Experimental and computational studies on the reaction of silanes with the diphosphine-bridged triruthenium clusters Ru3(CO)10(μ- dppf), Ru3(CO)10(μ-dppm) and Ru3(CO) 9{μ3-PPhCH2PPh(C6H4)}

Article abstract of DOI:10.1016/j.jorganchem.2014.05.040

Reactions of Ru₃(CO)₁₀(μ-dppf) (1) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), Ru₃(CO) ₁₀(μ-dppm) (2) (dppm = bis(diphenylphosphino)methane), and the orthometalated derivative Ru₃(CO)₉{μ₃- PPhCH₂PPh(C₆H₄)} (3) with silanes (Ph ₃SiH, Et₃SiH, Ph₂SiH₂) are reported. Treatment of 1 with Ph₃SiH and Ph₂SiH₂ at room temperature leads to facile Si-H bond activation to afford Ru ₃(CO)₉(μ-dppf)(SiPh₃)(μ-H) (4) (60% yield) and Ru₃(CO)₉(μ-dppf)(SiPh₂H)(μ-H) (6) (53% yield), respectively. The reaction of 1 with Ph₃SiH has been investigated by electronic structure calculations, and these data have facilitated the analysis of the potential energy surface leading to 4. Compound 1 does not react with Et₃SiH at room temperature but reacts at 68 °C to give Ru₃(CO)₉(μ-dppf)(SiEt ₃)(μ-H) (5) in 45% yield. Reaction of 2 with Ph₃SiH at room temperature yields two new products: Ru₃(CO)₉(μ- dppm)(SiPh₃)(μ-H) (7) in 40% yield and Ru₃(CO) ₆(μ₃-O)(μ-dppm)(SiPh₃)(μ-H) ₃ (8) in 15% yield. Interestingly, at room temperature compound 7 slowly reverts back to 2 in solution with decomposition and liberation of Ph₃SiH. Complex 8 can also be prepared from the direct reaction between 7 and H₂O. Similar reactions of 2 with Et₃SiH and Ph₂SiH₂ give only intractable materials. The orthometalated compound 3 does not react with Ph₃SiH, Et ₃SiH and Ph₂SiH₂ at room temperature but does react at 66°C to give Ru₃(μ-CO)(CO) ₇{μ₃-PPhCH₂PPh(C₆H ₄)}(SiR₂R¹)(μ-H)](9, R = R′ = Ph, 71% yield; 10, R = R′ = Et, 60% yield; 11, R = Ph, R′ = H, 66% yield) by activation of the Si-H bond. Compounds 4 and 8-11 have been structurally characterized. In 4, both the dppf and the hydride bridge a common Ru-Ru vector, whereas NMR studies on 7 indicate that two ligands span different Ru-Ru edges. Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh₃ ligand, and three bridging hydride ligands, whereas 9-11 represent simple oxidative addition products. In all of the compounds examined, the triruthenium framework retains its integrity and the silyl groups occupy equatorial sites.

Full text of DOI:10.1016/j.jorganchem.2014.05.040

Accepted Manuscript
Experimental and computational studies on the reaction of silanes with the
diphosphine-bridged triruthenium clusters Ru (CO) (μ-dppf), Ru (CO) (μ-dppm)
3
10
3
10
and Ru (CO) {μ -PPhCH PPh(C H )}
3
9 3 6 4
2
Md. Jakir Hossain , Subas Rajbangshi , Md. Mehedi M. Khan , Shishir Ghosh ,
Graeme Hogarth , Edward Rosenberg , Kenneth I. Hardcastle , Michael G.
Richmond , Shariff E. Kabir
PII:
S0022-328X(14)00286-1
10.1016/j.jorganchem.2014.05.040
JOM 18612
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 26 April 2014
Revised Date: 28 May 2014
Accepted Date: 29 May 2014
Please cite this article as: M.J. Hossain, S. Rajbangshi, M.M.M. Khan, S. Ghosh, G. Hogarth, E.
Rosenberg, K.I. Hardcastle, M.G. Richmond, S.E. Kabir, Experimental and computational studies on the
reaction of silanes with the diphosphine-bridged triruthenium clusters Ru (CO) (μ-dppf), Ru (CO) (μ-
3
10
3
10
dppm) and Ru (CO) {μ -PPhCH PPh(C H )}, Journal of Organometallic Chemistry (2014), doi:
3
9 3 6 4
2
10.1016/j.jorganchem.2014.05.040.
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ACCEPTED MANUSCRIPT
Experimental and computational studies on the reaction of silanes with the
diphosphine-bridged triruthenium clusters Ru3(CO)10(µ-dppf), Ru3(CO)10(µ-
dppm) and Ru3(CO)9{µ3-PPhCH2PPh(C6H4)}
a
a
a
b
Md. Jakir Hossain , Subas Rajbangshi , Md. Mehedi M. Khan , Shishir Ghosh , Graeme
e
f
Hogarth b,c, Edward Rosenberg d,*, Kenneth I. Hardcastle , Michael G. Richmond , Shariff E.
Kabir a,*
Graphical Abstract
The diphosphine-bridged clusters Ru3(CO)10(µ-dppf), Ru3(CO)10(µ-dppm), and Ru3(CO)9{µ3-
PPhCH2PPh(C6H4)} activate silanes (Ph3SiH, Et3SiH, Ph2SiH2) to give products containing η1-
silyl and bridging hydride groups. The Ru3 framework is maintained during the silane activation,
and the role of the ancillary diphosphine ligand in helping to preserve the cluster nuclearity is
discussed.

ACCEPTED MANUSCRIPT
Experimental and computational studies on the reaction of silanes with the
diphosphine-bridged triruthenium clusters Ru3(CO)10(µ-dppf), Ru3(CO)10(µ-
dppm) and Ru3(CO)9{µ3-PPhCH2PPh(C6H4)}
a
a
a
b
Md. Jakir Hossain , Subas Rajbangshi , Md. Mehedi M. Khan , Shishir Ghosh , Graeme
e
f
Hogarth b,c, Edward Rosenberg d,*, Kenneth I. Hardcastle , Michael G. Richmond , Shariff E.
Kabir a,*

ACCEPTED MANUSCRIPT
Experimental and computational studies on the reaction of silanes with
the diphosphine-bridged triruthenium clusters Ru3(CO)10(µ-dppf),
Ru3(CO)10(µ-dppm) and Ru3(CO)9{µ3-PPhCH2PPh(C6H4)}
a
a
a
b
Md. Jakir Hossain , Subas Rajbangshi , Md. Mehedi M. Khan , Shishir Ghosh ,
e
Graeme Hogarth b,c, Edward Rosenberg d,*, Kenneth I. Hardcastle , Michael G.
Richmond f, Shariff E. Kabir a,*
a Department of Chemistry, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh
b Department of Chemistry, University College London, 20 Gordon Street, London WC1H
OAJ, UK
c Department of Chemistry, King’s College London, Britannia House, 7 Trinity Street,
London SE1 1DB, UK
d Department of Chemistry, University of Montana, Missoula, MT 59812, USA
e Department of Chemistry, Emory University, Atlanta, GA 30322, USA
f Department of Chemistry, University of North Texas, Denton, TX 76209, USA
*Corresponding author. E-mail address: skabir_ju@yahoo.com (Shariff E. Kabir)
Telephone: +88027791099
Fax:
+88027791052
1

