Synthesis of [Pt12(CO)20(dppm)2]2- and [Pt18(CO)30(dppm)3]2- Heteroleptic Chini-type Platinum Clusters by the Oxidative Oligomerization of [Pt6(CO)12</

Article abstract of DOI:10.1021/acs.inorgchem.8b00447

The reactions of [Pt₆(CO)₁₂]^2- with CH(PPh₂)₂ (dppm), CH₂=C(PPh₂)₂ (P^P), and Fe(C₅H₄PPh₂)₂ (dppf) proceed via nonredox sub

Full text of DOI:10.1021/acs.inorgchem.8b00447

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Synthesis of [Pt12(CO)20(dppm)2]2− and [Pt18(CO)30(dppm)3]2−
Heteroleptic Chini-type Platinum Clusters by the Oxidative
Oligomerization of [Pt6(CO)12(dppm)]2−
Beatrice Berti, Cristiana Cesari, Francesco Conte, Iacopo Ciabatti, Cristina Femoni,
Maria Carmela Iapalucci, Federico Vacca, and Stefano Zacchini*
̀
Dipartimento di Chimica Industriale “Toso Montanari”, Universita di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
S
* Supporting Information
ABSTRACT: The reactions of [Pt6(CO)12]2− with CH(PPh2)2 (dppm),
CH2C(PPh2)2 (P^P), and Fe(C5H4PPh2)2 (dppf) proceed via
nonredox substitution and result in the heteroleptic Chini-type clusters
[Pt6(CO)10(dppm)]2−, [Pt6(CO)10(P^P)]2−, and [Pt6(CO)10(dppf)]2−,
respectively. Conversely, the reactions of [Pt6(CO)12]2− with Ph2P-
(CH2)4PPh2 (dppb) and Ph2PCCPPh2 (dppa) can be described as
redox fragmentation that afford the neutral complexes Pt(dppb)2,
Pt2(CO)2(dppa)3, and Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2. The
oxidation of [Pt6(CO)10(dppm)]2− results in its oligomerization to yield the larger heteroleptic Chini-type clusters
[Pt12(CO)20(dppm)2]2−, [Pt18(CO)30(dppm)3]2−, and [Pt24(CO)40(dppm)4]2− (for the latter there is only IR spectroscopic
evidence). All the clusters were characterized by means of IR and 31P NMR spectroscopies and electrospray ionization mass
spectrometry. Moreover, the crystal structures of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN, [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·
2dmf, [NEt4]2[Pt12(CO)20(dppm)2]·4dmf, [NEt4]2[Pt6(CO)10(dppf)]·2CH3CN, Pt2(CO)2(dppa)3·0.5CH3CN,
Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2·2thf, and Pt(dppb)2 were determined by single-crystal diffraction (dmf =
dimethylformamide; thf = tetrahydrofuran).
1. INTRODUCTION
(a) The nonredox substitution is favored by lower nuclearity
clusters, whereas larger clusters usually prefer redox
fragmentation. This may be explained on the basis of the
fact that the intertriangular bonding of Chini clusters is
mainly based on the negative charge of the clusters. Since
the charge (2−) is constant, the intertriangular Pt−Pt
bonds become weaker as the nuclearity of the cluster
increases.15−19 Thus, the nonredox substitution is
favored over redox fragmentation in the order
CO substitution is a general strategy to functionalize metal
carbonyl clusters.1−10 Nonetheless, a competition among CO
substitution with retention of the cluster structure, cluster
rearrangement, and/or cluster breakdown is generally ob-
served.1−10 This point has been well-exemplified by the studies
recently performed by our group on the reactions of
[Pt3n(CO)6n]2− (n = 2−5) Chini clusters with phosphine
ligands.11−14 These homoleptic Chini clusters are composed of
stacks of [Pt3(μ-CO)3(CO)3] triangular units arranged in
trigonal prismatic structures.15,16 Their redox chemistry has
been extensively investigated,17−19 and their employment as
conductive materials,20−22 catalysts,23−25 precursors of plati-
num nanoclusters and bimetallic clusters,26−31 and platinum
nanoparticles and nanowires32−38 has been studied.
A competition between the nonredox substitution with
retention of the nuclearity of the cluster and the redox
fragmentation is observed in the case of the reactions of
homoleptic Chini clusters with monodenate and bidentate
phosphines (Figure 1).11−14 The nonredox substitution results
in [Pt3n(CO)6n−x(L)x]2− (n = 1−5; x = 1 − n) heteroleptic
analogues of anionic Chini clusters. Conversely, redox
[Pt6(CO)12]2− > [Pt9(CO)18]2− > [Pt12(CO)24]2−
>
[Pt15(CO)30]2−.
(b) Monodentate (PPh3 and 1,3,5-triaza-7-phosphaadaman-
tane (PTA))12,14 and flexible bidentate phosphines
(Ph2PCH2CH2PPh2 (dppe); R-Ph2PCH(Me)CH2PPh2
(R-dppp))11 favor the nonredox substitution, whereas
more rigid bidentate ligands (CH2C(PPh2)2 (P^P);
CH2(PPh2)2 (dppm); o-C6H4(PPh2)2 (dppBz)) often
result in redox fragmentation affording neutral Pt
complexes.13
(c) The nonredox substitution is favored by the use of
stoichiometric amounts of the ligands, whereas an excess
of phosphine leads to redox fragmentation. Thus, by
employing stoichiometric amounts of PPh3, PTA, dppe,
and R-dppp, heteroleptic anionic Chini-type clusters can
fragmentation (elimination) reactions lead to lower nuclearity
homoleptic species [Pt3(n−1)(CO)6(n−1)
2−
]
as well as widely
varied neutral complexes Ptx(CO)y(L)z. The outcome of these
reactions depends on (a) the nuclearity of the cluster, (b) the
nature of the ligand, and (c) the stoichiometry of the reaction.
Received: February 19, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b00447
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. Some examples of the reactions of the [Pt12(CO)24]2− homoleptic anionic Chini cluster with phosphines: (a) nonredox substitution and
(b) redox fragmentation.
Figure 2. (a) Molecular structure of [Pt6(CO)10(dppm)]2− and (b) its Pt−P core (Pt, purple; P, orange; C, gray, O, red). H atoms were omitted for
clarity.
cases retained with local deformations; in some cases an
inversion of the cage from trigonal prismatic to octahedral
occurs, or eventually the reciprocal rotation of two trigonal
prismatic units with the loss of a Pt−Pt contact is observed.
For the purposes of this paper, it is remarkable that the
structure of [Pt12(CO)20(dppe)2]2− may be viewed as a dimer
composed of two monoanionic [Pt6(CO)10(dppe)]− units
joined by two Pt−Pt interactions (Figure 1).11 This
resemblance is not only formal, since [Pt12(CO)20(dppe)2]2−
can be obtained by the oxidation of [Pt6(CO)10(dppe)]2−.
