Platinum(II) and palladium(II) saccharinate complexes

Article abstract of DOI:10.1016/S0020-1693(98)00327-2

A number of platinum(II) and palladium(II) complexes containing the saccharinate ligand (sac^-), of the type [MCl(sac)L₂] (M = Pt, L = PPh₃, L₂ = Ph₂PCH₂CH₂PPh₂, dppe; M = Pd, L = PPh₃) have been synthesised by reaction of [MCl₂L₂] with sacNa in methanol. A single crystal X-ray diffraction study carried out on cis-[PtCl(sac)(PPh₃)₂]·4CHCl₃ shows the N-bonded saccharinate and platinum coordination planes to be nearly orthogonal. The results of an electrospray mass spectrometric study of the dppe complex are also reported.

Full text of DOI:10.1016/S0020-1693(98)00327-2

Inorganica Chimica Acta 285 (1999) 145±148
Note
Platinum(II) and palladium(II) saccharinate complexes
William Henderson*, Brian K. Nicholson, Louise J. McCaffrey
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 10 April 1998; accepted 17 June 1998
Abstract
A number of platinum(II) and palladium(II) complexes containing the saccharinate ligand (sac ), of the type [MCl(sac)L2] (M ˆ Pt,
L ˆ PPh3, L2 ˆ Ph2PCH2CH2PPh2, dppe; M ˆ Pd, L ˆ PPh3) have been synthesised by reaction of [MCl2L2] with sacNa in methanol. A
single crystal X-ray diffraction study carried out on cis-[PtCl(sac)(PPh3)2]Á4CHCl3 shows the N-bonded saccharinate and platinum
coordination planes to be nearly orthogonal. The results of an electrospray mass spectrometric study of the dppe complex are also reported.
# 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Platinum complexes; Palladium complexes; Saccharin complexes
1. Introduction
Platinum-group metal complexes of amide (amidate)
ligands are of interest for their fundamental coordination
chemistry [1±3] and biological activity [4,5] though to date,
relatively few complexes have been reported. We are cur-
rently investigating the syntheses and properties of platinum
amide complexes [6±8]. Saccharin (also known as 2,3-
dihydro-3-oxobenzisosulfonazole, 1,2-benzisothiazoline-3-
(2H)one 1,1-dioxide, o-benzosul®mide) (1) is an amide
widely used as an arti®cial sweetener, and because of the
biological importance of this molecule, there have been
many studies on coordination complexes with a range of
metal centres, especially ®rst-row transition metals [8,10±
16]. However, there has only been one report of a platinum
or palladium complex containing the sac ligand; complexes
trans-[PtH(sac)(EPh3)2] (E ˆ As, P) (2) were synthesised by
oxidative addition of the N±H bond of saccharin to
[Pt(EPh3)4] [17]. Here we report the synthesis of platinum
and palladium saccharinate complexes formed by reaction
of the saccharinate anion with metal±halide complexes.
2. Results and discussion
Reactions of the platinum(II) dichloride complexes cis-
[PtCl2L2] [L ˆ PPh3 and L2 ˆ Ph2PCH2CH2PPh2 (dppe)]
with excess sodium saccharinate (sacNa) in re¯uxing metha-
nol gives the platinum mono(sac) complexes 3a and 3b
respectively, after addition of water to precipitate the pro-
duct. A prolonged reaction time (70 h) and a large excess of
sacNa did not lead to substitution of the second chlorine of
cis-[PtCl2(PPh3)2]. In all preparations, the complex cis-
[PtCl(sac)(PPh3)2] was contaminated with a small quantity
of unreacted cis-[PtCl2(PPh3)2], even after the prolonged
reaction. Reaction of [PdCl2(PPh3)2] under analogous con-
ditions yielded the complex trans-[PdCl(sac)(PPh3)2] (4) as
shown by the single peak in the 31P {1H} NMR spectrum,
and by elemental analysis.
*Corresponding author: Tel.: +64-7-856-2889; fax: +64-7-838-4219;
e-mail: w.henderson@waikato.ac.nz
0020-1693/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00327-2