ACCEPTED MANUSCRIPT
Abstract
Reactions
of
Ru3(CO)10(µ-dppf)
(1)
(dppf
=
1,1ʹ
=
-bis(diphenylphosphino)ferrocene),
Ru3(CO)10(µ-dppm)
(2)
(dppm
bis(diphenylphosphino)methane), and the orthometalated derivative Ru3(CO)9{µ3-
PPhCH2PPh(C6H4)} (3) with silanes (Ph3SiH, Et3SiH, Ph2SiH2) are reported. Treatment of
1 with Ph3SiH and Ph2SiH2 at room temperature leads to facile Si-H bond activation to
afford Ru3(CO)9(µ-dppf)(SiPh3)(µ-H) (4) (60% yield) and Ru3(CO)9(µ-dppf)(SiPh2H)(µ-H)
(6) (53% yield), respectively. The reaction of 1 with Ph3SiH has been investigated by
electronic structure calculations, and these data have facilitated the analysis of the potential
energy surface leading to 4. Compound 1 does not react with Et3SiH at room temperature
o
but reacts at 68 C to give Ru3(CO)9(ꢀ-dppf)(SiEt3)(µ-H) (5) in 45% yield. Reaction of 2
with Ph3SiH at room temperature yields two new products: Ru3(CO)9(µ-dppm)(SiPh3)(µ-H)
(7) in 40% yield and Ru3(CO)6(µ3-O)(µ-dppm)(SiPh3)(µ-H)3 (8) in 15% yield.
Interestingly, at room temperature compound 7 slowly reverts back to 2 in solution with
decomposition and liberation of Ph3SiH. Complex 8 can also be prepared from the direct
reaction between 7 and H2O. Similar reactions of 2 with Et3SiH and Ph2SiH2 give only
intractable materials. The orthometalated compound 3 does not react with Ph3SiH, Et3SiH
and Ph2SiH2 at room temperature but does react at 66 ºC to give Ru3(µ-CO)(CO)7{µ3-
PPhCH2PPh(C6H4)}(SiR2R1)(µ-H)](9, R = Rʹ = Ph, 71% yield; 10, R = Rʹ = Et, 60% yield;
11, R = Ph, Rʹ = H, 66% yield) by activation of the Si–H bond. Compounds 4 and 8-11 have
been structurally characterized. In 4, both the dppf and the hydride bridge a common Ru-Ru
vector, whereas NMR studies on 7 indicate that two ligands span different Ru-Ru edges.
Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh3 ligand,
and three bridging hydride ligands, whereas 9-11 represent simple oxidative addition
products. In all of the compounds examined, the triruthenium framework retains its
integrity and the silyl groups occupy equatorial sites.
Keywords: Ruthenium carbonyl; Diphosphine; Silanes; Oxo-capped; Oxidative-addition;
X-ray structures
2

ACCEPTED MANUSCRIPT
1. Introduction
The activation of Si-H bonds by transition metal complexes is a key step in the catalytic
process known as hydrosilylation.1,2,3 The main entry into M-Si chemistry is by the facile
oxidative addition of hydrosilanes to a metal center, and in the case of metal clusters,
products with a bridging hydride and terminal silyl groups are produced.4 Although
examples of the ruthenium-carbonyl-catalyzed hydrosilylation using mononuclear
complexes exist, fewer reactions of hydrosilanes with ruthenium carbonyl clusters have
been published.5 It has been reported that the reactions of Ru3(CO)12 with hydrosilanes is
dependent on the structure of the silane and the reaction conditions, and in many such cases
cluster fragmentation was involved.6 Lewis et al. reported triruthenium clusters of the type
Ru3(CO)11(SiR3)(µ-H) from the reactions of the labile cluster Ru3(CO)11(NCMe) with
hydrosilanes under mild conditions.7 In terms of reactions and mechanisms concerning the
activation of silanes at triruthenium clusters, an early report by Süss-Fink and coworkers
stands out. There the reversible reaction of Ru3(CO)11(µ-H)- with two molecules of HSiR3
was shown to furnish the novel clusters Ru3(CO)10(SiR3)2(µ-H)-, which exhibit catalytic
activity in hydrosilylation.8 Cabeza et al. investigated the reactivity of the face-capped
clusters Ru3(CO)9(µ3-η3-ampy)(µ-H) and Ru3(CO)8(PPh3)(µ3-η3-ampy)(µ-H) (Hampy = 2-
amino-6-methylpyridine) and the edge-bridged cluster Ru3(CO)7(µ-CO)(µ-C4H4N2)
(C4H4N2 = pyridazine) with a wide range of tertiary silanes and obtained hydridosilyl
derivatives without cluster fragmentation upon oxidative addition of Si-H bonds.9,10,11
Nagashima and coworkers reported silyl complexes Ru3(CO)6(µ3-η2:η3:η5-
acenaphthylene)(SiR3)(µ-H) from the reactions of Ru3(CO)7(µ3-η2:η3:η5-acenaphthylene)
with trialkyl silanes.12 It has been reported that reaction of the triruthenium cluster
Ru3(CO)7(µ3-η5:η5-4,6,8-trimethylazulene) with PhMe2SiH resulted in the oxidative
addition of Si-H bond, followed by the hydrogenation of one of the carbon-carbon double
bonds in the azulene ligand to form the 46-electron cluster Ru3(CO)6(µ2-η3:η5-4,5-dihydro-
4,6,8-trimethylazulene)(PhMe2Si)(µ-H).13
Adams et al. reported two silyl-containing pentaruthenium compounds,
Ru5(CO)14(SiEt3)(µ5-C)(µ-H) and Ru5(CO)15(SiEt3)(µ5-C)(µ-H), from the oxidative
3

ACCEPTED MANUSCRIPT
addition of triethylsilane to Ru5(CO)15(µ5-C) in the presence of UV-vis irradiation.14
Finally, success in the oxidative addition of silanes to triosmium clusters has been achieved
15,16
using the reactive clusters Os3(CO)10(NCMe)2
Os3(CO)10(µ-H)2.17,18
and the 46-electron dihydride cluster
Cluster fragmentation following Si-H bond activation may be suppressed by edge-bridging
ligands that reinforce the cluster framework. We have previously found that the oxidative
addition of R3SiH (R
=
Ph, Et) to the unsaurated cluster Os3{µ3-
Ph2PCH2PPh(C6H4)}(CO)8(µ-H) gives rise to Os3(CO)9(µ-dppm)(SiR3)(µ-H) and
Os3(CO)7{µ3-PPh2CH2PPh(C6H4)}(SiR3)(µ-H)2 (R = Ph, Et) in which no cluster
fragmentation has occurred.19 The former products are also produced in the reaction of the
parent cluster Os3(CO)10(µ-dppm) with R3SiH (R = Ph, Et) at elevated temperatures.19 Kira
and co-workers reported that the reaction of Ru3(CO)10(µ-dppm) (1) with p-tol2SiH2
proceeds with cluster fragmentation to afford the dinuclear complexes Ru2(CO)6(µ-
dppm)(µ-Sitol2) and Ru2(CO)5(Sitol2H)(µ-dppm)(µ-η2-HSitol2);20 the latter was converted
to the µ-silane complex {Ru(CO)2(SiTol2H)}2(µ-dppm)(µ-η2:η2-H2Sitol2)2 upon further
reaction with p-tol2SiH2 under photochemical conditions, as summarized in Scheme 1.
SiH(p-tol)2
p-tol
p-tol
p-tol
p-tol
H
(CO)3
Ru
(CO)3
Ru
Ph2
P
Ph2
P
Ph2
(OC)4Ru
Ru
P
(CO)2
Si
Si
(p-tol)2SiH2
+
40oC
Ru
P
Ru
P
Ru
(CO)3
P
Ph2
Ph2
Ph2
(CO)3
(CO)3
(p-tol)2SiH2
hv
- CO
SiH(p-tol)2
Ph2
p-tol
H
Ru
P
Si
(CO)2
p-tol
H
Ru
(CO)2
P
Ph2
(p-tol)2HSi
Scheme 1.
Although the reactivity of the dppm-bridged triruthenium cluster 2 has extensively been
investigated,21,22,23 few studies have hitherto been published involving the dppf analog
4

