The reaction of alkynes with triangulo-clusters [Pt3(μ-CO)3(PR3)3]

Article abstract of DOI:10.1039/b103306a

The reaction of the cluster complexes [Pt₃(μ-CO)₃(PR₃)₃] (PR₃ = PPh₃ 1, PPh₂Bz 2, PCy₃ 3 and PⁱPr₃ 4) with dialkyl acetylenedicarboxylate, R′O₂CC≡CCO₂R′ (R′ = CH₃ or ^tBu) have been examined under various conditions. At low temperature the alkyne reacts quantitatively giving the unstable adducts [Pt₃(CO)₃(PR₃)₃(μ₃-alk yne)]. The stereochemistry of the intermediate [Pt₃(CO)₃(PPh₃)₃(μ₃- ^tBuO₂CC≡CCO₂^tBu)] 5has been deduced from low temperature ¹⁹⁵pt-{¹H}, ³¹P-{¹H} and ¹³C-{¹H} NMR spectra. At higher temperature a fluxional process renders two of the three platinum atoms equivalent on the NMR timescale. At room temperature the alkynes convert the starting clusters 1-4 to the stable dinuclear complexes [Pt₂(CO)₂(PR₃)₂(μ-R'O₂ CC≡CCO₂R′)] (R′ = CH₃, PR₃ = PPh₃ 6; R = ^tBu, PR₃ = PPh₃ 7; PPh₂Bz 8; PCy₃ 9 and PⁱPr₃ 10) in which the alkyne coordination has the C-C bond collinear with the Pt-Pt bond (6 and 7) or perpendicular to the Pt-Pt axis (9 and 10). The stereochemistry of these two types of dinuclear complexes has been established by NMR and IR studies and confirmed by X-ray diffraction analyses of 8 and 9.

Full text of DOI:10.1039/b103306a

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The reaction of alkynes with triangulo-clusters [Pt3(ꢀ-CO)3(PR3)3]
Renzo Ros,*a Augusto Tassan,a Raymond Roulet,*b Virginie Duprez,b Serena Detti,b
Gàbor Laurenczyb and Kurt Schenkc
a Dipartimento di Processi Chimici dell’Ingegneria, Via Marzolo 9, I-35131Padova, Italy
b Institut de Chimie Minérale et Analytique de l’Université, BCH, CH-1015 Lausanne,
Switzerland
c Institut de Cristallographie de l’Université, BSP, CH-1015Lausanne, Switzerland
Received 12th April 2001, Accepted 25th July 2001
First published as an Advance Article on the web 31st August 2001
The reaction of the cluster complexes [Pt3(µ-CO)3(PR3)3] (PR3 = PPh3 1, PPh2Bz 2, PCy3 3 and PiPr3 4) with dialkyl
t
᎐
acetylenedicarboxylate, RЈO CC᎐CCO RЈ (RЈ = CH or Bu) have been examined under various conditions. At low
᎐
2
2
3
temperature the alkyne reacts quantitatively giving the unstable adducts [Pt3(CO)3(PR3)3(µ3-alkyne)]. The
t
t
᎐
stereochemistry of the intermediate [Pt (CO) (PPh ) (µ - BuO CC᎐CCO Bu)] 5has been deduced from low
᎐
3
3
3
3
3
2
2
temperature 195Pt-{1H}, 31P-{1H} and 13C-{1H} NMR spectra. At higher temperature a fluxional process renders two
of the three platinum atoms equivalent on the NMR timescale. At room temperature the alkynes convert the starting
᎐
clusters 1–4 to the stable dinuclear complexes [Pt (CO) (PR ) (µ-RЈO CC᎐CCO RЈ)] (RЈ = CH , PR = PPh 6;
᎐
2
2
3
2
2
2
3
3
3
R = tBu, PR3 = PPh3 7; PPh2Bz 8; PCy3 9 and PiPr3 10) in which the alkyne coordination has the C–C bond
collinear with the Pt–Pt bond (6 and 7) or perpendicular to the Pt–Pt axis (9 and 10). The stereochemistry
of these two types of dinuclear complexes has been established by NMR and IR studies and confirmed
by X-ray diffraction analyses of 8 and 9.
identified at low temperature, slowly rearrange to dinuclear
acetylene-bridged complexes of µ-η1:η1- or µ-η2:η2- types.
