Hydroxo and oxo complexes of platinum(II) stabilized by phosphanes: Synthesis and characterization - X-ray structures of cis-[L2Pt(μ- OH)]2(NO3)2 (L = PMe2Ph, PMePh 2) and [{cis-(PMe2<

Article abstract of DOI:10.1002/ejic.200300446

The dinuclear hydroxo complexes cis-[L₂Pt(μ-OH)] ₂(NO₃)₂ (L = PMe₂Ph and PMePh ₂) have been characterized by single-crystal X-ray analysis, and their reactivity towards chloride ions has be

Full text of DOI:10.1002/ejic.200300446

FULL PAPER
Hydroxo and Oxo Complexes of Platinum(II) Stabilized by Phosphanes:
Synthesis and Characterization ؊ X-ray Structures of cis-[L2Pt(µ-OH)]2(NO3)2
(L ؍ PMe2Ph, PMePh2) and [{cis-(PMe2Ph)2Pt}3(µ-O)2]Cl2
Bruno Longato,*[a,c] Giuliano Bandoli,[b] and Alessandro Dolmella[b]
Keywords: Platinum / Oxo and hydroxo ligands / X-ray diffraction / Deprotonation reactions
The dinuclear hydroxo complexes cis-[L2Pt(µ-OH)]2(NO3)2
(L = PMe2Ph and PMePh2) have been characterized by
single-crystal X-ray analysis, and their reactivity towards
chloride ions has been investigated. Reaction of cis-[L2Pt(µ-
X-ray diffraction methods. Under the same experimental
conditions, the structurally analogous hydroxo complex, sta-
bilized by the less basic and more hindered PMePh2 ligand,
reacted with Cl− to give cis-[(PMePh2)2PtCl2] as the only isol-
= PMe3, PMe2Ph; X = NO3 , ClO4 )
with able species. The 31P NMR spectroscopic analysis of the reac-
−
−
OH)]2X2 (L
(NEt4)Cl·H2O or (AsPh4)Cl, in a 1:2 molar ratio, afforded a
mixture of cis-[L2PtCl2] and [{cis-L2Pt}3(µ-O)2]2+ in ca. equim-
olar amounts. The trinuclear oxo compounds, separated by
fractional crystallization of the reaction mixtures, were fully
tion mixtures allowed the detection of a moderately stable
product, which is most likely to be the neutral hydroxo com-
plex cis-[L2PtCl(OH)].
characterized by spectroscopic techniques, and the derivat- ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ive [{cis-(PMe2Ph)2Pt}3(µ-O)2]Cl2 was also characterized by
Germany, 2002)
Introduction
Oxo complexes of platinum() stabilized by phosphanes
of the type [L2Pt(µ-O)]2 (L ϭ PPh3, PMe2Ph; L2 ϭ biden-
tate phosphanes) have recently been described by P. R.
Sharp.[1] They were obtained by deprotonation of the corre-
sponding hydroxo bridged complexes [L2Pt(µ-OH)]22ϩ with
strong bases such as LiN(SiMe3)2. A common feature of the
bridging oxo ligands, and their chalcogenide analogues,[2] is
the ability to bind ions such as Liϩ, Agϩ, Cuϩ, and other
metal centers, thus affording stable and well-characterized
heteropolymetallic complexes. An exception is represented
by the adduct [cis-L2Pt(µ-O)]2·2LiBF4 (L ϭ PMe2Ph),
which decomposes in THF to give [{cis-L2Pt}3(µ-
O)2](BF4)2 (Scheme 1), the trinuclear species in which each
oxygen atom is symmetrically coordinated to three
[L2Pt]2ϩ units.[3]
Scheme 1
We have now found that oxo complexes of this type are
also formed when the hydroxo complexes cis-[L2Pt(µ-
2ϩ
OH)]2 (L ϭ PMe3 and PMe2Ph) react with chloride ions
in aprotic solvents. The nucleophilic attack of ClϪ at the
metal center affords a mixture of the mononuclear dichloro
cis-[L2PtCl2] species and the trinuclear [{cis-L2Pt}3(µ-
O)2]2ϩ species in which the relative quantity of the two com-
pounds is strongly dependent on the amount of added chlo-
ride. A large excess of ClϪ ions leads to the formation of
cis-[L2PtCl2] as the main product, whereas relatively good
yields of the oxo complex are formed when the molar ratio
[a]
Dipartimento di Chimica Inorganica, Metallorganica ed
`
Analitica, Universita di Padova,
Ϫ
n(Cl )/n(hydroxo complex) approaches the value of 2:1. This
Via Marzolo 1, 35131 Padova, Italy
Fax: (internat.) ϩ39-049-8275161
E-mail: longato@chin.unipd.it
finding contrasts the observations reported by Bushnell for
the strictly related hydroxo complex stabilized by PEt3.[4] In
that case, addition of LiCl to a solution of [cis-(PEt3)2Pt(µ-
OH)]22ϩ, in a 2:1 molar ratio, gave the substitution product
cis-[(PEt3)2PtCl2] and about half of the starting hydroxo
complex remained unreacted.
[b]
[c]
`
Dipartimento di Scienze Farmaceutiche, Universita di Padova,
Via Marzolo 5, 35131 Padova, Italy
Istituto di Scienze
e Tecnologie Molecolari, CNR, c/o
Dipartimento di Chimica Inorganica, Metallorganica ed
`
Analitica, Universita di Padova, Via Marzolo 1, 35131
Padova, Italy.