ACCEPTED MANUSCRIPT
Ru3(CO)10(µ-dppf) (1).24,25 We have recently explored the reactivity of the P(C4H3E)3 (E =
S, O) substituted derivatives of both 1 and 2, and find that the thermolytic behavior of the
dppm complexes Ru3(CO)9(µ-dppm){P(C4H3S)3} and Ru3(CO)9(µ-dppm){P(C4H3O)3} is
significantly different from the corresponding dppf clusters Ru3(CO)9(µ-dppf){P(C4H3S)3}
and Ru3(CO)9(µ-dppf){P(C4H3O)3}. The former clusters undergo carbon-hydrogen and
o
carbon-phosphorus bond scission under mild conditions (40 C) to afford thiophyne and
furyne complexes, respectively,23 whereas the latter clusters undergo ring cyclometalation,
but only under forcing conditions (100 oC).25 With the above reactivity differences in mind,
coupled with our interest in cluster-promoted substrate activation, we turned our attention
toward the comparative study of the reactivity of diphosphine-tethered clusters
Ru3(CO)10(µ-dppf) (1), Ru3(CO)10(µ-dppm) (2) and Ru3(CO)9{µ3-PPhCH2PPh(C6H4)} (3)
with silanes.
2. Experimental Section
2.1. General remarks
Unless otherwise noted, all reactions were carried out under a dry nitrogen atmosphere
using standard Schlenk techniques. Reagent grade solvents were dried using appropriate
drying agents and distilled prior to use by standard methods. Ph3SiH, Ph2SiH2 and Et3SiH
were purchased from Aldrich and used as received. The compounds Ru3(CO)10(µ-dppf)
(1),26 Ru3(CO)10(µ-dppm) (2),27 and Ru3(CO)9{µ3-PPhCH2PPh(C6H4)} (3)22a were prepared
according to published procedures. IR spectra were recorded on a Shimadzu FTIR 8101
spectrophotometer, and all NMR spectra were recorded on Varian Unity plus 400
spectrometers (1H NMR 400 MHz; 31P NMR 162 MHz). All chemical shifts are reported in
δ units and are referenced to the residual protons of the deuterated solvents (1H) and to
external H3PO4 (31P). Elemental analyses were performed by the Microanalytical
Laboratories of the Wazed Miah Science Research Centre at Jahangirnagar University.
Product separations were performed by TLC in air on 0.5 mm silica gel (HF254- type 60, E.
Merck, Germany) glass plates.
5

ACCEPTED MANUSCRIPT
2.2. Reaction of Ru3(CO)10(µ-dppf (1) with triphenylsilane
A dichloromethane solution (25 mL) of 1 (50 mg, 0.044 mmol) and Ph3SiH (24 mg, 0.088
mmol) was stirred at room temperature for 3 h, during which time the color changed from
orange to deep red. The solvent was removed under reduced pressure and the residue
chromatographed by TLC on silica gel. Elution with hexane/CH2Cl2 (7:3, v/v) developed
one major and one very minor band. The major band afforded Ru3(CO)9(µ-dppf)(SiPh3)(µ-
H) (4) (36 mg, 60%) as red crystals from hexane/CH2Cl2. Anal. Calcd. for
C61H44FeO9P2Ru3Si: C, 53.48; H, 3.24. Found: C, 53.65; H, 3.35%. IR (νCO, CH2Cl2):
2076 w, 2041 m, 2004 vs, 1967 sh cm-1. 1H NMR (CDCl3) 298 K: δ 7.74 (m, 6H), 7.45 (m,
20H), 7.26 (m, 9H), 4.44 (s, 4H), 4.16 (br, s, 4H), –16.53 (t, 1H, J = 9.8 Hz); 218 K: δ 7.55
(m, 22 H), 7.29 (m, 8 H), 7.25 (m, 3H), 7.09 (m, 2H), 4.60 (s, 1H), 4.53 (s, 1H), 4.50 (s,
1H), 4.37 (s, 2H), 4.28 (s, 1H), 4.00 (s, 1H), 3.74 (s, 1H), –16.68 (t, 1H, J = 9.8 Hz).
31P{1H}NMR (CDCl3) 298 K: δ 20.6 (s, 2P); 218 K: δ 20.5 (s, 1P), 21.4 (s, 1P) . FAB-MS:
m/z 1371.
2.3. Reaction of 1 with triethylsilane
A THF solution (30 mL) of 1 (50 mg, 0.044 mmol) and Et3SiH (10 mg, 0.088 mmol) was
heated to reflux for 1 h, during which time the color changed from orange to red. The
solvent was removed under reduced pressure and the residue chromatographed by TLC on
silica gel. Elution with hexane/CH2Cl2 (7:3, v/v) developed one major and two minor
bands. The major band afforded Ru3(CO)9(µ-dppf)(SiEt3)(µ-H) (5) as red crystals after
recrystallization from hexane/CH2Cl2 at 4°C (24 mg, 45%). Anal. Calcd. for
C49H44FeO9P2Ru3Si: C, 48.01; H, 3.62. Found: C, 48.25; H, 3.79. IR (νCO, CH2Cl2): 2073
w, 2036 m, 1998 vs, 1962 sh cm-1. 1H NMR (CDCl3) 293 K: δ 7.47 (m, 20H), 4.24 (s, 4H),
4.11 (br, s, 4H), 0.99 (t, 9H, J = 8.0 Hz), 0.62 (q, 6H, J = 8.0 Hz ) –16.63 (t, 1H, J = 10.4
Hz). 31P{1H}NMR (CDCl3): δ 28.3 (br, s, 2P). FAB MS: m/z 1227.
2.4. Reaction of 1 with diphenylsilane
A CH2Cl2 solution (15 mL) of Me3NO (4 mg, 0.053 mmol) was drop-wise added to a
CH2Cl2 solution (20 mL) of 1 (50 mg, 0.044 mmol) and Ph2SiH2 (16 mg, 0.088 mmol) over
6

ACCEPTED MANUSCRIPT
a period of 30 min, and the resulting solution was stirred for an additional 1 h. Similar work
up and chromatographic separation, as described above, developed one major and two very
minor bands. The major band gave Ru3(CO)9(µ-dppf)(SiPh2H)(µ-H) (6) (30 mg, 53%
yields) after recrystallization from hexane/CH2Cl2 at 4°C. Anal. Calcd for
C55H40FeO9P2Ru3Si: C, 51.05; H, 3.12. Found: C, 51.25; H, 3.23. IR (νCO, CH2Cl2): 2077
w, 2042 m, 2003 vs, 1967 sh cm-1. 1H NMR (CDCl3) 298 K: δ 7.82 (m, 4H), 7.46 (m, 22H),
7.32 (m, 2H), 7.24 (m, 2H), 5.70 (s, 1H), 4.32 (s, 4H), 4.12 (br, s, 4H), –16.68 (t, 1H, J =
10.4 Hz); 243 K: δ 7.83 (m, 4H), 7.57 (m, 20H), 7.33 (m, 3H), 7.25 (m, 3H), 5.63 (s, 1H),
4.39 (s, 4H), 4.27 (s, 1H), 4.14 (s, 1H) 3.78 (s, 1H) 3.72 (s, 1H), –16.82 (dd, 1H, J = 10.0,
10.8 Hz). 31P{1H}NMR (CDCl3) 298 K: δ 21.1 (br, s, 1P), 19.1 (br, s, 1P); 243 K: δ 21.0 (s,
1P), 19.0 (s, 1P). FAB MS: m/z 1295.
2.5. Reaction of Ru3(CO)10(µ-dppm) (2) with triphenylsilane
To a CH2Cl2 solution (30 mL) of 2 (100 mg, 0.103 mmol) and Ph3SiH (54 mg, 0.207 mmol)
was added drop-wise a CH2Cl2 solution (15 mL) of Me3NO (12 mg, 0.16 mmol) over a
period of 1 h, during which time the color changed from orange to deep red. The solvent
was removed under reduced pressure and the residue chromatographed by TLC on silica
gel. Elution with hexane/CH2Cl2 (3:1, v/v) developed three bands. The first band was
unreacted 2 (5 mg), the second band afforded Ru3(CO)9(µ-dppm)(SiPh3)(µ-H) (7) (65 mg,
40%), as red crystals after recrystallization from hexane/CH2Cl2 in the presence of Ph3SiH
o
(1 drop) at 4 C, and the third band yielded Ru3(µ3-O)(µ-dppm)(CO)6(SiPh3)(µ-H)3 (8) (9
mg, 15%), which was isolated as pale yellow crystals after recrystallization from
o
hexane/CH2Cl2 at 4 C. Analytical and spectroscopic data for 7: Anal. Calcd for
C52H38O9P2Ru3Si: C, 52.04; H, 3.19. Found: C, 52.25; H, 3.45%. IR (νCO, CH2Cl2): 2076
1
w, 2044 s, 2003 s, 1995 sh cm-1. H NMR (CD2Cl2): δ 7.31 (m, 9H), 7.41 (m, 11H), 7.55
(m, 15H), 4.47 (t, 2H, J = 10.8 Hz), –18.10 (d, 1H, J = 32.0 Hz). 31P{1H} NMR (CD2Cl2,):
δ 10.4 (d, J = 45.3 Hz), 8.9 (d, J= 45.3 Hz). FAB MS: m/z 1201. Spectroscopic data for 8:
Anal. Calcd for C49H40O7P2Ru3Si: C, 51.90; H, 3.56. Found: C, 52.05; H, 3.62%. IR (νCO,
1
CH2Cl2): 2040 vs, 2012 m, 1990 s, 1946 m cm-1. H NMR (CD2Cl2): δ 7.81 (m, 8H), 7.61
(m, 4H), 7.41 (m, 16H), 7.05 (m, 2H), 6.91 (m, 5H), 3.51 (m, 1H), 3.04 (m, 1H), –16.08
(br, s, 1H), –14.56 (d, 1H, J = 60.0 Hz), –11.75 (d, 1H, J = 74.4 Hz). 31P{1H} NMR
7

