Synthesis and Reactivity of N-Heterocyclic PSiP Pincer Iron and Cobalt Complexes and Catalytic Application of Cobalt Hydride in Kumada Coupling Reactions

Article abstract of DOI:10.1021/acs.organomet.5b00937

The new N-heterocyclic σ-silyl pincer ligand HSiMe(NCH₂PPh₂)₂C₆H₄ (1) was designed. A series of tridentate silyl pincer Fe and Co complexes were prepared. Most of them were formed by chelate-assisted Si-H activation. The typical iron hydrido complex FeH(PMe₃)₂(SiMe(NCH₂PPh₂)₂C₆H₄) (2) was obtained by Si-H activation of compound 1 with Fe(PMe₃)₄. The combination of compound 1 with CoMe(PMe₃)₄ afforded the Co(I) complex Co(PMe₃)₂(SiMe(NCH₂PPh₂)₂C₆H₄) (3). The Co(III) complex CoHCl(PMe₃)(SiMe(NCH₂PPh₂)₂C₆H₄) (5) was generated by the reaction of complex 1 with CoCl(PMe₃)₃ or the combination of complex 3 with HCl. However, when complex 3 was treated with MeI, the Co(II) complex CoI(PMe₃)(SiMe(NCH₂PPh₂)₂C₆H₄) (4), rather than the Co(III) complex, was isolated. The catalytic performance of complex 5 for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex 5 displayed efficient catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard reagents. This catalytic reaction mechanism is proposed and partially experimentally verified.

Full text of DOI:10.1021/acs.organomet.5b00937

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of N‑Heterocyclic PSiP Pincer Iron and
Cobalt Complexes and Catalytic Application of Cobalt Hydride in
Kumada Coupling Reactions
Zichang Xiong, Xiaoyan Li, Shumiao Zhang, Yaomin Shi, and Hongjian Sun*
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
S
* Supporting Information
ABSTRACT: The new N-heterocyclic σ-silyl pincer ligand HSiMe-
(NCH2PPh2)2C6H4 (1) was designed. A series of tridentate silyl pincer
Fe and Co complexes were prepared. Most of them were formed by
chelate-assisted Si−H activation. The typical iron hydrido complex
FeH(PMe3)2(SiMe(NCH2PPh2)2C6H4) (2) was obtained by Si−H
activation of compound 1 with Fe(PMe3)4. The combination of
compound 1 with CoMe(PMe3)4 afforded the Co(I) complex Co-
(PMe3)2(SiMe(NCH2PPh2)2C6H4) (3). The Co(III) complex CoHCl-
(PMe3)(SiMe(NCH2PPh2)2C6H4) (5) was generated by the reaction of
complex 1 with CoCl(PMe3)3 or the combination of complex 3 with
HCl. However, when complex 3 was treated with MeI, the Co(II)
complex CoI(PMe3)(SiMe(NCH2PPh2)2C6H4) (4), rather than the Co(III) complex, was isolated. The catalytic performance of
complex 5 for Kumada coupling reactions was explored. With a catalyst loading of 5 mol %, complex 5 displayed efficient
catalytic activity for Kumada cross-coupling reactions of aryl chlorides and aryl bromides with Grignard reagents. This catalytic
reaction mechanism is proposed and partially experimentally verified.
Ph2PC6H4)2SiMeH, [PSiP]-H). The hydrido iron(II) complex
[PSiP]Fe(H)(PMe3)2 was found to be an excellent catalyst for
the hydrosilylation of aldehydes and ketones under mild
conditions.7 In 2015, we reported the synthesis and character-
ization of stable tripodal silyl iron and nickel complexes.8
Hill’s group designed the first example of N-heterocyclic σ-
silyl pincer ligands bearing a PSiP-LXL donor triad.9 The noble
metals Ru and Rh were used to form tridentate silyl pincer
complexes via facile Si−H bond activation. On the basis of this,
we designed the novel N-heterocyclic σ-silyl pincer ligand 1 and
proved its good coordinating capability with non-noble metals.
The catalytic ability of these chelate compounds was explored.
