Catalytic hydrosilylation of acetylenes mediated by phosphine complexes of cobalt(I), rhodium(I), and iridium(I)

Article abstract of DOI:10.1016/S0022-328X(03)00582-5

The complexes [Co(PPh₃)₃Cl] (1), [Co(PPh₃)₂(CO)₂Cl] (2), [Co(PMe₃)₃Cl] (3), [Co(PMe₃)₂(CO)₂Cl] (4), [Rh(dppe)(CO)Cl] (5), [Rh(PPh₂Me)₂(CO)Cl] (6), [Ir(dppe)(CO)Br] (7), and [Ir(PPh₂Me)₂ (CO)Cl] (8) catalyse the hydrosilylation of a range of acetylenes including 1-hexyne, phenylacetylene, and 1-phenyl-1-propyne with triethylsilane. In the case of 1-hexyne and 1-phenyl-1-propyne, only the expected hydrosilylation products were observed; however, when the substrate was phenylacetylene, cyclotrimerisation and dimerisation products were observed in addition to the expected vinylsilanes. No hydrosilation was observed with alkene substrates; however, in the presence of some metal complexes, there was double bond migration and cis/trans-isomerisation probably mediated by the formation of metal hydrides in the reaction mixture.

Full text of DOI:10.1016/S0022-328X(03)00582-5

Journal of Organometallic Chemistry 681 (2003) 91Á97
/
www.elsevier.com/locate/jorganchem
Catalytic hydrosilylation of acetylenes mediated by phosphine
complexes of cobalt(I), rhodium(I), and iridium(I)
Leslie D. Field *, Antony J. Ward
School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia
Received 9 January 2003; accepted 29 May 2003
Abstract
The complexes [Co(PPh3)3Cl] (1), [Co(PPh3)2(CO)2Cl] (2), [Co(PMe3)3Cl] (3), [Co(PMe3)2(CO)2Cl] (4), [Rh(dppe)(CO)Cl] (5),
[Rh(PPh2Me)2(CO)Cl] (6), [Ir(dppe)(CO)Br] (7), and [Ir(PPh2Me)2(CO)Cl] (8) catalyse the hydrosilylation of a range of acetylenes
including 1-hexyne, phenylacetylene, and 1-phenyl-1-propyne with triethylsilane. In the case of 1-hexyne and 1-phenyl-1-propyne,
only the expected hydrosilylation products were observed; however, when the substrate was phenylacetylene, cyclotrimerisation and
dimerisation products were observed in addition to the expected vinylsilanes. No hydrosilation was observed with alkene substrates;
however, in the presence of some metal complexes, there was double bond migration and cis/trans-isomerisation probably mediated
by the formation of metal hydrides in the reaction mixture.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Hydrosilation; Iridium; Rhodium; Alkyne; Vinylsilane
1. Introduction
In general, the term ‘hydrosilylation’ is used to
describe an addition reaction of hydrosilanes to double
and triple bonds and, in the laboratory, hydrosilylation
is a very convenient method for the synthesis of a range
of organosilicon compounds. Although hydrosilylation
Organosilicones have proven to be a versatile class of
compounds which have found applications as precursors
to photoresistors, semiconductors, preceramics, reagents
sometimes takes place at high temperatures (ꢀ300 8C)
/
for organic synthesis, bioactive compounds [1Á3], as
/
without any catalyst, the reaction is effectively promoted
by ultraviolet light, g-irradiation, electric discharge and
catalysts such as peroxides, metals, metal salts, metal
complexes, or, in some special cases, by amines. Among
a variety of catalysts that promote the addition of
well as being important industrially where such com-
pounds are employed as adhesives, binders, and cou-
pling agents [4]. Consequently, the synthesis of
organosilicon compounds has become increasingly im-
portant. However, the methods employed to form SiÃ
/C
hydrosilanes to carbonÁcarbon multiple bonds, hexa-
/
bonds are still limited to a few reactions, including
organic halide-based Wurtz-type or Grignard reactions
with halosilanes, hydrosilylation, and the Rochow
process [5].
chloroplatinic acid has been used most commonly.
Group VII and VIII transition metal complexes, such
as tertiary phosphine complexes of nickel, palladium,
platinum and rhodium, are also effective [4,6,7].
The hydrosilylation of various functional groups
catalysed by transition metal complexes provides con-
venient routes to organosilicon compounds. This reac-
tion also serves as a unique and effective method for the
Hydrosilylation is the addition of SiÃ
/
H across an
unsaturated bond such as CÄ
/
C, CÅ
/
C, CÄO, or CÅN.
/
/
Although details of the mechanism are still controver-
sial, transition-metal-catalysed reactions are generally
selective reduction of carbonÁ/heteroatom bonds (in-
rationalised in terms of the ChalkÁHarrod mechanism
/
cluding asymmetric reduction) [4].
[8] in which the alkene, alkyne, carbonyl compound, or
imine initially coordinates to the metal to give a p-
complex, which adds oxidatively to the SiÃ
/
H bond of
* Corresponding author. Fax: ꢀ61-29-357-6650.
