Activation of Carbon Dioxide by Silyl Triflate-Based Frustrated Lewis Pairs

Article abstract of DOI:10.1002/chem.201501904

Silyl triflates of the form R_4-nSi(OTf)_n (n=1, 2; OTf=OSO₃CF₃) are shown to activate carbon dioxide when paired with bulky alkyl-substituted Group15 bases. Combinations of silyl triflates and 2,2,6,6-tetramethylpiperidine react with CO₂ to afford silyl carbamates via a frustrated Lewis pair-type mechanism. With trialkylphosphines, the silyl triflates R₃Si(OTf) reversibly bind CO₂ affording [R′₃P(CO₂)SiR₃][OTf] whereas when Ph₂Si(OTf)₂ is used one or two molecules of CO₂ can be sequestered. The latter bis-CO₂ product is favoured at low temperatures and by excess phosphine.

Full text of DOI:10.1002/chem.201501904

DOI: 10.1002/chem.201501904
Full Paper
&
Frustrated Lewis Pairs
Activation of Carbon Dioxide by Silyl Triflate-Based Frustrated
Lewis Pairs
Sarah A. Weicker and Douglas W. Stephan*[a]
Abstract: Silyl triflates of the form R4ÀnSi(OTf)n (n=1, 2;
OTf=OSO3CF3) are shown to activate carbon dioxide when
paired with bulky alkyl-substituted Group 15 bases. Combi-
nations of silyl triflates and 2,2,6,6-tetramethylpiperidine
react with CO2 to afford silyl carbamates via a frustrated
Lewis pair-type mechanism. With trialkylphosphines, the silyl
triflates R3Si(OTf) reversibly bind CO2 affording [R’3P(CO2)SiR3]
[OTf] whereas when Ph2Si(OTf)2 is used one or two mole-
cules of CO2 can be sequestered. The latter bis-CO2 product
is favoured at low temperatures and by excess phosphine.
Introduction
Nature delicately balances carbon dioxide levels through the
processes of photosynthesis, cellular respiration, and organic
decomposition. In the past two centuries, however, this global
carbon cycle has been disrupted by human activities. Anthro-
pogenic carbon dioxide emissions, most significantly from
fossil fuel combustion, have resulted in increased atmospheric
CO2 concentrations and have been a strong contributor to
global climate change.[1] As such, CO2 is very attractive for use
as a cheap, abundant, and environmentally-friendly C1 build-
ing block. The development of systems designed to sequester
or chemically modify CO2 to fuels or compounds of higher
value has garnered significant attention.[2] Frustrated Lewis
pairs (FLPs), combinations of sterically hindered Lewis acids
and bases with unquenched reactivity, can capture CO2 by si-
multaneous nucleophilic attack of the Lewis base at carbon
and binding of the Lewis acid to oxygen (Figure 1). In 2009,
we described the activation of CO2 by boron Lewis acids in
conjunction with phosphines.[3] Subsequent studies by Piers,[4]
O’Hare,[5] Fontaine,[6] and ourselves[7] revealed that B/N, B/P, or
Al/P based FLPs can effect the stoichiometric or catalytic re-
duction of the activated CO2 moiety upon treatment with an
appropriate reducing agent.
Figure 1. Selected examples of CO2 activation by frustrated Lewis pairs.
tion with hydrosilanes to stoichiometrically reduce CO2 to yield
formic acid or methanol after an aqueous quench. The
Müller[10] and Ashley[11] groups have also described CO2 seques-
tration by silylium/phosphine Lewis pairs.
The application of neutral four-coordinate silicon Lewis acids
in the context of FLP chemistry has been quite limited, al-
though Manners and co-workers[12] have described the reac-
tions of Group 14 triflates/amine based FLPs with amine and
phosphine–borane adducts. As electronically-saturated, four-
coordinate silicon compounds can display Lewis acidic proper-
ties, they have been previously employed as Lewis acid cata-
lysts for organic carbonÀcarbon bond forming reactions such
as the Diels–Alder reaction,[13] Mukaiyama aldol,[14] and cou-
plings of acetals or acetal-like compounds with nucleophiles.[15]
Recently, Tilley and co-workers[16] have also reported catalytic
aldehyde hydrosilylation by bis(perfluorocatecholato)silane.
Motivated by the above findings and targeting FLP chemis-
try beyond traditional Lewis acids, we have probed the use of
electronically-saturated silicon Lewis acids, demonstrating that
combinations of four-coordinate silyl triflates and amine or
phosphine bases can be exploited in FLP/CO2 chemistry.
Main Group Lewis acids outside of Group 13 have also been
employed in the activation of CO2. In 2012, we[8] reported the
insertion of CO2 into the PÀN bonds of strained amidophos-
phoranes. This reactivity was compared to a frustrated Lewis
pair, as the amidophosphoranes contained both acidic and
basic P,N functionalities. Efforts to apply silicon Lewis acids in
CO2 activation have focused on highly Lewis acidic silylium cat-
ions. Müller and co-workers[9] used silylium cations in conjunc-
[a] S. A. Weicker, Prof. Dr. D. W. Stephan
Department of Chemistry, University of Toronto
80 St. George St. Toronto, Ontario, M5S 3H6 (Canada)
E-mail: dstephan@chem.utoronto.ca
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501904.
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Results and Discussion
A CD2Cl2 solution of Ph2Si(OTf)2 (1) was added to one equiva-
lent of 2,2,6,6-tetramethylpiperidine (TMP) in a J-Young NMR
tube. The 1H NMR spectrum of this mixture appeared un-
changed from the starting materials, indicating that an adduct
was not formed. The NMR tube was degassed and backfilled
with carbon dioxide gas prompting precipitation of a white
solid. Analysis of the CD2Cl2 soluble components by 1H NMR
spectroscopy revealed two sets of aromatic resonances in a 1:1
ratio, corresponding to a mixture of free 1 and a new com-
pound containing phenyl substituents. The resonance attribut-
able to the tetramethylpiperidine N-H proton was absent from
Figure 2. POV-ray depiction of the molecular structure of 3. H atoms and dis-
order in the TMP moiety omitted for clarity.
1
the H NMR spectrum, implying complete consumption of TMP.
less than 2, while the O1-C19-O2 angle of 107.5(3)8 is signifi-
cantly smaller than the idealized carbonyl bond angle of 1208.
These parameters suggest the donation of electron density
from O2 into the s*-orbital of the SiÀO3 bond.
