Hydrosilylation of Carbonyl Compounds Catalyzed by a Nickel Complex Bearing a PBP Ligand

Article abstract of DOI:10.1002/ejic.202100425

The efficient catalytic hydrosilylation of ketones and aldehydes has been investigated using a nickel pincer hydride complex supported by a diphosphino-boryl ligand (PBP). It was found that the presence of the boryl group within the skeleton of the ligand has a beneficial effect on the catalytic activities observed for ketones compared to related pincer systems. The analysis of the reaction mechanism allows for the synthesis and characterization of a nickel alkoxide derivative by insertion of the carbonyl moiety into the Ni?H bond. Combined experimental and theoretical analysis (DFT) support a reaction mechanism that involves the initial formation of an alkoxide complex followed by reaction with the silane to release the corresponding silyl ether and regenerate the catalyst.

Full text of DOI:10.1002/ejic.202100425

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Hydrosilylation of Carbonyl Compounds Catalyzed by a
Nickel Complex Bearing a PBP Ligand
José Antonio Fernández,[a] Juan Manuel García,[a] Pablo Ríos,[a] and Amor Rodríguez*[a]
Dedicated to the memory of Professor Víctor Riera
The efficient catalytic hydrosilylation of ketones and aldehydes
has been investigated using a nickel pincer hydride complex
supported by a diphosphino-boryl ligand (PBP). It was found
that the presence of the boryl group within the skeleton of the
ligand has a beneficial effect on the catalytic activities observed
for ketones compared to related pincer systems. The analysis of
the reaction mechanism allows for the synthesis and character-
ization of a nickel alkoxide derivative by insertion of the
carbonyl moiety into the NiÀ H bond. Combined experimental
and theoretical analysis (DFT) support a reaction mechanism
that involves the initial formation of an alkoxide complex
followed by reaction with the silane to release the correspond-
ing silyl ether and regenerate the catalyst.
Introduction
nates the field, whereas studies with other metals such as nickel
are less common.[6–22]
Reduction of carbonyl compounds, mainly aldehydes and
ketones, into their respective primary or secondary alcohols, is a
fundamental reaction in organic chemistry that finds numerous
applications in the pharmaceutical and cosmetic industries.[1]
Consequently, in the last decades an intense search for different
catalytic methodologies that effectively achieve this trans-
formation has taken place.[2] Although the hydrogenation of
CÀ O bonds using high pressure of H2 gas or by means of
hydrogen transfer reactions using alcohols as the source of
hydrogen are the preferred procedures by industry,[3] the
homogeneous catalytic hydrosilylation represents a valuable
strategy for the synthesis of alcohols under milder reaction
conditions. This two-step process allows the addition of a SiÀ H
bond to a carbonyl group to generate a silyl ether that, after
hydrolysis, provides the corresponding alcohol. Still, the silyl
group may also behave as a protecting group that facilitate
different protocols in organic synthesis.[4] To date, most reports
on catalytic hydrosilylation have been focused on precious
metals such as Ru, Rh, Ir or Pt;[2] however the scarcity and high
cost of these metals press the need for cheaper and more
abundant alternatives. Accordingly, over the past decade, we
have witnessed the development of efficient catalysts based on
first-row transition metals,[5] being iron the metal that domi-
In 2009 Guan et al. reported one of the first studies on
nickel-catalyzed hydrosilylation of aldehydes employing
a
POCOP pincer hydride complex that, on the other hand,
exhibited low catalytic activity and only partial hydrosilylation
of ketones.[8] Shortly after, Mindiola and coworkers tested a
nickel complex supported by an amido-phosphino ligand that
demonstrated increased efficiency in the reduction of ketones.[9]
In 2012, two different papers, by the groups of Royo and
Ritleng, appeared simultaneously using N-Heterocyclic carbene
complexes of nickel that are active for the reduction of both,
aldehydes and ketones, with remarkable catalytic activity.[11,12]
More recently, the family of carbene ligands employed in
hydrosilylation reactions was expanded using a variety of
systems based on triazolylidene bearing different hemilabile
groups containing donor atoms (N, S, O or P) and two
independent papers by Albrecht and Ritleng reported highly
efficient nickel-based catalysts for the hydrosilylation of
aldehydes with comparable catalytic activities at room
temperature.[15,16] To our knowledge, apart from Guan’s catalyst,
only three nickel pincer complexes have been tested in the
catalytic hydrosilylation of aldehydes or ketones (Fig-
ure 1).[8,10,21,22] It is worth mentioning that all these catalysts
proved to be quite active for the hydrosilylation of aldehydes,
being Guan’s system the most active one, but showed very low
(if any) catalytic activity with ketones.