Herein, we report a detailed study of the reactions of
[Pt6(CO)12]2− with widely varied bidentate phosphines, that is,
dppm, P^P, Fe(C5H4PPh2)2 (dppf), Ph2P(CH2)4PPh2 (dppb),
and Ph2PCCPPh2 (dppa). Some of these ligands (dppm,
P^P) have been previously employed in the reactions with
be obtained through nonredox substitution. Conversely,
when used in excess, redox fragmentation occurs
affording mixtures of lower nuclearity anionic clusters
and zerovalent species such as Pt3(CO)3(PPh3),
Pt6(CO)6(dppe)3, Pt4(CO)4(dppe)2, and Pt-
(dppe)2.11−14
The heteroleptic Chini clusters so far structurally charac-
terized are [Pt6(CO)10(PPh3)2]2−, [Pt6(CO)10(dppe)]2−,
[Pt9(CO)16(PPh3)2]2−, [Pt9(CO)16(dppe)]2−, [Pt9(CO)16(R-
dppp)]2−, [Pt12(CO)22(PPh3)2]2−, [Pt12(CO)20(PTA)4]2−,
[Pt12(CO)20(dppe)2]2−, and [Pt15(CO)30(PTA)5]2−.11−14 Sev-
eral other species have been spectroscopically identified but not
structurally characterized. In all these clusters, the triangular Pt3
units present in the parent homoleptic species are preserved,
whereas their overall trigonal prismatic structures are in some
B
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Table 1. Main Bond Distances of [Pt6(CO)10(dppm)]2− and [Pt6(CO)10(dppf)]2− Compared to [Pt6(CO)12]2−,
[Pt6(CO)10(dppe)]2−, and [Pt6(CO)10(PPh3)2]2−
a
Pt−Pt intratriangular
Pt−Pt intertriangular
Pt−P
structure
[Pt6(CO)10(dppm)]2−
[Pt6(CO)10(dppf)]2−
2.6336(12)−2.6634(10) average
2.9715(14)−3.0202(14) average
2.228(2)−2.238(2) average
trigonal prismatic
g
2.646(3)
2.991(2)
2.233(3)
2.6533(4)−2.6703(4) average
2.9659(4)−3.3550(4) average
2.2525(17)−2.2531(17) average
distorted trigonal
prismatic
h
2.6620(10)
3.0962(7)
2.253(2)
b
[Pt6(CO)10(dppe)]2−
[Pt6(CO)10(dppe)]2−
2.6513(3)−2.6839(3) average
2.9839(4)−3.1797(3) average
2.2456(13)
2.251(4)
2.240(3)
2.247(3)
distorted octahedral
distorted octahedral
distorted octahedral
distorted octahedral
I
2.6625(9)
3.1285(8)
c
2.6573(8)−2.6758(8) average
3.0437(10)−3.359(2) average
j
2.6644(14)
3.202(2)
d
e
k
[Pt6(CO)10(PPh3)2]2−
[Pt6(CO)10(PPh3)2]2−
2.6558(6)−2.6743(6) average
3.0353(6)
2.6644(10)
2.6584(6)−2.6787(6) average
3.1380(6)−3.2079(6) average
l
2.6694(10)
3.1729(8)
f
[Pt6(CO)12]2−
2.644(7)−2.659(3) average
3.026(16)−3.049(17) average
trigonal prismatic
2.653(10)
3.03(3)
a
b
c
Only Pt−Pt interactions less than or equal to 3.36 Å were included. As found in [NMe4]2[Pt6(CO)10(dppe)]. From ref 11. As found in
d
e
[NEt4]2[Pt6(CO)10(dppe)]. From ref 11. As found in [NBu4]2[Pt6(CO)10(PPh3)2]. From ref 12. As found in [NBu4]2[Pt6(CO)10(PPh3)2]·2thf.
f
g
h
From ref 12. From ref 15. The shortest diagonal intertriangular Pt−Pt contacts are 3.628(5) and 3.411(2) Å. The shortest diagonal intertriangular
I
Pt−Pt contacts are 3.625 (3), 3.722(3), and 3.762(3) Å. Four intertriangular Pt−Pt bonding contacts are present. The remaining two Pt−Pt
j
k
contacts are 3.526(2) Å. Six intertriangular Pt−Pt bonding contacts are present. Three sets of intertriangular Pt−Pt contacts are present:
l
3.0353(6), 3.3581(6), 3.5070(6) Å. Three sets of intertriangular Pt−Pt contacts are present: 3.1380(6), 3.2079(6), 3.4310(6) Å.
higher nuclearity Chini clusters and resulted in redox
fragmentation.13 Thus, we focused our attention on
[Pt6(CO)12]2−, which is more prone to nonredox substitution.
Indeed, the heteroleptic clusters [Pt6(CO)10(dppm)]2−,
[Pt6(CO)10(dppf)]2−, and [Pt6(CO)10(P^P)]2− were obtained
and will be described in the following sections. Then, the
oxidative oligomerization of [Pt6(CO)10(dppm)]2− affording
[Pt12(CO)20(dppm)2]2− and [Pt18(CO)30(dppm)3]2− (as well
as IR spectroscopic evidence of [Pt24(CO)40(dppm)4]2−) will
be presented.
Conversely, in the case of the more flexible dppe and the
monodentate PPh3 ligands, the [Pt6(CO)10(dppe)]2− and
[Pt6(CO)10(PPh3)2]2− preferred to adopt distorted octahedral
structures, probably to release steric repulsion. Moreover, it
must be noticed that both [Pt6(CO)10(dppe)]2− and
[Pt6(CO)10(PPh3)2]2− were crystallized into two different
salts, showing some slight differences in their octahedral
cores due to different packing effects. This points out that the
intertriangular bonds in Chini clusters are rather weak and
easily deformed by small changes in the van der Waals forces
within the crystals or by variations of the properties of the
ancillary ligands.
2. RESULTS AND DISCUSSION
2.1. Synthesis and Structure of [Pt6(CO)10(dppm)]2−.
The reaction of [Pt6(CO)12]2− (νCO 2000(vs), 1800(s) cm−1)
with a slight excess of dppm in CH3CN afforded the new
dianionic cluster [Pt6(CO)10(dppm)]2− (νCO 2006(s),
1980(vs), 1780(s), 1770(s) cm−1) in high yields (eq 1). The
reaction was monitored by IR spectroscopy (Figure S.1), and
the reaction was completed after ca. 2 h. The IR spectrum of
[Pt6(CO)10(dppm)]2− in the νCO region was very similar to
that previously reported for the related anion
[Pt6(CO)10(dppe)]2−.11
Crystals of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN displayed
νCO bands in the IR spectrum recorded as mineral oil mull at
2000(s), 1980(s), 1949(s), 1778(m), 1756(m), and 1750(m)
cm−1, in accord to the solution spectrum. Their ESI-MS
spectrum in CH3CN solution (Figure S.2a) showed a main
peak in the negative mode at m/z 917, corresponding to the
molecular ion [Pt6(CO)10(dppm)]2−. Interestingly, a minor
peak was observed at m/z 1833, which was assigned to
[Pt12(CO)20(dppm)2]2−. This was likely to be formed by the
oxidation of [Pt6(CO)10(dppm)]2− operated by air (see next
section for details). This was confirmed by letting some air
enter into the sample and repeating the analysis. As a
consequence, the peak at m/z 1833 considerably increased
(Figure S.2b).
