Catalytic hydrosilylation of terminal alkynes promoted by organoactinides

Article abstract of DOI:10.1021/om990655c

Organoactinide complexes of the type Cp*₂AnMe₂ (An = Th, U) have been found to be efficient catalysts for the hydrosilylation of terminal alkynes. The chemoselectivity and regiospecificity of the reactions depend strongly on the nature of the catalyst, the nature of the alkyne, the silane substituents, the ratio between the silane and alkyne, the solvent, and the reaction temperature. The hydrosilylation reaction of the terminal alkynes with PhSiH₃ at room temperature produces the trans-vinylsilane as the major product along with the silylalkyne and the corresponding alkene. At higher temperatures (50-80°C), besides the products obtained at room temperature, the cis-vinylsilane and the double-hydrosilylated alkene, in which the two silicon moieties are connected at the same carbon atom, are obtained. The catalytic hydrosilylation of (TMS)C≡CH and PhSiH₃ with Cp*₂ThMe₂ was found to proceed only at higher temperatures, although no cis-vinylsilane or double-hydrosilylated products were observed. When the catalytic hydrosilylation reaction is carried out using a 1:2 ratio of ⁱPrC≡CH to PhSiH₃ with Cp*₂ThMe₂, the yield of the double-hydrosilylated product is increased from 6 to 26%. When the same reaction is conducted using a 2:1 ratio between ⁱPrC≡CH and PhSiH₃, the alkene was found to be the major product with the concomitant formation of the tertiary silane ⁱPrCH≡CHSi(HPh)(C≡CPrⁱ). For bulky silanes, nonselective alkyne oligomerization and trace amounts of the hydrosilylation products were produced. Mechanistic studies on the hydrosilylation of ⁱPrC≡CH and PhSiH₃ in the presence of Cp*₂ThMe₂ show that the first step in the catalytic cycle is the insertion of an alkyne into a thorium-hydride bond. A delicate balance between alkyne protonolysis and σ-bond metathesis by the silane determines the ratio among the vinylsilanes, the double-hydrosilylated product, the silylalkyne, and the alkene. The kinetic rate law is first order in organoactinide, silane, and alkyne, with ΔH?= 6.3(3) kcal mol^-1 and ΔS? = -51.1(5) eu. The turnover-limiting step is the release of the hydrosilylated product from the alkenyl-actinide complex. The key organoactinide intermediates for the cis-vinylsilane and the double-hydrosilylation products are the Cp*₂An(C≡CR)(C(PhSiH₂)=CHR) (An = Th, U) complexes. These complexes have been trapped (for R = ⁱPr) and characterized by spectroscopic methods and water poisoning experiments. A plausible mechanistic scenario is proposed for the hydrosilylation of terminal alkynes.

Full text of DOI:10.1021/om990655c

4724
Organometallics 1999, 18, 4724-4741
Ca ta lytic Hyd r osilyla tion of Ter m in a l Alk yn es P r om oted
by Or ga n oa ctin id es
Aswini K. Dash, J i Quan Wang, and Moris S. Eisen*
Department of Chemistry and Institute of Catalysis Science and Technology, Technion-Israel
Institute of Technology, Haifa 32000, Israel
Received August 13, 1999
Organoactinide complexes of the type Cp*2AnMe2 (An ) Th, U) have been found to be
efficient catalysts for the hydrosilylation of terminal alkynes. The chemoselectivity and
regiospecificity of the reactions depend strongly on the nature of the catalyst, the nature of
the alkyne, the silane substituents, the ratio between the silane and alkyne, the solvent,
and the reaction temperature. The hydrosilylation reaction of the terminal alkynes with
PhSiH3 at room temperature produces the trans-vinylsilane as the major product along with
the silylalkyne and the corresponding alkene. At higher temperatures (50-80 °C), besides
the products obtained at room temperature, the cis-vinylsilane and the double-hydrosilylated
alkene, in which the two silicon moieties are connected at the same carbon atom, are obtained.
The catalytic hydrosilylation of (TMS)CtCH and PhSiH3 with Cp*2ThMe2 was found to
proceed only at higher temperatures, although no cis-vinylsilane or double-hydrosilylated
products were observed. When the catalytic hydrosilylation reaction is carried out using a
i
1:2 ratio of PrCtCH to PhSiH3 with Cp*2ThMe2, the yield of the double-hydrosilylated
product is increased from 6 to 26%. When the same reaction is conducted using a 2:1 ratio
i
between PrCtCH and PhSiH3, the alkene was found to be the major product with the
concomitant formation of the tertiary silane iPrCHtCHSi(HPh)(CtCPri). For bulky silanes,
nonselective alkyne oligomerization and trace amounts of the hydrosilylation products were
produced. Mechanistic studies on the hydrosilylation of iPrCtCH and PhSiH3 in the presence
of Cp*2ThMe2 show that the first step in the catalytic cycle is the insertion of an alkyne into
a thorium-hydride bond. A delicate balance between alkyne protonolysis and σ-bond
metathesis by the silane determines the ratio among the vinylsilanes, the double-
hydrosilylated product, the silylalkyne, and the alkene. The kinetic rate law is first order in
organoactinide, silane, and alkyne, with ∆Hq) 6.3(3) kcal mol-1 and ∆Sq ) -51.1(5) eu. The
turnover-limiting step is the release of the hydrosilylated product from the alkenyl-actinide
complex. The key organoactinide intermediates for the cis-vinylsilane and the double-
hydrosilylation products are the Cp*2An(CtCR)(C(PhSiH2)dCHR) (An ) Th, U) complexes.
These complexes have been trapped (for R ) iPr) and characterized by spectroscopic methods
and water poisoning experiments. A plausible mechanistic scenario is proposed for the
hydrosilylation of terminal alkynes.
In tr od u ction
ever, examples of organoactinide-catalyzed reactions are
still limited to C-H activation11 and hydrogenation,12
and recently we have studied the hydroamination,13
oligomerization, and selective dimerization of alkynes.14
The metal-catalyzed hydrosilylation reaction, which is
During the past decade, the chemistry of electrophilic
d0/fn lanthanide and actinide organometallic compounds
has been under intense investigation, reaching a high
level of sophistication.1,2 This broad interest originates
from the novelty in their structure-reactivity relation-
ships and the capacious opportunities in using these
compounds, especially as homogeneous catalysts in
demanding chemical transformations. For organolan-
thanides, many catalytic processes are known;3-10 how-
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dimerization, oligomerization, or polymerization, see: (a) Boff, L. S.;
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DeCoster, P. M.; Greaves, J . Macromolecules 1995, 28, 7929. (c)
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10.1021/om990655c CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/13/1999

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4725
the addition of a Si-H bond across a carbon-carbon
multiple bond, is one of the most important reactions
in organosilicon chemistry and has been studied exten-
sively for half a century. The hydrosilylation reaction
has been used in the industrial production of organo-
silicon compounds (adhesives, binders, and coupling
agents) and in research laboratories as an efficient route
for the syntheses of a variety of organosilicon com-
pounds, silicon-based polymers, and new types of den-
drimeric materials.15 Since the discovery of Speier’s
catalyst (H2PtCl6/iPrOH) in 1957,16 catalytic asymmetric
hydrosilylation, applied to organic syntheses, and new
reactions related to hydrosilylation have been discovered
and developed, mainly using late-transition-metal
complexes.15,17-18 More recently, metallocene complexes
of either group 3 or 4, which exhibit distinctive features
in comparison to late-transition-metal complexes, have
been reported to catalyze the hydrosilylation reactions
of unsaturated hydrocarbons very effectively.6,19
compounds are considered to be important building
blocks in organic synthesis.20 For examples, electrophilic
substitutions of the silyl moiety on vinylsilanes have
been used for the stereoselective synthesis of substituted
alkenes.20 The heteroatom-substituted silyl moiety on
vinylsilane provides a method for functional group
transformation, as in the synthesis of phenylacetalde-
hyde from cis-PhCHdCHSi(OEt)2.21 The syntheses of
vinylsilanes have been extensively studied, and one of
the most convenient and straightforward methods is the
hydrosilylation of alkynes.20,22 In general, hydrosilyla-
tion of terminal alkynes produces three different iso-
mers, cis, trans, and geminal, as a result of both 1,2-
(syn and anti) and 2,1-additions, respectively, as shown
in eq 1. The distribution of the products is found to vary
The versatile and rich chemistry of vinylsilanes has
attracted considerable attention in recent years as these
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T. J . J . Am. Chem. Soc. 1998, 120, 4871. (b) Li, Y.; Marks, T. J . J . Am.
Chem. Soc. 1996, 118, 9295. (c) Li, Y.; Marks, T. J . Organometallics
1996, 15, 3770. (d) Li, Y.; Marks, T. J . J . Am. Chem. Soc. 1996, 118,
707 and references therein.
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Chem. Soc. 1995, 117, 7157. (b) Schumann, H.; Keitsch, M. R.;
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559, 181. (c) Molander, G. A.; Dowdy, E. D.; Noll, B. C. Organometallics
1998, 17, 3754. (d) Onozawa, S.; Sakakura, T.; Tanaka, M. Tetrahedron
Lett. 1994, 35, 8177.
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J . Macromolecules 1994, 27, 4625.
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activation processes, see: (a) Smith, G. M.; Carpenter, J . D.; Marks,
T. J . J . Am. Chem. Soc. 1986, 108, 6805. (b) Fendrick, C. M.; Schertz,
L. D.; Day, V. W.; Marks, T. J . J . Am. Chem. Soc. 1988, 7, 1828.
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nometallics 1996, 15, 3773. (b) Straub, T.; Frank, W.; Reiss, G. J .;
Eisen. M. S. J . Chem. Soc., Dalton Trans. 1996, 2541.
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Chem. Soc. 1995, 117, 6364. (b) Haskel, A.; Straub, T.; Dash, A. K.;
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J . Q.; Straub, T.; Gueta-Neyroud, T.; Eisen, M. S. J . Am. Chem. Soc.
1999, 121, 3025.
considerably with the nature of the catalyst and sub-
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hydrosilylation process, and one of the most widely
accepted mechanisms was first proposed by Chalk and
Harrod in 1965 for the Pt-catalyzed hydrosilylation of
alkenes.23 The key feature in the Chalk-Harrod mech-
anism (Scheme 1a) was the insertion of a coordinated
alkene into a metal-hydrogen bond followed by reduc-
tive elimination of the alkyl and silyl ligands. If the
intermediate alkyl complex undergoes reversible â-hy-
dride elimination and reinsertion with opposite regio-
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4726 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
Sch em e 1. Ch a lk -Ha r r od (a ) a n d Mod ified Ch a lk -Ha r r od (b) Mech a n ism s for th e Hyd r osilyla tion of
Alk en es
chemistry, then the Chalk-Harrod mechanism provides
an explanation for the olefin isomerization and deute-
rium scrambling in the hydrosilylation reactions.15a
However, this mechanism was unable to account for the
formation of vinylsilanes from the hydrosilylation reac-
tion of alkenes. In some cases vinylsilanes are produced
more readily than the hydrosilylation product.24 To
explain this competing process, a number of different
so-called modified Chalk-Harrod mechanisms have
been proposed.25 In the basic mechanism (Scheme 1b),
a coordinated alkene inserts into a metal-silicon bond,
forming a silaalkyl moiety. The subsequent reductive
elimination of the â-silaalkyl group with the hydride
ligand leads to the hydrosilylation products. A compet-
ing â-hydride elimination from the â-silaalkyl moiety
allows the formation of vinylsilanes.
Although there is some evidence showing that the
insertion of an alkene into a metal-hydrogen bond is
faster than insertion into a metal-silicon bond, these
findings are not enough to conclude that a Chalk-
Harrod mechanism is more favorable than the modified
Chalk-Harrod mechanism for late-transition-metal
complexes.19a,b,26 For organolanthanide and organoyt-
trium complexes, the hydrosilylation of alkenes is
proposed to proceed via the Chalk-Harrod type mech-
anism, except for the inclusion of a σ-bond metathesis
instead of a classical oxidative-addition-reductive-
elimination process.6a,19h
the oligomerization reaction, producing selectively the
formation of dimers and/or trimers.14c These findings
prompted us to study the catalytic hydrosilylation
reaction promoted by organoactinide complexes. Here
we report a thorough study for the hydrosilylation
reaction of terminal alkynes catalyzed by organoactinide
complexes. We present a full discussion, including scope,
stoichiometry and catalytic effects, substrate substitu-
ent, and metal effects. In addition, we have successfully
trapped some of the key organometallic intermediates
in the catalytic cycle. Kinetic and thermodynamic stud-
ies are presented as well, along with their mechanistic
implications.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All manipulations of air-sensitive
materials were performed with the rigorous exclusion of
oxygen and moisture in flamed Schlenk-type glassware on a
dual-manifold Schlenk line, interfaced to a high-vacuum (10-5
Torr) line, or in a nitrogen-filled Vacuum Atmospheres glove-
box with a medium-capacity recirculator (1-2 ppm O2). Argon
and nitrogen were purified by passage through a MnO oxygen-
removal column and a Davison 4 Å molecular sieve column.
The hydrocarbon solvents THF-d8, benzene-d6, and toluene-
d8 were distilled under nitrogen from Na/K alloy. All solvents
for vacuum-line manipulations were stored in vacuo over Na/K
alloy in resealable bulbs. Cp*2AnMe2 (An ) Th, U) compounds
were prepared according to the literature procedure.27 Acety-
lenic compounds (Aldrich) were dried and stored over activated
molecular sieve (4 Å), degassed and freshly vacuum-distilled.
PhSiH3 (Aldrich) were dried and stored over activated molec-
ular sieves (4 Å), degassed, and freshly vacuum-distilled. NMR
spectra were recorded on Bruker AM 200 and Bruker AM 400
Recently we have reported that organoactinide com-
plexes of the type Cp*2AnMe2 (An ) Th, U) are active
catalytic precursors for the linear oligomerization of
terminal alkynes, and the extent of oligomerization was
found to be strongly dependent on the electronic and
steric hindrance of the alkyne substituents.14 For ex-
ample, bulky alkynes reacted with high regioselectivity
toward dimers and/or trimers, whereas for nonbulky
alkynes, the oligomerization afforded dimers to hep-
tamers with total lack of regioselectivity. Addition of
primary amines to the catalytic cycle allows us to control
1
spectrometers. Chemical shifts for H NMR and 13C NMR are
referenced to internal solvent resonances and are reported
relative to tetramethylsilane. NMR spectra for alkenes were
confirmed by comparison with those in the published litera-
ture. For 29Si NMR, Si(TMS)4 was used as internal standard
(SiMe3 at -7.80 ppm), and the experiments were measured
using either the INEPT or DEPT program. GC/MS experi-
ments were conducted in
a GC-MS (Finnigan Magnum)
spectrometer. The NMR experiments were conducted in Tef-
lon-valve-sealed tubes (J . Young) after vacuum transfer of the
liquids in a high-vacuum line. Microanalysis was carried out
at the Hebrew University of J erusalem.
Gen er a l P r oced u r e for th e Ca ta lytic Hyd r osilyla tion
of Ter m in a l Alk yn es. In a typical procedure, the specific
alkyne and an equimolar amount of PhSiH3 were vacuum-
transferred in a high-vacuum line into an J . Young NMR tube
(24) (a) Tanke, R. S.; Crabtree, R. H. Organometallics 1991, 10, 415.
(b) Takeuchi, R.; Yasue, H. Organometallics 1996, 15, 2098. (c) Christ,
M. L.; Sabo-Etienne, S.; Chaudert, B. Organometallics 1995, 14, 1082.
(25) Three main modified Chalk-Harrod mechanisms have been
postulated: (a) Seitz, F.; Wrighton, M. S. Angew. Chem., Int. Ed. Engl.
1988, 27, 289. (b) Duckett, S. B.; Perutz, R. N. Organometallics 1992,
11, 90. (c) Ruiz, J .; Bentz, P. O.; Mann, B. E.; Spencer, C. M.; Taylor,
B. F.; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1987, 2709. (d)
Brookhart, M.; Grant, B. E. J . Am. Chem. Soc. 1993, 115, 2151.
(26) (a) Bode, B. M.; Day, P. N.; Gordon, M. S. J . Am. Chem. Soc.
1998, 120, 1552. (b) Sakaki, S.; Mizoe, N.; Sugimoto, M. Organome-
tallics 1998, 17, 2510. (c) Sakaki, S.; Ogawa, M.; Musashi, Y.; Arai, T.
J . Am. Chem. Soc. 1994, 116, 7258.
(27) (a) Fagan, P. J .; Manriquez, J . M.; Maatta, E. A.; Seyam, A.
M.; Marks, T. J . J . Am. Chem. Soc. 1981, 103, 6650. (b) Aitken, C.;
Barry, J . P.; Gauvin, F. G.; Harrod, J . F.; Malek, A.; Rousseau, D.
Organometallics 1989, 8, 1732.

