Hydrosilylation of Aldehydes and Ketones Catalyzed by a Terminal Zinc Hydride Complex, [κ3-Tptm]ZnH

Article abstract of DOI:10.1021/acs.organomet.5b00506

Tris(2-pyridylthio)methyl zinc hydride, [κ³-Tptm]ZnH, is an effective catalyst for multiple insertions of carbonyl groups into the Si-H bonds of Ph_xSiH_4-x (x = 1, 2). Specifically, [κ³-Tptm]ZnH catalyzes the insertion of a variety of aldehydes and ketones into the Si-H bonds of PhSiH₃ and Ph₂SiH₂ to afford PhSi[OCH(R)R′]₃ and Ph₂Si[OCH(R)R′]₂, respectively. The mechanism for hydrosilylation is proposed to involve insertion of the carbonyl group into the Zn-H bond to afford an alkoxy species, followed by metathesis with the silane to release the alkoxysilane and regenerate the zinc hydride catalyst. Multiple insertion of prochiral ketones results in the formation of diastereomeric mixtures of alkoxysilanes that can be identified by NMR spectroscopy.

Full text of DOI:10.1021/acs.organomet.5b00506

Article
pubs.acs.org/Organometallics
Hydrosilylation of Aldehydes and Ketones Catalyzed by a Terminal
Zinc Hydride Complex, [κ3‑Tptm]ZnH
Wesley Sattler, Serge Ruccolo, Mahnaz Rostami Chaijan, Tawfiq Nasr Allah, and Gerard Parkin*
Department of Chemistry, Columbia University, New York, New York 10027, United States
S
* Supporting Information
ABSTRACT: Tris(2-pyridylthio)methyl zinc hydride, [κ3-Tptm]ZnH, is an
effective catalyst for multiple insertions of carbonyl groups into the Si−H bonds
of PhxSiH4−x (x = 1, 2). Specifically, [κ3-Tptm]ZnH catalyzes the insertion of a
variety of aldehydes and ketones into the Si−H bonds of PhSiH3 and Ph2SiH2 to
afford PhSi[OCH(R)R′]3 and Ph2Si[OCH(R)R′]2, respectively. The mechanism
for hydrosilylation is proposed to involve insertion of the carbonyl group into the
Zn−H bond to afford an alkoxy species, followed by metathesis with the silane to
release the alkoxysilane and regenerate the zinc hydride catalyst. Multiple insertion
of prochiral ketones results in the formation of diastereomeric mixtures of
alkoxysilanes that can be identified by NMR spectroscopy.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
Catalytic hydrosilylation of carbonyl compounds to afford
alkoxysilanes is an area of interest in that it provides a method
to achieve the overall reduction to the alcohol via subsequent
hydrolysis of the alkoxysilane.1,2 Furthermore, alkoxysilanes3,4
have applications in organic synthesis5 and materials chemistry
(including stone consolidation,6 the synthesis of mesoporous
silica nanoparticles,7 and silsesquioxane derivatives8). In
addition to obtaining improved catalysts for this trans-
formation, it is important to develop effective catalysts that
are based on abundant non-precious metals.9 Zinc is one such
metal,10 and we have recently demonstrated that the tris(2-
pyridylthio)methyl zinc hydride complex, [κ3-Tptm]ZnH
(Figure 1),11 can serve as an effective catalyst for the
hydrosilylation of aldehydes, ketones, and carbon
dioxide.12−14 Here, we extend the scope of the catalytic
hydrosilylation transformations that are mediated by [κ3-
Tptm]ZnH.
We have previously reported that [κ3-Tptm]ZnH is capable of
catalyzing insertion of both acetaldehyde and acetone into all
three of the Si−H bonds of PhSiH3 to afford PhSi(OEt)3 and
PhSi(OPri)3, respectively (Scheme 1).12,15,16 Such compounds
are of interest because aryltrialkoxysilanes have applications in
cross-coupling reactions,4 but are traditionally synthesized via
the reaction of Grignard or lithium reagents with Si(OR)4.17
Scheme 1. Zinc-Catalyzed Insertion of Carbonyl
Compounds into the Si−H Bonds of PhSiH3
a
a
See Table 1 for conditions.
Special Issue: Gregory Hillhouse Issue
Received: June 15, 2015
Figure 1. [κ3-Tptm]ZnH, a mononuclear zinc hydride catalyst.
© XXXX American Chemical Society
A
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Table 1. [κ3-Tptm]ZnH-Catalyzed Insertion of Aldehydes and Ketones into the Si−H Bonds of PhSiH3
a
1
1.0 mol % catalyst based on PhSiH3; reactions performed at room temperature in C6D6, and conversions determined by H NMR spectroscopy;
b
TON = 100; product mixture contains excess PhSiH3. 3.3 mol % catalyst based on PhSiH3; reactions performed at room temperature in C6D6, and
conversions determined by H NMR spectroscopy; TON = 90. In view of the high activity, these values represent the minimum TOF.
c
1
Thus, even though metal-catalyzed insertion of aldehydes and
ketones into Si−H bonds is well established,2,18 the insertion of
carbonyl groups into three Si−H bonds had not been reported
as a general synthetic method for PhSi(OR)3 derivatives.
For example, catalysts such as [(C6H3Pri2)N]Mo-
(PMe3)3(Cl)H,19 [Tp][(C6H3Pri2)N]Mo(PMe3)H,20 [Tp]-
[(C6H3Pri2)N]Mo(PMe3)H,21 [{κ2-Ph2PC6H4)2O}Mo(NO)-
Tptm]ZnH (3.3 mol %) results in the rapid formation of
PhSi[OCH(Me)Ph]3. The effectiveness of [κ3-Tptm]ZnH as a
catalyst to achieve triple insertion of a ketone into PhSiH3 is
made evident by the fact that the TOF (77 h−1) for insertion of
acetophenone in benzene solution at room temperature is
greater than that for the manganese catalyst, (Ph PPrPDI)Mn (47
2
h−1).25b Furthermore, a heterogeneous cesium catalyst
possessed a TOF of only 1.7 h−1 at an elevated temperature
(80 °C).27
(NCMe)3][BArF ],22 [Fe{N(SiMe3)2}2],2f and Et2OFe(CAT-
4
POP)23 only efficiently insert aldehydes and ketones into two
of the Si−H bonds of PhSiH3, with insertion into all three Si−
H bonds occurring only to a small extent.24 Compounds that
catalyze the insertion of aldehydes and ketones into all three
Si−H bonds of PhSiH3 have, nevertheless, been described25,26
subsequent to our report.12,27 Thus, in view of the fact that
triple insertion of carbonyl compounds into PhSiH3 is not well
established, we have examined further the ability of [κ3-
Tptm]ZnH to catalyze such transformations.
While selective triple insertion is observed upon treatment of
PhSiH3 with 3 equiv of RC(O)R′, a mixture of single, double,
and triple insertion products, PhSiH2[OCH(R)R′], PhSiH-
[OCH(R)R′]2, and PhSi[OCH(R)R′]3, is observed upon
treatment of PhSiH3 with fewer equivalents of RC(O)R′. For
example, a 1:1 mixture of PhC(O)Me and PhSiH3 gives a
mixture that contains predominantly PhSiH[OCH(Me)Ph]2,
together with a small amount of PhSiH2[OCH(Me)Ph] (3%)
and unreacted PhSiH3 (Table 1), while a 2:1 mixture of
PhC(O)Me and PhSiH3 gives a mixture that contains
PhSi[OCH(Me)Ph]3 and PhSiH[OCH(Me)Ph]2. The obser-
vation that both 1:1 and 2:1 mixtures of PhC(O)Me and
PhSiH3 give primarily the double insertion product indicates
that, whereas incorporation of one alkoxy group significantly
promotes the insertion into the remaining Si−H bonds, the
effect is less pronounced upon incorporation of a second alkoxy
substituent.
Multiple Insertion of RC(O)R′ into PhSiH3. Illustrative
examples of aldehydes and ketones that undergo [κ3-Tptm]-
ZnH-catalyzed insertion into the Si−H bonds of PhSiH3 are
summarized in Table 1. In each case, treatment of a 1:3.3
mixture of PhSiH3 and RC(O)R′ with 3.3 mol % of catalyst
(relative to PhSiH3) results in the quantitative formation of the
triple insertion product, PhSi[OCH(R)R′]3. Aldehydes are the
most active, and the reactions proceed to completion in less
than 20 min, with turnover frequencies (TOFs) > 200 h−1 over
this period.28 Dialkyl ketones are the slowest but proceed
smoothly to completion over a period of 1 day. In contrast to
dialkyl ketones, however, the diaryl ketone Ph2CO is very
reactive, and the reaction proceeds to completion in less than
10 min at room temperature. The reactions can also be
performed in the absence of solvent. For example, addition of
PhC(O)Me (3.3 equiv) to PhSiH3 in the presence of [κ3-
A noteworthy feature of the reactions of prochiral ketones is
that the triple insertion products, PhSi[OCH(R)R′]3, display
interesting spectroscopic properties. For example, rather than
1
exhibiting in the H NMR spectrum a simple doublet that is
often associated with the methyl group of a [CH(Me)] moiety,
the methyl groups of PhSi[OCH(Me)Ph]3 are characterized by
eight signals in a ca. 1:1:1:1:1:1:1:1 ratio (Figure 2).
B
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Figure 2. 1H NMR spectra (C6D6) of methine (left) and methyl
(right) regions for enantiopure (S,S,S)-PhSi[OCH(Me)Ph]3 (top) and
the mixture of isomers of PhSi[OCH(Me)Ph]3 (bottom).
Figure 4. Stereoisomers of PhSi[OCH(Me)Ph]3 (the phenyl groups
and oxygen atoms attached to the asymmetric carbon centers are
omitted for clarity). Molecules with either RRS or SSR configurations
are statistically a factor of 3 more prevalent than those with either RRR
or SSS configurations.
Figure 3. 13C{1H} NMR spectra (C6D6) of methine (left) and methyl
(right) signals for the mixture of RRR/SSS and RSS/RRS isomers of
PhSi[OCH(Me)Ph]3.
Correspondingly, the 13C{1H} NMR spectrum of PhSi[OCH-
(Me)Ph]3 exhibits four signals for the methyl groups (Figure
3). Thus, both the 1H and 13C{1H} NMR spectra indicate that,
in solution, the methyl groups of PhSi[OCH(Me)Ph]3 are in
four equally populated unique chemical environments.
Figure 5. 29Si{1H} NMR spectrum of PhSi[OCH(Me)Ph]3 illustrating
a 3:1 ratio of diastereomers in C6D6.
Albeit unusual, the spectroscopic patterns are, nevertheless,
easily rationalized by recognizing that PhSi[OCH(Me)Ph]3
exists as two diastereomers by virtue of the fact that the
molecule contains three chiral centers. Specifically, a molecule
with three chiral centers can have a maximum of 8 (i.e., 23)
stereoisomers, which are determined by the R and S
configurations at each center; however, in view of the local
three-fold symmetry of PhSi[OCH(Me)Ph]3, the number of
isomers is reduced to four. Thus, PhSi[OCH(Me)Ph]3 consists
of two diastereomers, each of which exists as an enantiomeric
pair, i.e., RRR/SSS and RRS/SSR, as illustrated in Figure 4.
Statistically, however, the RRS/SSR set of isomers are a factor
of 3 more prevalent than the RRR/SSS isomers, evidence for
which is provided by the fact that the 29Si{1H} NMR spectrum
exhibits two signals at −59.85 and −59.92 ppm in a 3:1 ratio
(Figure 5), while the enantiopure compound shows only a
signal at −59.92 ppm. Both of these chemical shifts are
consistent with a PhSi(OR)3 species, as illustrated by the data
for PhSiH3−x(OR)x (x = 0−3) in Table 2.29
equivalent.36 On the other hand, the RRS/SSR isomers are
devoid of symmetry, with the result that the three methyl
groups are chemically inequivalent. As such, a 1:3 statistical
mixture of RRR/SSS and RRS/SSR isomers of PhSi[OCH-
(Me)Ph]3 would give rise to spectroscopic signals associated
with four equally abundant sets of methyl groups (Figure 6).
Thus, the 13C{1H} NMR spectrum exhibits four signals in a
1:1:1:1 ratio, while the 1H NMR spectrum exhibits eight signals
in a 1:1:1:1:1:1:1:1 ratio, corresponding to four doublets.
