Hydrosilylation of ketones, imines and nitriles catalysed by electrophilic phosphonium cations: Functional group selectivity and mechanistic considerations

Article abstract of DOI:10.1002/chem.201406356

The electrophilic phosphonium salt, [(C₆F₅)₃PF][B(C₆F₅)₄], catalyses the efficient hydrosilylation of ketones, imines and nitriles at room temperature. In the presence of this catalyst, adding one equivalent of hydrosilane to a nitrile yields a silylimine product, whereas adding a second equivalent produces the corresponding disilylamine. [(C₆F₅)₃PCl][B(C₆F₅)₄] and [(C₆F₅)₃PBr][B(C₆F₅)₄] are also synthesised and tested as catalysts. Competition experiments demonstrate that the reaction exhibits selectivity for the following functional groups in order of preference: ketone>nitrile>imine>olefin. Computational studies reveal the reaction mechanism to involve initial activation of the Si-H bond by its interaction with the phosphonium centre. The activated complex then acts cooperatively on the unsaturated substrate. Proceed with cation: The electrophilic phosphonium salt, [(C₆F₅)₃PF][B(C₆F₅)₄], catalyses the efficient hydrosilylation of ketones, imines and nitriles at room temperature. In the presence of this catalyst, adding one equivalent of hydrosilane to a nitrile yields a silylimine product, whereas adding a second equivalent produces the corresponding disilylamine.

Full text of DOI:10.1002/chem.201406356

DOI: 10.1002/chem.201406356
Full Paper
&
Hydrosilylation
Hydrosilylation of Ketones, Imines and Nitriles Catalysed by
Electrophilic Phosphonium Cations: Functional Group Selectivity
and Mechanistic Considerations
Manuel Pꢀrez,[a] Zheng-Wang Qu,[b] Christopher B. Caputo,[a] Vitali Podgorny,[a]
Lindsay J. Hounjet,[a] Andreas Hansen,[b] Roman Dobrovetsky,[a] Stefan Grimme,*[b] and
Douglas W. Stephan*[a, c]
Abstract: The electrophilic phosphonium salt, [(C6F5)3PF]
[B(C6F5)4], catalyses the efficient hydrosilylation of ketones,
imines and nitriles at room temperature. In the presence of
this catalyst, adding one equivalent of hydrosilane to a nitrile
yields a silylimine product, whereas adding a second equiva-
lent produces the corresponding disilylamine. [(C6F5)3PCl]
[B(C6F5)4] and [(C6F5)3PBr][B(C6F5)4] are also synthesised and
tested as catalysts. Competition experiments demonstrate
that the reaction exhibits selectivity for the following func-
tional groups in order of preference: ketone>nitrile>
imine>olefin. Computational studies reveal the reaction
mechanism to involve initial activation of the SiÀH bond by
its interaction with the phosphonium centre. The activated
complex then acts cooperatively on the unsaturated
substrate.
Introduction
Beller and co-workers showed that [Bu4N]F functions as a cata-
lyst;[5g] however this method requires the use of a highly reac-
tive silane.
Hydrosilylation reactions account for some of the most impor-
tant catalytic processes employed industrially,[1] due to the di-
verse applications of silicon-containing materials. For example,
silicones are used extensively within sealants, adhesives, lubri-
cants, medicines, cookware, and insulation.[2] A plethora of
transition metal catalysts have been exploited for the hydrosi-
lylations of ketones,[3] imines[4] and nitriles.[5] Furthermore,
metal-free methods have also been developed using acids,[6]
bases[7] or alkali fluorides[8] to effect these transformations, al-
though such methods have mostly required harsh reaction
conditions. Tin[9] and aluminium[10] species have also been used
as catalysts. Piers and co-workers demonstrated that B(C6F5)3
acts as a highly effective catalyst for hydrosilylation,[11] and the
reaction mechanism was further illuminated by Oestreich and
co-workers.[12] More recently, Piers and co-workers[13] isolated
a borole–silane adduct, a model intermediate. Furthermore,
While the field of organocatalysis has emerged from efforts
to develop metal-free catalysts,[14] our efforts to these ends
have focused on developing a variety of metal-free Lewis acids
for frustrated Lewis pair (FLP) chemistry.[15] Whereas the bulk of
the early work exploited boron-based Lewis acids, more re-
cently we have turned our attention to Lewis acidic phospho-
nium cations. Previous work showed that PV cations can cata-
lyse additions to polar unsaturated compounds[14c] and Diels-
Alder reactions.[16] Gabba¨ı and co-workers recently demonstrat-
ed the utility of such phosphonium species as acceptors for
fluoride ion sensing applications.[17] Radosevich and co-workers
also recently exploited the redox chemistry of PIII and PV sys-
tems within transfer hydrogenation catalysis.[18] In our initial in-
vestigation, we used a Lewis acidic PV centre to capture CO2.[19]
Targeting amplified Lewis acidity, we then prepared [(C6F5)3PF]
[B(C6F5)4]. The electrophilic phosphonium cation (EPC),
[(C6F5)3PF]+, was shown to catalyse the hydrodefluorination of
fluoroalkanes in the presence of hydrosilane.[20] Subsequently,
we demonstrated that [(C6F5)3PF][B(C6F5)4] catalysed olefin iso-
merisations, hydrosilylations of olefins and alkynes,[21] and de-
hydrocouplings of hydrosilanes with amines, thiols, phenols or
carboxylic acids.[22] Furthermore, the H2 generated by the dehy-
drocoupling reaction could be transferred to an olefin in situ.
This reactivity clearly demonstrates that the presence of the
electron-withdrawing fluoro and perfluoroaryl substituents at P
provides a potent Lewis acid. Herein we extend our earlier
work dealing with the hydrosilylation of olefins and alkynes by
demonstrating that the salts, [(C6F5)3PX][B(C6F5)4] (X=F, Cl, Br),
[a] Dr. M. Pꢀrez, C. B. Caputo, V. Podgorny, Dr. L. J. Hounjet, Dr. R. Dobrovetsky,
Prof. Dr. D. W. Stephan
Department of Chemistry, University of Toronto
80 St. George Street, Toronto, Ontario, M5S 3H6 (Canada)
E-mail: dstephan@chem.utoronto.ca
[b] Dr. Z.-W. Qu, A. Hansen, Prof. Dr. S. Grimme
Mulliken Center for Theoretical Chemistry
Institut fꢁr Physikalische und Theoretische Chemie, Universitꢂt Bonn
Beringstr. 4, 53115 Bonn (Germany)
[c] Prof. Dr. D. W. Stephan
Chemistry Department, Faculty of Science
King Abdulaziz University (KAU), Jeddah 21589 (Saudi Arabia)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201406356.
Chem. Eur. J. 2015, 21, 1 – 11
1
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
also catalyse the hydrosilylation of ketones, imines, and nitriles.
The reaction’s selectivity for these functional groups is probed
experimentally, and a computational study supports a mecha-
nism for metal-free hydrosilylation catalysis.
Table 1. Hydrosilylation of substrates 1, 3, and 5.
Entry Substrate
1
HSiEt3 [equiv] T [8C]
t [h] Yield [%][a]
2.0
2.0
1.2
25
25
25
1
1
99 (83)
99 (86)
99 (97)
Results and Discussion
2
3
Hydrosilylation catalysis
12
Aliphatic ketones were found to undergo efficient hydrosilyla-
tion using [(C6F5)3PF][B(C6F5)4] as the catalyst (Scheme 1).
4
5
1.2
1.2
25
25
72
24
99
99
6
1.2
25
24
99
7
8
1.2
1.2
25–100 24
0
25
100
100
24
24
24
99 (88)[b]
9
2.4
2.4
99 (98)[c]
96[b]
10
Scheme 1. [(C6F5)3PF][B(C6F5)4]-catalysed hydrosilylation of ketones (1),
imines (3), and nitriles (5) to silyl enol ethers (2), N-silylamines (4), and N-
silylimines (6) or N,N-disilylamines (7), respectively.
11
12
13
2.4
2.0
2.0
100
25
48
6
99[c]
95
The reaction of 1-cyclohexylethanone 1a with an excess of
Et3SiH in the presence of [(C6F5)3PF][B(C6F5)4] (1.5 mol%) afford-
ed the hydrosilylated product, CyCH(Me)OSiEt3 2a in an isolat-
ed yield of 83% (Table 1, entry 1). In a similar manner, treat-
ment of heptan-4-one 1b with Et3SiH in the presence of
[(C6F5)3PF][B(C6F5)4] yielded the hydrosilylated product,
nPr2CH(OSiEt3) 2b (Table1, entry 2). Extending this reactivity to
a series of aldimines also proved possible. The hydrosilylation
of N-benzylidene-tert-butylamine 3a with Et3SiH by [(C6F5)3PF]
[B(C6F5)4] gave the corresponding N-silylated amine 4a in 97%
yield after 12 h (Table1, entry 3). Similarly 4- and 3-bromoben-
zylidene, and 4-tert-butylbenzylidene derivatives (3b, c and d,
respectively) were catalytically reduced in quantitative yields
(Table1, entries 4–6, respectively). It is noteworthy that using
less sterically encumbering substituents at N did not result in
imine hydrosilylation, presumably because the relatively unpro-
tected N atom is able to interact with the Lewis acidic phos-
phonium centre (Table1, entry 7).