ACCEPTED MANUSCRIPT
(CD2Cl2): δ 27.9 (d, J = 61.0 Hz), 24.1 (d, J = 61.0 Hz). FAB MS: m/z 1133. Similar
reactions of 2 with Et3SiH or Ph2SiH2 afforded only intractable materials.
2.6. Reaction of 7 with water
To a CH2Cl2 solution of 7 (10 mg, 0.008 mmol) was added one drop of water and stirred for
3 h at room temperature. The solvent was removed under reduced pressure and the residue
chromotagraphed by TLC on silica gel. Elution with hexane/CH2Cl2 (3:1, v/v) developed
three bands which afforded, in order of elution, 1(2 mg, 25 %), unreacted 7 (5 mg, 50%)
and 8 (1.5 mg, 16%).
2.7. Reaction of Ru3(CO)9{µ3-PPhCH2PPh(C6H4)} (3) with triphenylsilane
Triphenylsilane (54 mg, 0.217 mmol) was added to a THF solution (25 mL) of 3 (80 mg,
0.093 mmol) and the reaction mixture refluxed for 3.5 h, during which the color changed
from orange to red. The solvent was removed under reduced pressure and the residue
chromatographed by TLC on silica gel. Elution with hexane/CH2Cl2, (4:1, v/v) afforded
Ru3(µ-CO)(CO)7{µ3-PPhCH2PPh(C6H4)}(SiPh3)(µ-H) (9) (45 mg, 71%) as pale yellow
crystals from hexane/CH2Cl2 at 4 oC. Anal. Calcd for C45H32O8P2Ru3Si: C, 49.41; H, 2.95.
Found: C, 49.65; H, 3.05. IR (νCO, CH2Cl2): 2079 vs, 2044 vs, 2027 s, 2015 m, 1975 m,
1
1869 w cm-1. H NMR (CDCl3): δ 7.83 (m, 1H), 7.55 (m, 5H), 7.32 (m, 10H), 7.24 (m,
10H), 6.98 (m, 1H), 6.71 (m, 1H), 6.14 (m, 1H), 4.43 (m, 1H), 3.75 (m, 1H), –16.10 (m,
1H). 31P{1H}NMR (CDCl3): δ 88.6 (d, J = 81.9 Hz), – 0.7 (d, J = 81.9 Hz).
2.8. Reaction of 3 with triethylsilane
A THF solution (50 mL) of 3 (100 mg, 0.116 mmol) and triethylsilane (68 mg, 0.580
mmol) was heated to reflux for 30 min, during which time the color changed from orange to
red. After removal of the solvent under reduced pressure, the residue was purified by TLC
on silica gel. Elution with hexane/CH2Cl2 (7:3, v/v) developed two bands. The major band
afforded Ru3(µ-CO)(CO)7{µ3-PPhCH2PPh(C6H4)}(SiEt3)(µ-H) (10) in 60% yield (34mg)
o
as red crystals after recrystallization from hexane/CH2Cl2 at 4 C. Anal. Calcd. for
C33H32O8P2Ru3Si: C, 41.73; H, 3.40. Found: C, 42.05; H, 3.65%. IR (νCO, CH2Cl2): 2077
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vs, 2040 vs, 2021 vs, 2008 m 1970 m, 1863 w cm-1. 1H NMR (CDCl3): δ 7.86 (m, 1H), 7.70
(m, 3H), 7.62 (m, 2H), 7.37 (m, 5H), 7.02 (m, 1H), 6.75 (m, 1H), 6.22 (m, 1H), 3.77 (m,
31
1H), 3.13 (m, 1H), 0.91 (m, 6H), 0.83 (m, 9H), –16.50 (m,1H). P{1H}NMR (CDCl3): δ
80.9 (d, J = 82.5 Hz), – 0.09 (d, J = 82.5 Hz). The minor band was too small for complete
characterization.
2.9. Reaction of 3 with diphenylsilane
Diphenylsilane (22 mg, 0.116 mmol) was added to a THF solution (15 mL) of 3 (50 mg,
0.058 mmol) and the reaction mixture was refluxed for 3.5 h. The solvent was removed
under reduced pressure and the residue chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2, (4:1, v/v) afforded Ru3(µ-CO)(CO)7{µ3-PPhCH2PPh(C6H4)}-
o
(SiPh2H)(µ-H) (11) (40 mg, 66%) as pale yellow crystals from hexane/CH2Cl2 at 4 C.
Anal. Calcd. for C39H28O8P2Ru3Si: C, 46.02; H, 2.77. Found: C, 46.26; H, 2.95%. IR
1
(νCO, CH2Cl2): 2079 vs, 2044 vs, 2028 vs, 2014 sh, 1975 w, 1867 w cm-1. H NMR
(CD2Cl2): δ7.92 (m, 1H), 7.53 (m, 9H), 7.35 (m, 8H), 7.17 (m, 1H), 7.06 (m, 3H), 6.75 (m,
1H), 6.19 (m, 1H), 5.75 (d, 1H, J = 4.0 Hz), 2.85 (m, 1H), 2.56 (m, 1H), –16.39 (m, 1H).
31P{1H}NMR (CD2Cl2): δ 89.7 (d, J = 78.3 Hz), – 1.5 (d, J = 78.3 Hz).
2.10. Crystal Structure Determinations
Single crystals of 4, 8, 10 and 11 were mounted on fibers and diffraction data collected at
293 K on a Bruker SMART APEX CCD diffractometer using Mo Kα radiation (λ =
0.71073 Å). Data reduction and integration was carried out with SAINT +, and absorption
corrections were applied using the program SADABS.28 The structures were solved by
direct methods and developed using alternating cycles of least-squares refinement and
difference Fourier synthesis. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms except those directly bonded to ruthenium were placed in the calculated
positions and their thermal parameters linked to those of the atoms to which they were
attached (riding model). We were unable to locate the hydride on cluster 4 but all three
hydrides on cluster 8 were located from the difference map. The quality of crystal of 4 used
for the diffraction had large mosaic spread, so even after final refinement the R values are
high. Several attempts have been made to grow good quality crystals but were unsuccessful.
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The SHELXTL PLUS V6.10 program package was used for structure solution and
refinement.29 Final difference maps did not show any residual electron density of
stereochemical significance. The details of the data collection and structure refinement are
given in Table 1.
A suitable crystal of 9 was coated with Paratone-N oil, suspended in a small fiber loop, and
placed in a cooled nitrogen gas stream at 100 K on a Bruker D8 SMART APEX CCD
sealed tube diffractometer with graphite-monochromated Mo-Kα (0.71073Å) radiation. All
data were measured using a series of combinations of phi and omega scans with 10 s frame
exposures and 0.3 frame widths. Data collection, indexing, and initial cell refinements
were all carried out using SMART software.30 Frame integration and final cell refinements
were done using SAINT software.31 The final cell parameters were determined from least-
squares refinement. The SADABS32 program was used to carry out absorption corrections.
The structures were solved using direct methods and difference Fourier techniques
(SHELXTL, V6.12).33 Hydrogen atoms were placed in their expected chemical position
using the HFIX command and were included in the final cycles of least squares with
isotropic Uij’s related to the atoms ridden on. The hydrides were positioned by using the
XHYDEX program in the WinGX suite of programs.34 All non-hydrogen atoms were
refined anisotropically. Scattering factors and anomalous dispersion corrections are taken
from International Tables for X-ray Crystallography.35 One of the phenyl rings in 9 was
disordered and no attempt has been made to model this. Structure solution, refinement,
graphics, and generation of publication materials were performed by using SHELXTL,
V6.12 software. Additional details of data collection and structure refinement are given in
Table 1.
Place Table 1
2.11. Computational Details and methodology
The DFT calculations were conducted using Morokuma’s ONIOM method,36 as
implemented by the Gaussian 09 program software.37 The different species were optimized
via a two-level approach with the phenyl groups of the silane reagent Ph3SiH and the Ph3Si
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and dppf ligands treated as the lower of the two levels; the atoms in all other compounds
were optimized by ab initio DFT methods. For those species analyzed within the two-level
treatment, we employed an ONIOM method that was defined by a B3LYP/PM6
composition. The phenyl groups (low level) were treated at the semiempirical PM6 level of
theory, while the remaining atoms (high level) were treated within the B3LYP framework.
With respect to the high-level treatment of atoms, the ruthenium atoms were described by
Stuttgart-Dresden effective core potentials (ecp) and SDD basis set, while a 6-31G(d’) basis
set was employed for the remaining atoms. All reported geometries were fully optimized
and evaluated for the correct number of imaginary frequencies through calculation of the
vibrational frequencies, using the analytical Hessian. Zero imaginary frequencies (positive
eigenvalues) represent ground-state structures, while a species with an imaginary frequency
(negative eigenvalue) designates a transition state. The transition states on the potential
energy surface were evaluated by IRC calculations in order to confirm the connecting
reactant and product species. The computed frequencies were used to make zero-point and
thermal corrections to the electronic energies, and the reported potential energies are quoted
in kcal/mol relative to the starting cluster Ru3(CO)10(dppf) (A) and Ph3SiH (C). The
geometry-optimized structures depicted in Figures 1 and 2 have been drawn with the JIMP2
molecular visualization and manipulation program [38].
3. Results and discussion
3.1. Oxidative addition of silanes to Ru3(CO)10(µ-dppf) (1)
Reactions of 1 with excess Ph3SiH and Ph2SiH2 at room temperature afforded Ru3(CO)9(ꢀ-
dppf)(SiPh3)(ꢀ-H) (4) (60% yield) and Ru3(CO)9(ꢀ-dppf)(SiPh2H)(ꢀ-H) (6) (53% yield),
respectively (Scheme 2). However, compound 1 does not react with Et3SiH at room
temperature but does react at 68 oC to give (ꢀ-H)Ru3(CO)9(ꢀ-dppf)(SiEt3) (5) (45% yield).
Compounds 4-6 are formed by dissociation of a CO from 1, followed by oxidative addition
of a Si-H bond. Characterization of 4-6 has been made by elemental analysis, mass
31
spectrometry, IR and NMR (1H and P{1H}) spectroscopy and by single crystal X-ray
diffraction analysis in the case of 4.
11