Similar patterns are also observed for the methine and phenyl
groups, although they are less easily identified due to overlap.
Evidence that the above assignment is correct is provided by
the synthesis of enantiopure (R,R,R)-PhSi[OCH(Me)Ph]3 and
(S,S,S)-PhSi[OCH(Me)Ph]3 by the [κ3-Tptm]ZnH-catalyzed
alcoholysis of PhSiH3 with (R)-(+)-1-phenylethanol and (S)-
(−)-1-phenylethanol, respectively (Scheme 2). For example,
the 1H NMR spectrum of (S,S,S)-PhSi[OCH(Me)Ph]3 exhibits
a simple doublet for the methyl groups (Figure 2), while the
13C{1H} NMR spectrum exhibits a singlet. Comparison of the
In view of the fact that the RRR/SSS isomers possess a C3
axis, the three methyl groups of these isomers are chemically
C
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Table 2. 29Si{1H} NMR Chemical Shift Data for
PhSiH3−x(OR)x
PhSiH3−x(OR)x
δ (ppm)
ref
x = 0
a
PhSiH3
−60.1
29b
x = 1
a
a
a
PhSiH2(OEt)
PhSiH2(OPri)
−28.6
−22.5
−20.4
30, 31
30, 31
30, 31
PhSiH2[OCH(Me)Ph]
Figure 6. Origin of eight signals for the methyl groups of
PhSi[OCH(Me)Ph]3 in the 1H NMR spectrum, with chemically
equivalent methyl groups coded by color. The methyl groups of the
RRR isomer are chemically equivalent, whereas the methyl groups of
the RRS isomer are chemically inequivalent; however, since the RRS
isomer is statistically a factor of 3 more prevalent than the RRR isomer,
four equally abundant methyl groups are observed. A similar argument
pertains to comparison of their enantiomers, i.e., SSS and SSR.
x = 2
a
a
PhSiH(OEt)2
−30.53
−30.8
this work
30
a
PhSiH(OPri)2
−34.58
this work
30
a
−34.8
−34.3
b
32
PhSiH[OCH(Me)Et]2
−33.24 (RsS), −33.66 (RR/SS),
this work
a
−34.18 (RrS)
a
PhSiH(OCHEt2)2
PhSiH(OCy)2
−32.55
−34.63
this work
this work
this work
Scheme 2. Synthesis of (S,S,S)-PhSi[OCH(Me)Ph]3 and
(S,S)-PhHSi[OCH(Me)Ph]2 via Alcoholysis
a
PhSiH[OCH(Me)Ph]2
−32.15 (RR/SS), −32.25 (RsS),
a
−32.41 (RrS)
a
−32.6
19, 30, 31
this work
a
PhSiH(OCHPh2)2
−30.09
x = 3
a
PhSi(OEt)3
−57.9
−60.3
−60.5
−58.2
−56.4
−55.7
−61.8
this work
32
b
c
33
b
34
a
PhSi(OCH2Ph)3
this work
35
b
a
PhSi(OPri)3
this work
this work
PhSi[OCH(Me)Et]3
−62.26 (RRR/SSS), −62.30
a
(RSS/RRS)
a
PhSi(OCHEt2)3
PhSi(OCy)3
−63.04
−61.62
this work
this work
this work
a
PhSi[OCH(Me)Ph]3
−59.85 (RRR/SSS), −59.92
a
(RSS/RRS)
ad
,
−32.7
−58.1
19, 30
a
PhSi(OCHPh2)3
this work
a
b
c
d
C6D6. CDCl3. Neat. This value is not characteristic of PhSi(OR)3
consists of a mixture of RR/SS, RrS, and RsS diastereomers
(Figure 8), each of which has a unique H NMR spectrum.
compounds and is presumably erroneous.
1
The existence of the RrS and RsS diastereomers is a
consequence of the fact that the silicon in (R,S)-PhSiH[OCH-
(Me)Ph]2 is a “pseudoasymmetric center”,41 a term that is used
to describe a stereogenic center in an achiral molecule, and is
given the notation r and s. Since the RR and SS isomers are
enantiomers, there are three sets of diastereomers, namely RR/
SS, RrS, and RsS, each of which has a unique spectral signature,
as clearly indicated by the observation of three signals in the
29Si{1H} NMR spectrum (Figure 9) and three signals
1H and 13C{1H} NMR spectra of (R,R,R)-PhSi[OCH(Me)Ph]3
and (S,S,S)-PhSi[OCH(Me)Ph]3 with the statistical mixture of
RRR/SSS and RRS/SSR isomers thus enables the spectral
assignment for the RRS/SSR diastereomers.
Interestingly, although PhSi[OCH(Me)Ph]3 has been
previously reported, the occurrence of isomers has not been
explicitly discussed. In this regard, it is pertinent to note that
1
1
the original report actually describes the H NMR spectro-
associated with the [SiH] moieties in the H NMR spectrum
scopic signals of methyl groups as a doublet at δ 1.36 ppm (J =
6 Hz) in C6D6,19,37 which is not consistent with the
interpretation described herein.38−40
(Figure 10). The distribution of RR/SS, RrS, and RsS isomers is
2:1.06:0.93,42,43 which corresponds closely to the statistical
distribution of 2:1:1.
As discussed above for PhSi[OCH(Me)Ph]3, the bis(alkoxy)
compound PhSiH[OCH(Me)Ph]2 also exists as a mixture of
diastereomers resulting from the different R and S config-
urations of the alkoxy groups, with the result that the methyl
However, while the spectral features of PhSiH[OCH(Me)-
Ph]2 associated with the [SiH] moieties provide evidence for
the three chemical environments that are consistent with the
1
presence of three diastereomers, the methyl region of the H
1
groups do not appear as a simple doublet in the H NMR
NMR spectrum exhibits signals due to four chemically
inequivalent methyl groups. The observation of four different
spectrum (Figure 7). Specifically, PhSiH[OCH(Me)Ph]2
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1
Figure 9. 29Si{1H} NMR spectrum illustrating the three RR/SS, RrS,
and RsS diastereomers of PhSiH[OCH(Me)Ph]2 (bottom), and
enantiopure (S,S)-PhSiH[OCH(Me)Ph]2 (top).
Figure 7. Methyl region of the H NMR spectrum of PhSiH[OCH-
(Me)Ph]2 illustrating four doublets associated with the three RR/SS,
RrS (“r”), and RsS (“s”) diastereomers (bottom) and two doublets
associated with (S,S)-PhSiH[OCH(Me)Ph]2 (top). Note that of the
RrS and RsS diastereomers, RrS is arbitrarily assigned to the more
abundant isomer.
1
Figure 10. Si−H region of the H NMR spectrum of PhSiH[OCH-
(Me)Ph]2 illustrating the three RR/SS, RrS, and RsS diastereomers.
with the [SiH] moiety in both the 29Si{1H} and H NMR
spectra.
1
Figure 8. Isomers of PhSiH[OCH(Me)Ph]2, with chemically
equivalent methyl groups coded by color (the phenyl groups and
oxygen atoms attached to the asymmetric carbon centers are omitted
for clarity). While the methyl groups of the RR and SS isomers are
chemically inequivalent, the methyl groups of the RrS and RsS isomers
are chemically equivalent due to the presence of a mirror plane. As
such, the methyl region of the H NMR spectrum consists of four
doublets in a ratio that reflects the relative abundance of the RR/SS,
RrS, and RsS diastereomers.
As noted above for PhSi[OCH(Me)Ph]3, the NMR data
presented for PhSiH[OCH(Me)Ph]2 in the literature are highly
varied. For example, the appearance of the methyl groups has
been described in terms of a doublet,44 three doublets,45
a
1
multiplet,25b and a “few” overlapping doublets,46 with there
being no report of which we are aware that refers to the pattern
as four doublets. The SiH region of the 1H NMR spectrum has
been described as comprising three singlets,45,46 which is
consistent with our observations, but has also been described as
a singlet.44 Finally, the 29Si{1H} NMR spectrum has been
described as a singlet,44 in contrast to the three signals that we
observe.
chemical environments for the methyl groups of three
diastereomers is a consequence of the fact that the RR and
SS enantiomers do not possess a mirror plane, thereby resulting
in diastereotopic methyl groups. In contrast, both the RrS and
RsS diastereomers exhibit chemically equivalent methyl groups
because the molecules possess a mirror plane. The methyl
Multiple Insertion of RC(O)R′ into Ph2SiH2. Ph2SiH2 is
also a commonly used reagent for the hydrosilylation of
aldehydes and ketones, although it often exhibits reduced
reactivity compared to PhSiH3.47 Therefore, it is significant that
[κ3-Tptm]ZnH is also an effective catalyst for room temper-
ature hydrosilylation reactions employing Ph2SiH2, affording
products derived from both single and double insertion
(Scheme 3 and Tables 3 and 4). The ability of [κ3-Tptm]ZnH
to achieve double insertion of ketones into Ph2SiH2 is of note
since only the monoinsertion product is typically observed.48
The reactivity of Ph2SiH2 towards insertion is, nevertheless,
lower than that of PhSiH3, as illustrated by the fact that the
zinc-catalyzed reaction of PhC(O)Me with an excess of a ca. 1:1
mixture of PhSiH3 and Ph2SiH2 results in the formation of a
1
region of the H NMR spectrum of PhSiH[OCH(Me)Ph]2
thus exhibits eight signals (i.e., four doublets) with an intensity
distribution that is consistent with the 2:1.06:0.93 diastereo-
meric composition as indicated by the SiH signals.
Support for this assignment is provided by the synthesis of
the SS isomer by the [κ3-Tptm]ZnH-catalyzed alcoholysis of
PhSiH3 with 2 equiv of (S)-(−)-1-phenylethanol (Scheme 2),
thereby demonstrating that (S,S)-PhSiH[OCH(Me)Ph]2 1 is
characterized by two doublets in the methyl region of the H
NMR spectrum. Furthermore, the synthesis of (S,S)-PhSiH-
[OCH(Me)Ph]2 allows identification of the signals associated
E
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methyl groups of the RR/SS isomers of Ph2Si[OCH(Me)Ph]2
are chemically equivalent by virtue of a C2 axis and thus give
rise to a single doublet in the 1H NMR spectrum. Likewise, the
methyl groups of the RS isomer are rendered equivalent by a
mirror plane, and therefore also give rise to a doublet. As such,
the diastereomeric mixture of Ph2Si[OCH(Me)Ph]2 exhibits
two doublets (with ratios that correspond to the relative
abundance of the RR/SS and RS diastereomers) in the methyl
Scheme 3. Zinc-Catalyzed Insertion of Carbonyl
Compounds into the Si−H Bonds of PhSiH3
a
54
1
region of the H NMR spectrum (Figure 13).
The signals attributable to (S,S)-Ph2Si[OCH(Me)Ph]2 (δ =
1.40, J = 7 Hz) have been assigned by its independent synthesis
via the zinc-catalyzed reaction between Ph2SiH2 and (S)-(−)-1-
phenylethanol (Figure 13). On the basis of this assignment, it is
evident that the RR/SS and RS diastereomers are formed in a
ratio of 1:0.62,55 which is significantly different to the statistical
ratio of 1.0:1.0. It is, therefore, evident that the diastereo-
selectivity for double insertion of a prochiral ketone into
Ph2SiH2 is greater than that for insertion into PhSiH3.
3. Mechanism of Hydrosilylation. A large variety of
mechanisms for hydrosilylation of carbonyl compounds has
been discussed in the literature.56 For example, two of the
earliest proposed mechanisms involve sequential (i) oxidative
addition of a Si−H bond, (ii) coordination of the carbonyl
compound, (iii) insertion of the carbonyl moiety into either the
M−H or M−Si bond, and (iv) Si−O or C−H bond reductive
elimination.1,57,58 A variant for silanes that have more than one
hydride involves, after oxidative addition of the Si−H bond: (i)
coordination of the carbonyl group to silicon, (ii) transfer of a
silicon hydride to carbon, and (iii) Si−H bond reductive
elimination.59 Another class of proposed mechanisms involves
the attack of a carbonyl oxygen upon a coordinated silicon
species (e.g., silylene moieties,58,60 silane adducts,56a,61−64 and
hypervalent silyl groups).65,66 Mechanisms that involve σ-bond
a
See Table 3 for conditions.
mixture of monophenylsilane derivatives, PhSiH2[OCH(Me)-
Ph] and PhSiH[OCH(Me)Ph]2, and the diphenylsilane
derivative, Ph2SiH[OCH(Me)Ph], of which the latter is a
minor component with a mole fraction of 0.19.
