Low-Coordinate NHC-Cobalt(0)-Olefin Complexes: Synthesis, Structure, and Their Reactions with Hydrosilanes

Article abstract of DOI:10.1021/acs.inorgchem.7b01763

The one-pot reaction of CoCl₂ with 1 or 2 equiv of N-heterocyclic carbene (NHC) ligands, vinyltrimethylsilane (vtms), and 2 equiv of reducing reagents (KC₈ or Na(Hg)) proved an effective protocol for the synthesis of three-coordinate NHC-cobalt(0)-olefin complexes, and by which the new low-coordinate cobalt(0) complexes [(NHC)Co(vtms)₂] (NHC = 1,3-di(2′,6′-diethylphenyl)-4,5-(CH₂)₄-imidazol-2-ylidene (cyIDep), 6; 1,3-diadamantylimidazol-2-ylidene (IAd), 7) and [(NHC)₂Co(vtms)] (NHC = 1-(2′,4′,6′-trimethylphenyl)-3-cyclohexylimidazol-2-ylidene (IMesCy), 8; 1,3-dicyclohexylimidazol-2-ylidene (ICy), 9) were prepared in moderate yields and further characterized by spectroscopic methods. The NHC-cobalt(0)-vtms complexes can serve as low-coordinate NHC-cobalt(0) precursors to react with hydrosilanes. From the reactions of Ph₂SiH₂ with the corresponding NHC-cobalt(0)-vtms complexes, the cobalt silyl complexes [(cyIDep)(H)Co(μ-η²:η²-H₂SiPh₂)(μ- η²-HSiPh₂)₂Co(H)(cyIDep)] (10), [(NHC)Co(μ- η²-SiHPh₂)₂Co(NHC)] (NHC = IPr, 13; IAd, 14), and [(IMesCy)₂Co(H)(SiHPh₂)] (15) were synthesized. Further reactivity studies established the thermal decomposition of 10 to give [(cyIDep)Co(μ- η²-HSiPh₂)₂Co(cyIDep)] (11), H₂, and Ph₂SiH₂, the reaction of 11 with Bu^tNC (4.5 equiv) to afford [(cyIDep)(Bu^tNC)Co(μ- η²-HSiPh₂)₂Co(CNBu^t)₃] (12) and cyIDep, as well as the conversion of 15 to a silyl-functionalized NHC-cobalt(II) complex 16 upon eliminating H₂. These cobalt silyl complexes have been characterized by single-crystal X-ray diffraction studies, NMR, absorption, and infrared spectroscopies, as well as elemental analyses. The diversified reaction outcomes demonstrate the rich reaction chemistry of low-coordinate NHC-cobalt(0) complexes.

Full text of DOI:10.1021/acs.inorgchem.7b01763

Article
pubs.acs.org/IC
Low-Coordinate NHC-Cobalt(0)-Olefin Complexes: Synthesis,
Structure, and Their Reactions with Hydrosilanes
Jian Sun, Yafei Gao, and Liang Deng*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of
Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai, 200032, P. R. China
*
S Supporting Information
ABSTRACT: The one-pot reaction of CoCl with 1 or 2 equiv of N-
2
heterocyclic carbene (NHC) ligands, vinyltrimethylsilane (vtms), and
2
equiv of reducing reagents (KC or Na(Hg)) proved an effective
8
protocol for the synthesis of three-coordinate NHC-cobalt(0)-olefin
complexes, and by which the new low-coordinate cobalt(0) complexes
[
(NHC)Co(vtms) ] (NHC = 1,3-di(2′,6′-diethylphenyl)-4,5-(CH ) -
2
2 4
imidazol-2-ylidene (cyIDep), 6; 1,3-diadamantylimidazol-2-ylidene
(
IAd), 7) and [(NHC) Co(vtms)] (NHC = 1-(2′,4′,6′-trimethyl-
2
phenyl)-3-cyclohexylimidazol-2-ylidene (IMesCy), 8; 1,3-dicyclohex-
ylimidazol-2-ylidene (ICy), 9) were prepared in moderate yields and
further characterized by spectroscopic methods. The NHC-cobalt(0)-
vtms complexes can serve as low-coordinate NHC-cobalt(0)
precursors to react with hydrosilanes. From the reactions of Ph SiH with the corresponding NHC-cobalt(0)-vtms complexes,
2
2
2
2
2
2
the cobalt silyl complexes [(cyIDep)(H)Co(μ-η :η -H SiPh )(μ-η -HSiPh ) Co(H)(cyIDep)] (10), [(NHC)Co(μ-η -SiHPh ) -
2
2
2 2
2 2
Co(NHC)] (NHC = IPr, 13; IAd, 14), and [(IMesCy) Co(H)(SiHPh )] (15) were synthesized. Further reactivity studies
2
2
2
established the thermal decomposition of 10 to give [(cyIDep)Co(μ-η -HSiPh ) Co(cyIDep)] (11), H , and Ph SiH , the
2
2
2
2
2
t
t
2
t
reaction of 11 with Bu NC (4.5 equiv) to afford [(cyIDep)(Bu NC)Co(μ-η -HSiPh ) Co(CNBu ) ] (12) and cyIDep, as well as
2
2
3
the conversion of 15 to a silyl-functionalized NHC-cobalt(II) complex 16 upon eliminating H . These cobalt silyl complexes have
2
been characterized by single-crystal X-ray diffraction studies, NMR, absorption, and infrared spectroscopies, as well as elemental
analyses. The diversified reaction outcomes demonstrate the rich reaction chemistry of low-coordinate NHC-cobalt(0)
complexes.
INTRODUCTION
While the known cobalt(0) complexes are dominated in
numbers by the ones with the coordination numbers of five and
four, there are a few low-coordinate cobalt(0) complexes
scattering in the literature. In his seminal study on Co(PMe ) ,
■
Cobalt(0) complexes are an important class of low-valent
cobalt species, and their capability of performing oxidative
addition with versatile covalent bonds forms the basis of many
3
4
Klein briefly noted the preparation of the three-coordinate
1
,2
cobalt-mediated or catalyzed reactions.
The most well-
2
cobalt complex (PMe ) Co(η -PhNNPh) from the reaction of
3
2
studied cobalt(0) complex is probably the dinuclear complex
Co (CO) that can function as an equivalent of two molecules
3
Co(PMe3)4 with PhNNPh. The structure of this three-
coordinate complex has not been unambiguously established.
More recently, Peters reported the first example of two-
coordinate formal cobalt(0) complex [Co(Et -cAAC) ] utiliz-
2
8
−
of the 17e species Co(CO) to react with substrates, giving
4
cobalt(I) complexes as the products of oxidative addition
2
2
1
,2
reactions. While the four-coordinate species Co(CO) could
4
ing cyclic alkylaminocarbene ligand Et -cAAC (3,3-diethyl-5,5-
2
only exist transiently, analogue phosphine complexes, e.g.,
dimethyl-1-(2′,6′-diisopropylphenyl)pyrrolidine-2-ylidene) as
11
Co(PMe3 )
4
and Co(dppf)2 (dppf = 1,1′-bis-
diphenylphosphino)ferrocene), are isolable and their oxidative
addition reactions with organic substrates have been extensively
ligands. We found that the combination of N-aryl-substituted
NHCs with vinylsilane presents an effective ligand environment
for the stabilization of three-coordinate cobalt(0) complexes
[(IMes)Co(dvtms)] (1 in Chart 1, dvtms = divinyltetrame-
(
3
−9
studied.
As a notable recent example, Li showed that
Co(PMe ) reacts with perfluorinated toluene to give the
thyldisiloxane) and [(NHC)Co(vtms) ] (2−5 in Chart 1,
3
4
2
2
9
cobalt(II) benzyne complex [Co(PMe ) (η -C F (4-CF ))].
NHC = IMes, IPr, sIPr, cyIPr; vtms = vinyltrimethylsi-
3
3
6
3
3
12−14
In addition to phosphine ligands, isocyanides are also known to
stabilize four-coordinate cobalt(0) species. Using the bulky
lane).
Preliminary reactivity study revealed the reactions
of these three-coordinate cobalt(0) complexes with organic
Mes2
isocyanide ligand CNAr , Figueroa achieved the synthesis of
Mes2
Mes2
[
Co(CNAr )4] (Ar
= 2,6-di(2′,4′,6′-trimethylphenyl)-
Received: July 10, 2017
1
0
phenyl).
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b01763
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Inorganic Chemistry
Article
Chart 1. Schematic Representations of the NHC-Cobalt(0)-
Olefin Complexes and the Designations for NHCs
stabilization of low-coordinate NHC-cobalt(0) complexes since
the reduction of (IMes) CoCl2 with 2 equiv of sodium
2
amalgam in the absence of olefins resulted in the formation
of the cobalt(II) cyclometalated NHC complex [Co-
15
(
IMes′) ].