INTRODUCTION
■
In recent years, cyclometalated phosphine-based “PSiP” pincer
complexes have enjoyed intense study,1 especially tridentate
silyl pincers of the type ((2-R′2PC6H4)2SiMeH, R′ = Ph, Cy,
tBu, iPr).2 Researchers reported a series of tridentate silyl pincer
complexes containing noble metals (Pd, Pt, Ir, etc.).2c,3 Most of
these complexes are obtained by Si−H bond activation, and
they have many applications. Iwasawa’s group used silyl pincer-
type palladium complex to realize catalytic hydrocarboxylation
of allenes with CO2.4 In Shimada’s group, tridentate pincer-type
bis(phosphino)silyl ligands (PSiP-R, R = Cy, Pr, Bu) were
used to synthesize the series of iridium tetrahydrido complexes
[Ir(H)4(PSiP-R)] under argon. When the same reaction was
transferred to a nitrogen atmosphere, a rare example of a
thermally stable iridium(III)−dinitrogen complex, [Ir-
(H)2(N2)(PSiP-R)], was isolated.5 Li’s group reported the
novel cyclometalated iridium(III) complex [IrCl(H)(PSiP)]
and this compound showed catalytic activity to the transfer
hydrogenation of ketones to the corresponding secondary
alcohols moderately with 2-propanol as the hydrogen source.2b
In the same year, Iwasawa’s group had developed an efficient
method for the synthesis of various types of diborylalkenes
from alkenes via a new PSiP-pincer palladium-catalyzed double
dehydrogenative borylation.6 Our group has expended a great
deal of effort in this field as well. In 2013, we reported the
synthesis and characterization of a series of Ni, Co, and Fe
complexes bearing a tridentate bis(phosphino)silyl ligand ((o-
i
t
RESULTS AND DISCUSSION
■
Similar to the strategy by Hill,9 1,3-siladiazoles HSiMe-
(NCH2PPh2)2C6H4 (1; Scheme 1) was synthesized by the
Scheme 1. Synthesis of Compound 1
Received: November 10, 2015
© XXXX American Chemical Society
A
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reaction of C6H4(NHCH2PPh2)2 with the chlorosilane
MeHSiCl2 in the presence of triethylamine in a yield of 75%.
In the IR spectrum of 1, the typical ν(Si−H) stretching band is
found at 2115 cm−1. The characteristic Si−H signal is registered
at 5.17 ppm as a multiplet in the 1H NMR spectrum of 1. In the
29Si NMR spectrum of 1, the characteristic silicon signal was
1
found at −3.42 ppm as a doublet with the H−29Si coupling
constant JHSi = 237 Hz.
Reaction of Fe(PMe3)4 with HSiMe(NCH2PPh2)2C6H4
(1). When compound 1 was treated with 1 equiv of Fe(PMe3)4
in THF (Scheme 2), the solution slowly turned dark red-
Scheme 2. Synthesis of Complex 2
1
Figure 2. H NMR of PCHaHbN and PCHa′Hb′N of complex 2.
X-ray crystallography was used to confirm the structure of
complex 2 (Figure 3). The structure of complex 2 is a distorted
brown. After 14 h, complex 2 was isolated as orange bulk
crystals from diethyl ether. In the IR spectrum of 2, the typical
ν(Fe−H) stretching band of complex 2 is found at 1840 cm−1.
1
In the H NMR spectrum of 2, the characteristic iron hydrido
Figure 3. ORTEP plot of complex 2 at the 50% probability level (most
of the hydrogen atoms are omitted for clarity). Selected bond lengths
(Å) and angles (deg): Fe1−P1 2.2095(6), Fe1−P1a 2.2095(6), Fe1−
P2 2.2742(9), Fe1−P3 2.226(1), Fe1−Si1 2.2643(9), Fe1−H 1.47(3);
P1−Fe1−H 74.66(2), P1−Fe1−P3 104.05(2), Si1−Fe1−P2
166.30(4).
hexacoordinate octahedral structure. The axial angle P2−Fe1−
Si1 is 166.30°, deviating from 180°. The sum of equatorial
plane bond angles is 357.41°, deviating from 360°. Due to the
strong trans influence of Si and H atoms, Fe1−P2 (2.2742(9)
Å) and Fe1−P3 (2.226(1) Å) are remarkably longer than Fe1−
P1 (2.2095(6) Å) and Fe1−P1a (2.2095(9) Å). The Fe1−H
bond (1.47 Å) is in the normal scope of an Fe−H bond.10 The
whole molecule has the symmetry plane [Si1P3P2H]. Complex
2 belongs to point group Cs.