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4727
containing 10 mg of Cp*2AnMe2 (An ) Th, U) in 0.6 mL of
THF-d8 or C6D6. The sealed tube was then heated in an oil
bath or kept at room temperature until 100% conversion of
the alkyne was detected by the disappearance of the acetylenic
hydrogen of the alkyne by 1H NMR spectroscopy. The percent-
age of the converted products is given related only to the
alkyne. The organic products were vacuum-transferred (10-6
mmHg) to another J . Young NMR tube and sealed, and both
(2) H yd r osilyla t ion of tBu CtCH w it h P h SiH 3 b y
Cp *2Th Me2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of tBuCt
CH (0.638 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at room temperature for 24 h,
producing trans-tBuCHdCHSiH2Ph (1; 48%), tBuCtCSiH2Ph
t
(4; 28%), and BuCHdCH2 (7; 24%).
(b) According to the general procedure described above,
t
1
the residue and volatiles were identified by H, 13C, 29Si, and
100% conversion was obtained by the reaction of BuCtCH
(0.638 mmol) and PhSiH3(0.637 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at 78 °C for 12 h, producing 1
(21%), 4 (46%), and 7 (34%).
2D (COSY, C-H correlation, Si-H correlation, NOESY) NMR
spectroscopy and GC-MS spectroscopy and by comparing with
compounds known in the literature.
(1) H yd r osilyla t ion of tBu CtCH w it h P h SiH 3 b y
Cp *2UMe2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of tBuCt
CH (0.638 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at room temperature for 48 h,
producing trans-tBuCHdCHSiH2Ph (1; 47%), tBuCtCSiH2Ph
(c) According to the general procedure described above, 100%
conversion was obtained by the reaction of BuCtCH (0.638
mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2ThMe2
(0.0187 mmol) in THF-d8 at 65 °C for 12 h, producing 1 (21%),
4 (31%), and 7 (48%).
t
(3) H yd r osilyla t ion of iP r CtCH w it h P h SiH 3 b y
Cp *2UMe2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of iPrCt
CH (0.768 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at room temperature for 48 h,
t
(4; 31%), and BuCHdCH2 (7; 22%).
1
Ch a r a cter iza tion Da ta for 1. H NMR (200 MHz, C6D6):
δ 7.05-7.17 (m, 3H, o,p-H Ph), 7.60-7.64 (m, 2H, m-H Ph),
3
3
6.39 (d, 1H, J trans ) 18.8 Hz, HCBut), 5.62 (dt, 1H, J trans
)
i
producing trans-iPrCHdCHSiH2Ph (2; 62%), PrCtCSiH2Ph
3
3
18.8 Hz, J HH(Si) ) 3.2 Hz, HC(PhSiH2)), 4.79 (d, 2H, J ) 3.2
Hz, PhSiH2), 0.90 (s, 9H, C(CH3)3). 13C NMR (50 MHz, C6D6):
δ 164.1 (d, 1J ) 152 Hz, HCBut), 135.6, 129.8, 128.3 (C-H
Ph), 132.5 (s, CC5H5), 114.2 (d, 1J ) 141 Hz, HC(PhSiH2)), 32.2
i
(5; 27%), and PrCHdCH2 (8; 12%).
1
Ch a r a cter iza tion Da ta for 2. H NMR (200 MHz, C6D6):
δ 7.52-7.65 (m, 2H, m-H Ph), 7.05-7.22 (m, 3H, o,p-H Ph),
3
3
1
6.31 (dd, 1H, J trans ) 18.5 Hz, J HH( Pr) ) 5.9 Hz, HCPri), 5.62
3 3 4
i
i
(s, CMe3), 28.8 (q, J ) 128 Hz, C(CH3)3). 29Si NMR (79.5 Hz,
1
3
(dtd, 1H, J trans ) 18.7 Hz, J HH(Si) ) 3.32 Hz, J H-H( Pr) ) 1.66
Hz, HC(PhSiH2)), 4.78 (d, 2H, 3J ) 3.32 Hz, PhSiH2), 2.33 (m,
C6D6): δ 15.62 (tt, J Si-H ) 198 Hz, J Si-H ) 7.3 Hz, PhSiH2).
GC/MS data: m/z 190 (M+), 189 (M+ - H), 175 (M+ - CH3),
162 (M+ - C2H4), 148 (M+ - C(CH3)2), 133 (M+ - C(CH3)3),
120 (M+ - (CH3)3CCH), 105 (PhSi+, 100%)
1H, CHMe2), 0.85 (d, 6H, J ) 6.69 Hz, CH(CH3)2). 13C NMR
3
(50 MHz, C6D6): δ 160.4 (d, 1J ) 150.3 Hz, CHPri), 135.7,
1
130.2, 128.3 (C-H Ph), 132.5 (s, CC5H5), 116.9 (d, J ) 140.1
1
Ch a r a cter iza tion Da ta for 4. H NMR (200 MHz, C6D6):
1
Hz, CH(PhSiH2)), 34.78 (d, J ) 122.8 Hz, CHMe2), 21.55 (q,
δ 7.35-7.40 (m, 3H, o,p-H Ph), 7.52-7.57 (m, 2H, m-H Ph),
4.85 (s, 2H, PhSiH2), 1.06 (s, 9H, C(CH3)3). 13C NMR (50 MHz,
C6D6): δ 135.4, 130.2, 128.4 (C-H Ph), 132.5 (s, CC5H5), 73.6
1J ) 125.6 Hz, CH(CH3)2). 29Si NMR (79.5 MHz, C6D6): δ 14.79
(t, 1J ) 199 Hz, PhSiH2). GC/MS data: m/z 176 (M+), 175 (M+
- H), 159 (M+ - CH3), 148 (M+ - C2H4), 133 (M+ - CH(CH3)2),
120 (M+ - CHPri), 105 (PhSi+, 100%), 98 (M+ - C6H6), 69 (M+
- SiH2Ph).
1
(s, CtCBut), 67.3 (s, CtCSiPhH2), 35.6 (s, CMe3), 30.8 (q, J
) 128 Hz, C(CH3)3). 29Si NMR (79.5 Hz, C6D6): δ -8.98
3
(tt,1J Si-H ) 211 Hz, J Si-H ) 6.1 Hz, PhSiH2). GC/MS data:
1
Ch a r a cter iza tion Da ta for 5. H NMR (200 MHz, C6D6):
m/z 188 (M+), 187 (M+ - H), 173 (M+ - CH3), 159 (M+ - C2H5),
145 (M+ - C3H7), 131 (M+ - C(CH3)3), 105 (PhSi+, 100%), 81
(M+ - PhSiH2).
δ 7.52-7.65 (m, 2H, m-H Ph), 7.05-7.22 (m, 3H, o,p-H Ph),
4.80 (d, 2H, 5J ) 1.07 Hz, PhSiH2), 2.16 (m, 1H, CHMe2), 0.97
3
(d, 6H, J ) 6.81 Hz, CH(CH3)2). 13C NMR (50 MHz, C6D6): δ
(b) According to the general procedure described above,
100% conversion was obtained after 24 h by the reaction of
tBuCtCH (0.638 mmol) and PhSiH3 (0.637 mmol), catalyzed
by Cp*2UMe2 (0.0186 mmol) in THF-d8 at 65 °C, producing 1
(15%), 4 (36%), 7 (7%), cis-tBuCHdCHSiH2Ph (13; 24%), and
the double-hydrosilylation product tBuCHdC(SiH2Ph)2 (16;
19%).
135.4, 129.8, 128.3 (C-H Ph), 132.5 (s, CC5H5), 78.6 (s,
CtCPri), 67.8 (s, CtCSiPhH2), 34.7 (d, 1J ) 122.8 Hz, CHMe2),
22.5 (q, 1J ) 125.6 Hz, CH(CH3)2). 29Si NMR (79.5 MHz,
C6D6): δ -9.0 (t, 1J ) 213 Hz, PhSiH2). GC/MS data: m/z 174
(M+), 173 (M+ - H), 159 (M+ -CH3), 145 (M+ - C2H5), 131
(M+ - CH(CH3)2), 119 (M+ - CPri), 105 (PhSi+, 100%), 96 (M+
- C6H6), 67 (M+ - SiH2Ph).
Ch a r a cter iza tion Da ta for 13. 1H NMR (200 MHz, THF-
(b) According to the general procedure described above,
3
i
d8): δ 7.29-7.57 (m, 5H, Ph), 6.65 (d, 1H, J cis ) 14.95 Hz,
100% conversion was obtained by the reaction of PrCtCH
3
3
HCBut), 5.54 (dt, 1H, J cis ) 14.95 Hz, J HH(Si) ) 4.15 Hz,
(0.768 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at 65 °C for 24 h, producing 2
(4%), 5 (31%), 8 (35%), cis-iPrCHdCHSiH2Ph (14; 27%), and
the double-hydrosilylation product iPrCHdC(SiH2Ph)2 (17;
2%).
3
HCSiH2Ph), 4.76 (d, 2H, J ) 4.15 Hz, SiH2Ph), 1.16 (s, 9H,
C(CH3)3). 13C NMR (50 MHz, THF-d8): δ 167.1 (d, J ) 150.2
1
Hz, HCBut), 137.6, 133.1, 131.3 (C-H Ph), 132.6 (s, CC5H5),
1
118.4 (d, J ) 137.7 Hz, HCSiH2Ph), 42.7 (s, CMe3), 33.2 (q,
1J ) 125.4 Hz, C(CH3)3). 29Si NMR (79.5 MHz, THF-d8): δ 4.60
(t, 1J ) 210 Hz, PhSiH2). GC/MS data: m/z 190 (M+), 189 (M+
- H), 175 (M+ - CH3), 162 (M+ - C2H4), 148 (M+ - C(CH3)2),
133 (M+ - C(CH3)3), 120 (M+ - (CH3)3CCH), 105 (PhSi+,
100%).
Ch a r a cter iza tion Da ta for 14. 1H NMR (200 MHz, THF-
3
d8): δ 7.20-7.68 (m, 5H, Ph), 6.42 (dd, 1H, J cis ) 13.3 Hz,
3
3
3
J HH( Pr) ) 5.8 Hz, HCPri), 5.57 (dt, 1H, J cis ) 13.3 Hz, J HH(Si)
i
) 4.15 Hz, HCSiH2Ph), 4.63 (d, 2H, 3J ) 4.15 Hz, PhSiH2),
2.37 (m, 1H, CHMe2), 1.03 (d, 1H, 3J ) 6.64 Hz, CH(CH3)2).
13C NMR (50 MHz, THF-d8): δ 162.7 (d, 1J ) 150.2 Hz, HCPri),
Ch a r a cter iza tion Da ta for 16. 1H NMR (200 MHz, THF-
d8): δ 7.29-7.57 (m, 10H, Ph), 7.34 (s, 1H, HCBut), 4.84 (s,
2H, SiH2Ph), 4.7 (s, 2H, SiH2Ph), 1.15 (s, 9H, C(CH3)3). 13C
1
138.4, 132.9, 131.1 (C-H Ph), 132.6 (s, CC5H5), 121.9 (d, J )
1
140 Hz, HCSiH2Ph), 38.1 (d, J ) 126.8 Hz, CHMe2), 24.5 (q,
1J ) 125.2 Hz, CH(CH3)2). 29Si NMR (79.5 MHz, THF-d8): δ
1
NMR (50 MHz, THF-d8): δ 180.2 (d, J ) 146.3 Hz, HCBut),
1.60 (t, J ) 195.5 Hz, PhSiH2). GC/MS data: m/z 176 (M+),
1
137.2, 133.1, 131.6 (C-H Ph), 132.6 (s, CC5H5), 42.4 (s, CMe3),
175 (M+ - H), 159 (M+ - CH3), 148 (M+ - C2H4), 133 (M+
CH(CH3)2), 120 (M+ - CHPri), 105 (PhSi+, 100%), 98 (M+
C6H6), 69 (M+ - SiH2Ph).
-
-
1
33.0 (q, J ) 125.4 Hz, C(CH3)3). 29Si NMR (79.5 MHz, THF-
1
1
d8): δ 30.22 (t, J ) 215.4 Hz, PhSiH2), 5.20 (t, J ) 210 Hz,
PhSiH2). GC/MS data: m/z 296 (M+), 295 (M+ - H), 281 (M+
Ch a r a cter iza tion Da ta for 17. 1H NMR (200 MHz, THF-
d8): δ 7.72-7.60 (m, 4H, m-H Ph), 7.52-7.25 (m, 6H, o,p-H
- CH3), 265 (M+ - C2H6 - H), 253 (M+ - C3H7), 239 (M+
-
C(CH3)3), 219 (M+ - C6H5), 187 (M+ - PhSiH3 - H), 183 (Ph2-
SiH), 131 (M - PhSiH3 - C(CH3)2), 105 (PhSi+, 100%).
Ph), 6.82 (d, 1H, J ) 9.25 Hz, HCPri), 4.66 (s, 2H, PhSiH2),
3

