Tris(oxazolinyl)boratomagnesium-catalyzed cross-dehydrocoupling of organosilanes with amines, hydrazine, and ammonia

Article abstract of DOI:10.1021/ja207641b

We report magnesium-catalyzed cross-dehydrocoupling of Si-H and N-H bonds to give Si-N bonds and H₂. A number of silazanes are accessible using this method, as well as silylamines from NH₃ and silylhydrazines from N₂H₄. Kinetic studies of the overall catalytic cycle and a stoichiometric Si-N bond-forming reaction suggest nucleophilic attack by a magnesium amide as the turnover-limiting step.

Full text of DOI:10.1021/ja207641b

COMMUNICATION
pubs.acs.org/JACS
Tris(oxazolinyl)boratomagnesium-Catalyzed Cross-Dehydrocoupling
of Organosilanes with Amines, Hydrazine, and Ammonia
James F. Dunne, Steven R. Neal, Joshua Engelkemier, Arkady Ellern, and Aaron D. Sadow*
Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States
S Supporting Information
b
report to be an effective precatalyst for the cross-dehydrocou-
ABSTRACT: We report magnesium-catalyzed cross-dehy-
pling of SiꢀH bonds in organosilanes and NꢀH bonds in amines
drocoupling of SiꢀH and NꢀH bonds to give SiꢀN bonds
and H2. A number of silazanes are accessible using this
method, as well as silylamines from NH3 and silylhydrazines
from N2H4. Kinetic studies of the overall catalytic cycle and
a stoichiometric SiꢀN bond-forming reaction suggest nu-
cleophilic attack by a magnesium amide as the turnover-
limiting step.
to give SiꢀN bonds and H2 (eq 1).
With this catalyst system, a range of silazanes can be prepared in
high conversion and high yield, as shown in Table 1.
Thus, primary aliphatic amines and anilines are effective
coupling partners, and primary and secondary silanes are selective
silylating agents. In reactions for which multiple dehydrocoupling
steps could give mixtures and oligomers, carefully controlled
silane/amine ratios allow the isolation of a single product. Forma-
tion of polysilazane, ꢀ[R0NSiR2]nꢀ, and poly(aminosilane),
ꢀ[SiR(NR02)]nꢀ, is not detected. In the absence of ToMMgMe
as a catalyst, only starting materials are observed.
ompounds containing SiꢀN bonds have important applica-
C
tions in synthetic chemistry as bases,1 silylating agents,2
ligands for metal centers, and polymeric precursors for ceramic
materials.3 Amines are often protected with tertiary silanes as
silazanes,4 and amines serve as useful protecting groups in silicon
chemistry for the selective conversion of chlorosilanes because
the SiꢀN bond forms readily and is easily transformed into SiꢀX
species (X = halide, alkoxide).5 However, the HCl produced
and/or basic conditions needed to neutralize the reaction can
limit its functional group tolerance, and a stoichiometric equiva-
lent of salt is formed; moreover, chlorosilanes are hydroscopi-
cally sensitive and must be stored under carefully controlled
conditions. Additionally, the products are controlled only by the
substituents on the chlorosilane and the amine partners, limiting
control over the selectivity. Catalytic dehydrocoupling of amines
and hydrosilanes offers a complementary synthetic method for
SiꢀN bond formation.
The catalytic reaction rates and product identities are notice-
ably affected by the steric bulk of the organosilane and amine
reactants. For example, 3.5 equiv of n-PrNH2 and PhSiH3
provide the tris(amido)silane (n-PrHN)3SiPh within 15 min
(Table 1, entry 1) with ToMMgMe as the catalyst, while i-PrNH2
and PhSiH3 form only the bis(amido) (i-PrHN)2SiHPh after
45 min at room temperature. Use of excess i-PrNH2 and heating
at 100 °C does not afford (i-PrHN)3SiPh. t-BuNH2 requires 24 h
for quantitative conversion to monodehydrocoupled t-BuHN-
SiH2Ph. Similar effects are observed in ToMMgMe-catalyzed
dehydrocoupling of anilines and silanes, as (PhHN)2SiHPh
forms rapidly while the reaction of Ph2SiH2 and PhNH2 requires
heating at 60 °C. The more hindered secondary amine Ph2NH
and PhSiH3 give a 10% yield of Ph2NSiH2Ph after 72 h at 110 °C,
and i-Pr2NH does not form detectable silazane products in the
presence of ToMMgMe after 5 days at 100 °C. The low reactivity
of secondary amines likely inhibits polysilazane formation, which
would require coupling of disubstituted R0HNSiR3. Additionally,
only starting materials are observed from mixtures of tertiary
BnMe2SiH and Et3SiH (Bn = CH2Ph) with primary amines
(PhNH2, t-BuNH2, i-PrNH2, n-PrNH2) under catalytic condi-
tions at 110 °C after 72 h.