2
Complexes 6−9 are air- and moisture-sensitive. As isolated, 6
presents as a green crystalline solid resembling 1−5, the IAd
complex 7 as blue crystals, and the bis(NHC) complexes 8 and
9
as red solids. They are soluble in low-polarity solvents, e.g.,
benzene, toluene, Et O, and THF. The measured solution
2
magnetic susceptibilities of 6−9 (around 2.9 μ ) are close to
B
those of 1−5. The moments are larger than the spin-only value
of 1.73 μ for an S = 1/2 system, which might be due to strong
B
spin−orbit coupling and/or the presence of trace paramagnetic
1
impurities in the samples. The H NMR spectra of these
cobalt(0) complexes all exhibit broad paramagnetically shifted
resonances (Figures S12−S14 and S17). The spectra of 6 and 7
in C D show 13 and 8 sets of peaks, respectively, indicating
6
6
their idealized C molecular symmetry. There are 35 and 22
signals appearing on the corresponding H NMR spectra of 8
2
azides to furnish mononuclear cobalt(II) and cobalt(IV) imido
complexes in the forms of (NHC)Co(NAr) and (NHC)Co-
1
and 9, consistent with their C molecular symmetry revealed by
s
(
NAr) , respectively. The results hint at the synthetic utility of
2
X-ray crystallographic studies (vide infra).
Figures 1, 2, and S1 depict the molecular structures of 7−9
established by single-crystal X-ray diffraction studies. The
this type of low-coordinate cobalt(0) complexes and prompt
further exploration on their reactivities. In this regard, we report
herein a systematic synthetic study on three-coordinate NHC-
cobalt(0)-vtms complexes featuring different NHCs, and, more
intriguingly, the diversified reactivity of these low-coordinate
cobalt(0) complexes toward hydrosilanes as shown below.
RESULTS AND DISCUSSION
■
Preparation of NHC-Cobalt(0)-vtms. In the previous
study, we found that the vtms complex 2 exhibits higher
reactivity over 1 toward bulky organic azide, which might arise
from the ease of vtms in 2 to dissociate from the metal’s
13
coordination sphere than the chelate ligand dvtms in 1.
Noted this, we targeted on cobalt(0)-vtms complexes bearing
different NHCs. Employing the synthetic protocol used for 1−
5
, four new NHC-cobalt(0)-vtms complexes 6−9 (Chart 1)
were prepared from the one-pot reactions of CoCl with vtms,
2
reducing-agents (KC8 or Na(Hg)) and the corresponding
NHC ligands in THF at room temperature. The reactions can
be described by the stoichiometries shown in eqs 1 and 2 in
Scheme 1. In practice, vtms was used in excess amounts to
Figure 1. Molecular structure of 7 showing 30% probability ellipsoids
and a partial atom-numbering scheme. Hydrogens were omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1−C1
1
.929(4), Co1−C2 2.023(3), Co1−C3 2.050(3), C2−C3 1.429(4),
C1−Co1−C2 90.45(8), C2−Co1−C2A 179.11(15), C2−Co1−C3A
Scheme 1. Stoichiometries of the Reaction for the
Preparations of the NHC-Co(0)-vtms Complexes
1
38.03(11), C1−Co1−C3 131.52(8), C2−Co1−C3 41.08(10), C3A−
Co1−C3 96.95(15).
trigonal planar core in the structure of 7 resembles those of
reported NHC-cobalt(0)-olefin complexes 1 and 2 and also
their analogue nickel, palladium, and platinum complexes
1
6−18
(
NHC)M(dvtms) (M = Ni, Pd, Pt).
Characteristic
ensure the moderate isolated yields (34−53%) of the cobalt(0)
complexes. The ratio of NHC-to-vtms in 2−9 (1:2 or 2:1)
seems to be determined by the steric property of the NHCs as
structure data of 7 include a short Co−C(carbene) distance
of 1.929(4) Å, a long C(olefin)−C(olefin) separation of
1.429(4) Å that is longer than the CC bond in vinylsilane
19,20
the attempts to prepare (cyIDep) Co(vtms) with bulky ligand
(1.32 Å),
and the near perpendicular alignment of the C2−
2
on the stoichiometry of eq 2 furnished 6 as the sole isolable
cobalt(0) product (Figure S40), and the reaction to prepare
C3−Co1−C2A−C3A plane toward the imidazole plane
(dihedral angle of 88 deg). The bis(NHC) complexes 8 and
9 also feature trigonal planar cores with the Co−C(carbene)−
C(carbene)−C(olefin)−C(olefin) atoms being coplanar. The
distances of the two Co−C(carbene) bonds in 8 and 9 are
comparable to each other (1.923(2) and 1.929(2) Å in average,
respectively) and also close to those in 1, 2, and 7. The
(
IMesCy)Co(vtms) according to the stoichiometry of eq 1
2
formed complex 8 (Figure S41). The relatively low isolated
yields should be due to the formation of insoluble species,
presumably cobalt black, in these reactions. It should also be
mentioned that the use of olefin as coligand is important for the
B
DOI: 10.1021/acs.inorgchem.7b01763
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Scheme 2. Reactions of (NHC)Co(vtms) with Ph SiH and
2
2
2
the Further Conversions of the Resulting Silyl Complexes
Figure 2. Molecular structure of 8 showing 30% probability ellipsoids
and a partial atom-numbering scheme. Hydrogens were omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1−C1
1
.922(2), Co1−C2 1.924(2), Co1−C3 1.979(2), Co1−C4 2.038(2),
C3−C4 1.441(3), C1−Co1−C2 107.43(9), C1−Co1−C3 98.16(9),
C1−Co1−C4 140.09(9), C2−Co1−C3 153.58(10), C2−Co1−C4
1
11.93(9), C3−Co1−C4 42.02(9).
C(olefin)−C(olefin) distances (1.441(3) and 1.443(2) Å for 8
and 9, respectively) are marginally longer than that in 7
(
2
1.429(4) Å). The Co−C(olefin) distances (1.979(2) and
.038(2) Å in 8; and 1.986(2) and 2.013(2) Å in 9) are slightly
shorter than those in 7 (2.023(3) and 2.050(3) Å). These data
hint at the enhanced 3d(Co)-to-π*(olefin) back-donation in
the (NHC) Co(vtms) complexes as compared that in (NHC)-
2
Co(vtms)2.
The Reactions of (NHC)Co(vtms) with Hydrosilanes.
2
With the series of three-coordinate cobalt(0) complexes in
hands, we further investigated their reactions with hydrosilanes.
These cobalt(0) complexes could react with the primary
Figure 3. Core molecular structure of 10 showing 30% probability
ellipsoids and a partial atom-numbering scheme. Except the carbon
atoms connecting with silicon and cobalt atoms, the phenyl groups and
the NHC moieties are omitted for clarity. Selected bond lengths (Å):
Co1−Co2 2.578(1), Co1−Si1 2.325(1), Co1−Si2 2.362(1), Co1−Si3
hydrosilane PhSiH to give diamagnetic species featuring high-
3
1
field H NMR signals attributable to cobalt-bound hydride.
However, the attempts to isolate the resulting cobalt-containing
products were generally unsuccessful. The exploration on the
reactions with tertiary hydrosilanes indicated the inertness of
these NHC-cobalt(0)-vtms complexes toward Ph SiH, Et SiH,
2
.255(1), Co1−C1 1.932(3), Co2−Si1 2.340(1), Co2−Si2 2.246(1),
Co2−Si3 2.366(1), Co2−C2 1.929(3), Co1−H1B 1.53(3), Co1−H3A
.42(3), Co1−H2 1.55(3), Co2−H3B 1.57(3), Co2−H1A 1.53(3),
Co2−H 1.38(3), Si1−H1A 1.60(3), Si1−H1B 1.62(3), Si2−H2
.55(3), Si3−H3B 1.64(3).
3
3
1
and (EtO) SiH at ambient temperature, probably due to steric
3
reason. On the other hand, the study on the reactions of NHC-
1
cobalt(0)-vtms with the secondary hydrosilane Ph SiH2 is
2
fruitful, leading to the isolation of diverse cobalt silyl complexes.