Recently, several hydrido iron pincer complexes have been
reported as catalysts for the reduction of unsaturated
compounds.11 In addition, our group has reported iron hydrido
complexes for the reduction of aldehydes and ketones.7,12
These all proved that hydrido iron pincer complexes are
potential effective catalysts. Therefore, the catalytic activity of
complex 2 was tested for the reduction of aldehydes. Several
aldehydes were chosen as substrates with (EtO)3SiH as a
hydrogen source. The reactions were carried out with 30 mol %
catalyst and a reaction temperature of 60−80 °C. Unfortu-
nately, low conversions of substrates were found (determined
by GC). The result might be because the large electronegativity
of nitrogen atoms makes the silicon atom become a better π
acceptor. This structure makes the metal center more stable.
Therefore, the PMe3 ligand cannot easily dissociate from the
Figure 1. Hydrido resonance of complex 2.
signal (Figure 1) is found at −18.70 ppm as a tdd peak with the
31P−1H coupling constants JPH = 66, 24, 6 Hz. The resonance is
first split into a triplet by the two phosphorus atoms of the
PPh2 groups. Then, each phosphorus atom of the PMe3 group
splits the triplet into a doublet of doublets. In preligand 1, the
four methylene hydrogen atoms have the same chemical
1
environment; therefore, they cannot be distinguished by H
NMR spectroscopy. In complex 2, the four methylene
hydrogen atoms have different chemical environments due to
the formation of the structure of complex 2. Even the two
hydrogen atoms of the same methylene group can be also
1
distinguished by H NMR spectroscopy. For example, the Ha
atom is coupled with Hb and then further coupled with the
nearby phosphorus atom to split into a pseudotriplet (Scheme
2 and Figure 2). However, the chemical shifts of Ha and Ha′
are very close and much different from those of Hb and Hb′.
This result is further proved by 13C NMR spectroscopy. Two
methylene carbon atoms were recorded at 63.86 and 64.02
ppm. This phenomenon can be explained by the fixation of the
two methylene groups caused by the coordination of the
preligand.
B
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iron center and there is no coordination vacancy for the
catalytic reaction.
Scheme 4. Synthesis of Complex 4
R e a c t i on o f C o M e ( P M e 3 ) 4 w i t h H S i M e -
(NCH2PPh2)2C6H4 (1). Compound 1 in 40 mL of THF was
combined with CoMe(PMe3)4 in 20 mL of THF (Scheme 3);
Scheme 3. Synthesis of Complex 3
the solution turned dark red from bright transparent red after
being stirred for 48 h. Complex 3 was isolated as red crystals
from a mixed solvent (diethyl ether/pentane, 1/1). The PMe3
signals of complex 3 in the 1H NMR spectrum (δ 0.82 and 1.29
ppm) and in the 31P NMR spectrum (δ −2.42 and 16.89 ppm)
clearly indicate that the two trimethylphosphine ligands are not
in the same chemical environment. X-ray crystallography data
indicate that the structure of 3 has a trigonal-bipyramidal
coordination geometry (Figure 4). [P2P3P4] is the equatorial
Figure 5. ORTEP plot of complex 4 at the 50% probability level
(hydrogen atoms are omitted for clarity). Selected bond lengths (Å)
and angles (deg): I1−Co1 2.6099(5), Co1−P1 2.208(1), Co1−P2
2.235(1), Co1−P3 2.265(1), Co1−Si1 2.280(1); P1−Co1−P2
110.19(4), P3−Co1−Si1 176.01(4), P1−Co1−I1 139.44(3), P2−
Co1−I1 104.09(3).
176.01°, deviating from 180°, and the sum of equatorial plane
bond angles is 353.72°, deviating from 360°. The Co−P bonds
of complex 4 are longer than those of complex 3. The Co−Si
bond (2.28 Å) of complex 4 is particularly long in this series of
cobalt complexes. It is conjectured that the process from 3 to 4
is a radical mechanism. The addition of iodo radical, formed via
homolytic cleavage of iodomethane, to the cobalt(I) center of 3
gives rise to the cobalt(II) center of 4. Two methyl radicals
form one molecule of ethane. The formation of ethane was
confirmed by an in situ 1H NMR spectrum with a chemical shift
of 0.89 ppm.7 In this process the pentacoordinate 18-electron
cobalt(I) complex 3 transforms to the pentacoordinate 17-
electron cobalt(II) species 4.
Synthesis of CoHCl(PMe3)(SiMe(NCH2PPh2)2C6H4) (5).
