Synthesis of a Silyl Cobalt Hydride and Its Catalytic Performance in Kumada Coupling Reactions

Article abstract of DOI:10.1002/asia.201700144

Four silyl [P,Si]-chelate cobalt complexes (2–5) have been synthesized through the chelate-assisted Si?H activation of bidentate preligand ortho-HSi(Me)₂(PPh₂)C₆H₄ (1) with CoMe(PMe₃)₄ and CoCl(PMe₃)₃. The silyl Co^I complex, Co(PMe₃)₃(1-Si(Me)₂-2-(PPh₂)C₆H₄) (2), was synthesized by Si?H activation of 1 with CoMe(PMe₃)₄ or by combining complex 5 with MeLi and PMe₃. Complex 2 was treated with CH₃I or EtBr, generating the silyl Co^II products CoI(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) (3) and CoBr(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) (4). The silyl Co^III hydride, CoHCl(PMe₃)₂(1-Si(Me)₂-2-(PPh₂)C₆H₄) (5), was obtained by the reaction of complex 1 with CoCl(PMe₃)₃. The catalytic performance of complex 5 was explored for Kumada coupling reactions, showing good to excellent catalytic efficiency with 2 mol % catalyst loading for the reactions of aryl chlorides or aryl bromides with Grignard reagents. It is noteworthy that the synthesis of 5 as a chelate complex is easier than that of previously reported [PSiP]-pincer cobalt hydride. With similar catalytic efficiency for Kumada reactions, the catalyst loading (2 %) of 5 was lower than that (5 %) of [PSiP]-pincer cobalt hydride.

Full text of DOI:10.1002/asia.201700144

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Synthesis of Silyl Cobalt Hydride and its Catalytic Performance in
Kumada Coupling Reactions
Authors: Hongjian Sun
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To be cited as: Chem. Asian J. 10.1002/asia.201700144
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10.1002/asia.201700144
Chemistry - An Asian Journal
Synthesis of Silyl Cobalt Hydride and its Catalytic Performance in Kumada
Coupling Reactions
Shilu Xu,[a] Peng Zhang,[a] Xiaoyan Li,[a] Benjing Xue,[a] Hongjian Sun,*[a] Olaf
Fuhr,[b] Dieter Fenske[b]
The first two authors contribute to this work equally.
Abstract:
In this paper, we reported the syntheses of four silyl [P,Si]-chelate cobalt complexes
(2-5) through the chelate-assisted Si-H activation of bidentate preligand
o-HSi(Me)2(PPh2)C6H4(1) with CoMe(PMe3)4 and CoCl(PMe3)3. The silyl Co(I)
complex, Co(PMe3)3(1-Si(Me)2-2-(PPh2)C6H4) (2), was synthesized by Si-H
activation of 1 with CoMe(PMe3)4 or the combination of complex 5 with MeLi and
PMe3. Complex 2 was treated with CH3I or EtBr and generating the silyl Co(II)
products
CoI(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4)
(4). The
(3)
Co(III)
and
hydride,
CoBr(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4)
silyl
CoHCl(PMe3)2(1-Si(Me)2-2-(PPh2)C6H4) (5), was obtained by the reaction of
complex 1 with CoCl(PMe3)3. The catalytic performance of complex 5 was explored
for the Kumada coupling reactions. With a load of 2 mol% of catalyst, complex 5
displayed good to excellent catalytic efficiency for the reactions of aryl chlorides or
aryl bromides with Grignard reagents. It is noteworthy that the synthesis of 5 as a
chelate complex is easier than that of our early reported [PSiP]-pincer cobalt hydride.
With similar catalytic efficiency for the Kumada reactions, the catalyst loading (2%)
of 5 is lower than that (5%) of [PSiP]-pincer cobalt hydride.