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DOI: 10.1002/ejic.200300446
Eur. J. Inorg. Chem. 2004, 1092Ϫ1099

Hydroxo and Oxo Complexes of Platinum(II)
FULL PAPER
In this paper, in addition to the X-ray structures of cis- OH)]2(NO3)2 (2), which was prepared in a good yield using
[L2Pt(µ-OH)]2(NO3)2 (L ϭ PMe2Ph, PMePh2), we report a slightly modified procedure, is virtually insoluble in water.
on the details of the reaction of this class of dinuclear com-
The dinuclear nature of 1a and 2 has been confirmed by
pounds with chloride ions. The facile deprotonation of the single-crystal X-ray analysis. The ORTEP drawings of the
bridging hydroxo ligands, induced by the presence of the two cations, cis-[L2Pt(µ-OH)]22ϩ, are shown in Figures 1
nucleophile ClϪ, offers an alternative route for the synthesis and 2, while the relevant bond lengths and angles are re-
of the oxo compounds [{cis-L2Pt}3(µ-O)2]2ϩ (L ϭ PMe2Ph, ported in Table 1. The unit cell of 1a comprises two moiet-
and PMe3), one of which has not previously been described. ies denoted as I and II.
The products have been isolated as pure compounds and
characterized by spectroscopic methods, and the species
[{cis-(PMe2Ph)2Pt}3(µ-O)2]Cl2 has also been characterized
by single-crystal X-ray diffraction analysis. Moreover, the
study of the reaction by 31P NMR spectroscopy allowed the
detection of unstable products, which are tentatively attri-
buted to the mononuclear complexes cis-[L2PtCl(OH)] (L ϭ
PMe3, PMe2Ph, PMePh2).
Results and Discussion
Synthesis and Characterization of the Hydroxo Complexes
؊
؊
cis-[(PMe2Ph)2Pt(µ-OH)]2X2 [X ؍ NO3 (1a), ClO4 (1b)]
and cis-[(PMePh2)2Pt(µ-OH)]2(NO3)2 (2)
We have already shown that the removal of the chloride
ligands from the trimethylphosphane complex cis-
[(PMe3)2PtCl2] with AgNO3, followed by neutralization of
the resulting solution, afforded the hydroxo compound
cis-[L2Pt(µ-OH)]2(NO3)2 (L ϭ PMe3). This compound is a
dinuclear cationic complex, which is very soluble in water
Figure 2. ORTEP drawing of 2 showing 40% probability thermal
ellipsoids and the essential atom numbering scheme; for clarity, the
nitrate anions are omitted
˚
Table 1. Selected bond lengths [A] and angles [°] for the complexes
when the anion is the nitrate group.[5] More recently, we 1a and 2
have
prepared
the
complex
cis-[(PMe2Ph)2Pt(µ-
1a
2
OH)]2(NO3)2 (1a) using the same procedure. This com-
pound is still moderately soluble in water.[6] As previously
observed for the PMe3 analogue, the conversion of 1a into
the perchlorate salt results in a drastic decrease in the solu-
bility. The compound cis-[(PMe2Ph)2Pt(µ-OH)]2(ClO4)2 PtϪO(1)
(1b) can be obtained in a quantitative yield from 1a by
Unit I
Unit II
PtϪP(1)
PtϪP(2)
2.217(4)
2.236(4)
2.06(1)
2.08(1)
3.233(1)
2.234(4)
2.219(4)
2.08(1)
2.07(1)
3.211(1)
2.211(3)
2.219(2)
2.053(9)
2.073(8)
3.174(1)
PtϪO(1)[a]
Pt···Pt[a]
metathetical exchange. The complex cis-[(PMePh2)2Pt(µ-
P(1)ϪPtϪP(2)
93.6(2)
172.3(3)
171.4(3)
77.5(4)
95.0(3)
94.0(3)
102.5(4)
94.9(2)
171.7(3)
171.5(3)
78.5(4)
93.6(3)
93.1(3)
101.5(4)
96.5(1)
170.0(2)
172.4(3)
79.4(4)
91.1(2)
93.0(2)
100.6(2)
P(1)ϪPtϪO(1)
P(2)ϪPtϪO(1)[a]
O(1)ϪPtϪO(1)[a]
P(2)ϪPtϪO(1)[a]
P(2)ϪPtϪO(1)
PtϪO(1)ϪPt[a]
[a]
At x, y, 1 Ϫ z in 1a; at x, 1 Ϫ y, z in 2.