25
12
96
14
2.0
25
12
99
[a] Conditions: To a solution of the catalyst [(C6F5)3PF][B(C6F5)4] (6 mg,
1.5 mol%) in CH2Cl2 or C6H5Br (2.5 mL) was added Et3SiH (1.0–2.4 equiv)
and then substrate (1.0 equiv) at 258C. Values in parentheses refer to
yields of isolated product; [b] yield of N-silylimine product (6); [c] yield of
N,N-disilylamine product (7).
cumbered mesityl nitrile 5b did not undergo hydrosilylation at
room temperature. At 1008C, however, selective formation of
N-silylimine 6b was observed to occur independently of the
amount of silane employed (Table1, entry 10). Conversely, pro-
pionitrile underwent hydrosilylation in the presence of excess
Et3SiH at 1008C to afford N,N-disilylamine 7c (Table1, entry 11)
after 2 d.
The catalyst was also found to effect the hydrosilylation of
benzonitrile (5a). In the presence of 1.2 equivalents of Et3SiH
Competition studies were undertaken to determine the se-
at room temperature, the corresponding N-silylimine, PhC(H)= lectivity of [(C6F5)3PF][B(C6F5)4]-catalysed hydrosilylations with
NSiEt3 (6a) was obtained after 1 d at 258C (Table1, entry 8).
However, in the presence of 2.4 equivalents of Et3SiH at 1008C,
benzonitrile was completely reduced to the N,N-disilylamine,
PhCH2N(SiEt3)2 (7a; Table1, entry 9). Interestingly, sterically en-
respect to the various functional groups. Initially, reaction mix-
tures containing a ketone, imine, or nitrile in the presence of
1-decene, were subjected to HSiEt3 in the presence of
[(C6F5)3PF][B(C6F5)4]. In each case, the olefin was unaltered and
&
&
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
2
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
For example, hex-6-en-2-one 1c was treated with Et3SiH in the
presence of [(C6F5)3PF][B(C6F5)4], resulting in the exclusive for-
mation of the silyl ether containing the unchanged olefinic
fragment (Table 1, entry 12). Similar treatment of 2-methylcy-
clohex-2-enone 1d gave the silyl enol ether via a formal 1,4-
addition (Table 1, entry 13). Lastly the hydrosilylation of 4-ace-
tylbenzonitrile 1e resulted in the selective reduction of the car-
bonyl group with the nitrile being unaffected (Table 1,
entry 14).
As a comparative study, we prepared analogous phosphoni-
um salts by exchanging the halide from fluoride to chloride or
bromide to give [(C6F5)3PCl][B(C6F5)4] and [(C6F5)3PBr][B(C6F5)4],
respectively (Scheme 3). The syntheses of these compounds
Scheme 3. Preparation of [(C6F5)3PCl][B(C6F5)4] and [(C6F5)3PBr][B(C6F5)4].
are similar to that of [(C6F5)3PF][B(C6F5)4], albeit with alternate
oxidants; initial oxidation of the phosphine, (C6F5)3P, was done
with either SO2Cl2 or Br2, resulting in the corresponding dihalo-
phosphoranes. Subsequent halide abstraction was performed
with [Et3Si][B(C6F5)4]. The bromophosphonium salt [(C6F5)3PBr]
[B(C6F5)4] was characterised crystallographically (Figure 1) and
incorporates a PÀBr bond length of 2.1314(9) ꢂ, which is con-
siderably longer than the PÀF bond length in the related
cation [(C6F5)2PhPF]+ (1.533(2) ꢂ).[20]
Scheme 2. Functional group competition experiments. Percentage values in
parentheses are yields determined by H NMR spectroscopy.
1
the polar unsaturated compound underwent hydrosilylation
(Scheme 2). In a similar fashion, the polar unsaturated com-
pounds themselves were systematically compared to each
other to determine their relative propensity to undergo
[(C6F5)3PF][B(C6F5)4]-catalysed hydrosilylation. For instance,
heptan-4-one 1b was selectively reduced in the presence of
benzonitrile 5a, whereas 5a was selectively reduced in the
presence of N-benzylidene-tert-butylamine 3a (Scheme 2). In-
terestingly, the competition experiment involving heptan-4-
one 1b and N-benzylidene-tert-butylamine 3a resulted in no
reaction at 258C, even on standing for 2 d. However, heating
the reaction mixture to 1008C for 12 h resulted in the com-
plete reduction of the imine 3a to amine 9 with concomitant
formation of silyl enol ether 10. In this case, stabilisation of an
intermediate is thought to result from the imine’s Brønsted ba-
sicity, which, at elevated temperatures, triggers deprotonation
of the activated ketone with simultaneous delivery of hydride
to the iminium carbon.
Figure 1. POV-Ray depiction of the cation of [(C6F5)3PBr][B(C6F5)4]. The anion
is not shown.
To explore the reactivity of the new phosphonium cations,
1-decene was treated with Et3SiH in the presence of 1.5 mol%
of [(C6F5)3PCl][B(C6F5)4] or [(C6F5)3PBr][B(C6F5)4]. In both cases,
the reaction required longer times than the corresponding
[(C6F5)3PF][B(C6F5)4]-catalysed reaction. Both reactions went to
completion, although that catalysed by [(C6F5)3PCl][B(C6F5)4]
Generally, these competition experiments indicate that hy-
drosilylation occurs in the following order of decreasing prefer-
ence: ketone>nitrile>imine>olefin. This notion was further
confirmed by some examples of intramolecular competitions.
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
3
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
To determine the precise mechanism of hydrosilylation catal-
ysis, a state-of-the-art DFT study using B2PLYP-D3/def2-QZVP
calculations together with TPSS-D3/def2-TZVP (COSMO) ther-
mal corrections and COSMO-RS solvation corrections in toluene
was performed (see the Supporting Information). This level of
theory was used successfully by Grimme and co-workers for
several years to obtain mechanistic information relating to pro-
cesses involving a variety of FLP systems,[23] and provided ex-
tensive thermochemical benchmarking.[24] Free energies and
optimised geometries were computed, and the reliability of
this method was confirmed by comparison with results from
both TPSS-D3 and PW6B95 DFT functionals and highly correlat-
ed local CCSD(T) methods.
Table 2. Hydrosilylation of substrates 1, 3, 5 and 8.
Entry Substrate
Cat.
HSiEt3 [equiv] T [8C] t [h] Conv. [%]
1
2
3
[(C6F5)3PF]+ 1.1
[(C6F5)3PCl]+ 1.1
[(C6F5)3PBr]+ 1.1
25
25
25
<0.5 99
3
1
99
99
4
5
[(C6F5)3PCl]+ 2.0
[(C6F5)3PBr]+ 2.0
25
25
1
99
<1 99
6
7
8
9
[(C6F5)3PCl]+ 1.2
[(C6F5)3PCl]+ 1.2
[(C6F5)3PBr]+ 1.2
[(C6F5)3PBr]+ 1.2
25
100
25
24
6
24
6
0
99
0
100
99
The origin of Lewis acidity within [(C6F5)3PF]+ is interesting.
TPSS-D3-optimised geometries of this cation reveal its C3 sym-
metry with a F-P-C angle of 105.48. This value indicates that
the P centre is less pyramidal than that of the parent Lewis
base (C6F5)3P, which exhibits a clearly sp3-hybridised P centre,
despite larger steric repulsion expected when replacing the
electron lone pair on P centre by fluoride. Upon addition of
fluoride or hydride to [(C6F5)3PF][B(C6F5)4], the resulting neutral
compounds, (C6F5)3PF2 or (C6F5)3PFH, show bipyramidal geome-
tries with respective linear F-P-F and F-P-H arrangements
about the C3 axis (Figure 2), consistent with idealised sp3d hy-
10
11
[(C6F5)3PCl]+ 2.4
[(C6F5)3PCl]+ 2.4
25
100
24
0
24 90 (6a)
10 (7a)
24
24 44 (6a)
56 (7a)
12
13
[(C6F5)3PBr]+ 2.4
[(C6F5)3PBr]+ 2.4
25
100
0
[a] Conditions: To a solution of the catalyst (6 mg, 1.5 mol%) in CH2Cl2 or
C6H5Br (2.5 mL) was added Et3SiH (1.0–2.4 equiv) followed by substrate
(1.0 equiv) at 258C or 1008C.
proceeded at the slowest rate (Table 2, entries 2 and 3). Using
heptan-4-one as the substrate, the reaction proceeded to com-
pletion in 1 h or less regardless of the catalyst used (Table 2,
entries 4 and 5). In contrast, hydrosilylation of the imine, N-
benzylidene-2-methylpropan-2-amine, was not catalysed by
[(C6F5)3PCl][B(C6F5)4] or [(C6F5)3PBr][B(C6F5)4] after 24 h at 258C,
whereas [(C6F5)3PF][B(C6F5)4] was effective under these condi-
tions (Table 1, entry 3). Nevertheless, after 6 h at 1008C, both
[(C6F5)3PCl][B(C6F5)4] and [(C6F5)3PBr][B(C6F5)4] could effect com-
plete conversion (Table 2, entries 6–9). Lastly, the hydrosilyla-
tion of benzonitrile with Et3SiH showed that [(C6F5)3PF][B(C6F5)4]
was the superior catalyst. Again, [(C6F5)3PBr][B(C6F5)4] and
[(C6F5)3PCl][B(C6F5)4] were ineffective at room temperature but
gave mixtures of imine 6a and amine 7a after 24 h at 1008C
(Table 2, entries 10–13).