————————————
[a]
School of Chemistry and Chemical Engineering, Key Laboratory of Special
Functional Aggregated Materials, Ministry of Education, Shandong University,
Shanda Nanlu 27, 250199 Jinan, People’s Republic of China
[b]
Institut für Nanotechnologie (INT) und Karlsruher Nano-Micro-Facility (KNMF),
Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344
Eggenstein-Leopoldshafen, Germany
Supporting
information
of
this
article
can
be
found
under
http://dx.doi.orxxxxxxxxxxxx
1
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Introduction:
The silyl transition metal complexes have received much attention due to the
growing interest of silicon chemistry. Transition metal silyl complexes synthesized via
Si-H bond activation have extensive application and they can be used either as
reactants or as catalysts in organic reactions.[1-5] Iwasawa’s group used pincer-type
hydrido palladium complexes to realize hydrocarboxylation of allene with CO2.[6] In
Turculet’s work, tridentate pincer-type bis(phosphino)silyl ligand [PSiP] was used to
synthesize a ruthenium(II) dinitrogen complexes [Ru(H)(N2)(PSiP-Ph)] under
nitrogen atmosphere.[7] Shimada reported that the tridentate pincer-type
i
t
bis(phosphino)silyl ligands (PSiP-R, R = Cy, Pr, or Bu) were used to prepare a rare
example of thermally stable iridium(III) dinitrogen complex [Ir(H)2(N2)(PSiP-R)].[8]
Li’s group prepared several cyclometalated iridium(III) compounds [IrCl(H)(PSiP)]
via Si-H bond activation and they showed good to excellent catalytic activity in the
transfer hydrogenation of ketones.[9] In 2013, we disclosed an iron hydrido complex
with a tridentate bis(phosphino)silyl ligand ((σ-Ph2PC6H4)2SiMeH, [PSiP]-H).[10] In
2015, we published the synthesis and characterization of a series of Co, and Fe
complexes bearing a tridentate bis(phosphino)silyl ligand (HSiMe(NCH2PPh2)2C6H4,
[PSiP]-H). The hydrido cobalt(III) complex [PSiP]Co(H)(Cl)(PMe3) was found to be
an excellent catalyst for Kumada coupling reactions under mild condition.[11]
In comparison with the silyl tridentate transition metal complexes, although the
synthesis of the silyl bidentate transition metal complexes is easier, the reports on the
silyl bidentate transition metal complexes are very few.[12-16] Because silyl bidentate
ligands can form only one chelate ring, their transition metal complexes have less
stability, but higher reactivity. Sabo-Etienne and co-workers used
pyridine-2-amino(methyl)dimethylsilane ligands to afford a series of ruthenium
complexes with multicenter Ru-H-Si interactions. In hydrogen atmosphere, these
complexes display different degrees of Si−H bond activation.[17-19] Chou’s group
reported several phosphine-substituted organo silanes and their Ir(III) complexes.[20]
In 2015, Maleczka and Smith III reported several cyclometalated [P,Si]-chelate
iridium complexes and found that they are catalytically effective for ortho-borylation
2
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10.1002/asia.201700144
Chemistry - An Asian Journal
reaction.[3]
In addition, most of the research in this field is based on precious metals. Similar
study on non-noble metals is rare. Therefore, we selected a bidentate [P,Si]-chelate
silyl preligand to synthesize its cobalt complexes. It was also confirmed that the
[P,Si]-chelate silyl hydrido cobalt complex is catalytically active for the Kumada
coupling reaction. Our results indicate that the synthesis of 5 as a chelate complex is
easier than that of our early reported [PSiP]-pincer cobalt hydride.[11] With similar
catalytic efficiency for the Kumada reactions, the catalytic loading (2%) of 5 is lower
than that (5%) of [PSiP]-pincer cobalt hydride.
Results and discussion
Syntheses and Structures of the [P,Si]-Chelate Cobalt Complexes
When preligand 1 was combined with MeCo(PMe3)4 at -78oC, the color of the
solution changed from orange to red. The mixture was stirred at room temperature for
12 h. The resulted deep red solution was evaporated to dryness and the residue was
extracted with pentane and diethyl ether. Complex 2 as deep red crystals was obtained
from pentane solution (eq. (1)). In the IR spectrum of complex 2, no signal at 2122
cm-1 ((Si-H) for preligand 1) was observed. This indicates that the activation of the
Si-H bond occurred. In the 1H NMR spectrum of complex 2, two sets of signals were
identified at 0.86 and 1.18 ppm for two chemically different PMe3 ligands in the
integral ratio of 1 : 2. In the 31P NMR of complex 2, three sets of signals were
distinguished at -2.40，20.94 and 71.32 ppm, respectively, corresponding to the three
kinds of P atoms in the integral ratio of 2 : 1 : 1.
