Selective hydrosilylation of alkynes and ketones: Contrasting reactivity between cationic 3-iminophosphine palladium and nickel complexes

Article abstract of DOI:10.1039/c7dt00832e

The catalytic hydrosilylation of alkynes and ketones has been explored utilizing palladium- and nickel(allyl) complexes supported by 3-iminophosphine ligands. Palladium and nickel demonstrated distinctly different reactivity profiles, with palladium provi

Full text of DOI:10.1039/c7dt00832e

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Selective hydrosilylation of alkynes and ketones:
contrasting reactivity between cationic
Cite this: DOI: 10.1039/c7dt00832e
3-iminophosphine palladium and nickel complexes†
Hosein Tafazolian, Robert Yoxtheimer, Rajendr S. Thakuri and
Joseph A. R. Schmidt
*
The catalytic hydrosilylation of alkynes and ketones has been explored utilizing palladium- and nickel
(allyl) complexes supported by 3-iminophosphine ligands. Palladium and nickel demonstrated distinctly
different reactivity profiles, with palladium proving very effective for the hydrosilylation of electron-
deficient alkynes, while nickel excelled with ketones and internal alkynes. Additionally, in many cases,
regioselective hydrosilylation was observed.
Received 7th March 2017,
Accepted 4th April 2017
DOI: 10.1039/c7dt00832e
rsc.li/dalton
give a hydridopalladium species that is likely the active catalyst
when using [(3-iminophosphine)Pd(allyl)]OTf for the hydro-
Introduction
Hydrosilylation is a useful catalytic transformation, facilitating silylation of allenes. This was further supported by a simple
access to organosilicon reagents.1–3 Among the many available H/D crossover experiment.28 In addition to allenes, the selec-
organosilicon species, allyl- and vinylsilanes have been key tive hydrosilylation of imines using this precatalyst was also
targets in catalytic hydrosilylation reactions because of their reported by our group.13 The simple activation of these com-
indispensable role as substrates in subsequent coupling plexes in the presence of silanes led us to further expand our
reactions.4–8 In addition to the hydrosilylation of carbon– study to the hydrosilylation of alkynes, while also investigating
carbon double and triple bonds, the catalytic hydrosilylation the nickel analogues of these palladium complexes in the
of unsaturated carbon–heteroatom systems as a means for hydrosilylation of unsaturated systems, as detailed herein.
selective reduction has grown rapidly.9–18 While there are
many reports of olefin hydrosilylation, common catalysts for
use with CvC bonds are second or third row late transition
Results and discussion
metals, and efforts to take advantage of first row transition
metals have only recently proven successful.7,19–27 This appli-
In this report, we examine the hydrosilylation of alkynes and
carbonyl groups, in particular electron-deficient alkynes and
cation to olefin chemistry is likely inspired by the very
ketones. Additionally, to better understand the role of the
common usage of first row transition metals in the hydrosilyl-
metal center, cationic complexes of both palladium and nickel
ation of carbonyl or imine groups, although selectivity remains
supported by the same 3-iminophosphine ligand were investi-
an ongoing challenge in this chemistry.
gated (Fig. 1).
Recently, we reported a very efficient palladium precatalyst
for the hydrosilylation of allenes.28 Mechanistic studies and
Initially, electron-deficient alkynes were examined, as
recent reports of palladium-catalyzed hydrosilylation of these
the observed regioselectivity suggested that primary and
alkynes with tertiary hydrosilanes yielded vinylsilane products
secondary unhindered hydrosilanes activated the precatalyst to
Department of Chemistry and Biochemistry, School of Green Chemistry and
Engineering, College of Natural Sciences and Mathematics, The University of Toledo,
2801 W. Bancroft St. MS 602, Toledo, Ohio, 43606-3390, USA.
E-mail: joseph.schmidt@utoledo.edu
†Electronic supplementary information (ESI) available: Full experimental
section, including characterization data and spectra for all hydrosilylation pro-
ducts. Crystallographic data is summarized in the ESI file, while a CIF file pro-
vides additional crystallographic data, including bond lengths and angles for
compound 1b. CCDC 1535923. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c7dt00832e
Fig. 1 Palladium and nickel complexes (1a and 1b) utilized.
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that function as very useful reagents for Hiyama coupling.29,30
Furthermore, the mechanism invoked in these previous
reports centered on the reactivity of a palladium-hydride
generated via oxidative addition of the hydrosilane to palla-
dium.29,30 With the belief that our system also proceeds via
hydrido-palladium intermediates,28 it seemed a promising
candidate for similar catalytic reactions.
Table 1 Hydrosilylation of electron-deficient alkynes with primary and
secondary silanes catalyzed by 1aa
Indeed, precatalyst 1a regioselectively hydrosilylated elec-
tron-deficient alkynes via syn addition with 100% conversion
to produce the corresponding vinylsilane products in moderate
to excellent isolated yields (Table 1). For 2j and 2k, performing
the catalysis at room temperature gave mixtures of E and Z
isomers, although these very rapid reactions were complete in
less than 30 minutes. Unfortunately, the ratio of these isomers
was not consistent from run to run, likely due to minor
changes in ambient temperature and the relatively slow cata-
lyst activation in this system. In order to achieve better selecti-
vity, they were instead performed at 0 °C, which lengthened
the reaction time to 2–3 hours, but formed solely the E isomer.