The reaction of [(cyIDep)Co(vtms) ] (6) with an excess
(2.578(1) Å) is longer than the separation found in dinuclear
24
2
amount of Ph SiH (3.4 equiv) in diethyl ether at room
cobalt complexes (2.47−2.52 Å) and suggests the weak Co−
Co interaction in the molecule. A close examination on the
interactions of the silane moieties with the cobalt centers then
revealed that one of the silane bridges could be viewed as a μ-
2
2
temperature gave the dinuclear complex [(cyIDep)(H)Co(μ-
2
2
2
η :η -H SiPh )(μ-η -HSiPh ) Co(H)(cyIDep)] (10) in 87%
2
2
2 2
isolated yield as a yellow solid (Scheme 2). Complex 10 has
1
13
29
2
2
been fully characterized by H, C, and Si NMR spectros-
copies, infrared spectroscopy, and elemental analysis (C, H, and
N). In addition to the dinuclear cobalt complex 10, the
hydrosilylation product Me SiCH CH SiHPh was also de-
η :η -H SiPh ligand (Si1 in Figure 3), and that the other two
2 2
(Si2 and Si3 in Figure 3) are best described as silyl ligands [μ-
2
−
2
2
η -SiHPh ] . The μ-η :η -H SiPh ligand has the comparable
2
2
2
Si1−Co1 and Si1−Co2 distances of 2.325(1) and 2.340(1) Å,
the equal H1B−Co1 and H1A−Co2 distances of 1.53(3) Å,
and the Si1−H1A and Si1−H1B distances of 1.60(3) and
1.62(3) Å. These Si−H separations locate on the short end of
3
2
2
2
tected by GC-MS as the byproduct. However, neither 6 nor 10
proved efficient catalyst for the hydrosilylation of vtms with
Ph SiH .
2
2
2
25
Figure 3 shows the core structure of 10. At a glance, the
typical η -(Si−H)-transition-metal complexes (1.6−1.9 Å).
dinuclear complex shows an idealized C molecular symmetry
The Co−Si distances are apparently longer than those of the
2
5
with each cobalt center being coordinating with a cyIDep ligand
reported cobalt silyl complexes, e.g., 2.246(3) Å in [(η -
t
26
and three bridging Ph SiH moieties. The long Si···Si
C H CH CH PBu )(H)CoSiHPhMe], 2.256−2.261 Å in
2
2
5
4
2
2
2
27
separations (3.19, 3.12, and 3.60 Å for Si1−Si2, Si1−Si3, and
[Cp*Co(SiHPh ) (H) ], and 2.228(1) Å in [(NHC-silyl-
2 2 2
28
Si2−Si3, respectively) indicate the absence of Si−Si bond
NHC)Co(N )]. Different from the bridging hydrosilane
2
2
1−23
2
−
between the silane moieties.
The Co−Co distance
ligand, each of the two silyl ligands [μ−η -SiHPh ] has
2
C
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3
6
nonequivalent Si−Co separations toward the two cobalt center
Ph SiH . In the latter case, the silyl-bridged dinickel complex
2 2
(
2.362(1) and 2.246(1) Å for Si2; 2.255(1) and 2.366(1) Å for
[(IPr H )Ni(μ-HSiPh ) Ni(IPr H )] was formed. Noting this,
2 2 2 2 2 2
Si3). The shorter Co−Si distances are consistent with those of
the aforementioned cobalt silyl complexes, whereas the longer
ones are comparable to those of the reported complexes having
we further examined the thermal decomposition reaction of 10
with the aim to achieve the synthesis of analogue cobalt(I) silyl
complex. Indeed, heating the solid of 10 at 120 °C under a
vacuum could result in the production of the dinuclear
2
η -(Si−H)-Co interactions. In addition, the H···Co distances of
2
2
these η -(Si−H)-Co interactions (1.55(3) and 1.57(3) Å) are
cobalt(I) silyl complex [(cyIDep)Co(μ-η -HSiPh ) Co-
2
2
25
also consistent with those of the reported ones. In contrast to
these H···Co separations, the distances of Co1−H3A and
Co2−H of the hydride ligands in 10 (1.42(3) and 1.38(3) Å)
are shorter and typical of Co−H bonds (1.40−1.50
(cyIDep)] (11) (Scheme 2). In this decomposition reaction,
Ph SiH and H are the probable byproducts as heating a
2
2
2
solution of 10 with styrene led to the formation of
ethylbenzene and the Ph HSiCH CH Ph (Figure S39) along
2
2
2
2
6,27,29−31
Å).
In accord with this, the infrared spectrum of 10
with 11. The two organic products should come from cobalt-
mediated hydrogenation and hydrosilylation of styrene.
The molecular structure of 11 (Figure 4) resembles those of
−1
in solid state exhibits resonances at 1944 cm , assignable to
the Co−H stretching resonances.
While the crystal structure data suggest the identity of 10 as a
dinuclear cobalt(II) silyl hydride (B in Chart 2), its solution
the group 10 complexes [(L)M(μ-SiHR )M(L)] (M = Ni, Pd,
2
Chart 2. Canonical Forms of 10
Figure 4. Molecular structure of 11 showing 30% probability ellipsoids
and a partial atom-numbering scheme. Besides the hydrogen atoms on
silicon, all other hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (deg): Co1−Co1A 2.599(1), Co1−C1
1
.931(2), Co1−Si1 2.246(1), Co1−Si1A 2.336(1), Co1−H 1.58(3),
Si1−H 1.66(3), Si1A−Co1−Co1A 53.829(16), Si1−Co1−Si1A
NMR data indicate the presence of fluxional process in solution
phases. Complex 10 is diamagnetic in nature. Its C D solution
1
10.926(19), C1−Co1−Si1 111.00(6), C1−Co1−Si1A 137.94(6).
6
6
1
exhibits a characteristic high-field H NMR peak at −8.97 ppm,
assignable to cobalt-bound hydride. Peak integrations suggest a
cyIDep/hydride ratio of 1:3. The high-field signal does not
3
4,36−38
Pt; L = PCy
, IPr
H
; R = alkyl and aryl).
It contains a
3
2
2
show decoalescence even when the toluene-d solution of 10
Co Si diamond core with a Co−Co distance of 2.599(1) Å, a
2 2
8
was cooled to −60 °C (Figure S30), hinting at fast conversion
Si−Si distance of 3.78 Å, and nonequivalent Co−Si distances of
2.246(1) and 2.336(1) Å. The Co−Si distances, in addition
with the distances of Co1−H and Si1A−H (1.58(3) and
1.66(3) Å, respectively), suggest the 3c-2e bond nature of the
2
between the Co···(η -H-Si) and H−Co−Si forms. There is only
one 29Si{ H} NMR signal at 64.5 ppm in the spectrum of 10.
1
2
9
This signal is slightly broaden in the Si NMR spectrum, and a
2
small JSi−H value of 18 Hz could be estimated by the hydride
Co-(η -H-Si) interactions. The paramagnetic nature of 11 (μeff
= 2.7 μ in C D at room temperature) made the assignment of
the Co-H-Si signal in its H NMR spectrum difficult.
Fortunately, the further reaction of 11 with Bu NC (4.5
1
29
signal on the H NMR spectrum. The chemical shift of the Si
NMR signal is much different from those of the reported
diamagnetic bridging diarylsilylene complexes and bridging
diarylhydrosilyl complexes, e.g., [Cp*Ru(μ-H) (μ -SiPh ) -
B 6 6
1
t
equiv) could furnish the diamagnetic complex [(cyIDep)-
2
2
2 2
33
32
t
t
RuCp*] (110 ppm), [(Me P) Pt (μ -SiPh ) ] (279 ppm),
(Cy P)Pt(μ-SiPh )(μ-SiH Et )Pt(PCy )] (230 ppm),
(dppm)Ru (CO) (μ -Si(p-tolyl) )] (173 ppm), [(dppm)-
(Bu NC)Co(μ-HSiPh
2
)
2
Co(CNBu )
3
] (12) (Scheme 2),
3
3
3
2
2 3
3
4
1
[
[
whose H NMR spectrum shows a hydride signal at −5.3
ppm. Comparing the molecular structures of 12 (Figure 5) and
11 indicated that the reaction has rendered in the dissociation
3
2
2
2
3
35
2
6
2
2
3
5
Ru (CO) (μ -Si(p-tolyl) )(H)(SiH(p-tolyl) )] (150 ppm),
2
5
2
2
2
1
[
(dppm)Ru (CO) (μ -Si(p-tolyl) )(H) (SiH(p-tolyl) ) ] (155
of a cyIDep ligand, which was also detected by H NMR
2
4
2
2
2
2 2
3
5
ppm), [(Cy P)Pt(μ-SiHPh )(μ-SiHEt )Pt(PCy )] (196
ppm), and [(IPr H )Ni(μ-HSiPh ) Ni(IPr H )] (118 ppm,
IPr H = 1,3-diisopropylimidazol-2-ylidene). On the basis of
experiment. The two hydrosilyl bridges in 12 are coordinating
with one cobalt center (Co2) via Co−Si σ-bond and the other
cobalt center (Co1) via 3c-2e Co-(η -H-Si) interactions. The
Co−H and Co−Si distances of the 3c-2e bonds are similar to
those in 11. Being consistent with the solid state structure, the
3
2
2
3
3
4
2
2
2 2
2
2
3
6
2
2
2
these NMR data, we speculate that the fluxional process of 10
in solution might operate between the structures of A and B
with little contribution C and D that contain silylene bridges
29
Si NMR spectrum of 12 measured on its C
D solution
6
6
(
Chart 2).
exhibits a peak at 101 ppm with a large Si−H coupling constant
29
The formation of 10 in the reaction of [(cyIDep)Co(vtms)2]
6) with Ph SiH differs from that of the reaction of the
of J
= 80 Hz. The Si NMR data are comparable to that of
Si−H
(
[(IPr H )Ni(μ-HSiPh ) Ni(IPr H )] (118 ppm and 63 Hz)
2
2
2
2
2 2
2
2
36
nickel(0) complex [(IPr H )Ni(COD)Ni(IPr H )] with
reported by Radius. According to these data, we tentatively
2
2
2
2
D
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
39
to the presence of the isopropyl groups on the NHC ligands.