/
E-mail address: l.field@chem.usyd.edu.au (L.D. Field).
the hydrosilane. It has also been proposed [9] that the
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00582-5

92
L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á97
/
reaction could proceed via initial oxidative addition of
the hydrosilane to the metal, followed by p-coordination
of the alkene and then by insertion of the p-bound
spectra were recorded on a Bruker AMX400 spectro-
meter or a Bruker DRX400 spectrometer at 400.13 and
100.62 MHz, respectively. In the presentation of NMR
data, chemical shifts (d) are quoted in ppm, the down-
field direction being positive. H-NMR chemical shifts
are referenced to residual solvent resonances.
GC analyses were performed using a Hewlett Packard
moiety into the MÃ/Si bond.
1
Extensive studies of platinum-catalysed hydrosilyla-
tion reactions [8,10] have shown that electron-with-
drawing groups on the hydrosilane increase the rate of
hydrosilylation and electron-donating groups on the
unsaturated moiety accelerate the rate of addition of
hydrosilane [11].
Hydrosilylation of monosubstituted alkynes should
give three isomeric products: b-(Z) 9, b-(E) 10 and a 11
(Scheme 1).
This paper examines the catalytic hydrosilylation of 1-
hexyne, phenylacetylene, and 1-phenyl-1-propyne with
triethylsilane using the metal complexes [Co(PPh3)3Cl]
(1), [Co(PPh3)2(CO)2Cl] (2), [Co(PMe3)3Cl] (3),
5890A gas chromatograph equipped with a splitÁsplit-
/
less capillary inlet and flame ionisation detector. Helium
was used as the carrier gas at a head pressure of 110 kPa.
The column used was an SGE 25QC2/BPX5-0.25. The
profile used was as follows: initial oven temperature
60 8C; initial hold time 2 min; rate 10 8C minꢁ1; final
oven temperature 300 8C; and, final time 20 min.
The metal complexes [Co(PPh3)3Cl] (1) [13],
[Co(PPh3)2(CO)2Cl] (2) [13], [Co(PMe3)3Cl] (3) [14],
[Co(PMe3)2(CO)2Cl] (4) [14], [Rh(dppe)(CO)Cl] (5)
[15], [Rh(PPh2Me)2(CO)Cl] (6) [16], [Ir(dppe)(CO)Br]
(7) [17], and [Ir(PPh2Me)2(CO)Cl] (8) [18] were synthe-
sised following literature methods.
[Co(PMe3)2(CO)2Cl]
(4),
[Rh(dppe)(CO)Cl]
(5),
[Rh(PPh2Me)2(CO)Cl] (6), [Ir(dppe)(CO)Br] (7), and
[Ir(PPh2Me)2(CO)Cl] (8) at 65 8C.
2.1. General protocol for the hydrosilylation of acetylenes
2. Experimental
The hydrosilylation of acetylenes with triethylsilane
was performed using 2 mol% of the metal complex in
THF-d8 (in the case of complexes 4, 5, 6, 7, and 8) and
heating the reaction mixture to 65 8C. For the para-
magnetic metal complexes (1, 2, and 3), the reaction was
heated for 24 h at 65 8C in THF before the solvent was
removed in vacuo, the residue extracted with hexane and
passed through a silica plug, eluting with hexane. In the
case of the hydrosilylation of 1-hexyne and 1-phenyl-1-
propyne, the relative proportion of products was
determined by careful integration of the vinylic reso-
The synthesis and manipulation of the air-sensitive
phosphines and metal complexes was performed under
an inert atmosphere of nitrogen either by performing
reactions in a glove-box (nitrogen atmosphere) or using
standard Schlenk or vacuum-line techniques.
All compressed gases were obtained from B.O.C.
Gases. Nitrogen (ꢀ
(ꢀ99.0%) were used as received without further pur-
ification.
/99.5%) and carbon monoxide
/
Phenylacetylene, 1-hexyne, 1-phenyl-1-propyne, 1-
pentene, cis-2-pentene, trans-2-pentene, and triethylsi-
lane were obtained from Aldrich and distilled immedi-
ately prior to use. Hexane, tetrahydrofuran (THF) and
THF-d8 were distilled from benzophenone over sodium
wire. Deuterated solvents were degassed by three con-
1
nances in the H-NMR spectrum. The relative propor-
tion of products for the hydrosilylation of
phenylacetylene was determined by careful integration
of the 1H-NMR spectrum and by GC analysis. The
assignment for the b-(Z), b-(E), and a-vinylsilanes was
based upon spectroscopic comparison with literature
secutive freezeÁ
/
pumpÁthaw cycles, stored under va-
/
[19Á/21].
cuum in an ampoule, and distilled immediately prior to
use.