As observed for hydrosilylation involving PhSiH3, the double
insertion of prochiral ketones into the two Si−H bonds of
Ph2SiH2 results in the formation of diastereomeric mixtures.
Thus, Ph2Si[OCH(Me)Ph]2 exists as a mixture of RR/SS and
RS diastereomers (Figure 11), which can be distinguished by
29Si{1H} NMR spectroscopy (Figure 12).
In contrast to PhSiH[OCH(Me)Ph]2, however, in which the
methyl groups of the RR/SS isomers are diastereotopic, the
Table 3. [κ3-Tptm]ZnH-Catalyzed Insertion of Aldehydes and Ketones into the Si−H Bonds of Ph2SiH2
a
1.0 mol % catalyst based on Ph2SiH2; reactions performed at room temperature in C6D6, and conversions determined by 1H NMR spectroscopy;
b
TON = 100; product mixture contains excess Ph2SiH2. 2.2 mol % catalyst based on Ph2SiH2; reactions performed at room temperature in C6D6,
and conversions determined by H NMR spectroscopy; TON = 91. In view of the high activity, these values represent the minimum TOF.
c
1
F
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Table 4. 29Si{1H} NMR Data for Ph2SiH2−x(OR)x
Ph2SiH2−x(OR)x
δ (ppm)
ref
x = 0
a
Ph2SiH2
−33.4
49
50
−35.7
x = 1
a
a
a
Ph2SiH(OEt)
−11.98
−17.6
this work
51
b
Ph2SiH(OPri)
−14.81
this work
51
b
−20.5
Ph2SiH(OCH2Ph)
−10.27
this work
51
b
−16.1
a
a
a
Ph2SiH[OCH(Me)Et]
Ph2SiH(OCHEt2)
Ph2SiH(OCy)
−14.14
−13.38
−15.03
this work
this work
this work
51
Figure 12. 29Si{1H} NMR spectrum illustrating the RR/SS and RS
diastereomers of Ph2Si[OCH(Me)Ph]2 in C6D6 (bottom) and (S,S)-
Ph2Si[OCH(Me)Ph]2 (top).
b
−20.9
a
a
c
Ph2SiH[OCH(Me)Ph]
Ph2SiH(OCHPh2)
−12.94
−11.52
−19.30
this work
this work
52
x = 2
a
a
a
Ph2Si(OEt)2
−32.11
−32.6
this work
32
b
Ph2Si(OCH2Ph)2
−30.02
this work
53
b
−30.0
Ph2Si(OPri)2
−35.53
this work
this work
this work
this work
this work
this work
27
a
Ph2Si[OCH(Me)Et]2
Ph2Si(OCHEt2)2
Ph2Si(OCy)2
−35.65, −35.69
a
−35.55
−35.65
a
a
b
Ph2Si[OCH(Me)Ph]2
−33.30, −33.23
−33.91, −33.97
−39.45, −33.77
bd
,
a
Ph2Si(OCHPh2)2
−30.71
this work
a
b
c
d
C6D6. CDCl3. CD2Cl2. The reported value of −39.45 is very
different from the value that we observe in the same solvent.
1
Figure 13. Methyl region of the H NMR spectrum of Ph2Si[OCH-
(Me)Ph]2 illustrating two doublets associated with the RR/SS and RS
diastereomers (bottom), and enantiopure (S,S)-Ph2Si[OCH(Me)Ph]2
(top).
hydride complex, [M]−H, that undergoes insertion of the
carbonyl compound to generate an alkoxide species, [M]−
OC(H)(R)R′, which undergoes metathesis with a silane to
release the alkoxysilane and thereby regenerate the hydride
catalyst, [M]−H.
In view of the presence of the hydride ligand, a reasonable
mechanism for the [κ3-Tptm]ZnH-catalyzed hydrosilylation of
carbonyl compounds is illustrated in Scheme 4, and consists of
two principal steps, namely (i) insertion of the carbonyl group
into the Zn−H bond of [κ3-Tptm]ZnH to form an alkoxide,
[Tptm]ZnOCH(R)R′, and (ii) metathesis of the Zn−O and
H−Si bonds to regenerate [κ3-Tptm]ZnH and release the
alkoxysilane, PhSiH2[OCH(R)R′].70 Additional cycles allow for
the subsequent formation of the double and triple insertion
products, PhSiH[OCH(R)R′]2 and PhSi[OCH(R)R′]3. A
similar mechanism would also apply for the insertion of the
carbonyl group into the Si−H bonds of Ph2SiH2. Precedent for
these steps is provided by the observations that (i) CO2 inserts
into the Zn−H bond of [κ3-Tptm]ZnH,11,71 and (ii) silanes are
capable of reacting with the Zn−O bonds of [Tptm]ZnOR and
[Tptm]ZnO2CH to form [κ3-Tptm]ZnH.11,12
Figure 11. Isomers of Ph2Si[OCH(Me)Ph]2, with chemically
equivalent methyl groups coded by color (the phenyl groups and
oxygen atoms attached to the asymmetric carbon centers are omitted
for clarity). The methyl groups of the RR and SS isomers are
chemically equivalent due to the presence of a C2 axis, while the
methyl groups of the RS isomer are chemically equivalent due to the
presence of a mirror plane. As such, the 1H NMR spectrum consists of
two doublets in a ratio that reflects the relative abundance of the RR/
SS and RS diastereomers.
metathesis processes have been proposed for both early67 and
late68,69 transition metals, and also main group metals.70 The
active catalytic species for such mechanisms is a terminal
G
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It is also worth discussing the observation that the ratio of
the RRR/SSS and RRS/SSR diastereomers of PhSi[OCH(Me)-
Ph]3 is close to statistical (i.e., 1:3), as is the ratio of the RR/SS,
RrS, and RsS diastereomers of PhSiH[OCH(Me)Ph]2 (i.e.,
2:1:1), whereas the RR/SS and RS diastereomers of Ph2Si-
[OCH(Me)Ph]2 are formed in a 1:0.62 ratio that is distinctly
different than the statistical value (i.e., 1:1).
Scheme 4. Possible Mechanism for the Zinc-Catalyzed
Insertion of a Carbonyl Group into Si−H Bonds, As
Illustrated for PhSiH3
In order to examine whether it is feasible for isomer
interconversion to occur under the reaction conditions, we
investigated the possibility that a mixture of (R,R,R)-PhSi-
[OCH(Me)Ph]3 and (S,S,S)-PhSi[OCH(Me)Ph]3 enantiomers
could convert to the RRS and RSS diastereomers. Significantly,
1H NMR spectroscopy demonstrated that isomer interconver-
sion did not occur at room temperature (or at 100 °C), either
in the presence or absence of the zinc catalyst, [κ3-Tptm]ZnH.
Thus, it is evident that the approximately statistical distribution
of RRR/SSS and RRS/SSR diastereomers of PhSi[OCH(Me)-
Ph]3 represents a kinetic distribution, although this distribution
may also be coincidentally the same as the thermodynamic
distribution.
With respect to the formation of Ph2Si[OCH(Me)Ph]2, we
note that monitoring of the zinc-catalyzed reaction between
Ph2SiH2 and PhC(O)Me as a function of the extent reaction
indicates that the ratio of RR/SS and RS diastereomers is
constant throughout the reaction. Since the ratio is constant,
the observation indicates that the distribution either reflects the
kinetic selectivity or the thermodynamic selectivity if isomer
interconversion is facile. On the basis that the RRR and SSS
isomers of PhSi[OCH(Me)Ph]3 do not redistribute readily
(vide supra), it is most likely that the 1:0.62 ratio of RR/SS and
RS diastereomers of Ph2Si[OCH(Me)Ph]2 corresponds to a
kinetic selectivity. We have also observed that a different
diastereomeric ratio (1:0.87) is obtained employing a cesium
catalyst,18 and that the 1:0.62 ratio does not change upon
heating at 100 °C, an observation which indicates that isomer
interconversion is not facile under these conditions.
However, while compounds that contain a terminal hydride
ligand are potential candidates for a catalytic cycle involving σ-
bond metathesis pathways, it must be noted that the hydride
ligand need not be directly involved in the mechanism; rather,
it is possible that the hydride remains on the metal center
during the course of the transformation and serves a role as a
spectator ligand.21,72−74 Several pieces of evidence, however,
indicate that the hydride ligand of [κ3-Tptm]ZnH plays a
critical role in the mechanism.
1
As an illustration, H NMR spectroscopy demonstrates that
insertion of the carbonyl group into the Zn−H bond of [κ3-
Tptm]ZnH to form an alkoxide, [Tptm]ZnOCH(R)R′, is
facile, and that subsequent treatment with PhSiH3 regenerates
[κ3-Tptm]ZnH and liberates an alkoxysilane. For example,
treatment of [κ3-Tptm]ZnH with Ph2CO generates [Tptm]-
ZnOCHPh2, of which the alkoxy group is identified by a singlet
at δ 6.28 in the 1H NMR spectrum. The corresponding reaction
of [κ3-Tptm]ZnD results in the formation of the isotopologue,
1
[Tptm]ZnOCDPh2, as indicated by H NMR spectroscopy.
Furthermore, the deuterium incorporation into the alkoxide
ligand is maintained upon release of the alkoxysilane when
treated with PhSiH3. Likewise, treatment of [κ3-Tptm]ZnH
with PhC(O)Me generates [Tptm]ZnOCH(Me)Ph,75 of which
the alkoxy group is identified by a quartet at δ 5.41 and a
doublet at δ 1.59 in the 1H NMR spectrum. The corresponding
reaction of [κ3-Tptm]ZnD results in the formation of the
isotopologue, [Tptm]ZnOCD(Me)Ph, and deuterium incor-
poration into the alkoxide ligand is maintained upon release of
the alkoxysilane when treated with PhSiH3.
In addition to probing for isomer interconversion, we have
also examined the possibility of alkoxide exchange between
different pairs of molecules, namely (i) PhSi(OPri)3 and
(S,S,S)-PhSi[OCH(Me)Ph]3, and (ii) Ph2Si(OPri)2 and (S,S)-
Ph2Si[OCH(Me)Ph]2. Significantly, no scrambling of alkoxide
ligands is observed under the reaction conditions, or upon
heating,77 which also supports the above observation that
isomer interconversion does not occur readily.
[κ3-Tptm]ZnH also reacts with PhCHO to generate
[Tptm]ZnOCH2Ph, and the corresponding reaction of [κ3-
Tptm]ZnD generates [Tptm]ZnOCD(H)Ph, but does not
result in deuterium incorporation into excess PhCHO. This
observation demonstrates that insertion of the carbonyl
compound into the Zn−H bond is irreversible on the time
scale of the experiments.
With respect to the final step, i.e., cleavage of the Zn−OR
bond by the silane to regenerate [κ3-Tptm]ZnH, recent
theoretical calculations have demonstrated that this reaction
is facile and that the transformation involves a 4-centered
transition state in which the silicon has an approximately
trigonal bipyramidal geometry.76 Thus, the data are consistent
with a general mechanism for hydrosilylation of aldehydes and
ketones that involves carbonyl insertion into the Zn−H bond
to form a alkoxide species, [Tptm]ZnOCH(R)R′, followed by
metathesis with either PhSiH3 or Ph2SiH2 to liberate the
alkoxysilane and regenerate the zinc hydride catalyst.
CONCLUSIONS
■
In summary, the zinc hydride complex, [κ3-Tptm]ZnH, is an
effective catalyst for the multiple insertion of carbonyl
compounds into the Si−H bonds of PhSiH3 and Ph2SiH2, via
a mechanism that is proposed to involve insertion of the
carbonyl group into the Zn−H bond to afford an alkoxy
species, followed by metathesis with the silane to release the
alkoxysilane and regenerate the zinc hydride catalyst. Multiple
insertion of prochiral ketones results in the formation of
diastereomeric mixtures of alkoxysilanes that can be identified
by NMR spectroscopy. Since the alkoxysilanes can also be
obtained via the zinc-catalyzed dehydrocoupling of alcohols
with silanes, the reactions with (R)-(+)-1-phenylethanol and
(S)-(−)-1-phenylethanol provide a means of identifying the
diastereomers that result from the hydrosilylation of
acetophenone.
