Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2- (n = 2-4)

Article abstract of DOI:10.1021/acs.inorgchem.6b02750

The reactions of [Pt_3n(CO)_6n]^2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph₂PCH₂CH₂PPh₂ (dppe) result in the heteroleptic Chini-type clusters [Pt₆(CO)₁₀(dppe)]^2-, [Pt₉(CO)₁₆(dppe)]^2-, and [Pt₁₂(CO)₂₀(dppe)₂]^2-. Their formation is accompanied by slight amounts of neutral species such as Pt₄(CO)₄(dppe)₂, Pt₆(CO)₆(dppe)₃, and Pt(dppe)₂. A similar behavior was observed with the chiral ligand R-Ph₂PCH(Me)CH₂PPh₂ (R-dppp), and two isomers of [Pt₉(CO)₁₆(R-dppp)]^2- were identified. All the new species were spectroscopically characterized by means of IR and ³¹P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh₃, as well as more rigid bidentate ligands, that is, CH₂C(PPh₂)₂ (P^P), CH₂(PPh₂)₂ (dppm), and o-C₆H₄(PPh₂)₂ (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt₃ units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt₉(CO)₁₆(dppe)]^2-, [Pt₉(CO)₁₆(R-dppp)]^2-, [Pt₁₂(CO)₂₂(PPh₃)₂]^2-, and [Pt₉(CO)₁₆(PPh₃)₂]^2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt₆(CO)₁₀(dppe)]^2- and [Pt₆(CO)₁₀(PPh₃)₂]^2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt₁₂(CO)₂₀(dppe)₂]^2-.

Full text of DOI:10.1021/acs.inorgchem.6b02750

Article
pubs.acs.org/IC
Heteroleptic Chini-Type Platinum Clusters: Synthesis and
Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2− (n = 2−
4)
Cristiana Cesari, Iacopo Ciabatti, Cristina Femoni, Maria Carmela Iapalucci, Federica Mancini,
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 [Pt3n(CO)6n]2− (n = 2−4)
homoleptic Chini-type clusters with stoichiometric amounts of
Ph2PCH2CH2PPh2 (dppe) result in the heteroleptic Chini-
type clusters [Pt6(CO)10(dppe)]2−, [Pt9(CO)16(dppe)]2−, and
[Pt12(CO)20(dppe)2]2−. Their formation is accompanied by
slight amounts of neutral species such as Pt4(CO)4(dppe)2,
Pt6(CO)6(dppe)3, and Pt(dppe)2. A similar behavior was
observed with the chiral ligand R-Ph2PCH(Me)CH2PPh2 (R-
dppp), and two isomers of [Pt9(CO)16(R-dppp)]2− were
identified. All the new species were spectroscopically
characterized by means of IR and 31P NMR, and their
structures were determined by single-crystal X-ray diffraction.
The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh3, as well as more rigid
bidentate ligands, that is, CH2C(PPh2)2 (P^P), CH2(PPh2)2 (dppm), and o-C6H4(PPh2)2 (dppb). From a structural point of
view, functionalization of anionic platinum Chini clusters preserves their triangular Pt3 units, whereas the overall trigonal
prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such
transformations may be just local deformations, as found in [Pt9(CO)16(dppe)]2−, [Pt9(CO)16(R-dppp)]2−
,
[Pt12(CO)22(PPh3)2]2−, and [Pt9(CO)16(PPh3)2]2−; an inversion of the cage from trigonal prismatic to octahedral, as observed
in [Pt6(CO)10(dppe)]2− and [Pt6(CO)10(PPh3)2]2−; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt−
Pt contact as found in [Pt12(CO)20(dppe)2]2−.
undergo fragmentation, rearrangement, and/or redox reactions
upon addition of ligands and nucleophiles.
1. INTRODUCTION
After the seminal work of Chini and Longoni,1,2
[Pt3n(CO)6n]2− (n = 1−8) clusters have represented a
milestone in the chemistry of molecular clusters and metal
carbonyls. These Chini clusters are composed of a stack of
triangular Pt3 units and can interconvert by simple redox
reactions.3−5 The higher nuclearity clusters (n = 5−8) display
the tendency to self-assemble into continuous chains, whose
solid-state structures are dependent upon the nature of the
charge-balancing cations as well as the sizes of the cluster
anions.6−8 Many of the higher ordered structures display
remarkable electric conductive properties, leading to interest in
their use as conductive materials.9−11 Moreover, they can be
used as catalysts, as well as precursors of heterogeneous
catalysts, metal nanoparticles, and nanowires.12−16 The thermal
decomposition of Chini clusters under milder conditions
affords globular platinum nanoclusters and Pt browns,17−21
whereas their redox condensation with metal carbonyls and
salts can lead to bimetallic clusters.22−24 Conversely, function-
alization of Chini clusters via CO substitution has been
investigated to a less extent, in view of their tendency to
These are general problems while studying the reactions of
metal carbonyl clusters with soft nucleophiles (e.g., CO, PR3,
−
RCCR, R2CCR2, pyridine, NO2 , halides), as they may result
either in the formation of addition or substitution products, or
in cluster breakdown. The nature of the species formed
depends on the nucleophile (which may or may not undergo
transformation on the cluster surface), the type of metal cluster,
and the conditions employed in the reaction.25−29 It must be
remarked that CO substitution with stronger σ-donors such as
phosphines becomes less favored when passing from cationic to
neutral and, eventually, anionic metal carbonyls. Indeed, most
of the examples reported in the literature of CO substitution
with PR3 in anionic carbonyl clusters involve low nuclearity
species possessing a robust metal cage, due to the presence of
heavier transition metals and/or interstitial heteroatoms.30−33
More often, larger (and more charged) anionic carbonyl
clusters do not react with phosphines, or the reaction results in
Received: November 17, 2016
© XXXX American Chemical Society
A
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degradation to lower nuclearity species.11,25,34 In a very few
cases, an opposite process has been observed, that is, cluster
condensation to higher nuclearity species upon treatment with
PR3.35
the reaction after workup. This is confirmed by the fact that
[Pt9(CO)16(dppe)]2− can be directly obtained from the
reaction of [Pt9(CO)18]2− and dppe in acetone, by periodically
removing CO in vacuo. In all cases, trace amounts of the
neutral Pt6(CO)6(dppe)3 cluster may be extracted in CH2Cl2
from the crude reaction mixture, in accord to eq 2.
Pt6(CO)6(dppe)3 was fully characterized by means of IR and
31P NMR spectroscopy and X-ray crystallography. In addition,
traces of the neutral complexes Pt(dppe)2 and
Pt4(CO)4(dppe)2 were sometimes isolated during the workup
of the reaction mixture. In particular, formation of Pt(dppe)2 is
favored by employing excess of dppe, and this species was, thus,
spectroscopically and structurally characterized. Conversely,
only a few crystals of Pt4(CO)4(dppe)2 were obtained,
hampering any further characterization, apart from X-ray
crystallography.
The formation of different neutral zerovalent species, that is,
Pt6(CO)6(dppe)3, Pt(dppe)2, and Pt4(CO)4(dppe)2, may be
explained assuming that CO/dppe substitution in
[Pt9(CO)18]2− may be followed by elimination of Pt(0)
fragments and formation of the lower nuclearity homoleptic
Chini cluster [Pt6(CO)12]2−. Elimination may be favored by
employing excess dppe. Then, depending on the experimental
conditions, the Pt(0) fragments may rearrange affording
different neutral species, as mentioned above. A similar trend
was previously observed in the case of the reaction of
[Pt9(CO)18]2− with PPh3, which, depending on the exper-
imental conditions, afforded the substitution products
[Pt9(CO)18−x(PPh3)x]2− (x = 1−3) and/or a mixture of
[Pt6(CO)12]2− and Pt3(CO)3(PPh3)3 via elimination of
Pt(0).36 Conversely, in the case of rigid diphosphines such as
dppm, P^P, and dppb, only the elimination products were
observed, probably because of the instability of the substitution
products.37
Within this framework, we recently reported that CO ligands
of [Pt3n(CO)6n]2− (n = 2−4) may be partially replaced by PPh3
l e a d i n g t o t h e f o r m a t i o n o f m i s c e l l a n e o u s
[Pt3n(CO)6n−m(PPh3)m]2− (m = 1−3) heteroleptic Chini-type
clusters.36 Conversely, their reactions with rigid bidentate
ligands, such as CH2C(PPh2)2 (P^P), CH2(PPh2)2 (dppm),
and o-C6H4(PPh2)2 (dppb), lead to neutral species, that is,
Pt4(CO)4(P^P)2, Pt6(CO)6(dppm)3, and Pt(dppb)2.37 Herein,
we report a detailed spectroscopic (IR and 31P NMR) and
structural study of the reactions of Chini clusters
[Pt3n(CO)6n]2− (n = 2−4) with a more flexible diphosphine
ligand, that is, Ph2PCH2CH2PPh2 (dppe). By using stoichio-
metric amounts of dppe, it is possible to observe CO/dppe
substitution with formation of dppe-functionalized Chini
clusters, among which [Pt9 (CO)1 6 (dppe)]2 −
,
[Pt6(CO)10(dppe)]2−, and [Pt12(CO)20(dppe)2]2− were struc-
turally characterized. In addition, the neutral species
Pt4(CO)4(dppe)2, Pt6(CO)6(dppe)3, and Pt(dppe)2 were
identified as side products of these reactions. Finally, a similar
trend was observed by employing a chiral analogue of dppe,
that is, R-Ph2PCH(Me)CH2PPh2 (R-dppp). In particular, two
isomers of the chiral Chini cluster [Pt9(CO)16(R-dppp)]2−
were obtained and fully characterized.
