Alkyne hydrosilylation catalyzed by nickel complexes of N-heterocyclic carbenes

Article abstract of DOI:10.1016/j.tet.2006.03.120

The addition of triethylsilane, triphenylsilane, and triethoxysilane to a variety of alkynes is catalyzed by complexes derived from Ni(COD)₂ and N-heterocyclic carbenes. A description of the reaction scope and potential mechanistic implications

Full text of DOI:10.1016/j.tet.2006.03.120

Tetrahedron 62 (2006) 7560–7566
Alkyne hydrosilylation catalyzed by nickel complexes of
N-heterocyclic carbenes
*
Mani Raj Chaulagain, Gireesh M. Mahandru and John Montgomery
Department of Chemistry, University of Michigan, 930 N. University Ave. Ann Arbor, MI 48109-1055, USA
Received 7 December 2005; revised 1 March 2006; accepted 1 March 2006
Available online 19 June 2006
Dedicated to Professor G €u nther Wilke for his seminal contributions to the field of organonickel chemistry
Abstract—The addition of triethylsilane, triphenylsilane, and triethoxysilane to a variety of alkynes is catalyzed by complexes derived from
Ni(COD) and N-heterocyclic carbenes. A description of the reaction scope and potential mechanistic implications in nickel-catalyzed addi-
2
tions of aldehydes, alkynes, and silanes is provided.
Ó 2006 Elsevier Ltd. All rights reserved.
1
. Introduction
Regioselectivity is typically highly dependent upon struc-
ture of the catalyst, alkyne, and silane, and either cis- or
trans-additions may be observed.
Vinyl silanes are useful building blocks for a variety of syn-
thetic processes including electrophilic substitutions and
palladium-catalyzed cross-couplings. While many methods
for preparation of vinyl silanes exist, catalytic additions of
silanes to alkynes are perhaps the most powerful. In
metal-catalyzed alkyne hydrosilylations, regioselectivity
and stereoselectivity issues are both important to control.
1
2
We have become interested in the nickel-catalyzed hydro-
silylation of alkynes not only because of the synthetic interest
in vinyl silanes, but also because we felt that understanding
the addition chemistry of silanes and alkynes could poten-
tially shed light on mechanistic issues in the three-component
3
OTES
Ni(0)
R3
O
+
Et SiH
3
R1
R3
+
R1
R2
H
R2
1
Path A
L
L
n
H
n
R3
Ni
R3
TESO L Ni
Ni
n
O
O
1
R1
R3
R2
R1
R2
R1
R2
Path B
O
R1
R2
R3
LnNi
H
R1
O
H
H
LnNi
H
1
LnNi
R2
R3
R2
R3
Path C
O
R1
R1
H
R1
R2
R3
O
NiLn
LnNi SiEt3
O
1
Et Si
3
Et Si
NiLn
3
R2
R3
Scheme 1.
*
0
Corresponding author. Tel.: +1 734 764 4424; fax: +1 734 763 1106; e-mail: jmontg@umich.edu
040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.03.120

M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
7561
coupling of aldehydes, alkynes, and silanes to produce pro-
tected allylic alcohols 1 being developed in our laboratory.
toluene, ether, and t-butanol were also effective solvents
although yields were highest in THF (Table 1). Only cis
addition products were observed, and the regioisomer 5a
was the sole product except for one instance in which 5b
was observed in low yield.
4
Prior studies in our lab involving crossover experiments
had demonstrated that the mechanism of aldehyde/alkyne/
silane couplings catalyzed by nickel phosphine complexes
proceeded by a different mechanism than the corresponding
couplings involving nickel complexes of N-heterocyclic
Table 1
4
c,5
carbenes.
The related system developed by Jamison in-
SiEt3
H
Ni(COD) , 3a
Ph
2
volving triethylborane-mediated aldehyde/alkyne couplings
poses similar questions, and evidence for a ligand-based
mechanistic switch in alkene-directed couplings of 1,5-
H
Et Si
3
+
Et SiH
+
3
Ph
Ph
Me
t-BuOK, rt
Me
5a
Me
5b
2a
6
enynes was provided. A multitude of mechanistic possibili-
ties for these processes exist, including the formation of
metallacycles from Ni(0), aldehydes, and alkynes (path A,
Scheme 1), hydrometallation of alkynes followed by alde-
hyde insertion (path B), and silylmetallation of aldehydes
Entry
Solvent
Combined yield (%)
5a:5b Ratio
1
2
3
4
THF
74
56
49
37
>95:5
89:11
>95:5
>95:5
Toluene
Ether
t-BuOH
7
followed by alkyne insertion (path C). In path B, the trialkyl-
silyl may or may not be directly coordinated to nickel through-
out the sequence shown. Similarly, in path C, a hydride may
or may not be directly coordinated to nickel throughout the
sequence shown. Variation in the active catalyst structure
and oxidation state leads to several possibilities within each
of these three pathways. Given these mechanistic complex-
ities, we envisioned that understanding the reactivity patterns
of simple alkyne hydrosilylations could be useful in further
understanding the corresponding three-component couplings
with aldehydes.
