Base-promoted synthesis of monometallic and bimetallic platinum complexes containing chelating O,O- or S,S-donor ligands

Article abstract of DOI:10.1016/j.ica.2006.08.060

Dichloroplatinum complexes [PtCl₂L₂] (L₂ = cod, dppp) react with 1,2-C₆H₄E₂ (E = O, S) in the presence of a base to produce mononuclear complexes. The diene was not readily displaced from [Pt(E₂C₆H₄-EE)(cod)]. A second approach to complexes containing dianionic chelating ligands involved [Pt(acac)₂] as precursor. Reaction with dppp and oxalic acid gave [Pt(C₂O₄)(dppp)], whereas the analogous reaction with Ph₂PC{triple bond, long}CPPh₂ produced the bimetallic complex [Pt(C₂O₄-OO)(μ-Ph₂PC{triple bond, long}CPPh₂)]₂. Similar reactions with 1,2-C₆H₄E₂ (E = O, S) also gave bimetallic products. The structures of [Pt(C₂O₄)(dppp)] and [Pt(C₂O₄-OO)(μ-Ph₂PC{triple bond, long}CPPh₂)]₂ have been determined by X-ray crystallography.

Full text of DOI:10.1016/j.ica.2006.08.060

Inorganica Chimica Acta 360 (2007) 1767–1770
www.elsevier.com/locate/ica
Note
Base-promoted synthesis of monometallic and bimetallic
platinum complexes containing chelating O,O- or S,S-donor ligands
*
Ngamjit Praingam, Gordon K. Anderson , Nigam P. Rath
Department of Chemistry and Biochemistry, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO 63121, USA
Received 14 July 2006; accepted 15 August 2006
Available online 7 October 2006
Abstract
Dichloroplatinum complexes [PtCl2L2] (L2 = cod, dppp) react with 1,2-C6H4E2 (E = O, S) in the presence of a base to produce mono-
nuclear complexes. The diene was not readily displaced from [Pt(E2C6H4-EE)(cod)]. A second approach to complexes containing dian-
ionic chelating ligands involved [Pt(acac)2] as precursor. Reaction with dppp and oxalic acid gave [Pt(C2O4)(dppp)], whereas the
analogous reaction with Ph2PC„CPPh2 produced the bimetallic complex [Pt(C2O4-OO)(l-Ph2PC„CPPh2)]2. Similar reactions with
1,2-C6H4E2 (E = O, S) also gave bimetallic products. The structures of [Pt(C2O4)(dppp)] and [Pt(C2O4-OO)(l-Ph2PC„CPPh2)]2 have
been determined by X-ray crystallography.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Platinum complexes; Oxalate complexes; Bimetallic complexes; Chelate complexes; X-ray crystal structure
1. Introduction
with chelating dianionic ligands (which might subsequently
be used to prepare neutral squares), and their initial use to
prepare monometallic and bimetallic derivatives.
The design of transition metal molecular squares typi-
cally has involved the use of square planar complexes with
chelating ligands that occupy mutually cis positions,
thereby forcing the potential bridging groups to also adopt
90° angles with respect to each other [1–4]. Charged molec-
ular squares have been prepared using platinum(II) or pal-
ladium(II) centers with chelating diamine or diphosphine
ligands and linear linkers such as 4,40-bipyridine [5–19].
We recognized that neutral molecular squares could be
generated either by incorporating neutral chelating ligands
and dianionic linkers, or through the use of dianionic che-
lating groups and neutral bridging moieties. We and others
have shown previously that neutral squares may be gener-
ated with diphosphineplatinum corner units and butadiy-
nyl edges [20–22]. In this paper we report on two
methods aimed at the generation of platinum(II) centers
2. Results and discussion
Treatment of [PtCl2(cod)] with 1,2-dihydroxybenzene
(catechol) or benzene-1,2-dithiol in methanol, in the pres-
ence of KOH or Et3N, results in proton abstraction from
the –OH or –SH groups and displacement of the chlorides
from platinum to give [Pt(E2C6H4-EE)(cod)] (E = O, S)
(Eq. (1)). The reaction to form the thioplatinum derivative
2ꢀ
occurs more rapidly, since the softer C6H4S2 anion is a
better ligand towards platinum(II). Similarly, reactions of
[PtCl2(dppp)] generate the corresponding [Pt(E2C6H4-EE)-
(dppp)] complexes, the thioplatinum species again being
produced more rapidly.