The presence of unreacted 1 suggested that the stoichiometry
of this reaction was not 1:1 with respect to the Lewis acid and
Lewis base. Adjusting the ratio of reagents to a 2:1 mixture of
TMP and 1 followed by exposure to CO2 yielded the same
white precipitate. The precipitate was isolated by filtration and
dissolved in CD3CN. Proton NMR spectroscopy revealed
a broad downfield 1:1:1 triplet at dH =6.53 ppm (1JHN =12 Hz)
and aliphatic proton signals, while the 19F spectrum exhibited
a single free triflate resonance at dF =À79.39 ppm. These ob-
servations suggested the formulation of this species as [TMPH]
[OTf] (2). The 13C{1H} NMR spectrum of the CD2Cl2 soluble prod-
uct displays a resonance at dC =165.02 ppm, attributable to
a carbonyl carbon. Repeating this reaction again using 13CO2
resulted in augmentation of this resonance, confirming the in-
corporation of carbon dioxide into this product. While the
spectroscopic data was consistent with the formulation
C9H18NCO2SiPh2(OTf) (3) (Scheme 1), the identity of this species
was ultimately confirmed by X-ray crystallographic studies
(Figure 2). Compound 3 was isolated as a white solid in 88%
yield.
The silyl triflates (C6F5)3Si(OTf) (4), Ph3Si(OTf) (5), and
Me3Si(OTf) (6) were found to react in an analogous fashion
when combined with two equivalents of TMP and exposed to
CO2 gas. Following reaction and removal of the salt by-prod-
uct, the corresponding silyl carbamates 7–9 were isolated in
yields of 86, 95, and 83%, respectively (Scheme 2). Single crys-
tals of 7 and 8 suitable for X-ray diffraction analysis were ob-
tained by slow evaporation of pentane solutions (Figures 3
and 4).
Scheme 2. Synthesis of 7–9.
Scheme 1. Synthesis of 3.
Figure 3. POV-ray depiction of the molecular structure of 7. H atoms omitted
for clarity.
The solid-state molecular structure of 3 reveals a five-coordi-
nate silicon centre with a distorted trigonal bipyramidal geom-
etry. Interestingly, the CO2 moiety is bound to silicon in a k2
fashion. The Si1ÀO1 and Si1ÀO2 bond lengths are not equal in
magnitude, with values of 1.747(3) and 1.938(3) Š, respectively.
Additionally, the Si1ÀO3 bond length of 1.823(3) Š is elongated
relative to the SiÀO bond in 1 (1.6792(2) Š). The C19ÀO2 bond
length of 1.283(5) Š is consistent with a CÀO bond order of
The solid-state molecular structures of 7 and 8 (Figures 3
and 4) display tetrahedral geometries about silicon. In contrast
to the structure of 3, the CO2 moieties are not bound in a che-
lating fashion. In fact, the Si1ÀO2 contact distances for 7 and 8
are quite long, with distances of 2.390(1) and 2.8280(1) Š, re-
spectively. This suggests only weak donation from the carbonyl
oxygen to silicon in 7, while there is no evidence for such in-
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À15.5 ppm (10, shifted due to equilibrium) and dP =38.4 ppm
(11). Repetition of this experiment with isotopically enriched
13CO2 gas resulted in the same broad singlet at dP =À15.5 ppm
as well as a doublet at dP =38.4 ppm (1JPC =115 Hz) in the
31P{1H} NMR spectrum. The 13C NMR spectrum displayed a corre-
sponding broad doublet at dC =163.14 ppm with a matching
coupling constant (1JCP =115 Hz). This one bond P-C coupling
suggests reversible insertion of CO2 into the Si–P adduct 10.
Insertion of CO2 into weak Lewis acid-base adducts is
known,[20] as has been reported for PMes3/AlX3 (X=Cl, Br) ad-
ducts.[7b]
Figure 4. POV-ray depiction of the molecular structure of 8. H atoms omitted
for clarity.
Variable-temperature NMR experiments using labeled 13CO2
demonstrate that at À208C, full conversion to the CO2 inser-
tion product is observed (Figure 5); however, due to the rever-
sible nature of this CO2 insertion, the product 11 was not isola-
ble. Nonetheless, all NMR spectroscopic data supports the for-
mulation [Et3PCO2SiMe3][OTf] (11) (Scheme 3).
In a similar manner, the stoichiometric reaction of 5 with
PEt3 yields a weak adduct, [Ph3SiPEt3][OTf] (12), evidenced by
the singlet in the 31P NMR spectrum at dP =À16.4 ppm which
is slightly downfield from free PEt3. Addition of CO2 to this
adduct results in the rapid formation of an equilibrium be-
tween the Si–P donor–acceptor adduct and a new species (13)
at dP =41.0 ppm. The 13C NMR spectrum of this mixture dis-
teraction in 8. The C19ÀO2 bond length of 1.237(2) Š and O1-
C19-O2 angle of 114.2(1)8 for 7 show slight deviations from
typical carbamate metric parameters;[17] however, those for 8
(C19-O2 1.2200 Š; O1-C19-O2 119.448) are consistent with a
C=O double bond and very close to the idealized sp2 hybrid-
ized carbon angle of 1208.[18] The degree of the Si1-O2 interac-
tion in 3, 7 and 8 appears to be strongly dependent on the
electrophilicity of the silicon centre.
A comparison of the NMR data reveals that the 29Si signal
for compound 3 (dSi =À72.0 ppm) is more upfield than those
of
7
(dSi =À49.9 ppm),
8
(dSi =À12.1 ppm), and
9 (dSi =
19.2 ppm), and the parent Lewis
acid Ph2SiOTf2 (dSi =À24.6 ppm).
Such upfield shifts in the 29Si
NMR signal have been previously
seen for five coordinate silicon[19]
and suggests the k2 binding of
CO2 is present for 3 in solution.
Furthermore, the more down-
field 13C carbonyl resonance of 3
(dC =165.02) is also consistent
with
a different CO2 binding
motif than in 7 (dC =157.67), 8
(dC =155.92), and 9 (dC =156.36).
When these silyl carbamates
3, 7–9 are placed under vacuum,
no release of CO2 is observed.
This stands in contrast to
Figure 5. Variable-temperature 31P{1H} NMR study depicting the conversion between 10 and 11 in a 13CO2 filled
NMR tube. * denotes [HPEt3]+ impurity arising from moisture in the CO2 gas.
a
related species, [TMPH]
[C9H18NCO2B(C6F5)3], reported by
Piers and co-workers,[4b] which
liberates CO2 on exposure to vacuum. The increased stability
of silyl carbamates 3, 7–9 is presumably a consequence of the
isolation from the salt by-product, which precludes the reverse
reaction.
In a similar fashion, treatment of 6 with one stoichiometric
equivalent of PEt3 resulted the formation of an adduct
[Me3SiPEt3][OTf] (10), as evidenced by a sharp singlet in the
31P{1H} NMR spectrum at dP =À11.5 ppm (Figure 5). Interesting-
ly, the 29Si spectrum of this adduct did not display Si–P cou-
pling, suggesting that the adduct dissociates reversibly on the
NMR time scale. This mixture was exposed to CO2 gas in a J-
Young NMR tube, and the 31P{1H} NMR spectrum of the reac-
tion mixture after 20 min revealed two broad singlets at dP =
Scheme 3. Synthesis of 10–15.