The structure of 2 was confirmed by single crystal X-ray crystal diffraction as a
trigonal bipyramid with the cobalt atom in the center (Fig. 1). The axial direction was
determined by the angle Si1-Co1-P2 (173.22(2)o), deviating from 180o. The equatorial
3
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10.1002/asia.201700144
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plane is constructed by P1, P3, P4 and Co1 atom. The sum of the bond angles
centered at Co1 in the equatorial plane (P1-Co1-P3 112.36(2); P3-Co1-P4 115.12(2)
and P1-Co1-P4 130.05(2)o) is 357.53o. This implies that the planarity of the equatorial
plane is not good. The distortion observed in the X-ray parameters for 2 might
presumably arise from the chelating bonding of the ligand. The distance of Co1-P2
(2.2193(5) Å) located at the opposite position of the silicon atom is longer than those
of the other three Co-P distances(Co1-P1 2.1679(5); Co1-P3 2.1722(5); Co1-P4
2.1912(5) Å) due to the strong trans-influence of silyl group.
Fig. 1 ORTEP plot of complex 2 at the 50% probability level (hydrogen atoms are
omitted for clarity). Selected bond lengths (Å) and angles (deg): Co1-P2 2.2193(5),
Co1-Si1 2.3353(5), Co1-P4 2.1912(5), Co1-P1 2.1679(5),Co1-P3 2.1722(5);
P2-Co1-Si1
173.22(2),P4-Co1-P2
92.29(2),P4-Co1-Si1
86.42(2),P1-Co1-P2
96.38(2),P1-Co1-Si1 79.46(2),P1-Co1-P4 130.05(2), P3-Co1-P2 97.28(2),P3-Co1-Si1
89.29(2),P3-Co1-P4 115.12(2)
The silyl [P,Si]-chelate cobalt(I) complex 2 could react with MeI to afford the
single-electron oxidative product 3 (eq (2)). Complex 3 was obtained as red crystals
from diethyl ether in a yield of 69%. The NMR results have confirmed the
4
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10.1002/asia.201700144
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paramagnetic character of complex 3 due to the existence of the single electron. This
reaction might undergo a radical mechanism. CH3I split into methyl radical and iodine
radical via homolytic cleavage. Two methyl radicals formed ethane and the iodine
radical combined with the cobalt center of complex 2 to furnish complex 3 with the
dissociation of PMe3 ligand.
Fig. 2 ORTEP plot of complex 3 at the 50% probability level (hydrogen atoms are
omitted for clarity). Selected bond lengths (Å) and angles (deg): Co1-P1 2.1722(9),
Co1-P2 2.2383(9), Co1-P3 2.2926(9), Co1-Si1 2.3368(9), Co1-I1 2.5923(5);
P1-Co1-P3 107.30(4), P1-Co1-P2 100.20(3), P3-Co1-P2 97.22(4), P1-Co1-Si1
80.25(3), P3-Co1-Si190.45(4), P2-Co1-Si1 171.77(4), P1-Co1-I1 136.73(3),
P3-Co1-I1 112.92(3), P2-Co1-I1 90.16(3), Si1-Co1-I1 84.07(3).
The structure of complex 3 was confirmed by single crystal X-ray diffraction.
Complex 3 has a triangular bipyramid coordination geometry, similar with that of
complex 2. The bond angle Si1-Co1-P2 (171.77(4)o) formed the axial position. The
equatorial plane was determined by I1, P1, P3 and Co1 atom. In the equatorial plane,
the angle I1-Co1-P1 (136.73(3)o) is larger than the angle I1-Co1-P3 (112.92(3)o)
because of the steric effect of the bulky diphenyl phosphino group (-PPh2).
5
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The reaction of complex 2 with EtBr afforded Co(II) bromide 4. Complex 4 as a
derivative of complex 3 is also paramagnetic. Complex 4 as red crystals was isolated
from the diethyl ether solution in a yield of 77%.