Introduction
The interaction of olefins and alkynes with metal surfaces is
important for heterogeneous catalysis.1,2 Since there is a remark-
ableresemblancebetweenthewaysinwhichsmallmoleculesbind
to the coordinatively unsaturated platinum cluster complexes
and a Pt-surface,3,4 a study of the coordination of organic spe-
cies to [Pt3(µ-CO)3(PR3)3] (PR3 = PPh3 1, PPh2Bz 2, PCy3 3 and
PiPr3 4)5–9 should be a useful model for substrate chemisorp-
tion in heterogeneous catalysis. For mononuclear complexes
the binding of simple substrates, such as olefins and alkynes,
is well understood and can be readily rationalised based on the
Dewar–Chatt–Duncanson model.10 However, for complexes
which involve more than one metal center, additional complex-
ity is introduced owing to the presence of adjacent metals and
hence the possibility of bridging modes for the substrate
molecule. For dinuclear complexes two geometries have been
found to occur, one with the carbon–carbon bond collinear
to the M–M bond, the other perpendicular (structures I and
Results and discussion
Spectroscopic evidence for the adduct [Pt3(CO)3(PPh3)3-
t
t
᎐
(ꢀ - BuO CC᎐CCO Bu)] 5
᎐
3
2
2
The addition reaction between an equimolecular amount of
di(tert-butyl)acetylenedicarboxylate and [Pt3(µ-CO)3(PPh3)3] 1
occurs rapidly in CH2Cl2 below Ϫ50 ЊC to give a red-brown
solution of the adduct [Pt3(µ-CO)3(PPh3)3(µ3-η1:η1:η2-
t
t
᎐
BuO CC᎐CCO Bu)] 5. Attempts to isolate this adduct were
᎐
2
2
unsuccessful, due to disproportionation to the starting
triangulo-cluster 1 and the dimeric complex [Pt2(CO)2(PPh3)2(µ-
1
1
t
t
η :η - BuO CC᎐CCO Bu)] 7. The 31P-{1H} NMR spectrum at
᎐
᎐
2
2
Ϫ80 ЊC shows three resonances of approximately equal inten-
sity with satellites, indicative of three non-equivalent phosphine
environments in a trinuclear complex having only two Pt–Pt
bonds (Fig. 1 and Table 1). The spectrum is a superposition of
the subspectra related to eight isotopomers, i.e. one without
195Pt (29.01% abundance), three isotopomers containing one
195Pt nucleus (14.81% each), three isotopomers with two 195Pt
(7.56% each) and one with three 195Pt nuclei (3.86%). A com-
puter simulation using the program gNMR 4.0 has confirmed
the assignment of the coupling constants.15 Warming the
solution causes reversible changes in the satellite pattern of the
P1 resonance, with a simultaneous broadening of the signals at
17.5 and 27.2 ppm (P2 and P3, respectively) and a shift of both
resonances ending in coalescence at 21.5 ppm (Fig. 1).
II, respectively).11 Interconversion of these two bonding modes
᎐
has also been proposed for the [Pt (µ-CF C᎐CCF )(COD) ]
᎐
2
3
3
2
complex.12
The 13C-{1H} NMR spectrum of a 13CO enriched (>99%)
sample of 5, in CD2Cl2 at Ϫ86 ЊC also contains signals for three
non-equivalent carbonyl ligands with satellites, located in the
region of terminal COs. Formally this unsymmetrical adduct,
having a µ3-η1:η1:η2-alkyne bonding mode, is a 46-electron
cluster and should thus contain only two Pt–Pt bonds (Scheme
in Table 1). Its 13C-{1H) variable temperature NMR shows a
broadening of the signal at 178.2 (C2) and 189.9 ppm (C3) upon
Recently, we have described the reactions of triangulo-cluster
compounds of platinum [Pt3(µ-CO)3(PR3)3] with sulfur diox-
ide13 and activated olefins,14 giving [Pt3(µ-SO2)n(µ-CO)3 Ϫ n
-
(PR3)3] (n = 1–3) and [Pt(CO)(PR3)(olefin)], respectively, the
latter via the adduct [Pt3(µ-CO)3(PR3)3(olefin)].
In this paper we describe the reactivity of some trinuclear
clusters with acetylenes. The unstable intermediate adducts,
2858
J. Chem. Soc., Dalton Trans., 2001, 2858–2863
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103306a

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t
t
Table 1 Variable temperature 31P-{1H} and 13C NMR data for [Pt3(CO)3(PPh3)3(µ3- BuO2CC᎐CCO2 Bu)] 5 in CD2Cl2 (δ/ppm; J/Hz)
᎐
᎐
T /ЊC
δ(P1)
δ(P2)
δ(P3)
1J(P1–Pt1) 1J(P2–Pt2) 1J(P3–Pt3) 2J(P1–Pt3) 2J(P3–Pt1) 3J(P1–P3) 3J(P2–P3) 4J(P1–P2)
Ϫ80
Ϫ74
Ϫ50
Ϫ38
12.66
13.22
13.64
14.14
17.53
17.72
18.45
27.16
26.96
25.40
4283
4268
4177
4107
3565
3568
3406
3408
362
361
234
238
207
62
61
42
40
6
8
a
a
207
a
a
a
a
a
≈3560
≈3330
a
a
a
21.49
184.2
δ(C1)
δ(C2)
δ(C3)
1J(C1–Pt1) 1J(C2–Pt2) 1J(C3–Pt3) 2J(C2–Pt3) 3J(C2–P3)
Ϫ86
Ϫ66
Ϫ46
Ϫ35
191.2
191.5
191.9
192.1
178.2
178.4
179.4
189.9
189.6
189.0
1634
1633
1624
1612
1886
1281
211
28.1
1873
1279
199
23
a
a
a
a
a
a
a
a
a Not observed.
