Dinuclear, tricyclometallated platinum(II) derivatives - Substitution reactions and reactivity of the platinum-carbon bonds

Article abstract of DOI:10.1002/ejic.200400371

In the recently reported dinuclear cyclometallated species [Pt ₂(R)(L)(DMSO)₂] [H₃L = 6-phenyl-2,2′- bipyridine; R = Me (1a), Ph (1b)] the threefold deprotonated ligand L links the two platinum atoms acting as an N′,C(3) and a C,N,C donor. Aspects of their reactivity have been studied first with regards to the substitution of the two DMSO ligands, which are coordinated to the platinum atom trans to a nitrogen and a carbon atom, respectively. Substitution of DMSO with neutral two-electron donors affords several new species, all having the same bridging ligand L: [Pt₂(R)(L)(L′)₂] [L′ = PPh ₃ (2a, 2b), CO (3a, 3b)] and [Pt₂(R)(L)(L′((DMSO)] [L′ = 3,5-Me₂-py (4a)]. The potentially bidentate diphosphane Ph₂P(CH₂)₃PPh₂ (dppp) gives a more complex species having both chelating and bridging dppp ligands [{Pt(Me)(L)(dppp)}₂(μ-dppp)] (5a). The reactivity of the platinum-carbon bonds with HCl has been studied in complexes 1a, 1b and 2a, 2b and found to be strongly dependent on the nature of the ancillary ligands. To discern the most labile of the four metal-carbon bonds, the reaction has been carried out with 1 equiv. of HCl under mild conditions. Although the reaction is not selective and minor species are formed, cleavage of the Pt-Me (1a) and Pt-Ph (1b) bonds is favoured - [Pt₂(L)Cl(DMSO)₂] (6) can be isolated and spectroscopically characterised from the reaction with either 1a or 1b. Substitution of PPh₃ for DMSO in 6 gives [Pt ₂(L)Cl(PPh₃)₂] (7) as the thermodynamically stable isomer having a trans Cl-Pt-C arrangement. The structure of complex 7 has been solved by X-ray crystallography. In contrast, reaction of 2a or 2b with HCl proceeds by another route: even with excess HCl the Pt-Me and Pt-Ph bonds are unaffected whereas one of the Pt-C bonds of the pincer-like C,N,C system is cleaved to selectively give [Pt₂(R)(HL)Cl(PPh₃] ₂) [R = Me (8a), Ph (8b)]. The same bond is cleaved also in 1a and 1b by excess HCl to give [Pt₂(HL)(Cl)₂(DMSO)₂] (9). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400371

FULL PAPER
Dinuclear, Tricyclometallated Platinum(II) Derivatives ؊ Substitution
Reactions and Reactivity of the Platinum؊Carbon Bonds
Antonio Zucca,*[a] Maria Agostina Cinellu,[a] Giovanni Minghetti,[a] Sergio Stoccoro,[a] and
Mario Manassero*[b]
Keywords: Cyclometallated compounds / N ligands / Platinum / X-ray diffraction
In the recently reported dinuclear cyclometallated species
[Pt2(R)(L)(DMSO)2] [H3L = 6-phenyl-2,2Ј-bipyridine; R = Me
(1a), Ph (1b)] the threefold deprotonated ligand L links the
carried out with 1 equiv. of HCl under mild conditions.
Although the reaction is not selective and minor species are
formed, cleavage of the Pt−Me (1a) and Pt−Ph (1b) bonds is
two platinum atoms acting as an NЈ,C(3) and a C,N,C donor. favoured — [Pt2(L)Cl(DMSO)2] (6) can be isolated and
Aspects of their reactivity have been studied first with re-
gards to the substitution of the two DMSO ligands, which are
coordinated to the platinum atom trans to a nitrogen and a
carbon atom, respectively. Substitution of DMSO with
neutral two-electron donors affords several new species, all
having the same bridging ligand L: [Pt2(R)(L)(LЈ)2] [LЈ = PPh3
spectroscopically characterised from the reaction with
either 1a or 1b. Substitution of PPh3 for DMSO in 6 gives
[Pt2(L)Cl(PPh3)2] (7) as the thermodynamically stable isomer
having a trans Cl−Pt−C arrangement. The structure of com-
plex 7 has been solved by X-ray crystallography. In contrast,
reaction of 2a or 2b with HCl proceeds by another route:
even with excess HCl the Pt−Me and Pt−Ph bonds are
unaffected whereas one of the Pt−C bonds of the pincer-
like C,N,C system is cleaved to selectively give
[Pt2(R)(HL)Cl(PPh3)2] [R = Me (8a), Ph (8b)]. The same bond
(2a, 2b), CO (3a, 3b)] and [Pt2(R)(L)(LЈ)(DMSO)] [LЈ
3,5-Me2-py (4a)]. The potentially bidentate diphosphane
Ph2P(CH2)3PPh2 (dppp) gives more complex species
having both chelating and bridging dppp ligands
=
a
[{Pt(Me)(L)(dppp)}2(µ-dppp)] (5a). The reactivity of the is cleaved also in 1a and 1b by excess HCl to give
platinum−carbon bonds with HCl has been studied in com-
plexes 1a, 1b and 2a, 2b and found to be strongly dependent
on the nature of the ancillary ligands. To discern the most
labile of the four metal−carbon bonds, the reaction has been
[Pt2(HL)(Cl)2(DMSO)2] (9).
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
Both five- and six-membered rings are known, and both
PtϪC(sp2) and PtϪC(sp3) bonds have been reported, the
former being more common. The variety of possible coordi-
nation modes allows one to obtain species with different
properties and an array of potential applications. In par-
ticular, it is worth noting that species of type II,[3] with a
trans CϪPtϪC arrangement, are still rare and often cannot
be obtained by direct activation of a CϪH bond.