Only a few metal-catalyzed cross-couplings of silanes and
amines have been described.6 Palladium on Al2O3 catalyzes the
aminolysis of optically active tertiary naphthylphenylmethylsi-
lane with inversion of the silicon stereocenter, while Pd/C gives
the racemic product.7 Ammonia and the tertiary silazane HN-
(SiHMe2)2 react at 135 °C in the presence of Ru3CO12 to give
polysilazanes and H2,8 while rhodium dimers give mixtures of
oligosilazanes from amines and organosilanes.9 A chromium
catalyst provides Ph2HSiꢀNHPh from Ph2SiH2 and aniline.10
Dimethyltitanocene catalyzes the coupling of silanes with am-
monia and hydrazine,11 while cuprous chloride catalyzes the
coupling of silanes and primary amines.12 Finally, a number of
silazanes have been prepared using [U(NMe2)3][BPh4] as a
catalyst.13 These few examples show the general challenge of
controlling the selectivity, and in addition, there have been few
opportunities for direct investigation of the siliconꢀnitrogen
bond-forming steps of these catalytic reactions.
The interaction between the tris(oxazolinyl)borate ancillary
ligand and the magnesium(II) center is not disrupted in the
presence of excess primary amine. For example, ToMMgNHt-Bu
is robust in the presence of 10 equiv of t-BuNH2 (although
amineꢀamide exchange occurs). Therefore, we decided to
investigate the reductive silylation of hydrazine as a multiple
Some of these issues are addressed by the catalytic behavior of
the four-coordinate magnesium complex ToMMgMe [ToM
=
Received: August 12, 2011
Published: September 29, 2011
tris(4,4-dimethyl-2-oxazolinyl)phenylborate],14 which we now
r
2011 American Chemical Society
16782
dx.doi.org/10.1021/ja207641b J. Am. Chem. Soc. 2011, 133, 16782–16785
|

Journal of the American Chemical Society
COMMUNICATION
Table 1. ToMMgMe-Catalyzed Aminolysis of Silanesa
amine (equiv)
silane
product
% yield (isolated)
n-PrNH2 (3.5)
n-PrNH2 (3)
n-PrNH2 (0.5)
n-PrNH2 (3)
n-PrNH2 (0.5)
i-PrNH2 (2.5)
i-PrNH2 (0.5)
i-PrNH2 (2)
i-PrNH2 (2)
t-BuNH2 (2.5)
t-BuNH2 (2)
t-BuNH2 (2)
PhNH2 (2.5)
PhNH2 (2)
PhSiH3
(n-PrHN)3SiPh
(n-PrHN)2SiMePh
n-PrHNSiHMePh
(n-PrHN)2SiPh2
n-PrHNSiHPh2
(i-PrHN)2SiHPh
i-PrHNSiH2Ph
i-PrHNSiHMePh
i-PrHNSiHPh2
t-BuHNSiH2Ph
t-BuHNSiHMePh
t-BuHNSiHPh2
(PhHN)2SiHPh
PhHNSiHMePh
PhHNSiHPh2
99 (99)
99 (90)
99 (78)
99 (99)
99 (96)
99 (99)
99 (45)
89 (67)
99 (97)
99 (90)
90 (60)
99 (81)
99 (97)
43b (19)
53b (19)
PhMeSiH2
PhMeSiH2
Ph2SiH2
Ph2SiH2
PhSiH3
PhSiH3
PhMeSiH2
Ph2SiH2
PhSiH3
PhMeSiH2
Ph2SiH2
PhSiH3
Figure 1. ORTEP diagram of ToMMgNHt-Bu. Ellipsoids are plotted
at 50% probability, and only the H atom bonded to N4 is shown.