A short study of the range of alkynes tolerated was carried
out (Table 2). Hydrosilylation of symmetrical internal al-
kynes 2b and 2c proceeded cleanly to afford products 6
and 7, respectively, and unsymmetrical alkynes 2a and 2d–
2f underwent efficient couplings with varying degrees of re-
gioselection. As noted above, couplings of phenylpropyne
2a were completely selective, whereas the regioselectivity
with internal doubly aliphatic substituted alkynes 2d and
2e varied according to the steric difference in alkyne substit-
uents. Interestingly, terminal alkyne 2f was an effective par-
ticipant, but with relatively poor regioselection. In all cases
other than activated aromatic alkynes, the silicon unit was
preferentially installed at the least hindered alkyne carbon.
2
. Results
The catalyst derived from Ni(COD) and tributylphosphine
2
is ineffective in promoting the hydrosilylation of either
alkynes or aldehydes with triethylsilane under conditions
that are effective in three-component couplings of alkynes,
Table 2
8
SiEt3
R1
H
aldehydes, and triethylsilane. This observation was an im-
portant feature that led us to propose the metallacycle-based
mechanism in the first reports of the nickel-catalyzed reduc-
R1
Ni(COD)2, 3a
H
Et Si
3
+
Et3SiH
+
R1
R2
t-BuOK, THF, rt
R2
R2
5b-10b
2a-f
4
a,e
tive coupling of alkynes and aldehydes. The catalyst de-
rived from Ni(COD) and N-heterocyclic carbenes, however,
are effective in alkyne hydrosilylations. Direct treatment of
5a-10a
2
1
2
R
9
Alkyne
R
Product (% yield)
a:b Ratio
1-phenyl-1-propyne and triethylsilane in THF with the cata-
lyst derived from Ni(COD) , t-butoxide, and imidazolium
salt 3a provided a 6:1 mixture of adducts derived from the
2
a
2b
Ph
Me
n-Propyl
Ph
n-Pentyl
t-Bu
n-Hexyl
5 (74)
6 (87)
7 (92)
8 (99)
9 (74)
10 (80)
>95:5
—
—
75:25
>95:5
67:33
2
n-Propyl
Ph
Me
Me
H
2c
2d
2e
2f
2
2
:1 coupling of the alkyne and silane in 50% yield (Scheme
). The major isomer of the 2:1 coupling was determined
1
0
to be structure 4. In order to suppress incorporation of the
second alkyne, the above experiment was repeated with sy-
ringe drive addition of the alkyne, and product 5, derived
from 1:1 coupling of the alkyne and silane, was obtained
Considering the poor regioselection with alkyne 2d, we ex-
amined the impact of varying ligand and silane structures
with this alkyne (Table 3). Whereas 3:1 selectivity was noted
(
Scheme 2). A brief study of solvent effects illustrated that
SiEt3
Me SiEt3
Ni(COD) , 3a
2
Ph
Ni(COD) , 3a
2
H
Ph
+ Et SiH
3
Ph
Ph
t-BuOK, THF, rt
t-BuOK, THF, rt
Me
Me
H
Me
2a
5
a (74 %, single isomer)
4
(50 %, 6:1 isomeric mixture)
(
2a added over 20 min)
(
2a added over 1 min)
3
a, Ar = 2,4,6-trimethylphenyl
+
N
N
3b, Ar = 2,6-diisopropylphenyl
3c, Ar = 4-methylphenyl
Ar
Ar
_
Cl
Scheme 2.

7562
M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
Table 3
H
SiR3
Ni(COD) , ligand
Me
2
+
H
R Si
3
+
R SiH
C5H11
C5H11
3
Me
t-BuOK, THF, rt
Me
Me
8b
2
d
8
a (R = Et)
1
1a (R = OEt)
2a (R = Ph)
11b
12b
1
Entry
Ligand
R
3
SiH
Product (% yield)
a:b Ratio
1
2
3
4
5
3a
3b
3c
3a
3a
Et
Et
Et
3
3
3
SiH
SiH
SiH
8 (99)
8 (99)
8 (75)
11 (71)
12 (53)
75:25
90:10
67:33
60:40
76:24
(EtO) SiH
3
3
Ph SiH
with 3a, reactions with more hindered ligand derived from
b proceeded in near quantitative yield with very good re-
triethoxysilane, and the ligand derived from 3a favored the
internal silane isomer 13b in 3:1 regioselection. Coupling
of 2f and triphenylsilane with the ligand derived from 3b af-
forded improved regioselectivity (relative to reactions with
3a) in favor of 14a, whereas the coupling of 2f and triethoxy-
silane with the ligand derived from 3b provided the reversed
regioselectivity (relative to reactions with 3a) in favor of
13a. Surprisingly, the ligand from 3b was not effective in
couplings of 2f and triethylsilane. Thus, variation of the
silane structure provides a good handle for controlling regio-
selection in hydrosilylations of terminal alkynes, but the
impact of ligand variation is highly substrate dependent.
3
gioselection (Table 3, entry 2). With smaller p-tolyl carbene
derived from 3c, regioselectivity worsened to 2:1 in dimini-
shing yield (Table 3, entry 3). In varying the silane structure,
we found with alkyne 2d that the regioselectivity was only
minimally impacted. Triethylsilane and triphenylsilane af-
forded nearly identical regioselectivities with the carbene
derived from 3a, whereas triethoxysilane participated with
lower regioselectivity and yield (Table 3, entries 4–5).
Thus, with internal alkynes possessing aliphatic substituents,
ligand structure provides the best strategy for controlling
regioselection.