Air-sensitive NMR samples were prepared in a
nitrogen-filled glove-box or by vacuum transfer of
solvent on a high vacuum line into an NMR tube fitted
2.2. cis-1-(Triethylsilyl)-1-hexene (9a)
1H-NMR (THF-d8): d 6.48 (dt, 1H, J1,2
ꢂ14.1 Hz,
/
3
1
with a concentric teflon valve [12]. H- and 13C-NMR
3
7.3 Hz), 5.50 (dt, 1H, J1,2
4
14.10 Hz, J1,3
3J2,3
1.30 Hz), 2.24 (m, 2H), 1.49 (m, 2H), 1.08 (m, 14H),
ꢂ
/
ꢂ
/
ꢂ
/
3
0.74 (q, JCH ÃCH
ꢂ7.8 Hz, 6H) ppm.
/
/
2
3
2.3. trans-1-(Triethylsilyl)-1-hexene (10a)
3
1H-NMR (THF-d8): d 6.17 (dt, 1H, J1,2
ꢂ18.6 Hz,
/
3
6.3 Hz), 5.67 (dt, 1H, J1,2
4
18.6 Hz, J1,3
1.50 (m, 2H), 1.06 (m, 14H),
3J2,3
ꢂ
/
ꢂ
/
ꢂ1.5
/
Hz), 2.27 (m, 2H), 1.70Á
/
3
Scheme 1.
0.69 (q, JCH ÃCH
ꢂ/7.8 Hz, 6H) ppm.
/
2
3

L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á
/97
93
2.4. 2-(Triethylsilyl)-1-hexene (11a)
2.12. cis-1-Phenyl-2-(triethylsilyl)-1-propene (17)
2
1H-NMR (THF-d8): d 5.76 (dt, 1H, Jgem
ꢂ
/
3.1 Hz,
1H-NMR (THF-d8): d 7.41Á
/
7.22 (m, 5H, Ph), 6.21 (q,
6.5 Hz, CH Ä), 1.67 (d, 3H,
6.5 Hz, Ä
7.8 Hz, CH3), 0.72 (q, 6H, JCH ÃCH
2
1.6 Hz), 5.42 (dt, 1H, Jgem
4
3.1 Hz, J1,3
4
4J1,3
ꢂ
/
ꢂ
/
ꢂ
/
1.3
1.50 (m, 2H), 1.08 (m, 14H),
1H, JHÃCÄCÃCH
ꢂ
/
/
3
3
Hz), 2.26 (m, 2H), 1.70Á
/
4JHÃCÄCÃCH
ꢂ
/
/
CCH3), 1.04 (t, 9H, JCH Ã
/
3
3
3
3
0.71 (q, JCH ÃCH
ꢂ/7.8 Hz, 6H) ppm.
ꢂ
/
ꢂ
/
7.8 Hz,
/
/
CH2
2
3
3
2
CH2) ppm.
2.13. trans-1-Phenyl-2-(triethylsilyl)-1-propene (18)
2.5. cis-2-(Triethylsilyl)styrene (9b)
3
1H-NMR (THF-d8): d 7.56 (d, 1H, JHCÄCH
Hz, PhCH Ä), 7.38Á
3JHCÄCH
15.4 Hz, Ä
7.8 Hz, CH3), 0.58 (q, 6H, JCH ÃCH
ꢂ
/
15.4
1H-NMR (THF-d8): d 7.41Á
/
7.22 (m, 5H, Ph), 6.88 (q,
1.7 Hz, CH Ä), 2.05 (d, 3H,
CCH3), 1.13 (t, 9H,
/
/
7.29 (m, 5H, Ph), 5.87 (d, 1H,
CH(SiEt3)), 0.91 (t, 9H,
4
1H, JHÃCÄCÃCH
ꢂ
/
/
3
3
ꢂ
/
/
J
/
CH2Ã
4
3
J
ꢂ
/
1.7 Hz, Ä
/
J
CH3Ã
3
/
HÃCÄCÃCH3
ꢂ
/
ꢂ
/
7.8 Hz,
/
CH3
3
2
3
ꢂ
/
7.8 Hz, CH3), 0.84 (q, 6H, JCH ÃCH
ꢂ7.8 Hz,
/
/
CH2
3
2
CH2) ppm.
CH2) ppm.
2.6. trans-2-(Triethylsilyl)styrene (10b)
2.14. General protocol for the hydrosilylation of alkenes
1H-NMR (THF-d8): d 7.38Á
/
7.29 (m, 5H, Ph), 7.10 (d,
15.4 Hz, PhCH Ä), 6.56 (d, 1H,
15.4 Hz, ÄCH(SiEt3)), 1.01 (t, 9H,
7.8 Hz, CH3), 0.58 (q, 6H, J ꢂ7.8 Hz,
The hydrosilylation of alkenes was attempted using 2
3
1H, JHCÄCH
ꢂ
/
/
mol% of the metal complexes 1Á8 in THF-d8 and
/
3JHCÄCH
ꢂ
/
/
J
CH2Ã
3
/
heating the reaction mixture at 65 8C. When the para-
magnetic metal complexes were used, the volatiles were
removed by trap-to-trap distillation under reduced
3
ꢂ
/
/
/
CH3
CH2ÃCH3
CH2) ppm.
pressure into an NMR tube at ꢁ180 8C. The ratio of
/
cis-2-pentene to trans-2-pentene was determined by
2.7. 1-(Triethylsilyl)styrene (11b)
1
careful integration of equivalent peaks in the H-NMR
spectrum.