Fig. 1 Variable temperature and simulated (Ϫ80 ЊC) 31P-{1H} NMR
t
᎐
spectra (161.93 MHz) of adduct [Pt3(CO)3(PPh3)3(µ3- BuO2CC᎐CCO2-
᎐
tBu)], 5, in CD2Cl2.
heating which is accompanied by a convergent shift of reson-
ances to 184.2 ppm; the coalescence temperature was estimated
at ca. Ϫ30 ЊC (Fig. 2).
Fig. 2 Variable temperature 13C-{1H} NMR spectra (99.55 MHz) of
13
t
t
᎐
adduct [Pt3( CO)3(PPh3)3(µ3- BuO2CC᎐CCO2 Bu)], 5, in CD2Cl2.
᎐
The non-rigid structure of adduct 5 is confirmed by the 195Pt-
{1H} NMR spectrum in CD2Cl2 at Ϫ95 ЊC, which shows only
the resonance of Pt1 (Ϫ4427 ppm) as a doublet of doublets, due
to the P1–195Pt1–Pt2–P2 and P1–195Pt1–Pt3–P3 equivalent iso-
topomers (1J(Pt1–P) = 3414 Hz, 2J(Pt1–P) = 372 Hz), flanked
by low intensity signals arising from the subspectrum for the
J. Chem. Soc., Dalton Trans., 2001, 2858–2863
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Table 2 Selected 195Pt-{1H}, 31P-{1H} and 13C NMRa data for com-
plexes 6–10 at 25 ЊC (δ/ppm, J/Hz)
6
7
8
9
10
δ(Pt)
Ϫ5007
783.8
Ϫ5018
372.0
Ϫ4977
477.4
Ϫ4703
Ϫ4764
1J(Pt–Pt)
2J(Pt–Pt)
505.4
537.1
Fig. 3 Observed (left) and simulated (right) spectra of [Pt2(CO)2-
1
1
t
t
δ(P)
19.40
2409
783.5
18.87
2873
490.3
9.25
2638
647.1
29.64
3169
43.57
3162
᎐
(PPh2Bz)2(µ-η :η - BuO2CC᎐CCO2 Bu)], 8, in CD2Cl2 at 25 ЊC: (a)
᎐
1J(P–Pt)
2J(P–Pt)
3J(P–Pt)
3J(P–P)
4J(P–P)
195Pt-{1H} (77.38 MHz), (b) 31P-{1H} (161.93 MHz) and (c) 13C-{1H}
NMR (50.32 MHz), the latter for the 13CO enriched (>99%) complex.
Ϫ41.7
Ϫ17.5
163.9
116.1
149.6
P1–195Pt1–195Pt2–P2 and the symmetrically equivalent P1–195Pt1–
195Pt3–P3 isotopomer (see A and B in Table 1), which allow an
estimation of the 195Pt–195Pt coupling constant as ca. 1021 Hz.
No signals for the other two Pt atoms were detected. At higher
temperature this single signal broadens, and disappears into
the base line above Ϫ70 ЊC. This type of dynamic process
involving trinuclear platinum acetylene complexes has not been
8.4
14.4
δ(C)a
193.0
1235
8.0
190.5
1332
<8
191.8
1258
10.4
186.8
1687
190.2
1678
1J(C–Pt)
2J(C–Pt)
3J(C–Pt)
2J(C–P)
3J(C–P)
4J(C–P)
3J(C–C)
4J(C–C)
Ϫ15.6
4.6
Ϫ14.3
4.6
3.5
3.2
<2
<2
4.1
3.3
<0.5
<0.5
previously observed. The site exchange mechanism of [Pt-
3.0
<2
4.0
᎐
(CO) (PCy ) (MeO CC᎐CCO Me)] has not been ascertained,
᎐
3
3
3
2
2
≈0.8
≈0.9
and another type of dynamic process, i.e. the rotation of the
a 13C NMR data for the carbonyl ligands of the complexes enriched
acetylenic ligand above one of the Pt3 faces of [Pt6(CO)6(µ-
(>99%) in 13CO.
dppm) (MeO CC᎐CCO Me)] has been reported recently.16b The
᎐
᎐
2
2
2
A
B exchange proposed in Table 1 explains the dynamics
which renders the Pt2 and Pt3 environments equivalent on the
NMR timescale. Unfortunately no other acetylene adduct of
the other triangulo-cluster complexes could be observed in the
slow exchange domain.
ically equivalent Pt atoms and is made of three isotopomers, i.e.
43.82% of the molecules are without 195Pt, 2 × 22.37% contain
one 195Pt nucleus and 11.42% contain two 195Pt nuclei. The
observed spectrum is a superimposition of the spectra of each
of these isotopomers taking into account their respective
natural abundances. For example, the 31P-{1H} NMR spectrum
of 8 (Fig. 3b) is composed of a singlet due to the A2 spin system,
8 signals due to the AAЈ part of the AAЈX spin system, and
10 signals due to the AAЈ part of the AAЈXXЈ spin system,
respectively. All spectra could be analysed using first order
approximation and spectral simulation using the gNMR 4.0
program confirmed all values, except for the negative sign of the
coupling constants 3J(P–Pt) and 3J(C–Pt) of 9 and 10.