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Scheme 2.
The molecular structure of 4 is shown in Figure 1, and the caption contains selected bond
distances and angles. The structure consists of a triangular array of ruthenium atoms with
two short [Ru(2)–Ru(3) 2.868(1), Ru(1)–Ru(3) 2.866(1) Å] and one comparatively long
[Ru(1)–Ru(2) 3.033(1) Å] ruthenium-ruthenium interactions, the latter being the metal-
metal vector spanned by the dppf and hydride ligands. The disposition of the hydride along
the Ru(1)-Ru(2) edge is confirmed by NMR spectroscopy and DFT calculations (see
below). This edge is much longer than the other two Ru-Ru bonds in 4 and is also longer
than the corresponding dppf-bridged Ru-Ru bond in 1 [2.9284(5) Å],38 as is typically found
for metal-metal bonds that are bridged by a hydride ligand(s). Nine CO ligands are bound
to the cluster, and each ruthenium atom has three CO ligands. The coordination geometry at
each Ru atom is closely octahedral, with the hydride occupying one of the octahedral sites
at the Ru(1) and Ru(2) centers. The unbridged Ru-Ru distances are very similar to those
distances reported for 1 [2.8600(4) Å], while the two Ru-P distances are almost equal
[Ru(1)–P(1) 2.323(3), Ru(2)–P(2) 2.327(3) Å] and compare favorably with the Ru–P
distances [2.3503(8) Å ] found in 1.39 In the crystal structure, the ferrocene moiety shows
no adverse interactions with the triruthenium framework. The SiPh3 moiety is bound to the
Ru(3) atom at the sterically least crowded equatorial site in the cluster and the Ru–Si
distance is 2.417(3) Å. The Ru–Si bond distance is similar to those found in related
triruthenium clusters such as 2.441(3) Å, 2.450(2) Å in Ru3(CO)10(SiEt3)2(µ-H)-;8b 2.460(6)
Å, 2.455(5) Å in Ru3(CO)8(SiEt3)2(µ-C4H4N2)(µ-H)2;10 2.435(4) Å in Ru3(CO)8(SiEt3)(µ3-
HNC6H3Me)(µ-H)2.9 While the overall structure of 4 is similar to those complexes of the
type Ru3(CO)9(µ-diphosphine)(PR3),23,25,39,40 it is only the second example of a
triruthenium cluster that possesses a bridging dppf ligand and one additional monodentate
12

