Facile synthesis of platinum based heterobimetallic carbonyl clusters from bis(1-alkenyl)Pt(II) precursors

Article abstract of DOI:10.1016/j.poly.2013.06.011

A new route for the high yield synthesis of platinum containing mixed bimetallic carbonyl clusters of the type [PtRu₂(CO)₈L ₂] (where L₂ = dppe, 1,2-bis(diphenylphosphino)ethane or dppp, 1,3-bis(diphenylphos-phino)propane; L=PPh₃) by the reaction of platinum-alkenyl [PtL₂(1-alkenyl)₂] precursors with [Ru₃(CO)₁₂] is reported. An unexpected multinuclear mixed cluster, [PtRu₄(CO)₁₃(μ₄-PCH ₂CH₂CH₂PPh₂)], obtained under prolonged refluxing conditions was also isolated. All the products were isolated and characterized by various spectroscopic and analytical techniques. In solution, the complex [PtRu₂(CO)₈(P Ph3)₂] gives [Pt₂Ru(-CO)₃(CO)₂(PPh₃) ₃] and Ru₃(CO)₁₁(PPh₃). The structures and relative energies of the intermediates and transition states in the proposed reaction mechanism for the {PtRu₂} clusters have been investigated using density functional theory.

Full text of DOI:10.1016/j.poly.2013.06.011

Polyhedron 62 (2013) 169–178
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Facile synthesis of platinum based heterobimetallic carbonyl clusters
from bis(1-alkenyl)Pt(II) precursors
a
Chinduluri Sravani a, Sadhana Venkatesh a, Akella Sivaramakrishna a, , Kari Vijayakrishna ,
⇑
Hadley S. Clayton b, John R. Moss c, Viktor Moberg c, Hong Su c
a Chemistry Division, School of Advanced Sciences, VIT University, Vellore 632 014, Tamil Nadu, India
b Department of Chemistry, University of South Africa, Pretoria, South Africa
c Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
A new route for the high yield synthesis of platinum containing mixed bimetallic carbonyl clusters of the
type [PtRu2(CO)8L2] (where L2 = dppe, 1,2-bis(diphenylphosphino)ethane or dppp, 1,3-bis(diphenylphos-
phino)propane; L = PPh3) by the reaction of platinum-alkenyl [PtL2(1-alkenyl)2] precursors with
Received 17 May 2013
Accepted 4 June 2013
Available online 27 June 2013
[Ru3(CO)12] is reported. An unexpected multinuclear mixed cluster, [PtRu4(CO)13(l4-PCH2CH2CH2PPh2)],
obtained under prolonged refluxing conditions was also isolated. All the products were isolated and char-
acterized by various spectroscopic and analytical techniques. In solution, the complex [PtRu2(CO)8(P
Ph3)2] gives [Pt2Ru(-CO)3(CO)2(PPh3)3] and Ru3(CO)11(PPh3). The structures and relative energies of the
intermediates and transition states in the proposed reaction mechanism for the {PtRu2} clusters have
been investigated using density functional theory.
Keywords:
Platinum–ruthenium mixed cluster
Platinum-alkenyl complex
Synthesis
Reactivity
Structure
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
The reaction between [Ru3(CO)11(CNBut)] and [Pt(
g-C2H4)
(PPh3)2] at ꢀ30 °C afforded [Ru2Pt(CO)7(PPh3)3], [RuPt2(CO)5
(PPh3)3], [RuPt2(CO)6(CNBut)(PPh3)], [Ru2Pt2(CO)9(CNBut)(PPh3)]
and the hexanuclear complexes [Ru2Pt4(CO)5ꢀn(CNBut)(PPh3)4+n],
where n = 0 and 1 [4]. The reaction of Pt[COD]2 with Ru(CO)5 at
25 °C produced the hexanuclear metal complex, [PtRu2(CO)9]2,
which consists of an open cluster containing two ruthenium atoms
bonded to two platinum atoms, followed by two additional ruthe-
nium atoms. This dimeric compound has also been used to synthe-
size other known trinuclear Pt–Ru cluster derivatives with various
ligand systems [5], but in low yields. The rearrangement of the
The chemistry of mixed-metal clusters has received much
attention because of their interesting structural features, synergis-
tic effects and catalytic potential [1]. The design of nanoparticle
catalysts has been imperative in the initial synthesis of bimetallic
clusters and hence the need for reliable and efficient synthetic
routes is inevitable [2]. Among them, platinum based heterobime-
tallic carbonyl clusters are very well known [3]. The main methods
used for the synthesis of these Pt based heterobimetallic clusters
are (i) reaction of either Pt(0)L4 or L2Pt(II)Cl2 (L = PPh3 and other li-
gands) with various M3(CO)12 clusters or their derivatives (where
M = Os or Ru) and (ii) by splitting larger clusters into smaller ones
and, (iii) aggregating small clusters into multinuclear heterobime-
tallic clusters. It is known that these carbonyl clusters react by; (i)
cleavage of bonds in larger clusters to form smaller clusters, (ii)
condensation of two mixed metal clusters, thus forming high nu-
clear cluster compounds, (iii) ligand substitution and/or addition
(ligands include phosphines, diphosphines, thioethers, carbonyls,
1,5-cyclooctadiene (COD), alkynyls, vinylidenes and mononuclear
systems), (iv) the reaction with different substrates, and (v)
intramolecular M–M rearrangement of ligands and/or dynamical
fluxionality within clusters [3].
spiked triangular cluster [Ru3Pt(-H)(4-
solution into the butterfly cluster [Ru3Pt(4-
(CO)9(dppe)] has been reported [6]. The cluster complex PtRu5
(CO)15(PMe2Ph)( 6-C) has also been shown to exhibit a facile intra-
g
2-CCBut)(CO)9(dppe)] in
2-C = CHBut)
g
l
molecular exchange of the phosphine ligand between the platinum
and a ruthenium atom. The reaction of Pt2M4(CO)18 (where M = Ru
or Os) with cyclooctadiene in the presence of UV irradiation re-
sulted the formation of different mixed metal clusters [7]. The syn-
thesis of new Sn and Ge containing PtRu5 clusters was also
t
achieved by the reaction of PtRu5(CO)14(PBu3 )(
l-H)2(
l
6-C) with
HGePh3 and HSnPh3 under reflux Eqs. (2) and (3) [8]. They are
widely used in the petroleum industry [9] as precursors for catalyt-
ically active metal nanoparticles and in fuel cells [10]. Ruthenium
based catalysts modified with Group 10 metals, e.g. Pt and Pd, were
found to be exceptionally active and selective in a number of
industrially important hydrogenation processes [11].