Mechanistic considerations
11B and 19F NMR spectroscopic analyses of reaction mixtures
consistently indicated that the [B(C6F5)4]À anion remained
intact after the hydrosilylation reactions were complete, ruling
out any possibility that a borane generated in situ may have
catalysed this process. We also considered a mechanism
whereby fluoride liberated from [(C6F5)3PF][B(C6F5)4] might
enable fluoride ion-catalysed hydrosilylation. To probe this pos-
sibility, mesityl nitrile was treated with Et3SiH (2.4 equiv) and
[Bu4N]F (30 mol%) in C6D5Br, and the mixture was heated to
1008C for 3 d. In this case, no reaction was observed. Given
this observation, and considering that the analogous
[(C6F5)3PF][B(C6F5)4]-catalysed hydrosilylation described herein is
complete in only 1 d, with much less catalyst under the same
conditions, we were able to rule out the occurrence of such
a mechanism.
Figure 2. Optimised geometries of some P- and B-containing Lewis acids
and bases. Bond lengths are given in ꢂ angles in degrees.
bridisation. The computed d-orbital Mulliken population at the
P centre of related compounds increases in the order (C6F5)3P
(0.30)<[(C6F5)3PF]+
(0.73)<(C6F5)3PFH
(0.75)<(C6F5)3PF2
(0.79)<PF5 (1.04), depending on the electronegativity and
number of ligands. These d populations are approaching the
value of unity expected for true sp3d hybridisation at a neutral
five-coordinate P centre, and are larger than values for boron-
containing species such as [(C6F5)3BH]À (0.14), (C6F5)3B (0.15) or
[(C6F5)3BF]À (0.24). Therefore, a plausible conceptualisation of
&
&
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
4
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
the high Lewis acidity of [(C6F5)3PF]+ should involve the term
“strongly 3d-polarised 3p orbital”[25] or alternatively “sp3d-hybri-
dised orbital as base acceptor.” For comparison, the well-
known sp2-hybridised Lewis acid (C6F5)3B uses the vacant 2p
orbital as base acceptor, but with a 20.8 kcalmolÀ1 smaller hy-
dride affinity (free energy at TPSS-D3 level). The hydride affini-
ties of [(C6F5)3PBr]+ and [(C6F5)3PCl]+ are 2.3 and 2.7 kcalmolÀ1
smaller than that of [(C6F5)3PF]+, respectively, consistent with
relatively lower experimentally observed reactivities. Despite
the higher electronegativity of Cl, the hydride affinity of
[(C6F5)3PCl]+ is found to be slightly smaller than that of
[(C6F5)3PBr]+, likely due to over-compensation of electron back-
donation along the comparatively (ca. 0.2 ꢂ) shorter PÀCl bond
into the empty 3d orbitals at the Lewis acidic P-centre.
tive action of ketone and phosphonium to heterolytically acti-
vate the SiÀH bond, resulting in simultaneous transfer of hy-
dride to the P centre and binding of the carbonyl oxygen to
the Si cation (Figure 3). This process generates a five-coordi-
nate neutral phosphorane complex and a carbocation. This ter-
molecular reaction encounters
a low free-energy barrier
(14.2 kcalmolÀ1), which originates mainly from entropic effects.
Stabilised by adjacent phenyl and siloxy groups, the carbocat-
ion E+ is not very reactive but abstracts hydride with a higher
free-energy barrier (19.0 kcalmolÀ1) via transition structure
TS E+/F to produce the hydrosilylation product while regener-
ating the catalytically active cation, [(C6F5)3PF]+.
Consideration was also given to the alternative pathway in
which [(C6F5)3PF]+ and silane cooperatively act on the ketone.
However, this route (see the Supporting Information, Figure S1,
Considering the hydrosilylation mechanism, several path-
ways were considered with the necessity of [(C6F5)3PF]+ estab-
lished. Indeed, computations show that the direct hydrosilyla-
tion of ketone is prevented by a very high free-energy barrier
(43.1 kcalmolÀ1) under ambient conditions (see the Supporting
Information, Figure S1, Path C). Turning attention to the crucial
role of the Lewis acid, the cation, [(C6F5)3PF]+ (A+; Figure 3)
was shown to form weak donor–acceptor complexes with the
Path B) includes a higher free-energy barrier of 21.5 kcalmolÀ1
.
At the corresponding transition structure TS A+/G, initial hy-
dride transfer from silane generates a reactive silicon cation in
an endergonic step. As same-side Si···O attack is likely to occur,
this would produce the same adduct as path A. In addition, it
is noted that the potential Si···F fluoride abstraction, involving
a free cation intermediate, is highly exergonic and thus may
represent an undesirable catalyst
deactivation pathway.
Collectively, these data are
consistent with an FLP hydrosily-
lation mechanism, in which the
silane and phosphonium ion act
cooperatively on the ketone
(Scheme 4). In principle, other
heteroatomic Lewis bases may
also participate in analogous ter-
molecular reactions. Thus, the
mechanism is thought to be
general for ketones, imines and
nitriles. Moreover it is directly
analogous to the mechanism of
hydrosilylation previously estab-
lished for the boron-based Lewis
acid catalyst, B(C6F5)3.[12] Interest-
ingly, Piers and co-workers have
recently established experimen-
tal support for the initial interac-
tion of a B-based Lewis acidic
boro-indole with silane[26] In this
regard, it is noteworthy that we
Figure 3. Reaction pathway for the hydrosilylation of ketones catalysed by A+. Relative free energies were calcu-
lated using B2PLYP-D3 and are given in kcalmolÀ1; enthalpies given in parentheses. Hydrogen atoms on substitu-
ents are omitted for clarity.
have previously established that
the cation [(C6F5)3PF]+ exhibits
greater Lewis acidity than
B(C6F5)3.
Lewis basic silane B and acetophenone C via P···HÀSi (Figure 3)
Conclusion
and P···O=C interactions, respectively, with the former silane
complex being slightly more stable. At room temperature,
both complexes can easily dissociate, and thus may act effec-
tively as a “frustrated Lewis pair” (FLP) for bond activation.
Indeed, the transition structure TS A+/D reveals the coopera-
The electrophilic phosphonium cation [(C6F5)3PF][B(C6F5)4] me-
diates the efficient catalytic hydrosilylation of ketones, imines
and nitriles. Competition experiments demonstrate that these
reactions can be performed in the presence of other functional
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
5
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
olution mass spectra (HRMS) were obtained using either a micro
mass 70S-250 (EI) spectrometer, an ABI/Sciex QStar Mass (DART)
spectrometer, or a JOEL AccuTOF-DART spectrometer.
Syntheses
(C6F5)3PCl2: In a 20 mL vial, (C6F5)3P (100 mg, 188 mmol) was dis-
solved in CH2Cl2 (1 mL) and then a 2.0m solution of SO2Cl2 in
CH2Cl2 (0.19 mL, 190 mmol) was added dropwise via syringe. After
30 min the solvent was removed under reduced pressure and the
remaining solid was washed with n-pentane (3ꢄ2 mL). The solid
was dried under vacuum, producing the product as a white
powder (90 mg, 79% yield). 13C{1H} NMR (125 MHz, CD2Cl2): d
147.45 (br d, J=256.5 Hz), 144.20 (br d, J=257.4 Hz), 137.98 (br d,
J=254.3 Hz), 119.45 ppm (br d, J=181.0 Hz); 31P{1H} NMR
(162 MHz, CD2Cl2): d=À104.50 ppm (s); 19F{1H} NMR (377 MHz,
CD2Cl2): d=À128.35 to À128.63 (m, 6F), À146.20 to À146.40 (m,
3F), À158.68 to À158.95 ppm (m, 6F); elemental analysis calcd (%)
for C18F15PCl2: C 35.85; found: C 36.09.
Scheme 4. Proposed mechanism for hydrosilylation catalysis by [(C6F5)3PF]+.
groups and that the preferred reactivity follows the order
ketone>nitrile>imine>olefin. In addition, the halophospho-
nium cations [(C6F5)3PCl][B(C6F5)4] and [(C6F5)3PBr][B(C6F5)4] were
prepared and their ability to catalyse a variety of hydrosilyla-
tion reactions was studied. These results uncovered the follow-
ing reactivity trend: [(C6F5)3PF]+ >[(C6F5)3PBr]+ >[(C6F5)3PCl]+.
