Hydrogen/deuterium exchange reactions and transfer hydrogenations catalyzed by [C5Me5Rh(olefin)2] complexes: Conversion of alkoxysilanes to silyl enolates

Article abstract of DOI:10.1021/ja984409o

A series of [C₅Me₅Rh(CH₂=CHR)₂] complexes (1a-e) have been prepared in which the olefin bears a bulky silyl substituent, R = (a) SiMe₃, (b) SiMe₂OEt, (c) Si(OⁱPr)₃, (d) SiMe(OSiMe₃)₂, (e) SiPh₂Oⁱ-Pr. The solid-state structure of 1c has been determined by X-ray crystallography. When complex 1a is heated (50°C) in deuterated solvents (C₆D₆, C₆D₅CD₃, C₆D₅Cl, or (CD₃)₂CO), deuterium is incorporated into the olefinic sites. Thermolysis at higher temperatures results in further H/D exchange and deuteration of both the SiMe₃ and C₅Me₅ groups. Heating 1a in C₆D₆ with added substrates (aniline, MeO^tBu, MeOSiMe₃, Cp₂Fe, cyclopentene, or EtOAc) results in deuteration of these substrates via shuttling of deuterium from C₆D₆ to the olefinic sites and then into certain sites of the substrates. Thermolysis of 1a in the presence of vinyltrimethylsilane at higher temperatures results in C-Si bond cleavage and generation of a silacyclopentadiene complex (6) whose structure was determined by X-ray analysis. Thermolysis of 1c in C₆D₆ results in facile H/D exchange and incorporation of deuterium not only into the vinylic positions but also into the methine and methyl groups of the isopropyl substituents. At 90°C in the presence of CH₂=CHSi(OⁱPr)₃ a catalytic transfer hydrogenation is observed which converts the vinylsilane to the silyl enolate, Et(ⁱPrO)₂SiOCMe=CH₂. A series of catalytic transfer hydrogenations were carried out in which alkoxysilanes CH₂=CHSiMe₂OR (R = Et, n-Bu, CHMeEt, C₂H_4tBu, C₂H₄Ph, CHMePh, CHMeCH₂Ph) were converted to the corresponding silyl enolates. Catalytic conversion of the vinylaminosilane CH₂=CHSiMe₂NHC₂H₄Ph to the silyl enamine EtSiMe₂NHC₂H₂Ph is also reported.

Full text of DOI:10.1021/ja984409o

J. Am. Chem. Soc. 1999, 121, 4385-4396
4385
Hydrogen/Deuterium Exchange Reactions and Transfer
Hydrogenations Catalyzed by [C5Me5Rh(olefin)2] Complexes:
Conversion of Alkoxysilanes to Silyl Enolates†
Christian P. Lenges, Peter S. White,‡ and Maurice Brookhart*
Contribution from the Department of Chemistry, UniVersity of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
ReceiVed December 22, 1998
Abstract: A series of [C5Me5Rh(CH2dCHR)2] complexes (1a-e) have been prepared in which the olefin
bears a bulky silyl substituent, R ) (a) SiMe3, (b) SiMe2OEt, (c) Si(OiPr)3, (d) SiMe(OSiMe3)2, (e) SiPh2Oi-
Pr. The solid-state structure of 1c has been determined by X-ray crystallography. When complex 1a is heated
(50 °C) in deuterated solvents (C6D6, C6D5CD3, C6D5Cl, or (CD3)2CO), deuterium is incorporated into the
olefinic sites. Thermolysis at higher temperatures results in further H/D exchange and deuteration of both the
SiMe3 and C5Me5 groups. Heating 1a in C6D6 with added substrates (aniline, MeOtBu, MeOSiMe3, Cp2Fe,
cyclopentene, or EtOAc) results in deuteration of these substrates via shuttling of deuterium from C6D6 to the
olefinic sites and then into certain sites of the substrates. Thermolysis of 1a in the presence of vinyltrimethylsilane
at higher temperatures results in C-Si bond cleavage and generation of a silacyclopentadiene complex (6)
whose structure was determined by X-ray analysis. Thermolysis of 1c in C6D6 results in facile H/D exchange
and incorporation of deuterium not only into the vinylic positions but also into the methine and methyl groups
of the isopropyl substituents. At 90 °C in the presence of CH2dCHSi(OiPr)3 a catalytic transfer hydrogenation
is observed which converts the vinylsilane to the silyl enolate, Et(iPrO)2SiOCMedCH2. A series of catalytic
transfer hydrogenations were carried out in which alkoxysilanes CH2dCHSiMe2OR (R ) Et, n-Bu, CHMeEt,
t
C2H4 Bu, C2H4Ph, CHMePh, CHMeCH2Ph) were converted to the corresponding silyl enolates. Catalytic
conversion of the vinylaminosilane CH2dCHSiMe2NHC2H4Ph to the silyl enamine EtSiMe2NHC2H2Ph is
also reported.
Introduction
An example that illustrates a functionalization process is the
transfer hydrogenation reaction. Early reports have focused
mainly on late metals which will activate hydrocarbons to
generate, after â-hydride elimination from the activated sub-
strate, an unsaturated product, in general an olefin.15-26 The
traditional approach utilizes a sacrificial hydrogen acceptor,
usually a hindered olefin, to drive the catalytic process. Only
recently have examples been reported that allow direct dehy-
drogenation of alkanes to generate an olefin and dihydrogen;
Transition metal mediated C-H bond activation combined
with the functionalization of the activated substrate has been a
topic of increasing interest in recent years.1,2 Initial efforts were
directed toward the actual C-H bond activation reaction
mediated by a transition metal.3-6 The focus of many recent
studies has moved toward the application of these findings in
catalytic processes. Several systems have been described which
generate functionalized products based on catalytic carbon-
heteroatom or carbon-carbon bond-forming processes.7-14
(13) Jones, W. D.; Foster, G. P.; Putinas, J. M. J. Am. Chem. Soc. 1987,
109, 5047.
† Dedicated to Joseph L. Templeton on occasion of his 50th birthday.
‡ Contact this author for further details regarding the X-ray analyses.
(1) Shul’pin, G. B.; Shilov, A. E. Chem. ReV. 1997, 97, 2879-2932.
(2) (a) Jones, W. D. In SelectiVe Hydrocarbon ActiVation Principles
and Progress; Davies, J. A., Watson, P. L., Greenberg, A., Liebman, J. F.,
Eds.; VCH Publishers: New York, 1990; p 113. (b) Ryabov, A. D. Chem.
ReV. 1990, 90, 403.
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Organometallics 1984, 3, 816.
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10.1021/ja984409o CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/27/1999