PhMeSiH2
PhNH2 (2)
Ph2SiH2
ToMMgMe (relative to the silane), and the reaction provided
BnMe2SiNH2 as the sole product after 15 h. BnMe2SiNH2 was
isolated by Kugelrohr distillation (175 °C, 150 mmHg). In the
presence of catalytic ToMMgMe, (C3H5)Me2SiH reacts more
rapidly with ammonia than BnMe2SiH, and quantitative forma-
tion of (C3H5)Me2SiNH2 was observed after 5 h in micromolar-
scale experiments monitored by 1H NMR spectroscopy (eq 3).
a Conditions: 5 mol % ToMMgMe, C6H6, 24 h, room temperature.
b 60 °C.
NH-containing compound that could undergo one or more
dehydrogenative silylations. Remarkably, monosilylhydrazines
are accessible from the ToMMgMe-catalyzed reactions of N2H4
with Et3SiH, (C3H5)Me2SiH, or BnMe2SiH (eq 2).
(C3H5)Me2SiH reacts quantitatively over 7 h, giving (C3H5)Me2-
SiNHNH2, whereas BnMe2SiH and Et3SiH proceed only to 50%
yield after 12 h. The magnesium species (k2-ToM)2Mg was
Et3SiNH2, however, requires 15 h for quantitative formation (5 mol %
ToMMgMe, benzene, room temperature). Disilazanes such as (Et3-
Si)2NH are not detected by 1H NMR spectroscopy, in contrast to the
case of transition-metal-catalyzed dehydrogenative silylations of am-
monia.11,12
1
observed in H NMR spectra of micromolar-scale reactions in
benzene-d6, and this species appears to form from the transient
intermediate ToMMgNHNH2 as the catalyst decomposition path-
way. This intermediate, ToMMgNHNH2, forms upon reaction of
ToMMgMe and N2H4, but attempts to isolate it by evaporation of
volatiles afforded mixtures of H[ToM] and ToM2Mg. ToMMgMe
also catalyzes reactions of hydrazine with primary and secondary
silanes, but mixtures of products are obtained. Still, the monosilyla-
tion of hydrazine highlights the impressive selectivity available in
these magnesium-catalyzed reactions.
Attempts to isolate ToMMgNHNH2 or ToMMgNH2 as pos-
sible intermediates by treatment of ToMMgMe with N2H4 or
NH3 provided the ligand redistribution product ToM2Mg and
unidentified species. Therefore, we focused our mechanistic
studies on catalytic aminolysis reactions that are conveniently
monitored by 1H NMR spectroscopy. Spectra of reaction
mixtures revealed that H2 is formed as the dehydrocoupling
reactions proceed and that the catalyst resting state is a tris-
(oxazolinyl)borate magnesium amide. No other resonances that
could be attributed to a ToMMg species were observed in the
reaction mixture. These ToMMgNHR species (R = Pr, i-Pr, Ph;
see below and the Supporting Information for synthesis and
characterization) are formed rapidly upon addition of RNH2 to
ToMMgMe. Over 2 h, ToMMgNHi-Pr and ToMMgNHn-Pr
precipitate from benzene.18 During independent synthesis,
ToMMgMe and t-BuNH2 were heated in benzene at 75 °C for
18 h to ensure quantitative formation of ToMMgNHt-Bu. In this
compound, all three oxazoline donors coordinate to magnesium-
(II) in the ground state [15N NMR: ꢀ158.4 (N-oxazoline) and
ꢀ117.8 (NHt-Bu); νCN = 1590 cmꢀ1]; an ORTEP diagram is
shown in Figure 1.