[Pt6(CO)12]2− + dppm → [Pt6(CO)10(dppm)]2− + 2CO
(1)
The new cluster [Pt6(CO)10(dppm)]2− was characterized by
means of electrospray ionization mass spectrometry (ESI-MS)
and IR and 31P NMR spectroscopies, and its molecular
structure was determined via single-crystal X-ray diffractometry
as the [NEt4]2[Pt6(CO)10(dppm)]·CH3CN salt (Figure 2 and
Table 1). The structure of the heteroleptic anion
[Pt6(CO)10(dppm)]2− can be formally derived from that of
[Pt6(CO)12]2−, after replacing two terminal CO ligands, one
per Pt3-triangular unit, with dppm. The Pt6-cage of the cluster
retained the trigonal prismatic structure of the parent
h o m o l e p t i c C h i n i c l u s t e r , 1 , 2 w h e r e a s b o t h
[Pt6(CO)10(dppe)]2− and [Pt6(CO)10(PPh3)2]2− displayed
distorted octahedral structures.11,12 Probably, in the case of
[Pt6(CO)10(dppm)]2−, the presence of a single −CH2− group
in the dppm ligand hampered the rotation of the Pt3-triangle.
In keeping with the solid-state structure, the 31P{1H} NMR
spectrum of [Pt6(CO)10(dppm)]2− recorded in CD3CN at 298
K displayed a resonance centered at δP 51.0 ppm, in view of the
equivalence of the two P atoms of the unique dppm ligand
1
(Figure 3 and Table 2). This resonance showed a large JPtP
coupling to one Pt atom (4960 Hz) as well as a second-order
2JPP (88 Hz).39−45 In addition, two very different 2JPtP coupling
constants were observed; the larger one (602 Hz) corre-
sponded to two equivalent Pt atoms, and the smaller one (15
Hz) corresponded to a single Pt atom. On the basis of the
2
crystal structure, the larger JPtP values correspond to coupling
to the two Pt atoms of the triangle to which the P atom is
directly bonded, whereas the smaller 2JPtP values correspond to
intertriangle coupling to the Pt atom bonded to the other P of
C
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PPh3. Conversely, redox fragmentation was observed, with
concomitant formation of lower-nuclearity anionic Chini
clusters and neutral species such as Pt6(CO)6(dppm)3. For
instance, the reaction of [Pt12(CO)24]2− with 2−3 equiv of
dppm afforded [Pt9(CO)18]2− and Pt6(CO)6(dppm)3.13
Similarly, the reaction of [Pt9(CO)18]2− with a slight excess
of dppm resulted in a mixture of [Pt6(CO)12]2−
,
[Pt6(CO)10(dppm)]2−, and Pt6(CO)6(dppm)3. Thus, the
heteroleptic clusters [Pt3n(CO)6n−2(dppm)]2− (n = 3−5)
could not be directly obtained by substitution, but they must
be synthesized by means of redox condensations. For instance,
[Pt9(CO)16(dppm)]2− was conveniently obtained by reacting
[Pt12(CO)20(dppm)2]2− (see below for its synthesis) and
[Pt6(CO)12]2− in a 1:1 ratio in accord to reaction (2).
Conversely, the redox condensation of equimolar amounts of
[Pt6(CO)10(dppm)]2− and [Pt12(CO)24]2− resulted in a 1:1
mixture of [Pt9(CO)16(dppm)]2− and [Pt9(CO)18]2−, as
depicted in reaction (3). The nature of [Pt9(CO)16(dppm)]2−
was established on the basis of its IR and 31P NMR spectra (see
experimental and Figure S.3), which were very similar to those
previously reported for the related [Pt9(CO)16(dppe)]2− anion.
[Pt12(CO)20(dppm)2]2− + [Pt6(CO)12]2−
→ 2[Pt9(CO)16(dppm)]2−
(2)
[Pt6(CO)10(dppm)]2− + [Pt12(CO)24]2−
→ [Pt9(CO)16(dppm)]2− + [Pt9(CO)18]2−
(3)
Figure 3. 31P{1H} NMR spectrum of [Pt6(CO)10(dppm)]2− in
CD3CN at 298 K: (a) experimental; (b) simulated. δ (ppm): 51.0
2.2. Oxidation of [Pt6(CO)10(dppm)]2−: Synthesis of
[Pt12(CO)20(dppm)2]2− and [Pt18(CO)30(dppm)3]2−. As
reported in the previous section, [Pt6(CO)10(dppm)]2− was
readily oxidized by air resulting in the formation of
[Pt12(CO)20(dppm)2]2−. Alternatively, the same reaction was
performed by employing HBF4·Et2O as an oxidant, in accord to
reaction (4). The reaction was reversed by adding [NBu4]-
[OH] under CO to a solution of [Pt12(CO)20(dppm)2]2− in
dimethylformamide (dmf), in agreement with eq 5.
(1JPtP = 4960 Hz (1Pt), 2JPtP = 602 Hz (2Pt), and 15 Hz (1Pt), 2JPP
=
88 Hz).
the same dppm ligand. The assignment of the 31P{1H} NMR
spectrum was fully corroborated by simulation with gNMR
5.0.6.0.46 A similar coupling pattern was observed in the case of
[Pt6(CO)10(dppe)]2−. The most significant difference was the
fact that, because of the presence of two CH2 groups in the
3
backbone of dppe, the JPP coupling constant of
2[Pt6(CO)10(dppm)]2− + 2H+
→ [Pt12(CO)20(dppm)2]2− + H2
[Pt6(CO)10(dppe)]2− was too small to be resolved. This
suggested that the P−P coupling observed in the case of
[Pt6(CO)10(dppm)]2− (2JPP = 88 Hz) occurred through the P−
CH2−P backbone of the ligand and not the metal skeleton of
the cluster.
(4)
[Pt12(CO)20(dppm)2]2− + 2OH− + CO
→ 2[Pt6(CO)10(dppm)]2− + CO2 + H2O
The reaction of higher-nuclearity Chini clusters
[Pt3n(CO)6n]2− (n = 3−5) with dppm did not afford the
expected isonuclear heteroleptic anionic clusters, as previously
observed in the case of analogous reactions with dppe and
(5)
It is well-known that Chini clusters are oxidized by strong
acids by means of the H+/H2 redox couple and reduced by CO
Table 2. 31P NMR Data of [Pt6(CO)10(dppm)]2−, [Pt12(CO)20(dppm)2]2−, [Pt18(CO)30(dppm)3]2−, [Pt9(CO)16(dppm)]2−,
[Pt6(CO)10(P^P)]2−, [Pt6(CO)10(dppf)]2−
δP
1JPtP
2JPtP (intratriangle)
2JPtP (intertriangle)
2JPP
[Pt6(CO)10(dppm)]2−
[Pt12(CO)20(dppm)2]2−
51.0
46.2
38.7
46.1
43.8
36.2
47.3
39.0
62.2
49.3
4960
4962
5144
5105
4952
5095
4941
5047
5059
5247
602
546
626
548
540
601
562
697
453
543
15
88
83
83
[Pt18(CO)30(dppm)3]2−
15
17
70
78
78
[Pt9(CO)16(dppm)]2−
85
85
[Pt6(CO)10(P^P)]2−
[Pt6(CO)10(dppf)]2−
120
D
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Scheme 1. Proposed Mechanism for the Oxidation of [Pt6(CO)10(dppm)]2− to [Pt12(CO)20(dppm)2]2−
Figure 4. Molecular structure of (a) [Pt12(CO)20(dppm)2]2− and (b) its Pt−P core. (Pt, purple; P, orange; C, gray, O, red). H atoms were omitted
for clarity.