Being supportive to this speculation, 13 exhibits poor solubility
in common low-polarity solvents (benzene, Et O, and THF),
2
which prevented further characterization by solution NMR
spectroscopies. Complex 14 shows improved solubility over 13,
1
and its H NMR spectrum (Figure S27) resembles that of 11
with broad paramagnetically signals in the range 12 to −9 ppm.
In addition, the absorption spectra of 11 and 14 (Figures S8
and S10) are also similar.
The Reactions of (NHC) Co(vtms) with Ph SiH . Being
2
2
2
different from the aforementioned reactions affording dinuclear
cobalt complexes, the interactions of (NHC) Co(vtms) with
2
Ph SiH gave mononuclear cobalt complexes. Treatment of
2
2
[
−
(IMesCy) Co(vtms)] (8) with Ph SiH (2 equiv) in Et O at
20 °C resulted in a reddish brown solution, and from which
2 2 2 2
yellow crystals of the cobalt(II) complex [(IMesCy) Co(H)-
2
(
SiHPh )] (15) were isolated in 21% yields when performing
2
Figure 5. Molecular structure of 12 showing 30% probability ellipsoids
and a partial atom-labeling scheme. Besides of the hydrogen atom
connecting with Si, all the other hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (deg): Co1−Co2
recrystallization at low temperature (−30 to −20 °C) (Scheme
3
). As shown in Figure 6, 15 displays a square planar
Scheme 3. Reactions of [(IMesCy) Co(vtms)] with Ph SiH
2
2
2
2
.657(1), Co1−Si1 2.303(2), Co1−Si2 2.283(2), Co1−C1 1.934(4),
Co1−C2 1.761(4), Co1−H2 1.60(6), Co1−H1 1.62(4), Co2−Si1
.288(2), Co2−Si2 2.286(2), Co2−C3 1.827(4), Co2−C4 1.802(4),
Co2−C5 1.830(4), Si2−Co1−Si1 89.31(4), C1−Co1−Si1
2
1
31.15(12), C1−Co1−Si2 126.44(11), C2−Co1−C1 95.93(16),
C3−Co2−Co1 115.64(12), C4−Co2−Co1 135.38(15), C5−Co2−
Co1 115.35(13).
assigned 12 as a silyl-bridged Co(0)−Co(II) complex
t
0
II
t
(
cyIDep)(Bu NC)Co (μ-HSiPh ) Co (Bu NC) .
2 2 3
The cobalt(0) complexes containing more steric demanding
NHCs [(IPr)Co(vtms) ] (3) and [(IAd)Co(vtms) ] (7) are
2
2
also reactive toward Ph SiH . The reactions of 3 and 7 with
2
2
Ph SiH (2 equiv) occurred readily at room temperature, and
2
2
from which the brown crystalline solids of [(NHC)Co(μ-
HSiPh ) Co(NHC)] (NHC = IPr, 13; IAd, 14) were isolated
2
2
in 26% and 47% yields, respectively (Scheme 2). Complexes 13
and 14 were characterized by infrared spectroscopy and
elemental analysis. The molecular structure of 13 was further
confirmed by X-ray crystallographic study (Figure S2). As listed
in Table 1, the Co Si diamond core in 13 has the
2
2
corresponding Co−Si distances comparable to those of 11.
Interestingly, the Co−Co distance in 13 (2.497(1) Å) is shorter
than that those in 11 by ca. 0.10 Å. The origin of the short Co−
Co distance in 13 is unclear. A plausible cause might be the
pronounced intramolecular London dispersion force in 13 due
Figure 6. Molecular structure of 15 showing 30% probability ellipsoids
and a partial atom-labeling scheme. Except the hydrides on cobalt and
silicon atoms, all other hydrogen atoms were omitted for clarity.
Selected bond lengths (Å) and angles (deg): Co1−H 1.47(4), Co1−
Si1 2.249(1), Co1−C1 1.937(4), Co1−C2 1.909(4), C1−Co1−Si1
Table 1. Selected Bond Distances (Å) of the Dinuclear
Cobalt Complexes 10−13
1
0
11
2.599(1) 2.657(1)
3.78 3.22
12
13
Co−Co
Si−Si
2.578(1)
2.497(1)
3.80
1
57.9(1), C2−Co1−Si1 97.2(1), C2−Co1−C1 104.9(2).
3.19, 3.12,
.60
3
a
coordination geometry with the cobalt center coordinating with
Co-SiA
2.325(1),
.362(1)
2.336(1) 2.303(2),
2.283(2)
2.317(1)
−
2
one terminal hydride ligand, one hydrosilyl ligand [SiHPh ] ,
2
2
.340(1),
and two IMesCy ligands in a cis-form. The short Co−H and
Co−Si distances (1.47(4) and 2.249(1) Å, respectively) and
long Si−H separation (2.17 Å) suggest the cobalt(II) silyl
hydride nature of 15 that is analogous to the group 10
2
.366(1)
b
Co-SiB
2.255(1),
.246(1)
2.246(1) 2.288(2),
2.286(2)
2.228(1)
1.927(2)
2
Co−C(carbene)
1.932(3),
.929(3)
1.931(2) 1.934(4)
complexes cis-[L M(H)(SiHPh )] (M = Pt, L = Cy P, Ph P; M
1
2
2
3
3
=
Ni, L = IPr H ; M = Ni, L = 1,2-bis(di(tert-butyl)-
2
2
2
a
b
40−42
Co−Si distances of the 3c-2e Co−H−Si interactions. Co−Si
phosphino)ethane).
(vtms)] (9) with Ph SiH indicated the formation of similar
A NMR scale reaction of [(ICy) Co-
2
distances of Co-SiPh H.
2
2 2
E
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
paramagnetic species as 15 (Figures S31 and S32). But, the
attempts to isolate the species via preparative scale reactions
were unsuccessful. The distinct outcome of the reactions of
spectroscopies, single-crystal X-ray diffraction studies, as well
as elemental analyses. They represent the rare examples of low-
coordinate cobalt(0) complexes.
(
NHC)Co(vtms) and (NHC) Co(vtms) with Ph SiH should
Examining the reactions of these NHC-cobalt(0)-olefin
2
2
2
2
associate with the different steric nature of the NHC-cobalt
complexes with Ph SiH revealed their capability of serving as
2
2
fragments (NHC)Co versus (NHC) Co. The latter fragment
might be more sterically shielding, preventing the dimerization
NHC-cobalt(0) precursors to perform oxidative addition
reactions with Si−H bonds. The reactions of [(cyIDep)Co-
(vtms) ], [(IPr)Co(vtms) ], [(IAd)Co(vtms) ], and
2
of the mononuclear cobalt silyl species (NHC) Co(H)-
2
2
2
2
(
SiHPh2).
