Synthesis and Reactivities of Polyhydrido Osmium Arylsilyl Complexes Prepared from OsH3Cl(PPh3)3

Article abstract of DOI:10.1021/acs.organomet.7b00512

Reactions of silanes with transition-metal complexes are of interest because their relevance to Si-H bond activation, the structural properties of polyhydrides, and catalytic hydrosilylation reactions. This work presents the results derived from reactions

Full text of DOI:10.1021/acs.organomet.7b00512

Article
pubs.acs.org/Organometallics
Synthesis and Reactivities of Polyhydrido Osmium Arylsilyl
Complexes Prepared from OsH3Cl(PPh3)3
Guomei He,†,‡ Linlin Wu,† Wei Bai,† Jiangxi Chen,*,‡ Herman H. Y. Sung,† Ian D. Williams,†
Zhenyang Lin,*,† and Guochen Jia*,†
†Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, People’s
Republic of China
‡Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen, People’s Republic of China
S
* Supporting Information
ABSTRACT: Reactions of silanes with transition-metal com-
plexes are of interest because their relevance to Si−H bond
activation, the structural properties of polyhydrides, and catalytic
hydrosilylation reactions. This work presents the results derived
from reactions of arylsilanes Ph2SiH2 and PhSiH3 with
OsH3Cl(PPh3)3 (1). Reaction of 1 with 1 equiv or excess
Ph2SiH2 affords OsH3(SiClPh2)(PPh3)3 (2) or OsH4(SiClPh2)-
(SiHPh2)(PPh3)2 (3), respectively. These silyl complexes are formed via the oxidative addition of Si−H bonds and H/Cl
exchange via silylene intermediates. Similarly, reaction of 1 with excess PhSiH3 produced the analogous bis(silyl) complex
OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4). The bis(silyl) complexes are dodecahedral tetrahydride complexes containing weak Si···H
interactions. The complex 3 reacts with PPh3 and CH3CN to selectively eliminate Ph2SiH2. Computational studies show that the
preference for reductive eliminations from 3 follows the order Ph2SiH2 > H2 > Ph2SiHCl > Ph2HSi-SiClPh2.
(silyl) complexes OsH3(SiClR2)(PPh3)3 obtained from the
reactions of OsH3Cl(PPh3)3 with R2SiH2. The reductive
elimination reactions of the bis(silyl) complex OsH4(SiClPh2)-
(SiHPh2)(PPh3)2 are also described.
INTRODUCTION
■
Reactions of silanes with transition-metal complexes are of
interest because their relevance to Si−H bond activation,1a−c
the structural properties of polyhydrides,1d,e and catalytic
hydrosilylation reactions.1a−d In the area of osmium chemistry,
reactions of silanes have been reported with Os(0) mono-
nuclear2 and cluster complexes,3 Os(II) halo,4,5 hydride, and
alkyl/aryl complexes,6−9 Os(IV) hydride10,11 and halohydride12
complexes, and OsO4.13
The results are interesting for the following reasons. (1) The
complexes OsH4(SiClR2)(SiHR2)(PPh3)2 represent a new type
of organometallic complexes formed from the reactions of
silanes with osmium complexes. The complexes are structurally
related to the bis(η2-silane) complexes RuH2(η2-H-
SiR3)2(PR′3)2, which were known as early as 1997.14 (2) The
SiClR2 group in the complexes OsH3(SiClR2)(PPh3)3 and
OsH4(SiClR2)(SiHR2)(PPh3)2 is apparently formed via H/Cl
exchange of the Si−H/Os−Cl bonds, which has rarely been
observed previously in the reactions of silanes with osmium
complexes. (3) The reductive elimination reactions of the
bis(silyl) complex OsH4(SiClPh2)(SiHPh2)(PPh3)2 provide an
opportunity to compare the relative ease of reductive
elimination of H2, Ph2ClSiH, Ph2SiH2, or Ph2ClSi-SiHPh2.
The reactions of silanes with osmium complexes can give
varied products depending on the structures of silanes as well as
the ligands of osmium complexes. The most common products
of the reactions are hydridosilyl complexes LnOsHx(SiR3) (e.g.,
OsCl(SiEt3)(H2)(CO)(PiPr3)2,8b,c Cp*OsHBr(SiR3)-
(PiPr3),5,6a,11 and OsH3(SiR3)(CO)(PR′3)2,7a,8a,9a) formed by
oxidative addition of R3Si−H to unsaturated osmium centers
and/or silyl complexes LnOs−SiR3 (e.g., OsCl(SiR3)(CO)-
(PPh3)2,7c,8a,c,9e−k OsH3(SiR3)(PPh3)3,10 and Cp*(Me3P)2Os-
(SiCliPr2)6b) formed as a result of metathesis reactions between
R3Si−H and LnOs−X (X = halide, H, alkyl). Other interesting
products include the osmium silylene complexes LnOsH(
SiR2) (e.g., Cp*OsH(SiHR)(PiPr3),6a OsH3(SiPhCl){2,6-
(CH2PtBu2)2C6H3},12 and OsH2(SiR2)(CO){PMe-
(tBu)2}27a) formed by α-H elimination of silyl intermediates
LnOs(SiHR2) and/or bis(silyl) complexes LnOs(SiHR2)2 (e.g.,
RESULTS AND DISCUSSION
■
Reactions of OsH3Cl(PPh3)3 with Silanes. This work
stems from our interest in comparing the structural properties
of OsH3(SiR3)(PR′3)3 and OsClH2(SiR3)(PR′3)3. Chloride and
hydride are known to have different effects on the structures of
polyhydridosilyl complexes. For example, the complex
OsH3(SiHPh2)(CO)(PiPr3)2, which was obtained from the
reaction of OsH2(CH2CHEt)(CO)(PiPr3)2 with Ph2SiH2, is
3a
Os(SiR3)2(CO)4 and Cp*(Me3P)OsH(SiMe2Cl)26d) formed
by further reactions of silanes with initially generated
mono(silyl) intermediates.