Computational studies are consistent with an FLP hydrosilyla-
tion mechanism whereby the silane is activated by the phos-
phonium cation, and the resulting complex acts cooperatively
on the substrate. The reactivity of these readily accessible and
highly reactive phosphonium-based Lewis acids is the subject
of ongoing study in our laboratories.
[(C6F5)3PCl][B(C6F5)4]: In a 20 mL vial, (C6F5)3PCl2 (63 mg, 105 mmol)
was fully dissolved in toluene (2 mL). A stir-bar was added and the
solution was placed in cold-well (ca. À358C). [Et3Si·tol][B(C6F5)4]
(86 mg, 100 mmol) was added, and the solution turned a slight
yellow colour over time. The solution was taken out of the cold
well and allowed to stir for 30 min. Toluene was then pipetted off,
and the solution was washed with toluene (2ꢄ1 mL) before re-
moving the solvent under reduced pressure. The resulting solid
was isolated as a white powder (106 mg, 85% yield). 13C{1H} NMR
(125 MHz, CD2Cl2): d=148.40 (br d, J=272.0 Hz), 148.05 (br d, J=
241.8 Hz), 139.35 (br d, J=255.4 Hz), 138.12 (br d, J=261.3 Hz),
136.22 ppm (br d, J=238.3 Hz); 31P{1H} NMR (162 MHz, CD2Cl2): d=
27.35 ppm (s); 19F{1H} NMR (377 MHz, CD2Cl2): d=À124.81 to
À125.04 (m, 6F), À125.05 to À125.28 (m, 3F), À133.44 (br s, 8F),
À150.47 to À150.71 (m, 6F), À163.89 (t, J=20.4 Hz, 4F),
À167.90 ppm (br t, J=18.3 Hz, 8F); 11B NMR (128 MHz, CD2Cl2): d=
À16.69 (s). elemental analysis calcd (%) for C42F35PClB: C 40.47;
found: C 40.45.
Experimental Section
General procedures
(C6F5)3PBr2: In a 20 mL vial, (C6F5)3P (100 mg, 188 mmol) was fully
dissolved in CH2Cl2 (1 mL), and then a 1.0m solution of Br2 in
CH2Cl2 (0.19 mL, 190 mmol) was added dropwise via syringe. The
solution turned a dark orange colour and after a few minutes a pre-
cipitate formed. After 30 min, the solvent was removed under re-
duced pressure and the remaining solid was washed with n-pen-
tane (3ꢄ2 mL). The solid was dried under vacuum and isolated as
a light yellow powder (121 mg, 93% yield). 13C{1H} NMR (125 MHz,
CD2Cl2): d=146.65 (br d, J=248.2 Hz), 144.39 (br d, J=260.5 Hz),
138.01 (br d, J=257.5 Hz), 107.49 ppm (br d, J=57.2 Hz); 31P{1H}
NMR (203 MHz, CD2Cl2): d=À86.68 ppm (s); 19F{1H} NMR (377 MHz,
CD2Cl2): d=À128.59 (br t, 6F, J=19.1 Hz), À145.21 (br t, 3F, J=
20.2 Hz), À158.72 ppm (br t, 6F, J=20.1 Hz); elemental analysis
calcd (%) for C18F15PBr2: C 31.24; found: C 25.20, N 0.44.
All preparations and manipulations were carried out under an an-
hydrous N2 atmosphere using standard Schlenk and glove box
techniques. All glassware was oven-dried and cooled under
vacuum before use. Commercial reagents were purchased from
Sigma-Aldrich, Strem Chemicals or Apollo Scientific, and were used
without further purification unless indicated otherwise. The com-
pound, [(C6F5)3PF][B(C6F5)4] was prepared by the reported proce-
dure.[20,27] Solvents, CH2Cl2, Et2O, n-pentane, and toluene, were
dried using an Innovative Technologies solvent purification system,
whereas CD2Cl2 and CDCl3 (Aldrich) were deoxygenated, distilled
over CaH2, then stored over 4 ꢂ molecular sieves before use. The
solvent, C6D5Br (Aldrich), was deoxygenated and stored over 4 ꢂ
molecular sieves before use. Reactions were monitored by NMR
spectroscopy or thin-layer chromatography (TLC) on EMD Silica Gel
60 F254 plates. TLC visualisation of the developed plates was per-
formed under UV light (254 nm) using either KMnO4 or anisalde-
hyde stains. Neutral silica (Silica-P, 40–63 mm, Silicycle, Quꢀbec,
Canada) for flash column chromatography was used as received.
Organic solutions were concentrated under reduced pressure on
a Bꢃchi rotary evaporator. NMR spectra were obtained on a Bruker
[(C6F5)3PBr][B(C6F5)4]: In
a
20 mL vial, (C6F5)3PBr2 (106 mg,
153 mmol) was partially dissolved in toluene (2 mL) with the aid of
a stir-bar. The orange suspension was placed in a cold well (ca.
À358C), and [Et3Si·tol][B(C6F5)4] (126 mg, 146 mmol) was added.
After 30 min, the suspension was taken out of the cold well. The
top layer of toluene was pipetted off, and the orange solid was
then washed with toluene (2ꢄ1 mL) before removing the solvent
under reduced pressure. The resulting solid was isolated as an off-
white powder (138 mg, 73% yield). 13C{1H} NMR (125 MHz, CD2Cl2):
d=148.30 (br d, J=250.1 Hz), 148.05 (br d, J=236.7 Hz), 139.21 (br
d, J=255.8 Hz), 138.19 (br d, J=235.6 Hz), 136.22 (br d, J=
243.8 Hz), 124.02 ppm (br s); 31P{1H} NMR (162 MHz, CD2Cl2): d=
1
AvanceIII-400 MHz spectrometer. H NMR data, referenced to exter-
nal Me4Si, are reported as follows: chemical shift (d/ppm), multi-
plicity (s=singlet, d=doublet, t=triplet, q=quartet, quin=quin-
tet, sex=sextuplet, m=multiplet, dm=doublet of multiplets, br=
broad), coupling constant (Hz), normalised integrals. 13C{1H} NMR
chemical shifts (d/ppm) are referenced to external Me4Si. High-res-
&
&
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
6
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
À5.73 ppm (s); 19F{1H} NMR (377 MHz, CD2Cl2): d=À124.69 (br s,
6F), À126.30 (br s, 3F), À133.34 (br s, 10F), À150.94 (br s, 6F),
À163.82 (t, J=20.21 Hz, 5F), À167.82 ppm (br t, J=17.45 Hz, 10F);
11B NMR (128 MHz, CD2Cl2): d=À16.71 ppm (s); elemental analysis
calcd (%) for C42F35PBrB: C 39.07; found: C 36.69, N 0.65. CCDC-
1037077 contains the crystallographic data for [(C6F5)3PBr][B(C6F5)4].
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Et3SiN(tBu)CH2(C6H4-4-Br), 4b: 1.2 equivalents of Et3SiH were used
relative to 3b, and the reaction was conducted for 72 h at 258C
(99% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=7.31 (d, J=8.8 Hz, 2H), 7.12 (d, J=8.9 Hz,
2H), 3.90 (s, 2H), 1.06 (s, 9H), 0.93 (t, J=8.0 Hz, 9H), 0.60 ppm (q,
J=7.8 Hz, 6H); 13C{1H} NMR (101 MHz, C6D5Br): d=144.7, 130.4
(2C), 127.6 (2C), 118.8, 54.2, 47.9, 30.2 (3C), 7.5 (3C), 6.9 ppm (3C);
29Si NMR (79.5 MHz, C6D5Br): d=9.5 ppm (s); MS (DART ionisation):
m/z (%): 242.1 ([MÀEt3Si+2H]+, 100), 244.1 ([MÀEt3Si+2H]+, 90);
HRMS (ESI): m/z calcd for C11H17BrN [MÀEt3Si+2H]+: 242.0539 and
244.0544; found: 242.0540 and 244.0518, respectively.
Representative protocol for hydrosilylation reactions
Et3SiN(tBu)CH2(C6H4-3-Br), 4c: 1.2 equivalents of Et3SiH were used
relative to 3c, and the reaction was conducted for 24 h at 258C
(99% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=7.56 (s, 1H), 7.19 (m, 2H), 6.99 (t, J=7.8 Hz,
1H), 3.93 (s, 2H), 1.06 (s, 9H), 0.94 (t, J=7.9 Hz, 9H), 0.59 ppm (q,
J=7.7 Hz, 6H); 13C{1H} NMR (101 MHz, C6D5Br): d=148.3, 129.0,
128.9, 128.2, 124.2, 121.9, 54.1, 47.9, 30.1 (3C), 7.5 (3C), 6.8 ppm
(3C); 29Si NMR (79.5 MHz, C6D5Br): d=9.7 ppm (s); MS (ESI): m/z (%):
168.9 ([MÀEt3SiNtBu]+, 100), 170.9 ([MÀEt3SiNtBu]+, 90), 242.1
([MÀEt3Si+2H]+, 60), 244.1 ([MÀEt3Si+2H]+, 55); HRMS (ESI) m/z
calcd for C11H17BrN [MÀEt3Si+2H]+: 242.0539 and 244.0544;
found: 242.0541 and 244.0520.