In our early work, CoCl(PMe3)3 was proven to be an effective
Si−H activation reagent.7,8 Thus, compound 1 and CoCl-
(PMe3)3 were combined in THF (Scheme 5). After the mixture
was stirred for 20 h, hydrido cobalt(III) complex 5 as a Si−H
activation product was isolated from diethyl ether. Complex 5
Figure 4. ORTEP plot of complex 3 at the 50% probability level
(hydrogen atoms are omitted for clarity). Selected bond lengths (Å)
and angles (deg): Co1−P4 2.1820(5), Co1−P3 2.1885(5), Co1−P2
2.1964(5), Co1−P1 2.2148(5), Co1−Si1 2.2559(5), Co2−P8
2.1817(5), Co2−P7 2.1958(5), Co2−P5 2.2180(5), Co2−P6
2.2232(5), Co2−Si2 2.2748(5); P4−Co1−P3 122.67(2), P4−Co1−
P2 106.84(2), P3−Co1−P2 124.97(2), P4−Co1−P1 99.22(2), P3−
Co1−P1 96.99(2), P2−Co1−P1 7.31(2), P1−Co1−Si1 172.79(2).
plane, and the Si1−Co1−P1 group is in the axial position. This
is accompanied by some distortions from ideality. The axial
angle of P1−Co1−Si1 is 172.79(2)°, deviating from 180°. The
sum of the equatorial plane bond angles is 354.48°, deviating
from 360°. The Co−P bonds of complex 3 are shorter than
usual Co−P bonds.13
Scheme 5. Different Strategies for Preparing Complex 5
Re acti on o f Me I wi th Co(PMe 3 ) 2 (SiMe-
(NCH2PPh2)2C6H4) (3). Complex 3 was treated with CH3I in
THF (Scheme 4). The solution turned dark brown quickly
from red. Finally, complex 4 was isolated as orange crystals
from a mixed solvent (THF/pentane, 1/1). Cobalt(II) complex
4 is paramagnetic. The crystal data of complex 4 indicate that it
has a trigonal-bipyramidal coordination geometry (Figure 5).
[P1P2I1] is the equatorial plane, and the Si1−Co1−P3 group is
in the axial position. The P3−Co1−Si1 axial bond angle is
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can also be prepared by combining complex 3 with HCl in
THF. The typical ν(Co−H) stretching band is found at 1985
some complexes containing Co−Cl bond can catalyze Kumada
coupling reactions.15 Encouraged by these results, we studied a
series of Kumada coupling reactions catalyzed by complex 5.
At the beginning, the Kumada cross-coupling of chlor-
obenzene with (4-methylphenyl)magnesium bromide catalyzed
by complex 5 was used as a probe reaction. When the
temperature was below 60 °C, there was little homocoupling
product of the Grignard reagent. However, when the
temperature was increased to 60 °C, the homocoupling
product of the Grignard reagent was obviously formed
according to GC analysis. When the temperature was increased
to 80 °C with dioxane as solvent, the conversion declined
sharply. A gray precipitate appeared in the solution. The
catalyst should have decomposed. Finally, the reaction
conditions 50 °C, 48 h, and THF as the solvent (Table 1,
entry 4) were adopted.
1
cm−1 in the IR spectrum of 5. In the H NMR of 5, the
resonance of the hydrido hydrogen is at −28.78 ppm (Figure
6). It is split into a quartet because the hydrogen atom is
Table 1. Kumada Cross-Coupling Reactions of
Chlorobenzene with (4-Methylphenyl)magnesium Bromide
Catalyzed by 5
Figure 6. Hydrido resonance of complex 5.
coupled with three phosphorus atoms in PPh2 and PMe3.
Similar to the case for complex 2, the two hydrogen atoms in
the methylene group of complex 5 also lie in different chemical
environments. However, the difference between two chemical
shifts is smaller than that of complex 2. X-ray crystallography
data indicate that the structure of 5 features octahedral
coordination (Figure 7). [P1P3Si1P2] is the equatorial plane,
entry
time (h)
temp (°C)
solvent
conversn (%)
1
2
3
4
5
6
7
24
48
48
48
48
48
48
25
25
40
50
50
60
80
THF
30
60
THF
THF
75
THF
90
toluene
THF
60
85
dioxane
<10
Under the optimized conditions, a series of reactions of 4-R1-
chlorobenzene with (4-R2-phenyl)magnesium bromide were
examined (Table 2). It can be summarized from Table 2 that
Table 2. Kumada Cross-Coupling Reactions of Aryl
a
Chlorides with Grignard Reagents Catalyzed by 5
b
entry
R1
R2
yield (%)
1
2
3
4
5
6
H
Me
OMe
H
84
70
80
72
65
67
Figure 7. ORTEP plot of complex 5 at the 50% probability level (most
hydrogen atoms are omitted for clarity). Selected bond lengths (Å)
and angles (deg): Co1−P1 2.2364(5), Co1−P2 2.2063(4), C1−P3
2.1976(4), Co1−Si1 2.2480(5), Co1−Cl1 2.3316(4), Co1−H50
1.38(2); Cl1−Co1−H50 178.8(1), P2−Co1−Si1 78.909(2), P3−
Co1−Si1 78.079(2), P1−Co1−P3 105.438(2), P1−Co1−P2
97.957(2).