Selective conversion of ammonia is also challenging.15 The
NꢀH bond is strong (104 kcal/mol)16 and nonacidic (pKa = 41
in DMSO).17 Silylation of ammonia increases the acidity of the
remaining NH moieties, potentially increasing their reactivity
and making monosilylation difficult. Furthermore, ammonia is a
good ligand for metal centers and can shield the (typically Lewis
acidic) catalytic site from interactions with other substrates.
While this can also be a problem with amines, bulky ancillary
ligands sterically inhibit coordination of substituted amines. This
strategy is not effective with ammonia because of its small size.
The successful reductive silylation of hydrazine and the apparent
coordinative saturation of ToMMgNHR suggested that the
coordination of ammonia would not be an issue. Controlling
the extent of silylation might remain a problem, as a mono-
silylamine is significantly more acidic than ammonia and might
be expected to be more reactive. To test our magnesium catalyst
for ammonolysis of silanes, excess ammonia was condensed into
a storage flask containing BnMe2SiH, benzene, and 5 mol %
In the solid state, ToMMgNHt-Bu contains a planar amido
group [Mg1ꢀN2ꢀC22, 137.2(4)°; Mg1ꢀN4ꢀH4, 113(6)°;
C22ꢀN4ꢀH4, 107(6)°; ∑(XꢀNꢀX) = 357°] and a four-
coordinate magnesium center. Solid-angle analysis revealed
that the ToM (7.38 sr) and NHt-Bu (2.81 sr) ligands occupy
16783
dx.doi.org/10.1021/ja207641b |J. Am. Chem. Soc. 2011, 133, 16782–16785

Journal of the American Chemical Society
COMMUNICATION
Scheme 1. Catalytic Cycle for Organosilane Aminolysis
Scheme 2. Proposed Mechanism for ToMMg-Mediated
SiꢀN Bond Formation
58.8 and 22.4% of the space surrounding the magnesium
center, respectively.19
In catalytic reactions, the consumption of organosilane and
the formation of the silazane product are evident from the SiH
resonances, which shift downfield as the hydrides are replaced
with amides. Additionally, the 3JHH coupling constants (∼3 Hz)
between the SiH and NH groups give rise to doublet SiH
resonances in RH2SiNHR0 and triplets in RHSi(NHR0)2, and
therefore, the SiH signal assists in product identification. Further-
more, all of the silazane products in Table 1 are isolable. The
in situ concentrations of ToMMgNHt-Bu, t-BuNH2, and PhMe-
isotope effects for SiꢀC bond formation of ca. 1.1,21 highly negative
ΔSq values, and small ΔHq values that are similar to those for the
magnesium-mediated SiꢀN bond formation.
A few studies probing electronic effects in σ-bond metathesis
have shown small changes in rate with electron-donating or
electron-withdrawing groups, consistent with small polarization
in the transition state.22 Similarly small electronic effects were
observed in the [2σ + 2π] four-center transition state of styrene
insertion into ZrꢀH bonds [F = ꢀ0.46(1)], whereas β-elimina-
tion provides a large negative F value of ꢀ1.8(5) and large KIEs
(kH/kD = 3.9ꢀ4.5).23 The aryl group is pendent from the
β-position of the four-center transition state in both of these
transformations.
1
SiH2 in catalytic reactions were monitored by H NMR spec-
troscopy, and under conditions of excess t-BuNH2 (17ꢀ43 equiv
vs PhMeSiH2) and 20ꢀ50 mol % ToMMgNHt-Bu at 335 K, the
rate law was found to be ꢀd[PhMeSiH2]/dt = k0[ToMMgNHt-
Bu]1[PhMeSiH2]1[t-BuNH2]0, with k0 = 0.060(4) Mꢀ1 sꢀ1
.
This rate law indicates that the turnover-limiting step involves
an interaction of the catalyst and PhMeSiH2; t-BuNH2 is not
present in that transition state. As noted above, 1H NMR spectra
of the catalytic reaction mixture suggest that ToMMgNHt-Bu is
the catalyst resting state. These observations are consistent with
the general mechanism shown in Scheme 1, where both steps are
irreversible and the interaction of ToMMgNHR and the organo-
silane is turnover-limiting.