[a] J. Antonio Fernández, J. Manuel García, P. Ríos, Dr. A. Rodríguez
Instituto de Investigaciones Químicas-Departamento de Química Inorgánica
Centro de innovación en Química Avanzada (ORFEO-CINQA)
Universidad de Sevilla-Consejo Superior de Investigaciones Científicas
Calle Américo Vespucio 49, 41092, Seville, Spain
E-mail: marodriguez@iiq.csic.es
https://sconejero.wixsite.com/amorysalva-chemistry
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202100425
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© 2021 The Authors. European Journal of Inorganic Chemistry published by
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reproduction in any medium, provided the original work is properly cited.
Figure 1. Previously reported nickel pincer catalysts for the hydrosilylation of
aldehydes and ketones.
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Recently, we have reported the synthesis of a nickel hydride
(Scheme 2). We found the best catalyst performance using
5 mol% of 1 in C6D6, employing Ph2SiH2 as reductant at room
temperature (Table 1). Different conditions such as triethylsi-
lane, Me2PhSiH or poly(methylhydrosiloxane) (PMHS) as reduc-
tants, or THF or pure silane as solvent did not translate into
greater catalytic activity even at higher temperatures. PhSiH3
leads to fast conversions (1 h at RT) but mixtures of PhSiH2(OBn)
and PhSiH(OBn)2 were obtained (product distribution 75:25).
Reducing the amount of nickel to 2.5 or 1 mol% increased the
reaction time to 12 and 24 h, respectively. Increasing the
complex supported by a pincer diphosphino-boryl ligand (1)
that turned out to be a very efficient catalyst for the highly
selective hydrosilylation of CO2 to bis(silyl)acetal derivatives,
using B(C6F5)3 as co-catalyst (Scheme 1).[23] We reasoned that the
strong σ-donor properties along with the high trans-influence
of the boryl ligand in 1 could increase the nucleophilic
character of the hydride group which might translate into a
high catalytic efficiency for the reduction of CÀ O bonds.[24,25] In
fact, the results reported by Guan et al[8] and Jones et al,[10]
using POCOP- and PONOP-pincer nickel hydride complexes for
the hydrosilylation of aldehydes support this hypothesis (Fig-
ure 1). In these systems, as expected, a high trans-influence
ligand such as a carbon-based donor eases the insertion of the
carbonyl functionality while the nitrogen-based ligand reacts
slowly.
°
temperature to 50 C decreases the reaction time to 3.5 h,
however, since the catalytic studies reported by Guan were
performed at room temperature, we decided to carry out this
study at the same temperature to compare both systems.
Using the optimized reaction conditions, both aliphatic
aldehydes as well as benzaldehydes having substituents with
different electronic effects at the para position of the phenyl
ring, were tested (Table 2). Cyclohexylcarbaldehyde was readily
reduced to the hydrosilylated product after only 3.5 h (Table 2,
entry 1). Benzaldehydes substituted with both electron-donat-
ing and electron-withdrawing groups are all reduced in
Results and Discussion
Bearing in mind these previous results, as a first approach to
test the catalytic behavior of 1, we analyzed the reduction of
benzaldehyde under several experimental conditions
excellent
yields.
Hydrosilylation
of
4-dimeth-
ylaminobenzaldehyde was completed after 3.5 h while p-
anisaldehyde and 4-chlorobenzaldehyde required 9 h and 24 h
respectively for completion (Table 2, entries 3–5). The catalyst
was not affected by using the halogenated derivative and no
decomposition was observed. Similarly to the results reported
by Guan, the substituents on the phenyl ring do affect the
kinetics of the reaction, requiring longer reaction times when
electro-withdrawing groups are used. A potential explanation
Scheme 1. Reactivity of complex 1 with CO2.