Table 3. Main Bond Distances of [Pt12(CO)20(dppm)2]2− Compared to [Pt12(CO)24]2−, [Pt12(CO)20(dppe)2]2−, and
[Pt12(CO)20(PTA)4]2−
a
Pt−Pt intratriangular
Pt−Pt intertriangular
Pt−P
b
c
[Pt12(CO)20(dppm)2]2−
[Pt12(CO)20(dppm)2]2−
2.6435(6)−2.6902(6) average 2.6630(15)
2.626(4)−2.649(4) average 2.640(9)
2.6487(16)−2.689(2) average 2.660(8)
2.6520(8)−2.6795(7) average 2.669(2)
2.6513(5)−2.6780(5) average 2.6671(12)
2.6539(9)−2.6756(9) average 2.666(2)
2.6587(5)−2.6707(5) average 2.6656(12)
2.9798(6)−3.0741(6) average 3.0135(13)
2.986(5)−3.026(5) average 3.011(10)
2.9427(17)−3.2178(18) average 3.091(7)
2.9765(8)−3.1939(8) average 3.068(2)
2.9728(5)−3.2075(5) average 3.0632(12)
3.0184(9)−3.2067(11) average 3.086(2)
2.241(3)−2.263(3) average 2.252(4)
2.239(16)−2.262(14) average 2.25(2)
2.222(9)−2.276(9) average 2.24(2)
2.254(4)−2.272(4) average 2.263(6)
2.251(2)−2.270(2) average 2.260(3)
2.281(4)
d
[Pt12(CO)20(PTA)4]2−
[Pt12(CO)20(dppe)2]2−
[Pt12(CO)20(dppe)2]2−
[Pt12(CO)22(PPh3)2]2−
e
f
g
h
[Pt12(CO)24]2−
3.0465(5)−3.0597(5) average 3.0535(12)
b
a
c
Only Pt−Pt interactions less than or equal to 3.36 Å were included. As found in [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf. As found in
[NEt4]2[Pt12(CO)20(dppm)2]·4dmf. From ref 14. As found in [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN. From ref 11. As found in
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN. From ref 11. From ref 12. From ref 15.
d
e
f
g
h
in the presence of a base.15−19 Nonetheless, the direct oxidation
of [Pt6(CO)12]2− afforded [Pt9(CO)18]2− and not
[Pt12(CO)24]2−. In addition, we previously observed that,
under the same experimental conditions, the oxidation of
[Pt6(CO)10(dppe)]2− afforded [Pt12(CO)20(dppe)2]2−.11 Thus,
it is likely that, in the presence of a bidentate ligand, the
oxidation of [Pt6(CO)10(LL)]2− (LL = dppm, dppe) proceeds
through a [Pt6(CO)10(LL)]− radical monoanion, which
immediately dimerizes resulting in [Pt12(CO)20(LL)2]2−
(Scheme 1).
structure was determined through single-crystal X-ray crystal-
lography as the [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf
and [NEt4]2[Pt12(CO)20(dppm)2]·4dmf solvated salts, which
contained the same cluster anion with very similar geometries
and bonding parameters (Figure 4 and Table 3). The structure
and spectroscopic data of [Pt12(CO)20(dppm)2]2− are very
s i m i l a r t o t h o s e p r e v i o u s l y r e p o r t e d f o r
[Pt12(CO)20(dppe)2]2−.11 The cluster may be viewed as
composed of two trigonal prismatic [Pt6(CO)10(dppm)] units
rotated by 180° and joined by the two symmetry-equivalent
Pt−Pt bonds [2.9798(6) and 2.986(5) Å, for the two salts,
respectively]. As a consequence, there is one μ-CO ligand per
[Pt6(CO)10(dppm)] unit that weakly interacts with one Pt
The new compound [Pt12(CO)20(dppm)2]2− was fully
characterized through IR (Figure S.4), ESI-MS (Figure S.5),
and 31P NMR spectroscopy (Figure S.6). Its molecular
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Scheme 2. Oxidation of [Pt6(CO)10(dppm)]2− Resulting in [Pt12(CO)20(dppm)2]2− and [Pt18(CO)30(dppm)3]2− (ox = H+ and/
or air; red = CO/OH−)
Figure 5. Molecular structure of (a) [Pt6(CO)10(dppf)]2− and (b) its Pt−P core. (Pt, purple; P, orange; C, gray, O, red; Fe, blue). H atoms were
omitted for clarity.
atom of the second [Pt6(CO)10(dppm)] unit [Pt···C(O)
3.226(12) and 3.285(18) Å, for the two salts, respectively].
[Pt12(CO)20(dppm)2]2− displayed νCO bands in the IR
spectrum recorded as mineral oil mull at 2013(vs), 1856(m),
1819(s), and 1810(s) cm−1 and at 2020(vs), 1851(m), 1829(s),
and 1808(m) cm−1 in CH3CN solution. The ESI-MS spectrum
of the same solution displayed, in the negative mode, the
expected peak of the molecular ion at m/z 1834. The 31P NMR
spectrum of [Pt12(CO)20(dppm)2]2− (Figure S.6) was fully
consistent with its solid-state structure and displayed the
presence of two nonequivalent P atoms in a 1:1 ratio. Thus, it
displayed two resonances at δP 46.2 and 38.7 ppm. Both
is reversibly reduced to [Pt12(CO)20(dppm)2]2− by reaction
with [NBu4][OH] under CO atmosphere in dmf. The nature of
[Pt18(CO)30(dppm)3]2− was fully corroborated through ESI-
MS (Figure S.8) and 31P NMR spectroscopy (Figures S.9 and
S.10). Unfortunately, all the attempts to obtain single crystals of
[Pt18(CO)30(dppm)3]2− suitable for X-ray crystallography
failed. In particular, the IR spectrum of [Pt18(CO)30(dppm)3]2−
displayed νCO bands at 2032(vs), 1871(m), 1856(s), 1843(m),
and 1821(m) cm−1, considerably moved toward higher
wavenumbers compared to the parent [Pt12(CO)20(dppm)2]2−.
Its nature was further corroborated by the presence of a main
peak in the ESI-MS spectrum (negative mode) at m/z 2752
attributable to the [Pt18(CO)30(dppm)3]2− molecular ion.
Moreover, the 31P{1H} NMR spectrum recorded in dmf-d7 at
298 K displayed three resonances attributable to the three
nonequivalent types of P atoms present within the structure,
each type consisting of two P atoms. The resulting spectrum
was rather complex (Figures S.9 and S.10), in view of the
presence of different isotopomers, second-order effects, and the
rich P−Pt and P−P coupling patterns, and its quality was not
very high due to the reduced solubility of this cluster compared
1
resonances showed JPtP coupling to one Pt atom (4962 and
2
5144 Hz, respectively), a JPtP coupling constant to two Pt
2
atoms (546 and 626 Hz, respectively), and a smaller JPP (83
Hz).