4386 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Lenges et al.
the most elementary hydrocarbon functionalization process.27-31
Productivity and selectivity of these catalysts have been
generally moderate, but recently promising improvements have
been made. Application of catalytic transfer hydrogenation for
preparation of functionalized olefins of utility in organic
synthesis has received only limited attention.
of olefin and the participation of the second 1 equiv of olefin
in insertion reactions are expected to be reversible. In this work
we have investigated the reactivity of labile rhodium bis-olefin
complexes in bond activation and functionalization reactions.
We report here a variety of H/D exchange reactions toward a
series of substrates and catalytic transfer hydrogenation of vinyl
alkoxysilanes to generate vinyl silyl ethers using complexes of
the type [C5Me5Rh(C2H3R)2] as catalysts.
We have recently investigated C-H bond activations by the
first-row metal cobalt and reported the use of [C5Me5Co(C2H3-
SiMe3)2] as a catalyst for H/D exchange in aromatic solvents
and for hydroacylation of olefins.32-34 The key to the increased
reactivity of this complex is the bulky trimethylvinylsilane which
is lost in a dissociative first step to generate the reactive 16-
electron fragment [C5Me5Co(C2H3SiMe3)] capable of C-H
bond activations. In this contribution we have applied this
strategy to analogous rhodium complexes and have prepared
rhodium(I) bis-olefin complexes in which the olefin bears bulky
substituents which increases the rate of ligand dissociation and
thus finds application in bond activation catalysis. As early as
1974 it was shown that the parent rhodium complex [C5H5Rh-
(C2H4)2] heated in benzene-d6 will activate the solvent to
reversibly exchange deuterium for hydrogen in the coordinated
olefin following a reversible olefin insertion-deinsertion se-
quence.35 A mechanism for this exchange process is shown in
Scheme 1 and is supported by our investigations with cobalt
and earlier work regarding the rhodium bis-ethylene complexes.
The first step, which in part controls the rate of the exchange
reaction, is the dissociation of olefin which generates the reactive
16-electron fragment for subsequent bond activation chemistry.
Results and Discussion
A. Synthesis of Rhodium(I) Olefin Complexes. A general
route into rhodium olefin complexes of the type [C5Me5Rh-
(olefin)2] was developed and involves the reduction of the
chloro-bridged dimer [C5Me5RhCl2]2 with zinc powder in
tetrahydrofuran in the presence of an excess of the desired
olefin.36 A series of new rhodium bis-olefin complexes (1a-e)
was accessible using this pathway. Extraction into pentane and
removal of the solvent allows the isolation of the bis-olefin
complexes as yellow-orange crystalline materials or oils which
are pure by NMR and elemental analysis (eq 2).
Scheme 1. Reversible C-H Bond Activation of Benzene-d6
with [C5R5M(C2H4)2] (M ) Co, Rh) and H/D Exchange
The coordination of two monosubstituted olefins to the [C5-
Me5Rh] fragment frequently results in the formation of a mixture
of isomers in which the substituent can either face toward or
away from the Cp* ligand as well as being disposed on the
same or opposite side as the substituent on the second
olefin.37-39 The NMR analysis of the new rhodium olefin
complexes shows that the solids or oils obtained from the
pentane filtrates consist of a mixture of isomers with one major
isomer accounting for at least 75% (1d) and up to 98% (1a) of
the olefin complexes present. The oil initially obtained in the
synthesis of 1a (which likely contains a mixture of isomers)
solidifies during the course of 1 h at room temperature to yield
an orange-yellow solid. It was also possible to recrystallize
complexes 1a,c from acetone at -78 °C to obtain yellow
crystalline materials which contained the rhodium bis-olefin
complex as a single isomer by NMR analysis.
The configuration drawn in eq 2 for the rhodium bis-olefin
complexes is based on the structurally characterized cobalt
analogue of 1a34 and is expected to be the one most favored.
NMR data are consistent with this assumption with a single
Cp* resonance at 1.68 ppm and a single SiMe3 resonance
accounting for two SiMe3 groups at 0.05 ppm along with olefinic
The low reactivity found in this system stands in clear contrast
to the high reactivity of the 16-electron fragment [C5R5Rh(L)]
in bond activation reactions. The dissociative loss of 1 equiv
(27) Jensen, C. M.; Kaska, W. C.; Flesher, R. J.; Hagen, C.; Gupta, M.
Chem. Commun. 1996, 2083.
(28) Goldman, A. S.; Krogh-Jespersen, K.; Kaska, W. C.; Jensen, C.
M.; Gupta, M.; Rosini, G.; Xu, W.-W. Chem. Commun. 1997.
(29) Jensen, C. M.; Kaska, W. C.; Cramer, R. E.; Hagen, C.; Gupta, M.
J. Am. Chem. Soc. 1997, 119, 840.
(30) Jensen, C. M.; Kaska, W. C.; Gupta, M. Chem. Commun. 1997,
461.
(36) The synthesis of [C5Me5Rh(CO)2] by zinc reduction in methanol
has been reported with moderate yields. Maitlis, P. M.; Kang, J. W. J.
Organomet. Chem. 1970, 26, 393.
(37) The coordination of vinyltrimethylsilane to a rhodium acetylaceto-
nato system has been reported. Fitch, J. W.; Osterlih, W. T. J. Organomet.
Chem. 1981, 213, 493.
(31) Leitner, W.; Six, C. Chem. Ber. 1997, 130, 555.
(32) Lenges, C. P.; Brookhart, M. J. Am. Chem. Soc. 1997, 119, 3165.
(33) Lenges, C. P.; Brookhart, M.; Grant, B. E. J. Organomet. Chem.
1997, 528, 199.
(34) Lenges, C. P.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 1998,
120, 6965.
(38) Perutz and co-workers have investigated the photochemical synthesis
of [C5H5Rh(olefin)2] complexes including the bis(vinyltrimethylsilane)
complex. The formation of two isomers is observed in contrast to 1a, which
shows essentially one isomer. Perutz, R. N.; Haddleton, D. M.; Duckett, S.
B.; Belt, S. T. Organometallics 1989, 8, 748.
(39) Mueller, J.; Hirsch, C.; Qiao, K.; Ha, K. Z. Anorg. Allg. Chem.
1996, 622, 1441.
(35) Seiwell, L. J. Am. Chem. Soc. 1974, 96, 7134.

[C5Me5Rh(olefin)2]-Catalyzed H/D Exchange Reactions
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4387
Scheme 2. [C5Me5M] Bis-olefin Complexes (E ) -CO2Me)
substituent is further removed from rhodium, the C2-Rh-C4
angle (93.8) is considerably smaller than the C3-Rh-C1 angle
(109.1). The solid-state structure confirms the observed NMR
characteristics for 1c, in which the coordinated olefins are
inequivalent, as opposed to 1a (or the structurally characterized
cobalt analogue of 1a), in which a local C2 symmetry is
observed.
Figure 1. ORTEP view of [C5Me5Rh(C2H3Si(OiPr)3)2] (1c). All atoms
are drawn at 50% probability ellipsoids. Selected bond distances (Å)
and angles (deg): Rh-C(1) 2.135(4), Rh-C(2) 2.167(4), Rh-C(3)
2.138(4), Rh-C(4) 2.172(4), Si(2)-C(4) 1.823(4), Si(1)-C(2) 1.841-
(4), C(1)-C(2) 1.412(6), C(3)-C(4) 1.422(6), C(1)-Rh-C(2) 38.31-
(15), C(1)-Rh-C(3) 109.16(16), C(1)-Rh-C(4) 93.84(15), C(2)-
Rh-C(3) 86.84(15), C(2)-Rh-C(4) 95.47, C(3)-Rh-C(4) 38.53(15),
Rh-C(4)-C(3) 69.43(21), Si(2)-C(4)-C(3) 125.2(3), Rh-C(1)-C(2)
72.07(23), Rh-C(2)-Si(1) 122.08(20), Rh-C(2)-C(1) 69.61(22), Si-
(1)-C(2)-C(1) 126.6(3), Rh-C(3)-C(4) 72.05(23), Rh-C(4)-Si(2)
128.06(21).
In other structurally characterized rhodium bis-olefin com-
plexes, C2 symmetry has also been observed. In the methyl-
acrylate complex 440 and the propene complex 341 (Scheme 2),
the influence of the substituent is less severe and orientation
toward the Cp* ligand is observed. It is interesting to note that
both 3 and 4 in solution show a rapid isomerization to a mixture
of three rotational isomers. With an increase in size of the olefin
substituent to trimethylsilyl, the olefins are oriented as in
complex 2, facing away both from each other and from the Cp*
ligand. The solution 1H NMR spectrum shows a single isomer
consistent with the simple C2 symmetry.
The rhodium complex 1a, analogous to 2, also shows two
equivalent olefinic ligands by NMR spectroscopy. On the other
hand, in complex 1c, the steric bulk of the silyl substituent does
not allow the coordination of the two olefins to generate a
structure with higher symmetry. The planes generated by the
olefinic carbons and the silicon atom of each olefin are nearly
perpendicular to each other in 1c, [C5Me5Rh(C2H3Si(OiPr)3)2]
(Figure 1). This arrangement is consistent with the observed
increased rate of ligand dissociation in this new bis-olefin
complex, allowing easier access to the reactive 16-electron
fragment (see below).
B. H/D Isotope Scrambling in 1a by Reversible C-H Bond
Activation. The reactivity of the new rhodium olefin complexes
in bond activation reactions is illustrated in a reaction with
benzene-d6. After 3 days at 20 °C the olefin resonances for
coordinated vinyltrimethylsilane of 1a are decreased in intensity
along with the partial disappearance of coupling due to
deuterium incorporation. Correspondingly, the integration of the
residual 1H solvent resonance (benzene-d5) is increased in
intensity. The resonance of the R-hydrogen atoms integrates at
this stage for 55% of its original value whereas the â-hydrogen
atoms still show 75% of the initial integrated intensity. No other
resonances are changed under these conditions. This reaction
of 1a was investigated in more detail at 78 °C in benzene-d6.
1H NMR analysis confirms faster H/D exchange processes; after
only 9 min the integral of the resonance for the R-hydrogen
has been reduced by 80% due to deuteration whereas the
integration for the â-hydrogen signals is reduced by 50%. After
17 min, the resonance for the R-hydrogen has disappeared and
the resonances for the â-hydrogens are reduced by 75%. The
13C NMR spectrum at this stage confirms exchange and shows
a 1:1:1 triplet at 45 ppm for CR and a pentet at 48 ppm for Câ.
After about 2 h the only resonances observed (besides the now
more intense C6D5H resonance) are the unchanged C5Me5 and
the SiMe3 resonances.
resonances at 2.11 (ddd, 2H) and 1.15 (m, 4H) ppm. The 13C
NMR spectrum shows only five resonances accounting for the
Cp* unit and two equivalent coordinated olefins. Using the same
procedure, complex 1b was isolated as a yellow-brown oil.
NMR analysis also showed one dominant rhodium species
(>98%), but signs for further reactivity were observed (vide
infra). In complex 1c a significant difference in the coordination
of the two bulky olefins to the rhodium center is observed.
Again, an orange oil of 1c was isolated after reduction and
pentane extraction; crystalline material in this case was obtained
only after cooling an acetone solution of 1c to -78 °C. NMR
analysis of this material showed a single rhodium species with
1
a Cp* H resonance at 1.72 ppm. In the region of 1.10-1.22
ppm the isopropyl methyl groups are observed as an overlapping
series of doublets integrating for 36 protons (see Figure 3 in
the Supporting Information). Two separate septet resonances
are observed at 4.22 and at 4.32 ppm which integrate together
for the six methine protons of the two coordinated triisopro-
poxyvinylsilane ligands. Most interesting are six different
resonances integrating each for one proton which are assigned
as the olefinic protons of two inequivalent ligands at 3.23, 2.11,
2.01, 1.88 (dd, 18, 15 Hz), 0.66, and 0.48 (dd, 18, 15 Hz) ppm.
The lack of symmetry in this bis-olefin complex is also
confirmed by 13C NMR analysis. Four doublets for the olefinic
carbons are observed as well as resonances for inequivalent
isopropyl groups and one Cp* unit. After recrystallization from
acetone it was possible to determine the structure of 1c by X-ray
crystallography (Figure 1).The structural analysis confirms the
coordination of 2 equiv of triisopropoxyvinylsilane ligands to
the Rh(I) center. The bulky substituent on the olefins clearly
dominates the structure which results in the observed orientation
of the substituents facing away from each other. The bond
distances in the coordinated olefin are within the expected range
(C1-C2, 1.412 Å; C3-C4, 1.422 Å). The rhodium-olefinic
carbon distances reflect the steric effect of the substituent. The
Rh-C2 bond distance at 2.167 Å is longer than the Rh-C1
distance at 2.135 Å. Similar bond distances are obtained for
the second olefin. Even though the carbon atom bearing the
(40) Hauptman, E.; Sabo-Etienne, S.; White, P. S.; Brookhart, M.; Garner,
J. M.; Fagan, P. J.; Calabrese, J. C. J. Am. Chem. Soc. 1994, 116, 8038.
(41) Lenges, C.; Brookhart, M. Manuscript in preparation.

