Nonclassical ruthenium silyl dihydride complexes TpRu(PPh 3)(I?·3-HSiR3H) [Tp = hydridotris(pyrazolyl)borate]: Catalytic hydrolytic oxidation of organosilanes to silanols with TpRu(PPh3)(I?·3-HSiR 3H)

Article abstract of DOI:10.1002/ejic.201000951

An X-ray crystallographic study showed that it is more appropriate to describe the complexes TpRu(PPh₃)"H₂SiR ₃" as TpRu(PPh₃)(I?·³- HSiR₃H), a static structure containing HA?·A? ·A?·SiA?·A?·A?·H bonding rather than a highly fluxional pair ofI?-silane hydride species TpRu(PPh₃)(H_a)(I?·²-H _bSiR₃) [rlhar2] TpRu(PPh₃)(H _b)(I?·²-H_aSiR₃). One of the complexes was used for the catalytic hydrolytic oxidation of organosilanes to silanols. A mechanism, which does not involve the usual oxidative addition of silane to the metal center to form the silyl hydride species, is proposed, which is supported by theoretical calculations.

Full text of DOI:10.1002/ejic.201000951

FULL PAPER
DOI: 10.1002/ejic.201000951
Nonclassical Ruthenium Silyl Dihydride Complexes TpRu(PPh3)(η3-HSiR3H)
[Tp = Hydridotris(pyrazolyl)borate]: Catalytic Hydrolytic Oxidation of
Organosilanes to Silanols with TpRu(PPh3)(η3-HSiR3H)
Ting Yan Lee,[a] Li Dang,[b] Zhongyuan Zhou,[a] Chi Hung Yeung,[a] Zhenyang Lin,*[b] and
Chak Po Lau*[a]
Keywords: Silanes / Hypervalent compounds / Oxidation / Reaction mechanisms / Density functional calculations
An X-ray crystallographic study showed that it is more ap-
propriate to describe the complexes TpRu(PPh3)“H2SiR3” as
for the catalytic hydrolytic oxidation of organosilanes to sil-
anols. A mechanism, which does not involve the usual oxi-
dative addition of silane to the metal center to form the silyl
hydride species, is proposed, which is supported by theoreti-
cal calculations.
TpRu(PPh3)(η3-HSiR3H),
a
static structure containing
H···Si···H bonding rather than a highly fluxional pair of
σ-silane hydride species TpRu(PPh3)(Ha)(η2-HbSiR3)
h
TpRu(PPh3)(Hb)(η2-HaSiR3). One of the complexes was used
from silane activation on the CpFe(iPr2MeP)H moiety; the
complex is most appropriately formulated as CpFe-
(iPr2MeP)(η3-H2SiR3) (Figure 1).[3]
Introduction
By virtue of the hypervalency around the Si center, a
nonclassical interligand interaction might be present in
complexes containing a silyl group and two or more hydride
ligands. For example, a silyl group in a complex could
simultaneously interact with two hydrides and generate a
structure with H···Si···H bonding. Crabtree and co-workers
first suggested an M(η3-H2SiR3) arrangement in the silyl
polyhydride complex [Re(PPh3)2H6(SiPh3)] based on the
close contacts between the Si atom and two of the hydride
ligands disclosed in the X-ray crystallography study; the hy-
dride positions in the structure are, however, only a working
hypothesis.[1] The complex RuH2(η2-H2)(η2-HSiPh3)-
(PCy3)2 (Cy = cyclohexyl), originally formulated as a dihy-
drogen σ-silane complex, in fact contains the [H2SiPh3]–
moiety where the Si atom is almost symmetrically bonded
to two hydrogen atoms with the two Si–H bond lengths
measuring 1.72 and 1.83 Å.[2] Nikonov and co-workers have
recently provided evidence from X-ray and DFT studies for
the existence of H···Si···H bonding in the complex resulting
Figure 1. Structure of CpFe(iPr2MeP)(η3-H2SiR3).
Several years ago, we synthesized a series of ruthenium
complexes TpRu(PPh3)“H2SiR3” [Tp = hydridotris(pyraz-
olyl)borate]. On the basis of NMR and DFT studies, we
formulated these complexes as σ-silane hydride species,
which rapidly exchange between two forms: TpRu(PPh3)-
(Ha)(η2-HbSiR3)
h
TpRu(PPh3)(Hb)(η2-HaSiR3).[4] We
have now successfully obtained single crystals of three com-
plexes of this type and carried out X-ray crystallographic
studies, the results of which are more consistent with a
static structure TpRu(PPh3)(η3-HSiR3H) containing
H···Si···H bonding. In addition to the X-ray structures of
three Ru(η3-HSiR3H) complexes, we report catalytic hydro-
lytic oxidation of organosilanes to silanols with one of these
complexes.
Silanols are widely utilized as building blocks for silicon-
based polymeric materials[5] and as the nucleophilic part-
ners in cross-coupling reactions.[6] Well-known preparative
methods for silanols include hydrolysis of chlorosilanes,[7]
oxidation of organosilanes with stoichiometric amounts of
oxidants,[8] and reactions of siloxanes with alkali reagents.[9]
The obvious shortcoming of these methods is the genera-
[a] Department of Applied Biology and Chemical Technology,
The Hong Kong Polytechnic University
Hung Hom, Kowloon, Hong Kong, P. R. China
Fax: +852-2364-9932
E-mail: bccplau@polyu.edu.hk
[b] Department of Chemistry, The Hong Kong University
of Science and Technology
Clear Water Bay, Kowloon, Hong Kong, P. R. China
Fax: +852-2358-1594
E-mail: chzlin@ust.hk
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000951.