4728 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
4.64 (s, 2H, PhSiH2), 2.64 (m, 1H, 3J ) 6.76 Hz, CHMe2), 1.18
3J HH(Bu) ) 6.64 Hz, HCBun), 5.75 (dt, 1H, 3J cis ) 13.3 Hz, 3J HH(Si)
) 4.15 Hz, HCSiH2Ph), 4.62 (d, 3J ) 4.15 Hz, 2H, PhSiH2),
2.20 (m, 2H, dCHCH2CH2), 1.50 (m, 4H, CH2CH2CH3), 0.9 (t,
3H, 3J ) 6.9 Hz, CH2CH3). 13C NMR (50 MHz, THF-d8): δ
156.8 (d, 1J ) 150.1 Hz, HCBun), 138.8, 133.1, 131.1 (C-H
Ph), 132.6 (s, CC5H5), 122.4 (d, 1J ) 146.3 Hz, HCSiH2Ph),
40.0 (t, 1J ) 125.6 Hz, dCHCH2), 34.1 (t, 1J ) 127.1 Hz, CH2-
3
(d, 6H, J ) 6.76 Hz, CH(CH3)2). 13C NMR (50 MHz, THF-d8):
δ 174.0 (d, 1J ) 150.5 Hz, HCPri), 136.5, 130.6, 128.8 (C-H
Ph), 132.8 (s, CC5H5), 116.9 (s, C(PhSiH2)2), 34.7 (d, 1J ) 122.8
Hz, CHMe2), 22.8 (q, 1J ) 125.6 Hz, CH(CH3)2). 29Si NMR (79.5
MHz, THF-d8): δ 27.5 (t, 1J ) 198 Hz, PhSiH2), 7.3 (t, 1J )
203 Hz, PhSiH2). GC/MS data: m/z 282 (M+), 281 (M+ - H),
267 (M+ - CH3), 251 (M+ - 2CH3), 239 (M+ - Pri), 225 (M+
-
CH2CH3), 25.7 (t, J ) 127 Hz, CH2CH3), 16.9 (q, J ) 123.8
1
1
CHPri - H), 205 (M+ - C6H6), 173 (M+ - PhSiH3 - H), 148
((CH3)2CdSiHPh+), 131 (M+ - PhSiH3 - Pri), 105 (PhSi+,
100%).
Hz, CH3). 29Si NMR (79.5 MHz, THF-d8): δ 1.44 (t, J ) 195
1
Hz, PhSiH2). GC/MS data: m/z 190 (M+), 189 (M+ - H), 175
(M+ - CH3), 161 (M+ - CH3CH2), 147 (M+ - CH2CH2CH3),
133 (M+ - Bun), 120 (M+ - CHBun), 105 (PhSi+, 100%).
Ch a r a cter iza tion Da ta for 18. 29Si NMR (79.5 MHz, THF-
d8): δ 23.84 (t, 1J ) 208 Hz, PhSiH2), 4.14 (t, 1J ) 211 Hz,
PhSiH2). GC/MS data: m/z 296 (M+), 295 (M+ - H), 279 (M+
- CH3 - 2H), 265 (M+ - CH3CH2 - 2H), 239 (M+ - Bun), 145
(M+ - PhSiH3 - CH2CH2CH3), 131 (M+ - PhSiH3 - Bun), 105
(PhSi+, 100%).
i
(4) Hyd r osilyla tion of P r CtCH w ith P h SiH3 by Cp *2-
Th Me2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of iPrCt
CH (0.768 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at room temperature for 24 h,
i
producing trans-iPrCHdCHSiH2Ph (2; 42%), PrCtCSiH2Ph
i
i
(5; 28%), PrCHdCH2 (8; 26%) and PrCH2CH3 (10; 5%).
(6) Hyd r osilyla t ion of n Bu CtCH w it h P h SiH 3 b y
Cp *2Th Me2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of nBuCt
CH (0.684 mmol) and PhSiH3 (0.716 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at room temperature for 24 h,
producing trans-nBuCHdCHSiH2Ph (3; 56%), nBuCtCSiH2-
Ph (6; 22%), and nBuCHdCH2 (9; 22%).
(b) According to the general procedure described above,
100% conversion was obtained by the reaction of nBuCtCH
(0.684 mmol) and PhSiH3 (0.716 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at 78 °C for 12 h, producing 3
(43%), 6 (34%), and 9 (23%).
(b) According to the general procedure described above,
i
100% conversion was obtained by the reaction of PrCtCH
(0.768 mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2-
ThMe2 (0.0187 mmol) in C6D6 at 78 °C for 12 h, producing 2
(37%), 5 (38%), 8 (23%), and the double-hydrosilylation product
iPrCHdC(SiH2Ph)2 (17; 2%).
(c) According to the general procedure described above, 100%
i
conversion was obtained by the reaction of PrCtCH (0.768
mmol) and PhSiH3 (0.637 mmol), catalyzed by Cp*2ThMe2
(0.0187 mmol) in THF-d8 at 65 °C for 12 h, producing 2 (33%),
5 (25%), 8 (36%), and 17 (6%).
(5) Hyd r osilyla t ion of n Bu CtCH w it h P h SiH 3 b y
Cp *2UMe2. (a) According to the general procedure described
above, 100% conversion was obtained by the reaction of nBuCt
CH (0.684 mmol) and PhSiH3 (0.716 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at room temperature for 48 h,
producing trans-nBuCHdCHSiH2Ph (3; 74%), nBuCtCSiH2-
Ph (6; 2%), and nBuCHdCH2 (9; 24%).
(7) Hyd r osilyla tion of (TMS)CtCH w ith P h SiH3 by
Cp *2UMe2. (a) According to the general procedure described
above, the reaction of (TMS)CtCH (0.556 mmol) and PhSiH3
(0.557 mmol), catalyzed by Cp*2UMe2 (0.0186 mmol) in THF-
d8 at room temperature for 48 h, produced trans-(TMS)CHd
CHSiH2Ph (11; 8%) and (TMS)CtCSiH2Ph (12; 16%).
Ch a r a cter iza tion Da ta for 11. 1H NMR (200 MHz,
C6D6): δ 7.51-7.60 (m, 2H, m-H Ph), 7.05-7.12 (m, 3H, o,p-H
1
Ch a r a cter iza tion Da ta for 3. H NMR (200 MHz, C6D6):
δ 7.52-7.66 (m, 3H, o,p-H Ph), 7.11-7.17 (m, 2H, m-H Ph),
3
3
6.29 (dt, 1H, J trans ) 18.37 Hz, J HH(
) 6.25 Hz, HCBun),
4
n
n
Bu)
Ph), 6.92 (d, 1H, 3J ) 22.4 Hz, HCTMS), 6.64 (dt, 1H, 3J trans
)
)
3
3
5.66 (dtt, 1H, J trans ) 18.37 Hz, J HH(Si) ) 3.12 Hz, J HH(
)
Bu)
3
3
22.4 Hz, J HH(Si) ) 2.6 Hz, HC(PhSiH2), 4.84 (d, 2H, J HH(Si)
1.55 Hz, HC(PhSiH2)), 4.77 (d, 2H, 3J ) 3.12 Hz, PhSiH2), 1.98
2.6 Hz, PhSiH2), 0.09 (s, 9H, Si(CH3)3).13C NMR (50 MHz,
C6D6): δ 158.9 (d, 1J ) 138.5 Hz, HCTMS), 140.8 (d, 1J ) 149.5
Hz, HC(PhSiH2)), 136.0, 135.8, 130.0 (C-H Ph), 138.2 (s,
CC5H5), -0.45 (q, 1J ) 119 Hz, Si(CH3)3). 29Si NMR (79.5 MHz,
C6D6): δ 15.46 (t, 1J ) 196 Hz, PhSiH2), GC/MS data: m/z
206 (M+), 205 (M+ - H), 191 (M+ - CH3), 178 (M+ - C2H4),
161 (M+ - 3CH3), 135 (PhSiH2CH2CH2+), 121 (PhSiH2CH2+),
105 (PhSi+, 100%), 73 (Me3Si+).
3
3
(dt, 2H, J ) 5.14 Hz, J gem ) 1.55 Hz, dCCH2), 1.20 (m, 4H,
CH2CH2), 0.8 (t, 3H, J ) 7.02 Hz, CH3). 13C NMR (50 MHz,
3
C6D6): δ 154.1 (d, 1J ) 150 Hz, HCBun), 135.7, 129.8, 128.3
(C-H Ph), 132.4 (s, CC5H5), 120.4 (d, 1J ) 140 Hz, HC(Ph-
SiH2)), 36.9 (t, 1J ) 125.4 Hz, dCCH2), 30.7 (t, 1J ) 126.3 Hz,
1
1
CH2CH2CH3), 22.5 (t, J ) 124.2 Hz, CH2CH3), 14.0 (q, J )
125.6 Hz, CH3). 29Si NMR (79.5 MHz, C6D6): δ 14.04 (t, J )
1
196.5 Hz, PhSiH2). GC/MS data: m/z 190 (M+), 189 (M+ - H),
175 (M+ - CH3), 161 (M+ - CH3CH2), 147 (M+ - CH2CH2-
CH3), 133 (M+ - Bun), 120 (M+ - CHBun), 105 (PhSi+, 100%).
Ch a r a cter iza tion Da ta for 12. 1H NMR (200 MHz,
C6D6): δ 7.34-7.40 (m, 2H, m-H Ph), 7.05-7.12 (m, 3H, o,p-H
Ph), 4.74 (s, 2H, PhSiH2), 0.18 (s, 9H, Si(CH3)3). 13C NMR (50
MHz, C6D6): δ 135.5, 130.4, 128.4 (C-H Ph), 107.1 (s,
1
Ch a r a cter iza tion Da ta for 6. H NMR (200 MHz, C6D6):
δ 7.52-7.65 (m, 3H, o,p-H Ph), 7.11-7.17 (m, 2H, m-H Ph),
1
3
CtCSiH2Ph), 93.2 (s, CtCTMS), -1.81 (q, J ) 120.5 Hz, Si-
4.81 (s, 2H, PhSiH2), 1.97 (t, J ) 6.16 Hz, 2H, CH2), 1.20 (m,
(CH3)3). 29Si NMR (79.5 MHz, C6D6): δ -9.8 (t, 1J ) 214.9 Hz,
PhSiH2). GC/MS data: m/z 204 (M+), 203 (M+ - H), 189 (M+
- CH3), 163 (M+ - C3H5), 145 (PhSiH2CtCCH2+), 135
(PhSiH2CH2CH2+), 121 (PhSiH2CH2+), 105 (PhSi+, 100%), 73
(Me3Si+).
3
4H, CH2CH2)), 0.71 (t, J ) 7.13 Hz, 3H, CH3). 13C NMR (50
MHz, C6D6): δ 135.4, 130.2, 128.4 (C-H Ph), 132.4 (s, CC5H5),
75.6 (s, nBuCtC), 67.2 (s, CtCSiH2Ph), 30.5 (t, 1J ) 125.4
1
1
Hz, dCCH2), 22.1 (t, J ) 126.3 Hz, CH2CH2CH2), 19.9 (t, J
) 124.2 Hz, CH2CH3), 13.6 (q, J ) 125.6 Hz, CH3). 29Si NMR
1
(79.5 MHz, C6D6): δ -9.17 (t, 1J ) 212.4 Hz, PhSiH2). GC/MS
data: m/z 188 (M+), 187 (M+ - H), 173 (M+ - CH3), 159 (M+
- CH3CH2), 146 (M+ - C3H6), 131 (M+ - Bun), 105 (PhSi+,
100%).
(b) According to the general procedure described above,
100% conversion was obtained by the reaction of (TMS)Ct
CH (0.556 mmol) and PhSiH3 (0.557 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at 65 °C for 24 h, producing
11 (6%), 12 (40%), cis-(TMS)CHdCHSiH2Ph (19; 26%), and
(TMS)CHdCH2 (20; 29%).
(b) According to the general procedure described above,
100% conversion was obtained by the reaction of nBuCtCH
(0.684 mmol) and PhSiH3 (0.716 mmol), catalyzed by Cp*2-
UMe2 (0.0186 mmol) in THF-d8 at 65 °C for 24 h, producing 3
(5%), 6 (9%), 9 (16%), cis-nBuCHdCHSiH2Ph (15; 54%), and
the double-hydrosilylation product nBuCHdC(SiH2Ph)2 (18;
3%).
Ch a r a cter iza tion Da ta for 19. 1H NMR (200 MHz, THF-
3
d8): δ 7.25-7.70 (m, 5H, Ph), 7.01 (d, 1H, J cis ) 13.3 Hz
3
3
HCTMS), 6.64 (dt, 1H, J cis ) 13.3 Hz, J HH(Si) ) 4.4 Hz,
3
HCSiH2Ph). 4.65 (d, 2H, J HH(Si) ) 4.4 Hz, H2SiPh), 0.18 (s,
9H, Si(CH3)3). 13C NMR (50 MHz, THF-d8): δ 160.7 (d, J )
1
Ch a r a cter iza tion Da ta for 15. 1H NMR (200 MHz, THF-
138.5 Hz, HCTMS), 144.5 (d, 1J ) 149.5 Hz, HCSiH2Ph), 138.5,
132.8, 130.9 (C-H Ph), 132.6 (s, CC5H5), 0.6 (q, 1J ) 116.6
3
d8): δ 7.30-7.65 (m, 5H, Ph), 6.61 (dt, 1H, J cis ) 13.3 Hz,