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ligand within the coordination sphere of the cluster. The only other paradigm being
Ru3(CO)9(µ-dppf)(PFu3), which was recently reported by us from the Me3NO-induced
decarbonylation reaction between Ru3(CO)10(µ-dppf) and PFu3.25
Place Figure 1 Here
The bonding in 4 was also investigated by DFT calculations, and the geometry-
optimized structure (G) is shown alongside the X-ray diffraction structure. The hydride
ligand spans the dppf-bridged Ru-Ru vector and lies essentially in the plane defined by the
three metals. The two non-bridged Ru-Ru vectors display a mean distance of 3.000 Å and
the hydride-bridged Ru-Ru bond distance in G is computed as 3.205 Å. These distances
and the disposition of the ligands about the cluster core in G are in concert with the solid-
state structure.
1
Compounds 4-6 are fluxional in solution, as evidenced by their temperature-dependent H
31
and P{1H} NMR spectra, which have been probed for clusters 4 and 6. As the three
species exhibit similar behavior in solution, only the VT NMR of 4 will be discussed in
detail (Figure 2). At 15 oC, the 31P{1H} NMR spectrum exhibits a sharp signal at δ 20.6. On
cooling to -20 oC, the signal becomes very broad and at -55 oC this signal separates into two
sharp, equal intensity singlets at δ 21.4 and 20.5, showing that the fluxionality is fully
arrested at this temperature. The slow-exchange spectrum reveals a ∆ν of 149 Hz for these
resonances, and in conjunction with the coalescence temperature of 248 K (Tc), we estimate
a ∆G≠ value of 11.2 kcal/mol for this equilibration process involving the two phosphine
1
o
groups.41 The H NMR spectra also shed light on the fluxional process. At 15 C, the
cyclopentadienyl protons appear as two equal intensity singlets, one very broad singlet at δ
o
4.16 and another comparatively sharp singlet at δ 4.44. At 0 C the broad singlet at δ 4.16
becomes barely indistinguishable from the base line and the other cyclopentadienyl
resonance becomes broad. These signals separate into seven singlets at -55 oC, six of equal
intensity that integrate for 1H each, with the remaining resonance integrating for 2H,
confirming the arrested fluxionality. In terms of the bridging hydride, the hydride appears
o
as a triplet at δ –16.53 at 15 C. The observed splitting pattern indicates that the two
phosphines are equally coupled to the bridging hydride. Apart from a slight high-field shift
(δ –16.68) upon cooling to -55 oC, the hydride remains a well-defined binomial triplet. We
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interpret these temperature-dependent spectral changes to the conformational flexibility of
the dppf ligand in 4. The behavior of the dppf ligand in 4 is analogous to that found by us
in the dppf-bridged cluster Os3(CO)10(dppf).26
Place Figure 2 Here
Compounds 5 and 6 exhibit spectroscopic properties similar to that of 4. All three products
exhibit four carbonyl absorptions bands in the carbonyl region of their IR spectrum, and the
31
intensities and spectral patterns reinforce their isostructural nature. Each P{1H} NMR
spectrum displays two singlets at low temperature, which confirms that the phosphorus
atoms are nonequivalent in the limiting spectrum. The dynamic behavior of the
cyclopentadienyl hydrogens and the phosphine groups in the 1H and 31P spectra of 5 and 6
indicates that the ancillary dppf is conformationally flexible. These data support a
common, low-energy exchange process involving the diphosphine ligand in this genre of
Ru3(CO)9(µ-dppf)(SiR3)(ꢀ-H) clusters.
The reaction path responsible for the formation of 4 (species G) was examined
computationally, starting from 1. Figures 3 and 4 show the pertinent geometry-optimized
structures and the potential-energy profile leading to G. The optimized structure of A
shows an excellent correspondence to the solid-state structure,39 including the pronounced
D3 twist in the axial CO groups. Silane activation is initiated by the site-selective loss of an
axial CO in A to generate the unsaturated species B and free CO, which lie 33.0 kcal/mol
above the parent cluster. The transition state TSBCD reveals that the oxidative addition of
the silane occurs at the axial site originally occupied by the liberated CO, and the resulting
product D contains axial Ph3Si and bridging hydride groups. A turnstile rotation of the
groups at the Ru(CO)3(SiPh3) center, which proceeds via TSDE, promotes the formation of
the equatorial Ph3Si group and yields species E. The axial-to-equatorial migration of the
Ph3Si group is thermodynamically favorably and E is 11.8 kcal/mol more stable than D.
Migration of the edge-bridging hydride in D to an interstitial locus in F constitutes the
penultimate step in the reaction. Continued transit of the hydride to the thermodynamically
preferred Ru-Ru edge that is tethered by the dppf ligand affords the final species G. While
the formation of G and CO relative to A and Ph3SiH is uphill by 12.2 kcal/mol, the release
14

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of CO in the first step of the reaction is entropically favored, and this serves to drive the
overall reaction to the experimentally observed silyl-hydride G.
Place Figures 3 and 4 Here
3.2. Oxidative addition of H–Si bonds to Ru3(CO)10(µ-dppm) (2)
With the aim of comparing the reactivity of the relatively rigid dppm analogue 2 with that
of more flexible dppf compound 1, we have studied the reactions of 2 with silanes. Scheme
3 illustrates the course of these reactions. Compound 2 has been shown to exhibit
significantly greater reactivity than the comparatively unreactive Ru3(CO)12, and the small-
bite angle dppm ligand helps to maintain the integrity of the trinuclear cluster framework.
In contrast to the reaction of 2 with p-tol2SiH2 which afforded Ru2(CO)6(µ-dppm)(µ-Sitol2)
and Ru2(CO)5(Sitol2H)(µ-dppm)(µ-η2-HSitol2),14 treatment with excess Ph3SiH at room
temperature is accompanied by loss of CO ligand and oxidative addition of silane to afford
the silyl cluster Ru3(CO)9(µ-dppm)(SiPh3)(ꢀ-H) (7) in 40% yield, in addition to the
trihydrido oxo-capped silyl compound Ru3(µ3-O)(µ-dppm)(CO)6(SiPh3)(ꢀ-H) (8) (15%
yield). Interestingly, in solution 7 slowly converts back to 2 by addition of CO to the
putative cluster Ru3(CO)9(µ-dppm), whose formation is expected upon reductive
elimination of Ph3SiH from 7. Here the extra CO needed for the regeneration of 2 is
presumed to originate from cluster degradation. Compound 8 was neither observed in the
solution at the start of the reaction nor in the crude product before chromatographic
separation. In separate experiment we found that 7 reacts with H2O to yield 8 suggesting
that the latter being formed on the TLC plate from the reaction between 7 and H2O present
in the chromatographic support. Examples of µ3-oxo triruthenium carbonyl clusters are
relatively rare. The triruthenium clusters Ru3(CO)8(µ-dppm)2, Ru3(CO)6(µ-dppm)3 and
Ru3(CO)9(µ-dppm){P(C4H3S)3} react with molecular oxygen at elevated temperatures to
yield oxo-capped Ru3(µ3-O)(µ3-CO)(CO)5(µ-dppm)2,42 Ru3(µ3-O)(µ3-CO)(CO)3(µ-
43
dppm)3 and Ru3(µ3-O)(µ3-CO)(CO)6(µ-dppm){P(C4H3S)3},44 respectively. Although 2
exhibits rich and diverse chemistry with respect to substrate activation,21 its reaction with
molecular oxygen is unknown and, to our knowledge, compound 8 represents the first
example of an oxo-capped triruthenium carbonyl cluster containing a single dppm ligand as
the phosphine auxiliary.
15

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Scheme 3
We were unable to grow X-ray quality crystals of 7; therefore, its characterization was
based on elemental analysis, infrared, 1H NMR, 31P{1H} NMR and mass spectral data. The
FAB mass spectrum displays a molecular ion peak at m/z 1201. The carbonyl stretching
frequencies of 7 are similar to those of Ru3(CO)9(µ-dppf)(SiPh3)(ꢀ-H) (4), indicating that
1
the two clusters have a similar distribution of carbonyl ligands. The H NMR spectrum
shows, in addition to the resonances corresponding to the phenyl protons of the dppm and
silyl ligands, a triplet at δ 4.47 that is assigned to the methylene protons of the dppm ligand,
along with a high-field doublet at δ –18.10 for the bridging hydride. This latter resonance is
coupled to one of the neighboring non-equivalent phosphorus nuclei, one of which is
assumed to be cis (geminal) to the hydride ligand based on a JP-H 32 Hz. A similar JP-H
coupling constant has been reported for the structurally characterized osmium analog
31
Os3(CO)9(µ-dppm)(SiPh3)(ꢀ-H) (JP-H 30.4 Hz).19 The P{1H} NMR spectrum of 7 shows
two doublets at δ 10.4 and 8.9 (JP-P 45.3 Hz) for the two non-equivalent 31P atoms of dppm
31
ligand, both of which are equatorially bonded to adjacent Ru atoms. These P NMR data
mirror those results found in the osmium analog Os3(CO)9(µ-dppm)(SiPh3)(ꢀ-H) (JP-P 46.5
Hz), whose SiPh3 ligand adopts an equatorial site proximal to the hydride.19 Cluster 7
contains 48 valence electrons, and each ruthenium atom formally has an 18-electron
16

