(Salicylaldiminato)Ni(ii)-catalysts for hydrosilylation of olefins

Article abstract of DOI:10.1039/c5cy00270b

A series of (salicylaldiminato)methylnickel complexes efficiently catalyse hydrosilylation of various olefins. The complexes are highly active for secondary hydrosilanes and exhibit excellent selectivity for monohydrosilylation. A possible mechanism, whic

Full text of DOI:10.1039/c5cy00270b

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IJSalicylaldiminato)NiIJII)-catalysts for
hydrosilylation of olefins†
Cite this: Catal. Sci. Technol., 2015,
5, 2081
*
Venu Srinivas, Yumiko Nakajima, Wataru Ando, Kazuhiko Sato
*
and Shigeru Shimada
Received 24th February 2015,
Accepted 26th February 2015
DOI: 10.1039/c5cy00270b
www.rsc.org/catalysis
A series of (salicylaldiminato)methylnickel complexes efficiently
catalyse hydrosilylation of various olefins. The complexes are
highly active for secondary hydrosilanes and exhibit excellent
selectivity for monohydrosilylation. A possible mechanism, which
includes a silylnickel complex as a key active species, is proposed.
presence of 0.5 mol% of 1a smoothly proceeded in CH3CN at
room temperature for 1 h to give Et2IJnOct)SiH (2, 93%, nOct =
CH3IJCH2)7) with high selectivity, along with a small amount of
dioctyl product Et2IJnOct)2Si (3, 4%) (entry 1). The use of other
solvents (benzene, toluene, hexane or THF) resulted in the for-
mation of a complicated mixture containing 2, 3, EtIJnOct)SiH2,
EtIJnOct)2SiH and Et2IJnOct)2Si probably via substituent redistri-
bution on the Si atom. Hence the reaction was conducted in
CH3CN for further investigation. Complex 1b exhibited a simi-
lar catalytic activity forming 2 and 3 in 90% and 2% yields,
respectively (entry 2). Complexes 1c and 1d were slightly less
active than 1a and 1b, and required longer reaction times (8 h
and 2.5 h, respectively) to give 2 in high yields (entries 3 and 4).
The rather low activities of 1c and 1d are likely due to the bulky
aryl substituent on the imino-N atom in 1c and the strongly
coordinating DMAP in 1d (vide infra). To our surprise, complex
1e, which was reported to be more active towards ethylene poly-
merization than 1a,5b was not active even at elevated tempera-
ture up to 100 °C (entry 5). It was confirmed that transforma-
tion of 1e gradually proceeded upon treatment with 1-octene
and Ph2SiH2 to give unidentified compounds including insolu-
ble black precipitates.6
Transition metal catalysed hydrosilylation of olefins is an
excellent tool for synthesis of various organosilicon
compounds and for cross-linking of silicone polymers in
industry.1 To date, hydrosilylation has depended on precious
metal catalysts, particularly platinum.1 Due to the high cost
of these metals, there is an increasing demand for the devel-
opment of non-precious metal catalysts. Thus far, first-row
transition metal complexes containing Fe,2 Co,3 Ni,4 etc. have
attracted much attention due to their potential applicability as
low-cost alternatives. However, examples of well-defined first-
row transition metal catalyst systems still remain scarce
because of the difficulty in controlling their complicated reac-
tivity, which sometimes leads to an unwanted product mixture.
In this study, we found out that (salicylaldiminato)methyl-
nickel complexes 1a–e (Fig. 1), which have been so far inten-
sively studied as olefin polymerization catalysts,5 act as good
hydrosilylation precatalysts of various olefins with excellent
product selectivity and diverse substrate scope.
We next investigated the substrate scope using the most
effective precatalyst, 1a. The results are summarized in
Table 2. In the reaction of 1-octene with R2SiH2 (R = Ph,
nHex), selective monohydrosilylation also proceeded to give
R2IJnOct)SiH (4 or 6) (90–94% yield) as a major product
accompanied by a small amount of R2IJnOct)2Si (entries 1 and 2).
Complex 1a catalysed hydrosilylation of 1-octene with primary
silanes, PhSiH3 and (nOct)SiH3, rather slowly to selectively give
NiIJII) complexes 1a–e were prepared by the reaction of
ijNiIJCH3)2IJtmeda)] (tmeda = N,N,N′,N′-tetramethylethylenediamine)
with a respective salicylaldimine derivative and pyridine or
DMAP (DMAP = 4-dimethylaminopyridine) in diethyl ether.5
Complexes 1b–d are new compounds and were fully char-
acterized by 1H and 13C NMR spectroscopy as well as ele-
mental analysis.