Given the utility of a crossover study in illustrating the
mechanistic differences between phosphine and N-hetero-
cyclic catalyst systems in three-component alkyne, alde-
With terminal alkyne 2f, however, silane structure displayed
an enormous impact (Table 4). Whereas reactions with the
ligand derived from 3a afforded a 2:1 ratio of products
4
c
hyde, and silane additions, we examined the crossover
reaction of 1-phenyl-1-propyne 2a with 3.0 equiv each of
Et SiD and Pr SiH in the presence of the catalyst derived
1
0a/10b with triethylsilane, the corresponding reaction
with triphenylsilane afforded the terminal silane 14a with
:1 regioselection. In contrast, the coupling of alkyne 2f,
3
3
7
from 3a (Scheme 3). In this experiment, only a small amount
Table 4
H
SiR3
Ni(COD) , ligand
2
R Si
+
H
Me
3
+
R SiH
C6H13
C6H13
3
t-BuOK, THF, rt
H
H
H
2
f
1
0a (R = Et)
3a (R = OEt)
4a (R = Ph)
10b
1
13b
14b
1
Entry
Ligand
R
3
SiH
Product (% yield)
a:b Ratio
1
2
3
4
5
3a
3a
3a
3b
3b
Et
Ph
3
SiH
10 (80)
14 (76)
13 (72)
14 (63)
13 (70)
67:33
89:11
25:75
>95:5
83:17
3
SiH
(EtO) SiH
Ph SiH
3
3
3
(EtO) SiH
SiEt3
Ph
Me
56.5 %
SiEt3
Ph
Me
<1.0 %
SiEt3
Me
Ph
1.3 %
D
H
D
+
+
+
Ph
Ni(COD) , 3a
2
+
Et SiD
+
n-Pr SiH
3
3
t-BuOK, THF, rt
Me
2a
SiPr3
Ph
SiPr3
Ph
SiPr3
Me
H
D
H
+
+
Me
Me
Ph
39.3 %
2.0 %
0.8 %
Scheme 3.

M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
7563
(<2%) of crossover products were observed, illustrating that
the R Si and H units in the product are largely derived from
imidazolium salts, and potassium tert-butoxide were stored
and weighed in an inert atmosphere glove box. All reactions
were conducted in flame-dried glassware under argon or
nitrogen.
3
a single molecule of trialkylsilane. Control experiments
illustrated that Et SiD and Pr SiH underwent addition at
similar rates.
3
3
5.2. General procedure for Ni(COD) /carbene catalyzed
hydrosilylation of alkynes
2
3. Discussion
Ni(COD) (28 mg, 0.10 mmol), ligand (0.10 mmol), and
2
Several points from the above study are potentially relevant
in analyzing the mechanism of three-component nickel-
catalyzed couplings of aldehydes, alkynes, and silanes. In
particular, the regioselection of phenylpropyne, benzalde-
hyde, and triethylsilane with Ni(0)/IMes ligand from 3a is
very clean for the production of isomer 15 (Scheme 4). In
contrast, the identical reaction carried out in the absence
of benzaldehyde cleanly affords compound 5a. Notably,
the position of introduction of the silane-derived hydrogen
atom is reversed in these two reactions. This suggests that
hydrometallation of the alkyne (path B, Scheme 1) is not
a common first step in both reactions unless coordination
of the aldehyde has a dramatic and an unexpected effect
on the regioselection.
potassium tert-butoxide (11 mg, 0.10 mmol) were weighed
together in a 15-mL flask in a glove box. Solvent (8 mL)
was added to the mixture under an inert atmosphere at rt.
The solution was stirred for 10 min and silane (2.0 mmol)
was added dropwise to the stirring mixture and allowed to
stir for 10 min. Alkyne (1.00 mmol) was dissolved in 2 mL
solvent under nitrogen and was added to the mixture over
20 min via syringe drive. Reactions were usually complete
after the addition of alkyne was complete. Solvents were
removed in vacuo and the crude product was purified by
column chromatography (SiO , hexanes, unless otherwise
2
noted) and the vinyl silanes were isolated as colorless oils
unless otherwise noted.
5
.2.1. ((1Z,3E)-2,3-Dimethyl-1,4-diphenylbuta-1,3-di-
enyl)triethylsilane (4). Following the general procedure
(except that alkyne was added over 1 min), Ni(COD)
(28 mg, 0.10 mmol), imidazolium salt, 3a (34 mg,
0.10 mmol), t-BuOK (11 mg, 0.10 mmol), triethylsilane
Et SiO
H
3
O
Ph
Ni(COD)2, 3a
+
Et SiH
3
+
Ph
Ph
2
t-BuOK, THF, rt
H
Ph
H3C
CH3
1
5 (>97:3)
(0.32 mL, 2.0 mmol), and 1-phenylpropyne (116 mg,
1.00 mmol) were employed to give 6:1 mixture of re-
SiEt3
Ph
Ph
Ni(COD)2, 3a
t-BuOK, THF, rt
+
Et SiH
H
3
gioisomers of 4 (176 mg, 0.50 mmol, 50%), after column
chromatography (SiO , hexanes). H NMR (400 MHz,
H C
3
CH3
1
2
5
a (>97:3)
CDCl ) d 7.15–7.42 (m, 8H), 6.97–7.10 (m, 2H), 6.54 (q,
3
J¼1.2 Hz, 0.14H, minor regioisomer), 6.44 (m, 0.86H, major
Scheme 4.
regioisomer), 2.06 (d, J¼1.6 Hz, 2.59H, major regioisomer),
1
0
.77 (d, J¼1.2 Hz, 0.41H, minor regioisomer), 1.71 (s,
Additionally, since crossover was not observed to an appre-
ciable extent in either the two component couplings of
alkynes and silanes or the three-component couplings of
alkynes, silanes, and aldehydes, then both reactions involve
mechanisms in which the silicon and hydrogen atoms of the
Si–H bond are simultaneously delivered to a metal complex.