Table 2. Nickel catalyzed hydrosilylation of aldehydes.
Entry[a]
Substrate
Time [h]
Conversion
[%][b]
Yield
[%]
Scheme 2. Nickel catalyzed hydrosilylation of benzaldehyde.
1
2
a
3.5
9
>99
>99
68
64
Table 1. Optimization of the reaction conditions for the hydrosilylation of
benzaldehyde.
b
Entry[a]
Catalyst
[mol%]
Silane
Time [h]
Conversion [%][b]
1
2
5
2.5
1
5
5
5
5
5
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Et3SiH
Et3SiH
Et3SiH
Me2PhSiH
PMHS
PhSiH3
9
>99
>99
>99
>99
0
0
0
3
4
5
c
3.5
9
>99
>99
>99
81
60
63
12
24
3.5
15
2
2
2
3
4[c]
5
d
e
6[c]
7[d]
8[d]
9[d]
10
0
5
5
10
1
0
24
[e]
[a] Reaction conditions: benzaldehyde (1 mmol); silane (1 equivalent), C6D6
(0.4 ml), RT. [b] Conversions determined by crude 1H NMR. [c] Reaction
[a] Reaction conditions: aldehyde (0.196 mmol); silane (1 equivalent), C6D6
(0.4 ml), RT. [b] Conversions determined by 1H NMR of the reaction
mixture.
°
°
performed at 50 C. [d] Reactions performed at 70 C. [e] mixture of PhSiH
(OBn)2 and PhSiH2(OBn) was obtained (product distribution 75:25).
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to this phenomenon may lie on the stabilization of some
Table 3. Nickel catalyzed hydrosilylation of ketones.
intermediate species (vide infra).
However, comparison of 1 with Guan’s catalyst revealed a
superior catalytic activity in hydrosilylation of aldehydes for the
latter (0.2 mol% catalyst loading and 2 h at RT for the reduction
of benzaldehyde to obtain the corresponding alcohol in 79%
yield vs 68% yield in 3.5 h using 5 mol% of catalyst loading
with our system).[8] Other systems, for example the Royo's
catalyst, yields 89% of the alcohol at room temperature in 5
minutes using 1 mol% of catalyst. Although, our results in the
hydrosilylation of aldehydes were not remarkable, we consid-
ered of interest to explore the hydrosilylation of ketones.
Usually, ketones are viewed as more challenging substrates due
to the greater steric hindrance around the carbonyl group
compared to aldehydes. For instance, the nickel catalyst
reported by Albrecht et al. has no catalytic activity towards
ketones but is extremely active towards aldehydes.[15] In line
with this, harsher reaction conditions and/or lower catalytic
activities compared to those for the reduction of aldehydes,
were reported for all of the nickel catalysts previously
described.
Entry[a]
Substrate
Time [h]
Conversion
[%][b]
Yield
[%]
1
2
f
6
>99
>99
50
56
50
37
g
h
6.5
3
4
24
5
i
j
>99
>99
67
54
Gratifyingly, reduction of acetophenone was readily com-
5
1
°
pleted in 6 h at 70 C using 5 mol% of catalyst (Table 3, entry 1).