All hydrosilylation experiments were performed in
a similar
manner, and therefore only one reaction is described in detail. Iso-
lated product yields determined for several products were com-
1
pared with those determined by H NMR spectroscopy. To a solu-
tion of the catalyst [(C6F5)3PF][B(C6F5)4] (6 mg, 5 mmol) in CD2Cl2,
CDCl3 or C6D5Br (2.5 mL) was added Et3SiH (98 mg, 850 mmol) fol-
lowed by heptan-4-one 1b (40 mg, 350 mmol) at 258C. Monitoring
the reaction by NMR spectroscopy and TLC showed that the
ketone had been completely consumed within 1 h. To the reaction
mixture was then added CH3CN (0.02 mL). The mixture was diluted
with CH2Cl2 (10 mL), filtered over silica gel and the solvent evapo-
rated to afford a mixture of the hydrosilylated compound 2b and
8% of (Et3Si)2O as a colourless oil (73 mg , 86% yield).
Et3SiN(tBu)CH2(C6H4-4-tBu), 4d: 1.2 equivalents of Et3SiH were used
relative to 3d, and the reaction was conducted for 24 h at 258C
(99% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=7.32 (s, 4H), 4.04 (s, 2H), 1.23 (s, 9H), 1.11 (s,
9H), 0.96 (t, J=8.4 Hz, 9H), 0.64 ppm (q, J=8.4 Hz, 6H); 13C{1H}
NMR (101 MHz, C6D5Br): d=147.5, 142.5, 125.5 (2C), 124.2 (2C),
54.2, 48.0, 33.6, 31.0 (3C), 30.4 (3C), 7.6 (3C), 7.0 ppm (3C); 29Si NMR
(79.5 MHz, C6D5Br): d=8.7 ppm (s); MS (DART ionisation): m/z (%):
220.2 ([MÀEt3Si+2H]+, 100); HRMS (ESI) m/z calcd for C15H26N
[MÀEt3Si+2H]+: 220.2060; found: 220.2061.
Et3SiN=CHPh, 6a: 1.2 equivalents of Et3SiH were used relative to
5a, and the reaction was conducted for 24 h at 258C. The crude
product was diluted with CH2Cl2 (10 mL), filtered through silica gel
and evaporated (32 mg, 88% yield, colourless oil). 1H NMR
(400 MHz, CD2Cl2): d=9.08 (s, 1H), 7.83 (m, 2H), 7.47 (m, 3H), 1.04
(t, J=8.0 Hz, 9H), 0.80 ppm (q, J=7.8 Hz, 6H); 13C{1H} NMR
(101 MHz, CD2Cl2): d=169.3, 139.8, 131.6, 129.1 (2C), 128.9 (2C), 7.4
(3C), 4.2 ppm (3C); 29Si NMR (79.5 MHz, CD2Cl2): d=7.6 ppm (s); MS
(DART ionisation): m/z (%): 220.2 ([M+H]+, 100); HRMS (DART ioni-
sation): m/z calcd for C13H22NSi, [M+H]+: 220.15215; found:
220.15305.
Reaction conditions and product characterisations
Et3SiOCH(Me)Cy, 2a: 2.0 equivalents of Et3SiH were used relative to
1a, and the reaction was conducted for 1 h at 258C. (82 mg of
a mixture of the hydrosilylated compound 2a and 15% of (Et3Si)2O,
1
83% yield of 2a, colourless oil). H NMR (400 MHz, CD2Cl2): d=3.57
(quint, J=6.3 Hz, 1H), 1.80 (m, 1H), 1.74 (m, 2H), 1.66 (m, 2H),
1.29–1.12 (m, 4H), 1.08 (d, J=6.3 Hz, 3H), 1.05–0.90 (m, 2H), 0.96
(t, J=8.2 Hz, 9H), 0.59 ppm (q, J=7.9 Hz, 6H); 13C{1H} NMR
(101 MHz, CD2Cl2): d=73.1, 45.4, 29.4, 29.3, 27.4, 27.2, 27.1, 21.2,
7.4 (3C), 5.7 ppm (3C); 29Si NMR (79.5 MHz, CD2Cl2): d=15.1 ppm
(s); MS (DART ionisation): m/z, (%): 247.2 (50), 243.2 ([M+H]+, 20),
133.2 ([HOSiEt3]+, 50), 111.1 ([MÀOSiEt3]+, 100).
Et3SiOCHPr2, 2b: 2.0 equivalents of Et3SiH were used relative to 1b,
and the reaction was conducted for 1 h at 258C (73 mg of a mix-
ture of the hydrosilylated compound 2b and 8% of (Et3Si)2O, 86%
yield of 2b, colourless oil). 1H NMR (400 MHz, CD2Cl2): d=3.63
(quint, J=5.5 Hz, 1H), 1.38 to 1.22 (m, 8H), 0.91 (t, J=7.9 Hz, 9H),
0.85 (t, J=7.1 Hz, 6H), 0.55 ppm (q, J=7.7 Hz, 6H); 13C{1H} NMR
(101 MHz, CD2Cl2): d=72.7, 40.3 (2C), 19.3 (2C), 14.8 (2C), 7.4 (3C),
5.8 ppm (3C); 29Si NMR (79.5 MHz, CD2Cl2): d=14.9 ppm (s); MS
(DART ionisation): m/z (%): 231.2 ([M]+, 75), 133.1; HRMS (DART ion-
isation): m/z calcd for C13H31OSi, [M+H]+: 231.21442; found:
231.21496.
(Et3Si)2NCH2Ph, 7a: 2.4 equivalents of Et3SiH were used relative to
5a, and the reaction was conducted for 24 h at 1008C. The crude
product was diluted with CH2Cl2 (10 mL), filtered through silica gel
and evaporated (55 mg, 98% yield, colourless oil). 1H NMR
(400 MHz, CD2Cl2): d=7.34 to 7.23 (m, 4H), 7.18 (t, J=6.9 Hz, 1H),
4.17 (s, 2H), 0.96 (t, J=7.8 Hz, 18H), 0.64 ppm (q, J=7.6 Hz, 12H);
13C{1H} NMR (101 MHz, CD2Cl2): d=145.3, 128.3 (2C), 127.1 (2C),
126.5, 49.5, 8.1 (6C), 6.6 ppm (6C); 29Si NMR (79.5 MHz, CD2Cl2): d=
12.2 ppm (s); MS (DART ionisation): m/z (%): 336.2 ([M+H]+, 100);
HRMS (DART ionisation): m/z calcd for C19H38NSi2, [M+H]+:
336.25428; found: 336.25475.
Et3Si(N(tBu)CH2Ph), 4a: 1.2 equivalents of Et3SiH were used relative
to 3a, and the reaction was conducted for 12 h at 258C. The crude
product was diluted with CH2Cl2 (10 mL), filtered through silica gel
and evaporated (46 mg, 97% yield, colourless oil). 1H NMR
(400 MHz, CD2Cl2): d=7.35 (d, J=7.9 Hz, 2H), 7.25 (t, J=7.9 Hz,
2H), 7.12 (t, J=7.9 Hz, 1H), 4.10 (s, 2H), 1.17 (s, 9H), 0.97 (t, J=
8.0 Hz, 9H), 0.66 ppm (q, J=8.0 Hz, 6H); 13C{1H} NMR (101 MHz,
CD2Cl2): d=147.00, 128.3 (2C), 126.9 (2C), 126.0, 55.4, 49.4, 31.2
(3C), 8.2 ppm (3C), 7.9 (3C); 29Si NMR (79.5 MHz, CD2Cl2): d=
9.5 ppm (s); MS (DART ionisation): m/z (%): 164.1 ([MÀEt3Si+2H]+,
100); HRMS (DART ionisation): m/z calcd for C11H18N [MÀEt3Si+
2H]+: 164.14392; found: 164.14415.
Et3SiN=CH(C6H2-2,4,6-Me3), 6b: 2.4 equivalents of Et3SiH were used
relative to 5b, and the reaction was conducted for 24 h at 1008C
(96% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=9.42 (s, 1H), 6.71 (s, 2H), 2.42 (s, 6H), 2.16 (s,
3H), 1.03 (t, J=8.0 Hz, 9H), 0.73 ppm (q, J=7.9 Hz, 6H); 13C{1H}
NMR (101 MHz, C6D5Br): d=169.1, 138.2, 137.2 (2C), 129.3 (2C),
128.6, 20.7, 20.2 (2C), 6.8 (3C), 3.4 ppm (3C); 29Si NMR (79.5 MHz,
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
7
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
C6D5Br): d=7.7 ppm (s); MS (DART ionisation): m/z (%): 280.2 ([M+
timised at the TPSS-D3/def2-TZVP+COSMO level of theory, which
combines the TPSS meta-GGA density functional[29] with the BJ-
damped DFT-D3 dispersion correction[30] and the def2-TZVP basis
set,[31] using the Conductor-like Screening Model (COSMO) continu-
um solvation model[32] for CH2Cl2 solvent (dielectric constant e=
8.93, refractive constant n=1.424, Rsolv =2.94 ꢂ). For the present
NH4]+, 100), 149.2 ([MesCHNH2]+, 75).