Cyclometallated platinum() complexes containing sub-
stituted pyridines and 2,2Ј-bipyridines are well docu-
mented.[1] They comprise mono- and dimetallated species
(IϪIV) with various donor sequences.[2Ϫ5]
Recently, a new type of cyclometallation, which entails
activation of a CϪH bond of a pyridine ring, has been de-
scribed: reaction of 6-substituted 2,2Ј-bipyridines with cis-
[Pt(R)2(DMSO)2] (R ϭ Me, Ph) gave a series of ‘‘rollover’’
cyclometallated species (V).[6]
[a]
`
Dipartimento di Chimica, Universita di Sassari,
Via Vienna 2, 07100 Sassari, Italy
E-mail: zucca@uniss.it
[b]
Dipartimento di Chimica Strutturale
e
Stereochimica
`
Inorganica, Universita di Milano, Centro CNR,
Via Venezian 21, 20133 Milano, Italy
E-mail: m.manassero@istm.cnr.it
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DOI: 10.1002/ejic.200400371
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Dinuclear, Tricyclometallated Platinum(II) Derivatives
FULL PAPER
In the case of 6-phenyl-2,2Ј-bipyridine (6-Ph-2,2Ј-bipy), conditions to give the disubstituted complexes
further reaction of complexes of type with cis- [Pt2(R)(L)(PPh3)2] [R ϭ Me (2a), Ph (2b)] in high yields
V
[Pt(R)2(DMSO)2] allowed us to isolate the dinuclear com- (ca. 90%).
plexes 1a (R ϭ Me) and 1b (R ϭ Ph).[7]
With 1 equiv. of PPh3 a mixture of starting material and
mono- and disubstituted products is obtained, indicating
nonselective DMSO substitution.
Compounds 2a,b were characterised by analytical and
spectroscopic methods: in particular the 31P{1H} NMR
spectra show two resonances [e.g. δ ϭ 26.52 and 32.44 ppm
(2a)] with very different 195Pt-31P coupling constants (3931
and 2412 Hz) in agreement with phosphorus atoms trans to
donors with a low (N) and high (C) trans influence, respec-
tively.[8] In the 1H NMR spectrum of 2a the Me group,
which is slightly shielded with respect to 1a, appears as a
doublet due to coupling with a 31P nucleus (3JP,H ϭ 7.6 Hz),
suggesting a PPh3 ligand in a cis position.
The coordinated DMSO can also be easily displaced
from 1a and 1b by CO at atmospheric pressure. In this case,
however, the reaction products, compounds 3a and 3b, are
almost insoluble in common organic solvents, hampering
their characterisation by NMR spectroscopy. Analytical
and spectroscopic data fit the formulation [Pt2(R)(L)(CO)2]:
in particular the IR spectra show two bands in the region
of terminal carbonyl ligands (2050, 2063 cmϪ1 for 3a and
2066, 2073 cmϪ1 for 3b) supporting substitution of both the
DMSO ligands. To completely rule out the possibility of
the coordination of only one CO ligand, compound 3a was
treated with PPh3 in a 1:1 Pt/P molar ratio. The almost
insoluble complex 3a reacts immediately with loss of gas
(CO): the 1H NMR spectrum of the solution shows the for-
mation of complex 2a, and no free or coordinated DMSO
is detected.
Compounds 1a and 1b were fully characterised by means
of NMR spectroscopy and FAB mass spectrometry, and, in
the case of 1b, by X-ray crystallography. They are rare ex-
amples of multiple CϪH bond activation: indeed 6-Ph-2,2Ј-
bipy displays an unprecedented behaviour, acting as a three-
fold deprotonated ligand. Compounds 1a and 1b are unique
in several aspects, having (i) three five-membered rings as-
sembled in the same molecule, (ii) a ten-electron bridging
ligand, and (iii) a rare C,N,C sequence of donor atoms. Fur-
thermore, in each of the two molecules a pincer-like system
with a trans CϪPtϪC arrangement coexists with an
NЈϪC(3) cycle having two cis platinumϪcarbon bonds. Due
to these interesting features, we deemed it worthwhile to
synthesise analogous species by substitution of neutral li-
gands for DMSO and to study some aspects of the reactiv-
ity of the four different platinumϪcarbon bonds assembled
in each of these unusual molecules.
Results and Discussion
With a nitrogen donor such as 3,5-Me2-py, only one of
the
DMSO
ligands
is
substituted,
yielding
Reaction with Neutral Ligands
1
[Pt2(Me)(L)(DMSO)(3,5-Me2-py)] (4). The H NMR spec-
tra give evidence for a DMSO coordinated trans to a nitro-
gen atom (δ ϭ 3.63, JPt,H ϭ 25.6 Hz);[9] only the more labile
DMSO trans to the carbon atom is displaced. Even with
excess 3,5-Me2-py or at higher temperature the disubsti-
tuted product is not obtained. The low affinity of the nitro-
gen donor for platinum() likely accounts for this behav-
iour.