E
HE
Cl
Cl
base
*
Pt
Pt
+
Corresponding author. Present address: College of Arts and Sciences,
-
2HCl
East Tennessee State University, Johnson City, TN 37614, USA. Tel.: +1
423 439 5671; fax: +1 423 439 4565.
E
HE
ð1Þ
E-mail address: andersgk@etsu.edu (G.K. Anderson).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.08.060

1768
N. Praingam et al. / Inorganica Chimica Acta 360 (2007) 1767–1770
The complexes have been characterized by NMR spec-
troscopy and mass spectrometry and, for the cyclooctadi-
ene complexes, they have been confirmed by X-ray
crystallography. The 1H and 13C NMR spectra of the
cod complexes show the expected NMR signals for the
diene and the aromatic ligand; those for the dppp com-
plexes are less informative due to the broad signals arising
from the diphosphine. The 31P NMR spectra of
[Pt(E2C6H4-EE)(dppp)] (E = O, S) each consist of a single
1
resonance that exhibits coupling to 195Pt; the JPtP
couplings of 3318 and 2665 Hz, respectively, illustrate the
greater trans-influence of the S-containing ligand [23].
The cyclooctadiene complexes [Pt(1,2-E2C6H4-EE)(cod)]
(E = O, S) do undergo protonation under FAB conditions
and provide satisfactory high-resolution mass spectra, but
they ionize more efficiently in the presence of AgOCOCF3.
In the case of [Pt(1,2-S2C6H4-SS)(cod)], clusters of peaks
are found for M + Ag+, M + AgOCOCF3 + Ag+ and
2M + Ag+, in addition to those for M + H+, indicating
that extensive chemistry takes place in the gas phase. The
molecular structures of [Pt(1,2-E2C6H4-EE)(cod)] (E = O,
S) have been reported previously [24,25]. To confirm the
identities of these complexes here, their structures were
determined by X-ray crystallography.
We postulated that displacement of the diene from
[Pt(E2C6H4-EE)(cod)] (E = O, S) by linear bidentate
ligands, such as 4,40-bipyridine or bis(diphenylphosph-
ino)ethyne, might provide a method for the generation of
neutral molecular squares with chelating dianionic corner
groups. Even reactions with chelating diphosphine ligands,
such as dppe or dppp, to generate mononuclear complexes
do not proceed cleanly, however, so we decided to consider
a second approach.
Fig. 1. Molecular structure of [Pt(C2O4-OO)(dppp)]. Selected bond
distances (A) and angles (°): Pt–P(1) 2.2245(8), Pt–P(2) 2.2244(8), Pt–
O(1) 2.065(2), Pt–O(3) 2.064(2); P(1)–Pt–P(2) 96.45(3), P(1)–Pt–O(1)
170.94(7), P(1)–Pt–O(3) 90.51(7), P(2)–Pt–O(1) 91.27(7), P(2)–Pt–O(3)
172.99(7), O(1)–Pt–O(3) 81.72(9).