[(IMesCy) Co(vtms)] with excess amounts of Ph SiH give
[(cyIDep)(H)Co(μ-H SiPh )(μ-HSiPh ) Co(H)(cyIDep)]
2 2 2 2
2
2
2
Complex 15 is unstable at room temperature. In C D , its
6
6
decomposition could give rise to the cobalt(II) complex
(cyCSi)Co(IMesCy′)] (16) that features a silyl-functionalized
NHC chelate (cyCSi) and a cyclometalated IMesCy ligand
IMesCy′) (Scheme 3 and Figure S33). Alternatively, 16 could
be synthesized directly from the reaction of 8 with Ph SiH
(10), [(IPr)Co(μ-SiHPh ) Co(IPr)] (13), [(IAd)Co(μ-
SiHPh ) Co(IAd)] (14), and [(IMesCy) Co(H)(SiHPh )]
2 2 2 2
(15), respectively. Complex 10 is the adduct of three molecules
2 2
[
(
of Ph SiH with two (cyIDep)Co fragments. NMR character-
2
2
ization on the solutions of 10 suggest the presence of the
2
2
2
(Scheme 3). As shown in Figure 7, the two carbene moieties in
fluxional process between the Co···(η -H-Si) and H−Co−Si
forms. Complexes 13 and 14 are dinuclear cobalt(I) silyl
2
complexes with Co···(η -H-Si) interactions, and might result
from the reductive elimination of H from their dinuclear
2
cobalt(II) hydride silyl precursors (NHC)(H)Co(μ-SiHPh ) -
2
2
Co(H)(NHC). Complex 15 is a cobalt(II) silyl hydride and can
be viewed as the oxidative addition of (IMesCy) Co(0) with
2
Ph SiH . The diversified reaction outcomes demonstrate the
2
2
effect of the steric property of the NHC ligands on the
reactivity of the NHC-cobalt(0)-olefin complexes. With these
understandings, we are now exploring the catalytic applications
of these NHC-cobalt(0)-olefin complexes in hydrosilylation
reactions.
EXPERIMENTAL SECTION
Figure 7. Molecular structure of 16 showing 30% probability ellipsoids
and a partial atom-labeling scheme. Hydrogen atoms were omitted for
clarity. Selected bond length (Å) and angles (deg): Co1−Si1 2.292(1),
Co1−C1 1.906(2), Co1−C2 1.902(2), Co1−C3 2.051(2), C1−Co1−
Si1 96.28(7), C1−Co1−C3 82.33(10), C2−Co1−Si1 89.60(7), C2−
Co1−C1 172.21(10), C2−Co1−C3 93.44(10), C3−Co1−Si1
■
General Procedures. All experiments were performed under an
atmosphere of dry dinitrogen or argon with the rigid exclusion of air
and moisture using standard Schlenk techniques, or in a glovebox. All
organic solvents were dried with a solvent purification system
(Innovative Technology) and bubbled with dry N gas prior to use.
2
1
63.82(7).
Ph SiH was further dried by 4 Å molecular sieves. 1,3-Bis(2′,6′-
2
2
4
4
diethylphenyl)imidazol-2-ylidene) (cyIDep), 1,3-bis-adamantyl-imi-
4
5
46
dazol-2-ylidene) (IAd), [HIMesCy]Cl, 1,3-bis-cyclohexyl-imidazol-
4
7
48
13
2
-ylidene (ICy), KC8, and 3 were prepared according to previous
1
6 are in trans-configuration. The silyl side arm has the Co−Si
distance of 2.2918(7) Å and the Si−Co−C(benzyl) angle of
63.82(7) deg, which are in analogy to the reported complexes
literatures. All other chemicals were purchased from either Strem or
1
J&K Chemical Co. and used as received unless otherwise noted. H,
1
13
29
C and Si NMR spectra were recorded on Agilent 400 MHz or
15,43
[
(MesCSi)M(IMes′)]
(M = Fe, Co; IMes′ denoted for the
Agilent 600 MHz spectrometer. Chemical shifts were reported in units
with references to the residual protons of the deuterated solvents for
cyclometalated IMes ligand) prepared from the reactions of the
13
bis-cyclometalated IMes complexes [M(IMes′) ] with hydro-
2
proton chemical shifts, the C of deuterated solvents for carbon
2
9
silanes. The mechanism for the conversion of 15 to 16 should
be complicated. As the processes of C−H bond activation and
Si−C bond formation must be involved in the conversion, we
speculate that cobalt silylene (IMesCy) Co(SiPh ) (E in
chemical shifts, and the Si of SiMe for silicon chemical shifts. The
4
29
1
1
Si{ H} NMR spectra required the inverse gated H-decoupling
techniques. Elemental analyses were performed by the Analytical
Laboratory of Shanghai Institute of Organic Chemistry (CAS).
Magnetic moments were measured by the method originally described
2
2
Scheme S1) or cyclometalated NHC cobalt silyl (IMesCy)Co-
by Evans with stock and experimental solutions containing a known
(
IMesCy′)(SiHPh ) (F in Scheme S1) are the probable
2
49,50
amount of a (CH ) SiOSi(CH ) standard.
Absorption spectra
3
3
3 3
intermediate. The validation of these routes needs further
study.
were recorded with a Shimadzu UV-3600 UV−vis-NIR spectropho-
tometer. IR spectra were recorded with a NICOLET AVATAR 330
FT-IR spectrophotometer.
CONCLUSIONS
■
X-ray Structure Determination. Diffraction-quality crystals were
In this study, we showed that the one-pot reaction of CoCl2
with NHC, vtms, and alkali metals is a useful protocol for the
preparation of three-coordinate NHC-cobalt(0)-olefin com-
plexes. Depending on the steric property of NHC ligands,
obtained as 7−9,10·2C
7 8 6 6 2
recrystallizations in Et O, Et O, Et O, toluene/n-hexane, THF/
H , 11, 12, 13·C H , 15·Et O, and 16 from
2
2
2
toluene, n-pentane, benzene, Et O, and Et O respectively, at room
2
2
temperature or −20 °C (12 and 15). Crystals were coated with
Paratone-N oil and mounted on a Bruker APEX CCD-based
diffractometer equipped with an Oxford low-temperature apparatus.
Data were collected at 140(2) K. Cell parameters were retrieved with
SMART software and refined using SAINT software on all reflections.
Data integration was performed with SAINT, which corrects for
Lorentz polarization and decay. Absorption corrections were applied
either (NHC)Co(vtms) (NHC = IPr, sIPr, cyIPr, cyIDep,
2
IMes, IAd) or (NHC) Co(vtms) (NHC = IMesCy, ICy) can
2
be obtained from the reaction using one or two equiv of NHCs
(
relative to CoCl ). These paramagnetic NHC-cobalt(0)
2
1
complexes are characterized by H NMR and UV−vis
F
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
5
1
using SADABS. Space groups were assigned unambiguously by
analysis of symmetry and systematic absences determined by XPREP.
mL) and dried under vacuum to give 8 as reddish brown solid (0.77 g,
53%). Single-crystals of 8 were obtained by standing its Et O solution
2
52
1
All structures were solved and refined using SHELXTL. Metal and
first coordination sphere atoms were located from direct-methods E-
maps. Non-hydrogen atoms were found in alternating difference
Fourier synthesis and least-squares refinement cycles and during final
cycles were refined anisotropically. Hydrogen atoms on the
coordination sphere of cobalt were located from the difference maps
and refined. Other hydrogen atoms were placed in calculated positions
employing a riding model. CCDC 1560269−1560277 contain the
supplementary crystallographic data for these complexes. These data
can be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
at room temperature after evaporation of solvent. H NMR (400 MHz,
C D , 19 °C): δ (ppm) 87.17 (v = 1447 Hz), 72.49 (v1/2 = 1673
6
6
1/2
Hz), 54.29 ((v1/2 = 1016 Hz), 27.23 (v1/2 = 40 Hz), 21.05 (v1/2 = 39
Hz), 19.86 (v1/2 = 64 Hz), 16.39 (v1/2 = 99 Hz), 15.58, 15.52, 13.54
(v1/2 = 220 Hz), 11.87 (v1/2 = 46 Hz), 10.28 (v1/2 = 64 Hz), 6.30 (v1/2
= 78 Hz), 4.64 (v1/2 = 73 Hz), −2.38 (v1/2 = 24 Hz), −2.71, −2.77,
−3.12 (v1 = 27 Hz), −3.34 (v = 16 Hz), −3.86, −4.02 (v = 51
/2
1/2
1/2
Hz), −4.35 (v = 15 Hz), −4.98 (v = 29 Hz), −5.55 (v = 27
1/2
1/2
1/2
Hz), −6.26 (v = 29 Hz), −8.99 (v = 26 Hz), −10.02 (v = 26
1/2
1/2
1/2
Hz), −15.18 (v = 85 Hz), −17.35 (v = 68 Hz), −17.76 (v = 64
1/2
1/2
1/2
Hz), −19.65 (v = 130 Hz), −22.33 (v = 50 Hz), −25.10 (v
=
1/2
1/2
1/2
Preparation of IMesCy. To the suspension of [HIMesCy]Cl
3.00 g, 9.84 mmol) in THF (50 mL) was added KOBu (1.44 g, 12.8
53 Hz), −134.46 (very br), −139.03 (very br). Because of peak
overlap, the half-peak widths of some signals were not listed. Magnetic
susceptibility (C D , 20 °C): μ = 3.2(1) μ . Anal. Calcd for
t
(
mmol). After stirring at room temperature for 14 h, the reaction was
subjected to a vacuum to remove the volatiles. The residue was
extracted by a mixture of n-hexane and toluene (50/50, 100 mL), and
filtered. The filtrate was then subjected to vacuum to remove the
volatiles, affording the free NHC ligand IMesCy as a white solid (2.00
6
6
eff
B
C H CoN Si: C, 70.76; H, 8.69; N, 8.05. Found: C, 71.46; H, 8.46;
4
1
60
4
−1
−1
N, 7.87. Absorption spectrum (THF): λmax (ε, M cm ) = 264
(11340), 368 (6030), 664 (70) nm.