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plays a characteristic doublet at dC =163.49 ppm exhibiting
a PÀC coupling of 112 Hz as well as resonances for constituent
silicon and phosphorus fragments. This spectroscopic data
supports the reversible formation of an analogous CO2 inser-
tion product [Et3PCO2SiPh3][OTf] (13) (Scheme 3); similarly, at-
tempts to isolate 13 were unsuccessful due to loss of CO2
under a nitrogen atmosphere.
denced by a small doublet in in the 31P{1H} spectrum dP =
57.5 ppm (1JPC =85 Hz) and a corresponding doublet in the 13C
spectrum at dC =162.93 ppm. Allowing this mixture to stand
for a day at room temperature led to no change in composi-
tion, with free PtBu3 still remaining as the predominant species
in solution.
We anticipated that reactions of CO2 with 1 and trialkylphos-
phines would yield more stable products due to the potential
for k2 binding of CO2. Treatment of 1 with one stoichiometric
equivalent of PEt3 did not result in adduct formation. Follow-
ing addition of CO2, the 31P{1H} NMR spectrum revealed two
new resonances at dP =43.9 ppm (16, major) and dP =
41.7 ppm (17, minor). Repetition of this reaction with 13CO2 gas
In an effort to minimize adduct formation and promote CO2
capture, the more sterically hindered phosphine PtBu3 was ex-
amined as the Lewis base partner. In contrast to PEt3, PtBu3
(Tolman cone angle of 1828 vs 1328)[21] in combination with 6
shows no Lewis acid/base interaction by NMR spectroscopy.
Exposure to 13CO2 in a sealed J-Young NMR tube shows reso-
nances in the 31P and 1H NMR spectra that are significantly
broadened in comparison to that of free PtBu3; however, no
phosphorus–carbon coupling was observed. The 13C NMR spec-
trum of this mixture showed a broadened resonance attributa-
ble to free CO2 as well as an extremely broad signal in the
baseline from dC =158–166 ppm,
revealed that both new signals in the 31P NMR spectrum
1
couple to 13C nuclei with similar coupling constants of JPC
=
1
112 Hz (16) and JPC =119 Hz (17). Changing the relative ratio
of the 1 and PEt3 reagents had a significant effect on the ratio
of 16 and 17 in solution (Figure 6).
suggesting very weak CO2 bind-
ing by 6 and PtBu3.
Cooling of the reaction mix-
ture to 08C, revealed a very
broad doublet (due to 31P–13C
coupling),
visible
at
dP =
51.6 ppm inferring an equilibri-
um with free PtBu3. Further cool-
ing to À408C, resulted in the
disappearance of the free PtBu3
resonance and yields a spectrum
with a sharp doublet at dP =
50.2 ppm (1JCP =87 Hz) corre-
sponding to a CO2 captured spe-
cies. The low temperature 13C{1H}
NMR spectrum displays the ex-
pected resonances for the con-
Figure 6. 31P{1H} NMR spectra depicting the activation of 13CO2 by 1 and different stoichiometric equivalents of
PEt3. * denotes [HPEt3]+ impurity arising from moisture in the CO2 gas.
stituent silicon and phosphorus fragments, as well as a doublet
at dP =161.45 ppm with a matching PÀC coupling of 87 Hz.
This spectroscopic data supports the proposed formulation
[tBu3PCO2SiMe3][OTf] (14) (Scheme 3).
With 0.5 stoichiometric equivalents of PEt3, 16 is the pre-
dominant species in solution; however, with 4.0 equivalents of
PEt3, the major species, 17, appears to be in equilibrium with
free phosphine giving rise to a broadened 31P{1H} spectrum. In-
creasing the equivalents of phosphine in the reaction mixture
presumably shifts the equilibrium towards species 17.
It is interesting and perhaps counterintuitive that 10 is only
observable in solution at low temperature. By contrast, CO2
capture by 6 and PEt3 readily occurs at room temperature. As
PtBu3 is actually a slightly stronger donor than PEt3 (Tolman
electronic parameters: PEt3 2061.7 cmÀ1, PtBu3 2056.1 cmÀ1)[21]
this difference in reactivity must be attributable to steric ef-
fects. It is proposed that the weak and reversible adduct for-
mation between 6 and PEt3 allows for pre-association of the
Lewis acid and base components and facilitates CO2 activation.
At room temperature, pre-organization of more hindered
Lewis bases, such as PtBu3, with tetrahedral Lewis acids may
be less favourable due to increased steric congestion.
The 13C NMR spectra of these reaction mixtures reveal that
the carbonyl carbon resonances of 16 and 17 have nearly iden-
tical chemical shifts of dC =162.83 and 162.65 ppm. For each
reaction, the 19F NMR spectrum displays only one triflate signal
at room temperature. As a greater amount of PEt3 is utilized,
this 19F NMR resonance shifts upfield. At 0.5 equivalents of
PEt3, the triflate signal appears at dF =À76.57 ppm, whereas
with 4.0 equivalents the resonance appears at dF =
À78.78 ppm (cf. dF =À76.10 ppm for 1). A more upfield reso-
nance is consistent with a greater degree of dissociation of the
triflate anion. These chemical shifts imply the dissociation of
a single triflate in 16 and both triflate anions in 17. Thus, it is
proposed that 16 and 17 correspond to stepwise CO2 activa-
tion products in which one or two molecules of CO2 are
bound, [Et3P(CO2)SiPh2(OTf)][OTf] (16) and [(Et3PCO2)2SiPh2]
The analogous reaction employing 5 similarly displayed
weak CO2 binding at room temperature. Upon addition of
13CO2 gas to a 1:1 stoichiometric mixture of 5 and PtBu3, NMR
spectroscopy revealed minor conversion (~10%) to a new CO2
captured species [tBu3PCO2SiPh3][OTf] (15) (Scheme 3) as evi-
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[OTf]2 (17), respectively (Scheme 3). This is further supported
by the low temperature NMR spectrum of the reaction be-
tween 1, excess PEt3, and CO2. At low temperatures, the P–Et
1
resonances of 17 and free PEt3 split in the H NMR spectrum.
Although still broad, integration of the CH2-PCO2 resonance rel-
ative to the aromatic signals reveals a ratio of two PEt3 moiet-
ies per equivalent of Lewis acid.
Examples of double activation of small molecules by FLP sys-
tems are relatively rare. In 2011, we reported that the bis-
borane (C6F5)2B(C6F4)B(C6F5)2 could activate two molecules of
nitrous oxide using two equivalents of PtBu3 to afford the bis-
zwitterion tBu3P(N2O)B(C6F5)2C6F4(C6F5)2B(ON2)PtBu3.[22] For this
system, it is proposed that N2O activation occurs in a stepwise
fashion. In 2012, our group also reported the double activation
of CO2 using the diamidophosphorane (C6H4(NMe))2PPh.[8] This
process occurs by the insertion of two molecules of CO2 into
the PÀN bonds to yield the bis(carbamato)phosphorane
(C6H4NMe(CO2))2PPh.[8] In contrast to the bis-borane system,
which contains two different Lewis acidic centres, the diamido-
phosphorane uses a single phosphorus Lewis acidic centre for
the double activation process.