4388 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Lenges et al.
Table 1. H/D Exchange of Vinyl Sites in 1a in Deuterated
increase of the original intensity for one site), with the ortho
positions being most slowly activated (5 h, 50 °C, 25% increase
compared to the original intensity for one site). These results
support previous observations that a methyl substituent has
considerable impact on reactivity and regioselectivity in the
activation reaction.33,43 The residual 1H NMR resonance for the
methyl group increases only by 20% (50 °C), consistent with
the reported lower reactivity of benzylic C-H bonds relative
to aromatic C-H bonds in oxidative additions to Rh(I).43
Solventsa
time for 50% reduction in signal
intensity (site of deuteration) (min)
Not only solvents containing aromatic sp2 CH bonds partici-
pate in this reversible H/D exchange process. An acetone-d6
solution of 1a also exhibits H/D exchange by incorporation of
deuterium into the coordinated olefin. Exchange rates are
comparable to those in aromatic solvents (Table 1). While η2-
arene adducts of [C5Me5Rh(L)] complexes have been previously
observed,44 we have not spectroscopically observed the likely
[C5Me5Rh(olefin)(acetone)] adduct as an intermediate in any
of these exchange reactions. These results clearly demonstrate
the ability of these systems, in which olefin dissociation is facile,
to activate not only sp2 C-H bonds but also sp3 C-H bonds
under moderately mild thermal conditions.
solvent
C6D6
C6D5CD3
C6D5Cl
(CD3)2CO
C6D6
C6D5CD3
temp (°C)
R
â
50
50
50
50
78
78
115
120
125
120
<5
250
960
230
210
18
<5
18
a 0.01 g of 1a (2.3 × 10-5 mol), 0.6 mL of solvent, capillary insert
with ferrocene
The mechanism for this process is similar to that outlined in
Scheme 1 with the modification that the regiochemistry of olefin
insertion is guided by the trimethylsilyl substituent which
explains the observed differences in the rates of deuterium
incorporation (eq 3). In the analogous cobalt system (2),
Since the olefinic hydrogens are deuterated initially by
exchange with solvent, further bond activation reactions fol-
lowed by reversible insertion and reductive elimination processes
can essentially shuttle deuterium from the solvent via the
coordinated olefin into other, undeuterated, substrates. The first
evidence for this reactivity was observed when a toluene-d8
solution of 1a was continuously heated at 78 °C. After all
resonances for olefinic protons disappeared, a decrease of the
SiMe3 resonance was observed with a half-life of 10 h (pseudo-
first-order rate constant: 7 × 10-6 s-1). In the 1H NMR
spectrum a 1:1:1 triplet (JHD ) 2 Hz) was observed just upfield
of the singlet SiMe3 resonance. Extended heating for a total of
1
24 h resulted in the complete disappearance of all H NMR
features of the trimethylvinylsilane ligand in this experiment.45
If additional trimethylvinylsilane is added to a reaction mixture
prepared in this fashion, olefin substitution chemistry is observed
under these conditions to regenerate protio-1a and deuterovi-
nyltrimethylsilane; ongoing H/D exchange will eventually result
in complete deuteration of vinyltrimethylsilane (10 equiv) if
heating is continued for 1 week at 78 °C.
comparable deuterium incorporation is observed but with a half-
life of 1 h at 20 °C and with highly regioselective incorporation
of deuterium into the R-position of the coordinated olefin.
It is interesting to compare this observation with the ther-
molysis of the parent bis-ethylene complex [C5Me5Rh(C2H4)2]
(5) in benzene-d6. Jones and co-workers have reinvestigated this
system42 and found that at 78 °C in benzene-d6 5 will incorporate
In the deuteration reactions described thus far, the C5Me5
ligand has not been involved in H/D exchange catalysis;
however, thermolysis of 1a in toluene-d8 at 120 °C for 12 h
eventually results in considerable deuteration of the C5Me5
ligand. Referencing to a ferrocene standard in a capillary insert
established that the remaining Cp* resonance decreased while
the resonance for benzene-d5h increased. Throughout this
process the reaction mixture is homogeneous (eq 4);46 continued
thermolysis results eventually in decomposition to unassigned
products. The integrity of 1a during this process was confirmed
by a ligand exchange reaction. Addition of trimethylvinylsilane
1
deuterium into coordinated ethylene to decrease the H NMR
integration after 2 h by 25% of its original value. This indicates
that the dissociative lability of the coordinated olefin is
significantly increased in 1a and should therefore allow more
effective access to the reactive 16-electron fragment [C5Me5-
RhL] under relatively mild conditions.
This H/D exchange process is also observed in other aromatic
solvents. In a series of experiments the intensity of the R- and
â-sites of the coordinated olefin of 1a was monitored by NMR
spectroscopy and half-lives for the deuterium incorporation
extracted (Table 1, pseudo-first-order rate constants are given
in the Supporting Information). Interesting differences are
observed for the deuterium incorporation into the â-sites of
coordinated vinyltrimethylsilane. Incorporation of H atoms into
toluene is somewhat slower than in benzene and chlorobenzene.
The regiochemistry of H incorporation into toluene-d8 indicates
that the para site is favored (5 h, 50 °C, the integration of the
residual resonance for the para position is increased by 300%
in intensity), followed by the meta positions (5 h, 50 °C, 100%
1
resulted in regeneration of the characteristic H NMR features
of coordinated protio-olefin in 1a, while the Cp* region
remained complex due to extensive deuterium incorporation.
(43) Less than 1% activation of the benzylic position of toluene is
observed in the reaction of [C5Me5Rh(PMe3)] with toluene. Jones, W. D.;
Feher, J. F. J. Am. Chem. Soc. 1984, 106, 1650.
(44) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984, 106, 1650.
(45) 13C NMR analysis of these reaction mixtures shows a broad, ill-
defined resonance at 0-2 ppm with extensive coupling to deuterium; for
the olefin resonances see ref 33.
(46) Besides the residual singlet resonance at 1.57 ppm (toluene-d8) a
triplet (1:1:1) resonance at 1.52 ppm (J ) 1.8 Hz) is observed in addition
to small amounts of unassigned decomposition products.
(42) Jones, W. D.; Duttweiler, R. P. J.; Feher, F. J.; Hessell, E. T. New
J. Chem. 1989, 13, 725.