Preparation of [(ICy) Co(vtms)] (9). To the solution of ICy (1.04
2
1
g, 76%). H NMR (400 MHz, C D , 25 °C): δ (ppm) 6.79 (s, 2H),
g, 4.48 mmol) in THF was added CoCl (0.29 g, 2.23 mmol) at room
6
6
2
6
1
0
.68 (s, 1H), 6.47 (s, 1H), 4.25−4.05 (m, 1H), 2.21−2.03 (m, 11H),
.76−1.56 (m, 4H), 1.52−1.40 (m, 1H), 1.26−1.10 (m, 2H), 1.10−
.95 (m, 1H). 13C NMR (101 MHz, C D , 25 °C): δ (ppm) 216.18
temperature. After stirring for 1.5 h, vinyltrimethylsilane (0.67 g, 6.68
mmol) was added, and then after 10 min, KC (0.60 g, 4.44 mmol)
8
6
6
was added. After stirring at room temperature for 17 h, the mixture
was filtered to give a reddish brown solution. Removal of the solvent
by a vacuum gave a reddish brown residue that was further washed by
n-hexane (5 mL) and dried under a vacuum to give 9 as reddish brown
(
br, Ccarbene), 139.70, 136.97, 135.51, 129.05, 119.90, 116.49, 59.96,
3
5.28, 25.95, 25.85, 21.04, 18.17.
Preparation of [(cyIDep)Co(vtms) ] (6). To a mixture of cyIDep
2
(
(
1.60 g, 4.14 mmol) and CoCl (0.54 g, 4.11 mmol) was added THF
30 mL). After stirring at room temperature for 3 h, vinyl-
solid (0.964 g, 34%). Single-crystals of 9 were obtained by standing its
Et O solution at room temperature after evaporation of solvent. H
2
2
1
trimethylsilane (1.30 g, 13.0 mmol) and KC (1.30 g, 9.62 mmol)
NMR (400 MHz, C D , 25 °C) δ (ppm) 117.22 (v = 483 Hz),
8
6
6
1/2
were added to the resulting blue solution. After further stirring at room
temperature for 21 h, the mixture turned into to a dark green
suspension. After filtration, the filtrate was subjected to a vacuum to
remove the solvent. The green residue was then extracted by n-hexane
113.20, 25.66 (v1/2 = 730 Hz), 20.67 (v1/2 = 138 Hz), 17.26 (v1/2 = 94
Hz), 14.09 (v1/2 = 109 Hz), 12.14 (br), 5.41 (very br), 0.92, −1.93
(very br), −2.91 (v = 167 Hz), −4.35 (v = 134 Hz), −4.90, −5.76
1
/2
1/2
(v = 35 Hz), −11.11 (v1/2 = 92 Hz), −15.40 (very br), −21.84 (very
1/2
(
20 mL), and filtered. The filtrate was standing at room temperature to
br), −24.38 (v1 = 93 Hz), −26.09 (v = 144 Hz), −35.03 (very br),
/2
1/2
evaporate the solvent, by which green crystals of 6 were obtained (0.92
−48.15 (very br), −127.63 (very br). Due to peak overlap, the half-
peak widths of some signals were not listed. Magnetic susceptibility
(C D ): μ = 2.8(2) μ . Anal. Calcd for C H CoN Si: C, 67.38; H,
1
g, 35%). H NMR (400 MHz, C D , 20 °C): δ (ppm) 70.64 (v =
1/2
6
6
1
679 Hz), 52.54 (v1/2 = 1234 Hz), 44.51 (v1/2 = 1709 Hz)), 12.31 (v1/2
138 Hz), 5.47 (v1/2 = 15 Hz), 5.09 (v1/2 = 34 Hz), 4.26(v1/2 = 34
Hz), 3.68 (v1/2 = 18 Hz), −0.66 (v = 22 Hz), −1.95 (v = 25 Hz),
6
6
eff
B
35 60
4
=
9.69; N, 8.98.; Found: C, 67.07; H, 10.07; N, 9.26. Absorption
−1
−1
1/2
1/2
spectrum (THF): λmax (ε, M cm ) = 241 (14090), 358 (8670), 489
−
3.40 (v1/2 = 84 Hz), −3.64 (v = 24 Hz), −5.52 (v = 22 Hz).
(3620), 659 (60) nm.
1/2
1/2
2
2
2
Magnetic susceptibility (C D , 20 °C): μ = 2.8(1) μ . Anal. Calcd for
Preparation of [(cyIDep)(H)Co(μ-η :η -H SiPh )(μ-η -
6
6
eff
B
2 2
C H CoN Si : C, 68.79; H, 9.05; N, 4.34; Found: C, 68.86; H, 9.24;
N, 4.60. Absorption spectrum (THF): λmax (ε, M cm ) = 254
HSiPh
[(cyIDep)Co(vtms)
added Ph SiH (0.83 g, 4.51 mmol) dropwisely. The solution changed
)
2
2
Co(H)(cyIDep)] (10). To a green solution of complex
3
7
58
2
2
−1
−1
] (0.85 g, 1.31 mmol) in Et O (15 mL) was
2
2
(
17970), 646 (70), 829 (30) nm.
2
2
Preparation of [(IAd)Co(vtms) ] (7). To a mixture of IAd (0.50 g,
to a yellowish brown suspension with the precipitation of a yellowish
brown solid. After stirring at room temperature for 0.5 h, the mixture
2
1
.47 mmol) and CoCl (0.19 g, 1.49 mmol) was added THF (15 mL).
2
After stirring at room temperature for 4 h, vinyltrimethylsilane (0.45 g,
was filtrated to leave a yellow residue. The solid was washed by Et O
2
4
.49 mmol) and KC (0.40 g, 2.96 mmol) were added. The mixture
(20 mL) and dried under a vacuum to afford 10 as a yellowish solid
(0.82 g, 87%). Yellowish crystals of 10·2C H were obtained by slow
8
gradually changed to blue suspension after stirring at room
temperature for 20 h. After filtration, the filtrate was subjected to
vacuum to remove the solvent. The green residue was then extracted
by Et O (10 mL), and filtered. The filtrate was standing at room
temperature to evaporate the solvent, by which blue crystals of 7 were
7
8
1
diffusion of n-hexane into the toluene solution of 10. H NMR (400
MHz, C D , 20 °C): δ (ppm) 7.12−7.03 (m, 18H), 7.02−6.95 (t, J =
6
6
7.6 Hz, 5H), 6.91 (t, J = 7.4 Hz, 12H), 6.85 (d, J = 7.6 Hz, 7H), 2.60−
2.45 (m, 8H), 2.45−2.30 (m, 8H), 1.58 (s, 8H), 1.12 (s, 8H), 0.96 (t, J
2
1
13
obtained (0.34 g, 38%). H NMR (400 MHz, THF-d , 19 °C): δ
= 7.5 Hz, 24H, −CH ), −8.97 (s, 6H). C NMR (101 MHz, C D , 19
8
3
6
6
(
ppm) 13.84 (v1/2 = 484 Hz), 11.69 (v1/2 = 156 Hz), 2.28 (v1/2 = 76
°C): δ (ppm) 189.08 (C
), 144.85, 140.77, 138.12, 137.64, 129.76,
128.51, 126.23, 126.19, 125.76, 24.48, 22.69, 22.49, 12.67. Si{ H}
NMR (119.2 MHz, C D , 25 °C): δ (ppm) 64.46. Si NMR (119.2
carbene
2
9
1
Hz), −1.06 (v1 = 187 Hz), −4.06 (v = 172 Hz), −5.51 (v = 157
/2
1/2
1/2
29
Hz), −16.74 (v
= 1908 Hz), −31.10 (very br). Magnetic
1
/2
6 6
susceptibility (C D ): μ = 2.9(1) μ . Anal. Calcd for C H CoN Si :
MHz, C D , 25 °C): δ (ppm) 64.50 (m). Anal. Calcd for
6 6
6
6
eff
B
33 56
2
2
C, 66.51; H, 9.47; N, 4.70; Found: C, 66.57; H, 9.94; N, 4.78.