After reaction completion at 0 °C, giving only the E isomer, the
catalytic mixture was removed from the ice bath and moni-
tored for 12 hours at room temperature. No signs of isomeriza-
tion to the Z isomer were observed. In previous reports, partial
isomerization of the E isomer was postulated to occur via an
insertion and β-hydride elimination sequence in the presence
of Pd–H species,30 but such a mechanism seems absent in our
catalytic system. In nearly all previous reports involving the
hydrosilylation of electron-deficient alkynes, tertiary silanes
were utilized due to unwanted continued hydrosilylation reac-
tivity observed with the resulting primary and secondary
hydrosilanes after the first hydrosilylation catalytic turnover,
leading to complicated mixtures. Fortuitously, this did not
occur with our catalyst, as summarized in Table 1, allowing
for clean isolation of the product secondary and tertiary
vinylsilanes. In fact, tertiary silanes such as triethylsilane,
tert-butyldimethylsilane, and dimethylphenylsilane did not
undergo hydrosilylation with any of the electron-deficient
alkynes at all, consistent with our previously proposed mech-
anism for precatalyst activation where tertiary silanes react to
form the Pd–Si species, rather than the necessary Pd–H cata-
lyst.28 Other than the usage of these vinylsilane products as
substrates in Hiyama coupling, they can also be easily trans-
formed to the corresponding vinyliodides and then utilized in
Suzuki–Miyaura coupling.31 Although hydrosilylation of elec-
tron-deficient alkynes with primary and secondary silanes
worked very well, internal unactivated alkynes such as
4-octyne, diphenylacetylene and phenylmethylacetylene
a Catalytic procedure: Reactions were carried out at ambient tempera-
ture in NMR tubes prepared in a glovebox using CDCl3 (800 µl), 1a
(0.01 mmol, 2 mol%), hydrosilane (0.5 mmol), and alkyne (0.5 mmol),
followed by frequent monitoring of the reaction by 1H NMR spec-
troscopy. b Product was not isolated due to the formation of a complex
mixture. c Reaction was carried out at 0 °C.
showed no evidence of reaction after 24 hours under the same optimization by screening different ligands was required to
catalytic conditions. Simple terminal alkynes, such as phenyl- achieve selective internal hydrosilylation of the C–C triple
acetylene, led to intractable product mixtures.
bond.32 To our surprise, both enynes tested with our system
Having observed excellent results with alkynyl esters, we underwent hydrosilylation with diphenylsilane regioselectively
proceeded on to investigate the electronically similar 1,3- to form a single isomer (Scheme 1), although the specific
enynes, although cautious of the regioselectivity issues poss- isomer produced depended on the enyne employed. The regio-
ible in an extended carbon π-system of this sort. In fact, regio- selectivity in these two reactions seems driven entirely by the
selectivity difficulties in the hydrosilylation of 1,3-enynes were steric hindrance in the enyne substrate. Similar reactions with
recently detailed by Zhou and Moberg, in which reaction phenylsilane, methylphenylsilane and diisopropylsilane were
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Scheme 1 Hydrosilylation of 1,3-enynes with diphenylsilane catalyzed
by 1a.
unsuccessful due to the formation of complex product mix-
tures. As before, tertiary silanes were again unreactive in the
hydrosilylation of 1,3-enynes, likely due to the formation of
Pd–Si intermediates rather than the necessary Pd–H species.
These Pd–Si intermediates have much greater steric hindrance
at the catalyst center, preventing alkyne insertion.33
Fig. 3 Time-resolved 31P NMR spectra from equimolar reaction of 1a
Since diphenylsilane had proven useful in the hydrosilyl-
ation of both substrate classes, it was chosen in order to study
the intermediates present in this catalytic system. Reactions
utilizing equimolar amounts of palladium precatalyst 1a and
diphenylsilane were monitored over time. Although complete
conversion to a distinct palladium intermediate was not
observed, the presence of a Pd–H complex was observed in situ
as a triplet via proton NMR spectroscopy (JH–P = 92.4 Hz;
Fig. 2). The observation of this resonance as a triplet is consist-
ent with the formation of a dinuclear palladium complex, due
to the unsaturated coordination sphere in the resulting mono-
and diphenylsilane (recorded every 15 minutes).
catalytic activity of this Pd–H species at this point since other
species within the rather complicated reaction mixture could
instead serve as the actual functional catalyst.