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4729
Hz, Si(CH3)3).29Si NMR (79.5 MHz, THF-d8): δ 6.56 (t, 1J )
205 Hz, PhSiH2). GC/MS data: m/z 206 (M+), 205 (M+ - H),
191 (M+ - CH3), 178 (M+ - C2H4), 161 (M+ - 3CH3), 135
(PhSiH2CH2CH2+), 121 (PhSiH2CH2+), 105 (PhSi+, 100%), 73
(Me3Si+).
- CH3 - 2H), 207 (100%, M+ - Pri), 182 (Ph2Si+), 172 (M+
-
C6H6), 105 (PhSi+).
GC/MS Da ta for 23: m/z 252 (M+), 251 (M+ - H), 237 (M+
- CH3), 224 (M+ - C2H4), 209 (M+ - Pri), 196 (M+ - CHPri),
183 (M+ - CHCHPri), 174 (M+ - C6H6), 105 (PhSi+).
Ch a r a cter iza tion Da ta for 20. 1H NMR (200 MHz,
(b) In a typical procedure, 0.098 mL of iPrCtCH (0.96 mmol)
and 0.118 mL of PhMeSiH2 (0.86 mmol) were vacuum-
transferred in a high-vacuum line into a J . Young NMR tube
containing 10 mg of Cp*2ThMe2 (0.0187 mmol) in 0.6 mL of
C6D6. The sealed tube was then heated in an oil bath at 78 °C
for 36 h, producing iPrCtCSiHMePh (24; 31.1%) trans-iPrCHd
3
3
C6D6): δ 6.15 (dd, 1H, J trans ) 19.9 Hz, J cis ) 14.6 Hz,
3
2
HCTMS), 5.88 (dd, 1H, J cis ) 14.6 Hz, J gem) 4.4 Hz, HCH),
3
2
5.63 (dd, 1H, J trans ) 19.9 Hz, J gem ) 4.4 Hz, HCH), 0.03 (s,
9H, Si(CH3)3).13C NMR (50 MHz, C6D6): δ 140.1 (d, 1J ) 130.6
1
1
Hz, HCTMS), 131.0 (t, J ) 147.4 Hz, CH2), -2.2 (q, J ) 118
Hz, Si(CH3)3).
i
CHSiHMePh (25; 2%), PrCHdCH2 (8; 20%), and the alkyne
(8) Hyd r osilyla tion of (TMS)CtCH w ith P h SiH3 by
Cp *2Th Me2. According to the general procedure described
above, 100% conversion was obtained by the reaction of
(TMS)CtCH (0.556 mmol) and PhSiH3 (0.557 mmol), catalyzed
by Cp*2ThMe2 (0.0187 mmol) in C6D6 at 78 °C for 48 h,
producing trans-(TMS)CHdCHSiH2Ph (11; 15%), (TMS)Ct
CSiH2Ph (12; 46%), and (TMS)CHdCH2 (20; 39%). No reaction
was observed at room temperature.
oligomerization products dimer (10%), trimer (traces), tetram-
ers (1%), and pentamers (36%).
Ch a r a cter iza tion Da ta for 24. 1H NMR (200 MHz,
3
C6D6): δ 7.10-7.70 (m, 5H, o,p-H Ph), 4.94 (q, 1H, J ) 4.14
Hz, PhMeSiH), 2.39 (m, 1H, CHMe2), 1.00 (d, 6H, 3J ) 7.48
Hz, CH(CH3)2), 0.39 (d, 3H, 3J ) 4.14 Hz, PhCH3SiH). 13C-
{1H} NMR (50 MHz, C6D6): δ 134.7, 129.7, 128.2 (m, Ph), 132.4
(s, CC5H5), 79.9 (s, CtCPri), 78.6 (s, CtCPri), 34.8 (s, CHMe2),
22.0 (s, CH(CH3)2), -3.17 (s, PhCH3SiH). 29Si NMR (79.5 MHz,
C6D6): δ 12.23 (d, 1J ) 223.4 Hz, PhMeSiH). GC/MS data: m/z
188 (M+), 187 (M+ - H), 173 (M+ - CH3), 161 (M+ - C2H3),
145 (100%, M+ - Pri), 121 (M+ - CtCPri), 105 (PhSi+).
GC/MS Da ta for 25: m/z 190 (M+), 189 (M+ - H), 175 (M+
(9) Ca ta lytic Hyd r osilyla tion Rea ction a s a F u n ction
of Su bstr a te Stoich iom etr y. (a) In a typical procedure, 0.079
mL of iPrCtCH (0.768 mmol) and 0.158 mL of PhSiH3 (1.536
mmol) were vacuum-transferred in a high-vacuum line into a
J . Young NMR tube containing 10 mg of Cp*2ThMe2 (0.0187
mmol) in 0.6 mL of THF-d8. The sealed tube was then heated
in an oil bath at 65 °C for 4 h, producing trans-iPrCHdCHSiH2-
Ph (2; 52%), iPrCtCSiH2Ph (5; 6%), iPrCHdCH2 (8; 17%), and
the double-hydrosilylation product iPrCHdC(SiH2Ph)2 (17;
26%).
- CH3), 162 (M+ - C2H4), 147 (M+ - C2H4 - CH3), 134 (M+
CHPri), 121 (100%, M+ - CHCHPri), 105 (PhSi+), 69 (M+
PhSiHMe).
-
-
(11) Syn th esis of Cp *2U(Me)(CtCP r i) (26). A 50 mL
Schlenk tube was charged in the glovebox with 52 mg (0.097
mmol) of Cp*2UMe2. A 6 mL portion of C6H6 was added to the
Schlenk tube by vacuum transfer at -78 °C, and then 0.01
mL (0.097 mmol) of isopropylacetylene was vacuum-trans-
ferred. The solution was stirred at room temperature for 4 h.
The reaction was monitored to completion by following the
disappearance of the methyl signals of the starting complex.
The mono(acetylide) complex Cp*2U(Me)(CtCPri) (1) was
formed together with the bis(acetylide) complex.
i
(b) In a typical procedure, 0.079 mL of PrCtCH (0.768
mmol) and 0.04 mL of PhSiH3 (0.384 mmol) were vacuum-
transferred in a high-vacuum line into a J . Young NMR tube
containing 10 mg of Cp*2ThMe2 (0.0187 mmol) in 0.6 mL of
THF-d8. The sealed tube was then heated in an oil bath at 65
°C for 4 h, producing trans-iPrC(H)dC(H)SiH2Ph (2; 20%),
iPrCtCSiH2Ph (5; 11%), iPrCHdCH2 (8; 48%), iPrCHdC(SiH2-
Ph)2 (17; 9%), and trans-iPrCHdCHSi(HPh)CtCPri (21; 13%).
Ch a r a cter iza tion Da ta for 21. 1H NMR (200 MHz, THF-
d8): δ 7.41-7.70 (m, 2H, m-H Ph), 7.25-7.37 (m, 3H, o,p-H
1H NMR (200 MHz, C6D6): δ 7.26 (s, 30H, Cp*), -14.74 (d,
3
3
6H, J HH ) 7.30 Hz, CH(CH3)2), -37.39 (septet, 1H, J HH
)
Ph), 6.41 (dd, 1H, 3J trans ) 18.5 Hz, 3J HH( Pr) ) 6.15 Hz, HCPri),
7.3 Hz, CHMe2), -133.27 (s, 3H, CH3). 13C NMR (50 MHz,
C6D6): δ 169.7 (s, CtCCHMe2), 154.1 (s, CtCCHMe2), 119.5
i
3
5.67 (dd, 1H,3J trans ) 18.5 Hz, J HH(Si) ) 2.7 Hz, HCSiHPh),
3
1
1
4.76 (d, 1H, J ) 2.7 Hz, PhSiH), 2.67 (m, 1H, CCHMe2), 2.36
(s, C5Me5), 44.1 (d, J ) 122 Hz, CHMe2), -25.0 (q, J ) 125
1 1
3
3
(septet, 1H, J ) 3.9 Hz, CHMe2), 1.19 (d, 6H, J ) 3.88 Hz,
Hz, C5(CH3)5), -29.5 (q, J ) 125 Hz, U-CH3), -45.2 (q, J )
125 Hz, CH(CH3)2).
CH(CH3)2), 1.15 (d, 3J ) 3.9 Hz, CH(CH3)2) ppm. 13C NMR (50
MHz, THF-d8): δ 160.1 (d, J ) 151 Hz, HCPri), 135.9, 130.7,
1
(12) Syn th esis of Cp *2U(CtCP r i)2 (27). A 50 mL Schlenk
tube was charged in the glovebox with 52 mg (0.097 mmol) of
Cp*UMe2. A 6 mL portion of C6H6 was added to the Schlenk
tube by vacuum transfer at -78 °C, and then 0.02 mL (0.195
mmol) of isopropylacetylene was vacuum-transferred into the
tube. The solution was stirred at room temperature for 4 h.
The reaction was monitored to completion by following the
disappearance of the methyl signal of the starting complex.
The bis(acetylide) complex was also obtained quantitatively
by addition of a second equivalent of isopropylacetylene (0.01
mL) to a solution of the mono(acetylide) complex Cp*2U(Me)-
(CtCPri). Mp: 85 °C dec.
128.7 (C-H Ph), 132.5 (s, CC5H5), 119.3 (d, 1J ) 135 Hz,
HCSiHPh), 77.4 (s, CtCPri), 76.51 (s, CtCPri), 35.4 (d, J )
1
126.8 Hz, CHMe2), 35.2 (d, 1J ) 126.8 Hz, CHMe2), 22.9 (q, 1J
) 127 Hz, CH(CH3)2), 22.1 (q, 1J ) 127 Hz, CH(CH3)2). 29Si
NMR (79.5 MHz, THF-d8): δ 11.78 (d, 1J ) 212.4 Hz, PhSiH).
GC/MS data: m/z 242 (M+), 241 (M+ - H), 227 (M+ - CH3),
214 (M+ - C2H4), 199 (M+ - Pri), 186 (M+ - Pr - CH), 173
i
(M+ - PrCHCH, 100%) 157 (M+ - 173 - CH3 - H), 131
i
(PhSiH2CtC+), 105 (PhSi+), 69 (M+ - PrCtCSiHPh).
i
(10) Effect of Sila n e Su bstitu en ts on th e Ca ta lytic
Hyd r osilyla tion Rea ction s. (a) In a typical procedure, 0.079
i
1H NMR (200 MHz, C6D6): δ 9.49 (s, 30H, Cp*), -15.87 (d,
mL of PrCtCH (0.77 mmol) and 0.158 mL of Ph2SiH2 (0.78
3
3
mmol) were vacuum-transferred in a high-vacuum line into a
J . Young NMR tube containing 10 mg of Cp*2ThMe2 (0.0187
mmol) in 0.6 mL of C6D6. The sealed tube was then heated in
12H, J HH ) 4.5 Hz, CH(CH3)2), -38.03 (septet, 2H, J HH
)
4.5 Hz, CHMe2). 13C NMR (50 MHz, C6D6): δ 169.0 (s, Ct
CCHMe2), 154.0 (s, CtCCHMe2), 119.1 (s, C5Me5), 39.7 (d, J
1
i
1
an oil bath at 78 °C for 24 h, producing PrCtCSiHPh2 (22;
) 122 Hz, CHMe2), 19.4 (q, J ) 125 Hz, C5(CH3)5), -44.0 (q,
47%), trans-iPrCHdCHSiHPh2 (23; 4%), iPrCHdCH2 (8; 39%),
and the alkyne oligomerization products (dimers-pentamers,
7%).
1J ) 125 Hz, CH(CH3)2).
(13) Syn th esis of Cp*2Th (CtCP r i)2 (28). A 50 mL Schlenk
tube was charged in the glovebox with 50 mg (0.0939 mmol)
of Cp*2ThMe2. An 8 mL portion of C6H6 was added to the
Schlenk tube by vacuum transfer at -78 °C, and then 0.019
mL of isopropylacetylene (0.187 mmol) was vacuum-trans-
ferred into the tube. The solution was stirred at room tem-
perature for 6 h. The reaction was monitored to completion
by following the disappearance of the methyl signals of the
Ch a r a cter iza tion Da ta for 22. 1H NMR (200 MHz,
C6D6): δ 7.10-7.78 (m, 10H, Ph), 5.51 (s, 1H, Ph2SiH), 2.37
3
(m, 1H, CH(CH3)2), 1.0 (d, 6H, J ) 7 Hz, CH(CH3)2). 13C{1H}
NMR (50 MHz, C6D6): δ 135.5, 130.1, 128.3, 132.4, 77.1, 34.5,
1
22.6. 29Si NMR (79.5 MHz, C6D6): δ 11.37 (d, J ) 212.4 Hz,
Ph2SiH). GC/MS data: m/z 250 (M+), 249 (M+ - H), 233 (M+