The catalytic performance of 1a–e is summarized in
Table 1. Hydrosilylation of 1-octene with Et2SiH2 in the
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba
Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
E-mail: s-shimada@aist.go.jp
† Electronic supplementary information (ESI) available: Experimental details
and compound characterization data. See DOI: 10.1039/c5cy00270b
Fig. 1 (Salicylaldiminato)methylnickel complexes 1a–e.
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Table 1 Hydrosilylation of 1-octene with Et2SiH2 catalysed by 1
Product [yield/%]a
Precatalyst
Entry
(0.5 mol%)
t/h
2
3
1
2
3
1a
1b
1c
1d
1e
1
1.3
8
2.5
24
93
90
88
92
0
4
2
5
4
0
4
5b
a
GC yield. b Starting materials were fully recovered.
Table 2 Reaction of various olefins with hydrosilanes catalysed by 1aa
Entry
1
Silane
Olefin
t/h
Products; yield/%b
Ph2SiH2
1-Octene
1
Ph2IJnOct)SiH (4); 90(91)
Ph2IJnOct)2Si (5); 8(9)
IJnHex)2IJnOct)SiH (6); 94IJ−)
IJnHex)2IJnOct)2Si (7); 3IJ−)
IJnOct)IJR)SiH2
2
3
IJnHex)2SiH2
1-Octene
1-Octene
2
RSiH3
24c
R = Ph (8); 15(20)
= nOct (9); 20(24)
4
5
R3SiH
(R = Et, OEt)
R2SiH2
1-Octene
48
1
No reaction
R = Et (10); 90(94)
= Ph (11); 94(99)
Et2IJnOct)SiH (2); 85(90)
6
7
Et2SiH2
R2SiH2
2-Octene
12d
10–36
R = Et (12a); −IJ9)
= Ph (13a); 55IJ−)
R = Et (12b); 85(90)
Ph (13b); 40IJ−)
8
9
R2SiH2
0.5
R = Et (14); 92IJ−)
= Ph (15); 65IJ−)
R2SiH2
Et2SiH2
1
R = Et (16); 96IJ−)
= Ph (17); 98IJ−)
10
36d
(18); 34IJ−)
a
b
c
1a (0.0025 mmol), silane (0.5 mmol), olefin (0.6 mmol) in CH3CN (2 mL) at 25 °C. Isolated yield (GC yield). Toluene (2 mL) was used as a
solvent. d Reaction at 50 °C.
monohydrosilylated products PhIJnOct)SiH2 (8) and IJnOct)2SiH2
(9) in 15% and 20% yields, respectively (entry 3). In these cases,
large amounts of the starting materials were recovered from the
resulting reaction mixture. Notably, even though a small excess
of olefin was employed, the reactions did not form isomerized
internal olefins, which are normally the major by-products in
olefin hydrosilylation reactions catalysed by conventional plati-
num catalysts.7 Tertiary silanes such as Et3SiH and (EtO)3SiH
were not applicable in this system probably due to the steric
bulkiness of the silanes (entry 4).
Hydrosilylation of 2-norbornene with Et2SiH2 or Ph2SiH2
smoothly took place to selectively provide exo-10 (90%) or exo-11
(94%), respectively (entry 5). Interestingly, hydrosilylation of an
unstrained internal olefin, 2-octene, also efficiently proceeded at
50 °C, selectively giving terminally silylated product 2 in a good
yield (entry 6), likely via successive olefin isomerization and
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hydrosilylation. Styrene was also hydrosilylated with Et2SiH2 or
Ph2SiH2 to yield α- and β-hydrosilylated products (entry 7).
While in the case of Et2SiH2, α-silylated (Markovnikov addition)
product 12b (85%) was predominantly obtained, and
a
nonselective mixture of α- and β-silylated products (13b, 40%,
and 13a, 55%, respectively) was formed in the case of Ph2SiH2.
Perfect 1,4-selectivity was observed in the hydrosilylation of iso-
prene with Et2SiH2 and Ph2SiH2 to form allylsilanes 14 (92%)
and 15 (65%), respectively (entry 8), which are useful precursors
for the construction of a plethora of carbo- and heterocyclic
systems.8 Hydrosilylation of N,N-dimethylallylamine with
Et2SiH2 and Ph2SiH2 quantitatively took place to furnish
silylpropylamines 16 and 17 in 1 h at 25 °C (96–98%, entry 9).
But-3-en-1-ylIJphenyl)sulfane also underwent hydrosilylation with
Et2SiH2 at 50 °C to produce 18, albeit in a low yield (entry 10).
Despite their industrial importance, examples of hydrosilylation
of functionalized olefins are still limited,2d,e,9 since they some-
times poison the conventional platinum catalysts.10 The above
results observed for the olefins having nitrogen and sulfur
functionalities strongly indicate potential compatibility of 1a
towards important functionalized substrates.