Scheme 4. Synthesis of 16–19.
PEt3 or PtBu3 as the Lewis base partner, Ph2Si(OTf)2 has been
proposed to activate either one or two molecules of CO2 de-
pending on the stoichiometric equivalents of phosphine used
as well as the temperature. Reactions employing PtBu3 tended
to yield less CO2 incorporation at equilibrium than their PEt3
counterparts. The increased steric hindrance of PtBu3 is pre-
sumably less conducive to the prearrangement of the Lewis
acidic and basic components when used with tetrahedral
Lewis acids.
Treatment of 1 with one stoichiometric equivalent of PtBu3
did not result in adduct formation. Addition of 13CO2 to this
mixture resulted in a 31P{1H} NMR spectrum that displayed
a broadened PtBu3 resonance and a broad doublet (dP =57.5,
1JPC =80 Hz) corresponding to the CO2 captured product
[tBu3P(CO2)SiPh2(OTf)][OTf2] (18) (Scheme 4). Attempts to pro-
mote the generation of a bis-CO2 activation product analogous
to 17 by addition of excess PtBu3 only accelerated degradation
of 18. However, upon cooling to À308C, a 1:2 stoichiometric
mixture of 1 and PtBu3 pressurized with 13CO2 showed con-
sumption of PtBu3 and 18 and the generation of a species pro-
posed to be [(tBu3P(CO2))2SiPh2][OTf2]2 (19) (Scheme 4) (see
Supporting Information). Interestingly at room temperature,
there is no evidence for the formation of a bis-CO2 activation
product. Over time, decomposition of 18 occurs at room tem-
perature. The major decomposition species can be identified
by a doublet in the 13C NMR spectrum at dC =181.61 ppm
(1JPC =45 Hz) and a corresponding signal in the 31P NMR spec-
trum at dP =49.7 ppm. Resonances arising from isobutylene
These findings illustrate that CO2 activation can be achieved
with electronically saturated Lewis acids. We are continuing to
investigate the application of four-coordinate silicon Lewis
acids in FLP chemistry and their use in the activation of CO2.
Experimental Section
General methods: All preparations and manipulations were carried
out under an anhydrous N2 atmosphere using standard glovebox
and Schlenk-line techniques. Glassware was oven-dried and cooled
under vacuum prior to use. Unless specified, all reagents were
used as received without further purifications. 2,2,6,6-Tetramethyl-
piperidine was distilled from CaH2 prior to use. (C6F5)3Si(OTf) (4)
was prepared by literature methods.[23] Me3Si(OTf) (6) was pur-
chased from Strem Chemicals. Solvents (CH2Cl2 and pentane) were
dried using an Innovative Technologies solvent purification system,
degassed, and stored over molecular sieves. CD2Cl2 was dried over
CaH2, degassed, and stored over activated molecular sieves. NMR
spectra were obtained on a Bruker Avance III-400 MHz, Varian
400 MHz, Agilent DD2 500 MHz, Agilent DD2 600 MHz, or Varian
Mercury 300 MHz spectrometer. All NMR experiments were con-
1
were also observed in the H NMR spectrum and the product
was presumed to be the phosphinoformate species,
tBu2P(CO2)SiPh2(OTf). This could be formed by the deprotona-
tion of a tert-butyl substituent of 18 and loss of isobutylene.
ducted at a temperature of 258C unless otherwise noted. H, 11B,
1
Conclusion
13C, 19F, 29Si, and 31P NMR spectra were referenced using (residual)
solvent resonances relative to SiMe4 (1H and 13C) or relative to an
external standard (11B: (Et2O)BF3, 19F: CFCl3, 29Si: SiMe4, 31P: 85%
H3PO4). Chemical shifts are reported in ppm and coupling con-
stants as scalar values in Hz. Combustion analyses were performed
by ANALEST at the University of Toronto with a PerkinElmer CHN
Analyzer.
Silyl triflates and tetramethylpiperidine are shown to react with
CO2 to yield silyl carbamates in the form of C9H18N(CO2)SiR3
and the ammonium triflate salt [TMPH][OTf]. In these carba-
mate products, the CO2 moiety was found to bind to silicon in
either a k1 or k2 fashion depending on the electrophilicity of
the silicon centre. Silyl triflates (R3SiOTf) are also shown to be
active in the complexation of CO2 in combination with PEt3 or
PtBu3 to yield species of the general form [R’3P(CO2)SiR3][OTf].
These species are unstable with respect to CO2 liberation and
thus are only stable in a CO2 filled vessel. When employing
Ph2Si(OTf)2 (1):
A solution of Ph2SiCl2 (534 mg, 2.11 mmol,
1.0 equiv) in CH2Cl2 (2 mL) was added to a suspension of AgOTf
(1.084 g, 4.22 mmol, 2.0 equiv) in CH2Cl2 (3 mL). The resulting mix-
ture was left stirring at room temperature in the dark for 24 h The
AgCl precipitate was removed by filtration and the solvent was re-
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moved in vacuo. The resulting solid was washed with minimal pen-
tane (1 mL) to give a white powder (930 mg, 92%). Crystals suita-
ble for X-ray diffraction were grown from a concentrated CH2Cl2 so-
lution at room temperature. The product can also be recrystallized
C9H18N(CO2)Si(C6F5)3
(7),
C9H18N(CO2)SiPh3
(8)
and
C9H18N(CO2)SiMe3 (9): These compounds were prepared in a similar
fashion to 3 and thus only one preparation is detailed. 7: Scale: 4
(20 mg, 0.0295 mmol, 1.0 equiv), 2,2,6,6-tetramethylpiperidine
(8 mg, 0.0590 mmol, 2.0 equiv). The product was obtained as
a white solid (20 mg, 95%). Single crystals suitable for X-ray diffrac-
tion were grown by slow evaporation of a pentane solution.
1H NMR (500.0 MHz, CD2Cl2): d=1.41 (s, 12H, CH3), 1.61 (m, 2H,
1
from pentane in the freezer at À358C. H NMR (400.0 MHz, CD2Cl2):
3
3
3
d=7.61 (dd, 4H, JHH =8 Hz, JHH =8 Hz, m-C6H5), 7.76 (tt, 2H, JHH
=
4
3
4
8 Hz, JHH =1 Hz, p-C6H5), 7.83 ppm (dd, 4H, JHH =8 Hz, JHH =1 Hz,
o-C6H5); 13C{1H} NMR (75.4 MHz, CD2Cl2): d=118.60 (q, JCF =318 Hz,
1
3
CF3), 122.73 (s, i-C6H5), 129.47 (s, m-C6H5), 134.75(s, p-C6H5),
135.60 ppm (s, o-C6H5); 19F{1H} NMR (376.4 MHz, CD2Cl2): d=
À76.10 ppm (s, CF3); 29Si NMR (79.5 MHz, CD2Cl2): d=À24.6 ppm
(s); elemental analysis calcd for (%): C14H10F6O6S2Si: C 35.00, H 2.10;
found: C 34.57, H 2.39.