Displacement of the DMSO ligands from 1a was also
attained by reaction with a bidentate phosphane such as
1,3-bis(diphenylphosphanyl)propane (dppp). The outcome
of the reaction, however, was unexpected: the analytical val-
ues point to a species, 5a, with a Pt/dppp molar ratio of
We have recently reported that the reaction of cis-
[Pt(Me)2(DMSO)2] and cis-[Pt(Ph)2(DMSO)2] with 6-Ph-
2,2Ј-bipy gives compounds 1a and 1b, respectively, in fairly
good yields (ca. 60Ϫ65%).[7]
The neutral ligands PPh3 and CO easily displace both the
DMSO molecules, whereas only one DMSO is substituted
by a nitrogen donor such as 3,5-dimethylpyridine (3,5-Me2-
py; Scheme 1). With PPh3 the reaction proceeds under mild
1
4:3. The H NMR spectrum shows, in the aliphatic region,
a methyl resonance at δ ϭ 0.30 ppm, at high field with re-
spect to 1a, coupled to 195Pt (2JPt,H ϭ 67 Hz) and to two
phosphorus nuclei (3JP,H ϭ 8.0 Hz and 6.7 Hz). The
31P{1H} spectrum exhibits a singlet at δ ϭ 17.71 ppm
(1JPt,P ϭ 3913 Hz) and two doublets at δ ϭ Ϫ0.31 ppm
Scheme 1
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A. Zucca, M. A. Cinellu, G. Minghetti, S. Stoccoro, M. Manassero
FULL PAPER
(1JPt,P ϭ 1918, 2JP,P ϭ 22.9 Hz) and δ ϭ 1.35 ppm (1JPt,P ϭ the IR spectrum supports the thermodynamically favoured
2
2106, JP,P ϭ 22.9 Hz). Coupling of the methyl group to isomer having the chlorine atom trans to a carbon atom.[10]
two 31P nuclei indicates an endobidentate diphosphane
whereas the chemical shift of the singlet, δ ϭ 17.71 ppm,
and the absence of a P-P coupling, suggests a bridging dppp
1
ligand. The high value of JPt,P (3913 Hz) observed for the
latter resonance is consistent with a phosphorus atom trans
to a nitrogen atom. In the absence of X-ray data, a plausible
description of 5a which accounts for the experimental, ana-
lytical and spectroscopic data is shown in Figure 1.
Reaction of complex 6 with PPh3 under mild conditions
leads to substitution of the DMSO ligands to give
[Pt2Cl(L)(PPh3)2] (7) for which crystals suitable for an X-
ray structure determination were obtained.
The structure consists of the packing of 7 and CHCl3
molecules in the molar ratio 2:3. An ORTEP view of 7 is
shown in Figure 2 and principal bond parameters are listed
Figure 1. A plausible description of complex 5a
in Table 1. The two platinum atoms are essentially square-
planar coordinated with slight square-pyramidal distor-
tions. For Pt(1) the maximum distances from the best plane
3
The small differences between the two JP,H coupling
constants (8.0, 6.7 Hz), makes a pentacoordinate arrange-
ment more likely than a square-planar one. In the latter
geometry, which entails the cleavage of the PtϪN bond of
the chelated NЈ,C(3) ring, the phosphorus atoms of the che-
lated dppp should be cis and trans, respectively, to the
methyl group.
It seems, therefore, that a variety of molecules with ancil-
lary ligands having different electronic and steric properties
can be synthesised from compounds 1 by substitution reac-
tions without disruption of the dinuclear cyclometallated
core of the system. All the new species 2Ϫ5 exhibit high
thermal stability.
˚
are ϩ0.041(1) and Ϫ0.055(4) A for Pt(1) and N(2), respec-
tively. For Pt(2) the maximum distances from the best plane
˚
are ϩ0.017(1) and Ϫ0.021(3) A for Pt(2) and N(1), respec-
tively. The dihedral angle between these two least-squares
planes is 7.5(2)°, a value which shows that the overall plan-
arity of the Pt2ClP2N2C16 moiety is less rigorous than
that of the analogous Pt2S2N2C17 fragment of
[Pt2Ph(L)(DMSO)2],[7] where the analogous dihedral angle
Reaction with Acids
Compounds 1a and 1b have four PtϪC bonds: in 1a one
of them is a C(sp3)ϪPt bond, whereas in 1b all of them are
C(sp2)ϪPt bonds. Regardless of the presence of two
PtϪC(sp2) bonds in mutual trans positions, the trimetal-
lated compounds are stable in air both in solution and in
the solid state. With the aim of investigating the reactivity
of these platinumϪcarbon bonds, we have studied the be-
haviour of 1a and 1b toward HCl, an acid having a coordin-
ating anion. To detect the most labile of the PtϪC bonds,
the reaction was first carried out under mild conditions
with a 1:1 L/HCl molar ratio. Under these conditions the
platinumϪmethyl and the platinumϪphenyl bond in 1a and
1b, respectively, were preferentially cleaved. The reaction is
not selective and other species are also formed; however,
1
according to their H NMR spectra none of them contains
an Me or a Ph group bound to the metal atom. One prod-
uct could be isolated in pure form by chromatography, al-
beit in low yield. It was fully characterised and the analyti-
cal and spectroscopic data agree with the formulation
Figure 2. ORTEP view of 7; ellipsoids are drawn at the 30% prob-
ability level; only the first carbon atoms of the phosphane phenyl
[Pt2Cl(L)(DMSO)2] (6). In particular, a band at 292 cmϪ1 in rings are shown for clarity
4486
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Dinuclear, Tricyclometallated Platinum(II) Derivatives
FULL PAPER
˚
Table 1. Selected distances [A] and angles [°] in 7·1.5CHCl3 with
estimated standard deviations in parentheses
Pt(1)ϪCl(1)
Pt(1)ϪN(2)
Pt(2)ϪP(2)
Pt(2)ϪC(8)
Cl(1)ϪPt(1)ϪP(1)
2.347(1) Pt(1)ϪP(1)
2.119(3) Pt(1)ϪC(3)
2.231(1) Pt(2)ϪN(1)
2.103(4) Pt(2)ϪC(13)
2.225(1)
2.010(4)
2.024(3)
2.071(4)
89.6(1)
94.1(1)
Cl(1)ϪPt(1)ϪN(2)
Cl(1)ϪPt(1)ϪC(3) 171.3(1)
P(1)ϪPt(1)ϪN(2)
N(2)ϪPt(1)ϪC(3)
P(2)ϪPt(2)ϪC(8)
N(1)ϪPt(2)ϪC(8)
173.9(1)
81.8(1)
103.3(1)
80.6(1)
P(1)ϪPt(1)ϪC(3)
P(2)ϪPt(2)ϪN(1)
P(2)ϪPt(2)ϪC(13)
N(1)ϪPt(2)ϪC(13)
94.5(1)
175.7(1)
97.3(1)
78.8(1)
C(8)ϪPt(2)ϪC(13) 159.4(1)
Figure 3. Complex 8a with selected NOE contacts
˚
is 1.7(6)°. The Pt(1)ϪN(2) bond length [2.119(3) A] is nor-
Complex 2b reacts with HCl in a similar manner to 2a,
to give 8b, as shown, in particular, by the 31P NMR spec-
trum, which is similar to that of 8a. In this case the two
platinumϪcarbon bonds — PtϪPh and PtϪC(sp2) — in the
five-membered NЈ,C(3) cycle are unaffected.