(Et3Si)2NHBu, 7c: 2.4 equivalents of Et3SiH were used relative to 5c,
and the reaction was conducted for 48 h at 1008C (99% yield as
1
determined by NMR spectroscopy). H NMR (400 MHz, C6D5Br): d=
2.72 (m, 2H), 1.40 (m, 2H), 1.17 (sex, J=7.5 Hz, 2H), 0.96 (t, J=
8.0 Hz, 18H), 0.87 (t, J=7.5 Hz, 3H), 0.61 ppm (q, J=8.0 Hz, 12H);
13C{1H} NMR (101 MHz, C6D5Br): d=44.9, 37.5, 20.1, 13.7, 7.3 (6C),
5.4 ppm (6C); 29Si NMR (79.5 MHz, C6D5Br): d=10.4 ppm (s); MS
(DART ionisation): m/z (%): 273.2 ([MÀEt]+, 20), 259.2 (20), 217.2
(25), 203.2 (30), 193.2 (40), 144.1 (60), 130.1 ([MÀBuÀSiEt3]+, 100).
Et3SiOCHMe(CH2)3CH=CH2, 2c: 2.0 equivalents of Et3SiH were used
relative to 1c, and the reaction was conducted for 6 h at 258C
(95% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=5.78 (m, 1H), 4.97 (m, 2H), 3.74 (sex. J=
6.1 Hz, 1H), 2.08 (m, 2H), 1.46 (m, 2H), 1.09 (d, J=6.5 Hz, 3H), 0.95
(m, 9H), 0.54 ppm (m, 6H); 13C{1H} NMR (101 MHz, C6D5Br): d=
138.2, 113.8, 126.9 (2C), 67.3, 38.5, 29.6, 23.5, 6.6 (3C), 4.7 ppm (3C);
29Si NMR (79.5 MHz, CD2Cl2): d=15.42 ppm (s); MS (DART ionisa-
tion): m/z (%): 232.2 ([M+NH4]+, 80), 215.2 ([M+H]+, 35), 187.2
(45), 133.1 (100).
A
+ +C+Et3SiH reaction system with 75 atoms, it leads to 1737
basis functions (35, 23, 17 atoms and 1091, 319, 327 basis func-
tions, respectively) in our DFT calculations. The density-fitting RI-J
approach[33] was used to accelerate the geometry optimisation and
numerical harmonic frequency calculations in solution. The opti-
mised structures were characterised by frequency analysis to iden-
tify the nature of located stationary points (no imaginary frequency
for true minima and only one imaginary frequency for transition
state) and to provide thermal corrections according to a modified
ideal gas-rigid rotor-harmonic oscillator model.[34]
The final solvation energies in toluene solvent were computed
with the COSMO-RS solvation model in the COSMOtherm program
package[35] on the above TPSS-D3-optimised structures. To check
the effects of the chosen DFT functional on the reaction energies
and barriers, gas-phase single-point calculations using the TPSS-
D3, hybrid PW6B95-D3[36] and double-hybrid B2PLYP-D3[37] were
performed using a larger def2-QZVP basis set.[38] The final reaction
enthalpies (DH) and Gibbs free energies (DG) were determined
from the gas-phase single-point energies plus thermal corrections
plus COSMO-RS solvation energies. The results from different DFT
functionals are in good mutual agreement. In our discussion, the
B2PLYP-D3 Gibbs free energies (in kcalmolÀ1, at 298.15 K, 1 atm)
were used unless specified otherwise.
Et3SiOC=C(Me)(C4H8), 2d: 2.0 equivalents of Et3SiH were used rela-
tive to 1d, and the reaction was conducted for 12 h at 258C (96%
yield as determined by NMR spectroscopy). 1H NMR (400 MHz,
C6D5Br): d=1.99 (m, 2H), 1.89 (m, 2H), 1.61 (s, 3H), 1.56 (m, 2H),
1.47 (m, 2H), 0.98 (t, J=8.0 Hz, 9H), 0.61 ppm (q, J=8.0 Hz, 6H);
13C{1H} NMR (101 MHz, C6D5Br): d=142.6, 109.9, 29.9 (2C), 29.8 (2C),
23.5 (2C), 22.7 (2C), 16.0, 6.6 (3C), 5.4 ppm (3C); 29Si NMR
(79.5 MHz, C6D5Br): d=15.9 ppm (s); MS (DART ionisation): m/z (%):
226.2 ([M]+, 30), 211.2 ([MÀMe]+, 60), 209.2 (75), 113.1 (100).
Et3SiOCHMe(C6H4-4-CN), 2e: 2.0 equivalents of Et3SiH were used
relative to 1e, and the reaction was conducted for 12 h at 258C
(99% yield as determined by NMR spectroscopy). 1H NMR
(400 MHz, C6D5Br): d=7.27 (d, J=8.3 Hz, 2H), 7.20 (d, J=8.2 Hz,
2H), 4.71 (q, J=6.3 Hz, 1H), 1.26 (d, J=6.5 Hz, 3H), 0.88 (t, J=
8.0 Hz, 9H), 0.51 ppm (m, 6H); 13C{1H} NMR (101 MHz, C6D5Br): d=
151.3, 131.3 (2C), 125.2 (2C), 118.1, 110.3, 69.4, 26.5, 6.5 (3C),
4.4 ppm (3C); 29Si NMR (79.5 MHz, C6D5Br): d=18.9 ppm (s); MS
(DART ionisation): m/z (%): 279.2 ([M+NH4]+, 100), 262.2 ([M+H]+,
75), 165.1 (50); HRMS (DART ionisation): m/z calcd for C15H23NOSi,
[M+H]+: 262.16272; found: 262.16289.
Further ab initio calculations were also performed using the ORCA
3.0.1 suite of programs.[39] MP2/CBS calculations were performed
using the frozen core and RI approximations (def2-TZVP/C and
def2-QZVP/C auxiliary basis sets, respectively) and Halkier CBS ex-
trapolation using def2-TZVP and def2-QZVP basis sets.[40] Highly
correlated DLPNO-CCSD(T) calculations[41] using the large and dif-
fuse aug-cc-pVTZ basis set[42] and default setup for the thresholds
were also performed to benchmark our B2PLYP-D3 calculations, re-
sulting in systematically lower free-energy barriers by about 4 kcal
molÀ1 (The computed relative free energies for TS 1/2+, TS 2/3+,
and TS 1/4+ were 9.8, À5.0 and 16.3 kcalmolÀ1, respectively). This
agreement between high-level wavefunction theory and DFT
methods further supports the reliability of the applied theory.
Larger scale hydrosilylation reactions
Acknowledgements
Et3SiOCHPr2, 2b: To a solution of the catalyst [(C6F5)3PF][B(C6F5)4]
(30 mg, 0.024 mmol) in CD2Cl2 (2.5 mL) was added Et3SiH (394 mg,
3.4 mmol) followed by heptan-4-one 1b (194 mg, 1.7 mmol) at
258C. Monitoring the reaction by NMR spectroscopy showed that
the ketone had been completely consumed within 1 h. (95% yield
as determined by NMR spectroscopy).
NSERC of Canada and the Deutsche Forschungsgemeinschaft
(SFB 813) are thanked for financial support. D.W.S. is grateful
for the award of a Canada Research Chair. C.B.C. is grateful for
the award of an NSERC postgraduate scholarship and a Wal-
ter C. Sumner Fellowship.
Et3Si(N(tBu)CH2Ph), 4a: To a solution of the catalyst [(C6F5)3PF]
[B(C6F5)4] (30 mg, 0.024 mmol) in CD2Cl2 (2.5 mL) was added Et3SiH
(209 mg, 1.8 mmol) followed by 3a (274 mg, 1.7 mmol) at 258C.
The reaction was monitored by NMR spectroscopy, which showed
that the reaction was completed after 24 h at 258C or 2 h at 508C.
The crude product was diluted with CH2Cl2 inside of glove box, fil-
tered through silica gel and evaporated (430 mg, 91% yield, col-
ourless oil).
Keywords: homogeneous catalysis
phosphonium · reaction mechanisms · selectivity
·
hydrosilylation
·
[1] a) D. Troegel, J. Stohrer, Coord. Chem. Rev. 2011, 255, 1440; b) A. K. Roy,
Adv. Organomet. Chem. 2007, 55, 1; c) R. M. Hill in Surfactants Science
Series, Vol. 86 (Ed.: R. M. Hill), Marcel Dekker, New York, 1999, pp. 1–48;
d) E. Plueddemann, Silane Coupling Agents, 2nd ed., Plenum Press, New
York, 1991; e) A. F. Noels, A. J. Hubert in Industrial Applications of Homo-
geneous Catalysis (Ed. A. Mortreux), Kluwer, Amsterdam, 1985, pp. 80–
91.