⇑
Corresponding author. Tel.: +91 4162202351; fax: +91 4162243092.
E-mail address: asrkrishna@rediffmail.com (A. Sivaramakrishna).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.06.011

170
C. Sravani et al. / Polyhedron 62 (2013) 169–178
The present paper describes a facile and novel route for the syn-
2.1.3. GC–MS analysis
thesis of mixed trinuclear metal carbonyl clusters of the type
[PtRu2(CO)8L2] (L = PPh3; L2 = dppe or dppp) using the reaction of
[Ru3(CO)12] with [PtL2(1-alkenyl)2], which have exhibited a rich
chemistry in the recent past [12] (Scheme 1).
GC analyses were carried out using a Varian 3900 gas chromato-
graph equipped with an FID and a 30 m ꢁ 0.32 mm CP-Wax 52 CB
column (0.25 lm film thickness). The carrier gas was helium at
5.0 psi. The oven was programmed to hold the temperature at
32 °C for 4 min and then to ramp to 200 °C at 10 °C/min and hold
for 5 min. GC–MS analyses for peak identification were performed
using an Agilent 5973 gas chromatograph equipped with MSD and
2. Experimental part
a 60 m ꢁ 0.25 mm Rtx-1 column (0.5
lm film thickness). The car-
2.1. Materials and methods
rier gas was helium at 0.9 mL/min. The oven was programmed to
hold the temperature at 50 °C for 2 min and then ramp to 250 °C
at 10 °C/min and hold for 8 min.
All reactions and manipulations were carried out under an inert
atmosphere of dry nitrogen using standard Schlenk and vacuum-
line techniques. [Pt(COD)Cl2] [13] (COD = 1,5-cyclooctadiene), [Pt
(dppp)Cl2] (dppp = 1,3-bis(diphenylphosphino)propane) (1a), [Pt
(dppe)Cl2] (dppe = 1,2-bis(diphenylphosphino)ethane) (1b), [Pt(P
Ph3)2Cl2] (PPh3 = triphenylphosphine) (1c), [Pt(dppm)Cl2] (dpp
m = 1,1-(bis(diphenylphosphino)methane) (1d), [Pt(dppp){(CH2)3-
CH = CH2}2] (2) [8], [Pt(dppe){(CH2)3CH = CH2}2] (3) [9], [Pt(PPh3)2
{(CH2)3CH = CH2}2] (4) [9] and [Pt(dppm){(CH2)3CH = CH2}2] (8)
[12] were prepared as previously described. [Pt(COD)Me2] (Sig-
ma–Aldrich) was purchased and used as received. [Pt(dppe)Me2]
was prepared from [Pt(COD)Me2] by treatment with dppe in
CH2Cl2. The solvents were purchased from commercially available
sources and distilled from dark purple solutions of sodium/benzo-
phenone ketyl prior to use.
2.1.4. Infrared spectroscopy
Infrared spectra were recorded on
spectrometer.
a Perkin-Elmer FT-IR
2.1.5. UV irradiation studies
Irradiations were carried out with an Englehard Hanovia Lamp
(125 W) at a distance of 16 cm from the reaction vessel.
2.1.6. Mass spectrometry
Mass spectral data was obtained using a VG70SE with 8 kV
acceleration and the FAB gun was an Iontech Saddlefield, using
xenon gas and operating at 8 kV. All matrices were made with
3-nba.
2.1.7. Crystallographic data for the compound [PtRu4(CO)13(l4-PCH2
CH2CH2PPh2)] (5a)
2.1.1. Nuclear magnetic resonance spectroscopy
1H and 31P NMR spectra were recorded on a Bruker DXM-400
spectrometer. All 1H chemical shifts are reported referenced to
the residual proton resonance in the deuterated solvent used. All
31P chemical shifts are 1H decoupled and referenced to an 85%
phosphoric acid external peak at 0 ppm.
X-ray single crystal intensity data were collected on a Nonius
Kappa-CCD diffractometer using graphite monochromated Mo K
radiation. The temperature was controlled by an Oxford Cryo-
stream cooling system (Oxford Cryostat). The strategy for the data
collection was evaluated using the Bruker Nonius ‘‘Collect’’ pro-
gram. Data were scaled and reduced using DENZO-SMN software
[14].
2.1.2. Elemental analysis
Micro analyses were conducted with a Thermo Flash 1112 Ser-
ies CHNS–O analyzer instrument.
The structure was solved by direct methods and refined
employing full-matrix least-squares with the program SHELXL-97
L
L
Cl
Cl
1a, L2 = dppp
1b
Pt
L
L
Ru(CO)4
Ru(CO)4
, L2 = dppe
1c, L = PPh3
Pt
80 oC
8 h
(80-90%)
BrMgCH2(CH2)2CH=CH2
Et2O
5, L2 = dppp
6, L2 = dppe
Ru3(CO)12
L
L
Ru(CO)4
L
L
Toulene
( )n
( )n
50 o
4 h
C
Pt
[Ru3(CO)11(PPh3)]
Pt
+
- [2,8-Decadiene]
Ru(CO)4
(50-60%)
7, L = PPh3
n = 2
2
3
, L2 = dppp
, L2 = dppe
4, L = PPh3
OC
CO
CO
CO
CO
OC
Ru
CO
Ru
CO
80 o
C
Ru
OC
OC
OC
5
+
Pt
3 days
Ru
PPh2
OC
OC
P
5a, minor product
Scheme 1.