To obtain information on the reaction mechanism, reac-
tions of 1a with a stoichiometric amount of 1-octene or
Ph2SiH2 were performed in CD3CN followed by 1H NMR
spectroscopy. Complex 1a did not react with 1-octene at room
temperature. On the other hand, 1a was completely con-
sumed by the treatment with Ph2SiH2 after 15 min and a
new SiH signal appeared at δ 5.85 ppm, whereas no signal
assignable to NiH was observed in the hydride region (δ 0 to
−30 ppm). In addition, formation of CH4 (δ 0.24 ppm) was
detected. The non-decoupled 29Si NMR spectrum exhibited one
doublet at −19.0 ppm IJ1JSiH = 219 Hz). The correlation between
the two signals, δH 5.85 ppm and δSi −19.0 ppm, was confirmed
by two dimensional NMR (Si–H HSQC) spectroscopy. Thus, for-
mation of an intermediary silyl complex was strongly indicated,
although full identification is still underway.11 Subsequent
addition of 1-octene (1.0 equiv.) and Ph2SiH2 (1.0 equiv.) to the
reaction mixture resulted in the formation of the correspond-
ing hydrosilylation products 4 and 5. In this reaction, broaden-
ing of the coordinated pyridine signal was detected, indicating
the rapid dissociation equilibrium of pyridine during the reac-
tion. It was also confirmed that 1a did not react with Et3SiH,
suggesting that the reaction is significantly influenced by the
steric bulkiness of hydrosilanes. These observations success-
fully explain the lower activity of 1c and 1d, which have the
bulky aryl group-substituted imino group and the strongly
coordinating DMAP ligand, respectively.
Scheme
hydrosilylation.
1
Proposed mechanism of complex 1-catalysed olefin
As mentioned above, complex 1a did not catalyse the
hydrosilylation reaction of tertiary hydrosilanes, Et3SiH and
(EtO)3SiH, with 1-octene. Thus, the observed formation of 3
in the hydrosilylation of 1-octene with Et2SiH2 is not likely by
double hydrosilylation of silanes via the intermediate tertiary
hydrosilane Et2IJnOct)SiH (2). Actually, it was indicated that 3
was formed via disproportionation of 2; i.e. octyl group dis-
proportionation of 2 proceeded in the presence of 1a (1
mol%) and Et2SiH2 (10 mol%) to furnish 3 in 15% yield after
24 h. In this reaction, Et2SiH2 was necessary to generate cata-
lytically active species.
In conclusion, well-defined IJsalicylaldiminato)NiIJII)-
precatalysts for hydrosilylation of olefins have been
established. In this system, selective tertiary hydrosilane for-
mation was achieved via predominant monohydrosilylation
of secondary hydrosilanes with a variety of olefins. The
precatalyst is also applicable for the hydrosilylation of amino-
and sulfur-functionalized olefins, showing its good functional
group tolerance.
Although several Ni complexes were thus far employed as
hydrosilylation catalysts, it was reported that the previous sys-
tems suffer from limited substrate scope and improper reac-
tion selectivity.4 It is therefore worth noting that this study
successfully presents the high potential of nickel complexes
as hydrosilylation catalysts. Further modification to expand
the scope of our Ni system is now underway and will be
reported in due course.
Acknowledgements
This work was supported by the “Development of Innovative
Catalytic Processes for Organosilicon Functional Materials”
project (PL: K. Sato) from the Ministry of Economy, Trade and
Industry, Japan (METI), and the New Energy and Industrial
Technology Development Organization (NEDO).
Based on these observations, one possible mechanism for
the complex 1-catalysed hydrosilylation is proposed (Scheme 1).
Precatalyst 1 initially reacts with a hydrosilane to give silyl inter-
mediate A via elimination of CH4. Intermediate A further
undergoes olefin insertion, possibly via olefin-coordinated
intermediate B, to give C. Reaction of C with hydrosilane regen-
erates A accompanied by the formation of the hydrosilylated
product. Through the reaction cycle, ligand exchange between
pyridine and 1-octene/acetonitrile could occur.
Notes and references
1 (a) B. Marciniec, J. Gulinski, W. Urbaniak and Z. W. Kornetka,
Comprehensive Handbook on Hydrosilylation, Pergamon, Oxford,
UK, 1992; (b) B. Marciniec, Hydrosilylation: A Comprehensive
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Review on Recent Advances, Springer, Berlin, 2009; (c) D. Troegel
Catalysis Science & Technology
evidenced by 1H and 13C NMR spectroscopy, possibly
indicating the occurrence of C–I bond cleavage.
and J. Stohrer, Coord. Chem. Rev., 2011, 255, 1440; (d)
L. N. Lewis, J. Stein, Y. Gao, R. E. Colborn and G. Hutchins,
Platinum Met. Rev., 1997, 41, 66.