2. RESULTS AND DISCUSSION
2.1. Reactions of [Pt3n(CO)6n]2− (n = 2,3,4) with dppe.
The reaction of [Pt9(CO)18]2− with a slight excess of dppe in
acetone results, after workup, in the new dianionic cluster
[Pt9(CO)16(dppe)]2−, formally in accord to eq 1. The new
species was characterized through IR and 31P NMR spectros-
copy, and its molecular structure was crystallographically
determined as its [NEt4]2[Pt9(CO)16(dppe)]·2CH3COCH3
salt.
The IR spectrum of [Pt9(CO)16(dppe)]2− displays both
terminal and bridging νCO bands (2013(vs), 1831(ms) cm−1) at
lower frequencies than [Pt9(CO)18]2− in view of the greater
basicity of dppe compared to CO, very close to those
previously reported for [Pt9(CO)16(PPh3)2]2− (νCO 2016(s),
1824(m) cm−1). The 31P{1H} NMR spectrum recorded in
CD3CN at 298 K displays two complex resonances centered at
δP 48.1 and 41.6 ppm (Figure 1; see Scheme 1 for an
[Pt9(CO)18]2− + dppe ↔ [Pt9(CO)16(dppe)]2− + 2CO
(1)
Even if formation of [Pt9(CO)16(dppe)]2− is formally
accounted for by eq 1, IR monitoring of the reaction indicates
a more complex evolution. Thus, after the addition of dppe to
[Pt9(CO)18]2− under N2, the IR spectra indicate the formation
of a mixture of [Pt9(CO)18]2− (νCO 2030(vs), 1855(sh),
1840(s), 1830(sh), 1810(m) cm−1) and [Pt6(CO)12]2− (νCO
1995(vs), 1818(m), 1795(s) cm−1) according to eq 2. The
(νCO 1794(vs) cm−1) band of Pt6(CO)6(dppe)3 is hidden by
the acetone solvent. Then, [Pt9(CO)16(dppe)]2− (νCO
2013(vs), 1831(ms) cm−1) is formed after removal of CO
under vacuum, probably through a condensation process (eq
3).
[Pt9(CO)18]2− + 1.5dppe
↔ [Pt6(CO)12]2− + 0.5Pt6(CO)6(dppe)3 + 3CO
(2)
[Pt9(CO)18]2− + 2[Pt6(CO)12]2− + Pt6(CO)6(dppe)3
Figure 1. 31P{1H} NMR spectrum of [Pt9(CO)16(dppe)]2− in CD3CN
at 298 K. The main peak of the resonances of the two inequivalent P
↔ 3[Pt9(CO)16(dppe)]2−
(3)
■
▲
atoms is indicated with , P(1), and , P(2). Arrows are used for the
1
2
1
2
It is likely that equilibria 1−3 are mainly shifted under
r e d u c e d p r e s s u r e t o w a r d t h e f o r m a t i o n o f
[Pt9(CO)16(dppe)]2−, which is actually the main product of
coupling constants: JPtP(1), red; JPtP(1), yellow; JPtP(2), blue; JPtP(2)
,
green. The intensities of some Pt satellites are lower than expected
because of second-order effects.
B
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a
the mononuclear complex Pt(dppe)2 shows a first-order AX
spectrum as indicated by a pseudotriplet centered at δP 29.8
ppm (1JPt−P = 3734 Hz) in the 31P{1H} NMR spectrum (Figure
S.4).
Scheme 1. Coupling Pattern of the Two P Atoms of
[Pt9(CO)16(dppe)]2−
In a similar manner, the reaction of [Pt12(CO)24]2− with 1
equiv of dppe results immediately in a mixture of
[Pt12(CO)24]2− and [Pt9(CO)18]2−, as evidenced by IR
spectroscopy. Nonetheless, as above, after workup (see
Experimental) a new species displaying νCO bands at
2036(vs) and 1839(s) cm−1 is formed. Analogously to the
above-described reaction involving [Pt9(CO)18]2− and dppe,
and based on the similarity of the IR spectrum of the new
species with that reported for [Pt12(CO)22(PPh3)2]2−, the new
species may be formulated as [Pt12(CO)22(dppe)]2−. Unfortu-
nately, all attempts to crystallize it failed. The 31P NMR spectra
of the purported [Pt12(CO)22(dppe)]2− dianion recorded in the
temperature range of 213−298 K display always a broad
resonance centered at 43 ppm (line width ca. 150 Hz) with
1JPt−P = 5020 Hz and 2JPt−P = 545 Hz. This indicates a fluxional
behavior at all the temperatures considered. Formation of
[Pt12(CO)22(dppe)]2− is accompanied by neutral side-products,
such as Pt6(CO)6(dppe)3 and Pt(dppe)2.
a
3JPP is not displayed.
explanation of the observed coupling pattern). Both resonances
show a large 1JPtP coupling to one Pt atom (5060 and 4995 Hz
for the two resonances, respectively) as well as a very small 3JPP
(8 Hz).38−41 In addition, two very different JPtP coupling
2
constants are observed; the larger one (521 and 632 Hz,
respectively) corresponds to two equivalent Pt atoms, and the
smaller one (17 and 9 Hz, respectively) corresponds to a single
Conversely, the reaction of [Pt12(CO)24]2− with 2 equiv of
dppe affords in a few minutes a dark red solution containing
[Pt9(CO)18]2− as the major species together with traces of
unreacted [Pt12(CO)24]2− (by IR). In this case, after removal of
the solvent in vacuo and dissolution of the solid in CH3CN, a
green solution of the new cluster [Pt12(CO)20(dppe)2]2− was
obtained. Its formation is accompanied by neutral species as
above, which may be separated based on their different
solubilities in organic solvents. The structure of this new
heteroleptic anionic cluster was fully determined by X-ray
crystallography as its [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·
CH3CN and [NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN salts.
These crystals display νCO bands at 2008(vs), 1974(m),
1854(w), and 1810(s) cm−1 in nujol mull and at 2015(vs),
1854(w), 1828(s), and 1807(m) in CH3CN solution. A
downshift of 25−30 cm−1 compared to the starting
[Pt12(CO)24]2− is observed for both terminal and edge-bridging
νCO bands, in agreement with substitution of four CO ligands
with two bidendate dppe. The 31P NMR spectrum of
[Pt12(CO)20(dppe)2]2− (Figure 3) is fully consistent with its
solid-state structure (see Section 2.3), which contains two
equivalent dppe ligands, whereas the two P atoms within each
dppe are not equivalent. As a result, the pattern of the 31P
NMR spectrum of [Pt12(CO)20(dppe)2]2− is similar to that of
[Pt9(CO)16(dppe)]2−. Thus, it displays two resonances at δP
2
Pt atom. On the basis of the 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 inter-triangle coupling to the
Pt atom bonded to the other P of the same dppe ligand. It is
noteworthy that inter-triangle coupling to any nucleus (13C,
195Pt, 31P) is not usually observed in related clusters containing
only monodenate ligands, that is, [Pt9(CO)18]2−
,
[Pt9(CO)17(PPh3)]2−, and [Pt9(CO)16(PPh3)2]2−.5 Thus, it is
2
likely that the small inter-triangle JPtP coupling observed in
[Pt9(CO)16(dppe)]2− is due to the bidentate nature of dppe.