Second-order rate constants were determined for the reac-
tions of ToMMgNHt-Bu and several Ph(aryl)SiH2 (aryl = Ph,
p-C6H4F, p-C6H4Me, p-C6H4OMe, p-C6H4CF3).24 The orga-
nosilanes with electron-withdrawing groups react more rapidly
than those with electron-donating groups. A Hammett plot of
log(kX/kH) versus σ provides a positive slope (F = 1.4). Thus, the
activation barrier is decreased with electron-withdrawing sub-
stituents on silicon. This effect is consistent with a reaction
pathway involving a five-coordinate silicon species ToMMgHt-
BuNꢀSiPh(aryl)H2 that is stabilized by electron-withdrawing
groups. However, the magnitude of the inductive electronic
effect is inconsistent with a concerted bond-breaking and bond-
forming process; electron-withdrawing groups are expected to
have counteracting effects on bond formation and bond cleav-
age by simultaneously increasing the barrier for hydride transfer
to magnesium while stabilizing the five-coordinate silicon center.
The temperature-independent primary isotope effect of unity
further supports little SiꢀH bond cleavage in the transition
state.
Considering these points, we suggest that these reactions
involve nucleophilic attack of the amide on silicon to form a
five-coordinate silicon center in the rate-determining step, which
is followed by rapid hydrogen transfer to magnesium in a step
reminiscent of β-elimination (Scheme 2).
Two additional observations suggest that this mechanism is
more reasonable than the concerted four-centered transition-
state-like pathway. First, the reaction rate is decreased with the
less nucleophilic anilide versus the aliphatic amide, which is
consistent with nucleophilic attack playing an important role in
the rate-limiting step. Second, a zeroth-order amine concentra-
tion dependence was observed in the catalytic rate law even at
very high concentrations without evidence of inhibition by amine
coordination. Thus, these reactions may be performed even in
liquid NH3. In contrast, intermolecular σ-bond metathesis reac-
tions require coordinative unsaturation and are inhibited by
Under stoichiometric conditions, isolated ToMMgNHt-Bu reacts
with hydrosilanes, and this step models SiꢀN bond formation
under catalytic conditions. For example, ToMMgNHt-Bu and
PhMeSiH2 (1.4 equiv, ꢀ20 to 80 °C) react quantitatively to give
t-BuHNSiHMePh. A black precipitate forms as the reaction pro-
ceeds, and this material is presumed to be the decomposition
product from a putative ToMMgH species. Linear second-order
integrated rate law plots of ln{[PhMeSiH2]/[ToMMgNHt-Bu]}
versus time provided a rate law of ꢀd[ToMMgNHt-Bu]/dt =
kobs[ToMMgNHt-Bu][PhMeSiH2], with k
= (3.9 ( 0.3) ꢁ
273K
obs
10ꢀ3 Mꢀ1 sꢀ1. The curve obtained from linear regression analysis of
a plot of ln(k/T) versus 1/T was used to calculate the second-order
335K
obs
rate constant k
= 0.04 Mꢀ1 ꢀ1, which is in reasonable
s
agreement with the rate constant obtained from the catalytic
experiments [0.060(4) Mꢀ1 sꢀ1].
The activation parameters calculated from a plot of ln(k/T) versus
1/T from ꢀ20 to 80 °C are ΔHqH = 5.9(2) kcal molꢀ1 and ΔSqH
=
ꢀ46.5(8) cal molꢀ1 Kꢀ1, suggesting a highly ordered transition
state.20 A primary kinetic isotope effect of kH/kD = 1.0(2) at 0 °C was
measured for the reaction of ToMMgNHt-Bu and PhMeSiD2. This
small primary isotope effect was essentially temperature-independent
from ꢀ20 to 80 °C, and activation parameters identical to those for
PhMeSiH2 were obtained for PhMeSiD2 (ΔHqD = 5.7(2) kcal molꢀ1
and ΔSqD = ꢀ46.1(8) cal molꢀ1 Kꢀ1). For comparison, kinetic
studies of SiꢀC bond formations mediated by early transition metals
and rare-earth elements, which are proposed to involve concerted,
four-center transition states (i.e., σ-bond metathesis), have primary
16784
dx.doi.org/10.1021/ja207641b |J. Am. Chem. Soc. 2011, 133, 16782–16785

Journal of the American Chemical Society
COMMUNICATION
coordinating groups.22,25 Our hydroamination studies suggest
that amines coordinate to the magnesium center in ToMMgNHR
compounds, either to give a five-coordinate magnesium or
substitute an oxazoline.14 Thus, the zeroth-order amine depen-
dence (rather than an inverse dependence) suggests that an open
coordination site is not important in the current SiꢀN bond
formation.