The P4Pt2O2 skeleton is essentially planar, within 0.03,
˚
0.04, and 0.05 A in 1aϪI, 1aϪII, and 2, respectively. Com-
parison of the structural parameters of 1a and 2 with those
of the PMe3 analogue shows only minor differences. In par-
ticular, the PϪPtϪP and OϪPtϪO angles are 93.6(2) and
77.5(4), 94.9(2) and 78.5(4), and 96.5(1)° and 79.4(4)° in
1aϪI, 1aϪII, and 2, respectively, while the corresponding
values in the PMe3 analogue are 95.4(1) and 75.9(4)°. How-
ever, more significant changes are observed in the O···O and
Pt···Pt distances. The O···O distance is relatively short in the
Figure 1. ORTEP drawing of 1a showing 40% probability thermal
ellipsoids and the essential atom numbering scheme; for clarity, the
nitrate anions are omitted and only unit I is shown
˚
PMe3 derivative (2.54 A), however, this distance is longer in
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B. Longato, G. Bandoli, A. Dolmella
FULL PAPER
˚
˚
Table 2. 1H and 31P NMR spectroscopic data for cis- [L2Pt(µ-
OH)2PtLЈ2](NO3)2 in [D6]DMSO at 27 °C
1a and 2, 2.61 A and 2.64 A, respectively; the latter value
is the same as that observed for the structurally analogous
complex that is stabilized by NH3 ligands,[7] and only
slightly shorter than that found in the PPh3 derivative (2.66
L,L
δp [ppm]
Ϫ24.5
1JP,Pt [Hz]
3358
δOH [ppm]
3.46
[3]
˚
A). An increase in the O···O separation is accompanied
by a decrease in the Pt···Pt distance; 3.222 A (average) in
L ϭ LЈ ϭ PMe3
L ϭ LЈ ϭ PMe2Ph
L ϭ LЈ ϭ PMePh2
˚
˚
˚
1a, 3.174(1) A in 2 and 3.261 A in the PMe3 complex. This
trend probably reflects the different repulsion effects at the
metal centers due to the diverse basicity of the PR3 li-
gands.[3]
As found in the PMe3 analogue, in 1a the hydroxo ligands
interact via hydrogen-bonding with the nitrate anions. In
particular, the atoms that are involved in this hydrogen-
bonding interaction are O(6) (at x, y, 1 Ϫ z) in unit I (O···O
Ϫ15.5
3457
4.11
Ϫ5.32
3571
3.53
L ϭ PMe3
LЈ ϭ PMe2Ph
Ϫ24.30
Ϫ15.73
3363
3446
3.40
L ϭ PMe3
LЈ ϭ PMePh2
Ϫ24.87
Ϫ4.94
3377
3522
4.01
3.90
˚
separation of 2.74 A and an OϪH···O angle of 167°) and
O(2) (at x, y ϩ 1, z) in unit II (separation of 2.79 A and an
L ϭ PMe2Ph
LЈ ϭ PMePh2
Ϫ16.15
Ϫ5.15
3478
3541
˚
angle of 178°). This hydrogen-bonding system is not present
in the crystal packing of 2, where the shortest O···O dis-
˚
tance is 3.18 A.
The spectroscopic characterization of compounds 1 and
2 has been carried out in [D6]DMSO. In the 1H NMR spec-
tra, the OH resonances are observed as broad singlets at
δ ϭ 4.11 (L ϭ PMe2Ph) and 3.53 (L ϭ PMePh2), values
similar to that observed for the PMe3 analogue (δ ϭ 3.46).[5]
The 31P NMR spectra, obtained at 36.23 MHz, exhibit a
singlet flanked by the typical pattern due to the 195Pt satel-
lites. Each component of the doublet, which is assigned to
the isotopomer [L2195Pt(OH)2PtL2]2ϩ (1JP,Pt ϭ 3457 Hz for
1 and 3571 Hz for 2), is flanked by a couple of very weak
resonances, separated by 304 Hz for 1 and 232 Hz for 2,
due to the contribution of the less abundant isotopomer
[L2195Pt(OH)2195PtL2]2ϩ (relative abundance 11.4%). As
previously noticed for cis-[(PMe2Ph)2Pt(µ-OH)]2(BF4)2,[3]
the main resonance does not show resolved satellites, which
In all the cases, the NMR spectrum of the resulting mix-
ture shows the resonances of the starting complexes and
two new singlets which are assigned to the species cis-
[L2Pt(µ-OH)2PtLЈ2]2ϩ (L ϭ PMe3, LЈ ϭ PMe2Ph or
PMePh2). After a few hours at room temperature, the rela-
tive intensities of the signals due to the mixed complexes are
approximately the same as those expected for a statistical
distribution of the cis-[L2Pt(OH)]ϩ units according to the
equilibrium reaction [Equation (1)].
2ϩ Ǟ
cis-[L2Pt(µ-OH)] 22ϩ ϩ cis-[LЈ2Pt(µ-OH)]2
ǟ
(1)
2 cis-[L2Pt(µ-OH)2PtLЈ2]2ϩ
This exchange reaction is followed by a further redistri-
bution of the neutral ligands around the metal center as
indicated by the appearance of additional doublets due to
the {cis-LLЈPt} moieties in the 31P NMR spectra.[8] The
lability of the bridging hydroxo ligands has previously been
observed in the structurally related NiII complexes
[NiR(PMe3)(µ-OH)]2 (Rϭ CH2Ph; CH2CMe2Ph).[9]
3
are assigned to the JP,Pt coupling, indicating that the mag-
netic interaction between the 31P and 195Pt nuclei through
three bonds is presumably too small to be observed.