Eur. J. Inorg. Chem. 2010, 5675–5684
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5675

T. Y. Lee, L. Dang, Z. Zhou, C. H. Yeung, Z. Lin, C. P. Lau
FULL PAPER
tion of large amounts of environmentally damaging waste.
Moreover, these methods have limited scopes. Highly ef-
ficient and environmentally more friendly synthetic meth-
ods for the conversion of readily available organosilanes to
silanols are therefore highly desirable, and some promising
homogeneous[10] and heterogeneous[11] systems that cata-
lyze the conversion with the use of water as an oxygen
source have recently been reported.
(1)
Crystals of 1a–c suitable for X-ray crystallographic stud-
ies were obtained by layering n-hexane on dichloromethane
solutions of the complexes. The molecular structures of 1a–
c are shown in Figures 2, 3, and 4, respectively. The crystal
data and refinement details are given in Table 1. Selected
bond lengths and angles are listed in Table 2. It is worth
noting that the two hydrogen atoms HM1 and HM2 in each
of the structures were located and refined. A common fea-
Results and Discussion
Synthesis and X-ray Crystallographic Study of
TpRu(PPh3)“H2SiR3”
The complex TpRu(PPh3)“H2SiPh3” (1a) is one of the ture of the structures of 1a–c is that the silicon atom inter-
members of the series of complexes TpRu(PPh3)“H2SiR3”, acts almost symmetrically with the two hydrogen atoms
which we have previously reported.[4] Complexes TpRu- HM1 and HM2; the Si–H bond lengths lie at the long end
(PPh3)“H2SiPh2Me” (1b) and TpRu(PPh3)“H2SiPhMe2” of the 2 Å limit normally observed for σ-Si–H bonds.[12]
(1c) are new members of the series synthesized according The ruthenium–hydrogen (Ru–HM1 and Ru–HM2) bond
to our previously reported procedure, i.e. by treating the lengths (1.49–1.568 Å) are within the normal range of clas-
solvento hydride precursor TpRu(PPh3)(CH3CN)H with sical ruthenium–hydride bond lengths. In addition, the two
the corresponding organosilanes [Equation (1)]. Similar to H–Ru–Si angles in each of the complexes are very close to
those of other complexes in the series, the 1H NMR spectra each other (53.9° and 57.3° in 1a; 52.6° and 54.8° in 1b;
of 1b and 1c each show a doublet hydride signal in the 53.9° and 54.8° in 1c). The X-ray structures of 1a–c reveal
upfield region, which integrates for two hydrogen atoms that these complexes are more appropriately formulated as
and does not show decoalescence down to –100 °C [1b: δ = TpRu(PPh3)(η3-HSiR3H) containing a nearly symmetrical
–9.93 ppm, J(HP) = 22.6 Hz; 1c: δ = –11.06 ppm, J(HP) = H···Si···H bonding in the [HSiR3H]– moiety. On the basis
22.8 Hz]. The hydride signals of 1b and 1c are flanked by of the model previously used in the B3LYP calculations, it
29Si satellites, and the observed J(SiH) values are 25.0 and was shown that the rapidly interchanging σ-silane hydride
19.2 Hz for 1b and 1c, respectively. These values are com- enantiomeric pair TpRu(PPh3)(Ha)(η2-HbSiR3) h TpRu-
parable to those of other complexes in the series.
(PPh3)(Hb)(η2-HaSiR3) is slightly lower in energy
Figure 2. ORTEP view (30% probability) of TpRu(PPh3)(η3-HSiPh3H) (1a) showing the atom-labeling scheme.
5676 Eur. J. Inorg. Chem. 2010, 5675–5684
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Nonclassical Ruthenium Silyl Dihydride Complexes
Figure 3. ORTEP view (30% probability) of TpRu(PPh3)(η3-HSiPh2MeH) (1b) showing the atom-labeling scheme.
Figure 4. ORTEP view (30% probability) of TpRu(PPh3)(η3-HSiPhMe2H) (1c) showing the atom-labeling scheme.
(2.1 kJmol-1) than the corresponding symmetrical structure, was performed on a model complex in which the Tp, PPh3,
which was regarded as the transition state for the inter- and SiR3 moieties were replaced by (H2C=NNH)3BH, PH3,
change of the enantiomeric pairs. The B3LYP calculation and SiH3, respectively.
Eur. J. Inorg. Chem. 2010, 5675–5684
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5677

T. Y. Lee, L. Dang, Z. Zhou, C. H. Yeung, Z. Lin, C. P. Lau
FULL PAPER
Table 1. Crystal and structure refinement data for 1a, 1b, and 1c.