C. Sravani et al. / Polyhedron 62 (2013) 169–178
171
[15] refining on F2. Packing diagrams were produced using the pro-
gram PovRay and graphic interface X-seed [16]. All non-H atoms
were refined anisotropically. All the hydrogen atoms, except the
amino hydrogens H1A and H1B, were included in idealized posi-
tions in a riding model with Uiso set at 1.2 or 1.5 times those of
the parent atoms. H1A and H1B were located by difference Fourier
methods and refined independently with a simple bond length
constraint. The structure was refined successfully with R = 0.0238.
(CCDC number 900110) [16]: C28H16O13P2PtRu4, M.w.t = 1221.
72 g molꢀ1, monoclinic, space group P21/c, a = 9.4382(2) Å, b =
11.4153(3) Å, c = 31.4264(6) Å, = 90°, = 95.801(2)°, = 90°, V = 33
68.54(13) Å3, Z = 4, calcd = 2.409 Mg/m3, T = 173(2) K, = 6.048 m
mꢀ1, F(000) = 2288, crystal size 0.15 ꢁ 0.14 ꢁ 0.14 mm3. Intensity
data were collected with a Nonius Kappa CCD diffractometer.
94236 reflections, 6393 independent (Rint = 0.0519), multi-scan
the GAUSSIAN basis set of the same size [19]. This combination of ba-
sis set and functional has been used successfully in previous stud-
ies of Pt and Ru complexes [20,21] Geometry optimizations were
performed without any symmetry constraints and the relative
energies were compared taking into account the total number of
molecules present. The convergence criteria for these optimiza-
tions consisted of the following threshold values: 1 ꢁ 10ꢀ5 Ha for
energy; 0.002 Ha Åꢀ1 for gradient and 0.005 Å for displacement
convergence, while a self-consistent field density convergence
threshold of 1 ꢁ 10ꢀ6 Ha was specified. All optimized geometries
were subjected to a full frequency analysis at the same level of the-
ory (GGA/PW91/DNP) to verify the nature of the stationary points.
Equilibrium geometries were characterized by the absence of
imaginary frequencies.
The phenyl substituents on the bis-phosphino ligand contain a
large number of atoms which contribute little to the electronic
structure of these complexes, and consequently they were replaced
by H atoms in the calculations to reduce the computational de-
mands of the system.
absorption correction
(SADABS), structure solution using direct
methods (SHELXS-97), structure refinement on F2 using full-matrix
least-squares procedures (SHELXL-97), R1 = 0.0238 [I > 2(I)], wR2
= 0.0449 (all data), GOF = 1.194, max./min. residual electron
density = 0.929/ꢀ0.686 e Åꢀ3 [17].1
2.2. Synthetic methodology
2.1.8. Crystallographic data for the compound [Pt2Ru(CO)2
2.2.1. Preparation of [PtRu2(CO)8(dppp)] (5)
(l-CO)3(PPh3)3] (13)
2 (256 mg, 0.3433 mmol) and [Ru3(CO)12] (220 mg, 0.3441
mmol) were dissolved in 10 mL of toluene. The reaction mixture
was then heated to 80 °C in a closed flask under reduced pressure
for 8 h. A dark colored solution was formed. The reaction was mon-
itored by 31P NMR until the completion of the reaction. All the vol-
atiles were removed by a high vacuum pump and the residue was
dissolved in 5 mL of CH2Cl2 and added to the top of a silica gel col-
umn. An orange red band was collected by eluting with a solvent
mixture of 4:1 CH2Cl2: n-hexane. The product was obtained as a
bright orange red solid (5). Yield: 319 mg (90%). M.p.: 166–
169 °C (dec.). Anal. Calc. for C35H26O8P2PtRu2 (1034.88): C, 40.67;
(CCDC number 671765) [14]: C59H45P3Ru1Pt2O5, M.w.t = 14
18 g molꢀ1, triclinic, space group P1, a = 12.5217(1) Å, b = 13.4675
(1) Å, c = 15.6595(1) Å, = 85.026(1)°, = 77.121(1)°, = 72.026(1)°,
V = 2448.23(3) Å3, Z = 2, calcd = 1.924 Mg/m3, T = 113 (2) K, = 6.15
5 mmꢀ1, F(000) = 1368, 5.70 < 2 < 51.83, (Mo k) = 0.71073 Å, crys-
tal size 0.14 ꢁ 0.18 ꢁ 0.18 mm3. Intensity data were collected [17]
with a Nonius Kappa CCD diffractometer. 61236 reflections, 9276
independent (Rint = 0.0315), multi-scan absorption correction
ꢀ
(
SADABS), structure solution using direct methods (SHELXS-97),
structure refinement on F2 using full-matrix least-squares proce-
dures (SHELXL-97), R1 = 0.0195 [I > 2(I)], wR2 = 0.0420 (all data),
GOF = 1.102, max./min. residual electron density = 0.693/
H, 2.54. Found: C, 40.48; H, 2.92%. IR (m
CO/cmꢀ1) in CH2Cl2:
2066 m, 2023vs, 1997sh, 1983s, 1960sh. 1H NMR (CDCl3) d: 6.85–
7.73 (m, 20H, Ph), 1.84–2.40 (m, 6H, P–CH2); 31P NMR (CDCl3) d:
8.35 (JPt–P = 3079 Hz). Mass Data, m/z: 1034.9 [M]+; 607.1
[(dppp)Pt]+.
ꢀ0.583 e Åꢀ3
.