146
W. Henderson et al. / Inorganica Chimica Acta 285 (1999) 145±148
plexes derived from 5,5-diethylbarbituric acid, of type 5 [7],
which are analogous to the complexes reported in this paper
in having cis chloride and amidate ligands. For these com-
plexes, the chloride ligand was more readily lost than the
amide, by a solvolysis reaction with the MeCN solvent,
‡
giving ions of the type [Pt(debarb)(MeCN)L2] . However,
for the saccharinate complex [PtCl(sac)(dppe)] (3b) the sac
and Cl ligands are both relatively easily lost; the positive-ion
spectrum of 3b recorded in MeCN±H2O solvent at a cone
There have been numerous structural determinations of
metal±saccharinate complexes of ®rst-row transition metals
[11±16], cadmium [18,19], mercury [20±23], and silver
[24,25] but no structures of platinum group metals have
been reported. Crystals of the triphenylphosphine complex
3a suitable for a single crystal X-ray diffraction study were
obtained by allowing a saturated chloroform solution to
stand at room temperature for several weeks. The structure
of 3a shows an approximately square-planar platinum cen-
tre which is coordinated by a chloride and two cis-triphe-
nylphosphine ligands, together with an N-bonded sac-
charinate ligand. Coordination about the platinum atom is
‡
voltage of 50 V showed two main ions due to [PtCl(dppe)]
‡
(m/z 629) and [Pt(sac)(dppe)] (m/z 775). At the lower cone
voltage of 20 V, ions solvated with MeCN were observed,
‡
together with a minor ion assigned as [M ‡ H] .
The IR spectra of the sac complexes 3 and 4 show
the expected features for such complexes [9,10]. Strong
1
CO stretches were observed in the range 1661±1684 cm
and strong SO2 symmetric stretches were observed
,
Ê
planar to within Æ 0.03 A, and the planar core of the sac
Table 1
Crystal data and structure refinement for 3aÁ4CHCl3
ligand forms a dihedral angle of 788 to the coordination
plane. As is typical for complexes of this type, the P(1)±
Pt(1)±P(2) angle is greater than the idealised 908, in this case
99.09(8)8. The N(1)±Pt(1)±Cl(1) angle is correspondingly
reduced at 87.0(2)8. The platinum±phosphorus bond lengths
Crystal data
Empirical formula
Formula weight
Temperature (K)
C
43H34NClO3P2PtSÁ4CHCl3
1414.72
203(2)
Ê
are identical (Pt(1)±P(1) 2.266(2), Pt(1)±P(2) 2.264(2) A),
Ê
Wavelength (A)
0.71073
monoclinic
C2/c
suggesting that the saccharinate and chloride ligands have
very similar trans in¯uences, though the values of 1J(PtP) in
the 31P NMR spectrum of 3a are signi®cantly different
(3770 and 3483 Hz). The platinum(II) complex 5 containing
the anion of 5,5-diethylbarbituric acid (H debarb) together
with a chloride ligand, provides a useful complex for
comparison [7]. The Pt±P bond lengths of 5 are different,
Crystal system
Space group
Unit cell dimensions
Ê
a (A)
43.3254(15)
10.4480(4)
23.9703(8)
93.444(1)
10830.9(7)
8
Ê
b (A)
Ê
c (A)
ꢀ (8)
Volume (A )
Ê 3
Z
Ê
with the one trans to chloride (2.241(2) A) being slightly
shorter than that trans to the higher trans-in¯uence amide
3
)
Density (calc.) (Mg m
1.735
Ê
ligand (2.274(2) A). The Pt(1)±N(1) bond length of the sac
Ê
complex 3a (2.064(6) A) is similar to that of 5, and to
platinum±nitrogen bond lengths in other platinum amidate
complexes [6±8].
Data collection
Diffractometer
Siemens SMART CCD
6.0
Crystal to detector distance (cm)
1
Absorption coefficient (mm
F(000)
Crystal size (mm)
)
3.372
5568
0.43 Â 0.18 Â 0.06
1.70 to 25.80
52 ꢀ h ꢀ 52
0 ꢀ k ꢀ 12
0 ꢀ l ꢀ 29
24711
ꢁ Range for data collection (8)
Index ranges
Reflections collected
Independent reflections
Observed reflections [I > 2ꢂ(I)]
Max., min. transmission
9274 [Rint ˆ 0.0401]
7539
0.8838, 0.5784
One feature of the structure is the high level of solvation.
There are four molecules of CHCl3 in the asymmetric unit,
three ordered and one disordered over two sites. One is
hydrogen-bonded to the Cl(1) of the complex, one to O(3) of
the sac ligand, while the other two make no unusually short
contacts.
Electrospray mass spectrometry (ESMS) has recently
been used in the study of a number of different types of
platinum-group metal amidate complexes, including com-
Structural analysis and refinement
Solution by
Patterson methods
Full-matrix least-squares on F2
9274/0/606
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢂ(I)]
R indices (all data)
1.135
R1 ˆ 0.0597, wR2 ˆ 0.1333
R1 ˆ 0.0782, wR2 ˆ 0.1440
2.488, 1.907(adjacenttoPtatom)
SHELXS 86 [29] and SHELXL 93 [30]
3
Ê
Largest difference peak, hole (e A
)
Programs used