1a
1b
1c·3CH2Cl2
Empirical formula
Formula mass
T [K]
λ [Å]
Crystal system
Space group
C45H42BN6PRuSi
837.79
296(2)
0.71073
monoclinic
P21/c
C40H40BN6PRuSi
775.72
296(2)
0.71073
triclinic
P1
C38H44BCl6N6PRuSi
968.43
296(2)
0.71073
triclinic
P1
Unit cell dimensions:
a [Å]
b [Å]
c [Å]
α [°]
β [°]
16.1421(3)
12.2111(2)
21.2219(4)
90
105.2180(10)
90
4036.42(13)
4
1.379
10.4776(2)
11.3027(2)
11.1167(4)
77.8800(10)
74.1180(10)
72.9730(10)
1845.54(6)
2
10.8951(2)
12.6105(2)
17.6399(3)
87.5410(10)
79.7450(10)
69.5820(10)
2234.56(7)
2
γ [°]
V [Å3]
Z
Density (calcd.) [gcm–3]
1.396
0.539
1.439
0.807
µ [mm–1]
0.498
F(000)
1728
800
988
Crystal size [mm]
θ range for data collection [°]
Index ranges [°]
0.32ϫ0.3ϫ0.28
1.94 to 27.39
–20Յ h Յ20
–15Յ k Յ15
–27Յ l Յ27
87540
0.50ϫ0.48ϫ0.32
2.09 to 27.33
–13Յ h Յ13
–14Յ k Յ14
–22Յ l Յ21
25782
0.42ϫ0.36ϫ0.30
1.17 to 27.46
–14Յ h Յ14
–16Յ k Յ16
–22Յ l Յ22
48788
Reflection collected
Independent reflections
Completeness to θ = 27.39° [%]
Absorption correction
Max. transmission
Min. transmission
Refinement method
9136 [R(int) = 0.3921]
99.8
8282 [R(int) = 0.0347]
99.1
10102 [R(int) = 0.0558]
98.8
semi-empirical from equivalents semi-empirical from equivalents semi-empirical from equivalents
1.000
0.840
1.000
0.819
1.000
0.805
full-matrix least squares on F2 full-matrix least squares on F2 full-matrix least squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
9136/0/508
0.735
8282/0/459
1.004
R1 = 0.0320, wR2 = 0.0758
R1 = 0.0416, wR2 = 0.0812
0.505/–0.525
10102/499
1.004
R1 = 0.0437, wR2 = 0.1069
R1 = 0.0649, wR2 = 0.1181
0.695/–0.609
R1 = 0.0335, wR2 = 0.0528
R1 = 0.2735, wR2 = 0.0645
Largest difference peak/hole [eÅ–3] 0.409/–0.303
Table 2. Selected bond lengths [Å] and angles [°] for 1a, 1b, and 1c. Table 3 shows the results of the hydrolytic oxidation of si-
lanes to silanols catalyzed by 1c. The reactions did not pro-
1a
1b
1c·3CH2Cl2
ceed at room temperature and were performed at 90 °C. Tri-
alkylsilanes (Entries 4–9) were oxidized more readily than
the silanes bearing aryl substituents (Entries 1–3 and 10).
In all the reactions reported, disiloxanes resulting from con-
Ru–HM(1)
Ru–HM(2)
1.491(15)
1.502(15)
2.016(14)
1.928(14)
2.3816(5)
57.3
53.9
38.5
39.0
1.568(16)
1.492(16)
1.903(15)
1.955(16)
2.3905(4)
52.6
54.8
40.9
38.5
1.49(2)
1.49(2)
1.94(2)
1.965(18)
2.4006(5)
53.9
54.8
38.2
38.3
Si(1)–HM(1)
Si(1)–HM(2)
Ru–Si(1)
HM(1)–Ru–Si(1)
HM(2)–Ru–Si(1)
HM(1)–Si(1)–Ru
HM(2)–Si(1)–Ru
Table 3. Hydrolytic oxidation of organosilanes to silanols with 1c.[a]
Entry
Silane
Time [h] Conversion [%][b]
1
2
3
4
5
6
7
8
9
Ph3SiH
Ph2MeSiH
PhMe2SiH
tBuMe2SiH
EtMe2SiH
24
24
20
4
2
2
4
4
4
24
24
84
99
96
96
97
94
94
97
85
65
91[c]
Catalytic Hydrolytic Oxidation of Organosilanes to
CyMe2SiH
CH3(CH2)16CH2Me2SiH
Et3SiH
Et2MeSiH
1,4-(SiMe2 H)C6H4
(+)-(R)-Me(α-Np)PhSiH
Silanols with TpRu(PPh3)(η3-HSiPhMe2H) (1c)
Complexes 1a–1c are readily synthesized, and we suspect
that it would make no difference using any one of them for
the catalytic hydrolytic oxidation of silanes [Equation (2)].
10
11
[a] Reaction conditions: silane (0.5 mmol), H2O (40 equiv.), 1c
(10 μmol, 2 mol-% with respect to silane), 1,4-dioxane (2 mL),
90 °C, under nitrogen flow. [b] Determined by 1H NMR spec-
troscopy. [c] Product: (+)-(S)-Me(α-Np)PhSiOH, isolated yield,
(2) 90% ee.
5678
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5675–5684

Nonclassical Ruthenium Silyl Dihydride Complexes
Figure 5. NMR study of the hydrolysis of PhMe2SiH to PhMe2SiOH catalyzed by 1c.
densation of silanols were not detected (see Supporting In- Relative Stability of 1c and TpRu(PPh3)(η3-HSiEtMe2H)
formation). It is important to note that the optically active (1d)
silane (+)-(R)-Me(α-Np)PhSiH (98% ee) was hydrolyzed to
yield (+)-(S)-Me(α-Np)PhSiOH with retention (Entry 11).