[C5Me5Rh(olefin)2]-Catalyzed H/D Exchange Reactions
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4389
Table 2. H/D Exchange between Benzene-d6 to Other Substrates
Catalyzed by 1a
Finally, the thermolysis of 1a in hexane-d14 was investigated.
At 78 °C no H/D exchange was observed. However, after 5 h
at 120 °C, only two major resonances remain in the H NMR
1
spectrum corresponding to the Cp* and SiMe3 groups of 1a
next to a series of broad signals in the Cp* region assigned as
decomposition products. The olefinic sites have been deuterated,
and thus, these resonances are absent. In addition, the SiMe3
resonance clearly shows signs for deuterium incorporation. This
was confirmed by 13C NMR spectroscopy as discussed above.
Compared to the other solvent systems, hexane shows the lowest
reactivity and solvent activation is not observed without some
catalyst decomposition. In contrast, it is significant to point out
that no signs for solvent activation and H/D exchange were
observed in a series of thermolysis experiments performed in
cyclohexane-d12. This observation is consistent with the marked
difference in reactivity previously observed between primary
and secondary C-H bonds in bond activation reactions.3,4,44
Equation 4 summarizes the sequence for deuterium incorporation
into complex 1a in order of site selectivity.
a 1a (0.01 g, 2.3 × 10-5 mol), substrate (4.6 × 10-4 mol) in C6D6
1
at 110 °C. b % deuteration estimated from residual H NMR signal
intensities.
of the SiMe3 group in entry 3 in place of the tBu group of entry
2 suggests a slight preference in the exchange process for the
substrate with the second-row element which renders the methyl
C-H bonds more acidic. In comparison to aromatic substrates,
both substrates are ca. 1 order of magnitude less reactive. The
rate of deuteration of ferrocene, on the other hand, compares
well to the H/D exchange rate of aromatic substrates (Table 2,
entry 4), and complete deuteration is observed readily.
These solvent activation reactions are encouraging for possible
applications in catalysis since the general bond activation
reactivity of the fragment [C5Me5RhL] has been well-established
and is here incorporated into a reversible sequence of C-H
activation steps of sp2 as well as sp3 bonds. The use of the more
labile olefin trimethylvinylsilane facilitates olefin dissociation
to generate the reactive 16-electron intermediate in combination
with the second olefin which can participate in an insertion
reaction in a possible catalytic cycle. The deuteration of the
SiMe3 group as well as the Cp* ligand is believed to occur
through intermolecular C-H bond activation processes.47 In
addition, vinylic C-H bond activation of the coordinated olefin
can contribute to the observed process but no further evidence
was observed to support this scenario.
To illustrate the intermolecular reactivity of the olefin
complex toward other C-H bonds, a benzene-d6 solution of
1a was heated in the presence of a variety of substrates.
Deuterium incorporation into these substrates was observed via
a shuttle process in which deuterium from benzene is exchanged
into the olefinic positions of the vinyl silane and then, upon
substrate activation, the deuterium is passed on to substrate.
Table 2 illustrates several substrates which have been subjected
to the shuttle exchange process.
Olefins with â-hydrogens are in general isomerized by
rhodium systems of type 1. This is also supported by the
observation in entry 5, in which the most likely mechanism
involves olefin substitution in 1a by cyclopentene followed by
reversible solvent activation, insertion, and deuterium exchange.
Rapid olefin isomerization will incorporate the label with equal
rates into all positions of the substrate as is observed. The bis-
cyclopentene rhodium complex was not accessible using the
synthetic strategies applied here, but the deuteration results
indicate that cyclopentene complexes are generated in these
reactions49 and suggests that complex 1a is a useful general
precursor for catalytic reactions with a variety of olefins. The
reaction of ethyl acetate with 1a and benzene-d6 results in
selective deuteration of the R-methyl group; deuterium incor-
poration into other C-H sites is not observed. This compares
well with the reversible activation of acetone as discussed above.
Twenty equivalents of aniline (Table 2, entry 1) react in this
process to show after 5 h at 110 °C considerable reduction of
the aromatic resonances in the 1H NMR spectrum. Deuteration
of the meta and para positions is fastest, which indicates the
steric impact of the amino substituent. It is noteworthy to point
out that the NH2 group does not show deuterium incorporation
on the time scale of these experiments.48 Interesting are also
entries 2 and 3 in which two similar substrates show selective
H/D exchange at a sp3 CH bond R to the heteroatom. (For an
1H NMR spectrum which illustrates deuterium incorporation
into MeOSiMe3 see the Supporting Information.) The presence
These H/D exchange results indicate that 1a can effectively
activate a variety of C-H bonds and shows selectivity in this
process. In addition the presence of a series of functional groups
is tolerated. It is noteworthy to point out that some of these
reactions were conducted under conditions where compound
1a was essentially stable (80 °C, >150 h). However, complete
deuteration of certain substrates required longer reaction times.
(48) Reaction mixtures containing aniline and 1a in benzene-d6 were
thermolyzed for 1 week at 110 °C without any signs for deuterium
incorporation into the -NH2 group; complex 1a decomposes after extensive
deuteration to unassigned products. This result also indicates that protic
mechanisms for H/D exchange catalyzed by possible decomposition products
are not operative.
(49) Addition of cyclopentene to 1a in cyclohexane-d12 at 50 °C results
in the formation of new olefin complexes assigned as mono- and
bis-cyclopentene rhodium species. Isolation of these materials was not
successful.
(47) (a) An alternative mechanism for deuteration of the Cp* ligand
follows a route via a fulvene rhodium hydride intermediate which operates
under different conditions as applied in the reactions of 1a. Maitlis, P. M.;
Moseley, K. J. Am. Chem. Soc. 1969, 91, 5970. (b) The activation of the
C5Me5 moiety in d0 transition metal systems has been observed; see refs 1
and 2 for general references.

4390 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Lenges et al.
At 110 °C, catalytic H/D exchange is efficient and fast but
the catalyst lifetime is reduced depending on the substrate
(Table 2).
C. Thermolysis of 1a in the Presence of Excess Trimeth-
ylvinylsilane. Complex 1a is stable for long times at high
temperatures but reactive as indicated by the ongoing H/D
scrambling processes in solvents such as benzene-d6. The inert
solvent cyclohexane-d12 was investigated to study the reactivity
of 1a under thermolysis conditions. A solution of complex 1a
was heated to 140 °C in cyclohexane-d12 in the presence of 10
equiv of vinyltrimethylsilane. After 4 h new singlet resonances
at 6.28 and 6.59 ppm are observed along with a singlet at 5.28
ppm identified as ethylene; in addition, new signals in the SiMe3
region are observed. After 24 h at 140 °C these resonances
account for roughly 30% of all vinyltrimethylsilane present, the
major rhodium species (95%) remains complex 1a. The new
singlets in the olefinic region at 6.59 and 6.28 ppm are assigned
to (E)-1,2-bis(trimethylsilyl)ethene (13C: 151.1, d) and 1,1-bis-
(trimethylsilyl)ethene (13C: 140.2, t) and agree well with
literature values.50-52 This result indicates that either vinylic
C-H bond can be activated by rhodium. Insertion followed by
â-silyl elimination and reductive elimination from a Rh(III)
vinylsilyl intermediate generates ethene and the observed bis-
silylated ethene derivatives (eq 5). The rhodium species is
trapped by additional vinyltrimethylsilane to regenerate 1a.
Figure 2. ORTEP view of 6. Selected distances (Å) and angles (deg):
Rh-Si(1) 2.8472(2), Rh-C(1) 2.135(4), Rh-C(2) 2.152(5), Rh-C(3)
2.166(5), Rh-C(4) 2.233(5), Si(1)-C(3) 1.849(5), Si(1)-C(4) 1.861-
(5), Si(2)-C(4) 1.850(5), Si(3)-C(10) 1.908(5), Si(4)-C(10) 1.909-
(5), C(1)-C(2) 1.434(7), C(1)-C(4) 1.445(7), C(2)-C(3) 1.437(7),
C(2)-C(10) 1.528(7); C(1)-Rh-C(2) 39.07(2), C(1)-Rh-C(3) 66.69-
(2), C(2)-Rh-C(3) 38.88(2), C(3)-Rh-C(4) 71.12(2), C(2)-C(1)-
C(4) 115.0(4), C(1)-C(2)-C(3) 110.9(4), C(1)-C(2)-C(10) 124.4(4),
Si(1)-C(4)-Si(2) 128.3(3), C(3)-Si(1)-C(4) 87.19(2), Si(1)-C(4)-
C(1) 106.9(4), Si(2)-C(4)-C(1) 119.9(4), Si(3)-C(10)-Si(4) 112.99-
(2); C(4)-Si(1)-C(3)-C(2) 29.7(4), C(4)-C(1)-C(2)-C(3) 2.4(4),
C(1)-C(2)-C(3)-Si(1) 24.1(4), C(4)-Si(1)-C(3)-C(2) 29.7(4).
Me5Rh] moiety.53 Two vinyltrimethylsilane molecules and two
SiMe3 groups are utilized to generate this η4-silacyclopentadiene
complex. The Rh-C1, Rh-C2, and Rh-C3 distances are all
very similar and in the range of 2.15 Å. The Rh-C4 distance
of 2.23 Å is considerably elongated and reflects the steric impact
of the SiMe3 group at C4. The bond distances in the diene unit
also reflect this influence with C1-C4 being notably longer
(1.45 Å) and C1-C2 or C2-C3 essentially identical (1.43 Å).
The torsion angle of 24° for C1-C2-C3-Si1 is also charac-
teristic for this complex.
Continuous heating of this reaction mixture for 1 week at
140 °C results eventually in 80% conversion of vinyltrimeth-
ylsilane to 1,2-bis(trimethylsilyl)ethene (72%) and 1,1′-bis-
(trimethylsilyl)ethene (28%). Significantly, under these condi-
tions, 1a has been completely converted to new rhodium
complexes. Removal of the volatiles by vacuum transfer
confirms the observations made during catalysis. Besides
vinyltrimethylsilane, ethene, and the two bis(trimethylsilyl)-
ethene isomers, ethyltrimethylsilane (t, 0.92 and q, 0.42 ppm)
is also observed in the volatile fraction. Analysis of the
remaining organometallic material indicates a mixture of
rhodium complexes incorporating a series of SiMe3 groups with
the dominant thermolysis product accounting for 75% of all
organometallic material. Cooling of an acetone solution of this
mixture to -30 °C for 1 week results in the formation of orange
crystalline material which corresponds to the major decomposi-
tion product, 6, whose 1H NMR spectrum shows one Cp*
resonance at 1.92 ppm and three 9H singlets accounting for
three SiMe3 groups. Analysis by 13C NMR spectroscopy also
shows three SiMe3 groups and four resonances which show
coupling to rhodium at 45.0 (18 Hz), 43.5 (15 Hz), 87.7 (6 Hz),
and 90.0 (9 Hz) ppm.
The formation of complex 6 during the thermolysis of 1a in
the presence of excess trimethylvinylsilane can be viewed as a
stepwise process in which first silation of vinyltrimethylsilane
occurs as observed during the thermolysis. The silacyclopen-
tadiene is then formed from two 1,1-bis(trimethylsilyl)ethene
units via dehydrogenative coupling and isomerization. It is
significant that in this deactivation process the sp3 CH bond of
a SiMe3 group must be activated and coupled in a reductive
elimination process with a second molecule of olefin. Additional
vinyltrimethylsilane functions as the hydrogen acceptor and
ethyltrimethylsilane is generated.
D. Deuteration of Complex 1c. The reactivity of complex
1c follows the general features observed for complex 1a but
with significant differences. A benzene-d6 solution of 1c shows
considerable deuterium incorporation into the R-positions of the
coordinated olefin after 3 days at 20 °C.54 This experiment was
repeated at higher temperatures, and a toluene-d8 solution of
1c was heated to 50 °C while the reaction was monitored by
NMR spectroscopy.55 Deuterium incorporation into multiple
The structure of 6 was determined by X-ray crystallography.
The ORTEP diagram of 6 is shown in Figure 2 and confirms
the incorporation of additional SiMe3 groups to generate a
silacyclopentadiene fragment which is coordinated to the [C5-
(50) Wakatsuki, Y.; Yamazaki, H.; Nakano, M.; Yamamoto, Y. J. Chem.
Soc., Chem. Commun. 1991, 703.
(51) Birkofer, L.; Kuehn, T. Chem. Ber. 1978, 111, 3119.
(52) Seki, Y.; Takeshita, K.; Kawamoto, K. J. Organomet. Chem. 1989,
369, 117.
(53) Hayashi, J.; Sakurai, H. J. Organomet. Chem. 1973, 63, C10.
(54) The doublet splitting of the â-protons disappears to generate a singlet
for all four inequivalent positions, while the resonances for the R-protons
are reduced to 30% in intensity at this stage.