In this work, we report the isolation and characterization of
bis(silyl) complexes OsH4(SiClR2)(SiHR2)(PPh3)2 and mono-
Received: July 10, 2017
© XXXX American Chemical Society
A
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a classical trihydride complex,8a while OsCl(SiEt3)(H2)(CO)-
(PiPr3)2, which was obtained from the reaction of OsHCl-
(CO)(PiPr3)2 with Et3SiH, is a nonclassical dihydrogen
complex.8b,c
The hydridosilyl complexes OsH3(SiR3)(PPh3)3 (R =
pyrrolyl, Et, Ph) are known to display interesting weak Si···H
interactions.10 It is therefore of interest to prepare complexes of
the formula OsClH2(SiR3)(PPh3)3 in order to further examine
the chloride effect on the structure of polyhydridosilyl osmium
complexes. The complexes OsH3(SiR3)(PPh3)3 can be
prepared from the reactions of OsH4(PPh3)3 with R3SiH.10
One might anticipate that the complexes OsClH2(SiR3)(PPh3)3
could be similarly prepared from the reactions of OsH3Cl-
(PPh3)3 (1) with R3SiH.
We first investigated the reaction of OsH3Cl(PPh3)3 (1) with
Ph2SiH2. To our surprise, the reaction did not produce the
expected complex OsClH2(SiHPh2)(PPh3)3 but instead gave
the mono(silyl) complex OsH3(SiClPh2)(PPh3)3 (2) and
bis(silyl) complex OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3) with a
SiClPh2 group derived from H/Cl exchange of the Si−H/Os−
Cl bonds (Scheme 1).
OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4) was obtained from the
reaction of OsH3Cl(PPh3)3 with excess PhSiH3. As monitored
by in situ 31P{1H} NMR, the reaction of 1 equiv of PhSiH3 with
OsH3Cl(PPh3)3 produced the bis(silyl) complex 4 as the major
product. The reaction also produced a minor species with a
singlet 31P{1H} signal at 5.2 ppm, which could be the trihydride
complex OsH3(SiClHPh)(PPh3)3 considering that the 31P
chemical shift is similar to that (4.9 ppm) of OsH3(SiClPh2)-
(PPh3)3. Unfortunately, we have failed to obtain a pure sample
of the minor product by either recrystallization or chromatog-
raphy. Under the same conditions, Ph3SiH and tBu2SiH2 were
unreactive.
Characterization of Bis(silyl) Complexes. The presence
1
of four hydride ligands in 3 is indicated by the H NMR
spectrum, which shows two broad hydride signals of equal
intensity at −6.0 and −9.7 ppm at room temperature (Figure
1
1). The H NMR spectra of 3 are temperature dependent.
Scheme 1. Reactions of OsH3Cl(PPh3)3 with Silanes
Figure 1. Hydride region of the 1H NMR spectra of 3 in C6D5CD3 at
295−242 K.
The in situ 31P{1H} NMR spectrum indicated that, after a
mixture of 1 and 10 equiv of Ph2SiH2 in toluene was stirred at
room temperature for 2 h, the starting hydride complex was
consumed completely and the reaction produced a new species
with a singlet 31P{1H} signal at 9.5 ppm along with free PPh3.
When only 1 equiv of Ph2SiH2 was used, the in situ 31P{1H}
NMR spectrum indicated that the starting hydride complex
partially reacted with Ph2SiH2 to give two products with singlet
31P{1H} signals at 9.5 and 4.9 ppm, respectively.
We have tried to isolate the reaction products. From the
reaction with 3 equiv of Ph2SiH2, the species with the singlet
31P{1H} signal at 9.5 ppm was isolated as a white solid, which
was subsequently identified to be the bis(silyl) complex
OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3) (Scheme 1). From the
reaction with 1 equiv of Ph2SiH2, a species with a singlet
31P{1H} signal at 4.9 ppm was isolated also as a white solid,
which was subsequently identified to be the monosilyl complex
OsH3(SiClPh2)(PPh3)3 (2). When OsH3Cl(PPh3)3 (1) was
replaced by OsHCl(PPh3)3 (5), the reaction also gave
complexes 2 and 3. Further experiments showed that the
bis(silyl) complex 3 could also be produced from the reaction
of Ph2SiH2 with isolated monosilyl complex 2.
Coalescence of the two hydride signals to give a single signal at
−7.9 ppm is obtained when the temperature is above 326 K.
When the temperature is below 262 K, the hydride signals
become sharp. At 252 K, two hydride signals appear at −5.9
and −9.6 ppm as sharp multiplets. At 248 K and 400 MHz, the
peaks at −5.9 and −9.6 ppm have rather long T1 values of 359
and 366 ms, respectively, indicating that the complex does not
have an η2-H2 ligand. The 31P{1H} NMR spectrum of the
bis(silyl) complex 3 displays a singlet signal at ca. 9.5 ppm in
the temperature range of 323−243 K.