In the course of growing single crystals for X-ray crystal-
lographic studies, we learned that complexes containing tri-
alkylsilanes are less stable than those containing silanes
with aryl groups. The trialkylsilane complexes undergo de-
composition more readily, and we have been unable to ob-
tain single crystals of them. We therefore carried out ligand
NMR Monitoring of the Hydrolytic Oxidation of
PhMe2SiH to PhMe2SiOH Catalyzed by 1c
PhMe2SiH (5 equiv.) and water (200 equiv.) were added substitution of 1c with HSiEtMe2 [Equation (3)] to gain a
to a [D8]-1,4-dioxane solution of 1c in a J. Young valved more quantitative comparison of the thermal stability of 1c
NMR tube, which was heated in an oil bath at 90 °C. Fig- and 1d. It was learned that after heating a [D8]-1,4-dioxane
1
ure 5 shows the 31P{1H} and H NMR spectra of the solu- solution of 1c in the presence of HSiEtMe2 (5 equiv.) at
tion measured at different times; the column on the far right 90 °C for 3 h, the relative equilibrium concentrations of 1c/
shows the percentage conversions to the products (esti- 1d was ca. 50:50, and the equilibrium constant Keq was esti-
mated from the integrations of the methyl peaks of the mated to be 1.1ϫ10–1. This experiment shows that the ther-
1
PhMe2SiH and PhMe2SiOH in the H NMR spectra). The mal stability of 1c is about nine times that of 1d. The
31P{1H} NMR spectrum of the solution taken after 10 min [H2SiR3]– moiety, in bonding to the metal fragment, trans-
of heating showed that 1c was present as the overwhelming fers electron density from the occupied orbitals ψ1 and ψ2
species; around 2% of the dihydrogen hydride complex to the metal center orbitals; on the other hand, the metal
TpRu(PPh3)(H2)H (2)[13] was also formed. As the reaction back-donates a lone pair into the empty ψ3 orbital of
proceeded, the amount of 2 increased at the expense of that [H2SiR3]–.[14] Here, ψ1 is the all-in-phase combination of the
of 1c, and at the end of the reaction, 1c was nearly all con- two H 1s orbitals and the SiR3 sp3-hybridized orbital, ψ2 is
verted to 2. The presence of 1c and 2 and the variation of the out-of-phase combination of the two H 1s orbitals only,
1
their amounts at different times were corroborated by H and ψ3 is the all-out-of-phase combination of the two H
NMR spectra of the solution, which showed the hydride 1s orbitals and the SiR3 sp3-hybridized orbital. The higher
signals of 1c and 2 in the upfield region. It should be stability of 1c vs. 1d is probably due to the phenyl group of
pointed out that in this experiment the H2 by-product was the silane ligand in the former being able to invite more
trapped in the NMR tube.
back-donation from the metal atom.
Eur. J. Inorg. Chem. 2010, 5675–5684
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5679

T. Y. Lee, L. Dang, Z. Zhou, C. H. Yeung, Z. Lin, C. P. Lau
FULL PAPER
(3)
Proposed Mechanism for the Catalytic Hydrolytic
Oxidation of Silanes to Silanols
The NMR monitoring experiment above shows that in
the course of catalysis, 1c and 2 were the only detectable
organometallic complexes, and these two complexes are in-
terconvertable by ligand exchange. We believe that 1c is the
key species reacting directly with water to generate the sil-
anol. The fact that hydrolytic oxidation of the chiral silane
(+)-(R)-Me(α-Np)PhSiH to give the silanol product (+)-(S)-
Me(α-Np)PhSiOH with retention is a strong indication that
the water molecule attacks the silicon center in the manner
shown in Scheme 1. A dihydrogen bonding interaction be-
tween the proton of the attacking water molecule and the
hydride of the [H2Si(Me)(α-Np)Ph]– moiety is expected to
be present. We have reported a similar dihydrogen bonding
interaction between the hydride ligand and the proton of
the attacking water molecule in hydration of nitriles cata-
lyzed by Ru–H complexes.[15,16]
Scheme 2.
To study the feasibility of the proposed reaction mecha-
nism shown in Scheme 2 for the catalytic hydrolytic oxi-
dation of silanes, DFT calculations were performed to ex-
amine the catalytic cycle by using TpRu(PMe3)(η3-HSiH-
Me2H) (1A) as the model catalyst. The potential energy
profile is shown in Figure 6 with the calculated relative elec-
tronic energies. The reaction of 1A with water occurs by a
nucleophilic attack of the water oxygen atom on the silicon
center of the η2-silane ligand in a six-membered-ring transi-
tion state to give silanol and the dihydrogen complex 2A.
From the dihydrogen complex 2A, ligand substitution with
silane occurs to regenerate 1A and to release a dihydrogen
molecule, completing the catalytic cycle. The overall reac-
tion barrier shown in Figure 5 is 90.0 kJmol–1 and the hy-
drolysis reaction is thermodynamically favorable. These re-
sults support the proposed mechanism discussed above.
Figure 7 presents the optimized structures with selected
structural parameters for the species shown in Figure 5. The
bond lengths calculated for the Ru–Si, Si–H, and Ru–H
bonds in 1A are similar to those determined experimentally
in TpRu(PPh3)(η3-HSiR3H). In 1A, both hydride ligands
maintain strong interactions with the silicon center of the
silyl ligand, indicating the hypervalency around the silicon
center.[12b] The double silyl–hydrido interactions have been
Scheme 1.
Scheme 2 shows a possible mechanism for the hydrolytic also found in Cp(iPr2MeP)FeH2SiR3 reported recently.[3]
oxidation of silanes to silanols. We propose the existence of 2A is a dihydrogen complex with an H–H distance of
a dihydrogen bonding interaction between one of the hy- 0.90 Å. The transition structure TSA(1–2) displays a strong
drides of the [H2SiR3]– moiety and a water proton during dihydrogen bonding with an H···H distance of 1.29 Å.