Notably, the nature of nucleophilic substitution at silicon and
the role of electrophilic assistance have long been debated,
primarily by assessing retention or inversion of stereochemistry
in chiral silicon centers.26 In fact, n-Bu4NF catalyzed silane
aminolysis is proposed to involve five-coordinate silicon centers
without electrophilic assistance.27 Despite the importance of
SiꢀE bond formations (E = C, Si, O, N) in catalytic chemistry,
experimental investigations of electronic effects in d0- and fn-
metal-mediated SiꢀE bond formations are scarce. Thus, we
are currently examining the kinetic features of other d0- and
fnd0-metal-mediated SiꢀE bond formations to identify the
features (coordinative unsaturation, bond polarity, steric con-
straints, and related effects of ancillary ligands) that influence the
mechanism of these types of reactions in order to develop new
catalysis.
K. A.; Laine, R. M.; Kennish, R. A.; Cronin, T. R.; Balavoine, G. A. In
Better Ceramics through Chemistry III; Brinker, C. J., Clark, D. E., Ulrich,
D. R., Eds.; Materials Research Society: Warrendale, PA, 1988; pp
489ꢀ495. (d) Chow, W.; Hamlin, R. D.; Blum, Y.; Laine, R. M. J. Polym.
Sci., Part C: Polym. Lett. 1988, 26, 103. (e) Blum, Y. D.; Schwartz, K. B.;
Laine, R. M. J. Mater. Sci. 1989, 24, 1707.
(9) Wang, W. D.; Eisenberg, R. Organometallics 1991, 10, 2222.
(10) Matarasso-Tchiroukhine, E. J. Chem. Soc., Chem. Commun.
1990, 681.
(11) (a) Liu, H. Q.; Harrod, J. F. Organometallics 1992, 11, 822.
(b) He, J. L.; Liu, H. Q.; Harrod, J. F.; Hynes, R. Organometallics 1994,
13, 336.
(12) Liu, H. Q.; Harrod, J. F. Can. J. Chem. 1992, 70, 107.
(13) Wang, J. X.; Dash, A. K.; Berthet, J. C.; Ephritikhine, M.; Eisen,
M. S. J. Organomet. Chem. 2000, 610, 49.
(14) (a) Dunne, J. F.; Fulton, D. B.; Ellern, A.; Sadow, A. D. J. Am.
Chem. Soc. 2010, 132, 17680. (b) Dunne, J. F.; Su, J.; Ellern, A.; Sadow,
A. D. Organometallics 2008, 27, 2399.
(15) For an in-depth discussion of catalytic reactions of NH3, see:
Klinkenberg, J. L.; Hartwig, J. F. Angew. Chem., Int. Ed. 2011, 50, 86.
(16) Darwent, B. de B. Natl. Stand. Ref. Data Ser. 1970, 31, 1.
(17) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456.
(18) Three νCN bands in the IR spectra suggest ToMMgNHi-Pr and
ToMMgNHn-Pr are not monomeric as solids (see the Supporting
Information), although the 1H NMR spectra of species generated
in situ suggest monomeric structures. Precipitated ToMMgNHi-Pr and
ToMMgNHn-Pr are sufficiently insoluble that solution NMR data were
not obtained.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures, data
b
(19) (a) White, D.; Coville, N. J. Adv. Organomet. Chem. 1994,
36, 95. (b) Guzei, I. A.; Wendt, M. Dalton Trans. 2006, 3991. (c) Guzei,
I. A.; Wendt, M. Solid-G UW-Madison, WI, 2004.
from kinetic measurements, and crystallographic data (CIF).