Absorption spectrum (THF): λmax (ε, M cm ) = 252 (15450), 592
C H Co N Si : C, 74.86; H, 7.26; N, 3.88. Found: C, 74.88; H,
90 104 2 4 3
−1
−1
−1
−1
7.46; N, 3.71. Absorption spectrum (THF): λmax (ε, M cm ) = 266
−
1
(
40), 672 (40) nm.
(25800), 318 (16190), 470 (1770) nm. IR spectrum (KBr, cm ): ν =
3038 (s), 2965 (s), 2935 (s), 2874 (s), 2851 (s), 1944 (m), 1684 (m),
1426 (s), 1384 (m), 1351 (s), 1275 (s), 1234 (m), 1187 (m), 1145
(m), 1093 (m), 1061 (m), 1038 (m), 987 (m), 807 (m), 732 (s), 699
(s), 486 (s), 459 (m), 438 (s).
Preparation of [(IMesCy) Co(vtms)] (8). To the solution of
2
IMesCy (1.09 g, 4.00 mmol) in THF was added CoCl (0.25 g, 1.92
mmol). After stirring at room temperature for 7 h, vinyltrimethylsilane
2
(
0.32 g, 3.19 mmol) and KC (0.54 g, 4.03 mmol) were added. The
8
mixture changed to reddish brown gradually after further stirring at
room temperature for 24 h. The mixture was then filtered to afford a
reddish brown solution. Removal of the solvent by vacuum gave a
reddish brown residue that was further washed by n-hexane (3 × 10
Preparation of [(cyIDep)Co(μ-HSiPh ) Co(cyIDep)] (11). To a
2
2
10 mL flask was added 10 (0.12 g, 0.083 mmol). Under vacuum, the
solid was heated at 120 °C for 4 h, during which the solid changed to
dark brown. After being cooled to room temperature, the solid was
G
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
extracted with by n-hexane (5 mL) to afford a dark brown solution.
Single-crystals of 11 were obtained by standing its THF/toluene
(v1/2 = 15 Hz), 0.35 (v1/2 = 16 Hz), −1.74 (v = 25 Hz), −2.25 (v
1/2
1/2
= 19 Hz), −4.01 (v1 = 188 Hz), −5.88 (very br). Anal. Calcd for
/2
solution at room temperature after evaporation of solvent (0.050 g,
C H Co N Si : C, 72.64; H, 7.49; N, 4.84. Found: C, 72.38; H, 7.50;
7
0
86
2
4
2
1
−1
−1
4
8%). H NMR (400 MHz, C D , 20 °C): δ (ppm) 8.34 (v = 20
N, 4.84. Absorption spectrum (THF): λmax (ε, M cm ) = 266
(29600), 317 (20480), 380 (14690), 547(840), 1080 (180). Because
of the poor solubility of 14 even in C H , THF or 1,2-difluorobenzene,
6
6
1/2
Hz), 5.60 (v1/2 = 19 Hz), 4.58, 4.39, 2.44 (v1/2 = 19 Hz), 2.04 (v1/2
=
2
6 Hz), 1.93 (v1/2 = 17 Hz), 1.74 (v1/2 = 17 Hz), 1.29 (v1/2 = 19 Hz).
6
6
Because of peak overlap, the half-peak widths of some signals were not
the solution magnetic susceptibility was not measured. IR spectrum
−1
listed. Magnetic susceptibility (C D , 20 °C): μ = 2.7(2) μ . Anal.
(KBr, cm ): ν = 3125 (w), 3042 (m), 2907 (s), 2850 (s), 2678 (w),
2044 (w), 1948 (w), 1948 (w), 1874 (w), 1810 (w), 1651 (w), 1578
(w), 1537 (w), 1474 (w), 1451 (m), 1424 (m), 1388 (m), 1375 (m),
1349 (m), 1305 (m), 1278 (m), 1261 (m), 1244 (m), 1227 (m), 1193
(m), 1160 (m), 1102 (s), 1077 (m), 1077 (m), 1042 (m), 999 (m),
980 (m), 953 (m), 901 (m), 840 (m), 816 (m), 773 (m), 730 (m),
701 (s), 680 (m), 667 (m), 499 (s), 463 (m), 432 (m), 409 (m).
6
6
eff
B
Calcd for C H Co N Si : C, 74.49; H, 7.21; N, 4.46. Found: C,
7
8
90
2
4
2
−
1
7
4.21; H, 7.01; N, 4.66. Absorption spectrum (THF): λ (ε, M
cm ) = 261 (16960), 384 (6980), 578 (1400), 1297 (80) nm. IR
max
−1
−
1
spectrum (KBr, cm ): ν = 3037 (m), 2964 (s), 2933 (s), 2875 (m),
852 (m), 1703 (s), 1670 (m), 1589 (w), 1564 (m), 1461 (s), 1425
m), 1384 (m), 1352 (m), 1327 (m), 1277 (m), 1232 (m), 1188 (m),
170 (m), 1144 (m), 1111 (m), 1091 (m), 1039 (m), 1023 (m), 998
m), 906 (m), 863 (m), 808 (m), 767 (m), 733 (s), 700(s), 487 (s),
42 (m), 430 (m).
Preparation of [(cyIDep)(Bu NC)Co(μ-HSiPh ) Co(CNBu ) ]
2
(
1
(
Preparation of [(IMesCy)
(vtms)] (8, 0.21 g, 0.30 mmol) was dissolved in Et
Co(H)(SiHPh
)] (15). [(IMesCy)
Co-
2
2
2
O (20 mL) to
2
4
afford a reddish brown solution. After filtration and cooling at −20 °C,
diphenylsilane (0.13 g, 0.71 mmol) was added. The mixture was kept
t
t
2
2
3
(
12). To a solution of 11 (0.10 g, 0.08 mmol) in toluene (5 mL)
at −20 °C for days without stirring, which led to the precipitation of
t
1
was added Bu NC (0.030 g, 0.36 mmol). After stirring for 8 h at room
temperature, the color of the solution changed to dark brown. After
removal of the solvent under vacuum, the brown residue was extracted
by n-pentane (5 mL) and filtered. Dark brown crystals of 12 were
obtained by standing its n-pentane solution at −20 °C for days (0.028
g, 28%). The low yield is due to the high solubility of 12 in n-pentane.
15·Et O as yellowish crystals (0.050 g, ca. 21%). H NMR
2
characterization (Figures S28 and S31) indicated the coexistence of
unknown impurity in the sample. Attempts to get pure sample of 15
by recrystallization were unsuccessful. The existence of the impurity
prevented the further characterization.
Preparation of [(cyCSi)Co(IMesCy′)] (16). To a suspension of
1
H NMR (400 MHz, C D , 21 °C): δ (ppm) 7.75 (dd, J = 6.4, 3.0 Hz,
[(IMesCy) Co(vtms)] (8, 0.27 g, 0.39 mmol) in Et O (10 mL) was
6
6
2
2
4
8
4
H), 7.51 (dd, J = 7.2, 1.5 Hz, 4H), 7.22−7.17 (m, 12H), 7.01 (dd, J =
.2, 6.9 Hz, 2H), 6.93 (d, J = 7.6 Hz, 4H), 2.92 (dq, J = 15.5, 7.6 Hz,
H), 2.60 (dq, J = 15.3, 7.5 Hz, 4H), 1.80 (s, 4H), 1.53 (s, 9H), 1.24
added diphenylsilane (0.14 g, 0.78 mmol). After stirring at room
temperature for 12 h, the solvent was removed by vacuum to afford a
reddish-brown residue. Toluene (10 mL) was added to redissolve the
residue. The resulting mixture was further heated at 70 °C for 4 h.