The presence of SiHPh2 and SiClPh2 groups in 3 is indicated
by the 29Si{1H} NMR spectrum, which displays two triplets at
19.7 (2JPSi = 12.2 Hz) and −16.8 ppm (2JPSi = 6.6 Hz). The 29Si
DEPT135 NMR experiment indicates that the signal at 19.7
ppm is due to SiClPh2 while the other at −16.8 ppm is due to
SiHPh2. In the 29Si NMR spectrum (see Figure S9 in the
Supporting Information), the signal of SiHPh2 appears as a
broad doublet (w1/2 = 36 Hz) with a 1JHSi coupling of 204.6 Hz
and the signal of SiClPh2 appears as a broad singlet (w1/2 = 40
Hz) with no observable JHSi coupling. As additional Si−H
coupling was not resolved, we conclude that the coupling
between silicon and the hydrides, if present, should be less than
40 Hz (considering the half-width of the broad peaks).
Similar reactions occurred between OsH3Cl(PPh3)3 and the
primary silane PhSiH3 . The bis(silyl) complex
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The structure of the bis(silyl) complex 3 has been confirmed
by X-ray diffraction. As shown in Figure 2, the complex
Support for the proposed structure of 3 comes from our
DFT calculations. Figure 4 shows the B3LPY optimized
Figure 4. B3LYP optimized structure of complex 3 that reproduces the
X-ray data. Selected bond lengths (Å) and angles (deg): Os−H1
1.674, Os−H2 1.625, Os−H3 1.673, Os−H4 1.632, H1−H2 2.068,
H2−H3 2.824, H1−H4 2.706, H3−H4 2.118, H2−H4 2.672, Os−P2
2.530, Os−P1 2.518, Os−Si1 2.488, Os−Si2 2.462, Si1−H1 2.231,
Si1−H2 2.453, Si1−H4 2.152, Si2−H2 2.309, Si2−H3 2.165, Si2−H4
2.549; P1−Os−P2 98.28, Si1−Os−Si2 92.87, Si1−Os−P2 106.14,
Si1−Os−P1 132.02, Si2−Os−P2 130.32, Si2−Os−P1 101.93, H1−
Os−H2 77.61, H1−Os−H3 158.72, H1−Os−H4 109.86, H1−Os−P2
87.39, H1−Os−P1 79.81, H1−Os−Si1 61.18, H1−Os−Si2 140.57,
H2−Os−H3 117.79, H2−Os−H4 110.29, H2−Os−P2 164.62, H2−
Os−P1 75.91, H2−Os−Si1 69.64, H2−Os−Si2 65.06.
Figure 2. ORTEP drawing of OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3)
with thermal ellipsoids at the 50% probability level. The phenyl groups
of the phosphines are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Os(1)−Si(1) 2.408(3), Os(1)−Si(2) 2.425(15);
Si(2)−Cl(2) 2.068(3), Os(1)−P(1) 2.403(2), Os(1)−P(2) 2.414(2);
P(1)−Os(1)−P(2) 99.31(8), P(1)−Os(1)−Si(1) 128.99(8), P(1)−
Os(1)−Si(2) 106.4(4), P(2)−Os(1)−Si(2) 126.1(6), Si(1)−Os(1)−
P(2) 107.25(8), Si(1)−Os(1)−Si(2) 92.0(6).
contains SiHPh2 and SiClPh2 groups which are cis to each
other with a Si−Os−Si angle of 92.0(6)°. The two phosphine
ligands are also cis to each other with a P−Os−P angle of
99.31(8)°. Unfortunately, the positions of the hydride ligands
could not be accurately located by the X-ray diffraction study.
Complexes 6 and 7 (see Figure 3 for their structures) are
reported examples of complexes having a set of ligands similar
structure of complex 3 that reproduces the X-ray data.
Consistent with the solution NMR data, the optimized
structure contains two types of hydrides: two of the hydrides
are essentially trans to phosphorus atoms (P2−Os−H2,
164.62°; P1−Os−H4, 169.20°), and the other two are
approximately trans to each other (H1−Os−H3, 158.72°).
The Os−H bonds for the mutually trans hydrides are of similar
bond distances and are longer than the Os−H bonds (which
are also of similar bond distances) trans to the phosphine
ligands. In agreement with a classical hydride structure, the
separations between the hydride ligands are in all cases longer
than 2.068 Å. The two hydride signals at −5.9 and −9.6 ppm
Figure 3. Selected bond angles (deg) of complexes 3, 6, and 7.
1
displayed by the low-temperature H NMR spectrum of 3 can
be assigned to the hydrides trans and cis to the phosphine
ligands, respectively.
to that of 3. Complex 6 is a bis(η2-silane) complex with the
silane ligands cis to the phosphine ligands.14c Complex 7 is a
bis(stannyl) tetrahydride complex with a dodecahedral
structure.15 As indicated by the structural parameters shown
in Figure 3, the P−Os−P, Si−Os−Si, and P−Os−Si angles of 3
are different from those of 6 and 7. When only the P−M−Si
angles are considered, the geometry of 3 is closer to that of the
dodecahedral tetrahydride complex 7. Considering the
structural and NMR data, we propose that the complex 3 has
a structure closer to that of 7.
We noted that square-planar complexes of the type
Pt(SiR′3)2(PR3)2 with two cis-disposed SiR3 groups and two
cis PR3 ligands are known.16 In such complexes, the Si−Pt−Si
angles are appreciably smaller. For example, the complex
Pt(SiHPh2)2(PPh3)2 has a Si−Pt−Si angle of 80.37(7)°.16a
A close look at the optimized structure of 3 reveals that there
are Si···H contacts which are shorter than the sum (3.3 Å) of
the van der Waals radii of H (1.2 Å) and silicon (2.1 Å),17
indicating the presence of weak secondary Si···H interactions.
The Si(1) is in close contact with H(1) and H(4) (Si(1)−
H(1), 2.231 Å; Si(1)−H(4), 2.152 Å), while Si(2) is in close
contact with H(2) and H(3) (Si(2)−H(2), 2.309 Å; Si(2)−
H(3), 2.165 Å) (Figure 4).
The structure of the bis(silyl) complex 4 can be assigned on
1
the basis of its NMR data. The H NMR spectroscopic data of
4 are similar to those of 3 (see the Experimental Section for
details). Due to the presence of the chiral Si center in the
SiHClPh group, the two phosphorus atoms are magnetically
inequivalent. Thus, the 31P{1H} NMR spectrum shows an AB
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pattern centered at 13.50 ppm with ΔδAB = 0.13 ppm and JAB
16.2 Hz.
=
Ph2SiH2 to 5 would produce the hydridosilyl intermediate 12,
which eventually evolves to complexes 2 and 3.