Synthesis and characterisation of dinuclear complexes
[Pt2(CO)2(PR3)2(ꢀ-alkyne)]
᎐
Excess of dialkyl acetylenedicarboxylate, RЈO CC᎐CCO RЈ
᎐
2
2
(RЈ = CH3 or tBu) reacts at room temperature with [Pt3-
(µ-CO)3(PR3)3] (PR3 = PPh3, PPh2Bz, PCy3 and PiPr3) to give
not the expected monoplatinum(0) complexes [Pt(CO)-
᎐
(PR )(RЈO CC᎐CCO RЈ)] but the dinuclear platinum() com-
᎐
3
2
2
1
1
᎐
pounds [Pt (CO) (PR ) (µ-η :η -RЈO CC᎐CCO RЈ)] (RЈ = CH ,
᎐
2
2
3
2
2
2
3
PR3 = PPh3 6; RЈ = tBu, PR3 = PPh3 7, PPh2Bz 8) or
All spectra show a single resonance, with similar patterns
of satellites, thus indicating that the dinuclear complexes have
two chemically equivalent platinum environments with linear
R3P–Pt–Pt–PR3 (6–8) or angular (9, 10) arrangements. The
coordination geometry about the metal centres of 6–8 could be
viewed as a distorted square plane, in which the phosphines
invariably prefer to be trans to the Pt–Pt bond whilst the
carbonyls are cis. There appears to be no obvious explanation
for this preference apart from the steric problems raised if the
phosphines were cis to the Pt–Pt bond.
2
2
t
t
᎐
[Pt (CO) (PR ) (µ-η :η - BuO CC᎐CCO Bu] (PR3 = PCy3 9,
᎐
2
2
3
2
2
2
PiPr3 10), the latter two having two “cis-Pt(CO)(PR3)” frag-
ments bridged by bis-π alkyne interactions. The dinuclear
platinum() complex 6 has been prepared by addition of
dimethyl acetylenedicarboxylate to Pt(CO)2(PPh3)2,16a as well
1
1
᎐
as [Pt (CO) (PCy ) (µ-η :η -CH O CC᎐CCO CH )] which is
᎐
2
2
3
2
3
2
2
3
isostructural with 6.16b
The IR spectra of the three complexes 6–8 show two bands
Ϫ1
᎐
(ν(C᎐O) B and A ) in the 2010–2050 cm region, indicating
᎐
1
1
1
CO groups terminally bonded to platinum(); the spectra of 9
and 10 present a single absorption shifted to lower wavelengths
(1994 and 1999 cmϪ1, respectively) in agreement with the
increased basicity of the metal.14,17 All derivatives showed an
additional strong absorption in the 1679–1703 cmϪ1 region due
The rather low values for the J(Pt–Pt) coupling constant
(372.0 and 477.4 Hz for 7 and 8, respectively) compared with
that for the isostructural dinuclear complex 6 (783.8 Hz) may be
associated with the steric bulkiness of the di(tert-butyl)acetyl-
enedicarboxylate ligand leading to an increase in the Pt–Pt
bond distance (see crystallographic section below). The rel-
atively higher values of 2J(Pt–Pt) (505.4 and 537.1 Hz for 9 and
10, respectively) may due to additional metal–metal inter-
actions. The values of the coupling constants 3J(P–Pt) and
4J(P–P) are respectively smaller than those of 2J(P–Pt) and
3J(P–P) found in 6–8. On the basis of molecular orbital
studies20 it has been stated that the values of 1J(Pt–Pt), J(Pt–P)
to ν(C᎐O) of the carboxylate groups of the acetylene ligands. In
᎐
this region no IR and Raman bands were found which could be
18,19
᎐
assigned to the ν(C᎐C) of the coordinated alkyne.
᎐
The 195Pt-{1H}, 31P-{1H} and 13C-{1H} NMR spectra of 8 are
shown in Fig. 3a–c and selected data for 6–10 are collected in
Table 2. Owing to the existence of isotope 195Pt (I = ½, natural
abundance 33.8%) each dinuclear complex contains two chem-
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J. Chem. Soc., Dalton Trans., 2001, 2858–2863

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Table 3 Selected bond lengths [Å] and angles [Њ] for 8 and 9a
and J(P–P) should be larger for dinuclear complexes where the
C–C bond is parallel to the Pt–Pt axis relative to complexes
where the C–C bond is perpendicular to that axis. On compar-
ing the data for complexes 6–10 (Table 2), this statement holds
for J(Pt–Pt) vs. J(Pt–P) and J(P–P) vs. J(P–P), but not for
1J(Pt–Pt). Perhaps the best criterion for distinguishing between
the two bonding modes of the alkyne ligand is the opposite sign
of the J(Pt–P) and J(Pt–C) coupling constants: positive for 6–8
(µ-η1:η1-type), negative for 9–10 (µ-η2:η2-type).