mal for a PtϪN bond trans to phosphorus.[11] The
Pt(2)ϪN(1) distance [2.024(3) A], however, is much shorter.
This shortness is a common feature of the central bonds of
bicyclic systems: see, for instance, the PtϪN bond length
˚
˚
[1.937(7) A] in [PtCl(LЈ)] (HLЈ ϭ 6-tert-butyl-2,2Ј-bipyri-
Finally, it is worth noting that the same
platinumϪcarbon bond of the pincer C,N,C ligand can also
be broken in complexes 1a and 1b upon addition of excess
dine).[5c] Similarly, the C(8)ϪPt(2)ϪC(13) angle [159.4(1)°]
is very far from 180° because of the relative rigidity of the
tricyclic ligand. All the other bond lengths and angles are
as expected if the trans influence of the carbon atoms is
taken into account.
1
HCl to give [Pt2Cl2(HL)(DMSO)2] (9). The H NMR spec-
trum is consistent with a species having two DMSO ligands
trans to nitrogen atoms [δ ϭ 3.47 (3JPt,C ഠ 24.5 Hz), 3.64
(3JPt,C ഠ 22 Hz) ppm] and ten aromatic protons with a pat-
tern similar to that of compound 8.
The reactions of compound 1 (a and b) and 2 (a and b)
with HCl are summarised in Scheme 2. The reactivity of the
PtϪC bonds appears to be strongly dependent on the nat-
ure of the spectator ligands. Substitution of PPh3 for
The reaction with HCl was also studied in the case of
complexes 2a and 2b. In contrast with the behaviour of 1a,
in the case of 2a the platinumϪmethyl bond is not cleaved,
even with an excess of HCl. The H NMR spectrum of the
reaction product 8a [δ ϭ 0.68 (d, JPt,H ϭ 80.8, JP,H
7.3 Hz, Me) ppm] indicates that the NЈ,C(3) chelated part
of the complex does not undergo substantial changes. In
agreement, in the 31P{1H} spectrum one of the resonances,
assignable to a phosphorus atom trans to a carbon atom
(δ ϭ 33.07 ppm, JPt,P ϭ 2405 Hz) is observed at a value
very close to that of complex 2a (δ ϭ 32.44 ppm, JPt,P
1
2
3
ϭ
1
1
ϭ
2412 Hz) as well as to that of the analogous mononuclear
1
species [Pt(Me)(H2L)(PPh3)] (δ ϭ 33.01 ppm, JPt,P
ϭ
2233 Hz).[6] However, the environment of the platinum
atom coordinated by the C,N,C pincer part of the bridging
ligand is significantly modified. (e.g. 31P NMR: δ ϭ 13.14
vs. δ ϭ 26.53 ppm in 2a), suggesting that one of the PtϪC
bonds of the strained [5ϩ5] fused-ring system has been
1
cleaved. A H 2D-COSY spectrum allowed us to ascribe
three spin systems, with three, two and five protons, respec-
tively, to the bridging ligand, the latter being assignable to
a monosubstituted phenyl ring [δ ϭ 8.56 (d, 2 H, Hortho),
1
7.86 (m, 2 H, Hmeta), 7.71 (t, 1 H, Hpara) ppm]. A H NOE
difference spectrum shows contacts between the PtϪMe
group, the ortho protons of the coordinated PPh3 ligand,
and the 4-H proton, as well as between the 4-H and the 5-
H protons and between 5-H and the doublet at δ ϭ 8.56
ppm ascribed to the ortho protons of the phenyl ring. On
the whole the 1H NMR spectra taken together with the
31P{1H}NMR spectra provide evidence for complex 8a be-
ing [Pt2Cl(Me)(HL)(PPh3)2] (Figure 3).
Scheme 2
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A. Zucca, M. A. Cinellu, G. Minghetti, S. Stoccoro, M. Manassero
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1
ppm. 31P NMR (CDCl3): δ ϭ 26.86 (s, JP,Pt ϭ 3937 Hz, P trans
DMSO makes the PtϪMe (or PtϪPh) bond less prone to
cleavage by HCl. Indeed, even in the related mononuclear
‘‘rollover’’ derivatives [Pt(R)(H2L)(DMSO)] the reaction
with HCl gives selective and fast attack at the PtϪMe and
PtϪPh centres, respectively, whereas [Pt(Me)(H2L)(PPh3)]
reacts slowly. After 4 h, about half of the starting com-
pound is recovered unchanged, and prolonged reaction
times are required to achieve quantitative attack at the
PtϪMe bond. A more marked effect is observed in the case
of the dinuclear species: the methyl group of compound 2a
is not cleaved even with excess HCl, suggesting a non-negli-
gible degree of electronic communication between the two
platinum atoms through the unsaturated bridging ligand.