1H-NMR (THF-d8): d 7.38Á
7.29 (m, 5H, Ph), 5.98 (d,
/
2
2
1H, JHÃCÃH
ꢂ
/
3.1 Hz, Ä
/
CH2), 5.70 (d, 1H, JHÃCÃH
ꢂ
/
3
3.1 Hz, Ä
0.70 (q, 6H, JCH ÃCH
/
CH2), 0.98 (t, 9H, JCH ÃCH
ꢂ7.8 Hz, CH3),
/
/
2
3
3
3. Results and discussion
ꢂ7.8 Hz, CH2) ppm.
/
/
2
3
3.1. Hydrosilyation of 1-hexyne
2.8. 1,2,4-Triphenylbenzene (13)
Table 1 summarises the hydrosilation of 1-hexyne
with triethylsilane catalysed by a range of metal com-
plexes. The hydrosilylation of 1-hexyne resulted in the
formation of three isomeric vinylsilanes, b-(Z) 9a, b-(E)
10a, and a-11a (Scheme 1).
This product was identified and characterised by GC/
MS.
2.9. 1,3,5-Triphenylbenzene (14)
The cobalt complexes studied were, in general,
ineffective as catalysts for the hydrosilylation of 1-
hexyne. The only Co complex which displayed any
catalytic activity was [Co(PPh3)(CO)2Cl] (2) which
formed the b-(E)- and b-(Z)-vinylsilanes exclusively;
however, the yield was only 8% (two turnovers) after 24
h at 65 8C (Entry 2, Table 1).
3
1H-NMR (THF-d8): d 7.97 (s, 3H), 7.88 (d, Jꢂ
/
7.40
7.40 Hz,
Hz, 6H), 7.57 (t, 3Jꢂ
/
7.40 Hz, 6H), 7.46 (t, 3Jꢂ
/
3H) ppm. 13C{1H}-NMR (THF-d8): d 144.5, 143.3,
130.8, 129.4, 129.3, 126.9 ppm.
2.10. trans-1,4-Diphenylbut-3-en-1-yne (15)
The rhodium complexes, [Rh(dppe)(CO)Cl] (5) and
[Rh(PPh2Me)2(CO)Cl] (6), proved effective catalysts for
the hydrosilylation of 1-hexyne. In the case of
[Rh(dppe)(CO)Cl] (5), only 79% of the 1-hexyne was
converted to products after 20 h at 65 8C, with the major
product being the b-(Z)-vinylsilane (Entry 5, Table 1).
Complete conversion to products was achieved, after
54 h at 65 8C, when [Rh(PPh2Me)2(CO)Cl] (6) was used
as the catalyst (Entry 6, Table 1). In this case the major
product was the b-(Z)-vinylsilane, with no a-isomer
observed.
1H-NMR (THF-d8): d 7.56 (m, 6H, Ph), 7.43 (m, 4H,
3
Ph), 7.15 (d, J1,2
ꢂ
/
16.2 Hz, 1H, CH Ã
/
CÅ
/
), 6.60 (d,
3J1,2
(THF-d8): d 143.4, 138.7, 133.4, 130.7, 130.6, 130.4,
ꢂ
/
16.2 Hz, 1H, PhÃ
/
CÄCH Ã
/
/
) ppm. 13C{1H}-NMR
130.1, 128.3, 125.8, 110.1, 93.5, 91.0 ppm.
2.11. cis-1,4-Diphenylbut-3-en-1-yne (16)
This product was identified by GC/MS.

94
L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á97
/
Table 1
Distribution of products obtained from the catalytic hydrosilylation of 1-hexyne with triethylsilane at 65 8C
a
Entry
Catalyst
Time
(h)
Yield b
(%)
Vinylsilanes (%)
12
(%)
b-(Z) 9a
b-(E) 10a
a-11a
1
2
3
4
5
6
7
8
[Co(PPh3)3Cl] (1)
[Co(PPh3)2(CO)2Cl] (2)
[Co(PMe3)3Cl] (3)
24
24
24
24
20
54
20
36
0
8
0
0
0
5
0
3
0
0
0
0
0
0
0
[Co(PMe3)2(CO)2Cl] (4)
[Rh(dppe)(CO)Cl] (5)
[Rh(PPh2Me)2(CO)Cl] (6)
[Ir(dppe)(CO)Br] (7)
[Ir(PPh2Me)2(CO)Cl] (8)
0
0
0
0
0
79
100
100
100
38
71
53
12
19
25
35
65
19
0
3
5
7
10
6
13
a
All reactions were performed using 2 mol% of catalyst.
