Tunable stereoselective hydrosilylation of PhC≡CH catalyzed by Cp*Rh complexes

Article abstract of DOI:10.1021/om010978k

The catalysts [Cp*RhCl₂]₂ and [Cp*Rh-(BINAP)](SbF₆)₂ (Cp* = pentamethylcyclopentadienyl; BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) are effective for the hydrosilylation of phenylacetylene with triethy

Full text of DOI:10.1021/om010978k

Organometallics 2002, 21, 1743-1746
1743
Tu n a ble Ster eoselective Hyd r osilyla tion of P h CtCH
Ca ta lyzed by Cp *Rh Com p lexes
J . W. Faller* and Darlene G. D’Alliessi
Department of Chemistry, Yale University, New Haven, Connecticut 06520
Received November 13, 2001
Sch em e 1. Hyd r osilyla tion of P h en yla cetylen e
Summary: The catalysts [Cp*RhCl2]2 and [Cp*Rh-
(BINAP)](SbF6)2 (Cp* ) pentamethylcyclopentadienyl;
BINAP ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl)
are effective for the hydrosilylation of phenylacetylene
with triethylsilane, triethoxysilane, and triphenylsilane
under mild conditions. [Cp*RhCl2]2 promotes the atypi-
cal anti addition to yield the â-Z isomer, whereas
[Cp*Rh(BINAP)](SbF6)2 gives syn addition to form the
â-E isomer. Extraordinarily high regioselectivity and
stereoselectivity were observed for reactions involving
triphenylsilane. Thus, tuning of the ligand set of Cp*Rh
allows preparation of either the â-Z or â-E product.
The hydrosilylation of alkynes offers a simple and
direct means of producing vinylsilanes.1,2 The main
products formed are the R, â-E/trans, and â-Z/cis
isomers (Scheme 1). Regio- and stereoselective syntheses
of these products are desirable, since vinylsilanes are
important intermediates in organic synthesis.3 Selective
formation of the â-Z product would be especially useful,
inasmuch as it is the thermodynamically less stable
isomer.4-6
In early work, transition-metal hydrosilylation cata-
lysts tended to give the â-E isomer.7-9 This formation
of the trans isomer was consistent with syn addition.
Cationic rhodium complexes were later found to catalyze
the hydrosilylation of 1-alkynes to give â-(E)-vinyl-
silanes as the major product, whereas neutral rhodium
compounds catalyzed the reaction to give predominantly
â-(Z)-vinylsilanes.10,11 This was exceptional, in that it
suggested an abnormal anti addition. The original
studies were with monocationic complexes of rhodium;
hence, we sought to examine a dicationic system and a
different neutral system for the potential of greater
selectivity. Dicationic [Cp*Rh(BINAP)](SbF6)2, where
BINAP ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl,
and neutral [Cp*RhCl2]2 were applied as catalysts in
the hydrosilylation of phenylacetylene by triethylsilane,
triethoxysilane, and triphenylsilane. Commercially avail-
able [Cp*RhCl2]2 is easily prepared by heating penta-
methylcyclopentadiene and rhodium trichloride under
reflux.12 [Cp*Rh(BINAP)](SbF6)2 is also easily pre-
pared from [Cp*RhCl2]2, BINAP, and silver hexafluoro-
antimonate. The procedure for hydrosilylation catalysis
involves stirring the appropriate silane with the catalyst
for 15 min at room temperature or 45 °C, prior to
addition of phenylacetylene. Reaction with the trialkyl-
silane can be confirmed by the appearance of rhodium
hydride resonances in the upfield region of the 1H NMR
spectrum. The observed hydride resonances appear
where expected, on the basis of published values for
analogous compounds.13-15 In particular, for the com-
plex derived from [Cp*Rh(BINAP)](SbF6)2, the hydride
appears as a doublet of triplets owing to coupling to one
103Rh and two 31P nuclei. Furthermore, the Cp* methyls
appear as a triplet from coupling to phosphorus. These
resonances persist after the catalytic reaction is com-
plete, but this observation does not, of course, indicate
that this complex lies directly in the catalytic loop. In
fact, the same resonances are observed when the di-
cation is treated with H2, suggesting that the complex
observed in the NMR is [Cp*Rh(BINAP)H]+. After the
addition of phenylacetylene most of the reactions are
complete within a few hours. Overall, reactions per-
formed at 45 °C gave better results. [Cp*Rh(BINAP)]-
(SbF6)2, which probably exists as the solvento or water
complex,16-18 is the first dicationic rhodium complex
(1) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai,
S., Rappoport, Z., Eds.; Wiley: New York, 1989; p 1479.