8
9
2
3
3
4
Pt–C(1)
Pt–C(2)
C(2)–Pt#1
Pt–P
1.893(4)
2.044(3)
1.859(4)
2.089(3)
2.054(3)
2.3271(8)
3.0299(5)
1.152(4)
1.205(4)
1.338(4)
1.475(4)
1.399(6)
1.482(4)
1.503(6)
1.505(6)
1.523(7)
1.838(3)
2.3277(8)
2.6538(2)
1.126(5)
1.213(4)
1.341(4)
1.469(5)
1.334(6)
1.485(4)
1.488(7)
1.511(6)
1.516(7)
1.819(3)
Pt–Pt#1
O(1)–C(1)
O(2)–C(3)
O(3)–C(3)
O(3)–C(4)
C(2)–C(2)#1
C(2)–C(3)
C(4)–C(6)
C(4)–C(5)
C(4)–C(7)
P–C(10)
Crystal structures of 8 and 9
The molecular structures of 8 and 9 are shown in Fig. 4 and 5,
respectively, and selected bond lengths and angles are collected
in Table 3. Both complexes are dimers in which the two parts
are related by a twofold axis. Alkyne coordination in 8 is of the
µ-η1:η1-type with the C–C bond nearly collinear with the metal
atoms. The structure is similar to that of [Pt2(CO)2(PPh3)3-
16
C(1)–Pt–C(2)
C(1)–Pt–C(2)#1
C(1)–Pt–P
164.64(14)
111.62(14)
151.05(14)
99.29(11)
149.07(9)
121.36(11)
42.56(8)
120.47(2)
136.2(2)
68.9(2)
125.2(2)
124.5(3)
110.6(3)
124.9(3)
᎐
(MeO CC᎐CCO Me)]. The Pt–Pt bond is longer in 8 (2.654
᎐
2
2
Å) than in the methyl derivative (2.635 Å). This is accompanied
by a greater deviation from coplanarity of the atoms consti-
tuting the mean plane Pt–C(2)–C(2)#1–Pt#1 (mean deviation
0.134 Å for 8, 0.03 Å for the methyl derivative). The latter is
probably due to the bulkiness of the tert-butyl groups relative to
the methyl groups which is reflected in the greater value of the
dihedral angle C(3)–C(2)–C(2)#1–C(3)#1 (16.4Њ vs. 5.8Њ).
97.74(12)
96.99(8)
95.73(12)
70.03(8)
165.65(2)
123.3(2)
106.61(11)
129.9(2)
126.8(3)
109.4(3)
123.7(3)
C(2)–Pt–P
C(1)–Pt–Pt#1
C(2)–Pt–Pt#1
P–Pt–Pt#1
C(2)#1–C(2)–C(3)
C(2)#1–C(2)–Pt
C(3)–C(2)–Pt
C(2)–C(3)–O(2)
C(2)–C(3)–O(3)
O(2)–C(3)–O(3)
Alkyne coordination in 9 is of the µ-η2:η2-type with the C–C
bond nearly perpendicular to the Pt–Pt axis (92Њ). The Pt–Pt
distance is considerably longer (3.030 Å) than that in 8 and
᎐
a Symmetry transformations used to generate equivalent atoms: for 8:
#1 = 1 Ϫ x, y, ½ Ϫ z; for 9 #1 = 1 Ϫ x, ½ Ϫ y, z.
is relatively similar to that found in [Pt (PMe ) (PhC᎐CPh)]
᎐
2
3 4
(2.905 Å)21 where the diphenyl acetylene ligand is coordinated
perpendicularly to the Pt–Pt axis. The Pt–C(2)–C(2)#1–Pt#1
dihedral angle is also greater (101.9Њ) than that in 8 (26.1Њ) and
in the Me derivative (6.6Њ). Its C(3)–C(2)–C(2)#1–C(3)#1
dihedral angle is similar to that of 8 (19.2 vs. 16.4Њ) and is
therefore not indicative of a change in the hybridisation mode
of the acetylenic carbon atoms.
s(Pt)–s(P) were found to be greater for the di-σ model (0.030
and Ϫ0.019, respectively) than those for the µ-bridging model
(0.005 and Ϫ0.004, respectively). Therefore, the Pt–Pt σ bond-
ing should be relatively weakened and the Pt–P σ bonding
strengthened in the latter, which in turn should lower the 1J(Pt–
An EHMO calculation20 on the model complex [Pt2-
1
᎐
(CO) (PH ) (HC᎐CH)] with the perpendicular orientation of
Pt) and enhance the J(Pt–P) coupling constants. The Pt–Pt
᎐
2
3 2
acetylene to the Pt–Pt axis (µ-bridging model) against the paral-
lel one (di-σ model) has shown that the orientation of the
acetylene ligand strongly affects the HOMO characteristics.
The magnitude of the s-coefficient products for s(Pt)–s(Pt) and
distance indeed increases with the increase in the Pt–C(2)–C(2)–
Pt dihedral angle on going from the Me derivative to 8 and then
to 9. However, the corresponding values for J(Pt–Pt) do not
1
follow the same sequence as shown in Table 2.
Fig. 4 Molecular structure of 8. The symmetry transformation #1 stands for: 1 Ϫ x, y, ½ Ϫ z.
J. Chem. Soc., Dalton Trans., 2001, 2858–2863
2861

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[Pt3(µ-CO)3(PPh3)3] according to NMR spectroscopic evidence
of their solutions at higher temperature (>Ϫ30 ЊC). However,
the dinuclear complex is the only species formed in the presence
of excess acetylene.