There are two possible routes for the conversion of complex
12 to complex 2: one involves a silylene intermediate (path A),
and the other involves reversible reductive elimination and
oxidative addition of Ph2SiClH (path B).
One of the most interesting aspects of the reactions of
OsH3(PPh3)3 with Ph2SiH2 and PhSiH3 is the Os−Cl/Si−H
exchange to give chlorine-substituted silyl complexes. Similar
H/X exchange reactions have been observed occasionally for
reactions involving IrX18,19 and RuCl12,20 complexes. In the
case of osmium chemistry, the only reported examples are the
reactions of PhSiH3 with [OsH2Cl{CH(C2H4PR2)2}] (8) and
[OsH2Cl{2,6-(CH2PR2)2C6H3}] (10, R = t-Bu), which
produced [OsH5(SiClPh2)(SiH2PR2(CH2)5PR2)] (9) and
[OsH3(SiPhCl){2,6-(CH2PR2)2C6H3}] (11, R = t-Bu),
respectively (Scheme 2).12
In path A, the complex 12 first dissociates a PPh3 ligand to
give the 16e species 13, which can then undergo α-H
elimination to give the silylene complex 14. Migratory insertion
of the silylene group into the osmium−chloride bond of 14 can
give the unsaturated intermediate 15, which could then react
with PPh3 to give the complex 2. We noted that silylene
intermediates have been suggested previously for the reaction
of Ir−X complexes with silanes Ph2SiH2 to give Ir−SiXPh2
complexes. Examples include the reaction of Cp*(PMe3)Ir-
(CH3)(OTf) with Ph2SiH2 to produce Cp*(PMe3)IrH-
{SiPh2(OTf)},18a the reactions of Ph2SiH2 with the triflato
complexes Ir(OTf)(TFB)(PR3) (R = i-Pr, Cy; OTf = triflate;
TFB = tetrafluorobenzobarrelene) to give (R3P)(TFB)(H)2Ir-
{Si(OTf)Ph2},18a the reaction of Ir(OCOCH3)(TFB)L (L =
py, PPh3, PCy3, PiPr3) with Ph2SiH2 to give IrH2{Si-
(OCOCH3)Ph2}(TFB)(PR3),18b and the reaction of Ir(η1-
OCOCH3)(CO)2(PCy3) with Ph2SiH2 to give IrH2{Si-
(OCOCH3)Ph2}(CO)2(PCy3).18c
Scheme 2. Reactions of Pincer Osmium Hydride Complexes
with PhSiH3
In path B, the complex 12 first isomerizes via intermediate 13
to 16, which then undergoes reductive elimination involving
the chloride and the SiHPh2 ligands to give Ph2SiClH and the
five-coordinate intermediate OsH2(PPh3)3 (17). The complex
2 could then be formed by oxidative addition of the Si−H bond
of Ph2SiClH to 17. A similar reaction sequence has been
suggested for the reaction of Cp*RuCl(PiPr3) with mesitylsi-
lane (MesSiH3) to give Cp*RuH2(SiHClMes)(PiPr3).19
The complex 3 could be formed by the oxidative addition
reaction of Ph2SiH2 with the intermediate OsH3(SiClPh2)-
(PPh3)2 (15). We have shown experimentally that the complex
3 could also be formed from the reaction of the complex 2 with
excess Ph2SiH2, presumably also via the intermediate 15
generated by dissociation of a PPh3 ligand from the complex 2.
To confirm whether the proposed mechanism shown in
Scheme 3 is reasonable or not and to determine which pathway
is more likely involved in the formation of 2, we have calculated
the energy profiles for the two reaction pathways starting from
the reaction of OsHCl(PPh3)3 (5) with Ph2SiH2.
Mechanistic Considerations. Scheme 3 shows plausible
pathways for the formation of the monosilyl complex 2 and the
Scheme 3. Proposed Mechanisms for the Formation of 2 and
3
As shown in Figure 5, the oxidative addition of OsHCl-
(PPh3)3 (5) with Ph2SiH2 to give OsH2Cl(SiHPh2)(PPh3)3
(12) is almost thermodynamically neutral (or slightly favored
by 0.2 kcal/mol) with a barrier of 18.5 kcal/mol. The complex
12 can evolve to complex 2 exothermically (by 15.0 kcal/mol)
with reasonably low reaction barriers, in agreement with
experimental observation that the complex 2 rather than the
complex 12 was isolated from the reaction.
The path for converting 12 to 2 involving a silylene
intermediate (path A) has an overall barrier of 22.1 kcal/mol.
In this pathway, the complex 12 dissociates a PPh3 ligand to
give the complex 13 in a slightly endothermic process (by 4.4
kcal/mol) with a barrier of 12.7 kcal/mol. The complex 13 then
isomerizes to the complex 13A also in a slightly endothermic
process (by 2.0 kcal/mol) with a small barrier of 6.5 kcal/mol.
α-H elimination in 13A to give the silylene complex 14 occurs
slightly endothermically (by 4.1 kcal/mol) with a small barrier
of 6.2 kcal/mol. The silylene complex 14 undergoes a migration
insertion reaction to give the silyl complex 15A in an
exothermic process (by 4.1 kcal/mol) with a barrier of 11.5
bis(silyl) complex 3. Since complexes 2 and 3 can also be
formed from reactions of OsHCl(PPh3)3 (5) with Ph2SiH2, we
assume that the first step of the reaction is the dissociation of
one molecule of H2 from the trihydride complex 1 to give the
monohydride OsHCl(PPh3)3 (5). Si−H oxidative addition of
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Figure 5. Reaction profile for the reaction of OsH3Cl(PPh3)3 (1) with Ph2SiH2. The relative free energies and electronic energies (in parentheses)
are given in kcal/mol.
kcal/mol. This step is the rate-determining step. Subsequent
reaction of the silyl complex 15A with PPh3 can proceed in an
exothermic process (by 21.4 kcal/mol) via intermediate 15 with
a very low barrier of ca. 5 kcal/mol.
more stable than complexes 12 and 16 by 15.0 and 18.9 kcal/
mol, respectively.