This material is available free of charge via the Internet at http://
pubs.acs.org.
(20) (a) Espenson, J. H. Chemical Kinetics and Reaction Mechanisms,
2nd ed.; McGraw-Hill: New York, 1995. (b) Morse, P. M.; Spencer,
M. D.; Wilson, S. R.; Girolami, G. S. Organometallics 1994, 13, 1646.
(21) (a) Gountchev, T. I.; Tilley, T. D. Organometallics 1999,
18, 5661. (b) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127, 643.
(22) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am.
Chem. Soc. 1987, 109, 203.
(23) Chirik, P. J.; Bercaw, J. E. Organometallics 2005, 24, 5407.
(24) Rate constants used in the Hammett plot were determined
from second-order integrated rate law plots of ln{[Ph(XC6H4)SiH2]/
[ToMMgNHt-Bu]} vs Δ0t (X = OMe, Me, H, F) for reactions at 313 K;
for X = CF3, the rate constant was calculated from an Eyring plot for
reactions measured over the range 245ꢀ313 K because the rate at 313 K
was sufficiently high to require verification.
’ AUTHOR INFORMATION
Corresponding Author
sadow@iastate.edu
’ ACKNOWLEDGMENT
Financial support for this work was provided by the National
Science Foundation (CHE-0955635) and (CRIF-0946687) and
the ACS-PRF-Green Chemistry Institute. S.R.N. was supported
by a GAANN Fellowship. A.D.S. is an Alfred P. Sloan Fellow.
’ REFERENCES
(1) As bases: Fieser, L. F.; Fieser, M. Reagents in Organic Chemistry;
Wiley: New York, 1967.
(2) As silylation agents: Roth, C. A. Ind. Eng. Chem. Prod. Res. Dev.
1972, 11, 134. (b) Tanabe, Y.; Murakami, M.; Kitaichi, K.; Yoshida, Y.
Tetrahedron Lett. 1994, 35, 8409. (c) Tanabe, Y.; Misaki, T.; Kurihara,
M.; Iida, A.; Nishii, Y. Chem. Commun. 2002, 1628. (d) Iida, A.; Horii, A.;
Misaki, T.; Tanabe, Y. Synthesis 2005, 16, 2677.
(25) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51.
(26) Bassindale, A. R.; Taylor, P. G. In The Chemistry of Organic
Silicon Compounds; Wiley: New York, 1989; Vol. 3, pp 839ꢀ892.
(27) Corriu, R. J. P.; Leclercq, D.; Mutin, P. H.; Planeix, J. M.; Vioux,
A. J. Organomet. Chem. 1991, 406, C1.
(3) (a) Neugebauer, P.; Jaschke, B.; Klingebiel, U. In The Chemistry
of Organic Silicon Compounds; Wiley: Chichester, England, 1989; Vol. 3,
pp 429ꢀ468. (b) Armitage, D. A. In The SiliconꢀHeteroatom Bond;
Wiley: Chichester, England, 1991; pp 365ꢀ484.
(4) Wuts, P. G. M.; Greene, T. W. Protecting Groups in Organic
Synthesis, 4th ed.; Wiley: New York, 2006.
(5) (a) Eaborn, C. Organosilicon Compounds; Butterworths: London,
1960; p 333. (b) Fessenden, R.; Fessenden, J. S. Chem. Rev. 1961,
61, 361. (c) Passarelli, V.; Carta, G.; Rossetto, G.; Zanella, P. Dalton
Trans. 2003, 413.
(6) Reichl, J. A.; Berry, D. H. Adv. Organomet. Chem. 1998, 43, 197.
(7) Sommer, L. H.; Citron, J. D. J. Org. Chem. 1967, 32, 2470.
(8) (a) Blum, Y.; Laine, R. M. Organometallics 1986, 5, 2081.
(b) Laine, R. M. Platinum Met. Rev. 1988, 32, 64. (c) Youngdahl,
16785
dx.doi.org/10.1021/ja207641b |J. Am. Chem. Soc. 2011, 133, 16782–16785