H
Me
Me
OMe
H
OMe
OMe
Me
a
b
Conditions: 50 °C, 48 h. Isolated yields.
and the Cl1−Co1−H50 group is in the axial position. This is
accompanied by some distortions from ideality as well. The
axial bond angle of Cl1−Co1−H50 is 178.8°, slightly deviating
from 180°. The sum of equatorial plane bond angles is 360.38°,
very close to 360°. In addition, because of the strong trans
influence of Si, the Co1−P1 bond (2.2364(5) Å) is longer than
both Co1−P2 (2.2063(4) Å) and Co1−P3 (2.1976(4) Å)
bonds.
Catalytic Application of Complex 5 in Kumada
Coupling Reactions. Complex 5 is a Co(III) compound
containing a Co−H and a Co−Cl together. This structure was
assumed to be an unstable structure sometimes,14 making the
complex a potential catalyst. Early work demonstrated that
aryl chlorides with an H or Me group give higher yields than
aryl chlorides with an OMe group. These reactions prove that
complex 5 is an effective catalyst for Kumada cross-coupling
reactions. In Table 3, we examined cross-coupling reactions of
dihalogenated phenyl with (4-R2-phenyl)magnesium bromide.
The yields of these reactions are relatively lower than those for
monosubstituted Kumada coupling reactions. From entries 1
and 2, it could be seen that, due to the potential steric
hindrance effect, lower yields were obtained for o-dichlor-
obenzene as the substrate in comparison to those for m-
dichlorobenzene and p-dichlorobenzene.
At the same time, a series of Kumada cross-coupling
reactions of different aryl bromides with Grignard reagents
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Table 3. Kumada Cross-Coupling Reactions of Aryl
Dichlorides with Grignard Reagents Catalyzed by 5
Scheme 6. Proposed Mechanism for Complex 5 Catalyzed
Kumada Coupling Reactions
a
b
entry
X
R2
yield (%)
1
2
3
4
5
6
o-Cl
o-Cl
m-Cl
m-Cl
p-Cl
p-Cl
H
56
48
68
72
75
65
Me
H
Me
H
Me
a
b
Conditions: 50 °C, 48 h. Isolated yields.
catalyzed by complex 5 were explored. The reaction temper-
ature was 10 °C, lower than that for the aforementioned
reactions. The reaction time was shortened to half of the time
used for the above reactions. From Table 4, it is concluded that
Table 4. Kumada Cross-Coupling Reactions of Aryl
Bromides with Grignard Reagents Catalyzed by Complex 5
a
b
entry
R4
R2
yield (%)
1
2
3
4
5
6
7
8
9
H
H
Me
OMe
H
88
75
85
82
78
85
83
80
70
p-Me
p-Me
p-OMe
p-OMe
o-Me
intermediate 5a, another stoichiometric reaction between
complex 5 and (4-methylphenyl)magnesium bromide was
carried out in THF again in the presence of 1 equiv of
trimethylphosphine as a supporting ligand. The reaction
solution was heated to 50 °C for 24 h. Finally, complex 3
was isolated from n-pentane. This gave evidence for the
presence of 5a. A stoichiometric reaction between complex 5
and chlorobenzene was also operated. However, these two
substances did not react with each other.
OMe
H
Me
H
o-Me
Me
OMe
o-Me
a
b
Conditions: 40 °C, 24 h. Isolated yields.
complex 5 showed better catalytic activity for Kumada cross-
coupling reaction of aryl bromides with Grignard reagents.
Through literature retrieval, we found that it is the first hydrido
cobalt(III) chloride catalyst for Kumada cross-coupling
reactions.