The reaction of [Pt12(CO)20(dppm)2]2− in dmf with a slight
excess of HBF4·Et2O in the presence of air afforded
[Pt18(CO)30(dppm)3]2− (Scheme 2) as indicated by the shift
of the νCO bands in the IR spectrum toward higher
wavenumbers (Figure S.7). In turn, [Pt18(CO)30(dppm)3]2−
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Figure 6. Comparison of the Pt6 metal cores of (a) [Pt6(CO)12]2−, (b) [Pt6(CO)10(dppm)]2−, (c) [Pt6(CO)10(dppf)]2−, (d, e)
[Pt6(CO)10(dppe)]2− (as found in [NMe4]2[Pt6(CO)10(dppe)] and [NEt4]2[Pt6(CO)10(dppe)]), and (f, g) [Pt6(CO)10(PPh3)2]2− (as found in
[NBu4]2[Pt6(CO)10(PPh3)2] and [NBu4]2[Pt6(CO)10(PPh3)2]·2thf). Only Pt−Pt contacts less than or equal to 3.36 Å were drawn as bonds.
to [Pt12(CO)20(dppm)2]2− and [Pt6(CO)10(dppm)]2−. The full
assignment and interpretation of the spectrum was possible
only by simulation with gNMR 5.0.6.0.46
with the proposed structures and comparable to those
p r ev i ou sl y r e po r te d f o r th e c lo s el y re la t ed
12
11
[Pt6(CO)10(PPh3)2]2−
,
[Pt6(CO)10(dppe)]2−
,
and
I t m u s t b e r e m a r k e d t h a t , b y r e a c t i n g
[Pt18(CO)30(dppm)3]2− in air with an excess of HBF4·Et2O,
there was evidence by IR spectroscopy of a new species
displaying νCO bands at 2045(vs), 1859(s), and 1826(m) cm−1.
The instability and low solubility of this species hampered its
isolation as well as its characterization by ESI-MS and/or 31P
NMR spectroscopy. Nonetheless, on the basis of its IR
spectrum in the νCO region (Figure S.7), we can tentatively
formulate it as [Pt24(CO)40(dppm)4]2−. These observations
indicated the possibility that heteroleptic Chini clusters
containing bidentate ligands may grow after oxidation by the
sequential addition of {Pt6(CO)10(LL)} units resulting in
[{Pt6(CO)10(LL)}x]2− (x = 1,2,3,4) molecular clusters. This
should be contrasted with the “normal” growing mode of
homoleptic Chini clusters, which involve the addition of
{Pt3(CO)6} triangular units.15−19
[Pt6 (CO)1 0 (dppm)]2 −
. In particular, all these
[Pt6(CO)10(LL)]2− clusters displayed two main IR absorptions
in the νCO region, one attributable to the terminal carbonyls
(LL = P^P 1979 cm−1, dppm 1979 cm−1,dppe 1976 cm−1, PPh3
1973 cm−1, dppf 1993 cm−1) and the other to the μ-CO ligands
(LL = P^P 1774 cm−1, dppm 1779 cm−1, dppe 1765 cm−1,
PPh3 1756 cm−1, dppf 1782 cm−1). It must be remarked that
the wavenumbers of all these νCO bands were very similar,
except the dppf derivative, which showed slightly higher
wavenumbers, probably because of the larger electron-with-
drawing character of the ferrocene backbone of the ligand.
In agreement with the equivalence of the two P atoms in the
[Pt6(CO)10(LL)]2− clusters, their 31P NMR spectra showed a
single multiplet with the typical coupling pattern of a single P
1
atom bonded to a Pt3 triangle: a larger JPtP coupling constant
2
(4960−5301 Hz) to a single Pt, and a smaller JPtP coupling
2.3. Reactivity of [Pt6(CO)12]2− with Other Bidentate
Phosphine Ligands. The reactions of [Pt6(CO)12]2− with
P^P and dppf were very similar to that described in Section 2.1
with dppm, resulting in the formation of [Pt6(CO)10(P^P)]2−
and [Pt6(CO)10(dppf)]2−, respectively. These compounds were
characterized through IR and 31P NMR spectroscopies (Figures
S.11 and S.12), and the molecular structure of
[Pt6(CO)10(dppf)]2− was determined by single-crystal X-ray
diffraction (Figure 5 and Table 1). The spectroscopic data of
[Pt6(CO)10(P^P)]2− and [Pt6(CO)10(dppf)]2− were consistent
constant (453−602 Hz) to two equivalent Pt atoms. Moreover,
in the case of [Pt6(CO)10(P^P)]2−, [Pt6(CO)10(dppm)]2−, and
2
[Pt6(CO)10(dppe)]2− a second and even smaller JPtP coupling
constant (17, 15, and 21 Hz, respectively) to one Pt was
observed. This is an intertriangular coupling made possible by
the bidentate nature of the P^P, dppm, and dppe ligands, which
keeps the two P-bonded Pt atoms in close proximity and in a
relative cis position [(P)Pt−Pt(P) 2.9715(14) Å for dppm,
3.0437(10) Å for dppe; the crystal structure of
[Pt6(CO)10(P^P)]2− was not determined]. Conversely, no
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Figure 7. Molecular structure of (a) Pt(dppb)2 and (b) a simplified view. (Pt, purple; P, orange; C, gray). H atoms were omitted for clarity.
2
intertriangular JPtP coupling was observed in the case of
monodentate ligands, that is, [Pt6(CO)10(PPh3)]2− (which
adopted a trans geometry of the PPh3 ligands), and
[Pt6(CO)10(dppf)]2− [(P)Pt−Pt(P) 3.3550(4) Å]. In addition,
Pt(dppb)2 showed a tetrahedral structure as expected for a
zero-valent Pt(LL)2 complex (Figure 7).47,48 Similarly,
Pt2(CO)2(dppa)3 is composed of two tetrahedral Pt(0) centers
bonded each to a CO ligand and three P atoms of three
different dppa ligands (Figure 8). The structure of
Pt2(CO)2(dppa)3 was similar to that reported for
Pt2(dppaO)2(dppa)3, where the two CO ligands were formally
replaced by two Ph2P−CC−P(O)Ph2 (dppaO) ligands.49
a
2JPP coupling constant was present in the spectra of
[Pt6(CO)10(P^P)]2− and [Pt6(CO)10(dppm)]2− (120 and 88
Hz, respectively) but not in the other clusters. As discussed in
Section 2.1, this coupling was likely to occur through the
backbone of the bidentate phosphine. Thus, it was larger in the
case of P^P, whose backbone contained a single sp2 carbon,
smaller in the case of dppm (a single sp3 carbon in the
backbone) and absent in the case of dppe (two sp3 carbons in
the backbone), as well as diphosphines with longer backbones.
From a structural point of view, the metal core of
[Pt6(CO)10(dppf)]2− can be described as a distorted Pt6
trigonal prism, which is intermediate between the almost
regular trigonal prismatic structures found in [Pt6(CO)12]2−
and [Pt6(CO)10(dppm)]2− and the distorted octahedral
structures displayed by [Pt6(CO)10(dppe)]2− and
[Pt6(CO)10(PPh3)2]2− (Figure 6). This observation further
points out that the intertriangular bonds in Chini clusters are
easily deformable and adapt themselves to the ancillary ligands
or even to packing effects.
The reactions of dppa and dppb with [Pt6(CO)12]2− were
rather different from those reported for dppm, P^P, and dppf
(as well as dppe, PPh3, and PTA, described in previous
papers),11−14 resulting in the formation of Pt2(CO)2(dppa)3
and Pt(dppb)2, respectively. As previously noticed, a competi-
tion between the nonredox substitution with retention of the
nuclearity and the redox fragmentation was observed in the case
of the reactions of [Pt3n(CO)6n]2− Chini clusters with
phosphine ligands.11−14 The nonredox substitution resulted in
heteroleptic analogues of anionic Chini clusters, whereas redox
Figure 8. Molecular structure of (a) Pt2(CO)2(dppa)3 and (b) its Pt−
P core. (Pt, purple; P, orange; C, gray, O, red). H atoms were omitted
for clarity.