It must be mentioned that the same catalytic reaction using
Guan’s nickel catalyst required extended reaction times to
6
7
k
l
10
>99
>99
72
47
°
obtain a conversion of 18% (24 h at 70 C) with 1 mol% catalyst
loading.[8c] In our case, 92% conversion was obtained after 13 h
4.5
°
at 70 C using 1 mol% catalyst loading. The substrate scope of
this reaction was then investigated, and the results are
presented on Table 3. We analyzed a variety of acetophenone
derivatives presenting different substituents on the para-
position of the phenyl ring. We found that while 4‘-meth-
oxyacetophenone was rapidly reduced in 5 h, the CF3 sub-
stituted analogue required longer reaction times (Table 3,
entries 2–4). Only 50% conversion was observed after 24 hours
8
9
m
n
6
>99
46
–
24
50
°
at 70 C when 4-acetylbenzonitrile was employed. In addition,
other aliphatic (2-hexanone; 4-phenylbutan-2-one), cyclic (cyclo-
hexanone; α-tetralone) and heteroaromatic ketones (2-acetylth-
iophene; 2-acetylpyridine) were also studied under the same
conditions. Cyclohexanone was hydrosilylated in only 1 h
(Table 3, entry 5) while the reduction of α-tetralone, 2-hexanone
and 4-phenylbutan-2-one (Table 3, entries 6–8) required from
4.5 to 10 hours to reach completion. The reduction of 2-
acetylthiophene proceeded slowly and only 50% of the
10
o
p
q
12
2
–
–
–
–
11[c,d]
Mixture[d]
Mixture[d]
12[c,d]
5
°
corresponding silyl ether was obtained after 24 h at 70 C
(Table 3, entry 9). No hydrosilylation was observed for 2-
acetylpyridine (Table 3, entry 10). Finally, analysis of α,β-unsatu-
rated ketones (trans-4-phenyl-3-buten-1-one and 2- cyclohexen-
1-one) ended up giving a mixture of reduction products of both
[a] Reaction conditions: ketone (0.196 mmol); Ph2SiH2 (1 equivalent), C6D6
(0.4 ml), 70 C. [b] Conversions determined by 1H NMR of the reaction
°
mixture. [c] 2 equivalents of Ph2SiH2 were used. [d] >99% conversion by
1H NMR. See ref. [26].
alkene and carbonyl functionalities (Table 3, entries 11–12).[26]
A
comparative analysis of the data previously reported positioned
our catalyst among the most active nickel catalysts for hydro-
silylation of ketones in terms of conversions but, in general, the
isolated yields of the corresponding alcohols are lower that
what has been observed using other well defined nickel
catalysts.,[11][12] However, it is important to mention that many
variables have to be considered when comparing two different
catalytic systems (temperature, catalyst loading, reaction time,
…..) so an accurate comparison cannot be made.
With these experimental results in hand, we were interested
on the mechanism of this reaction. Different pathways that can
be operative in metal-catalyzed aldehyde and ketone hydro-
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silylation reactions have been described. In most of the cases, a
group very nucleophilic.[25] Furthermore, treatment of a solution
of the nickel deuteride complex [(PBP)NiÀ D] (1-D) (prepared by
reaction of tBu(PBP)NiMe with 2 bar of D2) with 4 equivalents of
benzaldehyde leads to the formation of a mixture (1:2) of
complex [(PBP)Ni-OCH2Ph] (2) and [(PBP)Ni-OCHDPh] (2-D)
proving the existence of an equilibrium that interconverts the
benzyloxide and the hydride nickel complexes. In fact, β-
hydrogen elimination processes are frequently observed in
nickel alkoxide complexes and constitutes a common decom-
position pathway, however the stability of these species seems
to be associated to the reactivity of the nickel hydride complex
more than to the β-hydrogen elimination process itself.[28] Then,
we confirmed that complex 2 reacts slowly with Ph2SiH2 at
room temperature to produce PhCH2OSiHPh2 and nickel
hydride complex 1 (Scheme 3). Additionally, we conducted a
second experiment consisting of the stoichiometric reaction of
benzaldehyde with Ph2SiH2 and 1 in a 1:1:1 ratio. Monitoring
metal hydride mechanism, based on the initial carbonyl insertion
into the metal-hydride bond to give an alkoxide, is postulated.
However, other possibilities based on a non-hydride mechanism
have also been demonstrated. Recently, Nikonov and co-work-
ers reported a series of labeling experiments to certainly
discriminate between the hydride mechanism (commonly
accepted) and the non-hydride one.[27] To find experimental
evidence to distinguish between different pathways, we studied
the stoichiometric reaction between complex 1 and benzalde-
hyde (Scheme 3).