CONCLUSION
■
The new silyl pincer proligand HSiMe(NCH2PPh2)2C6H4 (1)
is designed. A series of studies of the reactions of complex 1
with electron-rich iron and cobalt complexes supported by
trimethylphophine ligands were carried out. Novel tridentate
silyl pincer Fe and Co complexes 2−5 were prepared via Si−H
bond activation. With a catalyst loading of 5 mol %, complex 5
displays efficient catalytic activity for Kumada cross-coupling
reactions of aryl chlorides and aryl bromides with Grignard
reagents. A catalytic reaction mechanism was proposed and
partially experimentally verified.
On the basis of related literatures,16 the reaction mechanism
is hypothesized (Scheme 6). At first, complex 5 reacts with
Grignard reagent to form intermediate 5a with one vacant
coordination site. Then oxidative addition of R′Cl to
intermediate 5a gives rise to intermediate 5b, followed by
transmetalation of RMgBr to form intermediate 5c. Finally,
reductive elimination of intermediate 5c leads to formation of
R-R′ with the recovery of intermediate 5a. In order to verify the
reaction mechanism proposed in Scheme 6, the following three
experiments were designed. A stoichiometric reaction between
complex 5 and (4-methylphenyl)magnesium bromide was
carried out in THF. The reaction solution was placed at 50
°C for 24 h. This solution turned red from dark yellow. Before
further operation, GC-MS measurements were used to analyze
the solution. Toluene was detected (page s20 in theSupporting
Information). After that, volatiles were removed in vacuo.
Diethyl ether and n-pentane were used to extract the solid.
However, attempts to isolate intermediate 5a failed. Perhaps 5a
as an unstable intermediate decomposed to the unknown gray
white solid. In the process of isolating and confirming the
EXPERIMENTAL SECTION
■
General Procedures and Materials. All air-sensitive materials
were prepared and used under a nitrogen atmosphere with the
standard Schlenk techniques. n-Pentane, diethyl ether, THF, and
toluene were dried by distillation from Na−benzophenone under
nitrogen before use. Fe(PMe3)4,17 CoMe(PMe3)4,18 and CoCl-
19
(PMe3)3 were prepared by the literature methods. The Grignard
reagents were prepared from the corresponding bromide and
magnesium turnings in anhydrous tetrahydrofuran (THF) according
to the known procedures20 and were titrated prior to use. All other
chemicals were purchased and used as received without further
purification. Infrared spectra (4000−400 cm−1), as obtained from
Nujol mulls between KBr disks, were recorded on a Bruker ALPHA
E
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1
FT-IR instrument. H, 13C{1H}, 29Si{1H}, and 31P{1H} NMR spectra
g, 0.95 mmol) was dissolved in 60 mL of THF. The resultant mixture
was stirred at room temperature for 24 h. After removal of the volatiles
under reduced pressure the residue was extracted with pentane and
diethyl ether. Compound 5 (0.49 g, 0.69 mmol) was isolated as yellow
crystals in 80% yield from diethyl ether at room temperature.
(300, 75, 60, and 121 MHz, respectively) were recorded on a Bruker
Avance 300 spectrometer with C6D6 as the solvent without an internal
reference at room temperature. Elemental analyses were carried out on
an Elementar Vario ELIII instrument.
Synthesis of HSiMe(NCH2PPh2)2C6H4 (1). Triethylamine (2.93 g,
29.00 mmol) was added to a stirred solution of C6H4(NHCH2PPh2)2
(7.3 g, 14.48 mmol) in THF (100 mL). Dichloromethylsilane (3.0 g,
26.09 mmol) was added dropwise to the stirred solution. The resultant
suspension was stirred for 2 days and then stored at 4 °C for 2 h. The
supernatant was isolated by filtration, and volatiles were removed in
vacuo, leaving a sticky solid. This was extracted with benzene, and the
residual precipitate was removed by filtration. The benzene was
removed in vacuo; then trituration of the solid in pentane/diethyl
ether (1/1, 50 mL) yielded a white precipitate, which was isolated by
cannula filtration. Yield: 74.8%. IR (Nujol, KBr, cm−1): 3050 (Ar−H),
(b) HCl (0.59 mL, 1.26 mol/L in Et2O) was added to complex 3
(0.57 g, 0.75 mmol) in 40 mL of THF with stirring at room
temperature for 12 h. After removal of the volatiles under reduced
pressure the residue was extracted with pentane and diethyl ether.
