Alkene Hydrosilylation Using Tertiary Silanes with α-Diimine Nickel Catalysts. Redox-Active Ligands Promote a Distinct Mechanistic Pathway from Platinum Catalysts

Article abstract of DOI:10.1021/acscatal.6b01134

Combination of the readily available α-diimine ligand, ((ArN=C(Me))₂ Ar = 2,6-ⁱPr₂-C₆H₃), (^iPrDI) with air-stable nickel(II) bis(carboxylates) generated a highly active catalyst exhibiting anti-Markovnikov selectivity for the hydrosilylation of alkenes with a variety of industrially relevant tertiary alkoxy- and siloxy-substituted silanes. A combination of the method of continuous variations with stoichiometric studies identified the formally Ni(I) hydride dimer, [(^iPrDI)NiH]₂ as the nickel compound formed following reduction of the carboxylate ligands. For the hydrosilylation of 1-octene with (EtO)₃SiH, a rate law of [Ni]^1/2[1-octene][(EtO)₃SiH] in combination with deuterium-labeling studies establish dissociation of the nickel hydride dimer followed by fast and reversible alkene insertion into (^iPrDI)NiH, consistent with turnover-limiting C-Si bond formation. The hydrosilylation of 1-octene with triethoxysilane, a reaction performed commercially in the silicones industry on a scale of >5000000 kg/year, was conducted on a 10 g scale with 96% yield and >98% selectivity for the desired product. Silicone cross-linking, another major industrial application of homogeneous hydrosilylation, was also demonstrated using the air-stable nickel and ligand precursors.

Full text of DOI:10.1021/acscatal.6b01134

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Letter
Alkene Hydrosilylation using Tertiary Silanes with #-
Diimine Nickel Catalysts. Redox-Active Ligands Promote
a Distinct Mechanistic Pathway from Platinum Catalysts.
Iraklis Pappas, Sean Treacy, and Paul J. Chirik
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b01134 • Publication Date (Web): 24 May 2016
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ACS Catalysis
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Alkene Hydrosilylation Using Tertiary Silanes With α-Diimine
Nickel Catalysts. Redox-Active Ligands Promote a Distinct
Mechanistic Pathway From Platinum Catalysts.
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Iraklis Pappas, Sean Treacy, and Paul J. Chirik*
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Department of Chemistry, Frick Laboratory, Princeton University, Princeton, New Jersey, 08544, United States
Supporting Information Placeholder
likely arise from Pt nanoparticles formed from catalyst decomposi-
ABSTRACT: Combination of the readily available α-diimine ligand,
1
1
i
iPr
tion. For catalysts with earth abundant transition metals to be consid-
ered as practical alternatives to current platinum technology emphasis
should be placed on those compounds that are reactive toward com-
mercially relevant silanes and siloxanes, promote the hydrosilylation of
internal alkenes to terminally functionalized products and are easily
prepared and handled.
((ArN=C(Me))
2
Ar = 2,6- Pr
2
-C
6
H
3
), ( DI) with air-stable nickel(II)
bis(carboxylates) generated a highly active catalyst exhibiting anti-
Markovnikov selectivity for the hydrosilylation of alkenes with a variety
of industrially-relevant tertiary alkoxy- and siloxy-substituted silanes. A
combination of the method of continuous variations with stoichio-
metric studies identified the formally Ni(I) hydride dimer,
iPr
[
( DI)NiH]
2
as the nickel compound formed following reduction of
the carboxylate ligands. For the hydrosilylation of 1-octene with
Chalk-Harrod:
Si]-H
R
1/2
R
(
EtO)
3
SiH, a rate law of [Ni] [1-octene][(EtO)
3
SiH] in combina-
[Si]
[Si]
[
Si]
[Si]
[Si]
[
[
M]
[M]
[M]
[M]
[M]
tion with deuterium labeling studies establish dissociation of the nickel
-
[M]
[M]
H
H
R
R
hydride dimer followed by fast and reversible alkene insertion into
Modified Chalk-Harrod:
R
iPr
(
DI)NiH, consistent with turnover limiting C-Si bond formation.
[Si]
[M]
R
R
The hydrosilylation of 1-octene with triethoxysilane, a reaction per-
formed commercially in the silicones industry on a scale of >5,000,000
kg/year, was conducted on a 10 g scale with 96 % yield and >98 %
selectivity for the desired product. Silicone crosslinking, another major
industrial application of homogenous hydrosilylation, was also demon-
strated using the air-stable nickel and ligand precursors.