We observed the rapid insertion of the carbonyl group into
the NiÀ H bond to form a new complex 2 that shows a signal at
4.7 ppm in the 1H NMR spectrum that correlates with a signal in
the 13C NMR spectrum at 72.9 ppm, attributable to the meth-
ylene fragment of a benzyloxide group.[8] The 31P and 11B NMR
spectra exhibit signals (δ31P 82.1 ppm; δ11B 38 ppm) at a higher
field than those observed for 1 (See Experimental Section). This
result, in accordance with a hydride mechanism, is not
surprising considering the strong σ-donor properties and high
trans-influence of the boryl group that renders the hydride
1
the progress of this reaction by H and 31P NMR allowed us to
observe, initially, the formation of 2 followed by the slow
release of the silyl ether and formation of 1 (See ESI). In order to
get more information about this catalytic process, we per-
formed a DFT analysis of the hydrosilylation of benzaldehyde
catalyzed by 1 using the PBE0/def2TZVP/def2QZVP level of
theory, including Grimme’s D3 (PBE0-D3) dispersion correction
(see ESI for more information and references).[29] The overall
Gibbs free energy profile is represented on Figure 2, using
complex 1, benzaldehyde and diphenylsilane as energy refer-
ence. The first step of the catalytic cycle involves the insertion
of the aldehyde C=O group into the nickel-hydride bond via
TS1 (18.9 kcalmolÀ 1) to afford nickel alkoxide complex 2 which
Scheme 3. Reactivity studies of 1 with benzaldehyde and Ph2SiH2; *
conversion determined by 1H NMR spectroscopy.
Figure 2. Gibbs energy profile in benzene for the reaction of 1 with Ph2SiH2 and benzaldehyde. Relative Gibbs energies at 298 K and 1 M in kcalmolÀ 1. The
phosphine groups (PtBu2) have been abbreviated as P for clarity.
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is 7.6 kcalmolÀ 1 more stable than the origin. Then, Ph2SiH2
interacts with 2 through TS2 (16.9 kcalmolÀ 1), and this step is
associated to the highest energy barrier (24.5 kcalmolÀ 1) of the
whole process. Lastly, from TS2, the resulting silyl ether product
is released, and the nickel hydride complex is regenerated,
closing the catalytic cycle. The values extracted from this
theoretical analysis are consistent with the experimental
observations: i) during the catalytic reaction 2 was the only
nickel species observed by NMR spectroscopy at room temper-
ature; ii) the formation of 2 is instantaneous at room temper-
ature while the hydrosilylation step requires several hours to
reach completion.
received. Solution NMR spectra were recorded on Bruker DRX-400
spectrometer and they were referenced to external SiMe4 (δ 0 ppm)
using the residual protio solvent peaks as internal standard (1H
NMR experiments) or the characteristic resonances of the solvent
nuclei (13C NMR experiments). 11B NMR spectra were referenced to
an external standard of BF3·Et2O. 31P NMR chemical shifts were
referenced to an external 85% solution of H3PO4 in the adequate
solvent. NiBr2(dme) was purchased from Aldrich and used as
received. [(tBuPBP)NiBr], [(tBuPBP)NiMe] and [(tBuPBP)NiH] (1) were
prepared as previously described.[21]
Synthetic procedures
Finally, we have investigated the electronic effect of the
substituents in the para position of the aryl fragment calculat-
ing the energy profile for this reaction with p-NO2-benzalde-
hyde and p-NMe2-benzaldehyde (See ESI).The insertion of the
CÀ O bond into the NiÀ H bond to form the corresponding
alkoxide complex is exergonic in both cases (ΔG=À 12.7 and
À 1.4 kcalmolÀ 1 respectively) and the activation energy is lower
for the aldehyde bearing the more electrophilic carbonyl carbon
(Ea(NO2)=15.4 vs Ea(NMe2)=25.6 kcalmolÀ 1) which is in accord-
ance with a mechanism involving a nucleophilic hydride
addition. The second step, the hydrosilylation of the alkoxide
complex, requires higher activation barriers than the first step,
as observed for benzaldehyde, though the reaction is facilitated
by electron-donor substituents on the para position (Ea(NMe2)=
23.5 vs Ea(NO2)=25.3 kcalmolÀ 1) that increase the nucleophilic
character of the alkoxide species easing the reaction towards
Ph2SiH2. These numbers are consistent with the experimental
observations (See Table 2 and Table 3).