When preligand 1 was combined with CoCl(PMe3)3 in THF at low temperature, the
color of the solution changed from blue to yellow immediately (Eq (4)). After stirring
for 18h at room temperature, the volatiles were evaporated under reduced pressure
and residue was extracted with pentane and diethyl ether. Complex 5 as yellow
crystals were obtained in a yield of 74%. In the IR spectrum of complex 5, the typical
1
Co-H vibration was found at 1931 cm-1. In the H NMR of complex 5, the hydrido
signal appeared at -11.68 ppm and split into ddd peak due to the coupling effect of
two chemically different PMe3 ligands and -PPh2 group. Three sets of signals
appeared at -5.04, 9.90 and 77.68 ppm, respectively in the 31P NMR of complex 5.
Fig. 3 ORTEP plot of complex 5 at the 50% probability level (hydrogen atoms are
omitted for clarity). Selected bond lengths (Å) and angles (deg): Co1-P1 2.1844(10),
6
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Co1-P3 2.2076(12), Co1-P2 2.2202(10), Co1-Si1 2.2735(10), Co1-Cl1 2.3746(9),
Co1-H 1.30(5); P1-Co1-P3 157.19(4), P1-Co1-P2 102.41(4), P3-Co1-P2 99.36(5),
P1-Co1-Si1 88.28(4), P3-Co1-Si1 95.56(4), P2-Co1-Si1 97.63(4), P1-Co1-Cl1
85.82(4), P3-Co1-Cl1 84.82(4), P2-Co1-Cl1 97.02(4), Si1-Co1-Cl1 165.07(4),
P1-Co1-H 85(2), P3-Co1-H 75(2), P2-Co1-H 166(2), Si1-Co1-H 70.8(19),
Cl1-Co1-H 95.0(19).
Single crystal X-ray diffraction has verified that complex 5 has a distorted
octahedral coordination geometry with the cobalt atom in the center. If the angle
H-Co1-P2 (166(2)o) was taken as the axial direction, Si1, Cl1, P1, P3 and Co1 atom
are in the equatorial plane. The five-membered chelate ring [Co1P1C4C3Si1] and the
phenyl ring [C3C4C5C6C7C8] are in one plane. The angle P1-Co1-P3 (157.19(4)o)
orientates towards the Co1-H direction due to the small size of the hydrido ligand.
Co1-H distance is 1.30 Å. This value is remarkably shorter than those of the known
Co-H bonds (1.40-1.50 Å).[10]
Complex 5 is the result of an oxidative addition of the Si-H bond of the prelignad 1
at the cobalt(I) center. Although PMe3 is stronger Lewis base, no reductive
elimination between Co-H and Co-Cl in complex 5 was observed. Nevertheless, if a
strong base, like MeLi, was added to the solution of complex 5, complex 5 could be
reduced to the cobalt(I) complex 2 in the presence of PMe3 ligand. During this
process, HCl was formed via reductive elimination. HCl reacted with MeLi to afford
LiCl and CH4. The newly-added PMe3 filled the uncoordinated sites at the cobalt
center.
Catalytic Application of Silyl Hydrido Complex 5 in Kumada Coupling Reaction
We reported that [PSiP]-pincer silyl hydrido cobalt chloride could catalyze the
7
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10.1002/asia.201700144
Chemistry - An Asian Journal
Kumada coupling reactions.[11] Complex 5 is a hydrido silyl [P,Si]-chelate Co(III)
chloride with a Co-H and a Co-Cl bond together. This structure was assumed to be an
unstable structure under certain conditions. Therefore, it is possible that complex 5
could be a potential catalyst. Encouraged by these results, a series of Kumada
coupling reactions catalyzed by complex 5 were studied (Table 1).
At first, the reaction of 1-chloro-4-methoxybenzene with phenyl magnesium
bromide was studied as a test reaction (Table 1, entries 1-12). It was found that there
was little homocoupling product of the Grignard reagents could be detected by GC
analysis when the reaction temperature was below 80oC. If toluene was replaced by
THF or dioxane, the conversion declined sharply. It could be speculated that the
catalyst decomposed under this conditions. According to the entries 7, 9 and 10, the
best yield could be reached when the catalyst loading was 2 mol%. Therefore, the
optimized catalytic conditions can be summarized as follows: 80oC, 48 hours, catalyst
loading of 2 mol% and toluene as the solvent (Table 1, entry 7).