Computational details
The quantum chemical DFT calculations were performed with the
TURBOMOLE 6.4 suite of programs.[28] The structures were fully op-
&
&
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
8
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
[2] a) V. B. Pukhnarevitch, E. Lukevics, L. I. Kopylova, M. Voronkov, Perspec-
tives of Hydrosilylation, Institute for Organic Synthesis Riga, Latvia,
1992; b) I. Ojima in The Chemistry of Organic Silicon Compounds, Vol.
(Eds.: S. Patai, Z. Rappoport), Wiley Interscience, New York, 1989, pp.
1479–1526.
dron 1997, 53, 1627–1634; k) M. D. Drew, N. J. Lawrence, D. Fontaine, L.
Sehkri, Synlett 1997, 989–991; l) Y. Kawanami, H. Yuasa, F. Toriyama, S.
Yoshida, T. Baba, Catal. Commun. 2003, 4, 455–459.
[9] N. Lawrence, S. M. Bushell, Tetrahedron Lett. 2000, 41, 4507–4512.
[10] J. Koller, R. G. Bergman, Organometallics 2012, 31, 2530–2533.
[11] a) D. J. Parks, J. M. Blackwel, W. E. Piers, J. Org. Chem. 2000, 65, 3090–
3098; b) D. J. Parks, W. E. Piers, J. Am. Chem. Soc. 1996, 118, 9440–9441;
c) R. Roesler, B. J. N. Har, W. E. Piers, Organometallics 2002, 21, 4300–
4302; d) J. M. Blackwell, D. J. Morrison, W. E. Piers, Tetrahedron 2002, 58,
8247–8254; e) J. Hermeke, M. Mewald, M. Oestreich, J. Am. Chem. Soc.
2013, 135, 17537–17546; f) J. M. Blackwell, E. R. Sonmor, T. Scoccitti,
W. E. Piers, Org. Lett. 2000, 2, 3921–3923.
[12] a) S. Rendler, M. Oestreich, Angew. Chem. Int. Ed. 2008, 47, 5997–6000;
Angew. Chem. 2008, 120, 6086–6089; b) D. Hog, M. Oestreich, Eur. J.
Org. Chem. 2009, 5047–5056.
[13] A. Y. Houghton, J. Hurmalainen, A. Mansikkamꢅki, W. E. Piers, H. M. Tuo-
nonen, Nat. Chem. 2014, 6, 983–988.
[14] a) L. Ratjen, M. van Gemmeren, F. Pesciaioli, B. List, Angew. Chem. Int. Ed.
2014, 53, 8765–8769; b) T. Werner, Adv. Synth. Catal. 2009, 351, 1469–
1481; c) O. Sereda, S. Tabassum, R. Wilhelm, Lewis Acid Organocatalysts
2010, 349–393.
[15] D. W. Stephan, G. Erker, Angew. Chem. Int. Ed. 2010, 49, 46–76.
[16] M. Terada, M. Kouchi, Tetrahedron 2006, 62, 401–409.
[17] T. W. Hudnall, Y. M. Kim, M. W. P. Bebbington, D. Bourissou, F. P. Gabba¨ı,
J. Am. Chem. Soc. 2008, 130, 10890–10891.
[3] a) H. Nishiyama, H. Sakaguchi, T. Nakamura, M. Horihata, M. Kondo, K.
Itoh, Organometallics 1989, 8, 846–848; b) M. Sawamura, R. Kuwano, Y.
Ito, Angew. Chem. Int. Ed. Engl. 1994, 33, 111 – 113 ; Angew. Chem. 1994,
106, 92–93; c) B. Tao, G. C. Fu, Angew. Chem. Int. Ed. 2002, 41, 3892–
3894; Angew. Chem. 2002, 114, 4048–4050; d) L. H. Gade, V. Cesar, S.
Bellemin-Laponnaz, Angew. Chem. Int. Ed. 2004, 43, 1014–1017; Angew.
Chem. 2004, 116, 1036–1039; e) G. Zhu, M. Terry, X. Zhang, J. Organo-
met. Chem. 1997, 547, 97–101; f) Y. Nishibayashi, I. Takei, S. Uemura, M.
Hidai, Organometallics 1998, 17, 3420–3422; g) A. R. Chianese, R. H.
Crabtree, Organometallics 2005, 24, 4432–4436; h) J. Yun, S. L. Buch-
wald, J. Am. Chem. Soc. 1999, 121, 5640–5644; i) B. H. Lipshutz, K.
Noson, W. Chrisman, A. Lower, J. Am. Chem. Soc. 2003, 125, 8779–8789;
j) Y.-J. Zhang, W. Dayoub, G.-R. Chen, M. Lemaire, Tetrahedron 2012, 68,
7400–7407; k) H. Mimoun, J. Y. D. S. Laumer, L. Giannini, R. Scopelliti, C.
Floriani, J. Am. Chem. Soc. 1999, 121, 6158–6166; l) T. Inagaki, Y.
Yamada, L. Phong, A. Furuta, J. Ito, H. Nishiyama, Synlett 2009, 253;
m) S. Das, D. Addis, S. Zhou, K. Junge, M. Beller, J. Am. Chem. Soc. 2010,
132, 1770–1771; n) C. Bianchini, E. Farnetti, M. Graziani, M. Peruzzini, A.
Polo, Organometallics 1993, 12, 3753–3761; o) S. C. Bart, E. Lobkovsky,
P. J. Chirik, J. Am. Chem. Soc. 2004, 126, 13794–13807; p) S. C. Bart, E. J.
Hawrelak, E. Lobkovsky, P. J. Chirik, Organometallics 2005, 24, 5518–
5527; q) S. Enthaler, G. Erre, M. K. Tse, K. Junge, M. Beller, Tetrahedron
Lett. 2006, 47, 8095–8099; r) C. P. Casey, H. Guan, J. Am. Chem. Soc.
2007, 129, 5816–5817.
[18] N. Dunn, M. Ha, A. Radosevich, J. Am. Chem. Soc. 2012, 134, 11330–
11333.
[19] L. J. Hounjet, C. B. Caputo, D. W. Stephan, Angew. Chem. Int. Ed. 2012,
51, 4714–4717; Angew. Chem. 2012, 124, 4792–4795.
[4] a) X. Verdaguer, U. E. W. Lange, M. T. Reding, S. L. Buchwald, J. Am.
Chem. Soc. 1996, 118, 6784; b) H. Gruber-Woelfler, J. G. Khinast, Organo-
metallics 2009, 28, 2546; c) R. Becker, H. Brunner, S. Mahboobi, W. Wie-
grebe, Angew. Chem. Int. Ed. Engl. 1985, 24, 995; Angew. Chem. 1985,
97, 969; d) B. H. Lipshutz, H. Shimizu, Angew. Chem. Int. Ed. 2004, 43,
2228; Angew. Chem. 2004, 116, 2278; e) K. A. Nolin, R. W. Ahn, F. D.
Toste, J. Am. Chem. Soc. 2005, 127, 12462; f) K. A. Nolin, R. W. Ahn, Y. Ko-
bayashi, J. J. Kennedy-Smith, F. D. Toste, Chem. Eur. J. 2010, 16, 9555.
[5] a) S. Das, S. Zhou, D. Addis, S. Enthaler, K. Junge, M. Beller, Top. Catal.
2010, 53, 979–984; b) S. Das, B. Wendt, K. Mçller, K. Junge, M. Beller,
Angew. Chem. Int. Ed. 2012, 51, 1662–1666; Angew. Chem. 2012, 124,
1694–1698; c) S. Laval, W. Dayoub, A. Favre-Reguillon, M. Berthod, P.
Demonchaux, G. Mignani, M. Lemaire, Tetrahedron Lett. 2009, 50, 7005–
7007; d) A. M. Caporusso, N. Panziera, P. Pertici, E. Pitzalis, P. Salvadori,
G. Vitulli, G. Martra, J. Mol. Catal. A 1999, 150, 275–285; e) D. Addis, S.
Das, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2011, 50, 6004–6011;
Angew. Chem. 2011, 123, 6128–6135; f) T. Murai, T. Sakane, S. Kato, J.
Org. Chem. 1990, 55, 449–453; g) C. Bornschein, S. Werkmeister, K.
Junge, M. Beller, New J. Chem. 2013, 37, 2061–2065.
[6] a) Y. Izumi, N. Yusuke, H. Nanami, K. Higuichi, M. Ohaka, Tetrahedron
Lett. 1991, 32, 4741–4744; b) S. Fukuzumi, M. Fujita, Chem. Lett. 1991,
2059–2062; c) Y. Izumi, M. Onaka, J. Mol. Catal. A Chem. 1992, 74, 35–
42; d) M. Fujita, S. Fukuzumi, J. Otera, J. Mol. Catal. A Chem. 1993, 85,
143–148; e) N. Asao, T. Ohishi, K. Sato, Y. Yamamoto, J. Am. Chem. Soc.