.42H, minor regioisomer), 1.65 (s, 2.58H, major regio-
isomer), 0.99 (t, J¼8.0 Hz, 1.26H, minor regioisomer),
.89 (t, J¼8.0 Hz, 7.74H, major regioisomer), 0.73 (q,
J¼8.0 Hz, 0.84H, minor regioisomer), 0.51 (q, J¼8.0 Hz,
0
1
3
5
.16H, major regioisomer); C NMR (75 MHz, CDCl )
3
d 154.4, 145.3, 142.2, 137.8, 136.2, 129.2, 129.0, 128.47,
1
2
28.9, 128.3, 128.2, 128.1, 127.9, 126.3, 126.0, 124.8,
1.0, 20.7, 18.1, 17.5, 7.9, 7.8, 4.6, 4.3; HRMS (EI) m/z cal-
4. Conclusions
+
culated for C H Si 348.2273, found 348.2267 (M ).
24 32
In summary, an efficient method for the hydrosilylation of
alkynes involving Ni(0) complexes of N-heterocyclic car-
benes has been developed. The scope of both alkynes and
silanes tolerated is broad, and regioselectivities often depend
on the structure of the alkyne, silane, and N-heterocyclic
carbene ligand. The impact of these variables on the regio-
selectivity in alkyne hydrosilylations was compared to the
regioselectivity of three-component couplings of alkynes,
aldehydes, and silanes, and the comparison suggests that
alkyne hydrometallation is not a common first step in both
groups of reactions.
Compound 4 was converted into the previously reported
compound ((1E,3E)-2,3-dimethylbuta-1,3-diene-1,4-diyl)-
dibenzene by stirring with (n-Bu) NF for 24 h at rt. Spectro-
4
11
scopic data were identical to that previously reported.
5.2.2. (E)-Triethyl(1-phenylprop-1-enyl)silane (5). Follow-
ing the general procedure, Ni(COD) (28 mg, 0.10 mmol),
2
imidazolium salt, 3a (34 mg, 0.10 mmol), t-BuOK
(11 mg, 0.10 mmol), triethylsilane (0.32 mL, 2.0 mmol),
and1-phenyl-1-propyne(116 mg, 1.00 mmol)wereemployed
to give (E)-triethyl(1-phenylprop-1-enyl)silane (171 mg,
0.74 mmol, 74%, single regioisomer), after column chromato-
5
. Experimental
graphy (SiO , hexanes) as a colorless oil. Spectroscopic data
2
1
2
5
.1. General
were identical to that previously reported.
All reagents were used as received unless otherwise noted.
All alkynes were freshly distilled prior to use. Ni(COD)2,
5.2.3. (E)-Triethyl(oct-4-en-4-yl)silane (6). Following
the general procedure, Ni(COD)2 (28 mg, 0.10 mmol),

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M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
imidazolium salt, 3a (34 mg, 0.10 mmol), t-BuOK (11 mg,
HRMS (EI) m/z calculated for C H Si 212.1954, found
13 28
212.1968(M ).
+
0
4
.10 mmol), triethylsilane (0.32 mL, 2.0 mmol), and oct-
-yne (110 mg, 1.00 mmol) were employed to give (E)-tri-
ethyl(oct-4-en-4-yl)silane (197 mg, 0.87 mmol, 87%),
after column chromatography (SiO , hexanes) as a colorless
5.2.8. (E)-Triethyl(oct-1-enyl)silane (10a) and triethyl-
(oct-1-en-2-yl)silane (10b). Following the general proce-
dure, Ni(COD) (28 mg, 0.10 mmol), imidazolium salt, 3a
(34 mg, 0.10 mmol), t-BuOK (11 mg, 0.10 mmol), triethyl-
silane (0.32 mL, 2.0 mmol), and oct-1-yne (110 mg,
1.00 mmol) were employed to give a mixture of (E)-tri-
ethyl(oct-1-enyl)silane and triethyl(oct-1-en-2-yl)silane
(181 mg, 0.80 mmol, 80%, 2:1 mixture of regioisomers),
2
oil. Spectroscopic data were identical to that previously
reported.
2
1
3
5.2.4. (E)-(1,2-Diphenylvinyl)triethylsilane (7). Following
the general procedure, Ni(COD) (28 mg, 0.10 mmol), imi-
dazolium salt, 3a (34 mg, 0.10 mmol), t-BuOK (11 mg,
2
0
.10 mmol), triethylsilane (0.32 mL, 2.0 mmol), and 1,2-di-
phenylethyne (178 mg, 1.00 mmol) were employed to give
E)-(1,2-diphenylvinyl)triethylsilane (269 mg, 0.92 mmol,
2%), after column chromatography (SiO , hexanes) as
after column chromatography (SiO , hexanes) as a colorless
2
1
oil. H NMR (400 MHz, CDCl ) d 6.00 (dt, J¼18.4,
3
(
9
6.4 Hz, 0.66H, major isomer), 5.58–5.61 (m, 0.34H, minor
isomer), 5.50 (dt, J¼18.4, 1.6 Hz, 0.66H, major isomer),
5.25 (dt, J¼2.7, 0.8 Hz, 0.34H, minor isomer), 2.02–2.12
(m, 2H), 1.22–1.40 (m, 8H), 0.82–0.94 (m, 12H), 0.48–
2
a colorless solid. Spectroscopic data were identical to that
1
2
previously reported.