2.1.9. Crystallographic data for the compound PtRu2(CO)6(l-dppm)2]
(14)
(CCDC number 670301) [14]: C56H44O6P4PtRu2ꢂ2(C6H6), M.w.t =
1490.24 g molꢀ1, monoclinic, space group P21/c, a = 15.8482(10) Å,
b = 19.7322(12) Å, c = 18.9112(12) Å, = 94.072(3)°, V = 5899.0(6)
Åꢀ3, Z = 4, calcd = 1.678 Mg/m3, T = 100(2) K, F(000) = 2952, 3.30
< 2 < 105.98, (Mo k) = 0.71073 Å, crystal size 0.33 ꢁ 0.30 ꢁ 0.19
mm3. Intensity data were collected [14] with a Bruker KAPPA APEX
II diffractometer. 258672 reflections, independent reflections
66042 [Rint = 0.0657], multi-scan absorption correction (SADABS),
structure solution using direct methods (SHELXS-97), structure
refinement on F2 using full-matrix least-squares procedures
2.2.2. Preparation of [PtRu2(CO)8(dppe)] (6)
3 (225 mg, 0.3075 mmol) and [Ru3(CO)12] (200 mg, 0.3128
mmol) were dissolved in 10 mL of toluene and then the mixture
was heated to 80 °C in a closed flask under reduced pressure for
8 h. A similar work-up procedure was used as mentioned above
to isolate an orange red solid (6). Yield: 244 mg (78%). M.p.: 85–
90 °C (dec.). Anal. Calc. for C34H24O8P2PtRu2 (1019.72): C, 40.05;
H, 2.37. Found: C, 40.79; H, 2.44. IR (m
CO/cmꢀ1) in CH2Cl2: 2063s,
2025s, 1978br, 1953m. 1H NMR (CDCl3) d: 7.34–7.98 (m, 20H,
Ph), 1.92–2.20 (m, 4H, P–CH2); 31P {1H} NMR (CDCl3) d: 61.3
(JPt–P = 3117 Hz). Mass Data, m/z: 1019.7 [M]+, 593.1 [Pt(dppe)]+.
(
SHELXL-97), R1 = 0.0395 [I > 2(I)], wR2 = 0.0629 (36020 reflections),
GOF = 1.225 max./min. transmission = 0.5965/0.4343 e Åꢀ3
.
2.2.3. Preparation of [PtRu4(CO)13(l4-PCH2CH2CH2PPh2)] (5a)
2.1.10. Computational details
All calculations were carried out using the DMol3 density func-
tional theory (DFT) code as implemented in the Accelrys Material
StudioÒ 5.0 software package [17]. The non-local generalized gra-
dient approximation (GGA) using the PW91 exchange–correlation
functional was used for geometry optimizations in all cases [18].
A double numeric, polarized split valence (DNP) basis set was used
in this study with a DFT semi-core pseudo potential to account for
relativistic effects in Ru and Pt. The size of the DNP basis set is
comparable to GAUSSIAN 6-31G⁄⁄, but the DNP is more accurate than
2 (186 mg, 0.2494 mmol) and [Ru3(CO)12] (164 mg, 0.2565
mmol) were dissolved in 10 mL of toluene. The reaction mixture
was then heated to 80 °C in a closed flask under reduced pressure
for 3 days. An intense red colored solution was formed. The 31P
NMR spectrum of the crude reaction mixture indicated the forma-
tion of 5 as a major product at 8.35 ppm (JPt–P = 3079 Hz) and a
new doublet at 13.2 ppm (JPt–P = 3126 Hz). All the volatiles were
removed by a high vacuum pump and the residue was dissolved
in 5 mL of CH2Cl2 and added to the top of a silica gel column. An
orange red band was collected by eluting with a solvent mixture
of 4:1 CH2Cl2:n-hexane. The major product, a bright orange red so-
lid (5), was obtained in 72% yield and isolated as mentioned above.
Then using CH2Cl2:n-hexane (10:1) as the eluant, an intense green
1
Crystallographic data have been deposited at the CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK and copies can be obtained on request, free of charge, by
quoting the publication citation and the deposition number 670301.

172
C. Sravani et al. / Polyhedron 62 (2013) 169–178
band was separated, and it was found to be a stable and new
heterobimetallic carbonyl cluster containing a {PtRu4} template
(5a) in 2% yield. M.p.: 206–208 °C (dec.). Anal. Calc. for C28H16O13-
P2PtRu4 (1221.73): C, 27.53; H, 1.32. Found: C, 27.48; H, 1.30%. IR
ward, and recently Adams, have extensively studied the synthesis
as well as novel reactivity patterns of platinum based bi- and tri-
metallic carbonyl clusters [24–26]. Usually the literature methods
for the carbonyl cluster synthesis indicate a mixture of clusters and
low yields. To the best of our knowledge, there is no direct method
available for the synthesis of trinuclear heterobimetallic clusters
selectively.
The bis(1-alkenyl)platinum(II) complexes 2–4 were prepared
by the reactions of 1a-c with the appropriate Grignard reagents,
as shown in Scheme 1. Investigations on the reactions of 2–4 with
ruthenium-carbonyls were carried out with the aim of forming
mixed metal complexes via olefin coordination to ruthenium. In
contrast, the formation of trinuclear cluster compounds with a
{PtRu2} core, [L2PtRu2(CO)8] (where L2 = dppp (2) or dppe (3);
L = PPh3 (4)) (Scheme 1), by the subsequent elimination of the or-
ganic fragment was observed. The products 5–7 were identified by
IR, 1H and 31P NMR spectroscopy, mass spectrometry and elemen-
tal analysis. The data for the compounds 6 [5] and 13 [4] are con-
sistent with the literature reports and the yields were found to be
superior to the reported methods [5,27].
(m
CO/cmꢀ1) in CH2Cl2: 2061m, 2044vs, 2031m, 2013s; 1H NMR
(CDCl3) d: 6.78–7.64 (m, 10H, Ph), 1.82–2.32 (m, 6H, P-CH2); 31P
2
1
{1H} NMR (CDCl3) d: 13.2 (d, JP–P = 14 Hz, JPt–P = 3126 Hz, Pt–P),
2
1
408.0 (d, JP–P = 14 Hz, JPt–P = 864 Hz, Pt–P).
2.2.4. Preparation of [PtRu2(CO)8(PPh3)2] (7)
4 (266 mg, 0.31 mmol) and [Ru3(CO)12] (202 mg, 0.316 mmol)
were dissolved in 10 mL of toluene and then the mixture was
heated to 50 °C in a closed flask under reduced pressure for 4 h.
A similar work-up procedure was used as mentioned above to iso-
late an orange red solid (7). Yield: 195 mg (55%). M.p.: 188–192 °C
(dec.). Anal. Calc. for C44H30O8P2PtRu2 (1145.88): C, 46.12; H, 2.64.