4730 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
starting complex. The bis(acetylide) complex 3, in the absence
of an excess of alkyne, slowly decomposes at room temperature.
Mp: 92 °C dec.
sample was prepared as described in the typical NMR scale
catalytic reactions section and maintained at -78 °C until
kinetic measurements were initiated. The sealed tube was kept
inside the probe of the NMR instrument, and at regular time
intervals NMR data were acquired using eight scans with a
long pulse delay to avoid saturation of the signal. The kinetics
were usually monitored by the intensity changes in the
substrate resonances and in the product resonances over 3 or
more half-lives. The substrate concentration (C) was measured
from the area (As) of the 1H-normalized signal of the solvent
(Ab). All the data collected could be convincingly least-squares-
fit (R > 0.98) to eq 2, where C0 (C0 ) As,0/Ab,0) is the initial
concentration of substrate and C(As/Ab) is the substrate
concentration at time t.
3
1H NMR (200 MHz, C6D6): δ 2.52 (septet, J HH ) 6.8 Hz,
3
2H, CHMe2), 2.21 (s, 30H, C5(CH3)5), 1.16 (d, J HH ) 6.8 Hz,
12H, CH3). 13C NMR (50 MHz, C6D6): δ 174.9 (s, CtCCHMe2),
1
125.3 (s, C5Me5), 116.1 (s, CtCCHMe2), 23.9 (q, J ) 125 Hz,
CH(CH3)2), 21.6 (d, 1J ) 125 Hz, CHMe2), 11.7 (q, 1J ) 126
Hz, C5(CH3)5).
(14) Syn th esis of Cp *2U(CtCP r i)[C(P h SiH2)dC(H)P r i]
(29). A 50 mL Schlenk tube was charged in the glovebox with
53 mg of Cp*2UMe2 (0.0985 mmol). A 10 mL portion of C6H6
was added to the Schlenk tube by vacuum transfer at -78 °C
followed by 0.02 mL of isopropylacetylene (0.195 mmol). The
reaction mixture was stirred for 4 h, producing the bis-
(acetylide) complex Cp*2U(CtCPri)2, as indicated by a change
in color and also confirmed by spectroscopic methods. Then a
0.012 mL portion of PhSiH3 (0.0985 mmol) was added by
vacuum transfer, and the mixture was stirred for an additional
6 h, affording the quantitative formation of Cp*U(CtCPri)-
{C(PhSiH2)dCH(Pri)}. Anal. Calcd for C36H52SiU: C, 57.60;
H, 6.93. Found: C, 57.01; H, 7.00.. Mp: 86 °C dec.
mt ) log(C/C0)
(2)
The ratio of catalyst to substrate was accurately measured
by calibration with internal FeCp2. Turnover frequencies (Nt,
h-1) were calculated from the least-squares-determined slopes
(m) of the resulting plots. Typical initial alkyne and PhSiH3
concentrations were in the range of 1.028-5.144 and 0.4264-
4.264 M, respectively, and typical catalyst concentrations were
in the range of 4.45-44.5 mM.
1
1H NMR (200 MHz, C6D6): δ 18.59 (s, 2H, J H-Si ) 192 Hz
(satellites), PhSiH2), 9.67 (d, 2H, 3J ) 7.3 Hz, o-H Ph), 8.14 (t,
3
3
2H. J ) 7.3 Hz, m-H Ph), 7.83 (t, 2H. J ) 7.3 Hz, p-H Ph),
7.47 (d, 1H, 3J ) 5.7 Hz, dCH), 3.75 (s, 30H, C5(CH3)5), -3.28
(d, 6H, 3J ) 6.8 Hz, dC-CH(CH3)2), -8.18 (m, 1H, dC-
Resu lts
3
CHMe2), -15.87 (d, 6H, J ) 6.68 Hz, C-CH(CH3)2), -21.46
The goal of this investigation was to examine the
scope, chemoselectivity, regioselectivity, actinide metal
sensitivity, kinetics, and mechanism of the hydrosily-
lation reaction of terminal alkynes. This study repre-
sents an extension of the unique reactivities of organo-
actinides with alkynes in the presence of silanes and a
complementary comparison to group 3, group 4, and
organolanthanide chemistry.6,19 In the following discus-
sion, we focus on the reaction scope, metal effect,
kinetics, rate law expression, and thermodynamics. We
start the discussion with the reaction scope for the
organoactinide-catalyzed hydrosilylation of terminal
alkynes at room temperature.
(septet, 1H, 3J ) 6.68 Hz, C-CHMe2). 13C NMR (50 MHz,
C6D6): δ 247.8 (s, UCdCH), 231.0 (s, UCtC), 162.1 (UCtC),
138.4 (d, 1J ) 155 Hz, o-CH Ph), 135.6 (s, CC5H5), 135.5 (d, 1J
1
) 120 Hz, dCH), 130.9 (d, J ) 155 Hz, m-CH Ph), 129.8 (d,
1J ) 155 Hz, p-CH Ph), 128.3 (s, C5Me5), 107.3 (d, J ) 128.2
1
Hz, tC-CHMe2), 74.3 (d, 1J ) 128.2 Hz, dC-CHMe2), -24.9
(q, 1J ) 125.1 Hz, dC-CH(CH3)2), -32.7 (q, 1J ) 125.7 Hz,
C5(CH3)5), -35.1 (q, 1J ) 125.1 Hz, tC-CH(CH3)2). 29Si NMR
1
(79.5 Hz, C6D6): δ 34.33 (t, J Si-H ) 192 Hz, PhSiH2).
(15) Syn t h esis of Cp *2Th (CtCP r i)[C(P h SiH 2)dCH -
(P r i)] (30). A 50 mL Schlenk tube was charged into the
glovebox with 52 mg of Cp*2ThMe2 (0.0977 mmol). A 10 mL
portion of C6H6 was added to the Schlenk flask by vacuum
transfer at -78 °C followed by 0.02 mL of isopropylacetylene
(0.195 mmol). The reaction mixture was stirred for 12 h at
room temperature, producing the bis(acetylide) complex Cp*2-
Th(CtCPri)2, as indicated by a change in color and confirmed
Or ga n oa ct in id e-Ca t a lyzed H yd r osilyla t ion of
Ter m in a l Alk yn es. (i) Rea ction Scop e a t Room
Tem p er a tu r e. The room-temperature reaction of Cp*2-
AnMe2 (An ) Th, U) with an excess of terminal alkynes
RCtCH (R ) tBu, iPr, nBu) and PhSiH3 (alkyne:silane:
catalyst ) 40:40:1) in either benzene or tetrahydrofuran
results in the catalytic formation of trans-vinylsilanes
1
by H NMR spectroscopy. Then a 0.012 mL portion of PhSiH3
(0.0985 mmol) was added by vacuum transfer and the reaction
mixture was stirred for an additional 6 h, yielding quantita-
tively Cp*Th(CtCPri){C(PhSiH2)dCH(Pri)}. The color of the
reaction mixture changed from pale yellow to dark red.
Poisoning experiments with equimolar amounts of H2O al-
lowed the production of the starting alkyne and the cis-
hydrosilylated compound 14. Anal. Calcd for C36H52SiUTh: C,
58.06; H, 6.99. Found: C, 56.70; H, 6.93.. Mp: 90 °C dec.
1H NMR (200 MHz, C6D6): δ 7.80-7.82 (m, 2H, m-H Ph),
7.21-7.28 (m, 3H, o,p-H Ph), 6.79 (d, 1H, 3J ) 6.73 Hz, d
t
i
RCHdCHSiH2Ph (R ) Bu (1), Pr (2), nBu (3)), the
dehydrogenated silylalkynes RCtCSiH2Ph (R ) tBu (4),
iPr (5), Bu (6)), and the corresponding alkenes RCHd
n
CH2 (R ) Bu (7), Pr (8), nBu (9)), as shown in eq 3
t
i
1
CH), 5.27 (s, 2H, J H-Si (satellites) ) 203 Hz, PhSiH2), 3.17 (m,
1H, dCH-CHMe2), 2.68 (septet, 1H, 3J ) 6.94 Hz, tC-
CHMe2), 2.07 (s, 30H, C5(CH3)5), 1.26 (d, 6H, 3J ) 6.94 Hz,
3
tC-CH(CH3)2), 1.08 (d, 6H, J ) 6.44 Hz, dCH-CH(CH3)2).
13C NMR (50 Hz, C6D6): δ 209.8 (s, ThCdCH), 156.8 (s, ThCt
1
1
C), 142.8 (d, J ) 119.2 Hz, ThCdCH), 135.8 (d, J ) 155 Hz,
1
o-CH Ph), 129.3 (d, J ) 155 Hz, m-CH Ph), 135.3 (s, CC5H5),
128.2 (d, 1J ) 155 Hz, p-CH Ph), 123.8 (s, C5Me5), 120.6 (s,
1
1
ThCtC), 34.0 (d, J ) 129.2 Hz, dC-CHMe2), 24.18 (q, J )
128.8 Hz, dC-CH(CH3)2), 22.7 (q, 1J ) 128.8 Hz, tC-CH-
1
1
(CH3)2), 21.8 (d, J ) 129.2 Hz, C-CHMe2), 11.6 (q, J ) 126.3
Hz, C5(CH3)5). 29Si NMR (79.5 Hz, C6D6): δ 5.9 (tdt, J Si-H
)
1
3
3
203.3 Hz, J Si-H(C) ) 23.2 Hz, J Si-H(Ph) ) 6.1 Hz, PhSiH2).
(16) Kin etic Stu d y of th e Hyd r osilyla tion of Ter m in a l
Alk yn es w ith P h SiH3. In a typical experiment, an NMR

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4731
Ta ble 1. P r od u ct Distr ibu tion s of th e Cp *2An Me2
(An ) Th , U) Ca ta lyzed Hyd r osilyla tion of
Ter m in a l Alk yn es w ith P h SiH3 a t Room
Tem p er a tu r ea
ture. The reactions were found to be sensitive to the
nature of the catalysts, the substituent on the alkyne
and silanes, the stoichiometry of the substrates, and the
polarity of the solvents.
trans-
t
i
The hydrosilylation of RCtCH (R ) Bu, Pr, nBu)
with PhSiH3 catalyzed by Cp*2UMe2 (alkyne:silane:
catalyst ) 40:40:1) at high temperature (65-78 °C)
produced, in addition to the hydrosilylation products at
room temperature (eq 3), the corresponding cis-hydrosi-
lylated compounds cis-RCHdCHSiH2Ph (R ) tBu (13),
R in
RCHdCHSiH2Ph RCtCSiH2Ph RCHdCH2
entry cat. RCtCH
(%)
(%)
(%)
1
2
3
4
5
6
7
8
Th
U
Th
U
Th
U
Th
U
iPr
42
62
48
47
56
74
-
28
27
28
31
22
24
-
26 (5)b
12
24
22
22
2
iPr
tBu
tBu
nBu
nBu
TMS
TMS
n
iPr (14), Bu (15)), and small to moderate yields of the
-
-
unexpected double-hydrosilylation products RCHdC(SiH2-
Ph)2 (R ) tBu (16), Pr (17), Bu (18)), in which the two
silyl moieties are attached to the same carbon atom (eq
5) (Table 2). For the bulky substituents (tBu), a maxi-
8
16
i
n
a
When the reactions were carried out in either C6D6 or THF-
d
8 for both catalytic systems, no significant changes in the product
b
selectivities were observed. The number in parentheses corre-
i
sponds to the alkane PrCH2CH3.
(Table 1). Interestingly, for Cp*2ThMe2 and only for
isopropylacetylene, the formation of the fully reduced
i
alkane PrCH2CH3 (10) was observed.
Irrespective of the alkyl substituents and the metal
center, the major product in the hydrosilylation reaction
at room temperature is the regio- and stereoselective
trans-vinylsilane, without any trace formation of the
other two hydrosilylation isomers (gem or cis). For bulky
alkynes (tBuCtCH), the product distributions are nearly
the same for both catalytic systems, whereas for other
terminal alkynes, they vary from one catalytic system
to another. It is worth pointing out that in the hydrosi-
lylation reaction of the alkynes with Cp*2ThMe2 and
PhSiH3, similar amounts of both the alkene and the
corresponding silylalkyne are obtained. This result
suggests a mechanistic pathway involving two organo-
metallic complexes that are formed in a consecutive
fashion, each one being responsible only for one of the
products.
mum yield of 19% for the double-hydrosilylation product
tBuCHdC(SiH2Ph)2 (16), was obtained, whereas for
i
nBuCtCH or PrCtCH only ∼3% of the corresponding
double-hydrosilylated products 17 and 18 were obtained.
The amounts of either the cis isomers 13-15 or the
corresponding silylalkynes 4-6 are much higher than
those of the trans isomers (1-3), which were the major
hydrosilylated products at room temperature. These
results strongly suggest a competing pathway toward
the cis isomers at high temperature. A comparison of
the concentrations of the silylalkyne and the corre-
sponding alkene for each alkyne shows that each
catalytic system gives a different ratio of the two
products. This result suggests that, at high temperature,
an additional competing route is responsible for the
formation of both the alkene and the silylalkyne.
Furthermore, it seems also possible that the silylalkyne
may be transformed, during the catalytic cycle, to other
products, inducing a lower concentration, as compared
to the corresponding alkene (entries 2, 3, 5, 8, 11, and
12 in Table 2).
The reaction of Cp*2UMe2 with (TMS)CtCH (TMS
) Me3Si) and PhSiH3 at room temperature is very slow,
producing only, after 48 h, 8% and 16% of trans-(TMS)-
CHdCHSiH2Ph (11) and the silylalkyne (TMS)Ct
CSiH2Ph (12), respectively (eq 4). For the analogous
The corresponding hydrosilylation reactions using
Cp*2ThMe2 with PhSiH3 and the terminal alkynes RCt
CH (R ) tBu, Pr, Bu) (alkyne:silane:catalyst ) 40:40:
1), at high temperature, follow the regioselectivity and
chemoselectivity as obtained for the hydrosilylation
reaction at room temperature (eq 3). The only difference
was found for isopropylacetylene, for which no fully
hydrogenated alkane 10 was produced and the double-
hydrosilylated product iPrCHdC(SiH2Ph)2 (14) was
obtained in 2% yield (C6D6) or up to 6% (THF), as
i
n
Cp*2ThMe2, with (TMS)CtCH and PhSiH3 no hydrosi-
lylation or dehydrogenative coupling products were
observed under similar reaction conditions. In addition,
neither the oligomerization dimer nor trimers of the
(TMS)CtCH were observed.14
(ii) Rea ction Scop e a t High Tem p er a tu r e. At high
temperature (65-78 °C), the chemoselectivity and the
regioselectivity of the vinylsilanes formed in the orga-
noactinide-catalyzed hydrosilylation of terminal alkynes
with PhSiH3 were found to be different, as compared to
the hydrosilylation results obtained at room tempera-
1
confirmed from the H, 13C, and 29Si NMR spectra. The
use of a polar solvent increased the yield of the
hydrogenated products RCHdCH2 (7 and 8) as com-
pared to that for the reaction carried out in C6D6, under
similar reaction conditions (entries 1 and 2 or 4 and 5