.2.5. (E)-Triethyl(oct-2-en-2-yl)silane (8a) and (E)-tri-
ethyl(oct-2-en-3-yl)silane (8b) with 3a. Following the
0
.60 (m, 6H). Data for 10a matches those previously
reported.
1
4
5
general procedure, Ni(COD) (28 mg, 0.10 mmol), imidazo-
2
lium salt, 3a (34 mg, 0.10 mmol), t-BuOK (11 mg, 0.10
mmol), triethylsilane (0.32 mL, 2.0 mmol), and oct-2-yne
5.2.9. (E)-Triethoxy(oct-2-en-2-yl)silane (11a) and (E)-
triethoxy(oct-2-en-3-yl)silane (11b). Following the general
procedure, Ni(COD) (28 mg, 0.10 mmol), imidazolium salt,
2
(
(
110 mg, 1.00 mmol) were employed to give a mixture of
E)-triethyl(oct-2-en-2-yl)silane and (E)-triethyl(oct-2-en-
-yl)silane (225 mg, 0.99 mmol, 99%, 3:1 mixture of regio-
3a (34 mg, 0.10 mmol), t-BuOK (11 mg, 0.10 mmol), tri-
ethoxysilane (0.37 mL, 2.0 mmol), and oct-1-yne (110 mg,
1.00 mmol) were employed to give a 1.5:1 mixture of
(E)-triethoxy(oct-2-en-3-yl)silane and (E)-triethoxy(oct-
3
isomer), after column chromatography (SiO , hexanes) as
a colorless oil. H NMR (500 MHz, CDCl ) d 5.82 (q,
3
2
1
2-en-2-yl)silane, after column chromatography (SiO , hex-
2
1
J¼6.5 Hz, 0.25H, minor isomer), 5.71 (tq, J¼6.5, 1.5 Hz,
anes) as a colorless oil. H NMR (400 MHz, CDCl3)
d 6.15 (qt, J¼6.4, 0.8 Hz, 0.4H, minor regioisomer), 6.06
0
.75H, major regioisomer), 2.07–2.15 (m, 2H), 1.71 (d,
J¼6.5 Hz, 0.75H, minor regioisomer), 1.66 (m, 2.25H),
(tq, J¼6.8, 1.6 Hz, 0.6H, major regioisomer), 3.72–3.80
13
1
6
3
7
1
.26–1.43 (m, 6H), 0.89–0.93 (m, 12H), 0.47–0.62 (m,
H); C (125 MHz, CDCl ) d 141.4, 139.0, 135.5, 132.6,
(m, 6H), 2.03–2.11 (m, 2H), 1.63–1.67 (m, 3H), 1.22–1.38
1
3
(m, 6H), 1.13–2.0 (m, 9H), 0.81–0.86 (m, 3H);
C
(125 MHz, CDCl ) d 146.0, 139.6, 134.0, 126.9, 58.3,
3
2.5, 31.8, 29.8, 29.6, 29.2, 28.5, 22.8, 15.1, 14.3, 14.2,
.6, 6.9, 6.6, 3.3, 2.8; IR (film, cm ) 2972, 2910, 2860,
434, 1425, 1332, 1254, 1064, 965, 912, 697, 617; HRMS
3
ꢀ1
58.2, 32.0, 31.5, 29.0, 28.6, 28.5, 28.2, 22.4, 18.1, 14.1,
14.0, 13.9; IR (film, cm ) 2973, 2927, 1620, 1442, 1389,
ꢀ
1
(
2
EI) m/z calculated for C H Si 226.2116, found
1
26.2113(M ).
1167, 1104, 1081, 957, 779; HRMS (EI) m/z calculated for
C H O Si 274.1964, found 274.1759(M ).
4 30
+
+
1
4 30 3
5.2.6. (E)-Triethyl(oct-2-en-2-yl)silane (8a) and (E)-tri-
ethyl(oct-2-en-3-yl)silane (8b) with 3b. Following the
general procedure, Ni(COD) (28 mg, 0.10 mmol), imidazo-
2
5.2.10. (E)-Oct-2-en-2-yltriphenylsilane (12a) and (E)-
oct-2-en-3-yltriphenylsilane (12b). Following the general
procedure (with the modification in silane stoichiometry),
Ni(COD)2 (28 mg, 0.10 mmol), imidazolium salt, 3a
(34 mg, 0.10 mmol), t-BuOK (11 mg, 0.10 mmol), triphe-
nylsilane (260 mg, 1.0 mmol in 2 mL THF), and oct-2-yne
(110 mg, 1.00 mmol) were employed to give a 3.2:1 mixture
of regioisomers (E)-oct-2-en-2-yltriphenylsilane and (E)-
oct-2-en-3-yltriphenylsilane (196 mg, 0.53 mmol, 53%),
lium salt, 3b (43 mg, 0.10 mmol), t-BuOK (11 mg,
0.10 mmol), triethylsilane (0.32 mL, 2.0 mmol), and oct-2-
yne (110 mg, 1.00 mmol) were employed to give a mixture
of (E)-triethyl(oct-2-en-2-yl)silane and (E)-triethyl(oct-
2-en-3-yl)silane (225 mg, 0.99 mmol, 99%, 9:1 mixture of
regioisomer), after column chromatography (SiO , hexanes)
as a colorless oil.