Following this study of palladium chemistry, the related
nickel complex 1b was also investigated in hydrosilylation reac-
tions. Although we reported 1b previously, with full character-
ization by NMR spectroscopy and elemental analysis, during
the intervening period crystals of 1b suitable for X-ray analysis
were grown by layering a saturated solution of 1b in tetrahydro-
furan with pentane. Its solid state structure was determined by
X-ray crystallography via direct methods (Fig. 4) and is
included herein. The approximately square planar coordi-
nation sphere of the cationic nickel portion, folding of the
ligand backbone, and overall metrical parameters were quite
similar to the other 3-iminophosphine palladium and nickel
complexes previously investigated by the Schmidt group.34–39
Unlike the related palladium complex 1a (Table 1), no cata-
lytic hydrosilylation of methylpropiolate was observed over
24 hours with 5 mol% of nickel complex 1b. Instead, a
complex mixture of products was formed. Moreover, when an
meric Pd–H species. Interaction with two spin 31P nuclei
1
2
then gives the observed coupling pattern. Time-resolved 31P
NMR analysis of this reaction, as recorded every 15 minutes,
supported these same assertions, showing diminishment of
the precatalyst 31P resonance in tandem with growth of a new
31P doublet resonance (Fig. 3). Our efforts to isolate this
hydride proved unsuccessful. Over time, the hydride decom-
posed during the attempted workup with formation of palla-
dium black and ligand reduction via what appeared to be a
hydride attack on the imine carbon atom. Resonances for this
same hydride were also observed in equimolar reactions of the
palladium precatalyst with either phenylsilane or methyl-
phenylsilane (primary and secondary silanes), but not in stoi-
chiometric reactions with the aforementioned tertiary silanes.
Unfortunately, we cannot draw any solid conclusions about the
Fig. 2 1H NMR spectrum for the equimolar reaction of 1a with diphe-
nylsilane, resulting in the formation of a Pd–H species.
Fig. 4 Crystal structure of complex 1b (50% thermal ellipsoids; hydro-
gen atoms and triflate anion omitted for clarity).
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Table 3 Hydrosilylation of ketones with diphenylsilane catalyzed by 1ba
equimolar reaction of 1b with diphenylsilane was monitored
by H NMR spectroscopy over time, unlike the Pd complex 1a,
1
no hydride triplet was observed, but instead the resulting
mixture gave an uninterpretable 1H NMR spectrum. Thus, it
seemed that complex 1b was ineffective in the hydrosilylation
of such alkynes.
Completion
time (h)
Isolated
yield (%)
Given the recent interest in the hydrosilylation of carbo-
nyls,40,41 we instead set out to utilize 1b in the hydrosilylation
of aldehydes and ketones, and this nickel complex proved to
be quite active for this catalysis. To provide better comparison,
both nickel and palladium complexes (1a and 1b) were investi-
gated in the hydrosilylation of benzaldehyde and aceto-
phenone as initial test reactions (Table 2). This data showed
quite conclusively that the nickel complex 1b was far superior to
the palladium complex 1a in the hydrosilylation of CvO deriva-
tives, with quantitative conversion to the silylether product for
both benzaldehyde (2 hours) and acetophenone (12 hours),
while the palladium complex proved to be almost inactive
under these conditions (<5% conversion after 24 hours, even
at increased temperature). We attribute the different affinities
of Pd and Ni for alkynes and carbonyl groups to their general
polarizability and hard–soft acid–base theory, in which the Ni
would be expected to form a stronger interaction with the
oxygen than Pd, leading to preferred coordination at the Ni
center and the subsequent insertion reaction that leads to
hydrosilylation.
Entry
1
Product
12
21
36
94
85
71
2
3
4
5
6
7
48
30
86
66
Having established the superiority of 1b, this nickel
complex was then utilized for a broad range of ketone hydro-
silylation reactions, as summarized in Table 3. The necessary
reaction time for these catalyses is highly dependent on the
sterics of the ketone, and only a very small amount of product
was detected with a bulky mesityl group present (Table 3,
entry 6). Entries 7 and 8, with ortho-methoxyphenyl and ortho-
b
—
Table 2 Catalytic activity of 1a and 1b in the hydrosilylation of benz-
aldehyde and acetophenone with diphenylsilanea
44
77
Completion
time (h) 1a
Completion
time (h) 1b
b
Entry
Substrate
Solvent
8
9
—
c
1
2
3
4
Benzaldehyde
Acetophenone
Benzaldehyde
Acetophenone
CDCl3
CDCl3
C6D6
NRb
NRb
NRb
NRb
—
c
—
2
12
C6D6
a Catalytic procedure: Reactions were carried out at ambient tempera-
ture in NMR tubes prepared in a glovebox using solvent-d (800 µl),
catalyst 1a or 1b (0.01 mmol, 2 mol%), hydrosilane (0.5 mmol), and
carbonyl compound (0.5 mmol), followed by frequent monitoring of
the reaction by 1H NMR spectroscopy. b Trace amount of product
detected after 24 h at 60 °C. c <5% conversion was observed after 24 h
at rt.
3
89
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Table 3 (Contd.)
Completion
time (h)
Isolated
yield (%)
Entry
10
Product
8
82
11
12
36c
24c
76
83
13d
30c
79
Scheme 2 Gram-scale catalytic reactions of 1a and 1b.