Found: C, 45.89; H, 2.72%. IR (m
CO/cmꢀ1) in CH2Cl2: 2045w, 2028s,
2013w. 1H NMR (CDCl3) d: 7.36–8.43 (m, 30H, Ph); 31P NMR
(CDCl3) d: 35.2 (JPt–P = 4577 Hz). Mass Data, m/z: 1146.92 [M]+,
719.15 [(PPh3)2Pt]+.
The formation of mixed platinum bimetallic trinuclear clusters
was observed when reacted with [Ru3(CO)12]. It is noteworthy that
no similar clusters were observed with the dppm ligand (8). Reac-
tions of 2–4 with [Co2(CO)8] yielded known trinuclear and tetranu-
2.2.5. Preparation of [Pt2Ru(CO)2(l-CO)3(PPh3)3] (13)
7 (120 mg, 0.1046 mmol) was taken in 5 mL of CH2Cl2 and the
solution was irradiated with UV light in a closed flask under
reduced pressure for 18 h at room temperature. The solvent was
removed under vacuum and then the residue was chromato-
graphed on a silica gel column using CH2Cl2 as the eluent. A red
band was isolated and dried under vacuum for a few hours. The
residue was recrystallized from CH2Cl2:n-hexane (1:3) to obtain
single crystals. Yield: 27 mg (36%). M.p.: 225–226 °C (dec.). Anal.
Calc. for C44H30O8P2Pt2Ru (1418.08): C, 49.97; H, 3.20. Found: C,
clear carbonyl clusters of the type [Co2Pt(l-CO)(CO)6(L2)] and
[Co2Pt2( -CO)3(CO)5(PPh3)2] [28]. It is interesting to note that no
l
cluster formation was observed when reacting 2 with other metal
carbonyls, including [W(CO)6] and [Mo(CO)6], under identical reac-
tion conditions.
Attempts were made to observe the formation of intermediate
complexes in the overall reaction of 2 and 3 separately with [Ru3
(CO)12] in toluene at 80 °C by monitoring the samples with IR
and 1H and 31P NMR spectroscopy at 30 min intervals. The 1H
decoupled 31P NMR chemical shift of 2 at d 3.48 (JPt–P = 1645 Hz))
was changed to d 8.9 (JPt–P = 3079 Hz) (5). In a similar way, 3
(d 46.4 (JPt–P = 1619 Hz)) forms 6 (d 61.2 (JPt–P = 3157 Hz)). It is pre-
dicted that Ru3(CO)12 at 80 °C can form the very reactive interme-
diate 9 along with coordinatively unsaturated Ru(CO)4 species in
the presence of 5 or 6 [29]. Then the corresponding allylic hydride
species (10) can result from 9, and this can be envisaged based on
literature reports [30] (i.e. the isomerization of a terminal olefin to
an internal olefin is consistent with the allylic metal hydride inter-
mediate pathway (10)). This is also in accordance with a similar re-
ported mechanism on the selective isomerization of 1-alkenes to
the corresponding 2-alkenes by various metal–carbonyl cluster
compounds, particularly with [Ru3(CO)12] [31]. The progress of
the reaction for 3 ? 6 was monitored by 31P NMR spectroscopy,
as shown in Scheme 2. The bis(2-alkenyl)Pt(II) species were con-
sidered to be the intermediates that were identified by 31P NMR
spectroscopy. The broad signals observed in the range d 46.3–
46.8 for 6 reveal the presence of three different isomers, E/E, E/Z,
Z/Z (11), as shown in Scheme 2. This is validated by our earlier
observations of the quantitative isomerization of bis(1-alke-
nyl)Pt(II) to bis(2-alkenyl)Pt(II) complexes under similar condi-
tions [10]. Fig. 1 illustrates the formation of various species
during the reaction of 3 with Ru3(CO)12 at 80 °C in toluene after dif-
ferent time intervals, and this directly supports the proposed isom-
erized species 11 (Scheme 2). When the infra red spectrum of
Ru3(CO)12 was compared with the crude reaction mixture, as well
as the product (L2)PtRu2(CO)8 (where L2 = dppe or dppp), signifi-
cant changes in the region from 2122 to 1977 cmꢀ1 were
observed.2 They have been attributed to the formation of interme-
49.89; H, 3.52%. IR (m
CO/cmꢀ1) in CH2Cl2: 2020s, 1947s, 1852w,
1791vs. 1H NMR (CDCl3) d: 7.46–8.69 (m, 30H, Ph); 31P NMR
(CDCl3) d: 35.2 (JPt–P = 4577 Hz) (Pt–P), 26.6 (Ru–P). Mass Data,
m/z: 1417.8 [M]+ and loss of CO and PPh3 groups at 1334, 1306,
896, 868 and comparison with the literature values [25].
2.2.6. Preparation of [PtRu2(CO)6(l-dppm)2] (14)
8
(322 mg, 0.44866 mmol) and [Ru3(CO)12
]
(292 mg,
0.4567 mmol) were suspended in 5 mL of toluene and the mixture
was heated at 80 °C for 8 h. The solvent from the resulting dark or-
ange red solution was removed under vacuum and then the resi-
due was chromatographed on a silica gel column using CH2Cl2 as
the eluent. The orange red band was isolated, and dried under vac-
uum after removing the solvent. The solid residue was recrystal-
lized from CH2Cl2/n-hexane to obtain single crystals of 14. Yield:
160 mg (26%). M.p.: 236–238 °C (dec.). Anal. Calc. for C56H44O6P4-
PtRu2 (1411.17): C, 50.41; H, 3.32. Found: C, 50.45; H, 3.42. IR
(m ) in CH2Cl2: 2007s, 1960s, 1940sh, 1924s, 1893s,
CO/cmꢀ1
1878b; 1H NMR (CDCl3) d: 4.5 (m, 4H, P–CH2), 6.95–7.98 (m,
2
40H, Ph); 31P {1H} NMR (CDCl3) d: 16.4 (d, JP–P = 48 Hz, Ru–P),
2
1
8.0 (d, JP–P = 48 Hz, JPt–P = 3130 Hz, Pt–P).