2
after column chromatography (SiO , hexanes) as a colorless
2
1
oil. H NMR (400 MHz, CDCl ) d 7.52–7.58 (m, 6H),
3
5
(
0
.2.7. (E)-(4,4-Dimethylpent-2-en-2-yl)triethyl silane
9a). Following the general procedure, Ni(COD) (28 mg,
.10 mmol), imidazolium salt, 3a (34 mg, 0.10 mmol),
7.32–7.42 (m, 9H), 6.05 (q, J¼6.4 Hz, 0.24H, minor
regioisomer), 5.94 (tq, J¼6.8, 1.6 Hz, 0.76H, major
regioisomer), 2.16–2.25 (m, 2H), 1.81–1.84 (m, 0.24H,
minor regioisomer), 1.79 (d, J¼6.4 Hz, 0.76H, major re-
gioisomer), 1.24–1.42 (m, 4H), 1.05–1.11 (m, 2H), 0.88 (t,
J¼6.8 Hz, 2.27H, major regioisomer), 0.72 (t, J¼6.8 Hz,
2
t-BuOK (11 mg, 0.10 mmol), triethylsilane (0.32 mL, 2.0
mmol), and 4,4-dimethylpent-2-yne (96 mg, 1.00 mmol)
were employed to give (E)-(4,4-dimethylpent-2-en-2-yl)-
triethyl silane (157 mg, 0.74 mmol, 74%, single regio-
1
3
0.73H, minor regioisomer);
C (125 MHz, CDCl )
3
isomer), after column chromatography (SiO , hexanes) as
2
a colorless oil. H NMR (400 MHz, CDCl ) d 5.58 (q,
3
d 147.3, 141.0, 136.3, 136.2, 134.9, 134.5, 129.9, 129.5,
129.2, 127.7, 127.6, 32.0, 31.6, 29.9, 29.1, 28.8, 28.7,
1
ꢀ
1
J¼1.6 Hz, 1H), 1.74 (d, J¼1.6 Hz, 3H), 1.09 (s, 9H), 0.87
22.5, 16.1, 14.8, 14.1, 13.9; IR (film, cm ) 3068, 2955,
2927, 2856, 1613, 1428, 1188, 1108, 741, 512; HRMS
(EI) m/z calculated for C H Si 370.2116, found
1
3
(
CDCl ) d 150.1, 131.2, 34.4, 30.7, 15.7, 7.3, 2.5; IR (film,
t, J¼8.0 Hz, 9H), 0.51 (q, J¼8.0 Hz, 6H); C (125 MHz,
3
26 30
ꢀ1
+
cm ) 2954, 2910, 2875, 1463, 1362, 1074, 1007, 729;
370.2120(M ).

M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
7565
ꢁ
53–55 C). H NMR (400 MHz, C D ) d 7.58–7.66 (m,
6 6
1
5.2.11. (E)-Triethoxy(oct-1-enyl)silane (13a) and tri-
ethoxy(oct-1-en-2-yl)silane (13b) with 3a. Following the
general procedure, Ni(COD) (28 mg, 0.10 mmol), imida-
2
6H), 7.10–7.14 (m, 9H), 6.25 (dt, J¼18.4, 5.6 Hz, 0.89H,
major isomer), 6.19 (d, J¼18.8 Hz, 0.89H, major isomer),
5.93–5.96 (m, 0.11H, minor isomer), 5.64–5.66 (d,
J¼2.8 Hz, 0.11H, minor isomer), 2.26 (t, J¼7.8 Hz,
0.22H, minor regioisomer), 2.00–2.08 (m, 1.78H, major
regioisomer), 1.20–1.34 (m, 8H), 0.72–0.84 (m, 3H);
(125 MHz, C D ) d 153.7, 136.3, 136.0, 135.1, 129.3,
127.8, 123.6, 36.9, 31.5, 28.8, 28.4, 22.5, 13.8; IR (film,
cm ) 3068, 2926, 2855, 1615, 1465, 1428, 1187, 1110,
zolium salt, 3a (34 mg, 0.10 mmol), t-BuOK (11 mg,
0
1
.10 mmol), triethoxysilane (0.37 mL, 2.0 mmol), and oct-
-yne (110 mg, 1.00 mmol) were employed to give a 3:1
1
3
mixture of regioisomers triethoxy(oct-1-en-2-yl)silane and
E)-triethoxy(oct-1-enyl)silane (196 mg, 0.72 mmol, 72%),
after column chromatography (SiO , ethyl acetate/hexanes,
C
(
6
6
2
1
ꢀ1
1
:19) as a colorless oil. H NMR (300 MHz, CDCl3)
d 6.38 (dt, J¼18.8, 6.4 Hz, 0.25H, minor regioisomer),
998, 784, 737; HRMS (EI) m/z calculated for C H Si
2
370.2117, found 370.2103(M ).