˚
Mononuclear complexes are formed, as expected, in the
case of dppp. The rigid nature of bis(diphenylphosph-
ino)ethyne, Ph2PC„CPPh2, should preclude chelation,
and it appeared possible that it would provide tetrametallic
species. Spectroscopic and crystallographic data, however,
of the product obtained by the analogous reaction shown
in Eq. (3), and those involving 1,2-C6H4(EH)2 (E = O, S),
indicate that bimetallic species are produced. The oxalate
complex formed with Ph2PC„CPPh2 contains a single res-
onance, with 195Pt satellites, in its 31P NMR spectrum, indi-
cating that it has a symmetrical structure. Its molecular
structure (Fig. 2) confirms its dimeric nature, the two plat-
inum-oxalate units being bridged by two diphosphine
ligands. Each platinum is again approximately square pla-
nar (the sums of the angles at platinum are 360.2° and
360.4°), the smallest angles again being within the plati-
num-oxalate chelates. The carbon–carbon distances con-
firm that the triple bond character is maintained,
although there is some bending at the carbons (P–C–C
angles 171.7–174.2°). The two metal square planes are
inclined at an angle of 25.5° to each other, giving a Pt–Pt
Our second synthetic strategy was to use [Pt(acac)2] as
the starting material. First, we sought to determine if this
method could be used to prepare mononuclear com-
plexes. When an acetone suspension of [Pt(acac)2] is trea-
ted with 1,2-C6H4(EH)2 (E = O, S) or oxalic acid in the
presence of dppp, acetylacetone is formed along with the
chelated platinum complex. This is illustrated for the case
of oxalic acid in Eq. (2). The oxalate complex has been
characterized by NMR spectroscopy and by X-ray crys-
tallography. Its 1H and 13C NMR spectra are quite
2uninformative, whereas [Pt(C2O4)(dppp)] exhibits a sin-
˚
distance of 6.985 A.
Ph2
P
Ph2
O
O
O
O
O
O
O
P
1
gle 31P resonance at ꢀ10.2 ppm, with JPtP = 3451 Hz
Pt
Pt(acac)2
Pt
P
Ph2
+
Ph2PC CPPh2
+
H2C2O4
P
Ph2
O
[26]. Its solid state structure (Fig. 1) reveals the antici-
pated planar geometry (the sum of the angles around
platinum is 360.0°), the smaller O–Pt–O angle of the che-
lated oxalate being balanced by the larger bite angle of
the dppp ligand. The solid state structures of the analo-
gous oxalate complexes [Pt(C2O4)L2] (L2 = dppm, dppf)
have been reported previously [27,28].
ð3Þ
The 31P NMR spectra of [Pt(E2C6H4-EE)(l-Ph2PC„
CPPh2)]2 (E = O, S) each exhibit a single resonance with
1
195Pt satellites, the value of JPtP being much smaller in
[Pt(S2C6H4-SS)(l-Ph2PC„CPPh2)]2 than in the O-com-
plexed dimers. The high resolution mass spectrum for
[Pt(S2C6H4-SS)(l-Ph2PC„CPPh2)]2 confirms its bimetallic
nature, a molecular ioþn being obtained that corresponds to
Ph2
O
O
P
O
O
dppp +
Pt
Pt(acac)2
+
H2C2O4
ð2Þ
the C64H48P4S4AgPt unit, the Ag+ deriving from the
P
Ph2
2
AgOCOCF3 used in the experiment.

N. Praingam et al. / Inorganica Chimica Acta 360 (2007) 1767–1770
1769
conditions, using AgOCOCF3 in a nitrobenzyl alcohol
matrix.
3.2. Preparation of [Pt(O2C6H4-OO)(cod)]
A 1.0 M solution of KOH in methanol (1.0 mL) was
added with stirring to a colorless solution of 1,2-C6H4-
(OH)2 (0.030 g, 0.27 mmol) and [PtCl2(cod)] (0.101 g,
0.27 mmol) in methanol (50 mL). The solution immediately
turned yellow, and it was refluxed for 2 h. The solvent was
removed in vacuo, and the residue was crystallized from
CH2Cl2 to give the product as yellow crystals (0.073 g,
64%). 1H NMR: dH 2.32 (m), 2.66 (m), 5.39 (1JPtH
=
66 Hz), 6.61 (m), 6.80 (m). 13C{1H} NMR: dC 30.1, 88.6,
115.1, 118.9, 161.8.