[
Si]
[Si]
[
Si]-H
R
[M]
[M]
-
H
H
H
R
This Work:
M]
[
H
Chain Walking
[
Si]
H-[Si]
+
R
[M]
[M]
R1
-[M]-H
R
R1
R
KEYWORDS: nickel, silicone, hydrosilylation, diimine, car-
boxylate, hydride, mechanism
Figure 1. Comparison of Chalk-Harrod, modified Chalk-Harrod, and
the mechanistic pathway likely operative in this work.
1
2
The hydrosilylation of alkenes with tertiary silanes promoted by
Based on periodicity, nickel has long been recognized as inexpen-
sive and terrestrially abundant alternative to platinum. The nickel ana-
log of Karstedt’s catalyst, Ni {[(CH =CH)SiMe ] O} as well as other
platinum catalysts such as Pt
2
{[(CH
2
=CH)SiMe
2
]
2
O}
3
(Karstedt’s
catalyst) and H PtCl ·6H O (Speier’s catalyst) is an enabling technol-
2
6
2
2
2
2
2
3
ogy in the silicones industry used in the manufacture of release coat-
ings, adhesives, surfactants, moldings, and other consumer products.1
Discovery of practical catalysts based on earth abundant metals is a
long-standing challenge owing to the high cost and deleterious envi-
common nickel precursors such as Ni(COD) and Ni(acac) (COD =
2
2
1,5-cyclooctadiene; acac = acetylacetonate) promote dehydrogenative
silylation.13 More recent efforts have focused on nickel(II) complexes
1
4
15
16
17
18
bearing indenyl, allyl, phosphine, amido, salicylaldiminato (sp),
2
19
20
ronmental profile associated with platinum mining. Highly active and
naphthyridine diimine (NDI), and anionic pincer-type ligands for
catalytic alkene hydrosilylation. Notably, Hu and coworkers have re-
cently described a nickel catalyst with broad substrate scope and excel-
3
4
selective iron and cobalt catalysts have been reported but many lack
the robustness, ease of handling, and air stability associated with plati-
num. In cases where air stable metal precursors are used, catalyst acti-
vation with reactive borohydride, alkyl lithium or Grignard reagents is
20a
lent selectivity for olefin hydrosilylation using Ph SiH . Despite the
2
2
successful demonstration of anti-Markovnikov addition, all of these
catalysts utilize primary or secondary silanes; commercially relevant
and less expensive tertiary silanes produced either no reaction or lead
5
required. Often these highly reducing activators are incompatible with
trialkoxysilanes promoting disproportionation to silicates and pyro-
6
21
phoric silane gas.
to significant quantities of dehydrogenative silylation products. The
presence of residual Si-H bonds decreases product stability and hence
commercial utility. Here we describe nickel catalysts derived from
straightforward combination of a readily available and inexpensive α-
diimine ligand with nickel(II) bis(carboxylates) that generate a rare
example of a highly active and anti-Markovnikov selective catalyst for
the hydrosilylation of terminal alkenes with tertiary silanes. All of the
catalyst precursors are air stable and no exogeneous reductants or acti-
vators are required, representing a significant advance in hydrosilyla-
tion catalysis with earth abundant transition metals. Determination of
the rate law, isolation of a nickel hydride complex and deuterium label-
Mechanistic studies on industrially preferred Karstedt’s catalyst es-
tablished the so-called Chalk-Harrod pathway whereby rate limiting
olefin insertion into a Pt-H is followed by relatively rapid C-Si bond
7
formation (Figure 1). In this pathway, the platinum catalyst operates
by a Pt(0)-Pt(II) redox couple with the reduced platinum species stabi-
8
lized by alkene ligands. An alternative possibility, dubbed the modified
9
Chalk-Harrod pathway invokes insertion into a metal-silyl and is often
implicated in catalytic dehydrogenative silylation reactions.10 With
platinum catalysts, competing alkene isomerization is deleterious as the
internal olefin byproducts are unreactive toward hydrosilylation and
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ACS Catalysis
Page 2 of 5
iPr
ing experiments support a metal-hydride pathway that is distinct from
ward in situ protocol using 1 mol% each of Ni(2-EH) and ( DI) in a
2
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the mechanism established in platinum catalysis and highlights the
chemistry enabled with redox-active ligands.
neat mixture of 1-octene and the appropriate silane at 23 ºC and in all
cases reached complete conversion (Figure 2).
Given the industrial importance of the hydrosilylation of 1-octene
1 mol% iPrDI
with (EtO)
3
SiH and precedent with iron and cobalt catalysts,22 this
1 mol% Ni(2-EH)2
[Si]
hex
+ [Si]-H
hex
reaction was used to evaluate combinations of nickel precursors and
ligands for catalytic activity (Table S1). Nickel(II) bis(carboxylates)
were attractive as the metal source due to their low cost, air-stability
and known ability of carboxylate ligands to undergo substrate-induced
activation with main group hydrides to generate active first row transi-
6 hr, 23 °C, neat
[Si] =
% Conversion (% Yield)
>98 % (97%)
Si(OEt)3
SiMe(OEt)2
>98 % (86%)
2
3,4a
SiMe (OEt)
>98 % (93%)
tion metal catalysts.