The complex 2 is more stable than complexes 12 and 16
probably because a Si−Cl bond is stronger than a Si−H bond.
For example, the Si−H bond energy in Me3SiH is 90.3 kcal/
mol, while the Si−Cl bond energy in Me3SiCl is 113 kcal/
mol.21 In addition, the Os−Si bonds in complexes 12 and 16
are weaker than that in complex 2, as reflected by the Os−Si
distances in complexes 12 (2.470 Å), 16 (2.480 Å), and 2
(2.380 Å) shown in Figure 6. The complex 12 is more stable
than complex 16 probably because the steric interaction of the
three facially bound PPh3 ligands in 16 is larger than that of the
three meridionally bound PPh3 ligands in 12.
The path for converting 12 to 2 involving reversible
reductive elimination and oxidative addition of Ph2SiHCl
(path B) has an overall barrier of 26.6 kcal/mol. In this
pathway, the complex 12, which contains three meridionally
bound PPh3 ligands, first isomerizes to the isomeric complex 16
containing three facially bound PPh3 ligands via intermediate
13. Reductive elimination of Ph2SiHCl from 16 to give the
complex 16B containing a bound Ph2SiHCl (through the
chloride atom) proceeds in an endothermic process (by 15.2
kcal/mol) with a barrier of 22.7 kcal/mol. This step is the rate-
determining step. Dissociation of Ph2SiHCl from 16B occurs
exothermically (by 5.0 kcal/mol) with a barrier of 3.5 kcal/mol
to give the dihydride complex 17, which then reacts with PPh3
to give complex 2 in an exothermic process (by 29.1 kcal/mol)
with a very low barrier of 5.1 kcal/mol.
We have also considered conversion of 16 to 2 by a
concerted process involving Cl− side-attacking the Si center and
H-shifting to the metal center simultaneously. However, we
were unable to locate such a transition state, implying that the
concerted process is unlikely.
The calculated reaction barriers for the two pathways suggest
that conversion of 12 to 2 most likely proceeds through the
path involving a silylene intermediate (path A) rather than the
path involving reversible reductive elimination and oxidative
addition of Ph2SiClH (path B). It is noted that silylene
intermediates have been suggested previously for the reactions
of M−X complexes with R2SiH2 to give M−SiXR2 com-
plexes,17,18 but the process has not been studied computation-
ally.
Comments on the Energies and Structures of 2, 12,
and 16. Complexes 2, 12, and 16 are structural isomers with
the same coordination number. Interestingly, they have
different stabilities and the complex 2 is thermodynamically
Figure 6. Optimized structures and selected structural parameters (Å)
of complexes 2, 12, and 16.
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At this point, it might be worthwhile to comment on the
structures of the trihydrido complex 2 and the chloro dihydrido
complexes 12 and 16 in a bit more detail. As shown in Figure 6,
the trihydrido complex and the chloro dihydrideo complexes
adopt different coordination geometries around osmium. The
trihydrido complex 2 can be best viewed as a distorted capped
octahedron with the SiClPh2 group capping one of the
triangular faces. The chloro dihydrido complexes 12 and 16,
despite their different ligand arrangements, can both be viewed
as a distorted pentagonal bipyramid with the SiClPh2 group
lying approximately on the pentagonal plane. Like OsH3(SiR3)-
(PPh3)3 (R = pyrrolyl, Et, Ph),10 there are weak Si···H
interactions in trihydrido complex 2 and the chlorodihydrido
complexes 12 and 16. It is also noted that the Si atom in
complex 12 is in close contact with the chloride ligand with a
Si···Cl distance of 3.022 Å, which is less than the sum (3.85 Å)
of the van der Waals radii of Si (2.10 Å) and Cl (1.75 Å).16 The
calculated structural parameters of complexes 16 and 2 indicate
that the presence of the chloride ligand on osmium does not
change the Si···H interaction remarkably.
It has been reported that the complex OsH3(SiHPh2)(CO)-
(PiPr3)2 is a classical trihydride complex8a while the complex
OsCl(H2)(SiEt3)(CO)(PiPr3)2 is a dihydrogen complex.8b,c
Thus, replacement of a hydride ligand in OsH3(SiHPh2)(CO)-
(PR3)2 with a chloride enhances the H···H interaction. In our
system, replacement of a hydride ligand in OsH3(SiR3)(PPh3)2
with a chloride does not lead to enhanced H···H or Si···H
interaction.
Reactions of OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3) with
PPh3 and CH3CN. Complex 3 contains four terminal hydride
ligands and two different silyl ligands. Its reductive elimination
is interesting, as it provides an opportunity to compare the
relative ease of reductive eliminations of H2, Ph2ClSiH,
Ph2SiH2, and Ph2ClSi-SiHPh2. We have therefore studied the
reactions of 3 with CH3CN and PPh3. The complex 3 was
found to react with PPh3 and CH3CN to give the trihydride
complexes OsH3(SiClPh2)(PPh3)3 (2) and OsH3(SiClPh2)-
(PPh3)2(NCMe) (18), respectively, via elimination of Ph2SiH2
(Scheme 4).
Figure 7. ORTEP drawing of OsH3(SiClPh2)(NCMe)(PPh3)2 (18)
with thermal ellipsoids at the 50% probability level. The phenyl groups
of the phosphines are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Os1−P1 2.3773(4), Os1−P2 2.3459(4), Os1−Si1
2.3254(5), Os1−N1 2.0885(16), Os1−H1 1.5917(239), Os1−H2
1.6077(255), Os1−H3 1.6003(313); P2−Os1−P1 101.324(15), Si1−
Os1−P1 124.572(16), Si1−Os1−P2 123.868(16), N1−Os1−P1
92.19(4), N1−Os1−P2 96.28(4).
noted that the P−Os−P angle 101.324(15)° is much smaller
than that (146.06(7)°) in OsH3(SiHPh2)(CO)(PiPr3)2.8a The
three hydride ligands are approximately trans to CH3CN and
the PPh3 ligands, as reflected by the H−Os−P or H−Os−N
angles (H(3)−Os−N(1), 177.59(1.90)°; H(2)−Os−P(2),
179.46(0.90)°; H(1)−Os−P(1), 175.73(0.88)°). Thus, the
complex can be viewed as either a distorted tetrahedron with
three face-capped hydrides or a distorted octahedron with a
face-capped SiClPh2 group.