3.3. Preparation of [Pt(S2C6H4-SS)(cod)]
This complex was prepared similarly from [PtCl2(cod)]
and 1,2-C6H4(SH)2 and obtained as colorless crystals in
72% yield. 1H NMR: dH 2.54 (m), 3.06 (m), 5.48
(1JPtH = 66 Hz), 6.90 (m), 7.52 (m). 13C{1H} NMR: dC
30.5, 92.8, 123.0, 128.0, 146.1. HRMS calc. for
C14H16S109Ag194Pt or C14H16S107Ag196Pt: 550.9382. Found:
Fig. 2. Molecular structure of [Pt(C2O4-OO)(Ph2PC„CPPh2)]2. Selected
bond distances (A) and angles (°): Pt(1)–P(1) 2.226(2), Pt(1)–P(3) 2.227(2),
˚
Pt(1)–O(1) 2.031(6), Pt(1)–O(3) 2.045(6), Pt(2)–P(2) 2.220(2), Pt(2)–P(4)
2.211(2), Pt(2)–O(5) 2.036(5), Pt(2)–O(7) 2.052(6), C(5)–C(6) 1.199(10),
C(7)–C(8) 1.195(10); P(1)–Pt(1)–P(3) 94.58(7), P(1)–Pt(1)–O(1) 91.13(17),
P(1)–Pt(1)–O(3) 172.37(17), P(3)–Pt(1)–O(1) 173.11(17), P(3)–Pt(1)–O(3)
92.71(17), O(1)–Pt(1)–O(3) 81.8(3), P(2)–Pt(2)–P(4) 94.87(8), P(2)–Pt(2)–
O(5) 93.23(18), P(2)–Pt(2)–O(7) 172.34(17), P(4)–Pt(2)–O(5) 171.45(18),
P(4)–Pt(2)–O(7) 89.87(16), O(5)–Pt(2)–O(7) 82.4(2), P(1)–C(5)–C(6)
171.9(7), C(5)–C(6)–P(2) 171.7(7), P(3)–C(7)–C(8) 174.2(8), C(7)–C(8)–
P(4) 171.7(8).
2
2
550.9399.
3.4. Preparation of [Pt(O2C6H4-OO)(dppp)]
This complex was prepared from [PtCl2(dppp)] and 1,2-
1
C6H4(OH)2 and obtained as a white solid in 67% yield. H
NMR: dH 2.11 (m), 2.52 (m), 7.37–7.79 (m). 13C{1H}
NMR: dC 24.7, 116.8, 120.2, 128.6, 131.1, 131.5, 133.6.
31P{1H} NMR: dP ꢀ10.0 (1JPtP = 3318 Hz).
Although we have not yet been able to use this approach
to generate neutral molecular squares with dianionic cor-
ners, we have shown that [Pt(acac)2] is a useful precursor
in such endeavors and Ph2PC„CPPh2 has been used as a
bridging ligand in a series of bimetallic platinum complexes.
3.5. Preparation of [Pt(S2C6H4-SS)(dppp)]
This complex was prepared analogously from [PtCl2-
(dppp)] and 1,2-C6H4(SH)2 and isolated as a white solid
3. Experimental
1
in 74% yield. H NMR: dH 2.43 (m), 2.58 (m), 6.62 (m),
7.31 (m), 7.64 (m). 13C{1H} NMR: dC 122.5, 125.7,
3.1. General
128.3, 128.7, 131.1, 133.8. 31P{1H} NMR: dP ꢀ5.3 (1JPtP
=
All reactions were carried out under an atmosphere of
argon. Dichloromethane was distilled from CaH2; HPLC
grade acetone and methanol were dried over molecular
sieves. 1,2-Benzenediol, 1,2-benzenedithiol, and oxalic acid
were obtained from ACROS and were used as received.
Bis(diphenylphosphino)ethyne was obtained from Strem.
[Pt(acac)2] was obtained from Engelhard, and recrystallized
from CH2Cl2 prior to use. [PtCl2(cod)] was prepared by a
standard method; [PtCl2(dppp)] was prepared by displace-
ment of cyclooctadiene from [PtCl2(cod)].
NMR spectra were recorded on a Bruker Avance
300 MHz spectrometer using CDCl3 as solvent. 1H and
13C chemical shifts were measured relative to the residual
CHCl3 and CDCl3 signals, respectively; 31P shifts were
measured relative to external H3PO4. High resolution mass
spectra were obtained on a JEOL M station under FAB
2665 Hz).
3.6. Preparation of [Pt(C2O4-OO)(dppp)]
A mixture of [Pt(acac)2] (0.10 g, 0.26 mmol), oxalic acid
(0.023 g, 0.26 mmol) and dppp (0.11 g, 0.26 mmol) was stir-
red in acetone (50 mL) for 2 h. The solvent was removed
and the residue was crystallized from CH2Cl2 to give the
product as colorless crystals (0.050 g, 84%). 31P{1H}
NMR: dP ꢀ10.2 (1JPtP = 3451 Hz).