6 30
+
5
0
.65–5.68 (m, 0.75H, major regioisomer), 5.56–5.59 (m,
.75H, major regioisomer), 5.36 (dt, J¼18.8, 1.6 Hz, minor
regioisomer), 3.77 (q, J¼7.2 Hz, 6H), 2.06–2.12 (m, 2H),
5.3. Crossover reaction
1
9
1
2
.32–1.44 (m, 2H), 1.21–1.27 (m, 6H), 1.18 (t, J¼7.2 Hz,
1
3
H), 0.80–0.86 (m, 3H); C (125 MHz, CDCl ) d 154.0,
3
Ni(COD)2 (3 mg, 0.01 mmol), ligand, 3a (4 mg,
0.01 mmol), and t-BuOK (1 mg, 0.01 mmol) were weighed
in glove box and 1.5 mL THF was added to the mixture
under argon. The dark green solution obtained was stirred
for 10 min at rt. Triethylsilane-d (48 mL, 0.30 mmol) and
tripropylsilane (56 mL, 0.30 mmol) were added simulta-
neously and stirred for 10 more minutes. Alkyne (12 mg,
0.10 mmol) was dissolved in 0.5 mL THF under argon and
was added to the reaction mixture over 20 min via syringe
drive. The progress of the reaction was monitored in 10
and 20 min in GCMS.
43.7, 128.9, 118.6, 58.3, 36.5, 35.9, 31.7, 31.6, 29.0,
8.7, 28.6, 28.1, 22.6, 22.5, 18.2, 18.1, 14.0, 13.9; IR
ꢀ
1
(
(
film, cm ) 2925.8, 1389.5, 1074.7, 956.2, 734.4; HRMS
EI) m/z calculated for C H O Si 274.1964, found
1
4 30 3
+
2
74.1963(M ).
5.2.12. (E)-Triethoxy(oct-1-enyl)silane (13a) and tri-
ethoxy(oct-1-en-2-yl)silane (13b) with 3b. Following the
general procedure, Ni(COD) (28 mg, 0.10 mmol), imida-
2
zolium salt, 3b (43 mg, 0.10 mmol), t-BuOK (11 mg,
0
1
.10 mmol), triethoxysilane (0.37 mL, 2.0 mmol), and oct-
-yne (110 mg, 1.00 mmol) were employed to give a 1:5
5.3.1. Analysis of the crossover experiment. Pure samples
of products derived from Et SiH (MW 232), Et SiD (MW
233), and Pr SiH (MW 274) were independently prepared
3
mixture of regioisomers triethoxy(oct-1-en-2-yl)silane and
E)-triethoxy(oct-1-enyl)silane (192 mg, 0.70 mmol, 70%,
single regioisomer), after column chromatography (SiO ,
3
3
(
and GCMS analysis was performed. Based on the similarity
of the molecular ion regions of the Et SiH and Et SiD-
derived product, the molecular ion region of the Pr SiD-
2
1
ethyl acetate/hexanes, 1:19) as a colorless oil. H NMR
(
3
3
400 MHz, CDCl ) d 6.37 (dt, J¼18.8, 6.4 Hz, 0.83H, major
3
3
regioisomer), 5.64–5.67 (m, 0.17H, minor regioisomer),
.55–5.58 (m, 0.17H, minor regioisomer), 5.35 (dt,
derived product was assumed to appear as the molecular
ion region of the Pr SiH-derived product, shifted by one
5
3
J¼18.8, 1.6 Hz, 0.83H, major regioisomer), 3.77 (m, 6H),
mass unit. Relative peak heights in the molecular ion region
of the spectra of each pure compound were normalized, with
a value of 1 assigned to the base peak.
2
1
1
2
1
.06–2.13 (m, 2H), 1.30–1.40 (m, 2H), 1.12–1.28 (m,
5H), 0.80–0.86 (m, 3H); C (125 MHz, CDCl ) d 154.0,
1
3
3
43.7, 118.6, 59.0, 58.3, 36.5, 31.7, 31.6, 28.7, 28.1, 22.6,
2.5, 18.2, 18.1, 14.0, 13.9; IR (film, cm ) 2925.8,
389.5, 1074.7, 956.2, 734.4; HRMS (EI) m/z calculated
ꢀ
1
In the crude product of an experiment that employed 1 equiv
each of Et SiD and Pr SiH, the ratio of Et Si products to
Pr Si products was determined by GC. From the crude
3
3
3
+
for C H O Si 274.1964, found 274.1963(M ).