The Os−Si bond length in complex 18 is 2.3254(5) Å, which
is appreciably shorter than those in OsH3(SiHPh2)(CO)-
(PiPr3)2 (2.448(2) Å)8a and OsH3(SiMe3)(CO)(PPh3)2
(2.4533(8) Å).9f
The solid-state structure is supported by the solution NMR
spectroscopic data. The 31P{1H} NMR spectrum in CD2Cl2
showed a singlet at 17.6 ppm in the temperature range of 295−
193 K. The IR spectrum showed ν(Os−H) signals at 2070 and
1991 cm−1. Like OsH3(SiR3)(CO)(PR′3)2, the 1H NMR
spectra of OsH3(SiClPh2)(PPh3)2(NCMe) (18) are temper-
ature dependent (Figure S22 in the Supporting Information).
At room temperature, the 1H NMR spectrum in CD2Cl2 shows
a broad hydride signal at −11.0 ppm. As expected, the hydride
signal is split into two signals in a 2:1 intensity ratio when the
temperature was lowered below 233 K. At 193 K, the two
hydride signals appeared at −9.1 (dd, 2JPH = 47.6, 22.0 Hz) and
Scheme 4. Reactions of OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3)
with PPh3 and CH3CN
2
−15.1 ppm (t, JPH = 19.6 Hz). As in the case of
Complex 2 has been characterized by NMR spectroscopy
OsH3(SiR3)(CO)(PR’3), the H−H coupling was not resolved
and elemental analysis. The 31P{1H} NMR spectrum in CD2Cl2
for 18.
1
10
showed a singlet at 4.9 ppm. The H NMR spectrum showed
Complexes OsH3(SiR3)(PR′3)3 and OsH3(SiR3)(CO)-
8a
characteristic hydride signal at −10.4 ppm. The IR spectrum
showed ν(Os−H) at 2064 and 2012 cm−1. The chemical shift
and the IR frequencies of Os−H of 2 are similar to those
reported for OsH3(SiPh3)(PPh3)3.10
(PR′3)2 are classical hydride complexes with weak Si···H
interaction. Our computational work confirms that such weak
Si···H interaction is also present in complexes 2 and 18 (see
Figures S23 and S34 in the Supporting Information).
The structure of 18 has been confirmed by X-ray diffraction.
As shown in Figure 7, the non-hydrogen donor atoms are
arranged in an approximately tetrahedral manner around
osmium. The Si−Os−N and P−Os−P angles are 110.78(4)°
and 101.324(15)°, respectively. The two Si−Os−P angles are
124.572(16) and 123.868(16)°. The structural parameters are
similar to those observed for OsH3(SiMe3)(CO)(PPh3)2.9f It is
In the reaction of 3 with PPh3 and CH3CN, complexes 2 and
18 are apparently formed by elimination of Ph2SiH2. In
principle, elimination of H2, Ph2SiClH, and Ph2ClSi-SiHPh2 are
also possible. However, we have no evidence for such processes.
To understand the selectivity of the reductive elimination
reactions, we have calculated the reaction energy changes for
the reactions of 3 with CH3CN. Our computational studies
F
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Article
suggest that the elimination reaction is thermodynamically
controlled, as illustrated in Figure 8.22 Consistent with our
OsH3(SiClPh2)(L)(PPh3)2, as a result of selective elimination
of Ph2SiH2. Computational studies show that preference for the
possible reductive eliminations from OsH4(SiClPh2)(SiHPh2)-
(PPh3)2 follows the order Ph2SiH2 > H2 > Ph2SiHCl > Ph2HSi-
SiClPh2.
EXPERIMENTAL SECTION
■
All manipulations were carried out under a nitrogen atmosphere using
standard Schlenk techniques unless otherwise stated. Solvents were
distilled under nitrogen from sodium benzophenone (hexane, ether),
sodium (toluene), or calcium hydride (CH2Cl2, CH3CN). OsH3Cl-
(PPh3)3 (1) was prepared according to the procedure reported in the
literature.23 The silanes and other reagents were used as purchased
from Aldrich Chemical Co. USA. Microanalyses were performed by
M-H-W Laboratories (Phoenix, AZ). 1H, 13C{1H}, 31P{1H}, and
29Si{1H} NMR spectra were collected on a Bruker ARX-400
spectrometer (400 MHz) or Bruker Advance II-300 spectrometer
1
(300 MHz). H and 13C NMR shifts are relative to TMS, and 31P
chemical shifts are relative to 85% H3PO4. Infrared (IR) spectra were
recorded on a Nicole Avator 360 apparatus (Nicolet, USA).
OsH3(SiClPh2)(PPh3)3 (2). Method A. To a suspension of
OsH3Cl(PPh3)3 (1; 200 mg, 0.197 mmol) in toluene (4.0 mL) was
added Ph2SiH2 (37 μL, 0.199 mmol). The reaction mixture was stirred
for 3 h to give a gray suspension. The solvent was removed under
vacuum, and the residue was washed with DCM (0.5 mL × 3) and
then with ether (2 mL × 3) to give a white solid, which was dried
under vacuum. Yield: 47.0 mg (0.0392 mmol), 19.9%.
Figure 8. Free energy changes for the reactions of 3 with CH3CN. The
relative free energies and electronic energies (in parentheses) are given
in kcal/mol.
experimental observation, only the elimination of Ph2SiH2 from
3 to give 18 is thermodynamically favored (by 0.9 kcal/mol).