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configuration. Given the spectroscopic similarity of 7 to Os3(CO)9(µ-dppm)(SiPh3)(ꢀ-H),19
the hydride in 7 is assumed to bridge one of the unsupported Ru-Ru edges. This is
consistent with our previous observations that the dppm-bridged Ru-Ru edge in 7 does not
have enough room to accommodate both the hydride and the dppm ligand at a common
edge.45
The molecular structure of 8 is shown in Figure 5, and selected bond angles and lengths are
listed in the caption. The molecule consists of a triangular framework of ruthenium atoms,
where one of the polyhedral faces is best viewed as symmetrically capped by the triply
bridging oxo-ligand [Ru(1)–O(1) 2.0506(15), Ru(2)–O(1) 2.0561(15), Ru(3)–O(1)
2.0701(16) Å]. The other ligands in 8 consist of a bridging dppm group, a terminally
coordinated triphenylsilyl group, and six terminal carbonyl groups. The Ru(1)–Ru(3) bond
[2.8272(3) Å] bridged by the dppm ligand is slightly shorter than the distance of other two
Ru-Ru bonds [Ru(1)–Ru(2) 2.8409(3), Ru(2)–Ru(3) 2.8335(3) Å], and these Ru-Ru
distances are in accordance with their single bond designation. The Ru-Si bond distance of
2.4142(7) Å is comparable to that found in 4. The dppm ligand occupies equatorial sites in
the cluster and the Ru-P distances [Ru(1)–P(2) 2.3477(6) and Ru(3)–P(1) 2.3492(6) Å],
which are almost equal in length, are unexceptional relative to the Ru-P distances in 2
[2.322(2) and 2.334(2) Å].46 The three hydride ligands bridging three ruthenium-ruthenium
edges were crystallographically located but not refined. Their positions, as shown in
Scheme 3, are confidently assigned on the basis of the NMR data (vide infra). Significantly,
the Ru-P vectors do not lie significantly out of the equatorial plane that is defined by the
metal triangle. The disposition of the hydrides and the O(1) oxo atom are situated trans to
each other, and these groups reside on opposite sides of the metallic plane. The
triruthenium framework of 8 is comparable with those oxo-capped clusters Ru3(µ3-
+ 47
+ 48
O)(C6H2Me4)3(µ-H)3 ,
Ru3(µ3-O)(C6H6)(C6Me6)2(µ-H)3 ,
and Ru3(µ3-O)(Fc-
+ 49
arene)(C6Me6)2(µ-H)3 , showing similar polyhedral architecture and arrangement of the
oxo and hydride ligands.
Place Figure 5 Here
The spectroscopic data for 8 are fully consistent with the solid-state structure. The
IR spectrum exhibits four terminal ν(CO) bands over the region of 2040-1946 cm-1. The
17

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FAB mass spectrum displays a molecular ion peak at m/z 1135, along with fragmentation
31
peaks corresponding to the loss of up to six carbonyl groups. The P{1H} NMR spectrum
displays two doublets at δ 27.9 and 24.1 (J 61.0 Hz), indicating that 8 contains two non-
equivalent phosphorus nuclei. In addition to the phenyl proton resonances of the dppm and
Ph3Si ligands in the aromatic region, the 1H NMR spectrum shows two multiplets at δ 3.51
and 3.04 that are assigned to the diastereotopic methylene protons of the diphosphine
ligand, as well as three distinct hydride resonances (each integrating for 1H) that appear as
two doublets at δ –11.75 (J 74.4 Hz) and δ –14.56 (J 60 Hz), and a broad singlet at δ –
16.08.
The reactivity of 2 with Et3SiH and Ph2SiH2 was also investigated. Unfortunately,
the addition of excess Et3SiH or Ph2SiH2 to a CH2Cl2 solution of 2 led to the rapid
formation of unidentified decomposition products. Attempts to isolate the reaction
products were not successful. The silyl-substituted cluster products that are formed here
are less stable than 7.
3.3. Oxidative addition of H–Si bonds to Ru3(CO)9{µ3-PPhCH2PPh(C6H4)} (3)
In order to compare the chemistry of the orthometalated derivative 3 with that of the
parent cluster 2, we investigated the reactions of 3 with silanes. The orthometalated
compound 3 does not react with Ph3SiH, Et3SiH and Ph2SiH2 at room temperature, but it
does react at 66 ºC to give Ru3(µ-CO)(CO)7{µ3-PPhCH2PPh(C6H4)}(SiR2Rʹ)(ꢀ-H) (9, R =
Rʹ = Ph, 71% yield; 10, R = Rʹ = Et, 60% yield; 11, R = Ph, Rʹ = H, 66% yield) (Scheme 3).
Compounds 9-11 have been characterized by a combination of spectroscopic methods, and
the molecular structures determined by X-ray crystallography. The solid-state structures of
the isostructural clusters 9-11 are depicted in Figures 6, 7, and 8, respectively, with the
captions containing selected bond distances and angles. The basic cores of the three
clusters are the same, having a triangular metal-framework of ruthenium atoms and three
distinctly different ruthenium-ruthenium bond lengths [Ru(1)–Ru(2) 3.0537(5), Ru(2)–
Ru(3) 2.8675(4), Ru(1)–Ru(3) 2.9702(4) Å for 9; Ru(1)–Ru(2) 3.0159(9), Ru(2)–Ru(3)
2.8521(7) , Ru(1)–Ru(3) 2.9706(7) Å for 10 ; Ru(1)–Ru(2) 2.9822(6), Ru(2)–Ru(3)
2.8344(6) , Ru(1)–Ru(3) 2.9544(6) Å for 11]. Of the seven terminal carbonyl ligands, two
each are located at the Ru(1) and Ru(3) centers, and three at the Ru(2) atom. The three
products each exhibit one semi-bridging carbonyl ligand involving the Ru(1) and Ru(3)
18