In addition to carbonyl hydrosilylation, it was found that
nickel complex 1b also worked well in the cis-hydrosilylation of
internal alkynes to form the corresponding vinylsilane pro-
ducts (Table 4). Although a few other examples of first row
transition metal-catalyzed hydrosilylation of alkynes have been
reported to date,19,25,27 overall selectivity is variable in all
cases, often yielding more than one product isomer. These pre-
vious reports include a cobalt system by Mo and coworkers
that works perfectly for terminal alkynes, but lacks regio-
selectivity with unsymmetric internal alkynes.25 Additionally,
recent reports of nickel-catalyzed hydrosilylation by Srinivas
a Catalytic procedure: Reactions were carried out at ambient tempera-
ture in NMR tubes prepared in a glovebox using C6D6 (800 µl), 1b
(0.01 mmol, 2 mol%), hydrosilane (0.5 mmol), and ketone (0.5 mmol),
followed by frequent monitoring of the reaction by 1H NMR spectro-
scopy. b Trace amount of product was detected by 1H NMR spectro-
scopy. c Reaction was carried out at 60 °C. d 2 eq. of diphenylsilane was
used due to sluggish reaction with 1 eq. of hydrosilane.
chlorophenyl groups, provide evidence of the advantageous and coworkers form two regioisomers in the hydrosilylation of
effect of an electron-donating group (OMe) on the rate of the an unsymmetric alkyne (1-phenyl-1-propyne).19,26 This con-
reaction. In general, as previously noted,40 electron-donating trasts with our observation of strong regioselectivity with the
groups on the aryl unit of ketones and imines promote η2- same substrate, where a 92 : 8 ratio of regioisomers was
coordination of the carbonyl or imine to the metal center, a formed. Another interesting result using our catalyst involved
required step for successful insertion of the CvO or CvN the telomerization of 1-hexyne when treated with an equimolar
group into the metal hydride. The hydrosilylation of E-4-phe- amount of diphenylsilane. For the result given (Table 4, entry 6),
nylbut-3-en-2-one (Table 3, entry 13) resulted in exclusive for- the reaction was repeated with 2 eq. of 1-hexyne in order to
mation of the conjugate addition 1,4-hydrosilylation product. reflect the product stoichiometry, since the initial equimolar
Previously, 1,4-hydrosilylation of α,β-unsaturated ketones has reaction had yielded telomerized product and unreacted
been obtained with rhodium complexes,42,43 although nearly diphenylsilane. Unfortunately, other terminal alkynes (phenyl-
all nickel-catalyzed examples favor direct hydrosilylation of the acetylene, trimethylsilylacetylene, methyl propiolate, and
carbonyl functionality, with only a single exception reported 2-methylbut-1-en-3-yne) did not form the telomerized product,
recently.44 Although further investigation of other but rather gave intractable mixtures. As discussed above,
α,β-unsaturated carbonyl compounds is necessary, entry 13 hydrosilylation of electron-deficient alkynes was effective uti-
suggests the strength and capability of nickel as a replacement lizing palladium (Table 1). Although the nickel complex 1b
for more expensive transition metal-catalyzed systems.
was not successful in hydrosilylation of methylpropiolate, it
To test the scale-up robustness of 1a and 1b in the hydro- did show moderate reactivity for the hydrosilylation of methyl
silylation of π-compounds, representative gram scale hydro- hept-2-ynoate. As with most organotransition metal chemistry,
silylation reactions with each catalyst were performed, result- it should be emphasized that the reactivity and selectivity
ing in excellent isolated yields in both cases (Scheme 2).
observed in catalytic hydrosilylation is highly dependent on
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Table 4 Substrate scope of alkyne hydrosilylation catalyzed by 1ba
primary or secondary silanes. Our previous experiments, along
with the time-resolved 1H NMR data in this work, provide sup-
porting evidence for the proposed mechanism. On the other
hand, the nickel analogue of the palladium complex showed
poor reactivity for hydrosilylation of electron-deficient alkynes,
but performed regio- and stereoselectively in the hydrosilyl-
ation of unactivated internal alkynes with diphenylsilane.
Additionally, the nickel precatalyst functioned well in ketone
hydrosilylation. Although the mechanism involved in acti-
vation of the nickel precatalyst remains unknown at present,
continued mechanistic investigations and expansion of reac-
tion substrate scope are ongoing research avenues in this
project.