4732 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
Ta ble 2. P r od u ct Distr ibu tion s of th e Cp *2An Me2 (An ) Th , U) Ca ta lyzed Hyd r osilyla tion of RCtCH w ith
P h SiH3 a t High Tem p er a tu r ea
RCHdC(SiH2Ph)2
trans-RCHdCHSiH2Ph
cis-RCHdCHSiH2Ph
RCtCSiH2Ph
RCHdCH2
entry
cat.
R
solvent
(%)
(%)
(%)
(%)
(%)
1
2
3
4
5
6
7
8
Th
Th
U
Th
Th
U
Th
U
Th
U
Thb
Thc
iPr
C6D6
THF
THF
C6D6
THF
THF
C6D6
THF
C6D6
THF
THF
THF
2
6
2
37
33
4
21
21
15
43
5
15
6
52
20 (13)d
trace
trace
27
trace
trace
24
trace
54
-
26
38
25
31
46
31
36
34
9
23
36
35
37
48
7
23
16
39
29
17
48
iPr
iPr
tBu
tBu
tBu
nBu
nBu
TMS
TMS
iPr
trace
trace
19
trace
3
-
-
9
46
40
6
10
11
12
26
9
trace
trace
iPr
11
a
b
The reactions were carried in either reflux of C6D6 or THF-d8. A stoichiometric ratio of 1:2 for iPrCtCH:PhSiH3 was used. c A
stoichiometric ratio of 2:1 for PrCtCH:PhSiH3 was used. The number in parentheses corresponds to trans-iPrCHdCHSi(H)(Ph)CtCPri.
i
d
in Table 2). Whereas Cp*2UMe2 catalyzed the hydrosi-
lylation of terminal alkynes at high temperature, yield-
ing a mixture of both cis- and trans-vinylsilanes, strik-
ingly, the analogue Cp*2ThMe2 afforded only the trans-
vinylsilane.
on the silane concentrations (eq 7).
In the high-temperature hydrosilylation reaction of
(trimethylsilyl)acetylene with PhSiH3 catalyzed by Cp*2-
UMe2, besides the trans-vinylsilane (11) and the sily-
lalkyne (12) products, which were also obtained at room
temperature, the cis-vinylsilane (19) and the olefin
(TMS)CHdCH2 (20) were obtained in good yields (eq 6
and Table 2). For Cp*2ThMe2, in contrast to the room-
Thus, when the hydrosilylation reaction is carried out
using a 1:2 ratio of iPrCtCH to PhSiH3 with Cp*2ThMe2
in THF (65 °C), the trans-vinylsilane is the major
product of the reaction (52%). The amount of the double-
hydrosilylation product 17 is increased to 26%, as
compared to the 6% obtained using a 1:1 ratio among
the substrates (eq 7 and Table 2, entry 11). When the
reaction is conducted under the same conditions, but
with an opposite ratio between the substrates (iPrCt
i
CH:PhSiH3 ) 0.5), the olefin PrCHdCH2 (8) was found
to be the major product. In addition to trans-iPrCHd
CHSiH2Ph (2), iPrCtCSiH2Ph (5), and the double-
hydrosilylated olefin 17, the tertiary silane trans-
iPrCHdCHSi(HPh)(CtCPri) (21) was also observed.
This last compound is obtained as the metathesis
dehydrocoupling product from the reaction of the trans-
alkenylsilane with the metal acetylide complex (vide
infra).
(iv) Effect of th e Sila n e Su bstitu en t in th e
Hyd r osilyla t ion R ea ct ion a t High Tem p er a t u r e.
The inductive and steric effects of the silane substitu-
ents for the Cp*2ThMe2-catalyzed hydrosilylation reac-
tion of iPrCtCH were studied (eq 8, Table 3). Replacing
temperature reaction, in which no products were found,
the same products as in the hydrosilylation reaction
promoted by Cp*2UMe2 were formed except for the cis-
vinylsilane (19) (eq 6). In neither case was the double
hydrosilylation of (TMS)CtCH observed.
(iii) E ffect of t h e R a t io of Alk yn e t o Sila n e. A
basic conceptual question regarding the effect of PhSiH3
toward the formation of the different products was
investigated by performing two parallel experiments.
Two reactions were designed in which the concentration
ratio between the catalyst and alkyne was maintained
constant (1:40) but the concentration of PhSiH3 as
compared to that of the alkyne was either doubled or
reduced to half. We have found that the chemoselectivity
and regioselectivity of the products are highly dependent
one hydrogen on PhSiH3 by either an alkyl or a phenyl

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4733
i
a
Ta ble 3. P r od u ct Distr ibu tion s of th e Cp *2Th Me2 Ca ta lyzed Hyd r osilyla tion of P r CtCH w ith P h RSiH2
entry
R
reacn time (h)
iPrCtCSiHRPh (%)
trans-iPrCHdCHSiHRPh (%)
iPrCHdCH2 (%)
alkyne oligomers (%)
1
2
3
Hb
Ph
Me
12
24
36
38
47
31
37
4
2
23
39
20
-
11
47
a
b
The reaction was carried out in C6D6 at 78 °C. A yield of 2.2% of the double-hydrosilylation product iPrCHdC(SiH2Ph)2 was
observed.
i
When an equivalent amount of PrCtCH was added
ring generates a retardation in the rate of the hydrosi-
lylation reaction as compared to the rate obtained util-
izing phenylsilane. Moreover, the selectivities of the pro-
ducts were significantly different as compared to those
obtained using PhSiH3 as the hydrosilylating agent.
The reaction of an equimolar mixture of iPrCtCH and
Ph2SiH2 in the presence of a catalytic amount of Cp*2-
ThMe2 in C6D6 at 78 °C produced the silylalkyne adduct
to a benzene solution of Cp*2UMe2 at room temperature,
methane gas evolved, leading to the formation of the
orange mono(acetylide) methyl complex Cp*2U(CtCPri)-
(Me) (26). This transient species was found to be very
reactive, and the consecutive addition of a second
i
equivalent of PrCtCH converted complex 26 rapidly
into the deep red-brown bis(acetylide) complex Cp*2U-
(CtCPri)2 (27). Due to the paramagnetic behavior of the
uranium(IV) complexes and the rapid electron spin-
lattice relaxation times, chemically and magnetically
nonequivalent ligand protons in 26 and 27 exhibit
generally sharp, well-separated signals and can be
readily resolved in the 1H NMR spectra. Attempts to
spectroscopically trap any other mono(acetylide) methyl
organoactinide complexes were unsuccessful. For tho-
rium, the reaction with stoichiometric amounts of iPrCt
CH produced half the amount of the bis(acetylide)
complex Cp*2Th(CtCPri)2 (28). Addition of 1 equiv of
PhSiH3 at room temperature to a benzene solution of
any of the bis(acetylide) organoactinide complexes af-
forded the quantitative formation of the silylalkenyl
acetylide actinide complexes Cp*2An(PhSiH2CdCHiPr)-
(CtCiPr) (An ) U (29), Th (30)), which were found to
be intermediates in the catalytic cycle for the hydrosi-
lylation reactions (eq 10).
i
iPrCtCSiHPh2 (22) and the alkene PrCHdCH2 (8) as
the major products. Trace amounts of the hydrosilyla-
i
tion product PrCHdCHSiHPh2 (23) was identified by
GC/MS spectroscopy, together with the alkyne oligo-
merization products (dimer-pentamers). The reaction
i
of PhMeSiH2 with PrCtCH under similar reaction con-
ditions afforded large amounts of iPrCtCSiHMePh (24),
iPrCHdCH2 (8), and alkyne oligomerization products
(dimer-pentamers), in addition to a small quantity of
trans-iPrCHdCHSiHMePh (25) (entries 2 and 3, Table
3). This result indicates that, for secondary silanes, the
insertion of an alkyne into the active bis(acetylide)-
actinide complex, inducing the oligomerization reac-
tion,14 is in competition with the dehydrogenative
coupling reaction, producing the corresponding silyla-
lkynes and the other observed products (vide infra).
Stoich iom etr ic Rea ction s a n d Tr a p p in g of th e
Key Or ga n om eta llic In ter m ed ia te Com p lex. To
detect some of the key organometallic intermediates in
the hydrosilylation process, a consecutive series of
stoichiometric reactions were carried out, using the
organoactinide precursor Cp*2AnMe2 (An ) Th, U),
iPrCtCH, and PhSiH3. The stoichiometric reaction of
PhSiH3 with Cp*2ThMe2 induced the dehydrogenative
coupling of the silane to the dimer and trimer, as
already reported in the literature.27 Since we have not
been able to detect any traces of these dimers or
oligomers for either organometallic complex, we decided
to start the stoichiometric reaction studies from the
i
addition of 1 and/or 2 equiv of PrCtCH to a benzene
solution of Cp*2AnMe2 at room temperature.
The reactions of the organoactinide metallocene com-
plexes Cp*2AnMe2 (An ) Th, U; Cp* ) C5Me5) with
alkynes in stoichiometric amounts allow the preparation
and characterization of mono- and bis(acetylide) com-
plexes of organoactinides, as described in eq 9.
The formation of such an intermediate was indicated
by the change in color of the reaction from orange to
dark orange-brown for complex 29 and from pale yellow
to dark red for 30. Both of the complexes were found to
be stable in their solutions for long periods of time under
an inert atmosphere. The structures of 29 and 30 were
unambiguously confirmed by 1H, 13C, and 29Si NMR
1
spectroscopy as well as by NOE experiments. The H
NMR spectra of 29 and 30 each displayed, in addition
to the signals for the phenyl and Cp* protons, two
signals for the CH3 protons (two different isopropyl
groups), two signals for the CH-(CH3)2 protons, and one
signal for each of the olefinic CH and silane (SiH2)
1
protons. Figure 1 shows the comparison of the H NMR

4734 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
to the isopropyl group in the organometallic complex
was found to be cis. The full stereochemical assignment
of the signals, in each of the complexes, was confirmed
by NOE experiments. For example, irradiation at the
CH proton of the isopropyl group in the silylalkenyl
moiety in 30 enhanced the corresponding PhSiH2 and
methyl signals in the 1H NMR by 3.12% and 1.56%,
respectively. A corroboration for the stereochemistry of
the organometallic intermediate 30 was found by a
quenching experiment of 30 with H2O. The addition of
an equimolar amount of water to complex 30 generated
the corresponding cis-vinylsilane product 14 (eq 11).
1
F igu r e 1. (I) H NMR spectrum of Cp*2Th(CtCPri)2 in
THF-d8 (signals marked as d and h). The signals marked
a and e correspond to the methyl and Cp* signals of
remaining Cp*2ThMe2. Signal b corresponds to CH4, and
the signals c, f, and g, correspond to the CH3, Cp*, and CH
hydrogens of Cp*2Th(CtCPri)2, respectively. (II) 1H NMR
spectra of 30 in THF-d8. Signals i, j, and l, m correspond
to the CH3 and CH hydrogens of the two different isopropyl
groups, respectively. Signals k, n, and o correspond to the
Cp*, SiH2, and vinylic CH protons, respectively. Signals p
and q correspond to the aromatic hydrogens.
Further addition of a second equivalent or even an
excess of PhSiH3 or alkyne to complex 29 or 30 did not
change the complex into a new organometallic com-
pound. After long periods of time, some decomposition
of the complexes was observed and the gem dimer was
found in the reaction mixture. This result strongly
suggests that, at room temperature, neither the silane
nor the alkyne is able to induce the σ-bond metathesis
or protonolysis of the hydrosilylated alkene or the
alkyne. The addition of an excess of alkyne at room
temperature to complex 30, only in the presence of
PhSiH3, yields the trans-hydrosilylated alkyne, alkene,
silylalkyne, and bis(acetylide) complex. This result
indicates that the silane is responsible for the σ-bond
metathesis of a different organometallic complex leading
to the trans-hydrosilylated product, which must be in
equilibrium with the organoactinide complex 30. This
equilibrium is proposed due to the trans stereochemistry
of the observed products as compared to the expected
cis stereochemistry, if the intermediate organoactinide
30 were to undergo protonolysis. This result also cor-
roborates a consecutive pathway for the formation of
the silylalkyne and alkene as presented in the room-
temperature scope of the reaction (vide supra).
F igu r e 2. 29Si INEPT spectrum of complex 30 at 300 K.
spectra for complexes 28 and 30. In Figure 1(II), the
downfield doublet signal at 6.79 ppm (3J ) 6.73 Hz) is
assigned to the olefinic proton, split by the CH proton
of the isopropyl group, indicating that both isopropyl
and olefinic proton moieties are in gem positions in the
organometallic complex.
When complex 30 is warmed with PhSiH3, the double-
hydrosilylation compound RCHdC(SiH2Ph)2 is pro-
duced. This result indicates that PhSiH3 is not the
protonolytic source, suggesting that the possible Th-
Si bond is not formed. When complex 29 is warmed with
1 equiv of alkyne, the cis-vinylsilane product is obtained.
Similar reaction of 29 with 1 equiv of PhSiH3 produces
the double-hydrosilylation product. These high-temper-
ature results account for the alkyne as the major
protonolytic agent, whereas the Si-H bond will induce
the σ-bond metathesis, producing the double-hydrosi-
lylation product and the corresponding organometallic
hydrides.
The signal at 5.27 ppm corresponds to the SiH2
protons (1J SiH (satellite) ) 203 Hz). Interestingly, the
proton-coupled 29Si NMR of 30 (Figure 2) displays a
triplet signal at 5.9 ppm (1J Si-H ) 203.3 Hz), which is
split into a doublet due to the trans vinylic hydrogen
(3J Si-H ) 23.19 Hz), which is also split into a triplet by
the ortho hydrogens of the phenyl ring (3J Si-H ) 6.19
Hz). For the corresponding complex 29, the signal is
observed at 34.33 ppm (1J Si-H ) 192 Hz). Low-temper-
ature INEPT measurements (-50 °C) induced neither
a broadening of the signals nor a reduction in the J
couplings. This result argues that even at low temper-
ature no η2-Th-H-Si interactions are detected, indicat-
ing the rapidity of such a process if operative.19a The
geometric arrangement of the silyl group with regard
Kin etic Stu d ies on th e Hyd r osilyla tion of iP r Ct
CH w ith P h SiH3 Ca ta lyzed by Cp *2Th Me2. A kinetic
study of the Cp*2ThMe2-catalyzed hydrosilylation of
iPrCtCH with PhSiH3 in C6D6 was carried out by in
1
situ H NMR spectroscopy. The reaction of an ∼40-fold
i
excess of PrCtCH was monitored with constant phe-
nylsilane and catalyst concentration at 303 K, until