Finally, the reaction of [Pt9(CO)18]2− with a slight excess of
dppa afforded [Pt6(CO)12]2− in mixture with the neutral
complex Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2 in poor yields.
Crystals of Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2·2thf (thf =
tetrahydrofuran) were obtained by slow diffusion of n-hexane
on the reaction mixture (Figure 9). This compound was not
soluble in any organic solvent, hampering any spectroscopic
characterization, except recording the IR spectrum in the solid
state as mineral oil mull (νCO 2023(vs), 2008(ms) cm−1). The
metal part of the structure was composed of two isolated Pt
atoms (formally zero valent) and two V-shaped Pt3 units. The
ligands present were six terminal carbonyls, two neutral dppa
ligands (each bonded to three different Pt atoms via the two P
atoms and the CC triple bond), two edge-bridging
phosphido [PPh2]− anions, and two [CCPPh2]− acetylides
(each bonded to four Pt atoms, via the phosphine group, the
CC triple bond and the terminal C atom). Thus, we can
fragmentation (elimination) reactions afforded lower-nuclearity
2−
homoleptic species [Pt3(n−1)(CO)6(n−1)
]
as well as widely
varied neutral complexes. In the case of PPh3, PTA, dppe, and
R-dppp ligands, it was possible to favor substitution over
fragmentation by employing stoichiometric amounts of the
ligands in the reactions with [Pt3n(CO)6n]2− (n = 2−4),
whereas redox fragmentation was observed in the case of the
higher nuclearity cluster [Pt15(CO)30]2−. In the cases of dppm,
P^P, and dppf, the nonredox substitution was observed in the
case of [Pt6(CO)12]2−, whereas redox fragmentation was
observed for all higher nuclearity Chini clusters. Finally, by
employing dppa, dppb, and dppBz13 redox fragmentation was
always observed, independently of the Chini cluster employed.
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Figure 9. Two views of the molecular structure of (a) Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2 and (b) simplified views with the same orientations.
(Pt, purple; P, orange; C, gray, O, red). H atoms were omitted for clarity.
assign a +2 charge to each of the two Pt3 units. The formation
of Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2 suggested that par-
tial cleavage of some dppa molecules occurred during the
reaction, resulting in [PPh2]− and [CCPPh2]− with
concomitant oxidation of the Pt-cluster.
unit after each oxidation step, instead of a Pt6 trigonal prismatic
unit.
From a mechanistic point of view, it is likely that the
oxidative oligomerization of [Pt6(CO)10(dppm)]2− proceeds
via [Pt6(CO)10(dppm)]− radical intermediates. Similarly,
monoanionic radicals of the type [Pt3n(CO)6n]− are sought to
be intermediates in the oxidation of homoleptic Chini
clusters.50 In this respect, a monoanionic [Pt3(μ-
CO)3(CNR)3]− (R = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) cluster
with terminal isocyanide ligands has been recently fully
charactreized.51
3. CONCLUSIONS
The stronger intertriangular Pt−Pt bonds of [Pt6(CO)12]2−
compared to larger Chini clusters favored the nonredox
substitution reactions over redox fragmentation. This allowed
the synthesis and characterization of the heteroleptic anionic
Chini clusters [Pt6(CO)10(dppm)]2−, [Pt6(CO)10(P^P)]2−, and
[Pt6(CO)10(dppf)]2−. Conversely, the reactions of dppm, P^P,
and dppf with [Pt3n(CO)6n]2− (n = 3−5) resulted in redox
fragmentation. Because of the steric properties of dppb (very
long backbone) and dppa (perfectly linear and rigid backbone),
their reactions with any Chini cluster resulted in redox
fragmentation.
4. EXPERIMENTAL SECTION
4.1. General Procedures. All reactions and sample manipulations
were performed using standard Schlenk techniques under nitrogen and
in dried solvents. All the reagents were commercial products (Aldrich)
of the highest purity available and used as received, except
[NEt4]2[Pt6(CO)12], which was prepared according to the literature.15
Analyses of C, H, and N were obtained with a Thermo Quest FlashEA
1112NC instrument. IR spectra were recorded on a PerkinElmer
Spectrum One interferometer in CaF2 cells. 31P{1H} NMR measure-
ments were performed on a Varian Mercury Plus 400 MHz
instrument. The phosphorus chemical shifts were referenced to
external H3PO4 (85% in D2O). 31P{1H} NMR spectra were simulated
with gNMR 5.0.6.0, using the experimental parameters (δ in ppm, J in
Hz).46 ESI mass spectra were recorded on a Waters Micromass
ZQ4000 instrument. Structure drawings were performed with
SCHAKAL99.52
4.2. Synthesis of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN. A portion
of dppm (0.310 g, 0.806 mmol) was added as a solid to a solution of
[NEt4]2[Pt6(CO)12] (0.700 g, 0.396 mmol) in CH3CN (15 mL). The
resulting mixture was stirred at room temperature for 2 h, and then,
the solvent was removed in vacuo. The residue was washed with
toluene (20 mL) and extracted with CH3CN (20 mL). Crystals of
[NEt4]2[Pt6(CO)10(dppm)]·CH3CN suitable for X-ray analyses were
[Pt6(CO)10(dppm)]2− was employed for the synthesis of
larger heteroleptic Chini clusters via redox condensation and
oxidative oligomerization. The latter process is rather
interesting, since it represents a new growing mode for
Chini-type clusters. This consists in the growth of
[Pt6(CO)10(dppm)]2− via the formal addition of one
[Pt6(CO)10(dppm)] fragment after each oxidation step and
2−
results in the formation of [Pt6(CO)10(dppm)]n (n = 2−4)
heteroleptic clusters. Further oxidation should afford infinite
molecular wires, as already found while studying the oxidation
of homoleptic Chini clusters.15−19 These reactions can be
reversed by the addition of reducing agents. Conversely, the
usual growing mode upon oxidation of homoleptic Chini
clusters consists in the addition of a single Pt3(CO)6 triangular
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2
obtained by layering n-hexane (4 mL) and diisopropyl ether (30 mL)
on the CH3CN solution (yield 0.550 g, 65% based on Pt).
C53H63N3O10P2Pt6 (2134.54): calcd. C 29.82, H 2.97, N 1.97;
62.2 (1JPtP = 5059 Hz (1Pt), JPtP = 453 Hz (2Pt) and 17 Hz (1Pt),
2JPP = 120 Hz).
4.7. Synthesis of [NEt4]2[Pt6(CO)10(dppf)]·2CH3CN. A portion
of dppf (0.695 g, 0.806 mmol) was added as a solid to a solution of
[NEt4]2[Pt6(CO)12] (0.700 g, 0.396 mmol) in CH3CN (15 mL). The
resulting mixture was stirred at room temperature for 2 h, and, then,
the solvent was removed in vacuo. The residue was washed with
toluene (20 mL) and extracted with CH3CN (20 mL). Crystals of
[NEt4]2[Pt6(CO)10(dppf)]·2CH3CN suitable for X-ray analyses were
obtained by layering n-hexane (4 mL) and diisopropyl ether (30 mL)
on the CH3CN solution (yield 0.558 g, 60% based on Pt).