The assignment of the 31P{1H} NMR spectrum is fully
corroborated by simulation with gNMR 5.0.6.0 (Figures S.1
and S.2 in Supporting Information).42
The neutral Pt6(CO)6(dppe)3 cluster is closely related to the
previously reported Pt6(CO)6(dppm)3 and Pt3(CO)3(PPh3)3
species.43,44 It displays a νCO band at 1797 cm−1 corresponding
to the six μ-CO ligands. The 31P{1H} NMR spectrum recorded
in CD2Cl2 at 298 K (Figure 2) shows a complex resonance at δP
52.1 ppm (1JPtP = 4825 Hz (1Pt), JPtP = 527 Hz (2Pt), JPP
=
2
3
62 Hz (2P)) corresponding to a second-order
AA′A″A‴A⁗A‴″XX′X″X‴X⁗X‴″ system only partially re-
solved (see Figure S.3 for the simulated spectrum). Conversely,
Figure 2. 31P{1H} NMR spectrum of Pt6(CO)6(dppe)3 in CD2Cl2 at
Figure 3. 31P{1H} NMR spectrum of [Pt12(CO)20(dppe)2]2− in
298 K.
CD3CN at 298 K.
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47.7 and 41.7 (see Figures S.5 and S.6 for the simulated
It is noteworthy that the oxidation of [Pt6(CO)10(dppe)]2−
with stoichiometric amounts of HBF4·Et2O results in the
formation of [Pt12(CO)20(dppe)2]2− as indicated by IR
spectroscopy. Conversely, the oxidation of the homoleptic
analogue [Pt6(CO)12]2− affords [Pt9(CO)18]2− via the formal
addition of a single triangular unit. Indeed, this is the general
1
spectra). Both resonances show JPtP coupling to one Pt atom
2
(5024 and 5076 Hz, respectively), a larger JPtP coupling
constant to two Pt atoms (513 and 528 Hz, respectively), a
2
smaller JPtP coupling constant to one Pt atom (19 and 17 Hz,
3
respectively), and a very small JPP (8 Hz).
[Pt6(CO)12]2− apparently does not react with a slight excess
(1−4 equiv) of dppe under N2, whereas [Pt6(CO)10(dppe)]2−
is formed in good yields under vacuum. It is likely that
equilibrium 4 is shifted toward the formation of
[Pt6(CO)10(dppe)]2− only after removing the CO; otherwise,
[Pt6(CO)12]2− is the main species present in solution. The
substitution reaction is always accompanied by formation of
neutral compounds such as Pt6(CO)6(dppe)3 and Pt(dppe)2,
which were identified on the basis of IR, 31P NMR
spectroscopy, and X-ray crystallography (see above).
behavior observed for the oxidation of homoleptic Chini
2−
clusters [Pt3n(CO)6n]2− resulting in [Pt3(n+1)(CO)6(n+1)
]
species.1−4,7,8 The same behavior was observed for all the
PPh3 derivatives previously reported, as well as the other
species herein described that contain a single dppe ligand. It is
noteworthy that a mono-anionic [Pt3(μ-CO)3(CNR)3]− (R =
2,6-(2,6-(i-Pr)2C6H3)2C6H3) cluster with terminal isocyanide
ligands was recently reported, supporting the idea that
oxidation of Chini clusters proceeds via transient monoradical
intermediates and exchange on triangular units.6 It is likely that
the unique behavior observed for the oxidation of
[Pt6(CO)10(dppe)]2− is due to the fact that both its triangular
units are held together by the bridging dppe and it does not
contain any unsubstituted Pt3(CO)6 unit as, conversely, for all
the other species reported. Thus, its oxidation cannot proceed
via removal of one electron and formal addition of one
Pt3(CO)6 unit, but the monoelectronic oxidation is followed by
dimerization resulting in [Pt12(CO)20(dppe)2]2− (Scheme 2).
Finally, it must be remarked that the addition of excess HBF4·
Et2O to [Pt6(CO)10(dppe)]2− results in the formation of a
complex mixture of degradation products, among which
[Pt(dppe)2][Pt12(CO)24]·2DMF (DMF = dimethylformamide)
was crystallographically identified (Figure S.9).
[Pt6(CO)12]2− + dppe ↔ [Pt6(CO)10(dppe)]2− + 2CO
(4)
The crystal structure of the new cluster [Pt6(CO)10(dppe)]2−
was determined as its [NMe4]2[Pt6(CO)10(dppe)] and
[NEt4]2[Pt6(CO)10(dppe)] salts. These crystals show νCO
bands at 1975(s), 1955(vs), 1756(s), and 1732(ms) cm−1 in
nujol mull and at 1976(vs), 1784(s), and 1765(s) in CH3CN
solution. In keeping with the solid-state structure, the 31P NMR
spectrum of [Pt6(CO)10(dppe)]2− displays a single resonance
at δP 51.2 ppm, in view of the equivalence of the two P atoms of
the unique dppe ligand (Figure 4). The following coupling
2.2. Reactions of [Pt3n(CO)6n]2− (n = 2,3,4) with R-
dppp. The reactions of [Pt3n(CO)6n]2− (n = 2,3,4) with R-
dppp are very similar to those described in the previous section
involving dppe. A complication arises from the fact that the two
P atoms of R-dppp are not equivalent, and thus, different
isomers may be formed upon coordination to the clusters. This
point is well-exemplified by the reaction of [Pt9(CO)18]2− with
1 equiv of R-dppp which, after workup, results in the
[Pt9(CO)16(R-dppp)]2− cluster. This compound displays an
IR spectrum very similar to [Pt9(CO)16(dppe)]2−. Its molecular
structure was determined as [NEt4]2[Pt9(CO)16(R-dppp)]·
2CH3COCH3, which actually contains a 1:1 mixture of two
isomers, differing in the orientation of the R-dppp ligand with
respect to the cluster (Scheme 3). Both isomers contain two
inequivalent P atoms, resulting in a very complex 31P NMR
spectrum (Figure 5) that displays four main resonances with
coupling patterns similar to [Pt9(CO)16(dppe)]2−. The assign-
ment of the 31P{1H} NMR spectrum is fully corroborated by
simulation with gNMR 5.0.6.0 (Figure S.10).42 Thus, isomer I
Figure 4. 31P{1H} NMR spectrum of [Pt6(CO)10(dppe)]2− in DMF/
CD3CN at 298 K.
constants are observed: 1JPtP = 5086 Hz to one Pt atom; 2JPtP
550 Hz to two Pt atoms; JPtP = 21 Hz to one Pt atom (see
=
2
Figures S.7 and S.8 for the simulated spectra).
Scheme 2. Proposed Mechanism for the Oxidation of [Pt6(CO)10(dppe)]2− to [Pt12(CO)20(dppe)2]2−
D
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Scheme 3. Two Isomers of [Pt9(CO)16(R-dppp)]2−
2.3. Crystal Structures of the Heteroleptic Chini-Type
Clusters. The molecular structures of [Pt9(CO)16(dppe)]2−,
[Pt9(CO)16(R-dppp)]2−, [Pt6(CO)10(dppe)]2−, and
[Pt1 2 (CO)2 0 (dppe)2 ]2 −
, as determined as their
[ N E t 4 ] 2 [ P t 9 ( C O ) 1 6 ( d p p e ) ] · 2 C H 3 C O C H 3 ,
[ N E t 4 ] 2 [ P t 9 ( C O ) 1 6 ( R - d p p p ) ] · 2 C H 3 C O C H 3 ,
[NMe4]2[Pt6(CO)10(dppe)], [NEt4]2[Pt6(CO)10(dppe)],
[NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN, and
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN salts, are represented
in Figures 6−9, whereas their main bonding parameters are
Figure 6. Molecular structure of [Pt9(CO)16(dppe)]2− (Pt, purple; P,
orange; O, red; C, gray; H, white).
Figure 5. 31P{1H} NMR spectrum of [Pt9(CO)16(R-dppp)]2− in
CD3COCD3 at 298 K.
displays two resonances at δP (ppm) 59.8 (1JPtP = 5037 Hz
2
3
(1Pt), JPtP = 517 Hz (2Pt), JPP = 11 Hz) and 48.0 (1JPtP
=
2
3
4436 Hz (1Pt), JPtP = 529 Hz (2Pt), JPP = 11 Hz).
Conversely, Isomer II shows two resonances at 51.2 (1JPtP
4944 Hz (1Pt), 2JPtP = 649 Hz (2Pt), 3JPP = 10 Hz), 41.2 (1JPtP
=
2
3
= 5033 Hz (1Pt), JPtP = 648 Hz (2Pt), JPP = 10 Hz). By
comparison, the free R-dppp ligand displays two resonances at
3
δ (ppm) 0.5 and −21.5 with JPP = 20 Hz.
The reaction of [Pt6(CO)12]2− with R-dppp, under
conditions similar to those employed in the case of dppe,
affords, after workup, [Pt6(CO)10(R-dppp)]2− as evidenced by
IR and 31P NMR spectroscopies (Figure S.11). In this case, a
single product is formed in view of the fact that the hexanuclear
cluster contains two equivalent triangular units. [Pt6(CO)10(R-
dppp)]2− displays two inequivalent P atoms with δP (ppm) 61.4
(1JPtP = 4937 Hz (1Pt), 2JPtP = 540 Hz (2Pt), 3JPP = 5 Hz) and
49.0 (1JPtP = 5032 Hz (1Pt), 2JPtP = 564 Hz (2Pt), 3JPP = 5 Hz).