CH2), 1.68 ppm (t, 4H, JHH =6 Hz, CH2); 13C{1H} NMR (125.73 MHz,
CD2Cl2): d=16.10 (s, CH2), 29.37 (s, CH3), 41.36 (s, CH2), 58.89 (s, C-
Me2), 106.99 (t, 2JCF =28 Hz, i-C6F5), 137.81 (dm, 1JCF =253 Hz, m-
C6F5), 142.78 (dm, 1JCF =257 Hz, p-C6F5), 149.19 (dm, 1JCF =245 Hz,
o-C6F5), 157.67 ppm (s, NCO2); 19F{1H} NMR (376.4 MHz, CD2Cl2): d=
3
3
À128.35 (d, 6F, JFF =18.1 Hz, o-C6F5), À149.22 (t, 3F, JFF =19.9 Hz,
p-C6F5), À161.16 ppm (m, 6F, m-C6F5); 29Si NMR (79.5 MHz, CD2Cl2):
d=À49.9 ppm (s); elemental analysis calcd for (%) C28H18F15NO2Si:
C 47.13, H 2.54, N 1.96; found: C 46.89, H 2.26, N 2.00.
[TMPH][OTf] (2): The precipitate from reactions yielding 3, 7–9
was isolated by filtration of the reaction mixtures. The white solid
was washed with CH2Cl2 and pentane (5 mL) and then dried in
vacuo. NMR spectroscopy and X-ray diffraction identified this spe-
cies as [TMPH][OTf]. Single crystals suitable for X-ray diffraction
8: Scale: 5 (30 mg, 0.0734 mmol, 1.0 equiv), 2,2,6,6-tetramethylpi-
peridine (21 mg, 0.147 mmol, 2.0 equiv). The product was obtained
as a white solid (27 mg, 83%). Single crystals suitable for X-ray dif-
fraction were grown by slow evaporation of a pentane solution.
1H NMR (400.0 MHz, CD2Cl2): d=1.47 (s, 12H, C-CH3), 1.64 (m, 2H,
1
were grown at room temperature from CH2Cl2. H NMR (400.0 MHz,
CD3CN): d=1.41 (s, 12H, CH3), 1.65 (m, 4H, CH2), 1.74 (m, 2H, CH2),
6.53 ppm (brt, 2H, 1JHN =12 Hz, NH); 13C{1H} NMR (75.4 MHz,
CD3CN): d=16.71 (s, CH2), 27.39 (s, CH3), 35.36 (s, CH2), 59.04 (s, C-
Me2), 121.78 ppm (q, 1JCF =320 Hz, CF3); 19F{1H} NMR (376.4 MHz,
CD3CN): d=À79.39 ppm (s, CF3).
3
3
3
CH2), 1.71 (t, 4H, JHH =6 Hz, CH2), 7.39 (dd, 6H, JHH =7 Hz, JHH
=
7 Hz, m-C6H5), 7.45 (t, 3H, 3JHH =7 Hz, p-C6H5), 7.66 ppm (d, 6H,
3JHH =7 Hz, o-C6H5); 13C{1H} NMR (125.73 MHz, CD2Cl2): d=15.95 (s,
CH2), 29.94 (s, CH3), 40.40 (s, CH2), 57.06 (s, C-Me2), 128.13 (s, m-
C6H5), 130.39 (s, p-C6H5), 134.23 (s, i-C6H5), 136.04 (s, o-C6H5),
155.92 ppm (s, NCO2); 29Si NMR (79.5 MHz, CD2Cl2): d=À12.1 ppm
(s); elemental analysis calcd for (%) C13H27NO2Si: C 75.80, H 7.50, N
3.16; found: C 76.49, H 7.50, N 2.97.
C9H18N(CO2)SiPh2(OTf) (3): A J-Young NMR tube was charged with
1 (34 mg, 0.0708 mmol, 1.0 equiv) and 2,2,6,6-tetramethylpiperi-
dine (20 mg, 0.142 mmol, 2.0 equiv) in CD2Cl2 (1 mL). The J-Young
was degassed and filled with CO2. Following this, a white solid
started to precipitate from solution. The progress of the reaction
was monitored by 1H NMR spectroscopy; upon reaction comple-
tion, the contents of the J-Young were transferred to a vial and
pentane was added (3 mL). The mixture was filtered to remove the
precipitate 2. Volatiles were removed from the filtrate in vacuo af-
fording 3. The product is a white solid which can be recrystallized
from pentane or CH2Cl2/pentane solutions at À308C (32 mg, 88%).
Single crystals suitable for X-ray diffraction were grown by slow
evaporation of a pentane solution. 1H NMR (400.0 MHz, CD2Cl2): d=
1.58 (s, 12H, CH3), 1.66 (m, 2H, CH2), 1.76 (m, 4H, CH2), 7.45 (ddm,
9: Scale: 6 (30 mg, 0.135 mmol, 1.0 equiv), 2,2,6,6-tetramethylpiper-
idine (38 mg, 0.270 mmol, 2.0 equiv). The product was obtained as
1
a colourless oil (30 mg, 86%). H NMR (500.0 MHz, CD2Cl2): d=0.26
(s, 9H, Si-CH3), 1.39 (s, 12H, C-CH3), 1.58 (m, 2H, CH2), 1.64 ppm (t,
3
4H, JHH =6 Hz, CH2); 13C{1H} NMR (125.73 MHz, CD2Cl2): d=0.24 (s,
Si-CH3), 16.25 (s, CH2), 29.94 (s, C-CH3), 41.11 (s, CH2), 56.53 (s, C-
Me2), 156.36 ppm (s, NCO2); 29Si NMR (79.5 MHz, CD2Cl2): d=
19.2 ppm (s); elemental analysis calcd for (%) C13H27NO2Si: C 60.65,
H 10.57, N 5.44; found: C 60.05, H 11.01, N 6.13.
3
3
3
4
4H, JHH =7 Hz, JHH =7 Hz, m-C6H5), 7.51 (tt, 2H, JHH =8 Hz, JHH
=
=
2 Hz, p-C6H5), 7.84 ppm (ddd, 4H, 3JHH =7 Hz, 4JHH =1 Hz, JHH
1 Hz, o-C6H5); 13C{1H} NMR (100.6 MHz, CD2Cl2): d=16.14 (s, CH2),
4
[Me3SiPEt3][OTf] (10) and [Ph3SiPEt3][OTf] (12): These compounds
were prepared in a similar fashion and thus only one is detailed.