Yields based on 1-hexyne.
b
The most effective catalyst for the hydrosilylation of
1-hexyne was the complex [Ir(dppe)(CO)Br] (7), which
achieved complete conversion of the 1-hexyne to hydro-
silated products after 20 h at 65 8C, and producing the
b-(Z)-vinylsilane as the major product (Entry 7, Table
1). The complex [Ir(PPh2Me)2(CO)Cl] (8) also proved
effective, producing the b-(E)-isomer as the major
product (Entry 8, Table 1).
formed by the oxidative addition of hydrosilane, can
eliminate a chlorosilane to form an iridium (or rhodium)
hydride (20) which could directly trap the terminal
acetylene or react with excess hydrosilane to form the
dihydridosilyliridium(III) complex 21 [22]. The forma-
tion of an iridium or rhodium hydride in the reaction
medium provides the avenue for reduction of the
terminal alkyne to compete with hydrosilation. An
iridium complex 22 (analogous to 21) has been observed
The trans-complexes, [Rh(PPh2Me)2(CO)Cl] (6) and
[Ir(PPh2Me)2(CO)Cl] (8), display greater stereoselectiv-
ity than their cis-analogues, [Rh(dppe)(CO)Cl] (5) and
[Ir(dppe)(CO)Br] (7). In the case of the rhodium
complexes, both 5 and 6 favoured the formation of the
b-(Z)-vinylsilane 9a: complex 5 achieved 38% conver-
sion to 9a, while the trans complex 6 achieved 71%
conversion. In the case of the iridium complexes, the
stereospecificities are different: the cis-complex 7 pro-
duces the b-(Z)-vinylsilane 9a as the major product,
whereas the trans-complex 8 primarily produces the
trans-vinylsilane 10a.
The reduction of 1-hexyne to 1-hexene (12) was also
observed with rhodium and iridium catalysts. This
product can be rationalised by the possible formation
of rhodium or iridium dihydrides by the stepwise
addition of two equivalents of silane to starting metal
complexes (Scheme 2). The hydridosilyl complex (19),
in the reaction of [Ir(dppe)(CO)X] (XꢂCl, Br) with
triethylsilane [23].
/
3.2. Hydrosilylation of phenylacetylene
Table 2 summarises the hydrosilation of phenylace-
tylene with triethylsilane catalysed by a range of metal
complexes. The hydrosilylation of phenylacetylene re-
sulted in the formation of three isomeric vinylsilanes, b-
(Z) 9b, b-(E) 10b, and a-11b (Scheme 1). However, there
were also two other competing reaction pathways: the
cyclotrimerisation of the phenylacetylene to form 1,2,4-
triphenylbenzene (13) and 1,3,5-triphenylbenzene (14)
(Scheme 3); and the tail-to-tail dimerisation of the
phenylacetylene to form trans-1,4-diphenylbut-1-en-3-
yne (15) and cis-1,4-diphenylbut-1-en-3-yne (16)
(Scheme 4) [24].
Of the cobalt complexes examined, the most effective
hydrosilylation catalyst was [Co(PPh3)(CO)2Cl] (2)
which converted all of the phenylacetylene substrate to
products after 24 h at 65 8C. Vinylsilanes comprised 79%
of the product mixture with the a-vinylsilane being the
major product (Entry 2, Table 2). The other cobalt
Scheme 2.

L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á
/97
95
Table 2
Distribution of products obtained from the catalytic hydrosilylation of phenylacetylene with triethylsilane
a
Entry Catalyst
Temperature Time Yield b Vinylsilanes (%)
Triphenylbenzenes (%)
Dimers (%)
trans 15 cis 16
(8C)
(h)
(%)
b-(Z) 9b b-(E) 10b a-11b 1,2,4- 13
1,3,5- 14
1
2
[Co(PPh3)3Cl] (1)
[Co(PPh3)2(CO)2Cl] (2)
[Co(PMe3)3Cl] (3)
65
65
65
65
40
65
80
65
65
65
24
24
24
18
24
16
4
100
100
100
89
6
5
1
1
10
18
19
56
0
0
1
1
1
1
2
3
1
1
8
21
19
7
57
1
B
/
1
1
1
B
/
3
B
B/
/
B/1
B/1
78
76
B
/
4
[Co(PMe3)2(CO)2Cl] (4)
[Rh(dppe)(CO)Cl] (5)
[Rh(dppe)(CO)Cl] (5)
[Rh(dppe)(CO)Cl] (5)
[Rh(PPh2Me)2(CO)Cl] (6)
[Ir(dppe)(CO)Br] (7)
[Ir(PPh2Me)2(CO)Cl] (8)
2
B/1
B
B/
/
13
3
5
100
100
100
100
100
100
41
48
51
4
22
21
20
19
67
10
29
23
18
45
14
62
5
B/
1
0
0
6
6
1
7
9
B/
1
3
1
1
8
18
16
18
8
19
0
9
10
19
28
B
/
B/1
B
/
B/
B/1
B/
1
B/
a
All reactions were performed using 2 mol% of catalyst.
Yields based on phenylacetylene.
b
however, the proportion of the b-(Z)-isomer 9b in-
creased with increasing temperature with a correspond-
ing systematic decrease in the amount of the a-isomer
11b formed. The proportion of the b-(E)-isomer 10b
formed remained relatively constant with temperature.