13
(
s, 4H), 1.14 (t, J = 7.6 Hz, 12H), 0.95 (s, 27H), −5.29 (s, 2H). C
NMR (101 MHz, C D , 21 °C): δ (ppm) 195.58 (C ), 173.22,
After removal of the solvent, the residue was extracted by Et
and filtered. Green crystals of 16 were obtained by standing its Et
solution at room temperature after evaporation of solvent (0.08 g,
2
O (5 mL)
6
6
carbene
1
1
2
72.74, 151.61, 147.44, 140.77, 138.60, 137.42, 137.28, 129.41, 125.94,
25.93, 125.80, 125.78, 125.36, 54.85, 54.26, 31.28, 30.82, 24.52,
O
2
29
1
1
2.91, 22.35, 13.21. Si{ H} NMR (119.2 MHz, C D , 25 °C): δ
26%). H NMR (400 MHz, C D , 19 °C) δ (ppm) 30.31 (v1/2 = 705
6 6
6
6
(
(
6
ppm) 101.24. 29Si NMR (119.2 MHz, C D , 25 °C): δ (ppm) 101.24
Hz), 27.74 (v1/2 = 151 Hz), 26.56 (v1/2 = 239 Hz), 23.78, 23.43, 22.19
(v1/2 = 140 Hz), 20.65 ((v1/2 = 117 Hz), 18.00, 17.64 (v1/2 = 170 Hz),
14.55 (v1/2 = 153 Hz), 14.02 (v1/2 = 170 Hz), 12.88 (v1/2 = 170 Hz),
10.94 (v1/2 = 110 Hz), 10.04 (v1/2 = 16 Hz), 7.71 (v1/2 = 17 Hz), 6.82
6
6
d, J = 80 Hz). Anal. Calcd for C H Co N Si : C, 70.85; H, 7.70; N,
71
92
2
6
2
.98. Found: C, 71.05; H, 8.01; N, 6.88. Absorption spectrum (THF):
−1
−1
λmax (ε, M cm ) = 287 (37110), 560 (6320) nm. IR spectrum (KBr,
−1
(
(
v1/2 = 15 Hz), 6.16 (v1/2 = 35 Hz), 4.02 (v1/2 = 38 Hz), 3.43, 2.62
v1/2 = 31 Hz), 0.37, −0.82 (v = 59 Hz), −0.98 (v = 59 Hz),
cm ): ν = 3044 (m), 2971 (s), 2933 (s), 2874 (s), 2104 (s), 2033 (s),
580 (w), 1460 (m), 1424 (m), 1385 (m), 1363 (m), 1352 (m), 1275
m), 1212 (m), 1188 (m), 1145 (w), 1088 (m), 1059 (w), 1036 (w),
026 (w), 987 (w), 808 (m), 770 (m), 734 (m), 696 (s), 679 (m), 502
1
(
1/2
1/2
−
−
−
1.12 (v = 11 Hz), −1.26 (v = 33 Hz), −1.41, −1.47, −2.87,
1/2
1/2
2.97 (v1/2 = 15 Hz), −3.25 (v = 51 Hz), −3.50 (v = 53 Hz),
1
1/2
1/2
4.39 (v1/2 = 36 Hz), −5.16 (v = 85 Hz), −5.90, −6.14 (v = 72
(
s), 483 (s), 441 (m).
1/2
1/2
Hz), −7.28 (v = 22 Hz), −7.99 (v = 31 Hz), −8.34 (v = 54
Preparation of [(IPr)Co(μ-HSiPh ) Co(IPr)] (13). To a solution
1/2
1/2
1/2
2
2
Hz), −8.86 (v = 74 Hz), −9.11 (v = 10 Hz), −9.74, −9.95,
of [(IPr)Co(vtms) ] (3, 0.36 g, 0.56 mmol) in toluene (15 mL) was
1/2
1/2
2
−
11.51 (v = 139 Hz), −12.65 (v = 94 Hz), −15.11 (v = 121
afford added diphenylsilane (0.21 g, 1.12 mmol) dropwisely. During
the course, the color of the mixture changed to brown. The mixture
was then allowed to stand at room temperature without stirring for
overnight, and a brown crystalline solid of 13 then precipitated out.
After filtration, washed by hexane, and dried under vacuum, brown
solid of 13 was obtained (0.18 g, 26%). The single-crystals of 13·C H6
were obtained by the same method using benzene as solvent. Anal.
1/2
1/2
1/2
Hz), −16.39 (v = 138 Hz), −20.20 (v = 189 Hz), −21.86, −22.65,
1/2
1/2
−
28.98 (v = 370 Hz), −30.73. Because of peak overlap, the half-
1/2
peak widths of some signals were not listed. Anal. Calcd for:
C H CoN Si: C, 74.29; H, 7.22; N, 7.27. Found: C, 74.00; H, 7.10;
48 56
4
−1
−1
N, 7.40. Absorption spectrum (THF): λmax (ε, M cm ) = 297
6
(9260), 327 (7300), 620 (270), 1169 (40) nm.
Calcd for C H Co N Si ·C H : C, 75.30; H, 7.52; N, 4.18; Found:
7
8
94
2
4
2
6
6
−1
C, 75.46; H, 7.84; N, 3.91. IR spectrum (KBr, cm ): ν = 3136 (w),
ASSOCIATED CONTENT
■
3
(
1
058 (m), 3044 (m), 2962 (s), 2927 (s), 2867 (s), 1698 (m), 1646
w), 1588 (w), 1534 (w), 1459 (m), 1426 (w), 1403 (m), 1382 (m),
362 (m), 1327 (m), 1287 (m), 1257 (m), 1180 (w), 1149 (w), 1115
* Supporting Information
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01763.
(
(
(
m), 1058 (m), 1041 (m), 1023 (m), 957 (m), 932 (m), 800 (m), 752
m), 736 (m), 699 (m), 678 (m), 546 (m), 491 (m), 464 (m), 454
m), 410 (m). The poor solubility of 13 prevented further detailed
Tables for crystal data, molecular structures, absorption
spectra, NMR, IR, and GC-MS spectra (PDF)
characterization.
Preparation of [(IAd)Co(μ-HSiPh ) Co(IAd)] (14). To a blue
2
2
solution of [(IAd)Co(vtms) ] (7, 0.13 g, 0.22 mmol) in Et O (6 mL)
2
2
Accession Codes
was added Ph SiH (0.10 g, 0.54 mmol) dropwisely. The color of the
2
2
CCDC 1560269−1560277 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
solution gradually changed to light green and then yellowish brown
gradually. After stirring at room temperature for 10 min, the mixture
was filtrated to leave a brown filtrate. Slow evaporation of solvent by
standing the solution at room temperature afforded 14 as yellowish
1
brown crystals (0.060 g, 47%). H NMR (400 MHz, THF-d , 21 °C):
8
δ (ppm) 11.07 (very br), 9.70 (v1/2 = 12 Hz), 7.89 (v1/2 = 14 Hz), 6.86
H
DOI: 10.1021/acs.inorgchem.7b01763
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
15) Mo, Z.; Liu, Y.; Deng, L. Anchoring of Silyl Donors on a N-
AUTHOR INFORMATION
Corresponding Author
E-mail: deng@sioc.ac.cn.
■
Heterocyclic Carbene through the Cobalt-Mediated Silylation of
Benzylic C-H Bonds. Angew. Chem., Int. Ed. 2013, 52, 10845−10849.
*
(16) Wu, J.; Faller, J. W.; Hazari, N.; Schmeier, T. J. Stoichiometric
ORCID
and Catalytic Reactions of Thermally Stable Nickel(0) NHC
Complexes. Organometallics 2012, 31, 806−809.
Jian Sun: 0000-0001-9397-3191
Liang Deng: 0000-0002-0964-9426
Notes
(17) Jackstell, R.; Harkal, S.; Jiao, H.; Spannenberg, A.; Borgmann,
̈
C.; Rottger, D.; Nierlich, F.; Elliot, M.; Niven, S.; Cavell, K.; Navarro,
O.; Viciu, M. S.; Nolan, S. P.; Beller, M. An Industrially Viable Catalyst
System for Palladium-Catalyzed Telomerizations of 1,3-Butadiene with
Alcohols. Chem. - Eur. J. 2004, 10, 3891−3900.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
́ ́
(18) Marko, I. E.; Sterin, S.; Buisine, O.; Mignani, G.; Branlard, P.;
■
Tinant, B.; Declercq, J.-P. Selective and Efficient Platinum(0)-Carbene
The work was supported by the National Key R&D Program of
China (2016YFA0202900), the National Natural Science
Foundation of China (Nos. 21690062, 21421091, and
Complexes As Hydrosilylation Catalysts. Science 2002, 298, 204−206.
(
̃
́
19) Bruna, S.; Gonzalez-Vadillo, A. M.; Nieto, D.; Pastor, C.;
Cuadrado, I. Vinyl-Functionalized Silanes and Disiloxanes with
2
1432001), and the Strategic Priority Research Program of
Electronically Communicated Ferrocenyl Units. Organometallics
the Chinese Academy of Sciences (No. XDB20000000). We
thank Mr. Lingbo Wang and Mr. Jingzhen Du for their
assistance on the preparation of the NHC-Co(0)-vtms
complexes.
2
(
010, 29, 2796−2807.
20) Strasser, U. H.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W.
Synthesis and Molecular Structures of Tetrasilyl Ethers of Calix[4]-
arenes. Z. Anorg. Allg. Chem. 2010, 636, 1249−1254.
2
(
21) Pham, E. K.; West, R. Platinum η -Disilene Complexes:
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