Isolated
Completion yield
Entry Alkyne
Product
time (h)
(%)
1
R1 = R2 = nPr
22 (12b)
84
2
R1 = R2 = Ph
30 (16b)
14 (10b)
77
80
Experimental
General methods and instrumentation
3
R1 = Me
R2 = Ph
All NMR-scale reactions were set up in a nitrogen-filled glove-
box. CDCl3 and C6D6 were purchased from Cambridge Isotope
Laboratories and for air-sensitive usage, dried over calcium
hydride and sodium, respectively, freeze–pump–thawed three
times, vacuum-transferred, and stored over molecular sieves in
a nitrogen-filled glovebox. Precatalysts 1a and 1b were syn-
thesized via the previously reported procedures.36,39
Hydrosilanes for catalytic hydrosilylation reactions were pur-
chased from Gelest, AK Scientific, or Acros, dried neat over
calcium hydride and distilled under nitrogen, freeze–pump–
thawed, and transferred to the glovebox. All aromatic alde-
hydes and ketones were supplied from Alfa Aesar, AK
Scientific, Sigma-Aldrich, and Acros. Alkynes were purchased
from either Sigma-Aldrich or AK Scientific. 1H and 13C NMR
data were obtained either on a 400 MHz Varian VXRS NMR
spectrometer at 399.95 MHz for 1H and 100.56 MHz for 13C
NMR spectroscopy or on a 600 MHz Bruker Avance III at
4
5
R1 = Et
24 (14b)
16 (12b)
81
71
R2 = 2-Propenyl
R1 = nPr
R2 = Methyl
formate
6c
R1 = nBu
R2 = H
36 (24b)
86
1
599.9 MHz for H and 150.8 MHz for 13C NMR spectroscopy.
a Catalytic procedure: Reactions were carried out at room temperature
in NMR tubes prepared in a glovebox using C6D6 (800 µl), 1b
(0.01 mmol, 2 mol%), hydrosilane (0.5 mmol), and ketone (0.5 mmol),
followed by frequent monitoring of the reaction by 1H NMR spec-
troscopy. b Reaction was carried out at 60 °C. c 2 eq. of alkyne was used.
High resolution mass spectrometry data were determined by
the University of Illinois Mass Spectrometry Laboratory,
Urbana, IL, USA.
Catalytic reactions and isolation of hydrosilylation products
For the hydrosilylation reactions of alkynes, unless otherwise
noted, 1a or 1b was suspended in CDCl3 or C6D6, followed by
addition of hydrosilane (1 eq.) and alkyne (1 eq.). In the case
of carbonyl hydrosilylation, the carbonyl derivative was added
before the hydrosilane. Then, the resulting solution was trans-
ferred to an NMR tube, sealed and reaction progress was moni-
the combination of metal and ligand used in the catalyst
as well as the electronic and steric parameters of the
hydrosilane.28,45,46
1
tored by acquiring H NMR data frequently. Gram scale reac-
tions were set up in 20 ml vials, sealed with gentle stirring,
Conclusions
In summary, efficient systems for the hydrosilylation of and reaction completion was monitored by TLC analysis of the
1
alkynes and ketones were developed using cationic complexes reaction mixture. After detection of reaction completion by H
of palladium and nickel supported by the 3-iminophosphine NMR spectroscopy (based on diminishing starting material
ancillary ligand. The palladium precatalyst showed satisfactory peaks), all volatiles were removed under vacuum, and the
reactivity in the hydrosilylation of activated alkynes. The mech- crude reaction mixture was extracted with hexanes and passed
anism for this system involved reactive palladium-hydride through a short plug of silica gel to remove inorganics. This
intermediates formed after treatment of the precatalyst with mixture was concentrated and purified by flash chromato-
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2
3
graphy (hexanes for vinylsilane products and 90 : 10 hexanes : 6.17 (d, J = 3.6 Hz, 1H), 3.75 (s, 3H), 3.65 (t, J = 3.6 Hz, 1H),
ethylacetate for silylether products) as a colorless oily liquid. 1.20–1.15 (m, 2H), 1.05 (d, 3J = 7.2 Hz, 6H), 0.98 (d, 3J = 7.2 Hz,
Isolated yields are calculated based on unsaturated substrate 6H); 13C{1H} NMR (CDCl3, 600 MHz): 169.6, 143.3, 139.0,
(alkyne or carbonyl derivative). For silylether products, due to 51.8, 18.9, 18.8, 10.7; HRMS (CI) (m/z): [M + H]+ calc. for
partial hydrolysis of the product on silica gel, yields are based C10H21O2Si, 201.1311; found, 201.1313.
on total of silylether and corresponding alcohol. All vinyl-
silanes were characterized by 1H and 13C NMR spectroscopy
and high resolution mass spectrometry. Silylether products
were characterized only by 1H and 13C NMR spectroscopy.
Hydrosilylation products 3a,47 3b,48 3d,49 3i,49 3j,50 3k,49 3l,51
3m,52 4a,53 4b,54 and 4c54 were identified by comparison to
previously reported NMR spectral data.
Methyl (E)-2-(phenylsilyl)hex-2-enoate (2e). 93% isolated
1
yield (109 mg), H NMR (CDCl3, 400 MHz): 7.62–7.60 (m, 2H),
3
7.42–7.36 (m, 3H), 6.68 (t, J = 6.8 Hz, 1H), 4.66 (s, 2H), 3.70
(s, 3H), 2.62 (q, 3J = 6.8 Hz, 2H), 1.53–1.47 (m, 2H), 0.95 (t, 3J =
7.2 Hz, 3H); 13C{1H} NMR (CDCl3, 400 MHz): 168.7, 162.9,
135.6, 131.5, 129.9, 128.1, 127.5, 51.4, 33.9, 22.2, 13.9; HRMS
(EI) (m/z): [M − H]+ calc. for C13H17O2Si, 233.0998; found,
233.0990.