1
N), 30.58 (s, JP,Pt ϭ 2363 Hz, P trans C) ppm.
[Pt2(Me)(L)(CO)2] (3a): CO (1 atm) was bubbled for 1 h through a
solution containing 1a (63.5 mg, 0.080 mmol) in 20 mL of CH2Cl2.
The precipitate formed was filtered and washed with Et2O (3 ϫ
5 mL), to give the analytical sample as an orange-yellow solid.
Yield: 82% (45.4 mg); m.p. 245 °C (dec.). C19H12N2O2Pt2 (690.5):
calcd. C 33.05, H 1.74, N 4.06; found C 33.07, H 1.34, N 3.93. IR
(Nujol): ν˜ ϭ 1037 (w), 1127 (m), 1558 (m), 1580 (m), 2050 (s), 2063
(s) cmϪ1
.
[Pt2(Ph)(L)(CO)2] (3b): Complex 3b was obtained as for 3a using
1b instead of 1a. Yield: 64%; m.p. 235 °C (dec.). C24H14N2O2Pt2
(752.5): calcd. C 38.30, H 1.88, N 3.72; found C 37.94, H 1.80, N
4.02. IR (Nujol): ν˜ ϭ 1024 (w),1065 (w), 1560 (m), 1575 (m), 2066
(s), 2073 (s) cmϪ1
.
Experimental Section
[Pt2(Me)(L)(3,5-Me2-py)DMSO] (4a): 3,5-Dimethylpyridine (3,5-
Me2-py; 42 mg, 0.39 mmol) was added, under vigorous stirring, to
a solution of 1a (58 mg, 0.073 mmol) in CH2Cl2 (20 mL) The solu-
tion, whose colour changed immediately to orange yellow, was
stirred for 30 min, then concentrated to a small volume and treated
with Et2O (10 mL). The precipitate formed was filtered and washed
with Et2O (3 ϫ 5 mL) to give an analytical sample as a yellow
solid. Yield: 45% (26.9 mg); m.p. Ͼ 250 °C. C26H27N3OPt2S
(819.7): calcd. C 38.10, H 3.32, N 5.13; found C 38.26, H 3.46, N
General: All the reactions were carried out under argon. The sol-
vents were purified and dried according to standard methods.[12]
Elemental analyses were performed with a PerkinϪElmer Elemen-
tal Analyser 240B by Mr. A. Canu (Dipartimento di Chimica, Un-
`
iversita di Sassari). Infrared spectra were recorded with
a
PerkinϪElmer 983 spectrometer as Nujol mulls. H, 13C{1H} and
31P{1H} NMR spectra were recorded with a Varian VXR 300 spec-
trometer operating at 300.0, 75.4 and 121.4 MHz, respectively.
Chemical shifts are given in ppm relative to internal TMS (1H,
13C) or external 85% H3PO4 (31P). 2D-COSY and NOE difference
spectra were performed by means of standard pulse sequences. The
mass spectrometric measurements were performed with a VG
7070EQ instrument, equipped with a PDP 11-250J data system and
operating under positive ion fast atom bombardment (FAB) con-
ditions with 3-nitrobenzyl alcohol as supporting matrix. cis-
[Pt(Me)2(DMSO)2] and cis-[Pt(Ph)2(DMSO)2] were prepared ac-
cording to literature procedures,[13] as were the ligand HL[14] and
complexes 1a and 1b.[7]