nucleophilic attack of the water molecule at the silicon cen-
An alternative mechanism for the hydrolytic oxidation of
ter. Several studies of metal–silane interactions indicate that silanes catalyzed by 1 is shown in Scheme 3. The cycle be-
silane is a strong σ*-accepting ligand because of the weaker gins with the generation of the aqua hydride complex 3 by
H–Si σ-bonding. The metal (dπ)-to-silane (σ*) back-bond- H2O/silane exchange, 3 then generates the hydroxido species
ing is deemed very important for the metal–(η2-silane) in- 4 probably through σ-bond metathesis.[18] Displacement of
teraction.[17] The lower activity of the arylsilanes in com- the dihydrogen ligand in 4 by silane and subsequent intra-
parison to the trialkylsilanes in hydrolytic oxidation reac- molecular hydroxylation of the silane ligand yields the
tions can be explained in terms of the diminished electro- product and metal hydride. Although we have not observed
philicity of the silicon center resulting from more back- the aqua hydride complex 3 in the NMR monitoring experi-
bonding from the metal atom and the stronger Ru–Si bond ment, we cannot, however, exclude the possibility that it
in A (Scheme 2) when R3 contains one or more phenyl might be present in trace amounts, which eludes NMR de-
groups. The lower electrophilicity at the silicon center ren- tection.
ders nucleophilic attack by the water more sluggish, and the
strong Ru–Si bond would slow down the extrusion of the of HSiHMe2 by a water molecule is endothermic [Equa-
silanol product from the metal center.
tion (4)]; 3A is less stable than 1A by 36.4 kJmol–1, consis-
Our theoretical calculations show that the replacement
5680
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5675–5684

Nonclassical Ruthenium Silyl Dihydride Complexes
Figure 6. Energy profile calculated for the hydrolysis reaction of HSiHMe2 catalyzed by TpRu(PMe3)(η3-HSiHMe2H) (1A). The calculated
relative electronic energies are given in kJmol–1.
Figure 7. Optimized structures for the species involved in the hydrolysis reaction of HSiHMe2 catalyzed by TpRu(PMe3)(η3-HSiHMe2H)
(1A) (Figure 5). Bond lengths are given in Å.
Eur. J. Inorg. Chem. 2010, 5675–5684
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5681

T. Y. Lee, L. Dang, Z. Zhou, C. H. Yeung, Z. Lin, C. P. Lau
FULL PAPER
cial step of the catalytic process is the nucleophilic attack of
the water oxygen atom at the silicon center of the [H2SiR3]–
moiety; a strong dihydrogen bonding interaction between
one of the hydrides of [H2SiR3]– and a water proton is pres-
ent in the transition state. This work provides experiental
evidence, which is scarce, for the presence of the [H2SiR3]–
ligand and establishes a unique mechanism for the transi-
tion metal catalyzed hydrolytic oxidation of silanes to silan-
ols. An alternative mechanism, which involves intramolecu-
lar hydroxido attack at the silane ligand is also proposed.
However, theoretical calculations indicate that this alterna-
tive mechanism is less favorable.
Experimental Section
General: All manipulations were carried out under nitrogen by
using standard Schlenk techniques. Solvents were dried, degassed,
and distilled prior to use: THF, 1,4-dioxane, and diethyl ether from
Na benzophenone ketyl; n-hexane and toluene from Na; acetoni-
trile and dichloromethane from CaH2. All chemicals were commer-
cially available (Aldrich, Acros, Strem, and International Labora-
tory) and used without further purification. The chiral silane (+)-
(R)-Me(α-Np)PhSiH (98% ee)[19] and the complexes TpRu(PPh3)-
(CH3CN)H[13] and TpRu(PPh3)(η3-HSiPh3H)[4] (1a) were prepared
according to literature methods. Deuterated NMR solvents, pur-
chased from Armar and Cambridge Isotope Laboratories, were
Scheme 3.
tent with the experimental results that the aqua hydride
complex 3A was not observed. The energy required to dis-
sociate a silane molecule from 1A was estimated to be
124.3 kJmol–1, indicating that the replacement of water by
silane is relatively difficult to achieve.
1
dried with P2O5 prior to use. H NMR spectra were obtained with
Varian (500 MHz) or Bruker DPX (400 MHz) spectrometers, and
chemical shifts are reported relative to residual protons of the deu-
terated solvents. 13C NMR spectra were recorded with a Bruker
DPX 400 spectrometer at 100.61 MHz, and chemical shifts are ref-
erenced to internal CD2Cl2 (δ = 53.8 ppm). 31P NMR spectra were
recorded with a Bruker DPX 400 spectrometer at 161.70 Mz, and
chemical shifts are referenced to external 85% H3PO4 in D2O (δ =
0.00 ppm). 29Si NMR spectra were obtained with a Bruker DPX
400 spectrometer at 79.50 MHz, and chemical shifts are referenced
to external Me4Si in CDCl3 (δ = 0.00 ppm). IR spectra were ob-
tained with a Bruker Vector 22 FTIR spectrophotomer. Optical
rotations were recorded with a Perkin–Elmer 341 polarimeter in a
10 cm cell. Electrospray ionization mass spectrometry was carried
out with a Finnigan MAT 95S mass spectrometer with the samples
dissolved in dichloromethane. Elemental analyses were performed
by M-H-W Laboratories, Phoenix, AZ.