Catalytic reactions and Spectroscopic Characterization Data for
the Alcohol Products
In a glove box, the corresponding aldehyde or ketone and Ph2SiH2
were added (first the carbonyl derivative (0.196 mmol) followed by
the silane (0.196 mmol) to a J. Young NMR tube containing a
solution of 1 (0.0098 mmol) in 400 μL of C6D6. Then, the tube was
sealed, and the reaction progress was monitored by 1H NMR
spectroscopy. The catalytic hydrosilylation reaction was performed
°
at room temperature for aldehydes and at 70 C for ketones. The
conversion was determined by 1H NMR. Once the reaction was
completed, the solution was treated with a THF solution of TBAF
(200 μl, 0.2 mmol) and stirred at room temperature for 15 minutes.
Then, the volatiles were removed under vacuum and 5 mL of water
were added. The organic product was extracted with diethyl ether
(2 x 6 mL). The combined organic layers were dried over anhydrous
MgSO4, filtered and the solvent was removed under reduce
pressure. The alcohol products with high boiling points were
purified by short silica gel column chromatography using ethyl
acetate-hexanes mixtures (5 to 10%). Those alcohols with low
boiling points were purified by distillation. All the alcohol products
have been characterized by 1H NMR and the spectroscopic data
were identical to previously reported data (See ESI for details).
Conclusion
Synthesis and NMR characterization of [tBu(PBP)Ni(OCH2Ph)]
(2)
Our catalytic studies indicate that, by using a pincer ligand with
a boryl group at the central atom, the enhanced nucleophilic
character of the hydride group trans to it facilitates the
hydrosilylation of ketones compared to other analogous pincer
systems. On the contrary, our system proved to be less active
for the hydrosilylation of aldehydes. We observed that both
aromatic and aliphatic substrates are easily reduced to the
corresponding silyl ether being the latter more efficiently
reduced that the former. Electron-donating groups on the para
position of the aryl ring increase the rate of the reaction while
no conversion was observed with ketones bearing heteroar-
omatic substituents such as pyridine or thiophene. Both DFT
analysis and the experimental observations point to a hydride
mechanism for the hydrosilylation of aldehydes and ketones.
Complex 2 was prepared following a slightly modified procedure to
that previously reported by our group: (11 mg, 0.02 mmol) of
[
tBu(PBP)NiMe] were dissolved in 400 μL of C6D6 in a J. Young valve
NMR tube, then the tube was degassed via three freeze-pump-thaw
°
cycles, charged with H2 (4 bar) and heated at 70 C for 4 hours. After
checking by 1H and 31P {1H} NMR spectroscopy that the reaction
was completed, the tube was degassed again and 2.2 μL
1
(0.02 mmol) of benzaldehyde were added at room temperature. H
and 31P{1H} NMR spectra confirmed the instantaneous and clean
formation of complex 2. Attempts to purify it or isolate it led to its
1
3
decomposition. H NMR (400 MHz, C6D6): 1.28 (t, JHP =6.4 Hz, 36H,
tBu); 3.49 (s, 4H, NCH2); 5.35 (s, 2H, OCH2); 6.87 (dd, (3JHH =6 Hz, JHH
4
=3 Hz, CH aromatic); 7.09 (dd, (3JHH =6 Hz, 4JHH =3 Hz, CH aromatic);
3
3
7.18 (t, JHH =8 Hz; p-CH phenyl); 7.40 (t, JHH =8 Hz; m-CH phenyl);
7.80 (t, JHH =8 Hz; o-CH phenyl). 31P{1H} (162 MHz, C6D6): 82.1 ppm;
3
11B{1H} (128 MHz, C6D6): 38 ppm; 13C{1H} (100 MHz, C6D6): 29.3 (s, tBu-
3
t
3
CH3); 34.4 (t, JCP =4.5 Hz, BuÀ Cq); 39.8 (t, JCP =18.5 Hz, NCH2); 72.9
(s, OCH2); 107.9 (s, CH aromatic-PBP); 118.2 (s, CH aromatic-PBP);
124.8 (s, CH aromatic-Ph); 126.2 (s, CH aromatic-Ph); 133.5 (s,
CqÀ Ph); 139.2 (s, Cq aromatic-PBP).