1
2
5.17. 1H NMR (CDCl3): δ ϭ 1.00 (s, JPt,H ϭ 85.7 Hz, 3 H,
CH3Pt), 2.38 (s, 6 H, CH3 of 3,5-Me2-py), 3.63 (s, 3JPt,H ϭ 25.6 Hz,
6 H, CH3 of DMSO), 6.88Ϫ7.49 (m, 8 H), 7.93 (d, 3JH,H ϭ 8.0 Hz,
1 H, 4-H), 8.17 (dd, 3JH,H ϭ 7.6 Hz, 1 H), 8.48 (s, 3JPt,H ϭ 22.7 Hz,
2 H, 2-H of 3,5-Me2-py) ppm.
[{Pt2(Me)(L)(dppp)2}2(µ-dppp)] (5a): dppp (97.2 mg, 0.236 mmol)
was added, under vigorous stirring, to a solution of 1a (88.3 mg;
0.112 mmol) in CH2Cl2 (20 mL). The solution, whose colour
changed immediately from yellow to orange-yellow, was stirred for
90 min, then concentrated to a small volume and treated with hex-
ane (15 mL). The precipitate formed was filtered off and washed
with hexane (3 ϫ 5 mL) to give the analytical sample as a yellow
solid. Yield 43% (60.6 mg); m.p. 211Ϫ214 (dec.). C115H102N4P6Pt4
(2506.2): calcd. C 55.11, H 4.10, N 2.24; found C 54.80, H 4.14, N
2.28. IR (Nujol): ν˜ ϭ 1100 (m), 1549 (w), 1569 (w) cmϪ1. 1H NMR
[Pt2(Me)(L)(PPh3)2] (2a): PPh3 (84.9 mg, 0.324 mmol) was added,
under vigorous stirring, to a solution of 1a (125.0 mg, 0.158 mmol)
in CH2Cl2 (15 mL). The solution was stirred for 2 h, then concen-
trated to a small volume and treated with hexane (15 mL). The
precipitate formed was filtered and washed with hexane to give the
analytical sample as a yellow solid. Yield: 90% (169.0 mg), m.p. 210
°C. C53H42N2P2Pt2·1/3C6H14 (1187.7) calcd. C 55.62, H 3.96, N
2.36; found C 55.48, H 3.95, N 2.37. IR (Nujol): ν˜ ϭ 1097 (s), 1557
2
3
(CDCl3): δ ϭ 0.30 (dd, JPt,H ϭ 67, JP,H ϭ 6.7, 8.0 Hz, 6 H,
CH3Pt), 2.06Ϫ2.94 [br. m, 18 H, CH2 (dppp)], 6.32Ϫ8.21 (m, 78
1
H, aromatic H) ppm. 31P NMR (CDCl3): δ ϭ Ϫ0.31 (d, JP,Pt
ϭ
1918, 2JP,P ϭ 22.9 Hz, 2 P), 1.35 (d, 1JP,Pt ϭ 2106, 2JP,P ϭ 22.9 Hz,
1
2
3
(w) cmϪ1. H NMR (CD2Cl2): δ ϭ 0.62 (d, JPt,H ϭ 76.2, JP,H
ϭ
1
2 P), 17.71 (s, JP,Pt ϭ 3913 Hz, 2 P) ppm.
7.6 Hz, 3 H, CH3Pt, 5.95 (m, 2 H), 6.28 (d, JH,H ϭ 7.3 Hz, 1 H),
6.59 (m, 1 H), 6.88 (m, 1 H), 6.98 (m, 1 H), 7.26Ϫ7.50 (m, 20 H),
[Pt2(Cl)(L)(DMSO)2] (6): Aqueous 0.1  HCl (2.0 mL) was added,
under vigorous stirring, to a solution of 1a (152.3 mg, 0.193 mmol)
in acetone (25 mL). The mixture was stirred for 2 h, then concen-
trated to a small volume. The brick-red precipitate formed was fil-
tered and washed with EtOH (3 ϫ 5 mL) and Et2O (3 ϫ 5 mL).
The crude product thus obtained was purified by chromatography
on silica gel (Merck, 230Ϫ400 mesh; eluent: benzene/acetone, 2:1)
to give an analytical sample as a yellow solid. Yield: 25% (39.0 mg);
m.p. 206 (dec.). C20H21ClN2O2Pt2S2 (811.1): calcd. C 29.61, H 2.61,
N 3.45; found C 30.52, H 2.33, N 3.82. IR (Nujol): ν˜ ϭ 292 (m)
4
7.68Ϫ7.77 (m, 6 H), 7.80Ϫ7.89 (m, 6 H), 8.07 (dd, JP,H ϭ 4.8,
3
3JH,H ϭ 7.7, JPt,H ϭ 38 Hz, 1 H, 4-H) ppm. 31P NMR (CD2Cl2):
1
1
δ ϭ 26.52 (s, JP,Pt ϭ 3931 Hz, P trans N), 32.44 (s, JP,Pt
ϭ
2412 Hz, P trans C) ppm. MS (FABϩ): m/z ϭ 1143 [M Ϫ CH3]ϩ,
895 [M Ϫ PPh3 Ϫ H]ϩ, 801 [M ϪPPh3 Ϫ C6H6 Ϫ CH3 Ϫ 2 H]ϩ,
725 [M Ϫ PPh3 Ϫ 2 C6H6 Ϫ CH3]ϩ. Compound 2a can be obtained
in almost quantitative yield also by reaction of [Pt2(CO)2(CH3)(L)]
with PPh3 in a 1:2 molar ratio.
[Pt2(Ph)(L)(PPh3)2] (2b): Complex 2b was obtained as for complex cmϪ1
.
1H NMR (CDCl3): δ ϭ 3.61 (s, JPt,H not resolved, 6 H,
2a, using 1b instead of 1a. Yield: 88%; m.p. 260 °C. CH3 of DMSO), 3.63 (s, JPt,H not resolved, 6 H, CH3 of DMSO),
Ͼ
3
4
C58H44N2P2Pt2·2H2O (1257.1): calcd. C 55.41, H 3.85, N 2.23;
found C 55.69, H 3.91, N 2.25. IR (Nujol): ν˜ ϭ 1096 (s), 1560 (w)
7.03Ϫ7.44 (m, 6 H), 8.23 (dd, JH,H ϭ 7.3, JH,H ϭ 1.2 Hz, 1 H,
3
3
4Ј-H), 8.32 (d, JH,H ϭ 8.3 Hz, 1 H, 4-H), 8.77 (d, JH,H ϭ 5.7,
cmϪ1 1H NMR (CDCl3): δ ϭ 5.94 (m, 2 H), 6.19 (d, JHϪH
. ϭ
4JH,H ϭ 1.2 Hz, 1 H, 6Ј-H) ppm. MS (FABϩ): m/z ϭ 811 [MH]ϩ,
7.1 Hz, 1 H), 6.59 (m, 4 H), 6.84 (t, JHϪH ϭ 7.4 Hz, 1 H), 810 [M]ϩ, 775 [M Ϫ Cl]ϩ, 732 [M Ϫ DMSO]ϩ, 697 [M Ϫ DMSO
6.93Ϫ7.44 (m, 24 H), 7.48Ϫ7.55 (m, 6 H), 7.82Ϫ7.89 (m, 6 H) Ϫ Cl]ϩ, 654 [M Ϫ 2 DMSO]ϩ, 619 [M Ϫ 2 DMSO Ϫ Cl]ϩ.