Lability of the Bridging Hydroxo Ligands in cis-[L2Pt(µ-
2؉
OH)]2 (L ؍ PMe3, PMe2Ph, and PMePh2)
Synthesis and Characterization of the Oxo Complexes [{cis-
L2Pt}3(µ-O)2]X2 (L ؍ PMe3, X؍ ClO4؊, 3; L ؍ PMe2Ph,
X ؍ Cl؊, 4)
The 1H and 31P NMR spectroscopic parameters of 1 and
2 do not exhibit appreciable changes with the concentration
(in the 10Ϫ2 to 10Ϫ3  range), suggesting that these di-
nuclear hydroxo-bridged complexes do not dissociate signif-
When chloride ions were added to solutions of cis-
icantly in DMSO solution. However, the lability of the [L2Pt(µ-OH)]2X2 (X ϭ NO3Ϫ, ClO4Ϫ; L ϭ PMe3, PMe2Ph)
PtϪO bonds becomes evident when solutions of 1 and 2 in DMSO or CH2Cl2/DMSO, at room temperature, a mix-
are mixed. The 31P NMR spectrum of a freshly prepared ture of the species cis-[L2PtCl2] and [{cis-L2Pt}3(µ-O)2]2ϩ
mixture shows, after a few minutes, the growth of two new (L ϭ PMe3, 3; PMe2Ph, 4) was formed. {1H}31P NMR
singlets, symmetrically flanked by 195Pt satellites at δ ϭ analysis of the resulting pale yellow solutions shows that
Ϫ5.15 (1JP,Pt ϭ 3541 Hz) and Ϫ16.15 (1JP,Pt ϭ 3478 Hz). the relative quantity of the two products is strongly depen-
These values for the chemical shifts and the coupling con- dent on the stoichiometric ratio of the reactants. A large
stants are intermediate between those found for the pure excess of ClϪ ions (molar ratio Ͼ 10), added as solid
compounds (Table 2), and are consistent with the formation (NEt4)Cl·H2O or (PPh4)Cl, affords the corresponding cis-
of
OH)2Pt(PMePh2)2]2ϩ. A similar exchange also occurs when trations of the chloride ions, the solutions contain increas-
1 or 2 are mixed with cis-[(PMe3)2Pt(µ-OH)]2(NO3)2.
ing amounts of the oxo complexes [{cis-L2Pt}3(µ-O)2]2ϩ
the
mixed
complex
cis-[(PMe2Ph)2Pt(µ- [L2PtCl2] as the only detectable species. At lower concen-
.
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Hydroxo and Oxo Complexes of Platinum(II)
FULL PAPER
Ϫ
When the molar ratio n(Cl )/n(Pt complex) is in the range 1Ϫ2,
the relative intensity of the 31P resonances which are as-
signed to the dichloro and oxo complexes approach the
value expected from the following reaction [Equation (2)].
2 cis-[L2Pt(µ-OH)]22ϩ ϩ 2 ClϪ Ǟ
ǟ
(2)
cis-[L2PtCl2] ϩ [{cis-L2Pt}3(µ-O)2]2ϩ ϩ 2 H2O
The trinuclear complexes were obtained as pure com-
pounds (31P NMR spectroscopy) after precipitation with
Et2O, followed by fractional crystallization. The elemental
analysis of the product isolated from the reaction of cis-
[(PMe3)2Pt(µ-OH)]2(ClO4)2 with (NEt4)Cl was consistent
with the separation of the oxo species as the perchlorate
salt, [{cis-(PMe3)2Pt}3(µ-O)2](ClO4)2 (3). The presence of
Ϫ
the ClO4 ion was clearly evidenced by the typical absorp-
tion at 1093 cmϪ1 in the IR spectrum of the solid.
The crystallization of the product obtained from the reac-
tion of cis-[(PMe2Ph)2Pt(µ-OH)]2(ClO4)2 with ClϪ gave
crystals of [{cis-(PMe2Ph)2Pt}3(µ-O)2]Cl2 (4), i.e. the chlo-
ride salt of the oxo species, as established by single-crystal
X-ray analysis. The structure of the dication of 4 is shown
Figure 4. The dication of 4 viewed along the O(1)···O(1A) line
˚
Table 3. Selected bond lengths [A] and angles [°] for complex 4
in Figures 3 and 4, while the relevant data are presented Pt(1)ϪO(1)
2.089(5)
2.078(5)
2.094(5)
2.883(1)
2.886(1)
Pt(1)ϪP(1)
Pt(1)ϪP(2)
Pt(2)ϪP(3)
Pt(2)···Pt(1A)
2.229(2)
2.230(2)
2.233(2)
2.883(1)
Pt(1)ϪO(1A)[a]
in Table 3.
Pt(2)ϪO(1)
Pt(1)···Pt(2)
Pt(1)···Pt(1A)
P(3)ϪPt(2)ϪO(1)
P(3)ϪPt(2)ϪP(3A)
O(1)ϪPt(2)ϪO(1A)
P(3)ϪPt(2)ϪO(1A)
Pt(1)ϪO(1)ϪPt(2)
Pt(1)ϪO(1)ϪPt(1A)
Pt(2)ϪO(1)ϪPt(1A)
94.2(2)
97.9(1)
73.9(3)
167.6(2)
87.1(2)
87.7(2)
87.4(2)
P(1)ϪPt(1)ϪP(2)
P(1)ϪPt(1)ϪO(1)
O(1)ϪPt(1)ϪO(1A)
O(1A)ϪPt(1)ϪP(2)
P(1)ϪPt(1)ϪO(1A)
P(2)ϪPt(1)ϪO(1)
97.1(1)
94.8(1)
74.3(2)
94.2(1)
167.5(1)
167.7(1)
[a]
At 1/2 Ϫ x, y Ϫ 1/2, 1/2 Ϫ z.
Attempts to determine the structure of 3 by X-ray analy-
sis were unsuccessful. However the 31P NMR spectrum of
this complex shows a pattern that is very similar to that
shown in the spectrum of 4. Both complexes are charac-
terized by a singlet (at δ ϭ Ϫ30.3 and Ϫ19.5 ppm for 3 and
4, respectively, in [D6]DMSO) that is symmetrically flanked
3
by satellites which can be assigned to the JP,Pt (ca. 13 Hz)
1
and JP,Pt couplings (in the range 3356Ϫ3396 Hz for 3 and
3410Ϫ3460 Hz for 4).
Dinuclear oxo complexes of platinum() stabilized by
phosphanes are obtained by reacting the corresponding
hydroxo compounds with strong bases [Equation (3)].