Under the optimized conditions, more substrates were selected to explore the
scope of this catalytic system (Table 1, entries 13-18). It can be concluded that higher
yield could be obtained from chlorobenzene than from the substituted chlorobenzene.
The electron-donating groups (methyl or methoxy group) make the yields poor.
At the same time, from Table 1 (entries 19-30) it can be summarized that the
optimized catalytic conditions for the reaction between 1-bromo-4-methylbenzene and
phenyl magnesium bromide catalyzed by 5 are: 40oC, 24h, THF and 2 mol% loading
of complex 5. It is obvious that the conditions are milder (lower temperature and
shorter reaction time) than those of entries 1-12 because aryl bromide is more active
than aryl chloride for the Kumada coupling reaction.
Under the optimized conditions, more substrates of aryl bromides were selected to
explore the scope of this catalytic system (Table 1, entries 31-39). These results
showed us that the positions of the substituents (Me- or MeO-) at the phenyl ring of
the bromo benzene have no significant influence upon the yields of the products.
8
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Table 1 Kumada Reactions of Grignard Reagents with Aromatic Halides Catalyzed by 5
Entry
1
ArMgX
Ar’X
Product
t/h
24
Temp./oC
25
Cayalst/mol%
2
Solvent
THF
Conversion/Yield(%)
20a
2
3
4
5
6
7
8
9
48
48
48
48
24
48
48
48
25
50
25
2
2
2
2
2
2
2
5
THF
50a
60a
30a
65a
70a
85a
30a
70a
THF
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
50
80
80
100
80
9
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10
11
12
13
14
15
16
17
18
19
20
21
22
48
48
48
48
48
48
48
48
48
24
24
24
24
80
25
50
80
80
80
80
80
80
25
25
25
25
10
2
2
2
2
2
2
2
2
2
2
2
2
Toluene
Dioxane
Dioxane
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
65a
2a
5a
84b
70b
80b
72b
65b
67b
88a
77a
45a
57a
Toluene
DMF
Dioxane
10
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23
24
25
26
27
28
29
30
31
32
33
34
35
24
24
24
24
24
24
24
24
24
24
24
24
24
40
40
40
40
40
25
25
40
40
40
40
40
40
2
2
THF
Toluene
DMF
Dioxane
THF
92a
85a
65a
72a
85a
65a
40a
55a
82b
69b
80b
72b
74b
2
2
5
1
THF
0.5
0.5
2
THF
THF
THF
2
THF
2
THF
2
THF
2
THF
11
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36
37
38
24
24
24
40
40
40
2
2
2
THF
THF
THF
75b
83b
72b
39
24
40
2
THF
63b
a Conversions.
b Isolated Yields.
12
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Conclusion
The silyl [P,Si]-chelate cobalt complexes 2 – 5 were obtained via Si-H bond
activation. With a catalyst loading of 2mol%, complex 5 displayed good activity in the
Kumada cross-coupling reactions of aryl chlorides or aryl bromides with Grignard
reagents. It is noteworthy that the synthesis of 5 as a chelate complex is easier than
that of our early reported [PSiP]-pincer cobalt hydride.[11] With similar catalytic
efficiency for the Kumada reactions, the catalytic loading (2%) of 5 is lower than that
(5%) of [PSiP]-pincer cobalt hydride.
Experimental section
General Procedures and Materials. Standard vacuum techniques were used in the
manipulations of volatiles and air-sensitive materials. Solvents were dried by metal
sodium and distilled under nitrogen before use. The ligand 1 was prepared according
to the literature.[20] The MeCo(PMe3)4 and CoCl(PMe3)4 were prepared according to
literature procedures.[21] Infrared spectra (4000-400 cm-1), as obtained from Nujol
mulls between KBr disks, were recorded on a Bruker ALPHA FT-IR instrument.
NMR spectra were recorded using Bruker Avance 300 MHz spectrometer. Elemental
analyses were carried out on an Elementar Vario ELIII instrument.