4488
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4484Ϫ4490

Dinuclear, Tricyclometallated Platinum(II) Derivatives
FULL PAPER
[Pt2(Cl)(L)(PPh3)2] (7): PPh3 (0.020 mmol) was added to an NMR X-ray Data Collection and Structure Determination: Crystal data
tube containing a solution of 6 (8.1 mg, 0.010 mmol) in CDCl3. are summarised in Table 2. The diffraction experiment was carried
The reaction was monitored by 1H and 31P NMR spectroscopy,
showing a fast reaction that produced complex 7 almost quantitat-
out with a Bruker SMART CCD area-detector diffractometer at
223 K. No crystal decay was observed, therefore no time-decay cor-
ively. A slow evaporation of the solvent gave crystals suitable for rection was needed. The collected frames were processed with the
an X-ray analysis. 1H NMR (CDCl3): δ ϭ 6.12 (d, JHϪH ϭ 7.5 Hz, software SAINT,[15] and an empirical absorption correction was
1 H), 6.24 (d, JHϪH ϭ 8.1 Hz, 1 H), 6.58 (m, 2 H), 6.80 (t, broad, applied (SADABS)[16] to the collected reflections. The calculations
1 H), 7.13 (d, JHϪH ϭ 7.1 Hz, 1 H), 7.30Ϫ7.49 (m, 22 H),
were performed using the Personal Structure Determination Pack-
7.74Ϫ7.90 (m, 10 H), 8.88 (m, 1 H, 6Ј-H) ppm. 31P NMR (CDCl3): age[17] and the physical constants tabulated therein.[18] The struc-
1
1
δ ϭ 25.93 (s, JPt,P ϭ 4146 Hz, P trans N), 18.32 (s, JPt,P
3952 Hz, P trans N) ppm.
ϭ
ture was solved by direct methods (SHELXS)[19] and refined by
full-matrix least squares using all reflections and minimising the
function Σw(F2o Ϫ kFc2)2 (refinement on F2). One of the two chloro-
form solvent molecules is disordered around a twofold axis and
its atoms have been given occupancy factors of 0.50. All the non-
hydrogen atoms were refined with anisotropic thermal factors. The
hydrogen atoms were placed in their ideal positions (CϪH ϭ 0.97
[Pt2(Me)(HL)(Cl)(PPh3)2] (8a): Aqueous 0.1  HCl (1.7 mL,
0.17 mmol, molar ratio 1:2), was added, under vigorous stirring, to
a solution of 2a (67.4 mg, 0.085 mmol) in acetone (20 mL). The
solution became pale yellow and was stirred for 16 h. The precipi-
tate formed was filtered and washed with (CH3)2CO (3 ϫ 5 mL).
From the filtered solution a second pale-yellow sample was ob-
tained by concentration and filtration. The filtered precipitate was
washed with (CH3)2CO and Et2O and added to the first sample.
Yield: 89% (94.6 mg); m.p. 215 (dec.). C53H43N2ClP2Pt2·3H2O
(1249.5): calcd. C 50.94, H 3.95, N 2.24; found C 50.27, H 3.51, N
2.28. IR (Nujol): ν˜ ϭ 1097 (s),1292 (s), 1585 (m), 1595 (m), 1715
˚
A), with the thermal parameter B set to 1.10-times that of the car-
bon atom to which they are attached, and not refined. In the final
Ϫ3
˚
˚
Fourier map the maximum residual was 3.86(20) e·A at 0.62 A
from Pt(1). CCDC-236975 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: ϩ 44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
2
(s), 296 m, 305 (m) cmϪ1. 1H NMR (CDCl3): δ ϭ 0.68 (d, JPt,H ϭ
3
3
80.8 Hz JP,H ϭ 7.3 Hz, 3 H, CH3Pt), 5.98 (dd, JH,H ϭ 7.9,
3JH,H ϭ 5.2 Hz, 1 H, 5Ј-H), 6.94Ϫ7.00 (m, 6 H), 7.16Ϫ7.26 (m, 10
H), 7.38Ϫ7.46 (m, 9 H), 7.47 (d, 1 H, 4Ј-H or 6Ј-H), 7.54Ϫ7.69
(m, 5 H), 7.71 (t, JHϪH ϭ 7.8 Hz, 1 H, Hpara, Ph bipy), 7.78 (d,
3JH,H ϭ 8.0 Hz, 1 H, 5-H), 7.86 (t, 3JH,H ϭ 7.8 Hz, 2 H, Hmeta, Ph
bipy), 8.01 (d, 3JH,H ϭ 7.9 Hz, 1 H, 6Ј-H or 4Ј-H), 8.56 (d, 3JH,H ϭ
Table 2. Crystallographic data of 7·1.5CHCl3
Empirical formula
Formula mass
Colour
C53.5H40.5Cl5.5N2P2Pt2
1358.55
yellow
monoclinic
C2/c
31.238(3)
17.779(2)
18.688(2)
110.48(1)
9723(2)
8
3
4
7.8 Hz, 2 H, Hortho, Ph bipy), 8.74 (dd, JH,H ϭ 8.0, JP,H ϭ 5.7,
3JPt,H ϭ 52 Hz, 1 H, 4-H) ppm. 31P NMR (CDCl3): δ ϭ 33.07 (s,
1
1JP,Pt ϭ 2405 Hz, P trans C), 13.14 (s, JP,Pt ϭ 4580 Hz, P trans
Crystal system
Space group
N) ppm.