Experimental
General procedures
All manipulations were carried out under nitrogen atmosphere
using standard Schlenk techniques. All solvents were dried by
conventional methods and distilled prior to use. Infrared
spectra of solids (KBr, Nujol mulls) and of CH2Cl2 solutions
(KBr or CaF2 cells) were recorded on Perkin-Elmer 983 or FT-
IR-2000 spectrometers, and NMR spectra on Bruker AC 200
(1H at 200.13 MHz, 31P at 81.02 MHz and 13C at 50.32 MHz),
on Bruker WH 360 (1H at 360.14 MHz, 13C at 90.55 MHz) and
on Bruker DRX 400 (31P at 161.93 MHz, 13C at 99.55 MHz and
195Pt at 77.38 MHz) spectrometers. The chemical shifts (δ) are
referenced to Me4Si (1H and 13C), to external 85% H3PO4 (31P)
Syntheses
1
1
᎐
[Pt (CO) (PPh ) {ꢀ-ꢁ :ꢁ -CH O CC᎐CCO CH }] (6).
A
᎐
2
2
3
2
3
2
2
3
suspension of [Pt3(µ-CO)3(PPh3)3] (0.35 g, 0.24 mmol) in 20 ml
of a 1 : 1 n-octane–benzene mixture was cooled to Ϫ10 ЊC and
dimethyl acetylenedicarboxylate (0.13 g, 0.91 mmol) was added
via a syringe. The resulting mixture was stirred for 15 minutes in
the cold and then for 2 h at room temperature. The obtained
ochre-orange suspension was concentrated under vacuum to ca.
3 ml and heptane (10 ml) was added to complete precipitation.
The solid was filtered, washed with cold heptane and recrystal-
lised from dichloromethane–heptane at Ϫ20 ЊC. Yield 0.276 g
(69%) as ochre-yellow microcrystals of 1. Mp 191–195 ЊC dec.
and to external Na2PtCl6 (
195Pt). The spectra of all nuclei
1
1
(except H) were H decoupled. Simulations were made with
the gNMR 4.0 program, taking into account only the relative
population of platinum isotopomers since all samples for
13C-{H} NMR were enriched to ≥99% 13CO.13
(Found: C, 47.13; H, 3.20%. C44H36O6P2Pt2 requires C, 47.49;
᎐
H, 3.26%). IR (CH Cl ): ν(C᎐O) 2052vs, 2015m; ν(C᎐O) 1703s
᎐
᎐
2
2
The compounds [Pt3(CO)3(PR3)3] (L = PPh3,13 PPh2Bz,13,22
cmϪ1
.
23
PCy3 and PiPr3 23) were prepared by literature methods; the
13C isotopically labeled derivatives were prepared similarly,
1
1
t
t
᎐
[Pt (CO) (PPh ) {ꢀ-ꢁ :ꢁ - BuO CC᎐CCO Bu}] (7). A solu-
᎐
2
2
3
2
2
2
using 13CO enriched to 99%. CH O CC᎐CCO CH and
᎐
᎐
3
2
2
3
tion of di(tert-butyl)acetylenedicarboxylate (77 mg, 0.34
mmol) in dichloromethane (2 ml) was added to a stirred
solution of [Pt3(µ-CO)3(PPh3)3] (0.22 g, 0.15 mmol) in dichloro-
methane (15 ml) at Ϫ20 ЊC. After 10 minutes in the cold the
solution was stirred at room temperature for 30 minutes (the
reaction progress was monitored by IR spectra). Evaporation
of the solvent under reduced pressure gave a pale brown resi-
due which was washed with cold pentane (2 × 3 ml) and crys-
tallised from dichloromethane–heptane at Ϫ20 ЊC. Yield 0.209
g (77%) as pale ochre microcrystals of 2. Mp 167–168 ЊC dec.
(Found: C, 49.93; H, 4.01%. C50H48O6P2Pt2 requires C, 50.17;
t
t
᎐
BuO CC᎐CCO Bu (Fluka) were used as purchased. Carbon
᎐
2
2
monoxide (>99% 13CO) was used as received from I.C.M.,
Innerberg.
Spectroscopic evidence for the alkyne adduct [Pt3(ꢀ-CO)3-
t
t
᎐
(PPh ) (ꢀ - BuO CC᎐CCO Bu)] (5)
᎐
3
3
3
2
2
A suspension of [Pt3(µ-CO)3(PPh3)3] (2 ÷ 3 × 10Ϫ4 mol) in
CD2Cl2 (0.4 ml) was cooled to Ϫ78 ЊC and a slight excess of
di(tert-butyl)acetylenedicarboxylate (3 ÷ 4 × 10Ϫ4 mol) in
CD2Cl2 (0.3 ml) at Ϫ78 ЊC was added via syringe. The resulting
mixture was stirred for some minutes at low temperature
(<Ϫ50 ЊC) and the red-brown solution examined by NMR
spectroscopy was found to contain [Pt3(µ-CO)3(PPh3)3-
᎐
H, 4.04%). IR (CH Cl ): ν(C᎐O) 2048vs, 2016m; ν(C᎐O) 1692s
᎐
᎐
2
2
cmϪ1
.
t
t
1
1
t
t
᎐
᎐
᎐
(µ - BuO CC᎐CCO Bu)]. This adduct is stable for several days
[Pt (CO) (PPh Bz) {ꢀ-ꢁ :ꢁ - BuO CC᎐CCO Bu}] (8). As for
᎐
3
2
2
2
2
2
2
2
2
in cold solution, but all preparative-scale attempts to isolate it
as a solid resulted in rearrangement to [Pt2(CO)2(PPh3)2-
7 starting with [Pt3(µ-CO)3(PPh2Bz)3] (0.37 g, 0.25 mmol) and
di(tert-butyl)acetylenedicarboxylate (0.116 g, 0.51 mmol). Yield
0.328 g (72%) as pale yellow microcrystals. Mp 149–151 ЊC dec.