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4735
complete disappearance of the normalized CtCH (δ 1.83
ppm) signal in the H NMR. The turnover frequency of
mol-1, arguing presumably for the high reactivity of
these actinide-silyl bonds.29 Since no dehydrogenative
coupling products of PhSiH3 or alkyne oligomers are
observed for the catalytic reaction between alkyne and
PhSiH3, we focus our studies on the stoichiometric
reactions, at room temperature, starting from the bis-
(acetylide) complexes.
Syn th esis of Bis(a cetylid e) a n d Mon o(a cetyl-
id e)-Sila a lk en yl Actin id e Com p lexes: Stoich io-
m etr ic Rea ction s. The σ-bond metathesis reaction of
the acidic proton of a terminal alkyne with an organo-
actinide complex of the type Cp*2AnMe2 (An ) Th, U)
is a fast reaction which is thermodynamically driven by
the elimination of methane. A number of bis(acetylide)
complexes can be easily prepared and characterized.13b,14
The enthalpy of reaction for such a process is highly
exothermic and can be calculated from tabulated bond
disruption energies that have been measured for these
organoactinide complexes (eq 13).29a,30
1
the reaction was calculated from the slope of the kinetic
plots of substrate to catalyst ratio vs time. When the
initial concentrations of PhSiH3 and catalyst were held
constant and the concentration of the alkyne was varied
over a 10-fold concentration range, a plot of the reaction
rate vs alkyne concentration displayed a linear depen-
dence, indicating that the reaction has a first-order
dependence on alkyne.28 When the concentrations of the
alkyne and catalyst were maintained constant and the
concentration of PhSiH3 was varied over a 10-fold
concentration range, a plot of the reaction rate vs silane
concentration also displays a linear dependence indicat-
ing that the reaction has a first-order dependence on
silane.28 When the concentrations of alkynes and Ph-
SiH3 were kept constant and the concentration of the
catalyst was varied over a 10-fold concentration range,
a plot of the reaction rate vs precatalyst concentration
indicated the reaction to be first order in catalyst.28
When all these facts are taken together, the empirical
rate law expression for the Cp*2ThMe2-catalyzed hy-
drosilylation of iPrCtCH with PhSiH3 can be given by
eq 12. The derived rate constant for the production of 2
at 30 °C is k ) [1.13(5)] × 10-3 s-1
.
ν ) k[iPrCtCH][PhSiH3][Cp*2ThMe2] (12)
A similar kinetic dependence on alkyne, PhSiH3, and
catalyst concentrations is observed over a 30-80 °C
temperature range. The derived activation parameters
Ea, ∆Hq, and ∆Sq from an Eyring analysis are 6.9(3) kcal
mol-1, 6.3(3) kcal mol-1, and 51.1(5) eu, respectively.28
The mono(acetylide) complex was only observed, as a
transient organometallic moiety, for the uranium com-
plex with isopropylacetylene (26). Stoichiometric reac-
tions for other alkynes did not form the mono(acetylide)
complex but rather the bis(acetylide) complexes, indi-
cating that the second σ-bond metathesis has an energy
of activation much lower than that of the corresponding
first σ-bond metathesis. The symmetric NMR spectra
which are obtained for these bis(acetylide) complexes,
similarly to other early-transition-metal bis(acetylide)
complexes,31 indicate that they do not form bridging
acetylide species as in the group 3/organolanthanide
complexes. Interestingly, only when Cp*2HfCl2 is re-
acted with an excess of NaCtCH is the mono(acetylide)
bridging complex Cp*2(CtCH)HfCtCHf(CtCH)Cp*2
obtained.32
Discu ssion
The discussion of the results will be presented by
starting with some controlling experiments detailed in
the literature that show the versatility of these orga-
noactinides toward the hydrosilylation reaction. Then
we will present a thorough discussion regarding the
formation of the organoactinide bis(acetylide) complexes,
the key organoactinide mono(acetylide) silaalkenyl com-
plexes, the reaction scope, and the mechanistic implica-
tions.
Con tr ollin g Exp er im en ts. The catalytic reaction of
the actinides Cp*2AnMe2 (An ) Th, U) with an excess
of terminal alkynes, at high temperature (T > 80 °C)
and in the absence of silanes, induces the alkyne
oligomerization reaction (dimers-heptamers).14a,b In
this process the bis(acetylide) complexes, which are
rapidly formed at room temperature, were found to be
the active species. The reaction of Cp*2UMe2 with an
excess of PhSiH3 in the absence of alkyne, induces the
dehydrogenative coupling of the silane toward oligo-
mers, whereas the reaction with Cp*2ThMe2 produces
the dehydrogenated dimer and the corresponding [Cp*2-
The reaction of either 27 or 28 with PhSiH3 induced
the quantitative isolation of complex 29 or 30, for
uranium and thorium, respectively. These complexes
are formed by the σ-bond metathesis of complexes 27
and 28 by the silane, forming the corresponding actinide
(29) (a) King, W. A.; Marks, T. J . Inorg. Chim. Acta 1995, 229, 343.
(b) Radu, N. S.; Engeler, M. P.; Gerlach, C. P.; Tilley, T. D.; Rheingold,
A. L. J . Am. Chem. Soc. 1995, 117, 3261.
(30) (a) Nolan, S. P.; Stern, D.; Hedden, D.; Marks, T. J . ACS Symp.
Ser. 1990, 428, 159. (b) Marthino Simoes, J . A.; Beauchamp, J . L.
Chem. Rev. 1990, 90, 629. (c) Nolan, S. P.; Stern, D.; Marks, T. J . J .
Am. Chem. Soc. 1989, 111, 7844.
(31) For related group IV bis(acetylide) compounds, see: (a) Erker,
G.; Fro¨mberg, W.; Benn, R.; Mynott, R.; Augermund, K.; Kru¨ger, C.
Organometallics 1989, 8, 911. (b) Lang, H.; Herres, M.; Zsolnai, L.;
Imhof, W. J . Organomet. Chem. 1991, 409, C7.
27
ThH(µ-Η)]2. Interestingly, for these types of organo-
actinides no actinide-silyl complexes have been iso-
lated. The uranium-silicon bond dissociation enthalpies
have been measured to be as low as ca. 37 ( 3 kcal
(28) See the Supporting Information for kinetic and thermodynamic
plots.
(32) Southard, G. E.; Curtis, M. D.; Kampf, J . W. Organometallics
1996, 15, 5, 4667.

4736 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
Sch em e 2. P la u sible Or ga n oa ctin id e In ter m ed ia tes Exp ected in th e Stoich iom etr ic Hyd r osilyla tion of
Ter m in a l Alk yn es th r ou gh a Tr a n sien t Or ga n oa ctin id e-Silicon Bon d
hydrides and the silylalkyne, which rapidly reinsert to
produce 29 or 30 (eq 14). For the thorium complex a
reactivity) would be expected to induce the rapid forma-
tion of either the acetylide alkenyl complex with a trans
or gem stereochemistry, 32 or 33, respectively, or the
hydride complex 34. If this mechanism is operative, we
can conclude that this is not a major route to products
because (i) the quenching experiments with water gave
exclusively the cis-vinylsilane, (ii) under the stoichio-
metric conditions, the addition of silane did not induce
the protonolysis of the acetylide-alkenylsilane complex
(29 or 30), arguing how difficult the production of
complex 31 will be, (iii) no gem hydrosilylated product
was obtained (if complex 33 is an intermediate, it would
be observed), (iv) no cis hydrosilylated products can be
obtained from complex 31, and (v) no cis double-
hydrosilylated products are observed (the result of
σ-bond metathesis from complex 32 or 33).
The reactions of complexes 29 and 30 at high tem-
perature with silane yield the double-hydrosilylated
product (eq 15). This σ-bond metathesis reaction is
hydride signal at 13.64 ppm is observed, which has a
chemical shift similar to that for the thorium hydride
[Cp*2ThH(µ-Η)]2 (19.20 ppm), 27 although our attempts
to trap this organometallic complex were unsuccessful.
The obtained regioselective mode of insertion for
PhSiH2CtCPri approaching the actinide hydride com-
plex is fully electronically favored, as expected for the
polarization of the organoactinides and the π* orbital
of the alkyne.33 In addition, since the insertion followed
a four-center transition state mechanism, a cis stereo-
chemistry between the two alkyne substituents is
expected, as corroborated by the H2O poisoning experi-
ment and the high-temperature reactions with alkyne
or silane. A similar regioselective insertion of (TMS)Ct
CH into an organothorium alkenyl complex has been
observed in the organoactinide-catalyzed oligomeriza-
tion of alkynes.14
Theoretically, the formulation of the organoactinide-
silane intermediate 31 is also possible, as described in
Scheme 2. Complex 31 could be obtained from the
corresponding bis(acetylide) complex. The low bond
enthalpy calculated for an actinide-silicon bond (high
stereoselectively favored due to the putative polarization
of the PhSiH3 toward the metal center, as well as the
preferred thermodynamics, as compared to the proto-
nolysis by the silane producing complex 31 and the cis
(33) For reviews, see: (a) Fleming, I. CHEMTRACTS: Org. Chem.
1993, 6, 113. (b) Apeloig, Y. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; Wiley-Interscience: New
York, 1989; pp 57-225. (c) Gabelica, V.; Kresge, A. J . J . Am. Chem.
Soc. 1996, 118, 3838 and references therein.

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4737
hydrosilylated product (∆ΗTh ) +15(4) kcal mol-1; ∆ΗU
) -3(2) kcal mol-1).30
hydrosilylation products are observed as compared to
other alkynes under the same catalytic conditions
(entries 7 and 9 in Tables 1 and 2, respectively). This
type of reactivity is found in general as the result of a
kinetic effect. Therefore, this result strongly suggests,
and again corroborates, an equilibrium between an
The most remarkable and puzzling observation re-
gards the products of reaction of complexes 29 and 30
with alkyne at either low or high temperature. The
reaction at high temperature (65-80 °C) yields the
expected cis-hydrosilylated product. This reaction is the
protonolysis of 29 or 30 by the alkyne, producing the
bis(acetylide) organoactinide complex (eq 16). The reac-
i
organometallic complex, similar to 30, in which the Pr
group is replaced by a TMS moiety (35), with the
organometallic complex 36 (Scheme 3). Complex 36 is
obtained by the insertion of the silylalkyne into a
hydride complex. Complex 36 is able to react with
another alkyne, yielding the alkene and the bis(acetyl-
ide) complex (protonolysis route) or to react with a
silane, producing the organometallic hydride and the
trans product (σ-bond metathesis route). The low activ-
ity obtained for (TMS)CtCH argues for a high energy
of activation to perform either the metathesis or pro-
tonolysis of complex 36, as compared with the energy
required for other alkynes.
The ratio between the silane and the alkyne seems
to govern the kinetics toward the different products.
Thus, when the PhSiH3:iPrCtCH ratio is 2, the trans
and double-hydrosilylation products are the major
products (metathesis route) (entry 11 in Table 2). When
the same ratio is halved, large amounts of the alkene
are obtained. This result is consistent with an organo-
metallic structure similar to that of 36 (Scheme 3). An
increase in the alkyne concentration will route the
reaction toward the alkene and the bis(acetylide) com-
plex (protonolysis route). The large concentration of the
bis(acetylide) complex will be able to react with the
trans-vinylsilane product, allowing the formation of 21
and the corresponding hydride complex (eq 17).
tion at room temperature in the presence of alkyne and
silane yields exclusively the unexpected trans isomer.
Thus, an operative competitive mechanism should be
in equilibrium, giving the different hydrosilylation
products at different temperatures.
Ca ta lytic Rea ction Scop e a n d Mech a n ism . The
present catalytic results for the hydrosilylation of
terminal alkynes with PhSiH3 producing, at room
temperature, the trans-hydrosilylated product and, at
high temperature, the cis and the double-hydrosilylation
products besides the hydrogenated alkyne and the
intermediate silylalkyne, demonstrate the ability to
tailor the hydrosilylation reaction catalyzed by organo-
actinides.34 Moreover, this is the first time in which
organoactinides or any other metal complexes have been
able to catalyze the double hydrosilylation of alkynes
in which the two silyl groups are in gem positions.35
With regard to the alkynes, (TMS)CtCH exhibits at
room temperature a total lack of reactivity with PhSiH3
in the presence of Cp*2ThMe2; however, at high tem-
perature it produced the trans-vinylsilane, the silyla-
lkyne, and the alkene. Interestingly, no cis or double-
The absence of the expected oligomerization products
under these PhSiH3 starving conditions indicates that
the metathesis reaction of the bis(acetylide) complex
with the hydrosilylated product (eq 17) is much faster
than that of the insertion of an alkyne into the bis-
(acetylide) complex. This is a plausible route, as indi-
cated by the higher temperature needed to run the
oligomerization reactions as compared to the hydrosi-
lylation.14 Interestingly, by using more bulky silanes
such as Ph2SiH2 and PhMeSiH2 a large retardation in
the kinetics toward the hydrosilylated products is
noticed. It seems that the secondary silanes are unable
to induce the metathesis of the organometallic alkenyl
complex, yielding the hydrosilylated trans product (me-
tathesis pathway as described in Scheme 3). The sily-
lalkyne and the alkene are the major products (proto-
(34) The hydrosilylation of terminal alkynes by organolanthanides
is not operative due to the rapid competing oligomerization of the
alkyne.4 For internal alkynes, only Cp*2YR has been reported as an
active catalyst, producing both (E)- and (Z)-vinylsilanes.6,19
(35) The bis-silylation of a C-C triple bond is a reaction in which
two Si-C bonds are created in the same molecule. Palladium complexes
are the most often used catalysts. The mechanism consists of the
oxidative addition of the Si-Si bond to palladium(0) and the transfer
of the two organosilyl groups to the C-C triple bond in
a cis
stereochemistry, regenerating the palladium(0). See ref 19a and: (a)
Murakami, M.; Yoshida, T.; Ito, Y. Organometallics 1994, 13, 2900.
(b) Murakami, M.; Yoshida, T.; Kawanami, S.; Ito, Y. J . Am. Chem.
Soc. 1995, 117, 6408. (c) Ozawa, F.; Sugawara, M.; Hayashi, T.
Organometallics 1994, 13, 3237. (d) J acobsen, H.; Ziegler, T. Organo-
metallics 1995, 14, 224.