Finally, the reaction of [Pt12(CO)24]2− with R-dppp is rather
complicated, and only a few hypotheses may be drawn on the
basis of spectroscopic data. As in the case of the analogous
reactions with dppe, it seems that both [Pt12(CO)22(R-
dppp)]2− and [Pt12(CO)20(R-dppp)2]2− may be formed,
depending on the stoichiometry of the reaction. Unfortunately,
it has not been possible to obtain the crystal structures of these
clusters. In the case of [Pt12(CO)22(R-dppp)]2−, its 31P NMR
spectrum shows two very broad resonances at 50 and 35 ppm,
indicative of a fluxional behavior, as previously described for
[Pt12(CO)22(dppe)]2−. Conversely, the purported
[Pt12(CO)20(R-dppp)2]2− displays a rather complex and ill-
defined 31P NMR spectrum. This may be due to the presence
of side products as well as the fact that three different isomers
of [Pt12(CO)20(R-dppp)2]2− should be formed in a statistical
2:1:1 ratio, based on the orientation of the Me groups of the
two R-dppp ligands compared to the four Pt3 units of the
cluster.
Figure 7. Molecular structure of the two isomers (a, b) of
[Pt9(CO)16(R-dppp)]2− (Pt, purple; P, orange; O, red; C, gray; H,
white).
compared in Table 1 to those of the parent [Pt12(CO)24]2−,
[Pt9(CO)18]2−, and [Pt6(CO)12]2−,1,2 as well as the related
[Pt12(CO)22(PPh3)2]2−, [Pt9(CO)16(PPh3)2]2−, and
[Pt6(CO)10(PPh3)2]2−.36 In drawing Figures 6−9 it was
arbitrarily decided to represent Pt−Pt bonds up to 3.36 Å,
which is slightly below twice the van der Waals radius of Pt and
ca. 20% greater than twice its covalent radius (covalent radius
1.36 Å; van der Waals radius 1.72 Å).45
The molecular structure of [Pt9(CO)16(dppe)]2− (Figure 6
and Table 1) can be formally obtained from that of
[Pt9(CO)18]2−, after replacing two terminal CO ligands, one
in the inner and one in one of the outer Pt3 triangular units,
with dppe. It is noteworthy that in the case of the related
[Pt9(CO)16(PPh3)2]2−, the two monodentate PPh3 ligands
E
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group in R-dppp may statistically attack the external or internal
Pt3 units, and both orientations are energetically equivalent. It
is also noteworthy that the distortion of the trigonal prismatic
Pt6 unit bonded to R-dppp is greater than in the case of dppe,
with the shortest diagonal Pt−Pt contact, which is now weakly
bonding [Pt(1)−Pt(5) 3.357(2) Å].
[Pt6(CO)10(dppe)]2− displays a distorted octahedral geom-
etry (Figure 8 and Table 1), in contrast to the parent
[Pt6(CO)12]2−, which adopts a trigonal prismatic structure.
Moreover, some slight differences in the octahedral core of
[Pt6 (CO)1 0 (dppe)]2 − were found in the two
[NMe4]2[Pt6(CO)10(dppe)] and [NEt4]2[Pt6(CO)10(dppe)]
salts. A similar behavior was observed for the related
[Pt6(CO)10(PPh3)2]2− cluster.36 In particular, the Pt6 cage of
[Pt6(CO)10(dppe)]2− displays six inter-triangular Pt−Pt
bonding contacts in [NEt4]2[Pt6(CO)10(dppe)] [3.0437(10)−
3.359(2) Å; average 3.202(2) Å] as expected for an octahedron,
even if some of them are slightly elongated. Conversely, in the
case of [NMe4]2[Pt6(CO)10(dppe)], there are four inter-
triangular Pt−Pt contacts [2.9839(4)−3.1797(3) Å; average
3.1285(8) Å] at bonding distance, whereas the remaining two
distances are nonbonding [Pt(1)−Pt(2′) and Pt(1′)−Pt(2)
3.526(2) Å]. These differences between the two salts can be
ascribed to packing forces due to the presence of different
cations. Similarly, analogous differences in the distorted
octahedral structures of [Pt6(CO)10(PPh3)2]2− were observed
due to different packing effects resulting from inclusion of
tetrahydrofuran (THF) in one salt. This points out that the
inter-triangular bonds are rather weak and easily deformed by
small changes in the van der Waals forces within the crystals.
Finally, the structure of [Pt12(CO)20(dppe)2]2− was
d e t e r m i n e d a s t w o d i ff e r e n t s a l t s , t h a t i s ,
[NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN and
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN, displaying very sim-
ilar geometries and bonding parameters (Figure 9 and Table 1).
[Pt12(CO)20(dppe)2]2− adopts an unprecedented structure for
a Chini-type cluster. Indeed, it is composed of two trigonal
prismatic [Pt6(CO)10(dppe)] units rotated of 180° and joined
by the two symmetry-equivalent Pt(2)−Pt(3′) and Pt(2′)−
Pt(3) bonds [2.9765(8) and 2.9728(5) Å, for the two salts,
respectively]. As a consequence, there is one μ-CO ligand per
[Pt6(CO)10(dppe)] unit, which sits above one Pt atom of the
second [Pt6(CO)10(dppe)] unit [Pt(1)···C(O) 3.324(14) and
3.286(10) Å, for the two salts, respectively].
Figure 8. Molecular structure of [Pt6(CO)10(dppe)]2− as found in (a)
[NEt4]2[Pt6(CO)10(dppe)] and (b) [NMe4]2[Pt6(CO)10(dppe)] (Pt,
purple; P, orange; O, red; C, gray; H, white).
Figure 9. Molecular structure of [Pt12(CO)20(dppe)2]2− (Pt, purple;
P, orange; O, red; C, gray; H, white).
were found bonded to two different external triangles to release
steric repulsion. Overall, [Pt9(CO)16(dppe)]2− retains the
trigonal prismatic structure of the parent homoleptic Chini
cluster, even if the Pt6 trigonal prism bonded to dppe is
considerably distorted. This causes an elongation of the inter-
triangular Pt−Pt contacts of [Pt9(CO)16(dppe)]2−
[2.9968(9)−3.2744(9) Å; average 3.114(2) Å] compared to
[Pt9(CO)18]2− [3.04(2)−3.06(2) Å; average 3.05(4) Å] and
[Pt9(CO)16(PPh3)2]2− [3.0015(9)−3.1098(8) Å; average
3.043(2) Å]. The shortest diagonal Pt−Pt contact in the
distorted trigonal prismatic dppe-substituted cage is Pt(1)−
Pt(5) [3.4360(10) Å], indicating an incipient octahedral
structure. Conversely, the intra-triangular contacts
[2.6485(10)−2.6841(9) Å; average 2.667(3) Å] are in keeping
with other homoleptic and heteroleptic Chini-type clusters.
The structural differences observed for the [Pt9(CO)18]2−,
[Pt9(CO)16(PPh3)2]2−, and [Pt9(CO)16(dppe)]2− clusters are
attributable to both steric and electronic effects. It may be also
the case that the phosphine-substituted clusters partially
attempt to align the π* systems of bridging COs, thereby
leading to a distortion of stacked rings.
2.4. Crystal Structures of the Neutral Side-Products.
The molecular structures of the neutral Pt4(CO)4(dppe)2,
Pt6(CO)6(dppe)3, and Pt(dppe)2 species will be briefly
discussed, since they closely resemble those of analogous
compounds previously reported with other diphosphine
ligands.