C64H74FeN4O10P2Pt6 (2347.60): calcd. C 32.74, H 3.18, N 2.39;
found: C 32.92, H 2.89, N 2.51%. IR (CH3CN, 293 K) νCO: 2005(sh),
1993(vs), 1802(sh), 1782(s) cm−1. 31P{1H} NMR (CD3CN, 298 K) δ
found: C 30.05, H 3.11, N 1.74%. IR (mineral oil, 293 K) νCO
:
2000(s), 1980(s), 1949(s), 1778(m), 1756(m), 1750(m) cm−1. IR
(CH3CN, 293 K) νCO: 2006(s), 1980(vs), 1780(s), 1770(s) cm−1.
31P{1H} NMR (CD3CN, 298 K) δ (ppm): 51.0 (1JPtP = 4960 Hz
2
2
(1Pt), JPtP = 602 Hz (2Pt), and 15 Hz (1Pt), JPP = 88 Hz).
4.3. Synthesis of [NEt4]2[Pt9(CO)16(dppm)]. A solution of
[NEt4]2[Pt12(CO)20(dppm)2] (0.823 g, 0.198 mmol) in CH3CN (15
mL) was added to a solution of [NEt4]2[Pt6(CO)12] (0.350 g, 0.198
mmol) in CH3CN (15 mL). The resulting mixture was stirred at room
temperature for 2 h, and, then, the solvent was removed in vacuo. The
residue was washed with toluene (20 mL) and extracted with CH3CN
(20 mL). The resulting CH3CN solution was employed for the IR and
31P{1H} NMR analyses.
(ppm): 49.3 (1JPtP = 5247 Hz (1Pt), JPtP = 543 Hz (2Pt).
2
4.8. Synthesis of Pt(dppb)2. A portion of dppb (0.511 g, 1.200
mmol) was added as a solid to a solution of [NEt4]2[Pt6(CO)12]
(0.700 g, 0.396 mmol) in CH3CN (15 mL). The resulting mixture was
stirred at room temperature for 4 h affording a microcrystalline solid,
which was recovered by filtration. The solid was extracted with CH2Cl2
(10 mL). Crystals of Pt(dppb)2 suitable for X-ray analyses were
obtained by layering n-hexane (25 mL) on the CH2Cl2 solution (yield
0.489 g, 20% based on Pt).
IR (CH3CN, 293 K) νCO: 2018(vs), 1828(s) cm−1. 31P{1H} NMR
(CD3CN, 298 K) δ (ppm): 47.3 (1JPtP = 4941 Hz (1Pt), 2JPtP = 562 Hz
2
2
(2Pt), JPP = 85 Hz), 39.0 (1JPtP = 5047 Hz (1Pt), JPtP = 697 Hz
2
(2Pt), JPP = 85 Hz).
4.4. Synthesis of [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf. A
solution of HBF4·Et2O (80 μL, 0.588 mmol) was added dropwise to a
solution of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN (0.550 g, 0.258
mmol) in dmf (15 mL). The reaction was monitored by IR, and the
final product was precipitated by the addition of a saturated solution of
[NEt4]Br in H2O (40 mL). After filtration, the solid was washed with
H2O (40 mL), dried under reduced pressure, and extracted with dmf
(10 mL). Crystals of [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf
suitable for X-ray analyses were obtained by layering isopropanol (30
mL) on the dmf solution diluted with some CH3CN (5 mL) (yield
0.319 g, 59% based on Pt).
C56H56P4Pt (1047.97): calcd. C 64.17, H 5.39; found: C 64.44, H
5.61%. 31P{1H} NMR (CD2Cl2, 298 K) δ (ppm): 0.5 (1JPtP = 3750
Hz).
4.9. Synthesis of Pt2(CO)2(dppa)3·0.5CH3CN. A portion of dppa
(0.473 g, 1.200 mmol) was added as a solid to a solution of
[NEt4]2[Pt6(CO)12] (0.700 g, 0.396 mmol) in CH3CN (15 mL). The
resulting mixture was stirred at room temperature for 4 h affording a
microcrystalline solid, which was recovered by filtration. The solid was
extracted with CH2Cl2 (10 mL). Crystals of Pt2(CO)2(dppa)3·
0.5CH3CN suitable for X-ray analyses were obtained by layering n-
hexane (2 mL) and diisopropyl ether (30 mL) on the crude CH3CN
solution before any workup (yield 0.392 g, 20% based on Pt).
C81H61.5N0.5O2P6Pt2 (1649.80): calcd. C 58.97, H 3.76, N 0.42;
Crystals of [NEt4]2[Pt12(CO)20(dppm)2]·4dmf can be obtained by
following an analogous procedure, without the final addition of
CH3CN.
C96H104N6O22P4Pt12 (4158.81): calcd. C 27.73, H 2.52, N 2.02;
found: C 27.51, H 2.89, N 1.91%. IR (mineral oil, 293 K) νCO
:
:
found: C 59.19, H 3.51, N 0.62%. IR (mineral oil, 293 K) νCO
:
2013(vs), 1856(m), 1819(s), 1810(s) cm−1. IR (CH3CN, 293 K) νCO
1928(vs) cm−1. IR (CH2Cl2, 293 K) νCO: 1930(vs) cm−1. IR (toluene,
293 K) νCO: 1935(vs) cm−1. 31P{1H} NMR (CD2Cl2, 298 K) δ (ppm):
−19.9 (1JPtP = 3391 Hz).
2020(vs), 1851(m), 1829(s), 1808(m) cm−1. 31P{1H} NMR (dmf-d7,
2
298 K) δ (ppm): 46.2 (1JPtP = 4962 Hz (1Pt), JPtP = 546 Hz (2Pt),
2JPP = 83 Hz), 38.7 (1JPtP = 5144 Hz (1Pt), 2JPtP = 626 Hz (2Pt), 2JPP
=
4.10. Synthesis of Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2·2thf. A
portion of dppa (0.473 g, 1.200 mmol) was added as a solid to a
solution of [NEt4]2[Pt9(CO)18] (0.895 g, 0.396 mmol) in thf (15 mL).
The resulting mixture was stirred at room temperature for 4 h and
layered with n-hexane (15 mL). After slow diffusion of the solvent, a
few crystals of Pt8(CO)6(PPh2)2(CCPPh2)2(dppa)2·2thf suitable for
X-ray analyses were obtained (yield 0.077 g, 5% based on Pt). These
crystals are completely not soluble in any organic solvent.
83 Hz).
4.5. Synthesis of [NEt4]2[Pt18(CO)30(dppm)3]. A solution of
HBF4·Et2O (20 μL, 0.147 mmol) was added dropwise to a solution of
[NEt4]2[Pt12(CO)20(dppm)2]·4dmf (0.258 g, 0.061 mmol) in dmf (10
mL). The reaction was monitored by IR, and the final product was
precipitated by the addition of a saturated solution of [NEt4]Br in
H2O (40 mL). After filtration, the solid was washed with H2O (40
mL), dried under reduced pressure, and extracted with dmf (10 mL).
The resulting dmf solution was employed for the IR and 31P{1H}
N M R a n a l y s e s . A l l a t t e m p t s t o c r y s t a l l i z e
[NEt4]2[Pt18(CO)30(dppm)3] failed, affording crystals of
[NEt4]2[Pt12(CO)20(dppm)2] instead.