H
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Article
which demonstrated the formation of a mixture of monophenyl
derivatives, PhSiH2[OCH(Me)Ph] and PhSiH[OCH(Me)Ph]2, and
the diphenyl derivative, Ph2SiH[OCH(Me)Ph], of which the latter is a
minor component, with a mole fraction of 0.19.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed using
a combination of glovebox, high-vacuum, and Schlenk techniques
under an argon atmosphere unless otherwise specified.78 Solvents were
purified and degassed by using standard procedures. H NMR spectra
were measured on Bruker 300 DRX, Bruker 300 DPX, Bruker 400
Spectroscopic Evidence for an Alkoxide Intermediate,
[Tptm]ZnOCH(R)R′. (i) A suspension of [κ3-Tptm]ZnH (5 mg,
0.012 mmol) in C7D8 (0.7 mL) in an NMR tube equipped with a J.
Young valve was treated with PhC(O)Me and monitored by 1H NMR
spectroscopy, thereby demonstrating the immediate formation of an
alkoxide compound, [Tptm]Zn[OCH(Me)Ph], as indicated by the
observation of a quartet signal at δ 5.41 assignable to [Tptm]Zn-
[OCH(Me)Ph] and a doublet at δ 1.59 assignable to [Tptm]Zn-
[OCH(Me)Ph]. Addition of an excess of PhSiH3 to the intermediate
results in the formation of a mixture of alkoxysilanes and [κ3-
Tptm]ZnH.
(ii) A suspension of [Tptm]ZnD (5 mg, 0.012 mmol) in C6D6 (0.7
mL) in an NMR tube equipped with a J. Young valve was treated with
PhC(O)Me and monitored by 1H NMR spectroscopy, thereby
demonstrating the immediate formation of an alkoxide compound,
[Tptm]Zn[OCD(Me)Ph], as indicated by the observation of a singlet
signal at δ 1.65 assignable to [Tptm]Zn[OCD(Me)Ph]. Addition of
an excess of PhSiH3 to the intermediate results in the formation of a
mixture of deuterated alkoxysilanes and [κ3-Tptm]ZnH.
1
Avance III, Bruker 400 Cyber-enabled Avance III, and Bruker 500
1
DMX spectrometers. H chemical shifts are reported in ppm relative
to internal SiMe4 (δ = 0). 13C NMR spectra are reported in ppm
relative to internal SiMe4 (δ = 0). 29Si chemical shifts are reported in
ppm and were referenced internally with respect to SiMe4 (δ = 0).
Coupling constants are given in hertz. [κ3-Tptm]ZnH was prepared by
the literature method,11 PhSiH3, PhCHO, PhC(O)Me, Ph2CO,
Me2CO, MeC(O)H, MeC(O)Et, Et2CO, cyclohexanone, 1-phenyl-
ethanol, (R)-(+)-1-phenylethanol, and (S)-(+)-2-butanol were ob-
tained from Sigma-Aldrich, Ph2SiH2 was obtained from Alfa Aesar, and
(S)-(−)-1-phenylethanol was obtained from Fluka. PhCHO was
distilled prior to use.
General Procedure for Catalytic Comparisons of Hydro-
silylation Reactions. 1:1 PhSiH3:RC(O)R′. A solution of PhSiH3 (79
mg, 0.73 mmol) and RC(O)R′ (0.73 mmol) in C6D6 (0.7 mL) was
treated with [κ3-Tptm]ZnH (3 mg, 0.0073 mmol) in an NMR tube
equipped with a J. Young valve. The catalytic reactions were
monitored by 1H NMR spectroscopy and the products were identified
by a combination of 1H, 13C, and 29Si NMR spectroscopy (see below).
1:3.3 PhSiH3:RC(O)R′. A solution of PhSiH3 (24 mg, 0.22 mmol)
and RC(O)R′ (0.73 mmol) in C6D6 (0.7 mL) was treated with [κ3-
Tptm]ZnH (3 mg, 0.0073 mmol) in an NMR tube equipped with a J.
(iii) A suspension of [κ3-Tptm]ZnH (5 mg, 0.012 mmol) in C6D6
(0.7 mL) in an NMR tube equipped with a J. Young valve was treated
with Ph2CO and monitored by 1H NMR spectroscopy, thereby
demonstrating the immediate formation of an alkoxide compound,
[Tptm]Zn[OCHPh2], as indicated by the observation of a singlet at δ
6.28 assignable to [Tptm]Zn[OCHPh2]. Addition of an excess of
PhSiH3 to the intermediate results in the formation of a mixture of
alkoxysilanes and [κ3-Tptm]ZnH.
(iv) A suspension of [Tptm]ZnD (5 mg, 0.012 mmol) in C6D6 (0.7
mL) in an NMR tube equipped with a J. Young valve was treated with
Ph2CO and monitored by 1H NMR spectroscopy, thereby
demonstrating the immediate formation of an alkoxide compound,
[Tptm]Zn[OCDPh2], with the site of deuterium incorporation being
demonstrated by the absence of a signal at δ 6.28. Addition of an
excess of PhSiH3 to the intermediate results in the formation of a
mixture of deuterated alkoxysilanes and [κ3-Tptm]ZnH.
1
Young valve. The catalytic reactions were monitored by H NMR
spectroscopy, and the products were identified by H, 13C, and 29Si
1
NMR spectroscopy (see below).
1:1 Ph2SiH2:RC(O)R′. A solution of Ph2SiH2 (134 mg, 0.73 mmol)
and RC(O)R′ (0.73 mmol) in C6D6 (0.7 mL) was treated with [κ3-
Tptm]ZnH (3 mg, 0.0073 mmol) in an NMR tube equipped with a J.
1
Young valve. The catalytic reactions were monitored by H NMR
spectroscopy, and the products were identified by a combination of
1H, 13C, and 29Si NMR spectroscopy (see below).
1:2.2 Ph2SiH2:RC(O)R′. A solution of Ph2SiH2 (61 mg, 0.33 mmol)
and RC(O)R′ (0.73 mmol) in C6D6 (0.7 mL) was treated with [κ3-
Tptm]ZnH (3 mg, 0.0073 mmol) in an NMR tube equipped with a J.
(v) A suspension of [κ3-Tptm]ZnH (5 mg, 0.012 mmol) in C6D6
(0.7 mL) in an NMR tube equipped with a J. Young valve was treated
with PhCHO and monitored by 1H NMR spectroscopy, thereby
demonstrating the immediate formation of an alkoxide compound,
[Tptm]Zn[OCH2Ph], as indicated by the observation of a singlet at δ
5.39 assignable to [Tptm]Zn[OCH2Ph]. Addition of an excess of
PhSiH3 to the intermediate resulted in the formation of a mixture of
alkoxysilanes and [κ3-Tptm]ZnH.
1
Young valve. The catalytic reactions were monitored by H NMR
spectroscopy, and the products were identified by a combination of
1H, 13C, and 29Si NMR spectroscopy (see below).
Synthesis of PhSi(OPri)3. A suspension of [κ3-Tptm]ZnH (6 mg,
0.015 mmol) in C6D6 (ca. 1.5 mL) in an NMR tube equipped with a J.
Young valve was treated with PhSiH3 (48 mg, 0.44 mmol). Acetone
(85 mg, 1.46 mmol) was added, and the solution was allowed to stand
at room temperature for a period of ca. 12 h. After this period, the
volatile components were removed in vacuo, and the oily residue was
dissolved in benzene (ca. 1 mL). The solution was passed through a
short plug of silica, and the volatile components were removed in
vacuo to yield PhSi(OPri)3 as a colorless oil (78 mg, 57% yield).
Catalytic Hydrosilylation of PhC(O)Me by PhSiH3 in the
Absence of a Solvent. A suspension of [κ3-Tptm]ZnH (6 mg, 0.015
mmol) in PhSiH3 (48 mg, 0.44 mmol) was treated with PhC(O)Me
(175 mg, 1.5 mmol) in a vial. The mixture was shaken, and an
exothermic reaction ensued. An aliquot was removed after 2 min and
analyzed by 1H NMR spectroscopy, thereby showing complete
conversion of PhSiH3 to a 0.53:1 mixture of PhSiH[OCH(Me)Ph]2
and PhSi[OCH(Me)Ph]3 (TON = 78, TOF = 2310 h−1). Another
aliquot was removed after 1 h and analyzed by 1H NMR spectroscopy,
thereby demonstrating that the mixture had converted completely to
PhSi[OCH(Me)Ph]3 (TON = 88, TOF = 88 h−1).
(vi) A suspension of [κ3-Tptm]ZnD (5 mg, 0.012 mmol) in C6D6
(0.7 mL) in an NMR tube equipped with a J. Young valve was treated
with PhCHO and monitored by 1H NMR spectroscopy, thereby
demonstrating the immediate formation of an alkoxide compound,
[Tptm]Zn[OCH(D)Ph], with the site of deuterium incorporation
being demonstrated by reduction in the intensity of the signal at δ 5.39
(there is no observable incorporation of deuterium into the aldehyde
site on the basis of integration). Addition of an excess of PhSiH3 to the
intermediate resulted in the formation of a mixture of deuterated
alkoxysilanes and [κ3-Tptm]ZnH.
[κ3-Tptm]ZnH-Catalyzed Alcoholysis of PhSiH3 with 1-
Phenylethanol To Give PhSi[OCH(Me)Ph]3. Racemic 1-Phenyl-
ethanol. A suspension of [κ3-Tptm]ZnH (8 mg, 0.02 mmol) in C6D6
(ca. 0.7 mL) in an NMR tube equipped with a J. Young valve was
treated with PhSiH3 (88 mg, 0.81 mmol). 1-Phenylethanol (393 μL,
3.26 mmol) was added, thereby resulting in evolution of H2 over a
period of ca. 2.5 h. The sample was analyzed by 1H NMR
spectroscopy, thereby demonstrating the conversion to PhSi[OCH-
(Me)Ph]3 as a statistical mixture of RRR/SSS and RRS/RSS
diastereomers. Mass spectrum: m/z = 467.3 {M−1}+.
Comparison of Hydrosilylation by PhSiH3 and Ph2SiH2. A
solution (0.3 mL) of a ca. 1:1 mixture of PhSiH3 (0.15 M) and
Ph2SiH2 (0.15 M) in C6D6 was diluted with C6D6 (0.7 mL) in an
NMR tube equipped with a J. Young valve and was treated sequentially
with [κ3-Tptm]ZnH (3 mg, 0.0073 mmol) and PhC(O)Me (0.8 μL,
0.0066 mmol). The sample was monitored by 1H NMR spectroscopy,
(S)-(−)-1-Phenylethanol. A suspension of [κ3-Tptm]ZnH (3 mg,
0.0073 mmol) in C6D6 (ca. 0.7 mL) in an NMR tube equipped with a
J. Young valve was treated with PhSiH3 (24 mg, 0.22 mmol). (S)-
I
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(−)-1-Phenylethanol (89 mg, 0.73 mmol) was added, thereby
resulting in evolution of H2 over a period of ca. 2 h. The sample
(iv) A mixture of (S,S,S)-PhSi[OCH(Me)Ph]3 (ca. 10 mg),
PhSi(OPri)3 (ca. 10 mg), and [κ3-Tptm]ZnH (3 mg, 0.0073 mmol)
in C6D6 (0.7 mL) in an NMR tube equipped with a J. Young valve was
allowed to stand at room temperature for 12 h and was then heated at
100 °C. The sample was monitored by 1H NMR spectroscopy, thereby
demonstrating the absence of scrambling.
1
was analyzed by H NMR spectroscopy, thereby demonstrating the
1
conversion to (S,S,S)-PhSi[OCH(Me)Ph]3. H NMR (C6D6): δ 1.44
[d, J = 6 Hz, 9H, PhSi[OCH(CH3)Ph]3], 5.13 [q, J = 6 Hz, 3H,
PhSi([OCH(CH3)Ph]3], 7.04−7.24 [m, 18H, PhSi[OCH(CH3)Ph]3],
7.82−7.84 [m, 2H, PhSi[OCH(CH3)Ph]3]. 13C{1H} NMR (C6D6): δ
26.93 [s, 3C, PhSi[OCH(CH3)Ph)]3], 71.62 [s, 3C, PhSi[OCH-
(CH3)Ph]3], 125.66 [s, 6C, PhSi[OCH(CH3)Ph]3], 127.17 [s, 3C,
PhSi[OCH(CH3)Ph]3], 128.06 [s, 2C, PhSi[OCH(CH3)Ph]3],
128.39 [s, 6C, PhSi[OCH(CH3)Ph]3], 130.56 [s, 1C, PhSi[OCH-
(CH3)Ph]3], 132.24 [s, 1C, PhSi[OCH(CH3)Ph]3], 135.36 [s, 2C,
PhSi[OCH(CH3)Ph]3], 146.09 [s, 3C, PhSi[OCH(CH3)Ph]3]. 29Si-
{1H} NMR (C6D6): δ −60.01 (SSS).