Synthesis of 2. (a) At -78oC, MeCo(PMe3)4 (0.47 g, 1.25 mmol) in 10 mL pentane
was added to a solution of 1 (0.40 g, 1.25 mmol) in 20 mL pentane, the mixture was
warmed to room temperature and the color changed to deep red. After stirring for 12 h,
the solution was evaporated to dryness at reduced pressure. The residue was extracted
with pentane and diethyl ether. Complex 2 was obtained as red cubic crystals from
pentane in a yield of 72% (0.55 g, 0.9 mmol). (b) To a solution of 5 (0.49 g, 0.87
mmol) in 20 mL diethyl ether was added CH3Li (0.54 mL / 1.6 M Et2O, 0.87 mmol)
and PMe3 (0.066 g, 0.87 mmol) at -78oC, the mixture was warmed to room
temperature and the color changed from yellow to red. After stirring at room
temperature for 6 h, the volatiles were evaporated to dryness and the residue was
extracted with pentane and diethyl ether, complex 2 was obtained as a red powder in a
13
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10.1002/asia.201700144
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yield of 81% (0.43 g, 0.70 mmol). Anal. Calcd. for C29H47CoP4Si (606.17 g/mol): C,
57.46; H, 7.81. Found: C, 57.87; H, 7.66. IR: (Nujol, KBr): 3046 (ArH), 1576
(ArC=C), 939 (PMe3) cm-1. 1H NMR: (300 MHz, benzene-d6, 300 K, δ): 0.46 (s, SiMe,
6H), 0.86 (d, J = 6 Hz, PMe3 9H), 1.18 (s, PMe3, 18H), 7.01 (s, Ar, 7H), 7.18-7.25 (m,
Ar, 2H), 7.5 (br, Ar, 4H), 7.73 (d, J = 7 Hz, Ar, 1H); 31P NMR (121 MHz, benzene-d6,
300 K, δ): -2.4 (m, PMe3, 2P), 20.9 (m, PMe3,1P), 71.3 (m, PPh2, 1P) ppm. 13C NMR
(75 MHz, benzene-d6, 300 K, δ): 14.20 (PCH3), 22.66 (PCH3), 30.16 (SiCH3), 34.38
(SiCH3), 133.11 (CPh), 141.01 (CPh) , 148.80 (CPh), 150.53 (CPh), 152.24 (CPh), 158.78
(CPh), 159.99 (CPh) ppm. 29Si NMR (79.5MHz, benzene-d6, 300K, δ): 41.65 (m) ppm.
Synthesis of 3. At 0oC, MeI (0.04 g, 0.28 mmol) was added into a solution (20 mL) of
complex 2 (0.16 g, 0.26 mmol). After stirring for 24h at room temperature, the
volatiles were removed at reduced pressure. The residue was extracted with diethyl
ether. Complex 3 as dark red crystals was isolated from its diethyl ether solution in a
yield of 73% (0.12 g, 0.19 mmol). Anal. Calcd. for C26H38CoIP3Si (657.43 g/mol): C,
47.50; H, 5.83. Found: C, 47.87; H, 5.65. IR: (Nujol, KBr): 3043 (ArH), 1582
(ArC=C), 935 (PMe3) cm-1. Complex 3 was paramagetic.
Synthesis of 4. At 0oC, EtBr (0.03 g, 0.27 mmol) was added into a solution (20 mL)
of complex 2 (0.15 g, 0.25 mmol). After stirring for 24 h at room temperature, the
volatiles were removed at reduced pressure. The residue was extracted with diethyl
ether. Complex 4 as dark red crystals was isolated from its diethyl ether solution in a
yield of 77% (0.12 g, 0.19mmol). IR: (Nujol, KBr): 3043 (ArH), 1582 (ArC=C), 935
(PMe3) cm-1. Anal. Calcd. for C26H38BrCoP3Si (610.43 g/mol): C, 51.16; H, 6.27.
Found: C, 51.37; H, 6.56. IR: (Nujol, KBr): 3047 (ArH), 1581 (ArC=C), 935 (PMe3)
cm-1. Complex 4 was paramagetic.
Synthesis of 5. To a solution of 1 (0.4 g, 1.25 mmol) in 20 mL THF was added
CoCl(PMe3)3 (0.4 g, 1.25 mmol) in 30 mL THF at 0oC. The mixture was allowed to
warm to the ambient temperature. The color changed from blue to yellow. After
14
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10.1002/asia.201700144
Chemistry - An Asian Journal
stirred at room temperature for 12 h, the volatiles were evaporated under reduced
pressure. The resulting yellow powder was extracted with pentane and diethyl ether.