Thus, the structure of Pt4(CO)4(dppe)2 is closely related to
37
Pt4(CO)4(P^P)2 and consists of a tetrahedral Pt4 core
elongated along its C2 axis (Figure 10). The two edges of the
elongated tetrahedron perpendicular to the C2 axis are bridged
by two dppe ligands, and the coordination sphere of the cluster
is completed by four terminal CO ligands, one per each Pt
atom. The six Pt−Pt contacts are divided into three sets
consisting of two bonds each. The shortest contacts are those
bridged by the dppe ligands [2.5771(3) and 2.5890(3) Å] and
perpendicular to the elongation axis. The two bonds almost
parallel to the C2 axis [2.6165(3) and 2.6228(3) Å] have
intermediate values. Conversely, the two diagonals of the
elongated tetrahedron [2.9995(3) and 3.0164(3) Å] are the
The structure of [Pt9(CO)16(R-dppp)]2− (Figure 7 and
Table 1) is very similar to that of [Pt9(CO)16(dppe)]2−. The
main difference is that, in view of the asymmetric nature of R-
dppp, two different isomers are present in a 1:1 ratio in the
solid-state structure. This is because the P atom close to the Me
F
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Table 1. Main Bond Distances of [Pt12(CO)20(dppe)2]2−, [Pt9(CO)16(dppe)]2−, [Pt9(CO)16(R-dppp)]2−, and
[Pt6(CO)10(dppe)]2− Compared to the Parent [Pt12(CO)24]2−, [Pt9(CO)18]2−, and [Pt6(CO)12]2−, and the PPh3-Substituted
Clusters [Pt12(CO)22(PPh3)2]2−, [Pt9(CO)16(PPh3)2]2−, and [Pt6(CO)10(PPh3)2]2−
Pt−Pt
Pt−Pt
a
intra-triangular
inter-triangular
Pt−P
b
c
[Pt12(CO)20(dppe)2]2−
[Pt12(CO)20(dppe)2]2−
[Pt12(CO)22(PPh3)2]2−
2.6520(8)−2.6795(7)
average 2.669(2)
2.9765(8)−3.1939(8)
average 3.068(2)
2.254(4)−2.272(4)
average 2.263(6)
2.251(2)−2.270(2)
average 2.260(3)
2.281(4)
2.6513(5)−2.6780(5)
average 2.6671(12)
2.6539(9)−2.6756(9)
average 2.666(2)
2.9728(5)−3.2075(5)
average 3.0632(12)
3.0184(9)−3.2067(11)
average 3.086(2)
d
e
[Pt12(CO)24]2−
2.6587(5)−2.6707(5)
average 2.6656(12)
2.6485(10)−2.6841(9)
average 2.667(3)
3.0465(5)−3.0597(5)
average 3.0535(12)
2.9968(9)−3.2744(9)
average 3.114(2)
[Pt9(CO)16(dppe)]2−
2.263(4)−2.282(4)
average 2.272(6)
2.277(6)−2.280(6)
average 2.278(8)
2.265(4)−2.287(4)
average 2.276(6)
[Pt9(CO)16(R−dppp)]2−
2.64913)−2.6843(12)
average 2.667(4)
3.0088(14)−3.357(2)
average 3.127(4)
d
[Pt9(CO)16(PPh3)2]2−
2.6597(8)−2.6814(9)
average 2.670(2)
3.0015(9)−3.1098(8)
average 3.043(2)
e
[Pt9(CO)18]2−
2.65(2)−2.67(8)
3.04(2)−3.06(2)
average 2.66(9)
average 3.05(4)
f
[Pt6(CO)10(dppe)]2−
2.6513(3)−2.6839(3)
average 2.6625(9)
2.6573(8)−2.6758(8)
average 2.6644(14)
2.6558(6)−2.6743(6)
average 2.6644(10)
2.6584(6)−2.6787(6)
average 2.6694(10)
2.644(7)−2.659(3)
average 2.653(10)
2.9839(4)−3.1797(3)
average 3.1285(8)
2.2456(13)
2.251(4)
2.240(3)
2.247(3)
g
h
[Pt6(CO)10(dppe)]2−
3.0437(10)−3.359(2)
i
average 3.202(2)
j
k
[Pt6(CO)10(PPh3)2]2−
3.0353(6)
l
[Pt6(CO)10(PPh3)2]2−
3.1380(6)−3.2079(6)
average 3.1729(8)
m
e
[Pt6(CO)12]2−
3.026(16)−3.049(17)
average 3.03(3)
a
b
c
Only Pt−Pt interactions ≤3.36 Å were included (see text). As found in [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN. As found in
d
e
f
g
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN. From ref 36. From ref 12. As found in [NMe4]2[Pt6(CO)10(dppe)]. Four inter-triangular Pt−Pt
h
i
bonding contacts are present. The remaining two Pt−Pt contacts are 3.526(2) Å. As found in [NEt4]2[Pt6(CO)10(dppe)]. Six inter-triangular Pt−
j
k
Pt bonding contacts are present. As found in [NBu4]2[Pt6(CO)10(PPh3)2]. From ref 36. Three sets of inter-triangular Pt−Pt contacts are present:
l
m
3.0353(6), 3.3581(6), 3.5070(6) Å. From ref 36. As found in [NBu4]2[Pt6(CO)10(PPh3)2]·2THF. From ref 36. Three sets of inter-triangular Pt−
Pt contacts are present: 3.1380(6), 3.2079(6), 3.4310(6) Å. From ref 36.
and the bonding parameters closely resemble those of
[Pt6(CO)12]2− and Pt6(CO)6(dppm)3.
Figure 10. Molecular structure of Pt4(CO)4(dppe)2 (Pt, purple; P,
orange; O, red; C, gray; H, white).
Figure 11. Molecular structure of Pt6(CO)6(dppe)3 (Pt, purple; P,
orange; C, gray, O, red).
Finally, Pt(dppe)2 shows a tetrahedral structure as expected
for a zerovalent Pt(LL)2 complex (Figure 12).47,48
loosest Pt−Pt contacts. The cluster possesses 56 CVE as
predicted for a Pt4 tetrahedral cluster on the basis of theoretical
considerations.46
Pt6(CO)6(dppe)3 is isostructural with Pt6(CO)6(dppm)3,43
being composed of a Pt6 trigonal prismatic core possessing D3h
symmetry to which are coordinated six μ-CO and three μ-dppe
ligands (Figure 11 and Table 2). The structure of the cluster
3. CONCLUSIONS
A competition between the nonredox substitution with
retention of the nuclearity and the redox fragmentation is
observed in the case of the reactions of [Pt3n(CO)6n]2− Chini
G
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Table 2. Main Bond Distances (Å) of Pt6(CO)6(dppe)3 Compared to Pt6(CO)6(dppe)3 and [Pt6(CO)12]2−
Pt−Pt
Pt−Pt
intra-triangular
inter-triangular
Pt−P
Pt6(CO)6(dppe)3
Pt6(CO)6(dppm)3
2.6586(4)−2.6715(4)
average 2.6667(10)
2.6427(5)−2.6945(5)
average 2.6748(12)
2.644(7)−2.659(3)
average 2.653(10)
3.1110(4)−3.1589(4)
average 3.1393(7)
3.0159(5)−3.1048(5)
average 3.0567(9)
3.026(16)−3.049(17)
average 3.03(3)
2.2502(17)−2.2667(17)
average 2.258(4)
a
2.248(2)−2.273(2)
average 2.260(5)
b
[Pt6(CO)12]2−
a
b
From ref 43. From ref 12.
triangular Pt−Pt bonds, the overall trigonal prismatic structures
present in the homoleptic clusters are readily deformed and
transformed upon functionalization. Such transformations,
which are due to both steric and electronic effects, may be
just local deformations, as found in [Pt9(CO)16(dppe)]2−,
[Pt9(CO)16(R-dppp)]2−, [Pt12(CO)22(PPh3)2]2−, and
[Pt9(CO)16(PPh3)2]2−; an inversion of the cage from trigonal
prismatic to octahedral, as observed in [Pt6(CO)10(dppe)]2−
and [Pt6(CO)10(PPh3)2]2−; the reciprocal rotation of two
trigonal prismatic units with the loss of a Pt−Pt contact as
found in [Pt12(CO)20(dppe)2]2−. The latter structure is
remarkable, since it may be viewed as a dimer composed of
two mono-anionic [Pt6(CO)10(dppe)]− units joined by two
(and not three) Pt−Pt interactions. Mono-anionic radicals of
the type [Pt3n(CO)6n]− are sought to be intermediates in the
oxidation of homoleptic Chini clusters,49 and the present
findings give some experimental support to this. In this respect,
a mono-anionic [Pt3(μ-CO)3(CNR)3]− (R = 2,6-(2,6-(i-
Pr)2C6H3)2C6H3) cluster with terminal isocyanide ligands was
recently fully charactreized.6 Overall, it seems that, 40 years
since their discovery, platinum Chini clusters still display a
rather rich and fascinating chemistry.