(2) Ojima, I.; Li, Z.; Zhu, J . In The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998;
p 1687.
(3) Luh, T.; Liu, S. In The Chemistry of Organic Silicon Compounds;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998; Vol. 2, p 1793.
(4) Tanke, R. S.; Crabtree, R. H. J . Am. Chem. Soc. 1990, 112, 7984.
(5) Ojima, I.; Clos, N.; Donovan, R. J .; Ingallina, P. Organometallics
1990, 9, 3127.
(6) Na, Y.; Chang, S. Org. Lett. 2000, 2, 1887.
(7) Ojima, I.; Kumagai, M.; Nagai, Y. J . Organomet. Chem. 1974,
66, C14.
(8) Hill, J . E.; Nile, T. A. J . Organomet. Chem. 1977, 137, 293.
(9) Watanabe, H.; Kitahara, T.; Motegi, T.; Nagai, Y. J . Organomet.
Chem. 1977, 139, 215.
(10) Takeuchi, R.; Nitta, S.; Watanabe, D. J . Org. Chem. 1995, 60,
3045.
(11) Mori, A.; Takahisa, E.; Kajiro, H.; Hirabayashi, K.; Nishihara,
Y.; Hiyama, T. Chem. Lett. 1998, 443.
(12) White, C.; Yates, A.; Maitlis, P. M.; Heinekey, D. M. Inorg.
Synth. 1992, 29, 228.
(13) Fernandez, M.; Maitlis, P. M. J . Chem. Soc., Dalton Trans.
1984, 2063.
(14) Fernandez, M.; Bailey, P. M.; Bentz, P. O.; Ricci, J . S.; Koetzle,
T. F.; Maitlis, P. M. J . Am. Chem. Soc. 1984, 106, 5458.
(15) Bentz, P. O.; Ruiz, J .; Mann, B. E.; Spencer, C. M.; Maitlis, P.
M. J . Chem. Soc., Chem. Commun. 1985, 1374.
(16) Davies, D. L.; Fawcett, J .; Garratt, S. A.; Russell, D. R. Chem.
Commun. 1997, 1351.
10.1021/om010978k CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/07/2002

1744 Organometallics, Vol. 21, No. 8, 2002
Ta ble 1. Hyd r osilyla tion of P h en yla cetylen ea
Notes
catalyst
silane
reacn time (h)
conversion of PhCCHb (%)
â-Z b,c (%)
â-E b,c (%)
R
b,c (%)
[Cp*Rh(BINAP)](SbF6)2
[Cp*Rh(BINAP)](SbF6)2
[Cp*Rh(BINAP)](SbF6)2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
Ph3SiH
(EtO)3SiH
Et3SiH
Ph3SiH
(EtO)3SiH
Et3SiH
2.5d
2.5
21
100
100
99.5
100
100
9.5
<1
0
0
>97
96.5
92.9
>99
81.2
97.4
<3
0
18.8
2.6
0
0
1.5
6d
2.5
3.5
2.5e
5.5
a
Catalyst (5 mol %) and silane (1.1 equiv) were stirred in CH2Cl2 at 45 °C, unless otherwise noted, for 15 min before addition of
PhCCH (1 equiv). The reaction was continued at the same temperature until 100% conversion or 21 h. Determined by 1H and 13C NMR.
b
Comparison of minor isomer 1H resonance to 13C satellites of the major isomer can provide intensity calibration for weak resonances.
c The percentages of Z, E, and R are in relation to each other only. Same result for reaction performed at room temperature and 45 °C.
d
e Reaction at room temperature.