1
29.16 (s, CH3), 41.52 (s, CH2), 61.22 (s, C-Me2), 119.29 (q, JCF
=
10: 6 (30 mg, 0.135 mmol, 1.0 equiv) and PEt3 (10 mg, 0.135 mmol,
318 Hz, CF3), 128.49 (s, m-C6H5), 131.42 (s, p-C6H5), 132.84 (s, i-C6H5),
135.53 (s, o-C6H5), 165.02 ppm (s, NCO2); 19F{1H} NMR (376.4 MHz,
CD2Cl2): d=À77.77 (s, CF3); 29Si NMR (79.5 MHz, CD2Cl2): dSi =
À72.0 ppm (s); elemental analysis calcd for (%) C23H28F3NO5SSi: C
53.58, H 5.47, N 2.72; found: C 53.88, H 5.69, N 3.23.
1.0 equiv) were combined in CD2Cl2 and the resulting adducts
were examined by multinuclear NMR spectroscopy. 1H NMR
3
(400.0 MHz, CD2Cl2): d=0.53 (s, 9H, Si-CH3), 1.16 (dt, 9H, JHP
=
16 Hz, P-CH2CH3), 1.83 ppm (m, 6H, P-CH2); 13C{1H} NMR
(100.6 MHz, CD2Cl2): d=À0.53 (s, Si-CH3), 8.26 (s, P-CH2CH3), 14.81
(br, P-CH2), 119.73 ppm (q, 1JCF =318 Hz, CF3); 19F{1H} NMR
(376.4 MHz, CD2Cl2): d=À78.09 ppm (s, CF3); 29Si NMR (79.5 MHz,
CD2Cl2): d=30.9 ppm (s); 31P{1H} NMR (161.9 MHz, CD2Cl2): d=
À11.5 ppm (s);
Ph3Si(OTf) (5): A solution of Ph3SiCl (460 mg, 1.56 mmol, 1.0 equiv)
in CH2Cl2 (2 mL) was added to a suspension of AgOTf (400 mg,
1.56 mmol, 1.0 equiv) in CH2Cl2 (3 mL). The resulting mixture was
stirred in the dark for 12 h. The AgCl precipitate was removed by
filtration and the solvent was removed in vacuo, affording a white
solid (495 mg, 78%). Single crystals suitable for X-ray diffraction
were grown from a concentrated pentane solution at room tem-
12: Scale:
5 (22 mg, 0.0539 mmol, 1.0 equiv), PEt3 (4 mg,
0.0539 mmol, 1.0 equiv); 1H NMR (400.0 MHz, CD2Cl2): d=1.04 (dt,
9H, 3JHP =15 Hz, 2JHH =8 Hz, CH3), 1.53 (qd, 6H, 2JHH =8 Hz, JHP
=
2
1
3
perature. H NMR (400.0 MHz, CD2Cl2): d=7.53 (dd, 6H, JHH =8 Hz,
3JHH =8 Hz, m-C6H5), 7.63 (t, 3H, 3JHH =8 Hz, p-C6H5), 7.75 ppm (d,
2 Hz, P-CH2), 7.52 (ddm, 6H, 3JHH =7 Hz, 3JHH =7 Hz, m-C6H5), 7.62
3
3
(tm, 3H, JHH =7 Hz, p-C6H5), 7.69 ppm (dm, 6H, JHH =7 Hz, o-C6H5);
13C{1H} NMR (100.6 MHz, CD2Cl2): d=9.01 (d, 1JCP =8 Hz, P-CH2),
17.41 (s, P-CH2CH3), 119.40 (q, 1JCF =318 Hz, CF3), 128.24 (brs, i-
C6H5), 129.13 (s, m-C6H5), 132.58 (s, p-C6H5), 136.13 ppm (s, o-C6H5);
19F{1H} NMR (376.4 MHz, CD2Cl2): d=À77.32 ppm (s, CF3); 29Si{1H}
NMR (HMBC) (99.3 MHz, CD2Cl2): d=À1.0 ppm (s); 31P{1H} NMR
(161.9 MHz, CD2Cl2): dP =À16.4 ppm (s).
6H, JHH =8 Hz, o-C6H5); 13C{1H} NMR (100.6 MHz, CD2Cl2): d=118.86
3
(q, 1JCF =318 Hz, CF3), 128.94 (s, m-C6H5), 129.11 (s, i-C6H5), 132.46 (s,
p-C6H5), 136.03 ppm (s, o-C6H5); 19F{1H} NMR (376.4 MHz, CD2Cl2):
d=À76.87 ppm (s, CF3); 29Si{1H} NMR (79.5 MHz, CD2Cl2): d=
1.7 ppm (s); elemental analysis calcd for (%) C19H15F3O3SSi: C 55.87,
H 3.70; found: C 55.84, H 3.92.
Chem. Eur. J. 2015, 21, 13027 – 13034
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Full Paper
[Et3PCO2SiMe3][OTf]
(11),
[Et3PCO2SiPh3][OTf]
(13),
(79.5 MHz, CD2Cl2): d=1.6 ppm (s); 31P{1H} NMR (161.9 MHz,
CD2Cl2): d=57.5 (brs, 15), 62.5 ppm (brs, free PtBu3).
[tBu3PCO2SiMe3][OTf] (14), [tBu3PCO2SiPh3][OTf] (15): These com-
pounds were prepared in a similar fashion and thus a general pro-
cedure is detailed. A J-Young NMR tube was charged with the ap-
propriate silyl triflate (1.0 equiv) and PEt3 (1.0 equiv) in CD2Cl2
(1 mL); The reaction mixture was then examined for adduct forma-
tion by multinuclear NMR spectroscopy. Following this, the J-
Young NMR tube was degassed and CO2 gas was added. In each
case, NMR spectra obtained after one hour revealed the presence
a CO2 sequestered species in equilibrium with free starting materi-
als or an adduct. The Si/P CO2 captured species were not isolable
and thus were characterized in a CO2-filled J-Young NMR tube.
[Et3P(CO2)SiPh2(OTf)][OTf] (16) and [(Et3PCO2)2SiPh2][OTf]2 (17): A
J-Young NMR tube was charged with 1 (1.0 equiv) and PEt3 (0.5,
1.0, 2.0, or 4.0 equiv) in CD2Cl2 (1 mL). No adduct formation was
observed between Ph2Si(OTf)2 and PEt3 by 31P NMR spectroscopy.
The J-Young NMR tubes were degassed and CO2 gas was added.
The relative amounts of 16 and 17 observed in the reaction mix-
tures are strongly dependent on the number of equivalents of PEt3
used. NMR spectroscopic data is provided for the reactions using
0.5 equiv and 4.0 equiv PEt3.