(v) A mixture of Ph2Si(OPri)2 (ca. 10 mg) and (S,S)-Ph2Si[OCH-
(Me)Ph]2 (ca. 10 mg) in C6D6 (0.7 mL) in an NMR tube equipped
with a J. Young valve was allowed to stand at room temperature for 12
1
h and was then heated at 100 °C. The sample was monitored by H
NMR spectroscopy, thereby demonstrating the absence of scrambling.
(vi) A mixture of Ph2Si(OPri)2 (ca. 10 mg), (S,S)-Ph2Si[OCH-
(Me)Ph]2 (ca. 10 mg), and [κ3-Tptm]ZnH (3 mg) in C6D6 (0.7 mL)
in an NMR tube equipped with a J. Young valve was allowed to stand
at room temperature for 12 h and was then heated at 100 °C. The
sample was monitored by 1H NMR spectroscopy, thereby
demonstrating the absence of scrambling.
NMR Spectroscopic Data for PhSiH3−x[OCH(R)R′]x and
Ph2SiH2−x[OCH(R)R′]x. The alkoxysilanes PhSi(OCH2Ph)3,35 PhSiH-
(OCH2Ph)2,79 PhSi[OCH(Me)Ph]3,19,25b,79 PhSiH[OCH(Me)-
Ph]2,19,25b PhSi(OCHPh2)3,19 PhSiH(OCHPh2)2,19 PhSi-
H2(OCHPh2),80 PhSi(OEt)3,25b,32 PhSiH(OEt)2,25b,30 PhSi-
H2(OEt),30 PhSi(OPri2)3,19 PhSiH(OPri2)2,25b,30,32 PhSiH2(OPri2),30
PhSi[OCH(Me)Et]3,81 PhSiH2[OCH(Me)Et],82 PhSi(OCy)3,83
PhSiH(OCy)2,83 PhSiH2(OCy),83 Ph2Si(OCH2Ph)2,15b Ph2SiH-
(OCH2Ph),2f,51 Ph2Si[OCH(Me)Ph]2,18,27 Ph2SiH[OCH(Me)Ph],2f
Ph2Si(OCHPh2)2,18 Ph2SiH(OCHPh2),18 Ph2Si(OEt)2,32,84−86
Ph2SiH(OEt),51,87 Ph2Si(OPri)2,15b Ph2SiH(OPri2),15b,51 Ph2SiH-
[OCH(Me)Et],88 Ph2SiH(OCHEt2),2f Ph2Si(OCy)2,18 and Ph2SiH-
(OCy)2f,18,51 have been previously described, and NMR spectra for
these compounds have been listed for a variety of solvents. Additional
data obtained here for solutions in C6D6 are provided below.
PhSi[OCH(Me)Ph]3. PhSi[OCH(Me)Ph]3 exists as a statistical
mixture of RRR/SSS and RRS/RSS diastereomers. 1H NMR
(CDCl3): (a) RRR/SSS: δ 1.42 [d, J = 6 Hz, 9H, PhSi[OCH(CH3)-
Ph]3], 4.99 [q, J = 6 Hz, 3H, PhSi[OCH(CH3)Ph]3, overlapping with
RRS/RSS], 7.16−7.39 [m, 18H, PhSi[OCH(CH3)Ph]3, overlapping
with RRS/RSS], 7.57−7.60 [m, 2H, PhSi[OCH(CH3)Ph]3, over-
lapping with RRS/RSS]. (b) RRS/RSS: δ 1.30 [d, J = 6 Hz, 3H,
PhSi[OCH(CH3)Ph]3], 1.32 [d, J = 6 Hz, 3H, PhSi[OCH(CH3)-
Ph]3], 1.39 [d, J = 6 Hz, 3H, PhSi[OCH(CH3)Ph]3], 4.95−5.08 [m,
3H, PhSi(OCH(CH3)Ph)3, overlapping with RRR/SSS], 7.16−7.39
[m, 18H, PhSi[OCH(CH3)Ph]3, overlapping with RRR/SSS], 7.53−
7.56 [m, 2H, PhSi[OCH(CH3)Ph]3]. 1H NMR (C6D6): (a) RRR/SSS:
δ 1.45 [d, J = 6 Hz, 9H, PhSi[OCH(CH3)Ph]3], 5.12 [q, J = 6 Hz, 3H,
PhSi[OCH(CH3)Ph]3, overlapping with RRS/RSS], 7.04−7.32 [m,
18H, PhSi(OCH(CH3)Ph)3, overlapping with RRS/RSS], 7.82−7.85
[m, 2H, PhSi(OCH(CH3)Ph)3]. (b) RRS/RSS: δ 1.35 [d, J = 6 Hz,
3H, PhSi[OCH(CH3)Ph]3], 1.37 [d, J = 6 Hz, 3H, PhSi[OCH-
(CH3)Ph]3], 1.44 [d, J = 6 Hz, 3H, PhSi[OCH(CH3)Ph]3], 5.10−5.21
[m, 3H, PhSi[OCH(CH3)Ph]3, overlapping with RRR/SSS], 7.05−
7.30 [m, 18H, PhSi(OCH(CH3)Ph)3, overlapping with RRR/SSS],
7.78−7.81 [m, 2H, PhSi[OCH(CH3)Ph]3]. 13C{1H} NMR (CDCl3):
(a) RRR/SSS: δ 26.76 [s, 3C, PhSi[OCH(CH3)Ph]3], 71.28 [s, 3C,
PhSi[OCH(CH3)Ph]3, overlapping with RRS/RSS], 125.54 [s, 6C,
PhSi[OCH(CH3)Ph]3], 127.04 [s, 3C, PhSi[OCH(CH3)Ph]3],
127.78 [s, 2C, PhSi[OCH(CH3)Ph]3], 128.23 [s, 6C, PhSi[OCH-
(CH3)Ph]3], 130.33 [s, 1C, PhSi[OCH(CH3)Ph]3], 131.72 [s, 1C,
PhSi[OCH(CH3)Ph]3], 135.08 [s, 2C, PhSi[OCH(CH3)Ph]3, over-
lapping with RRS/RSS], 145.80 [s, 3C, PhSi[OCH(CH3)Ph]3]. (b)
RRS/RSS: δ 26.60 [s, 1C, PhSi[OCH(CH3)Ph]3], 26.62 [s, 1C,
PhSi[OCH(CH3)Ph]3], 26.72 [s, 1C, PhSi[OCH(CH3)Ph]3], 71.25
[s, 2C, PhSi[OCH(CH3)Ph]3], 71.28 [s, 1C, PhSi[OCH(CH3)Ph]3,
overlapping with RRR/SSS], 125.47 [s, 6C, PhSi[OCH(CH3)Ph]3],
126.96 [s, 3C, PhSi[OCH(CH3)Ph]3], 127.80 [s, 2C, PhSi[OCH-
(CH3)Ph]3], 128.18 [s, 6C, PhSi[OCH(CH3)Ph]3], 131.56 [s, 1C,
PhSi[OCH(CH3)Ph]3], 135.08 [s, 2C, PhSi[OCH(CH3)Ph]3, over-
lapping with RRR/SSS], 145.84 [s, 1C, PhSi[OCH(CH3)Ph]3], 145.90
[s, 1C, PhSi[OCH(CH3)Ph]3], 145.93 [s, 1C, PhSi[OCH(CH3)Ph]3].
13C{1H} NMR (C6D6): (a) RRR/SSS: δ 26.95 [s, 3C, PhSi[OCH-
(R)-(+)-1-Phenylethanol. A suspension of [κ3-Tptm]ZnH (8 mg,
0.02 mmol, 0.8 mol %) in C6D6 (ca. 0.7 mL) in an NMR tube
equipped with a J. Young valve was treated with PhSiH3 (88 mg, 0.81
mmol). (R)-(+)-1-Phenylethanol (393 μL, 3.26 mmol) was added,
thereby resulting in evolution of H2 over a period of ca. 2.5 h. The
sample was analyzed by 1H NMR spectroscopy, thereby demonstrating
the conversion to (R,R,R)-PhSi[OCH(Me)Ph]3. The volatile
components were removed in vacuo, and the colorless oil obtained
was redissolved in CH2Cl2 (ca. 1 mL) and purified by flash column
chromatography (silica gel, ca. 3 mL) to give (R,R,R)-PhSi[OCH-
(Me)Ph]3 as a colorless oil after removal of the solvent in vacuo.
[κ3-Tptm]ZnH-Catalyzed Alcoholysis of PhSiH3 with (S)-
(−)-1-Phenylethanol To Give (S,S)-PhSiH[OCH(Me)Ph]2. A
suspension of [κ3-Tptm]ZnH (3 mg, 0.0073 mmol) in C6D6 (0.7
mL) in an NMR tube equipped with a J. Young valve was treated with
PhSiH3 (24 mg, 0.22 mmol). (S)-(−)-1-Phenylethanol (52 μL, 0.43
mmol) was added, thereby resulting in evolution of H2 over a period of
ca. 20 min. The sample was analyzed by 1H NMR spectroscopy,
thereby demonstrating the conversion to (S,S)-PhSiH[OCH(Me)-
1
Ph]2. H NMR (C6D6, selected resonances): δ 1.38[d, J = 6 Hz, 3H,
PhSiH[OCH(Me)Ph]2], 143 [d, J = 6 Hz, 3H, PhSiH[OCH(Me)-
Ph]2], 4.991 [q, J = 6 Hz, 1H, PhSiH[OCH(Me)Ph]2, 4.987 [q, J = 6
Hz, 1H, PhSiH[OCH(Me)Ph]2, 5.29 [s, 1H, PhSiH[OCH(Me)Ph]2.
13C{1H} NMR: δ 26.68 [s, 1C, PhSiH[OCH(Me)Ph]2], 26.74 [s, 1C,
PhSiH[OCH(Me)Ph]2], 72.32 [s, 1C, PhSiH[OCH(Me)Ph]2], 72.36
[s, 1C, PhSiH[OCH(Me)Ph]2]. 29Si{1H} NMR (C6D6): δ −32.13.
[κ3-Tptm]ZnH-Catalyzed Alcoholysis of Ph2SiH2 with (S)-
(−)-1-Phenylethanol To Give (S,S)-Ph2Si[OCH(Me)Ph]2. A
suspension of [κ3-Tptm]ZnH (7 mg, 0.017 mmol, 2.5 mol %) in
C6D6 (ca. 0.7 mL) in an NMR tube equipped with a J. Young valve
was treated with Ph2SiH2 (61 mg, 0.33 mmol) and (S)-(−)-1-
1
phenylethanol (89 mg, 0.73 mmol). The sample was analyzed by H
NMR spectroscopy, thereby demonstrating the conversion to (S,S)-
1
PhSiH[OCH(Me)Ph]2 over a period of 45 min. H NMR (C6D6,
selected resonances): δ 1.39 [d, J = 6 Hz, 6H, Ph2Si[OCH(Me)Ph]2,
5.05 [q, J = 6 Hz, 2H, Ph2Si[OCH(Me)Ph]2. 13C{1H} NMR (C6D6,
selected resonance): δ 27.08 [s, 2C, Ph2Si[OCH(Me)Ph]2], 71.61 [s,
2C, Ph2Si[OCH(Me)Ph]2]. 29Si{1H} NMR (C6D6): δ −33.23.
Investigation of Potential Scrambling in PhSi(OR)3 and
Ph2Si(OR)2. (i) A mixture of (S,S,S)-PhSi[OCH(Me)Ph]3 (ca. 10 mg)
and (R,R,R)-PhSi[OCH(Me)Ph]3 (ca. 10 mg) in C6D6 (0.7 mL) in an
NMR tube equipped with a J. Young valve was allowed to stand at
room temperature for 12 h and was then heated at 100 °C. The sample
1
was monitored by H NMR spectroscopy, thereby demonstrating the
absence of scrambling.
(ii) A mixture of (S,S,S)-PhSi[OCH(Me)Ph]3 (ca. 10 mg), (R,R,R)-
PhSi[OCH(Me)Ph]3 (ca. 10 mg), and [κ3-Tptm]ZnH (3 mg, 0.0073
mmol) in C6D6 (0.7 mL) in an NMR tube equipped with a J. Young
valve was allowed to stand at room temperature for 12 h and was then
heated at 100 °C. The sample was monitored by 1H NMR
spectroscopy, thereby demonstrating the absence of scrambling.