2001, 123, 6931–6932; f) N. Asao, T. Ohishi, K. Sato, Y. Yamamoto, Tetra-
hedron 2002, 58, 8195–8203.
[7] a) M. Onaka, K. Higuchi, H. Nanami, Y. Izumi, Bull. Chem. Soc. Jpn. 1993,
66, 2638–2645; b) M. Hojo, A. Fuji, C. Murakami, H. Aihora, A. Hosomi,
Tetrahedron Lett. 1995, 36, 571–574; c) M. Hojo, C. Murakami, A. Fuji, A.
Hosomi, Tetrahedron Lett. 1999, 40, 911–914; d) F. Le Bideau, C. T, D.
Gourier, J. H nique, E. Samuel, Tetrahedron Lett. 2000, 41, 5215–5218.
[8] a) M. Deneux, I. C. Akhrem, D. V. Avetisson, E. I. Mysoff, M. E. Vol’pin,
Bull. Chim. Soc. Fr. 1973, 2638–2642; b) J. Boyer, R. J. P. Corriu, R. Perz,
C. Reye, J. Organomet. Chem. 1979, 172, 143–152; c) J. Boyer, R. J. P.
Corriu, R. Perz, M. Poirier, C. Reye, Synthesis 1981, 558–559; d) R. J. P.
Corriu, R. Peu, C. Rayl, Tetrahedron 1983, 39, 999–1009; e) D. Yang,
D. D. Tanner, J. Org. Chem. 1986, 51, 2267–2270; f) M. Fujita, T. Hiyama,
J. Org. Chem. 1988, 53, 5405–5415; g) Y. Goldberg, E. Abele, M. Shy-
manska, E. Lukevics, J. Organomet. Chem. 1989, 372, C9–C11; h) Y. Gold-
berg, E. Abele, M. Shymanska, E. Lukevics, J. Organomet. Chem. 1991,
410, 127–133; i) C. Chuit, R. J. P. Corriu, J. C. Young, Chem. Rev. 1993, 93,
1371–1448; j) Y. Kobayashi, E. Takahisa, M. Akano, K. Watatani, Tetrahe-
[20] C. B. Caputo, L. J. Hounjet, R. Dobrovetsky, D. W. Stephan, Science 2013,
341, 1374–1377.
[21] M. Pꢀrez, L. J. Hounjet, C. B. Caputo, R. Dobrovetsky, D. W. Stephan, J.
Am. Chem. Soc. 2013, 135, 18308–18310.
[22] M. Perez, C. B. Caputo, R. Dobrovetsky, D. W. Stephan, Proc. Natl. Acad.
Sci. USA 2014, DOI: 10.1073/pnas.1407484111.
[23] a) M. Sajid, A. Lawzer, W. S. Dong, C. Rosorius, W. Sander, B. Schirmer, S.
Grimme, C. G. Daniliuc, G. Kehr, G. Erker, J. Am. Chem. Soc. 2013, 135,
18567–18574; b) J. C. Pereira, M. Sajid, G. Kehr, A. M. Wright, B. Schirm-
er, Z. W. Qu, S. Grimme, G. Erker, P. C. Ford, J Am Chem. Soc 2014, 136,
513–519; c) M. Sajid, L.-M. Elmer, C. Rosorius, C. G. Daniliuc, S. Grimme,
G. Kehr, G. Erker, Angew. Chem. Int. Ed. 2013, 52, 2243; Angew. Chem.
2013, 125, 2299.
[24] L. Goerigk, S. Grimme, Phys. Chem. Chem. Phys. 2011, 13, 6670–6688.
[25] a) A. E. Reed, P. V. Schleyer, J. Am. Chem. Soc. 1990, 112, 1434–1445;
b) T. H. Dunning Jr, D. E. Woon, J. Leiding, L. Chen, Acc. Chem. Res. 2013,
46, 359–368.
[26] A. Y. Houghton, V. A. Karttunen, C. Fan, W. E. Piers, H. M. Tuononen, J.
Am. Chem. Soc. 2013, 135, 941–947.
[27] L. J. Hounjet, C. B. Caputo, D. W. Stephan, Dalton Trans. 2013, 42, 2629–
2635.
[28] a) R. Ahlrichs, M. Bꢅr, M. Hꢅser, H. Horn, C. Kçlmel, Chem. Phys. Lett.
1989, 162, 165–169; b) R. Ahlrichs, M. K. Armbruster, R. A. Bachorz, M.
Bꢅr, H.-P. Baron, R. Bauernschmitt, F. A. Bischoff, S. Bçcker, N. Crawford,
P. Deglmann, F. D. Sala, M. Diedenhofen, M. Ehrig, K. Eichkorn, S. Elliott,
F. Furche, A. Glçß, F. Haase, M. Hꢅser, C. Hꢅttig, A. Hellweg, S. Hçfener,
H. Horn, C. Huber, U. Huniar, M. Kattannek, W. Klopper, A. Kçhn, C.
Kçlmel, M. Kollwitz, K. May, P. Nava, C. Ochsenfeld, H. ꢆhm, M. Pabst, H.
Patzelt, D. Rappoport, O. Rubner, A. Schꢅfer, U. Schneider, M. Sierka,
D. P. Tew, O. Treutler, B. Unterreiner, M. v. Arnim, F. Weigend, P. Weis, H.
Weiss, N. Winter, TURBOMOLE Vol. TURBOMOLE GmbH, 2012.
[29] J. Tao, J. P. Perdew, V. N. Staroverov, G. E. Scuseria, Phys. Rev. Lett. 2003,
91, 146401.
[30] a) S. Grimme, S. Ehrlich, H. Krieg, J. Chem. Phys. 2010, 132, 154104; b) S.
Grimme, S. Ehrlich, L. Goerigk, J. Comput. Chem. 2011, 32, 1456–1465.
[31] a) A. Schꢅfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 1994, 100, 5829–
5835; b) F. Weigend, M. Hꢅser, H. Patzelt, R. Ahlrichs, Chem. Phys. Lett.
1998, 143, 294; c) F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys.
2005, 7, 3297–3305.
[32] A. Klamt, G. Schꢃꢃrmann, J. Chem. Soc. Perkin Trans. 1 1993, 2, 799.
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
9
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[33] a) K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theor. Chem. Acc.
1997, 97, 119; b) P. Deglmann, K. May, F. Furche, R. Ahlrichs, Chem. Phys.
Lett. 2004, 384, 103.
[34] S. Grimme, Chem. Eur. J. 2012, 18, 9955.
[35] F. Eckert, A. Klamt, COSMOtherm, COSMOlogic GmbH & Co. KG, Leverku-
sen, Germany, 2010.
[36] Y. Zhao, D. G. Truhlar, J. Phys. Chem. A 2005, 109, 5656.
[37] S. Grimme, J. Chem. Phys. 2006, 124, 034108–034116.
[38] F. Weigend, F. Furche, R. Ahlrichs, J. Chem. Phys. 2003, 119, 12753.
[39] a) F. Neese, Comp. Mol. Sci. 2012, 2, 73–78; b) F. Neese, Vol. MPI fꢃr
Chemische Energiekonversion, Mꢃlheim a. d. Ruhr (Germany), 2014.
[40] a) A. Halkier, T. Helgaker, P. Jørgensen, W. Klopper, J. Olsen, Chem. Phys.
Lett. 1999, 302, 437; b) A. Halkier, T. Helgaker, P. Jørgensen, W. Klopper,
H. Koch, J. Olsen, A. K. Wilson, Chem. Phys. Lett. 1998, 286, 243.
[41] C. Riplinger, B. Sandhoefer, A. Hansen, F. Neese, J. Chem. Phys. 2013,
139, 134101.
[42] a) T. H. J. Dunning, J. Chem. Phys. 1989, 90, 1007–1023; b) D. E. Woon,
T. H. J. Dunning, J. Chem. Phys. 1993, 98, 1358–1371.
Received: December 4, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
10
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Proceed with cation: The electrophilic
phosphonium salt, [(C6F5)3PF][B(C6F5)4],
catalyses the efficient hydrosilylation of
ketones, imines and nitriles at room
temperature. In the presence of this cat-
alyst, adding one equivalent of hydrosi-
lane to a nitrile yields a silylimine prod-
uct, whereas adding a second equiva-
lent produces the corresponding disilyl-
amine.
&
Hydrosilylation
M. Pꢀrez, Z.-W. Qu, C. B. Caputo,
V. Podgorny, L. J. Hounjet, A. Hansen,
R. Dobrovetsky, S. Grimme,*
D. W. Stephan*
&& – &&
Hydrosilylation of Ketones, Imines and
Nitriles Catalysed by Electrophilic
Phosphonium Cations: Functional
Group Selectivity and Mechanistic
Considerations
Chem. Eur. J. 2015, 21, 1 – 11
www.chemeurj.org
11
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