Reaction mixture with 0.5 equiv PEt3: Scale:
1
(29 mg,
11: Scale:
6 (30 mg, 0.135 mmol, 1.0 equiv), PEt3 (10 mg,
0.0604 mmol, 1.0 equiv), PEt3 (2 mg, 0.0302 mmol, 0.5 equiv);
1H NMR (400.0 MHz, CD2Cl2): d=1.35 (m, 16 PCH2CH3), 2.69 (brm,
16 P-CH2), 7.61 (brdd, 3JHH =8 Hz, 3JHH =8 Hz, m-C6H5), 7.76 (tt,
0.135 mmol, 1.0 equiv); (Reaction mixture with 10): 1H NMR
(400.0 MHz, CD2Cl2): d=0.48 (s, Si-CH3), 1.16–1.42 (br, 11 P-Et),
1.54–1.80 (br, 10 P-Et), 2.25–2.40 (br, 10 P-Et), 2.40–2.90 ppm (br, 11
P-Et); 13C{1H} NMR (100.6 MHz, CD2Cl2): d=À0.10 (s, Si-CH3), 6.36
(br, P-CH2CH3), 12.45 (br, P-CH2), 120.06 (q, 1JCF =319 Hz, CF3),
4
3JHH =8 Hz, JHH =2 Hz, p-C6H5), 7.83 ppm (dm, 3JHH =8 Hz, o-C6H5);
13C{1H} NMR (100.6 MHz, CD2Cl2): d=6.15 (d, 2JPC =6 Hz, 16 P-
CH2CH3), 12.66 (d, 1JPC =42 Hz, 16 P-CH2), 118.97 (q, 1JCF =318 Hz,
CF3), 122.84 (s, i-C6H5), 125.30 (s, free CO2), 129.52 (s, m-C6H5),
134.79 (s, p-C6H5), 135.65 (s, o-C6H5), 162.83 ppm (d, 1JPC =112 Hz,
16 P-CO2); 19F{1H} NMR (376.4 MHz, CD2Cl2): d=À76.57 ppm (s,
CF3); 29Si NMR (79.5 MHz, CD2Cl2): d=À24.6 ppm (s, 16); 31P{1H}
NMR (161.9 MHz, CD2Cl2): d=41.7 (br, trace, 17), 43.9 ppm (s, 16).
125.28 (br, free CO2), 163.14 ppm (brd, JCP =115 Hz, P-CO2); 19F{1H}
1
NMR (376.4 MHz, CD2Cl2): d=À78.39 ppm (s, CF3); 29Si{1H} NMR
(HMBC) (99.3 MHz, CD2Cl2): d=40.3 ppm (br); 31P{1H} NMR
(161.9 MHz, CD2Cl2): d=À13.9 (br, 10), 38.4 ppm (br, 11).
13: Scale:
5 (22 mg, 0.0539 mmol, 1.0 equiv), PEt3 (4 mg,
0.0539 mmol, 1.0 equiv); (Reaction mixture with 12): 1H NMR
Reaction mixture with 4.0 equiv PEt3: Scale: 1 (29 mg, 0.603 mmol,
3
(400.0 MHz, CD2Cl2): d=1.04 (brm, 12 P-CH2CH3), 1.28 (dt, JHP
=
1
1.0 equiv), PEt3 (18 mg, 0.241 mmol, 4.0 equiv); H NMR (400.0 MHz,
20 Hz, 3JHH =8 Hz, 13 P-CH2CH3), 1.48 (brm, 12 P-CH2), 2.62 (dq,
2JHP =14 Hz, 3JHH =8 Hz, 13 P-CH2), 7.51 (br, m-C6H5), 7.60 (br, p-
C6H5), 7.68 ppm (br, o-C6H5); 13C{1H} NMR (100.6 MHz, CD2Cl2): d=
CD2Cl2): d=0.90–1.50 (br, overlapping PEt3 and 17 P-Et), 2.40–2.80
3
3
(br, 17 P-CH2CH3), 7.59 (dd, JHH =7 Hz, JHH =7 Hz, m-C6H5), 7.69 (t,
3JHH =7 Hz, p-C6H5), 7.83 ppm (dd, 3JHH =7 Hz, 4JHH =1 Hz, o-C6H5);
13C{1H} NMR (100.6 MHz, CD2Cl2): d=6.00 (br, 17 P-CH2CH3), 9.30
(br, PEt3 P-CH2CH3), 12.24 (br, 17 P-CH2), 18.48 (br, PEt3 P-CH2),
2
6.24 (d, JPC =6 Hz, 13 P-CH2CH3), 9.05 (br, 12 P-CH2CH3), 12.62 (d,
1JPC =42 Hz, 13 P-CH2), 17.58 (br, 12 P-CH2), 118.90 (q, JCF =318 Hz,
1
CF3), 125.27 (s, free CO2), 128.86 (s, 12 i-C6H5), 128.95 (s, 13 m-C6H5),
129.00 (s, 12 m-C6H5), 129.15 (s, 13 i-C6H5), 132.27 (s, 12 p-C6H5),
132.46 (s, 13 p-C6H5), 136.02 (s, 13 o-C6H5), 163.49 ppm (d, JCP
112 Hz, P-CO2); 19F{1H} NMR (376.4 MHz, CD2Cl2): d=À78.20 ppm (s,
CF3); 29Si{1H} NMR (HMBC) (99.3 MHz, CD2Cl2): d=À0.5 (s, 12),
0.5 ppm (s, 13); 31P{1H} NMR (161.9 MHz, CD2Cl2): d=À15.2 (s, 12),
41.0 ppm (s, 13).
1
121.14 (q, JCF =320 Hz, CF3), 124.56 (s, i-C6H5), 125.25 (br, free CO2),
129.33 (s, m-C6H5), 133.92 (s, p-C6H5), 135.66 (s, o-C6H5), 162.65 ppm
(brd, 1JPC =119 Hz, PCO2); 19F{1H} NMR (376.4 MHz, CD2Cl2): d=
À78.78 ppm (s, CF3); 29Si NMR (79.5 MHz, CD2Cl2): dSi =À21.0 ppm
(s, 17); 31P{1H} NMR (161.9 MHz, CD2Cl2): d=À18.6 (br, PEt3), 41.7
(br, 17), 43.9 ppm (br, trace, 16).
1
=
[tBu3P(CO2)SiPh2(OTf)][OTf2] (18) and [(tBu3PCO2)2SiPh2][OTf]2
(19): A J-Young NMR tube was charged with 1 (1.0 equiv) and
PtBu3 (1.0 or 2.0 equiv) in CD2Cl2 (1 mL). No adduct formation was
observed between 1 and PtBu3 by 31P NMR spectroscopy. The J-
Young NMR tubes were degassed and CO2 gas was added. Partial
conversion to 18 was observed at room temperature, while forma-
tion of 19 was only observable at low temperature (À308C).