Using the hydrocarbon soluble Ni(2-EH)
2
, (2-
2
0
1
2
3
4
5
6
7
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0
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2
3
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0
SiMe(OSiMe3)2
>98 % (99%)
EH = 2-ethylhexanoate) evaluation of 13 total ligands (5 mol% load-
ing, 12 hrs, 23 °C, see Table S1) identified several ligand combinations
with promising hydrosilylation activity. Pure σ-donating ligands such as
SiMe (OSiMe )
>98 % (90%)
2
3
nhex
0.1 mol% Ni(2-EH)2
.1 mol% iPrDI
0
Si(OEt)3
1
,2-Bis(diphenylphosphino)ethane (dppe) or tetramethylethylenedi-
+
nhex
40 °C, 6 hr, neat
amine (tmeda) produced either no reaction or products derived from
dehydrogenative silylation. By contrast, potentially redox-active 2,2’-
bipyridine (bpy), the aryl-substituted pyridine(imine) ( PI) and the
(EtO) SiH
> 99% Conversion
(96% yield)
3
iPr
10 gram scale
iPr
related aryl-substituted α-diimine, ( DI) all promoted anti-
O
O
Markovnikov hydrosilylation. Using this straightforward protocol, the
Si
Si
+
Si
hydrosilylation of 1-octene with (EtO)
3
SiH was conducted on a 10 g
1
20
100 ppm Nia
2 h, 80 ºC
iPr
Crosslinked
Silicone Polymer
scale with 0.1 mol% loading of DI / Ni(2-EH)
2
and produced >99%
n
24
of the desired octylSi(OEt) product (Figure 2). These results are
noteworthy in light of the success of redox-active, tridentate pyri-
dinediimines in supporting high activity iron and cobalt hydrosilylation
H
Si
Si
Si
Si
O
O
O
15
30
2
5
catalysts.
(olefin:Si-H) = 1:2
The observation of high yields coupled with the ease of synthesis of
iPr
Figure 2. Top: Scope of nickel catalysed hydrosilylation. 10-gram
scale hydrosilylation using air-stable nickel catalyst precursors. Bottom:
α-diimine ligands resulted in selection of DI for subsequent studies.
Efforts were devoted to optimization of the catalytic reaction, identifi-
cation of the active nickel species, exploration of the silane scope and
a
Silicone fluid crosslinking catalyzed by [Ni] at ppm loadings. Added
iPr
as a 0.15 M toluene solution containing 1 equiv. DI and 6 equiv.
elucidation of the mechanism of turnover. Notably, addition of
iPr
(EtO) SiH.
3
(
EtO)
3
SiH to an equimolar mixture of ( DI) and Ni(2-EH)
2
generat-
ed a blue solution, (λmax = 515 nm) suggesting ligand complexation,
activation of the carboxylate groups by the silane, and formation of the
active Ni species.
Our laboratory has previously reported multiple generations of Fe
and Co catalysts for olefin hydrosilylation that are compatible with
3i,j,k,l,4b
industrially-relevant tertiary silanes.
of 1-octene with HSiMe(OSiMe
The hydrosilylation reaction
Using the UV/Vis absorbance at 515 nm, the method of continu-
3
)
2
(MD’M) is a useful benchmark to
26
ous variations (“Job plot”) was applied to determine the optimal
compare the present Ni catalyst to the most active Fe and Co catalysts.
Me
Me
number of equivalents of silane required for catalyst activation (Figure
S6). A reaction stoichiometry corresponding to a 6:1 ratio of
With
[( APDI)Fe(N
2
)]
2
(μ
2
-N
2
)
( APDI
=
2,6-
(MeN=CMe)
2
C
5
3
H N) this reaction is complete (>98% yield anti-
[(EtO)
3
SiH]:[Ni] was established. Both (EtO)
3
SiOSi(OEt) and 2-
3
Markovnikov product) within 15 minutes at 23 °C with a catalyst load-
3
j
TF
ethylhexanol were observed by GC-MS as byproducts of the activation
procedure suggesting that Si-O-Si bond formation is likely the driving
force behind catalyst activation.