Sch em e 2. Selectivity for Neu tr a l a n d Dica tion ic Ca ta lysts
reported as a hydrosilylation catalyst precursor. As
expected, either rac- or (S)-BINAP can be used without
a change in results. [Cp*Rh(BINAP)](SbF6)2 produces
predominantly â-E isomers, and [Cp*RhCl2]2 produces
a greater proportion of â-Z isomers, in accord with
expectations. The isomers were identified by their 1H
and 13C NMR resonances.6,19,20 Particularly character-
istic are the olefinic proton couplings for the â-E isomer,
the â-Z isomer, and the R isomer, which are 18-20 Hz
(trans), 12-16 Hz (cis), and 2-3 Hz (gem), respectively.
The product ratios obtained in the triphenylsilane and
triethoxysilane hydrosilylations of phenylacetylene are
most significant, since other transition-metal catalysts
which give high selectivity for this hydrosilylation most
often involve triethylsilane.4,6,10,11,21,22 Commonly used
platinum catalysts, H2PtCl6‚6H2O23 and [Bu4N]2[PtCl6],24
give 3-â-E stereoselectively, but, at best, the 3-â-E to
3-R ratio is 95:5 after reaction at 140 °C for 3 h.24 The
most commonly used rhodium catalyst, RhCl(PPh3)3,25
gives a mixture of the isomers, although 3-â-E is
preferred. Another rhodium catalyst, [(nbd)(dppe)Rh]-
PF6 (nbd ) norbornadiene, dppe ) 1,2-bis(diphenylphos-
phino)ethane),22 gives no 3-â-Z but there is some R
isomer formed. The best catalyst to date, [cymene-
RuCl2]2, exhibited high selectivity for 3-â-Z (â-Z:â-E:R
) 96:4:0).6 In this work very high regioselectivity and
stereoselectivity were obtained for the hydrosilyl-
ation of phenylacetylene by triphenylsilane catalyzed
by the Cp*Rh catalysts. [Cp*RhCl2]2 produced >97%
3-â-Z, while [Cp*Rh(BINAP)](SbF6)2 produced >99%
3-â-E (Table 1). This high selectivity was also observed
in room-temperature reactions.
The selectivities obtained from the Cp*Rh-catalyzed
reaction of triethoxysilane with phenylacetylene are not
as high as with triphenylsilane, but to our knowledge,
they are the highest thus far reported. Karstedt’s
platinum catalyst yields 0% 2-â-Z, 70% 2-â-E, and 30%
2-R,19 whereas the distribution of products resulting
from the [Cp*Rh(BINAP)](SbF6)2 catalyst, 0% 2-â-Z,
81% 2-â-E, and 18% 2-R (Table 1), shows some improve-
ment in regioselectivity. In addition, the 2-â-Z isomer
is formed in only 50, 60, and 74% yield by [(C4H6)-
RhCl]2,20 RhCl(PPh3)3/NaI,11 and [(1,5-COD)RhCl-
(p-MeC6H4NCMe2)] (COD ) cyclooctadiene),26 respec-
tively, as compared to 90-96% achieved by [Cp*RhCl2]2
(Table 1).
The results in Table 1 exhibit how changing the
catalyst can affect the product distribution. In particu-
lar, a very high stereoselectivity is achieved, producing
the â-E isomer and no observable â-Z isomer, with
[Cp*Rh(BINAP)](SbF6)2. Since, as mentioned, cationic
rhodium complexes do tend to give â-E products, the
double positive charge appears to enhance the selectivity
in this case. There regioselectivity is not >99% in all
cases. The varying yields of the R-isomer by this catalyst
depend on the nature of the silane, with more being
produced from triethoxysilane. [Cp*RhCl2]2 overall gives
better regioselectivity, but, except for the triphenyl-
silane reaction, it is not 97% stereoselective for â-Z
products. In summary, the primary products are those
shown in Scheme 2.