1
t
t
᎐
(µ-η - BuO CC᎐CCO Bu)] together with the starting material
᎐
2
2
Fig. 5 Molecular structure of 9. The symmetry transformation #1 stands for: 1 Ϫ x, ½ Ϫ y, z.
2862
J. Chem. Soc., Dalton Trans., 2001, 2858–2863

View Article Online
Table 4 Crystallographic data for compounds 8 and 9
each. The intensities were corrected for Lorentz and polariz-
ation effects and an absorption correction based on the crystal
habitus was carried out as well. The structure was solved with
the help of DIRDIF 96,26 and refined by means of SHELXTL
5.05.25 All non-hydrogen atoms were refined anisotropically,
and all hydrogens were made to ride on their associated
carbons.
CCDC reference numbers 163707 and 163708.
See http://www.rsc.org/suppdata/dt/b1/b103306a/ for crystal-
lographic data in CIF or other electronic format.
8
9
Molecular formula
M
Crystal system
a/Å
b/Å
c/Å
C52H52O6P2Pt2
1225.1
C50H84O6P2Pt2
1233.30
Tetragonal
17.737(3)
17.737(3)
33.472(7)
Monoclinic
18.0590(7)
16.2947(7)
18.5105(8)
116.2990(10)
4883.2(4)
293(2)
β/Њ
U/Å3
10530(3)
293(2)
T /K
Space group
C2/c
4
5.836
21362/8336
0.0311
I41/a
8
5.412
33314/4119
0.0549
Acknowledgements
Z
µ/mmϪ1
We thank the Swiss National Science Foundation and Murst
Cofin-2000 for financial support.
Reflections collected/unique
Rint
Final R1,wR2 [I > 2σ(I )]
(all data)
0.0488, 0.0713
0.0544, 0.0719
0.0192, 0.0355
0.0270, 0.0365
References
1 H. C. Clark and V. K. Jain, Coord. Chem. Rev., 1984, 55, 151.
2 R. Whyman, Transition Metal Clusters, B. F. G. Johnson, ed., Wiley,
New York, 1980, pp. 471–608.
3 E. L. Muetterties, T. N. Rodin, E. Band, C. F. Bruker and W. R.
Pretzer, Chem. Rev., 1979, 79, 91.
(Found: C, 50.83; H, 4.16%. C52H52O6P2Pt2 requires C, 50.98;
᎐
H, 4.28%). IR (CH Cl ): ν(C᎐O) 2046vs, 2009m; ν(C᎐O) 1687s
᎐
᎐
2
2
cmϪ1
.
4 P. Braunstein and J. Rose, in Stereochemistry of Organometallic and
Inorganic Compounds, I. Bernal, ed., Elsevier, Amsterdam, 1988,
vol. 3.
5 K. H. Dahmer, A. Moor, R. Naegli and L. M. Venanzi, Inorg.
Chem., 1991, 30, 4285.
6 A. Albinati, A. Moor, P. S. Pregosin and M. L. Venanzi, J. Am.
Chem. Soc., 1982, 104, 7672.
7 A. Albinati, K.-H. Dahmer, A. Togni and M. L. Venanzi, Angew.
Chem., 1985, 97, 760.
2
2
t
t
᎐
[Pt (CO) (PCy ) {ꢀ-ꢁ :ꢁ - BuO CC᎐CCO Bu}] (9). As for 7
᎐
2
2
3
2
2
2
starting with [Pt3(µ-CO)3(PCy3)3] (0.26 g, 0.17 mmol) and
di(tert-butyl)acetylenedicarboxylate (75 mg, 0.33 mmol). Yield
0.223 g (70%) as ivory coloured microcrystals. Mp 182–185 ЊC
dec. (Found: C, 48.55; H, 6.91%. C50H84O6P2Pt2 requires C,
48.69; H, 6.86%). IR (CH Cl ): ν(C᎐O) 1994s; ν(C᎐O) 1679s
᎐
᎐
᎐
2
2
cmϪ1
.
8 D. M. P. Mingos and T. Slee, J. Organomet. Chem., 1990, 394, 679.
9 A. D. Burrows and D. M. P. Mingos, Coord. Chem. Rev., 1996, 154,
19.
i
2
2
t
t
᎐
[Pt (CO) (P Pr ) {ꢀ-ꢁ :ꢁ - BuO CC᎐CCO Bu}] (10). A sol-
᎐
2
2
3
2
2
2
ution of di(tert-butyl)acetylenedicarboxylate (174 mg, 0.77
mmol) was added to a stirred solution of [Pt3(µ-CO)3(PiPr3)3]
(0.46 g, 0.40 mmol) in cyclohexane (25 ml) at 5 ЊC. After 10
minutes at this temperature the solution was allowed to stir at
room temperature. After 20 minutes a pale orange solution was
obtained. Its IR spectrum showed the disappearance of the
ν(CO) absorption at 1770 cmϪ1 of the starting trinuclear cluster.