Figure 3. ORTEP drawing of 4 showing 35% probability thermal
ellipsoids and the essential atom numbering scheme; for clarity, the
chloride anions are omitted
The oxygen atoms cap a triangle formed by three
(PMe2Ph)2Pt units in which the average Pt···Pt distance is
Ǟ
cis-[L2Pt(µ-OH)]2(BF4)2 ϩ 2 LiNR2 ǟ
˚
2.884 A. Comparison of this structure with that containing
(3)
[cis-L2Pt(µ-O)]2·2LiBF4 ϩ 2 HNR2
Ϫ
BF4 as the counterion[3] does not reveal any significant
differences. For example, the PtϪO distances and the angles
around the oxygen atoms are almost equal, averaging
The bridging oxo ligands generally associate one or two
˚
˚
2.087(5) A and 87.4(2)° in 4 and 2.083(8) A and 87.4(3)° in molecules of LiBF4, depending on the type of phosphane
that previously determined. The three dihedral angles used. In solution, when L is PMe2Ph, the dinuclear oxo
formed by the three P2PtO2 mean planes are 61.3, 58.7, and complex decomposes to form the stable species [{cis-
61.3° in 4 and compare with the values of 61.8, 59.1, and (PMe2Ph)2Pt}3(µ-O)2](BF4)2 in a high yield.[3] In the reac-
Ϫ
59.5° in the BF4 derivative.
tion of 1, and its PMe3 analogue, with ClϪ ions [Equa-
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B. Longato, G. Bandoli, A. Dolmella
1
FULL PAPER
tion (2)], the 31P NMR spectra obtained immediately after doublet at lower field (δ ϭ Ϫ11.97, JP,Pt 3930 Hz) is as-
the addition of the chloride ions do not show signals which signed to the PMe2Ph molecule trans to the chloride ion,
can be assigned to the dinuclear oxo complex. The forma- and the resonance at Ϫ23.86 ppm, with a lower PϪPt coup-
tion of cis-[L2PtCl2] and [{cis-L2Pt}3(µ-O)2]2ϩ instead is ac- ling constant (3020 Hz), is assigned to the phosphane trans
companied by the formation of a relatively stable species; it to the hydroxo ligand. The intensities of these signals slowly
has tentatively been suggested that this species is the mixed decrease, whereas the relative intensities of the signals at
complex cis-[L2PtCl(OH)], although a dinuclear species of δ ϭ Ϫ19.5 and Ϫ14.4 ppm remain apparently unchanged
the type [{cis-L2Pt}2(µ-Cl)(µ-OH)]2ϩ cannot be ruled as shown in Figure 5(c), which represents the spectrum of
out.[10] In a typical experiment, increasing amounts of the same solution left for 12 h at 33 °C.
(AsPh4)Cl as a solid were added to a CD2Cl2 solution of
A similar behavior was observed with the hydroxo com-
1a and the 31P NMR spectrum of the resulting solution plex stabilized by PMe3. The spectrum of a mixture con-
immediately obtained. Figure 5(a) shows the spectrum that taining cis-[(PMe3)2Pt(µ-OH)]2X2 and ClϪ in a 1:2 molar
Ϫ
is observed when the molar ratio n(1a)/n(Cl is 1.0. The ratio shows, in addition to the resonances assigned to the
)
main resonance signal is the singlet, whose chemical shift oxo complex 3 (52% of relative intensity) and cis-
and coupling constant are very similar to those of un- [(PMe3)2PtCl2] (relative intensity 20%), an AX multiplet
changed 1a. The signals of the oxo species (at δ ϭ Ϫ19.5) (2JP,P ϭ 20 Hz) at δ ϭ Ϫ21.0 and Ϫ34.0 ppm which disap-
and the dichloro complex (at δ ϭ Ϫ14.4) exhibit relative pears after 24 h. These results lead to conclusion that the
intensities of 5.6:1, whereas the resonances assigned to cis- species responsible for the AX multiplet, the mononuclear
[L2PtCl(OH)], characterized by an AX multiplet, (at ca. δ ϭ hydroxo complex cis-[(PMe3)2PtCl(OH)], slowly decom-
Ϫ12 and Ϫ 24 ppm; 2JP,P ϭ 24 Hz) are only just detectable. poses leaving a pale yellow solution in which the only de-
tectable resonances are those of the colorless species cis-
[L2PtCl2] and [{cis-L2Pt}3(µ-O)2]2ϩ
.
Once formed, the species [{cis-L2Pt}3(µ-O)2]2ϩ are unre-
active towards an excess of ClϪions. In fact, the 31P NMR
spectrum of the isolated complex 3 (in 4) in DMSO is unaf-
fected by the addition of AsPh4Cl (molar ratio 1:3), after
several days at room temperature. The stability of the PtϪO
bonds in these trinuclear oxo complexes is confirmed by
the observation that they do not undergo intermolecular
exchange. Unlike their hydroxo precursors, when mixed in
DMSO, 3 and 4 maintain their structure as is observed by
the absence of new resonances in the 31P NMR spectrum
of the resulting mixture.