Figure 12. Molecular structure of Pt(dppe)2 (Pt, purple; P, orange; C,
gray, O, red).
clusters with phosphine ligands. The nonredox substitution
results in heteroleptic analogues of anionic Chini clusters,
4. EXPERIMENTAL SECTION
whereas redox fragmentation (elimination) reactions afford
2−
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 [Pt9 (CO)1 8 ], [NMe3 (CH2 Ph)]2 [Pt1 2 (CO)2 4 ],
[ N M e 4 ] 2 [ P t 1 2 ( C O ) 2 4 ] , [ N E t 4 ] 2 [ P t 6 ( C O ) 1 2 ] , a n d
[NMe4]2[Pt6(CO)12], which were prepared according to the
literature.1,2 Analysis of Pt was performed by atomic absorption on a
Pye-Unicam instrument. Analyses of C, H, and N were obtained with a
Thermo Quest Flash EA 1112NC instrument. IR spectra were
recorded on a PerkinElmer Spectrum One interferometer in CaF2
cells. 31P{1H} NMR measurements 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, J).42 Structure drawings were performed with
SCHAKAL99.50
lower nuclearity homoleptic species [Pt3(n−1)(CO)6(n−1)
]
as
well as miscellaneous neutral complexes. In the case of the
monodentate PPh3 and bidentate dppe and R-dppp ligands, it
has been possible to favor substitution over fragmentation by
employing stoichiometric amounts of the ligands. Thus, the
heteroleptic Chini clusters [Pt9(CO)16(dppe)]2−
,
[Pt9(CO)16(R-dppp)]2−, [Pt6(CO)10(dppe)]2−, and
[Pt12(CO)20(dppe)2]2− have been structurally characterized in
this work, whereas the analogous PPh3-derivatives
[Pt12(CO)22(PPh3)2]2−, [Pt9(CO)16(PPh3)2]2−, and
[Pt6(CO)10(PPh3)2]2− have been previously described.36
Conversely, in the case of more rigid bidentate ligands, such
as P^P, dppm, and dppb, it is not possible to isolate the
substitution products, since fragmentation (elimination)
proceeds very fast leading to neutral complexes.
The present work clearly demonstrates the possibility to
functionalize anionic platinum Chini clusters and extend the
scope of our previous work on monodentate ligands36 also to
bidentate and chiral phosphines. Heteroleptic and chiral Chini
clusters might be in the future investigated for applications in
catalysis.
Finally, from a structural point of view, the analysis of the
structures of the heteroleptic anionic platinum Chini clusters so
far characterized and their comparison to the homoleptic
analogues, points out a high flexibility of the inter-triangular
Pt−Pt interactions along the pseudo-C3 axis. Indeed, while the
triangular Pt3 units are preserved in view of stronger intra-
4.2. Synthesis of [NEt4]2[Pt9(CO)16(dppe)]·2CH3COCH3. dppe
(0.115 g, 0.289 mmol) was added as a solid to a solution of
[NEt4]2[Pt9(CO)18] (0.520 g, 0.206 mmol) in acetone (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 water
(20 mL), toluene* (15 mL), and CH2Cl2 (15 mL) and extracted with
acetone (15 mL). Crystals of [NEt4]2[Pt9(CO)16(dppe)]·
2CH3COCH3 suitable for X-ray analyses were obtained by layering
n-hexane (30 mL) on the acetone solution (yield 0.31 g, 51% based on
Pt).
C64H76N2O18P2Pt9 (2979.02): calcd. C 25.80, H 2.57, N 0.94, Pt
58.94; found: C 26.02, H 2.78, N 0.79, Pt 59.13%. IR (nujol, 293 K)
ν(CO): 2047(w), 2015(vs), 1997(sh), 1858(w), 1831(m), 1820(m),
H
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Table 3. Crystal Data and Experimental Details for [NMe4]2[Pt6(CO)10(dppe)], [NEt4]2[Pt6(CO)10(dppe)],
[NEt4]2[Pt9(CO)16(dppe)]·2CH3COCH3, [NEt4]2[Pt9(CO)16(R-dppp)]·2CH3COCH3, [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·
CH3CN, [NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN, [Pt(dppe)2][Pt12(CO)24]·2DMF, Pt(dppe)2·CH2Cl2, Pt6(CO)6(dppe)3·
3CH2Cl2, and Pt4(CO)4(dppe)2·2THF
[NEt4]2[Pt9(CO)16(dppe)]·2C-
[NMe3(CH2Ph)]2[Pt12(CO)20(dpp-
[NMe4]2[Pt6(CO)10(dppe)] [NEt4]2[Pt6(CO)10(dppe)]
H3COCH3
e)2]·CH3CN
formula
Fw
C44H48N2O10P2Pt6
1997.32
C52H64N2O10P2Pt6
2109.53
C64H76N2O18P2Pt9
2979.02
C94H83N3O20P4Pt12
4039.59
T, K
100(2)
100(2)
291(2)
100(2)
λ, Å
0.710 73
0.710 73
0.710 73
0.710 73
crystal system
space group
a, Å
monoclinic
C2/c
monoclinic
C2/c
orthorhombic
Pna21
triclinic
P1
̅
22.7406(8)
11.3119(4)
22.0638(8)
90
25.2580(7)
11.2170(3)
21.8096(6)
90
29.341(6)
14.916(3)
17.883(4)
90
13.4798(5)
13.9719(6)
14.6962(6)
95.293(2)
104.089(2)
112.579(2)
2424.94(17)
1
b, Å
c, Å
α, deg
β, deg
120.489(2)
90
116.1000(10)
90
90
γ, deg
cell volume, Å3
90
4890.9(3)
4
5549.0(3)
4
7826(3)
Z
4
Dc, g cm−3
μ, mm−1
F(000)
2.713
2.525
2.528
2.766
17.217
15.183
16.121
17.365
3616
3872
5400
1824
crystal size, mm
θ limits, deg
index ranges
0.15 × 0.13 × 0.10
2.08−27.00
−28 ≤ h ≤ 28
−14 ≤ k ≤ 14
−28 ≤ l ≤ 28
40 003
0.15 × 0.13 × 0.11
1.80−25.02
−30 ≤ h ≤ 30
−13 ≤ k ≤ 13
−25 ≤ l ≤ 25
38 717
0.21 × 0.16 × 0.13
1.39−25.03
−34 ≤ h ≤ 33
−17 ≤ k ≤ 17
−21 ≤ l ≤ 21
72 956
0.15 × 0.12 × 0.09
1.46−26.51
−16 ≤ h ≤ 16
−17 ≤ k ≤ 17
−18 ≤ l ≤ 18
38 438
reflections collected
independent reflections
completeness to θ max
data/restraints/parameters
goodness on fit on F2
R1 (I > 2σ(I))
5351 [Rint = 0.0511]
100.0%
4906 [Rint = 0.0953]
99.9%
13 712 [Rint = 0.0703]
99.6%
9972 [Rint = 0.0651]
98.9%
5351/30/289
1.102
4906/12/325
1.119
13 712/450/768
1.025
9972/299/538
1.053
0.0218
0.0479
0.0392
0.0508
wR2 (all data)
0.0451
0.1261
0.0850
0.1625
largest diff. peak and hole,
e Å−3
1.069/−1.394
4.217/−1.900
0.970/−1.351
2.965/−3.266
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN
[Pt(dppe)2][Pt12(CO)24]·2DMF
Pt4(CO)4(dppe)2·2THF
formula
Fw
C84H78N4O20P4Pt12
3928.46
C82H62N2O26P4Pt13
4151.39
C64H64O6P4Pt4
1833.39
T, K
100(2)
100(2)
100(2)
λ, Å
0.710 73
0.710 73
0.710 73
triclinic
crystal system
space group
a, Å
triclinic
monoclinic
Cc
P1
̅
P1
̅
13.3433(4)
13.8993(4)
14.5522(4)
95.896(2)
103.899(2)
113.0710(10)
2351.04(12)
1
12.8023(2)
34.8688(6)
20.7130(4)
90
13.2249(2)
13.4846(2)
18.7808(3)
79.9740(10)
71.7440(10)
67.4040(10)
2930.97(8)
2
b, Å
c, Å
α, deg
β, deg
98.8280(10)
90
γ, deg
cell volume, Å3
9136.8(3)
4
Z
Dc, g cm−3
μ, mm−1
F(000)
2.775
3.018
2.077
17.906
19.959
9.677
1766
7400
1736
crystal size, mm
θ limits, deg
index ranges
0.16 × 0.13 × 0.12
1.48−26.00
−16 ≤ h ≤ 16