Characterization of hydrosilylation products
Methyl 2-(phenylsilyl)acrylate (2a). 86% isolated yield
(83 mg), 1H NMR (CDCl3, 400 MHz): 7.64–7.61 (m, 2H),
7.44–7.37 (m, 3H), 7.03 (d, 2J = 2.0 Hz, 1H), 6.26 (d, 2J = 2.0 Hz,
1H), 4.69 (s, 2H), 3.76 (s, 3H); 13C{1H} NMR (CDCl3, 400 MHz):
168.5, 144.6, 137.2, 135.7, 130.5, 130.2, 128.2, 52.1; HRMS (EI)
Methyl (E)-2-(diphenylsilyl)hex-2-enoate (2f). (Same regio-
and stereoisomers from either 1a or 1b) 88% isolated yield
(137 mg), 1H NMR (CDCl3, 400 MHz): 7.64–7.62 (m, 4H),
(m/z): [M
191.0530.
−
H]+ calc. for C10H11O2Si, 191.0528; found,
3
7.45–7.39 (m, 6H), 6.60 (t, J = 7.2 Hz, 1H), 5.23 (s, 1H), 3.63
(s, 3H), 2.62 (q, 3J = 7.2 Hz, 2H), 1.55–1.49 (m, 2H), 0.97 (t, 3J =
7.2 Hz, 3H); 13C{1H} NMR (CDCl3, 400 MHz): 169.3, 161.7,
135.6, 133.1, 129.9, 129.5, 128.0, 51.3, 33.9, 22.3, 13.9; HRMS
(EI) (m/z): [M − H]+ calc. for C19H21O2Si, 309.1311; found,
309.1306.
Methyl 2-(diphenylsilyl)acrylate (2b). 91% isolated yield
(122 mg), 1H NMR (CDCl3, 400 MHz): 7.66–7.63 (m, 4H),
7.47–7.41 (m, 6H), 7.15 (d, 2J = 2.8 Hz, 1H), 6.25 (d, 2J = 2.8 Hz,
1H), 5.31 (s, 1H), 3.73 (s, 3H); 13C{1H} NMR (CDCl3, 400 MHz):
168.9, 145.0, 138.9, 135.7, 132.4, 130.1, 128.2, 52.0; HRMS (EI)
(m/z): [M
−
H]+ calc. for C16H15O2Si, 267.0841; found,
267.0841.
Methyl (E)-2-(methyl(phenyl)silyl)hex-2-enoate (2g). 85% iso-
lated yield (106 mg), 1H NMR (CDCl3, 400 MHz): 7.60–7.57
(m, 2H), 7.41–7.38 (m, 3H), 6.52 (t, 3J = 7.2 Hz, 1H), 4.67 (q,
3J = 4.0 Hz, 1H), 3.69 (s, 3H), 2.54 (q, 3J = 7.2 Hz, 2H), 1.49
(sext, 3J = 7.2 Hz, 2H), 0.95 (t, 3J = 7.2 Hz, 3H), 0.54 (d, 3J =
4.0 Hz, 3H); 13C{1H} NMR (CDCl3, 400 MHz): 169.5, 159.2,
134.9, 134.7, 131.0, 129.6, 127.9, 51.2, 33.8, 22.3, 13.9, −5.0;
HRMS (EI) (m/z): [M − H]+ calc. for C14H19O2Si, 247.1154;
found, 247.1153.
Methyl 2-(methyl(phenyl)silyl)acrylate (2c). 80% isolated
1
yield (83 mg), H NMR (CDCl3, 400 MHz): 7.60–7.58 (m, 2H),
7.42–7.37 (m, 3H), 6.96 (d, 2J = 2.8 Hz, 1H), 6.16 (d, 2J =
3
3
2.8 Hz, 1H), 4.72 (q, J = 4.0 Hz, 1H), 3.75 (s, 3H), 0.57 (d, J =
4.0 Hz, 3H); 13C{1H} NMR (CDCl3, 400 MHz): 169.0, 142.9,
140.3, 134.8, 133.5, 129.8, 128.0, 51.9, −5.3; HRMS (EI) (m/z):
[M − H]+ calc. for C11H13O2Si, 205.0685; found, 205.0684.