(iii) A mixture of (S,S,S)-PhSi[OCH(Me)Ph]3 (ca. 10 mg) and
PhSi(OPri)3 (ca. 10 mg) in C6D6 (0.7 mL) in an NMR tube equipped
with a J. Young valve was allowed to stand at room temperature for 12
h and then heated at 100 °C. The sample was monitored by 1H NMR
spectroscopy, thereby demonstrating the absence of scrambling.
J
DOI: 10.1021/acs.organomet.5b00506
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(CH3)Ph]3], 71.58 [s, 3C, PhSi[OCH(CH3)Ph]3, overlapping with
RRS/RSS], 125.65 [s, 6C, PhSi[OCH(CH3)Ph]3], 127.24 [s, 3C,
PhSi[OCH(CH3)Ph]3, overlapping with RRS/RSS], 128.06 [s, 2C,
PhSi[OCH(CH3)Ph]3], 128.39 [s, 6C, PhSi[OCH(CH3)Ph]3, over-
lapping with RRS/RSS], 130.56 [s, 1C, PhSi[OCH(CH3)Ph]3], 132.18
[s, 1C, PhSi[OCH(CH3)Ph]3], 135.36 [s, 2C, PhSi[OCH(CH3)Ph]3,
overlapping with RRS/RSS], 146.07 [s, 3C, PhSi[OCH(CH3)Ph]3].
(b) RRS/RSS: δ 26.83 [s, 1C, PhSi[OCH(CH3)Ph]3], 26.85 [s, 1C,
PhSi[OCH(CH3)Ph]3], 26.92 [s, 1C, PhSi[OCH(CH3)Ph]3], 71.58
[s, 2C, PhSi[OCH(CH3)Ph]3, overlapping with RRR/SSS], 71.61 [s,
1C, PhSi[OCH(CH3)Ph]3], 125.63 [s, 3C, PhSi[OCH(CH3)Ph]3],
125.68 [s, 3C, PhSi[OCH(CH3)Ph]3], 127.17 [s, 2C, PhSi[OCH-
(CH3)Ph]3, overlapping with RRR/SSS], 127.24 [s, 1C, PhSi[OCH-
(CH3)Ph]3], 127.25 [s, 1C, PhSi[OCH(CH3)Ph]3], 128.06 [s, 6C,
PhSi[OCH(CH3)Ph]3], 128.39 [s, 2C, PhSi[OCH(CH3)Ph]3, over-
lapping with RRR/SSS], 128.45 [s, 2C, PhSi[OCH(CH3)Ph]3], 130.56
[s, 1C, PhSi[OCH(CH3)Ph]3 overlapping with RRR/SSS], 132.00 [s,
2C, PhSi[OCH(CH3)Ph]3], 135.35 [s, 2C, PhSi[OCH(CH3)Ph]3],
135.36 [s, 2C, PhSi[OCH(CH3)Ph]3, overlapping with RRR/SSS],
146.13 [s, 1C, PhSi[OCH(CH3)Ph]3], 146.17 [s, 1C, PhSi[OCH-
(CH3)Ph]3], 146.20 [s, 1C, PhSi[OCH(CH3)Ph]3]. 29Si{1H} NMR
(CDCl3): δ −60.59 (RRR/SSS), −60.50 (RRS/SRR). 29Si{1H} NMR
(C6D6): δ −59.92 (RRR/SSS), −59.85 (RRS/RSS).
9.98 [s, 2C, PhSi[OCH(Me)CH2CH3]3], 9.99 [s, 1C, PhSi[OCH-
(Me)CH2CH3]3, overlapping with RRR/SSS], 23.07 [s, 1C, PhSi-
[OCH(Me)Et]3], 23.08 [s, 1C, PhSi[OCH(Me)Et]3], 23.10 [s, 1C,
PhSi[OCH(Me)Et]3], 32.51 [s, 3C, PhSi[OCH(Me)CH2CH3]3,
overlapping with RRR/SSS], 70.60 [s, 3C, PhSi[OCH(Me)Et]3,
overlapping with RRR/SSS], 70.61 [s, 6C, PhSi[OCH(Me)Et]3],
127.97 [s, 2C, PhSi[OCH(Me)Et]3, overlapping with RRR/SSS],
130.15 [s, 1C, PhSi[OCH(Me)Et]3, overlapping with RRR/SSS],
134.08 [s, 1C, PhSi[OCH(Me)Et]3, overlapping with RRR/SSS],
135.29 [s, 2C, PhSi[OCH(Me)Et]3, overlapping with RRR/SSS].
29Si{1H} NMR (C6D6): δ −62.26 (RRR/SSS), −62.30 (RSS/SRR).
PhSiH[OCH(Me)Et]2.89 The compound exists as a mixture of the
1
RR/SS, RrS, and RsS diastereomers in a 2:1.10:0.93 ratio. H NMR
(C6D6, selected resonances): (a) RrS: δ 0.892 [t, J = 7 Hz, 6H,
PhSiH[OCH(Me)CH2CH3]2], 1.169 [d, J = 6 Hz, 6H, PhSiH[OCH-
(Me)Et]2], 1.39−1.47 [m, 8H, PhSiH[OCH(Me)CH2CH3]2, over-
lapping RrS and RsS], 3.94−4.00 [m, 2H, PhSiH[OCH(Me)Et]2,
overlapping RrS, RsS, and RR/SS], 5.30 [s,1H, PhSiH[OCH(Me)-
Et]2]. (b) RsS: δ 0.890 [t, J = 7 Hz, 6H, PhSiH[OCH(Me)-
CH2CH3]2], 1.167 [d, J = 6 Hz, 6H, PhSiH[OCH(Me)Et]2], 3.94−
4.00 [m, 2H, PhSiH[OCH(Me)Et]2, overlapping RrS, RsS, and RR/
SS], 5.29 [s, 1H, PhSiH[OCH(Me)Et]2]. (c) RR/SS: δ 0.87 [t, J = 7
Hz, 6H, PhSiH[OCH(Me)CH2CH3]2], 1.18 [d, J = 6 Hz, 3H,
PhSiH[OCH(Me)Et]2], 1.19 [d, J = 6 Hz, 3H, PhSiH[OCH(Me)-
Et]2], 1.52−1.60 [m, 4H, PhSiH[OCH(Me)CH2CH3]2], 3.94−4.00
[m, 2H, PhSiH[OCH(Me)Et]2, overlapping with RrS and RsS], 5.29
[s, 1H, PhSiH[OCH(Me)Et]2]. 13C{1H} NMR (C6D6, selected
resonances): (a) RrS: δ 10.07 [s, 2C, PhSiH[OCH(Me)CH2CH3]2,
overlapping with RsS and RR/SS], 23.20 [s, 2C, PhSiH[OCH(Me)-
Et]2], 32.44 [s, 2C, PhSiH[OCH(Me)CH2CH3]2, overlapping with
RsS], 71.29 [s, 2C, PhSiH[OCH(Me)Et]2]. (b) RsS: δ 10.07 [s, 2C,
PhSiH[OCH(Me)CH2CH3]2, overlapping with RrS and RR/SS],
23.12 [s, 2C, PhSiH[OCH(Me)Et]2], 32.44 [s, 2C, PhSiH[OCH-
(Me)CH2CH3]2 overlapping with RrS], 71.57 [s, 2C, PhSiH[OCH-
(Me)Et]2]. (c) RR/SS: δ 10.07 [s, 2C, PhSiH[OCH(Me) CH2CH3]2,
overlapping with RrS and RrS], 23.16 [s, 2C, PhSiH[OCH(Me)Et]2],
32.41 [s, 2C, PhSiH[OCH(Me) CH2CH3]2], 71.24 [s, 1C, PhSiH-
[OCH(Me)Et]2], 71.62 [s, 1C, PhSiH[OCH(Me)Et]2]. 29Si{1H}
NMR (C6D6): δ −33.24 (RsS), −34.18 (RrS), −33.66 (RR/SS).
PhSiH2[OCH(Me)Et].90 1H NMR (C6D6, selected resonances): δ
0.82 [t, J = 7 Hz, 3H, PhSiH2[OCH(Me)CH2CH3]], 1.08 [d, J = 6 Hz,
3H, PhSiH2[OCH(Me)Et]], 3.66−3.72 [m, 1H, PhSiH2[OCH(Me)-
Et]], 5.24 [s, 2H, PhSiH2[OCH(Me)Et]]. 13C{1H} NMR (C6D6,
selected resonances): δ 22.61 [s, 1C, PhSiH2[OCH(Me)CH2CH3]],
32.13 [s, 1C, PhSiH2[OCH(Me)Et]], 73.20 [s, 1C, PhSiH2[OCH-
(Me)Et]].
PhSiH[OCH(Me)Ph]2.89 The compound exists as a mixture of the
1
RR/SS, RrS, and RsS diastereomers in a 2:1.06:0.93 ratio. H NMR
(C6D6, selected resonances): (a) RrS: δ 1.36 [d, J = 6 Hz, 6H,
PhSiH[OCH(Me)Ph]2], 4.97−5.06 [m, 2H, PhSiH[OCH(Me)Ph]2,
overlap with RsS and RR/SS], 5.37 [s, 1H, PhSiH[OCH(Me)Ph]2].
(b) RsS: δ 1.36 [d, J = 6 Hz, 6H, PhSiH[OCH(Me)Ph]2], 4.97−5.06
[m, 2H, PhSiH[OCH(Me)Ph]2, overlap with RrS and RR/SS], 5.24 [s,
1H, PhSiH[OCH(Me)Ph]2]. (c) RR/SS: δ 1.38 [d, J = 6 Hz, 3H,
PhSiH[OCH(Me)Ph]2], 1.43 [d, J = 6 Hz, 3H, PhSiH[OCH(Me)-
Ph]2], ], 4.97−5.06 [m, 2H, PhSiH[OCH(Me)Ph]2, overlap with RrS
and RsS], 5.30 [s, 1H, PhSiH[OCH(Me)Ph]2]. 13C{1H} NMR (C6D6,
selected resonances): (a) RrS: δ 26.16 [s, 2C, PhSiH[OCH(Me)Ph]2],
72.27 [s, 2C, PhSiH[OCH(Me)Ph]2]. (b) RsS: δ 26.07 [s, 2C,
PhSiH[OCH(Me)Ph]2], 72.31 [s, 2C, PhSiH[OCH(Me)Ph]2]. (c)
RR/SS: δ 26.68 [s, 2C, PhSiH[OCH(Me)Ph]2], 26.74 [s, 2C,
PhSiH[OCH(Me)Ph]2], 72.33 [s, 2C, PhSiH[OCH(Me)Ph]2],
72.37 [s, 2C, PhSiH[OCH(Me)Ph]2]. 29Si{1H} NMR (C6D6): δ
−32.15 (RR/SS), −32.25 (RsS), −32.41 (RrS).
PhSiH2(OCHPh2).90 1H NMR (C6D6, selected resonances): δ 5.20
[s, 2H, PhSiH2(OCHPh2)], 5.81 [s, 1H, PhSiH2(OCHPh2)]. 13C{1H}
NMR (C6D6, selected resonances): δ 79.50 [s, 1C, PhSi-
H2(OCHPh2)].
PhSi[OCH(Me)Et]3.91 The compound exists as a statistical mixture
1
of the RRR/SSS and RSS/SRR diastereomers in a 1:3 ratio. H NMR
PhSi(OCHEt2)3.90 1H NMR (C6D6): δ 0.93 [t, J = 7 Hz, 18H,
PhSi[OCH(CH2CH3)2]3], 1.55−1.67 [m, 12H, PhSi[OCH-
(CH2CH3)2]3], 4.03 [quint, J = 6 Hz, 3H, PhSi(OCHEt2)3], 7.21
[m, 3H, PhSi(OCHEt2)3], 7.90−7.92 [m, 2H, PhSi(OCHEt2)3].
13C{1H} NMR (C6D6): δ 9.72 [s, 6C, PhSi[OCH(CH2CH3)2]3],
29.21 [s, 6C, PhSi[OCH(CH2CH3)2]3], 75.58 [s, 3C, PhSi-
(OCHEt2)3], 127.93 [s, 1C, PhSi(OCHEt2)3], 130.09 [s, 1C,
PhSi(OCHEt2)3], 134.21 [s, 1C, PhSi(OCHEt2)3], 135.33 [s, 1C,
PhSi(OCHEt2)3]. 29Si{1H} NMR (C6D6): δ −63.04.