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atoms [Ru(1)–C(3) 2.564(4), Ru(3)–C(3) 1.968(4) Å, Ru(3)–C(3)–O(3) 158.8(4)° for 9;
Ru(1)–C(8) 2.505(4), Ru(3)–C(8) 1.971(4) Å, Ru(3)–C(8)–O(8) 156.7(4)° for 10 and
Ru(1)–C(8) 2.565(3), Ru(3)–C(8) 1.950(4) Å, Ru(3)–C(8)–O(8) 159.9(9)° for 11]. The
silyl groups are terminally bound to the Ru(1) atom and the Ru-Si bond distances [Ru(1)–
Si(1) 2.4254(12) Å for 9; Ru (1)–Si(1) 2.405(2) Å for 10 and Ru(1)–Si(1) 2.3829(10) Å for
11] are very similar to those found in 4 and 8. The hydride ligand in 9, which was located
using the program WinGX, is associated with the longest ruthenium-ruthenium edge
[Ru(1)–Ru(2) 3.0537(5) Å]. Significantly, the SiPh3 ligand is cis to the hydride at the
sterically least crowded equatorial site. The hydrides for 10 and 11 could not be
crystallographically located but their position, as shown in Scheme 3, is confidently
inferred from the NMR data. The tridentate phosphine ligand in 9 maintains the same
coordination mode as that found in the parent cluster 3.22a The product contains three Ru-
Ru single bonds and possesses a closed-shell configuration with an 18-electron count at
each Ru atom.
Place Figures 5-7 Here
The solution spectroscopic data for 9-11 are consistent with the solid-state structure of
each product. The IR spectrum of each compound exhibits, in addition to five terminal νCO
bands, an absorption at lower wave number (1863 w cm-1 for 9; 1869 w cm-1 for 10; 1867 w
31
cm-1 for 11), that supports the presence of a semi-bridging carbonyl group. The P{1H}
NMR spectrum for each compound displays two doublets [δ 88.6, –0.73 (J 81.9 Hz) for 9, δ
80.9, –0.09 (J 82.5 Hz) for 10, and δ 89.7, –1.5 ( J 78.3 Hz) for 11], consistent with the
solid-state structures. In addition to the aryl resonances from the diphosphine and silyl
1
ligands, each H NMR spectrum shows two multiplets in the aliphatic region (δ 3.75 and
4.43 for 9; δ 3.13 and 3.77 for 10; δ 2.56 and 2.85 for 11) that are assigned to the
diastereotopic methylene protons of the diphosphine ligand. Finally, each cluster exhibits a
single, high-field hydride (δ – 16.10 for 9 and – 16.50 for 10; –16.39 for 11) as a result of
silane activation.
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4. Conclusions
The reactions described in this study are summarized in Schemes 2 and 3. As described in
the introduction, oxidative addition of Si-H bonds to Ru3(CO)12 was investigated in early
1970s; however, the reactions with trialkyl silanes typically induced the cleavage and
recombination of ruthenium-ruthenium bonds in the initially formed products to yield silyl-
substituted ruthenium complexes with lower nuclearity.6 Successful formation of the
trinuclear oxidative-addition products 4-6 from the reactions of 1 with Ph3SiH, Et3SiH and
Ph2SiH2 can be attributed to the fact that the dppf ligand in 4-6 helps to suppress cluster
fragmentation. The reaction of 2 with Ph3SiH gives 7, which is isostructural with
Os3(CO)9(µ-dppm)(SiPh3)(µ-H) reported by us earlier,19 reacts with H2O to give the oxo-
capped cluster 8. The reaction of 2 with hydrosilanes yields products of differing stability,
and only in the case of Ph3SiH was the oxidative-addition product 8 found to be stable. The
dppf analog of 8 was not formed from 4 during chromatography indicating greater stability
of the dppf bridged molecules compared to those bridged by dppm. This stands in contrast
to the reaction of the orthometalated compound 3 and silanes, which affords the
isostructural hydride clusters 9-11 through activation of the silane reagent. Clusters 1 and 2
maintian their nuclearity, even after significant substrate activation involving the oxidative
cleave of Si-H bonds in hydrosilanes, a process of fundamental importance in hydrosilation
catalysis, because of the stabilizing effect the small bite angle ligands dppf and dppm exert
on the cluster frame. Future studies will probe the catalytic activity of these clusters in the
hydrosilyation of organic substrates.
5. Acknowledgements
This research has been partly sponsored by the Ministry of Education, Government of the
People’s Republic of Bangladesh. SG thanks Commonwealth Commission for a
scholarship. We gratefully acknowledge Prof. A. J. Deeming and our deceased friend Prof.
D. T. Haworth for collecting XRD data of cluster 8 and 10 respectively. Financial support
from the Robert A. Welch Foundation (Grant B-1093-MGR) and the NSF (CHE-0741936)
are acknowledged. We also thank Prof. Michael B. Hall (TAMU) for providing us a copy
of his JIMP2 program.
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6. Supplementary information
CCDC 997408, 923714, 921503, 956408 and 997409 contain supplementary
crystallographic data for 4, 8, 9, 10 and 11 successively. These data may be obtained free
of
charge
from
The
Cambridge
Crystallographic
Data
Center
via
www.ccdc.cam.ac.uk/data_request/cif, while the atomic coordinates of all optimized
structures are available from MGR upon request.
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Table 1 Crystallographic Data and Structure Refinement for 4, 8 and 9
Compound
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Cryst system
Space group
a (Å)
4
C61H44FeO9P2Ru3Si
1370.05
8
C49H40O7P2Ru3Si
1134.05
9
C45.13H32Cl0.50O8P2Ru3Si
1113.17
150(2)
293(2)
100(2)
0.71073
0.71073
0.71073
triclinic
monoclinic
P 21/n
monoclinic
C2/c
P 1
11.470(3)
12.921(4)
20.603(6)
89.139(5)
82.770(6)
69.517(5)
2836.3(15)
2
11.5517(9)
14.8235(12)
27.905(2)
90
14.554(3)
11.1260(7)
19.526(12)
90
b (Å)
c (Å)
α (°)
β (°)
99.8050(10)
90
96.391(2)
90
γ (°)
Volume (Å3)
4708.5(6)
4
8971.4(10)
8
Z
D
calc (Mg m−3)
1.604
1.600
1.648
ꢀ (Mo Kα) (mm−1)
1.168
1.093
1.176
F(000)
1368
2264
4410
Crystal size (mm)
θ range (°)
0.44 × 0.26 × 0.25
1.56−28.26
−15≤ h ≤ 15,
−19≤ k ≤ 19,
−35≤ l ≤ 36
41078
0.47 × 0.32 × 0.18
1.90−28.39
−55≤ h ≤ 55,
−14 ≤ k ≤ 14,
−26≤ l ≤ 26
60596
0.22 × 0.16 × 0.12
2.57−28.55
−15≤ h ≤ 14,
−16 ≤ k ≤ 17,
−26≤ l ≤ 27
23891
Limiting indices
Reflections collected
Independent reflections (Rint)
Max. and min. transmission
Data/restraints/parameters
Goodness of fit on F2
12757 (0.0952)
0.8726 and 0.7832
12757 / 0 / 685
0.830
11244 (0.0213)
0.7680 and 0.6443
11244/0/571
0.819
11197 (0.0304)
0.8162and 0.6079
11197/9/335
1.109
Final R indices [F2> 2σ]
R1 = 0.0773,
wR2 = 0.1784
R1 = 0.1688,
wR2 = 0.2165
2.936 and −1.781
R1 = 0.0300,
wR2 = 0.0782
R1 = 0.0355,
wR2 = 0.0827
0.829 and − 0.355
R1 = 0.0534,
wR2 = 0.1663
R1 = 0.0560,
wR2 = 0.1694
3.476 and −1.903
R indices (all data)
Largest difference in peak and hole (e
Å−3)
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Table 1 (continued) Crystallographic Data and Structure Refinement for 10 and 11
Compound
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Cryst system
Space group
a (Å)
10
C33H31O8P2Ru3Si
948.82
11
C39H28O8P2Ru3Si
1017.85
100(2)
150(2)
0.71073
0.71073
orthorhombic
Pbca
monoclinic
P 21/n
17.648(5)
18.641(5)
22.144(6)
90
13.079(3)
12.632(3)
23.323(5)
104.921(4)
3723.5(14)
4
b (Å)
c (Å)
β (°)
Volume (Å3)
7285(3)
Z
8
D
calc (Mg m−3)
1.730
1.816
ꢀ (Mo Kα) (mm−1)
1.396
1.372
F(000)
3752
2008
Crystal size (mm)
θ range (°)
0.38 × 0.30 × 0.11
1.84−31.98
0≤ h ≤ 26,
0 ≤ k ≤ 27,
0≤ l ≤ 32
0.46 × 0.20 × 0.16
2.64−28.32
−17≤ h ≤ 17,
−16≤ k ≤ 16,
−30≤ l ≤ 29
29971
Limiting indices
Reflections collected
12200
Independent reflections (Rint)
Max. and min. transmission
Data/restraints/parameters
Goodness of fit on F2
12200 (0.0535)
0.8616 and 0.6191
12200/12/458
1.162
8649 (0.0509)
0.8103 and 0.5709
8649/0/490
0.898
Final R indices [F2> 2σ]
R1 = 0.0500,
wR2 = 0.1087
R1 = 0.0637,
wR2 = 0.1133
1.713 and – 0.958
R1 = 0.0324,
wR2 = 0.0614
R1 = 0.0538,
wR2 = 0.0639
0.715 and −0.651
R indices (all data)
Largest difference in peak and
hole (e Å−3)
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Figure 1. ORTEP drawing of the molecular structure of Ru3(CO)9(SiPh3)(µ-dppf)(µ-H) (4) (left) and DFT-optimized structure G (right). Selected X-
ray difftraction data [bond lengths (Å) and angles (°)] for 4: Ru(1)–Ru(2) 3.033(1), Ru(2)–Ru(3) 2.868(1), Ru(1)–Ru(3) 2.866(1), Ru(1)–P(1)
2.323(3), Ru(2)–P(2) 2.327(3), Ru(3)–Si(1) 2.417(3), Ru(1)–Ru(2)–Ru(3) 58.04(3), Ru(1)–Ru(3)–Ru(2) 63.86(3), Ru(3)–Ru(1)–Ru(2) 58.10(3), P(2)–
Ru(2)–Ru(3) 171.47(8), P(2)–Ru(2)–Ru(1) 114.80(8), P(1)–Ru(1)–Ru(3) 174.85(9), P(1)–Ru(1)–Ru(2) 120.69(8), Si(1)–Ru(3)–Ru(1) 110.63(8),
Si(1)–Ru(3)–Ru(2) 170.57(8), P(1)–C(15)–Fe(1) 132.7(6), P(2)–C(10)–Fe(1) 131.2(6).
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Figure 2. 31P{1H} NMR spectra of Ru3(CO)9(SiPh3)(µ-dppf)(µ-H) 4
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Figure 3. B3LYP-optimized structures for the intermediates A-F and the corresponding transition
states. The structures for the liberated CO and Ph3SiH (C) are not shown.
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TSDE
40.5
TSBCD
38.7
TSEF
27.2
TSFG
25.4
B+CO
33.0
D
30.2
F
23.3
E
18.4
G
12.2
A+C
0.0
Figure 4. Potential energy surface for the conversion of A to G in the presence of Ph3SiH (C). Energy values are ꢁE in kcal/mol with respect to
A and C.
27