14: Scale:
6 (22 mg, 0.0990 mmol, 1.0 equiv), PtBu3 (20 mg,
0.0990 mmol, 1.0 equiv); Reaction mixture (258C): 1H NMR
(400.0 MHz, 258C, CD2Cl2): d=0.49 (s, 9H, Si-CH3), 1.19–1.50 ppm
(br, 27H, PC(CH3)3); 13C{1H} NMR (100.6 MHz, 258C, CD2Cl2): d=0.32
(s, Si-CH3), 32.36 (br, PC(CH3)3), 34.70 (br, P-C), 119.54 (q, JCF
1
=
319 Hz, CF3), 161.97 ppm (br, P-CO2); 19F{1H} NMR (376.4 MHz,
CD2Cl2): d=À77.86 ppm (s, CF3); 29Si{1H} NMR (HMBC) (99.3 MHz,
CD2Cl2): d=43.7 ppm(s); 31P{1H} NMR (161.9 MHz, 258C, CD2Cl2): d=
62.5 (brs); (À408C): 1H NMR (500.0 MHz, À408C, CD2Cl2): d=0.44
(s, 9H, Si-CH3), 1.65 ppm (d, 27H, 3JHP =15 Hz, PC(CH3)3); 13C{1H}
NMR (100.6 MHz, À408C, CD2Cl2): d=À0.67 (s, Si-CH3), 29.86 (s,
18: Reaction mixture with 1.0 equiv PtBu3: Scale:
1 (30 mg,
0.0624 mmol, 1.0 equiv), PtBu3 (13 mg, 0.0624 mmol, 1.0 equiv);
(258C): 1H NMR (400.0 MHz, CD2Cl2): d=1.30 (br, free PtBu3), 1.70
3
3
(br, 18 P-C(CH3)3), 7.62 (dd/br, JHH =8 Hz, JHH =8 Hz, m-C6H5), 7.76
(brt, 3JHH =8 Hz, p-C6H5), 7.81 ppm (dd, 3JHH =8 Hz, 4JHH =1 Hz, o-
C6H5); 13C{1H} NMR (125.7 MHz, CD2Cl2): d=30.58 (br), 32.51 (br),
34.63 (brd, 1JCP =30 Hz, P-C), 42.76 (brd, 1JCP =12 Hz, P-C), 119.41
(q, 1JCF =319 Hz, CF3), 122.80 (brs, i-C6H5), 122.89 (brs, i-C6H5),
125.29 (brs, free CO2), 129.51 (brs, m-C6H5), 129.75 (brs, m-C6H5),
134.80 (s, overlapping p-C6H5), 135.58 (brs, overlapping o-C6H5),
162.96 ppm (brd, 1JCP =80 Hz, PCO2); 19F{1H} NMR (376.4 MHz,
CD2Cl2): d=À77.32 ppm (s, CF3); 29Si{1H} NMR (HMBC) (99.3 MHz,
CD2Cl2): d=À24.6 (s, Ph2Si(OTf)2), À20.7 ppm (s, 18); 31P{1H} NMR
(161.9 MHz, CD2Cl2): d=57.5 (brs, 18), 62.5 ppm (brs, free PtBu3).
1
1
PC(CH3)3), 40.99 (d, JCP =18 Hz, P-C), 120.49 (q, JCF =321 Hz, CF3),
161.45 ppm (d, 1JCP =87 Hz, P-CO2); 19F{1H} NMR (376.4 MHz,
CD2Cl2): dF =À79.07 ppm (s, CF3); 29Si{1H} NMR (HMBC) (99.3 MHz,
CD2Cl2): d=38.2 ppm (s); 31P{1H} NMR (202.4 MHz, À408C, CD2Cl2):
1
d=50.23 ppm (d, JCP =87 Hz).
15: Scale:
5 (30 mg, 0.0734 mmol, 1.0 equiv), PtBu3 (15 mg,
0.0734 mmol, 1.0 equiv); Reaction mixture: 1H NMR (400.0 MHz,
3
3
CD2Cl2): d=1.31 (d, JHP =10 Hz, free PtBu3), 1.66 (d, JHP =15 Hz, 15
P-C(CH3)3), 7.51 (dd/br, 3JHH =7 Hz, 3JHH =7 Hz, m-C6H5), 7.61 (brt,
3JHH =7 Hz, p-C6H5), 7.71 ppm (brd, JHH =7 Hz, o-C6H5); 13C{1H} NMR
3
(100.6 MHz, CD2Cl2): d=30.69 (br, P-C), 32.61 (d, 3JCP =13 Hz, P-
19: Reaction mixture with 2.0 equiv PtBu3: Scale:
1 (29 mg,
1
C(CH3)3), 119.43 (q, JCF =321 Hz, CF3), 125.32 (s, free CO2), 128.91 (s,
0.0603 mmol, 1.0 equiv), PtBu3 (24 mg, 0.121 mmol, 2.0 equiv);
1
3
m-C6H5), 129.09 (s, i-C6H5), 132.44 (s, p-C6H5), 136.02 (s, o-C6H5),
162.93 ppm (brd, 1JPC =85 Hz, 15 P-CO2); 19F{1H} NMR (376.4 MHz,
258C, CD2Cl2): d=À77.42 ppm (brs, CF3); 29Si NMR (HMBC)
(À308C): H NMR (500.0 MHz, CD2Cl2): d=1.64 (d, 54H, JHP =16 Hz,
3
3
P-C(CH3)3), 7.62 (dd, 4H, JHH =8 Hz, JHP =8 Hz, m-C6H5), 7.76 ppm
(m, 6H, overlapping p-C6H5 o-C6H5); 13C{1H} NMR (125.7 MHz,
Chem. Eur. J. 2015, 21, 13027 – 13034
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13033
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
CD2Cl2): d=29.91 (s, P-C(CH3)3), 45.04 (d, 1JCP =16 Hz), 120.57 (q,
1JCF =320 Hz, CF3), 122.08 (s, i-C6H5), 129.55 (s, m-C6H5), 134.49 (s, p-
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1
C6H5), 135.09 (s, o-C6H5), 163.26 ppm (d, JCP =80 Hz, PCO2); 19F{1H}
NMR (470.4 MHz, CD2Cl2): d=À78.9 ppm (s, CF3); 31P{1H} NMR
1
(202.4 MHz, CD2Cl2): d=55.6 (d, JPC =81 Hz, 18, trace), 56.1 ppm (d,
1JPC =80 Hz, 19); 29Si{1H} NMR (HMBC) (99.3 MHz, CD2Cl2): d=
À17.7 ppm(s).
X-ray diffraction studies: Single crystals were coated with Para-
tone-N oil and mounted under a cold nitrogen stream. Data sets
were collected on a Bruker Kappa Apex II CCD diffractometer using
a graphite monochromater with MoKa radiation (l=0.71073 Š).
Data reduction was performed using the Bruker SMART software
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SADABS. The structures were solved by direct methods using XS
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and disordered. The TMP moiety is disordered over two positions
(50:50). The disordered atoms were refined isotropically, while the
remaining non-hydrogen atoms were refined anisotropically.
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Acknowledgements
D.W.S. gratefully acknowledges the financial support of the
NSERC of Canada and is thankful for the award of a Canada Re-
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CGS-M scholarship.
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Published online on July 28, 2015
Chem. Eur. J. 2015, 21, 13027 – 13034
www.chemeurj.org
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