The complexes [Rh(PPh2Me)2(CO)Cl] (6) and
[Ir(PPh2Me)2(CO)Cl] (8) also effectively catalysed the
hydrosilylation of phenylacetylene. Both complexes
achieved complete conversion to products within 18 h
at 65 8C. When [Rh(PPh2Me)2(CO)Cl] (6) was used, the
major product was the a-vinylsilane 11b; however,
dimerisation and cyclotrimerisation products comprised
33% of the product mixture (Entry 8, Table 2). The
complex [Ir(PPh2Me)2(CO)Cl] (8) converted 99% of the
phenylacetylene to vinylsilanes, with 11b being the
major product (Entry 10, Table 2).
Scheme 3.
Scheme 4.
3.3. Hydrosilylation of 1-phenyl-1-propyne
complexes produced trans-1,4-diphenylbut-1-en-3-yne
(15) as the major product. In the case of [Co(PMe3)3Cl]
(3) and [Co(PMe3)2(CO)2Cl] (4), only traces of the
hydrosilylation products were identified (Entries 3 and
4, Table 2).
The most effective catalysts for hydrosilation of
phenylacetylene were the complexes [Rh(dppe)(CO)Cl]
(5) and [Ir(dppe)(CO)Br] (7). At 65 8C both complexes
achieved total conversion of the phenylacetylene to
products after 16 h: complex 5 producing the b-(Z)-
vinylsilane 9b as the major product (Entry 6, Table 2),
while complex 7 formed the b-(E)-vinylsilane 10b as the
predominant product (Entry 9, Table 2). With these
catalysts, only traces of dimerisation and cyclotrimer-
isation products were observed.
Table 3 summarises the hydrosilation of 1-phenyl-1-
propyne with triethylsilane catalysed by a range of metal
complexes. 1-Phenyl-1-propyne is a non-terminal acet-
ylene and the hydrosilylation with triethylsilane can
result in the formation of four possible vinylsilanes, b-
(Z) 17, b-(E) 18, a-(Z) 23, and a-(E) 24 (Scheme 5).
When the cobalt complexes [Co(PPh3)3Cl] (1),
[Co(PPh3)2(CO)2Cl] (2), [Co(PMe3)3Cl] (3), and [Co(P-
Me3)2(CO)2Cl] (4), and the rhodium complex
[Rh(PPh2Me)2(CO)Cl] (6) were heated for 24 h at
65 8C in the presence of 1-phenyl-1-propyne with
triethylsilane, no reaction was observed. Similarly, the
complex [Ir(PPh2Me)2(CO)Cl] (8) showed little activity,
achieving only a 3% yield of vinylsilanes after 36 h at
65 8C (Entry 8, Table 3). This is probably due to the fact
that the internal triple bond is inherently more crowded
and this reduces the reactivity of the alkyne.
Catalytic reactions with [Rh(dppe)(CO)Cl] (5) were
also performed at 40 8C and 80 8C to establish the effect
of varying temperature (Entries 5, 6, and 7, Table 2). In
all cases, the b-(Z)-isomer 9b was the major product;
The most effective catalyst for the hydrosilylation of
1-phenyl-1-propyne with triethylsilane was the rhodium

96
L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á97
/
Table 3
Distribution of products obtained from the hydrosilylation of 1-phenyl-1-propyne with triethylsilane at 65 8C
a
Entry
Catalyst
Time (h)
Yield (%)
Vinylsilanes (%)
17
18
1
2
3
4
5
6
7
8
[Co(PPh3)3Cl] (1)
[Co(PPh3)2(CO)2Cl] (2)
[Co(PMe3)3Cl] (3)
24
24
24
24
20
24
54
36
0
0
0
0
0
0
0
0
0
[Co(PMe3)2(CO)2Cl] (4)
[Rh(dppe)(CO)Cl] (5)
[Rh(PPh2Me)2(CO)Cl] (6)
[Ir(dppe)(CO)Br] (7)
[Ir(PPh2Me)2(CO)Cl] (8)
0
0
0
100
0
38
0
62
0
54
3
37
2
17
1
a
2 mol% of the metal complex was used.
When [Co(PMe3)4Cl] (3) was used as the catalyst, the
ratio of 25:26 was 58:42 (24 h; 65 8C). After additional
heating (24 h; 65 8C) the ratio remained unchanged.
After 24 h at 65 8C, complex 5 achieved the ratio of
25:26 of 22:78, while a ratio of 28:72 was obtained when
7 was used. Similar ratios of 25 and 26 were obtained
over the same time period when the complexes 6 and 8
were used. A trace of 1-pentene was still present in the
reaction mixtures after heating for 36 h, irrespective of
the metal complex employed and this probably reflects
an equilibration between all of the isomers of pentene.
The triethylsilane remained unreacted throughout the
course of the reactions.