Interestingly, the elimination of Ph2SiHCl to give 19 is
significantly thermodynamically unfavorable (by 14.3 kcal/
mol). The reaction involving elimination of H2 to give bis(silyl)
complex 20 is thermodynamically slightly unfavored by 1.5
kcal/mol. The reaction involving elimination of Ph2ClSiSiHPh2
to give the dihydrogen complex 21 is thermodynamically most
unfavorable by 17.9 kcal/mol.
Method B. A solution of OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3; 35
mg, 0.0313 mmol) and PPh3 (10 mg, 0.0381 mmol) in C6D6 (0.40
mL) was heated at 55 °C for 12 h to give a white precipitate, which
was collected by filtration, washed with ether (0.5 mL × 3) and then
DCM (0.3 mL × 2), and dried under vacuum. Yield: 30.7 mg (0.0256
1
mmol), 82.1%. 31P{1H} NMR (161.98 MHz, CD2Cl2): δ 4.9 (s). H
NMR (400.13 MHz, CD2Cl2): δ −10.4 (m, 3H, OsH3), 6.8−7.1 (m,
42H, Ph), 7.18 (t, JHH = 7.2 Hz, 9H, Ph), 7.30 (d, JHH = 6.8 Hz, 4H,
Ph). IR: ν 2064, 2012 cm−1 (Os−H). Anal. Calcd for C66H58ClOsSiP3:
C, 66.18; H, 4.88. Found: C, 66.29; H, 5.08.
A plausible explanation for the selectivity of the elimination
reactions is as follows. Formation of 21 is least favorable
because the eliminated species (Ph2ClSiSiHPh2) has a weak
Si−Si bond. Formation of 20 is slightly thermodynamically
unfavorable probably because complex 20 is sterically very
crowded, which weakens the Os−ligand bond. In agreement
with this argument, the Os−Si(Cl) (2.590 Å) bond in the
optimized structure of 20 is appreciably longer than the
corresponding distance (2.370 Å) of 18. Elimination of
Ph2SiH2 from 3 to give 18 is preferred over elimination of
Ph2SiHCl from 3 to give 19, probably because the Os−SiClPh2
bond is stronger than Os−SiHPh2. Indeed, in the calculated
structure of 3, the Os−SiClPh2 (2.462 Å) bond is shorter than
the Os−SiHPh2 bond (2.488 Å) (Figure 4).
OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3). A suspension of OsH3Cl-
(PPh3)3 (1; 1.0 g, 0.985 mmol) in toluene (10 mL) was added
Ph2SiH2 (0.55 mL, 2.96 mmol). The reaction mixture was stirred for 2
h to give a pale brown solution. The solvent was removed under
vacuum, and the residue was washed with ether (2 mL × 3) then with
hexane (3 mL × 3) to give a white solid, which was dried under
vacuum. Yield: 0.963 g (0.86 mmol), 87.3%. 31P{1H} NMR (121.49
1
MHz, C6D6): δ 9.5 (s). H NMR (400.13 MHz, C6D5CD3): δ −9.7
(br, 2H, OsH4), −6.0 (br, 2H, OsH4), 6.27 (t, 1H, JPH = 6.8 Hz, JSiH
=
204.0 Hz, SiH), 6.8−7.6 (m, 50H, Ph). 13C{1H} NMR (100.62 MHz,
CD2Cl2): δ 147.5 (s, Ph), 143.4 (s, Ph), 136.1−135.6 (m, Ph), 135.1
(s, Ph), 134.5−134.4 (m, Ph), 130.3 (s, Ph), 128.5 (s, Ph), 128.2−
128.1 (m, Ph), 127.5 (s, Ph), 127.2 (s, Ph). 29Si{1H} NMR (59.63
MHz, C6D6): δ 19.7 (t, JPSi = 12.2 Hz, OsSiClPh2), −16.8 ppm (t, JPSi
= 6.6 Hz, OsSiHPh2). At 400 MHz and 248 K, the hydride signals at
−5.8 and −9.6 ppm have T1 values of 359 and 366 ms, respectively.
Anal. Calcd for C60H55ClOsSi2P2: C, 64.35; H, 4.95. Found: C, 64.37;
H, 5.14.
CONCLUSION
■
In summary, we have found that complex OsH3Cl(PPh3)3 can
react with R2SiH2 to give the mono(silyl) complexes
OsH3(SiClR2)(PPh3)3 and bis(silyl) complexes OsH4(SiClR2)-
(SiHR2)(PPh3)2. Computational studies reveal that the SiClR2
group was generated through an H/Cl exchange process
involving Si−H/Os−Cl bonds via a silylene intermediate.