2؉
Reactivity of cis-[(PMePh2)2Pt(µ-OH)]2 with Cl؊
Under the same conditions as those used for the PMe3
and PMe2Ph analogues, complex 2 does not form stable oxo
species when treated with ClϪ. The 31P NMR spectrum of
a solution of 2 in CDCl3 (or CH2Cl2/[D6]DMSO mixtures)
containing (NEt4)Cl·H2O (or AsPh4Cl) in a 1:2 molar ratio,
exhibit an intense singlet at δ ϭ Ϫ1.08 (1JP,Pt ϭ 3634 Hz)
1
and an AX multiplet (δ ϭ 1.97, JP,Pt ϭ 4030 Hz and
Figure 5. {1H}31P NMR spectrum (at 36.23 MHz) of a solution
(3.73·10Ϫ2 ) of 1a in CD2Cl2 at 27 °C: (a) immediately after the
addition of (AsPh4)Cl (molar ratio 1a/ClϪ ϭ 1:1); the labels (solid
1
2
Ϫ9.03 ppm, JP,Pt ϭ 3100 Hz, with JP,P ϭ 23 Hz) as the
main resonance signals. These signals are assigned to cis-
[(PMePh2)2PtCl2] and to the neutral complex cis-
[(PMePh2)2PtCl(OH)]. Two relatively weak signals are seen
circle and solid diamond) refer to the complexes cis-
2ϩ
[(PMe2Ph)2Pt(µ-OH)]2
and
cis-[{(PMe2Ph)2Pt}3(µ-O)2]2ϩ
,
respectively; (b) ca. half an hour after (a), following the addition
1
at δ ϭ Ϫ8.85 (singlet, JP,Pt ϭ 3602 Hz) and at δ ϭ Ϫ5.72
of a further amount of (AsPh4)Cl (molar ratio 1a/ClϪ ϭ 1:2); (c)
after 12 h at 33 °C); the labels (open circle and open diamond) refer (broad singlet). After 12 h at room temperature, the AX
to the complexes cis-[(PMe2Ph)2PtCl2] and cis-[(PMe2Ph)2Pt-
Cl(OH)], respectively
multiplet disappears, the resonance at δ ϭ Ϫ5.72 ppm also
disappears and is replaced by a very weak singlet at δ ϭ
Ϫ5.92 due to unchanged complex 2. A further change in
the 31P NMR spectrum occurs after several days, leading to
Ϫ
The further addition of chloride ions (n(1a)/n(Cl ϭ 1:2), the complete disappearance of the resonance at δ ϭ Ϫ8.85.
)
carried out after ca. 0.5 h, leads to the almost complete dis- The low concentration and the moderate stability of the
appearance of the resonances due to the starting complex, species responsible for this singlet prevents better charac-
whereas the AX multiplet became more intense to allow the terization. The absence of the fine structure observed for 3
detection of the platinum-195 satellites (Figure 5, b). The and 4, however, seems to exclude the formation of the anal-
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Eur. J. Inorg. Chem. 2004, 1092Ϫ1099

Hydroxo and Oxo Complexes of Platinum(II)
FULL PAPER
ogous trinuclear species cis-[{(PMePh2)2Pt}3(µ-O)2]2ϩ. On
the other hand, the formation of a mononuclear species of
the type cis-[(PMePh2)2Pt(OH)2], (the analogue cis-
[(PMe3)2Pt(OH)2] (known to be unstable in chlorinated sol-
vents) as has been seen before),[11] is not supported by the
Syntheses of the Complexes
Preparation of cis-[(PMe2Ph)2Pt(µ-OH)]2(ClO4)2 (1b): A solution
of AgNO3 (1.15 g, 6.77 mmol) in H2O (20 mL) was added to a
suspension of cis-[(PMe2Ph)2PtCl2] (1.84 g, 3.38 mmol) in H2O
(200 mL). The AgCl precipitate formed immediately was removed
by filtration, and the resulting solution was neutralized with NaOH
(0.092 ). Addition of NaClO4·H2O (0.48 g, 3.4 mmol) led to the
immediate precipitation of a white microcrystalline solid, which
was collected by filtration, washed with H2O, EtOH, and Et2O.
The yield of the dry product 1b was 1.29 g (92%). C16H23ClO5P2Pt
1
value of JP,Pt coupling constant. The observed value
(3602 Hz), in fact, is only slightly lower than that of the
dichloro complex, cis-[(PMePh2)2PtCl2] (1JP,Pt ϭ 3627 Hz);
however, the difference between the observed value and
those for cis-[(PMe3)2Pt(OH)2] (3254 Hz, in CD2Cl2) and
cis-[(PMe3)2PtCl2] (3470 Hz) is large.[11] Similar consider-
ations seem to exclude the formation of cis-[(PMePh2)2Pt(µ-
O)]2 since such oxo species should have a 1JP,Pt value that is
much lower than that of the precursor hydroxo complex.[3]
1
(587.8): calcd. C 32.69, H 3.94; found C 32.41, H 4.01. H NMR
at 89.55 MHz in [D6]DMSO: δ ϭ 7.5Ϫ7.7 (5 H, Ph), 4.09 (broad
3
s, 1 H, OH), 1.54 (apparent doublet, JPH ϭ 11.7, JPtH ϭ 35.6 Hz,
6 H, CH3) ppm. {1H}31P NMR at 36.23 MHz in [D6]DMSO: δ ϭ
1
2
Ϫ14.50 (s, JP,Pt ϭ 3456 Hz; JPt,Pt ϭ 304 Hz) ppm.
Caution: The above perchlorate is a potential explosive!