3
14
30
3
GCMS, the relative intensity of the 232 and 233 products
were normalized, with the value of 1 assigned to the base
peak. The ratio of the Et Si-(H) product to Et Si-(D) product
5
2
.2.13. (E)-Oct-1-enyltriphenylsilane (14a) and oct-1-en-
-yltriphenylsilane (14b). Following the general procedure
3
3
(
with the modification in silane stoichiometry), Ni(COD)2
was determined as follows:
intensity of 232 peak in crossover experiment
intensity of 233 peak in crossover experiment
½
Xꢃ ꢂ ½rel height of 232 peak in pure Et
Xꢃ ꢂ ½rel height of 233 peak in pure Et
3
3
Si-ðHÞ productꢃ þ ½Yꢃ ꢂ ½rel height of 232 peak in pure Et
Si-ðHÞ productꢃ þ ½Yꢃ ꢂ ½rel height of 233 peak in pure Et
3
3
Si-ðDÞ productꢃ
Si-ðDÞ productꢃ
¼
½
(
0
(
1
28 mg, 0.10 mmol), imidazolium salt, 3a (34 mg,
.10 mmol), t-BuOK (11 mg, 0.10 mmol), triphenylsilane
260 mg, 1.0 mmol in 2 mL THF), and oct-1-yne (110 mg,
.00 mmol) were employed to give a 8:1 mixture of regio-
X ¼ 1/100ꢂrelative % of Et Si-(H) product
3
Y ¼ 1/100ꢂrelative % of Et Si-(D) product ¼ 1ꢀX
3
isomers (E)-oct-1-enyltriphenylsilane and oct-1-en-2-yl-
triphenylsilane (280 mg, 0.74 mmol, 74%), after column
chromatography (SiO , hexanes) as a colorless solid (mp
2
In the above equation, after substitution of [1ꢀX] for [Y],
the experimental values were inserted and the equation
was solved for [X]. The ratio of Pr Si-(H) product to the
3

7566
M. R. Chaulagain et al. / Tetrahedron 62 (2006) 7560–7566
Pr Si-(D) products was determined in a similar fashion.
3
see: (a) Sato, Y.; Sawaki, R.; Mori, M. Organometallics 2001,
20, 5510; (b) Sawaki, R.; Sato, Y.; Mori, M. Org. Lett. 2004, 6,
1131; (c) Ng, S.-S.; Jamison, T. F. J. Am. Chem. Soc. 2005, 127,
7320; (d) Ng, S.-S.; Jamison, T. F. Tetrahedron 2005, 61,
Merging the GC ratios of Et Si products to Pr Si products
3
3
with the data calculated from the above equation, an overall
ratio of the six products were obtained.
1
1405.
. Miller, K. M.; Jamison, T. F. J. Am. Chem. Soc. 2004, 126,
5342.
. For a review, see: Montgomery, J. Angew. Chem., Int. Ed. 2004,
3, 3890.
. For examples of nickel-catalyzed hydrosilylations that employ
phosphine ligands under conditions different from those em-
ployed in our three-component couplings, see: (a) Lappert,
M. F.; Nile, T. A.; Takahashi, S. J. Organomet. Chem. 1974,
6
7
8
Acknowledgements
1
We thank the National Institutes of Health (GM57014) for
support of this research. Beth Knapp-Reed and Kanicha
Sa-ei are thanked for helpful discussions.
4
References and notes
7
2, 425; (b) Tillack, A.; Pulst, S.; Baumann, W.; Baudisch,
1
. (a) Fleming, I.; Dunogues, J.; Smithers, R. Org. React. 1989,
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1
986, 86, 857.
9. For preparation and characterization of nickel complexes of
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10. (a) For examples of 2:1 couplings of alkynes and silanes, see:
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ences therein; (b) For related nickel-catalyzed silaborative
dimerization of alkynes, see: Suginome, M.; Matsuda, T.; Ito,
Y. Organometallics 1998, 17, 5233; (c) For palladium-cata-
lyzed 2:1 couplings of alkynes and silanes, see: Kawanami,
Y.; Yamamoto, K. Synlett 1995, 1232.
11. Yang, L.; Liu, R. S. H.; Wendt, N. L.; Liu, J. J. Am. Chem. Soc.
2005, 127, 9378.
12. Chauhan, M.; Hauck, B. J.; Keller, L. P.; Boudjouk, P.
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13. Cornish, A. J.; Lappert, M. F. J. Organomet. Chem. 1984, 271,
153.
14. Takeuchi, R.; Nitta, S.; Watanabe, D. J. Org. Chem. 1995, 60,
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2
. (a) Hatanaka, Y.; Hiyama, T. Synlett 1991, 845; (b) Denmark,
S. E.; Sweis, R. F. Acc. Chem. Res. 2002, 35, 835.
3
. For a comprehensive overview of hydrosilylations of alkynes,
see: (a) Trost, B. M.; Ball, Z. T. Synthesis 2005, 6, 853; For rep-
resentative additional recent methods, see: (b) Maifeld, S. V.;
Tran, M. N.; Lee, D. Tetrahedron Lett. 2005, 46, 105; (c)
Takahashi, T.; Bao, F.; Gao, G.; Ogasawara, M. Org. Lett.
2003, 5, 3479; (d) Kawanami, Y.; Sonoda, Y.; Mori, T.;
Yamamoto, K. Org. Lett. 2002, 4, 2825.
. (a) Tang, X.-Q.; Montgomery, J. J. Am. Chem. Soc. 1999, 121,
6098; (b) Tang, X.-Q.; Montgomery, J. J. Am. Chem. Soc. 2000,
4
5
122, 6950; (c) Mahandru, G. M.; Liu, G.; Montgomery, J.
J. Am. Chem. Soc. 2004, 126, 3698; (d) Knapp-Reed, B.;
Mahandru, G. M.; Montgomery, J. J. Am. Chem. Soc. 2005,
127, 13156; (e) Oblinger, E.; Montgomery, J. J. Am. Chem.
Soc. 1997, 119, 9065.
. For other three-component couplings involving aldehydes, si-
lanes, and nickel catalysts with N-heterocyclic carbene ligands,