Compound 5 (0.32 g, 0.45 mmol) was isolated as yellow crystals in
60% yield from diethyl ether at room temperature. IR (Nujol, KBr,
1
cm−1): 3050 (Ar−H), 1985 (Co−H), 937 (PMe3). H NMR (300
MHz, C6D6, δ/ppm): −28.78 (q, J = 45 Hz, 1H, Co-H), 0.00 (s, 3H,
SiCH3), 0.97 (d, J = 7.2 Hz, 9H, PCH3), 4.65−4.77 (m, 4H, CH2),
7.08−7.34 (m, 20H, C6H5), 8.02 (m, 4H, C6H4). 31P NMR (121 MHz,
C6D6, δ/ppm): 5.18 (s, 1P, PMe3), 84.39 (s, 2P, PPh2). 13C NMR (75
MHz, C6D6, δ/ppm): 10.64 (d, SiCH3), 19.45 (m, PCH3), 57.31 (m,
CH2), 112.93 (Ar), 119.78 (Ar), 129.69 (Ar), 133.43 (Ar), 134.53
(Ar), 149.90 (Ar). Anal. Calcd for C36H41ClCoN2P3Si (717.09 g/
mol): C, 60.29; H, 5.76; N, 3.91. Found: C, 60.43; H, 5.78; N, 3.87.
X-ray Structure Determination. Diffraction data were collected
on a Bruker SMART Apex II CCD diffractometer equipped with
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The
structures were resolved by direct or Patterson methods with the
SHELXS-97 program and were refined on F2 with SHELXTL.
Hydrogen atoms were included in calculated positions and were
refined using a riding model. A summary of crystal data, data collection
parameters, and structure refinement details is given in the Supporting
Information. CCDC-1427407 (2), CCDC-1427422 (3), CCDC-
1427421 (4), and CCDC-1427423 (5) contain supplementary
crystallographic data for this paper. Copies of the data can be
obtained free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (+44)1223-336-033; e-mail, deposit@
ccdc.cam.ac.uk).
Representative Experimental Procedure for Cross-Coupling
Reaction. Under a N2 atmosphere complex 5 (2 mL, 0.025 mmol/mL
in THF) was placed in a Schlenk tube. Chlorobenzene (0.106 g, 1
mmol) and (4-methylphenyl)magnesium bromide (1 mL, 1.22 mmol/
mL in THF) were added. The reaction mixture was stirred for 48 h at
50 °C and was quenched with 10 mL of H2O. The product was
extracted three times with 50 mL of Et2O. The organic layers were
combined and dried over Na2SO4. All volatiles were removed under
reduced pressure. The crude product was purified by column
chromatography over silica gel with petroleum ether as eluent to
provide the corresponding product.
1
2116 (Si−H). H NMR (300 MHz, CDCl3, δ/ppm): 0.12 (m, 3H,
CH3), 3.94 (m, 4H, CH2), 5.17 (m, 1H, SiH), 6.74 (s, 4H, C6H4),
7.33−7.48 (m, 20H, C6H5). 31P NMR (121 MHz, CDCl3, δ/ppm):
−22.99 (s, P, PPh2). 13C NMR (75 MHz, CDCl3, δ/ppm): 0.00 (t,
SiCH3), 44.02 (d, CH2), 106.08 (d, Ar), 127.00 (dd, Ar), 127.51 (d,
Ar), 131.11−131.64 (m, Ar), 135.31−135.85 (m, Ar), 139.24 (d, Ar).
29Si NMR (79.45 MHz, CDCl3, δ/ppm): −3.42 (d, J = 237 Hz). Anal.
Calcd for C33H32N2P2Si (546.18 g/mol): C, 72.51; H, 5.90; N, 5.12.
Found: C, 72.70; H, 5.72; N, 5.34.