(C6D6): (a) RRR/SSS: δ 0.914 [t, J = 7 Hz, 9H, PhSi[OCH(Me)-
CH2CH3]3], 1.236 [d, J = 6 Hz, 9H, PhSi[OCH(Me)Et]3], 1.45−1.66
[m, 6H, PhSi[OCH(Me)CH2CH3]3, overlapping with RRS/RSS],
4.13−4.19 [m, 3H, PhSi[OCH(Me)Et]3, overlapping with RRS/RSS],
7.21−7.28 [m, 3H, PhSi[OCH(Me)Et]3, overlapping with RRS/RSS],
7.90 [m, 2H, PhSi[OCH(Me)Et]3, overlapping with RRS/RSS]. (b)
RRS/RSS: δ 0.916 [t, J = 7 Hz, 3H, PhSi[OCH(Me)CH2CH3]3],
0.918 [t, J = 7 Hz, 3H, PhSi[OCH(Me)CH2CH3]3], 0.920 [t, J = 7 Hz,
3H, PhSi[OCH(Me)CH2CH3]3], 1.230 [d, J = 6 Hz, 3H, PhSi[OCH-
(Me)Et]3], 1.233 [d, J = 6 Hz, 3H, PhSi[OCH(Me)Et]3], 1.234 [d, J =
6 Hz, 3H, PhSi[OCH(Me)Et]3], 1.45−1.66 [m, 6H, PhSi[OCH-
(Me)CH2CH3]3, overlapping with RRR/SSS], 4.12−4.19 [m, 3H,
PhSi[OCH(Me)Et]3, overlapping with RRR/SSS], 7.21−7.28 [m, 3H,
PhSi[OCH(Me)Et]3, overlapping with RRR/SSS], 7.90 [m, 2H,
PhSi[OCH(Me)Et]3, overlapping with RRR/SSS]. 13C{1H} NMR
(C6D6): (a) RRR/SSS: δ 9.99 [s, 3C, PhSi[OCH(Me)CH2CH3]3,
overlapping with RRS/RSS], 23.11 [s, 3C, PhSi[OCH(Me)Et]3], 32.51
[s, 3C, PhSi[OCH(Me)CH2CH3]3, overlapping with RRS/RSS], 70.60
[s, 3C, PhSi[OCH(Me)Et]3, overlapping with RRS/RSS], 127.97 [s,
2C, PhSi[OCH(Me)Et]3, overlapping with RRS/RSS], 130.15 [s, 1C,
PhSi[OCH(Me)Et]3, overlapping with RRS/RSS], 134.08 [s, 1C,
PhSi[OCH(Me)Et]3, overlapping with RRS/RSS], 135.29 [s, 2C,
PhSi[OCH(Me)Et]3, overlapping with RRS/RSS]. (b) RRS/RSS: δ
PhSiH2(OCHEt2).90 1H NMR (C6D6, selected resonances): δ 0.85 [t,
J = 7 Hz, 6H, PhSiH2[OCH(CH2CH3)2]], 1.37−1.60 [m, 4H,
PhSiH2[OCH(CH2CH3)2]], 3.51 [tt, J = 5 Hz, J = 7 Hz, 1H,
PhSiH2(OCHEt2)], 5.27 [s, 2H, PhSiH2(OCHEt2)]. 13C{1H} NMR
(C6D6, selected resonances): δ 10.06 [s, 2C, PhSiH2[OCH-
(CH2CH3)2]], 29.55 [s, 2C, PhSiH2[OCH(CH2CH3)2]], 78.62 [s,
1C, PhSiH2(OCHEt2)].
PhSiH(OCHEt2)2.89 1H NMR (C6D6, selected resonances): δ 0.88 [t,
J = 7 Hz, 6H, PhSiH[OCH(CH2CH3)2]2], 0.93 [t, J = 7 Hz, 6H,
PhSiH[OCH(CH2CH3)2]2], 1.37−1.60 [m, 8H, PhSiH[OCH-
(CH2CH3)2]2], 3.80 [tt, J = 5 Hz, J = 7 Hz, 2H, PhSiH(OCHEt2)2],
5.33 [s, 1H, PhSiH(OCHEt2)2]. 13C{1H} NMR (C6D6, selected
resonances): δ 9.95, [s, 2C, PhSiH[OCH(CH2CH3)2]2], 9.96 [s, 2C,
PhSiH[OCH(CH2CH3)2]2], 29.60 [s, 4C, PhSiH[OCH-
K
DOI: 10.1021/acs.organomet.5b00506
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(CH2CH3)2]2], 76.56 [s, 2C, PhSiH(OCHEt2)2]. 29Si{1H} NMR
overlapping with RS]. 13C{1H} NMR (C6D6, selected resonances): (a)
RR/SS: δ 9.92 [s, 2C, Ph2Si[OCH(Me)CH2CH3]2, overlapping with
RS], 23.13 [s, 2C, Ph2Si[OCH(Me)Et]2], 32.49 [s, 4C, Ph2Si[OCH-
(Me)CH2CH3]2, overlapping with RS], 70.77 [s, 2C, Ph2Si[OCH-
(Me)Et]2, overlapping with RR/SS]. (b) RS: δ 9.91 [s, 2C,
Ph2Si[OCH(Me)CH2CH3]2], 9.92 [s, 2C, Ph2Si[OCH(Me)-
CH2CH3]2, overlapping with RR/SS], 23.06 [s, 2C, Ph2Si[OCH(Me)-
Et]2], 32.49 [s, 4C, Ph2Si[OCH(Me)CH2CH3]2 overlapping with RR/
SS], 70.77 [s, 2C, Ph2Si[OCH(Me)Et]2, overlapping with RR/SS].
29Si{1H} NMR (C6D6): δ −35.65 (RR/SS), −35.69 (RS).
(C6D6): δ −32.55.
1
PhSi(OCy)3. H NMR (C6D6): δ 1.13−1.25 [m, 4H, PhSi[OCH-
(C5H10)]3], 1.31−1.39 [m, 4H, PhSi[OCH(C5H10)]3], 1.53−1.62 [m,
4H, PhSi[OCH(C5H10)]3], 1.66−1.73 [m, 4H, PhSi[OCH(C5H10)]3],
1.92−1.95 [m, 4H, PhSi[OCH(C5H10)]3], 4.14 [tt, J = 4 Hz, J = 9 Hz,
3H, PhSi[OCH(C5H10)]3], 7.23−7.29 [m, 3H, PhSi(OCy)3], 7.94−
7.97 [m, 2H, PhSi(OCy)3]. 13C{1H} NMR: δ 24.13 [s, 6C,
PhSi[OCH(C5H10)]3], 26.01 [s, 3C, PhSi[OCH(C5H10)]3], 35.88
[s, 6C, PhSi[OCH(C5H10)]3], 71.13 [s, 3C, PhSi[OCH(C5H10)]3],
130.21 [s, 1C, PhSi(OCy)3], 134.13 [s, 1C, PhSi(OCy)3], 135.24 [s,
2C, PhSi(OCy)3]. 29Si{1H} NMR: δ −61.62.
1
Ph2SiH[OCH(Me)Et]. H NMR (C6D6): δ 0.85 [t, J = 7 Hz, 3H,
Ph2SiH[OCH(Me)CH2CH3]], 1.13 [d, J = 6 Hz, 3H, Ph2SiH[OCH-
(Me)Et]], 1.34−1.60 [m, 2H, Ph2SiH[OCH(Me)CH2CH3]], 3.85 [m,
1H, Ph2SiH[OCH(Me)CH2CH3]], 5.71 [s, 1H, Ph2SiH[OCH(Me)-
CH2CH3]], 7.18 [m, 6H, Ph2SiH[OCH(Me)Et]], 7.70 [m, 4H,
Ph2SiH[OCH(Me)Et]]. 13C{1H} NMR (C6D6, selected resonances):
δ 10.12 [s, 1C, Ph2SiH[OCH(Me)CH2CH3]], 22.9 [s, 1C, Ph2SiH-
[OCH(Me)Et]], 32.29 [s, 1C, Ph2SiH[OCH(Me)CH2CH3]], 72.33
[s, 1C, Ph2SiH[OCH(Me)Et]]. 29Si{1H} NMR (C6D6): δ −14.14.
PhSiH(OCy)2.89 1H NMR (C6D6, selected resonances): δ 3.97 [tt, J
= 9 Hz, J = 4 Hz, 2H, PhSiH[OCH(C5H10)]2], 5.34 [s, 1H,
PhSiH(OCy)2]. 13C{1H} NMR: δ 72.01 [s, 2C, PhSiH[OCH-
(C5H10)]2]. 29Si{1H} NMR: δ −34.63.
PhSiH2(OCy).90 1H NMR (C6D6, selected resonances): δ 3.68 [tt, J
= 9 Hz, J = 4 Hz, 1H, PhSiH2[OCH(C5H10)]], 5.26 [s, 2H,
PhSiH2(OCy)]. 13C{1H} NMR (C6D6, selected resonances): δ 73.69
[s, 1C, PhSiH2[OCH(C5H10)]].
1
Ph2Si(OCHEt2)2. H NMR (C6D6, selected resonances): δ 0.87 [t, J
Ph2Si[OCH(Me)Ph]2. The compound exists as a mixture of the two
diastereomers, RR/SS and RS, in a 1:0.62 ratio. 1H NMR (C6D6,
selected resonances): (a) RR/SS: δ 1.39 [d, J = 6 Hz, 6H,
Ph2Si[OCH(Me)Ph]2], 5.05 [q, J = 6 Hz, 2H, Ph2Si[OCH(Me)Ph]2,
overlapping with RS] (b) RS: δ 1.30 [d, J = 6 Hz, 6H,
Ph2Si[OCH(Me)Ph]2], 5.08 [q, J = 6 Hz, 2H, Ph2Si[OCH(Me)Ph]2,
overlap with RR/SS]. 13C{1H} (C6D6, selected resonances): (a) RR/
SS: δ 27.06 [s, 2C, Ph2Si[OCH(Me)Ph]2], 71.60 [s, 2C, Ph2Si[OCH-
(Me)Ph]2]. (b) RS: δ 26.86 [s, 2C, Ph2Si[OCH(Me)Ph]2], 71.64 [s,
2C, Ph2Si[OCH(Me)Ph]2]. 29Si{1H} (C6D6): −33.30 (RS), −33.23
(RR/SS).
= 8 Hz, 12H, Ph2Si[OCH(CH2CH3)2]2], 1.55 [m, 8H, Ph2Si[OCH-
(CH2CH3)2]2], 3.83 [quintet, J = 6 Hz, 2H, Ph2Si[OCH-
(CH2CH3)2]2]. 13C{1H] NMR (C6D6, selected resonances): δ 9.74
[s, 4C, Ph2Si[OCH(CH2CH3)2]2], 29.24 [s, 4C, Ph2Si[OCH-
(CH2CH3)2]2], 75.84 [s, 2C, Ph2Si(OCHEt2)2]. 29Si{1H} NMR-
(C6D6): δ −35.55.
Ph2SiH(OCHEt2). 1H NMR (C6D6, selected resonances): δ 0.85 [t, J
= 8 Hz, 6H, Ph2SiH[(OCH(CH2CH3)2]], 1.49 [m, 4H, Ph2SiH-
[OCH(CH2CH3)2]], 3.68 [tt, J = 5 Hz, J = 6 Hz, 1H, Ph2SiH-
(OCHEt2)], 5.73 [s, 1H, Ph2SiH(OCHEt2)]. 13C{1H} NMR (C6D6,
selected resonances): δ 9.98 [s, 2C, Ph2SiH[OCH(CH2CH3)2]], 29.46
[s, 2C, Ph2SiH[OCH(CH2CH3)2]], 77.42 [s, 1C, Ph2SiH(OCHEt2)].
29Si{1H} NMR(C6D6): δ −13.38.
1
Ph2Si(OCHPh2)2. H NMR (C6D6, selected resonances): δ 6.02 [s,
2H, Ph2Si(OCHPh2)2]. 13C{1H} NMR (C6D6, selected resonances): δ
77.53 [s, 2C, Ph2Si(OCHPh2)2]. 29Si{1H} NMR (C6D6): δ −30.71.
Ph2Si(OCy)2. 1H NMR (C6D6, selected resonances): δ 1.49 [m,
20H, Ph2Si[OCH(C5H10)]2], 4.02 [tt, J = 4 Hz, J = 8 Hz, 2H,
Ph2Si[OCH(C5H10)]2]. 13C{1H} NMR (C6D6, selected resonances): δ
24.01 [s, 4C, Ph2Si[OCH(C5H10)]2], 25.94 [s, 2C, Ph2Si[OCH-
(C5H10)]2], 35.88 [s, 4C, Ph2Si[OCH(C5H10)]2], 71.21 [s, 2C,
Ph2Si[OCH(C5H10)]2]. 29Si{1H} NMR: δ −35.65.
1
Ph2SiH(OCHPh2). H NMR (C6D6, selected resonances): δ 5.98 [s,
1H, Ph2SiH(OCHPh2)], 5.67 [s, 1H, Ph2SiH(OCHPh2)]. 13C{1H}
NMR (C6D6, selected resonances): δ 78.62 [s, 1C, Ph2SiH-
(OCHPh2)]. 29Si{1H} NMR (C6D6): δ −11.52.
Ph2Si(OEt)2. 1H NMR (C6D6): δ 1.15 [t, J = 7 Hz, 6H,
Ph2Si(OCH2CH3)2], 3.79 [q, J = 7 Hz, 4H, Ph2Si(OCH2CH3)2 ].
7.21 [m, 6H, Ph2Si(OCH2CH3)2], 7.80 [m, 4H, Ph2Si(OCH2CH3)2].
13C{1H} NMR (C6D6, selected resonances): δ 18.48 [s, 2C,
Ph2Si(OCH2CH3)2], 58.97 [s, 2C, Ph2Si(OCH2CH3)2]. 29Si{1H}
NMR (C6D6): δ −32.11.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00506.
Ph2SiH(OEt).92 1H NMR (C6D6, selected resonances): δ 1.11 [t, J =
6 Hz, 3H, Ph2SiH(OCH2CH3)], 3.71 [q, J = 6 Hz, 2H, Ph2SiH-
(OCH2CH3)], 5.66 [s, 1H, Ph2SiH(OCH2CH3)]. 13C{1H} NMR
(C6D6, selected resonances): δ 18.29 [s, 1C, Ph2SiH(OCH2CH3)],
60.53 [s, 1C, Ph2SiH(OCH2CH3)]. 29Si NMR (C6D6): δ −11.98.
Ph2Si(OPri)2. 1H NMR (C6D6, selected resonances): δ 1.16 [d, J = 6
Hz, 12H, Ph2Si(OCHMe2)2], 4.22 [hept, J = 6 Hz, 2H, Ph2Si-
(OCHMe2)2]. 13C{1H} NMR (C6D6, selected resonances): δ 25.78 [s,
4C, Ph2Si(OCHMe2)2], 65.80 [s, 2C, Ph2Si(OCHMe2)2]. 29Si{1H}
NMR (C6D6): δ −35.53.
1H NMR spectra (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail for G.P.: parkin@columbia.edu.
■
Notes
Disclaimer. This report was prepared as an account of work
sponsored by an agency of the United States Government.
Neither the United States Government nor any agency thereof,
nor any of their employees, makes any warranty, express or
implied, or assumes any legal liability or responsibility for the
accuracy, completeness, or usefulness of any information,
apparatus, product, or process disclosed, or represents that its
use would not infringe privately owned rights. Reference herein
to any specific commercial product, process, or service by trade
name, trademark, manufacturer, or otherwise does not
necessarily constitute or imply its endorsement, recommenda-
tion, or favoring by the United States Government or any
agency thereof. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United
States Government or any agency thereof.
Ph2SiH(OPri2). 1H NMR (C6D6, selected resonances): δ 1.14 [d, J =
6 Hz, 6H, Ph2SiH(OCHMe2)], 4.07 [hept, J = 6 Hz, 1H,
Ph2SiH(OCHMe2)], 5.70 [s, 1H, Ph2SiH(OCHMe2)]. 13C{1H}
NMR (C6D6 selected resonances): δ 25.40 [s, 2C, Ph2SiH-
(OCHMe2)], 67.37 [s, 1C, Ph2SiH(OCHMe2)]. 29Si{1H} NMR
(C6D6): δ −14.81.
Ph2Si[OCH(Me)Et]2.93 The compound exists as a mixture of two
diastereomers, RR/SS and RS, in a 1:1 ratio. 1H NMR (C6D6, selected
resonances): (a) RS: δ 0.87 [t, J = 7 Hz, 6H, Ph2Si[OCH(Me)-
CH2CH3]2, overlapping with RR/SS], 1.158 [d, J = 6 Hz, 6H,
Ph2Si[OCH(Me)Et]2], 1.40−1.65 [m, 4H, Ph2Si[OCH(Me)-
CH2CH3]2, overlapping with RR/SS], 3.98−4.06 [m, 2H, Ph2Si-
[OCH(Me)Et]2, overlapping RR/SS]. (b) RR/SS: δ 0.87 [t, J = 7 Hz,
6H, Ph2Si[OCH(Me)CH2CH3]2, overlapping with RS], 1.165 [d, J = 6
Hz, 6H, Ph2Si[OCH(Me)Et]2], 1.40−1.65 [m, 4H, Ph2Si[OCH(Me)-
CH2CH3]2, overlapping with RS], 4.02 [m, 2H, Ph2Si[OCH(Me)Et]2,
L
DOI: 10.1021/acs.organomet.5b00506
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2014, 53, 2716−2721. (d) Wu, X. F. Chem. - Asian J. 2012, 7, 2502−
2509.
The authors declare no competing financial interest.
(11) Sattler, W.; Parkin, G. J. Am. Chem. Soc. 2011, 133, 9708−9711.
(12) Sattler, W.; Parkin, G. J. Am. Chem. Soc. 2012, 134, 17462−
17465.
ACKNOWLEDGMENTS
■
This material is based upon work supported by the U.S.
Department of Energy, Office of Science, Office of Basic Energy
Sciences (DE-FG02-93ER14339). Aaron Sattler is thanked for
helpful discussions.
(13) In addition, we also demonstrated that PhSiH3 can reduce
bicarbonate and carbonate to formate in molecular zinc complexes.
See: Sattler, W.; Parkin, G. Catal. Sci. Technol. 2014, 4, 1578−1584.
(14) For a review of main group catalysis of unsaturated bonds, see:
Revunova, K.; Nikonov, G. I. Dalton Trans. 2015, 44, 840−866.
(15) For examples of zinc hydride compounds as hydrosilylation
catalysts and as catalysts for dehydrocoupling of silanes, see refs 2u,v
and the following: (a) Rit, A.; Zanardi, A.; Spaniol, T. P.; Maron, L.;
Okuda, J. Angew. Chem., Int. Ed. 2014, 53, 13273−13277. (b) Kahnes,
M.; Gorls, H.; Gonzalez, L.; Westerhausen, M. Organometallics 2010,
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Catal. 2013, 3, 2336−2340. (d) Mukherjee, D.; Thompson, R. R.;
Ellern, A.; Sadow, A. D. ACS Catal. 2011, 1, 698−702.
(16) Zinc hydride compounds can also serve the role as
hydrogenation catalysts. See, for example: Jochmann, P.; Stephan, D.
W. Angew. Chem., Int. Ed. 2013, 52, 9831−9835.
(17) Manoso, A. S.; Ahn, C.; Soheili, A.; Handy, C. J.; Correia, R.;
Seganish, W. M.; DeShong, P. J. Org. Chem. 2004, 69, 8305−8314.
(18) For a hetereogeneous catalytic synthesis of α-NpSi(OR)3, see:
Boyer, J.; Corriu, R. J. P.; Perz, R.; Reye, C. J. Organomet. Chem. 1979,
172, 143−152.
(19) Peterson, E.; Khalimon, A. Y.; Simionescu, R.; Kuzmina, L. G.;
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(20) Shirobokov, O. G.; Gorelsky, S. I.; Simionescu, R.; Kuzmina, L.
G.; Nikonov, G. I. Chem. Commun. 2010, 46, 7831−7833.
(21) Shirobokov, O. G.; Kuzmina, L. G.; Nikonov, G. I. J. Am. Chem.
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(22) Chakraborty, S.; Blacque, O.; Fox, T.; Berke, H. ACS Catal.
2013, 3, 2208−2217.
(23) Kraft, S. J.; Sanchez, R. H.; Hock, A. S. ACS Catal. 2013, 3,
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(24) For example, catalytic insertion of PhC(O)Me into the Si−H
bonds of PhSiH3 by Cp*2NdCH(SiMe3)2 gives PhSi(OCH2Ph)3 in
only 12% yield,a while catalytic insertion of PhC(O)Me into the Si−H
bonds of PhSiH3 by [(C6H3Pri2)N]Mo(PMe3)3(Cl)H gives a mixture
of products, of which PhSi[OCH(Me)Ph]3 is only present in 5%
yield.b (a) Onozawa, S.; Sakakura, T.; Tanaka, M.; Shiro, M.
Tetrahedron 1996, 52, 4291−4302. (b) Reference 19.
(25) (a) Trovitch, R. J. Synlett 2014, 25, 1638−1642. (b) Mukho-
padhyay, T. K.; Flores, M.; Groy, T. L.; Trovitch, R. J. J. Am. Chem.
Soc. 2014, 136, 882−885. (c) Chidara, V. K.; Du, G. D. Organometallics
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(26) A zinc compound that achieves triple insertion of aldehydes has
also recently been described. See: Mou, Z.; Xie, H.; Wang, M.; Liu, N.;
Yao, C.; Li, L.; Liu, J.; Li, S.; Cui, D. Organometallics DOI: 10.1021/
acs.organomet.5b00413.
(27) Furthermore, a heterogeneous system for triple insertion
involving PhSiH3 has been reported. See: Zhao, M. D.; Xie, W. L.; Cui,
C. M. Chem. - Eur. J. 2014, 20, 9259−9262.
DEDICATION
■
This paper is dedicated to the memory of Gregory L. Hillhouse,
an inspirational chemist, friend, and colleague.
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(54) It is pertinent to note that other descriptions of the H NMR
be isochronous. Another illustration is provided by [TpMe ]Pt(H)2Si-
2
spectrum of Ph2Si[OCH(Me)Ph]2 have been presented. For example,
the methyl groups have been described as a pattern corresponding to
two doublets and a doublet of doublets, each of which is assigned to
two hydrogen atoms, i.e., six hydrogen atoms in total [δ 1.46 (d, J = 6.4
Hz, 2H), 1.37 (dd, J = 6.4 Hz, 1.4 Hz, 2H), 1.33 (d, J = 6.4 Hz, 2H)]
(see ref 27). Furthermore, rather than being described as two quartets,
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discrepancy is unknown, although it may be linked to the possibility
that other methods of synthesis may give rise to samples with a
statistical distribution of diastereomers. An early report describes the
methyl and methine groups in terms of a triplet and a quartet (see ref
18), but it is possible that this could be a consequence of poor
resolution.
(CH2CH3)3, for which the ethyl groups appear as a singlet.e Obviously,
the CH2 and CH3 groups cannot be classified as being chemically
equivalent but, because they are coincidentally isochronous, the ethyl
group appears as a singlet. A related example is provided by the
observation of a singlet for the ethyl group corresponding to one set of
199Hg satellite signals of EtHgCl.f Other issues concerned with the
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(55) A similar ratio is observed upon zinc-catalyzed dehydrocoupling
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(56) (a) Iglesias, M.; Fernandez-Alvarez, F. J.; Oro, L. A.
ChemCatChem 2014, 6, 2486−2489. (b) Chakraborty, S.; Guan, H.
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(37) Furthermore, it was also described as a doublet in CDCl3 (δ =
1.53, J = 6.5 Hz). See ref 27.
(38) Subsequent reports on PhSi[OCH(Me)Ph]3 have likewise not
discussed the spectroscopic features of PhSi[OCH(Me)Ph]3 in terms
of the diastereomeric mixture. For example, the methyl group has been
described as an unspecified multiplet (ref 25b), and as a range of
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1
PhSi[OCH(Me)Ph]3 in the H NMR spectrum (Figure 2) could be
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(39) Also inconsistent is the observation of a single 29Si NMR
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values of −59.84 and −59.92 ppm that we have observed for the two
diastereomers. The value of −32.7 ppm reported for PhSi[OCH-
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O
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