3.7. Preparation of [Pt(C2O4-OO)(l-Ph2PC„CPPh2)]2
This complex was prepared from [Pt(acac)2], oxalic acid
and Ph2PC„CPPh2 and obtained as colorless crystals in
1
86% yield. H NMR: dH 7.30–7.76 (m). 13C{1H} NMR:

1770
N. Praingam et al. / Inorganica Chimica Acta 360 (2007) 1767–1770
dC 122.9, 123.9, 129.6 (t), 133.1 (t), 164.6; 31P{1H} NMR:
dP ꢀ14.2 (1JPtP = 3760 Hz). HRMS calc. for C56H41O8-
P1495Pt2: 1355.1046. Found: 1355.1025.
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:
10.1016/j.ica.2006.08.060.
3.8. Preparation of [Pt(O2C6H4-OO)(l-Ph2PC„CPPh2)]2
This complex was generated from [Pt(acac)2], 1,2-
C6H4(OH)2 and Ph2PC„CPPh2 and isolated as colorless
1
crystals in 79% yield. H NMR: 5.53 (m), 6.50–7.66 (m).
13C{1H} NMR: 115.4, 117.3, 120.2, 128.8, 131.9, 133.3,
References
144.7. 31P{1H} NMR: ꢀ13.8 (1JPtP = 3867 Hz).
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3.9. Preparation of [Pt(S2C6H4-SS)(l-Ph2PC„CPPh2)]2
This complex was generated from [Pt(acac)2], 1,2-
C6H4(SH)2 and Ph2PC„CPPh2 and isolated as colorless
1
crystals in 85% yield. H NMR: 6.79 (m), 7.20–7.81 (m).
13C{1H} NMR: 123.6, 130.0, 133.1, 134.9, 160.0. 31P{1H}
NMR: ꢀ4.2 (1JPtP = 2815 Hz). HRMS calc. for C64H48-
P4S107Ag195Pt2: 1566.9939. Found: 1566.9878.
4
3.10. X-ray crystallography
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Crystals of [Pt(C2O4-OO)(dppp)] are monoclinic, space
group P21/n, with a = 10.5049(4) A, b = 15.3915(5) A,
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˚
˚
3
˚
˚
c = 16.5893(5) A, b = 103.185(2)°, V = 2611.55(15) A ,
Z = 4, and qcalcd = 1.769 g cmꢀ3 for fw = 695.53. A total
of 7416 independent reflections were collected at 155(2) K
in the h range 1.83–30.00°, wR2 = 0.0538 and R1 = 0.0316.
Crystals of [Pt(C2O4-OO)(l-Ph2PC„CPPh2)]2 are tri-
˚
ꢀ
clinic, space group Pð1Þ, with a = 14.6729(3) A, b =
˚
˚
15.0925(3) A, c = 15.9589(3) A, a = 81.8850(10)°, b =
3
˚
71.5070(10)°, c = 70.4240(10)°, V = 3155.48(11) A , Z =
2, and qcalcd = 1.803 g cmꢀ3 for fw = 1713.04. A total of
14488 independent reflections were collected at 160(2) K
in the h range 1.73–27.50°, wR2 = 0.1072 and R1 = 0.0639.
Acknowledgement
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Thanks are expressed to the University of Missouri-St.
Louis for a Research Award for support of this work,
and to NSF (Grant Numbers CHE-9318696, 9309690
and 9974801), the US Department of Energy (Grant Num-
ber DE-FG02-92CH10499) and the University of Missouri
Research Board for instrumentation grants. The authors
thank Dr. R. Winter and Mr. J. Kramer for assistance with
the mass spectra.
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Appendix A. Supplementary material
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Tables of crystal data, atomic coordinates and displace-
ment parameters, and complete lists of bond distances and
angles for [Pt(C2O4)(dppp)] and [Pt(C2O4-OO)(l-Ph2P-
C„CPPh2)]2 are available from CCDC. The data can be