(17) Carmona, D.; Cativiela, C.; Elipe, S.; Lahoz, F. J .; Lamata, M.
P.; Lopez-RamdeViu, M. P.; Oro, L. A.; Vega, C.; Viguri, F. Chem.
Commun. 1997, 2351.
(18) Carmona, D.; Cativiela, C.; Garcia-Correas, R.; Lahoz, F. J .;
Lamata, M. P.; Lopez, J . A.; Lopez-Ram de Viu, M. P.; Oro, L. A.; san
J ose, E.; Viguri, F. Chem. Commun. 1996, 1247.
(19) Lewis, L. N.; Sy, K. G.; Bryant, G. L., J r.; Donahue, P. E.
Organometallics 1991, 10, 3750.
(20) Donskaya, N. A.; Yur’eva, N. M.; Voevodskaya, T. I.; Sigeev,
A. S.; Beletskaya, I. P. Russ. J . Org. Chem. (Engl. Transl.) 1994, 30,
853.
(21) Esteruelas, M. A.; Herrero, J .; Oro, L. A. Organometallics 1993,
12, 2377.
(22) Cervantes, J .; Gonzalez-Alatore, G.; Rohack, D.; Pannell, K. H.
Appl. Organomet. Chem. 2000, 14, 146. The catalyst is claimed to be
[(nbd)(dppe)2Rh]PF6 in this paper; however, it is almost certainly
[(nbd)(dppe)Rh]PF6.
(23) Lukevics, E.; Sturkovich, R. Y.; Pudova, O. A. J . Organomet.
Chem. 1985, 292, 151.
Styrene is only produced as a byproduct in less than
1% yield with triethoxysilane or triphenylsilane. More
of the phenylacetylene, ∼25%, is converted to styrene
in the reaction involving triethylsilane, particularly in
reactions catalyzed by [Cp*Rh(BINAP)](SbF6)2. The
conversion of phenylacetylene to products is also slower
(24) Iovel, I. G.; Goldberg, Y. S.; Shymanska, M. V.; Lukevics, E.
Organometallics 1987, 6, 1410.
(25) Onopchenko, A.; Sabourin, E. T.; Beach, D. L. J . Org. Chem.
1983, 48, 5101.
(26) Brockman, M.; tom Dieck, H.; Klaus, J . J . Organomet. Chem.
1986, 301, 209.

Notes
Organometallics, Vol. 21, No. 8, 2002 1745
Sch em e 3. Mech a n ism for th e Obser va tion of An ti
Ad d ition
when triethylsilane is involved rather than triethoxy-
silane or triphenylsilane. As the [Cp*RhCl2]2-catalyzed
triethylsilane reaction is allowed to proceed in order to
increase phenylacetylene conversion, isomerization of
the initially predominant product, 1-â-Z, to the more
stable thermodynamic product, 1-â-E, occurs. Higher
temperature speeds up this isomerization. Others have
reported product isomerization when there is either
excess silane in solution or prolonged contact with the
catalyst.9,27,28 To evaluate this, the catalysis involving
[Cp*RhCl2]2 was performed with excess alkyne. The
same Z to E isomerization was observed from the NMR
spectra, indicating that the contact with the catalyst and
not excess silane is largely inducing the isomerization.
In addition, no significant changes in product ratios
were observed when phenylacetylene was added to the
solution prior to addition of silane.
The active catalyst from the neutral complex presum-
ably arises from Cp*Rh(H)2(SiR3)2, which should form
upon addition of R3SiH, removal of chloride from
[Cp*RhCl2]2 as R3SiCl, and loss of H2, followed by
oxidative addition of two molecules of R3SiH.15,29
A
reactive 16-electron intermediate capable of interaction
with acetylene would then be available by loss of HSiR3
to yield [Cp*Rh(H)(SiR3)].
catalytic process which involved isomerization of the
â-Z-olefin. If the â-Z product of the Cp*RhCl2 catalyst
is allowed to stand in the presence of the catalyst for
an extended time, it gradually isomerizes to the â-E
isomer. This is more likely to be the result of a
background catalysis of reversible â-hydride addition/
elimination to the olefin, but it is an alternative isomer-
ization path which is available. This much slower
process might not involve the same catalyst as that
responsible for the production of the â-Z product.