˚
a [A]
˚
[Pt2(Ph)(HL)(Cl)(PPh3)2] (8b): Aqueous 0.1
 HCl (0.7 mL,
b [A]
˚
c [A]
0.07 mmol) was added, under vigorous stirring, to a solution of 2b
(81.7 mg, 0.067 mmol) in acetone (20 mL). The solution became
yellow and was stirred for 13 h. The precipitate formed was filtered
and washed with acetone (3 ϫ 5 mL) to give the analytical sample
β [°]
3
˚
V [A ]
Z
F(000)
1284
1.856
223
as
a yellow solid. Yield: 55% (47.3 mg); m.p. 205 °C.
Dcalcd. [g cmϪ3
T [K]
]
C58H45N2ClP2Pt2·H2O (1275.6): calcd. C 54.61, H 3.71, N 2.20;
found C 54.75, H 3.53, N 2.28. IR (Nujol): ν˜ ϭ 700 (s), 750 (s),
Crystal dimensions [mm]
0.338 ϫ 0.450 ϫ 0.507
62.2
1
1100 (s), 1550 (m) cmϪ1. H NMR (CDCl3): δ ϭ 5.99 (m, 1 H, 5Ј-
µ(Mo-Kα) [cmϪ1
]
H), 6.62Ϫ7.75 (m, 39 H), 7.83 (t, JHϪH ϭ 7.5 Hz, 2 H, Hmeta, Ph
bipy), 8.01 (d, JHϪH ϭ 8.3 Hz, 1 H, 6Ј-H or 4Ј-H), 8.47 (d, JHϪH ϭ
7.5 Hz, 2 H, Hortho, Ph bipy) ppm. 31P NMR (CDCl3) ϭ 30.68 (s,
Min./max. transmission factors
Scan mode
Frame width [°]
Time per frame [s]
No. of frames
DetectorϪsample distance [cm]
θ range [°]
0.759/1.000
ω
0.30
15
2750
4.00
3Ϫ28
full sphere
89654/14815
0.0326
1
1JP,Pt ϭ 2352 Hz, P trans C), 13.10 (s, JP,Pt ϭ 3725 Hz, P trans
N) ppm.
[Pt2(HL)(Cl)2(DMSO)2] (9): Aqueous 0.1
 HCl (0.65 mL,
Reciprocal space explored
No. of reflections (total/independent)
Rint
0.065 mmol) was added, under vigorous stirring, to a solution of
1b (52.3 mg, 0.061 mmol) in acetone (20 mL). After 4 h, a second
quantity of HCl was added (1.35 mL). The mixture was stirred for
15 h, then concentrated to dryness and crystallised from CH2Cl2/
Et2O to give an analytical sample as a yellow solid. Yield: 46%
(24.0 mg); m.p. 215Ϫ218 °C (dec.). C20H22Cl2N2O2Pt2S2
(847.6):calcd. C 28.34, H 2.62, N 3.31; found C 28.09, H 2.33, N
3.24. 1H NMR (CDCl3): δ ϭ 3.47 (s, JPt,H ഠ 24.5 Hz, 6 H, CH3 of
Final R2 and R2w indices[a]
(F2/all reflections)
0.053/0.110
Conventional R1 index[b][I Ͼ 2σ(I)]
Reflections with I Ͼ 2σ(I)
No. of variables
0.036
11770
604
Goodness of fit[c]
1.29
3
DMSO), 3.64 (s, JPt,H ഠ 22 Hz, 6 H, CH3 of DMSO), 7.07 (dd,
[a]
2
2
2
2
2 2
R2 ϭ [Σ(|Fo Ϫ kFc |/ΣFo ], R2w ϭ [Σw/(Fo Ϫ kFc ) /Σw-
JHϪH ϭ 5.6 Hz, JHϪH ϭ 7.8 Hz, 1 H, 5Ј-H), 7.18 (d, JHϪH
ϭ
2 2 1/2 [b]
[c]
2
2 2
(Fo ) ]
.
R1 ϭ [Σ(|Fo Ϫ k|Fc||/ΣFo).
[Σw(Fo Ϫ kFc ) /(No
Ϫ
,
Nv)]1/2, where w ϭ 4Fo /σ(Fo ) , σ(Fo ) ϭ [σ2(Fo ) ϩ (pFo ) ]
2
2 2
2
2
2 2 1/2
8.1 Hz, 1 H, 5-H), 7.42Ϫ7.48 (m, 3 H, Hmeta and Hpara), 7.73 (d,
JHϪH ϭ 8.1 Hz, 2 H, Hortho), 8.63Ϫ8.69 (m, 2 H, 4Ј-H and 4-H),
8.98 (dd, JHϪH ϭ 5.6 Hz, JHϪH ϭ 1.2 Hz, 1 H, 6Ј-H) ppm.
where No is the number of observations, Nv the number of vari-
ables, and p, the ignorance factor (0.06).
Eur. J. Inorg. Chem. 2004, 4484Ϫ4490
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4489

A. Zucca, M. A. Cinellu, G. Minghetti, S. Stoccoro, M. Manassero
FULL PAPER
Chelucci, S. Gladiali, F. Demartin, M. Manassero, J. Or-
Acknowledgments
Financial support from Universita di Sassari and Ministero
dell’Istruzione, dell’Universita e della Ricerca (MIUR) is grate-
fully acknowledged.
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[4b] M. A. Albrecht, G. van Koten, Angew. Chem. Int. Ed. 2001,
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Type IV, NN,C systems:
Early View Article
Published Online September 13, 2004
[5a]
G. Minghetti, M. A. Cinellu, G.
4490
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4484Ϫ4490