Preparation of cis-[(PMePh2)2Pt(µ-OH)]2(NO3)2 (2): A solution of
AgNO3 (0.794 g, 4.67 mmol) in EtOH (10 mL) and H2O (2 mL)
Conclusions
was added to
a solution of cis-[(PMePh2)2PtCl2] (1.56 g,
The structures of complexes 1 and 2 reported here rep-
resent further examples of the preference for the
{L2Pt(OH)}ϩ moiety (L ϭ phosphanes or diphosphanes)
to form dinuclear species. This feature is in common with
most of the monohydroxo complexes of PtII with N-donor
ligands, although examples of the formation of hydroxo
complexes with higher nuclearity from some diamines are
known.[12]
2.34 mmol) in CH2Cl2 (20 mL). The AgCl precipitate formed im-
mediately was filtered, and an aqueous solution (25.4 mL) of
NaOH (0.092 ) was added to the resulting solution. The solution
was concentrated under vacuum, and a white precipitate was ob-
tained, which was recovered by filtration, washed twice with H2O
(10 mL) and dried under vacuum. The yield of the pure product 2
was 1.11 g (70%). C26H27NO4P2Pt (674.5): calcd. C 46.29, H 4.03,
1
N 2.08; found C 45.73, H 3.96, N 1.99. H NMR at 89.55 MHz in
[D6]DMSO: δ ϭ 7.5Ϫ7.8 (10 H, Ph), 3.53 (s broad, 1 H, OH), 1.62
An interesting feature of the phosphano-based complexes
[apparent doublet, JPH ϭ 10.7 Hz, 3 H, CH3] ppm. {1H}31P NMR
2ϩ
in [D6]DMSO: δ ϭ Ϫ5.32 (s, JP,Pt ϭ 3578, 2JPt,Pt ϭ 232 Hz) ppm.
1
cis-[L2Pt(µ-OH)]2 (L ϭ PMe3, PMe2Ph, and PMePh2) is
their reactivity towards ClϪ ions. Unlike the isostructural
hydroxo compounds containing the chelate ligands 2,2Ј-bi-
pyridine or phenanthroline, which are inert towards LiCl
even at 100 °C,[13] they react with ClϪ ions under very mild
conditions. When an excess of chloride ions is used, the
substitution of the OHϪ ligands, to give cis-[L2PtCl2], is the
predominant process. At lower concentrations of ClϪ ions,
however, other reaction pathways become competitive, lead-
ing to the concomitant formation of the stable complexes
Preparation of [{cis-(PMe3)2Pt}3(µ-O)2](ClO4)2 (3): A solution of
(NEt4)Cl·H2O (228 mg, 1.24 mmol) in CH2Cl2 (20 mL) was added
to a stirred solution of cis-[(PMe3)2Pt(µ-OH)]2(ClO4)2 (576 mg,
0.62 mmol) in DMSO (15 mL), and the resulting pale yellow solu-
tion was left at room temperature for 18 h. Addition of Et2O
(100 mL) afforded a white precipitate which was recovered by fil-
tration, dissolved in a minimum amount of CH2Cl2 and precipi-
tated by addition of Et2O. The crude solid (265 mg) was further
purified from CH2Cl2/Et2O, and a microcrystalline product was ob-
[{cis-L2Pt}3(µ-O)2]2ϩ when L is PMe3 or PMe2Ph, but an tained which was recovered by filtration, washed with EtOH and
dried under vacuum. The yield of the pure compound 3 was 91 mg
[23%, based on Equation (2)]. C18H54Cl2O10P6Pt3 (1272): calcd. C
16.99, H 4.28; found C 16.78, H 4.16. 1H NMR in [D6]DMSO:
unstable and not yet fully characterized species when L is
PMePh2.
3
δ ϭ 1.59 (d, JH,P ϭ 10.3, JH,Pt ϭ 34 Hz) ppm. {1H}31P NMR in
CD2Cl2 (at 36.23 MHz): δ ϭ Ϫ31.7 (1JP,Pt ϭ 3376Ϫ3406 Hz) ppm.
Crystallization of the solid from CH2Cl2/CHCl3 (1:1) gave needle-
shaped colorless crystals unsuitable for X-ray diffraction analysis.
Experimental Section
Preparation of [{cis-(PMe2Ph)2Pt}3(µ-O)2]Cl2 (4): A solution of
(NEt4)Cl·H2O (166 mg, 0.90 mmol) in CH2Cl2 (10 mL) was added
dropwise to a stirred solution of 1b (533 mg, 0.49 mmol) in DMSO
(6 mL). The resulting pale yellow solution was left at ca. 20 °C for
24 h. Addition of Et2O (120 mL) gave a waxy solid which was rap-
idly washed with H2O and then with Et2O. The dried solid (360 mg)
was purified twice by dissolution in CH2Cl2 and precipitation with
toluene. The yield of 4, free of the perchlorate salt, was 126 mg
[yield 34%, based on Equation (2)]. C48H66Cl2O2P6Pt3 (1517.0):
Reagent and Chemicals: Reagent grade chemicals (NEt4)Cl·H2O
(Ega-Chemie) and (AsPh4)Cl (Fluka) were used as received. The
complexes cis-[(PMePh2)2PtCl2],[14] cis-[(PMe3)2Pt(µ-OH)]2X2
[6]
(X ϭ NO3,[5] ClO4),[15] and cis-[(PMe2Ph)2Pt(µ-OH)]2(NO3,)2
were synthesized as previously reported.
Instrumentation: 1H and {1H}31P spectra were obtained with JEOL
90Q and/or Bruker 300AVANCE spectrometers. 1H chemical shifts
are referred to the residual peak of the deuterated solvent
([D6]DMSO), whereas the external reference for 31P is H3PO4 (85% calcd. C 38.00, H 4.38; found C 37.85, H 4.29. 1H NMR in
w/w in H2O). IR spectra in the range 4000Ϫ400 cmϪ1 were re-
corded as KBr pellets with a PerkinϪElmer 283 spectrophoto-
meter.