Scheme 5.
complex [Rh(dppe)(CO)Cl] (5), where 100% conversion
to vinylsilanes was achieved at 65 8C in 20 h. In this
case, only the b-(Z) 17 and b-(E) 18 vinylsilanes were
observed in yields of 38 and 62%, respectively (Entry 5,
Table 3). The iridium analogue, [Ir(dppe)(CO)Br] (7),
afforded a 54% yield of vinylsilanes after 54 h at 65 8C,
with only the b-(Z) 17 and b-(E)-vinylsilanes 18
observed (Entry 7, Table 3).
The
[Rh(dppe)(CO)Cl] (5) in the presence of triethylsilane
isomerisation
of
cis-2-pentene
by
(40 h; 65 8C), afforded a ratio of 25:26 of 16:84 with a
trace of 1-pentene (B1%). When the same isomerisation
/
was performed using 7, the ratio of 25:26 was 27:73 with
ca. 2% 1-pentene after 72 h. The isomerisation of trans-
2-pentene by [Rh(dppe)(CO)Cl] (5) under the same
conditions (72 h, 65 8C) resulted in a 25:26 ratio of
12:88 with the formation of B
complex [Ir(dppe)(CO)Br] (7) produced a ratio of
25:26 of 5:95 with only a trace of 1-pentene (B1%).
The isomerisation of alkenes will result in the forma-
tion of the thermodynamically more favourable trans-
isomer. In the isomerisation of 2-pentenes, the rhodium
/
1% 1-pentene; the
3.4. Attempted hydrosilylation of 1-pentene
/
When the hydrosilylation of 1-pentene was attempted
in the presence of the complexes [Co(PPh3)3Cl] (1),
[Co(PPh3)2(CO)2Cl] (2), and [Co(PMe3)2(CO)2Cl] (4) no
reaction was observed after 24 h at 65 8C.
complexes
[Rh(dppe)(CO)Cl]
(5)
and
When
the
complexes
[Co(PMe3)4Cl]
(3),
[Rh(PPh2Me)2(CO)Cl] (6) display a greater turnover
rate than the iridium complexes [Ir(dppe)(CO)Br] (7)
and [Ir(PPh2Me)2(CO)Cl] (8), based upon the rate of
conversion of cis-2-pentene to the thermodynamically
more favoured trans-2-pentene. Complex 5 shows the
lowest cis:trans ratio of 2-pentenes for the isomerisation
of 1-pentene after 24 h.
When the metal complexes, [Rh(dppe)(CO)Cl] (5) or
[Ir(dppe)(CO)Br] (7), was added to 1-pentene (in the
absence of triethylsilane) no isomerisation was observed
after 3 days at 65 8C. It is most likely that a metal
hydride such as 20, formed by the reduction of the metal
halide by the silane, is the critical intermediate in the
[Rh(dppe)(CO)Cl] (5), [Rh(PPh2Me)2(CO)Cl] (6),
[Ir(dppe)(CO)Br] (7), and [Ir(PPh2Me)2(CO)Cl] (8)
were used to mediate the hydrosilylation of alkenes,
no hydrosilylation products were detected after 24 h at
65 8C. However, the isomerisation of 1-pentene to a
mixture of cis-2-pentene 25 and trans-2-pentene 26 was
observed (Scheme 6).
Scheme 6.

L.D. Field, A.J. Ward / Journal of Organometallic Chemistry 681 (2003) 91Á
/97
97
isomerisation and that bond migration occurs by
reversible hydride addition/elimination to the metal
centre [25].
References
[1] R. West, J. Organomet. Chem. 300 (1986) 327.
[2] E.W. Colvin, Silicon in Organic Synthesis, Butterworth, London,
1981.
[3] R.J. Fessenden, J.S. Fessenden, Adv. Organomet. Chem. 18
(1980) 275.
4. Conclusions
[4] I. Ojima, in: S. Patai, Z. Rappoport (Eds.), The Chemistry of
Organic Silicon Compounds, Wiley, London, 1989 (Chapter 25).
[5] T. Sakakura, Y. Tokunaga, T. Sodeyama, M. Tanaka, Chem.
Lett. (1987) 2375.
A range of metal complexes in the CoÃ
/
RhÃ/Ir triad
were examined for their ability to catalyse the thermal
hydrosilylation of acetylenes with triethylsilane. The
most effective complex examined was the rhodium
complex [Rh(dppe)(CO)Cl] (5) which successfully cata-
lysed the hydrosilation of both terminal and non-
terminal acetylenes and both aliphatic and aromatic
acetylenes. In general, cobalt complexes examined
exhibited much less catalytic activity for hydrosilylation
of acetylenes, than the corresponding rhodium and
iridium compounds, although for aromatic acetylenes
the cobalt complexes were more effective in catalysing
competitive dimerisation and cyclotrimerisation pro-
cesses.
[6] J.A. Reichl, D.H. Berry, Adv. Organomet. Chem. 43 (1998) 197.
[7] T. Hiyama, T. Kusumoto, in: I. Fleming (Ed.), Comprehensive
Organic Synthesis, vol. 8, Pergamon Press, Oxford, 1991.