−17 ≤ k ≤ 17
−17 ≤ l ≤ 17
36 872
0.16 × 0.12 × 0.10
1.53−26.00
−15 ≤ h ≤ 15
−42 ≤ k ≤ 42
−25 ≤ l ≤ 25
71 622
0.15 × 0.12 × 0.10
1.64−27.00
−16 ≤ h ≤ 163
−17 ≤ k ≤ 17
−23 ≤ l ≤ 23
49 701
reflections collected
independent reflections
completeness to θ max
9212 [Rint = 0.0677]
99.6%
17 911 [Rint = 0.0552]
100.0%
12 703 [Rint = 0.0556]
99.3%
I
DOI: 10.1021/acs.inorgchem.6b02750
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 3. continued
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN
[Pt(dppe)2][Pt12(CO)24]·2DMF
Pt4(CO)4(dppe)2·2THF
data/restraints/parameters
goodness on fit on F2
R1 (I > 2σ(I))
9212/444/603
17 911/32/1145
1.019
12 703/184/749
1.023
1.047
0.0355
0.0273
0.0318
wR2 (all data)
largest diff. peak and hole, e Å−3
0.0826
0.0625
0.0699
2.052/−2.418
[NEt4]2[Pt9(CO)16(R-dppp)2]·2CH3COCH3
1.713/−1.575
Pt(dppe)2·CH2Cl2
1.408/−1.654
Pt6(CO)6(dppe)3·3CH2Cl2
formula
Fw
C65H78N2O18P2Pt9
2993.04
C53H50Cl2P4Pt
1076.80
C87H78Cl6O6P6Pt6
2788.55
T, K
100(2)
100(2)
100(2)
λ, Å
0.710 73
0.710 73
0.710 73
crystal system
space group
a, Å
monoclinic
P21
monoclinic
P21/n
triclinic
P1
̅
14.6912(9)
17.7718(11)
14.7316(9)
90
9.9225(4)
20.8279(9)
22.0699(9)
90
15.3436(5)
15.7219(6)
18.4766(7)
92.720(2)
98.368(2)
98.969(2)
4344.5(3)
2
b, Å
c, Å
α, deg
β, deg
94.221(4)
90
90.396(2)
90
γ, deg
cell volume, Å3
3835.8(4)
2
4561.0(3)
4
Z
Dc, g cm−3
μ, mm−1
F(000)
2.591
1.568
2.132
16.447
3.371
9.970
2716
2160
2616
crystal size, mm
θ limits, deg
index ranges
0.19 × 0.16 × 0.11
1.39−25.10
−17 ≤ h ≤ 17
−21 ≤ k ≤ 21
−17 ≤ l ≤ 17
38 838
0.22 × 0.15 × 0.13
1.85−28.00
−12 ≤ h ≤ 13
−27 ≤ k ≤ 27
−29 ≤ l ≤ 29
80 477
0.16 × 0.13 × 0.12
1.36−27.00
−19 ≤ h ≤ 19
−20 ≤ k ≤ 20
−23 ≤ l ≤ 23
73 574
reflections collected
independent reflections
completeness to θ max
data/restraints/parameters
goodness on fit on F2
R1 (I > 2σ(I))
13 605 [Rint = 0.0899]
99.8%
10 975 [Rint = 0.0669]
99.8%
18 871 [Rint = 0.0747]
99.3%
13 605/505/876
0.989
10 975/0/541
1.018
18 871/0/1000
1.017
0.0566
0.0280
0.0377
wR2 (all data)
largest diff. peak and hole, e Å−3
0.1560
0.0726
0.0870
3.952/−2.651
1.368/−1.754
3.530/−2.626
2
3
1804(ms) cm−1. IR (acetone, 293 K) ν(CO): 2013(vs), 1831(ms)
cm−1. 31P{1H} NMR (CD3CN, 298 K) δ (ppm): 48.1 (1JPtP = 5060 Hz
(1Pt), 2JPtP = 521 Hz (2Pt) and 17 Hz (1Pt), 3JPP = 8 Hz), 41.6 (1JPtP
= 4995 Hz (1Pt), JPtP = 632 Hz (2Pt) and 9 Hz (1Pt), JPP = 8 Hz).
*The toluene washing was dried in vacuo, and the residue was
dissolved in THF (10 mL). Slow diffusion of n-hexane (25 mL) on the
THF solution afforded a few crystals of Pt4(CO)4(dppe)2·2THF
suitable for X-ray analyses. IR (nujol, 293 K) ν(CO): 1978(s),
1952(m) cm−1.
4.3. Synthesis of [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN.
dppe (0.088 g, 0.221 mmol) was added as a solid to a solution of
[NMe3(CH2Ph)]2[Pt12(CO)24] (0.350 g, 0.106 mmol) in acetone (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 CH2Cl2* (15 mL) and extracted with CH3CN (15 mL). Crystals
of [NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN suitable for X-ray
analyses were obtained by layering n-hexane (3 mL) and diisopropyl
ether (30 mL) on the CH3CN solution (yield 0.19 g, 44% based on
Pt).
C94H83N3O20P4Pt12 (4039.59): calcd. C 27.94, H 2.07, N 1.04, Pt
57.95; found: C 27.76, H 2.21, N0.88, Pt 58.12%. IR (nujol, 293 K)
ν(CO): 2008(vs), 1974(m), 1854(w), 1810(s) cm−1. IR (acetone, 293
K) ν(CO): 2015(vs), 1854(w), 1832(s), 1810(m) cm−1. IR (CH3CN,
293 K) ν(CO): 2015(vs), 1854(w), 1828(s), 1807(m) cm−1. IR
(DMF, 293 K) ν(CO): 2012(vs), 1854(w), 1831(s), 1808(m) cm−1.
31P{1H} NMR (DMF/CD3CN, 298 K) δ (ppm): 47.7 (1JPtP = 5024
Hz (1Pt), JPtP = 513 Hz (2Pt) and 19 Hz (1Pt), JPP = 8 Hz), 41.7
(1JPtP = 5076 Hz (1Pt), 2JPtP = 528 Hz (2Pt) and 17 Hz (1Pt), 3JPP = 8
Hz).
2
3
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN was obtained employing a
similar procedure starting from [NMe4]2[Pt12(CO)24].
*Slow diffusion of n-hexane (25 mL) on the CH2Cl2 washing
afforded a few crystals of Pt6(CO)6(dppe)3·3CH2Cl2 suitable for X-ray
analyses. IR (nujol, 293 K) ν(CO): 1792(vs) cm−1. IR (CH2Cl2, 293
K) ν(CO): 1794(vs) cm−1. 31P{1H} NMR (CD2Cl2, 298 K) δ (ppm):
52.1 (1JPtP = 4825 Hz (1Pt), 2JPtP = 527 Hz (2Pt), 3JPP = 62 Hz (2P)).
4.4. Synthesis of [NEt4]2[Pt6(CO)10(dppe)]. dppe (0.238 g, 0.597
mmol) was added as a solid to a solution of [NEt4]2[Pt6(CO)12]
(0.480 g, 0.272 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* (15 mL) and CH2Cl2
(15 mL) and extracted with DMF (15 mL). Crystals of
[NEt4]2[Pt6(CO)10(dppe)] suitable for X-ray analyses were obtained
by layering isopropanol (30 mL) on the DMF solution (yield 0.26 g,
45% based on Pt).
C52H64N2O10P2Pt6 (2109.53): calcd. C 29.60, H 3.06, N 1.33, Pt
55.49; found: C 29.41, H 2.84, N 1.52, Pt 55.22%. IR (nujol, 293 K)
ν(CO): 1975(s), 1955(vs), 1756(s), 1732(ms) cm−1. IR (CH3CN,
293 K) ν(CO): 1976(vs), 1784(s), 1765(s) cm−1. 31P{1H} NMR
(DMF/CD3CN, 298 K) δ (ppm): 51.2 (1JPtP = 5086 Hz (1Pt), 2JPtP
=
550 Hz (2Pt) and 21 Hz (1Pt)).
J
DOI: 10.1021/acs.inorgchem.6b02750
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
[NMe4]2[Pt6(CO)10(dppe)] was obtained employing a similar
procedure starting from [NMe4]2[Pt6(CO)12].
*The toluene washing was dried in vacuo, and the residue dissolved
in CH2Cl2 (10 mL). Slow diffusion of n-hexane (25 mL) on the
CH2Cl2 solution afforded a few crystals of Pt(dppe)2·CH2Cl2 suitable
for X-ray analyses. 31P{1H} NMR (CD2Cl2, 298 K) δ (ppm): 29.8
(1JPt−P = 3734 Hz).
4.5. Synthesis of [NEt4]2[Pt9(CO)16(R-dppp)]·2CH3COCH3. R-
dppp (0.119 g, 0.289 mmol) was added as a solid to a solution of
[NEt4]2[Pt9(CO)18] (0.520 g, 0.206 mmol) in acetone (15 mL). The
resulting mixture was stirred at room temperature for 2 h, and then,
the solvent removed in vacuo. The residue was washed with toluene
(15 mL) and extracted with acetone (15 mL). Crystals of
[NEt4]2[Pt9(CO)16(R-dppp)]·2CH3COCH3 suitable for X-ray anal-
yses were obtained by layering n-hexane (30 mL) on the acetone
solution (yield 0.31 g, 51% based on Pt).