(4)
Conclusions
Based on the X-ray crystallographic structures of 1a–c,
it is more appropriate to describe this class of Ru–silane
complexes TpRu(PPh3)“H2SiR3” as having a static struc-
ture TpRu(PPh3)(η3-HSiR3H) containing H···Si···H bond-
ing, rather than a highly fluxional pair of σ-silane hydride
complexes TpRu(PPh3)(Ha)(η2-HbSiR3) h TpRu(PPh3)-
(Hb)(HaSiR3). The complex TpRu(PPh3)(η3-HSiPhMe2H)
(1c) was used to catalyze the hydrolytic oxidation of silanes
to silanols. Although the catalytic activity of 1c might not
Synthesis of TpRu(PPh3)(η3-HSiPh2MeH) (1b): TpRu(PPh3)-
(CH3CN)H (0.20 g, 0.32 mmol) was loaded into a 50 mL two-
necked pear-shaped flask, which was evacuated and filled with ni-
trogen for four cycles. Freshly distilled toluene (10 mL) and Ph2Me-
SiH (0.8 mL, 4 mmol) were then added by syringe into the flask,
and the resulting solution was heated at 90 °C with stirring for 4 h.
be as high as that of some of the catalytic systems reported The solution was cooled to room temperature, and the volume was
reduced to 1 mL in vacuo before cooled hexane (10 mL) was added
to precipitate the product as orange solid. The solid was collected,
washed with cooled hexane (5 mL) and dried under vacuum. Yield:
0.14 g (55%). C40H40BN6PRuSi (775.73): C 61.93, H 5.20, N 10.83;
by others, we have, however, been able to present a much
clearer picture of the mechanistic aspects of the reaction.
More importantly, this is a rare example of employing a
complex containing the [H2SiR3]– moiety for a catalytic
study. The reaction mechanisms of most of the previously
studied catalytic systems have not been studied in detail. It
was generally suggested that the catalysis involves oxidative
addition of the silane molecule to the metal atom to form
the silyl hydride species. From our study, a new mechanism
found C 61.93, H 5.25, N 10.85. IR (KBr): ν = 1942 [m, ν(Ru–H)],
˜
2468 [m, ν(B–H)]. 1H NMR (400.13 MHz, CD2Cl2, 25 °C): δ =
1
2
–9.93 (d, JSiH = 25.0, JHP = 22.6 Hz, 2 H, RuH); 0.70 (s, 3 H,
Si–CH3), 5.48 (t, 1 H of Tp), 5.77 (t, 2 H of Tp), 7.52 (d, 1 H of
Tp), 7.68 (d, 2 H of Tp), 7.82 (d, 1 H of Tp), 8.35 (d, 2 H of
Tp), 6.93–7.60 (m, 25 H of Ph) ppm. 13C{1H} NMR (100.61 MHz,
was proposed. Theoretical calculations show that the cru- CD2Cl2, 25 °C):
δ
=
9.49 (s, SiCH3) ppm. 31P{1H} NMR
5682
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2010, 5675–5684

Nonclassical Ruthenium Silyl Dihydride Complexes
(161.7 MHz, CD2Cl2, 25 °C): δ = 70.3 ppm. 29Si{1H} NMR refined by full-matrix least squares on F2 by using the Bruker smart
(79.50 MHz, CD2Cl2, 25 °C): δ = 16.8 (s) ppm. ESI-MS: m/z = 576
and Bruker SHELXTL program packages. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed in ideal
positions and refined as rigid atoms. The R and Rw values of 1a,
1b, and 1c are 0.0335 and 0.0528, 0.0320 and 0.0758, and 0.0437
and 0.1069, respectively. CCDC-763941 (1a), -763942 (1b) and
-763943 (1c) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[M–Ph2MeSiH]+.
Synthesis of TpRu(PPh3)(η3-HSiPhMe2H) (1c): This complex was
synthesized by using the same procedure as described above for 1b,
except that PhMe2SiH was used in place of Ph2MeSiH. Yield:
0.11 g (48%). C35H38BN6PRuSi (713.66): C 58.90, H 5.37, N 11.78;
found C 58.91, H 5.41, N 11.80. IR (KBr): ν = 2013 [m, ν(Ru–H)],
˜
2464 [m, ν(B–H)]. 1H NMR (400.13 MHz, CD2Cl2, 25 °C): δ =
1
2
–11.06 (d, JSiH = 19.2, JHP = 22.8 Hz, 2 H, RuH); 0.36 [s, 6 H,
Si(CH3)2]; 5.33 (t, 1 H of Tp), 5.77 (t, 2 H of Tp), 5.88 (d, 1 H of
Tp), 7.58 (d, 2 H of Tp), 7.66 (d, 1 H of Tp), 7.93 (d, 2 H of
Tp), 6.03–7.30 (m, 20 H of Ph) ppm. 13C{1H} NMR (100.61 MHz,
CD2Cl2, 25 °C): δ = 13.05 [s, Si(CH3)2] ppm. 31P{1H} NMR
(161.7 MHz, CD2Cl2, 25 °C): δ = 71.0 ppm. 29Si{1H} NMR
(79.50 MHz, CD2Cl2, 25 °C): δ = 15.1 (s) ppm. ESI-MS: m/z = 576
[M–PhMe2SiH]+.