[C5Me5Rh(olefin)2]-Catalyzed H/D Exchange Reactions
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4391
Table 3. Selective H/D Exchange of 1c in Aromatic Solvents
Characteristic for 8 are 1H NMR features which indicate the
formation of a Si-bound ethyl group (5H), a singlet resonance
at 1.71 ppm (3H), and two isopropoxy groups (septet at 4.18
(2H) and d at 1.13 (12H) ppm) in addition to two singlets at
4.32 and 4.02 ppm (each 1H).
site of deuteration (% 1H integral reduction)
temp
To investigate this catalytic process in more detail, the
reaction of 20 equiv of 7 with 1c in cyclohexane-d12 was fol-
solvent (°C) time
R
â
OCHMe2
OCHMe2
C6D5CD3 50 4 h
C6D5CD3 50 12 h
>99
>99
15
43
60
14
43
64
91
14
44
64
85
1
lowed by H NMR spectroscopy at 90 °C. A plot of turnover
number vs time is given in the Supporting Information. In the
initial part of catalysis (about 10 h) there is a linear relationship
between turnover number (TO) and the time which corresponds
to a turnover frequency (TOF) of 0.7 TO/h. However, after 20
h under these conditions, >99% conversion to 8 is observed,
which indicates that the TOF increases toward complete conver-
sion of substrate. After 95% conversion of 7 to 8 complex 1c
still amounts to 90% of the initially charged catalyst load. Only
after complete conversion of all 7 to 8 does 1c decay to unas-
signed products, which indicates that 1c is the resting state dur-
ing catalysis. Since reversible olefin dissociation must occur to
initiate catalysis, the presence of free vinylsilane will reduce
the TOF in this transfer hydrogenation process. Close to com-
plete conversion of 7 the TOF increases on the basis of the re-
duced binding affinity of the transfer hydrogenation product 8.
It is efficient to use neat vinylsilane as solvent for the catalytic
transfer hydrogenation since the products can be directly used
for further applications or freed from rhodium-containing
materials by simple vacuum transfer. Catalyst 1a is also effective
in these reactions since fast ligand exchange under reaction
conditions will generate the corresponding alkoxyvinylsilane
complex in situ. In the case of 7, addition to 1a will generate
1c. Therefore, in a series of experiments, 1a (0.01 g, 2.3 ×
10-5 mol) was dissolved in neat silane 7 (1 g, 188 equiv) and
heated at 140 °C and the reaction mixture sampled at various
times. The following time-turnover data were observed: 30
min, 38 TO; 45 min, 61 TO; 65 min, 81 TO; 95 min, 117 TO.
This result indicates that the TON is essentially linear with time.
Only close to complete conversion is a faster TOF observed.
Quantitative conversion (>99%) to 8 is observed after roughly
2 h reaction time. It is possible to achieve very high turnovers
with this catalyst system. For example, heating 0.01 g of 1a
and 10 g of 7 for 5 days at 140 °C results in quantitative
conversion of 7 to 8, which corresponds to 1900 turnovers.
During catalytic transfer hydrogenation the only rhodium-
containing species observable is 1c; the formation of a possible
rhodium enol complex in which 8 is utilized to stabilize the
rhodium fragment is not observed. This was tested by heating
1c in cyclohexane-d12 at 100 °C. After 8 h 60% of olefin 7 in
complex 1c is converted to enol 8; however, the only assignable
species in the reaction mixture is complex 1c besides decom-
position products.
C6D6
C6D6
70 4 min >99
70 10 h
>99
>99
sites of the coordinated olefin was observed, and the results of
these H/D exchange reactions are summarized in Table 3.
A significant reactivity difference is observed for the ex-
change of the R-protons compared to the other sites of the olefin.
Complete deuteration of the R-protons is observed after 4 min
at 70 °C. The rate of deuterium incorporation for all other sites
during the exchange process is very similar. The sequence of
deuterium incorporation is illustrated in eq 6.
Complex 1c-d2 is generated first and functions to shuttle
deuterium from the solvent into the C-H bonds of the
isopropoxy groups. The deuteration of the â-protons of the
vinyltriisopropoxysilane is considerably slower than the deu-
teration of the â-protons in 1a. This is likely a consequence of
the increased steric bulk of the olefin in 1c which disfavors
olefin insertion with opposite regiochemistry (see eq 3). It is
also remarkable that the isopropyl groups of the olefinic ligand
are deuterated on the time scale of reversible solvent activation
(similar H/D exchange results are also observed in acetone-d6).
In these exchange reactions the total 1H intensity of the methyl
groups decreases at the same rate as the isopropyl methine
signal. Taking statistical factors into account, this observation
suggests that the methyl groups are activated more easily than
the less accessible methine protons. In comparison to MeOSiMe3
(entry 3, Table 2) a significant increase in H/D exchange
reactivity is observed for this system, indicating a potential
preference for an intramolecular bond activation pathway (vide
infra).
E. Alkoxysilane Isomerization: Transfer Hydrogenation.
Reversible C-H bond activation of triisopropoxyvinylsilane (7)
in 1c indicated by the deuterium incorporation experiment is
not the only reaction observed with this ligand system. In a
reaction of excess silane 7 with 1c in cyclohexane-d12, the
catalytic formation of a new organic product is observed at 90
°C while excess olefin is depleted. The vinylsilane 7 has
undergone intramolecular transfer hydrogenation to generate the
bis(isopropoxysilyl)ethyl-protected enol of acetone, compound
8 (eq 7).
On the basis of the deuterium exchange experiments, the
general mechanism of transfer hydrogenation must involve
oxidative addition of the C-H bond either R or â to oxygen in
7 to the 16-electron species [C5Me5Rh(olefin)], migration of
the resulting rhodium hydride to the vinyl group, then â-hydride
elimination to yield the silyl vinyl ether functionality. This
process can occur in an intra- or intermolecular fashion. Scheme
3a illustrates a possible catalytic cycle via an intramolecular
mechanism employing the C-H bond â to oxygen (a similar
cycle could be written employing the C-H bond R to oxygen).
The H/D exchange experiments suggest that at least reactions
A, B, and C are reversible.
(55) In the course of 2 h a second Cp*-containing species is generated
which amounts to 21% of the rhodium complexes present relative to 1c.
Additional olefin resonances suggest that this second species is an isomer
of 1c. A fresh solution of crystallized 1c shows one isomer as indicated.
Monitoring this solution over 1 week at 25 °C shows that a second species
with analogous NMR features as the complex indicated here is generated.