7 (a) I. E. Markó, S. Stérin, O. Buisine, G. Mignani, P. Branlard,
B. Tinant and J.-P. Declercq, Science, 2002, 298, 204; (b)
I. E. Markó, S. Stérin, O. Buisine, G. Berthon, G. Michaud,
B. Tinant and J.-P. Declercq, Adv. Synth. Catal., 2004, 346, 1429.
8 (a) C. E. Masse and J. S. Panek, Chem. Rev., 1995, 95, 1293;
(b) M. D. Groaning, G. P. Brengel and A. I. Meyers, J. Org.
Chem., 1998, 63, 5517; (c) H. J. Knolker, G. Baum, O. Schmitt
and G. Wanzl, Chem. Commun., 1999, 1737; (d) S. R. Angle
and N. A. El-Said, J. Am. Chem. Soc., 2002, 124, 3608.
9 (a) G. A. Molander and P. J. Nichols, J. Am. Chem. Soc.,
1995, 117, 4415; (b) H. Zhou, S. R. Venumbaka, J. W. Fitch
and P. E. Cassidy, Macromol. Symp., 2003, 192, 115; (c) N.
Sabourault, G. Mignani, A. Wagner and C. Mioskowski, Org.
Lett., 2002, 13, 2117; (d) M. Igarashi, T. Matsumoto, T.
Kobayashi, K. Sato, W. Ando, S. Shimada, M. Hara and H.
Uchida, J. Organomet. Chem., 2014, 749, 421; (e) J. B. Perales
and D. L. Van Vranken, J. Org. Chem., 2001, 66, 7270.
2 (a) J. Y. Wu, B. N. Stanzl and T. Ritter, J. Am. Chem. Soc.,
2010, 132, 13214; (b) A. M. Tondreau, C. C. H. Atienza, K. J.
Weller, S. A. Nye, K. M. Lewis, J. G. P. Delis and P. J. Chirik,
Science, 2012, 335, 567; (c) K. Kamata, A. Suzuki, Y. Nakai
and H. Nakazawa, Organometallics, 2012, 31, 3825; (d) D.
Peng, Y. Zhang, X. Du, L. Zhang, X. Leng, M. D. Walter and
Z. Huang, J. Am. Chem. Soc., 2013, 135, 19154; (e) M. D.
Greenhalgh, D. J. Frank and S. P. Thomas, Adv. Synth. Catal.,
2014, 356, 584.
3 (a) F. Seitz and M. S. Wrighton, Angew. Chem., Int. Ed. Engl.,
1988, 27, 289; (b) M. Brookhart and B. E. Grant, J. Am. Chem.
Soc., 1993, 115, 2151.
4 (a) Y. Kiso, M. Kumada, K. Tamao and M. Umeno,
J. Organomet. Chem., 1973, 50, 297; (b) B. Marciniec, H.
Maciejewski and I. Kownacki, J. Mol. Catal. A: Chem.,
1998, 135, 223; (c) D. Gareau, C. Sui-Seng, L. F. Groux, F.
Brisse and D. Zargarian, Organometallics, 2005, 24, 4003; (d)
I. Hyder, M. Jiménez-Tenorio, M. C. Puerta and P. Valerga,
Dalton Trans., 2007, 3000; (e) M. I. Lipschutz and T. D.
Tilley, Chem. Commun., 2012, 48, 7146.
10 (a) J. Li, C. Niu, J. Peng, Y. Deng, G. Zhang, Y. Bai, C. Ma, W.
Xiao and G. Lai, Appl. Organomet. Chem., 2014, 28, 454; (b)
Y. Yoshikawa, K. Yamamoto and K. M. Tanaka, EP Pat.
0.604.104, 1994; (c) C. A. Hoag and S. W. Wilson, US Pat.
5346723, 1994.
5 (a) A. Osichow, I. Göttker-Schnetmann and S. Mecking,
Organometallics, 2013, 32, 5239; (b) F. M. Bauers and S.
Mecking, Macromolecules, 2001, 34, 1165.
6 During the reaction, collapse of the salicylaldiminato ligand
skeleton, which was not observed in the case of 1a–d, was
11 Examples of silylnickel complexes: (a) D. Adhikari, M. Pink
and D. J. Mindiola, Organometallics, 2009, 28, 2072; (b) S. N.
MacMillan, W. H. Harman and J. C. Peters, Chem. Sci.,
2014, 5, 590; (c) W. Chen, S. Shimada, M. Tanaka, Y.
Kobayashi and K. Saigo, J. Am. Chem. Soc., 2004, 126, 8072.
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