ing of 0.004 mol%. The air-stable cobalt pre-catalyst, APDICo(2-
TF
EH) ( APDI = 2,6-(3,4-dihydro-2H-pyrrole) requires 1 mol% catalyst
loading and 1 hour at 23 °C to reach a similar level of comple-
4
b
iPr
tion. {( DI)NiH} is markedly less active – requiring 1 mol% catalyst
2
Application of the optimized (EtO)
3
SiH:[Ni] ratio on a prepara-
loading and 6 hours at 23 °C to produce the anti-Markovnikov product
in high yield. Despite the comparatively lower activity of the Ni cata-
lyst, the ease with which the α-diimine scaffold can be modified and the
convenience of the in-situ activation protocol enables catalyst diversifi-
cation (Table S1) and should provide a straightforward path to more
active catalysts based on the specific application.
tive scale resulted in isolation of a deep blue (λmax = 515 nm; ε515
=
-
1
-1
iPr
3,225 M cm ) diamagnetic solid identified as [( DI)NiH]
2
, a com-
pound previously identified by Yang and coworkers.27 To account for
the formal reduction from Ni(II) to Ni(I), a Toepler pump28 experi-
ment was conducted and 0.45 equivalents of H were collected - con-
2
sistent with liberation of the expected 0.5 equivalents of dihydrogen en
iPr
A second major class of commercially important hydrosilylation
reactions involves the crosslinking of silicone polymer fluids, whereby a
polymeric vinyl silane is combined with a polymeric hydridosilane
containing tertiary Si-H linkages to form silicone polymers that are
widely employed as release coatings, fast setting molds, or extruded to
route to [( DI)NiH]
2
(see SI). This compound was also independent-
ly prepared and isolated in 42% yield following treatment of
iPr
(
DI)NiBr
2
with two equivalents of NaBEt H and the spectroscopic
3
data for material obtained from the two routes were identical. These
experiments unequivocally demonstrate that the in situ protocol gener-
iPr
29
ates [( DI)NiH]
2
in solution.
form ubiquitous consumer products. The morphology of the cross-
linked silicones prevents catalyst recovery and highlights the potential
The high activity, selectivity and scalability of isolated or in situ
iPr
economic benefit of base metal catalysts. With a concentrated (~0.15
generated [( DI)NiH]
2
prompted additional studies into the scope of
iPr
M) toluene pre-mix of ( DI), Ni(2-EH)
2
, and 6 eq. (EtO) SiH effi-
3
the catalytic reaction. Efforts were devoted to alkoxy and siloxy silanes,
as these substrate are the most relevant to commercial hydrosilylation
and have not been successfully used in nickel-catalyzed reactions. Each
catalytic hydrosilylation reaction was conducted using the straightfor-
cient hydrosilylation to yield crosslinked product was observed after
two hours at 80 °C (Figure 2). The crosslinked product is colorless, an
important characteristic for commercial viability.30
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ACS Catalysis
The mechanism of alkene hydrosilylation promoted by
reversible insertion of 1-octene (Figure 4). Interaction of the nickel
iPr
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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6
[( DI)NiH]
2
was of interest to not only understand the remarkable
alkyl with the silane is turnover limiting. Based on the current data,
both σ-bond metathesis and oxidative addition / reductive elimination
are viable mechanistic pathways for product release and regeneration of
the active catalyst. These observations are consistent with the deuteri-
um labeling studies and the isomerization to internal alkenes when the
catalytic performance but also to compare to the mechanism of plati-
iPr
num catalysts. Reaction of alkene with [( DI)NiH]
2
offers two possi-
bilities: insertion into the nickel-hydride, likely following dissociation
into a monomer or asymmetric rupture of the bridging hydrides to
iPr
iPr
1
form ( DI)Ni(alkene) and ( DI)NiH
2
. The latter path would be
catalytic reaction was monitored by H NMR spectroscopy in benzene-
reminiscent of platinum catalysis. To distinguish these possibilities, 5
d
6
solution.
iPr
2
31
mol % of ( DI)Ni(η -C
2
H ) was added to a mixture of 1-octene and
4
Ar
N
Ar
Ar
H
N
(
EtO)
3
SiH. After 12 hours at 23°C, <5% conversion was observed. By
R
iPr
N
iPr
N
Ni
H
iPr
olefin
isomers
comparison, the same procedure with [( DI)NiH]
2
reached >98%
1/2
iPr
N
Ni
R
N
Ni
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
H
[Ni]
conversion. To eliminate the possibility that ethylene is a catalyst poi-
iPr
iPr
iPr
son, the reaction of (EtO)
3
SiH with ethylene and 5 mol% Ni(2-EH) /
2
iPr
R
DI was also performed and quantitative formation of
R
(
EtO)
3
SiCH
2
CH
3
was obtained after 12 hours. These experiments
(EtO)3Si
iPr
eliminate the catalytic competency of ( DI)Ni(alkene) compounds
and suggest a distinct mechanistic pathway from platinum catalysts.
Ar
Ar
R
N
N
Insight into the catalyst resting state was obtained by monitoring
iPr
iPr
N
Ni
H
N
Ni
the hydrosilylation of 1-octene with (EtO)
by H NMR spectroscopy. With 1 mol% each of Ni(2-EH)
resonances diagnostic with formation of [( DI)NiH]
3
SiH in benzene-d
6
solution
and DI,
Si(OEt)3
1
iPr
2
iPr
iPr
iPr
R
2
were observed.
Significant isomerization to internal octene isomers occurred over the
n
(EtO)3SiH
course of the experiment but octySi(OEt)
3
eventually formed over the
Figure 4. Proposed mechanism for the hydrosilylation of 1-octene
course of hours as the sole hydrosilylation product. The concentration
iPr
iPr
with (EtO)
3
SiH and [( DI)NiH] .
2
of [( DI)NiH]
2
was unchanged throughout the reaction, implicating
the dimeric nickel hydride as an off-cycle catalyst resting state.
The presence of a redox-active α-diimine ligand raises questions as
to the oxidation state of the nickel throughout the catalytic cycle. Be-
Ni(2-EH)2
iPr
cause only [( DI)NiH]
2
was observed, DFT (B3LYP level) calcula-
6
(EtO)3SiH
+
DI
iPr
PhMe, 2 h
tions were conducted on this compound and related intermediates.
Ar
N
iPr
+
The electronic structure of diamagnetic [( DI)NiH]
2
is best described
iPr
N
Ni
H
(EtO) SiD
Ar
3
as two Ni(II) centers each with one-electron reduced diimine ligands.
34
1
/2
H
Ni
N
N
iPr Pr
i
Ar
The metrical parameters from the X-ray structure also support the
bond distance perturbations associated with this electronic structure
assignment. Unrestricted Kohn Sham calculations of the correspond-
N
Si(OEt)3
D
iPr
2 NaHBEt3
PhMe, 5 d
N
Ni Br
Br
iPr
% Deuterium Incorporation
Position: H C (CH2)
iPr
3
5
CH2 CH2
Si(OEt)3
iPr
35
ing monomer, ( DI)NiH, converge to a broken symmetry (2,1)
%
D:
8.0 % 36 % 35 % 21 %
solution with strong antiferromagnetic coupling (S=0.72) between the
S = 1 Ni(II) metal center and the one electron reduced α-diimine lig-
and (Figure 5). Similarly, the electronic structures of two putative
Figure 3. Left: Comparison of the one-step procedure (top) to the
iPr
multi-step procedure (bottom) for the synthesis of [ DINiH]
2
. Right:
Deuterium isotope incorporation studies related to catalytic hydrosi-
iPr
iPr
iPr
nickel alkyl intermediates, ( DI)Ni(n-octyl) and ( DI)Ni(2-octyl),
were computed and both converged to a BS (2,1) solution best de-
scribed as Ni(II) with a one electron reduced α-diimine ligand. Elec-
tronic participation of the diimine ligand serves to stabilize the formally
Ni(I) metal center in the putative nickel monohydride and alkyl com-
plexes. The accessibility and stability of these 3-coordinate 15-electron
complexes may explain their unprecedented reactivity compared to
other Ni hydrosilylation catalysts.
lylation of 1-octene with (EtO)
3
SiD using [ DINiH]
2
. Conditions: 0.1
iPr
mol% [ DINiH]
2
, 6hr, 23 °C, neat.
Deuterium labeling studies were also conducted. Catalytic deu-
terosilylation of 1-octene with (EtO)
3
SiD in the presence of 0.5 mol%
iPr
[( DI)NiH]
2
yielded the alkyl silane with deuterium in all positions of
2
the alkyl chain as judged by H NMR spectroscopy (Figure 3). These
experiments establish that β-H elimination is fast and reversible relative
to carbon-silicon bond formation and release of alkyl silane. The pro-
pensity for cationic α-diimine Ni(II) alkyls to undergo facile chain
a.
b.
3
2
walking is well-established in the context of alkene polymerization;
this property is preserved in the one electron reduced examples de-
scribed here. Hydrosilylation of 4-octene with (EtO)
3
SiH in the pres-
iPr
ence of 0.5 mol% [( DI)NiH]
2
was performed, yielding exclusive
n
formation of octylSi(OEt)
3
(>98 % conversion, 92% isolated yield)
after 6 hrs at 23 °C offering a distinct advantage over platinum catalysis
and previously-reported Co catalysts for which isomerization / hydros-
4b,33
ilylation is not operative.
iPr
Figure 5. a. Spin Density plot of ( DI)NiH. Mulliken Spin popula-
Kinetic studies in the form of initial rates were performed to estab-
lish the rate law for the nickel-catalyzed hydrosilylation of 1-octene and
iPr
tions are 1.5 (Ni) and -0.5 ( DI ligand). b. Spin Density plot of
iPr
iPr
( DI)Ni(n-octyl). Mulliken Spin populations are 1.5 (Ni) and -0.6
(
EtO)
3
SiH with [( DI)NiH]
2
in hexane solvent. The following rate
iPr
law was established:
( DI ligand).
iPr
]1/2 [1-octene] [(EtO)
Rate = kobs [{( DI)NiH}
2
3
SiH]
In summary, a highly active, anti-Markovnikov selective and scala-
ble nickel catalyst has been discovered for the hydrosilylation of 1-
octene with commercially relevant silanes and siloxanes. Both the lig-
The observed fractional order in nickel is consistent with dissocia-
iPr
tion of the hydride dimer to ( DI)NiH which undergoes fast and
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Page 4 of 5
and and metal precursors are air-stable and inexpensive and no addi-
tional pyrophoric activators are required. Investigations into the olefin
scope are forthcoming, but initial studies indicate that rapid olefin
isomerization has deleterious implications for functional group com-
patibility. The mechanism of the nickel-catalyzed hydrosilylation is
distinct from the established Chalk-Harrod mechanism established for
currently used platinum alternatives and involves nickel(II) intermedi-
ates with one-electron reduced α-diimines.
Soc. 2014, 136, 17414-17417. d) Mo, Z.; Liu, Y; Deng, L. Angew. Chem. Int.
Ed. 2013, 52, 10845-10849. e) Brookhart, M.; Grant, B. E. J. Am. Chem. Soc.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
1
1
993, 115, 2151-2156. f) Reichel, C. L.; Wrighton, M. S. Inorg. Chem. 1980,
9, 3858-3860. g) Harrod, J. F.; Chalk, A. J. J. Am. Chem. Soc. 1965, 87, 1133-
133.
(
5) a) Chen, C.; Hecht, M. B.; Kavara, A.; Brennessel, W. W.; Mercado, B.
Q.; Weix, D. J.; Holland, P. L. J. Am. Chem. Soc. 2015, 137, 13244-13247. b)
Chirik, P. J.; Tondreau, A. M.; Delis, J. G. P.; Lewis, K. M.; Weller, K. J.; Nye, S.
A. US Patent 8,765,987, 2014. For additional examples of this type of catalyst
activation for hydrosilylation reactions, see references 3(c), 3(e) 3(f), and 3(h).
(
6) a) Buchwald, S. L. Chem. Eng. News 1993, 71 (2), 13-16. b) Ryan, J. W.
J. Am. Chem. Soc. 1962, 84, 4730-4734.
ASSOCIATED CONTENT
(7) a)Meister, T. K.; Riener, K.; Gigler, P.; Stohrer, J.; Herrmann, W. A.;
Kühn, F. E. ACS Catal. 2016, 6, 1274-1284. b) Roy, A. K.; Taylor, R. B. J. Am.
Chem. Soc. 2002, 124, 9510-9524.
(8) a) Troegel, D.; Stohrer, J. Coord. Chem. Rev. 2011, 255, 1440-1459. b)
Marciniec, B. Coord. Chem. Rev. 2005, 249, 2374-2390.
0
1
2
3
4
5
6
7
8
9
0
1
2
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4
5
6
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Supporting Information
Experimental procedures, Deuterium labeling experiments, method of
continuous variations, Toepler pump results, 10-gram scale hydrosi-
lylation, Silicone fluid crosslinking, Kinetics experiments, Computa-
tional details, and General protocols. This material is available free of
charge via the Internet at http://pubs.acs.org.
(9) a) Schroeder, M. A.; Wrighton, M. S. J. Organomet. Chem. 1977, 128,
45-358. b) Mitchener, J. C.; Wrighton, M. S. J. Am. Chem. Soc. 1981, 103,
75-977.
3
9
(
10) a) Atienza, C. C. H.; Diao, T.; Weller, K. J.; Nye, S. A.; Lewis, K. M.;
Delis, J. G. P.; Boyer, J. L.; Roy, A. K.; Chirik, P. J. J. Am. Chem. Soc. 2014, 136,
12108-12118. b) Delpech, F.; Mansas, J.; Leuser, H.; Sabo-Etienne, S.;
Chaudret, B.; Organometallics 2000, 19, 5750-5757. c) Marciniec, B.;
Majchrzak, M. Inorg. Chem. Commun. 2000, 3, 371-375. d) Lippert, T.;
Dauth, J.; Deubzer, B.; Weis, J.; Wokaun, A. Radiat. Phys. Chem. 1996, 47,
AUTHOR INFORMATION
Corresponding Author
pchirik@princeton.edu
8
89-897.
11) Stein, J.; Lewis, L. N.; Gao, Y.; Scott, R. A. J. Am Chem. Soc. 1999,
(
Notes
121, 3693-3707.
(12) Ananikov, V. P.; ACS Catal. 2015, 1964-1971.
The authors declare the following competing financial interest(s): One
patent related to this work has been filed: Chirik, P. J.; Pappas, I.; US
Patent Application filed November 2015 (unpublished).
(
13) a) Marciniec, B. Coord. Chem. Rev. 2005, 249, 2374-2390. b)
Maciejewski, H.; Marciniec, B.; Kownacki, I. J. Organomet. Chem. 2000, 597,
75-181.
14) Chen, Y.; Sui-Seng, C.; Boucher, S.; Zargarian, D. Organometallics
2005, 24, 149-155.
15) Junquera, L. B.; Puerta, M. C.; Valerga, P. Organometallics 2012, 31,
175-2183.
1
ACKNOWLEDGMENT
(
We thank Momentive Performance Materials Inc. (MPM) for financial
support. We also acknowledge Drs. Kenrick Lewis (MPM), Aroop Roy
(MPM), Keith Weller (MPM), Julie Boyer (MPM), and Jos Delis
(MPM) for helpful discussions.
(
2
(
(
(
16) Kuznetsov, A.; Gevorgyan, V. Org. Lett. 2012, 14, 914-917.
17) Lipschutz, M. I.; Tilley, T. D. Chem. Commun. 2012, 48, 7146-7148.
18) Srinivas, V.; Nakajima, Y.; Ando, W.; Sato, K; Shimada, S. Catal. Sci.
Technol. 2015, 5, 2081-2084.
19) Steiman, T. J.; Uyeda, C. J. Am. Chem. Soc. 2015, 137, 6104-6110.
REFERENCES
(
st
(20) a) Buslov, I.; Becouse, J.; Mazza, S.; Montandon-Clerc, M.; Hu, X. An-
gew. Chem. Int. Ed. 2015, 54, 14523-14526. b) Vasudevan, K. V.; Scott, B. L.;
Hanson, S. K. Eur. J. Inorg. Chem. 2012, 4898-4906.
(
1) (a) Marciniec, B. Comprehensive Handbook on Hydrosilylation, 1 ed.;
Pergamon Press: Oxford, UK, 1992; pp 204 - 215. (b) Marciniec, B.; Maciejew-
ski, H.; Pietraszok, C.; Pawluc, P. Hydrosilylation: A Comprehensive Review on
Recent Advances. In Advances in Silicone Science; Matisons, J. Ed.; Springer:
New York, 2009; Vol. 1; pp 159-181.
(21) Nakajima, Y.; Shimada, S. RSC Adv. 2015, 5, 20603-20616.
(
22) a) Karstedt, B. US Patent 3,775,452, 1973 b) Lamoreaux, H. F. US Pa-
tent 3,220,972, 1965. c) Ashby, B. A. US Patent 3,159,601, 1964. d) Speier, J.
L.; Webster, J. A.; Garrett, H. B. J. Am. Chem. Soc. 1957, 79, 974-979.
(2) a) Mudd, G. M.; Glaister, B. J. The Environmental Costs of Platinum-
PGM Mining: An Excellent Case Study In Sustainable Mining. Proc. “48th
Annual Conference of Metallurgists”, Canadian Metallurgical Society, Sudbury,
Ontario, Canada, August 2009. b) Hilliard, H. E. US Geological Survey, Plati-
num-Group Metals Mineral Commodity Summary (Jan. 2003) (accessible on
the internet at minerals.usgs.gov/minerals/pubs/commodity/platinum/.
(3) a) Marciniec, B.; Kownacka, A.; Kownacki, I.; Hoffmann, M.; Taylor, R.
J. J. Organomet. Chem. 2015, 791, 58-65. b) Sunada, I.; Noda, D.; Soejima, H.;
Tsutsumi, H.; Nagashima, H. Organometallics 2015, 34, 2896-2906. c) Chen,
J.; Cheng, B.; Cao, M.; Lu, Z. Angew. Chem. Int. Ed. 2015, 54, 4661-4664. d)
Marciniec, B.; Kownacka, A.; Kownacki, I.; Taylor, I. Appl. Cat. A. Gen. 2014,
486, 230-238. e) Greenhalgh, M. D.; Frank, D. J.; Thomas, S. P. Adv. Synth.
Catal. 2014, 356, 584-590. f) Peng, D.; Zhang, Y.; Du, X.; Zhang, L.; Leng, X.;
Walter, M. D.; Huang, Z. J. Am. Chem. Soc. 2013, 135, 19154-19166. h) Ka-
mata, K.; Suzuki, A.; Nakai, Y.; Nakazawa, H. Organometallics 2012, 31, 3825-
(
23) a) Bleith, T.; Gade, L. H.; J. Am. Chem. Soc. 2016, 138, 4972-4983. b)
Noda, D.; Tahara, A.; Sunada, Y.; Nagashima, H. J. Am. Chem. Soc. 2015, 138,
2480-2483. c) Scheuermann, M. L.; Johnson, E. J.; Chirik, P. J. Org. Lett. 2015,
1
7, 2716-2719.
24) This reaction is performed commercially in the silicones industry on a
(
scale of >12,000,000 lbs/year. See Chemical Data Reporting database. Envi-
ronmental Protection Agency. U.S. Government Printing Office: Washington,
DC, 2012. Available online at http://www2.epa.gov/chemical-data-reporting.
(25) See 3(i), 3(j), 3(k), 3(l), and 4(a).
(
26) Renny, J. S.; Tomasevich, L. L.; Tallmadge, E. H.; Collum, D. B. Angew.
Chem. Int. Ed. 2013, 52, 11998-12013.
27) Dong, Q.; Zhao, Y.; Su, Y.; Su, J. H.; Wu, B.; Yang, X. J. Inorg. Chem.
(
2
012, 51, 13162-13170.
(28) Schriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive
3
828. i) Atienza, C. C. H.; Tondreau, A. M.; Weller, K. J.; Lewis, K. M.; Cruse,
Compounds, 2nd ed.; John Wiley & Sons: New York, 1986; pp 113-117.
29) Mark, H. F. Encyclopedia of Polymer Science and Technology, Con-
cise. Wiley 2013, pp. 1102-1114.
30) a) Momentive Performance Materials, SilForce SL6000 Technical Data
R. W.; Nye, S. A.; Boyer, J. L.; Delis, J. G. P.; Chirik, P. J. ACS Catal. 2012, 2,
2169-2172. j) Tondreau, A. M.; Atienza, C. C. H.; Weller, K. J.; Nye, S. A.;
Lewis, K. M.; Delis, J. G. P.; Chirik, P. J. Science 2012, 335, 567-570. k) Archer,
A. M.; Bouwkamp, M. W.; Cortez, M. P.; Lobkovsky, E.; Chirik, P. J. Organo-
metallics 2006, 25, 4269-4278. l) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am.
Chem. Soc. 2004, 126, 13794-13807.
(
(
Sheet. 2016, HCD-10896. b) Dow Corning, Silicone Mold Making. 2005.
Form No. 10–1681A–01. c) Shin-Etsu Silicone, Characteristic Properties of
Silicone Rubber Compounds. 2005.
(4) a) Ibrahim, A. D.; Entsminger, S. W.; Zhu, L.; Fout, A. R. ACS Catal.
2016, 6, 3589-3593. b) Schuster, C. H.; Diao, T.; Pappas, I.; Chirik, P. J. ACS
Catal. 2016, 6, 2632-2636. c) Mo, Z.; Xiao, J.; Gao, Y.; Deng, L. J. Am. Chem.
(
31) Zhao, Y.; Wang, Z.; Jing, X.; Dong, Q.; Gong, S.; Li, Q. S. Zhang, J.; Wu,
B.; Yang, X. J. Dalt. Trans. 2015, 44, 16228-16232.
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ACS Catalysis
(
32) a) Leatherman, M. D.; Svejda, S. A.; Johnson, L. K.; Brookhart, M. J.
Am Chem. Soc. 2003, 125, 3068-3081. b) Svejda, S. A.; Johnson, L. K.;
Brookhart, M. J. Am Chem. Soc. 1999, 121, 10634-10635.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
33) Schuster, C. H.; Diao, T.; Pappas, I.; Chirik, P. J. Unpublished Results.
See ref 4(b)
(
34) Muresan, N.; Chlopek, K.; Weyhermüller, T.; Neese, F.; Wieghardt, K.
Inorg. Chem. 2007, 46, 5327-5337.
(
35) The BS(m,n) notation refers to a broken symmetry state with m un-
paired spin-up electrons on the Ni metal center and n unpaired spin-down
electrons essentially localized on the diimine fragment. See F. J. Neese, Phys.
Chem. Solids 2004, 65, 781-785.
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TOC Graphic
Commercially-Relevent
Hydrosilylation
in-situ Catalyst Formation
Mechanistic Studies
R
Ar
N
iPr
Ar
H
N
Ar
N
N
+
Ni(O2R)2
Crosslinked silicone
OEt
iPr
N
Ni
N
Ni
R
Ar
Ar
pent
Si OEt
OEt
[Si]-H
Commercial silanes
Up to 1,000 TON
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