The R-olefin presumably results from insertion of the
acetylene into the Rh-Si bond with the opposite regio-
chemistry. Insertion into the Rh-Si bond was generally
regarded as improbable in the past,32,33 but there is now
ample evidence to the contrary.4,5,30,34-39 This suggests
that the observed “selectivity” of some of the catalysts
may not actually reflect the initial selectivity in the
formation of the metal silane silyl olefin intermediate
but the relative rates of subsequent isomerization
processes.
The nature of the active catalyst with the dicationic
system is less clear. Oxidative addition of HSiR3 to the
16-electron [Cp*Rh(BINAP)]2+ should initially produce
[Cp*Rh(BINAP)(H)(SiR3)]2+ or [Cp*Rh(BINAP)(HSiR3)]2+,
which are 18-electron species. It is clear from the
product ratios that a different path is involved with
the dicationic complex precursor. Following generally
accepted mechanisms, one would expect that after
oxidative addition of the silane to the metal, acetylene
insertion into the metal-hydride bond would occur and
subsequent reductive elimination would yield the
olefin. A normal syn addition, however, would yield the
â-E isomer. The formation of the â-Z isomer can be
accounted for by acetylene insertion into the metal-
silicon bond, isomerization to place the metal trans to
the silicon, which is more favorable sterically, and
reductive elimination.4,5,30 Crabtree et al.4,30 suggest
that the isomerization occurs via an η2-vinyl group,
and thus a mechanism as shown in Scheme 3 may be
operative.
If the primary process is insertion into the metal-
silicon bond, then the E/ Z stereoselectivity is deter-
mined by the relative rates of reductive elimination and
isomerization. Regardless, after interaction of the di-
cation with the silane, there is no site available for
interaction with the acetylene. Thus, the detachment
of at least one donor would be anticipated in order to
produce the real catalytically active species. Without
further evidence it would appear unwarranted to specu-
late further on the nature of this species.
In brief, the tunable selectivity afforded by the readily
prepared Cp*Rh compounds [Cp*RhCl2]2 and [Cp*Rh-
(BINAP)](SbF6)2 make them attractive catalysts for the
hydrosilylation of phenylacetylene under mild condi-
tions. The â-E products are also available via silylative
coupling or metathesis of styrene with vinylsilanes;40,41
however, higher temperatures are often required.
(31) Randolph, C. L.; Wrighton, M. S. J . Am. Chem. Soc. 1986, 108,
3366.
(32) Dickers, H. M.; Haszeldine, R. N.; Mather, A. P.; Parish, R. V.
J . Organomet. Chem. 1978, 161, 91.
(33) Brady, K. A.; Nile, T. A. J . Organomet. Chem. 1981, 206, 299.
(34) Onopchenko, A.; Sabourin, E. T.; Beach, D. L. J . Org. Chem.
1984, 49, 3389.
(35) Fernandez, M. J .; Esteruelas, M. A.; J imenez, M. S.; Oro, L. A.
Organometallics 1986, 5, 1519.
(36) Murai, S.; Chatani, N. J . Synth. Org. Chem. J pn. 1993, 51, 421.
(37) Bergens, S. H.; Noheda, P.; Whelan, J .; Bosnich, B. J . Am.
Chem. Soc. 1992, 114, 2128.
(38) Bosnich, B. Acc. Chem. Res. 1998, 31, 667.
(39) Esteruelas, M. A.; Olivan, M.; Oro, L. A.; Tolosa, J . I. J .
Organomet. Chem. 1995, 487, 143.
One should also note that the additions might be
reversible,31 although this is less likely for a vinyl silane.
The â-E isomer could also be produced as a secondary
(27) Dickers, H. M.; Haszeldine, R. N.; Malkin, L. S.; Mather, A. P.;
Parish, R. V. Dalton Trans. 1980, 308.
(28) Tanke, R. S.; Crabtree, R. H. J . Chem. Soc., Chem. Commun.
1990, 1056.
(29) Djurovich, P. I.; Carroll, P. J .; Berry, D. H. Organometallics
1994, 13, 2551.
(30) J un, C. H.; Crabtree, R. H. J . Organomet. Chem. 1993, 447,
177.
(40) Reichl, J . A.; Berry, D. H. In Adv. Organomet. Chem. 1999, 43,
197-265.
(41) Marciniec, B.; Walczuk-Gusciora, E.; Pietraszuk, C. Organo-
metallics 2001, 20, 3423-3428 and references therein.

1746 Organometallics, Vol. 21, No. 8, 2002
Notes
(B) [Cp*RhCl2] 2 (13.6 mg, 0.022 mmol) in CH2Cl2 (2.0 mL)
was stirred with Ph3SiH (120.6 mg, 0.46 mmol), (EtO)3SiH
(0.087 mL, 0.47 mmol), or Et3SiH (0.074 mL, 0.46 mmol) for
15 min at 45 °C or room temperature (see Table 1).
Exp er im en ta l Section
All manipulations were carried out under an atmosphere
of nitrogen using standard Schlenk techniques. Dichloro-
methane was dried and distilled over CaH2. AgSbF6, (S)-
BINAP, phenylacetylene, triphenylsilane, triethylsilane, tri-
ethoxysilane (Aldrich), and rac-BINAP (Strem) were used as
Hyd r osilyla tion . Phenylacetylene (0.049 mL, 0.45 mmol)
was added, and stirring at the appropriate temperature was
continued until 100% conversion of PhCCH was determined
12
1
received. [Cp*RhCl2]2 was prepared according to literature
from the H NMR spectrum or until 21 h passed. The solvent
methods. 31P{1H} NMR spectra were recorded at room tem-
perature on a GE Omega 300 MHz (operating at 121 MHz for
31P) or Bruker 400 MHz (operating at 161 MHz for 31P)
spectrometer. 1H NMR spectra were recorded at room tem-
perature on a Bruker 400 MHz spectrometer. Chemical shifts
are reported in ppm relative to residual solvent peaks (1H),
an 85% H3PO4 external standard (31P), or TMS external
standard (29Si). Elemental analyses were carried out by
Atlantic Microlabs.
was removed under reduced pressure. NMR (1H and 13C)
spectra were recorded of the residue in CDCl3, and chemical
shifts and couplings were compared to published values.6,19,20,30,39
P r epar ative-Scale Reaction s. (â-E)-P h (H)CdC(SiP h 3)H.
[Cp*Rh(η2-BINAP)Cl]Cl (22.3 mg, 0.024 mmol) and AgSbF6
(16 mg, 0.047 mmol) were stirred in CH2Cl2 (2.0 mL) for
20 min, and the mixture was then centrifuged to remove the
AgCl precipitate. The purple supernatant was stirred with
Ph3SiH (131 mg, 0.50 mmol) for 15 min at 45 °C, during which
time it turned orange. Phenylacetylene (0.053 mL, 0.48 mmol)
was added and stirring at 45 °C was continued until 100%
conversion of PhCCH was determined from the 1H NMR
spectrum or until 21 h passed. The solvent was removed under
reduced pressure. Products were separated from leftover
catalyst by column chromatography, and 164 mg of the E
isomer was collected in a 94% isolated yield as clear, colorless
needles upon recrystallization from CH2Cl2/MeOH. Compari-
son of its vinylic 1H NMR resonances to those reported in the
literature19 showed it to be (â-E)-Ph(H)CdC(SiPh3)H. 1H NMR
(400 MHz, CDCl3, δ): 7.05, 7.00 (2 H, AB quartet, J ) 19.2
Hz). 29Si{1H} HMQC NMR (99 MHz, CDCl3, δ): -16.25 (s).
(â-Z)-P h (H)CdC(SiP h 3)H. [Cp*RhCl2]2 (15.0 mg, 0.024
mmol) in CH2Cl2 (2.0 mL) was stirred with Ph3SiH (133.9 mg,
0.51 mmol) for 15 min at 45 °C, turning it orange. Phenyl-
acetylene (0.053 mL, 0.48 mmol) was added, and stirring at
45 °C was continued until 100% conversion of PhCCH was
P r ep a r a tion of [Cp *Rh Cl(η2-BINAP )]Cl. [Cp*RhCl2]2
(385 mg, 0.62 mmol) and BINAP (773 mg, 1.24 mmol) were
stirred in CH2Cl2 (40 mL) at room temperature for 40 min.
Solvents were removed under reduced pressure, and the
product was dried in vacuo. The yield of the red-orange product
1
was 1.067 g (92%). H NMR (400 MHz, CDCl3, δ): 7.98-5.96
(32 H, m, aromatic); 1.21 (15 H, pseudo-t, J PH ) 3.6 Hz, Cp*).
31P{1H} NMR (121 MHz, CDCl3, δ): 34.09 (dd, J RhP ) 137 Hz,
J PP ) 64 Hz); 20.58 (dd, J RhP ) 133 Hz, J PP ) 64 Hz).
P r epar ation of [Cp*Rh Cl(η2-BINAP )]SbF6. To [Cp*RhCl-
(η2-BINAP)]Cl (97.4 mg, 0.10 mmol) in CH2Cl2 (6 mL) was
added AgSbF6 (36 mg, 0.10 mmol). The mixture was stirred
for 1 h, filtered through Celite, and recrystallized from
dichloromethane/ether. The yield of the red-orange product
1
was 103 mg (91%). H NMR (400 MHz, CDCl3, δ): 7.94-5.95
(32 H, m, aromatic); 1.14 (15 H, pseudo-t, J PH ) 3.6 Hz, Cp*).
31P{1H} NMR (121 MHz, CDCl3, δ): 34.15 (dd, J RhP ) 137 Hz,
J PP ) 64 Hz); 20.69 (dd, J RhP ) 134 Hz, J PP ) 64 Hz). Anal.
Calcd for C54H47P2RhClSbF6: C, 57.30; H, 4.18. Found: C,
57.57; H, 4.34.
1
determined from the H NMR spectrum or until 21 h passed.
The solvent was removed under reduced pressure. Products
were separated from residual catalyst by column chromatog-
raphy, and 161 mg of the Z isomer was collected in a 92%
isolated yield as clear, colorless needles upon recrystallization
In Sit u P r ep a r a t ion of [Cp *R h (η2-BINAP )](Sb F 6)2.
Met h od A. [Cp*Rh(η2-BINAP)Cl]Cl (21.0 mg, 0.023 mmol)
and AgSbF6 (16 mg, 0.046 mmol) were stirred in CH2Cl2
(2.0 mL) for 20 min and then centrifuged to remove the AgCl
precipitate.
Meth od B. [Cp*Rh(η2-BINAP)Cl]SbF6 (26.0 mg, 0.023
mmol) and AgSbF6 (8 mg, 0.023 mmol) were stirred in CH2Cl2
(2.0 mL) for 20 min and then centrifuged to remove the AgCl
precipitate.
The NMR spectra were identical from either A or B. 1H
NMR (400 MHz, CD2Cl2, δ): 8.09-6.42 (32 H, m, aromatic);
1.35 (15 H, pseudo-t, J PH ) 3.3 Hz, Cp*). 31P{1H} NMR
(121 MHz, CD2Cl2, δ): 33.81 (d, J RhP ) 148 Hz). Note that only
one 31P doublet is observed at room temperature.
In ter a ction of HSiP h 3 w ith [Cp *Rh (η2-BINAP )](SbF 6)2.