Experimental Section
General: All manipulations were carried out using standard Schlenk
and glove box techniques under an atmosphere of argon or of high
purity nitrogen, respectively. All solvents were dried and degassed
prior to use. Benzene-d6 (C6D6) was distilled under argon over
sodium and then degassed and dried over 4 Å molecular sieves. All
other compounds were commercially available and were used as
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Patai, Z. Rappoport), Wiley, Chichester, 1989.
[3] H.-U. Blaser, C. Malan, B. Pugin, F. Spindler, H. Steiner, M. Studer, Adv.
Synth. Catal. 2003, 345, 103.
[4] a) R. D. Crouch, Synth. Commun. 2013, 43, 2265–2279; b) R. D. Crouch,
Tetrahedron 2013, 69, 2383–2417.
Experimental procedure for the NMR tube reaction of 2with
Ph2SiH2
2.2⊥⊥μL (0.02 mmol) of benzaldehyde were added at room temper-
ature to a solution of 0.02 mmol of complex 1 in 400 μL of C6D6 in a
J. Young NMR tube (prepared as indicated in the previous section).
1H and 31P{1H} NMR spectra confirmed the instantaneous and clean
formation of complex 2. Then 4 μL (0.02 mmol) of Ph2SiH2 were
[5] For selected reviews, see: hydrosilylation with Mn: a) R. J. Trovitch, Acc.
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Fernández, ACS Catal. 2019, 9, 5400; d) D. Wei, C. Darcel, Chem. Rev.
2019, 119, 2550; General reviews about catalytic hydrosilylation with
First Row Transition Metals: e) M. Bhunia, S. P. S. K. Mandal, Coord.
Chem. Rev. 2020, 405, 213110; f) B. Royo, Advances in Organometallic
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1
added and the reaction progress was monitored by H NMR. After
4 hours at room temperature, the 1H NMR spectrum showed the
formation of the corresponding silyl ether (PhCH2OSiPh2H) along
with nickel hydride complex 1 (40%). After 9 hours at room
temperature 2 was completely transformed into 1.
Stoichiometric reaction between 1and an equimolar mixture
of Ph2SiH2 and benzaldehyde
A solution of an equimolar mixture of Ph2SiH2 and benzaldehyde in
100 μL of C6D6 [4 μL of Ph2SiH2 (0.02 mmol) and 2.2 μL of
benzaldehyde (0.02 mmol)] were added at room temperature to a
solution of 0.02 mmol of complex 1 in 400 μl of C6D6 in a NMR J.
Young tube (prepared as indicated in the previous section). The
1
reaction progress was followed by H NMR. After 5 minutes 1 was
fully transformed into complex 2 and the formation of a very small
amount of the corresponding silyl ether (Ph2HSiOCH2Ph) was
observed along with the presence of unreacted Ph2SiH2. After
9 hours at room temperature, Ph2SiH2 was completely consumed
and complex 2 was transformed into 1.
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Acknowledgements
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Financial support (FEDER contribution) from the MINECO (Projects
PID2019-109312GB-IOO and RED2018-102387-T), the CSIC (AEPP-
CTQ2016-76267-P) and the use of computational facilities of the
Supercomputing Center of Galicia (CESGA) is gratefully acknowl-
edged.
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metallics 2012, 31, 8225; b) S. Chakraborty, P. Bhattacharya, H. Dai, H.
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Conflict of Interest
[25] J. Zhu, Z. Lin, T. B. Marder, Inorg. Chem. 2005, 44, 9384.
[26] For substrate p and q: A mixture of products was obtained and the
disappearance of the characteristic olefinic resonances and those
corresponding to the starting materials was observed but not further
purification was done.
The authors declare no conflict of interest.
Keywords: Boron
· Carbonyl compounds · Homogeneous
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catalysis · Hydrosilylation · Nickel
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Gaussian 09, Revision E.01, Gaussian, Inc, Wallingford CT, 2013, the full
Gaussian citation can be found in the ESI.
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Manuscript received: May 16, 2021
Revised manuscript received: June 22, 2021
Accepted manuscript online: June 23, 2021
Eur. J. Inorg. Chem. 2021, 2993–2998
www.eurjic.org
2998
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH