS-97 [27]. The structures of the cation and anion were
developed routinely. Later difference maps showed significant electron density
associated with disordered solvents in the lattice, possibly two CH2Cl2 and one ether
molecules. These could not be sensibly modeled, so they were eliminated using the
SQUEEZE procedure of PLATON [28] and were not included in the refinement.
Full-matrix least-squares refinement (SHELXL-97) [29] was based on F2o with all
non-hydrogen atoms anisotropic and hydrogen in calculated positions converged with
R1 ¼ 0.0247 (I ꢃ 2ꢃ(I)), wR2 ¼ 0.0596 (all data), goodness-of-fit ¼ 1.068. A final
difference map showed no feature greater than 1.039 and ꢂ0.932 e Aꢂ3. All calculations
˚
were carried out by the SHELX-97 suite of programs.
3.5. Crystal data for C110H91BN4O4P4Pt2S2
˚
˚
Mr ¼ 2121.86; triclinic; space group P-1; a ¼ 14.4408(2) A; b ¼ 16.5455(3) A; c ¼
3
ꢁ
ꢁ
ꢁ
˚
˚
22.9006(2) A; ꢄ ¼ 89.355(1) , ꢅ ¼ 72.784(1) , ꢆ ¼ 78.209(1) ; V ¼ 5109.12(12) A ; Z ¼ 2,
T ¼ 83(2) K, ꢇ(Mo-Kꢄ) ¼ 0.71073 A; m(Mo-Kꢄ) ¼ 2.891 mmꢂ1; dcalcd ¼ 1.379 g cmꢂ3
;
˚
48, 989 reflections collected; 20, 704 unique (Rint ¼ 0.0224).

2790
O.T. Ujam et al.
Supplementary material
CCDC no. 824691 contains the supplementary crystallographic data for this article.
These data can be obtained free of charge from The Cambridge Crystallographic Data
Centre, via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
We thank the University of Waikato for financial support of this study and Dr Tania
Groutso (University of Auckland) for collection of the X-ray data set. We also thank
Pat Gread for assisting with mass spectrometry instrumentation.
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