W. Henderson et al. / Inorganica Chimica Acta 285 (1999) 145±148
147
from 1303 to 1310 cm 1. The CO stretching frequencies are
3.1. Synthesis of cis-[PtCl(sac)(PPh3)2] (3a)
notably higher than those of ®rst-row transition metal
complexes of the type [M(sac)2(H2O)4], which occur at
The complex cis-[PtCl2(PPh3)2] (259 mg, 0.327 mmol)
with sodium saccharinate hydrate (337 mg, 1.64 mmol) was
re¯uxed for 65 min in methanol (45 ml). Water (70 ml) was
added, and the white solid ®ltered and washed with water
(20 ml), ether (20 ml), and dried under vacuum. Yield
271 mg (88%), m.p. > 2308C. Found: C, 53.9; H, 3.75; N,
1.5%. C43H34NClO3P2PtS requires: C, 55.1; H, 3.7; N, 1.5%
31P {1H} NMR (CDCl3 ‡ 10% DMSO), ꢃ 15.2 (d, P trans
Cl, 1J(PtP) 3770, 2J(PP) 17) and 7.9 (d, P trans N, 1J(PtP)
3483). IR: ꢄ(CO) 1673; ꢄsym(SO2) 1310 cm 1. Recrystalli-
sation from a saturated chloroform solution at room tem-
perature gave X-ray quality crystals of the tetra(chloroform)
solvate, which lose chloroform on exposure to air.
1
ca. 1610 cm [9,10]. Two bands were observed for all
three complexes in the SO2 asymmetric stretching region,
at 1155 and 1172 cm 1, and a de®nitive assignment has
not been made.
3. Experimental
General experimental procedures were as described pre-
viously [7,8]; reactions were carried out in air, using LR
grade solvents which were not further puri®ed. Electrospray
mass spectra were recorded in positive-ion mode, in MeCN±
H2O (1:1, vol./vol.) solvent, and cone voltages were varied
between 20 and 50 V. Assignment of ions was assisted
by comparison of experimental and calculated isotope
patterns, the latter obtained by means of the ISOTOPE program
[26].
3.2. Synthesis of cis-[PtCl(sac)(dppe)] (3b)
The complex [PtCl2(dppe)] (300 mg, 0.451 mmol), with
sodium saccharinate hydrate (464 mg, 2.26 mmol) in
methanol (20 ml) was re¯uxed for 60 min. Water (70 ml)
was added, the mixture stirred overnight, and the white
product ®ltered off, washed with water (20 ml), ether
(20 ml), and dried under vacuum. Yield 240 mg (66%),
m.p. > 2308C. Found: C, 48.0; H, 3.7; N, 1.6%.
C33H28NClO3P2PtS requires: C, 48.9; H, 3.5; N, 1.7%
31P {1H} NMR, ꢃ 42.4 (d, P trans Cl, 1J(PtP) 3623,
2J(PP) 45) and 35.7 (d, P trans N, 1J(PtP) 3457). IR
Sodium saccharinate hydrate (Aldrich) was used as sup-
plied. The complexes [PtCl2(cod)] [27] and [PdCl2(cod)]
[28] were prepared by the literature procedures, and the
complexes
cis-[PtCl2(PPh3)2],
[PtCl2(dppe)],
and
[PdCl2(PPh3)2] prepared from them by reaction with the
appropriate molar amount of the phosphine in dichloro-
methane, followed by precipitation with petroleum spirits
(b.p. 40±608C).
Fig. 1. Molecular structure of the complex cis-[PtCl(sac)(PPh3)2]Á4CHCl3 (3aÁ4CHCl3), showing the atom numbering scheme. The chloroform molecules of
Ê
crystallisation have been omitted. Selected bond lengths (A) and angles (8): Pt(1)±N(1) 2.064(6), Pt(1)±P(2) 2.264(2), Pt(1)±P(1) 2.266(2), Pt(1)±Cl(1)
2.340(2), N(1)±Pt(1)±P(2) 89.8(2), N(1)±Pt(1)±P(1) 170.8(2), P(2)±Pt(1)±P(1) 99.09(8), N(1)±Pt(1)±Cl(1) 87.0(2), P(2)±Pt(1)±Cl(1) 176.71(7), P(1)±Pt(1)±
Cl(1) 84.17(7). The inset shows the orthogonality of the sac ligand and platinum coordination planes; PPh3 carbons are omitted.

148
W. Henderson et al. / Inorganica Chimica Acta 285 (1999) 145±148
ꢄ(CO) 1684; ꢄsym(SO2) 1303 cm 1. ESMS: cone voltage
edged. Wendy Jackson and Ralph Thomson are thanked for
technical assistance and literature searches respectively.
‡
20 V (m/z, %) [M sac ‡ MeCN] (670, 100), [M Cl ‡
‡
‡
‡
MeCN] (816, 62), [M Cl] (775, 17), [M sac] (629,
10), [M ‡ H] (812, 5), plus several other minor unassigned
‡
‡
‡
References
ions. Cone voltage 50 V: [M sac] (629, 100), [M Cl]
‡
(775, 85), [M sac ‡ MeCN] (670, 13).
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Yield 247 mg (68%), m.p. > 2308C, decomp. > ca. 1958C.
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Acknowledgements
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We thank the University of Waikato for ®nancial support
of this work, the New Zealand Lottery Grants Board for a
grant-in-aid towards the mass spectrometer. The loan of
platinum from Johnson Matthey plc is gratefully acknowl-
È
University of Gottingen, 1986.
[30] G.M. Sheldrick, SHELXL 93, Program for refining crystal structures,
È
University of Gottingen, 1993.