C118H96O8P8Pt8 (3450.42): calcd. C 41.07, H 2.80; found: C 41.31,
H 2.68%. IR (mineral oil, 293 K) νCO: 2023(vs), 2008(ms) cm−1.
4.11. X-ray Crystallographic Study. Crystal data and collection
d e t a i l s f o r [ N E t 4 ] 2 [ P t 6 ( C O ) 1 0 ( d p p m ) ] · C H 3 C N ,
[ N E t 4 ] 2 [ P t 1 2 ( C O ) 2 0 ( d p p m ) 2 ] · 2 C H 3 C N · 2 d m f ,
IR (dmf, 293 K) νCO: 2032(vs), 1871(m), 1856(s), 1843(m),
[NEt4]2[Pt12(CO)20(dppm)2]·4dmf, [NEt4]2[Pt6(CO)10(dppf)]·
2CH3CN, Pt2(CO)2(dppa)3·0.5CH3CN, Pt8(CO)6(PPh2)2(C
CPPh2)2(dppa)2·2thf, and Pt(dppb)2 are reported in Table 1. The
diffraction experiments were performed on a Bruker APEX II
diffractometer equipped with a PHOTON100 detector using Mo Kα
radiation. Data were corrected for Lorentz polarization and absorption
effects (empirical absorption correction SADABS).53 Structures were
solved by direct methods and refined by full-matrix least-squares based
on all data using F2.54 Hydrogen atoms were fixed at calculated
positions and refined by a riding model. All non-hydrogen atoms were
refined with anisotropic displacement parameters, unless otherwise
stated.
1821(m) cm−1. 31P{1H} NMR (dmf-d7, 298 K) δ (ppm): 46.1 (1JPtP
=
5105 Hz (1Pt), 2JPtP = 548 Hz (2Pt) and 15 Hz (1Pt), 2JPP = 70 Hz),
43.8 (1JPtP = 4952 Hz (1Pt), 2JPtP = 540 Hz (2Pt), 2JPP = 78 Hz), 36.2
2
2
(1JPtP = 5095 Hz (1Pt), JPtP = 601 Hz (2Pt), JPP = 78 Hz).
4.6. Synthesis of [NEt4]2[Pt6(CO)10(P^P)]. P^P (0.319 g, 0.806
mmol) was added as a solid to a solution of [NEt4]2[Pt6(CO)12]
(0.700 g, 0.396 mmol) in CH3CN (15 mL). The resulting mixture was
stirred at room temperature for 2 h, and, then, the solvent was
removed in vacuo. The residue was washed with toluene (20 mL) and
extracted with CH3CN (20 mL). An amorphous powder of
[NEt4]2[Pt6(CO)10(P^P)] was obtained after CH3CN was removed
under reduced pressure from the filtrate (yield 0.517 g, 62% based on
Pt).
[NEt4]2[Pt6(CO)10(dppm)]·CH3CN. The asymmetric unit of the unit
cell contains one cluster anion, two [NEt4]+ cations, and one CH3CN
molecule (all located on general positions). All the C, O, and N atoms
were restrained to isotropic behavior (ISOR command in SHELXL,
s.u. 0.01). Similar U restraints were applied to the dppm ligands, the
C52H62N2O10P2Pt6 (2107.47): calcd. C 29.64, H 2.97, N 1.33;
found: C 29.38, H 3.12, N 1.14. IR (CH3CN, 293 K) νCO: 2006(s),
1979(vs), 1774(s) cm−1. 31P{1H} NMR (CD3CN, 298 K) δ (ppm):
J
DOI: 10.1021/acs.inorgchem.8b00447
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
[NEt4]+ cations, and the CH3CN molecule (SIMU command in
SHELXL, s.u. 0.02). All the aromatic rings were constrained to fit
regular hexagons (AFIX 66 command in SHELXL).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: stefano.zacchini@unibo.it. Phone: +39 051 2093711.
Web: https://www.unibo.it/sitoweb/stefano.zacchini/en.
[NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf. The asymmetric unit of
the unit cell contains half of a cluster anion (located on an inversion
center), one [NEt4]+ cation, one CH3CN, and one dmf molecule
(located on general positions). All the aromatic rings were constrained
to fit regular hexagons (AFIX 66 command in SHELXL). Similar U
restraints were applied to the [NEt4]+ cation and the dmf and CH3CN
molecules (SIMU command in SHELXL, s.u. 0.02). Restraints to bond
distances were applied as follows (s.u. 0.02): 1.47 Å for C−N and 1.53
Å for C−C in [NEt4]+.
ORCID
Cristina Femoni: 0000-0003-4317-6543
Stefano Zacchini: 0000-0003-0739-0518
Notes
The authors declare no competing financial interest.
[NEt4]2[Pt12(CO)20(dppm)2]·4dmf. The asymmetric unit of the unit
cell contains half of a cluster anion (located on an inversion center),
one [NEt4]+ cation, and two dmf molecules (located on general
positions). The crystals appeared to be nonmerohedrally twinned. The
TwinRotMat routine of PLATON55 was used to determine the
twinning matrix and to write the reflection data file (.hkl) containing
the two twin components. Refinement was performed using the
instruction HKLF 5 in SHELXL and one BASF parameter, which
refined as 0.333(5). All the C, O, and N atoms were restrained to
isotropic behavior (ISOR command in SHELXL, s.u. 0.005). All the
aromatic rings were constrained to fit regular hexagons (AFIX 66
command in SHELXL). Similar U restraints were applied to the
[NEt4]+ cation and to the dmf molecules (SIMU command in
SHELXL, s.u. 0.02). Restraints to bond distances were applied as
follows (s.u. 0.02): 1.47 Å for C−N and 1.53 Å for C−C in [NEt4]+.
[NEt4]2[Pt6(CO)10(dppf)]·2CH3CN. The asymmetric unit of the unit
cell contains one cluster anion, two [NEt4]+ cations, and two CH3CN
molecules (all located on general positions).
ACKNOWLEDGMENTS
■
We thank the Univ. of Bologna for financial support.
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00447.
I R s p e c t r a o f [ P t 6 ( C O ) 1 0 ( d p p m ) ] 2 −
,
[Pt12(CO)20(dppm)2]2−, [Pt18(CO)30(dppm)3]2−, and
[Pt24(CO)40(dppm)4]2−. ESI-MS spectra of
[Pt6(CO)10(dppm)]2−, [Pt12(CO)20(dppm)2]2−, and
[Pt18(CO)30(dppm)3]2−. Experimental and simulated
31P{1H} NMR spectra of [Pt9(CO)16(dppm)]2−
[Pt12(CO)20(dppm)2]2−, [Pt18(CO)30(dppm)3]2−
,
,
[Pt6(CO)10(P^P)]2−, and [Pt6(CO)10(dppf)]2−. Crystals
and experimental details (PDF)
Accession Codes
CCDC 1824418−1824424 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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soluble derivatives of platinum carbonyl Chini clusters: synthesis,
molecular structures and cytotoxicity of [Pt12(CO)20(PTA)4]2− and
[Pt15(CO)25(PTA)5]2−. Dalton Trans. 2018, 47, 4467.
K
DOI: 10.1021/acs.inorgchem.8b00447
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DOI: 10.1021/acs.inorgchem.8b00447
Inorg. Chem. XXXX, XXX, XXX−XXX