[8] (a) J.F. Harrod, A.J. Chalk, J. Am. Chem. Soc. 86 (1964) 1776;
(b) A.J. Chalk, J.F. Harrod, J. Am. Chem. Soc. 87 (1965) 16;
(c) J.F. Harrod, A.J. Chalk, J. Am. Chem. Soc. 87 (1965) 1133;
(d) J.F. Harrod, A.J. Chalk, J. Am. Chem. Soc. 88 (1966) 3491.
[9] (a) I. Ojima, K. Hidai, Asymmetric hydrosilylation and hydro-
carbonylation, in: J.D. Morrison (Ed.), Asymmetric Synthesis,
vol. 5, Academic Press, New York, 1985 (Chapter 4);
(b) M.A. Schroeder, M.S. Wrighton, J. Organomet. Chem. 128
(1977) 345;
(c) M. Brookhart, B.E. Grant, J. Am. Chem. Soc. 115 (1993)
2151;
(d) Y. Wakatsuki, H. Yamazaki, M. Nakano, Y. Yamamoto, J.
Chem. Soc. Chem. Commun. (1991) 703.
None of the complexes examined successfully hydro-
silylated alkenes; however, the complexes [Co(PMe3)3Cl]
(3), [Rh(dppe)(CO)Cl] (5), [Rh(PPh2Me)2(CO)Cl] (6),
[Ir(dppe)(CO)Br] (7), and [Ir(PPh2Me)2(CO)Cl] (8) were
effective catalysts for the isomerisation of alkenes.
Alkene isomerisation only occurs in the presence of
the silyl hydride and the active isomerisation catalyst is
probably a metal hydride formed in situ from the
reaction between the metal complex and the silane.
In this study, the range of metal complexes examined
as potential catalysts for alkyne hydrosilation was
limited and the reaction conditions were generally not
optimised. However, the results obtained demonstrate
that the product distribution is sensitive to changes in
the metal catalyst as well as reaction conditions and this
lays the foundation for work both searching out better
catalyst systems and optimising reaction conditions
towards desired product distributions.
[10] A.J. Chalk, J.F. Harrod, in: I. Wender, P. Pino (Eds.), Organic
Synthesis via Metal Carbonyls, Wiley, New York, 1977, p. 673.
[11] V.D. Sheludyakov, et al., Zh. Obshch. Khim. 55 (1985) 1544.
[12] Purchased from J. Young Ltd, Cat. No. VNMR/5.
[13] M. Aresta, M. Rossi, A. Sacco, Inorg. Chim. Acta 3 (1969) 227.
[14] (a) H.-F. Klein, Angew. Chem. Int. Ed. Engl. 10 (1971) 343;
(b) H.-F. Klein, H.H. Karsch, Inorg. Chem. 14 (1975) 473.
[15] A.R. Sanger, J. Chem. Soc. Dalton Trans. (1977) 120.
[16] S.E. Boyd, L.D. Field, T.W. Hambley, M.G. Partridge, Organo-
metallics 12 (1993) 1720.
[17] (a) B.J. Fisher, R. Eisenberg, Inorg. Chem. 23 (1984) 3216;
(b) C.E. Johnson, R. Eisenberg, J. Am. Chem. Soc. 107 (1985)
3148.
[18] (a) J.P. Collman, J.W. Kang, J. Am. Chem. Soc. 89 (1967) 844;
(b) L.D. Field, E.T. Lawrenz, A.J. Ward, Polyhedron 18 (1999)
3031.
[19] M.A. Esteruelas, M. Oliva´n, L.A. Oro, J.I. Tolosa, J. Organomet.
Chem. 487 (1995) 143.
[20] I. Ojima, N. Clos, R.J. Donovan, P. Ingallina, Organometallics 9
(1990) 3127.
[21] S. Elgafi, Ph.D. Thesis, University of Sydney, 1996.
[22] See for example: (a) M.A. Bennett, R. Charles, P.J. Fraser, Aust.
J. Chem. 30 (1977) 1201. (b) F. Glocking, M.D. Wilbey, J. Chem.
Soc. (A) (1970) 1675. (c) F. Glocking, G.J. Irwin, Inorg. Chim.
Acta 6 (1972) 355. (d) J. Chalk, J. Chem. Soc. Chem. Commun.
(1969) 1207.
Acknowledgements
[23] C.E. Johnson, R. Eisenberg, J. Am. Chem. Soc. 107 (1985) 6531.
[24] L.D. Field, A.J. Ward, Aust. J. Chem. 52 (1999) 1085.
[25] (a) R.H. Crabtree, The Organometallic Chemistry of the Transi-
tion Metals, Wiley, New York, 1988;
We gratefully acknowledge financial support from the
Australian Research Council and the Australian Gov-
ernment for an Australian Postgraduate Award (AJW).
We also thank Johnson Matthey Pty. Ltd for the
generous loan of rhodium and iridium salts.
(b) S.G. Davies, Organotransition Metal Chemistry: Applications
to Synthesis, Pergamon Press, Oxford, 1982.