3. Results and discussion
3.1. Synthesis and characterization
Most of the reported methods for synthesizing platinum con-
taining bi- and polynuclear metal carbonyl cluster complexes are
based on the reactions of the appropriate metal–carbonyls with
Pt(0) species as precursors [22]. In addition, a secondary method
for the synthesis of heteronuclear multimetallic clusters of plati-
num containing cobalt or molybdenum has been reported using
the carbonylmetallate salts Na[Co(CO)4] or Na[
with cis- or trans-PtCl2(PPh3)2 [23]. The groups of Stone and Wood-
g-C5H5)Mo(CO)3]
2
See supporting information Fig. 7 for the corresponding FT-IR data.

C. Sravani et al. / Polyhedron 62 (2013) 169–178
173
Ru(CO)4
L
L
L
L
80 oC
Pt
+ Ru(CO)4
Pt
+
Ru3(CO)12
Toluene
Ru(CO)4
9
H
H
H
-2 CO
L
L
CO
OC
Ru
H
Pt
CO
H
H
H
+
+
L
Pt
L
L
L
+2 CO
H
+
2 Ru(CO)4
Pt
Pt
H
H
H
10
L
L
H
Ru
CO
OC CO
H
H
11
Ru(CO)4
L
L
5, L2 = dppp
Pt
Ru(CO)4
Pt
6
, L2 = dppe
L
Ru(CO)4
+
7, L = PPh3
L
Ru(CO)4
12
Scheme 2. Proposed reaction mechanism for the formation of the trinuclear {PtRu2} carbonyl clusters.
supports the intermediacy of the hexacoordinate Pt(IV) species.
In all the reactions, the organic product distribution reveals the
presence of 2,8-decadiene (98%), traces of n-pentane (0.5%), 2-pen-
tene (0.5%, a mixture of cis- and trans- isomers) and 1,4-pentadiene
(1.0%).
In contrast, the reaction with prolonged heating gave smaller
amounts of 5a and afforded 5 as the major product. The green prod-
uct 5a, formed unexpectedly, was isolated by column chromatogra-
phy in very low yields. As the formation of multi nuclear clusters is
known by different routes [5b], the structural characterization of 5a
showed a novel cluster with a bridging diphosphine. Spectroscopi-
cally, 5a is characterized by its infrared spectrum and by proton
decoupled 31P NMR resonances at low field. The formation of 5a
clearly results from cluster aggregation to form the mixed Pt–Ru
cluster Ru4(CO)13Pt(CO)(l4-PCH2CH2CH2PPh2) (5a) (Scheme 1).
In order to try and shed more light on the mechanism of the
reaction, similar experiments were carried out using other organo-
platinum complexes, bearing either different ligand systems or dif-
ferent alkyl groups. Thus, attempts to react [Ru3(CO)12] with
[Pt(COD)Me2] and [Pt(dppe)Me2] under similar reaction conditions
did not yield the clusters 5–7. It appears that the pendant olefinic
group plays a key role in activating the metal carbonyl precursors
to produce these heterobimetallic cluster compounds.
An ORTEP diagram of compound 5a is shown in Fig. 2. The
ruthenium atoms are arranged in a square-based pyramidal geom-
etry with the phosphorus atom of the phosphinidene ligand occu-
pying one of the basal sites. The square base is capped with the
platinum center, resulting in an octahedral arrangement of the
six core cluster atoms. The platinum center is bound by one car-
bonyl and one diphenylphosphino end of the dppp ligand, while
each ruthenium center has three terminal carbonyl ligands.
The phosphorus atom of second end of dephenylated dppp li-
Fig. 1. Proton decoupled 31P NMR spectra recorded during the reaction of 3 with
Ru3(CO)12 at 80 °C in toluene to obtain 6: (a) before heating the reaction mixture;
(b) after 1 h heating; (c) after 10 h heating; (d) after 12 h heating.
diates 10, 11 and 12 (see Scheme 2). No spectroscopic evidences
were obtained for the identification of compounds 9 and 12.
To investigate this further, the reaction between
3 and
Ru3(CO)12 in toluene-d8 was followed in situ at 100 °C using NMR
spectroscopy. The 1H NMR spectra revealed a signal at d ꢀ15.2,
which was attributed to Ru–H and a broad multiplet at d 2.2–2.5,
indicating the presence of an allylic ruthenium hydride intermedi-
ate (10) that forms the bis(2-alkenyl)Pt(II) species (11). Further,
these isomerized species (11) undergo an oxidative addition reac-
tion with [Ru(CO)4] fragments to yield unstable heaxacoordinate
Pt(IV) species (12). The identification of long chain dienes by GC–
MS confirms the reductive elimination pathway, which further
gand (
l4-PCH2CH2PPh2) lies on the Ru(1), Ru(3), Ru(4), Pt(1) atoms
by forming a six membered ring with platinum, resulting in an

174
C. Sravani et al. / Polyhedron 62 (2013) 169–178
shows peaks at d 408 and 13.2 for the phosphinidene and phos-
phine ligands, respectively. The two bond P–P coupling constant
is 14 Hz. This small coupling constant reflects the relative cis
arrangement of these two ligands on platinum. A 195Pt coupling
constant of 3126 Hz is observed in the satellites of the diphenyl-
phosphino resonance, while the 195Pt coupling to the phosphinid-
ene phosphorus atom is much smaller, being 864 Hz.
The platinum–carbonyl interactions are almost linear [O(1)–
C(1)–Pt(1) = 175.9(4)°]. The Ru–C–O angles [ranging from
171.0(3) to 179.2(4)°] are much closer to linearity, without any
semi-bridging CO ligands. As well, the Ru–C distances [ranging
from 1.895(4) to 1.927(5) Å] are slightly longer than the Pt–C dis-
tance [1.882(4) Å]. These parameters confirm that the platinum–
carbonyl interactions are relatively strong and may suggest that
the removal of electron density from the electron-rich Pt center
is not easy. In solution, the infrared spectrum of 5a also shows
no evidence for bridging carbonyls, with the lowest frequency
band occurring at 2013 cmꢀ1
.