4392 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Lenges et al.
Scheme 3
with 1a are observed. When 1b is treated with 9 (5 equiv) in
C6D12 at 90 °C and the reaction is monitored by H NMR
1
spectroscopy, 10 is formed with an initial turnover frequency
of 2 TO/h. In the initial phase of catalysis, 1b is the only
rhodium species present. As catalysis proceeds, a second
rhodium complex begins to build up which accounts for 50%
of the rhodium complexes after 5% conversion of 9 to 10. After
quantitative conversion of 9 to 10 all rhodium-containing
material corresponds to the new species 11. Isolation of pure
samples of this complex has not been possible due to its thermal
lability, but spectral data57 suggest it is the bis-vinyl ether
complex, 11.
The same species is observed when 1b is thermolyzed in
benzene-d6 or acetone-d6 for several hours at 20 °C; however,
again the thermal instability of the complex prevents its isolation
as a pure compound.
To survey the utility of 1a as a transfer hydrogenation catalyst,
a series of vinylalkoxysilanes was prepared from dimethylvi-
nylchlorosilane and various alcohols and subjected to catalyst
1a. Results are summarized in Table 4. All reactions were
carried out without solvent. Column I describes results using 2
mol % catalyst in 3 h runs at 140 °C, while column II
summarizes results of reactions run at 140 °C, 48 h with 0.5
mol % catalyst. Products and isomer ratios were analyzed by
1H and 13C NMR spectroscopy.
Shown in Scheme 3b is an abbreviated form of the intermo-
lecular mechanism, again employing the â-C-H bond. It is
significant to note that the initial products of hydrogen transfer
are ethyltriisopropoxysilane (7′) and a silyl enolate (7′′) which
still possesses a vinyl substituent. While a detailed mechanistic
study has not yet been carried out on this hydrogen transfer
reaction, we currently favor the intramolecular pathway since
(1) spectroscopic evidence (1H, 13C) indicates that 7′ and 7′′
are not formed at any time during the reaction, (2) the
intermolecular transfer hydrogenation using an olefin as hy-
drogen acceptor and an alkoxysilane was not successful in
preliminary experiments using 1a as a catalyst under these
conditions,56 and (3) the reactivity of the unactivated methyl
groups in 7 in the H/D exchange reaction increased compared
to methyl groups which require intermolecular activation (see
Table 2).
The intramolecular transfer hydrogenation of vinylalkoxysi-
lanes has been extended to other substrates. Reaction of
vinyldimethylethoxysilane 9 (2.4 g, 1.84 × 10-2 mol) with 1a
(0.01 g, 2.3 × 10-5 mol) (neat, 140 °C, 72 h) results in
quantitative formation of the ethyldimethylsilyl-protected enol
of acetaldehyde, 10 (eq 8, 800 total turnovers). Vacuum transfer
of 10 away from residual rhodium catalyst results in isolation
of analytically pure 10.
Entries 1 and 2 have already been discussed. Using the
n-butoxy-substituted silane, 12 (entry 3), conversion to the
silylvinyl ethers are good (95% in series II) but little selectivity
is seen with nearly equal amounts of E and Z isomers observed.
The isobutoxy silane 14 (entry 4) generates not only E and Z
isomers but also regioisomers with little selectivity apparent for
activating a methyl vs ethyl group. Yields in series II are 78%;
however, under these conditions, all starting material has been
consumed. The remainder of the product appears to be derived
from C-Si bond cleavage as described above in eq 6.
The comparison of entries 5 and 6 suggests that the â-tert-
butyl group sterically inhibits C-H bond activation whereas
the high yields and quantitative conversion of 18 to 19a,b (E:Z
of ca. 53:47) indicate that the â-phenyl group activates the
â-C-H bond in this case. Conversion of 18 to 19a,b was
1
followed by H NMR spectroscopy in cyclohexane-d12 at 90
°C with a 20:1 ratio of 18:1a. After 12 h, 90% conversion to
19 was achieved with as E:Z ratio for 19a:19b of 6:1. This result
suggests that there is a significant kinetic selectivity for
formation of the E isomer but that at higher temperatures and
longer reaction times E/Z equilibration occurs (see the Sup-
porting Information). Conversion of substrate 20 bearing an
R-phenyl substituent to the silyl enolate 21 (entry 7) is clean
with high conversions (>99% under column II conditions). In
the case of 22 (entry 8), yields of transfer hydrogenation
products are high (99%, column II) but a mixture of both regio-
and stereoisomers are obtained.
The structure of the vinylsilane was varied in a different way
with substrate 24. Catalytic transfer hydrogenation of 24 to 25
Complex 1b also can be used to catalyze transfer hydrogena-
tion reactions and, in general, results identical to those obtained
(57) Characteristic for complex 11: 1H NMR 1.65 (s, 15H), 2.57 (dd,
7.2, 2.3 Hz, 2H), 1.55 (dd, 7.2, 2.3 Hz, 2H), 1.22 (ddd, 7.2, 6.0, 2.4 Hz,
2H), -0.04 (s, 3H), 0.28 (s, 3H), -Et resonances obscured; 13C NMR 101.1
(C5Me5), 52.2 (d, 13.5 Hz, H2Cd), 42.9 (d, 14.1 Hz, dCHOSi), 9.1 (C5Me5),
2.6, 1.8 (-SiMe), 9.85, 6.8 (-CH2CH3).
(56) Using n-propoxytrimethylsilane as substrate, reactions with nor-
bornene, trimethylvinylsilane, or tert-butylethylene using 1a as a catalyst
did not result in the formation of a silyl enolate and hydrogenation products.

[C5Me5Rh(olefin)2]-Catalyzed H/D Exchange Reactions
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4393
Table 4. Catalytic Transfer Hydrogenation of Vinylalkoxysilanes to Vinyl Silyl Ethersa
a All reactions run without solvent. *2% 1a, 3 h at 140 °C, by NMR. **0.5% 1a, 48 h at 140 °C, by NMR.
Table 5. Experimental Details for X-ray Analyses of 1c and 6
1c
6
mol formula
FW
RhSi2C32H63O6
702.91
RhC26H51Si4
578.93
crystal dimensions (mm)
0.40 × 0.20 × 0.15 0.30 × 0.30 × 0.30
Column I conditions (Table 3) resulted also in >99%
conversion to product in both cases. Reactions run at 120 °C
for 1 h with 2% catalyst gave with substrate 7 only 5%
conversion to 8, while 10% of 24 was converted to 25. These
preliminary results suggest that the increase in steric bulk at
silicon has a small but measurable effect on the rate of the
catalytic process.58
no. of reflns for cell
determn
a (Å)
b (Å)
c (Å)
5688
8192
8.9137(11)
13.0204(16)
16.9604(21)
100.845(2)
1890.2(4)
P1h
10.9528(5)
11.8066(5)
12.4378(6)
96.827(1)
1565.85(12)
P1h
â (deg)
V (Å3)
space group
Z
Transfer hydrogenation catalysis of vinyl amino silanes was
also briefly examined. Treatment of 26 with 1a under catalytic
conditions (140 °C, 12 h, 0.5 mol % 1a) results in formation of
silyl enamine 27 in 70% yield after 95% conversion of 26 (eq
10). Only a single isomer of 27 is observed, which is assigned
2
2
µ (Mo KR, mm -1
F(000)
)
0.55
0.71
750.45
-100
13301
614.61
-100
8855
T (°C)
no. of reflns
merging R-value on intens 0.029
no. of unique reflns 6684
0.025
5490
no. of obsns (I > 3.0σ(I)) 5212
4347
RFRW
0.040, 0.046
0.029, 0.054
0.034, 0.054
1.88
all reflns: RFRW
GOF
0.051, 0.053
2.05
(58) A bis-olefin complex analogous to 1 using triphenylvinylsilane was
prepared but not isolated without excess olefin present. This complex is
more reactive in catalytic H/D exchange as discussed above due to the
increased steric demand.
was observed under standard conditions using either 1a or 1e
as catalysts (eq 9).

4394 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Table 6. NMR Data for Vinyl Silyl Ethers
Lenges et al.
as the E isomer on the basis of the observed 12 Hz coupling
between the vicinal olefinic hydrogens (δ 5.55, 6.72). The
remaining 30% of the products are produced from C-Si bond
activation as discussed above. Under catalytic conditions
analogous to those in series I, Table 3, a 22% yield (42%
conversion of 26) of 27 is obtained.
These reactions offer the possibility of synthesis of silyl vinyl
ethers under base-free conditions. In addition, since a mild
hydrolysis of the vinyl ethers generates ketones or aldehydes,
these transformations represent oxidations of alcohols under
simple thermal isomerization conditions. The (apparent) in-
tramolecular nature of these reactions has synthetic advantages
for selective conversion of alcohols to silyl enolates and selective
protection and unmasking of alcohols as the oxidized products.
We are currently exploring more detailed mechanistic aspects
of these catalytic transfer hydrogenation reactions and the
application of the labile rhodium bis-olefin complexes in other
synthetic transformations.
Summary
The use of [C5Me5Rh(olefin)2] complexes for catalytic H/D
exchange reactions and transfer hydrogenation has been de-
scribed. Employing bulky olefins that readily dissociate from
the Rh(I) center allows facile access to the 16-electron species
[C5Me5Rh(L)] which is capable of C-H bond activation through
oxidative addition. Using L ) olefin as the ancillary ligand
provides a pathway for migratory insertion reactions of the C-H
activated substrate and thus catalytic cycles can be closed. The
results described here illustrate catalytic H/D exchange reactions
in which deuterium can be transferred from deuterated solvents
to the bound olefin and, further, can be shuttled to various
substrates in solution. Potential utility in synthesis has been
demonstrated by constructing a cycle in which, via the C-H
bond activation reaction, a catalytic transfer hydrogenation cycle
can be established which converts alkyl silyl ethers (readily
prepared from alcohols) to silyl vinyl ethers (silyl enolates).
Experimental Section
General Considerations. All manipulations of air- and/or water-
sensitive compounds were performed using standard high-vacuum or
Schlenk techniques. Argon and nitrogen were purified by passage
through columns of BASF R3-11 catalyst (Chemalog) and 4 Å
molecular sieves. Solid organometallic compounds were transferred in
an argon-filled Vacuum Atmospheres drybox. 1H and 13C NMR
chemical shifts were referenced to residual 1H NMR signals and to the
13C NMR signals of the deuterated solvents, respectively. NMR probe
temperatures were measured using an anhydrous ethylene glycol sample.
Elemental analyses were performed by Atlantic Microlabs, Inc., of
Norcross, GA.