4738 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
Sch em e 3. P r oton olysis a n d σ-Bon d Meta th esis Rou tes for th e High -Tem p er a tu r e Hyd r osilyla tion of
(TMS)CtCH w ith P h SiH3 Ca ta lyzed by Cp *2Th Me2
nolysis pathways), whereas only trace amounts of the
trans-hydrosilylated product are observed. This result
is also in agreement for a situation similar to that
depicted in Scheme 3. The low reactivity of the second-
ary silanes and their intrinsic inability toward the
σ-bond metathesis route to produce the corresponding
vinylsilane seem to be responsible for allowing the
production of alkene and the bis(acetylide) complex,
which may either react slowly with the silane, producing
the silylalkyne and the corresponding hydride, or react
with an alkyne, yielding the observed oligomers.14
σ-bond metathesis by a silane, and protonolysis by an
acidic alkyne hydrogen. The precatalyst Cp*2ThMe2 in
the presence of alkyne is converted to the bis(acetylide)
complex C (eq 9). Complex C reacts with PhSiH3,
yielding the silylalkyne and the organoactinide hydride
A (step 1), which is in equilibrium with the intermediate
D after reinsertion of the silylalkyne with the prefer-
ential stereochemistry (step 2).36 Complex D was found
to be the predominant complex under alkyne and silane
starvation. Although â-H elimination is not a favored
process in organoalkylactinide chemistry, interestingly,
t
the reaction of complex 30 with BuCtCH and PhSiH3
Regarding the rate, the present hydrosilylation pro-
cess exhibits larger turnover frequencies as compared
to Cp*2YCH3.19i The yttrium complex is able to induce
the hydrosilylation reaction of internal alkynes prefer-
entially toward the E isomer, although in some case the
Z isomer is found in similar quantities. Mechanistically,
the active species for the yttrium hydrosilylation of
internal alkynes is proposed to be the corresponding
hydride. For alkenes, the hydrosilylation reaction pro-
moted by organolanthanides of the type Cp*2LnR (Ln
) Sm, La, Lu) proceeds with similar turnover frequen-
cies, as compared to the organoactinides with terminal
alkynes. Mechanistically, the lanthanide hydrides have
been proposed as the primordial pathway toward the
hydrosilylated products.6a
produces only trans-tBuCHdCHSiH2Ph (1) and the
corresponding silylalkyne (4), supporting the equilibri-
um between complexes A and D. Complex A rapidly
inserts an alkyne, producing the alkenyl acetylide
organothorium complex B (step 3), which is presumably
in rapid equilibrium with complex A (as indicated by
the first-order dependence on alkyne). For example, in
the hydrogenation of alkenes by the metallocene tho-
rium bis(hydride) complex, this insertion step has been
found to be in rapid equilibrium.12 Complex B will react
with PhSiH3, as the rate-determining step producing the
hydride and the trans-hydrosilylated product (step 4).
Under the catalytic conditions, complex B may also
react with a second alkyne, producing the alkene and
the bis(acetylide) complex C (step 5). A similar insertion
of the alkene into complex A with the concomitant
A plausible mechanism for the hydrosilylation of
terminal alkynes catalyzed by Cp*2ThMe2 is described
in Scheme 4.
(36) Under the catalytic conditions, trace amounts of PhSiH2Me
are produced and characterized by 1H NMR and GC/MS tech-
niques, indicating that the Cp*2ThMe2 or the mono(acetylide) Cp*2-
ThMe(CtCR) is able to react with PhSiH3, yielding the corresponding
hydride.
The mechanism presented in Scheme 4 consists of a
sequence of well-established elementary reactions, such
as insertion of acetylene into a metal-hydride σ-bond,

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4739
Sch em e 4. P la u sible Mech a n ism for th e Room - a n d High -Tem p er a tu r e Hyd r osilyla tion of
a
Isop r op yla cetylen e w ith P h SiH3 P r om oted by Cp *2Th Me2
a
The transformation of the Cp*2ThMe2 complex into the bis(acetylide) complex is described in eq 9 and omitted for clarity.
reaction with an additional alkyne, will produce the
double-hydrogenated product (10), as found for isopro-
pylacetylene. At high temperature, complex D may react
with a silane (step 6), yielding complex A and the
double-hydrosilylation product, or with an alkyne (step
7), yielding complex C and the cis isomer. Thus, the
reaction rate law presented in eq 12 is compatible with
rapid, operationally irreversible phenylsilane metath-
esis with complex C, rapid preequilibrium involving the
hydride and alkenyl complexes A and B, and a slow
metathesis by the PhSiH3 inducing the trans product.
It is important to point out that, for the thorium
complex, step 6 is much faster than step 7, since the cis
product is obtained in trace amounts. The rate law
presented in eq 12 is operative for the production of the
hydrosilylated compound 2, between 30 and 80 °C. It is
important to point out that, since other pathways are
observed at higher temperatures, the kinetics for each
possible product may change as a function of tempera-
ture.
The activation energy parameters for the hydrosily-
lation of iPrCtCH with PhSiH3 promoted by Cp*2ThMe2
are characterized by a rather small enthalpy of activa-
tion (∆Hq ) 6.3(3) kcal mol-1, Ea ) 6.9(3) kcal mol-1
)
and a large negative (even for an intermolecular reac-
tion) entropy of activation (∆Sq ) -51.1(5) eu, ∆Gq )
21.5(6) kcal mol-1 at 298 K). These parameters suggest
a highly ordered transition state with considerable bond
making to compensate for bond breaking. Thus, the
process proceeds with a high degree of entropic reorga-
nization on approaching the transition state. The low
enthalpy of activation indicates that the σ-bond me-
tathesis of the alkenyl complex by PhSiH3, which is the
rate-determining step, is faster as compared to the
insertion of an alkyne into the bis(acetylide) complex
(∆Hq ) 11.1(3) kcal mol-1), which will produce alkyne
oligomers. On the basis of the obtained results, we can
argue that the formation of the silylalkyne and the
corresponding organoactinide hydride and the concomi-
tant alkyne insertion forming the alkenyl complex are
faster steps than the metathesis reaction of the alkenyl
complex yielding the trans-vinylsilane.
The mechanistic pathway proposed takes into account
the similar yields for the alkene and silylalkyne cata-
lyzed by the thorium complex even when the alkyne
concentration is in excess (in this case the sum of the
silylated products is equal to the amount of the alkene).
For the thorium or uranium complexes, the amount of
the hydrosilylated product is either similar to or larger
than that of the alkene. For example (entry 6, Table 1),
at room temperature the amount of 1-hexene (2%) is
much lower than that of the corresponding silylalkyne
(24%), indicating that an optional competing equilibri-
um route should be operative, responsible for the
transformation of the hydride complex back to the
biacetylide complex, allowing the production of the
silylalkyne without producing the alkene (eq 18).
Solven t Effect. Recently the use of polar solvents
to allow the stereoselective controlling of vinylsilanes
obtained by the hydrosilylation of terminal alkynes by
[Rh(COD)Cl2]2 has been reported.22c When the hydrosi-
lylation reaction is conducted in polar and/or protic
solvents (EtOH, DMF), the (Z)-vinylsilane is obtained
as the predominant species due to the stabilization of a

4740 Organometallics, Vol. 18, No. 23, 1999
Dash et al.
Ta ble 4. 29Si NMR Ch em ica l Sh ifts (p p m ) for th e Si-H-Con ta in in g P r od u cts Obta in ed in th e
Hyd r osilyla tion of RCtCH w ith P h SiH3 P r om oted by Cp *2An Me2 (An ) U, Th )
trans-RCHdCHSi(H)-
entry
1
R
RCHdC(SiH2Ph)2
trans-RCHdCHSiH2Ph
(Ph)CtCR
cis-RCHdCHSiH2Ph
RCtCSiH2Ph
tBu
30.2 (t, J ) 215 Hz)
15.6 (tt, J ) 198 Hz,
4.6 (t, J ) 210 Hz)
-8.98 (tt, J ) 211 Hz;
1
1
1
1
1
5.2 (t, J ) 210 Hz)
3J ) 7.3 Hza)
3J ) 6.1 Hza)
1
1
1
1
2
3
iPr
27.5 (t, J ) 198 Hz)
14.7 (t, J ) 199 Hz)
11.7 (d, J ) 212 Hz)
1.6 (t, J ) 196 Hz)
-9.0 (t, J ) 213 Hz)
1
7.3 (t, J ) 203 Hz)
nBu 23.8 (t, J ) 208 Hz)
14.0 (t, J ) 196 Hz)
1.4 (t, J ) 195 Hz)
-9.1 (t, J ) 212 Hz)
1
1
1
1
1
4.1 (t, J ) 211 Hz)
a
Only in these compounds were the 3J couplings of the ortho hydrogens with the silicon atom observed.
zwitterionic intermediate. However, using less polar
solvents, such as CH3CN, the E isomer is the predomi-
nant species obtained. For organoactinides, the use of
polar solvents (THF) did not induce any changes in
stereoselectivities but produced a significant shift in the
yields of the alkenes as compared to the reaction carried
out in C6H6. Thus, in polar solvents, the protonolysis of
the metal-alkenyl complex by the alkyne (step 5 in
Scheme 4) is much faster than the σ-bond metathesis
of the phenylsilane (step 4 in Scheme 4), possibly due
to the solvent-silane interactions.37
Thermodynamically, it is very interesting to compare
the enthalpy of the reactions for the possible silane and
hydride intermediates toward the formation of the trans
hydrosilylation product as presented in eqs 19 and 20,
respectively.
The calculated enthalpies of reaction for the insertion
of an alkyne into an actinide-silane bond (eq 19) (∆HTh
) -52 kcal mol-1; ∆HU ) -34 kcal mol-1) or into an
actinide-hydride bond (eq 20) (∆HTh ) -33 kcal mol-1
;
∆HU ) -36 kcal mol-1) are expected to be rapid and
exothermic. However, the protonolysis by the silane,
yielding back the An-Si bond and the trans product (eq
19), is for thorium an endothermic process (∆HTh ) +
15 kcal mol-1), as compared to the exothermic σ-bond
metathesis (eq 20) of the thorium alkenyl complex by
the silane (∆HTh ) -19 kcal mol-1), yielding the
corresponding Th-H bond and the trans product. For
the corresponding uranium complexes, the latter pro-
cesses are exothermic, although the σ-bond metathesis
route (eq 20) is by far more exothermic (∆HU ) -26 kcal
mol-1) than the protonolysis route (eq 19) (∆HU ) -3
kcal mol-1).
29Si Ch em ica l Sh ift Beh a vior . We have shown that
many types of silicon-containing organic compounds are
obtained in the hydrosilylation of terminal alkynes
promoted by organoactinide complexes. Table 4 compiles
the different 29Si chemical shifts for the corresponding
Si-H-containing products.
In the double-hydrosilylation products, the downfield
29Si signal was found to correspond to the silicon atom
that is in the position trans to the alkyl group. These
signals (23-30 ppm) appear at a lower field as compared
to those of similar silicon atoms in the trans-vinylsilane
compounds (14-16 ppm). No major changes are ob-
served in the chemical shifts of the silicon atom cis to
the alkyl group in the double-hydrosilylation product
as compared to the cis-vinylsilane (2-8 ppm). As
expected, silicon atoms at the vinylic positions (cis or
trans) are deshielded as compared to silicon atoms
(37) Bassindale, A. R.; Glynn, S. J .; Taylor, P. G In The Chemistry
of Organic Silicon Compounds; Apeloig, Y., Rappoport, Z., Eds.;
Wiley: Chichester, U.K., 1998; Vol. 2, Part 1, Chapter 7, pp 355-430.

Hydrosilylation of Alkynes Promoted by Organoactinides
Organometallics, Vol. 18, No. 23, 1999 4741
bonded to alkyne sp carbons as in the silylalkyne
tively and catalytically only desired products. The
striking difference in reactivity of the thorium complex
as compared to the corresponding uranium complex may
be a result of the involvement of the f orbitals for the
latter complex.
products (∼-9 ppm).19
Con clu sion s
In conclusion, we have shown that organoactinides
are active species for the hydrosilylation of terminal
alkynes by a mechanism that consists of several inser-
tions and σ-bond metathesis. A delicate balance between
alkyne protonolysis and σ-bond metathesis by the silane
determines the ratio among the silaalkyne, alkene, and
trans-hydrosilylated product. The present work repre-
sents the first study on the synthetic, spectroscopic,
kinetic, and reactivity properties of bis(acetylide) orga-
noactinide complexes in the presence of silanes. It
provides insights into the mechanistic process and
stability of the key intermediate compounds, providing
a basis for the rational modification of the metallocene
complexes for future organoactinide arrays. It also lays
the groundwork necessary to understand the approach
to control the hydrosilylation reaction to obtain selec-
Ack n ow led gm en t. The research was supported by
the Israel Science Foundation, administered by the
Israel Academy of Sciences and Humanities under
contract 67/97-1, by the Fund for the Promotion of
Research at the Technion, and by the Technion VPR
Fund. A.K.D. thanks the Technion for a postdoctoral
fellowship.
Su p p or tin g In for m a tion Ava ila ble: Figures giving ki-
netic and thermodynamic plots for the hydrosilylation of
isopropylacetylene with phenylsilane catalyzed by Cp*2ThMe2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM990655C