As the electronegativity of the group on phosphorus increases,
the phosphorus chemical shift moves further downfield [32]. A
parallel trend is observed in the phosphinidene phosphorus-plati-
num coupling constants, which increase as the electronegativity of
the phosphorus substituent increases.
The mass spectrum of the isolated compound 5, showed the
step-wise CO dissociation pattern from the molecular ion (m/
z = 1034.7) with the mass fragments corresponding to Pt(dppp)+
(m/z = 607.4) and other species of lower mass (Fig. 3). A similar
fragmentation pattern was observed in the dppe and PPh3
analogues.
Relative energies of the intermediates on the potential energy
surface are summarized in Fig. 4. Our calculations indicate that
the proposed reaction mechanism for the formation of a plati-
num-ruthenium trinuclear cluster via a hexacoordinate Pt(IV) spe-
cies is kinetically and thermodynamically feasible. The method
used in these calculations show the overall reaction to be exother-
mic by 79.8 kcal/mol, while the alkenyl dissociation energy from
(V) to (VI) is exothermic by 45.5 kcal/mol. The rate-determining
Fig. 2. ORTEP diagram of Ru4(CO)13Pt(CO)(l4-PCH2CH2CH2PPh2) (5a) with ellipsoi-
dal model of probability level = 40%. All H are omitted. Selected bond distances (Å)
and angles (°): Pt(1)–C(1) 1.882(4); Pt(1)–P(1) 2.3015(10); Pt(1)–P(2) 2.3196(10);
Ru(1)–P(1) 2.4179(10); Ru(3)–P(1) 2.3537(10); Ru(4)–P(1) 2.3784(10); Pt(1)–Ru(2)
2.7452(3); Pt(1)–Ru(4) 2.8769(3); Pt(1)–Ru(1) 2.9122(3); Ru(1)–Ru(2) 2.7823(4);
C(1)–Pt(1)–P(1) 161.27(13); C(14)–P(1)–Pt(1) 120.32(12); C(1)–Pt(1)–P(2)
99.81(12); P(1)–Pt(1)–P(2) 96.75(3); C(1)–Pt(1)–Ru(2) 87.92(12); P(1)–Pt(1)–Ru(2)
77.01(2); P(2)–Pt(1)–Ru(2) 168.96(3); C(1)–Pt(1)–Ru(4) 109.61(13); P(1)–Pt(1)–
Ru(4) 53.29(3).
step appears to be the isomerization of the terminal
x-alkenyl to
the internal alkenyl complex via the ruthenium–hydride(III). The
optimized geometries of (II) and (IV) do not show any agostic inter-
action between the ruthenium center and the allylic protons or C
protons respectively.
a
approximately cis arrangement of the two phosphorus ligands on
the platinum, while the carbonyl is directed away from the phos-
phinidene. The Ru–Ru and Ru–Pt bond lengths fall within the range
2.7823(4)–2.8755(4) Å. Careful examination of these bond lengths
reveals a distortion of the apical Ru(3) atom away from the center
of the square. The metal–phosphinidene phosphorus bond lengths
also show a distortion. All the Ru–P distances to the phosphinidene
ligand are unsymmetrical and in this case one distance, P(1)–Ru(1)
[2.4179(10) Å] is long compared to the others [P(1)–Pt = 2.3015
(10) Å, P(1)–Ru(3) = 2.3537(10) Å, P(1)–Ru(4) = 2.3784(10) Å].
The P(1)–C bond distance in the carbophosphinidene ligand of
1.841(4) Å is comparable to those observed in other phosphinidene
complexes [32] and longer than the P(2)–C bond distance. The Pt–
P(2) distance of 2.3196(10) Å is a normal Pt–PPh2 distance, longer
than the P(1)–Pt bond, 2.3015(10) Å. The 31P NMR spectrum of 5a
3.2. Transformations of the PPh3 derivatives
In CH2Cl2 solution, compound 7 undergoes a slow and irre-
versible transformation reaction Eq. (1) in air or under UV light
at room temperature within a few hours to give the known prod-
uct 13 [4] in a reasonable yield (36%). During this reaction the
{PtRu2} framework of 7 is been completely changed into a cluster
with a {Pt2Ru} core (13) and Ru3(CO)11(PPh3). It was found that
this transformation reaction Eq. (1) was selective to the PPh3
derivatives of the {PtRu2} clusters and was not observed with
the dppp and dppe analogues 5 and 6. Compound 13 was charac-
terized by a combination of IR, 1H and 31P NMR spectroscopy, and
single crystal X-ray diffraction analysis. The ORTEP diagram of the
PPh3
OC
CO
O
O
Ru
Ru(CO)4
Ru(CO)4
Ph3P
Ph3P
CH2Cl2
+ Ru3(CO)11(PPh3)
Pt
2
Pt
Pt
Ph3P
PPh3
7
O
13

C. Sravani et al. / Polyhedron 62 (2013) 169–178
175
SCAN GRAPH. Flagging=Low Resolution M/z.
Scan 9#0:49 - 11#1:00. Entries=1185. Base M/z=154. 100% Int.=0.75221. FAB. POS.
100
90
80
70
60
50
40
30
20
10
0
154
922.8
1034.7
867.8
307
289
977.8
1000
816.8
176
200
424
400
442.1
(*20)
800
100
300
500
600
700
900
1100
Low Resolution M/z
Fig. 3. Mass spectra of 5 showing the step-wise ‘CO’ dissociation pattern from the molecular ion (m/z = 1034.7).
Fig. 4. Energy profile for proposed intermediates and transition states in the reaction mechanism. The relative energies are given in kcal/mol.

176
C. Sravani et al. / Polyhedron 62 (2013) 169–178
molecular structure 13 is shown in Fig. 5. The crystallographic
data was collected at 113 K which generated better refinement
with more precise molecular parameters, as compared to the
same structure of 13 previously reported by Bruce et al. [4].