[D6]DMSO: δ ϭ 7.96Ϫ7.53 (complex multiplets, 5 H, Ph), 1.52 (d,
JH,P ϭ 10.2 Hz with unresolved 195Pt satellites) ppm. {1H}31P
NMR in CD2Cl2: δ ϭ Ϫ20.1 (1JP,Pt ϭ 3460Ϫ3487 Hz) ppm.
Eur. J. Inorg. Chem. 2004, 1092Ϫ1099
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1097

B. Longato, G. Bandoli, A. Dolmella
FULL PAPER
Table 4. Crystal and refinement data for complexes 1a, 2, and 4
Complex
1a
2
4
Formula
Molecular mass
Color
C32H46N2O8P4Pt2
1100.8
C52H54N2O8P4Pt2
1349.0
colorless
monoclinic
P 21/n (No. 14)
9.772(2)
C48H66Cl2O2P6Pt3
1517.0
colorless
monoclinic
C 2/c (No. 15)
23.160(2)
colorless
triclinic
P Ϫ1 (No. 2)
10.642(2)
11.830(2)
16.129(3)
105.66(1)
93.78(1)
94.75(1)
1940.3(5)
2
Crystal system
Space group
˚
a [A]
˚
b [A]
16.292(3)
16.040(4)
13.404(4)
17.996(4)
˚
c [A]
α [°]
β [°]
γ [°]
100.48(2)
99.36(2)
3
˚
V [A ]
2510.9(9)
2
1.784
1320
5512(2)
4
1.828
2912
Z
Dcalc [g cmϪ3
F(000)
]
1.884
1064
7.41
µ (Mo-Kα) [mmϪ1
]
5.75
7.90
Crystal dimensions [mm]
Θ limits [°]
0.20·0.20·0.30
2.0 / 21.0
4186
3162
366
0.050
0.121
1.3
1.004
0.15·0.25·0.20
2.0 / 22.5
3286
2815
308
0.049
0.131
1.7
0.30·0.15·0.08
1.8 / 25.0
4549
3779
286
0.031
0.066
0.8
No. of independent data
No. of data with I Ͼ 2σ (I)
No. of variables
R(F)[a]
wR(F2)[b]
Ϫ3
˚
Largest peak in ∆F [e·A
]
GOF[c]
1.193
1.011
[a]
[b]
[c]
2
R(F) ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|. wR(F2) ϭ [Σw(|Fo|2 Ϫ |Fc|2)2/Σw(|Fo|2)2]1/2
.
GOF ϭ [Σw(|Fo| Ϫ |Fc|2)2/(n Ϫ p)]1/2
.
X-ray Data Collection, Structure Solution and Refinement of 1a, 2,
Acknowledgments
and 4:[16] The X-ray data collections were performed at room tem-
perature with a NicoletϪSiemens four-circle R3m/V diffractometer
on single-crystals mounted in thin-walled glass capillaries with
This work was financially supported by the Ministero dell’Univer-
˚
`
sita e della Ricerca Scientifica e Tecnologica (PRIN 2001).
graphite-monochromated Mo-Kα radiation (λ ϭ 0.71073 A).
Crystals of 1a and 2 were obtained by slow diffusion of vapors of
Et2O into a saturated solution of the corresponding compound in
ethanol, whereas crystals of 4 were obtained by slow evaporation of
a CH2Cl2/C6H5CH3 solution of the complex, at room temperature.
[1]
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[2]
A summary of the X-ray analyses carried out on the complexes
is listed in Table 4. The cell dimensions for the complexes were
determined from the setting angles of 50 centered reflections. Inten-
sity data were collected for unique portions of reciprocal space to
the limit of observable diffraction. Corrections for X-ray absorp-
tion effects were applied on the basis of azimuthal scan data.[17]
The absorption effects have been noticeable only in complex 4, the
transmission factors ranging from 0.637 to 0.996.
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[7]
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The unit cell of 1a comprises two moieties denoted as I and II. The
structures were solved by heavy-atom methods and refined by full-
matrix least-squares against F2. Pt, P, and phenyl C atoms of 1a
and all non-hydrogen atoms of 2 and 4 were assigned anisotropic
displacement parameters. As expected, the nitrate groups of 1a and
2 endure high thermal motions and they have been treated iso-
tropically.
Chem. Soc. 1977, 99, 777Ϫ781.
D. G. Cooper, J. Powell, J. Am. Chem. Soc. 1973, 95,
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Final difference syntheses showed no chemically significant fea-
tures, the largest maxima being close to the platinum. Refinements
converged smoothly to residuals given in Table 4. All calculations
were made with programs of the SHELXTL/PC[18] system and
SHELXL-93[19] program.
[12]
1098
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2004, 1092Ϫ1099

Hydroxo and Oxo Complexes of Platinum(II)
FULL PAPER
bridge CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
A. C. T. North, D. C. Phillips, F. S. Mathews, Acta Crystallogr.,
Sect. A 1968, 24, 351Ϫ359.
G. M. Sheldrick, SHELXTL/PC, Version 5.03, Siemens Ana-
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G. M. Sheldrick, SHELXL-93, Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1993.
Received July 9, 2003
[13]
S. Wimmer, P. Castan, F. L. Wimmer, N. P. Johnson, J. Chem.
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[18]
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[15]
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Chem. 2001, 3021Ϫ3029.
CCDC-168694 (for 1a), -168695 (for 2), and -168696
[16]
(for 4) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
Early View Article
Published Online February 5, 2004
Eur. J. Inorg. Chem. 2004, 1092Ϫ1099
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1099