Complex 5 was obtained as light yellow cubic crystals from diethyl ether in a yield of
74% (0.52 g, 0.9 mmol). Anal. Calcd. for C26H39ClCoP3Si (566.95 g/mol): C, 55.08;
H, 6.93. Found: C, 54.87; H, 7.16. IR: (Nujol, KBr): 3054 (ArH), 1931 (Co-H), 1575
(ArC=C), 940 (PMe3) cm-1. 1H NMR: (300 MHz, benzene-d6, 300 K, δ): -11.68 (ddd,
J = 87, 48, 57 Hz, CoH, 1H), 0.63 (s, SiMe, 6H), 0.86 (d, J = 6 Hz, PMe3, 9H), 1.54 (d,
J = 9 Hz, PMe3, 9H), 7.11 (m, Ar, 6H), 7.45 (m, Ar, 1H), 7.71 (m, Ar, 2H), 8.29 (m,
31
Ar, 5H); P NMR (121 MHz, benzene-d6, 300 K, δ): -5.04 (s, PMe3, 1P), 9.9 (m,
PMe3,1P), 77.68 (m, PPh2, 1P) ppm. 13C NMR (75 MHz, benzene-d6, 300 K, δ): 5.83
(d, J = 5 Hz, SiCH3), 12.96 (d, J = 6 Hz, SiCH3), 18.48 (d, J = 22 Hz, PCH3), 20.00 (d,
J = 28 Hz, PCH3), 131.66 (s, CPh), 131.69 (t’, J = 5 Hz, CPh), 131.82 (s, CPh), 133.81
(s, CPh), 133.88 (d, J = 10 Hz, CPh), 134.41 (d, J = 8 Hz, CPh), 137.50 (s, CPh), 137.92
(s, CPh), 138.90 (d, J = 5 Hz, CPh), 139.60 (d, J = 5Hz, CPh), 143.05 (s, CPh), 143.70 (s,
CPh), 159.90 (d, J = 3 Hz, CPh), 160.63 (d, J = 4 Hz, CPh) ppm. 29Si NMR (79.5MHz,
benzene-d6, 300K, δ): 38.48 (s) ppm.
General procedure for the Kumada reaction catalyzed by complex 5. In 25 mL
Schlenk tube was added 1 mmol bromo toluene, 1.1 mmol Grignard reagent, 0.02
mmol 5, and 2.5 mL THF. The resulting solution was sealed and stirred at room
temperature for 24 h and monitored by TLC and GC. Then the mixture was added 10
ml 10% HCl and stirred vigorously for 2 h at room temperature. The resulting mixture
was extracted by 50 mL diethyl ether for three times. The organic phase was
combined and dried over Na2SO4. The yield was determined by GC with n-dodecane
as an internal standard.
Single crystal X-ray diffraction. Single crystal X-ray diffraction data of the
complexes 2, 3 and 5 were collected on a STOE STADIVARI Cu or Stoe IPDS2
diffractometer. Using Olex2,[22] the structures were solved with ShelXS[23] structure
solution program using Direct Methods and refined with the ShelXL[24] refinement
15
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10.1002/asia.201700144
Chemistry - An Asian Journal
package using Least Squares minimization. CCDC-1534302 (2), 1534303 (3) and
1534301 (5) contain supplementary crystallographic data for this paper. Copies of the
data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge
CB2
1EZ,
UK
(fax:
(+44)1223-336-033;
e-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgements. We gratefully acknowledge the financial support by NSF China
No. 21272138/21572119.
Keywords: Cobalt hydride · Si-H activation · Silyl cobalt complex · Kumada
Coupling
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Chemistry - An Asian Journal
TOC
Synthesis of Silyl Cobalt Hydride and its Catalytic Performance in Kumada
Coupling Reactions
Shilu Xu,[a] Peng Zhang,[a] Xiaoyan Li,[a] Benjing Xue,[a] Hongjian Sun,*[a] Olaf
Fuhr,[b] Dieter Fenske[b]
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