Computational Details: Molecular geometries of the model com-
plexes were optimized without constraints by DFT calculations
using the mPW1K[20] functional. Frequency calculations at the
same level of theory have also been performed to identify all the
stationary points as minima (zero imaginary frequencies) or transi-
tion states (one imaginary frequency). Transition states were lo-
cated by using the Berny algorithm. Intrinsic reaction coordi-
nates[21] were calculated for the transition states to confirm that
such structures indeed connect two relevant minima. The effective
core potentials of Hay and Wadt with double-ζ valence basis sets
(LanL2DZ)[22] were used to describe Ru, P, and Si. Polarization
functions were also added for Ru (ζf = 1.235), P (ζd = 0.387), and
Si (ζd = 0.284).[23] The 6-311G (d, p) Pople basis set was used for
the water molecule and H atoms that were directly bonded to the
metal center.[24] The 6-311G basis set was used for all the other
atoms.[25] All of the DFT calculations were performed with the
Gaussian 03 package.[26]
General Procedure for the Hydrolysis of Silanes Catalyzed by 1c:
The catalyst 1c (7.1 mg, 0.01 mmol) was loaded into a 25 mL two-
necked pear-shaped flask, which was then evacuated and flushed
with nitrogen for four cycles. Silane (0.5 mmol), water (0.36 mL,
20 mmol), and 1,4-dioxane (2 mL) were then added by syringe into
the flask (in the case of Ph3SiH, the solid was loaded into the flask
prior to system evacuation and nitrogen flushing), and the resulting
solution was stirred under a nitrogen flow in a preheated 90 °C
silicone oil bath for the predesignated times. At the end of the reac-
tion, the flask was cooled to room temperature before a 0.1 mL
1
aliquot of the solution was withdrawn and analyzed by H NMR
Supporting Information (see footnote on the first page of this arti-
cle): 1H NMR spectra of the reaction mixture of the
TpRu(PPh3)(η3-HSiPhMe2H)-catalyzed hydrolytic oxidation of or-
ganosilanes to silanols and cartesian coordinates for all the com-
plexes calculated in this study.
spectroscopy (in CD3COCD3 or CD3CN). Conversions were deter-
mined by comparison of the integrations of the characteristic peaks
of the product and the unreacted silane.
Monitoring of the Hydrolytic Oxidation of PhMe2SiH to PhMe2-
SiOH Catalyzed by 1c with NMR Spectroscopy: A sample of 1c
(31.2 mg) was loaded into a J. Young valved NMR tube. The tube
was evacuated and filled with nitrogen for four cycles. PhMe2SiH
(33 μL, 5 equiv.), water (157 μL, 200 equiv.), and [D8]-1,4-dioxane
(1 mL) were added by syringe into the tube. The resulting solution
was heated to 90 °C. At different time intervals, the tube was cooled
to room temperature, and 1H and 31P NMR spectra of the solution
were measured.
Acknowledgments
We thank the Hong Kong Research Grant Council (Project No.
PolyU 5010/06P) for financial support.
[1] X.-L. Luo, D. Baudry, P. Boydell, P. Charpin, M. Nierlich, M.
Ephritikhine, R. H. Crabtree, Inorg. Chem. 1990, 29, 1511.
[2] K. Hussein, C. J. Marsden, J.-C. Barthelat, V. Rodriguez, S.
Conejero, S. Sabo-Etienne, B. Donnadieu, B. Chaudret, Chem.
Commun. 1999, 1315.
[3] D. V. Gutsulyak, L. G. Kuzmina, J. A. K. Howard, S. F.
Vyboishchikov, G. I. Nikonov, J. Am. Chem. Soc. 2008, 130,
3732.
Monitoring of the Reaction Between 1c and EtMe2SiH: A sample
of 1c (31.2 mg) was loaded into a J. Young valved NMR tube. The
tube was evacuated and filled with nitrogen for four cycles. EtMe2-
SiH (28 μL, 5 equiv.) and [D8]-1,4-dioxane (1 mL) were added by
syringe into the tube. The solution was heated to 90 °C for 3 h. The
tube was cooled to room temperature, and 1H and 31P NMR spec-
tra of the solution were measured.
[4] S. M. Ng, C. P. Lau, M. F. Fan, Z. Lin, Organometallics 1999,
Crystallographic Structure Analysis of 1a–c: Orange crystals of
1a–c suitable for study by X-ray diffraction were obtained by
layering of n-hexane on a dichloromethane solution of the com-
plexes. Suitable crystals of 1a (0.32ϫ0.3ϫ0.28 mm), 1b
(0.50ϫ0.48ϫ0.32 mm), and 1c (0.42ϫ0.36ϫ0.30 mm) were
mounted on a Bruker CCD area detector diffractometer and sub-
jected to Mo-Kα radiation (λ = 071073 Å) from a generator operating
at 50 kV and 30 mA. The intensity data of 1a–c were collected in
the range θ = 1.94–27.39°, 2.09–27.33°, and 1.17–27.46°, respec-
tively, with oscillation frames of Ψ and ω and in the range 0–180°.
A total of 1728 frames for 1a, 800 for 1b, and 988 for 1c were taken
in four shells. An empirical absorption correction of the SADABS
(G. M. Sheldrick, 1996) program based on Fourier coefficient fit-
ting was applied. The crystal structures were solved by Patterson
function methods, expanded by difference Fourier synthesis, and
18, 2484.
[5] a) I. Ojima, Z. Li, J. Zhu in The Chemistry of Organic Silicon
Compounds (Eds.: S. Rappoport, Y. Apeloig), Wiley, New York,
1998, chap. 29; b) E. W. Colvin, Silicon Reagents in Organic
Synthesis, Academic Press, London, 1988, p. 7; c) P. D. Lickiss,
Adv. Inorg. Chem. 1995, 42, 147.
[6] a) K. Hirabayashi, Y. Nishihara, A. Mori, T. Hiyama, Tetrahe-
dron Lett. 1998, 39, 7893; b) K. Hirabayashi, J. Kawashima, Y.
Nishihara, A. Mori, T. Hiyama, Org. Lett. 1999, 1, 299; c) S. E.
Denmark, D. Wehrli, Org. Lett. 2000, 2, 565; d) K. Hirabaya-
shi, A. Mori, J. Kawashima, M. Suguro, Y. Nishihara, T. Hi-
yama, J. Org. Chem. 2000, 65, 5342.