Methyl (E)-2-(diisopropylsilyl)hex-2-enoate (2h). 83% iso-
1
3
lated yield (101 mg). H NMR (CDCl3, 400 MHz): 6.38 (t, J =
7.6 Hz, 1H), 3.68 (s, 3H), 3.56 (t, 3J = 3.2 Hz, 1H), 2.42
Methyl 2-(diisopropylsilyl)acrylate (2d). 64% isolated yield (q, 3J = 7.6 Hz, 2H), 1.50–1.41 (m, 2H), 1.13–1.05 (m, 2H),
(64 mg), H NMR (CDCl3, 600 MHz): 6.92 (d, J = 3.6 Hz, 1H), 1.01 (d, 3J = 6.8 Hz, 6H), 0.97 (d, 3J = 6.8 Hz, 6H), 0.90
1
2
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(t, 3J = 7.6 Hz, 3H); 13C{1H} NMR (CDCl3, 400 MHz): 170.4, 18.1; HRMS (EI) (m/z): [M]+ calc. for C17H18Si, 250.1178; found,
158.1, 129.9, 51.1, 33.8, 22.4, 18.8, 18.7, 13.8, 11.0. HRMS (EI) 250.1172.
(m/z): [M
−
H]+ calc. for C13H25O2Si, 241.1624; found,
241.1624.
(E)-(2-Methylhexa-1,3-dien-3-yl)diphenylsilane (2n). (Same
regio- and stereoisomers from either 1a or 1b) 81% isolated
yield (113 mg), 1H NMR (CDCl3, 600 MHz): 7.60 (dd, 3J =
4
3
7.8 Hz, J = 1.4 Hz, 4H), 7.42–7.26 (m, 6H), 5.89 (t, J = 7.1 Hz,
Methyl (E)-2-(diphenylsilyl)-3-phenylacrylate (2j). 93% iso-
lated yield (160 mg), 1H NMR (CDCl3, 600 MHz): 7.69–
7.68 (m, 4H), 7.48–7.45 (m, 2H), 7.43–7.41 (m, 4H), 7.38–
7.32 (m, 5H), 7.10 (s, 1H), 5.34 (s, 1H), 3.58 (s, 3H);
13C{1H} NMR (CDCl3, 600 MHz): 171.2, 148.8, 136.2,
135.8, 132.0, 131.7, 130.3, 129.3, 128.7, 128.5, 128.2, 51.8;
HRMS (EI) (m/z): [M]+ calc. for C22H20O2Si, 344.1233; found,
344.1238.
2
3
1H), 5.09 (s, 1H), 4.86 (d, J = 1.3 Hz, 1H), 4.53 (d, J = 1.3 Hz,
1H), 2.20 (quint, 3J = 7.1 Hz, 2H), 1.71 (s, 3H), 0.99 (t, 3J =
7.1 Hz, 3H); 13C{1H} NMR (CDCl3, 600 MHz): 147.5,
145.4, 139.2, 135.9, 133.9, 129.7, 128.0, 112.2, 24.5, 23.8, 14.4;
HRMS (EI) (m/z): [M]+ calc. for C19H22Si, 278.1491; found,
278.1491.
Diphenyl(1-(p-tolyl)ethoxy)silane (3c). 71% isolated yield
(113 mg), 1H NMR (CDCl3, 400 MHz): 7.72 (d, 3J = 7.6 Hz,
Methyl (E)-2-(methyl(phenyl)silyl)-3-phenylacrylate (2k).
79% isolated yield (112 mg), 1H NMR (CDCl3, 400 MHz):
7.66–7.64 (m, 2H), 7.44–7.31 (m, 8H), 7.03 (s, 1H), 4.81
(q, 3J = 3.6 Hz, 1H), 3.67 (s, 3H), 2.62 (d, 3J = 3.6 Hz, 3H);
13C{1H} NMR (CDCl3, 400 MHz): 171.5, 146.6, 136.3, 134.9,
133.4, 130.8, 130.1, 129.0, 128.53, 128.50, 128.2, 51.8, −5.3;
HRMS (EI) (m/z): [M]+ calc. for C17H18O2Si, 282.1076; found,
282.1079.
3
3
2H), 7.67 (d, J = 7.2 Hz, 2H), 7.52–7.41 (m, 6H), 7.33 (d, J =
8.0 Hz, 2H), 7.21 (d, 3J = 8.0 Hz, 2H), 5.51 (s, 1H), 5.07
(q, 3J = 6.0 Hz, 1H), 2.42 (s, 3H), 1.59 (d, 3J = 6.0 Hz, 3H);
13C{1H} NMR (CDCl3, 400 MHz): 142.4, 136.8, 135.9, 134.83,
134.79, 134.4, 130.41, 130.36, 129.0, 128.1, 128.0, 125.6, 72.7,
26.4, 21.4.
(1-(4-Chlorophenyl)ethoxy)diphenylsilane (3e). 66% isolated
yield (112 mg), 1H NMR (CDCl3, 400 MHz): 7.62 (dd, 3J =
Methyl (E)-2-(diisopropylsilyl)-3-phenylacrylate (2l). 68% iso-
lated yield (94 mg), 1H NMR (CDCl3, 600 MHz): 7.33–
7.24 (m, 5H), 7.05 (s, 1H), 3.77–3.75 (m, 1H), 3.69 (s, 3H),
1.24–1.19 (m, 2H), 1.12 (d, 3J = 7.6 Hz, 6H), 1.10 (d, 3J = 7.6 Hz,
6H); 13C{1H} NMR (CDCl3, 600 MHz): 172.3, 158.8, 146.4,
136.5, 128.8, 128.5, 128.4, 51.7, 18.61, 18.56, 11.1; HRMS
(EI) (m/z): [M − H]+ calc. for C16H23O2Si, 275.1467; found,
275.1471.