[NMe3(CH2Ph)]2[Pt12(CO)20(dppe)2]·CH3CN. The asymmetric unit
of the unit cell contains half of a cluster anion (located on 1), one
̅
[NMe3(CH2Ph)]+ cation (located on a general position), and half of a
CH CN molecule disordered over two symmetry related (by 1)
̅
3
positions. The CH3CN molecule was refined isotropically. The C
atoms of the dppe ligands, the C and N atoms of the
[NMe3(CH2Ph)]+ cations, and the C and N atoms of the CH3CN
molecule were restrained to have similar U parameters (SIMU
command in SHELXL, s.u. 0.01). The [NMe3(CH2Ph)]+ cations were
restrained to isotropic behavior (ISOR command in SHELXL, s.u.
0.01). All the aromatic rings were constrained to fit regular hexagons
(AFIX 66 command in SHELXL). Restraints to bond distances were
applied as follows (s.u. 0.02): 1.47 Å for C−N and 1.51 Å for C−C in
[NMe3(CH2Ph)]+; 1.14 Å for C−N and 1.47 Å for C−C in CH3CN.
[NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN. The asymmetric unit of the
unit cell contains half of a cluster anion (located on 1), one [NMe ]+
̅
4
cation (located on a general position), and two halves of two CH3CN
C65H78N2O18P2Pt9(2993.04): calcd. C 26.08, H 2.63, N 0.94, Pt
58.66; found: C 26.21, H 2.44, N 1.10, Pt 58.47%. IR (acetone, 293 K)
ν(CO): 2014(vs), 1812(ms) cm−1. 31P{1H} NMR (CD3COCD3, 298
molecules disordered over symmetry related (by 1) positions. The C
̅
atoms of the dppe ligands, the C and N atoms of the [NMe4]+ cations,
and the C and N atoms of the CH3CN molecules were restrained to
have similar U parameters (SIMU command in SHELXL, s.u. 0.02).
All the aromatic rings were constrained to fit regular hexagons (AFIX
66 command in SHELXL). The [NMe4]+ cations were restrained to
isotropic behavior (ISOR command in SHELXL, s.u. 0.02). Restraints
to bond distances were applied as follows (s.u. 0.02): 1.14 Å for C−N
and 1.47 Å for C−C in CH3CN.
2
K) δ (ppm) isomer I: 59.8 (1JPtP = 5037 Hz (1Pt), JPtP = 517 Hz
3
2
(2Pt), JPP = 11 Hz), 48.0 (1JPtP = 4436 Hz (1Pt), JPtP = 529 Hz
3
2
(2Pt), JPP = 11 Hz); isomer II: 51.2 (1JPtP = 4944 Hz (1Pt), JPtP
=
649 Hz (2Pt), JPP = 10 Hz), 41.2 (1JPtP = 5033 Hz (1Pt), JPtP = 648
3
2
3
Hz (2Pt), JPP = 10 Hz).
4.6. X-ray Crystallographic Study. Crystal data and collection
details for [NMe4]2[Pt6(CO)10(dppe)], [NEt4]2[Pt6(CO)10(dppe)],
[NEt4]2 [Pt9(CO)16(dppe)]·2CH3COCH3, [NEt4]2[Pt9(CO)16(R-
dppp)]·2CH3COCH3, [NMe3(CH2Ph)]2 [Pt12(CO)20(dppe)2]·
CH3CN, [NMe4]2[Pt12(CO)20(dppe)2]·2CH3CN, [Pt(dppe)2]-
[Pt12(CO)24]·2DMF, Pt(dppe)2·CH2Cl2, Pt6(CO)6(dppe)3·3CH2Cl2,
and Pt4(CO)4(dppe)2·2THF are reported in Table 3. The diffraction
experiments were performed on a Bruker APEX II diffractometer
equipped with a CCD detector using Mo Kα radiation. Data were
corrected for Lorentz polarization and absorption effects (empirical
absorption correction SADABS).51 Structures were solved by direct
methods and refined by full-matrix least-squares based on all data using
F2.52 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. Among the 10
crystal structures herein reported, five do not show any alert of levels A
or B in their checkcifs. Three structures present alerts of levels A and
B, and two structures present alerts of level B. All the alerts of levels A
and B are due to high values for the residual electron density. These
maxima are located close to the Pt atoms, in positions that are not
realistic for any atom, and they are series termination errors, which are
common with heavy atoms such as Pt, especially in the case of high
nuclearity clusters.
[NMe4]2[Pt6(CO)10(dppe)]. The asymmetric unit of the unit cell
contains half of a cluster anion (located on 2) and one [NMe4]+ cation
(located on a general position). Similar U restraints were applied to
the [NMe4]+ cation (SIMU command in SHELXL, s.u. 0.01).
[NEt4]2[Pt6(CO)10(dppe)]. The asymmetric unit of the unit cell
contains half of a cluster anion (located on 2) and one [NEt4]+ cation
(located on a general position). One CO ligand was restrained to
isotropic behavior (ISOR command in SHELXL, s.u. 0.01).
[NEt4]2[Pt9(CO)16(dppe)]·2CH3COCH3. The asymmetric unit of the
unit cell contains one cluster anion, two [NEt4]+ cations, and two
CH3COCH3 molecules (all located on general positions). The
CH3COCH3 molecules were refined isotropically. Some C and O
atoms of the cluster anion were restrained to isotropic behavior (ISOR
command in SHELXL, s.u. 0.04). The P and C atoms of the dppe
ligands, the C and N atoms of the [NEt4]+ cations, and the C and O
atoms of the CH3COCH3 molecules were restrained to have similar U
parameters (SIMU command in SHELXL, s.u. 0.02). All the aromatic
rings were constrained to fit regular hexagons (AFIX 66 command in
SHELXL). The CH3COCH3 molecules were restrained to have similar
geometries (SAME 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]+; 1.21 Å for C−O and 1.51 Å for C−C
in CH3COCH3.
[Pt(dppe)2][Pt12(CO)24]·2DMF. The asymmetric unit of the unit cell
contains one cluster anion, one [Pt(dppe)2]2+ cation, and two DMF
molecules (all located on general positions). The crystals are
racemically twinned with refined batch factor 0.513(6). The structure
could not be solved in C2/c, and Cc is the correct space group, which
gave the best refinement.
Pt4(CO)4(dppe)2·2THF. The asymmetric unit of the unit cell
contains one cluster molecule and two THF molecules (all located
on general positions). One THF molecule is disordered and was split
into two positions and refined using one occupancy factor. The THF
molecules were restrained to have similar geometries (SAME
command in SHELXL, s.u. 0.02). The U parameters of the disordered
THF molecule were restrained to be similar (SIMU command in
SHELXL, s.u. 0.01). Restraints to bond distances were applied as
follows (s.u. 0.01): 1.43 Å for C−O and 1.53 Å for C−C in the
disordered THF molecule.
[NEt4]2[Pt9(CO)16(R-dppp)]·2CH3COCH3. The asymmetric unit of
the unit cell contains one cluster anion, two [NEt4]+ cations, and two
CH3COCH3 molecules (all located on general positions). The cluster
anion is actually a mixture of two isomers because of the disorder of
the Me group, which can be found bonded to C(61) or C(62) in ca. a
1:1 ratio. Some C and O atoms of the cluster anion and C atoms of the
cations were restrained to isotropic behavior (ISOR command in
SHELXL, s.u. 0.01). The U parameters of the R-dppp ligand, [NEt4]+
cations, and CH3COCH3 molecules were restrained to be similar
(SIMU command in SHELXL, s.u. 0.02).
Pt(dppe)2·CH2Cl2. The asymmetric unit of the unit cell contains one
cluster molecule and one CH2Cl2 molecule (all located on general
positions).
Pt6(CO)6(dppe)3·3CH2Cl2. The asymmetric unit of the unit cell
contains one cluster molecule and three CH2Cl2 molecules (all located
on general positions).
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.6b02750.
Comparison of the experimental and simulated 31P NMR
spectra of [Pt9(CO)16(dppe)]2−, Pt6(CO)6(dppe)3, Pt-
(dppe)2, [Pt12(CO)20(dppe)2]2−, [Pt6(CO)10(dppe)]2−,
[Pt9(CO)16(R-dppp)]2−, [Pt6(CO)10(R-dppp)]2−. Mo-
K
DOI: 10.1021/acs.inorgchem.6b02750
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
lecular structure of [Pt(dppe)2][Pt12(CO)24]·2DMF
Article
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(PDF)
Crystallographic data in CIF format (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: stefano.zacchini@unibo.it.
■
ORCID
Stefano Zacchini: 0000-0003-0739-0518
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The Univ. of Bologna is acknowledged for financial support of
this work (FARB−Linea d’Intervento 2, “Catalytic trans-
formation of biomass-derived materials into high added-value
chemicals”, 2014-2016).
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