[C5Me5Rh(olefin)2]-Catalyzed H/D Exchange Reactions
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4395
Materials. All solvents used for synthesis were deoxygenated and
dried via passage over a column of activated alumina.59 Tetrahydrofuran
was distilled from sodium benzophenone-ketyl prior to use. [C5Me5-
RhCl2]2 was prepared by following literature procedures.60 Trimeth-
ylvinylsilane, triisopropoxyvinylsilane, dimethylethoxyvinylsilane, bis-
(trimethylsiloxy)methylvinylsilane, chlorodimethylvinylsilane, and
chlorodiphenylvinylsilane are commercially available (Celeste). Benzene-
d6, toluene-d8, and cyclohexane-d12 were dried over potassium ben-
zophenone-ketyl, chlorobenzene-d5, and acetone-d6 were dried over
CaH2, vacuum transferred, and degassed by repeated freeze-pump-
thaw cycles.
(s, 18H), 0.38 (s, 6H); 13C (75.5 MHz, 20 °C, C6D6) δ 97.5 (d, 4 Hz,
C5Me5), 9.5 (C5Me5), 3.0 (-SiMe), 2.3, 2.3 (-OSiMe3), 48.0 (d, 11.6
Hz), 43.4 (d, 13.6 Hz).
Preparation of [C5Me5Rh(C2H3SiPh2OiPr)2] (1e). The synthesis
follows the general method outlined for the synthesis of 1a. Complex
1e was isolated after extraction with pentane and removal of all volatiles
as an orange-red oil. Attempts to crystallize 1e from pentane or acetone
were not successful. Complex 1e contained usually small amounts of
additional vinylsilane. Column chromatography at low temperatures
was not successful to remove excess olefin; decomposition was
observed. Complex 1e was isolated as an orange-red semisolid. Further
reactivity at 20 °C to generate 26 is slow and allowed characterization
by NMR spectroscopy: 1H (300 MHz, 20 °C, acetone-d6) δ 3.36 (d,
11.2 Hz, 1H), 2.45 (d, 14.8 Hz, 1H), 2.40 (d, 11.5 Hz, 1H), 2.05 (d, 15
Hz, 1H), 1.36 (dd, 11.8, 15 Hz, 1H), 0.66 (dd, 11, 15 Hz, 1H), 1.08
(m, 6H), 0.90 (m, 6H), 1.58 (s, 15H), 4.13 (m, 1H), 4.02 (m, 1H), 7.89
(m, 2H), 7.76 (m, 4H), 7.58 (m, 2H), 7.40 (m, 12H); 13C (75.5 MHz,
20 °C, acetone-d6) δ 98.1 (d, 4.5 Hz, C5Me5), 8.9 (C5Me5), 66.2, 65.8
(-CHMe2), 25.3 (-CHMe2), 47.8 (d, 13.3 Hz), 47.0 (d, 17.8 Hz), 42.4
(d, 14.4 Hz), 37.3 (d, 16.2 Hz), 138.9, 138.5, 138.2, 137.6, 135.2, 135.1,
135.0, 134.9, 129.4, 129.3, 129.2, 129.0, 127.6, 127.5, 127.4, 127.3 (s,
aromatic). Anal. Calcd for C44H55O2Si2Rh: H, 7.15; C, 68.89. Found:
H, 7.26; C, 69.05.
Preparation of [C5Me5Rh(C2H3SiMe3)2] (1a). The precursor [C5-
Me5RhCl2]2 (0.4 g, 6.5 × 10-4 mol) was combined with an excess of
zinc powder (∼10×, 0.85 g) in a Schlenk flask. To this was added
5-10 mL of tetrahydrofuran and vinyltrimethylsilane (10×, 1.3 g).
This reaction mixture was stirred at 20 °C for 12 h. A red-orange
homogeneous solution has been generated with only excess zinc powder
as the remaining insoluble material. After filtration, the solvent was
removed in vacuo and the remaining solids were extracted with pentane
until further pentane washings remained colorless. The volatiles of the
filtrate were removed, and complex 1a was obtained as a yellow-orange
oil (0.41 g, 72% yield) that solidified in the course of 1 h. This material
is pure by NMR and elemental analysis. Recrystallization in acetone
at -70 °C results in yellow material which shows only one isomer by
NMR spectroscopy: 1H (400 MHz, 20 °C, acetone-d6) δ 2.11 (ddd, 10
Hz, 2.4 Hz, 1.6 Hz, 2H), 1.15 (m, 4H), 1.68 (s, 15H), 0.04 (s, 18H);
13C (100.6 MHz, 20 °C, acetone-d6) δ 98.2 (C5Me5), 47.8 (d, 15 Hz,
H2Cd), 45.5 (d, 15 Hz, )CHSi), 9.8 (C5Me5), 2.2 (-SiMe3). Anal.
Calcd for C20H39Si2Rh: C, 54.77; H, 8.96. Found: C, 54.88; H, 8.99.
Preparation of [C5Me5Rh(C2H3SiMe2OEt)2] (1b). The synthesis
follows the general method outlined for the synthesis of 1a. Complex
1b was isolated after extraction with pentane and removal of all volatiles
as an orange-brown oil. Attempts to crystallize 1b from pentane or
acetone were not successful. Complex 1b will react at room temperature
slowly to generate 11 and deactivation products and its instability
precludes elemental analysis: 1H (300 MHz, 20 °C, C6D12) δ 2.12 (dd,
11.5 Hz, 2.3 Hz, 2H), 1.05 (m, 4H), 1.66 (s, 15H), 0.16 (s, 6H), 0.10
(s, 6H), 3.61 (q, 15 Hz, 2H), 3.62 (q, 15 Hz, 2H), 1.11 (t, 7.2 Hz, 6H);
13C (75.5 MHz, 20 °C, C6D12) δ 97.4 (C5Me5), 47.9 (d, 13.5 Hz,
H2Cd), 44.2 (d, 13.7 Hz, dCHSi), 9.4 (C5Me5), 1.00 (-SiMe3), 17.9
(-OCH2CH3), 58.2 (-OCH2CH3).
Preparation of 6. Complex 6 was prepared by heating a solution
of 1a (0.06 g, 1.4 × 10-4 mol) and 10 equiv of vinyltrimethylsilane in
1 mL of cyclohexane for 2 weeks at 140 °C in a glass tube with Teflon
plug. The volatiles were removed in vacuo, and the residue was
dissolved in acetone. The reaction mixture was cooled to -20 °C.
Orange crystalline material was isolated which was suitable for X-ray
analysis: 1H (400 MHz, 20 °C, C6D6) δ 1.92 (s, 15H), 1.22 (s, 1H),
0.18 (s, 3H), 0.37 (s, 3H), 0.19 (s, 9H), 0.21 (s, 9H), 0.23 (s, 9H), 4.69
(d, 16 Hz, 1H); 13C (100.6 MHz, 20 °C, C6D6) δ 94.8 (d, 6 Hz, C5-
Me5), 11.9 (s, C5Me5), 11.2, 2.1, 1.3 (s), 3.7, 0.5, -1.1 (s, -SiMe3),
45.0 (d, 18 Hz), 43.5 (d, 15 Hz), 87.7 (d, 6 Hz), 90.0 (d, 9 Hz).
X-ray Structure Determination of 1c and 6. Data were collected
on a Siemens SMART diffractometer, using the ω-scan technique. The
structures were solved by direct methods. Refinement was done by
full-matrix least squares with weights based on counter statistics. All
non-hydrogen atoms were refined anisotropically, while H atoms were
refined using a riding model. Crystal data and collection parameters
are given in Table 2. All computations were performed using the
NRCVAX suite of programs.61
Preparation of [C5Me5Rh(C2H3Si(OiPr)3)2] (1c). The synthesis
follows the general method outlined for the synthesis of 1a. Complex
1c was isolated after extraction with pentane and removal of all volatiles
as a yellow oil. The material was pure at this stage by elemental
analysis; however, NMR spectroscopy showed the presence of one
minor isomer. Recrystallization from acetone gave a yellow material
which was suitable for X-ray crystallography and showed one isomer
by NMR analysis. In the solid form 1c was stored at 20 °C under argon.
Complex 1c will react in solution at room temperature slowly to
generate a mixture of isomers and eventually olefin 8 and decomposition
products: 1H (300 MHz, 20 °C, C6D12) δ 3.23 (d, 18 Hz, 1H), 2.11 (d,
18 Hz, 1H), 2.01 (d, 15 Hz, 1H), 1.88 (d, 15 Hz, 1H), 0.66 (dd, 18, 15
Hz, 1H), 0.48 (dd, 15, 18 Hz, 1H), 4.22 (spt, 6 Hz, 3H), 4.32 (spt, 6
Hz, 3H), 1.72 (s, 15 H), 1.10-1.21 (-CHMe2, d, 6 Hz, 36H); 13C (75.5
MHz, 20 °C, C6D12) δ 97.4 (d, 4.2 Hz, C5Me5), 49.1 (d, 13.6 Hz), 48.6
(d, 13.1 Hz), 39.5 (d, 14.3 Hz), 34.5 (d, 16.6 Hz), 65.0 (s, OCH), 65.2
(s, OCH), 25.9, 26.0, 26.1, 26.2, 26.2 (overlapping -CHMe2), 9.8
(C5Me5). Anal. Calcd for C32H63O6Si2Rh: H, 9.03; C, 54.68. Found:
H, 8.98; C, 54.87.
Preparation of Vinylalkoxysilanes. The substrates triisopropoxyvi-
nylsilane and dimethylethoxyvinylsilane are commercial and were used
as received. The general procedure for the synthesis of vinylalkoxysi-
lanes is analogous to the synthesis described below for n-butoxydim-
ethylvinylsilane.
n-Butanol (5 g, 0.067mol) was added to 30 mL of tetrahydrofuran
and the mixture cooled to 0 °C. To this was added slowly a 2.5 M
solution of n-butyllithium in hexanes (27 mL). The THF solution was
stirred for 1 h while warming to 20 °C. To this was added slowly over
the course of 1 h vinyldimethylchlorosilane (8.1 g, 0.067 mol). Close
to complete addition a white percipitate formed. The mixture was stirred
for 8-12 h and filtered, and the tetrahydrofuran was removed in vacuo
to leave a colorless oil that was further purified by distillation. All
vinylalkoxysilanes used here were prepared in this manner and were
pure by NMR spectroscopy and elemental analysis.
1
n-BuOSiMe2C2H3 (12): H (400 MHz, 20 °C, C6D6) δ 5.84, 6.03,
6.20 (dd, -CHdCH2, 3H), 3.63 (t, -OCH2-, 2H), 1.57 (m, 2H), 1.44
(m, 2H), 0.95 (t, -CH3, 3H), 0.26 (s, 6H); 13C (100.6 MHz, 20 °C,
C6D6) δ 138.6, 132.8 (-CHdCH2), 62.5 (-OCH2-), 35.2, 19.3, 14.0
(-C3H7), -2.0 (-SiMe2). Anal. Calcd: H, 11.46; C, 60.69. Found:
H, 11.64; C, 60.62.
Preparation of [C5Me5Rh(C2H3SiMe(OSiMe3)2)2] (1d). The syn-
thesis follows the general method outlined for the synthesis of 1a.
Complex 1d was isolated after extraction with pentane and removal of
all volatiles as an orange-red oil. Attempts to crystallize 1d from pentane
or acetone were not successful. NMR data for the major isomer: 1H
(300 MHz, 20 °C, C6D6) δ 1.96 (dd, 12 Hz, 4 Hz, 2H), 1.35 (d, 15 Hz,
2H), 0.91 (dd, 12 Hz, 15 Hz, 2H), 1.57 (s, 15H), 0.28 (s, 18H), 0.29
1
EtMeCHOSiMe2C2H3 (14): H (400 MHz, 20 °C, C6D6) δ 5.60,
5.82, 5.95 (dd, -CHdCH2, 3H), 3.58 (m, -OCH, 1H), 1.25 (m, 2H),
0.95 (d, 3H), 0.73 (t, -CH3, 3H), 0.15 (s, 6H); 13C (100.6 MHz, 20
°C, C6D6) δ 139.6, 133.0 (-CHdCH2), 70.5 (-OCH-), 33.1, 24.0,
10.6 (-Me, -Et), -2.9 (-SiMe2). Anal. Calcd: H, 11.46; C, 60.69.
Found: H, 11.59; C, 60.71.
(59) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(60) White, C.; Yates, A.; Maitlis, P. M.; Heinekey, D. M. Inorg. Synth.
1992, 29, 228.
(61) Gabe, E. J.; LePage, Y.; Charland, J. P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384.