4
3
4
8.0 Hz, J = 1.6 Hz, 2H), 7.57 (dd, J = 8.0 Hz, J = 1.6 Hz, 2H),
7.46–7.33 (m, 6H), 7.27 (s, 4H), 5.40 (s, 1H), 4.96 (q, 3J =
6.4 Hz, 1H), 1.48 (d, 3J = 6.4 Hz, 3H); 13C{1H} NMR (CDCl3,
400 MHz): 143.9, 134.81, 134.76, 134.1, 133.9, 132.9, 130.6,
130.5, 128.5, 128.2, 128.1, 127.1, 72.2, 26.4.
(1-(2-Methoxyphenyl)ethoxy)diphenylsilane (3g). 77% iso-
1
3
(3-Methylbuta-1,3-dien-1-yl)diphenylsilane (2m). 92% iso- lated yield (129 mg), H NMR (CDCl3, 400 MHz): 7.64 (dd, J =
lated yield (115 mg), 1H NMR (CDCl3, 400 MHz): 7.60–7.58 8.0 Hz, J = 1.6 Hz, 2H), 7.59 (dd, J = 8.0 Hz, J = 1.6 Hz, 2H),
4
3
4
(m, 4H), 7.43–7.37 (m, 6H), 6.83 (d, 4J = 18.8 Hz, 1H), 6.09 7.45–7.34 (m, 6H), 7.23 (t, J = 8.4 Hz, 1H), 6.93–6.90 (m, 2H),
3
(dd, 4J = 18.8 Hz, 2J = 3.2 Hz, 1H), 5.17 (d, 2J = 3.2 Hz, 1H), 5.14 6.79 (dm, 3J = 8.4 Hz, 1H), 5.42 (s, 1H), 4.99 (q, 3J = 6.4 Hz,
(s, 1H), 5.06 (s, 1H), 1.92 (s, 3H); 13C{1H} NMR (CDCl3, 1H), 3.77 (s, 3H), 1.51 (d, 3J = 6.4 Hz, 3H); 13C{1H} NMR
400 MHz): 152.1, 143.3, 135.6, 133.9, 129.8, 128.2, 121.4, 119.0, (CDCl3, 400 MHz): 159.7, 147.1, 134.84, 134.82, 134.3, 134.1,
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130.5, 130.4, 129.4, 128.14, 128.07, 118.1, 112.8, 111.1, 72.7, 15 W. Sattler, S. Ruccolo, M. R. Chaijan, T. N. Allah and
55.3, 26.4.
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17 C. Ghosh, T. K. Mukhopadhyay, M. Flores, T. L. Groy and
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20 D. Noda, A. Tahara, Y. Sunada and H. Nagashima, J. Am.
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(E)-(2-Butyl-3-methylenehept-1-en-1-yl)diphenylsilane (4e).
86% isolated yield (150 mg, 2,3-dinbutyl/2,4-dinbutyl isomer:
1/0.27 from crude mixture), 1H NMR (CDCl3, 600 MHz):
3
4
7.56–7.54 (dd, J = 7.6 Hz, J = 1.6 Hz, 4H), 7.37–7.33 (m, 6H),
3
3
2
5.64 (d, J = 5.7 Hz, 1H), 5.14 (d, J = 5.7 Hz, 1H), 4.80 (d, J =
2
3
2.0 Hz, 1H), 4.77 (d, J = 2.0 Hz, 1H), 2.28 (t, J = 7.6 Hz, 2H),
3
3
2.05 (t, J = 7.1 Hz, 2H), 1.44–1.24 (m, 8H), 0.92 (t, J = 7.3 Hz,
3H), 0.86 (t, J = 6.9 Hz, 3H); 13C{1H} NMR (CDCl3, 600 MHz):
3
166.3, 150.9, 136.3, 135.1, 128.0, 127.9, 118.1, 113.1, 38.8, 34.6,
30.4, 29.6, 22.8, 22.4, 14.11, 14.08; HRMS (EI) (m/z): [M]+ calc.
for C24H32Si, 348.2273; found, 348.2269.
24 Z. D. Miller, R. Dorel and J. Montgomery, Angew. Chem.,
Int. Ed., 2015, 54, 9088–9091.
25 Z. Mo, J. Mao, Y. Gao and L. Deng, J. Am. Chem. Soc., 2014,
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Acknowledgements
26 V. Srinivas, Y. Nakajima, W. Ando, K. Sato and S. Shimada,
Catal. Sci. Technol., 2015, 5, 2081–2084.
This work was based on financial support by the National
Science Foundation under CHE-0841611.
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