The structure of 13 is isostructural with the osmium analogue
of the type {PtOs2} [4] and consists of a triangular array of two
platinum atoms and one ruthenium atom. There are two terminal
carbonyl ligands bonded to each Ru atom and three carbonyls are
bridging along the three metal–metal edges. The Pt(1)–P(1) and
Pt(2)–P(2) bond lengths of 2.263(2) and 2.270(6) Å, respectively,
are similar in distance and are in the range of usual Pt–P bond
distances (2.26–2.28 Å) [33]. The presence of the bridging CO li-
gands across the Ru–Pt bonds does not influence the Pt–P bond
distances.
L
L
Ph2P
PPh2
( )
( )
n
+
Pt
3
2 Ru3(CO)12
Toulene, 80 oC, 8 h
n
3, L2 = dppe
n = 2
Ph2
P
Ph2
P
Pt
L
2 Ru3(CO)12
Toulene, 80 oC, 8 h
( )
n
n
3
Pt
Ph2P
PPh2
CO
( )
Ru
Ru
L
OC
OC CO OC CO
8, L2 = dppm
n = 2
14
Ru(CO)4
Ru(CO)4
L
Ph2P PPh2
Toulene, 80 oC, 6 h
Pt
L
3.3. Reaction of dppm derivatives
5, L2 = dppp
In contrast to the dppp and dppe analogues, the reaction of
Scheme 3.
[Pt(dppm)(
x
-pentenyl)2] (8) with [Ru3(CO)12] yielded a known
-dppm)2] (14) [34], as
dppm bridging complex, [PtRu2(CO)6(
l
shown Scheme 3. The 31P NMR spectrum of complex 14 shows
two resonances at d 16.8 (d) for the less shielded Ru bonded P
and at d 8.3 (d) for the more shielded Pt bonded P, with equal
intensities. The benzene solvated crystal structure of 14 is shown
in Fig. 6. The platinum atom and the two ruthenium atoms form
a triangular structure. Two dppm ligands bridge both Pt–Ru me-
tal–metal edges, but not along the Ru–Ru vector. All six carbonyl
ligands are terminal and are found to coordinate selectively to
the two ruthenium atoms in the cluster. It is clearly evident from
the packing diagram that the two molecules of benzene in the crys-
tal lattice do not show any disorder or molecular interactions with
the structure of the cluster. Further, characterization data of com-
pound 14 are in agreement with the literature values [34].
Attempts to make a mixed ligand trinuclear complex, substitut-
ing the dppp ligand by dppm, were not successful as the same
product 14 was obtained when a CHCl3 solution of 5 was refluxed
with dppm (Scheme 3).
0
Fig. 5. Molecular structure of 13 (ORTEP diagram; 40% probability ellipsoids). Hydrogen atoms are omitted for clarity. Selected bond lengths (ÅA): Pt(1)–P(1) 2.269(6); Pt(2)–
P(2) 2.270(6); Ru(1)–P(1) 2.437(5); Pt(1)–Ru(1) 2.734(1); Pt(2)–Ru(1) 2.741(2); Ru–CO(4) 1.889(11); Ru–CO(2) 1.900(10).

C. Sravani et al. / Polyhedron 62 (2013) 169–178
177
0
Fig. 6. Molecular structure of 14 (ORTEP diagram; 40% probability ellipsoids). Hydrogen atoms and two benzene molecules are omitted for clarity. Selected bond lengths (ÅA)
and angles (°): Pt(1)–P(2) 2.2464(3); Pt(1)–P(3) 2.2536(3); Pt(1)–C(6) 2.5832(13); Pt(1)–Ru(1) 2.67272(15); Pt(1)–Ru(2) 2.67870(16); Ru(1)–Ru(2) 2.8486(2); Ru(2)–C(5)
1.8967(14); Ru(2)–C(6) 1.9113(13); Ru(2)–C(4) 1.9258(14); O(1)–C(1)–Ru(1) 174.26(11); O(6)–C(6)–Ru(2) 173.52(11); O(6)–C(6)–Pt(1) 113.26(10); Ru(2)–C(6)–Pt(1)
71.39(4).
[4] (a) M.I. Bruce, J.G. Matisons, B.W. Skelton, A.H. White, Aust. J. Chem. 35 (1982)
4. Summary
687;
(b) M.I. Bruce, M.R. Snow, E.R.T. Tiekink, Aust. J. Chem. 39 (1986) 2145.
A new route has been used to synthesize a series of platinum
based mixed bimetallic carbonyl clusters from bis(1-alkenyl)Pt(II)
compounds as precursors, and the unexpected synthesis of a
substituted phosphinidene mixed metal cluster containing a qua-
druply bridging phosphorus atom was also achieved. The potential
energy surface, optimized using density functional theory, is fully
consistent with the postulated reaction mechanism and provides
insight into the mechanisms by which the clusters are formed.
Studies on the synthesis of novel carbonyl clusters of the type
{PtOs2}, {PtFe2}, {NiRu2} and {NiFe2} are underway.
[5] R.D. Adams, G. Chen, J.G. Wang, W. Wu, Organometallics 9 (1990) 1339.
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Acknowledgements
(b) R. Raja, T. Khimyak, J.M. Thomas, S. Hermans, B.F.G. Johnson, Angew.
Chem., Int. Ed. Engl. 22 (2001) 4638;
(c) R. Raja, G. Sankar, S. Hermans, D.S. Shephard, S. Bromley, J.M. Thomas,
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251 (2007) 1294;
Dr. ASRK is highly grateful to Council of Scientific and Industrial
Research India (CSIR-INDIA) for the financial support of this work
through research grants Ref. No. 01(2541)/11/EMR-II. Also we
thank Dr. M.W. Day (California Institute of Technology, California)
for the X-ray structural data of compound 13. Mr. Sadhana Venk-
atesh is grateful to CSIR for the fellowship to carry out the pro-
posed research work. Dr. ASRK and his group members thank
DST-VIT-FIST for NMR and SAIF-VIT Universiy for other instrumen-
tation facilities.
(b) K. Dralle, N.L. Jaffa, T.L. Roex, J.R. Moss, S. Travis, N.D. Watermeyer, A.
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(c) A. Sivaramakrishna, H. Su, J.R. Moss, Angew. Chem., Int. Ed. Engl. 46 (2007)
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