Evaporation of the solvent under vacuum gave an oily residue
which was treated with 4 ml of pentane and kept at Ϫ20 ЊC for
2 days. The pale yellow crystals were washed with cold pentane
(3 × 2 ml) and dried under vacuum. Yield 0.29 g (49%). Mp
10 M. J. S. Dewar, Bull. Soc. Chim. Fr., 1951, 18, C79; J. Chatt and L. A.
Duncanson, J. Chem. Soc., 1953, 2339; M. J. S. Dewar, R. C.
Haddon, A. Komorniki and H. Rzepa, J. Am. Chem. Soc., 1977, 99,
377; M. J. S. Dewar and G. P. Ford, J. Am. Chem. Soc., 1979, 101,
783.
11 D. M. Hoffman, R. Hoffman and C. R. Fisel, J. Am. Chem. Soc.,
1982, 104, 3858 and references therein.
12 R. S. Dickson and G. N. Pain, J. Chem. Soc., Chem. Commun., 1979,
277; N. M. Boag, M. Green and F. G. A. Stone, J. Chem. Soc., Chem.
Commun., 1980, 1281.
13 R. Ros, A. Tassan, G. Laurenczy and R. Roulet, Inorg. Chim. Acta,
2000, 303, 94.
14 R. Ros, G. Facchin, A. Tassan, R. Roulet, G. Laurenczy and
F. Lukas, J. Cluster Sci., 2001, 12, 99.
15 gNMR, version 4.0, Cherwell Scientific Publishing Limited, Oxford,
1995–1997.
116–118 ЊC dec. (Found: C, 38.90; H, 6.15%. C32H60O6P2Pt2
᎐
requires C, 38.71; H, 6.09%). IR (CH Cl ): ν(C᎐O) 1999vs;
᎐
2
2
ν(C᎐O) 1681s cmϪ1
.
᎐
16 (a) Y. Koie, S. Shinoda, Y. Saito, B. J. Fitzgerald and C. G. Pierpont,
Inorg. Chem., 1980, 19, 770; (b) G. J. Spivak and R. J. Puddephatt,
J. Organomet. Chem., 1998, 551, 383.
17 S. Braterman, Metal Carbonyl Spectra, Academic Press, New York,
1975.
18 H. C. Clark and L. E. Manzer, Inorg. Chem., 1974, 13, 1291.
19 N. M. Boag, M. Green, D. M. Grove, J. A. K. Howard, J. L. Spencer
and F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1980, 2170 and
references therein.
20 Y. Koie, S. Shinoda and Y. Saito, Inorg. Chem., 1981, 20, 4408.
21 N. M. Boag, J. Browning, C. Crocker, P. L. Goggin, R. J.
Goodfellow, M. Murray and J. L. Spencer, J. Chem. Res. (M), 1978,
2962.
22 J. Chatt and P. Chini, J. Chem. Soc. A, 1970, 1538.
23 K. H. Dalmer, A. Moor, R. Naegli and L. M. Venanzi, Inorg. Chem.,
1991, 30, 4285.
24 SAINT, Program for the Reduction of Data from an Area Detector,
version 4.05, Bruker Analytical X-Ray Instruments, Inc., Madison,
WI, 1996.
Crystal structures
Crystal data for 8. A yellow crystal the habitus of which
¯
¯¯
consisted of a {110} prism, a {112} pinacoid and a {112} bevel
face was brought onto a Bruker SMART CCD system
equipped with Mo radiation. A hemisphere of reflections were
collected as ω scans over twelve hours. Using the SAINT pack-
age,24 lattice constants were optimized (Table 4) and intensities
were integrated and corrected for Lorentz and polarization
effects. A semi-empirical absorption correction based on ψ-
scans was computed with the help of the XPREP program.25
The structure was solved with the help of DIRDIF 96,26 and
refined by means of SHELXTL 5.05.25 All non-hydrogen atoms
were refined anisotropically, and all hydrogens were made to
ride on their associated carbons.
25 G. M. Sheldrick, SHELXTL 5.05, Bruker Analytical X-Ray
Instruments, Inc., Madison, WI, 1996.
26 P. T. Beurskens, G. Beurskens, W. P. Bosman, R. de Gelder,
S. García-Granda, R. O. Gould, R. Israël and M. M. Smits,
The DIRDIF 96 System of Programs, Laboratorium voor
Kristallografie, Katholieke Universiteit Nijmegen, 1996.
Crystal data for 9. A yellow crystal the habitus of which
consisted of a not fully developed {112} dipyramid was meas-
ured on a Stoe IPDS system equipped with Mo radiation. A
crystal–image plate distance of 80 mm was chosen and 200
images, in oscillation steps of 1Њ, were exposed for five minutes
J. Chem. Soc., Dalton Trans., 2001, 2858–2863
2863