Synthesis of FeH(PMe3)2(SiMe(NCH2PPh2)2C6H4) (2). Com-
pound 1 (0.8 g, 1.46 mmol) in 40 mL of THF was treated with
Fe(PMe3)4 (0.55 g, 1.53 mmol) in 20 mL of THF with stirring at
room temperature for 24 h. After removal of the volatiles under
reduced pressure, the residue was extracted with pentane and diethyl
ether. Compound 2 (0.74 g, 0.98 mmol) was isolated as yellow crystals
in 67% yield from diethyl ether at room temperature. IR (Nujol, KBr,
1
cm−1): 3050 (Ar−H), 1840 (Fe−H), 937 (PMe3). H NMR (300
MHz, C6D6, δ/ppm): −18.6 (tdd, J = 66, 24, 6 Hz, 1H, Fe-H), 0.60 (d,
9H, PMe3), 0.87 (s, 3H, SiCH3), 1.28 (d, 9H, PMe3), 4.21 (m, 2H,
PCHaHbN), 4.99 (m, 2H, PCHa′Hb′N), 6.82−7.31 (m, 20H, C6H5),
7.84 (s, 4H, C6H4). 31P NMR (121 MHz, C6D6, δ/ppm): 17.42 (m,
1P, PMe3), 21.47 (m, 1P, PMe3), 110.26 (m, 2P, PPh2). 13C NMR (75
MHz, C6D6, δ/ppm): 12.88 (d, SiCH3), 25.08 (d, PCH3), 28.16 (d,
PCH3), 63.85 (m, CH2), 64.02 (m, CH2), 112.78 (Ar), 117.96 (Ar),
129.48 (Ar), 132.55 (Ar), 135.54 (Ar), 140.90 (Ar), 145.87 (Ar),
149.49 (Ar). Anal. Calcd for C39H50FeN2P4Si (754.63 g/mol): C,
62.07; H, 6.68; N, 3.71. Found: C, 61.99; H, 6.48; N, 3.68.
Synthesis of Co(PMe3)2(SiMe(NCH2PPh2)2C6H4) (3). Com-
pound 1 (0.53 g, 0.97 mmol) in 40 mL of THF was combined with
CoMe(PMe3)4 (0.38 g, 1.02 mmol) in 20 mL of THF with stirring at
room temperature for 48 h. After removal of the volatiles under
reduced pressure the residue was extracted with pentane and mixed
solvent (diethyl ether/pentane, 1/1). Compound 3 (0.53 g, 0.70
mmol) was isolated as red crystals in 72% yield from mixed solvent
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00937.
1
(diethyl ether/pentane, 1/1) at 0 °C. H NMR (300 MHz, C6D6, δ/
ppm): 0.65 (s, 3H, SiCH3), 0.82 (d, J = 6.3 Hz, 9H, PCH3), 1.29 (d, J
= 5.4 Hz, 9H, PCH3), 4.24 (m, 4H, CH2), 6.93−7.41 (m, 20 H, C6H5),
7.79 (s, 4H, C6H4). 31P NMR (121 MHz, C6D6, δ/ppm): −2.42 (m,
1P, PMe3), 16.89 (m, 1P, PMe3), 77.48 (m, 2P, PPh2). 13C NMR (75
MHz, C6D6, δ/ppm): 12.26 (m, SiCH3), 24.09 (d, PCH3), 26.94 (d,
PCH3), 61.97 (m, CH2), 114.90 (Ar), 119.87 (Ar), 132.97 (Ar),
142.39 (Ar), 148.37 (Ar). Anal. Calcd for C39H49CoN2P4Si (756.70 g/
mol): C, 61.90; H, 6.53; N, 3.70. Found: C, 62.13; H, 6.80; N, 3.92.
Synthesis of ColPMe3SiMe(NCH2PPh2)2C6H4 (4). Complex 3
(0.62 g, 0.82 mmol) in 40 mL of THF was treated with MeI (0.12g,
0.82 mmol) in 20 mL of THF with stirring at room temperature for 24
h. After removal of the volatiles under reduced pressure the residue
was extracted with pentane and THF/diethyl ether. Compound 4
(0.50 g, 0.62 mmol) was isolated as dark yellow crystals in 68% yield
from THF/diethyl ether at −30 °C. IR (Nujol, KBr, cm−1): 3057 (Ar−
H), 950 (PMe3). Anal. Calcd for C36H40CoIN2P3Si (807.53 g/mol):
C, 53.54; H, 4.99; N, 3.47. Found: C, 53.35; H, 5.18; N, 3.60.
Synthesis of CoHClPMe3SiMe(NCH2PPh2)2C6H4 (5). (a) A
mixture of complex 1 (0.47 g, 0.86 mmol) and CoCl(PMe3)3 (0.30
1
Crystallographic data for 2−5 and the original IR, H
NMR, 31P NMR, 13C NMR, and 29Si NMR spectra of the
complexes (PDF)
Crystallographic data for 2−5 (CIF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for H.S.: hjsun@sdu.edu.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support by NSF China No.
21272138/21572119 and support from Prof. Dr. Dieter Fenske
F
DOI: 10.1021/acs.organomet.5b00937
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and Dr. Olaf Fuhr (Karlsruhe Nano-Micro Facility) in the
determination of the crystal structures.
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DOI: 10.1021/acs.organomet.5b00937
Organometallics XXXX, XXX, XXX−XXX