[7] a) E. G. Rochow, W. F. Gilliam, J. Am. Chem. Soc. 1941, 63,
798; b) R. O. Sana, J. Am. Chem. Soc. 1944, 66, 1707.
[8] W. Adam, R. Mello, R. Curci, Angew. Chem. Int. Ed. Engl.
1990, 29, 890.
Eur. J. Inorg. Chem. 2010, 5675–5684
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5683

T. Y. Lee, L. Dang, Z. Zhou, C. H. Yeung, Z. Lin, C. P. Lau
FULL PAPER
[9] a) S. M. Sieburth, W. Mu, J. Org. Chem. 1993, 58, 7584; b) K.
Hirabayashi, A. Mori, T. Hiyama, Tetrahedron Lett. 1997, 38,
461.
[20]
[21]
B. J. Lynch, P. L. Fast, M. Harris, D. G. Truhlar, J. Phys. Chem.
A 2000, 104, 4811.
a) J. Fukui, J. Phys. Chem. 1970, 74, 4161; b) K. Fukui, Acc.
Chem. Res. 1981, 14, 363.
[10] a) M. Lee, S. Ko, S. Chang, J. Am. Chem. Soc. 2000, 122,
12011; b) Y. Lee, D. Seomoon, S. Kim, H. Han, S. Chang, P. H.
Lee, J. Org. Chem. 2004, 69, 1741; c) E. A. Ison, R. A. Corbin,
M. M. Abu-Omar, J. Am. Chem. Soc. 2005, 127, 11938.
[11] a) K. Mori, M. Tano, T. Mizugaki, K. Ebitani, K. Kaneda,
New J. Chem. 2002, 26, 1536; b) E. Choi, C. Lee, Y. Na, S.
Chang, Org. Lett. 2002, 4, 2369; c) T. Mitsudome, S. Arita, H.
Mori, T. Mizugaki, K. Jitsukawa, K. Kaneda, Angew. Chem.
Int. Ed. 2008, 47, 7938.
[12] a) U. Schubert, Adv. Organomet. Chem. 1990, 30, 151; b) Z.
Lin, Chem. Soc. Rev. 2002, 31, 239.
[13] Y.-Z. Chen, W. C. Chan, C. P. Lau, H. S. Chu, H. L. Lee, G.
Jia, Organometallics 1997, 16, 1241. We are not sure of the
exact structure of 2, it might be analogous to those of 1a–1c,
containing an [η3-H3]– moiety instead of the hydride and η2-
H2 ligands.
[14] a) S. F. Vyboischchikov, G. I. Nikonov, Chem. Eur. J. 2006, 12,
8518; b) G. I. Nikonov, Angew. Chem. Int. Ed. 2001, 40, 3353.
[15] C. W. Leung, W. Zheng, D. Wang, S. M. Ng, C. H. Yeung, Z.
Zhou, Z. Lin, C. P. Lau, Organometallics 2007, 26, 1924.
[16] W. K. Fung, X. Huang, M. L. Man, S. M. Ng, M. Y. Hung, Z.
Lin, C. P. Lau, J. Am. Chem. Soc. 2003, 125, 11539.
[17] a) M.-F. Fan, G. Jia, Z. Lin, J. Am. Chem. Soc. 1996, 118,
9915; b) M.-F. Fan, Z. Lin, Organometallics 1997, 16, 494; c)
M.-F. Fan, Z. Lin, Organometallics 1999, 18, 286.
[18] a) J. F. Hartwig, S. Bhandari, P. R. Rablen, J. Am. Chem. Soc.
1994, 116, 1839; b) J. C. Lee, E. Peris, A. L. Rheingold, R. H.
Crabtree, J. Am. Chem. Soc. 1994, 116, 11014; c) M. Schlaf,
R. H. Morris, J. Chem. Soc., Chem. Commun. 1995, 625; d)
D. G. Musaev, A. M. Mebel, K. Morokuma, J. Am. Chem. Soc.
1994, 116, 10693; e) P. E. M. Siegbahn, R. H. Crabtree, J. Am.
Chem. Soc. 1996, 118, 4442; f) C. Hinderling, D. Feichtinger,
D. A. Plattner, P. Chen, J. Am. Chem. Soc. 1997, 119, 10793;
g) A. Milet, A. Dedieu, G. Kapteijin, G. van Koten, Inorg.
Chem. 1997, 36, 3223.
[22]
[23]
P. J. Hay, W. R. Wadt, J. Chem. Phys. 1995, 82, 299.
a) A. W. Ehlers, M. Böhme, S. Dapprich, A. Gobbi, A.
Höllwarth, V. Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp,
G. Frenking, Chem. Phys. Lett. 1993, 208, 111; b) A.
Höllwarth, M. Böhme, S. Dapprich, A. W. Ehlers, A. Gobbi, V.
Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp, G. Frenking,
Chem. Phys. Lett. 1993, 208, 237.
[24] R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem.
Phys. 1980, 72, 650.
[25] a) M. S. Gordon, Chem. Phys. Lett. 1980, 76, 163; b) P. C.
Hariharan, J. A. Pople, Theor. Chim. Acta 1973, 28, 213; c)
R. C. Binning Jr, L. A. Curtiss, J. Comput. Chem. 1990, 11,
1206.
[26] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven Jr,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Sal-
vador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D.
Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Ba-
boul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Lia-
shenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03, revision B05;
Gaussian, Inc., Pittsburgh, PA, 2003.
Received: September 8, 2010
Published Online: November 9, 2010
[19] L. H. Sommer, C. L. Frye, G. A. Parker, K. W. Michael, J. Am.
Chem. Soc. 1964, 86, 3271.
5684
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5675–5684