4396 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Lenges et al.
t-BuCH2CH2OSiMe2C2H3 (16): 1H (400 MHz, 20 °C, C6D6) δ 5.80,
6.03, 6.20 (dd, -CHdCH2, 3H), 3.68 (t, -OCH2-, 2H), 1.55 (t,
-CH2-, 2H), 0.94 (s, 9H), 0.20 (s, 6H); 13C (100.6 MHz, 20 °C, C6D6)
δ 138.5, 132.7 (-CHdCH2), 60.0 (-OCH2-), 46.5 (-CH2-), 29.8
(-CMe3), -2.0 (-SiMe2). Anal. Calcd: H, 11.90; C, 64.45. Found:
H, 11.87; C, 63.50.
Hydrogen-Deuterium Exchange Reactions. All H/D exchange
reactions were conducted in purified, degassed solvents in either sealed
NMR tubes (J-young tubes) or thick-walled Kontes flasks sealed with
Teflon screw caps. All conditions are clearly indicated in the text and
Tables 1-3. Samples were monitored by both 1H NMR and 13C NMR
spectroscopies. When necessary, internal sealed capillaries containing
ferrocene were used as integration standards.
Procedure for Catalytic Transfer Hydrogenation. Complex 1a
(0.01 g, 2.3 × 10-5 mol) was dissolved in the appropriate amount of
neat alkoxyvinylsilane (see Table 4, I and II), which was added by
weight in a drybox. The vessel was closed with a Teflon plug and the
reaction mixture heated to 140 °C for the indicated time in an oil bath.
The solutions remained yellow-orange and homogeneous throughout
the reaction. After being cooled to room temperature, the vessel was
opened and the product analyzed directly by 1H and 13C NMR
spectroscopy. In all cases, with the exception of 15 (see text), NMR
analysis showed only the presence of starting material and silyl enolate-
(s) and traces of catalyst. Conversions of 95-99% were observed using
column II, Table 4 conditions for 8, 10, 13, 19, 21, and 23. Vacuum
transfer allowed easy separation from catalyst and access to rhodium-
free silyl enolates.
PhCH2CH2OSiMe2C2H3 (18): 1H (400 MHz, 20 °C, C6D6) δ 7.15-
7.13 (m, -Ph, 5H), 5.80, 6.01, 6.17 (dd, -CHdCH2, 3H), 3.81 (t,
-OCH2-, 2H), 2.86 (t, Ph-CH2-, 2H), 0.19 (s, 6H); 13C (100.6 MHz,
20 °C, C6D6) δ 139.4, 133.0 (-CHdCH2), 137.9, 129.4, 128.5, 126.4
(-Ph), 64.3 (-OCH2-), 39.8 (-CH2-), -2.0 (-SiMe2). Anal.
Calcd: H, 8.79; C, 69.84. Found: H, 8.86; C, 70.00.
PhCHMeOSiMe2C2H3 (20): 1H (400 MHz, 20 °C, C6D6) δ 7.11-
7.25, 7.32 (m, -Ph, 5H), 5.84, 6.03, 6.20 (dd, -CHdCH2, 3H), 4.88
(q, -OCHMe-, 1H), 1.42 (d, 3H), 0.19 (s, 3H), 0.15 (s, 3H); 13C (100.6
MHz, 20 °C, C6D6) δ 138.2, 132.8 (-CHdCH2), 137.9, 128.5, 127.3,
125.8 (-Ph), 71.0 (-OCHMe-), 27.5 (-CH3), -1.4, -1.6 (-SiMe2).
Anal. Calcd: H, 8.79; C, 69.84. Found: H, 8.84; C, 69.93.
PhCH2CHMeOSiMe2C2H3 (22): 1H (400 MHz, 20 °C, C6D6) δ
7.08-7.32 (m, Ph, 5H), 5.84, 5.95, 6.15 (dd, -CHdCH2, 3H), 3.95
(m, -OCH-, 1H), 2.58-2.77 (m, -CH2, 2H), 1.17 (d, -Me, 3H),
0.18 (s, 3H), 0.08 (s, 3H); 13C (100.6 MHz, 20 °C, C6D6) δ 139.8,
130.1, 128.5, 126.5 (-Ph), 138.6, 132.7 (-CHdCH2), 70.5
(-OCH-), 46.8 (-CH2), 24.1 (-CH3), -1.6, -1.8 (-SiMe). Anal.
Calcd: H, 9.15; C, 70.85. Found: H, 9.26; C, 71.12.
Acknowledgment. Acknowledgment is made to the National
Institutes of Health (Grant GM 28938) for financial support.
C.P.L. thanks the Fonds der Chemischen Industrie (Germany)
for a Kekule´ fellowship.
1
Me2CHOSiPh2C2H3 (24): H (400 MHz, 20 °C, C6D6) δ 7.22 (m,
4H), 6.71 (m, 6H), 5.43, 5.62, 6.05 (dd, -CHdCH2, 3H), 3.65 (m,
-OCH-, 1H), 0.71 (d, -Me, 6H); 13C (100.6 MHz, 20 °C, C6D6) δ
135.5, 135.0, 128.1 (-Ph), 136.6, 130.1 (-CHdCH2), 66.3
(-OCH-), 25.9 (-Me). Anal. Calcd: H, 7.51; C, 76.07. Found: H,
7.61; C, 75.92.
Supporting Information Available: Tables of crystal data,
structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for 1c
and 6, kinetic plots for H/D exchange of 1a, spectra for
deuteration of 1c, and catalytic analysis of transfer hydrogena-
tion (PDF). This material is available free of charge via the
Internet at http://pubs.acs.org.
PhCH2CH2NHSiMe2C2H3 (26): 1H (400 MHz, 20 °C, C6D6) δ
7.28-7.45 (-Ph, 5H), 5.90, 6.12, 6.35 (dd, -CHdCH2, 3H), 3.19 (q,
-NHCH2-, 2H), 2.83 (m, 2H), 0.72 (t, broad, 1H), 0.29 (s, 6H); 13C
(100.6 MHz, 20 °C, C6D6) δ 140.7, 129.4, 128.7, 126.4 (-Ph), 139.9,
131.8 (-CHdCH2), 44.1 (-NHCH2-), 41.9 (-CH2-), -1.3 (-SiMe2).
Anal. Calcd: H, 9.32; C, 70.18. Found: H, 9.48; C, 70.37.
JA984409O