Treatment of [Cp*Rh(η2-BINAP)](SbF6)2 with HSiPh3 in CD2Cl2
apparently ultimately yields the hydride [Cp*Rh(η2-BINAP)H]-
(Sb2F11) and FSiPh3. 1H NMR (400 MHz, CD2Cl2, δ): 8.09-6.42
(32H, m, aromatic); 1.44 (15 H, pseudo-t, J PH ) 2.6 Hz, Cp*),
-10.39 (1H, ddd, J Rh-H ) 20.7, J P-H ) 28.6, J P-H ) 28.7).
31P{1H} NMR (162 MHz, CD2Cl2, δ): 49.75 (dd, J RhP ) 141,
J PP ) 37 Hz); 49.29, 49.75 (dd, J RhP ) 141, J PP ) 37 Hz).
29Si{1H} HMQC NMR: δ -3.70 (d, J SiF ) 238 Hz). Identical
1H and 31P NMR parameters were obtained upon treatment
of the dication with H2. Eluting the mixture through silica gel
with CH2Cl2 yields [Cp*Rh(η2-BINAP)H](SbF6). Anal. Calcd
for C54H48P2RhSbF6: C, 59.09; H, 4.41. Found: C, 59.33; H, 4.53.
H yd r osilyla t ion of P h en yla cet ylen e: Gen er a l P r o-
ced u r e. Ad d it ion of Sila n e t o Ca t a lyst . (A) A purple
solution of [Cp*Rh(η2-BINAP)](SbF6)2 (0.023 mmol, prepared
in situ) in CH2Cl2 (2 mL) was stirred with Ph3SiH (126 mg,
0.48 mmol), (EtO)3SiH (0.09 mL, 0.49 mmol), or Et3SiH
(0.08 mL, 0.50 mmol) for 15 min at 45 °C or room temperature
(see Table 1).
1
from CH2Cl2/MeOH. Comparison of its vinylic H NMR reso-
nances to those reported in the literature6,19 showed it to be
(â-Z)-Ph(H)CdC(SiPh3)H. 1H NMR (400 MHz, CDCl3, δ): 7.77
(1 H, d, J ) 15.6 Hz); 6.38 (1 H, d, J ) 15.6 Hz). 29Si{1H}
HMQC NMR (99 MHz, CDCl3, δ): -20.70 (s).
â-(E)-P h (H)CdC(SiEt3)H.19,30,39 Colorless oil. 1H NMR (400
MHz, CDCl3, δ): 6.90 (1 H, d, J ) 19.2 Hz); 6.43 (1 H, d, J )
19.2 Hz).
â-(Z)-P h (H)CdC(SiEt3)H.6,30,39 Colorless oil. 1H NMR (400
MHz, CDCl3, δ): 7.45 (1 H, d, J ) 15.2 Hz); 5.77 (1 H, d, J )
15.2 Hz).
r-P h (SiEt3)CdCH2.19,30,39 Colorless oil. 1H NMR (400 MHz,
CDCl3, δ): 5.87 (1 H, d, J ) 3.2 Hz); 5.58 (1 H, d, J ) 3.2 Hz).
â-(E)-P h (H)CdC(Si(EtO)3)H.19,20 Colorless oil. 1H NMR
(400 MHz, CDCl3, δ): 7.20 (1 H, d, J ) 19.2 Hz); 6.17 (1 H, d,
J ) 19.2 Hz).
â-(Z)-P h (H)CdC(Si(EtO)3)H.20 Colorless oil. 1H NMR (400
MHz, CDCl3, δ): 7.41 (1 H, d, J ) 15.6 Hz); 5.57 (1 H, d, J )
15.6 Hz).
r-P h (Si(EtO)3)CdCH2.19,20 Colorless oil. 1H NMR (400
MHz, CDCl3, δ): 6.13 (1 H, d, J ) 2.8 Hz); 5.95 (1 H, d, J )
2.8 Hz).
Ack n ow led gm en t. This work was supported by the
National Science Foundation (NSF Grant CHE0092222).
We also thank R. H. Crabtree for helpful discussions.
Su p p or tin g In for m a tion Ava ila ble: A summary table
of all hydrosilylation experiments. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM010978K