Unlike the bis(η2-silane) ruthenium complexes RuH2(η2-H-
SiR3)2(PR′3)2, the osmium complexes OsH4(SiClR2)(SiHR2)-
(PPh3)2 can be best described as dodecahedral tetrahydride
complexes with weak Si···H interactions, suggesting that metals
can significantly affect the structures of polyhydridosilyl
complexes. The bis(silyl) complex OsH4(SiClPh2)(SiHPh2)-
(PPh3)2 reacts with L (L = PPh3, CH3CN) to give
OsH4(SiClHPh)(SiH2Ph)(PPh3)2 (4). To a suspension of OsH3Cl-
(PPh3)3 (1; 1.0 g, 0.985 mmol) in toluene (10 mL) was added PhSiH3
(0.32 mL, 2.59 mmol). The reaction mixture was stirred for 1 h to give
a pale brown solution. The solvent was removed under vacuum, and
the residue was washed with ether (2 mL × 3) then with hexane (3 mL
× 3) to give a white solid, which was dried under vacuum. Yield: 0.586
g (0.86 mmol), 61.5%. 31P{1H} NMR (161.98 MHz, C6D6): δ 13.50
(ABq, ΔδAB = 0.13, JAB = 16.2 Hz). 1H NMR (400.13 MHz, C6D6): δ
−7.8 (br, 4H, OsH4), 5.45 (dd, 1H, JHH = 6.0 Hz, JPH = 4.0 Hz,
SiH2Ph), 5.59 (dd, 1H, JHH = 6.0 Hz, JPH = 4.2 Hz, SiH2Ph), 6.7−7.5
(m, 37H, 36H for Ph and 1H for SiHClPh), 7.79 (dd, 2H, JHH = 7.8,
1.4 Hz, Ph), 7.84 (dd, 2H, JHH = 7.8, 1.4 Hz, Ph). 13C{1H} NMR
(100.62 MHz, CD2Cl2): δ 146.6 (s, Ph), 141.9 (s, Ph), 136.0−133.7
(m, Ph), 130.4 (s, Ph), 129.0 (s, Ph), 128.5−127.9 (m, Ph). 29Si{1H}
G
DOI: 10.1021/acs.organomet.7b00512
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Article
NMR (59.63 MHz, C6D6): δ 9.2 (dd, JPSi = 12.3, 9.4 Hz, OsSiHClPh),
−44.9 ppm (dd, JPSi = 7.2, 5.6 Hz, OsSiH2Ph). The hydride signals at
−6.0 and −9.8 ppm have T1 values of 477 and 400 ms, respectively, at
400 MHz and 233 K. Anal. Calcd for C48H47ClOsSi2P2: C, 59.58; H,
4.90. Found: C, 59.52; H, 5.10.
OsH3(SiClPh2)(PPh3)2(NCCH3) (18). Method A. To a suspension
of OsH3Cl(PPh3)3 (1; 1.0 g, 0.985 mmol) in toluene (10 mL) was
added Ph2SiH2 (0.55 mL, 2.96 mmol). After the mixture was stirred
for 2 h, 6 mL of CH3CN was added, and this reaction mixture was
further stirred for 6 h to give a white solid, which was collected by
filtration, washed with hexane (5 mL × 3), and dried under vacuum.
Yield: 0.56 g (0.573 mmol), 58.2%.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00512.
■
S
Experimental procedures and spectroscopic data for all
new compounds (PDF)
Cartesian coordinates for calculated structures (XYZ)
Accession Codes
CCDC 1550734 and 1550737 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Method B. To a solution of OsH4(SiClPh2)(SiHPh2)(PPh3)2 (3;
100 mg, 0.0893 mmol) in toluene (2 mL) was added CH3CN (2 mL).
The reaction mixture was stirred for 24 h to give a white solid and a
light purple solution. The volume of the reaction mixture was reduced
to ca. 1 mL. The white solid was then collected by filtration, washed
with ether (2 mL × 3) and hexane (3 mL × 3), and dried under
vacuum. Yield: 78.0 mg (0.0799 mmol), 89.4%. 31P{1H} NMR (161.98
MHz, C6D6): δ 17.6 (s). 1H NMR (400.13 MHz, C6D6): δ −10.2 (br,
3H, OsH3), 0.59 (s, grease), 0.63 (s, 3H, CH3CN), 6.8−7.4 (m, 36H,
Ph), 8.20 (d, JHH = 7.2 Hz, 4H, Ph). 13C{1H} NMR (100.62 MHz,
CD2Cl2): δ 150.4 (s, Ph), 136.0−132.9 (m, Ph), 128.0 (s, Ph), 126.6−
126.3 (m, Ph), 125.7 (s, Ph), 119.3 (s, CH3CN), 2.7 (s, CH3CN).
29Si{1H} NMR (79.49 MHz, C6D6): δ 19.9 (t, JPSi = 6.8 Hz,
OsSiClPh2). IR: ν 2070, 1991 cm−1 (Os−H). Anal. Calcd for
C50H46ClOsNSiP2: C, 61.49; H, 4.75; N, 1.43. Found: C, 61.39; H,
4.87; N: 1.35.
Crystal Structure Analyses. Crystals of 3 and 18 suitable for X-
ray diffraction were grown from toluene solution layered with hexane
under a hydrogen atmosphere. The crystal was mounted on glass fibers
with epoxy glue. The diffraction intensity data of 3 and 18 were
collected on a Rigaku Oxford Diffraction SuperNova, Dual, Cu at zero,
Atlas diffractometer with monochromated Cu Kα radiation (λ =
1.54178 Å) at 100 K. Diffraction data were processed using the
CrysAlisPro software (version 1.171.35.19). Empirical absorption
corrections were performed using spherical harmonics, implemented
in SCALE3 ABSPACK scaling algorithm in the CrysAlisPro software
suite. Structure solution and refinement data for all compounds were
obtained using the Olex224 software package (which embedded
ShelXS25 and SHELXTL26). All of the structures were solved by direct
methods, expanded by difference Fourier syntheses, and refined by
full-matrix least squares on F2. All non-hydrogen atoms were refined
anisotropically with a riding model for the hydrogen atoms except
where noted separately. Further crystallographic details are summar-
ized in Table S1 in the Supporting Information.
AUTHOR INFORMATION
Corresponding Authors
*E-mail for J.C.: chenjx@xmu.edu.cn.
*E-mail for Z.L.: chzlin@ust.hk.
*E-mail for G.J.: chjiag@ust.hk.
■
ORCID
Wei Bai: 0000-0001-8585-9321
Jiangxi Chen: 0000-0001-6534-2552
Zhenyang Lin: 0000-0003-4104-8767
Guochen Jia: 0000-0002-4285-8756
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Hong Kong Research Grants
Council (Project Nos. 601812, 602113, CUHK7/CRF/12G-2,
16321516) and by the National Natural Science Foundation of
China (No. 21302158).
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DOI: 10.1021/acs.organomet.7b00512
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DOI: 10.1021/acs.organomet.7b00512
Organometallics XXXX, XXX, XXX−XXX